If the news from a town in Alabama is any indication, residential wood waste is the next great feedstock for biodiesel. Fifteen of Hoover's police SUVs became the first in the nation to be fueled by "cellulose-based ethanol" on April 16.

Since last year public works has sent ground-up tree branches to Gulf Coast Energy Inc., a 2-year-old alternative-fuel manufacturer, to experiment with at a demonstration plant. The company is raising money to build three commercial plants throughout the state that are expected to produce 200 gallons of ethanol for every ton of wood chips.

"There's enough wood waste in Hoover to make 400,000 gallons of ethanol a year," says Mayor Tony Petelos. When the plants are up and running within the next five years, the city could save $100,000 in tipping fees to landfill the 2,000 tons of trees, limbs and branches it collects each year.

Almost 90% of the city's fleet runs on alternative fuel: 186 trucks and pieces of equipment use biodiesel the Fleet Department makes from used cooking oil, and 196 more vehicles use ethanol. General Motors has authorized the city to use the cellulose-based ethanol on its police fleet of flexible-fuel 2005 Chevrolet Tahoes, Petelos says.

"There was absolutely no difference in performance from corn-based ethanol," says Fleet Management Director David Lindon.The process that converts cellulose -- gasification has been used mainly on coal. In this case, the wood waste is ground and fed into a dryer. It's subjected to intense heat that forms a synthetic gas by separating the carbon monoxide, carbon dioxide, and hydrogen. A microorganism introduced to the process then ingests the gas and produces ethanol and water.

"Our goal all along has been to be cellulosic," says Lindon. "Corn's not the answer because you can't raise enough to fuel the country." Corn and soybeans are the feedstock for most ethanol produced in the United States. "Once that plant is up, we could be self-sufficient within 18 months."