Abstract: The analytically pure Fe₃O₄(d₅₀=1 μm) and magnetite concentrate(d₅₀=20 μm) were modified by polyacrylamide and chitosan under the action of ultrasonic dispersion，and four kinds of magnetic flocculants were prepared，including polyacrylamide-ferroferric oxide，polyacrylamide-magnetite，chitosan-ferroferric oxide，chitosan-magnetite. XRD，FTIR and SEM analysis on these four flocculants showed that a thick layer of needles on the surfaces of two magnetic materials was achieved through bounding effect of polyacrylamide，while chitosan was in had a bad effect. With use of the four magnetic flocculants to purify domestic sewage in Maanshan，and blue-green algae in Chaohu，the results showed that the removal rate of dirt and blue-green algae reached 98.13%，99.61% and 93.75%，99.02% respectively by polyacrylamide-ferromagnetic oxide and polyacrylamide-magnetite magnetic flocculants，while the removal rate was only 67.50%，35.29% and 49.38%，67.50% by using chitosan-ferromagnetic oxide and chitosan-magnetite magnetic flocculant. Polyacrylamide-magnetite magnetic flocculants can achieve a good effect in wastewater treatment and owns actual application significance in dealing with sewage，so it is worth of further investigation.

Key words: Magnetic flocculants, Blue-green algae, Domestic sewage, Flocculation