Removal of Microcystis aeruginosa using nano-Fe3O4 particles as a coagulant aid

Zhang, Bo; Jiang, Dan; Guo, Xiaochen; He, Yiliang; Ong, Choon Nam; Xu, Yongpeng; Pal, Amrita

Removal of Microcystis aeruginosa using nano-Fe3O4 particles as a coagulant aid

2015

Blue-green algae bloom is of great concern globally since they adversely affect the water ecosystem and also drinking water treatment processes. This work investigated the removal of Microcystis aeruginosa (M. aeruginosa) by combining the conventional coagulant polyaluminum chloride (PACl) with nano-Fe₃O₄ particles as a coagulant aid. The results showed that the addition of nano-Fe₃O₄ significantly improved the removal efficiency of M. aeruginosa by reducing the amount of PACl dosage and simultaneously hastening the sedimentation. At the M. aeruginosa density of an order of magnitude of 10⁷, 10⁶, and 10⁵ pcs/mL, respectively, the corresponding PACl dose of 200, 20, and 2 mg/L and the mass ratio of PACl to nano-Fe₃O₄ of 4:1, the removal efficiency of M. aeruginosa could be increased by 33.0, 44.7, and 173.1 %, respectively. Compared to PACl, PACl combined with the nano-Fe₃O₄ as a coagulant aid had higher removal efficiency at a wider pH range. SEM images showed that nano-Fe₃O₄ first combined with PACl to form clusters and further generated the flocs with algae. Results from the laser particle analyzer further suggested that the floc size increased with the addition of nano-Fe₃O₄. It was noted that the addition of nano-Fe₃O₄ led to aluminum species change after PACl hydrolyzed in the algae solution, from Alₐ to Alb and Alc subsequently. As a coagulant aid, the nano-Fe₃O₄, in conjunction with PACl, apparently provided nucleation sites for larger flocs to integrate with M. aeruginosa. In addition, increased floc density improved the removal of M. aeruginosa.

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