Life-cycle assessment of microalgae liquid biofuel production in biofilm cultivation system via conversion technologies of transesterification, hydrothermal liquefaction and pyrolysis

Biofilm seems to be an ideal cultivation system for microalgae liquid biofuel conversion technologies due to the advantage of high biomass concentration. However, research on the biofilm cultivation system for microalgae liquid biofuel producing were limited. In this study, a life-cycle assessment was conducted for microalgae liquid biofuel production in this system via three conversion technologies: transesterification, hydrothermal liquefaction and pyrolysis. The result shows that scenario hydrothermal liquefaction seems to be the most feasible technology to produce liquid biofuel in biofilm system because only hydrothermal liquefaction achieved positive energy and environment benefits with a net energy ratio of 0.87 and Greenhouse gas emissions of −39.91 g CO2-eq MJ−1. For transesterification and pyrolysis, the net energy ratio (2.18 and 2.06) were larger than 1, while Greenhouse gas emissions (3.28 and 59.25 g CO2-eq) were greater than 0. This indicated that these scenarios exhibited negative energy and environment benefits due to heavy use of chemicals and high energy consumption during biomass drying process, respectively. Additionally, according to the sensitivity analysis, bio-crude mass yield exhibited a more significant impact on the energy and environment loads for scenario hydrothermal liquefaction than the other factors.