Separation of lipids and proteins from clarified microalgae lysate: The effect of lipid-protein interaction on the cross-flow and shear-enhanced microfiltration performances

Abstract

For microalgae biorefinery, membrane process is a suitable technology for biomolecules (i.e., proteins, lipids or carbohydrates) fractionation due to the simplicity in operation, the flexibility for implementation and the potential for processing large volumes. Here the objective was to microfiltrate microalgae aqueous extracts, after cell disruption and clarification, to concentrate lipids in retentate and recover hydrophilic proteins in permeate. However, the optimization of the membrane process requires a large amount of raw material and the composition of real microalgae extracts is so complex that it limits the in-depth understanding of the membrane / molecules interactions on the modification of the filtration performances. Thus, simplified model mixtures of clarified microalgae lysates were formulated, aiming at quite a high complexity with constant composition but a nice representativity with respect to the real mixture. Through the microfiltration of three model mixtures containing lipids, proteins or both kinds of molecules, it was demonstrated that the strong interaction between the biomolecules in solution modified the membrane fouling and had a clear impact on the membrane permeation and selectivity, similarly to the real mixtures. The dynamic filtration was tested to enhance the performances compared to cross-flow filtration. The higher shear rate favored an increase in flux and therefore productivity, but did not modify membrane selectivity. It was therefore demonstrated that the interaction between molecules existing in the cell or generated during the cell disruption drives the separation efficiency and should be mitigated in future works to allow the whole biomass biorefining.