Ozonation of representative endocrine disrupters (EDs) in water

The effects of ozone dose, bicarbonate concentration and pH on endocrine disruptors (EDs) removal, such as E1, E2, EE2, DES and 4-n-NP, were investigated through batch experiment. The results indicated that the removal rates were enhanced by increasing ozone dose, and O₃ exposures of only 63.6 μg/L were calculated to achieve ≥ 92.0% EDs removal efficiency. The presence of bicarbonate (0-100 mg/L) inhibited EDs ozonation. Furthermore, the EDs removal rates increased significantly as pH increased. The five apparent rate constants (20°C ± 0.5°C of ozone with the five EDs were in the range of (1.67-3.89) × 10⁶ L·(mol·s)^-1 at neutral pH (pH ≈7.0) and (0.93-1.75) × 10⁹ L·(mol·s)^-1 at basic pH (pH > 10.6). It was indicated that the five EDs were removed rapidly by O₃ in water. At the same time, the elementary reaction ozone rate constants (20°C ± 0.5°) were calculated, and the reactivity of ozone with ionized EDs [i.e. 1.21 × 10⁹-3.81 × 10⁹ L·(mol·s)^-1] was 10³-10⁴ times higher than with neutral EDs [i.e. 7.62 × 10⁵-2.55 × 10⁶ L· (mol·s)^-1]. The comparative test of EDs ozonation under different water quality conditions indicated that the removal rates of EDs in filtrated water and river water were reduced 26.5%-50.3% and 57.3%-72.0% respectively compared with the case using ultrapurified water as the background. It showed that organics in real water would compete with EDs for ozonation.