BioCycle October 2004, Vol. 45, No. 10, p. 35
California dairy creates methane recovery system to convert manure into energy that fuels cheese plant and sends excess electricity back into utility grid.

IN ATWATER, California, Cottonwood Dairy – operated by Joseph Gallo Farms – will begin operating a biogas-powered generator next month with the capacity to produce up to 2,500,000-kilowatt hours per year from its dairy manure. The new anaerobic digester will save an estimated $275,000 in annual electrical costs, while at the same time reducing greenhouse gas emissions.
Cottonwood Dairy has about 5,000 lactating cows, generating about 483,000 gallons/day of manure at 1.07 percent solids. At the heart of the methane recovery system is a seven-acre covered lagoon digester, designed and managed by Williams Engineering Associates. Flushed manure from the dairy is pumped to the lagoon, where microbial action converts the nutrients in the manure into methane. A custom-engineered high-density polyethylene cover over the lagoon captures this biogas and channels it into a pipeline, where it is transported to the company’s cheese plant.
The gas is first cleaned and treated, then used to fuel a 300-kilowatt generator operating around the clock. The electricity generated provides a substantial portion of the plant’s electrical needs. Heat from the generator engine and exhaust system is captured and used to produce steam for the cheese plant, saving an estimated 145,000 gallons of propane per year at a cost of more than $100,000 annually.
Mike Gallo, CEO of Joseph Gallo Farms, is enthusiastic about the project’s multiple benefits. “The digester, lagoon and flush systems provide improved wastewater treatment and storage for the dairy,” he points out. “The cover reduces the release of greenhouse gases into the atmosphere, while steam generation reduces air emissions caused by propane combustion, refining and transportation.”
Funded in part by California’s SB5x alternative energy grant program, the Cottonwood Dairy digester is the second in the state to take advantage of the 2003 net metering law which allows the facility to run its meters in reverse as excess electricity is sent back into the grid. “The generation of electricity reduces the strain on the California power grid,” notes Gallo, “and reduces the need for electricity generation at central power plants.”
The Dairy Power Production Program, administered for the California Energy Commission by Western United Resource Development, provides financial assistance in two ways: Buy-down grants that cover a percentage of the capital costs of the proposed biogas system, or incentive payments for generated electricity.
“We are very pleased to see the second methane generator funded by this project go online,” said Michael Marsh, CEO, Western United Resource Development. The grant program has approved a total of $5,792,370 for 14 projects, with a total estimated generating capacity of 3.5 megawatts. “We are looking forward to seeing these other projects come online as California’s dairy families demonstrate once again their commitment to saving energy and dealing with the environmental challenges presented by cow manure.”
Adds Allen Dusault, senior project manager with Sustainable Conservation, whose organization has partnered with Western United on the Cottonwood digester: “The commitment of Gallo Farms to improving air and water quality sets a standard for California dairies for which the industry should be very proud.” An overview of Sustainable Conservation’s work with digesters and composting appears on its website: www.suscon.org. – J.G.