Generation of Reactive Nitrogen Species in UV Photolysis of Dichloramine and Their Incorporation into Nitrogenous Byproducts.

Dichloramine (NHCl 2 ) often coexists with monochloramine (NH 2 Cl) in reverse osmosis (RO) permeate in potable reuse scenarios when NH 2 Cl is added upstream of RO for membrane fouling control such that UV photolysis of NHCl 2 occurs during the downstream UV/chloramine process. However, the formation of reactive nitrogen species (RNS) and their incorporation into byproducts during the UV/NHCl 2 process are largely unknown. This study quantitatively evaluated the generation of RNS in the UV/NHCl 2 process and investigated the role of RNS in micropollutant transformation. UV photolysis of NHCl 2 produced comparable RNS concentration to that of NH 2 Cl at the same oxidant dosage (100 μM) at pH 5.5. Under the experimental conditions, the RNS contributed greatly (40.6%) to N , N -diethyl-3-methylbenzamide (DEET) degradation. By using 15 N-labeling and mass spectrometry methods, seven nitrogenous byproducts of DEET degradation with the incorporation of nitrogen originating from the RNS were detected. Among these seven byproducts, six were identified to contain a nitro group (-NO 2 ). While the UV/NHCl 2 process formed comparable intensities of -NO-containing products to those in the UV/NH 2 Cl process, the later process formed 3-91% higher intensities of -NO 2 -containing products. These findings are essential in furthering our understanding of the contribution of the UV/NHCl 2 process in potable reuse scenarios.