Enhanced Lipid Recovery from Marine Chlorella Sp. by Ultrasonication with an Integrated Process Approach for Wet and Dry Biomass

Lipid extraction from microalgal biomass faces some challenges such as the selection of a suitable biomass type and its quality, lipid yield (LY), and process energy consumption. This study aimed to develop optimized processing conditions using response surface methodology, for the ultrasonic extraction (UE) of lipids from wet and dried marine Chlorella sp. Integrated process approaches with different extraction and solvent recovery steps were developed for the evaluation of the lipid recovery and process energy consumption. The effects of other processing factors, such as the biomass-to-solvent ratio, solvent type, and solvent-to-solvent ratio were investigated. The biomass and lipids extracted were characterized by scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) and gas chromatography-flame ionization detection (GC-FID) analysis, respectively. With a single extraction and single-solvent recovery (1-1 cycle) process, the LYs from fresh and stored paste were 11.7% and 6%, respectively, while freeze-dried biomass produced an 18.5% LY. The energy consumption was 6000 MJ/kg lipid for the wet route and 8200 MJ/kg lipid for the dry route in the 1-1-cycle process. Dried biomass was selected for further investigation due to its longer storage-period capability and higher LY. The LY of the 2-1-cycle process using methanol/hexane (2/1 v/v) with a biomass-to-solvent ratio of 1/20 g/mL was 31% and was considered as a base case scenario of this study, which is 40.3% and 9.7% greater than those of the 1-1 cycle and 2-2 cycle, respectively. The lipids obtained from the 2-1 cycle at the optimum condition were mainly saturated fatty acids which are suitable for a biodiesel feedstock.