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Evaluation of factors that influence microbial communities and methane production in coal microcosms
Gallagher, Lisa K.
Gallagher, Lisa K.
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2014
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2014
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Abstract
Vast reserves of coal represent a largely untapped resource that can be used to produce methane gas, a cleaner energy alternative compared to burning oil or coal. The methane produced in subsurface coal seams, referred to as coalbed methane, represents an increasingly important source of domestic energy in the United States comprising approximately 10% of natural gas production. Biogenic coalbed methane is formed via the activity of microorganisms and contributes about 40% to the total amount of CBM produced in the world. Enhancement of biogenic coalbed methane has become an area of active research due to its potential impact on energy reserves as well as the positive environmental implications associated with its use. Enrichment cultures from coal were incubated and evaluated by DNA sequencing, qPCR analysis and gas chromatography to determine whether the presence of specific organisms was correlated to methane production and whether microbial community structure differed between productive and unproductive coal microcosms. Additionally, microcosm experiments were designed to assess how prior exposure of coal to oxygen might influence methane production and microbial community structure and dynamics. Microcosms with oxidized coal consistently produced between 50 and 100 micromoles less methane per gram of coal than the un-oxidized coal microcosms. Additionally, un-inoculated microcosms produced levels of methane comparable to their inoculated counterparts, demonstrating the importance of native, coal-associated microbial assemblages in biogenic methane production. Pelobacter was strongly correlated to methane production, suggesting its relevance for methane production. Productive microcosms in this study also had methanogenic populations that were dominated by Methanosarcina, a group of metabolically versatile methanogens. Copy number thresholds for methanogens (mcrA gene; 10[superscript 7] copies/mL), sulfate reducing bacteria (dsrA; 10[superscript 6] copies/mL) and acetogens (fhs; 10[superscript 5] copies/mL) were identified, below which methane production was limited. The results of this research add to the existing body of knowledge and provide findings that may help with increasing natural gas yields by stimulating existing seam activity or by reviving depleted wells. Further work is needed to better understand the intricacies of this process and ways to ensure coalbed methane remains a feasible energy resource.
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