1996 Discover Awards: Environment

Monday, July 01, 1996
Ashok Gadgil knows how devastating dysentery can be. Growing up in India, he lost several cousins to the disease and saw how it can stunt the growth of those who survive it. Three years ago, as a particularly virulent strain of cholera was sweeping his native country, it occurred to him that he might be able to make a water purifier based on ultraviolet light that would be inexpensive enough for the poorest villages.

The key to the invention is the effect ultraviolet light has on bacteria and viruses: it triggers the formation of peptide bonds between certain amino acids in the pathogens’ dna molecules, which robs them of the ability to reproduce and renders them harmless. Gadgil’s biggest challenge was to make the purifier cheap, reliable, efficient, and easy to maintain. All the time our focus was on cost, says the physicist from Lawrence Berkeley National Laboratory. Using only off-the-shelf gear such as sheet metal, uv lamps, and stainless-steel piping, he came up with a simple apparatus. Water, powered by gravity, flows down through pipes, passing into a tray where it is exposed to 12 seconds of ultraviolet light before it flows out a spigot. 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. Urminus Industries in Bombay is investing $700,000 in a new plant that will manufacture a solar-powered version capable of supplying 1,000 villagers with clean water. It costs $250 to make and is expected to go on sale next year.


Watts in the Dump

EPA’s Landfill Power Generator

Innovator: Ronald Spiegel

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. First the gases pass through a carbon bed that removes any hydrogen sulfide. The remaining gases are then dried, refrigerated, and filtered again before the residual is burned in a flare. In recent tests at a Los Angeles landfill, the filter removed more than 30 contaminants with 99.95 percent efficiency. About the only thing that goes into the atmosphere is carbon dioxide and some traces of carbon monoxide, Spiegel says.

With the exception of the carbon beds, which fill with sulfur every six months or so and must be replaced, the system can run virtually unattended. Happily, a landfill should go on producing gas for about the 20-year expected life of the fuel cells. The epa and Northeast Utilities, a power company in Berlin, Connecticut, are testing the prototype on a Groton, Connecticut, landfill. Although the generator now costs several hundred thousand dollars, Spiegel is trying to simplify it to make it less expensive.

Smokestack Lightning

MIT’s Microwave Plasma Sensor

Innovator: Paul Woskov

The best way to know for sure if manufacturers are complying with toxic and hazardous-metal pollution laws is to monitor what comes out of their smokestacks. Scientists do this periodically by sampling the exhaust and then analyzing it back in their labs. Although they’d prefer to monitor the emissions right at the source, 24 hours a day, seven days a week, the harsh environment of the average smokestack has precluded using the delicate equipment needed to record the measurements.

But all that’s about to change. mit engineer Paul Woskov has invented hardier measuring equipment. His method entails using microwaves to create a small cloud of hot, ionized gas, called a plasma, inside the smokestack. When the exhaust passes through the plasma, it obliterates metals such as lead and chromium into their constituent atoms. Free electrons in the plasma collide with these atoms, causing them to emit light, which is picked up by an optical fiber and fed to a spectrometer. Scientists see the spectrum displayed on a computer screen, and they can tell from looking at it what chemicals the emissions contain--watching in particular for lead, mercury, beryllium, arsenic, plutonium, and other poisons. Like a fingerprint, says Woskov, each element has its own spectrum.

In tests last year at an mit furnace, the microwave plasma detected chromium in concentrations as low as three parts per 10 billion. Although Woskov hasn’t licensed the innovation to a manufacturer, the laboratory version cost about $50,000 to build, most of which was the cost of the spectrometers. Because you can mass-produce microwave ovens for $100, Woskov said, maybe we can get our costs down a lot lower--to, say, $10,000.

Rubber Reborn

Pacific Northwest National Laboratory’s Tire-Recycling Microbes

Innovator: Robert Romine

Most people appreciate Yellowstone National Park for its beauty. Robert Romine has another reason: the park’s hot springs support a microbe that may hold the key to recycling the nation’s 2 billion discarded rubber tires.

Romine, a chemist at Pacific Northwest National Laboratory in Richland, Washington, was working on a way of using recycled tire rubber in asphalt pavement when his wife, Margaret, who is a microbiologist, introduced him to Sulfolobus acidocaldarius. As the name implies, the bug likes to dine on sulfur found among the minerals in the hot springs. When added to a vat of powdered tire rubber, the microbe attacks the sulfur in the rubber.

That turns out to be the best way of decomposing this chemically tough material that is hard to recycle. Although virgin rubber is like a plate of wet noodles, as Romine says, when heated the sulfur atoms combine with carbon to form a stiff lattice. Sulfolobus breaks the lattice down.

Automobile tires generally cannot contain any more than 3 percent of recycled rubber because of high performance requirements: inert impurities would cause too much heat to build up when the rubber meets the road, making the tires wear out quickly. For this reason, Romine makes sure to curb his bacteria, either by lowering the temperature or raising the pH, before they break down all the sulfur-carbon bonds. That way the rubber can be made to bond more thoroughly with virgin rubber during recycling. Because these bonds dissipate heat, tires can contain up to 15 percent of the recycled rubber without sacrificing quality.

Having demonstrated the process in a 200-liter vat last year, Romine is now working with Rouse Rubber Industries in Vicksburg, Mississippi, to build a 2,000-liter fermentation reactor capable of producing rubber for 3,000 tires a month. He expects the reactor to be ready in September. If we can satisfy the tire market, Romine says, other rubber markets will be wide open.

Cold War Cleanup

University of Southern California’s Rocket-Fuel Disposal System

Innovator: Teh Fu Yen

Although Teh Fu Yen had spent most of his career coming up with ways of extracting oil and other natural resources from the earth, he got his toughest challenge in 1992 when United Technologies asked him to find a way of safely returning some of those resources to the environment. Specifically, the company wanted a mild, gentle way of decomposing volatile solid rocket fuel left over from cold war missiles. Each year these missiles sat in their stockpiles, their chemical components grew more and more dangerously unstable, which did not make Yen’s task any easier.

Last year Yen, an engineering professor at the University of Southern California, finally perfected a technique. First he uses nontoxic solvents to attack the polyurethane web that binds the mix of metals and explosive chemicals. It’s largely a physical type of reaction, Yen explains. There are boxes, or pigeonholes, in these giant networks of polyurethane molecules. The tiny solvent molecules fill up these boxes, causing the web of molecules to expand and break, and the fuel swells to a jellylike mass at least ten times its original volume. As a result, some chemicals leak out, rendering the fuel harmless. Next Yen adds water and a catalyst to the jelly and bombards it with pulses of ultrasound, which shake and break the giant molecular web of plastic, decomposing it further.

After extracting the leftover aluminum, magnesium, and other metals, Yen delivers the coup de grâce. White rot fungi eat the remaining, and by now soluble, bits of the fuel’s polyurethane web. Then anaerobic Pseudomonas bacteria reduce the fuel’s highly explosive nitrogen compounds to harmless methane, carbon dioxide, ammonia, and other easily disposable substances.

Yen has grown fond of his bacteria. Your heart has to feel that they are like human beings, he says. You supply them with what they want, like perhaps a bit of clay in addition to food, and they work for free. Last year he successfully dismantled 50 grams of rocket fuel on the roof of a campus building.
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