Methane, Volume 4, Issue 2 (June 2025) – 6 articles

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. Full article

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 (CO_2e), 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 tCO_2e, 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. Full article

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. Full article

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. Full article

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. Full article

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. Full article