Vitamin B-12 and reduced titanium for remediation of residual chlorinated solvents: Field experiment

A first pilot-scale field experiment using vitamin B-12 and reduced titaniu m was conducted in an in situ vertical circulation column at CFB Borden. Th e objective of the experiment was to test the applicability of the technolo gy for restoring aquifer source zones contaminated by chlorinated solvents- tetrachloroethene (PCE) and 1,1,1-trichloroethane (1,1,1-TCA)-in a mixture of dense nonaqueous phase liquids (DNAPLs). Vitamin B-12 promotes the reduc tive dechlorination of chlorinated organics. A highly reducing and slightly alkaline environment must be maintained (Eh < -480 mV and 7 < pH < 9) to m aximize the rate of degradation. In this field test, PCE and 1,1,1-TCA degr aded to a limited extent under experimental conditions, with 1,1,1-TCA degr ading more readily. Indigenous bacteria were found to metabolize citrate, w hich caused titanium to precipitate, limiting degradation. The addition of glucose at the end of a second field season effectively limited citrate deg radation and helped recover the optimal redox potential by keeping reduced titanium in solution. A laboratory column was used to confirm field results . The column also produced a significant biomass, which provided an additio nal source of organic carbon onto which the solvents sorbed.