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Holsum Dairy - Elm Road

Location Hilbert, Wisconsin
Project Type Farm Scale
Animal Type Dairy
Population Feeding Digester 4,000
Baseline System Storage Tank or Pond or Pit
Digester Type Mixed Plug Flow
Co-Digestion Food waste (non-farm food processing waste from 3 industries)
System Designer DVO, Inc. (formerly GHD, Inc.)
Biogas Generation 363,000 ft3/day
Biogas Use Cogeneration
Generating Capacity 1,200 kW
Receiving Utility Wisconsin Public Service Corporation

Farm Bill Funded Project


Photo of one end of the digester near the equipment shed

Photo: Energy Center of Wisconsin

Elm Road Dairy is the newer of two Holsum dairies operating a digester in Wisconsin. Manure at the dairy is scraped and collected three times each day. Waste from three area food processing industries is added to the waste influent stream and sent to two plug flow digesters.

In 2007, the farm installed two concrete, below-grade mixed plug flow digesters with fixed concrete covers. The digesters operate at a temperature between 95°F and 100°F and have a hydraulic retention time of 22 days. The system, designed by DVO, Inc. (formerly GHD, Inc.), utilizes passive gas-induced mixing and has return of activated sludge to help sustain bacteria colonies.

Biogas generated from the digester is dehydrated by running it through a condensate trap and chiller, and then sent to two 600 kW engine generator sets for electricity production. All electricity produced on the farm is sold to the Wisconsin Public Service Corporation under a sell-all contract. Recovered heat is used to heat the digester, milking parlor, office, shop, and holding and transfer areas. The facility has an on-site dual fuel boiler for backup heat that can run on either biogas or diesel.

Two Fan screw presses are used to separate digester effluent. The farm produces approximately 16 tractor trailer truckloads of digested solids each week. The facility uses about one third of the fibrous solids for bedding and sells the rest to other dairies.

Elm Road's digester project includes the following benefits:

  • Revenue from waste tipping fees
  • Sale of excess gas and solids helps recover capital investments
  • Electricity and heat production

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