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Harrisburg Advanced Wastewater Treatment FacilityBiosolids Facilities Improvement Plan Existing Conditions Report

February 2017

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March 2018

Harrisburg Advanced Wastewater Treatment Facility Biosolids Facilities Improvement Plan

Capital Region Water

Table of Contents | i

N:\14342-001\Engineering\Reports\Biosolids Facilities Improvement Plan\Final\Capital Region Water Report FINAL.docx

Executive Summary ............................................................................................................................................. ES-1

1 Background .........................................................................................................................................................1

1.1 Introduction .................................................................................................................................................1

1.2 Objectives for Biosolids Management ........................................................................................................1

1.3 Purpose of Plan ..........................................................................................................................................1

2 Existing Conditions ..............................................................................................................................................2

2.1 Overall Process Description .......................................................................................................................2

2.2 Current Solids Loadings .............................................................................................................................2

Influent Flow........................................................................................................................................2

Influent Total Suspended Solids and Biochemical Oxygen Demand .................................................4

Primary Sludge ...................................................................................................................................5

Waste Activated Sludge ......................................................................................................................7

Sludge Thickening ..............................................................................................................................8

Sludge Digestion .............................................................................................................................. 10

Sludge Dewatering .......................................................................................................................... 11

2.2.7.1 Biogas Production ........................................................................................................................ 12

2.3 Existing Solids Handling Facilities ........................................................................................................... 14

Introduction ...................................................................................................................................... 14

2.3.1.1 Gravity Thickeners ....................................................................................................................... 14

2.3.1.2 Primary Digesters ........................................................................................................................ 15

2.3.1.3 Secondary Digesters ................................................................................................................... 15

2.3.1.4 Dewatering Facilities .................................................................................................................... 16

2.3.1.5 Boiler Building .............................................................................................................................. 16

2.3.1.6 Cogeneration Facility ................................................................................................................... 17

2.3.1.7 Gas Collection and Storage ......................................................................................................... 17

2.3.1.8 Sludge Storage Facilities ............................................................................................................. 17

3 Biosolids Projections ........................................................................................................................................ 18

3.1 Design/Future Biosolids Projections ........................................................................................................ 18

3.2 Proposed Hauled Waste Projections ....................................................................................................... 19

3.3 Biogas Utilization ..................................................................................................................................... 20

4 Biosolids Technology Assessment ................................................................................................................... 22

4.1 Sludge Thickening ................................................................................................................................... 22

Gravity Belt Thickener (GBT)........................................................................................................... 23

Dissolved Air Flotation (DAF) Thickener ......................................................................................... 23

Centrifuge ........................................................................................................................................ 24

Rotary Drum Thickener .................................................................................................................... 24

Volute Thickener .............................................................................................................................. 24



Table of Contents | ii


WAS Thickening Recommendations ............................................................................................... 25

4.2 Hauled Waste Handling ........................................................................................................................... 25

4.3 Anaerobic Digestion ................................................................................................................................. 25

4.4 Dewatering ............................................................................................................................................... 27

Centrifuge ........................................................................................................................................ 27

Screw Press and Volute Dewatering Press ..................................................................................... 28

Rotary Press .................................................................................................................................... 29

4.5 Vivianite Control ....................................................................................................................................... 30

4.6 Biogas Utilization Assessment ................................................................................................................ 31

Expected Energy Potential from Biogas .......................................................................................... 32

Heating Requirements for Digestion and Building Heating ............................................................. 33

Biogas Utilization Technology Assessment ..................................................................................... 33

4.6.3.1 Fuel Cells ..................................................................................................................................... 33

4.6.3.2 Reciprocating Engines ................................................................................................................. 34

4.6.3.3 Biogas Pretreatment .................................................................................................................... 34

4.6.3.4 Natural Gas Pipeline Injection ..................................................................................................... 35

5 Future Regulatory Trends ................................................................................................................................ 36

5.1 Standards ................................................................................................................................................ 36

5.2 Pollutants ................................................................................................................................................. 36

5.3 Pathogen Reduction ................................................................................................................................ 38

5.4 Vector Attraction Reduction ..................................................................................................................... 39

5.5 Biosolids Management ............................................................................................................................ 40

General Permit ................................................................................................................................. 40

Land Application 30-Day Notice ...................................................................................................... 41

Recordkeeping ................................................................................................................................. 41

Land Application Requirements ....................................................................................................... 41

5.6 Regulatory and Non-Regulatory Drivers .................................................................................................. 41

Phosphorus Management ................................................................................................................ 41

Hauled Waste Acceptance .............................................................................................................. 42

Odor ................................................................................................................................................. 42

Farmland Availability and Demand for Product ............................................................................... 42

6 Summary of Improvement Plan ........................................................................................................................ 44

6.1 Biosolids Facility Overall Improvements .................................................................................................. 44

Separately Thicken Waste Activated Sludge and Primary Sludge .................................................. 44

Increase Utilization of the Existing Anaerobic Digesters ................................................................. 44

Combined Heat and Power Generation ........................................................................................... 44

Anaerobic Digestion Improvements ................................................................................................. 45



Table of Contents | iii


6.2 Specific Facility Recommended Improvements ...................................................................................... 48

Gravity Thickener Facilities .............................................................................................................. 49

Hauled Waste Facility ...................................................................................................................... 49

Waste Activated Sludge Thickening Facility .................................................................................... 53

Sludge Blending Tank ...................................................................................................................... 53

Primary Digesters and Control House ............................................................................................. 54

Secondary Digesters and Control House ........................................................................................ 55

Dewatering Facilities ........................................................................................................................ 56

Boiler Building .................................................................................................................................. 56

Cogeneration Building ..................................................................................................................... 56

Vivianite Management ..................................................................................................................... 57

Sludge Storage Sheds ..................................................................................................................... 57

Gas Collection, Storage and Pretreatment ...................................................................................... 58

7 Improvements Phasing and Cost Analysis ....................................................................................................... 60

7.1 Age and Condition of Existing Processes................................................................................................ 60

7.2 Maintain Biosolids Facilities in Service .................................................................................................... 60

7.3 Availability of Funding in Relation to Other Infrastructure Needs ............................................................ 60

7.4 Analysis of Hauled Waste Alternatives .................................................................................................... 60

Alternative 1 - Hauled Waste Base Case ........................................................................................ 61

Alternative 2 - 30% Hauled Waste ................................................................................................... 61

Alternative 3 - No Hauled Waste ..................................................................................................... 61

Hauled Waste Cost Analysis Parameters and Assumptions ........................................................... 62

Net Present Value ............................................................................................................................ 63

Risks to the Hauled Waste Alternatives .......................................................................................... 64

Sensitivity Analysis .......................................................................................................................... 64

Other Biosolids Improvement Plan Benefits .................................................................................... 65

Hauled Waste Recommendation ..................................................................................................... 65

7.5 Summary and Cost of Improvements ...................................................................................................... 65

7.6 Biosolids Facilities Improvements Phasing Plan ..................................................................................... 71



List of Figures | iv


List of Figures

Figure ES-1. Schematic of Recommended Biosolids Improvements .................................................................. ES-4

Figure ES-2. Biosolids Facilities Improvement Phasing Plan ............................................................................. ES-7

Figure 2-1. Existing Solids Process Flow Diagram ....................................................................................................2

Figure 2-2. Daily Influent Flow ....................................................................................................................................3

Figure 2-3 Average Monthly Influent Flow ..................................................................................................................3

Figure 2-4. Average Monthly Influent BOD5 and TSS Concentration ........................................................................4

Figure 2-5. Average Monthly Influent BOD5 and TSS Loads ....................................................................................5

Figure 2-6. Daily Primary Sludge Flow .......................................................................................................................6

Figure 2-7. Daily Primary Sludge Total Solids Load ...................................................................................................6

Figure 2-8. Daily Waste Activated Sludge Flow .........................................................................................................7

Figure 2-9. Daily Waste Activated Sludge Total Solids Load .....................................................................................8

Figure 2-10. Daily Thickener Underflow .....................................................................................................................9

Figure 2-11. Average Monthly Thickener Underflow Total Solids Load .....................................................................9

Figure 2-12. Average Monthly Primary Digester Solids Load ................................................................................. 10

Figure 2-13. Average Monthly Primary Digester Volatile Solids Load .................................................................... 11

Figure 2-14. Average Monthly Belt Folter Press Dry Cake Load ............................................................................ 11

Figure 2-15. Average Monthly Primary Digester Gas Production ........................................................................... 12

Figure 2-16. Monthly Gas Usage: January 2014 – July 2017 ................................................................................. 14

Figure 4-1. Schematic of Two Phase Anaerobic Digestion ..................................................................................... 26

Figure 4-2. Cutaway View of Biosolids Dewatering Centrifuge ............................................................................... 27

Figure 4-3. Screw Press .......................................................................................................................................... 28

Figure 4-4. Volute Dewatering Press ....................................................................................................................... 29

Figure 4-5. Six Channel Rotary Press ..................................................................................................................... 30

Figure 4-6. Schematic of CHP Option for Biogas Utilization ................................................................................... 31

Figure 4-7. Schematic of Natural Gas Injection Option for Biogas Utilization ......................................................... 32

Figure 6-1. Schematic of Recommended Biosolids Improvements ........................................................................ 46

Drawing 01 ............................................................................................................................................................... 47

Drawing 02 ............................................................................................................................................................... 51

Drawing 03 ............................................................................................................................................................... 52

Figure 6-2. Proposed Storage Shed ........................................................................................................................ 58

Figure 7-1. Phasing Implementation ........................................................................................................................ 71



List of Tables | v


List of Tables

Table ES-1. Solids Digestion Capacity ................................................................................................................ ES-3

Table ES-2. Hauled Waste Alternatives Cost Analysis ....................................................................................... ES-4

Table ES-3. Recommended Biosolids Facilities .................................................................................................. ES-5

Table ES-4. Project Cost Estimates .................................................................................................................... ES-6

Table 2-1. Digester Performance Summary ............................................................................................................ 13

Table 2-2. Existing Total Boiler Data ....................................................................................................................... 17

Table 2-3. Existing Total Enginator Data ................................................................................................................. 17

Table 3-1. Sludge Design Criteria (AWTF) .............................................................................................................. 18

Table 3-2. Solids Digestion Capacity ....................................................................................................................... 19

Table 3-3. VSS Loadings from Selected HSW Generators ..................................................................................... 19

Table 3-4. Ratio of HSW to AWTF Solids at Selected Loadings ............................................................................. 20

Table 3-5. Current Biogas Generation with New CHP System ............................................................................... 20

Table 3-6. CHP: Future Conditions ......................................................................................................................... 21

Table 4-1. Typical Design Criteria for Gravity Thickeners1 ..................................................................................... 22

Table 4-2. Projected Gas Generation at Facilities Plan Digester Theoretical Design Capacity.............................. 32

Table 4-3. Lean Burn Reciprocating Engine Values ............................................................................................... 33

Table 5-1. Biosolids Pollutant Concentrations Limits1 ............................................................................................. 37

Table 5-2. CRW 2015 Pollutant Analyses Summary ............................................................................................... 38

Table 5-3. AWTF Historical Pathogen Reduction Monitoring Summary ................................................................. 39

Table 5-4. CRW Historical Vector Attraction Reduction Monitoring Summary ........................................................ 40

Table 6-1. Recommended Improvements by Facility .............................................................................................. 48

Table 6-2. Hauled Waste Receiving Station ............................................................................................................ 50

Table 6-3. Gravity Belt Thickeners .......................................................................................................................... 53

Table 6-4. Sludge Blending Tank ............................................................................................................................ 54

Table 6-5. Acid Phase Digester ............................................................................................................................... 55

Table 6-6. Secondary Digesters .............................................................................................................................. 55

Table 6-7. Proposed Storage Shed ......................................................................................................................... 57

Table 7-1. Incremental Capital for Hauled Waste Alternatives ............................................................................... 62

Table 7-2. Hauled Waste Alternatives Cost Analysis .............................................................................................. 63

Table 7-3. NPV for Hauled Waste Alternatives ....................................................................................................... 64

Table 7-4 Summary of Improvements ..................................................................................................................... 66

Table 7-5. Project Cost Estimates ........................................................................................................................... 70



Executive Summary | ES-1


Executive Summary

Overview

Capital Region Water (CRW) owns and operates the Harrisburg Advanced Wastewater Treatment Facility (AWTF), permitted for a maximum month flow of 37.7 million gallons a day (MGD). A recent upgrade of the liquid treatment process to provide biological nutrient removal (BNR) levels of treatment was brought online in April 2016. The solids handling and treatment facilities were not upgraded as part of that contract. A team led by Whitman, Requardt & Associates, LLP (WRA) has evaluated the biosolids facilities at the AWTF and developed a plan that allows CRW to meet their goals and objectives for these facilities. This Biosolids Facility Improvement Plan provides the long-term planning for the AWTF biosolids facilities and outlines recommended facility improvements. The Biosolids Facility Improvement Plan is presented in seven sections: 1.) Background 2.) Existing Conditions 3.) Biosolids Projections 4.) Biosolids Technology Assessment 5.) Future Regulatory Trends 6.) Summary of Improvement Plan 7.) Improvements Phasing and Cost Analysis The Background section provides an overview of the Improvement Plan including the objectives for biosolids management and the purpose of the plan. The Existing Conditions section reviews the historical and current solids handling facilities and operation. The Biosolids Projections section establishes the expected biosolids generation for the 25-year planning period. Alternatives for biosolids operations and equipment are presented in the Biosolids Technology Assessment section. The advantages and disadvantages are considered in the context of making the best use of existing infrastructure and attainment of the biosolids management goals. The expectations for future biosolids regulation are included in the Future Regulatory Trends section. The Summary of Improvement Plan section summarizes the improvements for each biosolids facility. The Improvements Phasing and Cost Analysis section includes a phasing plan and cost estimates for each improvement.

Condition Assessment

Prior to the development of the Biosolids Facility Improvement Plan, WRA completed a condition assessment of the existing biosolids facilities. Existing biosolids facilities include:

Two (2) Gravity Thickeners

Two (2) Fixed Cover Primary Anaerobic Digesters

Two (2) Secondary Anaerobic Digesters, one with fixed cover and one with floating cover

Two (2) 2.5 Meter Belt Filter Presses

Covered Biosolids Storage

One (1) Gas Storage Tank

Two (2) Biogas Driven 400 kW Internal Combustion Engine Driven Generators

Three (3) Concentric Tube Heat Exchangers

Two (2) Biogas Fueled Hot Water Boilers

Polymer feed systems, pumps, piping and conveyance systems to support the operations.





The condition assessment found many of the biosolids facilities to be operating well beyond their expected useful life, and some are not operating as intended. In general, the biosolids facilities are in need of extensive upgrades of the existing process equipment and supporting facilities. Additionally, there are potential opportunities to improve the energy efficiency and resource recovery from the solids and biogas utilization processes.

Summary of Evaluations

Through improvements to the solids treatment processes, additional biogas could be generated, and the associated energy recovered. Biogas is the methane rich gas produced during the anaerobic digestion of organics, and is a valuable resource produced by the AWTF. To capitalize on this resource, two areas must be addressed:

Maximize the biogas production efficiency

Optimize the energy recovery process The AWTF has been utilizing the biogas generated in the digester to produce electric power and generate heat. To increase the total energy recovered from the electric power generation process, the existing separate heat and power system is recommended to be replaced by a combined heat and power (CHP) system. By utilizing an efficient CHP system, the waste heat from the electrical energy generation process can provide the majority of the heat required for heating the digesters, at a relatively low operational cost. There are several opportunities to improve the biogas production efficiency (volume of biogas generated for each pound of organics fed to the digester) of the primary digesters including:

Increase the percent solids of the sludge sent to the digester

Improve digester mixing

Improve digester operation, including maintaining a near constant temperature

Co-digest high strength hauled waste from outside sources The proposed primary digester improvements that are currently being implemented at the AWTF will include new mechanical linear motion mixing, replacement of recirculation and transfer pumps, a new electrical and controls building, and replacement of sludge piping and valves, which will result in sludge heating improvements. These improvements will increase mixing efficiency and temperature control in the digesters, allowing for the digesters to accept a higher concentration of feed sludge. To increase the percent solids of the thickened sludge, it is recommended that the primary sludge and waste activated sludge (WAS) be separately thickened. To accomplish this, the primary sludge will continue to be thickened in the existing gravity thickeners. WAS will be thickened using gravity belt thickeners (GBTs). The two thickened sludges will be combined prior to entering the digesters. The GBTs will be installed in a new two story building adjacent to the existing primary clarifiers. A thickened WAS storage tank will be constructed adjacent to the new building. The primary digesters will have excess capacity over that needed to digest the sludge generated by the AWTF.

Table ES-1 includes the capacity of the two (2) digesters after the ongoing refurbishment, the projected amount of

sludge generated by the AWTF, and the resulting available digester capacity, that could be available for accepting

outside high strength wastes (referred to “hauled waste”).





Table ES-1. Solids Digestion Capacity

After Primary Digester Upgrades and Before WAS Thickening After WAS Thickening

Condition VS Loading (lbs / day)

VS Loading (lbs / day)

Digester Capacity

37,000

61,000

Projected Loading from

AWTF 24,2401 36,5602

Available Capacity

12,760 24,400

1 Estimated for the calendar year 2020 2 Ultimate AWTF generated

Hauled Waste Evaluation

Hauled waste is a potential source of revenue from tipping fees, as well as a source of solids that can be converted to biogas in the digesters. To efficiently receive and handle high strength hauled waste, a receiving station and equalization tank is recommended. The hauled waste receiving station would be installed on the first level of the proposed WAS thickening building. The receiving station would provide screens, and the ability to remove grit and floating solids prior to entering the equalization tank, which will be sized for a volume of 100,000 gallons. There will be pumps in order to transfer the hauled waste from a truck to the screening and grit removal system. The hauled waste would then be combined, using hose pumps, with the thickened WAS and thickened primary sludge in a blending tank, of volume equivalent to one day’s volume of hauled waste or approximately 75,000 gallons, prior to digestion. There will be a set of pumps to transfer the blended sludge to the digesters. In addition to the infrastructure needed, accepting hauled waste will require operational and maintenance support. Accepting hauled waste also introduces risks to the digestion process, and identifying, negotiating, and receiving high quality hauled waste will also add complexity to the overall AWTF operation. At the same time, the opportunity to provide a positive net economic impact to the AWTF as well as providing environmental and public relations benefits makes receiving hauled waste an attractive alternative. A cost analysis was conducted on three alternatives to assist in the recommendation to receive hauled waste. The three alternatives that were considered are:

Base Case – Hauled Waste received at about 50-60% of the total feed to operate at design capacity

30% Hauled Waste – Hauled Waste quantity is limited to 30% of the total feed to the digesters

No Hauled Waste – Only AWTF biosolids are digested.

The results of the simple rate of return and payback period for the alternatives is included in Table ES-2.





Table ES-2. Hauled Waste Alternatives Cost Analysis

Alternative Incremental

Capital

Annual

Benefit1

Simple Rate of

Return

Payback

Period

Hauled Waste

Base Case $15,470,000 $892,166 5.8% 17

30% Hauled

Waste $5,910,100 $529,491 9.0% 11

No Hauled

Waste $0 $272,454 N/A N/A

1. Annual Benefit = First Year Revenue from Electric generated + Offset of purchase of Nat Gas for heating + tipping revenue - HW disposal costs - Maintenance Costs (2% of Incremental Capital)

The alternative limiting hauled waste to 30% of the digester feed was found to have a shorter payback period compared to the base case. This alternative merits further consideration since it offers the potential for the plant to incrementally increase the volume of hauled waste received while the plant monitors and evaluates the stability of the digestion process. The benefits derived from co-digesting hauled waste will be affected by many factors that will vary over time. The tipping fee, price for electricity sold to the utility, availability and characteristics of hauled waste are each significant contributors to the benefit received. A sensitivity analysis of the effect some of the variables will have on the project financial returns is presented in Section 7.4.

Summary of Improvements

A schematic of the recommended improvements program is shown as Figure ES-1.

Figure ES-1. Schematic of Recommended Biosolids Improvements A summary of the recommended biosolids facilities is shown in Table ES-3.

Gravity Thickeners

Primary Anaerobic Digesters

Belt Filter Presses

Secondary Anaerobic Digesters

Primary Sludge

Diluent Water

Gas Storage Sphere

Polymer

Combined Heat and Power Waste Flare

Biosolids Storage

Land Application

Waste Activated Sludge

Hauled

Unloading With

Rock Trap

Screen Waste

Equalization Tank

Biogas Pretreatment Gravity Belt

Thickeners

Acid Phase

Digester FUTURE Higher Cake Solids Dewatering Process

followed by Heat Drying

Blending Tank





Table ES-3. Recommended Biosolids Facilities

Gravity Thickeners, Existing

Two (2) Existing

Diameter 80 ft, each

Hauled Waste Receiving Station, New

New Building with WAS Thickening

New Receiving Station

600 gpm Unloading Rate

Screening, Grit, and Grease Removal

75,000 gal Holding Tank

Hauled Waste Transfer Pumps

WAS Thickening, New

3 – New 2 m Gravity Belt Thickeners

600 gpm Hydraulic Loading Rate Each

2 In Operation 16.5 hrs/day at Design Capacity

New Building with Hauled Waste

100,000 gallon Blending Tank

Sludge Transfer Pumps

Primary Digesters, Refurbish and Upgrade

Mechanical Mixing

Provisions for Direct Steam Heating

Replace Pumps and Piping

Two Phase Digestion, New

One (1) 300,000 gallon Acid Phase Digester

1.5 Days SRT

Refurbish Secondary Digesters

Replace Roof on Both Digesters

Refurbish Concrete and Brick

Replace Piping

Upgrade One (1) Secondary Digester

Upgrade One Existing Digester to Function as a Primary Digester with Mechanical Mixer, and Recirculation with Temperature Control.

Install Mechanical Mixer on One Existing Digester

Sludge Dewatering, Upgrade

Two (2) New Centrifuges

Boiler Building, Upgrade One (1) New Steam Boiler, 6,000,000 BTU/hr in

Existing Building

Cogeneration Building, Upgrade

Two (2) New 500kW Biogas Reciprocating Engine Drive Generator Units, with Provisions for a Third Unit

Combined Heat Recovery

Gas Collection, Storage and Pretreatment, Refurbish and Upgrade

Replace Two (2) Low Pressure Compressors

Replace Hydrogen Sulfide Removal Unit

Replace Particulate and Condensate Removal Unit

Existing Storage Tank

Sludge Storage Sheds, Expand

Two (2) Existing

One (1) New 15,000 cu ft Capacity Sludge Storage Shed





A rough order of magnitude (ROM) project cost estimate for each improvement is summarized in Table ES-4. The point estimates are based on the available information gathered in 2017, and are in 2017 dollars. The ENR Construction Cost Index on August 2017 was 10842. Recognizing the scope of each improvement is conceptual in nature, a low estimate and high estimate are also presented, the Low Estimate including a negative 20% contingency, and the High Estimate including a 50% contingency.

Table ES-4. Project Cost Estimates

Included Projects

Low Estimate

-20%

Contingency

High Estimate

+50%

Contingency

Point Estimate

0%

Contingency

Primary Digester

Improvements $9,500,000 $13,400,000 $11,100,000(1)

CHP Evaluation & Enginator

Rehabilitation $600,000 $1,125,000 $750,000

Hauled Waste and Gas &

Power Generation Market

Evaluation

$160,000 $300,000 $200,000

Secondary Digester

Rehabilitation $2,900,000 $5,400,000 $3,600,000

Gravity Thickeners $1,500,000 $2,800,000 $1,900,000

CHP and Gas System

Upgrades $10,700,000 $20,100,000 $13,400,000

WAS Thickening and Hauled

Waste $7,800,000 $14,600,000 $9,700,000

Secondary Digester

Rehabilitation $2,900,000 $5,400,000 $3,600,000


CHP and Gas System

Upgrades $10,700,000 $20,100,000 $13,400,000


Waste $7,800,000 $14,600,000 $9,700,000

Secondary Digester Retrofit to

Primary Digester & Acid

Phase Digestion

$7,650,000 $14,340,000 $9,560,000

Dewatering $6,100,000 $11,500,000 $7,600,000

1. Primary Digester Improvement Point, Low, and High Estimates based on July 2017 75% Basis of Design Estimate.





A phased implementation plan, presented in Figure ES-2, was developed following the preparation of the biosolids facilities improvement projects and in consultation with CRW. The phased approach is intended to address immediate priorities while balancing recommended future improvements with CRW’s other system-wide infrastructure needs. The immediate priority for the AWTF Biosolids Facilities is the rehabilitation of the primary anaerobic digesters and related equipment, such that the plant can fully utilize existing equipment and maintain a stable and reliable digestion process. The Primary Digester Improvements, identified as Phase 1, will provide greater reliability for digestion with improvements in mixing, recirculation and heating, and will be starting construction in 2018. Phase 2 will include the refurbishment of the enginators to provide more reliable service in the short term and will also include an investigation of alternative biogas utilization options. Phase 3 will include an expanded market analysis of hauled waste generators, and will develop recommendations for a fee structure for the implementation of a hauled waste program. Phase 4 addresses the reliability of the gravity thickeners and the secondary digesters with a planned refurbishment of each facility. Phases 5 and 6 include major infrastructure improvements to biosolids handling and resource (energy) recovery systems, and allow for an expanded hauled waste receiving program at the AWTF. It is anticipated that the Phase 5 and 6 projects will be further refined through evaluations performed in Phases 2 and 3.

Figure ES-2. Biosolids Facilities Improvement Phasing Plan

Background | 1


1 Background

1.1 Introduction

The solids handling facilities at the AWTF were originally constructed in 1959 and included primary digesters, vacuum filtration dewatering and incineration. The original digesters were converted to secondary digesters in the 1970s when new primary digesters and support facilities were installed. At the same time, gravity thickeners, gas storage, and a digested sludge pumping station were added. Following the 1970s upgrade, digested sludge was pumped off site to an incinerator facility which included vacuum filtration for dewatering, sludge drying, and incineration. A cogeneration facility was added in 1984 to generate electricity from digester gas. The original vacuum filtration dewatering facilities were replaced in 1988 with belt filter presses and dewatered solids were hauled to a landfill. The belt filter presses were replaced in 2011. Currently, dewatered solids are land applied on local farms and occasionally sent to landfill. In general, the findings from the Harrisburg Advanced Wastewater Treatment Facility Biosolids Facilities Improvement Plan Existing Conditions Report (February 2017) indicated that the biosolids related tanks and buildings are in fair to good physical condition. The mechanical, electrical, HVAC and Instrumentation and Controls systems on the other hand are in poor condition and are operating well beyond their expected life. One exception was the dewatering belt filter presses, which were installed in 2011, and are fully operational.

1.2 Objectives for Biosolids Management

CRW is progressive with their goals and objectives for the biosolids facilities. They have long recognized there is real value in the biosolids which are generated by the AWTF, both through beneficial reuse of the biosolids, and also through utilization of the biogas that is generated during anaerobic digestion. Due to improvements in technology and advancements in operational philosophies, e.g. focus on energy efficiency and resource recovery since the AWTF biosolids facilities were installed, there are opportunities to expand on the resources recovered from the biosolids. CRW’s goals for biosolids management include:

• Increase the energy recovery from biosolids, • Develop facilities that provide operational and energy efficiency, • Improve long term sustainability, • Increase CRW revenue.

1.3 Purpose of Plan

The purpose of the Biosolids Facilities Improvement Plan is to:

Review the existing biosolids infrastructure at the AWTF,

Determine existing and planning level solids handling capacities and opportunities for supplementing facilities for accepting and processing hauled waste,

Identity alternatives for biosolids handling, hauled waste handling, digestion, and biogas utilization,

Determine the biosolids facility needs and develop a plan for future improvements to address the need



Existing Conditions | 2


2 Existing Conditions

2.1 Overall Process Description

The AWTF existing solids handling processes consist of gravity thickening of combined primary sludge and WAS, anaerobic sludge digestion, belt filter press dewatering, and sludge storage. Gas generated from the anaerobic digesters is stored on site and utilized for boilers to provide heat to the anaerobic digestion process, building heat and fuel for a supplemental electrical cogeneration system. Figure 2-1 shows the process flow diagram for the existing solids handling facilities.

Figure 2-1. Existing Solids Process Flow Diagram

2.2 Current Solids Loadings

Operating records for the time period from August 2013 to June 2017 were evaluated. The assessment of the liquid treatment data was limited to aspects that affect sludge production.

Influent Flow

The AWTF influent flow was reviewed to determine long term trends and evaluate peaking factors. Figure 2-2 shows the daily influent flow to the AWTF, and Figure 2-3 shows the monthly average influent flow. It should be noted that the influent flow stream does not include recycle streams from the sludge thickening, nor the sludge dewatering process.

Gravity Thickeners


Belt Filter Presses Secondary

Anaerobic Digesters

Primary Sludge

Diluent Water

Gas Storage Sphere

Polymer

Enginators Boilers

Waste Flare

Biosolids Storage

Land Application

WAS





Figure 2-2. Daily Influent Flow

Figure 2-3 Average Monthly Influent Flow

The average daily flow for the period reviewed was 21.5 MGD, the maximum month was 37.5 MGD, and the maximum day flow was 74.4 MGD. The maximum month peaking factor is 1.7, and the maximum day peaking factor is 3.5.





The influent flow to the AWTF demonstrates fluctuations typical of a system with a combined storm and sanitary collection system, which exhibits much higher peaking factors than a separate sewer collection system. CRW is developing a long-term control plan for controlling combined sewer overflows, which may result in more flow conveyed to the AWTF. These system improvements would be expected to increase the amount of solids that are processed at the AWTF by a nominal amount. The storm water itself contributes minimal quantity of solids from normal runoff activity, but the storm water inlets do collect some solids which are eventually flushed to the AWTF.

Influent Total Suspended Solids and Biochemical Oxygen Demand

Figure 2-4 presents the average monthly influent concentrations of total suspended solids (TSS) and biochemical oxygen demand (BOD5) in milligrams per liter Figure 2-4. Average Monthly Influent BOD5 and TSS Concentration

. The influent BOD5 and TSS loads, in pounds per day, directly influence the amount of sludge that the plant produces, and are presented in Figure 2-5.





Figure 2-5. Average Monthly Influent BOD5 and TSS Loads

Although there are significant fluctuations in the BOD5 and TSS loads, they have varied within the same range for the three year period reviewed, indicating they would expect to continue within the same range for some time into the future. The Long-Term Control Plan (LTCP) could result in more flow conveyed to the AWTF, and therefore result in a nominally higher influent solids (TSS) loading. The average BOD5 load for the time period was 24,600 lb/day, while the average TSS load was 27,700 lb/day, resulting in an average BOD5/TSS ratio of 0.89 lb/lb, which is typical of medium strength raw municipal wastewater.

Primary Sludge

Primary sludge is drawn off of the four primary clarifiers and pumped to the gravity thickeners. The daily primary sludge flow rate and the primary sludge solids loadings are shown in Figure 2-6 and Figure 2-7, respectively.





Figure 2-6. Daily Primary Sludge Flow

Figure 2-7. Daily Primary Sludge Total Solids Load





The daily primary sludge flow has been generally consistent during the time period studied. The daily load appears to be quite variable, but is indicative of variable results of periodic grab sampling concentrations multiplied by more consistent flow rates. The average primary sludge load was 22,500 lb/day.


WAS is pumped from the mixed liquor channel following the aerobic / post anoxic reactors and prior to the polymer mix tank and discharged to the gravity thickeners. The daily WAS flow rate and WAS solids loadings are shown in Figure 2-8 and Figure 2-9, respectively. Figure 2-8. Daily Waste Activated Sludge Flow

The period for which the WAS data were reviewed captures process changes resulting from the 2013 AWTF Improvements Project which included liquid process upgrades to provide for Biological Nutrient Removal (BNR), which were substantially complete at the end of April 2016. During the construction period, from March 2014 through April 2016, aeration basins and secondary clarifiers were sequentially taken offline. The data from this period are not relevant to the biosolids planning. The May and June 2017 WAS data were higher than the other months due to a draw down in mixed liquor suspended solids (MLSS) concentration to meet the warm weather MLSS target, which is less than the cold weather target concentration. Although this transition will occur each year, the transition will be carried out over a longer period to keep the WAS flow rates within a more narrow range than that in 2017. WAS pumping operation was modified through the upgrades, changing from wasting settled solids from the final clarifiers to wasting mixed liquor solids. Flow rate increased to compensate for the lower concentration. The WAS load prior to October 2015 averaged 6,100 lb/day, while the WAS load since May 2016 has averaged 16,600 lb/day. During the period October 2015 through May 2016, due to startup of nutrient removal upgrades, highly variable wasting of activated sludge occurred. The increased WAS rates since May 2016 correspond to the change of operation as a result of the BNR upgrade and therefore this increase in WAS solids production is expected to continue. Thus, the recent upgrades have increased the WAS component of the solids load from 22% to 39% of the total load.

BNR Construction BNR Online





Figure 2-9. Daily Waste Activated Sludge Total Solids Load

Sludge Thickening

The combined average total primary and WAS solids sent to the gravity thickeners from May 2016 to June 2017 was 40,500 lb/day with a 61 to 39 percent split of primary sludge to WAS. As the sludge settles, the thickened sludge is drawn off from the bottom, or underflow, of the thickeners, and is pumped to the primary digesters. The daily flow rate and monthly average solids load of gravity thickener underflow are shown in Figure 2-10 and Figure 2-11, respectively.

BNR Construction BNR Online





Figure 2-10. Daily Thickener Underflow

Figure 2-11. Average Monthly Thickener Underflow Total Solids Load

The thickener underflow (i.e. feed to the primary digesters) has averaged 3% solids concentration for the period reviewed. The thickener underflow daily solids load has increased since May 2016 as a result of the BNR upgrade. The BNR upgrade included the addition of a supplemental carbon (methanol) to promote the denitrification reaction. The denitrification bacteria will utilize the supplemental carbon, and therefore yield more waste solids.





The average thickened solids load increased from approximately 25,100 lb/day before October 2015 to approximately 30,400 lb/day since May 2016. A solids balance between the overall average thickener influent and underflow since May 2016 shows a difference of 9,500 lb/day. Some loss would be expected to represent the solids being lost over the perimeter weir, or thickener supernatant. The data, however, show an average thickener supernatant load of 2,300 lb/day, about a quarter of what is expected based on the solids balance calculations derived from the measured loads in and out of the gravity thickeners. This imbalance is likely a symptom of irregular grab sampling of the supernatant. The supernatant is returned to the head of the activated sludge process.

Sludge Digestion

The thickener underflow load is a measure of the feed solids to the primary digesters, see Figure 2-12. Total suspended solids digester loading prior to October 2015 was 25,000 lbs/day, and 30,400 lbs/day since May 2016. Figure 2-12. Average Monthly Primary Digester Solids Load

The volatile suspended solids (VS) component of the primary digester feed averaged 19,800 lbs/day prior to October 2015, and 23,700 lb/day since May 2016, see Figure 2-13.





Figure 2-13. Average Monthly Primary Digester Volatile Solids Load

Sludge Dewatering

Figure 2-14 shows the monthly average dry cake solids discharged from the belt filter presses. The belt filter presses are generally operated 24 hours a day, 7 days per week. Figure 2-14. Average Monthly Belt Folter Press Dry Cake Load





Since May 2016, the average daily primary digested solids feed to the belt filter presses was 20,600 lb/day, while the dewatered cake solids averaged 16,300 lb/day (and 20% solids) suggesting a belt filter press solids capture efficiency of 79%. Although this is less than the typical 90-95% efficiency, other factors should be considered such as the variabilities in the grab sampling, especially when considering the secondary digesters are not mixed. Also, the belt filter press operations are variable from month to month depending on several factors including biosolids disposal limitations and available storage capacity within the secondary digesters. As shown in Figure 2-14, the volume of cake solids processed varies significantly from month to month.

2.2.7.1 Biogas Production

Anaerobic digestion of sludge results in methane gas production. Figure 2-15 illustrates the average monthly gas production during the review period. Although the data are somewhat limited, and influenced by variable operating conditions and digestion process equipment issues, the data suggest that the digestion process is performing either below or at the low end of typical ranges for gas production parameters. Based on the available plant data, digester performance including volatile solids loading and destruction, and associated gas production, were not satisfactory when the process should have been more stable, before and after BNR upgrade startup. Data shown in Figure 2-15 is for the period August 2013 – June 2017. Figure 2-15. Average Monthly Primary Digester Gas Production

Data prior to BNR Upgrade startup are for the period August 2013 – October 2015. The daily average methane gas production was approximately 150,000 cubic feet per day (cfd). The maximum month was about 184,000 cfd and maximum daily gas production was 291,500 cfd. Primary digester gas flows have been fairly consistent, with several significant drops that took several months from which to recover. It is unknown what caused these drops, but the BNR Upgrade construction, and fouling of heat exchangers are possible contributing factors. CRW has also reported issues with the gas flow metering. The BNR Upgrade startup period extended from October 2015 to May 2016, and post startup from May 2016. Digester performance data for the entire period of data, and before and after the startup period, is summarized in Table 2-1.





Table 2-1. Digester Performance Summary

Period Description of

Time Period

Feed

VSS

(lb/day)

Digested

Sludge

VSS

(lb/day)

Destroyed

VSS

(lb/day)

Destroyed

VSS

(%)

Digester

Gas (cfd)

Gas

Produced

(cf/VSS

fed)

Gas

Produced

(cf/VSS

destroyed)

Aug 13 –

Oct 15

Prior to BNR

Upgrade

Construction

19,850 8,900 10,950 55.2 150,000 7.5 13.7

May 16 –

June 17

After BNR

Upgrade 23,700 12,370 11,330 47.8 134,000 5.7 11.8

Aug 13 –

June 17

Overall

Period

Reviewed

21,300 10,000 11,300 53.1 145,000 6.8 12.8

Gas production should fall within the following ranges:

8-12 cf gas / lb VSS fed (Averages for the 3 periods range from 5.7 – 7.5.)

12-18 cf gas / lb VSS destroyed (Averages for the 3 periods range from 11.8 – 13.7)

Although cf gas / lb VSS destroyed is within the typical range, the fact that the cf gas / lb VSS fed is low indicates that the destruction should be better. Several factors, with combined effects contribute to the poor performance:

1. Low feed solids concentration, causing a low solids retention time. 2. Insufficient digester temperature. (Optimum 98 deg F, minimum 95 deg F.) 3. Variations in digester temperature. 4. Inadequate mixing. 5. Batch feeding of hauled waste to digester (2017)

Collectively, these factors will be addressed later in this report, especially related to sludge thickening and digester heating and mixing. These improvements will allow for increased VSS destruction and associated gas production, in particular with respect to the increase in WAS since the BNR upgrade. Biogas Utilization The methane gas is compressed and stored in a spheroidal storage tank, and it is also used within the facility as fuel for boilers that provide heating of buildings and digester sludge and as fuel for two (2) cogeneration units, referred to as enginators. Excess gas that cannot be used is sent to be flared at a waste gas burner. Figure 2-16 illustrates the monthly total usage for the period evaluated, divided into usage for each gas consumer. CRW provided air flow data for total gas production, boiler usage, and the waste flare. Enginator gas use was calculated using these values.





Figure 2-16. Monthly Gas Usage: January 2014 – July 2017

The majority of gas produced by the digesters is utilized by CRW either as building heat or generated electricity.

2.3 Existing Solids Handling Facilities

Introduction

The existing solids handling facilities are briefly reviewed in this section. Included in the discussion are key design and operating information. More detailed process and specific equipment information is included in the Harrisburg Advanced Wastewater Treatment Facility Biosolids Facilities Improvement Plan Existing Conditions Report (February 2017).

2.3.1.1 Gravity Thickeners

Primary sludge is pumped from the primary clarifiers by pumps in the Control Building basement through pipe tunnels 1 and 2 to the gravity thickeners. Scum is collected from the surface of the primary clarifiers and is sent to two holding pits. Supernatant from these pits is pumped to the gravity thickeners, while scum is pumped out and removed offsite by a contracted hauler. Scum from the secondary clarifiers is pumped with scum pumps to combine with WAS Pump Station force main. The primary sludge and WAS force mains combine with diluent water (plant effluent from the chlorine contact tanks and pumped from the Settled Sewage Pump Station) prior to a thickener distribution box, which distributes flow to both gravity thickener tanks. The thickened sludge is drawn off the cone bottom of the thickeners by three (3) recessed-impeller, non-clog sewage pumps, which send thickened sludge to the primary digesters. Overflow from the gravity thickeners is returned to a manhole (MH-7) and is returned to the head of activated sludge process.





At the current conditions, the average combined sludge sent to the gravity thickeners is approximately 39,900 lb/day (18,100 kg/day). With a total surface area of approximately 10,000 ft2 (934 m2), the average mass loading rate to the gravity thickeners is 0.17 lb/ft2hr (0.81 kg/m2hr).

2.3.1.2 Primary Digesters

Currently, the combined thickened sludge is transferred to two primary digesters for anaerobic digestion. The primary digesters are circular reinforced concrete tanks with sloped bottoms and covered by fixed roofs. Within the tanks, anaerobic bacteria convert the volatile solids in the sludge to volatile acids, and then to carbon dioxide and methane. The facility has only been operating one digester. The contents of each digester are mixed by drawing off digester gas from the top of the digester roof, compressing

the gas with a rotary lobe compressor, and then discharging it through eight nozzles located approximately 1/3

below the liquid level in each of three 5-foot diameter eductor tubes. The rising gas bubbles pull sludge up with

them through each eductor tube and mix the tank contents.

To keep the digestion process at an optimal level, the temperature in the digester should be maintained at

approximately 98° F. To accomplish this, sludge is recirculated through heat exchangers, which are provided with

hot water from the boiler house. Three recessed impeller pumps pull sludge from the bottom of the digesters,

circulate it through three concentric tube heat exchangers and back into the top of the digesters.

The two digesters, their associated piping, and equipment have experienced vivianite precipitation and buildup.

Vivianite is a hydrated iron phosphate mineral and has accumulated to such an extent that Digesters No. 2’s valves

are no longer operational.

The refurbishment of the primary digesters is currently being designed. Improvements will include:

Replacement of gas mixing system with a mechanical mixing system,

Replacement of the primary digester fixed covers,

Replacement of the gas and sludge piping internal to the digesters and piping and valves within the Primary Digester Control House,

Replacement of the waste gas flare,

Replacement of the primary sludge recirculation pumps,

Replacement of the primary sludge transfer pumps,

Addition of a new Electrical Building to house motor control centers and control panels for the Biosolids Facilities.

The primary digester concentric tube heat exchangers are not being modified with the current project. The heat exchangers are sufficiently sized for the digester operation when not fouled with mineral buildup (vivianite). Currently, the heat exchangers become fouled and cannot maintain digester temperature within 18-24 months of operation. When fouled, the affected piping and heat exchanger tubes are replaced at a cost of approximately $50,000. However, accommodations for steam lances are being implemented into the primary digester improvements. These along with direct steam injection in the feed stream and recirculation lines will provide a future means of eliminating vivianite buildup and for maintaining optimal digester temperatures.

2.3.1.3 Secondary Digesters

Sludge from the primary digesters can be transferred by gravity to the secondary digesters. The secondary digesters are primarily serving as digested sludge storage from where excess liquid can be decanted. The settled solids are drawn off from multiple draw off points and pumped to dewatering. Supernatant from the secondary digesters flows by gravity to the inlet channel of the primary clarifiers. There is also a pipeline which allows for truck loading of liquid digested sludge into tanker trucks. Truck loading has not been utilized for many years. There are also two progressing cavity pumps that can be used when necessary to overcome the head in the secondary digester, e.g. when lowering the level in the primary digester for maintenance or inspection. Each





digester includes piping, accumulator and compressor to withdraw digester gas from the roofs of the digesters and send it into the digester gas system.

2.3.1.4 Dewatering Facilities

Digested sludge flows by gravity through two separate pipelines with in-line sludge grinders, and then is pumped to the belt filter presses with hose pumps. Polymer is added through a ring injector, which is upstream of a mixing valve. The sludge is then fed to the gravity section of the belt filter presses. The AWTF currently operates two (2) belt filter presses (BFP) to dewater digested sludge. The two (2) in-line sludge grinders break down larger solids, and replace the function of the in-line grinder pumps in the digested sludge pumping station. Discharges from the three (3) belt filter press hose pumps can be directed to either of the 2.5 meter wide belt filter presses.

Prior to being deposited on the belt filter press, the sludge is conditioned with polymer to promote the coagulation of solids. The polymers are first received as a powdered solid, delivered in supersaks. The polymer supersak is then placed on a skid, from which polymer is metered by a screw conveyor into a pneumatic line that pushes it into a 3,300 gallon fiberglass polymer mix tank. Water is added to the polymer and the contents are mixed. Once the polymer is conditioned, it is pumped by two progressing cavity pumps to a storage/feed tank, also a 3,300 gallon fiberglass tank. The polymer solution is then pumped into an injection ring located on each belt filter press feed pipeline. During the dewatering operation, as the dewatered cake is discharged, the press belts are continuously washed with spray water. A wash water skid equipped with three booster pumps provides the pressure to adequately wash the belts. The cake is discharged from the belt filter press onto a ribbed belt conveyor which conveys the cake into a dump truck that transports it to the covered storage area. The AWTF currently uses belt filter presses for dewatering. Belt filter presses have many advantages including:

Low capital cost

Low energy consumption

Simple operation and maintenance

Ability to handle stringy solids (i.e. rags) and plastics

Historically the belt filter presses are fed at an average flow rate of 60 gpm, and the two units operate an average of 27-30 hours total a day. This corresponds to a solids feed rate of approximately 700 lbs/hour. After the implementation of separate WAS thickening (discussed later in this report), which would increase the digested sludge feed concentration, the solids loading rate to the BFPs could be increased while producing dry cake solids of 20%. Although the current dewatering operations are having difficulty meeting the 20% dry cake solids, a study is being pursued to investigate potential improvements to the dewatering operations. A conservative design solids feed rate at the higher digested sludge solids content would be 1,000 lbs/hour. At this increased solids loading rate, two BFPs each operating an average of 16 hours a day, the AWTF could process 32,000 lbs dry solids/day.

2.3.1.5 Boiler Building

Digester gas is burned in two boilers to provide hot water for heating the primary digesters, and space heating for buildings. The boilers can also be fired with fuel oil, but there has been sufficient digester gas available for many years. The amount of biogas received by both boilers and the heat produced from both is summarized in Table 2-2.





Table 2-2. Existing Total Boiler Data

Winter1 Summer2

Biogas Usage (cf/day) 34,400 13,200

Heat Production (BTU/day) 20,600,000 8,000,000

1. October to March averaged from 2013-2017

2. April to September averaged from 2014-June 2017

2.3.1.6 Cogeneration Facility

Digester gas is also used to power two internal combustion engine driven electric power generators. The power generated is exported onto the utility grid. The amount of biogas received by both enginators and the electricity in kW produced by both enginators in total on a daily basis can be seen in Table 2-3. Prior to combustion, the digester gas is filtered by a condensing filter to remove condensable water vapor from the gas. The engine cooling is performed with roof mounted radiators, with closed loop circulation back to the engine blocks.

1. October to March averaged from 2013-2017

2. April to September averaged from 2014-June 2017

2.3.1.7 Gas Collection and Storage

The digester gas is routed through the pipe tunnels, through the Digested Sludge Pump Station, then compressed in the Gas Compressor Building and stored in a spherical tank. The tank has a pressure relief valve to avoid damage to the tank. Excess gas is burned off at an adjacent ground level waste gas flare.

2.3.1.8 Sludge Storage Facilities

Dewatered sludge is stored in two sludge storage sheds located at the north end of the plant site. Each sludge storage shed has a concrete floor and partial walls, and is covered with a metal roof supported by steel beams. Dewatered sludge is stored while awaiting transportation to the land application site. Dewatered sludge that is less than 20% cake solids cannot be stored at the land application site, nor can it be applied to frozen ground. Therefore, anytime cake solids are less than 20% the dewatered sludge is stored at the AWTF until it can be land applied. A separate study is being undertaken to improve existing dewatering operations.

Table 2-3. Existing Total Enginator Data

Winter1 Summer2


Electricity (kW) 2,200 2,260



Biosolids Projections | 18


3 Biosolids Projections

3.1 Design/Future Biosolids Projections

A review of 3 years of influent flows, BOD5, and TSS as summarized in the Biosolids Facilities Improvement Existing Conditions Report, February 2017, concluded the loadings to the plant vary within a consistent range. At the same time, CRW anticipates only a modest number of new connections to the collection system, indicating that the future primary sludge and WAS generated at the AWTF can be expected to remain within the same ranges. For the period since the BNR upgrade was completed (April 2016), the WAS volumes have increased substantially, coinciding with the modification to wasting mixed liquor rather than settled sludge from the final settling tanks. Taking this into consideration, Table 3-1 includes the current average and projected AWTF sludge design criteria.

Table 3-1. Sludge Design Criteria (AWTF)

Average, Current1

Projected Design Values

Influent

Wastewater Flow

19.5 MGD

37.7 MGD2

Primary Sludge

25,600 lbs/day @ 5,800 mg/L

0.44 MGD

27,750 lbs/day2 @ 5,800

mg/L

0.60 MGD

WAS

16,600 lbs/day @ 2,700 mg/L

0.72 MGD

25,000 lbs/day3 @ 2,500 mg/L4

1.2 MGD

1. Data from May 2016 to June 2017 (after BNR upgrade online) 2. AWTF BNR Upgrade Design Maximum Month 3. Calculated using a peaking factor of 1.3 times the current annual average WAS mass rates 4. Based on continued wasting from mixed liquor channel, concentrations may range from 2,000

to 3,000 mg-TSS/L Table 3-2 compares the AWTF generated solids to the digester capacity. The remaining digester capacity could be available for hauled waste, discussed further in Section 3.2.





Table 3-2. Solids Digestion Capacity

Condition VS Loading (lbs / day)

Digester Capacity

61,000

Current Loading 23,700

Projected Loading from

AWTF 36,560

Available Loading

24,400

3.2 Proposed Hauled Waste Projections

Approximately 100 potential high strength waste (HSW) generators were contacted to determine whether their wastes could be valuable waste streams to be hauled waste for co-digestion at CRW’s AWTF. Of the potential sources, five were identified as promising sources within the 50-mile survey radius. Table 3-3 identifies these potential sources along with projected waste characteristics. A more comprehensive market assessment is included in Appendix A as Technical Memorandum No. 5.

Table 3-3. VSS Loadings from Selected HSW Generators

HSW Source Daily Volume (MGD) % Solids TVS % VSS (lbs. day)

Utz Quality Foods1 0.012 9% 80% 7,126

Empire Poultry1 0.02 5% 80% 6,672

Hershey Creamery1 0.003 24% 98% 5,848

Grease Trap Waste2 0.0012 6% 80% 480

Warrell1 0.00033 5% 80% 110

Total volume per day (gallons) 36,530

Weighted average % solids 7.9%

Volume lbs. of VSS per day 20,236 1. Daily volume provided by generator; % solids and TVS% estimated 2. Calculated based on population served and typical per capita volumes generated

In addition to optimizing the type and composition of hauled waste the AWTF should receive, the quantity of hauled waste needs to be considered. The total digester capacity in terms of volatile solids is finite, thus the ratio of solids generated by the AWTF to the amount of hauled waste can be a useful indicator of digester capacity. Table 3-4 shows the ratios of HSW required to maximize the capacity of the digesters at different loadings.





Table 3-4. Ratio of HSW to AWTF Solids at Selected Loadings

Loading Rate AWTF Solids Loading (lbs.

VSS/day)

HSW Solids Loading (lbs.

VSS/day)

Total Solids Loading (lbs.

VSS/day)

% HSW to solids feed

Current Average 21,300 20,240 41,540 49%

Digester Capacity (37.7 MGD)

36,560 24,440 61,000 40%

The five identified sources represent substantial volatile solids loadings, which represent 40% of the total VSS loading of the two anaerobic digesters at design flow. At the current loading, the five HSW sources nearly double the current VSS loading. Accepting only the Utz or Empire Poultry feedstock provides approximately 49% of the feed rate to the digesters at current VSS loadings, which could correspond to an increase of 50-80% in biogas volumes, based on the available data.

3.3 Biogas Utilization

The addition of new CHP technology would increase the amount of heat and electricity outputted from the same amount of biogas. In addition, the amount of biogas generated will increase with increased volumes of hauled waste. However, the projected biogas increase will take many years to reach its design level, thus calculations were initially performed to determine the CHP outputs based on current biogas conditions, which assumes no additional biogas production from increased hauled waste. The results are shown in Table 3-5.

Table 3-5. Current Biogas Generation with New CHP System

Winter1 Summer2


Size (kW) 600 600

Electric Efficiency (%) 41.4 41.4

Heat Efficiency (%) 43.7 43.7

Heat Production (Btu/day) 37,000,000 36,000,000

Electric Production (kW) 10,800 10,600

1. October to March averaged from 2013-June 2017 2. April to September averaged from 2014-June 2017

When compared to the existing heat and electricity production from the boilers and enginators (as summarized in Tables 2-2 and 2-3 respectively), the production from the CHP System is significantly more for the current biogas production rates. Further, once identified project upgrades have been constructed and on-line, and hauled waste contributions are at design capacity, biogas emissions will increase significantly. Table 3-6 shows the CHP outputs based on future conditions.





Table 3-6. CHP: Future Conditions

Winter Summer


Size (kW) 600 600

Electric Efficiency (%) 41.4 41.4

Heat Efficiency (%) 43.7 43.7

Heat Production (BTU/day) 98,600,000 98,600,000

Electric Production (kW/day) 28,900 28,900

Comparing Table 3-5 to Table 3-6, CHP will produce approximately three times the amount of heat and electricity at the future conditions as it will under current conditions.



Biosolids Technology Assessment | 22


4 Biosolids Technology Assessment

4.1 Sludge Thickening

Gravity thickeners which only thicken primary sludge can be loaded at higher mass rates than those that thicken combined primary and waste activated sludge. In addition, with only primary sludge, the thickened primary sludge in the underflow is expected to settle to a higher concentration of solids. Therefore, separating the primary sludge and waste activated sludge would allow for a higher percent solids to be fed into the digesters. Table 4-1 summarizes typical design criteria for gravity thickeners.

Table 4-1. Typical Design Criteria for Gravity Thickeners1

Type of Solids Influent Solids Conc. % solids

Expected Underflow Concentration % solids

Mass Loading Rate lb/sq ft/hr (kg/m2/hr)

Max. Overflow Rate gal/sq ft/d (m3/m2/d)

Primary 2-7 5-10 0.82 – 1.23

(4 - 6) 380 – 760 (15.5 – 31)

Primary and WAS and Iron

1.5 3 0.31 (1.5)

N/A

1. WEF Manual of Practice No. 8

The thickener underflow is currently averaging 3% for the period reviewed. Increasing this to 5-6% solids would nearly double the solids retention time in the digesters. At an average mixed liquor suspended solids concentration of 2,700 mg/L, there is currently an average of 0.72 million gallons a day of WAS. WAS could be thickened separately from the primary sludge to a solids concentration of 5-6%. The overflow rate of the thickener was evaluated to determine if the rate when thickening only primary sludge is too low. The primary sludge flow rate has averaged 0.44 MGD over the period studied. Thickening this stream separately with a 4:1 dilution water to sludge ratio would result in an overflow rate of 220 gal/sq ft/d (9.0 m3/m2/d), which is low and subject to floating sludge, odors and septicity. Operating one thickener would be recommended to keep the dilution water quantity reasonable, and result in an overflow rate of 440 gal/sq ft/d (18.0 m3/m2/d). Gravity thickening is not well suited to thickening WAS due to the limited settleability equating to much larger thickeners needed than for combined sludge. In addition, the volume of WAS is relatively high due to mixed l iquor being wasted rather than clarifier underflow, resulting in an average total suspended solids of the WAS of approximately 2,700 mg/L. A more conservative value of 2,000 mg-TSS/L is utilized in the thickening equipment sizing. In addition to gravity thickening, there are several proven technologies in widespread use for thickening waste activated sludge including:

Gravity Belt Thickeners

Dissolved Air Flotation Thickeners

Centrifuges

Rotary Drum Thickeners





Volute Thickeners The potential also exists for sludge in the future to be wasted from the return activated sludge (RAS) stream, which would have higher solids content. This would require piping and pumping changes. Under this scenario, solids content of the WAS would be 4,000 to 5,000 mg-TSS/L, greatly reducing the volume of sludge to be pumped and thickened. The thickening equipment will need to take this into consideration, and will also be a positive benefit in all regards. Seasonal changes in activated sludge mixed liquor suspended solids (MLSS) targets can result in WAS volumes much higher than average, depending on the length of time the reduction in solids is desired. The WAS thickening equipment will be sized to operate with one unit out of operation for no more than 18 hours a day, 7 days a week at the design WAS volumes of 1.2 MGD.

Gravity Belt Thickener (GBT)

The GBT is well suited to thickening the low solids content (0.2 % solids) of the AWTF WAS to reliably above 5% solids. GBTs are similar in operation and construction to the belt filter presses that the AWTF currently uses to dewater stabilized sludge. GBTs offer the following advantages:

Relatively low capital cost

Relatively low power consumption

High thickened solids concentrations (>6%) are possible

GBTs have the same disadvantages as belt filter presses, so the AWTF operations are already familiar with them. Disadvantages include:

Reliance on the use of polymer

Required ongoing housekeeping efforts

Building corrosion due to high humidity

GBTs are hydraulically limited, rather than solids loading limited. A typical gravity belt thickener can thicken 300 gpm per meter of effective belt width, of WAS at 2,000 mg/L, and produce 5-6% solids thickened WAS (or TWAS). Alternatively, if waste sludge were taken from the RAS stream, the volume of WAS would be significantly less. The GBTs would therefore operate fewer hours, and there would be the potential for less polymer to be required to consistently attain 5-6% solids.

Dissolved Air Flotation (DAF) Thickener

Dissolved air flotation (DAF) has been successfully applied to thickening WAS for many decades. In the DAF thickening system, solids and liquids are separated by introducing fine air bubbles into the liquid phase, the bubbles tend to attach to the solids and lift the solids to the surface where they are collected by a skimmer system. The main components of the DAF thickener are a tank and an air introduction system. The air introduction system would include recycle pumps to return a portion of the subnatant liquid into an air saturation tank where pressurized air is introduced, typically up to 75 psi. The saturated recycle stream is then introduced into the WAS stream at the influent into the DAF tank. The reduction in pressure from the air saturation tank to the DAF tank causes the creation of small air bubbles distributed throughout the influent stream. The floating solids are then collected by a skimmer mechanism, and the subnatant is returned to the head of the plant. DAF tanks are also outfitted with bottom solids removal as well, for heavier solids that sink to the tank floor. In a rectangular tank configuration, this can be a screw conveyor. In a circular tank configuration, scraper blades mounted on a rotating truss, similar to a settling clarifier, are utilized to collect the solids to a sump.





The lower than typical TSS in the WAS (nominally 0.2 % TSS) will lower the expected thickened concentration possibly only to within the range of 3-4 %. Additionally, until pilot testing could be conducted, the design would be kept on the conservative side of the typical criteria, making the DAF tank approximately 1,300 sq ft. This could be configured as a rectangular steel tank (approximately 16 feet by 80 feet long), or more likely as a concrete circular tank (approximately 40 foot diameter) similar in configuration to a settling clarifier. Two DAF tanks would be required to provide redundancy.

Centrifuge

Use of a centrifuge would also be considered a common application for thickening WAS, and is applicable to low solids concentration WAS. The centrifuge utilizes an outer shell, referred to as the bowl, and an inner screw, referred to as the scroll. The bowl will rotate at speeds in excess of 1,500 rpm to produce centrifugal forces of hundreds of times the gravitational force. The scroll rotates slightly faster (or slower in some manufacturer’s designs) than the bowl to create a differential speed. The WAS stream is introduced into the center of the centrifuge through a hollow scroll shaft. The solids are forced to the inside face of the bowl and the scroll will push them towards the discharge. The liquid portion flows on top of the solids and past the scroll and moves towards the opposite end where it overflows a weir and goes into the effluent piping. Polymers are generally used to improve the performance of the centrifuge. There are many factors that affect the centrifugal thickening process results including flow rate, bowl and scroll geometry, maximum operating speed, feed rate, and the solids characteristics. Therefore, there are no specific design criteria for centrifuges, but instead pilot testing would be recommended to determine the design criteria. Properly sized, the centrifuge can consistently produce thickened WAS in the 5-6% target range, with solids capture rates of at least 90%, even with the low WAS TSS concentrations. The centrifuge has some disadvantages that need to be considered, including significant relative power consumption, high noise levels, and specialized maintenance skills requirements. For CRW the advantages are a smaller footprint which may reduce the building size required, thereby providing a competitive capital cost comparison between the advantages and disadvantages.

Rotary Drum Thickener

Rotary drum thickeners have many successful installations in regards to thickening waste activated sludge. Rotary drum thickeners have low power demands, are simple to operate and maintain, and generally have low overall life cycle costs. The footprint of a rotary drum thickener is less than that required by a comparably sized gravity belt thickener. However, few installations are reported to be thickening WAS with TSS as low as 2,000 mg/L. The low TSS of the AWTF WAS, will likely require relatively high rates of polymer, and could result in poor solids capture. The use of a rotary drum thickener would not be recommended without first piloting to determine its cost effectiveness in this application.

Volute Thickener

The volute thickener has a center conveying screw pushing the solids that are larger than the openings in the dewatering drum towards the discharge end. The volute thickener utilizes the annular space between donut shaped plates to separate out the solids. The volute thickener has relatively low capital costs and low energy consumption. The volute thickener has relatively few installations in the United States, but has fewer moving parts than the belt filter press or centrifuge which could translate to lower maintenance costs.





WAS Thickening Recommendations

The GBT has several advantages over the centrifuge and DAFs including:

Low capital cost

Low energy consumption

Simple operation and maintenance

Ability to handle stringy solids (i.e. rags) and plastics In addition, the AWTF operations staff is familiar with the operation of a GBT, as the equipment is very similar to a belt filter press. One of the disadvantages of the GBT is the physical size is larger than a similar capacity centrifuge. The use of a centrifuge will reduce the overall size of the thickening building, which would offset some of the higher capital costs of the centrifuge. A proposed thickening building would house the GBT facilities including the wash water booster pumps, the polymer handling system, and thickened WAS (TWAS) transfer pumps. The TWAS would be stored in a holding tank to allow consistent flow to the digesters when blended with the gravity thickened primary sludge. The existing gravity thickeners would continue to thicken primary sludge, but only one thickener would need to be online at a time.

4.2 Hauled Waste Handling

WAS thickening will increase the solids concentration fed to the digesters, and the existing digesters will then have additional excess capacity, over what is needed to stabilize the AWTF generated solids. The excess capacity can be utilized to digest hauled waste. The hauled waste generators would be charged tipping fees. The hauled waste will also produce additional biogas that can be utilized to generate electricity. Hauled waste will be delivered on tanker trucks varying in size. Handling the waste will require unloading, pretreatment, flow equalization, and pumping to the digesters, including the following facilities.

Truck unloading station with containment

Automated billing ticket generation

Rock trap

Two (2) Screening washing units with bypass for grease

Two (2) transfer pumps

One (1) equalization tank totaling a working volume of one (1) times the daily expected volume

Tank aeration/mixing system with odor control

Two (2) Transfer pumps to the primary digesters The mechanical equipment for handling hauled waste could be housed in the same building as the proposed WAS thickening process equipment. Although one screening unit could be sized to handle all of the projected hauled wastes, two units are recommended for redundancy.

4.3 Anaerobic Digestion

Over the years there have been many variations on anaerobic digestion of wastewater sludge, which include:

Operation at mesophilic (95–99º F) and thermophilic (122–135º F) temperatures

Two stage (Primary and Secondary) mesophilic (Harrisburg AWTF)

Two stage mesophilic and thermophilic operation

Use of egg shaped digesters

Operating two digesters in series with one at mesophilic and one at thermophilic temperatures (Temperature Phased Anaerobic Digestion or TPAD)





Two phase (acid phase) digestion

Given that the existing digesters at the AWTF are structurally sound, and there are plans to refurbish the mechanical systems, the use of egg shaped digesters is not considered. Thermophilic digestion is more difficult to control than mesophilic and requires more energy input to maintain the higher temperatures. Advantages of thermophilic digestion over mesophilic include the potential to produce more biogas, and better dewatering characteristics. Redesigning the digesters and heating system for thermophilic operation is not warranted based on the current plans for biosolids at the facility. Two phase digestion separates the two major types of reactions that take place during anaerobic digestion - acid formation and methane generation. Two phase digestion with an acid phase digester would take advantage of the AWTF existing infrastructure and would allow for more effective use of the anticipated biosolids and hauled waste. Figure 4-1 is a schematic of two phase digestion. Minimizing potential for foaming in the main digesters is another of the advantages of two phase digestion. The acid phase digester would be designed with a greater than 1:1 ratio of height to diameter to minimize the footprint, and reduce unmixed zones within the tank. See Section 6 for more information on the acid phase digester. The practicality of capturing the biogas from the secondary digesters was also considered. The primary digesters currently destroy an average of 54% of the feed volatile solids. Even by making the aggressive assumption that the secondary digesters could increase this by another 5 percentage points to 59% total volatile solids destruction, the biogas released in the secondary digesters would equate to 40,000 cubic feet of biogas per day at capacity (37.7 MGD). Considering that the value of electricity generated by this additional gas is approximately $50,000 per year, the simple payback on installing new covers and gas collection system, would be more than 50 years, and is therefore not justified. Figure 4-1. Schematic of Two Phase Anaerobic Digestion

Biogas

Feed

Sludge

Acid

Phase

Digester

Methane Phase

Digesters (Existing

Primary Digesters)

To

Secondary

Digesters

(Holding

Tanks)

Heat

Exchanger





4.4 Dewatering

Given the restrictions on storing dewatered sludge with less than 20% solids offsite, the dewatering process design target will be a minimum of 20% solids. Additional acceptance of hauled waste will increase the digested sludge that will need to be dewatered. These two conditions are considered, along with the current and proposed dewatering requirements in evaluating alternative dewatering technologies. Several dewatering technologies claim consistent biosolids cake dewatered to above 20% solids, including:

Centrifuge

Screw Press

Volute Dewatering Press

Rotary Press Other than the centrifuge, pilot testing would be highly recommended to confirm actual average percent solids performance at the AWTF.

Centrifuge

The centrifuge is widely utilized in dewatering biosolids, with high cake solids and high throughput as major advantages over most other technologies. Figure 4-2 shows an illustration of a centrifuge. Figure 4-2. Cutaway View of Biosolids Dewatering Centrifuge

Credit: Centrisys

Compared to the other technologies below, the disadvantages of the centrifuge include:

High energy consumption

High capital and maintenance cost

Specialized maintenance skills The centrifuge has several advantages compared to other technologies including:

High volumetric and solids loading capacity compared to unit size

High dewatered cake solids

Fully enclosed operation





Screw Press and Volute Dewatering Press

The screw press and volute dewatering press are similar in overall configuration, with a center conveying screw pushing the solids that are larger than the openings in the dewatering drum towards the discharge end. See Figure 4-3 for a typical screw press, and Figure 4-4 for a volute dewatering press. The screw press uses a static perforated, or slotted drum which separates the solids. The volute press utilizes the annular space between donut shaped plates to separate out the solids. The screw and volute press both have low capital costs and low energy consumption. The volute dewatering press has relatively few installations in the United States, but has fewer moving parts than the belt filter press or screw press which should translate to lower maintenance costs. Figure 4-3. Screw Press

Credit: Schwing Bioset, Inc.





Figure 4-4. Volute Dewatering Press

Credit: Process Wastewater Technologies, LLC

Rotary Press

The rotary press utilizes two vertically oriented plates with slotted openings, see Figure 4-5 for a general arrangement of a six channel rotary press. Flocculated biosolids are pumped in between the plates which separates the solids from the filtrate. The slow rotation speed of the plates provides friction to restrict the solids movement and provides compression of the solids cake to control the cake solids. The rotary press has a lower throughput than the screw press or belt filter press and therefore requires more floor space. The room where the existing belt filter presses are located may not be large enough for the required rotary presses, so that aspect would require evaluation.





Figure 4-5. Six Channel Rotary Press

Credit: Fournier Industries

4.5 Vivianite Control

The AWTF encounters significant mineral deposit buildup in the anaerobic digester recirculation/heating piping and heat exchangers. Every 18-24 months the buildup becomes significant enough to cause the degradation of heat exchanger, pump and valve performance. The AWTF currently replaces the piping and heat exchanger tubes each time the ability to maintain the digester temperature degrades. Considering the AWTF utilizes ferric chloride for phosphorus precipitation and removal, and that the worst buildup is in the heat exchangers and downstream, i.e. the hottest sludge temperatures in the system, the mineral is likely vivianite (iron phosphate). Vivianite can be identified by its characteristic blue-green color, is soluble in hydrochloric and nitric acids, and loses solubility when temperatures rise. There is currently no economical method from recovering the phosphorus from the iron phosphate. There are two primary methods to control vivianite deposits: reduce the temperature of the sludge coming out of the heat exchanger and/or reduce areas of high turbulence. Changing phosphorus precipitant chemical to an aluminum salt was also considered, but aluminum salts tend to have a higher cost, and struvite (solid magnesium ammonium phosphate) buildup is also a possibility. Given the congestion of piping within the primary digester pumping station there are few opportunities to address areas of high turbulence in the piping by removing bends and tees or introducing longer sweep elbows. Reducing the temperature rise of the sludge in the heat exchanger was investigated, but minimal improvement is expected. To mitigate vivianite buildup, it is recommended to heat the primary digesters with direct steam injection. In the primary digester improvements, provisions for steam lances, to be installed in the future, will be installed into the primary digesters. When the proposed CHP technology is installed, steam can then be produced from the heat output of the technology and conveyed to the steam lances to keep the digesters at a consistent, optimal temperature. Direct steam heating will help eliminate vivianite build up in the heating loop as well as eliminate the





need for the existing external heat exchangers. During the detailed design of the steam heating system, an external direct steam heat injection exchanger should be evaluated to supplement the steam lances.

4.6 Biogas Utilization Assessment

There are several potential beneficial uses for biogas including the following:

Combust the biogas and recover the heat and kinetic energy, e.g., combined or separate heat and power generation

Use a fuel cell to generate electricity and heat

Off-site use of the biogas, e.g., as natural gas substitute

Use as fuel to heat the digesters

Use as fuel for heat drying biosolids The AWTF is currently utilizing a hybrid heat and power generation, with partial recovery of heat from the engine driven generator, and the use of separate boilers for additional heat generation capacity. Integrating the heat and power generation into a combined heat and power system would improve the overall energy efficiency. In combined heat and power, all of the biogas is burned in the engine or turbine driven generator, and the heat for the digesters is supplied by the waste heat generated by the engine. A fuel cell can also be used in the generation of combined heat and power. See Figure 4-6 for a schematic of the proposed CHP system integrated in the AWTF biosolids process. Figure 4-6. Schematic of CHP Option for Biogas Utilization

Another alternative to consider is the use of the biogas off site, e.g., direct injection into a natural gas pipeline, or use in compressed natural gas vehicles. In any beneficial reuse alternative the biogas requires a certain level of pretreatment prior to use. Technologies have varying requirements for pretreatment. In order from fewer to more pretreatment requirements are the internal combustion engine, turbine, fuel cell, and then off site use. The use of the biogas off site, e.g. direct injection into natural gas pipeline, or use in compressed natural gas vehicles, requires removal of carbon dioxide, in addition to reducing levels of hydrogen sulfide, water and siloxanes over what is required for powering internal combustion engines or fuel cells for power generation. Once treated to a sufficient quality, an odorant is added and the biogas is then referred to as biomethane and can be injected into a utility system natural gas pipeline. See Figure 4-7 for a schematic of the pipeline injection within the AWTF biosolids process.

Digesters H2S

Removal Cogeneration

Sludge

Digester Gas

Heat Recovery

Back-up Boiler

AWTF Buildings

Particulate & Moisture Removal

Siloxane Removal

Treated Digester Gas

Electricity

Direct Steam Heating





Figure 4-7. Schematic of Natural Gas Injection Option for Biogas Utilization

Expected Energy Potential from Biogas

The biogas currently being produced at CRW is expected to be typical for municipal anaerobic digesters. When high strength (with a higher biochemical oxygen demand than the biosolids) hauled waste is brought in, the quantity of the biogas will increase.

Typical digester design criteria were used to estimate the potential biogas production. Summary information on the anaerobic digester design capacity and resulting biogas generation is provided in Table 4-2. The digester capacity in Table 4-2 is the theoretical capacity, and would need to include hauled waste in addition to the solids generated by the AWTF to reach the loading and biogas production rates indicated.

Table 4-2. Projected Gas Generation at Facilities Plan Digester Theoretical Design Capacity

TSS in Digester Feed 76,900 lbs/day

VS in Digester Feed 61,000 lbs/day

VS Fed/ Destruction Ratio

0.50

VS Destroyed in Digesters

30,500 lbs/day

Gas Produced 13.0 cf biogas per lb of VS destroyed

Digester Gas Produced 397,000 cfd

Digesters H2S

Removal Process Heating

Digester Gas Upgrading System and

Compression

Sludge Digester

Gas

Biomethane to Natural Gas Grid

Biomethane

To Boilers

AWTF Buildings





Heating Requirements for Digestion and Building Heating

In addition to heating the digesters, some of the heat generated by the proposed CHP system could be used to heat building spaces. Table 4-3 compares heat generated at current production rates and at the digester capacity. Building heating is not included.

1. Average from May to August, 2016 2. Average from September 2016 to April 2017 3. Based on average flow from May 2016 to June 2017 = 0.127 MGD, Cp = 8.33 BTU/gal - ºF, and 10% heat loss

An economic analysis based on the current natural gas and fuel oil pricing would need to be conducted once the CHP system is installed, and more data are gathered on the effects of hauled waste on biogas production. The analysis would determine if burning biogas to produce only heat would be economically justified rather than utilizing all of the biogas for electric production and supplementing building heat with natural gas or fuel oil.

Biogas Utilization Technology Assessment

4.6.3.1 Fuel Cells

Fuel cells use an electrochemical process to convert hydrogen from hydrocarbons, such as methane, into electricity. As of 2015, there are 126 fuel cells in the United States, with a combined capacity of 67 MW. The average installed fuel cell has a capacity of 532 kW. The thermal energy from the fuel cells can be recovered and used for heating demands. The fuel cell is made up of three primary structures: fuel cell stack, fuel processor, and power conditioner. The cell stack generates the direct current electricity which is then used in the fuel processor to convert the fuel into a hydrogen-rich feed stream and finally the power conditioner processes the direct current electric into alternating current. There are several types of fuel cells which have been used for CHP, including phosphoric acid, molten carbonate, solid oxide, and proton exchange membrane. Fuel cells are known for achieving high efficiency levels and generating constant power when supplied an uninterrupted supply of biogas. Fuel cells typically have a power to heat ratio of 1.26, which is advantageous for systems that require more electricity than heat. Another advantage of a fuel cell is the low emissions of carbon dioxide (CO2) and even lower emissions of oxides of nitrogen (NOx). Fuel cells can produce CO2 emissions ranging from 555 to 729 lbs/MWh, whereas a typical natural gas combined cycle power plant will produce 800-999 lbs/MWh. Besides less air pollution, fuel cells also do not create any noise. Currently, fuel cells have a higher capital cost per kWh than internal combustion technologies. A fuel cell can have

Table 4-3. Lean Burn Reciprocating Engine Values

Current

Summer (1)

Current

Winter (2)

Capacity

Summer (1)

Capacity

Winter (2)

Biogas Generated (cf/day) 117,000 145,000 397,000 397,000

Digester Heat Required

(MBTU/day) (3) 23.3 46.5 33.0 66.0

Electricity Generated kWh 283 351 960 960

Heat Generated (MBTU/day) 23.2 33.1 90.5 90.5

Additional Heat Required

(MBTU/day) 0.1 13.4 0 0





an installed cost ranging from $4,600 to $10,000/kWh. While fuel cells are fairly reliable, with a reported 90-95% electricity production rate, they do require periodic replacement and maintenance of their catalysts and fuel cell stacks. Fuel cells also have slow start times, ranging from 3 hours to 2 days. Fuel cells are newer and less prevalent than reciprocating engines.

4.6.3.2 Reciprocating Engines

Another option that utilizes CHP are reciprocating engines. As of 2015, there are nearly 2,400 reciprocating engine based CHP systems in the United States. Reciprocating engines are available in sizes ranging from 10 kW to 10 MW. There are two designs for reciprocating engines: spark ignition Otto-cycle engines and compression ignition Diesel-cycle engines. The two designs are mechanically the same, but differ on the method of fuel ignition. Spark ignition uses a spark plug to ignite a pre-mixed air fuel mixture and for CHP most reciprocating engines use a 4-stroke spark ignition. Compression ignition systems rely on the elevated temperatures produced during the compression cycle, to ignite the fuel. Further, reciprocating engines are usually characterized as either rich-burn or lean-burn. Rich-burn engines operate near the stoichiometric air/fuel ratio, thus air and fuel quantities result in complete combustion, with little excess air. Lean-burn engines run at significantly higher levels than the stoichiometric ratio. Reciprocating engines have electric efficiencies that are not as high as fuel cells, ranging from 25-50% (Based on the lower heating value (LHV) of the fuel). The installation cost and maintenance cost is lower for reciprocating engines. Reciprocating engines, with proper maintenance, can be available 90-96% of the time, with a 60 second start-up time. Rich-burn reciprocating engines have a power to heat ratio of approximately 0.62 and lean-burn engines have a ratio of 0.86, as compared to the fuel cell’s ratio of 1.26. Reciprocating engines produce more heat than electricity. One of the most significant differences between the two CHP technologies is the emissions of criteria pollutants. Reciprocating engines emit significant amounts of NOx, carbon monoxide (CO), and volatile organic compounds (VOCs).

4.6.3.3 Biogas Pretreatment

Biogas pretreatment is another component that must be analyzed in relation to CHP technologies. Depending on the technology, biogas has to be treated in order to remove certain elements that can negatively impact the technology’s performance. Further, pretreating the biogas can increase its heating value. Biogas from digesters is typically pretreated to remove solid particulates, siloxanes, hydrogen sulfide (H2S), and water vapor. Before the biogas can be utilized by CHP technology, it needs to be pretreated to remove certain components: H2S, moisture, and siloxanes. If not pretreated, these components can negatively impact the CHP’s equipment. Biogas typically consists of 55-80% methane (CH4), 20-45% carbon dioxide (CO2), 5-10% hydrogen gas (H2), trace

amounts of H2S, and other impurities. Therefore, the critical impurities are small in relation to the compounds found

in biogas, but their impact is still significant if not treated. Without pretreatment, H2S concentrations vary from 50-

10,000 ppm and can cause corrosion to the engine and the equipment’s metal parts from the emission of sulfur

dioxide (SO2) from combustion. This is especially the case if the engine is not operated continuously. Additionally,

these emissions produce toxic H2S/SO2 concentrations. Common H2S removal technologies fall into one of the

following categories: (1) absorption into a liquid, (2) adsorption on a solid, and (3) biological conversion. Currently,

the AWTF uses the second option through the use of a Varec gas purifier that utilizes a bed of iron sponge to

convert H2S into ferric sulfide deposits. The first option can result in the generation of wastewater and the third

option is a commercially expensive removal process. The SO2 formed from combustion results in corrosion and

results in a significant oil pH drop. By removing H2S, there is less piping and equipment corrosion and bearing

damage, less oil acidification, and less oil lubricity reductions.

After treating for H2S, the moisture content has to be removed. Biogas contains high amounts of moisture, and this

moisture condenses when temperatures cool in piping and biogas treatment vessels. This is an issue because





engine manufacturers require no water droplets in the biogas when in the engine and that the fuel gas be less than

saturated. Gas condensation can become even more of an issue in the colder weather and, besides potentially

damaging the engine, moisture can collect in low spots and become an operational issue in regards to drainage

and potential for freezing. Moisture can also combine with other contaminants to form corrosive substances.

Therefore, it is important to remove moisture not only to prevent the aforementioned impacts, but because there

are also positive impacts when moisture is removed: the efficiency of the engine increases, there is a reduction in

engine oil contamination, and less corrosion of pipework and components. Typically, moisture is removed by cooling

the gas to condense the water which can be drained from the system.

Finally, siloxanes have to be removed. Siloxanes are silicon compounds and are found in small amounts in biogas.

The prior removal of H2S and moisture will be beneficial in protecting the siloxane removal systems. Cogeneration

becomes more complicated when biogas contains organic silicon compounds. The combustion inside the engine,

transforms these compounds into oxides which precipitate and collect inside the machinery. Consequently, these

deposits can result in breakdowns and wear down the metal parts in engine, reducing the useful lifetime of the

system. Studies have found that most cogeneration engine problems involve the presence of siloxanes in the

biogas. There are numerous procedures for the removal of siloxanes, however, the only industrial scale method is

adsorption with activated carbon. The prior removal method, iron sponge bed, for H2S will also result inadvertently

in the removal of siloxanes.

Fuel cells and natural gas line injection require a more full treatment; i.e., removal of water vapor, CO2, and trace elements, in addition to those discussed above.

4.6.3.4 Natural Gas Pipeline Injection

Another alternative for beneficial use of biogas is injecting it into a utility’s natural gas pipeline. However, this process requires an advanced biogas upgrading system. The capital investment for natural gas pipeline injection can be less than a combined heat and power system. A heat source for the primary digesters would still be required if a CHP process is not utilized. Typically the biogas has to undergo treatment to remove contaminants and excessive CO2, an odorant has to be added, and finally be compressed and then sold to a local utility. It can also be used onsite as a vehicle fuel but this is very capital intensive. There is a water-wash technology available through Greenlane biogas that is ideal for grid injection and requires no heat or chemicals. It removes H2S without pretreatment and has reliable compression technology. Essentially it combines all the steps and results in a product that is pipeline acceptable. The company also claims ~99% energy available to pipeline from biogas produced. If the site requires natural gas, this would be a useful option, however, selling treated biogas as a natural gas supplement compared to utilizing the biogas to generate electricity does not appear to be economically justified.



Future Regulatory Trends| 36


5 Future Regulatory Trends

Every component of a biosolids management program is regulated including biosolids quality, storage and

application sites, and agronomic rates for beneficial use. Federal and state regulations and requirements are

intended to protect surface and ground water quality and protect public health.

The purpose of this section is to review the regulatory and non-regulatory pressures and drivers which impact

market and business choices for biosolids management. Included are:

Federal and state regulations and requirements for biosolids quality and management

Agricultural requirements for application of nutrients to farms, particularly phosphorus

Non-regulatory drivers such as public acceptance, odor, and sustainability demands

Emerging regulations and trends which can impact the choices on business and management decisions.

5.1 Standards

The United States Environmental Protection Agency (USEPA) regulates biosolids land application, surface

disposal, and incineration under The Code of Federal Register Title 40 Part 503. Part 503 includes metal

concentration limits, requirements for the reduction of pathogens and vector attraction, and management practices

/ site restrictions for land applying biosolids. Class B biosolids are specifically defined in Part 503 regulations

requiring specific pathogen density and application site management. Application site management is intended to

protect groundwater and surface waters from runoff or infiltration of nutrients, pathogens and metals contained in

the Class B biosolids. The PADEP developed standards in the Pennsylvania Code Title 25 Chapter 271 for Class

B quality and processing that parallel USEPA Part 503 regulations. Compliance with both USEPA Part 503 and

PADEP Chapter 271 regulations is required for all Pennsylvania utilities.

5.2 Pollutants

To meet Class A/EQ standards identified in Pennsylvania Code Title 25, §271.914, the pollutants shall never exceed

the ceiling limits and the average shall never exceed the monthly average concentration limits defined in tables

therein. To meet Class B standards, the concentration of any pollutant must not exceed the ceiling concentrations,

but do not need to comply with the monthly average concentrations. Table 5-1 summarizes prescribed ceiling and

monthly average concentrations.





Table 5-1. Biosolids Pollutant Concentrations Limits1

Contaminant Ceiling Concentration

(mg per kg) 2,3

Monthly Average

Concentration

(mg per kg)2

Arsenic 75 41

Cadmium 85 39

Copper 4,300 1,500

Lead 840 300

Mercury 57 17

Molybdenum 75 N/A

Nickel 420 420

PCBs 86 4

Selenium 100 100

Zinc 7,500 2,800

1. Source: Pennsylvania Code Title 25, § 271.914 (b)(1) – Ceiling Concentration, § 271.914 (b)(3) – Monthly Average Concentration

2. Dry weight basis 3. These values are a maximum levels, not to be exceeded.

The biosolids generated at the AWTF consistently meet the pollutant limits under Pennsylvania Code Title 25

Chapter 271.914, as summarized in Table 5-2. Note that the AWTF biosolids consistently meet the more stringent

Monthly Average Concentration limits in Table 5-1, although Class B biosolids are not required to meet these

limits. CRW is encouraged to continue to meet the higher quality standards.





Sample Data

Sample Result, mg/kg

Ars

en

ic

Cad

miu

m

Co

pp

er

Lead

Merc

ury

Mo

lyb

den

um

Nic

ke

l

PC

B's

Sele

niu

m

Zin

c

1/15/2015 <9.6 <2.4 504 72.1 1.4 11.3 23.9 <0.31 <24.0 1,860

3/3/2015 <9.9 <2.5 481 50.4 1.6 10.2 22.7 <0.43 <24.7 1,750

5/7/2015 <9.1 <2.3 439 56 1.2 9.6 21.2 <0.41 <22.6 1,370

7/13/2015 <8.6 4.6 484 81.9 1.8 11.1 24.3 0.34 <21.4 1,540

9/15/2015 <8.1 <2.0 423 50.8 1 17.9 28.1 <0.16 <20.2 1,670

11/24/2015 <10.4 <2.6 504 57.9 1.1 16.6 28.1 <0.19 <26.0 2,040

1/27/2016 <8.1 2.1 507 56.8 2.2 11.2 23.5 <0.29 <20.1 1,810

3/16/2016 <9.4 <2.4 388 54.5 1 <9.4 23.8 <0.24 <23.6 1,320

6/8/2016 <8.2 2.4 557 90.8 1.4 17.9 33.1 <0.22 <20.4 1,720

7/12/2016 <8.6 <2.1 424 77.2 1.2 15.6 36 <.015 <21.5 1,230

9/22/2016 <9.2 7.3 438 136 2.9 22.9 99.8 0.047 <23.0 1,270

Maximum <10.4 7.3 557 136 2.9 22.9 99.8 0.047 <26.0 2,040

5.3 Pathogen Reduction

There are three general alternatives for compliance with Class B pathogen reduction (PR), as required under 25

PA Code 271.932:

Alternative 1 - Demonstrate < 2,00,000 MPN or coliform-forming units (CFU) of fecal coliforms per gram of

total solids;

Alternative 2 - Apply a “Process to Significantly Reduce Pathogens” treatment; or

Alternative 3 - Apply a process that is equivalent to a “Process to Significantly Reduce Pathogens”, as

determined by USEPA.

There are five “Processes to significantly reduce pathogens (PSRP),” which include aerobic and anaerobic

digestion, air drying, composting and lime stabilization. The only alternative that applies to the AWTF is the

anaerobic digestion PSRP which requires that:

“sewage sludge is treated in the absence of air for a specific mean cell residence time at a specific

temperature. Values for the mean cell residence time and temperature shall be between 15 days at 95 ºF

to 60 days at 68 ºF.”

This PR alternative is available to CRW, although is not currently used for compliance purposes. With the completion

of biosolids facilities improvements, the second primary digester will be operational, the heat exchangers will be

rehabilitated, and the facility should be capable of consistently meeting the time and temperature PSRP

requirements.

Table 5-2. CRW 2015 Pollutant Analyses Summary





PR requirements are satisfied by CRW in accordance with the criteria under 25 PA Code §271.932(b)(3) [Class B

- Alternative 2], Fecal Coliform. As such, the Fecal Coliform test must be conducted on a series of at least seven

(7) samples during a monitoring event and the geometric mean calculated. The results of all such testing confirm

that the AWTF processed solids meet the standards established for Class B biosolids.

Testing results show that the geometric mean of Fecal Coliform of the anaerobically stabilized biosolids is

consistently less than 2 million colonies per gram of total solids (dry weight basis). Table 5-3 provides a summary

of the Fecal Coliform data collected throughout 2015 and 2016 showing that the geometric mean of the Fecal

Coliform test is less than 2 million CFU per gram of dry solids for the dewatered biosolids.

Table 5-3. AWTF Historical Pathogen Reduction Monitoring Summary

Monitoring Period

Sample Date

Sample Number / Units Geometric Mean

(CFU/g dry

solids)

1 2 3 4 5 6 7

colony forming units per gram of dry solids

Jan/Feb 1/15/15 11,800 14,100 17,600 15,900 12,600 23,200 13,600 15,173

Mar/Apr 3/3/15 3,700 2,280 2,780 8,720 4,410 1,830 2,290 3,244

May/Jun 5/7/15 3,090 2,430 10,000 3,300 2,570 2,090 3,050 3,277

Jul/Aug 7/13/15 123 40 125 123 82 82 82 89

Sep/Oct 9/15/15 133,000 170,000 48,100 29,500 51,300 38,100 41,800 59,439

Nov/Dec 11/24/15 23,800 17,500 24,800 18,900 130,000 127,000 18,200 34,541

Jan/Feb 1/27/16 5,790 4,720 6,380 7,910 6,700 6,090 12,200 6,820

Mar/Apr 3/16/16 12,900 11,100 8,620 7,180 11,800 5,050 7,510 8,762

May/Jun 6/8/16 12,000 199,000 13,000 10,700 11,200 13,300 10,800 17,654

Jul/Aug 7/12/16 10,700 14,600 20,000 14,100 21,400 10,900 15,300 14,823

Sep/Oct 9/22/16 0 27,000 165,000 187,000 316,000 218,000 272,000 25,842

5.4 Vector Attraction Reduction

There are eleven options specified in the regulation for vector attraction reduction (VAR) that relate to solids

generated from wastewater treatment. The application of VAR options depends on the type of biosolids and the

disposal/reuse method, and is an indication of the level of stability. Options 1 through 8 relate to treatment processes

(process VAR), and Options 9 and 10 relate to injection or incorporation within 6 hours of application, respectively

(barrier VAR). For land application programs, meeting process VAR is necessary to comply with farm conservation

plan requirements (related soil erosion) and the ability to store at the farm. The only process VAR option that applies

to CRW is Option 1, which requires volatile solids be reduced by a minimum of 38 percent.





VAR requirements are achieved through anaerobic digestion and is satisfied in accordance with the criteria under

25 PA Code §271.933 [Option 1]. Option 1 requires a minimum of 38% reduction in the Volatile Solids (VS) across

the digestion facilities. Analyses for VS are taken on samples entering and exiting the Primary Digester. Inflow VS

(VSin) are sampled from the thickener underflow and outflow VS (VSout) are sampled from sampling port on the belt

filter press feed line. VS Reduction (VSR) analyses and calculations are performed several times per month. The

Van Kleeck method is used to calculate the overall VS reduction.

Table 5-4 provides a summary of the VSR data collected throughout 2015 and 2016 showing that the VSR is

typically above the 38% necessary to demonstrate VAR is achieved. With process changes associated with the

BNR facilities start-up in April 2016, however, VSR was close to and below the 38% required to meet Option 1.

Material Matters, Inc. (MMI) worked with CRW personnel to undertake several measures to improve digester

performance and closely monitor digester operations data. It is recommended that CRW continue to monitor VAR

closely, until the digester improvements have been completed.

Table 5-4. CRW Historical Vector Attraction Reduction Monitoring Summary

Monitoring

Period VSin VSout VSR

Jan/Feb 2015 82.0% 62.1% 64.1%

Mar/Apr 2015 78.7% 57.9% 62.8%

May/Jun 2015 78.0% 58.9% 59.6%

Jul/Aug 2015 81.4% 60.7% 64.8%

Sep/Oct 2015 80.8% 66.1% 53.7%

Nov/Dec 2015 81.2% 67.0% 52.9%

Jan/Feb 2016 81.2% 64.0% 59.0%

Mar/Apr 2016 80.7% 60.6% 63.3%

May/Jun 2016 77.4% 62.5% 51.3%

Jul/Aug 2016 74.2% 64.6% 36.5%

5.5 Biosolids Management

All utilities that generate and land apply biosolids in Pennsylvania must follow the general requirements,

management practices, and operational standards found in 25 PA Code Chapter 271.915, Management Practices.

General Permit

All facilities that generate Class B biosolids and plan to land apply must apply for coverage under the state-wide

General Permit (GP). Once a Notice of Intent (NOI) application is submitted to PADEP for coverage under the GP,

the PADEP reviews the submittal and ultimately issues a Notice of Coverage. The GP for the Land Application of

Non-Exceptional Quality Biosolids (Class B) PAG-08, was issued by PADEP on April 3, 2009 and was effective

from April 3, 2009 through April 2, 2014. The PADEP has administratively extended the PAG-08 GP through April

2, 2017. PADEP has indicated that the GPs will be renewed during 2017, and new phosphorus management and

hauled waste requirements will be included in the GPs.





Land Application 30-Day Notice

New land application sites for beneficial use of Class B biosolids must be approved by PADEP, which has 30 days

to review the application. Class A/EQ biosolids are exempt from this requirement. The land applier must provide

the detailed information necessary to determine if a proposed application site is appropriate for land application of

biosolids. Detailed information about the site includes, but not limited to: types of crops, how agronomic rates will

be calculated, methods of application, landowner agreements, and a detailed map that identifies all setbacks and

land application areas.

Recordkeeping

Recordkeeping for Class B biosolids is more comprehensive than Class A/EQ biosolids. As with Class A/EQ,

biosolids quality, including pollutants, PR and VAR processes, and the corresponding certification statement must

be reported. However, unlike Class A/EQ biosolids, the facility must also report a summary of biosolids applied to

each field, the number of acres that received biosolids, and the type of crop, projected yield, and nitrogen

requirements where biosolids were applied. Additionally, the pollutant loading rate for each farm field must be

calculated annually and added to biosolids pollutants applied in past applications (cumulative pollutant loading rate

or CPLR). The facility must also indicate how public access was restricted from the site.

Land Application Requirements

Class B biosolids must be land applied at an agronomic rate to provide the amount of available nitrogen needed by

the crop or vegetation in the application area. The nitrogen need is based on two factors: the type of crop and the

projected yield. The projected yields must be realistic and based on site-specific factors. Using five-year historic

site yields is typical and recommended; however, recommendations by the farmer, written recommendations from

the Pennsylvania State University (PSU) extension, and the county yield average can be used if historic site yields

are not available.

To calculate the amount of biosolids needed to meet crop needs, it is necessary to calculate the amount of plant

available nitrogen (PAN) available in the biosolids, which is dependent on the mineralization rate of the biosolids

nitrogen. Land application of Class B biosolids on agricultural land, forest, and reclamation sites are subject to

setbacks around streams, sinkholes, dwellings, and water sources, but are not required for Class A/EQ biosolids.

These management practices are found under 25 PA Code Title Chapter 271.915.

Additionally, biosolids may not be applied within 11-inches of the seasonal high water table nor within 3.3-feet of

the regional groundwater table. Agricultural utilization cannot be conducted on slopes that exceed 25% or where

soil pH is less than 6.0. Land appliers must also complete training courses sponsored by PADEP within one (1)

year of beginning to conduct land application operations.

5.6 Regulatory and Non-Regulatory Drivers

There are several regulatory and non-regulatory drivers that could potentially affect biosolids land application

programs including limiting phosphorus application, odor considerations, and farmland availability. There are no

federal biosolids regulatory changes planned; however, PADEP plans revisions to the GPs to be reissued in 2017.

Phosphorus Management

The nutrients supplied by biosolids are not present in the same ratio as they are required by plants. Therefore,

biosolids supplied at an agronomic rate for nitrogen supply an excess of some nutrients, especially phosphorus.

When applied to meet crop nitrogen needs, biosolids supply large quantities of phosphorus. In soils that already





have high phosphorus content, application of phosphorus can increase the potential for phosphorus loss from the

field through runoff to surface waters, causing eutrophication.

Indications are that PADEP will pursue phosphorus management through the phosphorus index (P-Index) as part

of the upcoming reissued GPs. The P-Index is a tool used to assess the potential for phosphorus to move from

agricultural fields to surface water. It uses an integrated approach that considers soil features, as well as soil

conservation and phosphorus management practices in individual fields. In a study conducted on biosolids

application farms, MMI found that:

"…implementation of the P-Index will have a significant impact on land application of biosolids in

Pennsylvania. However, it appears that the Pennsylvania P Index contains sufficient flexibility for land-

appliers to credit biosolids characteristics and practices to reduce the risk of P loss, and maintain effective

land application programs.”

Of the 46 fields included in this study, use of the P Index allowed for 35 fields to continue with nitrogen management

(76% of the fields), seven with phosphorus management, and one field would be excluded from biosolids

applications. One conclusion from the study noted that biosolids programs should be able to accommodate

phosphorus management, but land application practices must evolve to meet the challenge.

CRW should periodically have a “phosphorus source coefficient” test performed by PSU Analytical Labs as part of

routine monitoring. The results of this analysis will be utilized in the future in site index calculations if phosphorus

management is implemented by PADEP. CRW may also want to consider conducting an assessment of their current

qualified acreage to determine the impact of phosphorus management.

Hauled Waste Acceptance

PADEP Central Office staff have indicated that the Department intends to incorporate hauled waste conditions in

the upcoming reissued GPs. While the exact language and requirements are unknown at this time, these revisions

may potentially impact either CRW’s biosolids land application program and/or its hauled waste program.

Odor

Nuisance odors from land application sites are the primary source of public opposition for biosolids recycling

(USEPA Biosolids and Residuals Management Fact Sheet- Odor Control in Biosolids Management. Office of Water.

September 2000. Washington, D.C). According to a 1999 Biocycle nationwide survey, nuisance odors at a land

application site are usually the initial operating problem leading to public opposition. Nuisance odors created by

biosolids are detrimental to aesthetics, property values, and the quality of life in an area. Therefore, if a utility fails

to acknowledge the potential for product odor, unintended odors can result in adverse public relations including

non-acceptance, complaints, and even a shutdown of the biosolids recycling program (USEPA 2000). Treatment

technologies are most effective if designed with odor reduction in mind. The proposed rehabilitation as part of

CRW’s biosolids facilities improvements should improve digester performance and VSR, thereby reducing VS of

the final biosolids product. Reducing the VS content of the dewatered biosolids produces a more stable product

and minimizes nuisance odors.

Farmland Availability and Demand for Product

Farmland availability and demand for the biosolids product is critical when evaluating the end use options. CRW

currently has over 700 acres qualified for biosolids land application of their Class B biosolids and MMI recommends

that CRW add 230 more acres to the program (approximately two new farms). Central Pennsylvania contains many

farms that are located within 50 miles of the CRW AWTF which provides opportunities with relatively low

transportation costs. Biosolids often compete with animal manures and litters as a nutrient supplement. Additionally,





biosolids imported from outside the region (i.e. Philadelphia, Maryland, New York, and New Jersey areas) produces

competition for farmland. While ample farmland is available throughout the region, pressure from manures and

imported biosolids is increasing. CRW should continue to work with the existing farmers in its program to deliver

high quality biosolids with low odors that supply cost effective nutrients for their farms, as well as search for

additional acreage and farmers to add to the program.



Summary of Improvement Plan | 44


6 Summary of Improvement Plan

6.1 Biosolids Facility Overall Improvements

WRA has evaluated the biosolids treatment process and has determined there are beneficial changes that can be made to the biosolids facilities to allow CRW to better attain their goals. Recommendations include the following major modifications:

Separately Thicken Waste Activated Sludge and Primary Sludge

This process modification has been proven at many facilities to greatly increase the percent solids in the thickened sludge sent to the anaerobic digesters. The current practice of co-thickening sludge at the AWTF is averaging approximately 3% solids (feed to the primary digesters). Separate thickening of primary and WAS is expected to result in 4-6% solids in each sludge stream. This in turn will increase the solids retention time in the anaerobic digesters, which will increase volatile solids reduction, increase biogas generation, and reduce the quantity of digester gas required to heat the sludge. WAS thickening with Gravity Belt Thickeners (GBTs) is recommended. The GBTs will be installed in a new building adjacent to the existing primary clarifiers. A thickened WAS blending tank will be constructed adjacent to the new building, where thickened primary sludge will be blended, resulting in a continuous feed to the digesters.

Increase Utilization of the Existing Anaerobic Digesters

Based on current and design (37.7 MGD) flows and loads, only one of the two primary digesters is needed. With the expected decrease in required volume from separate sludge thickening, there will be additional capacity in the digesters. This additional available capacity can be utilized by accepting hauled waste, e.g. food processing waste. In 2017, CRW began experimenting with feeding hauled waste to the anaerobic digesters. Based on the current and projected capacity of the anaerobic digesters, there is an opportunity to expand the receipt of hauled waste, with the goal of generating additional biogas and revenue. A hauled waste receiving station is recommended. The receiving station will be constructed in the new WAS thickening building. The receiving station will screen the hauled waste and remove grit prior to being discharged to an equalization tank adjacent to the WAS thickening building. The hauled waste will be blended with the combined primary sludge and WAS to target a uniform feed consistency to the digesters.

Combined Heat and Power Generation

With the improved digester efficiency, along with the increase in hauled waste and the resulting increase in biogas, there is an opportunity to better optimize heat and electrical power recovered from the biogas generated. A combined heat and power station would provide an opportunity to improve the overall energy recovery efficiency. Two new 500 kW reciprocating internal combustion engine driven generators are recommended. They will be installed in the existing cogeneration building. As the hauled waste program becomes more established, a third generator could be installed. The electricity generated will be put back on the utility grid through a new transformer. Biogas pretreatment equipment will be installed upstream of the generators to better control the gas quality to the units and decrease the maintenance required. The biogas pretreatment and heat recovery equipment will be located within, on the roof of, and adjacent to, the cogeneration building as needed.





Anaerobic Digestion Improvements

The planned improvements to the primary digesters are necessary to provide reliability and efficiently handle the increased sludge solids concentration and the hauled waste. These improvements include:

Gas mixing system replaced with mechanical mixing system

Replacement of the primary digester fixed covers

Replacement of the gas and sludge piping internal to the digesters

Replacement of sludge piping and valves within the digester control house gallery

Replacement of the waste gas flare

Replacement of the primary digester recirculation pumps

Replacement of primary digester transfer pumps

Provisions for future direct steam injection to the digesters

New electrical and controls building Mineral buildup in the digester recirculation line and heat exchanger has also been an operational difficulty. It is believed the mineral is vivianite, (i.e. solid hydrated iron phosphate), which provides limited economical options to address. As an alternative, the direct steam injection heating of the digesters is recommended. This will require a steam boiler, either from the CHP system, or the replacement boiler in the boiler building would be outfitted to generate steam and steam headers, to be installed in the digesters. Provisions for the steam lances will be included in the primary digester improvements. Direct steam injection in the sludge feed line, and the recirculation lines will be included in the future. The secondary digesters are currently used as digested sludge settling tanks prior to dewatering. With the expected increase in digested solids concentrations from separate thickening of primary and WAS sludge, this settling of digested sludge will not be necessary. One of the secondary digesters could be converted into a third primary anaerobic digester. This would require similar upgrades as the primary digesters, listed above. Direct steam injection would also be applied in the converted secondary digester. In addition, a recirculation loop would be recommended to provide further homogenization of the solids in the tanks. Another alternative is to keep both as secondary digesters and retrofit them with linear motion mixers to allow a more consistent feed to dewatering. Hauled waste can have an adverse effect on the digesters due to large variations in volume and characteristics. Equalization tanks can help provide for a more consistent feed to the digesters and one equalization tank is recommended to be included with the hauled waste receiving system. As a further improvement in anaerobic digester performance and gas production, the addition of an acid phase digester should be considered. One of the widely reported benefits of acid phase digestion is the reduction in foaming events, like those caused by inconsistent feed to the digesters. Figure 6-1 shows a schematic of the recommended biosolids improvements plan.





Figure 6-1. Schematic of Recommended Biosolids Improvements

A site plan of the proposed improvements is shown on Drawing 01.

Gravity Thickeners


Belt Filter Presses

Secondary Anaerobic Digesters

Primary Sludge

Diluent Water

Gas Storage Sphere

Polymer

Combined Heat and Power

Waste Flare

Biosolids Storage

Land Application


Hauled

Unloading With

Rock Trap

Screen Waste

Equalization Tank

Biogas Pre-Treatment Gravity Belt

Thickeners

Acid Phase

Digester FUTURE: Centrifuge or similar

Blending Tank

Whitman, Requardt & Associates, LLP

801 South Caroline Street, Baltimore, Maryland 21231

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SHEET 1

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SIGNATURE

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GRAPHIC SCALES

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KEY PLAN

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REVISIONS

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CLIENT INFORMATION

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TOWN OF CENTREVILLE CENTREVILLE, MD

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WWTP UPGRADE

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01

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DIGESTED SLUDGE PUMPING STATION

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SECONDARY DIGESTER NO.2

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SECONDARY DIGESTER NO.1

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THICKENER NO.1

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THICKENER NO.2

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SECONDARY DIGESTER CONTROL HOUSE

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PIPE TUNNEL NO.1

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GAS COMPRESSOR BUILDING

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GAS STORAGE SPHERE

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THICKENED SLUDGE PUMPING STATION

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PUMP TUNNEL NO.2

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PLANT DRAIN PUMPING STATION

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PROPOSED ELECTRICAL BUILDING

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FUEL OIL STORAGE TANK

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BOILER BUILDING

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PRIMARY DIGESTER NO.1

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PRIMARY DIGESTER NO.2

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COGENERATION BUILDING

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PRIMARY DIGESTER CONTROL HOUSE

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ELECTRIC GEAR

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CHLORINE CONTACT TANKS

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CHAMBER "C"

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CHAMBER "E"

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SETTLED SEWAGE PUMPING STATION

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PRIMARY SETTLING TANKS

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PARKING LOT

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CONTROL BUILDING

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GARAGE

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CHLORINE BUILDING

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WASTE GAS BURNER

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RAILROAD TRACK

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PROPOSED ACID PHASE DIGESTER

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PROPOSED HAULED WASTE RECEIVING STATION & WAS THICKENING & POLYMER HANDLING & PUMP STATION

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PROPOSED HAULED WASTE TANK

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PROPOSED BLENDING TANK





6.2 Specific Facility Recommended Improvements

Included in this section is a summary of design criteria for the recommended facilities, and key details for the individual facilities. A summary of the recommended biosolids facilities improvements, including key design criteria, are included in Table 6-1.

Table 6-1. Recommended Improvements by Facility

Gravity Thickeners

Replace Sludge Mechanisms

Replace Sludge Pumps, VFD

Replace Scum Pumps

Hauled Waste Receiving Station

New Building with WAS Thickening

New Receiving Station

600 gpm Unloading Rate

Screening, Grit, and Grease Removal

75,000 gal Holding Tank


WAS Thickening

3 – New 2 m Gravity Belt Thickeners

600 gpm Hydraulic Loading Rate Each

2 In Operation 16.5 hrs/day at Design Capacity

New Building with Hauled Waste

100,000 gallon Blending Tank

Sludge Transfer Pumps

Primary Digesters

Replace Mixing System with Mechanical Mixer

Replace Gas a Sludge Piping Inside the Digester and Inside the Control Building

New Electrical and Controls Building

Replace Waste Gas Flare

Replace Recirculation Pumps

Replace Transfer Pumps

Install Provisions for Direct Steam Injection into Digesters

Capacity after Upgrades and with WAS Thickening will be 61,000 lbs VS/day

Two Phase Digestion Install One (1) 300,000 gallon Acid Phase Digester

1.5 Days SRT

Secondary Digesters Rehabilitation

Replace Roof on Both Digesters

Replace Piping

Refurbish Concrete and Exterior Brick

Secondary Digester Upgrade

Upgrade One Existing Digester to Function as a Primary Digester with Mechanical Mixer, and Recirculation with Temperature Control.

Install Mechanical Mixer on One Existing Digester

Sludge Dewatering

Two (2) New Centrifuges

Hydraulic Loading Rate, 110 gpm each

Solids Loading Rate, 2,000 lbs dry solids/hr each





Table 6-1. Recommended Improvements by Facility

Boiler Building One (1) New Steam Boiler in Existing Building

Cogeneration Building Two (2) New 500kW Biogas Reciprocating Engine Drive

Generator Units, with Provisions for a Third Unit

Combined Heat Recovery

Gas Collection, Storage and Pretreatment

Replace Two (2) Low Pressure Compressors

Replace Hydrogen Sulfide Removal Unit

Replace Particulate and Condensate Removal Unit

Existing Storage Tank

Sludge Storage Sheds One (1) New 15,000 cu ft Capacity Sludge Storage

Shed

Gravity Thickener Facilities

Primary sludge will be thickened in the existing gravity thickeners without waste activated sludge (after implementation of WAS Thickening). The overflow rate of the thickeners was evaluated to determine if the rate when thickening only primary sludge is too low. The primary sludge flow rate has averaged 0.44 MGD over the period studied. Thickening this stream separately with a 4:1 dilution water to sludge ratio would result in an overflow rate of 220 gal/sq ft/d, which is low and subject to floating sludge, odors and septicity. Operating one thickener would be recommended to keep the dilution water quantity reasonable, result in an overflow rate of 440 gal/sq ft/d, and avoid excessive detention time. Also, chlorine can be added to reduce odors and maintain fresher sludge with less septicity and reduce potential for gasification. With the separate thickening of WAS, the existing gravity thickeners are expected to thicken the primary sludge to 4-6% solids. Since the gravity thickeners are well beyond their expected life, the sludge mechanisms and sludge and scum pumps will need to be replaced within the planning horizon of the biosolids improvement plan. The pumps and mechanism will be replaced in kind.

Hauled Waste Facility

Hauled waste will be delivered in tanker trucks varying in size. Handling the hauled waste will require unloading, pretreatment, flow equalization, blending with thickened primary and waste activated sludges, and pumping to the digesters. Equalization of the hauled waste reduces the potential for foaming and upset conditions as there may be considerable variability in waste volumes and characteristics. The hauled waste facility would include the following components, at a minimum.

Truck unloading station with containment

Automated billing ticket generation

Rock trap

One (1) screening washing unit with bypass for grease

One (1) grit trap with grease removal system

One (1) transfer pump

One (1) equalization tank, both totaling to a working volume of one (1) times the daily expected volume

Tank aeration/mixing system with odor control

Two (2) transfer pumps to convey pretreated waste to the primary digesters





The mechanical equipment for handling hauled waste would be housed in the same building as the proposed WAS thickening process. Additional pretreatment equipment may be necessary depending on the characteristics of the hauled waste anticipated to be accepted by the AWTF. The hauled waste truck unloading station will be equipped with an automated dump station control panel. The panel will read the driver’s access card, then open an automated valve, and record the totalized flow from a flow meter. This information will be stored in the panel and can be communicated across a network or downloaded for billing purposes. The truck will connect to an unloading station with a hose. The hauled waste will be pretreated during the truck unloading operation for the removal of inorganics (grit and screenings). Hauled waste may also include fats, oils and grease (referred to as FOG) which will bypass the screening operation. Screenings will be washed, compacted and conveyed into a dumpster. The grit that is removed will also be conveyed into the same dumpster. Table 6-2 shows key design criteria for the hauled waste receiving station.

Hauled waste will be pumped into a holding tank to provide flow equalization prior to being blended with primary

sludge and WAS and pumped into the primary anaerobic digesters. The flow equalization tank will have a working

volume equal to one day of expected hauled waste volume. The tank will be agitated with coarse bubble diffusers

and equipped with an odor control system.

Hauled waste transfer pumps will pump from the hauled waste holding tank to the sludge blending tank and then to

either of the primary anaerobic digesters, normally through the direct steam injection system in the recirculation

loop, so the combined sludge could be heated prior to entering the digester.

The hauled waste receiving station will be installed in the waste activated sludge thickening building. See Drawings 02 and 03 for a conceptual floor plans of the lower and upper levels of the proposed building showing the hauled waste receiving equipment.

Table 6-2. Hauled Waste Receiving Station

Quantity 1

Hydraulic Capacity

1.37 MGD

Drum Screen Diameter

47 inches

Screen Openings

1/4 to 3/8 inch

Screenings Compacted Water Content

65%, maximum

Location Rating

Class 1, Division 2



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CAPITAL REGION WATER

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3

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MARCH 2018

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GRAVITY BELT THICKENER, DIMENSIONS OF ASHBROOK AQUABELT, 2M UNIT

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Waste Activated Sludge Thickening Facility

Gravity belt thickeners will be installed for the separate thickening of WAS. The GBTs will be sized to operate 12 to 18 hours per day, 7 days a week with the preliminary design criteria in Table 6-3.

Table 6-3. Gravity Belt Thickeners

GBT Units No. of Units Hydraulic Loading, design Belt Width Hydraulic Capacity Solids Capacity Operating Schedule, each Volume of WAS, total Volume of thickened WAS, total

3, in parallel 300 gpm/meter of belt width 2 m, each 600 gpm, each 1,000 lbs/hr, each 16.5 hrs/day with 2 units in operation, 7 days a week 1,200,000 gpd 1,200 gpm when operating 50,000 gpd 56 gpm when operating

Blending a portion of the thickened primary sludge with the WAS will improve the solids capture of the gravity belt thickener. Provisions in the piping should be considered to allow for this flexibility. The thickened WAS will be pumped to a blending tank to provide flow equalization and mixing with thickened primary sludge and hauled waste prior to being pumped into the primary anaerobic digesters. The blending tank will have a working volume equal to 100,000 gallons. The tank will be covered and agitated with coarse bubble diffusers. Digester feed pumps will pump from the blending tank to either of the primary anaerobic digesters, normally through the heat exchanger recirculation loop, so the digester feed could be heated prior to entering the digester. The wasting of RAS, rather than MLSS, has also been examined. If RAS is utilized, the volume of sludge will be reduced to 50-60% of the MLSS related volume, or a range of 0.6 to 0.72 MGD rather than 1.2 MGD. If this change is made before the construction of the GBT facility, then the GBT sizing could be modified to 3 units, with a belt width of 1.5 meters each. Thus, the belt width of 2 meters as shown in Table 6-3 would change to 1.5 meter. Reducing the size of the GBTs further is not recommended to allow for greater flexibility when wasting volumes increase during periods of higher than average wasting, e.g., during the spring when reducing the target MLSS. See Drawing 01 for a site plan of the proposed WAS thickening and hauled waste receiving building. See Drawings 02 and 03 for conceptual floor plans of the lower and upper levels of the proposed building, showing the gravity belt thickener and related equipment.

Sludge Blending Tank

A new sludge blending tank will be provided to blend the thickened WAS, and the hauled waste. Thickened primary sludge will also be pumped to the proposed blending tank. Providing a blending tank in addition to the hauled waste tank will allow for the isolation of unloaded hauled waste, if necessary, and for control of the ratio of hauled waste, thickened WAS and thickened primary sludge that is pumped to the digesters. The blending tank





will be a cast in place concrete tank with common wall construction with the hauled waste tank. The blending tank will be covered and mixed. Key design criteria are presented in Table 6-4.

Table 6-4. Sludge Blending Tank

No. of Units Working Volume Length and Width Side Water Depth

1 100,000 gallons 40 feet by 28 feet 12 feet

Primary Digesters and Control House

The refurbishment of the primary digesters and associated upgrades is currently being implemented. Improvements will include:

Gas mixing system replaced with mechanical mixing system

Replacement of the primary digester fixed covers

Replacement of the gas and sludge piping internal to the digesters

Replacement of sludge piping and valves within the digester control house gallery

Replacement of the waste gas flare

Replacement of the primary digester recirculation pumps

Replacement of primary digester transfer pumps

New electrical and controls building The primary digester concentric tube heat exchangers are not being modified with the current project. The heat exchangers are sufficiently sized for the digester operation when not fouled with mineral buildup. Currently, the heat exchangers get too fouled to maintain digester temperature within 18-24 months of operation. The heat exchangers will be replaced by the direct steam injection into the digesters. A steam boiler will eventually be installed in the existing boiler building to replace the existing hot water boilers. Steam distribution piping will be extended to the floor of the digesters and steam will be distributed through a series of nozzles. Once the primary digesters refurbishment is completed, both digesters will be put in operation to provide additional solids and gas production capacity. The secondary digesters will remain as holding tanks until the capacity is needed, but will need to be refurbished with new covers and new process piping as a course of maintenance to replace aged infrastructure. When the two existing primary digesters are approaching capacity, CRW will need to determine if one of the secondary digesters should be converted to a primary digester and a new acid phase digester tank should be constructed. Conversion of a secondary digester to a primary digester will require similar upgrades to those of the existing primary digesters. Converting a secondary digester to a third primary digester and construction of an acid phase digester depend on the viability of a sustained hauled waste program and other economic factors described in Section 7.4. A new separate acid phase digester tank would be sized for a solids retention time of 1-2 days, where the acid formation phase of digestion would primarily take place. The feed biosolids would be pumped through a heat exchanger to mesophilic temperatures, and into the acid phase tank. The low-pH environment would be established





in this digester, suspended solids would be hydrolyzed, and fatty acids would be formed. The sludge from the acid phase digester would be pumped into the main digesters which can be operated to maintain optimum environment for methanogenic bacteria formation. Table 6-5 summarizes design criteria for acid phase digestion.

Table 6-5. Acid Phase Digester

No. of Units Volatile Solids Loading, design SRT, Design Working Volume Height to Diameter Ratio Diameter Side Water Depth

1 1.5 lbs volatile solids/cu ft/day 1.5 days 300,000 gallons 1.2:1 to 1.5:1 35 feet 45 feet

See Drawing 01 for the site plan indicating the proposed location for the acid phase digester.

Secondary Digesters and Control House

The secondary digesters are currently operated as holding tanks for storage and equalization of digested sludge prior to being pumped to dewatering operations. The secondary digesters need to be refurbished with new covers and new process piping as a course of maintenance to replace aged infrastructure. If the quantity of hauled waste and sludge generated at the AWTF exceeds the capacity of the existing primary digesters, one of the secondary digesters can be converted to operate as an anaerobic digester. As mentioned above, the conversion would require similar upgrades to those currently being implemented for the primary digesters. Providing mechanical mixing in both secondary digesters should be considered to provide a more uniform feed to the dewatering facilities. The design criteria of the existing secondary digesters are presented in Table 6-6.

Table 6-6. Secondary Digesters

No. of Units Clean Tank Volume Roof Type Diameter Side Water Depth

2 924,000, and 839,000 gallons One (1) Fixed, One (1) Floating 85 feet 28 feet





Dewatering Facilities

The existing dewatering facilities are anticipated to meet the needs of the Biosolids Facility Improvement Plan, including the hauled waste projections. The most significant disadvantage of the belt filter press (BFP) technology for the AWTF is that the dry cake solids are lower than typically produced by some of the other technologies, such as centrifuges or screw presses. Rather than replace the relatively new BFPs to increase the cake solids, it is recommended to investigate improvements to the BFP operation such as:

Modifications to polymer conditioning

Improve the digested sludge degree of stabilization and characteristics

Review the belt filter press condition and operation

In addition, pretreatment technologies should be investigated, such as the SLG (Solid Liquid Gas) process by Orege. A separate study is being undertaken to investigate alternatives to optimize dewatering operations.

Local biosolids regulations are likely to become more stringent in the foreseeable future, i.e., 5-10 year timeframe. There may be more reporting requirements, a higher quality of biosolids required for land application, and restrictions on land available for application. While these changes in regulations are developed and finalized, a reasonable course of action is to continue utilizing the existing belt filter presses. As more stringent biosolids disposal regulations become implemented in the future, the production of Class A biosolids should be considered.

Boiler Building

The existing hot water boilers would be replaced with one (1) 6,000,000 BTU/hr steam generating boiler to provide supplemental heat to that from the CHP units. The boiler would be dual fuel capable of burning either biogas or propane.

Cogeneration Building

The use of a combined heat and power system will provide higher energy recovery efficiency than the existing separate system. Considering that both the existing boilers, and engine driven generators are beyond their expected life, and if CRW decides to implement and expand hauled waste acceptance, investing in a combined heat and power system is recommended. The reciprocating engine driven generator is well known to the AWTF operations staff and is projected to provide an economic benefit to the facility. Therefore, it is recommended that the AWTF plan to install a lean burn reciprocating engine based CHP system. The amount of projected biogas is based on typical values for municipal biosolids anaerobic digestion. This implies that the biogas generated from the anticipated hauled wastes will average similar values to that of the biosolids. In fact, the actual blend of hauled waste may vary significantly over time, as will the ratio of hauled waste solids to biosolids. Therefore, the amount projected biogas will have a large variation over time. Therefore, the CHP system should be designed to provide for significant flexibility. Manufacturer’s generally carry a nominally sized 500 kW continuous rated 3 phase 60 Hz biogas fueled generator. Assuming a hauled waste program is pursued as recommended, and considering redundancy and turn down flexibility, three (3) 500 kW units would be recommended. Preliminary sizing based on catalog information would indicate that the three units could fit in the existing cogeneration building. Pretreatment equipment, and some of the heat recovery equipment would be installed adjacent to, or on the roof of, the building. The 480V power that is provided by the generator is stepped up to medium voltage prior to connecting to the utility power lines by a transformer. The existing transformer would need to be replaced, as would the cables from the cogeneration building to the utility power lines.





Vivianite Management

Vivianite buildup will be mitigated through the direct steam injection heating of the digesters. See above sections for discussions on the steam heating of the digesters and steam generation.

Sludge Storage Sheds

The existing sludge storage sheds are in good physical condition, and will provide many years of service with continued maintenance. The steel columns should be repainted and the metal roof replaced as needed. Due to the doubling in digested sludge that will be produced from the aforementioned upgrades including hauled waste co-digestion, and the need for additional storage when sludge cannot be moved off-site, due to either weather or unintended circumstances, a new sludge storage shed is proposed. Its location and approximate size can be seen in Figure 6-2. Table 6-7 shows the design criteria for the proposed storage shed.

Table 6-7. Proposed Storage Shed

Area, Dimensions

2600 sq ft, 52 x 50 ft

Sludge Height

6 ft

Sludge Density

64.3 lb/cf

Sludge Production Rate, design

52,000 lbs TSS/day (including hauled

waste)

Detention Time 19 days

Due to space constraints, the tipping scale will need to be relocated to accommodate the new storage shed. Its proposed location can also be seen in Figure 6-2. This new location will result in rerouting the trucks to go in a counter-clockwise direction when entering the facility.





Figure 6-2. Proposed Storage Shed

Gas Collection, Storage and Pretreatment

The gas compressors and pretreatment system are beyond their useful life expectancy, and are not designed for the flow or pressure required by the CHP system, and therefore the compressors will be replaced. Before the biogas can be utilized by CHP technology, it needs to be pretreated to remove certain components: H2S,

moisture, and siloxanes. If not pretreated, these components can negatively impact the CHP’s equipment.

Without pretreatment, H2S concentrations vary from 50-10,000 ppm and can cause corrosion to the engine and the

equipment’s metal parts from the emission of SO2 from combustion. This is especially the case if the engine is not

operated. Additionally, these emissions produce toxic H2S/SO2 concentrations. Currently, the AWTF uses the

second option through the use of a Varec gas purifier that utilizes a bed of iron sponge to convert H2S into ferric

sulfide deposits. It is a simple system that requires limited operational oversight. A larger replacement iron sponge

system will be installed for the proposed CHP system.

Biogas is typically saturated with water, and after treating for H2S, the moisture content has to be removed. The

efficiency of the engine increases, there is a reduction in engine oil contamination, and less corrosion of pipework

and components. Moisture will be removed by cooling the gas to condense the water which can be drained from

the system.





Siloxanes are silicon compounds and are found in small amounts in biogas. Combustion inside the engine, transforms these compounds into oxides which precipitate and collect inside the machinery. Consequently, these deposits can result in breakdowns and wear down the metal parts in engine, reducing the useful lifetime of the system. The only industrial scale method of removing siloxanes is adsorption with activated carbon. The activated carbon siloxane removal system will be located downstream of the hydrogen sulfide and moisture removal units.



Improvements Phasing and Cost Analysis | 60


7 Improvements Phasing and Cost Analysis

There are several factors that must be considered when determining when to implement the biosolids facility improvements. Some of the factors include:

Age and Condition of Existing Processes

Requirement to Maintain Biosolids Facilities in Operation

Availability of Funding in Relation to Competing Infrastructure Needs Outside of the AWTF

Analysis of Hauled Waste Alternatives

Cost of Recommended Improvements

This section presents costs of the various recommended improvements as well as an implementation schedule which was developed in conjunction with CRW.

7.1 Age and Condition of Existing Processes

A separate condition assessment was completed in advance of this evaluation which identified significant infrastructure needs within the AWTF biosolids facilities. The implementation plan addresses these needs in order of priority as discussed with CRW, beginning with the improvements to the primary digester facilities.

7.2 Maintain Biosolids Facilities in Service

Maintaining facilities in full operation in order to process biosolids is an important consideration in developing the implementation plan phasing. Projects need to be phased in order to maintain access for plant operations.

7.3 Availability of Funding in Relation to Other Infrastructure Needs

In addition to the AWTF, CRW owns and operates other significant infrastructure that serves the City of Harrisburg and the surrounding municipalities. Infrastructure includes a surface water storage reservoir, water conveyance and distribution, a water treatment plant, and sewer collection system and pumping stations. The amount of available funding is limited so implementation of capital projects recommended as part of this plan need to be phased in order to limit impacts to ratepayers. Further evaluation also should be done on gas production and utilization alternatives in the context of available grant funding to offset costs of the recommended program.

7.4 Analysis of Hauled Waste Alternatives

Co-digestion of hauled waste will require significant new infrastructure and additional ongoing labor and maintenance. The anaerobic digestion facility will also require additional testing and operational monitoring to reduce the impacts co-digestion could have on the anaerobic digestion facility. Identifying, scheduling, and receiving acceptable hauled waste to provide a consistent feed to the digester, will also require additional efforts. To assess the merits of expanding the hauled waste program, an evaluation was performed to consider the costs and benefits of the co-digestion of hauled waste, and the beneficial use of biogas to generate heat and electricity. The continued anaerobic digestion of the biosolids produced by the AWTF was not included in this economic evaluation. The benefits of biogas production, and biosolids stabilization and reduction are well established for municipal wastewater treatment plants of similar size.





In addition, the ‘do nothing’ alternative in which the biogas utilization facilities (existing boilers and engine driven generators) are not replaced, would result in the open flaring of the biogas. The environmental impacts and public perception of open flaring makes the ‘do nothing’ option undesirable, and is also not included in the cost analysis. Three alternatives were considered:

Base Case – Hauled Waste received at about 50-60% of the total feed to the digesters (VSS mass basis) and needed to keep digesters operating at design capacity

30% Hauled Waste – Hauled Waste quantity is limited to 30% of the total feed to the digesters (VSS mass basis)

No Hauled Waste – Only AWTF biosolids are digested.

Alternative 1 - Hauled Waste Base Case

In the base case, sufficient hauled waste is received to feed the two existing primary digesters at their design capacity loading rate. To account for the unavailability of the digesters, including for maintenance and repairs, 95% of the theoretical digester capacity (VSS mass basis) is used in the cost analysis. The percentage of hauled waste to total digester feed will change as the amount of AWTF biosolids changes, but will be approximately 50-60% by volatile solids load. Operating with hauled waste at this loading rate poses a potential risk to the stable operation of the digestion process. Many factors impact the stable operation of the digestion process, but the key is consistency of the feed. A higher percentage of hauled waste can result in more variable or undesirable characteristics of feed to the digesters, as well as difficulty in maintaining consistency, and thus poses a higher risk. The quality and consistency of the hauled waste (i.e., the hauled waste’s ease of digestibility) and stable operational control will be crucial to the successful operation of the digestion process. Upsets to the digestion process could result in decreased solids reduction, and therefore reduced biogas production. Excessive foaming is also commonly encountered when the digestion process is out of balance. Provisions have been included in this Improvements Plan to incorporate hauled waste pretreatment, storage, flow equalization, and blending with thickened primary and waste activated sludge, feed control and a digester mixing system to reduce the risk of these potential issues. In addition, provisions need to be in place to allow one of the digesters to be taken offline for cleaning and maintenance. Operating with high percentages of hauled waste with only one digester is not recommended. To mitigate these risks, the base case not only includes costs for the hauled waste facility and equalization tank, but also includes the installation of an acid phase digester to provide two phase digestion, and the upgrading of a secondary digester to have the capabilities of the primary digesters, including mixing and heating.

Alternative 2 - 30% Hauled Waste

In the second alternative, the hauled waste is limited to 30% of the total feed to the digesters. By limiting the percentage of hauled waste, a more stable digestion process is likely when compared with higher hauled waste percentages. The total feed to the digester will vary based on the AWTF biosolids, but in general the digesters will be operating at 60-70% of their design capacity. Operating with the digester feed at 30% hauled waste (VSS mass basis) will allow one digester to be taken off line for maintenance and cleaning, with only a moderate risk to the digestion process. Therefore, the secondary digester upgrade would not be required in this alternative. In addition, two phase digestion would not be justified. Therefore, this alternative includes costs of the hauled waste facility and equalization tank, but does not include capital costs for the acid phase digester or secondary digester upgrades.

Alternative 3 - No Hauled Waste

In the third alternative, no hauled waste is received and only AWTF biosolids coming in from the collection system are digested. This alternative does not include any costs for a hauled waste facility or equalization tank.





Hauled Waste Cost Analysis Parameters and Assumptions

In all three alternatives considered in the economic analysis to receive hauled waste, the following biosolids projects are not impacted by hauled waste.

Primary Digester Improvements

Secondary Digester Rehabilitation

Gravity Thickener Refurbishment

Dewatering Upgrades The total cost of the CHP and biogas handling facilities is $13,400,000, which includes infrastructure to address additional gas production anticipated with a hauled waste program. The incremental cost attributed to hauled waste is $2,700,000. Therefore, without hauled waste (Alternative No. 3), the CHP and biogas handling facilities could be reduced in capacity, with a cost reduction of $2,700,000. Thus, the incremental cost of CHP associated with Alternative Nos. 1 and 2 is $2,700,000. For all alternatives, WAS Thickening is assumed to be required regardless of the acceptance of hauled waste. The estimated cost of the combined WAS Thickening and Hauled Waste Facility is $9,700,000. If the hauled waste components were removed from this facility, the estimated facility cost could be reduced by $3,210,100. Therefore, the incremental cost associated with Alternative Nos. 1 and 2 is $3,210,100. The cost of the Acid Phase Digester, and conversions of a Secondary Digester to a Primary Digester of $9,560,000, are included as an incremental capital cost for Alternative 1. Since these facilities are not required for Alternative Nos. 2 and 3, there is no corresponding incremental cost assigned. The total incremental increase in capital costs relative to the no hauled waste alternative, are shown in Table 7-1.

Table 7-1. Incremental Capital for Hauled Waste Alternatives

Alternative CHP

WAS

Thickening /

Hauled Waste

Facility

Acid Phase

Digester and

Secondary

Digester Retrofit

Total

Incremental

Capital

1 - Hauled Waste –

Base Case $2,700,000 $3,210,100 $9,560,000 $15,470,100

2 - 30% Hauled

Waste $2,700,000 $3,210,100 $0 $5,910,100

3 - No Hauled

Waste $0 $0 $0 $0

The cost analysis includes assumptions for several key factors that will vary with market conditions, including electricity and fuel costs. Also, the new facilities will require ongoing maintenance, which is included. The tipping fee to be charged by CRW for hauled waste will be based on the volume of waste delivered, and will be influenced by market conditions, transportation costs and other variables. The cost analysis uses the following assumptions:

Electricity rates (based on current) of $0.05 per kWh purchased and $0.06964 per kWh sent to the grid from the generators.

The recovered heat will offset the cost of purchasing another fuel, for example natural gas.

Natural gas cost (based on current) of $5.30 per 1,000 cu ft.





Only the recovered heat that can be used for heating the digesters (year round) and heating the building space (during winter months only), is included in each alternative.

Maintenance and operating costs of 2.2% of the total project cost annually, beginning the year following the time of capital expenditures.

Tipping fee received for hauled waste of $40 per 1,000 gallons.

To provide a straightforward analysis of the costs and benefits of receiving hauled waste, a simple rate of return, the payback period was calculated. This type of analysis ignores the time value of money, and the potential growth of AWTF biosolids. Although these parameters are significant in this case, the simple rate of return and payback period remains meaningful and provide an easily interpreted analysis. The simple rate of return is calculated by dividing the annual benefit by the incremental capital and converting to a percentage. The simple rate of return could be compared to other investment opportunities, or to the cost of funding the project. The payback period represents the number of years the project would have to be operated at the assumed conditions, to provide a benefit equal to the incremental capital. The simple rate of return and the years to payback for the three hauled waste alternatives are included in Table 7-2. The financial analysis in Table 7-2 are based on the single point of capital costs, and input values described above. A sensitivity analysis of some of the variables that could affect the economics of the Alternatives are discussed below.

Table 7-2. Hauled Waste Alternatives Cost Analysis

Alternative Incremental

Capital

Annual

Benefit1

Simple Rate of

Return

Payback

Period

1 - Hauled Waste

Base Case $15,470,100 $892,166 5.8% 17

2 - 30% Hauled

Waste $5,910,100 $529,491 9.0% 11

3 - No Hauled

Waste $0 $276,964 N/A N/A

1. Annual Benefit = First Year Revenue from Electric Generated + Offset of Natural Gas that would otherwise be required for Heating + Tipping Fee Revenue – Hauled Waste Disposal – Maintenance Costs of the Incremental Capital Facilities

Since the incremental capital in Alternative 3 is zero (0), the simple rate of return and payback period cannot be determined. However, the annual benefit for the three alternatives can be directly compared. The annual benefit for Alternative 2 is nearly twice that of Alternative 3, and the annual benefit of Alternative 1 is more than three times more than that of Alternative 3. For Alternative 2, the rate of return on the incremental capital needed for this alternative is 9.0% and will pay back the capital investment in eleven (11) years. To operate reliably with Alternative 1, the rate of return on the incremental capital is only 5.8%, and it will take 17 years to pay back. The lower rate of return is due to the greater increase in capital than increase in annual benefit when compared to Alternative 2.

Net Present Value

The Net Present Value (NPV) was also calculated to provide a time dependent analysis of the costs and benefits of the three hauled waste alternatives. The cost of disposal of hauled waste was included in the NPV calculation. A 60% destruction of volatile solids in the hauled waste and a 22% dewatered cake was assumed in calculating the wet tons of hauled waste associated solids.





The net present value included the incremental capital and maintenance costs, the benefits of the electricity generated, and heat recovered, and the time value of money (3% discount rate, assumed). The NPV is calculated over a 25-year period starting in 2019. The NPV spreadsheets are included in Appendix B, and a summary is provided in Table 7-3.

Table 7-3. NPV for Hauled Waste Alternatives

Alternative NPV

1 - Hauled Waste – Base Case $1,100,000

2 - 30% Hauled Waste $6,000,000

3- No Hauled Waste $5,500,000

The NPV values for Alternatives 2 and 3 are essentially the same given the relatively long period being considered, and the numerous assumptions. Alternative 2 results in the highest net present value. Alternative 2 is conservative in the assumptions used for the NPV, providing opportunity for the hauled waste program to perform better than expected, which could potentially increase the NPV. Tax credits and grants may also be available for the hauled waste Alternatives 1 and 2 that may enhance the economic viability of those options.

Risks to the Hauled Waste Alternatives

The simple economic analysis and NPV calculation provide a comparison of three hauled waste alternatives. Understanding the risks involved with the three alternatives provides further justification to selecting an alternative. Risks to accepting hauled waste include:

The analysis assumes hauled waste that is amenable to co-digestion with municipal biosolids

Identifying and receiving the actual quantity of hauled waste compared to the projected quantity in the analysis

Obtaining the projected tipping fee ($40/1000 gallons) on average for the highest quality hauled waste

The growth of the biosolids from the AWTF service area growth may or may not occur

Monitoring of incoming hauled waste and close attention to the operation of the digesters are critical to consistent digestion and gas production.

Both tipping fee and the costs of maintenance can have a significant impact on the NPV. Selecting equipment with low maintenance requirements and maximizing tipping fees within the available source market can both result in a positive NPV result.

Sensitivity Analysis

A limited sensitivity analysis was also conducted on the hauled waste cost analysis. Included in the sensitivity analysis were the following variations: Increase capital costs by 20% Decrease capital costs by 15% Increase electricity costs by 50% Decrease electricity costs by 20% Increase natural gas costs by 50%





Increase Hauling Cost by 15% The spreadsheets for each of the NPV scenarios, taken individually and not collectively, are included in Appendix B. The range of NPV, Simple Rate of Return and Payback Period from the sensitivity analysis were also evaluated. For Alternative 1, the NPV ranges from ($900,000) to $6,300,000. The negative NPV indicating the project benefits would not break even with the project costs after 25 years. The simple rate of return range from 4 to 8%, and the years to payback range from 13 to 23 years. The simple rate of return and payback do not incorporate the time value of money resulting in more optimistic results. For Alternative 2, the NPV ranges from $4,500,000 to $9,900,000. By limiting the hauled waste received to a conservative 30% of the volatile solids fed to the digesters, the capital costs are reduced, and for the variations studied, the project results in a net benefit to CRW. The simple rate of return range from 7 to 12%, and the years to payback range from 8 to 14 years.

Other Biosolids Improvement Plan Benefits

There are other benefits that should be considered in evaluating the justification for the biogas utilization projects. Providing emergency back-up power, for critical treatment operations, to the AWTF is one benefit. Currently the AWTF is supplied power from two different sources, but in the event of a catastrophic weather event, both sources could be lost. Providing back-up power from the CHP system would not be affected by most weather events. Biogas is a renewable resource and utilizing it to generate electricity and heat offsets the use of non-renewable resources such as petroleum and coal. Another benefit not included in the cost analysis calculation, is the possibility that that portions of the capital costs may qualify for ‘green energy’ tax credits, grants, and low interest funding.

Hauled Waste Recommendation

Accepting hauled waste will require new infrastructure and operational and maintenance support. Accepting hauled waste also introduces risks to the digestion process, and identifying, negotiating, and receiving high quality hauled waste will also add complexity to the overall AWTF operation. At the same time, the potential opportunity to provide a long-term positive net economic impact to the AWTF as well as providing environmental and public relations benefits merits further evaluation of the hauled waste program. Alternative 2, or limiting hauled waste to 30% of the digester feed, was found to have a shorter payback period compared to Alternative 1, the base case. This alternative merits further consideration since it offers the potential for the plant to incrementally increase the volume of hauled waste received while the plant monitors and evaluates the stability of the digestion process.

7.5 Summary and Cost of Improvements

A summary of capital improvements is presented in Table 7-4. Estimated costs of each of the capital improvements are shown in Table 7-5.





Table 7-4 Summary of Improvements

Process Summary Description Key Design Criteria

Primary Digesters

(Upgraded)

Two (2) existing primary

digesters on line

Replace gas mixing system with

mechanical mixing system

Replace primary digester fixed

covers

Replace gas and sludge piping

internal to the digesters

Replace sludge piping and

valves within the digester control

house gallery

Replace waste gas flare

Replace primary digester

recirculation pumps

Replacement of primary digester

transfer pumps

New electrical and controls

building

At Digester Capacity:

Solids Loading Rate: 76,900 lbs

TSS/day

61,000 lbs VS/day

0.18 MGD

5% Solids

Loading Rate: 0.12 lbs VS/cu

ft/d

SRT: 20 days

Enginator Refurbishment Refurbish Enginator Equipment Two (2) 400 kW Units

Secondary Digesters

Refurbishment

Replace Roofs

Clean Tank Volumes: 924,000

and 839,000 gallons

Diameter: 85 ft

Side Water Depth: 28 ft

Gravity Thickeners

(Upgraded)

Replace Sludge Mechanisms (2)

Replace Thickened Sludge

Pumps (3)

Replace Scum Pumps (2)

80 Foot Diameter with scum

collection

210 gpm with VFD

50 gpm







Combined Heat and Power

Facility

(Existing Building, New

Equipment)

Reciprocating Engine Driven

Generator Units (3)

Generator Output, each: 500 kW

Electricity Generated, 480 V 3

phase 60 Hz 4 wire

Gas Collection, Storage and

Pretreatment

(Upgraded)

Replace low pressure gas

compressors (2)

Replace Hydrogen Sulfide

Removal and

Particulate/Condensate Units

Existing One (1) Storage Tank

Size: 4 x 4 inches

Output Pressure: 15.71 psia

Capacity, each: 240 cfm

Treatment volume: 40 cf

Capacity: 45,000 scf/day

Pressure drop: 0.5 in of water

column

Size: 42 ft diameter

Pressure, max: 50 psig

Capacity: 38,793 ft

Boiler Building

(Existing Building, New

Equipment)

New Steam Boiler (1), Back up

to CHP 6,000,000 Btu/hr







WAS Thickening

(New)

Gravity Belt Thickeners (3)

Thickened Sludge transfer

pumps(2)


New building for GBT and

hauled waste receiving facilities

Volumetric Loading Rate: 300

gpm per meter of belt width

Solids Loading Rate: 500 lbs

TSS per hour per meter of belt

width

Feed % Solids: 0.2 – 0.3% TSS

TWAS % Solids:

4-6% TSS

Number of Operating Hours a

Day: 33 hrs per day – 16.5

hrs/day with two GBT units

operating

30-60 gpm

50 ft head

VFD driven motor

100,000 gallon Capacity

Two Story

45 feet by 75 feet


Primary Digester & Acid Phase

Digestion (New)

Acid Phase Digester

Convert one secondary digester

to functioning anaerobic digester

with upgrades similar to primary

digester scope listed above.

Retrofit one secondary digester

1.5 days SRT

300,000 gallons volume







with linear motion mixer and

replacement roof

Hauled Waste Receiving

(New)

One hauled waste receiving

station with automated access

station including

- Rock Trap

- Screen

- Grit Removal

- Grease Removal

- FOG Bypass

Holding Tank


(2)

600 gpm unloading rate

75,000 gallons Capacity

40 – 100 gpm

50 ft head

VFD driven motor

Dewatering Facilities

(Upgraded)

Two (2) new centrifuges

Volumetric Loading Rate: 75-

110 gpm, each

150-220 gpm total

Solids Loading Rate: 2,000 lbs

dry solids/hr, each, 4,000 lbs dry

solids/hr total

Sludge Storage Facilities

(Existing)

Maintain Structure

Recoat Structure as needed

Replace Roofing as needed







Additional Storage Shed

Relocation of Tipping Scale

52 feet by 50 feet, with 6 ft

sludge height

19 day sludge capacity

A rough order of magnitude (ROM) project cost estimate for each phase is shown in Table 9-5. The information is based on data gathered in 2017. The ENR Construction Cost Index on August 2017 was 10842.

Table 7-5. Project Cost Estimates

Included Projects

Low Estimate

-20%

Contingency

High Estimate

+50%

Contingency

Point Estimate

0%

Contingency

Primary Digester

Improvements $9,500,000 $13,400,000 $11,100,000(1)

CHP Evaluation & Enginator

Rehabilitation $600,000 $1,125,000 $750,000

Hauled Waste and Gas &

Power Generation Market

Evaluation

$160,000 $300,000 $200,000

Secondary Digester

Rehabilitation $2,900,000 $5,400,000 $3,600,000


CHP and Gas System

Upgrades $10,700,000 $20,100,000 $13,400,000


Waste $7,800,000 $14,600,000 $9,700,000


Primary Digester & Acid Phase

Digestion

$7,650,000 $14,340,000 $9,560,000

Dewatering $6,100,000 $11,500,000 $7,600,000

1. Primary Digester Improvement Point, Low, and High Estimates based on July 2017 75% Basis of Design Estimate





7.6 Biosolids Facilities Improvements Phasing Plan

A phased implementation plan, presented in Figure 7-1, was developed following the preparation of the biosolids facilities improvement projects and in consultation with CRW. The phased approach is intended to address immediate priorities while balancing recommended future improvements with CRW’s other system-wide infrastructure needs. The immediate priority for the AWTF Biosolids Facilities is the rehabilitation of the primary anaerobic digesters and related equipment, such that the plant can fully utilize existing equipment and maintain a stable and reliable digestion process. The Primary Digester Improvements, identified as Phase 1, will provide greater reliability for digestion with improvements in mixing, recirculation and heating, and will be starting construction in 2018. Phase 2 will include the refurbishment of the enginators to provide more reliable service in the short term and will also include an investigation of alternative biogas utilization options. Phase 3 will include an expanded market analysis of hauled waste generators, and will develop recommendations for a fee structure for the implementation of a hauled waste program. Phase 4 addresses the reliability of the gravity thickeners and the secondary digesters with a planned refurbishment of each facility. Phases 5 and 6 include major infrastructure improvements to biosolids handling and resource (energy) recovery systems, and allow for an expanded hauled waste receiving program at the AWTF. It is anticipated that the Phase 5 and 6 projects will be further refined through evaluations performed in Phases 2 and 3.

Figure 7-1. Phasing Implementation



Appendices | 72


Appendices

Appendix A – Technical Memoranda

TM-1 Proposed Biosolids Plan

Capital Region WaterAWTF Biosolids Facilities Improvement Plan Technical Memorandum No. 1

August 2017 1 Whitman, Requardt & Associates, LLPN:\14342-001\Engineering\Design\Biosolids Facilities Imp Plan Tech Memos\Final\TM01 - Biosolids Overview .docx

AWTF BIOSOLIDS FACILITIES IMPROVEMENT PLANHARRISBURG, PA

TASK ORDER NO.: 2016-16-01PROJECT NO.: 14342-001

TECHNICAL MEMORANDUM No. 1

SUBJECT: Biosolids Master Plan Overview

Prepared by: D. Nixson, N. Cohen

Reviewed by: M. Olivier, J. Emerson

Distribution:

Date: June 9, 2017

Revised on: August 11, 2017

CONTENTS

I. INTRODUCTION

II. DESIGN CRITERIA

ATTACHMENTS:

1.) Not applicable.

REFERENCE DRAWINGS:

2.) Not applicable.



I. INTRODUCTION

The Harrisburg Advanced Wastewater Treatment Facility (AWTF) is owned and operated by CapitalRegion Water (CRW) and was originally constructed in 1959, and currently is permitted to treat anaverage of 37.7 million gallons per day (MGD) of wastewater collected from the City of Harrisburgand outlying areas. The liquid-side biological treatment process was recently upgraded, to meet morestringent nitrogen and phosphorous limits.

A team led by Whitman, Requardt & Associates, LLP (WRA) has been retained to evaluate thebiosolids facilities at the AWTF and develop a plan that allows CRW to meet their goals and objectivesfor these facilities. This technical memorandum briefly reviews the work completed to date andprovides an outline to establish the long term planning for the AWTF biosolids facilities.

WRA completed a condition assessment of the biosolids facilities in February 2017. Biosolids facilitiesinclude:

· Two (2) Gravity Thickeners· Two (2) Fixed Cover Primary Anaerobic Digesters· Two (2) Secondary Anaerobic Digesters, one with fixed cover and one with floating

cover· Two (2) 2.5 Meter Belt Filter Presses· Covered Biosolids Storage· One (1) Gas Storage Tank· Two (2) Biogas Driven 400 kW Internal Combustion Engine Driven Generators· Three (3) Concentric Tube Heat Exchangers· Two (2) Biogas Fueled Hot Water Boilers· Polymer feed systems, pumps, piping and conveyance systems to support the

operations.

Sludge from the primary sedimentation tanks is mixed with waste activated sludge (WAS) prior to thesolids handling processes. The combined sludges are thickened in gravity thickeners, anaerobicallydigested in primary digesters, stored in secondary digesters and dewatered using the belt filter presses.The dewatered sludge is stored onsite temporarily before being hauled away by a contractor and landapplied to local farms. Biogas is stored and used for building heat and to provide fuel to generateelectricity to sell back to the power company to offset plant power costs.

In general, the Harrisburg Advanced Wastewater Treatment Facility Biosolids Facilities ImprovementPlan Existing Conditions Report (February 2017) found the biosolids related tanks and buildings to bein fair to good physical condition. The mechanical systems on the other hand are in poor condition andare operating well beyond their expected life. Exception to this were the dewatering belt filter presseswhich were installed in 2007, and are fully operational.

CRW is progressive with their goals and objectives for the biosolids facilities. They have longrecognized there is real value in the biosolids which are generated by the AWTF, both throughbeneficial reuse of the biosolids, and also through utilization of the biogas that is generated during



anaerobic digestion. Due to improvements in technology and advancements in operationalphilosophies, e.g. focus on energy efficiency and resource recovery, since the AWTF biosolids facilitieswere installed, there are opportunities to expand on the resources recovered from the biosolids.

CRW current goals for biosolids include:

· Increase the energy recovery from biosolids,· Develop facilities that provide operational and energy efficiency,· Improve long term sustainability.

WRA has evaluated the biosolids treatment process and has determined there are beneficial changesthat can be made to the biosolids facilities to allow CRW to better attain their goals. Recommendationsinclude the following major modifications:

Separately Thicken Waste Activated Sludge and Primary Sludge

This process modification has been proven at many facilities to greatly increase the percent solids inthe thickened sludge sent to the anaerobic digesters. The co-thickened sludge at AWTF is currentlyaveraging approximately 3% solids. Separate thickening is expected to result in 4-6% solids in eachsludge stream. This in turn will increase the solids retention time in the anaerobic digesters, whichincreases volatile solids reduction and biogas generation, and reduces the quantity of digester gasrequired to heat the sludge.

Increase Utilization of the Existing Anaerobic Digesters

CRW currently only needs to operate one of their two primary digesters. With the decrease in volumefrom separate sludge thickening, there will be additional capacity in the digesters. This additionalcapacity can be put to beneficial use for CRW by accepting hauled waste, e.g. food processing waste.In 2017, CRW began experimenting with feeding hauled waste into their anaerobic digesters. Based onthe current and projected capacity of the anaerobic digesters, there is an opportunity to formalize andexpand the receipt of hauled waste, with the goal of generating additional biogas and revenue.

Combined Heat and Power Station

With the improved digester efficiency, along with the increase in hauled waste and the resultingincrease in biogas, there is an opportunity to better optimize heat and electrical power recovered fromthe biogas generated. A combined heat and power station would provide an opportunity to improve theoverall energy recovery efficiency.

Anaerobic Digestion Improvements

The anaerobic digesters are planned to be refurbished with new mixing, and pumping equipment andthe replacement of the fixed covers. In addition to these improvements, the mineral build up in the heatexchangers was evaluated, along with the addition of an acid phase digester.

Hauled waste can have an adverse effect on the digesters due to large variations in volume and



characteristics. Equalization tanks can help provide for a more consistent feed to the digesters and willbe included with the hauled waste receiving system. As a further improvement in anaerobic digesterperformance and gas production, the addition of an acid phase digester should be considered. One ofthe widely reported benefits of acid phase digestion is the reduction in foaming events, like those causedby inconsistent feed to the digesters.

Outline of Biosolids Facilities Technical Memorandum

Separate Technical Memoranda will be developed to provide further details of the plans for the majorbiosolids facilities. The following is a list of anticipated Technical Memoranda and their subject matter.Once the Technical Memoranda are completed and reviewed with CRW, a report summarizing thefacilities plan will be developed and the Technical Memoranda will be included as appendices. Table1-1 indicates of anticipated technical memoranda.

Table 1-1. Technical MemorandumTechnical

MemorandumNumber

Facilities/Processes

1 Proposed Biosolids Facilities Plan

2 Waste Activated Sludge Thickening

3 Hauled Waste Receiving

4 Anaerobic Digesters

Ongoing Upgrades

Acid Phase Digestion

Mineral Deposits and Heat Exchangers

5 Hauled Waste Projections

6 Dewatering Facility

7 Biogas Utilization

Biogas Projections

Biogas Pretreatment

Utilizing Biogas for Heat and Power Generation

II. DESIGN CRITERIA

Biosolids Generated

A review of the 2013 to 2016 AWTF influent flows, biological oxygen demand (BOD5), and TSSconducted in the Biosolids Facilities Improvement Existing Conditions Report concluded theloadings to the plant vary within a consistent range. CRW anticipates only a modest number of



new connections will be made to the collection system. Therefore, future primary and wasteactivated sludge quantities can be expected to generally remain within the current ranges,experienced following the recent nutrient removal upgrades.

The WAS volumes have increased substantially since the nutrient removal process modification,which included wasting mixed liquor rather than settled sludge. The WAS volumes and loads arecurrently exceeding the recent biological nutrient removal (BNR) upgrade expected values. Thepractice of wasting mixed liquor is expected to continue for the foreseeable future. As such, Table1-2 contains the WAS and primary sludge volumes and quantities that will be utilized in theremainder of the Biosolids Facilities Improvement Plan.

Table 1-2. Sludge Design Criteria

Average,Current1

Projected DesignValues2

InfluentFlow

19.5 MGD 37.7 MGD

PrimarySludge

25,600 lbs/day @5,800 mg/L

0.44 MGD

27,750 lbs/day @5,800 mg/L

0.60 MGD

WAS16,600 lbs/day @

2,700 mg/L

0.72 MGD

25,000 lbs/day3 @2,500 mg/L4

1.2 MGD

1 Data from May 2016 to June 2017 (after BNR upgrade online)2 AWTF BNR Upgrade Design Maximum Month3 Calculated using a peaking factor of 1.3 times the current annual average WAS mass rates4 Based on continued wasting from mixed liquor channel, concentrations may range from 2,000 to 3,000 mg-

TSS/L

Thickened Solids

With the separate thickening of WAS, the existing gravity thickeners are expected to thicken theprimary sludge to 4-6% solids. The gravity belt thickeners for the WAS thickening would have thepreliminary design criteria shown in Table 1-3.




Units 3, in parallel

Type Horizontal Gravity Belt

LoadingRate,Volumetric

300 gpm per meter of belt width

LoadingRate, Solids

500 lbs TSS per hourper meter of belt width

FeedPercentSolids

0.2 % TSS

The thickened WAS would flow by gravity to a blending tank to provide flow equalization priorto being pumped into the primary anaerobic digesters. The flow equalization tank will be sized tohold 24 hours of thickened WAS. The tank would be aerated with coarse bubble diffuser to alsoprovide agitation.

Hauled Waste

A hauled waste receiving station would include the major components in Table 1-4.

Table 1-4. Hauled Waste Receiving System

Capacity 700 gpm max flowrate

Screening 10 mm openings perforated platewith Washer/Compactor

Grit andGreaseRemoval

Inclined grit removal screw withintegrated grease skimmer

HoldingTank

Square Concrete with capacity of 1 dayat max day receiving rate



Table 1-4. Hauled Waste Receiving System

Accessories

Rock TrapFlow MeterScreenings and grit dumpsterHauler Access Station - Scan CardReader and Billing System

Anaerobic Digesters

The primary and secondary digesters would operate as they are currently configured, with thesecondary digesters mainly performing as holding tanks. Design criteria for the primary digestersare shown in Table 1-5.

Table 1-5. Primary Digesters


WorkingCapacity

1,833,000 gallons, each3,667,000 gallons, total

Design FeedRate

2.2 kg-VSS/m3/d0.14 lbs-VSS/ft3/d

DesignSolidsRetentionTime

15 days, minimum20 days, design with both on line

VolatileSolidsDestruction

50%, design

Currently the AWTF encounters mineral buildup in the digester heat exchangers and piping. Froma laboratory test of the mineral, along with circumstantial evidence, the mineral appears to behydrated iron phosphate, or as the mineral is known, vivianite. There is the potential to address themineral build up in the heat exchanger with alternate heat exchanger technologies such as the spiralheat exchanger, and the scraped surface heat exchanger. The capital costs of this equipmentcompared to the cost of replacing piping and valves, and heat exchanger tubes, is not likely to bea cost effective strategy. The existing concentric tube sludge heat exchangers would remain inservice.

Alternatively, the AWTF could evaluate the use of aluminum salts rather than ferric chloride, butthe aluminum salts tend to be more expensive. Regardless, the increased chemical costs may be



offset by increased operational and maintenance efficiencies.

The recommendation for addressing vivianite build up is with direct steam injection. In Phase 1 –Primary Digester Improvements, steam lances will be built into the primary digesters. Steam lanceswill eliminate vivianite build up in the heating loop along with eliminate the use of external heatexchangers.

Acid Phase Digestion

The stabilization (digestion) of biosolids occurs in three steps, hydrolysis, acidogenesis (acidformation), and methanogenesis (methane generation). Acid formation and methane generationare performed by different bacteria, which prefer different conditions. Currently all three stepsoccur in the primary digesters, and therefore there is a compromise of environmental conditions.

To provide conditions that favor the acid forming bacteria, a digester can be installed upstreamand in series with the primary digesters. The acid phase digester is designed with a short solidsretention time (SRT) compared to the primary digester. Acid phase digestion has the followingreported benefits:

· Greater consistency in feed rate and temperature to the primary digesters· Increased biogas generation in the primary digesters· Reduced digester upsets (fewer occurrences of foaming)

A cost effective way to incorporate acid phase digestion at the AWTF would be through theaddition of a single digester tank. The feeds from the gravity thickener underflow, thickened WASholding tank, and hauled waste equalization tank would be blended and pumped into the acid phasedigester. The key design parameters of the acid phase digester are in Table 1-6.

Table 1-6. Acid Phase Digester

Units 1

WorkingCapacity 300,000 gallons

Design FeedRate 0.15 MGD

Design SolidsRetention Time 2 days, minimum

OperatingTemperature Mesophilic, 96-99º F



The potential in increased biogas production through the addition of an acid phase digester willnot economically justify the digester. As the AWTF receives more hauled waste, especially hauledwaste from a variety of sources, the operational benefits of an acid phase digester will becomemore important. Therefore provisions for acid phase digester, including maintaining open space,should be incorporated into currently planned projects. The value of the acid phase digester wouldbe re-evaluated periodically to determine when it should be constructed.

Dewatering Facility

Considering that the existing belt filter presses are in good working condition, and generallyproduce cake solids with sufficiently high solids, they would continue to be utilized. A separatestudy on improving the dewatered cake solids is anticipated to supplement this report.

Table 1-7 provides some of the key design parameters of the existing belt filter presses.

Table 1-7. Belt Filter Press, Existing

Units 2

Type Dual belt with separate gravity andcompression sections

Belt Width 2.5 meters

Design FeedRate 2,000 lbs dry solids/hour

TypicalDewateredCake Solids

19 - 21 % solids

The belt filter presses would need to operate more hours a day to accommodate increased solidsproduction that would result from hauled waste. The existing belt filter presses are insufficient todewater the solids when the digesters are operating at design conditions. Prior to reaching theircapacity, a third belt filter press would need to be installed.

Biogas Utilization

The ongoing upgrades to the primary digesters, along with the increased solids retention time, andincreased acceptance of hauled waste, the volume of biogas generated is expected to increase,potentially by more than 250% over current average volumes. To make the most use of this asset,a combined heat and power plant is proposed.



The AWTF currently separately generates heat in two (2) boilers and electricity in two (2)reciprocating engine driven generators. They also recover some of the waste heat from thereciprocating engine. Combining heat recovery and electricity generation in one package unitincreases the total energy recovered from the biogas. The United States Department of Energyreports a nationwide average energy recovery from separate heat and power of 50%. For combinedheat and power (CHP) systems, the overall energy efficiency is typically around 75%1.

More than 50% of CHP installations are reciprocating engine driven. Reciprocating engines are amature technology with well-established and wide spread parts availability and servicerepresentatives. AWTF personnel are also familiar with operating and maintaining thereciprocating engine driven system.

The fuel cell CHP system is another technology which is being reviewed. Fuel cells produceelectricity by separating the hydrogen from the methane, and then combining it with oxygen fromthe atmosphere to produce electricity. The process produces waste heat which is recovered. Thefuel cells have no emissions, high overall energy efficiency, and good performance at partialloadings. Fuel cells have a higher capital cost than reciprocating engines, and do wear out overtime and need replacement. In addition, the biogas requires additional pre-treatment to provide thehigh quality fuel required. For either the reciprocating engine or the fuel cell, biogas pre-treatmentwould be installed.

1 https://energy.gov/eere/amo/combined-heat-and-power-basics



Appendices | 73


TM-2 Sludge Thickening


August 2017 1 Whitman, Requardt & Associates, LLPN:\14342-001\Engineering\Design\Biosolids Facilities Imp Plan Tech Memos\Final\TM02 - Sludge Thickening.docx




SUBJECT: Sludge Thickening

Prepared by: D. Nixson


Distribution:

Date: June 9, 2017


CONTENTS

I. INTRODUCTION

II. DESIGN CRITERIA

ATTACHMENTS:

1.) Alfa Laval Ashbrook Budgetary Proposal Dated May 18, 20172.) General Arrangement Drawing of Ashbrook Simon-Hartley 2.0 Meter Aquabelt

Enclosed

REFERENCE DRAWINGS:

1.) Not applicable.



I. INTRODUCTION

See Technical Memorandum No. 1 for a description of the Harrisburg AWTF and the overallbiosolids process. Technical Memorandum No. 2 provides summary design information regardingthe thickening of sludge at the AWTF.

The AWTF currently combines primary sludge collected from the primary clarifiers, wasteactivated sludge (WAS) from the mixed liquor channel, and diluting water and co-thickens theblended sludge in two (2) gravity thickeners. The thickener underflow averages 3% suspendedsolids, which is pumped to the primary digesters. At current flows and loads, the primary digesterhas a solids retention time (SRT) of 14.4 days in the one primary digester. This calculation assumesthe digester is free of debris and the full volume of the tank is usable.

By increasing the solids content of the sludge to a minimum of 5% solids, the volume of sludgewould be reduced from 159,500 gallons per day to 95,700 gallons per day. This would increasethe SRT to 19 days, potentially increasing volatile solids reduction and biogas production.Alternatively, and to greater benefit to CRW, more hauled waste can be loaded into the digestersresulting in additional gas production.

Although there are several proven technologies for thickening WAS, the gravity belt thickener(GBT) and the centrifuge are best suited to thickening the low solids content (0.2 % solids) of theAWTF WAS to reliably above 5% solids.

Another technology that should be considered is the volute thickener, a relatively new technology.The volute thickener would have several advantages over the gravity belt thickener and centrifugeincluding:

· Small footprint (comparable to centrifuge)· Low energy demand· Simple maintenance requirements· Low capital costs

There are relatively few installations of volute thickeners in the United States, and it is unknownif any of these installations are thickening WAS as low in solids (0.2% TSS) as the AWTF.Therefore a pilot test would be recommended prior to proceeding with this option.

The GBT has several advantages over the centrifuge including:

· Low capital cost· Low energy consumption· Simple operation and maintenance· Ability to handle stringy solids (i.e. rags) and plastics

In addition, the AWTF operations is familiar with the operation of a GBT, as the equipment is verysimilar to a belt filter press. One of the disadvantages of the GBT is the physical size is larger than



a similar capacity centrifuge. The use of a centrifuge will reduce the overall size of the thickeningbuilding, which would offset some of the higher capital costs of the centrifuge.

A proposed thickening building would house the GBT facilities including the wash water boosterpumps, the polymer handling system, and thickened WAS (TWAS) transfer pumps. The TWASwould be stored in a holding tank to allow consistent flow to the digesters when blended with thegravity thickened primary sludge.

The existing gravity thickeners would continue to thicken primary sludge, but only one thickenerwould need to be online at a time.

II. DESIGN CRITERIA

The design quantities and solids content for primary and waste activated sludge are in Table 2-1.

Table 2-1. Sludge Design Criteria

Average,Current1

Projected DesignValues2

InfluentFlow

19.5 MGD 37.7 MGD

PrimarySludge

25,600 lbs/day @5,800 mg/L

0.44 MGD

27,750 lbs/day @5,800 mg/L

0.60 MGD

WAS16,600 lbs/day @

2,700 mg/L

0.72 MGD

25,000 lbs/day3 @2,500 mg/L4

1.2 MGD1 Data from May 2016 to June 2017 (after BNR upgrade online)2 AWTF BNR Upgrade Design Maximum Month3 Calculated using a peaking factor of 1.3 times the current annual average WAS mass rates4 Based on continued wasting from mixed liquor channel, concentrations may range from 2,000 to 3,000 mg-TSS/L



Key design information for the existing gravity thickeners are in Table 2-2.

Table 2-2. Thickening Tanks

TanksNo. of UnitsDimensions, eachDiameterSide Water DepthFreeboard

Total VolumeTotal Surface AreaTotal Weir Length

2, in parallel

80 feet10 feet1.5 feet

968,775 gallons10,053 sq ft503 feet

Table 2-3 provides typical design criteria for gravity thickeners.

Table 2-3. Typical Design Criteria for Gravity Thickeners1

Type ofSolids

Primary

Primary andWAS andIron

InfluentSolids Conc.

% solids

2-7

1.5

ExpectedUnderflow

Concentration% solids

5-10

3

Mass LoadingRate

lb/sq ft/hr(kg/m2/hr)

0.82 – 1.23(4 - 6)

0.31(1.5)

Max. OverflowRate

gal/sq ft/d(m3/m2/d)

380 – 760(15.5 – 31)

N/A

1 WEF Manual of Practice No. 8

As can be seen in Table 2-3, gravity thickeners thickening only primary sludge can be loaded athigher mass rates than with combined primary and waste activated sludge. In addition, the primarysludge, and the thickened primary sludge is expected to be at a higher percent solids. Thereforeseparating the primary sludge and waste activated sludge would allow for a higher percent solidsbeing fed into the digesters.

The overflow rate of the thickener was evaluated to determine if the rate when thickening onlyprimary sludge is too low. The primary sludge flowrate has averaged 0.44 MGD over the periodstudied. Thickening this stream separately with a 4:1 dilution water to sludge ratio would result inan overflow rate of 220 gal/sq ft/d, which is low and subject to floating sludge, odors and septicity.Operating one thickener would be recommended to keep the dilution water quantity reasonable,and result in an overflow rate of 440 gal/sq ft/d. Also, chlorine can be added to reduce odors andmaintain fresher sludge with less septicity and reduce potential for gasification.



With the separate thickening of WAS, the existing gravity thickeners are expected to thicken theprimary sludge to 4-6% solids.

Gravity Belt Thickening

The gravity belt thickeners for the WAS thickening would have the preliminary design criteria inTable 2-4.


Quantity 3, in parallel, 2 duty, 1 standby

Size 2 meter belt

Type Horizontal Gravity Belt

LoadingRate,volumetric

300 gpm per meter of belt width

LoadingRate, Solids

500 lbs TSS per hourper meter of belt width

FeedPercentSolids

0.2 % TSS

Number ofOperatingHours a Day

33 hrs per day -16.5 hrs/day with two GBT units inoperation

Blending a portion of the thickened primary sludge with the WAS would improve the solidscapture of the gravity belt thickener. Provisions in the piping should be considered to allow forthis flexibility.

The thickened WAS would flow by gravity to a blending tank to provide flow equalization priorto being pumped into the primary anaerobic digesters. The flow blending tank will have a workingvolume equal to 48 hours of thickened WAS, or 100,000 gallons. The tank would be agitated withcoarse bubble diffusers.



TWAS pumps will pump from the TWAS holding tank to either of the primary anaerobic digesters,normally through the heat exchanger recirculation loop, so the TWAS could be heated prior toentering the digester. The TWAS pumps will have the design criteria in Table 2-5.

Table 2-5. TWAS Transfer Pumps

Quantity 2, in parallel, 1 duty 1 standby

Capacity 30 – 60 gpm @ 50 ft Head

Type Hose Pump with VFD Driven Motor



Appendices | 74


TM-3 Hauled Waste Receiving


August 2017 1 Whitman, Requardt & Associates, LLPN:\14342-001\Engineering\Design\Biosolids Facilities Imp Plan Tech Memos\Final\TM03 - Hauled Waste Receiving.docx




SUBJECT: Hauled Waste Receiving and Holding Tank



Distribution:

Date: June 9, 2017


CONTENTS

I. INTRODUCTION

II. DESIGN CRITERIA

ATTACHMENTS:

1.) PortALogic DS-200 Waste Dump Station

REFERENCE DRAWINGS:

1.) Huber Technology Rotamat Wash Drum RoFAS Conceptual Layout Drawing



I. INTRODUCTION

See Technical Memorandum No. 1 for a description of the Harrisburg AWTF and the overallbiosolids process. Technical Memorandum No. 3 provides summary design information regardingthe proposed hauled waste receiving system at the AWTF.

Hauled waste will be delivered in tanker trucks varying in size. Handling the waste will requireunloading, pretreatment, flow equalization, blending with thickened primary and waste activatedsludges, and pumping to the digesters. Equalization of these wastes reduces the potential forfoaming and upset conditions as there may be considerable variability in waste volumes andcharacteristics. The hauled waste system would include the following components, at a minimum.

· Truck unloading station with containment· Automated billing ticket generation· Rock trap· One (1) screening washing unit with bypass for grease· One (1) grit trap with grease removal system· Automatic sampler· One (1) transfer pump· One (1) equalization tank, totaling a working volume of one (1) times the daily

expected volume· Tank aeration/mixing system with odor control· Two (2) transfer pumps to convey pretreated waste to the primary digesters

The mechanical equipment for handling hauled waste would be housed in the same building as theproposed WAS thickening process. Additional pretreatment equipment may be necessarydepending on the characteristics of the potential hauled waste.

II. DESIGN CRITERIA

The daily design quantities and characteristics of the hauled waste are being concurrentlydeveloped. The daily quantities do not affect the size of the receiving station as it is sized for theunloading rate of a single truck. The hauled waste truck would park so the outlet of the truck iswithin a concrete containment area which would be sloped to a plant drain.

The hauled waste truck unloading station would be equipped with an automated dump stationcontrol panel. The panel would read the driver’s access card, then open an automated valve, andrecord the totalized flow from a flow meter. This information would be stored in the panel and canbe communicated across a network or downloaded for billing purposes.



The truck would connect to an unloading station with a hose. The hauled waste will be pretreatedduring the truck unloading operation for the removal of inorganics (grit and screenings). Hauledwaste may also include fats, oils and grease (referred to as FOG) which would bypass the screeningoperation. Screenings will be washed, compacted and conveyed into a dumpster. The grit that isremoved will also be conveyed into the same dumpster. Table 3-1 shows key design criteria forthe hauled waste receiving station.

Table 3-1. Hauled Waste Receiving Station

Quantity 1

HydraulicCapacity 1.37 MGD

DrumScreenDiameter

47 inches

ScreenOpenings 1/4 to 3/8 inch

ScreeningsCapacity 53 cubic feet per hour

ScreeningsCompactedWaterContent

65%, maximum

LocationRating Class 1 Div 2

Hauled waste would be pumped into to a holding tank to provide flow equalization prior to beingblended with primary sludge and WAS and pumped into the primary anaerobic digesters. The flowequalization tank will have a working volume equal to one day of expected hauled waste volume.The expected daily hauled waste volume is concurrently being developed. The tank would beagitated with coarse bubble diffusers and equipped with an odor control system.



Hauled waste transfer pumps will pump from the hauled waste holding tank to either of the primaryanaerobic digesters, normally through the heat exchanger recirculation loop, so the hauled wastecould be heated prior to entering the digester. The Hauled Waste Transfer pumps will have thedesign criteria shown in Table 3-2.

Table 3-2. Hauled Waste Transfer Pumps

Quantity 2, in parallel, 1 duty 1 standby

Capacity 40 – 100 gpm @ 50 ft Head

Type Hose Pump with VFD Driven Motor



Appendices | 75


TM-4 Anaerobic Digestion


August 2017 1 Whitman, Requardt & Associates, LLPN:\14342-001\Engineering\Design\Biosolids Facilities Imp Plan Tech Memos\Final\TM04 - Anaerobic Digestion.docx




SUBJECT: Anaerobic Digesters, Primary and Secondary



Distribution:

Date: June 13, 2017


CONTENTS

I. INTRODUCTION

II. DESIGN CRITERIA

ATTACHMENTS:

1.) Alfa Laval Spiral Heat Exchanger Quote dated May 25, 20172.) Alfa Laval Spiral Heat Exchanger Brochure3.) HRS Scraping Heat Exchanger Quote dated May 25, 20174.) HRS Unicus Series Brochure

REFERENCE DRAWINGS:

1.) Alfa Laval Spiral Heat Exchanger Model 2500K General Drawing



I. INTRODUCTION

See Technical Memorandum No. 1 for a description of the Harrisburg AWTF and the overallbiosolids process. Technical Memorandum No. 4 provides summary design information regardingthe primary and secondary digesters at the AWTF.

The thickened sludge is transferred to the two (2) primary digesters for anaerobic digestion. Theprimary digesters are circular reinforced concrete tanks with sloped bottoms. The tanks are coveredby fixed roofs. Anaerobic bacteria convert the volatile solids in the sludge to volatile acids, andthen to carbon dioxide and methane. The gas mixture (known as digester gas or biogas) iscombustible and is used to generate heat and electricity for use at the plant. Table 4-1 summarizesthe existing primary digesters.

Table 4-1. Existing Primary Digesters


Clean TankVolume

1,833,000 gallons, each3,667,000 gallons, total

Diameter 90 Feet

Side WaterDepth 35 Feet

Roof Type Fixed

Mixing,Type Gas bubble eductor

The contents of each digester are mixed by drawing off digester gas from the top of the digesterroof, compressing the gas with a rotary lobe compressor, and then discharging it through eight (8)nozzles located approximately 1/3 below the liquid level in each of three (3) 5-foot diametereductor tubes. The rising gas bubbles pull sludge up with them through each eductor tube and mixthe tank contents.

To keep the digestion process at an optimal level, the temperature in the digester should bemaintained at approximately 98° F. To accomplish this, sludge is continually recirculated throughheat exchangers, which are provided with hot water from the boiler house. Three (3) recessedimpeller pumps pull sludge from the bottom of the digesters, circulate it through three (3)concentric tube heat exchangers and back into the top of the digesters.



Both digesters and the associated piping and equipment have experienced vivianite (a hydratediron phosphate mineral) precipitation and buildup. Digester No. 2 has valves which are no longeroperational from vivianite accumulation, which has resulted in this digester being out of serviceindefinitely.

Sludge from the primary digesters can be transferred by gravity to the secondary digesters. Thereare also two (2) progressing cavity pumps that can be used when necessary to overcome the headin the secondary digester, e.g. when lowering the level in the primary digester for maintenance orinspection.

The secondary digesters are currently being used as holding tanks with no mixing or heating.Table 4-2 summarizes the existing secondary digesters.

Table 4-2. Existing Secondary Digesters


Clean TankVolume

924,000 gallons and839,000 gallons

Diameter 85 Feet

Side WaterDepth 28 Feet

Roof Type 1 with Fixed, 1 with Floating

The refurbishment of the primary digesters is currently being designed. Improvements willinclude:

· Gas mixing system replaced with mechanical mixing system· Replacement of the primary digester fixed covers· Replacement of the gas and sludge piping internal to the digesters· Replacement of sludge piping and valves within the digester control house gallery· Replacement of the waste gas flare· Replacement of the primary digester recirculation pumps· Replacement of primary digester transfer pumps· New electrical and controls building



The primary digester concentric tube heat exchangers are not being modified with the currentplans. The heat exchangers are sufficiently sized for the digester operation when not fouled withmineral buildup. Currently, the heat exchangers get too fouled to maintain digester temperaturewithin 18-24 months of operation. When fouled, the affected piping and heat exchanger tubes arereplaced at a cost of approximately $10,000-20,000.

Once the primary digesters refurbishment is completed, both digesters will be put in operation toprovide additional gas production capacity. The secondary digesters will remain as holding tanks.

Converting the digestion process to two-phase digestion through the addition of a single acid phasedigester, should be considered, especially to provide more consistent operations when receivingthe larger volumes of hauled waste in the future. This modified process, two-phase digestion, isdiscussed in more detail in Section II.

II. DESIGN CRITERIA

Digester Capacity

The average operating conditions for a clean digester (i.e. no debris build up in the digester) forthe primary anaerobic digesters as they are being currently operated with only one digester on lineare shown in Table 4-3.

Table 4-3. Current Operating Criteriafor Primary Digesters, Average Flow of 19.5 MGD

Primary Digesters On Line 1

Solids Loading Rate toDigester

38,100 lbs TSS/day23,700 lbs VS/day0.13 MGD3.0% Solids

Solids Retention Time(SRT) 14.4 days

Loading Rate 0.10 lbs VS/cu ft/day

1 Average values for May 2016 to June 2017, i.e., after BNR Upgrade Start Up



The maximum month design criteria for the primary anaerobic digesters based on the BiosolidsFacilities Improvement Plan volumes and quantities of thickened sludge are in Table 4-4.

Table 4-4. Facility Planning Max Month Design Criteriafor Primary Digesters (Plant Flows at 37.7 MGD)



47,750 lbs TSS/day36,560 lbs VS/day0.11 MGD5% Solids

SRT 16.7 days

Loading Rate 0.15 lbs VS/cu ft/day

Although the existing digester tanks are more than forty years old, after the planned refurbishment,they will be capable of operating as originally intended. With both digesters on line the digestershave the capacity to be loaded with additional solids above that expected from the primary andwaste activated sludge generated by the AWTF as presented above in Table 4-4. Table 4-5 providesthe full capacity of the primary digesters (assuming clean tanks).

Table 4-5. Primary Digesters Design Criteria,at Full Digester Capacity



76,900 lbs TSS/day61,000 lbs VS/day0.18 MGD5% Solids

SRT 20.4 days

Solids Loading Rate 0.12 lbs VS/cu ft/d

Estimated Digester Capacity Available for Hauled Waste

Comparing Tables 4-4 and 4-5 provides an estimate of the available capacity for hauled waste. Aconservative estimate is a TS loading of 25,000 lbs/day at 80% VS, or VS loading of 20,000



lbs/day. This estimated capacity assumes that there are no waste characteristics that would interferewith the digestion process, and the waste is readily degradable. The primary digester rehabilitationand improvements to WAS thickening, coupled with sludge blending and possibly two-phasedigestion, would offer a conservative approach to handling the additional loading of hauled waste.With VS of 20,000 lbs/day, the hauled waste would represent about one third of the digestionloading, which is very significant. As with any biological process, a gradual increase in loadingwould reduce the chances of upset, until the digestion process becomes acclimated to the additionalloads.

It is noted that the 20,000 lbs VS/day hauled waste is based on a maximum month flow at theAWTF of 37.7 MGD, and the AWTF solids generated at this flow. If the plant flows onlynominally increase over the past-three-year average flow of 21.7 MGD, to an annual average flowof 25 MGD, there would be additional capacity in the digesters for hauled waste, possibly up to30,000 lbs VS/day.


In order to improve digestion stability, especially with the expectation of future significantquantities of hauled wastes with variable volumes and characteristics, a sludge blending tanklocated ahead of digestion should be considered. The blending tank would provide mixing ofthickened primary and waste activated sludges and hauled wastes to achieve a more consistentdigester feed with respect to rate of feed and characteristics. This will reduce the impacts of diurnalloading variability and associated wide fluctuation in volatile solids in the feed from variablehauled waste sources. If a sludge blending tank is not included in the near term improvements,space for the tank and connections to the digestion process piping should be provided.

The Improvement Plan is providing a hauled waste pretreatment facility and holding/equalizationtank (TM 3). As an alternative to a separate sludge blending tank the hauled waste tank could besized and equipped with mixing to achieve blending of the thickened plant sludges and the hauledwaste. This alternative should be evaluated further.

Regardless of how blending is to be achieved, it should be evaluated in conjunction with the designof the primary digester rehabilitation and evaluation of two-stage digestion and associated additionof an acid phase digester. If two-phase digestion is not implemented, or if it is planned in the future,provisions to connect the blended sludge to the primary digester feed should be included in therehabilitation design.

Two-phase Digestion (Referred to as Acid Phase Digestion in Technical Memorandum No. 1)

Two-phase digestion separates the two major types of reactions that take place during anaerobicdigestion, acid formation, and methane generation. Two-phase digestion would take advantage ofthe AWTF existing infrastructure and would allow for more effective use of the anticipatedbiosolids and hauled waste. Minimizing foaming in the main digesters is another of the advantages



of the two-phase digester.

A new separate acid phase digester would be constructed sized for a solids retention time of 1-2days where the acid formation phase of digestion would primarily take place. The feed biosolidswould be pumped through a heat exchanger to increase temperature to the mesophilic range, andinto the two-phase tank. The low-pH environment would be established in this digester, suspendedsolids would by hydrolyzed, and fatty acids would be formed. Minimal methane is generated inthe acid phase digester, but any gas generated would be piped to the primary (methane phase)digester biogas system. The sludge from the acid phase digester would be pumped into the methanephase digesters which can be operated to maintain the optimum environment for methanogenicbacteria. Figure 1 illustrates a schematic incorporating two-phase digestion.

Figure 1. Schematic of Two-phase Anaerobic Digestion

HeatExchanger To

SecondaryDigesters(HoldingTanks)

AcidPhase

Digester

FeedSludge

Biogas

Hot Water

Methane PhaseDigesters (ExistingPrimary Digesters)



The acid phase digester for two-phase digestion would be designed using the criteria in Table 4-6.

Table 4-6. Acid Phase Digester Design Criteria

Units 1

Solids Loading Rate 1.5 lbs VS/cu ft/d

SRT 1.5 days

Clean Tank Volume 300,000 gallons

DimensionsDiameterSide Water Height

35 ft45 ft

Vivianite/Heat Exchangers

The AWTF encounters significant mineral deposit buildup in the anaerobic digesterrecirculation/heating piping and heat exchangers. Every 18-24 months the buildup becomessignificant enough to cause the degradation of heat exchanger, pump and valve performance. TheAWTF currently replaces the piping and heat exchanger tubes each time and, whenever this occurs,the ability to maintain the digester temperature degrades.

Considering the AWTF utilizes ferric chloride for phosphorus precipitation and removal, and thatthe worst buildup is in the heat exchangers and the downstream piping (i.e. the hottest sludgetemperatures in the system), the mineral is suspected to be vivianite, or iron phosphate. Vivianitecan be identified by its characteristic blue-green color, is soluble in hydrochloric and nitric acids,and it loses solubility at higher temperatures. A single sample taken from the built up material wastested and confirmed to be characteristic of vivianite.

There is currently no economical method from recovering the phosphorus from the iron phosphate.There are two primary methods to control vivianite deposits; reduce the temperature of the sludgecoming out of the heat exchanger, and to reduce areas of high turbulence.

Given the physical size of the primary digester pumping station there are few opportunities toaddress areas of high turbulence in the piping. Reducing the temperature rise of the sludge in theheat exchanger was investigated. Even when reducing the hot water temperature from 180ºF downto 140ºF, the solubility of vivianite would not be significantly improved.

The base components of the existing heat exchangers (e.g. frame, shell, etc) are in good physicalcondition and the replacement of the heat exchangers is not currently warranted. In an effort to



reduce the impacts of vivianite deposits on the operations of the digesters, two alternative heatexchangers were investigated, the scraped surface heat exchanger and the spiral heat exchanger.The scraped surface heat exchanger is also a concentric tube heat exchanger similar to the existing.In addition, it has a hydraulically driven rod within the heat exchanger tubes, with scraper bladesmounted along its length that extend out to the tube surface. Any buildup of material ismechanically scraped off by the reciprocating movement of the rod, and is carried away in thesludge flow. Figure 2 shows scraped surface heat exchanger mechanism.

Figure 2. Unicus Series Reciprocating Scraped Surface Heat Exchanger Exploded ViewCredit - HRS Heat Exchangers Ltd

The scraped surface heat exchanger has installations in many industries including wastewater.Design criteria for scraped surface heat exchangers can be seen in Table 4-7.

Table 4-7. Scraped Surface Heat Exchanger DesignCriteria


HeatTransfered

733 kW2.5 MBTU/hr

Sludge FlowRate 700 gpm

SludgeTemperatureRise

29 C inlet38 C outlet



Table 4-7. Scraped Surface Heat Exchanger DesignCriteriaWater FlowRate 400 gpm

WaterTemperatureRise

82 C inlet71 C outlet

OverallLength 21 feet

OverallHeight 5 feet

OverallWidth 2 feet

A single budgetary quote was received for three (3) scraped surface heat exchangers from HRSHeat Exchangers Ltd, in May 2017. The bare cost of the units totaled $683,600. Withoutconsidering the cost of purchasing and installing the units, the payback when compared to the$50,000 of pipe replacement cost every 18 to 24 months, is more than 20 years. Other driverswould need to be identified to pursue the scraped surface heat exchanger.

The spiral heat exchanger was also investigated. The heat exchange surface area is arranged inconcentric circles, see Figure 3. Utilizing this configuration the sludge flows through a narrowpassages resulting in higher velocity than in a straight tube. If buildup does occur, the velocity willincrease and will help erode the buildup. Spiral heat exchangers also have a more compact footprintthan concentric tube heat exchangers, and would easily fit in the existing space.

Figure 3. Spiral Heat Exchanger Flow DiagramsCredit – Alfa Laval

The spiral heat exchangers would be designed to the criteria shown in Table 4-8.



Table 4-8. Spiral Heat Exchanger Design Criteria


HeatTransfered

733 kW2.5 MBTU/hr

Sludge FlowRate 500 gpm

SludgeTemperatureRise

95 F inlet105 F outlet

Water FlowRate 400 gpm

WaterTemperatureRise

155 F inlet143 F outlet

Headloss 10 feet head, maximum

OverallLength 4 feet

OverallHeight 5 feet

OverallWidth 4 feet

A single budgetary quote was received for three (3) spiral heat exchangers from Alfa Laval, inMay 2017. The bare equipment cost of the three units totaled $125,000, compared to the $50,000of pipe replacement cost every 18 to 24 months. A rough order of magnitude installed capital costestimate is $400,000. The spiral heat exchanger simple payback would be approximately 12 years.

Vivianite deposits could still occur in the spiral heat exchanger, and it is not possible to predicthow long it would take before the deposits degrade performance. When the spiral heat exchangerdoes need to be cleaned, it is designed with a removable front plate for access to the heat exchangersurfaces, but the more narrow passages are more difficult to manually clean.



CRW could also consider doing routine chemical cleaning of the piping systems including the heatexchangers. There are many chemicals on the market that report excellent results when removingvivianite deposits with non-toxic cleaners. The piping could be modified to make cleaning morestraightforward. Steps in the cleaning cycle would include:

· Emptying the line of sludge,· Filling line with water and chemical cleaner,· Recirculate the cleaning solution,· Draining the cleaning solution.

Another consideration would be to change phosphorus precipitant to an aluminum salt, rather thanthe ferrous salt they are currently using. Aluminum salts tend to be more expensive than ferroussalts. The change to an aluminum salt would eliminate vivianite, but may have other unintendedmineral buildup consequences.

Modifying the liquid treatment process to utilize biological phosphorus (Bio-P) removal shouldalso be mentioned. If the AWTF were converted to Bio-P, the phosphorus could be removed fromthe waste activated sludge and recovered as a sellable product.

Converting the AWTF to Bio-P would require the installation of an anaerobic zone prior to thepure oxygen tanks. The anaerobic zone would be designed for a hydraulic retention time of 1 to1.5 hours, or 1.5 to 2.3 million gallons volume.

A final alternative considered is direct steam injection into the digesters. A steam generator wouldbe required, as would multiple steam injection lances mounted on the roof of each digester. Directsteam injection has been used successfully for many years at the City of Baltimore Back RiverWWTP. In Phase 1 – Primary Digester Improvements, steam lances will be constructed into theprimary digesters. This will eliminate the heat exchangers from the recirculation loop.

Further investigation and evaluation along with discussion with CRW is recommended todetermine the alternative that addresses their priorities most effectively.



Appendices | 76


TM-5 Hauled Waste


August 2017 1 Material Matters, Inc.TM05 - WRA_CRW_Co-digestion Market Assessment.docx


HARRISBURG, PA

TASK ORDER NO.: 2016-16-01

PROJECT NO.: 14342-001


SUBJECT: Co-Digestion Market Assessment for Capital Region Water

Prepared by: L. Boudeman, K. Turner

Reviewed by: T. Johnston

Distribution:

Date: June 15, 2017


TM05 - WRA_CRW_Co-digestion Market Assessment.docx

Table of Contents1.0 BACKGROUND....................................................................................................................................................5

1.1 INTRODUCTION ................................................................................................................................................5

1.2 GOALS AND OBJECTIVES..................................................................................................................................5

2.0 EXISTING CONDITIONS ...............................................................................................................................6

2.1 CURRENT HAULED WASTE PROGRAM .................................................................................................................6

2.2 BIOGAS PRODUCTION ..........................................................................................................................................8

2.3 HIGH STRENGTH WASTEWATER SURCHARGE FEE SCHEDULE .........................................................................8

3.0 MARKET ASSESSMENT APPROACH ............................................................................................................9

3.1 CONSIDERATIONS FOR PARTICIPATION IN HAULED WASTE PROGRAMS ..............................................................9

3.1.1 Transportation/Hauling Costs .....................................................................................................................9

3.1.2 Competition from Other Municipal WWTPs..............................................................................................10

3.1.3 High Strength Wastewater Surcharge Fees .........................................................................................12

3.1.4 Non-municipal Anaerobic Digesters.....................................................................................................13

On-Farm Digesters.......................................................................................................................................................... 13

Kline’s Septic Services ................................................................................................................................................... 13

3.1.5 Direct Land Application Programs .......................................................................................................14

3.2 IDENTIFYING HIGH STRENGTH WASTE GENERATORS ....................................................................................14

3.3 MARKET ASSESSMENT...................................................................................................................................16

4.0 MARKET ASSESSMENT FINDINGS..........................................................................................................16

4.1 HIGH STRENGTH WASTE GENERATORS .............................................................................................................16

4.1.1 Airport..................................................................................................................................................17

4.1.3 Breweries/Distilleries ...........................................................................................................................18

4.1.4 Candy ...................................................................................................................................................18

4.1.5 Dairy.....................................................................................................................................................19

4.1.6 Fats, Oils, and Grease ..........................................................................................................................21

4.1.8 Slaughterhouse/Meatpacking .............................................................................................................23

4.1.9 Snack Foods .........................................................................................................................................24

5.0 FINDINGS AND RECOMMENDATIONS ......................................................................................................26

5.1 FINDINGS .......................................................................................................................................................26

5.1.1 DIGESTER CAPACITY......................................................................................................................................26

5.1.2 PROMISING FEEDSTOCKS ...............................................................................................................................26

5.1.2.1 Grease Trap Waste from Area Restaurants ...........................................................................................26


5.1.2.2 DAF Solids / FOG from dairies, snack food processors / candy processors ............................................26

5.1.2.3 Potential volumes and biogas production..............................................................................................27

5.1.2.4 Operational limitations ..........................................................................................................................28

5.2 RECOMMENDATIONS..........................................................................................................................................29

5.2.1 Establish infrastructure for receiving hauled waste.............................................................................29

5.2.2 Utilize grease trap waste ordinance ....................................................................................................29

5.2.3 Follow up with identified facilities and haulers....................................................................................29

5.2.4 Develop experimental introduction plan..............................................................................................30

5.2.5 Pricing Strategies .................................................................................................................................30

5.2.6 Revisions needed to update the hauled waste program.....................................................................31

REFERENCES ..........................................................................................................................................................32

APPENDIX 1. IDENTIFIED HSW DISCHARGERS............................................................................................33

APPENDIX 2. SURVEY APPROACH....................................................................................................................36

FiguresFigure 1. Process hauled waste vs. digester gas production January 1, 2016 to April 1, 2017. ..... 8

Figure 2. Hauled waste categories accepted at utilities in southcentral Pennsylvania ................. 11

Figure 3. Hauled waste tipping fees for utilities in Southcentral Pennsylvania ........................... 12

Figure 4. Potential HSW feedstocks were identified within a 50-mile radius of CRW AWTF... 15

Figure 5. Food Processing and Industrial Facility Wastewater Handling and Management Practices........................................................................................................................................... 16

TablesTable 1. Hauled waste accepted at the CRW AWTF in 2016 and corresponding revenue ............ 6

Table 2. Hauled waste accepted at the CRW AWTF in 2017 and corresponding revenue ............ 7

Table 3. Maximum concentration of hauled waste constituents allowable .................................... 7

Table 4. Hauled waste general limitations...................................................................................... 8

Table 5. CRW High Strength Waste Fee Surcharge Concentration Limits.................................... 9

Table 6. Estimated Transportation Costs for Hauled Waste......................................................... 10

Table 7. Co-Digestion Feedstock Generator Categories............................................................... 15

Table 8. Typical ADF and AAF Runoff Characteristics .............................................................. 17

Table 9. Wastewater characteristics of a sweetener processing facility ....................................... 18


Table 10. Candy processing facilities within 50 miles of CRW AWTF ...................................... 19

Table 11. Waste characteristics of a dairy processing facility...................................................... 19

Table 12. Dairy processing facilities within 50 miles of CRW AWTF........................................ 20

Table 13. Hershey Creamery Waste Parameters........................................................................... 21

Table 14: Characteristics of Grease Trap Waste........................................................................... 22

Table 15. Estimated GTW generated in the City of Harrisburg ................................................... 22

Table 16. Major sources of slaughterhouse/meatpacking wastewater.......................................... 23

Table 17. Meat Processing Typical Wastewater Characteristics .................................................. 23

Table 18. Meatpacking facilities within 50 miles of CRW AWTF .............................................. 24

Table 19. Wastewater characteristics of UTZ DAF solids ........................................................... 25

Table 20. Snack-processing facilities within 50 miles of CRW AWTF....................................... 25

Table 21 Full Scale GTW Co-Digestion implementations (Long, 2012)Error! Bookmark notdefined.

Table 22. VSS Loadings from selected HSW generators ............................................................. 28

Table 23. Ratio of GSW to sludge at selected loadings................................................................ 28


1.0 Background

1.1 IntroductionThis Technical Memorandum is submitted in accordance with the scope of work outlined in TaskOrder 3, dated July 16, 2015, between Whitman, Requardt, and Associates (WRA) Inc. andMaterial Matters, Inc. (MM). This memorandum presents the findings of a Co-Digestion MarketAssessment conducted on behalf of Capital Region Water (CRW), which owns and operates theHarrisburg Advanced Wastewater Treatment Facility (AWTF). CRW initiated the marketassessment to identify regionally available high strength wastes (HSW) from industrial and non-residential dischargers suitable for co-digestion in the anaerobic digestion process at CRWAdvanced Wastewater Treatment Facility (AWTF), located in Harrisburg, PA.

The AWTF serves the city of Harrisburg and surrounding area, and operates with an average dailyflow of approximately 22 million gallons per day (mgd). The facility also accepted approximately4.6 million gallons of hauled-in waste in 2016. Under current operating conditions, solids from theprimary sedimentation tanks are blended with waste activated sludge (WAS), thickened in agravity thickener, digested in a primary anaerobic digester, stored in a secondary digester, anddewatered with a belt filter press (BFP). The anaerobic digestion process generates biogas, whichis stored and can be utilized to power two 400 kW turbine generators, three heat exchangers, andtwo boilers. CRW has operated engine generators since 1985. An agreement between the CRWand PPL Electric Utilities gives CRW the ability to export energy in excess of the plant’s needs tothe power company to generate revenue. However, as noted in the Existing Conditions report,aging and inoperable infrastructure has inhibited the AWTF from maximizing gas production andhas curtailed the conversion of biogas into energy.

1.2 Goals and ObjectivesCRW initiated an AWTF Biosolids Facilities Improvement Plan to assess the current condition ofthe solids handling equipment, and to identify and evaluate alternatives for improvements for eachmajor solids processing step. In the Existing Conditions report, MM noted a need to achievevolatile solids destruction to meet process Vector Attraction Reduction (VAR). An added benefitis that biogas production will be improved. Infrastructure upgrades will improve volatile solidsdestruction, increase biogas generated in the AD, and will allow the AWTF to expand its existinghauled waste program to include HSW.

This memorandum has been prepared to evaluate the potential to accept additional HSW streamsto better utilize available digestion process capacity, offset operating costs, and increase biogasproduction. HSW includes a number of materials sourced largely from food and beverageproduction and processing facilities, such as food processing wastes, off-spec beverage products,dairy wastes, brewery wastes, and fats, oils, and grease (FOG). Typically, these waste streams arehighly biodegradable, have higher volatile solids content than municipal wastewater solids, andcan increase biogas production if digested along with the solids produced or received at theWastewater Treatment Plant (WWTP) (USEPA, 2014).

Material Matters evaluated the regional availability of these HSW streams. To complete theassessment, it is important to understand CRW’s current hauled waste and industrial pretreatmentprogram, characterize current hauled waste management and beneficial use practices by the


industrial and non-residential dischargers in the region, and define the economic model foraccepting a particular waste stream.

2.0 Existing Conditions

2.1 Current Hauled Waste ProgramCRW maintains a moderately sized hauled waste program. Between January 2016 and April 2017,CRW accepted between 133,000 and 667,500 gallons of hauled waste per month (Tables 1 and 2).On average, CRW accepted ~384,150 gallons per month in 2016; in 2017, this average increasedto ~602,900 gallons per month. The increase is primarily due to initiating the acceptance ofdissolved air flotation (DAF) solids from UTZ Quality Foods (UTZ) in February 2017 throughMay of 2017.

CRW categorizes hauled waste into two categories: “Process” and “Septic.” Process includes highsolids material from municipal wastewater treatment plants, mobile home parks, food processingplants and landfill leachate, whereas “Septic” includes wastewater from septic and holding tanks.CRW does not accept grease trap waste (GTW), medical/infectious/or biohazard waste prioritypollutant waste, characteristic or listed hazardous waste, or digester, lagoon or tank cleaning wasteor grit.

Table 1. Hauled waste accepted at the CRW AWTF in 2016 and corresponding revenueProcess Septic Total

Month Gallons Revenue Gallons Revenue Gallons RevenueJanuary 479,600 $15,611.40 34,000 $1,224.00 513,600 $16,835.40February 439,700 $14,497.20 23,000 $828.00 462,700 $15,325.20March 451,660 $14,243.76 87,000 $3,132.00 538,660 $17,375.76April 261,760 $9,675.36 74,000 $2,664.00 335,760 $12,339.36May 245,380 $8,833.68 44,500 $1,602.00 289,880 $10,435.68June 133,580 $4,574.88 50,000 $1,800.00 183,580 $6,374.88July 202,839 $7,552.40 67,500 $2,430.00 270,339 $9,982.40August 160,800 $5,670.00 70,000 $2,520.00 230,800 $8,1 90.00September 397,500 $17,005.50 82,500 $2,970.00 480,000 $19,975.50October 341,500 $12,519.00 92,000 $3,312.00 433,500 $15,831.00November 240,980 $9,507.78 76,000 $2,736.00 316,980 $12,243.78December 504,020 $17,718.12 50,000 $1,800.00 554,020 $19,518.1 3Total 3,859,319 137,409.08 750,500 $27,018.00 4,609,819 $164,427.092016 Month Avg. 321,610 11,450.76 62,542 $2,251.50 384,152 $13,702.26


Table 2. Hauled waste accepted at the CRW AWTF in 2017 and corresponding revenueProcess Septic Total

Month Gallons Revenue Gallons Revenue Gallons RevenueJanuary 464,600 $16,107.30 30,000 $1,080.00 494,600 $17,187.30February 667,500 $23,733.00 10,000 $360.00 677,500 $24,093.00March 498,400 $19,790.10 30,000 $1,080.00 528,400 $20,870.10April 639,140 $26,306.04 72,000 $2,592.00 711,140 $28,898.04Total 2,269,640 $85,936.44 142,000.00 $5,112.00 2,411,640 91,048.442017 Month Avg. 567,410 $21,484.11 35,500 $1,278.00 602,910 $22,762.11

At present, CRW has a list of 36 registered hauled wastes to the AWTF; the majority (26 of 36)comes from municipal wastewater treatment plants (e.g. lower-strength waste streams). The otherwaste streams include wastewater from one compost facility, one mobile home park, two food-processing facilities, two landfills, two restaurants/service facilities, and two septic haulers. Mosthauled waste is accepted at the headworks; however, the UTZ DAF solids are accepted at thethickener just prior to the anaerobic digester. Discharging directly to the anaerobic digester or slowfeeding to the digester is the typical approach to process HSW. However, the infrastructure fordirect feed and equalized flow does not currently exist at the AWTF.

CRW has established hauled waste acceptance requirements. Prior to hauling the first load of wasteto CRW, the waste generator must complete the following requirements:

1. An application form from the hauled waste source;2. A $50 application fee;3. A waste sample for analysis in a CRW sample container ($299 fee), and4. Supplemental results of sampling and testing.

Once the wastewater is analyzed and approved (based on Table 3 and Table 4 limits/criteria), CRWissues a one-year contract. During the first month of hauling, wastewater generators are charged adischarge fee based on percent total solids (%TS) at $0.009/every 0.5% TS; the minimum fee is$0.027/gallon and 1,000 gallons. For months two through twelve of the contract, discharge feesare charged per truckload. In addition, a surveillance analysis is completed for every 200,000gallons, or once per year for those under 100,000 gal/year for a fee of $109.25.

Table 3. Maximum concentration of hauled waste constituents allowable

Parameter Concentration(dry wt. basis)

Cadmium, Total 39 mg/kgChromium, Total 1,200 mg/kgCopper, Total 1,500 mg/kgLead, Total 300 mg/kgMercury, Total 17 mg/kgNickel Total 420 mg/kgZinc, Total 2,500 mg/kg


Table 4. Hauled waste general limitations

Parameter LimitpH 5.0 – 10.0TVS 55% minimumOil/Grease 100 mg/LAmmonia Nitrogen 500 mg/L

2.2 Biogas ProductionIn general, co-digestion with HSW enhances biogas production relative to digestion of municipalwastewater solids alone. Digester gas production directly corresponds to the levels of “Process”hauled waste accepted at CRW (Figure 1). CRW experienced a decline in hauled waste in mid-2016 (equipment failures) that resulted in a decline in gas production. Data available through Aprilof 2017 shows that gas production is improving as more hauled waste is incorporated into theprogram. The addition of UTZ DAF solids in early 2017 led to some operational challenges withthe digester (foaming), and will need to be addressed as more hauled waste is accepted and addeddirectly to the digester. Section 5 includes discussion about challenges with HSW added directlyto the digesters. It is assumed that increasing the volume of HSW, in conjunction with solidshandling upgrades, will increase biogas production at the AWTF.

Figure 1. Process hauled waste vs. digester gas production January 1, 2016 to April 1, 2017.

2.3 High Strength Wastewater Surcharge Fee ScheduleCapital Region Water has an active high-strength wastewater surcharge program, which is a feecharged to dischargers of higher-than-domestic strength wastewater to recover the higher costassociated with treating these wastes. CRW’s high-strength wastewater surcharge schedule isfound in Table 5.

0

1000000

2000000

3000000

4000000

5000000

6000000

0

100000

200000

300000

400000

500000

600000

700000

800000

1/31/2016 3/31/2016 5/30/2016 7/29/2016 9/27/2016 11/26/2016 1/25/2017 3/26/2017

Gas P

rodu

ctio

n (c

ubic

feet

)

Proc

ess W

aste

wat

er (g

allo

ns)

Capital Region Water 2016-2017 Process Hauled Waste vs.Digester Gas Production

Process Wastewater (Gallons) Gas Production (cu. Ft.)


Table 5. CRW High Strength Waste Fee Surcharge Concentration Limits

Parameter SurchargeLevel (mg/L)

HarrisburgCustomers

($/1,000 gallons)

HarrisburgConveyance System

($/1,000 gallons)

SteeltonConveyance

System($/1,000 gallons)

BOD 290 $0.15 $0.15 $0.11SS 380 $0.11 $0.11 $0.11TP 10 $2.18 $2.21 $2.21

Surcharges are expressed as cents per volume of water consumed for each mg/L by which thepollutant exceeds the threshold. For example, if an industry discharges 1,000,000 gallons ofwastewater with a BOD of 300, it would be charged 1,000 * $0.15 * (300-290), or $1,500.Surcharge rates (per 1000 gallons) are determined for the current year based on the prior year’slaboratory analysis. For example, 2017 surcharge rates for specific companies would be based onBOD, SS, and TP from 2016.

With an active high-strength wastewater surcharge program, there is incentive for significantindustrial users in the CRW’s service area to divert high strength wastewater out of the collectionsystem and haul waste directly to the AWTF or other processing facilities. One industrialdischarger MM interviewed, Hershey Creamery, discharges 65,000-70,000 gallons of wastewaterto the collection system every day at the rate of $4.27/1000 gallons. At this rate, Hershey Creamerypays CRW approximately $300/day as a surcharge. If there is an economic incentive to encourageHershey Creamery to haul waste directly to the digester, they stated that they would be veryinterested. Harrisburg Dairies is another dairy in the CRW service area that may be interested indiverting waste out of the CRW collection system to the digester. Additionally, several foodprocessors, including Hershey Creamery, remove 3,000 gallons per day of DAF solids and divertthem to other digester facilities or land application. Capturing this HSW for addition to the CRWdigesters, if priced appropriately, would provide a benefit to both Hershey Creamery and CRW.

3.0 Market Assessment Approach

3.1 Considerations for Participation in Hauled Waste ProgramsThere are factors that must be considered when evaluating a generator’s potential participation ina co-digestion program. Important considerations for HSW generators includetransportation/hauling costs, proximity to other municipal wastewater treatment plants (WWTPs)that accept hauled wastes, high-strength wastewater surcharge fees, direct land applicationprograms, and options for on-farm anaerobic digesters.

3.1.1 Transportation/Hauling CostsMaterial Matters interviewed waste haulers to understand typical transportation and hauling costs,and to establish an economically viable radius appropriate to transport waste streams. Wastehaulers choose where to haul wastes based on economic incentives, and the availability andlocation of processing facilities. Waste haulers develop their fee schedule based on loading(merge), unloading (demerge) and transport times rather than wastewater volumes hauled or


distance transported, because the majority of their expenses are in labor and insurance. Ratestypically range between $100 and $120 per hour. For the majority of liquid waste streams, amaximum economically-viable hauling cost is $0.03 to $0.05 per gallon; transportation fees thatexceed this value create a combined tipping/transportation fee that typically exceeds other locallyavailable outlets. Table 6 shows that the tipping fee of $0.03 to $0.05 per gallon is equivalent to aone-hour, one-way transport. Therefore, assuming an average speed of 30-60 miles per hour, themaximum one-way radius for most waste streams is ~30-60 miles. However, haulers reported thatwaste streams with characteristics that are more difficult to treat (i.e. exceptionally high BOD,TSS, or other pollutant concentrations) are often hauled farther distances (50+ miles) to beprocessed.

Table 6. Estimated Transportation Costs for Hauled WasteHours Costs

(One Way) (Round Trip) (Demerge) Full Charge Cost per Gallon0.5 1 1 $200 $0.031 2 1 $300 $0.052 4 1 $500 $0.083 6 1 $700 $0.124 8 1 $900 $0.15

An economically viable hauling cost of $0.03-$0.05 per gallon is generally accepted, and mostwaste haulers will participate at CRW if HSW generators are located no more than one-hour (50miles) away. For this assessment, a radius of approximately 50 miles was assumed to be themaximum hauling distance for most waste streams.

In particular, Material Matters interviewed JG Environmental, a waste hauling company based inLancaster that has an established partnership with CRW. JG Environmental expressed interest inhauling HSW to CRW in the future and mentioned that contracts for high-BOD waste materialswere recently available. They suspect that similar opportunities would become available in thefuture and are looking forward to developing this business opportunity with CRW.

3.1.2 Competition from Other Municipal WWTPsThe competition for hauled waste revenue is a factor to be considered when expanding a hauledwaste program. When evaluating the regionally available hauled waste streams, it is critical toconsider the details of other management and beneficial use options available to HSW generators,including location and tipping fees.

A 2013 survey conducted by MM showed that, in addition to CRW, at least 11 municipalwastewater treatment plants in central/southern Pennsylvania accept hauled waste. Figure 2 showsthe waste stream categories accepted by these facilities. The “other” category includes high solidsfood waste, printing ink, meat-processing waste, and car wash waste. Note that CRW participatedin this survey.


Figure 2. Hauled waste categories accepted at utilities in southcentral Pennsylvania

Of the 11 utilities surveyed, less than half accept HSW: three accepted FOG, five accept industrialwaste, and three accept other HSW. Although the facilities that accept HSW are limited in number,some of these facilities are within 50 miles radius of CRW. Derry Township Municipal Authority(DTMA), located only 15 miles east of CRW, has a robust hauled waste program, but limiteddigester capacity. DTMA uses biogas to generate power for their thermal dryer and heat for theplant. The Manheim Area Water and Sewer Authority, located approximately 30 miles east of theCRW, also has a very robust hauled waste program, accepting more than one million gallons ofhauled waste each month. The Lancaster Area Sewer Authority, located approximately 40 milessoutheast of the AWTF, plans to accept hauled waste by the end of 2018, which will be additionalcompetition for CRW.

The tipping rates for each waste category varied considerably among the surveyed facilities. Theprimary billing method for all waste streams (except solid wastes) is a flat rate of dollars per 1,000gallons. For high solids materials, however, most surveyed facilities have a fee schedule based onthe percent total solids of the material.

0

2

4

6

8

10

12

14

Septage Holding TankWaste

Portable ToiletWaste

Leachate Solids FOG Industrial Other

Num

ber

of F

acili

ties

Categories of Hauled-In Waste

Hauled-in Waste Categories Accepted


*Solids numbers are only for facilities that charge a set rate for high solids waste streams.

Figure 3. Hauled waste tipping fees for utilities in Southcentral Pennsylvania

CRW’s HSW fees of $0.027 per gallon ($27 per 1,000 gallons) is comparable to the average feesfor septage, holding tank waste, portable toilet waste, and leachate. If CRW decides to accept HSW(including FOG) in the future, the average price in the region is about four times higher than theCRW’s current septage rate. Note that the value of the HSW (for biogas production) must also beconsidered when setting tipping fees.

3.1.3 High Strength Wastewater Surcharge FeesAs discussed in section 2.3, wastewater discharged from non-residential dischargers (categorizedas industrial, institutional, or commercial) can have higher levels of Biochemical Oxygen Demand(BOD5), Total Suspended Solids (TSS), Total Phosphorus (TP), or Total Nitrogen (TN) thandomestic wastewater and will require a higher level of treatment. On a volume basis, “highstrength” industrial, institutional, and commercial wastewaters cost more to treat than residentialwastewater because it has a higher oxygen demand, creates more solids to manage, and requiresmore chemicals for treatment.

A high-strength wastewater surcharge program provides utilities with a mechanism to recover theadditional treatment costs created by these discharges by charging a surcharge fee (in addition tothe quarterly user rate) to dischargers of high strength wastewater, when discharged to the head ofthe plant. Surcharge rates provide an equitable means of distributing treatment costs amongratepayers based on discharge characteristics. They are facility-specific and are calculated basedon actual facility operating data. By establishing high-strength surcharge rates, WWTPs have theability to distribute treatment costs based on actual discharge strength above an establishedsurcharge baseline concentration.

Effective HSW surcharge programs provide an economic incentive for HSW dischargers topretreat their wastewater or haul waste streams off-site, rather than directly discharge into the

$33.38

$24.21

$38.41

$19.95

$56.35

$107.47

$48.67

$23.70

$11.00

$22.50

$0.04

$35.60

$102.40

$15.00

$50.00 $50.00

$69.00

$35.70

$91.14

$110.00

$95.00

$0.00

$20.00

$40.00

$60.00

$80.00

$100.00

$120.00

Septage Holding TankWaste

Portable ToiletWaste

Leachate Solids* FOG Industrial

Bill

ing

Rat

e (d

olla

rs/1

000

gallo

n)

Hauled-in Waste Categories

Hauled-in Waste Billing Rates (dollars/1000 gallons)

Average

Minimum

Maximum


collection system. A facility that directly discharges high strength wastewater into the sewersystem, but is not subject to any HSW surcharge fees has no economic incentive to divert thewastewater for co-digestion. In contrast, a generator faced with HSW surcharge fees may find costsavings by paying to haul the wastewater off-site. Because the CRW has adopted a HSW surchargeprogram, industry subject to these surcharges will be more inclined to divert HSW to the anaerobicdigester at the AWTF, rather than directly discharge into the collection system. For example,Hershey Creamery, located in the CRW service area, hauls HSW (subject to the CRW surchargeand FOG limits) to the Kline’s anaerobic digester in Landisville.

Co-digestion of HSW generated in the service area of the AWTF, particularly when a surchargeprogram is being implemented, provides an opportunity to remove these wastes from the collectionsystem and divert them directly to the digester. As noted, the infrastructure to manage HSW feedto the digester is not in place, such as a receiving station and flow equalization. In addition, a co-digestion program that provides incentives (e.g., pricing, revising discharge limits) to HSWgenerators in their own service area, if the HSW has appropriate characteristics, should also beconsidered.

3.1.4 Non-municipal Anaerobic DigestersNon-municipal digesters include digesters located on farms (manure anaerobic digesters) andanaerobic digesters operated by contract haulers (e.g., Kline’s Septic Service).

On-Farm DigestersBeginning in the mid-2000’s, Pennsylvania farms had financing available from the state andfederal government for the construction of anaerobic digesters as a Best Management Practice formanure management. The funding sources include USDA’s REAP (Rural Energy for AmericaProgram), stimulus dollars from U.S. Treasury grants, and state financing assistance from bothPennVest (the Commonwealth Financing Authority) and the Pennsylvania Department ofEnvironmental Protection (PADEP). Most farms with on-farm digesters have generators to utilizethe biogas to produce electricity and heat. In order to maximize energy production and fill excesscapacity in the manure digesters, some farms choose to supplement their manure digester withfood processing waste. The PADEP issued a general permit WMGM042 that allows anaerobicdigestion of animal manure on a farm mixed with grease trap waste (collected from restaurants orgrocery stores) and pre-consumer and postconsumer food waste from commercial or institutionalestablishments. Farm digesters within the Harrisburg region include:

· Brubaker Farms: Mount Joy, PA· Keefer Hard Earned Acres: Shippensburg, PA· Sensenig Dairy: Kirkwood, PA· Oak Hill Farm: Avella, PA

Farm manure anaerobic digesters typically offer a competitive tipping fee because they receivedfinancial support from grants, and they are located at the land application site (for digestate).

Kline’s Septic ServicesKline’s Services is a wastewater hauling / management company headquartered in Landisville,PA. Kline’s owns and operates an anaerobic digester with capacity to accept and process up to50,000 gallons per day of high strength wastewater. Kline’s operates under a WMGR099, which


allows them to accept, process, and beneficially use (by land application) a combination of“domestic sewage and industrial wastewater treatment sludge.” Kline’s hauls wastewater solids toboth their own anaerobic digester and to other municipal wastewater treatment facilities.

Kline’s generally hauls higher strength waste (e.g. dairy, bakery, and FOG) to their own anaerobicdigester to maximize gas production, and lower strength solids (e.g. municipal solids) to othermunicipal wastewater treatment plants. Hershey Creamery, located in Harrisburg, PA, and TurkeyHill, located in Conestoga, PA, reported that Kline’s accepts their high strength waste (e.g., FOG)for a very competitive combined transportation / tipping fee of $0.05 or less per gallon.

3.1.5 Direct Land Application ProgramsThe food processing industry commonly recycles food processing wastewater and wastewatersolids as animal feed and as fertilizer. In Pennsylvania, land application of food processingresiduals (FPR) is covered under PA Code Chapter 283. Facilities that wish to land apply FPR arecovered by a “permit-by-rule” as long as they follow practices found in PADEP’s Food ProcessingResidual Management Manual. Southcentral Pennsylvania is a highly active agricultural area, witha significant acreage devoted to row cropping and a high animal population; as such, landapplication of FPR is a readily accessible, low-cost management option. Programs are typicallyarranged in one of the following ways:

· The farmer hauls and spreads the food processing residual for free (or farmer pays for theproduct)

· The food processor pays for transportation; farmer accepts FPR for free· The food processor pays for transportation; farmer is paid a management fee.

Due to the close proximity to agricultural land, the ease of the regulatory program, lowtransportation costs, and low tipping fees, land application is a significant competitor to anaerobicdigestion. Industries utilizing land application as a waste management option typically require analternative avenue for waste removal in winter months when the ground is frozen. Several of thefood processers Material Matters interviewed indicated that they use the services of a waste haulersuch as Kline’s Septic Services during conditions when land application is not practical.

3.2 Identifying High Strength Waste GeneratorsMM identified a list of potential HSW generators within a 50-mile radius of the CRW AWTF,which includes most of southcentral PA, and a portion of northern Maryland (Figure 4).


Figure 4. Potential HSW feedstocks were identified within a 50-mile radius of CRW AWTF

The following resources were utilized to identify potential HSW generators:1. Internet searches2. Liquid waste hauler lists3. Consultants from an industrial wastewater treatment firm

Potential HSW generators were divided into ten categories; a summary of the HSW generators isprovided in Table 7. A detailed list of the identified facilities is included in Appendix 1.

Table 7. Co-Digestion Feedstock Generator Categories

Category No. of HSW GeneratorsAirport 2

Animal Feed 2Bakery 5

Brewery 33Candy 11

Canned Food 3Dairy 12

Distillery 9Fats, Oils, Grease See 4.1.6

Food Production Facilities 6Slaughterhouse/meatpacking 7

Fresh Vegetable Packing 1Snack foods 8


3.3 Market AssessmentIndustrial and food processing facilities generate multiple waste streams that can be managed in avariety of ways. These facilities balance costs, risks, and environmental impacts when decidinghow each waste stream should be treated, transported, and utilized. Figure 5 depicts the potentialwaste streams generated, handling / processing options, and disposal or beneficial use outlets.Waste streams include wash water from cleaning activities, off-spec products (contaminated,damaged, or expired), excess raw materials, and wastewater treatment products such as highstrength side streams and DAF thickener solids. Facilities can discharge wastewater to the sewer(either with or without pretreatment), treat and discharge wastewater into a receiving water body,or haul material off-site to be beneficially used, disposed, or further processed.

Figure 5. Food Processing and Industrial Facility Wastewater Handling and ManagementPractices

In order to solicit information from sources of high strength wastewater, MM developed surveyquestions for each waste streams produced by the processing facilities (Appendix 2). Questionswere developed to obtain information in the following areas:

1. Quantity of high strength wastewater generated;2. High strength wastewater characteristics;3. Current handling practices; and4. Willingness to participate in an alternative program.

4.0 Market Assessment Findings

4.1 High Strength Waste GeneratorsA description of HSW generators within the CRW region, and typical waste stream characteristicsand energy values are described below

Potential HSWStreams

Handling

Disposal /Beneficial Use

Off-SpecProductsCleaning

Activities

Raw Materials DAF, HS sidestreams

Pretreatment (&discharge to sewer)

Discharge to Sewer NPDES Permit (w/direct discharge) Hauled off-site

LandfillDisposal

Municipal WWTP Beneficial use(fertilizer, animal

feed)

Other postprocessing(WWTP,

commercialprocessing)

ReceivingWaters


4.1.1 AirportAirports utilize aircraft deicing fluids (ADF) and aircraft anti-icing fluid (AAF) during winterweather conditions. Chemicals such as ethylene or propylene glycol, urea, potassium acetate,sodium acetate, sodium formate, calcium magnesium acetate, or an ethylene glycol based fluid arealso to clear airport paved surfaces (e.g. runways, taxiways, and gate areas). ADFs are used for theremoval of snow, ice, and frost from the exterior surfaces of aircrafts. ADFs are heated and applieddirectly onto aircraft surfaces immediately preceding takeoff. During times when there is activewinter precipitation (e.g. snow, sleet, and freezing rain), AAF is applied directly after the ADF toprovide production against new buildup of snow and ice. Alternatively, AAF can be applied to adry aircraft to prevent overnight frost from accumulating. The run-off from airport surfaces istypically collected and treated to reduce the potential toxicity of these chemicals from affectingwaterways. Other contaminates that may be found in industrial wastewater from an airport, inaddition to deicing/anti-icing fluids, are spilled fuel, lubricants, and wastewater fromvehicles/aircraft. Airports may either treat this wastewater on-site or discharge it to a municipalsewer system for treatment. Harrisburg International Airport is less than seven miles from theHarrisburg AWTF. While it is not clear if / how the deicing fluid at the HIA is treated, transportof spent fluid to the CRW AWTF is an excellent opportunity.

The base chemical of ADF and AAF is propylene or ethylene glycol, typically accounting for morethan 80% of the total product volume. ADF and AAF also contain a mix of water, corrosioninhibitors, wetting agents, thickeners and typically contain dye. As shown in Table 8 glycol exertsa high biochemical oxygen demand. According to the EPA, it is estimated that the majority ofADF and AAF is discharged to surface waters (21 million gallons per year), and only a smallfraction is treated by municipal treatment plants (2 million gallons per year).

Due to the high COD content, deicing wastewater is a good candidate for co-digestion. Studieshave shown that propylene glycol can be easily degraded under anaerobic conditions (Veltmen etal, 1998). Some additives in deicing fluids, such as methyl-benzotriazole (MEBT), however, canbe inhibitory to methanogenic bacteria at concentrations above the toxicity threshold. Studies havefound that the addition of airport deicing wastewater to anaerobic digesters generally yieldsbenefits, including increased biogas production (Zitomer et al, 2001). Because of the variousconstituents that can be found in this type of runoff, CRW may wish to first conduct treatabilitystudies of the Harrisburg International Airport’s wastewater prior to introduction to the digesters.This market may be viable; however, the volume of deicing fluids generated at the HarrisburgInternational Airport is unknown and will require additional follow-up.

Table 8. Typical ADF and AAF Runoff CharacteristicsParameter Concentration

BOD5 100 to 1,000,000 mg/LCOD 31,300 mg/L

Glycol 17,200 mg/LpH 7.50 to 9.3 s.u.


4.1.3 Breweries/DistilleriesBreweries generate two categories of waste in the brewing process – washwater and solids.Typically, smaller breweries (5,000 barrels or less per year) neutralize acidic wash water withbaking soda or caustic and discharge directly into the collection system. Large breweries typicallydischarge into their own pretreatment or wastewater treatment plant. Breweries report generatingbetween 5 and 10 gallons of wastewater per barrel of beer brewed. The solid stream consists ofspent grain, hops, and yeast; this material is typically collected by local farmers, hauled off site atno cost to the brewer or distiller, and used for animal feed. Based on interviews with a brewery(Appalachian Brewing Company, Harrisburg) and a distillery (Mid-State Distilling, Harrisburg),this appears to be standard for the industry.

Ten distilleries and 33 breweries were identified within 50 miles of the CRW AWTF. Overall, thismarket does not appear viable for co-digestion due to the low volumes of wastewater generated byeach source, and the low-cost accessibility to local agricultural markets.

4.1.4 CandyCandy manufacturing includes production of chocolate, hard candies, soft “gummy” or “chewy”candies, and other confectionaries. Process wastewater from these facilities is typically generatedduring the “first flush” of the washing process. In some cases, a demand for high strength sugarwater exists, in which case a portion of the wastewater can be segregated for other uses and asource of revenue for the manufacturer. In the case of chocolate, peanut, or other fat-containingcandies, process water from a candy manufacturing process will include a film of FOG that willfloat to the surface, or will be emulsified into the water. Free FOG will be scraped off andbeneficially used or disposed. In contrast, emulsified FOG will be treated with a coagulant toflocculate the FOG for removal from the wastewater; this is typically performed in a dissolved airflotation (DAF) unit. Characteristics from a processing facility of sweeteners (e.g. corn syrup,dextrose, molasses, etc.) are found in Table 9.

Table 9. Wastewater characteristics of a sweetener processing facility

Parameter ConcentrationpH 4 – 5 s.u.

BOD 15,000 to 60,000 mg/LTS 3-8%

MM identified and contacted 11 candy-manufacturing facilities within 50 miles of the CRWAWTF facility (Table 10). One facility operates their own wastewater treatment plant, one isstarting a land application program, one uses Kline’s hauling services, and eight facilities did notrespond. The Warrell Corporation currently separates DAF solids, which is then hauled out byKline’s. They produce 9,200 gallons of DAF solids every three to four weeks. The candy markethas limited potential; however, follow up with the facilities that could not be reached isrecommended.


Table 10. Candy processing facilities within 50 miles of CRW AWTF

Company Location RecommendationBlommer Chocolate Co East Greenville Potential; Contact again

Cargill Cocoa and Chocolate Mount Joy Potential; Contact againFitzkee's Candies York Very Small; not viableGardner's Candies Tyrone Potential; Contact again

Hershey Hershey Potential; Contact again

L&S Sweeteners Leola Operate low cost land applicationprogram; not viable

Mars Chocolate Elizabethtown Operate own WWTP; not interestedRM Palmer Co. Reading Potential; Contact again

Warrell Corporation Camp Hill DAF Solids hauled by Kline’s;Potential; Contact again

Wolfgang Candy Company York Potential; Contact againY&S Candies Lancaster Potential; Contact again

4.1.5 DairyDairy processing includes the processing and production of a variety of products including fluidmilk, butter and butter spreads, yogurt, and ice cream and frozen dessert producers. In southcentralPennsylvania, dairy processing facilities manufacture iced tea and other beverages as well. Dairyprocessing facilities typically have an on-site pretreatment facility followed by discharge into themunicipal collection system or an on-site treatment facility with direct discharge into a receivingwater body (i.e. NPDES Permit). There are two dairy processing facilities registered as significantindustrial dischargers in the CRW service area (Harrisburg Dairies and Hershey Creamery). Highstrength waste products from dairy processing facilities include first flush wash water, acid whey,off-spec/damaged products, and surplus of raw product. Facilities with on-site processing alsogenerate high-energy solids from the DAF process, and solids digestion processes. Fluid milk andDAF solids are an effective COD source if added directly into an AD. Typical wash watercharacteristics from a dairy processing facility are found in Table 11.

Table 11. Waste characteristics of a dairy processing facility

Parameter Wastewater from ProductsMilk Fluid Products Dry Products

pH (s.u.) 10.1 9.6 10.4COD(mg/L) 1,794 2,270 2,391TN(mg/L) 45 71 88TP (mg/L) 25 42 55

Oil & Grease (mg/L) 253 523 297

Dairy processing waste is typically utilized in agriculture as animal feed or as a soil amendment.During winter months when the ground is frozen and/or snow covered, however, land application


is limited. Dairy processors and waste haulers have reported that they need alternative outletsduring these times. MM contacted twelve dairy processing facilities within 50 miles of the CRWAWTF. A summary of the dairy processing facilities is found in Table 12.

Table 12. Dairy processing facilities within 50 miles of CRW AWTF

Company Location RecommendationLand O' Lakes Carlisle Potential; Contact again

Cumberland Valley Creamery Mechanicsburg Potential; Contact again

Harrisburg Dairy HarrisburgDAF Solids; Potential; Contact

againClover Farms Dairy Reading Potential; Contact again

Kreider Dairy Manheim Operate own digester; not viableSwiss Premium Lebanon Potential; Contact again

Rutters York Potential; Contact again

Hershey Creamery Company HarrisburgDAF Solids hauled by Kline’s;

Potential; Contact againDairiconcepts Hummelstown Potential; Contact again

Schreiber Foods, Inc. Shippensburg Potential; Contact againDairy Farmers of America Mechanicsburg Potential; Contact again

Turkey Hill ConestogaDAF Solids hauled by Kline’s

and JG Environmental:Potential; Contact again

MM interviewed Hershey Creamery, one of the significant industrial dischargers in the CRWservice area. CRW limits FOG to 100 ppm in discharged wastewater, and as a result, HersheyCreamery responded by establishing a treatment program to remove DAF solids from thewastewater before discharging to CRW. The DAF solids are hauled out by Kline’s Septic Servicesfor $300 per load ($0.05 per gallon). They typically produce 6,000 gallons of DAF solids everytwo days. Hershey Creamery expressed interest in utilizing CRW as an option for their FOG ifthere is an economic incentive. This market appears to have potential when considering two dairiesin the service area, and the number of other dairies locally. Characteristics of both the FOG andthe surcharged wastewater are included in Table 13.


Table 13. Hershey Creamery Waste Parameters

Parameter FOG Characteristics1 Discharged WastewaterConcentrations2

Daily Volume 3,000 gal 65-70,000 galTotal Suspended

Solids (mg/L) 238,500 171

pH 5.5 6.8

Hexane ExtractableOil and Grease n/a <5.45

BOD5 n/a 4015Total P n/a 5.9TVS% 98% n/a

1 FOG Characteristics provided from a single 6/3/2016 sample.2 Discharged Wastewater Characteristics are the average of three analysescompleted on 1/20/2017, 2/14/2017, and4/12/2017.

4.1.6 Fats, Oils, and GreaseFats Oils and Grease (FOG) are defined as organic, polar compounds derived from plant or animalsources that are composed of long chain triglycerides. FOG in municipal wastewater principallyconsists of cooking oil by-products, and can be broken into two major categories:

· Yellow grease: Inedible and unadulterated spent FOG formed from Food ServiceEstablishments (FSE). Yellow grease is principally comprised of spent grease that has beenutilized for frying foods. Yellow grease is responsive to co-digestion and requires minimalprocessing before adding to an AD.

· Brown grease: Floatable FOG, settled solids and associated wastewater retained by greaseinterceptors and grease traps. In order for brown grease to be suitable for AD, it must firstbe screened, heated, and blended with other feedstocks.

When directly discharged into the collection system, FOG accumulates on pipe walls, whichcauses reduced conveyance capacity, and increases the potential for sanitary sewer overflows. Toavoid these challenges, grease is removed from the discharge with the installation of grease traps(inside, under the sink) or grease interceptors (outside, underground tanks) where FOG isgenerated. Grease traps and interceptors are gravity separation devices used to retain aconglomeration of suspended grease and food solids referred to grease trap waste (GTW).Restaurant grease trap waste can vary significantly, but in general, contains organic matter in theform of fats, oils, grease, carbohydrates, sugars, and other organic compounds.


Many utilities have implemented ordinances for restaurants and large institutions (e.g., hospitals,schools) to install grease traps to remove grease from kitchen waste streams prior to entering thecollection system, and to clean out these traps on a regular basis (e.g. one time per 6 months).Grease trap and grease interceptor wastes are pumped and typically hauled to a WWTP orprocessing plant for treatment. Grease trap waste contains high BOD, a large fraction of lipids,and a typical energy content of roughly 7,000-10,000 BTUs/pound when dewatered. It has beenshown to increase the BTU and percent methane content of digester gas (Long et al., 2012) (Bailey,2007). While co-digestion of GTW can prove to be a benefit for methane production, it is importantto note that challenges exist including the potential for inhibition of methane generation. Table 14summarizes the typical elements in GTW.

Table 14: Characteristics of Grease Trap Waste

Parameter AmountVolatile solids content 5.6 %

Methane content of digester gas ~14,900 mg/LVSR 70%

Total solids content 6.00%Digester gas production 20 cf./lb. VS destruction

Source: Feasibility of High Strength Waste Co-Digestion from the San Francisco Public Utilities Commission (Abu-Orf et al, 2014)

The quantities of GTW available within the City of Harrisburg is shown in Table 15, as estimatedfrom a URS study (URS 2011). The brown grease fraction of the GTW was calculated first usinga per capita generation rate. Then the quantities of GTW were back-calculated from the browngrease quantities. The quantities in Table 14 represent total quantities of GTW, which may not beentirely available for co-digestion at CRW due to existing competition for this material.Characterization factors used in generating this table were also based on the URS study (URS,2011).

Table 15. Estimated GTW generated in the City of Harrisburg

Service Area PopulationServed1

Brown GreaseProduction

RecoverableBrown Grease GTW

lbs./day2 gpd3 gpd4 gpd5

City ofHarrisburg 49,082 1,798 240 60 1,199

1 2014 Census2 Grease trap generation factor of 13.37 lb./yr.-person, URS 20113 Conversion factor of 7.5 lbs./gallon of grease trap, URS 20114 25% recover factor, URS 20115 % brown grease composition factor, URS 2011

The City of Harrisburg has an ordinance requiring installation of grease traps in restaurants andregular monitoring and clean-out of those grease traps (Chapter 6-501.5-9). Additionally, CRWhas a limit for discharges of FOG to the collection system and the AWTF of 100 mg/L. FOGdischarged to the collection system and at the headworks of the AWTF is difficult to manage andresults in high maintenance costs. However, FOG and GTW directed to the digester is largelybroken down during digestion, increases gas production, and produces fewer solids than typical


municipal wastewater solids (Schafer et al., 2007). This potential market will require additionalstudy and revisions to the CRW pretreatment program requirements.

4.1.8 Slaughterhouse/MeatpackingThe meat-processing sector produces process wastewater with high loads of fats, oils, and grease,and solids resulting from the slaughtering of animals and cleaning of the slaughterhouse facilitiesand meat processing plants. Wastewater comes from the following sources listed in Table 16.

Table 16. Major sources of slaughterhouse/meatpacking wastewater

StageWastewater Source

Wash Blood BloodWater Curing Cooking

Slaughter X XBlood Processing XViscera Handling XHide Processing X X

Cutting XMeat Preparation X X

Rendering X

In general, pretreatment is required to remove the solids from the liquid due to the high grease /solids content of these waste streams. This may be a clarifier, DAF thickener, or a hydrosievescreen.

Based on the characteristics of slaughterhouse waste, these wastes are potential candidates for co-digestion due to high volatile solids and fat content (Table 17). While the COD of this waste streamis very high, the BOD may only be a fraction of the COD when wood shavings and other similarmaterials from the production process are present.

Table 17. Meat Processing Typical Wastewater Characteristics1

Parameter ConcentrationCOD 961,000 mg/LPercent Total Solids 8.2 %Volatile Solids 80.9%

Typically, fat is collected by a rendering facility, which is a facility that process animal by-productsto produce tallow, grease, and high-protein meat and bone meal (US EPA). Bones and blood arecommonly used to produce animal feed. Some waste streams may also be land applied as anagricultural fertilizer. As with other food processing sectors, most facilities reuse as much of theby-products as possible, because paying for the disposal of any of these animal byproducts willresult in loss of revenue and added costs for management. MM identified seven meatpacking or

1 Source: DAF solids from a Pennsylvania meat processor (September 2015)


rendering facilities within 50 miles of the CRW AWTF. A summary of the meatpacking facilitiesis found in Table 18.

Table 18. Meatpacking facilities within 50 miles of CRW AWTF

Company Location RecommendationVantage Foods Camp Hill Potential; Contact again

Brother and Sister Food Services Harrisburg Potential; Contact againKessler Foods Lemoyne Potential; Contact againSME Foods York Potential; Contact again

Empire Poultry Mifflintown Potential for DAF; Contact again

Keystone Protein FredericksburgExisting Hauled Waste

Customer (emergencies only);Has own treatment facility

Farmers Pride, Inc. Fredericksburg Has own treatment facility

Empire Poultry is a chicken processing facility located in Mifflintown, Pa that has an industrialwastewater treatment facility with direct discharge. The solids (food-processing waste) is landapplied; however, DAF solids are hauled off-site and treated at Valley Proteins. Empire Poultrycontacted Material Matters in late 2016 to identify cost effective options for handling their DAFsolids. Information provided by Empire indicated production of 20,000 gpd of DAF solids, or 4.2Mgal /yr. We estimated a tipping fee of $0.031 per gallon or less to make co-digestion at CRWattractive for Empire.

Keystone Protein is listed as an existing hauled waste customer at up to a maximum of 12,000 gpd.Keystone renders waste from Farmers Pride, Inc., which it makes into pet foods. MM interviewedNelson Weaver of Keystone Protein, and he indicated that Keystone has a contract with CRW foremergency situations only, with hauling to CRW by Kline’s. Keystone has its own wastewatertreatment facility and discharges wastewater to a local stream as per their NPDES permit allows.They are planning plant upgrades in 2018 that may require them to transfer a portion of their wasteto CRW. They also produce dewatered solids that are land applied by a local farmer.

4.1.9 Snack FoodsSnack food process wastewater is generated during production of a variety of food productsincluding potato chips and related potato snacks, pretzels, cheese curls and puffs, corn chips andrelated corn snacks, and popcorn. The HSW generated from snack processing facilities includeswash water (from raw product and processing areas), peelings (from potatoes), and spent oil.Facilities with on-site processing typically have high-energy solids from DAF thickeningprocesses. DAF solids such as the solids accepted from UTZ Quality Foods are an effective CODsource if fed slowly into an anaerobic digester. Typical characteristics from the UTZ DAF solidsare found in Table 19.


Table 19. Wastewater characteristics of UTZ DAF solids2

Parameter ConcentrationHexane Extractable

Oil and Grease 309,000 mg/kg

BOD5 20,100 mg/LCOD 77,800 mg/L

TVS% 82%

As with many other food categories, snack food processing waste is typically used in agricultureas animal feed or as a soil amendment. However, as is noted in section 4.1.5 (Dairy), manymanufacturing facilities sometimes seek alternative outlets during winter months when the groundis frozen or snow-covered, including on-farm digesters, constructing new on-farm storage tanks,and treatment at WWTPs.

Eight snack-processing facilities were identified within approximately 50 miles of the CRWAWTF (Table 20).

Table 20. Snack-processing facilities within 50 miles of CRW AWTF.

Company Location RecommendationDieffenbach's Potato Chips Womelsdorf Follow-upMiddleswarth Potato Chips Middleburg Follow-up

Herr's Potato Chips Nottingham Follow-up

Good's Potato Chips Adamstown Lard is only waste; not viableMartin's Potato Chips Lancaster Follow-up

Snyders-Lance(Hanover Manufacturing) Hanover Follow-up

Hartley's Chips Lewistown Low cost land app; not viableUtz Hanover Currently utilized

2 Source: Utz Quality Foods analytical Data (June 2016 and January 2017)


5.0 Findings and Recommendations

5.1 FindingsCapital Region Water’s Harrisburg AWTF has a robust hauled waste program (602,910 gal/monthor approx. 20,000 gpd), with frequent regular monitoring for pollutants/ BOD/ COD. However, itappears that there is capacity in the hauled waste program to include HSW for co-digestion.

MM conducted a market survey to determine the availability and characteristics of HSW that arevaluable for co-digestion at CRW’s Harrisburg AWTF. The identified categories of HSW werebased on suitability for co-digestion and location of sources relative to CRW AWTF. MMcontacted potential sources of HSW within 50 miles of the CRW AWTF. Major competitors formunicipal hauled waste and high strength wastewater were also identified.

Results of the market survey provided information relative to the number of generators andcharacteristics of HSW, current practices of the generators, typical transportation distances, andexpected pricing ranges for transportation and tipping. Market considerations for development ofa CRW co-digestion program were developed.

5.1.1 Digester CapacityCapital Region Water currently has two anaerobic digesters, each with a volume of 1.83 MG anda design loading of 30,500 lbs. VSS/day at 5% TS. Of this total capacity, CRW is currentlyoperating one anaerobic digester. This digester is currently loaded at an annual average daily rateof 27,500 lbs. VSS / day at 3% TS, and a maximum monthly loading rate of 36,560 lbs. VSS/dayat 5% TS. With both digesters in full operation, approximately 20,000 to 30,000 lbs. VSS/day or33 to 49% of the total capacity (i.e. 61,000 lbs. VSS/day) would remain available for co-digestionof HSW materials from outside sources.

5.1.2 Promising Feedstocks

5.1.2.1 Grease Trap Waste from Area RestaurantsA study by Schauer and Garbely in 2016 compared two digesters at an Oregon wastewatertreatment plant. One digester was co-digested with FOG/GTW, while the other was co-digestedwith food waste. While both digesters saw increases in biogas production compared to wastewatersolids only, the digester with FOG showed a much higher rate of biogas production than thedigester with food waste.

Grease trap waste (GTW) appears to be a good source for co-digestion. CRW currently does notaccept GTW, but as shown in Table 15, the expected volume of available GTW within the CRWservice area is estimated at 1,199 gal/day.

5.1.2.2 DAF Solids / FOG from dairies, snack food processors / candy processorsDissolved air flotation processes are designed to clarify wastewaters to remove oil and grease.These units are used in a variety of industrial applications, including food processing. UTZ is asnack food producer that discharges to a municipal collection system, and is required to meetpretreatment requirements for FOG and pays a surcharge based on conventional pollutants. When


land application is not possible, their DAF waste is hauled up to 150 miles for processing. TheDAF solids generated at UTZ are a good source of HSW for co-digestion.

MM conducted interviews with several food processors in the greater Harrisburg area that produceDAF waste, which could be potential options for CRW. In addition, we understand from wastehaulers that other unidentified sources are available.

5.1.2.3 Potential volumes and biogas productionIt has been demonstrated that the addition of HSW (specifically FOG) can provide a significantincrease in the biogas production from anaerobic digestion. A review of three studies (Long et al.,2012) demonstrated that adding grease trap waste to digesters in ranges from 10% to 30% byvolume yielded biogas production increases of 30-80% respectively. Other studies havedemonstrated biogas production increases of 30-197% using lab, pilot and full-scale co-digestionstudies, using feed rates of up to ~ 50% FOG (Long 2012, Schauer and Garbely, 2016).

References Location Reactor Loading Rate Response

Bailey (2007) Riverside, CA 28.1–30.4% GTW byvolume

81.9% Digester gasincrease, 9.5% BTUincrease, 5–6% increasein methane content

Cockrell (2007) Watsonville, CA Average 143,000 gallonsGTW/month

>50% Digester gasincrease

Muller et al. (2010)Vancouver, BritishColumbia 9.5% GTW by volume

32.4% Digester gasincrease

MM contacted approximately 100 potential HSW generators to determine whether their wastescould be valuable waste streams for co-digestion at CRW’s ATWF. Of the potential sources, fivewere identified as promising sources within the 50-mile survey radius.


Table 21. VSS Loadings from selected HSW generators

FOG Source Daily Volume (MGD) % Solids TVS % VSS (lbs. day)

Utz Quality Foods(2) 0.012 9% 80% 7,126

Empire Poultry (2) 0.02 5% 80% 6,672

Hershey Creamery(2) 0.003 24% 98% 5,848

Grease Trap Waste (1) 0.0012 6% 80% 480

Warrell (2) 0.00033 5% 80% 110

Total volume per day (gallons) 36,530

Weighted average % solids 7.9%

Volume lbs. of VSS per day 20,236

(1) Data from tables 14 and 15(2) Daily volume provided by generator; % solids and TVS% estimated

Table 22. Ratio of HSW to Solids at Selected Loadings

Loading RateAWTF SolidsLoading (lbs.

VS/day)

HSW SolidsLoading (lbs.

VS/day)

Total SolidsLoading (lbs.

VS/day)

% HSW to solidsfeed

Current Average 21,300 20,240 41,540 49%AWTF DesignMax. Month(37.7 MGD)

36,560 20,240 56,800 36%

Digester Capacity 36,560 24,440 61,000 40%

These five sources represent substantial volatile solids loadings that when co-digested represent25% of the total VSS loading of the two anaerobic digesters at design flow. At the current loading,these sources more than double the current VSS loading (Table 22). Providing a fraction of FOGto an anaerobic digester can provide a significant increase in biogas production. Accepting onlythe UTZ or Empire Poultry feedstock provides approximately 25% of the feed rate to the digestersat current VSS loadings, which could correspond to an increase of 50-80% in biogas volumes,based on the available data.

5.1.2.4 Operational limitationsAcceptance of HSW and subsequent co-digestion generates additional biogas, generating moreelectricity and heat onsite, with the potential to decrease operating costs. Increases in revenues inthe form of additional tipping fees are likely. However, operational challenges have been reported.If the HSW is not mixed and fed to the digester carefully, long chain fatty acids (LCFA) can causetoxicity to methanogens and other bacterial groups in a digester. Large increases in loading arealso known to cause foaming events in digesters (Schauer and Garbely, 2016), similar to


challenges seen when feeding large amounts of UTZ DAF solids at CRW in early 2017. Many ofthese challenges can be overcomes by careful mixing, flow, and loading design (Cockrell, 2007).

5.2 RecommendationsMM provides the following recommendations for establishing and sustaining a resilient co-digestion program, if CRW determines the program benefits and costs meet their operating goals.

5.2.1 Establish infrastructure for receiving hauled wasteThe infrastructure for direct feed into the digesters and equalized flow does not currently exist atthe AWTF. In order to provide flexibility in receiving hauled waste and allow gradual feeding ofhauled waste into the digester, a receiving facility or equalization basin with a pumping system atCRW will enable a more successful co-digestion program. The development of a hauled wastereceiving station and basins to allow for slow-feed of the hauled waste into the digester are criticalfor maintaining control of the digestion system and consistent production of biogas. Adding largequantities of hauled waste directly to the digester can overwhelm the microbial population andlead to foaming or loss of microbes. With the ability to gradually feed waste over a longer periodof time, any operational challenges with the digester can be detected and addressed. While buildinga receiving station would be a significant expense, the increased income from accepting additionalhauled waste and the increased biogas production have the potential to be economically viable.MM recommends CRW further investigate the economic viability of building and maintaining areceiving station and equalization system.

5.2.2 Utilize grease trap waste ordinanceGrease trap waste appears to be a reasonable opportunity as a preferred source for co-digestion.CRW does not currently accept grease trap waste. As mentioned previously, GTW is capable ofimproving biogas production. CRW does not currently take GTW as a hauled waste due to thepotential for clogged pipes / pumps and damage to equipment. By discharging GTW into thedigester rather than the headworks, collection system maintenance costs can be avoided. Hauledwaste pricing for GTW must reflect these avoided costs at the headworks and potential additionalbiogas production.

The City of Harrisburg has an ordinance requiring installation of grease traps in restaurants andregular monitoring and clean-out of those grease traps (Chapter 6-501.5-9). Area restaurants likelyuse waste haulers to periodically clean out their grease traps and remove the waste to anotherfacility. Restaurants should be contacted to determine which hauling/clean-out companies areused, and hauling companies contacted to determine competitive rates for them to bring GTW toCRW. It is also recommended that CRW become more involved in the enforcement of the greasetrap ordinance by required submittal of receipts showing that grease traps are being cleaned out ona regular basis. The frequency of required cleanout would depend on the volume of greaseproduced by the food service establishment and the capacity of their grease traps.

5.2.3 Follow up with identified facilities and haulersWhile MM interviewed a number of food processing facility representatives in the greaterHarrisburg area, we were unable to connect with a majority. Many of these facilities have potential,and additional effort will be needed to determine the availability and quantity of high strengthwaste available. Facilities MM contacted were very interested in learning more about when CRW


will consider co-digestion as an option for their waste management programs. These facilitiesshould be contacted with updates as to the progress of the co-digestion program and expandingCRW’s digesters to full capacity. Specifically, Hershey Creamery was interested in understandinghow they can utilize CRW’s anaerobic digesters in their program. Several facilities producing DAFsolids were identified in Southcentral Pennsylvania. These facilities should be notified prior to theexpansion of CRW digester capabilities (Hershey Creameries, Harrisburg Dairies, WarrellCorporation, other candy and dairy manufacturers in the area). All potential facilities are listed inAppendix 1.

In addition, any local waste haulers should be notified 6 months prior to developing andimplementing a co-digestion program to capture seasonal and other HSW from haulers. Inparticular, JG Environmental expressed interest in collaborating with CRW to bring high BODwaste to the CRW digesters.

5.2.4 Develop experimental introduction planWhen introducing new HSW sources into the digester, the impact to operations should beconsidered. With a receiving station, HSW can be added gradually to ensure microbes have timeto acclimate to the new food source and optimize biogas production. In early February 2017 andending in May 2017, CRW experienced foaming when adding UTZ DAF solids directly to thethickener for co-digestion. No other HSW is currently added directly to the thickener for co-digestion. Monthly volumes of material varied, but peaked at 120,000 gallons in the month ofMarch. This represents a significant portion of the total digester volume. After experiencingfoaming problems with the digester, CRW phased out the addition of UTZ DAF solids. Theexperience with UTZ confirms the importance of gradually adding materials to the digester,monitoring digestion parameters frequently, and establishing an experimental design to determinethe optimum amount of certain waste products in the co-digestion system.

DAF solids are an excellent feedstock for the production of biogas. In Figure 1 of this report,biogas production showed an increase from January through April of 2017, indicating that the UTZmaterial contributed to higher biogas production during that period. Before CRW considersresuming UTZ DAF feed into the digester (which is strongly encouraged), the impact of lowervolumes, additional monitoring, and gradual loading should be assessed. A similar experimentalplan is recommended for all future HSW sources added directly to the thickener or to the digester.

5.2.5 Pricing StrategiesCapturing HSW for co-digestion at CRW will require reasonable transportation costs and attractivetipping fee structure. Hauled waste is a very competitive market with generators looking for thelowest cost option, and haulers developing low cost options to gain the business. Transportationfees are dependent on distance from the AWTP, and are out of the control of CRW. As notedherein, a 50-mile travel distance will result in a transportation fee of $0.03 to $0.05 per gallon.Discussions with haulers indicated that disposal fees not exceeding $0.06 per gallon wouldencourage interest. Most municipalities base prices based on competition for haulers, despite thefact that this pricing strategy does not fully consider the capital and O&M costs for pretreatmentand other plant processes necessary treat the waste. A cost / benefit analysis to establish reasonabletipping fees must also include both the capital costs associated with a receiving station orequalization basin and the economic value of the additional biogas production.


Pricing strategies for hauled GTW, assuming it is added to the digesters, should reflect the costavoidance for removing it from wet end processes, the capital and O&M costs for pretreatmentfacilities, and value of the energy generated during co-digestion. However, competitive pricing forgrease trap waste must also be considered. Of the 11 municipalities with hauled waste programsSouthcentral PA, three accept grease trap waste with fees ranging from $0.102 to $0.11 per gallon.

CRW’s current pricing strategy is based on solids percentage. During the first month of hauling,wastewater generators are charged a discharge fee based on percent total solids (%TS) at$0.009/every 0.5% TS; the minimum fee is $0.027/gallon and 1,000 gallons. For months twothrough twelve of the contract, discharge fees are charged per truckload. MM recommendsconsidering a separate pricing strategy for HSW that will be discharge to the digester (or thickener)as opposed to the headworks. Rather than basing prices on % TS, pricing should reflect the valueof gas production of the material (%VS, BOD, COD). Dividing the pricing strategies into differentcategories allows CRW to offer competitive rates for materials that will work well with co-digestion.

5.2.6 Revisions needed to update the hauled waste programTables 3 and 4 of this report detail the CRW pollutant limits and general parameter limits forhauled waste acceptance at the headworks of the plant. Material Matters recommends developinga second set of criteria for HSW that will be accepted directly into the thickener or the digester.For example, FOG and GTW are a very good source of HSW for co-digestion in the CRW servicearea, but current requirements would not permit any material with O&G over 100 mg/L. Werecommend revising these numbers to allow FOG and GTW to be accepted into the thicker anddigester. Characteristics of potential HSW sources should be considered when updating theserequirements.


References

Abu-Orf, M., et al. "Feasibility of High Strength Waste Co-Digestion for the San FranciscoPublic Utilities Commission." Proceedings of the Water Environment Federation 2014.2(2014): 1-16.

Bailey, Regan S. "Anaerobic digestion of restaurant grease wastewater to improve methane gasproduction and electrical power generation potential." Proceedings of the WaterEnvironment Federation 2007.11 (2007): 6793-6805.Cockrell, Paul. "Grease digestion toincrease digester gas production–4 years of operation." Proceedings of the WaterEnvironment Federation 2007.11 (2007): 6706-6715.

Long, H.; Aziz, T.; de los Reyes III, F.; Ducosted, J. 2012. Anaerobic co-digestion of fat, oil, andgrease (FOG): A review of gas production and process limitations. Process Safety andEnvironmental Protection. 90: 231-245.

Muller, Christopher, et al. "Co-digestion at Annacis Island WWTP: Metro Vancouver's path torenewable energy and greenhouse gas emissions reductions." Proceedings of the WaterEnvironment Federation 2010.14 (2010): 2706-2722.

Schafer, Perry, et al. "Grease Processing for Renewable Energy, Profit, Sustainability, andEnvironmental Enhancement." Proceedings of the Water EnvironmentFederation 2007.14 (2007): 4497-4505.

Schauer, P. and Garbely, D. 2016. A FOGgy Day in Oregon. Proceedings of the WaterEnvironment Federation, WEFTEC 2016: Session 309 Co-Digestion, pp. 4777-4785(9).

URS. 2011, Implement Public Relations and Extend Project Findings of a FOG to BiodieselRefinery at a Municipal Wastewater Treatment Plant. August 2011.

USEPA. 2014. Food Waste to Energy: How Six Water Resource Recovery Facilities are BoostingBiogas Production and the Bottom Line. EPA 600/R-14/240.

Veltman, S.; Schoenbert, T.; & Switzenbaum, M.S. 1998. Acid and alcohol formation duringpropylene glycol degradation under anaerobic methanogenic conditions. Biodegradation.9(2):113-8.

Zitomer, D., Ferguson, N., McGrady, K., & Schilling, J. 2001. Anaerobic Co-Digestion ofAircraft Deicing Fluid and Municipal Wastewater Sludge. Water EnvironmentResearch, 73(6), 645–654.


Appendix 1. Identified HSW Dischargers

Material Matters identified eleven (11) different categories of HSW dischargers in the greaterHarrisburg region. Potential HSW sources were contacted and interviews were conducted withavailable contacts at the facilities.

Company Name City

AirportsFort Indiantown Gap Airport (Army) Fort Indiantown Gap

Harrisburg International Airport MiddletownAnimal Feed Manufacturers

Purina Food Mill MechanicsburgZeigler Brothers Gardners

BakeriesDawn Food Products, LLC York

Pellman Foods, Inc. New HollandSpecialty Bakers Marysville, also in LititzBimbo Bakeries Carlisle

Terranetti's Italian Bakery MechanicsburgBreweries

Appalachian Brewing Company HarrisburgBube's Brewery Mount Joy

Ever Grain Brewery Camp HillGunpowder Falls Brewing New FreedomHighway Manor Brewing Camp HillHowling Henry's Brewery Hummelstown

Iron Hill Brewery LancasterJoBoy's Brew Pub Lititz

Lancaster Brewing Company LancasterLiquid Hero Brewery York

Market Cross Pub CarlisleMolly Pitcher Brewing Company Carlisle

Moo Duck Brewery ElizabethtownMudhook Brewing Co. York

Old Forge Brewing Company DanvillePig Iron Brewing Company Marietta

Pizza Boy Brewery/Al's of Hampden East Pennsboro Twp.Rusty Rail Brewing Company Mifflinburg

Selin's Grove Brewing Company SelinsgroveSnitz Creek Brewery Lebanon

Something Wicked Brewing Company HanoverSouth County Brewing Co. Fawn Grove

Breweries (continued)


Spring Gate Brewery HarrisburgSpring House Brewing Company LancasterSt. Boniface Craft Brewing Co. Ephrata

Stoudt's Brewing Company AdamstownSwashbuckler Brewing Co. Manheim

The Millworks HarrisburgThe Vineyard and Brewery at Hershey Middletown

Troegs HersheyWacker Brewing Company Lancaster

Wyndridge Farm DallastownZeroday Brewing Company Harrisburg

Candy ManufacturingBlommer Chocolate Co East Greenville

Cargill Cocoa and Chocolate Mount JoyFitzkee's Candies YorkGardners Candies Tyrone

Hershey Foods HersheyL&S Sweeteners LeolaMars Chocolate ElizabethtownRM Palmer Co. Reading

Warrell Corporation Camp HillWolfgang Candy Company York

Y&S Candies LancasterFood Canning Operations

Hanover Foods HanoverKnouse Foods Co-Operative Inc Peach Glen

Toigo Orchards ShippensburgDairy Processing

Clover Farms Dairy ReadingCumberland Valley Creamery Mechanicsburg

Dairiconcepts HummelstownDairy Farmers of America Mechanicsburg

Harrisburg Dairy HarrisburgHershey Creamery Company Harrisburg

Kreider Dairy manheimLand O' Lakes Carlisle

Rutters YorkSchreiber Foods, Inc. Shippensburg

Swiss Premium LebanonTurkey Hill Conestoga

Distilleries


Big Spring Spirits BellefonteHidden Still Spirits Lebanon

Manatawny Still Works PottstownMason Dixon Distillery GettysburgOld Republic Distillery YorkShawneetown Distillery New Cumberland

Spirits of Gettysburg/Battlefield Brew Works GettysburgTattered Flag Brewery and Still Works Middletown

Thistle Finch Distilling LancasterFood Production Facilities

Advanced Food Products, llc New HollandASK Foods Palmyra

Dutch Valley Food Development, Inc MyerstownLancaster Fine Foods Lancaster

Philadelphia Macaroni Company HarrisburgWinter Gardens Quality Foods, Inc New Oxford

Slaughterhouse/MeatpackingBrother and Sister Food Services Harrisburg

Empire Poultry MifflintownKessler Foods LemoyneSME Foods York

Keystone Protein FredericksburgFarmers Pride, INC. Fredericksburg

Vantage Foods Camp HillFresh Vegetable Packaging

Fresh Express HarrisburgSnack Food Processing

Dieffenbach's Potato Chips WomelsdorfGood's Potato Chips Adamstown

Hartley's Chips LewistownHerr's Potato Chips Nottingham

Martin's Potato Chips LancasterMiddleswarth Potato Chips Middleburg

Snyders-Lance (Hanover Manufacturing) Hanover


Appendix 2. Survey Approach

The following questions were used in interviewing potential HSW producers. Initial contact wasmade by phone, and subsequent interviewing was completed via email.

1. Facility Background Information:a. Facility Information:

i. Nameii. Address

iii. Product(s) producediv. Plant Size (no. of employees/volume of product produced)

b. Contact Information:i. Name

ii. Positioniii. Phone numberiv. Email address

c. Does your company have a corporate environmental officer? Does each facilityhave a facility environmental officer? Who makes decisions about managing by-products from each facility?

i. Nameii. Phone number

iii. Email addressd. Are you familiar with co-digestion of municipal wastewater solids with other

commercial and industrial by-products to generate biogas?e. What industry organizations and/or associations does your facility participate in?

2. Waste streams Generateda. What types of wastewater generated:

i. Cleaning Activities / CIPii. Out-of-Spec Product

iii. Treatment side streams (i.e., DAF)iv. High strength waste streams (i.e., concentrated by-products)v. Solids (3% to 15% TS)

vi. Raw Productsvii. Other

b. Timing of waste stream generation (throughout typical shift)c. Volume of each type of wastewater is generated:

i. Dailyii. Weekly

iii. Monthlyiv. Annually


d. Are there seasonal variations in production?i. Explain

e. What are the characteristics for each waste stream (if known or available):i. BOD5

ii. CODiii. TSSiv. TVSv. TS

vi. Non-Petroleum O&Gvii. pH

viii. Brix

3. Current Handling Practicesa. Discharge to Local Sewer System

i. Pretreatment (Yes or No):1. What is treatment process2. What age/condition is the pretreatment facility3. What are discharge limits? Surcharge range?

a. Any upcoming new limits?4. What are high strength wastewater surcharge rates5. Other hauled out residuals?

b. Direct Discharge to Receiving Watersi. What is treatment process

ii. What age/condition is the treatment facilityiii. What are discharge limits?

1. Any upcoming new limits?iv. Other hauled out residuals?

c. Hauled Outi. Characteristics and volumes

ii. Hauler nameiii. Receiving Facilityiv. Hauling fee

1. Mileage portion2. Non-mileage portion (overhead)3. Tipping fee portion

v. Who makes decision on where hauled waste goes? (hauler or generator)d. Who makes decisions about residual waste treatment and/or final disposition?

i. Plant managerii. Corporate personnel

e. What factors are considered when determining how by-products will be managed?(Rate 1 to 5, 5 is big factor)

i. Costsii. Reliability


iii. Environmental impactiv. Other

f. What price point would you go from current provider to Harrisburg?

4. Current End Use and/or Disposal Practicesa. What is the final disposition of each waste stream?

i. Municipal WWTP or centralized waste treatment facilityii. Landfill

iii. Beneficial Use1. Type?2. Price?

b. What is the biggest challenge you face with the current waste treatment systemand/or disposition method?

i. Cost – capital and/or O&Mii. Reliability

iii. Operation5. Who decides where to go with waste? Hauler or industrial facility?



Appendices | 77


TM-6 Dewatering


August 2017 1 Whitman, Requardt & Associates, LLPN:\14342-001\Engineering\Design\Biosolids Facilities Imp Plan Tech Memos\Final\TM06 - Dewatering.docx




SUBJECT: Dewatering



Distribution:

Date: June 21, 2017


CONTENTS

I. INTRODUCTION

II. EXISTING BELT FILTER PRESS

III. PROCESS IMPROVEMENTS

IV. FUTURE DEWATERING REQUIREMENTS

V. ALTERNATIVES FOR FUTURE DEWATERING

VI. SUMMARY

ATTACHMENTS:

1.) N/A

REFERENCE DRAWINGS:

1.) N/A



I. INTRODUCTION

See Technical Memorandum No. 1 for a description of the Harrisburg AWTF and the overallbiosolids process. Technical Memorandum No. 6 provides summary design information regardingthe dewatering of digested biosolids at the AWTF.

Digested sludge flows by gravity through two separate pipelines with in-line sludge grinders, andthen is pumped to belt filter press with hose pumps. Polymer is added through a ring injector,which is upstream of a mixing valve. The sludge is then fed to the gravity section of the belt filterpresses.

The two (2) in-line sludge grinders break down larger solids, and replace the function of the in-line grinder pumps in the digested sludge pumping station. Discharges from the three (3) belt filterpress hose pumps can be directed to either of the two (2) 2.5 meter wide belt filter presses.

The polymers used in the dewatering process are received as a powdered solid, delivered insupersaks. The polymer supersak is placed on a skid, from which polymer is metered by a screwconveyor into a pneumatic line that pushes it into a 3,300 gallon fiberglass polymer mix tank.Water is added to the polymer and the contents are mixed. Once the polymer is conditioned, it ispumped by two (2) progressing cavity pumps to a storage/feed tank, also a 3,300 gallon fiberglasstank. The polymer solution is then pumped into an injection ring located on each feed pumppipeline which feeds the conditioned sludge to each belt filter press.

During the dewatering process, following discharge of the dewatered cake, the press belts arewashed with spray water. A wash water skid equipped with three (3) booster pumps provides thepressure to adequately wash the belts.

The cake is discharged from the belt filter press onto a ribbed belt conveyor which conveys thecake into a dump truck which transports it to a covered storage area. Table 6-1 summarizes theprocess criteria for the existing belt filter presses.

Dewatered cake produced by the belt filter presses has averaged more than 21% solids for the pastthree years, but the performance has been inconsistent. The monthly average cake solids was below20% for 7 months in 2016, and for all of the first 6 months of 2017. The dewatered cake cannot bestored for more than 10 days at the land application sites if it is less than 20% solids. When thecovered storage area is full, the biosolids are disposed of at a landfill. As an extension of theBiosolids Facilities Improvement Plan, a study of the dewatering of biosolids and the belt filterpress operation is being pursued. The study will be included as an appendix in the Final FacilitiesImprovement Plan.

II. Existing Belt Filter Presses

Belt Filter Press Condition

The existing belt filter presses were installed in 2011 and are in good physical and operatingcondition.



The ancillary equipment for the belt filter presses includes:· Polymer handling equipment· Polymer make down tanks and storage tanks· Digested sludge in-line grinders· BFP wash water booster pumps· BFP feed pumps.

The ancillary equipment is also in good physical and operating condition.

Belt Filter Press Capacity

The design criteria for the existing belt filter presses is presented in Table 6-1.

Table 6-1. Existing Belt Filter PressDesign Criteria


Manufacturer Ashbrook Simon-Hartley

Type Dual belt

Effective Belt Width 2.5 meters

Solids Loading Rate 2,000 lbs dry solids/hr, each4,000 lbs dry solids/hr, total

Feed Solids Content 2 - 6%

Runtime, both in operation 16 hours a day, 7 days a week

Capacity 32,000 lbs dry solids/day each64,000 lbs dry solids/day total

Information on the digested sludge at the facilities improvement plan digester capacity at a plantflow of 37.7 MGD, and the resulting belt filter press capacity are in Table 6-2.



Table 6-2. Belt Filter PressEstimated Required Capacity@ Plant Design Flow (37.7 MGD)

Digested Sludge atDigester Capacity 52,000 lbs TSS/day

Digested Sludge Volume atDigester Capacity 150,000 – 200,000 gallons per day

Digested Sludge, PercentSolids1 3 - 4 %

Solids Loading Rate 2,000 lbs dry solids/hr, each4,000 lbs dry solids/hr, total

Volumetric Loading Rate 75 – 110 gpm, each150 – 220 gpm, total

Runtime, both in operation 13 hours a day, 7 days a week

1 With separate WAS and primary sludge thickening to 5-6 % solids and average hauled waste 5-6% solids

Based on Table 6-2, the two existing belt filter presses have sufficient capacity to dewater thefuture quantity of sludge projected by the facilities improvement plan. Each belt filter press wouldbe operated more than 12 hours a day, 7 days a week, which does not allow for redundancy in thedewatering system when approaching the quantity of solids projected by the facilities improvementplan. Therefore, if one belt filter press were to be taken offline for more than 2-3 days, a rentaldewatering unit would be needed to dewater the projected sludge quantity.

The belt filter presses and the ancillary equipment have sufficient capacity, and are expected toprovide reliable service for their intended purpose for at least the next ten years.

III. Process Improvements

As mentioned above, the AWTF has intermittently produced dewatered biosolids at less than 20%cake solids which limits the dewatered biosolids storage options. There are many factors thatinfluence dewatering of biosolids, and contribute to the cake solids produced. Of these factors,some are within the control of the AWTF, and others are not. Some factors cannot be significantlyimproved until the addition of new processes and/or rehabilitation of existing facilities arecomplete. Those within the control of the AWTF include the following:

1.) Polymer conditioning2.) Digested sludge degree of stabilization3.) Digested sludge characteristics4.) Belt filter press condition and operation



The dewatering study portion of the Facilities Improvement Plan will review the existing belt filterpress operation. The goal of the study is to make recommendations to modify operation of the beltfilter presses, and possibly other aspects of the AWTF, to reliably maintain cake solids greater than20%. The study will also consider the effects the anticipated hauled waste will have on thedewaterability of the digested solids.

Polymer Conditioning

The dewatering study will include an evaluation of the chemical conditioning (i.e. polymeraddition) of the sludge. Technical support from the current polymer supplier will be engaged toevaluate polymer make down procedures, polymer dosing rates, location of the polymer injectionpoint and alternate polymers to determine what improvements could be made.

Digested Sludge Degree of Stabilization

The digestion process is affected by many factors including sludge characteristics and feed rate,mixing, temperature setpoint and variation in temperature, and solids retention time. A greaterdegree of biosolids digestion generally results in improved dewaterability. The planned digesterimprovements including mixing, heating, piping and pump replacement will result in improveddigestion efficiency.

Digested Sludge Characteristics

The cake solids will also be positively impacted by maintaining the digester temperature relativelyconstant at about 98ºF. Current variations in temperature are largely caused by rag buildup in thepiping and heat exchanger. The planned influent screening facility will reduce the amount of ragsin the sludge.

The recommendation to separately thicken primary sludge and WAS to increase the solidsconcentration of each, will result in a longer solids retention time, improving the degree ofdigestion. In addition, the digested sludge solids concentration and degree of stabilization will alsoincrease, and in turn positively impact the dewatered cake solids.

Belt Filter Press Condition and Operation

The belt filter press operation will also be evaluated including an inspection of the condition of thebelts, and testing of the belt tension and speeds. A review of the maintenance records of the beltfilter presses will identify if any maintenance items are overdue.

The feed rate to the belt filter press will also affect the cake solids, with higher feed rates negativelyimpacting the cake solids.

Summary of Belt Filter Press Improvements

Some of the belt filter press improvements and adjustments discussed in this section can be



implemented more rapidly than others. In addition, some will have a larger impact on dewateringcake solids than others. The polymer investigation and adjustment could be one of the first steps,and may provide a significant benefit. That would allow time for the remainder of theimprovements and adjustments above to be implemented and allow the belt filter presses to providethe required cake solids.

It is also recognized that depending on timing of the implementation and the actual results of theimprovements and in light of possible future dewatering requirements discussed in Section IV,other dewatering technologies may need to be investigated.

Sludge Pretreatment

In addition to thickening, digester and belt filter press improvements, sludge pretreatment couldbe investigated as another means of improving dewatered cake solids. Biosolids trap a portion ofwater within the cells of the microbes, and between the mesh of microbes and inert materials.Pretreatment is intended to release water, either or both, within the cells (primarily WAS) andbetween particles to improve dewatered cake solids. Although there are many research papersdescribing methods of pretreatment of biosolids for improved dewatering, including elevatedtemperature or pressure, ultrasound, and chemical, there are very few full scale applications.

The SLG process as manufactured by Orege has an installation in the Lehigh County AuthorityPretreatment WWTP in Pennsylvania. In the SLG process compressed air is combined with thesludge in a pressure vessel. When the sludge leaves the pressure vessel through a pressure reducingvalve the rapid change in pressure introduces small air bubbles into the sludge which provide apath for the interstitial water to drain out.

Pilot testing would be recommended prior to further evaluation of any technologies that are to beconsidered.

IV. Future Dewatering Requirements

Local biosolids regulations are likely to become more stringent in the foreseeable future, i.e., 5-10year timeframe. There may be more reporting requirements, a higher quality of biosolids requiredfor land application, and restrictions on land available for application. While these changes inregulations are developed and finalized, the best course of action is to continue utilizing theexisting belt filter presses.

As more stringent biosolids disposal regulations become imminent, the production of Class Abiosolids should be considered. To achieve Class A quality, the biosolids must undergo one of theEnvironmental Protection Agency (EPA) approved treatment methods. One of the commonmethods for producing Class A biosolids involves heat drying the dewatered cake to greater than90% solids. Even though significant energy (digester gas) will be required, an evaluation includingcost savings in disposal, i.e., through beneficial reuse instead of landfilling, and heat recovery, willshow benefits in heat drying.

The higher the percent solids in the dewatered cake, the less heat energy that must be used to dry



the cake. In fact, the capital and higher operating costs of new dewatering equipment canpotentially be fully offset by subsequent fuel savings in the heat drying operation.

Class A biosolids must be treated to further reduce pathogen levels beyond the requirements ofClass B biosolids. This is one of the reasons they have few restrictions on where they can be landapplied. Allowable disposal areas include publically accessible and residential lands. Heat dryingalso reduces transportation costs.

V. Alternatives for Future Dewatering

Depending on future regulations, the characteristics and volume of hauled waste, and many otherfactors, there may be need in the future to consider other dewatering technologies. This sectionbriefly discusses currently available dewatering technologies that claim consistent biosolids cakedewatered to above 20% solids, including:

· Plate and Frame Filter· Centrifuge· Screw Press· Volute Dewatering Press· Rotary Press

Other than the centrifuge, pilot testing would be highly recommended to confirm actual averagepercent solids performance at AWTF. The plate and frame filter is a batch process, is capitalintensive, has a large footprint and some plants have experienced operational difficulties.Therefore, it is not included for further consideration.

Centrifuge

The centrifuge is widely utilized in dewatering biosolids, with high cake solids and highthroughput as major advantages over most other technologies.

Figure 6-1. Cutaway View of Biosolids Dewatering CentrifugeCredit: Centrisys

Compared to the other technologies below, the disadvantages of the centrifuge include:



· High energy consumption· High capital and maintenance cost· Specialized maintenance skills

Screw Press and Volute Dewatering Press

The screw press and volute dewatering press are similar in overall configuration, with a centerconveying screw pushing the solids that are larger than the openings in the dewatering drumtowards the discharge end. See Figure 6-2 for a typical screw press, and Figure 6-3 for a volutedewatering press. The screw press uses a static perforated, or slotted drum which separates thesolids. The volute press utilizes the annular space between donut shaped plates to separate out thesolids. The screw and volute press both have low capital costs and low energy consumption.

Both the screw and volute press require sufficient space within the building for the removal of theconveyor screw. The existing belt filter press room is therefore unlikely to be compatible witheither technology.

The volute dewatering press has relatively few installations in the United States, but has fewermoving parts than the belt filter press or screw press which should translate to lower maintenancecosts.

Figure 6-2. Screw PressCredit: Schwing Bioset, Inc.



Figure 6-3. Volute Dewatering PressCredit: Process Wastewater Technologies, LLC

Rotary Press

The rotary press utilizes two vertically oriented plates with slotted openings, see Figure 6-4 for ageneral arrangement of a six channel rotary press. Flocculated biosolids are pumped in betweenthe plates which separates the solids from the filtrate. The slow rotation speed of the plates providesfriction to restrict the solids movement and provides compression of the solids cake to control thecake solids. The rotary press has a lower throughput than the screw press or belt filter press andtherefore requires more floor space. The room where the existing belt filter presses are located maynot be large enough for the required rotary presses, so that aspect would require evaluation.



Figure 6-4. Six Channel Rotary PressCredit: Fournier Industries

V. Summary

The existing belt filter presses have adequate capacity for the anticipated sludge production for theplanning period considered. They will likely require improvements, as discussed in Section III, toconsistently provide the 20% biosolids cake solids required. Depending on the results from theshort-term belt filter press operational and polymer modifications discussed above, the piloting ofthe Orege process would be a suggested next step.

The implementation of the thickening improvements and digester improvements discussed inSection III will further improve cake solids. It is therefore recommended to proceed with theseimprovements, including polymer conditioning modifications, and consider the replacement of thebelt filter presses only when future conditions dictate it.

When future regulations for higher cake solids, or further restrictions on Class B land application,force the landfilling of Class B biosolids, the overall case for producing Class A biosolids will bestrengthened. At that time the move to heat drying the biosolids to generate Class A biosolidswould be beneficial. Upgrading of the dewatering process to another technology capable ofproducing a drier cake to feed the drying process should be considered.



Appendices | 78


TM-7 Biogas Utilization


August 2017 1 Whitman, Requardt & Associates, LLPN:\14342-001\Engineering\Design\Biosolids Facilities Imp Plan Tech Memos\Final\TM07 - Biogas Utilization.docx




SUBJECT: Biogas Utilization

Prepared by: D. Nixson, N. Cohen


Distribution:

Date: June 22, 2017


CONTENTS

I. INTRODUCTION

II. EXISTING BIOGAS SYSTEM

III. BIOGAS PROJECTIONS

IV. ALTERNATIVES FOR BIOGAS UTILIZATION

V. PRELIMINARY COST ANALYSIS

VI. SUMMARY

ATTACHMENTS:

1.) N/A

REFERENCE DRAWINGS:

1.) N/A



I. Introduction

See Technical Memorandum No. 1 for a description of the Harrisburg AWTF and the overallbiosolids process. Technical Memorandum No. 7 provides summary design information regardingthe utilization of the biogas generated from the anaerobic digestion of biosolids at the AWTF.

There are several potential beneficial uses for biogas including the following:

A.) Combust the biogas and recover the heat and kinetic energy, e.g., combined orseparate heat and power generation

B.) Use a fuel cell to generate electricity and heatC.) Off-site use of the biogas, e.g., as natural gas substituteD.) Use as fuel to heat the digestersE.) Use as fuel for heat drying biosolids

AWTF is currently utilizing a hybrid heat and power generation, with partial recovery of heatfrom the engine driven generator, and the use of separate boilers for additional heat generationcapacity. By integrating the heat and power generation into a combined heat and power systemwould improve the overall energy efficiency. In combined heat and power all of the biogas isburned in the engine or turbine driven generator, and the heat for the digesters is supplied by thewaste heat generated by the engine.

A fuel cell can also be used in the generation of combined heat and power. Another alternative toconsider is the use of the biogas off-site, e.g., direct injection into natural gas pipeline, or use incompressed natural gas vehicles.

In any beneficial reuse alternative the biogas requires a certain level of pretreatment prior to use.In order of increasing pretreatment requirements is the internal combustion engine, turbine, fuelcell and then off site use.

II. Existing Biogas System

The digester gas is routed through the pipe tunnels, through the Digested Sludge Pump Station,then compressed in the Gas Compressor Building and stored in a spherical tank. The tank has apressure relief valve to avoid damage to the tank. Excess gas is burned off at an adjacent groundlevel flare. Tables 7-1, 7-2, 7-3 and 7-4 summarize gas collection, usage, and storage equipment.



Table 7-1. Existing Low PressureGas Compressors

Units 2

Manufacturer Spencer Turbine, Co.

Size 4 x 4 inches

OutputPressure 15.71 psia

Capacity,each 240 cfm

Table 7-2. Existing Gas Purifier

Units 2

Manufacturer Varec, Inc

Type Iron Sponge

TreatmentVolume 40 cubic feet

Capacity 45,000 standard cubic feet per day

PressureDrop 0.5 inches of water column



Table 7-3. Existing High PressureGas Compressors

Units 2

Manufacturer Ingersoll-Rand

Type Single Stage, Double Acting

DischargePressure 50 psig

Capacity 80 Actual cubic feet per minute

Table 7-4. Existing Storage Tank

Units 1

Manufacturer Pittsburgh-DesMoines Steel Co.

Size 42 feet diameter

Pressure,Maximum 50 psig

Capacity 38,793 cubic feet

Digester gas is burned in two (2) boilers to provide hot water for heating the primary digesters,and space heating buildings. The boilers can also be fired with fuel oil, but there has been sufficientdigester gas for many years. Information on the boilers follows. Table 7-5 summarizes the boilers.



Digester gas is also used to power two (2) internal combustion engine driven electric powergenerators. The power generated is put onto the utility grid. Prior to combustion, the digester gasis filtered by a condensing filter to remove condensable water vapor from the gas. The enginecooling is performed with roof mounted radiators, with closed loop circulation back to the engineblocks. Table 7-6 summarizes equipment in the cogeneration facility.

Table 7-5. Existing Boilers

Units 2

Manufacturer Weil-McLain

Fuel Biogas#2 Fuel Oil

Biogasconsumption 12,833 cfh @ 28 inches W.C.

Capacity,each

6,391,141 Btu/hr

Table 7-6. Existing Engine Drive Generators

Units 2

Manufacturer Waukesha

Fuel Biogas

GeneratorOutput, each 400 kW

ElectricGenerated 480 V 3 phase 60 Hz 4 wire

Feed GasRequirements 500 BTU/cu ft at 25 psig



III. Biogas Projections

Summary information on the existing digester performance and resulting biogas generation isprovided in Table 7-7.

Table 7-7. Existing Gas Generation1

TSS in DigesterFeed 38,100 lbs/day

VS in DigesterFeed 23,700 lbs/day

VS Destroyed inDigesters 11,300 lbs/day

VS Destruction /Fed Ratio 0.48

Digester GasProduced 134,000 cfd

Gas Produced 11.9 cf biogas per lb of VS destroyed

1 Average values for May 2016 to June 2017, i.e., after BNR Upgrade Start Up

The ratio of gas produced to pounds of volatile solids fed is below that typically found in municipalanaerobic digestion. This is likely due to the operational concerns discussed in TechnicalMemorandum No. 4 – Anaerobic Digester including thickened sludge low solids concentrationand its effect on solids retention time, incomplete mixing, and temperature control due to vivianitebuildup. Once the currently planned primary digester upgrades are completed, digesterperformance will improve. Implementing other improvements described in the Biosolids FacilitiesImprovement Plan will also improve performance and result in more typical biogas productionrates.

In addition to improving the digester performance, the introduction of carefully selected highstrength hauled waste is intended to not only increase the total gas produced, but also to improvebiogas generated per pound of volatile solids destroyed in the digester. Regardless, the FacilitiesImprovement Plan will utilize a conservative biogas production rate more typical of a welloperating anaerobic digester.

Summary information on the anaerobic digester design capacity and resulting biogas generation is



provided in Table 7-8.

Table 7-8. Projected Gas Generationat Facilities Plan Digester CapacityTSS inDigesterFeed

76,900 lbs/day

VS inDigesterFeed

61,000 lbs/day

VS Fed/DestructionRatio

0.50

VSDestroyed inDigesters

30,500 lbs/day

GasProduced 13.0 cf biogas per lb of VS destroyed

Digester GasProduced 397,000 cfd

IV. Alternatives For Biogas Utilization

Biogas is a product from anaerobic digestion that has traditionally been under-utilized. One methodfor improving the energy recovered from biogas is to use it as a fuel source utilizing a combinedheat and power (CHP) technology. CHP systems convert the biogas into electricity and recover theheat generated in the process. The heat can then be used to maintain optimal digester temperaturesand/or space heating buildings. Although other technologies exist, two promising CHPtechnologies that will be evaluated for the AWTF, are fuel cells and reciprocating engine drivengenerators.

Fuel Cells

Of the two, fuel cells are newer and less prevalent. Fuel cells use an electrochemical process toconvert hydrogen from hydrocarbons, such as methane, into electricity. As of 2015, there are 126fuel cells in the United States, with a combined capacity of 67 MW. The average installed fuel cellhas a capacity of 532 kW. The thermal energy from the fuel cells can be recovered and used forheating demands.

The fuel cell is made up of three primary structures: fuel cell stack, fuel processor, and powerconditioner. The cell stack generates the direct current electricity which is then used in the fuelprocessor to convert the fuel into a hydrogen-rich feed stream and finally the power conditioner



processes the direct current electric into alternating current. There are several types of fuel cellswhich have been used for CHP, including phosphoric acid (PAFC), molten carbonate (MCFC),solid oxide (SOFC), and proton exchange membrane (PEMFC).

Fuel cells are known for achieving high efficiency levels and generating constant power whensupplied an uninterrupted supply of biogas. Fuel cells typically have a power to heat ratio of 1.26,which is advantageous for systems that require more electricity than heat. Another advantage of afuel cell is the low emissions of carbon dioxide (CO2) and even lower emissions of oxides ofnitrogen (NOx). Fuel cells can produce CO2 emissions ranging from 555 to 729 lbs/MWh, whereasa typical natural gas combined cycle power plant will produce 800-999 lbs/MWh. Besides less airpollution, fuel cells also do not create any noise.

Currently fuel cells have a higher capital cost per kWh than internal combustion technologies. Afuel cell can have an installed cost ranging from $4,600 to $10,000/kWh. While fuel cells are fairlyreliable, 90-95%, they do require periodic replacement and maintenance of their catalysts and fuelcell stacks. Fuel cells also have slow start times, 3 hours – 2 days.

Reciprocating Engines

Another option that utilizes CHP are reciprocating engines. As of 2015, there are nearly 2,400reciprocating engine based CHP systems in the United States. Reciprocating engines are availablein sizes ranging from 10 kW to 10 MW. There are two designs for reciprocating engines: sparkignition Otto-cycle engines and compression ignition Diesel-cycle engines. The two designs aremechanically the same, but differ on the method of fuel ignition. Spark ignition uses a spark plugto ignite a pre-mixed air fuel mixture and for CHP most reciprocating engines use a 4-stroke sparkignition. Further, reciprocating engines are usually characterized as either rich-burn or lean-burn.Rich-burn engines operate near the stoichiometric air/fuel ratio, thus air and fuel quantities resultin complete combustion, with little excess air. Lean-burn engines run at significantly higher levelsthan the stoichiometric ratio.

Reciprocating engines have electric efficiencies that are not as high as fuel cells, ranging from 25-50% (LHV). The installation cost and maintenance cost is lower for reciprocating engines.Reciprocating engines, with proper maintenance, can be available 90-96% of the time, with a 60second start-up time.

Rich-burn reciprocating engines have a power to heat ratio of approximately 0.62 and lean-burnengines have a ratio of 0.86, which compared to the fuel cell’s ratio of 1.26, reciprocating enginesrespectively produce more heat than electricity. One of the most significant differences betweenthe two CHP technologies is the emissions of criteria pollutants. Reciprocating engines emitsignificant amounts of NOx, carbon monoxide (CO), and volatile organic compounds (VOCs).

Biogas Pretreatment

Biogas pretreatment is another component that must be analyzed in relation to CHP technologies.Depending on the technology, the biogas has to be treated in order to remove certain elements thatcan negatively impact the technology’s performance. Also pretreating the biogas can increase its



heating value. Biogas from digesters is typically pretreated to remove solid particulates, siloxanes,hydrogen sulfide (H2S), and water vapor. The presence of water in biogas is desirable forcombustion devices and fuel cells, by contributing to lower NOx emissions in the former and isused for stream reforming of methane in the latter. However, when H2S and water vapor react theyform sulfuric acid, which is very corrosive to engines. Thus for either technology, the biogas canbe cooled in a heat exchanger in order to remove water vapor. This is a more importantpretreatment step for fuel cells than reciprocating engines.

For both CHP technologies, it is essential to remove H2S. The most common hydrogen sulfideremoval method is adsorption (i.e., scrubbing) using a hydrated ferric oxide or other catalyticmedia. A gas analysis would need to be conducted to determine whether a two-stage sulfur removalsystem is needed. For fuel cells it’s important to also remove carbon dioxide (CO2) thus usingslaked lime (Ca(OH)2) as an absorption media is ideal as it removes both CO2 and H2S.

The term siloxanes refers to a series of volatile organic compounds. When siloxanes oxidize theyform silica (SiO2), which can deposit on surfaces, and is particularly dangerous to high temperaturefuel cells as it can fill the anode’s porous structure. The most common method for siloxane removalis adsorption using active carbon or silica gels. The media can be regenerated through temperatureswing adsorption (TSA) or pressure swing adsorption (PSA). The removal of siloxanes shouldoccur downstream of the H2S and water vapor removal methods.

In general, reciprocating engines need an H2S pretreatment removal, while fuel cells require fulltreatment (i.e., removal of water vapor, CO2, and trace elements).

Natural Gas Pipeline Injection

Another alternative for beneficial use of biogas is injecting it into a utility’s natural gas pipeline.However, this process requires an advanced biogas upgrading system and, as seen in Figure 1,selling biogas as a renewable natural gas, is not as valuable when compared to electricity, however,the price is more consistent over time. The capital investment for natural gas pipeline injection canbe less than a combined heat and power system. A heat source for the primary digesters would stillbe required if a CHP process is not utilized. A preliminary cost analysis is presented in Section Vto compare these alternatives.

Typically the biogas has to undergo treatment to remove contaminants and excessive CO2, anodorant has to be added, and finally be compressed and then sold to a local utility. It can also beused onsite as a vehicle fuel but this is very capital intensive. There is a water-wash technologyavailable through Greenlane biogas that is ideal for grid injection and requires no heat orchemicals. It removes H2S without pretreatment and has reliable compression technology.Essentially it combines all the steps and results in a product that is pipeline acceptable. Thecompany also claims ~99% energy available to pipeline from biogas produced. If the site requiresnatural gas, this would be a great option, however, selling treated biogas as a natural gassupplement compared to utilizing the biogas to generate electricity does not appear to beeconomically justified.



Figure 1: Historical Energy Costs Credit : Hazen 2017

In Figure 1, the potential revenue for biogas treated to natural gas (NG) pipeline quality is shownin light green (lowest on the chart). When natural gas is compressed sufficiently (i.e., 3,600 psi) itis referred to as compressed natural gas which is represented by the dark green line, andabbreviated as CNG.

V. Preliminary Cost Analysis

Typical municipal values for biogas were used to evaluate the two viable options discussed above,lean burn reciprocating engine driven generator, and fuel cell. The biogas design criteria, the actualcurrent prices for natural gas, and electricity sold to the utility are presented in Table 7-9.



Table 7-9. Biogas Utilization Design Criteria

MethaneContent 0.65 volume methane/volume biogas

DigesterHeatRequirement,Winter

40-50 degree F temperature rise, plus10% for heat losses

BiogasEnergyPotential1

600 BTU/ cubic foot

Natural Gas,Purchasedfrom Utility

$5.31 / 1000 cubic feet

Electricity,Sold toUtility

$0.07/kWh

1 Based on average lower heating value of biogas, Opportunities for Combined Heat and Power at Wastewater Treatment Facilities, October2011, US EPA

There are many established manufacturers of lean burn reciprocating engine driven generatorsutilized in combined heat and power systems. Most of the equipment manufacturers will team witha combined heat and power system integrator to design the system and supply the ancillaryequipment (e.g., pumps, heat exchangers, biogas pretreatment, etc.). Rather than performing aneconomic analysis based on a single manufacturer, we have utilized typical design parameters ascompiled by the US Environmental Protection Agency in their publication entitled Opportunitiesfor Combined Heat and Power at Wastewater Treatment Facilities, October 2011. Key designparameters are in Table 7-10.



Table 7-10. CHP Design Information1

Parameter UnitsLean BurnReciprocatingEngine Driven

Fuel Cell

ElectricEfficiency

BTU ElectricalOutput /BTU Combusted

0.33 0.42

Overall Heatand PowerEfficiency

BTU Recovered/BTU Combusted 0.71 0.76

Power to HeatRatio

BTU PowerOutput/ BTU HeatOutput

0.86 1.26

Capital Costs2 $/kW capacity $3,200 $5,500

MaintenanceCosts $/kWh 0.02 0.03

1 Based on averages, Opportunities for Combined Heat and Power at Wastewater Treatment Facilities, October 2011, US EPA2 Includes pretreatment equipment. Does not include any building or site improvements that may be required.

From Table 7-10, it can be seen that the fuel cell has a significantly higher energy conversionefficiency, and higher overall energy recovered efficiency than the lean burn reciprocatingengine. The capital costs and maintenance costs for fuel cells are higher than the lean burnreciprocating engine. These differences are discussed further in conjunction with Table 7-12below.

Based on the biogas generation at the facility improvement plan capacity (i.e., digester at fulldesign capacity) and the design information in Table Nos. 7-9 and 7-10, Table 7-11 contains theinformation regarding the capacity of the CHP system.



Table 7-11. CHP Capacity

Parameter,per day Units

Lean BurnReciprocatingEngine Driven

Fuel Cell

Biogas EnergyPotential BTU 238,000,000 238,000,000

EnergyProduced kWh 960 1,222

HeatRecovered BTU 90,500,000 81,000,000

Heat Deficit,Winter Only

Recovered minusBTU required byDigester Heat

-1,200,000 -10,700,000

A simple cost benefit analysis of the two types of CHP system is presented in Table 7-12. Thepurpose of this cost benefit analysis is not to determine the actual income AWTF can expect fromthe CHP, but to compare the two different technologies against one another. The analysis doesnot consider the time value of money, but instead uses a 20 year straight line depreciation of theinstalled capital costs. It also assumes biogas generation at full capacity beginning at start-up and100% utilization of the biogas.



Table 7-12. CHP Cost Benefit Analysis

Parameter UnitsLean BurnReciprocatingEngine Driven

Fuel Cell

Unit NominalSize kW 1,000 1,400

InstalledCapital Costs,CHPEquipment1

$ 4,000,000 9,600,000

InstalledCapital Costs,CHPEquipment2

$/year 200,000 481,000

ElectricGenerated kWh/day 960 1,222

Value ofElectric Sold toUtility

$/year 629,000 801,000

MaintenanceCosts $/year 168,000 320,000

Natural GasPurchased forDigesterHeating3

MBTU/year 106 964

Natural GasPurchased forDigesterHeating

$/year 600 5,200

Net Value ofElectricityGenerated

$/year 260,000 (5,000)

1 Includes a 25% contingency2 Uses a linear depreciation of capital costs over 20 year life for a per year cost3 Assumes 90 days a year need supplemental heating beyond what the CHP system generates

Based on the net value of the electricity generated in Table 7-12, the fuel cell based CHP is notappropriate for AWTF, and the lean burn reciprocating engine will provide an economic benefit.



VI. Summary

The use of a combined heat and power system will provide higher energy recovery efficiency thanthe existing separate system. Considering that both the existing boilers, and engine drivengenerators are beyond their expected life, investing in a combined heat and power system isrecommended. The reciprocating engine driven generator is well known to the AWTF operationsand is projected to provide an economic benefit to the facility. Therefore it is recommended thatthe AWTF plan to install a lean burn reciprocating engine based CHP system.

The amount of projected biogas is based on typical values for municipal biosolids anaerobicdigestion. This implies that the biogas generated from the anticipated hauled wastes will averageto similar values to that of the biosolids. In fact, the actual blend of hauled waste may varysignificantly over time, as will the ratio of hauled waste solids to biosolids. Therefore, the amountprojected biogas will have a large variation over time. Therefore the CHP system should bedesigned to provide for significant flexibility.

Manufacturer’s generally carry a nominally sized 500 kW continuous rated 3 phase 60 Hz biogasfueled generator. Considering redundancy and turn down flexibility, three (3) 500 kW units wouldbe recommended. Preliminary sizing based on catalog information would indicate that the threeunits could fit in the existing cogeneration building. Pretreatment equipment, and some of the heatrecovery equipment would be installed adjacent to, or on the roof of the building.

The 480V power that is provided by the generator is stepped up to medium voltage prior toconnecting to the utility power lines by a transformer. The existing transformer would need to bereplaced, as would the cables from the cogeneration building to the utility power lines.



Appendices | 79


Appendix B – Net Present Value Spreadsheets

AWTF Biosolids Improvement Plan

Simple Payback Methods 3/12/2018

Scenario Incremental Capital Annual Benefit1Simple Rate of Return Years to Payback

Base Case 15,470,010$ 892,166$ 5.8% 17

30% HW 5,910,100$ 529,491$ 9.0% 11

Without HW -$ 276,964$ N/A N/A

1 Annual Benefit = First Year Revenue from Electric generated + Offset of purchase of Nat Gas for

heating + tipping revenue - HW disposal costs - Maintenance and Operating Costs (2.2% of Incremental Capital)

Scenario Incremental Capital NPV

Base Case 15,470,010$ 1,100,000$

30% HW 5,910,100$ 6,000,000$

Without HW -$ 5,500,000$

N:\14342-001\Engineering\Cost_Est

NPV (25 Year Project Life)

Decrease

Elec. Cost

Increase

Hauling Cost

by 20% by 15%

BASE CASE 1,100,000$ (900,000)$ 3,740,000$ 6,300,000$ (900,000)$ 2,900,000$ (300,000)$

30%

HAULED

WASTE

6,000,000$ 4,700,000$ 7,000,000$ 9,900,000$ 4,500,000$ 7,200,000$ 5,300,000$

NO HAULED

WASTE5,500,000$ N/A N/A 7,500,000$ 4,700,000$ 6,200,000$ N/A

Incremental

Capital

Annual

Benefit

Simple Rate

of Return

Years to

Payback

Increase

Capital by 20%18,564,012$ 824,098$ 4% 23

Decrease Elec

by 20%15,470,010$ 757,956$ 5% 20

Increase Elec.

By 15%15,470,010$ 1,227,691$ 8% 13

Increase

Capital by 20%7,092,120$ 503,486$ 7% 14

Decrease Elec.

By 20%5,910,100$ 447,866$ 8% 13

Increase Elec.

By 15%5,910,100$ 733,551$ 12% 8


Base Case

30% HW

Decrease

Capital by 15%

Increase

Capital by

20%

Increase

Elec. Cost by

15%

Increase Gas

Cost by 50%

Summary NPV for Scenarios

Scenario

SCENARIO Baseline

Net Present Value Base Case

Client: Capital Region Water Electricity Generated ($/kWh) 0.06964

Project: Biosolids Facilities Improvement Plan Tipping Fee ($/1000 gallons) 40

NPV Scenario: Base Case - Digester and HW at AD Capacity Discount Rate 3.00%

Last Modified: 3/12/2018 Hauling Cost ($/wet ton) 33

Maintenance and Operating Cost Rate 2.20%

2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034

Digester Capacity (lbs VS/day) 37,000 37,000 37,000 37,000 37,000 37,000 37,000 37,000 61,000 61,000 61,000 61,000 61,000 61,000 61,000 61,000

AWTF Biosolids Generated (lbs VS/day) 24,000 24,240 24,482 24,727 24,974 25,224 25,476 25,731 25,989 26,248 26,511 26,776 27,044 27,314 27,587 27,863

Available Capacity for HW (lbs VS/day)1

11,150 10,910 10,668 10,423 10,176 9,926 9,674 9,419 31,961 31,702 31,439 31,174 30,906 30,636 30,363 30,087

Received HW (lbs VS/day) 11,150 10,910 10,668 10,423 10,176 9,926 9,674 9,419 31,961 31,702 31,439 31,174 30,906 30,636 30,363 30,087

Received HW (gallons/day) 26,739 26,163 25,582 24,995 24,402 23,803 23,198 22,587 76,646 76,023 75,393 74,758 74,116 73,467 72,812 72,150

Biogas Produced (cf/day) 222,000 222,000 222,000 222,000 222,000 222,000 222,000 222,000 397,000 397,000 397,000 397,000 397,000 397,000 397,000 397,000

Electricity Generated (kWh) 615 615 615 615 615 615 615 615 1,100 1,100 1,100 1,100 1,100 1,100 1,100 1,100

Construction Costs ($) - - - - - (5,910,010) (9,560,000) - - - - - - - - -

Electricity Revenue ($) 375,247.68 375,248 375,248 375,248 375,248 375,248 375,248 375,248 671,051 671,051 671,051 671,051 671,051 671,051 671,051 671,051

Offset Cost of Heating Digest.&Bldgs ($) 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124

HW Sludge Hauling Costs3

(259,447) (253,862) (248,222) (242,525) (236,771) (230,960) (225,091) (219,163) (743,703) (737,656) (731,548) (725,379) (719,149) (712,856) (706,500) (700,081)

Maintenance and Operating Costs ($) - - - - - - (130,020) (340,340) (340,340) (340,340) (340,340) (340,340) (340,340) (340,340) (340,340) (340,340)

Tipping Revenue ($) 390,384 381,981 373,494 364,922 356,265 347,521 338,689 329,769 1,119,034 1,109,934 1,100,744 1,091,462 1,082,088 1,072,619 1,063,056 1,053,397

Total 692,309 689,490 686,644 683,769 680,865 (5,232,078) (9,015,050) 331,638 892,166 889,114 886,031 882,918 879,774 876,598 873,390 870,151

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 692,309 669,408 647,228 625,745 604,940 (4,513,236) (7,549,962) 269,652 704,284 681,432 659,291 637,839 617,056 596,921 577,414 558,517

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044

Digester Capacity (lbs VS/day) 61,000 61,000 61,000 61,000 61,000 61,000 61,000 61,000 61,000 61,000

AWTF Biosolids Generated (lbs VS/day) 28,142 28,423 28,708 28,995 29,285 29,577 29,873 30,172 30,474 30,778

Available Capacity for HW (lbs VS/day)129,808 29,527 29,242 28,955 28,665 28,373 28,077 27,778 27,476 27,172

Received HW (lbs VS/day) 29,808 29,527 29,242 28,955 28,665 28,373 28,077 27,778 27,476 27,172

Received HW (gallons/day) 71,482 70,807 70,126 69,437 68,742 68,040 67,331 66,614 65,891 65,160

Biogas Produced (cf/day) 397,000 397,000 397,000 397,000 397,000 397,000 397,000 397,000 397,000 397,000

Electricity Generated (kWh) 1,100 1,100 1,100 1,100 1,100 1,100 1,100 1,100 1,100 1,100

Construction Costs ($) - - - - - - - - - -

Electricity Revenue ($) 671,051 671,051 671,051 671,051 671,051 671,051 671,051 671,051 671,051 671,051

Offset Cost of Heating Digest.&Bldgs ($) 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124 186,124

HW Sludge Hauling Costs2(693,598) (687,049) (680,436) (673,756) (667,009) (660,195) (653,312) (646,361) (639,341) (632,250)

Maintenance Costs ($) (340,340) (340,340) (340,340) (340,340) (340,340) (340,340) (340,340) (340,340) (340,340) (340,340)

Tipping Revenue ($) 1,043,641 1,033,788 1,023,837 1,013,786 1,003,634 993,381 983,025 972,566 962,002 951,333

Total 866,879 863,574 860,236 856,865 853,460 850,021 846,548 843,040 839,496 835,918

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 540,210 522,476 505,298 488,658 472,540 456,928 441,807 427,161 412,977 399,239

Total NPV: 1,100,000

2020 Capital Costs = Phase 2 : WAS Thickening and Hauled Waste & Phase 3 : CHP

2024 Capital Costs = Phase 4 : Secondary Digester Upgrades

2025 Capital Costs = Phase 5 : Acid Phase Digester

2 Cost for hauling digested, dewatered hauled waste. Assumes 60% destruction of VS from HW and digested sludge is dewatered to 22% dry solids.


1 Spreadsheet assumes 95% utilization of the digester. All digester capacity beyond that required for AWTF biosolids is assumed to be filled with Hauled Waste.

Year

Year

Net Present Value Base Case: Capital Cost Increase 20%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034



Available Capacity for HW (lbs VS/day)111,150 10,910 33,468 33,223 32,976 32,726 32,474 32,219 31,961 31,702 31,439 31,174 30,906 30,636 30,363 30,087






Electricity Revenue ($) 375,248 375,248 375,248 375,248 375,248 375,248 375,248 375,248 671,051 671,051 671,051 671,051 671,051 671,051 671,051 671,051


HW Sludge Hauling Costs3(259,447) (253,862) (778,749) (773,052) (767,299) (761,488) (755,618) (749,690) (743,703) (737,656) (731,548) (725,379) (719,149) (712,856) (706,500) (700,081)


Tipping Revenue ($) 390,384 381,981 1,171,767 1,163,196 1,154,538 1,145,794 1,136,962 1,128,043 1,119,034 1,109,934 1,100,744 1,091,462 1,082,088 1,072,619 1,063,056 1,053,397

Total 692,309 689,490 954,390 951,515 948,611 (6,146,334) (10,685,308) 531,316 824,098 821,046 817,963 814,850 811,706 808,530 805,322 802,083

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 692,309 669,408 899,604 870,771 842,829 (5,301,882) (8,948,777) 432,009 650,550 629,263 608,642 588,665 569,314 550,570 532,413 514,826

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 1,043,641 1,033,788 1,023,837 1,013,786 1,003,634 993,381 983,025 972,566 962,002 951,333

Total 798,811 795,506 792,168 788,797 785,392 781,953 778,480 774,972 771,428 767,850

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 497,792 481,294 465,315 449,840 434,852 420,338 406,283 392,672 379,492 366,729

Total NPV: (900,000)






1 Spreadsheet assumes full utilization of the digester. All digester capacity beyond that required for AWTF biosolids is assumed to be filled with Hauled Waste.

Year

Year

Net Present Value Base Case: Capital Cost Decrease 15%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034













Tipping Revenue ($) 390,384 381,981 373,494 364,922 356,265 347,521 338,689 329,769 1,119,034 1,109,934 1,100,744 1,091,462 1,082,088 1,072,619 1,063,056 1,053,397

Total 692,309 689,490 686,644 683,769 680,865 (4,345,576) (7,561,547) 382,689 943,217 940,165 937,082 933,969 930,825 927,649 924,441 921,202

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 692,309 669,408 647,228 625,745 604,940 (3,748,532) (6,332,677) 311,161 744,584 720,558 697,277 674,719 652,862 631,684 611,165 591,284

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 1,043,641 1,033,788 1,023,837 1,013,786 1,003,634 993,381 983,025 972,566 962,002 951,333

Total 917,930 914,625 911,287 907,916 904,511 901,072 897,599 894,091 890,548 886,969

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 572,023 553,363 535,285 517,772 500,806 484,371 468,450 453,028 438,090 423,621








Year

Year

Net Present Value Base Case: Electricity Cost Increase 50%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034









Electricity Revenue ($) 562,871.53 562,872 562,872 562,872 562,872 562,872 562,872 562,872 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577




Tipping Revenue ($) 390,384 381,981 373,494 364,922 356,265 347,521 338,689 329,769 1,119,034 1,109,934 1,100,744 1,091,462 1,082,088 1,072,619 1,063,056 1,053,397

Total 879,933 877,114 874,268 871,393 868,489 (5,044,454) (8,827,426) 519,262 1,227,691 1,224,639 1,221,557 1,218,444 1,215,299 1,212,123 1,208,916 1,205,676

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 879,933 851,567 824,081 797,448 771,641 (4,351,390) (7,392,830) 422,208 969,151 938,584 908,953 880,230 852,386 825,397 799,236 773,878

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044









Electricity Revenue ($) 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577 1,006,577




Tipping Revenue ($) 1,043,641 1,033,788 1,023,837 1,013,786 1,003,634 993,381 983,025 972,566 962,002 951,333

Total 1,202,404 1,199,099 1,195,762 1,192,390 1,188,986 1,185,547 1,182,073 1,178,565 1,175,022 1,171,443

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 749,299 725,475 702,384 680,004 658,312 637,290 616,915 597,169 578,033 559,488








Year

Year

Net Present Value Base Case: Electricity Cost Decrease 20%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034













Tipping Revenue ($) 390,384 381,981 373,494 364,922 356,265 347,521 338,689 329,769 1,119,034 1,109,934 1,100,744 1,091,462 1,082,088 1,072,619 1,063,056 1,053,397

Total 617,259 614,441 611,594 608,719 605,816 (5,307,127) (9,090,100) 256,589 757,956 754,904 751,821 748,708 745,564 742,388 739,180 735,941

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 617,259 596,545 576,486 557,064 538,259 (4,577,975) (7,612,815) 208,630 598,337 578,571 559,426 540,883 522,923 505,530 488,685 472,372

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 1,043,641 1,033,788 1,023,837 1,013,786 1,003,634 993,381 983,025 972,566 962,002 951,333

Total 732,668 729,364 726,026 722,655 719,250 715,811 712,338 708,829 705,286 701,708

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 456,575 441,277 426,464 412,120 398,231 384,784 371,764 359,158 346,954 335,139








Year

Year

Net Present Value Base Case: Natural Gas Cost Increase 50%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034









Electricity Revenue ($) 375,247.68 375,248 375,247.68 375,248 375,248 375,248 375,248 375,248 671,051 671,051 671,051 671,051 671,051 671,051 671,051 671,051




Tipping Revenue ($) 390,383.69 381,981 373,494 364,922 356,265 347,521 338,689 329,769 1,119,034 1,109,934 1,100,744 1,091,462 1,082,088 1,072,619 1,063,056 1,053,397

Total 785,371 782,553 779,706 776,831 773,927 (5,139,016) (8,921,988) 424,700 985,228 982,176 979,093 975,980 972,836 969,660 966,452 963,213

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 785,371 759,760 734,948 710,910 687,624 (4,432,960) (7,472,025) 345,320 777,748 752,756 728,537 705,069 682,327 660,291 638,939 618,250

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 1,043,641 1,033,788 1,023,837 1,013,786 1,003,634 993,381 983,025 972,566 962,002 951,333

Total 959,941 956,636 953,298 949,927 946,522 943,083 939,610 936,102 932,558 928,980

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 598,203 578,780 559,962 541,730 524,066 506,954 490,375 474,315 458,757 443,686








Year

Year

Net Present Value Base Case, Increase Hauling 15%




Last Modified: 3/12/2018 Hauling Cost ($/wet ton) 37.95


2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034













Tipping Revenue ($) 390,384 381,981 373,494 364,922 356,265 347,521 338,689 329,769 1,119,034 1,109,934 1,100,744 1,091,462 1,082,088 1,072,619 1,063,056 1,053,397

Total 653,392 651,411 649,411 647,390 645,349 (5,266,722) (9,048,814) 298,764 780,610 778,466 776,299 774,111 771,902 769,670 767,415 765,139

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 653,392 632,438 612,132 592,454 573,385 (4,543,120) (7,578,239) 242,922 616,221 596,629 577,640 559,234 541,396 524,108 507,352 491,113

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 1,043,641 1,033,788 1,023,837 1,013,786 1,003,634 993,381 983,025 972,566 962,002 951,333

Total 762,839 760,517 758,171 755,802 753,409 750,992 748,551 746,085 743,595 741,080

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 475,376 460,125 445,345 431,023 417,144 403,695 390,663 378,035 365,800 353,944







1 Spreadsheet assumes 95% utilization of the digester. All digester capacity beyond that required for AWTF biosolids is assumed to be filled with Hauled Waste.

Year

Year

Net Present Value HW at 30% of Digester Feed



NPV Scenario: HW at 30% of Total Digester Feed Discount Rate 3%



2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034



Available Capacity for HW (lbs VS/day) 13,000 12,760 12,518 12,273 12,026 11,776 11,524 11,269 35,011 34,752 34,489 34,224 33,956 33,686 33,413 33,137

HW Limited to 30% of AD Feed1 (lbs VS/day) 10,286 10,389 10,492 10,597 10,703 10,810 10,918 11,028 11,138 11,249 11,362 11,475 11,590 11,706 11,823 11,941



Electricity Generated (kWh) 618 624 631 637 643 650 656 663 669 676 683 690 697 704 711 718

Construction Costs ($) - - - - - - (5,910,100) - - - - - - - - -



Total Sludge Hauling Cost Savings by Thickening2- - - - - - - - - - - - - - - -


Maintenance and Operating Costs ($) - - - - - - - (130,022) (130,022) (130,022) (130,022) (130,022) (130,022) (130,022) (130,022) (130,022)

Tipping Revenue ($) 360,123 363,725 367,362 371,035 374,746 378,493 382,278 386,101 389,962 393,862 397,800 401,778 405,796 409,854 413,952 418,092

Total 609,165 615,147 621,762 627,790 633,842 640,529 (5,263,471) 523,341 529,491 536,275 543,084 549,919 556,779 563,666 570,578 577,517

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 609,165 597,230 586,070 574,517 563,161 552,526 (4,408,074) 425,524 417,985 411,010 404,106 397,273 390,514 383,829 377,219 370,686

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044



Available Capacity for HW (lbs VS/day) 32,858 32,577 32,292 32,005 31,715 31,423 31,127 30,828 30,526 30,222

HW Limited to 30% of AD Feed1 (lbs VS/day) 12,061 12,181 12,303 12,426 12,551 12,676 12,803 12,931 13,060 13,191



Electricity Generated (kWh) 725 732 740 747 754 762 770 777 785 793






Tipping Revenue ($) 422,273 426,496 430,761 435,068 439,419 443,813 448,251 452,734 457,261 461,834

Total 584,483 591,475 599,105 606,152 613,227 620,940 628,682 635,842 643,641 651,469

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 364,230 357,852 351,911 345,680 339,529 333,786 328,104 322,176 316,629 311,145





1 Spreadsheet assumes hauled waste received is limited to 30% of total digester feed.

Year

Year

Net Present Value HW at 30% of Digester Feed: Capital Cost Increase 20%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034














Tipping Revenue ($) 360,123 363,725 367,362 371,035 374,746 378,493 382,278 386,101 389,962 393,862 397,800 401,778 405,796 409,854 413,952 418,092

Total 609,165 615,147 621,762 627,790 633,842 640,529 (6,445,491) 497,337 503,486 510,270 517,080 523,915 530,775 537,661 544,574 551,513

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 609,165 597,230 586,070 574,517 563,161 552,526 (5,397,997) 404,380 397,457 391,080 384,756 378,487 372,275 366,121 360,027 353,995

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 422,273 426,496 430,761 435,068 439,419 443,813 448,251 452,734 457,261 461,834

Total 558,478 565,471 573,101 580,148 587,223 594,936 602,677 609,837 617,636 625,465

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 348,025 342,119 336,636 330,850 325,131 319,807 314,533 309,000 303,836 298,725






Year

Year

Net Present Value HW at 30% of Digester Feed: Capital Cost Decrease 15%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034














Tipping Revenue ($) 360,123 363,725 367,362 371,035 374,746 378,493 382,278 386,101 389,962 393,862 397,800 401,778 405,796 409,854 413,952 418,092

Total 609,165 615,147 621,762 627,790 633,842 640,529 (4,376,956) 542,845 548,994 555,778 562,588 569,422 576,283 583,169 590,082 597,020

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 609,165 597,230 586,070 574,517 563,161 552,526 (3,665,632) 441,382 433,381 425,958 418,618 411,363 404,193 397,110 390,113 383,205

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 422,273 426,496 430,761 435,068 439,419 443,813 448,251 452,734 457,261 461,834

Total 603,986 610,979 618,608 625,656 632,731 640,444 648,185 655,345 663,144 670,972

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 376,384 369,652 363,367 356,803 350,328 344,270 338,283 332,058 326,223 320,460






Year

Year

Net Present Value HW at 30% of Digester Feed: Electricity Cost Increase 50%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034














Tipping Revenue ($) 360,123 363,725 367,362 371,035 374,746 378,493 382,278 386,101 389,962 393,862 397,800 401,778 405,796 409,854 413,952 418,092

Total 797,669 805,481 814,231 822,090 829,972 838,794 (5,063,376) 725,572 733,551 742,471 751,415 760,385 769,381 778,402 787,450 796,524

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 797,669 782,020 767,491 752,329 737,420 723,551 (4,240,498) 589,956 579,072 569,042 559,123 549,318 539,628 530,054 520,597 511,258

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 422,273 426,496 430,761 435,068 439,419 443,813 448,251 452,734 457,261 461,834

Total 805,625 814,752 824,822 834,005 843,215 853,368 863,550 872,845 883,084 893,352

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 502,039 492,939 484,496 475,621 466,868 458,727 450,680 442,263 434,419 426,670






Year

Year

Net Present Value HW at 30% of Digester Feed: Electricity Cost Decrease 20%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034














Tipping Revenue ($) 360,123 363,725 367,362 371,035 374,746 378,493 382,278 386,101 389,962 393,862 397,800 401,778 405,796 409,854 413,952 418,092

Total 533,763 539,013 544,774 550,070 555,390 561,223 (5,343,509) 442,449 447,866 453,797 459,752 465,733 471,739 477,771 483,830 489,914

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 533,763 523,313 513,502 503,392 493,457 484,115 (4,475,105) 359,752 353,550 347,797 342,099 336,455 330,868 325,339 319,868 314,457

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 422,273 426,496 430,761 435,068 439,419 443,813 448,251 452,734 457,261 461,834

Total 496,026 502,164 508,818 515,011 521,232 527,969 534,735 541,041 547,864 554,716

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 309,107 303,818 298,877 293,704 288,594 283,810 279,074 274,141 269,513 264,935






Year

Year

Net Present Value HW at 30% of Digester Feed: Natural Gas Cost Increase 50%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034














Tipping Revenue ($) 360,123 363,725 367,362 371,035 374,746 378,493 382,278 386,101 389,962 393,862 397,800 401,778 405,796 409,854 413,952 418,092

Total 664,849 671,388 678,565 685,162 691,788 699,053 (5,204,361) 583,042 589,789 597,176 604,594 612,044 619,526 627,040 634,586 642,165

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 664,849 651,833 639,613 627,020 614,644 603,009 (4,358,571) 474,067 465,585 457,686 449,875 442,154 434,523 426,983 419,536 412,181

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 422,273 426,496 430,761 435,068 439,419 443,813 448,251 452,734 457,261 461,834

Total 649,777 657,422 665,712 673,425 681,173 689,565 697,993 705,846 714,345 722,880

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 404,919 397,751 391,035 384,045 377,149 370,675 364,277 357,646 351,410 345,252






Year

Year

Net Present Value HW at 30% of Digester Feed, Hauling Increased by 15%




Last Modified: 3/12/2018 Hauling Cost ($/wet ton) 37.95


Year

2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034














Tipping Revenue ($) 360,123 363,725 367,362 371,035 374,746 378,493 382,278 386,101 389,962 393,862 397,800 401,778 405,796 409,854 413,952 418,092

Total 573,264 578,887 585,140 590,802 596,484 602,797 (5,301,580) 484,851 490,616 497,011 503,428 509,866 516,326 522,808 529,312 535,838

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 573,264 562,026 551,550 540,668 529,969 519,978 (4,439,990) 394,228 387,297 380,918 374,598 368,338 362,141 356,007 349,937 343,934

Year

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) 422,273 426,496 430,761 435,068 439,419 443,813 448,251 452,734 457,261 461,834

Total 542,387 548,958 556,163 562,781 569,422 576,697 583,996 590,709 598,057 605,429

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 337,997 332,129 326,687 320,946 315,275 310,003 304,783 299,308 294,204 289,156






Net Present Value Without Hauled Waste



NPV Scenario: Without Hauled Waste Discount Rate 3%



Year

2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034




Received HW (lbs VS/day) - - - - - - - - - - - - - - - -

Received HW (gallons/day) - - - - - - - - - - - - - - - -



Construction Costs ($) - - - - - - - - - - - - - - - -



HW Sludge Hauling Costs3- - - - - - - - - - - - - - - -

Maintenance and Operating Costs ($) - - - - - - - - - - - - - - - -

Tipping Revenue ($) - - - - - - - - - - - - - - - -

Total 267,085 269,756 272,454 275,178 277,930 280,709 283,517 286,352 289,215 292,107 295,028 297,979 300,959 303,968 307,008 310,078

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 267,085 261,899 256,814 251,827 246,937 242,142 237,441 232,830 228,309 223,876 219,529 215,266 211,086 206,987 202,968 199,027

Year

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044




Received HW (lbs VS/day) - - - - - - - - - -

Received HW (gallons/day) - - - - - - - - - -





Offset Cost of Heating Digester & Bldgs ($) 82,613 83,439 82,613 83,439 82,613 83,439 82,613 83,439 82,613 83,439

HW Sludge Hauling Costs - - - - - - - - - -

Maintenance Costs ($) - - - - - - - - - -

Tipping Revenue ($) - - - - - - - - - -

Total 311,518 314,633 316,119 319,280 320,813 324,021 325,600 328,856 330,484 333,789

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 194,128 190,358 185,687 182,081 177,626 174,177 169,928 166,629 162,576 159,420


2020 Capital Costs = Phase 2 : WAS Thickening without Hauled Waste (Estimated at 67% of full Phase 3 cost with Hauled Waste) & Phase 3 : Estimated at 80% of Full Capacity CHP Cost


Net Present Value Without Hauled Waste: Electricity Cost Increase 50%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034













Tipping Revenue ($) - - - - - - - - - - - - - - - -

Total 364,693 368,340 372,023 375,743 379,501 383,296 387,129 391,000 394,910 398,859 402,848 406,876 410,945 415,054 419,205 423,397

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 364,693 357,611 350,667 343,858 337,182 330,634 324,214 317,919 311,746 305,692 299,757 293,936 288,229 282,632 277,144 271,762

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044









Electricity Revenue ($) 343,357.14 346,791 350,259 353,761 357,299 360,872 364,481 368,125 371,807 375,525




Tipping Revenue ($) - - - - - - - - - -

Total 425,970 430,230 432,872 437,201 439,912 444,311 447,094 451,565 454,420 458,964

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 265,451 260,296 254,267 249,329 243,569 238,839 233,335 228,804 223,544 219,204




Year

Year

Net Present Value Without Hauled Waste: Electricity Cost Decrease 20%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034













Tipping Revenue ($) - - - - - - - - - - - - - - - -

Total 228,042 230,323 232,626 234,952 237,302 239,675 242,072 244,492 246,937 249,407 251,901 254,420 256,964 259,534 262,129 264,750

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 228,042 223,614 219,272 215,015 210,840 206,746 202,731 198,795 194,935 191,149 187,438 183,798 180,229 176,730 173,298 169,933

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044









Electricity Revenue ($) 183,123.81 184,955 186,805 188,673 190,559 192,465 194,390 196,334 198,297 200,280




Tipping Revenue ($) - - - - - - - - - -

Total 265,737 268,395 269,418 272,112 273,173 275,904 277,003 279,773 280,910 283,719

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 165,599 162,383 158,255 155,182 151,249 148,312 144,566 141,759 138,189 135,506




Year

Year

Net Present Value Without Hauled Waste: Natural Gas Increase 50%






2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034













Tipping Revenue ($) - - - - - - - - - - - - - - - -

Total 303,021 306,051 309,111 312,202 315,325 318,478 321,663 324,879 328,128 331,409 334,723 338,071 341,451 344,866 348,314 351,798

Discount Factor 1.00 0.97 0.94 0.92 0.89 0.86 0.84 0.81 0.79 0.77 0.74 0.72 0.70 0.68 0.66 0.64

NPV 303,021 297,137 291,367 285,710 280,162 274,722 269,387 264,156 259,027 253,998 249,066 244,229 239,487 234,837 230,277 225,805

2035 2036 2037 2038 2039 2040 2041 2042 2043 2044













Tipping Revenue ($) - - - - - - - - - -

Total 352,825 356,353 357,426 361,000 362,119 365,740 366,907 370,576 371,791 375,509

Discount Factor 0.62 0.61 0.59 0.57 0.55 0.54 0.52 0.51 0.49 0.48

NPV 219,869 215,599 209,950 205,873 200,497 196,603 191,486 187,768 182,897 179,345




Year

Year

801 South Caroline Street, Baltimore, MD 21231 WRA W.O. 81488-059

dnixson

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WRA WO # 14342-001

harrisburg advanced wastewater treatment facility ... · harrisburg advanced wastewater treatment...

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