Marin County
University of California
Marin County

West Marin ranchers hope to turn pasture pollution into cow power

02/03/2010

West Marin ranchers are seeking ways to turn a source of greenhouse gas emissions into a renewable energy supply.

That source is dairy cows, which produce about 3 percent of the methane, nitrous oxide and carbon dioxide in the United States that researchers believe contribute to global warming. Farmers and ranchers gathered in Point Reyes Station to discuss the issue Tuesday at an event hosted by the University of California Cooperative Extension, Western United Dairymen and the Marin Resource Conservation District.

"The bottom line is that you get manure on your farm 24 hours a day, 365 days a year," said Point Reyes rancher Bob Giacomini, who uses a methane digester to turn his cattle's by-products into power. "That's not true for wind or solar - and you can get more in grant funding for a digester than you can for wind or solar."

Cows produce a smaller percentage of greenhouse gases here than in other nations, where farming is a much larger part of the economy, and where it's practiced much less efficiently than in the United States and Europe. A 2006 United Nations report suggests that livestock produce about 18 percent of the world's greenhouse gases - more than all sources of transportation combined - and researchers expect that number to grow as worldwide demand for meat doubles in the next 30 years.

In the United States, the 5.8 percent of greenhouse gases produced by all forms of agriculture is dwarfed by the 26 percent of gases emitted by cars, trucks

and other forms of transportation. Yet the emissions produced by cattle remain a cause for concern in California, particularly in the San Joaquin Valley, where 3.5 million cows produce about 21 percent of the nation's milk supply - and an average of 250 to 280 million pounds of manure every day.

Until recently, researchers believed most of the greenhouse gases produced by cattle came from the manure lagoons dairy farmers use to store animal waste. But a 2009 study by researchers at the University of California at Davis suggests that cows themselves produce much more methane and nitrous oxide than those lagoons.

"Lagoon waste is so heavily diluted that it's a smaller factor than fresh waste" emissions produced by cows, said Frank Mitoehner, lead researcher on the UC Davis study, which measured the gases emitted by nine cows in a controlled chamber, or "bovine bubble." The study concludes that one cow produces about 11.36 grams of methane and .02 grams of nitrous oxide each hour.

One solution to the problem of bovine pollution is to cut back on the number of cows. By increasing the efficiency of its operations, the U.S. dairy industry reduced the number of cows required to produce a billion kilograms of milk by 21 percent from 1994 to 2007. It also cut the amount of feed required by 23 percent, the amount of water required by 35 percent and the amount of land needed by 10 percent during the same period. Those changes caused the amount of methane generated to fall by 43 percent and the amount of nitrous oxide to plunge by 56 percent, Mitoehner said.

But that efficiency can mean turning away from the organic farming methods favored by many Marin ranchers. According to Mitoehner, grass-fed cattle produce a third more greenhouse gases than those living on feed lots.

"The microbes that produce greenhouse gases need roughage," Mitoehner said. "The more roughage they get, the more methane they produce."

Yet Albert Straus, who operates the organic Straus Creamery in Marshall, believes lowering emissions is only part of the environmental picture.

"Our mission is to work within a sustainable system," Straus said. "It's not just particulate emissions; it's water quality, it's the use of GMOs (genetically modified organisms) and antibiotics. It's switching from a diesel truck to one powered by electricity, which is powered by our methane digester - so that our cows are powering the truck that feeds them."

Another option, and one favored by Straus, is to turn much of the waste produced by cows into energy. By covering and aerating his five manure lagoons in 2001, Straus was able to transform them into a methane digester that provided 99 percent of the energy needed to power his West Marin dairy. On Tuesday, Straus finished installation of a more efficient digester that exceeds his needs, allowing him to sell methane-generated electricity to Pacific Gas and Electric.

Researchers at UC Davis are experimenting with a much larger methane digester. By combining the pounds of manure generated by the school's animal sciences program with the school's garbage and green waste, the methane plant is expected to satisfy the heat and electricity needs of a 500-home development while generating 11 tons of compost each day. Mitoehner believes the system will recoup its cost within five to six years, not least because the school will be able to reduce the amount of trash it hauls to a landfill.

"You could put this stuff in a landfill, and it will produce methane, but then it's just wasted," Mitoehner said. "If this is proven to be cost-effective on a community scale, people would be fools not to do it."

FROM GRASS TO GAS

Greenhouse gases may lead to global warming by trapping heat energy in the atmosphere. Methane, produced by cattle, is up to 21 times as effective in capturing heat than the carbon dioxide exhaled by humans, while nitrous oxide - also produced by cattle - is up to 310 times as effective.

The Intergovernmental Panel on Climate Change estimates that agriculture contributed 10 to 12 percent of the carbon dioxide, 40 percent of the methane and 60 percent of the nitrous oxide generated by humans in 2005, and the U.S. Department of Agriculture believes livestock contributes half of the greenhouse gases produced by agriculture in the U.S.

Source: University of California at Davis

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