Aqueous two-phase systems based on natural deep eutectic solvents for protein extraction from microalgal biomass grown in wastewater

The cultivation of microalgae in photobioreactors offers a sustainable approach for efficient treatment of nutrient-rich wastewater while producing biomass rich in valuable biocompounds that can be recovered. Aqueous two-phase systems (ATPSs) composed of the combination of two natural deep eutectic solvents (NADESs), betaine-levulinic acid (Bet:2LA) and choline chloride-urea (ChCl:2Urea), with di- and tripotassium phosphate salts, were evaluated as green extraction technologies for protein recovery from microalgal biomass cultivated in swine wastewater. The extraction capacity was compared with that of ATPSs formed by natural metabolites betaine or choline chloride and the phosphate salts. Binodal curves and tie-lines were experimentally determined for each system at 25 ºC to characterize the ATPS studied. Protein recovery yield (PRY) from the biomass was analyzed for the six ATPSs at three different extraction times at 25 ºC. The best compromise between PRY, selectivity relative to carbohydrate coextraction, and extraction time was achieved using the Bet:2LA NADES paired with K3PO4 after 30 min (PRY 16.4 %). This ATPS contains 50 % water, underscoring its environmentally friendly profile. These findings suggest the feasibility of NADES-based ATPS for efficient and fast protein extraction from wastewater-derived microalgal biomass in mild conditions.