Significant role of UV and carbonate radical on the degradation of oxytetracycline in UV-AOPs: Kinetics and mechanism

Overlooked role of CO3·- reactivity with different dissociation forms of organic micropollutants in degradation kinetics modeling: A case study of fluoxetine degradation in a UV/peroxymonosulfate system

Selective oxidizing agent carbonate radical (CO3•-) is an important secondary radical in radical-based advanced oxidation technology for wastewater treatment. However, the role of CO3•- in removing ionizable organic micropollutants (OMs) under environmentally relevant conditions remains unclear. Herein we investigated CO3•- effect on degradation kinetics of fluoxetine in UV/peroxymonosulfate (PMS) system based on a built radical model considering CO3•- reactivity differences with its different dissociation forms. Results revealed that the model, which incorporated CO3•- selective reactivity (with determined second-order rate constants, ksrc,CO3·-, of 7.33 ×106 and 2.56 ×108 M-1s-1 for cationic and neutral fluoxetine, respectively) provided significantly more accurate predictions of fluoxetine degradation rates (k). A good linear correlation was observed between ksrc,CO3·- from experiments and literatures for 24 ionizable OMs and their molecular orbital energy gaps and oxidation potentials, suggesting the possible electron transfer reaction mechanism. Cl- slightly reduced the degradation rates of fluoxetine owing to rapid transformation of Cl• with HCO3- into CO3•-, which partially compensated for the quenching effects of Cl- on HO• and SO4•-. Dissolved organic matter significantly quenched reactive radicals. The constructed kinetic model successfully predicted fluoxetine degradation rates in real waters, with CO3•- being the dominant contributor (∼90 %) to this degradation process.

Hydroxylamine promoted degradation of organic contaminants using peroxydisulfate activated by Fe-alginate

To overcome the shortcomings of Fe(Ⅱ)/peroxydisulfate (PDS) system including the limited working pH range and large iron sludge production, a Fe-doped alginate (Fe-Alg) catalyst was prepared and combined with hydroxylamine (HA) to continuously activate PDS for the removal of organic pollutants in neutral condition. Due to the strong reductive capability of HA, it could significantly enhance the catalytic capability of Fe-Alg for PDS. The results of characterization suggested that Fe(Ⅲ)/Fe(Ⅱ) was evenly distributed in Alg through its complexation with carboxyl groups, and the reduction of Fe(Ⅲ) to Fe(Ⅱ) initiated by HA enabled Orange G (OG) to be continuously degraded in the Fe-Alg/HA/PDS system. The results of quenching experiments suggested that S O 4 ∙ - and HO• played a dominant role for OG removal in the Fe-Alg/HA/PDS process. The effect of influence factors (e.g. initial pH, HA concentration, Fe-Alg dose and PDS concentration) and water matrix components (i.e. S O 4 2 - , N O 3 - , Cl-, HC O 3 - and dissolved organic matters (DOM)) on the performance of Fe-Alg/HA/PDS system was systematically investigated. Other refractory organic contaminants, including diclofenac (DCF), sulfamethoxazole (SMX), oxytetracycline (OTC) and bisphenol AF (BPAF) were also efficiently eliminated in Fe-Alg/HA/PDS system, suggesting the feasibility of this system for the treatment of organic pollutants. This work provides a method to optimize Fe(Ⅱ)/PDS system and a novel process applied to degrade refractory pollutants.

Photodegradation of the main synthetic musk (HHCB) in water: kinetic study and influencing factors

Galaxolide (HHCB) is the most common synthetic musk compound detected in numerous daily products. Despite its persistence in the aquatic environment, the photodegradation of HHCB remains poorly understood. In this study, we investigated the direct and indirect photolysis kinetics of HHCB under simulated sunlight and UVC light. Our aim was to determine the role of reactive oxygen species (ROS) responsible for HHCB degradation in the aquatic environment and to identify its transformation products. The influence of environmental factors on indirect photolysis was investigated by testing both synthetic waters (containing humic acid, carbonate (CO32-), and nitrate (NO3-)) and real waters (riverine and effluent). Hydrogen peroxide (H2O2/UVC) was tested to simulate the wastewater treatment process. Quencher experiments were conducted to identify the role of ROS in HHCB photodegradation, including hydroxyl radicals (˙OH), carbonate radicals (CO3˙-), triplet states of dissolved organic matter (3DOM*), and singlet oxygen (1O2). The results clearly indicated that HHCB was efficiently degraded by direct photolysis under both light conditions. The presence of H2O2 led to the most efficient HHCB degradation due to the high production of ˙OH induced under UVC. Indirect photolysis contribution was observed, induced by ˙OH, CO3˙-, 3DOM*, and 1O2 to different extents depending on the light and matrix composition. The experiments led to the detection of transformation products: HHCB lactone, a well-known transformation product, and two other substances with proposed structures. This study provides a comprehensive identification of the processes involved in the direct and indirect photodegradation of HHCB, which could serve as the basis for evaluating and modeling the fate of HHCB in aquatic environments.

A systematic review on percarbonate-based advanced oxidation processes in wastewater remediation: From theoretical understandings to practical applications

Percarbonate encompasses sodium percarbonate (SPC) and composite in-situ generated peroxymonocarbonate (PMC). SPC emerges as a promising alternative to hydrogen peroxide (H2O2), hailed for its superior transportation safety, stability, cost-effectiveness, and eco-friendliness, thereby becoming a staple in advanced oxidation processes for mitigating water pollution. Yet, scholarly literature scarcely explores the deployment of percarbonate-AOPs in eradicating organic contaminants from aquatic systems. Consequently, this review endeavors to demystify the formation mechanisms and challenges associated with reactive oxygen species (ROS) in percarbonate-AOPs, alongside highlighting directions for future inquiry and development. The genesis of ROS encompasses the in situ chemical oxidation of activated SPC (including iron-based activation, discharge plasma, ozone activation, photon activation, and metal-free materials activation) and composite in situ chemical oxidation via PMC (namely, H2O2/NaHCO3/Na2CO3, peroxymonosulfate/NaHCO3/Na2CO3 systems). Moreover, the ROS generated by percarbonate-AOPs, such as •OH, O2•-, CO3•-, HO2•-, 1O2, and HCO4-, can work individually or synergistically to disintegrate target pollutants. Concurrently, this review systematically addresses conceivable obstacles posing percarbonate-AOPs in real-world application from the angle of environmental conditions (pH, temperature, coexisting substances), and potential ecological toxicity. Considering the outlined challenges and advantages, we posit future research directions to amplify the applicability and efficacy of percarbonate-AOPs in tangible settings. It is anticipated that the insights provided in this review will catalyze the progression of percarbonate-AOPs in water purification endeavors and bridge the existing knowledge void.

Recent advances in the role of dissolved organic matter during antibiotics photodegradation in the aquatic environment

The presence of residual antibiotics in the environment is a prominent issue. Photodegradation behavior is an important way of antibiotics reduction, which is closely related to dissolved organic matter (DOM) in water. The review provides an overview of the latest advancements in the field. Classification, characterization of DOM, and the dominant mechanisms for antibiotic photodegradation were discussed. Furthermore, it summarized and compared the effects of DOM on different antibiotics photodegradation. Moreover, the review comprehensively considered the factors influencing the photodegradation of antibiotics in the aquatic environment, including the characteristics of light, temperature, dosage of DOM, concentration of antibiotics, solution pH, and the presence of coexisting ions. Finally, potential directions were proposed for the development of predictive models for the photodegradation of antibiotics. Based on the review of existing literature, this paper also considered several pathways for the future study of antibiotic photodegradation. This study allows for a better understanding of the DOM's environmental role and provides important new insights into the photochemical fate of antibiotics in the aquatic environment.

Graphitic-carbon-nitride-hydrophilicity-dependent photocatalytic degradation of antibiotics with different log Kow

The surface hydrophilicity of a photocatalyst is an important factor that directly influences its interactions with organic pollutants and significantly impacts its degradation. In this study, we investigated the impact of increased hydrophilicity of g-C3N4 (CN) by alkaline solvothermal treatment on the degradations of three antibiotics (oxytetracycline (OTC), oxolinic acid (OA), and sulfamethoxazole (SMX)) with different log Kow values. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier-transform infrared (FT-IR) spectroscopy showed no significant differences in the morphology, crystalline structure, and surface functional groups of CN after alkaline solvothermal treatment (Nv-HPCN). However, contact angle analysis revealed that Nv-HPCN (31.8°) was more hydrophilic than CN (61.1°). To assess the hydrophilicity of the antibiotics, the log Kow values of SMX (0.77), OA (0.43), and OTC (-0.34) were measured. Nv-HPCN showed faster OTC degradation than CN, whereas the opposite pattern was observed for the degradation of OA. Scavenger tests showed that O2•- and h+ mainly contributed to the degradation of these antibiotics. Furthermore, the influences of NOM and coexisting anions on antibiotic degradation were investigated. This study thus offers perspectives on the impact of surface hydrophilicity of photocatalysts on the degradation of antibiotics.

Potassium permanganate oxidation enhanced by infrared light and its application to natural water

Photocoupled permanganate (PM) is an effective way to enhance the oxidation efficiency of PM, however, the activation of PM by infrared has received little attention. This study aimed to investigate the ability of infrared light to activate PM. When coupled with infrared, the degradation rate of 4-chlorophenol (4-CP) is increased to 3.54 times of PM oxidation alone. The accelerated reaction was due to the formation of vibrationally excited PM by absorbing 3.1 kJ mol-1 infrared energy, which also leads to the primary reactive intermediates Mn(V/IV) in the reaction system. The infrared coupled PM system also showed 1.14-2.34 times promotion effect on other organic pollutants. Furthermore, solar composed of 45% infrared, coupled PM system showed excellent degradation performance, where the degradation of 4-CP in 10 L of tap water and river water was 68 and 23 times faster than in ultrapure water, respectively. The faster-increased degradation rate in natural waters is mainly due to the abundant inorganic ions, which can stabilize the manganese species, and then has a positive effect on 4-CP degradation. In summary, this work develops a energy-efficient photoactivated PM technology that utilizes infrared and provides new insights into the design of novel sunlight-powered oxidation processes for water treatment.

Aging of polystyrene microplastics by UV/Sodium percarbonate oxidation: Organic release, mechanism, and disinfection by-product formation

The occurrence and transformation of microplastics (MPs) in environment has attracted considerable attention. However, the release characteristics of MP-derived dissolved organic matter (MP-DOM) under oxidation conditions and the effect of DOM on subsequent chlorination disinfection by-product (DBP) still lacks relevant information. This study focused on the conversion of polystyrene microplastics (PSMPs) in the advanced oxidation of ultraviolet-activated sodium percarbonate (UV/SPC-AOP) and the release characteristics of MP-DOM. The DBP formation potential of MP-DOM was also investigated. As a result, UV/SPC significantly enhanced the aging and fragmentation of PSMPs. Under UV irradiation, the fluorescence peak intensity and position of humus-like and protein-like components of MP-DOM were correlated with SPC concentration. The aging MP suspension was analyzed by gas chromatography-mass spectrometry (GC-MS), and various alkyl-cleavage and oxidation products were identified. Quenching experiments and electron paramagnetic resonance (EPR) detection confirmed that carbonate and hydroxyl radicals jointly dominated the conversion of PSMPs. The formation of DBP was related to the components of MP-DOM. Overall, these results help to understand the aging behavior of MPs in AOP. Moreover, MP-DOM released by MPs after AOP oxidation may be a precursor of DBPs, which deserved more attention.

Thermo-activated periodate oxidation process for tetracycline degradation: Kinetics and byproducts transformation pathways

Periodate-based advanced oxidation processes have been diffusely practiced for pollutant decontamination. However, the thermo-activation of periodate process (heat/PI), an effective water pollution removal process, has been rarely discussed, and the degradation pathway of this heat/PI system requires investigation. In this work, tetracycline antibiotics were selected as the model micropollutant for the comprehensive evaluation of the heat/PI system. The heat/PI system exhibited good performance for tetracycline (TC) remediation with temperature increases. The principal reactive oxidative species in the heat/PI system was confirmed using quenching experiments and electron paramagnetic resonance experiments. Further, the potential reactive sites in the TC were identified based on the density functional theory calculation. Based on the detection results of intermediates, there was no significant difference in byproducts generated during TC degradation under various temperatures in the heat/PI system. The Toxicity Estimation Software Tool (T.E.S.T.) method was applied to calculate the individual toxicity of the byproducts. This study contributes to a comprehensive explanation of the process of the thermal activation of periodate, and in particular, it explains the source of oxidation power, the transformation of byproducts, and the toxicity of reaction systems.

Effect of bicarbonate on nitrate-induced photosensitive degradation of sulfamethoxazole under UV irradiation

In this study, the influence of HCO3- on NO3--induced photosensitive degradation of sulfamethoxazole (SMX) under UV irradiation was investigated. It was found that the removal of SMX by UV in the presence of NO3- improved significantly compared to its photolysis, which was confirmed to be due to the role of hydroxyl radical (HO•) formed through UV-activated NO3-. However, the addition of HCO3- in UV/NO3- system could further enhance SMX degradation, which was verified to be ascribed to the formed carbonate radical (CO3•-) through the reaction of HCO3- with HO•. The second-order rate constant of CO3•- with SMX was determined to be 2.58 × 108 M-1 s-1. In UV/NO3-/HCO3- system, the reactive species for SMX removal were HO• and CO3•-, and the contribution of CO3•- to SMX degradation might be much higher than that of HO•. The concentration of NO3- was almost unchanged after reaction in UV/NO3- and UV/NO3-/HCO3- systems because of its regeneration. Based on the detected four transformation products, the possible degradation pathways of SMX in UV/NO3-/HCO3- system were proposed including hydroxylation, amino-oxidation and bond cleavage.

Simultaneous adsorption and biodegradation of oxytetracycline in wastewater by Mycolicibacterium sp. immobilized on magnetic biochar

Due to the adverse effects of long-term oxytetracycline (OTC) residues in aquatic environments, an effective treatment is urgently needed. Immobilized microbial technology has been widely explored in the treatment of various organic pollutants in aquatic environments with its excellent environmental adaptability. Nevertheless, studies on its application in the removal of antibiotics are relatively scarce and not in sufficient depth. Only a few studies have further investigated the final fate of antibiotics in the immobilized bacteria system. In this study, a novel kind of OTC-degrading bacteria Mycolicibacterium sp. was immobilized on straw biochar and magnetic biochar, respectively. Magnetic biochar was proved to be a more satisfactory immobilization carrier due to its superior property and the advantage of easy recycling. Compared with free bacteria, immobilized bacteria had stronger environmental adaptability under different OTC concentrations, pH, and heavy metal ions. After 5 cycles, immobilized bacteria could still remove 71.8% of OTC, indicating that it had a stable recyclability. Besides, OTC in real swine wastewater was completely removed by immobilized bacteria within 2 days. The results of FTIR showed that bacteria were successfully immobilized on biochar and O-H, N-H, and C-N groups might be involved in the removal of OTC. The fate analysis indicated that OTC was removed by simultaneous adsorption and biodegradation, while biodegradation (92.8%) played a dominant role in the immobilized bacteria system. Meanwhile, the amount of adsorbed OTC (7.20%) was rather small, which could effectively decrease the secondary pollution of OTC. At last, new degradation pathways of OTC were proposed. This study provides an eco-friendly and effective approach to remedy OTC pollution in wastewater.

Ag2S Nanoparticles Supported on 3D Flower-Shaped Bi2WO6 Enhanced Visible Light Catalytic Degradation of Tetracycline

A three-dimensional flower-shaped Bi2WO6 has been prepared by a hydrothermal procedure without the addition of an auxiliary agent and under neutral conditions with ultrapure water serving as solvent, and the Ag2S-Bi2WO6 composite with weight ratios of 5, 10, and 15% was prepared by a hydrothermal method. The crystallinity, morphology, mode of binding, and optical properties of the Ag2S-Bi2WO6 composite were characterized, the results of which showed that the composite had excellent dispersion, crystallinity, and purity. The composite with a weight ratio of 10% had the best photocatalytic performance, and the degradation rate of tetracycline reached 95.51% within 120 min, an increase of 27.35% over Bi2WO6. In experiments, some focus was given to the effect of the initial solution pH and the concentrations of humic acid and inorganic anions on the degradation efficiency. Based on free radical capture experiments and the semiconductor theory, the main active substances and mechanisms in the optical catalytic reaction process were studied, and speculation was given concerning the degradation pathway for the target pollutants. This study has conceived novel methods for the development of dual semiconductor systems consisting of a Ag NP composite and in doing so has provided new approaches for the development and photocatalysis for water pollution control.

Eco-friendly oxidation of a reactive textile dye by CaO2: effects of specific independent parameters

Textile wastewater containing dyes poses significant risks to the environment. Advanced oxidation processes (AOPs) effectively eliminate dyes by converting them into harmless substances. However, AOPs have drawbacks such as sludge formation, metal toxicity, and high cost. As an alternative to AOPs, calcium peroxide (CaO2) offers an eco-friendly and potent oxidant for dye removal. Unlike certain AOPs that generate sludge, CaO2 can be directly employed without resulting in sludge formation. This study examines the use of CaO2 for oxidizing Reactive Black 5 (RB5) in textile wastewater without any activator. Various independent factors-pH, CaO2 dosage, temperature, and certain anions-were investigated for their influence on the oxidation process. The effects of these factors on dye oxidation were analyzed using the Multiple Linear Regression Method (MLR). CaO2 dosage was determined to be the most influential parameter for RB5 oxidation, while the optimal pH for oxidation with CaO2 was found to be 10. The study determined that 0.5 g of CaO2 achieved approximately 99% efficiency in oxidizing 100 mg/L of RB5. Additionally, the study revealed that the oxidation process is endothermic, with an activation energy (Ea) and standard enthalpy (ΔH°) for RB5 oxidation by CaO2 determined as 31.135 kJ mol-1 and 110.4 kJ mol-1, respectively. The presence of anions decreased RB5 oxidation, with decreasing effectiveness observed in the order of PO43-, SO42-, HCO3-, Cl-, CO32-, and NO3-. Overall, this research highlights CaO2 as an effective, easy-to-use, eco-friendly, and cost-efficient method for removing RB5 from textile wastewater.

Hydroxyl radical dominated ibuprofen degradation by UV/percarbonate process: Response surface methodology optimization, toxicity, and cost evaluation

Ibuprofen (IBP) is a typical nonsteroidal anti-inflammatory drug with a wide range of applications, large dosages, and environmental durability. Therefore, ultraviolet-activated sodium percarbonate (UV/SPC) technology was developed for IBP degradation. The results showed that IBP could be efficiently removed using UV/SPC. The IBP degradation was enhanced with prolonged UV irradiation time, with the decreasing IBP concentration and the increasing SPC dosage. The UV/SPC degradation of IBP was highly adaptable to pH ranging from 4.05 to 8.03. The degradation rate of IBP reached 100% within 30 min. The optimal experimental conditions for IBP degradation were further optimized using response surface methodology. IBP degradation rate reached 97.3% under the optimal experimental conditions: 5 μM of IBP, 40 μM of SPC, 7.60 pH, and UV irradiation for 20 min. Humic acid, fulvic acid, inorganic anions, and natural water matrix inhibited the IBP degradation to varying degrees. Scavenging experiments of reactive oxygen species indicated that hydroxyl radical played a major role in the UV/SPC degradation of IBP, while carbonate radical played a minor role. Six IBP degradation intermediates were detected, and hydroxylation and decarboxylation were proposed as the primary degradation pathways. An acute toxicity test, based on the inhibition of luminescence in Vibrio fischeri, indicated that the toxicity of IBP during UV/SPC degradation decreased by 11%. An electrical energy per order value of 3.57 kWh m^-3 indicated that the UV/SPC process was cost-effective in IBP decomposition. These results provide new insights into the degradation performance and mechanisms of the UV/SPC process, which can potentially be used for practical water treatment in the future.

Magnetic CuFe2O4 nanoparticles anchored on N-doped carbon for activated peroxymonosulfate removal of oxytetracycline from water: Radical and non-radical pathways

In this work, magnetic CuFe₂O₄ was prepared for the removal of oxytetracycline (OTC) by a self-propagating combustion synthesis method. Almost complete degradation (99.65%) of OTC was achieved within 25 min at [OTC]₀ = 10 mg/L, [PMS]₀ = 0.05 mM, CuFe₂O₄ = 0.1 g/L under pH = 6.8 at 25 °C for deionized water. Specially, the addition CO₃^2- and HCO₃^- induced the CO₃•^- appearance enhancing the selective degradation to electron-rich OTC molecule. The prepared CuFe₂O₄ catalyst exhibited desirable OTC removal rate (87.91%) even in hospital wastewater. The reactive substances were analyzed by free radical quenching experiments and electron paramagnetic resonance (EPR), and the results demonstrated that ¹O₂ and •OH were the main active substances. Liquid chromatography-mass spectrometry (LC-MS) was used to analyze the intermediates produced during the degradation of OTC and thus to speculate on the possible degradation pathways. Ecotoxicological studies were conducted to unveil large-scale application prospect.

Mechanism and security of UV driven sodium percarbonate for sulfamethoxazole degradation using DFT and metabolomic analysis

Recently, sodium percarbonate (SPC) as a solid substitute for H₂O₂ has aroused extensive attention in advanced oxidation processes. In current work, the degradation kinetics and mechanisms of antibiotic sulfamethoxazole (SMX) by ultraviolet (UV) driven SPC system were explored. The removal efficiency of SMX was enhanced as the increasing dosage of SPC. Moreover, hydroxyl radical (•OH), carbonate radical (CO₃^•-) and superoxide radical (O₂^•-) were verified to be presented by scavenger experiments and •OH, CO₃^•- exhibited a significant role in SMX degradation. Reactions mediated by these radicals were affected by anions and natural organic matters, implying that an incomplete mineralization of SMX would be ubiquitous. The screening four intermediates and transformation patterns of SMX were verified by DFT analysis. Metabolomic analysis demonstrated that a decreasing negative effect in E. coli after 24 h exposure was induced by intermediates products. In detail, SMX interfered in some key functional metabolic pathways including carbohydrate metabolism, pentose and glucuronate metabolism, nucleotide metabolism, arginine and proline metabolism, sphingolipid metabolism, which were mitigated after UV/SPC oxidation treatment, suggesting a declining environmental risk of SMX. This work provided new insights into biological impacts of SMX and its transformation products and vital guidance for SMX pollution control using UV/SPC technology.

Targeted Decomplexation of Metal Complexes for Efficient Metal Recovery by Ozone/Percarbonate

Traditional methods cannot efficiently recover Cu from Cu(II)-EDTA wastewater and encounter the formation of secondary contaminants. In this study, an ozone/percarbonate (O₃/SPC) process was proposed to efficiently decomplex Cu(II)-EDTA and simultaneously recover Cu. The results demonstrate that the O₃/SPC process achieves 100% recovery of Cu with the corresponding k_obs value of 0.103 min^-1 compared with the typical ^•OH-based O₃/H₂O₂ process (81.2%, 0.042 min^-1). The carbonate radical anion (CO₃^•-) is generated from the O₃/SPC process and carries out the targeted attack of amino groups of Cu(II)-EDTA for decarboxylation and deamination processes, resulting in successive cleavage of Cu-O and Cu-N bonds. In comparison, the ^•OH-based O₃/H₂O₂ process is predominantly responsible for the breakage of Cu-O bonds via decarboxylation and formic acid removal. Moreover, the released Cu(II) can be transformed into stable copper precipitates by employing an endogenous precipitant (CO₃^2-), accompanied by toxic-free byproducts in the O₃/SPC process. More importantly, the O₃/SPC process exhibits excellent metal recovery in the treatment of real copper electroplating wastewater and other metal-EDTA complexes. This study provides a promising technology and opens a new avenue for the efficient decomplexation of metal-organic complexes with simultaneous recovery of valuable metal resources.

Comprehensive understanding of fluoroquinolone degradation via MPUV/PAA process: Radical chemistry, matrix effects, degradation pathways, and toxicity

The wide occurrence of fluoroquinolones (FQs) in aquatic environments has aroused increasing concern about their potential adverse effects on human health. In this study, an emerging advanced oxidation process, i.e., the Medium-Pressure Ultraviolet/Peracetic Acid (MPUV/PAA) process, was used to degrade FQs (e.g., levofloxacin (LEV), norfloxacin, and ciprofloxacin). Compared with the MPUV process alone and the PAA process alone, the MPUV/PAA process significantly promoted degradation of FQs due to the considerable contribution of reactive radicals. Probe experiments revealed that PAA-specific organic radicals (e.g., CH₃C(O)O• and CH₃C(O)OO•) were the major radicals responsible for FQ elimination. Rapid degradation of FQs via the MPUV/PAA process was achieved within a wide range of pH values (5-9) by selecting LEV as the target compound, and higher pH values were more favorable for the reaction. The slight impacts of Cl^- and CO₃^2-/HCO₃^- on LEV removal were observed. The transformation products and pathways of LEV were identified, and nearly all of the transformation pathways occurred on the piperazine ring. Based on Quantitative Structure-Activity Relationship (QSAR) analysis, most of the products had lower toxicities than LEV. Overall, these findings improve our understanding and application of the MPUV/PAA process for degrading emerging contaminants in (waste)water treatment.

Efficient degradation of organic pollutants by S-NaTaO3/biochar under visible light and the photocatalytic performance of a permonosulfate-based dual-effect catalytic system

Removing large concentrations of organic pollutants from water efficiently and quickly under visible light is essential to developing photocatalytic technology and improving solar energy efficiency. This study used a simple hydrothermal method to prepare a non-metallic, S-doped NaTaO₃ (S-NTO) photocatalyst, which was then loaded onto biochar (BC) to form a S-NTO/BC composite photocatalyst. After uniform loading onto BC, the S-NTO particles transformed from cubic to spherical. The photogenerated electron-hole pair recombination probability of the composite photocatalyst was significantly lower than those of the NTO particles. The light absorption range of the catalyst was effectively widened from 310 nm UV region to visible region. In addition, a dual-effect catalytic system was constructed by introducing peroxymonosulfate (PMS) into the environment of the pollution to be degraded. The Rhodamine B, Methyl Orange, Acid Orange 7, tetracycline, and ciprofloxacin degradation efficiency at 40 mg/L reached 99.6%, 99.2%, 84.5%, 67.1%, and 70.7%, respectively, after irradiation by a 40 W lamps for 90 min. The high-efficiency visible-light catalytic activity of the dual-effect catalytic system was attributed to doping with non-metallic sulfur and loading of catalysts onto BC. The development of this dual-effect catalytic system provides new ideas for quickly and efficiently solving the problem of high-concentration organic pollution in aqueous environments, rationally and fully utilizing solar energy, and expanding the application of photocatalytic technology to practice.

Efficient microwave-assisted mineralization of oxytetracycline driven by persulfate and hypochlorite over Cu-biochar catalyst

Microwave (MW)-assisted catalytic degradation of organic pollutants draws increasing attention owing to its high efficiency in wastewater treatment. This work developed Cu-loaded biochar (CuBC) catalysts for time-efficient mineralization of refractory and high-concentration oxytetracycline (OTC). With only 1 min at 80 °C, Na₂S₂O₈ achieved 100% total organic carbon (TOC) removal over the Cu5BC, while NaClO mineralized 73.3% TOC over the metal-free BC, in contrast to a relatively low mineralization efficiency (< 35%) achieved by H₂O₂. The high efficiency in MW-assisted oxidation systems could be ascribed to reactive oxidizing species (^•SO₄^- or ^•ClO), which otherwise were barely detectable in a conventional heating system. The interactions between CuBC and MW were revealed by correlating the physiochemical characteristics to the MW absorption ability. The proposed catalytic systems can contribute to the development of a high-throughput and low-carbon wastewater treatment technology.

AOP-Based Transformation of Abacavir in Different Environments: Evolution Profile of Descyclopropyl-Abacavir and In Silico Toxicity Assessment of the Main Transformation Products

This study explores the photocatalytic transformation of the antiviral drug abacavir employing different advanced oxidation processes (AOPs) such as UV/TiO₂, UV/MOF/H₂O₂, UV/MOF/S₂O₈^2-, UV/Fe²⁺/H₂O₂, and UV/Fe²⁺/S²O₈^2-. All processes appear to be effective in eliminating abacavir within a few minutes, while the evolution profile of the basic transformation product, descyclopropyl-abacavir (TP-247) was also monitored. Moreover, the implementation of the most efficient technologies towards the removal of abacavir in different matrices such as wastewater effluent and leachate was also assessed, revealing that the organic matter present or the inorganic constituents can retard the whole process. Four major transformation products were detected, and their time-evolution profiles were recorded in all studied matrices, revealing that different transformation pathways dominate in each matrix. Finally, the prediction of the toxicity of the major TPs employing ECOSAR software was conducted and showed that only hydroxylation can play a detoxification role in the treated solution.

Revisiting UV/sulfite exposed to air: A redox process for reductive dechlorination and oxidative mineralization

2,4-Dichlorophenol (2,4-DCP) widely exists in many industrial wastewaters and is considered a priority pollutant due to its high toxicity. In this work, we proposed a UV/sulfite process without aeration for high-efficiency dechlorination and enhanced mineralization. The UV/sulfite system significantly improved the removal of 2,4-DCP (93.33 % in 60 min) and dechlorination rate (85.13 % in 60 min) compared with UV alone and sulfite alone, and the synergistic factor was 6.59. The UV/sulfite system without aeration improved the mineralization rate (49.80 %) compared with the nitrogen aeration system. UV/sulfite was a reduction-oxidation coupled process and was more suitable for neutral and alkaline conditions. Reducing species (hydrated electrons and H^•) made 2,4-DCP dechlorinate to form dechlorination products such as p-chlorophenol (4-CP), o-chlorophenol (2-CP), and phenol, which were further mineralized by oxidized species (SO₄^•-). UV/sulfite remained highly efficient in the presence of coexisting ions and under different water quality conditions. This process was also suitable for removing a wide range of chlorinated organic compounds. The UV/sulfite process without aeration can achieve high dechlorination and enhanced mineralization with simple operation and low cost (1.78 $·m^-3 order^-1), which has a broad and cost-effective application prospect in removing refractory halogenated organic pollutants.

Electrochemical degradation of indigo carmine, P-nitrosodimethylaniline and clothianidin on a fabricated Ti/SnO2-Sb/Co-βPbO2 electrode: Roles of radicals, water matrices effects and performance

In this study, the kinetic degradation of several typical organic pollutants was performed on a synthetic electrode (Ti/SnO₂-Sb/Co-βPbO₂). The surface structure and the electrochemical properties of the prepared electrode were investigated, confirming the successful preparation of the electrode using an electrochemical deposition method. The outer layer (Co-βPbO₂) played an important role in reducing the resistance of the electrode and improving its degradation efficiency. The results showed that indigo carmine (IC), p-nitrosodimethylaniline (RNO), and clothianidin (CLO) were effectively degraded within 20 min of electrolysis. Their degradation in the electrochemical process followed the first-order kinetic model with the degradation rate constant of IC being higher than that of RNO and CLO. This was proved by the difference in the reactivity of the target pollutants toward oxidizing radicals (i.e., •OH, SO₄^•-, and Cl•). Their second-order rate constant towards radicals were in the range of 10⁹ - 10¹⁰ M^-1 s^-1 with the highest value being that for IC: k_·OH,IC = 15.1 × 10⁹ M^-1 s^-1 and [Formula: see text]  = 7.4 × 10⁹ M^-1 s^-1. The study calculated the contribution of some oxidizing species, including direct electron transfer (DET), •OH, SO₄^•-, and other reactive oxygen species (ROS). Solution pH, supporting electrolyte, and water matrix affected the degradation efficiency of pollutants and the contribution of the oxidizing species. Br^- and I^- ions enhanced the degradation rate of organic pollutants, while Fe²⁺, HCO₃^-, and humic acid (HA) reduced it. In addition, the toxicity, total organic carbon (TOC) removal, mineralization current efficiency (MCE), energy consumption, recyclability and stability of the prepared electrode were studied, suggesting that the prepared Ti/SnO₂-Sb/Co-βPbO₂ is a good candidate for treating organic pollutants using the electrochemical oxidation process.

Advanced oxidation processes for water purification using percarbonate: Insights into oxidation mechanisms, challenges, and enhancing strategies

Percarbonate (SPC) has drawn considerable attention due to its merits in the safety of handling and transport, stability, and price as well as environmental friendliness, which has been extensively applied in advanced oxidation processes (AOPs) for water decontamination. Nevertheless, comprehensive information on the application of SPC-AOPs for the treatment of organic compounds in aquatic media is scarce. Hence, the focus of this review is to shed light on the mechanisms of reactive oxygen species (ROS) evolution in typical SPC-AOPs (i.e., Fenton-like oxidation, photo-assisted oxidation, and discharge plasma-involved oxidation processes). These SPC-AOPs enable the formation of multiple reactive species like hydroxyl radical (^•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), carbonate radicals (CO₃^•-), and peroxymonocarbonate (HCO₄^-), which together or solely contribute to the degradation of target pollutants. Simultaneously, the potential challenges in practical applications of SPC-AOPs are systematically discussed, which include the influence of water quality parameters, cost-effectiveness, available active sites, feasible activation approaches, and ecotoxicity. Subsequently, enhancing strategies to improve the feasibility of SPC-AOPs in the practical implementation are tentatively proposed, which can be achieved by introducing reducing and chelating agents, developing novel activation approaches, designing multiple integrated oxidation processes, as well as alleviating the toxicity after SPC-AOPs treatment. Accordingly, future perspectives and research gaps in SPC-AOPs are elucidated. This review will hopefully offer valuable viewpoints and promote the future development of SPC-AOPs for actual water purification.

Photodegradation of oxytetracycline by UV-assisted persulfate and percarbonate processes: kinetics, influencing factors, anion effect, and radical species

In this study, the performance of ultraviolet (UV)-assisted persulfate (PS) and percarbonate (PC) oxidation processes in oxytetracycline (OTC) removal was investigated. UVC lamps were used for the photolysis process and the effect of operating parameters (initial pH, oxidant dose, initial OTC concentration, UV intensity) on OTC removal efficiency was determined. Control experiments were carried out at pH 5.5 and 32 W UV power for 60 min by adding a 4 mM oxidant with 10 mg/L initial OTC concentration. The OTC removal efficiency obtained as a result of only photolysis was 17.3% and the removal efficiency obtained by PS and PC oxidation alone was 18.3% and 12.7%, respectively. The OTC removal efficiencies increased in the combined processes and reached 58.1% and 69.9% for the UV-PS and UV-PC processes, respectively. The reaction rates of the processes were ranked as UV-PC > UV-PS > PS > UV > PC. In the UV-PS and UV-PC processes, the highest removal efficiencies were achieved at alkaline pH values. The OTC removal efficiency was increased with the increase in oxidant dose; however, the efficiency decreased after a certain dose due to the scavenging effect. The removal efficiency also increased as the initial OTC concentration decreased. The UV intensity had a positive effect on OTC removal efficiency. The effect of the water matrix on OTC removal efficiency was investigated while the dominant radical types were determined in UV-assisted processes. The EE/O values for the UV-PS and UV-PC processes were calculated as 211 kWh/m³ and 153 kWh/m³, respectively for 60 min of reaction time. Although similar removal efficiencies were obtained with both UV-assisted processes, the UV-PC process steps forward in terms of being a novel, environmentally friendly, more economic, and promising technology for OTC removal.

Antibiotics degradation by advanced oxidation process (AOPs): Recent advances in ecotoxicity and antibiotic-resistance genes induction of degradation products

Antibiotic contamination could cause serious risks of ecotoxicity and resistance gene induction. Advanced oxidation processes (AOPs) such as Fenton, photocatalysis, activated persulfate, electrochemistry and other AOPs technologies have been proven effective in the degradation of high-risk, refractory organic pollutants such as antibiotics. However, due to the limited mineralization ability, a large number of degradation intermediates will be produced in the oxidation process. The residual or undiscovered ecological risks of degradation products are potential safety hazards and problems necessitating comprehensive studies. In-depth investigations especially on the full assessments of ecotoxicity and resistance genes induction capability of antibiotic degradation products are important issues in reducing the environmental problems of antibiotics. Therefore, this review presents an overview of the current knowledge on the efficiency of different AOPs systems in reducing antibiotics toxicity and antibiotic resistance.

Microwave-assisted Synthesis, Characterization, Photocatalytic Degradation of Antibiotics, and Fluorometric Selective Sensing Activity of g-C3N4 Supported CuO Composites

Herein, we have designed for the fabrication of a series of g-C₃N₄/CuO composite by using one-step microwave-assisted synthesis for the degradation of antibiotics and detection of nano-molar range of toxic heavy metal ions. The synthesized g-C₃N₄/CuO composites were analyzed and characterized to know the structure, phase, surface area, absorption region, bandgap, and size of the composites. From the observation of TEM and XRD measurements, g-C₃N₄/CuO composites have hexagonal shape with average diameter of the particles is 25 ± 5 nm. The observed band gap values from UV-vis DRS for g-C₃N₄ nanosheets and CuO NPs are 2.64 eV and 1.72 eV. The synthesized g-C₃N₄/CuO composite has prodigious specific surface area (32.47 m²/g), which is the evident for superior heterogeneous catalytic applications. Therefore, the synthesized g-C₃N₄/CuO composites were tested for the degradation of antibiotics such as tetracycline (TC) and ciprofloxacin (CIP) under UV light illumination, it shows 88.02% and 90.01% degradation was observed within 1 h due to the matching optical band gap and internal charge transfer of excitons with in the heterojunction surface among g-C₃N₄ and CuO in the composite than the individual components (g-C₃N₄ and CuO) due to the high surface area and tiny particles of CuO were randomly deposited on the surface of g-C₃N₄ nanosheets. The catalytic reduction reaction follows as pseudo-first order equation and reused for 5 consecutive cycles without remarkable loss of catalytic activity. Moreover, the synthesized CuO NPs and g-C₃N₄/CuO composites were used as a prominent fluorescence sensing probe for the selective detection of Pb²⁺ in nano-molar range of concentration with K_sv is 1.38 × 10⁴ mol^- 1dm³. It was observed as a linear relationship based on the change in intensity, the limit of detection was determined to be 0.184 nM.

Modeling carbonate/bicarbonate and nitrate disturbance during secondary effluent disinfection by UV/H2O2 and UV/ozone

The disinfection of effluents has been considered the main step to inactivate pathogenic organisms to prevent the spread of waterborne diseases. The variation in the matrix composition can lead to the use of inadequate oxidant dose and disturb a correct treatment. The objective of this study was to develop a simple and practical mathematical model to simulate the disturbance of inorganic anions (CO₃^2-/HCO₃^- and NO₃^-) during secondary effluent disinfection by UV/H₂O₂ and UV/O₃. The pathogenic agents chosen for this study were total coliforms and E. coli. To build the mathematical model, a modification of the Chick model (referred to as 'Modified Chick Model') was proposed by employing a weighted average in the calculation of the kinetic constant. Both treatments were affected by the presence of the anions. However, with the highest NO₃^- concentration, less inhibition of disinfection was observed in the UV/H₂O₂. The use of the arithmetic means to calculate the value of k, as indicated by the Chick model, demonstrates a lesser precision in the prediction of the microorganisms' concentrations. On the other hand, using the Modified Chick Model, a better prediction of the inactivation of the microorganisms was obtained, which can be confirmed by the validation performed.

Identification of Reactive Oxygen Species and Mechanism on Visible Light-Induced Photosensitized Degradation of Oxytetracycline

This study investigated the photolysis and TiO₂-assisted photosensitized degradation of oxytetracycline (OTC) under visible light, the active reactive oxygen species (ROS), and the degradation mechanisms in these two reactions. The results show that the deprotonated OTC could be photolyzed more easily under visible light because of the redshift of its absorption spectrum at high pH values. Due to the TiO₂-assisted self-photosensitized degradation of OTC, OTC removal in the visible light/TiO₂ system was more efficient with the addition of TiO₂, as demonstrated when TiO₂ was replaced with insulator SiO₂. The study's ROS scavenging experiments show that superoxide radical anion (O₂^•-) ROS was most responsible for the self-sensitized degradation of OTC in both reactions. OTC degradation under the visible light/TiO₂ system was enhanced with increasing TiO₂ load, while the elimination of total organic carbon (TOC) was very limited after 5 h of visible light irradiation. Based on the eight identified transformation products found, five potential reaction mechanisms, including hydroxylation, quinonization, decarbonylation, de-methylation, and dehydration, were proposed for the photolytic and TiO₂-assisted photosensitized degradation mechanisms of OTC under visible light. This study indicates that OTC can degrade under visible light with or without a semiconductor when conditions are suitable.

Removal of Pharmaceuticals and Personal Care Products (PPCPs) by Free Radicals in Advanced Oxidation Processes

As emerging pollutants, pharmaceutical and personal care products (PPCPs) have received extensive attention due to their high detection frequency (with concentrations ranging from ng/L to μg/L) and potential risk to aqueous environments and human health. Advanced oxidation processes (AOPs) are effective techniques for the removal of PPCPs from water environments. In AOPs, different types of free radicals (HO·, SO₄·^-, O₂·^-, etc.) are generated to decompose PPCPs into non-toxic and small-molecule compounds, finally leading to the decomposition of PPCPs. This review systematically summarizes the features of various AOPs and the removal of PPCPs by different free radicals. The operation conditions and comprehensive performance of different types of free radicals are summarized, and the reaction mechanisms are further revealed. This review will provide a quick understanding of AOPs for later researchers.

Wastewater preinteraction accelerates the photoaging of disposable box-derived polystyrene microplastics in water

Before being discharged into natural environment, almost all of microplastics (MPs) interact with wastewater constituents in wastewater treatment plants (WWTPs). This study investigated the photoaging of disposable box-derived polystyrene (PS) mediated by real wastewater by simulating the case flowing from WWTPs to natural water. Results showed that wastewater influent pretreatment significantly enhanced the photoaging of PSMPs through the sorption of wastewater constituents, e.g., 2.02 times of increase in photooxidation after 30 d of ultraviolet irradiation. Fulvic acid was identified as the leading contributor for the enhancing effect of wastewater relative to other wastewater constituents such as Cl, CO₃^2-, NO₃^- and clay particles. In-depth mechanism analysis showed that the observed enhancement was critically controlled by the photosensitization effect of wastewater itself and the enhanced utilization of PSMPs for ultraviolet energy. Specifically, various sorbed wastewater constituents can not only generate higher concentrations of •OH and O₂^⋅- than clean MPs without constituents, but also reinforce the utilization of PSMPs for light energy due to the increased dispersion in solution by increasing hydrophilicity and surface charges. Also, the light-shielding effect was induced by wastewater, but was less important. This study bridges wastewater source and MP aging and fate and suggests the shortened lifetime of (micro)plastic samples via WWTP input to deepen our understanding of MP pollution in the environment.

Impact of water matrices on oxidation effects and mechanisms of pharmaceuticals by ultraviolet-based advanced oxidation technologies: A review

The binding between water components (dissolved organic matters, anions and cations) and pharmaceuticals influences the migration and transformation of pollutants. Herein, the impact of water matrices on drug degradation, as well as the electrical energy demands during UV, UV/catalysts, UV/O₃, UV/H₂O₂-based, UV/persulfate and UV/chlorine processes were systemically evaluated. The enhancement effects of water constituents are due to the powerful reactive species formation, the recombination reduction of electrons and holes of catalyst and the catalyst regeneration; the inhibition results from the light attenuation, quenching effects of the excited states of target pollutants and reactive species, the stable complexations generation and the catalyst deactivation. The transformation pathways of the same pollutant in various AOPs have high similarities. At the same time, each oxidant also can act as a special nucleophile or electrophile, depending on the functional groups of the target compound. The electrical energy per order (EEO) of drugs degradation may follow the order of EEO_UV > EEO_UV/catalyst > EEO_UV/H2O2 > EEO_UV/PS > EEO_UV/chlorine or EEO_UV/O3. Meanwhile, it is crucial to balance the cost-benefit assessment and toxic by-products formation, and the comparison of the contaminant degradation pathways and productions in the presence of different water matrices is still lacking.

Performance Enhancement of Moisture-driven Power Generators by Photofragmentation of Inorganic Salt Particles

We developed a novel method based on the photofragmentation of inorganic salt particles for improving the moisture-electric energy transformation performance of a moisture-driven power generator (MPG). Infrared laser irradiation on cellulose nanofiber films (CNFs) prepared by a TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation of bleached pulp induced a photothermal conversion of CNFs to porous graphitic carbon films (GCFs) with the catalyst-derived Na₂O₂ particles. Since the laser beam was focused on the top surface of CNF, the gradients of the photothermal conversion of CNFs and Na₂O₂ concentration were created along the thickness direction. Subsequent irradiation with ultraviolet (UV) light induced the photofragmentation of the micrometer-sized Na₂O₂ particles into smaller ones, which increased the surface area of the salt particles in contact with the GCFs and consequently increased the number of effective dissociable charge carriers. When the GCF was exposed to moisture, the dissociated sodium ions migrated along the preformed concentration gradient, producing continuous outputs of current and voltage. At 90% relative humidity, the maximum voltage and current density outputs of the MPG increased from 0.91 V and 18.7 μA/cm² before UV irradiation to 1.10 V and 56.2 μA/cm² after UV irradiation, respectively. Additionally, we demonstrated that a green light-emitting diode could be turned on without capacitors or rectifiers during normal breathing while wearing a face mask with three GCF arrays attached (each 3 mm × 3 mm × 0.1 mm in size).

Enhanced removal of oxytetracycline from wastewater using bimetallic Fe/Ni nanoparticles combined with ZIF-8 nanocomposites

The integration of metal-organic frameworks with other functional materials has recently emerged as a promising approach for creating innovative materials for environmental remediation. Here, a nano-sized iron/nickel (Fe/Ni) functionalized zeolitic imidazolate framework-8 (ZIF-8-Fe/Ni) was fabricated for oxytetracycline (OTC) removal from wastewater. Cyclic voltammetry and amperometric I-t measurements indicated that OTC was degraded by ZIF-8-Fe/Ni. X-ray diffraction spectroscopy (XRD), transmission electron microscopy mapping (TEM-mapping) and X-ray photoelectron spectroscopy (XPS) indicated that Fe/Ni was evenly dispersed throughout ZIF-8 and partially oxidized after reaction with OTC. OTC adsorption isotherms and kinetics best fitted the Langmuir isotherm (R² > 0.982) and pseudo-second-order model (R² > 0.997), respectively. Reduction kinetics data followed the pseudo-first-order model (R² > 0.905), where the apparent activation energy (Ea) was 22.9 kJ mol^-1, demonstrating that OTC degradation was mainly via a chemical process. The practical removal efficiency of OTC from real wastewater by ZIF-8-Fe/Ni was 92.6%, where even after application of ZIF-8-Fe/Ni for 5 consecutive removal cycles, a high OTC removal of 74.9% was maintained. Thus ZIF-8-Fe/Ni exhibited both high removal efficiency and good recyclability.

Two novel and efficient plant composites for the degradation of oxytetracycline: nanoscale ferrous sulphide supported on rape straw waste

As a biomass waste, rape straw shows a good application prospect in heterogeneous catalyst preparation due to its low-cost and stable structure. In this study, FeS-modified rape straw (RS-FeS) and its biochar (RSBC-FeS) were firstly synthesized to remove oxytetracycline (OTC). The highest OTC removal capacities observed for RS-FeS and RSBC-FeS were 635.66 and 827.80 mg g^-1. When compared with the adsorption process, the degradation ratios of the total OTC removal capacity observed in the RS-FeS/H₂O₂ and RSBC-FeS/H₂O₂ systems were 70.14 and 79.35%. Degradation was the dominant process observed during the removal of OTC. Both radical (SO₄^•-, ^•OH, and O₂^•-) and non-radical (¹O₂ and Ov) pathways were involved in the degradation process. OTC was degraded into smaller molecules via hydroxylation, dehydration, quinonization, demethylation, decarbonylation, alcohol oxidation, and ring cleavage reaction, indicating two catalysts could efficiently mineralize organic pollutants. The highest total organic carbon removal efficiencies of observed for RS-FeS and RSBC-FeS in swine wastewater were 88.93 and 96.81%, respectively. In addition, OTC removal efficiency of RS-FeS was more than 80% in successive experiments, further suggesting the feasibility of rape straw to Fenton-like catalysts. In this study, FeS nanoparticles were directly loaded on rape straw for the first time. Compared with biochar, FeS-modified rape straw can also degrade OTC efficiently, which provides an eco-friendly, high-efficient, and sustainable strategy for the preparation of catalyst.

Insight into UV-LED/PS/Fe(Ⅲ) and UV-LED/PMS/Fe(Ⅲ) for p-arsanilic acid degradation and simultaneous arsenate immobilization

As a feed additive, p-arsanilic acid (p-ASA) is hardly metabolized in animal bodies and is excreted chemically unchanged via feces and urine, which can be transformed into more toxic inorganic arsenic species and other organic by-products upon degradation in the aquatic environment. In this study, UV-LED/persulfate (PS)/Fe(Ⅲ) and UV-LED/peroxymonosulfate (PMS)/Fe(Ⅲ) processes were developed to remove p-ASA and immobilize the formed inorganic arsenic via tuning solution pH. UV-LED/PMS/Fe(Ⅲ) (90.8%) presented the best performance for p-ASA degradation at pH 3.0, and the p-ASA degradation in these processes both followed the pseudo-first-order kinetics. The ∙OH played the major role in UV-LED/PS/Fe(Ⅲ) and UV-LED/PMS/Fe(Ⅲ) systems. Solution pH greatly affected the p-ASA degradation and the maximum removal can be achieved at pH 3.0 due to the presence of more Fe(OH)(H₂O)₅²⁺. The dosages of Fe(III) and PMS (PS), SO₄^2- and HCO₃^- significantly influenced the performance of p-ASA oxidation, while HA, Cl^- and NO₃^- slightly affected the p-ASA degradation. According to quantum chemical calculation, radical addition on the C atom in the C-As bond of p-ASA was corroborated to be the dominant reaction pathway by SO₄∙^- and ∙OH. Additionally, the reactive sites and reasonable degradation pathways of p-ASA were proposed based on DFT calculation and HPLC/MS analysis. The release of inorganic arsenic in both processes can be effectively immobilized and the toxicity of the reaction solution dramatically reduced by adjusting solution pH to 6.0. UV-LED/PMS/Fe(Ⅲ) process was found to be more cost-effective than UV-LED/PS/Fe(Ⅲ) process at the low oxidant dosages.

UV activated sodium percarbonate to accelerate degradation of atrazine: Mechanism, intermediates, and evaluation on residual toxicity by metabolomics

Efficient and safe removal of widely used herbicides such as atrazine has become a recent hotspot. Herein, UV driven sodium percarbonate system (UV/SPC) was established to have many advantages in remediation of atrazine contamination. The mechanism and environmental risk of intermediates were explored, which provided information for the feasibility of UV/SPC. The degradation efficiency of atrazine was significantly enhanced as the increasing dosage of SPC. Quenching assay identified that •OH and CO3•- were committed to degrading atrazine. Humic acid and HPO42- remarkably inhibited atrazine degradation. Several intermediates were generated through the dealkylation, dechlorination-hydroxylation, alkylic-hydroxylation, alkyl oxidation and olefination reactions. Toxicity prediction proved that acute toxicity and bioaccumulation of intermediates were mitigated comparing with atrazine. Based on metabolomics results, the alteration of key metabolites such as citrate, L-kynurenine, malic acid, putrescine, glutamine, spermine, ethanolamine and phytosphingosine in various metabolic pathways of E.coli verified that the toxicity of atrazine was weakened after UV/SPC treatment. The application of UV/SPC on atrazine removal in real waters was influenced by environmental factors, and might be improved through coupling with other treatment technologies.

Imidazolium ionic liquids as potential persistent pollutants in aqueous environments: Indirect photochemical degradation kinetics and mechanism

Ionic liquids (ILs) with promising application are likely to become ubiquitous contaminants in water environment for their high hydrophilicity, low biodegradability, and especially its potential toxicity. In this work, we have investigated photochemical transformation of six imidazolium ILs for fate prediction and ecological risk assessment. We found that the reaction rates of the ILs with •OH, CO₃^•─ and ¹O₂ enhanced with their increasing alkyl chain and varied slightly with the paired anions. Meanwhile, modelled results under different scenarios indicate that the primary contributors to transformation of the ILs are triplet-stated dissolved matter (³CDOM*), •OH and CO₃^•-. Besides, the overall half-lives of the ILs can reach 670 days, which indicates persistence of these ILs in the environment. Products for ILs in reaction with •OH and triplet-stated sodium anthraquinone-2-sulfonate (³AQ2S*) were probed by UHPLC-Q-TOF-MS/MS and there is a difference between their products: Products by •OH are likely formed by hydrogen abstraction from the side alkyl chain, followed by dehydrogenation, hydroxylation and carbonylation, while one of the products by ³AQ2S* is formed by dihydroxyl-addition of the imidazolium ring. Furthermore, the ILs and its products were estimated to have toxicity and non-readily biodegradability, suggesting potential eco-risk for the environmental water.

Degradation of dyes by UV/Persulfate and comparison with other UV-based advanced oxidation processes: Kinetics and role of radicals

This study investigated the degradation of methylene blue (MeB), methyl orange (MeO), and rhodamin B (RhB) by the UV/Persulfate (UV/PS) process. The dye degradation in the investigated UV-based Advanced Oxidation Processes (UV/AOPs) followed the first-order kinetic model. The second-order rate constant of the dyes with •OH, SO₄^•-, and CO₃^•- were calculated and found to be: k_•OH,MeB = 5.6 × 10⁹ M^-1 s^-1, [Formula: see text]  = 3.3 × 10⁹ M^-1 s^-1, [Formula: see text]  = 6.9 × 10⁷ M^-1 s^-1; k_•OH,MeO = 3.2 × 10⁹ M^-1 s^-1, [Formula: see text]  = 13 × 10⁹ M^-1 s^-1, [Formula: see text]  = 4.4 × 10⁶ M^-1 s^-1; k_•OH,RhB = 14.8 × 10⁹ M^-1 s^-1, [Formula: see text]  = 5 × 10⁹ M^-1 s^-1, [Formula: see text]  = 1 × 10⁷ M^-1 s^-1. The steady-state concentrations of •OH and SO₄^•- (including other reactive species) were determined using both chemical probes and modeling methods (Kintecus® V6.8). In the UV/PS, the dye degradation depends on the pH of the solution with the order: k_dye (at pH of 7) > k_dye (in acidic conditions) > k_dye (in alkaline conditions). The presence of water matrices had different impacts on dye degradation: 1) The HCO₃^- and Cl^- promoted the degradation efficiency of one dye, but also inhibited the degradation of other dyes; 2) Humic acid (HA) inhibited dye degradation as it scavenged both •OH and SO₄^•-. The degradation of the dyes by UV/PS was also compared with the UV/Chlorine (UV/HOCl) and UV/H₂O₂ and it was established that: 1) In UV/PS and UV/HOCl, SO₄^•- and RCS contributed to dye degradation more than •OH, while •OH played a major role in dye degradation by UV/H₂O₂; 2) The calculated toxicity in UV/PS was the lowest probably due to the low toxicity of by-products; 3) For MeO and RhB, the UV/PS process is more beneficial for the total organic carbon (TOC) removal compared to that of the UV/HOCl and UV/H₂O₂ processes; 4) The UV/PS showed lower cost than the UV/HOCl and UV/H₂O₂ systems for MeO, and RhB degradation but higher cost for MeB removal.

Oxytetracycline co-metabolism with denitrification/desulfurization in SRB mediated system

Aquaculture wastewater contained a high remnant of oxytetracycline (OTC) and nitrate. In this study, OTC co-metabolized with denitrification/desulfurization was investigated in terms of kinetic analysis, pathway, microbial communities and produces analysis in sulfate-reducing bacteria (SRB) mediated system. Long-term acclimatization with sulfate (300 mg-S/L) could markedly accelerate the removed rate of OTC from 0.9 to 1.4 mg/g-SS/d, with the kinetic constants increasing from 0.2760 to 0.5232 d^-1, mainly via enzymes including adenosine-5'-phos-phosulfate reductase and cytochrome P450, and non-enzymatic process related to intermediates (adenosine-5'-phos-phosulfate and S⁰). Furthermore, OTC was likely detoxified by SRB enriched sludge mainly via hydrolysis, dehydration, oxidation and reduction. The denitrification process would postpone the OTC degradation via outcompeting electron donors with the desulfurization process. Redundancy analysis suggested that sulfur-oxidizing bacteria (Acidithiobacillus, Ochrobactrum) were highly related to OTC degradation processes. This study provides deep insight and a new opportunity for the treatment of aquaculture wastewater containing OTC, sulfate and nitrate by SRB sludge.

In-situ electrodeposition synthesis of Z-scheme rGO/g-C3N4/TNAs photoelectrodes and its degradation mechanism for oxytetracycline in dual-chamber photoelectrocatalytic system

The dual-chamber photoelectrocatalytic (PEC) system possess advantages in the degradation efficiency and processing cost of organic contaminants. In this study, TiO₂ nanotube arrays modified by rGO and g-C₃N₄ (rGO/g-C₃N₄/TNAs) photoelectrodes were successfully prepared. The surface micromorphology, chemical structure, crystal structure, and basic element composition of rGO/g-C₃N₄/TNAs photoelectrodes were studied by SEM, FTIR, XRD, Raman, and XPS. UV-vis absorption, photoluminescence (PL) spectra, and photoelectrochemical (PECH) tests were used to explore the photoelectrochemical characteristics of rGO/g-C₃N₄/TNAs photoelectrodes. Under simulated sunlight illumination, the dual-chamber PEC system with external bias voltage was used to investigate the degradation of oxytetracycline (OTC) on rGO/g-C₃N₄/TNAs photoelectrodes. The results showed that rGO and g-C₃N₄ were successfully loaded on TNAs, and the separation efficiency of electrons and holes at rGO/g-C₃N₄/TNAs photoelectrodes was improved. The light absorption range of rGO/g-C₃N₄/TNAs photoelectrodes extends to the visible light region and has better light absorption performance. Compared with the photocatalytic process, when 1.2 V bias voltage was applied, the degradation efficiency of OTC in anode and cathode chambers in PEC were increased by 3.28% and 44.01% within 60 min, respectively. In addition, the anode and cathode chambers have different degradation effects on OTC. Both the external bias voltage and initial pH have significant effects in cathode chamber, but have little effect in photoanode chamber. The fluorescence excitation-emission matrix spectra and liquid chromatography-tandem mass spectrometry showed that there were different intermediates in the degradation process of OTC. This study indicated that for the dual-chamber PEC system, rGO/g-C₃N₄/TNAs photoelectrodes exhibited excellent photocatalytic performance and have potential application prospects in water environmental remediation.

Heat-activated peracetic acid for degradation of diclofenac: kinetics, influencing factors and mechanism

ABSTRACTHeat-activated peracetic acid (PAA) was used to degrade diclofenac (DCF) in this study. Electron paramagnetic resonance and radical scavenging experiments proved that organic radicals (i.e. CH₃C(=O)O• and CH₃C(=O)OO•) were the primary active species for DCF removal in the heat/PAA process. The degradation efficiency of DCF increased with the increase of temperature or initial PAA concentration in the heat/PAA process, and the optimal reaction pH for DCF removal was neutral. The presence of NO₃^- or SO₄^2- insignificantly affected DCF degradation, while Cl^- was favourable for DCF removal in this process. In contrast, an obvious inhibition on the removal of DCF was observed with the addition of natural organic matter, which might be responsible for the lower DCF removal in real waters. Finally, dechlorination, formylation, dehydrogenation and hydroxylation were proposed to be four degradation pathways of DCF in the heat/PAA system based on the five detected transformation products.