New electrochemical reactor design for emergent pollutants removal by electrochemical oxidation

This paper presents the theoretical and experimental confirmation of the performance of a novel pre-pilot reactor design implementing a boron-doped diamond (BDD) anode to destroy emerging pollutants by electrochemical oxidation. Turbulent flow simulation and secondary current distribution modeling with a COMSOL Multiphysics software were used to assess the engineering capabilities of the reactor along with the oxidant BDD(^·OH) electrogeneration at the anode. The antibiotic ciprofloxacin (CIP) was chosen as model molecule to assess the oxidation power achieved with the pre-pilot batch plant. In sulfate medium where BDD(^·OH) was the main oxidant, faster degradation was determined by increasing current density, CIP content, and pH. The effect of pH was explained by the transformation of the cationic form of CIP in acidic medium into its more easily oxidizable anionic form in alkaline medium. In chloride medium, CIP was more rapidly removed by the faster attack of the generated active chlorine. The degradation was decelerated in carbonate medium by its scavenging effect and in the presence of humic acid by its competitive oxidation with BDD(^·OH). The antibiotic abatement also dropped down in tap water and synthetic urine. An almost total mineralization was achieved with a constant energy cost per unit COD mass of 0.6 ± 0.1 kWh (g COD)⁻¹. The initial N of CIP was pre-eminently converted into nitrate, alongside nitrite and ammonia to lesser extent. Recalcitrant acetic, oxalic, and formic acids were detected as final carboxylic acids.