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

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.