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This state produces a lot of organic waste on its many dairy farms (all that cow manure) and food processing plants. These waste products could be turned into methane biogas, a renewable fuel that replaces natural gas, says the Wisconsin Bioenergy Initiative at UW-Madison. According to a new report from the group, this state already has a burgeoning biogas industry, but it has room to grow.

Biogas plant in Germany

Biogas plants work by trapping manure or food waste in an airless environment, often in a structure resembling a silo, where microbes break it down, releasing methane and leaving behind a solid byproduct that can be used as soil bedding or fertilizer. There are already 31 small-scale versions of these “anaerobic digesters” in the state, including 22 on farms, more than any other state in the country.

There are 151 in the country, but the U.S. lags far behind Germany, which has aggressively expanded its renewable energy sources in recent years with government incentives. There are now more than 5,000 biogas plants in that country, including 3,000 on farms.

Although digesters are multiplying in Wisconsin, “project development seems to have reached a plateau recently,” the report says. “It will likely take public policy to expand the opportunity in Wisconsin and the region.” Government incentives, including preferential rates for biogas-generated power sold back to utilities, could encourage the industry.

Biogas can be burned on-site in boilers to produce heat or electricity, or it can be treated and sold on existing natural gas pipelines. In 2009, Wisconsin’s small-scale plants generated about 11.6 megawatts, enough to power 10,000 homes, according to the Bioenergy Initiative.

As an energy source, the gas also has potential for large municipalities: The City of Toronto collects food and other organic waste in curbside bins for its power-generating biogas plant.

And earlier this year, UW-Oshkosh fired up a biogas plant and “began producing electricity and heat for the campus from about 8,000 tons of organic waste generated each year from campus cafeterias,” the report says. “The Oshkosh project is the first commercial-scale system of its kind in the U.S.”

The Bioenergy Initiative estimates the state could, with 1,000 digesters, produce 250 megawatts of power in the state. It also estimates that if all the dairy cow manure in the state was digested, the resulting biogas could offset 4.4 percent of the state’s natural gas consumption.

Despite the benefits, “anaerobic digesters are not currently economical investments for most farmers,” the report notes. Smaller farms benefit more financially, it says, from the mineral-rich bedding material produced than the electricity generated. At industrial-scale dairy farms, the “primary economic driver” is savings on wastewater treatment (cleaning up manure-contaminated water, etc.), followed by power generation.

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