Biofuel production from microalgae grown under mixotrophic and stress conditions

Energy plays a vital role in populations' daily lives around the world. Local communities, industries, and transportation systems depend on the continuous availability of energy that is often derived from fuel-based sources. Meanwhile, the increasing depletion of fuel resources poses a global challenge. Green microalgae offer a promising solution, as they can grow under both mixotrophic and autotrophic conditions. This study aimed to explore the potential of the microgreen alga Scenedesmus obliquus cultivated under mixotrophic conditions, using seawater supplemented with BG11 medium. The Face-centered Central Composite Design (FCCCD) was employed to optimize the conditions for algal biomass production, lipid production, Chl a and Chl b content. The experimental design consisted of 20 runs, evaluating the effects of varying concentrations of glucose (0, 2, and 4 g/L), glycerol (0, 2, and 4 g/L), and natural seawater (0, 20, and 40 %). The results showed that the highest dry weight (9.72 g/L) and lipid content (34.69 %) were achieved under conditions of 4 g/L glycerol and 4 g/L glucose without seawater. Based on the desirability function, the predicted optimal conditions for maximum lipid production (34.7 %) were 3.99 g/L glucose, 3.51 g/L glycerol, and 0.011 % seawater. The predicted optimal conditions for maximum dry weight (9.72 g/L) were 3.44 g/L glucose, 3.98 g/L glycerol, and 0.27 % seawater. The GC-Ms analysis was used to evaluate the lipid profile for potential biofuel production. The analysis revealed differences in the fatty acid composition of algae grown with and without seawater supplementation. Specifically, algae cultivated in seawater produced higher levels of monounsaturated fatty acids than those cultivated without seawater. These findings demonstrate that Scenedesmus obliquus can be effectively cultivated under mixotrophic conditions for biodiesel production. • Scenedesmus obliquus fresh green alga contain a high amount of lipids • S. obliquus can grow under mixotrophic conditions and stress conditions such as seawater • The high amount of lipids was obtained when S. obliquus grow in 3.99 g/L glucose and, 3.51 g/L glycerol, and 0.011 % seawater for optimal lipid content (34.70 %). • The increasing of lipids yields of S. obliquus above the control, (autotrophic and without seawater) by 69.51 % • The high amount of Polyunsaturated fatty acid was obtained when alga cultivated under mixotrophic conditions