Microbial production of methane and carbon dioxide from lignite, bituminous coal, and coal waste materials

The aim of this study was to examine microbial methane and CO2 production from bituminous coal waste, lignite, and bituminous coal materials. Bituminous coal and coal waste material were obtained from a Utah mine and lignite was obtained from a commercially available North Dakota sample. Microbial populations were cultured from hydrocarbon-rich environments and locations where natural methanogenesis was occurring. Various pulverized coal and coal waste materials were combined with selected microbial inocula and different types and levels of nutrient amendments. After a 30-day reaction period at about 23 °C, headspace methane and CO2 were analyzed using gas chromatography. With increasing nutrient concentrations (0, 10, and 50%), coal waste generated an extrapolated equivalent of 36, 53, and 16,000 scf of CH4/ton/year and 1870, 4400, and 8000 scf of CO2/ton/year. Methane produced from native and nutrient-amended bituminous coal waste materials was the same order of magnitude as that produced from bituminous coal but lower than that produced from lignite. CO2 generation from coal waste materials, with no nutrient addition was over twice as high as that produced from analogous bituminous coal. The results of this study suggest that coal waste products can be converted to useful fuel at volumes that may be commercially viable.