Search Results (187)

Anaerobic digestion (AD) is a sustainable and widely adopted technology for the treatment of organic solid wastes (OSWs). However, AD efficiency varies significantly across different substrates, primarily due to differences in the microbial community and metabolic pathways. This review provides a comprehensive summary of the AD processes for four types of typical OSWs (i.e., sewage sludge, food waste, livestock manure, and straw), with an emphasis on their universal characteristics across global contexts, focusing mainly on the electron transfer mechanisms, essential microbial communities, and key metabolic pathways. Special attention was given to the mechanisms by which substrate-specific structural differences influence anaerobic digestion efficiency, with a focused analysis and discussion on how different components affect microbial communities and metabolic pathways. This study concluded that the hydrogenotrophic methanogenesis pathway, TCA cycle, and the Wood–Ljungdahl pathway serve as critical breakthrough points for enhancing methane production potential. This research not only provides a theoretical foundation for optimizing AD efficiency, but also offers crucial scientific insights for resource recovery and energy utilization of OSWs, making significant contributions to advancing sustainable waste management practices. Full article

Sewage sludge, characterized by its high organic matter and nutrient content, as well as the presence of microbial pathogens and other contaminants, requires proper management due to its significant generation rate. The table olive sector, which is highly significant in Spain as a global leader in production and export, generates various waste streams such the Organic Solid By-Products from Table Olive Processing (OSBTOP), which are mainly derived from the olive pit after the pitting process. The main aim of this study was to enhance the methane production performance of sewage sludge through co-digestion with OSBTOP as a co-substrate. Batch assays demonstrated that employing OSBTOP as a co-substrate increased methane content by 35–41% across all tested mixtures. While the highest methane yield was produced at a 40:60 (sludge:OSBTOP) ratio, a 60:40 mixture proved to be a more advantageous option for scale-up and practical application. This is attributed to factors such as the higher availability of sludge and its inherent buffering capacity, which counteracts the accumulation of volatile fatty acids and promotes process stability, thereby contributing to the study’s objective of significantly enhancing methane production from sewage sludge through co-digestion. In semi-continuous operation, methane yields in the co-digestion scenario exceeded those of mixed sludge digestion, showing a yield of 180 versus 120 LCH₄⁻¹ · kgVS_added⁻¹, representing a 50% improvement. This study highlights the potential of anaerobic digestion as a strategy for valorizing OSBTOP, a by-product with no prior studies, while demonstrating that its co-digestion with sewage sludge enhances methane generation, offering a sustainable approach to organic waste treatment. 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

Volatile fatty acids (VFA) are valuable intermediates with growing demand in chemical, pharmaceutical, and environmental applications. Their sustainable production from organic waste is increasingly explored in the context of circular economy and biorefinery models. This study investigates the co-fermentation of waste-activated sludge (WAS) and the organic fraction of municipal solid waste (OFMSW) as a strategy for integrated VFA and biogas production. Semi-continuous experiments were carried out to assess the effect of the substrates ratio (WAS:OFMSW = 90:10 and 30:70), hydraulic retention time (HRT), and pH control (5, 9, no control) on VFA yield and composition. Results showed that higher OFMSW content and alkaline conditions favoured VFA production, with a maximum yield of 144.9 mgHAc·gVS⁻¹ at pH 9 and 70:30 ratio. Acetate dominated, while butyrate production peaked at 114.1 mgHBu·gVS⁻¹ under high sludge conditions. However, the addition of alkali required for pH control may lead to excessive accumulation of alkaline-earth metal ions, which can disrupt biological processes due to their potential toxicity. Anaerobic digestion of fermentation residues enhanced biomethane yields significantly (0.27 NL·gVS⁻¹ vs. 0.05 NL·gVS⁻¹ from raw sludge). The proposed process demonstrates potential for converting wastewater treatment plants into biorefineries, maximising resource recovery while reducing environmental impact. Full article

The environmental impacts of industrial processes have increased the demand for sustainable alternatives in wastewater treatment. Conventional chemical coagulants, though widely used, can generate toxic residues and pose environmental and health risks. Biocoagulants, derived from natural and renewable sources, offer a biodegradable and eco-friendly alternative. This review explores their potential to replace synthetic coagulants by analyzing their origins, mechanisms of action, and applications. A total of 15 studies published between 2020 and 2025 were analyzed, all focused on industrial wastewater. These studies demonstrated that biocoagulants can achieve similar, or the superior, removal of turbidity (>67%), solids (>83%), and heavy metals in effluents from food, textile, metallurgical, and paper industries. While raw materials are often inexpensive, processing costs may increase production expenses. However, life cycle assessments suggest long-term advantages due to reduced sludge and environmental impact. A textile industry case study showed a 25% sludge reduction and improved biodegradability using a plant-based biocoagulant compared to aluminum sulfate. Transforming this waste into inputs for wastewater treatment not only reduces negative impacts from disposal but also promotes integrated environmental management aligned with circular economy and cleaner production principles. The review concludes that biocoagulants constitute a viable and sustainable alternative for industrial wastewater treatment. Full article

This study evaluates Spain’s biomethane production potential for 2030 and 2050, focusing on agricultural residues, livestock manure, municipal solid waste (MSW), and wastewater treatment plant (WWTP) sludge. The research aims to provide a regional analysis based on historical data on livestock populations, cultivated land, waste availability, and demographic projections. Using utilization coefficients and technological assumptions derived from existing biogas infrastructure, the study estimates that Spain could generate 9.71 TWh of biomethane by 2030, slightly below the national target of 10.41 TWh. By 2050, agricultural and livestock residues are expected to contribute 30.04 TWh, accounting for nearly 80% of total biomethane production, while the relative share of MSW and WWTP sludge will decrease. Andalusia, Castilla-La Mancha, and Castilla y León emerge as key contributors due to their extensive agricultural and livestock sectors. Catalonia and Madrid maintain significant roles driven by urban waste generation. The findings underscore the need for infrastructure expansion, particularly enhancing biomethane injection facilities into the natural gas grid, alongside financial incentives to support industry growth. This study highlights the role of biomethane in Spain’s renewable energy sector, emphasizing its potential to reduce greenhouse gas emissions, optimize organic waste utilization, and contribute to a sustainable energy transition. Full article

Sludge is a semi-solid waste generated during the process of wastewater treatment. Due to the addition of polymerized ferric chloride in the flocculation process, the sludge produced by the sewage treatment plant in Liaocheng Jiaming Industrial Park contains a high content of iron oxide. In this paper, chemical analysis and particle size analysis of local sludge and sludge ash were conducted. In order to assess the potential of substituting cement as cementitious material with different dosages of sludge or sludge ash with high iron oxide content, setting time, compressive strength, microscopic analysis using microscopic testing (XRD, TG/DTG, SEM) and a toxicity characteristic leaching procedure (TCLP) were analyzed. These procedures determined the physical properties, compressive strength, hydration products, microstructure, and heavy metal contaminants of cement slurries replaced by local sludge or sludge ash with different dosages of high iron oxide content. The results show that less than 5% of local sludge or sludge ash can be incorporated into cement slurry as an alternative cementitious material for solid waste disposal. Full article

Microalgal biomass contributes to the valorization of urban and agro-industrial solid waste via hydrothermal co-liquefaction (co-HTL) for the production of biocrude, a sustainable substitute for petroleum. Tropical and populous countries like Brazil generate a lot of agro-industrial waste, such as sugarcane bagasse and malt bagasse, as well as sludge from sewage treatment plants. Such residues are potential sources of biocrude production via thermochemical conversion. To increase biocrude productivity, microalgal biomass has been successfully used in mixing the co-HTL process feed with different residues. In addition to biocrude, co-HTL generates an aqueous phase that can be used to produce H₂ and/or electricity via microbial energy cells. In this sense, this paper aims to present the potential for generating energy from solid waste commonly generated in emerging countries such as Brazil based on a simplified scheme of a conceptual biorefinery employing algal biomass co-HTL together with sugarcane bagasse, malt bagasse, and sludge. The biorefinery model could be integrated into an ethanol production plant, a brewery, or a sewage treatment plant, aiming at the production of biocrude and H₂ and/or electricity by bioelectrochemical systems, such as microbial electrolysis cells and microbial fuel cells. Full article

This paper reviews methods of municipal sewage sludge (MSS) disposal in the Republic of Poland. The MSS amount produced in 2022 in sewage treatment plants is 580.7 thousand tons of total solids. This is related to the increase in the amount of treated sewage and the use of the co-digestion of sewage sludge with waste. MSS generated in municipal sewage treatment plants constitutes waste with code 19 08 05—stabilized MSS. It is subjected to the rules of conduct specified in the Act on Waste. According to data from the Central Statistical Office, in 2022, the most popular disposal method was its use in agriculture (27.1%). Approximately 18% of the MSS from treatment plants was thermally treated. A significant part of MSS is also used for crops, compost production, and reclamation. MSS management requires an individual approach from sewage treatment plant operators and the use of effective disposal methods. Considering the assumption of the circular economy, it is necessary to consider the possibility of recovering valuable raw materials from MSS and producing products for reuse. One of the possibilities of reusing MSS is to generate porous materials. Moreover, MSS can be transformed into multiple types of soil improvers and fertilizers. Full article

Triclosan (TCS) is extensively detected in wastewater and waste-activated sludge (WAS). The occurrence and fate of TCS in anaerobic digestion have been well revealed, but the change in TCS during WAS pretreatment needs to be clarified. Thermal hydrolysis pretreatment has been proven to be efficient for both WAS hydrolysis and TCS removal, with a removal efficiency of 54.0% and a retention time of 90 min at 170 °C. Alkaline pretreatment remarkably changed the TCS distribution between the sludge and liquid, and the solid–liquid distribution coefficient decreased by three orders of magnitude as the pH increased to 13. Neither alkaline pretreatment nor thermal–alkaline pretreatment resulted in the obvious removal of TCS. UP demonstrated limited efficiency in the hydrolysis of WAS, as well as the migration and removal of TCS. Thus, this study demonstrated that pretreatment methods and operational parameters significantly influence the migration and removal of TCS. It also provides a valuable reference for future studies on the migration and degradation behavior of TCS during anaerobic digestion and lays a foundation for the development of WAS treatment engineering capable of efficiently removing TCS. Full article

This study investigates the synthesis of SMS-Ti-Mn (SMS-Ti-Mn stands for spent mushroom substrate activated carbon-Ti-Mn) nanocomposites and their application in removing the heavy metal antimony from water. In the process of antimony mining and smelting, the concentration of antimony in the waste residue can still reach as high as 80.5 mg/L. In addition, the soil in the electronic waste dismantling area is severely contaminated with antimony. In short, antimony enters the environment in various ways from mining, smelting, and manufacturing to the final waste process and continuously migrates in different environmental media, increasing the environmental exposure risk of antimony pollution. Single-factor experiments and response surface methodology were employed to determine the optimal conditions, including the adsorption time, pH, and solid–liquid ratio. Material characterization was performed to understand the role of nano-metals, and adsorption kinetics were analyzed using the quasi-first-order kinetic model. The research results revealed that the optimal conditions for antimony removal were an adsorption time of 40 min, a pH of 4, and a solid–liquid ratio of 2:1 (mg/mL). Under these conditions, the nanocomposites showed an adsorption capacity of 10.502 mg/g, which was 5.8 times higher than that of iron coagulants, 11 times higher than that of manganese-modified activated carbon, and 1.7 times higher than that of iron–manganese sludge adsorbents. Characterization revealed enhanced functional groups (carbonyl, Ti=O, Mn=O), contributing to improved adsorption. Kinetic analysis indicated physical adsorption as the dominant mechanism, and the regression model accurately predicted the adsorption capacity. SMS-Ti-Mn nanocomposites offer a promising strategy for treating antimony-contaminated water, with strong potential for practical applications in water treatment. They can decompose naturally after use, reduce secondary pollution, and promote ecological balance. Secondly, agricultural waste treated with heavy metal removal can be used as a fertilizer and soil amendment to improve soil quality and promote sustainable agricultural development. Full article

Cyclone separation is a widely utilized separation technique, which enables the self-rotation behaviors of particles in the internal flow field, in order to realize high-performance separation of mixtures. Oily sludges are solid wastes generated by the shale gas industry, which need to be properly treated for environmental protection. In the present investigation, we demonstrated that tuning the inlet flow pattern of the cyclone from linear flow to vortex flow is an effective approach to boost the rotation speed of oily sludge particles for obtaining significantly improved separation effects. Numerical simulations were carried out to investigate the influences of inlet flow pattern on the rotation behaviors of particles, which manifested in the rotation speed of particles being evidently increased up to 4500 rad/s when the inlet flow was tuned from a unidirectional pattern into vortex pattern. The effective rotation zone’s area was also found to increase significantly, with the area of the effective rotation zone enlarged by up to 400%. Further separation experiments on oily sludge were carried out using a cyclone equipped with a worm shell that generated vortex inlet flow with rotating blades. Separation results confirmed that the oily sludge was successfully purified by the cyclone equipped with a worm shell, which provided an extremely high oil removal percentage of 99.9%, showing a 49.1% enhancement in oil removal capability over the individual cyclone separation. Our investigations demonstrated an effective method for realizing oily sludge treatment and oil resource recovery by conventional cyclone separation. Full article

The mining and processing of coal resources generate substantial coal-based solid wastes, such as coal gangue and slag, which pose environmental challenges, occupy land, and are difficult to manage. However, utilizing these wastes for the stabilization and solidification (S/S) of municipal sludge containing chromium (Cr) and nickel (Ni) offers an effective solution for mitigating environmental and groundwater pollution while enabling sustainable waste treatment and resource utilization. This study applied an alkali-activated coal gangue–S95 granulated blast furnace slag-based binder (CGS) to the S/S treatment of municipal sludge. The effects of the liquid-to-solid ratio, alkali activator dosage, sludge content, and incineration on compressive strength and the leaching of Cr and Ni were analyzed. The results showed that compressive strength decreased with increases in the sludge content and liquid-to-solid ratio, while incinerated sludge (ESA) samples exhibited better strength than raw sludge (ES). Incineration decomposed the calcite (CaCO₃) into CaO, which facilitated the oxidation of Cr(III) to Cr(VI) and increased Cr leaching in the ESA. However, the ESA samples demonstrated superior heavy metal stabilization, as CGS reduced Cr(VI) to Cr(III) and immobilized it through the formation of chromite phases. Using ESA as a binder in CGS provides a safe, efficient approach for resource recovery and heavy metal stabilization, offering a novel solution for the environmental management and utilization of coal-based solid wastes. Full article

Arsenic (As) contamination in water poses significant environmental and health risks, particularly in mining regions. Scorodite (FeAsO₄·2H₂O) is a highly stable compound for As immobilization, traditionally synthesized under high As concentrations and extreme conditions, such as elevated temperatures and pressures. This study explores a sustainable alternative by utilizing Fe-sludge, a waste by-product from acid mine drainage (AMD) treatment, as a novel Fe source for biogenic scorodite formation mediated by the thermo-acidophilic archaeon Acidianus brierleyi. Through a systematic evaluation of Fe-sludge incorporation, the study investigates its impact on microbial activity, As immobilization efficiency, and scorodite crystallization mechanisms. Liquid and solid analyses demonstrate that Fe-sludge enhances the reaction rate and crystallinity of scorodite while bypassing the induction period required in Fe²⁺-only systems. Cross-sectional SEM imaging and EXAFS analysis reveal dynamic transformations on the Fe-sludge surface, supporting faster As adsorption and scorodite nucleation through Fe-S intermediates. Despite potential challenges to microbial activity at higher Fe-sludge concentrations, optimized conditions successfully balance cell viability and Fe utilization. This approach offers an eco-friendly, cost-effective pathway for As immobilization by repurposing AMD sludge, contributing to sustainable resource management and reducing environmental impact. Full article

Bacteria quickly acquire the ability to survive or grow in the presence of an antibacterial agent that should be able to inhibit or kill them, leading to increased mortality caused by infective diseases. The digestate from the anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) is spread on soil, but the knowledge on the presence and persistence of the antibiotic resistance genes (ARGs) is limited. Thus, this study aims to evaluate the presence of seven ARGs (bla_TEM, bla_OXA, ermB, qnrB, sulI, sulII, tetA, and tetW) in the OFMSW and their persistence after the AD, using the innovative droplet digital Polymerase Chain Reaction (ddPCR), not yet used on this matrix. A total of 31 samples were collected from the influent and effluent of the AD in two plants located in Northern Italy. ARG concentration ranged between 4 and 9 Log gene copies/kg of sludge. A limited reduction in the concentration of antibiotic resistance targets given by AD was observed in the study (<1 Log). The persistence of ARGs after mesophilic digestion of the OFMSW suggests a risk of horizontal transmission when directly spread on soil. Further evaluations are needed for safe and sustainable reuse of such sludges. Full article