Anaerobic Digesters

Three Wisconsin-based dairy farms and one Iowa-based dairy operation in Alliant Energy's service territory put a total of 0.88 megawatts of electricity on the grid in 2004 from energy produced by anaerobic digesters . Most recently, Vir-Clar Farms in Fond du Lac County, Wisconsin signed on to supply renewable energy from its anaerobic digester.

The methane captured by the digesters is used as fuel to produce electricity, as well as heat for milking parlors and to pre-heating water.

We predict that an additional 40 Alliant Energy farm customers will be interconnected digesters by 2015.

Environmental benefits

The environmental benefits of using manure to efficiently generate electricity are considerable:

• Methane, which has roughly 22 times the global warming effect of carbon dioxide, is no longer released into the atmosphere.
• Solids from the manure are used for livestock bedding and soil conditioner.
• Liquids are converted to fertilizer that has approximately one-half the phosphorus content of manure, thereby preventing soil problems caused by buildup
• Odor is reduced 90-95%, significantly reducing fly populations.

How an anaerobic digester works

The manure is stored in a 124-foot-long sealed concrete tanks and heated to 98 degrees Fahrenheit. The methane and carbon dioxide released from the heating process are fed through the connected piping to a 150 horsepower, 100 kilowatt generator and a 30 kilowatt Capstone™ MicroTurbine to create the electricity.

Brochures and fact sheets:

Anaerobic Digesters and Methane Production [PDF]
By Alliant Energy

Methane Energy Recovery on Iowa Farms [PDF]
By the Iowa Department of Natural Resources

Learn more:

Visit these informative sites to learn more about anaerobic digesters:

Iowa Department of Natural Resources

Midwest Rural Energy Council

U.S. Department of Energy: Energy Efficiency & Renewable Energy

U.S. Environmental Protection Agency