Revealing mechanism and influence of microalgae cells' periodical auto-agglomeration induced by high concentration of carbon dioxide

The efficient cultivation of microalgae using CO2 from flue gas can be a win-win situation for both environmental protection and energy accessibility. In general, 10-20% of CO2 in flue gas would decrease pH and inhibit microalgae growth. However, Chlorella sorokiniana MB-1 under 15% CO2 showed a periodical auto-agglomeration, which promoted microalgae growth on the contrary in this study. The maximum biomass concentration of 3.27 g L-1 was higher than that cultivated with an optimal CO2 concentration. The pH decreased to 6.04 after the mixed gas with 15% CO2 (v/v) was bubbled into medium for 0.5 h, which resulted in auto-agglomeration to protect microalgae from acidification and keep a high specific growth rate of 0.03 h-1. Then the pH recovered to 7 during stabilization phase, auto-agglomeration ratio was up to 100% because of lamellar extracellular polymeric substances. Therefore, the interesting periodical agglomeration both enhanced growth and simplified harvesting.