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The formation of chlorinated by-products is a major concern associated with electrochemical water treatment processes. This study investigated the formation of chlorinated by-products during surface water treatment by a newly developed electrochemical advanced oxidation process (EAOP), the electro-peroxone (E-peroxone) process, which couples ozonation with in situ electro-generation of hydrogen peroxide (H2O2) from cathodic oxygen reduction. Due to the enhanced ozone (O3) conversion to hydroxyl radicals (•OH) by electro-generated H2O2, the E-peroxone process considerably accelerated the abatement of ozone-refractory micropollutants such as clofibric acid and chloramphenicol in the selected surface water compared to conventional ozonation. In addition, the cathodically generated H2O2 effectively quenched hypochlorous acid (HOCl) derived from the anodic oxidation of chloride in the surface water. Therefore, the formation of trichloromethane (TCM) and chloroacetic acids (CAAs) from the reactions of HOCl with dissolved organic matter (DOM) was insignificant during the E-peroxone process, and similar levels of TCM and CAAs were generally observed in the conventional ozonation and E-peroxone treated water. In contrast, considerable amounts of HOCl could be generated from the anodic oxidation of chloride and then accumulated in the surface water during conventional electrolysis process, which resulted in significantly higher concentrations of TCM and CAAs in the electrolysis treated water. The results of this study suggest that the E-peroxone process can overcome the major limitation of conventional electrochemical processes and provide an effective and safe EAOP alternative for micropollutant abatement during water treatment.

The electro-peroxone (E-peroxone) process is an emerging ozone-based advanced oxidation process (AOP) that has shown large potential for micropollutant abatement in water treatment. To evaluate its performance under more realistic conditions of water treatment, a continuous-flow pilot E-peroxone system was developed and compared with conventional ozonation and a UV/O3 process for micropollutant abatements in various water matrices (groundwater, surface water, and secondary wastewater effluent) in this study. With a specific ozone dose of 1.5 mg O3/mg DOC, micropollutants that have high and moderate reactivity with ozone (O3) (diclofenac, naproxen, gemfibrozil, and bezafibrate) could be sufficiently abated (>90% abatement) in the various waters by all three processes. However, ozone-resistant micropollutants (ibuprofen, clofibric acid, and chloramphenicol) were abated only by ∼32–68%, 68–91%, and 73–90% during conventional ozonation of the selected groundwater, surface water, and secondary wastewater effluent, respectively. By electro-generating H2O2 or applying UV irradiation to enhance O3 transformation to •OH during ozonation, the E-peroxone and UV/O3 processes similarly enhanced the abatement efficiencies of ozone-resistant micropollutants by ∼15–43%, ∼5–15%, and ∼5–10% in the groundwater, surface water, and secondary wastewater effluent, respectively. In addition, the E-peroxone and UV/O3 processes significantly reduced bromate formation during the treatment of the three waters compared to conventional ozonation. Due to its higher efficiency, the E-peroxone process reduced ∼10–53% of the energy consumption required to abate the concentration of chloramphenicol (the most ozone-resistant micropollutant spiked in the waters) by 1 order of magnitude in the three waters compared to conventional ozonation. In contrast, the UV/O3 process consumed approximately 4–10 times higher energy than conventional ozonation. This pilot-scale study demonstrates that the E-peroxone process can provide a feasible, effective, and energy-efficient alternative for micropollutant abatement and bromate control in water and wastewater treatment.

The electro-peroxone (E-peroxone) process is an emerging ozone-based electrochemical advanced oxidation process that combines conventional ozonation with in-situ cathodic hydrogen peroxide (H2O2) production for oxidative water treatment. In this study, the effects of the E-peroxone pretreatment on disinfection by-product (DBP) formation from chlorination of a synthetic surface water were investigated and compared to conventional ozonation. Results show that due to the enhanced transformation of ozone (O3) to hydroxyl radicals ( OH) by electro-generated H2O2, the E-peroxone process considerably enhanced dissolved organic carbon (DOC) abatement and significantly reduced bromate (BrO3−) formation compared to conventional ozonation. However, natural organic matter (NOM) with high UV254 absorbance, which is the major precursors of chlorination DBPs, was less efficiently abated during the E-peroxone process than conventional ozonation. Consequently, while both conventional ozonation and the E-peroxone process substantially reduced the formation of DBPs (trihalomethanes and haloacetic acids) during post-chlorination, higher DBP concentrations were generally observed during chlorination of the E-peroxone pretreated waters than conventional ozonation treated. In addition, because of conventional ozonation or the E-peroxone treatment, DBPs formed during post-chlorination shifted to more brominated species. The overall yields of brominated DBPs exhibited strong correlations with the bromide concentrations in water. Therefore, while the E-peroxone process can effectively suppress bromide transformation to bromate, it may lead to higher formation of brominated DBPs during post-chlorination compared to conventional ozonation. These results suggest that the E-peroxone process can lead to different DBP formation and speciation during water treatment trains compared to conventional ozonation.

Pharmaceutical abatement in a groundwater (GW), surface water (SW), and secondary effluent (SE) by conventional ozonation, the conventional peroxone (O3/H2O2), and the electro-peroxone (E-peroxone) processes was compared in batch tests. SE had significantly more fast-reacting dissolved organic matter (DOM) moieties than GW and SW. Therefore, O3 decomposed much faster in SE than in GW and SW. At specific ozone doses of 0.5–1.5 mg O3/mg dissolved organic carbon (DOC), the application of O3/H2O2 and E-peroxone process (by adding external H2O2 stocks or in-situ generating H2O2 from cathodic O2 reduction during ozonation) similarly enhanced the OH yield from O3 decomposition by ∼5–12% and 5–7% in GW and SW, respectively, compared to conventional ozonation. In contrast, due to the slower reaction kinetics of O3 with H2O2 than O3 with fast-reacting DOM moieties, the addition or electro-generation of H2O2 hardly increased the OH yield ( OH yields, the abatement efficiencies of ozone-resistant pharmaceuticals (ibuprofen and clofibric acid) increased evidently in GW (up to ∼14–18% at a specific ozone dose of 1.5 mg O3/mg DOC), moderately in SW (up to 6–10% at 0.5 mg O3/mg DOC), and negligibly in SE during the O3/H2O2 and E-peroxone treatment compared to conventional ozonation. These results indicate that similar to the conventional O3/H2O2 process, the E-peroxone process can more pronouncedly enhance O3 transformation to OH, and thus increase the abatement efficiency of ozone-resistant pharmaceuticals in water matrices exerting relatively high ozone stability (e.g., groundwater and surface water with low DOM contents). Therefore, by installing electrodes in existing ozone reactors, the E-peroxone process may provide a convenient way to enhance pharmaceutical abatement in drinking water applications, where groundwater and surface water with low DOM contents are used as the source waters.

The degradation of irgarol, a frequently detected algaecide in the aquatic environment, by ozonation was investigated in this study. The second-order rate constants for the reaction of irgarol with ozone (O3) and hydroxyl radical ( OH) were determined to be 505 M−1 s−1 and 4.96 × 109 M−1 s−1, respectively. During ozonation, sixteen transformation products (TPs) of irgarol were proposed using an electrospray ionization quadrupole time-of-flight mass spectrometer. Most of the TPs are ozone-refractory compounds and therefore could only be further transformed by oxidation with OH generated from O3 decomposition during ozonation. Toxicity analysis using the ecological structure activity relationship class program indicates that some of the TPs (e.g., irgarol sulfoxide) still exhibit high acute or chronic toxicity to aquatic organisms (fish, daphnia, and algae) as the parent compound. With a typical ozone dose applied in water treatment (2 mg/L, corresponding to a specific ozone dose of 0.8 mg O3/mg dissolved organic carbon), irgarol could be completely abated in a selected surface water by ozonation. However, most of the TPs persisted in the ozonation effluent because of their low ozone reactivity. The results of this study suggest that ozonation with typical ozone doses applied in water treatment may not be able to sufficiently reduce the ecotoxicological effects of irgarol on aquatic organisms. More effective treatment processes such as ozone-based advanced oxidation processes may be required to enhance the removal of toxic TPs of irgarol in water treatment.

This study compares the degradation of diethyl phthalate (DEP) by the electro-peroxone (E-peroxone) process with three different carbon-based cathodes, namely, carbon-polytetrafluorethylene (carbon-PTFE), carbon felt, and reticulated vitreous carbon (RVC). Results show that the three cathodes had different electrocatalytic activity for converting sparged O2 to H2O2, which increased in order of carbon felt, RVC, and carbon-PTFE. The in-situ generated H2O2 then reacts with sparged O3 to yield OH, which can in turn oxidize ozone-refractory DEP toward complete mineralization. In general, satisfactory total organic carbon removal yields (76.4-91.8%) could be obtained after 60min of the E-peroxone treatment with the three carbon-based cathodes, and the highest yield was obtained with the carbon-PTFE cathode due to its highest activity for H2O2 generation. In addition, the carbon-PTFE and carbon felt cathodes exhibited excellent stability over six cycles of the E-peroxone treatment of DEP solutions. Based on the intermediates (e.g., monoethyl phthalate, phthalic acid, phenolics, and carboxylic acids) identified by HPLC-UV, plausible reaction pathways were proposed for DEP mineralization by the E-peroxone process. The results of this study indicate that carbon-based cathodes generally have good electrocatalytic activity and stability for application in extended E-peroxone operations to effectively remove phthalates from water.

This study investigated the degradation of clofibric acid and formation of perchlorate during the electro-peroxone (E-peroxone) treatment of chloride-containing (26.1-100 mg L(-1)) water (Na2SO4 electrolytes and secondary effluents). The E-peroxone process involves sparging O2 and O3 gas mixture into an electrolysis reactor where a carbon-based cathode is used to electrochemically convert the sparged O2 to H2O2. The electro-generated H2O2 then reacts with sparged O3 to produce OH, which can rapidly oxidize pollutants in the bulk solution. When boron-doped diamond (BDD) electrodes were used as the anode, perchlorate concentrations increased significantly from undetectable levels to ∼15-174 mg L(-1) in the different water samples as the applied current density was increased from 4 to 32 mA cm(-2). In contrast, no ClO4(-) was detected when Pt/Ti anodes were used in the E-peroxone process operated under similar reaction conditions. In addition, when sufficient O3 was sparged to maximize OH production from its peroxone reaction with electro-generated H2O2, the E-peroxone process with Pt/Ti anodes achieved comparable clofibric acid degradation and total organic carbon (TOC) removal yields as that with BDD anodes, but did not generate detectable ClO4(-). These results indicate that by optimizing operational parameters and using Pt/Ti anodes, the E-peroxone process can achieve the goal of both fast pollutant degradation and ClO4(-) prevention during the treatment of chloride-containing wastewater.

This study compared the removal of pharmaceuticals from secondary effluents of wastewater treatment plants (WWTPs) by conventional ozonation and the electro-peroxone (E-peroxone) process, which involves electrochemically generating H2O2 in-situ from O2 in sparged O2 and O3 gas mixture (i.e., ozone generator effluent) during ozonation. Several pharmaceuticals with kO3 ranging from

In this study methylisoborneol (MIB) and geosmin abatement in a surface water by conventional ozonation and the electro-peroxone (E-peroxone) process was compared. Batch tests with addition of ozone (03) stock solutions and semi-batch tests with continuous O-2/O-3 gas sparging (simulating real ozone contactors) were conducted to investigate O-3 decomposition, center dot OH production, MIB and geosmin abatement, and bromate formation during the two processes. Results show that with specific ozone doses typically used in routine drinking water treatment (0.5-1.0 mg O-3/mg dissolved organic carbon (DOC)), conventional ozonation could not adequately abate MIB and geosmin in a surface water. While increasing the specific ozone doses (1.0-2.5 mg O-3/mg DOC) could enhance MIB and geosmin abatement by conventional ozonation, this approach resulted in significant bromate formation. By installing a carbon-based cathode to electrochemically produce H2O2 from cathodic oxygen reduction, conventional ozonation can be conveniently upgraded to an E-peroxone process. The electro-generated H2O2 considerably enhanced the kinetics and to a lesser extent the yields of hydroxyl radical (center dot OH) from O-3 decomposition. Consequently, during the E-peroxone process, abatement of MIB and geosmin occurred at much higher rates than during conventional ozonation. In addition, for a given specific ozone dose, the MIB and geosmin abatement efficiencies increased moderately in the E-peroxone (by similar to 8-9% and similar to 10 25% in the batch and semi-batch tests, respectively) with significantly lower bromate formation compared to conventional ozonation. These results suggest that the E-peroxone process may serve as an attractive backup of conventional ozonation processes during accidental spills or seasonal events such as algal blooms when high ozone doses are required to enhance MIB and geosmin abatement. (C) 2016 Elsevier Ltd. All rights reserved.