Fast degradation of estrogen hormones in environmental matrices by photo-Fenton oxidation under simulated solar radiation

The efficiency of homogeneous Fenton oxidation induced by simulated solar radiation to remove 17α-ethynylestradiol (EE2), a synthetic estrogen hormone, from secondary treated effluents was investigated. Solar radiation was simulated with a 150 W xenon lamp and experiments were conducted varying initial effluent pH (3-8), EE2 concentration (70-315 μg/L), H₂O₂ concentration (1.5-86 mg/L) and Fe²⁺ concentration (1-5 mg/L). Changes in estrogen concentration were followed by high performance liquid chromatography. EE2 was readily oxidizable at acidic conditions (pH = 3) with complete conversion typically occurring in 5-10 min of irradiation at, e.g. 5 mg/L Fe²⁺, 4.3-15 mg/L H₂O₂ and 200 μg/L EE2 concentration. The process involves two distinct kinetic regimes, a fast one during the very first minutes followed by a far slower one. The contribution of dark Fenton reactions to degradation was found to be considerable, particularly at higher concentrations of Fenton's reagents; nonetheless, the beneficial role of simulated solar irradiation was noticeable at lower concentrations and even in the absence of hydrogen peroxide, as well as for the mineralization of the effluent organic matter. Two natural hormones, namely estrone and 17β-estradiol were also tested and their reactivity values were nearly equal to EE2. The implications for tertiary wastewater treatment (removal of pathogens and estrogenicity) are also discussed.