Rapid Algal Inactivation during a Harmful Algal Bloom in the Pingtan Sea Area by a Hydroxyl Radical-Mediated Method

Harmful algal blooms (HABs) pose a significant threat to aquatic ecosystems, public health, and economic activities worldwide. In this study, a highly efficient advanced oxidation process utilizing hydroxyl radicals (•OH) generated via strong ionization discharge at atmospheric pressure was applied to rapidly inactivate harmful algae collected during HABs in June 2022 in Pingtan coastal waters, which were dominated by the toxic species Karlodinium digitatum and Karenia papillonacea. Notably, the inactivation rates reached 98% ± 0.05% for a high algal density of 2500 cells/mL within an extremely short contact time of only 12 s, requiring low total reactive oxidant (TRO) concentrations of merely 0.5 to 1.0 mg/L. Meanwhile, •OH inactivated algal cells primarily while the cells remained morphologically intact, without visible lysis. This action mechanism effectively prevents the secondary release of intracellular organic matter and intracellular toxins, a common drawback of many physical and chemical treatments. Furthermore, the •OH treatment concurrently improved the overall water quality by significantly reducing total coliform counts. The technology demonstrated herein, characterized by its rapid response, high efficiency, minimal ecological impact, and dual function of algae inactivation and water purification, represents a highly promising and environmentally benign strategy for the emergency control and mitigation of HABs in water conservation projects.