High pH-induced flocculation–sedimentation and effect of supernatant reuse on growth rate and lipid productivity of Scenedesmus obliquus and Chlorella vulgaris

High pH-induced flocculation–sedimentation of Scenedesmus obliquus and Chlorella vulgaris was studied with the objective of improving the efficiency of microalgae harvesting, since it is one of the most expensive steps of production of microalgae. Desired pH values were achieved by addition of NaOH and Ca(OH)2. Growth rate and lipid productivity in fresh media prepared with tap water and with analytical-grade water, and in reused media prepared with culture centrifuged supernatant and the supernatant from high pH-induced flocculation–sedimentation were compared. Since the growth rates for reused media were about 1.7 times higher than in fresh media, and the lipid productivities were about 25 and 26 mg L−1 d−1 in flocculated and centrifuged reused media respectively, medium reuse is a suitable method of saving water and nutrients.