Characterization of the transformation of natural organic matter and disinfection byproducts after chlorination, ultraviolet irradiation and ultraviolet irradiation/chlorination treatment

• NOM fractions with a low O/C and high molecular weight were the most susceptible toward UV/chlorination. • Chlorination and UV/chlorination generated Cl-DBPs share only 30% similarity. • Chlorination formed more polycyclic aromatic CHNOCl groups than UV/chlorination. • UV irradiation increased the intensity of tannin- and lignin-like precursors of Cl-DBPs. • MFAssign-based package was promoted to automatically analyze mass spectra data and visualize DBPs. The ultraviolet (UV)/chlorination process provides an emerging strategy to disinfect and remove trace organic contaminants in drinking water and wastewater treatment plants. Different strategies for UV irradiation, chlorination, and UV/chlorination affect the characteristics of natural organic matter (NOM) and the formation of disinfection by-products (DBPs). The underlying effect remains poorly understood. In this work, Orbitrap-high resolution mass spectrometry, with a high accuracy for mass identification and a low cost, was used to investigate NOM transformation and DBP formation with UV irradiation, chlorination, and UV/chlorination. Of the untreated and treated (UV irradiation, chlorination, and UV/chlorination) NOM sample, most identified compounds were phenolic and highly unsaturated aliphatic compounds. Compared with UV irradiation, chlorination, and UV/chlorination had a stronger effect on the transformation of NOM molecular composition and resulted in more oxidized groups. A comparison of UV/chlorination with chlorination showed that UV/chlorination formed less nitrogen-containing Cl-containing DBPs, and more oxidized and saturated Cl-containing DBPs. After chlorination and UV/chlorination, more than 60% of the identified DBPs could track their precursors on the basis of electrophilic substitution and addition reactions. The UV/chlorination precursors were more saturated than for chlorination. This systematic investigation is expected to guide the future advanced development of water treatment strategies and provide a method to auto-analysis of mass spectra data and visualize the DBP character.