Auto-flocculation (AF) leads to co-precipitation with inorganic salt ions at high pH levels, and bio-flocculation (BF) depends on the production of extracellular polymeric substances during algal growth phases. This study examines the separation efficiency of Chlorella vulgaris formed in AF/BF conditions, without the addition of chemical coagulants. To improve the efficiency of conventional gravity sedimentation (CGS) and dissolved air flotation (DAF), AF/BF conditions were considered as pH/mixing-induced stress. The higher efficiency of DAF was affected by the mixing-stagnation condition for Chlorella vulgaris and influenced by the high temperature and condition under which no nutrients were added to AF/BF for Anabaena sp.