Microalgal lipid production for fatty acid methyl esters conversion: A response surface methodology optimisation of media nutrient in batch reactors

Biodiesel has the potential to reduce heavy dependence on petroleum diesel, and microalgae are considered a potential feedstock, owing to their ability to produce high lipids. In this study, the effect of brine salinity on the cell growth and lipid production was investigated. Brine salinity of 2.50 M NaCl was selected as the optimum salinity for high biomass (2480 ± 75 mgL−1), with high lipid content (18.00 %), and it was further used in the nutrient optimization processes by Response Surface Methodology (RSM). The Plackett-Burman and Box-Behnken designs of the RSM were used to select and optimize significant medium nutrients for culturing Dunalliela salina for maximum growth and high lipid production. The Plackett-Burman method identified NaHCO3, NaH2PO4·2H2O and NaNO3 as significant nutrients to biomass concentration, lipid content and lipid productivity. While the Box-Behnken design further optimized the significant nutrients and developed a lipid production model (R2 = 95.80 %) that yielded 181.10 mgL−1, which was 12.30 % improvement under optimum culture medium comprising of 1302.4 mgL−1 NaHCO3, 22.5 mgL−1 NaH2PO4·2H2O, 181.1 mgL−1 NaNO3, 44.7 mgL−1 CaCl2, 2355.0 mgL−1 MgSO4·7H2O, 5.6 mlL−1 of micronutrients solution. The extracted lipids were methanol-transesterified, and GC–MS analysis revealed fatty acid methyl esters with carbon chains between C14 and C20. The methyl esters were dominated by 8-octadecenoic acid (36.69 %), hexadecanoic acid (35.53 %) and 9-octadecenoic acid Z (17.85 %), signifying the characteristics of good quality biodiesel. Therefore, D. salina under optimized nutrients interaction is highly feasible as a source of lipids for sustainable and renewable biodiesel production on scaled up production.