Energy Recovery and Efficiency Improvements Enhance Wastewater Treatment Sustainability

Two approaches to resource recovery and sustainability are described together with other energy savings measures to enhance sustainability and reduce the carbon footprint of wastewater treatment. The two case studies describe the measures implemented at the Dallas, Texas Southside Wastewater Treatment Plant and the San Antonio, Texas Dos Rios Water Recycling Center. Both are large advanced secondary treatment activated sludge plants with anaerobic digestion. After considering various options, engine generators were installed at the Dallas Southside plant to convert biogas into electricity, which is used by the plant. The Dos Rios plant also collects biogas, but installed a gas processing plant to strip carbon dioxide and produce pipeline-quality natural gas that is then sold on the open market. Both facilities engaged a private power developer to construct and operate the energy recovery facilities. The paper describes these energy recovery systems together with the respective energy and solids balances for each facility. Other resource recovery methods used or considered by the plants are also described. The results and net cost savings achieved by the plants are quantified. This consists of over $3 million/year in energy savings for the Dallas Southside wastewater treatment plant and $200,000-$250,000 per year in revenue for the San Antonio Dos Rios wastewater treatment plant.