Harvesting Chlorella vulgaris via rapid sedimentation induced by combined coagulants and tapered shear

In this study, a rapid sedimentation induced by combined coagulants and gradual shear was developed to harvest Chlorella vulgaris. The microalgal harvesting efficiency was observably promoted by the synergistic effect between FeCl3 and PAM, especially in the first 10 min. A higher harvesting efficiency, 95.61%, could be achieved within approximately 3 min due to the large and dense flocs generated by the combined coagulants. In contrast, the efficiencies were only 54.25 and 60.20% with FeCl3 and PAM, independently. When coagulation was performed under gradually reduced shear (from 50 to 30 rpm), smaller clusters or cells filled the pores of the aggregates via interception, which caused the flocs to become larger and more compact. The sedimentation time was shortened to 30 s for microalgal coagulation induced by the simultaneous use of combined coagulants and tapered shear, providing an effective approach to harvesting microalgae.