Application of Emulsified Substrate Biobarrier to Remediate TCE-Contaminated Groundwater: Pilot-Scale Study

Abstract

Groundwater at many existing and former industrial areas and disposal sites is contaminated by halogenated organic compounds that were released into the environment. One cost-effective approach for the remediation of the chlorinated solvent contaminated aquifers is the installation of biobarriers within aquifers. The objective of this study was to assess the potential of using an in situ biobarrier system containing the emulsified substrate (ES) to bioremediate and contain the trichloroethylene (TCE) plume. The ES contained soybean oil, lactate, biodegradable surfactant, and nutrients, and thus it was able to provide carbon sources for the enhancement of the reductive dechlorination of TCE. A field-scale study was operated at a TCE-contaminated site, and 150 L of ES solution was pressure-injected into three remediation wells located in the upgradient area of the plume to form a biobarrier. Results show that the total organic carbon (TOC) went up from 12 mg/L (before ES injection) to 9,800 mg/L after 45 days of ES injection, and slowly declined to 1,500 mg/L after 230 days of operation. The increased TOC caused the complete consumption of groundwater dissolved oxygen in the injection wells (dropped from 0.6 to 0 mg/L) after 5 days of the ES injection. Results also show that the TCE concentrations dropped from 140 to below 1 μg/L after 10 days of ES injection in the biobarrier. The TCE degradation byproducts [e.g., 1,1-dichloroethene (1,1-DCE), vinyl chloride (VC)] were also observed in the injection and downgradient monitor wells. Results of microbial analyses show that various TCE-degrading bacteria exist in the subsurface, including Ralstonia sp., Clostridium sp., uncultured Burkholderiales bacterium, Hydrogenophaga sp., Acidovorax sp., Hydrocarboniphaga sp., uncultured Curvibacter sp., Pseudomonas sp., Comamonas sp., Aquabacterium sp., and Variovorax strains. Results indicate that the injected ES enhanced the anaerobic dechlorination of TCE, and the developed biobarrier could contain the TCE plume effectively. The biobarrier has the potential to be developed into an environmentally and economically acceptable remedial system.