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 (O-3) competition kinetics method was developed. Sixteen competitors with known second-order rate constants for their reaction with O-3 ranging between 1 and 10(8) M-1 s(-1) were applied to cover a wide range of the O-3 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 x 10(6) M-1 s(-1)) while k(app,O3) for tryptophan- and thioether-containing cyano-metabolites were significantly higher than expected (3.4-7.3 x 10(7) 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