The UV bulbs need to be replaced every year or two. Gadgil tested the purifier on water fouled with E. coli bacteria and found that fewer than 1 in 100,000 of the bugs survived. The purifier did just as well against 10 other pathogens, including typhoid and cholera. It doesn't work, however, with very muddy water, which is opaque to UV light, or on Giardia spores, which cause a mild form of diarrhea, because UV light cannot penetrate them. The 20 Indian villages that field-tested the purifier are reluctant to give it up now that the tests are over.
Most people regard a landfill as nothing but a smelly problem.
Ronald Spiegel, however, sees an untapped source of cheap energy. An engineer at the U.S. Environmental Protection Agency in Research Triangle Park, North Carolina, Spiegel believes that it is possible to harness the country's 7,500 landfills to produce 4.5 billion watts of electricity, enough to power a metropolis of about 5 million homes. In 1990 he conceived of a fuel-cell power plant that burns the methane gas that wafts up from most landfills. Fuel cells, which are quieter, cleaner, and more efficient than conventional engines or turbines, convert hydrocarbons such as methane into carbon dioxide and hydrogen, and then combine the hydrogen with oxygen in the air in a catalytic reaction that produces electricity. Since fuel cells require an ultraclean form of methane, Spiegel had to invent a way of filtering out the sulfides, halides, and other undesirables found in landfill gases.