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 capacity 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 wastewater generated by the estimated 1.25 million citizens of the city, along with eleven neighboring customer cities. The permitted treatment capacity for both plants is a total of 280 MGD.
While wastewater treatment is performed by both plant, the residuals (biosolids) resulting from the wastewater treatment is processed by Southside, only. Southside Plant does this by stabilizing the biosolids generated by both treatment plants. During the process of stabilizing the biosolids, biogas (which is about 65% methane) is produced as a by-product. Previously, the biogas was mostly flared as a means of disposal, with only a small portion of the inherent energy used to produce hot water for plant needs. The Cogeneration Project allows the City to recover and utilize more of the energy contained in 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 cubic feet of biogas per day, which is converted by engines into electricity and hot water. The electricity, about 33 million kWh/year, 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.
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 reduced the region’s overall emissions by eliminating the pollutants that would have been created by a power plant in the generation of 33 million kWh.
- The Cogeneration Project did not require any City capital funds (construction cost is about $10 million dollars).
- The plant reduced its grid-derived electrical needs by about 33 million kWh/year. This is a 45% reduction in electricity 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 process through its nationally recognized Defend Your Drains – Cease the Grease Program (DYD-CtG). DYD-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%.