Vitamin B-12-catalyzed dechlorination of perchloroethylene present as residual DNAPL

The goal of this study was the cleanup of residual solvents in the saturated zone using an in situ biochemical treatment. Perchloroethylene (PCE) was chosen as a model compound because it is the most commonly found organic ground water contaminant. A mixture of vitamin B-12 with titanium citrate was pumped as the remedial solution through a column containing 100 mu L of PCE residual. The rate of reaction was found to be first order with respect to the concentration of PCE and to the concentration of vitamin B-12. At 10 ppm B-12, more than 85 percent PCE was degraded to trichloroethylene (TCE) and dichloroethylene (DCE) in two hours. The presence of low to moderate concentrations of organic carbon had no significant effect on the reaction. Vitamin B-12 reduced by titanium citrate was found to be compatible with the survival of anaerobic bacteria. The four major advantages of the biochemical system over the use of anaerobic bacteria are that (1) the rate is faster; (2) there is no need for the careful balance of nutrients or the addition of an extraneous carbon source; (3) there is no restriction in the concentration range of the compound to be treated; and (4) the remedial solution is mobile, even in the presence of organic carbon.