Search Results (160)

Lactic acid bacteria (LAB), as the core microorganisms in silage fermentation, play a crucial role in improving silage quality and ensuring feed safety, making the screening, identification, and functional characterization of LAB strains a significant research focus. Researchers initially isolate and purify LAB from various samples, followed by identification through a combination of morphological, physiological, biochemical, and molecular biological methods. Systematic screening has been conducted to identify LAB strains tolerant to extreme environments (e.g., low temperature, high temperature, high salinity) and those possessing functional traits such as antimicrobial activity, antioxidant capacity, production of feruloyl esterase and bacteriocins, as well as cellulose degradation, yielding a series of notable findings. Furthermore, modern technologies, including microbiomics, metabolomics, metagenomics, and transcriptomics, have been employed to analyze the structure and functional potential of microbial communities, as well as metabolic dynamics during the ensiling process. The addition of superior LAB inoculants not only facilitates rapid acidification to reduce nutrient loss, inhibit harmful microorganisms, and improve fermentation quality and palatability but also demonstrates potential functions such as degrading mycotoxins, adsorbing heavy metals, and reducing methane emissions. However, its application efficacy is directly constrained by factors such as strain-crop specific interactions, high dependence on raw material conditions, limited functionality of bacterial strains, and relatively high application costs. In summary, the integration of multi-omics technologies with traditional methods, along with in-depth exploration of novel resources like phyllosphere endophytic LAB, will provide new directions for developing efficient and targeted LAB inoculants for silage. Full article

Tuna-processing facilities produce substantial amounts of concentrated organic residues and sludges containing high levels of proteins, lipids, and nitrogen, which are not easily handled by conventional waste treatment methods. In this work, the anaerobic digestion (AD) performance of tuna-processing by-products (TPB1–2) and associated wastewater sludges (TWS1–3) was investigated using a combination of biochemical methane potential (BMP) tests, theoretical methane yield calculations based on the Buswell–Boyle equation, semi-continuous mono-digestion experiments, and 16S rRNA gene-based microbial analyses. Among the evaluated materials, TWS2 produced the highest methane yield (554.6 N mL CH₄/g VS) and, when its annual production volume was taken into account, showed the greatest estimated energy recovery (approximately 1.88 × 10⁶ kWh per year). By contrast, TWS3 exhibited the lowest methane yield (239.8 N mL CH₄/g VS), which was attributed to the presence of lignocellulosic sawdust and its limited biodegradability. TWS1 showed a moderate level of performance, with an estimated biodegradability of 62.3%, which may have been influenced by the addition of ferric salts and polymeric coagulants during sludge conditioning. In the semi-continuous digestion experiments, reactors that were initiated under relatively high total ammonia nitrogen (TAN) concentrations achieved stable operation within a shorter period, with the acclimation phase reduced by approximately one hydraulic retention time. These trends were supported by the microbial community data, where an increase in Bacillota-associated families, such as Tissierellaceae and Streptococcaceae, was detected along with a clear shift in dominant methanogens from Methanothrix to the more ammonia-tolerant Methanosarcina. Taken together, it is suggested that, when ammonia levels are appropriately managed, mono-digestion of tuna-processing sludges can be operated at a moderate organic loading rate. The process stabilization and energy recovery in nitrogen-rich industrial wastes are closely linked to gradual microbial adaptation rather than immediate improvements in methane yield. Full article

Biogas and methane generated from the anaerobic digestion (AD) of organic waste present a highly effective alternative to fossil fuels. The study assessed using dragon fruit peel (DFP) as a co-substrate to enhance chicken manure (CM) biodegradability and stabilize the AD process for methane during co-digestion. The biochemical methane potential assays were conducted at mono-controls (CM and DFP) and co-digestion at CM-75:DFP-25, CM-50:DFP-50, and CM-25:DFP-75. Compared to the controls, mono-digestion produced 103.3 mL/g of volatile solids (VSs) of CM and 34.6 mL/g VS of DFP, while all treatment groups of co-digestion exhibited an increase in methane production. The highest yield was 180.3 mL/g VS at CM-25:DFP-75 (74.6% and 421.1% increase relative to mono-digestions of CM and DFP, respectively), followed by 148.3 mL/g VS at CM-50:DFP-50 (43.6% higher than CM) and 116.7 mL/g VS at CM-75:DFP-25 (13% higher than CM). Process stability at the optimal DFP co-substrate ratio (CM-25:DFP-75) was confirmed by total volatile fatty acid (VFA) conversion, as below 0.5 g/L VFAs were observed at the end of incubation, indicating highly acceptable performance. The relative abundance of Bacteroidetes and Bacillota in the treatment groups was higher as compared to the control reactors, correlating with enhanced substrate hydrolysis and VFA production. Moreover, the enrichment of acetoclastic methanogens Methanosarcina and Methanosaeta in co-digesters at CM-25:DFP-75 was associated with the efficient degradation of acetic acid and propionic acid, which aligns with the observed increase in methane yield. The study enhances the understanding of DFP as a co-substrate for optimizing methane recovery from AD of CM. Full article

This review relates the kinetics of anaerobic digestion (AD) to energy outcomes, including typical ranges of methane yields and volumetric methane productivities (down to hourly g L⁻¹ h⁻¹ scales relevant for industrial plants). It further translates these relationships into practical control principles that support stable, high methane productivity. Evidence spans substrate selection and co-digestion with emphasis on carbon/nitrogen (C/N) balance, pretreatment strategies, and reactor operation, linking process constraints with operating parameters to identify interventions that raise performance while limiting inhibition. Improving substrate accessibility is the primary step: pretreatment and co-digestion shift limitation beyond hydrolysis and allow safe increases in organic loading. Typical mesophilic operation involves hydraulic retention times of about 10–40 days for food waste and 20–60 days for different types of livestock manure and slowly degradable energy crops, with stable performance achieved when the solids retention time (SRT) is maintained longer than the hydraulic retention time (HRT). Stability is further governed by sustaining a low hydrogen partial pressure through hydrogenotrophic methanogenesis. Temperature and pH define practicable operating ranges; meanwhile, mixing should minimise diffusion resistance without damaging biomass structure. Early-warning indicators—volatile fatty acids (VFAs)/alkalinity, the propionate/acetate ratio, specific methanogenic activity, methane (CH₄)% and gas flow—enable timely adjustment of loading, retention, buffering, mixing intensity and micronutrient supply (Ni, Co, Fe, Mo). In practice, robust operation is generally associated with VFA/alkalinity ratios below about 0.3 and CH₄ contents typically in the range of 50–70% (v/v) in biogas. The review consolidates typical feedstock characteristics and biochemical methane potential (BMP) ranges, as well as outlines common reactor types with their advantages and limitations, linking operational choices to energy yield in combined heat and power (CHP) and biomethane pathways. Reported pretreatment effects span approximately 20–100% higher methane yields; for example, 18–37% increases after mechanical size reduction, around 20–30% gains at 120–121 °C for thermal treatments, and in some cases nearly a two-fold increase for more severe thermal or combined methods. Priorities are set for adaptive control, micronutrient management, biomass-retention strategies, and standardised monitoring, providing a coherent route from kinetic understanding to dependable energy performance and explaining how substrate composition, pretreatment, operating parameters, and kinetic constraints jointly determine methane and energy yield, with particular emphasis on early-warning indicators. Full article

Sheep manure and beet waste (the uneatable leaf part of the beet) are promising feedstock for biogas production due to their abundance and organic richness. However, their high lignocellulosic content reduces anaerobic digestibility and controls methane yield. This study investigates the effect of various pretreatment strategies, namely physical, thermal, and combined physical–thermal methods, on the Biochemical Methane Potential (BMP) of sheep manure and beet waste. Batch anaerobic digestion experiments were conducted under mesophilic conditions, with BMP values recorded for each treatment. The highest BMP for sheep manure, 125 Nml CH₄/g VS, was achieved using combined physical and thermal pretreatment. This approach enhanced methane production by 16%, 25%, and 60% compared to physical pretreatment (PP) alone, thermal pretreatment (TP) alone, and no pretreatment, respectively, while the one BMP for beet waste is 80 Nml CH₄/g VS and obtained with thermal pretreatment. To predict BMP outcomes, three machine learning approaches are applied, namely Linear Regression (LM), Random Forest Regression (RFR), and Gradient Boosting Machine (GBM), using digestion time (N days), total solids (Ts), volatile solids (Vs), pretreatment type, and biomass type. The variance analysis confirmed that the interaction between pretreatment and biomass type significantly improved model performance. While diagnostic checks revealed non-linear patterns limiting the linear model, ensemble methods achieved stronger results. The RFR model explained 79.5% of the variance with a Root Mean Square Error (RMSE) of about 15.7, whereas the GBM model achieved the lowest RMSE of 5.05. GBM captures complex non-linear interactions. In addition, variable importance analyses identified digestion time, solid content, and pretreatment as the most influential factors for methane yield, with the combined chemical and physical pretreatment producing the highest biogas outputs. These findings underscore the potential of advanced machine learning models, particularly GBM (Gradient Boosting Machine), for optimizing anaerobic digestion strategies and maximizing biogas recovery from sheep manure and beet waste. Full article

Olive tree pruning (OTP), a widely available agricultural residue in Mediterranean countries, represents a promising lignocellulosic feedstock for anaerobic digestion. However, its recalcitrant structure limits its biodegradability and methane yields, necessitating effective pretreatment approaches. In this context, hydrogen peroxide in combination with ultraviolet (UV) radiation (UV/H₂O₂) at ambient temperature was used as a pretreatment method for enhancing methane production from OTP. Three concentrations of H₂O₂ (0, 1, and 3% w/w) alone or in combination with UV radiation, at different retention times (8, 14, and 20 h), were evaluated to enhance OTP depolymerization and methane generation. In addition, the combination of UV/H₂O₂ with alkali (UV/H₂O₂/NaOH) was compared with the typical alkaline pretreatment (NaOH) in terms of lignocellulosic biomass fractionation and biochemical methane potential (BMP). Results showed that increasing H₂O₂ concentration during UV/H₂O₂ pretreatment enhanced hemicellulose solubilization. Both NaOH and UV/H₂O₂/NaOH pretreatment promoted lignin reduction (37.3% and 37.8%), resulting in enhanced BMP values of 330.5 and 337.9 L CH₄/kg TS, respectively. Considering operational energy requirements (heating at 80 °C and irradiance for 20 h) and methane energy recovery, net energy balances of 45.52 kJ and 66.65 kJ were obtained for NaOH and UV/H₂O₂/NaOH, respectively. Full article

With rising energy demand and the need for sustainable waste treatment, anaerobic digestion (AD) has emerged as a key technology for converting organic residues into renewable energy. However, predicting methane yield in full-scale facilities remains challenging due to the complexity of AD processes, the variability of feedstocks, and the impracticality of frequent biochemical methane potential (BMP) testing. In this study, we developed a simple, data-driven approach to forecast methane production in a commercial-scale digester co-digesting manure and food waste. The model employs weekly cumulative BMP of feedstock mixtures, calculated from literature values, as the explanatory variable. The model achieved an R² of 0.70 and a forecast mean absolute percentage error (MAPE) of 7.4, indicating its potential for full-scale AD prediction. Importantly, the analysis revealed a long-run equilibrium between BMP and methane yield, with deviations corrected within roughly one month—closely matching the system’s hydraulic retention time. These findings demonstrate that literature-based BMP values can be used to reliably predict methane yield in operating AD systems, offering a low-cost and scalable tool to support decision-making in waste management and biogas plant operations. Full article

Anaerobic digestion is a sustainable approach for waste treatment and renewable biogas production. A key parameter for large-scale applications is the Biochemical Methane Potential (BMP), which enables methane yield estimation and facilitates process scale-up. This study introduces an automated, low-cost prototype for BMP testing, comprising three 2-L reactors with provisions for future expansion. Control and data acquisition are carried out by low-cost embedded systems integrated with sensors for pressure, temperature, pH, and biogas flow. The system was evaluated using a mixture of pig manure and sludge from a local wastewater treatment plant. Real-time monitoring of temperature, pH, and biogas production was achieved. The heat exchanger, designed through transient energy balance modeling, increased the reactor temperature from 20 °C (lab temp.) to 38 °C in 400 s. Overall, the prototype demonstrated reliable performance, achieving rapid heating, stable monitoring, and precise biogas flow quantification through both displacement and pressure methods. Full article

The REPowerEU plan is aimed at a target of 35 bcm of biomethane annually by 2030, up from 4 bcm in 2023, requiring about EUR 37 billion in investment. Food waste is identified as a key feedstock, characterized by discrete homogeneity, although its availability may vary seasonally. In Italy, the Emilia-Romagna region generates approximately 450 kt/y of industrial waste from the food and beverage sector, primarily originating from meat processing (NACE 10.1), fruit and vegetable processing (NACE 10.3), and the manufacture of vegetable and animal oils and fats (NACE 10.4). Of this amount, food and beverage processing waste (EWC 02) accounts for about 302 kt from NACE 10 (food, year 2019) and 14 kt from NACE 11 (beverage, year 2019). This study provides a comprehensive screening of waste streams generated by the local food and beverage industry in Emilia-Romagna, evaluating the number of enterprises, their value added, and recorded waste production. The screening led to the identification of suitable streams for further valorization strategies: a total of ~93 kt/y was selected for the preliminary conceptual design of an integrated process combining anaerobic digestion with hydrothermal treatment, aimed at supporting national biomethane production targets while maximizing material recovery through hydrochar production. Preliminary estimations indicate that the proposed process may achieve a biochemical methane potential of approximately 0.23 Nm³/kg_VS, along with a hydrochar yield of about 130 kg/t_waste. Full article

This study was conducted to investigate the effect of hydrogen peroxide (H₂O₂) pretreatment on the anaerobic digestion performance of dairy wastewater. Initial physicochemical characterization revealed that the substrate is highly enriched in volatile solids (approximately 90.67%), indicating its strong potential for anaerobic biodegradation. Given this favorable composition, biochemical methane potential (BMP) assays were performed under mesophilic conditions (37 °C) to quantify biogas and methane generation from the untreated and pretreated dairy effluent. To enhance substrate biodegradability and increase methane yield, an oxidative pretreatment using various doses of H₂O₂ was applied. This pretreatment aimed to disrupt the complex organic matter and promote the solubilization of chemical oxygen demand (COD), especially in its soluble form (sCOD), which is more readily assimilated by methanogenic microorganisms. The experimental results demonstrated a significant improvement in biogas production efficiency. While the untreated sample yielded approximately 100 mL CH₄/g VS, the pretreated substrate achieved a maximum of 168 mL CH₄/g VS, marking a substantial enhancement. Gas composition analysis further revealed that methane accounted for nearly 45% of the total biogas produced under optimal conditions. The dosage of 0.2 g H₂O₂ per g of volatile solids (VS) resulted in the highest improvement in methane production after thermal treatment C1, followed by 1.35 g H₂O₂/g VS, and then 0.5 g H₂O₂/g VS. Furthermore, the kinetics of methane production were assessed by fitting the experimental data to the modified Gompertz model. This model enabled the determination of key parameters, such as the maximum specific methane production rate and the duration of the lag phase. The high coefficient of determination (R²) values obtained confirmed the excellent agreement between the experimental data and the model predictions, highlighting the robustness and reliability of the modified Gompertz model in describing the anaerobic digestion process of dairy waste subjected to oxidative pretreatment. Full article

Food waste (FW) management remains a critical challenge within the circular economy framework. This study examines low-temperature pretreatment (LT-PT) of food waste and its effects on physicochemical transformations and microbial community dynamics. Artificial food waste (AFW) was subjected to LT-PT at 60 °C for 24 h, 48 h, and 72 h to assess changes in organic matter solubilization, nitrogen and phosphorus transformations, microbial composition, and biomethane potential. The results show that LT-PT promotes volatile fatty acid (VFA) accumulation, ammonification, and organic matter solubilization, thereby enhancing substrate biodegradability. The largest VFA increase was observed for acetate, whose concentration increased by approximately 0.55 g/L between 0 h and 72 h of LT-PT. Metagenomic analysis revealed a pronounced shift in microbial communities, with fermentative bacteria (Leuconostocaceae) increasing to 53.08% after 24 h of LT-PT, while Cyanobacteria decreased from 81.31% at 0 h to 19.48% at 48 h. Biochemical methane potential (BMP) tests demonstrated that longer LT-PT durations improved methane yield, with the highest production (1170 NmL CH₄) recorded after 72 h of pretreatment. Kinetic modeling using first-order and modified Gompertz equations confirmed that LT-PT enhances methane production efficiency by accelerating substrate hydrolysis. These findings indicate that LT-PT is a promising strategy for optimizing food waste valorization via anaerobic digestion, supporting sustainable waste management and renewable energy generation. Full article

The biochemical conversion of biomass waste and organic slurries into clean methane is a valuable strategy for both reducing environmental pollution and advancing alternative energy sources to support energy security. Anaerobic digestion (AD), a mature renewable technology operated in high-performance bioreactors, continues to attract attention for improvements in energy efficiency, profitability, and long-term sustainability at scale. Recent efforts focus on optimizing biochemical reactions throughout all phases of the anaerobic process while mitigating the production of inhibitory compounds that reduce biodegradation efficiency and, consequently, economic viability. A relatively underexplored but promising strategy involves supplementing fermentation substrates with nanoscale additives to boost biomethane yield. Laboratory-scale studies suggest that nanoparticles (NPs) can enhance process stability, improve biogas yield and quality, and positively influence the value of by-products. This paper presents a comprehensive overview of recent advancements in the application of nanoparticles in catalyzing anaerobic digestion, considering both biochemical and economic perspectives. It evaluates the influence of NPs on bioconversion efficiency at various stages of the process, explores specific metabolic pathways, and addresses challenges associated with recalcitrant biomass. Additionally, currently employed and emerging pre-treatment methods are briefly discussed, highlighting how they affect digestibility and methane production. The study also assesses the potential of various nanocatalysts to enhance anaerobic biodegradation and identifies research gaps that limit the transition from laboratory research to industrial-scale applications. Further investigation is necessary to ensure consistent performance and economic feasibility before widespread adoption can be achieved. Full article

The integration of microalgae cultivation in the treatment of aquaculture wastewater (AWW) offers a sustainable solution for the recovery of nutrients and the valorisation of biomass. In this study, the potential of Chlorella vulgaris for growth in raw AWW and its variants was investigated and the efficiency of nutrient removal, biochemical composition of biomass, biodiesel potential by FAME analysis, and biogas production were evaluated. C. vulgaris was cultivated in three media: raw AWW, microelement-enriched AWW, and a synthetic base medium. Raw AWW allowed for the highest biomass production (2.4 g VS/L) and nutrient removal efficiency (ammonia: 100%, phosphate: 93.7%, nitrate: 37.8%). The addition of microelements did not significantly improve growth or nutrient uptake. The biomass grown on AWW showed a favourable lipid profile for biodiesel, dominated by C16:0 and C18:1. The highest biogas and methane yields were recorded for biomass from raw AWW as 358 ± 11 L/kg VS and 216 ± 7 L/kg VS, respectively. The results confirm that AWW is a suitable medium for the cultivation of C. vulgaris, enabling efficient wastewater treatment and the production of high-quality biomass. Full article

Interest in using warm-season grasses, including switchgrass (SG) (Panicum virgatum L.), as a bioenergy crop has increased in Europe. This study evaluated the effects of harvesting regimes with two cuts per year on the productivity, chemical composition and biochemical methane potential of the SG cultivars ‘Dacotah’, ‘Foresburg’ and ‘Cave in Rock’ in environments with cool and moderate climates in Europe with minimal fertilizer application. The results of two harvest years suggest that the biomass yield, chemical composition and energy potential depend on the grass cultivars and harvesting time. Significant effects (p < 0.05) of the harvest date and cultivar were observed for most of the measured parameters for biomass and silage quality. All three SG cultivars harvested on August 8 produced the lowest (p < 0.05) volume of methane per kg of biomass (181–202 normal litres (NL) per kg⁻¹ volatile solids (VS)) compared to the biomass of the respective cultivar harvested on 14 July (287–308 NL kg⁻¹ VS) or on October 3, as regrowth after the first cut made in mid-July (274–307 NL kg⁻¹ VS). The stands of all three SG cultivars, when the first harvest was completed in mid-July, achieved a higher annual area-specific methane yield than those harvested first in August (1128–1900 Nm³ ha⁻¹ and 888–1332 Nm³ ha⁻¹, respectively). Depending on the harvest regime and cultivar, the annual gross energy presented as a lower heating value varied from 31.8 GJ ha⁻¹ to 68.0 GJ ha⁻¹. It is concluded that SG growing under the cool temperate climate of Northern Europe could be an interesting alternative crop for methane production. Our study proves that the cultivar choice also plays an important role. 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