Degradation Mechanism Of Typical Fluoroquinolone Antibiotics By Chlorine Dioxide

Fluoroquinolones(FQs)antibiotics are widely used in China,which have been detected in different environmental media due to their intensive use.Fluoroquinolones(FQs)antibiotics residues in the environment media pose threats to the health of ecological systems and human,attracted great attention from many countries and regions.However,the traditional treatment technologies can not effectively remove FQs antibiotics from wastewater,that finding efficient removal methods is very important to control the pollution of FQs antibiotics.Chemical oxidation process is widely used in water treatment process because of its merits such as completely removal and easily handling.As a commonly used green disinfectant,Chlorine dioxide(ClO2)is wildly used in water treatment field because of its excellent functions,such as high redox potential,high stability,convenient use and less by-products.In this paper,by analyzing the removal efficiency of ClO2 on four typical FQs antibiotics and structural analogue flumequine(FLU),the effects of different initial chlorine dioxide concentration and different initial pH on the degradation efficiency were studied,the degradation kinetics,degradation products and reaction process of FQs were analyzed,and the reaction sites and reaction paths of ClO2 degradation of FQs were revealed.This research got the following conclusions:(1)The study on the degradation efficiency of ClO2 for ciprofloxacin(CIP),norfloxacin(nor),enrofloxacin(ENR)and fleroxacin(FLE)showed that the degradation efficiency of ClO2 for the four FQs antibiotics increased with the initial concentration of ClO2,and under different pH conditions,acidic conditions would inhibit the degradation of the four FQs antibiotics,and the degradation rate was relatively slow,but under alkaline conditions,it would promote the degradation of the four FQs antibiotics and the degradation efficiency was very fast.(2)The results showed that the oxidation reaction of four FQs antibiotics by ClO2 in aqueous solution followed the second-order reaction kinetic model.When ClO2 was excessive,the second-order reaction rate constants were kCIP=1.603×103 M-1·min-1,kNOR=33.4327 M-1·min1,kENR=4.6699×102 M-1·min-1 and kFLF=3.1314×104 M-1·min-1,respectively.FQs antibiotic anions had the highest reaction activity,the kFQ-values of CIP,NOR,ENR and FLE were respectively 1.908×103M-1·min-1,1.6944×104M-1·min-1,2.1941×104M-1·min-1和1.1015×105 M-1·min-1,while the value of kFQ+ and kFQ is relatively small.(3)In this study,based on the structure of the parent compound of FQs antibiotics,the charge ratio of oxidation products and literature analysis,the reaction sites and pathways of ClO2 degradation of FQs antibiotics were studied,the results showed that the main groups involved in the reaction of FQs antibiotics were piperazine ring,and the main reaction sites involved in the reaction were N1 atom and N4 atom on piperazine ring.At least five oxidation products and two pathways were found in this study.CIP,NOR,ENR and FLE were degraded mainly through the fracture of C-N bond and C-C bond.Decarboxylation reaction and dealkylation reaction were also very common in the oxidation of FQs antibiotics by ClO2,which was the mainly reaction pathway.This study provided an effective method of removing FQs antibiotics from aquatic environment.