Using Electrochemical Oxidation to Remove PFAS in Simulated Investigation-Derived Waste (IDW): Laboratory and Pilot-Scale Experiments

Repeated use of aqueous firefighting foams at military aircraft training centers has contaminated groundwater with per and polyfluorinated alkyl substances (PFAS). To delineate the extent of PFAS contamination, numerous site investigations have occurred, which have generated large quantities of investigation-derived wastes (IDW). The commonly used treatment of incinerating PFAS-tainted IDW is costly, and was recently suspended by the Department of Defense. Given long-term IDW storage in warehouses is not sustainable, our objective was to use electrochemical oxidation to degrade PFAS in contaminated water and then scale the technology toward IDW treatment. This was accomplished by conducting a series of laboratory and pilot-scale experiments that electrochemically oxidized PFAS using direct current with boron-doped diamond (BDD) electrodes. To improve destruction efficiency, and understand factors influencing degradation rates, we quantified the treatment effects of current density, pH, electrolyte and PFAS chain length. By using C-14-labeled perfluorooctanoic acid (PFOA) and tracking temporal changes in both C-14-activity and fluoride concentrations, we showed that oxidation of the carboxylic head (-(COOH)-C-14 -> (CO2)-C-14) was possible and up to 60% of the bonded fluorine was released into solution. We also reported the efficacy of a low-cost, 3D printed, four-electrode BDD reactor that was used to treat 189 L of PFOA and PFOS-contaminated water (C-o <= 10 mu g L-1). Temporal monitoring of PFAS with LC/MS/MS in this pilot study showed that PFOS concentrations decreased from 9.62 mu g L-1 to non-detectable (<0.05 mu g L-1) while PFOA dropped from a concentration of 8.16 to 0.114 mu g L-1. Efforts to improve reaction kinetics are ongoing, but current laboratory and pilot-scale results support electrochemical oxidation with BDD electrodes as a potential treatment for PFAS-tainted IDW.

Automated summary

Repeated use of aqueous firefighting foams at military aircraft training centers has led to groundwater contamination with PFAS. Incineration, the commonly used treatment, is costly and has been suspended. This study investigated the use of electrochemical oxidation with BDD electrodes to degrade PFAS in contaminated water and potentially treat investigation-derived wastes. Experimental results showed promising degradation efficiency and the potential for releasing fluorine into solution. A low-cost 3D printed BDD reactor was also demonstrated to effectively treat PFAS-contaminated water. Ongoing efforts are focused on improving reaction kinetics.