Background and purpose: Metronidazole is a serious environmental pollutant due to high consumption and persistence in biological degradation. This study aimed at removal of metronidazole using ozone (O₃) activated persulfate (PS) in presence of ultrasound (US).

Materials and methods: A laboratory scale study was carried out in batch reactor using US irradiation and O₃ generator apparatuses. The effects of operating parameters such as pH of the solution, different initial concentrations of persulfate, initial metronidazole concentration, different ion strength, and radical scavenger were evaluated. Metronidazole concentration was determined using DR-5000 Spectrophotometer in 320 nm wavelength.

Results: The results showed that removal of metronidazole decreased by increasing the pH of solution from 3 to 11. The removal rate of metronidazole was dependent on initial PS dosages and the highest rate of removal was found in 500 mg/l (94.7%), but in higher concentrations the removal rate decreased. Also, the metronidazole removal rate decreased by increase in initial concentration of metronidazole. The COD removal rate in optimum condition was 56%.

Conclusion: Activation of PS by US/O₃ process could serve as a novel treatment for removal of metronidazole in aqueous solution.