Column Studies of Anaerobic Carbon Tetrachloride Biotransformation with Hanford Aquifer Material



Continuous-flow and batch experiments were conducted using a column reactor system containing Hanford Aquifer material in order to assess the potential of in situ bioremediation of carbon tetrachloride (CT) at the Hanford site in south-central Washington state. Benzoate and acetate were evaluated as primary substrates both in the presence and absence of nitrate as a potential electron acceptor. Each of the four resulting test conditions was first run under continuous-flow mode until a pseudo–steady state was achieved and then switched to batch mode. The longer residence time of the batch portion of the test resulted in more complete transformations and helped elucidate zones of variable activity within the column. Reductions in CT concentration and chloroform (CF) production were observed in all test conditions. Benzoate generally supported faster and more complete CT transformations than acetate, even though substrate use and denitrification was more rapid for acetate. Sulfate was present in all cases; yet, sulfate reduction was never observed, even during extended absences of nitrate and nitrite. CT transformation was most rapid near the point of injection, with rates decreasing toward the effluent end of the column. These results indicate that the microbial population at Hanford is capable of transforming CT in the subsurface. However, methods to control the production of CF may be necessary before this technology can be successfully implemented in the field.