The award-winning Southside Wastewater Treatment Plant commenced operations in 1964. Since then, the plant has grown from treating less than 10 MGD (millions of gallons per day) to the current permitted design of 110 MGD. Southside is one of two wastewater treatment plants owned and operated by the City of Dallas Water Utilities (DWU). Both plants are responsible for treating all of the wastewater generated by the estimated 1.25 million citizens of the city, along with eleven neighboring customer cities, which is about 260 MGD.
Southside stabilizes and disposes of the biosolids generated by both of the wastewater treatment plants. During the process of stabilizing the biosolids, methane (biogas) is produced as a by-product. Previously, the biogas was flared as a means of disposal, with only a small portion being used to generate hot water for plant needs. The Cogeneration Project allows the City to recover and utilize all of the energy provided by the biogas.
The Cogeneration Project is a twenty year lease agreement between the City of Dallas and Ameresco, Inc., in which Ameresco finances, designs, constructs, operates, and maintains the cogeneration facility. The City of Dallas supplies the facility with approximately 1.3 million ft3 of biogas per day, which is converted by engines into electricity and heated water. The electricity is sold back to the plant, and the hot water is returned to the plant’s hot water system, and is used for heating purposes. The cogeneration facility produces approximately 27,000,000 kWh/year, which is sold back to the City at a cost of approximately 6.5 cents/kWh, less than what the City is paying for grid-derived electricity.
Some Benefits of the Project Include:
- The project generates Renewable Energy Credits (REC’s), which the City uses for LEED certification of City facilities.
- The project will reduce the region’s overall emissions by eliminating the pollutants that would have been created by a power plant in the generation of 27 million kWh.
- The Cogeneration Project did not require any City capital upfront to construct (it would have cost about $10 million dollars).
- The plant reduces its grid-derived electrical needs by 27,000,000 kWh/year. This is a 50-60% reduction for the plant, and a 4% reduction for the entire City.
DWU offers a way for its citizens to be a part of this waste-to-energy system through its nationally recognized Cease the Grease program (CtG). CtG is an education and outreach program started in 2005 that helps Dallas residents properly dispose of fats, oils, and grease (FOG) through residential cooking oil recycling. DWU has nearly 25 CtG drop-off stations, where anyone can leave a sealed container of used cooking oil. That oil is collected and taken to Southside and becomes part of the cogeneration process. By including citizens in the cogeneration process, DWU has decreased grease-related sanitary sewer overflows by 93%.