Reductive Dechlorination of Tetrachloroethene by a Mixed Bacterial Culture Growing on Ethyl Lactate

Abstract

Chloroethenes like tetrachloroethene (PCE) are the most prevalent groundwater contaminants in the USA. Their presence as nonaqueous phase liquids (NAPLs) makes remediation difficult. Among options for NAPL cleanup, co-solvent injection has demonstrated success. However, the process has the potential to leave considerable residue of the co-solvent as well as residual chloroethene. Our rationale in this study was to examine whether this residual solvent could be a potential electron donor for the remediation of the residual chloroethene. We hypothesized that ethyl lactate, a “green” solvent, could serve both as a NAPL extraction solvent and an electron donor for reductive dechlorination of residual chloroethene. We examined whether a mixed culture known to degrade PCE with lactate could also grow on ethyl lactate and whether it could stimulate PCE dechlorination. Biomass growth and PCE dechlorination were observed by protein and chloride production, respectively, in the culture; with a specific dechlorination rate of 50–150 µg (mg cell d)⁻¹. Ethyl lactate abiotically breaks down to ethanol and lactate, the latter being a rich source of hydrogen for reductive dechlorination. The results demonstrate that ethyl lactate may be promising for in situ bioremediation following NAPL extraction.

Keywords:

• Reductive dechlorination
• Bioremediation
• Ethyl lactate
• Perchloroethene
• Tetrachloroethene
• Chloroethene
• Green chemistry
• Solvent extraction
• NAPL

Acknowledgments

This work was supported in part by grants BES-0119972 and OCE-0120453 from the National Science Foundation and a grant from the Campus Research Board of the University of Illinois at Chicago. We thank Robert Sanford from the University of Illinois at Urbana-Champaign for supplying the microbial cultures used in these experiments.