Effects of UV-Based Treatment on Water and Air Chemistry in Chlorinated, Indoor Pools

摘要

Combined UV/chlorine treatment is commonly used in treatment of swimming pool waterrnbecause UV irradiation is known to be effective against (some) chlorine-resistant microbialrnpathogens (e.g., C. parvum), and it has the potential to promote photodecay of some DBPs (e.g.,rninorganic chloramines). However, it has been reported in the literature that UV-based treatmentrnhas the potential to promote formation of some DBPs (e.g., CNCl and CNCHCl_2). Promotion ofrnthese reactions also results in increases of free chlorine consumption rates. To further examinernthis issue and to explore the dynamics of UV-induced effects on water chemistry in chlorinatedrnindoor swimming pools, a three-year field experiment has been initiated at a high school, indoorrnswimming pool under operating conditions of: conventional chlorination (1~(st) year), chlorinationrnaugmented by MP UV irradiation (2nd year), and chlorination augmented by LP UV irradiationrn(3~rd year). The first year of sampling was recently completed and the MP UV system has beenrninstalled. Water samples were collected from the pool and analyzed for free and combinedrnchlorine, urea and volatile DBPs. Eleven volatile DBPs were identified: monochloraminern(NH_2Cl), dichloramine (NHCl_2), trichloramine (NCl_3), chloroform (CHCl_3), bromoformrn(CHBr3), dichlorobromomethane (CHBrCl_2), dibromochloromethane (CHBr_2Cl), cyanogenrnchloride (CNCl), cyanogen bromide (CNBr), dichloroacetonitrile (CNCHCl_2), andrndichloromethylamine (CH3NCl_2). Of these eleven compounds, ten were identified as regularlyrnoccurring, with dichlorobromomethane (CHBrCl_2) only appearing sporadically. Also since manyrnDBPs are volatile, air quality within indoor swimming pool facilities has become an importantrnissue with regard to human health. A large fraction of the current research regarding swimmingrnpool air quality has focused on trichloramine (NCl_3) exposure. Trichloramine in the gas phase isrnanalyzed by air sparging-DPD/KI analytical method. The results showed a correlation betweenrnbather loading and gas phase trichloramine concentration in the 1~(st) year of experiment underrnchlorination operating condition. The results of this study are expected to yield fundamentalrnimprovements in our understanding of how UV systems can be used to improve water chemistryrnin swimming pool facilities. At the end of these experiments the following questions will bernaddressed: ultimately, should we be using UV for water treatment in chlorinated, indoorrnswimming pool facilities? If so, MP UV or LP UV? The results of these experiments are alsornexpected to benefit UV/chlorine applications in other water treatment settings, such as treatmentrnof drinking water, wastewater, or in water reuse facilities.