Rapid extraction of lipid from wet microalgae biomass by a novel buoyant beads and ultrasound assisted solvent extraction method

Microalgae biomass is considered as a sustainable source of biofuels and co-products because of its rapid growth and high lipid yield. However, some challenging steps need to be solved such as biomass harvesting, lipid extraction and transesterification in industrial processing. In this study, a novel method using buoyant beads and ultrasound assisted solvent extraction was developed for efficient lipid extraction from microalgae. The central composite design was used to statistically analyze and evaluate the effects of exposure time, hexane: isopropanol ratio, solid concentration and transducer power on lipid yield. The optimum lipid yield of 18.75 wt% was obtained at exposure time of 13.05 min, hexane: isopropanol ratio of 4.04 v/v, solid concentration of 1.24 w/v% and transducer power of 38%. Compared with ultrasound-assisted solvent extraction method, the disruption efficiency was higher and the particle size was smaller with this novel method. Additionally, the content of polyunsaturated fatty acids was lower and degree of saturated fatty acids was higher compared to the biodiesel produced by modified Bligh & Dyer method. Thus, this work demonstrates that the use of buoyant beads and ultrasound assisted solvent extraction is an efficient method to produce fatty acid methyl ester and raw biodiesel.