Overlooked roles of Cl2O and Cl2 in micropollutant abatement and DBP formation by chlorination. (1st February 2023)

• Record Type: Journal Article
• Authors: Yang, Xin; Wang, Anna; Hua, Zhechao; Wei, Wenrui; Cao, Yilong; Fu, Bingyue; Chen, Shuping; Dong, Zijun; Fang, Jingyun
• Is Part Of: Water research. Volume 229(2023)
• Publication Date: 2023-02-01
• Subjects: Chlorine -- Micropollutants -- Disinfection byproducts (DBPs) -- Kinetics -- Water treatment; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2022.119449
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: pH, chlorine and Cl⁻ concentrations change micropollutant degradation by chlorination. A simplified method is developed to determine rate constants of chlorine toward micropollutants. Reactivities with micropollutants increase in the order of H2 OCl + ≈ OCl⁻ < HOCl << Cl2 O ≈ Cl2 . Cl2 O dominates micropollutant degradation in real drinking water and groundwater. Cl2 O and Cl2 significantly contribute to the formation of DBPs. Abstract: This study investigated the roles of diverse free available chlorine (FAC) species including HOCl/OCl −, H2 OCl +, Cl2 O, and Cl2 in the degradation of micropollutants. The degradation of 5 micropollutants was significantly affected by pH, FAC dosage, and chloride (Cl − ) concentration. The reaction orders in FAC ( n ) of 5 micropollutants (acetaminophen, carbamazepine, naproxen, gemfibrozil, and mecoprop) ranged from 1.4 ± 0.2 to 2.1 ± 0.3 at pH 3 − 5, evidencing the importance of Cl2 O and Cl2 for micropollutant abatement. A simplified method for the determination of second-order rate constants ( k ) of specific FAC species with micropollutants was developed. Herein, the k for neutral/dissociated forms of 5 micropollutants with Cl2 and Cl2 O were determined in the ranges of 9.3 (± 0.2) × 10 2 ∼ 2.9 (± 0.2) × 10 9 M −1 s −1 and 1.8 (± 0.1) × 10 4 ∼ 3.7 (± 0.6) × 10 9 M −1 s −1, respectively. They were 4 − 7 orders of magnitude higher than those of HOCl, whereas those of OCl − and H2 OCl + were negligible. By using kinetic modeling, Cl2 was more important under acidic conditions and higher Cl − levels with contributions of 37.9 – 99.2% at pH 5 in pure water. Cl2 O played a dominant role in micropollutant degradation in pure water (56.4 − 87.3%) under neutral conditions. Furthermore, both Cl2 and Cl2 O played vital roles in the formation of disinfection byproducts (DBPs) during chlorination of carbamazepine and natural organic matter. This study highlights the overlooked roles of Cl2 O and Cl2 in micropollutant abatement and DBP formation during chlorination. Graphical abstract: Image, graphical abstract