Toxicity Reduction of Microcystis Aeruginosa Using Microbubble Ozonation

The aim of this study was to investigate microbubble ozonation for the removal of toxic cyanobacteria, Microcystis aeruginosa. The microbubble ozonation (30 min) at 3.47 mg O₃ L⁻¹ decreased the M. aeruginosa concentration from 1.5 × 10⁷ to 0.8 × 10⁷ cell mL⁻¹. However, the acute toxicity (48 h) to Daphnia magna (<24 h old) was considerably increased after the microbubble ozonation, possibly owing to the release of intracellular microcystins (MCs). Considering the release of toxic MCs, the microbubble ozonation was optimized at an environmentally relevant concentration (1.74 × 10⁶ cell mL⁻¹) of M. aeruginosa. Microbubble ozonation at 0.26–1.92 mg O₃ L⁻¹ for 30 min removed M. aeruginosa by 26 to 83% without any acute toxicity on D. magna. Moreover, D. magna feeding enhanced the removal rate from 85 to 100% for 48 h. These findings suggest that microbubble ozonation, possibly combined with D. magna biomanipulation, can be a promising tool to control toxic cyanobacteria in ambient water.