A method of wet algal lipid recovery for biofuel production
Drying of algae is resource-intensive (land, energy) for biofuel production. A method to recover lipids from wet algae has been developed at lab scale. The method is based on introduction of polar solvent first into wet algae to replace the water inside the cells, followed by gradual introduction of non-polar solvent to replace the polar solvent and thus extract lipids. Extraction conditions are normal temperature and pressure (25 °C; 1 atm). Dunaliella tertiolecta was adopted for extraction due to its potential as promising biofuel candidate and non-requirement of pretreatment before extraction. 1 g of wet algal paste was treated with polar solvent, polar solvent: non-polar solvent mixture (1:1 volume ratio) and non-polar solvent in series. Solvents were added in 3 steps for each solvent type and at 3 times the volume of the algal paste at each step. Mixing time was 30 s for each step. 2-propanol/hexane was preferred as viable solvent system and methanol/methyl t-butyl ether was also found to be effective. Lipid recovery matched that of analytical method. Other reported methods for wet algal lipid recovery usually employ more intensive conditions or long extraction times. Classification of neutral lipids and polar lipids in total lipids extracted by the method (68:31% by weight) was similar to that of the analytical method. It was also found that sun drying and any similar prolonged wet state of harvested algae may lead to significant loss of lipids, stressing the need for immediate processing as in the case of wet algal lipid extraction.