Harvesting of Scenedesmus obliquus by Bioflocculation: Appropriate Chitosan Concentrations with Various pH Values at Different Growth Stages

摘要

The current study evaluates harvesting microalga Scenedesmus obliquus at different growth phases using chitosan, an anionic bioflocculating polymer. Different concentrations of chitosan were applied at different cultural pH levels and at different growth stages. The flocculation efficiency was evaluated in S. obliquus cultures with various cell densities. The optimum chitosan level for flocculating S. obliquus varied according to the cultural growth phase, cultural pH, and cells density. The highest flocculation efficacies (89.07 % and 88.48 %) at the late log phase were obtained when 80 ppm and 10 ppm of chitosan were applied to cultures with pH 10 (OD680nm ≈ 1) and pH 7 (OD680nm ≈ 3), respectively. Moreover, during the early stationary phase, the maximum coagulation value was achieved when 40 ppm of chitosan was used for cultures with pH 9 and OD680nm ≈3. At the late stationary growth phase, the highest flocculation efficacy (81.68% and 81.19 %) was achieved in cultures adjusted to pH 6 and treated with 20 ppm of chitosan and in the culture with pH 9 treated with 60 ppm of chitosan, correspondingly. Flocculation efficiency of S. obliquus could be improved by selecting a proper chitosan concentration according to the culture conditions (growth phase, pH, and cells density).