The final component of the “environmental trifecta” is harnessing methane gas generated during the wastewater treatment process as a renewable green energy source. This biogas, which is 60 percent methane, is a byproduct of the anaerobic digestion process from biosolids. Annually, San Antonio produces about 140,000 tons of biosolids.
SAWS partnered with Ameresco, Inc., a national energy company focusing on renewable energy, and by 2010 Ameresco began to process more than 1.5 million standard cubic feet of biogas a day and deliver a minimum of 900,000 cubic feet of natural gas each day to a nearby commercial pipeline to sell on the open market. (The 1.5 million cubic feet is enough gas to fill seven commercial blimps or 1,250 tanker trucks each day!)
By harnessing the biogas instead of burning the gas off using flares, the city enjoys one of the following annual carbon-reduction equivalents:
- The removal of 31,261 cars from the road.
- The planting of 38,736 acres of trees.
- The reduction of 19,739 tons of carbon dioxide.
- The heating of more than 4,689 average-size homes.
In addition to the environmental benefits, SAWS also receives about $200,000 in annual royalties through the sale of the biogas, which reduces the cost of SAWS operations and helps to keep rates affordable.
San Antonio is the first city to harness biogas using this unique renewable energy strategy. When combined with SAWS’ water recycling and compost efforts, it further demonstrates SAWS’ mission of providing sustainable, affordable water services for our growing city.