Excess of Water Enables Efficient Lipid Extraction from Wet Pulsed-Electric Field-Treated A. protothecoides Microalgae Using Immiscible Solvents

This article presents a new processing approach to perform lipid extraction on the wet microalgae A. protothecoides using nonpolar solvents or solvents of low polarity. It was demonstrated that solvents such as hexane, heptane, or 2-butanol exhibit a negligible extraction efficiency (<4% of total lipid content) when added to the pulsed-electric field (PEF)-treated and dewatered biomass slurry. In contrast, extraction efficiency after PEF treatment could substantially be increased by adding water and solvent to the biomass slurry. For this case, additional water admixture during extraction enabled to recover 67.3, 62, or 82.3% of the total lipid content, respectively. When utilizing methyl terbutyl ether (MTBE), ethylacetate, and 2-methyltetrahydrofuran (2-MeTHF) as extracting solvents, the yield increase by additional water admixture is far less pronounced. In all cases, the extraction process was performed after a PEF treatment using 1.50 MJ/kg(DW) plus 24-h incubation and 20 h of mixing time with the solvents and the solvent/water mixtures. Estimations on the energy required for the whole downstream process showed that this process variant allows an energy consumption of 31.48 MJ/kg(biodiesel) at maximum and 7.98 MJ/kg(biodiesel) at minimum. The low energy requirements (only <22% of the energy content of the lipids) open pathways to energetical applications of microalgae lipids.