The high cost of harvesting microalgae is a major hurdle for the microalgae industry, and an efficient pre-concentration method is required. In this study, the effects of using different pH values (between pH 3 and 11) and calcium (Ca2+) concentrations (between 0 and 5 mM) on Chlorella vulgaris sedimentation were investigated by evaluating the spacio-temporal distributions of microalgae cells. Fast and efficient sedimentation occurred (within 10 min) at a high Ca2+ concentration (5 mM) at pH 9 and 11. However, the sediment volume was lower at a Ca2+ concentration of 3 mM than at a Ca2+ concentration of 5 mM. This indicated that the Ca2+ concentration strongly affected the sediment volume. Fast sedimentation and a low sediment volume were found at pH 7 and a Ca2+ concentration of 5 mM, probably because of the neutral charge in the system (adhesion to calcium precipitates would have occurred at a high pH). The highest Ca2+ recovery (82%) was achieved when sediment produced at pH 11 and a Ca2+ concentration of 5 mM was acidified to pH 3.
Keywords: Calcium recovery; Harvesting; Microalgae; Sedimentation efficiency; Sedimentation rate.
© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.