Heterogeneous catalytic ozonation by Nano-MgO is better than sole ozonation for metronidazole degradation, toxicity reduction, and biodegradability improvement

In the current paper, the removal efficiency of metronidazole (MNZ) using a catalytic ozonation process (COP) in the presence of magnesium oxide nanocrystals, as a catalyst, was investigated in deionized water and compared with a sole ozonation process (SOP). The influence of several operational factors on both removal processes was evaluated: solution pH, MgO dosage, initial MNZ concentration, and reaction time. Biodegradability improvement, mineralization rate, oxidation intermediates, and toxicity were also studied for the COP. The results showed that MgO nanocrystals accelerated MNZ removal compared to the SOP. The optimum pH for both SOP and COP was obtained at 10 and optimum MgO dosage for the COP was determined 0.25g/L. Under optimum conditions, after 20min and 35min, the complete removal of 40mg/L MNZ solution occurred in COP and SOP, respectively. The COP significantly increased the biological oxygen demand/chemical oxygen demand ratio (from 0.09 to 0.43), caused 93.5% MNZ mineralization, and reduced the toxicity of the MNZ.