NOVEMBER 2008

San Antonio will turn sewage into energy

San Antonio Water System’s board of trustees approved a truly innovative contract that will make the utility the first in the nation to capture and sell methane generated while treating the city’s sewage.

The gas is generated by biosolids during the sewage treatment process. Eighty percent of biosolids – the solids remaining after liquid waste is removed – are used to generate compost. With the new contract, sewage treated at Dos Rios Water Recycling Center will now be used to generate environmentally friendly products, such as recycled water – which improves river quality and is used in place of potable water by industry and manufacturers – and compost, which is used to improve soil quality and energy.

“The citizens of San Antonio produce about 140,000 tons of biosolids each year,” said SAWS COO Steve Clouse. “Treating these biosolids generates an average of 1.5 million cubic feet of gas a day – that’s enough gas to fill seven commercial blimps or 1,250 tanker trucks each day.”

“Most of that gas is currently burned off using flares. We have been working hard over the last few years to develop a process to improve the consistent quality and quantity of gas produced. Now we’re very pleased that we can capture and sell it.”

This project includes a 20-year lease and operating agreement between SAWS and Ameresco. Ameresco will construct the gas conditioning and distribution facility and the pipelines necessary to transfer the gas to commercial gas pipelines. They will also be in charge of selling the gas on the open market. In return, SAWS will receive a 12 percent royalty on the sale of the gas – which helps reduce the cost of SAWS operations.

Said Clouse, “Early estimates put the revenue at about $200,000 to $250,000 a year. SAWS will be the only large wastewater utility actively selling biogas in the United States.”