Effects of UV-dechloramination of swimming pool water on the formation of disinfection by-products: A lab-scale study

Abstract

UV dechloramination has become a very popular process for reducing the concentration of chloramines in public swimming pool water. As the effects of this process on the formation of disinfection byproducts (DBPs) remain a controversial issue, a bench-scale study has been undertaken to examine the impact of UV dechloramination on the formation of various DBPs. Four pool water samples were exposed to UV radiation at 254 nm in the presence of free chlorine ([Cl 2 ] 0 = 3 mg L-1) and then chlorinated in the dark for 24 h ([Cl 2 ] 0 = 3 mg L-1). High UV doses (up to 47 kJ m-2) were used to simulate cumulative UV doses received by real pool waters. The data showed that UV irradiation led to a 90 % photodecay of free chlorine for UV doses ranging from 13 to 20 kJ m-2 , to the formation of chlorate ion (0.05-0.11 mole of chlorate/mole of free chlorine decomposed) and to a significant increase in the chlorine demand of pool water during the post-chlorination step. UV exposure followed by post-chlorination did not significantly affect the formation of haloacetic acids, led to a small increase in the concentrations of adsorbable organic halogen (AOX) and of chloral hydrate and markedly increased the formation of trihalomethanes (chloroform, bromodichloromethane, chlorodibromomethane), dichloroacetonitrile, 1,1,1-trichloropropanone and chloropicrin.

Effect of medium-pressure UV-lamp treatment on disinfection by-products in chlorinated seawater swimming pool waters

“…A similar trend has been reported in freshwater pool studies (Cheema et al, 2017;Cimetiere and De Laat, 2014;Spiliotopoulou et al, 2015) and also in drinking water, where it has been observed that UV treatment increases the fraction of low molecular organic matter, which in turn increases chlorine consumption (Choi and Choi, 2010 (Feng et al, 2007;Watts and Linden, 2007), which then might react with organic matter present in the pool water. Thereby, non-chlorine reactive molecules may become highly reactive after UV treatment, thus leading to an observed increase in chlorine consumption.…”

“…A possible explanation is that the breaking of large organic molecules, which increased the chlorine reactivity of dissolved organic matter, also promoted precursors in the pool water for THM formation. Previous studies on freshwater pools have also reported similar trends regarding an increase in THM concentration through UV irradiation (Cimetiere and De Laat, 2014). However, Spiliotopoulou et al (2015) reported that UV treatment accelerates THM formation instead of increasing it, since pool water without UV treatment had the same increase in THM formation with a high chlorine level.…”

“…An increase in bromoform and in dibromochloromethane is quite surprising; indeed, previous studies have shown that both low and medium-pressure UV lamps are efficient to remove brominated THMs (Cimetiere and De Laat, 2014;Nicole et al, 1991). In the present case, the observed increase in the concentrations of these two THMs in post-chlorinated water suggests that the amount formed during post-chlorination was higher than the amount photo-decomposed in the UV reactor.…”

“…Spiliotopoulou et al (2015) described that DBPs are only formed in secondary reactions after chlorine addition during the post-UV chlorination treatment of freshwater pools. Cimetiere and De Laat (Cimetiere and De Laat, 2014) also reported increased the formation of some DBPs with UV treatment followed by chlorination in freshwater pools during the post-chlorination step. However, no data have been reported for reaction pathways leading to an increase in the formation of THMs and some other DBPs in seawater.…”

“…However, as chloroform concentrations were close to or under the quantification limit, no definite trend was observed for chloroform. Spiliotopoulou et al (2015) reported that UV irradiation does not create chloroform in freshwater swimming pool waters, with or without free chlorine present, while Cassan et al (2006), Cimetiere and De Laat (2014) and Spiliotopoulou et al (2015) all reported chloroform formation as a result of chlorination following UV irradiation in freshwater pools.…”