Gas wars: Microbes fight water and soil pollution

MTBE, an additive to gasoline that comes straight from the pump, improves air quality but can contaminate water and soil

By Environmental News Network staff

Legislators, environmental groups and ordinary people are battling to get methyl tertiary butyl ether, or MTBE, out of gasoline. Until they do, Derek Lovley knows a way to get MTBE out of contaminated soil and water.

Lovley, head of the department of microbiology at the University of Massachusetts, devised a unique and relatively inexpensive method to clean up dangerous contaminants contained in gasoline by encouraging microorganisms already in the ground or water to degrade the pollutants.

Lovley and colleague Robert Anderson demonstrated in laboratory tests that it is possible to spur microbes to degrade benzene in petroleum-contaminated underground water, even where oxygen has been depleted by massive or long-term contamination. Benzene, a major constituent of many fuels, is a known carcinogen.

Now, Lovley and an assistant, Kevin Finneran, are conducting a similar project to degrade methyl tertiary butyl ether, or MTBE, another hazardous gasoline component, at contaminated sites.

Every day, nearly 200,000 gas stations across the country pump about a half-million gallons of gasoline into America’s motor vehicles, according to the Journal of Petroleum Marketing. Invariably, some gasoline escapes into the environment — at the pump, in accidents on the road and directly into water supplies and soil through ruptures in underground tanks or pipes.

In California, residents are fighting to clean up water supplies throughout the state and ban MTBE in the process. The Association of California Water Agencies sent a letter last month to President Clinton demanding prompt action to stop the use of MTBE.

The Environmental Protection Agency on March 20 said it would phase out MTBE in favor of ethanol, but no timetable is set. The association fears the action will take years to carry out.

Lovley and Anderson received funding from the American Petroleum Institute and Conoco to determine what they could accomplish in a site near Ponca City, Oklahoma, that had been contaminated with various forms of petroleum for more than 50 years. Conventional approaches to remediation of the area, which included more than 25 million gallons of contaminated water in an underground aquifer, were unsuccessful.

"We were faced with a massively contaminated site," said Lovley. "Sometimes they pump oxygen into badly contaminated soil and water like this to get the microbial remediation process started, but that approach is costly, and then you end up with other problems, including plugging up the aquifer with iron oxides.

Derek Lovley is chairman of the microbiology department at the University of Massachusetts

"We've shown it's not only possible but it's also easier and cheaper to remove benzene from these contaminated wells anaerobically, or, without oxygen, by pumping sulfate into the sediment below an aquifer. This encourages microorganisms deep in the soil to finish the remediation process for us."

Lovley and Anderson set up 40 injection wells over a section of the aquifer as well as a series of observation wells along the flow path of the groundwater. Sulfate was dripped into the contaminated area through the injection wells over a period of 200 days. Tests run in the observation wells demonstrated how effectively benzene was removed from the water.

"When we added sulfate to the aquifer, we saw virtually immediate stimulation of benzene removal. The bacteria oxidized benzene and produced carbon dioxide, which is not harmful to the environment," said Lovley. "To our knowledge, this is the first successful field demonstration in which the anaerobic degradation of benzene has been accelerated at the site of contamination.

"This process might not work in all petroleum-contaminated aquifers, but we have proved it works where there are sulfate-reducing microbes present in the environment."

Buoyed by one success, Lovley and Finneran went about transferring the benzene-removal technology to sites contaminated with MTBE. This additive tends to migrate quickly when it reaches underground pools of water and is difficult to remove at low concentrations through conventional treatment, Lovley explained.

The two researchers collected sediments from several MTBE-contaminated sites in the United States. By simulating an anaerobic process similar to what Lovley and Anderson used to extract benzene, they reduced the amount of MTBE in soil samples by about 3 percent a week. At this rate, they expect to remove all of the MTBE from the soil in less than a year.

"One of the major advantages of using an anaerobic technique is it lets you remove MTBE at the source, before it has a chance to spread," said Lovley.

Field tests using procedures similar to the benzene test will begin this fall in California.

Accidental spills can contaminate residential or agricultural soil or water supplies of an entire area. Lovley said the anaerobic bioremediation techniques he and his colleagues developed could be used to clean up some of those spills.

Their project is outlined in a recent issue of the journal Environmental Science and Technology.

Copyright 2000, Environmental News Network, All Rights Reserved

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USGS's MTBE
American Petroleum Institute
Conoco
California Energy Commission's study on MTBE
University of Massachusetts
Energy Information Administration
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