A process of flocculation followed by gravity sedimentation for algae separation has been studied (Golueke and Oswald, 1965). Treating high rate oxidation pond effluent, the process achieved up to 85% of the algal biomass using alum as a coagulant. The process was found reliable, and various algae species could be separated to achieve an algae slurry of 1.5% solids content. A comparison of the flocculation-sedimentation process with the flocculation — flotation method indicated that the latter exhibited very clear optima operating conditions for algae separation (Friedman et al., 1977; Moraine et al., 1980).