Contrasting the performance of photo-Fenton at neutral pH in the presence of different organic iron-complexes using hydrogen peroxide or persulfate as oxidants for naproxen degradation and removal of antimicrobial activity

This is the first study to compare the combination of different iron complexes (Fe3+-oxalate (FeOx), Fe3+-citrate (FeCit), Fe3+-nitrilotriacetic acid (FeNTA), Fe3+-ethylenediaminetetraacetic acid (FeEDTA) and Fe3+-ethylenediamine-N,N′-disuccinic acid (FeEDDS) with distinct oxidants (H2O2 and S2O82−) on the degradation of naproxen (NAP) via photo-Fenton. Experiments were performed in distilled water and in sewage treatment plant effluent and different Fe/organic ligand molar ratios, oxidant concentrations and radiation sources (black light and sunlight) were tested for each complex. Photo-Fenton at neutral pH was efficient for naproxen degradation in the presence of all iron complexes. Fe/ligand molar ratio was strongly affected by the ligand type, best results were obtained in the presence of Fe/EDDS (1:1) and Fe/NTA (1:1), Fe/EDTA (1:2), Fe/Cit (1:3) and Fe/Ox (1:12). Although NAP removal in distilled water was faster in the presence of H2O2 (max 20 kJ m−2 required) when compared to S2O82− (max 90 kJ m−2 required), better performance of S2O82− was observed in sewage treatment plant effluent. Antimicrobial activity was only observed in the presence of FeEDDS, yet it was eliminated after treatment in the presence of S2O82−. A critical comparison in terms of operational and electrical energy costs indicates that using FeCit complex with H2O2 is the most cost-effective alternative in both matrices.