Special Report
Making anaerobic digesters work
One of the features at both the old and new Statz Brothers Farms is anaerobic digesters. The digesters were built by DVO Anaerobic Digesters of Chilton, Wisconsin. Melissa Van Ornum says the digester is basically a recreation of the cow’s stomach except it holds the mass for 22 days so the anaerobic bacteria can break down the fats, proteins and starches giving off methane as they do that. That biogas then powers the engines which power the electric generators. The digester at the new facility produces two-to-four times the electricity used on the farm. Plus the burning of the methane removes the odor, the solids from the digester are allowed to dry to be used for bedding in the bans and the liquid which is 90 percent water is applied to the fields. Harmful pathogens are also destroyed by the digestion process.
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A digester isn’t a machine. It is a structure that houses a system. You need to consult with a digester construction company to find out the size of and cost of a digester for 5000 cows. There are a lot of variables that go into answering those questions. A digester will only make minimal contributions to improving water quality. The anaerobic digestion process fixes nitrogen in a plant available form. Digesters make much more significant contributions to protecting air quality.
No. You can’t drink water directly from a digester. A digester doesn’t reduce the N, P nor K content of the effluent. It only makes minimal reductions in the volume of solids in the effluent. While the pathogen reduction is significant, it isn’t complete. Besides, land application of raw effluent will reduce pathogens due to air and light exposure.
Digesters are not silver bullets. The will improve things but not solve everything. If a digester developer or consultant tells you otherwise, run.
Yes we have digesters working in Wisconsin, some better than others. I have a question of size and expense: If a farmer had 5000 milking cows how many tons of liquid manure would be produced by these cows each month? How big would the digester have to be? How much would this machine cost and how much does it cost to operate? I hear a lot about pathogens and liquid manure being the vehicle carrying this stuff, will your machine protect the water, can a person or animal drink the water from a digester?
So much miss information, I need your help.