The objective of this project is to validate the performance, scalability, and stable operability of a pilot-scale, continuous hydrothermal reactor for treatment of liquids impacted by per- and polyfluoroalkyl substances (PFAS). Aquagga has previously fabricated a continuous hydrothermal alkaline treatment (HALT) reactor capable of processing >1 gallons per hour (GPH) of PFAS-impacted liquids. Test bed-based evaluation is needed to confirm the performance of this system, evaluating such metrics as (i) PFAS destruction performance, (ii) energy usage, and (iii) chemical consumption. Several long run-time tests will be performed to confirm the long-term operating stability of the system, and to demonstrate the premise of remote system control and operation, leveraging a distributed infrastructure approach. Finally, the scalability of the continuous HALT processing platform will be evaluated through assessing the observed reaction rates achieved in the pilot-scale continuous reactor relative to bench-scale batch and continuous HALT reactors. Project partner Geosyntec Consultants will provide a supply of >100 gallons of PFAS-impacted feedstock for testing, while project partner Colorado School of Mines will perform quantitative analysis of PFAS in the reactor effluent. Project success will validate the use of continuous HALT processing for the disposal of PFAS-impacted liquids produced during the remediation of impacted Department of Defense (DoD) sites.

The HALT technology leverages high temperature, high pressure, high pH liquid water to fully mineralize PFAS into benign salts such as sodium fluoride. At temperatures and pressures below the critical point of water, caustic soda is highly soluble and can be leveraged to drive the defluorination of PFAS molecules. Previous studies at the Colorado School of Mines and University of Washington have consistently demonstrated that HALT is effective across the entire class of PFAS, regardless of chain length, hydrophobicity, or initial concentration. The technology that will be demonstrated in this project is a pilot-scale continuous HALT reactor, capable of processing >1 GPH of PFAS-impacted liquids, assuming reaction rate kinetics observed in batch reactor studies, and assuming >99% total destruction and removal efficiency. This project will demonstrate the performance of the scaled-up continuous HALT reactor, to confirm PFAS destruction performance, to demonstrate the ability to reliably operate scaled-up HALT reactors, and to demonstrate the ability to further scale the technology to industry-relevant throughputs. Project success will include achieving discharge numbers of <1 μg/L for all individually measured PFAS during multiple reactor runs and demonstrating stable continuous operation. The project will de-risk the pilot-scale system for field-based demonstrations.

Successful demonstration and scale-up of the HALT technology will provide a cheap alternative to granular activated carbon or ion exchange resin filtration coupled with incineration of spent media for the disposal of PFAS-impacted liquids during remediation projects at DoD sites. Incineration is a relatively expensive PFAS destruction option, driving the need for alternative technologies. HALT technology has potential for lower energy demands compared to other emerging PFAS destruction technologies, is inherently scalable, and has been shown to fully mineralize PFAS. This project will advance the technology readiness of continuous HALT processing, with anticipated commercial availability for deployment at DoD sites. (Anticipated Completion Date - 2025)