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Isolation of complex dissolved organic matter (DOM) from environmental water is a major challenge for unknown screening analysis by high-resolution mass spectrometry. In this study, DOM in process water during advanced drinking water treatment was fractionated sequentially by three solid-phase extraction (SPE) cartridges based on the polarity and charge of DOM molecules. By sequential SPE with unknown screening analysis, over 3000 DOM features were found in raw water, whereas around 2000 were obtained by a single SPE. The hydrophobic neutral (HPON) fraction contained CHO features with highest averaged molecular weight followed by hydrophobic acid (HPOA) and then hydrophilic acid (HPIA). The average degree of carbon double bond equivalents and carbon oxidation states indicated that the HPON fraction contained molecules that were more unsaturated and less oxidized than those of the HPOA and HPIA fractions. Ozone selectively decomposed (1) more unsaturated and less oxidized HPON features, (2) more unsaturated HPOA compounds, and (3) less oxidized HPIA molecules. Oxidation by-products were mostly HPON and HPIA compounds that were more oxidized than the decomposed molecules. During biological activated carbon (BAC) filtration, less oxidized HPON were preferentially removed, whereas HPOA were removed without selectivity. HPON and HPIA molecules with more oxidized character were found to be refractory to BAC treatment. HPON with more unsaturated and HPIA with more oxidized characters were decomposed by chlorine. Many types of HPIA decomposed during chlorination were the oxidation by-products of ozonation that were refractory to BAC treatment. Sequential SPE with unknown screening analysis provided previously unknown details of the molecular characteristics of DOM and its changes during advanced water treatment. • Sequential solid-phase extraction effectively recovers dissolved organic matter (DOM). • Ozone preferentially decomposes more unsaturated and less oxidized DOM. • Ozone oxidation by-products are found as highly oxidized hydrophobic neutral (HPON) and hydrophilic acid (HPIA). • Biological activated carbon filtration removes less oxidized HPON and hydrophobic acid (HPOA). • Chlorine selectively reacts with HPON and HPIA species. [ABSTRACT FROM AUTHOR]

This study aimed to classify the possible molecular formulas of precursors for disinfection by-products (DBPs) in raw, coagulated, and chlorinated water samples from the U-Tapao Canal, Songkhla, Thailand. The molecular formulas of DBPs in chlorinated water were investigated. Polyaluminum chloride (PACl) was employed as a coagulant. Orbitrap Fourier transform-mass spectrometry was able to estimate the composition of dissolved organic matter (DOM) with the carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) elements contained and DBPs at the molecular level. The molecular formulas of the DOM in the raw water primarily consisted of CHO and CHON when extracted by lichrolut EN. The CHO and CHON species were rich in lignin-, tannin-, and condensed aromatic-like substances. The DOM with high-molecular-weight from 300 to 500 Da were preferentially removed by coagulation. The PACl coagulation decreased the abundances of lignin-, tannin-, and condensed aromatic-like substances in the CHO formulas, while lignin- and condensed aromatic-like substances in the CHON formulas remained. The remaining precursors corresponded to CHON molecules in the coagulated water, which may result in the formation of some chlorine (Cl)-containing molecules. Several DBPs among the CHOCl and CHONCl species were produced in the chlorinated water through the addition reaction of chlorine. New chlorinated N-DBPs of 21 formulas were detected. Image 1 • The LiEN is selective for trapping DOM in a wide mass range (100–500 Da). • The non-targeted DBP precursors were evaluated by the Orbitrap mass spectrometry. • PACl coagulation mostly removed DOM with MW ranging from 300 to 500 Da. • Formation of CHOCl and CHONCl species corresponded to their putative precursors. [ABSTRACT FROM AUTHOR]