this page intentionally left blank - libros cientificos en...

Copyright © 2008, 1997, 1984, 1973, 1963, 1950, 1941, 1934 by The McGraw-Hill Companies, Inc. All rights reserved. Manufactured in the UnitedStates of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributedin any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher.

0-07-154229-9

The material in this eBook also appears in the print version of this title: 0-07-151145-8.

All trademarks are trademarks of their respective owners. Rather than put a trademark symbol after every occurrence of a trademarked name, we usenames in an editorial fashion only, and to the benefit of the trademark owner, with no intention of infringement of the trademark. Where such designations appear in this book, they have been printed with initial caps.

McGraw-Hill eBooks are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs.For more information, please contact George Hoare, Special Sales, at [email protected] or (212) 904-4069.

TERMS OF USE

This is a copyrighted work and The McGraw-Hill Companies, Inc. (“McGraw-Hill”) and its licensors reserve all rights in and to the work. Use of thiswork is subject to these terms. Except as permitted under the Copyright Act of 1976 and the right to store and retrieve one copy of the work, you maynot decompile, disassemble, reverse engineer, reproduce, modify, create derivative works based upon, transmit, distribute, disseminate, sell, publishor sublicense the work or any part of it without McGraw-Hill’s prior consent. You may use the work for your own noncommercial and personal use;any other use of the work is strictly prohibited. Your right to use the work may be terminated if you fail to comply with these terms.

THE WORK IS PROVIDED “AS IS.” McGRAW-HILL AND ITS LICENSORS MAKE NO GUARANTEES OR WARRANTIES AS TO THEACCURACY, ADEQUACY OR COMPLETENESS OF OR RESULTS TO BE OBTAINED FROM USING THE WORK, INCLUDING ANYINFORMATION THAT CAN BE ACCESSED THROUGH THE WORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIMANY WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY ORFITNESS FOR A PARTICULAR PURPOSE. McGraw-Hill and its licensors do not warrant or guarantee that the functions contained in the work willmeet your requirements or that its operation will be uninterrupted or error free. Neither McGraw-Hill nor its licensors shall be liable to you or anyone else for any inaccuracy, error or omission, regardless of cause, in the work or for any damages resulting therefrom. McGraw-Hill has noresponsibility for the content of any information accessed through the work. Under no circumstances shall McGraw-Hill and/or its licensors be liablefor any indirect, incidental, special, punitive, consequential or similar damages that result from the use of or inability to use the work, even if any ofthem has been advised of the possibility of such damages. This limitation of liability shall apply to any claim or cause whatsoever whether such claimor cause arises in contract, tort or otherwise.

DOI: 10.1036/0071511458

This page intentionally left blank

22-1

Section 22

Waste Management*

Louis Theodore, Eng.Sc.D. Professor of Chemical Engineering, Manhattan College;Member, Air and Waste Management Association (Section Editor, Pollution Prevention)

Kenneth N. Weiss, P.E., Diplomate AAEE Partner and North American Director ofCompliance Assurance, ERM; Member, Air and Waste Management Association (Introductionto Waste Management and Regulatory Overview)

John D. McKenna, Ph.D. President and Chairman, ETS International, Inc.; Member,American Institute of Chemical Engineers, Air and Waste Management Association (Air-PollutionManagement of Stationary Sources)

(Francis) Lee Smith, Ph.D., M.Eng. Principal, Wilcrest Consulting Associates, Houston,Texas; Member, American Institute of Chemical Engineers, Society of American Value Engineers,Water Environment Federation, Air and Waste Management Association (Biological APC Tech-nologies, Estimating Henry’s Law Constants)

Robert R. Sharp, Ph.D., P.E. Professor of Environmental Engineering, Manhattan Col-lege; Environmental Consultant; Member, American Water Works Association; Water Environ-ment Federation Section Director (Wastewater Management)

Joseph J. Santoleri, P.E. Senior Consultant, RMT Inc. & Santoleri Associates; Member,American Institute of Chemical Engineers, American Society of Mechanical Engineers (ResearchCommittee on Industrial and Municipal Waste), Air and Waste Management Association (SolidWaste Management)

Thomas F. McGowan, P.E. President, TMTS Associates; Member, American Institute ofChemical Engineers, American Society of Mechanical Engineers, Air and Waste ManagementAssociation (Solid Waste Management)

INTRODUCTION TO WASTE MANAGEMENT AND REGULATORY OVERVIEW

Multimedia Approach to Environmental Regulations in the United States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4

Plant Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-5Corporate Strategic Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-5United States Air Quality Legislation and Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-6Clean Air Act of 1970 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-6Prevention of Significant Deterioration (PSD) . . . . . . . . . . . . . . . . . . 22-6Nonattainment (NA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8Controlled-Trading Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9

Clean Air Act of 1990 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9Regulatory Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-12

United States Water Quality Legislation and Regulations . . . . . . . . . . . 22-12Federal Water Pollution Control Act . . . . . . . . . . . . . . . . . . . . . . . . . 22-12Source-Based Effluent Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-14Clean Water Act of 1977 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-15Control of Toxic Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-151987 CWA Amendments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-15Biological Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-15Metal Bioavailability and Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-16Total Maximum Daily Load (TMDL) . . . . . . . . . . . . . . . . . . . . . . . . . 22-16Water Quality Trading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-16Bioterrorism Act of 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-17

*The contributions of Dr. Anthony J. Buonicore to material from the seventh edition of this handbook are acknowledged.

Copyright © 2008, 1997, 1984, 1973, 1963, 1950, 1941, 1934 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Cooling Water Intake Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-17Water Reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-17Regulatory Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-17

United States Solid Waste Legislation and Regulations . . . . . . . . . . . . . 22-17Rivers and Harbors Act, 1899 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-17Solid Waste Disposal Act, 1965 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-17National Environmental Policy Act, 1969 . . . . . . . . . . . . . . . . . . . . . . 22-17Resource Recovery Act, 1970 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-17Resource Conservation and Recovery Act, 1976 . . . . . . . . . . . . . . . . 22-17Toxic Substances Control Act, 1976 . . . . . . . . . . . . . . . . . . . . . . . . . . 22-18Regulatory Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-18

POLLUTION PREVENTIONIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19Pollution-Prevention Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-20Multimedia Analysis and Life-Cycle Analysis . . . . . . . . . . . . . . . . . . . . . 22-21

Multimedia Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-21Life-Cycle Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-21

Pollution-Prevention Assessment Procedures . . . . . . . . . . . . . . . . . . . . 22-22Planning and Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-22Assessment Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-22Feasibility Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-22Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-23Sources of Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-23Industry Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-23

Assessment Phase: Material Balance Calculations . . . . . . . . . . . . . . . . . 22-23Barriers and Incentives to Pollution Prevention . . . . . . . . . . . . . . . . . . . 22-24

Barriers to Pollution Prevention (“The Dirty Dozen”) . . . . . . . . . . . . 22-24Pollution-Prevention Incentives (“A Baker’s Dozen”) . . . . . . . . . . . . 22-24

Economic Considerations Associated with Pollution-Prevention Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-25

Pollution Prevention at the Domestic and Office Levels . . . . . . . . . . . . 22-26Ethical Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-27Future Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-27

AIR-POLLUTION MANAGEMENT OF STATIONARY SOURCESIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-28

Gaseous Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-28Particulate Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-29Estimating Emissions from Sources . . . . . . . . . . . . . . . . . . . . . . . . . . 22-31Effects of Air Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-31

A Source-Control-Problem Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-35Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-35Factors in Control-Equipment Selection . . . . . . . . . . . . . . . . . . . . . . 22-36

Dispersion From Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-37Preliminary Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-37Design Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-39Miscellaneous Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-40

Control of Gaseous Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-41Absorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-41Adsorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-42Combustion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-44Condensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-47Biological APC Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-48Membrane Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-51

Source Control of Particulate Emissions . . . . . . . . . . . . . . . . . . . . . . . . 22-53Emissions Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-54

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-54Sampling Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-55

INDUSTRIAL WASTEWATER MANAGEMENTIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-58United States Legislation, Regulations, and Government Agencies . . . . . 22-58

Federal Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-58Environmental Protection Agency. . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-60State Water-Pollution-Control Offices. . . . . . . . . . . . . . . . . . . . . . . . . 22-60

Wastewater Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-60Priority Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-60Organics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-60Inorganics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-62pH and Alkalinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-62

Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-62Dissolved Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-62Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-62Nutrients and Eutrophication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-62Whole Effluent Toxicity (WET). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-63Oil and Grease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-63

Wastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-63Pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-63

Equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-63Neutralization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-63Grease and Oil Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-64Toxic Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-64

Primary Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-64Screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-64Grit Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-64Gravity Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-64Chemical Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-65

Secondary Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-65Design of Biological Treatment Systems . . . . . . . . . . . . . . . . . . . . . . . 22-66Reactor Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-67Determination of Kinetic and Stoichiometric Pseudo Constants . . . . . 22-68Activated Sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-69Lagoons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-72Fixed-Film Reactor Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-74Trickling Filters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-74Rotating Biological Contactors (RBCs) . . . . . . . . . . . . . . . . . . . . . . . . 22-74Packed-Bed Fixed-Film Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-74Biological Fluidized Beds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-75

Physical-Chemical Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-76Adsorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-76Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-77Stripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-77Chemical Oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-77Advanced Oxidation Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-77Membrane Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-78Membrane Bioreactors (MBRs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-78Industrial Reuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-78

Sludge Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-78Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-78Concentration: Thickening and Flotation . . . . . . . . . . . . . . . . . . . . . . 22-79Stabilization (Anaerobic Digestion, Aerobic Digestion, High Lime Treatment) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-79

Sludge Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-80Incineration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-80Sanitary Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-80Beneficial Reuse of Biosolids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-80

MANAGEMENT OF SOLID WASTESIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-81

Functional Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-81United States Legislation, Regulations, and Government Agencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-82

Generation of Solid Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-82Types of Solid Waste. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-82Hazardous Wastes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-83Sources of Industrial Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-84Properties of Solid Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-84Quantities of Solid Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-86

On-Site Handling, Storage, and Processing . . . . . . . . . . . . . . . . . . . . . . 22-88On-Site Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-89On-Site Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-89On-Site Processing of Solid Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-90

Processing and Resource Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-90Processing Techniques for Solid Waste . . . . . . . . . . . . . . . . . . . . . . . . 22-90Processing of Hazardous Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-91Materials-Recovery Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-92Recovery of Biological Conversion Products. . . . . . . . . . . . . . . . . . . . 22-92Thermal Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-92Concentration of WTE Incinerators . . . . . . . . . . . . . . . . . . . . . . . . . . 22-96

Regulations Applicable to Municipal Waste Combustors . . . . . . . . . . . 22-96Ultimate Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-98

Landfilling of Solid Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-98Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-106

22-2 WASTE MANAGEMENT

WASTE MANAGEMENT 22-3

3P Pollution prevention paysABS Alkyl benzene sulfonateACC Annualized capital costsBACT Best available control technologyBAT Best available technologyBCOD Biodegradable chemical oxygen demandBCT Best conventional technologyBOD Biochemical oxygen demandBSRT Biomass solids retention timeBTEX Benzene, toluene, xyleneCAA Clean Air ActCAAA Clean Air Act AmendmentsCCP Comprehensive costing proceduresCFR Code of federal regulationsCKD Cement kiln dustCOD Chemical oxygen demandCPI Chemical process industriesCRF Capital recovery factorCTDMPLUS Complex terrain dispersion model plus algorithms for

unstable situationsCWRT Center for Waste Reduction TechnologiesDCF Direct installation cost factorDO Dissolved oxygenDRE Destruction and removal efficiencyEBCT Empty bed contact timeEMAS Eco-management and audit schemeEMS Environmental management systemEPA Environmental Protection AgencyFML Flexible membrane linerGAX Granular activated carbonHAPS Hazardous air pollutantsHAZWOPER Hazardous waste operatorsHCS Hauled-container systemsHRT Reactor hydraulic retention timeHSWA Hazardous and Solid Waste ActI-TEF International toxic equivalency factorICF Indirect installation cost factorISO International Organization for StandardizationLCA Life cycle assessment

LCC Life cycle costingLOX Liquid oxygenMACT Maximum achievable control technologyMSDA Material safety data sheetsMSW Municipal solid wasteMWC Municipal waste combustorsMWI Medical waste incineratorsNBOD Nitrogenous biochemical oxygen demandNIMBY Not in my back yardNPDES National pollutant discharge elimination systemNSPS New source performance standardsPCB Polychlorinated biphenylPIES Pollution prevention information exchange systemsPM Particulate matterPOTW Publicly owned treatment workPPIC Pollution prevention information clearinghousePSD Prevention of significant deteriorationRCRA Resource Conservation and Recovery ActRDF Refuse-derived fuelSARA Superfund Amendments and Reauthorization ActSCR Selective catalytic reductionSCS Stationary-container systemsSE Strength of the treated wasteSMART Save money and reduce toxicsSO Strength of the untreated wasteSS Suspended solidsTCC Total capital costTCP Traditional costing proceduresTGNMO Total gas nonmethane organicsTOC Total organic carbonTSA Total systems approachTSCA Toxic Substances Control ActTSD Treatment, storage, and disposalUASB Upflow anerobic sludge blanketVOC Volatile organic compoundVOST Volatile organic sampling trainVSS Volatile suspended solidsWRAP Waste reduction always paysWTE Waste-to-energy (systems)

List of Abbreviations

Abbreviation Definition Abbreviation Definition

GENERAL REFERENCES1. United States EPA, Pollution Prevention Fact Sheet, Washington, DC,

March 1991.2. Keoleian, G., and D. Menerey, “Sustainable Development by Design: Review

of Life Cycle Design and Related Approaches,” Air & Waste, 44, May 1994.3. Theodore, L. Personal notes.4. Dupont, R., L. Theodore, and K. Ganesan, Pollution Prevention: The Waste

Management Approach for the 21st Century, Lewis Publishers, 2000.5. World Wildlife Fund, Getting at the Source, 1991, p. 7.6. United States EPA, 1987 National Biennial RCRA Hazardous Waste

Report—Executive Summary, Washington, DC, GPO, 1991, p. 10.7. ASTM, Philadelphia, PA.8. Theodore, L., and R. Allen, Pollution Prevention: An ETS Theodore Tutor-

ial, Roanoke, VA, ETS International, Inc., 1993.9. United States EPA, The EPA Manual for Waste Minimization Opportunity

Assessments, Cincinnati, OH, August 1988.10. Santoleri, J., J. Reynolds, and L. Theodore, Introduction to Hazardous

Waste Incineration, 2d ed., Wiley, 2000.11. ICF Technology Incorporated, New York State Waste Reduction Guidance

Manual, Alexandria, VA, 1989.12. Details available from L. Theodore.13. Neveril, R. B., Capital and Operating Costs of Selected Air Pollution Control

Systems, EPA Report 450/5-80-002, Gard, Inc., Niles, IL, December 1978.14. Vatavuk, W. M., and R. B. Neveril, “Factors for Estimating Capital and

Operating Costs,” Chemical Engineering, November 3, 1980, pp. 157–162.15. Vogel, G. A., and E. J. Martin, “Hazardous Waste Incineration,” Chemical

Engineering, September 5, 1983, pp. 143–146 (part 1).16. Vogel, G. A., and E. J. Martin, “Hazardous Waste Incineration,” Chemical

Engineering, October 17, 1983, pp. 75–78 (part 2).17. Vogel, G. A., and E. J. Martin, “Estimating Capital Costs of Facility Com-

ponents,” Chemical Engineering, November 28, 1983, pp. 87–90.18. Ulrich, G. D., A Guide to Chemical Engineering Process Design and Eco-

nomics, Wiley-Interscience, New York, 1984.19. California Department of Health Services, Economic Implications of Waste

Reduction, Recycling, Treatment, and Disposal of Hazardous Wastes: TheFourth Biennial Report, California, 1988, p. 110.

20. Wilcox, J., and L. Theodore, Engineering and Environmental Ethics, Wiley,1998.

21. Varga, A., On Being Human, Paulist Press, New York, 1978.22. Theodore, L., “Dissolve the USEPA . . . Now,” Environmental Manager

(AWMA publication), vol. 1, November 1995.23. Theodore, L., and R. Kunz, Nanotechnology: Environmental Implications

and Solutions, Wiley, 2005.24. Yang, Y., and E. R. Allen, “Biofiltration Control of Hydrogen Sulfide. 2. Kinet-

ics, Biofilter Performance, and Maintenance,” JAWA, vol. 44, p. 1315.25. Mycock, J., and J. McKenna, Handbook of Air Pollution Control and Tech-

nology, ETS, Inc., chap. 21.26. Ottengraf, S. P. P., “Biological Systems for Waste Gas Elimination,” 1987.27. Hubert, F. L., “Consider Membrane Pervaporation,” Chemical Engineering

Progress, July 1992, p. 46.28. Caruana, Claudia M., “Membranes Vie for Pollution Cleanup Role,” Chem-

ical Engineering Progress, October 1993, p. 11.29. Winston, W. S., and Kamalesh K. Sirkar, Membrane Handbook, Van Nos-

trand Reinhold, NY, 1992, p. 78.30. Tabak et al., “Biodegradability Studies with Organic Priority Pollutant Com-

pounds,” USEPA, MERL, Cincinnati, Ohio, April 1980.31. Levin, M. A., and M. A. Gealt, Biotreatment of Industrial and Hazardous

Waste, McGraw-Hill Inc., 1993.32. Sutton, P. M., and P. N. Mishra, “Biological Fluidized Beds for Water and

Wastewater Treatment: A State-of-the-Art Review,” WPCF Conference,October 1990.

33. Envirex equipment bulletin FB. 200-R2 and private communication,Waukesha, WI, 1994.

34. Donavan, E. J., Jr., “Evaluation of Three Anaerobic Biological SystemsUsing Paper Mill Foul Condensate,” HydroQual, Inc., EPA, IERL contract68-03-3074.

35. Mueller, J. A., K. Subburama, and E. J. Donavan, Proc. 39th Ind. WasteConf., 599, Ann Arbor, 1984.

36. ASME Research Committee on Industrial and Municipal Waste—KeepingSociety’s Options Open—MWCs, A Case Study on Environmental Regulation.

37. Chartwell Information, EBI, Inc., San Diego, June 2004.38. Wilson, D. G. (ed.), Handbook of Solid Waste Management, Van Nostrand

Reinhold, New York, 1997.39. Wastes: Engineering Principles and Management Issues, McGraw-Hill,

New York, 1977.40. Montenay Montgomery LP, 2001.

In this section, a number of references are made to laws and proce-dures that have been formulated in the United States with respect towaste management. An engineer handling waste-management prob-lems in another country would well be advised to know the specificlaws and regulations of that country. Nevertheless, the treatmentgiven here is believed to be useful as a general guide.

MULTIMEDIA APPROACH TO ENVIRONMENTAL REGULATIONS IN THE UNITED STATES

Among the most complex problems to be faced by industry during the1990s is the proper control and use of the natural environment. In the1970s the engineering profession became acutely aware of its respon-sibility to society, particularly for the protection of public health andwelfare. The decade saw the formation and rapid growth of the U.S.Environmental Protection Agency (EPA) and the passage of federaland state laws governing virtually every aspect of the environment.The end of the decade, however, brought a realization that only themore simplistic problems had been addressed. A limited number of

large sources had removed substantial percentages of a few readilydefinable air pollutants from their emissions. The incremental costs toimprove the removal percentages would be significant and wouldinvolve increasing numbers of smaller sources, and the health hazardsof a host of additional toxic pollutants remained to be quantified andcontrol techniques developed.

Moreover, in the 1970s, air, water, and waste were treated as sepa-rate problem areas to be governed by their own statutes and regula-tions. Toward the latter part of the decade, however, it becameobvious that environmental problems were closely interwoven andshould be treated in concert. The traditional type of regulation—command and control—had severely restricted compliance options.

The 1980s began with EPA efforts redirected to take advantageof the case-specific knowledge, technical expertise, and imaginationof those being regulated. Providing plant engineers with an incen-tive to find more efficient ways of abating pollution would greatlystimulate innovation in control technology. This is a principal objec-tive, for example, of EPA’s “controlled trading” air pollution pro-gram, established in the Offsets Policy Interpretative Ruling issuedby the EPA in 1976, with statutory foundation given by the CleanAir Act Amendments of 1977. The Clean Air Act Amendments of

INTRODUCTION TO WASTE MANAGEMENT AND REGULATORY OVERVIEW

22-4

1990 expanded the program even more to the control of sulfuroxides under Title IV. In effect, a commodities market on “cleanair” was developed.

The rapidly expanding body of federal regulation presents an awe-some challenge to traditional practices of corporate decision-making,management, and long-range planning. Those responsible for newplants must take stock of the emerging requirements and construct afresh approach.

The full impact of the Clean Air Act Amendments of 1990, theClean Water Act, the Safe Drinking Water Act, the Resource Conser-vation and Recovery Act, the Comprehensive Environmental Respon-sibility, Compensation and Liability (Superfund) Act, and the ToxicSubstances Control Act is still not generally appreciated. The combi-nation of all these requirements, sometimes imposing conflictingdemands or establishing differing time schedules, makes the task ofobtaining all regulatory approvals extremely complex.

One of the dominant impacts of environmental regulations is thatthe lead time required for the planning and construction of newplants is substantially increased. When new plants generate majorenvironmental complexities, the implications can be profound. Ofcourse, the exact extent of additions to lead time will vary widely fromone case to another, depending on which permit requirements applyand on what difficulties are encountered. For major expansions inany field of heavy industry, however, the delay resulting from federalrequirements could conceivably add 2 to 3 years to total lead time.Moreover, there is always the possibility that regulatory approval willbe denied. So, contingency plans for fulfilling production needs mustbe developed.

The 1990s saw the emergence of environmental management sys-tems (EMSs) across the globe including the ISO 14001 environmentalmanagement system and the European Union’s Eco-Management andAudit Scheme (EMAS). Any EMS is a continual cycle of planning,implementing, reviewing, and improving the processes and actions thatan organization undertakes to meet its business and environmentalgoals. EMSs are built on the “Plan, Do, Check, Act” model (Fig. 22-1)that leads to continual improvement. Planning includes identifyingenvironmental aspects and establishing goals (plan); implementingincludes training and operational controls (do); checking includes mon-itoring and corrective action (check); and reviewing includes progressreview and acting to make needed changes to the EMS (act). Organiza-tions that have implemented an EMS often require all their suppliers tobecome EMS-certified as environmental programs become part ofeveryday business.

Any company planning a major expansion must concentrate on envi-ronmental factors from the outset. Since many environmental approvalsrequire a public hearing, the views of local elected officials and the com-munity at large are extremely important. To an unprecedented degree,the political acceptability of a project can now be crucial.

PLANT STRATEGIES

At the plant level, a number of things can be done to minimize theimpact of environmental quality requirements. These include:

1. Maintaining an accurate source-emission inventory2. Continually evaluating process operations to identify potential

modifications that might reduce or eliminate environmental impacts3. Ensuring that good housekeeping and strong preventive-

maintenance programs exist and are followed4. Investigating available and emerging pollution-control technologies5. Keeping well informed of the regulations and the directions in

which they are moving6. Working closely with the appropriate regulatory agencies and

maintaining open communications to discuss the effects that new reg-ulations may have

7. Keeping the public informed through a good public-relationsprogram

8. Implementing an EMSIt is unrealistic to expect that at any point in the foreseeable future

Congress will reverse direction, reduce the effect of regulatory con-trols, or reestablish the preexisting legal situation in which privatecompanies are free to construct major industrial facilities with little orno restraint by federal regulation.

CORPORATE STRATEGIC PLANNING

Contingency planning represents an essential component of soundenvironmental planning for a new plant. The environmental uncer-tainties surrounding a large capital project should be specified andrelated to other contingencies (such as marketing, competitive reac-tions, politics, foreign trade, etc.) and mapped out in the overall cor-porate strategy.

Environmental factors should also be incorporated into a com-pany’s technical or research and development program. Since theplanning horizons for new projects may now extend to 5 to 10years, R&D programs can be designed for specific projects. Thesemay include new process modifications or end-of-pipe controltechnologies.

Another clear need is to integrate environmental factors intofinancial planning for major projects. It must be recognized thatstrategic environmental planning is as important to the long-rangegoal of the corporation as is financial planning. Trade-off decisionsregarding financing may have to change as the project goes throughsuccessive stages of environmental planning and permit negotia-tions. For example, requirements for the use of more expensive pol-lution control technology may significantly increase total projectcosts; or a change from end-of-pipe to process modification tech-nology may preclude the use of industrial revenue bond financingunder Internal Revenue Service (IRS) rules. Regulatory delays canaffect assumptions as to both the rate of expenditure and inflationfactors. Investment, production, environmental, and legal factorsare all interrelated and can have a major impact on corporate cashflow.

Most companies must learn to deal more creatively with local offi-cials and public opinion. The social responsibility of companies canbecome an extremely important issue. Companies should applythoughtfulness and skill to the timing and conduct of public hearings.Management must recognize that local officials have views and con-stituencies that go beyond attracting new jobs.

From all these factors, it is clear that the approval and constructionof major new industrial plants or expansions is a far more complicatedoperation than it has been in the past, even the recent past. Stringentenvironmental restrictions are likely to preclude construction of cer-tain facilities at locations where they otherwise might have been built.In other cases, acquisition of required approvals may generate aheated technical and political debate that can drag out the regulatoryprocess for several years.

In many instances, new requirements may be imposed while a com-pany is seeking approval for a proposed new plant. Thus, companiesintending to expand their basic production facilities should anticipatetheir needs far in advance, begin preparation to meet the regulatorychallenge they will eventually confront, and select sites with carefulconsideration of environmental attributes. It is the objective of thissection to assist the engineer in meeting this environmental regulatorychallenge.

INTRODUCTION TO WASTE MANAGEMENT AND REGULATORY OVERVIEW 22-5

PLAN

DO

CHECK

ACT

FIG. 22-1 “Plan, Do, Check, Act” model.

UNITED STATES AIR QUALITY LEGISLATION AND REGULATIONS

Although considerable federal legislation dealing with air pollutionhas been enacted since the 1950s, the basic statutory framework nowin effect was established by the Clean Air Act of 1970; amended in1974 to deal with energy-related issues; amended in 1977, when anumber of amendments containing particularly important provisionsassociated with the approval of new industrial plants were adopted;and amended in 1990 to address toxic air pollutants and ozone nonat-tainment areas.

Clean Air Act of 1970 The Clean Air Act of 1970 was foundedon the concept of attaining National Ambient Air Quality Standards(NAAQS). Data were accumulated and analyzed to establish the qual-ity of the air, identify sources of pollution, determine how pollutantsdisperse and interact in the ambient air, and define reductions andcontrols necessary to achieve air-quality objectives.

EPA promulgated the basic set of current ambient air-quality stan-dards in April 1971. The specific regulated pollutants were particu-lates, sulfur dioxide, photochemical oxidants, hydrocarbons, carbonmonoxide, and nitrogen oxides. In 1978, lead was added. Table 22-1enumerates the present standards.

To provide basic geographic units for the air-pollution control pro-gram, the United States was divided into 247 air quality controlregions (AQCRs). By a standard rollback approach, the total quantityof pollution in a region was estimated, the quantity of pollution thatcould be tolerated without exceeding standards was then calculated,and the degree of reduction called for was determined. States wererequired by EPA to develop state implementation plans (SIPs) toachieve compliance.

The act also directed EPA to set new source performance standards(NSPS) for specific industrial categories. New plants were required touse the best system of emission reduction available. EPA graduallyissued these standards, which now cover a number of basic industrialcategories (as listed in Table 22-2). The 1977 amendments to theClean Air Act directed EPA to accelerate the NSPS program andincluded a regulatory program to prevent significant deterioration inthose areas of the country where the NAAQS were being attained.

Finally, Sec. 112 of the Clean Air Act required that EPA promul-gate National Emission Standards for Hazardous Air Pollutants

(NESHAPs). Between 1970 and 1989, standards were promulgatedfor asbestos, beryllium, mercury, vinyl chloride, benzene, arsenic,radionuclides, and coke-oven emissions.

Prevention of Significant Deterioration (PSD) Of all the fed-eral laws placing environmental controls on industry (and, in particu-lar, on new plants), perhaps the most confusing and restrictive are thelimits imposed for the prevention of significant deterioration (PSD) ofair quality. These limits apply to areas of the country that are alreadycleaner than required by ambient air-quality standards. This regula-tory framework evolved from judicial and administrative action underthe 1970 Clean Air Act and subsequently was given full statutory foun-dation by the 1977 Clean Air Act Amendments.

EPA established an area classification scheme to be applied in allsuch regions. The basic idea was to allow a moderate amount of indus-trial development but not enough to degrade air quality to a point atwhich it barely complied with standards. In addition, states were todesignate certain areas where pristine air quality was especially desir-able. All air-quality areas were categorized as Class I, Class II, or ClassIII. Class I areas were pristine areas subject to the tightest control.Permanently designated Class I areas included international parks,national wilderness areas, memorial parks exceeding 5000 acres, andnational parks exceeding 6000 acres. Although the nature of theseareas is such that industrial projects would not be located within them,their Class I status could affect projects in neighboring areas wheremeteorological conditions might result in the transport of emissionsinto them. Class II areas were areas of moderate industrial growth.Class III areas were areas of major industrialization. Under EPA reg-ulations promulgated in December 1974, all areas were initially cate-gorized as Class II. States were authorized to reclassify specified areasas Class I or Class III.

The EPA regulations also established another critical conceptknown as the increment. This was the numerical definition of theamount of additional pollution that may be allowed through the com-bined effects of all new growth in a particular locality (see Table 22-3).To assure that the increments would not be used up hastily, EPA spec-ified that each major new plant must install best available controltechnology (BACT) to limit emissions. BACT is determined based ona case-by-case engineering analysis and is more stringent than NSPS.

To implement these controls, EPA requires that every new sourceundergo preconstruction review. The regulations prohibited a company


TABLE 22-1 National Ambient Air Quality Standards

Pollutant Primary stds. Averaging times Secondary stds.

Carbon monoxide 9 ppm (10 mg/m3) 8-ha None35 ppm (40 mg/m3) 1-ha None

Lead 1.5 µg/m3 Quarterly average Same as primaryNitrogen dioxide 0.053 ppm (100 µg/m3) Annual (arithmetic mean) Same as primaryParticulate matter (PM10) 50 µg/m3 Annualb (arithmetic mean) Same as primary

150 µg/m3 24-ha

Particulate matter (PM2.5) 15.0 µg/m3 Annualc (arithmetic mean) Same as primary65 µg/m3 24-hd

Ozone 0.08 ppm 8-he Same as primary0.12 ppm 1-hf Same as primary

Sulfur oxides 0.03 ppm Annual (arithmetic mean) —0.14 ppm 24-ha —

— 3-ha 0.5 ppm (1300 µg/m3)aNot to be exceeded more than once per year.bTo attain this standard, the expected annual arithmetic mean PM10 concentration at each monitor within an area must not

exceed 50 µg/m3.cTo attain this standard, the 3-year average of the annual arithmetic mean PM2.5 concentrations from single or multiple com-

munity-oriented monitors must not exceed 15.0 µg/m3.dTo attain this standard, the 3-year average of the 98th percentile of 24-h concentrations at each population-oriented mon-

itor within an area must not exceed 65 µg/m3.eTo attain this standard, the 3-year average of the fourth-highest daily maximum 8-h average ozone concentrations measured

at each monitor within an area over each year must not exceed 0.08 ppm.f(1) The standard is attained when the expected number of days per calendar year with maximum hourly average concen-

trations above 0.12 ppm is ≤ 1.(2) The 1-h NAAQS will no longer apply to an area 1 year after the effective date of the designation of that area for the 8-h

ozone NAAQS. The effective designation date for most areas is June 15, 2004. [40 CFR 50.9; see Federal Register of April 30,2004 (69 FR 23996)].


TABLE 22-2 New Source Performance Standards (NSPS) from 40 CFR Part 60 as of June 2004

40 CFR 60 NSPS

Subpart C Emission Guidelines and Compliance TimesSubpart Ca (Reserved)Subpart Cb Emissions Guidelines and Compliance Times for Large Municipal Waste Combustors That Are Constructed

On or Before September 20, 1994Subpart Cc Emission Guidelines and Compliance Times for Municipal Solid Waste LandfillsSubpart Cd Emission Guidelines and Compliance Times for Sulfuric Acid Production UnitsSubpart Ce Emission Guidelines and Compliance Times for Hospital/Medical/Infectious Waste IncineratorsSubpart D Standards of Performance for Fossil-Fuel-Fired Steam Generators for Which Construction is Commenced

After August 17, 1971Subpart Da Standards of Performance for Electric Utility Steam Generating Units for Which Construction Is

Commenced After September 18, 1978Subpart Db Standards of Performance for Industrial-Commercial-Institutional Steam Generating UnitsSubpart Dc Standards of Performance for Small Industrial-Commercial-Institutional Steam Generating UnitsSubpart E Standards of Performance for IncineratorsSubpart Ea Standards of Performance for Municipal Waste Combustors for which Construction is Commenced after

December 20, 1989 and on or before September 20, 1994Subpart Eb Standards of Performance for Large Municipal Waste Combustors for Which Construction is Commenced

after September 20, 1994 or for which Modification of Reconstruction is Commenced after June 19, 1996Subpart Ec Standards of Performance for Hospital/Medical/Infectious Waste Incinerators for which Construction Is

Commenced after June 20, 1996Subpart F Standards of Performance for Portland Cement PlantsSubpart G Standards of Performance for Nitric Acid PlantsSubpart H Standards of Performance for Sulfuric Acid PlantsSubpart I Standards of Performance for Hot Mix Asphalt FacilitiesSubpart J Standards of Performance for Petroleum RefineriesSubpart K Standards of Performance for Storage Vessels for Petroleum Liquids Constructed After June 11, 1973 and

Prior to May 19, 1978Subpart Ka Standards of Performance for Storage Vessels for Petroleum Liquids for Which Construction, Reconstruction,

or Modification Commenced After May 18, 1978, and Prior to July 23, 1984Subpart Kb Standards of Performance for Volatile Organic Liquid Storage Vessels (Including Petroleum Liquid Storage

Vessels) for Which Construction, Reconstruction, or Modification Commenced after July 23, 1984Subpart L Standards of Performance for Secondary Lead SmeltersSubpart M Standards of Performance for Secondary Brass and Bronze Production PlantsSubpart N Standards of Performance for Primary Emissions from Basic Oxygen Process Furnaces for Which

Construction Is Commenced After June 11, 1973Subpart Na Standards of Performance for Secondary Emissions From Basic Oxygen Process Steelmaking Facilities for

Which Construction Is Commenced After January 20, 1983Subpart O Standards of Performance for Sewage Treatment PlantsSubpart P Standards of Performance for Primary Copper SmeltersSubpart Q Standards of Performance for Primary Zinc SmeltersSubpart R Standards of Performance for Primary Lead SmeltersSubpart S Standards of Performance for Primary Aluminum Reduction PlantsSubpart T Standards of Performance for the Phosphate Fertilizer Industry: Wet-Process Phosphoric Acid PlantsSubpart U Standards of Performance for the Phosphate Fertilizer Industry: Superphosphoric Acid PlantsSubpart V Standards of Performance for the Phosphate Fertilizer Industry: Diammonium Phosphate PlantsSubpart W Standards of Performance for the Phosphate Fertilizer Industry: Triple Superphosphate PlantsSubpart X Standards of Performance for the Phosphate Fertilizer Industry: Granular Triple Superphosphate Storage

FacilitiesSubpart Y Standards of Performance for Coal Preparation PlantsSubpart Z Standards of Performance for Ferroalloy Production FacilitiesSubpart AA Standards of Performance for Steel Plants: Electric Arc Furnaces Constructed After October 21, 1974, and

On or Before August 17, 1983 Subpart AAa Standards of Performance for Steel Plants: Electric Arc Furnaces and Argon-Oxygen Decarburization Vessels

Constructed After August 17, 1983 Subpart BB Standards of Performance for Kraft Pulp Mills Subpart CC Standards of Performance for Glass Manufacturing Plants Subpart DD Standards of Performance for Grain Elevators Subpart EE Standards of Performance for Surface Coating of Metal Furniture Subpart FF (Reserved) Subpart GG Standards of Performance for Stationary Gas Turbines Subpart HH Standards of Performance for Lime Manufacturing Plants Subpart KK Standards of Performance for Lead-Acid Battery Manufacturing Plants Subpart LL Standards of Performance for Metallic Mineral Processing Plants Subpart MM Standards of Performance for Automobile and Light Duty Truck Surface Coating Operations Subpart NN Standards of Performance for Phosphate Rock Plants Subpart PP Standards of Performance for Ammonium Sulfate Manufacture Subpart QQ Standards of Performance for the Graphic Arts Industry: Publication Rotogravure Printing Subpart RR Standards of Performance for Pressure Sensitive Tape and Label Surface Coating Operations Subpart SS Standards of Performance for Industrial Surface Coating: Large Appliances Subpart TT Standards of Performance for Metal Coil Surface Coating Subpart UU Standards of Performance for Asphalt Processing and Asphalt Roofing Manufacture Subpart VV Standards of Performance for Equipment Leaks of VOC in the Synthetic Organic Chemicals

Manufacturing Industry Subpart WW Standards of Performance for the Beverage Can Surface Coating Industry Subpart XX Standards of Performance for Bulk Gasoline Terminals Subpart AAA Standards of Performance for New Residential Wood Heaters


NAAQS. Continuous monitoring is also required for other CAA pol-lutants for which the EPA or the state determines that monitoring isnecessary. The EPA or the state may exempt any CAA pollutant fromthese monitoring requirements if the maximum air-quality impact ofthe emissions increase is less than the values in Table 22-6 or ifpresent concentrations of the pollutant in the area that the newsource would affect are less than the Table 22-6 values. The EPA orthe state may accept representative existing monitoring data col-lected within 3 years of the permit application to satisfy monitoringrequirements.

EPA regulations provide exemption from BACT and ambient air-impact analysis if the modification that would increase emissions isaccompanied by other changes within the plant that would net a zeroincrease in total emissions. This exemption is referred to as the “nonet increase” exemption.

A full PSD review would include a case-by-case determination ofthe controls required by BACT, an ambient air-impact analysis todetermine whether the source might violate applicable increments orair-quality standards; an assessment of the effect on visibility, soils, andvegetation; submission of monitoring data; and full public review.

Nonattainment (NA) Those areas of the United States failingto attain compliance with ambient air-quality standards are consid-ered nonattainment areas. New plants could be constructed innonattainment areas only if stringent conditions are met. Emissionshave to be controlled to the greatest degree possible, and more thanequivalent offsetting emission reductions have to be obtained fromother sources to assure progress toward achievement of the ambientair-quality standards. Specifically, (1) the new source must beequipped with pollution controls to assure lowest achievable emis-sion rate (LAER), which in no case can be less stringent than anyapplicable NSPS; (2) all existing sources owned by an applicant inthe same region must be in compliance with applicable state imple-mentation plan requirements or be under an approved schedule or

from commencing construction on a new source until the review hadbeen completed and provided that, as part of the review procedure,public notice should be given and an opportunity provided for a pub-lic hearing on any disputed questions.

Sources Subject to Prevention of Significant Deterioration(PSD) Sources subject to PSD regulations (40 CFR, Sec. 52.21) aremajor stationary sources and major modifications located in attainmentareas and unclassified areas. A major stationary source was defined asany source listed in Table 22-4 with the potential to emit 100 tons peryear or more of any pollutant regulated under the Clean Air Act(CAA) or any other source with the potential to emit 250 tons per yearor more of any CAA pollutant. The “potential to emit” is defined asthe maximum capacity to emit the pollutant under applicable emis-sion standards and permit conditions (after application of any air pol-lution control equipment) excluding secondary emissions. A “majormodification” is defined as any physical or operational change of amajor stationary source producing a “significant net emissionsincrease” of any CAA pollutant (see Table 22-5).

Ambient monitoring is required of all CAA pollutants with emis-sions greater than or equal to Table 22-5 values for which there are

TABLE 22-3 PSD Air Quality Increments (/m3)

Class I area Class II area Class III area

Sulfur dioxideAnnual 2 20 4024-h 5 91 1823-h 25 512 700

PM10

Annual 4 17 3424-h 8 30 60

Nitrogen dioxideAnnual 2.5 25 50

TABLE 22-2 New Source Performance Standards (NSPS) from 40 CFR Part 60 as of June 2004 (Concluded )

40 CFR 60 NSPS

Subpart BBB Standards of Performance for the Rubber Tire Manufacturing Industry Subpart CCC (Reserved) Subpart DDD Standards of Performance for Volatile Organic Compound (VOC) Emissions from the Polymer

Manufacturing Industry Subpart EEE (Reserved) Subpart FFF Standards of Performance for Flexible Vinyl and Urethane Coating and Printing Subpart GGG Standards of Performance for Equipment Leaks of VOC in Petroleum Refineries Subpart HHH Standards of Performance for Synthetic Fiber Production Facilities Subpart III Standards of Performance for Volatile Organic Compound Emissions From the Synthetic Organic Chemical

Manufacturing Industry (SOCMI) Air Oxidation Unit Processes Subpart JJJ Standards of Performance for Petroleum Dry Cleaners Subpart KKK Standards of Performance for Equipment Leaks of VOC From Onshore Natural Gas Processing Plants Subpart LLL Standards of Performance for Onshore Natural Gas Processing: SO(2) Emissions Subpart MMM (Reserved) Subpart NNN Standards of Performance for Volatile Organic Compound Emissions from Synthetic Organic Chemical

Manufacturing Industry Distillation Operations Subpart OOO Standards of Performance for Nonmetallic Mineral Processing Plants Subpart PPP Standard of Performance for Wool Fiberglass Insulation Manufacturing Plants Subpart QQQ Standards of Performance for VOC Emissions From Petroleum Refinery Wastewater Systems Subpart RRR Standards of Performance for Volatile Organic Compound Emissions From Synthetic Organic Chemical

Manufacturing Industry (SOCMI) Reactor Processes Subpart SSS Standards of Performance for Magnetic Tape Coating Facilities Subpart TTT Standards of Performance for Industrial Surface Coating: Coating of Plastic Parts for Business Machines Subpart UUU Standards of Performance for Calciners and Dryers in Mineral Industries Subpart VVV Standards of Performance for Polymeric Coating of Supporting Substrates Facilities Subpart WWW Standards of Performance for Municipal Solid Waste Landfills Subpart AAAA Standards of Performance for Small Municipal Waste Combustion Units for Which Construction Is

Commenced After August 30, 1999 or for Which Modification or Reconstruction Is Commenced After June 6, 2001

Subpart BBBB Emission Guidelines and Compliance Times for Small Municipal Waste Combustion Units Constructed On or Before August 30, 1999

Subpart CCCC Standards of Performance for Commercial and Industrial Solid Waste Incineration Units for Which Construction Is Commenced After November 30, 1999 or for Which Modification or Reconstruction Is Commenced on or After June 1 , 2001

Subpart DDDD Emissions Guidelines and Compliance Times for Commercial and Industrial Solid Waste Incineration Units that Commenced Construction On or Before November 30, 1999


an enforcement order to achieve such compliance; (3) the applicantmust have sufficient offsets to more than make up for the emissionsto be generated by the new source (after application of LAER); and(4) the emission offsets must provide “a positive net air quality ben-efit in the affected area.”

LAER was deliberately a technology-forcing standard of control.The statute stated that LAER must reflect (1) the most stringentemission limitation contained in the implementation plan of anystate for such category of sources unless the applicant can demon-strate that such a limitation is not achievable, or (2) the most strin-gent limitation achievable in practice within the industrial category,whichever is more stringent. In no event could LAER be less strin-gent than any applicable NSPS. While the statutory language defin-ing BACT directed that “energy, environmental, and economicimpacts and other costs” be taken into account, the comparableprovision on LAER provided no instruction that economics be con-sidered.

For existing sources emitting pollutants for which the area is nonat-tainment, reasonable available control technology (RACT) would berequired. EPA defines RACT by industrial category.

Minor Source Preconstruction Permits Commonly after theapplication of air pollution controls the emissions associated with newfacilities or modifications of existing facilities will be less than theemissions thresholds necessary to trigger PSD or nonattainment newsource review. In such instances, a minor source preconstruction per-mit is required from the state permitting authority and new sourceperformance standards (NSPS) apply.

Controlled-Trading Program The legislation enacted underthe Clean Air Act Amendments of 1977 provided the foundation forEPA’s controlled-trading program, the essential elements of whichinclude:• No-net-increase provisions of PSD• Offsets policy (under nonattainment)• Banking and brokerage (under nonattainment)

While these different policies vary broadly in form, their objectiveis essentially the same: to substitute flexible economic-incentive sys-tems for the current rigid, technology-based regulations that specifyexactly how companies must comply. These market mechanisms havemade regulating easier for EPA and less burdensome and costly forindustry.

PSD No-Net-Increase Provisions Under the PSD program, theaffected source is the entire plant. This source definition allows acompany to determine the most cost-effective means to control pollu-tion any time a plant is modified. Emission increases associated with anew process or production line may be compensated for by emissionincreases at other parts of the plant. As long as the entire site net emis-sions increase is maintained below the levels identified in Table 22-5,a PSD review is not required.

Offsets Policy Offsets were EPA’s first application of the conceptthat one source could meet its environmental protection obligationsby getting another source to assume additional control actions. Innonattainment areas, pollution from a proposed new source, even onethat controls its emissions to the lowest possible level, would aggravateexisting violations of ambient air-quality standards and trigger thestatutory prohibition. The offsets policy provided these new sourceswith an alternative. The source could proceed with construction plans,provided that:

1. The source would control emissions to the lowest achievablelevel.

2. Other sources owned by the applicant were in compliance or onan approved compliance schedule.

3. Existing sources were persuaded to reduce emissions by anamount at least equal to the pollution that the new source would add.

Banking and Brokerage Policy EPA’s banking policy is aimedat providing companies with incentives to find more offsets. Underthe original offset policy, a firm shutting down or modifying a facilitycould apply the reduction in emissions to new construction elsewherein the region only if the changes were made simultaneously. However,with banking a company can “deposit” the reduction for later use orsale. Such a policy will clearly establish that clean air (or the right touse it) has direct economic value.

Clean Air Act of 1990 In November 1990, Congress adoptedthe Clean Air Act Amendments of 1990, providing substantial

TABLE 22-4 Sources Subject to PSD Regulation If TheirPotential to Emit Equals or Exceeds 100 Tons per Year

Fossil-fuel-fired steam electric plants of more than 250 million Btu/h heatinput

Coal-cleaning plants (with thermal dryers)Kraft-pulp millsPortland-cement plantsPrimary zinc smeltersIron and steel mill plantsPrimary aluminum-ore-reduction plantsPrimary copper smeltersMunicipal incinerators capable of charging more than 250 tons of refuse per dayHydrofluoric, sulfuric, and nitric acid plantsPetroleum refineriesLime plantsPhosphate-rock-processing plantsCoke-oven batteriesSulfur-recovery plantsCarbon-black plants (furnace process)Primary lead smeltersFuel-conversion plantsSintering plantsSecondary metal-production plantsChemical-process plantsFossil-fuel boilers (or combinations thereof) totaling more than 250 millionBtu/h heat input

Petroleum-storage and -transfer units with total storage capacity exceeding300,000 bbl

Taconite-ore-processing plantsGlass-fiber-processing plantsCharcoal-production plants

TABLE 22-5 Significant Net Emissions Increase

Pollutant Tons/yr

PM10 15SO2 40NOx 40VOC 40CO 100Lead 0.6PM 25Fluorides 3Sulfuric acid mist 7Hydrogen sulfide 10Total reduced sulfur 10Municipal waste combustorAcid gases 40Metals 15Organics 3.5 × 10−6

CFCs (11, 12, 113, 114 & 115) Any increaseHalons (1211, 1301, 2402) Any increaseAny emissions increase resulting in a >1 µ/m3

24-h impact in a Class I area

TABLE 22-6 Concentration Impacts below Which AmbientMonitoring May Not Be Required

µg/m3 Average time

CO 575 8-h maximumNO2 14 AnnualPM10 10 24-h maximumSO2 13 24-h maximumLead 0.1 3-monthFluorides 0.25 24-h maximumTotal reduced sulfur 10 1-h maximumH2S 0.2 1-h maximumReduced-sulfur compounds 10 1-h maximum


changes to many aspects of the existing CAAA. The concepts ofNAAQS, NSPS, and PSD remain virtually unchanged. However, sig-nificant changes have occurred in several areas that directly affectindustrial facilities and electric utilities and air-pollution control atthese facilities. These include changes and additions in the followingmajor areas:

Title I Nonattainment areasTitle III Hazardous air pollutantsTitle IV Acid deposition controlTitle V Operating permitsTitle VI Stratospheric ozone protectionTitle I: Nonattainment Areas The existing regulations for

nonattainment areas were made more stringent in several areas. TheCAAA of 1990 requires the development of comprehensive emissioninventory-tracking for all nonattainment areas and establishes a classi-fication scheme that defined nonattainment areas into levels of sever-ity. For example, ozone nonattainment areas were designated asmarginal, moderate, serious, severe (two levels), and extreme, withcompliance deadlines of 3, 6, 9, 15–17, and 20 years, respectively, witheach classification having more stringent requirements regardingstrategies for compliance (see Table 22-7). Volatile organic compound(VOC) emissions reductions of 15 percent were required in moderateareas by 1996 and 3 percent a year thereafter for severe or extremeareas until compliance was achieved. In addition, the definition of amajor source of ozone precursors (previously 100 tons per year ofNOx, CO, or VOC emissions) was redefined to as little as 10 tons peryear in the extreme classification, with increased offset requirementsof 1.5 to 1 for new and modified sources. In 2004, EPA adopted a new8-h ozone ambient air quality standard. Ultimately the 8-h standardwill replace the 1-h standard although both standards apply during aseveral year transition period. The new standard adopted the sameregulatory approach as previously existed for the 1-h standard. Newextended deadlines for compliance are being adopted based on thesame marginal to extreme area approach previously described withthe new deadlines identified in Table 22-8. These requirements placemajor constraints on affected industries in these nonattainment areas.A similar approach is being taken in PM10 and CO nonattainmentareas.

Title III: Hazardous Air Pollutants The Title III provisions onhazardous air pollutants (HAPs) represent a major departure from theprevious approach of developing NESHAPs. While only eight HAPswere designated in the 20 years since enactment of the CAAA of 1970,the new CAAA of 1990 designated 189 pollutants as HAPs requiringregulation. The state allows EPA to list additional HAPs or to delistany HAP. As of 2004 there were 188 HAPs identified in Table 22-9.Major sources are defined as any source (new or existing) that emits(after control) 10 tons a year or more of any regulated HAP or 25 tonsa year or more of any combination of HAPs. A major source of HAPsmust comply with emissions standards known as MACT standardsthat EPA has been adopting since 1992. Table 22-10 provides a list ofMACT standards as of 2004 that affect all named existing and newmajor HAP sources. If a proposed new source is not of a type identi-fied in Table 22-10, then the new source must undergo a case-by-caseMACT evaluation to identify the appropriate level of control which isgenerally the most stringent achieved in practice.

For existing sources, MACT is defined as a stringency equivalent tothe average of the best 12 percent of the sources in the category. For

new sources, MACT is defined as the best controlled system. Newsources are required to meet MACT immediately, while existingsources have three years from the date of promulgation of the appro-priate MACT standard.

Title IV: Acid Deposition Control The Acid Deposition Con-trol Program is designed to reduce emissions of SO2 in the UnitedStates by 10 million tons per year, resulting in a net yearly emission of8.9 million tons by the year 2000. Phase I of the program requires 111existing uncontrolled coal-fired power plants (≥ 100 MW) to reduceemissions to 2.5 pounds of SO2 per 106 Btu by 1995 (1997 if scrubbersare used to reduce emissions by at least 90 percent). The reduction isto be accomplished by issuing all affected units emission “allowances”equivalent to what their annual average SO2 emissions would havebeen in the years 1985–1987 based on 2.5 pounds SO2 per 106 Btucoal. The regulations represent a significant departure from previousregulations where specified SO2 removal efficiencies were mandated;rather, the utilities will be allowed the flexibility of choosing whichstrategies will be used (e.g., coal washing, low-sulfur coal, flue gasdesulfurization, etc.) and which units will be controlled, as long as theoverall “allowances” are not exceeded. Any excess reduction in SO2 bya utility will create “banked” emissions that can be sold or used atanother unit.

Phase II of Title IV limits the majority of plants ≥ 20 MW and allplants ≥ 75 MW to maximum emissions of 1.2 pounds of SO2 per 106

Btu after the year 2000. In general, new plants would have to acquirebanked emission allowances in order to be built. Emission allowanceswill be traded through a combination of sell/purchase with other util-ities, EPA auctions and direct sales.

Control of NOx under the CAAA of 1990 will be accomplishedthrough the issuance of a revised NSPS in 1994, with the objective ofreducing emissions by 2 million tons a year from 1980 emission levels.The technology being considered is the use of low-NOx burners(LNBs). The new emission standards will not apply to cyclone and wetbottom boilers, unless alternative technologies are found, as thesecannot be retrofitted with existing LNB technologies.

Title V: Operating Permits Title V of the 1990 Clean Air ActAmendments established a new operating permit program to beadministered by state agencies in accordance with federal guidelines.The program basically requires a source to obtain a permit that covers

TABLE 22-7 Ozone Nonattainment Area Classifications and Associated Requirements

One-hour ozone Major sourceNonattainment concentration threshold level, Offset ratio for

area classification design value, ppm Attainment date tons VOCs/yr new/modified sources

Marginal 0.121–0.138 Nov. 15, 1993 100 1.1 to 1Moderate 0.138–0.160 Nov. 15, 1996 100 1.15 to 1Serious 0.160–0.180 Nov. 15, 1999 50 1.2 to 1Severe 0.180–0.190 Nov. 15, 2005 25 1.3 to 1

0.190–0.280 Nov. 15, 2007 25 1.3 to 1Extreme 0.280 and up Nov. 15, 2010 10 1.5 to 1

TABLE 22-8 The 8-h Ozone NAAQS Classifications andAttainment Dates*

8-h ozone concentration,Area classification† ppm Attainment date†

Marginal 0.081–0.092 2007Moderate 0.092–0.107 2010Serious 0.107–0.120 2013Severe-15 0.120–0.127 2019Severe-17 0.127–0.187 2021Extreme 0.187 and up 2024

*Areas newly designated as nonattainment under the 8-h standard whichwere never previously nonattainment must comply with the standard within 5years of being designated nonattainment or generally in 2009.

†These classifications and attainment dates apply to areas previously designatednonattainment under the 1-h ozone NAAQS.


CAS no. HAP

75070 Acetaldehyde60355 Acetamide75058 Acetonitrile98862 Acetophenone53963 Acetylaminofluorene107028 Acrolein79061 Acrylamide79107 Acrylic acid107131 Acrylonitrile107051 Allyl chloride92671 4-Aminobiphenyl62533 Aniline90040 o-Anisidine1332214 Asbestos71432 Benzene (including benzene from gasoline)92875 Benzidine98077 Benzotrichloride100447 Benzyl chloride92524 Biphenyl117817 Bis(2-ethylhexyl)phthalate (DEHP)54288 Bis(chloromethyl)ether75252 Bromoform106990 1,3-Butadiene156627 Calcium cyanamide133062 Captan63252 Carbaryl75150 Carbon disulfide56235 Carbon tetrachloride463581 Carbonyl sulfide120809 Catechol133904 Chloramben57749 Chlordane7782505 Chlorine79118 Chloroacetic acid532274 2-Chloroacetophenone108907 Chlorobenzene510156 Chlorobenzilate67663 Chloroform107302 Chloromethyl methyl ether126998 Chloroprene1319773 Cresols/Cresylic acid (isomers and mixture)95487 o-Cresol108394 m-Cresol106445 p-Cresol98828 Cumene94757 2,4-D, salts and esters3547044 DDE334883 Diazomethane132649 Dibenzofurans96128 1,2-Dibromo-3-chloropropane84742 Dibutylphthalate106467 1,4-Dichlorobenzene(p)91941 3,3-Dichlorobenzidene111444 Dichloroethyl ether (Bis (2-chloroethyl)ether)76448 Heptachlor118741 Hexachlorobenzene87683 Hexachlorobutadiene77474 Hexachlorocyclopentadiene67721 Hexachloroethane822060 Hexamethylene-1,6-diisocyanate680319 Hexamethylphosphoramide110543 Hexane302012 Hydrazine7647010 Hydrochloric acid7664393 Hydrogen fluoride (Hydrofluoric acid)123319 Hydroquinone78591 Isophorone58899 Lindane (all isomers)108316 Maleic anhydride67561 Methanol72435 Methoxychlor74839 Methyl bromide (Bromomethane)74873 Methyl chloride (Chloromethane)71556 Methyl chloroform (1,1,1-Trichloroethane)78933 Methyl ethyl ketone (2-Butanone)60344 Methyl hydrazine74884 Methly iodide (lodomethane)

CAS no. HAP

108101 Methyl isobutyl ketone (Hexone)624839 Methyl isocyanate80626 Methyl methacrylate1634044 Methyl tert butyl ether101144 4,4-Methyiene bis(2-chloroaniline)75092 Methylene chloride (Dichloromethane)101688 Methylene diphenyl diisocyanate (MDI)101779 4,4-Methylenedianiline91203 Naphthalene98953 Nitrobenzene92933 4-Nitrobiphenyl100027 4-Nitrophenol79469 2-Nitropropane684935 N-Nitroso-N-methylurea62759 N-Nitrosodimethylamine59892 N-Nitrosomorpholine56382 Parathion82688 Pentachloronitrobenzene (Quintobenzene)87865 Pentachlorophenol108952 Phenol106503 p-Phenylenediamine75445 Phosgene7803512 Phosphine7723140 Phosphorus85449 Phthalic anhydride1336363 Polychlorinated biphenyls (Aroclors)1120714 1,3-Propane sultone57578 beta-Propiolactone123386 Propionaldehyde114261 Propoxur (Baygon)78875 Propylene dichloride (1,2-Dichloropropane)542756 1,3-Dichloropropene62737 Dichlorvos111422 Diethanolamine121697 N,N-Diethyl aniline (N,N-Dimethylaniline)64675 Diethyl sulfate119904 3,3-Dimethoxybenzidine60117 Dimethyl aminoazobenzene119937 3,3′-Dimethyl benzidine79447 Dimethyl carbamoyl chloride68122 Dimethyl formamide57147 1,1-Dimethyl hydrazine131113 Dimethyl phthalate77781 Dimethyl sulfate534521 4,6-Dinitro-o-cresol, and salts51285 2,4-Dinitrophenol121142 2,4-Dinitrotoluene123911 1,4-Dioxane (1,4-Diethyleneoxide)122667 1,2-Diphenylhydrazine106898 Epichlorohydrin (I-Chloro-2,3-epoxypropane)106887 1,2-Epoxybutane140885 Ethyl acrylate100414 Ethyl benzene51796 Ethyl carbamate (Urethane)75003 Ethyl chloride (Chloroethane)106934 Ethylene dibromide (Dibromoethane)107062 Ethylene dichloride (1,2-Dichloroethane)107211 Ethylene glycol151564 Ethylene imine (Aziridine)75218 Ethylene oxide96457 Ethylene thiourea75343 Ethylidene dichloride (1,1-Dichloroethane)50000 Formaldehyde75569 Propylene oxide75558 1,2-Propylenimine (2-Methyl aziridine)91225 Quinoline106514 Quinone100425 Styrene96093 Styrene oxide1746016 2,3,7,8-Tetrachlorodibenzo-p-dioxin79345 1,1,2,2-Tetrachloroethane127184 Tetrachloroethylene (Perchloroethylene)7550450 Titanium tetrachloride108883 Toluene95807 2,4-Toluene diamine584849 2,4-Toluene diisocyanate95534 o-Toluidine

TABLE 22-9 Regulated Hazardous Air Pollutants (HAPs) from 40 CFR Part 63 as of June 2004

affected equipment, and detailed records must be maintained. Table22-11 identifies common ODS compounds.

Regulatory Direction The current direction of regulations andair-pollution control efforts is clearly toward significantly reducing theemissions to the environment of a broad range of compounds, including:

1. Volatile organic compounds and other ozone precursors (COand NOx)

2. Hazardous air pollutants, including carcinogenic organic emis-sions and heavy metal emissions

3. Acid rain precursors, including SOx and NOx

In addition, the PM2.5 NAAQS will continue to place emphasis on quan-tifying and reducing particulate emissions in the less than 2.5 µm parti-cle-size range. Particle size-specific emission factors have beendeveloped for many sources, and size-specific emission standards havebeen developed in a number of states. These standards are addressingconcerns related to nitrates and suitable condesates in the atmosphere.

Although it is not possible to predict the future, it is possible to pre-pare for it and influence it. It is highly recommended that maximumflexibility be designed into new air-pollution control systems to allowfor increasingly more stringent emission standards for both particu-lates and gases. Further, it is everyone’s responsibility to provide athorough review of existing and proposed new processes and to makeevery attempt to identify economical process modifications and/ormaterial substitutions that reduce or, in some cases, eliminate boththe emissions to the environment and the overdependency on retro-fitted or new end-of-pipe control systems.

UNITED STATES WATER QUALITY LEGISLATION AND REGULATIONS

Federal Water Pollution Control Act In 1948, the originalFederal Water Pollution Control Act (FWPCA) was passed. This actand its various amendments are often referred to as the Clean WaterAct (CWA). It provided loans for treatment plant construction andtemporary authority for federal control of interstate water pollution.The enforcement powers were so heavily dependent on the states as tomake the act almost unworkable. In 1956, several amendments to theFWPCA were passed that made federal enforcement procedures lesscumbersome. The provision for state consent was removed by amend-ments passed in 1961, which also extended federal authority to includenavigable waters in the United States.


each and every requirement applicable to the source under the CleanAir Act. A major impact of the Title V program is that sources arerequired to implement measures to demonstrate routinely that theyare operating in compliance with permit terms. This represents a dra-matic shift from previous practices where, to bring an enforcementaction, regulatory authorities were required to demonstrate that asource was in noncompliance.

Initially, all “major” sources of air pollution are required to obtainan operating permit. However, any state permitting authority mayextend the applicability of the operating permit to minor sources aswell. Once a source is subject to the permit program as a major sourcefor any one pollutant, emissions of every regulated air pollutant mustbe addressed in the permit application.

The operating permit must outline specifically how and when asource will be allowed to operate over the five-year term of the permit.The permit the state develops from an application becomes the prin-cipal mechanism for enforcement of all air-quality regulations. Assuch, it is critically important to submit an application that allows max-imum operating flexibility.

Sources must also include in their permit applications monitoringprotocols sufficient to document compliance with each permit termand condition.

The Title V operating permit requires the submission of at least fivetypes of reports:

1. The initial compliance report2. The annual compliance certification3. Monitoring reports submitted at least every six months4. Progress reports for sources not in compliance when the appli-

cation is submitted5. Prompt reports on any deviations from the permit termsPermit fees are a mandatory element of the Title V program. In

most cases, fees are assessed for emissions on a dollars-per-ton-emitted basis.

Title VI: Stratospheric Ozone Protection Title VI of the 1990Clean Air Act Amendments established a program to implement theprovisions of the Montreal Protocol, a worldwide agreement to reducethe use and emission of ozone-depleting substances. EPA’s regulationsadopted in response to Title VI outline a series of requirements forfacilities that use equipment containing ODS compounds. Facilitiesmust be certain that they handle and manage ODS compounds as pre-scribed in the rules. Only certified technicians and staff may maintain

CAS no. HAP

8001352 Toxaphene (chlorinated camphene)120821 1,2,4-Trichlorobenzene79005 1,1,2-Trichloroethane79016 Trichloroethylene95954 2,4,5-Trichlorophenol88062 2,4,6-Trichlorophenol121448 Triethylamine1582098 Trifluralin540841 2,2,4-Trimethylpentane108054 Vinyl acetate593602 Vinyl bromide75014 Vinyl chloride75354 Vinylidene chloride (1,1-Dichloroethylene)1330207 Xylenes (isomers and mixture)95476 o-Xylenes108383 m-Xylenes106423 p-Xylenes

CAS no. HAP

— Antimony compounds— Arsenic compounds (inorganic including arsine)— Beryllium compounds— Cadmium compounds— Chromium compounds— Cobalt compounds— Coke oven emissions— Cyanide compounds1

— Glycol ethers2

— Lead compounds— Manganese compounds— Mercury compounds— Fine mineral fibers3

— Nickel compounds— Polycylic organic matter4

— Radionuclides (including radon)5

— Selenium compounds

TABLE 22-9 Regulated Hazardous Air Pollutants (HAPs) from 40 CFR Part 63 as of June 2004 (Concluded)

NOTE: For all listings above which contain the word “compounds” and for glycol ethers, the following applies: Unless otherwise specified, these listings are definedas including any unique chemical substance that contains the named chemical (i.e., antimony, arsenic, etc.) as part of that chemical’s infrastructure.

1X′CN where X = H′ or any other group where a formal dissociation may occur, for example, KCN or Ca (CN)2.2Includes mono- and di-ethers of ethylene glycol, diethylene glycol, and triethylene glycol R-(OCH2CH2)n-OR′ where n = 1, 2, or 3; R = alkyl or aryl groups; R′ =

R, H, or groups which, when removed, yield glycol ethers with the structure R-(OCH2CH)n-OH. Polymers are excluded from the glycol category. 3Includes mineral fiber emissions from facilities manufacturing or processing glass, rock, or slag fibers (or other mineral derived fibers) of average diameter 1

micrometer or less.4Includes organic compounds with more than one benzene ring, and which have a boiling point greater than or equal to 100°C.5A type of atom which spontaneously undergoes radioactive decay.


40 CFR 63 MACT Standard

Subpart F National Emission Standards for Organic Haz-ardous Air Pollutants from the Synthetic OrganicChemical Manufacturing Industry

Subpart G National Emission Standards for Organic HazardousAir Pollutants From Synthetic Organic ChemicalManufacturing Industry Process Vents, StorageVessels, Transfer Operations, and Wastewater

Subpart H National Emission Standards for Organic Haz-ardous Air Pollutants for Equipment Leaks

Subpart I National Emission Standards for Organic HazardousAir Pollutants for Certain Processes Subject to theNegotiated Regulation for Equipment Leaks

Subpart J National Emission Standards for Organic Haz-ardous Air Pollutants for Polyvinyl Chloride andCopolymers Production

Subpart K (Reserved)Subpart L National Emission Standards for Coke Oven BatteriesSubpart M National Perchloroethylene Air Emission Stan-

dards for Dry Cleaning FacilitiesSubpart N National Emission Standards for Chromium Emis-

sions from Hard and Decorative ChromiumElectroplating and Chromium Anodizing Tanks

Subpart O Ethylene Oxide Emissions Standards for Steriliza-tion Facilities

Subpart Q National Emission Standards for Hazardous AirPollutants for Industrial Process Cooling Towers

Subpart R National Emission Standards for Gasoline Distrib-ution Facilities (Bulk Gasoline Terminals andPipeline Breakout Stations)

Subpart S National Emission Standards for Hazardous AirPollutants from the Pulp and Paper Industry

Subpart T National Emission Standards for HalogenatedSolvent Cleaning

Subpart U National Emission Standards for Hazardous Air Pol-lutant Emissions: Group I Polymers and Resins

Subpart W National Emission Standards for Hazardous AirPollutants for Epoxy Resins Production and Non-Nylon Polyamides Production

Subpart X National Emission Standards for Hazardous AirPollutants From Secondary Lead Smelting

Subpart Y National Emission Standards for Marine Tank Ves-sel Tank Loading Operations

Subpart AA National Emission Standards for Hazardous AirPollutants From Phosphoric Acid ManufacturingPlants

Subpart BB National Emission Standards for Hazardous AirPollutants From Phosphate Fertilizers ProductionPlants

Subpart CC National Emission Standards for Hazardous AirPollutants From Petroleum Refineries

Subpart DD National Emission Standards for Hazardous AirPollutants from Off-Site Waste and RecoveryOperations

Subpart EE National Emission Standards for Magnetic TapeManufacturing Operations

Subpart GG National Emission Standards for Aerospace Manu-facturing and Rework Facilities

Subpart HH National Emission Standards for Hazardous AirPollutants From Oil and Natural Gas ProductionFacilities

Subpart II National Emission Standards for Shipbuilding andShip Repair (Surface Coating)

Subpart JJ National Emission Standards for Wood FurnitureManufacturing Operations

Subpart KK National Emission Standards for the Printing andPublishing Industry

Subpart LL National Emission Standards for Hazardous Air Pol-lutants for Primary Aluminum Reduction Plants

Subpart MM National Emission Standards for Hazardous AirPollutants for Chemical Recovery CombustionSource at Kraft, Soda, Sulfite, and Stand-AloneSemichemcial Pulp Mills

Subpart OO National Emission Standards for Tanks—Level 1Subpart PP National Emission Standards for ContainersSubpart QQ National Emission Standards for Surface

Impoundments


Subpart RR National Emission Standards for Individual DrainSystems

Subpart SS National Emission Standards for Closed VentSystems, Control Devices, Recovery Devices andRouting to a Fuel Gas System or a Process

Subpart TT National Emission Standards for EquipmentLeaks—Control Level 1

Subpart UU National Emission Standards for EquipmentLeaks—Control Level 2 Standards

Subpart VV National Emission Standards for Oil-Water Separa-tors and Organic-Water Separators

Subpart WW National Emission Standards for Storage Vessels(Tanks)—Control Level 2

Subpart XX National Emission Standards for Ethylene Manu-facturing Process Units: Heat Exchange Systemsand Waste Operations

Subpart YY National Emission Standards for Hazardous AirPollutants for Source Categories: Generic Maxi-mum Achievable Control Technology Standards

Subpart CCC National Emission Standards for Hazardous AirPollutants for Steel Pickling—HCI Process Facil-ities and Hydrochloric Acid Regeneration Plants

Subpart DDD National Emission Standards for Hazardous AirPollutants for Mineral Wool Production

Subpart EEE National Emission Standards for Hazardous AirPollutants From Hazardous Waste Combustors

Subpart GGG National Emission Standards for PharmaceuticalsProduction

Subpart HHH National Emission Standards for Hazardous AirPollutants From Natural Gas Transmission andStorage Facilities

Subpart III National Emission Standards for Hazardous Air Pol-lutants for Flexible Polyurethane Foam Production

Subpart JJJ National Emission Standards for Hazardous Air Pol-lutant Emissions: Group IV Polymers and Resins

Subpart LLL National Emission Standards for Hazardous AirPollutants From the Portland Cement Manufac-turing Industry

Subpart MMM National Emission Standards for Hazardous Air Pol-lutants for Pesticide Active Ingredient Production

Subpart NNN National Emission Standards for Hazardous AirPollutants for Wool Fiberglass Manufacturing

Subpart OOO National Emission Standards for Hazardous AirPollutant Emissions: Manufacture of Amino/Phe-nolic Resins

Subpart PPP National Emission Standards for Hazardous AirPollutant Emissions for Polyether Polyols Pro-duction

Subpart QQQ National Emission Standards for Hazardous AirPollutants for Primary Copper Smelting

Subpart RRR National Emission Standards for Hazardous AirPollutants for Secondary Aluminum Production

Subpart TTT National Emission Standards for Hazardous AirPollutants for Primary Lead Smelting

Subpart UUU National Emission Standards for Hazardous AirPollutants for Petroleum Refineries: CatalyticCracking Units, Catalytic Reforming Units, andSulfur Recovery Units

Subpart VVV National Emission Standards for Hazardous AirPollutants: Publicly Owned Treatment Works

Subpart XXX National Emission Standards for Hazardous AirPollutants for Ferroalloys Production: Ferroman-ganese and Silicomanganese

Subpart AAAA National Emission Standards for Hazardous AirPollutants: Municipal Solid Waste Landfills

Subpart CCCC National Emission Standards for Hazardous AirPollutants: Manufacturing of Nutritional Yeast

Subpart EEEE National Emission Standards for Hazardous AirPollutants: Organic Liquids Distribution (Non-Gasoline)

Subpart FFFF National Emission Standards for Hazardous AirPollutants: Miscellaneous Organic ChemicalManufacturing

Subpart GGGG National Emission Standards for Hazardous AirPollutants: Solvent Extraction for Vegetable OilProduction

TABLE 22-10 Maximum Achievable Control Technology (MACT) Standards from 40 CFR Part 63 as of June 2004


In 1965 the Water Quality Act established a new trend in water pollu-tion control. It provided that the states set water quality standards inaccordance with federal guidelines. If the states failed to do so, the fed-eral government, subject to a review hearing, would set the standards. In1966, the Clean Water Restoration Act transferred the Federal WaterPollution Control Administration from the Department of Health,Education, and Welfare to the Department of the Interior. It also gavethe Interior Department the responsibility for the Oil Pollution Act.

After the creation of EPA in 1970, the EPA was given the responsi-bility previously held by the Department of the Interior with respectto water pollution control. In subsequent amendments to the FWPCAin 1973, 1974, 1975, 1976, and 1977, additional federal programs wereestablished. The goals of these programs were to make waterways ofthe United States fishable and swimmable by 1983 and to achieve zerodischarge of pollutants by 1985. The National Pollutant DischargeElimination System (NPDES) was established as the basic regulatorymechanism for water pollution control. Under this program, the states

TABLE 22-10 Maximum Achievable Control Technology (MACT) Standards from 40 CFR Part 63 as of June 2004 (Concluded)

TABLE 22-11 Common ODS Compounds

Class I-CFCs Class II-HCFCs

CFC-11 HCFC-22CFC-12 HCFC-123CFC-13 HCFC-124CFC-111 HCFC-141CFC-112 HCFC-142CFC-113CFC-114CFC-115

Halons OthersHalon-1211 Carbon tetrachlorideHalon-1301 Methyl chloroformHalon-1202 Methyl bromide


Subpart HHHH National Emission Standards for Hazardous AirPollutants for Wet-Formed Fiberglass Mat Pro-duction

Subpart JJJJ National Emission Standards for Hazardous AirPollutants: Paper and Other Web Coating

Subpart KKKK National Emission Standards for Hazardous AirPollutants: Surface Coating of Metal Cans

Subpart MMMM National Emission Standards for Hazardous AirPollutants for Surface Coating of Miscellaneous

Subpart NNNN National Emission Standards for Hazardous AirPollutants: Surface Coating of Large Appliances

Subpart OOOO National Emission Standards for Hazardous AirPollutants: Printing, Coating, and Dyeing of Fab-rics and Other Textiles

Subpart QQQQ National Emission Standards for Hazardous AirPollutants: Surface Coating of Wood BuildingProducts

Subpart RRRR National Emission Standards for Hazardous AirPollutants: Surface Coating of Metal Furniture

Subpart SSSS National Emission Standards for Hazardous AirPollutants: Surface Coating of Metal Coil

Subpart TTTT National Emission Standards for Hazardous AirPollutants for Leather Finishing Operations

Subpart UUUU National Emission Standards for Hazardous AirPollutants for Cellulose Products Manufacturing

Subpart VVVV National Emission Standards for Hazardous AirPollutants for Boat Manufacturing

Subpart WWWW National Emission Standards for Hazardous Air Pol-lutants: Reinforced Plastic Composites Production

Subpart XXXX National Emission Standards for Hazardous AirPollutants: Rubber Tire Manufacturing

Subpart YYYY National Emission Standards for Hazardous AirPollutants for Stationary Combustion Turbines

Subpart AAAAA National Emission Standards for Hazardous AirPollutants for Lime Manufacturing Plants

Subpart BBBBB National Emission Standards for Hazardous AirPollutants for Semiconductor Manufacturing


Subpart CCCCC National Emission Standards for Hazardous AirPollutants for Coke Ovens: Pushing, Quenching,and Battery Stacks

Subpart FFFFF National Emission Standards for Hazardous AirPollutants for Integrated Iron and Steel Manufac-turing Facilities

Subpart GGGGG National Emission Standards for Hazardous AirPollutants: Site Remediation

Subpart HHHHH National Emission Standards for Hazardous AirPollutants: Miscellaneous Coating Manufacturing

Subpart IIIII National Emission Standards for Hazardous AirPollutants: Mercury Emissions from MercuryCell Chlor-Alkali Plants

Subpart JJJJJ National Emission Standards for Hazardous AirPollutants for Brick and Structural Clay ProductsManufacturing

Subpart KKKKK National Emission Standards for Hazardous AirPollutants for Clay Ceramics Manufacturing

Subpart LLLLL National Emission Standards for Hazardous AirPollutants: Asphalt Processing and Asphalt Roof-ing Manufacturing

Subpart MMMMM National Emission Standards for Hazardous AirPollutants: Flexible Polyurethane Foam Fabrica-tion Operations

Subpart NNNNN National Emission Standards for Hazardous AirPollutants: Hydrochloric Acid Production

Subpart PPPPP National Emission Standards for Hazardous AirPollutants for Engine Test Cells/Stands

Subpart QQQQQ National Emission Standards for Hazardous AirPollutants for Friction Materials ManufacturingFacilities

Subpart RRRRR National Emission Standards for Hazardous AirPollutants: Taconite Iron Ore Processing

Subpart SSSSS National Emission Standards for Hazardous AirPollutants for Refractory Products Manufacturing

Subpart TTTTT National Emission Standards for Hazardous AirPollutants for Primary Magnesium Refining

were given the authority to issue permits to “point-source” dischargersprovided the dischargers gave assurance that the following standardswould be met:

1. Source-specific effluent limitations [including new source perfor-mance standards (NSPS)]

2. Toxic pollutant regulations (for specific substances regardless ofsource)

3. Regulations applicable to oil and hazardous substance liabilityTo achieve that stated water quality goal of fishable and swimmable

waters by 1983, each state was required by EPA to adopt water qualitystandards that met or exceeded the federal water quality criteria. Aftereach state submitted its own water quality standards, which were sub-sequently approved by EPA, the federal criteria were removed fromthe Code of Federal Regulations. The state water quality standards areused as the basis for establishing both point-source-based effluent lim-itations and toxic pollutant limitations used in issuing NPDES permitsto point-source discharges.

Source-Based Effluent Limitations Under the FWPCA, EPAwas responsible for establishing point-source effluent limitations formunicipal dischargers, industrial dischargers, industrial users ofmunicipal treatment works, and effluent limitations for toxic sub-stances (applicable to all dischargers).

Standards promulgated or proposed by EPA under 40 CFR, Parts402 through 699, prescribe effluent limitation guidelines for existingsources, standards of performance for new sources, and pretreat-ment standards for new and existing sources. Effluent limitationsand new source performance standards apply to discharges madedirectly into receiving bodies of water. The new standards requirebest-available technology (BAT) and are to be used by the stateswhen issuing NPDES permits for all sources 18 months after EPAmakes them final. Pretreatment standards apply to waste streamsfrom industrial sources that are sent to publicly owned treatmentworks (POTW) for final treatment. These regulations are meant to

protect the POTW from any materials that would either harm thetreatment facility or pass through untreated. They are to beenforced primarily by the local POTW. These standards are applica-ble to particular classes of point sources and pertain to dischargesinto navigable waters without regard to the quality of the receivingwater. Standards are specific for numerous subcategories undereach point-source category.

Limitations based upon application of the best practicable controltechnology currently available (BPT) apply to existing point sourcesand should have been achieved by July 1, 1977. Limitations basedupon application of the BATEA (best-available technology economi-cally achievable) that will result in reasonable further progress towardelimination of discharges had to be achieved by July 1, 1984.

Clean Water Act of 1977 The 1977 Clean Water Act directedEPA to review all BAT guidelines for conventional pollutants in thoseindustries not already covered.

On August 23, 1978 (43 FR 37570), the EPA proposed a newapproach to the control of conventional pollutants by effluent guidelinelimitations. The new guidelines were known as best conventional (pol-lutants control) technology (BCT). These guidelines replaced theexisting BAT limitations, which were determined to be unreasonablefor certain categories of pollutants.

To determine if BCT limitations would be necessary, the cost-effec-tiveness of conventional pollutant reduction to BAT levels beyondBPT levels had to be determined and compared to the cost of removalof this same amount of pollutant by a publicly owned treatment worksof similar capacity. If it was equally cost-effective for the industry toachieve the reduction required for meeting the BAT limitations as thePOTW, then the BCT limit was made equal to the BAT level. Whenthis test was applied, the BAT limitations set for certain categorieswere found to be unreasonable. In these subcategories EPA proposedto remove the BAT limitations and revert to the BPT limitations untilBCT control levels could be formulated.

Control of Toxic Pollutants Since the early 1980s, EPA’swater quality standards guidance placed increasing importance ontoxic pollutant control. The agency urged states to adopt criteriainto their standards for priority toxic pollutants, particularly thosefor which EPA had published criteria guidance. EPA also providedguidance to help and support state adoption of toxic pollutant stan-dards with the Water Quality Standards Handbook (1983) and theTechnical Support Document for Water Quality Toxics Control(1985 and 1991).

Despite EPA’s urging and guidance, state response was disappoint-ing. A few states adopted large numbers of numeric toxic pollutant cri-teria, primarily for the protection of aquatic life. Most other statesadopted few or no water quality criteria for priority toxic pollutants.Some relied on “free from toxicity” criteria and “action levels” for toxicpollutants or occasionally calculated site-specific criteria. Few statesaddressed the protection of human health by adopting numerichuman health criteria.

State development of case-by-case effluent limits using proceduresthat did not rely on the statewide adoption of numeric criteria for thepriority toxic pollutants frustrated Congress. Congress perceived thatstates were failing to aggressively address toxics and that EPA was notusing its oversight role to push the states to move more quickly andcomprehensively. Many in Congress believed that these delays under-mined the effectiveness of the act’s framework.

1987 CWA Amendments In 1987, Congress, unwilling to tol-erate further delays, added Section 303(c)(2)(B) to the CWA. Thesection provided that whenever a state reviews water quality stan-dards or revises or adopts new standards, the state has to adopt cri-teria for all toxic pollutants listed pursuant to Section 307(a)(1) ofthe act for which criteria have been published under Section 304(a),discharge or presence of which in the affected waters could reason-ably be expected to interfere with those designated uses adopted bythe state, as necessary to support such designated uses. Such criteriahad to be specific numerical criteria for such toxic pollutants. Whennumerical criteria are not available, wherever a state reviews waterquality standards, or revises or adopts new standards, the state has toadopt criteria based on biological monitoring or assessment methodsconsistent with information published pursuant to Section 304(a)(8).

Nothing in this section was to be construed to limit or delay the useof effluent limitations or other permit conditions based on or involv-ing biological monitoring or assessment methods or previouslyadopted numerical criteria.

In response to this new congressional mandate, EPA redoubled itsefforts to promote and assist state adoption of numerical water qualitystandards for priority toxic pollutants. EPA’s efforts included thedevelopment and issuance of guidance to the states on acceptableimplementation procedures. EPA attempted to provide the maximumflexibility in its options that complied not only with the express statu-tory language but also with the ultimate congressional objective:prompt adoption of numeric toxic pollutant criteria. The agencybelieved that flexibility was important so that each state could complywith Section 303(c)(2)(B) within its resource constraints. EPA distrib-uted final guidance on December 12, 1988. This guidance was similarto earlier drafts available for review by the states. The availability ofthe guidance was published in the Federal Register on January 5,1989 (54 FR 346).

The structure of Section 303(c) is to require states to review theirwater quality standards at least once each 3-year period. Section303(c)(2)(B) instructs states to include reviews for toxics criteriawhenever they initiate a triennial review. EPA initially looked atFebruary 4, 1990, the 3-year anniversary of the 1987 CWA amend-ments, as a convenient point to index state compliance. The April17, 1990, Federal Register Notice (55 FR 14350) used this indexpoint for the preliminary assessment of state compliance. However,some states were very nearly completing their state administrativeprocesses for ongoing reviews when the 1987 amendments wereenacted and could not legally amend those proceedings to addressadditional toxics criteria. Therefore, in the interest of fairness, andto provide such states a full 13-year review period, EPA’s FY 1990Agency Operating Guidance provided that states should completeadoption of the numeric criteria to meet Section 303(c)(2)(B) bySeptember 30, 1990.

Section 303(c) does not provide penalties for states that do notcomplete timely water quality standard reviews. In no previous casehad an EPA Administrator found that state failure to complete areview within 3 years jeopardized the public health or welfare to suchan extent that promulgation of federal standards pursuant to Section303(c)(4)(8) was justified. However, the pre-1987 CWA never man-dated state adoption of priority toxic pollutants or other specific crite-ria. EPA relied on its water quality standards regulation (4O CFR131.11) and its criteria and program guidance to the states on appro-priate parametric coverage in state water quality standards, includingtoxic pollutants. With congressional concern exhibited in the legisla-tive history for the 1987 Amendments regarding undue delays bystates and EPA, and because states have been explicitly required toadopt numeric criteria for appropriate priority toxic pollutants since1983, the agency is proceeding to promulgate federal standards pur-suant to Section 303(c)(4)(B) of the CWA and 40 CFR 131.22(b).

States have made substantial recent progress in the adoption, andEPA approval, of toxic pollutant water quality standards. Further-more, virtually all states have at least proposed new toxics criteria forpriority toxic pollutants since Section 303(c)(2)(B) was added to theCWA in February 1987. Unfortunately, not all such state proposalsaddress, in a comprehensive manner, the requirements of Section303(c)(2)(B). For example, some states have proposed to adopt crite-ria to protect aquatic life, but not human health; other states have pro-posed human health criteria that do not address major exposurepathways (such as the combination of both fish consumption anddrinking water). In addition, in some cases final adoption of proposedstate toxics criteria that would be approved by EPA has been substan-tially delayed due to controversial and difficult issues associated withthe toxic pollutant criteria adoption process.

Biological Criteria While the overall mandate of the CleanWater Act may now be more clearly stated and understood, the toolsneeded are still under development, and their full application is beingworked out. The direction is toward a more comprehensive approachto water quality protection, which might be more appropriatelytermed water resource protection to encompass the living resourcesand their habitat along with the water itself.


In 1991, EPA directed states to adopt biological criteria into theirwater quality standards by September 30, 1993. To assist the states,EPA issued its “Policy on the Use of Biological Assessments and Cri-teria in the Water-Quality Program,” which sets forth the key policydirections governing the shift to the use of biological criteria:• “Biological surveys shall be fully integrated with toxicity and chemical-

specific assessment methods in state water-quality programs.”• “Biological surveys should be used together with whole-effluent

and ambient toxicity testing, and chemical-specific analyses toassess attainment/nonattainment of designated aquatic life uses instate water-quality standards.”

• “If any one of the three assessment methods demonstrate thatwater-quality standards are not attained, it is EPA’s policy thatappropriate action should be taken to achieve attainment, includinguse of regulatory authority” (the independent applicability policy).

• “States should designate aquatic life uses that appropriately addressbiological integrity and adopt biological criteria necessary to protectthose uses.”

These policy statements are founded on the existing language andauthorities in Clean Water Act Sections 303(c)(2)(A) and (B). EPAdefined biological criteria as “numerical values or narrative expres-sions used to describe the expected structure and function of theaquatic community.”

Most states currently conduct biological surveys. These consist ofthe collection and analysis of resident aquatic community data and asubsequent determination of the aquatic community’s structure andfunction. A limiting factor in the number of surveys conducted is sim-ply the funding to support field sampling. Most states also take theirsurvey data through the next level of analysis, which is a biologicalassessment, in which the biological condition of the water body is eval-uated. A state needs to conduct a biological assessment to justify des-ignated waters as having uses less than the Clean Water Act goal of“fishable/swimmable” [Sec. 101(a)(2)].

Implementing biological criteria requires that the state establishwhat the expected condition of a biological community should be.This expected condition (or reference condition) is based on mea-surements at either unimpacted sites or sites that are minimallyimpacted by human activities. A key element of developing and adopt-ing biological criteria is to develop a set of metrics (biological mea-surements) and indices (summations of those metrics) that aresensitive to reflecting the community changes that occur as a result ofhuman perturbation. Metrics may include measures of species rich-ness, percentages of species of a particular feeding type, and measuresof species abundance and condition. The development of metrics andindices has been a major technical advance that effectively broughtthe field to the point of implementing biological integrity measures.

Aside from the need for additional monitoring and data as a basis forbiological criteria, the largest impediment is currently related to thequestion of how or whether biological criteria should be translateddirectly to NPDES permit requirements. A strict reading of theNPDES regulations leads some individuals to conclude that every waterquality standard potentially affected by a discharge must have a specificeffluent limit. In the case of biological criteria, the direct translationisn’t always possible. The preferred approach is to use biological criteriaas a primary means to identify impaired waters that will then need addi-tional study. Appropriate discharge controls can then be applied.

The other area of contention in adopting biocriteria is the EPA pol-icy of independent applicability. This policy recognizes that chemical-specific criteria, toxicity testing (WET tests), and biological criteriaeach have unique as well as overlapping attributes, limitations, andprogram applications. No single approach is superior to another;rather, the approaches are complementary. When any one of theseapproaches indicates that water quality is impaired, appropriate regu-latory action is needed. Critics of this approach most frequently citebiological criteria as the superior, or determining, measure and woulduse it to override an exceedance of chemical-specific criteria.

EPA and many states are now moving toward a watershed or basinmanagement approach to water management. This is a holisticapproach that looks at the multiple stresses and activities that affect abasin and evaluates these effects in the context of the survival of eco-logical systems. Biological criteria are recognized by states as a necessary

tool for detecting impacts to important aquatic resources that wouldotherwise be missed, particularly those caused by non-point-sourceactivities, and for defining the desired endpoint of environmentalrestoration activities.

To assist states, EPA has issued programmatic guidance (BiologicalCriteria: National Program Guidance for Surface Waters, April 1990;Procedures for Initiating Narrative Biological Criteria, October1992). In addition, EPA will be issuing over the next couple of yearstechnical guidance specific to developing biological criteria forstreams and small rivers, lakes and reservoirs, estuaries, and wetlands.

Metal Bioavailability and Toxicity Another area of policy andregulatory change that bears directly on questions of biological integrityis the application of toxic metal water quality criteria. EPA is in the midstof reconsidering its approach to implementing toxic metals criteria. Thiswas prompted in part by the difficulty that some dischargers are havingin meeting the state ambient water quality criteria for metals, which gen-erally are expressed as total recoverable metals (a measurement thatincludes the metal dissolved in water plus metal that becomes dissolvedwhen the sample is treated with acid). At issue is whether the criteria canbe expressed in a form that more accurately addresses the toxicity of themetal to aquatic life, thereby providing the desired level of aquatic lifeprotection, while allowing greater leeway in the total amount of metaldischarged. This is a technically complex issue that will require long-term research even if short-term solutions are implemented.

The bioavailability, and hence the toxicity, of metal depends on thephysical and chemical form of the metal, which in turn depends on thechemical characteristics of the surrounding water. The dissolved formof the metal is generally viewed as more bioavailable and thereforemore toxic than the particulate form. Particulate matter and dissolvedorganic matter can bind the metal, making it less bioavailable. What isnot well known or documented is the various chemical transforma-tions that occur both within the effluent stream and when the effluentreaches and mixes with the receiving water. Metal that is not bioavail-able in the effluent may become bioavailable under ambient chemicalconditions.

The NPDES regulations (40 CFR 122.45) require effluent limits tobe expressed as total recoverable metal. This requirement makessense as a means to monitor and regulate both the total metal loadingand the effectiveness of wastewater treatment that involves chemicalprecipitation of the metal.

From the perspective of ecological integrity called for in the CleanWater Act, any adjustment to the implementation of toxic metals cri-teria needs to be integrated with both sediment criteria and biologicalcriteria to provide ecosystem protection envisioned by the act.

Total Maximum Daily Load (TMDL) Under Section 303(d) ofthe 1972 Clean Water Act, states, territories, and authorized tribeswere required to develop a list of impaired waters. The impairedwaters do not meet water quality standards that states, territories, andauthorized tribes have set for them, even after point sources of pollu-tion have installed the minimum required levels of pollution controltechnology. The law requires that these jurisdictions establish priorityrankings for waters on the lists and develop TMDLs for these waters.

This part of the Clean Water Act was relatively neglected until1996. A Federal Advisory Committee was convened and produced in1998 a report and subsequent proposed changes for implementationof the TMDL program and associated changes in the National Pollu-tant Discharge Elimination System for point sources. A number ofcourt orders were also motivating factors in the implementation andproposed changes to the rule.

The TMDL specifies the amount of a particular pollutant that maybe present in a water body, allocates allowable pollutant loads amongsources, and provides the basis for attaining or maintaining waterquality standards.

The TMDL regulations were issued as draft in 1999 and finallypublished on July 13, 2000.

Water Quality Trading Within the approach to TMDL rulesand subsequent management policy, the emphasis on Pollutant trad-ing or water quality trading has evolved. Trading allows sources withresponsibility for discharge reductions the flexibility to determinewhere reduction will occur. Within the trading approach, the economicadvantages are emphasized. This is driven by the TMDL or more



stringent water quality-based requirement in an NPDES permit andthe potential fact that discharge sources have significantly differentcosts to control the pollutant of concern.

In January 2003, EPA published the Water Quality Trading Policy.The policy outlines the trading objectives, requirements, and elementsof a trading program. While barriers exist to the implementation of aneffective water quality trading program, the cost of discharge qualitycompliance would warrant consideration of the approach.

Bioterrorism Act of 2003 While not directly related to waterquality regulations, the security and vulnerability of community drink-ing water systems were addressed in the Public Health Security andBioterrorism Preparedness and Response Act of 2002 (BioterrorismAct). The vulnerability assessments were intended to examine a facil-ity’s ability to defend against adversarial actions that might substan-tially disrupt the ability of a water system to provide a safe and reliablesupply of drinking water.

For community drinking water systems serving more than 3300persons, it was required to conduct a vulnerability assessment (VA),certify and submit a copy of the VA to the EPA Administrator, prepareor revise an emergency response plan based on the results of the VA,and within 6 months certify to the EPA Administrator that an emer-gency response plan has been completed or updated. The VA require-ment was to be completed by all facilities in June 2004.

Cooling Water Intake Regulation The EPA establishedrequirements for facilities with cooling water intake structure toimplement best-available technologies to minimize adverse environ-mental impacts. Under Section 316(b) of the CWA, the protection ofaquatic organisms from being killed or injured by impingement orentrainment was established. The rule was divided into three phases.Phase I was published in December 2001 and addressed new facili-ties. Phase II was published in July 2004. The Phase II rule addressedexisting electric generating plants that withdraw greater than 50 mil-lion gallons per day and use at least 25 percent of their withdrawnwater for cooling purposes only. Phase III was prepublished inNovember 2004. The Phase III rule addresses other electric generat-ing facilities and industrial sectors that withdraw water. It is antici-pated that Phase III will be published within 1 to 2 years.

The rule provides that the facility may choose one of five compli-ance alternatives for establishing best available technology for mini-mizing adverse environmental impact at the site. Under currentNPDES program regulations, the 316(b) requirements would occurwhen an existing NPDES permit was reissued or when an existingpermit was modified or revoked and reissued.

Water Reuse With increasing water sustainability and scarcityissues in the United States, the U.S. Environmental ProtectionAgency (EPA) and the U.S. Agency for International Development(USAID) are revising portions of the 1992 EPA Guidelines for WaterReuse to reflect significant technical advancements and institutionaldevelopments since 1992. The guidelines will also address new areas,including national reclaimed water use trends, endocrine disrupters,and approaches to integrated water resources management.

Across the world, reclaimed water is becoming a critical watersource, and reuse strategies are recognized in many U.S. states as anintegral part of water resources management. The original guidelines,published in 1980, gave many state agencies direction in establishingreuse permits and helped to foster state water reuse regulations. Therevised guidelines will include an updated inventory of state reuseregulations.

Regulatory Direction EPA and states are directed by the CleanWater Act to develop programs to meet the act’s stated objective: “torestore and maintain the chemical, physical, and biological integrity ofthe Nation’s waters” [Section 101 (a)]. Efforts to date have empha-sized “clean water” quite literally, by focusing on the chemical makeupof discharges and their compliance with chemical water quality stan-dards established for surface water bodies. These programs have suc-cessfully addressed many water pollution problems, but they are notsufficient to identify and address all of them. A continuing large gap inthe current regulatory scheme is the absence of a direct measure ofthe condition of the biological resources that we are intending to pro-tect (the biological integrity of the water body). Without such a mea-sure it will be difficult to determine whether our water management

approaches are successful in meeting the intent of the act. Takentogether, chemical, physical, and biological integrity is equivalent tothe ecological integrity of a water body. It is highly likely the futurewill see the interpretation of biological integrity and ecologicalintegrity, and the management of ecological systems, assume a muchmore prominent role in water quality management.

To ensure technically sound decision making, EPA should review itswater quality criteria at a minimum of every 10 years. EPA’s waterquality criteria consist of information regarding the concentrations ofchemicals or levels of parameters in water that protect aquatic life andhuman health, and act as regulatory thresholds for determination ofimpaired waters. Many of EPA’s current water quality criteria are out-dated, and have not been developed using consistent methodologies.

To the extent that EPA does pursue changes or additions to the cur-rent water quality standards program, it is critical that such modifica-tions not be simply added onto existing requirements as independentnew program elements. In pursuing any modifications EPA shouldcarefully examine opportunities for coordinating and streamliningrequirements within the context of the overall water quality standardsprogram to maximize efficiency in the face of substantial resourceconstraints.

UNITED STATES SOLID WASTE LEGISLATION AND REGULATIONS

Much of the current activity in the field of solid waste management,especially with respect to hazardous wastes and resources recovery, isa direct consequence of recent legislation. Therefore, it is importantto review the principal legislation that has affected the entire field ofsolid-waste management.

What follows is a brief review of existing legislation that affects themanagement of solid wastes. The actual legislation must be consultedfor specific detail. Implementation of the legislation is accomplishedthrough regulations adopted by federal, state, and local agencies.Because these regulations are revised continuously, they must bemonitored continuously, especially when design and constructionwork is to be undertaken.

Rivers and Harbors Act, 1899 Passed in 1899, the Rivers andHarbors Act directed the U.S. Army Corps of Engineers to regulatethe dumping of debris in navigable waters and adjacent lands.

Solid Waste Disposal Act, 1965 Modern solid-waste legislationdates from 1965, when the Solid Waste Disposal Act, Title II of Pub-lic Law 88-272, was enacted by Congress. The principal intent of thisact was to promote the demonstration, construction, and applicationof solid waste management and resource-recovery systems that pre-serve and enhance the quality of air, water, and land resources.

National Environmental Policy Act, 1969 The National Envi-ronmental Policy Act (NEPA) of 1969 was the first federal act thatrequired coordination of federal projects and their impacts with thenation’s resources. The act specified the creation of the Council onEnvironmental Quality in the Executive Office of the President. Thisbody has the authority to force every federal agency to submit to thecouncil an environmental impact statement on every activity or proj-ect which it may sponsor or over which it has jurisdiction.

Resource Recovery Act, 1970 The Solid Waste Disposal Act of1965 was amended by Public Law 95-512, the Resources RecoveryAct of 1970. This act directed that the emphasis of the national solid-waste-management program should be shifted from disposal as its pri-mary objective to that of recycling and reuse of recoverable materialsin solid wastes or the conversion of wastes to energy.

Resource Conservation and Recovery Act, 1976 RCRA is theprimary statute governing the regulation of solid and hazardous waste.It completely replaced the Solid Waste Disposal Act of 1965 and sup-plemented the Resource Recovery Act of 1970; RCRA itself was sub-stantially amended by the Hazardous and Solid Waste Amendments of1984 (HSWA). The principal objectives of RCRA as amended are to:• Promote the protection of human health and the environment from

potential adverse effects of improper solid and hazardous wastemanagement

• Conserve material and energy resources through waste recyclingand recovery

• Reduce or eliminate the generation of hazardous waste as expedi-tiously as possibleTo achieve these objectives, RCRA authorized EPA to regulate the

generation, treatment, storage, transportation, and disposal of haz-ardous wastes. The structure of the national hazardous waste regula-tory program envisioned by Congress is laid out in Subtitle C of RCRA(Sections 3001 through 3019), which authorized EPA to:• Promulgate standards governing hazardous waste generation and

management• Promulgate standards for permitting hazardous waste treatment,

storage, and disposal facilities• Inspect hazardous waste management facilities• Enforce RCRA standards• Authorize states to manage the RCRA Subtitle C program, in whole

or in part, within their respective borders, subject to EPA oversightFederal RCRA hazardous waste regulations are set forth in 40 CFR

Parts 260 through 279. The core of the RCRA regulations establishesthe “cradle to grave” hazardous waste regulatory program throughseven major sets of regulations:• Identification and listing of regulated hazardous wastes (Part 261)• Standards for generators of hazardous waste (Part 262)• Standards for transporters of hazardous waste (Part 263)• Standards for owners/operators of hazardous waste treatment, stor-

age, and disposal facilities (Parts 264, 265, and 267)• Standards for the management of specific hazardous wastes and

specific types of hazardous waste management facilities (Part 266)• Land disposal restriction standards (Part 268)• Requirements for the issuance of permits to hazardous waste facili-

ties (Part 270)• Approved state hazardous waste management programs (Part 272)• Standards for unusual waste management (Part 273)• Standards for management of used oil (Part 279)• Standards and procedures for authorizing state hazardous waste

programs to be operated in lieu of the federal program (Part 271)EPA, under Section 3006 of RCRA, may authorize a state to admin-

ister and enforce a state hazardous waste program in lieu of the federalSubtitle C program. To receive authorization, a state program must:• Be equivalent to the federal Subtitle C program• Be consistent with, and no less stringent than, the federal program

and other authorized state programs• Provide adequate enforcement of compliance with Subtitle C

requirementsToxic Substances Control Act, 1976 The two major goals of the

Toxic Substances Control Act (TSCA), passed by Congress in 1976, are(1) the acquisition of sufficient information to identify and evaluatepotential hazards from chemical substances and (2) the regulation of themanufacture, processing, distribution, use, and disposal of any substancethat presents an unreasonable risk of injury to health of the environment.

Under TSCA, the EPA has issued a ban on the manufacture, pro-cessing, and distribution of products containing PCBs. Exporting ofPCBs has also been banned. TSCA also required that PCB mixturescontaining more than 50 ppm PCBs must be disposed of in an accept-able incinerator or chemical waste landfill. All PCB containers orproducts containing PCBs had to be clearly marked and records main-tained by the operator of each facility handling at least 45 kilograms ofPCBs. These records include PCBs in use in transformers and capac-itors, PCBs in transformers and capacitors removed from service,PCBs stored for disposal, and a report on the ultimate disposal of thePCBs. Additionally, PCB transformers, must be registered, andrecords must be kept of hydraulic systems, natural gas pipeline sys-tems, voltage regulators, electromagnetic switches, and ballasts.

TSCA also placed restrictions on the use of chlorofluorocarbons,asbestos, and fully halogenated chlorofluoroalkanes such as aerosolpropellants.

Regulatory Direction There is no doubt that pollution preven-tion continues to be the regulatory direction. The development of newand more efficient processes and waste minimization technologies willbe essential to support this effort.

An area certain to receive regulatory attention in the future is nan-otechnology. The applications and implications of nanotechnology notonly are changing lives every day, but also are moving so fast that many


have not yet grasped their tremendous impact (Theodore, L., and R. Kunz, Nanotechnology: Environmental Implications and Solutions,Wiley, Hoboken, N.J., 2002). It is clear that nanotechnology will revo-lutionize the way industry operates, creating chemical processes andproducts that are more efficient and less expensive. A primary obstacleto achieving this goal will be the need to control, reduce, and ultimatelyeliminate the environmental and related problems associated with nan-otechnology, or dilemmas that may develop through its misuse.

Completely new legislation and regulatory rulemaking may be nec-essary for environmental control of nanotechnology. However, in themeantime, one may speculate on how the existing regulatory frame-work might be applied to the nanotechnolgy area as this emergingfield develops over the next several years.

Commercial applications of nanotechnology are likely to be regulatedunder the Toxic Substances Control Act (TSCA), which authorized EPAto review and establish limits on the manufacture, processing, distribu-tion, use, and/or disposal of new materials the EPA determines to pose“an unreasonable risk of injury to human health or the environment.”The term chemicals is defined broadly by TSCA. Unless qualifying foran exemption under the law [R&D (a statutory exemption requiring nofurther approval by EPA), low-volume production, low environmentalreleases along with low volume, or plans for limited test marketing], aprospective manufacturer is subject to the full-blown premanufacturenotice (PMN) procedure. This requires submittal of said notice, alongwith toxicity and other data to EPA at least 90 days before commencingproduction of the chemical substance. (Theodore, L., and R. Kunz,Nanotechnology: Environmental Implications and Solutions, Wiley,Hoboken, N.J., 2002).

Approval then involves recordkeeping, reporting, and otherrequirements under the statute. Requirements will differ, dependingon whether EPA determines that a particular application constitutes a“significant new use” or a “new chemical substance.” EPA can imposelimits on production, including an outright ban when it is deemednecessary for adequate protection against “an unreasonable risk ofinjury to health or the environment.” EPA may revisit a chemical’s sta-tus under TSCA and change the degree or type of regulation whennew health and environmental data warrant. EPA is expected to beissuing several new TSCA test rules in 2004 [Bergeson, L. L., “Expecta Busy Year at EPA,” Chem. Processing 17 (April 14, 2004)]. If theexperience with genetically engineered organisms is any indication,there will be a push for EPA to update regulations in the future toreflect changes, advances, and trends in nanotechnology [Bergeson,L. L., “Genetically Engineered Organisms Face Changing Regula-tions,” Chem. Processing (March 2004)].

Workplace exposure to chemical substances and the potential for pul-monary toxicity are subject to regulation by the Occupational Safety andHealth Administration under the Occupational Safety and Health Act(OSHA), including the requirement that potential hazards be disclosedon material safety data sheets (MSDS). (An interesting question arisesas to whether carbon nanotubes, chemically carbon but with differentproperties because of their small size and structure, are indeed to beconsidered the same as or different from carbon black for MSDS pur-poses.) Both government and private agencies can be expected todevelop the requisite threshold limit values (TLVs) for workplace expo-sure. Also, EPA may once again utilize TSCA to assert its own jurisdic-tion, appropriate or not, to minimize exposure in the workplace.

Wastes from a commercial-scale nanotechnology facility would betreated under the Resource Conservation and Recovery Act (RCRA),provided that they meet the criteria for RCRA waste. RCRA require-ments could be triggered by a listed manufacturing process or the act’sspecified hazardous waste characteristics. The type and extent of regu-lation would depend on how much hazardous waste is generated andwhether the wastes generated are treated, stored, or disposed of on-site.

Finally, opponents of nanotechnology, especially, may be able to usethe National Environmental Policy Act (NEPA) to impede nanotech-nology research funded by the U.S. government. A “major Federalaction significantly affecting the quality of the human environment” issubject to the environmental impact provision under NEPA. (Variousstates also have environmental impact assessment requirements thatcould delay or put a stop to construction of nanotechnology facilities.)Time will tell.

POLLUTION PREVENTION 22-19

This subsection is drawn in part from “Pollution Prevention Overview,”prepared by B. Wainwright and L. Theodore, copyright 1993.

FURTHER READING: American Society of Testing and Materials, StandardGuide for Industrial Source Reduction, draft copy dated June 16, 1992. AmericanSociety of Testing and Materials, Pollution Prevention, Reuse, Recycling and Envi-ronmental Efficiency, June, 1992. California Department of Health Services, Eco-nomic Implications of Waste Reduction, Recycling, Treatment, and Disposal ofHazardous Wastes: The Fourth Biennial Report, California, 1988. Citizen’s Clear-inghouse for Hazardous Waste, Reduction of Hazardous Waste: The Only SeriousManagement Option, Falls Church, CCHW, 1986. Congress of the United States.Office of Technology Assessment, Serious Reduction of Hazardous Waste: ForPollution Prevention and Industrial Efficiency, Washington, D.C., GPO, 1986.Dupont, R., L. Theodore, and K. Ganesan, Pollution Prevention: The Waste Man-agement Option for the 21st Century, Lewis Publishers, 2000. Friedlander, S.,“Pollution Prevention—Implications for Engineering Design, Research, andEducation,” Environment, May 1989, p. 10. Theodore, L., and R. Kunz, Nan-otechnology: Environmental Implications and Solutions, Wiley, 2005. Theodore,L. and R. Allen, Pollution Prevention: An ETS Theodore Tutorial, Roanoke, VA,ETS International, Inc., 1994. Theodore, L., A Citizen’s Guide to Pollution Pre-vention, East Williston, NY, 1993. United States EPA, Facility Pollution Preven-tion Guide. (EPA/600/R-92/088), Washington, D.C., May 1992. United StatesEPA, “Pollution Prevention Fact Sheets,” Washington, D.C., GPO, 1991. UnitedStates EPA, 1987 National Biennial RCRA Hazardous Waste Report—ExecutiveSummary, Washington, D.C., GPO, 1991. United States EPA, Office of PollutionPrevention, Report on the U.S. Environmental Protection Agency’s Pollution Pre-vention Program, Washington, D.C., GPO, 1991. Wilcox, J., and L. Theodore,Engineering and Environmental Ethics, Wiley, 1998. World Wildlife Fund, Get-ting at the Source—Executive Summary, 1991.

INTRODUCTION

The amount of waste generated in the United States has reached stag-gering proportions; according to the United States EnvironmentalProtection Agency (EPA), 250 million tons of solid waste alone aregenerated annually. Although both the Resource Conservation andRecovery Act (RCRA) and the Hazardous and Solid Waste Act(HSWA) encourage businesses to minimize the wastes they generate,the majority of the environmental protection efforts are still centeredaround treatment and pollution clean-up.

The passage of the Pollution Prevention Act of 1990 has redirectedindustry’s approach to environmental management; pollution preven-tion has now become the environmental option of the 21st century.Whereas typical waste-management strategies concentrate on “end-of-pipe” pollution control, pollution prevention attempts to handle wasteat the source (i.e., source reduction). As waste handling and disposalcosts increase, the application of pollution prevention measures isbecoming more attractive than ever before. Industry is currentlyexploring the advantages of multimedia waste reduction and develop-ing agendas to strengthen environmental design while lessening pro-duction costs.

There are profound opportunities for both industry and the indi-vidual to prevent the generation of waste; indeed, pollution preven-tion is today primarily stimulated by economics, legislation, liabilityconcerns, and the enhanced environmental benefit of managing wasteat the source. The Pollution Prevention Act of 1990 established pollu-tion prevention as a national policy, declaring that “waste should beprevented or reduced at the source wherever feasible, while pollutionthat cannot be prevented should be recycled in an environmentallysafe manner” (Ref. 1). The EPA’s policy establishes the following hier-archy of waste management:

1. Source reduction2. Recycling/reuse3. Treatment4. Ultimate disposalThe hierarchy’s categories are prioritized so as to promote the

examination of each individual alternative prior to the investigation ofsubsequent options (i.e., the most preferable alternative should bethoroughly evaluated before consideration is given to a less acceptedoption). Practices that decrease, avoid, or eliminate the generation of

waste are considered source reduction and can include the imple-mentation of procedures as simple and economical as good house-keeping. Recycling is the use, reuse, or reclamation of wastes and/ormaterials that may involve the incorporation of waste recovery tech-niques (e.g., distillation, filtration). Recycling can be performed at thefacility (i.e., on-site) or at an off-site reclamation facility. Treatmentinvolves the destruction or detoxification of wastes into nontoxic orless toxic materials by chemical, biological, or physical methods, orany combination of these control methods. Disposal has beenincluded in the hierarchy because it is recognized that residual wasteswill exist; the EPA’s so-called “ultimate disposal” options include land-filling, land farming, ocean dumping, and deep-well injection. How-ever, the term ultimate disposal is a misnomer, but is included herebecause of its earlier adaptation by the EPA.

Table 22-12 provides a rough timetable demonstrating the UnitedStates’ approach to waste management. Note how waste managementhas begun to shift from pollution control-driven activities to pollutionprevention activities.

The application of waste-management practices in the UnitedStates has recently moved toward securing a new pollution preven-tion ethic. The performance of pollution prevention assessments andtheir subsequent implementation will encourage increased activityinto methods that will further aid in the reduction of hazardouswastes. One of the most important and propitious consequences ofthe pollution-prevention movement will be the development of life-cycle design and standardized life-cycle cost-accounting proce-dures. These two consequences are briefly discussed in the twoparagraphs that follow. Additional information is provided in a latersubsection.

The key element of life-cycle design is Life-Cycle Assessment(LCA). LCA is generally envisioned as a process to evaluate the envi-ronmental burdens associated with the cradle-to-grave life cycle of aproduct, process, or activity. A product’s life cycle can be roughlydescribed in terms of the following stages:

1. Raw material2. Bulk material processing3. Production4. Manufacturing and assembly5. Use and service6. Retirement7. Disposal

Maintaining an objective process while spanning this life cycle can bedifficult given the varying perspective of groups affected by differentparts of that cycle. LCA typically does not include any direct or indi-rect monetary costs or impacts to individual companies or consumers.

Another fundamental goal of life-cycle design is to promote sus-tainable development at the global, regional, and local levels. Thereis significant evidence that suggests that current patterns of humanand industrial activity on a global scale are not following a sustainablepath. Changes to achieve a more sustainable system will require thatenvironmental issues be more effectively addressed in the future.Principles for achieving sustainable development should include(Ref. 2):

POLLUTION PREVENTION

TABLE 22-12 Waste Management Timetable

Prior to 1945 No control1945–1960 Little control1960–1970 Some control1970–1975 Greater control (EPA is founded)1975–1980 More sophisticated control1980–1985 Beginning of waste-reduction management1985–1990 Waste-reduction management1990–1995 Formal pollution prevention programs

(Pollution Prevention Act)1995–2000 Widespread acceptance of pollution

preventionAfter 2000 The sky’s the limit


1. Sustainable resource use (conserving resources, minimizingdepletion of nonrenewable resources, using sustainable practices formanaging renewable resources). There can be no product develop-ment or economic activity of any kind without available resources.Except for solar energy, the supply of resources is finite. Efficientdesigns conserve resources while also reducing impacts caused bymaterial extraction and related activities. Depletion of nonrenewableresources and overuse of otherwise renewable resources limits theiravailability to future generations.

2. Maintenance of ecosystem structure and function. This is aprincipal element of sustainability. Because it is difficult to imaginehow human health can be maintained in a degraded, unhealthy naturalworld, the issue of ecosystem health should be a more fundamentalconcern. Sustainability requires that the health of all diverse species aswell as their interrelated ecological functions be maintained. As onlyone species in a complex web of ecological interactions, humans cannotseparate their success from that of the total system.

3. Environmental justice. The issue of environmental justicehas come to mean different things to different people. Theodore(Ref. 3) has indicated that the subject of environmental justice con-tains four key elements that are interrelated: environmental racism,environmental health, environmental equity, and environmental pol-itics. (Unlike many environmentalists, Theodore has contended thatonly the last issue, politics, is a factor in environmental justice.) Amajor challenge in sustainable development is achieving both inter-generational and intersocietal environmental justice. Overconsum-ing resources and polluting the planet in such a way that it enjoinsfuture generations from access to reasonable comforts irresponsiblytransfer problems to the future in exchange for short-term gains.Beyond this intergenerational conflict, enormous inequities in thedistribution of resources continue to exist between developed andless developed countries. Inequities also occur within nationalboundaries.

Life cycle is a perspective that can consider the true costs of productproduction and/or services provided and utilized by analyzing the priceassociated with potential environmental degradation and energy con-sumption, as well as more customary costs like capital expenditure andoperating expenses. A host of economic and economic-related termshave appeared in the literature. Some of these include total cost assess-ment, life-cycle costing, and full-cost accounting. Unfortunately, theseterms have come to mean different things to different people at differ-ent times. In an attempt to remove this ambiguity, the following threeeconomic terms are defined below.

1. Traditional costing procedure (TCP). This accounting proce-dure only takes into account capital and operating (including environ-mental) costs.

2. Comprehensive costing procedure (CCP). The economic pro-cedure includes not only the traditional capital and operating costs butalso peripheral costs such as liability, regulatory related expenses, bor-rowing power, and social considerations.

3. Life-cycle costing (LCC). This type of analysis requires that allthe traditional costs of project or product system, from raw-materialacquisition to end-result product disposal, be considered.

The TCP approach is relatively simple and can be easily applied tostudies involving comparisons of different equipment, differentprocesses, or even parts of processes. CCP has now emerged as themost realistic approach that can be employed in economic projectanalyses. It is the recommended procedure for pollution-preventionstudies. The LCC approach is usually applied to the life-cycle analysis(LCA) of a product or service. It has found occasional application inproject analysis.

The remainder of this subsection on pollution prevention will beconcerned with providing the reader with the necessary background tounderstand the meaning of pollution prevention and its useful imple-mentation. Assessment procedures and the economic benefits derivedfrom managing pollution at the source are discussed along with meth-ods of cost accounting for pollution prevention. Additionally, regula-tory and nonregulatory methods to promote pollution prevention andovercome barriers are examined, and ethical considerations are pre-sented. By eliminating waste at the source, all can participate in theprotection of the environment by reducing the amount of waste mate-

Dec

reas

ing

pref

eren

ce

Source reduction

Recycling

Treatment

Ultimatedisposal

FIG. 22-2 Pollution prevention hierarchy.

rial that would otherwise need to be treated or ultimately disposed;accordingly, attention is also given to pollution prevention in both thedomestic and business office environments.

POLLUTION-PREVENTION HIERARCHY

As discussed in the Introduction, the hierarchy set forth by the EPA inthe Pollution Prevention Act establishes an order to which waste-management activities should be employed to reduce the quantity ofwaste generated. The preferred method is source reduction, as indi-cated in Fig. 22-2. This approach actually precedes traditional wastemanagement by addressing the source of the problem prior to itsoccurrence.

Although the EPA’s policy does not consider recycling or treatmentas actual pollution prevention methods per se, these methods presentan opportunity to reduce the amount of waste that might otherwise bedischarged into the environment. Clearly, the definition of pollutionprevention and its synonyms (e.g., waste minimization) must beunderstood to fully appreciate and apply these techniques.

Waste minimization generally considers all of the methods in theEPA hierarchy (except for disposal) appropriate to reduce the volumeor quantity of waste requiring disposal (e.g., source reduction). The def-inition of source reduction as applied in the Pollution Prevention Act,however, is “any practice that reduces the amount of any hazardous sub-stance, pollutant, or contaminant entering any waste stream or other-wise released into the environment . . . prior to recycling, treatment ordisposal” (Ref. 1). Source reduction reduces the amount of waste gen-erated; it is therefore considered true pollution prevention and has thehighest priority in the EPA hierarchy.

Recycling (or reuse) refers to the use (or reuse) of materials thatwould otherwise be disposed of or treated as a waste product. A goodexample is a rechargeable battery. Wastes that cannot be directlyreused may often be recovered on-site through methods such as dis-tillation. When on-site recovery or reuse is not feasible due to qualityspecifications or the inability to perform recovery on-site, off-siterecovery at a permitted commercial recovery facility is often a possi-bility. Such management techniques are considered secondary tosource reduction and should only be used when pollution cannot beprevented.

The treatment of waste is the third element of the hierarchy andshould be utilized only in the absence of feasible source reduction orrecycling opportunities. Waste treatment involves the use of chemical,biological, or physical processes to reduce or eliminate waste material.The incineration of wastes is included in this category and is consid-ered “preferable to other treatment methods (i.e., chemical, biologi-cal, and physical) because incineration can permanently destroy the


hazardous components in waste materials” (Ref. 4). It can also beemployed to reduce the volume of waste to be treated.

Several of these pollution-prevention elements are used by industryin combination to achieve the greatest waste reduction. Residualwastes that cannot be prevented or otherwise managed are then dis-posed of only as a last resort.

Figure 22-3 provides a more detailed schematic representation ofthe two preferred pollution prevention techniques (i.e., source reduc-tion and recycling).

MULTIMEDIA ANALYSIS AND LIFE-CYCLE ANALYSIS

Multimedia Analysis In order to properly design and thenimplement a pollution prevention program, sources of all wastes mustbe fully understood and evaluated. A multimedia analysis involves amultifaceted approach. It must not only consider one waste streambut all potentially contaminated media (e.g., air, water, land). Pastwaste-management practices have been concerned primarily withtreatment. All too often, such methods solve one waste problem bytransferring a contaminant from one medium to another (e.g., airstripping); such waste shifting is not pollution prevention or wastereduction.

Pollution prevention techniques must be evaluated through a thor-ough consideration of all media, hence the term multimedia. Thisapproach is a clear departure from previous pollution treatment orcontrol techniques where it was acceptable to transfer a pollutantfrom one source to another in order to solve a waste problem. Suchstrategies merely provide short-term solutions to an ever increasingproblem. As an example, air pollution control equipment prevents orreduces the discharge of waste into the air but at the same time canproduce a solid (hazardous) waste problem.

Life-Cycle Analysis The aforementioned multimedia approachto evaluating a product’s waste stream(s) aims to ensure that the treat-ment of one waste stream does not result in the generation or increasein an additional waste output. Clearly, impacts resulting during theproduction of a product or service must be evaluated over its entire

history or life cycle. This life-cycle analysis or total systems approach(Ref. 3) is crucial to identifying opportunities for improvement. Asdescribed earlier, this type of evaluation identifies “energy use, mate-rial inputs, and wastes generated during a product’s life: from extrac-tion and processing of raw materials to manufacture and transport ofa product to the marketplace and finally to use and dispose of theproduct” (Ref. 5).

During a forum convened by the World Wildlife Fund and the Con-servation Foundation in May 1990, various steering committees rec-ommended that a three-part life-cycle model be adopted. This modelconsists of the following:

1. An inventory of materials and energy used, and environmentalreleases from all stages in the life of a product or process

2. An analysis of potential environmental effects related to energyuse and material resources and environmental releases

3. An analysis of the changes needed to bring about environmentalimprovements for the product or process under evaluation

Traditional cost analysis often fails to include factors relevant tofuture damage claims resulting from litigation, the depletion of nat-ural resources, the effects of energy use, and the like. As such,waste-management options such as treatment and disposal mayappear preferential if an overall life-cycle cost analysis is not per-formed. It is evident that environmental costs from cradle to gravehave to be evaluated together with more conventional productioncosts to accurately ascertain genuine production costs. In the future,a total systems approach will most likely involve a more careful eval-uation of pollution, energy, and safety issues. For example, if onewas to compare the benefits of coal versus oil as a fuel source for anelectric power plant, the use of coal might be considered economi-cally favorable. In addition to the cost issues, however, one must beconcerned with the environmental effects of coal mining (e.g., trans-portation and storage prior to use as a fuel). Society often has a ten-dency to overlook the fact that there are serious health and safetymatters (e.g., miner exposure) that must be considered along withthe effects of fugitive emissions. When these effects are weighedalongside standard economic factors, the full cost benefits of coal

Pollution preventiontechniques

Source reduction Recycling(on-site and off-site)

Sourcecontrol

Product changes• Substitution• Conservation• Product composition

Use and reuse• Return to original process• Raw material for another process

Reclamation• Processed for recovery• Processed as by-product

Good operation practices• Procedural measures• Management practice• Material handling improvements• Production scheduling

Technology changes• Process changes• Equipment changes• Additional automation• Changes in operation settings

Input material changes• Material purification• Material substitution

FIG. 22-3 Pollution prevention techniques.


usage may be eclipsed by environmental costs. Thus, many of theeconomic benefits associated with pollution prevention are oftenunrecognized due to inappropriate cost-accounting methods. Forthis reason, economic considerations are briefly detailed later.

POLLUTION-PREVENTION ASSESSMENT PROCEDURES

The first step in establishing a pollution prevention program is theobtainment of management commitment. This is necessary given theinherent need for project structure and control. Management will deter-mine the amount of funding allotted for the program as well as specificprogram goals. The data collected during the actual evaluation is thenused to develop options for reducing the types and amounts of wastegenerated. Figure 22-4 depicts a systematic approach that can be usedduring the procedure. After a particular waste stream or area of concernis identified, feasibility studies are performed involving both economicand technical considerations. Finally, preferred alternatives are imple-mented. The four phases of the assessment (i.e., planning and organiza-tion, assessment, feasibility, and implementation) are introduced in thefollowing subsections. Sources of additional information as well as infor-mation on industrial programs are also provided.

Planning and Organization The purpose of this phase is to obtainmanagement commitment, define and develop program goals, andassemble a project team. Proper planning and organization are crucial tothe successful performance of the pollution-prevention assessment.Both managers and facility staff play important roles in the assessmentprocedure by providing the necessary commitment and familiarity withthe facility, its processes, and current waste-management operations. Itis the benefits of the program, including economic advantages, liability

reduction, regulatory compliance, and improved public image that oftenleads to management support.

Once management has made a commitment to the program andgoals have been set, a program task force is established. The selectionof a team leader will be dependent upon many factors including theability to effectively interface with both the assessment team and man-agement staff.

The task force must be capable of identifying pollution reductionalternatives as well as be cognizant of inherent obstacles to theprocess. Barriers frequently arise from the anxiety associated with thebelief that the program will negatively affect product quality or resultin production losses. According to an EPA survey, 30 percent of indus-try comments responded that they were concerned that product qual-ity would decline if waste minimization techniques were implemented(Ref. 6). As such, the assessment team, and the team leader in partic-ular, must be ready to react to these and other concerns (Ref. 2).

Assessment Phase The assessment phase aims to collect dataneeded to identify and analyze pollution-prevention opportunities.Assessment of the facility’s waste-reduction needs includes the exam-ination of (hazardous) waste streams, process operations, and theidentification of techniques that often promise the reduction of wastegeneration. Information is often derived from observations made dur-ing a facility walk-through, interviews with employees (e.g., operators,line workers), and review of site or regulatory records. One profes-sional organization suggests the following sources of information bereviewed, as available (Ref. 7):

1. Product design criteria2. Process flow diagrams for all solid waste, wastewater, and air

emissions sources3. Site maps showing the location of all pertinent units (e.g., pollu-

tion-control devices, points of discharge)4. Environmental documentation, including: Material Safety Data

Sheets (MSDS), military specification data, permits (e.g., NPDES,POTW, RCRA), SARA Title III reports, waste manifests, and anypending permits or application information

5. Economic data, including: cost of raw materials; cost of air,wastewater, and (hazardous) waste treatment; waste managementoperating and maintenance costs; and waste disposal costs

6. Managerial information: environmental policies and procedures;prioritization of waste-management concerns; automated or comput-erized waste-management systems; inventory and distribution proce-dures; maintenance scheduling practices; planned modifications orrevisions to existing operations that would impact waste-generationactivities; and the basis of source reduction decisions and policies

The use of process flow diagrams and material balances are worth-while methods to quantify losses or emissions and provide essentialdata to estimate the size and cost of additional equipment, other datato evaluate economic performance, and a baseline for tracking theprogress of minimization efforts (Ref. 3). Material balances should beapplied to individual waste streams or processes and then utilized toconstruct an overall balance for the facility. Details on these calcula-tions are available in the literature (Ref. 8). In addition, an introduc-tion to this subject is provided in the next section.

The data collected is then used to prioritize waste streams andoperations for assessment. Each waste stream is assigned a prioritybased on corporate pollution-prevention goals and objectives. Oncewaste origins are identified and ranked, potential methods to reducethe waste stream are evaluated. The identification of alternatives isgenerally based on discussions with the facility staff; review of techni-cal literature; and contacts with suppliers, trade organizations, andregulatory agencies.

Alternatives identified during this phase of the assessment are eval-uated using screening procedures so as to reduce the number of alter-natives requiring further exploration during the feasibility analysisphase. Some criteria used during this screening procedure include:cost-effectiveness; implementation time; economic, compliance,safety and liability concerns; waste-reduction potential; and whetherthe technology is proven (Refs. 4, 8). Options that meet establishedcriteria are then examined further during the feasibility analysis.

Feasibility Analysis The selection procedure is performed by anevaluation of technical and economic considerations. The technicalFIG. 22-4 Pollution prevention assessment procedure.

evaluation determines whether a given option will work as planned.Some typical considerations follow:

1. Safety concerns2. Product quality impacts or production delays during implemen-

tation3. Labor and/or training requirements4. Creation of new environmental concerns5. Waste reduction potential6. Utility and budget requirements7. Space and compatibility concerns

If an option proves to be technically ineffective or inappropriate, it isdeleted from the list of potential alternatives. Either following or con-current with the technical evaluation, an economic study is per-formed, weighing standard measures of profitability such as paybackperiod, investment returns, and net present value. Many of these costs(or, more appropriately, cost savings) may be substantial yet are diffi-cult to quantify. (Refer to Economic Considerations Associated withPollution Prevention.)

Implementation The findings of the overall assessment are usedto demonstrate the technical and economic worthiness of programimplementation. Once appropriate funding is obtained, the programis implemented not unlike any other project requiring new proce-dures or equipment. When preferred waste-pollution-preventiontechniques are identified, they are implemented and should becomepart of the facility’s day-to-day management and operation. Subse-quent to the program’s execution, its performance should be evalu-ated in order to demonstrate effectiveness, generate data to furtherrefine and augment waste-reduction procedures, and maintain man-agement support.

It should be noted that waste reduction, energy conservation, andsafety issues are interrelated and often complementary to each other.For example, the reduction in the amount of energy a facility consumesusually results in reduced emissions associated with the generation ofpower. Energy expenditures associated with the treatment and trans-port of waste are similarly reduced when the amount of waste gener-ated is lessened; at the same time, worker safety is elevated due toreduced exposure to hazardous materials. However, this is not alwaysthe case. Addition of air-pollution control systems at power plantsdecreases net power output due to the power consumed by the equip-ment. This in turn requires more fuel to be combusted for the samepower exported to the grid. This additional fuel increases pollutionfrom coal mining, transport, ash disposal, and the like. In extremecases, very high recovery efficiencies for some pollutants can raise, notlower, overall total emissions. Seventy percent removal might producea 2 percent loss in power output; 90 percent recovery could lead to a 3percent loss; 95 percent, a 5 percent loss; 99 percent, a 10 percent loss,and so on. The point to be made is that pollution control is generallynot a “free lunch.”

Sources of Information The successful development andimplementation of any pollution prevention program is not onlydependent on a thorough understanding of the facility’s operationsbut also requires an intimate knowledge of current opportunities andadvances in the field. In fact, 32 percent of industry respondents toan earlier EPA survey identified the lack of technical information as amajor factor delaying or preventing the implementation of a waste-minimization program (Ref. 6). One of EPA’s positive contributionshas been the development of a national Pollution Prevention Infor-mation Clearinghouse (PPIC) and the Pollution Prevention Informa-tion Exchange System (PIES) to facilitate the exchange ofinformation needed to promote pollution prevention through effi-cient information transfer (Ref. 2).

PPIC is operated by the EPA’s Office of Research and Develop-ment and the Office of Pollution Prevention. The clearinghouse iscomprised of four elements:

1. Repository, including a hard copy reference library and collec-tion center and an on-line information retrieval and ordering system.

2. PIES, a computerized conduit to databases and document order-ing, accessible via modem and personal computer: (703) 506-1025.

3. PPIC uses the RCRA/Superfund and Small Business Ombuds-man Hotlines as well as a PPIC technical assistance line to answerpollution-prevention questions, access information in the PPIC, and

assist in document ordering and searches. To access PPIC by tele-phone, call:

RCRA/Superfund Hotline, (800) 242-9346Small Business Ombudsman Hotline, (800) 368-5888PPIC Technical Assistance, (703) 821-48004. PPIC compiles and disseminates information packets and bul-

letins, and initiates networking efforts with other national and inter-national organizations.

Additionally, the EPA publishes a newsletter entitled Pollution Pre-vention News that contains information including EPA news, tech-nologies, program updates, and case studies. The EPA’s RiskReduction Engineering Laboratory and the Center for Environmen-tal Research Information has published several guidance documents,developed in cooperation with the California Department of HealthServices. The manuals supplement generic waste reduction informa-tion presented in the EPA’s Waste Minimization Opportunity Assess-ment Manual (Ref. 9).

Pollution prevention or waste minimization programs have beenestablished at the State level and as such are good sources of informa-tion. Both Federal and State agencies are working with universitiesand research centers and may also provide assistance. For example,the American Institute of Chemical Engineers has established theCenter for Waste Reduction Technologies (CWRT), a program basedon targeted research, technology transfer, and enhanced education.

Industry Programs A significant pollution-prevention resourcemay very well be found with the “competition.” Several large compa-nies have established well-known programs that have successfullyincorporated pollution-prevention practices into their manufacturingprocesses. These include, but are not limited to: 3M—Pollution Pre-vention Pays (3P); Dow Chemical—Waste Reduction Always Pays(WRAP); Chevron—Save Money and Reduce Toxics (SMART); and,the General Dynamics Zero Discharge Program.

Smaller companies can benefit by the assistance offered by theselarger corporations. It is clear that access to information is of majorimportance when implementing efficient pollution-prevention pro-grams. By adopting such programs, industry is affirming pollution pre-vention’s application as a good business practice and not simply a“noble” effort.

ASSESSMENT PHASE: MATERIAL BALANCECALCULATIONS

(The reader is directed to Refs. 4 and 10 for further information.)One of the key elements of the assessment phase of a pollution pre-

vention program involves mass balance equations. These calculationsare often referred to as material balances; the calculations are per-formed via the conservation law for mass. The details of this often-used law are described below.

The conservation law for mass can be applied to any process or sys-tem. The general form of the law follows:

mass in – mass out + mass generated = mass accumulated

This equation can be applied to the total mass involved in a process orto a particular species, on either a mole or mass basis. The conservationlaw for mass can be applied to steady-state or unsteady-state processesand to batch or continuous systems. A steady-state system is one inwhich there is no change in conditions (e.g., temperature, pressure) orrates of flow with time at any given point in the system; the accumula-tion term then becomes zero. If there is no chemical reaction, the gen-eration term is zero. All other processes are classified as unsteady state.

To isolate a system for study, the system is separated from the sur-roundings by a boundary or envelope that may either be real (e.g., areactor vessel) or imaginary. Mass crossing the boundary and enteringthe system is part of the mass-in term. The equation may be used forany compound whose quantity does not change by chemical reactionor for any chemical element, regardless of whether it has participatedin a chemical reaction. Furthermore, it may be written for one pieceof equipment, several pieces of equipment, or around an entireprocess (i.e., a total material balance).

The conservation of mass law finds a major application during theperformance of pollution-prevention assessments. As described earlier,


a pollution-prevention assessment is a systematic, planned procedurewith the objective of identifying methods to reduce or eliminate waste.The assessment process should characterize the selected waste streamsand processes (Ref. 11)—a necessary ingredient if a material balance isto be performed. Some of the data required for the material balance cal-culation may be collected during the first review of site-specific data;however, in some instances, the information may not be collected untilan actual site walk-through is performed.

Simplified mass balances should be developed for each of theimportant waste-generating operations to identify sources and gain abetter understanding of the origins of each waste stream. Since a massbalance is essentially a check to make sure that what goes into aprocess (i.e., the total mass of all raw materials) is what leaves theprocess (i.e., the total mass of the products and by-products), thematerial balance should be made individually for all components thatenter and leave the process. When chemical reactions take place in asystem, there may be an advantage to performing “elemental bal-ances” for specific chemical elements in a system. Material balancescan assist in determining concentrations of waste constituents whereanalytical test data are limited. They are particularly useful whenthere are points in the production process where it is difficult oruneconomical to collect analytical data.

Mass-balance calculations are particularly useful for quantifyingfugitive emissions such as evaporative losses. Waste stream data andmass balances will enable one to track flow and characteristics of thewaste streams over time. Since in most cases the accumulation equalszero (steady-state operation), it can then be assumed that any buildupis actually leaving the process through fugitive emissions or othermeans. This will be useful in identifying trends in waste/pollutant gen-eration and will also be critical in the task of measuring the perfor-mance of implemented pollution prevention options. The result ofthese activities is a catalog of waste streams that provides a descriptionof each waste, including quantities, frequency of discharge, composi-tion, and other important information useful for material balance. Ofcourse, some assumptions or educated estimates will be needed whenit is impossible to obtain specific information.

By performing a material balance in conjunction with a pollutionprevention assessment, the amount of waste generated becomesknown. The success of the pollution prevention program can there-fore be measured by using this information on baseline generationrates (i.e., that rate at which waste is generated without pollution pre-vention considerations) (Ref. 12).

BARRIERS AND INCENTIVES TO POLLUTION PREVENTION

As discussed previously, industry is beginning to realize that there areprofound benefits associated with pollution prevention, including costeffectiveness, reduced liability, enhanced public image, and regula-tory compliance. Nevertheless, there are barriers or disincentivesidentified with pollution prevention. This section will briefly outlineboth barriers and incentives that may need to be confronted or con-sidered during the evaluation of a pollution prevention program.

Barriers to Pollution Prevention (“The Dirty Dozen”)There are numerous reasons why more businesses are not reducingthe wastes they generate. The following “dirty dozen” are commondisincentives:

1. Technical limitations. Given the complexity of present manu-facturing processes, waste streams exist that cannot be reduced withcurrent technology. The need for continued research and develop-ment is evident.

2. Lack of information. In some instances, the informationneeded to make a pollution-prevention decision may be confidentialor is difficult to obtain. In addition, many decision makers are simplyunaware of the potential opportunities available regarding informa-tion to aid in the implementation of a pollution-prevention program.

3. Consumer preference obstacles. Consumer preference stronglyaffects the manner in which a product is produced, packaged, and mar-keted. If the implementation of a pollution-prevention program resultsin an increase in the cost of a product or decreased convenience oravailability, consumers might be reluctant to use it.

4. Concern over product quality decline. The use of a less haz-ardous material in a product’s manufacturing process may result indecreased life, durability, or competitiveness.

5. Economic concerns. Many companies are unaware of the eco-nomic advantages associated with pollution prevention. Legitimateconcerns may include decreased profit margins or the lack of fundsrequired for the initial capital investment.

6. Resistance to change. The unwillingness of many businesses tochange is rooted in their reluctance to try technologies that may beunproven or based on a combination of the barriers discussed in thissection.

7. Regulatory barriers. Existing regulations that have createdincentives for the control and containment of wastes are at the sametime discouraging the exploration of pollution-prevention alterna-tives. Moreover, since regulatory enforcement is often intermittent,current legislation can weaken waste-reduction incentives.

8. Lack of markets. The implementation of pollution-preventionprocesses and the production of environmentally friendly productswill be of no avail if markets do not exist for such goods. As an exam-ple, the recycling of newspaper in the United States has resulted in anoverabundance of waste paper without markets prepared to takeadvantage of this raw material.

9. Management apathy. Many managers capable of making deci-sions to begin pollution-prevention activities do not realize the poten-tial benefits of pollution prevention.

10. Institutional barriers. In an organization without a strong infra-structure to support pollution-prevention plans, waste-reduction pro-grams will be difficult to implement. Similarly, if there is no mechanismin place to hold individuals accountable for their actions, the successfulimplementation of a pollution-prevention program will be limited.

11. Lack of awareness of pollution prevention advantages. Asmentioned in reason no. 5, decision makers may merely be unin-formed of the benefits associated with pollution reduction.

12. Concern over the dissemination of confidential productinformation. If a pollution-prevention assessment reveals confi-dential data pertinent to a company’s product, fear may exist thatthe organization will lose a competitive edge with other businessesin the industry.

Pollution-Prevention Incentives (“A Baker’s Dozen”) Vari-ous means exist to encourage pollution prevention through regulatorymeasures, economic incentives, and technical assistance programs.Since the benefits of pollution prevention can surpass prevention bar-riers, a “baker’s dozen” incentives is presented below:

1. Economic benefits. The most obvious economic benefitsassociated with pollution prevention are the savings that result fromthe elimination of waste storage, treatment, handling, transport,and disposal. Additionally, less tangible economic benefits are real-ized in terms of decreased liability, regulatory compliance costs(e.g., permits), legal and insurance costs, and improved processefficiency. Pollution prevention almost always pays for itself, partic-ularly when the time required to comply with regulatory standardsis considered. Several of these economic benefits are discussed sep-arately below.

2. Regulatory compliance. Quite simply, when wastes are notgenerated, compliance issues are not a concern. Waste-managementcosts associated with record keeping, reporting, and laboratory analy-sis are reduced or eliminated. Pollution prevention’s proactiveapproach to waste management will better prepare industry for futureregulation of many hazardous substances and wastes that are currentlyunregulated. Regulations have, and will continue to be, a moving tar-get.

3. Liability reduction. Facilities are responsible for their wastesfrom “cradle-to-grave.” By eliminating or reducing waste generation,future liabilities can also be decreased. Additionally, the need forexpensive pollution liability insurance requirements may be abated.

4. Enhanced public image. Consumers are interested in purchas-ing goods that are safer for the environment, and this demand,depending on how they respond, can mean success or failure for manycompanies. Businesses should therefore be sensitive to consumerdemands and use pollution-prevention efforts to their utmost advan-tage by producing goods that are environmentally friendly.



5. Federal and state grants. Federal and state grant programshave been developed to strengthen pollution-prevention programs ini-tiated by states and private entities. The EPA’s “Pollution Prevention byand for Small Business” grant program awards grants to small busi-nesses to assist their development and demonstration of new pollution-prevention technologies.

6. Market incentives. Public demand for environmentally pre-ferred products has generated a market for recycled goods and relatedproducts; products can be designed with these environmental charac-teristics in mind, offering a competitive advantage. In addition, manyprivate and public agencies are beginning to stimulate the market forrecycled goods by writing contracts and specifications that call for theuse of recycled materials.

7. Reduced waste-treatment costs. As discussed in reason no. 5 ofthe dirty dozen, the increasing costs of traditional end-of-pipe waste-management practices are avoided or reduced through the imple-mentation of pollution-prevention programs.

8. Potential tax incentives. In an effort to promote pollution pre-vention, taxes may eventually need to be levied to encourage wastegenerators to consider reduction programs. Conversely, tax breakscould be developed for corporations that utilize pollution-preventionmethods to foster pollution prevention.

9. Decreased worker exposure. By reducing or eliminating chem-ical exposures, businesses benefit by lessening the potential forchronic workplace exposure and serious accidents and emergencies.The burden of medical monitoring programs, personal exposure mon-itoring, and potential damage claims are also reduced.

10. Decreased energy consumption. As mentioned previously,methods of energy conservation are often interrelated and comple-mentary to each other. Energy expenditures associated with the treat-ment and transport of waste are usually but not always reduced whenthe amount of waste generated is lessened, while at the same time thepollution associated with energy consumed by these activities isabated.

11. Increased operating efficiencies. A potential beneficial sideeffect of pollution-prevention activities is a concurrent increase in oper-ating efficiency. Through a pollution-prevention assessment, the assess-ment team can identify sources of waste that result in (hazardous) wastegeneration and loss in process performance. The implementation of areduction program will often rectify such problems through moderniza-tion, innovation, and the implementation of good operating practices.

12. Competitive advantages. By taking advantage of the manybenefits associated with pollution prevention, businesses can gain acompetitive edge.

13. Reduced negative environmental impacts. Through an evalu-ation of pollution-prevention alternatives, which consider a total sys-tems approach, consideration is given to the negative impact ofenvironmental damage to natural resources and species that occurduring raw-material procurement and waste disposal. The perfor-mance of pollution-prevention endeavors will therefore result inenhanced environmental protection.

ECONOMIC CONSIDERATIONS ASSOCIATED WITH POLLUTION-PREVENTION PROGRAMS

The purpose of this subsection is to outline the basic elements of apollution-prevention cost-accounting system that incorporates bothtraditional and less tangible economic variables. The intent is not topresent a detailed discussion of economic analysis but to help identifythe more important elements that must be considered to properlyquantify pollution-prevention options.

The greatest driving force behind any pollution-prevention plan isthe promise of economic opportunities and cost savings over the longterm. Pollution prevention is now recognized as one of the lowest-costoptions for waste/pollutant management. Hence, an understanding ofthe economics involved in pollution prevention programs/options isquite important in making decisions at both the engineering and man-agement levels. Every engineer should be able to execute an eco-nomic evaluation of a proposed project. If the project cannot bejustified economically after all factors—and these will be discussed in

more detail below—have been taken into account, it should obviouslynot be pursued. The earlier such a project is identified, the fewerresources will be wasted.

Before the true cost or profit of a pollution-prevention program canbe evaluated, the factors contributing to the economics must be rec-ognized. There are two traditional contributing factors (capital costsand operating costs), but there are also other important costs and ben-efits associated with pollution prevention that need to be quantified ifa meaningful economic analysis is going to be performed. Table 22-13demonstrates the evolution of various cost-accounting methods.Although Tables 22-12 (see Introduction) and 22-13 are not directlyrelated, the reader is left with the option of comparing some of thesimilarities between the two.

The Total Systems Approach (TSA) referenced in Table 22-13 aimsto quantify not only the economic aspects of pollution prevention butalso the social costs associated with the production of a product or ser-vice from cradle to grave (i.e., life cycle). The TSA attempts to quan-tify less tangible benefits such as the reduced risk derived from notusing a hazardous substance. The future is certain to see more empha-sis placed on the TSA approach in any pollution-prevention program.As described earlier, a utility considering the option of convertingfrom a gas-fired boiler to coal-firing is usually not concerned with theenvironmental effects and implications associated with such activitiesas mining, transporting, and storing the coal prior to its usage as anenergy feedstock. Pollution-prevention approaches since the mid-to-late 1990s have become more aware of this need.

The economic evaluation referred to above is usually carried outusing standard measures of profitability. Each company and organiza-tion has its own economic criteria for selecting projects for imple-mentation. (For example, a project can be judged on its paybackperiod. For some companies, if the payback period is more than 3 years,it is a dead issue.) In performing an economic evaluation, various costsand savings must be considered. As noted earlier, the economic analy-sis presented in this subsection represents a preliminary, rather than adetailed, analysis. For smaller facilities with only a few (and perhapssimple) processes, the entire pollution-prevention assessment proce-dure will tend to be much less formal. In this situation, several obvi-ous pollution-prevention options such as the installation of flowcontrols and good operating practices may be implemented with littleor no economic evaluation. In these instances, no complicated analy-ses are necessary to demonstrate the advantages of adopting theselected pollution-prevention option. A proper perspective must alsobe maintained between the magnitude of savings that a potentialoption may offer and the amount of manpower required to do thetechnical and economic feasibility analyses. A short description of thevarious aforementioned economic factors—including capital andoperating costs and other considerations—follows.

Once identified, the costs and/or savings are placed into their appro-priate categories and quantified for subsequent analysis. Equipmentcost is a function of many variables, one of the most significant of whichis capacity. Other important variables include operating temperatureand/or pressure conditions, and degree of equipment sophistication.Preliminary estimates are often made using simple cost-capacity rela-tionships that are valid when the other variables are confined to a nar-row range of values.

TABLE 22-13 Economic Analysis Timetable

Prior to 1945 Capital costs only1945–1960 Capital and some operating costs1960–1970 Capital and operating costs1970–1975 Capital, operating, and some environmental control costs1975–1980 Capital, operating, and environmental control costs1980–1985 Capital, operating, and more sophisticated environmental

control costs1985–1990 Capital, operating, and environmental controls, and some

life-cycle analysis (Total Systems Approach)1990–1995 Capital, operating, and environmental control costs and

life-cycle analysis (Total Systems Approach)1995–2000 Widespread acceptance of Total Systems ApproachAfter 2000 To be detailed at a later date

5. Dealings with state and local regulatory bodies6. Elimination or reduction of fines and penalties7. Potential tax benefits8. Customer relations9. Stockholder support (corporate image)

10. Improved public image11. Reduced technical support12. Potential insurance costs and claims13. Effect on borrowing power14. Improved mental and physical well-being of employees15. Reduced health-maintenance costs16. Employee morale17. Other process benefits18. Improved worker safety19. Avoidance of rising costs of waste treatment and/or disposal20. Reduced training costs21. Reduced emergency response planningMany proposed pollution-prevention programs have been squelched

in their early stages because a comprehensive economic analysis was notperformed. Until the effects described above are included, the truemerits of a pollution-prevention program may be clouded by incorrectand/or incomplete economic accounting. Can something be done byindustry to remedy this problem? One approach is to use a modifiedversion of the standard Delphi panel. In order to estimate these othereconomic benefits of pollution prevention, several knowledgeableindividuals within and perhaps outside the organization are asked toindependently provide estimates, with explanatory details, on theseeconomic benefits. Each individual in the panel is then allowed toindependently review all responses. The cycle is then repeated untilthe group’s responses approach convergence.

Finally, pollution-prevention measures can provide a company withthe opportunity of looking their neighbors in the eye and truthfullysaying that all that can reasonably be done to prevent pollution isbeing done. In effect, the company is doing right by the environment.Is there an economic advantage to this? It is not only a difficult ques-tion to answer quantitatively but also a difficult one to answer qualita-tively. Industry is left to ponder the answer to this question.

POLLUTION PREVENTION AT THE DOMESTIC AND OFFICE LEVELS

Concurrent with the United States’ growth as an international eco-nomic superpower during the years following World War II, a newparadigm was established whereby society became accustomed to theconvenience and ease with which goods could be discarded after a rel-atively short useful life. Individuals have come to expect these every-day comforts with what may be considered an unconscious ignorancetowards the ultimate effect of the throwaway lifestyle. In fact, many,while fearful of environmental degradation, are not aware of the illeffect these actions have on the world as a whole. Many individualswho abide by the “not in my back yard” (NIMBY) mind-set also feelpollution prevention does not have to occur “in my house.”

The past three decades have seen an increased social awareness ofthe impact of modern-day lifestyles on the environment. Public envi-ronmental concerns include issues such as waste disposal; hazardous-material regulations; depletion of natural resources; and air, water,and land pollution. Nevertheless, roughly one-half of the total quan-tity of waste generated each year can be attributed to domesticsources!

More recently, concern about the environment has begun to stimu-late environmentally correct behavior. After all, the choices madetoday affect the environment of tomorrow. Simple decisions can bemade at work and at home that conserve natural resources and lessenthe burden placed on a waste-management system. By eliminatingwaste at the source, society is participating in the protection of theenvironment by reducing the amount of waste that would otherwiseneed to be treated or ultimately disposed.

There are numerous areas of environmental concern that can bedirectly influenced by the consumer’s actions. The first issue, which isdescribed above, is that of waste generation. Second, energy conserva-tion has significantly affected Americans and has resulted in cost-saving


The usual technique for determining the capital costs (i.e., totalcapital costs, which include equipment design, purchase, and installa-tion) for the facility is based on the factored method of establishingdirect and indirect installation costs as a function of the known equip-ment costs. This is basically a modified Lang method, whereby costfactors are applied to known equipment costs (Refs. 13 and 14). Thefirst step is to obtain from vendors the purchase prices of the primaryand auxiliary equipment. The total base price, designated by X, whichshould include instrumentation, control, taxes, freight costs, and soon, serves as the basis for estimating the direct and indirect installa-tion costs. These costs are obtained by multiplying X by the cost fac-tors, which are available in the literature (see Refs. 13–19).

The second step is to estimate the direct installation costs by sum-ming all the cost factors involved in the direct installation costs, whichinclude piping, insulation, foundation and supports, and so on. Thesum of these factors is designated as the DCF (direct installation costfactor). The direct installation costs are then the product of the DCFand X. The third step consists of estimating the indirect installationcost. Here all the cost factors for the indirect installation costs (engi-neering and supervision, startup, construction fees, and so on) areadded; the sum is designated by ICF (indirect installation cost factor).The indirect installation costs are then the product of ICF and X.Once the direct and indirect installation costs have been calculated,the total capital cost (TCC) may be evaluated as follows:

TCC = X + (DCF)(X) + (ICF)(X)

This can then be converted to annualized capital costs (ACC) with theuse of the capital recovery factor (CRF). The CRF can be calculatedfrom the following equation:

CRF =

where n = projected lifetime of the project, yearsi = annual interest rate, expressed as a fraction

The annualized capital cost (ACC) is the product of the CRF and TCCand represents the total annualized installed equipment cost distrib-uted over the lifetime of the project. The ACC reflects the cost asso-ciated with the initial capital outlay over the depreciable life of thesystem. Although investment and operating costs can be accountedfor in other ways such as present-worth analysis, the capital recoverymethod is often preferred because of its simplicity and versatility. Thisis especially true when comparing somewhat similar systems havingdifferent depreciable lives. In such decisions, there are usually otherconsiderations besides economic, but if all other factors are equal, thealternative with the lowest total annualized cost should be the mostviable.

Operating costs can vary from site to site since these costs reflectlocal conditions (e.g., staffing practices, labor, utility costs). Operatingcosts, like capital costs, may be separated into two categories: directand indirect costs. Direct costs are those that cover material and laborand are directly involved in operating the facility. These include labor,materials, maintenance and maintenance supplies, replacement parts,wastes, disposal fees, utilities, and laboratory costs. However, themajor direct operating costs are usually those associated with laborand materials. Indirect costs are those operating costs associated with,but not directly involved in, operating the facility; costs such as over-head (e.g., building/land leasing and office supplies), administrativefees, property taxes, and insurance fees fall into this category.

The main problem with the traditional type of economic analysis isthat it is difficult—nay, in some cases impossible—to quantify some ofthe not-so-obvious economic merits of a pollution-prevention pro-gram. Several considerations have just recently surfaced as factors thatneed to be taken into account in any meaningful economic analysis ofa pollution-prevention effort. What follows is a summary listing ofthese considerations, most which have been detailed earlier.

1. Decreased long-term liabilities2. Regulatory compliance3. Regulatory recordkeeping4. Dealings with the EPA

(i)(1 + i)n

��(1 + i)n − 1


measures that have directly reduced pollution. As mentioned previ-ously, energy conservation is directly related to pollution preventionsince a reduction in energy use usually corresponds to less energy pro-duction and, consequently, less pollution output. A third area of concernis that of accident and emergency planning. Relatively recent accidentslike Chernobyl and Bhopal have increased public awareness and helpedstimulate regulatory policies concerned with emergency planning.Specifically, Title III of the Superfund Amendments and Reauthoriza-tion Act (SARA) of 1986 established the Emergency Planning andCommunity Right-to-Know Act, which has forever changed the con-cept of environmental management. This law attempts to avert poten-tial emergencies through careful planning and the development ofcontingency plans. Planning for emergency situations can help protecthuman health and the environment (Ref. 3).

Based on the above three areas of potential concern, a plethora ofwaste reduction activities can be performed at home or in an officeenvironment. One can easily note the similarities between these activ-ities and those pollution-prevention activities performed in industry.The following few examples are identified by category according tothis notation (Ref. 3):

● Waste reduction★ Accidents, health, and safety■ Energy conservation

At home● Purchase products with the least amount of packaging● Borrow items used infrequently★ Handle materials to avoid spills (and slips, trips)★ Keep hazardous materials out-of-reach of children■ Use energy-efficient lighting (e.g., fluorescent)■ Install water-flow restriction devices on sink faucets and

showerheads

At the office● Pass on verbal memos when written correspondence isn’t

required● Reuse paper before recycling it★ Know building evacuation procedures★ Adhere to company medical policies (e.g., annual physicals)■ Don’t waste utilities simply because you are not paying for

them■ Take public transportation to the office

The use of pollution-prevention principles on the home front clearlydoes not involve the use of high-technology equipment or majorlifestyle changes; success is only dependent upon active and willingpublic participation. All can help to make a difference.

Before pollution prevention becomes a fully accepted way of life,considerable effort still needs to be expended to change the way onelooks at waste management. A desire to use “green” products and ser-vices will be of no avail in a market where these goods are not avail-able. Participation in pollution-prevention programs will increasethrough continued education, community efforts, and lobbying forchange. Market incentives can be created and strengthened by taxpolicies, price preferences, and packaging regulations created at thefederal, state, and local levels. Individuals should take part by com-municating with industry and expressing their concerns. For example,citizens should feel free to write letters to decision makers at bothbusiness organizations and government institutions regarding specificproducts or legislation. Letters can be positive, demonstrating per-sonal endorsement of a green product, or disapproving, expressingdiscontent and reluctance to use a particular product because of itsnegative environmental effect (Ref. 3).

By starting now, society will learn through experience to bettermanage its waste while providing a safer and cleaner environment forfuture generations.

ETHICAL CONSIDERATIONS

Given the evolutionary nature of pollution prevention, it is evidentthat as technology changes and continued progress is achieved, society’s

opinion of both what is possible and desirable will also change. Gov-ernment officials, scientists, and engineers will face new challengesto fulfill society’s needs while concurrently meeting the require-ments of changing environmental regulations. It is now apparentthat attention should also be given to ethical considerations andtheir application to pollution prevention policy. How one makesdecisions on the basis of ethical beliefs is clearly a personal issuebut one that should be addressed. In order to examine this issue, themeaning of ethics must be known, although the intent here is not toprovide a detailed discussion regarding the philosophy of ethics ormorality.

Ethics can simply be defined as the analysis of the rightness andwrongness of an act or actions. According to Dr. Andrew Varga, direc-tor of the Philosophical Resources Program at Fordham University, inorder to discern the morality of an act, it is customary to look at the acton the basis of four separate elements: its object, motive, circum-stances, and consequences (Ref. 21). Rooted in this analysis is thebelief that if one part of the act is bad, then the overall act itself can-not be considered good. Of course, there are instances where thegood effects outweigh the bad, and therefore there may be a reason topermit the evil. The application of this principle is not cut and dry andrequires decisions to be made on a case-by-case basis. Each mustmake well-judged decisions rooted in an understanding of the interac-tion between technology and the environment. After all, the decisionsmade today will have an impact not only on this generation but onmany generations to come. If one chooses today not to implement awaste-reduction program in order to meet a short-term goal ofincreased productivity, this might be considered a good decision sinceit benefits the company and its employees. However, should a majorrelease occur that results in the contamination of a local sole-source ofdrinking water, what is the good?

As an additional example, toxicological studies have indicated thattest animals exposed to small quantities of toxic chemicals had betterhealth than control groups that were not exposed. A theory has beendeveloped that says that a low-level exposure to the toxic chemicalresults in a challenge to the animal to maintain homeostasis; this chal-lenge increases the animal’s vigor and, correspondingly, its health.However, larger doses seem to cause an inability to adjust, resulting innegative health effects. Based on this theory, some individuals wouldbelieve that absolute pollution reduction might not be necessary.

FUTURE TRENDS

The reader should keep an open mind when dealing with the types ofissues discussed above and facing challenges perhaps not yet imag-ined. Clearly, there is no simple solution or answer to many of thequestions. The EPA is currently attempting to develop a partnershipwith government, industry, and educators to produce and distributepollution-prevention educational materials. Given EPA’s past historyand performance, there are understandable doubts as to whether thisprogram will succeed (Ref. 22).

Finally, no discussion on pollution prevention would be completewithout reference to the activities of the 50-year-old InternationalOrganization for Standardization (ISO) and the general subject ofnanotechnology (Ref. 23). Both are briefly described below.

ISO created Technical Committee 207 (TC 207) to develop newstandards for environmental management systems (EMS). The rami-fications, especially to the chemical industry, which has become heav-ily involved in the continued development and application of thesestandards, will be great. TC 207’s activities are being scrutinizedclosely. The new environmental management set of standards is enti-tled ISO 14000. With this new standard in place, it is expected thatcustomers will require their product suppliers to be certified by ISO14000. In addition, some service suppliers who have an impact on theenvironment are expected to obtain an ISO 14000 certification. Certi-fication will imply to the customer that, when the product or servicewas prepared, the environment was not significantly damaged in theprocess. This will effectively require that the life-cycle design mental-ity discussed earlier be applied to all processes. Implementing the life-cycle design framework will require significant organizational andoperational changes in business. To effectively promote the goals of


sustainable development, life-cycle designs will have to successfullyaddress cost, performance, and cultural and legal factors.

Nanotechnology is concerned with the world of invisible minisculeparticles that are dominated by forces of physics and chemistry thatcannot be applied at the macro or human-scale level. These particleshave come to be defined by some as nanomaterials, and these materi-als possess unusual properties not present in traditional and/or ordi-nary materials. The new technology allows the engineering of matterby systems and/or processes that effectively deal with atoms. Interest-ingly, the classic laws of science are different at the nanoscale.Nanoparticles possess large surface areas and essentially no innermass; i.e., their surface-to-mass ratio is extremely high. This new “sci-ence” is based on the knowledge that particles in the nanometerrange, and nanostructures or nanomachines that are developed fromthese nanoparticles, possess special properties and exhibit uniquebehavior; and can significantly impact physical, chemical, electrical,biological, mechanical, etc., functional qualities. These new character-istics can be harnessed and exploited by applied scientists to engineer“Industrial Revolution II” processes. Present-day and future applica-tions include chemical products, e.g., parts, plastics, specialty metals,powders; computer chips and computer systems; pollution preventionareas that can include energy conservation, environmental control,and health/safety issues, plus addressing crime and terrorism con-cerns. In effect, the sky’s the limit regarding efforts in this area. As faras the environment is concerned, this new technology can terminatepollution as it is known today. By ingeniously controlling the building

of small and large products via a process of precise controlled build-ing, there is no waste since environmental engineering is built in bydesign. However, activists have begun to organize against the science,calling for a moratorium on nanotechnology products until the social(health) and environmental risks are better understood. At the time ofthe preparation of this manuscript, justifiably (in the opinion of theauthor) no nanoregulations had been put into place. One of the mainobstacles to achieving this goal will be to control, reduce, and ulti-mately eliminate environmental and related problems, or problemsthat may develop through the misuse or use of nanotechnolgy.

The impact of all of the above on both the industry and the con-sumer will be significant. All have heard the expression “I’ve met theenemy . . . and we’re it.” After all, it is the consumer who can and willultimately have the final say. Once the consumer refuses to buy and/oraccept products and/or services that damage the environment, thatindustry is either out of business or must change its operations to envi-ronmentally acceptable alternatives. With the new standards, cus-tomers (in addition to other organizations) of certified organizationswill be assured that the products or services they purchase have beenproduced in accordance with universally accepted standards of envi-ronmental management. Organizational claims, which today can bemisleading or erroneous, will, under the standards, be backed up bycomprehensive and detailed environmental management systems thatmust withstand the scrutiny of intense audits.

Can all of the above be achieved in the near future? If it can, then soci-ety need only key its environmental efforts on educating the consumer.

AIR-POLLUTION MANAGEMENT OF STATIONARY SOURCES

FURTHER READING: Billings and Wilder, Fabric Filter Handbook, U.S. EPA,NTIS Publ. PB 200-648 (vol. 1), PB 200-649 (vol. 2), PB 200-651 (vol. 3), and PB200-650 (vol. 4), 1970. Buonicore, “Air Pollution Control,” Chem, Eng., 87(13), 81(June 30, 1980). Buonicore and Theodore, Industrial Control Equipment forGaseous Pollutants, vols. I and II, CRC Press, Boca Raton, Florida, 1975. Calvert,Scrubber Handbook, U.S. EPA, NTIS Publ. PB 213-016 (vol. 1) and PB 213-017(vol. 2), 1972. Danielson, Air Pollution Engineering Manual, EPA Publ. AP-40,1973. Davis, Air Filtration, Academic, New York, 1973. Kleet and Galeski, FlareSystems Study, EPA-600/2-76-079 (NTIS), 1976. Lund, Industrial Pollution Con-trol Handbook, McGraw-Hill, New York, 1971. Oglesby and Nichols, Manual ofElectrostatic Precipitator Technology, U.S. EPA, NTIS Publ. PB 196-380 (vol. 1),PB 196-381 (vol. 2), PB 196-370 (vol. 3), and PB 198-150 (vol. 4), 1970. PackageSorption System Study, EPA-R2-73-202 (NTIS), 1973. Rolke et al., AfterburnerSystems Study, U.S. EPA, NTIS Publ. PB 212-500, 1972. Slade, Meteorology andAtomic Energy, AEC (TID-24190), Oak Ridge, Tennessee, 1969. Stern, Air Pollu-tion, Academic, New York, 1974. Strauss, Industrial Gas Cleaning, Pergamon,New York, 1966. Buonicore and Theodore, Industrial Control Equipment forGaseous Pollutants, vol. 1, 2d ed., CRC Press, Boca Raton, Florida, 1992.Theodore and Buonicore, Air Pollution Control Equipment: Selection, Design,Operation, and Maintenance, Prentice Hall, Englewood Cliffs, New Jersey, 1982.Treybal, Mass Transfer Operations, 3d ed., McGraw-Hill, New York, 1980. Turner,Workbook of Atmospheric Dispersion Estimates, U.S. EPA Publ. AP-26, 1970.White, Industrial Electrostatic Precipitation, Addison-Wesley, Reading, Massa-chusetts, 1963. McKenna, Mycock, and Theodore, Handbook of Air PollutionControl Engineering and Technology, CRC Press, Boca Raton, Florida, 1995.Theodore and Allen, Air Pollution Control Equipment, ETSI Prof. Training Inst.,Roanoke, VA, 1993. Air Pollution Engineering Manual, 2d ed., Wiley, New York,2000. Guideline on Air Quality Models (GAQM), rev. ed., EPA-450/2-78-027R,July 1986. Compilation of Air Pollution Emission Factors (AP-42), 4th ed., U.S.EPA, Research Triangle Park, North Carolina, September, 1985. McKenna andTurner, Fabric Filter—Baghouses I—Theory, Design, and Selection, ETSI Prof.Training Inst., Roanoke, Virginia, 1993. Greiner, Fabric Filter—Baghouses II—Operation, Maintenance, and Troubleshooting, ETS Prof. Training Inst., Roanoke,Virginia, 1993. Yang, Yonghua, and Allen, “Biofiltration Control of Hydrogen Sul-fide. 2. Kinetics Biofilter Performance and Maintenance,” JAWA, 44, p. 1315.

INTRODUCTION

Air pollutants may be classified into two broad categories: (1) naturaland (2) human-made. Natural sources of air pollutants include:• Windblown dust• Volcanic ash and gases

• Ozone from lightning and the ozone layer• Esters and terpenes from vegetation• Smoke, gases, and fly ash from forest fires• Pollens and other aeroallergens• Gases and odors from biologic activities• Natural radioactivitySuch sources constitute background pollution and that portion ofthe pollution problem over which control activities can have little, ifany, effect.

Human-made sources cover a wide spectrum of chemical and phys-ical activities and are the major contributors to urban air pollution. Airpollutants in the United States pour out from over 10 million vehicles,the refuse of approximately 300 million people, the generation of bil-lions of kilowatts of electricity, and the production of innumerableproducts demanded by everyday living. Hundreds of millions of tons ofair pollutants are generated annually in the United States alone. The sixpollutants identified in the Clean Air Act are shown in Table 22-14.Annual emission statistics for these six pollutants are considered majorindicators of the U.S. air quality. During the 1970 to 2003 period, thetotal emissions of the six pollutants declined by 51 percent, while at thesame time the gross domestic product increased by 176 percent, thepopulation by 39 percent, and energy consumption by 45 percent.Total emissions in the United States are summarized by source cate-gory for the year 1998 in Table 22-15.

Air pollutants may also be classified as to the origin and state of matter:1. Origina. Primary. Emitted to the atmosphere from a processb. Secondary. Formed in the atmosphere as a result of a chemical

reaction2. State of mattera. Gaseous. True gases such as sulfur dioxide, nitrogen oxide,

ozone, carbon monoxide, etc.; vapors such as gasoline, paint solvent,dry cleaning agents, etc.

b. Particulate. Finely divided solids or liquids; solids such as dust,fumes, and smokes; and liquids such as droplets, mists, fogs, and aerosols

Gaseous Pollutants Gaseous pollutants may be classified asinorganic or organic. Inorganic pollutants consist of:

1. Sulfur gases. Sulfur dioxide, sulfur trioxide, hydrogen sulfide2. Oxides of carbon. Carbon monoxide, carbon dioxide

AIR-POLLUTION MANAGEMENT OF STATIONARY SOURCES 22-29

3. Nitrogen gases. Nitrous oxide, nitric oxide, nitrogen dioxide,other nitrous oxides

4. Halogens, halides. Hydrogen fluoride, hydrogen chloride,chlorine, fluorine, silicon tetrafluoride

5. Photochemical products. Ozone, oxidants6. Cyanides. Hydrogen cyanide7. Ammonium compounds. Ammonia8. Chlorofluorocarbons. 1,1,1-trichloro-2,2,2-trifluoroethane;

trichlorofluoromethane, dichlorodifluoromethane; chlorodifluoro-methane; 1,2-dichloro-1,1,2,2-tetrafluoroethane; chloropentafluo-roethane

Organic pollutants consist of:1. Hydrocarbons

a. Paraffins. Methane, ethane, octaneb. Acetylenec. Olefins. Ethylene, butadiened. Aromatics. Benzene, toluene, benzpyrene, xylene, styrene

2. Aliphatic oxygenated compoundsa. Aldehydes. Formaldehydeb. Ketones. Acetone, methylethylketonec. Organic acidsd. Alcohols. Methanol, ethanol, isopropanole. Organic halides. Cyanogen chloride bromobenzyl cyanidef. Organic sulfides. Dimethyl sulfideg. Organic hydroperoxides. Peroxyacetyl nitrite or nitrate (PAN)

The most common gaseous pollutants and their major sources andsignificance are presented in Table 22-16.

Particulate Pollutants Particulates may be defined as solid orliquid matter whose effective diameter is larger than a molecule butsmaller than approximately 100 µm. Particulates dispersed in agaseous medium are collectively termed an aerosol. The termssmoke, fog, haze, and dust are commonly used to describe particulartypes of aerosols, depending on the size, shape, and characteristicbehavior of the dispersed particles. Aerosols are rather difficult toclassify on a scientific basis in terms of their fundamental propertiessuch as settling rate under the influence of external forces, opticalactivity, ability to absorb an electrical charge, particle size and struc-ture, surface-to-volume ratio, reaction activity, physiological action,and so on. In general, particle size and settling rate have been themost characteristic properties for many purposes. On the otherhand, particles on the order of 1 µm or less settle so slowly that, forall practical purposes, they are regarded as permanent suspensions.Despite possible advantages of scientific classification schemes, theuse of popular descriptive terms such as smoke, dust, and mist,which are essentially based on the mode of formation, appears to bea satisfactory and convenient method of classification. In addition,this approach is so well established and understood that it undoubt-edly would be difficult to change.

Dust is typically formed by the pulverization or mechanical disinte-gration of solid matter into particles of smaller size by processes suchas grinding, crushing, and drilling. Particle sizes of dust range from alower limit of about 1 mm up to about 100 or 200 µm and larger. Dustparticles are usually irregular in shape, and particle size refers to someaverage dimension for any given particle. Common examples include

TABLE 22-14 Six Principal Pollutants’ Annual Emission Statistics, Millions of Tons per Year

1970 1975 1980 1985a 1990 1995 2000a 2002 2003b

Carbon monoxide (CO) 197.3 184.0 177.8 169.6 143.6 120.0 102.4 96.4 93.7Nitrogen oxides (NOx)c 26.9 26.4 27.1 25.8 25.1 24.7 22.3 20.8 20.5Particulate matter (PM)d

PM10 12.2a 7.0 6.2 3.6 3.2 3.1 2.3 2.4 2.3PM2.5

e NA NA NA NA 2.3 2.2 1.8 1.8 1.8Sulfur dioxide (SO2) 31.2 28.0 25.9 23.3 23.1 18.6 16.3 15.3 15.8Volatile organic 33.7 30.2 30.1 26.9 23.1 21.6 16.9 15.8 15.4compounds (VOC)

Lead f 0.221 0.16 0.074 0.022 0.005 0.004 0.003 0.003 0.003Totalsg 301.5 275.8 267.2 249.2 218.1 188.0 160.2 150.2 147.7

NOTES:aIn 1985 and 1996 EPA refined its methods for estimating emissions. Between 1970 and 1975, EPA revised its methods for estimating particulate matter emissions.bThe estimates for 2003 are preliminary.cNOx estimates prior to 1990 include emissions from fires. Fires would represent a small percentage of the NOx emissions.dPM estimates do not include condensable PM, or the majority of PM2.5 that is formed in the atmosphere from “precursor” gases such as SO2 and NOx.eEPA has not estimated PM2.5 emissions prior to 1990.f The 1999 estimate for lead is used to represent 2000 and 2003 because lead estimates do not exist for these years.gPM2.5 emissions are not added when calculating the total because they are included in the PM10 estimate.SOURCE: EPA 2003 Emissions Report (www.EPA.gov./air/urbanair/6poll.html).

TABLE 22-15 1998 National Point and Area Emissions by Source Category and Pollutant, 1000 Short Tons

CO NOx VOC SO2

Source category Point Area Total Point Area Total Point Area Total Point Area Total

Fuel comb. elec. util. 413 4 417 6,095 8 6,103 54 0 54 13,217 0 13,217Fuel comb. industrial 908 206 1,114 2,142 827 2,969 144 17 161 2,075 820 2,895Fuel comb. other 83 3,760 3,843 142 975 1,117 12 666 678 191 418 609Chemical & allied product mfg. 1,129 0 1,129 152 0 152 312 84 396 299 0 299Metals processing 1,494 1 1,495 88 0 88 75 0 76 444 0 444Petroleum & related industries 365 3 368 122 16 138 223 273 496 344 0 345Other industrial processes 629 3 632 402 6 408 388 62 450 366 3 370Solvent utilization 2 0 2 2 0 2 639 4,640 5,278 1 0 1Storage & transport 80 0 80 7 0 7 298 1,025 1,324 3 0 3Waste disposal & recycling 31 1,123 1,154 38 59 97 27 406 433 19 24 42Highway vehicles 0 50,386 50,386 0 7,765 7,765 0 5,325 5,325 0 326 326Off-highway 0 19,914 19,914 0 5,280 5,280 0 2,461 2,461 0 1,084 1,084Natural sources 0 0 0 0 0 0 0 14 14 0 0 0Miscellaneous 0 8,920 8,920 1 327 328 2 770 772 0 12 12

Total 5,134 84,319 89,454 9,190 15,264 24,454 2,174 15,743 17,917 16,960 2,688 19,647

SOURCE: National Air Pollution Trends: 1900–1998, EPA 454/R-00-002, March 2000 (www.epa.gov/ttn/chief/trends/index.html).

www.EPA.gov./air/urbanair/6poll.html

www.epa.gov/ttn/chief/trends/index.html


fly ash, rock dusts, and ordinary flour. Smoke implies a certain degreeof optical density and is typically derived from the burning of organicmaterials such as wood, coal, and tobacco. Smoke particles are veryfine, ranging in size from less than 0.01 µm up to 1 µm. They are usu-ally spherical in shape if of liquid or tarry composition and irregular inshape if of solid composition. Owing to their very fine particle size,smokes can remain in suspension for long periods of time and exhibitlively brownian motion.

Fumes are typically formed by processes such as sublimation, con-densation, or combustion, generally at relatively high temperatures.They range in particle size from less than 0.1 µm to 1 µm. Similar tosmokes, they settle very slowly and exhibit strong brownian motion.

Mists or fogs are typically formed either by the condensation ofwater or other vapors on suitable nuclei, giving a suspension of smallliquid droplets, or by the atomization of liquids. Particle sizes of nat-ural fogs and mists lie between 2 and 200 µm. Droplets larger than200 µm are more properly classified as drizzle or rain. Many of theimportant properties of aerosols that depend on particle size are pre-sented in Sec. 17, Fig. 17-34.

When a liquid or solid substance is emitted to the air as particulatematter, its properties and effects may be changed. As a substance isbroken up into smaller and smaller particles, more of its surface area isexposed to the air. Under these circumstances, the substance, whateverits chemical composition, tends to combine physically or chemically

TABLE 22-16 Typical Gaseous Pollutants and Their Principal Sources and Significance

Air pollutants From manufacturing sources such as these In typical industries Cause these damaging effects

Used as a solvent in coatingsResults from thermal decomposition of fats,

oil, or glycerol; used in some glues andbinders

Used in refrigeration, chemical processessuch as dye making, explosives, lacquer,fertilizer

Used as a solvent in coatings

Any soldering, pickling, etching, or platingprocess involving metals or acids contain-ing arsenic

Fuel combustion; calcining

Fuming of metallic oxides, gas-operatedfork trucks

Manufactured by electrolysis, bleachingcotton and flour; by-product of organicchemicals

Used in refrigeration and production ofporous foams; degreasing agent

Combustion of coal or wastes containingchlorinated plastics

From metal plating, blast furnaces, dyestuffworks

Catalyst in some petroleum refining, etch-ing glass, silicate extraction; by-product inelectrolytic production of aluminum

Refinery gases, crude oil, sulfur recovery,various chemical industries using sulfurcompounds

Used as a solvent in coatingsIncineration, smelting and casting, trans-

portationHigh-temperature combustion: metal clean-

ing, fertilizer, explosives, nitric acid; car-bon-arc combustion; manufacture ofH2SO4

Slaughtering and rendering animals, tan-ning animal hides, canning, smokingmeats, roasting coffee, brewing beer, pro-cessing toiletries

Reaction product of VOC and nitrogenoxides

Thermal decomposition of chlorinatedhydrocarbons, degreasing, manufacture ofdyestuffs, pharmaceuticals, organic chemi-cals

Fuel combustion (coal, oil), smelting andcasting, manufacture of paper by sulfiteprocess

Surface coatings, printingFood processing, light process, wood furni-

ture, chip board

Textiles, chemicals

Surface coatings, printing

Chemical processing, smelting

Industrial boilers, cement and lime produc-tion

Primary metals; steel and aluminum

Textiles, chemicals

Refrigeration, plastic foam production,metal fabricating

Coal-fired boilers, incinerators

Metal fabricating, primary metals, textiles

Petroleum, primary metals, aluminum

Petroleum and chemicals; Kraft pulpingprocess

Surface coatings, printingCopper and lead smelting, MSWs

Metal fabrication, heavy chemicals

Food processing, allied industries

Not produced directly

Metal fabrication, heavy chemicals

Primary metals (ferrous and nonferrous);pulp and paper

Sensory and respiratory irritationAn irritating odor, suffocating, pungent,

choking; not immediately dangerous tolife; can become intolerable in a very shorttime

Corrosive to copper, brass, aluminum, andzinc; high concentration producing chemi-cal burns on wet skin

Irritation of mucous membranes, narcoticeffects; some are carcinogens

Breakdown of red cells in blood

Greenhouse gas

Reduction in oxygen-carrying capacity ofblood

Attacks entire respiratory tract and mucousmembrane of eye

Attacks stratospheric ozone layer; green-house gas

Irritant to eyes and respiratory system

Capable of affecting nerve cells

Strong irritant and corrosive action on allbody tissue; damage to citrus plants, effecton teeth and bones of cattle from eatingplants

Foul odor of rotten eggs; irritating to eyesand respiratory tract; darkening exteriorpaint

Sensory and respiratory irritationNeurological impairments; kidney, liver, and

heart damage.Irritating gas affecting lungs; vegetation

damage

Objectionable odors

Irritant to eyes and respiratory system

Damage capable of leading to pulmonaryedema, often delayed

Sensory and respiratory irritation, vegeta-tion damage, corrosion, possible adverseeffect on health

AlcoholsAldehydes

Ammonia

Aromatics

Arsine

Carbon dioxide

Carbon monoxide

Chlorine

Chlorofluoro-carbons

Hydrochloric acid

Hydrogen cyanide

Hydrogen fluoride

Hydrogen sulfide

Ketones

Lead

Nitrogen oxides

Odors

Ozone

Phosgenes

Sulfur dioxide


with other particles or gases in the atmosphere. The resulting combi-nations are frequently unpredictable. Very small aerosol particles(from 0.001 to 0.1 µm) can act as condensation nuclei to facilitate thecondensation of water vapor, thus promoting the formation of fog andground mist. Particles less than 2 or 3 µm in size (about half by weightof the particles suspended in urban air) can penetrate the mucousmembrane and attract and convey harmful chemicals such as sulfurdioxide. In order to address the special concerns related to the effectsof very fine, inhalable particulates, EPA now has ambient standards inplace for both PM10 and PM2.5.

By virtue of the increased surface area of the small aerosol particlesand as a result of the adsorption of gas molecules or other such prop-erties that are able to facilitate chemical reactions, aerosols tend toexhibit greatly enhanced surface activity. Many substances that oxidizeslowly in their massive state will oxidize extremely fast or possibly evenexplode when dispersed as fine particles in the air. Dust explosions,for example, are often caused by the unstable burning or oxidation ofcombustible particles, brought about by their relatively large specificsurfaces. Adsorption and catalytic phenomena can also be extremelyimportant in analyzing and understanding the problems of particulatepollution. The conversion of sulfur dioxide to corrosive sulfuric acidassisted by the catalytic action of iron oxide particles, for example,demonstrates the catalytic nature of certain types of particles in theatmosphere. Finally, aerosols can absorb radiant energy and rapidlyconduct heat to the surrounding gases of the atmosphere. These aregases that ordinarily would be incapable of absorbing radiant energyby themselves. As a result, the air in contact with the aerosols canbecome much warmer.

Estimating Emissions from Sources Knowledge of the typesand rates of emissions is fundamental to evaluation of any air pollutionproblem. A comprehensive material balance on the process can oftenassist in this assessment. Estimates of the rates at which pollutants aredischarged from various processes can also be obtained by utilizing pub-lished emission factors. See Compilation of Air Pollution Emission Fac-tors (AP-42), 4th ed., U.S. EPA, Research Triangle Park, NorthCarolina, September, 1985, with all succeeding supplements and theEPA Technology Transfer Network’s CHIEF. The emission factor is astatistical average of the rate at which pollutants are emitted from theburning or processing of a given quantity of material or on the basis ofsome other meaningful parameter. Emission factors are affected by thetechniques employed in the processing, handling, or burning opera-tions, by the quality of the material used, and by the efficiency of the air-pollution control. Since the combination of these factors tends to beunique to a source, emission factors appropriate for one source may notbe satisfactory for another source. Hence, care and good judgmentmust be exercised in identifying appropriate emission factors. If appro-priate emission factors cannot be found or if air-pollution control equip-ment is to be designed, specific source sampling should be conducted.The major industrial sources of pollutants, the air contaminants emit-ted, and typical control techniques are summarized in Table 22-17.

Effects of Air PollutantsMaterials The damage that air pollutants can do to some materi-

als is well known: ozone in photochemical smog cracks rubber, weak-ens fabrics, and fades dyes; hydrogen sulfide tarnishes silver; smokedirties laundry; acid aerosols ruin nylon hose. Among the most impor-tant effects are discoloration, corrosion, the soiling of goods, andimpairment of visibility.

1. Discoloration. Many air pollutants accumulate on and discolorbuildings. Not only does sooty material blacken buildings, but it canaccumulate and become encrusted. This can hide lines and decora-tions and thereby disfigure structures and reduce their aestheticappeal. Another common effect is the discoloration of paint by certainacid gases. A good example is the blackening of white paint with a leadbase by hydrogen sulfide.

2. Corrosion. A more serious effect and one of great economicimportance is the corrosive action of acid gases on building materials.Such acids can cause stone surfaces to blister and peel; mortar can bereduced to powder. Metals are also damaged by the corrosive action ofsome pollutants. Another common effect is the deterioration of tires

and other rubber goods. Cracking and apparent “drying” occur whenthese goods are exposed to ozone and other oxidants.

3. Soiling of goods. Clothes, real estate, automobiles, and house-hold goods can easily be soiled by air contaminants, and the more fre-quent cleaning thus required can become expensive. Also, morefrequent cleaning often leads to a shorter life span for materials and tothe need to purchase goods more often.

4. Impairment of visibility. The impairment of atmospheric visi-bility (i.e., decreased visual range through a polluted atmosphere) iscaused by the scattering of sunlight by particles suspended in the air.It is not a result of sunlight being obscured by materials in the air.Since light scattering, and not obscuration, is the main cause of thereduction in visibility, reduced visibility due to the presence of air pol-lutants occurs primarily on bright days. On cloudy days or at nightthere may be no noticeable effect, although the same particulate con-centration may exist at these times as on sunny days. Reduction in vis-ibility creates several problems. The most significant are the adverseeffects on aircraft, highway, and harbor operations. Reduced visibilitycan reduce quality of life and also cause adverse aesthetic impressionsthat can seriously affect tourism and restrict the growth and develop-ment of any area. Extreme conditions such as dust storms or sand-storms can actually cause physical damage by themselves.

Vegetation Vegetation is more sensitive than animals to many aircontaminants, and methods have been developed that use plantresponse to measure and identify contaminants. The effects of air pol-lution on vegetation can appear as death, stunted growth, reduced cropyield, and degradation of color. It is interesting to note that in somecases of color damage such as the silvering of leafy vegetables by oxi-dants, the plant may still be used as food without any danger to the con-sumer; however, the consumer usually will not buy such vegetables onaesthetic grounds, so the grower still sustains a loss. Among the pollu-tants that can harm plants are sulfur dioxide, hydrogen fluoride, andethylene. Plant damage caused by constituents of photochemical smoghas been studied extensively. Damage has been attributed to ozone andperoxyacetyl nitrites, higher aldehydes, and products of the reaction ofozone with olefins. However, none of the cases precisely duplicates allfeatures of the damage observed in the field, and the question remainsopen to some debate and further study.

Animals Considerable work continues to be performed on theeffects of pollutants on animals, including, for a few species, experi-ments involving mixed pollutants and mixed gas-aerosol systems. Ingeneral, such work has shown that mixed pollutants may act in severaldifferent ways. They may produce an effect that is additive, amount-ing to the sum of the effects of each contaminant acting alone; theymay produce an effect that is greater than the simply additive (syner-gistic) or less than the simply additive (antagonistic); or they may pro-duce an effect that differs in some other way from the simply additive.

The mechanism by which an animal can become poisoned in manyinstances is completely different from that by which humans areaffected. As in humans, inhalation is an important route of entry inacute air-pollution exposures such as the Meuse Valley and Donoraincidents (see the paragraph on humans below). However, probablythe most common exposure for herbivorous animals grazing within azone of pollution will be the ingestion of feed contaminated by air pol-lutants. In this case, inhalation is of secondary importance.

Air pollutants that present a hazard to livestock, therefore, are thosethat are taken up by vegetation or deposited on the plants. Only a fewpollutants have been observed to cause harm to animals. These includearsenic, fluorides, lead, mercury, and molybdenum.

Humans There seems to be little question that, during many ofthe more serious episodes, air pollution can have a significant effect onhealth, especially upon the young, elderly, or people already in illhealth. Hundreds of excess deaths have been attributed to incidents inLondon in 1952, 1956, 1957, and 1962; in Donora, Pennsylvania, in1948; in New York City in 1953, 1963, and 1966; and Bhopal, India in1989. Many of the people affected were in failing health, and they weregenerally suffering from lung conditions. In addition, hundreds ofthousands of persons have suffered from serious discomfort and incon-venience, including eye irritation and chest pains, during these andother such incidents. Such acute problems are actually the lesser of thehealth problems. There is considerable evidence of a chronic threat to


TABLE 22-17 Control Techniques Applicable to Unit Processes at Important Emission Sources

Industry Process of operation Air contaminants emitted Control techniques

Aluminum reduction Materials handling: Particulates (dust) Exhaust systems and baghouseplants Buckets and belt

Conveyor or pneumatic conveyorAnode and cathode electrode Exhaust systems and mechanicalpreparation: collectorsCathode (baking) Hydrocarbon emissions from binderAnode (grinding and blending) Particulates (dust)

Baking Particulates (dust), CO, SO2, High-efficiency cyclone, electrostatic hydrocarbons, and fluorides precipitators, scrubbers, catalytic

combustion or incinerators, flares, baghouse

Pot charging Particulates (dust), CO, HF, SO2, High-efficiency cyclone, baghouse, CF4, and hydrocarbons spray towers, floating-bed scrubber,

electrostatic precipitators, chemisorp-tion, wet electrostatic precipitators

Metal casting Cl2, HCl, CO, and particulates (dust) Exhaust systems and scrubbers

Asphalt plants Materials handling, storage and Particulates (dust) Wetting; exhaust systems with a classifiers: elevators, chutes, vibrating scrubber or baghousescreens

Drying: rotary oil- or gas-fired Particulates, SO2, NOx, VOC, CO, and Proper combustion controls, fuel-oilsmoke preheating where required; local

exhaust system, cyclone and a scrubber or baghouse

Truck traffic Dust Paving, wetting down truck routes

Cement plants Quarrying: primary crusher, secondary Particulates (dust) Wetting; exhaust systems with fabriccrusher, conveying, storage filters

Dry processes: materials handling, air Particulates (dust) Local exhaust system with mechanical separator (hot-air furnace) collectors and baghouse

Grinding Particulates (dust) Local exhaust system with cyclones Pneumatic, conveying and storage Particulates (dust) and baghouseWet process: materials handling, Wet materials, no dustgrinding, storage

Kiln operations: rotary kiln Particulates (dust), CO, SOx, NOx, Electrostatic precipitators, acoustic hydrocarbons, aldehydes, ketones horns and baghouses, scrubber

Clinker cooling: materials handling Particulates (dust) Local exhaust system and electrostaticprecipitators or fabric filters

Grinding and packing, air separator, Particulates (dust) Local exhaust system and fabric filtersgrinding, pneumatic conveying,materials handling, packaging

Coal-preparation Materials handling: conveyors, Particulates (dust) Local exhaust system and cyclonesplants elevators, chutes

Sizing: crushing, screening, classifying Particulates (dust) Local exhaust system and cyclonesDedusting Particulates (dust) Local exhaust system, cyclone

precleaners, and baghouseStoring coal in piles Blowing particulates (dust) Wetting, plastic-spray coveringRefuse piles H2S, particulates, and smoke from Digging out fire, pumping water onto

burning storage piles fire area, blanketing with incombus-tible material

Coal drying: rotary, screen, suspension, Dust, smoke, particulates, sulfur oxides, Exhaust systems with cyclones and fluid-bed, cascade H2S fabric filters

Coke plants By-product-ovens charging Smoke, particulates (dust) Pipe-line charging, careful charging techniques, portable hooding andscrubber or baghouses

Pushing Smoke, particulates (dust), SO2 Minimizing green-coke pushing,scrubbers and baghouses

Quenching Smoke, particulates (dust and mists), Baffles and spray towerphenols, and ammonia

By-product processing CO, H2S, methane, ammonia, H2, Electrostatic precipitator, scrubber, phenols, hydrogen cyanide, N2, flaringbenzene, xylene, etc.

Material storage (coal and coke) Particulates (dust) Wetting, plastic spray, fire-prevention techniques

Electric utilities Coal-fired boilers Particulates SOx, NOx Baghouses(industrial and Precipitators, SCR, and SNCRcommercial facilities) Acid gas scrubbers

Fertilizer industry Phosphate fertilizers: crushing, Particulates (dust) Exhaust system, scrubber, cyclone, (chemical) grinding, and calcining baghouse

Hydrolysis of P2O5 PH3, P2O5PO4 mist Scrubbers, flareAcidulation and curing HF, SiF4 ScrubbersGranulation Particulates (dust)(product recovery) Exhaust system, scrubber, or baghouseAmmoniation NH3, NH4Cl, SiF4, HF Cyclone, electrostatic precipitator,

baghouse, high-energy scrubber


TABLE 22-17 Control Techniques Applicable to Unit Processes at Important Emission Sources (Continued)


Fertilizer industry Nitric acid acidulation NOx, gaseous fluoride compounds Scrubber, addition of urea(chemical) Superphosphate storage and shipping Particulates (dust) Exhaust system, cyclone or baghouse

Ammonium nitrate reactor NH3, NOx ScrubberPrilling tower NH4, NO3 Proper operation control, scrubbers

Foundries: Melting (cupola:)Iron Charging Smoke and particulates Closed top with exhaust system, CO

Melting Smoke and particulates, fume afterburner, gas-cooling device andPouring Oil, mist, CO scrubbers, baghouse or electrostatic Bottom drop Smoke and particulates precipitator, wetting to extinguish fire

Brass and bronze Melting:Charging Smoke particulates, oil mist Low-zinc-content red brass: use of Melting Zinc oxide fume, particulates, smoke good combustion controls and slag Pouring Zinc oxide fume, lead oxide fume cover; high-zinc-content brass: use of

good combustion controls, local exhaust system, and baghouse or scrubber

Aluminum Melting: charging, melting, pouring Smoke and particulates Charging clean material (no paint orgrease); proper operation required; no air-pollution-control equipment ifno fluxes are used and degassing isnot required; dirty charge requiringexhaust system with scrubbers andbaghouses

Zinc Melting:Charging Smoke and particulates Exhaust system with cyclone and

baghouse, charging clean material (no paint or grease)

Melting Zinc oxide fume Careful skimming of drossPouring Oil mist and hydrocarbons from Use of low-smoking die-casting

diecasting machines lubricantsSand-handling shakeout Particulates (dust), smoke, organic vaporsMagnetic pulley, conveyors, and Particulates (dust) Exhaust system, cyclone, and baghouseelevators, rotary cooler, screening, crusher-mixer

Coke-making ovens Organic acids, aldehydes, smoke, Use of binders that will allow ovens hydrocarbons to operate at less than 204°C (400°F)

or exhaust systems and afterburners

Galvanizing Hot-dip-galvanizing-tank kettle: Fumes, particulates (liquid), vapors: Close-fitting hoods with high in-draft operations dipping material into the molten zinc; NH4Cl, ZnO, ZnCl2, Zn, NH3, oil, velocities (in some cases, the hood

dusting flux onto the surface of the and carbon may not be able to be close to the molten zinc kettle, so the in-draft velocity must be

very high), baghouses, electrostaticprecipitators

Kraft pulp mills Digesters: batch and continuous Mercaptans, methanol (odors) Condensers and use of lime kiln, boiler, or furnaces as afterburners

Multiple-effect evaporators H2S, other odors Caustic scrubbing and thermaloxidation of noncondensables

Recovery furnace H2S, mercaptans, organic sulfides, and Proper combustion controls fordisulfides fluctuating load and unrestricted

primary and secondary air flow tofurnace and dry-bottom electrostaticprecipitator; noncontact evaporator

Weak and strong black-liquor H2S Packed tower and cycloneoxidation

Smelt tanks Particulates (mist or dust) Demisters, venturi, packed tower, orimpingement-type scrubbers

Lime kiln Particulates (dust), H2S Venturi scrubbers

Municipal and Single-chamber incinerators Particulates, smoke, volatiles, CO, SOx, Afterburner, combustion controlsindustrial ammonia, organic acids, aldehydes, incinerators NOx, dioxins, hydrocarbons, odors,

HCl, furansMultiple-chamber incinerators Particulates, smoke, and combustion Operating at rated capacity, using(retort, inline): contaminants auxiliary fuel as specified, and good

maintenance, including timelycleanout of ash

Flue-fed Particulates, smoke, and combustion Use of charging gates and automaticcontaminants controls for draft; afterburner

Wood waste Particulates, smoke, and combustion Continuous-feed systems; operation atcontaminants design load and excess air; cyclones

Municipal incinerators (50 tons and up Particulates, smoke, volatiles, CO, Preparation of materials, includingper day): ammonia, organic acids, aldehydes, weighing, grinding, shredding; control

NOx, furans, hydrocarbons, SOx, of tipping area, furnace design with


TABLE 22-17 Control Techniques Applicable to Unit Processes at Important Emission Sources (Continued)


Municipal and Municipal incinerators (50 tons and up hydrogen chloride, dioxins and odors proper automatic controls; properindustrial per day): start-up techniques; maintenance ofincinerators design operating temperatures; use of

electrostatic precipitators, scrubbers,and baghouses; proper ash cleanout

Pathological incinerators Odors, hydrocarbons, HCl, dioxins, Proper charging, acid gas scrubber, furans baghouse

Industrial waste Particulates, smoke, and combustion Modified fuel feed, auxiliary fuel andcontaminants dryer systems, cyclones, scrubbers

Nonferrous smelters,primary:Copper Roasting SO2, particulates, fume Exhaust system, settling chambers,

cyclones or scrubbers and electrostaticprecipitators for dust and fumes andsulfuric acid plant for SO2

Reverberatory furnace Smoke, particulates, metal oxide fumes, Exhaust system, settling chambers,SO2 cyclones or scrubbers and electrostatic

precipitators for dust and fumes and sulfuric acid plant for SO2

Converters: charging, slag skim, Smoke, fume, SO2 Exhaust system, settling chambers,pouring, air or oxygen blow cyclones or scrubbers and electrostatic

precipitators for dust and fumes and sulfuric acid plant for SO2

Lead Sintering SO2, particulates, smoke Exhaust system, cyclones and bag-house or precipitators for dust andfumes, sulfuric acid plant for SO2

Blast furnace SO2, CO, particulates, lead oxide, Exhaust system, settling chambers,zinc oxide afterburner and cooling device,

cyclone, and baghouseDross reverberatory furnace SO2, particulates, fume Exhaust system, settling chambers,

cyclone and cooling device, baghouseRefining kettles SO2, particulates Local exhaust system, cooling device,

baghouse or precipitator

Cadmium Roasters, slag, fuming furnaces, Particulates Local exhaust system, baghouse ordeleading kilns precipitator

Zinc Roasting Particulates (dust) and SO2 Exhaust system, humidifier, cyclone,scrubber, electrostatic precipitator, and acid plant

Sintering Particulates (dust) and SO2 Exhaust system, humidifier, electro-static precipitator, and acid plant

Calcining Zinc oxide fume, particulates, Exhaust system, baghouse, scrubber or SO2, CO acid plant

Retorts: electric arc

Nonferrous smelters, Blast furnaces and cupolas-recovery of Dust, fumes, particulates, oil vapor, Exhaust systems, cooling devices, COsecondary metal from scrap and slag smoke, CO burners and baghouses or precipitators

Reverberatory furnaces Dust, fumes, particulates, smoke, Exhaust systems, and baghouses orgaseous fluxing materials precipitators, or venturi scrubbers

Sweat furnaces Smoke, particulates, fumes Precleaning metal and exhaust systemswith afterburner and baghouse

Wire reclamation and autobody burning Smoke, particulates Scrubbers and afterburners

Paint and varnish Resin manufacturing: closed reaction Acrolein, other aldehydes and fatty Exhaust systems with scrubbers andmanufacturing vessel acids (odors), phthalic anhydride fume burners

(sublimed)Varnish: cooking-open or closed vessels Ketones, fatty acids, formic acids, Exhaust system with scrubbers and

acetic acid, glycerine, acrolein, other fume burners; close-fitting hoodsaldehydes, phenols and terpenes; required for open kettlesfrom tall oils, hydrogen sulfide, alkyl sulfide, butyl mercaptan, and thiofen (odors)

Solvent thinning Olefins, branched-chain aromatics Exhaust system with fume burnersand ketones (odors), solvents

Rendering plants Feedstock storage and housekeeping Odors Quick processing, washdown of allconcrete surfaces, paving of dirtroads, proper sewer maintenance, enclosure, packed towers

Cookers and percolators SO2, mercaptans, ammonia, odors Exhaust system, condenser, scrubber,or incinerator

Grinding Particulates (dust) Exhaust system and scrubber

Roofing plants Felt or paper saturators: spray section, Asphalt vapors and particulates (liquid) Exhaust system with high inlet velocity(asphalt saturators) asphalt tank, wet looper at hoods (3658 m/s [>200 ft/min])

with either scrubbers, baghouses, ortwo-stage low-voltage electrostatic precipitators


human health from air pollution. This evidence ranges from the rapidrise of emphysema as a major health problem, through identification ofcarcinogenic compounds in smog, to statistical evidence that peopleexposed to polluted atmospheres over extended periods of time sufferfrom a number of ailments and a reduction in their life span. Theremay even be a significant indirect exposure to air pollution. As notedabove, air pollutants may be deposited onto vegetation or into bodies ofwater, where they enter the food chain. The impact of such indirectexposures is still under review.

A large body of evidence is available to indicate that atmospheric pol-lution in varying degrees does affect health adversely. [Amdur, Melvin,and Drinker, “Effect of Inhalation of Sulfur Dioxide by Man,” Lancet, 2,758 (1953); Barton, Corn, Gee, Vassallo, and Thomas, “Response ofHealthy Men to Inhaled Low Concentrations of Gas-Aerosol Mixtures,”Arch. Environ. Health, 18, 681 (1969); Bates, Bell, Burnham, Hazucha,and Mantha, “Problems in Studies of Human Exposure to Air Pollu-tants,” Can. Med. Assoc. J., 103, 833 (1970); Ciocco and Thompson, “AFollow-Up of Donora Ten Years After: Methodology and Findings,” Am.J. Public Health, 51, 155 (1961); Daly, “Air Pollution and Causes ofDeath,” Br. J. Soc. Med., 13, 14 (1959); Jaffe, “The Biological Effect ofPhotochemical Air Pollutants on Man and Animals,” Am. J. PublicHealth, New York, 57, 1269 (1967); New York Academy of Medicine,Committee on Public Health, “Air Pollution and Health,” Bull. N.Y.Acad. Med., 42, 588 (1966); Pemberton and Goldberg, “Air Pollutionand Bronchitis,” Br. Med. J., London, 2, 567 (1954); Snell andLuchsinger, “Effect of Sulfur Dioxide on Expiratory Flowrates and TotalRespiratory Resistance in Normal Human Subjects,” Arch. Environ.Health, Chicago, 18, 693 (1969); Speizer and Frank, “A Comparison ofChanges in Pulmonary Flow Resistance in Healthy Volunteers AcutelyExposed to SO2 by Mouth and by Nose,” J. Ind. Med., 23 75 (1966);Stocks, “Cancer and Bronchitis Mortality in Relation to AtmosphericDeposit and Smoke,” Br. Med. J. London, 1, 74 (1959); Toyama, “Air Pol-lution and Its Health Effects in Japan,” Arch. Environ. Health, Chicago,8, 153 (1963); U.K. Ministry of Health, “Mortality and Morbidity DuringLondon Fog of December 1952,” Report on Public Health and MedicalSubjects No. 95, London, 1954; U.S. Public Health Service, “Air Pollu-tion in Donora, Pa.: Preliminary Report,” Public Health Bull. 306.] Itcontributes to excesses of death, increased morbidity, and earlier onset ofchronic respiratory diseases. There is evidence of a relationship betweenthe intensity of the pollution and the severity of attributable health effectsand a consistency of the relationship between these environmentalstresses and diseases of the target organs. Air pollutants can both initiateand aggravate a variety of respiratory diseases including asthma. In fact,the clinical presentation of asthma may be considered an air pollutionhost-defense disorder brought on by specific airborne irritants: pollens,infectious agents, and gaseous and particulate chemicals. The bron-chopulmonary response to these foreign irritants is bronchospasm andhypersecretion; the airways are intermittently and reversibly obstructed.

Air-pollutant effects on neural and sensory functions in humansvary widely. Odorous pollutants cause only minor annoyance; yet, ifpersistent, they can lead to irritation, emotional upset, anorexia, andmental depression. Carbon monoxide can cause death secondary tothe depression of the respiratory centers of the central nervous sys-tem. Short of death, repeated and prolonged exposure to carbonmonoxide can alter sensory protection, temporal perception, andhigher mental functions. Lipid-soluble aerosols can enter the bodyand be absorbed in the lipids of the central nervous system. Oncethere, their effects may persist long after the initial contact has beenremoved. Examples of agents of long-term chronic effects are organicphosphate pesticides and aerosols carrying the metals lead, mercury,and cadmium.

The acute toxicological effects of most air contaminants are reason-ably well understood, but the effects of exposure to heterogenous mix-tures of gases and particulates at very low concentrations are onlybeginning to be comprehended. Two general approaches can be usedto study the effects of air contaminants on humans: epidemiology,which attempts to associate the effect in large populations with thecause, and laboratory research, which begins with the cause andattempts to determine the effects. Ideally, the two methods shouldcomplement each other.

EPA recognizes that scientific studies show a link between inhal-able PM (alone and in combination with other pollutants in the air)and a series of health effects. While both coarse and fine particlesaccumulated in the respiratory system and are associated with numer-ous adverse health effects, fine particles have been more clearly tiedto the most serious health effects. Fine particles have been associatedwith decreased lung functions, disease, and even premature death.The elderly and children are notable in the sensitive groups thatappear to be at greatest risk (JAWMA Special Issues, July and August2000; PM2000, Particulate Matter and Health—The Scientific Basisfor Regulatory Decision Making).

Epidemiology, the more costly of the two, requires great care inplanning and often suffers from incomplete data and lack of controls.One great advantage, however, is that moral barriers do not limit itsapplication to humans as they do with some kinds of laboratoryresearch. The method is therefore highly useful and has producedconsiderable information. Laboratory research is less costly than epi-demiology, and its results can be checked against controls and verifiedby experimental repetition.

A SOURCE-CONTROL-PROBLEM STRATEGY

Strategy Control technology is self-defeating if it creates unde-sirable side effects in meeting objectives. Air pollution control mustbe considered in terms of regulatory requirements, total technologicalsystems (equipment and processes), and ecological consequences,

TABLE 22-17 Control Techniques Applicable to Unit Processes at Important Emission Sources (Concluded)


Roofing plants Crushed rock or other minerals Particulates (dust) Local exhaust system, cyclone or(asphalt saturators) handling multiple cyclones

Steel mills Blast furnaces: charging, pouring CO, fumes, smoke, particulates (dust) Good maintenance, seal leaks; use ofhigher ratio of pelletized or sinteredore; CO burned in waste-heat boilers,stoves, or coke ovens; cyclone,scrubber, and baghouse

Electric steel furnaces: charging, Fumes, smoke, particulates (dust), CO Segregating dirty scrap; properpouring, oxygen blow hooding, baghouses or electrostatic

precipitatorOpen-hearth furnaces: oxygen blow, Fumes, smoke, SOx, particulates Proper hooding, settling chambers,

pouring (dust), CO, NOx waste-heat boiler, baghouse, electro-static precipitator, and wet scrubber

Basic oxygen furnaces: oxygen blowing Fumes, smoke, CO, particulates (dust) Proper hooding (capturing of emissions and dilute CO), scrubbers, or electrostatic precipitator

Raw material storage Particulates (dust) Wetting or application of plastic sprayPelletizing Particulates (dust) Proper hooding, cyclone, baghouseSintering Smoke, particulates (dust), SO2, NOx Proper hooding, cyclones, wet

scrubbers, baghouse, or precipitator


such as the problems of treatment and disposal of collected pollutants.It should be noted that the 1990 Clean Air Act Amendments (CAAA)have impacted on the control approach in a significant manner. In par-ticular, the CAAA have placed an increased emphasis on control tech-nology by requiring Best Available Control Technology (BACT) onnew major sources and modifications, and by requiring MaximumAchievable Control Technology (MACT) on new and existing majorsources of Hazardous Air Pollutants (HAPs).

The control strategy for environmental-impact assessment oftenfocuses on five alternatives whose purpose would be the reductionand/or elimination of pollutant emissions:

1. Elimination of the operation entirely or in part2. Modification of the operation3. Relocation of the operation4. Application of appropriate control technology5. Combinations thereofIn light of the relatively high costs often associated with pollution-

control systems, engineers are directing considerable effort towardprocess modification to eliminate as much of the pollution problem aspossible at the source. This includes evaluating alternative manufac-turing and production techniques, substituting raw materials, andimproving process-control methods. Unfortunately, if there is no alter-native, the application of the correct pollution-control equipment isessential. The equipment must be designed to comply with regulatoryemission limitations on a continual basis, interruptions being subject tosevere penalty depending upon the circumstances. The requirementfor design performance on a continual basis places very heavy empha-sis on operation and maintenance practices. The escalating costs ofenergy, labor, and materials can make operation and maintenance con-siderations even more important than the original capital cost.

Factors in Control-Equipment Selection In order to solve anair-pollution problem, the problem must be defined in detail. A num-ber of factors must be considered prior to selecting a particular pieceof air-pollution-control equipment. In general, these factors can begrouped into three categories: environmental, engineering, and eco-nomic.

Environmental Factors These include (1) equipment location,(2) available space, (3) ambient conditions, (4) availability of adequateutilities (i.e., power, water, etc.) and ancillary-system facilities (i.e.,waste treatment and disposal, etc.), (5) maximum allowable emission(air pollution codes), (6) aesthetic considerations (i.e., visible steam orwater-vapor plume, etc.), (7) contributions of the air-pollution-controlsystem to wastewater and land pollution, and (8) contribution of theair-pollution-control system to plant noise levels.

Engineering Factors These include:1. Contaminant characteristics (e.g., physical and chemical proper-

ties, concentration, particulate shape and size distribution [in the case ofparticulates], chemical reactivity, corrosivity, abrasiveness, and toxicity)

2. Gas-stream characteristics (e.g., volume flow rate, temperature,pressure, humidity, composition, viscosity, density, reactivity, com-bustibility, corrosivity, and toxicity)

3. Design and performance characteristics of the particular controlsystem (i.e., size and weight, fractional efficiency curves [in the case ofparticulates]), mass-transfer and/or contaminant-destruction capabil-ity (in the case of gases or vapors), pressure drop, reliability, turndowncapability, power requirements, utility requirements, temperaturelimitations, maintenance requirements, operating cycles (includingstartup and shutdown) and flexibility toward complying with morestringent air-pollution codes.

Economic Factors These include capital cost (equipment, installa-tion, engineering, etc.), operating cost (utilities, maintenance, etc.),emissions fees, and life-cycle cost over the expected equipment lifetime.

Comparing Control-Equipment Alternatives The final choice inequipment selection is usually dictated by the equipment capable ofachieving compliance with regulatory codes at the lowest uniform annualcost (amortized capital investment plus operation and maintenancecosts). To compare specific control-equipment alternatives, knowledgeof the particular application and site is essential. A preliminary screening,however, may be performed by reviewing the advantages and disadvan-tages of each type of air-pollution-control equipment. General advan-tages and disadvantages of the most popular types of air-pollution

equipment for gases and particulates are presented in Tables 22-18through 22-30. Other activities that must be accomplished before finalcompliance is achieved are presented in Table 22-31.

In addition to using annualized cost comparisons in evaluating anair-pollution-control (APC) equipment installation, the impact of the1990 Clean Air Act Amendments (CAAA) and resulting regulationsalso must be included in the evaluation. The CAAA prescribes specificpollution-control requirements for particular industries and locations.As an example, the CAAA requires that any major stationary source ormajor modification plan that is subject to Prevention of SignificantDeterioration (PSD) requirements must undergo a Best AvailableControl Technology (BACT) analysis. The BACT analysis is done on acase-by-case basis. The process involves evaluating the possible typesof air-pollution-control equipment that could be used for technologyand energy and in terms of the environment and economy. The analy-sis uses a top-down approach that lists all available control technolo-gies in descending order of effectiveness. The most stringenttechnology is chosen unless it can be demonstrated that, due to tech-nical, energy, environmental, or economic considerations, this type ofAPC technology is not feasible.

The 1990 CAAA introduced a new level of control for hazardous(toxic) air pollutants (HAPs). As a result, EPA has identified 188 HAPsfor regulation. Rather than rely upon ambient air quality standards toset acceptable exposures to HAPs, the CAAA requires that EPA pro-mulgate through the end of the decade Maximum Achievable ControlTechnology (MACT) standards for controlling HAPs emitted fromspecified industries. These standards are based on the level of controlestablished by the best performing 12 percent of industries in each ofthe categories identified by EPA.

TABLE 22-18 Advantages and Disadvantages of Cyclone Collectors

Advantages1. Low cost of construction2. Relatively simple equipment with few maintenance problems3. Relatively low operating pressure drops (for degree of particulate

removal obtained) in the range of approximately 2- to 6-in water column4. Temperature and pressure limitations imposed only by the materials of

construction used5. Collected material recovered dry for subsequent processing or disposal6. Relatively small space requirements

Disadvantages1. Relatively low overall particulate collection efficiencies, especially on

particulates below 10 µm in size2. Inability to handle tacky materials

TABLE 22-19 Advantages and Disadvantages of Wet Scrubbers

Advantages1. No secondary dust sources2. Relatively small space requirements3. Ability to collect gases as well as particulates (especially “sticky” ones)4. Ability to handle high-temperature, high-humidity gas streams5. Capital cost low (if wastewater treatment system not required)6. For some processes, gas stream already at high pressures (so pressure-

drop considerations may not be significant)7. Ability to achieve high collection efficiencies on fine particulates (how-

ever, at the expense of pressure drop)8. Ability to handle gas streams containing flammable or explosive materials

Disadvantages1. Possible creation of water-disposal problem2. Product collected wet3. Corrosion problems more severe than with dry systems4. Steam plume opacity and/or droplet entrainment possibly objectionable5. Pressure-drop and horsepower requirements possibly high6. Solids buildup at the wet-dry interface possibly a problem7. Relatively high maintenance costs8. Must be protected from freezing9. Low exit gas temperature reduces exhaust plume dispersion

10. Moist exhaust gas precludes use of most additional controls


DISPERSION FROM STACKS

Stacks discharging to the atmosphere have long been the most com-mon industrial method of disposing of waste gases. The concentra-tions to which humans, plants, animals, and structures are exposed atground level can be reduced significantly by emitting the waste gasesfrom a process at great heights. Although tall stacks may be effectivein lowering the ground-level concentration of pollutants, they do notin themselves reduce the amount of pollutants released into the atmo-sphere. However, in certain situations, their use can be the most prac-tical and economical way of dealing with an air-pollution problem.

Preliminary Design Considerations To determine the accept-ability of a stack as a means of disposing of waste gases, the acceptableground-level concentration (GLC) of the pollutant or pollutants mustbe determined. The topography of the area must also be considered sothat the stack can be properly located with respect to buildings andhills that might introduce a factor of air turbulence into the operationof the stack. Awareness of the meteorological conditions prevalent inthe area, such as the prevailing winds, humidity, and rainfall, is alsoessential. Finally, an accurate knowledge of the constituents of thewaste gas and their physical and chemical properties is paramount.

Wind Direction and Speed Wind direction is measured at theheight at which the pollutant is released, and the mean direction willindicate the direction of travel of the pollutants. In meteorology, it isconventional to consider the wind direction as the direction fromwhich the wind blows; therefore, a northwest wind will move pollu-tants to the southeast of the source.

The effect of wind speed is twofold: (1) Wind speed will deter-mine the travel time from a source to a given receptor; and (2) windspeed will affect dilution in the downwind direction. Generally, theconcentration of air pollutants downwind from a source is inverselyproportional to wind speed.

Wind speed has velocity components in all directions so that thereare vertical motions as well as horizontal ones. These random motionsof widely different scales and periods are essentially responsible forthe movement and diffusion of pollutants about the mean downwindpath. These motions can be considered atmospheric turbulence. If thescale of a turbulent motion (i.e., the size of an eddy) is larger than thesize of the pollutant plume in its vicinity, the eddy will move that por-tion of the plume. If an eddy is smaller than the plume, its effect willbe to diffuse or spread out the plume. This diffusion caused by eddymotion is widely variable in the atmosphere, but even when the effectof this diffusion is least, it is in the vicinity of three orders of magni-tude greater than diffusion by molecular action alone.

Mechanical turbulence is the induced-eddy structure of the atmo-sphere due to the roughness of the surface over which the air is passing.Therefore, the existence of trees, shrubs, buildings, and terrain featureswill cause mechanical turbulence. The height and spacing of the ele-ments causing the roughness will affect the turbulence. In general, thehigher the roughness elements, the greater the mechanical turbulence.In addition, mechanical turbulence increases as wind speed increases.

TABLE 22-20 Advantages and Disadvantages of Dry Scrubbers

Advantages1. No wet sludge to dispose of2. Relatively small space requirements3. Ability to collect acid gases at high efficiencies4. Ability to handle high-temperature gas streams5. Dry exhaust allows addition of fabric filter to control particulate

Disadvantages1. Acid gas control efficiency not as high as with wet scrubber2. No particulate collection—dry scrubber generates particulate3. Corrosion problems more severe than with dry systems4. Solids buildup at the wet-dry interface possibly a problem5. Relatively high maintenance costs6. Must be protected from freezing7. Low exit gas temperature reduces exhaust plume dispersion

TABLE 22-21 Advantages and Disadvantages of Electrostatic Precipitators

Advantages1. Extremely high particulate (coarse and fine) collection efficiencies

attainable (at a relatively low expenditure of energy)2. Collected material recovered dry for subsequent processing or disposal3. Low pressure drop4. Designed for continuous operation with minimum maintenance

requirements5. Relatively low operating costs6. Capable of operation under high pressure (to 150 lbf/in2) or vacuum

conditions7. Capable of operation at high temperatures [to 704°C(1300°F)]8. Relatively large gas flow rates capable of effective handling

Disadvantages1. High capital cost2. Very sensitive to fluctuations in gas-stream conditions (in particular,

flows, temperature, particulate and gas composition, and particulateloadings)

3. Certain particulates difficult to collect owing to extremely high- or low-resistivity characteristics

4. Relatively large space requirements required for installation5. Explosion hazard when treating combustible gases and/or collecting

combustible particulates6. Special precautions required to safeguard personnel from the high

voltage7. Ozone produced by the negatively charged discharge electrode during

gas ionization8. Relatively sophisticated maintenance personnel required9. Gas ionization may cause dissociation of gas stream constituents and

result in creation of toxic byproducts10. Sticky particulates may be difficult to remove from plates11. Not effective in capturing some contaminants that exist as vapors at

high temperatures (e.g., heavy metals, dioxins)

TABLE 22-22 Advantages and Disadvantages of Fabric-Filter Systems

Advantages1. Extremely high collection efficiency on both coarse and fine (sub-

micrometer) particles2. Relatively insensitive to gas-stream fluctuation; efficiency and pressure

drop relatively unaffected by large changes in inlet dust loadings forcontinuously cleaned filters

3. Filter outlet air capable of being recirculated within the plant in manycases (for energy conservation)

4. Collected material recovered dry for subsequent processing or disposal5. No problems with liquid-waste disposal, water pollution, or liquid

freezing6. Corrosion and rusting of components usually not problems7. No hazard of high voltage, simplifying maintenance and repair and

permitting collection of flammable dusts8. Use of selected fibrous or granular filter aids (precoating), permitting

the high-efficiency collection of submicrometer smokes and gaseouscontaminants

9. Filter collectors available in a large number of configurations, resultingin a range of dimensions and inlet and outlet flange locations to suitinstallment requirements

10. Relatively simple operation

Disadvantages1. Temperatures much in excess of 288°C (550°F) requiring special refrac-

tory mineral or metallic fabrics that are still in the developmental stageand can be very expensive

2. Certain dusts possibly requiring fabric treatments to reduce dust seep-ing or, in other cases, assist in the removal of the collected dust

3. Concentrations of some dusts in the collector (∼50 g/m3) forming a pos-sible fire or explosion hazard if a spark or flame is admitted by accident;possibility of fabrics burning if readily oxidizable dust is being collected

4. Relatively high maintenance requirements (bag replacement, etc.)5. Fabric life possibly shortened at elevated temperatures and in the pres-

ence of acid or alkaline particulate or gas constituents6. Hygroscopic materials, condensation of moisture, or tarry adhesive com-

ponents possibly causing crusty caking or plugging of the fabric orrequiring special additives

7. Replacement of fabric, possibly requiring respiratory protection formaintenance personnel

8. Medium pressure-drop requirements, typically in the range 4- to 10-inwater column


Thermal turbulence is turbulence induced by the stability of theatmosphere. When the Earth’s surface is heated by the sun’s radiation,the lower layer of the atmosphere tends to rise and thermal turbulencebecomes greater, especially under conditions of light wind. On clearnights with wind, heat is radiated from the Earth’s surface, resulting inthe cooling of the ground and the air adjacent to it. This results inextreme stability of the atmosphere near the Earth’s surface. Underthese conditions, turbulence is at a minimum. Attempts to relate differ-ent measures of turbulence of the wind (or stability of the atmosphere)to atmospheric diffusion have been made for some time. The measure-ment of atmospheric stability by temperature-difference measurementson a tower is frequently utilized as an indirect measure of turbulence,particularly when climatological estimates of turbulence are desired.

Lapse Rate and Atmospheric Stability Apart from mechanicalinterference with the steady flow of air caused by buildings and otherobstacles, the most important factor that influences the degree of tur-bulence and hence the speed of diffusion in the lower air is the variationof temperature with height above the ground, referred to as the “lapserate.” The dry-adiabatic lapse rate (DALR) is the temperature changefor a rising parcel of dry air. The dry-adiabatic lapse rate can be approx-imated as −1°C per 100 m, or dT/dz = −10−2 °C/m or −5.4°F/1000 ft. Ifthe rising air contains water vapor, the cooling due to adiabatic expan-sion will result in the relative humidity being increased, and saturationmay be reached. Further ascent would then lead to condensation ofwater vapor, and the latent heat thus released would reduce the rate ofcooling of the rising air. The buoyancy force on a warm-air parcel iscaused by the difference between its density and that of the surround-ing air. The perfect-gas law shows that, at a fixed pressure (altitude), thetemperature and density of an air parcel are inversely related; tempera-ture is normally used to determine buoyancy because it is easier to mea-sure than density. If the temperature gradient (lapse rate) of theatmosphere is the same as the adiabatic lapse rate, a parcel of air dis-placed from its original position will expand or contract in such a man-ner that its density and temperature remain the same as itssurroundings. In this case there will be no buoyancy forces on the dis-placed parcel, and the atmosphere is termed “neutrally stable.”

If the atmospheric temperature decreases faster with increasing alti-tude than the adiabatic lapse rate (superadiabatic), a parcel of air dis-placed upward will have a higher temperature than the surroundingair. Its density will be lower, giving it a net upward buoyancy force. Theopposite situation exists if the parcel of air is displaced downward, andthe parcel experiences a downward buoyancy force. Once a parcel ofair has started moving up or down, it will continue to do so, causingunstable atmospheric conditions. If the temperature decreases moreslowly with increasing altitude than the adiabatic lapse rate, a displacedparcel of air experiences a net restoring force. The buoyancy forcesthen cause stable atmospheric conditions (see Fig. 22-5).

Strongly stable lapse rates are commonly referred to as inversions.The strong stability inhibits mixing across the inversion layer. Normallythese conditions of strong stability extend for only several hundredmeters vertically. The vertical extent of the inversion is referred to as theinversion depth. Two distinct types are observed: the ground-level inver-sion, caused by radiative cooling of the ground at night, and inversionsaloft, occurring between 500 and several thousand meters above theground (see Fig. 22-6). Some of the more common lapse-rate profileswith the corresponding effect on stackplumes are presented in Fig. 22-7.

From the viewpoint of air pollution, both stable surface layers andlow-level inversions are undesirable because they minimize the rate ofdilution of contaminants in the atmosphere. Even though the surfacelayer may be unstable, a low-level inversion will act as a barrier to ver-tical mixing, and contaminants will accumulate in the surface layer

TABLE 22-23 Advantages and Disadvantages of Absorption Systems (Packed and Plate Columns)

Advantages1. Relatively low pressure drop2. Standardization in fiberglass-reinforced plastic (FRP) construction per-

mitting operation in highly corrosive atmospheres3. Capable of achieving relatively high mass-transfer efficiencies4. Increasing the height and/or type of packing or number of plates capa-

ble of improving mass transfer without purchasing a new piece of equip-ment

5. Relatively low capital cost6. Relatively small space requirements7. Ability to collect particulates as well as gases8. Collected substances may be recovered by distillation

Disadvantages1. Possibility of creating water (or liquid) disposal problem2. Product collected wet3. Particulates deposition possibly causing plugging of the bed or plates4. When FRP construction is used, sensitive to temperature5. Relatively high maintenance costs6. Must be protected from freezing

TABLE 22-24 Comparison of Plate and Packed Columns

Packed column1. Lower pressure drop2. Simpler and cheaper to construct3. Preferable for liquids with high-foaming tendencies

Plate column1. Less susceptible to plugging2. Less weight3. Less of a problem with channeling4. Temperature surge resulting in less damage

TABLE 22-25 Advantages and Disadvantages of Adsorption Systems

Advantages1. Possibility of product recovery2. Excellent control and response to process changes3. No chemical-disposal problem when pollutant (product) recovered and

returned to process4. Capability of systems for fully automatic, unattended operation5. Capability to remove gaseous or vapor contaminants from process

streams to extremely low levels

Disadvantages1. Product recovery possibly requiring an exotic, expensive distillation (or

extraction) scheme2. Adsorbent progressively deteriorating in capacity as the number of

cycles increases3. Adsorbent regeneration requiring a steam or vacuum source4. Relatively high capital cost5. Prefiltering of gas stream possibly required to remove any particulate

capable of plugging the adsorbent bed6. Cooling of gas stream possibly required to get to the usual range of

operation (less than 49°C [120°F])7. Relatively high steam requirements to desorb high-molecular-weight

hydrocarbons8. Spent adsorbent may be considered a hazardous waste9. Some contaminants may undergo a violent exothermic reaction with the

adsorbent

TABLE 22-26 Advantages and Disadvantages of Combustion Systems

Advantages1. Simplicity of operation2. Capability of steam generation or heat recovery in other forms3. Capability for virtually complete destruction of organic contaminants

Disadvantages1. Relatively high operating costs (particularly associated with fuel require-

ments)2. Potential for flashback and subsequent explosion hazard3. Catalyst poisoning (in the case of catalytic incineration)4. Incomplete combustion, possibly creating potentially worse pollution

problems5. Even complete combustion may produce SO2, NOx, and CO2

6. High temperature components and exhaust may be hazardous to main-tenance personnel and birds

7. High maintenance requirements—especially if operation is cyclic


below the inversion. Stable atmospheric conditions tend to be morefrequent and longest in persistence in the autumn, but inversions andstable lapse rates are prevalent at all seasons of the year.

Design Calculations For a given stack height, the calculationalsequence begins by first estimating the effective height of the emis-sion, employing an applicable plume-rise equation. The maximumGLC may then be determined by using an appropriate atmospheric-diffusion equation. A simple comparison of the calculated GLC for theparticular pollutant with the maximum GLC permitted by the local air-pollution codes dictates whether the stack is operating satisfactorily.Conversely, with knowledge of the maximum acceptable GLC stan-dards, a stack that will satisfy these standards can be properly designed.

Effective Height of an Emission The effective height of anemission rarely corresponds to the physical height of the stack. If theplume is caught in the turbulent wake of the stack or of buildings inthe vicinity of the stack, the effluent will be mixed rapidly downwardtoward the ground. If the plume is emitted free of these turbulentzones, a number of source emission characteristics and meteorologicalfactors influence the rise of the plume. The source emission charac-teristics include the gas flow rate and the temperature of the effluentat the top of the stack and the diameter of the stack opening. Themeteorological factors influencing plume rise include wind speed, airtemperature, shear of the wind speed with height, and atmosphericstability. No theory on plume rise presently takes into account all ofthese variables. Most of the equations that have been formulated forcomputing the effective height of an emission are semi-empirical.When considering any of these plume-rise equations, it is important toevaluate each in terms of the assumptions made and the circum-stances existing at the time that the particular correlation was formu-lated. The formulas generally are not applicable to tall stacks (above305 m [1000 ft] effective height).

The effective stack height (equivalent to the effective height of theemission) is the sum of the actual stack height, the plume rise due tothe exhaust velocity (momentum) of the issuing gases, and the buoy-ancy rise, which is a function of the temperature of the gases beingemitted and the atmospheric conditions.

Some of the more common plume-rise equations have been sum-marized by Buonicore and Theodore (Industrial Control Equipmentfor Gaseous Pollutants, vol. 2, CRC Press, Boca Raton, Florida, 1975)and include:

TABLE 22-27 Advantages and Disadvantages of Condensers

Advantages1. Pure product recovery (in the case of indirect-contact condensers)2. Water used as the coolant in an indirect-contact condenser (i.e., shell-

and-tube heat exchanger), not in contact with contaminated gas stream,and is reusable after cooling

3. May be used to produce vacuum to remove contaminants from process

Disadvantages1. Relatively low removal efficiency for gaseous contaminants (at concen-

trations typical of pollution-control applications)2. Coolant requirements possibly extremely expensive3. Direct-contact condenser may produce water discharge problems

FIG. 22-5 Stability criteria with measured lapse rate.

FIG. 22-6 Characteristic lapse rates under inversion conditions.

Temperature gradient Observation Description

Strong lapse—looping (unstable)This is usually a fair-weather daytime condition, since strong solar heating of the groundis required. Looping is not favored by cloudiness, snow cover, or strong winds.

Weak lapse—coning (slightly unstable or neutral)This is usually favored by cloudy and windy conditions and may occur day or night. Indry climates it may occur infrequently, and in cloudy climates it may be the most fre-quent type observed.

Inversion—fanning (stable)This is principally a nighttime condition. It is favored by light winds, clear skies, andsnow cover. The condition may persist in some climates for several days at a time duringwinter, especially in the higher latitudes.

Inversion below, lapse aloft—lofting (transition from unstable to stable)This condition occurs during transition from lapse to inversion and should be observedmost frequently near sunset; it may be very transitory or persist for several hours. Theshaded zone of strong effluent concentration is caused by trapping by the inversion ofeffluent carried into the stable layer by turbulent eddies that penetrate the layer for ashort distance.

Lapse below, inversion aloft—fumigation (transition from stable to unstable)This occurs when the nocturnal inversion is dissipated by heat from the morning sun.The lapse layer usually starts at the ground and works its way upward (less rapidly inwinter than in summer). Fumigation may also occur in sea-breeze circulations duringlate morning or early afternoon. The shaded zone of strong concentration is that portionof the plume which has not yet been mixed downward.

FIG. 22-7 Lapse-rate characteristics of atmospheric-diffusion transport of stack emissions.


• ASME, Recommended Guide for the Prediction of the Dispersion ofAirborne Effluents, ASME, New York, 1968.

• Bosanquet-Carey-Halton, Proc. Inst. Mech. Eng. (London), 162,355 (1950).

• Briggs, Plume Rise, AEC Critical Review ser., U.S. Atomic EnergyCommission, Div. Tech. Inf.

• Brummage et al., The Calculation of Atmospheric Dispersion froma Stack, CONCAWE, The Hague, 1966.

• Carson and Moses, J. Air Pollut. Control Assoc., 18, 454 (1968) and19, 862 (1969).

• Csnaday, Int. J. Air Water Pollut., 4, 47 (1961).• Davison-Bryant, Trans. Conf. Ind. Wastes, 14th Ann. Meet. Ind.

Hyg. Found. Am., 39, 1949.• Holland, Workbook of Atmospheric Dispersion Estimates, U.S.

EPA Publ. AP-26, 1970.• Lucas, Moore, and Spurr, Int. J. Air Water Pollut., 7, 473 (1963).• Montgomery et al., J. Air Pollut. Control Assoc., 22(10), 779, TVA

(1972).• Stone and Clarke, British Experience with Tall Stacks for Air Pollu-

tion Control on Large Fossil-Fueled Power Plants, American PowerConference, Chicago, 1967.

• Stumke, Staub, 23, 549 (1963).See also:

• Briggs, G. A., Plume Rise Predications: Lectures on Air Pollution andEnvironmental Impact Analyses, Workshop Proceedings, AmericanMeteorological Society, Boston, Massachusetts, 1975, pp. 59–111.

• Randerson, Darryl (ed.), Plume Rise and Buoyancy Effects, Atmos-pheric Science and Power Production, DOE Report DOE/TIC-27601, 1981.Maximum Ground-Level Concentrations The effective height

of an emission having been determined, the next step is to study itspath downward by using the appropriate atmospheric-dispersion for-mula. Some of the more popular atmospheric-dispersion calculationalprocedures have been summarized by Buonicore and Theodore (op.cit.) and include:• Bosanquet-Pearson model [Pasquill, Meteorol. Mag., 90, 33, 1063

(1961), and Gifford, Nucl. Saf., 2, 4, 47 (1961).]• Sutton model [Q.J.R. Meteorol. Soc., 73, 257 (1947).]• TVA Model [Carpenter et al., J. Air Pollut. Control Assoc., 21(8),

(1971), and Montgomery et al., J. Air Pollut. Control Assoc., 23(5),388 (1973).]See also:

• Bornstein et al., Simulation of Urban Barrier Effects on Polluted UrbanBoundary Layers Using the Three-Dimensional URBMET\TVMModel with Urban Topography, Air Pollution Proceedings, 1993.

• EPA, Guidance on the Application of Refined Dispersion Models forAir Toxins Releases, EPA-450/4-91-007.

• Zannetti, Paolo, Air Pollution Modeling: Theories, ComputationalMethods, and Available Software, Van Nostrand, Reinhold, NewYork, 1990.

• Zannetti, Paolo, Numerical Simulation Modeling of Air Pollution:An Overview, Ecological Physical Chemistry, 2d InternationalWorkshop, May 1992.

Miscellaneous EffectsEvaporative Cooling When effluent gases are washed to absorb

certain constituents prior to emission, the gases are cooled and becomesaturated with water vapor. Upon release of the gases, further coolingdue to contact with cold surfaces of ductwork or stack is likely. This cool-ing causes water droplets to condense in the gas stream. Upon release ofthe gases from the stack, the water droplets evaporate, withdrawing thelatent heat of vaporization from the air and cooling the plume. Theresulting negative buoyancy reduces the effective stack height. The resultmay be a plume (with a greater density than that of the ambient atmo-sphere) that will fall to the ground. If any pollutant remains after scrub-bing, its full effect will be felt on the ground in the vicinity of the stack.

Aerodynamic Downwash Should the stack exit velocity be toolow as compared with the speed of the crosswind, some of the effluentcan be pulled downward by the low pressure on the lee side of thestack. This phenomenon, known as “stack-tip downwash,” can be min-imized by keeping the exit velocity greater than the mean wind speed(i.e., typically twice the mean wind speed). Another way to minimizestack-tip downwash is to fit the top of the stack with a flat disc thatextends for at least one stack diameter outward from the stack.

If it becomes necessary to increase the stack-gas exit velocity toavoid downwash, it may be necessary to remodel the stack exit. A ven-turi-nozzle design has been found to be the most effective. Thisdesign also keeps pressure losses to a minimum.

Building Downwash A review must be conducted for each stackto determine if building downwash effects need to be considered.Atmospheric flow is disrupted by aerodynamic forces in the immedi-ate vicinity of structures or terrain obstacles. The disrupted flow neareither building structures or terrain obstacles can both enhance thevertical dispersion of emissions from the source and reduce the effec-tive height of the emissions from the source, resulting in an increasein the maximum GLC.

EPA Air Dispersion Models EPA addresses modeling tech-niques in the “Guideline on Air Quality Models” [Appendix W (July2003) of 40 CFR Part 51]. The guideline provides a common basis forestimating the air quality concentrations of criteria pollutants used inassessing control strategies and developing emission limits. The con-tinuing development of new air quality models in response to regula-tory requirements and the expanded requirements for models tocover ever more complex problems have emphasized the need forperiodic review and update of guidance on these techniques. Infor-mation on the current status of modeling guidance can always beobtained from EPA’s regional offices.

The guideline recommends air quality modeling techniques thatshould be applied to State Implementation Plan (SIP) revisions forexisting sources and to new source reviews (NSRs), including preven-tion of significant deterioration (PSD). In addition the guideline servesto identify, for all interested parties, those techniques and databases thatEPA considers acceptable. Dispersion models, while uniquely filling

TABLE 22-28 Advantages and Disadvantages of Biofiltration

Advantages1. Uses natural biological processes and materials2. Relatively simple and economical3. High destruction efficiencies for oxygen-rich, low-contaminant concen-

tration gas streams4. Waste products are CO2 and water

Disadvantages1. Raw gas must not be lethal to microorganisms2. Gas stream must be maintained at proper temperature and humidity3. Heavy particulate loadings can damage pore structure of filter bed

TABLE 22-29 Advantages and Disadvantages of Membrane Filtration

Advantages1. Low energy utilization2. Modular design3. Low capital costs4. Low maintenance5. Superior separation ability

Disadvantages1. Potential particulate fouling problems if not properly designed

TABLE 22-30 Advantages and Disadvantages of Selective Catalytic Reduction of Nitrogen Oxides

Advantages1. Capable of 90% NOx removal2. Uses readily available urea reagent3. Exhaust products are N2 and water

Disadvantages1. Spent catalyst may be considered hazardous waste2. Gas stream must be maintained at proper temperature and humidity3. Heavy particulate loadings can damage pore structure of filter bed


one program need, have become a primary analytical tool in most airquality assessments. Air quality measurements can be used in a comple-mentary manner to dispersion models, with due regard for the strengthsand weaknesses of both analysis techniques. The diversity of the nation’stopography and climate, and variations in source configurations andoperating characteristics dictate against a strict modeling “cookbook.”There is no one model capable of properly addressing all conceivable sit-uations even within a broad category such as point sources.

The guideline provides a consistent basis for selection of the mostaccurate models and databases for use in air quality assessments.There are two levels of sophistication of models. The first level con-sists of relatively simple estimation techniques that generally use pre-set, worst-case meteorological conditions to provide conservativeestimates of the air quality impact of a specific source, or source cate-gory. These are called screening techniques or screening models. Thepurpose of such techniques is to eliminate the need for more detailedmodeling for those sources that clearly will not cause or contribute toambient concentrations in excess of either the National Ambient AirQuality Standards (NAAQS) or the allowable PSD concentrationincrements. The second level consists of those analytical techniquesthat provide more detailed treatment of physical and chemical atmos-pheric processes, require more detailed and precise input data, andprovide more specialized concentration estimates. Most of the screen-ing and refined models discussed in the guideline, codes, associateddocumentation, and other useful information are available for down-load from EPA’s Support Center for Regulatory Air Modeling(SCRAM) Internet web site at http://www.epa.gov/scram001.

CONTROL OF GASEOUS EMISSIONS

There are four chemical-engineering unit operations commonly usedfor the control of gaseous emissions:

1. Absorption. Sec. 4, “Thermodynamics”; and Sec. 18, “LiquidGas Systems.” For plate columns, see Sec. 18, “Gas-Liquid Contact-ing: Plate Columns.” For packed columns, see Sec. 18, “Gas-LiquidContacting: Packed Columns.”

2. Adsorption. See Sec. 16, “Adsorption and Ion Exchange.”3. Combustion. See Sec. 9, “Heat Generation” and “Fired Process

Equipment.” For incinerators, see material under these subsections.4. Condensation. See Sec. 10, “Heat Transmission”; Sec. 11, “Heat-

Transfer Equipment”; and Sec. 12, “Evaporative Cooling.” For direct-

contact condensers, See Sec. 11, “Evaporator Accessories”; and Sec.12, “Evaporative Cooling.” For indirect-contact condensers, see Sec.10, “Heat Transfer with Change of Phase” and “Thermal Design ofHeat-Transfer Equipment”; and Sec. 11, “Shell and Tube HeatExchangers” and “Other Heat Exchangers for Liquids and Gases.”

These operations, which are routine chemical engineering opera-tions, have been treated extensively in other sections of this handbook.

There are three additional chemical engineering unit operationsthat are increasing in use in recent years. They are:

1. Biofiltration2. Membrane filtration3. Selective catalytic reduction

and are discussed further in this section.Absorption The engineering design of gas absorption equipment

must be based on a sound application of the principles of diffusion,equilibrium, and mass transfer as developed in Secs. 5 and 14 of thehandbook. The main requirement in equipment design is to bring thegas into intimate contact with the liquid; that is, to provide a largeinterfacial area and a high intensity of interface renewal and to mini-mize resistance and maximize driving force. This contacting of thephases can be achieved in many different types of equipment, themost important being packed and plate columns. The final choicebetween them rests with the various criteria that must be met. Forexample, if the pressure drop through the column is large enough thatcompression costs become significant, a packed column may bepreferable to a plate-type column because of the lower pressure drop.

In most processes involving the absorption of a gaseous pollutantfrom an effluent gas stream, the gas stream is the processed fluid;hence, its inlet condition (flow rate, composition, and temperature)are usually known. The temperature and composition of the inlet liq-uid and the composition of the outlet gas are usually specified. Themain objectives in the design of an absorption column, then, are thedetermination of the solvent flow rate and the calculation of the prin-cipal dimensions of the equipment (column diameter and height toaccomplish the operation). These objectives can be obtained by eval-uating, for a selected solvent at a given flow rate, the number of theo-retical separation units (stage or plates) and converting them intopractical units, column heights or number of actual plates by means ofexisting correlations.

The general design procedure consists of a number of steps to betaken into consideration. These include:

TABLE 22-31 Compliance Activity and Schedule Chart

Milestones

1. Date of submittal of final control plan to appropriate agency2. Date of award of control-device contract3. Date of initiation of on-site construction or installation of emission-control equipment4. Date by which on-site construction or installation of emission-control equipment is completed5. Date by which final compliance is achieved

Activities

Designation Activity Designation Activity

A-C Preliminary investigation. K-L Review and approval of assembly drawings.A-B Source tests, if necessary. L-M Vendor prepares fabrication drawings.C-D Evaluate control alternatives. M-N Fabricate control device.D-E Commit funds for total program. L-O Prepare engineering drawings.E-F Prepare preliminary control plan and O-P Procure construction bids.

compliance schedule for agency. P-Q Evaluate construction bids.F-G Agency review and approval. Q-3 Award construction contract.G-I Finalize plans and specifications. 3-N On-site construction.I-H Procure control-device bids. N-R Install control device.H-J Evaluate control-device bids. R-4 Complete construction (system tie-in).J-2 Award control-device contract. 4-5 Startup, shakedown, source test.2-K Vendor prepares assembly drawings.

http://www.epa.gov/scram001

1. Solvent selection2. Equilibrium-data evaluation3. Estimation of operating data (usually consisting of a mass and

energy in which the energy balance decides whether the absorptionbalance can be considered isothermal or adiabatic)

4. Column selection (should the column selection not be obviousor specified, calculations must be carried out for the different types ofcolumns and the final based on economic considerations)

5. Calculation of column diameter (for packed columns, this is usu-ally based on flooding conditions, and, for plate columns, on the opti-mum gas velocity or the liquid-handling capacity of the plate)

6. Estimation of column height or number of plates (for packedcolumns, column height is obtained by multiplying the number oftransfer units, obtained from a knowledge of equilibrium and operat-ing data, by the height of a transfer unit; for plate columns, the num-ber of theoretical plates determined from the plot of equilibrium andoperating lines is divided by the estimated overall plate efficiency togive the number of actual plates, which in turn allows the columnheight to be estimated from the plate spacing)

7. Determination of pressure drop through the column (for packedcolumns, correlations dependent of packing type, column-operating data,and physical properties of the constituents involved are available to esti-mate the pressure drop through the packing; for plate columns, the pres-sure drop per plate is obtained and multiplied by the number of plates)

Solvent Selection The choice of a particular solvent is mostimportant. Frequently, water is used, as it is very inexpensive andplentiful, but the following properties must also be considered:

1. Gas solubility. A high gas solubility is desired, since thisincreases the absorption rate and minimizes the quantity of solventnecessary. Generally, solvents of a chemical nature similar to that ofthe solute to be absorbed will provide good solubility.

2. Volatility. A low solvent vapor pressure is desired, since the gasleaving the absorption unit is ordinarily saturated with the solvent, andmuch may thereby be lost.

3. Corrosiveness.4. Cost.5. Viscosity. Low viscosity is preferred for reasons of rapid

absorption rates, improved flooding characteristics, lower pressuredrops, and good heat-transfer characteristics.

6. Chemical stability. The solvent should be chemically stableand, if possible, nonflammable.

7. Toxicity.8. Low freezing point. If possible, a low freezing point is favored,

since any solidification of the solvent in the column makes the columninoperable.

Equipment The principal types of gas-absorption equipmentmay be classified as follows:

1. Packed columns (continuous operation)2. Plate columns (staged operations)3. MiscellaneousOf the three categories, the packed column is by far the most com-

monly used for the absorption of gaseous pollutants. Miscellaneousgas-absorption equipment could include acid gas scrubbers that arecommonly classified as either “wet” or “dry.” In wet scrubber systems,the absorption tower uses a lime-based sorbent liquor that reacts withthe acid gases to form a wet/solid by-product. Dry scrubbers can begrouped into three catagories: (1) spray dryers; (2) circulating spraydryers; and (3) dry injection. Each of these systems yields a dry prod-uct that can be captured with a fabric filter baghouse downstream andthus avoids costly wastewater treatment systems. The baghouse ishighly efficient in capturing the particulate emissions, and a portion ofthe overall acid gas removal has been found to occur within the bag-house. Additional information may be found by referring to the appro-priate sections in this handbook and the many excellent texts available,such as McCabe and Smith, Unit Operations of Chemical Engineer-ing, 3d ed., McGraw-Hill, New York, 1976; Sherwood and Pigford,Absorption and Extraction, 2d ed., McGraw-Hill, New York, 1952;Smith, Design of Equilibrium Stage Processes, McGraw-Hill, NewYork, 1963; Treybal, Mass Transfer Operations, 3d ed., McGraw-Hill,New York, 1980; McKenna, Mycock, and Theodore, Handbook of AirPollution Control Engineering and Technology, CRC Press, Boca

Raton, Florida, 1995; Theodore and Allen, Air Pollution ControlEquipment, ETSI Prof. Training Inst., Roanoke, Virginia, 1993.

Adsorption The design of gas-adsorption equipment is in manyways analogous to the design of gas-absorption equipment, with a solidadsorbent replacing the liquid solvent (see Secs. 16 and 19). Similarityis evident in the material- and energy-balance equations as well as inthe methods employed to determine the column height. The finalchoice, as one would expect, rests with the overall process economics.

Selection of Adsorbent Industrial adsorbents are usually capa-ble of adsorbing both organic and inorganic gases and vapors. How-ever, their preferential adsorption characteristics and other physicalproperties make each of them more or less specific for a particularapplication. General experience has shown that, for the adsorption ofvapors of an organic nature, activated carbon has superior properties,having hydrocarbon-selective properties and high adsorption capacityfor such materials. Inorganic adsorbents, such as activated alumina orsilica gel, can also be used to adsorb organic materials, but difficultiescan arise during regeneration. Activated alumina, silica gel, and mole-cular sieves will also preferentially adsorb any water vapor with theorganic contaminant. At times this may be a considerable drawback inthe application of these adsorbents for organic-contaminant removal.

The normal method of regeneration of adsorbents is by use ofsteam, inert gas (i.e., nitrogen), or other gas streams, and in themajority of cases this can cause at least slight decomposition of theorganic compound on the adsorbent. Two difficulties arise: (1)incomplete recovery of the adsorbate, although this may be unimpor-tant; and (2) progressive deterioration in capacity of the adsorbent asthe number of cycles increases owing to blocking of the pores fromcarbon formed by hydrocarbon decomposition. With activated car-bon, a steaming process is used, and the difficulties of regenerationare thereby overcome. This is not feasible with silica gel or activatedalumina because of the risk of breakdown of these materials when incontact with liquid water.

In some cases, none of the adsorbents has sufficient retaining capac-ity for a particular contaminant. In these applications, a large-surface-area adsorbent can be impregnated with an inorganic compound or, inrare cases, with a high-molecular-weight organic compound that canreact chemically with the particular contaminant. For example, iodine-impregnated carbons are used for removal of mercury vapor andbromine-impregnated carbons for ethylene or propylene removal. Theaction of these impregnants is either catalytic conversion or reaction toa nonobjectionable compound or to a more easily adsorbed compound.For this case, general adsorption theory no longer applies to the overalleffects of the process. For example, mercury removal by an iodine-impregnated carbon proceeds faster at a higher temperature, and a bet-ter overall efficiency can be obtained than in a low-temperature system.

Since adsorption takes place at the interphase boundary, theadsorption surface area becomes an important consideration. Gener-ally, the higher the adsorption surface area, the greater its adsorptioncapacity. However, the surface area has to be “available” in a particu-lar pore size within the adsorbent. At low partial pressure (or concen-tration) a surface area in the smallest pores in which the adsorbate canenter is the most efficient. At higher pressures the larger poresbecome more important; at very high concentrations, capillary con-densation will take place within the pores, and the total micropore vol-ume becomes the limiting factor.

The action of molecular sieves is slightly different from that ofother adsorbents in that selectivity is determined more by the pore-sizelimitations of the particular sieve. In selecting molecular sieves, it isimportant that the contaminant to be removed be smaller than theavailable pore size. Hence, it is important that the particular adsor-bent not only have an affinity for the contaminant in question but alsohave sufficient surface area available for adsorption.

Design Data The adsorbent having been selected, the next stepis to calculate the quantity of adsorbent required and eventually con-sider other factors such as the temperature rise of the gas stream dueto adsorption and the useful life of the adsorbent under operating con-ditions. The sizing and overall design of the adsorption system dependon the properties and characteristics of both the feed gas to be treatedand the adsorbent. The following information should be known oravailable for design purposes:



1. Gas streama. Adsorbate concentration.b. Temperature.c. Temperature rise during adsorption.d. Pressure.e. Flow rate.f. Presence of adsorbent contaminant material.2. Adsorbenta. Adsorption capacity as used on stream.b. Temperature rise during adsorption.c. Isothermal or adiabatic operation.d. Life, if presence of contaminant material is unavoidable.e. Possibility of catalytic effects causing an adverse chemical reac-

tion in the gas stream or the formation of solid polymerizates on theadsorbent bed, with consequent deterioration.

f. Bulk density.g. Particle size, usually reported as a mean equivalent particle diam-

eter. The dimensions and shape of particles affect both the pressuredrops through the adsorbent bed and the diffusion rate into the parti-cles. All things being equal, adsorbent beds consisting of smaller parti-cles, although causing a higher pressure drop, will be more efficient.

h. Pore data, which are important because they may permit elimi-nation from consideration of adsorbents whose pore diameter will notadmit the desired adsorbate molecule.

i. Hardness, which indicates the care that must be taken in han-dling adsorbents to prevent the formation of undesirable fines.

j. Regeneration information.The design techniques used include both stagewise and continu-

ous-contacting methods and can be applied to batch, continuous, andsemicontinuous operations.

Adsorption Phenomena The adsorption process involves threenecessary steps. The fluid must first come in contact with the adsor-bent, at which time the adsorbate is preferentially or selectivelyadsorbed on the adsorbent. Next the fluid must be separated from theadsorbent-adsorbate, and, finally, the adsorbent must be regeneratedby removing the adsorbate or by discarding used adsorbent andreplacing it with fresh material. Regeneration is performed in a vari-ety of ways, depending on the nature of the adsorbate. Gases or vaporsare usually desorbed by either raising the temperature (thermal cycle)or reducing the pressure (pressure cycle). The more popular thermalcycle is accomplished by passing hot gas through the adsorption bed inthe direction opposite to the flow during the adsorption cycle. Thisensures that the gas passing through the unit during the adsorptioncycle always meets the most active adsorbent last and that the adsor-bate concentration in the adsorbent at the outlet end of the unit isalways maintained at a minimum.

In the first step, in which the molecules of the fluid come in contactwith the adsorbent, an equilibrium is established between the adsorbedfluid and the fluid remaining in the fluid phase. Figures 22-8 through22-10 show several experimental equilibrium adsorption isotherms for anumber of components adsorbed on various adsorbents. Consider Fig.22-8, in which the concentration of adsorbed gas on the solid is plottedagainst the equilibrium partial pressure p0 of the vapor or gas at constanttemperature. At 40ºC, for example, pure propane vapor at a pressure of550 mm Hg is in equilibrium with an adsorbate concentration at pointP of 0.04 lb adsorbed propane per pound of silica gel. Increasing thepressure of the propane will cause more propane to be adsorbed, whiledecreasing the pressure of the system at P will cause propane to be des-orbed from the carbon.

The adsorptive capacity of activated carbon for some common sol-vent vapors is shown in Table 22-32.

Adsorption-Control Equipment If a gas stream must be treatedfor a short period, usually only one adsorption unit is necessary, pro-vided, of course, that a sufficient time interval is available betweenadsorption cycles to permit regeneration. However, this is usually notthe case. Since an uninterrupted flow of treated gas is often required,it is necessary to employ one or more units capable of operating in thisfashion. The units are designed to handle gas flows without interrup-tion and are characterized by their mode of contact, either staged orcontinuous. By far the most common type of adsorption system usedto remove an objectionable pollutant from a gas stream consists of a

number of fixed-bed units operating in such a sequence that the gasflow remains uninterrupted. A two- or three-bed system is usuallyemployed, with one or two beds bypassed for regeneration while oneis adsorbing. A typical two-bed system is shown in Fig. 22-11a, while atypical three-bed system is shown in Fig. 22-11b. The type of systembest suited for a particular job is determined from several factors,including the amount and rate of material being adsorbed, the timebetween cycles, the time required for regeneration, and the coolingtime, if required.

Typical of continuous-contact operation for gaseous-pollutantadsorption is the use of a fluidized bed. During steady-state staged-contact operation, the gas flows up through a series of successive flu-idized-bed stages, permitting maximum gas-solid contact on eachstage. A typical arrangement of this type is shown in Fig. 22-12 formultistage countercurrent adsorption with regeneration. In theupper part of the tower, the particles are contacted countercurrently

FIG. 22-8 Equilibrium partial pressures for certain organics on silica gel.

FIG. 22-9 Equilibrium partial pressures for certain organics on carbon.


on perforated trays in relatively shallow beds with the gas stream con-taining the pollutant, the adsorbent solids moving from tray to traythrough downspouts. In the lower part of the tower, the adsorbent isregenerated by similar contact with hot gas, which desorbs and car-ries off the pollutant. The regenerated adsorbent is then recirculatedby an airlift to the top of the tower.

Although the continuous-countercurrent type of operation hasfound limited application in the removal of gaseous pollutants fromprocess streams (for example, the removal of carbon dioxide and sul-fur compounds such as hydrogen sulfide and carbonyl sulfide), by farthe most common type of operation presently in use is the fixed-bedadsorber. The relatively high cost of continuously transporting solidparticles as required in steady-state operations makes fixed-bedadsorption an attractive, economical alternative. If intermittent orbatch operation is practical, a simple one-bed system, cycling alter-nately between the adsorption and regeneration phases, will suffice.

Additional information may be found by referring to the appropri-ate sections of this handbook. A comprehensive treatment of adsorberdesign principles is given in Buonicore and Theodore, Industrial Con-trol Equipment for Gaseous Pollutants, vol. 1, 2d ed., CRC press, BocaRaton, Florida, 1992.

Combustion Many organic compounds released from manufac-turing operations can be converted to innocuous carbon dioxide andwater by rapid oxidation (chemical reaction): combustion. However,combustion of gases containing halides may require the addition ofacid gas treatment to the combustor exhaust.

Three rapid oxidation methods are typically used to destroy com-bustible contaminants: (1) flares (direct-flame-combustion), (2) ther-mal combustors, and (3) catalytic combustors. The thermal and flaremethods are characterized by the presence of a flame during combus-

tion. The combustion process is also commonly referred to as “after-burning” or “incineration.”

To achieve complete combustion (i.e., the combination of the com-bustible elements and compounds of a fuel with all the oxygen thatthey can utilize), sufficient space, time, and turbulence and a temper-ature high enough to ignite the constituents must be provided.

The three T’s of combustion—time, temperature, and turbu-lence—govern the speed and completeness of the combustion reac-tion. For complete combustion, the oxygen must come into intimatecontact with the combustible molecule at sufficient temperature andfor a sufficient length of time for the reaction to be completed. Incom-plete reactions may result in the generation of aldehydes, organicacids, carbon, and carbon monoxide.

Combustion-Control Equipment Combustion-control equip-ment can be divided into three types: (1) flares, (2) thermal incinera-tors, (3) catalytic incinerators.

Flares In many industrial operations and particularly in chemicalplants and petroleum refineries, large volumes of combustible wastegases are produced. These gases result from undetected leaks in theoperating equipment, from upset conditions in the normal operationof a plant in which gases must be vented to avoid dangerously highpressures in operating equipment, from plant startups, and fromemergency shutdowns. Large quantities of gases may also result fromoff-specification product or from excess product that cannot be sold.Flows are typically intermittent, with flow rates during major upsets ofup to several million cubic feet per hour.

The preferred control method for excess gases and vapors is torecover them in a blowdown recovery system. However, large quantitiesof gas, especially those during upset and emergency conditions, are dif-ficult to contain and reprocess. In the past all waste gases were venteddirectly to the atmosphere. However, widespread venting caused safetyand environmental problems, and, in practice, it is now customary tocollect such gases in a closed flare system and to burn them as they aredischarged.

Although flares can be used to dispose of excess waste gases, suchsystems can present additional safety problems. These include theexplosion potential, thermal-radiation hazards from the flame, and theproblem of toxic asphyxiation during flameout. Aside from these safetyaspects, there are several other problems associated with flaring thatmust be dealt with during the design and operation of a flare system.These problems include the formation of smoke, the luminosity of theflame, noise during flame, and the possible emission of by-product airpollutants during flaring.

The heat content of the waste stream to be disposed is anotherimportant consideration. The heat content of the waste gas falls intotwo classes. The gases can either support their own combustion or not.In general, a waste gas with a heating value greater than 7443 kJ/m3

FIG. 22-10 Equilibrium partial pressures for certain gases on molecular sieves. (A. J. Buonicore and L. Theodore, Industrial Control Equipment for Gaseous Pollu-tants, vol. I, CRC Press, Boca Raton, Fla., 1975.)

TABLE 22-32 Adsorptive Capacity of Common Solvents on Activated Carbons*

Solvent Carbon bed weight, %†

Acetone 8Heptane 6Isopropyl alcohol 8Methylene chloride 10Perchloroethylene 20Stoddard solvent 2–71,1,1-Trichloroethane 12Trichloroethylene 15Trichlorotrifluoroethane 8VM&P naphtha 7

*Assuming steam desorption at 5 to 10 psig.†For example, 8 lb of acetone adsorbed on 100 lb of activated carbon.


(200 Btu/ft3) can be flared successfully. The heating value is based onthe lower heating value of the waste gas at the flare. Below 7443 kJ/m3,enriching the waste gas by injecting another gas with a higher heatingvalue may be necessary. The addition of such a rich gas is called“endothermic flaring.” Gases with a heating value as low as 2233 kJ/m3

(60 Btu/ft3) have been flared but at a significant fuel demand. It is usu-ally not feasible to flare a gas with a heating value below 3721 kJ/m3

(100 Btu/ft3). If the flow of low-Btu gas is continuous, thermal or cat-alytic incineration can be used to dispose of the gas. For intermittentflows, however, endothermic flaring may be the only possibility.

Although most flares are used to dispose of intermittent wastegases, some continuous flares are in use, but generally only for rela-tively small volumes of gases. The heating value of large-volume con-tinuous-flow waste gases is usually too valuable to lose in a flare. Vaporrecovery or the use of the vapor as a fuel in a process heater is pre-ferred over flaring. Since auxiliary fuel must be added to the gas inorder to flare, large continuous flows of a low-heating-value gas areusually more efficient to burn in a thermal incinerator than in theflame of a flare.

Flares are mostly used for the disposal of hydrocarbons. Wastegases composed of natural gas, propane, ethylene, propylene, butadi-

ene, and butane probably constitute over 95 percent of the materialflared. Flares have been used successfully to control malodorous gasessuch as mercaptans and amines, but care must be taken when flaringthese gases. Unless the flare is very efficient and gives good combus-tion, obnoxious fumes can escape unburned and cause a nuisance.

Flaring of hydrogen sulfide should be avoided because of its tox-icity and low odor threshold. In addition, burning relatively smallamounts of hydrogen sulfide can create enough sulfur dioxide to causecrop damage or a local nuisance. For gases whose combustion prod-ucts may cause problems, such as those containing hydrogen sulfide orchlorinated hydrocarbons, flaring is not recommended.

Thermal Incinerators Thermal incinerators or afterburners canbe used over a fairly wide but low range of organic vapor concentration.The concentration of the organics in air must be substantially belowthe lower flammable level (lower explosive limit). As a rule, a factor offour is employed for safety precautions. Reactions are conducted atelevated temperatures to ensure high chemical-reaction rates for theorganics. To achieve this temperature, it is necessary to preheat thefeed stream using auxiliary energy. Along with the contaminant-ladengas stream, air and fuel are continuously delivered to the incinerator(see Fig. 22-13). The fuel and contaminants are combusted with air ina firing unit (burner). The burner may utilize the air in the process-waste stream as the combustion air for the auxiliary fuel, or it may usea separate source of outside air. The products of combustion and theunreacted feed stream are intensely mixed and enter the reaction zoneof the unit. The pollutants in the process-gas stream are then reactedat the elevated temperature. Thermal incinerators generally requireoperating temperatures in the range of 650 to 980°C (1200 to 1800°F)for combustion of most organic pollutants (see Table 22-33). A resi-dence time of 0.2 to 1.0 is often recommended, but this factor is dic-tated primarily by complex kinetic considerations. The kinetics ofhydrocarbon (HC) combustion in the presence of excess oxygen can besimplified into the following first-order rate equation:

= −k[HCl] (22-1)d(HCl)�

dt

FIG. 22-12 Multistage countercurrent adsorption with regeneration.

FIG. 22-11 (a) Typical two-bed adsorption system. (b) Typical three-bedadsorption system.

(a)

(b)


where k = pseudo-first-order rate constant (s−1). If the initial concen-tration is CA,o, the solution of Eq. (22-1) is:

ln� = −kt (22-2)

Equation (22-2) is frequently used for a kinetic modeling of a burnerusing mole fractions in the range of 0.15 and 0.001 for oxygen and HC,respectively. The rate constant is generally of the following Arrheniusform:

k = Ae−E/RT (22-3)

where: A = pre-exponential factor, s- (see Table 2, Air PollutionEngineering Manual, Van Nostrand Reinhold, New York,1992, p. 62)

E = activation energy, cal/gmol (see Table 2, Air PollutionEngineering Manual, Van Nostrand Reinhold, New York,1992, p. 62)

R = universal gas constant, 1.987 cal/gmol °KT = absolute temperature, °K

The referenced table for A and E is a summary of first-order HCcombustion reactions.

The end combustion products are continuously emitted at the out-let of the reactor. The average gas velocity can range from as low as 3m/s (10 ft/s) to as high as 15 m/s (50 ft/s). These high velocities arerequired to prevent settling of particulates (if present) and to mini-mize the dangers of flashback and fire hazards. Space velocity calcula-tions are given in the “Incinerator Design and Performance Equation”section.

The fuel is usually natural gas. The energy liberated by reactionmay be directly recovered in the process or indirectly recovered bysuitable external heat exchange (see Fig. 22-14).

Because of the high operating temperatures, the unit must be con-structed of metals capable of withstanding this condition. Combustion

CA�CA,o

devices are usually constructed with an outer steel shell that is linedwith refractory material. Refractory-wall thickness is usually in the0.05- to 0.23-m (2- to 9-in) range, depending upon temperature con-siderations.

Some of the advantages of the thermal incinerators are:1. Removal of organic gases2. Removal of submicrometer organic particles3. Simplicity of construction4. Small space requirementsSome of the disadvantages are:1. High operating costs2. Fire hazards3. Flashback possibilitiesCatalytic Incinerators Catalytic incinerators are an alternative

to thermal incinerators. For simple reactions, the effect of the pres-ence of a catalyst is to (1) increase the rate of the reaction, (2) permitthe reaction to occur at a lower temperature, and (3) reduce the reac-tor volume.

In a typical catalytic incinerator for the combustion of organicvapors, the gas stream is delivered to the reactor continuously by a fanat a velocity in the range of 3 to 15 m/s (10 to 30 ft/s), but at a lowertemperature, usually in the range of 350 to 425ºC (650 to 800ºF), thanthe thermal unit. (Design and performance equations used for calcu-lating space velocities are given in the next section). The gases, whichmay or may not be preheated, pass through the catalyst bed, wherethe combustion reaction occurs. The combustion products, whichagain are made up of water vapor, carbon dioxide, inerts and unre-acted vapors, are continuously discharged from the outlet at a highertemperature. Energy savings can again be effected by heat recoveryfrom the exit stream.

Metals in the platinum family are recognized for their ability to pro-mote combustion at low temperatures. Other catalysts include variousoxides of copper, chromium, vanadium, nickel, and cobalt. These cat-alysts are subject to poisoning, particularly from halogens, halogenand sulfur compounds, zinc, arsenic, lead, mercury, and particulates.It is therefore important that catalyst surfaces be clean and active toensure optimum performance.

Catalysts may be porous pellets, usually cylindrical or spherical inshape, ranging from 0.16 to 1.27 cm (1⁄16 to 1⁄2 in) in diameter. Smallsizes are recommended, but the pressure drop through the reactorincreases. Among other shapes are honeycombs, ribbons, and wiremesh. Since catalysis is a surface phenomenon, a physical property ofthese particles is that the internal pore surface is nearly infinitelygreater than the outside surface.

The following sequence of steps is involved in the catalytic conver-sion of reactants to products:

1. Transfer of reactants to and products from the outer catalystsurface

2. Diffusion of reactants and products within the pores of the catalyst3. Activated adsorption of reactants and the desorption of the

products on the active centers of the catalyst

FIG. 22-13 Thermal-combustion device.

TABLE 22-33 Thermal Afterburners: Conditions Required forSatisfactory Performance in Various Abatement Applications

Afterburner Temperature,Abatement category residence time, s °F

Hydrocarbon emissions: 90 + % destruction of HC 0.3–0.5 1100–1250*

Hydrocarbons + CO: 90 + % destruction of HC + CO 0.3–0.5 1250–1500

Odor50–90% destruction 0.3–0.5 1000–120090–99% destruction 0.3–0.5 1100–130099 + % destruction 0.3–0.5 1200–1500

Smokes and plumesWhite smoke (liquid mist)

Plume abatement 0.3–0.5 800–1000†90 + % destruction of HC + CO 0.3–0.5 1250–1500

Black smoke (soot and combustible particulates) 0.7–1.0 1400–2000

*Temperatures of 1400 to 1500°F (760 to 816°C) may be required if thehydrocarbon has a significant content of any of the following: methane, cello-solve, and substituted aromatics (e.g., toluene and xylenes).

†Operation for plume abatement only is not recommended, since this merelyconverts a visible hydrocarbon emission into an invisible one and frequently cre-ates a new odor problem because of partial oxidation in the afterburner. FIG. 22-14 Thermal combustion with energy (heat) recovery.

4. Reaction or reactions on active centers on the catalyst surfaceAt the same time, energy effects arising from chemical reaction can

result in the following:1. Heat transfer to or from active centers to the catalyst-particle

surface2. Heat transfer to and from reactants and products within the cat-

alyst particle3. Heat transfer to and from moving streams in the reactor4. Heat transfer from one catalyst particle to another within the

reactor5. Heat transfer to or from the walls of the reactorSome of the advantages of catalytic incinerators are:1. Lower fuel requirements as compared with thermal incinerators2. Lower operating temperatures3. Minimum insulation requirements4. Reduced fire hazards5. Reduced flashback problemsThe disadvantages include:1. Higher initial cost than thermal incinerators2. Catalyst poisoning3. Necessity of first removing large particulates4. Catalyst-regeneration problems5. Catalyst disposalIncinerator Design and Performance Equations The key

incinerator design and performance calculations are the required fuelusage and physical dimensions of the unit. The following is a generalcalculation procedure to use in solving for these two parameters,assuming that the process gas stream flow, inlet temperature, com-bustion temperature, and required residence time are known. Thecombustion temperature and residence time for thermal incineratorscan be estimated using Table 22-33 and Eqs. (22-1) through (22-3).

1. The heat load needed to heat the inlet process gas stream to theincinerator operating temperature is:

Q = ∆H (22-4)

2. Correct the heat load for radiant heat losses, RL:

Q = (1 + RL) (∆H); RL = fractional basis (22-5)

3. Assuming that natural gas is used to fire the burner with a knownheating value of HVG, calculate the available heat at the operatingtemperature. A shortcut method usually used for most engineeringpurposes is:

HAT = (HVG)� ref

(22-6)

where the subscript “ref” refers to a reference fuel. For natural gaswith a reference HVG of 1059 Btu/scf, the heat from the combustionusing no excess air would be given by:

(HAT)ref = −0.237(t) + 981; T = F (22-7)

4. The amount of natural gas needed as fuel (NG) is given by:

NG = ; consistent units (22-8)

5. The resulting volumetric flow rate is the sum of the combustionof the natural gas q and the process gas stream p at the operating tem-perature:

qT = qp + qc (22-9)

A good estimate for qc is:

qc = (11.5)(NG) (22-10)

6. The diameter of the combustion device is given by:

S = (22-11)

where vt is defined as the velocity of the gas stream at the incineratoroperating temperature.

Condensation Frequently in air-pollution-control practice, itbecomes necessary to treat an effluent stream consisting of a con-

qT�vt

Q�HA

HAT�HVG

densable pollutant vapor and a noncondensable gas. One controlmethod to remove such pollutants from process-gas streams that isoften overlooked is condensation. Condensers can be used to collectcondensable emissions discharged to the atmosphere, particularlywhen the vapor concentration is high. This is usually accomplished bylowering the temperature of the gaseous stream, although an increasein pressure will produce the same result. The former approach is usu-ally employed by industry, since pressure changes (even small ones)on large volumetric gas-flow rates are often economically prohibitive.

Condensation Equipment There are two basic types of con-densers used for control: contact and surface. In contact condensers,the gaseous stream is brought into direct contact with a coolingmedium so that the vapors condense and mix with the coolant (seeFig. 22-15). The more widely used system, however, is the surfacecondenser (or heat exchanger), in which the vapor and the coolingmedium are separated by a wall (see Fig. 22-16). Since high removalefficiencies cannot be obtained with low-condensable vapor concen-trations, condensers are typically used for pretreatment prior to someother more efficient control device such as an incinerator, absorber, oradsorber.

Contact Condensers Spray condensers, jet condensers, andbarometric condensers all utilize water or some other liquid in directcontact with the vapor to be condensed. The temperature approachbetween the liquid and the vapor is very small, so the efficiency of thecondenser is high, but large volumes of the liquid are necessary. If thevapor is soluble in the liquid, the system is essentially an absorptiveone. If the vapor is not soluble, the system is a true condenser, inwhich case the temperature of the vapor must be below the dew point.Direct-contact condensers are seldom used for the removal of organicsolvent vapors because the condensate will contain an organic-watermixture that must be separated or treated before disposal. They are,however, the most effective method of removing heat from hot gasstreams when the recovery of organics is not a consideration.

In a direct-contact condenser, a stream of water or other coolingliquid is brought into direct contact with the vapor to be condensed.The liquid stream leaving the chamber contains the original coolingliquid plus the condensed substances. The gaseous stream leaving the


( a ) ( b ) ( c )

FIG. 22-15 Typical direct-contact condensers. (a) Spray chamber. (b) Jet.(c) Barometric.

FIG. 22-16 Typical surface condenser (shell-and-tube).

to their release into the environment. Biological processes can be par-ticularly desirable because they neither transfer the identified pollu-tants into another phase (as with carbon adsorption, condensation,etc.) nor produce additional, collateral air pollution from fuel combus-tion [as does incineration (SOx, NOx, CO, CO2, particulates, etc.)].

Biomass: The Community of Microorganisms* The microor-ganisms which make up the biomass in these devices are similar tothose found in soil and in biological wastewater treatment plants: bac-teria, often with smaller populations of fungi, ciliates, and other pro-tists. Bacteria are extremely diverse in their biochemical degradationabilities. They all lack cellular nuclei. Individually, a bacterium has lim-ited metabolic capabilities, because a single bacterium has limitedquantities of DNA. However, individual bacteria can modify theirDNA by exchange and transfer with other bacteria present. Neverthe-less, this limited DNA restricts the ability of one kind of bacterium toproduce all the different enzymes needed to completely break down allavailable substrates. Consequently, at steady state, differing bacterialive together in mixed consortia (communities) such that, takentogether, these consortia can produce all the enzymes needed to com-pletely break down the available substrates to CO2, H2O, salts, etc.

In bioscrubbers, biotrickling filters, and biofilters, the principal micro-bial populations metabolize the primary substrates, the biodegradableair pollutants. The secondary and generally smaller microbial popula-tions assist the process of total breakdown by consuming bacterial meta-bolic intermediates from the primary substrates as well as other wasteproducts produced by the other bacteria. In biotrickling filters and biofil-ters, the biomass exists within the airstream as a fixed biofilm, a thin layerof microbes growing on an inert attachment surface. An importantadvantage of an attached biofilm is that the microbes tend to become dis-tributed along chemical gradients by depth within the biofilm. Often, themost rapidly growing microbes are concentrated near the outer surface,where both oxygen and the primary substrate are most abundant, andthe slower-growing, secondary microbes are concentrated near theattachment surface. This configuration protects the secondary microbeswith an outer layer of expendable microbes. It also provides a nearly infi-nite mean cell residence time for the often slow-growing but essentialsecondary microbes, needed for complete breakdown of the pollutants.These bacterial populations are consumed by still other predatory micro-bial populations, which decompose them, recycling their substances tothe consortia. Acting together, these microbial populations finish thecomplete breakdown of the primary substrates.

Biofiltration: Theoretical ConsiderationsMaximum biofilter inlet pollutant concentration For an aerobic

fixed-film device, the local total flux for all pollutants into the biofilmmust not exceed the local flux of oxygen into the biofilm, on a stoi-chiometric basis. Therefore, the maximum acceptable total pollutantconcentration is fixed, at the biofilter inlet, by the low maximum oxygensolubility in the biofilm, at the biofilm interface. This oxygen concen-tration is about 8 mg/L (8 ppm) for air at ambient conditions. If thetotal pollutant concentration exceeds this maximum limit, aerobic bio-logical conditions cannot be maintained throughout the biofilter, acondition which can result in biofilter failure.

For a single pollutant biofilter application, using the stoichiometriccoefficients v for complete pollutant oxidation, diffusivities D, andmolecular weights (MW), the maximum acceptable inlet biofilminterface pollutant POL concentration SPOL can be estimated from themaximum available biofilm interface oxygen concentration SO2:

SPOL = � �� SO2(22-12)

Pollutant solubility At these very low biofilm interface concentra-tions, biodegradable pollutant solubility in water can be described byusing Henry’s law:

pi = HiCi (22-13)

where p is the partial pressure of the solute i in the gas phase; C is theconcentration of the solute in the aqueous liquid phase; and H is the

MWPOL�MWO2

DO2�DPOL

νPOL�νO2


chamber contains the noncondensable gases and such condensablevapor as did not condense; it is reasonable to assume that the vapors inthe exit gas stream are saturated. It is then the temperature of the exitgas stream that determines the collection efficiency of the condenser.

The advantages of contact condensers are that (1) they can be usedto produce a vacuum, thereby creating a draft to remove odorousvapors and also reduce boiling points in cookers and vats; (2) they usu-ally are simpler and less expensive than the surface type; and (3) theyusually have considerable odor-removing capacity because of thegreater condensate dilution (13 lb of 60ºF water is required to con-dense 1 lb of steam at 212ºF and cool the condensate to 140ºF). Theprincipal disadvantage is the large water requirement. Depending onthe nature of the condensate, odor in the wastewater can be offset byusing treatment chemicals.

Direct-contact condensers involve the simultaneous transfer of heatand mass. Design procedures available for absorption, humidification,cooling towers, and the like may be applied with some modifications.

Surface Condensers Surface condensers (indirect-contact con-densers) are used extensively in the chemical-process industry. Theyare employed in the air-pollution-equipment industry for recovery,control, and/or removal of trace impurities or contaminants. In thesurface type, coolant does not contact the vapor condensate. Thereare various types of surface condensers including the shell-and-tube,fin-fan, finned-hairpin, finned-tube-section, and tubular. The use ofsurface condensers has several advantages. Salable condensate can berecovered. If water is used for coolant, it can be reused, or the con-denser may be air-cooled when water is not available. Also, surfacecondensers require less water and produce 10 to 20 times less con-densate. Their disadvantage is that they are usually more expensiveand require more maintenance than the contact type.

Biological APC TechnologiesGENERAL REFERENCES

BIOFILTRATION: Ottengraph, S. S. P., “Exhaust Gas Purification,” in Biotech-nology, vol. 8, Rehn, H. J., and G. Reed, eds., VCH Verlagsgesellschaft, Wein-heim, Germany, 1986; Ottengraph, S. S. P., “Biological Elimination of VolatileXenobiotic Compounds in Biofilters,” Bioprocess Eng., 1986, 1: 61–69; Smith,F. L., et al., “Development and Demonstration of an Explicit Lumped Parame-ter Biofilter Model and Design Equation Incorporating Monod Kinetics,” J. Air& Waste Manage. Assoc., 2002, 52(2): 208–219; Margulis, L., Microcosmos,Summit Books, New York, 1986.

HENRY’S LAW CONSTANTS: Subsection “Solubilities” in Sec. 2 of this handbook;DIPPR 911; ENVIRON, EPCON International, Houston; “Environmental Simu-lation Program”: OLI Systems, Inc., Morris Plains, N. J. (www.olisystems.com);Mackay, D., et al., “A Critical Review of Henry’s Law Constants for Chemicals ofEnvironmental Interest,” J. Phys. Chem. Ref. Data, 1981, 10(4): 1175–1199; Tse,G., et al., “Infinite Dilution Activity Coefficients and Henry’s Law Coefficients ofSome Priority Water Pollutants Determined by Relative Gas ChromatographicMethod,” Environ. Sci. Technol., 1992, 26: 2017–2022; Smith, F. L., and A. H.Harvey, “Avoid Common Pitfalls When Using Henry’s Law,” Chem. Eng. Prog.103(9), 2007.

PHASE-EQUILIBRIUM DATA: Shaw, D. G., and A. Maczynski (eds.), IUPAC Sol-ubility Data Series, Vol. 81: “Hydrocarbons in Water and Seawater—Revised andUpdated,” published in 12 parts in J. Phys. Chem. Ref. Data, 2005 and 2006;Gmehling, J., et al., “Vapor-Liquid Equilibrium Data Collection: Aqueous-Organic Systems,” DECHEMA Chemistry Data Series, Vol. I, Part 1-1d, Schön &Wetzel GmbH, Frankfurt/Main, Germany, 1988.

Bioscrubbers, biotrickling filters, and biofilters are biological APCtechnologies which use enzymatic catalytic oxidation to completelybreak down (metabolize) biodegradable air pollutants to H2O, CO2,and salts. These pollutants, present in the airstream as vapors, can beeither organic or inorganic (H2S, NH3, CO, etc.). The oxidation cata-lysts (enzymes) are produced and maintained within moist, living,active biomass, which operates near ambient temperature and pres-sure. In practice, these biological APC processes represent a subclassof gas adsorption processes, in which pollutant mass transfer from thegas phase to the liquid phase is enhanced by a fast chemical reaction inthe liquid phase, which contains the biomass. Unlike incineration,biodegradation of compounds containing sulfur, nitrogen, and halo-gens produces benign by-products, biomass, and inorganic ions (SO4

−2,NO3

−1, Cl−1, etc.), which require little or no subsequent treatment prior*The contributions to this subsection by Prof. Lynn Margulis, University of

Massachusetts, Amherst, are gratefully appreciated.

www.olisystems.com

where the variables are the empty-bed residence time τ, a dimension-less variable H, liquid-phase local mass-transfer coefficient kL, and air-liquid phase effective specific surface af. (The units used for thedimensionless H must be the same as those used for Sg [Eq. (22-17)].)If the mass-transfer coefficient were for an ideal, single-component,fast first-order reaction system, for a biofilm having no external liquidlayer of any significant thickness (i.e., not more than a moist surface),and all other variables are assumed to have constant magnitudes, then

kL = �k1Df� =� (22-18a)

where Df is the pollutant diffusion coefficient within the biofilm andkL has a single magnitude, a function of temperature. For a singlecomponent following Monod reaction kinetics, kL is defined as

kL =� �Si − S min − K S ln (22-18b)

where Si and Smin are the pollutant biofilm concentrations, at thebiofilm interface (maximum) and at the biofilm attachment surface(minimum), respectively. All other variables are assumed to have con-stant magnitudes throughout the biofilter. (For a “deep biofilm,” Smin

is assumed to approach the limit of zero.) Therefore, kL is a functionof the local pollutant concentration as well as a function of tempera-ture. Note that Eq. (22-18b) predicts a lower value for kL than doesEq. (22-18a), until the pollutant concentration approaches the limit ofzero, where they are equal.

General Process Description For any APC design it is difficult toaccurately characterize variations of temperature, flow rate, and com-position for the polluted source stream, especially during the engineer-ing design of the upstream process source. For biological APC design isadded the state of the art, the imperfect scientific understanding of thebehavior of biomass under long-term steady-state operation, but moreimportantly as the biomass and media respond to stream variations,especially significant step change variations. This APC field remains atechnical art. The magnitude of kLaf cannot be calculated with confi-dence for any media formulation from first principles, especially formultiple pollutants. Consequently, and especially for multiple compo-nents, responsible vendors can be expected to recommend field pilottesting for unfamiliar applications, as an appropriate expense for achiev-ing a minimum annualized system cost design. What follows is writtento assist chemical engineers to effectively discuss their project needswith responsible vendors of biological APC technologies, and to com-prehend what they receive from such vendors.

Most natural, and most artificial, organic compounds can be biode-graded. However, only some biodegradable compounds are candi-dates for economical biological APC, which typically means aresidence time measured in minutes [Eq. (22-17)]. Although kLaf isimportant, its practical range of magnitudes is modest, and candidatesuitability for treatment is principally determined by its solubility, cou-pled with the ratio of the design inlet and outlet concentrations. Note,for instance, that economical designs are achievable for pollutants withlow concentrations and low solubility (flavors and fragrances) or forhigh concentrations and high solubility (ethanol, butyric acid). In prac-tice, compounds such as ethanol, acetone, formaldehyde, acetic acid,and diethylether are good candidates; BTEX, pinenes, and similarlysoluble compounds are acceptable candidates; and largely nonpolarhydrocarbons such as alkanes (and highly halogenated compounds ingeneral) are poor candidates. The most expensive media typically canoffer the highest values for kLaf and are generally justified throughreduction of the required EBRT (reduced media volume) needed for aspecific application.

An ID fan, which minimizes leakage of polluted air, is normallyused to maintain airflow through the process and to overcome thetotal system pressure drop, typically measured in centimeters ofwater. The optimum design temperature is determined by the trade-off between solubility, which decreases with temperature, and biolog-ical kinetics, which increases. Another optimization factor is howmuch heating or cooling is necessary for the inlet stream. Operation is

KS + Si�

KS + Smin

2kXfDf�

Si2

kXfDf�

KS


proportionality constant, generally referred to as the Henry’s law con-stant. (Henry’s law constants are not true constants but rather functionsof temperature.) Experimental data are needed to estimate H, how-ever, because pollutant-water mixtures are highly nonideal. The bestreference for these solubilities is corroborated data from a computer-ized data bank that specializes in environmental aqueous systems. Suchdata banks are especially helpful for calculating solubilities for uncom-mon pollutants of environmental interest, as well as for compoundsthat dissociate in water, i.e., are acidic or basic.

Estimating Henry’s law constants Henry’s law constants can beestimated from extensive data published for solute-water LLE(liquid-liquid equilibria):

Hi = (22-14)

where xwater is the equilibrium mole fraction of water in the organicphase (often negligible), Pi

sat is the vapor pressure of the organic solute,and xi is the equilibrium mole fraction of the solute in the water phase.

Extensive, reviewed tabulated pollutant data also exist (see subsec-tion “Solubilities” in Sec. 2 of this handbook). Any single tabulatedHenry’s law constant H is published with its measurement tempera-ture, typically 20 or 25ºC. The constant H for a subcritical pollutant(i.e., toluene) is proportional to its pure component vapor pressurePsat, and therefore H is an exponential function of temperature T.Using Henry’s and Raoult’s laws, a pollutant’s constant H for a givenambient design temperature can be estimated by using its tabulatedvalue and its vapor pressure, by extrapolating ≤ 25°C over the ambienttemperature range (4°C < T < 50°C), from T1 to T2:

H2 = H1 ≅ H1 (22-15a)

For a more soluble (or completely miscible) pollutant (i.e., ethanol), aHenry’s law constant can be similarly estimated by using its tabulatedinfinite dilution activity coefficient γ∞, measured at T1, by extrapola-tion using P2

sat, from T1 to T2:

H2 = γ∞2P2sat ≅ γ∞1P2

sat (22-15b)

Such estimations for H2 are single-point extrapolations of nonlinearfunctions, and therefore should be used with caution. In both casesestimation error is introduced due to the nonlinear temperaturedependence of the activity coefficient.

Biofilter kinetics and design model These biological systems arecomplex, so that normal simplifying assumptions are approximate atbest: biomass homogeneity, independent and uniform multisubstratekinetics, etc. Nevertheless, for understanding the basics of thesebioabsorbers, it is helpful to consider them in terms of a single sub-strate system, with uniform classic kinetics and mass transfer, and noliquid layer external to the fixed biofilm. Chemical and environmentalengineers use different expressions to describe the kinetics of sub-strate (pollutant) utilization—the shifting order form and the Monod(or Michaelis-Menten) form:

= = (22-16)

where the variables are rate-limiting substrate concentration Sf, first-order reaction rate coefficient k1 = k1, zero-order rate coefficient k0 =k1/k2, maximum utilization rate coefficient for the rate-limiting sub-strate k, density of the active substrate degraders Xf, and Monod half-velocity coefficient KS.

Biofilters are chemically enhanced absorbers, and therefore masstransfer limited (see “Absorption with Chemical Reaction” in Sec. 14).The magnitudes for the Hatta [= Damkohler II = (Thiele modulus)2]numbers are quite low, perhaps below 5. Nevertheless, for design sim-plicity, mass-transfer limitation is generally assumed to be in the liquidphase (the biofilm). For a single-component biofilter, the simplifiedbiofilter model and design equation is

τ = ln (22-17)Sg(IN)�Sg(OUT)

H�kLaf

kXfSf�KS + Sf

k1Sf�1 + k2Sf

d(Sf)�dt

P2sat

�P1

sat

γ2P2sat

�γ1P1

sat

(1 − xwater)Pisat

��xi


generally controlled to within a narrow range of a couple of degrees.The selected design temperature may range from perhaps 20 to 45ºC,commonly 30 to 35ºC. Particulates or aerosols, including organic liq-uid droplets, should be removed (perhaps > 15 µm). The inlet streamis usually prehumidified to 95 to nearly 100 percent relative humidity.Finally, temperature, particulate, and humidity control is often man-aged in a single step.

Biofilters Biofilters fall into two categories: soil bed biofilter(open bed) and artificial media biofilters (confined media).

Soil bed biofilters consist of an air distribution system of perforatedpiping buried under a layer of soil media, typically exposed outdoors.The treated air is emitted directly to atmosphere (Fig. 22-17). The soilmedia used can consist of a blend of natural soil components and othermaterials. This is a fixed-film bioreactor, with the biofilm attached toother inert soil materials. Soil media are biologically self-sustaining,hydrophilic, and self-buffering and often last for decades of use. Overa hundred are in operation. Although most soil beds are employed forodor control, any otherwise suitable candidate pollutant should betreatable in a soil bed. Soil bed operating temperature is maintained byinlet air temperature control, and soil biofilters are practical for any cli-mate, including very cold conditions (i.e., Calgary, Alberta, Canada).

Artificial media biofilters employ a biologically active mediumhoused in a containment vessel (Fig. 22-18). The support media canconsist of natural and synthetic materials, including compost, peat,bark, wood chips, etc., and polymer foam, activated carbon, rubbertire waste, ceramic pellets, etc., respectively. The media are typicallyblended, wetted, and biologically seeded (inoculated) before installa-tion. Inert materials, such as polystyrene beads, may be blended withthe media to prevent compaction and pressure drop increase and tomaintain biofilm specific surface. Media moisture content can be acritical operating parameter. Secondary humidification is oftenemployed, via water spraying, which can be accurately controlled byweigh cell measurement of the total media bed mass. Media replace-ment may be required 1 to 2 times per decade. Depending on themedia and the pollutants, nutrients and/or pH buffers may be appliedwith the water spray. Some biofilters are maintained wet enough todrip, to purge soluble waste salts. Generally, artificial media biofilterscan be designed for higher loadings than can soil bed biofilters.Upflow and downflow designs are practical.

Bioscrubbers Bioscrubbers combine physical absorption with bio-logical degradation, using two separate unit operations. The pollutantsare absorbed into water within the scrubber. This water is then directedto an external biological reactor, where the pollutants are degraded. Thetreated liquid is recycled to the bioscrubber. One configuration employswater and a fixed-film bioreactor, while a second configuration employsMLSS and a slurry reactor. In both cases, separating absorption fromreaction permits scrubbing pollutant concentrations far above thosewhich a fixed-film system would survive (due to O2 limitation). Scrub-bing can be designed to attenuate substantial and rapid compositionchange in the inlet, assisting the performance of a downstreambiotreatment step. The scrubber can be multistaged (packed column,Fig. 22-18) or single-staged (a venturi scrubber or spray chamber, Fig.22-19). Scrubbers with horizontal airflow are also available. Nutrients,pH buffers, and makeup water are added, and biomass and waste saltsare purged, as needed. Bioscrubbing is commonly combined with

Biofilter Media Grass

Gravel

Air Inlet

Laterals

FIG. 22-17 Pretreated contaminated air flows into an inlet manifold, lateralpiping, and into a continuous layer of gravel or crushed stone, providing even airdistribution across the bottom of the media. Air is biofiltered, flowing upwardthrough the biofilter media, exiting to atmosphere through the media surface ora grass cover. (Courtesy of Bohn Biofilter, www.bohnbiofilter.com.)

FIG. 22-18 Contaminated air is pretreated (shown: a countercurrent bioscrubber), before passing into the biofilter. Air is biofiltered, flowingdownward through the media. Biomedia moisture content is accurately controlled via load-cell control of water sprays on media surface. (Courtesyof Waterleau Biofilter–Bioton, Bel-Air, www.waterleau.com.)

www.bohnbiofilter.com

www.waterleau.com


temperature, particulate, and humidity control as feed pretreatment tobiotrickling filters and biofilters. A combined multipollutant plot of logH = f(1/T) is a helpful design aid in the selection of the optimumstream composition for the scrubber effluent stream.

Biotrickling Filters Biotrickling filters are a hybrid of bioscrub-bers and biofilters. A fixed biofilm (often a deep biofilm) is employed,typically attached to a synthetic medium containing blocks of polymerfoam, lava rock, sintered ceramics, etc. (Fig. 22-19). Water permeabilityis preferred for the biofilm support media. Inert materials, such as Pallrings or other distillation-type packing materials, may be blended withthe media to prevent compaction and pressure drop increase and tomaintain biofilm specific surface. Water is recirculated through the fil-ter. Although the water layer forms a resistance to pollutant mass trans-fer into the fixed biofilm, the water stream also absorbs pollutants whichcan be removed from the filter for separate biological treatment, asdescribed above for bioscrubbers. As for a bioscrubber, this hybrid canrespond more effectively to rapid changes in the feed, and can survive

higher inlet concentrations, than can a biofilter. This feature, in turn,can assist the performance of a downstream biotreatment step. Nutri-ents, pH buffers and makeup water are added, and biomass and wastesalts are purged, as needed. Upflow, downflow, and horizontal airflowdesigns are practical.

Use of Activated Carbon Activated carbon (AC) can be used toenhance these processes in at least three ways. Positioned in front of theprocess, AC can provide pollutant concentration capacitance, reducingconcentration peak magnitudes and rapid rate of variation and provid-ing minimum concentrations during periods of no or low source pollu-tant flow. Positioned behind the process, AC can increase the overallprocess elimination efficiency, as well as scavenging nonbiologicallydegradable compounds (i.e., poly-halogenated organics). Mixed withthe media, AC is reported to combine these two functions, enhancingbiological removal and protecting the system during periods of high pol-lutant inlet variation. Note that AC positioned in front can present a firehazard for certain pollutants, such as acetone. AC positioned in back isexposed to very high humidity, which restricts adsorption capacity.

Relative Biofiltration Treatment Costs The true final annual-ized cost for treating a polluted airstream with any specific APC tech-nology is complex and will be affected by many factors, includingproject-specific factors. Nevertheless, Fig. 22-20 can provide helpfulguidance to the relationships between the probable final costs fortreating a polluted airstream using different APC technologies.

Membrane Filtration Membrane systems have been used forseveral decades to separate colloidal and molecular slurries by thechemical process industries (CPI). Membrane filtration was notviewed as a commercially viable pollution control technology untilrecently. This conventional wisdom was due to fouling problems exhib-ited when handling process streams with high solid content. Thischanged with the advent of membranes composed of high-flux cellu-lose acetate. In Europe and Asia, membrane filtration systems havebeen used for several years, primarily for ethanol dewatering for syn-thetic fuel plants. Membrane systems were selected in these cases fortheir (1) low energy utilization; (2) modular design; (3) low capitalcosts; (4) low maintenance; and (5) superior separations. In the UnitedStates, as EPA regulations become increasingly stringent, a renewedinterest in advanced membrane filtration systems has occurred. In thiscase, the driving factors are the membrane system’s ability to operate ina pollution-free, closed-loop manner with minimum wastewater out-put. Low capital and maintenance costs also result from the smallamount of moving parts within the membrane systems.

CONTAMINATEDAIR

AIR TOATMOSPHEREVENTURI

SCRUBBER

BIOTRICKLING FILTER

MAKEUP WATER

IMMOBILIZED CELL BIOREACTOR

HONEYWELLPACKING

SPACER

FOAM

P1 P2

FIG. 22-19 Contaminated air is pretreated (shown: a Venturi scrubber),before passing into the biotrickling filter. Air is biofiltered, flowing downwardthrough the media. (Courtesy of Honeywell PAI—Biological Air Treatment Sys-tem, www.honeywellpai.com.)

100

10

A A. Thermal incineration (+ heat exchanger)B. Catalytic incineration (+ heat exchanger)C. Carbon adsorption (without reactivation)D. Carbon adsorption (with reactivation)E. Carbon adsorption + thermal incinerationF. Water scrubberG. Chemical scrubber (2-stage)H. BioscrubberI. Biofilter (compost)

E

F G

H I

B

CD

100 1,000

Carbon content of influent air (mg/m3)

Relative treatment cost in arbitrar

y units

10,000

80

60

40

20

0

FIG. 22-20 Relative (and approximate) treatment costs for removing VOCs from air (Kosky and Neff, 1988). Assumption:40,000 m3/h at 1982 price level. (Note: Current costs for chemical scrubbing can be 2 or more times greater than for biofil-tration.)

www.honeywellpai.com


Process Descriptions Selectively permeable membranes havean increasingly wide range of uses and configurations as the need formore advanced pollution control systems are required. There are fourmajor types of membrane systems: (1) pervaporation; (2) reverseosmosis (RO); (3) gas absorption; and (4) gas adsorption. Only mem-brane pervaporation is currently commercialized.

Membrane Pervaporation Since 1987, membrane pervapora-tion has become widely accepted in the CPI as an effective means ofseparation and recovery of liquid-phase process streams. It is mostcommonly used to dehydrate liquid hydrocarbons to yield a high-purity ethanol, isopropanol, and ethylene glycol product. The methodbasically consists of a selectively-permeable membrane layer separat-ing a liquid feed stream and a gas phase permeate stream as shown inFig. 22-21. The permeation rate and selectivity is governed by thephysicochemical composition of the membrane. Pervaporation differsfrom reverse osmosis systems in that the permeate rate is not a func-tion of osmotic pressure, since the permeate is maintained at satura-tion pressure (Ref. 24).

Three general process groups are commonly used when describingpervaporation: (1) water removal from organics; (2) organic removalfrom water (solvent recovery); and (3) organic/organic separation.Organic/organic separations are very uncommon and therefore willnot be discussed further.

Ethanol Dehydration The membrane-pervaporation process fordehydrating ethanol was first developed by GFT in West Germany inthe mid 1970s, with the first commercial units being installed in Braziland the Philippines. At both sites, the pervaporation unit was coupledto a continuous sugarcane fermentation process that produced ethanolat concentrations up to 96 percent after vacuum pervaporation. Thekey advantages of the GFT process are (1) no additive chemicals arerequired; (2) the process is skid-mounted (low capital costs and smallfootprint); (3) and there is a low energy demand. The low energyrequirement is achieved because only a small fraction of the water isactually vaporized and that the required permeation driving force isprovided by only a small vacuum pump. The basic ethanol dehydrationprocess schematic is shown in Fig. 22-22. A key advantage of all perva-poration processes is that vapor-liquid equilibria and possible resultingazeotropic effects are irrelevant (see Fig. 22-23 and Ref. 24).

Solvent Recovery The largest current industrial use of pervapo-ration is the treatment of mixed organic process streams that havebecome contaminated with small (10 percent) quantities of water.Pervaporation becomes very attractive when dehydrating streamsdown to less than 1 percent water. The advantages result from thesmall operating costs relative to distillation and adsorption. Also, dis-

tillation is often impossible, since azeotropes commonly form in mul-ticomponent organic/water mixtures.

Pervaporation occurs in three basic steps:1. Preferential sorption of chemical species2. Diffusion of chemical species through the membrane3. Desorption of chemical species from the membrane

Steps 1 and 2 are controlled by the specific polymer chemistry and itsdesigned interaction with the liquid phase. The last step, consisting ofevaporation of the chemical species, is considered to be a fast, nonse-lective process. Step 2 is the rate-limiting step. The development bythe membrane manufacturers of highly selective, highly permeablecomposite membranes that resist fouling from solids has subsequentlybeen the key to commercialization of pervaporation systems. Themembrane composition and structure are designed in layers, witheach layer fulfilling a specific requirement. Using membrane dehy-dration as an example, a membrane filter would be composed of asupport layer of nonwoven porous polyester below a layer of polyacry-lonitrile (PAN) or polysulfone ultrafiltration membrane and a layer of0.1-µm-thick crosslinked polyacrylate, polyvinyl alcohol (PVA). Otherseparations membranes generally use the same two sublayers. The toplayer is interchanged according to the selectivity desired.

FIG. 22-21 Pervaporation of gas from liquid feed across membrane to vaporous permeate. (SOURCE:Redrawn from Ref. 24.)

FIG. 22-22 Ethanol dehydration using pervaporation membrane. (SOURCE:Redrawn from Ref. 24.)


attention to reductions in the other ingredients in ozone formation,nitrogen oxides (NOx). In such areas, ozone concentrations are con-trolled by NOx rather than VOC emissions.

Selective catalytic reduction (SCR) has been used to control NOx

emissions from utility boilers in Europe and Japan for over a decade.Applications of SCR to control process NOx emissions in the chemicalindustry are becoming increasingly common. A typical SCR system isshown in Fig. 22-24.

NOx-laden fumes are preheated by effluent from the catalyst vesselin the feed/effluent heat exchanger and then heated by a gas- or oil-fired heater to over 600ºF. A controlled quantity of ammonia isinjected into the gas stream before it is passed through a metal oxide,zeolite, or promoted zeolite catalyst bed. The NOx is reduced to nitro-gen and water in the presence of ammonia in accordance with the fol-lowing exothermic reactions:

6NO + 4NH3 → 5N2 + 6H2O

4NO + 4NH3 + O2 → 4N2 + 6H2O

2NO2 + 4NH3 + O2 → 3N2 + 6H2O

NO + NO2 + 2NH3 → 2N2 + 3H2O

NOx analyzers at the preheater inlet and catalyst vessel outlet monitorNOx concentrations and control the ammonia feed rate. The effluentgives up much of its heat to the incoming gas in the feed/effluentexchanger. The vent gas is discharged at about 350ºF.

SOURCE CONTROL OF PARTICULATE EMISSIONS

There are four conventional types of equipment used for the controlof particulate emissions:

1. Mechanical collectors2. Wet scrubbers3. Electrostatic precipitators4. Fabric filtersEach is discussed in Sec. 17 of this handbook under “Gas-Solids Sep-

arations.” The effectiveness of conventional air-pollution-control equip-ment for particulate removal is compared in Fig. 22-25. These fractionalefficiency curves indicate that the equipment is least efficient in remov-ing particulates in the 0.1- to 1.0-µm range. For wet scrubbers and fab-ric filters, the very small particulates (0.1 µm) can be efficientlyremoved by brownian diffusion. The smaller the particulates, the moreintense their brownian motion and the easier their collection by diffu-sion forces. Larger particulates (>1 µm) are collected principally byimpaction, and removal efficiency increases with particulate size. Theminimum in the fractional efficiency curve for scrubbers and filtersoccurs in the transition range between removal by brownian diffusionand removal by impaction.

A somewhat similar situation exists for electrostatic precipitators.Particulates larger than about 1 µm have high mobilities because theyare highly charged. Those smaller than a few tenths of a micrometercan achieve moderate mobilities with even a small charge because ofaerodynamic slip. A minimum in collection efficiency usually occurs inthe transition range between 0.1 and 1.0 µm. The situation is furthercomplicated because not all particulates smaller than about 0.1 µmacquire charges in an ion field. Hence, the efficiency of removal of verysmall particulates decreases after reaching a maximum in the submi-crometer range.

The selection of the optimum type of particulate collection device(i.e., ESP or fabric filter baghouse) is often not obvious without con-ducting a site-specific economic evaluation. This situation has beenbrought about by both the recent reductions in the allowable emis-sions levels and advancements with fabric filter and ESP technologies.Such technoeconomic evaluations can result in application and evensite-specific differences in the final optimum choice (see PrecipNewsletter, 220, June, 1994 and Fabric Filter Newsletter, 223, June,1994).

Improvements in existing control technology for fine particulatesand the development of advanced techniques are top-priorityresearch goals. Conventional control devices have certain limitations.Precipitators, for example, are limited by the magnitude of charge on

FIG. 22-23 Comparison of two types of pervaporation membranes to distilla-tion of ethanol-water mixtures. (SOURCE: Redrawn from Ref. 24.)

Emerging Membrane Control Technologies The recentimprovements in membrane technology have spawned several poten-tially commercial membrane filtration uses.

Reverse Osmosis (RO) Membranes A type of membrane systemfor treating oily wastewater is currently undergoing commercializa-tion by Bend Research, Inc. The system uses a tube-side feed modulethat yields high fluxes while being able to handle high-solids-contentwaste streams (Ref. 25). Another type of reverse osmosis technique isbeing designed to yield ultrapurified HF recovered from spent etchingsolutions. It is estimated that 20,000 tons of spent solution is annuallygenerated in the United States and that using membrane RO couldsave 1 million bbl/yr of oil.

In Situ Filter Membranes In situ membranes are being fittedinto incinerator flue-gas stacks in an attempt to reduce hydrocarbonemissions. Two types of commercially available gas separation mem-branes are being studied: (1) flat cellulose acetate sheets; and (2) hol-low-tube fiber modules made of polyamides.

Vibratory Shear-Enhanced Membranes The vibratory shear-enhancing process (VSEP) is just starting commercialization by LogicInternational, Emeryville, CA. It employs the use of intense sinusiodalshear waves to ensure that the membrane surfaces remain active andclean of solid matter. The application of this technology would be inthe purification of wastewater (Ref. 2).

Vapor Permeation Vapor permeation is similar to vapor perva-poration except that the feed stream for permeation is a gas. Thefuture commercial viability of this process is based upon energy andcapital costs savings derived from the feed already being in the vapor-phase, as in fractional distillation, so no additional heat input would berequired. Its foreseen application areas would be the organics recov-ery from solvent-laden vapors and pollution treatment. One commer-cial unit was installed in Germany in 1989 (Ref. 26).

Selective Catalytic Reduction of Nitrogen Oxides The tradi-tional approach to reducing ambient ozone concentrations has been toreduce VOC emissions, an ozone precursor. In many areas, it has nowbeen recognized that elimination of persistent exceedances of theNational Ambient Air Quality Standard for ozone may require more


The electrostatic effect can be incorporated into wet scrubbing bycharging the particulates and/or the scrubbing-liquor droplets. Elec-trostatic scrubbers may be capable of achieving the same efficiency forfine-particulate removal as is achieved by high-energy scrubbers, but atsubstantially lower power input. The major drawbacks are increasedmaintenance of electrical equipment and higher capital cost.

Flux-force-condensation scrubbers combine the effects of fluxforce (diffusiophoresis and thermophoresis) and water-vapor conden-sation. These scrubbers contact hot, humid gas with subcooled liquid,and/or they inject steam into saturated gas, and they have demon-strated that a number of these novel devices can remove fine particu-lates (see Fig. 22-26). Although limited in terms of commercialization,these systems may find application in many industries.

EMISSIONS MEASUREMENT

Introduction An accurate quantitative analysis of the dischargeof pollutants from a process must be determined prior to the designand/or selection of control equipment. If the unit is properly engi-neered by utilizing the emission data as input to the control device andthe code requirements as maximum-effluent limitations, most pollu-tants can be successfully controlled.

Sampling is the keystone of source analysis. Sampling methods andtools vary in their complexity according to the specific task; therefore,a degree of both technical knowledge and common sense is needed todesign a sampling function. Sampling is done to measure quantities orconcentrations of pollutants in effluent gas streams, to measure theefficiency of a pollution-abatement device, to guide the designer ofpollution-control equipment and facilities, and/or to appraise contam-ination from a process or a source. A complete measurement requiresa determination of the concentration and contaminant characteristicsas well as the associated gas flow. Most statutory limitations requiremass rates of emissions; both concentration and volumetric-flow-ratedata are therefore required.

FIG. 22-24 Selective catalytic reduction of nitrogen oxides.

the particulate, the electric field, and dust reentrainment. Also, theresistivity of the particulate material may adversely affect both chargeand electric field. Advances are needed to overcome resistivity andextend the performance of precipitators not limited by resistivity (seeBuonicore and Theodore, “Control Technology for Fine ParticulateEmissions,” DOE Rep. ANL/ECT-5, Argonne National Laboratory,Argonne, Illinois, October 1978). Recent design developments withthe potential to improve precipitator performance include pulse ener-gization, electron beam ionization, wide plate spacing, and prechargedunits [Balakrishnan et al., “Emerging Technologies for Air PollutionControl,” Pollut. Eng., 11, 28-32 (Nov. 1979); “Pulse Energization,”Environ. Sci. Technol. 13(9), 1044 (1974); and Midkaff, “Change inPrecipitator Design Expected to Help Plants Meet Clean Air Laws,”Power, 126(10), 79 (1979)]; Robert A. Mastropietro, “Impact of ESPPerformance on PM2.5,” European Particulate Control Users GroupMeeting, Pisa, Italy, Nov. 7, 2000.

Fabric filters are limited by physical size and bag-life considera-tions. Some sacrifices in efficiency might be tolerated if higher air-cloth ratios could be achieved without reducing bag life (improvedpulse-jet systems). Improvements in fabric filtration may also be pos-sible by enhancing electrostatic effects that may contribute to rapidformation of a filter cake after cleaning. J.C. Mycock, J. Turner, and J.Farmer, “Baghouse Filtration Products Verification Testing, How ItBenefits the Boiler Baghouse Operator,” Council of Industrial BoilerOwners Conference, May 6, 2002; C. Jean Bustard et al. “Long TermEvaluation of Activated Carbon Injection for Mercury ControlUpstream of a Cohpac Fabric Filter,” Air Quality IV, Arlington, Va.,Sept. 22, 2003.

Scrubber technology is limited by scaling and fouling, overall reli-ability, and energy consumption. The use of supplementary forces act-ing on particulates to cause them to grow or otherwise be more easilycollected at lower pressure drops is being closely investigated. Thedevelopment of electrostatic and flux-force-condensation scrubbers isa step in this direction.


The selection of a sampling site and the number of sampling pointsrequired are based on attempts to get representative samples. Toaccomplish this, the sampling site should be at least eight stack or ductdiameters downstream and two diameters upstream from any flowdisturbance, such as a bend, expansion, contraction, valve, fitting, orvisible flame.

Once the sampling location has been decided on, the flue cross sec-tion is laid out in a number of equal areas, the center of each being thepoint where the measurement is to be taken. For rectangular stacks, thecross section is divided into equal areas of the same shape, and the tra-verse points are located at the center of each equal area, as shown inFig. 22-27. The ratio of length to width of each elemental area shouldbe selected. For circular stacks, the cross section is divided into equalannular areas, and the traverse points are located at the centroid of eacharea. The location of the traverse points as a percentage of diameterfrom the inside wall to the traverse point for circular-stack sampling isgiven in Table 22-34. The number of traverse points necessary on eachof two perpendiculars for a particular stack may be estimated from Fig.22-28.

Once these traverse points have been determined, velocity mea-surements are made to determine gas flow. The stack-gas velocity isusually determined by means of a pitot tube and differential-pressuregauge. When velocities are very low (less than 3 m/s [10 ft/s]) andwhen great accuracy is not required, an anemometer may be used.For gases moving in small pipes at relatively high velocities or pres-sures, orifice-disk meters or venturi meters may be used. These arevaluable as continuous or permanent measuring devices.

Once a flow profile has been established, sampling strategy can beconsidered. Since sampling collection can be simplified and greatly

reduced depending on flow characteristics, it is best to complete theflow-profile measurement before sampling or measuring pollutantconcentrations.

Sampling Methodology The following subsections reviewthe methods specified for sampling commonly regulated pollutantsas well as sampling for more exotic volatile and semivolatileorganic compounds. In all sampling procedures, the main concernis to obtain a representative sample; the U.S. EPA has published

FIG. 22-26 Fractional efficiency curves for novel air-pollution-controldevices. [Chem. Eng., 87(13), 85 (June 30, 1980).]

FIG. 22-25 Fractional efficiency curves for conventional air-pollution-controldevices. [Chem. Eng., 87(13), 83 (June 30, 1980).]

FIG. 22-27 Example showing rectangular stack cross section divided into 12equal areas, with a traverse point at centroid of each area.


reference sampling methods for measuring emissions of specificpollutants so that uniform procedures can be applied in testing toobtain a representative sample. Table 22-35 provides a list of someof the most commonly employed test methods. A complete listingof all EPA test methods can be found by going online to theUSEPA Technology Transfer Network Emission MeasurementCenter at www.epa.gov/ttn/emc/promgate.html. These are theCFR Promulgated test methods published in the Federal Registerand are the federal government’s official legal versions. The testmethods reviewed in the following subsections address measuringthe emissions of the following pollutants: particulate matter, sulfurdioxide, nitrogen oxides, carbon monoxide, fluorides, hydrogenchloride, total gaseous organics, multiple metals, volatile organiccompounds, and semivolatile organic compounds.

Each sampling method requires the use of complex samplingequipment that must be calibrated and operated in accordance withspecified reference methods. Additionally, the process or source thatis being tested must be operated in a specific manner, usually at ratedcapacity, under normal procedures.

Velocity and Volumetric Flow Rate The U.S. EPA has pub-lished Method 2 as a reference method for determining stack-gasvelocity and volumetric flow rate. At several designated samplingpoints, which represent equal portions of the stack volume (areas inthe stack), the velocity and temperature are measured with instru-mentation shown in Fig. 22-29.

Measurements to determine volumetric flow rate usually requireapproximately 30 min. Since sampling rates depend on stack-gasvelocity, a preliminary velocity check is usually made prior to testingfor pollutants to aid in selecting the proper equipment and in deter-mining the approximate sampling rate for the test.

The volumetric flow rate determined by this method is usuallywithin ±10 percent of the true volumetric flow rate.

Sources of Methods and Information For the person trying toobtain current information or to enter into the field of source mea-surements, several particularly helpful information sources are avail-able. The U.S. EPA methods fall in two groups—those used by EPA’sOffice of Air Quality Planning and Standards (OAQPS) and thoseused by EPA’s Office of Solid Waste (OSW).

The Emission Measurement Technical Information Center (EMTIC)at Research Triangle Park, N.C., is supported by EPA’s Office of Air Qual-ity Planning and Standards. Perhaps the most efficient of several availableforms of assistance is the EMTIC Bulletin Board System (BBS). Testmethods are included along with announcements, utility programs, mis-cellaneous documents, and other information. The EMTIC/BBS may bereached through TTN 2000 on the Internet at http://www.epa.gov/ttn. AnEMTIC representative can be reached by telephone at 919-541-0200.EMTIC sponsors workshops and training courses jointly with EPA’s AirPollution Training Institute. Training videotapes, a newsletter, and othermailings are also available from EMTIC.

An excellent source for information concerning OSW’s SW-846 Meth-ods is the Methods Information Communication Exchange (MICE).MICE can be reached on the Internet at [email protected]. Atelephone call to the MICE line, at 703-821-4690, will put the informa-tion seeker in touch with an automated information service or with a liverepresentative. Although the function of MICE is to provide informa-tion, they will usually send copies of up to three methods. They will notprovide copies of the entire SW-846 Methods Manual. The SW-846Methods Manual may be obtained on CD-ROM or hard copy fromNational Technical Information Service (NTIS). The NTIS order num-ber for the CD-ROM which includes the third edition and updates 1–3is PB97-501928INQ. NTIS has a web site at http://www.ntis.gov andmay also be reached by telephone at 703-487-4650. SW-846 may also beobtained from the Government Printing Office (GPO). Ordering infor-mation for GPO is Test Methods for Evaluating Solid Waste,Physical/Chemical Methods, SW-846 Manual, 3d ed., Document No.955-001-000001. Available from Superintendent of Documents, U.S.Government Printing Office, Washington, D.C., November 1986.

The full document is available from the U.S. Government PrintingOffice, telephone 202-783-3238. GPO also has a web site at http://www.access.gpo.gov.

For more information or copies of the California Environmental Pro-tection Agency, Air Resources Board Methods (a.k.a. CARB Methods),contact http://www.arb.ca.gov/testmeth/testmeth.htm or telephone theEngineering and Laboratory Branch at 916-263-1630.

EPA reports may be ordered from NTIS at the web site or tele-phone number given above.

TABLE 22-34 Location of Traverse Points in Circular Stacks(Percent of stack diameter from inside wall to traverse point)

Number of traverse points on a diameter

Traverse point number on a diameter 2 4 6 8 10 12 14 18 20 22 24

1 14.6 6.7 4.4 3.2 2.6 2.1 1.8 1.4 1.3 1.1 1.12 85.4 25.0 14.6 10.5 8.2 6.7 5.7 4.4 3.9 3.5 3.23 75.0 29.6 19.4 14.6 11.8 9.9 7.5 6.7 6.0 5.54 93.3 70.4 32.3 22.6 17.7 14.6 10.9 9.7 8.7 7.95 85.4 67.7 34.2 25.0 20.1 14.6 12.9 11.6 10.56 95.6 80.6 65.8 35.6 26.9 18.8 16.5 14.6 13.27 89.5 77.4 64.4 36.6 23.6 20.4 18.0 16.18 96.8 85.4 75.0 63.4 29.6 25.0 21.8 19.49 91.8 82.3 73.1 38.2 30.6 26.2 23.0

10 97.4 88.2 79.9 61.8 38.8 31.5 27.211 93.3 85.4 70.4 61.2 39.3 32.312 97.9 90.1 76.4 69.4 60.7 39.813 94.3 81.2 75.0 68.5 60.214 98.2 85.4 79.6 73.8 67.715 89.1 83.5 78.5 72.816 92.5 87.1 82.0 77.017 95.6 90.3 85.4 80.818 98.6 93.3 88.4 83.919 96.1 91.3 86.820 96.7 94.0 89.521 96.5 92.122 98.9 94.523 96.824 96.9

www.epa.gov/ttn/emc/promgate.html

http://www.epa.gov/ttn

http://www.ntis.gov

http://www.access.gpo.gov

http://www.access.gpo.gov

http://www.arb.ca.gov/testmeth/testmeth.htm


Disturbance

Disturbance

Measurementsite

8 or 9a

24 or 25a

From point of any type of disturbance(bend, expansion, contraction, etc.)

Stack diameter = 0.30 to 0.61 m (12–24 in)

*

aHigher number is for rectangular stacks or ducts

12

16

20

2 3 4 5 6 7Duct diameters downstream from flow disturbance* (distance B)

8 9 10

0.550

40

30

20

Min

imum

num

ber

of tr

aver

se p

oint

s

10

0

1.0 1.5Duct diameters upstream from flow disturbance* (distance A)

2.0 2.5

Stack diameter > 0.61 m (24 in.)

A

B

( a )

8 or 9a

Stack diameter = 0.30 to 0.61 m (12–24 in)

aHigher number is for rectangular stacks or ducts

*From point of any type of disturbance (bend, expansion, contraction, etc.)

12

16

2 3 4 5 6 7Duct diameters downstream from flow disturbance* (distance B)

8 9 10

0.550

40

30

20

Min

imum

num

ber

of tr

aver

se p

oint

s

10

0

1.0 1.5Duct diameters upstream from flow disturbance* (distance A)

2.0 2.5

Stack diameter > 0.61 m (24 in.)

( b )

Disturbance

Disturbance

Measurementsite

A

B

FIG. 22-28 Minimum number of traverse points for (a) particulate traverse and (b) velocity (nonparticulate)traverse.


INDUSTRIAL WASTEWATER MANAGEMENT

FURTHER READING: Eckenfelder, W. W., Industrial Water Pollution Control,2d ed., McGraw-Hill, 1989. Metcalf & Eddy, Inc., Wastewater Engineering,Treatment, Disposal and Reuse, 3d ed., McGraw-Hill, 1990. Nemerow, N. L.and A. Dasgupta, Industrial and Hazardous Waste Treatment, Van NostrandReinhold, New York, 1991.

INTRODUCTION

All industrial operations produce some wastewaters which must bereturned to the environment. Wastewaters can be classified as (1)domestic wastewaters, (2) process wastewaters, and (3) coolingwastewaters. Domestic wastewaters are produced by plant workers,shower facilities, and cafeterias. Process wastewaters result fromspills, leaks, product washing, and noncooling processes. Coolingwastewaters are the result of various cooling processes and can beonce-pass systems or multiple-recycle cooling systems. Once-passcooling systems employ large volumes of cooling waters that areused once and returned to the environment. Multiple-recycle cool-ing systems have various types of cooling towers to return excessheat to the environment and require periodic blowdown to preventexcess buildup of salts.

Domestic wastewaters are generally handled by the normal sani-tary-sewerage system to prevent the spread of pathogenic microor-ganisms which might cause disease. Normally, process wastewatersdo not pose the potential for pathogenic microorganisms, but they dopose potential damage to the environment through either direct orindirect chemical reactions. Some process wastes are readily biode-graded and create an immediate oxygen demand. Other processwastes are toxic and represent a direct health hazard to biological lifein the environment. Cooling wastewaters are the least dangerous, butthey can contain process wastewaters as a result of leaks in the cool-ing systems. Recycle cooling systems tend to concentrate both inor-ganic and organic contaminants to a point at which damage can becreated.

Recently, concern for subtle aspects of environmental damage hasstarted to take precedence over damage referred to above. It has beenrealized that the presence of substances in water at concentrations farbelow those that will produce overt toxicity or excessive reduction ofdissolved oxygen levels can have a major impact by altering the pre-domination of organisms in the aquatic ecosystem. This is beginningto have an effect on water-quality standards and, consequently, allow-

able discharges. Unfortunately, the extent of knowledge is not suffi-cient upon which to base definitive standards for these subtle effects.Emerging chemicals of concern include pharmaceutically activeagents, endocrine disrupters, and low concentrations of heavy metalsand metalloids. Over the next decade, it is anticipated that accumula-tion of knowledge will make it possible to delineate defensible stan-dards. Another recent concern is that of contaminated storm waterfrom industrial sites. Federal guidelines to control this wastewater arepresently being developed. Most concern is for product spills on plantproperty but outside the production facility and from rain contact withspoil piles.

UNITED STATES LEGISLATION, REGULATIONS, AND GOVERNMENT AGENCIES

Federal Legislation Public Law 92-500 promulgated in 1972created the primary framework for management of water pollution inthe United States. This act has been amended many times since 1972.Major amendments occurred in 1977 (Public Laws 95-217 and 95-576), 1981 (Public Laws 97-117 and 97-164), and 1987 (Public Law100-4). This law and its various amendments are referred to as theClean Water Act. The Clean Water Act addresses a large number ofissues of water pollution management. A general review of theseissues has been presented in an earlier chapter in this handbook. Pri-mary with respect to control of industrial wastewater is the NationalPollutant Discharge Elimination System (NPDES), originally estab-lished by PL 92-500. Any municipality or industry that dischargeswastewater to the navigable waters of the United States must obtain adischarge permit under the regulations set forth by the NPDES.Under this system, there are three classes of pollutants (conventionalpollutants, priority pollutants, and nonconventional/nonpriority pollu-tants). Conventional pollutants are substances such as biochemicaloxygen demand (BOD), suspended solids (SS), pH, oil and grease,and coliforms. Priority pollutants are a list of 129 substances originallyset forth in a consent decree between the Environmental ProtectionAgency and several environmental organizations. This list was incor-porated into the 1977 amendments. Most of the substances on this listare organics, but it does include most of the heavy metals. These sub-stances are generally considered to be toxic. However, the toxicity isnot absolute; it depends on the concentration. In addition, many of

TABLE 22-35 Selected EPA Test Methods

Commonly Used in Stationary Source Compliance Tests

Method Test parameter(s)

Office of Air Quality Planning and Standards (OAQPS)Methods 1–4 Test location, volumetric flow, gas composition,

moisture contentMethod 5 Particulate matterMethod 6 Sulfur dioxideMethod 7 Nitrogen oxidesMethod 9 OpacityMethod 10 Carbon monoxideMethod 13 Total fluorideMethod 23 Dioxins and furansMethod 25 VOCsMethod 26 Halogens, halidesMethod 29 MetalsMethod 201 Particulate PM10

Method 202 Condensible particulate matter

Office of Solid Waste (OSW)Method 0010 Modified Method 5, semivolatile organicsMethod 0030 Volatile organics

FIG. 22-29 Velocity-measurement system.

INDUSTRIAL WASTEWATER MANAGEMENT 22-59

the organics on the list are under appropriate conditions biodegrad-able. In reality, substances for inclusion on the priority pollutant listwere chosen on the basis of a risk assessment rather than only a haz-ard assessment. The third class of pollutants could include any pollu-tant not in the first two categories. Examples of substances that arepresently regulated in the third category are nitrogen, phosphorous,sodium, and chlorine residual. The overall goals of the Clean WaterAct are to restore and maintain water quality in the navigable watersof the United States. The initial standard was to ensure that thesewaters would be clean enough for recreation (swimmable) and eco-logically secure (fishable). Initially this was to be achieved by curtail-ment of the discharge of pollutants. Eventually the regulatory systemwas essentially to phase out discharge of any pollutant into water.Obviously, if no discharge of pollutants occurs, the waters will bemaintained in close to a pristine condition. However, the early reduc-tion of pollutant discharge to zero was realized as impractical. Thus, atpresent, the NPDES has prescribed the limits on discharges as a func-tion of the type of pollutant, the type of industry discharging, and thedesired water quality. The specific requirements for each individualdischarger are established in the NPDES permit issued to the dis-charger. These permits are reviewed every five years and are subjectto change at the time of review.

A major tactic that was adopted in the Clean Water Act was toestablish uniform technology standards, by class of pollutant and spe-cific industry type, which applied nationwide to all dischargers. Thus,a kraft mill in Oregon would have to meet essentially the same dis-charge standards as a kraft mill in New York. In establishing thesestandards, the EPA took into account the state of the art of wastetreatment in each particular industry as well as cost and ecologicaleffectiveness. These discharge standards have been published in theFederal Register for more than thirty industrial categories and severalhundred subcategories (the Commerce Department Industrial Classi-fication System was used to establish these categories) in the FederalRegister. These have been promulgated over an extensive period oftime. The reader is advised to consult the index to this document toascertain regulations that apply to a particular industry. Table 22-36presents the major industrial categories.

As indicated above, not only are the discharge standards organizedon an industry-by-industry basis, but they are different dependingupon which of the three classes of pollutants is being regulated. Thestandards for conventional pollutants are referred to as best conven-tional technology (BCT). The standards for priority pollutants arereferred to as best available technology (BAT), as are those for non-conventional, nonpriority pollutants. These standards envision thatthe technology will not be limited to treatment but may include revi-sion in the industrial processing and/or reuse of effluents (pollutionprevention). They are usually presented as mass of pollutant dis-charged per unit of product produced.

In some situations it is anticipated that application of BCT and BATmay not be sufficient to ensure that water-quality standards areachieved in a stream segment. Studies have indicated that approxi-mately 10 percent of the stream segments in the United States willhave their water-quality standards violated, even if all the dischargersto that stream segment meet BCT and BAT regulations. These seg-ments are referred to as water quality limited segments. The NPDESpermit for those who discharge into water quality limited segmentsmust provide for pollutant removal in excess of that required by BCTand BAT so that water-quality standards (which are jointly establishedby each state and EPA) are achieved. The stream segments in whichwater-quality standards will be met by application of BCT and BATare referred to as “effluent quality limited segments.”

For industrial discharges that enter municipal sewers and thuseventually municipal treatment plants, NPDES regulations are nomi-nally the same as for industries that discharge directly to navigablewaters; i.e., they must meet BCT and BAT standards. These arereferred to as “categorical industrial pretreatment standards.” How-ever if it can be demonstrated that the municipal treatment plant canremove a pollutant in the industrial waste, a “removal credit” can beassigned to the permit, thus lowering the requirement on the indus-trial discharger. The monetary charge to the industry by the munici-pality for this service is negotiable but must be within parametersestablished by EPA for industrial user charges if the municipalityreceived a federal grant for construction of the treatment plant. Aremoval credit cannot be assigned if removal of the industrial pollu-tant results in difficulty in ultimate disposal of sludge from the munic-ipal plant. In addition, an industry cannot discharge any substancethat can result in physical damage to the municipal sewer and/or inter-fere with any aspect of treatment plant performance even if the sub-stance is not covered by BCT or BAT regulations.

The EPA has established a National Pretreatment Program toaddress the growing impacts industrial effluents have on publiclyowned treatment works (POTWs). These impacts include biologicaltoxicity and inhibition causing biological upsets that can reduce plantefficiency; accumulation of heavy metals in primary and secondarysludge that may impact beneficial reuse applications; increase inwhole effluent toxicity (WET) which can impact plant discharge per-mit requirements; and increasing organic and solid loadings on plantsthat are reaching their design capacity. The EPA has established twosets of rules that are the basis of the National Pretreatment Program,the categorical pretreatment standards and prohibited dischargestandards. The categorical pretreatment standards are industry- ortechnology-based limitations on pollutant discharges to POTWs pro-mulgated by USEPA in accordance with Section 307 of the CleanWater Act. These standards apply to specific process wastewaters ofparticular industrial categories (see 40 CFR 403.6 and 40 CFR Parts405 to 471). The prohibited discharge standards forbid certain chem-icals and discharges by any sewer system. These specific dischargesare described in full in the Federal Register and include 126 specificchemicals. The program requires all POTWs with a flow greater than5 mgd or those receiving significant industrial flow to establish anindustrial pretreatment program. States and individual municipalitiescan develop their own pretreatment programs to address system-specific industrial wastewater impacts. Currently, over 1500 munici-palities have established their own pretreatment programs that eithermeet or exceed the EPA pretreatment standards. Along with settingstandards for pretreatment, the EPA identifies best-available technolo-gies to economically control industrial effluents. In addition to indus-trial discharges, the EPA has initiated a program to better control

TABLE 22-36 Industry Categories

1. Adhesives and sealants2. Aluminum forming3. Asbestos manufacturing4. Auto and other laundries5. Battery manufacturing6. Coal mining7. Coil coating8. Copper forming9. Electric and electronic components

10. Electroplating11. Explosives manufacturing12. Ferroalloys13. Foundries14. Gum and wood chemicals15. Inorganic chemicals manufacturing16. Iron and steel manufacturing17. Leather tanning and finishing18. Mechanical products manufacturing19. Nonferrous metals manufacturing20. Ore mining21. Organic chemicals manufacturing22. Pesticides23. Petroleum refining24. Pharmaceutical preparations25. Photographic equipment and supplies26. Plastic and synthetic materials manufacturing27. Plastic processing28. Porcelain enamelling29. Printing and publishing30. Pulp and paperboard mills31. Soap and detergent manufacturing32. Steam electric power plants33. Textile mills34. Timber products processing

stormwater discharges associated with industrial activity. This pro-gram is part of the national NPDES Phase I Stormwater Program.

Environmental Protection Agency President Nixon createdthe EPA in 1970 to coordinate all environmental pollution-controlactivities at the federal level. The EPA was placed directly under theOffice of the President so that it could be more responsive to the polit-ical process. In the succeeding decade, the EPA produced a series offederal regulations increasing federal control over all wastewater-pol-lution-control activities. In January 1981, President Reagan reversedthe trend of greater federal regulation and began to decrease the roleof the federal EPA. However, during the 1980s, an equilibrium wasachieved between those who wish less regulation and those who wishmore. In general, industry and the EPA reached agreement on theoptimum level of regulation.

State Water-Pollution-Control Offices Every state has its ownwater-pollution-control office. Some states have reorganized along thelines of the federal EPA with state EPA offices, while others have kepttheir water-pollution-control offices within state health departments.Prior to 1965, each state controlled its own water-pollution-controlprograms. Conflicts between states and uneven enforcement of stateregulations resulted in the federal government’s assuming the leader-ship role. Unfortunately, conflicts between states shifted to being con-flicts between the states and the federal EPA. By 1980, the statewater-pollution-control offices were primarily concerned with han-dling most of the detailed permit and paperwork for the EPA and infurnishing technical assistance to industries at the local level. In gen-eral, most of the details of regulation are carried out by state water-pollution-control agencies with oversight by EPA.

WASTEWATER CHARACTERISTICS

Wastewater characteristics vary widely from industry to industry.Obviously, the specific characteristics will affect the treatment tech-niques chosen for use in meeting discharge requirements. Some gen-eral characteristics that should be considered in planning are given inTable 22-37. Because of the large number of pollutant substances,wastewater characteristics are not usually considered on a substance-by-substance basis. Rather, substances of similar pollution effects aregrouped together into classes of pollutants or characteristics as indi-cated below.

Priority Pollutants Recently, greatest concern has been for thisclass of substances for the reasons given previously. These materialsare treated on an individual-substance basis for regulatory control.Thus, each industry could receive a discharge permit that lists anacceptable level for each priority pollutant. Table 22-38 presents a listof these substances; most are organic, but some inorganics areincluded. All are considered toxic, but, as indicated previously, there iswide variation in their toxicity. Most of the organics are biologicallydegradable despite their toxicity (Refs. 30 and 31). USEPA has col-lected data on the occurrence of these substances in various industrial

wastes and their treatability. A recent trend has been to avoid their usein industrial processing.

Organics The organic composition of industrial wastes varieswidely, primarily due to the different raw materials used by each spe-cific industry. These organics include proteins, carbohydrates, fats andoils, petrochemicals, solvents, pharmaceutical, small and large mole-cules, solids and liquids. Another complication is that a typical indus-try produces many diverse wastestreams. Good practice is to conducta material balance throughout an entire production facility. This sur-vey should include a flow diagram, location and sizes of piping, tanksand flow volumes, as well as an analysis of each stream. Results of anindustrial waste survey for an industry are given in Table 22-39. Note-worthy is the range in waste sources, including organic soap, toiletarticles, ABS (alkyl benzene sulfonate), and the relatively clean buthot condenser water that makes up half the plant flow, while thestrongest wastes—spent caustic and fly ash—have the lowest flows.See Tables 22-39 and 22-40 for information on the average character-istics of wastes from specific industries.

An important measure of the waste organic strength is the 5-daybiochemical oxygen demand (BOD5). As this test measures thedemand for oxygen in the water environment caused by organicsreleased by industry and municipalities, it has been the primaryparameter in determining the strength and effects of a pollutant. Thistest determines the oxygen demand of a waste exposed to biologicalorganisms (controlled seed) for an incubation period of five days. Usu-ally this demand is caused by degradation of organics according to thefollowing simplified equation, but reduced inorganics in some indus-tries may also cause demand (i.e., Fe2+, S2−, and SO3

2−).

Organic waste + O2 (D.O.) CO2 + H2O

This wet lab test measures the decrease in dissolved oxygen (D.O.)concentration in 5 days, which is then related to the sample strength.If the test is extended over 20 days, the BOD20 (ultimate BOD) isobtained and corresponds more closely to the Chemical OxygenDemand (COD) test. The COD test uses strong chemical oxidizingagents with catalysts and heat to oxidize the wastewater and obtain avalue that is almost always larger than the 5- and 20-day BOD values.Some organic compounds (like pyridene, a ring structure containingnitrogen) resists chemical oxidation giving a low COD. A major advan-tage of the COD test is the completion time of less than 3 hours, ver-sus 5 days for the BOD5 test. Unfortunately, state and federalregulations generally require BOD5 values, but approximate correla-tions can be made to allow computation of BOD from COD. A morerapid measure of the organic content of a waste is the instrumentaltest for total organic carbon (TOC), which takes a few minutes andmay be correlated to both COD and BOD for specific wastes. Unfor-tunately, BOD5 results are subject to wide statistical variations andrequire close scrutiny and experience. For municipal wastewaters,BOD5 is about 67 percent of the ultimate BOD and 40–45 percent ofthe COD, indicating a large amount of nonbiodegradable COD andthe continuing need to run BOD as well as COD and TOC. An exam-ple of BOD, COD, and TOC relationships for chemical industrywastewater is given in Table 22-40. The concentrations of the waste-waters vary by two orders of magnitude, and the BOD/COD,COD/TOC, and BOD/TOC ratios vary less than twofold. The tableindicates that correlation/codification is possible, but care and contin-ual scrutiny must be exercised.

Another technique for organics measurement that overcomes thelong period required for the BOD test is the use of continuousrespirometry. Here the waste (full-strength rather than diluted as inthe standard BOD test) is contacted with biomass in an apparatus thatcontinuously measures the dissolved oxygen consumption. This testdetermines the ultimate BOD in a few hours if a high level of biomassis used. The test can also yield information on toxicity, the need todevelop an acclimated biomass, and required rates of oxygen supply.

In general, low-molecular-weight water-soluble organics are biode-graded readily. As organic complexity increases, solubility andbiodegradability decrease. Soluble organics are metabolized moreeasily than insoluble organics. Complex carbohydrates, proteins, and

seed→microbes


TABLE 22-37 Wastewater Characteristics

Property Characteristic Example Size or concentration

Solubility Soluble Sugar >100 gm/LInsoluble PCB <1 mg/L

Stability, biological Degradable SugarRefractory DDT, metals

Solids Dissolved NaCl <10−9 mColloidal Carbon >10−6–<10−9 mSuspended Bacterium >10−6 m

Organic Carbon AlcoholInorganic Inorganic Cu2+

pH Acidic HNO3

Neutral Salt (NaCl) 1–12Basic NaOH

Temperature High–low Cooling >5°Heat exchange >30°

Toxicity Biological effect Heavy metals VariesPriority compounds

Nutrients N NH3 VariesP PO4

3−


TABLE 22-38 List of Priority Chemicals*

Compound name Compound name Compound name

1. Acenaphthene†2. Acrolein†3. Acrylonitrile†4. Benzene†5. Benzidine†6. Carbon tetrachloride†

(tetrachloromethane)

Chlorinated benzenes (other than dichloroben-zenes)

7. Chlorobenzene8. 1,2,4-Trichlorobenzene9. Hexachlorobenzene

Chlorinated ethanes† (including 1,2-dichloroethane, 1,1,1-trichloroethane, andhexachloroethane)

10. 1,2-Dichloroethane11. 1,1,1-Trichloroethane12. Hexachloroethane13. 1,1-Dichloroethane14. 1,1,2-Trichloroethane15. 1,1,2,2-Tetrachloroethane16. Chloroethane (ethyl chloride)

Chloroalkyl ethers† (chloromethyl, chloroethyl, and mixed ethers)

17. Bis(chloromethyl) ether18. Bis(2-chloroethyl) ether19. 2-Chloroethyl vinyl ether (mixed)

Chlorinated napthalene†20. 2-Chloronapthalene

Chlorinated phenols† (other than those listed elsewhere; includes trichlorophenols and chlorinated cresols)

21. 2,4,6-Trichlorophenol22. para-Chloro-meta-cresol23. Chloroform (trichloromethane)†24. 2-Chlorophenol†

Dichlorobenzenes†25. 1,2-Dichlorobenzene26. 1,3-Dichlorobenzene27. 1,4-Dichlorobenzene

Dichlorobenzidine†28. 3,3′-Dichlorobenzidine

Dichloroethylenes† (1,1-dichloroethylene and 1,2-dichloroethylene)

29. 1,1-Dichloroethylene30. 1,2-trans-Dichloroethylene31. 2,4-Dichlorophenol†

Dichloropropane and dichloropropene†32. 1,2-Dichloropropane33. 1,2-Dichloropropylene (1,2-

dichloropropene)34. 2,4-Dimethylphenol†

Dinitrotoluene†35. 2,4-Dinitrotoluene36. 2,6-Dinitrotoluene

83. Indeno (1,2,3-cd) pyrene (2,3-o-phenylenepyrene)

84. Pyrene85. Tetrachloroethylene†86. Toluene†87. Trichloroethylene†88. Vinyl chloride† (chloroethylene)

Pesticides and metabolites89. Aldrin†90. Dieldrin†91. Chlordane† (technical mixture and metabo-

lites)

DDT and metabolites†92. 4-4′-DDT93. 4,4′-DDE (p,p′-DDX)94. 4,4′-DDD (p,p′-TDE)

Endosulfan and metabolites†95. α-Endosulfan-alpha96. β-Endosulfan-beta97. Endosulfan sulfate

Endrin and metabolites†98. Endrin99. Endrin aldehyde

Heptachlor and metabolites†100. Heptachlor101. Heptachlor epoxide

Hexachlorocyclohexane (all isomers)†102. α-BHC-alpha103. β-BHC-beta104. γ-BHC (lindane)-gamma105. δ-BHC-delta

Polychlorinated biphenyls (PCB)†106. PCB-1242 (Arochlor 1242)107. PCB-1254 (Arochlor 1254)108. PCB-1221 (Arochlor 1221)109. PCB-1232 (Arochlor 1232)110. PCB-1248 (Arochlor 1248)111. PCB-1260 (Arochlor 1260)112. PCB-1016 (Arochlor 1016)113. Toxaphene†114. antimony (total)115. arsenic (total)116. asbestos (fibrous)117. beryllium (total)118. cadmium (total)119. chromium (total)120. copper (total)121. cyanide (total)122. lead (total)123. mercury (total)124. nickel (total)125. selenium (total)126. silver (total)127. thallium (total)128. zinc (total)129. 2,3,7,8-Tetrachlorodibenzo-p-dioxin

(TCDD)

37. 1,2-Diphenylhydrazine†38. Ethylbenzene†39. Fluoranthene†

Haloethers† (other than those listed elsewhere)40. 4-Chlorophenyl phenyl ether41. 4-Bromophenyl phenyl ether42. Bis(2-chloroisopropyl) ether43. Bis(2-chloroethoxy) methane

Halomethanes† (other than those listed else-where)

44. Methylene chloride (dichloromethane)45. Methyl chloride (chloromethane)46. Methyl bromide (bromomethane)47. Bromoform (tribromomethane)48. Dichlorobromomethane49. Trichlorofluoromethane50. Dichlorodifluoromethane51. Chlorodibromomethane52. Hexachlorobutadiene†53. Hexachlorocyclopentadiene†54. Isophorone†55. Naphthalene†56. Nitrobenzene†

Nitrophenols† (including 2,4-dinitrophenol and dinitrocresol)

57. 2-Nitrophenol58. 4-Nitrophenol59. 2,4-Dinitrophenol†60. 4,6-Dinitro-o-cresol

Nitrosamines†61. N-Nitrosodimethylamine62. N-Nitrosodiphenylamine63. N-Nitrosodi-n-propylamine64. Pentachlorophenol†65. Phenol†

Phthalate esters†66. Bis(2-ethylhexyl) phthalate67. Butyl benzyl phthalate68. Di-n-butyl phthalate69. Di-n-octyl phthalate70. Diethyl phthalate71. Dimethyl phthalate

Polynuclear aromatic hydrocarbons (PAH)†72. Benzo(a)anthracene (1,2-benzanthracene)73. Benzo(a)pyrene (3,4-benzopyrene)74. 3,4-Benzofluoranthene75. Benzo(k)fluoranthene (11,12-

benzofluoranthene)76. Chrysene77. Acenaphthylene78. Anthracene79. Benzo(ghl)perylene (1,12-benzoperylene)80. Fluorene81. Phenanthrene82. Dibenzo(a,h)anthracene (1,2,5,6-

dibenzanthracene)

*Adapted from Eckenfelder, W. W. Jr., Industrial Water Pollution Control, 2d ed., McGraw-Hill, New York, 1989.†Specific compounds and chemical classes as listed in the consent degree.

fats and oils must be hydrolyzed to simple sugars, aminos, and otherorganic acids prior to metabolism. Petrochemicals, pulp and paper,slaughterhouse, brewery, and numerous other industrial wastes con-taining complex organics have been satisfactorily treated biologically,but proper testing and evaluation is necessary.

Inorganics The inorganics in most industrial wastes are thedirect result of inorganic compounds in the carriage water. Soft-watersources will have lower inorganics than hard-water or saltwatersources. However, some industrial wastewaters can contain significantquantities of inorganics which result from chemical additions duringplant operation. Many food processing wastewaters are high insodium. While domestic wastewaters have a balance in organics andinorganics, many process wastewaters from industry are deficient inspecific inorganic compounds. Biodegradation of organic compoundsrequires adequate nitrogen, phosphorus, iron, and trace salts. Ammo-nium salts or nitrate salts can provide the nitrogen, while phosphatessupply the phosphorus. Either ferrous or ferric salts or even normalsteel corrosion can supply the needed iron. Other trace elementsneeded for biodegradation are potassium, calcium, magnesium,cobalt, molybdenum, chloride, and sulfur. Carriage water or deminer-alizer wastewaters or corrosion products can supply the needed traceelements for good metabolism. Occasionally, it is necessary to addspecific trace elements or nutrient elements.

pH and Alkalinity Wastewaters should have pH values between6 and 9 for minimum impact on the environment. Wastewaters withpH values less than 6 will tend to be corrosive as a result of the excesshydrogen ions. On the other hand, raising the pH above 9 will causesome of the metal ions to precipitate as carbonates or as hydroxides athigher pH levels. Alkalinity is important in keeping pH values at theright levels. Bicarbonate alkalinity is the primary buffer in waste-waters. It is important to have adequate alkalinity to neutralize theacid waste components as well as those formed by partial metabolismof organics. Many neutral organics such as carbohydrates, aldehydes,ketones, and alcohols are biodegraded through organic acids whichmust be neutralized by the available alkalinity. If alkalinity is inade-quate, sodium carbonate is a better form to add than lime. Lime tendsto be hard to control accurately and results in high pH levels and pre-

cipitation of the calcium which forms part of the alkalinity. In a fewinstances, sodium bicarbonate may be the best source of alkalinity.

Temperature Most industrial wastes tend to be on the warm side.For the most part, temperature is not a critical issue below 37°C ifwastewaters are to receive biological treatment. It is possible to oper-ate thermophilic biological wastewater-treatment systems up to 65°Cwith acclimated microbes. Low-temperature operations in northernclimates can result in very low winter temperatures and slow reactionrates for both biological treatment systems and chemical treatment sys-tems. Increased viscosity of wastewaters at low temperatures makessolid separation more difficult. Efforts are generally made to keepoperating temperatures between 10 and 30°C if possible.

Dissolved Oxygen Oxygen is a critical environmental resource inreceiving streams and lakes. Aquatic life requires reasonable dissolved-oxygen (DO) levels. EPA has set minimum stream DO levels at 5 mg/Lduring summer operations, when the rate of biological metabolism is amaximum. It is important that wastewaters have maximum DO levelswhen they are discharged and have a minimum of oxygen-demandingcomponents so that DO remains above 5 mg/L. DO is a poorly solublegas in water, having a solubility around 9.1 mg/L at 20°C and 101.3-kPa(1-atm) air pressure. As the temperature increases and the pressuredecreases with higher elevations above sea level, the solubility of oxy-gen decreases. Thus, DO is a minimum when BOD rates are a maxi-mum. Lowering the temperature yields higher levels of DO saturation,but the biological metabolism rate decreases. Warm-wastewater dis-charges tend to aggravate the DO situation in receiving waters.

Solids Total solids is the residue remaining from a wastewaterdried at 103–105°C. It includes the fractions shown in Fig. 22-30. Thefirst separation is the portion that passes through a 2-µm filter (dis-solved) and those solids captured on the filter (suspended). Combus-tion at 500°C further separates the solids into volatile and ash (fixed)solids. Although ash and volatile solids do not distinguish inorganicfrom organic solids exactly, due to loss of inorganics on combustion,the volatile fraction is often used as an approximate representation ofthe organics present. Another type of solids, settleable solids, refers tosolids that settle in an Imhoff cone in one hour. Industrial wastes varysubstantially in these types of solids and require individual wastewatertreatment process analysis. An example of possible variation is given inTable 22-41.

Nutrients and Eutrophication Nitrogen and phosphorus causesignificant problems in the environment and require special attentionin industrial wastes. Nitrogen, phosphorus, or both may cause aquatic


TABLE 22-39 Industrial Waste Components of a Soap,Detergents, and Toilet Articles Plant

Sampling COD, BOD, SS, ABS, Flow,Waste source station mg/L mg/L mg/L mg/L gal/min

Liquid soap D 1,100 565 195 28 300Toilet articles E 2,680 1,540 810 69 50Soap production R 29 16 39 2 30ABS production S 1,440 380 309 600 110Powerhouse P 66 10 50 0 550Condenser C 59 21 24 0 1100Spent caustic B 30,000 10,000 563 5 2Tank bottoms A 120,000 150,000 426 20 1.5Fly ash F 6750 10Main sewer 450 260 120 37 2150

NOTE: gal/min = 3.78 × 10−3 m3/min.SOURCE: Eckenfelder, W. W., Industrial Water Pollution Control, 2d ed.,

McGraw-Hill, New York, 1989.

TABLE 22-40 BOD, COD, and TOC Relationships

Type of BOD5, COD, TOC,waste mg/L mg/L mg/L BOD5/COD COD/TOC BOD5/TOC

Chemical 700 1,400 450 0.50 3.12 1.55Chemical 850 1,900 580 0.45 3.28 1.47Chemical 8,000 17,500 5,800 0.46 3.02 1.38Chemical 9,700 15,000 5,500 0.65 2.72 1.76Chemical 24,000 41,300 9,500 0.58 4.35 2.53Chemical 60,700 78,000 26,000 0.78 3.00 2.34Chemical 62,000 143,000 48,140 0.43 2.96 1.28

Adapted from Eckenfelder, W.W. and D.L. Ford, Water Pollution Control,Pemberton Press, Austin and New York, 1970.

FIG. 22-30 Solids identification. Abbreviations: TS, total solids; SS, suspendedsolid; D, dissolved; V, volatile.

TABLE 22-41 Solids Variation in Industrial Wastewater

Type of solids Plating Pulp and paper

Total High HighDissolved High HighSuspended Low HighOrganic Low HighInorganic High High


biological productivity to increase, resulting in low dissolved oxygenand eutrophication of lakes, rivers, estuaries, and marine waters.Table 22-42 gives the primary nutrient forms causing problems, whilethe following equation shows the biological oxidation or oxygen-consuming potential of the most common nitrogen forms.

When organics containing reduced nitrogen are degraded, theyusually produce ammonium, which is in equilibrium with ammonia.As the pK for NH3 ↔ NH4

+ is 9.3, the ammonium ion is the primaryform present in virtually all biological treatment systems, as they oper-ate at pH < 8.5 and usually in the pH range of 6.5–7.5. In aerobic reac-tions, ammonium is oxidized by nitrifying bacteria (nitrosomonas) tonitrite and each mg of NH4

+�N oxidized will require 3.43 mg D.O.Further oxidation of nitrite by nitrobacter yields nitrate and uses anadditional 1.14 mg of D.O. for a total D.O. consumption of 4.57 mg.Thus, organic and ammonium nitrogen can exert significant biochem-ical oxygen demand in the water environment. This nitrogen demandis referred to as nitrogenous or NBOD, whereas organic BOD isCBOD (carbonaceous). In treatment of wastewaters with organicsand ammonium, the total oxygen demand (TOD) may have to be sat-isfied in accordance with the approximate formula:

TOD � 1.5 BOD5 + 4.5 (TKN)

where TKN (total Kjeldahl nitrogen) Organic N � NH+4�N.

Phosphorus is not oxidized or reduced biologically, but ortho-P maybe formed from organic and poly-P. Ortho-P may be removed bychemical precipitation or biologically with sludges and will be coveredin a later section.

While many industrial wastes are so low in nitrogen and phosphorusthat these must be added if biologically based treatment is to be used,others contain very high levels of these nutrients. For example, paint-production wastes are high in nitrogen, and detergent productionwastes are high in phosphorus. Treatment for removal of these nutri-ents is required in areas where eutrophication is a problem.

Whole Effluent Toxicity (WET) Whole effluent toxicity testingis an important part of the EPA’s approach to protecting receivingwaters from toxic effluents. The EPA has established 17 analyticalmethods for testing acute and chronic toxicity of point sources(municipal and industrial wastewater effluents) and their impact onsurface water environments. WET is a term used to describe the toxiceffects imposed on a species or population of aquatic organismscaused by exposure to an effluent. WET is determined analytically byexposing sensitive indigenous organisms to effluents using WET testprotocols established by the EPA. WET tests report on the generalacute and chronic toxicity of all constituents in a complex effluent anddo not represent the toxicity of specific chemicals. To this end, theWET test results could represent the combined toxic effect of heavymetals, un-ionized ammonia, and other toxic constituents in an efflu-ent. The EPA and state regulators have been using WET as an analyt-ical tool for controlling industrial discharges and developing andenforcing industrial pretreatment programs.

Oil and Grease These substances are found in many industrialwastes (i.e., meat packing, petrochemical, and soap production). Theytend to float on the water surface, blocking oxygen transfer, interfer-ing with recreation, and producing an aesthetically poor appearance inthe water. Measurement is by a solvent extraction procedure. Manysomewhat different substances will register as oil and grease in thistest. Often oil and grease interfere with other treatment operations, sothey must be removed as part of the initial stages of treatment.

WASTEWATER TREATMENT

As indicated above, industrial wastewater contains a vast array of pol-lutants in soluble, colloidal, and particulate forms, both inorganic andorganic. In addition, the required effluent standards are also diverse,varying with the industrial and pollutant class. Consequently, therecan be no standard design for industrial water-pollution control.Rather, each site requires a customized design to achieve optimumperformance. However, each of the many proven processes for indus-trial waste treatment is able to remove more than one type of pollutantand is in general applicable to more than one industry. In the sectionsthat follow, waste-treatment processes are discussed more from thebroad-based generalized perspective than with narrow specificity.Generally, a combination of several processes is utilized to achieve thedegree of treatment required at the least cost.

Much of the experience and data from wastewater treatment hasbeen gained from municipal treatment plants. Industrial liquid wastesare similar to wastewater but differ in significant ways. Thus, typicaldesign parameters and standards developed for municipal wastewateroperations must not be blindly utilized for industrial wastewater. It isbest to run laboratory and small pilot tests with the specific industrialwastewater as part of the design process. It is most important tounderstand the temporal variations in industrial wastewater strength,flow, and waste components and their effect on the performance ofvarious treatment processes. Industry personnel in an effort to reducecost often neglect laboratory and pilot studies and depend on wastecharacteristics from similar plants. This strategy often results in fail-ure, delay, and increased costs. Careful studies on the actual waste ata plant site cannot be overemphasized.

PRETREATMENT

Many industrial-wastewater streams should be pretreated prior to dis-charge to municipal sewerage systems or even to a central industrialsewerage system. Many POTWs have pretreatment programs that fol-low the EPA program by regulating specific industries and specificchemical constituents. Product substitution, process alteration, orpretreatment should be considered to address wastewater streamsthat may fall under the local or federal pretreatment program. Pre-treatment may include single- or multiple-unit processes aimed atreducing the overall toxicity and adverse impact of the waste streamon the total treatment system.

Equalization Equalization is one of the most important pretreat-ment devices. The batch discharge of concentrated wastes is bestsuited for equalization. It may be important to equalize wastewaterflows, wastewater concentrations, or both. Periodic wastewater dis-charges tend to overload treatment units. Flow equalization tends tolevel out the hydraulic loads on treatment units. It may or may notlevel out concentration variations, depending upon the extent of mix-ing within the equalization basin. Mechanical mixing may be adequateif the wastes are purely chemical in their reactivity. Biodegradablewastes normally require aeration mixing so that the microbes are keptaerobic and nuisance odors are prevented. Diffused aeration systemsoffer better mixing under variable load conditions than mechanicalsurface aeration equipment. Mixing and oxygen transfer are bothimportant with biodegradable wastewaters. Operation on regularcycles determines the size of the equalization basin. There is noadvantage in making the equalization basin any larger than necessaryto level out wastewater variations. Industrial operation on a 5-day, 40-hweek will normally make a 2-day equalization basin as large as neededfor continuous operation of the wastewater-treatment system underuniform conditions.

Neutralization Acidic or basic wastewaters must be neutralizedprior to discharge. If an industry produces both acidic and basicwastes, these wastes may be mixed together at the proper rates toobtain neutral pH levels. Equalization basins can be used as neutral-ization basins. When separate chemical neutralization is required,sodium hydroxide is the easiest base material to handle in a liquidform and can be used at various concentrations for in-line neutraliza-tion with a minimum of equipment. Yet, lime remains the most widelyused base for acid neutralization. Limestone is used when reaction

TABLE 22-42 Nutrient Forms

Parameter Example

Organic N proteinAmmonia NH3

Ammonium NH4+

Nitrite NO2−

Nitrate NO3−

Organic P malathionOrtho-P PO4

3−

Poly-P (PO43−)x

rates are slow and considerable time is available for reaction. Sulfuricacid is the primary acid used to neutralize high-pH wastewaters unlesscalcium sulfate might be precipitated as a result of the neutralizationreaction. Hydrochloric acid can be used for neutralization of basicwastes if sulfuric acid is not acceptable. For very weak basic waste-waters carbon dioxide can be adequate for neutralization.

Grease and Oil Removal Grease and oils tend to form insolublelayers with water as a result of their hydrophobic characteristics.These hydrophobic materials can be easily separated from the waterphase by gravity and simple skimming, provided they are not too wellmixed with the water prior to separation. If the oils and greases formemulsions with water as a result of turbulent mixing, the emulsions aredifficult to break. Separation of oil and grease should be carried outnear the point of their mixing with water. In a few instances, air bub-bles can be added to the oil and grease mixtures to separate thehydrophobic materials from the water phase by flotation. Chemicalshave also been added to help break the emulsions. American Petro-leum Institute (API) separators have been used extensively by thepetroleum industry to remove oils from wastewaters. The food indus-tries use grease traps to collect the grease prior to its discharge. Unfor-tunately, grease traps are designed for regular cleaning of the trappedgrease. Too often they are allowed to fill up and discharge the excessgrease into the sewer or are flushed with hot water and steam to flu-idize the grease for easy discharge to the sewer. A grease trap shouldbe designed for a specific volume of grease to be collected over spe-cific time periods. Care should be taken to design the trap so that thegrease can easily be removed and properly handled. Neglected orpoorly designed grease traps are worse than no grease traps at all.

Toxic Substances Recent federal legislation has made it illegalfor industries to discharge toxic materials in wastewaters. Each indus-try is responsible for determining if any of its wastewater componentsare toxic to the environment and to remove them prior to the waste-water discharge. The EPA has identified a number of priority pollu-tants which must be removed and kept under proper control fromtheir origin to their point of ultimate disposal. Major emphasis hasrecently been placed on heavy metals and on complex organics thathave been implicated in possible cancer production. Pretreatment isessential to reduce heavy metals below toxic levels and to preventdischarge of any toxic organics. Many industries will be required topretreat waste streams under the local or federal pretreatment pro-gram. In the past, these pretreatment programs have focused onheavy metals and toxic organics. More recently they have begun toconcentrate on whole effluent toxicity, with future emphasis likely tobe on low concentrations of heavy metals and metalloids, pharmaceu-tical agents, endocrine disrupters, and other emerging pollutants ofconcern.

PRIMARY TREATMENT

Wastewater treatment is directed toward removal of pollutants withthe least effort. Suspended solids are removed by either physical orchemical separation techniques and handled as concentrated solids.

Screens Fine screens such as hydroscreens are used to removemoderate-size particles that are not easily compressed under fluidflow. Fine screens are normally used when the quantities of screenedparticles are large enough to justify the additional units. Mechanicallycleaned fine screens have been used for separating large particles. Afew industries have used large bar screens to catch large solids thatcould clog or damage pumps or equipment following the screens.

Grit Chambers Industries with sand or hard, inert particles intheir wastewaters have found aerated grit chambers useful for therapid separation of these inert particles. Aerated grit chambers arerelatively small, with total volume based on 3-min retention at maxi-mum flow. Diffused air is normally used to create the mixing patternshown in Fig. 22-31, with the heavy, inert particles removed by cen-trifugal action and friction against the tank walls. The air flow rate isadjusted for the specific particles to be removed. Floatable solids areremoved in the aerated grit chamber. It is important to provide forregular removal of floatable solids from the surface of the grit cham-ber; otherwise, nuisance conditions will be created. The settled grit isnormally removed with a continuous screw and buried in a landfill.

Gravity Sedimentation Slowly settling particles are removedwith gravity sedimentation tanks. For the most part, these tanks aredesigned on the basis of retention time, surface overflow rate, andminimum depth. A sedimentation tank can be rectangular or circular.The important factor affecting its removal efficiency is the hydraulicflow pattern through the tank. The energy contained in the incoming-wastewater flow must be dissipated before the solids can settle. Thewastewater flow must be distributed properly through the sedimenta-tion volume for maximum settling efficiency. After the solids have set-tled, the settled effluent should be collected without creating serioushydraulic currents that could adversely affect the sedimentationprocess. Effluent weirs are placed at the end of rectangular sedimen-tation tanks and around the periphery of circular sedimentation tanksto ensure uniform flow out of the tanks. Once the solids have settled,they must be removed from the sedimentation-tank floor by scrapingand hydraulic flow. Conventional sedimentation tanks have sludgehoppers to collect the concentrated sludge and to prevent removal ofexcess volumes of water with the settled solids. Cross-sectional dia-grams of conventional sedimentation tanks are shown in Figs. 22-32and 22-33.

Design criteria for gravity sedimentation tanks normally provide for2-h retention based on average flow, with longer retention periodsused for light solids or inert solids that do not change during theirretention in the tank. Care should be taken that sedimentation time isnot too long; otherwise, the solids will compact too densely and affect


FIG. 22-31 Schematic diagram of an aerated grit chamber.

FIG. 22-32 Schematic diagram of a circular sedimentation tank.

FIG. 22-33 Schematic diagram of a rectangular sedimentation tank.


solids collection and removal. Organic solids generally will not com-pact to more than 5 to 10 percent. Inorganic solids will compact up to20 or 30 percent. Centrifugal sludge pumps can handle solids up to5 or 6 percent, while positive-displacement sludge pumps can handlesolids up to 10 percent. With solids above 10 percent the sludge tendsto lose fluid properties and must be handled as a semi-solid ratherthan a fluid. Circular sedimentation tanks have steel truss boxes withangled sludge scrapers on the lower side. As the sludge scrapersrotate, the solids are pushed toward the sludge hopper for removal ona continuous or semicontinuous basis. The rectangular sedimentationtanks employ chain-and-flight sludge collectors or rail-mountedsludge collectors. When floating solids can occur in primary sedimen-tation tanks, surface skimmers are mounted on the sludge scrapers sothat the surface solids are removed at regular intervals.

The surface overflow rate (SOR) for primary sedimentation is nor-mally held close to 40.74 m3/(m2⋅day) [1000 gal/(ft2⋅day)] for averageflow rates, depending upon the solids characteristics. Lowering theSOR below 40.74 m3/(m2⋅day) does not produce improved effluentquality in proportion to the reduction in SOR. Generally, the mini-mum depth of sedimentation tanks is 3.0 m (10 ft), with circular sedi-mentation tanks having a minimum diameter of 6.0 m (20 ft) andrectangular sedimentation tanks having length-to-width ratios of 5:1.Chain-and-flight limitations generally keep the width of rectangularsedimentation tanks to increments of 6.0 m (20 ft) or less. Whilehydraulic overflow rates have been limited on the effluent weirs, oper-ating experience has indicated that the recommended limit of 186 m3/(m�day) [15,000 gal/(ft�day)] is lower than necessary for good opera-tion. A circular sedimentation tank with a single-edge weir providesadequate weir length and is easier to adjust than one with a double-sided weir. More problems appear to be created from improperadjustment of the effluent weirs than from improper length.

Chemical Precipitation Lightweight suspended solids and col-loidal solids can be removed by chemical precipitation and gravitysedimentation. In effect, the chemical precipitate is used to agglom-erate the tiny particles into large particles that settle rapidly in normalsedimentation tanks. Aluminum sulfate, ferric chloride, ferrous sul-fate, lime, and polyelectrolytes have been used as coagulants. Thechoice of coagulant depends upon the chemical characteristics of theparticles being removed, the pH of the wastewaters, and the cost andavailability of the precipitants. While the precipitation reaction resultsin removal of the suspended solids, it increases the amount of sludgeto be handled. The chemical sludge must be considered along withthe characteristics of the original suspended solids in evaluatingsludge-processing systems.

Normally, chemical precipitation requires a rapid mixing systemand a flocculation system ahead of the sedimentation tank. With arectangular sedimentation tank, the rapid-mixer and flocculation unitsare added ahead of the tank. With a circular sedimentation tank therapid-mixer and flocculation units are built into the tank. Schematicdiagrams of chemical treatment systems are shown in Figs. 22-34 and22-35. Rapid mixers are designed to provide 30-s retention at averageflow with sufficient turbulence to mix the chemicals with the incom-ing wastewaters. The flocculation units are designed for slow mixing at20-min retention. These units are designed to cause the particles tocollide and increase in size without excessive shearing. Care must betaken to move the flocculated mixture from the flocculation unit tothe sedimentation unit without disrupting the large floc particles.

The parameter used to design rapid mix and flocculation systems isthe root mean square velocity gradient G, which is defined by equa-tion

G = � 1/2

� where P = power input to the water (ft⋅lb/s)

V = mixer or flocculator volume (ft)3

U = absolute viscosity of water (lb⋅s/ft2)

Optimum mixing usually requires a G value of greater than 1000inverse seconds. Optimum flocculation occurs when G is in the range10–100 inverse seconds.

1�

sP

�VU

Chemical precipitation can remove 95 percent of the suspendedsolids, up to 50 percent of the soluble organics and the bulk of theheavy metals in a wastewater. Removal of soluble organics is a func-tion of the coagulant chemical, with iron salts yielding best resultsand lime the poorest. Metal removal is primarily a function of pH andthe ionic state of the metal. Guidance is available from solubilityproduct data.

SECONDARY TREATMENT

Secondary treatment utilizes processes in which microorganisms, pri-marily bacteria, stabilize waste components. The mixture of microor-ganisms is usually referred to as biomass. A portion of the waste isoxidized, releasing energy, the remainder is utilized as building blocksof protoplasm. The energy released by biomass metabolism is utilizedto produce the new units of protoplasm. Thus, the incentive for thebiomass to stabilize waste is that it provides the energy and basicchemical components required for reproduction. The process of bio-logical waste conversion is illustrated by Eq. (22-19).

(22-19)

As this equation indicates, the waste generally serves as an electrondonor, necessitating that an electron acceptor be supplied. A variety ofsubstances can be utilized as electron acceptors, including molecularoxygen, carbon dioxide, oxidized forms of nitrogen, sulfur, and organicsubstances. The characteristics of the end products of the reaction aredetermined by the electron acceptor. Table 22-43 is a list of typicalend products as a function of the electron acceptor. In general, theend products of this reaction are at a much lower energy level than thewaste components, thus resulting in the release of energy referred toabove. Although this process is usually utilized for the stabilization oforganic substances, it can also be utilized for oxidation of inorganics.For example, biomass-mediated oxidation of iron, nitrogen, and sulfuris known to occur in nature and in anthropogenic processes.

Equation (22-19) describes the biomass-mediated reaction and indi-cates that proper environmental conditions are required for the reac-tion to take place. These conditions are required by the biomass, not theelectron donor or acceptor. The environmental conditions include pH,temperature, nutrients, ionic balance, and so on. In general, biomasscan function over a wide pH range generally from 5 to 9. However,

Waste(electron donor)

Electronacceptor Proper

environmentalconditions

BiomassMore

biomass End products: Oxidized electron donor Reduced electron acceptor

+ + +

FIG. 22-34 Schematic diagram of a chemical precipitation system for rect-angular sedimentation tanks.

FIG. 22-35 Schematic diagram of a chemical precipitation system for circularsedimentation tanks.

some microbes require a much narrower pH range; i.e., effectivemethane fermentation requires a pH in the range of 6.5–7.5. It is just asimportant to maintain a relatively constant pH in the process as it is tostay within the range given above. Microorganisms can function effec-tively at the extremes of their pH range provided they are given theopportunity to acclimate to these conditions. Continual changes in pHare detrimental, even if the organisms are on the average near themiddle of their effective pH range. A similar situation prevails fortemperature. Most organisms can function well over a broad range oftemperature but do not adjust well to frequent fluctuations of even afew degrees. There are three major temperature ranges in whichmicroorganisms function. The psychrophilic range (5 to 20°C), themesophilic range (20 to 45°C), and the thermophilic range (45 to 70°C).In general the microbes that function in one of these temperatureranges cannot function efficiently in the other ranges. As it is generallyuneconomical to adjust the temperature of a waste, most processes areoperated in the mesophilic range. If the normal temperature of thewaste is above or below the mesophilic range, the process will be oper-ated in the psychrophilic or thermophilic range as appropriate. How-ever, occasionally the temperature of the waste is altered to improveperformance. For example, some anaerobic treatment processes areoperated under thermophilic conditions, even though the waste mustbe heated to achieve this temperature range. This is carried out in orderto speed up the degradation of complex organics and/or to achieve killof mesophilic pathogens. It should be noted that any time the biologicaloperation of a process moves away from its optimum or most effectiverange, be it pH, temperature, nutrients, or what have you, the rate ofbiological processing is reduced.

All microorganisms require varying amounts of a large number ofnutrients. These are required because they are necessary compo-nents of bacterial protoplasm. The nutrients can be divided intothree groups: macro, minor, and micro. The macronutrients are thosethat comprise most of the biomass. These are given by the commonlyaccepted formula for biomass (C60H87O23N12P). The carbon, hydro-gen, and oxygen are normally supplied by the waste and water, butthe nitrogen and phosphorous must often be added to industrialwastes to ensure that a sufficient amount is present. A good rule isthat the mass of nitrogen should be at least 5 percent of the BOD,and the mass of phosphorous should be at least 20 percent of themass of nitrogen. One of the major operational expenses is the pur-chase of nitrogen and phosphorous for addition to biologically basedtreatment processes. The quantities of nitrogen and phosphorousreferred to above as required are actually in excess of the minimumamounts needed. The actual amount required depends upon thequantity of excess biomass wasted from the system and the amount ofN and P available in the waste. This will be expanded upon later inthis section. The minor nutrients include the typical inorganic com-ponents of water. These are given in Table 22-44. The range of con-centrations required in the wastewater for the minor nutrients is1–100 mg/L. The micronutrients include the substances that we nor-mally refer to as trace metals and vitamins. It is interesting to notethat the trace metals include virtually all of the toxic heavy metals.This reinforces the statement made above that toxicity is a function ofconcentration and not an absolute parameter. Whether or not thesubstances referred to as vitamins will be required depends upon thetype of microorganisms required to stabilize the waste materials.Many microorganisms have the ability to make their own vitaminsfrom the waste components; thus, a supplement is not needed. How-ever, occasionally the addition of an external source of vitamins isessential to the success of a biologically based waste-treatment sys-

tem. In general, the trace nutrients must be present in a waste at alevel of a few micrograms per liter.

One aspect of the basic equation describing biological treatment ofwaste that has not been referred to previously is that biomass appearson both sides of the equation. As was indicated above, the only reasonthat microorganisms function in waste-treatment systems is because itenables them to reproduce. Thus, the quantity of biomass in a waste-treatment system is higher after the treatment process than before it.This is favorable in that there is a continual production of the organ-isms required to stabilize the waste. Thus, one of the major reactantsis, in effect, available free of charge. However, there is an unfavorableside in that unless some organisms are wasted from the system, anexcess level will build up, and the process could choke on organisms.The wasted organisms are referred to as sludge. A major cost compo-nent of all biologically based processes is the need to provide for theultimate disposal of this sludge.

Biologically based treatment processes probably account for themajority of the treatment systems used for industrial waste man-agement because of their low cost and because most substances areamenable to biological breakdown. However, some substances aredifficult to degrade biologically. Unfortunately, it is not possible atpresent to predict a priori the biodegradability of a specific organiccompound; rather, we must depend upon experience and testing.The collective experience of the field has been put into compendiaby EPA in a variety of documents. However, these data are primar-ily qualitative. There have been some attempts to develop a systemof prediction of biodegradability based on a number of compoundparameters such as solubility, presence or absence of certain func-tional groups, compound polarity, and so on. Unfortunately, none ofthese systems has advanced to the point where reliable quantitativepredictions are possible. Another complication is that some organ-ics that are easily biodegradable at low concentration exert a toxiceffect at high concentration. Thus, literature data can be confusing.Phenol is a typical compound that shows ease of biodegradationwhen the concentration is below 500 mg/L but poor biodegradationat higher concentrations. Another factor affecting both biodegrada-tion and toxicity is whether or not a substance is in solution. In gen-eral, if a substance is not in solution, it is not available to affect thebiomass. Thus, the presence of a waste in substances that can pre-cipitate, complex, or absorb other waste components can have a sig-nificant effect on reports of biodegradability and/or toxicity. Aquantitative estimate of toxicity can be obtained in terms of thechange in kinetic parameters of a system. These kinetic parametersare discussed below.

Design of Biological Treatment Systems In the past, thedesign of biologically based waste-treatment systems has beenderived from rules of thumb. During the past two decades, however,a more fundamental system has been developed and is presentlywidely used to design such systems. This system is based upon a fun-damental understanding of the kinetics and stoichiometry of biologi-cal reactions. The system is codified in terms of equations in whichfour pseudo constants appear. These pseudo constants are km, themaximum substrate utilization rate (1/time); Ks, the half maximalvelocity concentration (mg/L); Y, the yield coefficient; and b, theendogenous respiration rate (1/time). These are referred to aspseudo constants because, in the mathematical manipulation of theequations in which they appear, they are treated as constants. How-ever, the value of each is a function of the nature of the microbes, thepH, the temperature, and the components of the waste. It is impor-tant to remember that if any of these change, the value of the pseudo


TABLE 22-43 Electron Acceptors and End Products for Biological Reactions

Electron acceptors End product

Molecular oxygen Water, CO2, oxidized nitrogenOxidized nitrogen N2, N2O, NO, CO2, H2OOxidized sulfur H2S, S, CO2, H2OCO2, acetic acid, formic acid CH4, CO2, H2

Complex organics H2, simple organics, CO2, H2O

TABLE 22-44 Minor and Micro Nutrients Required for Biologically Mediated Reactors

Minor 1–100 mg/L

Sodium, potassium, calcium, magnesium, iron, chloride, sulfate

Micro 1–100 µg/L

Copper, cobalt, nickel, manganese, boron, vanadium, zinc, lead, molybdenum,various organic vitamins, various amino acids


constants may change as well. The kinetics of biological reactions aredescribed by Eq. (22-20).

(22-20)

where t = time (days)S = waste concentration (mg/L)X = biomass concentration (mg/L)

km = (mg/L substrate ÷ mg/L biomass) − time

The accumulation or growth of biosolids is given by Eq. (22-21).

Y � bX (22-21)

where X biomass level (mg/L).The equations that have been developed for design using these

pseudo constants are based on steady-state mass balances of the bio-mass and the waste components around both the reactor of the systemand the device used to separate and recycle microorganisms. Thus,the equations that can be derived will be dependent upon the charac-teristics of the reactor and the separator. It is impossible here topresent equations for all the different types of systems. As an illustra-tion, the equations for a common system (a complete mix – stirredtank reactor with recycle) are presented below.

Se = (22-22)

X = (22-23)

where Se = influent waste concentration (mg/L)So = treated waste concentration (mg/L)

HRT = reactor hydraulic retention time

Note that these equations predict some unexpected results. Thestrength of the untreated waste (So) has no effect on the strength ofthe treated waste (Se). Neither does the size of the reactor (HRT).Rather, a parameter referred to as the biomass solids retention time(BSRT) is the key parameter determining the system performance.This is illustrated in Fig. 22-36. As the BSRT increases, the concen-tration of untreated waste in the effluent decreases irrespective of thereactor size or the waste strength. However, the reactor size and wastestrength have a significant effect on the level of biomass (X) that ismaintained in the system at steady state. Since the development of anexcess level of biomass in the system can lead to system upset, it isimportant to take cognizance of the waste strength and the reactorsize. But treatment performance with respect to removal of the wastecomponents is again a function only of BSRT and the value of the

(BSRT)(Y)(So − Se)��HRT[1 + (b)BSRT]

Ks[1 + BSRT(b)]��BSRT(YKm − b) − 1

dS�dt

dX�dt

kmSX�Ks � S

dS�dt

pseudo constants referred to above. The BSRT also has an effect onthe level of biomass in the system and the quantity of excess biomassproduced (Fig. 22-37). The latter will determine the quantity of wastesludge which must be dealt with as well as the N and P requirement.The N and P in the biomass removed from the system each day mustbe replaced. From the formula given previously for biomass, N is 12percent and P is 2.3 percent by weight in biomass grown under idealconditions (see Fig. 22-37). Also, note that m, the minimum BSRT, isthe minimum time required for the microorganisms to double inmass. Below this minimum, washout occurs and substrate removalapproaches zero.

Although identical results are not obtained for other reactor config-urations, the design equations yield similar patterns. The dominantparameters in determining system performance are again the BSRTand the pseudo constants. The latter are not under the control of thedesign engineer as they are functions of the waste and the microor-ganisms that developed in the system. The BSRT is the major designparameter under the control of the design engineer. This parameterhas been defined as the ratio of the biomass in the reactor to the bio-mass produced from the waste each day. At steady state, the level ofbiomass in the system is constant; thus, the biomass produced mustequal the biomass wasted. The minimum BSRT that can be utilized isthat which will produce the degree of treatment required. Generally,this minimum value is less than the range of BSRT used in design andoperation. This provides not only a safety factor, but, in addition, it isnecessary in order to foster the growth of certain favorable groups ofmicroorganisms in the system. Generally, BSRT values in the range of3–15 days are utilized in most systems, although BSRT values ofless than 1 day for high rate systems are usually adequate to ensuregreater than 95 percent destruction of waste components in all butanaerobic systems. For the latter, a minimum BSRT of 8 days isneeded for 95 percent destruction. BSRT is controlled by the con-centration of biomass (X) in the system and the quantity wastedeach day; thus, the treatment plant operator can alter BSRT byaltering the rate of biomass wasting.

Reactor Concepts A large number of reactor concepts seem tobe used in biologically based treatment systems. However, this diversity

FIG. 22-36 Effect of BSRT on biological treatment process performance. m = minimum BSRT.

FIG. 22-37 Biomass production.

is more apparent than real. In reality, there are only two major reactortypes that are used. One is referred to as a suspended growth reactor,the other is referred to as a fixed film reactor. In the former, the wasteand the microorganisms move through the reactor, with the microor-ganisms constantly suspended in the flow. After exiting the reactor,the suspension flows through a separator, which separates the organ-isms from the liquid. Some of the organisms are wasted as sludge,while the remainder are returned to the reactor. The supernatant isdischarged either to the environment or to other treatment units(Fig. 22-38). The functioning of the separator is very important, aspoor performance of the separator will result in high solids in theeffluent and reduction of organisms in the recycle and eventually alsoin the reactor. As indicated above, the level of the BSRT used indesign of suspended growth systems is set to produce a biomass of theproper level in the system; i.e., a level at which waste degradation israpid but not so high that excess loading on the separator will occur.BSRT also influences the ability of biomass to self flocculate and thusbe removed in the separator (usually a clarifier).

In the fixed-film reactor, the organisms grow on an inert surfacethat is maintained in the reactor. The inert surface can be granularmaterial, proprietary plastic packing, rotating discs, wood slats, mass-transfer packing, or even a sponge-type material. The reactor can beflooded or have a mixed gas-liquid space (Fig. 22-39). The biomasslevel on the packing is controlled by hydraulic scour produced as thewaste liquid flows through the reactor. There is no need of a separatorto ensure that the biomass level in the reactor is maintained. The spe-cific surface area of the packing is the design parameter used toensure an adequate level of biomass. However, a separator is usuallysupplied to capture biomass washed from the packing surface by theflow of the waste, thus providing a clarified effluent. As with the sus-pended growth system, if this biomass escapes the system, it will result

in a return to the environment of organic laden material, thus negat-ing the effectiveness of the waste treatment. As indicated above, bio-mass level in a fixed film reactor is maintained by a balance betweenthe rate of growth on the packing (which is a function of the strengthof the waste, the yield coefficient and the BSRT), and the rate ofhydraulic flushing by the waste flow. Recycle of treated wastewater isused to control the degree of hydraulic flushing. Thus, typical designparameters for fixed film reactors include both an organic loading anda hydraulic loading. Details on the typical levels for these will be givenin a later section.

The reactor concepts described above can be utilized with any ofthe electron acceptor systems previously discussed, although somereactor types perform better with specific electron acceptors. Forexample, suspended growth systems are generally superior to fixedfilm systems when molecular oxygen is the electron acceptor becauseit is easier to supply oxygen to suspended growth systems.

On the other hand, fixed-film systems that use nitrate as the elec-tron acceptor can be superior to activated sludge systems since nitro-gen bubbles produced won’t affect sludge settling and oxygendiffusion limitations are not an issue. Different reactor types are bet-ter suited for different strengths and types of wastewater. Weakwastewaters are generally easier to treat with fixed-film systems sincethe appropriate amount of biomass is inherently maintained in thesystem. Very strong wastes are typically better treated using anaero-bic systems to eliminate oxygen limitation and significantly reducewaste sludge production. In addition, the yield coefficient Y is muchlower for anaerobic systems, reducing sludge production and exces-sive biomass accumulation. Different types and combinations of acti-vated and fixed-film reactor types can be utilized to perform tertiarytreatment on wastewaters and to reclaim hazardous waste streamsthat are contaminated with recalcitrant chemicals such as PCBs,halogenated aliphatics, and PAHs. Table 22-45 summarizes some ofthe advantages and disadvantages of various combinations of reactortype, electron acceptor, and waste strength.

Determination of Kinetic and Stoichiometric Pseudo Con-stants As indicated above, these parameters are most importantfor predicting the performance of biologically based treatment sys-tems. It would be ideal if tabulations of these were available for var-ious industrial wastes as a function of pH temperature and nutrientlevels. Unfortunately, little reliable data has been codified. Onlycertain trends have been established, and these are primarily theresult of studies on municipal wastewater. For example, the yieldcoefficient Y has been shown to be much higher for systems that areaerobic (molecular oxygen as the electron acceptor) than for anaer-obic systems (sulfate or carbon dioxide as the electron acceptors).Systems where oxidized nitrogen is the electron acceptor (termedanoxic) exhibit yield values intermediate between aerobic and


Clarifiedeffluent

Mixer

Biomass recycle

Waste

Excessbiomass

FIG. 22-38 Diagram of a suspended growth system.

Inert packing

Flow distributor

Waste

Effluent recycle

Excessbiomass

FIG. 22-39 Diagram of a fixed-film system.

TABLE 22-45 Favorable (F) and Unfavorable (U)Combinations of Electron Acceptor, Waste Strength, and Reactor Type

Suspended growth reactor

Electron acceptor Waste strength Condition

Aerobic Low–modest FAerobic High UAnoxic Low–modest FAnoxic High UAnaerobic Low–modest UAnaerobic High F

Fixed film reactor

Electron acceptor Waste strength Condition

Aerobic Low FAerobic Modest–high UAnoxic Low–modest FAnoxic High UAnaerobic Low–modest FAnaerobic High F


anaerobic systems. The endogenous respiration rate is higher foraerobic and anoxic systems than anaerobic systems. However, notrends have been established for values of the maximum specificgrowth rate or the half maximal velocity concentration. Thus, thevalues applicable to a specific waste must be determined from lab-oratory studies.

The laboratory studies utilized small-scale (1–5-L) reactors. Theseare satisfactory because the reaction rates observed are independentof reactor size. Several reactors are operated in parallel on the waste,each at a different BSRT. When steady state is reached after severalweeks, data on the biomass level (X) in the system and the untreatedwaste level in the effluent (usually in terms of BOD or COD) are col-lected. These data can be plotted for equation forms that will yield lin-ear plots on rectangular coordinates. From the intercepts and theslope of the lines, it is possible to determine values of the four pseudoconstants. Table 22-46 presents some available data from the litera-ture on these pseudo constants. Figure 22-40 illustrates the procedurefor their determination from the laboratory studies discussed previ-ously.

Activated Sludge This treatment process is the most widelyused aerobic suspended growth reactor system. It will consistentlyproduce a high-quality effluent (BOD5 and SS of 20–30 mg/L). Oper-ational costs are higher than for other secondary treatment processesprimarily because of the need to supply molecular oxygen usingenergy-intensive mechanical aerator- or sparger-type equipment.Removal of soluble organics, colloidal, particulates, and inorganics areachieved in this system through a combination of biological metabo-lism, adsorption, and entrapment in the biological floc. Indeed, manypollutants that are not biologically degradable are removed duringactivated sludge treatment by adsorption or entrapment by the floc.For example, most heavy metals form hydroxide or carbonate precip-itates under the pH conditions maintained in activated sludge, andmost organics are easily adsorbed to the surface of the biological floc.A qualitative guide to the latter is provided by the octanol-water par-tition coefficient of a compound.

All activated sludge systems include a suspended growth reactor inwhich the wastewater, recycled sludge, and molecular oxygen aremixed. The latter must be dissolved in the water; thus the need for anenergy-intensive pure oxygen or air supply system. Usually, air is thesource of the molecular oxygen rather than pure oxygen. Energy formixing of the reactor contents is supplied by the aeration equipment.All systems include a separator and pump station for sludge recycleand sludge wasting. The separator is usually a sedimentation tank thatis designed to function as both a clarifier and a thickener. Many mod-ifications of the activated sludge process have been developed overthe years and are described below. Most of these involve differencesin the way the reactor is compartmentalized with respect to introduc-tion of waste, recycle, and/or oxygen supply.

Modifications The modifications of activated sludge systemsoffer considerable choice in processes. Some of the most popular mod-ifications of the activated sludge process are illustrated in Fig. 22-41.Conventional activated sludge uses a long narrow reactor with airsupplied along the length of the reactor. The recycle sludge andwaste are introduced at the head end of the reactor producing a zoneof high waste to biomass concentration and high oxygen demand.

This modification is used for relatively dilute wastes such as munici-pal wastewater. Step aeration systems distribute the waste along thelength of the aerator, thus reducing the oxygen demand at the headend of the reactor and spreading the oxygen demand more uniformlyover the whole reactor. In the complete mix system, the waste andsludge recycle are uniformly distributed over the whole reactor,resulting in the waste load and oxygen demand being uniform in theentire reactor. Complete-mixing activated sludge is the most popularsystem for industrial wastes because of its ability to absorb shockloads better than other modifications. Contact stabilization is a mod-ification of activated sludge that is best suited to wastewaters havinghigh suspended solids and low soluble organics. Contact stabilizationemploys a short-term mixing tank to adsorb the suspended solids andmetabolize the soluble organics, a sedimentation tank for solids sep-aration, and a reaeration tank for stabilization of the suspendedorganics. Extended-aeration systems are actually long-term-aeration,completely mixed activated-sludge systems. They employ 24- to 48-haeration periods and high mixed-liquor suspended solids to providecomplete stabilization of the organics and aerobic digestion of theactivated sludge in the same aeration tank. The oxidation ditch is apopular form of the extended-aeration system employing mechanicalaeration. Pure-oxygen systems are designed to treat strong industrial

TABLE 22-46 Typical of Values for Pseudo Constants

kmax, Y, Ks, b,

Biomass type SubstrateRemarks

Mixed culture Sewage (COD) 5–10 0.5 50 0.05 Aerobic 20°CMixed culture Glucose (COD) 7.5 0.6 10 0.07–.1 Aerobic 20°CMixed culture Skim milk (COD) 5 — 100 0.05 Aerobic 20°CMixed culture Soybean waste (COD) 12 — 355 0.144 Aerobic 20°CMethane bacteria Acetic acid (COD) 8.7 .04 165 0.035 35°CAnaerobic mixed Propanoic acid (COD) 7.7 .04 60 0.035 35°CAnaerobic mixed Sewage sludge (COD) 6.7 .04 1,800 0.03 35°CAnoxic NO3 as N 0.375 0.8 0.1 0.04 Methanol feedAerobic NH4

+ as N 5 0.2 1.4 .05 20°C

1�day

mg substrate��

litermg biomass��mg substrate

mg substrate��mg biomass⋅day

FIG. 22-40 Determination of pseudo-kinetic constants.

wastes in a series of completely mixed units having relatively shortcontact periods. One of the latest modifications of activated sludgeemploys powdered activated carbon to adsorb complex organics andassist in solids separation. Another modification employs a redwood-medium trickling filter ahead of a short-term aeration tank withmixed liquor recycled over the redwood-medium tower to provideheavy microbial growth on the redwood as well as in the aerationtank.

As indicated previously, success with the activated sludge processrequires that the biomass have good self-flocculating properties. Sig-nificant research effort has been expended to determine the condi-tions that favor the development of good settling biomass cultures.These have indicated that nutritional deficiency, levels of dissolvedoxygen between 0 to 0.5 mg/L, and pH values below 6.0 will favorthe predomination of filamentous biomass. Filamentous organismssettle and compact poorly and thus are difficult to separate from liq-uid. By avoiding the above conditions, and with the application ofselector technology, the predomination of filaments in the biomasscan be eliminated. A selector is often a short contact (15–30 min)reactor set ahead of the main activated sludge reactor. All of therecycle sludge and all of the waste are routed to the selector. In theselector, either a high rate of aeration (aerobic selector) is used tokeep the dissolved oxygen above 2 mg/L, or no aeration occurs(anaerobic selector) so that the dissolved oxygen is zero. Because fil-amentous organisms are microaerophilic, they cannot predominatewhen the dissolved oxygen level is zero or high. The anaerobic selector

not only selects in favor of nonfilamentous biomass but also fostersluxury uptake of phosphorous and is used in systems where phos-phorous removal is desired.

Aeration Systems These systems control the design of aerationtanks. Aeration equipment has two major functions: mixing and oxy-gen transfer. Diffused-aeration equipment employs either a fixed-speed positive-displacement blower or a high-speed turbine blowerfor readily adjustable air volumes. Air diffusers can be located alongone side of the aeration tank or spread over the entire bottom of thetank. They can be either fine-bubble or coarse-bubble diffusers. Fine-bubble diffusers are more efficient in oxygen transfer but requiremore extensive air-cleaning equipment to prevent them from cloggingas a result of dirty air. Mechanical-surface-aeration equipment is moreefficient than diffused-aeration equipment but is not as flexible. Eco-nomics has dictated the use of large-power aerators, but tank configu-ration has tended to favor the use of greater numbers of lower-poweraerators. Oxidation ditches use horizontal rotor-type aerators. Mixingis a critical problem with mechanical-surface aerators since they are apoint-source pump of limited capacity. Experience has indicated thatbearings are a serious problem with mechanical-aeration equipment.Wave action generated within the aeration tank tends to produce lat-eral stresses on the bearings and has resulted in failures and increasedmaintenance costs. Slow-speed mechanical-surface-aeration unitspresent fewer problems than the high-speed mechanical-surface-aeration units. Deep tanks, greater than 3.0 m (10 ft), require drafttubes to ensure proper hydraulic flow through the aeration tank.


FIG. 22-41 Schematic diagrams of various modifications of the activated-sludge process. (a) Conventional activated sludge. (b) Step aeration. (c) Contact stabilization. (d) Complete mixing. (e) Pure oxygen. (f) Activated biofiltration (ABF). (g) Oxidation ditch.

( a ) ( d )

( b )( e )

( c ) ( f )

( g )


Short-circuiting is one of the major problems associated with mechan-ical aeration equipment. Combined mechanical- and diffused-aerationsystems have enjoyed some popularity for industrial-waste systemsthat treat variable organic loads. The mechanical mixers provide thefluid mixing with the diffused aeration varied for different oxygen-transfer rates.

Diffused-aeration systems transfer from 20 to 40 mg/(L O2�h).Combined mechanical- and diffused-aeration systems can transferup to 65 mg/(L O2�h), while mechanical-surface aerators can provideup to 90 mg/(L O2�h). Pure-oxygen systems can provide the highestoxygen-transfer rate, up to 150 mg/(L O2�h). Aeration equipmentmust provide sufficient oxygen to meet the peak oxygen demand;otherwise, the system will fail to provide proper treatment. For thisreason, the peak oxygen demand and the rate of transfer for thedesired equipment determine the size of the aeration tank in terms ofretention time. Economics dictates a balance between the size of theaeration tank and the size of the aeration equipment. As the cost ofpower increases, economics will favor constructing a larger aerationtank and smaller aerators. It is equally important to examine thehydraulic flow pattern around each aerator to ensure maximum effi-ciency of oxygen transfer. Improper spacing of aeration equipmentcan waste energy.

There is no standard aeration-tank shape or size. Aeration tankscan be round, square, or rectangular. Shallow aeration tanks aremore difficult to mix than deeper tanks. Yet aeration-tank depthshave ranged from 0.6 m (2 ft) to 18 m (60 ft). The oxidation-ditchsystems tend to be shallow, while some high-rate diffused-aerationsystems have used very deep tanks to provide more efficient oxygentransfer.

Regardless of the aeration equipment employed, oxygen-transferrates must provide from 0.6 to 1.4 kg of oxygen/kg BOD5 (0.6 to 1.4 lboxygen/lb BOD5) stabilized in the aeration tank for carbonaceous-oxy-gen demand. Nitrogen oxidation can increase oxygen demand at therate of 4.3 kg (4.3 lb) of oxygen/kg (lb) of ammonia nitrogen oxidized.At low oxygen-transfer rates more excess activated sludge must beremoved from the system than at high oxygen-transfer rates. Hereagain the economics of sludge handling must be balanced against thecost of oxygen transfer. The quantity of waste activated sludge willdepend upon wastewater characteristics. The inert suspended solidsentering the treatment system must be removed with the excess acti-vated sludge. The soluble organics are stabilized by converting a por-tion of the organics into suspended solids, producing from 0.3 to 0.8 kg(0.3 to 0.8 lb) of volatile suspended solids/kg (lb) of BOD5 stabilized.Biodegradable suspended solids in the wastewaters will result indestruction of the original suspended solids and their conversion to anew form. Depending upon the chemical characteristics of thebiodegradable suspended solids, the conversion factor will range from0.7 to 1.2 kg (0.7 to 1.2 lb) of microbial solids produced/kg (lb) of sus-pended solids destroyed. If the suspended solids produced by metab-olism are not wasted from the system, they will eventually bedischarged in the effluent. While considerable efforts have beendirected toward developing activated-sludge systems which totallyconsume the excess solids, no such system has proved to be practical.The concept of total oxidation of excess sludge is fundamentallyunsound and should be recognized as such.

A definitive determination of the waste sludge production and theoxygen requirement can be obtained using the pseudo constantsreferred to previously. The ultimate BOD in the waste will beaccounted for by the sum of the oxidation and sludge synthesis [Eq.(22-24)].

Thus:

Waste BODu = oxygen required + BODu of sludge produced (22-24)

where: BODU of sludge = (Ynet)(1.42)(Waste BODU)

Ynet =

1.42 = Factor converting biomass to oxygen units; i.e.,BODu ≈ COD

Y��1 + b(BSRT)

Sedimentation Tanks These tanks are an integral part of anyactivated-sludge system. It is essential to separate the suspendedsolids from the treated liquid if a high-quality effluent is to be pro-duced. Circular sedimentation tanks with various types ofhydraulic sludge collectors have become the standard secondarysedimentation system. Square tanks have been used with common-wall construction for compact design with multiple tanks. Mostsecondary sedimentation tanks use center-feed inlets and periph-eral-weir outlets. Recently, efforts have been made to employperipheral inlets with submerged-orifice flow controllers andeither center-weir outlets or peripheral-weir outlets adjacent tothe peripheral-inlet channel.

Aside from flow control, basic design considerations have centeredon surface overflow rates, retention time, and weir overflow rate. Sur-face overflow rates have been slowly reduced from 33 m3/(m2⋅day)[800 gal/(ft2⋅day)] to 24 m3/(m2⋅day) to 16 m3/(m2⋅day) [600gal/(ft2⋅day) to 400 gal/(ft2⋅day)] and even to 12 m3 (m2⋅day) [300gal/(ft2⋅day)] in some instances, based on average raw-waste flows.Operational results have not demonstrated that lower surface over-flow rates improve effluent quality, making 33 m3/(m2⋅day) [800gal/(ft2⋅day)] the design choice in most systems. Retention time hasbeen found to be an important design factor, averaging 2 h on thebasis of raw-waste flows. Longer retention periods tend to producerising sludge problems, while shorter retention periods do not providefor good solids separation with high-return sludge flow rates. Efflu-ent-weir overflow rates have been limited to 186 m3/(m⋅day) [15,000gal/(ft⋅day)] with a tendency to reduce the rate to 124 m3/(m⋅day)[10,000 gal/(ft⋅day)]. Lower effluent-weir overflow rates are obtainedby using dual-sided effluent weirs cantilevered from the periphery ofthe tank. Unfortunately, proper adjustment of dual-side effluent weirshas created more hydraulic problems than the weir overflow rate.Field data have shown that effluent quality is not really affected byweir overflow rates up to 990 m3/(m⋅day) [80,000 gal/(ft⋅day)] or even1240 m3/(m⋅day) [100,000 gal/(ft⋅day)] in a properly designed sedi-mentation tank. A single peripheral weir, being easy to adjust andkeep clean, appears to be optimal for secondary sedimentation tanksfrom an operational point of view.

Depth tends to be determined from the retention time and the sur-face overflow rate. As surface overflow rates were reduced, the depthof sedimentation tanks was reduced to keep retention time from beingexcessive. It was recognized that depth was a valid design parameterand was more critical in some systems than retention time. As mixed-liquor suspended-solids (MLSS) concentrations increase, the depthshould also be increased. Minimum sedimentation-tank depths forvariable operations should be 3.0 m (10 ft) with depths to 4.5 m (15 ft)if 3000 mg/L MLSS concentrations are to be maintained under variable hydraulic conditions. With MLSS concentrations above 4000 mg/L, the depth of the sedimentation tank should be increasedto 6.0 m (20 ft). The key is to keep a definite freeboard over the set-tled-sludge blanket so that variable hydraulic flows do not lift thesolids over the effluent weir.

Scum baffles around the periphery of the sedimentation tank andradial scum collectors are standard equipment to ensure that risingsolids or other scum materials are removed as quickly as they form.Hydraulic sludge-collection tubes have replaced the center sludgewell, but they have caused a new set of operational problems. Thesetubes were designed to remove the settled sludge at a faster rate thanconventional sludge scrapers. To obtain good hydraulic distribution inthe sludge-collection tubes, it was necessary to increase the rate ofreturn sludge flow and decrease the concentration of return sludge.The higher total inflow to the sedimentation tank created increasedforces that lifted the settled-solids blanket at the wall, causing loss ofexcessive suspended solids and lower effluent quality. Operating datatend to favor conventional secondary sedimentation tanks overhydraulic sludge-collection systems. Return-sludge rates normallyrange from 25 to 50 percent for MLSS concentrations up to 3300mg/L. Most return-sludge pumps are centrifugal pumps with capaci-ties up to 100 percent raw-waste flow.

Gravity settling can concentrate activated sludge to 10,000 mg/L,but hydraulic sludge-collecting tubes tend to operate best below 8,000mg/L. The excess activated sludge can be wasted either from the

return sludge or from a separate waste-sludge hopper near the centerof the tank. The low solids concentrations result in large volumes ofwaste activated sludge in comparison with primary sludge. Unfortu-nately, the physical characteristics of waste activated sludge preventsignificant concentration without the expenditure of considerableenergy. Gravity thickening can produce 2 percent solids, while airflotation can produce 4 percent solids concentration. Centrifuges areable to concentrate activated sludge from 10 to 15 percent solids, butthe capture is limited. Vacuum filters can equal the performance ofcentrifuges if the sludge is chemically conditioned. Filter presses andbelt-press filters can produce cakes with 15 to 25 percent solids. It isvery important that the excess activated sludge formed in the aerationtanks be wasted on a regular basis; otherwise, effluent quality willdeteriorate. Care should be taken to ensure that sludge-thickeningsystems do not control activated-sludge operations. Alternativesludge-handling provisions should be available during maintenanceon sludge-thickening equipment. At no time should final sedimenta-tion tanks be used for the storage of sludge beyond that required bydaily operational variations.

Anaerobic/Anoxic Activated Sludge The activated sludge con-cept (i.e., suspended growth reactor) can be used for anaerobic oranoxic systems in which no oxygen or air is added to the reactor. Ananoxic activated sludge is used for systems in which removal of nitrateis a goal or where nitrate is used as the electron acceptor. These sys-tems (denitrification) will be successful if the nitrate is reduced to lowlevels in the reactor so that nitrate reduction to nitrogen gas does nottake place in the clarifier-thickener. Nitrogen gas production in theclarifier will result in escape of biological solids with the effluent asnitrogen bubbles floating sludge to the clarifier surface. For nitrogenreduction, a source of organics (electron donor) is required. Any inex-pensive carbohydrate can be effectively used for nitrate removal.Many systems utilize methanol as the donor because it is rapidly

metabolized; others use the organics in sewage in order to reducechemical costs. Nitrate reduction is invariably used as part of a systemin which organics and nitrogen removal are goals. In such systems, thenitrogen in the waste is first oxidized to nitrate and then reduced tonitrogen gas. Figure 22-42 presents some flow sheets for such sys-tems. Table 22-47 presents some design parameters for nitrate-reduc-tion-activated sludge systems. Anaerobic activated sludge has beenused for strong industrial wastes high in degradable organic solids. Inthese systems, a high rate of gasification takes place in the sludge sep-arator so that a highly clarified effluent is usually not obtained. A vac-uum degasifier is incorporated in such systems to reduce solids loss.Such systems have been used primarily with meat packing wastes thatare warm, high in BOD and yield a high level of bicarbonate buffer asa result of ammonia release from protein breakdown. All of these con-ditions favor anaerobic processing. The use of this process schemeprovides a high BSRT (15–30 days), usually required for anaerobictreatment, at a low HRT (1–2 days).

Lagoons Lagoons are low-cost, easy-to-operate wastewater-treatment systems capable of producing satisfactory effluents. Nomi-nally, a lagoon is a suspended-growth no-recycle reactor with avariable degree of mixing. In lagoons in which mechanical or diffusedaeration is used, mixing may be sufficient to approach complete mixing


SCHN

Two-sludge systemOrganic

Aerobic Anoxic

CO2H2ONO3

Organic

SNO3 N2

NO3 N2N NO3SCH

Three-sludge system

Aerobic

CO2H2O

S

Aerobic

S

Anoxic

CH

NO3

Internal recycle

Anoxic

CO2H2O N2

SNO3 N2

CHN

Aerobic

CO2H2ONO3

Anoxic

CNH

Aerobic

CO2NO3H2O

FIG. 22-42 Nitrogen removal systems.

TABLE 22-47 Design Parameter for Nitrogen Removal

System BSRT, d HRT, h X, mg/L pH

Carbon removal† 2–5 1–3 1000–2000 6.5–8.0Nitrification† 10–20 0.5–3 1000–2000 7.4–8.6Denitrification† 1–5 0.2–2 1000–2000 6.5–7.0Internal recycle* 10–40 8–20 2000–4000 6.5–8.0

*Total for all reactors†Separate reactors


(i.e., solids maintained in suspension). In other types of lagoons, mostsolids settle and remain on the lagoon bottom, but some mixing isachieved as a result of gas production from bacterial metabolism andwind action. Lagoons are categorized as aerobic, facultative, or anaer-obic on the basis of degree of aeration. Aerobic lagoons primarilydepend on mechanical or diffused air supply. Significant oxygen sup-ply is also realized through natural surface aeration. A facultativelagoon is dependent primarily on natural surface aeration and oxygengenerated by algal cells. These two lagoon types are relatively shallowto encourage surface aeration and provide for maximum algal activity.The third type of lagoon is maintained under anaerobic conditions tofoster methane fermentation. This system is often covered with float-ing polystyrene panels to block surface aeration and help prevent adrop in temperature. Anaerobic lagoons are several meters deeperthan the other two types. Lagoon flow schemes can be complex,employing lagoons in series and recycle from downstream toupstream lagoons. The major effect of recycle is to maintain control ofthe solids. If solids escape the lagoon system, a poor effluent is pro-duced. Periodically controlled solids removal must take place or solidswill escape.

Lagoons are, in effect, inexpensive reactors. They are shallowbasins either cut below grade or formed by dikes built above grade ora combination of a cut and dike. The bottom must be lined with animpermeable barrier and the sides protected from wind erosion.These systems are best used where large areas of inexpensive land areavailable.

Facultative Lagoons These lagoons have been designed to useboth aerobic and anaerobic reactions. Normally, facultative lagoonsconsist of two or more cells in series. The settleable solids tend to set-tle out in the first cell and undergo anaerobic metabolism with theproduction of organic acids and methane gas, which bubbles out tothe atmosphere. Algae at the surface of the lagoon utilize sunlight fortheir energy in converting carbon dioxide, water, and ammonium ionsinto algal protoplasm with the release of oxygen as a waste product.Aerobic bacteria utilize the oxygen released by the algae to stabilizethe soluble and colloidal organics. Thus, the bacteria and algae form asymbiotic relationship as shown in Fig. 22-43. The interesting aspectof facultative lagoons is that the organic matter in the incoming waste-waters is not stabilized but rather is converted to microbial proto-plasm, which has a slower rate of oxygen demand. In fact, in somefacultative lagoons inorganic compounds in the wastewaters are con-verted to organic compounds with a total increase in organics withinthe lagoon system.

Facultative lagoons are designed on the basis of organic load in rela-tionship to the potential sunlight availability. In the northern part ofthe United States facultative lagoons are designed on the basis of2.2 g/(m2�day) [20 lb BOD5/(acre�day)]. In the middle part of theUnited States the organic load can be increased to 3.4 to 4.5 g/(m2�day)[30 to 40 lb BOD5/(acre�day)], while in the southern part the organicload can be increased to 6.7 g/(m2�day) [60 lb BOD5/(acre�day)]. Thedepth of lagoons is normally maintained between 1.0 and 1.7 m (3 and5 ft). A depth less than 1.0 m (3 ft) encourages the growth of aquatic

weeds and permits mosquito breeding. In dry areas the maximumdepth may be increased above 1.7 m (5 ft) depending upon evapora-tion. Most facultative lagoons depend upon natural wind action formixing and should not be placed in screened areas where wind actionis blocked.

Effluent quality from facultative lagoons is related primarily to thesuspended solids created by living and dead microbes. The long reten-tion period in the lagoons allows the microbes to die off, leaving asmall particle that settles slowly. The release of nutrients from thedead microbes permits the algae to survive by recycling the nutrients.Thus, the algae determine the ultimate effluent quality. Use of seriesponds with well-designed transfer structures between ponds permitsmaximum retention of algae within the ponds and the best-qualityeffluent. Normally the soluble BOD5 is under 5 or 10 mg/L with atotal effluent BOD5 under 30 mg/L. The effluent suspended solidswill vary widely during the different seasons of the year, being a maxi-mum of 70 to 100 mg/L in the summer months and a minimum of 10to 20 mg/L in the winter months. If suspended-solids removal isessential, chemical precipitation is the best method available at thepresent time. Slow sand filters and rock filters have been studied forsuspended-solids removal; they work well as long as the effluent sus-pended solids are relatively low, 40 to 70 mg/L.

Aerated Lagoons These lagoons originated from efforts tocontrol overloaded facultative lagoons. Since the lagoons were defi-cient in oxygen, additional oxygen was supplied by either mechani-cal surface aerators or diffused aerators. Mechanical surfaceaerators were quickly accepted as the primary aerators because theycould be quickly added to existing ponds and moved to strategiclocations. Unfortunately, the high-speed, floating surface aerationunits were not efficient, and large numbers were required for existinglagoons. The problem was simply one of poor mixing in a very shallowlagoon.

Eventually, diffused aeration equipment was added to relativelydeep lagoons [3.0 to 6.0 m (10 to 20 ft)]. Mixing became the most sig-nificant parameter for good oxygen transfer in aerated lagoons. Froman economical point of view, it was found that a completely mixedaerated lagoon with 24-h retention provided the best balancebetween mixing and oxygen transfer. As the organic load increased,the fluid-retention time also increased. Short-term aeration permit-ted metabolism of the soluble organics by the bacteria, but time didnot permit metabolism of the suspended solids. The suspended solidswere combined with the microbial solids produced from metabolismand discharged from the aerated lagoon to a solids-separation pond.Data from the short-term aerated lagoon indicated that 50 percentBOD5 stabilization occurred, with conversion of the soluble organicsto microbial cells. The problem was separation and stabilization ofthe microbial cells. Short-term sedimentation ponds permitted sepa-ration of the solids without significant algae growths but requiredcleaning at frequent intervals to keep them from filling with solidsand flowing into the effluent. Long-term lagoons permitted solidsseparation and stabilization but also permitted algae to grow andaffect effluent quality.

Aerated lagoons were simply dispersed microbial reactors whichpermitted conversion of the organic components in the wastewaters tomicrobial solids without stabilization. The residual organics in solutionwere very low, less than 5 mg/L BOD5. By adding oxygen and improv-ing mixing, the microbial metabolism reaction was speeded up, butthe stabilization of the microbial solids has remained a problem to besolved.

Anaerobic Lagoons These lagoons were developed when amajor fraction of the organic contaminants consisted of suspendedsolids that could be removed easily by gravity sedimentation. Theanaerobic lagoons are relatively deep [8.0 to 6.0 m (10 to 20 ft)], with ashort fluid-retention time (3 to 5 days) and a high BOD5 loading rate,up to 3.2 kg/(m3�day) [200 lb/(1000 ft3�day)]. Microbial metabolism inthe settled-solids layer produces methane and carbon dioxide, whichquickly rise to the surface, carrying some of the suspended solids. Ascum layer that retards oxygen transfer and release of obnoxious gasesis quickly produced in anaerobic lagoons. Mixing with a grinder pumpcan provide a better environment for metabolism of the suspendedsolids. The key for anaerobic lagoons is adequate buffer to keep theFIG. 22-43 Schematic diagram of oxidation-pond operations.

pH between 6.5 and 8.0. Protein wastes have proved to be the bestpollutants to be treated by anaerobic lagoons, with the ammoniumions reacting with carbon dioxide and water to form ammonium bicar-bonate as the primary buffer. High-carbohydrate wastes are poor inanaerobic lagoons since they produce organic acids without adequatebuffer, making it difficult to maintain a suitable pH for good microbialgrowth.

Anaerobic lagoons do not produce a high-quality effluent but areable to reduce the BOD load by 80 to 90 percent with a minimum ofeffort. Since anaerobic lagoons work best on strong organic wastes,their effluent must be treated by either aerated lagoons or facultativelagoons. An anaerobic lagoon is simply the first stage in the treatmentof strong organic wastewaters.

Fixed-Film Reactor Systems A major advantage of fixed film sys-tems is that a flocculent-type biomass is not necessary as the biomassremains in the reactor attached to inert packing. Biomass does periodi-cally slough off or break away from the packing, usually in large chunksthat can be easily removed in a clarifier. On the other hand, the time ofcontact between the biomass and the waste is much shorter than in sus-pended growth systems, making it difficult to achieve the same degreeof treatment especially in aerobic systems. Aerobic, anoxic, and anaero-bic fixed film systems are utilized for waste treatment.

Aerobic systems including trickling filters and rotating biologicalcontactors (RBC) are operated in a nonflooded mode to ensure ade-quate oxygen supply. Other aerobic, anoxic, and anaerobic systemsemploy flooded reactors. The most common systems are packed beds(anaerobic trickling filter) and fluidized or expanded bed systems.

Trickling Filters For years trickling filters were the mainstay ofbiological wastewater treatment systems because of their simplicity ofdesign and operation. Trickling filters were displaced as the primarybiological treatment system by activated sludge because of bettereffluent quality. Trickling filters are simply fixed-medium biologicalreactors with the wastewaters being spread over the surface of a solidmedium where the microbes are growing. The microbes remove theorganics from the wastewaters flowing over the fixed medium. Oxygenfrom the air permits aerobic reactions to occur at the surface of themicrobial layer, but anaerobic metabolism occurs at the bottom of themicrobial layer where oxygen does not penetrate.

Originally, the medium in trickling filters was rock, but rock haslargely been replaced by plastic, which provides greater void space perunit of surface area and occupies less volume within the filter. A plas-tic medium permitted trickling filters to be increased from a mediumdepth of 1.8 m (6 ft) to one of 4.2 m (14 ft) and even 6.0 m (20 ft). Thewastewaters are normally applied by a rotary distributor or a fixed-spray nozzle. The spraying or discharging of wastewaters above thetrickling-filter medium permits better distribution over the mediumand oxygen transfer before reaching the medium. The effluent fromthe trickling-filter medium is captured in a clay-tile underdrain systemor in a tank below the plastic medium. It is important that the bottomof the trickling filter be open for air to move quickly through the filterand bring adequate oxygen for the microbial reactions.

If a high-quality effluent is required, trickling filters must be oper-ated at a low hydraulic-loading rate and a low organic-loading rate.Low-rate trickling filters are operated at hydraulic loadings of 2.2 ×10−5 to 4.3 × 10−5 m3/(m2⋅s) [2 million to 4 million gal/(acre⋅day)].High-rate trickling filters are designed for 10.8 × 10−5 to 40.3 ×10−5 m3/(m2⋅s) [10 million to 40 million gal/(acre⋅day)] hydraulic load-ings and organic loadings up to 1.4 kg/(m3⋅day) [90 lb BOD5/(1000ft3⋅day)]. Plastic-medium trickling filters have been designed to oper-ate up to 108 × 10−5 m3/(m2⋅s) [100 million gal/(acre⋅day)] or evenhigher, with organic loadings up to 4.8 kg/(m3⋅day) [300 lb BOD5/(1000 ft3⋅day)]. Low-rate trickling filters will produce better than90 percent BOD5 and suspended-solids reductions, while high-ratetrickling filters will produce from 65 to 75 percent BOD5 reduction.Plastic-medium trickling filters will produce from 59 to 85 percentBOD5 reduction depending upon the organic-loading rate. It is im-portant to recognize that concentrated industrial wastes will requireconsiderable hydraulic recirculation around the trickling filter toobtain the proper hydraulic-loading rate without excessive organicloads. With high recirculation rates the organic load is distributed overthe entire volume of the trickling filter for maximum organic removal.

The short fluid-retention time within the trickling filter is the primaryreason for the low treatment efficiency.

Rotating Biological Contactors (RBCs) The newest form oftrickling filter is the rotating biological contactor with a series of cir-cular plastic disks, 3.0 to 3.6 m (10 to 12 ft) in diameter, immersed toapproximately 40 percent diameter in a shaped contact tank. TheRBC disks rotate at 2 to 5 r/min. As the disks travel through the waste-waters, a small layer adheres to them. As the disks travel into the air,the microbes on the disk surface oxidize the organics. Thus, only asmall amount of energy is required to supply the required oxygen forwastewater treatment. As the microbes build up on the plastic disks,the shearing velocity that is created by the movement of the disksthrough the water causes the excess microbes to be removed from thedisks and discharged to the final sedimentation tank.

Rotating biological contactors have been very popular in treatingindustrial wastes because of their relatively small size and their lowenergy requirements. Unfortunately, there have occurred a number ofproblems which should be recognized prior to using RBCs. Strongindustrial wastes tend to create excessive microbial growths which arenot easily sheared off and which create high oxygen-demand rateswith the production of hydrogen sulfide and other obnoxious odors.The heavy microbial growths have damaged some of the disks andcaused some shaft failures. The disks are currently being covered withplastic shells to prevent nuisance odors from occurring. Air must beforced through the covered RBC systems and be chemically treatedbefore being discharged back into the environment. Recirculation ofwastewater flow around the RBC units can distribute the load over allthe units and reduce the heavy initial microbial growths. RBC unitsalso work best under uniform organic loads, requiring surge tanks formany industrial wastes. The net result has been for the cost of RBCunits to approach that of other treatment units in terms of organicmatter stabilized.

RBCs should be designed on both a hydraulic-loading rate and anorganic-loading rate. Normally, hydraulic-loading rates of up to 0.16m3/(m2�day) [4 gal/(ft2�day)] of surface area are used with organicloading rates up to 44 kg/(m2�day) [9 lb BOD5/(ft2�day)]. Treatmentefficiency is primarily a function of the fluid-retention time and theorganic-loading rate. At low organic-loading rates the RBC units willproduce nitrification in the same way as low-rate trickling filters.

Packed-Bed Fixed-Film Systems These systems were originallytermed anaerobic trickling filters because the first systems were sub-merged columns filled with stones run under anaerobic conditions. Awide variety of packed media is now used ranging in size from granules40 mesh to 7.5-cm (3–in) stones. Many systems use open structureplastic packing similar to that used in aerobic trickling filters.

The systems using granular media packing are used for anoxic deni-trification. They are usually downflow, thus serving the dual functionof filtration and denitrification. Contact times are short (EBCT < 15min), but excellent removal is achieved due to the high level of bio-mass retained in the reactor. Pacing the methanol dose to the varyingfeed nitrate concentration is crucial. Frequent, short-duration back-wash (usually several times per day) is required or the nitrogen bub-bles formed will bind the system, causing poor results. Extendedbackwash every two to three days is required or the system will clog onthe biomass growth. Thus, several units in parallel or a large holdingtank are needed to compensate for the down time during backwash.Backwash does not remove all the biomass; a thin film remains coat-ing the packing. Thus, denitrification begins immediately when theflow is restored.

The systems using the larger packing are used in the treatment ofrelatively strong, low-suspended-solids industrial waste. These sys-tems are closed columns usually run in an upflow mode with a gasspace at the top. These are operated under anaerobic conditions withwaste conversion to methane and carbon dioxide as the goal. Effluentrecycle is often used to help maintain the pH in the inlet zone in thecorrect range 6.5–7.5 for the methane bacteria. Some wastes requirethe addition of alkaline material to prevent a pH drop. Sodium bicar-bonate is often recommended for pH control because it is easier tohandle than lime or sodium hydroxide, and because an overdose ofbicarbonate will only raise the pH modestly. An overdose of lime orsodium hydroxide can easily raise the pH above 8.0. Table 22-48 gives



some performance data with systems treating industrial wastes. HRTsof 1 to 2 days are used, as the buildup of growth on the packingensures a BSRT of 20–50 days. It should be possible to lower the HRTfurther, but in practice this has not been successful because biomassstarts to escape from the system or plugging occurs. Some escape isdue to high gasification rates, and some is due to the fact that anaero-bic sludge attaches less tenaciously to packing than aerobic or anoxicsludge. These systems can handle wastes with moderate solids levels.Periodically, solids must be removed from the reactor to prevent plug-ging of the packing or loss of solids in the effluent.

Biological Fluidized Beds This high-rate process has beenused successfully for aerobic, anoxic, and anaerobic treatment ofmunicipal and industrial wastewaters. Numerous small- and large-scale applications for hazardous waste, contaminated groundwater,nontoxic industrial waste and municipal wastewater have beenreported (Refs. 32 and 33). The basic element of the process is a bedof solid carrier particles, such as sand or granular activated carbon,placed in a reactor through which wastewater is passed upflow withsufficient velocity to impart motion or fluidize the carrier. An activegrowth of biological organisms grow as firmly attached mass sur-rounding each of the carrier particles. As the wastewater contami-nants pass by the biologically covered carrier, they are removed fromthe wastewater through biological and adsorptive mechanisms. Figure22-44 is a schematic of the process.

The influent wastewater enters the reactor through a pipe manifoldand is introduced downflow through nozzles that distribute the flowuniformly at the base of the reactor. Reversing direction at the bot-tom, the flow fluidizes the carrier when the fluid drag overcomes thebuoyant weight of the carrier and its attached biomass layer. Duringstartup (before much biomass has accumulated), the flow velocityrequired to achieve fluidization is higher than after the biomassattaches. Recycle of treated effluent is adjusted to achieve the desireddegree of fluidization. As biomass accumulates, the particles of coatedbiomass will separate to a greater extent at constant flow velocity.Thus, as the system ages and more biomass accumulates, the extent ofbed expansion increases (the volume of voids increases). This phe-nomenon is advantageous because it prevents clogging of the bed withbiomass. Consequently, higher levels of biomass attachment are possi-ble than in other types of fixed film systems. However, eventually, thedegree of bed expansion may become excessive. Reduction of recyclewill reduce expansion but may not be feasible because recycle has sev-eral purposes (i.e., supply of nutrients, alkalinity, and dilution of wastestrength). Control of the expanded bed surface level is automaticallyaccomplished using a sensor that activates a biomass growth controlsystem at a prescribed level and maintains the bed at the properdepth. A pump removes a portion of the attached biomass, separatesthe biomass and inert carrier by abrasion, and pumps the mixture intoa separator. Here the heavy carrier settles back into the fluidized bedand the abraded biomass, which is less dense, is removed from the sys-tem by gravity or a second pump. Other growth control designs arealso used. Effluent is withdrawn from the supernatant layer above thefluidized bed. The reactor is usually not covered unless it is operatingunder anaerobic conditions and methane, odorous gases, or othersafety precautions are mandated.

When aerobic treatment is to be provided to high concentrations oforganics, pure oxygen or hydrogen peroxide may be injected into thewastewater prior to entering the reactor. Liquid oxygen (LOX) orpressure swing absorption (PSA) systems have been used to supplyoxygen. Air may be used at low D.O. demands.

In full-scale applications, this process has been found to operate atsignificantly higher volumetric loading rates for wastewater treatmentthan other processes. The primary reasons for the very high rates ofcontaminant removal is the high biologically active surface area avail-able (approximately 1000 ft2/ft3 of reactor) and the high concentrationof reactor biological solids (8,000–40,000 mg/L) that can be main-tained (Table 22-49). Because of these atypical high values, designsusually indicate a 200–500 percent reduction in reactor volume whencompared to other fixed film and suspended growth treatmentprocesses. In Table 22-50, is a list of full-scale commercial applicationsof the process operated at high wastewater concentrations includingaerobic oxidation of organics, anoxic denitrification and anaerobictreatment systems.

TABLE 22-48 Anaerobic Process Performance on Industrial Wastewater UASB, Submerged Filter (SF), FBR

ReactorProcess Wastewater size, MG COD, g/l OVL, kg/m3d %CODr HRT-d °C

SF Rum slops 3.5 80–105 15 71 7.8 35SF Modified guar 0.27 9.1 7.5 60 1.0 37SF Chemical 1.5 14 11 90 0.7 HSF Milk 0.2 3 7.5 60 0.5 32SF PMFC 10−5 13.7 23 72 0.6 36UASB Potato 0.58 2.5 3 85 0.7 35UASB Sugar beet 0.21 3 16 88 — —UASB Brewery 1.16 1.6–2.2S 4.4 83 0.4 30UASB Brewery 1.16 2.0–2.4S 8.7 78 0.2 30UASB PMFC 10−5 13.7 4–5 87 2.9 36FBR PMFC 10−5 13.7 35–48 88 0.4 36FBR Soft drink 0.04 3.0 6–7 75 0.5 35FBR Chemical 0.04 35 14 95 2.5 35

OVL = organic volumetric load (COD); S = settled effluent; H = heated; PMFC = paper mill foul condensate (5,6).NOTE: MG = 3785 m3.

EffluentBiomass

growthcontrol

Recycle

Influent

Gas

Pump

Fluidized bedFluidized bedFluidized bed

O2

FIG. 22-44 Schematic of fluidized bed process.

Of special note is the enhancement to the process when granularactivated carbon (GAC) is used as the carrier. Because GAC hasadsorptive properties, organic compounds present in potable watersand wastewater at low concentrations, often less than ten mg/L, areremoved by adsorption and subsequently consumed by the biologicalorganisms that grow in the fluidized bed. The BTEX compounds,methylene chloride, chlorobenzene, plastics industry toxic effluent,and many others are removed in this manner. BTEX contamination ofgroundwater from leaking gasoline storage tanks is a major problem,and sixteen full-scale fluidized bed process applications have beenmade. Contaminated groundwater is pumped to the ground surfacefor treatment using the fluidized bed in the aerobic mode. Often thelevel of BTEX is 1–10 mg/L and about 99 percent is removed in lessthan ten minutes detention time. Installations in operation range insize from 30 to 3000 gpm. The smaller installations are often skid-mounted and may be moved from location to location at a given site.A major advantage of this process over stripping towers and vacuumsystems for treating volatile organics (VOCs) is the elimination ofeffluent gas treatment.

Pilot-plant studies and full-scale plants have shown successfultreatment of wastewaters with 5000 to 50,000 mg/L COD fromdairy, brewery, other food preparation wastes; paper pulp wastes;deicing fluids; and other hazardous and nonhazardous materials.Design criteria for biological fluidized-bed systems are included inTable 22-51.

A third type of reactor system is the upflow anaerobic sludge blan-ket (UASB) reactor system. The UASB is a continuous-flow systemthat maintains a dense flocculated biomass that is granular. The waste-water passes through this dense sludge blanket to achieve desiredtreatment efficiency. The UASB, anaerobic filter, and fluidized-bedsystems have all been applied successfully to treat a variety of indus-trial waste streams. Table 22-44 summarizes some of the applicationsof these treatment technologies.

Design criteria for satisfactory biological fluidized bed treatmentsystems include the major parameters given in Table 22-51.

PHYSICAL-CHEMICAL TREATMENT

Processes and/or unit operations that fall under this classificationinclude adsorption, ion exchange, stripping, chemical oxidation, andmembrane separations. All of these are more expensive than biologi-cal treatment but are used for removal of pollutants that are not easilyremoved by biomass. Often these are utilized in series with biologicaltreatment; but sometimes they are used as stand-alone processes.

Adsorption This is the most widely used of the physical-chemicaltreatment processes. It is used primarily for the removal of solubleorganics with activated carbon serving as the adsorbent. Most liquid-phase-activated carbon adsorption reactions follow a FreundlichIsotherm [Eq. (22-25)].

y kc1�m (22-25)

where: y = adsorbent capacity, mass pollutant/mass carbonc = concentration of pollutant in waste, mass/volume

k and n = empirical constants

EPA has compiled significant data on values of k and n for environ-mentally significant pollutants with typical activated carbons. Assum-ing equilibrium is reached, the isotherm provides the dose of carbonrequired for treatment. In a concurrent contacting process, the capac-ity is set by the required effluent concentration. In a countercurrentprocess, the capacity of the carbon is set by the untreated waste pollu-tant concentration. Thus countercurrent contacting is preferred.

Activated carbon is available in powdered form (200–400 mesh)and granular form (10–40 mesh). The latter is more expensive but iseasier to regenerate and easier to utilize in a countercurrent contactor.Powdered carbon is applied in well-mixed slurry-type contactors fordetention times of several hours after which separation from the flowoccurs by sedimentation. Often coagulation, flocculation, and filtra-tion are required in addition to sedimentation. As it is difficult toregenerate, powdered carbon is usually discarded after use. Granularcarbon is used in column contactors with EBCT of 30 minutes to 1hour. Often several contactors are used in series, providing for fullcountercurrent contact. A single contactor will provide only partialcountercurrent contact. When a contactor is exhausted, the carbon isregenerated either by a thermal method or by passing a solventthrough the contactor. For waste-treatment applications where a largenumber of pollutants must be removed but the quantity of each pol-lutant is small, thermal regeneration is favored. In situations where asingle pollutant in large quantity is removed by the carbon, solventextraction regeneration can be used, especially where the pollutantcan be recovered from the solvent and reused. Thermal regenerationis a complex operation. It requires removal of the carbon from thecontactor, drainage of free water, transport to a furnace, heating undercontrolled conditions of temperature, oxygen, time, water vapor par-tial pressure, quenching, transport back to the reactor, and reloadingof the column. Five to ten percent of the carbon is lost in this regen-eration process due to burning and attrition during each regenerationcycle. Multiple hearth, rotary kiln, and fluidized bed furnaces have allbeen successfully used for carbon regeneration.

Pretreatment prior to carbon adsorption is usually for removal ofsuspended solids. Often this process is used as tertiary treatment after


TABLE 22-49 Process Comparisons

MLVSS, Surface area,Biological process mg/L ft2/ft3

Activated sludge 1500–3000 —Pure oxygen activated sludge 2000–5000 —Suspended growth nitrification 1000–2000 —Suspended growth denitrification 1500–3000 —Fluidized bed-CBOD removal 12,000–20,000 800–1200Fluidized bed-nitrification 8,000–12,000 800–1200Fluidized bed-denitrification 25,000–40,000 800–1200Trickling filter-CBOD removal — 12–50RBC-CBOD removal — 30–40

TABLE 22-50 Full-Scale Commercial Applications of Fluidized Bed Process

ReactorApplication Type volume, m3

CBOD—paint—General Motors Aerobic 108C,NBOD—sanitary and automotive—GM Aerobic 165Chemical—Grindsted Products Denmark Aerobic 730Nitrification—fish hatchery—Idaho Aerobic 820BTEX, groundwater—Ohio Aerobic 250Chemical, Toxicity reduction—Texas Aerobic 225Denitrification, Nuclear Fuel, DOE, Fornald, OH Anoxic 53CBOD, Denitrification—municipal, Nevada Anoxic 1450Petrochemical—Reliance Ind. India Anaerobic 850Soft drink, Delaware Anaerobic 166Brewery—El Aguila, Spain Anaerobic 1570

TABLE 22-51 Typical Design Parameters for Fluidized Beds

VolatileInfluent Volumetric Hydraulic solids

concentration, load, detention (biosolids),Waste Mode mg/L lb/ft3⋅d time, hr g/L

Organic COD Aerobic <2000 0.1–0.6 0.5–2.5 12–20Organic COD Aerobic <10 0.02–0.1 0.1–0.5 4–8NH3-N Aerobic <25 0.05–0.3 0.1–0.5 7–14NO3

−-N Anoxic <5,000 0.4–2 0.1–2.4 20–40Organic COD Anaerobic >4000 0.5–4 2–24 20–40

NOTE: lb/ft3⋅d = 16 kg/m3⋅d.


primary and biological treatment. In either situation, the carboncolumns must be designed to provide for backwash. Some solids willescape pretreatment, and biological growth will occur on the carbon,even with extensive pretreatment. Originally carbon treatment wasviewed only as applicable for removal of toxic organics or those thatare difficult to degrade biologically. Present practice applies carbonadsorption as a procedure for removal of all types of organics. It isrealized that some biological activity will occur in virtually any acti-vated carbon unit, so the design must be adjusted accordingly.

Ion Exchange This process has been employed for many yearsfor treatment of industrial water supplies but not for wastes. How-ever, some new ion-exchange materials have recently been developedthat can be used for removal of specific pollutants. These new resinsare primarily useful for selective removal of heavy metals, eventhough the target metals are present at low concentration in a waste-water containing many other inorganics. An ion-exchange process isusually operated with the waste being run downflow through a seriesof columns containing the appropriate ion-exchange resins. EBCTcontact times of 30 min to 1 hour are used. Pretreatment for sus-pended solids and organics removal is practiced as well as pHadjustment.

The capacity of an ion-exchange resin is a function of the type andconcentration of regenerant. Because ion-exchange resins are soselective for the target compound, a significant excess of the regener-ant must be used. Up to a point, the more regenerant, the greater thecapacity of the resin. Unfortunately, this results in waste of most of theregenerant. In fact, the bulk of the operational cost for this process isfor regenerant purchase and its disposal; thus, regeneration must beoptimized. Regenerants used (selection depends on the ion exchangeresin) include sodium chloride, sodium carbonate, sulfuric acid,sodium hydroxide, and ammonia. Table 22-52 gives information onsome of the new highly selective resins. These resins may provide theonly practical method for reduction of heavy metals to the very lowlevels required by recent EPA regulations.

Stripping Air stripping is applied for the removal of volatile sub-stances from water. Henry’s law is the key relationship for use indesign of stripping systems. The minimum gas-to-liquid ratio requiredfor stripping is given by:

=

for a concurrent process and

=

for a countercurrent process where:G = airflow rate, mass/timeL = waste flow rate, volume/timeX = concentration of pollutant in waste, mass/volumeH = Henry’s constant for the pollutant in water, volume/mass

Higher ratios of gas to liquid flow are required than those computedabove because mass-transfer limitations must be overcome. Stripping

Xin − Xout�

(H)Xin

G�L

Sin − Xout�(H)Xout

G�L

can occur by sparging air into a tank containing the waste. Indeed,stripping of organics from activated sludge tanks is of concern becauseof the possibility that the public will be exposed to airborne pollutantsincluding odors. A much more efficient stripping procedure is to usecounterflow or crossflow contact towers. Procedures for design ofthese and mass-transfer characteristics of various packings are avail-able elsewhere in this handbook.

Stripping has been successfully and economically employed forremoval of halogenated organics from water and wastes with disper-sion of the effluent gas to the atmosphere. However, recent EPA reg-ulations have curtailed this practice. Now removal of these toxicorganics from the gas stream is also required. Systems employing acti-vated carbon (prepared for use with gas streams) are employed as wellas systems to oxidize the organics in the gas stream. However, the costof cleaning up the gas stream often exceeds the cost of stripping theseorganics from the water.

Chemical Oxidation This process has not been widely utilizedbecause of its high cost. Only where the concentration of the targetcompound is very low will the quantity of oxidant required be lowenough to justify treatment by chemical oxidation. The efficiency of thisprocess is also low, as many side reactions can occur that will consumethe oxidant. In addition, complete oxidation of organics to carbon diox-ide and water often will not occur unless a significant overdose is used.However, renewed interest has recently occurred for two reasons.

1. It has been found that partial oxidation is satisfactory as a pre-treatment to biological or carbon adsorption treatment. Partial oxida-tion often seems to make recalcitrant organics easier to degradebiologically and easier to adsorb.

2. A combination of ozone oxidation with simultaneous exposureto ultraviolet light seems to produce a self-renewing chain reactionthat can significantly reduce the dose of ozone needed to accomplishoxidation.

Oxidants commonly used include ozone, permanganate, chlorine,chlorine dioxide, and ferrate, often in combination with catalysts.Standard-type mixed reactors are used with contact times of severalminutes to an hour.

Advanced Oxidation Processes Advanced oxidation processes(AOPs) utilize the extremely strong oxidizing power of hydroxyl radi-cals to oxidize recalcitrant organic compounds to the mineral endproducts of CO2, H2O, HCL, etc. The hydroxyl radicals are pro-duced on-site using a combination of traditional oxidation processessuch as ozone/hydrogen peroxide, ultraviolet radiation/ozone, ultravi-olet radiation/hydrogen peroxide, Fenton’s reagent (ferrous iron andhydrogen peroxide) with ultraviolet radiation, and titanium dioxide/ultraviolet radiation (catalytic oxidation). The hydroxyl radical is apowerful nonselective oxidant, which can effectively and rapidly oxi-dize most organic compounds. As shown in Table 22-53, the hydroxylradical has greater oxidizing power than do traditional oxidizing reagents.AOPs can be used to remove overall organic content (COD) or todestroy specific compounds. Table 22-53 shows the relative oxidationpower of a select number of oxidizing species compared to chlorine.AOPs are most economical for treating industrial and hazardous wastestreams that have a low level of recalcitrant contamination (<50 ppm).AOPs are emerging as an efficient and cost-effective treatment tech-nology for specific industrial wastewaters and are likely to have broaderapplications as the various technologies are proved in the field.

TABLE 22-52 Selective Ion-Exchange Resins

Application Exchanger type Composition Regenerant

Softening Cation Polystyrene matrix NaClSulfonic acid functional groups

Heavy metals Cation Polystyrene matrix Mineral acidsChelating functional groups

Chromate Anion Polystyrene matrix Sodium carbonateTertiary or quaternary ammonium orfunctional groups alkaline NaCl

Nitrate Anion Polystyrene matrix NaClTributyl ammonium functional group

Membrane Processes These processes use a selectively perme-able membrane to separate pollutants from water. Most of the mem-branes are formulated from complex organics that polymerize duringmembrane preparation. This allows the membrane to be tailored todiscriminate by molecular size or by degree of hydrogen bondingpotential. Ultrafiltration membranes discriminate by molecular size orweight, while reverse osmosis membranes discriminate by hydrogen-bonding characteristics. The permeability of these membranes is low:from 0.38–3.8 m/day (10–100 gal/d/ft2). The apparatus in which theyare used must provide a high surface area per unit volume.

Membrane Bioreactors (MBRs) Membrane bioreactors are atechnology that combines biological degradation of waste productswith membrane filtration (Fig. 22-45). Typically, MBRs are operatedas activated sludge systems with high biomass concentrations (10,000to 15,000 mg/L MLSS) and long solids retention times (30 to 60 days).The membranes act as a solid-liquid separation to replace secondaryclarifiers and granular media polishing filters. With the developmentof more economical, durable, and efficient membrane components,MBR systems have become feasible options for aerobic treatment ofmunicipal wastewaters, and potentially for anaerobic treatment ofindustrial (i.e. low- to medium-strength) wastewaters. Two differentprocess configurations for MBRs (sidestream or submerged modules)are used within wastewater treatment. The sidestream process isoperated with high velocities and high transmembrane pressures (upto 5 bar). This results in high energy consumption and excessive shearforces within the reactor. The process with submerged modules wasespecially designed for biological wastewater treatment. The modulesare submerged in the aerobic activated sludge zone where flow acrossthe membrane surface is attained by aeration and mixing, resulting ina low flux rate with low transmembrane and vacuum pressures. Sub-merged membranes typically last longer (8+ years) and require lessfrequent cleaning and maintenance. With recent advances in mem-brane materials and process technology, MBRs have become morereliable, durable, and affordable. MBRs can be utilized for any level oftreatment, but are most cost-effective when high-quality effluent isrequired.

The submerged MBR system is a small-footprint, single-process unitthat can achieve a high-quality standard with low solids production. Themembrane systems typically utilize either micro- or ultramembranesconfigured as hollow fibers, flat sheets, or tubes depending upon themanufacturer. Experience over the past decade has proved MBRs tobe reliable and cost-effective for high-quality effluent applications, andrelatively easy to maintain and operate. The key parameters for MBR

design and operation are flux rate, transmembrane pressure, foulingrate, and membrane cleaning schedule. MBRs have many possibleapplications in industrial and advanced municipal wastewater treat-ment and are becoming the preferred technology for wastewaterreuse applications.

Industrial Reuse Many industries that use large volumes offreshwater are turning toward industrial reuse to minimize costs asso-ciated with attaining freshwater and disposing of wastewater. Theneed to minimize water consumption is a function of economics,water shortages caused by drought and overdevelopment, increasinglystringent regulations, and environmental awareness. Industrial reusewater is wastewater that is produced on-site that does not containsewage and has been adequately treated for use in some part of theindustrial operation. Reuse has become more economically feasible asa result of new treatment technologies (MBRs, AOPs, etc.) and risingcosts of freshwater and wastewater disposal.

There are many industrial sources and uses of industrial reusewater. Common industrial processes that require large quantities ofwater, such as evaporative cooling towers and power stations, can besupplied using reclaimed wastewater. Other industrial applications forreuse water include boilers; stack scrubbing; washing of vehicles,buildings, and mechanical parts; and process water. The key to effec-tive industrial reuse is to match the proper treatment processes(chemical, physical, biological) to achieve the desired quality of reusewater. Zero discharge industrial systems have recently been imple-mented in the United States and appear to be a growing trend, sus-taining water resources and promoting smart industrial development.Some common industries that have implemented water reuse includethe paper pulp industry, the pharmaceutical industry, chemical manu-facturers, power plants, and refineries.

SLUDGE PROCESSING

Objectives Sludges consist primarily of the solids removed fromliquid wastes during their processing. Thus, sludges could contain awide variety of pollutants and residuals from the application of treat-ment chemicals; i.e., large organic solids, colloidal organic solids,metal sulfides, heavy-metal hydroxides and carbonates, heavy-metalorganic complexes, calcium and magnesium hydroxides, calcium car-bonate, precipitated soaps and detergents, and biomass and precipi-tated phosphates. As sludge even after extensive concentration anddewatering is still greater than 50 percent by weight water, it can alsocontain soluble pollutants such as ammonia, priority pollutants, andnonbiologically degradable COD.

The general treatment or management of sludge involves stabiliza-tion of biodegradable organics, concentration and dewatering, andultimate disposal of the stabilized and dewatered residue. A largenumber of individual unit processes and unit operations are used in asludge-management scheme. Those most frequently used are dis-cussed below. Occasionally, only one of these is needed, but usuallyseveral are used in a series arrangement.

Because of the wide variability in sludge characteristics and thevariation in acceptability of treated sludges for ultimate disposal (thisis a function of the location and characteristics of the ultimate disposalsite), it is impossible to prescribe any particular sludge-managementplan. In the sections below, general performance of individual sludge-treatment processes and operations is presented.


TABLE 22-53 Relative Oxidation Power of Select OxidizingReagents

Oxidizing species Relative oxidation power

Chlorine 1.0Hypochlorous acid 1.1Permanganate 1.24Hydrogen peroxide 1.31Ozone 1.52Atomic oxygen 1.78Hydroxyl radical 2.05Titanium dioxide 2.35

(a) (b)

FIG. 22-45 Membrane bioreactor configurations for wastewater treatment. (a) With sidestream module; (b) with submerged module.


Concentration: Thickening and Flotation Generated sludgesare often dilute (1–2 percent solids by weight). In order to reduce thevolumetric loading on other processes, the first step in sludge pro-cessing is often concentration. The most popular process is gravitythickening which is carried out in treatment units similar to circularclarifiers. Organic sludges from primary treatment can usually be con-centrated to 5–8 percent solids. Sludges from secondary treatmentcan be thickened to 2 percent solids. The potential concentration withcompletely inorganic sludges is higher (greater than 10 percent solids)except for sludges high in metal hydroxides. Polymers are often usedto speed up thickening and increase concentration. Thickening isenhanced by long retention of the solids in the thickening apparatus.However, when biodegradable organics are present, solids retentiontime must be at a level that will not foster biological activity, lest odors,gas generation, and solids hydrolysis occur. Loading rates on thicken-ers range from 50–122 kg/m2/d (10–25 lb/ft2/d) for primary sludge to12–45 kg/m2/d (2.5–9 lb/ft2/d). Solids detention time is 0.5 days insummer to several days in winter.

Flotation Air flotation has proved to be successful in concentrat-ing secondary sludges to about 4 percent solids. The incoming solidsare normally saturated with air at 275 to 350 kPa (40 to 50 psig) priorto being released in the flotation tank. As the air comes out of solution,the fine bubbles are trapped under the suspended solids and carrythem to the surface of the tank. The air bubbles compact the solids asa floating mass. Normally, the air-to-solids ratio is about 0.01–0.05 L/g(0.16–0.8 ft3/lb). The thickened solids are scraped off the surface,while the effluent is drawn off the middle of the tank and returned tothe treatment system. In large flotation tanks with high flows theeffluent rather than the incoming solids is pressurized and recycled tothe influent. The size of the flotation tanks is determined primarily bythe solids-loading rate, directly or indirectly. A solids loading of 25 to 97 kg/(m2⋅day) [5 to 20 lb/(ft2⋅day)] has been found to be adequate.On a flow basis this translates into 0.14 to 2.7 L/(m2⋅day) [0.2 to 4 gal/(ft2⋅min)] surface area.

As with thickening, air flotation is enhanced by the addition of poly-mers. Flotation has been successfully used with wholly inorganicmetal hydroxide sludges. Polymers and surfactants are used as addi-tives. Engineering details on air flotation equipment has been devel-oped by and is available from various equipment manufacturingcompanies. Liquid removed during thickening and flotation is usuallyreturned to the head end of the plant.

Stabilization (Anaerobic Digestion, Aerobic Digestion, HighLime Treatment) Sludges high in organics can be stabilized bysubjecting them to biological treatment. The most popular system isanaerobic digestion.

Anaerobic Digestion Anaerobic digesters are large coveredtanks with detention times of 30 days, based on the volume of sludgeadded daily. Digesters are usually heated with an external heatexchanger to 35–37°C to speed the rate of reaction. Mixing is essentialto provide good contact between the microbes and the incomingorganic solids. Gas mixing and mechanical mixers have been used toprovide mixing in the anaerobic digester. Following digestion, thesludge enters a holding tank, which is basically a solids-separation unitand is not normally equipped for either heating or mixing. The super-natant is recycled back to the treatment plant, while the settled sludgeis allowed to concentrate to 3–6 percent solids before being furtherprocessed.

Anaerobic digestion results in the conversion of the biodegradableorganics to methane, carbon dioxide, and microbial cells. Because ofthe energy in the methane, the production of microbial mass is quitelow, less than 0.1 kg/kg (0.1 lb volatile suspended solids (VSS)/lb)BCOD metabolized except for carbohydrate wastes. The productionof methane is 0.35 m3/kg (5.6 ft3/lb) BCOD destroyed. Digester gasesrange from 50 to 80 percent methane and 20 to 50 percent carbondioxide, depending on the chemical characteristics of the waste organ-ics being digested. The methane is often used on site for heat andpower generation.

There are three major groups of bacteria that function in anaerobicdigestion. The first group hydrolyzes large soluble and nonsolubleorganic compounds such as proteins, fats and oils (grease), and carbo-hydrates, producing smaller water-soluble compounds. These are

then degraded by acid-forming bacteria, producing simple volatileorganic acids (primarily acetic acid) and hydrogen. The last group (themethane bacteria) split acetic acid to methane and carbon dioxide andproduce methane from carbon dioxide and hydrogen. Good operationrequires the destruction of the volatile acids as quickly as they are pro-duced. If this does not occur, the volatile acids will build up anddepress the pH, which will eventually inhibit the methane bacteria. Toprevent this from occurring, feed of organics to the digester should beas uniform as possible.

If continuous addition of solids is not possible, additions should bemade at as short intervals as possible. Alkalinity levels are normallymaintained at about 3000 to 5000 mg/L to keep the pH in the range6.5–7.5 as a buffer against variable organic-acid production with vary-ing organic loads. Proteins will produce an adequate buffer, but car-bohydrates will require the addition of alkalinity to provide a sufficientbuffer. Sodium bicarbonate should be used to supply the buffer.

An anaerobic digester is a no-recycle complete mix reactor. Thus,its performance is independent of organic loading but is controlled byhydraulic retention time (HRT). Based on kinetic theory and valuesof the pseudo constants for methane bacteria, a minimum HRT of 3 to4 days is required. To provide a safety factor and compensate for loadvariation as indicated earlier, HRT is kept in the range 10 to 30 days.Thickening of feed sludge is used to reduce the tank volume requiredto achieve the long HRT values. When the sludge is high in protein,the alkalinity can increase to greater than 5000 mg/L, and the pH willrise past 7.5. This can result in free ammonia toxicity. To avoid this sit-uation, the pH should be reduced below 7.5 with hydrochloric acid.Use of nitric or sulfuric acid will result in significant operational prob-lems.

Aerobic Digestion Waste activated sludge can be treated moreeasily in aerobic treatment systems than in anaerobic systems. Thesludge has already been partially aerobically digested in the aerationtank. For the most part, only about 25 to 35 percent of the waste acti-vated sludge can be digested. An additional aeration period of 15 to20 days should be adequate to reduce the residual biodegradable massto a satisfactory level for dewatering and return to the environment.One of the problems in aerobic digestion is the inability to concen-trate the solids to levels greater than 2 percent. A second problem isnitrification. The high protein concentration in the biodegradablesolids results in the release of ammonia, which can be oxidized duringthe long retention period in the aerobic digester. Limiting oxygen sup-ply to the aerobic digester appears to be the best method to handlenitrification and the resulting low pH.

A new concept is to use an on/off air supply cycle. During aeration,nitrates are produced. When the air is shut off, nitrates are reduced tonitrogen gas. This prevents acid buildup and removes nitrogen fromthe sludge. High power cost for aerobic digestion restricts the applic-ability of this process.

High Lime Treatment Uses doses of lime sufficient to raise thepH of sludge to 12 or above. As long as the pH is maintained at thislevel, biological breakdown will not occur. In this sense, the sludge isstable. However, any reduction of pH as a result of contact with CO2

in the air will allow biological breakdown to begin. Thus, this tech-nique should only be used as temporary treatment until further pro-cessing can occur. It is not permanent stabilization as is provided byanaerobic or aerobic digestion.

Sludge Dewatering Dewatering is different from concentrationin that the latter still leaves a substance with the properties of a liquid.The former produces a product which is essentially a friable solid.When the water content of sludge is reduced to <70–80 percent, itforms a porous solid called sludge cake. There is no free water in thecake, as the water is chemically combined with the solids or tightlyadsorbed on the internal pores. The operations below which are usedto dewater sludge can be applied at any stage of the sludge manage-ment process, but often they follow concentration and/or biologicalstabilization. Chemical conditioning is almost always used to aiddewatering.

Lime, alum, and various ferric salts have been used to conditionsludge prior to dewatering. Lime reacts to form calcium carbonatecrystals, which act as a solid matrix to hold the sludge particles apartand allow the water to escape during dewatering. Alum and iron salts

help displace some of the bound water from hydrophilic organics andform part of the inorganic matrix. Chemical conditioning increases themass of sludge to be ultimately handled from 10 to 25 percent,depending upon the characteristics of the individual sludge. Chemicalconditioning can also help remove some of the fine particles by incor-porating them into insoluble chemical precipitates. The water (super-natant) removed from the sludge during dewatering is often high insuspended solids and organics. Addition of polymers prior to, during,or after dewatering will often reduce the level of pollutants in thesupernatant.

Centrifugation Both basket and solid-bowl centrifuges havebeen used to concentrate waste sludges. Field data have shown that itis possible to obtain 10 to 20 percent solids with waste activatedsludge, 15 to 30 percent solids with a mixture of primary and wasteactivated sludge, and up to 30 to 35 percent solids with primary sludgealone. Centrifuges result in 85 to 90 percent solids capture with goodoperation. The problem is that the centrate contains the fine solids noteasily removed. The centrate is normally returned to the treatmentprocess, where it may or may not be removed. Economics do not favorcentrifuges unless the sludge cake produced is at least 25 to 30 per-cent solids. For the most part, centrifuges are designed by equipmentmanufacturers from field experience. With varying sludge characteris-tics centrifuge characteristics will also vary widely.

Vacuum Filtration Vacuum filtration has been the most com-mon method employed in dewatering sludges. Vacuum filters consistof a rotary drum covered with a cloth-filter medium. Various plasticfibers as well as wool have been used for the filter cloth. The filteroperates by drawing a vacuum as the drum rotates into chemicallyconditioned sludge. The vacuum holds a thin layer of sludge, which isdewatered as the drum rotates through the air after leaving the vat.When the drum rotates the cloth to the opposite side of the apparatus,air-pressure jets replace the vacuum, causing the sludge cake to sepa-rate from the cloth medium as the cloth moves away from the drum.The cloth travels over a series of rollers, with the sludge being sepa-rated by a knife edge and dropping onto a conveyor belt by gravity.The dewatered sludge is moved on the conveyor belt to the next con-centration point, while the filter cloth is spray-washed and returned tothe drum prior to entering the sludge vat. Vacuum filters yield thepoorest results on waste activated sludge and the best results on pri-mary sludge. Waste activated sludge will concentrate to between 12and 18 percent solids at a rate of 4.9 to 9.8 kg dry cake/(m2�h) [1 to 2lb/(ft2�h)]. Primary sludge can be dewatered to 25 to 30 percent solidsat a rate of 49 kg dry cake/(m2�h) [10 lb/(ft2�h)].

Pressure Filtration Pressure filtration has been used increas-ingly since the early 1970s because of its ability to produce a driersludge cake. The pressure filters consist of a series of plates andframes separated by a cloth medium. Sludge is forced into the filterunder pressure, while the filtrate is drawn off. When maximum pres-sure is reached, the influent-sludge flow is stopped and the pressurefilter is allowed to discharge the residual filtrate prior to opening thefilter and allowing the filter cake to drop by gravity to a conveyor beltbelow the filter press. The pressure filter operates at a pressurebetween 689 and 1380 kPa (100 and 200 psig) and takes 1.5 to 4 h forthe pressure cycle. Normally, 20 to 30 min is required to remove thefilter cake. The sludge cakes will vary from 20 to 25 percent for wasteactivated sludge to 50 percent for primary sludge. Chemical condi-tioning is necessary to obtain good dewatering of the sludges.

Belt-Press Filters The newest filter for handling waste activatedsludge is the belt-press filter. The belt press utilizes a continuouscloth-filter belt. Waste activated sludge is spread over the filtermedium, and water is removed initially by gravity. The open belt withthe sludge moves into contact with a second moving belt, whichsqueezes the sludge layer between rollers with ever-increasing pres-sure. The sludge cake is removed at the end of the filter press by aknife blade, with the sludge dropping by gravity to a conveyor belt.Belt-press filters can produce sludge with 20–30 percent solids.

Sand Beds Sand filter beds can be used to dewater either anaerobi-cally or aerobically digested sludges. They work best on relatively smalltreatment systems located in relatively dry areas. The sand bed consistsof coarse gravel graded to fine sand in a series of layers to a depth of 0.45to 0.6 m (1.5 to 2 ft). The digested sludge is placed over the entire filter

surface to a depth of 0.3 m (12 in) and allowed to sit until dry. Free waterwill drain through the sand bed to an open pipe underdrain system andbe removed from the filter. Air drying will slowly remove the remainingwater. The sludge must be cleaned from the bed by hand prior to addinga second layer of sludge. The sludge layer will drop from an initial thick-ness of 3 m (12 in) to about 0.006 m (1⁄4 in). An open sand bed can gen-erally handle 49 to 122 kg dry solids/(m2�year) [10 to 25 lb/(ft2�year)].Covered sand beds have been used in wet climates as well as in coldclimates, but economics does not favor their use.

SLUDGE DISPOSAL

Incineration Incineration has been used to reduce the volumeof sludge after dewatering. The organic fractions in sludges lendthemselves to incineration if the sludge does not have an excessivewater content. Multiple-hearth and fluid-bed incinerators have beenextensively used for sludge combustion.

A multiple-hearth incinerator consists of several hearths in a verti-cal cylindrical furnace. The dewatered sludge is added to the tophearth and is slowly pushed through the incinerator, dropping by grav-ity to the next lower layer until it finally reaches the bottom layer. Thetop layer is used for drying the sludge with the hot gases from thelower layers. As the temperature of the furnace increases, the organ-ics begin to degrade and undergo combustion. Air is used to add thenecessary oxygen and to control the temperature during combustion.It is very important to keep temperatures above 600°C to ensure com-plete oxidation of the volatile organics. One of the problems with themultiple-hearth incinerator is volatilization of odorous organics duringthe drying phase before the temperature reaches combustion levels.Even afterburners on the exhaust-gas line may not be adequate forcomplete oxidation. Air-pollution-control devices are required on allincinerators to remove fly ash and corrosive gases. The ash from theincinerator must be cooled, collected, and conveyed back to the envi-ronment, normally to a sanitary landfill for burial. The residual ash willweigh from 10 to 30 percent of the original dry weight of the sludge.Supplemental fuels are needed to start the incinerator and to ensureadequate temperatures with sludges containing excessive moisture,such as activated sludge. Heat recovery from wastes is being givenmore consideration. It is possible to combine the sludges with otherwastes to provide a better fuel for the incinerator.

A fluid-bed incinerator uses hot sand as a heat reservoir for dewa-tering the sludge and combusting the organics. The turbulence cre-ated by the incoming air and the sand suspension requires the effluentgases to be treated in a wet scrubber prior to final discharge. The ashis removed from the scrubber water by a cyclone separator. Thescrubber water is normally returned to the treatment process anddiluted with the total plant effluent. The ash is normally buried.

Sanitary Landfills Dewatered sludge, either raw or digested, isoften buried in a sanitary landfill to minimize the environmentalimpact. Increased concern over sanitary landfills has made it more dif-ficult simply to bury dewatered sludge. Sanitary landfills must bemade secure from leachate and be monitored regularly to ensure thatno environmental damage occurs. The moisture content of mostsludges makes them a problem at sanitary landfills designed for solidwastes, requiring separate burial even at the same landfill.

Beneficial Reuse of Biosolids Biosolids are biological treat-ment sludges that are stabilized by using a variety of methods includ-ing alkaline stabilization, anaerobic digestion, aerobic digestion,composting, or heat drying and pelletization. The disposal of biosolidshas typically been done through incineration and landfilling. With thesevere decline in the number of landfills and the difficulty with incin-eration meeting stringent Clean Air Act standards, biosolids areincreasingly being land-applied as a beneficial reuse. The specific typeof land application is a function of the quality of biosolids beingapplied. Beneficial reuse of biosolids is regulated by the EPA (Part503 Rules), which has established guidelines and specific criteria forreuse application. The EPA biosolids rules regulate chemical contam-inants in the biosolids (metals), pathogen and pathogen indicator con-tent, sludge stabilization methodology, land application site access andsetback distances, vector attraction reduction methods, and the croptype and harvesting schedule.


MANAGEMENT OF SOLID WASTES 22-81

EPA Class A or Class B biosolids can be land-applied. Land appli-cation serves two purposes: (1) to provide an inexpensive fertilizer andsoil conditioner and (2) to continue treatment of the sludge throughexposure to sunlight, plant uptake of metals, and desiccation ofpathogens. The benefits of biosolids land application include addition

of nutrients (micro and macro) to soil, replacing agricultural depen-dency on chemical fertilizer; improving soil texture and increasingbiological activity to promote root growth; slowly releasing nutrientsto reduce off-site transport of nutrients; and lower cost than landfill-ing or incineration.

MANAGEMENT OF SOLID WASTES

INTRODUCTION

Solid wastes are all the wastes arising from human and animal activi-ties that are normally solid and that are discarded as useless orunwanted. The term as used in this subsection is all-inclusive, and itencompasses the heterogeneous mass of throwaways. The three R’sshould be applied to solid wastes: reuse, recycle, and reduce. Whenthese techniques have been implemented, management of theremaining residual solid waste can be addressed.

Functional Elements The activities associated with the man-agement of solid wastes from the point of generation to final disposalhave been grouped into the functional elements identified in Fig. 22-46.By considering each fundamental element separately, it is possible to(1) identify the fundamental element and (2) develop, when possible,

quantifiable relationships for the purpose of making engineering com-parisons, analyses, and evaluations.

Waste Reduction Processes can be redesigned to reduce theamount of waste generated. For example, transfer lines betweenprocesses can be blown clear pneumatically to drive liquid into thebatch mix tank.

Waste Generation Waste generation encompasses those activi-ties in which materials are identified as no longer being of value andare either thrown away or gathered together for disposal. From thestandpoint of economics, the best place to sort waste materials forrecovery is at the source of generation.

Reuse Waste may be diverted to reuse. For example, containersmay be cleaned and reused, or the waste from one process maybecome the feedstock for another.

FIG. 22-46 Functional elements in a solid-waste management system. (Updated fromG. Tchobanoglous, H. Theisen, and R. Eliassen, Solid Wastes: Engineering and Manage-ment Issues, McGraw-Hill, New York, 1977.)

On-Site Handling, Storage, and Processing The functionalelement encompasses those activities associated with the handling,storage, and processing of solid wastes at or near the point of genera-tion. On-site storage is of primary importance because of the aes-thetic considerations, public health, public safety, and economicsinvolved.

Collection The functional element of collection includes the gath-ering of solid wastes and the hauling of wastes after collection to thelocation where the collection vehicle is emptied. As shown in Fig. 22-46,this location may be a transfer station, a processing station, or a landfilldisposal site.

Transfer and Transport The functional element of transfer andtransport involves two steps: (1) the transfer of wastes from thesmaller collection containers to the larger transport equipment and(2) the subsequent transport of the wastes, usually over long distances,to the disposal site.

Processing and Recovery The functional element of processingand recovery includes all the techniques, equipment, and facilitiesused both to improve the efficiency of the other functional elementsand to recover usable materials, conversion products, or energy fromsolid wastes. Materials that can be recycled are exported to facilitiesequipped to do so. Residues go to disposal.

Disposal The final functional element in the solid waste manage-ment system is disposal. Disposal is the ultimate fate of all solidwastes, whether they are wastes collected and transported directly toa landfill site, semisolid wastes (sludge) from industrial treatmentplants and air-pollution-control devices, incinerator residue, compost,or other substances from various solid waste processing plants that areof no further use.

Solid-Waste-Management Systems Practical aspects associatedwith solid-waste-management systems not covered in the presentationinclude financing, operations, equipment management, personnel,reporting, cost accounting and budgeting, contract administrationordinances and guidelines, and public communications.

UNITED STATES LEGISLATION, REGULATIONS, AND GOVERNMENT AGENCIES

Much of the current activity in the field of solid-waste management,especially with respect to hazardous wastes and resources recovery, isa direct consequence of legislation. It is imperative to have a workingknowledge of waste regulations, including RCRA and MACT (forEPA hazardous waste); TSCA (Toxic Substances Control Act) forPCBs and toxic waste; Solid Waste Disposal Act; the Clean Air Act;and PSD (prevention of significant deterioration) regulations. TheClean Air Act has far-reaching implications for any waste-relatedoperation (e.g., incineration or landfill) that emits particulates orgaseous emissions. Primary elements of the act are Title I, dealingwith fugitive emissions monitoring; Title III, with reduction of organichazardous air pollutants; and Title V, with operating permits. The 1990amendments have added a significant permitting burden for industrialplants and require additional controls for HAPs (hazardous air pollu-tants). In addition, state and local regulations apply to waste opera-tions. The process of initiating major technology improvements inpoor air quality areas, proving performance, and then spreading thattechnology elsewhere steadily ratcheted the emission limitations fornew plants down to ever-lower levels.

Particulate emissions are an example of the ratcheting process. Inthe 1960s, burning 1 ton of MSW emitted about 30 lb of smoke. In1971, the NSPS for incinerators reduced PM emissions to approxi-mately 1.9 lb of PM per ton of MSW burned, a 94 percent reduction.In the 1980s, the focus changed to minimizing sulfur dioxide and PM.New plant PM levels have been below 0.2 lb/ton of MSW burnedsince the late 1980s—a 99 percent reduction from 30 lb in about twodecades. Incremental improvements came from technology meetingthe more stringent emission criteria. Each incremental improvementalso used much more resources—energy, money and human talent—than the previous step.

Dioxin and furan emissions are another example of the ratchetingprocess. When first measured in the 1970s, concentrations were 1000

times greater than those routinely found 10 years later in state-of-the-art plants. The technology to control sulfur dioxide and hydrogenchloride emissions also reduced dioxin and furan emissions. Multi-pathway health risk assessments routinely show negligible risk fromthis level of dioxin and furan emissions. Even so, the 1995 EmissionsGuidelines call for these low-emitting systems to demonstrate dioxinemissions another 50 times lower. This reduction is the anticipated by-product of using activated carbon to reduce mercury emissions, as itwill also adsorb dioxins and furans.

The Maximum Achievable Control Technology (MACT) emissionlimitations required by the 1990 Clean Air Act Amendments (CAAA)show the ultimate effect of the ratcheting process. After a little morethan two decades of ratcheting, MWCs have become a comparativelyminor source of combustion-related air pollution. Other artificial andnatural sources such as automobiles, trucks, power plants, fireplaces,wood stoves, metal production furnaces, industrial manufacturingprocesses, volcanoes, forest fires, and backyard trash burning are nowthe major known sources of combustion-related pollutants.

Regulations have been adopted by federal, state, and local agenciesto implement the legislation. Before any design and construction workis undertaken, these regulations must be reviewed and care taken tofactor in the nearly continuous regulatory revisions, as noted above.

GENERATION OF SOLID WASTES

Solid wastes, as noted previously, include all solid or semisolid materi-als that are no longer considered of sufficient value to be retained in agiven setting. The types and sources of solid wastes, the physical andchemical composition of solid wastes, and typical solid-waste genera-tion rates are considered in this subsection.

Types of Solid Waste The term solid wastes is all-inclusive andencompasses all sources, types of classifications, compositions, andproperties. As a basis for subsequent discussions, it will be helpful todefine the various types of solid wastes that are generated. It is impor-tant to note that the definitions of solid-waste terms and the classifica-tions vary greatly in practice and in the literature. Consequently, theuse of published data requires considerable care, judgment, and com-mon sense. The following definitions are intended to serve as a guide.

1. Food wastes. Food wastes are the animal, fruit, or vegetableresidues (also called garbage) resulting from the handling, prepara-tion, cooking, and eating of foods. The most important characteristicof these wastes is that they are putrescible and will decompose rapidly,especially in warm weather.

2. Rubbish. Rubbish consists of combustible and noncom-bustible solid wastes, excluding food wastes or other putrescible mate-rials. Typically, combustible rubbish consists of materials such aspaper, cardboard, plastics, textiles, rubber, leather, wood, furniture,and garden trimmings. Noncombustible rubbish consists of itemssuch as glass, crockery, tin cans, aluminum cans, ferrous and othernonferrous metals, dirt, and construction wastes.

3. Ashes and residues. These are the materials remaining fromthe burning of wood, coal, coke, and other combustible wastes.Residues from power plants normally are composed of fine powderymaterials, cinders, clinkers, and small amounts of burned and partiallyburned materials. Fly ash from coal boilers and CKD (cement kilndust) are frequently sold for stabilization of waste, waste bulkingoperations, and incorporation into building products such as gypsumfrom sulfur dioxide scrubbing.

4. Construction and demolition wastes. C&D wastes that comefrom razed buildings and other structures are classified as demolitionwastes. Wastes from the construction, remodeling, and repair of com-mercial and industrial buildings and other similar structures are clas-sified as construction wastes. These wastes may include dirt, stones,concrete, bricks, plaster, lumber, shingles, and plumbing, heating, andelectrical parts.

5. Special wastes. Wastes such as street sweepings, roadside liter,catch-basin debris, dead animals, and abandoned vehicles are classi-fied as special wastes.

6. Treatment plant wastes. The solid and semisolid wastes fromwater, wastewater, and industrial waste-treatment facilities are includedin this classification.



7. Agricultural wastes. Wastes and residues resulting from diverseagricultural activities, such as the planting and harvesting of row, field,and tree and vine crops, the production of milk, the production of ani-mals for slaughter, and the operation of feedlots are collectively calledagricultural wastes.

Hazardous Wastes The US EPA has defined hazardous waste inRCRA regulations, CFR Parts 260 and 261. A waste may be hazardous ifit exhibits one or more of the following characteristics: (1) ignitability, (2)corrosivity, (3) reactivity, and (4) toxicity. A detailed definition of theseterms was first published in the Federal Register on May 19, 1980, pp.22, 121–122. A waste may be hazardous if listed in Appendix VIII.

In the past, hazardous wastes were often grouped into the followingcategories: (1) radioactive substances, (2) chemicals, (3) biologicalwastes, (4) flammable wastes, and (5) explosives. The chemical cate-gory included wastes that were corrosive, reactive, and toxic. The

principal sources of hazardous biological wastes are hospitals and bio-logical research facilities.

All hazardous waste combustors (HWCs), including hazardous wasteincinerators (HWIs), cement kilns (CKs), and lightweight aggregatekilns (LWAKs), are subject to the MACT standards regardless of size ormajor source status. HWCs are required to be in compliance with thestandards by September 30, 2003, and are required to demonstratecompliance by March 30, 2004, through a Comprehensive PerformanceTest (CPT). The rule allows for a 1-year extension of the compliancedate for facilities that need to install pollution control equipment tomeet standards.

The HWC MACT standards regulate emissions of the followingpollutants:• Dioxins and furans (D/F)• Mercury (Hg)

TABLE 22-54 Sources and Types of Industrial Wastes*

Code SIC group classification Waste-generating processes Expected specific wastes

19 Ordnance and accessories Manufacturing, assembling Metals, plastic, rubber, paper, wood, cloth, chemical residues

20 Food and kindred products Processing, packaging, shipping Meats, fats, oils, bones, offal, vegetables, fruits, nuts and shells, cereals

22 Textile mill products Weaving, processing, dyeing, shipping Cloth and filter residues23 Apparel and other finished products Cutting, sewing, sizing, pressing Cloth, fibers, metals, plastics, rubber24 Lumber and wood products Sawmills, millwork plants, wooden containers, Scrap wood, shavings, sawdust; in some

miscellaneous wood products, manufacturing instances, metals, plastics, fibers, glues, sealers, paints, solvents

25a Furniture, wood Manufacture of household and office furniture, Those listed under Code 24, in addition, partitions, office and store fixtures, mattresses cloth and padding residues

25b Furniture, metal Manufacture of household and office furniture, Metals, plastics, resins, glass, wood, rubber, lockers, springs, frames adhesives, cloth paper

26 Paper and allied products Paper manufacture, conversion of paper and Paper and filter residues, chemicals, paper paperboard, manufacture of paperboard boxes coatings and filters, inks, glues, fastenersand containers

27 Printing and publishing Newspaper publishing, printing, lithography, Paper, newsprint, cardboard, metals, engraving, bookbinding chemicals, cloth, inks, glues

28 Chemicals and related products Manufacture and preparation of inorganic Organic and inorganic chemicals, metals, chemicals (ranging from drugs and soaps to plastics, rubber, glass, oils, paints, solvents, paints and varnishes and explosives) pigments

29 Petroleum refining and related Manufacture of paving and roofing materials Asphalt and tars, felts, paper, cloth, fiberindustries

30 Rubber and miscellaneous Manufacture of fabricated rubber and plastic Scrap rubber and plastics, lampblack, curing plastic products products compounds, dyes

31 Leather and leather products Leather tanning and finishing, manufacture of Scrap leather, thread, dyes, oils, processing leather belting and packaging and curing compounds

32 Stone, clay, and glass products Manufacture of flat glass, fabrication or forming Glass, cement, clay, ceramics, gypsum, of glass,; manufacture of concrete, gypsum, and asbestos, stone, paper, abrasivesplaster products; forming and processing of stone products, abrasives, asbestos, and miscellaneous non-mineral products

33 Primary metal industries Melting, casting, forging, drawing, rolling, Ferrous and non-ferrous metals scrap, slag, forming, extruding operations sand, cores, patterns, bonding agents

34 Fabricated metal products Manufacture of metal cans, hand tools, general Metals, ceramics, sand, slag, scale, coatings, hardware, non-electrical heating apparatus, solvents, lubricants, pickling liquorsplumbing fixtures, fabricated structural products, wire, farm machinery and equipment, coating and engraving of metal

35 Machinery (except electrical) Manufacture of equipment for construction, Slag, sand, cores, metal scrap, wood, plastics,elevators, moving stairways, conveyors, resins, rubber, cloth, paints, solvents,industrial trucks, trailers, stackers, machine petroleum productstools, etc.

36 Electrical Manufacture of electrical equipment, appliances Metal scrap, carbon, glass, exotic metals, and communication apparatus, machining, rubber, plastics, resins, fibers, cloth drawing, forming, welding, stamping, winding, residues, PCBspainting, plating, baking, firing operations

37 Transportation equipment Manufacture of motor vehicles, truck and bus Metal scrap, glass, fiber, wood, rubber,bodies, motor-vehicle parts and accessories, plastics, cloth, paints, solvents, petroleum aircraft and parts, ship and boat building, productsrepairing motorcycles and bicycles and parts, etc.

38 Professional scientific Manufacture of engineering, laboratory and Metals, plastics, resins, glass, wood, rubber,controlling instruments research instruments and associated equipment fibers, abrasives

39 Miscellaneous manufacturing Manufacture of jewelry, silverware, plate ware, Metals, glass, plastics, resin, leather, rubber, toys, amusements, sporting and athletic goods, composition, bone, cloth, straw, adhesives, costume novelties, buttons, brooms, brushes, paints, solventssigns, advertising displays

*From C. L. Mantell (ed.), Solid Wastes: Origin, Collection, Processing, and Disposal, Wiley-Interscience, New York, 1975. PCBs added to item 36.

• Total chlorine (HCl/Cl2)• Semivolatile metals (SVMs)—lead and cadmium• Low-volatility metals (LVMs)—arsenic, beryllium, and chromium• Particulate matter (PM)• Carbon monoxide (CO)• Hydrocarbons (HC)The HWC MACT standards require continuous monitoring of bothemissions and operating parameters to demonstrate compliance at alltimes. Continuous emissions monitoring is required for CO or HC. Inthe future, facilities will also be required to use continuous emissionmonitors for PM. In addition, cement kilns may be required to use anopacity monitor.

The Federal Register (vol. 69, no. 76, April 20, 2004) issued ProposedRules for Existing and New Sources of HWCs. This included not onlythe HWIs, CKs, and LWAKs, but also for the first time the solid-fuel-fired boilers, liquid-fuel-fired boilers, and hydrochloric acid productionfurnaces. The boilers and HCl furnaces had been covered by the Boil-ers and Industrial Furnaces standards issued as Boiler and IndustrialFurnace Act (BIF) in 1991. When MACT was enacted for HWCs onSeptember 30, 1999, the BIFs were not included. The proposed stan-dards were listed in Tables 1 and 2 of the FR of April 20, 2004.

Sources of Industrial Wastes Knowledge of the sources andtypes of solid wastes, along with data on the composition and rates ofgeneration, is basic to the design and operation of the functional ele-ments associated with the management of solid wastes.

Conventional Wastes Sources and types of industrial solidwastes generated by Standard Industrial Classification (SIC) groupclassification are reported in Table 22-54. The expected specificwastes in the table are most readily identifiable.

Hazardous Waste Hazardous wastes are generated in limitedamounts throughout most industrial activities. In terms of generation,concern is with the identification of amounts and types of hazardouswastes developed at each source, with emphasis on those sourceswhere significant waste quantities are generated.

The USEPA released “National Biennial RCRA HazardousWaste Report” based on 2001 data. The three-volume report, whichrepresents comprehensive data on the generation and managementof hazardous waste in the United States during 2001, includes theNational Analysis, the State Detail Analysis, and the List ofReported RCRA Sites. The report noted a decrease to 40.8 million

tons compared to 206 million tons of hazardous waste generated in1991. The number of large-quantity generators decreased to 19,024from 23,426 in 1991. The number of waste treatment, storage, anddisposal (TSD) facilities decreased to 2479 from 3862 in 1991.

The majority—56.1 percent—of the hazardous wastes generated dur-ing 2001 were managed in aqueous waste treatment units. Land disposalaccounted for another 4.6 percent of the total, divided as follows: 2.1 mil-lion tons sent to landfills and 65,000 tons managed by land farming.Resource recovery operations managed 3.7 percent of the 46 milliontons, with solvent-recovery units managing 3.6 million tons; fuel-blend-ing units, 1.4 million tons; metals recovery, 1.46 million tons; and othermethods such as acid regeneration and waste oil recovery accounting for9.8 million tons. Thermal treatment systems burned 6.3 percent of thehazardous wastes generated in 2001: 1.65 million tons was incinerated,and 1.7 million tons was used as fuel in boilers and industrial furnaces.

The generation of hazardous wastes by spillage must also be con-sidered. The quantities of hazardous wastes that are involved inspillage usually are not known. After a spill, the wastes requiring col-lection and disposal are often significantly greater than the amount ofspilled wastes, especially when an absorbing material, such as straw,sand, and “oil-dry,” is used to soak up liquid hazardous wastes. Simi-larly, the volume and mass of contaminated soil requiring excavationare far greater than the waste volume involved in a spill. Both theadsorbing material and the liquid are classified as hazardous waste.

Properties of Solid Wastes Information on the properties ofsolid wastes is important in evaluating alternative equipment needs,systems, and management programs and plans.

Physical Composition Information and data on the physical com-position of solid wastes including (1) identification of the individualcomponents that make up industrial and municipal solid wastes, (2)density of solid wastes, and (3) moisture content are presented below.

1. Individual components. Components that typically make upmost industrial and municipal solid wastes and their relative distributionare reported in Table 22-55. Although any number of componentscould be selected, those listed in the table have been chosen becausethey are readily identifiable, are consistent with component categoriesreported in the literature, and are adequate for the characterization ofsolid wastes for most applications.

2. Density. Typical densities for various wastes as found in con-tainers are reported by source in Table 22-56. Because the densities of


TABLE 22-55 Typical Data on Distribution of Industrial Wastes Generated by Major Industries and Municipalities*

Percent by mass

SIC code SIC group classification Food wastes† Paper Wood Leather Rubber Plastics Metals Glass Textiles Miscellaneous

20 Food and kindred products 15–20 50–60 5–10 0–2 0–2 0–5 5–10 4–10 0–2 5–1522 Textile mill products 0–2 40–50 0–2 0–2 0–2 3–10 0–2 0–2 20–40 0–523 Apparel and other finished 0–2 40–60 0–2 0–2 0–2 0–2 0–2 0–2 30–50 0–5

products24 Lumber and wood products 0–2 10–20 60–80 0–2 0–2 0–2 0–2 0–2 0–2 5–1025a Furniture, wood 0–2 20–30 30–50 0–2 0–2 0–2 0–2 0–2 0–5 0–525b Furniture, metal 0–2 20–40 10–20 0–2 0–2 0–2 20–40 0–2 0–5 0–1026 Paper and allied products 0–2 40–60 10–15 0–2 0–2 0–2 5–15 0–2 0–2 10–2027 Printing and publishing 0–2 60–90 5–10 0–2 0–2 0–2 0–2 0–2 0–2 0–528 Chemicals and related products 0–2 40–60 2–10 0–2 0–2 5–15 5–10 0–5 0–2 15–2529 Petroleum refining and related 0–2 60–80 5–15 0–2 0–2 10–20 2–10 0–12 0–2 2–10

industries30 Rubber and miscellaneous plastic 0–2 40–60 2–10 0–2 5–20 10–20 0–2 0–2 0–2 0–5

products31 Leather and leather products 0–2 5–10 5–10 40–60 0–2 0–2 10–20 0–2 0–2 0–532 Stone, clay, and glass products 0–2 20–40 2–10 0–2 0–2 0–2 5–10 10–20 0–2 30–5033 Primary metal industries 0–2 30–50 5–15 0–2 0–2 2–10 2–10 0–5 0–2 20–4034 Fabricated metal products 0–2 30–50 5–15 0–2 0–2 0–2 15–30 0–2 0–2 5–1535 Machinery (except electrical) 0–2 30–50 5–15 0–2 0–2 1–5 15–30 0–2 0–2 0–536 Electrical 0–2 60–80 5–15 0–2 0–2 2–5 2–5 0–2 0–2 0–537 Transportation equipment 0–2 40–60 5–15 0–2 0–2 2–5 0–2 0–2 0–2 15–3038 Professional scientific controlling 0–2 30–50 2–10 0–2 0–2 5–10 5–15 0–2 0–2 0–5

instruments39 Miscellaneous manufacturing 0–2 40–60 10–20 0–2 0–2 5–15 2–10 0–2 0–2 5–15

Municipal Municipal 10–20 40–60 1–4 0–2 0–2 2–10 3–15 4–16 0–4 5–30

*Adapted in part from D. G. Wilson (ed.), Handbook of Solid Waste Management, Van Nostrand Reinhold, New York, 1977.†With the exception of food and kindred products, food wastes are from company cafeterias, canteens, etc.


solid waste vary markedly with geographic location, season of the year,and length of time in storage, great care should be used in selectingtypical values.

3. Moisture content. The moisture content of solid wastes usually isexpressed as the mass of moisture per unit mass of wet or dry material.In the wet-mass method of measurement, the moisture in a sample isexpressed as a percentage of the wet mass of the material; in the dry-mass method, it is expressed as a percentage of the dry mass of the mate-rial. In equation form, the wet-mass moisture content is expressed as

Moisture content (%) �a � � � 100 (22-26)

where a = initial mass of sample as delivered and b = mass of sampleafter drying. Typical data on the moisture content for the solid-waste

b�a

components are given in Table 22-56. For most industrial solid wastes,the moisture content will vary from 10 to 25 percent.

4. Particle size. The material handling properties of solid wastesare dependent upon particle size. This applies as well to feed prepa-ration and air pollution control which are affected by solid-waste par-ticle size and cohesiveness. For wastes such as bulk soils, the amountof fines (from clay and silt) is critical for system design. Cohesiveness,which varies with moisture content, is important for bin and conveyordesign.

Chemical Composition Information on the chemical composi-tion of solid wastes is important in evaluating alternative processingand recovery options. If solid wastes are to be used as fuel, the six mostimportant properties to be known are

1. Proximate analysisa. Moisture (loss at 105°C for 1 h)

TABLE 22-56 Typical Density and Moisture-Content Data for Domestic, Commercial, andIndustrial Solid Waste

Density, kg/m3 Moisture content, % by mass

Item Range Typical Range Typical

Residential (uncompacted)Food wastes (mixed) 130–480 290 50–80 70Paper 40–130 85 4–10 6Cardboard 40–80 50 4–8 6Plastics 40–130 65 1–4 2Textiles 40–100 65 6–15 10Rubber 100–200 130 1–4 2Leather 100–260 160 8–12 10Garden trimmings 60–225 100 30–80 60Wood 130–320 240 15–40 20Glass 160–480 195 1–4 2Tin cans 50–160 90 2–4 3Nonferrous metals 65–240 160 2–4 2Ferrous metals 130–1150 320 2–4 2Dirt, ashes, etc. 320–1000 480 6–12 8Ashes 650–830 745 6–12 6Rubbish (mixed) 90–180 130 5–20 15

Residential (compacted)In compactor truck 180–450 300 15–40 20In landfill (normally compacted) 360–500 450 15–40 30*In landfill (well-compacted) 590–740 600 15–40 30*

CommercialFood wastes (wet) 475–950 535 50–85 75Appliances 150–200 180 0–5Wooden crates 110–160 110 10–30 20Tree trimmings 100–180 150 20–80 50Rubbish (combustible) 50–180 120 5–25 15Rubbish (noncombustible) 180–360 300 5–15 10Rubbish (mixed) 140–180 160 5–20 12

Construction; demolition; remediationMixed demolition (noncombustible) 1000–1600 1420 2–10 4Mixed demolition (combustible) 300–400 360 4–15 8Mixed construction (combustible) 180–360 260 4–15 8Broken concrete 1200–1800 1540 0–5 —Contaminated soil 1200–1900 1600 5–25 10

Industrial wastesChemical sludges (wet) 800–1100 1000 75–99 80Fly ash 700–900 800 2–10 4Leather scraps 100–250 160 6–15 10Metal scraps (heavy) 1500–2000 1780 0–5Metal scraps (light) 500–900 740 0–5Metal scraps (mixed) 700–1500 900 0–5Oils, tars, asphalt 800–1000 950 0–5 2Sawdust 100–350 290 10–40 15Textile wastes 100–220 180 6–15 10Wood (mixed) 400–675 500 10–40 20

Agricultural wastesAgricultural (mixed) 400–750 560 48–80 50Fruit wastes (mixed) 250–750 360 60–90 75Manure (wet) 900–1050 1000 75–96 94Vegetable wastes (mixed) 200–700 360 50–80 65

*Depends on degree of surface water infiltration.

b. Volatile matter (additional loss on heating to 950°C)c. Ash (residue after burning)d. Fixed carbon (remainder)2. Fusion point of ash3. Ultimate analysis, percent of C (carbon), H (hydrogen), O (oxy-

gen), N (nitrogen), S (sulfur), and ash4. Heating value5. Organic chlorine6. Organic sulfur

Typical proximate-analysis data for the combustible components ofindustrial and municipal solid wastes are presented in Table 22-57.

Typical data on the inert residue and energy values for solid wastesmay be converted to a dry basis by using Eq. (22.27):

= � (22-27)

The corresponding equation on an ash-free basis is

=

× � (22-28)100

��100 − % ash − % moisture

kJ��kg (as discarded)

kJ��

kg (ash-free dry basis)

100��100 − % moisture

kJ��kg (as discarded)

kJ��kg (dry basis)

Representative data on the ultimate analysis of typical industrialand municipal-waste components are presented in Table 22-58. Ifenergy values are not available, approximate values can be determinedby using Eq. (22-29), known as the modified Dulong formula, and thedata in Table 22-58.

kJ�kg = 337C + 1428 �H − O + 95S (22-29)

where C = carbon, percentH = hydrogen, percentO = oxygen, percentS = sulfur, percent

Quantities of Solid Wastes Representative data on the quanti-ties of solid wastes and factors affecting the generation rates are con-sidered briefly in the following paragraphs.

Typical Generation Rates Typical unit waste generation ratesfrom selected industrial sources are reported in Table 22-59. Becausewaste generation practices are changing so rapidly, the presentation of“typical” waste generation data may not be reliable.

Factors That Affect Generation Rates Factors that influencethe quantity of industrial wastes generated include (1) the extent of sal-vage and recycle operations, (2) company attitudes, and (3) legislation

1�8


TABLE 22-57 Typical Proximate-Analysis and Energy-Content Data for Components in Domestic, Commercial, and Industrial Solid Waste*

Proximate analysis, % by mass Energy content, kJ/kg

Volatile Non- Moisture-Component Moisture matter Fixed carbon combustible As collected Dry and ash-free

Food and food productsFats 2.0 95.3 2.5 0.2 37,530 38,296 38,374Food wastes (mixed) 70.0 21.4 3.6 5.0 4,175 13,917 16,700Fruit wastes 78.7 16.6 4.0 0.7 3,970 18,638 19,271Meat wastes 38.8 56.4 1.8 3.1 17,730 28,970 30,516

Paper productsCardboard 5.2 77.5 12.3 5.0 16,380 17,278 18,240Magazines 4.1 66.4 7.0 22.5 12,220 12,742 16,648Newsprint 6.0 81.1 11.5 1.4 18,550 19,734 20,032Paper (mixed) 10.2 75.9 8.4 5.4 15,815 17,611 18,738Waxed cartons 3.4 90.9 4.5 1.2 26,345 27,272 27,615

PlasticsPlastics (mixed) 0.2 95.8 2.0 2.0 32,000 32,064 32,720Polyethylene 0.2 98.5 <0.1 1.2 43,465 43,552 44,082Polystyrene 0.2 98.7 0.7 0.5 38,190 38,266 38,216Polyurethane 0.2 87.1 8.3 4.4 26,060 26,112 27,316Polyvinyl chloride 0.2 86.9 10.8 2.1 22,690 22,735 23,224

Wood, trees, etc.Garden trimmings 60.0 30 9.5 0.5 6,050 15,125 15,316Green wood 50.0 42.3 7.3 0.4 4,885 9,770 9,848Hardwood 12.0 75.1 12.4 0.5 17,100 19,432 19,542Wood (mixed) 20.0 67.9 11.3 0.8 15,444 19,344 19,500

Leather, rubber, textiles, etc.Leather (mixed) 10 68.5 12.5 9.0 18,515 20,572 22,858Rubber (mixed) 1.2 83.9 4.9 9.9 25,330 25,638 28,493Textiles (mixed) 10 66.0 17.5 6.5 17,445 19,383 20,892

Glass, metals, etc.Glass and mineral 2 — — 96–99+ 196† 200 200Metal, tin cans 5 — — 94–99+ 1,425† 1,500 1,500Metals, ferrous 2 — — 96–99+ — — —Metals, nonferrous 2 — — 94–99+ — — —

MiscellaneousOffice sweepings 3.2 20.5 6.3 70 8,535 8,817 31,847

Multiple wastes 20 53 7 20 10,470 13,090 17,450(15–40) (30–60) (5–15) (9–30)

Industrial wastes 15 58 7 20 11,630 13,682 17,892(10–30) (30–60) (5–15) (10–30)

*Adapted in part from D. G. Wilson (ed.), Handbook of Solid Waste Management, Van Nostrand Reinhold, New York, 1977, and G. Tchobanoglous, H. Theisen, andR. Eliassen, Solid Wastes: Engineering Principles and Management Issues, McGraw-Hill, New York, 1977.

†Energy content is from coatings, labels, and attached materials.


and regulations. The existence of salvage and recycling operationswithin an industry definitely affects the quantities of wastes collected.Whether such operations affect the quantities generated is anothermatter. The subsection “Pollution Prevention” by Louis Theodorepoints out actions taken by industrial plants as a result of the 1990 Pol-lution Prevention Act. Significant reductions in the quantities of solidwastes generated will occur when and if companies are willing tochange—of their own volition—to conserve natural resources, to han-dle waste at its source rather than use “end-of-pipe” pollution control,and to reduce the economic burdens associated with the managementof solid wastes. Perhaps the most important factor affecting the gener-ation of certain types of waste is the existence of local, state, and fed-eral regulations concerning the use and disposal of specific material. Ingeneral, the more regulated the waste, the higher the cost for treat-ment and disposal and the greater the incentive to reduce generationof the waste.

In 2001, U.S. residents, businesses, and institutions producedmore than 229 million tons of MSW, which is approximately 4.4 lb of

waste per person per day, up from 2.7 lb per person per day in 1960.Several waste management practices, such as source reduction,recycling, and composting, prevent or divert materials from thewaste stream. Source reduction involves altering the design, manu-facture, or use of products and materials to reduce the amount andtoxicity of what gets thrown away. A portion of each material cate-gory was recycled or composted in 2001. The highest rates of recov-ery were achieved with yard trimmings, paper products, and metalproducts. About 57 percent (5.8 million tons) of yard trimmingswere recovered for composting in 2001. This represents a 4-foldincrease from 1990. About 45 percent (36.7 million tons) of paperand paperboard was recovered for recycling in 2001. Recyclingthese organic materials alone diverted nearly 23 percent of MSWfrom landfills and combustion facilities. In addition, about 6.3 mil-lion tons, or about 35 percent, of metals were recovered for recy-cling. See Figs. 22-47 and 22-48.

EPA has ranked the most environmentally sound strategies forMSW. Source reduction (including reuse) is the most preferred

TABLE 22-58 Typical Ultimate-Analysis Data for Components in Domestic, Commercial, and Industrial Solid Waste*

Percent by mass (dry basis)

Components Carbon Hydrogen Oxygen Nitrogen Sulfur Ash

Foods and food productsFats 73.0 11.5 14.8 0.4 0.1 0.2Food wastes (mixed) 48.0 6.4 37.6 2.6 0.4 5.0Fruit wastes 48.5 6.2 39.5 1.4 0.2 4.2Meat wastes 59.6 9.4 24.7 1.2 0.2 4.9

Paper products 45.4 6.1 42.1 0.3 0.1 6.0Cardboard 43.0 5.9 44.8 0.3 0.2 5.0Magazines 32.9 5.0 38.6 0.1 0.1 23.3Newsprint 49.1 6.1 43.0 < 0.1 0.2 23.3Paper (mixed) 43.4 5.8 44.3 0.3 0.2 6.0Waxed cartons 59.2 9.3 30.1 0.1 .1 1.2

PlasticsPlastics (mixed) 60.0 7.2 22.8 — — 10.0Polyethylene 85.2 14.2 — < 0.1 < 0.1 0.4Polystyrene 87.1 8.4 4.0 0.2 — 0.3Polyurethane† 63.3 6.3 17.6 6.0 < 0.1 4.3Polyvinyl chloride‡ 45.2 5.6 1.6 0.1 0.1 2.0

Wood, trees, etc.Garden trimmings 46.0 6.0 38.0 3.4 0.3 6.3Green timber 50.1 6.4 42.3 0.1 0.1 1.0Hardwood 49.6 6.1 43.2 0.1 < 0.1 0.9Wood (mixed) 49.5 6.0 42.7 0.2 < 0.1 1.5Wood chips (mixed) 48.1 5.8 45.5 0.1 < 0.1 0.4

Glass, metals, etc.Glass and mineral 0.5 0.1 0.4 < 0.1 — 98.9Metals (mixed) 4.5 0.6 4.3 < 0.1 — 90.5

Leather, rubber, textilesLeather (mixed) 60.0 8.0 11.6 10.0 0.4 10.0Rubber (mixed) 69.7 8.7 — — 1.6 20.0Textiles (mixed) 48.0 6.4 40.0 2.2 0.2 3.2

MiscellaneousOffice sweepings 24.3 3.0 4.0 0.5 0.2 68.0Oils, paints 66.9 9.6 5.2 2.0 — 16.3

Refuse-derived fuel (RAF) 44.7 6.2 38.4 0.7 < 0.1 9.9

*Adapted in part from D. G. Wilson (ed.), Handbook of Solid Waste Management, Van Nostrand Reinhold, New York, 1977, and G. Tchobanou-glous, H. Theissen, and R. Eliassen, Solid Wastes Engineering Principles and Management Issues, McGraw-Hill, New York, 1977.

†Organic content is from coatings, labels and other attached materials.‡Remainder is chlorine.

TABLE 22-59 Unit Solid-Waste Generation Rates for Selected Industrial Sources

Source Unit Range

Canned and frozen foods Metric tons/metric tons of raw product 0.04–0.06Printing and publishing Metric tons/metric tons of raw paper 0.08–0.10Automotive Metric tons/vehicle produced 0.6–0.8Petroleum refining Metric tons/(employee day) 0.04–0.05Rubber Metric tons/metric tons of raw rubber 0.01–0.3

method, followed by recycling and composting, and, lastly, disposal inMWCs and landfills. Currently, in the United States, 30 percent isrecovered and recycled or composted, 15 percent is burned at com-bustion facilities (MWCs and WTEs), and the remaining 56 percent isdisposed of in landfills. See Fig. 22-49.

Source reduction can be a successful method of reducing wastegeneration. Practices such as grass recycling, backyard composting,two-sided copying of paper, and transport packaging reduction byindustry have yielded substantial benefits through source reduction.Source reduction has many environmental benefits. It prevents emis-sions of many greenhouse gases, reduces pollutants, saves energy, con-serves resources, and reduces the need for new landfills and MWCs.Table 22-60 shows the total source reduction between 1992 and 2000in millions of tons. Note the rapid rise in the first 4 years from 0.6 mil-lion to 31.0 million tons. From 1996 to 2000, a period of 4 years, areduction of 77 percent has continued. The materials that made upthese reductions are noted in Table 22-61.

Recycling, including composting, diverted 68 million tons of mate-rial away from landfills and MWCs in 2001, up from 34 million tons in1990. See Fig. 22-50.

ON-SITE HANDLING, STORAGE, AND PROCESSING

The handling, storage, and processing of solid wastes at the sourcebefore they are collected are the second element of the six functionalelements in the solid-waste-management system.


FIG. 22-47 2001 total MSW generation—229 million tons.

250 mil tons

200 mil tons

150 mil tons

100 mil tons

50 mil tons1960 1970 1980 1990 2001

5 lb229.2

205.2

4.5

3.7

3.3

2.7

4.4

151.6

121.1

88.1

4 lb

3 lb

2 lb

Per capita generation (lb/person/day)

Total waste generation (mil tons)

FIG. 22-48 Trends in MSW generation, 1960–2001.


On-Site Handling On-site handling refers to the activities asso-ciated with the handling of solid wastes until they are placed in thecontainers used for storage before collection. Depending on the typeof collection service, handling may also be required to move loadedcontainers to the collection point and to return the empty containersto the point where they are stored between collections.

Conventional Solid Wastes In most office, commercial, andindustrial buildings, solid wastes that accumulate in individual officesor work locations usually are collected in relatively large containersmounted on casters. Once filled, these containers are removed bymeans of the service elevator, if there is one, and emptied into (1)large storage containers, (2) compactors used in conjunction with thestorage containers, (3) stationary compactors that can compress thematerial into bales or into specially designed containers, or (4) otherprocessing equipment.

Hazardous Wastes When hazardous wastes are generated, spe-cial containers are usually provided, and trained personnel (OSHA

1910.120 required such workers to have HAZWOPER training) areresponsible for the handling of these wastes. Hazardous wastes includesolids, sludges, and liquids; hence, container requirements vary withthe form of waste.

On-Site Storage Factors that must be considered in the on-sitestorage of solid wastes include (1) the type of container to be used, (2)the container location, (3) public health and aesthetics, (4) the collec-tion methods to be used, and (5) future transport method.

Containers To a large extent, the types and capacities of the con-tainers used depend on the characteristics of the solid wastes to becollected, the collection frequency, and the space available for theplacement of containers.

1. Containers for conventional wastes. The types and capacitiesof containers now commonly used for on-site storage of solid wastesare summarized in Table 22-62. The small containers are used in indi-vidual offices and workstations. The medium-size and large containersare used at locations where large volumes are generated.

2. Containers for hazardous wastes. On-site storage practices area function of the types and amounts of hazardous wastes generatedand the time period over which waste generation occurs. Usually,when large quantities are generated, special facilities are used thathave sufficient capacity to hold wastes accumulated over a period of

FIG. 22-49 Management of MSW in the United States, 2001.

80 mill

70 mill

60 mill

50 mill

40 mill

30 mill

20 mill

10 mill

0 mill1960 1970 1980 1990 2001

5%

10%

15%

20%

25%

30%

35%

68.029.7%

16.2%

9.6%6.6%6.4%

33.2

14.58.05.6

Total waste recycling (millions/year)Percent recycling

FIG. 22-50 Waste recycling rates, 1960–2001.

TABLE 22-60 Source Reduction of Municipal Solid Waste since1990

Million tons ofYear source reduced

1992 0.61994 8.01995 21.41996 31.01997 31.81998 37.31999 42.82000 55.1

TABLE 22-61 Source Reduction by Major Material Categories,2000

Million tons ofWaste stream source reduced

Durable goods (e.g., appliances, furniture) 5.4Nondurable goods (e.g., newspapers, clothing) 9.3Containers and packaging (e.g., bottles, boxes) 15.5Other MSW (e.g., yard trimmings, food scraps) 25.0

Total source reduction (1990 baseline) 55.1

several days. When only small amounts of hazardous wastes are gen-erated on an intermittent basis, they may be containerized, and lim-ited quantities may be stored for periods covering months or years.General information on the storage containers used for hazardouswastes and the conditions of their use is presented in Table 22-63.

Container Location The location of containers at existing com-mercial and industrial facilities depends on both the location of avail-able space and service-access conditions. In newer facilities, specificservice areas have been included for this purpose. Often, because thecontainers are not owned by the commercial or industrial activity, thelocations and types of containers to be used for on-site storage mustbe worked out jointly between the industry and the public or privatecollection agency.

On-Site Processing of Solid Wastes On-site processing methodsare used to (1) recover usable materials from solid wastes, (2) reducethe volume, or (3) alter the physical form. The most common on-siteprocessing operations as applied to large commercial and industrialsources include manual sorting, compaction, and incineration. Theseand other processing operations are considered in the portion of thissubsection dealing with processing and resource recovery. Factors thatshould be considered in the selection of on-site processing equipmentare summarized in Table 22-64.

PROCESSING AND RESOURCE RECOVERY

The purpose of this subsection is to introduce the reader to the tech-niques and methods used to recover materials, conversion products,

and energy from solid wastes. Topics to be considered include (1) pro-cessing techniques for solid waste, (2) processing techniques for haz-ardous wastes, (3) materials-recovery systems, (4) recovery ofbiological conversion products, (5) thermal processes, and (6) waste-to-energy systems.

Because so many of the techniques, especially those associated withthe recovery of materials and energy and the processing of solid haz-ardous wastes, are in a state of flux with respect to application anddesign criteria, the objective here is only to introduce them to thereader. If these techniques are to be considered in the development ofwaste-management systems, current engineering design and perfor-mance data must be obtained from consultants, operating records,field tests, equipment manufacturers, and available literature.

Processing Techniques for Solid Waste Processing techniquesused in solid-waste-management systems (1) improve the efficiency ofthe systems, (2) recover resources (usable materials), and (3) preparematerials for recovery of conversion products and energy. The moreimportant techniques used for processing solid wastes are summa-rized below:• Manual component separation. The manual separation of solid-

waste components can be accomplished at the source where solidwastes are generated, at a transfer station, at a centralized processingstation, or at the disposal site. Manual sorting at the source of gener-ation is the most positive way to achieve the recovery and reuse ofmaterials. The number and types of components salvaged or sorted(e.g., cardboard and high-quality paper, metals, and wood) dependon the location, the opportunities for recycling, and the resale market.


TABLE 22-62 Data on the Types and Sizes of Containers Used for On-Site Storage of Solid Wastes

Capacity Dimensions*

Container type Unit Range Typical Unit Typical

Small-capacityPlastic or metal (office type) L 16–40 28 mm (180 × 300)B × (260 × 380)T × 380HPlastic or galvanized metal L 75–150 120 mm 510D × 660HBarrel, plastic, aluminum, or fiber barrel L 20–250 120 mm 510D × 660HDisposable paper bags (standard, leak-resistant, and L 75–210 120 mm 380W × 380d × 1100H

leakproof)Disposal plastic bag L 20–200 170 mm 460W × 380d × 1000H

Medium-capacitySide or top loading m3 0.75–9 3 mm 1830W × 1070d × 1650HBulk bags m3 0.3–2 1 mm 1000W × 1000d × 1000H

Large-capacityOpen top, rolloff (also called debris bags) m3 9–38 27 mm 2440W × 1830H × 6100LUsed with stationary compactor m3 15–30 23 mm 2440W × 1830H × 5490LEquipped with self-contained compaction mechanism m3 15–30 23 mm 2440W × 2440H × 6710LTrailer-mounted

Open top m3 15–38 27 mm 2440W × 3660H × 6100LEnclosed, equipped with self-contained compaction m3 15–30 27 mm 2440W × 3660H × 7320Lmechanism

*B = bottom, T = top, D = diameter, H = height, W = width, L = length, and d = depth.

TABLE 22-63 Typical Data on Containers Used for Storage and Transport of Hazardous Waste

Container

Waste category Type Capacity Auxiliary equipment and conditions of use

Radioactive substances Lead encased in concrete Varies with waste Isolated storage buildings; high-capacity hoists and lighting Lined metal drums 210 L equipment; special container markings

Corrosive, reactive, and toxic chemicals Metal drums 210 L Washing facilities for empty containers, special blending Plastic drums 210 L, up to 500 L precautions to prevent hazardous reactions; incompatible Lined metal drums 210 L wastes stored separatelyLined and unlined storage tanks Up to 20 m3

Liquids and sludges Drums 142–3400 L Drums, hand-trucks, pallets, forkliftsTrucks 11–30 m3 Transfer piping, hoses, pumpsVacuum tankers 11–15 m3 Transfer piping, hoses, pumps

Biological wastes Sealed plastic bags 120 L Heat sterilization prior to bagging; special heavy-duty Lined boxes, lined metal drums 57 L bags with hazard warning printed on sides

Flammable wastes Metal drums 210 L Fume ventilation, temperature controlStorage tanks Up to 20 m3

Explosives Shock-absorbing containers Varies Temperature control; special container markings


tion of solid-waste-management systems. Vehicles equipped withcompaction mechanisms are used for the collection of most indus-trial solid wastes. To increase the useful life of landfills, wastes arecompacted there also via mobile compaction equipment. Paper forrecycling is baled for shipping to processing centers. When com-pacting industrial solid wastes, it has been found that the final den-sity (typically about 1100 kg/m3) is essentially the same regardless ofthe starting density and applied pressure. This fact is important inevaluating manufacturer’s claims.

• Chemical volume reduction. Incineration has been the methodcommonly used to reduce the volume of wastes chemically. One ofthe most attractive features of the incineration process is that it canbe used to reduce the original volume of combustible solid wastesby 80 to 90 percent. The technology of incineration has advancedwith many mass burn facilities now having two or more combustorswith capacities of 1000 tons/day of refuse per unit. However, regu-lations limiting low volatile and semivolatile metals, acid gases, freechlorine and hydrogen chloride, unburned hydrocarbons, polychlo-rinated dioxin and furan (PCDD/PCDF) emissions have resulted inhigher costs and operating complexity.

• Mechanical size alteration. The objective of size reduction is toobtain a final product that is reasonably uniform and considerablyreduced in size in comparison to its original form. It is important tonote that size reduction does not necessarily imply volume reduc-tion. In some situations, the total volume of the material after sizereduction may be greater than the original volume. Shredding ismost often used for size reduction. Two-stage (coarse, fine) low-speed shredders and a single-stage shredder with screen and recy-cle of oversize are the most common systems. The gain in ease ofmaterials handling must be weighed against the substantial operat-ing costs for shredding equipment. A substantial market for thetechnology lies in shredding tires to produce fuel for cement kilnsand utility boilers. With finer shredding, the product can be used tomake thick resilient mats for play areas or for inclusion in asphaltpavement.

• Mechanical component separation. Component separation is anecessary operation in the recovery of resources from solid wastesand in instances when energy and conversion products are to berecovered from process wastes.

• Magnetic and electromechanical separation. Magnetic separationof ferrous materials is a well-established technique. More recently,a variety of electromechanical techniques have been developed forthe removal of several nonferrous materials.

• Drying and dewatering. In many solid-waste energy-recovery andincineration systems, the shredded light fraction is predried todecrease weight. Although energy requirements for drying wastesvary with the application, the required energy input can be estab-lished by using a value of about 4300 kJ/kg of water evaporated.Drying can frequently increase waste throughput in many treat-ment systems. For incinerators, it produces more stable combus-tion and better ash quality.

• Bulking of liquid wastes. Liquid wastes are prohibited from land-fills. Wastes with free liquids are mixed with a bulking agent such asdry sawdust, cement kiln dust, or fly ash.Processing of Hazardous Waste As with conventional solid

wastes, the processing of hazardous wastes is undertaken for threepurposes: (1) to recover useful materials, (2) to reduce the amount ofwastes that must be disposed in landfills, and (3) to prepare the wastesfor ultimate disposal.

Processing Techniques The processing of hazardous wastes on abatch basis can be accomplished by physical, chemical, thermal, andbiological means. The various individual processes in each categoryare reported in Table 22-65. Clearly, the number of possible treat-ment-process combinations is staggering. In practice, the physical,chemical, and thermal treatment operations and processes are theones most commonly used.

Identification of Waste Constituents In any processing (anddisposal) scheme, the key item is knowledge of the characteristics ofthe waste being handled. Without this information, effective process-ing or treatment is impossible. For this reason, the characteristics ofthe wastes must be known before they are accepted and hauled to a

TABLE 22-64 Factors That Should Be Considered in EvaluatingOn-Site Processing Equipment

Factor Evaluation

Capabilities What will the device or mechanism do? Will its use be an improvement over conventional practices?

Reliability Will the equipment perform its designated functions with little attention beyond preventivemaintenance? Has the effectiveness of the equip-ment been demonstrated in use over a reasonableperiod of time or merely predicted?

Service Will servicing capabilities beyond those of the local building maintenance staff be required occasion-ally? Are properly trained service personnel avail-able through the equipment manufacturer or thelocal distributor?

Safety of operation Is the proposed equipment reasonably foolproof so that it may be operated by tenants or buildingpersonnel with limited mechanical knowledge orabilities? Does it have adequate safeguards to dis-courage careless use?

Ease of operation Is the equipment easy to operate by a tenant or building personnel? Unless functions and actualoperations of equipment can be carried out easily,they may be ignored or bypassed by paid person-nel and most often by “paying” tenants.

Efficiency Does the equipment perform efficiently and with a minimum of attention? Under most conditions,equipment that completes an operational cycleeach time that it is used should be selected.

Environmental effects Does the equipment pollute or contaminate the environment? When possible, equipment shouldreduce environmental pollution presently associ-ated with conventional functions.

Health hazards Does the device, mechanism, or equipment create or amplify health hazards?

Aesthetics Do the equipment and its arrangement offend the senses? Every effort should be made to reduce oreliminate offending sights, odors, and noises.

Economics What are the economics involved? Both first and annual costs must be considered. Future opera-tion and maintenance costs must be assessed care-fully. All factors being equal, equipment producedby well-established companies, having a provenhistory of satisfactory operations should be givenappropriate consideration.

Flexibility Will the equipment or its placement allow future changes to the process to handle wastes with dif-fering characteristics?

*From G. Tchobanouglous, H. Theissen, and R. Eliassen, Solid Wastes: Engi-neering Principles and Management Issues, McGraw-Hill, New York, 1977.

There has been an evolution in the solid-waste industry to combinemanual and automatic separation techniques to reduce overall costsand produce a cleaner product, especially for recyclable materials.Component separation is the heart of recycling, and it is required toraise the concentration of the material to the point that it is worthreclaiming, and reduce the amount of tramp materials to meet spec-ifications. Recycling occurs on a major scale, and for MSW, itaccounted for 30 percent of the waste stream in 2001.

• Storage and transfer. When solid wastes are to be processed formaterial recovery, storage and transfer facilities should be consid-ered an essential part of the processing operation. Important factorsin the design of such facilities include (1) the size of the materialbefore and after processing, (2) the density of the material, (3) theangle of repose before and after processing, (4) the abrasive char-acteristics of the materials, and (5) the moisture content.

• Mechanical volume reduction. Mechanical volume reduction isperhaps the most important factor in the development and opera-

treatment or disposal site. In most states, proper identification of theconstituents of the waste is the responsibility of the waste generator.

Materials-Recovery Systems Paper, rubber, plastics, textiles,glass, metals, and organic and inorganic materials are the principalrecoverable materials contained in industrial solid wastes.

Once a decision has been made to recover materials and/or energy,process flow sheets must be developed for the removal of the desiredcomponents, subject to predetermined materials specifications. A typ-ical flow sheet for the recovery of specific components and the prepa-ration of combustible materials for use as a fuel source is presented inFig. 22-51. The light combustible materials are often identified asrefuse-derived fuel (RDF).

The design and layout of the physical facilities that make up the pro-cessing-plant flow sheet are an important aspect in the implementationand successful operation of such systems. Important factors that must beconsidered in the design and layout of such systems include (1) processperformance efficiency, (2) reliability and flexibility, (3) ease and econ-omy of operation, (4) aesthetics, and (5) environmental controls.

Recovery of Biological Conversion Products Biological con-version products that can be derived from wastes include alcohols anda variety of other intermediate organic compounds. The principalprocesses that have been used are reported in Table 22-68. Compost-ing and anaerobic digestion, the two most highly developed processes,are considered further. The recovery of gas from landfills is discussedin the portion of this subsection dealing with ultimate disposal.

Composting If the organic materials, excluding plastics, rubber,and leather, are separated from municipal solid wastes and subjectedto bacterial decomposition, the end product remaining after dissimila-tory and assimilatory bacterial activity is called compost or humus. Theentire process involving both separation and bacterial conversion ofthe organic solid wastes is known as composting. Decomposition ofthe organic solid wastes may be accomplished either aerobically oranaerobically, depending on the availability of oxygen.

Most composting operations involve three basic steps—(1) prepa-ration of solid wastes, (2) decomposition of the solid wastes, and (3)size reduction—and moisture and nutrient addition are part of thepreparation step. Several techniques have been developed to accom-plish the decomposition step. Once the solid wastes have been con-

verted to a humus, they are ready for the third step of product prepa-ration and marketing. This step may include fine grinding, blendingwith various additives, granulation, bagging, storage, shipping, and, insome cases, direct marketing. The principal design considerationsassociated with the biological decomposition of prepared solid wastesare presented in Table 22-66.

Anaerobic Digestion Anaerobic digestion or anaerobic fermen-tation, as it is often called, is the process used for the production ofmethane from solid wastes. In most processes in which methane is tobe produced from solid wastes by anaerobic digestion, three basicsteps are involved. The first step involves preparation of the organicfraction of the solid wastes for anaerobic digestion and usuallyincludes receiving, sorting, separation, and size reduction. The secondstep involves the addition of moisture and nutrients, blending, pHadjustment to about 6.7, heating of the slurry to between 327 and 333K (130 and 140°F), and anaerobic digestion in a reactor with continu-ous flow, in which the contents are well mixed for a time varying from8 to 15 days. The third step involves capture, storage, and, if necessary,separation of the gas components evolved during the digestionprocess. The fourth step is the disposal of the digested sludge, an addi-tional task that must be accomplished. Some important design consid-erations are reported in Table 22-67. Because of the variability of theresults reported in the literature, it is recommended that pilot-plantstudies be conducted if the digestion process is to be used for the con-version of solid wastes.

Thermal Processes Conversion products that can be derivedfrom solid wastes include heat, gases, a variety of oils, and variousrelated organic compounds. The principal thermal processes that havebeen used for the recovery of usable conversion products from solidwastes are reported in Table 22-65.

Incineration with Heat Recovery Heat contained in the gasesproduced from the incineration of solid wastes can be recovered assteam. The low-level heat remaining in the gases after heat recoverycan also be used to preheat the combustion air, boiler makeup water,or solid-waste fuel.

1. In existing incinerators. With existing incinerators, waste-heatboilers can be installed to extract heat from the combustion gaseswithout introducing excess amounts of air or moisture. Typically,


TABLE 22-65 Biological and Thermal Processes Used for Recovery of Conversion Products from Solid Waste

Process Conversion product Preprocessing required Comments

BiologicalComposting Humuslike material Shredding, air separation Lack of markets a primary shortcoming;

technically proved in full-scale application

Anaerobic digestion Methane gas Shredding, air separation Technology on laboratory scale onlyBiological conversion to Protein, alcohol Shredding, air separation Technology on pilot scale onlyprotein

Biological fermentation Glucose, furfural Shredding, air separation Used in conjunction with the hydrolyticprocess

ThermalIncineration with heat recovery Energy in the form of steam None Markets for steam required; proved in

numerous full-scale applications;air-quality regulations possibly prohibiting use

Thermal desorption Clean soil used for fill or Sizing, blending, dilution In routine use for Superfund organicreclaimed raw materials such as contaminated soildeoiled metal turnings

Supplementary fuel firing in boilers Energy in the form of steam Shredding, air separation, If at least capital investment desired,magnetic separation existing air-quality regulations possibly

prohibiting useGasification Energy in the form of low-energy gas Shredding, air separation, Gasification also capable of being used

magnetic separation for codisposal for industrial sludgesPyrolysis Energy in the form of gas or oil Shredding, magnetic Technology proved only in pilot

and char separation applications but full-scale use has rarely succeeded due to high operating costs and lack of materials for gas, oil, and char only.

Hydrolysis Glucose, furfural Shredding, air separation Technology on pilot scale onlyChemical conversion Oil, gas, cellulose acetate Shredding, air separation Technology on pilot scale only

FIG. 22-51 Typical flow sheet for the recovery of materials and production of refuse-derived fuels (RDF). [Adapted in part from D. C. Wilson (ed.), Waste Management: Planning, Evaluation, Technologies, OxfordUniversity Press, Oxford, 1981.]

22

-93

incinerator gases will be cooled from a range of 1250 to 1375 K (1800to 2000°F) to a range of 500 to 800 K (600 to 1000°F) before beingdischarged to the air-pollution-control system. Apart from the pro-duction of steam, the use of a boiler system is beneficial in reducingthe volume of gas to be processed in the air-pollution-control equip-ment. The compounds in the waste stream will generate products ofcombustion and ash that may create serious corrosion and foulingproblems in waste-heat boilers (WHBs). WHBs also tend to generatedioxins and furans when particulates, combined with free chlorine andother dioxin/furan precursors, attach to the tubes at proper reforma-tion temperatures and time to cause the reformation of D/Fs.

2. In water-wall incinerators. The internal walls of the combus-tion chamber are lined with boiler tubes that are arranged verticallyand welded together in continuous sections. When water walls areemployed in place of refractory materials, they are not only useful forthe recovery of steam but also extremely effective in controlling fur-nace temperature without introducing excess air; however, they aresubject to corrosion by the hydrochloric acid produced from the burn-ing of some plastic compounds and the molten ash containing salts(chlorides and sulfates) that attach to the tubes.

Combustion Combustion of industrial and municipal waste is anattractive waste management option because it reduces the volume ofwaste by 70 to 90 percent. In the face of shrinking landfill availability,municipal waste combustion capacity in the United States has grownat a rate significantly faster than the growth rate for municipal refusegeneration.

Types of Combustors The three main classes of facilities used tocombust municipal refuse are mass-burn, modular, and RDF-fired facil-ities. Mass-burn combustors are field-erected and generally range in size

from 50 to over 1000 tons/day of refuse feed per unit (Fig. 22-52). Mod-ular combustors burn waste with little more preprocessing than do themass-burn units. These range in size from 5 to 100 tons/day. Total U.S.MSW waste-to-energy plants had a design capacity of 98,719 tons/dayper a 2004 survey. There were 72 plants in 2004. In addition to tradi-tional WTE contained in the first two classes, the third major class ofmunicipal waste combustor burns RDF. The types of waste-to-energyboilers used to combust RDF can include suspension, stoker, andfluidized-bed designs. RDF fuels can also be fired directly in large indus-trial and utility boilers that are now used for the production of powerwith pulverized or stoker coal, oil, and gas. Although the process is notwell established with coal, it appears that about 15 to 20 percent of theheat input can be from RDF. With oil as the fuel, about 10 percent of theheat input can be from RDF. Depending on the degree of processing,suspension, spreader-stoker, and double-vortex firing systems have beenused. RDF includes source-separated material, such as whole tires andchipped tires fired in cement kilns and boilers, and wood waste. Com-bustion of this material was estimated to be 2.4 million tons in 2001.

The system shown in Fig. 22-52 is a schematic of the MontenayMontgomery LP located in Plymouth Township, MontgomeryCounty, Pa. The facility specifications are as follows:

Waste throughput: 1200 tons/day ( 2 × 600)Technology: L&C Steinmuller, GmbhSteam output: 324,000 lb/h (2 × 162,000)Steam quality: 650 psig/750°FBoiler mfr.: L&C Steinmuller, GmbhExtraction turbine: 36 MW grossTurbine mfr. General ElectricGenerator: General Electric


TABLE 22-66 Important Design Considerations for Anaerobic Composting Processes*

Item CommentParticle size For optimum results the size of solid waste should be between 25 and 75 mm (1 and 3 in).Seeding and mixing Composting time can be reduced by seeding with partially decomposed solid wastes to the extent of about 1 to 5 percent by weight.

Sewage sludge can also be added to prepared solid wastes. When sludge is added, the final moisture content is the controlling variable.Mixing or turning To prevent drying, caking, and air channeling, material in the process of being composted should be mixed or turned on a regular

schedule or as required. Frequency of mixing or turning will depend on the type of composting operation.Air requirements Air with at least 50 percent of the initial oxygen concentration remaining should reach all parts of the composting material for

optimum results, especially in mechanical systems.Total oxygen requirements The theoretical quantity of oxygen required can be estimated.Moisture content Moisture content should be in the range between 50 and 60 percent during the composting process. The optimum value appears to

be about 55 percent.Temperature For best results, temperature should be maintained between 322 and 327 K (130 and 140°F) for the first few days and between 327

and 333 K (130 and 140°F) for the remainder of the active composting period. If temperature goes beyond 339 K (150°F), biologicalactivity is reduced significantly.

Carbon-nitrogen ratio Initial carbon-nitrogen ratios (by mass) between 35 and 50 are optimum for aerobic composting. At lower ratios ammonia is givenoff. Biological activity is also impeded at lower ratios. At higher ratios nitrogen may be a limiting nutrient.

pH To minimize the loss of nitrogen in the form of ammonia gas, pH should not rise above about 8.5.Control of pathogens If the process is properly conducted, it is possible to kill all the pathogens, weeds, and seeds during the composting process. To do

this, the temperature must be maintained between 333 and 334 K (140 and 160°F) for 24 h.*Adapted from G. Tchobanoglous, H. Theisen, and R. Eliassen, Solid Wastes: Engineering Principles and Management Issues, McGraw-Hill, New York, 1977.

TABLE 22-67 Important Design Considerations for Anaerobic Digestion*

Item CommentSize of material shredded Wastes to be digested should be shredded to a size that will not interfere with the efficient functioning of pumping and mixing

operations.Mixing equipment To achieve optimum results and to avoid scum buildup, mechanical mixing is recommended.Percentage of solid wastes Although amounts of waste varying from 50 to 90+ percent have been used, 60 percent appears to be a reasonable compromise.mixed with sludge

Hydraulic and mean cell residence Washout time is in the range of 3 to 4 days. Use 8 to 15 days for design of base design on results of pilot-plant studies.time, �h �C

Loading rate 0.6 to 1.6 kg/(m3 ⋅day) [0.04 to 0.10 lb/(ft3 ⋅day)]. It is not well defined at present. Significantly higher rates have been reported.Temperature Between 327 and 333 K (130 and 140°F)Destruction of volatile solid wastes Varies from about 60 to 80 percent; 70 percent can be used for estimating purposes.Total solids destroyed Varies from 40 to 60 percent, depending on amount of inert material present originally.Gas production 0.5 to 0.75 m3/kg (8 to 12 ft3/lb) of volatile solids destroyed (CH4 = 60 percent; CO2 = 40 percent)

*From G. Tchobanoglous, H. Theisen, and R. Eliassen, Solid Wastes: Engineering Principles and Management Issues, McGraw-Hill, New York, 1977.NOTE: Actual removal rates for volatile solids may be less, depending on the amount of material diverted to the scum layer.


Dry scrubber: Research-Cottrell (slaked lime)Baghouse: Research-Cottrell (reverse air)CEMs: Environmental elementsDeNOx: Fuel techMercury removal: SorbalineMaterial recovery: Ferrous metals

The construction of the facility began on May 23, 1989, and went into fulloperation on February 17, 1992, on an interim basis upon completion ofthe performance tests. The facility achieved full acceptance on May 23,1994, and began a 20-year service agreement with the Eastern District ofMontgomery County. The plant serves 24 municipalities in the EasternDistrict with a population of 425,000. The processing capacity is 1200tons/day; 377,000 tons/yr with an electrical capacity of 36 MW. The elec-tricity produced is sold to Philadelphia Electric Company (PECO).

See Fig. 22-53, which is typical of most waste-to-energy (WTE)plants burning MSW. Trucks deliver MSW to the scale house of thefacility, where the truck is weighed and identified. At (2), the trucksunload waste into a storage pit in an enclosed tipping hall. The truckfumes and waste odors are drawn into the furnaces by large fans toprovide combustion air and to prevent escape of odors. The waste isinspected in the storage pit (3), prior to feeding the waste into the fur-

nace by large overhead cranes. Waste is burned at high temperatures(over 2000°F) in the furnaces (4). The waste moves through the fur-naces through drying, combustion, and final burnout stages over a 60-min period.

The heat of combustion generates steam in the boiler (5). The steamis used in making electricity in a steam turbine/generator set. Afterproviding the in-plant electrical needs, excess energy is sold to the localelectric utility and/or utilized by nearby process steam industries. Afterthe combustion of the waste, ferrous metals are removed from theremaining residue by screening and magnetic separation (6). Theseferrous metals are then recycled. The remaining residue can be bene-ficially reused or recycled, further reducing reliance on landfilling.

State-of-the-art pollution control equipment (7) removes particu-lates, acid gases, and other air emissions following the waste combus-tion process. Clean Air Act and other environmental standards areachieved through a combination of equipment such as spray dryers,baghouses, and carbon injection systems. Exhaust gases are drawn intoan induced-draft fan which maintains a negative pressure throughoutthe entire system from waste feeding through the pollution controls.This prevents fugitive emissions from the process. These gases are thenpushed into the exhaust stack and into the atmosphere. Stack gas sam-pling is conducted on platforms in the vertical stack section.

Gasification The gasification process involves the partial com-bustion of a carbonaceous or hydrocarbon fuel to generate a com-bustible fuel gas rich in carbon monoxide and hydrogen. A gasifier issimilar to an incinerator operating under reducing conditions. Heat tosustain the process is derived from exothermic reactions, while thecombustible components of the low-energy gas are primarily gener-ated by endothermic reactions. The reaction kinetics of the gasifica-tion process are quite complex and still the subject of considerabledebate.

When a gasifier is at atmospheric pressure with air as the partial oxi-dant, the end products of the gasification process are a low-energy gastypically containing (by volume) 10 percent CO2, 20 percent CO, 15percent H2, and 2 percent CH4, with the balance being N2 and a car-bon-rich ash. Because of the diluting effect of the nitrogen in theinput air, the low-energy gas has an energy content in the range of the5.2 to 6.0 MJ/m3 (140 to 160 Btu/ft3). Dual-bed gasifiers produce a gaswith double this heating value. When pure oxygen is used as the oxi-dant, a medium-energy gas with an energy content in the range of 12.9to 13.8 MJ/m3 (345 to 370 Btu/ft3) is produced. Gasifiers were in wide-spread use on coal and wood until natural gas displaced them in the1930s through the 1950s. Some large coal gasifiers are in use today inthe United States and worldwide. While the process can work on solidwaste, incinerators (which gasify and burn in one chamber) arefavored over gasifiers.

FIG. 22-52 1200-tons/day MSW plant of Montenay Montgomery.

FIG. 22-53 1200-tons/day MSW plant schematic.

Pyrolysis Of the main alternative chemical conversion processesthat have been investigated, pyrolysis has received the most attention.Pyrolysis has been tested in countless pilot plants, and many full-scaledemonstration systems have operated. Few attained any long-termcommercial use. Major issues were lack of market for the unstable andacidic pyrolytic oils and the char and high operating costs.

Depending on the type of reactor used, the physical form of solidwastes to be pyrolyzed can vary from unshredded raw wastes to thefinely ground portion of the wastes remaining after two stages of shred-ding and air classification. Upon heating in an oxygen-free atmosphere,most organic substances can be split via thermal cracking and conden-sation reactions into gaseous, liquid, and solid fractions. Pyrolysis is theterm used to describe the process while the term destructive distilla-tion is also often used. In contrast to the combustion process, which ishighly exothermic, the pyrolytic process involves both highly endother-mic and exothermic reactions. For this reason, the term destructivedistillation is often used as an alternative for pyrolysis.

The characteristics of the three major component fractions result-ing from the pyrolysis are (1) a gas stream containing primarily hydro-gen, methane, carbon monoxide, reduced sulfur compounds, carbondisulfide, and various other gases, depending on the organic charac-teristics of the material being pyrolyzed; (2) a fraction that consists ofa tar and/or oil stream that is liquid at room temperature and has beenfound to contain hundreds of chemicals such as acetic acid, acetone,methanol, and phenols; and (3) a char consisting of almost pure car-bon plus any inert material that may have entered the process. It hasbeen found that distribution of the product fractions varies with thetemperature at which the pyrolysis is carried out. Under conditions ofmaximum gasification, the energy content of pyrolytic oils has beenestimated to be about 23.2 MJ/kg (10,000 Btu/lb).

Waste-to-Energy Systems The preceding subsection ended atthe production of steam. WTE systems take over at this point, usinghigh-pressure/high-temperature steam to drive turbines and produceshaft horsepower for prime movers at industrial plants or to generateelectricity.

This fuel may be solid or gas or oil or fuels from a gasifier or pyrol-ysis system.

Typical flow sheets for alternative energy-recovery systems areshown in Fig. 22-54. Perhaps the most common flow sheet for theproduction of electric energy involves the use of a steam turbine–generator combination. As shown, when solid wastes are used as thebasic fuel source, four operating modes are possible. A flow sheetusing a gas turbine–generator combination is shown in Fig. 22-54.The low-energy gas is compressed under high pressure so that it canbe used more effectively in the gas turbine. Use of low- or medium-Btu gas for gas turbines has been attempted, and success requiresgood design and operation of gas cleaning equipment prior to intro-duction into the combustor of the gas turbine.

Efficiency Factors Representative efficiency data for boilers,pyrolytic reactors, gas turbines, steam turbine–generator combina-tions, electric generators, and related plant use and loss factors aregiven in Table 22-68. In any installation in which energy is being pro-duced, allowance must be made for the power needs of that station orprocess and for unaccounted-for process-heat losses. Typically, theauxiliary power allowance varies from 4 to 8 percent of the power pro-duced. Process-heat losses usually will vary from 2 to 8 percent. Ingeneral, steam pressures of 600 psig and temperatures of 650°F areconsidered minimum for economical power generation. Industrialplants may choose a cogeneration topping cycle, with steam exhaustfrom the turbine at the plant’s process steam pressure, typically in the125 to 250 psig range. For commercial WTE plants, condensing tur-bines are the norm.

Determination of Energy Output and Efficiency for Energy-Recovery Systems An analysis of the amount of energy producedfrom a solid-waste energy conversion system using an incineratorboiler system turbine electric generator combination with a capac-ity of 1000 t/day of waste is presented in Table 22-69. If it isassumed that 10 percent of the power generated is used for thefront-end processing system (typical values vary from 8 to 14 per-cent), then the net power for export is 24,604 kW and the overallefficiency is 17.4 percent.

Concentration of WTE Incinerators The total number ofmunicipal waste incinerator facilities as listed in the Solid WasteDigest, vol. 14, no. 6, June 2004 (a publication of Chartwell Informa-tion, EBI, Inc., of San Diego, Calif.), is 72. This is an increase of 10facilities since September 1994 (a 10-year period). See Table 22-70.The wastes burned in these facilities total 8.96 percent of total munic-ipal wastes managed in landfills, incinerators, and transfer stations.This amounts to 98,719 tons/day of combusted municipal waste. Thisalso is an increase of 10,248 tons over the 88,471 tons in September1994, an average of 1000 tons/yr.

One notes that the heavily populated areas of the country also havethe highest number of WTE facilities as well as the highest intake ofmunicipal waste into incinerators. This is also due to the lack of low-cost land and open space for landfills compared to the midwest andwestern states. The amount of waste combusted in the northeasternstates is 25.6 percent of the total generated compared to 8.96 percentof all municipal wastes combusted nationwide. The WTE cost per tonaverages $62 in the northeastern states compared to $59 for thenation. Incinerator costs are similar to landfill costs in the northeast-ern states. However, landfill costs are far lower than WTE tippingfees across the nation. For example, in states such as Idaho (landfillcosts, $18.80/ton) and Texas (landfill costs $21.03/ton), WTE inciner-ator plants cannot compete at this time. However, it is interesting tonote that the landfill costs have doubled in 10 years while WTE tip-ping fees have dropped about 10 percent. The stricter regulationsapplied to landfills have caused this increase in landfill tipping fees.The NIMBY (Not In My Back Yard) syndrome concerning incinera-tion systems has also hurt the siting and permitting of many of thesefacilities. Figure 22-55 shows the range of costs for all solid-wastemanagement in June 2004. The national index was $39.49/ton in2004, up from $37.93/ton in 1994. This is an average increase of only0.1 percent per year, which is well below the inflation rate for this 10-year period.

REGULATIONS APPLICABLE TO MUNICIPAL WASTE COMBUSTORS

New Source Performance Standards (NSPS) were promulgatedunder Sections 111(b) and 129 of the CAA Amendments of 1990. TheNSPS applies to new municipal solid-waste combustors (MWCs) withcapacity to combust more than 250 tons/day of municipal solid wastethat commenced construction after September 20, 1994. The pro-posed standards and guidelines were published in the Federal Regis-ter on September 20, 1994. They are listed in Title 40, Protection ofthe Environment, Chapter 1, Part 60 Standards of Performance forNew Stationary Sources (http://a257.g.akamaitech.net/7/25/23422/14mar20010800/edocket.access.gpo.gov/cfr2001). Section 129 of theCAAA of 1990 applies to a range of solid-waste incinerators includingMWCs, medical waste incinerators (MWIs), and industrial wasteincinerators. On June 28, 2004, the Federal Register (vol. 69, no. 123)established that Section 129(a)(5) of the CAA requires EPA to review,and if necessary revise, those standards every 5 years. This rulemakingaddresses those requirements and is the first 5-year review of theMACT standards. Implementation of these MACT standards hasbeen highly effective and has reduced dioxin/furan emissions by morethan 99 percent since 1990. Similar reductions have occurred forother CAA Section 129 pollutants. Incinerators for hazardous solidand liquid wastes are covered under RCRA and MACT regulations(40 CFR Parts 260 through 272) and TSCA, Toxic Substances ControlAct, 1976 (40 CFR Parts 700 through 766).

Regulated Pollutants The NSPS regulates MWC emissions andnitrogen oxides (NOx) emissions from individual MWC units largerthan 250 tons/day capacity. MWC emissions are subcategorized asMWC metal emissions, MWC organic emissions, and MWC acid gasemissions. The NSPS establishes emission limits for organic emissions(measured as dioxins and furans), MWC metal emissions (measuredas particulate matter PM, opacity, cadmium, lead, and mercury), andMWC acid gas emissions as sulfur dioxide SO2 and hydrogen chlorideHCl, as well as NOx emission limits.


http://a257.g.akamaitech.net/7/25/23422/14mar20010800/edocket.access.gpo.gov/cfr2001

http://a257.g.akamaitech.net/7/25/23422/14mar20010800/edocket.access.gpo.gov/cfr2001

FIG. 22-54 Flow sheet—alternative energy recovery systems.22

-97

MWCs Organic Emissions The NSPS limits organic emissionsto a total dioxin plus furan emission mass limit of 13 ng/scfm (at 7 percentO2 dry volume). This level is approximately equivalent to a toxic equiv-alent (TEQ) of 2.0 ng/dscm, using the 1990 international toxic equiv-alency factor (I-TEF) approach.

MWCs Metal Emissions The NSPS includes a PM emissionlimit of 0.015 grain per dry standard cubic feet (gr/dscf) at 7 percentoxygen dry/volume and an opacity limit of 10 percent (6-min average).Cadmium is limited to 0.020 ng/dnm3 and lead to 0.3 ng/dnm3, all at7 percent O2 dry volume.

MWCs Acid Gas Emissions The NSPS requires a 95 percentreduction of HCl emissions and an 80 percent reduction of SO2 emis-sions for new MWCs or an emission limit of 25 ppmv for HCl and 30ppmv for SO2 (at 7 percent O2 dry volume).

Nitrogen Oxides Emissions The NSPS limits NOx emission to150 ppmv (at 7 percent O2 dry volume).

MWC Air-Pollution-Control Systems MWCs generate flue gasthat contains particulates, acid gases, and trace amounts of organicand volatile metals. Particulates have traditionally been removed byuse of cyclone separators, baghouses, and electrostatic precipitators.Acid gases require neutralization and removal from the gas stream.This can be accomplished by adding reagents or chemicals to the gasstream and removing products of the chemical reaction when thesematerials are mixed together. Two major types of APCs are employedfor PM, metals and acid gas removal:• Dry systems, where the gas stream is humidified and chemicals

(lime, sodium hydroxide, or carbonate and activated carbon) areadded to the system

• Wet systems, where large quantities of water-containing chemicals

(lime, sodium hydroxide or carbonates, activated carbon) wash thegas stream

MWC facilities are required to meet some of the toughest environ-mental air emissions standards in the country. Complying with thesestandards makes modern waste combustors among the cleanest pro-ducers of electricity—and may even provide a means of improving acommunity’s overall air quality.

ULTIMATE DISPOSAL

Disposal on or in the earth’s mantle is, at present, the only viablemethod for the long-term handling of (1) solid wastes that are col-lected and are of no further use, (2) the residual matter remainingafter solid wastes have been processed, and (3) the residual matterremaining after the recovery of conversion products and/or energy hasbeen accomplished. The three land disposal methods used most com-monly are (1) landfilling, (2) landfarming, and (3) deep-well injection.Although incineration is being used more often as a disposal method,it is, in reality, a processing method. Recently, the concept of usingmuds in the ocean floor as a waste storage location also has receivedsome attention.

Landfilling of Solid Waste Landfilling involves the controlleddisposal of solid wastes on or in the upper layer of the earth’s mantle.Important aspects in the implementation of sanitary landfills include(1) site selection, (2) landfilling methods and operations, (3) occur-rence of gases and leachate in landfills, (4) movement and control oflandfill gases and leachate, and (5) landfill design. Landfilling is alarge-scale operation. The number of landfills decreased substantiallyover the period from 1988 to 2001. There were nearly 8000 in 1988,


TABLE 22-68 Typical Thermal Efficiency and Plant Use and Loss Factors for Individual Components and Processes Used forRecovery of Energy from Solid Wastes

Efficiency*

Component Range Typical Comments

Incinerator-boiler 40–68 63 Mass-firedBoiler

Solid fuel 60–75 72 Processed solid wastes (RDF)Low-btu gas 60–80 75 Necessity to modify burnersOil-fired 65–85 80 Oils produced from solid wastes possibly required to be blended to reduce corrosiveness

Gasifier 60–70 70Pyrolysis reactor 65–75 70Turbines

Combustion gasSimple cycle 8–12 10Regenerative 20–26 24 Including necessary appurtenances

Expansion gas 30–50 40Steam turbine–generator system

Less than 10 MW 24–40 29†‡ Including condenser, heaters, and all other necessary appurtenances but not boiler10 MW 28–32 31.6†‡

Electric generatorLess than 10 MW 88–92 90Over 10 MW 94–98 96

* Theoretical value for mechanical equivalent of heat = 3600 kJ/kWh.†Efficiency varies with exhaust pressure. Typical value given is based on an exhaust pressure in the range of 50 to 100 mmHg.‡Heat rate = 11,395 kJ/kWh = (3600 kJ/kWh)/0.316.

TABLE 22-69 Energy Output and Efficiency for 1000 t/day of Waste Steam Boiler Turbine-Generator Energy-Recovery Plant Using Unprocessed Industrial Solid Wastes with Energy Contentof 12,000 kJ/kg

Item Value

Energy available in solid wastes, million kJ/h [(1000 t/day × 1000 kg/t × 12,000 kJ/kg) / 500(24 h/day × 106 kJ/million kJ)]

Steam energy available, million kJ/h (500 million kJ/h × 0.7) 350Electric power generation, kW (350 million kJ/h)/(11, 395 kJ/kWh) 30,715Station-service allowance, kW [30,715 (0.06)] −1,843Unaccounted heat losses, kW [30,715 (0.05)] 1,536Net electric power for export, kW 27,336Overall efficiency, percent {(27,336 kW)/[(500,000,000 kJ/h)/(3600 kJ/kWh)]}(100) 19.7

TABLE 22-70 Summary of Waste Disposal Pricing and Volumes by Type of Facility and State and Region, June 2004Average tipping fees by facility type Daily volume of waste by facility type

Landfills Transfer WTE All types Landfills Transfer WTE All types

12-mo 12-mo 12-mo 12-mo 12-mo 12-mo 12-mo 12-moRegion/state $/ton chg. $/ton chg. $/ton chg. Tons/day chg. Tons/day chg. Tons/day chg. Tons/day chg. Tons/day chg.

NortheastConnecticut 60.62 −11.6% 65.22 −4.0% 64.79 2.1% 64.60 −1.4% 1.060 −38.4% 4,310 −7.3% 7.830 0.5% 8.890 −6.5%Delawere 58.48 0.2% 54.93 −6.0% — N/A 57.87 −0.8% 4,240 −7.6% 880 −10.2% — N/A 4,240 −7.6%Maine 55.43 9.2% 38.53 11.5% 71.38 <1% 57.33 −10.2% 630 1.6% 1,880 382.1% 2,600 <1% 3,230 0.3%Maryland 52.90 5.5% 36.16 −3.1% 65.21 0.1% 49.64 1.5% 7,340 −14.8% 4,620 16.1% 2,490 <1% 9,900 −11.6%Massachusetts 67.66 8.7% 84.80 31.5% 67.30 −1.4% 73.47 13.8% 6.810 0.9% 11,220 −8.9% 10.150 −0.5% 17.750 2.8%New Hampshire 72.38 −5.1% 90.28 8.6% 79.71 −6.0% 77.10 −2.3% 4,640 −1.7% 1,510 −20.9% 760 −1.3% 5.390 −1.8%New Jersey 66.61 28.7% 77.61 5.4% 60.78 −7.0% 69.51 9.8% 13.250 −1.3% 12.500 −7.6% 6,360 −18.3% 20,300 −4.3%New York 48.46 0.5% 61.46 7.9% 58.11 −0.1% 54.92 2.9% 26,120 −3.9% 20,740 −16.6% 11,220 −2.2% 37.420 −3.4%Pennsylvania 56.47 2.8% 64.46 0.2% 56.76 <1% 57.86 2.1% 80,180 −1.5% 18,560 14.9% 10,380 <1% 90,600 −3.4%Rhode Island 64.37 11.4% 68.18 −7.3% — N/A 64.98 7.2% 3,660 1.4% 690 −13.8% — N/A 3,660 1.4%Vermont 70.46 9.7% 56.09 4.1% 42.83 <1% 60.49 6.8% 740 −23.7% 1,640 −37.6% 10 <1% 750 −23.5%

Northeast total 57.15 4.8% 66.67 6.6% 62.30 –1.1% 60.39 3.8% 148,663 –3.2% 78,556 –4.4% 51,792 –3.2% 202,120 –3.6%

SouthernAlabama 26.72 4.1% 32.23 8.6% 39.90 <1% 27.54 4.4% 20,150 −16.4% 1,870 −21.8% 630 −8.7% 20,780 −16.1%Arkansas 27.75 8.5% 23.98 −2.2% 9.97 −45.5% 27.00 6.6% 7,510 −15.1% 1.130 −49.3% 130 85.7% 7,640 −14.3%District of Columbia — N/A 59.77 5.3% — N/A 59.77 5.3% — N/A 3,150 16.7% — N/A — N/AFlorida 37.00 −1.3% 40.95 5.3% 57.43 −1.0% 42.03 1.0% 49.950 33.3% 17.170 3.0% 17,480 −1.2% 69,870 21.6%Georgia 33.13 6.7% 33.94 1.1% 60.00 <1% 33.26 4.6% 39.150 69.0% 6,290 −25.0% 390 29.0% 39.830 71.1%Kentucky 33.01 6.6% 33.89 105.8% — N/A 33.16 17.8% 17,930 −4.1% 3,730 −16.9% — N/A 17,930 −4.1%Louisiana 26.90 −1.7% 32.35 −0.5% — N/A 27.80 −1.4% 15,340 −4.2% 3,000 −2.9% — N/A 15,340 −4.2%Mississippi 26.88 6.3% 32.34 −1.4% — N/A 27.51 5.0% 10,300 −16.1% 1,330 −22.7% — N/A 10,300 −16.1%North Carolina 33.27 7.7% 38.57 1.1% 46.00 35.3% 34.63 5.6% 20,300 −8.2% 5,820 −27.9% 400 <1% 20,750 −8.6%South Carolina 33.41 −4.2% 33.94 −0.5% 59.50 <1% 34.19 −3.3% 19,340 −6.6% 2,670 −21.0% 620 <1% 19,960 −6.4%Tennessee 29.16 −0.5% 36.05 26.1% 30.56 85.8% 29.75 3.1% 22,280 −9.4% 1,750 −59.4% 420 −8.7% 22,830 −9.4%Virginia 40.05 3.0% 47.24 55.7% 45.36 0.5% 42.04 12.6% 41,510 −7.8% 10,680 −14.3% 6,640 −2.8% 49,580 −6.9%West Virginia 35.38 −1.0% 42.03 −17.6% — N/A 36.00 −3.7% 5,630 −15.0% 580 −26.6% — N/A 5,630 −15.0%

Southern total 33.43 3.2% 39.98 17.5% 53.28 0.3% 35.65 6.0% 269,370 3.8% 59,163 –16.3% 26,710 –0.6% 300,438 3.4%

MidwestIllinois 35.88 5.7% 48.66 65.7% 59.00 <1% 40.19 23.0% 63,880 7.3% 29,780 2.6% 1,200 <1% 65,450 7.1%Indiana 31.19 9.0% 39.17 43.1% 28.11 8.3% 33.28 18.1% 22,660 −7.9% 9,750 14.2% 2,070 7.8% 24,920 −6.6%Iowa 32.12 −3.0% 34.35 −9.1% — N/A 32.41 −4.0% 6,990 −21.2% 980 −31.9% — N/A 7,000 −21.1%Kansas 31.87 5.4% 35.62 9.9% — N/A 32.63 6.0% 9,560 5.3% 2,420 −19.9% — N/A 9,560 5.3%Michigan 35.32 7.3% 41.05 39.4% 54.43 −0.6% 37.04 9.3% 57,510 −1.1% 6,640 −10.3% 4,160 −2.8% 61,670 −1.2%Minnesota 58.80 11.8% 52.77 31.7% 62.25 23.7% 57.23 21.8% 6,040 −9.9% 6,670 −12.0% 4,210 −18.9% 10,320 −13.7%Missouri 36.17 4.3% 33.16 39.3% — N/A 35.48 11.2% 15,750 −2.2% 4,740 −14.6% — N/A 15.750 −2.2%Nebraska 25.61 −0.2% 35.27 1.1% — N/A 26,73 −0.3% 7,470 −8.6% 980 −16.2% — N/A 7,470 −8.6%North Dakota 27.89 11.6% 31.63 −10.5% — N/A 28.88 7.0% 1,690 −20.3% 500 −18.0% — N/A 1,710 −20.5%Ohio 33.60 10.7% 38.07 41.1% — N/A 34.97 19.1% 45,100 −1.3% 19,660 6.7% — N/A 45,180 −1.2%South Dakota 27.54 7.4% 60.67 18.3% — N/A 30.33 6.4% 1,380 −23.3% 130 −43.5% — N/A 1,380 −23.3%Wisconsin 38.00 4.0% 37.77 1.8% 50.36 <1% 38.17 3.5% 18,690 −5.2% 5,140 −14.6% 420 <1% 19,110 −5.1%

Midwest total 35.00 6.9% 42.72 41.6% 52.95 8.1% 37.22 14.2% 256,724 –1.5% 87,394 –1.8% 12,058 –7.3% 269,524 –1.7%

WesternArizona 26.93 3.7% 31.90 −0.7% — N/A 28.42 2.0% 19,520 −9.1% 8,290 −13.2% — N/A 19,530 −9.1%Colorado 22.27 8.5% 33.68 12.9% 25.00 <1% 23.83 8.5% 20,590 −0.7% 3,230 −14.3% 10 <1% 20,610 −0.6%Idaho 18.80 −7.3% 30.86 −32.9% — N/A 21.45 −8.4% 4,700 −41.3% 1,320 18.9% — N/A 4,700 −41.3%Montana 25.40 20.5% 45.28 9.4% 60.00 <1% 28.91 17.6% 2.470 <1% 410 −14.6% 50 <1% 2,570 <1%Nevada 18.74 28.4% 31.51 37.5% — N/A 21.19 29.2% 8,230 −1.2% 1,960 −15.5% — N/A 8,230 −1.2%New Maxico 20.65 0.4% 15.37 8.2% — N/A 19.77 2.4% 9.100 −10.5% 1,840 −26.7% — N/A 9,100 −10. 5%Oklahoma 22.22 3.2% 21.85 2.7% 55.00 <1% 24.71 4.0% 12,870 −12.3% 710 −30.4% 1.130 <1% 14,000 −11.4%Texas 21.03 4.2% 25.64 46.2% 55.49 33.0% 21.52 7.6% 74,920 −2.1% 7,570 −5.5% 60 −25.0% 75,210 −2.2%Utah 24.59 −2.2% 24.77 0.1% 25.00 <1% 24.68 −1.7% 13,210 20.2% 1,010 −17.2% 10 <1% 13,280 20.7%Wyoming 25.03 13.9% 46.56 −3.9% — N/A 28.94 6.8% 1,180 −36.2% 260 −40.9% — N/A 1,180 −36.2%

Western total 22.14 4.7% 28.92 11.0% 54.79 1.7% 23.17 5.7% 166,788 –4.8% 26,590 –12.6% 1,251 –1.6% 168,406 –4.8%

PacificAlaska 37.31 −24.4% 14.77 12.3% 140.81 −0.1% 40.63 −27.8% 2,100 18.6% 200 400.0% 120 −25.0% 2,220 15.0%California 36.58 5.1% 43.86 9.0% 37.58 −0.9% 39.12 6.0% 122,110 −1.7% 45,940 −14.0% 3,260 −5.0% 126,800 −2.1%Hawaii 62.00 2.3% 95.32 17.6% 81.27 <1% 71.22 2.3% 2,280 −6.9% 270 −41.3% 1,440 <1% 3,730 −4.1%Oregon 30.79 −2.7% 32.67 36.9% 65.52 0.9% 32.35 8.1% 12,650 3.5% 6.040 −13.1% 530 −14.5% 13,190 2.6%Washington 44.68 7.2% 80.38 3.2% 88.23 21.1% 60.73 3.5% 12,650 −2.8% 8,950 −22.3% 1,540 −8.9% 14,630 −3.3%

Pacific total 37.16 4.1% 48.21 7.4% 62.02 5.0% 41.30 4.9% 151,790 –1.3% 61,404 –15.2% 6,907 –5.9% 160,561 –1.7%

National total 36.06 4.8% 48.12 16.2% 58.60 0.7% 39.49 6.8% 993,335 –0.9% 313,107 –9.2% 98,719 –3.2% 1,101,049 –1.2%

SOURCE: Chartwell Information, a division of Environmental Business International, Inc.

22

-99

down to 1858 landfills in service nationwide in 2001 accepting approx-imately 160 million tons of waste. The number of landfills is decreas-ing, and the capacity of remaining landfills is rising, as new landfillsare larger. New landfills are more sophisticated than older ones andare therefore more costly to design and operate. Over the long term,the tonnage of MSW landfilled in 1990 was 140.1 million tons, butdecreased to 122.4 million tons in 1995. The tonnage increased to131.8 million tons in 1999, then declined to 127.6 in 2001. The ton-nage landfilled results from an interaction among generation, recy-cling, and combustion, which do not necessarily rise and fall at thesame time. Figure 22-56 shows the decrease of landfills that hasoccurred over the 13-year period from 1988 to 2001.

The landfilling of hazardous waste is considered separately.Site Selection Factors that must be considered in evaluating

potential solid-waste-disposal sites are summarized in Table 22-71.Final selection of a disposal site usually is based on the results of a pre-liminary site survey, results of engineering design and cost studies, andan environmental impact assessment.

Landfilling Methods and Operations To use the availablearea at a landfill site effectively, a plan of operation for the place-ment of solid wastes must be prepared. Various operational meth-ods have been developed primarily on the basis of field experience.The principal methods used for landfilling dry areas may be classi-fied as (1) area and (2) depression.

1. Area method. The area method is used when the terrain isunsuitable for the excavation of trenches in which to place the solidwastes. The filling operation usually is started by building an earthenlevee against which wastes are placed in thin layers and then com-pacted (see Fig. 22-57). Each layer is compacted as the filling pro-gresses until the thickness of the compacted wastes reaches a heightvarying from 2 to 3 m (6 to 10 ft). At that time, and at the end of eachday’s operation, a 150- to 300-mm (6- to 12-in) layer of cover materialis placed over the completed fill. The cover material must be hauledin by truck or earthmoving equipment from adjacent land or fromborrow-pit areas. In some newer landfill operations, the daily covermaterial is omitted, and reusable geotextile covers, similar to very


FIG. 22-55 Solid-waste management costs, June 2004.


large tarps, are used. A completed lift including the cover material iscalled a cell (see Fig. 22-58). Successive lifts are placed on top of oneanother until the final grade called for in the ultimate developmentplan is reached. A final layer of cover material is used when the fillreaches the final design height.

2. Depression method. At locations where natural or artificialdepressions exist, it is often possible to use them effectively for land-filling operations. Canyons, ravines, dry borrow pits, and quarrieshave been used for this purpose. The techniques to place and compactsolid wastes in depression landfills vary with the geometry of the site,

the characteristics of the cover material, the hydrology and geology ofthe site, and access of the site. In a canyon site, filling starts at the headend of the canyon (see Fig. 22-59) and ends at the mouth. The prac-tice prevents the accumulation of water behind the landfill. Wastesusually are deposited on the canyon floor and from there are pushedup against the canyon face at a slope of about 2 : 1. In this way, a highdegree of compaction can be achieved.

3. Landfills in wet areas. Because of the problems associatedwith contamination of local groundwater, the development of odors,and structural stability, landfills must be avoided in wetlands. If wet

FIG. 22-56 Number of landfills, 1988–2001.

TABLE 22-71 Important Factors in Preliminary Selection of Landfill Sites

Factor Remarks

Available land area In selecting potential land disposal sites, it is important to ensure that sufficient land area is available. Sufficient area to operate for at least 1 year at a given site is needed to minimize costs.

Impact of processing and It is important to project the extent of resource-recovery processing activities that are likely to occur in the future and determine resource recovery their impact on the quantity and condition of the residual materials to be disposed of.

Haul distance Although minimum haul distances are desirable, other factors must also be considered. These include collection-route location, types of wastes to be hauled, local traffic patterns, and characteristics of the routes to and from the disposal site (condition of theroutes, traffic patterns, and access conditions).

Soil conditions and topography Because it is necessary to provide material for each day’s landfill and a final layer of cover after the filling has been completed, data on the amounts and characteristics of the soils in the area must be obtained. Local topography will affect the type of landfill operation to be used, equipment requirements, and the extent of work necessary to make the site usable.

Climatological conditions Local weather conditions must also be considered in the evaluation of potential sites. Under winter conditions where freezing issevere, landfill cover material must be available in stockpiles when excavation is impractical. Wind and wind patterns must alsobe considered carefully. To avoid blowing or flying papers, windbreaks must be established.

Surface-water hydrology The local surface-water hydrology of the area is important in establishing the existing natural drainage and runoff characteristics that must be considered.

Geologic and hydrogeologic Geologic and hydrogeologic conditions are perhaps the most important factors in establishing the environmental suitability of theconditions area for a landfill site. Data on these factors are required to assess the pollution potential of the proposed site and to establish

what must be done to the site to control the movement of leachate or gases from the landfill.Local environmental conditions The proximity of both residential and industrial developments is extremely important. Great care must be taken in their

operation if they are to be environmentally sound with respect to noise, odor, dust, flying paper, and vector control.Ultimate uses Because the ultimate use affects the design and operation of the landfill, this issue must be resolved before the layout and

design of the landfill are started.

areas such as ponds, pits, or quarries must be used as landfill sites,special provisions must be made to contain or eliminate the move-ment of leachate and gases from completed cells. Usually this isaccomplished by first draining the site and then lining the bottom witha clay liner or other appropriate sealants. If a clay liner is used, it isimportant to continue operation of the drainage facility until the site isfilled to avoid the creation of uplift pressures that could cause theliner to rupture from heaving.

Occurrence of Gases and Leachate in Landfills The followingbiological, physical, and chemical events occur when solid wastes areplaced in a sanitary landfill: (1) biological decay or organic materials,either aerobically or anaerobically, with the evolution of gases and liq-uids; (2) chemical oxidation of waste materials; (3) escape of gasesfrom the fill; (4) movement of liquids caused by differential heads;(5) dissolving and leaching of organic and inorganic materials by waterand leachate moving through the fill; (6) movement of dissolved materialby concentration gradients and osmosis; and (7) uneven settlementcaused by consolidation of material into voids.

With respect to item 1, bacterial decomposition initially occursunder aerobic conditions because a certain amount of air is trappedwithin the landfill. However, the oxygen in the trapped air isexhausted within days, and long-term decomposition occurs underanaerobic conditions.

1. Gases in landfills. Gases found in landfills include air, ammo-nia, carbon dioxide, carbon monoxide, hydrogen, hydrogen sulfide,methane, nitrogen, and oxygen. Data on the molecular weight anddensity of these gases are presented in Sec. 2. Carbon dioxide andmethane are the principal gases produced from the anaerobic decom-position of the organic solid-waste components.

The anaerobic conversion of organic compounds is thought to occurin three steps. The first involves the enzyme-mediated transformation(hydrolysis) of higher-weight molecular compounds into compoundssuitable for use as a source of energy and cell carbon; the second isassociated with the bacterial conversion of the compounds resulting


( a )

( b )

FIG. 22-57 Area method for landfilling solid wastes. (a) Pictorial view of com-pleted landfill. (b) Section through landfill.

( a )

( b )

FIG. 22-58 Typical section through a landfill. (a) With daily or intermediatecover. (b) Without daily or intermediate cover.

( a )

( b )

FIG. 22-59 Depression method for landfilling solid wastes. (a) Plan view:canyon-site landfill. (b) Section through landfill.

from the first step into identifiable lower-molecular-weight intermedi-ate compounds; and the third step involves the bacterial conversion ofthe intermediate compounds into simpler end products, such as car-bon dioxide (CO2) and methane (CH4). The overall anaerobic conver-sion of organic industrial wastes can be represented with the followingequation:

CaHbOcNd → nCwHxOyNz + mCH4 + sCO2 + rH2O + (d − nz)NH3

(22-30)

where s = a = nw = m and r = c − ny − 2s. The terms CaHbOcNd andCwHxOyNz are used to represent on a molar basis the composition ofthe material present at the start of the process.

The rate of decomposition in unmanaged landfills, as measured bygas production, reaches a peak within the first 2 years and then slowlytapers off, continuing in many cases for periods of up to 25 years ormore. The total volume of the gases released during anaerobicdecomposition can be estimated in a number of ways. If all theorganic constituents in the wastes (with the exception of plastics, rub-ber, and leather) are represented with a generalized formula of theform CaHbOcNd, the total volume of gas can be estimated by usingEq. (22-30) with the assumption of completed conversion to carbondioxide and methane.

2. Leachate in landfills. Leachate may be defined as liquid thathas percolated through solid waste and has extracted dissolved or sus-pended materials from it. In most landfills, the liquid portion of theleachate is composed of the liquid produced from the decompositionof the wastes and liquid that has entered the landfill from externalsources, such as surface drainage, rainfall, groundwater, and waterfrom underground springs. Representative data on chemical charac-teristics of leachate are reported in Table 22-72.

Gas and Leachate Movement and Control Under ideal condi-tions, the gases generated from a landfill should be either vented tothe atmosphere or, in larger landfills, collected for the production ofenergy. Landfills with >2.5 million cubic meters of waste or >50 Mg/yrNMOC (nonmethane organic compounds) emissions may requirelandfill-gas collection and flare systems, per EPA support WWW,CFR 60 Regulations. The leachate should be either contained withinthe landfill or removed for treatment.

1. Gas movement. In most cases, over 90 percent of the gas vol-ume produced from the decomposition of solid wastes consists ofmethane and carbon dioxide. Although most of the methane escapesto the atmosphere, both methane and carbon dioxide have been foundin concentrations of up to 40 percent at lateral distances of up to 120m (400 ft) from the edges of landfills. Methane can accumulate belowbuildings or in other enclosed spaces or close to a sanitary landfill.With proper venting at the landfill source, methane should not pose aproblem.

Because carbon dioxide is about 1.5 times as dense as air and 2.8times as dense as methane, it tends to move toward the bottom of thelandfill. As a result, the concentration of carbon dioxide in the lowerportions of landfill may be high for years. Ultimately, because of itsdensity, carbon dioxide will also move downward through the under-lying formation until it reaches the groundwater. Because carbon diox-ide is readily soluble in water, it usually lowers the pH, which in turncan increase the hardness and mineral content of the groundwaterthrough the solubilization of calcium and magnesium carbonates.

Currently, MSW landfills are estimated to release approximately14,300 tons/yr of NMOC. Methane and carbon dioxide contribute tothe greenhouse effect, and the release of VOCs cause air quality issuessuch as smog and ozone formation. In the gas of a MSW landfill,VOCs comprise about 39 percent of NMOC.

2. Control of gas movement. The lateral movement of gases pro-duced in a landfill can be controlled by installing vents made of mate-rials that are more permeable than the surrounding soil. Typically, asshown in Fig. 22-60a, gas vents are constructed of gravel. The spacingof cell vents depends on the width of the waste cell but usually variesfrom 18 to 60 m (60 to 200 ft). The thickness of the gravel layer shouldbe such that it will remain continuous even though there may be dif-

ferential settling; 300 to 450 mm (12 to 18 in) thick is recommended.Barrier vents (see Fig. 22-60b) also can be used to control the lateralmovements of gases. Well vents are often used in conjunction with lat-eral surface vents buried below grade in a gravel trench (see Fig. 22-60c). Details of a gas vent are shown in Fig 22-61. Control of thedownward movement of gases can be accomplished by installing per-forated pipes in the gravel layer at the bottom of the landfill. If thegases cannot be vented laterally, it may be necessary to install gas wellsand vent the gas to atmosphere. This is considered a passive ventingsystem. See Fig. 22-62. The movement of landfill gases through adja-cent soil formation can be controlled by constructing barriers of mate-rials that are more impermeable than soil. See Fig. 22-63a. Some of thelandfill sealants that are available for this use are identified in Table 22-73. Of these, the use of compacted clays is the most common. Thethickness will vary depending on the type of clay and the degree of con-trol required; thicknesses ranging from 0.015 to 1.25 m (6 to 48 in)have been used. Covers of landfills are also typically multilayered andmay include foundation layer, clay layer, membrane, drainage layer(synthetic or natural), root zone layer, or soil.

3. Control of gas movement by recovery. The movement of gasesin landfills can also be controlled by installing gas-recovery wells incompleted landfills (see Fig. 22-63b). This is considered an activeventing system. Clay and other lines are used when landfill gas is to be


TABLE 22-72 Typical Leachate Quality of Municipal Waste

Overall rangeS1 number Parameter (mg/L except as indicated)

1 TDS 584–55,0002 Specific conductance 480–72,500 µ mho/cm3 Total suspended solids 2–140,9004 BOD ND–195,0005 COD 6.6–99,0006 TOC ND–40,0007 pH 3.7–8.9 units8 Total alkalinity ND–15,0509 Hardness 0.1–225,000

10 Chloride 2–11,37511 Calcium 3.0–2,50012 Sodium 12–6,01013 Total Kjeldahl nitrogen 2–3,32014 Iron ND–4,00015 Potassium ND–3,20016 Magnesium 4.0–78017 Ammonia–nitrogen ND–1,20018 Sulfate ND–1,85019 Aluminum ND–8520 Zinc ND–73121 Manganese ND–40022 Total phosphorus ND–23423 Boron 0.87–1324 Barium ND–12.525 Nickel ND–7.526 Nitrate–nitrogen ND–25027 Lead ND–14.228 Chromium ND–5.629 Antimony ND–3.1930 Copper ND–9.031 Thallium ND–0.7832 Cyanide ND–633 Arsenic ND–70.234 Molybdenum 0.07–1.4335 Tin ND–0.1636 Nitrite–nitrogen ND–1.4637 Selenium ND–1.8538 Cadmium ND–0.439 Silver ND–1.9640 Beryllium ND–0.3641 Mercury ND–3.042 Turbidity 40–500 Jackson units

From McGinely, P. M., and P. Kmet, Formation Characteristics, Treatment,and Disposal of Leachate from Municipal Solid Waste Landfills, Bureau ofSolid Waste Management, Wisconsin Department of Natural Resources,Madison, 1984.


( a )

( b )

( c )

FIG. 22-60 Vents used to control the lateral movement of gases in landfills. (a)Cell. (b) Barrier. (c) Well. (From G. Tchobanoglous, H. Theisen, and R. Eliassen,Solid Wastes: Engineering Principles and Management Issues, McGraw-Hill,New York, 1977.)

FIG. 22-61 Typical detail of an isolated gas vent. (From Bagchi, A., Design,Construction, and Monitoring of Sanitary Landfill, Wiley, 1990.)

recovered. In some gas-recovery systems, leachate is collected andrecycled to the top of the landfill and reinjected through perforatedlines located in drainage trenches. Typically, the rate of gas productionis greater in leachate-recirculation systems.

Gas recovery systems have been installed in some large municipallandfills, with the gas flared used to run spark-ignition diesel enginesto generate power for sale to the grid or the gas is cleaned up and pipedto nearby users. The economics of such operations must be reviewedfor each site. The end use of gas will affect the overall economics. The

FIG. 22-62 Typical detail of a passive gas venting system with a header pipe.(From Bagchi, A., Design, Construction, and Monitoring of Sanitary Landfill,Wiley, 1990.)

( a )

( b )

FIG. 22-63 Use of an impermeable liner to control the movement of gasesand leachate in landfills. (a) Without gas recovery. (b) With gas recovery. (FromG. Tchobanoglous, H. Theisen, and R. Eliassen, Solid Wastes: Engineering Prin-ciples and Management Issues, McGraw-Hill, New York, 1977.)

cost of gas cleanup and processing equipment will limit the recoveryof landfill gases, especially from small landfills.

4. Leachate movement. Under normal conditions, leachate isfound in the bottom of landfills. From there it moves through theunderlying strata, although some lateral movement may also occur,depending on the characteristics of the surrounding material. The rateof seepage of leachate from the bottom of a landfill can be estimated byDarcy’s law by assuming that the material below the landfill to the top ofthe water table is saturated and that a small layer of leachate exists at thebottom of the fill. Under these conditions, the leachate discharge rateper unit area is equal to the value of the coefficient of permeability K,expressed in meters per day. The computed value represents the maxi-mum amount of seepage that would be expected, and this value shouldbe used for design purposes. Under normal conditions, the actual ratewould be less than this value because the soil column below the landfillwould not be saturated. Models have been developed to aid in the esti-mation of leachate quantity. Bagchi has covered details of these modelsin the Design, Construction, and Monitoring of Sanitary Landfill.


TABLE 22-73 Landfill Sealants for the Control of Gas and Leachate Movement

Sealant

Classification Representative types Remarks

Compacted soil Should contain some clay or fine silt.Compacted clay Bentonites, illites, kaolinites Most commonly used sealant for landfills;

layer thickness varies from 0.15–1.25 m;layer must be continuous and not be allowed to dry out and crack.

Inorganic chemicals Sodium carbonate, silicate, or pyrophosphate Use depends on local soil characteristics.Synthetic chemicals Polymers, rubber, latex Experimental; use not well established.Synthetic membrane liners Polyvinyl chloride, butyl rubber, Hypalon, polyethylene, nylon-reinforced liners Expensive; may be justified where gas

is to be recovered.Asphalt Modified asphalt, asphalt-covered polypropylene fabric, Layer must be thick enough to maintain

asphalt concrete continuity under differential settling conditions.

Others Gunite concrete, soil, cement, plastic soil cement

*From G. Tchobanoglous, H. Theisen, and R. Eliasen, Solid Wastes: Engineering Principles and Management Issues, McGraw-Hill, New York, 1977.

TABLE 22-74 Short- and Long-Term Actions for Effective Industrial Solid-Waste Management*

Actions Remarks

Short-term1. Inventory wastes. Document all types, quantities, and sources of wastes (both nonhazardous and hazardous wastes).2. Inventory inactive sites. All inactive sites where wastes have been disposed of in the past should be inventoried. Data should be gathered

on buried wastes, including types, quantity, and sources. A groundwater-monitoring program should be developed.3. Characterize wastes. In addition to general information on the characteristics of the wastes, all hazardous wastes should be individually

characterized.4. Assign responsibilities. Assign responsibilities and authority at plant and headquarters for the storage, collection, treatment, and disposal

of all types of hazardous wastes.5. Track the movement of wastes. Develop a logging system for hazardous wastes containing the date, waste description, source, volume shipped or

hauled, name of hauler, and destination. Follow through to be sure that wastes reach their destination.6. Develop emergency procedures. Develop procedures for dealing with emergency situations involving the storage, collection, treatment, and

disposal of hazardous wastes.7. Obtain permits. Start obtaining the necessary waste-disposal permits as soon as possible.Long-term1. Remove all accumulated wastes. Develop a systematic program for removing all accumulated wastes stored on the plant site.2. Separate wastes. Institute a long-term program to separate wastes at the source of production.3. Reduce wastes. A systematic program should be undertaken to examine all sources of waste production and to develop alternative

operations and processes to reduce waste generation.4. Improve facilities. Upgrade facilities to meet RCRA requirements. A data-collection program should be instituted to obtain any

needed data.5. Review all waste-management Develop detailed contracts with outside waste-management firms. Define clearly the duties and responsibilities of

agreements. plant personnel and waste-collection personnel.6. Review and develop disposals-tie options. Develop long-term projections for landfill requirements and initiate a program to secure the needed sites.7. Secure appropriate engineering and Make sure that your engineering departments are involved early in the process.

consulting services. Retain outside consultants for specific tasks.8. Monitor legislative programs. Develop a program for monitoring new regulations and for inputting to appropriate federal, state, and local

agencies on the modification and development of new regulations.

*Adapted in part from R. Sobel, “How Industry Can Prepare for RCRA,” Chem. Eng., 86(1), 82 (Jan. 29, 1979).

5. Control of leachate movement. As leachate percolates throughthe underlying strata, many of the chemical and biological constituentsoriginally contained in it will be removed by the filtering and adsorptiveaction of the material composing the strata. In general, the extent of thisaction depends on the characteristics of the soil, especially the clay con-tent. Because of the potential risk involved in allowing leachate to perco-late to the groundwater, best practice calls for its elimination orcontainment. Ultimately, it will be necessary to collect and treat theleachate.

The use of clay has been the favored method of reducing or eliminat-ing the percolation of leachate (see Fig. 22-63 and Table 22-73). Mem-brane liners are used most often today but require care so that they willnot be damaged during the filling operations. Equally important incontrolling the movement of leachate is the elimination of surface-water infiltration, which is the major contributor to the total volume ofleachate. With the use of an impermeable clay layer, membrane liners,an appropriate surface slope (1 to 2 percent), and adequate drainage,surface infiltration can be controlled effectively.

6. Settlement and structural characteristics of landfills. The set-tlement of landfills depends on the initial compaction, characteristicsof wastes, degree of decomposition, and effects of consolidation whenthe leachate and gases are formed in the landfill. The height of thecompleted fill will also influence the initial compaction and degree ofconsolidation.

PLANNING

Because of the ever-growing number of federal regulations governingthe disposal of nonhazardous and hazardous solid wastes, it is prudentto develop both short-term and long-term action programs to dealwith all aspects of solid-waste management. Important short- andlong-term actions are identified in Table 22-74.
