Dispersed air flotation of Chlorella saccharophila and subsequent extraction of lipids – Effect of supercritical CO2 extraction parameters and surfactant pretreatment

Highlights: • Lipids were extracted from surfactant-exposed microalgae with supercritical CO₂. • Fatty acid methyl ester (FAME) content was optimized based on extraction parameters. • Maximum FAME recoveries obtained at longer extraction times and moisture removal. • Good yields also obtained without additional drying at shorter extraction times. -- Abstract: An environmentally sustainable approach was developed for recovering lipids from Chlorella saccharophila for biodiesel production. This involved harvesting the microalgae via foam-aided dispersed air flotation (DiAF) prior to supercritical CO₂ (SC–CO₂) extraction. Response surface methodology was used to investigate the extraction conditions that would affect the fatty acid composition within the lipids, measured analytically as total fatty acid methyl ester (T-FAME) and biodiesel dominant FAME (BD-FAME) content (% dcw). SC-CO₂ extraction parameters for maximum T-FAME (20.4 ± 1.9% dcw) and BD-FAME (9.8 ± 0.4% dcw) content in the extracted lipids were 90 min, 241 bar, 73 °C and 89% moisture (w/w), and 86 min, 241 bar, 73 °C and 86% moisture (w/w), respectively. Further analysis indicated that good T-FAME and BD-FAME content could be achieved when the extraction time was reduced to 30 min without drying, which may be more industrially favorable, as they would reduce processing expenses. Furthermore, the exposure of biomass to surfactant was found to have a significant effect on the composition of FAME in the extracted lipids. Surfactant exposed biomass, resulted in T-FAME and BD-FAME contents of 5.3 and 2.4% (dcw), respectively, and a longer exposure time resulted in higher contents. Centrifuged biomass had a FAME profile most suited for biodiesel. However, surfactant exposure resulted in higher levels of polyunsaturated fatty acids, which could be recovered as high value-added byproducts, and potentially improve the overall process economics. These findings suggest that the lipid composition can be tailored to suit specific applications by adjusting the extraction parameters and surfactant exposure.