Biomethane Production Research Articles

Prognostic Modelling of Biomethane Production from Waste: Application of Extreme Gradient Boosting

The escalating fossil fuel prices and greenhouse gases need urgent attention for a sustainable solution. The present study explores as modern machine learning approaches can be employed to prognosticate the complex biomethane generation process from organic wastes, like biowaste or food waste. The research investigates the use of organic sludges and how intelligent approaches can be employed to comprehend the complex nonlinear processes involved in biomethane production. Linear regression and Extreme gradient boosting (XGBoost) based prediction-models were developed and assessed employing a diverse set of statistical parameters, including R, R2, Mean Squared Error (MSE), Mean Absolute Error (MAE), and Kling-Gupta Efficiency (KGE). The results show that the XGBoost model beat the classical Linear Regression (LR) model in both the training and testing phases. During training, the XGBoost had an impressive R2 value of 0.99994, indicating a perfect fit to the data. In contrast, LR achieved an R2 value of 0.65464. Similarly, during the test period, XGBoost outperformed LR with R2 values ​​of 0.9553 to 0.9902. Furthermore, XGBoost reduced prediction errors, with significantly lower MSE and MAE values ​​than LR. Taylor’s graph better illustrates the excellent performance of the XGBoost over LR in both training and testing. These data demonstrate the ability of XGBoost to predict biomethane production, as well as its ability to improve the biomethane production process.

Bioaugmentation of anaerobic digesters with the enriched lignin-degrading microbial consortia through a metagenomic approach

The recalcitrance of lignin impedes the efficient utilization of lignocellulosic biomass, hindering the efficient production of biogas and value-added materials. Despite the emergence of anaerobic digestion as a superior alternative to the aerobic method for lignin processing, achieving its feasibility requires thorough characterization of lignin-degrading anaerobic microorganisms, assessment of their biomethane production potential, and a comprehensive understanding of the degradation pathway. This study aimed to address the aforementioned necessities by bioaugmenting seed sludge with three distinct enriched lignin-degrading microbial consortia at both 25 °C and 37 °C. Enhanced biomethane yields was detected in the bioaugmented digesters, while the highest production was observed as 188 mLN CH4 gVS−1 in digesters operated at 37 °C. Moreover, methane yield showed a significant improvement in the samples at 37 °C ranging from 110% to 141% compared to the control, demonstrating the efficiency of the enriched lignin-degrading microbial community. Temperature and substrate were identified as key factors influencing microbial community dynamics. The observation that microbial communities tended to revert to the initial state after lignin depletion, indicating the stability of the overall microbiota composition in the digesters, is a promising finding for large-scale studies. Noteworthy candidates for lignin degradation, including Sporosarcina psychrophila, Comamonas aquatica, Shewanella baltica, Pseudomonas sp. C27, and Brevefilum fermentans were identified in the bioaugmented samples. PICRUSt2 predictions suggest that the pathway and specific proteins involved in anaerobic lignin degradation might share similarities with those engaged in the degradation of aromatic compounds.

Exploring the potential of biological methanation for future defossilization scenarios: Techno-economic and environmental evaluation

The REPowerEU plan establishes the production objective of 35 billion m3 of biomethane in the European Union (EU) by 2030. Biomethane is an excellent energy vector to promote the defossilization of different sectors within a Power-to-Gas approach. The present study evaluates the economic and environmental implications of producing biomethane from the biogas generated in a municipal wastewater treatment plant (WWTP) with a treatment capacity of 100,000 m3/d and 500,000 population equivalents. The techno-economic analysis (TEA) and life cycle assessment (LCA) were conducted for a biomethane production plant based on biological methanation process using the hydrogen produced in a water electrolyser. The TEA illustrated that the electricity price (0–0.20 €/kWh) features an important impact on the biomethane cost (0.05–0.23 €/kWhHHV) due to the high electrolyser energy consumption. Flexible operation of the electrolyser is economically feasible at load factors above 35 %, which can be attributed to the lower impact of the electrolyser capital cost as the load factor increases. The LCA illustrated that biomethane has a lower global warming impact (<0.28 kgCO2-eq/kWhHHV) than fossil natural gas when the renewable electricity production in the mix is above 62 %. The results highlighted that high carbon prices under the EU Emission Trading System is an important driver to promote biomethane production in European countries since energy production from biomethane could be exempted to acquire emission allowances. This would provide a competitive advantage of biomethane over natural gas when considering the whole supply chain of the energy carrier. Overall, this study demonstrates that biological methanation has the potential to become an important biomethane production technology for future defossilization scenarios.

Constraints and dynamic assessment of biomethane generation from cyclically nutrients stimulation

The generation of biomethane in geological history is primarily influenced by multi-stage tectonic uplift and diverse groundwater charging conditions. To investigate and simulate this process, we conducted laboratory experiments involving cyclic addition of nutrients. The results demonstrate that continuous nutrient supplementation is a viable approach for achieving sustained biomethane production, with yields ranging from 1191.53 to 1316.90 μmol/g over three biodegradation cycles. Fitzhugh models prove to be the most suitable for predicting biomethane production. Biodegradation induces rearrangement of coal's pore structure, leading to increased pore sizes and numbers, facilitating the infiltration of biological enzymes, and enhancing methanogenesis rates. Our study elucidates the mechanisms underlying biomethane generation in geological history and offers strategies to expedite the practical application of coalbed methane bioengineering.

Is Biomethane Production from Common Reed Biomass Influenced by the Hydraulic Parameters of Treatment Wetlands?

Treatment wetlands (TWs) are Nature-Based Solutions which have been increasingly used worldwide for wastewater (WW) treatment as they are able to remove mineral and organic pollutants through both physical and biochemical processes. Besides the reusable effluent, the TWs produce, as their main output, plant biomass that needs to be harvested and disposed of at least once a year with significant management costs and causing the TW to be temporarily out of service. This study aims (i) to evaluate the potential of TWs’ biomass for local energy production and (ii) to understand the effects of TWs’ hydraulic conductivity (Ks) on the biomass biomethane yield. Specifically, this was addressed by determining the Biochemical Methane Potential of common reed (CR) (Phragmites australis) samples collected at three harvest times from the 10-year-old horizontal subsurface treatment wetland (HSTW) used as a secondary WW treatment system for the IKEA® store situated in Catania (Eastern Sicily, Italy). Furthermore, the falling-head test was conducted to assess the hydraulic conductivity (Ks) variation in the hydraulic conductivity (Ks) of the HSTW, in order to understand its influence on the CR biomethane production. The average methane content values were 130.57 Nm3CH4/tVS (±24.29), 212.70 Nm3CH4/tVS (±50.62) and 72.83 Nm3CH4/tVS (±23.19) in August, September, October 2022, respectively. Ks was correlated with both dry matter (R2 = 0.58) and fiber content (R2 = 0.74) and, consequently, affected the biomethane yield, which increased as the Ks increased (R2 = 0.30 in August; R2 = 0.57 in September). In the framework of a circular economy, the results showed the successful possibility of integrating bioenergy production into TWs. The research could contribute (i) to encouraging plant operators to reuse biomass from TWs for local energy production and (ii) to help plant operators to understand Ks effects on the biomass biomethane yield in order to increase the sustainability of the system and to reduce the maintenance costs.

Dual disintegration of microalgae biomass for cost-effective biomethane production: Energy and cost assessment

The present study aims to enhance the biomethane production potential of microalgae via a dual disintegration process. During this process, the microalgae biomass was firstly subjected to cell wall weakening by thermochemical disintegration (TC) (50 to 80 °C), pH adjustment with alkali, NaOH (6 to 10) and time (0 to 10 min) and, secondly, by bacterial disintegration (BD). TC-BD disintegration was comparatively higher (33 %) than BD (24 %), TC (8.5 %), and control (7 %). A more significant VFA accumulation of 2816 mg/L was recorded for TC-BD. Similarly, a greater substrate anaerobic biodegradability was achieved in TC-BD (0.32 g COD /g COD) than BD (0.21 g COD /g COD), TC alone (0.09 gCOD/g COD) and control (0.08 g COD /g COD), respectively. The TC-BD achieves a positive net profit and an energy ratio of + 0.12 GJ/d and 1.03. The proposed dual disintegration has a promising future for commercialization.

Seasonal tourism's impact on wastewater composition: Evaluating the potential of alternating activated adsorption in primary treatment

Primary treatment processes have gained attention in recent research and development due to their potential for redirecting carbon towards anaerobic digestion, which can subsequently be used for the production of biomethane. The alternating activated adsorption (AAA) process is implemented on full-scale at several wastewater treatment plants across Europe. However, there is a lack of full-scale studies of advanced carbon capture technology implementations in literature. This study demonstrates the ability of a full-scale AAA process to remove and redirect carbon in a region heavily influenced by tourism. Periods in high and off-season were compared to study the impact of tourism on the composition of the wastewater and the AAA-process. The wastewater characteristics of the high season differed significantly from the low season. During the high season, the PE increased by 37 %, total suspended solids went up by 75 % and chemical oxygen demand increased by 58 %, compared to the low season. Additionally, 80 % of the low volatile lipophilic substances (LVLS) measured were attributed to the impact of tourism. A mass-balance of primary treatment for chemical oxygen demand (COD) and LVLS was conducted for both trial periods. The primary treatment was able to eliminate 56 % of the COD and 62 % of the LVLS in the non-tourist season and 53 % of the COD and 54 % of the LVLS in the tourist season. The increased wastewater load was effectively managed in the AAA-process. Key process parameters like sludge settling characteristics, hydraulic retention time and total suspended solids removal rates remained stable during the high season in winter.

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 215.52mL/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.

Decarbonizing our environment via the promotion of biomass methanation in developing nations: a waste management tool

Abstract For a long time, fossil fuel has been a part of our everyday lives and has constantly led to the emission of carbon dioxide (CO2) into the environment. The release of methane (CH4) into our surroundings can be caused by the decomposition of organic wastes produced by our daily activities; CH4 produced by human activity is responsible for at least 25 % of global warming. CH4 is a known potent greenhouse gas that can trap about 35 times more heat than CO2. These greenhouse gases play a role in climate change and global warming. It, therefore, becomes important to explore measures for decarbonizing our environment. Biomethane production using our generated waste is a promising decarbonization approach with significant potential for mitigating greenhouse gas emissions. This paper overviews potential biomass methanation feedstocks and investigates several technologies, such as anaerobic digestion, combined pyrolysis and methanation, and combined gasification and methanation. SWOT analysis of waste conversion to biomethane was conducted, and important points related to the scaling-up of biomethane production processes were outlined. Also, insights into prospects for promoting biomass methanation deployment were provided. In conclusion, biomass methanation has great potential for producing sustainable energy. Hence, collaboration between industrialists, researchers, government agencies, and stakeholders including an understanding of the financial investments, return on investments, or potential subsidies and incentives could enhance the practicality of the proposed solution. Research and development should be continuously carried out as they are necessary to scale up and promote the technology. Also, there should be technical training for stakeholders as it is essential for the smooth development of the sector.

Biomethane production using goat manure and cheese whey: statistical analysis of the effect of mixture composition

Biomethane production using goat manure and cheese whey: statistical analysis of the effect of mixture composition

Temperature-phased anaerobic sludge digestion effectively removes antibiotic resistance genes in a full-scale wastewater treatment plant

Sludge is a major by-product and the final reservoir of antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs). Temperature-phased anaerobic digestion (TPAD), consisting of thermophilic anaerobic digestion (AD) (55 °C) and mesophilic AD processes (37 °C), has been implemented in WWTPs for sludge reduction while improving the biomethane production. However, the impact of TPAD on the ARGs' fate is still undiscovered in lab-scale experiments and full-scale WWTPs. This study, for the first time, investigated the fate of ARGs during the TPAD process across three seasons in a full-size WWTP. Ten typical ARGs and one integrase gene of class 1 integron (intI1) involving ARGs horizontal gene transfer were examined in sludge before and after each step of the TPAD process. TPAD reduced aac(6′)-Ib-cr, blaTEM, drfA1, sul1, sul2, ermb, mefA, tetA, tetB and tetX by 87.3–100.0 %. TPAD reduced the overall average absolute abundance of targeted ARGs and intI1 by 92.39 % and 92.50 %, respectively. The abundance of targeted ARGs in sludge was higher in winter than in summer and autumn before and after TPAD. During the TPAD processes, thermophilic AD played a major role in the removal of ARGs, contributing to >60 % removal of ARGs, while the subsequent mesophilic AD contributed to a further 31 % removal of ARGs. The microbial community analysis revealed that thermophilic AD reduced the absolute abundance of ARGs hosts, antibiotic resistant bacteria. In addition, thermophilic AD reduced the abundance of the intI1, while the intI1 did not reproduce during the mesophilic AD, also contributing to a decline in the absolute abundance of ARGs in TPAD. This study demonstrates that TPAD can effectively reduce the abundance of ARGs in sludge, which will suppress the transmission of ARGs from sludge into the natural environment and deliver environmental and health benefits to our society.

In situ preparation of oriented microbial consortium-based compound enzyme strengthens food waste disintegration and anaerobic digestion: Performance, mechanism, microbial communities and global metabolic pathways

This study used food waste (FW) as the substrate, under the co-culture system, innovatively developed the oriented and high matching degree microbial consortium-based compound enzyme (MCE) used for promoting FW hydrolysis and anaerobic digestion (AD). It was found that the highest hydrolysis efficiency and substrate biodegradability could be obtained after 1:100 MCE (i.e. the inoculation ratio of Aspergillus oryzae CICC 40214 as protease generator and Aspergillus niger CICC 40294 as amylase generator was 1:100) pretreatment, thereby harvesting the highest biomethane yield of 522.61 mL/g VS. The dissection of FTIR results indicated that the structure of main components of starch, protein and lipid in FW was destructed after MCE pretreatment, of which the protein was more susceptible to MCE and disintegrated first, while its structure also became looser. XPS C1s spectra and N1s spectra showed that the C-(C/H) and protein-N of the enzyme pretreated solid were respectively decreased from 77.82 % to 69.19 % and 69.43 % to 40.07 %, which further implied that more carbohydrates and proteins were released from solid phase to liquid phase after MCE pretreatment. The microbial community and metagenome analysis illustrated that MCE pretreatment regulated the microbial communities lead to a shift in the favorable direction of biomethane production. While based on the changes in gene abundance, the deciphering of global metabolic pathways revealed that the 80 %, 60 %, 75 % and 86 % of the functional genes related to glycolysis, amino acid metabolism, TCA cycle and methane metabolism were respectively intensified after 1:100 MCE pretreatment, thereby achieving the maximized biomethane yield.

Biomineralization of phosphorus during anaerobic treatment of distillery wastewaters

This study addresses the pressing environmental concerns associated with the rapidly growing distillery industry, which is a significant contributor to wastewater generation. By focusing on the treatment of distillery wastewater using anaerobic digestion, this research explores the potential to convert organic materials into biofuels (methane). Moreover, the study aims to recover both methane and phosphorus from distillery wastewater in a single anaerobic reactor, which represents a novel and unexplored approach. Laboratory-scale experiments were conducted using mesophilic and thermophilic upflow anaerobic sludge blanket reactors. A key aspect of the study involved the implementation of a unique strategy: the mixing of centrate and spent caustic wastewater streams. This approach was intended to enhance treatment performance, manipulate the microbial community structure, and thereby optimizing the overall treatment performance. The integration of the centrate and spent caustic streams yielded remarkable co-benefits, resulting in significant biomethane production and efficient phosphorus precipitation. The study demonstrated a phosphorus removal efficiency of ∼60 % throughout the 130–140 days operation period. The recovery of phosphorus via the reactor sludge offers exciting opportunities for its utilization as a fertilizer or as a raw material within the phosphorus refinery industry. The biomethane produced during the treatment exhibits significant energy potential, estimated at 0.5 GJ/(m3 distillery wastewater).

Optimization strategy of Co3O4 nanoparticles in biomethane production from seaweeds and its potential role in direct electron transfer and reactive oxygen species formation

In the present study, three process parameters optimization were assessed as controlling factors for the biogas and biomethane generation from brown algae Cystoceira myrica as the substrate using RSM for the first time. The biomass amount, Co3O4NPs dosage, and digestion time were assessed and optimized by RSM using Box-Behnken design (BBD) to determine their optimum level. BET, FTIR, TGA, XRD, SEM, XPS, and TEM were applied to illustrate the Co3O4NPs. FTIR and XRD analysis established the formation of Co3O4NPs. The kinetic investigation confirmed that the modified model of Gompertz fit the research results satisfactorily, with R2 ranging between 0.989–0.998 and 0.879–0.979 for biogas and biomethane production, respectively. The results recommended that adding Co3O4NPs at doses of 5 mg/L to C. myrica (1.5 g) significantly increases biogas yield (462 mL/g VS) compared to all other treatments. The maximum biomethane generation (96.85 mL/g VS) was obtained with C. myrica at (0 mg/L) of Co3O4NPs. The impacts of Co3O4NPs dosages on biomethane production, direct electron transfer (DIET) and reactive oxygen species (ROS) were also investigated in detail. The techno-economic study results demonstrate the financial benefits of this strategy for the biogas with the greatest net energy content, which was 2.82 kWh with a net profit of 0.60 USD/m3 of the substrate and was produced using Co3O4NPs (5 mg/L).

Biohybrid CO2 electrolysis under external mode: using pure formic acid extracted from CO2 electroreduction for diverse microbial conversion

The demand for converting CO2 into fuels or chemicals is on the rise to achieve a carbon-efficient circular economy. Biohybrid CO2 electrolysis shows potential for increasing production rates and diversifying product spectra by combining electrocatalysts and microbial catalysts. However, it is important to note that utilizing a shared catholyte for biohybrid CO2 electrolysis has not demonstrated significant performance improvements to date. In this study, we developed a biohybrid CO2 electrolysis system utilizing a solid electrolyte operating in an external mode. The produced formic acid was extracted and used as an intermediate for microbial conversion. Impressively, the solid-electrolyte CO2 electrolysers obtained a remarkable total Faraday efficiency of 81.4% for formic acid production. In-situ mechanism studies unveiled metallic tin as the probable real active site, prompting further exploration of strategies to boost the activity and stability of electrocatalysts. In the bioconversion step, we achieved a noteworthy 8-day duration for generating bioelectricity, nearly 100% electron recovery for biomethane production, and 90.8% for acetate generation. Additionally, when ethanol was co-fed, a C6 specificity of 41.1% was observed for the generation of medium-chain fatty acids (MCFAs). This study presents groundbreaking experimental data that demonstrates the numerous advantages of utilizing hybrid systems as advanced synthesis techniques.

Anaerobic co-digestion of food waste and bio flocculated sewage sludge towards bio-methane production

The existing sewage treatment plants are energy consumers rather than producers and integration of anaerobic reactor can be a viable approach for enhancing their commercial viability. Therefore, anaerobic co-digestion of food waste and bio-flocculated sewage sludge was studied in a continuous stirred tank reactors (R1 and R2) having a working volume of 6.5 Litre at organic loading rates of 2.5 and 2.4 g VS L−1D−1. At mesophilic temperature, the stabilisation of inoculum was performed in batch mode for 60 days followed by continuous mode feeding for 120 days. The feeding ratio was decided based on availability of food waste and bio-flocculated sewage sludge from a typical domestic household for analysing the effect of volatile fatty acids accumulation on reactor performance. The R1 was fed with equal proportion of bio-flocculated sewage sludge and food waste while R2 was fed in 98:2 (v/v), respectively. To analyse the mixing and temperature distribution within the digester, the velocity and temperature profiles were obtained using Ansys Fluent. In R1, more biogas yield were observed than R2 due to 80% average VS reduction as compared to 55% in case of R2. The highest volatile fatty acids accumulation of 10951 mg L−1 was observed in R1 whereas R2 showed 2800 mg L−1, respectively. The more fluctuations in pH were observed in R1 as compared to R2 due to more food waste concentration and maximum bio-methane production was 133 and 233 mL CH4 g−1 VSadded in R1 and R2, respectively.

Continuous biomethanation of flue gas-carbon dioxide using bio-integrated carbon capture and utilization

Biomethanation of carbon dioxide (CO2) from flue gas is a potential enabler of the green transition, particularly when integrated with the power-to-gas chain. However, challenges arise in achieving synthetic natural gas quality when utilizing CO2 from diluted carbon sources, and the high costs of CO2 separation using amine-based solutions make large-scale implementation unfeasible. We propose an innovative continuous biomethanation system that integrates carbon capture and CO2 stripping through microbial utilization, eliminating expenses with the stripper. Stable continuous biomethane production (83–92 % methane purity) was achieved from flue gas-CO2 using a biocompatible aqueous n-methyldiethanolamine (MDEA) solution (50 mmol/L) under mesophilic and hydrogen-limiting conditions. MDEA was found to be recalcitrant to biodegradation and could be reused after regeneration. Demonstrating the microbial ability to simultaneously strip and convert the captured CO2 and regenerate MDEA provides a new pathway for valorization of flue gas CO2.

Acidogenic fermentation of biowaste coupled with nitrogen recovery using selective membranes to produce a VFA-rich liquid with a high C/N ratio

This research focuses on the production of a liquid stream rich in volatile fatty acids (VFAs) and low ammoniacal nitrogen content (<0.1 g N/L) from biowaste. The liquid stream was obtained by combining (i) mixed culture acidogenic fermentation to maximise VFA production and (ii) gas-permeable membrane (GPM) contactor to recover ammoniacal nitrogen. Three batch fermentation tests of biowaste collected in a full-scale mechanical-biological treatment plant provided high and stable VFA concentrations (37–39 g CODVFA/L). VFAs represented 73–81 % of the soluble chemical oxygen demand (sCOD) concentration, with a predominance of acetic, propionic and butyric acids. A highly specialized microbial community was observed in all batch tests, with Bacteroidota and Firmicutes as predominant phyla (>90 % of relative abundance). The GPM contactor recovered more than 99 % of the ammoniacal nitrogen in the fermentation liquid without VFA losses. The suitability of the produced fermentation liquid with a high C/N ratio for downstream applications was evaluated using biomethane potential tests (BMP) at different total ammonium nitrogen (TAN) concentrations (0.76–3.15 g N/L) and circumneutral pH. Despite achieving similar ultimate methane yields (279–314 NmL CH4/g CODfeed), lower TAN concentrations in the biowaste fermentation liquid improved anaerobic biodegradation kinetics, enhancing its potential applicability for methane production.

Microbial community dynamics and functional potentials in the conversion of oil palm wastes into biomethane.

Oil palm processing generates substantial waste materials rich in organic content, posing various environmental challenges. Anaerobic digestion (AD), particularly for palm oil mill effluent (POME), offers a sustainable solution, by converting waste into valuable biomethane for thermal energy or electricity generation. The synergistic activities of the AD microbiota directly affect the biomethane production, and the microbial community involved in biomethane production in POME anaerobic digestion has been reported. The composition of bacterial and archaeal communities varies under different substrate and physicochemical conditions. This review discusses the characteristics of POME, explores the microbial members engaged in each stage of AD, and elucidates the impacts of substrate and physicochemical conditions on the microbial community dynamics, with a specific focus on POME. Finally, the review outlines current research needs and provides future perspectives on optimizing the microbial communities for enhanced biomethane production from oil palm wastes.

Improved Formation of Biomethane by Enriched Microorganisms from Different Rank Coal Seams.

The influence of enrichment of culturable microorganisms in in situ coal seams on biomethane production potential of other coal seams has been rarely studied. In this study, we enriched culturable microorganisms from three in situ coal seams with three coal ranks and conducted indoor anaerobic biomethane production experiments. Microbial community composition, gene functions, and metabolites in different culture units by 16S rRNA high-throughput sequencing combined with liquid chromatography-mass spectrometry-time-of-flight (LC-MS-TOF). The results showed that biomethane production in the bituminous coal group (BC)cc resulted in the highest methane yield of 243.3 μmol/g, which was 12.3 times higher than that in the control group (CK). Meanwhile, Methanosarcina was the dominant archaeal genus in the three experimental groups (37.42 ± 11.16-52.62 ± 2.10%), while its share in the CK was only 2.91 ± 0.48%. Based on the functional annotation, the relative abundance of functional genes in the three experimental groups was mainly related to the metabolism of nitrogen-containing heterocyclic compounds such as purines and pyrimidines. Metabolite analysis showed that enriched microorganisms promoted the degradation of a total of 778 organic substances in bituminous coal, including 55 significantly different metabolites (e.g., purines and pyrimidines). Based on genomic and metabolomic analyses, this paper reconstructed the heterocyclic compounds degradation coupled methane metabolism pathway and thereby preliminarily elucidated that enriched culturable bacteria from different coal-rank seams could promote the degradation of bituminous coal and intensify biogenic methane yields.