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.
The combination of chlorine and UV (i.e., chlorine-UV process) has been attracting more attention in recent years due to its ready incorporation into existing water treatment facilities to remove PPCPs. However, limited information is available on the impact of total ammonia nitrogen (TAN). This study investigated two model PPCPs, N,N-diethyl-3-toluamide (DEET) and caffeine (CAF), in the two stages of the chlorine-UV process (i.e., chlorination and UV/chlor(am)ine) to elucidate the impact of TAN. During chlorination, the degradation of DEET and CAF was positively correlated with the overall consumption of total chlorine by TAN. Reactive nitrogen intermediates, including HNO/NO and ONOOH/ONOO, along with OH were identified as major contributors to the removal of DEET and CAF. During UV irradiation, DEET and CAF were degraded under UV/chlorine or UV/NHCl conditions. OH andCl were the major reactive species to degrade DEET and CAF under UV/NHCl conditions, whereas OCl played a major role for degrading CAF under UV/chlorine conditions. Numerical models were developed to predict the removal of DEET and CAF under chlorination-UV process. Chlorinated disinfection byproducts were detected. Overall, this study presented kinetic features and mechanistic insights on the degradation of PPCPs under the chlorine-UV process in ammoniacal water.
There is increasing concern about the severe endocrine-related health problems because of the discharge of estrogenic disrupting chemicals (EDCs) into the natural environment. In this study, we investigated the activation of monochloramine (NH 2 Cl) by biochar [pyrolyzed by cotton straw at 350 °C (Cot350), wheat straw at 350 and 700 °C (WS350 and WS700), and corn straw at 350 and 700 °C (CS350 and CS700)] for the degradation of estradiol (E2) and ethinylestradiol (EE2). Approximately 95% of parent E2 and EE2 was removed by Cot350/NH 2 Cl in buffered solution, and 87% of E2 and 75% of EE2 were removed in urine within 24 h. Electronic paramagnetic resonance analysis and radicalquenching experiments showed that biochar activated NH 2 Cl and primarily generated • NO radicals for the degradation of the EDCs. The nitrogen and silicon elements of Cot350 served as primary catalytic sites for NH 2 Cl activation, whereas the sp 2hybridized carbon on WS700 and CS700 played a major role. The effect of major urine components (i.e., ammonia species, chloride, and bicarbonate) on the reaction pathways of biochar/NH 2 Cl was also elucidated. This study provides new insights into the reaction pathways of NH 2 Cl activation by biochar and suggests potential applications for other carbonaceous materials for NH 2 Cl activation.
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