The use of redox potential to monitor biochemical HCBD dechlorination.

The microbial reductive dechlorination of chlorinated solvents is a redox reaction in which the chlorinated carbon receives electrons from a suitable electron donor. Hexachloro-1,3-butadiene (HCBD) is a particularly recalcitrant chlorinated solvent. Its slow, cyanocobalamin-dependent biochemical dechlorination by mixed microbial consortia had been previously demonstrated. This study shows that the reductive dechlorination reaction of HCBD can be monitored in situ by recording the redox potential (E(Ag/AgCl)). The addition of HCBD to mixed anaerobic consortia triggered a rise of E(Ag/AgCl) and the formation of dechlorinated endproducts. This indicated that the change in E(Ag/AgCl) was linked to the dechlorination of HCBD. Total concentration of dechlorinated endproducts (C4 gases) equated to approximately 50% of HCBD added. The rise and subsequent fall in E(Ag/AgCl) after the addition of HCBD caused a peak. Peak areas obtained, from the change in E(Ag/AgCl), provided an indication of the amount of HCBD dechlorinated. Moreover, the saturation concentration of HCBD can be estimated from peak heights. This online monitoring of HCBD reductive dechlorination could potentially be used for improved process control of bioremediation reactors and on-site as online biosensors. Online monitoring of HCBD dechlorination via redox potential offers both reliability and portability at a low cost. In addition, this novel and innovative technique could potentially be used to monitor the dechlorination of contaminants other than HCBD.