MARGINALIA
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.
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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