Decomposition of ozone in water in the presence of organic solutes acting as promoters and inhibitors of radical chain reactions

Abstract

The decomposition of aqueous ozone is generally due to a chain reaction involving ·OH radicals. Many organic solutes (impurities) can react with ·OH to yield ·O2- upon addition of O2. ·O2-transfers its electron to a further ozone molecule in a rather selective reaction. The ozonide anion (·O3-) formed immediately decomposes into a further ·OH radical. Compounds that convert ·OH radicals into ozone-selective ·O2-, therefore, act as promoters of the chain reaction. The efficiencies of different ·OH to ·O2- converters (e.g., formic acid, primary and secondary alcohols (including sugars), glyoxylic acid, and humic acids) are tested in the presence of other ·OH radical scavengers that do not primarily produce ·O2- (carbonate, aliphatic alkyl compounds, and tert-butyl alcohol). The derived reaction kinetics allows one to qualitatively interpret the variation of the lifetime of O3 found in model solutions and even in natural waters and during drinking water treatment.