Ultrasound Applications in Lipid Extractions from Microalgae

Abstract

Microalgae have been identified as a promising next generation biofuel feedstock owing to their high lipid content and fast growth rate. Ultrasonication is one of the most effective methods of extracting the algal lipids for biofuel production. This chapter begins with a life cycle analysis of algal biofuel and the energy dynamics involved in the processing steps. A review of the ultrasound applications in lipid extractions from algal biomass and the challenges associated with the processes are described. The operation of continuous ultrasonication on wet algal culture is a good alternative to avoid the energy intensive drying step. The effect of operating parameters of continuous ultrasonication on extraction yield as well as the celldisruption and lipid releasing characteristics of two marine microalgal species—Tetraselmis suecica and Nannochloropsis sp., and one freshwater microalgal species— Chlorella sp. are presented. Marine microalgae are more susceptible to ultrasonic damage than freshwater microalgae. However, the soft marine microalgal cell membrane tends to roll up upon ultrasonic cell disruption and retain the membrane lipids. On the other hand, the rigid cell walls of freshwater microalgal cells can be shattered by ultrasonic cell disruption, which causes the release of their lipids. A mechanism for the temporal release of the lipid types is proposed.