Analysis of landfill leachate promoting efficient application of weathered coal anaerobic fermentation.

This research aimed to develop a new method for clean utilization and treatment of landfill leachate and solid waste weathered coal. Landfill leachate and weathered coal were adopted for combined anaerobic fermentation for methane production. The characteristics of microbial community, mechanism of biological methane production, and utilization characteristics of fermentation broth and solid residue for co-fermentation were analyzed through metagenomics, soluble organic matter detection and thermogravimetric (TG) analysis. The obtained results revealed that combined anaerobic fermentation increased methane production by 80.1%. Syntrophomonas, Salipiger, Methanosaeta and Methanothrix were highly correlated. Gene abundances of 2-oxoacid ferredoxin oxidoreductase and enolase were increased in methane conversion pathway mainly by acetic acid. Pyruvate-ferroredoxin oxidoreductase, 2-oxoglutarate synthase and succinate dehydrogenase acetate synthase intensified electron transfer pathways among microorganisms. Fulvic acid, tyrosine and tryptophan contents were high in fermentation broth. Volatile decomposition temperature, ignition point and residual char combustion temperature of residual coal were decreased and combustion was more stable. The obtained results showed that the co-fermentation of landfill leachate and weathered coal improved biological methane gas production, degraded weathered coal and improved combustion performance, which provided a new idea for weathered coal clean utilization.

Experimental Study on the Mechanism of Radial Change of Simulated Enrichment Nutrient Solution Injection into Coal Seams.

This paper deals with enhanced coal bed methane recovery and geological CO2 storage, combined with the dual effect of increasing coal-bed methane and achieving carbon emission reduction. Coal of different particle sizes were loaded into acrylic tanks of a certain height, and peristaltic pumps were used to enrich nutrient solution and CO2 into different layers of coal seams, to monitor the liquid phase pH, COD, OD600, aromatic structure, HCO3-, three-dimensional fluorescence data of the upper, middle, and lower layers, and the specific surface area of coal Poreginseng. The following conclusions were drawn: (1) the reaction with CO2 resulted in a lower pH than that without CO2, with weak acidity and higher concentration of HCO3- ions. The OD600 concentration and activity of the bacterial solution were stronger. Most of the solution was dominated by Clostridium acidophilum, and the three-dimensional fluorescence results are also shown. (2) Coal samples with small particle sizes had a larger surface area, more contact area with bacterial liquid, and a more complete reaction, so the physical property transformation of coal reservoirs with small particle sizes was more obvious, and the COD change was the largest. (3) The upper and middle layers were exposed to more bacterial fluid and CO2, resulting in a more complete degradation reaction.

Biogasification of methanol extract of lignite and its residue: A case study of Yima coalfield, China.

To investigate the biogas generation characteristics of the organic matter in lignite, methanol extraction was conducted to obtain the soluble fraction and the residual of lignite, which were subsequently taken as the sole carbon source for biogas production by a methanogenic consortium. Afterward, the composition of compounds before and after the fermentation was characterized by UV-Vis, GC-MS, and HPLC-MS analysis. The results indicated that the methanogenic microorganisms could produce H2 and CO2 without accumulating CH4 by utilizing the extract, and the methane production of the residue was 18% larger than that of raw lignite, reaching 1.03 mmol/g. Moreover, the organic compounds in the methanol extract were degraded and their molecular weight was reduced. Compounds such as 1, 6-dimethyl-4-(2-methylethyl) naphthalene, 7-butyl-1-hexylnaphthalene, simonellite, and retene were completely degraded by microorganisms. In addition, both aromatic and non-aromatic metabolites produced in the biodegradation were detected, some of which may have a negative effect on the methanogenesis process. These results revealed the complexity of the interaction between coal and organism from another point of view.

Potential of biogenic methane for pilot-scale fermentation ex situ with lump anthracite and the changes of methanogenic consortia.

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 CH4/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.

An Effective Method to Detect Volatile Intermediates Generated in the Bioconversion of Coal to Methane by Gas Chromatography-Mass Spectrometry after In-Situ Extraction Using Headspace Solid-Phase Micro-Extraction under Strict Anaerobic Conditions.

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.