Field demonstration of bioaugmentation in trichloroethene-contaminated groundwater

A pilot test was conducted to evaluate the effectiveness of bioaugmentation. Dechlorinating consortium in which the dominant microorganisms were Dehalococcoides species (DHC) possessing the vinyl chloride reductase gene (vcrA). The pilot test consisted of a direct injection system, including 2 injection wells. One injection well was for bioaugmentation, and the other, located approximately 20 m away, was for biostimulation. TCE was rapidly dechlorinated to cis-DCE in both wells. The first indication of reduction beyond cis-DCE and VC was the occurrence of ethene 63 days after bioaugmentation in the augmented injection well (AIW). In conjunction with the ethene production, the concentrations of the DHC-16S rRNA gene and the vcrA increased to approximately 10⁶ copies/mL. By day 119, the number of copies of those genes remained high in the AIW, and all chloroethenes declined to levels below the Environmental Quality Standards for Groundwater Pollution in Japan. Though the concentration of indigenous DHC also increased to approximately 10⁶ copies/mL 182 days after injection of nutrients in stimulated injection well, the concentration of cis-DCE and VC remained high until 371 days. These results confirmed that bioaugmentation contributed to shortening the clean-up time better than biostimulation by increasing the initial DHC population in the groundwater.