Almost twenty years ago John Pueschel, Dave Pueschel, and Larry Kelly, owners of Fairgrove Farms in Sturgis, Michigan, installed a system to generate electricity from cow manure.

Manure from the dairy barns and milking parlor is pumped to a digester. This “plug flow” digester was designed by Perennial Energy of West Plains, Missouri. The digester is in the form of a horizontal concrete tank, like a long swimming pool. It is covered so that the bio-gas from the digestion process is collected. This gas flows, without the aid of a booster blower, to a Caterpillar internal combustion engine. The engine drives an induction generator. The generator in turn produces about $3,200 worth of electricity per month.

An induction generator was selected although it is a little less efficient that other types of generators. Its advantage is it produces electricity that is automatically in phase with the power grid that supplies the farm. The result is that surplus electricity can be pumped into the grid (sold to the public utility) without the need for expensive switchgear.

Selecting a Caterpillar engine that would run on the low 600 BTU (mostly methane) biogas, without a need for filtration or pressure boosting, was a key element in minimizing the capital investment.

In 1999 Fairgrove Farms purchased a Vincent Model KP-10 Manure Separator. This machine is used to dewater the sludge from the digester. It is manufactured in Tampa, Florida.

This separator is an all-stainless screw press with only one moving part, the auger. This screw features three stages of compression with weld applied hardsurfacing in the high abrasion surfaces. A screw recently completed over 4,000 hours of service before refurbishment was required.

The screen of the press is made of perforated metal screen with 3/32″ openings.

The sludge is pumped to the screw press at the rate of about 40 gpm. The press liquor goes to the wastewater pond, while the press cake (at 70% moisture) is sold as bedding to nearby dairy farms. This generates an additional $3,000 in monthly revenue.