Reaction of chlorine dioxide with organic matter – formation of inorganic products

Abstract

Chlorine dioxide (ClO₂) is used for disinfection of water and pollutant control. Recently it was shown that free available chlorine (FAC) is formed during the oxidation of organic compounds with ClO₂. To investigate the moieties in natural organic matter (NOM) responsible for the FAC formation, reactions of ClO₂ with phenols and olefins were investigated. Thereby primary yields of the inorganic by-products chlorite, chloride, FAC, and chlorate were determined and compared with Suwannee River natural organic matter (SRNOM). The reaction of ClO₂ with the studied model compounds (vanillin, hydroquinone, indigotrisulfonate, and dimedone) revealed very different inorganic by-products. The main inorganic by-product of all investigated compounds was chlorite (>50% per consumed ClO₂). Besides chlorite, vanillin formed 35% chloride and 4% chlorate, indigotrisulfonate 25% chloride, 7% FAC and 3% chlorate and dimedone 50% chloride and 4% chlorate. Hydroquinone formed exclusively chlorite (90%). Yields of FAC 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. The yield of FAC decreased significantly after pre-ozonation, which can be explained by ozone induced formation of poly-hydroxylated aromatic compounds, which may mainly form chlorite in analogy to hydroquinone.