Alkaline Flocculation Optimization for Microalgae Harvesting: Phaeodactylum tricornutum, Scenedesmus sp. and Chlorella zofingiensis

A response surface methodology (RSM) was used to evaluate the effects of pH and microalgal biomass concentration (BC) on alkaline flocculating activity for harvesting two freshwater green algae Scenedesmus sp. G4, Chlorella zofingiensis G1 and one marine diatom Phaeodactylum tricornutum 863. The pH value and BC were in range of 9.0-12.0 and 0.16-3.03 g/L, respectively. Very high regression coefficient between the variables and the response indicates excellent evaluation of experimental data by second-order regressions, except Phaeodactylum tricornutum 863. Alkaline flocculation was not a good method for harvesting of Chlorella zofingiensis. Furthermore, the addition of synthetic ocean water (SOW) to the freshwater green algae culture can increase the flocculating activity to 57.15%, 80.92% in low algae concentration (Chlorella zofingiensis G1 0.34 g/L, Scenedesmus sp. G4 0.61 g/L), 39.67%, 90.55% in high concentration (Chlorella zofingiensis G1, 1.72 g/L, Scenedesmus sp. G4, 3.03 g/L).