Sunlight enhanced the formation of tribromomethane from benzotriazole degradation during the sunlight/free chlorine treatment in the presence of bromide

The coexistence of free chlorine and bromide under sunlight irradiation (sunlight/FC with Br−) is unavoidable in outdoor seawater swimming pools, and the formation of brominated disinfection byproducts could act more harmful than chlorinated disinfection byproducts. In this study, benzotriazole was selected as a model compound to investigate the degradation rate and the subsequent formation of disinfection byproducts via sunlight/FC with Br− process. The rate constants for the degradation of benzotriazole under pseudo first order conditions in sunlight/FC with Br− and sunlight/FC are 2.3 ± 0.07 × 10−1 min−1 and 6.0 ± 0.7 × 10−2 min−1, respectively. The enhanced degradation of benzotriazole can be ascribed to the generation of HO•, bromine species, and reactive halogen species (RHS) during sunlight/FC with Br−. Despite the fact that sunlight/FC with Br− process enhanced benzotriazole degradation, the reaction results in increasing tribromomethane (TBM) formation. A high concentration (37.8 μg/L) of TBM was detected in the sunlight/FC with Br−, which was due to the reaction of RHS. The degradation of benzotriazole was notably influenced by the pH value (pH 4 − 11), the concentration of bromide (0 − 2 mM), and free chlorine (1 − 6 mg/L). Furthermore, the concentration of TBM increased when the free chlorine concentrations increased, implying the formation potential of harmful TBM in chlorinated seawater swimming pools.