Search Results (739)

This study aims to evaluate the blanching process of wasted Undaria pinnatifida as a ruminant feed source by assessing chemical compositions, in vitro nutrient digestibility, rumen fermentation characteristics, greenhouse gas emissions, and rumen microbes. The blanching process was conducted at different temperatures (15 vs. 80 vs. 90 °C) and times (2 vs. 4 min) to assess the chemical and mineral contents. Supplementation levels of U. pinnatifida (0 vs. 0.5 vs. 1 vs. 2%) were observed with the blanching process (non-blanching (NBL) vs. blanching (LOS)). Increasing blanching temperature and time decreased (p < 0.05) dry matter, crude ash, and the mineral contents, including sodium, phosphorus, and arsenic. Moreover, LOS treatment increased (p < 0.01) in vitro dry matter and neutral detergent fiber digestibility, ruminal pH, and the acetate-to-propionate ratio, but reduced (p < 0.01) CH₄ (mL/g NDFD). Additionally, 2% of LOS treatment reduced the abundance of protozoa, fungi, fibrolytic microbes, methanogenic archaea, Methanobrevibacter ruminantium, Methanosarcina barkeri, and Methanosphaera stadtmanae (p < 0.01). Therefore, blanching at 80 °C for 2 min improved the nutritional profile by reducing antinutritional minerals. Subsequent in vitro fermentation suggested that supplementing the diet with 0.5–1% of LOS improved digestibility and altered fermentation, potentially reducing methane yield (per NDFD). Full article

Ruminants significantly contribute to global methane (CH₄) emissions, necessitating the development of dietary mitigation strategies. This study evaluated five Bangladeshi seaweeds (brown, red, and green types) from Saint Martin Island for their anti-methanogenic potential through phenotypic identification, proximate analysis, and in vitro fermentation assessment. Significant interspecies variation was (p < 0.001) observed in dry matter (DM: 82.1–99.9%), acid detergent fiber (ADF: 17.4–24.9%), neutral detergent fiber (NDF: 29.6–43.6%), and dry matter degradability (DMD: 43.9–58.7%), while crude protein (CP) remained consistent (p = 0.574). After 48 h of fermentation, total gas (1.3–22.1 mL/g DM) and CH₄ yield (0.04–1.6 mL/g DM) varied markedly (p < 0.01). DMD was strongly correlated with total gas and CH₄ production. Crucially, both ADF and NDF showed a positive correlation with total gas and CH₄ production. However, NDF displayed a weak positive correlation with DMD. These findings suggest atypical fiber fraction dynamics, contrasting with terrestrial forages. Supplementation effects of two red seaweeds, SW-4 (Gracilaria parvispora) and SW-5 (Asparagopsis taxiformis), on Napier grass were assessed at 5% and 10% inclusion levels. SW-5 reduced CH₄ by 52.7% when co-fermented with Napier grass at a 10% inclusion level for 48 h, whereas SW-4 showed no significant effect. These results highlight SW-5 as a promising dietary supplement to reduce enteric CH₄ in ruminants, suggesting further in vivo validation for optimal use. Full article

Rapid population growth is intensifying global energy demand and waste generation. Slaughterhouse waste is creating important environmental problems. Transforming this into renewable energy through technologies like anaerobic digestion offers a sustainable pathway to reduce environmental impacts and support the energy transition. The main objective of this study was to examine the biodegradability of the slaughterhouse semi-liquid fraction (S), slaughterhouse liquid fractions (L), and their mixtures (25%, 50%, and 75%) through a two-phase anaerobic co-digestion (TPAcD) process. Batch reactors were operated in two separate microbiological and thermal phases. In the first, a thermophilic 55 °C–acidogenic stage, biochemical hydrogen potential (BHP) assays were conducted to evaluate green hydrogen production, while in the second, a mesophilic 35 °C–methanogenic stage, biochemical methane potential (BMP) assays were carried out to assess biomethane generation. The most relevant findings revealed that while liquid fractions maximized hydrogen recovery, overall yields remained limited due to competitive metabolic pathways. Notably, the 25L:75S configuration optimized hydrolysis, with a 1280% increase in soluble COD, establishing the semi-liquid fraction as a critical organic reservoir for thermophilic–acidogenic activity. In the subsequent stage, the acidogenic pre-treatment significantly enhanced methanogenesis, where the same 25L:75S mixture exhibited a synergistic methane yield of 495.46 mL CH₄/g VS. This 13.8% improvement over the theoretical additive potential confirms that strategic substrate balancing overcomes individual feedstock limitations, maximizing energy recovery in sequential anaerobic digestion. These results highlight the potential of phase-separated anaerobic co-digestion as a strategy to improve the valorization of slaughterhouse wastes. Full article

Methanogens, or methanogenic archaea (MA), are among the most ancient and widely distributed microorganisms, characterized by a unique metabolism that generates methane (CH₄) as the terminal product of anaerobic respiration. Their ability to grow and/or survive across a wide range of environmental conditions has made methanogens key contributors to biogeochemical cycles throughout most of Earth’s history. Most importantly, these oxygen-sensitive microorganisms have regulated the climate since the early Archean and impacted biogeochemical cycles throughout Earth’s history by producing the potent greenhouse gas, CH₄, while consuming H₂, CO₂, and small organic molecules. Hence, methanogens are attributed a key role in the start and end of several Proterozoic glaciations and mass extinction events. Their specific roles in the long-term carbon cycle that focus on CH₄ production are well-established, but, in contrast, only very few studies report on interactions with CaCO₃ and long-term carbon storage. Methanogens evolved early during Earth’s history, likely during the Archaean Eon, in layered benthic microbial communities called microbial mats. When lithified, these mats form microbialites that represent some of the earliest evidence of life in the fossil record, dating back >3.5 Gy. Methanogens are an integral part of contemporary microbial mats and have been identified both in the anoxic and oxic zones of these sedimentary ecosystems; however, their adaptations to apparently unfavorable oxic conditions and their role in the precipitation of carbonate in mats are unclear. In addition to an important role in the evolution of our planet by producing CH₄, methanogens may also produce a biosignature that could be relevant for astrobiology research. This review will discuss the diversity, physiology, and ecology of methanogens in detail to clarify their role in some of the major biogeochemical processes and ecological climatic events through the fluctuating environmental conditions on Earth through geologic time. Full article

The effects of substituting pelleted diets manufactured from cassava, chaya, and mulberry leaves for concentrate on growth performance, feed intake, rumen fermentation, and microbial protein synthesis in beef cattle were evaluated. Four beef cattle (initial BW: 250 ± 50 kg) were assigned to four treatments: a control diet (T1) and diets in which 50% of the concentrate was replaced with cassava leaf pellets (T2), chaya leaf pellets (T3), or mulberry leaf pellets (T4). The data were analyzed using a 4 × 4 Latin square with animal as a period effect as appropriate. Rumen volatile fatty acids were determined by means of HPLC, and microbial protein synthesis was assessed using urinary purine derivatives. Cattle fed cassava leaf pellets (T2) showed the greatest average daily gain (0.79 kg/d) compared with the control (0.50 kg/d; p < 0.05). Compared with T1, T4 exhibited a higher ruminal propionate proportion and total VFA concentration, which was associated with a lower acetate-to-propionate pattern, suggesting reduced methanogenic potential. No adverse health effects were observed, as indicated by hematocrit and blood urea nitrogen values within normal ranges. Microbial protein production increased in the leaf-pellet treatments, with T4 showing the highest efficiency. Overall, cassava, chaya, and mulberry leaf pellets can partially replace concentrate while maintaining growth performance and improving rumen fermentation efficiency in beef cattle. Full article

Bioelectromethanogenesis, the microbial conversion of carbon dioxide (CO₂) into methane (CH₄) using a cathode, offers a promising route for biogas upgrading and renewable energy storage. The flow field is an essential factor influencing the performance of bioelectromethanogenesis, and the stability and efficiency of the biocathode play important roles in this process. This study systematically investigated the effect of different internal-circulation flow rates on the biocathode initiated without the electric field and the reactor effluent. It was found that the methane production of the biocathode initiated without the electric field was increased by around 30% at an internal-circulation flow rate of 18 mL/min, which was stronger than that of the biocathode initiated by the reactor effluent. The relative content of the extracellular polymeric substance (EPS) heme was increased by 4%, while the EPS electron accepting capacity was much higher than that initiated by reactor effluent. Furthermore, the microbial community analysis showed that the functional methanogen on the biocathode initiated without an electric field was Methanosaeta (17%) and Methanobacterium (8%). This study could provide support for the dynamic operation of biogas upgrading in microbial electrolysis cells. Full article

Solid-state fermentation (SSF) is a long-established biotechnological approach gaining renewed interest for its ability to enhance nutrient availability and improve the functional properties of agro-industrial by-products. This strategy is particularly relevant for early post-weaning piglets, which are highly susceptible to weaning stress due to an immature digestive system and a gut microbiota not yet adapted to solid feed. In this study, the fermentation parameters of flaxseed cake were optimized using a Plackett–Burman experimental design. Protease activity was selected as the response variable due to its relevance for improving protein degradation and potential digestibility in fermented feed ingredients. Accordingly, based on the statistical analysis, the conditions selected for the in vivo trial were 1% molasses, 0.5% yeast extract, 0.05% CaCl₂, 0.5% NaCl, 7.5% inoculum (4.12 × 10⁹ CFU/mL), 60% moisture, and 72 h fermentation. Fermentation time was identified as the main factor positively influencing protease production, while higher CaCl₂ concentrations and inoculum levels negatively affected enzyme activity. Optimization increased protease activity, microbial viability and free amino acid content. In addition, SSF reorganizes the carbohydrate profile by reducing structural fiber fractions, with neutral detergent fiber and acid detergent fiber decreasing by 27% and 29%, respectively, while simultaneously increasing soluble carbohydrates by 14.67%. Phytic acid content being also reduced by 23.81%. A pilot nutritional trial on post-weaned piglets (35 days old) showed that including 8% fermented flaxseed cakes (FFSC group) improved body weight, average daily gain, feed conversion ratio, and diarrhea score, without affecting average daily feed intake, compared with 8% unfermented flaxseed cakes (FSC group). These performance improvements were accompanied by changes in fermentation metabolites and gut microbial composition. Lower isovalerate concentrations suggested reduced proteolysis, while higher propionate levels may contribute to increased blood glucose availability in the FFSC group. These changes coincided with a shift in microbial composition, characterized by a reduced abundance of methanogenic archaea and increased abundances of taxa such as Lactobacillus, Enterococcus, and members of the Lachnospiraceae and Eubacteriaceae families. Full article

To broaden the application of biomethanation for energy storage and renewable integration, this study investigates the performance of a trickle-bed reactor (TBR) for hydrogen (H₂) utilisation in biogas upgrading, using both pure Carbon dioxide (CO₂) and biogas-derived CO₂ as substrates for methane (CH₄) production. Renewable sources such as wind and solar are inherently variable, increasing the need for scalable storage solutions. Converting surplus electricity into H₂ and CH₄ via biological methanation offers an efficient and safer alternative to direct H₂ storage. By reducing CO₂ produced by biogas plants, methanogenic archaea produce CH₄, enabling H₂ valorisation and enhanced biogas yields. This study demonstrates that TBR technology can achieve CH₄ formation rates up to 15 L-CH₄/L-reactor/day under optimised conditions. Siporax carrier material supported dense biofilm formation and effective gas–liquid mass transfer, facilitating high conversion efficiency. The system showed operational robustness, with rapid recovery after prolonged idle periods and stable production rates of 10–12 L-CH₄/L/day. Wastewater was used as a realistic medium to assess reactor performance under complex, variable conditions. Reactor design focused primarily on enhancing gas–liquid mass transfer and supporting sustained microbial activity through adequate nutrient supply, ensuring sufficient buffer capacity to maintain pH stability. These results demonstrate the potential of TBR-based systems for high-rate, stable biomethanation and highlight their applicability in future energy infrastructures for integrating H₂ through decentralised biogas upgrading. Full article

In the process of anaerobic digestion for manure treatment, adding conductive materials is one of the most used methods to enhance methane yield. Biochar, a stable conductive material, shows significant potential in facilitating direct interspecies electron transfer in anaerobic digestion systems. However, biochar’s structure and properties are influenced by its preparation method, and the mechanisms by which structural characteristics affect methane yield and microbial community structure in fermentation systems require further investigation. This study investigates the effects of pyrolysis duration (1 h for A3O and 2 h for A3T) at 550 °C using corn straw as raw material. Through characterization analyses including SEM, FTIR, conductivity, and elemental composition, we explore the impacts on gas production efficiency and key parameters in anaerobic digestion systems. By analyzing microbial community structure and changes in methanogenic functional bacteria, we elucidate the mechanisms by which biochar materials with different pyrolysis times influence anaerobic digestion processes and microbial community composition. These findings provide theoretical foundations and support for optimizing biochar preparation techniques and their targeted applications in anaerobic digestion fields. It was found that the biochar-treated group exhibited higher methane production. Compared with the CK group without biochar, the methane production of A3O and A3T increased by 8.53% and 5.16%, respectively. While methane yield differed little between A3O and A3T, longer pyrolysis time increased the biochar’s specific surface area, promoting the system’s reaction rate and enabling faster methanogenesis. High-throughput analysis showed that biochar enriched methanogenic archaea like Methanosarcina and Methanobrevibacter while upregulating methanogenesis metabolic pathways and enhancing system metabolic potential. This study elucidates the influence of pyrolysis conditions on biochar performance and its regulatory role in anaerobic digestion, providing a basis for energy recovery from organic waste and biochar application in anaerobic fermentation. Full article

This study explores the use of bentonite to enhance biological biogas upgrading in a bubble reactor (BR) operated under mesophilic conditions (39 ± 1 °C). The experimental setup consisted of a 2 L vertically oriented BR (height-to-diameter ratio 16:1) fed with a synthetic gas mixture (60% H₂, 15% CO₂, 25% CH₄, v/v) at a gas recirculation rate of 4 L L_R⁻¹ h⁻¹. The aim was to overcome hydrogen’s low gas–liquid mass transfer rate while avoiding the operational challenges typically associated with trickle-bed reactors (TBR). Bentonite increases the density and hydrostatic pressure of the liquid medium and likely alters its rheology, thereby extending the gas–liquid contact time without requiring elevated pressures or intensive gas recirculation. Additionally, bentonite is expected to provide microstructural support that promotes the formation of biofilm-like communities, creating favorable microenvironments for hydrogenotrophic methanogens. As a clay-based additive, bentonite may also contribute to improved process stability through adsorption of inhibitory compounds, enhanced biomass retention, and pH buffering. Under mesophilic conditions, the bentonite-modified BR achieved a methane production rate of 2.17 ± 0.06 LCH₄ L_R⁻¹ d⁻¹ at a gas retention time of 1.49 h, with methane purity reaching 96.25%. In comparison, a previously reported mesophilic BR operated under an identical reactor configuration and operating conditions but without bentonite exhibited substantially lower methane production rates, supporting the beneficial role of bentonite in biological methanation. The findings highlight bentonite’s potential dual role (physical and biological) in improving process efficiency and stability in biological methanation. Full article

Reducing enteric methane emissions from ruminants has emerged as a critical environmental priority in the face of global climate change, given the substantial contribution of methane to agricultural greenhouse gas outputs. This study evaluated the potential of spearmint essential oil (SEO) to reduce methane production and enhance energy utilization efficiency using an in vitro rumen fermentation system. The experiment comprised a control (CON, no additive), three SEO doses (L-SEO: 100 mg/L; M-SEO: 200 mg/L; H-SEO: 400 mg/L), and a commercial essential oil blend (AGL: 150 mg/L). Results indicated that M-SEO and H-SEO significantly reduced methane production at 24 h from 58.11 mL/g DM in CON to 47.93 and 46.58 mL/g DM, respectively (p < 0.001), corresponding to reductions of 17.5% and 19.8%. Furthermore, M-SEO increased total volatile fatty acid concentration from 48.41 to 58.10 mmol/L and elevated the molar proportion of propionate, while significantly enhancing microbial crude protein production (p < 0.001). Microbial community analysis revealed that M-SEO increased bacterial alpha-diversity (Shannon index) (p = 0.001) and significantly enriched specific functional guilds, particularly the propionate-producing genus Succiniclasticum and the butyrate-producing genus Butyrivibrio. Interestingly, the abundance of dominant methanogens (Methanobrevibacter) was not reduced, suggesting a metabolic inhibition mechanism rather than a biocidal effect. Functional prediction analysis further supported this, indicating a downregulation of pathways associated with methanogenesis, including key enzymes such as methyl-coenzyme M reductase. In conclusion, SEO supplementation at 200 mg/L effectively reduced methane production by redirecting metabolic hydrogen toward propionate formation, without affecting overall fermentation. Therefore, the current study indicated that SEO could serve as a sustainable feed additive for mitigating enteric methane emissions in ruminants. Full article

While essential oils are gaining momentum as a strategy to modulate rumen function and potentially reduce enteric methane in cattle, little is known about how their bioactive components, terpenes, affect rumen microbes. Our objective was to evaluate how in vivo doses of thymol affect the structure and function of the rumen microbial community via whole genome shotgun sequencing (WGS). Four beef steers were used in a 4 × 4 Latin square with four 28 d periods. Steers consumed ad libitum forage and received one of four thymol doses (0 [CON], 120 [120-T], 240 [240-T], and 480 [480-T] mg/kg forage intake). Rumen contents were separated into liquid and solid fractions, DNA was extracted, analyzed via WGS, and assessed with orthogonal contrasts. After FDR correction, no taxa were affected by thymol; however, raw p-values demonstrated responses to thymol supplementation for solid-associated uncultured Lachnospiraceae bacterium (p = 0.04), uncultured Methanobrevibacter (p = 0.05), and uncultured Coriobacteriaceae bacterium (p = 0.02). Liquid-associated uncultured Prevotellaceae bacterium (p = 0.03), Prevotella sp. (p = 0.04), and Bacteroides sp. (p = 0.02) also responded to thymol, with the highest abundances observed at various thymol doses. Genes involved in energy production and amino acid metabolism transport were observed at the highest abundances at 240-T, while genes associated with cell cycle control, cell division, and chromosome partitioning were present in the highest abundances at 120-T. The findings suggest that thymol exerts dose-dependent effects on rumen microbial abundances and functional pathways, with 240 mg/kg forage intake appearing to be the most effective dose to downregulate methanogenic enzymes while also enhancing the enzymes associated with metabolism without negatively impacting microbial diversity. Full article

The bioconversion of propionate, a well-known intermediate of anaerobic digestion (AD), to methane is energetically unfavorable under standard conditions, which typically occurs in the syntrophy of bacteria and methanogens via methylmalonyl-CoA (MMC) and the dismutation pathway. Since the latter, which is reported only in Smithella, possessed a thermodynamic advantage over the former, enriching Smithella and promoting the syntrophic interaction and metabolism of the microbiota are important for improving AD efficiency. In this study, lysine-modified Fe₃O₄ (Lys@Fe₃O₄) significantly enhanced the bioconversion of propionate to methane. The methane yield and the maximum methane production rate (R_max) in a Lys@Fe₃O₄ reactor were 278.7% and 271.7% of Blank, and the corresponding values were 201.9% and 201.6% of bare Fe₃O₄, respectively. The metaproteomic results indicated that Lys@Fe₃O₄ increased not only the abundance of Smithella but also the expression of cell surface and adhesion proteins, thereby promoting syntrophic interaction between Smithella and methanogens and facilitating electron and acetate transfer from Smithella to methanogens. Moreover, the expression of quorum-sensing proteins was enhanced, benefiting the cooperation of Smithella and its associated bacterium (Syntrophomonas). Furthermore, the expressions of key enzymes related to metabolism and electron transfer in propionate oxidation, butyrate oxidation, CO₂-reductive methanogenesis and acetoclastic methanogenesis were all significantly upregulated. The results are of great significance for maintaining low propionate concentration and stability of AD. Full article

Slaughterhouse by-products are promising feedstocks for anaerobic digestion due to their high lipid and protein content. However, their complex structures often limit hydrolysis, and excessive pretreatment can induce inhibitory conditions. This study evaluates the effects of ball-milling (BM), ball-milling with water (BM + water), and combined thermal hydrolysis and ball-milling (THP + BM) on the digestion performance of a mixed substrate of slaughterhouse and agricultural wastes. The results demonstrate that all BM-based pretreatments significantly improved digestion kinetics, reducing the lag phase by 26–66% and shortening the T₅₀ values by approximately 40% compared to the untreated substrate. While no statistically significant differences were observed in the ultimate methane yield, the onset of methanogenesis was markedly accelerated in the BM and BM + water treatments. In contrast, despite achieving superior solubilization, the THP + BM treatment failed to provide proportional kinetic enhancements. This was attributed to a severe initial metabolic imbalance—characterized by a pH drop below the inhibitory threshold (6.33)—which induced physiological stress and delayed the functional recovery of methanogens. These findings indicate that while ball-milling effectively facilitates digestion initiation by enhancing physical accessibility, the intensity of combined thermal-mechanical processes must be strategically optimized. For high-strength organic biomass, managing pretreatment severity is crucial to prevent initial acid stress and maximize process efficiency. Full article

In this study, the impact of zero-valent iron (ZVI) on methane production during sludge thermophilic anaerobic fermentation was investigated. The results showed that ZVI addition significantly enhanced cumulative methane production, with an optimum concentration of 5 g/L increasing the biochemical methane potential by 51.4% compared to the control. ZVI primarily promoted the acidogenesis and methanogenesis stages rather than hydrolysis, as indicated by the enhanced production of short-chain fatty acids and increased activities of key enzymes. Specifically, the activity of the methanogenic enzyme F₄₂₀ increased by 28.09%, which contributed to a higher methane yield. Moreover, the synergistic effect of ZVI and its decomposition products (Fe²⁺ > Fe³⁺) facilitated a more reduced environment. Furthermore, ZVI addition enriched acetate-utilizing methanogens, i.e., Methanosarcina, which helps rapidly degrade organic acids, thereby stabilizing the fermentation process. These findings demonstrated the potential of ZVI to improve methane recovery and process stability in thermophilic anaerobic fermentation systems. Full article