posted on 2013-05-07, 00:00authored byShihChi Weng, Ernest R. Blatchley
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.