Microalgae Biorefinery: Optimization of Starch Recovery for Bioplastic Production

Microalgae are a promising source of starch with the potential to reduce land and water footprints as compared to terrestrial plants. However, so far, there are no specific downstream processes to recover microalgal starch. In this work, the development of a lab-scale biorefinery to produce microalgal starch is described. Guidelines are provided on how to set up microalgae cultivation, attaining until 37% starch content and 0.48 g L-1 d(-1) starch productivity in 500 mL lab-scale photobioreactors. Cell lysis by ultrasonication in water and ethanol was studied, obtaining better disruption rates at a lower temperature (approximate to 30 C-degrees) in water. The refinery of the lysate was studied by comparing the conventional Percoll protocol with more potentially scalable methods: aqueous two-phase systems (ATPSs) and ethanol extraction. Ethanol allowed attainment of the best results, separating quantitatively lipids, with reduced pigment degradation, by ensuring higher starch recovery (91%) and starch content (57%) in the refined pellet. Finally, refined starch was used to produce a plastic film that showed mechanical properties comparable to those obtained by using corn starch. This study provides preliminary evidence that microalgal starch could replace conventional starch sources in the biobased industry, possibly with reduced environmental impacts.