The effects of light intensity and nitrogen concentration to enhance lipid production in four tropical microalgae

The manipulation of nutritional and culture parameters is one of the most promising methods for enhancing microalgal biomass and biofuel production. An earlier study analysed the ability of eight locally isolated microalgae to utilize standard nutrient sources in culture media to produce lipids. Four microalgae, Ankistrodesmus falcatus, Chlorella emersonii, Chaetoceros muelleri, and Isochrysis galbana, showed the desired biofuel properties (lipid/mass productivity, lipid content, and fatty acid profiles) and were selected for the present study. In this study, light intensity and nitrogen concentration were optimised to increase the growth rate, biomass, and lipid content of the four selected microalgae. Under optimal conditions of 135 μmol/m2/s light intensity and 5 g/l nitrogen, the isolates exhibited biomass productivity of 0.31–0.56 g/l/day, lipid content of 20.30–40.95% dry weight, and lipid productivity of 85.26–180.18 mg/l/day. Using the optimised parameters, the microalgae was further cultured with an upscaled volume of 5 L. The study found that C. muelleri and I. galbana produced the most promising results, with the highest lipid content, up to 43.40% dry weight, and the desired fatty acid profiles, which included a high concentration of saturated fatty acids (43.89–48.00%) and monounsaturated fatty acids (35.30–38.44%). Regardless, C. muelleri was chosen as a promising candidate for biodiesel application because of its high oleic acid proportion (27.68%), which was significantly higher than the other three microalgae (only 2.37–3.62% oleic acid). The study demonstrates the potential use of the tropical marine microalga C. muelleri as a feedstock for the production of biofuels. [Display omitted] •Four native microalgal strains were used in this study.•Lipid/biomass productivity, lipid content, and fatty acid profiles were analysed.•Optimised parameters were 135 μmol/m2/s illumination and 5 g/l nitrate.•The microalgae produced satisfactory lipid results under optimal conditions.•The microalga Chaetoceros muelleri is a promising biodiesel producer candidate.