chapter 20.1-20.2 revised_6th edition.pdf

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20-1 Copyright © 2006 Water Environment Federation. Section 1 Introduction The activated-sludge process is still the most widely used biological treatment process for reducing the concentration of organic pollutants in wastewater. Well-established design standards based on empirical data have evolved over the years. Our under- standing of the process has advanced from a system originally designed simply for bio- chemical oxygen demand (BOD) reduction, to one that now is designed to remove nutrients such as nitrogen and phosphorus. Despite these advances, poor process per- formance can still present problems for many plants. The objective of this manual is to help operators and other wastewater treatment professionals acquire a greater understanding of the process, solve performance prob- lems, and improve operations. The manual is intended as both a training and reference tool. The format will make the book useful to newcomers and experienced profession- als alike. This manual describes the process variations and focuses on operation, addressing pertinent process theory, alternative process control strategies, energy conservation, and troubleshooting the activated-sludge process. Since the last printing of this manual in 1987, there have been advancements and improvements in process configurations and control strategies to achieve higher degrees of treatment efficiency. Section 2 provides an overview of the activated-sludge process starting with the fundamental concepts of microbiology and biochemistry. It describes how the propa- gation and control of living organisms are key to achieving the basic process goals of removing BOD, nitrogen, and phosphorus. Conventional process configurations are dis- cussed along with current modifications including sequencing batch reactors, coupled systems, and combined systems. A description of facilities and equipment is provided. Control of activated-sludge systems is based on maintaining proper aeration and mixing in the biological reactor and controlling the biomass inventory of the system.

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  • 20-1Copyright 2006 Water Environment Federation.

    Section 1

    Introduction

    The activated-sludge process is still the most widely used biological treatment processfor reducing the concentration of organic pollutants in wastewater. Well-establisheddesign standards based on empirical data have evolved over the years. Our under-standing of the process has advanced from a system originally designed simply for bio-chemical oxygen demand (BOD) reduction, to one that now is designed to removenutrients such as nitrogen and phosphorus. Despite these advances, poor process per-formance can still present problems for many plants.

    The objective of this manual is to help operators and other wastewater treatmentprofessionals acquire a greater understanding of the process, solve performance prob-lems, and improve operations. The manual is intended as both a training and referencetool. The format will make the book useful to newcomers and experienced profession-als alike.

    This manual describes the process variations and focuses on operation, addressingpertinent process theory, alternative process control strategies, energy conservation,and troubleshooting the activated-sludge process. Since the last printing of this manualin 1987, there have been advancements and improvements in process configurationsand control strategies to achieve higher degrees of treatment efficiency.

    Section 2 provides an overview of the activated-sludge process starting with thefundamental concepts of microbiology and biochemistry. It describes how the propa-gation and control of living organisms are key to achieving the basic process goals ofremoving BOD, nitrogen, and phosphorus. Conventional process configurations are dis-cussed along with current modifications including sequencing batch reactors, coupledsystems, and combined systems. A description of facilities and equipment is provided.

    Control of activated-sludge systems is based on maintaining proper aeration andmixing in the biological reactor and controlling the biomass inventory of the system.

  • The secondary clarifier is integral to the activated-sludge process because it maintainscontrol of the biomass in the system. Section 3, Process Control, describes the differ-ent strategies for controlling the biomass inventory in the system to achieve and main-tain optimum process performance.

    Section 4 describes energy use in wastewater treatment plants and discusses energy-saving opportunities through process and equipment considerations. It alsodiscusses how automatic sensors and controls can be key tools in conserving power.

    Section 5 presents the procedures used for solving common operational problems.Included are easy-to-use troubleshooting tables that correlate observations to possiblecauses and remedies and items to check in the process of narrowing down the causes.This section has been updated to include troubleshooting for nitrogen- and phosphorus-removal systems.

    A new section on Aerobic Digestion has been included as Section 6. Althoughthe goal of aerobic digestion is to stabilize sludge, rather than reduce organic pollutantsand nutrients, the principles of mixing and aerating the organisms and controlling theprocess are similar to those of the activated-sludge process. Thus, a brief overview ofthe aerobic digestion process is given here.

    Appendices contain material that expands on the concepts presented in the sec-tions. Practical examples supported with sample calculations on subjects ranging fromhow to determine nutrient supplement requirements to chemical addition for pH con-trol or settling enhancement are included. Appendices covering preventive maintenanceand safety are also provided.

    20-2 Operation of Municipal Wastewater Treatment Plants

    Copyright 2006 Water Environment Federation.

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