Mineralization of flumequine in acidic medium by electro-Fenton and photoelectro-Fenton processes

The mineralization of flumequine, an antimicrobial agent belonging to the first generation of synthetic fluoroquinolones which is detected in natural waters, has been studied by electrochemical advanced oxidation processes (EAOPs) like electro-Fenton (EF) and photoelectro-Fenton (PEF) with UVA light. The experiments were performed in a cell containing a boron-doped diamond (BDD) anode and an air-diffusion cathode to generate H2O2 at constant current. The Fe2+ ion added to the medium increased the solubility of the drug by the formation of a complex of intense orange colour and also reacted with electrogenerated H2O2 to form hydroxyl radical from Fenton reaction. Oxidant hydroxyl radicals at the BDD surface were produced from water oxidation. A partial mineralization of flumequine in a solution near to saturation with optimum 2.0 mM Fe2+ at pH 3.0 was achieved by EF. The PEF process was more powerful, giving an almost total mineralization with 94–96% total organic carbon removal. Increasing current accelerated both treatments, but with decreasing mineralization current efficiency. Comparative treatments using a real wastewater matrix led to similar degradation degrees. The kinetics for flumequine decay always followed a pseudo-first-order reaction and its rate constant, similar for both EAOPs, raised with increasing current. Generated carboxylic acids like malonic, formic, oxalic and oxamic acids were quantified by ion-exclusion HPLC. Fe(III)–oxalate and Fe(III)–oxamate complexes were the most persistent by-products under EF conditions and their quicker photolysis by UVA light explains the higher oxidation power of PEF. The release of inorganic ions such as F−, NO3− and in lesser extent NH4+ was followed by ionic chromatography.

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► Partial mineralization by electro-Fenton and almost total mineralization by photoelectro-Fenton.
► Similar degradation behaviour in synthetic water and real wastewater.
► Added Fe2+ acting for complexing flumequine and for generating hydroxyl radicals.
► Malonic, oxalic, oxamic and formic acids generated as carboxylic acids.
► Release of fluoride ion, nitrate ion and in lesser extent ammonium ion in both processes.