PH-stat photoheterotrophic cultivation of indigenous Chlorella vulgaris ESP-31 for biomass and lipid production using acetic acid as the carbon source

The growth and lipid content of an isolated microalga Chlorella vulgaris ESP-31 were investigated under photoheterotrophic cultivation with different carbon sources (glucose, fructose, sucrose, glycerol, sodium acetate and acetic acid). In the absence of pH control, growing C. vulgaris ESP-31 on glucose obtained the highest biomass concentration (3.5g/L) and lipid content (26%). By controlling pH at 8.5, the growth on fructose and sodium acetate was improved, obtaining a biomass concentration of 3.2-3.6g/L and a lipid content of 24-25%. Moreover, a fed-batch operation with pH-stat feeding of acetic acid was employed to enhance biomass and lipid production. When the pH-stat culture was conducted at pH 7.0-7.5 with acetic acid feeding, the best photoheterotrophic growth performance was obtained, resulting in the highest biomass yield, lipid content, and lipid productivity of 0.68g/g CH ₃COOH, 50%, and 78mg/L/d, respectively. Regardless of the carbon sources used, the fatty acid profile of the microalgal lipid did not change significantly, as the lipid comprises over 60-80% of saturated fatty acids (mainly palmitic acid (C16:0) and stearic acid (C18:0)) and monounsaturated acids (mainly oleic acid (C18:1)). This lipid composition is suitable for the use in biodiesel synthesis.