Degradation Of Saccharin By Typical Advanced Treatment Process And DBPs Derived From Subsequent Chlorination

Artificial sweeteners(ASs)are synthetic sucrose substitutes,which are widely used in beverages,food,personal care products,drugs and animal feed.Saccharin(SAC)is the earliest artificial sweetener and suspected carcinogen,so its pollution in water environment has attracted much attention.The production and use of SAC in China are very large,but there are few studies on SAC pollution and control in China.In this paper,the mechanism and effect of SAC degradation by ozone and UV/H2O2,which are commonly used in water treatment,were discussed,and the effects of two oxidation processes on SAC derived disinfection by-products(DBPs)in the subsequent chlorination stage were investigated.Ozone can effectively degrade SAC,and the degradation rate of 20 mg/L SAC in water treated 60 min by 7.10 mg/min ozonation can reach 99%,and the salinity was 80%.The degradation process conforms to the pseudo-first-order kinetics.The higher the ozone flux,the greater the reaction rate constant.In the process of degradation of SAC by ozone,in addition to ozonation,hydroxyl radicals will also react with SAC.SAC’s benzene ring may hydroxylated by hydroxyl radical and C-N bond breaking,resulting in produced carboxylic acid and other intermediates.The degradation rate of UV/H2O2 oxidized SAC 60 min can reach 99%,and the salinity was 80%.The degradation process conforms to the pseudo-first-order kinetics.The higher the initial H2O2 concentration in the range of 0-1.00 mM,the greater the reaction rate constant.The lower initial SAC concentration,Acidity and higher temperature promoted the reaction.Common ions inhibited the reaction,and the order of action was:NO3->SO42>CO32->Cl-.The degradation of SAC by UV/H2O2 mainly depends on hydroxyl radical reaction.SAC ’s benzene ring may hydroxylated by hydroxyl radical and C-N bond breaking.SAC can react with chlorine,and the degradation rate of 20 mg/L SAC in water treated 60 min by 80 mg/L available chlorine was 22%.A variety of DBPs,can be produced,including trichloromethane(TCM),dichloroacetic acid(DCAA),trichloroacetic acid(TCAA)and dichloroacetonitrile(DCAN),with yields of 8.1,0.4,1.2 and 0.1 μg/mg,respectively.Advanced treatment processes such as ozone and UV/H2O2 have stronger ability to degrade SAC,but due to incomplete degradation,SAC may be transformed into more DBPs precursors.The TCM,DCAA,TCAA and DCAN produced by chlorination after ozonation of SAC were 3,39,41 and 178 times higher than those produced by direct chlorination.The main reason was that ozone degrades SAC into a small molecular structure that reacts more easily with chlorine.With the extension of ozonation time,the concentration of DBPs increased at first and then decreased,and reached the highest at 20 min.When the ozone dosage was 3.50-10.7 mg/min,the increase of ozone dosage promoted the DBPs production.In the range of pH 6 to 8,the higher the pH value of the solution was,the higher the amount of DCAA,TCAA and DCAN was,and the lower the amount of TCM was.20 mM Cl-,NO3-and CO32-inhibited the formation of TCM,DCAA and DCAN.The TCM,DCAA,TCAA and DCAN produced by chlorination after UV/H2O2 oxidation of SAC were 1.7,45,10 and 44 times higher than those produced by direct chlorination.Within 60 min,with the longer the oxidation time of UV/H2O2,the concentration of DBPs increased at first and then decreased,and reached the highest at 20 min.Within 60 min,the longer the oxidation time of chlorine was,the higher the concentration of DBPs was.The higher the initial H2O2 concentration in the range of 0-1.00 mM,the higher the concentration of TCM and DCAN,and the lower the concentration of DCAA and TCAA.In the range of pH 6 to 8,the formation of TCM,DCAA and TCAA was promoted under alkaline conditions,but the production of DCAN was the highest in neutral solution.Ozone and UV/H2O2 advanced treatment processes promote the degradation of SAC,and the resulting intermediates or end products may promote the production of subsequent chlorinated DBPs.Attention should be paid to the transformation and fate of trace organic pollutants,especially refractory or persistent organic matter,in the waterworks treatment process.