Carbon and hydrogen isotope fractionation during methanogenesis: a laboratory study using coal and formation water

Susilawati, Rita, Golding, Suzanne D., Baublys, Kim A., Esterle, Joan S. and Hamilton, Stephanie K. (2016) Carbon and hydrogen isotope fractionation during methanogenesis: a laboratory study using coal and formation water. International Journal of Coal Geology, 162 108-122. doi:10.1016/j.coal.2016.05.003


Author Susilawati, Rita
Golding, Suzanne D.
Baublys, Kim A.
Esterle, Joan S.
Hamilton, Stephanie K.
Title Carbon and hydrogen isotope fractionation during methanogenesis: a laboratory study using coal and formation water
Journal name International Journal of Coal Geology   Check publisher's open access policy
ISSN 0166-5162
1872-7840
Publication date 2016-05-15
Sub-type Article (original research)
DOI 10.1016/j.coal.2016.05.003
Open Access Status Not Open Access
Volume 162
Start page 108
End page 122
Total pages 25
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Collection year 2017
Language eng
Formatted abstract
Carbon and hydrogen isotope compositions of CH4 generated via methanogenesis in cultures of South Sumatra Basin (SSB) coalbed methane (CBM) formation waters grown on coal, acetate and H2+CO2 were investigated. CH4 production and molecular analysis confirmed the presence of active microbial communities that are able to convert coal into CH4 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.

CH4 produced in this study's culturing experiments has δ13C values in the range of -50 ‰ to -20 ‰, with most values falling outside the current understanding of the carbon isotopic boundaries for biogenic CH4 (-110 ‰ to -30 ‰). However, the corresponding apparent carbon isotopic α factor (αc = 1.02 ± 0.006), and isotopic effect (εc = -20.1 ‰ ± 15.3) showed that CH4 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 CO2 reduction from the δ13C values of coal-treated cultures was overall <50 %, further confirming the high contribution of the acetoclastic pathway to CH4 production in the SSB cultures. The outcome of this experimental study also suggests that δ2H-CH4 values may not provide a reliable basis for distinguishing methanogenic pathways, while apparent carbon isotopic fractionation factor (αc) and isotope effect (εc) are considered more useful indicators of the methanogenic pathway.

The high δ13C-CH4 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 δ13C-CH4 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 δ13C-CH4 values during the growth of cultures within a single experiment also showed a 13C-enrichment trend over time. At log phase of growth, the CH4 produced was 13C-depleted when compared to the stationary phase that also indicates substrate depletion effects. Finally, the δ13C-CH4 values encountered in this study (as high as -20 ‰) highlight the possible positive extension of δ13C-CH4 values of acetoclastic methanogenesis from those currently reported in the literature for natural and experimental samples (as high as -30 ‰)
Keyword Biogenic gas
Coal
Culture experiment
Isotopic composition
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Earth Sciences Publications
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Created: Fri, 22 Jul 2016, 12:09:25 EST by Professor Sue Golding on behalf of School of Earth Sciences