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January 2007

Chevron and Millbrae turn grease into biogas

Chevron Energy Solutions, a unit of Chevron Corporation, and the City of Millbrae completed a new facility at Millbrae's Water Pollution Control Plant that uses kitchen grease from restaurants to naturally produce biogas for generating renewable power and heat to treat the city's wastewater.

The system, engineered and installed by Chevron Energy Solutions, includes a grease receiving station and an expanded cogenerator as well as other upgrades that result in annual revenues and energy savings of $366,000 for Millbrae while nearly doubling the amount of "green power" produced at the plant.

More than 3,000 gallons of restaurant grease, the kind washed from grills and pans, will be delivered to the plant each day by grease hauling companies, which pay a city fee for disposals. Microorganisms in the plant's digester tanks eat the grease and other organic matter, naturally producing methane gas to fuel the plant's new 250-kilowatt microturbine cogenerator to produce electricity for wastewater treatment. Meanwhile, excess heat produced by the cogenerator warms the digester tanks to their optimum temperature for methane production.

Nationally, restaurants produce an average of 14 pounds of inedible grease per capita annually, a total of nearly 4.2 billion pounds each year in the United States alone. Much of this grease is disposed of in landfills, where it releases methane gas as it decomposes, sometimes directly to the atmosphere. Millbrae's grease receiving station will reduce the amount of grease sent to landfills.

The grease and other organic matter will produce enough biogas at the plant to generate about 1.7 million kilowatt hours annually, which will meet 80 percent of the plant's power needs and reduce its electricity purchases significantly. This lower demand for utility-generated power reduces carbon dioxide emissions by 1.2 million pounds annually, the same amount of carbon dioxide absorbed by planting about 170 acres of trees.

The total cost of the project, $5.5 million, was reduced by about $200,000 with a rebate awarded through the state of California's Self-Generation Incentive Program administered by Pacific Gas and Electric Company. The net amount, along with maintenance costs, is being funded entirely by savings from the new system and, therefore, will have no effect on the city's wastewater treatment rates.

"This is the only wastewater treatment plant in the United States to receive and process inedible grease in a self-funding, purpose-built system that successfully addresses so many challenges simultaneously," said Dick York, superintendent of the Millbrae plant. "It's a complete solution that could be adopted in many cities around the country."

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