Insight into PPCP degradation by UV/NH2Cl and comparison with UV/NaClO: Kinetics, reaction mechanism, and DBP formation

Simiao Li; Xiuwei Ao; Chen Li; Zedong Lu; Wenfeng Cao; Fangfang Wu; Shuming Liu; Wenjun Sun

doi:10.1016/j.watres.2020.115967

Insight into PPCP degradation by UV/NH₂Cl and comparison with UV/NaClO: Kinetics, reaction mechanism, and DBP formation

Water Res. 2020 Sep 1:182:115967. doi: 10.1016/j.watres.2020.115967. Epub 2020 May 27.

Authors

Simiao Li¹, Xiuwei Ao¹, Chen Li¹, Zedong Lu¹, Wenfeng Cao², Fangfang Wu¹, Shuming Liu¹, Wenjun Sun³

Affiliations

¹ School of Environment, Tsinghua University, Beijing, 100084, China.
² Suzhou University of Science and Technology, Suzhou, 215009, China.
³ School of Environment, Tsinghua University, Beijing, 100084, China. Electronic address: wsun@tsinghua.edu.cn.

PMID: 32721700
DOI: 10.1016/j.watres.2020.115967

Abstract

The UV/NH₂Cl process is an emerging advanced oxidation process (AOP) that is greatly effective in degrading pharmaceuticals and personal care products (PPCPs). However, detailed information regarding the process is lacking. The degradation of ibuprofen (IBP, an electron-withdrawing PPCP) and naproxen (NPX, an electron-donating PPCP) in UV/NH₂Cl and UV/NaClO processes was performed to investigate the applicability and security of the UV/NH₂Cl process and compare with those of UV/NaClO. UV/NH₂Cl was effective in degrading both IBP and NPX and the degradation followed pseudo-first order kinetics (k_IBP = 0.0037 cm²/mJ and k_NPX = 0.0044 cm²/mJ). This indicated the broad applicability of UV/NH₂Cl to different kinds of PPCPs. Ranges of values of UV intensity (0.3-1.0 mW/cm²) and pH (6.0-8.0) showed little effect on the degradation of PPCPs by UV/NH₂Cl based on UV Dose but HCO₃^- (2-8 mM), natural organic matter (NOM, 2-8 mg/L), and the natural water matrixes were inhibitory. Increasing the dosage of NH₂Cl from 0.15 mM to 0.75 mM, resulted in an even increase of k_IBP; however, k_NPX increased slowly after 0.3 mM NH₂Cl. Mechanism experiments involving nitrobenzene showed that •OH was the major radical involved in degrading IBP and NPX via UV/NH₂Cl. The electron spin resonance spectroscopy and kinetic modeling results also indicated the larger amount of •OH and weaker reactive chlorine species (mainly ClO• and ClO₂•) in UV/NH₂Cl compared with UV/NaClO. Compared to UV/NaClO in synthetic and natural water, UV/NH₂Cl was a more stable degrader with little pH- and substrate-dependence, while UV/NaClO preferred degrading the electron-donating PPCP and at low pH. The UV/NH₂Cl produced less halogenated disinfection byproducts (DBPs) (even nitrogenous DBPs) and was less cytotoxic theoretically than UV/NaClO based on the DBPs included in this study. Thus UV/NH₂Cl process may be an effective AOP for water treatment.

Keywords: Disinfection by-products; Drinking water; Hydroxyl radical; Pharmaceuticals and personal care products; UV/NH(2)Cl; UV/NaClO.

MeSH terms

Chlorine
Disinfection
Halogenation
Kinetics
Ultraviolet Rays
Water Pollutants, Chemical*
Water Purification*

Substances

Water Pollutants, Chemical
Chlorine