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Nothing to waste

Agriculture.com Staff 10/28/2006 @ 3:13pm

When dairy farmers Gale Gordon and his son, Kyle, built modern, free-stall facilities with a double-14 herringbone milking parlor, they included a biogas, or methane, digester. Adding one later for their 900 cows near Nelsonville, Wisconsin, would be too costly.

"We saw the biogas digester as a great way to complement the operation since it could generate energy and help save bedding and fertilizer costs," says Gale. It also improves nutrient management and control of odors and flies.

The digester's methane powers an eight-cylinder Caterpillar 3408 reciprocating engine that runs an electricity generator. The in-ground, insulated digester holds 650,000 gallons and produces about 65 cubic feet per minute (cfm) of methane. "That's enough volume for the engine and generator to crank out more than 130 kilowatts (kw) of electricity," says Gale. "We're delivering enough electricity on the grid to help provide power to more than 125 homes."

Alliant Energy owns and maintains the engine and generator, which can be nearly a third of a system's total price. "Essentially, we're just selling the methane gas to the utility," says Gale. The farm is paid 1.5¢ per kilowatt-hour generated and delivered to Alliant's power transmission system.

Once the manure is digested, the leftover, nutrient-rich effluent is pumped to a lagoon and applied later to cropland to reduce fertilizer costs. The coarse solids in the manure are squeezed out with an expeller screw-type press and used as an excellent and sanitary bedding material in the free-stall barns.

If you add up all the benefits, Gale says the biogas digester has generated income and energy savings of about $75,000 per year.

"We aimed for a payback period of about six years," he says. "So far, we seem to be very well on track since our initial outlay was slightly more than $300,000." When their project was built in 2001, it received no grants to help offset initial costs. That's another factor that can affect the payback period.

Today, however, there are more state and federal renewable energy grant and loan opportunities available to livestock producers to help offset some of the costs, especially for the engine and generator equipment.

"When I talk to other dairy producers, I tell them to expect a range of $800 to perhaps $1,000 per cow when calculating a very rough estimate on what a biogas system may cost," he says.

Bedding cost savings, odor control, better nutrient management, and environmental benefits are also very important. About 35 tons of separated solids from the digester are used for bedding each week, saving the dairy $60,000 a year. They also sell some of the solids to area gardeners. The Gordons' dairy operation uses about 2,000 acres for corn silage and grain, about 800 acres for alfalfa (on a three- to four-year rotation), and 400 acres for soybeans and other grains.

"The biogas digester also helps in managing the manure and nutrients better," says Gale. "What it boils down to is that you have a more manageable amount of phosphorus in the effluent for field applications," he explains. "This liquid fertilizer is either knifed in or broadcasted and then worked into the soil. It's also broadcast on growing crops, such as alfalfa and corn. In making those applications, however, we still rely on regular soil testing coupled with cropping maps to avoid nutrient overloading.

"Most of the organic nitrogen in the manure is converted to ammonia," says Gale. "When broadcasting, the liquid effluent doesn't burn the crops, and the nutrient uptake or utilization appears to be real good."

He estimates that the digested manure and effluent have helped trim out-of-pocket fertilizer expenses by about 25%. "In fact, during the past couple of cropping seasons, we actually sidedressed some of the corn with the liquid effluent."

When dairy farmers Gale Gordon and his son, Kyle, built modern, free-stall facilities with a double-14 herringbone milking parlor, they included a biogas, or methane, digester. Adding one later for their 900 cows near Nelsonville, Wisconsin, would be too costly.

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