Decomposition of carbon-bearing compounds and their influence on methane formation in a lignite incubation experiment

Abstract

Carbon-bearing compounds (glucose, sodium acetate, methanol, yeast extract, and nutrient broth) were added in different proportions to cultures to stimulate methanogenesis in a lignite incubation experiment. Their addition significantly influenced the isotopic composition of methane generated during the fermentation of lignite. Glucose was degraded mainly in the first 2 weeks of incubation, when the atmospheric air was present in the headspace and used for biomass growth. Sodium acetate, methanol, and, presumably, lignite were decomposed in the next phase, in which anaerobic conditions occurred. The simultaneous decomposition of sodium acetate and methanol (as single substrates or as a mixture) with lignite resulted in the formation of methane with δ¹³C(CH₄) values typical for methyl-type fermentation. The identification of decomposed compounds in the mixture of sodium acetate and methanol was accomplished via isotopic analysis of carbon and hydrogen in the methane. The δ²H(CH₄) values in the case of methanol biodegradation were characterized by a negative trend over time, in contrast to a positive trend observed when sodium acetate decomposed. This observation may help to identify a very good tracer for the determination of methane precursors during methyl-type fermentation.

Keywords:

• Fermentation pathways
• lignite
• methanogenesis
• stable isotopes

Acknowledgments

The authors would like to acknowledge the significant support of Dr Hans-Hermann Richnow and his co-workers at the Helmholtz Centre for Environmental Research (UFZ) in Leipzig in isotopic measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by the National Science Centre, Poland, through grant DEC-2015/16/S/ST10/00430 to Michał Bucha.