Conceptual Design Report Digester

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ConceptualDesign Report

Lewiston Auburn Water Pollution

Control Authority, MaineAnaerobic Digestion and Energy RecoveryProject

October 2009


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5816-72780

Contents

Section 1 Introduction1.1 Purpose ...................................................................................................................... 1-1

1.2 Existing Biosolids Treatment .................................................................................. 1-21.3 Project Drivers, Goals and Objectives .................................................................... 1-31.4 Project Components ................................................................................................. 1-31.5 Facility Layout Options ........................................................................................... 1-4

1.5.1 Option 1: New Separate Facility ............................................................. 1-51.5.2 Option 2: Retrofit of Existing Interior Process Space .......................... 1-5

Section 2 Biosolids Quantities and Characteristics2.1 Existing Sludge Quantities and Characteristics ................................................... 2-12.2 Existing Sludge Quantities and Characteristics with DAF Replacement ......... 2-22.3 Basis of Design .......................................................................................................... 2-3

Section 3 Waste Activate Sludge Thickening Improvements3.1 Background and Existing Conditions .................................................................... 3-13.2 Thickening Design Criteria ..................................................................................... 3-23.3 Thickening Alternatives Analysis .......................................................................... 3-2

3.3.1 Rotary Drum Thickeners .......................................................................... 3-33.3.2 Gravity Belt Thickeners ............................................................................ 3-43.3.3 Thickening Process Comparison and Recommendations ................... 3-5

3.4 Gravity Belt Thickener Design Criteria ................................................................. 3-83.4.1 WAS GBTS .................................................................................................. 3-9

3.4.2 GBT Washwater / Drain System ............................................................. 3-93.5 Thickened Waste Activated Sludge Transfer Pumping ...................................... 3-93.6 Maintenance of Plant Operations (MOPO) ........................................................ 3-11

Section 4 Anaerobic Digestion and Sludge Storage Improvements4.1 General ....................................................................................................................... 4-14.2 Anaerobic Digestion Tanks ..................................................................................... 4-1

4.2.1 Digester Sizing Criteria............................................................................. 4-14.2.2 Digester Tank Configuration Options .................................................... 4-2

4.3 Sludge Storage Tanks ............................................................................................... 4-3

4.3.1 Thickened Waste Activated Sludge Storage .......................................... 4-34.3.2 Digested Sludge Storage ........................................................................... 4-44.4 Digester Heating Requirements ............................................................................. 4-5

4.4.1 Heat Requirement for Incoming Sludge ................................................ 4-54.4.2 Digester Tank Heat Losses ....................................................................... 4-64.4.3 Heating Requirement Summary ............................................................. 4-7


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4.5 Digester System Equipment .................................................................................... 4-84.5.1 Digester Heating ........................................................................................ 4-84.5.2 Digester Mixing ......................................................................................... 4-94.5.3 Digester Covers........................................................................................ 4-10

4.6 Facility Site Location Options ............................................................................... 4-124.6.1 Option 1: New Separate Facility ........................................................... 4-124.6.3 Option 2: Retrofit of Existing Interior Process Space ........................ 4-12

4.7 Anaerobic Digester Conceptual Design Summary ............................................ 4-13

Section 5 Biogas Handling and Cogeneration Improvements5.1 General ....................................................................................................................... 5-15.2 Digester Gas Production .......................................................................................... 5-15.3 Digester Gas Usage ................................................................................................... 5-1

5.3.1 Cogeneration System Sizing .................................................................... 5-25.4 Recommended Cogeneration System .................................................................... 5-45.5 Biogas Conveyance and Storage ............................................................................. 5-4

5.5.1 Biogas Safety Equipment .......................................................................... 5-45.5.2 Moisture and Sediment Removal ............................................................ 5-55.5.3 Biogas Metering ......................................................................................... 5-55.5.4 Biogas Storage ............................................................................................ 5-5

5.6 Biogas Treatment ...................................................................................................... 5-65.6.1 Hydrogen Sulfide Biogas Treatment ...................................................... 5-65.6.2 Siloxane Removal ...................................................................................... 5-6

5.6.3 Biogas Pressure Boosting ......................................................................... 5-75.6.4 Recommended Biogas Treatment System .............................................. 5-7

5.7 Summary .................................................................................................................... 5-7

Section 6 Architectural and Structural Considerations6.1 Building Codes and Standards ............................................................................... 6-16.2 Architectural Considerations .................................................................................. 6-2

6.2.1 Option 1 Buildings and Structures ..................................................... 6-26.2.2 Option 2 Buildings and Structures ..................................................... 6-36.2.3 Building Systems ....................................................................................... 6-4

6.2.4 Building Materials and Finishes .............................................................. 6-46.2.5 Roofing Systems ........................................................................................ 6-56.2.6 Proposed Interior Finishes ....................................................................... 6-6

6.3 Structural Considerations ........................................................................................ 6-66.3.1 Design Loads and Serviceability ............................................................. 6-66.3.2 Serviceability ............................................................................................ 6-136.3.3 Foundation Design .................................................................................. 6-156.3.4 Concrete Design ....................................................................................... 6-16


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6.3.5 Masonry Design ....................................................................................... 6-186.3.6 General Design and Detailing ............................................................... 6-196.3.7 Structural Metal Design .......................................................................... 6-206.3.8 Modification of Existing Structures ...................................................... 6-226.3.9 Facility Specific Structural Design Considerations ............................. 6-22

Section 7 Electrical and Instrumentation Functions7.1 Electrical Systems ..................................................................................................... 7-1

7.1.1 Electrical System Overview ..................................................................... 7-17.1.2 Existing Electrical System ........................................................................ 7-17.1.3 Electrical Observations and Vulnerability ............................................. 7-27.1.4 Recommendations and Improvements .................................................. 7-37.1.5 Hazardous Areas ....................................................................................... 7-7

7.2 Instrumentation and Control .................................................................................. 7-77.2.1 General ........................................................................................................ 7-77.2.2 Objectives.................................................................................................... 7-77.2.3 Control System Description ..................................................................... 7-97.2.4 Naming Convention ............................................................................... 7-127.2.5 Control Philosophy ................................................................................. 7-147.2.6 SCADA System Design .......................................................................... 7-157.2.7 Summary Recommendations ................................................................. 7-15

Section 8 HVAC and Plumbing Functions

8.1 HVAC ......................................................................................................................... 8-18.1.1 General ........................................................................................................ 8-18.1.2 Design Conditions ..................................................................................... 8-18.1.3 Demolition .................................................................................................. 8-18.1.4 New Work .................................................................................................. 8-2

8.2 Plumbing .................................................................................................................... 8-48.2.1 General ........................................................................................................ 8-48.2.2 Demolition .................................................................................................. 8-48.2.3 New Work .................................................................................................. 8-58.2.4 Fire Protection ............................................................................................ 8-6

Section 9 Preliminary Geotechnical, Civil and Site Analysis and DesignRecommendations

9.1 General ....................................................................................................................... 9-19.2 Conceptual Geotechnical Recommendations ....................................................... 9-1

9.2.1 Existing Conditions ................................................................................... 9-19.2.2 Proposed Construction ............................................................................. 9-19.2.3 Purpose and Scope .................................................................................... 9-2


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9.2.4 Subsurface Investigations ......................................................................... 9-29.2.5 Geotechnical Laboratory Testing ............................................................ 9-39.2.6 Conceptual-Level Geotechnical Evaluation........................................... 9-59.2.7 Conceptual-Level Foundation Recommendations ............................... 9-69.2.8 Recommended Phase 2 Exploration Program ....................................... 9-7

9.3 Site Design Considerations ..................................................................................... 9-79.3.1 Codes and Standards ................................................................................ 9-79.3.2 Site Preparation.......................................................................................... 9-89.3.3 Materials ..................................................................................................... 9-89.3.4 Grading and Drainage .............................................................................. 9-99.3.5 Erosion and Sedimentation Control ....................................................... 9-99.3.6 Landscape ................................................................................................... 9-99.3.7 Layout Specific Site Design Considerations ........................................ 9-10

Section 10 Permitting 10.1 Purpose .................................................................................................................... 10-110.2 Local Permitting ...................................................................................................... 10-1

10.2.1 Urban Enterprise (UE) and Resource Conservation (RC) ZoningDistricts Provisions ................................................................................. 10-1

10.2.2 Local Flood Protection Provisions ........................................................ 10-110.2.3 Natural Resources Protection Act (NRPA) Permit ............................. 10-210.2.4 Stormwater Runoff and Flood Management Permitting ................... 10-210.2.5 Local Permit Application and Approval Schedule ............................. 10-2

10.3 Air Quality Permitting ........................................................................................... 10-3

Section 11 Preliminary Cost Estimate11.1 Project Cost Estimates: ........................................................................................... 11-111.2 Comparison of Options ......................................................................................... 11-2

Appendices Appendix A: Historical Boring Logs Appendix B: Recent Boring Logs Appendix C: Geotechnical Laboratory Test Results


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Tables

2-1 Plant Influent ............................................................................................................. 2-12-2 Thickened Primary Sludge ...................................................................................... 2-22-3 Thickened Waste Activated Sludge ....................................................................... 2-22-4 Thickened Waste Activated Sludge, DAF Replacement ..................................... 2-22-5 Combined Thickened Sludge, WAS thickened to 5% ......................................... 2-32-6 Combined Thickened Sludge Feed to Digester .................................................... 2-3

3-1 Estimated Loading Rates for WAS Thickening .................................................... 3-23-2 Non-Cost Comparison of Thickening Alternatives ............................................. 3-63-3 Performance Comparison for Thickening Alternatives ...................................... 3-73-4 Comparison Costs for Thickening Alternatives ................................................... 3-73-5 Design Criteria TWAS Transfer Pumps ......................................................... 3-10

4-1 Combined Thickened Sludge to Digester System, Basis of Design ................... 4-24-2 Digester System Configurations Summary .......................................................... 4-34-3 Sludge Heating Requirements ................................................................................ 4-64-4 Digester Tank Configuration .................................................................................. 4-74-5 Conductive Heat Loss .............................................................................................. 4-74-6 Digester Heating Requirements ............................................................................. 4-8

5-1 Biogas Production Rates and Energy Value of Biogas ........................................ 5-25-2 Utilizing Biogas in Engine Application ................................................................. 5-35-3 Digester and Facility Heating Needs vs. Heat from Engine ............................... 5-3

7-1 LAWPCA Facility Area Classification Summary ............................................ 7-8

9-1 Summary of Geotechnical Laboratory Testing ................................................... 9-129-2 Summary of Subsurface Conditions .................................................................... 9-13

10-1 Summary of Maximum Annual Emissions ......................................................... 10-4

11-1 Conceptual Estimate of Project Costs Based on 10% Level of Design ............ 11-111-2 Comparison of Facility Layout Options .............................................................. 11-2


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Figures

1-1 Anaerobic Digestion System Process Flow Diagram .......................................... 1-71-2 Anaerobic Digester/Cogen Facility Site Plan Option 1 ................................... 1-91-3 Anaerobic Digester/Cogen Facility Site Plan Option 2 ................................. 1-11

4-1 Digester Plan and Section ...................................................................................... 4-154-2 Gas Storage Facility Plan, Section, Detail and Schematic ................................. 4-174-3 Anaerobic Digester/Cogen Facility Digester Building Option 1 ................ 4-194-4 Existing Process Building Plan Option 2 ........................................................ 4-214-5 New Digesters Lower Level Option 2 ............................................................ 4-23

5-1 Waste Gas Burner, Gas Equipment Building, Gas Conditioning System,and Cogen Units ...................................................................................................... 5-9

7-1 Electrical Overall One Line Diagram ................................................................... 7-177-2 Electrical One Line Diagram Sludge Digesters MCC-6 ..................................... 7-19

9-1 Boring Location Plan Option 1 ........................................................................ 9-139-2 Boring Location Plan Option 2 ........................................................................ 9-15


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5816-72780

Section 1Introduction

1.1 PurposeThe purpose of this Conceptual Design Report (CDR) is to expand on therecommendations presented in the June 2009 Anaerobic Digestion/Energy RecoveryFeasibility Study (Feasibility Study) prepared for the Lewiston Auburn WaterPollution Control Authority (LAWPCA) by Camp Dresser & McKee Inc (CDM). ThisConceptual Design is defined herein as approximately a 10-percent level of designand is intended to be in accordance with Task 2A as outlined in the Agreementbetween LAWPCA and CDM dated August 17, 2009. This CDR provides the baselinefor design of the proposed digestion improvements.

The June 2009 Feasibility Study presented two conceptual options for the layout of thefacilities required for the anaerobic digestion system. Option 1 involved new

separate tanks and adjacent support building located remote from the existing processbuilding while Option 2 attempted to modify existing process building space toaccommodate the bulk of the mechanical equipment and build new digesters south ofthe existing gravity thickeners. In addition to providing criteria for the general basisof design of the proposed systems, this CDR further evaluates and recommends oneof these two facility layout options based on analysis of cost and non-cost factors.

As presented in the Feasibility Study, replacement of the existing Waste ActivatedSludge (WAS) thickening system at the facility is included in the proposed digesterimprovements in order to increase the solids percentage and decrease the totalvolume of sludge being fed to the anaerobic digestion system. This CDR expands

upon the recommended WAS thickening improvements by comparing potentialthickening system equipment and providing a recommended selection. It should alsobe noted that this thickening system replacement work is recommended irrespectiveof the facility layout option selected and the cost for this work has been carried inboth options.

This CDR includes design criteria and concepts of operation for each unit process.This basis of design has been supported herein through presentation of the following:

Conceptual site plans of the proposed facilities (both layout options);

Conceptual drawings of the new process areas as well as proposed modifications toexisting structures (both layout options);

Solids train process flow diagram;

Discussion of architectural and structural design considerations;

Evaluation of the existing and proposed power distribution system;


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Discussion related to instrumentation and control concepts, including the desireddegree of automation;

Consideration of current and future plant operations include operations duringconstruction;

Consideration of ease of construction and associated risks during construction;

Heating, ventilating and plumbing improvements considerations;

Site access improvements evaluation;

Results of initial geotechnical investigations; and

An update of the estimated project costs and comparison of layout alternatives.

1.2 Existing Biosolids TreatmentThe LAWPCA Facility is permitted to discharge an average daily flow of 14.2 milliongallons per day (MGD) and currently operates at an average daily flow ofapproximately 12.7 MGD. The influent wastewater is a mixture of residential,commercial and industrial wastewater, generated in the cities of Lewiston andAuburn. Approximately half of the total organic load to the facility is generated bythe Cascades Auburn-Fiber deinking facility. The LAWPCA Facility has a secondarylevel treatment process, with two primary sedimentation basins, two aeration basinsand two secondary clarifiers. Final effluent is disinfected with chlorine and thendechlorinated with sodium bisulfate prior to discharge into the Androscoggin River.

The NPDES permit requires the facility to disinfect on a seasonal basis.

Current solids handling equipment at the LAWPCA Facility thickens and dewaterssolids removed in the primary and secondary treatment process. Primary sludge ispumped from the primary clarifiers to two gravity thickeners, which thicken andstore primary solids. In the gravity thickeners, the primary sludge is thickened toapproximately 6% solids. Waste Activated Sludge (WAS) from the Secondary Processis pumped to two dissolved air floatation units for thickening, where WAS isthickened to between 2.6% to 3.3% solids. Thickened Waste Activated Sludge(TWAS) flows by gravity from the DAF units to four holding tanks. Facility operatorshave reported that when both DAF units are operating, the TWAS should be

approximately 3% solids or less to allow it to easily flow by gravity to the TWASholding tanks.

The thickened sludge is mixed in-line prior to dewatering using BFPs. The dewateredcake is then either transferred to a pug mill mixer for lime addition prior to landapplication or is hauled in raw cake form to the remotely located LAWPCAcomposting facility for in vessel composting or is directly transferred to disposal sites.Composting is used primarily in the winter and early spring months to stabilize


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biosolids while lime stabilization is used primarily in the late spring, summer andearly fall months.

1.3 Project Drivers, Goals and ObjectivesThe composting facility has served the LAWPCA well during its 15 years ofoperation. However, composting operation costs have increased, especially the costof amendments (sawdust, shavings or horse bedding) that is mixed with thedewatered sludge; and the facility is unable to manage peak seasonal biosolidsproduction, necessitating costly long distance disposal. Additionally, recent spikes inpower and fuel costs have increased the overall operations costs at the facility. This,in addition to factors such as potential grant funding for the project, LAWPCAs debtretirement schedule and sustainability considerations, has led the LAWPCA toconsider anaerobic digestion for biosolids stabilization and volume reduction.

As discussed in detail in the Feasibility Study, anaerobic digestion of biosolids beforedewatering and land applying or composting offers several advantages. Thesepotential advantages include:

Reduction of total solids by approximately 40%. This reduction in solids willreduce subsequent costs for conditioning, dewatering, stabilization, trucking anddisposal.

Elimination of the cost to transport excess biosolids that currently exceed thecapacity of the composting facility. Associated tipping fees will also be eliminated.

Reduction of biosolids odors, thereby making the LAWPCAs existing Class B land

application program more acceptable to nearby property owners. Biogas utilization from the anaerobic digestion process in a combined heat and

power (CHP) application to produce electricity and heat. The electricity producedwould offset a portion of power currently purchased and the heat would be usedfor digester and building heating.

Increase of the overall solids handling capacity of the plant by reducing the volumeof sludge through anaerobic digestion. Currently the plant is limited by thecapacity of the existing dewatering and biosolids stabilization equipment.

Establish LAWPCA and the Cities of Lewiston and Auburn as environmental andenergy conservation leaders in the State of Maine with the first anaerobic digestionfacility in the state.

1.4 Project ComponentsAs detailed in the Feasibility Study, it is estimated that two insulated concretedigester tanks, will meet the needs of the LAWPCA facility. Irrespective of layout


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option, additional facilities and equipment required to support the digesters wouldinclude the following:

Waste activated sludge thickening equipment replacement and associatedmodifications to the existing process building;

Digester tank covers;

Biogas and digested sludge storage tank;

Digester recirculation pumps;

Sludge heat exchangers;

Central dual-fuel boiler and hot water recirculation pumps;

Digester mixing system pumps;

Biogas cleaning system;

Anaerobic digester gas driven reciprocating engine generators;

Waste gas burner for burning any excess gas not utilized and to provide an outletfor gas production should gas treatment and utilization be out of service.

Yard piping modifications for digester overflow, drain, sludge feed, sludgerecirculation, sludge mixing and other utilities as required; and

Site layout, roadways, grading and drainage modifications.

It should also be noted that, in the event that Option 2 is selected, the layout of thisequipment and associated space constraints will require modifications to the influentscreening systems. In this event, the following equipment upgrades will also likely berequired as part of the project:

Replacement/upgrade of influent screening mechanisms;

New screenings wash compactors; and

New screenings conveyor and transport system.

Modifications to the existing screening garage to provide an isolated space for newequipment for the digestion process.

The solids process flow diagram associated with the proposed anaerobic digestionand energy recovery system systems and equipment is presented in Figure 1-1.


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1.5 Facility Layout OptionsThough the remaining sections of this report detail the design, operational and costdifferences between the two conceptual facility layout options, a brief introduction tothe layouts is presented below.

1.5.1 Option 1: New Separate FacilityDuring the Feasibility Study process, due to the current active use in most areas of theexisting process building and immediate surrounding area, it was initially assumedthat the new digesters and required process area would be constructed as separatefrom the existing facility. To keep space for future process expansion immediatelywest of the existing clarifiers and aeration tanks, as well as, the potential need for CSOpretreatment facilities on the east side of the site, the location selected for thedigestion improvements was south west of the existing chlorine contact tanks (northof the active compost area). Figure 1-2 depicts the overall facility layout for

Option 1.

1.5.2 Option 2: Retrofit of Existing Interior Process SpaceDuring development of the Feasibility Study, a second potential location for thedigesters was identified in an attempt to retrofit a portion of the existing processbuilding. Per CDMs conversations with LAWPCA personnel, it may be possible tomodernize and relocate the existing screening equipment to the east side of theProcess Control Building and install the digester equipment in the southwest cornerof the building (currently housing the screenings garage). It was initially assumedthat the advantages to this option could include the following:

Reduce the amount of new interior process space by installing a portion of thedigestion equipment within the existing building;

Minimize yard piping and pumping by locating the new digestion facility as closeas physically possible to the existing thickening and dewatering areas; and

Create operational advantages by relocating and modernizing the screeningshandling systems.

As shown in Figure 1-3, the current configuration of the Option 2 layout attemptedto reuse the space as previously intended. It should be noted however that, due tospace limitations within the screenings garage and adjacent areas, a new (subsurface)interior process space adjacent to the new digesters is still required. In addition, anew screenings garage located to the east of the process building is also needed toreplace the existing garage.

The advantages, disadvantages and cost implications of each layout option are furtherdetailed in subsequent sections of this report.


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Section 2Biosolids Quantities and Characteristics

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Average Day Max Month

MGD 0.024 0.035

Dry Solids, lbs/day 12,900 18,900

% Solids 6.3 6.5

Table 2-2

Thickened Primary Sludge, 2003-2007


MGD 0.051 0.066


% Solids 2.6 3.4

Table 2-3

Thickened Waste Activated Sludge, 2003-2007

2.2 Existing Sludge Quantities and Characteristics withDAF Replacement

Due to the age and thickening performance of the existing DAF units, the equipment

requires substantial rehabilitation or replacement in order to achieve TWASconcentrations required for optimal sizing and performance of the proposed digestionsystem. As a result, it is recommended that they be replaced by gravity beltthickeners (GBTs) (as described in detail in Section 3), capable of thickening the WASto a minimum of 5%. By thickening the WAS to 5% instead of the current 23.5%, thevolume of the digester can be reduced, resulting in lower capital costs to construct thedigester system. The volume and characteristics of WAS thickened to 5% are given inTable 2-4.


MGD 0.026 0.045


% Solids 5.0 5.0

Table 2-4

Thickened Waste Act ivated Sludge, DAF Replacement


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Section 3Waste Activated Sludge Thickening Improvements

3-2 A

3.2 Thickening Design CriteriaThe design criteria for the thickening equipment include residuals feed (loading) rate,sludge percent solids, desired thickened solids, duration of equipment operation,redundancy, and available space. Influent sludge to the thickening equipmentincludes secondary sludge (or waste activated) only. Primary sludge will continue tobe thickened independent of WAS via existing gravity thickener equipment.

The WAS thickening system will be designed for operating between 8.5 and 11 hoursper day and 7 days per week in order to provide continuous daily flow of TWAS tothe downstream anaerobic digester process. Plant operators have reported thatexisting plant staffing and operating schedules currently a minimum of 10 hrs pershift per day are adequate and will not require modification for the newlyproposed WAS thickening system operating schedule.

Full scale redundancy will be provided for WAS thickening and each unit will bedesigned to handle maximum conditions. This is required to ensure that solids can betreated on site in the event a unit is taken out of service during planned or unplannedmaintenance.

The following Table 3-1 provides the projected future characteristics of the sludgeconveyed to the WAS thickening equipment based on an 8.5 hour per day and 7 dayper week processing schedule which provides for up to 1.5 hours of startup/shutdown time per shift. The percent solids are based on the anticipated performanceof solids removal in the secondary facilities.

Condition

HydraulicLoading

HydraulicLoading

SolidsLoading

Percent Solids

(wet - gpd) (WET-GPM) (dry lb/hr) (%)

Average Day 208,000 408 1,500 0.71

Maximum Month 283,000 555 2,500 0.92

Table 3-1

Estimated Loading Rates for WAS Thickening

3.3 Thickening Alternatives AnalysisCurrent available technologies that were considered for sludge thickening includegravity belt thickeners (GBTs), Rotary Drum Thickeners, and DAFs.

Continued use of the existing DAFs is not being considered as an alternative forfuture thickening at the facility due to the limited and unreliable thickening


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Process Advant ages Disadvantages

Rotary DrumThickeners

Relatively low power consumption A very simple process Minimal ancillary equipment Compact Footprint Minimal operator attention

Polymer Dependent Floc Shear potential Lower Hydraulic Throughput Moderate Solids Capture at high

flows Odors generated

Gravity Belt

Thickening

Control capability for process

performance are flexible Relatively lower capital cost due to

higher throughput Relatively low power consumption High solids capture Higher thickened concentrations

are possible A very simple process to operate Moving parts are accessible Minimal ancillary equipment

More housekeeping / Startup time Polymer dependent Moderate operator attention

requirements Odors generated Building corrosion potential if not

ventilated adequately Higher washwater pressure requiring

a booster pump

Table 3-2

Non-Cost Comparison of Thickening Alternatives

Performance Comparison of AlternativesTable 3-3 provides a side by side performance comparison of the two thickeningalternatives based on available operating performance information as provided bymanufacturers for WAS thickening applications.


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3.6 Maintenance of Plant Operations (MOPO)To facilitate the installation of the new GBTs, construct the new electrical room, anddemolish the old DAF units, construction will require strict sequencing to maintainWAS thickening capability at all times. A brief summary of the proposed constructionsequence is provided below:

1. Provide temporary compressed air system (trailer mounted)/ Demo ExistingDAF Compressor system /

2. Construct new electrical room and install new electrical equipment switchoverfrom old to new MCC.

3. Demo DAF tank No.1

4. Install GBT No.1

5. Startup, Test and place into service GBT no.1

6. Demo DAF No.2

7. Install GBT No.2

8. Construct Thickening Room partition walls

9. Startup, Test and Place GBT No.2 into service.


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Section 4 Anaerobic Digestion and Sludge Storage Improvements

4-4 A

operate between 8.5 and 11 hours per day. As a result, storage volume is required tocontain and allow for continuous feed of TWAS to the digesters during the 13 to 15.5hours per day during which the WAS thickening system is not in operation.

For the proposed digestion project, it is recommended that the existing TWAS storagetanks, located west of the Process Building below grade, be used to feed TWAS to thedigesters continuously. The four tanks have a combined volume of approximately40,000 gallons, not all of which is considered to be active due to pumpingconsiderations. At average day conditions, approximately 17,000 gallons of the tankvolume will be utilized during off hours while using a continuous feed rate to thedigesters of approximately 20 gallons per minute (gpm). At maximum monthconditions, 24,000 gallons of TWAS storage will likely be needed, which would be fedcontinuously to the digesters at a rate of approximately 30 gpm. It should also benoted that the TWAS storage volume required will vary depending on the actualpercent solids, flow rates and daily processing schedule.

4.3.2 Digested Sludge StorageThe dewatering system at the LAWPCA facility is typically operated on a similardaily schedule as the WAS thickening system. When fed continuously, digestedsludge storage volume will be required during the 13 to 15.5 hours per day when thedewatering system is not in operation. Because the dewatering system does notoperate continuously, digested sludge may be stored in the digester itself or in aseparate sludge storage tank. Typically, it is most cost effective to construct a separatedigested sludge storage tank instead of using the digester itself to store digestedsludge

At average day conditions, the digester will provide a continuous output of 40 gpmwhich would equate to approximately 38,000 gallons of digested sludge tank volumeover 15.5 hours. At maximum month conditions, approximately 64 gpm would bedischarged over 11 hours, equating to a required storage volume of approximately50,000 gallons. As these volumes are in excess of any potentially unused existingTWAS storage tank volume, a new digested sludge storage tank is recommended.

The TWAS and digested sludge storage volumes above assume daily operation of allthickening and dewatering equipment and provide for storage of max month solidsloadings. Due to the need for some equipment downtime and the likelihood that thepeak daily solids loading at the facility will be in excess of the max month values, it is

recommended that additional storage volume be built into the new digester system,specifically within the new digested sludge storage tank. It is estimated thatapproximately 180,000 gallons of digested sludge storage would provideapproximately 3 days of digested sludge at average day flow and approximately2 days of storage at maximum month flow.

To accommodate this volume of storage, it is recommended that a digested sludgestorage tank 50 feet in diameter and 15 feet deep be constructed. Digested sludge,


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temperature of the sludge entering the digester is 45 F in the winter and 70 F in thesummer. Table 4-3 presents the estimated energy required to heat the sludge enteringthe digester. Heating requirements are given in millions of British Thermal Units perhour (MBTU/hr).

Average Day Maximum Month

Winter Summer Winter Summer

Sludge Volume to Both Digesters (gpd) 58,000 58,000 92,000 92,000

T2, Heated Sludge Temperature (F) 95 95 95 95

T1, Cold Sludge temperature (F) 45 70 45 70

Temperature Difference (F) 45 25 45 25

W, Flow to both digesters (lb sludge/hr) 20,000 20,000 32,000 32,000

Q 1, Sludge Heating Required For Both Digesters(MBTU/hr) 1.00 0.50 1.60 0.80

Table 4-3

Sludge Heating Requirements

4.4.2 Digester Tank Heat LossesHeat losses resulting from conduction through the digester tank roof, walls and floor

are calculated using the following relationship:

Where:

Q2 = heat loss (BTU/hr)

U = heat transfer coefficient (BTU/ ft 2/F/hr)

T2 = operating Temperature of Digester (F)

T1 = air temperature outside of tank (F)

A = Area of exposed surface (ft 2)

The design outside temperatures used in the heat loss analysis are based on the 2009Pluming Code for Portland, ME and are -1 F in winter and 72 F in summer. Thoughthe heat losses per digester, summarized in Table 4-4, were calculated based on thestandard digester tank configuration, it should be noted that similar calculations wereperformed for the cylinder tank option and yielded similar heat loss results.

( )122 T T AU Q =


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Average Day Maximum Month

Winter Summer Winter Summer

Q1, Heating Required to raise temperature of incoming sludge (MBTU/hr) 1.00 0.50 1.60 0.80

Q2, Heat required to compensate for conductionlosses insulated roof and walls (MBTU/hr) 0.74 0.18 0.74 0.18

Total Heat Required insu lated roof and wall s (MBTU/hr) 1.74 0.68 2.34 0.98

Table 4-6

Digester Heating Requirements

4.5 Digester System EquipmentAnaerobic digestion system equipment generally consists of the following three majorsystems:

Heating system

Mixing system

Digester covers

4.5.1 Digester Heating Maintaining a stable temperature within the digester is important, as the microbesresponsible for the digestion process are extremely sensitive to temperaturefluctuations. There are two primary types of digester heating systems: internal andexternal.

With an internal arrangement, heat is applied to the sludge while it remains in thedigester tank. In older digesters, heating arrangements include circulating hot waterthrough pipes mounted to the inside of the digester tank wall or through draft tubemixers equipped with hot water jackets.. In recent years, these arrangements havebecome less popular due to operational issues, including the buildup of sludge onheating surface and access restrictions. Because all internal heating systems rely onthe digester mixing system to circulate heat within the digester, the mixing systemmust be operated on a continuous basis. Without continuous mixing, a heat gradientwill develop in the tank and create biologically inactive zones.

Recent digester designs typically use external heating systems that recirculate sludgethrough external heat exchangers using a recirculation pump. Most external heatingsystems incorporate means to heat the sludge before it enters the digester. The feedsludge is typically interlocked with the sludge recirculation pumps, allowing the


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Fixed CoversFixed concrete and steel covers are also widely used throughout the wastewaterindustry. They have historically been the option with the lowest cost and leastpotential for operation and maintenance problems in comparison to floating covers.

However, fixed covers offer minimal biogas storage and limited flexibility withregard to sludge liquid level. One variation on the fixed concrete cover design is thesubmerged fixed cover (SFC). Compared to flat fixed cover designs, the submergedfixed cover is effective at utilizing the upper portion of the tank volume by inhibitingthe buildup of floating foam and scum and directs mixing energy for better efficiency.

SFCs are similar in costs to flat roof digesters and less costly to construct than domedroofs. The key to the submerged fixed cover digester is a sloped roof that leads to acentrally located gas dome. In a SFC design, the liquid level is allowed to rise into thegas dome above the side wall, submerging the underside of the cover. Submergingthe cover provides a gradual transition at the cover side wall connection, directing

mixing patterns more effectively. Operating the liquid level in the gas domeminimizes the gas to liquid interface. By minimizing this interface, foam and scumcan be removed more effectively. With minimal gas storage volume, a fixed coversystem must either rely on storage spheres, piping, flares, vacuum and pressure reliefvalves, or some other means of gas storage to keep the pressures consistent inside thetank.

Gas Membrane CoversGas membrane covers are a relatively new product that was first used in the U.S. inthe early 1990s. They provide a large volume of digester gas storage using a double-membrane design and may be installed on digester tanks or sludge storage tanks. The

outer membrane maintains a consistent dome shape, while the inner membranemoves up or down depending upon gas storage requirements. Ambient air fans andvalves add or release air from the space between the inner and outer membranes tomaintain the consistent outer membrane shape and constant biogas pressure. Thisalso allows for substantial changes in the depth of sludge in the digester.

Cover RecommendationSFCs are recommended for the digesters at LAWPA facility based on the followingconsiderations:

Fixed covers tend to be less costly than floating covers or gas holder membranes.

SFC minimize foaming, which is often expensive and difficult to control andcontain.

The digester tank configuration shown in Figure 4-1 depicts the general arrangementof the recommended SFC.

It is further recommended that the digested sludge storage tank, as discussed inSection 4.2 and shown in Figure 4-2, be installed with a gas membrane cover to store


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the multiple pipes and conduits which would be required between the existingprocess building and new sludge pumping area, a pipe tunnel has been providedunder this option between the new space and the existing process tunnel. Theexisting piping connecting to TWAS tank No. 4 in the area of the proposed tunnel

would need to be relocated as part of this work.

As shown on Figure 4-4, this option does require a substantial retrofit of the existingscreenings area. The existing wall between the intake screening area and the existingscreenings garage would be relocated to the east while the existing bathroom, laundryrooms and associated hallway would be removed to allow room for the newequipment. In addition, to facilitate screenings removal, a new screenings handlingsystem (new wash presses and conveyor system) along with a new screenings garageat the east end of the process building would be required. At the request ofLAWPCA, this alternative has also included the complete replacement of the existingintake screens with new multi-rake style screens.

Due to the site constraints inherent with Layout Option 2 which are apparent inFigure 1-3, the 65-ft diameter, less costly, standard tank was not a viable option. As aresult, the layout of this option has utilized the taller 50-ft diameter tanks that wouldbe installed as shown along with the 50-ft digested sludge/biogas storage tank.

4.7 Anaerobic Digester Conceptual Design SummaryThe following is a list of tankage and equipment included in the conceptual design.

Digester tanks:

9 Layout Option 1 Separate Facility. Standard Tanks two, 65 foot diameterconcrete tanks with insulation; SWD of each tank is 30.5 feet

9 Layout Option 2 Retrofit. Cylinder Tanks two, 50 foot diameter concretetanks with insulation; SWD of each tank is 52 feet

Digester feed Utilize existing TWAS storage tanks to continuously feed TWAS todigester system. Pump thickened primary sludge from gravity thickeners todigesters continuously.

Digester Roof Submerged fixed cover

Digester Mixing Pumped mixing system

Digester Heating External heat exchangers. Typically, waste heat from thecogeneration system provides hot water. In the event that the cogeneration systemis not operating or not producing enough heat to meet the digester heat needs, aboiler utilizing biogas or natural gas may be used.


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Digested Sludge Storage One 50-foot diameter by 15-foot deep tank to storedigested sludge prior to dewatering and new belt filter press feed pumps.

Biogas Storage Gas storage membrane on digested sludge storage tank.


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A 5-1

5816-72780

Section 5Biogas Handling and Cogeneration

5.1 GeneralGas generated by the anaerobic digestion of organic solids is often referred to asbiogas. This gas contains primarily methane and carbon dioxide and is an excellentsource of energy. The energy can be harnessed in a variety of ways, including boilersfor digester and building heating, and reciprocating engines and microturbines forelectricity production.

5.2 Digester Gas ProductionThe amount of biogas produced during the anaerobic digestion process depends uponthe amount volatile solids entering into and destroyed within the digester. Higheramounts of volatile solid destruction will, in turn, result in higher biogas production.

For systems that digest municipal biosolids, feed stock to these systems typicallyconsists of combined (primary and secondary) thickened sludge which containsapproximately 75% volatile solids, 50% of which is generally able to be destroyed.The addition of alternative feed stocks to the anaerobic digester, including fats, oilsand grease (FOG), should be considered, as they greatly enhance biogas production.In a recent study performed by the EPA, it was shown that food waste has up to threetimes the energy generation potential as municipal biosolids.

Though some alternative feed stocks may be fed to the LAWPCA digestion system,the design of the biogas system was conservatively based on the followingassumptions and those listed in Table 5-1:

Volatile solids comprise 75% of the total dry solids fed to the digesters.

Volatile solids destruction in digester of 55% (average) and 50% (maximum month).

Digester gas production typically ranges from 1218 cubic feet per pound ofvolatiles destroyed. For the purpose of the conceptual design, a value of 15 cubicfeet per pound of volatile solids destroyed is used.

Heating value of digester biogas typically ranges from 500 to 650 BTU/cubic foot.To be conservative for the purpose of this conceptual design, a value of 550BTU/cubic foot is used.

5.3 Digester Gas UsageDigester biogas is typically used at wastewater treatment plants (WWTPs) to heat thedigester. In recent years, as the cost of power has increased and there is greater focuson renewable energy, biogas generated from digestion at WWTPs is often used incogeneration to produce heat and power. The power is typically used onsite to offsetthe amount of power purchased from the utility, while the heat is used for digester


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Average DailyBiogas Produced

(MMBTU/hr)

RatedEnergy InputPer Engine(MMBTU/hr)

Number of Units

NetElectrical

Output(Output Parasitic

Load) (kW

Recoverable Heatfrom Units

(MMBTU/hr)

140 kW

3.88 1.38 3 at 94% load 374 2.01

220 kW

3.88 2.11 2 at 92% load 384 1.97

280 kW

3.88 2.60 2 at 75% load 399 1.95

Table 5-2

Utilizing Biogas in Engine Application

Based on average daily flow, there is enough biogas produced to operate three140-kW engines at 94% load, two 220-kW engines at 92% load, or two 270-kW enginesoperating at 75% load.

The heating needs of the digester system versus the amount heat provided by theengine system are summarized in Table 5-3. Based on this evaluation all three enginesystems produce enough recoverable heat to heat the digesters year-round at average

day conditions.

Average Day

Winter Summer

Facility and Digester Required (MMBTU/hr) 1.74 0.68

Energy Available for Heating with 140 kW System(MMBTU/hr) 2.01 2.01



Table 5-3

Digester and Facili ty Heating Needs vs . Heat from Engine


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5.4 Recommended Cogeneration SystemThe recommended technology for cogeneration at the treatment plant is two 220-kWreciprocating engines. At average day flow, enough biogas is generated to operateboth engines at 90% load. It is recommended that the engines be sized to operate asclose to 100% load as possible, as engines operating at full load are the most efficient.At maximum month flow, enough biogas is generated to operate both engines at fullload. Two 220-kW engines are recommended over three 140-kW engines to reduceengine installation costs.

Accounting for estimated parasitic loads from biogas conditioning and compression,the system will generate approximately 340 kW of electricity. With the recommendeddigester configuration and material of construction, it is estimated that the reclaimedheat from the 220-kW engine system can meet the thermal loads of the digesters yearround. Typically, heat in the form of hot water is recovered from the engine jacketand exhaust gases. A hot water loop circulating between the cogeneration system andthe heat exchanges provides heat for the digesters.

5.5 Biogas Conveyance and StorageThe objective of the conveyance system is to convey biogas from the digester to theplace it is being consumed or stored. Anaerobic digestion does not produce biogas ata constant rate, while biogas is typically used at a constant rate, especially in acogeneration system. As such, it is beneficial for biogas systems to include biogasstorage to balance production and use.

5.5.1 Biogas Safety EquipmentIn biogas conveyance systems, biogas safety equipment is critical. As biogas isexplosive at low concentrations, it is crucial that the biogas handling system be fittedwith appropriate gas-safety equipment, to protect against the risk of ignition andexplosion. As there are significant electrical code classification issues associated withbiogas handling equipment, it is required that certain gas equipment be physicallyseparate from the remainder of the digestion equipment, but in close proximity to thedigester tanks.

Any source of ignition, such as waste gas burner, engines, or boilers must beprotected against flashback through the piping with a flame arrestor or flame traps. Aflame arrestor works to quench the flame by dissipating any heat from a potential

explosion in the piping. A flame trap is a combination of a flame arrestor and athermal shutoff valve. If a propagating flame is stopped by the arrestor but continuesto burn in the piping, a thermal element in the shutoff valve will melt and seal off theremainder of the upstream piping from the biogas source.

Although the intention is to maximize utilization of the biogas in the cogenerationengines, a waste gas burner system is necessary to safely combust all digester gasproduced at the facility in the event the engines and boiler are off-line. A waste gas


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burner safely flares excess biogas to the atmosphere and eliminates the potential forhazardous accumulation of biogas within the conveyance and storage system. Forsafety considerations a minimum of 50 feet is required between the waste gas burnerand the digester tanks.

See Figure 5-1 for the proposed layout of the gas safety and handling equipment.

5.5.2 Moisture and Sediment RemovalAfter leaving the digester, the biogas, at approximately 95 F, comes into contact withcooler piping and condensate forms within the pipeline. The condensate saturates thebiogas and, as such, the biogas conveyance system must be designed to removecondensate. The moisture formed within the gas conveyance system can deteriorategas handling equipment including check valves, relief valves, gas meters, andregulators and affect their performance. Moisture can also combine with hydrogensulfide present in the biogas to form a sulfuric acid that will corrode piping if the

moisture is not removed.

To effectively remove moisture and sediment, the biogas piping must be sloped toconvey condensate to condensate and sediment traps. Condensate and sedimenttraps consist of a sealed vessel that slows down the velocity of the biogas and allowsmoisture and solids to settle out of the biogas flow stream. The first condensate andsediment trap should be located as close to the digester as possible. As such, it isrecommended that a condensate/sediment trap be located in the biogas safetyequipment building, as indicated on Figure 5-1. Others will be located at low pointsin the biogas piping as the design develops.

5.5.3 Biogas Metering To measure the amount of digester gas produced by each digester, it is recommendedthat thermal mass dispersion meters be installed. Similar to the moisture andsediment removal systems, due to electrical code classification reasons, it isrecommended that these meters be installed within the biogas safety equipmentbuilding.

5.5.4 Biogas StorageAs previously noted, because digesters do not produce biogas at a constant rate,biogas storage is recommended. One common gas storage system is a floating gas-holder digester cover which floats on the biogas produced in the tank. The covermoves up and down to create variable volume and allow a constant biogas pressurewithin the headspace of the cover. However, as submerged fixed covers are therecommended option for the digester tanks, another means of biogas storage isrequired.

As discussed in Section 4.3, because the volume of existing sludge storage onsite islimited, it is recommended that a digested sludge storage tank be constructed. This


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Biogas Utilization : two 220-kW reciprocating engines, producing electricity andhot water for use on-site; and

Biogas treatment : hydrogen sulfide removal and biogas pressure boosting.


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Section 6 Architectural and Structural Considerations

A 6-2

Where applicable, vehicular loads will be determined in accordance with:

AASHTO Standard Specification for Highway Bridges

6.2 Architectural Considerations6.2.1 Option 1 Buildings and StructuresFunctional areas which will be addressed as part of the plant upgrade with thisdesign approach are as follows ( indicates structures with architectural implications):

Existing Process Building There will be a New Gravity Belt Thickener Roomwith an area of approximately 2,084 sq. ft., comprised of two zones open into eachother and without any interruptions: one measuring approximately 45'-9 "x 36'-8" and the other measuring approximately 14'-7" x 28'-0". The Room will be accessedfrom the corridor through an air-lock vestibule with an area of 106 square feet andthrough two sets of double doors equipped with pressure gaskets. The walls willbe 2-hr rated and five vision panels equipped with rated safety glass will also beprovided. Additionally, a New Electrical Room with an area of 356 square feetwill be provided with approximate dimensions of 45'-9" x 7'-10". The NewElectrical Room will be provided with an independent set of 90-min. rated doubledoors. The two new rooms will be adjacent to each other and separated by a2-hour rated 6-inch CMU wall and communicating through a 90-min. rated singledoor.

Tanks There will be two new cast-in-place digester tanks with a 65-foot interiordiameter; provisions for the expansion to a future cast-inplace digester tank withthe same dimensions as the new proposed ones are also being made; additionallythere will be a cast-in-place sludge & gas holding tank with a 50-foot interiordiameter.

Tank Locations The four tanks are placed with their centers, each located onone of four vertices of an imaginary square with a side measuring approximately94 feet. The new digesters are located respectively on the West and South vertices,the future digester on the North vertex and the storage/gas holding tank on theEast vertex of the square. Please refer to paragraph 6.3.9 for additional facilityspecific structural design considerations.

New Digestion Building The building will have a square footprint with thesides measuring approximately 45 feet, and located in the center amongst all threeproposed and one future tank. The building is oriented in such a way so that itsvertices are diagonally oriented in relation to the imaginary square whose verticesare occupied by the centers of the tanks. The building vertices will be locatedrespectively at the North-South/West, and at the North-South East. The buildingwill have two levels. The lower level will be entirely occupied by a Sludge PumpRoom and by an enclosed Stairwell leading to the exterior through the upper levelat grade. The upper level will be occupied by the Boiler/Heat Exchanger Room,


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by the Electrical Room with its independent entrance opening directly to theexterior, and by the enclosed Stairwell leading to the exterior.

New Gas Safety Equipment Building The small approximately 12' x 20'

enclosed structure will primarily house gas safety equipment. It will beconstructed with reinforced 8-inch CMU and with a precast concrete hollow coreplanks and provided with an access door.

New Waste Gas Burner Exterior pad mounted flare system.

New Gas Treatment Skid The equipment will be installed on an exteriorconcrete pad measuring approximately 26'- " x 42'-8" and covered with aprefabricated steel canopy system measuring 24'-0 " x 40'-0". The canopy will bestructured with steel tubes along 4 frames spaced at 13'-4 " from each other andshaped in a gable fashion with a central ridge to span the 24'-0 " side of the canopy.

The roof will be built with corrugated metal deck and standing seam metal panels. New Cogeneration Engines Two exterior Pad mounted generators with

vendors enclosures.

6.2.2 Option 2 Buildings and StructuresFunctional areas which will be addressed as part of the plant upgrade with thisdesign approach are as follows ( indicates structures with architectural implications):

Existing Process Building Refer to Option 1 at paragraph 6.2.1 above plus thefollowing additional changes:

a. New Boiler/Heat Exchanger Room The new room with an area ofapproximately 1,516 square feet will be located in an area currently occupiedby the screening garage and by a portion of the headworks area. It will beseparated by 2-hr rated 8-inch reinforced CMU wall. One door will be used toegress the room to the exterior.

b. New Headworks The new space will have an area of approximately 1,085square feet, therefore reduced from the current size, and it will be separatedfrom the adjacent Boiler/Heat Exchanger Room by the new 2-hr ratedreinforced 8-inch CMU wall. The existing exterior door will have to berelocated to the south to accommodate a new dumpster garage on the Eastside.

c. New Screening Dumpster Garage The garage, with an approximate size of16'-0"x 20'-0", will be structured with a separate frame of cast-in-place concretecolumns and beams and with reinforced 8-inch CMU infill walls. The roof willbe structured with precast concrete hollow core planks. The dumpster can be


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accessed by a truck through a 12-foot wide by 14-foot high aluminum coilingroll-up door.

d. New Exterior Stair Due to the new screening dumpster garage the exterior

stair to the East side where the garage will be added, will need to bedemolished and rebuilt at its relocated position to the South of the current one.

Tanks There will be two new cast-in-place digester tanks with a 50-foot interiordiameter, and one cast-in-place sludge and gas holding tank with a 50-footinterior diameter.

New Sub-grade Sludge Pump Room and Tunnel The new Pump room will beentirely below grade between the two digester tanks, with an approximate area of1,656 square feet. The sides of the room flanking the two digesters will have anadditional segmented separation wall to follow the curvature of the digesters and

it will be built with reinforced 8-inch CMU. A cast-in-place concrete tunnel willconnect this room to the existing building below grade and a cast-in-placeconcrete egress stair will lead off the tunnel to the exterior above grade.

New Gas Safety Equipment Building Refer to Option 1 at paragraph 6.2.1above.

New Waste Gas Burner Refer to Option 1 at paragraph 6.2.1 above.

New Gas Treatment Skid Refer to Option 1 at paragraph 6.2.1 above.

New Cogeneration Engines Refer to Option 1 at paragraph 6.2.1 above.

6.2.3 Building SystemsThe existing plant buildings are constructed with reinforced concrete structuralsystems. Galleries, basements and above grade buildings have poured concrete walls,floors, columns and beams. Roofs are precast concrete double tees, except theDigester and Sludge Thickener Buildings have poured concrete roofs. Exterior wallsare masonry consisting of face brick exterior with concrete masonry backup, withoutinsulation. Interior partitions are concrete masonry. Windows are aluminum anddoors and louvers either aluminum or steel painted. These buildings are in soundcondition and can be repaired and reroofed, if necessary, to extend their useful life.

6.2.4 Building Materials and Finishes

6.2.4.1 Existing Process Building (both Options)The configuration, materials and finishes of the New Gravity Belt Thickener andElectrical Rooms will be the same in both design approaches, as described inparagraph 6.2.1 above. There is one additional element that needs to be taken intoconsideration, which is relevant to the staging for the removal of the existing


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equipment, but much more critical to the installation of the new Gravity Thickeners,and it is the temporary removal of the existing window system to allow theinstallation of the Thickeners and re-installation of the same in place. This additionalconsideration has been made with the assumption that the existing window systemcan be, indeed, temporarily removed and reinstalled. During final design,replacement of this with a new window or with a fully insulated wall should beconsidered. A hazardous materials assessment survey will be required in the existingbuildings to determine the location and approximate quantities of hazardousmaterials that are or might be present in areas subject to modifications.

6.2.4.2 New Digestion Building (Option 1)The walls below grade will be reinforced bearing cast-in-place concrete walls.Additional vertical loads within the building footprint will be handled by cast-in-place columns. Above grade, the building will be structured with reinforced 8-inchbearing CMU wall at the perimeter and additional intermediate locations of verticalload discharge will be handled by steel columns on top of the cast-in-place columns atthe lower level. The exterior walls will have a 4-inch cavity with rigid insulation andwill be faced with 4-inch ground face CMU, in a grey color to blend within thecomplex of the cast-in-place tanks around it. The flat roof will be structured withprecast concrete hollow core planks, and tapered insulation will provide the neededslope to direct the drainage of water to roof drainage inlets. The roof will be coveredwith Thermoplastic Polyolefin (TPO) roofing membrane. The enclosed stairwell willbe 2-hr rated, and structured similarly to the rest of the building with cast-in-placeconcrete below grade and CMU above grade.

6.2.4.3 New Gas Safety Equipment Building (both Options)In addition to the information provided at paragraph 6.2.1 above, the design willconsider the use of tapered insulation at a minimum, not for thermal reasons, but toprovide drainage slope to direct water to the proper outlets (i.e., two scuppers) andthe covering of the roof with TPO roofing membrane.

6.2.4.4 New Gas Treatment Skid (both Options)In addition to the information provided at paragraph 6.2.1 above, the design willconsider specifying galvanizing and, for added long-term protection, painting all thepre-engineered steel frames. Additionally, the system will require some braced baysto be determined by the vendor and to be approved by the Engineer, in order toprovide lateral stability.

6.2.5 Roofing SystemsThe proposed system for all new stand-alone structures or addition to existingbuildings is generally a TPO roofing membrane adhered to underlayment board overtapered rigid polyisocyanurate insulation over a vapor retarder sheet. The assemblywill be adhesive or mechanically attached to the roof deck. Insulation will be of


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thickness necessary to meet energy code requirements (New Digestion Building onlyin Option 1) and to provide drainage slopes.

6.2.6 Proposed Interior FinishesInterior finishes should be appropriate to the use of the space, durable and facilitatemaintenance of clean and sanitary conditions. Spaces such as the headworks, wherewastewater is processed, and moisture is constantly present, should have finishes thatresist physical abuse and moisture damage, are readily washed down and inhibitcorrosion of building elements. Pipe galleries, pump rooms and the garage, wherecondensation may occur, humidity may be high and occasional wash down isrequired, should have finishes that protect building elements from corrosion, as wellas resistant to damage from the atmosphere and usual activities occurring in thespace. Finishes in rooms intended for employees should be suited to their particularfunction, resistant to moisture and chemicals, readily cleanable and contribute togood illumination and acoustics.

The following are proposed finishes intended to fulfill these objectives:

6.2.6.1 Floors Subject to chemicals or regular wash down epoxy seamless flooring

Dry process areas, garage hardened concrete with sealer

6.2.6.2 Walls Process, electrical and mechanical rooms, garage epoxy painted

6.2.6.3 Ceilings Exposed structure, epoxy painted

6.2.6.4 Doors and Frames Exterior Stainless Steel for long life, ease of maintenance and durability.

Interior FRP for better responsiveness to moist environment with or withoutchemically aggressive conditions.

6.3 Structural Considerations

6.3.1 Design Loads and ServiceabilityApplicable loads and load combinations will be determined as required by thegoverning code, occupancy, site and environmental effects, equipment, and processes.Appropriate load combinations will be established, as well as, appropriate allowablestresses, load factors, and safety factors (as applicable). These criteria will beconfirmed at the beginning of final design.


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6.3.1.1 Dead LoadsDead loads are those resulting from the weight of fixed construction such as walls,partitions, floors, roofs, cladding, equipment bases, and permanent, non-removable,stationary furnishings. Numerical values for the dead load of well-definedcomponents of a structure will be used as documented in the following publications:

ASCE 7, Minimum Design Loads for Buildings and Other Structures

AISC Manual of Steel Construction

CRSI Handbook

Manufacturer's catalogs for fabricated components

6.3.1.2 Live Loads

Live loads will consist of loads due to occupancy, furnishings and equipment. Liveload reduction will not be employed for members of large influence area in the designof environmental facilities, due to the relatively high probability of simultaneousloads on all areas. Uniform live loads will be established in accordance with thegoverning code. Values are listed below for purposes of preliminary design. Actualusage and equipment will be considered during final design and higher loadings usedwhen appropriate.

General Administrative Buildings

Office areas 50 psf

Office file, record and mainframe computer areas 125 psf Personnel assembly areas 100 psf

Stairways, corridors, lobbies 100 psf

Partitions (present or future) 30 psf

Roofs 20 psf

Storage areas 250 psf

Catwalks 100 psf

Garages, passenger cars only 100 psf

Garages, other vehicles AASHTO load or design vehicle

Process Buildings and Structures

Office areas 150 psf

Office file, record and mainframe computer areas 150 psf

Personnel assembly areas 150 psf

Stairways, corridors, lobbies, catwalks 150 psf


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load, and 10 percent of the sum of the hoist capacity and total crane weightwill be applied as a longitudinal load.

9 Monorail supports 25 percent of hoist capacity. 10 percent of the sum of the

hoist capacity and hoist weight will be applied as a longitudinal load.9 Light machinery supports, shaft or motor driven 20 percent of the operating

weight (minimum) or manufacturer's recommendation.

9 Reciprocating machinery or power-driven unit supports 50 percent of theoperating weight (minimum) or manufacturer's recommendation.

9 Hangers supporting floors or balconies 33 percent of live load reaction

Construction Live LoadsWhen it is necessary to provide particular restrictions on construction sequencing,special load conditions may result. This is particularly applicable to work involvingthe modification of existing structures. These cases will be evaluated and appropriatecriteria established during final design. Such restrictions will be indicated in thedrawings or specifications.

6.3.1.3 Environmental LoadsSnow and Rainwater LoadsSnow loads will be developed from the following criteria in accordance with thegoverning code. Appropriate modification factors, drifting effects, and unevendistributions will be considered for each structure.

Ground snow load: 70 psf

Importance factor: Establish for each structure per governing codebased on occupancy

Roofs will be designed for retained water to its maximum depth (accounting fordeflection) assuming that the primary drainage system is blocked. Overflow scuppersor other secondary drainage systems may be used to minimize this load. Thiscriterion will be coordinated with architectural and plumbing disciplines.

Wind LoadsWind loads will be developed from the following criteria in accordance with thegoverning code. Appropriate shape modification factors, uneven distributions, andorthogonal effects will be considered for each structure. Main wind force resistingsystems, as well as appropriate components and cladding, will be designed forinternal and external effects. Increased allowable stresses or reduced load factors willbe used, as appropriate.


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The effects of any load type (other than dead load) will not be used to reduce theeffects of another load type. A maximum of 90 percent of the dead load will beused in any combination where it reduces the effects of another load type.

Liquid Containing or Below-grade StructuresDesign will be performed for structures that contain liquids, extend below grade, orboth, for the following load combinations.

Liquid-containing compartments full, no backfill for liquid containingcompartments. No reduction will be made for any counteracting soil pressure onthe face remote from a contained liquid unless approved.

Backfill and groundwater with liquid-containing compartments empty and full.

Liquid containing compartments empty or full in any combination.

6.3.2 ServiceabilityAdditional requirements for serviceability will be considered as provided insubsequent sections and referenced standards for specific materials.

6.3.2.1 DeflectionDesign will be performed to limit deflections to the following. In cases indicated withan asterisk (*), deflection limit will apply to live load effects only. For monorails andcranes, impact need not be included.

Monorails, including the effects of differential support deflection L/450

Bridge crane girders L/1000

Floor plates and gratings* L/360

Beams, lintels or slabs supporting masonry L/720 (3/8 inch maximum atwindows)

Roofs without plastered ceilings* L/240

Roofs with plastered ceilings* L/360

Floors, steel framed* L/360

Floors, concrete In accordance with ACI 318

6.3.2.2 Ponding Ponding refers to water retention due to the effects of deflection on a flat roof. Forflexible roof systems, sufficient stiffness will be provided to prevent successive waterretention and deflection leading to failure.


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6.3.3 Foundation Design6.3.3.1 ScopeCriteria will be established for the design of structure foundations in coordination

with the geotechnical recommendations. Permanent structure foundation elementswill be designed to distribute loads to the supporting soil in accordance with theirallowable loads, and to accommodate predicted deformations of the structure causedby settlement or movement of the supporting elements. Structure foundationelements will be designed to resist effects of groundwater, including buoyancy.

6.3.3.2 Frost ProtectionProtection will be provided for structures against excessive heave or settlement due tothe action of frost. In most cases, the bearing level of frost-susceptible foundationelements will be established below the frost depth as provided in the geotechnicalreport. For minor structures that are tolerant to some movement, bearing level may

be established above the frost depth, provided that frost formation can be inhibited inthe zone between the bearing level and frost depth by providing a layer of free-draining material.

6.3.3.3 Shallow Foundation SupportDesign of shallow foundation elements (footings and mats), including excavation andbackfill limits and details, will be performed in accordance with the recommendationsof the geotechnical report.

To the extent possible, buried piping and ductbanks will be maintained outside theinfluence zone of the foundation elements. Limits of this zone will be established

based on bearing materials characteristics as documented in the geotechnical report.A reinforced concrete encasement or other appropriate protection will be provided forany utilities extending into this zone.

6.3.3.4 Retaining WallsThe stability of retaining walls will be confirmed for appropriate lateral soil andgroundwater pressures, surcharges and other applicable loads. Passive pressuresfrom the soil in front of the wall or footing keys will not be used to reduce loads,stresses, or overturning and sliding effects, unless measures are taken to ensureagainst erosion or removal of the soil and approved. Design will be performed for thefollowing factors of safety.

Overturning: 2.0

Sliding: 1.5

For design of retaining walls with portions below the design groundwater level, theeffects of uplift pressures will be considered in stability analyses.


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will be performed by the fabricator or erector, in accordance with criteria provided inthe contract documents.

Precast site structures, including manholes, vaults, pipe, culverts, and headwalls

Precast, prestressed roof planks and tees

Precast architectural elements, including wall panels, copings, and sills

6.3.4.2 Codes and StandardsConcrete structures will be designed in accordance with the following, as appropriate.

General structures: ACI 318

Environmental engineering structures: ACI 350

Reinforcing steel, welding: AWS D1.4

Structures that convey, store or treat liquid, are subjected to severe exposures, or haverestrictive leakage requirements will be designed as environmental engineeringstructures.

Design of miscellaneous roadway structures, such as culverts and headwalls will beperformed in accordance with the state highway standards and the AASHTOSpecification.

6.3.4.3 Materials and Design StrengthsDesign will be performed for concrete with the following minimum 28-daycompressive strengths (f c).

Structural concrete: 4,000 psi

Concrete topping: 4,000 psi

Precast concrete: 5,000 psi

Prestressed concrete

Date post:	03-Apr-2018
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