Search Results (806)

Caproic acid (CA) production through ethanol-driven chain elongation (CE) is a promising pathway to valorize organic wastes. However, the effect of pH and inoculum source on substrate conversion properties and microbial communities was not fully explored. In this study, performance of caproic acid production with anaerobic methanogenic sludge (AMS), aerobic sludge (AS) and chain elongation sludge (CES) at different pH conditions (uncontrolled (UN), 5, 6, and 7) were investigated. It was found that microorganisms in all inocula could degrade ethanol, but the consumption rate was different. The AS mainly used substrate for biogas production, without CA accumulation, while AMS and CES could synthesize butyrate and caproate with ethanol and acetate as substrates. At pH UN and 5, excessive ethanol oxidation (EEO) was activated and transformed ethanol into acetate resulting in low CA yield. Increasing pH to 7, the AMS produced more caproate and achieved a higher CA yield (0.36 g-COD/g-COD) than that of CES (0.33 g-COD/g-COD). Microbial communities in raw inocula were different, which led to distinct substrate conversion pathways. After fermentation, Anaerolineaceae was the dominate family in AMS, while Corynebacteriaceae and Dysgonomonadaceae dominated in the reactor with CES, explaining the distinct caproate yield in both reactors. The results of this study provided useful information for constructing ethanol-driven CE processes from organic wastes. Full article

Developing efficient and sustainable catalysts for advanced oxidation processes (AOPs) to remove endocrine-disrupting compounds remains a critical challenge. In this study, a defect-engineered MnFe₂O₄@SBC composite was synthesized by loading spinel MnFe₂O₄ onto sewage sludge-derived biochar (SBC) prepared at different calcination temperatures, and applied for efficient periodate (PI) activation toward bisphenol A (BPA) degradation. The catalytic performance exhibited a volcano-type dependence on calcination temperature, with MnFe₂O₄@SBC-750 achieving the highest BPA removal efficiency (98.6% within 30 min). Structural characterization revealed that MnFe₂O₄@SBC-750 possessed an optimized carbon structure with a balance between defect sites and graphitized domains. Mechanistic investigations demonstrated that multiple reactive oxygen species, including ^•OH, O₂^•−, IO₃^• and ¹O₂, were involved in BPA degradation. LC-MS analysis identified key transformation intermediates and proposed degradation pathways, while toxicity assessment confirmed reduced ecological risks after treatment. Density functional theory (DFT) calculations indicated that MnFe₂O₄@SBC significantly enhanced PI adsorption and activation by promoting interfacial electron transfer and elongating the I-O bond in IO₄⁻. Notably, MnFe₂O₄@SBC-750 exhibited the strongest electron transfer capability, attributed to the optimal regulation of defect density and graphitization degree, which facilitated π-d electronic coupling at the MnFe₂O₄-SBC interface. Overall, this work elucidates the critical role of defect regulation in spinel biochar-based catalysts for oxidant activation and provides a sustainable strategy for converting sewage sludge into high-performance catalysts for water purification. Full article

Ammonium nitrogen pollution presents a significant challenge in wastewater treatment. Traditional activated sludge processes often suffer from limitations such as low efficiency and high energy consumption when treating high-ammonium nitrogen wastewater. This study utilized previously screened high-efficiency heterotrophic nitrification aerobic denitrification (HN-AD) bacterial strains (Pseudomonas alcaliphila and Paracoccus versutus) synergistically with microalgae to construct an immobilized bacteria algae symbiotic system (IBAS). The nitrogen removal performance and microbial community response of the system were investigated under different nitrogen sources, carbon to nitrogen (C/N) ratios, and light intensities. Results demonstrated that the system achieved a removal rate of over 95% for nitrite and nitrate. Under conditions of C/N = 15 and high light intensity (335.36 μmol/(m² · s)), the removal rates of NH₄⁺-N, TN, and COD exceeded 90% without nitrite accumulation. Microbial community analysis revealed that high C/N conditions significantly enriched HN-AD functional bacteria (such as Acinetobacter) in the Pseudomonadota phylum and Gammaproteobacteria class. High light intensity promoted the proliferation of microalgae (Chlorella and Halochlorella), enhanced algal bacterial interaction, and improved system stability. This study elucidated the nitrogen removal mechanism of the IBAS under multi-factor regulation, providing a theoretical foundation and demonstrating application potential for low-carbon and high-efficiency wastewater treatment technologies. Full article

The accelerating generation of waste streams is observed globally. Spanning lignocellulosic biomass, plastic waste, sewage sludge, and industrial residues, this review presents both an urgent management challenge and a compelling materials opportunity. Carbon materials derived from these waste streams offer a sustainable route to functional carbons applicable in electrochemical energy storage, adsorption, heterogeneous catalysis, and high-temperature applications. Yet their rational design remains constrained by incomplete understanding of the relationships between feedstock composition, processing pathway, structural characteristics, and functional performance. This review provides an integrated analysis of waste-derived carbon materials from processing pathways to structure–property–function relationships. The principal feedstock categories are examined for their compositional characteristics and implications for carbon yield and structure. Five primary processing routes are assessed. The five routes examined are pyrolysis, hydrothermal carbonisation, physical and chemical activation, and microwave-assisted processing. They are assessed comparatively with emphasis on structural outcomes and governing parameters. The resulting structural characteristics are discussed. These are morphology, hierarchical pore architecture, surface chemistry, heteroatom doping, and crystallinity. They are discussed alongside their characterisation methods and known limitations as performance predictors. Structure–property relationships are examined quantitatively. Heteroatom-doped hierarchical porous carbons achieve 612 F/g specific capacitance. Turbostratic hard carbons deliver 450 mAh/g sodium storage with over 90% retention. Hierarchical porous carbons demonstrate CO₂ uptake of 5.0 mmol/g and dye adsorption exceeding 9000 mg/g under optimised laboratory conditions; these values reflect individual studies and are not directly comparable across systems. Biomass-derived sulfonated carbon catalysts sustain biodiesel yields above 90% over multiple cycles. Challenges of feedstock variability, process scalability, environmental compliance, and economic feasibility are addressed, and machine learning-guided design, standardised characterisation methodology, and circular economy policy frameworks are identified as key enablers for translating laboratory performance into industrial reality. Full article

To address the problems of short-circuit flow and dead zones, complicated operation and control caused by intermittent influent, and the mismatch between aeration rate and oxygen demand in the Cyclic Activated Sludge System (CASS), a novel Multi-Compartment Fixed-Biofilm Cyclic Activated Sludge System (MCFCASS) was developed. This system operated in continuous-flow mode, and the aeration rate of each compartment was redistributed using a mathematical model. The results show that the plug flow ratio of the MCFCASS reactor increased from 18.75% to 31.25% compared with the CASS reactor. After aeration rate redistribution, the average total nitrogen (TN) removal efficiency of the MCFCASS reactor rose from 83.34% to 86.80%, and the effluent TN concentration consistently met the Grade I-A limit (15 mg/L) specified in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002). The average removal efficiencies of chemical oxygen demand (COD) and ammonium nitrogen (NH₄⁺-N) increased from 91.58% and 93.39% to 92.98% and 94.57%, respectively. Microbial community analysis revealed that after aeration rate redistribution, the relative abundances of Pseudomonadota, Bacteroidota, and Bacillota in the pre-reaction zone of MCFCASS were 39.17%, 17.78%, and 10.33%, respectively. In addition, the abundances of some functional bacterial groups in the first and fourth compartments of the main reaction zone shifted adaptively in response to the aeration rate redistribution, consistent with the trends in pollutant removal contributions in these compartments. Hierarchical clustering and principal coordinate analysis (PCoA) further indicated that aeration rate redistribution influenced the microbial community structure. The above laboratory-scale optimization results may provide a preliminary reference for aeration control and improvement of denitrification performance in similar processes. Full article

Industrial and municipal wastewater may contain substances that inhibit biological processes in wastewater treatment plants (WWTPs), posing risks to operational stability and environmental protection. The aim of this study is to evaluate the practical suitability of the ISO 8192:2007 respiration inhibition test for assessing the toxicity of wastewater. Nitrified activated sludge from a municipal WWTP was used to analyze wastewater from three industrial companies, wastewater from several discharge locations at a hospital, and WWTP influent. Oxygen consumption and inhibition were determined at sample-specific dilution levels and the reference substance 3,5-dichlorophenol. Two samples from the dental department of the hospital showed toxic effects on activated sludge respiration (inhibition > 50%), while no toxic effects were observed in the remaining samples. Several samples exhibited stimulatory effects (inhibition < 0%), indicating the presence of readily biodegradable organic matter. However, inhibitory effects (0–50% inhibition) were detected in individual wastewater samples at higher concentrations. This demonstrates that the method can detect toxicological changes in wastewater and is suitable for routine monitoring and early warning in WWTPs. Full article

In isolated areas, wastewater reuse is a key solution to water scarcity, enabling the completion of the integral water cycle. However, managing sludge from treatment plants in these regions poses significant environmental and economic challenges, particularly due to limited land availability. This study presents a cradle-to-gate comparative carbon footprint analysis of various sludge management pathways, ranging from traditional systems to advanced thermochemical conversion processes. The regional assessment reveals a significantly higher carbon footprint in Fuerteventura (23.0 kg CO_2,eq/capita · year) compared to Tenerife (13.2 kg CO_2,eq/capita · year). Centralized thermochemical processing shows the greatest decarbonization potential under the studied conditions; specifically, pyrolysis maximizes the reduction to 54% and 40% for Tenerife and Fuerteventura, respectively. This behavior is due to the carbon footprint recovery associated with pyrolysis byproducts. However, these findings are based solely on carbon footprint considerations and are subject to the technical and operational feasibility of thermochemical processing. These results provide a strategic framework for decarbonizing wastewater treatment plants in similar regions, identifying the most efficient pathways toward achieving carbon neutrality in the sludge line. Full article

The high-rate contact stabilization (HiCS) process is a potential technology for recovering energy from organic matter in wastewater; however, further performance improvement is required. This study proposes a biologically enhanced HiCS (BE-HiCS) process that introduces waste-activated sludge (WAS) from a separate conventional activated sludge (CAS) train within a wastewater treatment plant (WWTP) into the HiCS stabilization tank. The performance of the proposed process was verified using a pilot-scale plant. In a scenario combining the CAS and BE-HiCS processes, which is considered feasible for practical WWTP implementation due to the ready availability of WAS, a recovery of 0.24 ± 0.03 g-COD/g-COD of the influent COD mass was projected. This value was statistically significantly higher than that achieved by either the CAS process alone or the HiCS process alone. In this scenario, WAS was added to the BE-HiCS process at a ratio of 0.15 ± 0.03 g-COD/g-COD, resulting in a net recovery rate of 0.33 ± 0.04 g-COD/g-COD, after subtracting the COD contribution of the added WAS. The superior organic matter recovery of the BE-HiCS process was attributed to its enhanced ability to convert non-particulate organic matter into sludge through absorption and adsorption, while maintaining adequate sludge settleability for effective solid–liquid separation. Full article

The Fenton reaction remains one of the most widely investigated advanced oxidation processes for wastewater treatment due to its ability to generate highly reactive oxygen species capable of degrading persistent organic pollutants. However, classical homogeneous Fenton systems suffer from significant limitations, including narrow pH applicability, iron sludge generation, and poor catalyst reusability. In response, extensive research has focused on the development of heterogeneous and advanced Fenton-like catalysts aimed at overcoming these challenges while enhancing catalytic efficiency and operational stability. This review provides a comprehensive and critical analysis of the evolution of Fenton catalysis, from classical homogeneous systems to advanced materials, including nanostructured catalysts, carbon-based Fe–N–C systems, metal–organic frameworks, and single-atom catalysts. A unified evaluation framework is proposed, integrating key performance parameters such as catalytic activity, manufacturability, stability, and catalyst lifespan. Comparative analysis reveals that improvements in activity are often accompanied by trade-offs in cost and scalability, indicating that the most advanced materials do not necessarily provide the best practical performance. A life cycle-oriented perspective is incorporated, emphasizing catalyst reuse, lifespan, and iron leaching, and providing quantitative insight into cumulative catalytic performance. The results demonstrate that long-term efficiency is governed not only by intrinsic activity but also by durability and operational stability under realistic conditions. Finally, current challenges and future directions are discussed, including scalable synthesis, improved mechanistic understanding, and integration into hybrid treatment systems. This review bridges the gap between fundamental research and practical application by highlighting the importance of balancing performance, stability, and sustainability in the design of next-generation Fenton catalysts. Full article

The activated sludge process serves as the core barrier in pharmaceutical wastewater treatment, yet its stability is inherently challenged by the extreme complexity of influent composition and the unpredictability of toxic shocks, particularly under contract development and manufacturing organization (CDMO) operations. Current biotoxicity assessment methods face inherent trade-offs among timeliness, specificity, and matrix robustness, resulting in fragmented, reactive management that lacks predictive capacity. In response, this review critically synthesizes evidence on toxicity pathways and monitoring technologies, systematically evaluating their mechanistic basis and engineering applicability. Building on these findings, we propose a conceptual perception–cognition–response architecture that structures decision-making across three adaptive tiers: (i) a perception layer that tolerates false positives for rapid anomaly detection; (ii) a cognition layer that requires effect-based biological verification; and (iii) a response layer that authorizes resilience-oriented interventions. Rather than a linear pipeline, the three tiers form an adaptive feedback cycle that dynamically aligns monitoring intensity, verification depth, and response authority with real-time risk gradients and site-specific constraints. By explicitly linking biological mechanisms to assessment limitations and tiered decision rules, this review provides a hypothesis-generating roadmap that orients biotoxicity management from episodic, composition-based assessment toward adaptive, effect-driven control. The proposed framework is intended to guide future pilot validation, multi-sensor integration, and context-specific calibration, offering a unified narrative for advancing proactive biotoxicity control in complex pharmaceutical wastewater systems. Full article

The activated sludge process, along with its modifications, is currently the most widely used wastewater treatment method to achieve desired environmental outcomes. However, it is also characterized by operational instability resulting from changing conditions, a wide range of quantitative and qualitative wastewater parameters, and technical and technological factors. Multi-parameter analysis of biological processes enables more comprehensive control through the use of chemometric techniques, modeling, artificial neural networks, and AI in the decision-making process. This article presents the results of a multivariate data analysis of parameters of activated sludge suspension held under anaerobic conditions. Several correlations were identified between parameters characterizing activated sludge and sludge liquid. PCA and HCA analyses enabled the extraction of three sets of parametric clusters. They reflect specific stages of sludge transformation under anaerobic conditions: initial high biological activity (cluster I), degradation and nutrient release (cluster II), and stabilization with minimal sludge activity (cluster III). These clusters indicate characteristic qualitative changes in sludge and sludge liquid, which can serve as effective control and optimization tools for biological wastewater treatment processes. Statistical and chemometric analyses demonstrate the potential to rapidly assess the condition of activated sludge or the stage of anaerobic transformation by correlating individual parameters. This is an example of how these tools can be used to control wastewater treatment processes more effectively, including in anaerobic conditions. Such control may improve treatment quality and the energy efficiency of the process. It will also help reduce the impact of treatment plants on the aquatic environment and enable the reuse of wastewater that is more effectively treated, which is undoubtedly an important element of sustainable development. Full article

Deammonification, which is based on partial nitritation and anammox (PN/A), is a well-established sidestream treatment for nitrogen removal. However, transferring deammonification to mainstream wastewater treatment remains challenging due to low temperatures, the need to retain slow-growing anammox bacteria (AnAOB), and their competition for nitrite with nitrite-oxidizing bacteria (NOB) and heterotrophic denitrifiers. This work investigates cubic polyurethane foam carriers to promote growth and retention of AnAOB. A moving bed biofilm reactor (MBBR) and an integrated fixed-film activated sludge (IFAS) reactor were compared over a three-year experimental period at lab-scale. The feasibility of the biofilm carriers for deammonification was first evaluated under sidestream conditions, followed by a stepwise transition to mainstream operational conditions. The impact of operational parameters, including dissolved oxygen concentration, pH value, and aeration strategy, was evaluated with respect to the activity of aerobic ammonium-oxidizing bacteria (AOB), NOB, and AnAOB, as well as nitrogen removal rates. Deammonification reached nitrogen removal rates of 0.04–0.12 kg N m⁻³ d⁻¹ (IFAS reactor) and 0.02–0.28 kg N m⁻³ d⁻¹ (MBBR) at subphases with reactor bulk concentrations above 60 mg NH₄-N L⁻¹. Highest nitrogen removal degrees of 77 ± 6% (IFAS) and 76 ± 5% (MBBR) were achieved at reactor bulk concentrations of 96 mg NH₄ L⁻¹ and 97 mg NH₄ L⁻¹, respectively. Lower concentrations triggered NOB activity in both reactors, leading to an increase in nitrate concentration up to 22 mg NO₃-N L⁻¹. AOB and AnAOB activities were on average 6-fold higher on the carriers compared to suspended biomass throughout all experimental phases, demonstrating the feasibility of using cubic polyurethane foam carriers for deammonification. This was also confirmed by fluorescence in-situ hybridization (FISH) measurements. Median nitrogen removal rates over all experimental phases of 0.07 kg N m⁻³ d⁻¹ for the IFAS reactor and 0.05 kg N m⁻³ d⁻¹ for the MBBR were achieved, which are comparable to conventional activated sludge systems performing nitrogen removal via nitrification–denitrification. While at lower nitrogen concentrations, the IFAS reactor yielded superior nitrogen removal rates, peak nitrogen removal rates of 0.28 kg N m⁻³ d⁻¹ were measured in the MBBR configuration. However, controlling NOB activity at lower temperatures and concentrations remains a challenge in MBBR and IFAS configurations. In our study, in the IFAS reactor NOB activities were visible on fewer days than in MBBR. At mainstream-like conditions, higher nitrogen removal rates of IFAS (0.09–0.12 kg N m⁻³ d⁻¹) were achieved compared to the MBBR (0.06–0.09 kg N m⁻³ d⁻¹). This demonstrates the advantage of the IFAS reactor in treating mainstream wastewater via deammonification. As an autotrophic nitrogen removal process, the implementation of deammonification in the mainstream of municipal wastewater treatment plants enables enhanced recovery of biogas from sewage organic matter. The latter would otherwise be consumed during the conventional nitrification-denitrification pathway. Consequently, the overall energy balance for wastewater treatment can be improved, contributing to a more environmentally sustainable process. Full article

This study investigates the influence of waste-based materials, namely drinking water treatment sludge (DWTS) and expanded glass production waste (EGPW), on the properties of fine-grained concrete when used as partial Portland cement replacements. Fine-grained concrete mixtures containing different proportions of DWTS and EGPW were evaluated in terms of hydration behavior, microstructural development, mechanical performance, durability, and dimensional stability. Density, ultrasonic pulse velocity, water absorption, flexural and compressive strengths, drying shrinkage, and porosity parameters were determined, while frost resistance was assessed and predicted based on porosity characteristics. Hydration kinetics were analyzed using X-ray diffraction and semi-adiabatic calorimetry. The results showed that increasing EGPW content enhanced cement hydration processes and promoted matrix densification through pozzolanic reactions, resulting in reduced water absorption and improved mechanical properties. In contrast, DWTS exhibited an inhibiting effect on hydration due to its inert nature and high Fe₂O₃ content, acting primarily as a micro-filler; however, when combined with EGPW at moderate dosages, DWTS contributed positively to flexural strength and slightly reduced drying shrinkage. The combined use of DWTS and EGPW enabled the formation of a balanced pore structure and improved the durability of fine-grained concrete. Among the tested mixtures, ED-3 (7.5% EGPW + 5% DWTS) provided the most favorable balance between hydration activation and binder reduction, while the highest frost resistance was achieved by the ED-4 mixture, reaching approximately 603 predicted freeze–thaw cycles. Overall, the results indicate that properly optimized combinations of EGPW and DWTS can significantly enhance the performance and durability of fine-grained concrete while controlling drying shrinkage. Full article

This study systematically compared the performance of different composite magnetic materials in enhancing activated sludge treatment of municipal wastewater. A sequencing batch reactor (SBR) process was used as the model system. Four different composite magnetic materials were examined: Fe₃O₄ composite activated carbon, Fe₃O₄ composite diatomite, Fe₃O₄ composite composite kaolin, and Fe₃O₄ composite composite fly ash. Their performance in enhancing activated sludge treatment of municipal wastewater was evaluated in terms of pollutant removal, sludge physicochemical properties, and molecular biology analysis. Furthermore, the two best-performing composite magnetic materials were further investigated at different dosages to examine their pollutant removal performance and mechanisms. Furthermore, the two best-performing composite magnetic materials were further investigated at different dosages to examine their pollutant removal performance and mechanisms. The results showed that, compared with the control system (without material addition), the addition of four composite magnetic materials improved the average removal efficiencies as follows: for the Fe₃O₄ composite activated carbon, Fe₃O₄ composite diatomite, Fe₃O₄ composite kaolin, and Fe₃O₄ composite composite fly ash systems, COD removal increased by 2.55%, 2.77%, 1.67%, and 4.10%, respectively; TN removal increased by 1.71%, 3.33%, 4.82%, and 0.82%, respectively; and TP removal increased by 4.96%, 7.02%, 6.01%, and 5.76%, respectively. In the Fe₃O₄ composite diatomite system, the highest average removal efficiencies of COD, TN, and NH₄⁺-N were achieved at a dosage of 50 mg/L, whereas the highest average TP removal efficiency was achieved at a dosage of 200 mg/L. In the Fe₃O₄ composite kaolin system, the highest average removal efficiencies of COD, TP, and NH₄⁺-N were achieved at a dosage of 50 mg/L, while the highest average TN removal efficiency was achieved at a dosage of 200 mg/L. High-throughput sequencing indicated that the highest activity of denitrifying genera was observed in the Fe₃O₄ composite diatomite system at a dosage of 50 mg/L and in the Fe₃O₄ composite kaolin at a dosage of 200 mg/L, respectively. The addition of composite magnetic materials enhances the efficiency of municipal wastewater biological treatment. These findings provide theoretical and technical guidance for the selection of magnetic composite materials in municipal wastewater treatment. Full article

Microplastics (MPs) in wastewater treatment plants are predominantly retained in sewage sludge, making sludge processing a critical stage for MP transformation and potential pollutant release. However, the aging of polyethylene (PE) MPs and the release of MP-derived dissolved organic matter (MP-DOM) during sludge dewatering remain poorly understood. In this study, representative sludge conditioners were set up in dewatering experiments to investigate the changes in PE MP surface properties, pollutant-carrying potential, and MP-DOM release behavior. The results showed that sludge dewatering induced pronounced surface aging of PE MPs, including wrinkling, cracking, particle fragmentation, and the formation of polar oxygen-containing functional groups. These changes significantly increased the Cd adsorption potential of PE MPs, reaching 8228 ± 568 mg kg⁻¹. Lime conditioning promoted stronger fragmentation and a greater reduction in particle size than other conditionings, which likely increased the specific surface area. Meanwhile, a substantial release of PE MP-DOM was observed, with dissolved organic carbon concentrations in sludge process water being 2–30 times higher than those in deionized water. Fluorescence and molecular analyses showed that PE MP-DOM was dominated by protein-like and fulvic-like substances and also contained phthalates, fatty acids, and acetamide-based plasticizers. The magnitude and composition of PE MP-DOM release were strongly regulated by conditioner-induced pH and ionic strength. Alkaline conditions and increasing concentrations of Ca²⁺ (0.1–2.1 mol L⁻¹) and Fe³⁺ (0.006–0.6 mol L⁻¹) enhanced PE MP additive release. These findings demonstrate that sludge dewatering is an active process that accelerates PE MP aging and associated organic release. This work provides new insight into the environmental behavior of MPs during sludge treatment and offers a basis for developing sustainable sludge management. Full article