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22 Jul 2009: From Skins of Onions,
Farmers Develop Promising Biogas

A large onion processor in California is taking 300,000 pounds of onion waste a day — skins, tails, and tops — and converting much of it into a biogas that he uses to power his operation. Steven Gill, a partner in Gills Onions — which dices, slices, and purees onion for wholesale and retail customers — has worked with Southern California Gas Company to create an energy recovery system that produces 600 kilowatts per day, which meets up to 40 percent of the electricity needs of his processing plant. The onion waste is shredded and pressed to squeeze out the juice, which is then diverted to an anaerobic digester. Workers add microbes that convert the juice into methane gas, which helps power Gill’s facility. Gill used to spread the onion waste on fields but soon ran out of room. Southern California Gas provided $2.7 million in incentives for the $9.5 million energy recovery system. Gill estimates that converting the onion waste to biogas will save him $700,000 a year in electricity costs and $400,000 in waste disposal costs, meaning the plant will pay for itself in about six years. Nearby carrot and wine producers are interested in installing similar systems.

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