Search Results (805)

Small-scale biogas systems in developing regions are predominantly mono-digestion systems utilizing livestock manure as the primary feedstock. However, crop residues such as wheat straw offer significant potential for improving feedstock diversity and biogas production when applied in anaerobic co-digestion systems. Due to the recalcitrant nature of lignocellulosic biomass, pretreatment is required to enhance substrate degradability and methane production. In this study, the performance of integrated pretreatment and anaerobic co-digestion of cattle manure and wheat straw was evaluated using the modified ADM1_R3 model. Simulations were conducted under varying feedstock mixing ratios (0 to 100%wt wheat straw), pretreatment intensities (carbohydrate degradability levels of 50%, 67%, and 75%), organic loading rates (1 to 4 kgVSm⁻³day⁻¹), and digester volumes (2, 4, and 6 m³). The results showed that increasing the wheat straw fractions improved biogas production, although with a slight reduction in methane. Pretreatment further enhanced overall process performance, with biogas production enhancement of between 40% and 56% across the different mixing ratios and degradability increase from 50 to 75%, while higher loading rates combined with higher pretreatment intensities increased the risk of process instability. The findings demonstrate the feasibility of this innovative approach of flexible small-scale co-digestion systems supported by appropriate pretreatment strategies. This study advances the application of anaerobic digestion modelling to small-scale biogas systems by providing an integrated framework for evaluating the effects of operational and design parameters on technical performance. Full article

Wastewater sludge can improve soil fertility and support resource recycling, but potential heavy metal accumulation limits its agricultural application. In this study, we evaluated the effects of anaerobically digested wastewater sludge, applied alone or in combination with the purple non-sulfur bacterium (Rhodopseudomonas palustris), on two green manure crops, Sesbania cannabina and Glycine max. A 90-day pot experiment was conducted with five treatments: control, sludge at 10 and 20 t/ha, and each sludge level combined with R. palustris. Soil physicochemical properties, plant biomass production, and heavy metal concentrations in soil and plant tissues were analyzed. Sludge application increased soil total carbon, total nitrogen, and available phosphorus, while co-application with R. palustris further enhanced phosphorus availability. The greatest biomass production response was observed in G. max under 20 t/ha sludge plus R. palustris, with a 78% increase after 90 days. However, heavy metal concentrations and plant uptake generally increased with sludge dosage, particularly for Ni and Cr. These results indicate that sludge–PNSB application may improve soil fertility and biomass production, but heavy metal risks require careful evaluation. Full article

Efficient utilization of agricultural residues plays an important role in advancing sustainable bioenergy development in China. This study established a multi-criteria evaluation framework integrating energy quality, economic performance, and environmental impact to assess three representative straw-to-energy pathways: direct combustion for power generation, anaerobic digestion for biogas production, and lignocellulosic ethanol production. The Analytic Hierarchy Process (AHP) was applied to determine indicator weights and calculate composite scores using operational and pilot-scale data obtained for each pathway. The results showed that anaerobic biogas achieved the highest overall performance (composite score 0.41), with balanced performance in economic viability, energy utilization efficiency, and environmental performance. Direct combustion demonstrated favorable economic performance (0.37) but exhibited higher process emissions, whereas lignocellulosic ethanol showed superior environmental performance but suffered from low energy conversion efficiency and negative economic returns (0.00). Sensitivity analysis confirmed the stability of the pathway ranking and highlighted the dominant influence of economic and energy-related indicators on the overall sustainability assessment. The study demonstrated that anaerobic biogas exhibited the most balanced performance among the evaluated pathways under the investigated technological and economic conditions, while integrated biorefining approaches, such as co-production of ethanol and biogas, showed potential for further enhancing resource efficiency and sustainability. Full article

This study, conducted in the Ecuadorian Andes, evaluated the anaerobic co-digestion of local crop residues (amaranth and quinoa) with llama, vicuña, and pig manure to analyze methane production kinetics. The raw materials were characterized by proximate, elemental, and structural analyses, and biogas volume and the CH₄ fraction were monitored daily. The Amaranth-vicuña and Amaranth-llama treatments reached 77.29 ± 5.63 and 64.62 ± 3.62 mL biogas/g VS and 36.20 ± 7.29 and 31.78 ± 3.62 mL CH₄/g VS, respectively; in contrast, Quinoa-vicuña and Quinoa-llama produced only 1.04 ± 0.25 and 0.24 ± 0.03 mL CH₄/g VS. Monod-model parameters were estimated using an apparent formulation based on the methane production rate, and the kinetic behavior was compared with first-order, modified Gompertz, and modified logistic models. In addition, artificial neural networks (ANNs) were evaluated to predict the methane production curve from substrate characterization. Network 44, with a 13-15-10-1 architecture, yielded an overall R² = 0.998, validation R² = 0.997, and validation MSE = 0.415. Ten-times repeated five-fold cross-validation of the same architecture yielded R² = 0.985 ± 0.007 and RMSE = 1.21 ± 0.28 mL CH₄/g VS, supporting its interpolation capability within the experimental domain, although this does not demonstrate extrapolation to new substrate combinations. Overall, the proposed approach combines interpretable kinetic parameters with ANN-based prediction, but external validation with independent datasets is still required. The reported yields correspond to the specific production achieved in a low-cost batch system operated at room temperature and should not be interpreted as standardized biochemical methane potential (BMP) values. Full article

Anaerobic digestion (AD) plays a key role in the circular bioeconomy by converting organic waste into renewable energy and facilitating the sustainable utilisation of waste materials. Agricultural and agro-industrial by-products are increasingly recognised as valuable AD feedstocks due to their widespread availability and significant bioenergy potential. However, many of these substrates contain plant-derived bioactive compounds, such as polyphenols, tannins, flavonoids and terpenes, which can influence microbial communities and process performance. Depending on their concentration and chemical characteristics, these compounds may inhibit microbial activity, impair process stability, and ultimately decrease methane production. This review critically synthesises current knowledge on the occurrence, bioavailability and biological activity of plant-derived bioactive compounds in agricultural feedstocks used for anaerobic digestion, with particular emphasis on their implications for process performance and reactor stability. The principal mechanisms through which phytochemicals influence anaerobic digestion include enzyme inhibition, membrane disruption, interference with syntrophic interactions and trace metal chelation. The available evidence demonstrates a pronounced dose-dependent response, whereby low concentrations may exert neutral or selective modulatory effects. In contrast, elevated concentrations disrupt microbial activity, leading to volatile fatty acid accumulation, prolonged lag phases and reduced methane production. Current mitigation strategies include substrate pretreatment, co-digestion, microbial adaptation, adsorbent-assisted detoxification and the use of DIET-promoting materials. An integrated evidence matrix is proposed to link phytochemical composition with reactor configuration, operational parameters and mitigation strategies, thereby providing a practical framework for feedstock-specific process optimisation. Overall, the available evidence demonstrates that reliable evaluation of agricultural feedstocks should extend beyond conventional biochemical methane potential assessment to incorporate phytochemical composition, microbial functional responses and key operational parameters. Such an integrated approach can improve the prediction of methane recovery and support evidence-based optimisation of anaerobic digestion within circular bioeconomy systems. Full article

This study presents a kinetic evaluation of anaerobic co-digestion of pulsed electric field (PEF)-pretreated corn stover using three models: the Modified Gompertz (MG), Logistic, and Reaction Curve (RC). The objective was to assess model performance and improve the interpretation of biogas production dynamics beyond cumulative biogas yield analysis. Experimental data were obtained from batch mesophilic digestion of fine and coarse corn stover fractions subjected to PEF pretreatment with applied voltages of 350 V and 1 kV. All models achieved high coefficients of determination (R² ≥ 0.97), indicating good agreement between experimental and modeled biogas production curves. However, error metrics and information criteria revealed clear differences in predictive performance. The MG model provided the closest agreement with experimentally determined biogas production potential (Bmax), whereas the Logistic model consistently underestimated both Bmax and the maximum biogas production rate (Rmax). The RC model yielded the lowest prediction errors and favorable information criteria values but showed greater sensitivity to the initial phase of biogas production, occasionally overestimating Bmax and Rmax. Moderate PEF pretreatment increased both Bmax and Rmax, particularly in the fine fractions, without substantially prolonging the lag phase. In contrast, pretreatment at the higher applied voltage resulted in more heterogeneous kinetic responses, including prolonged lag phases and increased variability of kinetic parameters. 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

Resilience and adaptation to extreme climate events have become an urgent necessity. As cities grow denser, increasing numbers of people are exposed to water scarcity, flooding, and power grid disruptions. Immediate action is required to safeguard human lives and property. Residential buildings exert a significant environmental impact throughout their operational phase, contributing to air, land, and water pollution. A more sustainable and proactive approach to building management is essential to reduce the consumption, processing, and disposal of natural resources. This article explores the potential for biogas production from decentralised/on-site wastewater treatment systems through the co-digestion of blackwater (BW) and kitchen waste (KW) for existing residential buildings located in densely populated urban areas using hybrid grids. It addresses the importance of wastewater source separation, the use of BW and KW blends to achieve the best biogas production, and the environmental, economic and social aspects of these systems’ implementation. An extensive literature review and state-of-the-art analysis were conducted to assess the potential, main challenges, and research directions in this field. The results indicate that decentralised anaerobic systems can be technically feasible, reducing grid energy dependence, optimising water use, and valorising digestate as fertiliser—fully aligned with the EU’s Green Deal and the UN Sustainable Development Goals regarding sustainability and circularity. However, few studies address the feasibility of BW (vacuum toilet) and KW co-digestion for combined heat and power generation in hybrid grids. Further pilot- and full-scale research is therefore needed to increase system reliability and social acceptance. Full article

The environmental sustainability of farms can be improved by the adoption of sound manure management techniques, with anaerobic digestion (AD) being one of the most promising: AD offers the production of renewable fuel, biogas or biomethane, and prevents the emissions of odors and greenhouse gases. While anaerobic digestion (AD) is widely implemented for treating dairy, pig, and poultry manure, limited interest has been directed toward horse farms. A laboratory-scale experiment was performed to assess the biochemical methane potential of horse manure and straw-based horse litter. The test was conducted using a BioReactor Simulator system (six digesters, 2.0 L each) at 38 °C for 40 days, using inoculum from a 1 MWe biogas plant fed with dairy cow manure and silages. Horse manure presented total solids (TS) of 19.4% and volatile solids (VS) of 90.7% TS, while straw-based horse litter showed a TS of 49.8% and VS of 90.0% TS. Methane yields of 48.2 NL/kg, 237.6 NL/kgTS, and 262.1 NL/kgVS were obtained for horse manure, and 82.1 NL/kg, 164.9 NL/kgTS, and 183.2 NL/kgVS for the straw-based horse litter. These results are of practical interest for the management of large horse facilities or for the co-digestion of these feedstocks in existing AD plants. Full article

Anaerobic digestion (AD) is an effective technology for sustainable waste management, renewable energy production and resource recovery within a circular economy. This study offers a systematic bibliometric review of global advances in AD research and assesses their relevance to Ghana. Using the PRISMA framework, the literature from 2011 to 2025 was sourced from the Scopus database and analysed through bibliometric and thematic methods. The review emphasises four key factors affecting AD performance: municipal solid waste as feedstock, pretreatment technologies, biochemical methane potential (BMP) assessment and process optimisation. Studies were included if they addressed any of these themes. Non-English publications, inaccessible full texts and papers lacking bibliographic metadata were excluded. After screening 3424 records, 61 studies were included in the systematic review. After metadata screening, 3374 of the 3424 retrieved records were retained for bibliometric analysis. Results show that municipal solid waste, food waste, agricultural residues and sewage sludge are promising sources for biogas generation. Pretreatment techniques, including thermal, chemical, mechanical and biological, significantly enhance substrate biodegradability and methane production. BMP assessment is a reliable way to gauge feedstock suitability and energy recovery potential. Optimising parameters like pH, temperature, organic loading, hydraulic retention time and co-digestion ratios improves process stability and biogas yield. The review highlights the increasing use of modelling and optimisation to boost digester performance and facilitate scale-up. In Ghana, abundant organic waste offers significant opportunities for biogas development. Employing advanced feedstock characterisation, pretreatment, BMP evaluation and optimisation can improve AD efficiency, support renewable energy, reduce waste disposal issues and promote Ghana’s shift toward a sustainable circular bioeconomy. Full article

Intensive dairy farm wastewater (DFW) poses significant environmental challenges due to its high organic loading and complex composition. Anaerobic co-digestion with sewage sludge (SS) offers a promising strategy for simultaneous pollutant removal and bioenergy recovery. However, the optimal inoculation ratio for maximizing both methane production and volatile fatty acid (VFA) accumulation remains unclear for liquid DFW following a solid–liquid separation. This study investigated the effects of three SS addition ratios (0%, 15%, and 45%) on anaerobic co-digestion performance. Daily methane production, cumulative yield, VFA composition, pH, electrical conductivity (EC), ammonium nitrogen (NH₄⁺-N), and chemical oxygen demand (COD) were monitored over 26 days. The 45% SS treatment (S45) achieved the highest cumulative methane yield (2882.60 mL), representing 35.1% and 7.2% increases over S0 and S15. Modified Gompertz modeling confirmed S45 attained the highest methane potential (3056.8 mL) and production rate (569.8 mL/d), with the shortest lag phase (14.47 d). S45 also reached the highest total VFAs peak (2209.02 mg/L) on day 3, advancing acidification by 3 days. Process stability was maintained across all treatments (pH 6.94–8.44), with S45 showing the earliest pH recovery and lowest NH₄⁺-N accumulation. COD removal in S45 exceeded S0 by 25.1% at day 26. These findings indicate that 45% SS addition optimally balances methanogenic performance, acidogenic efficiency, and process stability in DFW anaerobic co-digestion. Full article

Anaerobic digestion of kitchen waste (KW) for biogas production has significant promise both economically and environmentally. However, low biogas production and fluctuating methane concentration remain key challenges that need to be overcome to make this a viable solution. This study implements a two-stage evaluation framework to link temperature-dependent microbial characteristics with process optimization. First, high-throughput sequencing was performed across a wide temperature gradient (25 °C, 37 °C, 45 °C, 50 °C, 55 °C, and 60 °C) to characterize the baseline microbial community screening and succession trajectories of methanogenic archaea. Based on the identified thermophilic transition threshold, five batch anaerobic reactors were subsequently configured under the target thermophilic condition (50 ± 1 °C) with substrate-to-inoculum (S/I) ratios calculated on a volatile solids (VS) basis (1:0, 1.5:1, 1:1, 1:1.5, and 1:2) to evaluate the biomethane potential, organic removal rates, and volatile fatty acid (VFA) conversion. The results showed that an optimal S/I ratio of 1:1 was crucial for maximizing methane production performance, achieving the highest cumulative biogas yield of 1494.07 mL/g VS and methane yield of 746.28 mL/g VS. Notably, Methanoculleus and Candidatus Methanoplasma were identified as the core functional methanogens enriched at high-temperature stages. Both genera are obligate hydrogenotrophic methanogens that consume H₂ and CO₂ as substrates, and their enrichment plays a vital syntrophic role in alleviating intermediate acid accumulation and maintaining steady methanogenesis. This study provides clear theoretical insights and experimental data supporting the efficient thermophilic utilization of KW via precise microbial load balancing. Full article

Aerobic composting of food waste (FW) is constrained by delayed temperature increase initially. This study evaluated the use of high-solid anaerobic digestion (HSAD) biogas residue as a composting initiator. In the co-composting treatment containing biogas residue and FW (C3), the temperature peaked at 69.8 °C on day 5. In comparison, the FW composting alone (C1) reached a lower peak temperature of 67.1 °C on day 8. Similarly, C3 sustained the thermophilic phase (>55 °C) for 10 days, comparable to the 11 days observed in C1. The incorporation of biogas residue adjusted the pH of FW toward neutrality, helping to reduce nitrogen loss. C3 also demonstrated a distinctive phytohormone profile, with salicylic acid (SA) content reaching 42.62 ng g⁻¹, significantly exceeding that of C1 (31.54 ng g⁻¹), suggesting enhanced bio-stimulatory potential. Compared with C1, N₂O emissions in C3 were both reduced and delayed, while cumulative CH₄ emissions were lower than those in the biogas-residue-alone composting (C2). Biogas residue addition introduced thermotolerant microbes, reduced acidification by suppressing acidophiles, and enhanced humification via cooperative networks. Metagenomics revealed that C3 developed a denitrification gene profile favoring net N₂O consumption under high pH. These results demonstrate that HSAD biogas residue can serve as an effective initiator for FW composting. Full article

Small-scale anaerobic digestion offers a decentralized pathway for organic waste recovery; however, its performance is often evaluated through fragmented modules that do not ensure formal traceability between design, operation, sustainability assessment, and decision-making. This study proposes an integrated five-stage methodological framework—diagnosis, design, operational control, economic-environmental assessment, and decision-making validation with feedback—whose ACT (Acceptance–Control–Traceability) decision block applies three sequential filters: data-quality control ($C_{data}\ge 0.90$), multivariable operational stability ($SR\ge 0.75$), and comprehensive sustainability verification ($\mathsf{\Omega }$: $GE{I}_{net}>0$, $NPV>0$, $\varphi <1$, and $\beta \ge 0.10$). A phased bibliographic mapping of 48 references confirmed the modular structure of the state of the art:60.4% address operation/optimization and 39.6% address economic-environmental evaluation, whereas only 2.1% incorporate a formal decision closure. The framework was inductively derived from two Peruvian case studies: Chillón, as a structural-predictive reference, and Huaycán, focused on active pH–EC control through stoichiometric NaHCO∗3 dosing. It was then prospectively evaluated on an independent 200-L co-digestion prototype in Lurín. The Lurín reactor delivered a mean biogas production of 96.9 L,d⁻¹, a methane fraction of 54.2%, and a specific methane yield of 177.4 L,CH∗4,kgVS⁻¹; nevertheless, the ACT decision yielded $SR=0.33$, classifying the system as not validated (Type A failure) due to ionic drift and thermal variability. Although the co-product scenario showed conditionally positive economic ($NPV>0$) and environmental ($GEI\ast net=38.2$ kgCO₂eq/a) indicators, $\mathsf{\Omega }$ could not be evaluated because Stage 1 territorial inputs ($E\ast dem$, $P\ast energy$) were undefined. By rejecting a system that a fragmented modular assessment would have classified as viable, the framework demonstrates the practical value of enforcing operational-stability verification before any sustainability claim and prescribes targeted feedback to Stage 3 for ionic and thermal management. Full article