Methane Production Research Articles

Biogas Purification by Methane and Acetate Manufacturing

ABSTRACTWastewater treatment plants have two persistent financial and energetic drains, the carbon dioxide content of biogas, which limits its commercial sale, and the presence of trace organics in the wastewater effluent, which damages the aquatic ecosystem, like the Great Barrier Reef. Biogas is a renewable methane resource that is underutilized due to the variable CO2 content (~40%). Biogas is energy intensive to purify and limited by the economy of scale (> 8.85 GJ/h) to large‐scale purification methods, thus small‐scale processes require development. Electrocatalytic microbes native to wastewater have been shown to convert CO2 to CH4 and acetate, however complete conversion of the CO2 content to CH4 is energy intensive. Here we show a low power bioelectrochemical fuel cell design to purify biogas to pipeline quality methane (98%), manufacture methane and/or acetate, and remove trace organics, using HCO3− as the transport charge carrier from dissolved CO2 from the biogas through an anion exchange membrane. This decreased the power required to separate CO2 from methane in biogas on a molar basis, resulting in a net energy recovery similar to current industrial systems. Magnesium anode use resulted in an energy positive system. Tests evaluated the influence of cathode potential on the current density, HCO3− ion flux and the rates and efficiencies of methane production, resulting in optimization at −0.7 V versus standard hydrogen electrode (SHE). A techno‐economic analysis modeled a positive return on investment for scaled‐up production to purify small biogas streams that are otherwise financially unrecoverable. Carbon sequestration by production of methane, acetate and solid fertilizers demonstrated profitable and energy efficient waste‐to‐resource conversion.

Nutrient digestibility, rumen fermentation and microbial nitrogen synthesis of swamp buffaloes fed urea-lime treated rice straw

This study aimed to evaluate the effects of urea-lime treatment on rice straw regarding its influence on nutrient digestibility and rumen fermentation efficiency in swamp buffaloes. Eight rumen-fistulated swamp buffaloes (353 ± 11 kg) were used in a completely randomised design experiment. They received one of the two diets (untreated rice straw (RS) and 2% urea + 2% lime treated rice straw (ULTRS)) during the feeding trial. Offered and residual feed were weight and collected during the 21–day experimental period while faeces and urine were sampled on the final 7 days when the animals were housed in metabolism crates. Rumen fluid and blood samples were collected on the last day for chemical analyses. The results showed a significant improvement in dry matter intake and digestibility with the use of ULTRS. Feeding ULTRS improved rumen NH3-N concentration, whereas blood and urine nitrogen contents were similar. The acetic acid concentration and methane production decreased while propionic acid content increased. Consequently, the ratio of acetic acid to propionic acid was significantly reduced in buffaloes that were fed ULTRS. Total viable bacteria, amylolytic, and cellulolytic bacteria enhanced in the ULTRS treatment. The efficiency microbial nitrogen synthesis and the microbial protein synthesis were both elevated in the ULTRS group. The findings suggest that ULTRS can be used as a source of roughage to enhance nutrient digestibility, rumen fermentation efficiency, microbial nitrogen and protein synthesis efficiency and methane reduction in swamp buffaloes.

The impact of global change factors on the functional genes of soil nitrogen and methane cycles in grassland ecosystems: a meta-analysis.

Soil functional genes in grasslands are crucial for processes like nitrogen fixation, nitrification, denitrification, methane production, and oxidation, integral to nitrogen and methane cycles. However, the impact of global changes on these genes is not well understood. We reviewed 84 studies to examine the effects of nitrogen addition (N), warming (W), increased precipitation (PPT +), decreased precipitation (PPT-), and elevated CO2 (eCO2) on these functional genes. For nitrogen cycling, global changes mainly boost genes involved in nitrification but reduce those in denitrification, with nirK being the most sensitive. Most nitrogen fixation-related genes did not show a significant response. Among single factors, N and PPT + have the most significant effects. The impact of global changes on nitrogen cycling genes is largely additive, and their interaction with N is particularly influential. For methane cycling, global changes notably affect mcrA, while only PPT + significantly reduces pmoA. The magnitude and duration of global change treatments are more critical than the treatment form for nitrogen cycling genes. For methane cycling, the form and intensity of nitrogen addition, along with treatment duration, affect pmoA abundance. We also identified a competitive relationship between methane oxidation and nitrification and a complex coupling with denitrification. This study provides new insights into microbial responses in nitrogen and methane cycling under global changes, with significant implications for experimental design and management strategies in grassland ecosystems.

Fracture Propagation Laws and Influencing Factors in Coal Reservoirs of the Baode Block, Ordos Basin

The expansion of hydraulic fractures in coalbed methane (CBM) reservoirs is key to effective stimulation, making it essential to understand fracture propagation and its influencing factors for efficient resource development. Using petrological characteristics, logging data, microseismic monitoring, and fracturing reports from the Baode Block on the eastern Ordos Basin, this study systematically investigates the geological and engineering factors influencing hydraulic fracture propagation. The real-time monitoring of fracture propagation in 12 fractured wells was conducted using microseismic monitoring techniques. The results indicated that the fracture orientations in the study area ranged from NE30° to NE60°, with fracture lengths varying between 136 and 226 m and fracture heights ranging from 8.5 to 25.3 m. Additionally, the fracturing curves in the study area can be classified into four types: stable, descending, fluctuating, and falling. Among these, the stable and descending types exhibit the most effective fracture propagation and are more likely to generate longer fractures. In undeformed–cataclastic coals and bright and semi-bright coals, long fractures are likely to form. When the Geological Strength Index (GSI) of the coal rock ranges between 60 and 70, fracture lengths generally exceed 200 m. When the coal macrolithotype index (Sm) is below 2, fracture lengths typically exceed 200 m. When the difference between the maximum and minimum horizontal principal stresses exceeds 5 MPa, fractures with length >180 m are formed, while fracture heights generally remain below 15 m. From an engineering perspective, for the study area, hydraulic fracturing measures with a preflush ratio of 20–30%, an average sand ratio of 13–15%, and a construction pressure between 15 MPa and 25 MPa are most favorable for coalbed methane production.

Response of Metabolic Gene Panel to Organic Loading Stress in Propionate-Degrading Methanogenic Anaerobic Digesters

Propionate, a critical intermediate in anaerobic digestion, and its syntrophic removal, is sensitive to stress. To our knowledge, this study investigates for the first time the response of a metabolic gene panel to organic loading rate (OLR) stress in propionate-degrading methanogenic consortia in lab-scale upflow anaerobic sludge blanket (UASB) reactors. The experimental phases included stabilisation (1.4–2.8 g COD/L/day), electroactive enrichment, OLR shock (6 g COD/L/day), and early recovery. Quantitative PCR was used to assess the abundance of key functional genes (16SrRNA, mcrA, pilA, and hgtR). During stabilisation, ~200 mLCH₄/h was produced, the mcrA/16SrRNA ratio was 0.78–2.64, and pilA and hgtR abundances were 1.29–2.27 × 105 and 2.12–4.37 × 104 copies/gVS. Following the OLR shock, methane production ceased entirely, accompanied by a sharp decline in the mcrA/16S ratio (0.08–0.24) and significant reductions in pilA (1.43-log) and hgtR (1.34-log) abundance. Partial recovery of pilA and hgtR abundance (1.19 × 105 and 8.57 × 104) was observed in the control reactor after the early recovery phase. The results highlight the utility of mcrA, 16SrRNA, pilA, and associated ratios, as reliable indicators of OLR stress in lab-scale UASB reactors. This study advances the understanding of molecular stress responses in propionate-degrading methanogenic consortia, focusing on direct interspecies electron transfer in process stability and recovery.

Mechanochemical-assisted Natural Deep Eutectic Solvent as a platform for an olive leaves biorefinery: Extraction of bioactive compounds and methane production

This study introduces an innovative biorefinery process aimed at maximizing the utilization of olive leaves. The proposed approach seeks to extract valuable phenolic compounds, lignocellulosic material, and biomethane from olive leaves. To achieve this, a combined technique involving mechanochemical extraction and sustainable solvents, specifically natural deep eutectic solvents (NADES), was employed. Unlike conventional methods, NADES were simultaneously formed and utilized for extraction within a ball mill. The optimal conditions for maximum extraction of high-value compounds were 0.5 g of OL using 10 mL of ChCl:Gl (3:1) and 1.1 h in a ball mill. The recovered yields were 14.5 ± 2.9 g/kg OL of lignocellulosic fraction and 1.3 ± 0.3 g gallic acid eq./kg OL of phenolic compounds. OL waste generated after the optimized extraction process was evaluated for methane production, obtaining 142 ± 53 mL CH4/g VS OL waste compared to 126 ± 30 mL CH4/g VS untreated OL. Therefore, NADES represent promising solvents for the biorefinery process and reduce dependence on organic solvents.

Chemical composition, rumen fermentation kinetics, and degradability of cassava stem hay ammoniated with urea using the in vitro gas production technique

ABSTRACT A completely randomised design was adopted with five treatments urea levels of 0, 2, 4, 6, and 8% of dry matter and five replicates per treatment. The fermentation products were analysed using an in vitro semiautomatic gas production technique. Ammoniation had a significant linear effect on DM, NDF, hemicellulose, acid detergent fiber, and neutral detergent insoluble nitrogen. Ammoniation had a positive linear effect on crude protein (CP) content; increasing urea by 1% caused an increase in CP by 5.19 g kg−1 DM. The gas production based on DM, OM, and NDF decreased linearly with increasing urea for every 1% urea added to the hay, there was a reduction in gas production of 1.40, 3.27, and 4.21 ml/g DM, OM, and NDF, respectively. The concentration of methane decreased linearly with urea dose; for each 1% reduction in urea, there was a 0.15, 0.34, and 0.41 ml/g reduction in methane concentration during the degradation of DM, OM, and NDF, respectively. Ammoniation with 8% urea improved the chemical composition of cassava stem hay and decreased methane production.

Polyethylene hydrogenolysis by dilute RuPt alloy to achieve H2-pressure-independent low methane selectivity

Chemical recycling of plastic waste could reduce its environmental impact and create a more sustainable society. Hydrogenolysis is a viable method for polyolefin valorization but typically requires high hydrogen pressures to minimize methane production. Here, we circumvent this stringent requirement using dilute RuPt alloy to suppress the undesired terminal C–C scission under hydrogen-lean conditions. Spectroscopic studies reveal that PE adsorption takes place on both Ru and Pt sites, yet the C–C bond cleavage proceeds faster on Ru site, which helps avoid successive terminal scission of the in situ-generated reactive intermediates due to the lack of a neighboring Ru site. Different from previous research, this method of suppressing methane generation is independent of H2 pressure, and PE can be converted to fuels and waxes/lubricant base oils with only <3.2% methane even under ambient H2 pressure. This advantage would allow the integration of distributed, low-pressure hydrogen sources into the upstream of PE hydrogenolysis and provide a feasible solution to decentralized plastic upcycling.

Effect of Temperature and Inoculum-to-Substrate Ratios on Two-Stage Biohydrogen and Methane Production from Sugarcane Molasses

Effect of Temperature and Inoculum-to-Substrate Ratios on Two-Stage Biohydrogen and Methane Production from Sugarcane Molasses

Technical–Economic Analyses of Electric Energy Generation by Biogas from Anaerobic Digestion of Sewage Sludge from an Aerobic Reactor with the Addition of Charcoal

This study aimed to obtain the energy recovery potential of the biogas produced from anaerobic digestion (AD) of the sludge from a wastewater treatment plant (WWTP), including the use of biochar as an additive for substrate co-digestion and catalyst for methane production. We carried out the following steps: chemical–physical laboratory analyses of sludge samples; the building, operation, and monitoring of an experimental prototype of a batch bioreactor of 2.5 L for the AD of the sludge (with and without the addition of charcoal); qualitative measurements of biogas; the study of charcoal morphology; and the projection of useful energy generation from the AD sludge after treatment. A study on the economic viability and avoided greenhouse gas (GHG) emissions was performed based on the experimental results. The substrate showed alterations in all the physicochemical parameters evaluated after AD, such as a reduction of 35% in the biochemical oxygen demand (BOD) analysis; the experiment carried out using biochar showed positive results regarding the speed of CH4 production and a greater potential for energy recovery. Enterprises from 2000 kW onwards would present an internal rate of return (IRR) equal to or higher than the minimum attractiveness rate (MAR) of 15%. The USD 95.28/MWh tariff presented economic feasibility for the studied scenarios. WWTPs that produce enough sludge to generate power of 2000 kW would need to process the waste of 117,200 inhabitants with charcoal addition and 136,000 without charcoal. It would be possible to avoid the emission of 2307.97 tCO2/year (2000 kW). According to the results obtained, this study revealed that using alternative energies based on anaerobic digestion and biochar can generate positive results regarding methane production, and its application as an energy source in a WWTP proved to be economically viable at a specific level of power production.

Impact and mechanism of polyethylene terephthalate microplastics with different particle sizes on sludge anaerobic digestion.

Municipal wastewater treatment plants (WWTPs) are important sinks for microplastics, and the vast majority of microplastics entering WWTPs are trapped in residual sludge. In order to investigate the effect of microplastics on anaerobic digestion of sludge, polyethylene terephthalate (PET) microplastics with common particle size and physical aging were selected to conduct a comparative study. Regardless of aging, the addition of 300 and 500 μm PET microplastics inhibited methane production, with their cumulative methane production reduced by 11.3-24.9% compared to the control group. In contrast, when 100 μm microplastics were added, the raw PET promoted methane production, yielding 337 L CH4/kg VS, while the aged experimental group showed similar yields to the control group. For the 800 μm microplastics treatment group, aged microplastics facilitated methane production while raw microplastics inhibited it, with methane production of 91.0% and 111% of the control group, respectively. The effects were also investigated by model fitting, stage discussion, and microbial community structure analysis. The results discovered that the main rate-limiting steps of adding microplastics with smaller or larger particle sizes (100, 800 μm) to methane production were solubilization and hydrolysis, while the main rate-limiting step of microplastics with medium particle sizes (300, 500 μm) was methanogenesis. Physically aged PET microplastics with smaller or larger sizes showed a more significant effect on methane production. Furthermore, PET microplastics altered the microbial community structure, shifting methanogens from acetotrophic pathways to hydrotrophic pathways. This study offers new insights into the performance analysis of sludge anaerobic digestion in practical WWTPs.

Graphite-enhanced methanogenesis in coal measure shale anaerobic digestion: Implications for increasing gas yield and CO2 utilization

Anaerobic digestion (AD) of coal measure shale (CMS) for methane production is a promising technology for increasing yield of coal measure gas (CMG) wells. However, improving methane production efficiency of CMS remains a challenge. Conductive material has been shown to promote biogas production in different AD systems, but its effectiveness in CMS requires investigation. In this study, graphite was selected as conductive material due to its low cost and suitability for field applications, and its effects on methane production was investigated. The results indicate that as graphite concentration increases from 0 to 1.6 g/L, the methane production of CMS increases. However, when the graphite concentration reaches 2.0 g/L, the methanogenesis is inhibited, resulting in lower methane production compared to the control group. In the group with a graphite concentration of 1.6 g/L, the abundances of Romboutsia and Pseudomonas increase, which improves the compatibility of the microbial community with the CMS AD system and causes the amount of the substrates for methanogenesis to increase. Also, the direct interspecies electron transfer between Methanobacterium, Methanosaeta and Pseudomonas is strengthened, which enhances the methane production. However, excessive addition of graphite (2.0 g/L) intensifies the competitions from dissimilatory iron reduction and sulfate reduction reactions for substrates and electrons with the methanogenesis, causing the methane production to decrease. This study confirms the effectiveness of graphite in enhancing methane production of CMS, and the promoted hydrogenotrophic methanogenesis enhances the CO2 methanation, which offers an efficient pathway for increasing CMG well yield and enabling CO2 underground utilization.

Novel application of Ru-based catalysts on MgAl oxides alkaline adsorbents for cyclic CO2 methanation

This study explores the performances of Ru-based catalysts with a low metal content (2 wt%) supported on MgO and Mg-Al Oxides (MgAl) for cyclic CO2 adsorption and methanation at atmospheric pressure. Adsorption and desorption tests demonstrated that MgAl-based catalysts are more promising for CO2 capture due to their larger surface area and better distribution of active sites (Mg2+–O2-). Moreover, doping the MgAl support with K2CO3 further improves surface alkalinity and, consequently, capture performance. During cyclic operations, all the catalysts proved effective and selective for methane production. To simulate realistic conditions, both dry and wet CO2 adsorptions were conducted before the methanation stage. The presence of moisture positively influenced gas carbonation for all catalysts, increasing the overall amount of CO2 captured. Specifically, Ru/MgAl exhibited the best performance in terms of adsorption and conversion to methane (approximately 85 % after dry adsorption and 79 % after wet adsorption), with a maximum methane production of 183 and 220 μmolCH4 g−1, respectively. The reaction yield was further enhanced with Ru-K/MgAl, achieving 327 μmolCH4 g−1 after dry adsorption and 333 μmolCH4 g−1 after wet adsorption. However, this catalyst displays different conversion kinetics, attributed to slowed carbonate migration, low Ru dispersion, limited specific surface area, and excessive carbonation strength. Operando FTIR tests revealed differences in reaction intermediates between Ru/MgAl and Ru-K/MgAl, by going deeper into the kinetic differences observed. The study concludes that Ru/MgAl materials are highly promising catalysts for CO2 adsorption and methane production, supporting the development of technologies for CO2 abatement and renewable energy utilisation.

Effect of thermal and alkaline pretreatments on polyhydroxybutyrate solubilization and subsequent anaerobic digestion: Solubilization efficiency, methane production and microbial community

Effect of thermal and alkaline pretreatments on polyhydroxybutyrate solubilization and subsequent anaerobic digestion: Solubilization efficiency, methane production and microbial community

Methanochimaera problematica gen. nov., sp. nov., a novel methanoarchaeon isolated from cold seep sediment and reclassification of Methanomicrobium antiquum as Methanoeremita antiquus gen. nov., comb. nov.

A hydrogenotrophic methanoarchaeon, designated strain FWC-SCC4T, was isolated from cold seep sediment of Four-Way Closure Ridge, offshore southwestern Taiwan. Strain FWC-SCC4Tutilizes H2/CO2 or formate, but not acetate, secondary alcohols, methylamines, methanol or ethanol for growth and methane production. Yeast extract is required for growth. The cell morphology is coccoid, with a diameter of 0.8-1.2 µm, and the cell envelope is composed of S-layer protein with Mr about 137.00 kDa. Cells possess multiple flagella and usually occur singly. Strain FWC-SCC4T grows at a temperature range of 20-40 °C (optimum 37 °C) and a pH range of 5.4-7.2 (optimum 7.0). The NaCl range for growth is 0-0.86 M (optimum 0.09 M). The result of phylogenetic analysis of 16S rRNA gene sequences indicates that the most closely related species are Methanoplanus limicola M3T and Methanoplanus endosymbiosus MC1T, with similarities of 95.95 and 95.63%, respectively. The G+C content of the genomic DNA is 40.3 mol%. The overall genome-relatedness indexes (OGRIs) and concatenated ribosomal protein (RBP) phylogenic analysis indicate that strain FWC-SCC4T is a novel lineage of Methanomicrobiaceae. In addition to strain FWC-SCC4T, the differences between Methanomicrobium antiquum MobHT and Methanomicrobium mobile BPT demonstrated by comparative analysis of genomic G+C content and phylogenetic analysis with non-type strain genomes are enough to support the establishment of a novel genus. In conclusion, strain FWC-SCC4T (BCRC AR10058T= NBRC 114595T) is proposed as the type strain of Methanochimaera problematica gen. nov., sp. nov., and Methanoeremita antiquus gen. nov., comb. nov. is proposed as the new name for Methanomicrobium antiquum MobHT (=DSM 21220T= NBRC 104160T).

Exploring pyrolysis-based alternatives for the valorization of used diapers through a comprehensive understanding of all generated products

This study provides an in-depth evaluation of a pyrolysis process designed for the valorization of baby diaper waste from the rejected fraction of municipal solid waste treatment facilities. The diapers were separated, identified, and classified into distinct fractions/layers, each subjected to Thermogravimetric Analysis to determine the optimal temperature range for operation. This study identified that hydrogen and methane production is maximized at 575 °C. At this temperature, yields reach up to 7.4 mmol of hydrogen and 6.3 mmol of methane, with a total of 23 mmol of non-condensable gases per gram of diaper waste. The temperature of 525 °C optimized the production of lighter liquid fractions. This temperature yielded compounds with boiling points similar to heavy naphtha and comprised over 63 % of the liquid products. The solid residue resulting from pyrolysis was a partially amorphous carbonaceous material, with a maximum surface area of 9.7 m2/g achieved at 575 °C, which is considered low. The analysis is completed with a study of the degradation of the used diapers by TGA/MS-FTIR and the determination of the effective activation energy as a function of conversion. This study highlights the significant potential of pyrolysis technology for treating diaper waste, which generates several potentially usable or valuable products, including hydrogen, methane, light liquid compounds, and carbonaceous material.

Improving methane production from waste-activated sludge by coupling thermal hydrolysis with potassium ferrate pretreatment

Thermal hydrolysis (TH) is effective in improving the solubilization of waste-activated sludge, but opportunities for enhancement remain, particularly in increasing organic matter conversion and reducing the generation of refractory substances. This study proposed a novel pretreatment method combining TH and potassium ferrate (PF) and evaluated its performance in improving sludge methane production. The results indicated that the combined pretreatment increased the methane yield from 118 ± 2 mL/g VS to 215 ± 7 mL/g VS, an increase of 82.2 % compared to the control. Combined pretreatment promoted the exposure of functional groups in the extracellular polymeric substances (EPS) and altered protein secondary structure composition, thereby disrupting EPS. PF improved the biodegradability of TH-treated sludge by degrading humic acids and Maillard reaction products. In addition, Fe(III) produced by PF induces dissimilar iron reduction, which enhances microbial electron transfer activity and facilitates subsequent hydrolysis and acidification processes. Combined pretreatment increased the abundance of hydrolyzing and acidifying bacteria, but reduced hydrogenotrophic methanogens. This article reveals that PF improves the biodegradability of TH-treated sludge and provides new ideas for advanced TH technologies for sludge resource recovery.

Influence of forage-to-concentrate ratio on the effects of a radiata pine bark extract on methane production and fermentation using the rumen simulation technique

Influence of forage-to-concentrate ratio on the effects of a radiata pine bark extract on methane production and fermentation using the rumen simulation technique

Regulatory effects of high concentrate diet synergistically fermented with cellulase and lactic acid bacteria: in vitro ruminal fermentation, methane production, and rumen microbiome

Regulatory effects of high concentrate diet synergistically fermented with cellulase and lactic acid bacteria: in vitro ruminal fermentation, methane production, and rumen microbiome

Pre-digestion of corn straw with kitchen waste improves synergistic methanogenic profiles at different carbon-to-nitrogen ratios

Anaerobic digestion (AD) has been widely applied for treating organic solid wastes. Particularly, the anaerobic co-digestion (AcoD) of representative lignocellulosic material and kitchen waste (KW), which exhibit distinct biodegradation behaviors, has garnered increasing attention. This study characterized the methanogenic performance of the AcoD of corn straw (CS) and KW, revealing initial-stage acidification with carbon-to-nitrogen ratios ranging from 20:1 to 30:1. The prolonged lag phase observed in this study poses a challenge for practical application. Nonetheless, composting both feedstocks prior to AD notably ameliorated acidification. Composting CS with KW played a crucial role in methane production, with the highest methane yield of 334.5mL/g VS achieved at a carbon-to-nitrogen ratio of 30:1, marking a 266.9% increase compared to the untreated group. The degradation of KW and microorganisms in composting proved beneficial for AcoD. Throughout the composting process, there was a substantial increase in the abundance of Firmicutes, Lentilactobacillus, and Limosilactobacillus. Furthermore, in the CS-pretreated samples, the archaeal community was dominated by acetoclastic methanogens, indicating increased resistance to acidification. Thus, this study offers novel insights into biomethane production through the AcoD of CS and KW.