An investigation of plasma-driven decomposition of per- and polyfluoroalkyl substances (PFAS) in raw contaminated ground water

Abstract

Per- and polyfluoroalkyl substances (PFAS) are contaminants of emerging concern owing to their ability to bioaccumulate in the body and subsequently cause cancer. PFAS, while recalcitrant to advanced oxidation, can be degraded by plasma action. In this work, we investigate the efficacy of two plasma reactors on degrading PFAS in ground water derived from two different contaminated sites. The reactors included an array of underwater plasma jets and a dielectric barrier discharge (DBD) with water dielectric barriers. While both reactors showed effectiveness in removing PFAS, the DBD with water barriers was most efficient with regard to the rate of degradation and power consumed. This better performance was attributed to the increased plasma–liquid contact area. Experiments indicate that air is a suitable working gas alternative to argon, and both AC and ns-pulsed power sources can generate the plasmas for these reactors. Furthermore, it was found that for both reactors, the removal rate for low and high PFAS concentration in ground water was the same, suggesting that the reactors are most efficient at treating heavily contaminated water. In this respect, a concentration step followed by plasma treatment may be a cost-effective means to treat the PFAS-contaminated water.

PFAS–CTAB Complexation and Its Role on the Removal of PFAS from a Lab-Prepared Water and a Reverse Osmosis Reject Water Using a Plasma Reactor

“…The EE/O value for RO reject water is one order of magnitude lower than that for the treatment of leachate (20–36 kWh/m 3 ) and two orders of magnitude lower than that for IX still bottom (380–830 kWh/m 3 ), respectively. Other studies reported the energy demand for the treatment of PFOA and PFOS to be 241 kWh/m 3 in a dielectric barrier discharge plasma jet system and 237 kWh/m 3 in a reverse vortex flow gliding arc plasma system, , which is comparable with our studies. The wide range of EE/O values for plasma technology (1.7–830 kWh/m 3 ) might be due to the water matrix, PFAS initial concentration, and experimental setup, among other factors.…”

“…We have recently conducted a series of plasma degradation studies investigating the removal of PFAS from highly conductive and complex water matrices including landfill leachate and IX still bottoms using an enhanced contact (EC) plasma reactor. , In this type of reactor, argon is bubbled through a diffuser that transports long-chain PFAS to the gas–liquid interface where they are degraded by plasma-generated species. − Solvated electrons, argon ions, and hot electrons have all been proposed to be responsible for the degradation of PFAS molecules . Our results indicate that for a range of aqueous matrices, long-chain PFAS (C ≥ 6 for perfluoroalkyl sulfonates (PFSAs) and C ≥ 8 for perfluoroalkyl carboxylates (PFCAs)) at typical groundwater concentrations (ng/L to μg/L) can typically be 90% degraded within minutes of treatment.…”

Rate, Efficiency, and Mechanisms of Electrochemical Perfluorooctanoic Acid Degradation with Boron-Doped Diamond and Plasma Electrodes

“…These results hint that 2 mA may correspond to too low of a current density (4 mA/cm 2 ) and reaction rate for the BDD, and in the future, electrodes must be designed with better matching of power density. That is, either smaller areas for the BDD or, preferably, larger currents spread over a large area for the plasma are needed …”

“…That is, either smaller areas for the BDD or, preferably, larger currents spread over a large area for the plasma are needed. 52 Role of Short-Lived Reactive Species. Although the split cell experiments indicated that both working electrodes can effectively degrade PFOA, where the plasma is assisted by the counter electrode, additional experiments are necessary for comparing major degradation pathways.…”

“…Examples of separation-based methods include adsorption, − ion exchange, , membrane separation, , and foam fractionation. − More recently, electrosorption-based technologies have demonstrated potential for selectively removing PFAS through functional surfaces. − Although these methods can physically remove PFAS from water, the PFAS ultimately remains as a persistent waste that needs to be chemically degraded. Examples of degradation-based methods include sonolysis, ,, photochemical, − electrochemical, ,− and plasma − processes. In the last decade, electrochemical and plasma-based processes have attracted much attention because of their capability to mineralize PFAS into F – and CO 2 .…”