Effects of Dissolved Inorganic Carbon and Mixing On Growth and Lipid Formation of Chlorella Vulgaris

Microalgae have recently received great interests as a potential alternative biofuel source because they can generate a large amount of triacylglycerols (e.g. 20-50 % dry cell weight) for biodiesel production.  Chlorella vulgaris has been extensively studied due to its relatively rapid growing rate and reasonable quantity of triacylglycerols (e.g. 14-22 % dry cell weight).  Dissolved inorganic carbon including carbon dioxide (CO₂(aq)) and bicarbonate ion (HCO₃^-) is an important carbon source for the autotrophic growth of microalgae.  However, the dissolved inorganic carbon concentration in culture mediums is not usually enough for the growth of microalgae in typical open ponds when CO₂(g) is added to the medium due to a narrow pH window suitable for the growth.  In this study, sodium bicarbonate (NaHCO₃) was used to increase the inorganic carbon concentration.  Then, different mixing speeds were employed to investigate the effect of dissolved inorganic carbon concentrations on the algal cell surface.  During the entire growth phase, the lipid content in algal cell was also monitored using fluorescence spectroscopy in vivo to trace neutral lipid formation.