 By EDIE LAU Sacramento Bee December 02, 2005
In the wrong hands, a stinky mess. But with some engineering finesse, food scraps can be transformed into fuel for electricity. That's the thinking behind a $100,000 pilot project at the Sacramento Municipal Utility District, given the catchy name "Leftovers to Lights." SMUD has contracted with Ruihong Zhang, a professor of biological and agricultural engineering at the University of California, Davis, to study the feasibility of collecting food waste from restaurants and institutions in the Sacramento area and feeding the waste to bacteria that make methane gas. Basically, it's a new twist on the old saw about turning trash to treasure.
"We can't call it 'waste' anymore," said Zhang. "It's a resource." The food waste SMUD is eyeing is organic stuff that's otherwise buried as garbage. Collecting it could serve two useful purposes, said Ruth MacDougall, a SMUD manager: It would keep it out of the landfill, and it would provide the utility district power from a renewable source - a source that doesn't run out or is easily replenished. MacDougall said SMUD has a goal by 2011 of obtaining 20 percent of its electricity from renewable sources - sources such as wind; the sun; the heat of the Earth's interior (geothermal); and biomass, biodegradable matter including farm remains such as rice straw, wood waste and food leftovers. At the moment, 10 percent of SMUD's electricity is derived from renewable sources, MacDougall said; biomass accounts for 2.5 percent, and she believes it could be more. "One of the most renewable things we have in Sacramento is our waste," she said. Citing figures from the state Integrated Waste Management Board, MacDougall said 18 percent of what goes into the landfill is food leavings. What SMUD is looking to do with Sacramento's leftovers is a variation on composting. In composting, bacteria - and sometimes other bugs and worms - are harnessed in the presence of oxygen to turn organic material into soil. The Leftovers project involves anaerobic digestion, which harnesses the power of bacteria that thrive in oxygen-less environments to convert organic material into useful gases. The topic could easily degrade into a crude junior high school joke, but the folks involved are careful not to let it. For example, asked whether foods with reputations for making gas in the human gut, such as beans and broccoli, are especially good for making methane, Zhang kept a straight face and answered with a simple no. "The digestion process is different," she said. "In our system, we don't have methane bacteria." In anaerobic digesters, some foods do, however, yield more methane than others. "Meat will produce more than potatoes," Zhang said.
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