Formulation of low-cost seawater medium for high cell density and high lipid content of Chlorella vulgaris BDUG 91771 using central composite design in biodiesel perspective

Microalgal biodiesel production depends on high biomass and lipid yielding strain grown in a low-cost medium. The present study had identified marine microalga Chlorella vulgaris BDUG 91771 as a potent strain among the screened 14 marine microalgal and 51 cyanobacterial strains since the strain yielded 22.2% lipid. Optimal physical conditions for high biomass and the lipid content of Chlorella vulgaris BDUG 91771 are 20 μmol m⁻² s⁻¹ light intensity, 27 ± 2 °C, pH 7 ± 0.2. Further, seawater amended with different consortia of analar (NaNO₃/K₂HPO₄) and commercial (urea and superphosphate) nitrogen, and phosphorus sources were optimized by central composite design to produce maximal biomass and lipid. To the best of our knowledge, there is no hitherto report on the central composite design based optimization of nutrient consortia of NaNO₃ and superphosphate or urea and K₂HPO₄ in a seawater based medium for high lipid content. High growth was observed with high urea (6.60 mM) and high superphosphate (0.07 mM), whereas low urea (2.20 mM) and low superphosphate (0.021 mM) positively increased the lipid content to 27.5%, which was equal to expensive analar nutrients dosed cells and further it was 4% higher over control. As the lipid content and fatty acid profile of the strain grown under analar and fertilizer grade nutrients are similar, formulation of seawater medium with low-cost urea and superphosphate adds novelty to this present research. Fatty acid characterization unveiled a profound abundance of C16:0, C16:1, C18:1, and low abundance of C18:3 fatty acid in low urea and low superphosphate supplemented cells over control. Further, fatty acid methyl ester had a desirable degree of unsaturation (65.49), cold filter plugging point (−7.36), and long chain saturation factor (2.9) to use it as a fuel.