Formation of trihalomethanes in swimming pool waters using sodium dichloroisocyanurate as an alternative disinfectant

Disinfection is essential to preventing infection caused by microbial pathogens in swimming pool water. The most commonly used disinfection methods are chlorine disinfectant, including sodium hypochlorite (NaOCl) and sodium dichloroisocyanurate (SDIC, C3O3N3Cl2Na) with characteristics of available chlorine formation and stability. In this study, we estimate the formation of trihalomethanes (THM4) in indoor swimming pools filled with seawater that adopt these disinfection methods, and we investigated the factors influencing the formation of THM4. Formation of THM4 by free chlorine (FC) and SDIC respectively is 327.8 μg L−1 and 307.6 μg L−1; Br-THMs is 226.7 μg L−1 for FC, 198 μg L−1 for SDIC. SDIC has less THM4 formation than FC in the same molar Br− dosage (10 μM) and total chlorine dosage (20 μM), and bromoform is the main Br-THMs species. The occurrence of THM4 is inhibited at high dosages of natural organic matter and Br−. The total Br-THMs increase from 75 μg L−1 to 189.7 μg L−1 and from 64.6 μg L−1 to 190 μg L−1 by FC and SDIC at pH 5.0–9.0, both of which are highly dependent on pH. In real water, similar results were found in Br−-containing water (1 mg-Br− L−1).