Overcoming the cell wall recalcitrance of heterotrophic Chlorella to promote the efficiency of lipid extraction

One of the major challenges associated with algal fuels production from heterotrophic Chlorella (H. Chr.) is the rigid and complex structure of the cell wall. The cell wall of H. Chr. consists mainly of hydrophilic carbohydrates that prevent contact between the extraction solvent and the microalgal cells. Moreover, the cross-link ether structure on the thick cell wall, which causes part of the lipid to bind to the biopolymers by means of a glycosidic bond, also prevents lipid extraction. Chemical pretreatment is necessary to overcome cell wall recalcitrance of H. Chr. and promote lipid extraction efficiency. Among the different pretreatment methods, acid could disrupt the cell wall more efficiently and make lipid extraction available without drying. The best result was obtained with H₂SO₄ at a concentration of 0.5 M, 120 °C for 1 h and the solid load was 10% (wt.). Under these conditions, the lipid yield was 41.41% (based on raw material) and the solid residue yield was 11.88%.