Treatment of Dense Non-Aqueous Phase Liquids Through Enhanced Bioremediation

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Courtesy of SIREM

Problem
As a result of trichloroethene (TCE) releases to groundwater during the 1960’s, TCE is now found in the sandy aquifer beneath the Site in the form of a dense, non-aqueous phase liquid (DNAPL). Testing for the vinyl chloride reductase (vcrA) gene (Gene-Trac-VC) and bench scale treatability testing indicated that native Dehalococcoides (Dhc) found at the Site were not uniformly capable of complete dechlorination of TCE to ethene (Hood et al., 2008).

Solution
NASA undertook a field testing program of KB-1® bioaugmentation to target TCE DNAPL in groundwater using LC34 as the demonstration site. The US EPA Superfund Innovative Technology Evaluation (SITE) program (EPA, 2004) collected parallel independent data to validate performance. Groundwater at the site was amended with dilute ethanol as an electron donor and recirculated through the demonstration plot to promote in situ microbial growth. The recirculated groundwater was bioaugmented with 60 liters of KB-1® culture with the goal of introducing large numbers of Dhc capable of complete dechlorination of TCE.

Results
Enhanced bioremediation, including KB-1® bioaugmentation, rapidly increased the rate of TCE biodegradation with ethene concentrations in stoichiometric excess of the initial TCE concentrations, indicating enhanced removal of TCE-DNAPL (>98% mass removal) and confirming that dechlorinating activity was not inhibited by high concentrations of TCE. Two years after this study, follow up testing confirmed that dechlorinating activity continued in the absence of ongoing treatment and resulted in further decreases in TCE concentrations; demonstrating that bioremediation is
an effective approach for both enhanced DNAPL removal and/or containment of TCE-impacted groundwater in DNAPL source zones. As a result, bioaugmentation technologies are currently being deployed as several sites at Kennedy Space Center and related facilities.

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