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

Abstract This is the first study to compare the combination of different iron complexes (Fe3+-oxalate (FeOx), Fe3+-citrate (FeCit), Fe3+-nitrilotriacetic acid (Fe3+-NTA), Fe3+-ethylenediaminetetraacetic acid (Fe3+-EDTA) and Fe3+-ethylenediamine-N,N´-disuccinic acid (Fe3+-EDDS) 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 water was faster in the presence of H2O2 (max20 kJ m―2 required) when compared to S2O82― (max90 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.