Biphasic optimization approach for maximization of lipid production by the microalga Chlorella pyrenoidosa

The aim of the study was to identify the optimum cultivation conditions for the microalgal growth and lipid production of the oleaginous microalga Chlorella pyrenoidosa Chick (IPPAS C2). Moreover, an appropriate NO₃^- concentration in the cultivation medium for maximized lipid accumulation was determined. The experimental design involved a biphasic cultivation strategy with an initial biomass accumulating phase under optimized light (400 μmol/m² per s), temperature (25 °C), and elevated CO₂ concentration in the air mixture (3%), followed by a mid-elevated CO₂ concentration (0.5%) for lipid induction. The highest lipid yields of 172.47 ± 18.1 and 179.65 ± 25.4 mg/L per day were detected for NO₃^- concentrations of 100 and 150 mg/L. The optimization approach presented here led not only to the maximization of lipid yield but also to the development of a biphasic cultivation strategy easily applicable to the cultivation process without the necessity for algal cell harvesting between the first and second cultivation phases.