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Microalgal flocculation and sedimentation: spatiotemporal evaluation of the effects of the pH and calcium concentration


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.

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This research was partially supported by Japan Science and Technology Agency (JST)/Japan International Cooperation Agency (JICA), Science and Technology Research Partnership for Sustainable Development (SATREPS) through the project for Continuous Operation System for Microalgae Production Optimized for Sustainable Tropical Aquaculture (COSMOS) <JPMJSA1509>.

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Correspondence to Yuanjun Xia.

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Xia, Y., Kishi, M., Sugai, Y. et al. Microalgal flocculation and sedimentation: spatiotemporal evaluation of the effects of the pH and calcium concentration. Bioprocess Biosyst Eng 45, 1489–1498 (2022).

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  • Microalgae
  • Harvesting
  • Sedimentation efficiency
  • Sedimentation rate
  • Calcium recovery