Optimization of photosynthetically active radiation, temperature, and urea deprivation for increasing neutral lipids and fatty acids in Scenedesmus obliquus and Chlorella vulgaris as biodiesels

The present study investigated the impact of photosynthetically active radiation (PAR), culture temperature, and urea addition on the biomass, total lipid, lipidomic profile, and fatty acid productivity in Scenedesmus obliquus (S. obliquus) and Chlorella vulgaris (C. vulgaris) for sustainable biodiesels. In this study, S. obliquus and C. vulgaris, respectively, showed generally high cell densities with 1.23 g/L and 1.22 g/L of dried cell weights and 18.2% and 17.65% of lipids. Of the various PARs tested (10, 20, 40, and 60 μmol/m2/sec), 60 μmol/m2/sec showed maximal biomass yields for both species (1.78 g/L of dried cell weight and 25.7% of lipids for S. obliquus; and 1.74 g/L of dried cell weight and 24.6% of lipids for C. vulgaris). Of the various temperatures (27 °C, 37 °C, and 47 °C), 27 °C showed maximal dried cell weights (1.22 g/L for S. obliquus and 1.23 g/L for C. vulgaris), whereas 47 °C accumulated high levels of lipids (23.5% for S. obliquus and 21.6% for C. vulgaris). On the other hands, urea deprivation in the medium increased lipid levels in both species compared to no deprivation (10% increase for S. obliquus and 8% increase for C. vulgaris). The fatty acid profile showed that palmitic acid with 16 carbons and double bonds was dominant among major fatty acids, accounting for 30.55% for S. obliquus and 26.6% for C. vulgaris. Furthermore, urea deprivation and 60 μmol/m2/sec of PAR showed the highest proportions of unsaturated fatty acids in both species (27.55% for urea deprivation and 30.55% for PAR in S. obliquus; and 28.33% for urea deprivation and 26.6% for PAR in C. vulgaris).