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  June 12, 2000

Research Yields New Environmental Clean-Up Technique

Faculty affiliated with the School of Engineering's Environmental Research Institute, collaborating with researchers from the United Technologies Research Center, have pioneered a new technique for removing dangerous chemical solvents from contaminated soil at industrial sites.

The new technique, recently awarded a U.S. patent, was developed to abate chlorinated solvents at industrial sites.

The work was conducted under ERI's Industrial Affiliates program - through which companies partner with ERI scientists to develop and commercialize key technologies - and with additional research contracts funded by UTC.

The collaboration was sparked by a desire at UTC to clean up a number of polluted sites, some acquired when UTC purchased smaller companies, where soil and groundwater were contaminated with a solvent commonly used to degrease industrial equipment. Although UTC has already reduced its use of solvents by 80 percent, the previously contaminated sites remain a challenge for cleanup.

"We are gratified by the promise and success of our new technique in not merely lessening the impact of pollutants, but eliminating contaminants at the source," says George Hoag, a professor of civil and environmental engineering and director of ERI. "We look forward to commercializing it for widespread use to reduce point pollution nationwide."

Working Together
The collaboration began in 1997 when UTC approached Hoag and his colleagues for help in identifying a method for eliminating solvents at the source. In addition to Hoag, the project team involved Pradeep Chheda, an assistant professor-in-residence with ERI, and Bernard Woody and Gregory Dobbs of the United Technologies Research Center.

The specific target contaminant at UTC sites is trichloroethylene, commonly used for degreasing and cleaning manufacturing and military equipment.

It was not until the late 1970s and early 1980s that scientists began to suspect solvents were a potential health risk. About the same time, testing methods became extremely refined, allowing for detection of minute quantities of pollutants.

TCE, also associated with the dry cleaning industry, is now considered a suspected carcinogen - cancer-

causing agent - by the Environmental Protection Agency.

When released into the soil, TCE slowly seeps through the soil layers until it encounters an impenetrable layer of clay or bedrock. Groundwater passing through the soil slowly dissolves and transports the solvent, where it can further migrate through the soil, potentially resulting in significant contamination of groundwater resources.

EPA has set a maximum concentration of five parts per billion as the acceptable level of human consumption. To put it in perspective, consider that one drop of human sweat in the average swimming pool is at a concentration of one part per million.

Hoag says thousands of sites nationwide are contaminated by TCE, including commercial businesses and government installations. Although various remediation methods are being marketed, most are unproven and many are effective only under very prescribed circumstances.

Conventional techniques for dealing with solvent pollution rely on so-called "pump-and-treat" methods. These employ a series of wells at intervals down-gradient from the pollution source. The wells collect contaminated groundwater, which then is treated and returned to drinking water sources.

"The process can take 20-30 years, and no site is ever considered fully 'clean'," says UTC's Woody. This method is effective in controlling only the pollutant "plume," that is, the migration through the soil away from the original pollution source.

Other methods involve simply digging up the polluted soil and storing it in containment devices.

Both approaches are effective in treating, but not eliminating, the contaminant. The time and cost involved make them impractical, however.

Winning Technique
Before hitting on the winning technique, the team investigated and discarded several processes. A promising chemical method of soil remediation, being tested in Canada, involved use of potassium permanganate.

In the laboratory, potassium permanganate was especially promising because it was found to degrade high concentrations of solvents very rapidly - within hours - and produce benign byproducts.

In both lab and field experiments, however, its strong reactivity with soil prevented it from moving through the soil as quickly as desired, before eventually reacting with the pollutant. Using a greater volume of potassium permanganate proved significantly more costly and produced additional chemical reactions that hindered oxidation of the contaminant.

So the team looked at three other oxidants, in hopes of reducing the amount of potassium permanganate needed and thereby decreasing the cost and increasing the effectiveness of this approach.

Among them was sodium persulfate, used commonly as a brightener in laundry formulations and as a chain initiator for making polymers. In tests, it did not react with the soil as quickly as permanganate.

A Serial Approach
Tests showed that combining potassium permanganate and sodium persulfate - with sodium persulfate introduced first - worked best. The method required less of the costly potassium permanganate and - most importantly - was effective in eliminating the TCE from the soil.

Rigorous testing is proving the viability of this new remediation technology. Large-scale testing of the technique is under way at a former UTC site in Indiana and at another site in California. The team is also looking for additional pilot test sites.

The patent was granted to Hoag and Chheda, and Bernard Woody and Gregory Dobbs of UTC in February. Besides continuing to treat contaminated UTC sites, the researchers are negotiating with several U.S. companies to license the new technology.

Last month, the U.S. Environmental Protection Agency conditionally accepted the researchers' proposal to demonstrate the cleanup technology at the contaminated Roosevelt Mills property in Vernon, Conn., under the agency's Superfund Innovative Technology Evaluation Program.

Formerly used in textile manufacture, the Roosevelt Mills site is severely contaminated with chlorinated solvents. Once cleaned up, the former mills may be transformed into a fish farm.

"This achievement is the culmination of a great deal of hard work between the United Technologies Research Center and the School of Engineering's Environmental Research Institute," says Hoag. "Bringing the technology to a commercially viable state - with the promise of adding

one more weapon in the war against environmental contaminants - is a wonderful reward."

Nan Cooper