Dallas Water Utilities Dallas Water Utilities

Southside Wastewater Treatment PlantSouthside Wastewater Treatment Plant

Cogeneration and Co-Digestion ProjectsCogeneration and Co-Digestion Projects

May 9, 2011May 9, 2011

Turning Waste Into EnergyTurning Waste Into Energy

OutlineOutline

What is Cogeneration

Biogas and It’s Uses

Cogeneration Project Details

What is Co-Digestion

Grease Trap Waste and How It Can Be Used

Future of Co-Digestion at SWWTP

Questions and Answers

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What is Cogeneration?What is Cogeneration?

Cogeneration is the production of two types of Cogeneration is the production of two types of energy such as heat and electricity from one fuel energy such as heat and electricity from one fuel source in such a way that both are useablesource in such a way that both are useable

43%43%

22%22%

35%35%

RecoverableRecoverableMechanical EnergyMechanical Energy

UnrecoverableUnrecoverable Waste HeatWaste Heat

RecoverableRecoverableWaste HeatWaste Heat

What is Biogas?What is Biogas? Biogas is the methane (CHBiogas is the methane (CH44) produced ) produced

as a by-product of the anaerobic as a by-product of the anaerobic digestion process at the Southside digestion process at the Southside Wastewater Treatment PlantWastewater Treatment Plant

DWU’s biogas was used to fire boilers DWU’s biogas was used to fire boilers to heat the digesters, but a large to heat the digesters, but a large portion was burned off in flaresportion was burned off in flares

Biogas is a renewable fuel source Biogas is a renewable fuel source that can be used to generate that can be used to generate electricity in lieu of using coal or electricity in lieu of using coal or natural gasnatural gas

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How Can Biogas Be Used? How Can Biogas Be Used?

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M M

ScreeningsScreenings GritGrit Primary Primary SludgeSludge

Secondary Secondary SludgeSludge

Treated Treated EffluentEffluent

Receiving

Stream

Screenings Screenings RemovalRemoval

Grit Grit RemovalRemoval

Primary Primary ClarificationClarification AerationAeration Secondary Secondary

ClarificationClarification FiltrationFiltration

Raw Raw SewageSewage

DigestersDigesters

Gas Gas FlareFlare

Heat and Heat and Power Power GenerationGeneration

Gas Gas StorageStorage

Gas Gas CompressionCompression

Hot Water Hot Water Supply and Supply and Return LinesReturn Lines

In lieu of current operations where a majority of the biogas is flared, the biogas can be sent to the generation facility for the production of electricity and hot water.

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As a fuel to generate electricity, DWU’s Biogas As a fuel to generate electricity, DWU’s Biogas has the potential to reduce the City of Dallas’ has the potential to reduce the City of Dallas’ total grid derived electricity consumption by total grid derived electricity consumption by almost 4%almost 4%

DWUDWU

7% Reduction7% Reduction(30,000,000 kWh/Year)(30,000,000 kWh/Year)

430,000,000 kWh / Year430,000,000 kWh / Year

60% Reduction 60% Reduction (30,000,000 kWh/Year)(30,000,000 kWh/Year)

50,000,000 kWh / Year50,000,000 kWh / Year

CITYCITY

790,000,000 kWh/Year790,000,000 kWh/Year

4% Reduction4% Reduction(30,000,000 kWh / Year)(30,000,000 kWh / Year)

SOUTHSIDESOUTHSIDEWWTPWWTP

Treatment Plant / Cogeneration Site LayoutTreatment Plant / Cogeneration Site Layout

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Biogas Hot Water

Electrical

CogenerationSite

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LESSEE/DEVELOPER RESPONSIBILITYLESSEE/DEVELOPER RESPONSIBILITYDWU RESPONSIBILITYDWU RESPONSIBILITY

Southside Southside DigestersDigesters

Gas Gas CompressionCompression

Natural Natural GasGas

Gas Gas StorageStorage

Southside Southside WWTP Main WWTP Main SubstationSubstation

MeterMeter

MeterMeter

WH

• Design/Build/Finance/Operate Design/Build/Finance/Operate Cogeneration FacilityCogeneration Facility

• Generate/Deliver ElectricityGenerate/Deliver Electricity• Generate/Deliver Hot WaterGenerate/Deliver Hot Water• Permit FacilityPermit Facility• Capitalize on Rebates/Tax CreditsCapitalize on Rebates/Tax Credits

L/D RESPONSIBILITIESL/D RESPONSIBILITIES

MeterMeterWH

From From OncorOncor• Provide Utility ConnectionsProvide Utility Connections

• Produce Guaranteed Quantity Produce Guaranteed Quantity and Quality of Biogasand Quality of Biogas

• Purchase ElectricityPurchase Electricity• Utilize REC’sUtilize REC’s

DWU RESPONSIBILITIESDWU RESPONSIBILITIES

MeterMeter

To WWTP To WWTP LoadsLoads WH

MeterMeter

To/From To/From OncorOncor

GuaranteedGuaranteed

Renewable Energy Leasing Project DetailsRenewable Energy Leasing Project Details

Hot Water Hot Water Supply and Supply and ReturnReturn

Biogas SupplyBiogas Supply

Benefits of the ProjectBenefits of the Project

The City will reduce its grid derived electricity needs by 30,000,000 kWh per year

Reduced cost of electricity will result in annual savings of approximately $1,500,000/year

Project will generate approximately 30,000 Renewable Energy Credits (REC’s) per year.

The REC’s generated may also be used towards LEED’s certification.

No need for additional labor or skill set above staff’s current capabilities

Project will reduce region wide emissions

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Co-DigestionCo-Digestion

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What is Co-Digestion?What is Co-Digestion?

High StrengthWastes

Receiving facility

Solids

Land ApplicationDewatering

Biogas

Co-generation

DigestersSolids from Wastewater

Treatment Plant

$

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High Strength Wastes and Related Gas ProductionHigh Strength Wastes and Related Gas Production

Cattle Manure

Poultry

Sugar Cane

Brewer's Grain

Raw Sludge

Food Waste

Restaurant Waste

Grease Trap Waste

Methane Yield, ft3gas/per ton

Brown Grease yields4x the amount of gas

as WWTP solids

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165

660

Grease Trap Waste (Brown Grease) Grease Trap Waste (Brown Grease)

First phase of Co-digestion to focus on brown grease

Items yet to be determined– Amount of grease that can be digested

– Hauling to the plant site

– Effects on the Cogeneration Facility

If successful future phases

will include other high strength

wastes

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Increase in biogas production, electricity and hot water

– 75,000 gallons/day = $760,000/year

Potential revenue from tipping fees

– 75,000 gallons/day = $1,600,000/year

Increased solids destruction

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Benefits of Brown Grease DigestionBenefits of Brown Grease Digestion

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Benefits of Brown Grease Digestion (cont’d)Benefits of Brown Grease Digestion (cont’d)

23 tons GHG

0.8 tons of GHG

1 MW of Electricity

1 ton

1 ton

Potential Drawbacks Potential Drawbacks

Increased digester maintenance will be necessary to prevent clogging in the mechanical systems

Digester upsets due to foreign and/or toxic substances

Increases in truck traffic could pose a nuisance to the surrounding neighborhood

Expansion of the Cogeneration Facility will adversely impact air quality and air permitting at the plant

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Treatment Plant / Cogeneration Site LayoutTreatment Plant / Cogeneration Site Layout

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CogenerationSite

Grease Receiving Facility

Digester Feed Line

Co-Digestion DetailsCo-Digestion Details

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Design RFP and Grease Hauling RFP are both scheduled for August 2011

Questions?Questions?