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 (3.5 g/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 3.2–3.6 g/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 0.68 g/g CH3COOH, 50%, and 78 mg/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.

► Effects of carbon sources on photoheterotrophic growth of a microalga were studied.
► pH control is a key factor affecting the performance of photoheterotrophic growth.
► pH-stat culture with acetic acid enhanced the lipid content and lipid productivity.
► Composition of the microalgal lipids is suitable for biodiesel production.