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CottonWood Dairy

Location Atwater, California
Project Type Farm Scale
Animal Type Dairy
Population Feeding Digester 5,000
Baseline System Storage Lagoon
Digester Type Covered Lagoon
Co-Digestion Wastewater (warm clean up water from cheese plant)
System Designer Williams Engineering Associates; Cover installed by Environmental Fabrics, Inc.
Biogas Generation 432,000 ft3/day
Biogas Use Cogeneration; Boiler/Furnace Fuel
Generating Capacity 700 kW

Photo of Cottonwood Dairy's engine-generator set

Photo: Joseph Farms

When Cottonwood Dairy covered its 40 million gallon anaerobic lagoon with a 7.5 acre bank-to-bank cover, the anaerobic digester captured so much biogas, the farm installed a second engine-generator set to utilize all of the gas. Power generated by the 700 kW system provides electricity for Joseph Farms Cheese Plant, which produces 33 million pounds of cheese each year.

Five thousand cows produce over 450,000 pounds of manure each day, which is flushed to the digester. Manure solids are separated prior to digestion and are used for animal bedding. Wastewater from the cheese plant is added to the digester to increase biogas production. Liquid digester effluent is used to irrigate cereal grains, corn, and alfalfa.

A 700 kW engine-generator set provides as much as 80 percent of the electricity required to operate the cheese plant and also offsets some of the plant's propane need. The biogas is scrubbed to remove hydrogen sulfide and dried prior to burning in the engine-generator set. Waste heat from the engine-generator set is used in the cheese plant to produce steam for pasteurizing and sterilizing. Additional heat may be used in the future to preheat air for the whey dryer.

The project has provided the following benefits:

  • Improves water quality and reduces greenhouse gas emissions
  • Allows four-year payback on initial investment
  • Saves an estimated $800,000 per year in electricity and propane expenses
  • Provides an outlet for cheese plant wastewater

The project received grants from the California Dairy Power Production Program and the California Self-Generation Incentive Program. In addition to methane recovery, the farm has been recognized for its efforts to preserve wildlife habitat.

We work as hard as anyone in business to turn a profit. And as a family, we have always had a strong commitment to the environment we conduct this business in. Putting this digester to work on our ranch was the right thing to do.
—Mike Gallo, CEO Joseph Gallo Farms

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