Effect of ethanol on the bioattenuation of BTEX compounds and their enhanced anaerobic biodegradation through biostimulation or bioaugmentation.

摘要

The replacement of the groundwater contaminant methyl tert-butyl ether (MTBE) with ethanol is increasing nationwide. Ethanol is a renewable fuel and can reduce United States dependency on foreign oil imports. Unfortunately, the likelihood of encountering ethanol as a co-contaminant in groundwater contaminated with gasoline constituents such as benzene, toluene, ethylbenzene, and xylenes (BTEX) is expected. Thus a better understanding of how ethanol will affect the fate and transport of BTEX in aquifers is needed to adapt our current risk assessment and remediation approaches.; Flow-through aquifer columns experiments were conducted to investigate how ethanol affects BTEX migration and natural attenuation. The feasibility and limitations of anaerobic biostimulation or bioaugmentation to enhance the biodegradation of BTEX and ethanol mixtures were also investigated.; The enhanced migration of BTEX due to the presence of ethanol was not observed at typical ethanol-blended gasoline concentrations, but could be important when dealing with higher ethanol concentrations.; During conditions simulating natural attenuation, ethanol was preferentially biodegraded consuming the available oxygen, nitrate, and sulfate that could be otherwise utilized for BTEX degradation. No significant benzene degradation occurred in the presence of ethanol even after 3 years of column acclimation.; Significant benzene removal was observed after biostimulation with nitrate, chelated-iron (III) or sulfate. However, no significant benzene degradation occurred in these columns under anoxic conditions, indicating that influent dissolved oxygen plays a critical role.; In experiments without electron acceptor amendments, benzene removal was only observed in a column bioaugmented with benzene-enriched methanogenic consortium, and this removal efficiency was sustained for one year with no decrease in effective porosity due to cell growth. Benzene removal was hindered by the presence of toluene. Soil DNA analysis showed high concentration of benzyl succinate synthase (bssA) gene (which codes for the enzyme responsible for the initial degradation of toluene under anaerobic conditions) where the highest toluene removal occurred. The persistence of bssA in the columns one year after exposure to BTEX ceased indicates the robustness of the added catabolic potential.; Overall, these results suggest that anaerobic biostimulation or bioaugmentation could be considered to enhance bioattenuation of BTEX in groundwater contaminated with ethanol-blended gasoline.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office.