Influence of water content and cell disruption on lipid extraction using subcritical dimethyl ether in wet microalgae

[Display omitted] •Lipid in microalgae is effectively extracted by subcritical dimethyl ether.•Effect of moisture content in sample on extraction performance is clarified.•Cell disruption highly improves the extraction efficiency.•Mechanism of the improvement relies on increasing cell wall’s permeability.•Microalgal residue after the extraction is sufficient to be used as solid fuel. Subcritical dimethyl ether, a green solvent, was used to extract lipids from microalgae. The effect of the water content on the process was firstly investigated. Secondly, microalgal samples were subjected to five cell disruptions, and the effects on raw lipid and fatty acid methyl ester, and its profile were evaluated. Among them, heating, microwave, and ultrasonic treatments greatly improved extraction. Mechanism analysis revealed the improvements by the three treatments were due to increased cell wall permeability rather than to complete cell disruption. After the extraction, microalgal cells with lipid being well-extracted were shriveled with extensive surface folds, indicating a loss of intracellular substances, but the cell structure was undamaged. As for dewatering performance, extraction process removed almost all of the free water but left bound water. Finally, the potential of the residues after lipid extraction to serve as solid fuel was evaluated by combustion characteristics and heating value calculation.