Flocculation of algae using chitosan

Flocculation of three freshwater algae, Spirulina, Oscillatoria and Chlorella, and one brackish alga, Synechocystis, using chitosan was studied in the pH range 4 to 9, and chlorophyll-a concentrations in the range 80 to 800 mg m(-3), which produces a turbidity of 10 to 100 nephelometric turbidity units (NTU) in water. Chitosan reduced the algal content effectively by flocculation and settling. The flocculation efficiency is very sensitive to pH, and reached a maximum at pH 7.0 for the freshwater species, but lower for the marine species. The optimal chitosan concentration that is required to effect maximum flocculation depended on the concentration of alga. Flocculation and settling were faster when concentrations of chitosan higher than optimal are used. The settled algal cells are intact and live, but will not be redispersed by mechanical agitation. The de-algated water may be reused to produce fresh cultures of algae.