Evaluation of Enhanced Reductive Dechlorination of Trichloroethylene Using Gene Analysis: Pilot-Scale Study

The industrial solvent trichloroethylene (TCE) is among the most ubiquitous chlorinated compounds found in groundwater contamination. The objective of this pilot-scale study was to evaluate the effectiveness of an in situ reductive dechlorination process to remediate TCE-contaminated groundwater at a TCE-spill site using specific gene analysis. An injection well was installed inside the TCE plume for substrate and inocula injection. Brown sugar and anaerobic activated sludge (collected from an industrial wastewater-treatment plant with influent containing TCE) as electron donor (primary substrate) and inocula, respectively, were injected to enhance the TCE biodegradation rate through anaerobic reductive dechlorination. Three monitor wells were installed downgradient of the injection well along the groundwater flow path to monitor the TCE degradation trend. Polymerase chain reaction (PCR) analytical results reveal that the major TCE degrader (Dehalococcoides) and TCE-degrading genes (vcrA and tceA) were not observed in site groundwater before sludge injection. Thus, anaerobic sludge was injected for inoculation. After sludge injection, Dehalococcoides and the vcrA and tceA genes were detected in the injection and downgradient monitoring wells. Results show that brown sugar could be fermented to volatile fatty acids (VFAs), which could be used as substrates to enhance TCE reductive dechlorination. Up to 97% of TCE removal was observed after 204 days of operation. This reveals that appropriate substrates and inocula are required to effectively enhance the anaerobic reductive dechlorinating rate of TCE. Results indicate that the enhanced in situ bioremediation is a promising technology to remediate TCE-contaminated groundwater, and gene analysis is a necessity to evaluate the feasibility and occurrence of enhanced bioremediation. DOI: 10.1061/(ASCE)EE.1943-7870.0000654. (C) 2013 American Society of Civil Engineers.