Performance of a Flow-Through Electro-Fenton Reactor for Dye Degradation: Influence of Hydrodynamics and Anodic Material

This study investigated the influence of a novel flow–through electro-Fenton (EF) reactor configuration on hydrodynamics and dye removal efficiency using Pt and boron-doped diamond (BDD) anodes coupled with a carbon–PTFE gas diffusion cathode. In this work, an innovative pre–pilot-scale reactor operating in recirculation mode was used to treat 100 mg L−1 Calcon dye solutions in 0.05 mol L−1 Na2SO4 at pH 3.0 under electrochemical oxidation (EO) with electrogenerated H2O2 (EO-H2O2), EF, and Photoelectro-Fenton (PEF) conditions. The effects of applied current density (30–90 mA cm−2) and Fe2+ concentration (0.25–0.75 mmol L−1) were evaluated through color removal, TOC decay, and identification of oxidation intermediates. The hydrodynamic characterization results revealed flow conditions in a transitional region between laminar and turbulent flow (Re = 3.6 × 103; Sh = 246). Comparing EF and EO-H2O2 processes, when Fe2+ was added to the solution, it significantly accelerated discoloration and, consequently, dye degradation in the former, while the absence of Fe2+ resulted in slower discoloration kinetics, reaching only 85.8% color removal after 180 min in the latter. The best performance was obtained with 0.50 mmol L−1 Fe2+ in EF, achieving >98% discoloration. Among the investigated processes, PEF exhibited the highest mineralization efficiency. TOC removals using BDD as the anode efficiently reached high mineralization levels of 83.88%, 86.99%, and 93.38% for EO-H2O2, EF, and PEF, respectively, while Pt as the anode achieved 81.80%, 85.14%, and 91.63%. Overall, the BDD/PEF system showed the best degradation and mineralization performance. The proposed reactor was designed at the pre-pilot scale and incorporates vertical recirculation flow with hydrodynamic optimization, enabling efficient mass transfer and improved oxidant generation. The study provides practical insights into the reactor engineering aspects required for the future scale-up of EF technologies.