Microbes fight gas additive

Contamination: A combination of bacteria and oxygen shows promise in cleaning up ground water polluted by MTBE.

Medicine & Science

July 12, 2004|By Timothy B. Wheeler | Timothy B. Wheeler,SUN STAFF

PORT HUENEME, Calif. -- Almost hidden by a low stockade fence, an unassuming tangle of white plastic pipe and metal tanks on the parade ground of a Navy base here could revolutionize cleanup of one of the nation's most vexing environmental messes.

The West Coast home of the Seabees, Port Hueneme (why-KNEE-me) is a major staging area for the naval engineers, with sprawling parking lots for their vehicles and hardware. Like many military bases, this 1,600-acre complex sits above ground water that has been contaminated -- in this case with a mile-long plume of a gasoline additive called methyl tertiary butyl ether, or MTBE.

Scientists say they hope their system -- which uses bacteria to devour the chemical -- could trim millions of dollars and decades from the current costly, time-consuming cleanups.

The foul-smelling MTBE got loose here in the late 1980s when 11,000 gallons of fuel leaked from underground tanks at the base exchange service station.

As owners of wells in Maryland and the rest of the country have discovered, the chemical shows up in the water virtually everywhere MTBE-laced gas is sold. It dissolves easily and spreads quickly, making the water unpalatable -- if not unsafe to drink -- at very low levels.

A few years back, the U.S. Geological Survey found MTBE in 9 percent of the community water sources checked randomly nationwide, including lakes, rivers and wells.

MTBE is notoriously stubborn: Cleaning up a tainted aquifer can take decades and cost untold millions. The City of Santa Monica, about 60 miles south of here, will spend almost $100 million on a treatment plant to remove MTBE from a well field contaminated in the mid-1990s. Oil companies whose leaky gas stations caused the problem will foot the bill.

The Navy likewise is under orders to clean up its MTBE here, even though no one on base or in the neighboring civilian community drinks water from the fouled aquifer.

For four years, the service has been pumping water from the ground and using traditional carbon filters to remove MTBE before it can seep into the harbor. Given the snail's pace at which ground water moves -- a few inches a year -- officials say it could take 240 years for that system to finish the job.

But the Navy has turned its problem here into a proving ground for new technologies that might restore aquifers more quickly and cheaply.

Scientists from private industry, the federal government and California's universities have tried breaking down the gasoline additive by bombarding it with high-energy electron beams. They've also tried to destroy the MTBE chemically by injecting ozone and hydrogen peroxide into the ground water.

The most promising MTBE-buster, however, might be the simplest and most natural -- bacteria that "eat" the chemical, producing harmless carbon dioxide. Researchers at the University of California, Davis and at private laboratories have tested at least three strains of microbes in the field.

The process is known as bio-remediation -- an increasingly common method of attacking toxic pollutants in soil and ground water. It's used to break down substances that range from cancer-causing benzene (also found in gasoline) to PCBs, another troublesome chemical once used in electric transformers.

Initially, studies suggested that microbes couldn't do much with MTBE, at least not without being fed another chemical first.

But then researchers heard about a Los Angeles County treatment plant that mysteriously and unexpectedly was removing MTBE from tainted refinery waste. Scientists traced the development to bacteria found growing on a filter in the plant. They ultimately succeeded in teasing out a strain partial to feeding on the gasoline oxygenate.

The strain, which has yet to be named, has been dubbed PM1. It is a type of proteobacteria, a diverse group of microorganisms that includes some that can cause diseases. PM1 appears relatively benign, however.

Interestingly enough, the microbes have been found growing on their own at a number of MTBE-contaminated sites around the state, said Kate M. Scow, professor of soil science at UC Davis. This leads researchers to think the solution could be to stimulate naturally occurring bacteria.

They decided that oxygen, required by all animals and many bacteria, could be the critical factor. But there's not much oxygen in ground water.

"The key, I think, is you need to add oxygen unless it's there," says Scow, a specialist in bioremediation . "There have been places where MTBE seems to be degrading without adding oxygen, and that's in places where ground water dumps into a stream."

Scow and other researchers have tested their microbes' ability to fight MTBE by injecting small amounts of bacteria into the tainted aquifer here, which lies 10 to 20 feet below the surface.

They set up their treatment system by punching holes in the asphalt that covers much of the base, then pumping in a bacteria-laced solution along with frequent doses of air or pure oxygen to keep the microbes alive.

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