Test landfills percolate as bioreactors.

On the outskirts of urban centers grow great manmade mountains of trash. Piled high, packed, and buried, these landfills -- which hold 70 percent of domestic refuse -- typically take years to amass and decades to decompose.

To manage the solid-waste stream responsibly, scientists seek speedier ways to break down garbage into useful components, extract energy-rich fuel, and recycle the remnants. Toward that end, Frederick G. Pohland and Robert E. Landreth, environmental engineers at, respectively, the University of Pittsburgh and the Environmental Protection Agency in Cincinnati, Ohio, describe a faster way to decompose rubbish using "landfill bioreactors."

Speaking at last week's meeting of the American Chemical Society in Washington, D.C., they explained that by recirculating leachates -- the liquid brew of decomposing wastes -- in a landfill, biological breakdown occurs up to 10 times faster than usual. "Normally, a landfill takes 20 to 30 years to decompose," says Pohland. "But using this method, it may only take 2 to 3 years."

Rain soaks and the sun bakes decaying rubbish, creating a great compost pile, says Pohland. Already rich in nutrients and microbes, the fermenting heap mostly requires nurturing to make methane gas, wastewater, and reclaimable solids. So engineers are testing landfill designs that mix wastes with leachates. Almost like an oven that bastes a roast, the new landfills use liners and collection systems whose pipes and pumps recirculate liquids and extract methane gas.

"We don't even have to add bacteria or chemicals," Pohland says. "The landfill is biologically active and nutrient rich. This process simply accelerates natural decomposition." Municipalities can later irrigate land with treated leachate waters, generate power from methane, and mine what remains for metals, plastics, and other recyclables.

Scientists are testing 20 landfill bioreactors, each site varying slightly in design, Landreth says. The EPA supports three of these sites: in Monroe County, N.Y., Gainesville, Fla., and Dover, Del. In Dover, the most advanced site, two 1-acre cells will soon give rise to a full-size 20-acre pilot site, Pohland says.

Landreth sees the possibility of "round robin" landfills serving communities and industrial parks. "Fill one up, move to the next. Fill that one up, then move to a third," Landreth says. "Keep going around, filling up sites and pumping out gas until the first one is fully cooked. Then dig up the first one, mine it for materials, and fill it again. You can go in a circle."