Effective extraction of microalgae lipids from wet biomass for biodiesel production

Producing biodiesel from lipid extracted from microalgae is a promising approach for sustainable fuel production. However, this approach is not yet commercialized due to the high costs of upstream processes that are associated with the time consuming and/or energy intensive drying, and lipid extraction processes. In this study, the possibility of avoiding the drying process, and extracting the lipid directly from the wet concentrated cells, using enzymatic disruption to enhance the extraction, has been tested. Results showed that lysozyme and cellulase were both efficient in disrupting cell walls and enhancing lipid extraction from wet samples, with highest lipid extraction yield of 16.6% achieved using lysozyme. The applicability of using supercritical CO2 (SC-CO2) in extracting lipid from wet biomass was also tested and the highest yield of 12.5% was achieved using lysozyme. In addition, a two-step culturing process was applied, using Scenedesmus sp., to combine both high biomass growth and lipid content. The strain was able to increase its biomass productivity in the first stage, reaching 174 mg l−1 d−1, with almost constant lipid content. In the second stage, the lipid content was enhanced by six-fold after three weeks of nitrogen starvation, but with lower biomass productivity.