Oxidative removal of benzotriazole using peroxymonosulfate/ozone/ultrasound: Synergy, optimization, degradation intermediates and utilizing for real wastewater

Degradation of UV328 by ozone/peroxymonosulfate system: Performance and mechanisms

2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV328) is an emerging persistent organic pollutant ubiquitously found in environmental matrices. Though some advanced oxidation processes have been tested to degrade UV328 in waste streams, the degradation mechanisms are largely unknown. In this study, the degradation of UV328 by ozone (O3) and peroxymonosulfate (PMS) was systemically investigated. At neutral pH, 97.0% UV328 was removed in 5 min with 6.4 mg/min O3 and 2 mM PMS, and the degradation rate was positively correlated with the concentration of oxidants. Hydroxyl radical (•OH), sulfate radical (SO4•-) and singlet oxygen (1O2) participated in the degradation of UV328, in which 1O2 played a key role. Based on the identified transformation intermediates and density functional theory simulations, three degradation pathways of dehydrogenation, cycloaddition and hydroxylation were proposed. •OH and SO4•- radicals could attack UV328 through hydrogen atom abstraction channel. 1O2-mediated cycloaddition reaction is favorable, and •OH could react with UV328 via radical adduct formation pathway. Toxicity assessment indicated that O3/PMS treatment mitigated the ecological risks of UV328.

Sonoelectrochemical degradation of aspirin in aquatic medium using ozone and peroxymonosulfate activated with FeS2 nanoparticles

The catalytic performance of nano-FeS2 in the sonoelectrochemical activation of peroxymonosulfate (PMS) and ozone to remove aspirin (ASP) was studied for the first time. The crystal structure and Fe bonds in the catalyst were confirmed through XRD and FTIR analysis. Within 30 min, ASP (TOC) was removed by 99.2 % (81.6 %) and 98.6 % (77.4 %) in nano-FeS2/PMS and nano-FeS2/O3 sonoelectrochemical systems, respectively. Water anions, especially (almost 50 %), had an inhibitory effect on ASP removal. The probes confirmed that SO4•-and HO• were the key to ASP degradation in nano-FeS2/PMS and nano-FeS2/O3 systems, respectively. The effective activation of oxidants due to the ideal distribution of Fe2+ by catalyst was the main mechanism of ASP removal, in which electric current (EC) and ultrasound (US) played a crucial role through the recycling of Fe ions, dissolution and cleaning of the catalyst. LC-MS analysis identified thirteen byproducts in the ASP degradation pathways. The energy consumption of the proposed sonoelectrochemical systems was lower than previous similar systems. This study presented economic and sustainable hybrid systems for pharmaceutical wastewater remediation.

High-performance activation of ozone by sonocavitation for BTEX degradation in water

This work presents a novel advanced oxidation process (AOP) for degradation of emerging organic pollutants - benzene, toluene, ethylbenzene and xylenes (BTEXs) in water. A comparative study was performed for sonocavitation assisted ozonation under 40-120 kHz and 80-200 kHz dual frequency ultrasounds (DFUS). Based on the obtained results, the combination of 40-120 kHz i.e., low-frequency US (LFDUS) with O3 exhibited excellent oxidation capacity degrading 99.37-99.69% of BTEXs in 40 min, while 86.09-91.76% of BTEX degradation was achieved after 60 min in 80-200 kHz i.e., high-frequency US (HFDUS) combined with O3. The synergistic indexes determined using degradation rate constants were found as 7.86 and 2.9 for LFDUS/O3 and HFDUS/O3 processes, respectively. The higher extend of BTEX degradation in both processes was observed at pH 6.5 and 10. Among the reactive oxygen species (ROSs), hydroxyl radicals (HO•) were found predominant according to scavenging tests, singlet oxygen also importantly contributed in degradation, while O2•- radicals had a minor contribution. Sulfate (SO42-) ions demonstrated higher inhibitory effect compared to chloride (Cl-) and carbonate (CO32-) ions in both processes. Degradation pathways of BTEX was proposed based on the intermediates identified using GC-MS technique.

Effect of tannic acid binding on the thermal degradation behavior and product toxicity of boscalid

The effect of tannic acid (TA) binding on the thermal degradation of boscalid was studied in this work. The results revealed that TA binding has a significant impact on boscalid degradation. The degradation rate constant of bound boscalid was reduced, and its corresponding half-life was significantly prolonged compared to the free state. Four identical degradation products were detected in both states through UHPLC-Q-TOF-MS, indicating that degradation products were not affected by TA binding. Based on DFT and MS analysis, the degradation pathways of boscalid included hydroxyl substitution of chlorine atoms and cleavage of CN and CC bonds. The toxicity of B2 and B3 exceeded that of boscalid. In summary, the binding of TA and boscalid significantly affected the thermal degradation rate of boscalid while preserving the types of degradation products. This study contributed to a fundamental understanding of the degradation process of bound pesticide residues in complex food matrices.

Research Progress on the Degradation of Organic Pollutants in Wastewater via Ultrasound/Periodate Systems: A Review

In recent years, the efficient removal of organic pollutants from wastewater has emerged as a critical area of global research interest. Against this backdrop, an array of innovative technologies for wastewater treatment has been developed. Among numerous advanced oxidation processes (AOPs), periodate (PI), an emerging oxidizing agent in AOPs, has garnered significant attention from researchers. Particularly, the integration of ultrasound (US)-activated PI systems has been recognized as an exceptionally promising approach for the synergistic degradation of organic pollutants in wastewater. In this paper, we conducted a thorough analysis of the mechanisms underlying the degradation of organic pollutants using the US/PI system. Furthermore, we comprehensively delineated the effects of ultrasonic power, periodate concentration, temperature, pH, coexisting inorganic ions, and dissolved organic matter on the removal efficiency of organic pollutants and summarized application cases of the US/PI system for the degradation of different pollutants. Finally, we also offered prospective discussions on the future trajectories of US/PI technology development.

Enhanced antibiotic degradation via photo-assisted peroxymonosulfate over graphitic carbon nitride nanosheets/CuBi2O4: Highly efficiency of oxygen activation and interfacial charge transfer

Improving the activation capacity of peroxymonosulfate (PMS) to increase radical and non-radical production is critical for antibiotic degradation. However, how to boost reactive oxygen species (ROS) and speed interfacial charge transfer remains an essential challenge. We report a coupling system of 10 %CNNS/CuBi2O4 photocatalyst and sulfate radical-based advanced oxidation processes (SO4--AOPs) to enhance the activation of PMS and improve antibiotic degradation. Owing to highly efficient oxygen activation and interfacial charge transfer, the degradation efficiency of the photo-assisted PMS system was as high as 51.6 times and 2.8 times that of photocatalyst and SO4--AOPs alone, respectively. Importantly, the highly efficient oxygen activation resulted in the production of O2-, which in turn could utilize the excess electrons generated through efficient interfacial charge transfer to convert into non-radical 1O2. The total organic carbon (TOC) elimination effectiveness of the photo-assisted PMS system reached 82 % via the synergy of radicals and non-radicals (O2-, OH, 1O2, SO4-, h+). This system also had excellent potential for reducing the generation and toxicity of disinfection by-products (DBPs), as evidenced through significant reductions in concentrations of trichloromethane (TCM), dichloroacetic acid (DCAA), and trichloronitromethane (TCNM) by 76 %, 64 %, and 35 %, respectively, providing an effective and eco-friendly strategy for antibiotic treatment.

New solution for predicting the removal efficiency of organic contaminants by UV/ H2O2: From a case study of 1H-benzotriazole

Rapid prediction of the removal efficiency and energy consumption of organic contaminants under various operating conditions is crucial for advanced oxidation processes (AOPs) in industrial application. In this study, 1H-Benzotriazole (BTZ, CAS: 95-14-7) is selected as a model micropollutant, a validated incorporated Computational Fluid Dynamics (CFD) model is employed to comprehensively investigate the impacts of initial concentrations of H2O2, BTZ and dissolved organic carbon (DOC) (i.e., [DOC]0, [BTZ]0 and [DOC]0), as well as the effective UV lamp power P and volumetric flow rate Qv. Generally, the operation performance depends on [DOC]0 and [BTZ]0 in similar trends, but with quantitatively different ways. The increase in [H2O2]0 and P/Qv can promote •OH generation, leading to the elimination of BTZ. It is worth noting that P/Qv is found to be linearly correlated with the removal order of BTZ (ROBTZ) under specific conditions. Based on this finding, the degradation of other potential organic contaminants with a wide range of rate constants by UV/H2O2 is further investigated. A model for predicting energy consumption for target removal rates of organic pollutants is established from massive simulation data for the first time. Additionally, a handy Matlab app is first developed for convenient application in water treatment. This work proposes a new operable solution for fast predicting operation performance and energy consumption for the removal of organic contaminants in industrial applications of advanced oxidation processes.

Advanced oxidation process for the treatment of industrial wastewater: A review on strategies, mechanisms, bottlenecks and prospects

Due to its complex and, often, highly contaminated nature, treating industrial wastewater poses a significant environmental problem. Many of the persistent pollutants found in industrial effluents cannot be effectively removed by conventional treatment procedures. Advanced Oxidation Processes (AOPs) have emerged as a promising solution, offering versatile and effective means of pollutant removal and mineralization. This comprehensive review explores the application of various AOP strategies in industrial wastewater treatment, focusing on their mechanisms and effectiveness. Ozonation (O3): Ozonation, leveraging ozone (O3), represents a well-established AOP for industrial waste water treatment. Ozone's formidable oxidative potential enables the breakdown of a broad spectrum of organic and inorganic contaminants. This paper provides an in-depth examination of ozone reactions, practical applications, and considerations involved in implementing ozonation. UV/Hydrogen Peroxide (UV/H2O2): The combination of ultraviolet (UV) light and hydrogen peroxide (H2O2) has gained prominence as an AOP due to its ability to generate hydroxyl radicals (ȮH), highly efficient in pollutant degradation. The review explores factors influencing the efficiency of UV/H2O2 processes, including H2O2 dosage and UV radiation intensity. Fenton and Photo-Fenton Processes: Fenton's reagent and Photo-Fenton processes employ iron ions and hydrogen peroxide to generate hydroxyl radicals for pollutant oxidation. The paper delves into the mechanisms, catalyst selection, and the role of photoactivation in enhancing degradation rates within the context of industrial wastewater treatment. Electrochemical Advanced Oxidation Processes (EAOPs): EAOPs encompass a range of techniques, such as electro-Fenton and anodic oxidation, which employ electrode reactions to produce ȮH radicals. This review explores the electrochemical principles, electrode materials, and operational parameters critical for optimizing EAOPs in industrial wastewater treatment. TiO2 Photocatalysis (UV/TiO2): Titanium dioxide (TiO2) photocatalysis, driven by UV light, is examined for its potential in industrial wastewater treatment. The review investigates TiO2 catalyst properties, reaction mechanisms, and the influence of parameters like catalyst loading and UV intensity on pollutant removal. Sonolysis (Ultrasonic Irradiation): High-frequency ultrasound-induced sonolysis represents a unique AOP, generating ȮH radicals during the formation and collapse of cavitation bubbles. This paper delves into the physics of cavitation, sonolytic reactions, and optimization strategies for industrial wastewater treatment. This review offers a critical assessment of the applicability, advantages, and limitations of these AOP strategies in addressing the diverse challenges posed by industrial wastewater. It emphasizes the importance of selecting AOPs tailored to the specific characteristics of industrial effluents and outlines potential directions for future research and practical implementation. The integrated use of these AOPs, when appropriately adapted, holds the potential to achieve sustainable and efficient treatment of industrial wastewater, contributing significantly to environmental preservation and regulatory compliance.

Peroxymonosulfate Activation by Cu-OMS-2 Nanofibers for Efficient Degradation of N-Containing Heterocycles in Aquatic Solution

In this research, the degradation of different types of N-containing heterocycle (NHC) contaminants by Cu-OMS-2 via peroxymonosulfate (PMS) activation in an aqueous environment was investigated. First, the effects of different reaction parameters were optimized using benzotriazole (BTR) as the model contaminant, and the optimal reaction conditions were 8 mM PMS, 0.35 g/L Cu-OMS-2, and 30 °C. Nine different types of NHC contaminants were effectively degraded under these reaction conditions, and the degradation efficiencies and the mineralization rates of those NHCs were more than 68 and 46%, respectively. Moreover, the Cu-OMS-2/PMS process presented excellent performance at a wide pH ranging from 3.0 to 11.0 and in the presence of some representative anions (NO3- and SO42-) and dissolved organic matter (fumaric acid). The inhibition sequence of anions on BTR removal during the Cu-OMS-2/PMS process was H2PO4- > HCO3- > Cl- > CO32- > NO3- > SO42-. It was also found that 74.5 and 71.3% BTR degradation rates were achieved in actual water bodies, such as tap water and Yellow River water, respectively. Besides, the Cu-OMS-2 heterogeneous catalyst had excellent stability and reusability, and the degradation rate of BTR was still at 77.0% after 5 cycles. Finally, electron paramagnetic resonance analysis and scavenging tests showed that 1O2 and SO4- • were the primary reactive oxygen species. Accordingly, Cu-OMS-2 nanomaterial was an efficient and sustainable heterogeneous catalyst to activate PMS for the decontamination of BTR in water remediation.

Oxygen doped graphite carbon nitride as efficient metal-free catalyst for peroxymonosulfate activation: Performance, mechanism and theoretical calculation

In this study, oxygen-doped graphitic carbon nitride (g-C3N4), named O-g-C3N4, was successfully fabricated and characterized, and its performance in activating peroxymonosulfate (PMS, HSO5-) for the removal of phenol, 2,4-dichlorophenol (2,4-DCP), bisphenol A (BPA), rhodamine B (RhB), reactive brilliant blue (RBB) and acid orange 7 (AO7) was evaluated. The catalytic performance of O-g-C3N4 for AO7 removal increased by 14 times compared to g-C3N4. In the presence of 0.2 g L-1 O-g-C3N4, 3.5 mM PMS at natural pH 5.8, 96.4% of AO7 could be removed in 60 min, reduced toxicity of the treated AO7 solution was obtained, and the mineralization efficiency was 47.2% within 120 min. Density functional theory (DFT) calculations showed that the charge distribution changed after oxygen doping, and PMS was more readily adsorbed by O-g-C3N4 with the adsorption energy (Eads) of -0.855 kcal/mol than that of the pristine g-C3N4 (Eads: -0.305 kcal/mol). Mechanism investigation implied that AO7 was primarily removed by the sulfate radicals (SO4•-) and hydroxyl radicals (•OH) on the surface of O-g-C3N4, but the role of singlet oxygen (1O2) to AO7 elimination was negligible. The results of cyclic experiments and catalyst characterization after reaction confirmed the favorable catalytic activity and structural stability of O-g-C3N4 particles. Furthermore, the O-g-C3N4/PMS system was very resistant to most of the environmental impacts, and AO7 removal was still acceptable in natural water environment. This study may provide an efficient metal-free carbonaceous activator with low dosage for PMS activation to remove recalcitrant organic pollutants (ROPs).

Generation and engineering applications of sulfate radicals in environmental remediation

Sulfate radical (SO4•-)-based advanced oxidation processes (AOPs) have become promising alternatives in environmental remediation due to the higher redox potential (2.6-3.1 V) and longer half-life period (30-40 μs) of sulfate radicals compared with many other radicals such as hydroxyl radicals (•OH). The generation and mechanisms of SO4•- and the applications of SO4•--AOPs have been examined extensively, while those using sulfite as activation precursor and their comparisons among various activation precursors have rarely reviewed comprehensively. In this article, the latest progresses in SO4•--AOPs were comprehensively reviewed and commented on. First of all, the generation of SO4•- was summarized via the two activation methods using various oxidant precursors, and the generation mechanisms were also presented, which provides a reference for guiding researchers to better select two precursors. Secondly, the reaction mechanisms of SO4•- were reviewed for organic pollutant degradation, and the reactivity was systematically compared between SO4•- and •OH. Thirdly, methods for SO4•- detection were reviewed which include quantitative and qualitative ones, over which current controversies were discussed. Fourthly, the applications of SO4•--AOPs in various environmental remediation were summarized, and the advantages, challenges, and prospects were also commented. At last, future research needs for SO4•--AOPs were also proposed consequently. This review could lead to better understanding and applications of SO4•--AOPs in environmental remediations.

Activation of peroxymonosulphate using a highly efficient and stable ZnFe2O4 catalyst for tetracycline degradation

Tetracycline (TC) is a widely used antibiotic that adversely affects ecosystems and, therefore, must be removed from the environment. Owing to their strong ability to oxidise pollutants, including antibiotics, and selectivity for these pollutants, an improved oxidation method based on sulphate radicals (SO4·-) has gained considerable interest. In this study, a novel technique for removing TC was developed by activating peroxymonosulphate (PMS) using a ZnFe2O4 catalyst. Using the co-precipitation method, a ZnFe2O4 catalyst was prepared by doping zinc into iron-based materials, which increased the redox cycle, while PMS was active and facilitated the production of free radicals. According to electron paramagnetic resonance spectroscopy results, a ZnFe2O4 catalyst may activate PMS and generate SO4·-, HO·, O2·-, and 1O2 to eliminate TC. This research offers a new method for creating highly effective heterogeneous catalysts that can activate PMS and destroy antibiotics. The study proposes the following degradation pathways: hydroxylation and ring-opening of TC based on the products identified using ultra-performance liquid chromatography-mass spectrometry. These results illustrated that the prepared ZnFe2O4 catalyst effectively removed TC and exhibited excellent catalytic performance.

Iron (III)-doped PbO2 and its application as electrocatalyst for decomposition of phthalocyanine dye

The textile industry contributes significantly to environmental pollution through dyeing and finishing processes that release dyes into wastewater. Even small amounts of dyes can have harmful effects and cause negative impacts. These effluents have carcinogenic, toxic, and teratogenic properties and can take a long time to be naturally degraded through photo/bio-degradation processes. This work investigates degradation of Reactive Blue 21 (RB21) phthalocyanine dye using anodic oxidation process with PbO₂ anode doped with iron III (0.1 M) (marked as Ti/PbO₂-0.1Fe) and compared with pure PbO₂. Ti/PbO₂ films with and without doping were successfully prepared by electrodeposition technology on Ti substrates. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS) was used to characterize the electrode morphology. Also, linear scanning voltammetry (LSV) and cyclic voltammetry (CV) tests were conducted to investigate the electrochemical response of these electrodes. The influence of operational variables on the mineralization efficiency was studied as a function of pH, temperature, and current density. Doping Ti/PbO₂ with Fe³⁺ (0.1 M) could reduce the particle to a smaller dimension and slightly increase the oxygen evolution potential (OEP). A large anodic peak was found for both electrodes prepared in the CV test, indicating that oxidation of the RB21 dye was easily achieved on the surface of the prepared anodes. No significant effect of initial pH on the mineralization of RB21 was observed. RB21 decolorization was more rapid at room temperature and increases with increasing current density. A possible degradation pathway for the anodic oxidation of RB21 in aqueous solution is proposed based on the identified reaction products. In general, it can be said that from the findings it was observed that the Ti/PbO₂ and Ti/PbO₂-0.1Fe electrodes show good performance on RB21 degradation. However, it was noted that the Ti/PbO₂ electrode tends to deteriorate over time and exhibits poor substrate adhesion, while the Ti/PbO₂-0.1Fe electrode displays superior substrate adhesion and stability.

Synergetic Photocatalytic Peroxymonosulfate Oxidation of Benzotriazole by Copper Ferrite Spinel: Factors and Mechanism Analysis

The development of oxidation processes with the efficient generation of powerful radicals is the most interesting and thought-provoking dimension of peroxymonosulfate (PMS) activation. This study reports the successful preparation of a magnetic spinel of CuFe₂O₄ using a facile, non-toxic, and cost-efficient co-precipitation method. The prepared material exhibited a synergetic effect with photocatalytic PMS oxidation, which was effective in degrading the recalcitrant benzotriazole (BTA). Moreover, central composite design (CCD) analysis confirmed that the highest BTA degradation rate reached 81.4% after 70 min of irradiation time under the optimum operating conditions of CuFe₂O₄ = 0.4 g L^-1, PMS = 2 mM, and BTA = 20 mg L^-1. Furthermore, the active species capture experiments conducted in this study revealed the influence of various species, including ^•OH, SO₄^•-, O₂^•-, and h⁺ in the CuFe₂O₄/UV/PMS system. The results showed that SO₄^•- played a predominant role in BTA photodegradation. The combination of photocatalysis and PMS activation enhanced the consumption of metal ions in the redox cycle reactions, thus minimizing metal ion leaching. Additionally, this maintained the reusability of the catalyst with reasonable mineralization efficiency, which reached more than 40% total organic carbon removal after four batch experiments. The presence of common inorganic anions was found to have a retardant effect on BTA oxidation, with the order of retardation following: HCO₃^- > Cl^- > NO₃^- > SO₄^2-. Overall, this work demonstrated a simple and environmentally benign strategy to exploit the synergy between the photocatalytic activity of CuFe₂O₄ and PMS activation for the treatment of wastewater contaminated with widely used industrial chemicals such as BTA.

Study on the ozonation degradation of methylene blue enhanced by microchannel and ultrasound

Azo dye-containing wastewater poses serious risks of environmental pollution because it is generally biologically toxic and resistant to conventional wastewater treatment methods. A novel degradation system integrating ozone, microchannel, and ultrasound was designed to effectively degrade azo dye-contaminated wastewater. The effects of discharge voltage of dielectric barrier discharge (DBD) reactor, liquid flow rate, microchannel width, ultrasonic power, initial pH, and reaction temperature on methylene blue (MB) decolorization were studied. A maximum MB decolorization efficiency of 92.7% was obtained in the ozone/microchannel/ultrasound (O₃/MC/US) system with 14 min of treatment. In addition, the 14-min decolorization efficiency and TOC removal efficiency obtained in O₃/MC/US system were increased by 12.6 and 6.5%, respectively, compared to those obtained in the pure O₃ system. Based on the results of scavenging experiments, the combined effects of microchannel and ultrasound were proved to improve the contribution rate of hydroxyl radicals, thus improving the decolorization efficiency. The present work clearly illustrates that ozonation degradation can be effectively enhanced by microchannel and ultrasound, and also provides a feasible method for the treatment of organic wastewater.

Core-shell magnetic CFO@COF composites toward peroxymonosulfate activation for degradation of sulfamethoxazole from aqueous solution: A comparative study and mechanistic consideration

A core-shell covalent organic framework encapsulated Co1.2Fe1.8O4 magnetic particles (CFO@COF) was designed and prepared successfully to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. It displays amazing catalytic reactivity since the unique interior structure and synergistic effect between COF shell and CFO core, reaching 99.8% removal of SMX (10 mg/L) within 30 min and 90.8% TOC removal. The synergy between bimetals vests high reactivity to CFO core. And the outer COF shell can stabilize the CFO core under intricate reaction conditions to restrain the leaching of Co ions (decreased from 0.75 to 0.25 mg/L). Further investigation compared the activation mechanism in two different system, CFO/PMS system and CFO@COF/PMS system. The result showed that the radical mechanism controlled by SO4⋅- guided the SMX degradation in CFO/PMS system whereas the 1O2 played a pivotal role in CFO@COF/PMS system called non-radical leading. The influences of various factors on degradation experiments and SMX degradation pathway were also studied. Most importantly, risk assessment in CFO@COF/PMS/SMX system was estimated via "ecological structure activity relationships". In most case, the toxicities of intermediates were lower than the initial samples, which confirmed the effectiveness of CFO@COF/PMS/SMX system in the reduction of toxicity of SMX.

Enhanced activation of peroxymonosulfate by a floating FeMo3Ox/C3N4 photocatalyst under visible-light assistance for oxytetracycline degradation: Performance, mechanisms and comparison with H2O2 activation

In this study, a floating FeMo₃O_x/C₃N₄-EP (FM-C-P) composite with highly stability and reusability was synthesized by an impregnation/calcination process and used to activate peroxymonosulfate (PMS) for oxytetracycline (OTC) degradation under visible light irradiation. The results demonstrated that 98.1% of OTC (50 mg/L) removal can be achieved by the activation of PMS (5 mM) using FM-C-P (1 g/L) in 30 min under visible light irradiation. The pseudo-first-order rate constant was calculated to be 0.181 min^-1. The degradation process with PMS was hardly affected by pH (3-11) and co-existing substance. ·SO₄^-, ·OH, ·O₂^- and ¹O₂ were produced in the Vis/PMS/FM-C-P system and ¹O₂ was determined to be the main reactive oxygen species (ROSs). The high efficiency of ROSs production mainly contributed to two mechanisms. Firstly, via the combination of ≡Fe (II)-·SO₅^- and free state ·SO₅^-, ¹O₂ could be generated on the Fe-N_x site. Secondly, photo-induced electrons in the FeMo₃O_x/g-C₃N₄ heterojunction could react with Fe (III) and Mo (VI) to form catalytically active species Fe (II) and Mo (IV). Moreover, the proposed degradation pathway and the toxicity of intermediated products was analyzed. Overall, this study was expected to deepen the understanding of the photo-assisted PMS activation and the generation of ¹O₂ with the presence of metal-oxide/C₃N₄ heterojunction.

Application of O3/PMS Advanced Oxidation Technology in the Treatment of Organic Pollutants in Highly Concentrated Organic Wastewater: A Review

The ozone/peroxymonosulfate (O3/PMS) system has attracted widespread attention from researchers owing to its ability to produce hydroxyl radicals (•OH) and sulfate radicals (SO4•−) simultaneously. The existing research has shown that the O3/PMS system significantly degrades refinery trace organic compounds (TrOCs) in highly concentrated organic wastewater. However, there is still a lack of systematic understanding of the O3/PMS system, which has created a significant loophole in its application in the treatment of highly concentrated organic wastewater. Hence, this paper reviewed the specific degradation effect, toxicity change, reaction mechanism, various influencing factors and the cause of oxidation byproducts (OBPs) of various TrOCs when the O3/PMS system is applied to the degradation of highly concentrated organic wastewater. In addition, the effects of different reaction conditions on the O3/PMS system were comprehensively evaluated. Furthermore, given the limited understanding of the O3/PMS system in the degradation of TrOCs and the formation of OBPs, an outlook on potential future research was presented. Finally, this paper comprehensively evaluated the degradation of TrOCs in highly concentrated organic wastewater by the O3/PMS system, filling the gaps in scale research, operation cost, sustainability and overall feasibility.

Mechanisms, toxicity and optimal conditions - research on the removal of benzotriazoles from water using Wolffia arrhiza

In the presented work, phytoremediation with the use of floating plant Wolffia arrhiza (L.) Horkel ex Wimm. was proposed as a method of removing the selected benzotriazoles (BTRs): 1H-benzotriazole (1H-BTR), 4-methyl-1H-benzotriazole (4M-BTR), 5-methyl-1H-benzotriazole (5M-BTR) and 5-chlorobenzotriazole (5Cl-BTR) from water. The efficiency of phytoremediation depends on three factors: daily time of exposure to light, pH of the model solution, and the amount of plans. Using a design of experiment (DoE) methods the following optimal values were selected: plant amount 1.8 g, light exposure 13 h and pH 7 per 100 mL of the model solution. It was found that the loss of BTRs in optimal conditions ranged from 92 to 100 % except for 4M-BTR, for which only 23 % of removal was achieved after 14 days of cultivation of W. arrhiza. The half-life values for studied compounds ranged from 0.98 days for 5Cl-BTR to 36.19 for 4M-BTR. The observed rapid vanishing of 5M-BTR is supposed by the simultaneous transformation of 5M-BTR into 4M-BTR. The detailed study of BTRs degradation pointed that the plant uptake is mainly responsible for the benzotriazoles concentration decrease. Toxicity tests showed that the tested organic compounds induce oxidative stress in W. arrhiza, which manifested among others, in reduced levels of chlorophyll in cultures with benzotriazoles compared to control.

Application of pier waste sludge for catalytic activation of proxy-monosulfate and phenol elimination from a petrochemical wastewater

This investigation aimed to remove phenol from real wastewater (taken from a petrochemical company) by activating peroxy-monosulfate (PMS) using catalysts extracted from pier waste sludge. The physical and chemical properties of the catalyst were evaluated by FE-SEM/EDS, XRD, FTIR, and TGA/DTG tests. The functional groups of O-H, C-H, CO₃^2-, C-H, C-O, N-H, and C-N were identified on the catalyst surface. Also, the crystallinity of the catalyst before and after reaction with petrochemical wastewater was 103.4 nm and 55.8 nm, respectively. Operational parameters of pH (3-9), catalyst dose (0-100 mg/L), phenol concentration (50-250 mg/L), and PMS concentration (0-250 mg/L) were tested to remove phenol. The highest phenol removal rate (94%) was obtained at pH=3, catalyst dose of 80 mg/L, phenol concentration of 50 mg/L, PMS concentration of 150 mg/L, and contact time of 150 min. Phenol decomposition in petrochemical wastewater followed the first-order kinetics (k> 0.008 min^-1, R²> 0.94). Changes in pH factor were very effective on phenol removal efficiency, and maximum efficiency (≈83%) was achieved in pH 3. The catalyst stability test was performed for up to five cycles, and phenol removal in the fifth cycle was reduced to 42%. Also, the energy consumption in this study was 77.69 kW h/m³. According to the results, the pier waste sludge catalyst/PMS system is a critical process for eliminating phenol from petrochemical wastewater.

Sulfate radicals induced from peroxymonosulfate on electrochemically synthesized TiO2-MoO3 heterostructure with Ti-O-Mo bond charge transfer pathway for potential organic pollutant removal under solar light irradiation

Here, a novel method for synthesis of heterostructured TiO₂-MoO₃ (MT) nanosheets photocatalyst by utilizing a facile electrochemical method and examined it's photocatalytic activity by the degradation of tetracycline hydrochloride (TCH), a model of organic pollutants, in the presence of peroxymonosulfate (PMS) under solar light irradiation (SL) was reported for the first time. The influence of several factors on the degradation efficiency including the initial concentration of TCH, solution pH, catalyst dosage, PMS concentration, and the existence of inorganic anions was explored. The MT-15/PMS system displayed a promising photocatalytic performance and up to 97% of TCH was degraded in 90 min the rate of the degradation reaction of MT-15/PMS was the highest (0.05299 min^-1) compared to 0.00251, 0.00337, 0.00546, 0.00735, 0.01337min^-1of TiO₂-P25, TiO₂-P25/PMS, MoO₃, MoO₃/PMS, and MT-15 respectively. The enhancement can be attributed to several reasons. First, the 2D morphology of the optimized heterostructure photocatalyst plays a significant role in providing much more active sites on its surface. Next, the boosted light absorption efficiency and higher photoproduced electron-hole pair separation ability, induced by the unique direct transformation of photogenerated electrons from the valance band of TiO₂ to the conduction band of MoO₃ via the Ti-O-Mo bond formed at the interface of MT heterostructure. Finally, the appropriate accessible reactive sites for the activation of PMS together with the synergistic effect between activation of PMS and photocatalytic processes eased the production of active species for the degradation of pollutants. Based on the scavenger experiments and EPR analysis, hydroxide and sulfate radicals were found to be the dominant free radical active species in the degradation process. Furthermore, the synergistic degradation reaction mechanism was proposed.

Attenuation of toxicity and occurrence of degradation products of the fungicide tebuconazole after combined vacuum UV and UVC treatment of drinking water

Antifungal azoles are the most frequently used fungicides worldwide and occur as active ingredients in many antifungal pharmaceuticals, biocides, and pesticides. Azole fungicides are frequent environmental contaminants and can affect the quality of surface waters, groundwater, and drinking water. This study examined the potential of combined vacuum UV (185 nm) and UVC (254 nm) irradiation (VUV/UVC) of the azole fungicide tebuconazole and the transformation product 1,2,4-trizole on degradation and changes in ecotoxicity. In vivo ecotoxicity was examined before and after UV treatment using bioassays with test organisms from different trophic levels to integrate changes in biological effect of the parent compound and the degradation products. The test battery included the luminescent bacterium Aliivibrio fischeri, the Gram-positive bacterium Bacillus subtilis, the fungus Fusarium graminearum, the green microalga Raphidocelis subcapitata, and the crustacean Daphnia magna. The combined VUV/UVC treatment of tebuconazole in drinking water efficiently degraded the parent compound at the µg/L-mg/L level and resulted in transformation products with lower toxicity than the parent compound. A direct positive correlation was observed between the applied UV dose (fluence, J/cm²), the disappearance of tebuconazole, and the decrease in ecotoxicity. The combined VUV/UVC process does not require addition of supplementary oxidants or catalysts and our study suggests that VUV/UVC-mediated photolysis of azole fungicides in water can decrease the overall toxicity and represent a potentially environmentally friendly treatment method.

Efficient activation of peroxymonosulfate by nanotubular Co3O4 for degradation of Acid Orange 7: performance and mechanism

Morphology optimization of catalysts has been considered as a viable strategy to improve the catalytic efficiency for peroxymonosulfate (PMS) activation by providing high surface area and abundant active sites. In this study, nanotubular Co₃O₄ (NT-Co₃O₄) was successfully synthesized as a PMS activator for the rapid removal of acid orange 7 (AO7) in aqueous solutions. Characterization results showed that NT-Co₃O₄ presented as aggregated nanotubes, with an average pore diameter of 10 nm. The specific surface area of NT-Co₃O₄ was as high as 41.8 m² g^-1. Catalytic experiments demonstrated that the degradation rate of AO7 in the NT-Co₃O₄/PMS system was 15 times greater than that in commercially available Co₃O₄/PMS system. The effects of various experimental parameters, including catalyst dose, PMS dose, pH, and temperature, were comprehensively investigated. The reactive species in the NT-Co₃O₄/PMS system were identified as sulfate radical (SO₄^•-) through both quenching tests and electron paramagnetic resonance (EPR) technology, and ≡CoOH⁺ played an important role in PMS activation. N atoms in the AO7 molecule were found to be preferentially attacked by SO₄^•-. Moreover, the good stability and reusability of NT-Co₃O₄ were confirmed by a five-cycle AO7 removal experiment. This study provides a broader view of the potential applications of nanotubular materials to achieve highly efficient PMS activation in treating dyes in wastewater.

ZrO2 supported perovskite activation of peroxymonosulfate for sulfamethoxazole removal from aqueous solution

In this study, A- and B-site doped perovskite La_0.5Sr_0.5Co_0.8Ni_0.2O₃ （LSCN) was prepared by sol-gel method. On this basis, ZrO₂ supported LSCN used to maintain high catalytic activity while inhibit the leaching of toxic Co ions. Compared with the non-doped LaCoO₃, the ZrO₂@La_0.5Sr_0.5Co_0.8Ni_0.2O₃ (Z@LSCN82)/PMS system could almost completely degrade SMX in 30 min. In addition, the leaching amount of Co ions was only 0.303 mg L^-1. Free radical quenching experiments and electron paramagnetic resonance experiments proved that active species SO₄^•-, •OH and ¹O₂ existed in the Z@LSCN82/PMS system, and SO₄^•- played a major role. Besides, the catalyst had high efficiency for SMX degradation in a wide pH range. In addition, co-existing anions in water such as HPO₄^- and Cl^- also showed slight inhibition of the system. It was indicated that the Z@LSCN82/PMS system had huge potential applications for practical wastewater treatment.

Understanding the Iron-Cobalt Synergies in ZSM-5: Enhanced Peroxymonosulfate Activation and Organic Pollutant Degradation

Iron- and cobalt-based heterogeneous catalysts are widely applied for activating peroxymonosulfate (PMS) to degrade organic pollutants. However, few studies have unveiled the clear synergistic mechanism of iron and cobalt in ZSM-5. In this paper, the synergistic mechanism of enhanced PMS activation was revealed by constructing iron and cobalt bimetal modified ZSM-5 zeolite catalysts (FeCo-ZSM-5). The tetracycline hydrochloride (TCH) degradation experiments showed that the catalytic activity of FeCo-ZSM-5-2:3 was much higher than those of Fe-ZSM-5 and Co-ZSM-5. In addition, the influences of catalyst dosage, PMS concentration, reaction temperature, initial pH, and coexisting ions on TCH removal were systematically investigated in this paper. Density functional theory calculations indicated that Co was the main active site for PMS adsorption, and Fe increased the area of Co's positive potential mapped to the electron cloud. The Fe-Co bimetallic doping increased the area of positive potential mapped to the electron cloud and benefited the adsorption of PMS on the catalyst surface, which revealed the synergistic mechanism of bimetals. Electron paramagnetic resonance spectra and quenching experiments showed that sulfate radicals, singlet oxygen, and hydroxyl radicals were involved in the degradation of TCH. Furthermore, liquid chromatography-mass spectrometry was conducted to propose possible degradation pathways. This work provides certain guiding significance in understanding the synergistic effect of heterogeneous catalysts for tetracycline wastewater treatment.

Enhanced utilization efficiency of peroxymonosulfate via water vortex-driven piezo-activation for removing organic contaminants from water

The efficient activation and utilization of peroxymonosulfate (PMS) in PMS-based advanced oxidation processes is a high-priority target for the removal of organic contaminants. This work introduces a water vortex-driven piezoelectric effect from few-odd-layered MoS2 into the PMS activation to remove benzotriazole (BTR) and other organic contaminants from the water. Approximately 91.1% of BTR can be removed by the MoS2 piezo-activated PMS process with a reaction rate constant of 0.428 min-1, which is 2.09 times faster than the sum of the individual MoS2, water vortex, and piezocatalysis rates. Meanwhile, the PMS utilization efficiency reached 0.0147 in the water vortex-driven piezo-activation system, which is 3.97 times that of the sum from the vortex/PMS and MoS2/PMS systems. These results demonstrate that the presence of MoS2 under a water vortex can trigger a piezoelectric potential and generate abundant free electrons to activate PMS to generate various active species for degradation of organic contaminants.

Effective degradation of azo dye from textile wastewater by electro-peroxone process

Color-producing chemicals emitted from many sources, such as textile or dye manufacturing industries, are a significant concern worldwide. The present study focuses on the electro-peroxone (EP) process for decolorizing a synthetic azo dye, C.I. Reactive Black 5 (RB5). Findings suggest that the EP process is more effective for dye degradation than ozonation and electrolysis. The EP process resulted in 100% decolorization after 60 min of contact time under optimum testing conditions such as pH 7, applied current 300 mA, and sulfate concentration 3.55 g L^-1. Based on the findings of the primary investigation, EP treatment of real textile effluent was carried out and 2 h of EP treatment resulted in 99% decolorization and 74%total organic carbon (TOC) removal. As an outcome, the EP process can treat textile wastewater in a cost-effective and environmentally friendly manner.

Advanced catalytic ozonation for degradation of pharmaceutical pollutants-A review

Various chemical treatment techniques are involved in removing refractory organic compounds from water and wastewater using the oxidation reaction of hydroxyl radicals (^•OH). The use of catalysts in advanced catalytic ozonation is likely to improve the decomposition of molecular ozone to generate highly active free radicals that facilitate the rapid and efficient mineralization and degradation of numerous organics. For the degradation of toxic organic pollutants in wastewater, the advanced catalytic ozonation process has been widely applied in recent years. Low utilization efficiency of ozone and ineffective mineralization of organic contaminants by ozone can be remedied with advanced catalytic ozonation. Advanced catalytic ozonation has gained popularity because of these merits. However, homogeneous catalytic ozonation has the disadvantage of producing secondary contaminants from the addition of metallic ions. Heterogeneous catalytic ozonation can overcome this drawback by utilizing metals, metallic oxides, and carbon materials as a catalyst of efficacy and stability. This review discusses various aspects of catalytic ozonation in wastewater treatment of pharmaceutical pollutants, application of catalytic ozonation process in typical wastewater, and prospects in advancing the techniques in heterogeneous catalytic ozonation.

Elimination of amoxicillin using zeolite Y-sea salt as a good catalyst for activation of hydrogen peroxide: Investigating degradation pathway and the effect of wastewater chemistry

The sea contains elements that can play a useful role in catalyzing reactions. Therefore, this research was done to focus on eliminating amoxicillin (AMX) from wastewater utilizing zeolite Y- sea salt catalyst in the presence of H₂O₂. The influences of furnace temperature (200-500 °C) and time duration in the furnace (1-4 h) were optimized during catalyst generation. Also, the effects of different parameters on AMX removal, such as pH (5.0-9.0), catalyst dose (0-10 g.L^-1), AMX concentration (50-300 mg.L^-1), contact time (10-130 min), and H₂O₂ concentration (0-6 mL/100 mL distilled water) were investigated. Different analyses like Brunauer-Emmett-Teller (BET), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were conducted to reveal catalyst properties. The BET-specific surface area of the catalyst (12.69 m²g^-1) insignificantly (p-value > 0.05) changed after AMX removal (13.04 m²g^-1), indicating the strength of the prepared catalyst. The active groups of N-H, O-H-O, O-Si-O, C-H, Si-O-Si, and Si-O-Al were determined in the catalyst structure. The highest removal of AMX (93%) was achieved in the zeolite-sea salt/H₂O₂ system at a pH level of 6.0 and an H₂O₂ concentration of 0.1 mL/100 mL. Elimination of the AMX followed pseudo-first-order kinetics. The catalyst was reclaimed up to 7 times and the removal efficiency was suitable up to the fifth stage. The by-products and reaction pathways were investigated by gas chromatography-mass spectrometry (GC-MS). The results showed that zeolite-sea salt can be utilized as an H₂O₂ activator for the effective degradation of AMX from wastewater.

Kinetics and mechanisms of flumequine degradation by sulfate radical based AOP in different water samples containing inorganic anions

Many studies have reported that hydroxyl radical (HO˙) driven advanced oxidation processes (AOPs) could degrade fluoroquinolones (FQs) antibiotics effectively. Compared with HO˙, sulfate radical (SO₄˙⁻) shows a similar oxidation capacity but a longer half-life. SO₄˙⁻ could cause chain reactions and resulted in the generation of halogen radicals and carbonate radicals from the main anions in sea water including Cl⁻, Br⁻ and HCO₃⁻. However, few studies were focused on the degradation of FQs in marine aquaculture water and seawater, as well as the bioaccumulation of transformation products. As a typical member of FQs, flumequine (FLU) was degraded by UV/peroxodisulfate (PDS) AOPs in synthetic fresh water, marine aquaculture water and seawater. The reaction rate constants in the three water samples were 0.0348 min⁻¹, 0.0179 min⁻¹ and 0.0098 min⁻¹, respectively. The reason was attributed to the inhibition of the anions as they could consume SO₄˙⁻ and initiate the quenching reaction of free radicals. When the pH value increased from 5 to 9, the reaction rate decreased from 0.0197 min⁻¹ to 0.0066 min⁻¹. The energy difference between HOMO and LUMO of FLU was calculated to be 8.07 eV indicating that FLU was a stable compound. The atoms on quinolone ring of FLU with high negative charge would be more vulnerable to attack by free radicals through electrophilic reactions. Two possible degradation pathways of FLU were inferred according to the degradation products. Preliminary bioaccumulation analysis of transformation products by the EPI suite software proved that the values of log K_ow and log BCF of the final product P100 were less than those of FLU and the intermediates.

Many studies have reported that hydroxyl radical (HO˙) driven advanced oxidation processes (AOPs) could degrade fluoroquinolones (FQs) antibiotics effectively.

PMS activation by magnetic cobalt-N-doped carbon composite for ultra-efficient degradation of refractory organic pollutant: Mechanisms and identification of intermediates

Refractory organic pollutant effluent has led to severe water pollution. In this study, magnetic Co-N-doped carbon hybrid catalysts (Co-NC-x) were fabricated using a facile cation exchange combined pyrolysis and self-reduction technique to activate peroxymonosulfate (PMS) for rehabilitation of the water environment. Factors affecting the catalytic activity of the Co-NC-850 were comprehensively examined. 100% of RhB degradation efficiency within 20 min was achieved in the Co-NC-850/PMS system at the optimum conditions (C₀ = 80 mg L^-1, catalyst loading 0.025 g L^-1, PMS concentration 0.8 mM, native pH and 25 °C). The electron paramagnetic resonance measurements and competitive quenching tests demonstrated that a sulfate radical (SO₄•^-) and singlet oxygen (¹O₂) account for RhB degradation in the Co-NC-850/PMS system, and ¹O₂ contributed ~86.2% to RhB removal. The synergistic effect of Co⁰ nanoparticles (NPs) and NC on Co-NC-850 might induce a predominant non-radical route to trigger PMS activation for RhB degradation. Direct oxidation of O₂•^- by a hydroxyl radical (•OH) might be the crucial process for forming ¹O₂. Magnetic response and successive cycles verified that Co-NC-850 has superior separable performance and reusability. This innovative magnetic Co-NC-850 hybrid catalyst for PMS activation delivered vast potential for disintegration of refractory organic contaminants.

Comparative investigation of acetaminophen degradation in aqueous solution by UV/Chlorine and UV/H2O2 processes: Kinetics and toxicity assessment, process feasibility and products identification

The degradation of acetaminophen (ACM) was comparatively studied by UV/chlorine and UV/H₂O₂ systems. An apparent reduction in the removal rate was observed above the optimum pH levels of 7.0 and 3.0 in UV/chlorine and UV/H₂O₂ processes, respectively. The relative contribution of each oxidizing agent in ACM removal using the two advanced oxidation processes (AOPs) was evaluated. Even though hydroxyl radicals, with the contribution percentage of 90.1%, were determined as the primary oxidizing species in ACM removal using the UV/H₂O₂ process, reactive chlorine species (RCS), with 43.8% of contribution percentage, were also found to play a pivotal role in ACM removal using the UV/chlorine process. For instance, dichlorine radical (Cl₂^•-) showed an acceptable contribution percentage of 32.2% in the degradation of ACM by the UV/chlorine process. The rate of ACM degradation significantly rose to 99.9% and 75.6%, as higher amounts of oxidants were used in the UV/chlorine and UV/H₂O₂ processes, respectively, within 25 min. The introduction of HCO₃^- ions and humic acid remarkably decreased the rate of ACM degradation in both techniques used in this study. The presence of NO₃^- and Cl^- ions did not considerably affect the removal rate in the UV/chlorine process. The acute toxicity analysis revealed that a more pronounced reduction in the ACM solution toxicity could be achieved by the UV/H₂O₂ process compared to the UV/chlorine process, which should be ascribed to the formation of chlorinated products in the UV/chlorine treatment. Eventually, plausible oxidation pathways were proposed for each process.

Removal of levofloxacin through adsorption and peroxymonosulfate activation using carbothermal reduction synthesized nZVI/carbon fiber

Nano zero-valent iron (nZVI) is widely used for decontamination. The main issues associated with nZVI are agglomeration and oxidation in the long term. In this study, the carbothermal reduction of cotton fiber was conducted for the synthesis of nZVI supported on cotton carbon fiber (nZVI/CF) to address the agglomeration and oxidation of nZVI. Synergistic adsorption and peroxymonosulfate (PMS) activation using nZVI/CF for removing levofloxacin (LEV) are reported herein. The nZVI concentration and morphology were conveniently adjusted by soaking cotton fiber in ferric nitrate solutions of various Fe³⁺ concentrations. The carbothermal reduction of the cotton fiber at 900 °C contributed to the reduction of Fe³⁺ into nZVI. A nZVI/CF-900-0.3 system was obtained through the carbothermal reduction of cotton fiber soaked in 0.3 M ferric nitrate. Favorable adsorption of nZVI/CF-900-0.3 to LEV facilitated LEV degradation under PMS activation. Approximately 93.83% of LEV (C₀ = 20 ppm) was removed within 60 min with 0.2 g/L of the catalyst and 1 mM PMS. It was preferable to use nZVI + CF-900 to activate PMS for degrading LEV, thus confirming the favorable effect of LEV adsorption on further degradation. The nZVI/CF-900-0.3 exhibited excellent long-term stability given that it was able to activate PMS after it was stored for 6 months. ·SO₄^- played an important role in LEV degradation in the presence of PMS.

Construction of Z-scheme CuFe2O4/MnO2 photocatalyst and activating peroxymonosulfate for phenol degradation: Synergistic effect, degradation pathways, and mechanism

Photocatalysis coupled with sulfate radical-based advanced oxidation process (SR-AOPs) is an efficient strategy to enhance the degradation efficiency of organic pollution. Herein, a Z-scheme CuFe₂O₄/MnO₂ composite catalyst was successfully fabricated by the hydrothermal method. A series of characterizations demonstrated that the higher CuFe₂O₄ particle dispersion and larger BET surface area of CuFe₂O₄/MnO₂ catalyst contributed to a high catalytic activity toward the phenol removal compared with pure CuFe₂O₄. The effects of catalyst concentration, pH, and peroxymonosulfate (PMS) concentration were studied according to the Box-Behnken Design (BBD) method. The results indicated that 100 mg/L 100 mL phenol could be degraded completely at 0.5 g/L CuFe₂O₄/MnO₂ catalyst, pH = 4.8 and 0.5 mM PMS within 30 min. Moreover, the excellent reusability and stability of CuFe₂O₄/MnO₂ were indicated by the results of recycling degradation and ion leaching test. The free radical quenching experiments and electron spin resonance (ESR) confirmed that h⁺, SO₄^•-, and ^•OH were the main reaction species for phenol oxidation. Based on the results of gas chromatography-mass spectrometry (GC-MS) and ion chromatography, the degradation pathway of phenol was proposed, and the toxicity of phenol degradation intermediates was evaluated. This work may provide new insights into the design of heterojunction photocatalysts for PMS activation to remove organic pollutants.

Application of hybrid oxidative processes based on cavitation for the treatment of commercial dye industry effluents

The present work demonstrates the significant role of ultrasound (US) in intensifying the efficacy of the combination with Fenton reagent and/or ozone for the treatment of real dye industry industrial effluent procured from the local industry. Initial part of the work focused on analysing the literature based on combination approaches of US with different oxidants applied for the treatment of real and simulated effluents focusing on the dyes. The work also provides guidelines for the selection of optimal operating parameters for maximizing the intensification of the degradation. The second part of the work presents an experimental study into combined approaches of ultrasound with ozone (O3) and Fenton's reagent for treatment of real effluent. Under optimized conditions (100 W, 20 kHz and duty cycle of 70%), maximum COD reductions of 94.79% and 51% were observed using a combined approach of US + Fenton oxidation followed by lime treatment for the treatment of effluent-I and effluent-II respectively at H2O2 loading of 17.5 g/L, H2O2/Fe2+ ratio of 3, pH of 4, CaO dose of 1 g/L and an overall treatment time of 70 min. US + Fenton + O3 followed by lime was also applied for treatment under ozone loading of 1 g/h for the treatment of effluent-I and it was found that maximum COD reduction of 95.12% was obtained within 30 min of treatment time, indicating use of ozone did not result in significant value addition in terms of COD reduction but resulted in faster treatment. HC (inlet pressure: 4 bar) + Fenton + Lime scheme was successfully replicated on a pilot-scale resulting in maximum COD reduction of 57.65% within 70 min of treatment time. Overall, it has been concluded that the hybrid oxidative processes as US + Fenton followed by lime treatment is established as the best approach ensuring effective COD reduction at the same time obtaining final colourless/reusable effluent.

A Review on the Treatment of Petroleum Refinery Wastewater Using Advanced Oxidation Processes

The petroleum industry is one of the most rapidly developing industries and is projected to grow faster in the coming years. The recent environmental activities and global requirements for cleaner methods are pushing the petroleum refining industries for the use of green techniques and industrial wastewater treatment. Petroleum industry wastewater contains a broad diversity of contaminants such as petroleum hydrocarbons, oil and grease, phenol, ammonia, sulfides, and other organic composites, etc. All of these compounds within discharged water from the petroleum industry exist in an extremely complicated form, which is unsafe for the environment. Conventional treatment systems treating refinery wastewater have shown major drawbacks including low efficiency, high capital and operating cost, and sensitivity to low biodegradability and toxicity. The advanced oxidation process (AOP) method is one of the methods applied for petroleum refinery wastewater treatment. The objective of this work is to review the current application of AOP technologies in the treatment of petroleum industry wastewater. The petroleum wastewater treatment using AOP methods includes Fenton and photo-Fenton, H2O2/UV, photocatalysis, ozonation, and biological processes. This review reports that the treatment efficiencies strongly depend on the chosen AOP type, the physical and chemical properties of target contaminants, and the operating conditions. It is reported that other mechanisms, as well as hydroxyl radical oxidation, might occur throughout the AOP treatment and donate to the decrease in target contaminants. Mainly, the recent advances in the AOP treatment of petroleum wastewater are discussed. Moreover, the review identifies scientific literature on knowledge gaps, and future research ways are provided to assess the effects of these technologies in the treatment of petroleum wastewater.

Sunlight-driven activation of peroxymonosulfate by microwave synthesized ternary MoO3/Bi2O3/g-C3N4 heterostructures for boosting tetracycline hydrochloride degradation

Design of direct Z-scheme heterojunction photocatalyst is considered as an effective strategy to fully use the high redox potential photogenerated charge carriers. This work reports a novel method for investigating the photosynergistic performance of the Z-scheme MoO₃/Bi₂O₃/g-C₃N₄ (MBG) photocatalyst with peroxymonosulfate (PMS) for the solar degradation of tetracycline hydrochloride (TCH), a model of organic pollutants in wastewater. The results showed a better strategy to activate PMS via accelerating the redox cycle (Mo⁶⁺/Mo⁵⁺), which ultimately induces the successive generation of highly reactive oxygen species. The effect of dosage of the catalyst, PMS, pH of the solution, initial concentrations of TCH and the presence of inorganic anions were investigated. It was found that the degradation of the TCH under sunlight irradiation (SL) was strongly enhanced by the presence of the PMS as an electron acceptor. The MBG/PMS/SL system was able to degrade an initial concentration (40 mg/L) of the TCH solution within 140 min. The good reusability and stability of the MBG catalyst were evaluated by recycling the degradation experiment. The main free radicals are OH and SO₄^─ which played an important role in the degradation reaction were identified by scavenger experiments and confirmed by EPR spectroscopy. X-ray photoelectron spectroscopy (XPS) study revealed the role of molybdenum ion in the activation process of PMS. The possible synergistic degradation reaction mechanism was proposed.

How neutral nitrogen-containing compounds are oxidized in oxidative-denitrogenation of liquid fuel with TiO2@carbon

Oxidative-denitrogenation (ODN) of indole (IND) and methyl-substituted INDs (methyl-INDs), representative neutral nitrogen-containing compounds (NCCs), was carried out with TiO₂@C and H₂O₂ as heterogeneous catalyst and oxidant, respectively, under ultrasound irradiation. The oxidation of INDs progressed through radical formation, as evidenced by electron spin resonance and radical scavenger experiments. The oxidized position of INDs in the ODN process was checked via characterization of the obtained products. It was observed that the oxidation finally occurred on the carbon rather than on the nitrogen atom of INDs, unlike the oxidation of basic NCCs (e.g., oxidation on the nitrogen atom, as respective N-oxides were formed) and sulfur-containing compounds. To understand the relative reactivity and oxidation position, electron density (ED) on the nitrogen atom of the studied INDs and relative stability of representative intermediates/products were calculated. It could be confirmed that ED on the nitrogen atom of the INDs is very important in the oxidation of INDs since the ODN reactivity of INDs was enhanced with increasing ED on the nitrogen atom of the investigated INDs. Moreover, theoretical analyses of the relative stability of substrate and intermediates/products (especially for IND) can explain the route for the observed final products in ODN. In other words, oxygen on the nitrogen atom, obtained via the first step of oxidation (electrophilic addition of an active oxygen atom on nitrogen), moves to the nearby carbon atom, because of the relative stability of the intermediates and products.

Synergistic mechanism and degradation kinetics for atenolol elimination via integrated UV/ozone/peroxymonosulfate process

The present research systematically investigates the atenolol (ATL) degradation in integrated UV/Ozone (O₃)/peroxymonosulfate (PMS) process focusing on the synergistic mechanism, reaction kinetics, pollutant degradation pathway and antibacterial activity. The results manifested that the integrated UV/O₃/PMS process showed the noteworthy superiority to ATL degradation compared with UV/PMS, UV/O₃ and O₃/PMS systems. Simultaneously, the impacts of operating parameters like PMS dosage, initial ATL concentration, solution pH and water matrix were comprehensively explored. The ATL elimination efficiency increased linearly with PMS dose and significantly enhanced in alkaline conditions. The ^•OH and SO₄^•- were the primary reactive radicals for ATL oxidation in UV/O₃/PMS system based on the radical scavenging experiments and electron paramagnetic resonance characterization. Besides, a simplified kinetic model on the basis of the dominant reactions and the steady-state assumption was established to foretell the relative contributions of reactive oxidants for ATL elimination in UV/O₃/PMS process. Main transformation products were determined via UPLC-QTOF-MS to infer the possible degradation pathways of ATL. Furthermore, the UV/O₃/PMS process could distinctly mitigate the antibacterial activity of ATL and its intermediates to E. coli and B. subtilis. Our findings may have critical implications for the development of novel oxidation processes for recalcitrant contaminants mitigation in water purification.

Recycling application of modified waste electrolytic manganese anode slag as efficient catalyst for PMS activation

Electrolytic manganese anode slag (EMAS) is the waste residue produced by electrolytic manganese metal industry. At present, no mature recycling system has been established, which causes a waste of resources and threatens the environment. Therefore, the resource utilization of EMAS has attracted increased attention. In this paper, the in-situ resource utilization of EMAS can be realized by pickling treatment was reported. Specifically, EMAS after pickling treatment (PEMAS) was first used as catalyst to activate PMS to degrade tetrachlorophenol (4-CP). Pickling could remove the inert inorganic components on EMAS and increase the specific surface area, pore volume and Mn distribution of the catalyst, thus improving the catalytic performance of the catalyst. Under the conditions of 4-CP of 40 ppm, PMS of 1 mM and PEMAS of 0.3 g L^-1, 85% of 4-CP could be degraded within 50 min. Mechanism studies proved that the main active species were O₂^- and ¹O₂. Some O₂^- contributed to the generation of ¹O₂ and some O₂^- directly contributed to the degradation of 4-CP. During the reaction, the valence state of Mn transformed between Mn(III)/Mn(IV) and Mn(II)/Mn(III) and kept the cycle. Moreover, PEMAS/PMS system exhibited excellent independence of the solution pH, resistance to the versatile inorganic ions and background organic matters, and stability of recycling. In a word, this study has achieved the resource utilization of EMAS and the goal of treating waste with waste, which is a win-win strategy of economic and environmental benefits.