Simulation and comparative study on the oxidation kinetics of atrazine by UV/H₂O₂, UV/HSO₅⁻ and UV/S₂O₈²⁻

Phototransformation of zinc oxide nanoparticles and coexisting pollutant: Role of reactive oxygen species

In this study, the photochemistry of ZnO NPs and their effect on phototransformation of coexisting pollutants (sulfamethazine, SMZ) were systematically investigated under UV illumination. SMZ (40 μM) degradation was accelerated by ZnO NPs, as the observed reaction rate constant (k_obs) increased from 0.0809 h^-1 to 0.7982 h^-1 at the concentration of 5-50 mg/L ZnO NPs. Free radical quenching and quantification experiments indicated the reactive oxygen species, especially the hydroxyl radicals (OH) and singlet oxygen (¹O₂), made great contributions to SMZ degradation. Moreover, SMZ was prone to be degraded at high pH with k_obs reaching upto 0.5734 h^-1 at pH 12.0. The presence of Cl^- (1000 mM) reduced the SMZ decomposition greatly by 2.4-fold while the effects of SO₄^2- (30 mM) were very limited. Natural organic matter including humic acid and tannic acid both inhibited the degradation of SMZ with k_obs decreasing by 35.4-fold and 132-fold, respectively. During the photoreaction process, ZnO NPs fragmented into relative small size pieces obviously along with the release of Zn²⁺. Finally, the possible cotransformation pathways of ZnO NPs and SMZ were proposed based on SMZ degradation intermediates and the above results. These findings of the present study suggested that the photoreactions of ZnO NPs greatly influenced the transformation of contaminants and ZnO NPs themselves in aquatic environment, which may have significant implications for the fate assessment of NPs and environmental pollutants.

A comparative study of UV/H2O2 and UV/PDS for the degradation of micro-pollutants: kinetics and effect of water matrix

Organic micro-pollutants such as pesticides and endocrine disruptors cause serious harm to human health and aquatic ecosystem. In this study, the potential degradation of atrazine (ATZ), triclosan (TCS), and 2,4,6-trichloroanisole (TCA) by UV-activated peroxydisulfate (UV/PDS) and UV-activated H₂O₂ (UV/H₂O₂) processes were evaluated under different conditions. Results showed that UV/PDS process was more effective than UV/H₂O₂ under the same conditions. Increasing oxidant dosage or decreasing the initial ATZ, TCS, and TCA concentrations promoted the degradation rates of these three compounds. The presence of natural organic matter (NOM) could effectively scavenge sulfate radical (SO₄•^-) and hydroxyl radical (HO•) and reduced the removal rates of target compounds. Degradation rates of ATZ and TCA decreased with pH increasing from 5.0 to 9.0 in UV/PDS process, while in UV/H₂O₂ process, the increase of solution pH had little effect on ATZ and TCA degradation. In the UV/PDS and UV/H₂O₂ oxidation process, when the solution pH increased from 5 to 8, the removal rates of TCS decreased by 19% and 1%, while when the solution pH increased to 9, the degradation rates of TCS increased by 23% and 17%. CO₃^2-/HCO₃^- had a small inhibitory effect on ATZ and TCA degradation by UV/H₂O₂ and UV/PDS processes but promoted the degradation of TCS significantly (> 2 mM). Cl^- had little effect on the degradation of ATZ, TCA, and TCS in UV/H₂O₂ process. Cl^- significant inhibited on the degradation of ATZ and TCS, but the influence of Cl^- on the degradation of TCA was weak in UV/PDS process. Based on these experimental results, the various contributions of those secondary radicals (i.e., carbonate radical, chlorine radical) were discussed. This study can contribute to better understand the reactivities when UV/PDS and UV/H₂O₂ are applied for the treatment of micro-pollutant-containing waters.

Enhanced mineralization of reactive brilliant red X-3B by UV driven photocatalytic membrane contact ozonation

The partial oxidation on refractory organics in ozonation process and the poor performance of mass transfer between ozone (O₃) phase and liquid phase by common O₃ distribution techniques inhibit the practical application of O₃. To overcome these defects, hollow fiber membrane was applied in membrane contact ozonation (MCO)-UV process for the reactive brilliant red X-3B (RBRX-3B) degradation. The efficiency of mass transfer was guaranteed due to the enormous gas/liquid contact area supplied in this bubble-less O₃ transfer process. UV photolysis not only significantly improved the O₃ utilization efficiency but also accelerated the mineralization of RBRX-3B by promoting O₃ to decompose to hydroxyl radicals (OH). When 15 mg/L of O₃ was supplied at flow rate of 0.2 L/min, and a liquid velocity of 0.453 m/s, the chemical oxygen demand (COD) removal and total organic carbon (TOC) removal reached 90 % and 77 %, respectively. The rate constant for TOC removal in the MCO-UV process (7.89 × 10^-3 min^-1) was 3.08 and 6.12 times higher than that in MCO and UV photolysis processes, respectively. Furthermore, the mineralization efficiency (ΔCOD/ΔO₃ = 0.84 mg/mg) and electrical energy per mass (E_EM = 4.7 kW h/kg) were calculated and these results indicated a promising future for the MCO-UV process.

Persulfate-Based Advanced Oxidation: Critical Assessment of Opportunities and Roadblocks

Reports that promote persulfate-based advanced oxidation process (AOP) as a viable alternative to hydrogen peroxide-based processes have been rapidly accumulating in recent water treatment literature. Various strategies to activate peroxide bonds in persulfate precursors have been proposed and the capacity to degrade a wide range of organic pollutants has been demonstrated. Compared to traditional AOPs in which hydroxyl radical serves as the main oxidant, persulfate-based AOPs have been claimed to involve different in situ generated oxidants such as sulfate radical and singlet oxygen as well as nonradical oxidation pathways. However, there exist controversial observations and interpretations around some of these claims, challenging robust scientific progress of this technology toward practical use. This Critical Review comparatively examines the activation mechanisms of peroxymonosulfate and peroxydisulfate and the formation pathways of oxidizing species. Properties of the main oxidizing species are scrutinized and the role of singlet oxygen is debated. In addition, the impacts of water parameters and constituents such as pH, background organic matter, halide, phosphate, and carbonate on persulfate-driven chemistry are discussed. The opportunity for niche applications is also presented, emphasizing the need for parallel efforts to remove currently prevalent knowledge roadblocks.

Comparative study of atrazine degradation by magnetic clay activated persulfate and H2O2

To effectively remove the endocrine disrupting chemicals (EDCs) in water, Fe3O4 was loaded on the surface of modified sepiolite clay by the method of co-precipitation to catalyze potassium persulfate (K2S2O8) and hydrogen peroxide (H2O2) respectively to generate SO4˙- and ·OH for atrazine (ATZ) removal. The magnetic clay catalyst was characterized by XRD, SEM, N2 adsorption-desorption and isoelectric point. The degradation efficiency of ATZ in the two systems was systematically compared in terms of initial pH, oxidant dosage and oxidant utilization rate. The results revealed that, after 90 minutes, systems with K2S2O8 and H2O2 can remove 65.7% and 57.8% of the ATZ under the given conditions (30 °C, catalyst load: 1 g L-1, initial pH: 5, [ATZ]0: 10 mg L-1, [H2O2]0: 46 mmol L-1, [PDS]0: 46 mmol L-1). The magnetic clay catalyst still maintained good catalytic activity and stability during the four consecutive runs. Based on the quenching experiments, it was demonstrated that the dominant radical species in the two systems were SO4˙-/·OH and ·OH, respectively. However, the degradation efficiency of the two systems presented different responses toward the condition variations; the system with K2S2O8 was relatively more sensitive to solution pH, the oxidant efficiency was generally higher than that of the H2O2 system (except 184 mmol L-1).

Improving the Fenton catalytic performance of FeOCl using an electron mediator

FeOCl Fenton-like catalyst has drawn much attention due to its high catalytic activity. Nevertheless, the potential application of FeOCl is significantly hindered by the sluggish reduction kinetics of Fe³⁺ to active Fe²⁺. Here, we report that the incorporation of Fe - O-Mo electron mediator into FeOCl via forming a FeOCl/MoS₂ composite can facilitate the Fe²⁺ regeneration through the oxidation of Mo⁴⁺ to Mo⁶⁺, which boosts the hydroxyl radicals yields, thus leading to a significantly improved catalytic performance. The removal efficiency of methylene blue (MB, 50 mg L^-1) achieves ∼100% within 2 min. with low dosage of FeOCl/MoS₂ (0.2 g L^-1) and H₂O₂ (0.6 mM). FeOCl/MoS₂ not only has broad working pH range (∼3 - 9) and high salinity tolerance (100 mM), but also capable to degrade various organic pollutants. For practical application, the fabricated FeOCl/MoS₂ membrane effectively degrades continuous MB flow. This study demonstrates that incorporating an electron mediator is an effective way to improve the catalytic performance of heterogeneous Fenton-like catalysts.

Sonolytic degradation of bisphenol S: Effect of dissolved oxygen and peroxydisulfate, oxidation products and acute toxicity

In this paper, the kinetics of bisphenol S (BPS) degradation in the presence of peroxydisulfate (PDS) or dissolved oxygen (DO) in ultrasound (US) system were investigated. For PDS (US/PDS), increased PDS concentration result in faster BPS degradation, but the enhancement was not remarkable with multiplying PDS dosages. Therefore, heterogeneous PDS activation model based on a Langmuir-type adsorption mechanism was proposed to explain the trait of BPS abatement. The equilibrium constant of PDS (K_PDS) was calculated to be 2.91 × 10^-4/μM, which was much lower than that of BPS, suggesting that PDS was hard to adsorb on the gas-liquid interface of the cavitation bubble following by activation. Besides, the formation of •OH and SO₄^•- in US/PDS system was reinvestigated. The result showed that SO₄^•- rather than •OH was the predominant radical, which was quite different from previous study. Dissolved oxygen largely improve the degradation of BPS in US system and •OH rather than O₂^•- was proved to be the main reactive oxygen species (ROS). The improvement of •OH generation possibly caused by the reaction of DO with •H so that it cannot recombine with •OH. The transformation of the BPS in US system mainly included BPS radical polymerization, hydroxylation and hydrolysis. Frustratingly, the acute toxicity assay of Vibrio fischeri suggests that the degradation products of BPS are more toxic. These results will improve the understanding on the activation mechanisms of PDS and the role of dissolved oxygen play in US. Further investigations may need to explore other treatment ways of BPS and evaluate the acute toxicity of degradation products.

Micropollutant elimination by O3, UV and plasma-based AOPs: An evaluation of treatment and energy costs

Over the last years, there has been a growing interest in the use of Advanced Oxidation Processes (AOPs) for the elimination of micropollutants. This work attempts to compare the efficiency of conventional UV, O₃ and H₂O₂ based AOPs with a relatively new AOP based on plasma-ozonation, in terms of removal and energy efficiency. The experimental study is performed in a synthetic water matrix spiked with four different micropollutants: atrazine (ATZ), alachlor (ALA), bisphenol A (BPA) and 1,7-α-ethinylestradiol (EE2). For the different processes examined in this study, O₃ - based AOPs are more effective compared to UV based techniques in terms of energy efficiency. Although the energy efficiency of plasma-ozonation falls between the energy cost of O₃ and UV-based AOPs, the removal kinetics generally proceed faster compared to other AOPs, achieving complete elimination (>99.8% removal) of the target compounds within 20 min of treatment. Moreover, the results suggest that improvement in the mass-transfer in the plasma-ozonation setup permits to further decrease the energy cost of this process up to electrical energy per order (EE/O) values between 2.54 and 0.124 kWh m^-³, which is already closer to the energy efficiency of ozonation (EE/O = 0.73-0.084 kWh m^-³).

Persulfate activation by natural zeolite supported nanoscale zero-valent iron for trichloroethylene degradation in groundwater

In the advanced oxidation processes, using persulfate (PS) as a radical precursor for pollutant degradation in groundwater has received increasing attention. In this study, zeolite supported nZVI composites (Z/nZVI) were synthesized through an ion exchange and borohydride reduction method to investigate their ability to activate PS for the TCE degradation. Based on preliminary screening of the PS activation by the Z/nZVI (PS-Z/nZVI) system in terms of TCE degradation, Z/nZVI composite with a zeolite to nZVI mass ratio of 1:1 (Z/nZVI (1)) was optimized as the best composition and chosen for further characterization and examination. Especially, for this PS-Z/nZVI system, PS concentration, solution matrix effects (i.e., solution pH, coexisting anions and natural organic matter) were studied. Characterization results revealed that the aggregation of nZVI particles was alleviated and they were good dispersed on the zeolite sheet with a large SSA (159.49 m²/g) compared to the unsupported nZVI (8.77 m²/g). The synthesized Z/nZVI (1) composite exhibited excellent activated ability towards PS (1.5 mM) and effectively degraded 98.8% of TCE at pH 7 within 120 min. The PS-Z/nZVI system was observed to operate effectively over a wide range of pH (i.e., 4-7) for TCE degradation. Moreover, the presence of nitrates (1 mM) and bicarbonates (10 mM) decreased the TCE degradation efficiency to 91.5% and 59.6%, respectively. Scavenger tests demonstrated that both sulfate and hydroxyl radicals participated in the TCE degradation. The ion chromatography analysis suggested the formation of oxalic acid and formic acid as the reaction intermediates during the TCE degradation process in the PS-Z/nZVI system.

The individual and Co-exposure degradation of benzophenone derivatives by UV/H2O2 and UV/PDS in different water matrices

Benzophenone derivatives, including benzophenone-1 (C₁₃H₁₀O₃, BP1), benzophenone-3 (C₁₄H₁₂O₃, BP3) and benzophenone-8 (C₁₄H₁₂O₄, BP8), that used as UV filters are currently viewed as emerging contaminants. Degradation behaviors on co-exposure benzophenone derivatives using UV-driven advanced oxidation processes under different aqueous environments are still unknown. In this study, the degradation behavior of mixed benzophenone derivatives via UV/H₂O₂ and UV/peroxydisulfate (PDS), in different water matrices (surface water, hydrolyzed urine and seawater) were systematically examined. In surface water, the attack of BP3 by hydroxyl radicals (HO∙) or carbonate radicals (CO₃^∙-) in UV/H₂O₂ can generate BP8, which was responsible for the relatively high degradation rate of BP3. Intermediates from BP3 and BP8 in UV/PDS were susceptible to CO₃^∙-, bringing inhibition of BP1 degradation. In hydrolyzed urine, Cl^- was shown the negligible effect for benzophenone derivatives degradation due to low concentration of reactive chlorine species (RCS). Meanwhile, BP3 abatement was excessively inhibited during co-exposure pattern. In seawater, non-first-order kinetic behavior for BP3 and BP8 was found during UV/PDS treatment. Based on modeling, Br^- was the sink for HO∙, and the co-existence of Br^- and Cl^- was the sink for SO₄^∙-. The cost-effective treatment toward target compounds removal in different water matrices was further evaluated using EE/O. In most cases, UV/H₂O₂ process is more economically competitive than UV/PDS process.

Further insights into the combination of permanganate and peroxymonosulfate as an advanced oxidation process for destruction of aqueous organic contaminants

Recent studies have reported a novel advanced oxidation process (AOP) by combining permanganate (KMnO₄) and peroxymonosulfate (PMS) for destruction of organic contaminants (i.e., acid orange 7, trichloroethylene, and benzene), where hydroxyl (^•OH) and sulfate radicals (SO₄^•-) are proposed to be generated from PMS activation by amorphous manganese dioxide (MnO₂) formed in situ from KMnO₄ reduction. In this work, appreciable degradation of p-chlorobenzoic acid (p-CBA) was confirmed in KMnO₄/PMS system, while KMnO₄ or PMS alone showed inert reactivity toward p-CBA. Moreover, it was found that pre-synthesized amorphous MnO₂ showed invalid PMS activation for p-CBA degradation, and pre-addition of inorganic or organic reducing agents to promote the formation of amorphous MnO₂ showed negligible influence on p-CBA degradation as well. In these regards, a tentative mechanism for PMS activation by KMnO₄ rather than its product MnO₂ was proposed, involving the substitution of oxo atoms of KMnO₄ by peroxo groups, subsequent reductive generation of peroxomanganese (VI) complexes, and intramolecular disproportionation of these complexes to generate radicals. Efficient degradation of p-CBA was achieved at acid or basic conditions with a maximum rate occurring at pH 3. The coexisting chloride anions showed suppressive effect on p-CBA degradation for scavenging SO₄^•- and ^•OH, while metal ions accelerated the degradation of p-CBA, possibly due to the cation bridging function between negatively-charged MnO₄^- and HSO₅^-. Hydroxylated intermediates of p-CBA were identified in KMnO₄/PMS system. This work improved the fundamental understanding of a new class of AOPs by combining KMnO₄ and PMS for environmental decontamination.

Evaluation of amicarbazone toxicity removal through degradation processes based on hydroxyl and sulfate radicals

The herbicide amicarbazone (AMZ), which appeared as a possible alternative to atrazine, presents moderate environmental persistence and is unlikely to be removed by conventional water treatment techniques. Advanced oxidation processes (AOPs) driven by ^•OH and/or SO₄^•- radicals are then promising alternatives to AMZ-contaminated waters remediation, even though, in some cases, they can originate more toxic degradation products than the parent-compound. Therefore, assessing treated solutions toxicity prior to disposal is of extreme importance. In this study, the toxicity of AMZ solutions, before and after treatment with different ^•OH-driven and SO₄^•--driven AOPs, was evaluated for five different microorganisms: Vibrio fischeri, Chlorella vulgaris, Tetrahymena thermophila, Escherichia coli, and Bacillus subtilis. In general, the toxic response of AMZ was greatly affected by the addition of reactants, especially when persulfate (PS) and/or Fe(III)-carboxylate complexes were added. The modifications of this response after treatment were correlated with AMZ intermediates, which were identified by mass spectrometry. Thus, low molecular weight by-products, resulting from fast degradation kinetics, were associated with increased toxicity to bacteria and trophic effects to microalgae. These observations were compared with toxicological predictions given by a Structure-Activity Relationships software, which revealed to be fairly compatible with our empirical findings.

Development of Fe-doped g-C3N4/graphite mediated peroxymonosulfate activation for degradation of aromatic pollutants via nonradical pathway

A new composite catalyst, i.e., Fe doped g-C₃N₄/graphite (Fe-CN/G), was successfully constructed to activate peroxymonosulfate (PMS) for efficient phenolic compounds (i.e., p-chlorophenol, 4-CP) degradation in the pH range of 3-10. The optimized Fe-CN/G, i.e., Fe_3.75-CN/G_5.0, was fabricated at the dosage of 3.75 mmol FeCl₃·6H₂O, 5.0 g dicyandiamide, and 5.0 mmol glucose. Fe complexed in the nitrogen pots of Fe_3.75-CN/G_5.0 was demonstrated to be the primary active site for PMS activation, and the introduction of graphite favored the exposure of more accessible active sites in Fe_3.75-CN/G_5.0, suggesting a synergistic effect between the Fe and graphite of Fe_3.75-CN/G_5.0 on 4-CP degradation. Multiple experiments confirmed that sulfate radical (SO₄^-), hydroxyl radical (HO), singlet oxygen (¹O₂) and superoxide radical (O₂^-) exerted negligible contribution on 4-CP degradation. The in-situ Fe K-edge X-ray absorption near-edge structure (XANEX) analysis revealed a redox cycle of Fe in PMS/Fe_3.75-CN/G_5.0, suggesting the formation of high-valent iron-oxo species (Fe^IVO) was responsible for 4-CP degradation. In addition, PMS/Fe_3.75-CN/G_5.0 exhibited acceptable degradation of 4-CP in the presence of coexisting anions and natural organic matters (NOM). We believe this study provides new insights into the design and development of Fe-based heterogeneous catalysts for PMS-based wastewater treatment.

Degradation of UV Filter Ethyl 4-Aminobenzoate (Et-PABA) Using a UV-Activated Persulfate Oxidation Process

In this paper, the ultraviolet/persulfate (UV/PDS) combined oxidation process was used to remove the ethyl 4-aminobenzoate (Et-PABA), one of the typical 4-aminobenzoic acid (PABA)-type UV filters. The effects of various factors on the removal of Et-PABA using the UV/PDS process were investigated, and the degradation mechanisms of Et-PABA were explored. The results showed that the UV/PDS process can effectively remove 98.7% of Et-PABA within 30 min under the conditions: UV intensity of 0.92 mW·cm−2, an initial concentration of Et-PABA of 0.05 mM, and a PDS concentration of 2 mM. The removal rate of Et-PABA increased with the increase in PDS dosage within the experimental range, whereas humic acid (HA) had an inhibitory effect on Et-PABA removal. Six intermediates were identified based on HPLC–MS and degradation pathways were then proposed. It can be foreseen that the UV/PDS oxidation process has broad application prospects in water treatment.

Intensification of UV-C tertiary treatment: Disinfection and removal of micropollutants by sulfate radical based Advanced Oxidation Processes

This study explores the enhancement of UV-C tertiary treatment by sulfate radical based Advanced Oxidation Processes (SR-AOPs), including photolytic activation of peroxymonosulfate (PMS) and persulfate (PS) and their photocatalytic activation using Fe(II). Their efficiency was assessed both for the inactivation of microorganisms and the removal or micropollutants (MPs) in real wastewater treatment plant effluents. Under the studied experimental range (UV-C dose 5.7-57 J/L; UV-C contact time 3 to 28 s), the photolysis of PMS and PS (0.01 mM) increased up to 25% the bacterial removal regarding to UV-C system. The photolytic activation of PMS led to the total inactivation of bacteria (≈ 5.70 log) with the highest UV-C dose (57 J/L). However, these conditions were insufficient to remove the MPs, being required oxidant's dosages of 5 mM to remove above 90% of carbamazepine, diclofenac, atenolol and triclosan. The best efficiencies were achieved by the combination of PMS or PS with Fe(II), leading to the total removal of the MPs using a low UV-C dosage (19 J/L), UV-C contact time (9 s) and reagent's dosages (0.5 mM). Finally, high mineralization was reached (>50%) with photocatalytic activation of PMS and PS even with low reagent's dosages.

Degradation of metronidazole by UV/chlorine treatment: Efficiency, mechanism, pathways and DBPs formation

Metronidazole (MET) is a widely used antibiotic but is recalcitrant in aquatic environment. This study investigated elimination of MET by UV/chlorine process systematically. The degradation of MET in the process well fitted pseudo first-order kinetics. Decreasing pH from 9 to 5 raised the rate constant from 0.0199 min^-1 to 0.1485 min^-1, possibly ascribed to change in species distribution and apparent quantum yields of radicals. Scavenging experiments indicated that both HO and Cl contributed to the degradation of MET, and that HO was the dominant species in the pH range studied. The second-order rate constant between Cl and MET was determined to be (5.64 ± 0.1) × 10⁹ M^-1 s^-1. Three products were identified by UPLC-Q-TOF MS and degradation pathway was thus proposed. Significant amounts of chlorinated disinfection by-products (DBPs) were produced and 1,1,1-TCP was the dominant (83.6%-92.3%) in the UV/chlorine process. The kinetic model developed fitted well with experimental results, and was used to examine the effects of typical water parameters, such as chorine dosage, pH, inorganic anions, NOM and real water matrix. Furthermore, removal efficiency of MET by the UV/chlorine process were assessed in terms of electrical energy per order (EE/O). The efficiency was about 0.43 kWh m^-3 order^-1, 0.54 kWh m^-3 order^-1, 0.57 kWh m^-3 order^-1, respectively, for the removal of MET in ultrapure water (UPW) and two types of real water samples, indicating that UV/chorine was a practical method for authentic drinking water treatment practices.

Mechanism and Kinetic Analysis of Degradation of Atrazine by US/PMS

The degradation effect, degradation mechanism, oxidation kinetics, and degradation products of Atrazine (ATZ) by Ultrasound/Peroxymonosulfate (US/PMS) in phosphate buffer (PB) under different conditions were studied. It turned out that the degradation rate of US/PMS to ATZ was 45.85% when the temperature of the reaction system, concentration of PMS, concentration of ATZ, ultrasonic intensity, and reaction time were 20 °C, 200 μmol/L, 1.25 μmol/L, 0.88 W/mL, and 60 min, respectively. Mechanism analysis showed that PB alone had no degradation effect on ATZ while PMS alone had extremely weak degradation effect on ATZ. HO• and SO₄⁻• coexist in the US/PMS system, and the degradation of ATZ at pH7 is dominated by free radical degradation. Inorganic anion experiments revealed that Cl⁻, HCO₃⁻, and NO₃⁻ showed inhibitory effects on the degradation of ATZ by US/PMS, with Cl⁻ contributing the strongest inhibitory effect while NO₃⁻ showed the weakest suppression effect. According to the kinetic analysis, the degradation kinetics of ATZ by US/PMS was in line with the quasi-first-order reaction kinetics. ETA with concentration of 1 mmol/L reduced the degradation rate of ATZ by US/PMS to 10.91%. Product analysis indicated that the degradation of ATZ by US/PMS was mainly achieved by dealkylation, dichlorination, and hydroxylation, but the triazine ring was not degraded. A total of 10 kinds of ATZ degradation intermediates were found in this experiment.

Performance and properties of coking nanofiltration concentrate treatment and membrane fouling mitigation by an Fe(ii)/persulfate-coagulation-ultrafiltration process

Coking nanofiltration (NF) concentrates, as typical wastewater with high salinity and refractory organics, have become one of the greatest challenges for "near-zero emission" processes. In our study, an advanced oxidation technology based on ferrous iron/persulfate (Fe(ii)/PS) and polyferric sulfate (PFS) coagulation coupled with ultrafiltration (UF) was used to treat NF concentrates and mitigate membrane fouling. Based on batch experiments, the optimal parameters of Fe(ii)/PS were obtained, during which we discovered that the slow reaction stage of total organic carbon (TOC) removal followed first-order degradation kinetics. Under the optimal reaction conditions, Fe(ii)/PS could efficiently mineralize 69% of organics in coking NF concentrates. In order to eliminate the iron floc generated in the Fe(ii)/PS step, a small amount of PFS (0.05 mM) was added to coagulate the iron floc, which could further improve the effluent quality so that the turbidity, iron content and TOC were significantly reduced by 79.18%, 98% and 21.79% respectively. Gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOFMS) and fluorescence excitation-emission matrix spectrometry (EEM) were performed to characterize the removal of phenols, PAHs, quinolines and humic acids in NF concentrates which were responsible for UF membrane fouling. Moreover, scanning electronic microscopy (SEM) and atomic force microscopy (AFM) were conducted to study the surface of the UF membrane after treatment of NF concentrates. The result exhibited that the organic pollutants deposited on the UF membrane surface were reduced by Fe(ii)/PS-PFS pretreatment, and UF membrane flux was thus enhanced. Our results show the potential of the approach of applying Fe(ii)/PS-PFS-UF in NF concentrate treatment.

Degradation of typical macrolide antibiotic roxithromycin by hydroxyl radical: kinetics, products, and toxicity assessment

The degradation of roxithromycin (ROX) by hydroxyl radical (·OH) generated by UV/H₂O₂ was systematically investigated in terms of degradation kinetics, effects of water chemistry parameters, oxidation products, as well as toxicity evaluation. The degradation of ROX by UV/H₂O₂ with varying light irradiation intensity, initial ROX concentration, and H₂O₂ concentration in pure water and wastewater all followed pseudo-first-order kinetics. The second-order rate constant for reaction between ROX and ·OH is 5.68 ± 0.34 × 10⁹/M/s. The degradation rate of ROX increased with the pH; for instance, the apparent degradation rates were 0.0162 and 0.0309/min for pH 4 and pH 9, respectively. The presence of natural organic matter (NOM) at its concentrations up to 10 mg C/L did not significantly affect the removal of ROX. NO₃^- and NO₂^- anions inhibited the degradation of ROX due to the consumption of ·OH in reactions with these ions. Fe³⁺, Cu²⁺, and Mg²⁺ cations inhibited the degradation of ROX, probably because of the formation of ROX-metal chelates. A total of ten degradation products were tentatively identified by HPLC/LTQ-Orbitrap XL MS, which mainly derived from the attack on the oxygen linking the lactone ring and the cladinose moiety, tertiary amine and oxime side chain moiety by ·OH. The toxicity evaluation revealed that UV/H₂O₂ treatment of ROX induced the toxicity to bioluminescent bacteria increased.

Degradation of iopamidol by three UV-based oxidation processes: Kinetics, pathways, and formation of iodinated disinfection byproducts

In this study, the degradation kinetics of iopamidol (IPM) by three different UV-based oxidation processes including UV/hydrogen peroxide (H₂O₂), UV/persulfate (PDS) and UV/chlorine (NaClO) were examined and the potential formation of iodinated disinfection byproducts (I-DBPs) in these processes followed by sequential chlorination was comparatively investigated. Increasing pH led to the decrease of IPM degradation rate in UV/NaClO, while it showed negligible impact in UV/PDS and UV/H₂O₂. Common background constituents such as chloride ions (Cl^-), carbonate (HCO₃^-) and natural organic matter (NOM) inhibited IPM degradation in UV/H₂O₂ and UV/PDS, while IPM degradation in UV/NaClO was only suppressed by NOM but not Cl^- and HCO₃^-. The differences in transformation products of IPM treated by hydroxyl radical (HO*), sulfate radical (SO₄*^-), as well as Cl₂*^- and ClO* generated in these processes, respectively, were also analyzed. The results suggested that hydroxyl radical (HO*) preferred to form hydroxylated derivatives. Sulfate radical (SO4*-) preferred to oxidize amino group of IPM to nitro group, while Cl₂*^- and ClO* favored the generation of chlorine-containing products. Moreover, specific I-DBPs (i.e., iodoform (IF) and monoiodacetic acid (MIAA)) were detected in the three processes followed by chlorination. The addition of NOM had little effect on IF formation of three processes, while MIAA formation decreased in all processes except UV/H₂O₂. Given that the formation of I-DBPs in UV/NaClO was less than those formed in the other two processes, UV/NaClO seems to be a more promising strategy for effectively removing IPM with alleviation of I-DBPs in treated water effluents.

Dechlorination-Hydroxylation of Atrazine to Hydroxyatrazine with Thiosulfate: A Detoxification Strategy in Seconds

Hydroxylation of atrazine to nontoxic hydroxyatrazine is generally considered an efficient detoxification method to remediate atrazine-contaminated soil and water. However, previous studies suggested that hydroxylation was not the dominant pathway for atrazine degradation in the hydroxyl radical-generating systems such as Fenton reaction, ozonation and UV/H₂O₂. Herein we report that the addition of sodium thiosulfate can realize rapid hydroxylation of atrazine to hydroxyatrazine at pH ≤ 4 under room temperature. High resolution mass spectra and isotope experiments results revealed that the hydroxylation of atrazine was involved with nucleophilic substitution and subsequent hydrolysis reaction as follows. HS₂O₃^-, as a species of thiosulfate only at pH ≤ 4, first attacked C atom connecting to chlorine of atrazine to dechlorinate atrazine and produce C₈H₁₄N₅S₂O₃^-. Subsequently, the S-S bond of C₈H₁₄N₅S₂O₃^- was cleaved easily to form SO₃ and C₈H₁₄N₅S^-. Next, C₈H₁₄N₅S^- was hydrolyzed to generate hydroxyatrazine and H₂S. Finally, the comproportionation of SO₃ and H₂S in situ produced S⁰ during hydroxylation of atrazine with thiosulfate. This study clarifies the importance of degradation pathway on the removal of pollutants, and also provides a nonoxidative strategy for atrazine detoxification in seconds.

Effects of water matrices on the degradation of naproxen by reactive radicals in the UV/peracetic acid process

The UV/peracetic acid (UV/PAA) process as a novel advanced oxidation process has been reported to produce carbon-centered radicals (RC•) for Naproxen (NAP) degradation, which is a representative of naphthyl structure substances. Real water matrices, such as carbonate and bicarbonate ions (CO₃^2-/HCO₃^-), humic acid (HA), and chloride ion (Cl^-), may react with these reactive radicals and change their contributions to NAP degradation. The results showed that RC• contributed 60.8% and •OH contributed 39.2% to NAP degradation in pure water by a competition method. CO₃^2-/HCO₃^- (0-20 mM) showed minimal effect on NAP degradation in the UV/PAA process, meanwhile, it has observable inhibition effect on NAP degradation in the UV/H₂O₂ process (mainly of •OH) and minimal effect in the UV/PAA process with tert-butanol (TBA) (mainly of RC•). Results suggested that CO₃^2-/HCO₃^- could react with •OH yielding CO₃•^- with low reactivity to NAP, CO₃•^- could further react with PAA to produce RC•. This speculation was confirmed by the increased contribution of RC• to NAP degradation with the increase of CO₃^2-/HCO₃^- concentration through the competition method. HA (0-5 mg/L) had a higher scavenging capacity for RC• than •OH because HA with naphthyl structure was likely to be attacked by RC•. Cl^- (0-200 mM) had little effect on NAP degradation in the UV/PAA and UV/H₂O₂ processes, while exerted an observable inhibition on NAP degradation in the UV/PAA process with TBA. This finding suggested that Cl^- could react with RC• to produce Cl•, which could further convert into HOCl•^-, and then excess •OH was formed. The new knowledge on the conversion of reactive radicals obtained in this study provides an important basis for facilitating further research on the UV/PAA advanced oxidation.

Simultaneous atrazine degradation and E. coli inactivation by UV/S2O82-/Fe2+ process under KrCl excilamp (222 nm) irradiation

This study is the first to reveal that the iron-catalyzed photo-activation of persulfate (UV/PS/Fe²⁺system) under mercury-free KrCl excilamp irradiation (222 nm) is capable of simultaneous degradation of an organic pollutant and inactivation of a microorganism in aqueous media using the herbicide atrazine (ATZ) and E. coli as model contaminants, respectively. Deionized water, natural water and wastewater effluents, contaminated with 4 mg/L ATZ and/or 10⁵ CFU/mL E. coli, were sequentially treated by direct UV, UV/PS and UV/PS/Fe²⁺ processes. Lowering the pH to 3.5 accelerated both the degradation and inactivation during the UV/PS/Fe²⁺ treatment of natural water. Comparison of the apparent UV dose-based pseudo first-order rate constants showed the negative effect of E. coli on ATZ degradation by decreasing rates in all of the examined water matrices. This can be due to the competitive effect between ATZ and bacterial cells for reactive oxygen species (ROS). By contrast, E. coli in the presence of ATZ was inactivated faster in natural water and wastewater (but not in deionized water), as compared to the case without ATZ. A scheme of possible synergistic inactivation under ROS exposure in water, containing ATZ, natural organic matter and chloride ions as primary constituents, was proposed. Radical scavenging experiments showed a major contribution of SO₄•^- to ATZ degradation by UV/PS/Fe²⁺ treatment of deionized water and natural water. The UV doses, required for 90% removal of ATZ from natural water and wastewater, achieve 160 mJ/cm² (pH 5.5) and concurrently provide 99.99% E. coli inactivation. These results make the UV/PS/Fe²⁺ system with narrow band UV light sources promising for simultaneous water treatment and disinfection.

Key structural features promoting radical driven degradation of emerging contaminants in water

Diverse contaminants of emerging concern (CECs) can be found in nowadays aquatic environment, possessing high potential to cause adverse ecological and human health effects. Due to their recalcitrance, conventional water treatment methods are shown to be inadequately effective. Thus, their upgrade by advanced oxidation processes, involving the generation of highly reactive species (HO and SO₄^-), is highly demanded. In order to assess the susceptibility of CECs by HO and SO₄^-, as well as to determine the corresponding reaction rate constants k_HO and k_SO4^-, the complex experimental studies has to be maintained. The alternative is the application of modeling approaches which correlate structural characteristics with activities/properties of interest, i.e. quantitative structure activity/property relationship (QSAR/QSPR). In this study k_HO and k_SO4^- of fifteen selected CECs were determined by competitive kinetics, and afterward used to elucidate key structural features promoting their degradation. In that purpose, QSPR models were constructed using multiple linear regression (MLR) combined with genetic algorithm (GA) approach. The models were submitted to the internal and external validation (using additional set of 17 CECs). Selected 3-variable models predicting k_HO and k_SO4^- were characterized with high accuracy and predictivity (R² = 0.876 and Q² = 0.847 and R² = 0.832 and Q² = 0.778, respectively). Although selected models at the first sight include descriptors derived through complicated calculation procedures, their weighting schemes indicate on their relevance and transparency toward established reaction theories and differences regarding radical type.

Enhanced mineralization of atrazine by surface induced hydroxyl radicals over light-weight granular mixed-quartz sands with ozone

A light-weight granular mixed-quartz sand (denoted as L-GQS) combined with stirring-assisted bubble column reactor was firstly applied in catalytic ozonation of atrazine. The L-GQS, with a density of 2.36 g cm^-3 and average diameter of ca. of 4 mm, was readily churned up and uniformly distributed within the solution in the reactor. The introduction of L-GQS was found to exhibit enhanced catalytic ozonation of atrazine, with the increase in degradation rate and the dissolved organic carbon (DOC) removal being more than 2-fold for the catalytic process (L-GQS dosage = 5 g L^-1, [atrazine]₀ = 50 μM, [O₃] = 25 mg L^-1, gas flow = 0.2 L min^-1, at pH 7.0 and 293 K). The L-GQS settled at the bottom of the reactor after experimentation, allowing its easy separation from the solution. A complete characterization of the material (XRD, XPS, FTIR, FE-SEM/EDS, BET and pH_pzc) revealed that L-GQS consisted of α-quartz, β-cristobalite, anorthoclase and small amount of iron oxy-hydroxides. Hydroxyl groups, Bronsted acid sites and Lewis acid sites on the surface of L-GQS all contributed to the atrazine adsorption, ozone decomposition and ·OH generation. The L-GQS catalyzed ozonation exhibited superior atrazine degradation and mineralization rates in a wide range of pH (3.0-9.0) and reaction temperatures (278 K-293 K). Also, an enhancement of DOC abatement was observed both in presence of natural organic matter isolates and natural water matrices (river water) when L-GQS was used. Finally, the degradation mechanism was proposed, based on the intermediates and by-products formation analyzed by LC-QTOF-MS/MS and ionic chromatography. Our results indicate that the L-GQS combined with stirring-assisted bubble column reactor could be utilized as an enhancement of ozone-based advanced oxidation processes.

Removal of micropollutants from water in a continuous-flow electrical discharge reactor

The emergence of micropollutants into our aquatic resources is regarded as an issue of increasing environmental concern. To protect the aquatic environment against further contamination with micropollutants, treatment with advanced oxidation processes (AOPs) is put forward as a promising technique. In this work, an innovative AOP based on electrical discharges in a continuous-flow pulsed dielectric barrier discharge (DBD) reactor with falling water film over activated carbon textile is examined for its potential application in water treatment. The effect of various operational parameters including feed gas type, gas flow rate, water flow rate and power on removal and energy efficiency has been studied. To this end, a synthetic micropollutant mixture containing five pesticides (atrazine, alachlor, diuron, dichlorvos and pentachlorophenol), two pharmaceuticals (carbamazepine and 1,7-α-ethinylestradiol), and 1 plasticizer (bisphenol A) is used. While working under optimal conditions, energy consumption was situated in the range 2.42-4.25 kW h/m³, which is about two times lower than the economically viable energy cost of AOPs (5 kW h/m³). Hence, the application of non-thermal plasma could be regarded as a promising alternative AOP for (industrial) wastewater remediation.

Oxidative Degradation of Tannic Acid in Aqueous Solution by UV/S2O82− and UV/H2O2/Fe2+ Processes: A Comparative Study

Tannic acid (TA) is a major pollutant present in the wastewater generated from vegetable tanneries process and food processing. This work studied TA degradation by two advanced oxidation processes (APOs): UV irradiation at the wavelength of 254 nm in the presence of hydrogen peroxide (H2O2) and ferrous iron (photo-Fenton) and in the presence of potassium persulfate. The influence of certain experimental parameters such as K2S2O8, H2O2, Fe2+, and TA concentrations, initial pH and temperature was evaluated in order to obtain the highest efficiency in terms of aromatics (decay in UV absorbance at 276 nm) and TOC removals. Chemical oxidation of TA (0.1 mM) by UV/persulfate achieved 96.32% of aromatics removal and 54.41% of TOC removal under optimized conditions of pH = 9 and 53.10 mM of K2S2O8 after 60 min. The treatment of TA by photo-Fenton process successfully led to almost complete aromatics removal (99.32%) and high TOC removal (94.27%) from aqueous solutions containing 0.1 mM of TA at natural pH = 3 using 29.4 mM of H2O2 and 0.18 mM of Fe2+ at 25 °C after 120 min. More efficient degradation of TA by photo-Fenton process than UV/persulfate was obtained, which confirms that hydroxyl radicals are more powerful oxidants than sulfate radicals. The complete removal of organic pollution from natural waters can be accomplished by direct chemical oxidation via hydroxyl radicals generated from photocatalytic decomposition of H2O2.

Mechanisms and toxicity evaluation of the degradation of sulfamethoxazole by MPUV/PMS process

In this work, a sulfate radical (SO4-)-based advanced oxidation process was applied to the degradation of sulfamethoxazole (SMX). In these experiments, a medium pressure UV (MPUV) lamp was employed to active peroxymonosulfate (PMS). It was found that 98% of SMX was removed by MPUV/PMS at a UV dose of 200 mJ cm-2 (3.95 μM SMX, 0.2 mM PMS, pH0 = 3.7). Direct MPUV photolysis played a remarkable role in SMX removal by MPUV/PMS process. As for the indirect photolysis, SO4- was the major reactive species under acidic and neutral conditions in MPUV/PMS system, while the hydroxyl radical (OH) became the predominant radical under alkaline conditions. The transformation products (TPs) of SMX that formed in the MPUV-only and MPUV/PMS experiments were identified, and the possible degradation pathways were proposed. Photoisomerization of the isoxazole ring was the major pathway of SMX during MPUV-only process. Hydroxylation/oxidation of the aniline and isoxazole ring was the predominant degradation mechanism of SMX by MPUV/PMS. Toxicity evaluation showed that MPUV/PMS was effective at reducing the antibacterial activity of SMX solutions, while MPUV-only was not. However, some TPs with equivalent or even higher antibacterial activity than SMX were formed during the initial degradation period in MPUV/PMS system. Ecotoxicity of SMX and its TPs was also hypothetically predicted via the ECOSAR program, and the results indicated that some TPs could be more toxic than SMX.

Oxidation of fluoroquinolone antibiotics by peroxymonosulfate without activation: Kinetics, products, and antibacterial deactivation

While fluoroquinolone (FQ) antibiotics are susceptible to degradation by sulfate and/or hydroxyl radicals formed in peroxymonosulfate (PMS) based advanced oxidation processes, here we report that unactivated PMS itself exhibits a specific high reactivity toward FQs for the first time. Reaction kinetics of PMS with two model FQs, ciprofloxacin (CF) and enrofloxacin (EF), showed a strong pH dependency with apparent second-order rate constants of 0.10-13.05 M^-1s^-1 for CF and 0.51-33.17 M^-1s^-1 for EF at pH 5-10. This pH dependency was well described by species-specific parallel reactions. On the basis of reaction kinetics and structure-activity assessment, the tertiary and secondary aliphatic N4 amines on the FQs' piperazine ring were proposed to be the main reaction sites. High performance liquid chromatography/electrospray ionization tandem mass analysis showed the formation of hydroxylated, N-oxide, and dealkylated products. Bacterial growth inhibition bioassays using Escherichia coli showed that oxidation products of FQs by PMS retained negligible antibacterial potency in comparison to parent FQs. Kinetic modeling using the rate constants estimated from pure water well predicted the oxidation kinetics of low levels of CF and EF by PMS in surface water. The degradation efficiency of FQs by PMS in surface water was slightly lower than that by ozone, comparable to that by ferrate, and much higher than that by permanganate. These results suggest that PMS is a promising oxidant for the treatment of FQs in water.

Effect of sulfate radical-based oxidation pretreatments for mitigating ceramic UF membrane fouling caused by algal extracellular organic matter

Algal extracellular organic matter (EOM) released from Microcystis aeruginosa can cause severe membrane fouling during algae-laden water treatment. To solve this problem, three typical sulfate radical-based advanced oxidation processes (SR-AOPs), i.e., ferrous iron/peroxymonosulfate (Fe(II)/PMS), UV/PMS and UV/Fe(II)/PMS, were employed as membrane pretreatment strategies. Their performance on mitigating EOM fouling of a ceramic UF membrane was systematically investigated and compared in the present study. The results indicated that SR-AOPs pretreatments could promote the reduction of DOC and UV₂₅₄, and the removal performance showed an apparent regularity of UV/Fe(II)/PMS > Fe(II)/PMS > UV/PMS. The pretreatments were very effective for decomposing high-MW biopolymers (>20,000 Da) into low-MW humic substances (1000-20,000 Da), thus reducing the accumulation of high-MW biopolymers on membrane surface. With respect to membrane fouling control, Fe(II)/PMS significantly mitigated both reversible and irreversible membrane fouling, whereas UV/PMS only reduced reversible fouling, and exhibited little effect on irreversible fouling. By contrast, UV/Fe(II)/PMS showed the best performance for fouling reduction due to the synergistic effect of UV and Fe(II) for PMS activation. The dominating fouling mechanism was governed by both pore blockage and cake filtration, likely due to the bimodal MW distribution of EOM, and SR-AOPs pretreatments delayed the transition from pore blockage to cake filtration. In addition, SR-AOPs prior to UF membrane were also very effective to improve the removal of micropollutants (i.e., ATZ, SMT and p-CNB). These results demonstrate the potential application of SR-AOPs as pretreatment for membrane fouling control during algae-laden water treatment.

Is Sulfate Radical Really Generated from Peroxydisulfate Activated by Iron(II) for Environmental Decontamination?

It is well documented that the traditional Fenton reagent (i.e., the combination of Fe(II) and H₂O₂) produces hydroxyl radical (^•OH) under acidic conditions, while at near-neutral pH the reactive intermediate converts to ferryl ion (Fe(IV)) that can oxidize sulfoxides to produce corresponding sulfones, markedly differing from their ^•OH-induced products. However, it remains unclear whether Fe(IV) is generated in the Fe(II) activated peroxydisulfate (PDS) process, where sulfate radical (SO₄^•-) is long recognized as the dominant intermediate in literature. Here we demonstrated that SO₄^•- oxidized methyl phenyl sulfoxide (PMSO, a model sulfoxide) to produce biphenyl compounds rather than methyl phenyl sulfone (PMSO₂). Interestingly, the formation of PMSO₂ was observed when PMSO was treated by the Fe(II)/PDS system over a wide pH range, and the yields of PMSO₂ were quantified to be ∼100% at acidic pH 3-5. The identification of Fe(IV) in the Fe(II)/PDS system could also reasonably explain the literature results on alcohol scavenging effect and ESR spectra analysis. Further, a Fe(IV)-based kinetic model was shown to accurately simulate the experimental data. This work urges re-evaluation of the Fe(II)/PDS system for environmental decontamination, given that Fe(IV) would have different reactivity toward environmental contaminants compared with SO₄^•- and/or ^•OH.

Efficient degradation of imipramine by iron oxychloride-activated peroxymonosulfate process

Synthesized iron oxychloride (FeOCl) was firstly applied to activate peroxymonosulfate (PMS) to degrade imipramine (IMI), a tricyclic antidepressant. Compared to some other Fe-based materials including zero valent iron, Fe₂O₃, Fe₃O₄ and ferric ions, FeOCl presented an impressive catalytic activity on PMS at near-neutral condition due to its unique structure containing abundant unsaturated iron atoms and oxo-bridged configuration. With an increase of FeOCl dose, PMS dose or initial pH in ranges of 0.02 - 0.5 g/L, 0.1 - 2.5 mM and 4.0 - 8.0, the degradation efficiency of IMI was effectively raised by 64.0%, 48.5% and 50.6%, respectively. The presence of either bicarbonate or chloride stimulated the removal of IMI. Moreover, 70.4% of IMI was degraded under the background of real water with 2 mM PMS. The possible reactive species were identified as sulfate and hydroxyl radicals. The formed hypochlorite through the reaction of PMS and the released chloride ions may also contribute to the degradation of IMI. Among the oxidants, sulfate radical was proven to be the dominate one in the system. Additionally, the FeOCl/PMS system can overall effectively degrade six other organic compounds including amitriptyline, desipramine, propranolol, nitrobenzene, methyl-paraben and ethyl-paraben, further suggesting the possible application of this system in treatment of vast aquatic micro-organic pollutants.

Ferrocene-catalyzed heterogeneous Fenton-like degradation mechanisms and pathways of antibiotics under simulated sunlight: A case study of sulfamethoxazole

Readily-available and efficient catalyst is essential for activating oxidants to produce reactive species for deeply remediating water bodies contaminated by antibiotics. In this study, Ferrocene (Fc) was introduced to establish a heterogeneous photo-Fenton system for the degradation of sulfonamide antibiotics, taking sulfamethoxazole as a representative. Results showed that the removal of sulfamethoxazole was effective in Fc-catalyzed photo-Fenton system. Electron spin resonance and radical scavenging experiments verified that there was a photoindued electron transfer process from Fc to H₂O₂ and dissolved oxygen resulting in the formation of OH that was primarily responsible for the degradation of sulfamethoxazole. The reactions of OH with substructure model compounds of sulfamethoxazole unveiled that aniline moiety was the preferable reaction site of sulfamethoxazole, which was verified by the formation of hydroxylated product and the dimer of sulfamethoxazole in Fc-catalyzed photo-Fenton system. This heterogeneous photo-Fenton system displayed an effective degradation efficiency even in a complex water matrices, and Fc represented a long-term stability by using the catalyst for multiple cycles. These results demonstrate that Fc-catalyzed photo-Fenton oxidation may be an efficient approach for remediation of wastewater containing antibiotics.

Impact of Chloride Ions on UV/H2O2 and UV/Persulfate Advanced Oxidation Processes

Chloride ion (Cl^-) is one of the most common anions in the aqueous environment. A mathematical model was developed to determine and quantify the impact of Cl^- on the oxidization rate of organic compounds at the beginning stage of the UV/persulfate (PS) and UV/H₂O₂ processes. We examined two cases for the UV/PS process: (1) when the target organic compounds react only with sulfate radicals, the ratio of the destruction rate of the target organic compound when Cl^- is present to the rate when Cl^- is not present (designated as r_R^Cl-/ r_R) is no larger than 1.942%; and (2) when the target organic compounds can react with sulfate radicals, hydroxyl radicals and chlorine radicals, r_R^Cl-/ r_R, can be no larger than 60%. Hence, Cl^- significantly reduces the organic destruction rate in the UV/PS process. In the UV/H₂O₂ process, we found that Cl^- has a negligible effect on the organic-contaminant oxidation rate. Our simulation results agree with the experimental results very well. Accordingly, our mathematical model is a reliable method for determining whether Cl^- will adversely impact organic compounds destruction by the UV/PS and UV/H₂O₂ processes.

Influence of process parameters on the effectiveness of photooxidative treatment of pharmaceuticals

In this study, UV-C/H₂O₂ and UV-C/[Formula: see text] processes as photooxidative Advanced oxidation processes were applied for the treatment of seven pharmaceuticals, either already included in the Directive 2013/39/EU "watch list" (17α- ethynylestradiol, 17β-estradiol) or with potential to be added in the near future due to environmental properties and increasing consumption (azithromycin, carbamazepine, dexamethasone, erythromycin and oxytetracycline). The influence of process parameters (pH, oxidant concentration and type) on the pharmaceuticals degradation was studied through employed response surface modelling approach. It was established that degradation obeys first-order kinetic regime regardless structural differences and over entire range of studied process parameters. The results revealed that the effectiveness of UV-C/H₂O₂ process is highly dependent on both initial pH and oxidant concentration. It was found that UV-C/[Formula: see text] process, exhibiting several times faster degradation of studied pharmaceuticals, is less sensitive to pH changes providing practical benefit to its utilization. The influence of water matrix on degradation kinetics of studied pharmaceuticals was studied through natural organic matter effects on single component and mixture systems.

Degradation of atrazine by electrochemically activated persulfate using BDD anode: Role of radicals and influencing factors

A novel advanced oxidation process using boron-doped diamond (BDD) anode to activate persulfate (PS) with low concentration of electrolyte was systematically investigated in this study. Compared to direct electrochemical oxidation of atrazine (ATZ) using BDD anode, the addition and activation of PS significantly declined the demand for electrolytes. It was confirmed by scavenger experiments that both radical and non-radical oxidation occurred in this system. Degradation of ATZ was enhanced with the increase of current density and dosage of PS, and decrease of initial pH. However, the increase of current density can also lead to the decrease of current efficiency, then increase of energy consumption. Besides, the inhibitory effect of anions on the degradation of ATZ followed the order of HCO₃^->H₂PO₄^->NO₃^-, while the presence of Cl^- accelerated the degradation of ATZ. Furthermore, the degradation products mainly resulting from de-alkylation, de-chlorination, and hydroxylation were detected. Due to the distinctive preference to ethyl group in BDD/PS system, the formation of deethyl-atrazine was quicker than that of deisopropyl-atrazine. The study aims to provide a comprehensive understanding on the potential application of BDD/PS system in water treatment.

Degradation of diethyl phthalate (DEP) by UV/persulfate: An experiment and simulation study of contributions by hydroxyl and sulfate radicals

Degradation of diethyl phthalate (DEP) by ultraviolet/persulfate (UV/PS) process at different reaction conditions was evaluated. DEP can be degraded effectively via this process. Both tert-butyl (TBA) and methanol (MeOH) inhibited the degradation of DEP with MeOH having a stronger impact than TBA, suggesting sulfate radical () and hydroxyl radical (HO) both existed in the reaction systems studied. The second-order rate constants of DEP reacting with and HO were calculated to be (6.4±0.3)×10⁷ M^-1s^-1 and (3.7±0.1)×10⁹ M^-1s^-1, respectively. To further access the potential degradation mechanism in this system, the pseudo-first-order rate constants (k_o) and the radical contributions were modeled using a simple steady-state kinetic model involving and HO. Generally, HO had a greater contribution to DEP degradation than . The k_o of DEP increased as PS dosages increased when PS dosages were below 1.9 mM. However, it decreased with increasing initial DEP concentrations, which might be due to the radical scavenging effect of DEP. The k_o values in acidic conditions were higher than those in alkaline solutions, which was probably caused by the increasing concentration of hydrogen phosphate (with higher scavenging effects than dihydrogen phosphate) from the phosphate buffer as pH values rose. Natural organic matter and bicarbonate dramatically suppressed the degradation of DEP by scavenging and HO. Additionally, the presence of chloride ion (Cl^-) promoted the degradation of DEP at low Cl^- concentrations (0.25-1 mM). Finally, the proposed degradation pathways were illustrated.

Degradation of dyes by peroxymonosulfate activated by ternary CoFeNi-layered double hydroxide: Catalytic performance, mechanism and kinetic modeling

Ternary CoFeNi-layered double hydroxide (CoFeNi-LDH) was synthesized and initially applied to activate peroxymonosulfate (PMS) for the degradation of Congo red (CR) and Rhodamine B (RhB). The results show that the CoFeNi-LDH/PMS system can efficiently degrade nearly 100% of 20 mg/L CR or 20 mg/L RhB within 6- and 10-min reaction times, respectively. And the catalyst exhibits higher degradation efficiency on CR than on RhB under identical conditions, which is confirmed by electron clouds of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) performed by DFT calculations. Quenching tests reveal that SO₄^- is the dominant active species participating in the degradation process. Mechanism investigation demonstrates that Co(II)-Co(III)-Co(II) cycle is responsible for activating PMS to generate radicals for dyes degradation. A dynamic kinetic model is successfully developed to simulate the concentration profiles of CR and RhB degradation in CoFeNi-LDH/PMS system. The empirical second order rate constants between SO₄^- and CR (k_SO4-/CR), HO and CR (k_OH/CR), SO₄^- and RhB (k_SO4-/RhB), HO and RhB (k_HO/RhB) are determined to be 2.47 × 10⁷, 3.44 × 10⁶, 8.39 × 10⁶ and 2.62 × 10⁷ M^-1s^-1, respectively. In addition, toxic assessment using ECOSAR program suggests that the overall toxicity of CR and RhB decreased after treatment with CoFeNi-LDH/PMS system. Repeating tests and application of CoFeNi-LDH in different water sources give us adequate confidence that the as-synthesized CoFeNi-LDH is favorable for the purification of dye-contaminanted waters in practical.

The removal of COD and NH3-N from atrazine production wastewater treatment using UV/O3: experimental investigation and kinetic modeling

In this study, a UV/O₃ hybrid advanced oxidation system was used to remove chemical oxygen demand (COD), ammonia nitrogen (NH₃-N), and atrazine (ATZ) from ATZ production wastewater. The removal of COD and NH₃-N, under different UV and O₃ conditions, was found to follow pseudo-first-order kinetics with rate constants ranging from 0.0001-0.0048 and 0.0015-0.0056 min^-1, respectively. The removal efficiency of ATZ was over 95% after 180 min treatment, regardless the level of UV power. A kinetic model was further proposed to simulate the removal processes and to quantify the individual roles and contributions of photolysis, direct O₃ oxidation, and hydroxyl radical (OH·) induced oxidation. The experimental and kinetic modeling results agreed reasonably well with deviations of 12.2 and 13.1% for the removal of COD and NH₃-N, respectively. Photolysis contributed appreciably to the degradation of ATZ, while OH· played a dominant role for the removal of both COD and NH₃-N, especially in alkaline environments. This study provides insights into the treatment of ATZ containing wastewater using UV/O₃ and broadens the knowledge of kinetics of ozone-based advanced oxidation processes.