Phaeodactylum tricornutum (P. tricornutum) is a model and unique species of marine diatom with high lipid content and rapid growth. Alkaline flocculation is considered as a potential method to concentrate microalgae biomass, which is critical for large-scale cultivation and harvesting. In this study, we developed an effective approach to the traditional alkaline flocculation method by utilizing the auto-flocculation ability of P. tricornutum. We studied the performance and mechanism of auto-flocculation by comparing the inorganic and organic processes, assisted by scanning electron microscope (SEM), X-ray diffraction (XRD), and zeta potential. And we found that the role of algae growth in mediating Mg(OH)2 precipitation was not only to help increase pH but also adsorb divalent cations around the cell wall, which thus made algae cells the seeds facilitating Mg(OH)2 precipitation. We thus discovered a new pathway named “wrapping-sedimentation” during the auto-flocculation process, besides the charge neutralization and sweeping mechanisms. Through the auto-alkaline flocculation method, higher harvesting efficiency with at least a 2/3 reduction in alkali addition could be achieved.
