Evaluation of strategies for anaerobic bioremediation of high concentrations of halomethanes

Bioremediation is being considered for groundwater at an industrial site contaminated with carbon tetrachloride (CT), trichlorofluoromethane (CFC-11), and chloroform (CF), at concentrations typically considered too high for biological treatment. 1,1-Dichloroethene is also present. The objective of this study was to evaluate in situ anaerobic remediation by biostimulation alone (lactate, emulsified vegetable oil, and corn syrup), biostimulation (corn syrup) supplemented with vitamin B₁₂ (cyanocobalamin), and bioaugmentation in combination with catalytic levels of B₁₂. Three cultures were evaluated for enhancing biotransformation of CT, CFC-11 and CF: two were sulfate reducing enrichments (grown on lactate and ethanol, respectively), based on a high concentration of sulfate in the groundwater; the other was a fermentative enrichment grown on corn syrup. A microcosm study with soil and groundwater (neutralized to pH 7) from the site revealed that bioaugmentation is a potentially feasible treatment approach, with complete biotransformation of 8.8 mg/L CT, 26 mg/L CFC-11, and 500 mg/L of CF in approximately 500 days. The lactate-grown sulfate reducing culture and the corn syrup-grown fermentative culture were the most effective. Subsequent bioaugmentation with a chloroethene-respiring culture yielded rapid reduction of 1,1-dichloroethene (9.1 mg/L) to ethene. Complete transformation of CT, CFC-11 and CF was also observed with corn syrup + B₁₂, although the time required was twice as long compared to bioaugmentation. In the presence of B₁₂, biotransformation of ¹⁴C]CT and ¹⁴C]CF yielded mainly CO, CO₂, and organic acids. CT was consistently transformed first, followed by CFC-11 and then CF. Corn syrup was only partially effective for halomethane removal without B₁₂, but was more effective than emulsified vegetable oil or lactate.