Reactivity of Cyanobacteria Metabolites with Ozone: Multicompound Competition Kinetics

Cyanobacterial blooms occur at increasing frequency and intensity, notably in freshwater. This leads to the introduction of complex mixtures of their products, i.e., cyano-metabolites, to drinking water treatment plants. To assess the fate of cyano-metabolite mixtures during ozonation, a novel multicompound ozone (O3) competition kinetics method was developed. Sixteen competitors with known second-order rate constants for their reaction with O3 ranging between 1 and 108 M–1 s–1 were applied to cover a wide range of the O3 reactivity. The apparent second-order rate constants (k app,O3) at pH 7 were simultaneously determined for 31 cyano-metabolites. k app,O3 for olefin- and phenol-containing cyano-metabolites were consistent with their expected reactivity (0.4–1.7 × 106 M–1 s–1) while k app,O3 for tryptophan- and thioether-containing cyano-metabolites were significantly higher than expected (3.4–7.3 × 107 M–1 s–1). Cyano-metabolites containing these moieties are predicted to be well abated during ozonation. For cyano-metabolites containing heterocycles, k app,O3 varied from