Search Results (743)

The use of methane as a carbon source for producing bacterial single-cell protein (SCP) has been one of the most interesting developments in recent years. Most of these upcoming industries are using a methanotroph, Methylococcus capsulatus Bath, for SCP production using natural gas as the substrate. In the present study, we have explored the possibility of using an indigenously isolated methanotroph from a rice field in India, Methylomagnum ishizawai strain KRF4, for producing SCP from biogas [derived from cow dung]. The process was eco-friendly, required minimal instruments and chemicals, and was carried out under semi-sterile conditions in a tabletop fish tank. As the name suggests, Methylomagnum is a genus of large methanotrophs, and the strain KRF4 had elliptical to rectangular size and dimensions of ~4–5 µm × 1–2 µm. In static cultures, when biogas and air were supplied in the upper part of the growing tank, the culture grew as a thick pellicle/biofilm that could be easily scooped. The grown culture was mostly pure, from the microscopic observations where the large size of the cells, with rectangular-shaped cells and dark granules, could easily help identify any smaller contaminants. Additionally, the large cell size could be advantageous for separating biomass during downstream processing. The amino acid composition of the lyophilized biomass was analyzed using HPLC, and it was seen that the amino acid composition was comparable to commercial fish meal, soymeal, Pruteen, and the methanotroph-derived SCP-UniProtein^®. The only difference was that a slightly lower percentage of lysine, tryptophan, and methionine was observed in Methylomagnum-derived SCP. Methylomagnum ishizawai could be looked at as an alternative for SCP derived from methane or biogas due to the comparable SCP produced, on the qualitative level. Further intensive research is needed to develop a continuous, sustainable, and economical process to maximize biomass production and downstream processing. Full article

Anaerobic digestion (AD) is a sustainable method of treating organic waste to generate methane-rich biogas. However, the complex lignocellulosic nature of organic waste in most cases limits its biodegradability and methane potential. This review evaluates pretreatment technology to optimize AD performance, particularly in developing countries like Ghana, where organic waste remains underutilized. A narrative synthesis of the literature between 2010 and 2024 was conducted through ScienceDirect and Scopus, categorizing pretreatment types as mechanical, thermal, chemical, biological, enzymatic, and hybrid. A bibliometric examination using VOSviewer also demonstrated global trends in research and co-authorship networks. Mechanical and thermal pretreatments increased biogas production by rendering the substrate more available, while chemical treatment degraded lignin and hemicellulose, sometimes more than 100% in methane yield. Biological and enzymatic pretreatments were energy-consuming and effective, with certain enzymatic blends achieving 485% methane yield increases. The study highlights the synergistic benefits of hybrid approaches and growing global interest, as revealed by bibliometric analysis; hence, the need to explore their potential in Ghana. In Ghana, this study concludes that low-cost, biologically driven pretreatments are practical pathways for advancing anaerobic digestion systems toward sustainable waste management and energy goals, despite infrastructure and policy challenges. Full article

CO₂-biomethanation was studied in the present manuscript by considering the direct injection of hydrogen into a conventional anaerobic digester treating sewage sludge within a simulated wastewater treatment plant (WWTP). The plant was simulated using the Python 3.12.4 software, and a Monte Carlo simulation was conducted to account for the high variability in the organic content of the wastewater and the methane potential of the sludge. Two modes of operation were studied. The first mode involves the use of an anaerobic digester to upgrade biogas, and the second mode considers using the digester as a CO₂ utilization unit, transforming captured CO₂. Upgrading biogas and utilizing the extra methane to generate electricity within the same plant leads to a negative economic balance (first scenario). A hydrogen injection of 1 L of H₂/L_r d (volumetric H₂ injection per liter of reactor per day) was required to transform the CO₂ present in the biogas into methane. The benefits associated with this approach resulted in lower savings regarding heat recovery from the electrolyzer, increased electricity production, and an additional oxygen supply for the waste-activated sludge treatment system. Increasing the injection rate to values of 5 and 30 L of H₂/L_r d was also studied by considering the operation of the digester under thermophilic conditions. The latter assumptions benefited from the better economy of scale associated with larger installations. They allowed for enough savings to be obtained in terms of the fuel demand for sludge drying, in addition to the previous categories analyzed in the biogas upgrading case. However, the current electricity price makes the proposal unfeasible unless a lower price is set for hydrogen generation. A standard electricity price of 7.6 c€/kWh was assumed for the analysis, but the specific operation of producing hydrogen required a price below 3.0 c€/kWh to achieve profitability. Full article

The integration of renewable energy with circular economy strategies offers effective pathways to reduce greenhouse gas emissions while enhancing local energy independence. This study analyses three real-world projects implemented in Spain that exemplify this synergy. LIFE Smart Agromobility converts pig manure into biomethane to power farm vehicles, using anaerobic digestion and microalgae-based upgrading systems. Smart Met Value refines biogas from a wastewater treatment plant in Guadalajara to produce high-purity biomethane for the municipal fleet, demonstrating the viability of energy recovery from sewage sludge. The UNDERGY project addresses green hydrogen storage by repurposing a depleted natural gas reservoir, showing geochemical and geomechanical feasibility for seasonal underground hydrogen storage. Each project utilises regionally available resources to produce clean fuels—biomethane or hydrogen—while mitigating methane and CO₂ emissions. Results show significant energy recovery potential: biomethane production can replace a substantial portion of fossil fuel use in rural and urban settings, while hydrogen storage provides a scalable solution for surplus renewable energy. These applied cases demonstrate not only the technical feasibility but also the socio-economic benefits of integrating waste valorisation and energy transition technologies. Together, they represent replicable models for sustainable development and energy resilience across Europe and beyond. Full article

The aim of the study was to evaluate the chemical composition and biogas potential of selected ruderal and expansive plant species: Heracleum sosnowskyi, Aegopodium podagraria, Chaerophyllum bulbosum, Acer negundo, and Urtica dioica. Plant material was collected from a 19th-century park in the village of Niegolewo (Greater Poland Voivodship) and analyzed for cellulose, lignin, hemicellulose, extractives, and ash content before and after methane fermentation. Fermentation followed DIN 38 414-S8, and chemical analyses used standardized methods (TAPPI, Seifert, and DIN). Statistical analyses included ANOVA, CVA, and hierarchical clustering. The highest biogas yield was obtained from A. podagraria, which is associated with low lignin and high hemicellulose degradation. The results confirm the potential of ruderal biomass as a diverse source for biogas production. Full article

Anaerobic digestion for biogas production represents a crucial approach to achieving the high-value utilization of agricultural solid waste. The adoption of multi-material co-digestion offers a viable solution to overcome the inherent constraints associated with single-substrate digestion, thereby significantly enhancing the efficiency of resource utilization. This study explored a co-digestion system using dairy manure and cucumber vines as substrates, uncovering how total solids (TS) influence the methane yield and microbial community characteristics. All treatments exhibited swift methane fermentation, with daily production initially increasing before declining. Cumulative methane production increased with the increasing TS contents. These results may be linked to pH value and the concentration of volatile fatty acids (VFAs). Except for the 6% TS treatment, digesters across different TS levels maintained a favorable final pH of 7.4–8.4, while VFA concentrations exhibited a downward trend as TS contents increased. The treatment with the highest TS concentration (25%) demonstrated superior performance, achieving the maximum volumetric methane yield. This yield was 1.6 to 9.1 times higher than those obtained at low (6–10%) and medium (12–18%) TS concentrations. Microbial community analysis revealed that during the peak methane production phase, Firmicutes and Methanoculleus were the predominant bacterial and archaeal phyla, respectively. The microbial community structure changed with different TS levels. This study offers valuable scientific insights for enhancing biogas production efficiency in co-digestion systems. Full article

This study investigates the optimization of enzymatic hydrolysis for enhancing carbohydrate release from microalgal biomass and its subsequent impact on methane production during anaerobic digestion. Using Response Surface Methodology with a Box–Behnken design comprising 15 experimental runs, the effects of enzyme loading (20–40 mg/gVS), pH (4.5–5.5), and incubation time (24–72 h) were evaluated. A quadratic regression model was developed to predict carbohydrate release, revealing significant interactions between these factors. The optimal conditions for enzymatic hydrolysis were determined to be a cellulase dose of 20 mg/gVS, pH 5.0, and an incubation period of 72 h. The model demonstrated excellent predictive accuracy, with an R² value of 0.9894 and an adjusted R² of 0.9704. Enzymatic hydrolysis significantly improved methane and biogas yields, with cumulative production reaching 52.50 mL/gVS and 95.62 mL/gVS, respectively, compared to 6.98 mL/gVS and 20.94 mL/gVS for untreated samples. The findings highlight the importance of optimizing enzyme loading and reaction time, while pH variations within the studied range had minimal impact. This study underscores the potential of enzymatic hydrolysis to enhance the bioavailability of organic matter, thereby improving the efficiency of anaerobic digestion for biogas production. Full article

Anaerobic digestion (AD) is a sustainable strategy for converting hazardous wastes into renewable energy while supporting Sustainable Development Goals (SDGs). This study aimed to evaluate the effect of inoculum on optimizing biogas production from sewage sludge (SS) and cattle manure (CM). Bench-scale digesters were fed with 0, 20, and 40% inoculum prepared at a 1:3 SS:CM ratio. Substrate and digestate were analyzed for physicochemical properties, and biogas production data were fitted using nonlinear models. Kinetic parameters ranged from 0.0770 to 0.4691 L·kg⁻¹ for Y_max, from 1.0263 to 2.1343 L·kg⁻¹·week⁻¹ for μ_max, and from 0.8168 to 8.0114 weeks for λ, depending on the ratio. The 1:3 SS:CM with 40% inoculum significantly improved biogas production by reducing the lag phase and increasing weekly yield, with the Gompertz model showing the best fit to the digestion kinetics. This was particularly evident due to the favorable conditions for microbial adaptation and efficient substrate degradation. The results reinforce the concept of optimization as defined in this study, wherein the application of inoculum enhances the performance of AD by improving the physicochemical conditions of the substrate and accelerating microbial activity, thereby resulting in increased methane (CH₄) generation and overall biogas yield. Full article

The ongoing global population growth and the corresponding rise in energy demand have contributed to increased greenhouse gas (GHG) emissions. The integration of alternative, locally sourced energy solutions such as biogas presents a promising strategy to partially offset conventional energy consumption. In this context, countries like Colombia—characterized by a high availability of organic waste such as palm oil mill effluent (POME), rice straw, and pig manure—have the potential to harness these residues for biogas production. This study integrates experimental assays of anaerobic co-digestion tests with the spatial analysis of substrate distribution through GIS tools, enabling the identification of optimal regions for biogas production. Methane yields reached 412 mL CH₄/g VS, comparable or superior to those reported in similar studies. In addition to laboratory assays, Geographic Information System (GIS) tools were used to generate a weighted heatmap index based on feedstock availability (POME, rice straw, pig manure) across 40 municipalities in Colombia. This integrated approach supports decentralized renewable energy planning and helps identify optimal locations for biogas plant development. Full article

Internal Dry Reforming of Methane (IDRM) in biogas fed Solid Oxide Fuel Cells (SOFCs) was investigated on Fe-Au modified Ni/GDC electrolyte-supported cells at 900 and 850 °C. The aim was to clarify the synergistic interaction between Fe and Au, focusing on the effect of X wt.% of Au loading (where X = 1 or 3 wt.%) in binary Au-Ni/GDC and ternary 0.5 wt.% Fe-Au-Ni/GDC fuel electrodes. The investigation combined i-V, Impedance Spectroscopy and Gas Chromatography electrocatalytic measurements. It was found that modification with 0.5Fe-Au enhanced significantly the electrocatalytic activity of Ni/GDC for the IDRM reaction, whereas the low wt.% Au content had the most promoting effect. The positive interaction of 0.5 wt.% Fe with 1 wt.% Au increased the conductivity of Ni/GDC and enhanced the corresponding IDRM charge transfer electrochemical processes, especially those in the intermediate frequency region. Comparative long-term measurements, between cells comprising Ni/GDC and 0.5Fe-1Au-Ni/GDC, highlighted the significantly higher IDRM electrocatalytic activity of the modified electrode. The latter operated for almost twice the time (280 h instead of 160 h for Ni/GDC) with a lower degradation rate (0.44 mV/h instead of 0.51 mV/h). Ni/GDC degradation was ascribed to inhibited charge transfer processes in the intermediate frequencies region and to deteriorated ohmic resistance. Stoichiometric analysis on the (post-mortem) surface state of each fuel electrode showed that the wt.% content of reduced nickel on Ni/GDC was lower, compared to 0.5Fe-1Au-Ni/GDC, verifying the lower re-oxidation degree of the latter. This was further correlated to the hindered H₂O production during IDRM operation, due to the lower selectivity of the modified electrode for the non-desired RWGS reaction. Full article

An integrated approach is sorely needed to treat biogas emanating from anaerobic digesters (AD) which is cost-effective, in terms of upgrade/purification to ~95–98% methane needed for pipeline injection. This is a very pressing environmental and waste-management problem. At present, biogas water-/solvent-washing operations require significant capital investment, with high operational and maintenance costs. In the present study, we deployed a facile and efficient novel nanobubble-formation approach using applied electric fields to boost biogas-enrichment operations: we achieve substantial methane enrichment via selective CO₂ and H₂S take-up in water in the form of nanobubbles. This enables an integrated waste-processing vision using cutting-edge engineering-science advances, and making anaerobic digestion a circular-economic and practical reality, that can be deployed at scale—initially developing at the small scale—and points the way for low-energy CO₂ capture in the form of nanobubbles by dint of the electric-field approach. In addition, we carried out nanobubble generation using various gases for water treatment for both up- and down-stream sludge-containing (waste)water, achieving meaningful operational successes in AD operations and organic-fertiliser production, respectively. Full article

The European Union views biogas production from landfills as a crucial element in achieving decarbonization goals by 2050. Biogas is primarily composed of methane (CH₄) and carbon dioxide (CO₂), produced through the anaerobic digestion of various residual materials. This study aimed to investigate CH₄ and CO₂ concentrations from municipal solid waste in biogas capture wells in a landfill in Romania between 2023 and 2024. A peak in CH₄ concentrations occurred in the fall of 2024 (P4 well), while the highest CO₂ content was recorded in the summer of 2023 (P3 well). The Aermod View software platform (version 11.2.0) was employed to model the dispersion of pollutants in the surrounding air. A worst-case scenario was applied to estimate the highest ground-level pollutant concentrations. The highest recorded CH₄ concentration was 90.1 mg/m³, while CO₂ reached 249 mg/m³ within the landfill. The highest CH₄ concentrations were found in the southern part of the site, less than 1 km from the landfill, while CO₂ was highest in the northern area. In conclusion, municipal solid waste landfills behave like unpredictable bioreactors, and without proper management and oversight, they can pose significant risks. An integrated system that combines prevention, reuse, and correct disposal is critical to minimizing these negative effects. Full article

Today, there is considerable interest in creating artificial microbial consortia to solve various biotechnological problems. The use of such consortia allows for the improvement of process indicators, namely, increasing the rate of accumulation of target products and enhancing the conversion efficiency of the original substrates. In this work, the prospects for creating artificial consortia based on anaerobic sludge (AS) with cells of different yeasts were confirmed to increase the efficiency of methanogenesis in glucose- and glycerol-containing media and obtain biogas with an increased methane content. Yeasts of the genera Saccharomyces, Candida, Kluyveromyces, and Pachysolen were used to create the artificial consortia. Their concentration in the biomass of consortium cells was 1.5%. Yeast cells were used in an immobilized form, which was obtained by incorporating cells into a cryogel of polyvinyl alcohol. The possibility of increasing the efficiency of methanogenesis by 1.5 times in relation to the control (AS without the addition of yeast cells) was demonstrated. Using a consortium composed of methanogenic sludge and yeast cells of the genus Pachysolen, known for their ability to convert glycerol into ethanol under aerobic conditions, the possibility of highly efficient anaerobic conversion of glycerol into biogas was shown for the first time. Analysis of the metabolic activity of the consortia not only for the main components of the gas phase (CH₄, CO₂, and H₂) and metabolites in the cell culture medium, but also for the concentration of intracellular adenosine triphosphate (ATP), controlled by the method of bioluminescent ATP-metry, showed a high level of functionality and thus, prospects for using such consortia in methanogenesis processes. The advantages and the prospect of using the developed consortia instead of individual AS for the treatment of methanogenic wastewater were confirmed during static tests conducted with several samples of real and model waste. Full article

The influence of introducing fluctuations in acetate feeding concentrations on the process stability of a lab-scale horizontal anaerobic reactor (HAR) was investigated to ascertain its effects on acetoclastic methanogenesis. Acetate concentrations were randomized at 85 g COD/L ± 20% and discontinuously fed in the duplicate HARs for five days per week (giving the system time to rest and equilibrate for two days). The reactors were monitored daily with respect to performance indicators (physicochemical variables). The residual acetate concentration was observed to fluctuate at the initial stages, followed by a converging trend (decrease in variance) until the end of operation. Furthermore, letting the system self-neutralize and equilibrate during rest days resulted in improved process performance. The daily acetate degradation efficiency at ~90% and methane concentration at ~60% were attained after operating the reactors for 80 days. The results divulged that introducing fluctuations in acetate feeding concentrations does not affect the stability of biogas production and methane concentration. The acclimatization of the methanogenic population (predominantly Methanosaeta, then shifting to Methanosarcina) was also observed. Full article

This study presents an integrated approach for the remediation of zinc- and ammonium-contaminated water using duckweed, followed by the valorization of the harvested biomass through anaerobic digestion for biogas production. Duckweed was cultured with various initial concentrations of zinc (Zn, 0 mg/L, 2.5 mg/L, and 5 mg/L) and ammonium (NH₄⁺-N, 0 mg/L, 20 mg/L, and 40 mg/L). Subsequently, duckweed was subjected to chemical pretreatment with sulfuric acid and the obtained residual solid and liquid fractions were evaluated as substrates for methane production. The liquid fraction consistently yielded higher methane production compared to the solid fraction. However, when duckweed was grown in zinc- and ammonium-rich conditions (2.5 or 5.0 mg/L Zn and 20 mg/L NH₄⁺-N), methane production from the liquid hydrolysate was significantly reduced (120.90 ± 12.03 mL/g COD and 129.82 ± 10.65 mL/g COD, respectively) compared to the control duckweed (201.67 ± 5.72 mL/g COD). The lowest methane yields were observed for duckweed grown solely in zinc (111.32 ± 5.72 and 99.88 ± 10.49 mL/g COD for 2.5 and 5.0 mg/L Zn, respectively), attributed to the inhibitory effect of high dissolved zinc concentrations in the liquid fraction. The applicability of this integrated system is particularly relevant for the agricultural and industrial sectors, where wastewater streams are often co-contaminated with nutrients and trace metals. By demonstrating that acid-pretreated, zinc-rich duckweed biomass can be used for biogas production—provided that process conditions are optimized to mitigate metal inhibition and acidification—this study provides actionable strategies for developing circular, sustainable wastewater treatment systems. The approach not only maximizes pollutant removal and resource recovery, but also addresses environmental safety concerns associated with residual metals in the digestate. Full article