BACKGROUND: Environmental engineers at the University of California, Davis, are building a full-scale anaerobic digester that can convert any type of solid organic waste into electricity -- even leftovers from restaurants. The system is part of the $100,000 Sacramento Municipal Utility District (SMUD pilot project), but an even larger digester system is being put into place in San Francisco.
HOW IT WORKS: In the process, food waste is collected from restaurants and institutions and then fed to bacteria that thrive in low-oxygen environments. It's called anaerobic digestion, a naturally occurring process of decomposition. One type of bacteria turns carbohydrates into simple sugars, amino acids and fatty acids. A second group of bacteria eats those compounds and turns them into hydrogen gas, carbon dioxide, and acetic acid -- the primary component of vinegar. Then a third group of bacteria takes those broken-down compounds and turns them into methane and carbon dioxide. Between 60 and 80 percent becomes methane. The methane can be used as fuel for an internal combustion engine that provides electricity.
TYPES OF DIGESTION: Anaerobic digestion is not the same thing as human digestion, since the type of bacteria that produce methane don't live in the human digestive tract. Industrial anaerobic digesters can also harness this natural process to treat waste, provide heat, and increase nutrients in soil. They are most commonly used for sewage treatment and for managing animal waste.
BENEFITS: The goal of SMUD is to obtain 20 percent of its electricity from renewable sources such as wind, solar, and biodegradable matter by 2011. Currently SMUD derives 10 percent of its electricity from renewable sources, of which biomass accounts for 2.5 percent. The UC-Davis digester would keep food and other biodegradable waste out of landfills; food leftovers account for 18 percent of a landfill's contents. One tone of leftover food can produce enough fuel to power 18 homes for one day.
WHAT ARE EXTREMOPHILES? An extremophile is any microbe that thrives in extreme conditions, such as temperature (extreme heat or cold), pressure, salinity, low oxygen environments, or high concentrations of hostile chemicals. Most extremophiles belong to a class known as archaeobacteria, but certain species of worm, crustacean and krill can also be considered extremophiles.
The Institute of Electrical and Electronics Engineers, Inc., contributed to the information contained in the TV portion of this report.