(180f) Wastewater to Sustainable Aviation Fuel Via Membrane-Assisted Methane-Arrested Anaerobic Digestion: Process Design, Techno-Economic and Life-Cycle Analyses

With the electrification of aircraft a far-off goal, sustainable aviation fuel (SAF) is considered a viable near-term solution for decarbonizing the aviation industry. Using new conversion technologies to turn waste materials into low-carbon fuels reduces the emissions from both waste management and fuel production. Recently, volatile fatty acids (VFAs) have been reported as promising intermediates for SAF production. By utilizing a robust microbial consortium, methane-arrested anaerobic digestion (MAAD) is a cost-effective alternative to sustainably produce VFAs from waste streams. Previous research efforts have been focused on either upstream VFAs production or downstream VFAs catalytic upgrading to SAF. However, the reported high VFAs production from MAAD results in VFAs salt formation (fermentation pH near neutral), whereas efficient conversions to SAF requires the acids in their undissociated form. In this study, experiments and process simulations were conducted to further enhance the existing MAAD technology with the aim to provide a comprehensive evaluation of VFAs separation on the overall wastewater-to-SAF process.

Specifically, two new membrane-assisted MAAD configurations (anaerobic submerged membrane digester and Resin Wafer Electrodeionization) were proposed and tested for VFAs production from wastewater. A blended stream of dairy and brewery wastewater with an elevated chemical oxygen demand (COD) concentration (>70 g/L) was selected as the feed solution. The feasibility of two MAAD configurations was evaluated using a lab-scale digester (14-L) under continuous operation mode. The results from the most stable conditions (e.g., hydraulic retention time around 3 days, pH 6.0) were applied for the process design of wastewater-to-SAF with multiple VFAs separation scenarios (cation/anion exchange resins) using Superpro Designer and Aspen Plus. The obtained mass and energy balances from the rigorous process simulation were then used for techno-economic analysis (TEA) and life-cycle analysis (LCA). The results suggest VFAs separation methods can significantly impact the feasibility of the VFAs-derived wastewater-to-SAF pathway. With a proper VFAs separation method, wastewater to SAF via MAAD can be a cost-effective alternative for lowering the carbon footprint of the aviation industry.