San Antonio has signed a contract with a Massachusetts company to collect the methane produced by processing the Texas city’s human waste and sell it to utility companies to burn and produce electricity. Although some U.S. communities have collected smaller amounts of methane from sewage to power waste treatment plants, this is the first time that an American city will be collecting gases from human waste on a large scale to sell to utilities. Under the new plan, more than 90 percent of the human waste flushed down San Antonio’s toilets will be recycled. The city will use the liquid for irrigation, the solids to produce compost, and the gases for energy generation. Sewage gases are similar to natural gas, which is primarily composed of methane.