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Promising Emerging Mechanisms
Citation:
Wilson, J. Promising Emerging Mechanisms. Presented at AFCEE Technology Transfer Workshop, San Antonio, TX, March 25 - 28, 2008.
Impact/Purpose:
To present information at the AFCEE Technology Transfer Workshop
Description:
Most applications of enhanced in situ bioremediation are based on biological reductive dechlorination. Anaerobic metabolism can also produce reactive minerals that allow for in situ biogeochemical transformation of chlorinated organic contaminants such as PCE, TCE, and cis-DCE. Sulfate reduction can produce iron sulfides including FeS and FeS2. Magnetite (FeO.Fe2O3) can be produced in situ by iron reduction. Magnetite can degrade chlorinated ethylenes to acetylene under either aerobic or anaerobic conditions. FeS can degrade chlorinated ethylenes to acetylene under anaerobic conditions. FeS is not stable under aerobic conditions. Both processes can degrade TCE and cis-DCE through an elimination reaction to produce acetylene. If the in situ biogeochemical transformation of chlorinated alkenes goes through acetylene, then production of vinyl chloride through the sequential reductive dechlorination pathway is avoided. Rates of TCE degradation by FeS that is chemically synthesized are near 0.067 per day at pH 7.0 in presence of 1.0 mole FeS in contact with 1.0 liter of water (M*). Rates of TCE degradation by FeS that is produced by biological sulfate reduction vary from 2.3 and 0.53 per day per M*. Magnetic susceptibility can serve as a very inexpensive screening test for the presence of magnetite. A magnetic susceptibility in the range of 0.1 to 1.0 X10-6 m3 kg-1 can sustain first order rates of removal near 0.3 per year.