Migration And Transformation Of Ofloxacin By Free Chlorine In Water Distribution System

In recent years,as the improvement of living standards and medical technology,antibiotics have been used extensively in the medical field.Ofloxacin?OFL?,a typical representative of fluoroquinolones,is widely used in clinical medicine.Although it has a good curative effect,it is also constantly detected in various environmental media such as water bodies,sediments,and soils.These environmental residues can affect the growth and development of plants,inhibit or even kill certain microorganisms in the environment,and have an impact on human health.In addition,in recent years,disinfection by-products such as trihalomethane?THMs?and haloacetic acid?HAAs?,which are carcinogenic,teratogenic and mutagenic,have also been detected in drinking water and the content has increased year by year,threatening human health.The environmental residue of OFL and the water pollution caused by disinfection by-products have been widely concerned.At the same time,the study on the migration and transformation of antibiotics such as OFL in the environment has also become a research hotspot in the field of drinking water safety.Currently,there have been many studies on the removal of OFL and the disinfection of drinking water.Great progress has been made in this area,but there are still some deficiencies.Previous research on OFL mainly focuses on the simple reaction environment such as beaker deionized water.However,the study of the degradation,migration and transformation of OFL in the complex environment of water supply network has not yet been reported.Therefore,based on the comprehensive simulation experiment platform of water quality of a large water supply pipe network in an university in Zhejiang,this study investigated the degradation kinetics,migration and transformation mechanism of OFL in the pipe network and the deionized water under the action of the free chlorine to provide a reference for the effective control of OFL into the urban water system and the protection of the human and living body.The migration and transformation of OFL in the water supply network and beaker deionized water under the action of free chlorine were systematically studied,which provided some reference significance for the effective control of OFL into the urban water system and the protection of human health and the environment.This study investigated the degradation kinetics and product generation of OFL in the pipe network under different pipe materials,flow rate,pH,free chlorine concentration and temperature.The results obtained in the beaker and pipe network were compared.The results showed that the reaction rate of OFL chlorination with free chlorine increased with the increase of free chlorine concentration in the pipe network and deionized water,and the degradation efficiency of OFL in the pipe network was higher than that in deionized water,satisfying second-order dynamics model.The degradation rate under different pH was:neutral>acidic>alkaline.The influence of flow rate is not significant while the influence of pipe materials and temperature is obvious.The degradation rate of OFL increased with the increase of temperature,indicating the OFL degradation was an endothermic process.Liquid chromatograph-mass spectrometer?LC-MS?was used to detect the chlorination intermediates,and the results showed that piperazine ring was the main group involved in the chlorination reaction and the main point involved in the chlorination reaction was the N4 atom on piperazine ring.OFL lost a CH₃ to form the oxidation product M-61,react on the N4 atom on piperazine ring,and removed C₃H₇N to form the oxidation product M-101 by free chlorine.Oxazine rings opened to form the oxidation product M-139.N2 atoms on the quinolone ring were replaced by Cl to form the oxidation product M-108.In addition,on the one hand,free chlorine attacked the hydroxyl group on piperazine ring,captured the hydrogen and lost one H₂O molecule to form the oxidation product M-18;on the other hand,free chlorine lost one CO₂ molecule to form the oxidation product M-44.With the progress of the reaction,a substitution reaction occurred and H atom is replaced by Cl atom to form the oxidation product M+44.It is also found that THMs mainly exist in the form of trichloromethane?TCM?while HAAs mainly exist in the form of monochloroacetic acid?MCAA?.In addition,the results showed that as the reaction time increases,the concentrations of THMs and HAAs increase.