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Lipid extraction is the bottleneck step for algae-based biodiesel production. Herein, 12 solvent mixture systems (mixtures of three non-polar and two polar organic solvents) were examined to evaluate their effects on the total lipid yield from Chlorella vulgaris (C. vulgaris). Moreover, the extraction yields of three solvent systems with maximum extraction efficiency of esterifiable lipids were determined by acidic transesterification and GC-FID analysis. Three solvent systems, which resulted in a higher extraction yield, were further subjected to fatty acid methyl ester (FAME) analysis. The total lipid extraction yields (based on dry biomass) were (38.57 ± 1.51), (25.33 ± 0.58), and (25.17 ± 1.14) %, for chloroform-methanol (1:2) (C1M2), hexane-methanol (1:2) (H1M2), and chloroform-methanol (2:1) (C2M1), respectively. The extraction efficiency of C1M2 was approximately 1.5 times higher than H1M2 and C2M1, whereas the FAME profile of extracted lipids by H1M2 and C1M2 were almost identical. Moreover, the esterifiable lipid extraction yields of (18.14 ± 2.60), (16.66 ± 0.35), and (13.22 ± 0.31) % (based on dry biomass) were obtained for C1M2, H1M2, and C2M1 solvent mixture systems, respectively. The biodiesel fuel properties produced from C. vulgaris were empirically predicted and compared to that of the EN 14214 and ASTM 6751 standard specifications.

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Microalgae are considered as a promising feedstock for the production of valuable fatty acids. In this study, individual fatty acid profiles during the growth period of Chlorella vulgaris were investigated. The results showed that the quantity and the type of fatty acids changed with varying rates during the growth of microalgal cells. Interchanging the fatty acid profiles may provide some metabolic information as a complementary method to radiolabeling studies. For C. vulgaris, two unsaturated fatty acids, oleic and linoleic acids, were the major components. Constant concentration of palmitic and oleic acids shows that they may serve as precursors for longer-chain fatty acids. Higher concentration of palmitic rather than palmitoleic acid (about 16 to 34 times depending on the cultivation day) shows that palmitic acid production rate is higher than its conversion rate to longer-chain fatty acids. In fact, palmitoleic acid might have been partly converted to oleic and linoleic acids. The fatty acid content variations during the growth period are not linear and can be fitted to a Sigmoidal model with R2 value higher than 0.98 and low RMSD values (except for oleic and palmitic acid).