Mechanisms of enhanced total organic carbon elimination from oxalic acid solutions by electro-peroxone process

Electro-peroxone (E-peroxone) is a novel electrocatalytic ozonation process that combines ozonation and electrolysis process to enhance pollutant degradation during water and wastewater treatment. This enhancement has been mainly attributed to several mechanisms that increase O3 transformation to OH in the E-peroxone system, e.g., electro-generation of H2O2 from O2 at a carbon-based cathode and its subsequent peroxone reaction with O3 to OH, electro-reduction of O3 to OH at the cathode, and O3 decomposition to OH at high local pH near the cathode. To get more insight how these mechanisms contribute respectively to the enhancement, this study investigated total organic carbon (TOC) elimination from oxalic acid (OA) solutions by the E-peroxone process. Results show that the E-peroxone process significantly increased TOC elimination rate by 10.2–12.5 times compared with the linear addition of the individual rates of corresponding ozonation and electrolysis process. Kinetic analyses reveal that the electrochemically-driven peroxone reaction is the most important mechanism for the enhanced TOC elimination rate, while the other mechanisms contribute minor to the enhancement by a factor of 1.6–2.5. The results indicate that proper selection of electrodes that can effectively produce H2O2 at the cathode is critical to maximize TOC elimination in the E-peroxone process. [Display omitted] •E-peroxone process combines ozonation with electrolysis and greatly enhances total organic carbon removal.•H2O2 is electro-generated from O2 in sparged O2 and O3 gas mixture at a carbon-base cathode.•O3 can be transformed to OH via several mechanisms in the E-peroxone process.•Electro-generation of H2O2 from O2 and its subsequent peroxone reaction with O3 is the major source of OH.•Boron-doped diamond anode can mineralize Fe3+-oxalate complexes that resist aqueous OH oxidation.