Monochloramine (NH2Cl)
can be irradiated by UV to create an advanced oxidation condition
(i.e., UV/NH2Cl) for the elimination of organic micropollutants
(OMPs) from source water. However, information in retrospective studies
was scarce on how UV/NH2Cl performance would be affected
by the water matrix and OMP molecular structures. In this study, the
degradation of five representative OMPs, including triclosan, carbamazepine,
sulfamethoxazole, estradiol (E2), and ethinylestradiol (EE2), was
examined in different water matrices. All OMPs were rapidly removed
by UV/NH2Cl but exhibited different degradation mechanisms.
Although •OH, •Cl, and direct photolysis mainly contributed
to the overall degradation of OMPs in buffered nanopure water, the
contribution of reactive nitrogen species (RNS) generated from the
photolysis of NH2Cl was not negligible in the degradation
of E2 and EE2. A phenolic group was identified as the moiety reactive
toward RNS. Based on quantitative analysis of the impact on OMP degradation
from cosolutes (including Cl–, HCO3
–, NOM) as well as pH and NH2Cl doses, we
developed a kinetic model for the prediction of OMP degradation in
complex water matrices. In environmental water matrices, the performance
and radical contributions in UV/NH2Cl and UV/H2O2 systems were taken into comparison, which showed faster
degradation of OMPs and a more significant contribution of CO3
•– in the UV/NH2Cl process.
Elimination of pharmaceuticals in source-separated human urine is a promising approach to minimize the pharmaceuticals in the environment. Although the degradation kinetics of pharmaceuticals by UV/H2O2 and UV/peroxydisulfate (PDS) processes has been investigated in synthetic fresh and hydrolyzed urine, comprehensive evaluation of the advanced oxidation processes (AOPs), such as product identification and toxicity testing, has not yet been performed. This study identified the transformation products of two commonly used antibiotics, trimethoprim (TMP) and sulfamethoxazole (SMX), by UV/H2O2 and UV/PDS in synthetic urine matrices. The effects of reactive species, including •OH, SO4(•-), CO3(•-), and reactive nitrogen species, on product generation were investigated. Multiple isomeric transformation products of TMP and SMX were observed, especially in the reaction with hydroxyl radical. SO4(•-) and CO3(•-) reacted with pharmaceuticals by electron transfer, thus producing similar major products. The main reactive species deduced on the basis of product generation are in good agreement with kinetic simulation of the advanced oxidation processes. A strain identified as a polyphosphate-accumulating organism was used to investigate the antimicrobial activity of the pharmaceuticals and their products. No antimicrobial property was detected for the transformation products of either TMP or SMX. Acute toxicity employing luminescent bacterium Vibrio qinghaiensis indicated 20-40% higher inhibitory effect of TMP and SMX after treatment. Ecotoxicity was estimated by quantitative structure-activity relationship analysis using ECOSAR.
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