Methane

Biogas production from organic waste is a promising renewable energy source, but achieving optimal production and digester stability can be challenging. This study investigated the impact of the Evogen microbial additive on biogas production and digester status in two biogas plants (BG01 and BG02). Microbial abundance and physicochemical parameters were analyzed to assess the effects. The results show distinct microbial community shifts in Evogen-treated digesters, with increased abundance of methanogenic archaea and hydrolytic bacteria, indicating improved anaerobic digestion. Evogen supplementation positively influenced digester performance, as evidenced by higher alkalinity buffer capacity (FOS/TAC ratios), indicating enhanced acidification and methanogenesis, along with reductions in total solids and volatile solids, demonstrating improved organic matter degradation. Evogen-treated digesters exhibited significantly higher biogas production and improved process stability, as indicated by volatile fatty acids (VFAs) profiling. The dominance of Firmicutes, Synergistetes, Proteolytic Bacteroidetes and Actinobacteria highlighted their roles in substrate degradation and VFA production. The findings contribute to optimizing biogas production systems and understanding complex microbial interactions within anaerobic digesters. The addition of Evogen influenced microbial community composition and dynamics, potentially altering substrate utilization, metabolic interactions and overall community structure. Full article

Enteric fermentation is one of the largest contributors of methane release to the environment from the livestock sector. Plant bioactive compounds can modulate rumen fermentation for reduced methanogenesis and fatty acid biohydrogenation. The present study investigates the effects of tannin extract from Ficus glomerata (FG) leaves on the rumen fermentation, methanogenesis, feed digestibility and fatty acid biohydrogenation of a total mixed ration with the aim of developing a feed supplement for enhanced livestock production and product quality with lower methane emission. The tannin extract (70% aqueous acetone extract) of FG leaves in the total mixed ration (oat hay/concentrate mixture; 1:1) was studied at four graded dose regimens (0.0 (control), 0.25 mL (FG-0.25), 0.50 mL (FG-0.50) and 1.0 mL (FG-1.0) per 60 mL of buffered rumen fluid) in three replicates for each treatment in a radio-frequency-based automatic gas production system (ANKOM-RF) at 39 °C for 24 h following the standard in vitro gas production protocol. The total gas production (mL or mL/g incubated dry matter (DM)) was gradually reduced (p < 0.01) at dose levels of FG-0.50 and FG-1.0; however, it remained intermediary and comparable (p > 0.05) for FG-0.25 with the control and FG-0.50. Compared to the control, the methane concentration (%) in the head space gas, as well as the total methane production (mL or mL/g DM incubated, or mL/g DM digested), were found to be gradually reduced (p < 0.01) with increasing doses (0.25–1.0 mL) of FG extract. The reduced (p < 0.05) feed degradability at higher levels (0.50–1.0 mL) of FG extract supplementation and the comparative (p > 0.05) effects with the control at a lower level of supplementation (FG-0.25) are suggestive of the dose-responsive detrimental effects of tannins on fibrolytic microbes in the rumen. However, the ammonia concentration decreased (p < 0.05) in all of the incubations compared to the control. Among the volatile fatty acids, acetate remained comparable (p > 0.05) with enhanced (p < 0.05) propionate at a lower dose (FG-0.25); however, a dose-dependent reduction was evident at higher dose levels (FG-0.50 and FG-1.0). The production of stearic acid (C18:0), which is a product of the rumen biohydrogenation process, was reduced (p < 0.05), irrespective of the concentration of the FG extract. Compared to the control, the concentration of t-vaccenic acid (C18:1), which is a precursor of conjugated linoleic acid (CLA) in animal products, was increased in all the FG-extract-supplemented groups. It may be concluded that Ficus glomerata leaf tannins can modulate rumen fermentation for reduced methanogenesis and fatty acid biohydrogenation in a total mixed ration. As a higher level of inclusion negatively affects feed digestibility, a lower dose (0.25 mL FG extract per 60 mL fermentation fluid or 4.17 mL FG extract per L of fermentation fluid) is suggested to achieve desirable effects on methane abatement (30%) and an improvement in fatty acid profiles in animal products. Full article

Biosurfactants are promising additives for gas hydrate technology applications. They are believed to have better eco properties than conventional kinetic hydrate promoters such as sodium dodecyl sulfate (SDS). In this article, the research advances on the use of biosurfactants for gas hydrate formation enhancement have been reviewed and discussed in detail to provide current knowledge on their progress in green chemistry technologies. Specifically, the use of bio promoters in carbon capture, gas storage and transportation are discussed. By far, biosurfactants seem to perform better than conventional hydrate promoters and have the potential to lead to the commercialization of gas hydrate-based technologies in terms of improving hydrate kinetics. Full article

Methane, a potent greenhouse gas, has gained significant attention due to its environmental impact and economic potential. Chemical industries have focused on specialized catalytic systems, like zeolites, to convert methane into methanol. However, inherent limitations in selectivity, irreversibility, and pore blockages result in high costs and energy requirements, thus hindering their commercial viability and profitability. In contrast, biological methane conversion using methanotrophs has emerged as a promising alternative, offering higher conversion rates, self-renewability, improved selectivity, and economically feasible upstream processes. Nevertheless, biological methane oxidation encounters challenges including the difficulty in cultivating methanotrophs and their slow growth rates, which hinder large-scale bioprocessing. Another highlighted limitation is the limited mass transfer of methane into liquid in bioreactors. Practical strategies to enhance methane oxidation in biological systems, including optimizing reactor design to improve mass transfer, altering metal concentrations, genetic engineering of methane monooxygenases, enzyme encapsulation, and utilizing microbial consortia are discussed. By addressing the limitations of chemical approaches and highlighting the potential of biological methods, the review concluded that the utilization of genetically engineered methanotrophic biofilms on beads within a biotrickling reactor, along with enhanced aeration rates, will likely enhance methane oxidation and subsequent methane conversion rates. Full article

Additives can improve the efficiency of anaerobic digestion by increasing biogas production, reducing air pollution, and preventing ammonia inhibition. Biological or chemical supplementation can also improve the economic efficiency of anaerobic digestion. However, the effects of specific additives on biogas production can vary, depending on the type of supplement used. This research utilizes the additives on an industrial scale and monitors the optimization of the anaerobic digestion operating parameters after their addition. The various AD additives were examined in a sufficient cycle of operation for three biogas plants located in northern Greece. In this manner, the effectiveness was investigated in multiple initial feeds and unstable operating situations caused by the seasonality of specific feedstocks. The existing operation state in the three biogas plants was recorded before and after adding the supplements. The addition of zeolite contributed to the reduction in the total ammoniacal nitrogen values in BG01 and BG03 plants. 8.4 tn of zeolite were added to the BG01 and BG03 plants over a period of two months. Low levels of trace element concentrations were observed in the BG02 plant; this issue was addressed by adding 5 kg of a trace element mixture every week over a period of 60 days. Introducing additives proved to be a stabilization factor in AD performance and an inhibition mediator. Full article

This study investigates the use of Au-doped Pd anodic electrocatalysts on ATO support for the conversion of methane to methanol. The study uses cyclic voltammetry, in situ Raman spectra, polarization curves, and FTIR analysis to determine the optimal composition of gold and palladium for enhancing the conversion process. The results demonstrate the potential for utilizing methane as a feedstock for producing sustainable energy sources. The Pd₇₅Au₂₅/ATO electrode exhibited the highest OCP value, and Pd₅₀Au₅₀/ATO had the highest methanol production value at a potential of 0.05 V. Therefore, it can be concluded that an optimal composition of gold and palladium exists to enhance the conversion of methane to methanol. The findings contribute to the development of efficient and sustainable energy sources, highlighting the importance of exploring alternative ways to produce methanol. Full article

Methane is one of the main greenhouse gases emitted by ruminants around the world. It is essential to investigate novel approaches to increasing animal production while reducing greenhouse gas emissions from ruminants. This study was conducted to examine the effect of methane inhibitors, such as nitrate, linseed oil, and anthraquinone, on nutritional digestibility, rumen fermentation processes, and methane emission in Sahiwal and Gir cattle calves. Twelve calves (6–12 months old), six of each Sahiwal and Gir breed, were selected and divided into four groups; Sahiwal control (C) and treated (T) calves; Gir control (C) and treated calves (T) of three calves each based on average body weight. Switch over a design was used as for periods 1 and 2. Animals in all groups were fed chopped oat fodder, wheat straw, and a concentrate mixture. Additionally, treated groups were fed a ration with potassium nitrate (1%), linseed oil (0.5%), and anthraquinone (4 ppm). The results revealed that the addition of methane inhibitors had no impact on nutrient intake and apparent digestibility. The levels of propionate, ammonia nitrogen, and total nitrogen were increased significantly (p < 0.05), while butyrate decreased in the treated groups of both breeds. However, there was no change in acetate and pH between the groups. Methane emission (g/d) was lower (p < 0.05) in the treated groups as compared to the control group. This study concludes that supplementation of methane inhibitors in calves feed can be utilized to lower methane emissions without affecting the intake and digestibility of nutrients. Combining diverse dietary mitigation strategies could be an effective way to mitigate methane emissions to reduce global warming while minimizing any negative impacts on ruminants to accomplish sustainable animal production. Full article

Rice husk (RH) co-combustion with natural gas in highly oxygen-enriched concentrations presents a net carbon-negative energy production opportunity while minimizing flue gas recycling. However, recent experiments have shown enhanced ash deposition rates in oxygen-enriched conditions, with deposition/shedding also being dependent on the particle size distribution (PSD) of the parent RH fuel. To uncover the causative mechanisms behind these observations, add-on models for ash deposition/shedding and radiative properties were employed in computational fluid dynamics simulations. The combustion scenarios investigated encompassed two types of RH (US RH, Chinese RH) with widely varying ash contents (by % mass) and inlet fuel PSD with air and O₂/CO₂ (70/30 vol %, OXY70) as oxidizers. Utilizing the measured fly-ash PSDs near the deposit surface and modeling the particle viscosity accurately, particle kinetic-energy (PKE)-based capture and shedding criteria were identified as the keys to accurate deposition/shedding rate predictions. The OXY70 scenarios showed higher ash-capturing propensities due to their lower PKE. Conversely, higher erosion rates were predicted in the AIR firing scenarios. In addition, the radiative characteristics across all the scenarios were dominated by the gases and were not sensitive to the fly-ash PSD. Therefore, the higher particle concentrations in the OXY70 conditions did not negatively impact the heat extraction. Full article

Sewage sludge to energy conversion is a sustainable waste management technique and a means of militating against the environmental concerns associated with its disposal. Amongst the various conversion technologies, anaerobic digestion and gasification have been identified as the two most promising. Therefore, this study is focused on a detailed evaluation of the anaerobic digestion and gasification of sewage sludge for energy production. Moreover, the key challenges hindering both technologies are discussed, as well as the practical measures for addressing them. The applicable pretreatment measures for efficient transformation into valuable energy vectors were further evaluated. Specifically, the study evaluated various properties of sewage sludge in relation to gasification and anaerobic digestion. The findings showed that a high ash content in sewage sludge results in sintering and agglomeration, while a high moisture content promotes tar formation, which has been identified as one of the key limitations of sewage sludge gasification. More importantly, the application of pretreatment has been shown to have some beneficial features in promoting organic matter decomposition/degradation, thereby enhancing biogas as well as syngas production. However, this has additional energy requirements and operational costs, particularly for thermal and mechanical methods. Full article

The Biochemical Methane Potential (BMP) assay is a vital tool for quantifying the amount of methane that specific biodegradable materials can generate in landfills and similar anaerobic environments. Applications of the protocol are extensive and while simple in design, the BMP assay can use anaerobic seed from many different types of sources to determine the methane potential from most biodegradable substrates. Many researchers use differing protocols for this assay, both including and excluding the use of synthetic growth medias, intended to provide vital nutrients and trace elements that facilitate methanogenesis and leave the substrate being tested as the only limiting factor in methane generation potential. The variety of previous approaches inspired this effort to determine the efficacy of adding synthetic growth media to BMP assays. The presented findings suggest the use of M-1 synthetic growth media, defined in this study, at a volumetric ratio of 10% active sludge: 90% M-1 media yielded optimal results in terms of gas yield and reduced variability. Full article

Electrocatalytic CO₂ reduction to valued products is a promising way to mitigate the greenhouse effect, as this reaction makes use of the excess CO₂ in the atmosphere and at the same time forms valued fuels to partially fulfill the energy demand for human beings. Among these valued products, methane is considered a high-value product with a high energy density. This review systematically summarizes the recently studied reaction mechanisms for CO₂ electroreduction to CH₄. It guides us in designing effective electrocatalysts with an improved electrocatalytic performance. In addition, we briefly summarize the recent progress on CO₂ electroreduction into CH₄ from the instructive catalyst design, including catalyst structure engineering and catalyst component engineering, and then briefly discuss the electrolyte effect. Furthermore, we also provide a simplified techno-economic analysis of this technology. These summaries are helpful for beginners to rapidly master the contents related to the electroreduction of carbon dioxide to methane and also help to promote the further development of this field. Full article

Pd_xNi_y/TiO₂ bimetallic electrocatalysts were used in fuel cell polymeric electrolyte reactors (PER-FC) to convert methane into methanol through the partial oxidation of methane promoted by the activation of water at room temperature. X-ray diffraction measurements showed the presence of Pd and Ni phases and TiO₂ anatase phase. TEM images revealed mean particle sizes larger than those reported for PdNi materials supported, indicating that TiO₂ promotes particle aggregation on its surface. Information on the surface structure of electrocatalysts obtained by Raman spectra indicated the presence or formation of NiO. The PER-FC tests showed the highest power density for the electrocatalyst with the lowest amount of nickel Pd₈₀Ni₂₀/TiO₂ (0.58 mW cm⁻²). The quantification of methanol through the eluents collected from the reactor showed higher concentrations of methanol produced, revealing that the use of TiO₂ as a support also increased the reaction rate. Full article

Isotopic fractionation of methane between gas and solid hydrate phases provides data regarding hydrate-forming environments, but the effect of pressure on isotopic fractionation is not well understood. In this study, methane hydrates were synthesized in a pressure cell, and the hydrogen isotope compositions of the residual and hydrate-bound gases were determined. The δ²H of hydrate-bound methane formed below the freezing point of water was 5.7–10.3‰ lower than that of residual methane, indicating that methane hydrate generally encapsulates lighter molecules (CH₄) instead of CH₃²H. The fractionation factors α_H-V of the gas and hydrate phases were in the range 0.9881–0.9932 at a temperature and pressure of 223.3–268.2 K and 1.7–19.5 MPa, respectively. Furthermore, α_H-V increased with increasing formation pressure, suggesting that the difference in the hydrogen isotopes of the hydrate-bound methane and surrounding methane yields data regarding the formation pressure. Although the differences in the hydrogen isotopes observed in this study are insignificant, precise analyses of the isotopes of natural hydrates in the same area enable the determination of the pressure during hydrate formation. Full article

Bioenergy recovery from biomass by-products is a promising approach for the circular bioeconomy transition. However, the management of agri-food by-products in stand-alone treatment facilities is a challenge for the low-capacity food processing industry. In this study, the techno-economic assessment of a small-scale anaerobic digestion process was evaluated for the management of jabuticaba by-product and the production of biomethane, electricity, heat, and fertilizer. The process was simulated for a treatment capacity of 782.2 m³ y⁻¹ jabuticaba peel, considering the experimental methane production of 42.31 L CH₄ kg⁻¹ TVS. The results of the scaled-up simulated process demonstrated the production of biomethane (13,960.17 m³ y⁻¹), electricity (61.76 MWh y⁻¹), heat (197.62 GJ y⁻¹), and fertilizer (211.47 t y⁻¹). Economic analysis revealed that the process for biomethane recovery from biogas is not profitable, with a net margin of −19.58% and an internal rate of return of −1.77%. However, biogas application in a heat and power unit can improve project feasibility, with a net margin of 33.03%, an internal rate of return of 13.14%, and a payback of 5.03 years. In conclusion, the application of small-scale anaerobic digestion can prevent the wrongful open-air disposal of jabuticaba by-products, with the generation of renewable energy and biofertilizer supporting the green economy toward the transition to a circular economy. Full article

Since WO₃ is a relatively abundant metal oxide and features the ability to absorb in the visible spectrum, this non-toxic semiconductor is a promising photocatalyst among sustainable materials. These properties have delivered intriguing catalytic results in the conversion of methane to methanol; however, initial investigations indicate low photocatalytic efficiency resulting from fast recombination of photogenerated charges. To explore this aspect of inefficiency, five different morphologies of WO₃ consisting of micron, nanopowder, rods, wires, and flowers were obtained and characterized. In addition, several electron capture agents/oxidizers were investigated as a means of improving the separation of photogenerated charges. The photocatalytic activity of different morphologies was assessed via CH₃OH formation rates. Based on our results, WO₃ flowers produced the highest methanol productivity (38.17 ± 3.24 µmol/g-h) when 2 mM H₂O₂ was present, which is approximately four times higher in the absence of H₂O₂. This higher methanol production has been attributed to the unique structure-related properties of the flower-like structure. Photoluminescence emission spectra and diffuse reflectance data reveal that flower structures are highly catalytic due to their reduced electron/hole recombination and multiple light reflections via petal-like hollow chambers. Full article

CO₂ methanation was studied on Ni-based yttria-stabilised zirconia (Ni/YSZ) catalysts. The catalysts were prepared by the wet impregnation method, where the amount of Ni content was varied from 5% to 75%. Thereafter, the prepared catalysts were analysed by BET, XRD, SEM and H₂-TPR. BET results showed an initial increase in the surface area with an increase in Ni loading, then a decrease after 30% Ni loading. The XRD results revealed that the Ni crystallite size increased as the Ni loading increased, while the H₂-TPR showed a shift in reduction peak temperature to a higher temperature, indicating that the reducibility of the catalysts decreased as the Ni loading increased. The activity of the synthesised catalysts for CO₂ methanation was studied by passing a mixture of H₂, CO₂ and N₂ with a total flow of 135 mL min⁻¹ and GHSV of 40,500 mL h⁻¹ g⁻¹ through a continuous flow quartz tube fixed-bed reactor (I.D. = 5.5 mm, wall thickness = 2 mm) containing 200 mg of the catalyst at a temperature range of 473 to 703 K under atmospheric pressure and a H₂:CO₂ ratio of 4. The tested Ni/YSZ catalysts showed an improvement in activity as the reaction temperature increased from 473 K to around 613 to 653 K, depending on the Ni loading. Beyond the optimum temperature, the catalyst’s activity started to decline, irrespective of the Ni loading. In particular, the 40% Ni/YSZ catalyst displayed the best performance, followed by the 30% Ni/YSZ catalyst. The improved activity at high Ni loading (40% Ni) was attributed to the increase in hydrogen coverage and improved site for both H₂ and CO₂ adsorption and activation. Full article

This paper presents the implementation of natural gas vehicles (NGVs) in Tanzania’s road transportation sector. The peculiarity of this analysis is the evaluation of the technical and economic performance of the converted gasoline and diesel engines to use compressed natural gas (CNG) as the cleanest-burning hydrocarbon. The technical performance involved vehicle mileage (MiCNG), fuel consumption (Fcons), speed drop, engine fuel enhancement (Fenh), and fuel saving, while the economic performance involved conversion cost (Cc), fuel cost saving (FCsaving), and payback (PB). Considering the conversion of gasoline vehicles, the MiCNG could reach an average of 100 to 500 km per filling, depending on the CNG cylinder size. The Fenh and fuel saving were ranging between 1.9 and 3.9 and 71 and 78%. With a proportion of 30:70 diesel-CNG fuel, the heavy-duty truck with 180 kg of CNG could reach 1300 km, saving about 440 L, which is 78.6% per roundtrip, while the medium passenger car with 15 kg of CNG could reach 350 km, presenting a fuel saving of about 75%. From an economic point of view, gasoline retrofitted NGVs cost about 50 to 200 TZS/km, yielding a fuel cost saving of up to 79% and starting to pay off between 2 and 7 months or 10,000 and 40,000 km, depending on the engine capacity. Considering dual fuel, the heavy-duty truck consumes about 496 TZS/km, saving about 62.3% of diesel fuel and starting to pay off after 2.5 months or 29,304 km. To conclude, NGV technologies have been successfully implemented in Tanzania’s road transportation sector, presenting significant fuel savings and reducing reliance on imported oil. While taking measures, this study paves a way for Tanzania and other sub-Saharan countries to promote NGV growth. Full article

The reforming of methane with CO₂ was carried out efficiently in a fluidized bed reactor at 973 K under atmospheric pressure, taking advantage of the nickel catalyst efficiency achieved with a bed of particulate fines. The fluidization operation was characterized by determining a minimum velocity of 3.11 × 10⁻³ ms⁻¹ and higher velocities. The reactor worked with surface speeds of up to 1.84 × 10⁻² ms⁻¹, providing conversions from 45% to 51% and a syngas yield of 97%. The control base of the operation focused on the use of CO₂ was established through the reaction steps assumed for the process, including methane cracking, reverse Boudouard reaction, and RWGS (reverse reaction of water gas-shift). The reactor designed to operate in two zones was able to simultaneously process surface reactions and catalyst regeneration using feed with 50% excess CO₂ in relation to methane. Predictions indicating the production of syngas of different compositions quantified with the H₂/CO ratio from 2.30 to 0.91 decreasing with space-time were validated with the results available for process design. Full article