Study on the mechanism of action of methane production by co-fermentation of sludge and lignite.

To improve the methanogenic efficiency of lignite anaerobic fermentation and explore innovative approaches to sludge utilization, a co-fermentation technique involving lignite and sludge was employed for converting biomass into biomethane. Volatile suspended solids were introduced as a native enrichment of the sludge and mixed with lignite for fermentation. The synergistic fermentation mechanism between sludge and lignite for biomethane production was analyzed through biochemical methane potential experiments, measurement of various parameters pre- and post-fermentation, observation of bacterial population changes during the peak of reaction, carbon migration assessment, and evaluation of rheological characteristics. The results showed that the addition of sludge in the anaerobic fermentation process improved the microorganisms' ability to degrade lignite and bolstered biomethane production. Notably, the maximum methane production recorded was 215.52 mL/g-volatile suspended solids, achieved at a sludge to coal ratio of 3:1, with a synergistic growth rate of 25.37%. Furthermore, the removal rates of total suspended solids, and total chemical oxygen demand exhibited an upward trend with an increasing percentage of sludge in the mixture. The relative abundance and activity of the methanogens population were found to increase with an appropriate ratio of sludge to lignite. This observation confirmed the migration of carbon between the solid-liquid-gas phases, promoting enhanced system affinity. Additionally, the changes in solid-liquid phase parameters before and after the reaction indicated that the addition of sludge improved the system's degradation capacity. The results of the study hold significant implications in realizing the resource utilization of sludge and lignite while contributing to environmental protection endeavors.

Research on the Biogas Production Mechanism of Mudstone in the Qaidam Basin under Different CO2 Pressures.

Mudstone, a class of sedimentary rocks rich in organic matter, possesses considerable potential for biogas production. Mudstones possess a rich biological origin, which is conducive to refining the mechanisms and enrichment patterns of biogenic gas reservoirs. This has significant theoretical and practical implications for guiding the exploration and development of Quaternary mudstone gas reservoirs. Furthermore, the Qaidam Basin is an excellent place for the geological storage of CO2 due to its rich petroleum reservoir conditions. Experimental research on biogas production under diverse CO2 pressure-mudstone-microorganism-water interactions is conducted to determine the biogas production mechanism of mudstone under different CO2 pressures during sequestration circumstances. According to the results: (1) under supercritical carbon dioxide conditions, there is a slight initial increase in biogas production, followed by a gradual decrease. The periods and peaks of gas production vary among the different reaction groups. As carbon dioxide pressure increases, the gas production cycle lengthens significantly, while the gas yield declines. (2) Siderite and secondary carbonate minerals have increased in the mudstone's mineral fraction both before and after biogas production, while clay mineral groups have decreased. Specifically, there was a notable drop in chlorite and kaolinite. (3) Microorganism species in the system were analyzed, and the results showed that there was a gap in each microorganism's ability to adapt to its surroundings, and the diversity and quantity of bacteria declined with increasing pressure. After carbon dioxide was fluxed, there was a considerable shift in the pattern of biogas generation, which consequently had a major impact on the alterations in mineral fractions.

Metabolism mechanisms of biogenic methane production by synergistic biodegradation of lignite and guar gum.

Coalbed methane (CBM) presents a promising energy source for addressing global energy shortages. Nonetheless, challenges such as low gas production from individual wells and difficulties in breaking gels at low temperatures during extraction hinder its efficient utilization. Addressing this, we explored native microorganisms within coal seams to degrade guar gum, thereby enhancing CBM production. However, the underlying mechanisms of biogenic methane production by synergistic biodegradation of lignite and guar gum remain unclear. Research results showed that the combined effect of lignite and guar gum enhanced the production, yield rate and concentration of biomethane. When the added guar gum content was 0.8 % (w/w), methane production of lignite and guar gum reached its maximum at 561.9 mL, which was 11.8 times that of single lignite (47.3 mL). Additionally, guar gum addition provided aromatic and tryptophan proteins and promoted the effective utilization of CC/CH and OCO groups on the coal surface. Moreover, the cooperation of lignite and guar gum accelerated the transformation of volatile fatty acids into methane and mitigated volatile fatty acid inhibition. Dominant bacteria such as Sphaerochaeta, Macellibacteroides and Petrimonas improved the efficiency of hydrolysis and acidification. Electroactive microorganisms such as Sphaerochaeta and Methanobacterium have been selectively enriched, enabling the establishment of direct interspecies electron transfer pathways. This study offers valuable insights for increasing the production of biogenic CBM and advancing the engineering application of microbial degradation of guar gum fracturing fluid. Future research will focus on exploring the methanogenic capabilities of lignite and guar gum in in-situ environments, as well as elucidating the specific metabolic pathways involved in their co-degradation.

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.

The characteristics of solid-phase substrate during the co-fermentation of lignite and straw.

Co-fermentation of lignite and biomass has been considered as a new approach in achieving clean energy. Moreover, the study of the characteristics of solid phase in the synergistic degradation process is of great significance in revealing their synergistic relationship. Accordingly, in order to produce biogas, lignite, straw, and the mixture of the two were used as the substrates, the solid phase characteristics of which were analyzed before and after fermentation using modern analytical methods. The results revealed that the mixed fermentation of lignite and straw promoted the production of biomethane. Moreover, the ratios of C/O and C/H were found to be complementary in the co-fermentation process. Furthermore, while the relative content of C-C/C-H bonds was observed to be significantly decreased, the aromatics degree of lignite was weakened. Also, while the degree of branching increased, there found to be an increase in the content of cellulose amorphous zone, which, consequently, led to an increase in the crystallinity index of the wheat straw. Hence, the results provide a theoretical guidance for the efficient utilization of straw and lignite.

Physical, chemical, and bio-pretreatments on microbial gas production in Baode Block coal.

Currently, the exploitation of Baode Block as a biogenic coal-bed gas field has been in the later stage of stable production; hence, exploration and activation of microbial gas production are of great practical significance for the enhancement and stabilization of block production. Pretreatment is the key process to improve anaerobic biodegradation performance and increase yield and production rate of gas. In this study, we examine physical, chemical, and biological pretreatment methods and compare their effectiveness toward microbial gas production in the coal seam. The obtained results indicate that: (1) grinding can enhance contact between the coal sample and bacteria liquid, and coal powder has greater gas-producing performance than the coal lump. (2) Chemical pretreatment of coal samples using acid and base can enhance gas production capacity. NaOH treatment has better gas-producing performance than HCl treatment, and the activity of microbial flora is higher after treatment. (3) Biological pretreatment can greatly enhance the microbial degradation of coal bed. The highest gas yield after white rot fungus pretreatment is 11.65 m3/t, and gas production cycle is shorter than before. This may be due to the white rot fungus effectively degrading macromolecules and, therefore, shortening the duration of methanogenic hydrolysis, which provides more organic matter for methanogens to decompose. During production, in addition to selecting a proper pretreatment method, the treatment cost and balance between energy input of pretreatment and gas energy output must also be considered. The joint pretreatment between different reagents and treatment methods is a possible solution to the problem and a current research trend to realize the large-scale degradation of coal. The simulated microbial methane production of coal seam is feasible for Baode Block in Ordos, where coal samples in this block have great gas-producing potential after treatment, and provides good references for further in-field tests.

Metagenomic insight of corn straw conditioning on substrates metabolism during coal anaerobic fermentation.

Increasing methane production from anaerobic digestion of coal is challenging. This study shows that the combined fermentation of coal and corn straw greatly enriched the substrates available to microorganisms. This was mainly manifested in the increased types and abundance of organic matter in the fermentation liquid, which enhanced methane production by 61%. Metagenomic analysis showed that the addition of corn straw enriched the abundance of Methanosarcina in the combined fermentation system and promoted the complementary advantages of the microorganisms. At the same time, the abundance of genes that convert glucose into acetic acid (K00927, K01689, K01905, etc.) in the combined fermentation system increased, which is conducive to acidification process and biomethane production. In addition, there were the two key methanogenic pathways, namely aceticlastic (57.1%-63.5%) and hydrogenotrophic (23.4%-25.1%) methanogenesis, identified in the single coal fermentation system and the combined coal and corn straw fermentation system. Combined fermentation enhanced the hydrogenotrophic and methylotrophic methanogenic pathways by increasing the gene abundance of K00200 (methane production from CO2 and oxidation of coenzyme M to CO2), K00440 (participates in the binding to other known physiological receptors with hydrogen as a donor), and K00577 (methyltransferase).

The characterization of organic nitrogen and sulfur functional groups in coals after biomethane production.

To study the change characteristics of nitrogen and sulfur functional types in the raw coal and coal residues after anaerobic fermentation, three different rank coals from Baiyinhua mine (BY coal), Qianqiu mine (QQ coal), and Malan mine (ML coal) in China were collected and treated with methanogenic microorganisms, then X-ray photoelectron spectroscopy (XPS) was used to test the nitrogen and sulfur functional types in raw coals and coal residues. The results show that the pyrrolic nitrogen (N-5) and aromatic sulfur are the main nitrogen type and sulfur type in three coals. The N-5 increases by 17.42% in BY coal residue and decreases by 2.37% and 8.51% in QQ and ML coal residues, respectively. The pyridinic nitrogen (N-6) in BY, QQ, and ML coal residues decreases by 2.18%, 5.44%, and 2.75%, respectively. The aromatic sulfur increases by 2.13%, 3.14%, and 4.02% in BY, QQ, and ML coal residues, respectively. The aliphatic sulfur has obvious changes in BY and QQ coal residues with the increment of 9.17% and decrement of 11.64%, respectively. The results reveal that the nitrogen and sulfur types have changed in the coal residues after the biomethane production, and the instable types such as N-5 and aliphatic sulfur have obvious changes in the low-rank BY and QQ coals. The research provides a sight to the changes about nitrogen and sulfur types after biomethane yield and more deep thoughts about the clean and effective utilization of coals.

The biochemical mechanism of enhancing the conversion of chicken manure to biogenic methane using coal slime as additive.

To improve the efficiency of methane production from chicken manure (CM) anaerobic digestion, the mechanism of coal slime (CS) as an additive on methane production characteristics were investigated. The results showed that adding an appropriate amount of CS quickened the start of the fermentation and effectively increased the methane yield. In addition, the pH changed in a stable manner in the liquid phase, and the concentrations of total ammonia nitrogen (TAN) and free ammonia nitrogen (FAN) were reduced. Moreover, organic matter was decomposed and volatile fatty acids (VFAs) were consumed effectively. The abundance of Bacteroides in the bacterial community and Methanosarcina in the archaea was increased. In addition, the reduction of CO2 was the main methanogenic pathway, and adding CS raised the abundance of genes for key enzymes in metabolic pathways during methane metabolism. The results provide a novel method for the efficient methane production from CM.

Culture medium optimization for producing biomethane by coal anaerobic digestion.

The culture medium in biogas field have been used in coalbed gas bioengineering (CBGB). However, there is a huge difference between the substrate of biogas fermentation and coal. It is necessary to study and optimize the culture medium in the anaerobic digestion (AD) system with coal as substrate. In this study, the single factor test and response surface curve analysis are used to clarify the essential components in the culture medium and the optimal content of these chemicals. The influence of a single component on microbial community structure and major metabolic pathways in AD system are discussed. Under the optimal conditions, SEM observation show that the coal surface sediment is significantly reduced after AD process. The results of GC-MS show that there is no significant difference in the composition and content of organic compounds in the liquid phase before and after the optimization; the microbial community structure and gene function did not weaken with the decrease of culture medium addition, but formed a more targeted and stable microbial community.

Preparation of valuable pyrolysis products from poplar waste under different temperatures by pyrolysis: Evaluation of pyrolysis products.

Poplar waste is used as feedstock to prepare valuable pyrolysis products by pyrolysis under different temperature. The bio-oil is rich in aldehyde with the maximum relative content of 47.15%, which has potential application in chemical industries. Pyrolysis temperature has significantly influenced the composition and heating value of bio-gas. The maximum heating value of bio-gas is 14.56 MJ/Nm3. Biochar is used as an adsorbent to adsorb Ag+ from aqueous solution with the adsorption capacity of 76.09 mg/g. Biochar forms the value-added Ag-Biochar composite by reduction after adsorption Ag+. While, Ag-Biochar composite can be used as catalyst for methyl orange removal with the maximum removal of 94.08%. Ag-Biochar composite is also used as lithium ion battery cathode material for energy storage with the specific capacity of 345 mAh/g. Besides, preliminary economic analysis is used to evaluate the economics of pyrolysis process with the total annual revenue of $115, 725/year.

Efficient utilization of coal slime using anaerobic fermentation technology.

In order to increase the utilization of coal slime, realize efficient utilization of resources and protect the environment, the feasibility of anaerobic fermentation technology employing coal slime was explored. The biodegradation of coal slimes and its influence on the utilization characteristics were analyzed using biogas production simulations, drying dehydration and thermogravimetric (TG) analysis. The results showed that the organic matter in various coal slimes could be converted to biomethane. In addition, the main methanogenic pathway was the reduction of CO2. Moreover, lower the metamorphic degree of coal slimes and higher the ash content, more conducive were they to the dehydration of coal slimes. After biodegradation, the temperatures of four coal slimes during the stages of release of moisture, volatile combustion, residual coke combustion and burnout advanced to varying degrees. Moreover, the combustion performance improved. The research results provided a novel idea for the efficient utilization of coal slime.

The mechanisms of biogenic methane metabolism by synergistic biodegradation of coal and corn straw.

The mechanisms associated with the biomethane metabolism through the synergistic biodegradation of both coal and corn straw were explored to improve the utilization rate of corn straw. This applies to the filling of the goaf with corn straw and the production of biomethane using indigenous bacteria in the mine water with coal. The results showed that new macromolecular substances (e.g., Tetracosane and Pentacosane) were produced on the third day. A lower coal rank leads to a lower biodegradation rate of low-molecular-weight substances (e.g., butyric acid and valeric acid). Under the addition of coal samples, the biodegradation rate of cellulose, hemicellulose and lignin in corn straw could reached up to 29.82%, 35.79% and 6.16%, respectively. The addition of corn straw promoted the complementary advantages of archaeal genera (such as Methanosarina and Methanospirillum) and decreased the adverse bacterial genera (such as Desulfovibrio and Pseudomonas) in the fermentation system of single coal.

Analysis of methanogens adsorption and biogas production characteristics from different coal surfaces.

The aim of this study was to examine the biogas production and the adsorption aspect of microorganism from different coals. Coal samples were obtained from Qianqiu mine and Guandi mine. Microbial populations were cultured from the coal mine drainage. After an anaerobic reaction period at about 35 °C, adsorption rate was determined by the spectrophotometer, while a scanning electron microscopy was used to observe the microorganisms on the coal and the headspace methane was analyzed using gas chromatography. Results show that the coal rank and particle size serve as important factors influencing the adsorption of microorganism and biogenic methane production. With decreasing particle size, the Qianqiu coal produced a considerable adsorption rate between 75 and 79%, while the adsorption rate of Guandi coal was between 52 and 74%. Meanwhile, the density of microorganisms from the Qianqiu coal surface demonstrated a higher level of adsorption than that of Guandi coal following the scanning electron microscopy images. Additionally, Qianqiu coal produced a higher level of biogas production (391.766-629.199 µmol/g) than that of Guandi coal (292.835-393.744 µmol/g) and the Qianqiu coal also generated a higher concentration of methane during the incubation. When the adsorption rate decreasing, the biogas production from various pulverized coals appeared to be decreased and demonstrated a positive correlation to the adsorption rate. The results of this study suggest that the adsorption behavior of microorganisms is closely related to the effect of coal biodegradation and contributes to the biogenic methane production potential.

The diversity of hydrogen-producing bacteria and methanogens within an in situ coal seam.

BACKGROUND: Biogenic and biogenic-thermogenic coalbed methane (CBM) are important energy reserves for unconventional natural gas. Thus, to investigate biogenic gas formation mechanisms, a series of fresh coal samples from several representative areas of China were analyzed to detect hydrogen-producing bacteria and methanogens in an in situ coal seam. Complete microbial DNA sequences were extracted from enrichment cultures grown on coal using the Miseq high-throughput sequencing technique to study the diversity of microbial communities. The species present and differences between the dominant hydrogen-producing bacteria and methanogens in the coal seam are then considered based on environmental factors. RESULTS: Sequences in the Archaea domain were classified into four phyla and included members from Euryarchaeota, Thaumarchaeota, Woesearchaeota, and Pacearchaeota. The Bacteria domain included members of the phyla: Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, Acidobacteria, Verrucomicrobia, Planctomycetes, Chloroflexi, and Nitrospirae. The hydrogen-producing bacteria was dominated by the genera: Clostridium, Enterobacter, Klebsiella, Citrobacter, and Bacillus; the methanogens included the genera: Methanorix, Methanosarcina, Methanoculleus, Methanobrevibacter, Methanobacterium, Methanofollis, and Methanomassiliicoccus. CONCLUSION: Traces of hydrogen-producing bacteria and methanogens were detected in both biogenic and non-biogenic CBM areas. The diversity and abundance of bacteria in the biogenic CBM areas are relatively higher than in the areas without biogenic CBM. The community structure and distribution characteristics depend on coal rank, trace metal elements, temperature, depth and groundwater dynamic conditions. Biogenic gas was mainly composed of hydrogen and methane, the difference and diversity were caused by microbe-specific fermentation of substrates; as well as by the environmental conditions. This discovery is a significant contribution to extreme microbiology, and thus lays the foundation for research on biogenic CBM.