Modeling the sulfamethoxazole degradation by active chlorine in a flow electrochemical reactor

The aim of this study is to propose a continuous physicochemical model accounting for the active chlorine production used to degrade recalcitrant sulfamethoxazole (SMX) in an electrochemical flow reactor. The computational model describes the fluid mechanics and mass transfer occurring in the re/actor, along with the electrode kinetics of hydrogen evolution reaction arising on a stainless steel cathode, and the chloride oxidation on a DSA. Specifically, the anodic contributions assume the heterogeneous nature of the adsorbed chlorine species formed on this surface, which are a model requirement to correctly define the experimental reactor performance and degradation efficiency of the contaminant. The experimental validation conducted at different applied current densities, volumetric flows, and chloride concentrations is adequately explained by the model, thus evidencing some of the phenomena controlling the electrocatalytic chlorine production for environmental applications. The best conditions to eliminate the SMX are proposed based on the theoretical analysis of the current efficiency calculated with the model, and experimentally confirmed. The use of the Ti/RuO₂-ZrO₂-Sb₂O₃ anode at the bench scale improves the SMX removal by using electro-generated chlorine species adsorbed on its surface, which remarkably increases the oxidation potential of the system along with chlorine desorbed from the electrode. This is a technological innovation concerning other mediated oxidation methods entirely using oxidants in solution.