Search

Pilot-scale fermentation is one of the important processes for achieving industrialization of biogenic coalbed methane (CBM), although the mechanism of biogenic CBM remains unknown. In this study, 16 samples of formation water from CBM production wells were collected and enriched for methane production, and the methane content was between 3.1 and 21.4%. The formation water of maximum methane production was used as inoculum source for pilot-scale fermentation. The maximum methane yield of the pilot-scale fermentation with lump anthracite amendment reached 13.66 μmol CH 4 /mL, suggesting that indigenous microorganisms from formation water degraded coal to produce methane. Illumina high-throughput sequencing analysis revealed that the bacterial and archaeal communities in the formation water sample differed greatly from the methanogic water enrichment culture. The hydrogenotrophic methanogen Methanocalculus dominated the formation water. Acetoclastic methanogens, from the order Methanosarcinales, dominated coal bioconversion. Thus, the biogenic methanogenic pathway ex situ cannot be simply identified according to methanogenic archaea in the original inoculum. Importantly, this study was the first time to successfully simulate methanogenesis in large-capacity fermentors (160 L) with lump anthracite amendment, and the result was also a realistic case for methane generation in pilot-scale ex situ.

Bioconversion of coal to methane has gained increased attention in recent decades because of its economic and environmental advantages. However, the mechanism of this process is difficult to study in depth, partly because of difficulties associated with the analysis of intermediates generated in coal bioconversion. In this investigation, we report on an effective method to analyze volatile intermediates generated in the bioconversion of coal under strict anaerobic conditions. We conduct in-situ extraction of intermediates using headspace solid-phase micro-extraction followed by detection by gas chromatography-mass spectrometry. Bioconversion simulation equipment was modified and combined with a solid-phase micro-extraction device. In-situ extraction could be achieved by using the combined units, to avoid a breakdown in anaerobic conditions and to maintain the experiment continuity. More than 30 intermediates were identified qualitatively in the conversion process, and the variation in trends of some typical intermediates has been discussed. Volatile organic acids (C2-C7) were chosen for a quantitative study of the intermediates because of their importance during coal bioconversion to methane. Fiber coating, extraction time, and solution acidity were optimized in the solid-phase micro-extraction procedure. The pressure was enhanced during the bioconversion process to investigate the influence of headspace pressure on analyte extraction. The detection limits of the method ranged from 0.0006 to 0.02 mmol/L for the volatile organic acids and the relative standard deviations were between 4.6% and 11.5%. The volatile organic acids (C2-C7) generated in the bioconversion process were 0.01-1.15 mmol/L with a recovery range from 80% to 105%. The developed method is useful for further in-depth research on the bioconversion of coal to methane., Competing Interests: The authors have declared that no competing interests exist.

This study addressed the effect of microbial methane production on the physical properties of a coal reservoir. Two kinds of coal samples before and after anaerobic degradation were tested by a low-temperature liquid nitrogen adsorption test and an isothermal adsorption and diffusion coefficient test. The influence of the characteristics of microbial gas production on the coal physical properties was analyzed. Due to the differences in the physical properties of the coal samples, the effect of microbial production is different. Coal is a macromolecular organic compound, mainly aromatic and lignin derivatives, containing carbon and nitrogen sources that can be used by microorganisms. Microorganisms secrete extracellular enzymes to decompose covalent bonds and functional groups of macromolecules in coal and eventually produce methane, which will change the physical properties of coal. It was found that microbial anaerobic degradation could increase the content of coalbed methane, change the pore structure of coal, reduce the fractal dimension of the coal surface and smooth the coal surface. At the same time, microbial degradation has changed the physical properties of coal reservoirs to some extent, increased the diffusion of coal reservoirs and improved the pore connectivity of coal reservoirs, which provides more of a scientific basis for the development of coalbed methane. [ABSTRACT FROM AUTHOR]

Coal slime can significantly enhance anaerobic digestion (AD) of chicken manure (CM) for methane production; However, the underlying mechanism is still unclear. This study has mainly discussed variation characteristics of key metabolic pathways in the AD process of CM by coal slime. Dry CM and coal slime (CS) were selected and coal seam mine water was applied as bacteria source. CS effects on the metabolic pathway of CM fermentation system were studied by biogas production simulation experiments and metagenomic analyses. The results indicated that variations in pH and CS amount exerted significant effects on the biogas generation in the contest of CM fermentation. Optimal conditions for enhanced biogas production were observed when the pH approached neutrality, and the CS quantity was 0.2 g, highlighting substantial potential of CM for biogas generation. The addition of CS resulted in a 13.1%, 1.9%, and 1.8% increase in the relative abundance of Bacteroides , Aminobacterium , and Methanothrix. This, in turn, elevated gene abundance of essential enzymes in the glycolytic pathway (glycolysis and pyruvate metabolism), promoting acetic acid production and providing a foundational basis for methanogen metabolic gas production. Furthermore, the addition of CS lead to a notable increase in the abundance of the pilA gene in Methanocorpusculuma (111.5%) and Methanothrix (66.1%). This suggested the involvement of CS in DIEF, thereby augmenting the anaerobic methane production potential of CM. These outcomes offer valuable theoretical insights for optimizing the biogas production potential of CM and maximizing the resource utilization of CS. [Display omitted] • Coal slime increased methane yield from chicken manure. • Biogas yield of chicken manure was analyzed by response surface methodology. • Key metabolic functions of substrate metabolism were efficiently expressed. • Coal slime enrichment led to an increased abundance of key genes related to DIET. [ABSTRACT FROM AUTHOR]