Biogenic coal-to-methane conversion efficiency decreases after repeated organic amendment stimulation
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Addition of organic amendments to coal-containing systems can increase the rate and extent of biogenic methane production for 60−80 days before production slows or stops. Understanding the effect of repeated amendment additions on the rate and extent of enhanced coal-dependent methane production is important if biological coal-to-methane conversion is to be enhanced on a commercial scale. Microalgal biomass was added at a concentration of 0.1 g/L to microcosms with and without coal on days 0, 76, and 117. Rates of methane production were enhanced after the initial amendment but coal-containing treatments produced successively decreasing amounts of methane with each amendment. During the first amendment period, 113% of carbon added as amendment was recovered as methane, whereas in the second and third amendment periods, 39% and 32% of carbon added as amendment was recovered as methane, respectively. Additionally, algae-amended coal treatments produced ∼38% more methane than unamended coal treatments and ∼180% more methane than amended coal-free treatments after one amendment. However, a second amendment addition resulted in only an ∼25% increase in methane production for coal versus noncoal treatments and a third amendment addition resulted in similar methane production in both coal and noncoal treatments. Successive amendment additions appeared to result in a shift from coal-to-methane conversion to amendment-to-methane conversion. The reported results indicate that a better understanding is needed of the potential impacts and efficiencies of repeated stimulation for enhanced coal-to-methane conversion.
Davis, Katherine J., Elliott P. Barnhart, Matthew W. Fields, and Robin Gerlach. “Biogenic Coal-to-Methane Conversion Efficiency Decreases after Repeated Organic Amendment.” Energy & Fuels 32, no. 3 (January 30, 2018): 2916–2925. doi:10.1021/acs.energyfuels.7b03426.