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Old Gas, New Gas

Methane—made and taken apart by microbes, in the Earth, by people

Roald Hoffmann

A Kiln on a Landfill

A few years ago, I spent some time at the Penland School for Crafts in the Blue Ridge country of North Carolina. There I met Jon Ellenbogen, a potter with a good background in technology. Jon showed me pictures of glass and ceramic kilns and of greenhouses on the site of the nearby Mitchell/Yancey county landfill. Once a smelly six-acre eyesore, the landfill now provides not only a home for artists and greenhouses, but also, importantly, the energy they consume. From methane.

Methanogenic microbes can digest...Click to Enlarge Image

The U.S. Environmental Protection Agency estimates that 33 percent of methane released into the atmosphere by human activity comes from landfills. This production is the result of microbes (they're at it, around the globe) that decompose the buried waste. Landfill gas is roughly 50 percent methane, 45 percent CO2 and a few other gases. The total gas-generation potential of the Mitchell/Yancey landfill is 2 cubic feet of methane per pound of refuse buried. Figuring that each year the dump operated, it swallowed perhaps 10,000 tons of waste, there's lots of methane there. EnergyXchange, Ellenbogen's nonprofit organization, reasoned, why not use it? If only more landfills around the country did so!

Biogas may be generated from any organic waste, but animal manure is an especially good source. Large-scale animal productions of swine, poultry or cattle are natural places to site biogas digesters—dedicated residences for domesticated methanogens. And there are already millions of small ones, adapted for household use, installed around the world, especially in China and India.

The Indian biodigesters work mainly with cow manure—it takes three good cows to provide a household with cooking gas and some lights. The Chinese digesters, a somewhat different design, use human nightsoil. In both designs, there is much useful digested manure left in the end.

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