The GL Dairy Biogas Project uses a digester and generator to create energy. Cow manure from the three farms is processed in three air-tight digester tanks. The tanks are heated to about 100 degrees—just like a cow’s stomach. Bacteria in manure thrives in these conditions, and they consume solids in the manure while releasing methane gas.
Instead of being released into the atmosphere, the methane is captured at the top of the digester and burned in a generator to create electricity. The excess heat from the generator warms the digester. The digester operation is expected to generate about 16 million kilowatt hours of electricity annually. The electricity is added to the local grid in Dane County through Madison Gas and Electric, enough to power approximately 2,500 homes and reduce fossil fuel carbon dioxide by 11,000 metric tons per year.
The process also creates a large amount of clean, organic -fiber by-product that has many horticultural uses or can be used on the farms as cow bedding.
In addition to producing cleaner energy, the digesters prevent more than 3,700 pounds of phosphorus runoff to the water ways in Dane County every year. Phosphorus is the leading cause of green algae and other weed growth in Dane County’s lakes and comes from both urban and rural sources. It is estimated that 370,000 pounds of algae will be reduced annually in the Yahara watershed as a result of this project.