The addition of sulfate to an anaerobic petroleum-contaminated aquifer in which benzene was a major soluble contaminant resulted in removal of benzene from the groundwater. The loss in benzene was associated with a decrease in sulfate along the groundwater flow path, relative to a conservative bromide tracer. Studies with [2-14C]acetate and molybdate demonstrated that sulfate reduction was the predominant terminal electron-accepting process (TEAP) in the sulfate-amended sediments, and studies with [14C]benzene indicated that benzene oxidation was dependent upon sulfate reduction. Abundant ferrous iron in the subsurface likely prevented the generation of free sulfide in the groundwater during the field trial. Comparisons of benzene and sulfate depletion in the treatment zone indicated that benzene degradation could account for 53% of the sulfate depletion. These results suggest that the addition of sulfate stimulated the activity of benzene-degrading, sulfate-reducing microorganisms. This is the first field study demonstrating that it is possible to stimulate anaerobic benzene degradation in a petroleum-contaminated aquifer.
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