The Missouri Senate gave initial approval Tuesday to a bill allowing methane gas produced by animal waste to count toward the state's renewable energy mandate for electricity providers.

A 2008 voter-approved law requires investor-owned utilities to get 15 percent of their electricity from renewable resources by 2021, with gradually increasing thresholds before then.

The law says at least 2 percent must come from solar energy. Other accepted resources include hydropower and biomass.

Methane gas created from landfills or human wastewater already is considered a renewable resource that fulfills the mandate. But state law doesn't count methane made from animal waste.

Bill sponsor Sen. Frank Barnitz, D-Lake Spring, said adding animal waste to the acceptable list provides another method for utility companies to meet the percentage mandates.

"If we constrain or reduce the number of renewable energy resources out there it won't be feasible," Barnitz said. "What I don't want to happen is that we set a standard so high that we have to go outside the state of Missouri" for more costly energy sources.

According to the U.S. Department of Energy, pulling methane gas from waste uses a process called anaerobic digestion or methane recovery. Similar to how natural gas is created, anaerobic bacteria digest organic material when there is no oxygen and then produce biogas.

The bacteria must be kept at a consistent temperature around 98 degrees. The biodigester — where waste is stored during the process — can be very expensive and usually is more economically viable for large scale livestock operations that produce a lot of waste.

"The technology is moving quickly to make those less expensive," Barnitz said.

No investor owned utility companies currently use methane gas from landfills or human wastewater, though several municipal utility companies do, said Lena Mantle, the energy department manager for the Missouri Public Service Commission. She said utility company AmerenUE recently announced a landfill-based methane project in St. Louis that is expected to open in 2011.

The federal Environmental Protection Agency counts 10 Missouri landfills that use their methane to generate electricity and has identified four others as potential candidates through its Landfill Methane Outreach Program.

Copyright 2010 The Associated Press.