Evolutions of dissolved organic matter and disinfection by-products formation in source water during UV-LED (275 nm)/chlorine process

• Published in: Water research (Oxford) 2023-09, Vol.243, p.120284-120284, Article 120284
• Main Authors: Zhao, Xiating, Chen, Chuze, Chen, Haoran, Guo, Yaxin, Zhang, Xueqi, Li, Mengting, Cao, Liu, Wang, Yuting, Gong, Tingting, Che, Lei, Yang, Guoying, Xian, Qiming
• Format: Article
• Language: English
• Subjects: Disinfection by-products; Dissolved organic matter; Source water; Two-dimensional correlation spectroscopy; UV-LED/chlorine
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2023.120284

•The non-fluorescent group of DOM contributed to the formation of HKs, HANs and HNMs.•Lower ratios of UTOX/TOX obtained in UV-LED/chlorine process than chlorination.•The formation and toxicity of N-DBPs and Br-DBPs increased at high UV fluence. Ultraviolet light-emitting diode (UV-LED) is a promising option for the traditional low-pressure UV lamp, but the evolutions of DOM composition, the formation of disinfection by-products (DBPs) and their toxicity need further study in raw water during UV-LED/chlorine process. In UV-LED (275 nm)/chlorine process, two-dimensional correlation spectroscopy (2DCOS) analysis on synchronous fluorescence and UV–vis spectra indicated the protein-like fractions responded faster than the humic-like components, the reactive sequence of peaks for DOM followed the order: 340 nm→240 nm→410 nm→205 nm→290 nm. Compared to chlorination for 30 mins, the UV-LED/chlorine process enhanced the degradation efficiency of three fluorescent components (humic-like, tryptophan-like, tyrosine-like) by 5.1%-46.1%, and the formation of carbonaceous DBPs (C-DBPs) significantly reduced by 43.8% while the formation of nitrogenous DBPs (N-DBPs) increased by 27.3%. The concentrations of C-DBPs increased by 17.8% whereas that of N-DBPs reduced by 30.4% in 24 h post-chlorination. The concentrations of brominated DBPs increased by 17.2% during UV-LED/chlorine process, and further increased by 18.5% in 24 h post-chlorination. According to the results of principal component analysis, the non-fluorescent components of DOM might be important precursors in the formation of haloketones, haloacetonitriles and halonitromethanes during UV-LED/chlorine process. Unlike chlorine treatment, the reaction of DOM in UV-LED/chlorine treatment generated fewer unknown DBPs. Compared with chlorination, the cytotoxicity of C-DBPs reduced but the cytotoxicity of both N-DBPs and Br-DBPs increased during UV-LED/chlorine process. Dichloroacetonitrile had the highest cytotoxicity, followed by monobromoacetic acid, bromochloroacetonitrile and trichloroacetic acid during 30 mins of UV-LED/chlorine process. Therefore, besides N-DBPs, the more toxic Br-DBPs formation in bromide-containing water is also not negligible in the practical applications of UV-LED (275 nm)/chlorine process. [Display omitted]