A comparison of bio-crude oil production from five marine microalgae – Using life cycle analysis

Abstract

Marine microalgae biomass could offer a viable feedstock for sustainably producing biofuel by hydrothermal liquefaction. In this study, five promising marine microalgae (i.e., Tetraselmis, Picochlorum, Synechococcus, Chroococcidiopsis, and Dunaliella), having different characteristics, were studied for biocrude oil production. The overall microalgal biocrude oil production process was divided into six unit operations: water supply, CO2 supply, nutrient supply, cultivation, harvesting, and HTL process. Models were developed for these unit processes such that once the key parameters of any unit process are known, the corresponding energy consumption could be determined. While the selection of the cultivation site influenced the energy requirements for sourcing seawater and CO2, the characteristics of the strain influenced energy requirements for the other four-unit operations. A cradle-to-grave concept was assumed to compare the life cycle assessment of the five strains. Among these strains, Tetraselmis sp. provided the most favorable energy balance with a net energy gain of 1.77 GJ/barrel of biocrude, an energy return on investment value of 2.81, and GHG reduction potential of 129 kg CO2 equivalent/barrel of biocrude. Further investigation with sensitivity analysis confirmed that the net energy yield for Tetraselmis sp. was least affected by a ±10% variation of the parameters of the unit processes.