Study On The Degradation Efficiency And Mechanism Of Carbamazepine And Ciprofloxacin By UV/chlorine Process

Pharmaceutially active compounds(PhACs)have been frequently detected in the environment,due to its strong polarity,cumulative effects and refractory,conventional water treatment processes cannot effectively remove PhACs.PhACs residues can disrupt the balance of the ecosystem and have a negative impact on human health.Therefore,the removal of PhACs has received widespread attention.The UV/chlorine process uses ultraviolet rays to stimulate free chlorine(HClO/ClOˉ)to produce free radicals with high oxidizing power to degrade pollutants,inactivate pathogens,achieve multiple barrier disinfection and reduce secondary pollution.As a new advanced oxidation process,the UV/chlorine process has important research significance for controlling the generation of disinfection by-products in water.This study took typical PhACs drugs carbamazepine(CBZ)and ciprofloxacin(CIP)as the research objects to investigate and evaluate the removal effect of UV/chlorine on CBZ and CIP;investigate the UV intensity,the initial concentration of residual chlorine,and the pH of the solution Analyze the relative contribution of different free radicals to the UV/chlorine degradation reaction;analyze the structural characteristics of CBZ and CIP;predict raman,infrared and vibrational circular dichroic spectroscopy of CBZ and CIP based on stable configurations;explore the degradation mechanism of CBZ and CIP in UV/chlorine processes based on mass spectrometry;identify degradation intermediates;Determine the reaction path of degradation products;evaluate the changes in toxicity during the degradation process.The results show that the UV/chlorine process is a water treatment process that efficiently removes CBZ and CIP from water.The reaction of CBZ and CIP degradation all fitted pseudo-first-order kinetics.The degradation effect of UV/chlorine process is obviously better than that of single UV and single chlorine.At 20 min,the CBZ removal rate was 99%;at 100 s,the CIP removal rate was 92.2%.In the UV/chlorine degradation process,the reaction rate constant is positively correlated with the ultraviolet light intensity and the initial concentration of residual chlorine,and negatively correlated with the ammonia nitrogen concentration.CBZ has the best degradation effect at pH=3;CIP has the best degradation effect at pH=9.Five intermediates of CBZ and Eight intermediates of CIP were identified by HRMS Q-E Plus Orbitrap LC-MS.In addition,five small-molecular acid intermediates of CBZ and two small-molecular acid intermediates of CIP in the late stage of AML degradation were also identified by GC-MS.NB is used as a free radical probe to quantitatively analyze the relative contribution of different active free radicals to the degradation of CBZ.It was found that ?OH is the main free radical that promotes the degradation of pollutants in the degradation process of UV/chlorine technology.The relative contributions of ?Cl and ?OH to CBZ degradation were 31.6% and 68.4%,respectively.The active radicals participate in a series of reactions,including chlorination,hydroxylation,and electron transfer.The frontier orbital theory analysis showed the C8 and C9 position of CBZ molecular structure and the N6 position of CIP molecular structure might be the most vulnerable to be attacked by radicals.Both luminescent bacteria experiment and ECOSAR prediction showed that the complete removal of pollutants does not guarantee the reduction of acute toxicity.Prolonging degradation may promote the detoxification of toxic intermediates,but may also generate intermediates with higher toxicity.Therefore,it is necessary to further explore the ecological risks of the UV/chlorine process to ensure the safety of water quality.