Life cycle assessment of biodiesel production from algal bio-crude oils extracted under subcritical water conditions

•Life cycle assessment of algal biodiesel production from bio-crude oil.•Estimation of energy consumption and greenhouse gas emissions.•Subcritical water extraction consumes 3–5 times less energy than solvent extraction.•Production of 1kg of algal biodiesel could consume as low as 28.23MJ of energy.•1kg of algal biodiesel fixes about 0.6kg of CO2. A life cycle assessment study is performed for the energy requirements and greenhouse gas emissions in an algal biodiesel production system. Subcritical water (SCW) extraction was applied for extracting bio-crude oil from algae, and conventional transesterification method was used for converting the algal oil to biodiesel. 58MJ of energy is required to produce 1kg of biodiesel without any co-products management, of which 36% was spent on cultivation and 56% on lipid extraction. SCW extraction with thermal energy recovery reduces the energy consumption by 3–5 folds when compared to the traditional solvent extraction. It is estimated that 1kg of algal biodiesel fixes about 0.6kg of CO2. An optimized case considering the energy credits from co-products could further reduce the total energy demand. The energy demand for producing 1kg of biodiesel in the optimized case is 28.23MJ.