In situ and enhanced coal-bed methane production from the Powder River Basin
Barnhart, Elliott Paul
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The majority of the coal in the Powder River Basin (PRB) is located in formations too deep to be economically mined but microorganisms within some of these deep coal seams generate coal-bed methane (CBM) which can be harvested and utilized as an energy source. However, little is known about the in situ microbial community, the environmental conditions conducive to CBM production, or the microbial community interactions that promote CBM production. Several sampling locations within the PRB were identified as methane-producing sites based on geochemical analysis of groundwater. A diffusive microbial sampler (DMS) was utilized for microbial sampling which was loaded with coal and only opened at the bottom of the wells where the coal seam was exposed. Pyrotag analysis of DMS coal identified the predominant in situ bacterial and archaeal populations, providing insight into microbes generating CBM within the PRB. Changes in the composition and structure of microbial communities that occur under stimulated conditions were investigated by applying molecular methods in combination with cultivation techniques (with and without nutrient supplementation) to identify conditions which maximize methane production in batch, bench-scale incubations. Results from these studies indicated the addition of yeast extract resulted in an increase in methane production as well as a shift to a microbial population capable of acetate production and/or acetate utilization. Isolation methods targeting coal utilizing Bacteria and methanogenic Archaea were applied in addition to DNA based methods to infer microbial community members present within coalbeds. The acetoclastic methanogen Methanosarcina was isolated which is the only identified methanogen with the high-efficiency acetate kinase (Ack) / phosphotransacetylase (Pta) methane production pathway. This pathway provides increased growth and methane production when acetate concentrations are high which can result from microbial stimulation with nutrients. Genomic analysis revealed Ack evolved through gene duplication and divergence of acetyl CoA synthetase within the methanogenic genome. This research provided novel insight into the evolution of the high-efficiency Ack/Pta pathway. Collectively, this dissertation presents a novel link between the Ack/Pta pathway, stimulated CBM production and genomic insight into the development of this pathway.