Reactivity of Cyanobacteria Metabolites with Ozone: Multicompound Competition Kinetics
Valentin Rougé, Urs von Gunten, Elisabeth M.‐L. Janssen
Abstract
High Resolution Image Download MS PowerPoint Slide 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 × 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 × 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 <10 2 to 5.0 × 10 3 M –1 s –1, giving first insights into the O 3 reactivity of this class of compounds. Due to lower O 3 reactivities, heterocycle- and aliphatic amine-containing cyano-metabolites may be only partially degraded by a direct O 3 reaction near circumneutral pH. Hydroxyl radicals, which are formed during ozonation, may be more important for their abatement. This novel multicompound kinetic method allows a high-throughput screening of ozonation kinetics.