The UV/H
2O
2 process is a commonly practiced advanced oxidation process (AOP) in drinking water treatment targeting micropollutant abatement. However, during the degradation of micropollutants by AOPs, the elemental composition and structural features of dissolved organic matter (DOM) are also altered. The alterations in DOM result in changes in the formation of disinfection byproducts (DBPs) during the subsequent disinfection step. Ultra-high-resolution mass spectrometry (UHRMS), which obtains accurate mass and elemental formula of molecules, can capture detailed molecular compositions of DOM and DBPs. This study established a new data processing software, HaloFormula, for the formula assignment from UHRMS mass spectra of DOM and DBPs. The alterations of the elemental composition of DOM...[
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The UV/H
2O
2 process is a commonly practiced advanced oxidation process (AOP) in drinking water treatment targeting micropollutant abatement. However, during the degradation of micropollutants by AOPs, the elemental composition and structural features of dissolved organic matter (DOM) are also altered. The alterations in DOM result in changes in the formation of disinfection byproducts (DBPs) during the subsequent disinfection step. Ultra-high-resolution mass spectrometry (UHRMS), which obtains accurate mass and elemental formula of molecules, can capture detailed molecular compositions of DOM and DBPs. This study established a new data processing software, HaloFormula, for the formula assignment from UHRMS mass spectra of DOM and DBPs. The alterations of the elemental composition of DOM due to the UV/H
2O
2 AOP and the connections with the changes in DBP formation during the subsequent disinfection step were investigated by using UHRMS and the newly established software.
The newly developed software, HaloFormula, rapidly and accurately assigns chemical formulas from UHRMS mass spectra of compounds containing C, H, O, N, P, S, Cl, Br, and I. The time required to finish the data processing of a typical DOM sample was less than 5 minutes. Both mass accuracy and isotopic pattern similarity were considered as the formula selection criteria, which further secured the accuracy of the formula assignment by HaloFormula. Compared to Formulatiry, an open-access software for the formula assignment of DOM and chlorinated compounds, HaloFormula showed significantly higher formula assignment ratio and accuracy for CHO, CHONS, Cl-containing, and Br-containing formulas.
Another method was developed to identify and track the nitrogen origins of nitrogenous-DBPs by using
14:15 = 1:1N-labeling of NH
2Cl, UHRMS and the newly established software HaloFormula. By using
14:15 = 1:1N-labeled NH
2Cl, the number of detectable isotope peaks were significantly increased, and the accuracy of formula assignment and nitrogen origin tracking were enhanced. After 3-d chloramination of 3 model C-compounds and 4 model N-compounds using
14:15 = 1:1N-labeled NH
2Cl, more than a hundred nitrogen-containing products were captured by HaloFormula from the UHRMS mass spectra.
The UV/H
2O
2 AOP increased the degree of oxidation and decreased the aromaticity of DOM. A total of 226 chlorinated DBPs with relatively lower aromaticity were newly formed after 3-d chlorination of the UV/H
2O
2-treated DOM compared to the DBPs formed from the DOM sample treated with 3-d chlorination alone. Links between the elemental compositions of DBPs and the corresponding precursors in DOM were visualized by network computation. For C
16HO formulas, only if the formula had an oxygen number of larger than 6 could it be a potential DBP precursor. HO• attack through hydroxylation and decarboxylation increased the number of formulas located in the pool of potential DBP precursors in van Krevelen space. A model compound study reconfirmed the transformation mechanism of DOM during the UV/H
2O
2 AOP and the corresponding influence on the DBP formation potential.
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