NSF-BSF Application: Developing Sustainable Approaches for Cometabolic Degradation of TCE and cDCE in Groundwater through Stable Isotope Techniques

Developing synergistic approaches that could reduce concentrations of multiple contaminants has the potential to result in considerable cost savings. Although anaerobic bioremediation has been successful for many chlorinated solvent sites, it has several significant limitations. Specifically, it is unlikely to be employed at large oxic sites because of the requirement for highly reducing conditions and the associated cost of driving such large sites anaerobic. Secondly, the approach will be less desirable at sites with multiple contaminants if those co-contaminants can be degraded more easily under aerobic conditions (e.g. benzene, toluene, 1,4-dioxane). Further, the accumulation of the known human carcinogen, vinyl chloride, from the dechlorination process represents a significant risk, if complete dechlorination does not occur. Additionally, driving sites anaerobic can result in long-term secondary groundwater impacts such as hydrogen sulfide, acidification, mobilization of reduced metals and methane accumulation. In contrast, aerobic approaches do not significantly impact site geochemistry. The proposed research will provide knowledge to enhance the aerobic remediation of two important groundwater contaminants (TCE and cDCE) for oxic sites.

An overall goal is to identify microorganisms capable of the most sustained TCE and cDCE removal at oxic sites. The data generated will then be used to test groundwater samples to determine if these microorganisms are present and active across sites. Specifically, the work will determine which microorganisms are associated with the most sustainable rates of co-metabolic biodegradation of TCE and cDCE. The research will also identify the most competitive microorganisms for both sustainable TCE and cDCE biodegradation and co-metabolic substrate uptake. Both aims will be achieved by examining the fate of carbon from both the co-metabolic substrates as well as TCE, cDCE and their degradation products using stable isotope probing (SIP). Another key aspect of the proposed work involves the application of compound specific isotope analysis (CSIA) to determine isotope enrichment patterns for these transformations, so that biodegradation pathways can be finally identified in the field and correlated to the microbial communities present. To our knowledge, no such combined approach has been applied for examining TCE or cDCE co-metabolism.