Expanding the application of photoelectro-Fenton treatment to urban wastewater using the Fe(III)-EDDS complex

This work reports the first investigation on the use of EDDS as chelating agent in photoelectro-Fenton (PEF) treatment of water at near-neutral pH. As a case study, the removal of the antidepressant fluoxetine was optimized, using an electrochemical cell composed of an IrO2-based anode an air-diffusion cathode for in-situ H2O2 production. Electrolytic trials at constant current were made in ultrapure water with different electrolytes, as well as in urban wastewater (secondary effluent) at pH 7.2. PEF with Fe(III)-EDDS (1:1) complex as catalyst outperformed electro-Fenton and PEF processes with uncomplexed Fe(II) or Fe(lll). This can be explained by: (i) the larger solubilization of iron ions during the trials, favoring the production of (OH)-O-center dot from Fenton-like reactions between H2O2 and Fe(II)-EDDS or Fe(III)-EDDS, and (ii) the occurrence of Fe(II) regeneration from Fe(III)-EDDS photoreduction, which was more efficient than conventional photo-Fenton reaction with uncomplexed Fe(III). The greatest drug concentration decays were achieved at low pH, using only 0.10 mM Fe(III)-EDDS, although complete removal in wastewater was feasible only with 0.20 mM Fe(III)-EDDS due to the greater formation of TH. The effect of the applied current and anode nature was rather insignificant. A progressive destruction of the catalytic complex was unveiled, whereupon the mineralization mainly progressed thanks to the action of (OH)-O-center dot adsorbed on the anode surface. Despite the incomplete mineralization using BDD as the anode, a remarkable toxicity decrease was determined. Fluoxetine degradation F(-)yielded and NO3- ions, along with several aromatic intermediates. These included two chloro-organics, as a result of the anodic oxidation of Cl- to active chlorine. A detailed mechanism for the Fe(III)-EDDS-catalyzed PEF treatment of fluoxetine in urban wastewater is finally proposed. (C) 2019 Elsevier Ltd. All rights reserved.