Molecular-Level Transformation of Dissolved Organic Matter during Oxidation by Ozone and Hydroxyl Radical

Abstract

Ozonation of drinking and wastewater relies on ozone (O3) and hydroxyl radical ( • OH) as oxidants. Both oxidants react with dissolved organic matter (DOM) and alter its composition, but the selectivity of the two oxidants and mechanisms of reactivity with DOM moieties are largely unknown. The reactions of O3 and • OH with two DOM isolates were studied by varying specific ozone doses (0.1 -1.3 mg-O3/mg-C) at pH 7. Additionally, conditions that favor O3 (i.e., addition of an • OH scavenger) or • OH (i.e., pH 11) were investigated. Ozonation decreases aromaticity, apparent molecular weight, and electron donating capacity (EDC) of DOM, with large changes observed when O3 is the main oxidant (e.g., EDC decreases 63 -77% for 1.3 mg-O3/mg-C). Both O3 and • OH react with highly aromatic, reduced formulas detected using high-resolution mass spectrometry (O:C = 0.48 ± 0.12; H:C = 1.06 ± 0.23), while • OH also oxidizes more saturated formulas (H:C = 1.64 ± 0.26). Established reactions between model compounds and O3 (e.g., addition of 1-2 oxygen atoms) or • OH (e.g., addition of one oxygen atom and decarboxylation) are observed and produce highly oxidized DOM (O:C > 1.0). This study provides molecular-level evidence for the selectivity of O3 as an oxidant within DOM.

Spatial and Temporal Variability of Dissolved Organic Matter Molecular Composition in a Stratified Eutrophic Lake

“…1 O 2 is a selective oxidant that preferentially oxidizes nucleophilic compounds and can be quenched by DOM (Hessler et al., 1996; Yang et al., 2013). • OH also reacts quickly with aromatic rings via oxygen addition to generate more oxidized products, which is consistent with the observed increases in O:C w (Figure 2f) and the shift toward more oxidized lignin‐ and tannin‐like formulas (Figure 3b; Remucal et al., 2020). Thus, the observed changes in weighted averages derived from FT‐ICR MS data could be attributed to either microbial or photochemical processing.…”

Insights into Adsorption of Humic Substances on Graphitic Carbon Nitride

“…Due to the heterogeneity of HSs, bulk parameters (such as DOC and UV absorbance) cannot completely describe the complicated adsorption behaviors of HSs. , As a rough indicator of HS aromaticity, , the SUVA of adsorbed HA and FA on CN-U was tracked based on mass balance as a function of contact time. As presented in Figure a, the SUVA of adsorbed HA remained stable at pH 3.0, indicating the homogeneous adsorption of bulk HA.…”

Selective Reactivity and Oxidation of Dissolved Organic Matter by Manganese Oxides

“…Dissolved organic matter (DOM) is a complex mixture of thousands of individual molecules containing carbon, hydrogen, oxygen, and heteroatoms (e.g., nitrogen). − DOM is heterogeneous across natural and engineered waters with differing reactive functional groups, molecular weights, and aromaticity. ,− The DOM source (e.g., allochthonous vs autochthonous) and extent of environmental processing alter its composition, ,− with implications for bioavailability, contaminant mobility, ,,− photochemical transformation, ,, and reactivity with oxidants (e.g., chlorine). ,,− …”