(125c) The Effect of High-Intensity Ultrasound on Cell Disruption and Lipid Extraction from Concentrated and Viscous Slurries of Nannochloropsis Sp. Biomass

The effect of ultrasonication on the cell rupture of marine microalgae species Nannochloropsis sp. was studied as a function of solids concentration and treatment time. The concentrated and viscous wet-biomass (11, 20 and 25% solids concentration) was subjected to ultrasonication (20 kHz high intensity ultrasound) at 11.4 for up to 5 minutes. The cell rupture was visualized using multi-ion beam microscopy that showed clear increase in cell rupture with an increase in ultrasonic treatment time. The non-polar lipids were extracted from the ultrasonic treated wet-biomass using hexane extraction at room temperature. The lipid extraction efficiency was measured as a function of solids concentration and treatment time. Compared to hexane extraction without cell rupture, sonication led to a significant increase in the extraction efficiency from ~11 to 62% within 5 minutes of sonication. The lipid extraction efficiency decreased slightly with increase in solids concentration from 11 to 20% but it decreased significantly when the solids concentration is increased to 25%. This is attributed to the attenuation of high intensity ultrasound in viscous biomass. In order to elucidate the effect of viscosity on ultrasound attenuation, we have measured the viscosity of biomass at various solids concentration as a function of shear rate. We found that the Nannochloropsis sp. was shear thinning. We also measured the speed of sound in the biomass as a function of solids concentration to calculate the attenuation of ultrasound. The speed of sound decreased with increase in solids concentration. The increase in viscosity and decrease in speed of sound with increase in solids concentration resulted in the attenuation of ultrasound resulting in low lipid extraction efficiencies at 25% solids concentration. The efficiencies from ultrasound cell rupture at 20% solids concentration were on par with the efficiencies from conventional method of High Pressure Homogeniser (HPH). The lipid oxidation during ultrasonic treatment was characterized by HPLC and found that the lipid profile did not change with ultrasonication. The specific energy requirements were calculated for ultrasonication cell rupture as a function of solids concentration, ultrasound power and treatment time and compared them to HPH and other cell rupture methods.