Solar photoelectro-Fenton-like process with anodically-generated HClO in a flow reactor: Norfloxacin as a pollutant with a particular structure

Abstract

The degradation and mineralization of the drug norfloxacin (NFX) has been assessed in a model solution, containing 15 mM NaCl +45 mM Na2SO4 at pH 3.0, using a flow plant with an FM01-LC filter-press reactor equipped with a Ti|Ir-Sn-Ru oxides anode to electrogenerate HClO from Cl- oxidation and a stainless-steel cathode. Unexpectedly, anodic oxidation with active chlorine (AO-HClO) outperformed electro-Fenton (EF-HClO), photoelectro-Fenton (PEF-HClO) and solar photoelectro-Fenton (SPEF-HClO) due to: (i) the formation of refractory complexes between iron ions and carboxyl group of NFX, and (ii) the conversion of HClO into less effective ¿OH upon its Fenton-like reaction with added Fe2+ catalyst. SPEF-HClO was superior among Fentonbased treatments because the ¿OH concentration was largely increased by the photolysis of Fe(III) species. At an initial NFX concentration in the range 0.103-0.146 mM, the optimum conditions for SPEF-HClO were 0.40 mM Fe2+ and 15 mA cm􀀀 2. A BDD anode allowed a higher production of ¿OH, accelerating the degradation and mineralization, with similar energy requirements as compared to trials with Ti|Ir-Sn-Ru oxides anode. The SPEFHClO process in urban wastewater was less powerful because of the parallel oxidation of natural organic matter. HClO, Fe2+ and Fetotal were quantified in both water matrices. The initial degradation sequence for NFX, proposed from 10 primary by-products identified by LC-MS/MS, revealed the occurrence of hydroxylation, chlorination and defluorination steps. Additionally, 5 stable by-products were detected by GC-MS.