TRANSFORMATION OF CARBON-TETRACHLORIDE UNDER SULFATE-REDUCING CONDITIONS

The removal of carbon tetrachloride under sulfate reducing conditions was studied in an anaerobic packed-bed reactor. Carbon tetrachloride, up to a concentration of 30 mu M, was completely converted. Chloroform and dichloromethane were the main transformation products, but part o f the carbon tetrachloride was also completely dechlorinated to unknow n products. Gram-positive sulfate-reducing bacteria were involved in t he reductive dechlorination of carbon tetrachloride to chloroform and dichloromethane since both molybdate, an inhibitor of sulfate reductio n, and vancomycin, an inhibitor of gram-positive bacteria completely i nhibited carbon tetrachloride transformation. Carbon tetrachloride tra nsformation by these bacteria was a cometabolic process and depended o n the input of an electron donor and electron acceptor (sulfate). The rate of carbon tetrachloride transformation by sulfate reducing bacter ia depended on the type of electron donor present. A transformation ra te of 5.1 nmol.ml(-1).h(-1) was found with ethanol as electron donor. At carbon tetrachloride concentrations higher than 18 mu M, sulfate re duction and reductive dechlorination of carbon tetrachloride decreased and complete inhibition was observed at a carbon tetrachloride concen tration of 56.6 mu M. It is not clear what type of microorganisms were involved in the observed partial complete dechlorination of carbon te trachloride. Sulfate reducing bacteria probably did not play a role si nce inhibition of these bacteria with molybdate had no effect on the c omplete dechlorination of carbon tetrachloride.