5-supplementary material-R1

Microalgae are a rich resource for valuable products, yet their biomass harvesting is challenging due to their small size and low density. The study introduced choline-alanine ([Cho][Ala]), an ionic liquid, as an efficient green flocculant for Coelastrella sp. CHZ. [Cho][Ala] significantly enhanced flocculation efficiency, increasing from 32% to 76% at a 200 mg L-1 concentration, and peaking at 85% at 290 mg L-1 after optimization. Employing response surface methodology and central composite design, optimal flocculation conditions were identified. Theoretical analysis using thermodynamic principles and Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory revealed that [Cho][Ala] increases cell hydrophobicity and reduces interaction energy, promoting aggregation. It also neutralizes the surface charge, similar to traditional flocculants, reducing intercellular repulsion. This research not only improves microalgae harvesting efficiency but also deepens the understanding of cell aggregation mechanisms. It highlights the potential of ionic liquids as greener and more efficient alternatives in the bioprocessing of microalgae harvesting.