August 15, 2004 | General

Methane Digesters Move Forward On California Dairy Farms

BioCycle August 2004, Vol. 45, No. 8, p. 62
An organic creamery is the most recent installer of an anaerobic digestion system to generate power from manure and wastewater, saving $6,000/month in electricity costs.

“This is one more step toward my goal of having our farm become completely self-sufficient in energy with minimal environmental impact,” says owner Albert Straus of his organic Straus Family Creamery in Marshall, California. Last spring, the digester began generating up to 600,000 kWh per year, and “operations are coming together nicely,” adds Straus., who is working with the utility company, PG&E. Funded by California’s SB5X alternative energy grant program, this is the first system to take advantage of regulations under the net metering legislation which effectively allows the entire operation to run meters in reverse as excess electricity is sent back into the grid. It also means that the dairy will save about $6,000/month energy costs.
At the heart of the methane recovery system is a 9,000-sq ft covered lagoon digester designed by Doug Williams of Williams Engineering Associates. Flushed manure (15,000 gallons/day) from the dairy along with wastewater from the creamery (4,000 gallons/day) are pumped to the 800,000-gallon lagoon for a 40-day hydraulic retention time. Maintained under anaerobic conditions the covered lagoon permits microbial action to convert organic matter into 20,000 to 30,000 cu ft/day of methane-rich biogas. The reinforced polypropylene cover (supplied by Sharp Energy) over the lagoon captures the biogas and channels it into a pipeline for transport to the engine-generator.
Gas is first dried and lightly compressed, then used to fuel a 75 kilowatt generator which provides a significant portion of the dairy’s electrical needs through net metering provisions of the interconnection agreement with PG&E. According to Straus, the plan is to recover heat from the generator engine and exhaust system to produce hot water for the dairy as well as heat for the lagoon digester.
It’s estimated that there are almost 2,000,commercial dairies in California with some two million cows. The Straus digester is reported to be the fifth in the state with 13 more currently under construction – all receiving matching funds from the California Energy Commission. A $10 million pool of matching funds for digesters was created under the SB5X program and some of those funds helped to finance the $280,000 cost of the Straus system. With the savings in electrical costs, Straus calculates he will pay back his capital investment in two to three years. Plus, the digester will eliminate tons of naturally-occurring greenhouse gases and close to 99 percent of organic pollutants from the wastewater.
Notes George Simons of the California Energy Commission: “I believe that PG&E should be congratulated for getting the Straus Farms project on line. These projects are small, but they are important. They aren’t that complex, yet they’re very beneficial to the industry. This is the way to go.”

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