Characterization of Anthracite-Degrading Methanogenic Microflora Enriched from Qinshui Basin in China

Abstract

Microorganisms are essential for the formation of biogenic coalbed methane (CBM) and the application of microbially enhanced CBM (MECoM). Anthracite-degrading methanogenic microflora was cultivated by enrichment and subculture from produced water obtained in Qinshui Basin where CBM is explored commercially. The maximum methane yield was 255 μmol/g of coal after 23 days of cultivation at 35 °C, 1.1–1.2% of salinity, <0.15 mm of coal particle size, pH 8–9, and 5 mL of inocula/g of coal. Microflora archaea, as revealed by MiSeq, were mainly composed of Methanosaeta, an acetic acid-consuming methanogen, followed by Methanocella, a hydrogen-consuming methanogen, suggesting a diversity of methanogenic pathways with a dominance of acetoclastic methanogenesis. The bacteria mainly included Enterobacter, Acetoanaerobium, Macellibacteroides, Clostridium, and Ercella. FTIR analysis showed that the oxygen-containing groups and aliphatic groups were the main targets for microbial degradation. XRD analysis indicated that crystal nucleus structures of coal decreased after degradation. The concentrations of aliphatics were shown to increase over the incubation period based on GC–MS analysis, while the concentrations of dissolved aromatics decreased. These results show the potential for enhancing CBM production by stimulating the activity of methanogenic consortia in situ in Qinshui Basin as well as other high-rank coal reservoirs.

The effect of NaOH pretreatment on coal structure and biomethane production

“…number of these organics were mostly less than 10 and they could be utilized by microorganisms [43]. It is noted that there were 13 organic compounds detected which was much less than that found after H 2 O 2 pretreatment [16].…”

Available methane from anthracite by combining coal seam microflora andH2O2pretreatment

“…Furthermore, the proportion of C‐O in phenols and ethers in pretreated coal was 5.59 and 3.07 times more than those in raw coal, respectively. The significant increment of the oxygen‐containing functional groups caused by H 2 O 2 pretreatment suggested that H 2 O 2 altered the coal structure by oxidation and it would be beneficial to subsequent biodegradation as the oxygen‐containing functional groups are the main targets for biodegradation 6 . During biodegradation, the proportions of all oxygen‐containing functional groups reduced significantly after 27 days of biodegradation.…”

“…Xiao et al confirmed that the methanogenic consortia from Qinshui Basin could use the compounds in anthracite to produce biomethane 33 . Guo et al reported that anthracite was available for bacterial and fungal flora to produce biomethane with the highest methane production of 255 μmol/g coal, 6,10,11,32 which was comparable to the reported biomethane productions from low rank coal which ranged from 70 to 230 μmol/g coal 34‐38 . Thus, anthracite, the typical high rank coal, can be used as the substrate for biodegradation.…”

“…However, the content of alkanes rings during the biodegradation with raw coal only increased by 16.8%, suggesting that H 2 O 2 pretreatment promoted the formation of alkanes rings by microflora which might be a part of methanogenesis. 6 The infrared spectra of oxygen-containing functional groups in raw coal and pretreated coal are shown in Figure 5, which were mainly divided into eight adsorption bands, such as aromatic C=C, conjugated C=O, C-O phenol, C-O alcohol, CH 3 -Ar, etc. (Table S2 in Online Resource).…”

“…The technology of converting coal to biomethane is one of coal gasification technologies by decomposing the organic matter in coal to produce biomethane via anaerobic microorganisms which has such advantages as low cost, little energy consumption, and environmentally friendly. Recent years, lots of literatures have reported the feasibility of coal biomethanation and also found that there are several limitations in the conversion of coal to biomethane, such as low content of effective biological substrate in coal, little know about the activation and degradation process of coal components 5‐10 . Thus, a number of techniques, including physical, chemical, and biological approaches, have been proposed to pretreat coal to increase the bioavailability of coal 11‐15 .…”