Summary: | Harmful algal blooms (HABs) caused by <i>Heterosigma akashiwo</i> are occurring in coastal waters frequently, posing a great risk to marine environments and subsequent treatment processes like desalination. UV-assisted permanganate oxidation (UV/KMnO<sub>4</sub>) is recognized as an innovative advanced oxidation process. This study investigated the inactivation and removal efficiencies of <i>H. akashiwo</i> cells by UV/KMnO<sub>4</sub>. Algal cells were effectively disintegrated into fragments by UV/KMnO<sub>4</sub>. Also, the degradation of photosynthetic pigments, membrane lipid peroxidation, and severe oxidative stress in algal cells was observed. The removal efficiency of algal cells reached 80.2% by 20 min of UV/KMnO<sub>4</sub> oxidation, with a KMnO<sub>4</sub> dosage of 5 mg L<sup>−1</sup>. In addition, the residual algal cells could be completely removed by a subsequent self-settling process, without an additional coagulation procedure. The fragmentation of algal cells caused by UV/KMnO<sub>4</sub> may facilitate the formation of algal flocs, thereby improving the cell settleability. Furthermore, UV<sub>254</sub> was significantly reduced by UV/KMnO<sub>4</sub>, which is expected to reduce the formation of disinfection byproducts and membrane fouling. This study elucidates that UV/KMnO<sub>4</sub> can be a promising technique for the efficient treatment of harmful marine algae.
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