Repetitive extraction of botryococcene from Botryococcus braunii: a study of the effects of different solvents and operating conditions
2019
Jackson, Brent A. | Bahri, Parisa A. | Moheimani, Navid R.
As global temperatures continue to increase the move to renewable energy sources is becoming an essential step in achieving a sustainable future. Biofuels from microalgae, while still more expensive to produce than fossil fuels, are of great interest for the high microalgae biomass growth rates, high lipid content, relatively low water requirements, and ability to be grown on non-arable land. Botryococcus braunii is a freshwater green microalga which grows in colonies supported by an extracellular matrix (ECM) of liquid hydrocarbons. Recent studies have investigated the efficiency of non-destructive in situ solvent extraction of lipids from B. braunii with a variety of solvents. These lipids are encapsulated in a retaining wall coated by a sheath of amphiphilic fibrils which have been found to act as a barrier to solvents. By carrying out repeated in situ solvent extraction in a high shear environment, we found that access to the ECM can be significantly improved. Sustainable botryococcene and total lipid productivities respectively of 29.9 ± 8.5 and 71.3 ± 20.3 mg L⁻¹ day⁻¹ were achieved with heptane extraction, a shear rate of 415 s⁻¹, initial culture density of 1.62 ± 0.12 g L⁻¹, contact period of 4 h, and a recovery period of 3 days. Nutrient supplementation to replace those lost in the emulsion entrained biomass will be required to maintain a sustainable process. The combined presence of heptane with high shear proved to be an effective colony disruption method which could be an effective pre-treatment followed by a low shear, high solvent contact, and extraction method.
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