Posted Aug 31, 2009
San Francisco’s East Bay Municipal Utility District has created a program to generate electricity from the methane gas produced by food decomposition, a newspaper report said on Monday.
The project is believed to be the first of its kind in the United States, the Los Angeles Times said.
Engineers have been testing and refining the process since the U.S. Environmental Protection Agency gave the utility 50,000 dollars in 2006 to study it, and they plan to sell energy to the grid beginning next year, the paper said.
“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, according to the paper.
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, allowing it to sell more than five megawatts of energy to Pacific Gas & Electric Co, said David Williams, director of wastewater.
The utility eventually hopes that about one 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 in remarks published by the paper.
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.
Besides creating energy, the program will reduce landfill waste and greenhouse gase.
Date: Aug 24, 2009