Effects of operating conditions on iron (hydr)oxides evolution and ciprofloxacin degradation in potassium...

In this study, a stepwise oxidation system of potassium ferrate (K₂FeO₄) combined with ozone (O₃) was used to degrade ciprofloxacin (CIP). The effects of pH and pre-oxidation time of K₂FeO₄ on the evolution of K₂FeO₄ reduction products (iron (hydr)oxides) and CIP degradation were investigated. It was found that in addition to its own oxidation capacity, K₂FeO₄ can also influence the treatment effect of CIP by changing the catalyst content. The presence of iron (hydr)oxides effectively enhanced the mineralization rate of CIP by catalyzing ozonation. The pH value can influence the content and types of the components with catalytic ozonation effect in iron (hydr)oxides. The K₂FeO₄ pre-oxidation stage can produce more iron (hydr)oxides with catalytic components for subsequent ozonation, but the evolution of iron (hydr)oxides components was influenced by O₃ treatment. It can also avoid the waste of oxidation capacity owing to the oxidation of iron (hydr)oxides by O₃ and free radicals. The intermediate degradation products were identified by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Besides, the degradation pathways were proposed. Among the degradation products of CIP, the product with broken quinolone ring structure only appeared in the stepwise oxidation system.