Protic ionic liquid-assisted cell disruption and lipid extraction from fresh water Chlorella and Chlorococcum microalgae

Protic ionic liquids (PILs) with their ability to host labile protons and form hydrogen bonds are likely to be efficient catalyst for bioprocessing. This is one of the first reports investigating PIL-assisted microalgal cell disruption and lipid extraction. The applicability of several PILs with butyrolactam, caprolactam, propylammonium and hydroxypropylammonium cations in combination with formate, acetate and hexanoate anions for cell disruption and lipid extraction from fresh water Chlorella and Chlorococcum sp. have been evaluated in this study. The investigations were performed with de-watered wet microalgae under ambient temperatures and hence do not require any energy intensive drying and/or processing steps. The PILs with formate and hexanoate anions when compared with conventional pre-treatment techniques: sonication, microwave and cellulase provided better microalgal cell disruption efficiencies. The FESEM analysis for the Butyrolactam hexanoate (BTH) treated cells show extensive pattern of microalgal cell disruption. The fluorescence imaging analysis coupled with culturing experiments indicates a near-complete disruption and loss in viability of the PIL-treated microalgal cells. The lipid yield from the formate and hexanoate anions-PILs was statistically comparable and/or higher to the Bligh & dyer control method. Among the PILs, BTH recorded 1.86 and 1.72 folds higher lipid yields than the control method with Chlorella and Chlorococcum sp. respectively. The lipids show predominance of C16 and C18 fatty acids similar to lipid profile obtained with the control method. Furthermore, the PILs were also found to have a beneficial role in reducing the chlorophyll pigments in the final lipid product. Overall, the results show PILs with formate and hexanoate anions can be utilized for a relatively energy efficient, one-step cell disruption and lipid extraction process from wet microalgae.