Power From Poop: Putting Manure to Use

July 24, 2008 -- Researchers have identified a climate-energy win-win, but it may put them in deep doo-doo.

That's what happens when you study poop for a living. Michael Webber and Amanda Cuéllar of the University of Texas at Austin estimate that digesting all of the nation's livestock manure to produce methane to burn for energy could supply more than 2 percent of the country's electricity needs.

Meanwhile, the process would avoid the greenhouse gas emissions created by burning the equivalent amount of coal, and it would prevent the release of the super-potent greenhouse gases methane and nitrous oxide released by normal manure degradation, allowing for a double-whammy of greenhouse gas reduction.

The combined savings could reduce U.S. greenhouse gas emissions from electricity by about 4 percent.

"We wanted to look at what would happen if we took all the manure in the nation, which is currently an environmental liability, and turned it into a commodity as a source of energy," Webber said. The pair's work is published today in Environmental Research Letters.

Livestock in the United States unload more than a billion tons of manure each year, most of which ends up in lagoons or other outdoor locations where it decomposes, emitting methane and nitrous oxide, greenhouse gases 21 and 310 times more potent at warming than CO2, respectively.

The proposed approach would send the manure to anaerobic digesters where microorganisms would produce biogas rich in methane that could be captured and burned for energy, releasing the less-potent greenhouse gas CO2. The remaining solids could be used for fertilizer.

This approach would reduce other problems associated with manure ponds, including odor, air pollution, and water pollution from runoff or groundwater contamination, Webber said.

Digesters exist in the United States, and many more are used in Europe. But this is the first time anyone has studied the total potential of biogas production in the United States, he added. "The numbers are big enough that they're worth paying attention to."