The formation of nitrogenous disinfection by-products (N-DBPs) is always found to increase during UV/chlorine treatment, while it is not well understood. The formation pathways and mechanism of dichloroacetonitrile (DCAN) from amino compounds during UV/chlorine treatment were investigated in this study. Phenylethylamine (PEA), L-phenylalanine (Phe), and L-phenylalanyl-L-phenylalanine (Phe-Phe) were selected to represent amines, amino acids and peptides, respectively, to investigate the formation pathways of DCAN during UV/chlorine treatment. Firstly, chlorination of amines, amino acids and peptides rapidly formed N-chloramines via chlorine substitution. Then, UV photolysis but not radicals promoted the transformation from N-chloramines to N-chloroaldimines and then to phenylacetonitrile (PAN). Finally, PAN was transformed to DCAN with conversion ratios of 14.2 – 25.6%, which was attributed to radical oxidation, as indicated by scavenging experiments and density functional theory (DFT) calculations. The formation of DCAN during UV/chlorine treatment is highly dependent on the participation of radicals.

Roles of UV photolysis and radicals in the formation of N-DBPs in UV/chlorine

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