Compost reduces landfill gas.

Mountains of decomposing garbage release about 10 million metric tons of methane each year in the United States alone. To reduce gas from landfills, communities should start treating them more like backyard gardens, a report in the Sept. 1 Environmental Science & Technology suggests.

In field tests at a landfill in Louisville, Ky., Morton A. Barlaz of North Carolina State University in Raleigh and his colleagues tried a new twist on the practice of covering garbage with soil. That practice keeps odors and rat populations down, but the North Carolina researchers reasoned that using compost laden with microbes could have the additional benefit of reducing methane emissions.

To test this idea, the researchers covered part of the landfill with a three-layer sandwich: a thin layer of clay soil on the bottom, a layer of shredded tires to spread out the emerging gas, and a top layer of compost. Another part of the landfill got a conventional cap of clay-rich soil. Then, the researchers measured how well each of the two types of covers biodegraded the landfill's methane.

"On average," says Barlaz, "the compost cover stimulated the biological uptake [and breakdown] of at least 2.5 times as much methane as the clay cover." The compost sandwich removed 55 percent of the methane, while the clay removed 21 percent.

The researchers say that their approach could give thousands of small landfills a cost-effective way of reducing methane emissions.