Developing a restricted chlorine-dosing strategy for UV/chlorine and post-chlorination under different pH and UV irradiation wavelength conditions. (November 2020)

• Record Type: Journal Article
• Authors: Cheng, Shi; Wu, Ji; Zuo, Yan-Ting; Han, Yu-Ze; Ji, Wen-Xiang; Li, Yan; Huo, Zong-Li; Li, Ai-Min; Li, Wen-Tao
• Is Part Of: Chemosphere. Volume 258(2020)
• Publication Date: 2020-11
• Subjects: Chlorine photolysis -- Natural organic matter -- Haloacetic acids -- Bromate -- Acute toxicity -- Chlorine-dosing strategy; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2020.127393
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: UV/chlorine and chlorination processes have drawn great interests of water treatment utilities for oxidation and disinfection purposes. This work proposed a restricted chlorine-dosing strategy for UV/chlorine and post-chlorination under different pH and UV irradiation conditions by comprehensively assessing the oxidation of natural organic matter (NOM), formation of 9 haloacetic acids (HAA9) and bromate, and alteration of toxicity. During UV/chlorine with restricted chlorine doses, the oxidation of NOM chromophores (i.e., ΔUVA254) showed an apparent dependence on cumulative exposures of free available chlorine ( CT FAC ); Meanwhile, HAA9 formation was determined by CT FAC values and could be linearly correlated with ΔUVA254 irrespective of pH and UV irradiation wavelength. Irradiated by 254 nm LP-Hg lamp, the faster chlorine photolysis produced relatively higher steady-state concentrations of Cl and HO species but resulted in lower CT FAC . Reducing CT FAC values by operation parameters (pH, UV wavelength and irradiation fluence) could mitigate HAA9 formation during UV/chlorine at a specific chlorine dose. Additionally, high bromide concentration and acidic pH promoted more bromo-HAAs formation, and the presence of NOM significantly suppressed bromate formation. Analogous to ozonation, the UV/chlorine pre-oxidation could reduce the HAA9 formation potentials during post-chlorination at mildly alkaline pH. The photobacterium bioassay further demonstrated that although the UV/chlorine treatment might have increased the acute toxicity, the post-chlorination treatment could polish the acute toxicity to the level of chlorination alone. These results suggest that with the restricted chlorine-dosing strategy, the trade-off between oxidation/disinfection efficiency and DBPs formation can be controlled by monitoring CT FAC and ΔUVA254 values during UV/chlorine treatment. Graphical abstract: Image 1 Highlights: Oxidation of NOM chromophores showed apparent dependence on CT FAC values in UV/Cl2 . HAA9 formation in UV/Cl2 was related to CT FAC values and ΔUVA254. The presence of NOM greatly suppressed bromate formation in UV/Cl2 . UV/Cl2 oxidation reduced HAA9 formation in post-chlorination at alkaline pH. Post-chlorination could reduce the acute toxicity formed in UV/Cl2 .