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The natural attenuation and engineered bioremediation of benzene in petroleum -contaminated aquifers under anaerobic conditions
The potential for in situ anaerobic benzene degradation in petroleum-contaminated aquifers was investigated. Sediments collected from a contaminated aquifer near Bemidji, MN in which Fe(III)-reduction was the dominant microbial process readily mineralized benzene when incubated with [U-14C]benzene while sediments from other aquifers did not. Benzene mineralization was localized within a narrow zone at the downgradient edge of the Fe(III) reduction zone. Analysis of MPN cultures and sediment by a variety of 16S rRNA-based techniques indicated a selective enrichment of Geobacteraceae in benzene degrading, Fe(III)-reducing sediments. Members of the Geobacteraceae are known to couple the oxidation of aromatic compounds to the reduction of Fe(III) and could be responsible for the observed benzene degradation at this site. Bemidji sediments also mineralized other aromatic compounds commonly found in hydrocarbon-contaminated groundwaters. Benzene-degrading sediments readily mineralized toluene and naphthalene indicating that these compounds were also being oxidized in situ. The unusual aromatic degradation activity at the Bemidji site could not be attributed to the presence of Fe(III)-chelators and/or electron shuttling compounds in the groundwater. Uncontaminated sediments could be adapted to benzene suggesting that Bemidji sediments naturally contain a microbial population capable of anaerobic benzene degradation. Results obtained from the Bemidji aquifer encouraged the investigation of anaerobic treatment alternatives for contaminated aquifers. Anaerobic bioremediation of benzene was evaluated at a petroleum-contaminated aquifer in Oklahoma. The injection of sulfate into the subsurface stimulated benzene degradation within a treatment zone located downgradient from an injection gallery. Benzene concentrations in the groundwater decreased by an average of 90% (100% in one well) during the study period. Sulfate concentrations, relative to a bromide tracer, decreased with distance from the injection gallery suggesting that benzene removal was coupled to the removal of sulfate from the groundwater. [U-14C]Benzene mineralization and [2-14C]acetate analysis of sediments confirmed that benzene degradation was indeed coupled to sulfate reduction within treatment zone sediments. Mass balance calculations suggested that as much as 42% of the removed sulfate within the treatment zone could be attributed to the anaerobic oxidation of benzene. The results demonstrate that stimulation of anaerobic processes can be an effective treatment alternative for heavily contaminated aquifers.
Anderson, Robert Todd, "The natural attenuation and engineered bioremediation of benzene in petroleum -contaminated aquifers under anaerobic conditions" (2000). Doctoral Dissertations Available from Proquest. AAI9960733.