MILWAUKEE — When dairy farmer Gary Boyke looks out at the manure his herd produces, he sees the prospect of profits rather than waste, odors and water pollution.

Boyke is one of a growing number of farmers turning animal waste into energy, and he's spreading the word to others. He was among those giving presentations at a conference Jan. 31 in Madison on ways farmers can turn manure into money.

Boyke, who has 1,300 cows on his Vir-Clar Farm near Fond du Lac, said he gets two to three times the energy he needs with an anaerobic digester, which uses bacteria on manure to produce a gas containing methane to power generators.

He sells it to a Madison-based utility and then buys back what he needs. He said the device produces enough power for 330 homes.

"I think we're just on the verge of something that is going to be big in the future," he said.

A dozen such digesters are in operation in Wisconsin, five are under construction and 15 others are planned, said Larry Krom, business sector manager of the state Focus on Energy's renewable energy program.

About 110 digesters are working around the country, with another 70 planned, said Kurt Roos, manager of the U.S. Environmental Protection Agency's AgSTAR program. Most of them are at dairy farms in the Midwest, California, New York and Pennsylvania.

The average cost of a digester is nearly $1.5 million, and it takes about six years to earn back that original investment without any grants, said Krom, whose organization is one of the sponsors of the Madison conference.

A group of smaller dairy farms could bring manure to one central community digester to make it financially feasible for them, Krom said, or they could use a less expensive process in which methane is burned to produce heat rather than electricity.

There's another benefit to digesters, too: Kenn Buelow, who operates Holsum Dairy at Hilbert and uses two of the digesters in his 3,100-cow operation, said the devices reduce odors from manure by 95 percent or more.

The conference discussed other uses for manure, including drying it to produce steam to power generators and create electricity; putting it in a pressurized chamber at high temperature to produce oil and a charcoal-like material, and — for smaller dairy operations — composting it and selling it to landscapers, gardeners and others, said Timm Johnson, executive director of the Wisconsin Agricultural Stewardship Initiative.