Achieving high lipid productivity of a thermotolerant microalga Desmodesmus sp. F2 by optimizing environmental factors and nutrient conditions

The optimal conditions for cultivating the thermotolerant lipid-rich microalga Desmodesmus sp. F2 to achieve maximal lipid productivity were determined in this study. The conditions were light intensity, 700 μmol/m2s; temperature, 35 °C; cultivation nitrogen source, nitrate; initial nitrogen level, 6.6 mM nitrogen. Carbon dioxide (2.5%, 0.2 vvm) was pumped into the cultures continuously. In the pre-optimized conditions, the maximal lipid productivity of this microalga was 113 mg/L/d, which was raised to 263 mg/L/d in the optimized conditions. This level of lipid productivity of microalgae is the highest ever reported in the literature. Fatty acid composition of the lipid produced by Desmodesmus sp. F2 in the optimal conditions was determined, in which C16 and C18 species accounted for 95% of the fatty acids. Saturated, monounsaturated and polyunsaturated fatty acids accounted for 38.9%, 33.1% and 22.6%, respectively. Based on the analysis, this lipid quality makes it a good feedstock for biodiesel production.