When Dane County Executive Kathleen Falk talks about cow manure, she uses phrases like “cow power” and “our oil fields.”

That's because she and the county government are in the process of helping develop a manure digester to be shared by several farms. It would convert manure into methane and bio-gas to power an engine capable of producing one megawatt of electricity valued at $1 million. The anaerobic (oxygen-free) digester would also generate other products such as fertilizer and livestock bedding.

If all goes well, ground will be broken this year for a $6 million to $13 million digester to be shared by five farms in the Waunakee area, northwest of Madison. Falk’s county budget for 2009 commits $1.1 million for developing the digester, and digesters are a top priority in Dane County’s requests for federal economic stimulus funds.

Manure digesters aren't new. There are now more than 20 in Wisconsin, the most of any state. What's distinctive about the Dane County project would be the sharing of the facility and the use of wastewater treatment techniques to take more than 85 percent of the phosphorous from the manure liquid.

The community digester and the phosphorous removal would be important to the economic and environmental health of the county. Dane County has some 50,000 dairy cows on 400 farms, most of which are too small on their own for the multi-million investment in construction and operation of a digester. Wisconsin's other digesters are concentrated on large farms with 1,000 cows or more.

As a measure of the importance of dairying to Dane County, a 2004 University of Wisconsin Extension study found that each of the county's cows generated $2,090 in direct income from milk sales and $15,000 to $17,000 in economic activity per year.

Yet, in the process, each cow also generates 120 pounds of manure per day, and the total for 50,000 cows adds up to 6 million pounds. Coping with manure is a major headache for dairy farmers. Storing, hauling and spreading manure increases costs and limits possible expansions in herd size.

Runoff from farm fields is believed to be a prime source of the phosphorous that helps algae increase in the county's lakes and streams.

“The [digester] project stemmed originally from the question: How do we keep our fabulous lakes and streams in Dane County blue instead of green?” Falk says.

Dane County's investment has paid for an initial feasibility study and is funding a more detailed development plan for the Waunakee-area digester. The major challenge still being worked out is who would own and operate the digester. Falk says that while county involvement was needed to get the project going, she isn’t making a policy statement that the county should be involved in running the digester.

Other possibilities, she says, might be for the county's two strong farm cooperatives to own and operate the digester or for an arrangement whereby an outside company would own and operate it. A third alternative might be for joint ownership by several of the farms involved.

Solving these challenges is important. The alternative, green electricity generated by the bio-gas could power the farms, and selling the excess power could supply additional income to farmers battered by slumping milk prices. Fertilizer and livestock bedding derived from the solid residue would be an additional source of revenue.

Building the digester could create 15 to 20 construction jobs for 12 to 18 months and two permanent jobs for technicians to operate it.

At the same time, the digester could help clean the waters of the county, remove almost 20,000 metric tons of greenhouse gases and contain much of the stench of the manure.

And the project could serve as a model for more digesters to take advantage of the millions of pounds of manure the state's 1.25 million cows generate every day.

By John Hill

You can contact John Hill by e-mail at jhoythill@sbcglobal.net.

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