Experimental investigation of the influence of growth medium on biomass composition and fatty acids profiles of Chlorella vulgaris micro-algae in sustainable biofuel production

Chlorella micro algae strains offer sustainable biomass feedstocks in biofuel production because of their resilience, diversity, high adaptability to environmental stresses, flexible cultivation alternatives and high biomass and total lipids production tendencies among others. In this study, the influence of growth medium on the biomass composition and fatty acids profiles of SAG 211-11b Chlorella vulgaris micro-algae strain in sustainable biofuel production was investigated by advanced experimental and analytical techniques. The micro-algae strain was cultured in the laboratory with modified-blue–green algae nutrients. The extraction was done in a Spe-edTM supercritical fluid extraction equipment by Applied Separations Inc (USA). The micro-algae biomass and its triglycerides were analysed by a Schimadzu Nexera 40D Series ultra high-performance liquid chromatography (UHPLC) system that was equipped with a photo-diode array detector (PDA) and a triple quadrupole, Iso-butane gas-source chemical ionization mass spectrometer (CI-MS/MS). Also, the influence of light intensity and glucose concentration on biomass productivity of C.vulgaris micro-algae strain as well as the quantification of the degree of these effects by ANOVA was investigated. Heterotrophic micro-algae have a biomass productivity of 7.11 ± 0.36 mgL −1day −1. Their fatty acids composition is predominantly mono-unsaturated (59.96%), with oleic acid (C18:1) contributing 46.87% and palmitoleic acid (C16:1) accounting for 9.14%. Poly-unsaturated fatty acids make up only 9.59%. Whereas the photoautotrophic micro-algae culture has a biomass productivity value of 2.8 ± 0.15 mgL −1day −1 and higher total poly-unsaturated fatty acids (41.82%) with linoleic (C18:2) and linolenic (C18:3) acids constituting 28.42% and 13.40% respectively. The practical implication of the different fatty acids moieties on biofuel production is that the Chlorella vulgaris micro-algae that was cultivated from the photoautotrophic route have lower lipids contents (22.18 ± 1.25mg/L) but better cold flow characteristics. Whereas, the heterotrophic micro-algae have higher total lipids contents (53.20 ± 2.75mg/L) and better biofuel qualities owing to lower quantities of poly-unsaturated fatty acids components. There is a strong positive relationship up to saturation point among light intensity, glucose concentration and biomass productivity. Finally, the heterotrophic micro-algae bio-fuel has higher cetane index value of 56.16 ± 2.75 and calorific value of 39.82 ± 2.17 MJ/Kg compared to the photoautotrophic micro-algae biofuel with lower values of 49.20 ± 2.30 and 39.33 ± 2.13 MJ/Kg. This represents better ignition quality and lower fuel consumption characteristics of the heterotrophic biofuel.