Optimization of Culture Conditions for Growth and Enhanced Lipid Accumulation in Green Microalgae <i>Chlorella sorokiniana</i> Using a Two-Stage Cultivation Process for Biodiesel Production

Chlorella, a genus of green algae, exhibits rapid growth and high lipid accumulation as self-defense against adverse conditions. This study aimed to identify optimal conditions for the growth and lipid accumulation of Chlorella sorokiniana in a two-stage process for biofuel production. In the first stage, C. sorokiniana grew best in BG-11 medium with 3 g L−1 NaNO3 and 10 g L−1 glucose, achieving highest dry cell weight (DCW) of 2.87 ± 0.35 g L−1 and lipid content of 23.25 ± 0.15 % DCW after 4 d of cultivation. The second stage cultivation reached a C. sorokiniana biomass concentration of 2.18 ± 0.08 g L−1 and lipid content of 40.78 ± 0.61 % DCW with the addition of 30 g L−1 NaCl, 6 g L−1 NaHCO3 and a light intensity of 150 µmol m−2 s−1 after 2 d cultivation in 1 L Erlenmeyer flasks. C. sorokiniana cultured in 20 L, 50 L, and 300 L closed photobioreactors (PBRs) achieved DCW ranging from 1.35 ± 0.06 to 1.94 ± 0.04 g L−1 and lipid contents from 33.21 ± 0.67 % to 38.48 ± 0.76 % DCW, respectively, after 4 d in the first and 2 d in the second stage under optimal conditions of cultivation. Fatty acids profile, including C16:0, C18:2, and C18:3, indicated high-quality biodiesel, meeting 4-5 out of 5 parameters according to US and European standards. Therefore, C. sorokiniana is a potential feedstock for biodiesel.