Search Results (2,945)

Anaerobic digestion (AD) of thickened waste-activated sludge (TWAS) is widely applied for sludge stabilization and renewable energy recovery; however, hydrolysis of complex organics often limits fermentation performance. This study evaluated the effects of multiple pretreatment strategies on solubilization, volatile fatty acids (VFAs) production, and extracellular polymeric substances (EPS) during 80 h mesophilic batch fermentation. Pretreatments included hydrothermal treatment (HTP; 70, 90, and 170 °C), ultrasonication (US; 3000, 5000, and 10,000 KJ/kg TS), chemical pretreatment (acidic pH 4 and alkaline pH 10), and biological augmentation using YDRO Process^® (YDRO^®; 5%, 10%, 15% v/v). Across feedstock pretreatments, HTP generated the greatest improvements in solubilization, increasing SCOD by 56–113-fold and producing substantial acetate levels, particularly at 70 °C, alongside substantial phosphorus release. Ultrasonication resulted in moderate solubilization (28–56-fold) and elevated soluble phosphorus and ammonia. Acidic pretreatment maximized soluble phosphorus, but showed limited VFAs production, whereas alkaline pretreatment rapidly increased soluble EPS due to pH-induced cell disruption. Bioaugmentation achieved the highest total COD but yielded comparatively low soluble fractions. Following fermentation, HTP 170 °C consistently outperformed other treatments, maintaining elevated soluble COD and producing the highest acetate concentration. EPS analysis revealed extensive protein and polysaccharide degradation in thermal and bioaugmented systems, indicating active utilization during fermentation. Overall, the results demonstrate that targeted pretreatment strategies significantly enhance organic solubilization, EPS disruption, and VFAs yields, with thermal pretreatment showing the greatest potential to accelerate hydrolysis and acidogenesis. These findings provide valuable insights for optimizing the pre-methanogenic stages of AD and improving the efficiency of sludge treatment and resource recovery. Full article

The circular valorization of biomass for sustainable energy recovery is a strategic priority in the transition toward low-carbon systems. In the last decade, anaerobic digestion (AD) has emerged as an efficient technology to produce an energetic vector to replace natural gas with biomethane and reduce waste; however, the hydrolysis of refractory fractions remains the main rate-limiting step. This study investigates an innovative electro-assisted pretreatment of biomass to promote the first rate-limiting hydrolysis step of refractory compounds in biomethane production. Lignocellulosic residues are employed not only as feedstock for the AD process but also as substrates in electrohydrolysis (EH) pretreatment using an Ir-Ta mixed metal oxide (MMO) anode coupled with advanced biomass-derived carbon felt cathodes. Two cathodes were functionalized with Phragmites Australis (PhA) hydrochars, untreated (PA) and KOH-activated (PA-KOH), to enhance the in situ generation of reactive oxygen species (ROS). Brassica napus (Bn) was chosen as the other biomass selected as a feedstock of AD, and was subjected to EH at varying energy inputs (500–5000 kJ·kg⁻¹), evaluating structural and biochemical shifts. The results demonstrate that EH effectively modifies the biomass matrix; the PA-KOH-CF cathode exhibited good selectivity to degrade lignocellulosic structures, but higher biomethane production was achieved at 2500 kJ·kg⁻¹ TS using PA-CF, reaching an increase of 52% compared with untreated samples. Kinetic analysis of the biomethane potential was performed using the modified Gompertz model. The model accurately captured the asymmetric sigmoidal transitions of methane production with different electrode configurations, and finally, energy balance assessment identified 2500 kJ·kg⁻¹ TS as the optimal operational threshold. These findings suggest that an excess of applied energy is critical to the availability of soluble organic matter and the presence of refractory compounds that reduce efficiency. This electro-assisted approach offers a robust strategy for intensifying AD, aligning with circular bioenergy objectives. Full article

In this study, the methane yield, substance conversion rate and microbial community structure of individual components of lignocellulose, synthetic mixtures, and corn straw subjected to different pretreatments (thermal hydrolysis, chemical, biological, and combined pretreatment) during anaerobic digestion were comparatively investigated. The synthetic mixture of cellulose and hemicellulose (MCXY) exerted a positive promoting effect on biomethane production, with a synergistic effect index of 101.51%. The methane yield per volatile solids (VS) of microcrystalline cellulose (MC), xylan (XY), and MCXY reached 320.81 ± 1.85 mL/g VS, 352.70 ± 6.58 mL/g VS, and 340.60 ± 10.94 mL/g VS, respectively. Lignin did not produce biogas in anaerobic digestion (AD) system, and its presence had an inhibitory effect on the methanogenesis of cellulose and hemicellulose, especially that of hemicellulose. Notably, pretreatment significantly improved the methane production potential of corn stover. Deep eutectic solvent-pretreated corn stover (DES_CS) achieved the highest methane yield of 356.57 ± 8.50 mL/g VS, which was 55.46% higher than that of the untreated group. DES pretreatment deconstructed lignocellulosic matrix and distinctly increased DOM molecular diversity, thus providing superior substrate conditions for improving anaerobic digestion performance. Microbial community analysis revealed that DES pretreatment significantly reshaped the bacterial structure, enriching syntrophic taxa over the carbohydrate-degrading Bacteroides found in raw corn stover, thereby fostering a more robust metabolic network for methane production. While acetoclastic Methanothrix dominated the pretreated groups, its synergistic coexistence with hydrogenotrophic Methanobacterium across all digesters facilitated stable dual-pathway methanogenesis. This work can provide a theoretical basis and technical reference for the optimization and application of pretreatment strategies for efficient anaerobic digestion of corn stover. Full article

A livestock farm in southern Taiwan produces wastewater with high concentrations of nitrogen and organics, which inhibit anaerobic methanogens and limit the efficiency of its biogas system. To enhance energy recovery, this study developed a liter-scale microbial fuel cell (MFC) system aimed at harvesting electricity from livestock wastewater, serving as a supplementary energy recovery pathway alongside the biogas process. According to the five analyses, the chemical oxygen demand (COD) of raw wastewater ranged from 14 to 21 g L⁻¹, with acetate concentrations ranging between 40 and 112 mM. Propionate and butyrate were consistently below 32 mM and 18 mM, respectively. Ammonium ranged from 1.1 to 1.7 g-N L⁻¹, indicating the wastewater’s high organic load and elevated nitrogen content. Two liter-scale MFCs, ch5 and ch7, were operated for over 70 d. From days 7 to 28, both MFCs employed a fill-and-draw mode, achieving optimal COD removal exceeding 80%. After resolving leakage issues between days 30 and 40, the system was restarted on day 40, yielding 76% (ch5) and 82% (ch7) of COD removal. Continuous operation began on day 59, and both reactors maintained COD removal rates above 80% for most of the subsequent two-week period. The best power outputs for ch5 and ch7 reached 1.11 and 0.82 W m⁻³, respectively. Although both liter-scale reactors achieved COD removal and measurable power output, the most important finding was obtained from the inoculum comparison experiments. After 54 days of acclimating to raw wastewater solids, no significant current was observed. In contrast, digestate solids acclimated with carbon powder for 22 d produced a peak current of 42.5 A m⁻³ at 147 h, with COD removal rates of 67–73% and complete removal of organic acids. The key conclusion of this study is that anaerobic digestate exhibits electroactive microbial potential, whether operated in liter-scale reactors or acclimated with carbon powder. Further investigation into the microbial community structure is warranted to optimize system performance. Full article

The overuse of mineral fertilizers has brought about numerous matters such as deteriorating soil health, crop safety concerns, and environmental pollution. The global requirements for effective waste handling and sustainable agricultural production have been growing continuously. Therefore, integrated nutrient management method might be a key way to achieve circular agriculture, such as replacing chemical fertilizers with organic fertilizers. In modern agriculture, digestate that is a byproduct of anaerobic digestion as a fertilizer is becoming increasingly favored as a viable method for improving crop yield and quality. However, the application of digestate in agriculture have not yet been fully explored. This review addresses a knowledge gap by synthesizing current research on digestate as a fertilizer. Firstly, the physical–chemical and biological properties of digestate are discussed. Following that, this review focuses on its specific impact on crop growth and quality. Lastly, it outlines the challenges faced in the application of digestate and looks ahead to future trends. With appropriate policy support and technological innovation, digestate holds promise for advancing environmental sustainability. This review aims to provide direction and reference for future research on the application of digestate. Full article

Wastewater treatment plants (WWTPs) are significant contributors to anthropogenic greenhouse gas (GHG) emissions through both direct biological processes generating methane (CH₄), nitrous oxide (N₂O), and biogenic carbon dioxide (CO₂) and indirect energy consumption. This comprehensive research paper synthesizes findings from 30 peer-reviewed studies to present a holistic analysis of carbon footprints in wastewater treatment, with a specific quantitative assessment of a sequencing batch reactor (SBR) facility processing 5000 m³/day. The SBR operates with anoxic–aerobic cycles (fill–anoxic react–aerobic react–settle–decant–idle). The analysis reveals that N₂O emissions can constitute up to 75% of a plant’s carbon footprint, while aeration accounts for 40–75% of total energy consumption. For the SBR facility, the baseline carbon footprint is 1648 tCO₂e/year [95% CI: 1420–1910] (0.90 kg CO₂e/m³) under conservative assumptions, with CH₄ yield of 0.03 kg CH₄/kg COD removed and N₂O yield of 0.008 kg N₂O-N/kg TN removed. A realistic baseline using median literature values gives 0.52 kg CO₂e/m³. The carbon footprint of WWTPs varies by treatment technology, scale, and operational conditions, ranging from 61 to 161 kg CO₂e per population equivalent (PE) annually. Through anaerobic digestion with biogas recovery and anoxic phase optimization, emissions can be reduced by 38% to 1018 tCO₂e/year [95% CI: 860–1190]. The findings underscore that achieving carbon neutrality requires extending accounting beyond plant boundaries to include effluent exports, sludge management, and urban infrastructure integration. This paper provides a transparent, practitioner-ready framework for understanding, quantifying, and mitigating carbon emissions from wastewater treatment, with particular emphasis on SBR technology. Full article

Three natural celluloses (softwood pulp, straw grass pulp, and degreased cotton) were used for anaerobic digestion tests to research methane yield, substrate conversion and microbial community structure, and further supplemented and clarified the metabolic pathway mechanisms of anaerobic digestion of cellulosic biomass. The results showed that natural cellulose could be significantly degraded and converted into methane by anaerobic microorganisms. The cumulative specific methane yields of wood pulp fiber (F1), straw pulp fiber (F2), and degreased cotton fiber (F3) were 373.57 ± 10.70 mL/g VS, 349.15 ± 13.20 mL/g VS and 346.16 ± 1.60 mL/g VS, respectively. The corresponding biodegradability values were 93.97%, 85.95% and 84.32%. Although the fermentation cycles in F1, F2, and F3 were identical (T95 was 12 days), the three groups exhibited distinct biogas production patterns. Metagenomic analysis indicated that F1 and F2 were dominated by the acetoclastic methanogenesis pathway, while the proportion of the hydrogenotrophic methanogenesis pathway increased in F3. Meanwhile, the cell motility pathway category was significantly enriched in F3. These results supplement the existing research on the anaerobic digestion of natural cellulose and provide theoretical support for the efficient anaerobic bioconversion of natural cellulosic biomass. Full article

Two-stage anaerobic digestion systems are extensively researched for enhancing process stability and phase separation when processing complex organic materials. Scaling from laboratory setups to pilot plants necessitates engineering modifications to ensure operational feasibility. In this study, a laboratory-scale system comprising a 100 L horizontal CSTR and a packed-bed reactor was scaled up 100-fold. The design separates solid and liquid retention times, with fibers retained in the first stage while liquids and volatile fatty acids flow into the second. Fiber retention in the lab was achieved using a 100 µm sieve dividing the CSTR into two chambers, allowing prolonged lignocellulosic degradation. During scale-up, a filtration and recirculation system was introduced, able to return the fibers to the first reactor through a 1000 µm edge-gap filter, which separates liquids for the second reactor and recycles undegraded fibers. An economic analysis indicated a scale-up exponent of 0.396, indicating that unit costs decrease with plant size and demonstrating economies of scale. Laboratory-based mass balance estimates biogas production at approximately 16.3 m³ daily at the pilot scale, equivalent to 90 kWh. The modular system aims to be transferred to small farms, promoting cost-effective biogas from manure and local residues to support decentralized renewable energy in agriculture. Full article

Anaerobic co-digestion of substrates offers synergistic benefits, enhancing methane production and improving the operational stability of wastewater treatment. The present study, for the first time, evaluated the biochemical methane potential and kinetics modeling performance of two regional wastewater streams—swine wastewater (SW) and nejayote wastewater (NW)—under mesophilic batch conditions. Five substrate ratios (SW/NW: 100/0 to 0/100) were tested, and interaction effects were measured using the co-digestion performance index (CPI). All mixtures demonstrated synergistic effects, with CPI values ranging from 1.12 to 1.26. NW exhibited the highest methane yield (438 ± 25 NL-CH₄/kgCOD_T-removed), nearly twice that obtained for SW (227 ± 18 NL-CH₄/kgCOD_T-removed). In addition, co-digestion improved the methane yield of SW as mono-digestion, with production increasing from 281.8 ± 12.4 to 304.7 ± 27.8 NL-CH₄/kgCOD_T-removed in all mixtures. The methane production kinetics were analyzed using six mathematical models. The multi-phase Gompertz model provided the best fit (R² > 0.99), while the two-phase model offered the best balance of accuracy and simplicity according to Akaike’s criterion. The present model effectively described the diauxic patterns of methane production resulting from substrate heterogeneity with an error of <8% for all experimental assays. Full article

Augmenting aquaculture feeds with black soldier fly (Hermetia illucens L.) larvae is an emerging solution to the industry’s fishmeal and fish oil dependence. However, the larva’s nutritional plasticity often results in bioaccumulation of metals from the rearing substrates. Larvae can be nutritionally enriched with microalgae, but research investigating growth impacts and metals uptake are lacking. In this study, a Stichococcaceae algae strain that is used to phycoremediate effluent from commercial anaerobic digesters was investigated as a rearing substrate. Larvae were reared on chicken feed enriched with stepped ratios of algae and spent coffee grounds (a reference waste feed). Growth, survival and metals content (ICP-OES) were recorded when 10% of larvae were prepupal. Survival was >98.5% across all treatments with a trend of increased growth with microalgal inclusion, and no significant impact of metals on growth. Metals uptake as determined by a bioaccumulation factor was significantly lower in the highest algae treatment compared to the coffee-only treatment. Larvae consistently accumulated cadmium and lead whereas arsenic bioaccumulation was only observed in three treatments. Cadmium had the highest bioaccumulation factor (up to 4.06) and arsenic the lowest (down to 0.41). Larvae did not exceed current European Union maximum metal ions levels for inclusion into aquafeeds. These findings highlight the potential of using Stichococcaceae to enrich black soldier fly larvae, offering a dual sustainable solution for wastewater remediation and aquaculture feed provision. Full article

Lignocellulose is degraded in the rumen by diverse microorganisms. This study aimed to select the top ruminal microbes associated with an anaerobic fungus (AF) capable of forming consortia that facilitate biogas production from wheat straw. The workflow included the following steps: (1) batch reactors, divided into three compartments with porous membrane bags containing wheat straw, were assembled. The outermost compartment was inoculated with freshly collected rumen content. The first microbes colonizing the wheat straw in the innermost compartment within 72 h were identified. (2) Synthetic consortia were assembled comprising the following identified microbes: an anaerobic fungus (AF) (Neocallimastix lanati); methanogenic archaea (M) (Methanobrevibacter ruminantium or Methanobrevibacter gottschalkii); bacteria (B) (Butyrivibrio hungatei or Succinoclasticum ruminis). (3) Wheat straw was subjected to 7-day pretreatments with these synthetic consortia. (4) The pretreated straw served as substrate in biochemical methane potential (BMP) tests that used a biogas reactor digestate as the inoculum. The pretreated straw produced elevated biomethane yields; nonetheless, this process needs further optimization. The cross-kingdom AF + M + B consortia increased methane production by 35–70%, and superior volatile fatty acid production was confirmed via HPLC. The results suggest novel strategies for advanced practical biogas/biomethane technologies. Full article

Olive pomace is an abundant agro-industrial residue whose recalcitrant composition limits its efficient valorisation, highlighting the need for sustainable recovery strategies. This study investigated the use of Hermetia illucens larvae for the bioconversion of olive pomace and its integration with anaerobic digestion to evaluate the simultaneous recovery of biomass and energy. Larvae were initially reared on olive pomace, goat manure, and their mixture to assess growth performance, survival, and substrate suitability. Subsequently, olive pomace was subjected to thermal pre-treatment and anaerobic digestion with goat manure, and the resulting digestates were reused as substrates for larval rearing. Their phytotoxicity was also evaluated through germination tests on alfalfa. Larval performance was higher on non-digested substrates, confirming the suitability of raw mixtures for insect rearing. Thermal pre-treatment did not result in a significant increase in methane production. In contrast, digestates, particularly those obtained under more severe thermal treatments, resulted in reduced larval growth and survival under the tested conditions and showed variable phytotoxic effects. Overall, although anaerobic digestion enabled energy recovery, its integration with insect-based bioconversion resulted in reduced larval performance under the tested conditions. These findings highlight the importance of optimising substrate treatment to ensure effective integration of insect rearing within circular bioeconomy systems. Full article

Urban buildings significantly contribute to global carbon emissions, with urbanization increasing energy demand and reliance on fossil fuels, leading to environmental damage. This study investigates the role of biogas in reducing urban carbon footprints through a thematic literature review of 526 publications from 2004 to 2024, refined to 33 relevant studies focusing on biogas, carbon emissions, and urban infrastructure. The research concludes that biogas systems present a clean, renewable energy alternative that enhances waste management and energy efficiency within urban settings. Despite facing economic, logistical, and social challenges, integrating biogas could provide substantial environmental benefits and is vital for meeting climate targets and transforming urban energy systems. Full article

The European Urban Wastewater Treatment Directive revision introduced the energy neutrality concept, accelerating the transition of wastewater treatment plants (WWTPs) towards a 100% renewable energy share. Energy audits must be initially conducted to assess current energy consumption levels, identifying deviations from benchmarking values, and energy efficiency measures must be implemented. Strategies should be then diversified according to WWTP size: anaerobic digestion (AD) is a core technology for large-scale plants. The refurbishment of conventional digesters into “enhanced” AD, including sludge pretreatment, co-digestion, or two-stage AD, significantly increases energy yields, providing most of the required electricity/heat. Enhanced AD can be complemented by photovoltaic (PV) panels and thermal energy recovery from effluents. For medium-scale plants, instead, PV implementation is a key solution for electricity production, coupled with hydroenergy recovery and, eventually, wind turbines, while heat can be provided by solar thermal panels or thermal energy recovery from effluents. Hybrid systems, which integrate multiple renewable sources, are often the best solution to reach energy neutrality, improving the system’s resiliency; however, dedicated mathematical models are needed to size and operate the different components, considering local factors. Future research must connect theoretical and in-field studies to allow a wider implementation of hybrid systems. Full article

This study designed an integration of anaerobic digestion, partial nitrification/Anammox (PN/A), and Fenton process to efficiently treat high-concentration organic liquor wastewater (HCLW). Results indicated that when the diluted ten-fold mixture of boiler bottom water and cellar bottom water with the ratio of 5:1 was used as influent, the average concentrations of COD, TN, NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N in effluent of biological treatment for this process were 180.00, 12.64, 1.74, 0.13, and 2.45 mg/L, respectively. To meet the requirement for direct discharge of HCLW, Fenton oxidation with 600 mg H₂O₂/L and 300 mg Fe²⁺/L was used to further reduce the COD concentration. Three-dimensional fluorescence spectra analysis revealed that the process effectively altered the organic molecular structure and degraded some large molecular proteins. Microbial community analysis showed that Methanobacterium (20.98% → 31.52%) and Methanosaeta (9.70% → 19.34%) in AD, Azoarcus (no detected → 10.49%) and Nitrosomonas (1.68% → 6.16%) in PN, and Candidatus_Brocadia (18.80% → 20.31%) and Ignavibacterium (no detected → 5.11%) in Anammox were dominant in this system. This study provided a pioneering industrial solution for the efficient and stable treatment of HCLW. Full article