Geographically-Resolved Techno-Economic and Life Cycle Assessment Comparing Microalgae-Based Renewable Diesel and Sustainable Aviation Fuel in the United States

This study integrates high-resolution thermal and biological modeling with techno-economic analysis and life cycle assessment to evaluate and compare two different microalgae biorefinery configurations targeting renewable diesel (RD) and sustainable aviation fuel (SAF) production in the United States at the county level. A dynamic engineering process model captures mass and energy balances for biomass growth, storage, dewatering, and conversion with hourly resolution. The modeled configurations enable large-scale biofuel production by supporting facilities in remote locations and cultivation on marginal lands. The two pathways under examination share identical biomass production and harvesting assumptions but differ in their conversion processes. The first pathway evaluates hydrothermal liquefaction (HTL) to produce RD, while the second pathway explores the hydroprocessed esters and fatty acids (HEFA) process to produce SAF. Results indicate that the minimum fuel selling price (MFSP) for HTL could decrease from 3.72-$7.26 to 1.48-$4.10 per liter of gasoline equivalent (LGE^-1), and for HEFA from 5.79-$10.93 to 1.73-$4.48 LGE^-1 under future scenarios with increased lipid content and reduced CO₂ delivery costs. Optimization analyses reveal pathways to achieve a MFSP of $0.75 LGE^-1 and 70% greenhouse gas emissions reductions compared to petroleum fuels for both pathways. The study also examines water footprint, land-use change emissions, and additional environmental impacts. Discussion focuses on outlining strategic research and development investments to reduce production costs and environmental burdens from microalgae biofuels.