Degradation Of Carboxylic Acid Drugs In UV/chlorine Disinfection Process:degradation Mechanism And Water Toxicity

In recent years,the exposure frequency and exposure levels of pharmaceuticals(PhACs)are increasing in the environment.It caused widely concern that PhACs had a potential threat to human health all over the world.The disinfection process can be more effective to remove the PhACs in the raw water,compared to the coagulation,precipitation and filtration in the conventional drinking water treatment process.Chlorination technology is the most widely used method of drinking water disinfection,which can effectively remove the PhACs in the original water.Compared with the individual chlorination,the removal mechanism of trace drugs in water is more complicated by UV/chlorine disinfection process.But at present,the research in this field is very limited.Therefore,it is of great significance to study the reaction kinetics,degradation pathway and water quality toxicity of PhACs during the UV/chlorine disinfection process.In this paper,two kinds of carboxylic acid drugs,clofibric acid(CA)and naproxen(NAP),were selected as the target PhACs.The degradation efficiency,reaction kinetics mechanism,influencing factors,active component contribution and degradation pathway in the process of UV/chlorine disinfection were explored.The changes in the genetic toxicity of water quality during the reaction process were tested.Furthermore,the degradation products of PhACs during the disinfection process and the potential water quality risk were revealed.This research has very important theoretical and practical significanceabout ensuring the safety of drinking water.The results show that two kinds of carboxylic acids can be effectively degraded by UV/chlorine disinfection.The degradation process could be degraded via pseudo first order kinetics.The apparent rate constants(kobs)are kobs,CA=0.0447min-1,kobs,NAP=0.418 min-1,respectively.The rate constant of degradation increased significantly with the increasing of chlorine dosage.The pH value of the solution has a similar effect on the degradation rate of the two target drugs,which means acid conditions(PH<7)can promote the reaction and alkaline condition(pH>7)inhibits the reaction due to the morphologic changes of the active component.Other reaction conditions,such as chloride ion(Cl-)and carbonate(HCO3-),also affect the rate of UV/chlorine disinfection degraded target drugs.HCO3-slightly inhibits the degradation of CA,but it has no effect on the degradation of NAP.Cl-has no effect on the degradation of CA,but it can significantly promote the degradation of NAP.By the study on contribution of active components to UV/chlorine disinfection degrading target drugs,it was found that Hydroxyl radical(·OH)has a significant degradation effect on CA under acidic conditions.And active chlorine radical(RCS)andUV photolysisdominated the main degradation of CAin neutral and alkaline solutions.Chlorinationdominated the degradation of NAPunder the acid condition and RCS dominated the degradation of NAP under the alkaline condition.In the process of UV/chlorine disinfection of target drugs,the cracking of Aryl oxygen carbon and Aryl halogen and the substitution of aryl ring were the main degradation pathways of CA.the reaction of demethylation,dehydroxylation and decarboxylation were the main degradation pathways of NAP.Comparison with separate UV disinfection and separate chlorination disinfection,UV/chlorine disinfectioncan effectively reduce the genetic toxicity of water quality of CA and NAP.