Methane doi: 10.3390/methane5030022

Authors: Marek Borowski Klaudia Zwolińska-Glądys Jianwei Cheng Artur Badylak Magdalena Wojtowicz

Methane emissions from coal mines pose significant environmental and operational challenges. Methane can be released from coal seams and surrounding rock layers as a result of mining operations. These emissions pose environmental risks and can lead to fire and explosion hazards. Therefore, reducing coal mine methane emissions is essential for both protecting miners’ safety and cutting greenhouse gas emissions. Additionally, capturing methane before it escapes into the atmosphere can be economically beneficial and used as a valuable energy source. This study proposes an integrated approach that combines advanced methane capture and hydrogen production technologies to enhance both environmental performance and energy recovery in coal mining operations. By combining methane capture with hydrogen production, the study presents a practical solution for lowering greenhouse gas emissions in the coal sector. This strategy promotes the adoption of low-carbon energy sources and offers a sustainable path forward for coal-dependent regions facing decarbonization challenges. A scenario-based techno-economic analysis is presented, including investment and operating costs, hydrogen yield, energy generation potential, and greenhouse gas mitigation. Further research should focus on process optimization, the integration of carbon capture technologies, and the valorization of by-products to further reduce the environmental footprint.

Methane doi: 10.3390/methane5030021

Authors: Amit Kumar Singh Madhubala

Methane (CH4) is the second most important anthropogenic greenhouse gas, accounting for approximately 30% of current global warming. Since 2007, atmospheric methane concentrations have been increasing at an accelerating rate, reaching a record 1945.85 ppb in November 2025. The emergence of high-resolution satellite constellations has transformed our ability to detect, quantify, and attribute methane emissions from space. This review provides a comprehensive analysis of the current state of high-resolution global methane mapping, examining: (1) the evolution of satellite missions from coarse-resolution sounders like TROPOMI (5.5 × 7 km) to very high-resolution imagers including WorldView-3 (3.7 m), GHGSat (50 m), and the recently launched Tanager-1 (30 m); (2) advances in retrieval algorithms, including the transition from physics-based matched filter methods to deep learning approaches such as U-Net architectures achieving F1-scores of 78.4% on Sentinel-2 imagery; (3) integration of satellite observations with atmospheric inverse models for flux estimation; (4) the impact of satellite-derived data on policy frameworks including the Global Methane Pledge and EPA’s Super-Emitter Program; and (5) remaining challenges including cloud contamination, detection limit trade-offs, and the need for sustained validation networks. We synthesize findings from over 200 peer-reviewed studies and analyze 42 years of NOAA global methane observations to demonstrate how the convergence of improved spatial resolution, machine learning, and international coordination is enabling unprecedented transparency in global methane monitoring. The review concludes with recommendations for future satellite missions and data assimilation strategies needed to meet the Global Methane Pledge target of 30% emission reductions by 2030.

Methane doi: 10.3390/methane5030020

Authors: Romeo M. Flores

Biogenic or microbial methane (CH4) emissions, believed to be the main driver of the recent surge in global atmospheric CH4 emissions, have altered monitoring, measurement, and mitigation of fossil-fuel emissions. As of 1981, over 20% of the world’s natural gas reserves were biogenic in origin. Additional biogenic CH4 reserves from coal have been discovered since 1981 mixed (40–80%) with thermogenic CH4. Biogenic CH4 accumulates up to 100% in coal reservoirs in the Powder River Basin (PRB), USA. Biogenic CH4 is generated by microbial breakdown of fossil organic matter as an early-stage (primary) type during burial over geologic time and is rarely preserved. Also, biogenic CH4 is generated as a late-stage (secondary) type from recent geologic to present times and is commonly preserved. Late-stage biogenic CH4 is sustained by nutrients and microbes in meteoric/surface waters discharged into coal aquifers. Groundwater is pumped from wells in coal aquifers to desorb and produce CH4 and dewater coal mines. The co-produced water with dissolved CH4 is discharged into diverse surface aquatic systems. The emission factors (EFs) of co-produced water are 2.0522 × 10−9 Gg CH4/gal of water in the PRB and 2.0694 × 10−3 Gg CH4/well in the Black Warrior Basin, U.S. Accurate data on biogenic CH4 emissions from coal sources is a major gap in the accounting of current global groundwater-driven CH4 whose average flux is estimated to be 3.9 ± 6.2 mmol/m2/day or accounting for up to 70% of CH4 emissions from surface aquatic systems. Biogenic CH4 emissions from coal mining and coalbed gas extractions and related infrastructures are overlooked because the focus has been on coalmine methane (CMM) emissions. CMM data from ground-based measurements is highly variable and used by the Intergovernmental Panel on Climate Change three-tier system to estimate EFs for national inventories. However, 90% of CMM emissions are attributable to a small group of the most coal-consuming-and-producing countries but fails to capture other coal sources worldwide. This created gaps and “blind spots” in “unstructured” low-concentration, diffused biogenic CH4 emission data. These key “blind spots” include sources from flooded, abandoned coal mines; coalbed methane (CBM) co-produced water with dissolved CH4 and infrastructures/facilities; and groundwater drawdown from water withdrawals during coal mining and CBM extraction. Also, a critical “blind spot” is the mixing of biogenic CH4 emissions from subsurface coals with biogenic CH4 generated at the surface from wetlands, agriculture, and landfills/wastes, which grew 85% from 2008 to 2020. Limited understanding of the mixing of biogenic CH4 from diverse sources and their contributions to global methane requires accurate attribution of overlapping isotopic signatures (δ13CCH4 and δD). This paper addresses knowledge gaps in coalbed biogenic CH4 emissions by a systematic review of the literature and specific study cases, which provided insights on key “blind spots” in their mitigation.

Methane doi: 10.3390/methane5030019

Authors: Monica Feksa Frasson José Ignacio Gere María Esperanza Cerón-Cucchi José Ignacio Arroquy Marisa Wawrzkiewicz Gustavo Jaurena

Feed intake and diet quality are key factors influencing enteric methane (CH4) emissions in ruminants. Low-quality C4 grasses typically limit intake and are associated with high CH4 yield. Nitrogen supplementation may improve rumen function and reduce CH4 emissions per unit of feed intake, although responses under low-quality forage conditions remain insufficiently characterized. The goal of the study was to evaluate the effects of nitrogen supplementation (urea- or nitrate-containing supplements) on the utilization of low-quality weeping lovegrass hay (Eragrostis curvula) and CH4 yield in beef steers. Twenty-four Aberdeen Angus steers (326 ± 27 kg body weight) were assigned to three treatments: (1) weeping lovegrass hay alone; (2) weeping lovegrass hay + sunflower expeller + urea; and (3) weeping lovegrass hay + sunflower expeller + potassium nitrate (KNO3). The proportion of non-protein nitrogen (NPN; urea and KNO3) included in the supplements was set according to the maximum tolerated threshold. Methane emissions were measured using the SF6 tracer technique. Compared with the hay-only treatment, supplemented animals increased dry matter intake (DMI) by 35% and 38% in the urea and nitrate treatments, respectively (p < 0.01). Total CH4 emissions (g/d) were not affected by treatment (p = 0.16). However, CH4 yield (g CH4/kg DMI) decreased by 27% and 38% in the urea and nitrate treatments, respectively (p < 0.01). The methane conversion factor (Ym) was also reduced in supplemented animals. Under the conditions of this study, supplementation of low-quality weeping lovegrass hay with nitrogen-containing supplements increased feed intake and reduced CH4 yield without affecting total CH4 emissions. These findings highlight the importance of considering CH4 emission intensity, in addition to absolute emissions, when evaluating mitigation opportunities in forage-based beef production systems.

Methane doi: 10.3390/methane5020018

Authors: Sitansu Kumar Das Malaya Mohanty Satya Ranjan Samal Sasmita Chand Jagdeep Kumar Nayak Kundan Samal

Municipal solid waste (MSW) landfills are major sources of greenhouse gas (GHG) emissions, particularly methane (CH4), which possesses a significantly higher global warming potential than carbon dioxide (CO2). This study evaluates methane emission and energy recovery potential from the Okhla landfill site, South Delhi, India, using the Landfill Gas Emissions Model (LandGEM). Site-specific model parameters suitable for Indian landfill conditions (k = 0.032 year−1 and L0 = 70 m3 Mg−1) were incorporated to improve prediction accuracy. The results showed that methane generation initiated in 1997 and is expected to continue until 2068. Peak methane emission of approximately 17.15 million m3 year−1 was observed in 2020 due to rapid degradation of the biodegradable organic fraction, especially food waste. The corresponding peak total landfill gas (LFG) and CO2 emissions were approximately 35.43 million m3 year−1 and 17.71 million m3 year−1, respectively. A strong correlation (R2 = 0.9557) between cumulative waste deposition and methane generation confirmed model reliability. The estimated maximum energy recovery potential was approximately 46.19 million kWh year−1. The study further discusses the applicability of the LandGEM under non-engineered landfill conditions commonly observed in developing countries. Overall, the findings emphasize the importance of methane recovery for greenhouse gas mitigation, sustainable waste management, and renewable energy generation in urban landfill systems.

Methane doi: 10.3390/methane5020017

Authors: Isabele Giordani Wenzel Oscar W. Perez-Lopez

The use of waste eggshell as a support material for nickel catalysts in the dry reforming of methane (DRM) aims to enhance hydrogen production while controlling catalyst deactivation caused by carbon deposition. Catalyst samples were prepared by wet impregnation and characterized by N2 adsorption–desorption measurements, X-ray diffractometry (XRD), thermogravimetric analysis (TGA), temperature-programmed reduction, desorption of CO2 and oxidation (H2-TPR, CO2-TPD and TPO), and scanning electron microscopy (SEM). Catalyst activity experiments were conducted at temperatures ranging from 500 to 750 °C, with both reduced and unreduced samples, utilizing a 1.5:1 mixture of CH4 and CO2 in a fixed-bed reactor, accompanied by online gas chromatography for analysis. By employing a low calcination temperature (500 °C), the integrity of the eggshell support was maintained. The Ni20 catalyst, with an intermediate nickel loading, exhibited the highest CH4 (24.5%) and CO2 (60.5%) conversion and showed minimal carbon formation. Notably, the basicity of the eggshell support contributed to the suppression of carbon deposition, as evidenced by the TPO and SEM analyses. The results suggest that the inherent basicity of the eggshell enhances catalyst resistance to coking while also contributing to the mitigation of eggshell waste.

Methane doi: 10.3390/methane5020016

Authors: Domingo Cabrera-Gallardo Maria Camila Quintero-Quintana Francisco M. Baena-Moreno Mónica Rodríguez-Galán Fernando Vidal-Barrero

Following the rising global demand for sustainable solutions within the chemical industry, this narrative review evaluates dimethyl ether (DME) production routes focusing on both economic performance and environmental sustainability. Special focus is given to landfill biogas (LFB) as a source to obtain DME. Assessment was performed through narrative comparison of facility capacity, DME pricing, environmental impacts, and Technology Readiness Level (TRL). Studies from 2015 onwards are considered, unless well-established methods are referenced. We searched for industrial-scale studies reporting economic viability and techno-economic-environmental feasibility, including modeling plants, government reports, and conference papers in English. Two primary routes for DME synthesis are identified: the commercially proven indirect route, and an emerging, future-focused direct synthesis in a single reactor. A comparative analysis reveals that natural gas (NG) and coal are the most economical feedstocks for DME synthesis (305–485 €/t), but carry the highest environmental impacts. Biogenic feedstocks offer economic competitiveness (270–550 €/t for biomass and 350–785 €/t for biogas) with lower CO2 emissions, while renewable hydrogen and carbon capture CO2 are recognized as long-term solutions (910–2610 €/t). The timeline for their industrial realization will be determined by advancements in innovation, research, and economic incentives to bridge the price gaps existing today.

Methane doi: 10.3390/methane5020015

Authors: Ali Hamidoğlu Hao Wang

Methane generation from anaerobic biodegradation of fugitive diluent hydrocarbons is an important source of greenhouse gas emissions from oil-sands tailings, yet predictive tools that preserve hydrocarbon-level information remain limited. This study develops a hydrocarbon-resolved methane-prediction model and tests it on a case study involving a twelve-component diluent mixture containing BTEX, normal alkanes, and iso-alkanes. The model integrates stoichiometric methane yields, compound-specific lag times, Monod-type hydrocarbon consumption, logistic activation, and a single methane-conversion factor to simulate cumulative methane production and group-level methane contributions through time. Model performance is evaluated against measured methane and residual hydrocarbon data using normalized mean square error. The model reproduces cumulative methane with improved normalized mean square error relative to the existing stoichiometric benchmarks, while group-resolved outputs and robustness analyses show that predictive performance is governed primarily by conversion efficiency and lag structure. On the other hand, inclusion of an unresolved biodegradable-substrate fraction did not strengthen model agreement. These results indicate that the modeled hydrocarbon set captures the principal methane-generating substrate pool and that the proposed framework provides an accurate and mechanistically interpretable basis for methane prediction in oil-sands tailings.

Methane doi: 10.3390/methane5020014

Authors: Xiaowen Zhu Edgar Blanco Manni Bhatti Aiduan Borrion

Predicting long-term anaerobic digestion (AD) performance for food waste remains challenging because of substrate variability, process disturbance, and limited routine monitoring data. This study developed a practical framework that combines biomethane potential (BMP) test results with time-series analyses to estimate methane production during steady-state long-term AD operation. Ten paired batch and long-term datasets from three research groups were analysed. Among four BMP kinetic models, the Cone model gave the best fit in eight of 10 datasets. For long-term prediction, a 3-day sliding-window method and two Kalman filter approaches were compared. The one-dimensional Kalman filter achieved the best overall predictive accuracy, while the two-dimensional Kalman filter, which incorporated substrate conversion efficiency, provided clearer identification of persistent abnormal deviations associated with potential inhibition. The proposed framework offers a simple and localised decision support tool for methane forecasting, noise reduction, and early warning of instability when only BMP data and routine methane measurements are available.

Methane doi: 10.3390/methane5020013

Authors: Bonface O. Manono Felix Lamech Mogambi Ming’ate

Anaerobic digestion (AD) plays an important role in the circular bioeconomy by converting organic waste into renewable methane and nutrient-rich fertilizer. However, consistent, high-quality biomethane production is hindered by four main factors: hydrolysis limitations, fluctuating feedstock quality, microbial instability, and the high cost/energy demand of purification. This review explores three key areas that improve biomethane production: (i) process intensification (pretreatments and advanced reactors), (ii) microbial regulation through additives, and (iii) biogas upgrading for pipeline use. Anaerobic digestion can be greatly improved by combining thermal or hybrid pretreatments, staged digestion, high-solids technology, and electrochemical systems. These methods speed up hydrolysis and help the system handle higher amounts of organic material more effectively. However, actual performance benefits depend on specific substrate characteristics, heat integration, and control complexity. Optimizing the C:N ratio, buffering capacity, and trace-element supplementation, while simultaneously diluting toxic inhibitors, makes co-digestion an effective and adaptable approach to enhancing anaerobic digestion processes. Additives like carbon, iron nanoparticles, enzymes, and buffers can optimize digestion, but their performance is highly dependent on dosage and substrate. Additionally, they lack validation in long-term, industrial-scale applications. Conventional physicochemical techniques continue to be standard for generating high-quality biomethane, but biological methanation and microalgal systems are playing a growing role in integrating Power-to-Gas technology and using CO2 efficiently. Critical research needs to focus on four areas: (1) standardized reporting metrics, (2) AI-enabled monitoring and control, (3) coupled techno-economic and life-cycle analysis (TEA-LCA), and (4) long-term pilot or full-scale validation. Overall, comprehensive optimization of the entire flow is more effective than improving isolated parts.

Methane doi: 10.3390/methane5020012

Authors: Morokolo J. Molele Khanyisile R. Mbatha Sanele T. Jiyana Francuois L. Müller Thamsanqa D. E. Mpanza

Livestock represent a key asset in the livelihood of smallholder farmers and play a critical role in the social dynamics and nutritional security of resource-poor communities. However, within these resource-poor communities, livestock productivity remains low. This is often due to seasonal changes in the quantity and quality of available feed from the natural veld, which in turn also contributes to methane production. This study aimed to evaluate the effects of supplementing Eragrostis curvula hay with Searsia lancea leaf or silage meal on in vitro fermentation efficiency and gas and methane production. Therefore, an in vitro study using a semi-automated pressure transducer technique was conducted on grass hay alone (control) and grass hay supplemented with 15% or 30% of either S. lancea leaf or silage meal. The dietary treatments were arranged in a complete randomized design, with each treatment replicated four times. Total gas and methane production was recorded at 3, 6, 12, 24 and 48 h using a pressure transducer attached to a data logger. After incubation, samples were collected to determine volatile fatty acids. Supplementing grass hay with 15% S. lancea leaf meal increased gas production by 76%, 52%, 32% and 12% in the first 24 h of incubation. Similarly, increasing the supplementation level to 30% increased gas production by 75%, 63%, 45% and 14%. However, supplementing grass hay with silage meal at 15% significantly reduced gas production by 37% during the first 3 h of incubation, whereas supplementation at 30% had no effect. Supplementing grass hay with S. lancea meals effectively reduced methane production at 24 and 48 h. Grass hay supplemented with 15% or 30% silage meal reduced methane by 46% and 39% at 24 h, while at 48 h, methane was reduced by 39% and 49%, respectively. Supplementing grass hay with S. lancea meals, however, did not affect volatile fatty acids. In conclusion, S. lancea can be strategically used as a supplementary feed source to modulate the rumen ecosystem by attenuating enteric methane production. Further studies are required to determine the effect of S. lancea on rumen microbial composition and its metabolic function.

Methane doi: 10.3390/methane5010011

Authors: Fanying Zhang Bin Lu Jihao Zhang

The reaction of CO2 hydrogenation into CH4 provides an industrial-scale pathway for CO2 recycling. The controllable design of catalysts with highly active and stable performance is challenging, and investigation of the reaction mechanism is of great significance. In this paper, the reasonable regulation scheme on designing excellent performance catalysts is proposed, and all the reaction paths on the surface of catalysts are also analyzed in detail. It emphasized the fundamental factors influencing the activity of catalysts, and it proposed some practical strategies to effectively improve the performance of the catalysts in combination with the structure–activity relationship. This work has great significance for the optimal performance catalysts of heterogeneous catalytic systems. Furthermore, it provided a rationalized approach to designing catalysts with specific nanostructures and surface properties, such as catalytic reforming, dehydrogenation, hydrogenation, electric catalysis, and many other reactions. In addition, a critical perspective on the future challenges and opportunities in designing high performance catalysts is provided.

Methane doi: 10.3390/methane5010010

Authors: Alvise Ferrari Valerio Pampanoni Giovanni Laneve Raul Alejandro Carvajal Tellez Simone Saquella

Methane is the second most important contributor to global warming, and monitoring super-emitters from space is critical for climate mitigation. Despite the advancements in hyperspectral remote sensing, comparing methane observations across diverse imaging spectrometers remains a challenging task. Different retrieval algorithms, plume segmentation techniques and uncertainty treatments make it very hard to perform fair comparisons between different products. To overcome these difficulties, this study presents HyGAS (Hyperspectral Gas Analysis Suite), a unified, open-source framework for sensor-agnostic methane retrieval and flux estimation. Starting from the established clutter-matched-filter (CMF) formalism and a physical calibration in concentration–path-length units (ppm·m), we propagate both instrument noise and surface-driven background variability consistently from methane enhancement to Integrated Mass Enhancement (IME) and flux. The framework further includes a spectrally matched background-selection strategy, scale-aware segmentation with fixed physical criteria across resolutions, and emission-rate estimation via an IME–Ueff approach informed by Large Eddy Simulation (LES). We demonstrate the framework on near-simultaneous observations of landfills and gas infrastructure in Argentina, Turkmenistan, and Pakistan, spanning Level-1 radiance workflows (PRISMA, EnMAP, Tanager-1) and Level-2 methane products (EMIT, GHGSat). The standardised chain enables systematic inter-comparison of methane enhancement products and reduces methodological bias, supporting robust multi-mission assessment and future global monitoring.

Methane doi: 10.3390/methane5010009

Authors: Azzedine Lakhlifi Pierre R. Dahoo Mustapha Meftah

This paper investigates the different relaxation channels of a single symmetric top NH3 and a spherical top CH4 molecule trapped at low temperature in a clathrate hydrate nano-cage in the infrared absorption domain of their vibrational degrees of freedom. The approach utilizes the Born–Oppenheimer approximation and the extended site inclusion model applied to CO2 in a previous work, which was based on pairwise atom–atom effective interaction potentials. The calculations show that trapping the methane or ammonia molecule is energetically more favorable in a type sI clathrate structure than in an sII one, and entropic considerations show that methane can be released much more easily than ammonia from clathrate hydrate nano-cages. In the small (s) and large (l) nano-cages with the sI structure, the CH4 molecule exhibits a more or less perturbed rotational motion, while the NH3 molecule shows a strongly hindered orientational motion that tends to a three-dimension librational motion (oscillation motion) around its orientational equilibrium configuration. The calculated orientational energy level schemes are quite different from those of the molecular free rotation. In the static field inside the cage, degenerate ν3 and ν4 vibrational modes of methane and ammonia molecules are shifted and split. Moreover, for ammonia molecules, the ν1 and ν2 modes are shifted, and the inversion motion is no longer allowed. The non-radiative and radiative relaxation channels of CH4, NH3 and CO2 in clathrate nano-cages are discussed with reference to the matrix isolation spectroscopic results. Upon laser excitation, then, from the energy levels calculated for the different degrees of freedom, NH3 and CO2 are expected to fluoresce, while for CH4, non-radiative relaxation should lead to evaporation at the surface of clathrates. Experimental setups are suggested to localize and study these species underneath ice surfaces on distant planets or planetesimals from mobile detectors such as drones or CubeSats equipped with appropriate laser sources and telescopes with 2D imaging detectors.

Methane doi: 10.3390/methane5010008

Authors: Rebecca Bastos Boschoski Lizandro de Sousa Santos

A digital twin (DT) is an automation strategy that integrates a physical plant with an adaptive, real-time simulation environment, with bidirectional communication between them. In process engineering, DTs promise real-time monitoring, prediction of future conditions, predictive maintenance, process optimization, and control. Dashboards for process monitoring are becoming increasingly relevant for tracking key metrics and supervising industrial units in real time. Supervisory Control and Data Acquisition (SCADA) systems are widely used for process automation, with ScadaBR, an open-source, freely licensed platform. This work presents the development of a computational tool that integrates the Aspen HYSYS/Python with the ScadaBR system for real-time monitoring and supervision of dynamic models. The virtual plant, which replicates the system’s physical behavior, was connected to the SCADA platform via the Modbus protocol, enabling bidirectional data exchange between the simulated model and the supervisory interface. The system supports operational analysis and control strategy validation. Two case studies were analyzed: (i) a simplified catalytic hydrocracking process, implemented in the Python environment, and (ii) a heat exchanger networks process, simulated using the HYSYS simulator. In the second case, the process was dynamically simulated, with real-time monitoring of a simple dynamic indicator that correlates the feed methane concentration with heat transfer fluids. The results demonstrate the feasibility and applicability of the proposed approach for educational purposes, operator training, and process engineering validation, fostering a more realistic and interactive simulation environment. Furthermore, the results show that the tool is promising for dynamic monitoring of environmental and energy indices, demonstrating that methane consumption relative to process feed can be evaluated and controlled over time.

Methane doi: 10.3390/methane5010007

Authors: Bonface O. Manono

Livestock operations significantly contribute to global methane (CH4) emissions, a potent greenhouse gas. This occurs primarily through enteric fermentation (a digestive process in ruminant animals that produce methane) and manure management. This review synthesizes the current understanding of the sources of methane within livestock farming systems. It focuses on the primary drivers of these emissions, namely methane production during ruminant digestion and emissions from manure handling. The review also explores the concept of methane sinks, highlighting the processes that remove methane from the atmosphere and their role in the global methane cycle. While natural methane sinks exist, their capacity to offset methane emissions from livestock operations is limited. This review therefore discusses a range of mitigation approaches, categorized into animal and feed management, diet manipulation, rumen manipulation, and advanced technologies. Synthesizing these elements provides a clear understanding of the challenges and opportunities in addressing livestock-related methane emissions. Effective strategies should aim to reduce methane production without negatively impacting animal productivity and health. This emphasizes that addressing sustainable livestock production requires integrated approaches that simultaneously tackle climate change mitigation.

Methane doi: 10.3390/methane5010006

Authors: Helio Danilo Quevedo Ricardo Hideo Taniwaki Janaina Braga do Carmo

This study evaluated the effects of ammonium sulfate [(NH4)2SO4] addition and land-use history on greenhouse gas emissions (CH4, CO2, N2O) and inorganic nitrogen dynamics (NH4+ and NO3−) in Brazilian Cerrado soils. The objective was to determine how fertilization interacts with native and agricultural soils to regulate key biogeochemical processes. Soil samples from native and agricultural areas were collected in four regions (Araras, Sorocaba, Itirapina, and Brasília), representing contrasting pedoclimatic conditions and soil textures under different cropping systems. Samples were incubated under controlled conditions, with greenhouse gas fluxes analyzed by gas chromatography and inorganic nitrogen concentrations determined by colorimetric methods. Nitrogen fertilization inhibited CH4 consumption in native and agricultural soils and reversed fluxes to emissions in sandy soils. CO2 emissions increased in native soils but decreased in agricultural soils, suggesting effects of soil fertility and carbon stocks. N2O emissions increased mainly in native soils, reflecting intensified nitrification and denitrification, whereas agricultural soils responded heterogeneously. Nitrogen addition altered NH4+ and NO3− consumption, indicating enhanced oxidation and microbial assimilation. These results demonstrate that land-use history influences soil biogeochemical responses to nitrogen, underscoring the importance of site-specific fertilization in mitigating emissions and promoting sustainability in the Cerrado.

Methane doi: 10.3390/methane5010005

Authors: Juan Sebastián Ramírez-Navas Ana María Carabalí-Banderas

Whey and its permeates constitute highly organic, low-alkalinity dairy streams whose management remains suboptimal in many processing facilities. This narrative review integrates recent evidence on the anaerobic digestion (AD) of whey, linking substrate composition and biodegradability with microbial pathways, inhibition mechanisms, biogas quality, and techno-economic and environmental feasibility in industrial settings. Data for sweet whey, acid whey, and their permeates are synthesized, with emphasis on operational windows, micronutrient requirements, and co-digestion or C/N/P/S balancing strategies that sustain resilient methanogenic communities. Options for biogas conditioning and upgrading towards combined heat and power, boiler applications, and compressed or liquefied biomethane are examined, and selection criteria are proposed based on impurity profiles, thermal integration, and methane-recovery performance. Finally, critical R&D gaps are identified, including mechanistic monitoring, bioavailable micronutrition, modular upgrading architectures, and the valorization of digestate as a recovered fertilizer. This review provides an integrated framework to guide the design and operation of technically stable, environmentally verifiable, and economically viable whey-to-biomethane schemes for the dairy industry.

Methane doi: 10.3390/methane5010004

Authors: Jerry Celumusa Dlamini David Chadwick Laura Maritza Cardenas

Food production systems associated with livestock management are significant sources of greenhouse gases (GHGs). Livestock excreta are one of the primary sources of GHG emissions from grazing livestock. Against this context, a field experiment was established in a UK grassland to establish the extent of soil methane (CH4), carbon dioxide (CO2), andN2O fluxes upon the deposition of (i) cattle urine (U), (ii) urine + dicyandiamide (DCD) (U + DCD), (iii) artificial urine (AU), and dung (D), and compared with a (iv) control, where neither urine nor dung was applied. Excreta applications were made at three experimental periods during the grazing season: early-, mid-, and late-season. Soil N2O emissions data have been published already by co-authors; hence, this paper summarizes the emissions of soil-borne CH4 and CO2 emissions, and explores in particular, the effects of the addition of DCD, a nitrification inhibitor used to reduce direct and indirect N2O emissions from urine patches, on these (carbon) C-GHGs. Soil moisture (p = 0.47), soil temperature (p = 0.51), and nitrate (NO3−) (p = 0.049) and ammonium (NH4+) (p = 0.66) availability, and C (p = 0.54) addition were key controls of both soil CH4 and CO2 emissions. The dung treatment stimulated the production and subsequent emissions of soil CH4 and CO2, a significantly high net CH4 and CO2-based global warming potential (GWP). The findings of the current study lay a foundation for an in-depth understanding of the magnitude and dynamics of soil-borne CH4 and CO2 upon urine and dung deposition during three different seasons. This study implies that the use of DCD may have the potential to reduce carbon-based GHGs from the urine and dung of grazing animals.

Methane doi: 10.3390/methane5010003

Authors: Emma J. Daigle Mirwais M. Qaderi

Aerobically produced methane (CH4) from plants is influenced by several environmental factors, but wind velocity has yet to be investigated for its potential role in plant-derived CH4 emissions. We tested three wind velocities (0, 6, and 12 km h−1) on a wind-susceptible, Raphanus sativus (radish), and a wind-tolerant, Brassica oleracea var. sabellica (kale) plant species to investigate the effects of wind on plant-derived CH4, and to compare how varying tolerances to wind affect CH4 emissions. We found that wind exposure resulted in a decrease in leaf surface area, root and total dry mass, and an increase in leaf water potential for radish plants, while kale plants were affected minimally by wind. Radish plants emitted more CH4 than kale plants, although the effect of wind velocity on CH4 emissions and several of the measured traits was insignificant. Our study revealed that short-term exposure to lower wind velocities is generally insufficient to induce significant changes in plant growth and functioning. However, we showed that radish plants were more stressed by exposure to wind compared to kale plants, as indicated by lower plant growth and higher CH4 emissions.

Methane doi: 10.3390/methane5010002

Authors: Jiaojiao Yang Baihui Cui Xiaodong Xin Yves Iradukunda Wangwang Yan

The compositional heterogeneity of food waste greatly influences its bioconversion in microbial electrolysis cell (MEC)-assisted anaerobic digestion (AD), but the underlying mechanism remains unclear. Therefore, this study assessed two typical food wastes, i.e., starch-rich rice and cellulose-rich vegetables, on methane production, microbial constituents, and digestate dewaterability in single-chamber MECs. The results demonstrated that, while the rice-fed MEC (258.56 mL/g VS) achieved a higher methane yield compared to the vegetable-fed MEC (161.79 mL/g VS), the latter achieved higher methane purity. Temporal profiles of volatile fatty acids (VFAs) revealed rapid acidification and consumption in rice-fed systems, whereas vegetable-fed MEC exhibited delayed degradation. Additionally, the substrate type greatly influenced digestate dewaterability, since digestate from the vegetable-fed MEC exhibited lower specific resistance to filtration (3.25 × 1012 m/kg vs. 12.46 × 1012 m/kg) and capillary suction time (8.16 s·L/g vs. 19.14 s·L/g) compared to that from the rice-fed MEC. This improvement was likely attributed to high polysaccharides in extracellular polymeric substances (EPS) and cellulose’s structural properties, which promoted the formation of a porous, less compressible sludge cake that facilitated sludge dewaterability. Microbial community analysis revealed a substrate-driven specialization, as the rice-fed MECs enriched exoelectrogens (e.g., Geobacter, Trichococcus) and hydrogenotrophic methanogens (i.e., Methanobacterium), while the vegetables enriched Bacteroides and Methanosarcina. Collectively, these results suggest substrate composition profoundly influences methane yield, metabolic pathways, microbial ecology, and digestate properties in MEC-assisted AD. This work provides key insights into the role of feedstock characteristics in shaping MEC-assisted AD systems.

Methane doi: 10.3390/methane5010001

Authors: Priyanka Srivastava Sheikh S. Rahman

Neutral red (NR) is a phenazine dye that has been implicated in electron transfer processes in methanogenic archaea. NR has been previously observed to enhance methane production but its effects on Methanosarcina barkeri are unknown. This study aimed to investigate the effects of NR on M. barkeri DSM-804. M. barkeri cultures were grown in the presence of 10 and 250 µM NR for four weeks, and proteomic analysis was performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results showed that methane production was significantly reduced in the presence of NR, at lower concentrations of both 10 and 250 µM NR treatments, compared to the control. Proteomic analysis revealed the downregulation of proteins related to substrate metabolism and methanogenesis, such as the heterodisulfide reductase subunits D (HDRD_METBF) and E (HDRE_METBF), suggesting that NR hindered essential metabolic processes. Proteomic analysis also revealed that M. barkeri lacked methanophenazine in its membrane, which is a component essential for electron transport via neutral red (NR) that supports enhanced growth and methane production. Further research is needed to explore the role of methanophenazine and understand the mechanisms underlying NR’s effects of NR on methanogenesis in M. barkeri.

Methane doi: 10.3390/methane4040030

Authors: Idowu Kolawole Odubote Chisoni Mumba Shimels Wassie Christian Adjogo Bateki Andreas Wilkes

Agriculture is a significant contributor to greenhouse gas (GHG) emissions, with enteric methane (EntCH4) from cattle production being a major source. In Zambia, cattle play a critical role in rural livelihoods and food security, yet the contribution of cattle production systems to national GHG emissions remains poorly quantified. This study used the Intergovernmental Panel on Climate Change (IPCC) Tier 2 method to estimate EntCH4 from Zambia’s cattle population from 1994 to 2022. The Tier 2 method provides a more accurate estimate than the Tier 1 method by incorporating country-specific data on cattle population demographics, husbandry, and feeding practices. The results show significant variations in EntCH4 over time, driven by changes in cattle population dynamics and production practices. This study underscored the importance of transitioning from the generalized Tier 1 to the Tier 2 method to capture the unique characteristics of Zambia’s cattle production systems. The present findings provide critical insights for developing targeted mitigation strategies that will support Zambia’s ongoing efforts to address climate change while promoting sustainable livestock production.

Methane doi: 10.3390/methane4040029

Authors: Stephen A. Lloyd William J. Atteridge

The cost of “carbon net zero by year 2050” for the UK will be high, and this target date can only be achieved if the project is undertaken in a progressive and timely manner; otherwise, costs will escalate. The base power source behind the UK approach to “net zero” is nuclear fission electricity power stations, and the ones currently on order are running significantly late. Renewables will provide some supply together with interconnectors, but only approx. twenty percent of the planned wind turbines are in place. The electricity distribution grid must change to satisfy the UK’s planned “electricity-based” future. Energy use for transport is also a significant fraction of total UK energy consumption and we include predictions for their associated emissions. These must be reduced in a progressive and timely fashion. Intermittent support for unreliable renewables is necessary and methods employing both liquid as well as gaseous fuels are suggested. Means to use and upgrade the existing infrastructure are considered, and a few of the basic building blocks of the future are examined regarding their installation without significant interruption to the basic UK economy. ANR/AMR and SMR are included as potential renewables support as well as base load generators, and the approx. quantity of CO2e emissions avoided is estimated. Even though methane is a powerful greenhouse gas, the main support for renewables will be UK natural gas (methane content ~95%), with Avtur/diesel as a recommended reserve. It is suggested that methane has a significant short- to medium-term future as a transition fuel.

Methane doi: 10.3390/methane4040028

Authors: Abira Sengupta Fathima Nuzla Ismail Shanika Amarasoma

Rice cultivation accounts for roughly 10% of worldwide anthropogenic greenhouse gas emissions, making it a significant source of methane (CH4) Despite modest observational constraints, estimates of worldwide CH4 emissions from rice agriculture range from 18–115 Tg CH4 yr−1. CH4 is a potent greenhouse gas, and its oxidation produces tropospheric ozone (O3), which is harmful to public health and crop production when combined with nitrogen oxides (NOx) and sunlight. Elevated O3 levels reduce air quality, crop productivity, and human respiratory health. This study presents an AI-driven framework that combines ensemble learning, hyperparameter optimisation (HPs), and SHAP-based explainability to enhance CH4 emission predictions from rice paddies in India, Bangladesh, and Vietnam. The model consists of two stages: (1) a classification stage to distinguish between zero and non-zero CH4 emissions, and (2) a regression stage to estimate emission magnitudes for non-zero situations. The framework also incorporates O3 and asthma incidence data to assess the downstream impacts of CH4-driven ozone formation on air quality and health outcomes. Understanding the factors that drive optimal model performance and the relative importance of features affecting model outputs is still an ongoing field of research. To address these issues, we present an integrated approach that utilises recent improvements in model optimisation and employs SHapley Additive ExPlanations (SHAP) to find the most relevant variables affecting methane (CH4) emission forecasts. In addition, we developed a web-based artificial intelligence platform to help policymakers and stakeholders with climate strategy and sustainable agriculture by visualising methane fluxes from 2018 to 2020, ensuring practical applicability. Our findings show that ensemble learning considerably improves the accuracy of CH4 emission prediction, minimises uncertainty, and shows the wider benefits of methane reduction for climate stability, air quality, and public health.

Methane doi: 10.3390/methane4040027

Authors: Sheila Barry Gabriele Maier Josh S. Davy Larry Forero Andrea Warner

While methane emissions from cattle contribute to greenhouse gases, supplementing with red seaweed Asparagopsis taxiformis (AT) demonstrates an up to 90% methane reduction in controlled feeding studies. However, methods for delivery of AT in grazing systems remain unexplored. This study evaluated AT with mineral supplementation to 112 weaned steers grazing on annual rangeland over 157 days. Cattle were randomly assigned to access mineral with freeze-dried AT (targeting 150 mg bromoform/head/day) or mineral without AT. Methane emissions were measured using laser methane detection (LMD) and body weight, mineral consumption, and blood selenium levels were monitored. Average daily mineral consumption was lower than targeted, resulting in suboptimal bromoform intake (89.2 mg/head/day). No significant differences were observed between treatments for mineral consumption, weight gain, or blood selenium levels. Cattle with access to mineral with AT had lower peak emissions than control cattle when measured at day 25, but no differences in peak emissions were measured at day 115 or day 157. The lack of methane reduction was attributed to insufficient bromoform dosing, potential compound degradationduring field storage, and limitations of laser methane detection. Achieving consistent dosing and accurate methane assessment in extensive grazing systems requires improved delivery mechanisms, compound stabilization, and measurement techniques.

Methane doi: 10.3390/methane4040026

Authors: Ahmad Abuhaiba

In micro gas turbines, electrical power from the high-speed generator is delivered to the grid through a converter that influences overall efficiency and energy quality. This subsystem is often overlooked in efforts to improve turbine performance, which have traditionally focused on combustors and turbomachinery. This study investigates how replacing conventional silicon switching devices in the converter with silicon carbide technology can directly reduce greenhouse gas emissions from micro gas turbines. Although silicon carbide is widely used in electric vehicles and distributed energy systems, its emission reduction impact has not been assessed in micro gas turbines. A MATLAB-based model of a 100 kW Ansaldo Energia micro gas turbine was used to compare the performance of silicon and silicon carbide converters across the 20–100 kW operating range. Silicon carbide reduced total converter losses from 4.316 kW to 3.426 kW at full load, a decrease of 0.889 kW. This improvement lowered carbon dioxide emissions by 5.7 g/kWh and increased net electrical efficiency from 30.03% to 30.29%. Each turbine can therefore avoid about 1.53 tonnes of carbon dioxide annually, or 11.61 tonnes over a 50,000 h service life, without altering turbine design, combustor geometry, or fuel composition. This work establishes the first quantitative link between wide-bandgap semiconductor performance and direct greenhouse gas mitigation in micro gas turbines, demonstrating that upgrading converter technology from silicon to silicon carbide offers a deployable pathway to reduce emissions from micro gas turbines and, by extension, lower the carbon intensity of distributed generation systems.

Methane doi: 10.3390/methane4040025

Authors: Tim Karsten Abigail Perez Ortiz Reinhard Schomäcker Jens-Uwe Repke

In this study, three different reactor concepts for the oxidative coupling of methane (OCM) reaction are examined at the miniplant scale. Their performance and response to variations in key process parameters, such as temperature and gas hourly space velocity (GHSV), are evaluated over a wide range. In addition to the conventional Packed Bed Reactor (PBR), Packed Bed Membrane Reactor (PBMR), and Chemical Looping Reactor (CLR) approaches were tested. The PBMR was realized with a porous ceramic α-Alumina membrane as air/O2 distributor. The CLR was operated in a poly-cyclic operation. Similarities of the different reactor concepts as well as layout-immanent differences with regard to changes in reaction conditions could be identified and advantages and disadvantages of the processes highlighted. The results show that C2 selectivity can be improved by both PBMR and CLR in comparison to conventional PBR, possibly reducing cost-intensive downstream units. While a PBMR can slightly improve selectivity (23%) while keeping the same conversion compared to a PBR, the use of a CLR allows for achieving exceptionally high selectivities of up to 90%. In order to address the low conversion, CLR tests were carried out with an additional O2 carrier material, which led to a significant improvement in terms of C2 yield. In addition to an evaluation and comparison of the different reactor concepts, the findings at the miniplant scale provide estimates of their potential use and scalability.

Methane doi: 10.3390/methane4040024

Authors: Alexander Sidorenkov Viktor Ivanov

We perform a molecular dynamics simulation of a bulk eight-component hydrocarbon mixture that roughly represents a composition of hydrocarbon fluid in a volatile oil reservoir. For that goal, we have developed a method for building molecular models of hydrocarbon mixtures which can include various branched molecules. We have used self-periodical simulation boxes with different aspect ratios. Our main focus here is the phase behavior of a multicomponent mixture in the presence of gas–liquid interfaces of different shapes: spherical, cylindrical, and slab-like gas bubbles. We have developed a method for calculating properties of coexisting phases in molecular simulations of multicomponent systems. In particular, it allows us to analyze the local composition of the mixture and to calculate the molar densities of components in liquid and gas phases, and inside the interface layer between them. For the values of model parameters that we have used so far, the mixture is homogeneous at a high pressure and undergoes liquid–gas phase separation upon decreasing the pressure. We have kept the same temperature T=375.15 K, the same composition and the same number of molecules in all systems and used several combinations of the simulation box size and shape to control the overall density, and therefore also the pressure, as well as the presence or absence of a liquid–gas interface and its shape. The gas bubble that appears in the system is mainly composed of methane. There is also a small number of ethane and butane molecules, a tiny number of hexane molecules, and no molecules of heavier components at all. In the liquid phase, all components are present. We also show that inside the gas–liquid interface layer, which is actually quite broad, the molar density of methane is also higher than that of other components and even reaches a maximum value in the middle of the interface. Ethane behaves similarly: its molar density also reaches a maximum inside the interface. The molar density of heavier components grows monotonically from the inner part of the interface towards its outer part and shows a very small (almost not visible) maximum at the outer side of the bubble.

Methane doi: 10.3390/methane4040023

Authors: Waaseyaaban-nooji’iwe Landgren Robert M. Handler David R. Shonnard Mary E. Lidstrom

Methane, a greenhouse gas which has a global warming potential 80 times greater than carbon dioxide on a 20-year time scale, greatly contributes to global warming. Removing 1 Gt of atmospheric methane by 2050 would limit global temperature increase from reaching 1.5 °C. Currently, biotrickling filter systems for removing atmospheric methane via methanotrophs exist, but not for very low methane concentrations (<1 v%). Recent work at the University of Washington to isolate and improve a microbial strain which thrives at 500 ppmv CH4 has removed one obstacle in making this technology feasible. In this study, techno-economic and environmental life cycle assessment analyses conducted on this process have assessed its economic feasibility, greenhouse gas reduction potential, and possible areas of improvement. Study results show that at 500 ppmv CH4, this process could remove atmospheric methane at a cost of USD 3992–5224/tCH4. The best-performing case also produces annual net reductions in warming potential by 276–311 tCO2e/120 m3 process unit deployed. Many opportunities exist to improve the outcomes of the baseline analysis even further, especially related to reducing the transport distance of media and harvested biomass.

Methane doi: 10.3390/methane4040022

Authors: Lian He Naomi E. Kern Sergey Stolyar Mary E. Lidstrom

In 2024, the global average temperature reached 1.55 °C above the pre-industrial level for the first time. However, we could still keep the long-term global average temperature below 2 °C if all possible measures are taken to mitigate greenhouse gases. It is widely accepted that methane (CH4) mitigation can slow global warming in the near term. Among all approaches toward this goal, the utilization of aerobic methanotrophs, which are natural catalysts for the conversion of CH4, emerges as a promising solution. Previously, we identified a candidate for CH4 mitigation, Methylotuvimicrobium buryatense 5GB1C, which exhibits a greater growth rate and CH4 consumption rate than other known methanotrophs at 500 ppm CH4. In this study, we address aspects of the practical applications of this methanotroph for CH4 mitigation. We first examined temperature and medium conditions to optimize M. buryatense 5GB1C growth at 500 ppm CH4. The results show that M. buryatense 5GB1C has a broad optimal temperature range for growth at 500 ppm, from 15 °C to 30 °C, and that its growth rate is consistently improved by 20–30% in 10-fold-diluted medium. Next, to demonstrate the feasibility of CH4 removal at low concentrations by this methanotroph, we applied it in a laboratory-scale packed-bed column reactor for the treatment of 500 ppm CH4 and tested different packing materials. The column reactor experiments revealed a maximum elimination capacity of 2.1 g CH4 m−3 h−1 with 2 mm cellulose beads as the packing material. These results demonstrate that with further technological innovation, this methanotroph has the potential for real-world methane mitigation.

Methane doi: 10.3390/methane4030021

Authors: Mohammadreza Mohammadabadi Mahmoud Amiri Roudbar Moslem Momen Seyedeh Fatemeh Mousavi Mehdi Momen

Methane emissions (CH4-em) from dairy cows are a major environmental concern, contributing to greenhouse gases and energy loss in dairy cows. This study implemented advanced data analysis techniques to understand how different diet ingredients and production traits in dairy production systems can affect methane emissions. We analyzed a comprehensive meta dataset compiled from 225 peer-reviewed studies including 303 observations across multiple traits, using Bayesian networks and various machine learning models to explore the relationships between MEs, diet chemical ingredients, and production traits in dairy cattle. Eight models were applied, including linear models (OLS, LASSO, ridge, elastic net) and non-linear models (PLSR, spline regression, support vector machine, Gaussian process), to assess predictive performance. CH4-em showed correlations ranged from −0.43 (with diet starch; STR) to 0.50 (with neutral detergent fiber; NDF) for diet-related factors, and 0.18 (with body weight; BW) to 0.29 (with milk yield; MY) for production traits. Also, Bayesian network analysis indicated that CH4-em was a downstream variable for diet-related factors and an upstream variable for production traits. Additionally, the likelihood ratio test identified NDF as significant variable among the diet-related factors, while MY and milk fat (FAT) were crucial for production traits. non-linear models, particularly spline regression (SPL) and Gaussian process (GP), outperformed linear models in predicting CH4-em. For production traits, support vector machine (SVM) and GP models showed superior predictive capabilities. Model performance was evaluated using R2 and mean squared error (MSE) metrics. We found that while larger cows emitted more methane overall, they were generally more efficient, as methane intensity decreased with increasing MY regardless of body size. These findings offer valuable insights for developing sustainable methane mitigation strategies in dairy cattle production.

Methane doi: 10.3390/methane4030020

Authors: Joseph Wheatley

Methane emissions are responsible for approximately 0.5°C, or about 30%, of total greenhouse-gas-induced warming. For many countries, methane represents an even larger share of their overall warming footprint. Assessing the warming contributions of individual methane-emitting countries to global warming is not straightforward due to methane’s short atmospheric lifetime and the non-linear (convex) relationship between radiative forcing and the atmospheric concentration of this gas. This study addresses this challenge using a simple climate model in combination with a warming allocation approach derived from cooperative game theory. Applying this method, the warming contributions of several high-methane-emitting countries and regional groupings are quantified relative to the early industrial period. The analysis reveals that the commonly used marginal attribution method underestimates methane-induced warming by approximately 20%. This discrepancy is due to the substantial rise in the atmospheric concentration of methane since early industrial times.

Methane doi: 10.3390/methane4030019

Authors: Emmanuel Nwanebu Sabahudin Hrapovic Fabrice Tanguay-Rioux Rihab Gharbi Boris Tartakovsky

This study assessed the effects of NiFe-based metal catalysts on CO2 conversion to methane (CH4) and carboxylic acids in microbial electrosynthesis (MES) cells. A NiFeBi alloy, when electrodeposited on a conductive bioring cathode, significantly decreased CH4 production from 0.55 to 0.12 L (Lc d)−1 while enhancing acetate production to 1.0 g (Lc d)−1, indicating suppressed methanogenic activity and improved acetogenic activity. On the other hand, NiFeMn and NiFeSn catalysts showed varied effects, with NiFeSn increasing both CH4 and acetate production and suggesting potential in promoting both chain elongation and CO2 uptake. When these alloys were electrodeposited on a 3D-printed conductive polylactide (cPLA) lattice, the production of longer-chain carboxylic acids like butyrate and caproate increased significantly, indicating enhanced biocompatibility and nutrient delivery. The NiFeSn-coated cPLA lattice increased caproate production, which was further enhanced using an acetogenic enrichment. However, the overall throughput remained low at 0.1 g (Lc d)−1. Cyclic voltammetric analysis demonstrated improved electrochemical responses with catalyst coatings, indicating better electron transfer. These findings underscore the importance of catalyst selection and cathode design in optimizing MES systems for efficient CO2 conversion to value-added products, contributing to environmental sustainability and industrial applications.

Methane doi: 10.3390/methane4030018

Authors: Ezekiel Alaba Bryan Rainwater Ethan Emerson Ezra Levin Michael Moy Ryan Brouwer Daniel Zimmerle

Accurate methane emission estimates are essential for climate policy, yet current field methods often struggle with spatial constraints and source complexity. Ground-based mobile approaches frequently miss key plume features, introducing bias and uncertainty in emission rate estimates. This study addresses these limitations by using small unmanned aerial systems equipped with precision gas sensors to measure methane alongside co-released tracers. We tested whether arc-shaped flight paths and alternative ratio estimation methods could improve the accuracy of tracer-based emission quantification under real-world constraints. Controlled releases using ethane and nitrous oxide tracers showed that (1) arc flights provided stronger plume capture and higher correlation between methane and tracer concentrations than traditional flight paths; (2) the cumulative sum method yielded the lowest relative error (as low as 3.3%) under ideal mixing conditions; and (3) the arc flight pattern yielded the lowest relative error and uncertainty across all experimental configurations, demonstrating its robustness for quantifying methane emissions from downwind plume measurements. These findings demonstrate a practical and scalable approach to reducing uncertainty in methane quantification. The method is well-suited for challenging environments and lays the groundwork for future applications at the facility scale.

Methane doi: 10.3390/methane4030017

Authors: Kajal Pardhi Shubha Manvi Rahul A. Bahulikar Yukta Patil Yash Kadam Shirish Kadam Chandani Saraf Monali C. Rahalkar

Wetlands are the most important natural sources of methane. Studies on the distribution and diversity of methanotrophs, especially in tropical wetlands, are limited. The studies on wetland methanotrophs help bridge the gap in the literature for understanding the community structure of methanotrophs in tropical wetlands. Our present study documents the methanotroph diversity from various wetland habitats across Western India. Samples from various sites, such as freshwater ponds, lake sediments, mangroves, etc., located in Western India, were collected and enriched for methanotroph isolation. An established protocol for the isolation of methanotrophs from Indian rice fields, involving serial dilution and long-term incubations, was slightly modified and used. Obtaining entirely pure cultures of methanotrophs is a labor-intensive and technically challenging process. Hence, for primary level characterization, ‘methanotroph monocultures’, which have a single methanotroph culture with minimal contamination, were established. Twenty monocultures and eight pure cultures of methanotrophs were obtained in this study. The pmoA gene has been used for the phylogenetic characterization of methanotrophs for the last 25 years. Monocultures were from seven genera: the Methylomonas, Methylocystis, Methylosinus, Methylocaldum, Methylocucumis, Methylomagnum, and Methylolobus genera. Eight pure cultures were obtained, which were strains of Methylomonas koyamae, Methylosinus sporium, and Methylolobus aquaticus. A maximum number of cultures belonged to the Type I genus Methylomonas and to the Type II genus Methylocystis. Thus, the cultivation-based community studies of methanotrophs from wetland habitats in India expanded the current knowledge about the methanotroph diversity in such regions. Additionally, the cultivation approach helped us obtain new methanotrophs from this previously unexplored habitat, which can be used for further biotechnological and environmental applications. The isolated monocultures can either be used as MMCs (mixed methanotroph consortia) for environmental applications or further purified and used as pure cultures.

Methane doi: 10.3390/methane4030016

Authors: Joshua M. Hollingshead Makayla L. L. Ianuzzi Alexandra C. Risha Jeffrey D. Moore Grant A. Risha

This work examined the effects of secondary annular flow area on flame stability in an experimental diffusion flame burner. The burner was composed of a horizontally mounted, rectangular chamber that utilized a retractable spark plug for ignition and an inverse coaxial injector. The primary and secondary gaseous reactants were oxygen and methane, respectively. Three injectors were assessed to have a fixed primary flow area and secondary flow impingement angle of 30 degrees with the primary flow and distinct secondary annular flow areas. Resultant flames and flame standoff distances were recorded via optical windows aligned parallel to the burner axis. Flame stability regime maps were generated based on the reactant equivalence ratio, the methane Reynolds number, and the injector secondary annular flow area. Results showed that among the injectors, the greater the secondary annular flow area with an impingement angle, the better the likelihood of generating a stable, anchored, fuel-rich diffusion flame for hydrogen production over the largest range of Reynolds numbers. As the secondary flow area decreased, stable diffusion flames transitioned from existing at highly turbulent flows to experiencing near-blowoff or no ignition under the same conditions. Secondary annular flow area significantly influences the location and range of stable, anchored methane/oxygen diffusion flames.

Methane doi: 10.3390/methane4030015

Authors: Donatello Fosco Maurizio De Molfetta Pietro Alexander Renzulli Bruno Notarnicola Francesco Astuto

Quantifying methane (CH4) emissions is essential for climate change mitigation; however, current estimation methods often suffer from substantial uncertainties, particularly at the site level. This study introduces a drone-based approach for measuring CH4 emissions using an open-path Tunable Diode Laser Absorption Spectroscopy (TDLAS) sensor mounted parallel to the ground, rather than in the traditional nadir-pointing configuration. Controlled CH4 release experiments were conducted to evaluate the method’s accuracy, employing a modified mass-balance technique to estimate emission rates. Two wind data processing strategies were compared: a logarithmic wind profile (LW) and a constant scalar wind speed (SW). The LW approach yielded highly accurate results, with an average recovery rate of 98%, while the SW approach showed greater variability with increasing distance from the source, although it remained reliable in close proximity. The method demonstrated the ability to quantify emissions as low as 0.08 g s−1 with approximately 4% error, given sufficient sampling. These findings suggest that the proposed UAV-based system is a promising, cost-effective tool for accurate CH4 emission quantification in sectors, such as agriculture, energy, and waste management, where traditional monitoring techniques may be impractical or limited.

Methane doi: 10.3390/methane4030014

Authors: Tarsida N. Wedraogo Souhila Djerid Jing Wu Huai Z. Li

Biogas is a renewable energy source produced by anaerobic digestion of organic waste. It can be upgraded to bio-methane by removing carbon dioxide, water and impurities. The present work focuses on carbon dioxide removal using both physical and chemical absorption in a micromixer. The absorption efficiency in the micromixer was studied under various conditions of co-current gas–liquid flow. With physical absorption, 25% of carbon dioxide could be removed from the biogas stream (with a liquid flowrate of 40 mL/min and a gas flowrate of 25 mL/min). In absorption with a chemical reaction, up to 88% of the carbon dioxide was eliminated with a catalyst concentration of 77.4 mol·m−3. In both cases, the space time was below 3 s. Liquid-side mass transfer coefficients as large as 3.5 s−1 were achieved, which is at least two orders of magnitude higher than those reported in conventional absorbers.

Methane doi: 10.3390/methane4020013

Authors: Hajer Khelil-Arfa Sara Maria Tondini Alejandro Belanche Juan Manuel Palma-Hidalgo Alexandra Blanchard David Yáñez-Ruiz Guillermo Elcoso Alex Bach

An in vitro and an in vivo study were conducted to investigate the effects of a blend of cinnamaldehyde, eugenol, and capsicum oleoresin (CEC) on rumen fermentation parameters, animal performance, and methane (CH4) emissions in dairy cows. Continuous culture fermenters (CCF) were utilized to test one of two treatments: (1) CON; no supplementation and (2) CEC supplemented at 0.0125 g/d. The basal diet consisted of grass hay and concentrate (50:50). Supplementation with CEC increased (p < 0.01) total volatile fatty acids (VFA; mM) and decreased (p = 0.02) CH4 concentration compared with CON in vitro. Additionally, protozoa abundance tended (p = 0.07) to decrease in CEC compared with CON. The in vivo experiment utilized forty Holstein-Friesian dairy cows (32% primiparous and 68% multiparous) averaging 163 ± 48 days in milk (DIM) and 38 ± 6.2 kg/d of milk yield (MY). Cows were blocked by parity and randomly assigned to one of two treatments: (1) CON; no supplementation and (2) CEC supplemented at 1.2 g/cow/d. The basal diet consisted of grass hay and concentrate (40:60). Individual CH4 emissions were recorded using the sniffer technique. Dry matter intake (DMI) and eating rate were increased (p < 0.01; 3.6% and 5.2%, respectively), while feed efficiency decreased (p < 0.05) in CEC compared with CON. Additionally, CEC decreased (p = 0.02) CH4 yield by 16.4% and tended to reduce daily CH4 production (p = 0.09) and CH4 intensity (p = 0.08) by 13.4% and 14.0%, respectively. Supplementing CEC decreased CH4 concentration in vitro and CH4 yield in vivo without negatively impacting performance parameters.

Methane doi: 10.3390/methane4020012

Authors: Gerutu Bosinge Gerutu Esebi Alois Nyari Frank Lujaji Mathew Khilamile Kenedy Aliila Greyson Oscar Andrew Zongo Pius Victor Chombo

This study assesses the energy, economic, and environmental implications of switching Tanzania’s road transport sector to natural gas, which is slowly transitioning. In energy, the main goal is to identify the energy demand for petroleum fuel (diesel and petrol) and natural gas during the transition, while in the economy, the government revenue in the form of taxes for shifted and unshifted vehicles, as well as the loss in government revenue from petroleum fuel revenue post-transition, is assessed. In the environment, carbon emission in terms of carbon dioxide equivalent (CO2e), carbon tax revenues, and carbon credit revenues post-transition is estimated. The shift involved 10, 20, and 30% of the road vehicle population. The 10, 20, and 30% shift targeted about 142,247, 183,893, and 225,540 vehicles, which in turn dropped diesel and petrol demand by 7 and 3.68%, 7 and 3.8%, and 15 and 7.5%, respectively. In natural gas, the demand started at 0.0916 billion kg and grew exponentially by 200% and later by 300%. The transition has consequences in government revenue, which takes the form of taxes on petroleum products. The shift from 10 to 30% could lead to foregone taxes amounting to Tanzania shilling TZS 0.09, 0.31, and 0.54 trillion (US$ 33,358,680, US$ 11,490,212, and US$ 20,015,208), indicating a tax loss of about 3, 9, and 15%. Contrary, the government may benefit from these losses by lowering the amount of foreign currency necessary for oil importation. In environmental benefits, the 10, 20, and 30% shift could offset approximately 8,959,198.92119, 8,438,863.65528, and 7,918,528.38937 tCO2e, equivalent to 5.4, 10.97, and 16.47% of the road emissions. The post-transition road emissions might result in a carbon tax revenue of about US$ 71,673,591.37, 67,510,909.24, and 63,348,227.11 per year. The post-transition carbon credit revenue of about US$ 20,813,410.64, 41,626,821.27, and 62,440,231.91 is expected annually. The findings are critical for policy design and promoting a transition in the road transport sector.

Methane doi: 10.3390/methane4020011

Authors: Ioannis Kontodimos Christos Evaggelou Nikolaos Margaritis Panagiotis Grammelis Maria Goula

The present study investigates a two-stage process aimed at producing biogas from food waste leachates (FWL) through an experimental approach. The first stage involves biohydrogen production via dark fermentation (DF), while the second focuses on biomethane production through anaerobic digestion (AD). The substrate consists of leachates derived from fruit and vegetable waste, which are introduced into two continuous stirred-tank reactors (CSTR1) with two different inoculum-to-substrate ratios (ISR). Dark fermentation occurs in these reactors. The effluent from the CSTRs is then fed into two additional reactors for methanogenesis. All reactors operated under mesophilic conditions. During the DF stage, hydrogen yields were relatively low, with a maximum of 8.2 NmL H2/g VS added (ISR = 0.3) and 6.1 NmL H2/g VS added (ISR = 0.5). These results were attributed to limited biodegradation of volatile solids (VS), which reached only 21.9% and 23.6% in each respective assay. Similarly, the removal of organic matter was modest. In contrast, the AD stage demonstrated more robust methane production, achieving yields of 275.2 NmL CH4/g VS added (ISR = 0.3) and 277.5 NmL CH4/g VS added (ISR = 0.5). The system exhibited significant organic matter degradation, with VS biodegradability reaching 66%, and COD removal efficiencies of 50.8% (ISR = 0.3) and 60.1% (ISR = 0.5). The primary focus of the study was to monitor and quantify the production of the two biofuels, biohydrogen and biomethane. In conclusion, this study provides an assessment of the two biochemical conversion pathways, detailing the generation of two valuable and utilizable gaseous products. This research examines the process-specific operational conditions governing gas production, with a focus on optimizing process parameters to enhance yield and overall efficiency.

Methane doi: 10.3390/methane4020010

Authors: Wilmer Cuervo Camila Gomez-Lopez Nicolas DiLorenzo

Ruminal methanogenesis represents considerable energy loss within the fermentative processes mediated by microbial populations, by means of which up to 12% of gross energy intake is driven away from microbial protein synthesis (MPS). This review explores the relationship between methane (CH4) synthesis and emission with MPS in beef cattle, focusing on the nutritional, biochemical, and microbial factors modulating these processes. The synthesis of CH4 by ruminal archaea is essential for maintaining redox balance during the fermentation of carbohydrates. This process diverts metabolic H2 from energy-efficient pathways like propionate synthesis, which could otherwise enhance microbial growth. Dietary factors, including carbohydrate fermentability, N synchronization, and passage rate, modulate MPS. Diets based on roughage might enhance CH4 synthesis while impairing MPS efficiency by reducing diet digestibility and promoting microbial shifts towards methanogenic populations. Potential mitigation strategies, including plant secondary metabolites, CH4 inhibitors, and controlled forage-to-concentrate ratios, demonstrate the potential to reduce CH4 emissions while enhancing nutrient utilization. This review underscores the need for integrated approaches combining dietary strategies, advanced feed additives, and improved prediction models to optimize ruminal fermentation, enhance MPS, and reduce the environmental footprint of beef cattle systems.

Methane doi: 10.3390/methane4020009

Authors: Merideth Kelliher Diana Bogueva Dora Marinova

Methane, a potent greenhouse gas, has a global warming potential over 84 times greater than carbon dioxide over its relevant lifespan. Current atmospheric methane concentrations are at a record high, significantly contributing to near-term climate warming. Agriculture, particularly livestock, is a major methane emitter, accounting for 40% of global total emissions, with enteric fermentation in ruminants accounting for 90% of agricultural methane emissions. The recent interest in mitigating these emissions has centered on seaweeds, such as Asparagopsis taxiformis, which contain bromoform, a bioactive compound shown to significantly reduce enteric methane production. However, bromoform raises environmental concerns including its potential carcinogenicity and ozone-depletion effects. This study systematically reviews the environmental and ozone-related impacts of scaling up seaweed production for enteric methane reduction in livestock. Key challenges include sustainability, biodiversity risks, and upstream emissions possibly offsetting the methane reduction gains. Animal health concerns, such as reduced weight gain and mucosal irritation, also warrant attention. Additionally, supply chain logistics, cultivation and harvesting practices, and bromoform retention remain underdeveloped. The limited assessment of the ozone depletion potential underscores the need for further research. These findings highlight the need for techno-feasibility and life cycle assessment before scaling up seaweed-based solutions. A broader approach to methane mitigation, beyond feed additives, is essential to ensure sustainable outcomes for livestock agriculture.

Methane doi: 10.3390/methane4020008

Authors: Angela Bywater Jethro A. H. Adam Sigrid Kusch-Brandt Sonia Heaven

Anaerobic digesters fed with dairy cow slurry struggle to achieve economic viability, particularly when animals are housed seasonally, so additional feedstocks are usually required. This study applied experimentally derived data from the co-digestion of cow slurry (CS) and food waste (FW) to the UK dairy herd as a whole, and at average (AH) and large (LH) herd sizes of 160 and 770 animals, respectively. The experimental data confirmed stable operation at an organic loading rate (OLR) of 5 g VS L−1 day−1 at CS:FW ratios of 3:1 and 6:1 on a wet weight basis, and these parameters were considered for both AH and LH by herd size and country (Scotland, England, Wales, Northern Ireland) in order to provide energy production and policy observations. The results showed that these scenarios could provide between 959 to 23,867 GJ per year, and that a targeted policy intervention could affect slurry treatment from a significant number of animals in a relatively small number of large herds across the UK. For a more detailed analysis, better data are required on non-domestic FW arisings and FW transportation needs.

Methane doi: 10.3390/methane4010007

Authors: Ulisses Raad da Silva Coelho Adriele Maria de Cássia Crispim Maria Auxiliadora de Barros Martins Regina Mambeli Barros Maria Luiza Grillo Reno Geraldo Lucio Tiago Filho Ivan Felipe Silva dos Santos Aylla Joani Mendonça de Oliveira Pontes

This study evaluates the energy recovery from biogas generated through the anaerobic co-digestion of the Organic Fraction of Urban Solid Waste (OFUSW) with lime mud (LM). This approach aims to mitigate environmental impacts such as greenhouse gas emissions and pollution while promoting energy recovery for a diversified power matrix. Life cycle assessment (LCA) methodology, in accordance with the NBR ISO 14040 and 14044 standards, was used to compare five scenarios for the disposal of LM. The results highlight that the co-digestion scenario showed significant environmental benefits in 8 out of the 18 categories evaluated, such as reductions in eutrophication, acidification, and climate change. Additionally, the digestate produced helped avoid further environmental impacts. The integration of urban and industrial waste demonstrates the potential to enhance biogas productivity, generate savings for the pulp and paper industry, and promote sustainable practices. The innovation lies in the synergistic use of LM as a co-substrate, improving the efficiency of the anaerobic process and maximizing biogas production. This research provides a solid scientific foundation for decision-making in public policies and industrial practices, positioning itself as a viable and innovative proposal for the integrated management of solid waste and sustainable energy.

Methane doi: 10.3390/methane4010006

Authors: Bruce M. Prince

This study employs DFT at the APFD/def2-TZVP level, with SMD solvation in THF, to investigate the catalytic activation of methane by [(κ3-CNC)Fe(N₂O)]2+ cation complexes. The catalytic mechanism encompasses three key steps: oxygen atom transfer (OAT), hydrogen atom abstraction (HAA), and oxygen radical rebound (ORR). The computational results identify OAT as the rate-determining step, with activation barriers of −10.2 kcal/mol and 5.0 kcal/mol for κ1-O- and κ1-N-bound intermediates in the gas and solvent phases, respectively. Methane activation proceeds via HAA, with energy barriers of 16.0–25.2 kcal/mol depending on the spin state and solvation, followed by ORR, which occurs efficiently with barriers as low as 6.4 kcal/mol. The triplet (S = 1) and quintet (S = 2) spin states exhibit critical roles in the catalytic pathway, with intersystem crossing facilitating optimal reactivity. Spin density analysis highlights the oxyl radical character of the FeIV=O intermediate as being essential for activating methane’s strong C–H bond. These findings underscore the catalytic potential of CNC-ligated iron complexes for methane functionalization and demonstrate their dual environmental benefits by utilizing methane and reducing nitrous oxide, a potent greenhouse gas.

Methane doi: 10.3390/methane4010005

Authors: Pier Paolo Dell’Omo

The effects of milling on the anaerobic degradability of wheat straw and corn stover were investigated. Pretreatment was carried out by an industrial-scale device, able to process over one ton per hour. After 28 days of digestion under mesophilic conditions, the cumulative methane production from the pretreated straw (250 Nm3 t−1 of volatile solids) was 49.2% greater than that from the raw material. Pretreated stover reached a cumulative methane yield of 219.8 Nm3 t−1 of volatile solids, gaining 10.1% as compared to the feedstock. The specific electrical energy requirements for pretreatment were 66.6 kWh t−1 for processed straw and 64.8 kWh t−1 for stover; these consumptions were not significantly different. With reference to biomethane production, the impact of raw material on the production cost decreased from EUR 0.418 Nm−3 to EUR 0.328 Nm−3 for pretreated straw, whereas it increased by 5.8% for corn stover, whose pretreatment, therefore, was not economically feasible.

Methane doi: 10.3390/methane4010004

Authors: Qing Ye Jialin Liu Zhenzhen Jia

In order to solve the wall damage problem of roadways with deep and high stress in methane explosion accidents, mathematical-physical analysis models for the dynamic response damage of roadway walls were established by LS-Dyna software in this paper, and the models were validated to be effective. The roadway wall displacement, stress, and deformation characteristics under the methane explosion impact load were numerical simulated and the response and damage evolution process of the roadway wall was studied. The results indicate that the model established in this study can reflect the dynamic response damage characteristics of the roadway wall. The damage of the roadway wall caused by the methane explosion impact load was mainly concentrated in the methane accumulation section, but the maximum principal stress of the roadway wall near the methane accumulation section was still high, and the damage possibility was also high. The dynamic response damage of the roadway wall decreased with the increase in the distance from the initiation explosion point. The stress response of the curved part of the roadway roof was the most severe, and the stress response of the side part was second to that of the roof. The stress changes at the corners were significant, but the deformation was small. The bottom plate was minimally affected by the methane explosion impact loads. The arch top and two sides of the roadway were first subjected to significant impact, resulting in a high-pressure zone. The peak pressure of the side part was relatively high, and the difference in peak pressure between the corner and the bottom plate was not significant.

Methane doi: 10.3390/methane4010003

Authors: Alberto Costantiello Lucio Laureti Angelo Quarto Angelo Leogrande

Methane is a strong green gas that has higher GWP. Methane emissions, therefore, form one of the critical focuses within climate change mitigation policy. Indeed, the present study represents a very novel analysis of methane emission within the ESG framework by using the data across 193 countries within the period of 2011–2020. Methane reduction on account of ESG delivers prompt climate benefits and thereby preserves the core environment, social, and governance objectives. In spite of its importance, the role of methane remains thinly explored within ESG metrics. This study analyzes how factors like renewable energy use, effective governance, and socioeconomic settings influence the emission rate of the study subject, as many previous ESG studies are deficient in considering methane. By using econometric modeling, this research identifies that increasing methane emissions remain unabated with the improvement of ESG performances around the world, particularly within key agricultural and fossil fuel-based industrial sectors. Renewable energy cuts emissions, but energy importation simply transfers the burdens to exporting nations. It therefore involves effective governance and targeted internationational cooperation, as socioeconomic elements act differently in different developed and developing countries to drive various emission sources. These findings strongly call for balanced, targeted strategies to integrate actions of mitigation into ESG goals related to methane abatement.

Methane doi: 10.3390/methane4010002

Authors: Joshua O. Ighalo Faith Uchechukwu Onyema Victor E. Ojukwu Johnbosco C. Egbueri

Steam reforming is an important industrial process for hydrogen production. Acetone, the by-product of phenol production from cumene peroxidation, is a useful source of hydrogen due to its availability and low value compared to hydrogen fuel. This study aimed to utilize the Gibbs free energy minimization method using the Soave–Redlich–Kwong (SRK) equation of state (EOS) to conduct a thermodynamic analysis of the steam reforming process for pure component acetone. The steam reforming process is temperature dependent, with increasing temperatures leading to higher hydrogen production. Competing reactions, particularly the exothermic reverse water–gas shift, impact hydrogen yields beyond 650 °C. The study identified 600 °C as the optimum temperature to strike a balance between maximizing hydrogen production and minimizing the reverse water–gas shift’s impact. The optimal hydrogen yield (70 mol%) was achieved at a steam-to-oil ratio (STOR) of 12. High STOR values shift the equilibrium of the water–gas shift reaction towards hydrogen production due to increased steam, effectively consuming acetone and favoring the desired product. Atmospheric pressure is optimum for hydrogen production because the equilibrium of gas phase reactions shifts in favor of the lighter components at lower pressures.

Methane doi: 10.3390/methane4010001

Authors: Adriaan M. H. van der Veen

The evaluation of measurement uncertainty of natural gas properties calculated from composition data are an essential aspect of fiscal metering in the trade of natural gas. For conformity assessment, and in gas allocation, it is essential to have a reliable value for the uncertainty. This need is also reflected in, e.g., ISO 6976, the standard for computing natural gas properties, which follows the requirements of the “Guide to the expression of uncertainty in measurement” much more closely. Normalised compositions and their associated standard uncertainties do not suffice for this purpose. A novel algorithm is provided to recover these correlations from the normalised fractions and associated standard uncertainties, enabling the industry work with the data already stored in their repositories. The standard uncertainties are reproduced within 2%, which is acceptable for uncertainty calculations. The correlation coefficients obtained from the recovery algorithm agree with the ones obtained by normalisation.

Methane doi: 10.3390/methane3040034

Authors: Cornélio Ribeiro Garcia Michael Danilo Vargas Hincapie Regina Mambeli Barros Maxi Estefany Huamán Córdova Hellen Luisa de Castro e Silva Ivan Felipe Silva dos Santos Electo Eduardo Silva Lora Geraldo Lucio Tiago Filho João Victor Rocha de Freitas Adriele Maria de Cássia Crispim Aylla Joani Mendonça de Oliveira Pontes

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.

Methane doi: 10.3390/methane3040033

Authors: Zhenzhen Jia Qing Ye Wei Xiong Jialin Liu

During the process of mining underground coal, the coal emits a large amount of methane into the mining space, which may lead to methane accumulation and exceed explosion safety limits When the methane encounters a fire source, a methane explosion may occur. The forceful impact caused by a methane explosion in an underground roadway can cause serious damage to the roadway structures and even lead to the collapse of the ventilation system. At the same time, the explosion impact may result in the death of workers and cause physical injury to the surviving workers. Therefore, it is necessary to study the damage effect and injury range of methane explosions. On the basis of the damage criteria and damage characteristics of methane explosions, according to the overpressure distribution of shock waves in the propagation process of a methane explosion, the explosion hazard range is divided into four ranges (from inside to outside): death range, serious injury range, minor injury range, and safety range. Four injury degrees of shock wave overpressure to personal body (slight, medium, serious injury, death), and seven damage degrees of overpressure to structures are also analyzed. The thresholds of their damage (destruction) are determined. On this basis, an experimental system and numerical simulation are constructed to measure damage characteristics, the overpressure value, and the range distance of a methane explosion with different initial explosion intensities. According to the experimental and numerical results, the attenuation formula of a methane explosion shock wave in the propagation process is derived. The research results show that the overpressure and impulse of shock waves are selected as the damage criteria for comprehensive evaluation, and the overpressure criterion is suitable of determining the injury (failure) range over long distances. The four injury ranges are in line with the actual situation and are reasonable. The injury degree also conforms to the medical results, which can be used to guide the injury degree of mine methane explosions. The injury range caused by methane explosions with different initial explosion intensities is reasonable and is basically consistent with the on-site situation. The derived attenuation formula and calculated safety distance are in good agreement with the experimental and numerical results. The research results can provide guidance and help in the escape, rescue, and protection of coal mine underground person.

Methane doi: 10.3390/methane3040032

Authors: Cíntia Minori Takeda Francisco Weshley Maciel-Silva Tânia Forster-Carneiro Miriam Gonçalves Miguel

Municipal solid waste (MSW) remains in sanitary landfills for many years. To maintain a circular economy, assessing the feasibility of reinserting MSW excavated from sanitary landfills into the production chain is important. This reduces environmental impacts, helping to minimize soil, water, and air pollution resulting from the decomposition of waste in landfills. In addition, it promotes economic benefits from the energy recovery of waste, such as biomass, which can generate electricity and heat, contributing to a sustainable energy matrix. The present study aimed to evaluate the easily degradable MSW group with 24 years of landfilling (ED-24) regarding its potential for methane generation. The ED group consisted of putrescible organic matter, wood, paper, cardboard, and pruning landfilled at a sanitary landfill in Southeastern Brazil. The feasibility of valuing ED-24 as a substrate for anaerobic digestion was assessed by analyzing its physical, chemical, and biochemical characterization and calculating its theoretical methane yield (TMY). The total volatile solids (TVS) and holo-cellulose contents of ED-24 were 73.45% and 61.39%, respectively, on a dry-weight basis. These values were in the range of those determined for non-landfilled lignocellulosic materials. Thus, 24 years of landfilling partially degraded the anaerobically lignocellulosic materials. The TMY of ED-24 was 233.41 mL CH4/g TVS, indicating a potential to generate methane. Despite the high lignin value, ED-24 can be valued as a substrate for anaerobic digestion.

Methane doi: 10.3390/methane3040031

Authors: Andrés Donoso-Bravo María Constanza Sadino-Riquelme Martín Vicencio Fernando Zorrilla Bastián Valdebenito Felipe Hansen

Anaerobic digestion plays a crucial role in the transition toward a circular economy. Incorporating system supervision through mathematical modelling can enhance control and resilience. This study aims to assess the impact of scheduled digester maintenance on the effectiveness of modelling as a tool for monitoring and control. Data from a pilot-scale plug-flow digester were analyzed using an adapted ADM1 model. The maintenance involved halting the digester and removing sedimented solids. Model calibration indicated solid retention in the first two zones of the reactor, while the hydrolysis coefficient and biogas potential remained at 0.122 d−1 and 100.4 mL CH4/gVS, respectively. The average biogas production decreased from 156 to 109 mL/gVS pre- and post-maintenance. Simulations showed a decline in the model’s predictive accuracy after maintenance. To improve model fit, the initial conditions, solids retention, and kinetic parameters were adjusted. Optimal performance was achieved with khyd at 0.045 d−1 and B0 at 52.28 mL gVS−1, revealing an issue with the digester’s heating system. In conclusion, maintenance can significantly alter digester conditions, requiring model recalibration to maintain its effectiveness as a digital copilot for process supervision.

Methane doi: 10.3390/methane3040030

Authors: Ryan J. Batley Alex V. Chaves Joel B. Johnson Mani Naiker Simon P. Quigley Mark G. Trotter Diogo F. A. Costa

Several additives have been shown to reduce enteric methane emissions from ruminants when supplied in feed. However, utilising this method to deliver such methane-reducing compounds (MRCs) in extensive grazing systems is challenging. Use of livestock drinking water presents a novel method to deliver MRCs to animals in those systems. This work evaluated 13 MRCs for suitability to be deployed in this manner. Compounds were analysed for solubility and stability in aqueous solution using Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Furthermore, aqueous solutions of MRCs were subjected to variations in temperature and starting pH of water used to assess solubility and stability of the MRCs in simulated water trough conditions, also using FTIR-ATR spectroscopy. In vitro batch culture fermentations were carried out using a medium-quality tropical grass feed substrate, to simulate pastures consumed by cattle in extensive grazing systems. Measurements were made of total gas and methane production, in vitro dry matter digestibility (IVDMD), and volatile fatty acid (VFA) concentration. Of the MRCs tested, 12 were found to be soluble and stable in water using the FTIR method employed, whilst the other could not be measured. Of the 12 soluble and stable MRCs, one containing synthetic tribromomethane (Rumin8 Investigational Veterinary Product) reduced methane production by 99% (p = 0.001) when delivered aqueously in vitro, without a reduction in IVDMD (p = 0.751), with a shift towards decreased acetate and increased propionate production and decreased total VFA production (p < 0.001). Other compounds investigated also appeared suitable, and the methods developed in this study could be used to guide future research in the area.

Methane doi: 10.3390/methane3030029

Authors: Marcela Moreira Albuquerque Gabriela de Bona Sartor Walter Jose Martinez-Burgos Thamarys Scapini Thiago Edwiges Carlos Ricardo Soccol Adriane Bianchi Pedroni Medeiros

Hydrogen (H2) is a highly efficient and clean energy source with the potential for renewable energy. The production of H2 from biological routes such as biophotolysis, photofermentation, dark fermentation, and bioelectrochemical production is characterized as a renewable alternative to current production, which is mainly based on energy-intensive electrochemical and thermochemical processes and responsible for the emission of high amounts of environmentally harmful compounds. Dark fermentation is the most efficient and cost-effective method for producing biohydrogen, making it a key research focus. This article offers a comprehensive overview of the dark fermentation process with the aim of enhancing hydrogen productivity and yields. Aspects related to the main substrates used, the inoculum sources and their pretreatment, and physical-chemical parameters of the process are covered. Furthermore, this manuscript addresses topics such as process integration, genetic and metabolic engineering of fermentative microorganisms, and the main types of bioreactors aimed at greater yields and productivity of biohydrogen to enable its production through dark fermentation on a larger scale.

Methane doi: 10.3390/methane3030028

Authors: Clifford Jaylen Louime Tariq Asleem Raza

This research project aimed to address the growing concern about methane emissions from seaweed by developing a Convolutional Neural Network (CNN) model capable of accurately predicting these emissions. The study used PANDAS to read and analyze the dataset, incorporating statistical measures like mean, median, and standard deviation to understand the dataset. The CNN model was trained using the ReLU activation function and mean absolute error as the loss function. The model performance was evaluated through MAPE graphs, comparing the mean absolute percentage error (MAPE) between training and validation sets and between true and predicted emissions, and analyzing trends in yearly greenhouse gas emissions. The results demonstrated that the CNN model achieved a high level of accuracy in predicting methane emissions, with a low MAPE between the expected and actual values. This approach should enhance our understanding of methane emissions from Sargassum, contributing to more accurate environmental impact assessments and effective mitigation strategies.

Methane doi: 10.3390/methane3030027

Authors: Jesús Cruz-Navarro Fabiola Hernández-García Arturo Sánchez-Mora María Moreno-Narváez Viviana Reyes-Márquez Raúl Colorado-Peralta David Morales-Morales

The electrochemical reduction of carbon dioxide (CO2) to methane (CH4) holds tremendous potential in mitigating greenhouse gas emissions and producing renewable fuels. Thus, this review provides a comprehensive overview of the utilization of copper-based metal–organic frameworks (Cu-MOFs) as catalysts for this transformative process. Diverse key aspects of Cu-MOFs that make them ideal candidates for CO2 reduction are discussed, including their high surface areas, tunable pore sizes, and customizable active sites. Furthermore, recent advances in the design and synthesis of Cu-MOFs tailored specifically for enhanced catalytic activity and selectivity towards CH4 production are highlighted. Additionally, mechanistic insights into the CO2 reduction process on Cu-MOF catalysts are examined. Moreover, the recent application of diverse Cu-MOFs and derived materials in electrochemical reduction systems is discussed, and future research directions and potential applications of Cu-MOFs in sustainable energy conversion technologies are outlined. Thus, this review provides valuable insights into the current state of the art and the prospects for utilizing Cu-MOFs as efficient catalysts for the electrochemical conversion of CO2 to CH4, offering a pathway towards a greener and more sustainable energy future.

Methane doi: 10.3390/methane3030026

Authors: Lizbeth E. Robles-Jimenez Navid Ghavipanje Ashley Ulloa Ali Rivero Pablo Gallardo Manuel Gonzalez Ronquillo

The sustainable meeting of the global quest for ruminant intensification dictates the need to identify alternative, eco-friendly, and safe feed ingredients. In this sense, macroalgae offer a new paradigm in sustainable ruminant feed supply. This study aimed to investigate the potential of sub-Antarctic macroalgae, including Lessonia flavicans, Macrocystis pyrifera, Gigartina skottbergii, and Ulva Lactuca, regarding their chemical composition, in vitro gas production, and CH4 production. A completely randomized design consisted of a 96 h (h) incubation that included four different species and a control (alfalfa hay) with buffered rumen fluid. In vitro total gas, fermentation characteristics, and CH4 production were evaluated. The highest and the lowest crude protein (CP) contents were for U. lactuca (185.9 g/kg) and G. skottsbergi (86 g/kg), respectively (p < 0.0001). All macroalage had lower levels of natural detergent fiber (NDF) and acid detergent fiber (ADF) compared to alfalfa hay (p < 0.0001). The highest potential of gas production (b) was for M. pyriphera (162.8 mL gas/g DM), followed by alfalfa (119.3 mL gas/g DM). However, G. skottsbergi and M. pyriphera showed the highest dry matter degradability at 96 h (68.49 and 67.62 mg/100 mg, respectively; p < 0.0001) and microbial crude protein (679.8 and 669.8 mg/g, respectively, p < 0.0001). All four tested algae produced lower amounts of methane compared to alfalfa hay (p < 0.0001). After 24 h of incubation, M. pyriphera, L. flavicons, G. skottsbergi, and U. lactuca reduced CH4 by 99.7%, 98.6%, 92.9%, and 79.8%, respectively, when compared with the control. Also, all tested algae had lower (p = 0.0001) CH4 production (ml CH4/g Dry matter degradability, DMD) than alfalfa hay. The current results suggest that M. pyriphera and L. flavicons are promising feed additives for ruminants with eco-friendly production and acceptable CP content and DMD that could effectively mitigate CH4 emissions. Overall, these findings suggest that macroalgae hold promise as a substitute feed source for sustaining ruminant production at the onset of global warming.

Methane doi: 10.3390/methane3030025

Authors: Ryan J. Batley Elieder Prates Romanzini Joel B. Johnson William Luiz de Souza Mani Naiker Mark G. Trotter Simon P. Quigley Guilhermo Francklin de Souza Congio Diogo Fleury Azevedo Costa

The addition of methane-reducing compounds (MRCs) to livestock drinking water presents an alternative method for enteric methane mitigation in extensive systems where these compounds cannot be fed through the diet. This work evaluated several such compounds with the potential to be deployed in this manner. Methane-reducing compounds were selected based on the existing literature and likelihood of dissolution when combined with a commercially available water-based nutrient supplement (uPRO) (uPRO ORANGE®, DIT AgTech, QLD, Australia). This, in turn, would demonstrate the capacity for MRCs to be administered through animal drinking water when such supplements are in use. This technique requires the analysis of MRC solubility and stability in solution, which was completed via Fourier transform infrared-attenuated total reflectance spectroscopy. The uPRO supplement is comprised of urea, urea phosphate, and ammonium sulfate, providing nitrogen, phosphorus, and sulfur—limiting nutrients for ruminants grazing extensive systems during drier periods of the year. Accordingly, medium-quality Rhodes grass hay was used in fermentation runs to simulate a basal diet during the dry season. Methane-reducing compounds were assessed in accordance with each variable measured (gas/methane production, dry matter digestibility, stability under different environmental conditions) along with existing research in the field to determine the most suitable compound for co-administration. Whilst most compounds examined in this study appeared to retain their structure in solution with uPRO, fermentation results varied in terms of successful methane mitigation. The additive Agolin Ruminant L emerged as the most promising compound for further in vivo investigation.

Methane doi: 10.3390/methane3030024

Authors: Julliana Alves da Silva Adriana F. M. Braga Larissa Quartaroli Fernando G. Fermoso Marcelo Zaiat Gustavo H. R. da Silva

To achieve optimal performance, anaerobic digestion (AD) requires well-balanced operation conditions, steady physical–chemical conditions, and adequate nutrient concentrations. The use of anaerobic structured-bed reactor (ASTBR) presents these conditions. However, several additional investigations are required to elucidate robustness to treat domestic sewage (DS). This pioneering study investigated the performance of an ASTBR in treating DS across four decreasing hydraulic retention times (HRTs) (12, 8, 6, and 5 h). The study aimed to assess organic matter removal, the influence on physical–chemical parameters, and the monitoring of trace metals (TMs) during long-term operation (614 days). Overall, the results underscore the viability of employing ASTBR for DS treatment, achieving an average chemical oxygen demand (COD) removal efficiency of 70%. The system demonstrated consistent long-term operation over 614 days, maintaining stability even with decreasing hydraulic retention times (HRTs). The average effluent concentration of volatile fatty acids (VFAs) was 20.4 ± 3.3 mg L−1, with a pH value averaging 7.2 ± 0.1. TM concentrations at an HRT of 12 h exhibited higher levels in the effluent compared to the influent, gradually decreasing over the course of operation and ultimately stabilizing at levels similar to those observed in the influent. The concentrations of metals, including Ba, Cr, Fe, Mn, Ni, Pb, Se, and Zn, monitored in the effluent samples adhered to the allowable discharge thresholds as stipulated by Brazilian regulations.

Methane doi: 10.3390/methane3030023

Authors: Yoshiaki Kitaya Siqinbatu Ryosuke Endo Toshio Shibuya

To develop technology to efficiently utilize digestate from methane fermentation in agricultural production, the application of digestate from methane fermentation for supplying nutrients in sweet potato cultivation was investigated in sandy soil. Different strengths of diluted digestate with water were applied to sweet potato plants as water and nutrient supplies to determine the appropriate strength of digestate from methane fermentation for sweet potato production in sandy soil. The growth of sweet potato cultivated with diluted digestate was also compared with that of sweet potato cultivated with a commercial chemical nutrient solution. The growth rate of the tuberous roots with the strength of 1/20 of the digestate was greatest among the treatments with different digestate strengths (1/80–1/2) and commercial nutrient solutions (1/4–1). Consequently, we proposed a sweet potato production system using a bottom irrigation method with digestate from methane fermentation, which will be applicable in semiarid regions. In conclusion, the results of this study can be effectively used in a regional agricultural system combined with a methane fermentation system and can contribute to increasing food production as well as the establishment of a resource recycling society.

Methane doi: 10.3390/methane3030022

Authors: Bradley Ridoutt

Ruminant livestock industries can support the climate stabilization ambitions of the Paris Agreement through interventions that reduce GHG emissions (predominantly biogenic methane) and sequester carbon in landscapes. This study explored pathways for the Australian red meat industry (grazing, feedlot finishing, and domestic processing) to become climate neutral, whereby the radiative forcing (RF) footprint is plateaued and there is no additional forcing contribution. Emissions timeseries (CO2, N2O, CH4) were compiled for 1990 to 2020 and projected to 2030 under a business-as-usual scenario (including an 18% increase in sheep and 13% increase in beef cattle) and with a range of production system and vegetation management interventions. The RF footprint peaked in 2018 at 7.13 mW/m2 and decreased to 7.07 mW/m2 in 2020. With the future expansion of the herd/flock and under business-as-usual conditions, the RF footprint is projected to increase by 2.8% by 2030. However, with a combination of interventions, production has the potential to increase with a decreasing RF footprint, a condition that can be described as climate neutral. The Australian red meat industry has made an historical contribution to global RF increase. However, with ongoing RF management, it is possible to increase food production within climate-neutral limits.

Methane doi: 10.3390/methane3030021

Authors: Mirwais M. Qaderi Kate Burton

Previous studies have shown that light quality and quantity affect methane emissions from plants. However, the role of photoperiod in plant-derived methane has not been addressed. We studied the effects of two photoperiods—long-day (16 h light/8 h dark), and short-day (8 h light/16 h dark)—on growth and methane emissions of lettuce (a long-day plant), mung bean (a short-day plant), and tomato (a day-neutral plant) under a temperature regime of 22/18 °C. All species were grown under both light durations. First, seeds were germinated in Petri dishes for one week, then plants were transferred to pots and randomly assigned to one of the two experimental conditions. Under each condition, twelve plants were grown for 21 days; at that time, plant growth and physiological traits, including plant dry mass, growth index, photosynthesis, chlorophyll fluorescence, total chlorophyll, nitrogen balance index, flavonoids, and anthocyanin, were measured. Lettuce plants under the short-day photoperiod had the highest methane emissions. Long-day plants that were exposed to short-day conditions and short-day plants that were exposed to long-day conditions were stressed; day-neutral plants were also stressed under short days (p < 0.05). All three species had decreased total dry mass under short-day conditions, most likely because of decreased photosynthesis and increased transpiration and stomatal conductance. Methane emission was positively correlated with shoot/root mass ratio, nonphotochemical quenching and anthocyanin; but was negatively correlated with stem height, dry mass, photosynthesis, water-use efficiency, total chlorophyll, and flavonoids (p < 0.05). This study revealed that, besides light intensity and quality, light duration can also affect methane emissions from plants.

Methane doi: 10.3390/methane3020020

Authors: Felipe Anchieta e Silva Thenner Silva Rodrigues

This study investigates the utilization of controlled nanocatalysts in methane conversion reactions, addressing the pressing need for the efficient utilization of methane as a feedstock for valuable chemicals and clean energy. The methods employed include a comprehensive review of recent advancements in nanocatalyst synthesis, characterization, and application, as well as the critical analysis of underlying mechanisms and controversies in methane activation and transformation. The main findings reveal significant progress in the design and synthesis of controlled nanocatalysts, enabling enhanced activity, selectivity, and stability in methane conversion reactions. Moreover, the study highlights the importance of resolving controversies surrounding metal–support interactions for rational catalyst design. Overall, the study underscores the pivotal role of nanotechnology in shaping the future of methane utilization and sustainable energy production, providing valuable insights for guiding future research directions and technological developments in this field.

Methane doi: 10.3390/methane3020019

Authors: Tarsida N. Wedraogo Jing Wu Huai Z. Li

In the present study, a comparison of the dry reforming of a gas mixture containing methane, carbon dioxide and nitrogen without contaminants to a ruthenium-based Ru/Al2O3 catalyst was carried out in a microreactor for the first time. The influence of the contact time, temperature and composition of the feed on the conversion was exhaustively investigated. The optimal operating conditions were found to be a contact time of 80 milliseconds, a temperature of 700 °C and a CH4:CO2 ratio of 1. The assessment of diffusional limitations reveals that there is no resistance to mass transfer, which reveals the potential benefit of the determination of intrinsic reaction kinetics within a microreactor.

Methane doi: 10.3390/methane3020018

Authors: Yuchen Liu Masanori Kurihara

To solve the sand problem during the depressurization of methane hydrate (MH), we proposed a method to build a porous grout body with sufficient permeability and strength around the wellbore through inhibitor pre-injection and grouting, and verified its effectiveness and potential in our previous research using artificial cores created with silica sand and alternative hydrates such as TBAB- hydrate and iso-butane hydrate. However, all of the artificial cores mentioned above were created with high homogeneity, injected, cured, and had their physical properties measured in the vertical direction, which differs from real reservoir conditions. To investigate the effects of grouting in a more realistic fluid flow, we conducted further experiments using horizontal 1D cores, 1D cubic models, and a 2D cross-sectional model mimicking the near wellbore. These experiments revealed that (1) the generated gas somewhat suppressed the effects of grouting as in the case of previous experiments, and (2) grouted reservoirs would be heterogenous and anisotropic due to the fluid densities and the distribution of grout particles and turbidite sediments, but sufficient permeability and satisfactory strength could still be attained. The above series of experiments demonstrated that our method has the potential to effectively produce actual MH, preventing sand problems even in heterogeneous and anisotropic grouted reservoirs.

Methane doi: 10.3390/methane3020017

Authors: Letícia Rodrigues de Melo Bruna Zerlotti Demasi Matheus Neves de Araujo Renan Coghi Rogeri Luana Cardoso Grangeiro Lucas Tadeu Fuess

This study mapped the bioenergy production from sugarcane vinasse according to the mesoregions of the State of São Paulo (SP), Brazil, assessing the magnitude of biogas-derived electricity and biomethane production and estimating the greenhouse gas (GHG) emissions. SP holds 45% of the Brazilian ethanol-producing plants, in which 1.4 million m3 of carbon-rich vinasse are generated daily. The electricity generated from vinasse has the potential to fully supply the residential consumption (ca. 6.5 million inhabitants) in the main sugarcane-producing mesoregions of the state (Ribeirão Preto, São José do Rio Preto, Bauru, Araçatuba and Presidente Prudente). In another approach, biomethane could displace almost 3.5 billion liters of diesel, which represents a 26% abatement in the annual state diesel consumption. Energetically exploiting biogas is mandatory to prevent GHG-related drawbacks, as the eventual emission of methane produced under controlled conditions (261.2 × 106 kg-CO2eq d−1) is ca. 7-fold higher than the total emissions estimated for the entire ethanol production chain. Meanwhile, replacing diesel with biomethane can avoid the emission of 45.4 × 106 kg-CO2eq d−1. Implementing an efficient model of energy recovery from vinasse in SP has great potential to serve as a basis for expanding the utilization of this wastewater in Brazil.

Methane doi: 10.3390/methane3020016

Authors: Stephen Okiemute Akpasi Joseph Samuel Akpan Ubani Oluwaseun Amune Ayodeji Arnold Olaseinde Sammy Lewis Kiambi

The role of methane (CH4) in the 21st century presents a critical dilemma. Its abundance and clean-burning nature make it a promising energy source, while its potent greenhouse effect threatens climate stability. Despite its potent greenhouse gas (GHG) nature, CH4 remains a crucial energy resource. However, advancements in CH4 capture, utilization, and emissions mitigation are rapidly evolving, necessitating a critical assessment of the advances, their potential, and challenges. This study aims to comprehensively evaluate the current state of the art in these advancements, particularly focusing on the emissions trends, with corresponding global warming potentials of projected CH4 emissions, and a discussion on the advances that have been made towards reducing the impacts of CH4 emissions. The areas of these advances include measurement, computational, numerical modeling, and simulation studies for CH4, emerging technologies for CH4 production, management and control, the nexus of CH4 –X, and case study applications in countries. This study reports on these advances, which involves a technical review of studies, mainly from the last decade, discussing the technical feasibility, economic viability, and environmental impact of these advancements. Our trend analysis reveals that even though the share of CH4 in the GHG mix has been around 19% compared with carbon dioxide (CO2), still, CH4 reduction would need to be highly subsidized because of the high global warming potential it has, compared with CO2. We conclude that while significant progress has been made, further research and development are essential to optimize the performance, scalability, and affordability of these advancements. Additionally, robust policy frameworks and international collaborations are crucial to ensure widespread adoption and maximize the potential that comes with the advancements in the mitigation of the impact of CH4 emission. This study contributes to the ongoing dialogue on balancing the potentials of CH4 with its environmental footprint, paving the way for a future where this versatile resource can be utilized sustainably.

Methane doi: 10.3390/methane3020015

Authors: Moritz Schroll Katharina Lenhart Thomas Bender Piet Hötten Alexander Rudolph Sven Sörensen Frank Keppler

Saprotrophic fungi, key players in global carbon cycling, have been identified as methane (CH4) sources not yet accounted for in the global CH4 budget. This study, for the first time, explores the influence of oxygen (O2) and temperature on CH4 production by two fungi, Laetiporus sulphureus and Pleurotus sapidus. To explore the relationship between these parameters and fungal CH4 formation, we examined CH4 formation under varying O2 levels (0 to 98%) and temperatures (17, 27, and 40 °C) during fungal growth on pine wood, beech wood, and grass under sterile conditions. Our findings show that fungal CH4 formation strongly depends on O2 levels. Methane formation was highest when O2 levels exceeded 5%, whilst no CH4 formation was observed after complete O2 consumption. Reintroducing O2 immediately resumed fungal CH4 production. Methane formation normalized to O2 consumption (CH4_norm) showed a different pattern. L. sulphureus showed higher CH4_norm rates with higher O2 levels, whereas P. sapidus showed elevated rates between 0 and 5%. Temperature also significantly influenced CH4 and CH4_norm rates, with the highest production at 27 °C, and comparatively lower rates at 17 and 40 °C. These findings demonstrate the importance of O2 levels and temperature in fungal CH4 emissions, which are essential for refining CH4 source predictions.

Methane doi: 10.3390/methane3020014

Authors: Xiaoyong Li Zhi Wang Yun He Yuzhong Wang Shilei Wang Zehui Zheng Songtao Wang Jingliang Xu Yafan Cai Hanjie Ying

Low and unstable digestion performance is a challenging issue for anaerobic digestion, which prompts researchers to develop new strategies. In addition to traditional approaches such as co-digestion, pre-treatment, and recirculation, some emerging strategies, namely additive processes and microaeration, have also been recognized and developed in recent years. Many studies have evaluated the effect of these strategies on digestion performance. However, their comprehensive analysis is lacking, especially regarding the mechanisms of the different strategies. This review presents a comprehensive overview of research progress on these strategies based on the latest research, considering the five main strategies listed above. Through critical thinking, a summary of their mechanism, reactor performance, and availability of these strategies is presented. The results demonstrate that the contribution of microaeration is mainly to balance the composition and activity of hydrolysis, acidogenesis, and methanogenic archaea. Recirculation and co-digestion mainly balance mass and reaction environments. Pre-treatment, such as removing lignin, reducing cellulose crystallinity, and increasing the substrate-specific surface area, makes the characteristics of the substrate more conducive to the digestion of microorganisms. The mechanism of additive strategies varies greatly depending on the type of additive, such as enhancing interspecies electron transfer through conductive materials, resisting adverse digestion conditions through functional microbial additives, and accelerating nutrient absorption by regulating the bioavailability of trace elements. Although these strategies have different mechanisms for promoting digestion performance, their ultimate effect is to allow the parameters of the reactor to reach an ideal status and then achieve a balance among the substance, microorganisms, and water in an anaerobic reactor.

Methane doi: 10.3390/methane3020013

Authors: Tzyy Shyuan Yang Carla Flores-Rodriguez Lorena Torres-Albarracin Ariovaldo José da Silva

Psychrophilic anaerobic digestion emerges as an appealing integrated solution for the management of agricultural waste, particularly for farmers in regions where the average temperature does not exceed 26 °C, as seen in coffee cultivation. Therefore, this study seeks to assess the biomethane potential of thermochemical-treated coffee husk through psychrophilic anaerobic digestion (C3-20 °C-w/pretreatment). To examine its viability, outcomes were compared with reactors operating at both mesophilic (C1-35 °C) and psychrophilic (C2-20 °C) conditions, albeit without the use of pretreated coffee husk. The C3-20 °C-w/pretreatment test demonstrated a 36.89% increase (150.47 NmL CH4/g VS; 161.04 NmL CH4/g COD), while the C1-35 °C test exhibited a 24.03% increase (124.99 NmL CH4/g VS; 133.77 NmL CH4/g COD), both in comparison to the C2-20 °C test (94.96 NmL CH4/g VS; 101.63 NmL CH4/g COD). Notably, the C3-20 °C-w/pretreatment trial yielded superior outcomes, accompanied by an associated energy output of 3199.25 GWh/year, sufficient to meet the annual energy demands of 494 residences. This marks an increase of 83 and 182 million residences compared to the mesophilic and psychrophilic AD of CH without pretreatment, respectively.

Methane doi: 10.3390/methane3010012

Authors: Andrew Curtis Benjamin McLellan

The global narrative around domestic energy security is dominated by the paradigm of import-dependent countries, and as a result the interactions of energy export activities with domestic energy systems are not generally considered. In this paper, we apply a systems approach to establish two potential blind spots in evaluating the whole-of-system energy security of energy resource exporters (actual primary energy self-sufficiency and export exposure of the domestic energy system), and examine some case studies, primarily in the Australian context, to validate the existence of these blind spots. The commencement of LNG exports from the state of Queensland is examined in detail. Furthermore, we propose two novel quantitative indicators to mitigate the blind spots established. First, a revised method is proposed to calculate energy self-sufficiency, showing for the exporters studied a less secure position than shown by the traditional method. Second, an indicator is proposed to quantify the extent of exposure of the domestic energy system to international markets through export linkages, which we have applied to Australia’s domestic energy system, showing the extent of the increase in international exposure since LNG exports from Queensland commenced in 2015–2016. Conclusions of this paper include the realization that domestic energy security for energy exporters, such as Australia and the other countries examined, is more complex and, in the cases examined, less secure than importer-oriented energy security frameworks have previously recognized. A further conclusion is established that the decoupling of energy resource exports from the domestic energy system through transition to a zero-carbon energy system based on domestic renewable energy sources can be an effective means of improving Australia’s energy security.

Methane doi: 10.3390/methane3010011

Authors: Santanu Ghosh Tushar Adsul Balram Tiwari Dinesh Kumar Atul Kumar Varma

This article furnishes a brief review of the geochemistry of waters produced during coal bed methane and shale gas exploration. Stable deuterium and oxygen isotopes of produced waters, as well as the stable carbon isotope of dissolved inorganic carbon in these waters, are influenced by groundwater recharge, methanogenic pathways, the mixing of formation water with saline water, water–rock interactions, well completion, contamination from water from adjacent litho-units, and coal bed dewatering, among many others. Apart from the isotopic fingerprints, significant attention should be given to the chemistry of produced waters. These waters comprise natural saturated and aromatic organic functionalities, metals, radioisotopes, salts, inorganic ions, and synthetic chemicals introduced during hydraulic fracturing. Hence, to circumvent their adverse environmental effects, produced waters are treated with several technologies, like electro-coagulation, media filtration, the coupling of chemical precipitation and dissolved air flotation, electrochemical Fe+2/HClO oxidation, membrane distillation coupled with the walnut shell filtration, etc. Although produced water treatment incurs high costs, some of these techniques are economically feasible and sustain unconventional hydrocarbon exploitation.

Methane doi: 10.3390/methane3010010

Authors: Rosy Paletta Rossella Girimonte Yessica A. Castro Jose Atilio De Frias Vincenza Calabrò

The collection and use of Sargassum spp. as feedstock for the production of valuable products such as biomethane by anaerobic digestion (AD) would mitigate the negative impact of the blooms and the costs related to waste management in the Dominican Republic. In this work, the effect of the particle size of pelagic Sargassum spp. biomass, as a result of mechanical pretreatments, on the biomethanation was determined. The granulometric analysis of the mechanically pre-treated biomass was carried out using a Mastersize2000. The Biochemical Methane Potential (BMP) of the samples was determined using an Automatic Potential System Test II (AMPTS® II). The kinetic parameters of the reaction were scientifically evaluated by using First order kinetic Model and modified Gompertz Model. The granulometric analysis showed a monomodal distribution on crushed biomass (505 µm) and a bimodal distribution on the milling sample (107 µm). The bimodal biomass means the biomass is characterized by the presence of fine and large particles. We observed that BMP increased by 78.85% when particles were reduced from 50,000 µm to 505 µm and by 73.61% when particles were reduced from 50,000 µm to 107 µm. A low methane yield from the milling biomass (107 µm) compared to the crushed biomass (505 µm) could be related to the excessive reduction of particle size. The fine particles are subject to the formation of aggregates and consequently, the contact area between the algae cells and the microorganisms that operate the anaerobic digestion process decreases.

Methane doi: 10.3390/methane3010009

Authors: Mohammed Benaouda Manuel González-Ronquillo Francisca Avilés-Nova Reynaldo Zaragoza-Guerrero Juan Carlos Ku-Vera Octavio Alonso Castelán-Ortega

Dairy cows are the highest daily and annual methane (CH4) producers among all cattle categories. So, the present study aimed to evaluate the effect of increasing supplementation levels of a low-quality forage on dry matter intake (DMI), DM digestibility (DMD), milk production, enteric CH4 emission, gross energy, and protein partitioning in Holstein cows. In total, eight cows (112 ± 38 days postpartum; mean ± s.d.) were randomly assigned to 4 treatments composed of 4 dietary neutral detergent fibre (NDF) inclusion levels (40.2% (control), 43.3%, 46.5%, and 50.5%) in a 4 × 4 repeated Latin square experimental design. The cows were fed corn + alfalfa silage and a concentrate (60:40 forage:concentrate ratio). To increase the contents of low-quality NDF, part of the silage was replaced with maize stover (MSTV). The CH4 production was measured in an open-circuit respiration chamber. The DMI increased significantly and linearly (p < 0.05) with increasing levels of MSTV. However, the CH4 yield decreased (p < 0.0001) as the NDF level increased (32.1, 28.1, 23.1, and 21.3 CH4 L/kg DMI, respectively). DMD decreased as NDF levels in the diet increased (p < 0.0001). The NDF digestibility (DNDF) explained the better (p < 0.0001) CH4 production response than DMD. It was concluded that low-quality forages can be used to regulate CH4 production in subtropical and tropical climate regions.

Methane doi: 10.3390/methane3010008

Authors: Fatemeh Ahmadi Tatiana Bodraya Maximilian Lackner

The ongoing yearly rise in worldwide methane (CH4) emissions is mostly due to human activities. Nevertheless, since over half of these emissions are scattered and have a concentration of less than 3% (v/v), traditional physical–chemical methods are not very effective in reducing them. In this context, biotechnologies like biofiltration using methane-consuming bacteria, also known as methanotrophs, offer a cost-efficient and practical approach to addressing diffuse CH4 emissions. The present review describes recent findings in biofiltration processes as one of the earliest biotechnologies for treating polluted air. Specifically, impacts of biotic (such as cooperation between methanotrophs and non-methanotrophic bacteria and fungi) and abiotic factors (such as temperature, salinity, and moisture) that influence CH4 biofiltration were compiled. Understanding the processes of methanogenesis and methanotrophy holds significant importance in the development of innovative agricultural practices and industrial procedures that contribute to a more favourable equilibrium of greenhouse gases. The integration of advanced genetic analyses can enable holistic approaches for unravelling the potential of biological systems for methane mitigation. This study pioneers a holistic approach to unravelling the biopotential of methanotrophs, offering unprecedented avenues for biotechnological applications.

Methane doi: 10.3390/methane3010007

Authors: Dipayan Samanta Tanvi Govil Priya Saxena Lee Krumholz Venkataramana Gadhamshetty Kian Mau Goh Rajesh K. Sani

Over the past decade, copper (Cu) has been recognized as a crucial metal in the differential expression of soluble (sMMO) and particulate (pMMO) forms of methane monooxygenase (MMO) through a mechanism referred to as the “Cu switch”. In this study, we used Methylosinus trichosporium OB3b as a model bacterium to investigate the range of Cu concentrations that trigger the expression of sMMO to pMMO and its effect on growth and methane oxidation. The Cu switch was found to be regulated within Cu concentrations from 3 to 5 µM, with a strict increase in the methane consumption rates from 3.09 to 3.85 µM occurring on the 6th day. Our findings indicate that there was a decrease in the fold changes in the expression of methanobactin (Mbn) synthesis gene (mbnA) with a higher Cu concentration, whereas the Ton-B siderophore receptor gene (mbnT) showed upregulation at all Cu concentrations. Furthermore, the upregulation of the di-heme enzyme at concentrations above 5 µM Cu may play a crucial role in the copper switch by increasing oxygen consumption; however, the role has yet not been elucidated. We developed a quantitative assay based on the naphthalene–Molisch principle to distinguish between the sMMO- and pMMO-expressing cells, which coincided with the regulation profile of the sMMO and pMMO genes. At 0 and 3 µM Cu, the naphthol concentration was higher (8.1 and 4.2 µM, respectively) and gradually decreased to 0 µM naphthol when pMMO was expressed and acted as the sole methane oxidizer at concentrations above 5 µM Cu. Using physical protein–protein interaction, we identified seven transporters, three cell wall biosynthesis or degradation proteins, Cu resistance operon proteins, and 18 hypothetical proteins that may be involved in Cu toxicity and homeostasis. These findings shed light on the key regulatory genes of the Cu switch that will have potential implications for bioremediation and biotechnology applications.

Methane doi: 10.3390/methane3010006

Authors: Minghui Wei Xuerong Shi

CO2 reforming of CH4 (DRM) utilizes the greenhouse gases of CH4 and CO2 to obtain the synthesis gas, benefiting the achievement of carbon neutrality. However, the deactivation of Ni-based catalysts caused by sintering and carbon deposition limits the industrial application. Focusing on stability improvement, this review first summarizes the reaction mechanism and deactivation mechanism in DRM and then discusses the impact of catalyst active components, supports, and interfacial structure. Finally, we propose the design direction of stable Ni-based catalysts towards DRM, providing guidance for the future development of catalysts suitable for industrial production.

Methane doi: 10.3390/methane3010005

Authors: Nghia Duc Tin Nguyen Gautham Krishnamoorthy

A Computational Fluid Dynamic study was carried out to match the measured outer ash deposition rates associated with the combustion of petroleum coke (PC)–natural gas in AIR and O2/CO2 (70/30 vol%, OXY70). The fly ash PSD associated with high-fixed-carbon, non-porous fuel was estimated using a shrinking sphere burnout model and employed in conjunction with particle kinetic energy (PKE), particle viscosity (µP), and a critical Weber-number-based capture criterion. Deposition rate predictions were sensitive to the fly ash composition employed for estimating µP due to the significant enrichment of Fe in the deposits. Predictions were insensitive to the specific µP model formulation employed or whether the V2O5 in the ash was assumed to play the role of a glass former or a glass modifier. OXY70 scenario impaction rates were significantly lower than the measured deposition rates when the fly ash PSD associated with the AIR scenario was employed in the calculations. This necessitated an ad hoc modification of the OXY70 fly ash PSD to a coarser range to match the measurements and attributing it to agglomeration resulting from longer residence times and higher temperatures. This shift in PSD was in line with AIR and OXY70 fly ash PSD measurements reported previously.

Methane doi: 10.3390/methane3010004

Authors: Maitê L. Gothe Adolfo L. Figueredo Laís R. Borges Ruben Ramos Andreia F. Peixoto Pedro Vidinha

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.

Methane doi: 10.3390/methane3010003

Authors: Umer Hayyat Muhammad Usman Khan Muhammad Sultan Umair Zahid Showkat Ahmad Bhat Mohd Muzamil

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.

Methane doi: 10.3390/methane3010002

Authors: Babak Darabighane Ilma Tapio Saija Rasi Ari-Matti Seppänen Lucia Blasco Seppo Ahvenjärvi Ali R. Bayat

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.

Methane doi: 10.3390/methane3010001

Authors: Michael L. Galyean Kristin E. Hales

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.

Methane doi: 10.3390/methane2040031

Authors: Vicente Pérez-Madrigal Edna Ríos-Valdovinos Elizabeth Rojas-García Miguel A. Valenzuela Francisco Pola-Albores

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.

Methane doi: 10.3390/methane2040030

Authors: Tarek Abichou Nizar Bel Hadj Ali Sakina Amankwah Roger Green Eric S. Howarth

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.

Methane doi: 10.3390/methane2040029

Authors: Gabriela P. Freitas Brenno Vinicius M. Lima Maria Paula C. Volpi Renata P. Rodriguez Bruna S. Moraes

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).

Methane doi: 10.3390/methane2040028

Authors: Eric A. Walker Joseph J. Marziale James Chen

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 (SiC), 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 SiC growth due to Si being far more reactive. Therefore, increasing the C content of the precursor is a logical CVI strategy. Methane (CH4) is more reactive than ethane (C2H6) and ethylene (C2H2) 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.

Methane doi: 10.3390/methane2040027

Authors: Jin Wang Qinghua Peter He

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.

Methane doi: 10.3390/methane2040026

Authors: Matheus Henrique Silva Cavalcante Ícaro Augusto Maccari Zelioli Emílio Émerson Xavier Guimarães Filho Julles Mitoura dos Santos Júnior Annamaria Dória Souza Vidotti Antonio Carlos Daltro de Freitas Reginaldo Guirardello

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.

Methane doi: 10.3390/methane2040025

Authors: Mykhailo Bludov Ivan Khyzhniy Sergey Uyutnov Elena Savchenko

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%.

Methane doi: 10.3390/methane2040024

Authors: Jyoti A. Mohite Kumal Khatri Kajal Pardhi Shubha S. Manvi Rutuja Jadhav Shilpa Rathod Monali C. Rahalkar

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.

Methane doi: 10.3390/methane2030023

Authors: Danielle F. Baffa Tadeu S. Oliveira Alberto M. Fernandes Michelle G. Camilo Ismael N. Silva José R. Meirelles Júnior Elon S. Aniceto

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.

Methane doi: 10.3390/methane2030022

Authors: Themistoklis Sfetsas Manthos Panou Afroditi G. Chioti Nikoleta Prokopidou Ioanna Dalla

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.

Methane doi: 10.3390/methane2030021

Authors: Ram Kumar Singh Avijit Dey Mala Singh

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.

Methane doi: 10.3390/methane2030020

Authors: Cornelius B. Bavoh Eric Broni-Bediako Solomon Adjei Marfo

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.

Methane doi: 10.3390/methane2030019

Authors: Dipayan Samanta Rajesh K. Sani

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.

Methane doi: 10.3390/methane2030018

Authors: Eleni Anna Economou Georgia Dimitropoulou Nikoleta Prokopidou Ioanna Dalla Themistoklis Sfetsas

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.