Ultrasonic Pretreatment of Microalgae for Enhanced Lipid Extraction

Oil extracted from algal biomass could provide a potential feed source for the production of bio-diesel to supplement current fossil fuels. Ultrasound pretreatment is a potential mechanical method to increase the yield of lipids extracted from the algae via solvents due to the cavitation breaking algae cell walls. A CCD was used to design experiments with varying power (350-750 W) and time (5-30 minutes). Chlorella vulgaris/Cyanobacteria leptolyngbya was harvested locally and pretreated at the powers and times specified by the CCD before extraction was done. Ultrasound pretreatment saw an increase yield up to 94% compared to the controls on non-treated algae suspension. Hexane (1:1 v/v) was evaluated as an alternative to the standard Bligh & Dryer (2:2:1.8 v/v/v chloroform/methanol/cell suspension). Yield was evaluated gravimetrically and Bligh & Dryer method yielded 134% greater yield than hexane. GCMS was used to evaluate composition of lipids after extraction. Lipids were found to be primarily composed of fatty acids and fatty acid methyl esters. SEM was used to analyze whether ultrasound had any effect on algae structure before and after treatment. Ultrasound proved to be a viable method in the pretreatment of algae for lipid extraction. Future research should be done into potential new solvents and finding the power and time that produced the maximum yield in lipids extracted.