Degradation of Parabens in Different Aqueous Matrices by Several O₃‑Derived Advanced Oxidation Processes

Ozonation is a promising technology for the treatment of biorefractory compounds. Parabens belong to a chemical family of apparently innocuous preservatives that have been used in the food and cosmetic industries for several years. Oxidation of different parabens, such as methylparaben (MP), ethylparaben (EP), propylparaben (PP), and butylparaben (BP), was carried out using O₃ in ultrapure water. A design of experiments procedure has been carried out in order to optimize the ozonation process as well as to study the interaction between the studied variables: pH and temperature (<i>T</i>). In addition to the application of the single ozonation, ozone-combined processes were studied under the optimal conditions obtained for O₃ (namely, pH 8 and <i>T</i> = 20 °C). The tested processes were O₃/Fenton, O₃/H₂O₂, O₃/UV, O₃/UV/H₂O₂, O₃/photo-Fenton, O₃/UV/TiO₂, and O₃/UV/TiO₂/H₂O₂. According to the experimental results, single ozonation is a more effective treatment than O₃/H₂O₂ and O₃/Fenton processes. In addition, the introduction of ultraviolet (UV) irradiation results, in all cases, in a faster and more efficient removal of the parabens, because of the contribution of ozone photolysis to the radical-mediated pathway. The most efficient method for the degradation of these emerging pollutants was O₃/UV/TiO₂/H₂O₂. The influence of different aqueous matrices (namely, ultrapure water, river water, wastewater treatment plant (WWTP) effluent, and reservoir water) on the removal of the target pollutants has been analyzed. The direct ozonation pathway is the predominant degradation mechanism and a remarkable synergistic effect of bicarbonate ions has been demonstrated