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Dallas Water Utilities Southside Wastewater Treatment Plant

Turning Waste Into Energy. Dallas Water Utilities Southside Wastewater Treatment Plant Cogeneration and Co-Digestion Projects May 9, 2011. Outline. What is Cogeneration Biogas and It’s Uses Cogeneration Project Details What is Co-Digestion Grease Trap Waste and How It Can Be Used

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Dallas Water Utilities Southside Wastewater Treatment Plant

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  1. Turning Waste Into Energy Dallas Water Utilities Southside Wastewater Treatment Plant Cogeneration and Co-Digestion Projects May 9, 2011

  2. Outline • 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 2

  3. What is Cogeneration? • Cogeneration is the production of two types of energy such as heat and electricity from one fuel source in such a way that both are useable Recoverable Mechanical Energy 35% Unrecoverable Waste Heat 22% Recoverable Waste Heat 43% 3

  4. What is Biogas? • Biogas is the methane (CH4) produced as a by-product of the anaerobic digestion process at the Southside Wastewater Treatment Plant • DWU’s biogas was used to fire boilers to heat the digesters, but a large portion was burned off in flares • Biogas is a renewable fuel source that can be used to generate electricity in lieu of using coal or natural gas 4

  5. M M 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. Gas Storage Heat and Power Generation Gas Compression Hot Water Supply and Return Lines How Can Biogas Be Used? Screenings Removal Grit Removal Primary Clarification Secondary Clarification Aeration Filtration Raw Sewage Treated Effluent Receiving Stream Screenings Grit Primary Sludge Secondary Sludge Gas Flare Digesters 5

  6. CITY As a fuel to generate electricity, DWU’s Biogas has the potential to reduce the City of Dallas’ total grid derived electricity consumption by almost 4% 7% Reduction (30,000,000 kWh/Year) 60% Reduction (30,000,000 kWh/Year) DWU SOUTHSIDE WWTP 430,000,000 kWh / Year 50,000,000 kWh / Year 4% Reduction (30,000,000 kWh / Year) 6 790,000,000 kWh/Year

  7. Cogeneration Site Electrical Biogas Hot Water Treatment Plant / Cogeneration Site Layout 7

  8. DWU RESPONSIBILITIES • Provide Utility Connections • Produce Guaranteed Quantity and Quality of Biogas • Purchase Electricity • Utilize REC’s L/D RESPONSIBILITIES • Design/Build/Finance/Operate Cogeneration Facility • Generate/Deliver Electricity • Generate/Deliver Hot Water • Permit Facility • Capitalize on Rebates/Tax Credits Renewable Energy Leasing Project Details DWU RESPONSIBILITY LESSEE/DEVELOPER RESPONSIBILITY WH Meter Southside WWTP Main Substation Natural Gas To/From Oncor Biogas Supply To WWTP Loads Meter WH From Oncor Gas Storage Gas Compression Meter WH Hot Water Supply and Return Meter Southside Digesters Meter 8 Guaranteed

  9. Benefits 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 9

  10. Co-Digestion 10

  11. What is Co-Digestion? High Strength Wastes Receiving facility $ Biogas Co-generation Digesters Solids from Wastewater Treatment Plant Solids Dewatering Land Application 11

  12. High Strength Wastes and Related Gas Production Grease Trap Waste 660 Restaurant Waste Food Waste 165 Raw Sludge Brewer's Grain Brown Grease yields 4x the amount of gas as WWTP solids Sugar Cane Poultry Cattle Manure Methane Yield, ft3gas/per ton 12

  13. 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 13

  14. Benefits of Brown Grease Digestion • 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 14

  15. 0.8 tons of GHG 1 MW of Electricity Benefits of Brown Grease Digestion (cont’d) 1 ton 1 ton 23 tons GHG 15

  16. 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 16

  17. Cogeneration Site Digester Feed Line Grease Receiving Facility Treatment Plant / Cogeneration Site Layout 17

  18. Co-Digestion Details • Cost is anticipated to be around $3 million dollars • Expected payback is 2 years • Design RFP and Grease Hauling RFP are both scheduled for August 2011 18

  19. Questions?

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