Anaerobic digesters are sealed tanks used to sustain the biological degradation of manure and other organic material in the absence of oxygen. Biogas is a product of this process. To date, all on-farm digesters in Michigan are on large farms. There are no digesters on small dairies (meaning dairies with an average herd size of 125 cows in Michigan). However, these farmers want the advantages of a digester.

They like the idea of using biogas to produce heat and generate electricity. But what they really like is the ability of a digester to mineralize nutrients and remove the manure odor from the digestate. With no odor issues to worry about and readily available plant nutrients, land application of manure becomes much simpler.

The primary reason there are no digesters on small dairies in Michigan is due to cost. Digesters are designed to take advantage of economies of scale inherent in large dairy and swine facilities. These digesters, depending on the type, can range in cost from $150 to $500 per dairy cow. This is beyond the budget of a small dairy. However, in recent years digesters have been designed for and marketed specifically to the small dairy.

To make a digester work on a small dairy requires thinking about the best use for the biogas and digestate on the farm. In other words, the benefits of a digester stay on the farm. Working through this thought process is one of the topics that will be covered at the 2011 Small Scale Anaerobic Digester Conference Thursday, Dec. 1 at the Michigan State University Bioeconomy Institute in Holland, Mich. This conference will outline the basic principles behind anaerobic digestion and highlight the key issues facing small scale digester adoption and options for the small scale farmer.

Information about the conference, including registration, can be found at It should be noted that while the target audience is small dairy owners and operators, the information that will be shared can be generalized to other applications. All are welcome to attend.