Integrating fermentation of Chlamydomonas mexicana by oleaginous Lipomyces starkeyi and switchable ionic liquid extraction for enhanced biodiesel production

The conversion of multi-bioconstituents of microalgal biomass such as carbohydrates and proteins to lipids can substantially reduce the downstream and overall process cost, as the bioprocessing can be aimed at single-desired biofuel product, e.g., biodiesel. The present study developed an integrated process to enhance the lipid yield through oleaginous yeast fermentation of microalgal biomass, and cost-effectively extract the lipids through permeable and switchable ionic liquid (IL). A 60 g/L of microalgal (Chlamydomonas mexicana) biomass was pretreated via microwave which showed 37% cell disruption efficiency. The pretreated biomass was fermented using an oleaginous yeast, L. starkeyi which effectively consumed the carbohydrates (92%) and proteins (91%) of C. mexicana and converted it to excessive lipids (188%) in comparison to the original microalgal lipids (12.6 g/L) before fermentation. The ionic liquid (IL), Dissopropanolamine-Im was used for high-thoughput disruption of the biomass and extraction of total lipids. It significantly improved cell disruption efficiency (95%) and lipid extraction efficiency (99%) than the conventional (Bligh & Dyer) lipid extraction method (87%) and previously reported methods using several ionic liquids (∼92%), and required a relatively shorter process time. More than 93% of IL could be recovored from the solution, and its recyclability was tested for >5 times where it could maintain an efficiency of >80% after five cycles. The integration of microalgal biomass and L. starkeyi mediated fermentation improved the overall lipid production (23.72 g/L) and yielded 2.2 times higher biodiesel than the conventional process. The outcomes of this study provides a economic and sustainable model to overcome the existing limitations of biodiesel production from microalgal biomass.