SOURCE OF HYDROGEN FOR BIOGENIC METHANE PRODUCTION FROM COAL AS REVEALED BY STABLE ISOTOPE ANALYSIS OF COAL ENRICHMENT CULTURES

Commercial CBM production has begun in Alberta, Canada. Geological and hydrogeological analyses of deep coal beds in Alberta suggest that microbial activity may be responsible for a large portion of the methane held within these coals. Several lines of evidence suggest that the reduction of CO2 with H2 as the electron donor is probably the preferred metabolic pathway in coal beds. However it is unclear what is the source of hydrogen molecules for methanogenesis. Hydrogen may be derived from water or it can derive from bacterial metabolism (or a combination of the two).

The microbial incorporation of deuterium into methane was investigated in order to elucidate the source of hydrogen used by mixed and pure methanogenic cultures for methane formation. Results from growth experiments using deuterated water and coal as the carbon substrate and either amended or un-amended with a nutrient only showed two of the hydrogen molecules in the produced methane coming from the water as opposed to all 4 of the hydrogen molecules as would be expected in the CO2-reduction pathway. Those cultures expected to produce methane by the acetoclastic pathway incorporated between 1 in 6 and 1 in 10 of the water hydrogen molecules into methane. It was expected that at least 1 in 4 of the hydrogen molecules would have come from water during acetoclastic methanogenesis. The presence of different methanogenic species in the enrichment cultures using different methanogenesis pathways and the contribution of coal and nutrient to hydrogen production may have contributed to the deuterium incorporation results observed.

This presentation will explore these contributing factors as well as link carbon stable isotope data to the molecular identification of the bacterial and archaeal species in the coal enrichment cultures. Research in the mechanisms for coal bed methanogenesis will contribute to the understanding of the conditions favourable for microbial-enhanced methane generation and for the microbial conversion of sequestered CO2 to methane.