Oxidation with a BDD electrode in an electrochemical reactor for paraquat degradation: Experimental and modeling study

Advanced oxidation processes for treating water contaminated with environmentally hazardous compounds represent a promising technology. However, many studies are conducted in non‑scalable systems, requiring modeling investigations in scalable reactors, where both reactor design and operating variables can be systematically analyzed. Such analyses are crucial for understanding the degradation of organic matter. Accordingly, this work proposes a CFD-based model that integrates Nernst–Planck species transport with electrochemical hydroxyl radical generation and paraquat degradation reactions in a scalable filter‑press electrochemical reactor. A simplified reaction scheme was proposed to render the model mathematically tractable, with only three kinetic parameters adjusted to experimental data from two types of degradation experiments. This ensured consistency across different current densities and between single‑stage and two‑stage processes, the latter involving an electrochemical reactor followed by a stirred reactor without electrical current, in which reactions occur solely in the bulk medium. The model successfully describes degradation in both configurations and closely predicts the effects of current density and flow rate in a reactor equipped with a spacer that reduces the electrode gap. Furthermore, it demonstrates that paraquat removal increases proportionally with current density. In contrast, variations in flow rate exert only a minor influence, thereby confirming that hydroxyl radical generation is the dominant factors governing reactor performance.