January 19, 2013

'Cow power' turns manure, food waste into mighty electricity source

Exeter Agri-Energy on track to produce about 8,000 megawatt-hours of electricity a year, enough to power 800 typical homes

By Ben McCanna bmccanna@centralmaine.com
Staff Writer

(Continued from page 1)

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Two of the 1,000 cows at the Stonyvale Farm in Exeter. Waste from the cows and food products are used to produce gas to power electric generators.

Staff photo by David Leaming

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John Wintle monitors the engine inside the control room, where gas produced by mixing cow manure and food waste powers a generator and produces 5.2 million kilowatt-hours of electricity, at the Stonyvale Farm in Exeter.

Staff photo by David Leaming

Additional Photos Below

As the mixture breaks down in the digesters and the pressure subsides, the system's computer automatically pumps more raw manure and food waste into the containers to keep the bacterial process rolling.

At the same time, spent material is pumped out of the containers, where it passes through a mechanical liquid separator. Plant fibers that aren't broken down during the anaerobic digestion process are separated from the water and reused. All day long, the fibers churn out of the machine in bone-dry clumps that fall into large piles that are used for cow bedding or compost.

The liquid from the separator is pumped back to the farm, where it spills into lagoons that once held raw manure. The liquid contains all the same fertilizing nutrients found in raw manure, but it's better. The liquid is easier to spread on fields than manure; plants absorb its nutrients more easily; and it is virtually odorless, said Wintle, 37.

Those two byproducts save the farm about $100,000 a year, Fogler said. The greatest savings are found in fertilizer costs. It's not that they produce more fertilizer; they can just use more of what they have.

"Manure before digestion stinks, so all summer long we would purchase (commercial) fertilizers because we didn't want to aggravate our neighbors with the odor," said Fogler, 35. "The digestion process removes the odor, so we're able to spread it all summer."

Donna Wagner has lived about a half mile from Stonyvale Farm for the past seven years. She said the odor reduction was immediately noticeable.

"It is less smelly, even during the summer," she said.

Town Manager Tressa Smith said the project is viewed favorably within the rural community of 1,062.

"Everyone from the town has supported it, and it has been great. I've heard no negative feedback whatsoever," she said.

Smith is also a neighbor of Stonyvale.

"I'm happy with it," she said of the project. "I don't smell the cow manure anymore. I can hang my clothes outside."

Why isn't manure power spreading?

In the United States there are about 100 cow-power facilities. Only a dozen combine food waste with manure. In Maine, there is only one.

Curt Gooch, dairy sustainability engineer at Cornell University in Ithaca, N.Y., said digesters first appeared in the U.S. in the 1970s, during the oil embargo; however, when oil prices dropped again, interest in the technology dried up. Then, in the late 1990s, there was a resurgence. Digesters have continued to crop up since then, but it's still not widespread

"The potential is huge," he said. "It's a big bud that's waiting to blossom."

In Europe, cow power is in full bloom. About 5,000 anaerobic digesters operate in Germany alone, Gooch said.

There are several reasons why, said Spencer Aitel, co-owner of Two Loons Farm in South China and board member at Maine Organic Farmers and Gardners Association in Unity.

Cow-power producers in Europe are paid three times as much per kilowatt hour; European countries are more densely populated, so odor control is highly valued; and European governments tightly regulate milk prices so they're always profitable for dairy farmers.

Installing cow power requires a substantial investment, which is extremely difficult for U.S. farmers, who are often in the red. On Friday, for instance, 110-year-old Garelick Farms ended production because the cost of making milk exceeds the amount dairy farmers receive.

Also, the technology is viable only for very large farms, Aitel said.

Prudence Flood is part owner of Maine's largest dairy farm -- Flood Bros., in Clinton. Flood said she has looked into the possibility of cow power and it looks promising; however, a system for her 3,800-cow farm would cost about $10 million. At the moment, the price of milk is too low to justify such a large expense.

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Additional Photos

click image to enlarge

Adam Wintle, left, Travis Fogler and John Wintle walk past the two digester buildings, where food waste and cow manure are mixed to produce gas that powers a generator for electricity, at Stonyvale Farm in Exeter.

Staff photo by David Leaming

click image to enlarge

Stonyvale Farm worker Joachin Hershbine pushes cow manure into a transport system that takes the manure to a digester, where it is mixed with food waste. The gases produced are used to power an electric generator at the Exeter farm.

Staff photo by David Leaming

click image to enlarge

John Wintle watches as food waste is unloaded in one of the receiving tanks at Exeter Agri-Energy, at the Stonyvale dairy farm in Exeter. The waste is mixed with cow manure and produces gas that is used to power a generator to make electricity.

Staff photo by David Leaming



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