Improving the efficiency of advanced photocatalytic oxidation process in the presence of sulfite for decomposition of metronidazole from aqueous solutions

Metronidazole antibiotic is belong to the nitroimidazole family. Non degradability, high solubility in water, toxicity, carcinogenicity and mutagenicity are important concerns related to antibiotics. Therefore, the aim of this study is to apply the new advanced oxidation process of UV/zinc oxide/sulfite (UZS) to degrade metronidazole from aqueous solutions. Methods: In this study, the effect of pH, sulfite to zinc oxide ratio, initial metronidazole concentration and contact time on the performance of the UV/sulfite/zinc oxide process in the degradation of metronidazole was studied. The residual concentration of metronidazole was measured by HPLC (Cecil model 4900 CE). Results: The results showed more than 90 % antibiotic is degraded at pH = 12 and the molar ratio of sulfite to zinc oxide 1 to 3 after 5 min of the reaction. Although the antibiotic degradation rate in the UZS process was very high, based on the GC-MASS analysis, the mineralization rate was not sufficient. The several metabolites were detected in the UZS process effluent and the degradation pathway was proposed based on the identified metabolites. It was observed the kinetic coefficient of robs (mg/L. min) to degrade the metronidazole by UZS was 6.92 time and 15 time of UV/zinc oxide and UV alone processes, respectively. Conclusion: According to the results, the UV/zinc oxide/sulfite process, due to the higher robs value as well as the higher efficiency value ​​than those of the UV/zinc oxide and UV alone processes, can be considered as a suitable and economical option in the degradation of metronidazole antibiotic and the similar compounds.