Search Results (793)

Keratin is an abundant, recalcitrant structural protein that constitutes the primary component of several animal wastes, particularly chicken feathers. Because of their potential and availability, various technologies, such as anaerobic biodigestion, have been used to degrade keratin and transform feathers into biogas and other value-added products. However, due to their fibrous architecture and rigid structure, keratinous materials are elastic, water-insoluble, and enzymatically resistant, which makes natural degradation difficult. In this sense, before using chicken feathers as feedstock in biodigesters, the keratin in the residue must be cleaved in pretreatment steps. Whether as a single substrate or in co-digestion processes, the keratin breakdown is critical for enhancing biogas production from feathers. In this context, there is growing emphasis on developing pretreatment methods to facilitate protein hydrolysis and digestion, thereby improving biogas generation. To evaluate progress in recycling waste keratin, a bibliometric analysis of original scientific publications on the pretreatment of chicken feathers for anaerobic digestion was conducted using the Scopus database. The findings indicate that researchers apply chicken feathers in processes, including standard biodigestion, co-digestion with food waste, animal manure, and slaughterhouse waste, for biomethane and biohydrogen production. Across the evaluated studies, the pretreatment methods showed notable improvements in feather solubilization and subsequent biogas yield; however, they still encounter key limitations, including ammonia (NH₃) inhibition, high chemical/reagent costs, and high energy demand. Full article

Conventional anaerobic digestion relies on diverse inocula present in sludge-based systems. A defined consortium approach was investigated as an alternative. Acetivibrio cellulolyticus was chosen as the cellulose degrader, and two strains of Methanosarcina barkeri were selected as methane producers. Initial cultivation following manufacturer protocols highlighted significant challenges in maintaining strict anaerobic conditions, particularly in the absence of specialized infrastructure. A simplified anaerobic cultivation workflow was therefore evaluated for pure cultures of the selected anaerobes and subsequently used to evaluate a defined consortium using microcrystalline cellulose (MCC) and industrial lignocellulosic biomass (LB) residue as growth substrates. The workflow enabled successful cultivation of pure cultures in their recommended nutrient media without detectable contamination, as assessed by microscopy, aerobic contamination checks, and gas chromatography analysis. Growth-associated observations were obtained on MCC after prolonged incubation (~30 days); however, a metabolically active cellulolytic–methanogenic consortium was not established, as methane was not detected and no activity was detected on the LB substrate. This study demonstrates that anaerobic cultivation of fastidious microorganisms is feasible using a simplified method without fully controlled anaerobic environments and highlights inherent challenges associated with the defined consortium on substrates such as MCC and complex LB residue. The simplified workflow may provide an accessible approach to anaerobic cultivation for sustainable biomethane research in laboratories lacking specialized anaerobic infrastructure. Further work is required to determine conditions supporting methane production using the defined consortium. Full article

This research proposes an approach based on a circular economy principle for the integral valorization of Sargassum from the Mexican Caribbean. The biomass was characterized through proximal and elemental analyses, and then an oxidative pretreatment was carried out to enhance a sequential processing scheme to extract sodium alginate and use the solid waste as a substrate for biogas production via anaerobic digestion. The oxidative pretreatment successfully reduces the recalcitrant content and the concentration of heavy metals. The sodium alginate extracted from treated biomass achieves a yield higher than 20%; the characterization of the polymer via nuclear magnetic resonance showed that the mannuronic-to-guluronic ratio was between 0.34 and 0.62, indicating the potential for its use for environmental and biomedical applications. The highest yield in methane production was 328 mL CH₄/g of volatile solids, with a purity of 90%, and was achieved using the waste from alginate extraction with an inoculum-to-substrate ratio of 1:1. The experimental data presented an excellent fit to a Gompertz model (R² > 0.99). The proposed valorization pathway improves the sustainability of Sargassum management, prioritizing the recovery of high-value compounds before energy production. This circular approach provides a framework for converting environmental challenges into opportunities in the Caribbean. Full article

Rapid population growth, urbanization, and industrialization are continuously increasing global energy demand while intensifying climate change associated with fossil fuel consumption. In this context, renewable energy production from organic waste has gained increasing attention as a sustainable and environmentally friendly strategy. Anaerobic digestion (AD) offers significant potential for simultaneous waste stabilization and biomethane generation. However, many previous studies investigating lignocellulosic or nutrient-rich substrates have relied on physical, chemical, or thermal pretreatment methods to enhance biodegradability, despite their additional operational costs, energy consumption, and environmental impacts. Therefore, developing low-cost and pretreatment-free co-digestion strategies remains an important research need. This study investigated the biomethane production potentials of untreated chicken manure (CM) and duckweed (Lemna minor-LM) collected from the final sedimentation tanks of wastewater treatment plants under mono-digestion and co-digestion conditions. The study hypothesized that rapidly growing and widely available LM biomass could enhance methane production without requiring pretreatment. Among all reactors, CM0.75 (75% of the total TS derived from CM and 25% from LM and inoculum) achieved the highest performance with a cumulative biogas production of 5350 mL (74.2% of CH4) and a methane yield of 327 mL CH4/g VS, while mono-digestion of CM resulted in the lowest methane yield of 104 mL CH4/g VS. The results demonstrated that LM biomass naturally proliferating in wastewater treatment plants can be directly utilized as an effective co-substrate to improve biomethane production from poultry wastes. The proposed approach provides a cost-efficient, eco-friendly, and circular-economy-oriented alternative by eliminating the need for pretreatment while simultaneously valorizing problematic biomass generated in wastewater treatment facilities. Full article

Horse manure is an abundant lignocellulosic feedstock with potential for circular biorefineries to diversify and upgrade the methane value chain. However, integrated fractionation strategies enabling the simultaneous valorization of both polysaccharides and lignin remain poorly explored. Here, we developed the Coffionic strategy, a closed-loop, green iono-organosolv fractionation combining, in a two-step, one-batch approach, the eco-acceptable ionic liquid 1-ethyl-3-methylimidazolium acetate and the food-grade solvent 2-methyltetrahydrofuran-3-one, with full solvent recovery and recycling. This strategy selectively recovered 70% w/w of the lignin from horse manure, yielding a Coffionic lignin fraction with a purity of 78% w/w and less than 2.5% w/w of residual sugars. The resulting polysaccharide-rich fraction showed enhanced enzymatic digestibility, achieving >99% cellulose conversion and increasing the biochemical methane potential by 17% compared with untreated horse manure. Coffionic lignin was further upgraded by enzymatic transesterification using immobilized Novozym435^® in the same food-grade solvent employed for fractionation, yielding lignin esters compatible with PLA. Esterified lignin–PLA films reached a total surface energy significantly higher than neat PLA and unmodified lignin–PLA films. Overall, the Coffionic strategy provides an integrated and low-waste biorefinery route enabling the simultaneous production of biomethane and high-value lignin-based materials from horse manure. Full article

Very large-scale biogas (biomethane) projects are important infrastructure systems for integrating organic waste treatment, renewable energy substitution, and carbon mitigation under China’s carbon peaking and carbon neutrality goals. However, their long process chains, concentrated hazardous media, and frequent confined-space operations create coupled safety risks that may undermine sustainable operation. To identify the dominant risk drivers and safety governance priorities, this study investigated five operating very large-scale biogas projects in Shanxi Province, China. On-site inspections, semi-structured interviews, and document reviews were used to identify ten safety-risk causative factors. The Decision-Making Trial and Evaluation Laboratory (DEMATEL) method was combined with Interpretive Structural Modeling (ISM) to quantify causal relationships and reveal the hierarchical transmission structure among the factors. The results show a structural imbalance between document-based compliance and operational implementation. Although basic safety documents were generally established, only 20% of the projects had scenario-specific emergency response plans for major accident scenarios; the compliance rate of explosion-proof electrical equipment, the configuration rate of fixed monitoring and alarm systems for combustible and toxic gases, and the effective operation rate of forced ventilation facilities were 40%, 60%, and 40%, respectively. Insufficient enterprise safety investment (M1) and unclear external regulatory responsibilities (M2) were the dominant root causes of system-level risk propagation, while inadequate control of high-risk operations (M9) and unsafe worker behavior (M10) were the final manifestations. A four-pillar governance pathway is proposed, including policy and standard improvement, technological support and equipment upgrading, personnel capacity enhancement, and sustainable funding mechanisms. The findings provide empirical evidence for risk-based supervision and indicate how operational safety governance can serve as an enabling condition for the long-term sustainability of the biomethane industry, rather than as a direct measurement of carbon-mitigation or energy-performance outcomes. Full article

Electrified steam methane reforming (eSMR) is emerging as a promising technology for the decarbonization of the chemical industry and low-carbon hydrogen production by coupling renewable electricity with renewable gaseous feedstocks such as biomethane. In this work, structured Ni-based catalysts washcoated on highly thermally conductive SiC open-cell foams (OCFs) were developed and evaluated for biomethane steam-reforming operating conditions. Two catalyst formulations, 30 wt.% Al₂O₃_30 wt.% CeO₂_20 wt.%Ni and SiC_30 wt.% Al₂O₃_30 wt.%Ce_0.25Zr0.75 O₂_20 wt.%Ni, were tested in a laboratory-scale indirectly electrically heated reformer. The high thermal conductivity of the SiC-structured support ensured efficient heat transfer throughout the reactor, limiting radial temperature gradients to below 10 °C. Both catalyst formulations exhibited excellent catalytic performance; however, the Ce_0.25Zr0.75O₂-promoted catalyst achieved the best results, maintaining equilibrium methane conversion at a gas hourly space velocity above 7000 h⁻¹ while reaching a specific electrical energy consumption of 2.06 kWh/Nm³ of produced H₂ projected for industrial-scale efficiency. Notably, these performances were obtained with a catalyst loading approximately 20–50% lower than that of conventional commercial alumina pellet catalysts. XRD characterization did not reveal the formation of crystalline graphitic carbon after catalytic operation. Furthermore, the structural evolution of the Ce–Zr–O highlights the active role of the mixed oxide in promoting redox processes and maintaining catalytic activity under reaction conditions. Overall, these results demonstrate that the combination of highly conductive SiC-structured supports and Ce–Zr-promoted Ni catalysts significantly enhances both the thermal and catalytic efficiency of eSMR. The proposed catalyst provides a promising route toward compact, energy-efficient, and decentralized hydrogen production from biomethane, supporting the electrification and decarbonization of future hydrogen generation technologies. Full article

The agricultural and livestock sectors of Latin America produce a large number of residues that could be converted into energy through bioenergy production processes. However, the bioenergy sector still faces several limitations across the region, including fragmented logistics systems, weak coordination among institutions, and limited integration of environmental, digital, and compliance-related performance indicators. This review systematically analyses residue-based bioenergy value chains in Latin America between 2015 and 2025 using the PRISMA methodology to evaluate selected peer-reviewed studies and regional reports indexed in Scopus, ScienceDirect, SpringerLink, and IEEE Xplore, and institutional repositories. The final synthesis included 37 studies and institutional contributions, which were further disaggregated into 208 country–residue observations for the regional and feedstock distribution analysis. The review identified three main research gap categories: the limited integration of collection and logistics systems, the insufficient treatment of uncertainty, circularity, and traceability within optimization models, and the weak incorporation of governance and institutional coordination into bioenergy value-chain design. The analysis includes biogas, biomethane and related residue-based systems, with attention to supply-chain optimization, policy alignment, methane mitigation metrics, and traceability requirements. Results indicate that although technologies such as biomass pretreatment, process intensification, and upgrading processes continue to improve conversion performance, most studies still focus mainly on technical feasibility and biomass potential. Less attention is given to governance constraints, uncertainty analysis, and monitoring systems capable of supporting regulatory compliance. This research introduced the Sustainable Bioenergy Chain Management Framework (SBCMF) to respond to these limitations and bring together different aspects of bioenergy management within one analytical structure. The framework combines supply-chain optimization under spatial and temporal constraints, circular economy valorisation, methane-related climate performance, and digital traceability, while also linking techno-economic system design with governance and monitoring requirements. In this way, it can help support the development of more transparent and low-carbon bioenergy systems across Latin America. Full article

The transition towards circular economy models is driving the transformation of wastewater treatment plants (WWTPs) from energy-intensive facilities into resource recovery systems capable of generating renewable energy. In this context, this study developed an integrated mass and energy balance methodology to assess sludge production, anaerobic digestion performance, biomethane recovery, and electricity generation in a full-scale urban WWTP. The proposed framework integrates the water treatment line, sludge processing line, and energy recovery system, combining primary and secondary sludge management with biogas upgrading and combined heat and power (CHP) generation. Representative operating parameters from the scientific literature were applied to a facility treating 204,000 m³ d⁻¹ and serving approximately 425,000 population equivalents. The results showed that primary sludge accounted for approximately 70% of the volatile solids fed to the anaerobic digester. Methane production was estimated at 1.12 × 10³ kg CH₄ d⁻¹, corresponding to a biogas production of 2.40 × 10³ m³ d⁻¹. Under two alternative valorisation scenarios, the maximum recovered biomethane flow was 1.48 × 10³ m³ d⁻¹, whereas the maximum annual electricity generation potential through CHP was 1.9 × 10⁶ kWh. These findings highlight the potential of integrated sludge valorisation strategies to enhance renewable energy recovery and support the transition of WWTPs towards energy-efficient and low-carbon resource recovery facilities. Full article

European smart cities face a distinct decarbonisation challenge in the gas component of urban energy consumption, which cannot be addressed through internal optimisation alone. The European Union (EU) Mission for Climate-Neutral and Smart Cities selected 112 cities for climate neutrality by 2030, including Bucharest Sector 2, Cluj-Napoca, and Suceava in Romania. The Mission timeline coincides with the Russian pipeline gas phase-out under Regulation (EU) 2026/261, the 5 August 2026 transposition deadline for the Hydrogen and Decarbonised Gas Market Package (also referred to as the Fourth Gas Package), and the post-Hormuz energy market environment of 2026. This paper develops a hinterland framework that links Romanian Mission cities to their rural renewable gas supply through biomethane and renewable hydrogen production, integrated with circular bioeconomy strategies and routed through the national transmission system operated by Transgaz. The empirical analysis combines documentary evidence from the May 2026 consultation on Government Emergency Ordinance 9/2026, institutional documentation of Transgaz and Romgaz, and the comparative European literature on smart city renewable energy integration. Findings show that Mission city decarbonisation pathways depend on rural-to-urban gas infrastructure calibration under the post-2024 regulatory cascade. The paper proposes specific deployment strategies for each Romanian Mission city. Full article

The article assesses the energy potential of biodegradable municipal waste in the Krakow Metropolitan Area, analyzing the feasibility of using derived biomethane for residential heating by 2050. Framed within the circular economy and the European Green Deal, the study highlights a significant technological gap in Poland, contrasting it with successful models in Austria, Germany, and Italy. Empirical data from 2023–2024 indicate that kitchen waste (code 20 01 08) is an optimal feedstock for methane fermentation due to its stable annual flow, whereas green waste (code 20 02 01) presents challenges due to high seasonality. Simulation modeling suggests that annual biomethane production from kitchen waste could range from approximately 1.23 million m³ (Variant 3) to over 1.42 million m³ (Variant 4). A key finding is the synergy between waste-to-energy transformation and building thermal modernization. By reducing energy demand, the consistent volume of kitchen waste processed from 2024 could potentially supply heating for between 4928 and 8180 apartments by 2050. Ultimately, the research underscores the role of metropolitan integration in achieving sustainable development goals, enhancing regional energy security, and reducing emissions. Full article

Anaerobic digestion (AD) is a common waste management method for producing renewable energy from biogas. However, animal manures typically have low C/N ratios, which can limit biogas recovery. This study aims to optimize biogas production through the co-digestion of goat manure (GM) with high-C/N lignocellulosic rice husk (RH) and sludge as the inoculum. Characterization of the substrate and inoculum revealed a low GM C/N ratio (GM = 21.3), whereas RH has a high-C/N (RH = 107.3). The volatile solids-to-total solids (VS/TS) ratios were around 82–85% for GM and RH. Batch experiments were conducted at different organic loading rates, with an inoculum-to-substrate ratio of 2:1 (mL:g), at 36 ± 1 °C for 65 days. This study investigates optimizing biomethane recovery by using serum-bottle biomethane potential (BMP) and compares kinetic performance and yields across different GM-to-RH ratios with the characteristics of the influent and effluent. The highest BMP values (mL CH₄/g_VS) occurred at 100% GM (245.1), followed by 90% GM (233.6) and 30% GM (232.5), indicating a strong synergy between GM and RH at specific mixing ratios. Kinetic modeling using both the modified Gompertz and first-order models effectively described digestion dynamics, allowing for estimation of potential lag phases and maximum production rates. These models aligned well with experimental data across substrates, aiding process design. Overall, the results show that strategic co-digestion of GM with RH can maximize methane recovery, with defined substrate ratios and a clear understanding of the kinetics essential for scale-up and sustainable biogas production. Full article

In this study, thermophilic anaerobic digestion (TAD, 60 °C) was evaluated as a downstream waste-to-energy step within a cascading thermophilic biorefinery using four interrelated substrates—primary cafeteria wastes (pCFWs) and primary corn stover wastes (pCSWs) were evaluated without physicochemical pretreatment. Their corresponding secondary substrates, secondary cafeteria waste (sCFW) and secondary corn stover wastes (sCSWs), were residual solids generated after thermophilic bioethanol production and exopolysaccharide production, respectively. To our knowledge, this is the first study to demonstrate sequential thermophilic valorization in which primary wastes are untreated and the remaining biotreated secondary residues are subsequently converted into biomethane, adding each step to bioeconomy. Biomethane potential was quantified to determine how substrate composition and upstream bioprocessing influence methane yield and biodegradability. In the batch, pCFW achieved the highest biodegradability (84% VS reduction) but suffered rapid acidification at higher loadings, whereas pCSW was hydrolysis-limited by lignocellulosic recalcitrance. Upstream bioprocessing (biological pretreatment) improved digestibility, with sCSW exhibiting a 1.8-fold increase in methane yield (300 L CH₄ kg⁻¹ VS) relative to pCSW. All co-digestion treatments outperformed monodigestion, with the best-performing (among the tested) sCFW:sCSW ratio of 3:1 delivering the highest methane yield (413 L CH₄ kg⁻¹ VS) and VS reduction (95.8%). Scale-up in a 40 L fed-batch reactor achieved methane productivities of 49–142 L CH₄ kg⁻¹ VS per feeding cycle, reaching stable operation after two cycles, with cumulative methane production of ~800 L CH₄ kg⁻¹ VS for secondary wastes compared to ~550 L CH₄ kg⁻¹ VS for primary wastes. Microbial analysis revealed dominance of syntrophic acetate-oxidizing bacteria (Acetomicrobium, 22.6%) and hydrogenotrophic methanogens (Methanothermobacter, 72.3%). Therefore, biologically pretreated wastes enabled higher methane recovery and improved solids destruction under thermophilic conditions and demonstrates circular conversion of wastes into renewable biomethane. Full article

Calcium hypochlorite (CH) is a strong oxidant that can be utilized to enhance sludge hydrolysis and anaerobic digestion (AD) performance; however, its suppressive effect on methanogens restricts the development of CH treatment technologies. This laboratory-scale study introduced zero-valent iron (ZVI) into a CH-treated sludge AD system to alleviate the adverse effect, thereby synergistically enhancing biomethane production, and the correlation between methane yield and the two key treatment parameters (ZVI and CH dosages) was explored. The experimental results revealed that the best conditions for the ZVI + CH method were 5 g/L of ZVI plus 0.12 g/g of volatile suspended solids (VSSs) of CH, under which the maximum biomethane yield of 275.8 mL/g VSS was achieved, representing increases of 81.5%, 43.2%, and 28.2% over the control, solo ZVI, and solo CH conditions, respectively. More organic matter in the sludge was found to be degraded during AD by the ZVI + CH treatment compared with the control, solo ZVI, or solo CH conditions. An enzyme activity analysis illustrated that the ZVI + CH treatment not only enhanced the bioactivity of anaerobes but also eliminated the suppression of methanogens by CH. A microbial analysis demonstrated that all functional microbes responsible for sludge AD were enriched by the ZVI + CH treatment, with total abundances of 8.41% and 20.58% in the control and ZVI + CH-treated reactors, respectively. Full article

Ex situ hydrogen biomethanation represents a promising approach to converting surplus renewable electricity into CH₄-rich gas through the biological reduction in CO₂ with H₂, mediated by hydrogenotrophic methanogens. In this study, an ex situ H₂ biomethanation process was investigated in a lab-scale mesophilic anaerobic reactor operated in fed-batch mode. The system followed a cyclic operational strategy comprising sequential gas feeding, reaction, and discharge phases. Hydrogen was supplied through a pressure-controlled feeding strategy, whereas CO₂ injection maintained dissolved CO₂ concentrations at 25, 17, and 2 mg L⁻¹ during the initial, intermediate, and final stages, respectively. During early operation, volatile fatty acids (VFAs) temporarily accumulated to 3 g L⁻¹, accompanied by a decrease in pH. Progressively lowering the dissolved CO₂ target restored process stability, reduced the VFA concentration to 618 mg L⁻¹, and increased the pH to 7.6. Under stable final-stage conditions, the reactor achieved an average CH₄ concentration of 93.3%, a hydrogen utilization efficiency of 99%, and a methane evolution rate (MER) of 3.95 NL CH₄ L_VR⁻¹ d⁻¹. These results show that combining pressure-controlled hydrogen injection with dissolved CO₂ regulation enhances methane production and maintains stable ex situ biomethanation. Full article