Harnessing Microelectrolysis to Enhance Clay-Based <i>Heterosigma akashiwo</i> Removal via Active Chlorine Generation and Surface Modification

Clay flocculation is a widely adopted method for controlling red tides, yet its low efficiency and high material demand limit its practical applications. This study introduces an innovative microelectrolysis-enhanced clay treatment, which significantly enhances the microalgal removal performance. Using Heterosigma akashiwo (a notorious red tide species) as a model red-tide organism, we demonstrate that the pretreatment of clay suspensions (10 g/L) with microelectrolysis (0.5 A/cm2, 5 min) achieved 93.91% microalgal removal efficiency at only 0.16 g/L clay, which drastically surpassed the 4.51% efficiency of untreated clay. The synergy stems from two key mechanisms. One is the generation and clay adsorption of active chlorine, which enhances algicidal activity. The other is the electrochemically modified clay properties, including increased zeta potential (from −20.43 to −11.90 mV) and optimized pore structure, which improves flocculation and sedimentation. Importantly, the integrated approach reduces algal cell rupture compared to that with electrolysis alone, while the clay matrix moderates the release of active oxidants to enable prolonged control effects. By dramatically lowering clay consumption and maintaining effective algal removal, this work offers a scalable and efficient alternative for red tide mitigation.