Ultraviolet-Induced Effects on Chloramine and Cyanogen Chloride Formation from Chlorination of Amino Acids

Ultraviolet (UV)-based treatment is commonly used to augment chlorination in swimming pools. However, the effects of combined application of UV₂₅₄/chlorine on disinfection byproduct (DBP) formation are incompletely defined. To examine this issue, experiments were conducted with amino acids (l-arginine, l-histidine, and glycine) that are representative of those introduced to swimming pools via human body fluids. For each precursor, stepwise experiments were conducted with chlorination and UV₂₅₄ exposure, with/without post-chlorination. Net formation and decomposition of chloramines and cyanogen chloride (CNCl) were measured for a range of chlorine/precursor (Cl/P) molar ratios and UV₂₅₄ doses. Substantial production of NH₂Cl from l-arginine and l-histidine was observed at Cl/P = 1.0 and 2.0 when post-chlorination was applied to UV₂₅₄-irradiated samples. These results suggested a mechanism of rapid N-chlorination, followed by cleavage of NH₃ by UV₂₅₄ irradiation. CNCl formation was observed from UV₂₅₄-irradiated samples of l-arginine and l-histidine when Cl/P = 2.0 and 3.0, as well as from glycine for Cl/P ≤ 1. Structurally related precursor compounds were examined for CNCl formation potential in chlorination/UV experiments. CNCl formation was promoted by UV₂₅₄ exposure of chlorinated imidazole and guanidine compounds, which suggested that these groups contributed to CNCl formation. The results have implications with respect to the application of chlorine and UV for water treatment in swimming pools and other settings, such as water reuse and advanced oxidation processes