Sonodegradation of 17α-ethynylestradiol in environmentally relevant matrices: laboratory-scale kinetic studies

The sonochemical degradation of 17α-ethynylestradiol (EE2) in secondary treated effluents was investigated. Ultrasound irradiation was provided by a horn-type sonicator operating at 80 kHz. The effect of various operating conditions such as estrogen concentration (25-160 μg/L), power density (18-46 W/L), liquid bulk temperature (15-60 °C), gas sparging (air, oxygen, and helium), solution pH (3 and 7.8), as well as the addition of radical promoters (hydrogen peroxide) or catalysts (TiO2 and Fe2+) on degradation kinetics was evaluated. Changes in estrogen concentration were followed by high performance liquid chromatography and the yeast estrogen screening (YES) assay. EE2 degradation in the range 25-110 μg/L follows first order kinetics in regard to its concentration, while lower order kinetics occur at higher concentrations. The reaction rate increases linearly with applied power and decreases exponentially with temperature at the conditions in question. Continuous sparging of air or oxygen has little effect on the kinetics relative to air-equilibrated conditions, while helium has a marginally positive effect. The inorganic and organic contents of the wastewater matrix appear to promote degradation at inherent conditions in comparison to experiments in ultrapure water. Nevertheless, the addition of H2O2 (8.6 and 86 mg/L), Fe2+ (2.5-25 mg/L) or TiO2 (50-2000 mg/L) has no or, in some cases, adverse effect on kinetics.