Search Results (329)

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

Anaerobic digestion is a widely adopted technique for biologically converting organic biomass to biogas under oxygen-limited conditions. However, several factors, including the properties of biomass and its complex structure, make it challenging to degrade biomass effectively, thereby reducing the overall efficiency of anaerobic digestion. This review examines the recent advancements in commonly used pretreatment techniques, including physical, chemical, and biological methods, and their impact on the biodegradability of organic waste for anaerobic digestion. Furthermore, this review explores integrated approaches that utilize two or more pretreatments to achieve synergistic effects on biomass degradation. This article highlights various additives and their physicochemical characteristics, which play a vital role in stimulating direct interspecies electron transfer to enhance biomethanation reaction rates. Direct electron interspecies transfer is a crucial aspect that accelerates electron transfer among syntrophic microbial communities during anaerobic digestion, thereby enhancing biomethane formation. Finally, this article reviews potential approaches, identifies research gaps, and outlines future directions to strengthen and develop advanced pretreatment strategies and novel additives to improve anaerobic digestion processes for generating high-value biogas. Full article

A three-year optimization study was conducted at a mechanical biological treatment plant with the aim of enhancing organic fractions recovery from mechanically separated fine fractions (MSFF) of residual waste using a screw press. The study aimed to optimize key operating parameters for the employed screw press, such as pressure, liquid-to-MSFF, feeding quantity per hour, and press basket mesh size, to enhance volatile solids and biogas recovery in the generated press water for anaerobic digestion. Experiments were performed at the full-scale facility to evaluate the efficiency of screw press extraction with other pretreatment methods, like press extrusion, wet pulping, and hydrothermal treatment. The results indicated that hydrolysis of the organic fractions in MSFF was the most important factor for improving organic extraction from the MSFF to press water for fermentation. Optimal hydrolysis efficiency was achieved with a digestate and process water-to-MSFF of approximately 1000 L/ton, with a feeding rate between 8.8 and 14 tons per hour. Increasing pressure from 2.5 to 4.0 bar had minimal impact on press water properties or biogas production, regardless of the press basket size. The highest volatile solids (29%) and biogas (50%) recovery occurred at 4.0 bar pressure with a 1000 L/ton liquid-to-MSFF. Further improvements could be achieved with longer mixing times before pressing. These findings demonstrate the technical feasibility of the pressing system for preparing an appropriate substrate for the fermentation process, underscoring the potential for optimizing the system. However, further research is required to assess the cost–benefit balance. Full article

This study evaluated the viability of using the solid residues (bagasse) of the mezcal industry produced with Agave durangensis as a substrate for biogas production, using two chemical pretreatments, acid (HCl) and alkaline (KOH + Ca(OH)₂), to enhance its biodegradability and improve the anaerobic digestion (AD) process. The chemical composition of bagasse was analyzed before and after the chemical pretreatments and then AD experiments were conducted in anaerobic sequential batch reactors (A-SBR) to analyze the effect of pretreatments on biogas production performance. The results showed that acid pretreatment increased cellulose content to 0.606 g, which represented an increase of 34%, and significantly reduced hemicellulose. In contrast, alkaline pretreatment did not show significant changes in cellulose composition, although it caused a swelling of the Agave durangensis mezcal bagasse (Ad-MB) fibers. In terms of biogas production, Ad-MB pretreated with acid (Ad-MB-acid) increased cumulative production by 76% compared to the Agave durangensis mezcal bagasse that was not pretreated (Ad-MB-not pretreated) and by 135% compared to Agave durangensis mezcal bagasse pretreated with an alkaline solution (Ad-MB-alkaline). These results confirmed that Agave durangensis solid waste from the mezcal industry that receives acidic chemical pretreatment has the potential to generate biogas as a sustainable biofuel that can be used to reduce the ecological footprint of this industry. Full article

Adequate treatment of the organic fraction of municipal solid waste (OFMSW) in co-digestion with sewage sludge (SS) through dark fermentation (DF) technologies has been widely studied and recognized. However, there is little experience with a high-solids approach, where practical and scalable conditions are established to lay the groundwork for further development of feasible industrial-scale projects. In this study, the biochemical hydrogen potential of OFMSW using a 7 L batch reactor at mesophilic conditions was evaluated. Parameters such as pH, redox potential, temperature, alkalinity, total solids, and substrate/inoculum ratio were adjusted and monitored. Biogas composition was analyzed by gas chromatography. The microbial characterization of SS and post-reaction percolate liquids was determined through metagenomics analyses. Results show a biohydrogen yield of 38.4 NmLH₂/gVS OFMSW, which forms ~60% of the produced biogas. Aeration was proven to be an efficient inoculum pretreatment method, mainly to decrease the levels of methanogenic archaea and metabolic competition, and at the same time maintain the required total solid (TS) contents for high-solids conditions. The microbial community analysis reveals that biohydrogen production was carried out by specific anaerobic and aerobic bacteria, predominantly dominated by the phylum Firmicutes, including the genus Bacillus (44.63% of the total microbial community), Clostridium, Romboutsia, and the phylum Proteobacteria, with the genus Proteus. Full article

Mechanical–biological treatment plants face challenges in effectively separating organic fractions from residual municipal solid waste for biological treatment. This study investigates the optimization measures carried out at the Erbenschwang MBT facility, which transitioned from solely aerobic treatment to integrated anaerobic digestion using a screw press. This study focused on evaluating the efficiency of each mechanical pretreatment step by investigating the composition of the residual waste, organic fraction recovery rate, and screw press performance in recovering organic material and biogas to press water. The results showed that 92% of the organic material from the residual waste was recovered into fine fractions after shredding and trommel screening. The pressing experiments produced high-quality press water with less than 3% inert material (0.063–4 mm size). Mass balance analysis revealed that 47% of the input fresh mass was separated into press water, corresponding to 24% of the volatile solids recovered. Biogas yield tests showed that the press water had a biogas potential of 416 m³/ton VS, recovering 38% of the total biogas potential. In simple terms, the screw press produced 32 m³ of biogas per ton of mechanically separated fine fractions and 20 m³ per ton of input residual waste. This low-pressure, single-step screw press efficiently and cost-effectively prepares anaerobic digestion feedstock, making it a promising optimization for both existing and new facilities. The operational configuration of the screw press remains an underexplored area in current research. Therefore, further studies are needed to systematically evaluate key parameters such as screw press pressure (bar), liquid-to-waste (L/ton), and feed rate (ton/h). Full article

Poisoning and suffocation accidents occurred frequently in the pre-treatment pool workshops of biogas plants, so this paper provided a multi-dimensional risk analysis model: Bow-Tie-Qualitative Comparative Analysis (QCA)-Bayesian Neural Network-Consequence Simulation. First, the reasons for biogas poisoning and suffocation accidents were clarified through Bow-Tie. Then, the QCA method explored the accident cause combination paths in management. Next, the frequency distribution of biogas poisoning and suffocation accidents in the pre-treatment pool workshop was predicted to be 0.61–0.66 using the Bayesian neural network model, and the uncertainty of the forecast outcome was given. Finally, the ANSYS Fluent 16.0 simulation of biogas diffusion in three different ventilation types and a grid-independent solution of the simulation were conducted. The simulation results showed the distribution of methane, carbon dioxide and hydrogen sulfide gases and the hazards of the three gases to workers were analyzed. In addition, according to the results, this paper discussed the importance and necessity of ventilation in pre-treatment pool workshops and specified the hazard factors in biogas poisoning and suffocation accidents in the pre-treatment pool workshops. Some suggestions on gas alarms were also proposed. Full article

This paper studies the potential of utilizing cocoa residues to address energy demands in post-conflict regions of Colombia. Through a systematic review, the findings indicate that cocoa byproducts from 170 municipalities could produce enough biogas to power a population nearing one million inhabitants. Three main residues can be obtained from processing cocoa—mucilage, cocoa bean shells, and cocoa pod husks—which are analyzed and recognized as the most significant in terms of potential biogas yield. The review highlights a considerable gap in existing research regarding the specific characteristics of cocoa residues and their biogas production rates. Additionally, this study emphasizes the need to investigate pretreatment methods for these materials, particularly cocoa pod husks, as well as the critical impact of transportation logistics. It also suggests exploring integrated valorization strategies and various energy conversion pathways. Finally, the article emphasizes the importance of establishing markets and promoting new initiatives to effectively utilize this abundant amount of waste. The insights gained from this analysis are relevant to similar regions, not only across South America but also in any cocoa-producing area worldwide. 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

Various pretreatment methods, often employed in wood biorefineries, aim to disrupt the wood architecture, thereby enhancing the efficiency of hemicellulose extraction for increasing the production of bio-ethanol, bio-gas, and bio-oil, as well as improving the pulping process. Pretreatment for the pulping process has advantages such as enhanced yield in biorefined products and reducing chemicals and energy consumption. This study examined the effect of an alkaline hydrolysis of birch sawdust on the chemical composition, aggregation ability, and surface activity of soda lignin obtained by soda pulping. The alkaline hydrolysis of birch sawdust led to a remarkable removal of hemicellulose and reduced its mechanical strength. The resorption of lignin fragments on the lignocellulosic matrix during the hydrolysis was observed. The soda pulping of the original and the treated sawdust was carried out under laboratory conditions at 165 °C for 90 min, using 4.5% sodium hydroxide. A higher yield of soda lignin and pulp was obtained from the treated sawdust. The reduced content of acidic and methoxyl groups in the chemical composition of the soda lignin from the hydrolyzed sawdust was explained by the predominance of polycondensation reactions in forming its primary structure. The changes in size and zeta potential values of the formed lignin particles, as well as in the modality of the size distribution with decreasing pH, were studied. The early-proposed suggestion about the existence of structural complementarity in the formation of the ordered lignin supermolecular structures has been testified. The higher surface activity at the air–water interface for the soda lignin extracted from the hydrolyzed sawdust, compared to the lignin from the original residue, was mainly attributed to a lower content of the acidic groups in its chemical composition, shifting the hydrophilic–hydrophobic balance of its structure toward hydrophobicity. Full article

Pre-treatment of lignocellulosic biomass is a necessary step to improve the degradability of these materials when used as substrates for biogas production, due to their resistance resulting from their complex composition and structural properties. The effect of using digestate for the pre-treatment of maize waste to enhance biogas production in an anaerobic digestion process was assessed through biogas potential tests and long-term operation of an anaerobic reactor model. The biogas potential tests confirmed the positive effect of soaking maize waste in digestate for pre-treatment compared to soaking it in water, as higher specific biogas production rates of 17%, 18%, and 29% were achieved after soaking it in digestate for 1 day, 2 days, and 5 days, respectively. The results from monitoring the long-term operation of the anaerobic reactor demonstrated the suitability of using digestate-soaked maize waste as a co-substrate to maize silage, which may significantly reduce the dependence on maize silage in practical applications. Stable operation of the reactor was also achieved during anaerobic treatment of the pre-treated maize waste itself, with an average specific biogas production of 403 mL/g VS. Full article

In line with the concept of sustainable agriculture, efforts should be made to increase the green energy yield and minimize the environmental impact of mineral fertilizers, maintaining high agricultural productivity. In alignment with the principles of sustainable development, plant biomass-based green energy is considered promising. A deep understanding of and enhancements to the anaerobic digestion process using plant biomass, along with digestate post-treatment for regenerative agriculture improvements, are key elements to achieve sustainability goals. This article describes innovative methods for plant biomass pre-treatment aimed at enhancing biogas yield and the fertilizing potential of the obtained digestate. Moreover, valuable insights into the process of digestate conditioning for valorization are discussed. Among these, separation and digestate stabilization techniques are emphasized. Furthermore, this article provides a comprehensive source of knowledge on the impact of digestate on soil quality, fertility, soil organic carbon sequestration, and microbiota. The findings contribute to a broader understanding of how digestate impacts regenerative agriculture. Full article

Biogas production from lignocellulosic biomass, such as wheat and rapeseed straw, is an essential strategy for sustainable energy generation. However, the efficiency of anaerobic digestion depends on the physical characteristics of the substrate, particularly the particle size, which influences microbial accessibility and biogas yield. This study aims to optimize straw particle size for enhanced methane production by evaluating different fractionation levels. The straw was processed using a hammer mill and separated into three size fractions (2.4 mm, 1 mm) alongside non-separated and finely ground (2 mm) samples. The chemical composition was analyzed using X-ray fluorescence (XRF), and key parameters such as pH, dry matter (DM), and organic dry matter (ODM) were assessed. The results indicated that rapeseed straw had lower pH (6.05) and DM than wheat straw (7.01). Biogas yield analysis demonstrated that methane production varied with particle size. For rapeseed straw, non-separated samples achieved the highest methane yield (132.87 m³ Mg⁻¹), whereas for wheat straw, methane yield decreased with increased fragmentation, with the highest yield observed for non-separated material (206.65 m³ Mg⁻¹). The carbon-to-nitrogen (C/N) ratio was highest in rapeseed straw (153.82), potentially limiting microbial activity, while finer fractions had more balanced ratios. These findings highlight the importance of mechanical pretreatment in optimizing biogas production and provide insights into improving the efficiency of straw-based anaerobic digestion systems. Full article

Fungal chlamydospores are asexual spores formed by fungi under adverse conditions and could be used in biological pretreatment for biogas projects fed by lignocellulosic substrates. In this study, Trichoderma viride (Tv) chlamydospores were used as the pretreatment agent to enhance the methane yield of spent mushroom substrates (SMSs). Lignocellulosic composition, methanogenesis performance, and anaerobic microbial communities were investigated for different Tv pretreatment durations (0 h, 12 h, 24 h, 48 h, 96 h, and 192 h). The results showed that the optimal Tv pretreatment duration was 24 h, and the cumulative methane yield reached 173.4 mL/gVS, which was 16.8% higher than that of the control. A pretreatment duration longer than 48 h was not conducive to methanogenesis. Sequencing analysis of anaerobic microbial communities showed that the pretreatment duration was directly proportional to the relative abundance of Tv at the beginning of digestion. When the initial Tv abundance was higher than 50%, Trichoderma became the absolute dominant fungus with an abundance higher than 97% in fungal communities in the later stage of digestion. The correlation network among fungi, bacteria, and archaea showed that Tv was directly related to 11 genera, and through these taxa, Tv affected 58% of the taxa in the whole microbial network. Cost accounting showed that Tv pretreatment has a net income of 45.5 CNY/1000 kg SMS, and is a promising technology. This study provides important guidance for the use of fungal chlamydospores in pretreatment and also promotes the understanding of fungi in anaerobic digestion. Full article

This study analyzed the effects of thermohydrolysis on the anaerobic conversion efficiency of lignocellulosic biomass, comparing conventional and microwave heating methods. The research aimed to identify the optimal temperature and duration for biomass pre-treatment to maximize biogas output. Four temperatures (100 °C, 130 °C, 150 °C, and 180 °C) and six durations (10, 15, 20, 25, 30, and 40 min) were tested. The results showed that microwave heating increased biogas production compared to conventional heating at the same temperatures and durations. At 150 °C, microwave heating for 20 min produced 1184 ± 18 NmL/gVS of biogas, which was 16% more than the 1024 ± 25 NmL/gVS achieved through conventional heating. Statistically significant differences in biogas output between microwave and conventional heating were observed at 130 °C, 150 °C, and 180 °C, with the greatest difference recorded between 130 °C and 150 °C: 13% for conventional heating and 18% for microwave heating. Notably, increasing the temperature from 150 °C to 180 °C did not result in a statistically significant rise in biogas production. The energy balance analysis revealed that microwave heating, despite its lower efficiency compared to conventional heating, resulted in higher net energy gains. The most favorable energy balance for microwave heating was observed at 150 °C, with a net gain of 170.8 Wh/kg, while conventional heating at the same temperature achieved a gain of 126.2 Wh/kg. Microwave heating became cost-effective starting from 130 °C, yielding an energy surplus of 18.2 Wh/kg. The maximum energy output from microwave conditioning was 426 Wh/kg at 150 °C, which was 158 Wh/kg higher than conventional heating. These findings suggest that microwave thermohydrolysis, particularly at 150 °C for 20 min, enhances both biogas production and energy efficiency compared to conventional methods. The results highlight the potential of microwave pre-treatment as an effective strategy to boost methane fermentation yields, especially at temperatures above 130 °C. Full article