Study On Oxidation Of Pyrazolone During Chlorine Dioxide Disinfection Process:transformation Behavior And Water Toxicity

Recent years,pharmaceuticals are frequently detected in aquatic environment and are receiving increasing attention for its potential threaten to human health.Compared with traditional drinking water treatment process such as coagulation,sedimentation and filtration,disinfection process appeared to be the most effective way to degrade pharmaceuticals in raw water.Chlorine dioxide(ClO2)is an efficient alternative disinfectant of chlorine for its high biocidal efficacy and less potential of chlorine disinfection by-products(DBPs)formation.Therefore,it's important to conduct a study on reaction kinetics,degradation pathway and water toxicity of pharmaceuticals during chlorine dioxide disinfection process.The target pharmaceuticals of this study are antipyrine(ANT),aminopyrine(AMP)and isopropylphenazone(PRP),the research object is to study the degradation efficiency and reaction kinetic parameters of pharmaceuticals by ClO2,identify major degradation products and conclude the degradation pathway,research the variation patterns of water toxicity.The results of this study demonstrated that,all of the three target pharmaceuticals could be degraded by ClO2,the reaction followed second-order kinetics and the second-order rate constant were determined to be kapp(ANT)=4.8×10-1 M-1s-1,kapp(PRP)=11.0 M-1s-1,kapp(AMP)=(1.30±0.01)×105 M-1s-1.pH value had similar effect pattern to reaction rate of the three pharmaceuticals,higher pH could accelerate the reaction when pH<9,while strong alkaline environment(pH>9)might significantly slow down the oxidation process due to disproportionation reaction of ClO2.Under simulative physical condition,ClO2 could degrade PRP and AMP within 30 min,which is the average duration of exposure in disinfection process,while the degradation rate of ANT was only 24.2%.Main active group of pharmaceuticals were also recognized,C=C double bond and C-N bond were most vulnerable under ClO2 electrophilic attack.The reaction pathway could be concluded as cleavage of C=C double bond,ring-opening reaction of pyrazolone ring and de-carbonyl reaction,the degradation products of three pharmaceuticals were highly similar.ClO2 could effectively reduce the genetic toxicity of PRP and AMP,while it barely had any effect on ANT.