Animal waste may supply cleaner power
NEW YORK - Cows, pigs and chickens in the U.S. produce enough manure to supply 2.4 per cent of the nation's electricity if the waste were converted into burnable gas, an energy option overlooked by the government, researchers said.
Igniting energy-rich biogas in turbines would cut U.S. global-warming emissions from power generation by 4 per cent, said Michael Webber, lead author of a study published today in the Institute of Physics' Environmental Research Letters. The paper is the first to assess the nation's ability to use livestock manure as a renewable fuel, said Webber, assistant professor at the University of Texas at Austin.
"It's a big enough number that we care,'' Webber said in an interview. "There's enough potential for biogas manure that it might be something policy makers consider.''
Farmers who already use systems that convert animal waste into fuel see thin profits, said Susan Wood, chief executive officer of SCC Americas, a Houston-based company that develops projects to eliminate greenhouse gases from farms, landfills and coal mines. Wider use of livestock excrement for fuel won't come without stronger incentives, she said.
"It'll probably take a dramatic shift in the carbon markets and in the price of carbon before people start looking at this on a regular basis,'' Wood said in an interview, referring to the price of a permit to release carbon dioxide, that main gas blamed for global warming.
SCC Americas is unit of Sindicatum Carbon Capital, a London- based developer of projects to curb planet-warming gases that's backed by Gulf One Investment Bank and American International Group Inc.
Farmers who produce biogas benefit by lowering their electricity costs, selling the gas, or selling carbon emissions permits that represent greenhouse gases destroyed before they reach the atmosphere. Profit depends on the cost of electricity and natural gas, and the price those permits, Wood said.
Cost benefits are "very area specific,'' Wood said. "Most of the projects are really marginal because of power and gas prices.''
Some farmers are realizing the benefits of converting manure to fuel, said Richard Sandor, chairman of the Chicago Climate Exchange, owner of emissions markets in London and Chicago. Members of the exchange buy credits from farms that destroy methane, and use them to meet voluntary greenhouse gas targets. A credit representing one ton of emissions cost $3.90 on the exchange at the close of trading Wednesday.
"We recently gave one dairy farmer $10,000 in biogas credits, so now he's got a new business model -- 80 per cent milk and 20 per cent environmental services,'' Sandor said today in an interview. "If I can get that with a $5 credit price. Could you imagine if it was $20 or $30?''
Some U.S. states and regions are developing programs to limit greenhouse gases, which may increase the value of carbon credits. Congress is debating a national climate program.
Livestock produce more than 1 billion tons of manure a year, according to the study, Cow Power: The Energy and Emissions Benefits of Converting Manure to Biogas. Most is collected in ponds or left outdoors to decompose, which produces air pollution and greenhouse gases such as methane. Methane has 21 times the global-warming potential as carbon dioxide.
Emissions from agriculture account for 7 per cent of U.S. greenhouse gases, according to the U.S. Environmental Protection Agency. Concentrations of methane in the atmosphere have tripled in the last two centuries, the United Nations Intergovernmental Panel on Climate Change said last year. Nitrous oxide, another gas from decomposing manure, has increased 25 per cent.
"Finding other approaches to manure management that decrease these emissions represents a valuable starting point for mitigating concerns about global climate change in the agricultural sector,'' according to the study.
Cows, which weigh about 1,000 pounds (454 kilograms), represent one animal unit, the measure used by researchers to calculate the amount of biogas energy from a farm animal. It takes four pigs or dozens of chickens to make up one animal unit, and there are 95 million animal units in the U.S.
While technology exists to capture the energy potential of livestock waste, tapping renewable fuel from all 95 million animal units is unrealistic, Webber said. The right government policies, such as subsidies or low-interest loans for equipment to convert feces into combustible gas, could help farmers harness energy from about half their animals.
Anaerobic digesters, which use microorganisms to convert the waste into biogas, may initially be best used on large farms with more of the raw material, Webber said. In Sweden and Germany, digesters are installed at smaller farms where the output is combusted to make electricity on site. Biogas, which is 60 per cent to 70 per cent methane, could also be sold to a central plant.
"Farmers are already handling it,'' Webber said. "They're just not getting money out of it while it's creating an environmental hazard'' left untreated.
U.S. global-warming emissions including methane and nitrous oxide reached 7.08 billion metric tons in 2006, according to a report from the Energy Department. Capturing gases from all livestock waste and using it to displace coal-fired electricity generators would cut emissions by 99 million tons, about 4 per cent of climate-change pollution from power generation.
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