Volatile Disinfection By-products Formation During Chlorination Of Water

Chlorination is the most common method for water treatment and disinfection.Although chlorine has been demonstrated to be effective forthe control of many microbial pathogens,it is also knownto react with aqueous constituents to yield disinfectionbyproducts（DBPs）.In this study,the volatile DBPs during chlorination was investigated Carbamate insecticides,as frequently detected pollution in resource water,were chosen to study.Four carbamate insecticides,including methomyl,carbofuran,carbaryl,and thiodicarb,were investigated over a range of reaction conditions,based on variables of chlorine/precursor（C1/P）molar ratios and temperature.CH₃NCl₂ was found to be the major product resulting from chlorination of all four carbamate insecticides,with a second-order rate constant of kfrom 0.010 to 0.375M-1s-1.Dichloromethlyamine（DMA）was found to be part of the emerging class of nitrogen based disinfection byproducts（N-DBPs）of health concern in chlorinated water.However,there is a limited understanding about its formation,stability,and toxicity.About ppb level CH₃NCl₂ were also detected in chlorination real water sample collected from different location in China.Further experiments proved that CH₃NCl₂ is relatively stable compound with a half-life 38 hours in water.The toxicity of CH₃NCl₂ was investigated by using human lung tumor cells,and it exhibited a relatively high toxic compared to CHC13.The GI50 values of CH₃NCl₂and CHCl3were calculated to be 61μmol/L and 14mmol/L respectively.The GI50 value of CH₃NCl₂was about three orders of magnitude more toxic than CHCl3.The toxicity of CH3NC12 was also investigated by using Vibrio fisheri,the IC50 values of CH₃NCl₂and CHCl3were calculated to be 0.02μmol/L and 23mmol/L respectively.According to the IC50 values,CH₃NCl₂ was six orders of magnitude toxic than CHC13,The results suggest that CH₃NCl₂ poses a hazard to public health and the environment and should be included as one of the important N-DBPs.The effects of chloride ion concentration on the formation of volatile DBPs resulting fromchlorination of typical precursors and body fluid analogue（BFA）in swimming poolswere investigated with variable chloride concentration and pH.The formation of three volatile DBPs（NC13,CHCl3 and CNCHCl2）was observed to be linearly correlated with chloride concentration,both in bench experiments and the real swimming pool water samples.Free chlorine consumption was also observed to increase with chloride concentration.These behaviors appear to be attributable to shifts in speciation of free chlorine,with higher chloride resulting in higher concentration of molecular chlorine（Cl2）,which is much more reactive than HOC1.The results of this work suggest potential changes to lower chloride concentration in pool management that could be important to control volatile DBP formation and economize free chlorine usage in chlorinated swimming pools.