The electro-peroxone process for the abatement of emerging contaminants: Mechanisms, recent advances, and prospects

Optimization of the Electro-Peroxone Process for Micropollutant Abatement Using Chemical Kinetic Approaches

The electro-peroxone (E-peroxone) process is an emerging electrocatalytic ozonation process that is enabled by in situ producing hydrogen peroxide (H₂O₂) from cathodic oxygen reduction during ozonation. The in situ-generated H₂O₂ can then promote ozone (O₃) transformation to hydroxyl radicals (•OH), and thus enhance the abatement of ozone-refractory pollutants compared to conventional ozonation. In this study, a chemical kinetic model was employed to simulate micropollutant abatement during the E-peroxone treatment of various water matrices (surface water, secondary wastewater effluent, and groundwater). Results show that by following the O₃ and •OH exposures during the E-peroxone process, the abatement kinetics of a variety of model micropollutants could be well predicted using the model. In addition, the effect of specific ozone doses on micropollutant abatement efficiencies could be quantitatively evaluated using the model. Therefore, the chemical kinetic model can be used to reveal important information for the design and optimization of the treatment time and ozone doses of the E-peroxone process for cost-effective micropollutant abatement in water and wastewater treatment.

The beneficial effect of cathodic hydrogen peroxide generation on mitigating chlorinated by-product formation during water treatment by an electro-peroxone process

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.

Enhanced organic removal for shale gas fracturing flowback water by electrocoagulation and simultaneous electro-peroxone process

Colloids and organics in shale gas fracturing flowback water (SGFFW) during shale gas extraction are of primary concerns. Coagulation combined with oxidation might be a promising process for SGFFW treatment. In this study, a novel electrocoagulation-peroxone (ECP) process was developed for SGFFW treatment by simultaneous coagulation and oxidation process with a Al plate as the anode and a carbon-PTFE gas diffusion electrode as the cathode, realizing the simultaneous processes of coagulation, H₂O₂ generation and activation by O₃ at the cathode. Compared with electrocoagulation (EC) and peroxi-electrocoagulation (PEC), COD removal efficiency mainly followed the declining order of ECP, PEC and EC under the optimal current density of 50 mA cm^-2. The appearance of medium MW fraction (1919 Da) during ozonation and PEC but disappearance in ECP indicated that these intermediate products couldn't be degraded by ozonation and PEC but could be further oxidized and mineralized by the hydroxyl radical produced by the cathode in ECP, demonstrating the hydroxyl radical might be responsible for the significant enhancement of COD removal. The pseudo-first order kinetic model can well fit ozonation and EC process but not the PEC and ECP process due to the synthetic effect of coagulation and oxidation. However, the proposed mechanism based model can generally fit ECP satisfactorily. The average current efficiency for PEC was 35.4% and 12% higher than that of ozonation and EC, respectively. This study demonstrated the feasibility of establishing a high efficiency and space-saving electrochemical system with integrated anodic coagulation and cathodic electro-peroxone for SGFFW treatment.

C3N4–Mn/CNT composite as a heterogeneous catalyst in the electro-peroxone process for promoting the reaction between O3and H2O2in acid solution

The C₃N₄–Mn/CNT catalyst promotes the reaction between O₃and H₂O₂in acid solution, and enhances the degradation efficiency of the electro-peroxone process.