Researchers pour on the heat to test waste cleanup technology
August 31, 1992
RICHLAND, Wash. –
For generations, heat has been used to sterilize medical instruments and food products. Now, a new technology is being developed to use heat to "sterilize" contaminated soils. Developers say the technique will be a superior and inexpensive way of cleaning up toxic materials such as chlorinated solvents, PCBs, pesticides and industrial fuel oils and lubricants.
The process will provide the means for removing and/or destroying hazardous contaminants within the soil. Depending on the type of contaminant, the system is designed either to draw pollutants from the soil and treat the gases above ground, or to destroy the hazardous material, in place, underground.
The soil treatment process, named Electrical Remediation At Contaminated Environs or ERACE, is being developed by a multidisciplinary research team at the U.S. Department of Energy's Pacific Northwest Laboratory in Richland, Washington. Battelle operates PNL for DOE.
In the ERACE process, electrodes are used to apply an electrical current to the soil. Moisture within the soil boils and forms steam, stripping volatile and semi-volatile contaminants from soil particles. The contaminated steam is vented, and contaminants are collected within an off-gas treatment system. In addition, a specialized off-gas treatment system is being developed to destroy contaminants escaping from the soil instead of just filtering and collecting them.
The soil heating step is being field tested by PNL at DOE's Hanford Site in southeastern Washington state, and it will be demonstrated at DOE's Savannah River Site in South Carolina beginning next year. Both sites are contaminated with chlorinated solvents from nuclear defense production activities. However, the initial field studies are being done on non- contaminated soils.
Laboratory tests at Hanford suggest that ERACE will be able to remove 99.99 percent of many soil contaminants, including trichloroethylene, a common but toxic solvent used in dry cleaning and industrial applications; PCBs, or polychlorinated biphenyls, which have been linked to cancer; carbon tetrachloride, a carcinogenic industrial solvent; and most hydrocarbon fuels such as gasoline, diesel and jet fuels.
The key to the ERACE technology is the splitting of conventional three-phase electricity into six separate electrical phases. This allows for more uniform and deeper heating at relatively low voltages making the process less expensive than other soil heating technologies. ERACE is rapid, requiring weeks to remediate a large site, versus months or years for other soil venting technologies.
The PNL process also may provide a unique method of destroying contaminants in place. "When we were working on removing contaminants through soil heating, we discovered a technique that not only can volatilize but actually decompose or destroy organic contaminants," said William O. Heath, PNL project manager.
Destruction was achieved in tests by applying electricity to the soil to the point where a low-temperature plasma was created in the soil. Plasma is similar to a match flame, but is produced by electricity and oxidizes or consumes non-volatile contaminants which are bound tightly within the soil and would not be released with the steam. Non-volatile contaminants include transformer oils containing PCBs as well as greases, pesticides and industrial compounds.
The destruction application of ERACE is being developed for use at Hanford beginning in 1994 as part of DOE's Integrated Demonstration of technologies for cleaning up volatile organic compounds at arid sites. The technology also holds promise for soil treatment at many contaminated industrial, military and municipal sites.
PNL researchers also are using the same low-temperature plasma technique to develop a unique off-gas system to destroy contaminants in steam that rises from the ERACE soil treatment process.
The steam passes through a plasma reactor where contaminants are oxidized or consumed, and the gases are scrubbed with water and neutralized with ordinary baking soda. The final products are water containing table salt and clean air with slightly higher levels of carbon dioxide. The water and air appear to meet standards for release to the environment.
Initial laboratory tests at PNL indicate the ERACE process will decompose a long list of contaminants identified as hazardous by the U.S. Environmental Protection Agency, including polycyclic naphthalene or "Town Gas," a widespread problem on the East Coast that is proving costly to clean up by conventional methods.
A patent is pending on the ERACE soil treatment technology.