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 1 kg of algal biodiesel could consume as low as 28.23 MJ of energy.
• 1 kg of algal biodiesel fixes about 0.6 kg 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. 58 MJ of energy is required to produce 1 kg 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 1 kg of algal biodiesel fixes about 0.6 kg of CO2. An optimized case considering the energy credits from co-products could further reduce the total energy demand. The energy demand for producing 1 kg of biodiesel in the optimized case is 28.23 MJ.

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