Millbrae, California’s Water Pollution Control Plant is using inedible 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 will 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.
“This project clearly demonstrates that cities can develop renewable energy economically, with multiple benefits to urban communities,” said Jim Davis, president of Chevron Energy Solutions. “By applying proven technologies and looking at the entire waste stream in new ways, the City of Millbrae has cost effectively upgraded its facilities, reduced its operating costs, created new revenue and solved environmental challenges all at the same time.”
“This innovative project brings new meaning to the term ‘sustainable development,'” said Millbrae Mayor Robert Gottschalk. “Through our partnership with Chevron Energy Solutions, we’re taking an urban waste and turning it into an asset for the city and the environment.”
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 U.S. alone. Much of this grease is disposed of in landfills, where it releases methane – a potent greenhouse 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 will have no effect on the city’s wastewater treatment rates.
“This is the only wastewater treatment plant in the U.S. 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.”