Stress-induced lipids are unsuitable as a direct biodiesel feedstock: A case study with Chlorella pyrenoidosa

The effects of various stresses on the suitability of lipid synthesized by Chlorella pyrenoidosa for biodiesel production were investigated. Lipids were characterized for detailed fatty acid methyl ester profiling and biodiesel properties like cetane number (CN), iodine value, cold filter plugging point (CFPP). Maximum biomass productivity (106.63 mg L−1 d−1) and lipid content (29.68%) were obtained at indoor cultivation (nitrate sufficient, pH 8–10, 24 h illumination). However, compared to this condition, other nitrate sufficient cultures [pH 6–8 and 10–12 (24 h illumination), and at ambient CO2 and 16:8 h light:dark photoperiod (pH unadjusted)] showed ∼12–14% lower lipid productivity. Upon 50% nitrate depletion (at indoor and outdoor; pH unadjusted) lipid content has increased by 7.62% and 17%, respectively. Though stress conditions helped enhancing lipid accumulation, there was two-fold increase in PUFA content compared to that observed at pH 8–10. This resulted in fuel properties which did not comply with the biodiesel standards.