In Situ Bioremediation of Carbon Tetrachloride: Field Test Results

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Abstract
Results of a 7-month field test of in situ bioremediation of carbon tetrachloride (CT) under denitrifying conditions are reported. The demonstration was conducted in a portion of a several-square-mile CT and nitrate plume. Pretest CT and nitrate levels were 12.5 ± 0.14 μM and 3.87 ± 0.26 mM, respectively. During the test, the CT concentration dropped by 3.71 ± μM, representing an estimated total of 1.42 kg of CT destroyed. The total quantities of acetate and nitrate injected during the demonstration were 221 and 300 kg, respectively. Nitra injection was composed of short-duration, high-concentration pulses added with acetate pulses, and continuously injected nitrate that was present in the surrounding groundwater. Biomass was distributed successfully within the flow field without fouling the injection well. Levels of planktonic denitrifiers increased 10- and 5-fold in monitoring wells 3 and 6 m downstream from the injection well, respectively. A distributed growth pattern was indicated through reductions in the concentrations of acetate, nitrate, and nitrite between these wells. Chloroform (CF) production was controlled by adjusting acetate and nitrate pulsing to keep low levels of nitrate in most of the flow field. Under this regime only 1 mol% of transformed CT appeared as CF. In contrast, approximately 33 mol% of CT transformed to appear as CF when nutrient-feeding conditions were adjusted so that nitrate was consistently absent.