Comparison of photolysis rates, radical concentrations and micropollutant degradation during the UV290/free chlorine and UV290/dichloramine advanced oxidation processes

• Published in: Separation and purification technology 2025-07, Vol.361, p.131562, Article 131562
• Main Authors: Xie, Anyin, Ma, Jinxing, Li, Xianhui, Tang, Baixuan, Zhou, Yang, Gao, Yuan, Yang, Tao, Wu, Zihao, Zhang, Zhong
• Format: Article
• Language: English
• Subjects: AOP; Disinfection byproducts; Free chlorine; NHCl2; Primidone; UV-LED
• ISSN: 1383-5866
• DOI: 10.1016/j.seppur.2025.131562

[Display omitted] •UV-LEDs at 290 nm were used for free chlorine/dichloramine photodecay and radical formation.•The modeling results were optimized using the innate quantum yields.•The steady-state concentrations of radicals were measured at different pHs.•The performance of two AOPs in degrading primidone was compared at different pHs.•Of the 28 halogenated DBPs we measured, UV/free chlorine AOP produced higher concentrations. UV-LEDs are promising UV light sources with potential to replace traditional UV lamps in future water treatment applications. In this study, UV-LED at 290 nm was used to investigate the photolysis kinetics of free chlorine and dichloramine and the associated generation of DBPs. We have derived innate quantum yields for radical generation by the UV photolysis of HOCl, OCl−, and NHCl2 of 0.85, 0.57, and 0.58, respectively. The formation of radicals (•OH, Cl•, Cl2•−, and ClO•) increased with the pH increasing from 6.0 to 8.0 in UV290/free chlorine AOP, while the concentration of radicals in UV290/NHCl2 AOP remained relatively stable. Meanwhile, ClO• was the main radical in UV290/free chlorine AOP, and Cl2•− dominated in UV290/NHCl2 AOP. However, in both UV290/AOPs, •OH was the largest contributor to primidone degradation. This study also assessed the formation of disinfection by-products (DBPs) after AOP treatment and chloramination, including 28 halogenated DBPs from eight categories and one N-nitrosamine (NDMA). The results indicated that, of the 28 halogenated DBPs we measured, UV290/free chlorine AOP yielded more, but the regulated haloacetic acids (HAA9) and trihalomethanes (THM4) remained below their 80 μg/L and 60 μg/L MCLs, respectively. UV290/NHCl2 AOP produced more NDMA, but consistently below the 10 ng/L California Notification Level for chlorinated drinking waters or reuse waters. HAA9, haloacetonitriles (HAN4) and haloacetamides (HAM4) increased for both AOPs after chloramination. When weighed by metrics of toxic potency, HAN4 and HAM4 were found to be the main contributors and the total toxicity produced by UV290/free chlorine AOP was slightly greater. This study provides theoretical guidance for selecting suitable oxidants in UV-LED AOPs across varying water quality conditions.