Body fluid analog chlorination:Application to the determination of disinfection byproduct formation kinetics in swimming pool water

Disinfection by-products(DBPs)are formed in swimming pools by the reactions of bather inputs with the disinfectant.Although a wide range of molecules has been identified within DBPs,only few kinetic rates have been reported.This study investigates the kinetics of chlorine consumption,chloroform formation and dichloroacetonitrile formation caused by human releases.Since the flux and main components of human inputs have been determined and formalized through Body Fluid Analogs(BFAs),it is possible to model the DBPs formation kinetics by studying a limited number of precursor molecules.For each parameter the individual contributions of BFA components have been quantified and kinetic rates have been determined,based on reaction mechanisms proposed in the literature.With a molar consumption of 4 mol Cl2/mol,urea is confirmed as the major chlorine consumer in the BFA because of its high concentration in human releases.The higher reactivity of ammonia is however highlighted.Citric acid is responsible for most of the chloroform produced during BFA chlorination.Chloroform formation is relatively slow with a limiting rate constant determined at 5.50×10^-3 L/mol/sec.L-histidine is the only precursor for dichloroacetonitrile in the BFA.This DBP is rapidly formed and its degradation by hydrolysis and by reaction with hypochlorite shortens its lifetime in the basin.Reaction rates of dichloroacetonitrile formation by L-histidine chlorination have been established based on the latest chlorination mechanisms proposed.Moreover,this study shows that the reactivity toward chlorine differs whether L-histidine is isolated or mixed with BFA components.

Impact of combining chlorine dioxide and chlorine on DBP formation in simulated indoor swimming pools

The main objective of this study was to assess the combined use of chlorine dioxide（ClO_2）and chlorine（Cl_2） on the speciation and kinetics of disinfection by-product（DBP） formation in swimming pools using synthetic pool waters prepared with a body fluid analog（BFA）and/or fresh natural water. At 1：25（mass ratio） of ClO_2 to Cl_2, there was no significant reduction in the formation of trihalomethanes（THMs） and haloacetic acids（HAAs） for both BFA solution and natural water compared to the application of Cl_2 alone. When the mass ratio of ClO_2 to Cl_2increased to 1：1, substantial decreases in both THMs and HAAs were observed in the natural water, while there was almost no change of DBP formations in the BFA solution. Haloacetonitriles and halonitromethanes levels in both water matrices remained similar. In the presence of bromide, the overall DBP formation increased in both BFA solution and natural water. For the DBP formation kinetics, after 72 hr of contact time,very low formation of THMs and HAAs was observed for the use of ClO_2 only. Compared to Cl_2 control, however, applying the 1：1 mixture of ClO_2/Cl_2 reduced THMs by 〉 60% and HAAs by 〉 50%. Chlorite was maintained below 1.0 mg/L, while the formation of chlorate significantly increased over the reaction time. Finally, in a bench-scale indoor pool experiment, applying ClO_2 and Cl_2simultaneously produced less THMs compared to Cl_2 control and kept chlorite at 〈 0.4 mg/L, while HAAs and chlorate accumulated over 4-week operation period.