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We investigated semiquantitative changes in almost 1000 dissolved organic matter (DOM) features during oxidation with 1 mg of O 3 per liter (mg O 3 /L), 4 mg O 3 /L, or 4 mg O 3 /L + 2.5 mg of H 2 O 2 per liter (advanced oxidation process, AOP) by unknown screening analysis with Orbitrap mass spectrometry. The consequential effects on formation of unknown disinfection by-products (DBPs) by chlorination were evaluated in laboratory-scale experiments. Several hundred unsaturated DOM features with positive oxygen-subtracted double bond equivalents per carbon ((DBE–O)/C) were decomposed by the ozone-only treatment and AOP. The AOP decomposed some saturated (negative (DBE–O)/C)) and reduced molecules, which had negative carbon oxidation states (C os). Several hundred saturated oxidation by-products were detected after ozonation and the AOP. After chlorination, the samples pre-treated with ozone alone resulted in higher formation of unknown DBPs than the AOP pre-treated sample or the sample without oxidation. Over half of the DBP precursors, estimated by electrophilic substitution, were not totally decomposed by any oxidation process, but they were increased after the ozone-only process and AOP. DBP precursors produced by the ozone-only process or AOP formed unique unknown DBPs. Therefore, post-treatment processes after oxidation and before chlorination are important to minimize formation of unknown DBPs. Image 1 • Changes of over 1000 DOM features by ozonation and peroxone were investigated. • Unsaturated DOM features were selectively decomposed by ozone and peroxone. • Several hundred of saturated oxidation byproducts were detected after ozonation and peroxone. • Ozone results in formation of unknown disinfection by-products more than peroxone. • Ozone and peroxone increase generate their specific unknown DBP precursors. [ABSTRACT FROM AUTHOR]

Reclaimed water has recently become an important water source for urban use, but the composition of dissolved organic matter (DOM) in reclaimed water has rarely been characterized at the compound level because of its complexity. In this study, the transformation and changes in composition of low molecular weight DOM in water reclamation processes, where secondary effluent of the municipal wastewater treatment plant was further treated by biofiltration, ozonation and chlorination, were investigated by “unknown” screening analysis using Orbitrap mass spectrometry (Orbitrap MS). The intense ions were detected over an m / z range from 100 to 450. In total, 2412 formulae with various heteroatoms were assigned, and formulae with carbon (C), hydrogen (H) and oxygen (O) only and C, H, O and sulfur (S) were the most abundant species. During biofiltration, CHO-only compounds with relatively high hydrogen to carbon (H/C) ratio or with saturated structure were preferentially removed, while CHOS compounds were mostly removed. Ozonation induced the greatest changes in DOM composition. CHOS compounds were mostly decreased after ozonation while ozone selectively removed CHO compounds with relatively unsaturated structure and produced compounds that were more saturated and with a higher degree of oxidation. After chlorination, 168 chlorine-containing formulae, chlorinated disinfection by-products (DBPs), were additionally detected. Candidate DBP precursors were determined by tracking chlorinated DBPs formed via electrophilic substitution, half of which were generated during the ozonation. [ABSTRACT FROM AUTHOR]

Image 1 • Orbitrap MS explores BOM compositions in drinking water. • BOM compositions in ozonated water and finished water differ. • Chlorine disinfection generates residual BOM in drinking water. [ABSTRACT FROM AUTHOR]