How the Haubenschild Farms anaerobic digester works
An anaerobic digester is a system for collecting and breaking down manure and other forms of biological waste and capturing the resulting gas. Haubenschild Farms uses a plug flow digester. This system works well for dairy cows because the solid content of their manure is 10 to 12 percent and is a viscous mixture that does not separate.
Marty Kramer, business development manager for East Central Energy, says, "It yields a little less gas than some other systems but it's more reliable and requires less maintenance."
Alley scrapers move across the dairy parlor floor 24 hours a day, scraping the cattle waste into a 250,000 gallon pit. The manure slurry flows into a mixing chamber where it is stirred up before moving into the digester, a 400,000 gallon manure lagoon covered with a rubbery lid.
A network of water heated pipes underneath the lagoon maintains a constant temperature of 95 to 100 degrees to speed up the bacteria's digestion process. As the bacteria break down the manure, it releases biogas which is 55 to 70 percent methane. The gas is pumped into a generator which burns the gas, producing electricity.
About one third of the electricity powers the Haubenschild dairy operation. East Central Energy buys the remaining renewable energy.