Toward Better Understanding Of Influencing Factors And Products Of Chloral Hydrate In Water

Disinfection byproduct(DBP)is a type of contaminant resulting from the reaction between disinfectant and natural organic matter(NOM)during water disinfection.Chloral hydrate(CH)is a disinfection byproduct commonly found in disinfected water,and once formed,CH may undergo several transformation processes in water.In order to understand its fate and occurrence in water,this study examined several factors that may affect the stability of CH in water,including pH,temperature,and initial CH concentration.Furthermore,this study also investigated the impact of free chlorine and ultraviolet(UV)on degradation of CH.The results of CH hydrolysis indicated that CH was a relatively stable compound(half-life ~7 d for 30 ?g/L)in ambient pH(7)and temperature(20 ?)conditions.However,the hydrolysis rate can be greatly facilitated by increasing pH and temperature or decreasing initial CH concentration.To quantify the influences of these factors on the CH hydrolysis rate,this study developed a multivariate model successfully used to predict the hydrolysis rate constants in 23 conditions.In terms of reaction products,CH hydrolysis yielded mostly chloroform and formic acid and a few of chloride,which confirmed decarburization as a dominant pathway and dehalogenation as a noticeable coexisting reaction,which decreased with an increase of hydrolysis rate.However,no trichloroacetic acid,dichloroacetic acid,monochloroacetic acid,or dichloro acetaldehyde was detected.The oxidation experiment shows that chloral hydrate could not be oxidized by free chlorine with 10 mg/L chlorine and 50 ?g/L chloral hydrate.Meanwhile,no trichloroacetic acid,one of possible oxidation product of chloral hydrate,was detected.This suggests that chlorine did not degrade CH under these reaction conditions.However,an introduction of free chlorine in reaction system without buffer,would accelerate the hydrolysis of CH due to an increase of pH.The photolysis of CH was affected by pH,UV power input,and initial concentration of CH.However,the presence of free chlorine(10 mg/L)poses little influence on the photolysis of CH.Direct photolyis was equal to indirect photolysis of CH.In terms of reaction mechanism,dehalogenation was the dominant pathway for CH photolysis.Chloride was the main product of CH photolysis.Mass balance of chlorine was achieved while mass balance of carbon was poor,indicating that carbon dioxide or halogen-free matters was likely to be photolysis by-product.