Synthetic dyes are used extensively in many industries, such as textile, printing among others. Some of the dyes, however, are discharged in industrial wastewaters and can cause serious aesthetic and environmental damage to receiving water bodies. Decolorization and pollutant degradation are two major tasks in dye wastewater treatment. Because of the strong decolorization ability of ozone, it has been widely used in dye wastewater treatment. However, ozone usually has limited oxidation ability to mineralize refractory synthetic dyes effectively to CO₂ and H₂O. To improve pollutant mineralization efficiency, ozone is often used in particularly with O₃ and H₂O₂ together (i.e., the so-called peroxone process) has a significant synergistic effect on organic mineralization [1]. The electro-peroxone (E-peroxone) process is a novel electrochemical advanced oxidation process (EAOP) that is enabled by in situ generation of hydrogen peroxide (H₂O₂) from cathodic oxygen (O₂) reduction during conventional ozonation. The electro-generated H₂O₂ can considerably enhance ozone (O₃) transformation to hydroxyl radicals (•OH), thus greatly enhancing pollutant degradation by the E-peroxone process than by conventional ozonation [2]. In this context, the experimental characterization and modeling of the reaction environment in electrochemical flow reactors is mandatory to control homogeneous fluid flow, mass transport to and from electrode surface and current and potential distribution, aiming to prevent parasitic reactions that impact negatively on the current efficiency and energy consumption. Furthermore, the modeling of EAOPs is also needed to enhance the reaction kinetics. The numerical simulation can also be a powerful tool to devise new reactors for EAOPs, thus contributing to a smarter scale-up [3]. So, in this work, the E-peroxone process for the degradation of the orange reactive 16 dye, using Ir-Sn-Sb oxides as anode, an unmodified graphite felt on top of carbon cloth as air-diffusion in the cathode fitted into an undivided filter-press cell, operating in recirculation mode, was simulated using a parametric model. The experiments were performed in a laboratory reactor with recirculation of 2 dm³ of 0.05M Na₂SO₄ solutions at pH 3.0 upon continuous air feeding (5 psi) to the cathode and continuous ozone feeding (0.5 dm³ min^-1) at the exit of the reactor. The potential to produce H₂O₂ is 0.695 V|SHE, reported by Perez et. al. (2018) [4], which was used in this case. In the degradation of the dye, different flows (1.9, 1.5, 1.1 and 0.75 dm³ min^-1) and then current densities (0.004-0.00625 A cm^-2) were tested to determine the optimal conditions of the degradation. The discoloration of the dye was measurement at 498 nm by a spectrophotometer uv/vis, and the degradation of the organic matter was followed by TOC. The results of the decolorization of reactive orange 16 dye show that the optimal flow is 1.9 dm³ min^-1, achieving a discoloration of 98.4% against 77.4% to 0.75 dm³ min^-1 in a time of one hour of process. Good agreement between simulations and experimental TOC decays was obtained.

[1] Bakheet, B. et al. Electro-peroxone treatment of Orange II dye wastewater, Water Research, 47 (2013) 6234-6243.

[2] Zhou, M., Oturan, M., Sirés I., Electro-fenton process, New trend and scale-up, Springer, Singapore, 2018.

[3] Perez, T., Sirés, I., Brillas, E., Nava, J.L., Solar photoelectro-fenton plant modeling for the degradation of the antibiotic erythtomycin in sulfate medium, Electrochimica Acta, 228 (2017) 45-56.

[4] Perez, T., Coria, G., Sirés, I., Nava, J.L., Uribe, A., Electrosynthesis of hydrogen peroxide in a filter-press flow cell using graphite felt as air-diffusion cathode, Journal of Electroanalytical Chemistry, 812 (2018) 54-58.