In view of several authors’ earlier findings, CP was chosen as the basic polymer grafted by a quaternary ammonium compound [25,26] for the wastewater treatment. However, it has not been reported as flocculating agent for removing harmful microalgae. Alexandrium tamarens has been a main causative HABs species. Since the late 1980s, blooms of this species have caused mass mortality of cultured fish and grass prawn and paralytic shellfish poisoning (PSP) contamination, as well as frequent intoxication of human being