Batch Growth of <i>Chlorella Vulgaris</i> CCALA 896<i> versus</i> Semi-Continuous Regimen for Enhancing Oil-Rich Biomass Productivity

The aim of this study was to induce lipid accumulation in <i>Chlorella </i>cells by creating stressful growth conditions. <i>Chlorella vulgaris</i> CCALA 896 was grown under various batch growth modes in basal and modified BG-11 and Kolkwitz culture broths, using a continuous light regimen of 150 µE/m²/s, at 30 °C. In order to perform the experiments, two indoor photobioreactor shapes were used: a cylindrical glass photobioreactor (C_GPBR) with a working volume of 350 mL, and a flat glass photobioreactor (F_GPBR) with a working volume of 550 mL. Stress-eliciting conditions, such as nitrogen and phosphorous starvation, were imposed in order to induce lipid accumulation. The results demonstrated that more than 56% of the lipids can be accumulated in <i>Chlorella</i> biomass grown under two-phase batch growth conditions. The highest biomass productivity of 0.30 g/L/d was obtained at the highest nominal dilution rate (0.167 day⁻¹) during a semi-continuous regimen, using a modified Kolkwitz medium. During the pH-stress cycles, the amount of lipids did not increase significantly and a flocculation of <i>Chlorella</i> cells was noted.