Unraveling the bioenergy production potential of native Scenedesmus and Nannochloropsis species by ameliorating non-polar lipids and desirable fatty acid production

This study investigated the biodiesel potential of aboriginal microalgal strains Scenedesmus sp. S01, Scenedesmus sp. S02, Nannochloropsis sp. S01, and Nannochloropsis sp. S02 under nitrogen-repletion (N+) and nitrogen-depletion (N-) conditions to minimize the energy sector's carbon footprint. Onset of the study, Nannochloropsis sp. S01 yielded higher biomass and chlorophyll of 1.41 g/L and 11.28 mg/g, respectively, over other species. Regarding macromolecules, Nannochloropsis sp. S01 had higher protein and lipid content of 37.09 % and 30 %, respectively, under the N+ condition, while it accumulated 34.27 % lipids in the N_ condition, of which non-polar lipids occupied 69 %. Among the Scenedesmus species, Scenedesmus sp. S02 showed high biomass, chlorophyll, and lipid content. The higher lipid-to-biodiesel conversion was noticed in Scenedesmus sp. S02, Nannochloropsis sp. S01 at about 71.02 %, which was further confirmed by FTIR. The biodiesel of all strains revealed palmitic acid as the most prevalent fatty type, accounting for between 30 and 37 %, and all species exhibited higher levels of SFAs between 37.21 and 46.54 %, followed by MUFAs (31–44 %) and low levels of PUFAs (8–20 %). Eventually, the mainstream fuel quality properties analyzed in this study, namely higher heating value, density, viscosity, oxidative stability, iodine value, and cetane number, satisfy the ASTM and EN biodiesel standards.