Effect of chloride on the formation of volatile disinfection byproducts in chlorinated swimming pools

Abstract

Chloride can accumulate in chlorinated swimming pool water. Although substantial efforts have been made to examine the effects of halide ions on the formation of volatile disinfection byproducts (DBPs), most have focused on bromide. The effects of chloride ion concentration on the formation of volatile DBPs in swimming pools remain largely unstudied. In this study, chlorination of typical precursors and body fluid analogue (BFA) were investigated with variable chloride concentration and pH. The formation of three volatile DBPs (NCl3, CHCl3 and CNCHCl2) was observed to be linearly correlated with chloride concentration, both in bench experiments and in actual 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 HOCl. The results of this work suggest that changes in pool management strategies to promote low chloride concentration could be important for control of volatile DBPs in pools and to economize free chlorine usage.