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

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