A farmer may have more than 1,000 cows on his land, which create a steady stream of revenue—and manure.
In fact, a dairy cow typically produces 150 pounds of manure per day. Multiply this by scores of cattle, and you get a large—and odoriferous—waste situation.
Concerned about groundwater contamination and fecal-borne disease, farmers are continually on the lookout for ways to ensure safety and make cleanup easier.
One approach involves methane digesters, which operate on an old technology and handle cleanup effectively. As an added bonus, they produce electric energy.
By definition, a methane digester is a wastewater and solids treatment technology, according to Sustainable Conservation, a San Francisco-based environmental advocacy organization. When used on a farm, a digester processes animal waste under anaerobic conditions, yielding methane gas and reducing the volume of solids and treated liquids. The methane can be sold or used to generate electricity on the farm. The solid matter left behind is a valuable soil amendment. And the liquids become an easily applied fertilizer, with plant-available nutrients and low pathogen levels.
Typically, large farms will store liquid and solid manure produced by livestock in large waste ponds. The manure is later pumped back onto fields as a source of fertilizer.
But this type of storage scenario poses a host of problems, including strong odors, pathogens in the manure, and flooding of ponds and land when heavy rains or storms occur (allowing manure to reach local water sources). A methane digester provides a workaround solution, and harnessing the methane—a greenhouse gas more powerful than carbon dioxide—benefits the environment.
To offset costs, the U.S. government has started giving subsidies to farmers who wish to install methane digesters. Some, however, believe digesters may not be the best solution for small farms. Other communities fight large-scale digester installation because of their industrial appearance and added traffic from waste haulers.
Nonetheless, many environmentalists say the positives outweigh the negatives.
- Organic Dairy Powered by Methane Digester (Straus Family Creamery)
- Manure Power: Dairies Harness Methane to Create Renewable Energy (Checkbiotech)
- Idaho Energy Czar Aims to Harness Cow Pie Power (Associated Press)
- A Refreshing Idea for Barnyard Odor(Boston Globe)
- A German Town Embraces Manure Energy(Fast Company)
- Introduction to Methane Digesters (Oregon Department of Agriculture)
- Energy Savers: Anaerobic Digesters for Farms and Ranches (U.S. Department of Energy)
- Anaerobic Digestion of Animal Wastes: Factors to Consider (National Sustainable Agriculture Information Service)