Princeton, Minn. — For a time last winter, Dennis Haubenschild’s dairy cows were earning him 40 cents a day from their milk and 30 cents a day from their electricity.
Electricity from cows? That’s right.
Haubenschild Farms is the first Minnesota farm to produce “cow power.” The 760-cow family farm uses anaerobic manure digestion to produce methane for electricity. The waste digester supplies enough power to run the entire farm, plus 78 average homes.
Farm digesters are attracting widespread interest. State experts say these manure treatment systems could bring important economic and environmental benefits to Minnesota agriculture. The technology lets farmers make a valuable new ag product — electricity — while reducing odor and creating high-quality fertilizer.
Manure to methane
The dairy cows at Haubenschild Farms produce 22,000 gallons of manure a day. That manure, in turn, yields about 80,000 cubic feet of “biogas” a day — enough to generate 3,000 kilowatt hours of electricity. How does it happen? It is microbe magic.
Cow manure, together with recycled newspaper bedding, is scraped from the freestall barn three times a day, mixed to a smooth consistency, then pumped into a 350,000-gallon covered digester tank, which looks like a long white sausage.
There, the manure is heated to about 100 degrees F, speeding the action of beneficial bacteria in the tank. As bacteria break the manure down, they give off gas — mostly methane, which collects under the tank cover. After three weeks in the digester, the manure — now a lot less smelly — empties into a storage lagoon for later application to the farm’s 1,000 acres of cropland.
Juice to run the farm
Captured methane is burned in a retrofitted natural gas engine, which drives a 150-kilowatt electrical generator. Recovered heat from the engine warms the digester and the barn floors.
About 45 percent of the Haubenschilds’ electrical output is distributed on the farm, offsetting $700 a week of electricity expense, Dennis Haubenschild says.
The rest of the electricity is sold to a local power cooperative, East Central Energy, which markets it as renewable energy. An enthusiastic partner in the project, East Central Energy pays 7.25 cents per kilowatt hour for the Haubenschilds’ excess electricity — the full retail rate.
Farm sales of electricity average $900 a week, Haubenschild says. When milk prices fell to all-time lows last year, his net returns from energy approached those from milk.
The Haubenschild digester, called a plug-flow, has been operating since September 1999, generating electricity with 98.6 percent reliability, Haubenschild says. But the system delivers other benefits besides electricity.
One of the most significant is odor reduction. “Odor is an important social issue,” one that often hamstrings livestock expansion, Haubenschild says. It’s also an issue that touches him where he lives: “I don’t like to smell manure any more than anyone else. We put in our first lagoon in 1978, right next door to our home. The smell! I thought, there has to be a better way.”
Even more important, he says, digestion creates a high-quality fertilizer, converting the nutrients in manure into a more usable form and destroying weed seeds. “That’s the biggest reason to work with digesters; manure is your true renewable resource,” says Haubenschild, who carries the value of stored manure on his farm balance sheet at $5 per thousand gallons.
The University of Minnesota is conducting a three-year field study to compare the performance of digested manure with raw manure and commercial fertilizers. But Haubenschild is already sold: “It’s saving our farm fertility.”
Committed over time
Three generations earn their living from the sandy soil of Haubenschild Farms.
In 1952, Dennis’ parents, Donald and Myrtle, began farming in Isanti County, running a diversified crop and livestock operation that included ten dairy cows. Over the years, they expanded the dairy herd to 24 head, then 44, installed a freestall barn, then doubled the herd again when Dennis and his wife Marsha joined the business in 1975.
By 1998, the family was milking 150 cows. When Dennis and Marsha’s sons, Tom and Bryan, wanted to start farming, too, “that meant we had to expand,” Dennis says.
The family planned a 1,000-head dairy. Dennis, a member of the Minnesota Feedlot and Manure Management Advisory Committee, was well aware of the manure and odor problems associated with a dairy feedlot of that size. Installing a digester was a way to expand “in an environmentally sound way.”
Digesting in the basement
Dennis, 53, has been interested in waste digesters since college. “I had a little digester in the basement. Instead of brewing wine, like other college kids, I was brewing methane. So I knew it worked.”
In fact, small anaerobic digesters have been used in China and India for decades, and more than 450 farm digesters generate fuel in Europe. In this country, dozens of manure digesters were built in the 1970s and ’80s, says Jack Johnson, AURI engineering services director in Waseca. Many of those failed, he says, because of high capital costs and a low return on investment. Now, he estimates, fewer than 45 manure digesters exist on U.S. farms.
But recently there has been renewed interest in the technology. Several states are supporting farm demonstrations of dairy and swine manure digesters, Johnson says. AgSTAR, a federal waste management program, sponsored 13 digester projects around the country, including the Haubenschilds’ digester.
Larger feedlots, new environmental regulations and public outcry over manure odor and greenhouse gases are all influencing the resurgence of digesters, Johnson says. Energy deregulation, rising fuel costs, and growing demand for green power have also spurred interest. In addition, digesters are better designed and more efficient now, he says.
The Haubenschilds have been swamped with inquiries about their system, especially as the energy crisis in California intensifies. In the past 18 months, Dennis says, several thousand people have toured the farm, “and we’ve had hundreds of calls and e-mails from all over the country.
“Interest in digesters is really growing.”