One-step Hydrothermal Liquefaction and Catalytic Upgrading of Wastewater-Grown Microalgae for Potential Sustainable Aviation Fuel Precursors

In the context of aviation decarbonization goals, this study investigated the conversion of wastewater-grown microalgae into sustainable aviation fuel (SAF) precursor via one-step hydrothermal liquefaction (HTL) and upgrading. The highest bio-oil yield achieved was 23.07% (dry basis), at 320 °C for 30 min with 10% NiMo/Al₂O₃ catalyst. The highest heating value, 41.77 MJ kg^-1, was obtained under the same temperature and catalyst concentration, but with a longer reaction time (120 min). Bio-oil yield was significantly influenced by temperature, while the catalyst played a key role in sulfur reduction. The response surface analysis identified an intersection region, around 324 °C with 15% NiMo/Al₂O₃ catalyst, that offers a favorable balance between high yield and low sulfur content. Since reaction time had no significant impact on the results, a 30 min process is recommended to improve energy efficiency. Bio-oil presented a predominance of aromatic hydrocarbons, with smaller fractions of alkanes and cycloalkanes, compounds that are desirable for SAF. These results highlight HTL as a promising pathway for wastewater-grown microalgae valorization. However, further refining and comprehensive technical, economic, and environmental assessments are needed to advance the use of this bio-oil as SAF precursor.