Surface-Modified Filter-Based Continuous Recovery of Microalgal Lipid-in-Solvent with High Recovery Efficiency, Long-Term Stability, and Cost Competitiveness

Microalgal lipid-derived biofuels have been regarded as promising candidate materials to replace fossil fuels, but their production cost, especially for lipid extraction, still must be lowered substantially for field application. Although lipid extraction from concentrated wet microalgae using a nonpolar solvent is considered as a feasible method, an effective recovery method to regain the nonpolar solvent with microalgal lipid from the emulsified extraction mixture has not yet been addressed significantly. In this study, microalgal lipid is cost-efficiently recovered in continuous manner directly from the emulsified, highly concentrated extraction mixture by utilizing a surface-modified filter. The surface of a highly porous sponge filter is modified conformally by an oil-absorbing but water-repellent polymer coating via an initiated chemical vapor deposition (iCVD) process. Concentrated wet Schizochytrium sp. ABC101 microalgal cells are disrupted, and the microalgal lipid components are extracted out by adding n-hexane in the aqueous disrupted microalgae. The surface-modified filter is capable of selective permeation of the n-hexane phase with microalgal lipid while blocking the water-phase permeation simply by immersing the filter into the emulsified extraction mixture. The absorbed n-hexane phase is recovered in a continuous manner by pumping it out. The continuous filter-based recovery system shows a high recovery yield of 95% and an extremely high permeation flux of 2640 L m^–2 h^–1. Moreover, the recovery performance is maintained for more than 24 h without any filter-cleaning step. Techno-economic analysis of the method developed in this study with the conventional phase recovery methods shows that the rapid but highly cost-efficient filter-based recovery method will be a useful platform for scalable, continuous microalgae lipid production.