Pipes that extract methane gas generated by waste decomposition are seen at the Simi Valley Landfill and Recycling Center in Simi Valley, California May 8, 2008. REUTERS / Hector Mata

SAN ANTONIO (Reuters) - San Antonio unveiled a deal on Tuesday that will make it the first U.S. city to harvest methane gas from human waste on a commercial scale and turn it into clean-burning fuel.

San Antonio residents produce about 140,000 tons a year of a substance gently referred to as “biosolids,” which can be reprocessed into natural gas, said Steve Clouse, chief operating officer of the city’s water system.

“You may call it something else,” Clouse said, but for area utilities, the main byproduct of human waste - methane gas - will soon be converted into natural gas to burn in their power plants.

The city approved a deal where Massachusetts-based Ameresco Inc will convert the city’s biosolids into natural gas, which could generate about 1.5 million cubic feet per day, he said.

Methane gas, which is a byproduct of human and organic waste, is a principal component of the natural gas used to fuel furnaces, power plants, and other combustion-based generators.

“The private vendor will come onto the facility, construct some gas cleaning systems, remove the moisture, remove the carbon dioxide content, and then sell that gas on the open market,” Clouse said.

The gas will be sold to power generators, he said.

Some communities are using methane gas harvested from solid waste to power smaller facilities like sewage treatment plants, but San Antonio is the first to see large-scale conversion of methane gas from sewage into fuel for power generation, he said.

Following the agreement, more than 90 percent of materials flushed down the toilets and sinks of San Antonio will be recycled, he said. Liquid is now used for irrigation, many of the solids are made into compost, and now the methane gas will be recycled for power generation.