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Carbon and hydrogen isotope compositions of CH 4 generated via methanogenesis in cultures of South Sumatra Basin (SSB) coalbed methane (CBM) formation waters grown on coal, acetate and H 2 + CO 2 were investigated. CH 4 production and molecular analysis confirmed the presence of active microbial communities that are able to convert coal into CH 4 using both acetoclastic and hydrogenotrophic pathways. The representative bacterial sequences were dominated by Bacteroidetes , Firmicutes and Deltaproteobacteria , while Methanosaeta and Methanosarcina were the most prevalent archaeal methanogens present in the cultures. CH 4 produced in this study's culturing experiments has δ 13 C values in the range of − 50 ‰ to − 20 ‰, with most values falling outside the current understanding of the carbon isotopic boundaries for biogenic CH 4 (− 110 ‰ to − 30 ‰). However, the corresponding apparent carbon isotopic α factor ( α c = 1.02 ± 0.006), and isotopic effect ( e c = − 20.1 ‰ ± 15.3) showed that CH 4 in SSB cultures was predominantly produced by acetoclastic methanogenesis, which is consistent with the results of molecular DNA analysis. In addition, the calculated contribution of CO 2 reduction from the δ 13 C values of coal-treated cultures was overall 4 production in the SSB cultures. The outcome of this experimental study also suggests that δ 2 H-CH 4 values may not provide a reliable basis for distinguishing methanogenic pathways, while apparent carbon isotopic fractionation factor ( α c ) and isotope effect ( e c ) are considered more useful indicators of the methanogenic pathway. The high δ 13 C-CH 4 values (≥ 30 ‰) and the dominance of Methanosaeta over Methanosarcina indicate that methanogens within the SSB cultures were operating at low substrate concentrations. An unusually positive δ 13 C-CH 4 suggests a substrate depletion effect, which is thought to be related to a decrease in the relative abundance of key bacterial coal degraders with formation water inoculum storage time. Closer observation of δ 13 C-CH 4 values during the growth of cultures within a single experiment also showed a 13 C-enrichment trend over time. At log phase of growth, the CH 4 produced was 13 C-depleted when compared to the stationary phase that also indicates substrate depletion effects. Finally, the δ 13 C-CH 4 values encountered in this study (as high as − 20 ‰) highlight the possible positive extension of δ 13 C-CH 4 values of acetoclastic methanogenesis from those currently reported in the literature for natural and experimental samples (as high as − 30 ‰).

Refereed/Peer-reviewed Temporal changes in microbial community structures during methanogenesis were investigated in cultures of South Sumatra Basin (SSB) coalbed methane (CBM) formation water (SSB5) grown on three coals of different rank (Burung sub bituminous Rv 039%, Mangus sub bituminous Rv 0.5%, Mangus anthracite Rv 22%). Methane production accelerated from day 6, peaked around day 17 and then levelled off around day 20. The initial bacterial community from the SSB formation water was predominantly Aceto bacterium, Acidaminobacter, Bacteroides and Pelobacter species, while the archaeal community consisted of Methanosaeta, Methanosarcina and Methanobacterium members. A general pattern was observed in all cultures with the three coals. Over time the bacterial members decreased in proportion whereas the archaeal component increased. The increase in the proportion of archaeal methanogens corresponded with an increase in methane production yield.Enrichment cultures produced similar communities when grown on coals from the same seam (Mangus sub bituminous and Mangus anthracite), rather than from different seams of similar type (Burung sub bituminous and Mangus sub bituminous). Methanosaeta was the dominant methanogen species in the sub-bituminous Burung coal culture, but was a lesser proportion in cultures of both Mangus sub bituminous and anthracite coals where Methanosarcina species were a greater proportion. Interestingly, obligate hydrogenotrophic methanogens from the genera of Methanobacterium, which were present at low levels in culture enrichment of all coal substrates, increased in proportion only in the absence of coal in the no-coal control enrichment cultures. These results suggest that the low rank Burung sub bituminous coal favours methane production by the obligate acetoclastic Methanosaeta members while both Mangus coals also favour metabolically versatile Methanosarcina members, and the absence of coal favours hydrogenotrophic methanogens. Despite the similarity of communities grown on coals from the same seam, greater quantities of methane were generated from the lower rank coals when compared to higher rank coals. (C) 2014 Elsevier B.V. All rights reserved. usc

The coal of the Miocene Bukit Asam deposit in south Sumatra is mostly sub-bituminous in rank, consistent with regional trends due to burial processes. However, effects associated with Plio–Pleistocene igneous intrusions have produced coal with vitrinite reflectance up to at least 4.17% (anthracite) in different parts of the deposit. The un-metamorphosed to slightly metamorphosed coals, with Rvmax values of 0.45–0.65%, contain a mineral assemblage made up almost entirely of well-ordered kaolinite and quartz. The more strongly heat-affected coals, with Rvmax values of more than 1.0%, are dominated by irregularly and regularly interstratified illite/smectite, poorly crystallized kaolinite and paragonite (Na mica), with chlorite in some of the anthracite materials. Kaolinite is abundant in the partings of the lower-rank coals, but is absent from the partings in the higher-rank areas, even at similar horizons in the same coal seam. Regularly interstratified illite/smectite, which is totally absent from the partings in the lower-rank coals, dominates the mineralogy in the partings associated with the higher-rank coal beds. A number of reactions involving the alteration of silicate minerals appear to have occurred in both the coal and the associated non-coal lithologies during the thermal metamorphism generated by the intrusions. The most prominent involve the disappearance of kaolinite, the appearance of irregularly interstratified illite/smectite, and the formation of regular I/S, paragonite and chlorite. Although regular I/S is identified in all of the non-coal partings associated with the higher-rank coals, illite/smectite with an ordered structure is only recognised in the coal samples collected from near the bases of the seams. The I/S in the coal samples adjacent to the floor of the highest rank seam also appears to have a greater proportion of illitic components. The availability of sodium and other non-mineral inorganic elements in the original coal to interact with the kaolinite, under different thermal and geochemical conditions, appears to be the significant factor in the formation of these new minerals, and distinguishes the mineralogical changes at Bukit Asam from those developed more generally with rank increases due to burial, and from the effects of intrusions into coals that were already at higher rank levels.