Phosphorus (P) in waste activated sludge (WAS) exists in both intracellular stores and fractions associated with extracellular polymeric substances (EPS). These EPS-bound phosphorus species are often stabilized through metal - phosphate - EPS linkages, which complicate their selective recovery. In this study, five single extraction methods (acidification, alkalization, heating, ultrasound, and EDTA chelation) and one combined approach (ultrasound-EDTA) were comparatively evaluated to elucidate their mechanisms of EPS disruption and P mobilization. Phosphorus speciation behavior under single treatments was characterized using 31P nuclear magnetic resonance with phytic acid and sodium hexametaphosphate as model compounds, revealing that strong alkaline extraction caused extensive Poly-P depolymerization and OP hydrolysis, whereas EDTA and low-intensity ultrasound preserved P speciation but showed limited extraction efficiency. The ultrasound-EDTA combination achieved a synergistic effect, yielding 62.63 mg·g-1 TSS of EPS and 9.6 mg·g-1 TSS of phosphorus with only 13.2% cell apoptosis, comparable to alkaline extraction yet with minimal biological disruption. Confocal microscopic analysis confirmed that the released phosphorus predominantly originated from the EPS matrix, indicating that the hybrid treatment effectively targeted EPS-P while preventing intracellular release. These findings establish a non-destructive extraction pathway based on the coupling of physical cavitation and selective chelation, providing mechanistic insight into EPS-mediated P binding and offering a new strategy for controlled, high-efficiency phosphorus recovery from sludge.
Soil dissolved organic matter (DOM) plays a pivotal role in governing the environmental behavior and fate of metal ions. The inherent heterogeneity of DOM, however, leads to complex and poorly understood interactions with heavy metals. In this study, soil DOM was fractionated into four pH-dependent fractions via PPL solid-phase extraction combined with sequential acid elution. The binding interactions of these fractions with Cu(II) were systematically investigated through and, coupled with two-dimensional correlation (2D-COS) analysis. The results indicated that low-pH fractions exhibited enhanced aromaticity and more pronounced spectral responses. Regardless of the DOM fraction, 2D-COS analysis revealed that short-wavelength chromophores (< 230 nm) preferentially coordinated with Cu(II), and the binding sequence of fluorescent components followed protein-like > fulvic-like > humic-like components. Moreover, functional group analysis showed that carboxyl C = O groups dominated the binding response, followed by aliphatic C-OH or phenolic O-H, while pH-based fractionation of DOM primarily influenced binding accessibility rather than binding mechanism. Meanwhile, the parallel factor analysis (PARAFAC) results revealed that protein-like substances exhibited higher conditional stability constants, whereas humic-like fractions provided more accessible binding sites among the pH-dependent DOM fractions. Collectively, these findings illuminated that the heterogeneous complexation mechanisms between DOM fractions and Cu(II), and provide a basis for assessing environmental geochemical risks of heavy metals.
The effects of moisture + extrusion and composting + extrusion treatments on the production of biogas from the anaerobic digestion (AD) of wheat straw (WS) were systematically investigated. The results showed that when the moisture content of WS was adjusted to 55% before extrusion and maintained for 24 h, the biogas production of both the unextruded and extruded samples reached the highest levels, which were 130.48 and 158.41 mL/g, respectively. Based on these results, the WS was further aerobically composted after adjusting its moisture content to 55%, and then extruded for biogas production. The biogas production of unextruded WS initially increased and then decreased, reaching the maximum of 129.40 mL/g when the composting temperature rose to 55°C. In contrast, the biogas production of extruded WS increased at all composting temperatures and reached the maximum of 150.83 mL/g at 55°C, which is 19.49% higher than the initial biogas production of extruded WS at the start of composting. Mechanistic analyses indicated that extrusion reduced particle size, increased specific surface area, and disrupted lignocellulosic structure, while composting promoted partial degradation of hemicellulose and lignin. These structural modifications enhanced substrate accessibility and microbial degradation, thereby boosting biogas production. In conclusion, the combination of composting and extrusion pretreatment can significantly improve the biogas production performance of anaerobic digestion of WS, with an increase ranging from 20.76% to 43.45%, which is worthy of further research.
The co-composting of Siraitia grosvenorii residue and pig manure frequently faces challenges associated with substantial nitrogen loss and insufficient humification. To address these issues, the Bacillus smithii strain XT-3 was inoculated into the co-composting system to enhance nitrogen retention and promote humus formation during composting. The underlying mechanisms were further elucidated through metagenomic analysis. Inoculation with strain XT-3 reduced cumulative NH3 emissions by 27.8% and increased humic acid content by 17.02%. Temporal variations in humic substances presented a synchronous decline in fulvic acid coupled with humic acid accumulation, facilitating faster attainment of compost maturity thresholds. Furthermore, XT-3 reshaped the microbial community involved in nitrogen metabolism by enhancing the relative enrichment of Bacillota during the thermophilic stage and elevating the relative abundance of Pseudomonadota and Bacteroidota during the cooling stage, along with strengthened positive microbial interactions. Functional annotation of KEGG orthologs indicated that XT-3 improved the genetic potential of ammonia assimilation pathways throughout composting. Collectively, these findings demonstrate that XT-3 may facilitate synergistic nitrogen retention and enhanced humification by modulating microbial community structure, strengthening positive microbial interactions, thereby providing a theoretical basis for the precise regulation of functional microorganisms during composting.
This study investigated the removal of U(VI) from multi-ion simulated groundwater using a uranium-tolerant indigenous strain Leifsonia sp. coupled with natural kaolinite and montmorillonite binary clay composites. Batch static experiments were performed to systematically quantify the independent and interactive effects of key variables (pH, reaction duration, initial U(VI) concentration, bacterial dry biomass dosage) and common groundwater coexisting ions on U(VI) immobilization efficiency. The binary clay-bacteria composite achieved optimal U(VI) removal performance, with a maximum removal efficiency of 94.23% under the optimized conditions of pH 6, 20 h reaction time, 10 mg·L-¹ initial U(VI) concentration, and 0.6 g·L-¹ bacterial biomass. Kinetic studies were further conducted to elucidate the adsorption behaviour, and the PSO model exhibited the best fitting performance, confirming the dominant chemisorption mechanism. Multi-technique characterizations including SEM-EDS, FTIR and XPS were applied to reveal the synergistic immobilization mechanism. Clay minerals significantly promoted bacterial cell attachment, alleviated bacterial aggregation and uranium cytotoxicity, and supplied abundant extra inorganic ion-exchange adsorption sites. FTIR spectra verified that hydroxyl, carboxyl, alkoxy and carbonyl functional groups from bacterial extracellular polymeric substances and clay lattices jointly coordinated uranyl ions. XPS high-resolution U4f spectra and quantitative peak fitting detected coexisting U(VI) and U(IV) species in solid reaction precipitates, realizing differentiation of passive surface adsorption (∼73%) and metabolism-dependent microbial bioreduction (∼21%) contributions to U(VI) immobilization. Overall, the natural binary clay-indigenous Leifsonia composite exhibited prominent cascade synergistic effects and shows promising application potential for in-situ remediation of uranium-contaminated groundwater.
Nostocoides, a key phosphate-accumulating organism (PAOs), is abundant in wastewater treatment plants (WWTPs); however, the mechanism of sludge reduction in biological phosphorus removal systems under its dominance remains largely unknown. This study employed a lab-scale, exploratory multiparameter approach to examine extracellular polymeric substance (EPS) profiles, intracellular metabolites, microbial community, membrane integrity, and physiological activity to elucidate how Nostocoides-enriched enhanced biological phosphorus removal (EBPR) configurations accomplished sludge reduction. Waste-activated sludge (WAS) was repurposed as fermentation feedstock in the EBPR process. The findings indicate that a 43.23% reduction in sludge was achieved without any preliminary sludge pretreatment. The phosphorus removal rate was 99% without any supplemental carbon, which broke free from the reliance on influent organics that typified conventional EBPR. Illumina-based sequencing indicated that Nostocoides was the dominant bacterial community. Excitation-emission matrix (EEM) spectra showed that aromatic proteins derived from tyrosine and tryptophan, along with soluble microbial by-products embedded in the EPS matrix, were broken down to accelerate sludge disintegration. Flow cytometry was employed to assess membrane integrity along with overall microbial vitality and revealed that microbial cells underwent extensive death and lysis under WAS fermentation conditions, thereby releasing DNA and elevating its concentration in the supernatant, which represent key physiological changes driving sludge disintegration and organic carbon release for nutrient removal in this system. Nostocoides-governed EBPR configuration enables concomitant sludge reduction and nutrient elimination. This preliminary mechanistic exploration within Nostocoides-led EBPR configurations provides exploratory fundamental insights for advancing EBPR technology, with further validation required for practical engineering application.
Sulphate-rich industrial wastewater is often contaminated with heavy metals, yet their influence on microbial sulphate reduction remains poorly understood. This study investigated the response of sulphate-reducing bacteria (SRB) in a microbial electrolysis cell (0.8 V, 48 h cycles) to stepwise increasing Cu2+ concentrations (8-125 mg/L) under stirred conditions. When Cu2+ concentration increased from 8 to 55 mg/L, sulphate reduction efficiency over 48 h remained stable at approximately 90%, suggesting good SRB tolerance. When Cu2+ concentration was 85 mg/L, sulphate reduction efficiency over 48 h dropped sharply to 30-60%, coinciding with persistent Cu2+ removal below 40%. Extracellular polymeric substances (EPS) extracted from cathode effluent, analysed by 3D-EEM and FTIR, showed metal complexation capacity. However, excess Cu2+ caused cell deformation and lysis, as observed by TEM. These results indicate a concentration-dependent response with a critical toxicity threshold, providing a basis for operating bioelectrochemical systems treating copper-laden sulphate wastewater.
In response to dual demands of advanced oxidation of organic pollutants and recycling of retired lithium-ion batteries, this research proposed a high-value recycling method to convert cobalt resources from retired lithium-ion batteries into high-performance cobalt ferrite (CoFe2O4) catalysts. Cobalt leaching and cobalt ferrite synthesis were coupled into an integrated process to achieve efficient cobalt leaching (> 98%). By optimising the sol-gel process, optimal conditions were identified: tartaric acid-to-total metal ion molar ratio 2:1, pH = 7.0, and calcination at 500°C for 2 h. The spinel-type cobalt ferrite particles obtained under these conditions are well-structured, with high catalytic activity, and stable magnetic properties. The cobalt ferrite material catalyzed the degradation of rhodamine B (RhB) by activated peroxymonosulfate (PMS) with excellent performance. Under the optimised reaction conditions (PMS concentration of 0.50 mmol/L, cobalt ferrite concentration of 75 mg/L, initial pH = 7, RhB concentration of 20 mg/L, and reaction time of 90 min), the degradation rate of RhB could reach 99.46%, with an apparent rate constant of 0.0387 min-1. The quenching experiments showed that sulfate radical (SO4-·) was the main reactive oxygen species for the degradation of RhB, while hydroxyl radical (·OH) and superoxide radical (·O2-) also promoted the activation of PMS. Moreover, the cobalt ferrite catalyst could maintain high catalytic activity after multiple cycles, with the degradation rate of RhB remaining above 81%, demonstrating favourable cycling stability. This research offers a novel approach for retired lithium-ion battery valorisation and theoretical support for advanced heterogeneous catalyst development.
This study assessed the feasibility and environmental implications of utilizing pig and cattle manure as solid fuels, with a focus on flue-gas emissions and ash recyclability. Cattle manure - derived solid fuel, produced by reducing moisture content to approximately 4%, achieved a lower heating value (LHV) of 14.6 MJ kg-¹ and an ash content of 21.5%, meeting Republic of Korea solid-fuel quality standards (LHV ≥ 12.6 MJ kg-¹, ash ≤ 30%, moisture < 20%). In contrast, pig manure - derived solid fuel exhibited a moisture content (12.5%) that satisfied the standard, but a lower LHV (8.5 MJ kg-¹) and higher ash content (34.6%), failing to meet fuel quality criteria. Stack measurements revealed distinct emission characteristics. For cattle manure, selective non-catalytic reduction (SNCR) enabled stable emission control, with dust (1.3 mg m-³), CO (105.7 ppm), NOx (46.8 ppm), and SOx (17.2 ppm) within regulatory limits. Conversely, pig manure combustion produced excessive SOx emissions (286 ppm vs. 60 ppm limit) even with SNCR, indicating need for additional desulfurization or alternative utilization pathways. Residue analysis showed that over 90% of ash was recovered as bottom ash, with phosphorus concentrated in this fraction, indicating reuse potential. However, pig manure ash contained elevated Cu and Zn levels, exceeding fertilizer standards and requiring stabilization before recycling. Overall, cattle manure demonstrated favorable environmental performance, whereas pig manure posed challenges related to sulfur-related air pollution and heavy-metal enrichment. These results highlight the need to jointly consider environmental risk management and resource recovery when promoting livestock manure as a renewable energy source.
This study addresses the pollution challenges posed by fluoride-containing wastewater in the photovoltaic industry and explores the potential for fluorine resource recovery. It proposes a seed-induced electrocoagulation-crystallization (EC-C) strategy to achieve efficient fluoride removal and high-value recovery of cryolite (Na3AlF6). The key operating parameters for electrocoagulation (EC) were systematically optimized, with optimal conditions determined as: electrode area of 150 cm2, electrode spacing of 1.2 cm, 0.05 M NaCl + NaHCO3 composite electrolyte, and initial fluoride concentration of 3000 mg/L. Under these conditions, fluoride removal efficiency reached 94.4% with minimal energy consumption and anode loss, conforming to pseudo-first-order kinetics. To regulate crystallization pathways and product quality, seed-assisted crystallization was introduced: Commercial Na3AlF6 seed crystals (CNSC) outperformed Autocatalysed seeds crystals (ASC), with an optimal dosage of 0.75 g administered via stepwise addition over 0-20 min, significantly enhancing product phase content. This yielded high-content cryolite with 97.5% content. FTIR/XRD analysis revealed that fluorinated aluminum intermediates undergo progressive dehydration and transformation into a cryolite crystal phase dominated by Al-F bonds. This study established an integrated pathway for efficient fluoride removal and high-value recovery through coupled regulation of parameter windows and seeding timing, providing theoretical and process foundations for the high-value utilization of fluorinated photovoltaic wastewater.
Perfluorooctanoic acid (PFOA), remains a major environmental challenge due to its exceptional chemical stability, resistance to conventional treatment technologies. In this study, a sustainable carboxymethyl cellulose-reinforced graphene oxide/molybdenum disulfide hydrogel (MoS₂/GO/CMC) was developed as a visible-light-responsive photocatalyst for PFOA degradation under low-power LED irradiation. The photocatalytic process was optimized using Response Surface Methodology based on a Box-Behnken Design, evaluating the effects of irradiation power (7-12 W), catalyst dosage (0-0.04 g), and initial PFOA concentration (10-50 mg L-¹). The optimized conditions (12 W, 0.04 g catalyst, and 30 mg L-¹ PFOA) achieved 99.8% degradation efficiency, with the developed quadratic model exhibiting excellent predictive capability (R² = 0.9974). Characterization results confirmed integration of MoS₂ and GO within the CMC matrix, producing a heterostructure with a narrow band gap of 1.12 eV, enhanced charge separation, and suppressed electron-hole recombination. Kinetic analysis revealed pseudo-first-order degradation behaviour with a rate constant of 0.013 min-¹ and a half-life of 0.89 h. Radical scavenging experiments identified superoxide radicals (O₂•-) as the dominant reactive species governing PFOA degradation. LC-MS analysis confirmed a stepwise chain-shortening degradation pathway involving intermediates such as PFHpA, PFPeA, and PFBA, indicating progressive defluorination and carbon-carbon bond cleavage. The hydrogel demonstrated excellent stability, retaining over 96% of its initial activity after seven cycles. An Electrical Energy per Order (EEO) value of 444.6 kWh m-³ order-¹ highlights the feasibility of low-energy operation. These findings demonstrate that MoS₂/GO/CMC hydrogels offer an environmentally benign, recoverable, and energy-efficient for PFAS remediation.
The development of efficient low-phosphorus water treatment formulations is essential for sustainable industrial water management. In this study, a novel quadri-component corrosion and scale inhibitor PPHZ was developed by rationally combining biodegradable polyaspartic acid (PASP), phosphonobutane-tricarboxylic acid (PBTCA), hydrolyzed polymaleic anhydride (HPMA), and ZnCl2. The formulation exhibits excellent dual-functional performance in both scale and corrosion inhibition. At a dosage of 50 mg/L, PPHZ achieves 95% CaCO3 scale inhibition by effectively distorting crystal growth and completely transforming calcite/aragonite into non-adherent vaterite. Notably, only 10 mg/L of PPHZ is sufficient to completely inhibit CaSO4 scale formation. In simulated circulating water, PPHZ achieves a corrosion inhibition efficiency of 90% for carbon steel at 30 mg/L. Electrochemical analysis reveals that PPHZ simultaneously suppresses both anodic and cathodic reactions through a 'Zn2+-bridging' hybrid film mechanism, while surface characterization (SEM-EDS, XRD) confirms the formation of a dense hybrid protective film. The formulation has a theoretical phosphorus content of only 2.296%, achieving >92% phosphorus reduction compared to conventional phosphorus-based agents, in line with the sustainable development trend of water treatment technologies. PPHZ provides an effective strategy for integrated corrosion and scale control in industrial water systems.
Bioelectrochemical systems offer a promising approach for nitrogen polishing of low-strength, carbon-limited wastewater; however, how electron-acceptor availability governs nitrogen conversion and electrochemical behaviour remains unclear. In this study, a bioelectrochemical sequencing batch reactor (BeSBR) and a control reactor were operated in sequencing batch mode, in which electron-acceptor conditions were sequentially varied within the same reactor system. The reactors were subjected to nitrite-abundant, nitrite-limited, nitrite-free, and oxygen-exposed phases, each maintained until stable performance was achieved. Nitrogen conversion was evaluated using cycle-based concentration profiles under steady-state conditions. Stable nitrogen polishing was achieved without external organic carbon addition, and powdered activated carbon (PAC) served as a conductive mediator supporting microbial retention and extracellular electron transfer. Nitrite-abundant conditions exhibited the most favourable electrochemical characteristics, while ammonium removal persisted under nitrite-limited and nitrite-free conditions, indicating adaptive nitrogen conversion under alternative electron acceptors. Kinetic analysis showed that ammonium removal exhibited approximately linear, zero-order-like behaviour under most conditions, with rates in the range of 2.0-2.5 mg N L-1 h-1, corresponding to removal of ∼25 mg N L-1 within 10-12 h. Biomass stabilised at approximately 3,000-3,500 mg/L after initial reduction, indicating microbial adaptation. Microbial and functional analyses suggested multiple coexisting pathways, including nitrite-associated processes, dissimilatory nitrate reduction to ammonium, and sulfur-linked reactions. Overall, nitrogen conversion was governed by dynamic redox reconfiguration driven by electron-acceptor availability, rather than a single dominant pathway, highlighting its potential as an energy-efficient nitrogen polishing strategy.
The contamination of wastewater by antibiotics poses significant ecological risks. Here, a novel Fe-Mn co-doped nitrogen-doped biochar (Fe-Mn@NBC) was synthesized from corn straw via impregnation-chelation-pyrolysis to activate periodate (PI) for oxytetracycline (OTC) degradation. The Fe-Mn@NBC/PI system demonstrated outstanding degradation performance, achieving an OTC removal rate of 96.2% within 90 min, with a reaction constant of 0.237 min-1. The unit degradation efficiency of OTC for Fe-Mn@NBC/PI system was calculated to be 320.7 mg·(g·mmol)-1, outperforming many similar catalysts reported in the literature. This enhanced performance is attributed to the porous structure, large surface area, and abundant active sites of Fe-Mn@NBC, which optimize charge distribution and facilitate electron transfer. The system maintained good degradability and reusability under various hydraulic conditions (pH, inorganic anions, humic acid, actual water). Mechanistic studies revealed that 1O2, O2•-, and IO3• were the dominant reactive species. Using HPLC-MS and Fukui function analysis, electron-rich groups (-CONH2, -COOH) were identified as primary attack sites, leading to three proposed OTC degradation pathways, with key intermediates showing low toxicity via T.E.S.T. analysis. This study not only presents a sustainable approach for repurposing waste corn stalk biomass but also offers a cost-effective and eco-friendly solution to combat antibiotic pollution in wastewater.
Efficient regeneration of spent activated carbon (SAC) is critical for sustainable VOC abatement, yet the multiscale structural evolution during thermal treatment remains poorly understood. This study elucidates the multiscale structural evolution mechanism of SAC during thermal regeneration - from contaminant desorption to carbon matrix reorganization - through integrated multi-technique characterization (BET, SEM, TGA, XRD, FTIR). Key findings reveal a three-stage 'cleaning-reconstruction-degradation' mechanism: (i) Low-temperature treatment (300-400°C) removes surface contaminants and oxygen-containing groups, reopening blocked micropores; (ii) Optimal treatment at 400-500°C for 1-2 h achieves near-complete contaminant removal (>95%) while inducing controlled graphitization and beneficial mesoporosity development, restoring SBET to 965-1020 m²/g with well-preserved microporous architecture, indicating high potential for adsorption capacity recovery; (iii) Excessive treatment (≥600°C for 3 h) causes micropore collapse and sintering, reducing surface area. These findings establish a scientifically grounded optimal regeneration window (400-500°C, 1-2 h) that balances contaminant desorption efficiency with carbon matrix preservation, offering practical guidance for energy-efficient industrial regeneration of VOC-laden activated carbon from organic chemical manufacturing processes.
Rapid population growth has intensified pressure on freshwater (FW) resources, significantly impacting agricultural practices and worsening food scarcity in many regions. The reuse of treated wastewater (TWW) for irrigation addresses water scarcity but carries the risk of spreading pathogenic microbes and antibiotic-resistant bacteria (ARB). Free-living amoebae (FLA) in soil prey on bacteria and have been proposed as biocontrol agents. Here, we suggest an eco-biological approach, investigating how key ions in TWW (phosphate, ammonium, and sulphate) affect predation by three FLA species (Vermamoeba vermiformis, Acanthamoeba castellanii and Heterolobosea sp.) on model bacterial prey GFP-tagged Escherichia coli and GFP-tagged Enterococcus mundtii. This approach aims to enhance soil microbial safety and reduce pathogen persistence in irrigation systems. We also develop a YOLOv5 deep-learning model to quantitatively track FLA behaviour in microscopy videos. Our results show that PO43- or NH₄⁺ (100 mg/L) enrichment greatly enhances Vermamoeba's grazing on E. coli (7 log10 reductions in 72 h) compared to controls or SO₄²- addition. Fluorescence microscopy images confirm extensive bacterial interaction and killing by Vermamoeba in PO43- and NH₄⁺ enrichment. In contrast, Acanthamoeba and Heterolobosea had weaker effects. A mixed FLA consortium, however, eliminated E. mundtii faster than any single FLA species. The YOLOv5 model trained on an annotated dataset and validated against manual viable-cell counts reliably tracked FLA movement. These findings suggest that tailoring nutrient levels in TWW can enhance the biocontrol function of FLAs. Our interdisciplinary approach lays groundwork for ecological and AI-informed strategies to make TWW reuse safer.
With the acceleration of global industrialization, the environmental risks posed by heavy metals in sludge have become increasingly prominent. Traditional treatment methods struggle to effectively reduce the bioavailability of these metals, whereas pyrolysis facilitates the fixation and transformation of heavy metals via high-temperature conversion. This study investigated the migration and transformation of heavy metals during sludge pyrolysis, focusing on the influence of pyrolysis temperature and heating rate on the distribution and morphology of these metals. The results revealed that both the pyrolysis temperature and heating rate significantly affected the fixation efficiency, migration behavior, and chemical form of the heavy metals. Pyrolysis temperature and heating rate significantly affect heavy metal behavior. Optimal stabilization is achieved at 700 and 10 °C min-1, which drastically reduces the potential ecological risk index (RI) from 156.97 to 9.83 and 10.80. These conditions facilitate metal migration into gas/liquid phases and convert active fractions (F1/F2) into the stable residual fraction (F4). The crystal structure and functional group changes of the pyrolysis products were further analyzed by X-ray diffraction and infrared spectroscopy. The results show that the higher pyrolysis temperature will weaken the characteristic peak intensity of SiO2. The faster heating rate will enhance the crystallization of graphite carbon and accelerate the dehydration/alkane decomposition reaction, which can be confirmed by the weakening of -OH and -CH stretching vibration intensity. This study provides a theoretical foundation for optimizing the sludge pyrolysis process and contributes to the realization of resource utilization in sludge treatment.
To mitigate the environmental risks posed by the herbicide acetochlor in aquatic ecosystems, this study systematically evaluated its degradation across three advanced UV-based reductive processes: UV/Na2SO3, UV/Na2S, and UV/Na2S2O4. Under 254 nm irradiation, the UV/sulphite (UV/Na2SO3) system demonstrated superior degradation efficiency, achieving optimal removal under neutral-to-weakly alkaline conditions (pH 7.0-10.0) with rates scaling proportionally to the initial sulphite concentration. Mechanistic investigations revealed that hydrated electrons (eaq-), sulphite radicals (SO3•-), and hydrogen atoms (H•) collectively drove the degradation, contributing 58.72%, 37.95%, and 3.33%, respectively. Matrix effect evaluations indicated that NO3-, NO2-, and HCO₃- significantly inhibited the eaq--mediated reduction, whereas Cl- and SO42- exhibited negligible interference. Crucially, density functional theory (DFT) and transition state calculations were employed to elucidate the microscopic degradation pathways. These theoretical models confirmed that the initial electron-induced dechlorination at the C-Cl bond is a barrierless process. Furthermore, transition state analysis uncovered a water-assisted, stepwise hydrogen transfer and hydrolysis mechanism, wherein water clusters function as essential proton shuttles to facilitate C-N bond activation. By seamlessly integrating experimental kinetics with advanced computational modelling, this study delineates the precise degradation mechanisms of acetochlor, providing a robust theoretical foundation and technical framework for the application of UV/sulphite processes in water remediation.
Anaerobic sludge digestion is widely applied in municipal wastewater treatment plants for sludge stabilisation and renewable energy recovery through biogas production. However, digestion performance is governed by upstream biological treatment configuration, which determines sludge origin and biodegradability. This study presents a comparative assessment based on experimentally generated from a full-scale high-rate activated sludge (HRAS) system and literature-based datasets for conventional activated sludge (CAS) systems. Long-term anaerobic batch digestion tests were conducted under mesophilic conditions using plant-representative mixed sludge prepared from primary and secondary sludges collected from HRAS treatment line of a full-scale municipal wastewater treatment plant in Türkiye. Methane production and solids reduction were evaluated. The experimental results were further interpreted using plant-wide modelling implemented in the SUMO simulation platform. Methane yields normalised to volatile solids fed varied substantially with sludge origin and sludge age. The HRAS plant operated at the lowest sludge age exhibited the highest methane yield (530 L CH4/kg VSfed), whereas literature reported CAS systems yielded between 193 and 375 L CH4/kg VSfed. When normalised to treated wastewater, biogas production from CAS systems in Türkiye was significantly lower than that from HRAS configurations and reported CAS systems in Europe and North America, reflecting differences in carbon capture and upstream processes. Good agreement between experimental observations and plant-wide modelling confirms that anaerobic digestion performance cannot be optimised independently of upstream treatment design. Overall, the results highlight the importance of high-rate carbon capture strategies and unit wastewater-based performance indicators for improving plant-wide energy recovery in wastewater treatment systems.
