UV254 irradiation of N-chloro-α-amino acids: Kinetics, mechanisms, and N-DBP formation potentials. (1st July 2021)

• Record Type: Journal Article
• Authors: Ruan, Xiaoxue; Zhang, Xinran; Lei, Yu; Lei, Xin; Wang, Chao; Yang, Xin
• Is Part Of: Water research. Volume 199(2021)
• Publication Date: 2021-07-01
• Subjects: N-chloro-α-amino acids -- Dissolved organic nitrogen -- UV254 irradiation -- Nitrogenous disinfection byproducts (N-DBPs) -- Water treatment; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.117204
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: l UV254 irradiation accelerated the degradation of N-chloro-α-amino acids. l The apparent quantum yields of sixteen N-chloro-α-amino acids were provided. l pH influenced the UV254 -induced degradation rate of N-chloro-α-amino acids. l UV254 irradiation enhanced the TCNM formation potential of N-chloro-α-amino acids. l The mechanisms of N-chlorotyrosine degradation were proposed. Abstract: This study explores the degradation kinetics and mechanisms of N-chloro-α-amino acids and the changes in the formation potential of nitrogenous disinfection byproducts (N-DBPs) upon UV254 irradiation. UV254 irradiation significantly accelerated the degradation of all the tested N-chloro-α-amino acids compared to those in the dark. Both direct photolysis-induced cleavage of the N-Cl bonds and radical oxidation (e.g., Cl and Cl2 − ) involved reactions that contributed to their enhanced degradation. The fluence-based photolysis rate constants of the N-chloro-α-amino acids varied in the range of (1.06—5.47) × 10 −3 cm 2 mJ −1 at pH 6.0 and (0.74—2.79) × 10 −3 cm 2 mJ −1 at pH 8.0. The apparent quantum yields (Φapp ) of the majority of the N-chloro-α-amino acids were in the range of 0.41−0.95 at pH 6.0 and 0.22−0.79 at pH 8.0, except N-chloroaspartic acid, N-chlorohistidine, and N-chloroalanine. UV254 irradiation significantly enhanced the formation of trichloronitromethane (TCNM) from the tested N-chloro-α-amino acids after post-chlorination, but exhibited various effects on the formation of dichloroacetonitrile (DCAN). A longer UV254 irradiation time generated more TCNM, and a lower pH produced more DCAN from the N-chloro-α-amino acids. The degradation pathways of N-chlorotyrosine, as a representative N-chloro-α-amino acid, are proposed, and the β -scission and 1, 2-H shift pathways led to the formation of different precursors of TCNM and DCAN. The results of this study improve our understanding of the fate of N-chloro-α-amino acids under UV254 irradiation and post-chlorination. Graphic abstract: Image, graphical abstract