Search Results (263)

Biogas slurry (BGS), a nutrient-rich by-product of anaerobic digestion, presents a promising opportunity for sustainable agriculture on sandy soils. This review explores the agronomic potential of using BGS for improving sorghum’s (Sorghum bicolor) productivity by enhancing soil fertility and the nutrient availability. It focuses on the sources and properties of BGS, its application methods, and their effects on the soil nutrient dynamics and crop productivity. The findings indicate that BGS improves the soil health and crop yields, offering an eco-friendly alternative to synthetic fertilizers, especially in resource-limited settings. Despite these benefits, research gaps persist, including the need for long-term field trials, the optimization of application strategies for sandy soils, and comprehensive economic evaluations. Additionally, concerns such as nutrient imbalances, phosphorus accumulation, and slurry composition variability must be addressed. This review recommends standardizing BGS nutrient profiling and adopting site-specific management practices to maximize its agronomic benefits and environmental safety. Integrating BGS into sustainable soil fertility programs could contribute significantly to achieving agricultural resilience and circular economy goals. 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 development of food waste anaerobic digestion (AD) is a contemporary research topic addressed in the scientific community to meet the requirements of food waste valorization and proper substrate configuration for an efficient AD process. In this study, multiple AD experiments were performed on food waste together with industrial inoculum using laboratory-scale bioreactors. Food waste consisted mainly of fruits and vegetables (80.9%) and boiled rice (19.1%). The effect of operating temperature (33 °C, 37 °C, 41 °C, 45 °C) and the ratio between food waste mixture and inoculum-FIR (1:1, 3:2 and 2:1, w/w) on the production and composition of biogas, and the conversion yield for CH₄ and organic carbon, were investigated. The best results were obtained at an FIR of 2:1 and a temperature of 37 °C, with a total biogas production of 468.59 NL h⁻¹ kg⁻¹_VSadded (51% v/v CH₄ conc.) and a conversion yield of 36.42% for CH₄. A modified Gompertz model was applied on the accumulated CH₄ and biogas to evaluate the process performance. The model parameters were investigated in conjunction with the physico-chemical characteristics of the substrate, inoculum taxonomic profile, pH measurements, and TG-DTA analysis. The conducted analyses emphasized the susceptibility of the selected substrate towards easy degradation and improved biotransformation reactions when temperature and FIR were increased. Full article

Maize (Zea mays) is one of the most cultivated crops in South Africa, serving as a staple food, stock feed, and a key element in several industrial applications. It contributes significantly to the growth of the South African agricultural economy. The cultivation of maize generates a large amount of agricultural waste, mainly in the form of maize stover (MS), which encapsulates leaves, stalks, cobs, and husks. Approximately 5.15 metric tons (Mt) yr⁻¹ of MS are generated in South Africa. This corresponds to an energy potential of 94 PJ. There is immense potential to surpass the annual yield of MS by 126% up to about 11.66 Mt yr⁻¹ through practices such as zero tillage and improved agricultural production systems. MS may pose a serious threat to the environment if not managed in a sustainable and eco-friendly manner. Valorization of MS into biogas presents an excellent opportunity to effectively control biomass waste while contributing to renewable energy production and mitigating dependence on depleting fossil fuels. However, MS continues to be overlooked as a sustainable bioenergy resource due to its lignocellulosic structure. This study explores the potential of converting MS into biogas for heat and power generation, addressing both energy needs and waste management in South Africa. The purpose is to provide knowledge that will inform researchers, innovators, industrialists, policy makers, investors, and other key stakeholders interested in renewable energy systems. Collaborative efforts among multiple stakeholders are vital to leverage biogas as a technology to promote socio-economic development in South Africa. Full article

This study proposes a novel integrated biorefinery approach that combines Hermetia illucens (Black Soldier Fly) larvae treatment, anaerobic digestion (AD), and hydrothermal carbonization (HTC) to enhance the valorisation of fat-rich food residues. The process was designed to improve biogas yields while mitigating the inhibitory effects of lipid accumulation in AD systems. Results from larval bioconversion showed effective fat removal and a promising potential for protein and biomass valorisation. Downstream integration with AD and HTC enabled thermal self-sufficiency, enhanced energy recovery, and improved digestate dewaterability. Additionally, HTC process water recirculation to the AD unit was evaluated, considering its acidic nature and impact on biomethane production. A thermally integrated process flow was proposed, enabling efficient heat exchange and reduced external energy input. The overall system allows for multi-product recovery—including biogas, hydrochar, and larval biomass—offering a sustainable pathway for circular bioeconomy applications. This study illustrates the feasibility of a synergetic process chain that maximises energy recovery and resource efficiency from food industry waste streams. Full article

With the global emphasis on sustainable growth and development, the depletion of natural energy reserves due to reliance on fossil fuels and non-renewable sources remains a critical concern. Despite strides in transitioning to electrical mobility, rural and agricultural communities depend heavily on liquefied petroleum gas and firewood for cooking, lacking viable, sustainable alternatives. This study focuses on community-led efforts to advance biogas adoption, providing an eco-friendly and reliable energy alternative for rural and farming households. By designing and developing balloon-type anaerobic biodigesters, this initiative provides a robust, cost-effective, and scalable method to convert farm waste into biogas for household cooking. This approach reduces reliance on traditional fuels, mitigating deforestation and improving air quality, and generates organic biofertilizer as a byproduct, enhancing agricultural productivity through organic farming. The study focuses on optimizing critical parameters, including the input feed rate, gas production patterns, holding time, biodigester health, gas quality, and liquid manure yield. Statistical tools, such as descriptive analysis, regression analysis, and ANOVA, were employed to validate and predict biogas output data based on experimental and industrial-scale data. Artificial neural networks (ANNs) were also utilized to model and predict outputs, inspired by the information processing mechanisms of biological neural systems. A comprehensive database was developed from experimental and literary data to enhance model accuracy. The results demonstrate significant improvements in cooking practices, health outcomes, economic stability, and solid waste management among beneficiaries. The integration of statistical analysis and ANN modeling validated the biodigester system’s effectiveness and scalability. This research highlights the potential to harness renewable energy to address socio-economic challenges in rural areas, paving the way for a sustainable, equitable future by fostering environmentally conscious practices, clean energy access, and enhanced agricultural productivity. Full article

Composite catalysts combining absorbers and active metal hold significant potential for improving the efficiency of biomass microwave-assisted pyrolysis (MAP). Compatibility optimization of composite catalysts can be facilitated through comparative analysis for the influential mechanisms of absorbers and catalysts. Therefore, decoupling experiments about the MAP of Sargassum and calculations based on density functional theory (DFT) were conducted in this research, to investigate the influential mechanisms of absorbers and active metal. The results show the introduction of both the absorbers (SiC) and active metal (MgO) increase the yields of high-value components, such as hydrogen and hydrocarbons. However, their influential mechanisms are different. The introduction of SiC enhances the heating rate within the reaction zone, shortening the duration of MAP and inhibiting the condensation of bio-oil and the interaction between bio-oil and bio-char, and thereby increasing the bio-oil yield by 4%. The introduction of MgO lowers the energy barriers for macromolecular decomposition and gas generation, promoting the decomposition of bio-char and bio-oil, and thus leading to a 12% increase in the yield of bio-gas. This research conclusion provides a theoretical basis for the optimization and design of composite catalysts. 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

This study evaluates the potential of spent coffee grounds (SCGs) as a co-substrate to improve anaerobic co-digestion (AcD) performance, with a focus on biogas yield, methane (CH₄) content, and the removal of volatile solids (VS) and total chemical oxygen demand (TCOD). Biochemical methane potential (BMP) tests were conducted in two stages. In Stage I, SCGs were blended with active sludge (AS) and the organic fraction of municipal solid waste (OFMSW) at varying ratios. The addition of 25% SCGs increased biogas production by 24.47% (AS) and 20.95% (OFMSW), while the AS50 mixture yielded the highest methane yield (0.302 Nm³/kg VS, 66.42%). However, SCG concentrations of 75% or higher reduced process stability. In Stage II, we evaluated the impact of mixing. The AS25 configuration maintained stable biogas under varying mixing conditions, showing system resilience, whereas OFMSW25 showed slight improvement. Biogas production kinetics were modeled using modified Gompertz, logistic, and first-order equations, all of which demonstrated high predictive accuracy (R² > 0.97), with the modified Gompertz model offering the best fit. Overall, SCGs show promise as a sustainable co-substrate for the improvement of methane recovery and organic matter degradation in AcD systems when applied at optimized concentrations. Full article

Biogas is a crucial renewable energy source for green hydrogen (H₂) production, reducing greenhouse gas emissions and serving as a carbon-free energy carrier with higher specific energy than traditional fuels. Currently, methane reforming dominates H₂ production to meet growing global demand, with biogas/landfill gas (LFG) reform offering a promising alternative. This study provides a comprehensive simulation-based evaluation of Steam Methane Reforming (SMR) and Dry Methane Reforming (DMR) of biogas/LFG, using Aspen Plus. Simulations were conducted under varying operating conditions, including steam-to-carbon (S/C) for SMR and steam-to-carbon monoxide (S/CO) ratios for DMR, reforming temperatures, pressures, and LFG compositions, to optimize H₂ yield and process efficiency. The comparative study showed that SMR attains higher specific H₂ yields (0.14–0.19 kgH₂/Nm³), with specific energy consumption between 0.048 and 0.075 MWh/kg of H₂, especially at increased S/C ratios. DMR produces less H₂ than SMR (0.104–0.136 kg H₂/Nm³) and requires higher energy inputs (0.072–0.079 MWh/kg H₂), making it less efficient. Both processes require an additional 1.4–2.1 Nm³ of biogas/LFG per Nm³ of feed for energy. These findings provide key insights for improving biogas-based H₂ production for sustainable energy, with future work focusing on techno–economic and environmental assessments to evaluate its feasibility, scalability, and industrial application. Full article

The dairy industry generates substantial nutrient-rich wastewater, posing environmental challenges if discharged untreated. This study explores the potential of using the cyanobacterium Arthrospira platensis for nutrient recovery from dairy wastewater, precisely the liquid biogas digestate (BD). The research investigates the feasibility of utilising BD and electrodialysis-concentrated BD (BD concentrate) as alternative media for A. platensis cultivation, with a focus on biomass productivity, nutrient uptake, and high-value product formation. Batch and continuous cultivation modes were employed. In batch experiments, biomass productivity was in the ratio of 0 and 0.27 g L⁻¹ d⁻¹, which was 8–100% lower than simulated values for all five tested media compositions. Phosphate fixation was limited with no fixation during batch cultivation and 8–69% during continuous cultivation, likely due to suboptimal N/P ratios, while ammonium removal remained consistently high (>98%). Phycocyanin yield decreased significantly by 92% at high BD concentrate concentrations compared to standard media. Continuous cultivation with 50% BD concentrate improved biomass productivity to 1.02 g L⁻¹ d⁻¹ and pigment yield to 107.9 mg g⁻¹, suggesting a sufficient supply of nutrients. The findings highlight the potential of BD-based media for nutrient recovery but emphasise the need for optimisation strategies, such as nutrient supplementation and microbial adaptation, to enhance performance. Full article

This study investigates the transformation of biogas (methane and carbon dioxide) into high-value liquid products using Ni/Al₂O₃, Fe/Al₂O₃, and Ni-Fe/Al₂O₃ catalysts in a non-thermal plasma (NTP)-assisted process within a dielectric barrier discharge (DBD) reactor, operating at room temperature and atmospheric pressure. We compared the effectiveness of these three catalysts, with the Ni-Fe/Al₂O₃ catalyst showing the highest enhancement in conversion rates, achieving 34.8% for CH₄ and 19.7% for CO₂. This catalyst also promoted the highest liquid yield observed at 38.6% and facilitated a significant reduction in coke formation to 10.4%, minimizing deactivation and loss of efficiency. These improvements underscore the catalyst’s pivotal role in enhancing the overall process efficiency, leading to the production of key gas products such as hydrogen (H₂) and carbon monoxide (CO), alongside valuable liquid oxygenates including methanol, ethanol, formaldehyde, acetic acid, and propanoic acid. The findings from this study highlight the efficacy of combining NTP with the Ni-Fe/Al₂O₃ catalyst as a promising approach for boosting the production of valuable chemicals from biogas, offering a sustainable pathway for energy and chemical manufacturing. Full article

Long-term excessive application of nitrogen fertilizers in sweet maize farmland in South China has led to low nitrogen absorption and high emissions of reactive nitrogen (RN). In this study, four kinds of organic materials, including maize straw, cow manure, biochar, and biogas residue, were applied to sweet maize farmland for three consecutive cropping seasons to substitute 20% of synthetic nitrogen fertilizer. We compared the effects of different nitrogen substitution practices on nitrogen use efficiency (NUE), nitrogen surplus (NSP), and nitrogen footprint (NF) in farmland, with conventional fertilization as the control (CK). Results demonstrated that nitrogen substitution practices increased crop nitrogen uptake by 18.80–52.37%, NUE by 16.00–43.03%, and nitrogen partial factor productivity (PFP_N) by 46.18–74.31%, while reducing nitrogen surplus and loss by 7.84–21.84% and 12.08–42.88%, respectively. From a life cycle assessment perspective, nitrogen footprint per unit area (NF_A) and per unit yield (NF_Y) decreased by 13.64–32.24% and 34.26–47.64%, respectively. The results demonstrated that partial substitution with organic fertilizers improved nitrogen utilization as well as reduced nitrogen surplus, loss and, footprint in the sweet maize cropping system in South China. Biochar substitution achieved the most significant improvements. This study provides a research basis for nitrogen management in the sweet maize cultivation system in South China and valuable information for achieving sustainable agricultural development in typical subtropical areas in East Asia. 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