Wastewater: a trifecta of resources

Wastewater is typically considered something to quickly dispose of, but in San Antonio, Texas wastewater is turned into valuable resources: an ‘environmental trifecta’ of recycled water, organic biosolids, and methane gas.

*By Robert C. Brears

To reduce San Antonio’s dependency on the drought-sensitive Edwards Aquifer for the city’s water needs, the San Antonio Water System (SAWS) has developed the largest direct recycled water system in the United States. More than 130 miles of pipeline deliver up to 35,000 acre-feet per year of high-quality recycled water for non-potable uses including golf courses, parks, and commercial and industrial customers throughout the city. The system is also designed to supplement flows in the San Antonio River and Salado Creek. In addition, recycled water supplies up to 50,000 acre-feet per year for CPS Energy’s power plants.

SAWS Composting Program

The SAWS Composting Program uses a combination of wood chips and biosolids to form compost, with the program diverting up to 150,000 cubic yards of wood chips from landfills each year while the biosolids component, the by-product of water recycling, diverts up to 208,000 cubic yards of biosolids from landfills each year. SAWS has partnered with New Earth to conduct all compost-related activities. This provides better service for compost customers and lowers the costs for SAWS ratepayers.

Harnessing methane gas

SAWS is harnessing methane gas generated during the wastewater treatment process as a renewable energy source. The biogas — which is 60% methane — is a by-product of the anaerobic digestion process from biosolids, with San Antonio producing around 140,000 tons of biosolids per annum. SAWS has partnered with Ameresco, Inc., a national energy company that focuses on renewable energy. Since 2010, Ameresco has processed more than 1.5 million standard cubic feet of biogas a day and delivered a minimum of 900,000 cubic feet of natural gas each day to the nearby commercial pipeline to sell on the open market. Economically, SAWS receives around $200,000 in annual royalties from the sale of the biogas, reducing the costs of SAWS operations and keeping rates affordable, while environmentally the harnessing of biogas instead of flaring reduces 19,739 tons of carbon dioxide each year.

The take-out

Wastewater creates new water, revenue, and material sources.

*Robert C. Brears is the author of Urban Water Security (Wiley), The Green Economy and the Water-Energy-Food Nexus(Palgrave Macmillan), Natural Resource Management and the Circular Economy (Palgrave Macmillan), Blue and Green Cities: The Role of Blue-Green Infrastructure in Managing Urban Water Resources (Palgrave Macmillan), and Climate Resilient Water Resources Management (Palgrave Macmillan). He is Founder of Our Future Water, Mitidaption, and Mark and Focus.

· LinkedIn Groups: Our Future Water / Urban Water Security

· Twitter: Mitidaption / YoungH20Leader / Our Future Water