Stimulating and Sustaining Reductive Dechlorination using In Situ Bioreactors
Electron donor injection and bioaugmentation are common approaches to enhance in situ reductive dechlorination. While these treatments are frequently successful, issues can arise that diminish the effectiveness of the treatment and cannot be easily corrected without incurring the expense of additional injections. These issues may include problems related to amendment delivery, decreased longevity of donor, or survivability of a lab-grown culture. The in situ bioreactor (ISBR) design presented here allows for controlled amendment delivery over a long period of time, which can decrease the overall amount of donor used and limit the need for bioaugmentation. Also, the lower substrate concentrations maintained by the ISBR can have less impact on secondary groundwater quality and hydraulic conductivity of an aquifer compared to the donor loads associated with batch injections. In the current study, 9 anaerobic ISBRs installed at an industrial facility in New Jersey were fed with electron donors in order to sustain high concentrations of indigenous dechlorinating bacteria and subsequently increase dechlorination rates.
Eight ISBRs were operated in duplicate and fed one of 4 different electron donors to determine the efficacy of each substrate when used with the ISBR. The ninth ISBR was inoculated with a bioaugmentation culture and then fed an electron donor. Lastly, a traditional batch injection of donor and culture was also evaluated. The 10 remediation wells and 5 adjacent monitoring wells were sampled quarterly. Significant growth in key microbial communities was observed after 3 months of treatment. All 8 ISBRs without bioaugmentation sustained indigenous dechlorinating bacteria, and there were no statistically significant differences in performance of the 4 electron donors in terms of total CVOC removal. The bioaugmented ISBR maintained higher concentrations of dechlorinators compared to the well that received a traditional injection of donor and culture.