Field demonstration of bioaugmentation in trichloroethene-contaminated groundwater

Abstract

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.

Exploiting the intrinsic microbial degradative potential for field-based in situ dechlorination of trichloroethene contaminated groundwater

“…However, substantial dechlorination still occurred in MNA wells (although at a slower rate) suggesting that it would be a cheaper bioremediation approach, if accelerated contaminant removal was not needed. If no indigenous dechlorinating community was present, augmentation with dechlorinators (Dhc mixed consortia) would be standard practice [7,17,41].…”

“…For example, Okutsu et al showed that the addition of "bioaugmentation agents contributed to shortening the clean-up time better than biostimulation by increasing the initial Dehalococcoides sp. (Dhc) population in the groundwater" in a pilot study of TCE contaminated groundwater [7]. Chemical compounds (biostimulation) can also be added to contaminated samples to stimulate the biological degradation of the pollutants [8].…”