Food goes from plate to plant
Leftovers from San Francisco Bay Area restaurants may soon help power the region.
The East Bay Municipal Utility District has created a program, believed to be the first of its kind in the nation, to generate electricity from the methane gas produced by food decomposition.
Engineers have been testing and refining the process since the U.S. Environmental Protection Agency gave the utility $50,000 in 2006 to study it, and they plan to sell energy to the grid beginning next year.
“The program could yield a significant amount of energy, long-term,” said John Hake, an associate civil engineer with the utility district. “It’s no silver bullet, but it could be one part of a portfolio of renewable energy sources.”
Food scraps are collected from about 2,300 restaurants and grocery stores in the Bay Area and taken to the utility district’s wastewater treatment plant in Oakland, where they are pumped into large tanks full of microbes that speed up decomposition. The food releases methane gas, which is used to generate electricity.
The utility now powers its wastewater treatment plant, which serves about 650,000 homes in Alameda and Contra Costa counties, by processing many kinds of waste, including the food scraps.
By the end of 2010, the utility expects to double its capacity to create power, said David Williams, director of wastewater, allowing it to sell more than 5 megawatts of energy to Pacific Gas & Electric Co. The utility eventually hopes that about 1 megawatt will come from food scraps, enough to power 1,300 homes, Williams said.
It would need to process about 100 tons of food per day to reach that goal, he said. Currently, the plant processes about 100 tons per week.
Contaminants such as forks and plastic bags, which often get mixed into the food scraps, have caused the most trouble for the food waste program, Williams said.
“Rags just wreck havoc on the pumps,” Williams said. “We get oyster shells, silverware and, for some reason, rocks.”
When the food reaches the plant, it is put through a “juicer” to sort out the contaminants. A metal blade grinds the food scraps, yielding liquid food waste. The liquid is then churned into a thick brown soup and pumped into the digestive tanks, which release the methane gas.
The gas is piped into on-site generators, which create the electricity. After about 20 days in the digestive tanks, the food waste is composted.
To cut back on contaminants, companies that collect food waste educate restaurant workers about separating food from other waste, said Robert Reed, a spokesman for Sunset Scavenger. The company provides special containers for the cast-off food.
Reed said about half of the restaurants approached are receptive.
The employees at Bakesale Betty in Oakland, which contributes food scraps to the utility district, have been trained to set aside food waste since the restaurant opened, said owner Michael Camp.
“We’re committed to separating food waste,” Camp said. “We emphasize to employees that if they don’t abide by it, they’ll be warned and then they’ll be fired.”
Besides creating energy, the program will reduce landfill waste and greenhouse gases.
“With compost, there are always concerns about the release of gases and other issues,” Williams said. “We thought, why not use it to generate renewable energy?”
Several water-treatment plants have been attempting to develop renewable energy.
The Sonoma County Water Agency, which prides itself on green innovation, generates solar power and is concentrating on developing a program to create energy using wave technology. “Anything that produces renewable energy will gain footing,” said Cordel Stillman, capital projects manager for the agency.
Stillman said he expects other agencies to follow the East Bay Municipal Utility District’s lead and begin trying to extract energy from food waste. His agency is interested, he said, but lacks some of the necessary equipment.
Williams hopes eventually to expand the program to food waste collected from homes.
“It’s a long process to educate the public,” he said. “The early growing pains are the hardest part.”