Methane, Volume 3, Issue 1 (March 2024) – 12 articles

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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 (µ_P), and a critical Weber-number-based capture criterion. Deposition rate predictions were sensitive to the fly ash composition employed for estimating µ_P due to the significant enrichment of Fe in the deposits. Predictions were insensitive to the specific µ_P 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. Full article

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·kg_cat⁻¹ of CH₄ can be generated. Full article

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. Full article

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. Full article

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. Full article