Hawaii
Energy Policy Forum > 2003
Articles
Farming for Energy: Anaerobic Digesters -- Cow Power
By E. M. Morrison
http://www.auri.org/news/ainjul01/05page.htm
A newsletter from WWW.Green-Trust.Org
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.
Smell begone
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.
Interest surges
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."
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