To satisfy the increasing water demand despite a more volatile supply, the only option is often potable water reuse. Such water reuse is currently achieved by purifying wastewater effluents with advanced treatment technologies, including reverse osmosis to reject unwanted pollutants and advanced oxidation processes (AOPs) to degrade permeated pollutants. The UV/chloramine AOP is one of the promising AOPs in this scenario because chloramines applied upstream can permeate through RO membranes and serve as the oxidant precursors. This thesis work tackled one critical challenge in the design and operation of the UV/chloramine AOP: understanding the unique complexity of the radical chemistry faced under advanced treatment conditions. The radical formation from UV photolysis of NH
2Cl was experimentally investigated using probe compounds. NH
2• that was generated from NH
2Cl photolysis was anticipated to be primarily consumed by the dissolved oxygen in water. HO•, Cl•, Cl
2•– and ClO• were the major reactive species that contributed to the degradation of micropollutants. ClO• was ignored in previously reported literature, but its steady-state concentration was found to be comparable to that of HO• in the UV/chloramine AOP. The steady-state concentration of the four radicals followed the trend of Cl
2•– > HO• ~ ClO• > Cl•. The UV photolysis of NHCl
2 also generated the four radicals, and their steady-state concentrations followed the trend of Cl
2•– > HO• > Cl• > ClO•. A kinetic model that incorporated the models in the literature with additional consideration of the non-negligible reactions relevant to nitrate/nitrite was established and used to predict the radical formation in the UV/chloramine AOP. By comparing with the experimental results, the model underestimated the HO• concentration, but overestimated the concentrations of reactive chlorine species in the UV/NH
2Cl AOP. However, the differences between the experimental and modeled results became smaller on the radical formation in the UV/NH
2Cl-NHCl
2 system, which was likely ascribed to the less significant NO
2– formation in the UV/mixture AOP compared with that in the UV/NH
2Cl AOP alone.
Two representative micropollutants, i.e., caffeine (CAF) and diclofenac (DCF), were selected and their degradation in the UV/chloramine AOP was investigated. HO• and UV photolysis were the predominant contributors to the degradation of CAF (~90%) and DCF (80–85%), respectively, under the conditions relevant to potable water reuse. Cl• also contributed to the degradation of CAF while the contribution from Cl
2•– and ClO• was negligible. The major contributing radicals in DCF degradation were HO•, Cl• and Cl
2•–. CAF degradation was suppressed at lower pH or in the presence of chloride (0.05–0.3 mM) and alkalinity (2.5–20.0 mg/L as CaCO
3), while it was barely affected by nitrate (0.05–0.2 mM). The degradation of DCF was less affected by the water matrices since direct UV photolysis was the major contributor to its degradation and the decreased contribution of HO• and Cl• by scavenging of chloride and bicarbonate was offset by the increased contribution of Cl
2•– and CO
3•–. By using a real RO permeate, the effect of chloramine dosing manners was investigated. The highest degradation constant of CAF and DCF were observed by using Approach 2, in which the overall chloramine concentration prior to RO filtration was 3 mg/L and the RO feed was not pre-acidified.
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