Is Bioaugmentation in Combination with Biostimulation Effective for in Situ Bioremediaiton of Chlorinated Solvents in Groundwater?

Abstract:

The purpose of the field-scale study was to evaluate the effectiveness of biostimulation and bioaugmentation for in situ biodegradation of chlorinated solvents in groundwater. Elevated levels of tetrachloroethene (PCE), trichloroethene (TCE), and cis-1,2-dichloroethene, were detected in groundwater. The natural attenuation evaluation showed that reductive dechlorination was occurring in several of the on-site monitor wells where the dissolved oxygen (DO) concentrations were less than 1 mg/L. However, the oxidation reduction potential (ORP) significantly varied in on-site and off-site wells.

The results of bench-scale testing indicated that a variety of carbon substrates were effective at reducing the DO to levels that were favorable for reductive dechlorination. The lactate amended bioaugmented microcosms showed the highest level of reductive dechlorination, followed by EOS^® amended. However, the indigenous microbial population was not able to successfully degrade PCE to ethene. When a microbial consortium including Dehalococcoides was added to the microcosms, complete reductive dechlorination was observed.

A pair of recirculation wells was installed to inject the carbon source and microbial population into the groundwater. After a push-pull test was performed to evaluate the mobility of the microbial amendment, lactate was injected to promote highly reduced conditions in the groundwater. Once the ORP was less -150 mV, the Dehalococcoides consortium was injected into the groundwater and recirculated using the paired recirculation wells.

Within 3 months after carbon substrate injection, more than a 70% reduction in PCE and TCE was observed in the downgradient monitor well. Likewise, there was a significant decrease in ORP in the impacted wells. This presentation will discuss how the amendments impacted the chlorinated solvent concentrations, microbial community and chemistry of the groundwater in the area around the recirculation wells compared to non-impacted wells.