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New 'Digester' Converts Garbage to Energy

October 4, 2004

More than 14 million tons of high-moisture, organic waste are generated in California each year. Some of it is composted, but too much finds its way into landfills. UC Davis bioenvironmental engineer Ruihong Zhang sees a vast untapped resource in those lawn clippings, household table scraps and other biodegradable materials: enough energy to keep the lights burning in thousands of California homes, high-quality soil amendments for the landscape industry, even fiberboard for construction purposes.

One promising key to unlocking this potential is currently under study at UC Davis. Zhang is building a prototypical anaerobic digester, part of a $4 million project funded by the California Energy Commission and industry partners. The concept is elegantly simple -- garbage in, good stuff out, including "biogas" to burn for electricity-producing turbines.

Previous biological conversion systems have failed because they required that the waste be ground up, which canceled the energy-production benefits. Zhang's anaerobic digester should be better because, she said, it is designed to process waste materials in their "natural" form, easing material handling and converting the material into biogas at a faster rate.

The prototype digester at UC Davis should be fired up this fall. It will consume about three tons of organic waste per day, delivered from collection facilities in Dixon and San Francisco. It will generate about 600 kilowatt-hours of electricity per day, enough to meet the needs of 15 typical California homes. The energy will go to the campus power supply.

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