This study examined how ozone and permanganate preoxidation affect coagulation of green algae (Chodatella sp.) and diatom (Navicula sp.) by alum and/or polymer. The results show that algae species exhibit noticeable responses to various combinations of preoxidation and coagulation processes. Preoxidation can improve green algae coagulation with either alum or cationic polymer as coagulant. For diatom, alum is more effective on cell coagulation than cationic polymer. Ozone preoxidation has detrimental effect on diatom coagulation removal, while permanganate preoxidation has only minor effect. These probably are due to the difference in interaction modes between the preoxidants, cell surface, and coagulants. It is, therefore, suggested that the strategy for algae removal from source water should be based on the dominant algae species.
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