Cushman Farm Digester

October 1, 2001                                                                                                                                                                                                      ISSUE #M19

The Cushman Dairy in Franklin, Connecticut is a show case farm. The electrical energy used at this farm comes from a manure digester system developed by CST Industries (better known as Harvestore - Slurrystore). The original installation was made in 1998. 

The farm has 700 head, utilizing coarse sawdust as bedding. A scraped barn system is used to collect the manure, which is pumped to the digester.

The digester is an insulated tank made of the traditional Harvestore glass porcelainized steel panels. Manure is pumped in at the two-thirds level. Agitation is achieved with a centrifugal pump that takes its suction off the bottom of the tank. Digested manure sludge floats over a weir at the top and goes to a Vincent screw press for dewatering.

The biogas collected from the top of the digester flows to a positive displacement blower and then to a Cummins internal combustion engine. The engine is coupled to an induction generator that fills the farm's electrical needs. Radiator cooling water goes through a tubular heat exchanger that heats water used to maintain the digester temperature.

Digested manure flows to a Vincent Model KP-10 manure separator that was installed in 1998. Typically this produces 20 gpm of press liquor which flows to the manure pond. Press cake production normally runs 600 pph, with the press operating about ten hours per day.