On the capacity of ozonation to remove antimicrobial compounds, resistant bacteria and toxicity from urban wastewater effluents

The degradation of erythromycin (ERY) and ethylparaben (EtP) in urban wastewater effluents at low concentration level during ozonation was investigated under different experimental conditions. Both substrates were rapidly eliminated within 2 min at low ozone dose of 0.3 mg L⁻¹ and the experimental data were well fitted in the pseudo-first-order kinetic model. The ratio of HO[rad]- and O₃-exposure (R_ct) at the inherent pH was found to be 1.9 × 10⁻⁸. The degradation of ERY and EtP was pronounced at pH 8 compared to acidic pH conditions, while the degradation rate of both substrates was found to be matrix-depended. It was also shown that both O₃- and HO[rad]-mediated pathways are involved in the degradation of EtP, whereas the saturated-rich structure of ERY renders it O₃-recalcitrant. Under the optimum O₃ dose, the BrO₃ ⁻ concentration was found to be lower than 10 μg L⁻¹. Five and fifteen transformation products were elucidated during ERY and EtP oxidation, respectively. The root and shoot inhibition can be attributed to the oxidation products formed upon dissolved effluent organic matter transformation. Escherichia coli harbouring resistance to ERY survived ozonation better than EtP-resistant E. coli. However, neither ERY- nor EtP-resistant E. coli were detected after 15 min of ozonation.