WisBusiness: Anaerobic digesters turning state’s dairy waste into power

By Brian E. Clark

WisBusiness.com

WATERLOO – For more than two decades, the Crave brothers — Charlie, George, Thomas and Mark — had mulled over installing an anaerobic digester to turn the methane from their cows’ plentiful manure into electricity.

But until their herd numbered 900, the finances never quite penciled out for the dairy, which is known for producing award-winning farmstead cheeses, including mascarpone, fresh mozzarella and a washed-rind variety they have appropriately dubbed “Les Freres” (The Brothers).

“An anaerobic digester is something my dad, Charlie, had been thinking about for a long time,” said Karl Crave, who works for Clear Horizons, which built and runs the digester on the Crave dairy.

“The technology has been around for a long time and he has friends who have had them for 10 or even 20 years,” Crave said. “But until the past few years, my dad didn’t think the systems weren’t as efficient or cost-effective as we needed.”

But with rising energy costs, the project became more feasible, he said.

“And we also wanted to do it for environmental reasons,” he said, noting that the digester process stabilizes the manure, making what is left over easier to store and use.

“My family has always tried to be good stewards of the land,” Crave said.

He said the dairy’s fully automoted digester began producing power 14 months ago, processing up to 10 million gallons of manure annually.

It is one of 18 now operating in the state, though another 10 are in various stages of construction around Wisconsin, according to state officials.

Those 18 digesters produce 55 million kilowatt hours of electricity a year, said Larry Krom, who works with the state’s Focus on Energy Program.

That’s enough to provide power to 5,500 homes and replaces the equivalent of 27,600 tons of coal or 108,700 barrels of oil.

“In the next year or two, we could have another 30 projects in the works,” added Krom.

Crave said his dairy’s digester, which creates enough electricity to power 150 homes a year, also helps the farm’s waste management and odor control while also producing a byproduct used for potting soil.

The Crave dairy currently has Clear Horizons’ only digester, which cost $2 million to build. But the company has several more in the design and permit process, Crave said.

Prior to installation of the digester, Crave said the manure was simply stored in a lined storage lagoon and then spread on the fields in the spring and fall.

Crave said the digestion process does not eliminate the manure, only converting around 5 percent of it from a solid state to a gas used to produce electricity.

“So you are still left with 95 percent of your volume to deal with. And the process doesn’t destroy any of the nutrients — mainly nitrogen and potassium — which ultimately are used to fertilize the fields.”

In addition to the smell reduction, Crave said the digester removes phosphorus from the remaining manure, another benefit to the dairy. Some of that phosphorus ends up in the potting soil or in bedding used by the cows, he said.

“In our farm’s case, by digesting that manure and separating it, we are able to remove about 40 to 50 percent of the phosphorus, which gives us a lot more flexibility and allows them to spread the liquid on growing crops.”

Crave said he would recommend anaerobic digesters to other large dairies.

“As renewable energy prices increase and utilities recognize the value of on-farm digestion, the economics should improve,” he said.

“If that happens, it should be a no-brainer for just about any large farm — not just financially, but from an environmental standpoint as well.” he said.

Crave said Clear Horizons sells the power it produces to We Energies for 5.5 cents a kilowatt.

“But the dairy buys its power from the utility for 10.5 cents a kilowatt,” explained Crave, who said he and others who run digesters are lobbying the state Public Service Commission and other agencies for a higher rate.

Roger Kasper, a chemical engineer and technical advisor who works at the state Agriculture Department’s Farm Center, said he believes digesters will play a growing role on dairies.

“They definitely have their place,” he said, but cautioned that they are not for every farm.

“It’s like that line in real estate,” he said. “It’s often location, location, location because if you are more than half a mile from a three-phase (heavy duty) distribution line, or a natural gas line, it’s probably not going to be practical economically.”

But Kasper said some dairies might consider using the manure gas directly to heat water.

“Even if it’s a small dairy, you could displace your entire water-heating bill,” he said.

Collecting gas is also an option for larger dairies, said John Frieze, who milks 2,700 cows on the Emerald and Baldwin dairies between Eau Claire and Minneapolis.

He is looking at a regional biogas pipeline that would help other farmers with waste stabilization and sell “scrubbed gas” that would be the same quality as natural gas.

Even dairies with only a few hundred cows might want to be part of the project, which he said could permitted this summer and operating by the fall.