Mechanistic insights on interactions of dissolved organic matter with chemical oxidants: quantification of reactive sites and identification of oxidation byproducts

Chemical oxidants including ozone (O3), chlorine (HOCl/OCl-) and chlorine dioxide (ClO2) are applied for disinfection of drinking water. To cope with water scarcity and the increased risks associated with the presence of micropollutants, water treatment systems are upgraded with an additional oxidation step to purify impaired water sources such as wastewater. However, there are two main drawbacks to oxidative water and wastewater treatment. (i) In most waters, dissolved organic matter (DOM) rather than micropollutants is by far the main sink for oxidants and (ii) oxidation is always accompanied by the formation of disinfection byproducts (DBPs). The formation of DBPs is only poorly understood and the identification of precursors in DOM responsible for DBP formation is difficult. Consequently, a better understanding of DOM and DOM-oxidant interactions is essential and was the main goal of this thesis.(1) An oxidative titration approach based on the kinetic selectivity of oxidants towards different electron-rich moieties in DOM was developed. Concentrations of phenolic moieties in five DOM isolates and two wastewater effluent samples were quantified by oxidative titration with ClO2 and in the range of 1.6-3.7 µmol phenols/mgC. The electron donating capacity (EDC) and inorganic ClO2-byproducts were linearly correlated. A novel molecular tagging for phenols in DOM, combined with the determination of EDC values of 27 tagged and non-tagged DOM model compounds, revealed a better understanding of reactive structures within DOM.(2) A non-target screening workflow was developed to analyse carbonyl compounds formed upon ozonation of DOM. A total of 178 carbonous and nitrogenous carbonyl compounds was detected upon ozonation of two lake waters, three wastewaters in the laboratory and one wastewater in a full-scale wastewater treatment plant. Five different formation trends of carbonyl compounds as a function of spe- cific ozone doses were observed. Ozonated municipal wastewater effluents showed a significantly higher fraction of N-containing carbonyl compounds (30%) compared to lake water (17%), highlighting the differences in the water types. Among the 178 carbonyl compounds are eight targets, which showed total concentrations of 1.1 and 1.9 µmol/mgC at specific ozone doses of 0.5 and 2 mgO3/mgC, respectively. Furthermore, 15 non-target carbonyl compounds were identified using MS2 spectra and kinetic and mechanistic information. Hydroxyacetone, unsaturated dialdehydes and ketoacids, potentially trialdehydes/ketones and the N-containing 2-oxo-propaneamide are reported for the first time in real ozonated water samples.(3) An analytical procedure for the measurement of 18O/16O in H2O2 was developed. d18O of H2O2 formed during ozonation (pH 3-8) of three olefins and phenol were determined. Criegee-type reactions always lead to a comparable baseline d18O of 59 permille in H2O2 and do not allow to distinguish precursors. However, mechanistic implications are possible for compounds with competing reaction pathways, which induce pH-dependent deviations of d18O of H2O2. For acrylate, a decarboxylation induced pathway leads to a lower d18O at higher pH (47 permille). For phenolate, competing pathways via an ozone-adduct (electron transfer and loss of 1O2) lead to an enrichment of 18O, leading to a lower d18O in H2O2 (49 permille).The results presented in this thesis enhance the knowledge of DOM-oxidant interactions significantly.