Photoactivated reductive defluorination (PRD) is a chemical reaction that can be implemented in existing ultraviolet (UV) water-remediation equipment and is considered an energetically favorable mechanism for per- and polyfluoroalkyl substance (PFAS) destruction in aqueous solutions. The commercial readiness of the technology has been advanced by testing it with various environmental samples and conducting preliminary cost comparisons with mainstream PFAS capture methods. This project aims to scale-up PRD from the laboratory benchtop to field-scale application by combining it with available PFAS concentration techniques for a complete PFAS treatment solution from concentration to full destruction. 

The scale-up process will be established in stepwise phases comprised of benchtop testing for early optimization of reaction variables (Phase I), commercial design reactor testing to determine full-scale UV system configuration parameters (Phase I), and field pilot-test employing existing commercial equipment (Phase II). The overall objective for Phase I was to obtain site-specific design parameters for a field-scale mobile treatment system to be employed in Phase II. This included selecting the most appropriate concentration techniques for pairing with PRD, assessing energy efficiency, estimating total cost associated with PRD destruction of concentrated PFAS liquid waste being generated at multiple DoD sites, and developing a cost estimate for construction of a mobile treatment system. Phase I was successful and the project has moved into Phase II testing. 

During Phase II, the project objectives are as follows: 

1. Assess the feasibility and applicability of implementing PFASigator™, a fully automatic commercial-scale equipment specialized in PRD reactions, in applied field scenarios.
2. Evaluate the ability of PFASigator™ to effectively achieve site-specific PFAS destruction in the applied field scenarios.
3. Calculate a detailed deployment cost.
4. Evaluate treated water discharge alternatives, and pair the PFASigator™ treatment with a discharge strategy that meets regulatory discharge limits.

PRD is a chemical reaction that breaks fluorine-carbon bonds and disassembles PFAS molecules in a linear fashion beginning with the hydrophilic functional group and proceeds through shorter molecules to complete destruction. The reaction is facilitated by self-assembly of a micelle cage formed from cetyl trimethylammonium bromide (CTAB) that traps PFAS. A second non-toxic liquid reagent associates with the micelle surface. When stimulated with ultraviolet light, the secondary reagent produces hydrated electrons that initiate a reductive chemical reaction that cleaves fluorine-carbon and other molecular bonds resulting in the final products of fluoride, water, and simple carbon molecules (e.g., formic acid and acetic acid). The self-assembled micelle system working as a reactive cage, greatly boosts the reductive defluorination reaction rate, and enables the reaction to occur over a wide range of water matrix, pH values, in both anaerobic and aerobic conditions under atmospheric pressure and temperature.

Phase I Results

During Phase I, the PRD met bench-scale success criteria for the destruction of PFAS in five of seven samples tested. In the successful samples, perfluorooctanesulfonic acid and perfluorooctanoic acid concentrations decreased 96% to >99% and 77% to 97%, respectively, during the allotted treatment duration. In the two unsuccessful samples, the reaction rate was inhibited when total dissolved solids were as high as 200,000 ppm. Key reaction parameters measured in benchtop studies translated very well to scaleup studies and support reasonable estimates of energy efficiency and overall treatment cost at commercial scale.

During Phase I, the PRD reaction demonstrated both technical effectiveness and economic feasibility for reducing PFAS concentrations in water. Some opportunities for improvement were observed and will be applied in future implementation of the technology. PFAS destruction reactions were more efficient at pH 10 than the native sample pH. The commercial scale equipment has been designed to maintain pH 10 throughout the reaction duration. The oxidation reaction conducted after PRD reduced CTAB concentration by >99% to non-detects. This is likely sufficient for permitted discharge at most locations, although site-specific evaluation of the need for further capture or recycling of CTAB should be evaluated. The PRD reaction in solutions with high, non-PFAS, surfactant concentrations can be improved by adjusting reagent addition from standard formula. Therefore, matrix-specific benchtop treatability studies are recommended to optimize reaction efficiencies. (Anticipated Phase II Completion - 2026)