Biofuels from microalgae: Lipid extraction and methane production from the residual biomass in a biorefinery approach

•More lipids are extracted by SCCO2 than using conventional extraction methods.•SCCO2 extracts most of neutral lipids for biodiesel production.•SCCO2 allows valorisation of the resulting microalgal biomass.•The highest methane yield was obtained after lipid extraction by SCCO2.•SCCO2 enhances microalgal biodegradability to increase methane production.

Renewable fuels and energy are of major concern worldwide and new raw materials and processes for its generation are being investigated. Among these raw materials, algae are a promising source of lipids and energy. Thus, in this work four different algae have been used for lipid extraction and biogas generation. Lipids were obtained by supercritical CO2 extraction (SCCO2), while anaerobic digestion of the lipid-exhausted algae biomass was used for biogas production. The extracted oil composition was analyzed (saturated, monounsaturated and polyunsaturated fatty acids) and quantified. The highest lipid yields were obtained from Tetraselmis sp. (11%) and Scenedesmus almeriensis (10%), while the highest methane production from the lipid-exhausted algae biomass corresponded to Tetraselmis sp. (236 mL CH4/g VSadded).