A new electrochemical technology for direct-air capture (DAC) of atmospheric CO2 can also produce freshwater from brackish water or brine waste from desalination or wastewater treatment facilities (diagram). The technology, developed by Capture6 (Berkeley, Calif.; www.capture6.org), splits the salt content from brine waste, forming an acid and a base. The derived base acts as a solvent, absorbing CO2 from the air and forming carbonates that can be sequestered. “By consuming salt from wastewater, the technology generates the solvent for DAC, while simultaneously producing freshwater,” explains Capture6’s chief technology officer Rahul Surana. According to the company, the process can recover over 50% of freshwater from desalination waste brine, and it can be configured to handle varying saltwater sources and to produce different byproducts.
This DAC process has several features that contribute to its scalability. First, it operates at ambient temperatures, making it compatible with renewable-energy sources, and it is a once-through process, meaning that fresh solvent is continuously created, says Surana. Also, the process comprises multiple technical components that are widely used in industry, such as nanofiltration and electrodialysis. Notably, the process’ air contactors expand upon traditional cooling-tower designs with Capture6’s AURA (Absorption Reactor Unit for Ambient Air) technology, for which the company was recently awarded funding from the U.S. Dept. of Energy. “This enhanced tower design will likely improve upon the mass-transfer characteristics of the process and reduce total energy demand. With the award, we expect to test various configurations that combine the laminar airflow in the cooling tower with turbulent airflows and atomize the liquid solvent as in a venturi,” says Surana. Optimizing AURA is expected to improve the efficiency and the energy intensity of the DAC process. The company estimates AURA can reduce the total energy required for DAC by 15% when compared to other solvent-based DAC technologies.
Capture6 is working with the Palmdale Water District in California on the Project Monarch pilot plant, which will be the first fully integrated water-management and CO2-removal facility of its kind. Groundbreaking for Project Monarch is expected in the second quarter of 2024.