Although wastewater streams with high organic content — such as those from breweries and dairy facilities — can be difficult to treat and expensive to dispose of, there is potential to valorize their carbon content with the right process. Based on a technology called membrane-assisted methane-arrested anaerobic digestion (MAAD), a process developed at Argonne National Laboratory (ANL; Lemont, Ill.; www.anl.gov) can readily convert high-strength organic wastewater into volatile fatty acids like butyric acid, a low-carbon-intensity feedstock suitable for sustainable aviation fuel (SAF) production. According to ANL, the process (diagram) boasts a considerably lower carbon footprint than other SAF feedstocks, such as energy crops or lignocellulosic sugars. “When we look at the production of cheese or beer, they are already using a lot of water in the process, and their waste streams are very carbon-rich. Valorization of these organic waste streams provides us negative or very low carbon-intensity feedstocks for SAF. Conversely, with crops, we need to look at the entire supply chain to understand what the carbon intensity of the feedstock will be,” says Meltem Urgun-Demirtas, department manager — Sustainable Materials and Processes at ANL.
The team from ANL developed a method to shut down the production of methane within the anaerobic digester, and use a “highly diverse and highly dynamic microbial community structure” to focus only on short-chain fatty acids needed for SAF production. The next step was to tackle the separation and purification of the desired product from the reactor system. “Separation and purification can account for up to 70% of total production costs, so we integrated both production and separation/purification technologies together,” adds Urgun-Demirtas, noting that the team also developed a new electrochemical separation method to accompany MAAD. “By combining separation and purification with the production process, we have not only reduced the costs, but are also reducing the concentrations of the high organic acid in the bioreactor, which can inhibit microorganism activity. Thus, we are increasing overall productivity for the SAF feedstock,” she notes.
The team is currently working on proposals to pilot the technology in the field using wastewater from cheese or beer production. Currently, they have demonstrated the technology at the 100-gal scale.