The fate of fuel releases largely depends on the poorly-understood response in pollutant mass balance and microbial community shift, and the explosion risk of methane via stimulating methanogenesis in impacted aquifers are focused in recent years. Here, we evaluate the impacts to the microbial community resulting from a pilot-scale fix-volume release (1L and 5L) of a 25% v:v ethanol solution mixed with benzene(B), toluene(T), m-xylene(X) and trimethylbenzene(TMB). In this study, the mass balance for BTX, TMB, ethanol and their degradation products were analyzed during and after different volume ethanol blend release. The low concentrations of methane observed in the groundwater are attributed to methanotrophic activity, which was highest at 3mg/L in the capillary fringe after two months of 5L ethanol solution release. Ethanol mass recovered in effluent were negligible compared to other components, and the transformation of ethanol to VFAs was 67.5% and was 58.2% of 1L and 5L ethanol blend release. Microbial population shifts were characterized by quantitative PCR and pyrosequencing-based 16S rRNA analysis. Microbial community and functional genes analysis showed that the release stimulated microbial growth, increased species richness and diversity, and selected for genotypes involved in fermentative degradation.The relative abundance of mcrA and fhs increased 18- and 6-folds, respectively. A significant correlations (p &lt; 0.05) between CH4 concentrations and mcrA gene abundance and between acetate concentrations and fhs gene abundance were observed. The growth of putative hydrocarbon degraders and commensal anaerobes, and increases in microbial diversity and in degradation rates suggest an adaptive response that increases the potential for natural attenuation of ethanol blend releases. Overall, this study shows the importance of ethanol degrading activity near the water table to attenuate methane generated from dissolved ethanol plumes and reduce its potential to migrate and accumulate at the surface.

Bioattenuation and adaptive shifts of microbial community in response to a fixed-volume pilot-scale release of an ethanol blend

256th National Meeting (2018)

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