Removal Characteristics of Steroid Estrogen in the Mixed System through an Ozone-Based Advanced Oxidation Process

In this work, the removal of estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2) in their coexisting micro-polluted solution through an ozone-based oxidation process was studied in depth. The results showed that all of the estrogens in the mixed solution could be completely degraded and their degradation processes fitted the pseudo-first-order kinetic model well. As the initial concentration of the mixed solution increased from 50 to 300 μg L⁻¹, the removal rate constants of E1, E2, and EE2 decreased by 65.9%, 66.5%, and 67.0%, respectively. However, when the initial solution pH increased from 2.0 to 7.0, the removal rate constant of E1, E2, and EE2 increased by 271.4%, 149.7%, and 152.4%, respectively. When the H₂O₂ or UV was introduced into the ozonation system, the removal efficiency of steroid estrogens in the mixed solution was substantially enhanced. Moreover, main intermediates of E1, E2, and EE2 were proposed. The synthetic estrogen EE2 was chosen as the representative compound to evaluate the estrogenic activities during O₃, O₃/H₂O₂, and O₃/UV processes. In the O₃/H₂O₂ and O₃/UV processes, the degradation products still possessed certain estrogenic activities, which led to a hysteresis of the decrease of estrogenic activity compared with that of the estrogen concentration. These findings provided some reliable research data, alternative oxidants, and oxidation manners for the removal of steroid estrogens from the aquatic environment.