Effect of inorganic carbon source on lipid production with autotrophic Chlorella vulgaris

We studied the effects of three inorganic carbon sources, Na ₂CO ₃, NaHCO ₃ and CO ₂, and their initial concentrations on lipid production of Chlorella vulgaris. Chlorella vulgaris could utilize Na ₂CO ₃, NaHCO ₃ and CO ₂ to produce lipids. After 10-day cultivation with each of the three inorganic carbon sources, lipid yield of Chlorella vulgaris reached its peak with the concentration increase of the inorganic carbon source, but dropped again by further increase of the concentration. The pH value of the culture medium for Chlorella vulgaris increased after the cultivation on inorganic carbon source. The optimal concentration of both Na ₂CO ₃ and NaHCO ₃ was 40 mmol/L, and their corresponding biomass dry weight was 0.52 g/L and 0.67 g/L with their corresponding lipid yield 0.19 g/L and 0.22 g/L. When the concentration of CO ₂ was 6%, Chlorella vulgaris grew the fastest and its biomass dry weight was 2.42 g/L with the highest lipid yield of 0.72 g/L. When the concentration of CO ₂ was too low, the supply of inorganic carbon was insufficient and lipid yield was low. A too high concentration of CO ₂ caused a low pH and lipid accumulation was inhibited. Na ₂CO ₃ and NaHCO ₃ were more favorable for Chlorella vulgaris to accumulate unsaturated fatty acids than that of CO ₂.