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

Outline u u What is Cogeneration u u Biogas and It’s Uses u u Cogeneration Project Details u u What is Co-Digestion u u Grease Trap Waste and How It Can Be Used u u Future of Co-Digestion at SWWTP u u Questions and Answers 2

3 What is Cogeneration? u 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 43% 22% 35% Recoverable Mechanical Energy Unrecoverable Waste Heat Waste Heat Recoverable Waste Heat

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

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

6 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% DWU 7% Reduction (30,000,000 kWh/Year) 430,000,000 kWh / Year 60% Reduction (30,000,000 kWh/Year) 50,000,000 kWh / Year CITY 790,000,000 kWh/Year 4% Reduction (30,000,000 kWh / Year) SOUTHSIDEWWTP

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

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

Benefits of the Project u The City will reduce its grid derived electricity needs by 30,000,000 kWh per year u Reduced cost of electricity will result in annual savings of approximately $1,500,000/year u Project will generate approximately 30,000 Renewable Energy Credits (REC’s) per year. u The REC’s generated may also be used towards LEED’s certification. u No need for additional labor or skill set above staff’s current capabilities u Project will reduce region wide emissions 9

Co-Digestion 10

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

High 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, ft 3 gas/per ton Brown Grease yields 4x the amount of gas as WWTP solids

Grease Trap Waste (Brown Grease) u u First phase of Co-digestion to focus on brown grease u u Items yet to be determined – –Amount of grease that can be digested – –Hauling to the plant site – –Effects on the Cogeneration Facility u u If successful future phases will include other high strength wastes 13

u u Increase in biogas production, electricity and hot water – –75,000 gallons/day = $760,000/year u u Potential revenue from tipping fees – –75,000 gallons/day = $1,600,000/year u u Increased solids destruction 14 Benefits of Brown Grease Digestion

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

Potential Drawbacks u u Increased digester maintenance will be necessary to prevent clogging in the mechanical systems u u Digester upsets due to foreign and/or toxic substances u u Increases in truck traffic could pose a nuisance to the surrounding neighborhood u u Expansion of the Cogeneration Facility will adversely impact air quality and air permitting at the plant 16

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

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

Questions?