Biogenic methane in Indonesian coal : assessing the potential using culture enrichment, molecular phylogenetic and isotopic analysis

Abstract

Biogenic coal bed methane (CBM) has gained considerable interest because of its potential to be regenerated. The research reported in this thesis evaluated the potential to develop Indonesian coals as CH 4 bioreactors using culture enrichment, molecular phylogenetic and isotopic composition analysis methods. The results increase the current understanding on microbial methanogenesis in coal, with a specific focus on Indonesian coals.Indonesian coals range in rank from lignite to bituminous, with anthracites occurring in specific areas. The coals are low in ash yield and dominated by vitrinite group macerals, with abundant liptinite group macerals, which is thought to make them good targets for methanogenesis.Stable isotope analysis of gas from pilot production wells confirmed the hypothesis that Indonesian CBM is partly biogenic in origin. Culture enrichment studies of formation water from these CBM pilot wells also indicated the presence of active coal to CH 4 consortia that has the capability for degrading native South Sumatra Basin (SSB) coals and foreign Surat Basin coal from Australia. Among the Indonesian coal basins, the SSB currently has the greatest CBM potential and good accessibility for gas, water, and coal sampling that is required to assess the biogenic CH 4 potential of Indonesian coal. Therefore, SSB was targeted for the experiments conducted in this thesis. The investigation of the microbial methanogen community structure grown on different coal substrates showed temporal changes in community structure over time, and suggested some influence of coal substrate on the microbial community composition. The community structure exhibited greater similarity when grown on coal from the same seam but of different ranks (Mangus iii sub-bituminous (SB) Rv 0.5% and Mangus Anthracite (A) Rv 2.2%) than for coal of similar types (Mangus SB Rv 0.5% and Burung SB Rv 0.39%). The obligate acetoclastic Methanosaeta members favor Burung SB coal, while metabolically versatile Methanosarcina members favor the Mangus coals and the obligate hydrogenotrophic methanogens are significant in the control cultures without coal. Regardless of the community structure similarities across all coal cultures, more CH 4 was generated from the lower rank sub-bituminous coal cultures relative to the one high-rank semi anthracite coal. These results suggest a potential relationship between coal type and rank, microbial community composition and CH 4 production, which warrants further investigation.While CH 4 measurements and molecular phylogenetic analysis confirmed the production of biogenic CH 4 in the cultures, the gas sampled from the culture headspace had δ 13 C-CH 4 values ( 52.2‰ to 22.6‰) that mostly fell outside the range currently considered to indicate a biogenic origin. In this study, the apparent carbon fractionation factor (α c =1.02±0.006) and isotope effect (ε c = 20.1‰±15.3) were found to be more useful indicators of methanogenic pathways than the absolute δ 13 C-CH 4 values. Both values agreed with the calculat...

Ecological Diversity of Microbial Consortium Feces of Beef Cattle and Lignite Coal

“…Based on MG-Rast result, the genus found in coal waste dominated by Clostridium 51.28%, followed with Bacillus 35.29%, Pyramidobacter 6.13%, Desulfovibrio 2.04%, Planctomyces 1.38%, and Syntrophomonas 0.56% (Figure 1). This was consistent with (Susilawati 2015), who stated that bacterial species from the Clostridium genus were geopolymer hydrolyzers in biogenic Coal Bed Methane (CBM) reservoirs. This showed that after applying the treatment and growing bacteria in waste, it still showed biogenic coal.…”