Chlorine dioxide (ClO2) is used for disinfection pollutant control in water treatment. Thereby reactions of ClO2 with matrix constituents can form free chlorine as a secondary oxidant. However, exact yields of free chlorine and other inorganic by-products of this reaction are yet lacking. The present study is a decent investigation on reactions of ClO2 with moieties in natural organic matter (NOM) which quickly react with ClO2 such as phenols and olefins. Thereby primary yields of the inorganic by-products chlorite, chloride, FAC, and chlorate were determined and compared with organic matter bulk material (i.e., Suwannee River natural organic matter (SRNOM)). The reaction of ClO2 with the studied model compounds (vanillin, hydroquinone, indigotrisulfonate and dimedone) revealed very different yields of inorganic by-products. Besides hydroquinone all investigated model compounds formed approximately 50% chlorite per consumed ClO2, while the remaining fraction of inorganic by-products largely varied. Vanillin formed 35% chloride and 4% chlorate, indigotrisulfonate 25% chloride, 7% free chlorine and 3% chlorate and dimedone 50% chloride and 4% chlorate. Only hydroquinone formed exclusively chlorite (90%). Yields of free chlorine formed by ClO2 oxidation of SRNOM were significant (22%) which principally could result in halogenated organic by-products. Additionally, chlorite (63%), chloride (8%), and chlorate (5%) were formed in this reaction. The yield of free chlorine decreased significantly after pre-ozonation, which can be explained by the ozone-induced formation of poly-hydroxylated aromatic compounds, which may mainly form chlorite in analogy to hydroquinone.

Formation of secondary oxidations in the reaction of chlorine dioxide with organic matter

ACS Fall 2021

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