Application of Non-Thermal Plasma Technology for the Removal of Per- and Polyfluorinated Substances from Investigation-Derived Wastes
Christopher Sales | Drexel University
The overarching goal of this project is to demonstrate the feasibility of applying dielectric barrier discharge (DBD) to enhance the use of cold plasma to degrade poly- and perfluoroalkyl substances (PFASs) in investigation-derived waste (IDW). The recent findings from Stratton et al. (2017), demonstrating that plasma could be an efficient method for removal of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS), are promising but only scratch the surface of the full potential of using plasma technology for environmental remediation of PFASs because the corona discharge system that they use is not as scalable as DBD and other types of more powerful, nonthermal plasma. In an effort to further advance the use of plasma to cost effectively and efficiently remove PFASs from contaminated environmental matrices, such as IDW, groundwater, and soils, this research aims to achieve the following objectives:
Objective 1: Adapt reactors designs and optimize plasma regimes using DBD, one of the most promising and advanced forms of cold plasmas, for treatment of PFASs in IDW;
Objective 2: Examine the removal efficiency and characterize the extent of mineralization of PFASs, specifically of perfluorobutane sulfonate (PFBS), perfluorohexane sulfonate (PFHxS), perfluoroheptanoate (PFHpA), PFOA, PFOS, perfluorononanoate (PFNA), and 6:2 and 8:2 fluorotelomer sulfonate (FtS), by DBD plasma technology;
Objective 3: Investigate potential matrix effects of IDW (i.e., presence of clays, natural organic matter) on the PFAS degradation by DBD plasma technology.
The approach has the potential to produce results that demonstrate the proof-ofconcept of using DBD cold plasma technologies to destructively degrade PFASs in IDW. Since IDW contaminated with PFASs can contain a mixture of liquids and solids, we plan to adapt and implement two types of reactors using DBD. The first reactor system will be used in this project for treatment of PFAS contaminated liquid solutions from site investigations, while the second reactor system is designed to treat solid materials contaminated with PFASs. Combining screening approaches, such as ion chromatography (IC) to detect production of fluoride ions (F-) and total inorganic carbon (TIC) analysis to detect production of CO2, with PFAS analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS) and the total oxidizable precursor (TOP) assay, will provide the chemical data needed to determine the removal efficiency and identify potential degradation pathways and mechanisms of plasma treatment of PFASs. Moreover, testing the ability of this new technologies to treat synthetic aqueous solutions with defined mixtures of PFASs and other constituents (i.e., clay, natural organic matter), as well as real IDW contaminated with PFASs, will allow researchers to investigate potential inhibitory effects that these other constituents may have on degradation performance. Lastly, this project will initiate studies in how to adapt cold plasma technology to produce and deliver reaction conditions for the treatment of solid materials, such as granular activated carbon (GAC), ion exchange (IX) resins and soils, contaminated with PFASs.
Due to the overwhelming realization that many Department of Defense sites are contaminated with PFASs, it is imperative that treatment technologies be developed that can degrade PFASs in a wide variety of environmental matrices, including IDW, soil, sediments, and groundwater. The work described in this limited-scope project will provide a foundation for building scalable and deployable forms of nonthermal plasma technologies capable of accomplishing efficient deflourination and mineralization of PFASs. It will demonstrate the potential advantages of using DBD plasma technology and other forms of non-thermal plasma (e.g., gliding arc) over the corona discharge plasma reactor system used by Stratton et al. (2017) in the treatment of PFASs. (Anticipated Completion - March 2019)