Journal Description
Methane
Methane
is an international, peer-reviewed, open access journal on all aspects of methane published quarterly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 17.3 days after submission; acceptance to publication is undertaken in 9.7 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: APC discount vouchers, optional signed peer review, and reviewer names published annually in the journal.
Latest Articles
High-Pressure Hydrogenation: A Path to Efficient Methane Production from CO2
Methane 2024, 3(1), 53-64; https://doi.org/10.3390/methane3010004 - 15 Jan 2024
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Methane has a rather relevant role in the “Power-to-Gas” concept, which is central in the current paradigm of climate change and renewable energies. Methane, the main component of natural gas, can be produced by catalytic hydrogenation reactions, particularly of CO2. A
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Methane has a rather relevant role in the “Power-to-Gas” concept, which is central in the current paradigm of climate change and renewable energies. Methane, the main component of natural gas, can be produced by catalytic hydrogenation reactions, particularly of CO2. A very effective catalyst in this reaction, hydrotalcite-derived nickel nanoparticles supported on alumina, Ni/Al2O3-HTC, can be employed in a high-pressure flow reactor to convert CO2 and H2 into CH4 at 100% selectivity and 84% conversion, whereas at atmospheric pressure, methane can be obtained with up to 90% selectivity. The high-pressure aspect also allows fast-paced production—over 5 m3·h−1·kgcat−1 of CH4 can be generated.
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Open AccessReview
A Review on Dry Anaerobic Digestion: Existing Technologies, Performance Factors, Challenges, and Recommendations
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, , , , and
Methane 2024, 3(1), 33-52; https://doi.org/10.3390/methane3010003 - 15 Jan 2024
Abstract
With the increase in the growing rate of municipal solid waste throughout the world and due to the high moisture and organic components of the organic fraction of municipal solid waste, dry anaerobic digestion has become the future direction to cope with this
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With the increase in the growing rate of municipal solid waste throughout the world and due to the high moisture and organic components of the organic fraction of municipal solid waste, dry anaerobic digestion has become the future direction to cope with this waste while reducing the impact on the environment, including climate change. Dry anaerobic digestion has become a promising technology that converts the organic fraction of municipal solid waste into combustible biogases, which can be used as an alternative energy source. However, the technology faces several challenges that must be addressed to enhance its performance and adoption. This paper provides a comprehensive analysis of the current technologies used for dry anaerobic digestion in OFMSW and delves into the various factors that influence the performance of these technologies. This review paper also identifies and discusses the challenges faced in optimizing and scaling up these technologies, such as feedstock pretreatment requirements, characteristics of inoculum, and other crucial parameters.
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(This article belongs to the Special Issue Anaerobic Digestion Process: Converting Waste to Energy)
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Open AccessFeature PaperArticle
The Trade-Off between Enteric and Manure Methane Emissions and Their Bacterial Ecology in Lactating Cows Fed Diets Varying in Forage-to-Concentrate Ratio and Rapeseed Oil
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, , , , , and
Methane 2024, 3(1), 12-32; https://doi.org/10.3390/methane3010002 - 09 Jan 2024
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An experiment was conducted to examine how dietary interventions reducing enteric methane (CH4) emissions influence manure CH4 emissions in biogas production (as biochemical methane potential (BMP)) or under static conditions mimicking natural manure storage conditions. Experimental treatments consisted of a
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An experiment was conducted to examine how dietary interventions reducing enteric methane (CH4) emissions influence manure CH4 emissions in biogas production (as biochemical methane potential (BMP)) or under static conditions mimicking natural manure storage conditions. Experimental treatments consisted of a factorial arrangement of high (HF: 0.65) or low (LF: 0.35) levels of forage and 0 or 50 g of rapeseed oil per kg of diet dry matter. Oil supplementation reduced daily enteric CH4 emissions, especially in the HF diet, by 20%. Greater dietary concentrate proportion reduced CH4 yield and intensity (6 and 12%, respectively) and decreased pH, increased total volatile fatty acids, and molar proportions of butyrate and valerate in feces incubated under static conditions. Oil supplementation increased daily BMP and BMP calculated per unit of organic matter (OM) (17 and 15%, respectively). Increased dietary concentrate had no impact on daily BMP and BMP per unit of OM, whereas it reduced daily CH4 production by 89% and CH4 per unit of OM by 91% under static conditions. Dietary oil supplementation tended to decrease fecal CH4 production per unit of digestible OM (23%) under static conditions. Diets had no impact on the alpha diversity of ruminal prokaryotes. After incubation, the fecal prokaryote community was significantly less diverse. Diets had no effect on alpha diversity in the BMP experiment, but static trial fecal samples originating from the HF diet showed significantly lower diversity compared with the LF diet. Overall, the tested dietary interventions reduced enteric CH4 emissions and reduced or tended to reduce manure CH4 emissions under static conditions, indicating a lack of trade-off between enteric and manure CH4 emissions. The potential for increasing CH4 yields in biogas industries due to dietary interventions could lead to a sustainable synergy between farms and industry.
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(This article belongs to the Special Issue Anaerobic Digestion Process: Converting Waste to Energy)
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Open AccessReview
Relationships between Dietary Chemical Components and Enteric Methane Production and Application to Diet Formulation in Beef Cattle
Methane 2024, 3(1), 1-11; https://doi.org/10.3390/methane3010001 - 09 Jan 2024
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We used published data consisting of 263 treatment mean observations from beef cattle and dairy steers and heifers, in which CH4 was measured via chambers or head boxes, to evaluate relationships between enteric CH4 production and dry matter intake (DMI) and
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We used published data consisting of 263 treatment mean observations from beef cattle and dairy steers and heifers, in which CH4 was measured via chambers or head boxes, to evaluate relationships between enteric CH4 production and dry matter intake (DMI) and dietary components. Daily DMI was positively related (slope = 15.371, p < 0.001) to total daily production (g/d) of CH4 (r2 = 0.821). Among chemical components, dietary neutral detergent fiber (NDF) concentration was the most highly related (r2 = 0.696; slope = 0.2001; p < 0.001) to CH4 yield (g/kg of DMI), with strong relationships also noted for dietary starch:NDF ratio (r2 = 0.662; slope = −2.4587; p < 0.001), starch (r2 = 0.495; slope = −0.106; p < 0.001), and the proportion of metabolizable energy relative to gross energy (r2 = 0.561; slope = −23.663; p < 0.001). The slope (−0.5871) and intercept (22.2295) for the dietary ether extract vs. CH4 yield were significant (p < 0.001), but the relationship was highly variable (r2 = 0.150). For dietary crude protein concentration, the slope for CH4 yield was not significant (−0.0344; p < 0.381) with an r2 value near zero. Decreasing DMI by programming body weight gain or restricting feed intake could decrease CH4 production in confined cattle, but these approaches might negatively affect growth performance and product quality, potentially negating positive effects on CH4 production. Feeding higher-quality forages or using grazing management systems that decrease dietary NDF concentrations or substituting grain (starch) for forage should decrease both CH4 yield from enteric production and manure CH4 production via increased digestibility. Effects of feeding management and diet formulation strategies should be additive with other mitigation approaches such as feed additives, allowing the cattle industry to achieve maximal decreases in enteric CH4 production, while concurrently maintaining optimal beef production.
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Open AccessArticle
Dry Reforming of Methane over Li-Doped Ni/TiO2 Catalysts: Effect of Support Basicity
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, , , and
Methane 2023, 2(4), 452-469; https://doi.org/10.3390/methane2040031 - 15 Dec 2023
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In this research, we investigate the impact of Li doping on a TiO2 support, synthesized through the sol-gel method, with a focus on varying the aging time. Our objective is to elucidate how aging duration and doping influence the surface basicity, thereby
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In this research, we investigate the impact of Li doping on a TiO2 support, synthesized through the sol-gel method, with a focus on varying the aging time. Our objective is to elucidate how aging duration and doping influence the surface basicity, thereby mitigating carbon formation and amplifying the catalytic efficacy of Ni-loaded catalysts (15 wt.%). Essential characterization techniques encompass X-ray diffraction, H2-TPR, FE-SEM, N2-physisorption, DLS, FTIR, and Raman spectroscopies. Our findings reveal that extended aging periods promote the development of a basic character, attributable to oxygen defects within TiO2. This inherent trait bears significant implications for catalyst performance, stability, and carbon formation during the reaction. Remarkably, the catalyst with the highest catalytic activity and stability boasts an 85% relative basicity, a property also induced by incorporating lithium into the TiO2 support.
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(This article belongs to the Special Issue Methane Dry Reforming)
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Using Ground- and Drone-Based Surface Emission Monitoring (SEM) Data to Locate and Infer Landfill Methane Emissions
Methane 2023, 2(4), 440-451; https://doi.org/10.3390/methane2040030 - 11 Dec 2023
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Ground- and drone-based surface emission monitoring (SEM) campaigns were performed at two municipal solid waste landfills, during the same week as mobile tracer correlation method (TCM) testing was used to measure the total methane emissions from the same landfills. The G-SEM and the
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Ground- and drone-based surface emission monitoring (SEM) campaigns were performed at two municipal solid waste landfills, during the same week as mobile tracer correlation method (TCM) testing was used to measure the total methane emissions from the same landfills. The G-SEM and the D-SEM data, along with wind data, were used as input into an inverse modeling approach combined with an optimization-based methane emission estimation method (implemented in a tool called SEM2Flux). This approach involves the use of backward dispersion modeling to estimate the whole-site methane emissions from a given landfill and the identification of locations and emission rates of major leaks. SEM2Flux is designed to exploit the measured surface methane concentration concurrently with wind data and tackle two problems: (1) inferring the estimates of methane rates from individual landfills, and (2) identifying the likely locations of the main emission sources. SEM2Flux results were also compared with emission estimates obtained using TCM. In Landfill B, the average TCM-measured methane emissions was 1178 Kg/h, with a standard deviation of 271 Kg/h. In Landfill C, the average TCM-measured emission rate was 601 Kg/h, with a standard deviation of 292 Kg/h. For both landfills, the D-SEM data yielded statistically similar estimates of methane emissions as the TCM-measured emissions. On the other hand, the G-SEM data yielded comparable estimates of emissions to TCM-measured emissions only for Landfill C, where the D-SEM and G-SEM data were statistically not different. The results of this study showcase the ability of this method using surface concentrations to provide a rapid and simple estimation of fugitive methane emissions from landfills. Such an approach can also be used to assess the effectiveness of different remedial actions in reducing fugitive methane emissions from a given landfill.
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Open AccessArticle
Anaerobic Co-Digestion of Vinasse and Pentose Liquor and the Role of Micronutrients in Methane Production within Sugarcane Biorefineries
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, , , and
Methane 2023, 2(4), 426-439; https://doi.org/10.3390/methane2040029 - 08 Dec 2023
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Anaerobic digestion (AD) of residues from integrated first- and second-generation ethanol (1G2G) biorefineries is a sustainable method for energy recovery through biogas production. This study evaluated the co-digestion of 1G vinasse, 2G vinasse and pentose liquor (from the pretreatment of sugarcane bagasse for
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Anaerobic digestion (AD) of residues from integrated first- and second-generation ethanol (1G2G) biorefineries is a sustainable method for energy recovery through biogas production. This study evaluated the co-digestion of 1G vinasse, 2G vinasse and pentose liquor (from the pretreatment of sugarcane bagasse for 2G ethanol production) compared to individual digestions using biochemical methane potential (BMP) assays. The results showed some “key” micronutrients from the substrates that affected methane (CH4) production, while their balance provided by co-digestion achieved high digestibility (95%). High iron (Fe) and nickel (Ni) concentrations, in addition to furfural (0.33 g L−1) in pentose liquor seemed to decrease its CH4 production potential. Despite these adverse effects observed in mono-digestion, co-digestion was beneficial for this substrate, increasing digestibility (52%) and BMP (118%). The highest BMP was observed in vinasse 2G (631 ± 6 NmL CH4 gTVS−1), with no significant difference compared to the adjusted modified Gompertz model (624 ± 10 NmL CH4 gTVS−1). The co-digestion system also presented the highest specific CH4 production rate (20 ± 1 NmL CH4 gTVS−1day−1) and shortened the lag phase by 19% compared to the AD of isolated 1G vinasse with the second lowest BMP value (494 ± 11 NmL CH4 gTVS−1).
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Open AccessFeature PaperArticle
Density Functional Theory Insight into Chemical Vapor Infiltration
Methane 2023, 2(4), 415-425; https://doi.org/10.3390/methane2040028 - 09 Nov 2023
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Chemical Vapor Infiltration (CVI) has proven remarkably successful in producing strong and lightweight ceramic matrix composite materials. This technology has matured to regular industrial use. However, two fundamental problems remain, and those are the formation of pores and depositing of weaker material than
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Chemical Vapor Infiltration (CVI) has proven remarkably successful in producing strong and lightweight ceramic matrix composite materials. This technology has matured to regular industrial use. However, two fundamental problems remain, and those are the formation of pores and depositing of weaker material than silicon carbide ( ), namely, Si. Definitive knowledge of the molecular mechanism would catalyze an advance in the chemical precursors used in CVI. In this work, the CVI reaction is modeled using density functional theory (DFT) calculations. The DFT calculations here use the Bayesian Error Estimation Functional with van der Waals correction (BEEF-vdW). The main findings begin with C deposition determining the rate of solid growth due to Si being far more reactive. Therefore, increasing the C content of the precursor is a logical CVI strategy. Methane ( ) is more reactive than ethane ( ) and ethylene ( ) and would be effective as an additive to the chemical precursor. Increasing the deposition rate of C has the benefit of decreasing pure Si deposits. Si melts at 1410 °C and CMCs are used in high-temperature settings beyond this melting point, including in aeroengines and nuclear fuel cladding.
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Open AccessFeature PaperReview
Methane Removal from Air: Challenges and Opportunities
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Methane 2023, 2(4), 404-414; https://doi.org/10.3390/methane2040027 - 01 Nov 2023
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Driven by increasing greenhouse gas (GHG) concentrations in the atmosphere, extreme weather events have become more frequent and their impacts on human lives have become more severe. Therefore, the need for short-term GHG mitigations is urgent. Recently, methane has been recognized as an
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Driven by increasing greenhouse gas (GHG) concentrations in the atmosphere, extreme weather events have become more frequent and their impacts on human lives have become more severe. Therefore, the need for short-term GHG mitigations is urgent. Recently, methane has been recognized as an important mitigation target due to its high global warming potential (GWP). However, methane’s low concentration in the atmosphere and stable molecular structure make its removal from the air highly challenging. This review first discusses the fundamental aspects of the challenges in atmospheric methane removal and then briefly reviews the existing research strategies following the mechanisms of natural methane sinks. Although still in its infancy, recent research on methane removal from the air holds great potential for slowing down global warming. At the same time, it is important to carefully examine the energy consumption of these methane removal strategies and whether they will be able to achieve net GHG reduction. In addition, due to the scale of methane removal from the air, any potential solution’s environmental impacts must be carefully evaluated before it can be implemented in practice.
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Open AccessArticle
Autothermal Reforming of Methane: A Thermodynamic Study on the Use of Air and Pure Oxygen as Oxidizing Agents in Isothermal and Adiabatic Systems
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, , , , , and
Methane 2023, 2(4), 389-403; https://doi.org/10.3390/methane2040026 - 08 Oct 2023
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In this paper, we analyze the autothermal reforming (ATR) of methane through Gibbs energy minimization and entropy maximization methods to analyze isothermic and adiabatic systems, respectively. The software GAMS® 23.9 and the CONOPT3 solver were used to conduct the simulations and thermodynamic
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In this paper, we analyze the autothermal reforming (ATR) of methane through Gibbs energy minimization and entropy maximization methods to analyze isothermic and adiabatic systems, respectively. The software GAMS® 23.9 and the CONOPT3 solver were used to conduct the simulations and thermodynamic analyses in order to determine the equilibrium compositions and equilibrium temperatures of this system. Simulations were performed covering different pressures in the range of 1 to 10 atm, temperatures between 873 and 1073 K, steam/methane ratio was varied in the range of 1.0/1.0 and 2.0/1.0 and oxygen/methane ratios in the feed stream, in the range of 0.5/1.0 to 2.0/1.0. The effect of using pure oxygen or air as oxidizer agent to perform the reaction was also studied. The simulations were carried out in order to maintain the same molar proportions of oxygen as in the simulated cases considering pure oxygen in the reactor feed. The results showed that the formation of hydrogen and synthesis gas increased with temperature, average composition of 71.9% and 56.0% using air and O2, respectively. These results are observed at low molar oxygen ratios (O2/CH4 = 0.5) in the feed. Higher pressures reduced the production of hydrogen and synthesis gas produced during ATR of methane. In general, reductions on the order of 19.7% using O2 and 14.0% using air were observed. It was also verified that the process has autothermicity in all conditions tested and the use of air in relation to pure oxygen favored the compounds of interest, mainly in conditions of higher pressure (10 atm). The mean reductions with increasing temperature in the percentage increase of H2 and syngas using air under 1.5 and 10 atm, at the different O2/CH4 ratios, were 5.3%, 13.8% and 16.5%, respectively. In the same order, these values with the increase of oxygen were 3.6%, 6.4% and 9.1%. The better conditions for the reaction include high temperatures, low pressures and low O2/CH4 ratios, a region in which there is no swelling in terms of the oxygen source used. In addition, with the introduction of air, the final temperature of the system was reduced by 5%, which can help to reduce the negative impacts of high temperatures in reactors during ATR reactions.
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(This article belongs to the Special Issue Methane Dry Reforming)
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Matrix-Assisted Processes in CH4-Doped Ar Ices Irradiated with an Electron Beam
Methane 2023, 2(4), 372-388; https://doi.org/10.3390/methane2040025 - 07 Oct 2023
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The relaxation processes induced by exposure of the Ar matrices doped with CH4 (0.1–10%) to an electron beam were studied with a focus on the dynamics of radiolysis products—H atoms, H2 molecules, CH radicals, and energy transfer processes. Three channels of
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The relaxation processes induced by exposure of the Ar matrices doped with CH4 (0.1–10%) to an electron beam were studied with a focus on the dynamics of radiolysis products—H atoms, H2 molecules, CH radicals, and energy transfer processes. Three channels of energy transfer to dopant and radiolysis products were discussed, including free charge carriers, free excitons and photons from the “intrinsic source” provided by the emission of the self-trapped excitons. Radiolysis products along with the total yield of desorbing particles were monitored in a correlated manner. Analysis of methane transformation reactions induced by free excitons showed that the CH radical can be considered a marker of the CH3 species. The competition between exciton self-trapping and energy transfer to the dopant and radiolysis products has been demonstrated. A nonlinear concentration behavior of the H atoms in doped Ar matrices has been established. Real-time correlated monitoring of optical emissions (H atom and CH3 radicals), particle ejection, and temperature revealed a nonmonotonic behavior of optical yields with a strong luminescence flash after almost an hour of exposure, which correlated with the explosive pulse of particle ejection and temperature. The connection of this phenomenon with the processes of energy transfer and recombination reactions has been established. It is shown that the delayed explosive ejection of particles is driven by both the recombination of H atoms and CH3 radicals. This occurs after their accumulation to a critical concentration in matrices at a CH4 content C ≥ 1%.
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Exploring the Potential of Methanotrophs for Plant Growth Promotion in Rice Agriculture
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, , , , , and
Methane 2023, 2(4), 361-371; https://doi.org/10.3390/methane2040024 - 27 Sep 2023
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Rice fields are one of the important anthropogenic sources of methane emissions. Methanotrophs dwelling near the rice roots and at the oxic–anoxic interface of paddy fields can oxidize a large fraction of the generated methane and are therefore considered to be important. Nitrogen
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Rice fields are one of the important anthropogenic sources of methane emissions. Methanotrophs dwelling near the rice roots and at the oxic–anoxic interface of paddy fields can oxidize a large fraction of the generated methane and are therefore considered to be important. Nitrogen fixation in rice root-associated methanotrophs is well known. Our aim in this study was to explore the potential of methanotrophs as bio-inoculants for rice and the studies were performed in pot experiments in monsoon. Ten indigenously isolated methanotrophs were used belonging to eight diverse genera of Type Ia, Type Ib, and Type II methanotrophs, including the newly described genera and/or species, Methylocucumis oryzae and Methylolobus aquaticus, as well as Ca. Methylobacter oryzae and Ca. Methylobacter coli. Additionally, two consortia (Methylomonas strains and Methylocystis-Methylosinus strains) were used. Nitrogen fixation pathways or nifH genes were detected in all of the used methanotrophs. Plant growth promotion (PGPR) was seen in terms of increased plant height and grain yield. Nine out of twelve (seven single strains and two consortia) showed positive effects on grain yield (6–38%). The highest increase in grain yield was seen after inoculation with Ca. Methylobacter coli (38%) followed by Methylomonas consortium (35%) and Methylocucumis oryzae (31%). Methylomagnum ishizawai inoculated plants showed the highest plant height. Methylocucumis oryzae inoculated plants showed early flowering, grain formation, and grain maturation (~17–18 days earlier). In all the pot experiments, minimal quantities of nitrogen fertilizer were used with no additional organic fertilizer inputs. The present study demonstrated the possibility of developing methanotrophs as bio-inoculants for rice agriculture, which would promote plant growth under low inputs of nitrogenous fertilizers. Although the effect of methanotrophs on methane mitigation is still under investigation, their application to reduce methane emissions from rice fields could be an added advantage.
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(This article belongs to the Special Issue Trends in Methane-Based Biotechnology)
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Evaluation of Associative Effects of In Vitro Gas Production and Fermentation Profile Caused by Variation in Ruminant Diet Constituents
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, , , , , and
Methane 2023, 2(3), 344-360; https://doi.org/10.3390/methane2030023 - 12 Sep 2023
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This study aimed to investigate the associative effects caused by changes in the proportions of feed ingredients (forage-to-concentrate ratio) and the forage source in ruminant diets on in vitro gas production and fermentation parameters. The study consisted of two assays conducted in a
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This study aimed to investigate the associative effects caused by changes in the proportions of feed ingredients (forage-to-concentrate ratio) and the forage source in ruminant diets on in vitro gas production and fermentation parameters. The study consisted of two assays conducted in a completely randomized design with a 3 × 10 factorial arrangement consisting of three forages (pineapple crop waste silage [PS], corn silage [CS], and Tifton hay [TH]) associated with concentrate feed (C) (binary mixture) in 11 proportions, with triplicates of each combination. For the first assay, the asymptotic volume of gas did not show any difference among (p = 0.059) CS and PS (p = 0.464) and their proportions. We evaluated the associative effect among forages and their proportions and noticed there was an effect on gas production between the combination of forage and concentrate for the CS (p = 0.003) and PS (p = 0.003). In the second assay, volatile fatty acids (VFA) and ammonia nitrogen (p < 0.05) were affected by the forage source and concentrate inclusion. In conclusion, forages with a high content of soluble carbohydrates presented the lowest gas production, as well as higher concentrations of propionic acid and ammonia nitrogen. The associative effect on in vitro gas production was more pronounced in the first 12 h incubation. The different forage sources and the inclusion of concentrate change fermentation parameters.
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Open AccessArticle
The Effects of Using Evogen Biogas Additive on the Microbiome and Performance of Full-Scale Biogas Plant
Methane 2023, 2(3), 329-343; https://doi.org/10.3390/methane2030022 - 03 Sep 2023
Cited by 1
Abstract
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
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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.
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(This article belongs to the Special Issue Anaerobic Digestion Process: Converting Waste to Energy)
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Modulating Natural Methane Release from Rumen Fermentation through the Use of Ficus glomerata Leaf Tannins in Murrah Buffalo (Bubalus bubalis)
Methane 2023, 2(3), 319-328; https://doi.org/10.3390/methane2030021 - 10 Aug 2023
Abstract
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
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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.
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(This article belongs to the Special Issue Natural Methane Release—from Old Subsurface Origins to Recent Biogenic Production)
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Review of Biosurfactants Gas Hydrate Promoters
Methane 2023, 2(3), 304-318; https://doi.org/10.3390/methane2030020 - 08 Aug 2023
Abstract
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
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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.
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(This article belongs to the Special Issue Perspective in Natural Gas Hydrate)
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Open AccessReview
Methane Oxidation via Chemical and Biological Methods: Challenges and Solutions
by
and
Methane 2023, 2(3), 279-303; https://doi.org/10.3390/methane2030019 - 19 Jul 2023
Cited by 1
Abstract
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
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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.
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(This article belongs to the Special Issue Trends in Methane-Based Biotechnology)
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Open AccessArticle
Anaerobic Digestion Remediation in Three Full-Scale Biogas Plants through Supplement Additions
by
, , , and
Methane 2023, 2(3), 265-278; https://doi.org/10.3390/methane2030018 - 18 Jul 2023
Abstract
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,
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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.
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(This article belongs to the Special Issue Anaerobic Digestion Process: Converting Waste to Energy)
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Open AccessCommunication
Methane to Methanol Conversion Using Proton-Exchange Membrane Fuel Cells and PdAu/Antimony-Doped Tin Oxide Nanomaterials
Methane 2023, 2(3), 252-264; https://doi.org/10.3390/methane2030017 - 25 Jun 2023
Abstract
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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
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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.
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Open AccessArticle
Evaluation of Rumen Methane Emission in Sahiwal and Gir Calves Supplemented with Combination of Methanogenic Inhibitors
Methane 2023, 2(2), 241-251; https://doi.org/10.3390/methane2020016 - 07 May 2023
Abstract
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,
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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.
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(This article belongs to the Special Issue Natural Methane Release—from Old Subsurface Origins to Recent Biogenic Production)
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