A Research On The Efficacy And Mechanisms For The Degradation Of Ciprofloxacin In Water By UV/NH₂Cl Advanced Oxidation Process

Antibiotics are a kind of organic microcontaminants that are ubiquitous in the global water environment.China is a big producer and consumer of antibiotics,and the levels of antibiotics detected in river systems are relatively high.Residual antibiotics in water environment will not only affect the ecological environment,but also potentially threaten human health.At present,the traditional drinking water treatment technologies have limited effect on the removal of antibiotics,and the advanced treatment processes,such as ozone biological activated carbon and membrane technology,also have certain technical limitations.UV/chloramine process is a new and promising UV-based advanced oxidation process,which can achieve efficient degradation of organic micropollutants and has become a new research hotspot in recent years.In this study,medium pressure UV/chloramine（MPUV/NH₂Cl）advanced oxidation process was used to degrade the typical antibiotic in aqueous environment.In this paper,ciprofloxacin（CIP）was selected as the target pollutant,and the efficiency and mechanism of removing CIP by MPUV/NH₂Cl were explored,aiming to comprehensively study and evaluate the performance of this process,and to provide basic theoretical basis and reference for the engineering application of this technology.The results showed that MPUV/NH₂Cl significantly improved the degradation efficiency of CIP compared with MPUV photolysis alone and NH₂Cl oxidation alone,and the degradation process was in line with the pseudo-first-order kinetics.The degradation of CIP in MPUV/NH₂Cl was promoted by reducing the initial concentration of CIP,increasing the dosage of NH₂Cl appropriately,and controlling the neutral p H value of the solution.The presence of NO₃^—and Br^—,which were common in water matrix,promoted the generation of active radicals in MPUV/NH₂Cl and thus accelerated the degradation of CIP,while the presence of HCO₃^—trapped free radicals and significantly inhibit the removal of CIP.CIP was degraded by MPUV/NH₂Cl mainly through defluorination and cracking of the piperazine ring,in which the fracture transformation of piperazine ring was the primary degradation pathway of CIP in MPUV/NH₂Cl.Most of the degradation products were produced by MPUV photolysis,so MPUV photolysis alone contributed the most to the degradation of CIP under neutral conditions.Oxidation of NH₂Cl alone in MPUV/NH₂Cl was independent of p H value.Under different p H values,the contribution of hydroxyl to CIP degradation was relatively weak.Under acidic and neutral conditions,the contribution of active halogen species（i.e.,active chlorine species and active nitrogen species）to CIP degradation was much greater than that of hydroxyl.During the degradation of CIP in real water,81.3%of trihalomethanes,15.8%of nitrogen-containing disinfection by-products,and 23.3%of haloacetic acids were reduced by the MPUV/NH₂Cl advanced oxidation process.Haloacetic acids was the dominant class of by-products formed during the degradation,in which trichloroacetic acid（TCAA）accounted for the largest proportion.MPUV/NH₂Cl advanced oxidation process could significantly reduce the theoretical cytotoxicity of disinfection by-products.Moreover,haloacetic acids and nitrogen-containing disinfection by-products were the major sources of the theoretical cytotoxicity.According to the prediction results of ECOSAR software,more than half of the degradation products of CIP showed higher acute or chronic ecotoxicity than that of CIP.