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In Situ Treatment of PCB-Contaminated Sediments Using Zero-Valent Iron
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Project Title: In situ Treatment of PCBs in Marine and Freshwater Sediments using Colloidal Zero-
Valent Iron
Research Locations: Narragansett Bay, RI
Last Update: 3-04-04
Polychlorinated biphenyls, or PCBs, are organic compounds used in many industrial and commercial applications from the 1930’s to the 1970’s. Dubbed the “perfect industrial chemicals,” PCBs are non-flammable and do not break down easily, properties that make them ideal for use in everything from industrial coolants to plastics and rubber products. However, evidence of severe health problems from exposure to PCBs led manufacturers to end their production in the late 1970’s. Hundreds of thousands of tons of these highly toxic contaminants were released into the environment over the course of decades, and remain in sediments around the country to this day. Because they do not biodegrade and they are readily stored in fats, they move up the food chain and accumulate in animal tissues at increasingly higher concentrations, impacting the environment and human health. Few successful and cost-effective management options exist to remediate PCB-polluted sediments. This project is developing a promising new technology to remediate large areas of contaminated sediments on-site, without disturbing the environment or risking direct human exposure.
The Approach
Current techniques for remediating contaminated sediments include dredging and removing large volumes of sediment material, and either burning it to eliminate contaminants, or depositing it in landfills. This
process is costly and time-consuming, and can damage the coastal marine ecosystem. Dredging can also stir up PCBs that lie beneath layers of non-toxic sediments, releasing them into the air and water, exposing them to people and organisms in the environment. On-site remediation can potentially avoid the high cost and possible hazards of these traditional clean-up methods.
The Science
The zero-valent iron (ZVI) technology involves introducing ZVI, or solid
metal iron, to the sediments in situ (that is, at the site), mixing
them together, and allowing a chemical reaction to break down the PCBs.
The process of breaking down the toxic chemicals is called dechlorination,
and results in a product that is much less harmful and more easily biodegraded
in the environment.
Results
Researchers injected ZVI into contaminated sediment samples obtained from two PCB-polluted sites in Massachusetts: the New Bedford Harbor and the Housatonic River. Results showed that PCB levels decreased significantly after the addition of ZVI, and in some instances nearly disappeared altogether. The type and composition of the sediments appeared to affect the removal rate, with loose, sandy sediments taking less time than sediments containing clay. As illustrated by Figure 2, 98% of the PCBs in sandy Housatonic River samples were removed in a single day; 38% were removed from the more clay-based New Bedford Harbor samples in the same period.
Technology Transfer: Getting the Word Out
The groundbreaking ZVI technology has generated significant interest in both the public and private sectors. Researchers have presented their findings to a wide audience that includes scientists, government officials, coastal zone managers and citizen's groups.
Beginning the Patenting Process
A patent for this new technology was submitted in the fall of 2003.
Commercialization: Putting New Technology to Use
Researchers are partnering with Dr. Warren Chesner of Seaway Environmental Technologies, Inc. to commercialize the zero-valent iron remediation technology. Seaway is fine-tuning the engineering aspects of applying zero-valent iron on-site, and researchers are continuing laboratory work to further demonstrate the effectiveness of the treatment. Visit the Seaway website at http://www.seawaytech.com to learn more.
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Project Coordinator
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Kevin Gardner (603) 862-4334 University of New Hampshire Environmental Research Group kevin.gardner@unh.edu |
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Start -End Date:
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09/01/2001 - 09/01/2003
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NERR Reserve(s):
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Narragansett Bay, RI
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| For more information: |
Dolores Jalbert Leonard Phone: (603) 862-3685 Email: dolores.leonard@unh.edu |