25x’25

Key to the 25x’25 renewable energy and carbon initiatives is the developing technology that is advancing anaerobic digestion. The process captures methane that is generated when biomass, usually animal waste, is broken down anaerobically, or without the presence of oxygen. The methane, a potent greenhouse gas (GHG), is often run through a generator to produce electricity. Methane digesters implemented on livestock operations to manage manure create a renewable source of electricity that can be used to help power the operation and, in some cases, sell electricity back to the grid. Digesters are also a proven way to reduce GHG emissions, which can provide offsets that could generate a significant revenue stream for the operation in a cap-and-trade climate change regulatory system.

While EPA estimates there were 111 commercial livestock digesters operating in 2007, the potential for anaerobic digesters to provide financial and environmental benefits to U.S. farms has prompted acceleration in the construction of digesters in recent years.

Successful examples are promoting that acceleration. The Crave Brothers Dairy Farm, a Waterloo. WI, is an operation that includes a regionally renowned cheese-making enterprise and runs a computer-controlled anaerobic digestion system that generates enough electricity to power the farm, cheese factory and 120 area homes. The Twin Birch Dairy is a 1,200-cow operation in Skaneateles, NY, where anaerobic digestion technology on the farm prompted the EPA in 2008 to selected Twin Birch as the northeast U.S. dairy to kick off the agency’s multi-year, manure and air quality study.

The Crave Brothers grow soybeans, corn and alfalfa on 1,700 acres to use as feed for their 950-cow herd. To handle current needs and plans for expansion, the operation hired Clear Horizons, a firm that specializes in organic waste management solutions and biogas energy systems, to install a computer-controlled digester which is run over the Internet from the Clear Horizon’s office in Milwaukee. The digester, which is owned by Clear Horizon, helps manage the farm’s manure, provides clean, renewable energy for the farm, and produces excess electricity, which Clear Horizons sells on the electrical grid. The digester reduces odor from the manure, and the Craves use the liquid byproduct as fertilizer on their fields. Solid byproducts are used as animal bedding, and in a line of organic potting mixes sold by the farm.

Twin Birch uses freestall housing that allows cattle to move around freely. To keep the barn floor manure free, an automatic alley scraper cleans the floor at regular intervals, emptying the manure into a holding area beneath the ground floor. Every 15 minutes the manure is pumped into an anaerobic digester, where the methane is extracted to reduce greenhouse emission. The methane gas is converted to electricity, and heat to kill pathogens, producing nutrients. The farm produces the majority of its needed electricity during the summer months. In the winter months, when tunnel fans are not needed, electricity costs will be fully paid for by the farm’s digester. After digestion, manure is separated into solids and liquids. The solid is used to create fiber for bedding for the cows and the liquid is pumped into a 6-million-gallon storage area until, at the appropriate time, it is spread on crops as a nutritional supplement.

Both operations reached their decisions to employ anaerobic digestion after considering issues of economics and scale. For those operations wishing to explore the technology, AgSTAR is a collaborative effort of the EPA, USDA and DOE that promotes the development and implementation of anaerobic digestion technologies. In addition to its environment value, the technology can enhance an operation’s financial performance when compared to traditional waste management systems such as manure storages and lagoons.

25x'25 Energy Resources Agriculture, anaerobic digestion, Emissions, Farms, Sustainability