Stirring-induced vortex augmented ultrasonic cavitation for algae inactivation

Ultrasonication (US) is an ecofriendly algae removal strategy with chemical additives-free; however, its standalone application is limited by low energy-conversion efficiency and insufficient cavitation effects. To address these limitations, this study investigated combining mechanical stirring with US to synergistically enhance cavitation dynamics and reactive oxygen species production. In situ measurements revealed the pressure from cavitation in the combined system was 1.71 times that in a system with only US. In the intensified hydrodynamic field, hydroxyl radicals, superoxide radicals and singlet oxygen concentrations were approximately 84, 7 and 18 times that of the US alone system, respectively. Comparative analyses of algal physiological responses after exposure to both systems showed pronounced functional impairments in the combined treatment group, with disruption of photosynthetic activity, exacerbation of oxidative stress, compromised cellular integrity, and metabolic dysfunction. Mechanistically, vortex-driven flow patterns optimized energy distribution by enhancing bubble nucleation and nonlinear oscillations, which amplify reactive oxygen species-mediated oxidative damage. This work establishes a paradigm for augmenting US treatment efficacy through hydrodynamic field modulation and offers a scalable solution for sustainable algal bloom mitigation.