Hydrocarbon recovery by extraction with a biocompatible solvent from free and immobilized cultures of Botryococcus braunii
Recovery of a substantial fraction of B. braunii hydrocarbons was achieved via short contact with hexane of algae concentrated by filtration. Growth and hydrocarbon production during subsequent cultures were not impaired, even after repeated extractions. In fact, the hydrocarbon content of the cultures derived from treated algae tends to be higher than in controls. Recovery yields can be influenced by the physiological stage of the extracted culture. In addition, algae corresponding to the early exponential stage afford higher recoveries when grown under air-lift conditions relative to standard conditions; this likely originates from the smaller average size of colonies in the former cultures. The scale-up of extraction indicates that the recovery yield falls off when relatively large amounts of algae are contacted with hexane (large clump formation due to the sharp polarity contrast between wet cells and the nonpolar solvent). Immobilization, via entrapment in alginate beads and adsorption on polyurethane foams, was used to overcome this problem. Contact with hexane does not affect subsequent growth and hydrocarbon production of immobilized cultures. Recovery yields are markedly increased, relative to free cells, especially in the case of polyurethane foams.