Reactivity of Reactive Nitrogen Species and Degradation Kinetics of Micropollutants in the UV/Monochloramine Process

Reactive nitrogen species (RNS) are thought to play a non-negligible role in the UV/monochloramine (NH2Cl) process. This work focuses on RNS (•NO, •NO2, •NH2). The degradation of eight organic micropollutants (OMPs), including phenolic (paracetamol, hydroquinone, estradiol, bisphenol A, and triclosan) and nonphenolic compounds (ibuprofen, carbamazepine (CBZ), and sulfamethoxazole), was examined. We compared the reactivity of RNS with OMPs based on reaction energies and activation energies using density functional theory (DFT) calculations. We verified the specificity of the reaction of •NH2 on phenolic groups: •NH2 degrades phenolic compounds by abstracting hydrogen atoms from phenolic groups. Additionally, DFT calculations demonstrate that •NH2 can react with CBZ to abstract hydrogen atoms from double bonds and amino groups. We established linear relationships between the Hammett ∑σp+ constants of OMPs and their rate constants with •NH2 and developed kinetic models considering the reactions of RNS with OMPs. The models were used to explain how water matrix constituents affect the OMP degradation by obtaining the evolution profiles of HO•, •Cl, and •NH2. The effects of OMPs on the decay of NH2Cl and the generation of inorganic nitrogen were also predicted. Nitro- and nitroso-transformation products of OMPs were detected, suggesting that RNS play essential roles.