Unused aqueous film-forming foam (AFFF) concentrate is of great concern due to the potential impact and risks caused to the ecosystem and human health by per- and polyfluoroalkyl substances (PFAS), which are persistent in the environment and recalcitrant to degradation by traditional remediation strategies. The goal of this project is to develop a novel, compact, and effective continuous-flow liquid-phase plasma discharge (CLPD) technology, as a proof-of-concept, to efficiently destroy carbon-fluorine bonds in unspent AFFF concentrate. Specific objectives include the following:

1. Evaluate the technical feasibility for CLPD to handle AFFF concentrate and destroy PFAS;
2. Establish a laboratory-scale CLPD process to achieve 99% total PFAS destruction in the AFFF concentrate by non-thermal defluorination and fluoride recovery; and
3. Elucidate the degradation pathways for perfluorooctane sulfonate (PFOS), 1H,1H, 2H, 2H-Perfluorooctane sulfonic acid (6:2FTS), and 1H,1H, 2H, 2H-Perfluorodecane sulfonic acid (8:2FTS) by CLPD based on a quantitative assessment of total fluorine mass balance.

The technical feasibility of initiating liquid-phase plasma discharge in 6% AFFF (Type 6) concentrate and its diluent will be determined with a CLPD reactor by determining the highest concentration of AFFF that can be handled by CLPD under varying electrical power and voltage. Upon characterization of the AFFF concentrate, the performance for the CLPD to efficiently destroy and mineralize PFAS will be evaluated based on removal and defluorination rates for total PFAS quantified for all targeted PFAS under draft EPA Method 1633.

Process variables, such as AFFF flow rate, pH, and applied power, will be screened for their impact on PFAS removal performance, and the selected significant CLPD operational parameters will be evaluated and optimized for removal and defluorination of the major PFAS component in the AFFF. To achieve 99% PFAS removal, a fluidized-bed precipitation process will be designed to couple with the CLPD reactor for continuous recovery of the produced fluoride ions. Energy efficiency for PFAS removal and the cost of the working CLPD process will be estimated by analyzing the energy consumption and capital/operational cost of the process running under the optimized operating condition that can achieve 99% PFAS removal. CLPD system running under the optimal operating condition will be specifically examined for PFOS, 6:2FTS, 8:2FTS and their degradation products in gas- and liquid-phase to assess the degradation/defluorination pathways and quantitative fluorine mass balance during the CLPD treatment.

This project will result in an improved understanding of a liquid-phase plasma-based treatment process and its ability for complete destruction of PFAS in unused AFFF concentrate. In addition, the technical feasibility of a transformative, green treatment technology for cost-effective and sustainable cleanup of AFFF impacted sites will be assessed. Successful completion of this project will lay the ground for an on-site demonstration of the CLPD process for pilot/full-scale destruction of PFAS in the AFFF concentrate in the next phase. (Anticipated Project Completion – 2024)