Abstract
The application of oxidants for disinfection or micropollutant abatement during drinking water and wastewater treatment is accompanied by oxidation of matrix components such as dissolved organic matter (DOM). To improve predictions of the efficiency of oxidation processes and the formation of oxidation products, methods to determine concentrations of oxidant-reactive phenolic, olefinic or amine-type DOM moieties are critical.Here, a novel selective oxidative titration approach is presented, which is based on reaction kinetics of oxidation reactions towards certain DOM moieties. Phenolic moieties were determined by oxidative titration with ClO2 and O3 for five DOM isolates and two secondary wastewater effluent samples. The determined concentrations of phenolic moieties correlated with the electron-donating capacity (EDC) and the formation of inorganic ClO2-byproducts (HOCl, ClO2−, ClO3−). ClO2-byproduct yields from phenol and DOM isolates and changes due to the application of molecular tagging for phenols revealed a better understanding of oxidant-reactive structures within DOM.Overall, oxidative titrations with ClO2 and O3 provide a novel and promising tool to quantify oxidant-reactive moieties in complex mixtures such as DOM and can be expanded to other matrices or oxidants.
Highlights
Chemical oxidants such as ozone, chlorine and chlorine dioxide are applied in water treatment to improve the microbial and chemical water quality (von Gunten, 2018)
Phenols react with ClO2 by a two-step mechanism where in a first step, phenolate and ClO2 react by a 1-electron transfer to a phenoxyl radical and ClO−2 Eq (1)
All dissolved organic matter (DOM) isolates and two secondary wastewater effluent samples could be included in the relationship, reinforcing the advantage of this novel quantification method in terms of accuracy of the results compared to previous attempts of phenol quantification. These results demonstrate that oxidative titration with ClO2 is a robust method to determine oxidant-reactive phenolic moieties in DOM, even when applied to DOM in real wastewater samples
Summary
Chemical oxidants such as ozone, chlorine and chlorine dioxide are applied in water treatment to improve the microbial and chemical water quality (von Gunten, 2018). Thereby, DOM-oxidant interactions decrease the effi ciency of oxidation processes and contribute to the formation of potentially toxic oxidation byproducts (OBPs) (Li and Mitch, 2018; Liu et al, 2020; Sedlak and von Gunten, 2011; von Gunten, 2003a) These problems may be aggravated when applying such processes for micro pollutant abatement during enhanced wastewater treatment or water reuse, because of higher concentrations and different types of DOM (von Gunten, 2018). In combination with UV measurements, EDC is a useful parameter to assess relative changes in the content of reactive DOM moieties and formation of OBPs from the reactions with various oxidants such as chlorine dioxide, chlorine or ozone (Onnby et al, 2018a; Wenk et al, 2013). High-resolution mass spectrometry (HRMS) has been applied to investigate molecular level changes induced by oxidation of DOM (Jiang et al, 2020; Liu et al, 2020; Maizel and Remucal, 2017; Remucal et al, 2020; These and Reemtsma, 2005)
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