IDENTIFYING THE SOURCE, PATHWAYS, AND RATES OF ENHANCED MICROBIAL COALBED METHANE PRODUCTION

From 2000 to 2012, combustion of coal accounted for 46% of the global primary energy supply. When used for electricity generation, coal combustion produces 2x the CO₂, 4x the NO_x, and >100x the SO₂ and Hg compounds per kWh than burning natural gas. In the Powder River Basin where most of the coal is too deep to be mined by conventional means, indigenous microorganisms produce biogenic coalbed methane (CBM). The rates of natural CBM production rates are slower than those of commercial gas collection, resulting in short well lifespan and many abandoned wells. Developing economically feasible in situ strategies for increasing the rate of coal to methane bioconversion will provide a cleaner and renewable alternative to conventional coal and extend the life of already existing CBM production wells.

Previous studies have demonstrated enhanced biogenic CBM production in the laboratory by stimulation with nutrient addition. To improve the understanding of the mechanisms of CBM stimulation, different biostimulants (microalgae, cyanobacteria and yeast) were added to coal from the Powder River Basin (Montana) and non-coal containing treatments at two concentrations (0.1 g/L and 0.5 g/l). In 111 days, the unstimulated, coal-only condition produced 676 µg CH₄/g coal at a maximum rate of 16.3 µg CH₄/g coal/day. All biostimulated treatments demonstrated CBM enhancement relative to the unstimulated treatments in excess of the expected methane production from the stimulant itself. The lower biostimulant concentration resulted in a 2.5X increase in total methane production and 3X the maximum rate. The higher biostimulant concentration resulted in a 3.5X increase in total methane and 4X the maximum rate. All non-coal conditions produced less methane overall and had lower maximum production rates when compared to coal conditions. However, methane production in non-coal conditions were greater for yeast extracts compared to the algal or cyanobacterial biostimulants. This presentation will provide details of our efforts to delineate the exact pathways of CBM enhancement by combining isotopic labelling and microbial community analysis approaches with traditional productivity enhancement experiments.