Plasma treatment of PFAS-laden material

Abstract

A method for treating a PFAS-laden solid material, comprising: treating a feed fluid with a gliding-arc plasma (GAP) to give rise to a plasma-activated fluid; fluidizing the PFAS-laden solid material; and contacting the PFAS-laden solid material and the plasma-activated fluid in a reaction zone under conditions sufficient to at least partly mineralize at least some of the PFAS so as to give rise to (i) a treated solid material having a reduced PFAS load and (ii) at least one degradation product, the PFAS-laden solid material optionally comprising any one or more of sand, soil, sediment, absorbent media, particulate activated carbon, and ion exchange resin. Other related systems and methods are also described.

Description

104889.001015 / 22-2414 PLASMA TREATMENT OF PFAS-LADEN MATERIAL RELATED APPLICATIONS

[0001] The present application claims priority to and the benefit of United States patent application no.63 / 672,272, “Plasma Treatment Of PFAS-Laden Material” (filed July 17, 2024). All foregoing applications are incorporated herein by reference in their entireties for any and all purposes. GOVERNMENT RIGHTS

[0002] This invention was made with government support under 950042 awarded by the Department of Defense. The government has certain rights in the invention. TECHNICAL FIELD

[0003] The present disclosure relates to the field of plasma treatment of PFAS-laden materials. BACKGROUND

[0004] Per- and polyfluoroalkyl substances (PFAS) have been widely used in multiple industries due to the physicochemical properties conferred by the recalcitrant C-F bonds in the hydrophobic tails and, for some PFAS, the hydrophilicity of the acidic (carboxylic, sulfonic) heads. The same properties that make these substances attractive (e.g., chemical inertness, water / oil repellent) have led to significant bioaccumulation (in all trophic levels) and pervasive contamination of soil, groundwater, and surface water worldwide. Given the recalcitrance, bioaccumulative potential, and toxicity of PFAS, it is imperative to develop cost-effective technologies that remove and mineralize these contaminants. Further, as existing approaches remain, in many instances, time intensive and / or cost prohibitive, there is a need for technologies that can cost-effectively treat PFAS-contaminated solids. SUMMARY

[0005] In meeting the described long-felt needs, the present disclosure provides a method for treating a PFAS-laden solid material, comprising: treating a feed fluid with a 4931-7710-2166.1 - 1 -104889.001015 / 22-2414 gliding-arc plasma (GAP) to give rise to a plasma-activated fluid; fluidizing the PFAS-laden solid material; and contacting the PFAS-laden solid material and the plasma-activated fluid in a reaction zone under conditions sufficient to at least partly mineralize at least some of the PFAS so as to give rise to (i) treated solid material having a reduced PFAS load and (ii) at least one degradation product, the PFAS-laden solid material optionally comprising any one or more of sand, soil, sediment, absorbent media, particulate activated carbon, and ion exchange resin.

[0006] Also provided is a method for treating a PFAS-laden solid material, comprising: treating a feed fluid with a gliding-arc plasma (GAP) to give rise to a plasma- activated fluid; and contacting the PFAS-laden solid material and the plasma-activated fluid in a reaction zone under conditions sufficient to at least partly mineralize at least some of the PFAS so as to give rise to treated solid material having a reduced PFAS load and to degradation products.

[0007] Further provided is a remediation system, comprising: a gliding-arc plasma (GAP) reactor, the GAP reactor configured to receive a PFAS-laden solid material therein, the GAP reactor configured to fluidize the solid material, the GAP reactor configured to output a fluid comprising degradation products resulting from contact between the solid material and a plasma-activated fluid within the reactor, the GAP reactor comprising an inlet to receive a feed fluid, and the GAP reactor configured to form the plasma-activated fluid from the feed fluid.

[0008] Also disclosed is a remediation system, comprising: a gliding-arc plasma (GAP) reactor, the GAP reactor configured to receive a PFAS-laden solid material therein, the GAP reactor configured to form a plasma-activated fluid from a GAP and a feed fluid, the GAP reactor configured to effect contact between the plasma-activated fluid and the PFAS- laden solid material, and the GAP reactor configured to output a fluid comprising degradation products resulting from contact between the solid material and the plasma-activated fluid within the reactor.

[0009] Additionally provided is a remediation system, comprising: a pre-treatment zone, the pre-treatment zone configured to contact a PFAS-laden solid material and a carrier fluid under conditions to remove PFAS from the PFAS-laden solid material and into the carrier fluid to give rise to PFAS-laden carrier fluid; and a remediation zone, the remediation 4931-7710-2166.1 - 2 -104889.001015 / 22-2414 zone configured to contact to PFAS-laden carrier fluid and a plasma-activated fluid so as to degrade fluorinate in the PFAS-laden carrier fluid.

[0010] Further provided is a method, comprising: contacting a PFAS-laden solid material with at least one of a first plasma and a first plasma-activated carrier fluid, the contacting being performed such that PFAS accumulates in a carrier fluid to give rise to a PFAS-laden carrier fluid and a plasma-treated solid material; optionally collecting plasma- treated solid material; contacting the PFAS-laden carrier fluid with at least one of a second plasma and a second plasma-activated carrier fluid, the contacting being performed so as to at least partially degrade PFAS accumulated in the PFAS-laden carrier fluid.

[0011] Also provided is a system, comprising: a first reactor, the first reactor configured to receive a PFAS-laden solid material and contact the PFAS-laden solid material with at least one of a first plasma and a first plasma-activated carrier fluid such that PFAS accumulate in a carrier fluid so as to give rise to a PFAS-laden carrier fluid and a plasma- treated solid material; and a second reactor, the second reactor being configured to receive the PFAS-laden carrier fluid and contact the PFAS-laden carrier fluid with at least one of a second plasma and a second plasma-activated carrier fluid so as to at least partially degrade PFAS accumulated in the PFAS-laden carrier fluid and give rise to PFAS degradation products. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present document. In the drawings:

[0013] FIGs.1A-1B.1A. Kinetics of PFAS degradation in the fluidized GAP reactor (FB-GAP). Conditions: 40 L air / min, 630 W, and 650 g of sand treated.1B. Kinetic of PFBS and PFBA degradation in the FB-GAP and in a furnace. The temperature profile set in the furnace matched that of the FB-GAP (dashed lines). Data represent the average concentration ± one standard deviation of triplicate samples.

[0014] FIGs.2A-2B.2A. Degradation of PFOS and B. temperature profiles under different gases and power settings. The current was manually set, and the resulting power 4931-7710-2166.1 - 3 -104889.001015 / 22-2414 (listed in panel 2B.) was a function of the breakdown voltage of the gas. In all cases, 650 g of spiked sand were treated, and the gas flow rate was 40 L / min. Data represent the average concentration ± one standard deviation of triplicate samples.

[0015] FIG.3. Comparison of specific energy inputs (SEI) for the removal of PFBA under air + methane, air. and nitrogen. The inset shows the temperatures developed in each case as a function of time. In all cases the air / N2 flow rate was 40 L / min, the CH4 flow rate was 2 L / min, and 650 g of spiked sand were treated. Data represent the average ± one standard deviation of triplicate samples.

[0016] FIG.4. Defluorination extents for three different tests – air + methane, air, and nitrogen. The base gas (air or nitrogen) was fed at 40L / min and the methane flow rate was 2 L / min. The defluorination was calculated based on the fluoride extracted from the solids and the total fluorine expected from the initial concentration of the six parent PFAS.

[0017] FIG.5. Exemplary workflow for treatment of a PFAS-laden solid material.

[0018] FIG.6. Improved fluoride recovery through the addition of TISAB III solution. A known amount of fluoride was spiked to deionized water (the control – ctrl) and a sand extract.

[0019] FIG.7. Decreasing absorbance at ~672nm with higher concentrations of fluoride in solution.

[0020] FIG.8. Fluidized bed GAP reactor and its major components. This version of the rector was not sealed, which enabled solid sampling throughout the treatment process.

[0021] FIG.9. Sealed fluidized bed GAP reactor. While no solid sampling was performed during the treatment process, the off-gas was passed through four based traps in series (0.1 M NaOH, 500 mL), thereby enabling detection / quantification of semi-volatile compounds.

[0022] FIGs.10A-D. PFAS degradation in the fluidized GAP reactor (FB-GAP). Conditions: 10A.40 L argon / min, 135 W; 10B.40 L air / min, 480 W; 10C.40 L air / min, 660 W; and 10D.40 L nitrogen / min, 780 W. In all cases, 650g of laboratory spiked sand was treated. Data represent the average concentration ± one standard deviation of triplicate samples.

[0023] FIGs.11A-D. First order fits to the PFAS degradation data under 11A., 11B. air at 630W and 11C., 11D. nitrogen at 780W. In all cases, 650g of laboratory spiked sand 4931-7710-2166.1 - 4 -104889.001015 / 22-2414 was treated. Data represent the average concentration ± one standard deviation of triplicate samples.

[0024] FIG.12. Degradation of PFAS in the FB-GAP under Air (40 L / min) and methane (2 L / min) at 200 W. Data represent the average concentration ± one standard deviation of triplicate samples. The dilutions of the samples between 30 and 50 minutes had concentrations below the LOQ (0.04 µg / g). As a conservative estimate, the concentrations for those points were set at the LOQ.

[0025] FIG.13. Shorter chain PFAS observed during the treatment of spiked sand. Conditions: 40 L air / min, 650 g sand, 630 W. Data represent the average concentration ± one standard deviation of triplicate samples.

[0026] FIG.14. Fluoride extracted from NaF-spiked sand. All tests were performed in triplicates in a muffle furnace in porcelain crucibles.

[0027] FIG.15. Reactor modification with methane injection, cooling loop and influent / effluent streams

[0028] FIG.16. Reactor modification with condensate trapping and influent / effluent streams.

[0029] FIG.17. Kinetics of PFAS degradation in the fluidized GAP reactor (FB- GAP). Conditions: 40 L air / min, 630 W, and 650 g of sand. Data represent the average concentration ± one standard deviation of triplicate samples (i.e., three replicates [from a single experiment] processed separately).

[0030] FIG 18. The effect of gas type and power setting on A. PFOS mass removals and B. temperature profiles. The current was manually set, and the resulting power (listed in panel B.) was a function of the breakdown voltage of the gas. In all cases, 650 g of spiked sand were treated, and the gas flow rate was 40 L / min. Data represent the average concentration ± one standard deviation of triplicate samples.

[0031] FIG.19. Mass removals of A. PFBA and PFBS and B. PFOA and PFOS in the FB-GAP system (blue) and in a furnace (orange). The temperature profile (secondary y- axis) set in the furnace matched that developed in the FB-GAP system under air at 630 W (‒ ‒ ‒ for FB-GAP and ‒ ‒ ‒ for furnace).

[0032] FIG.20. Comparison of specific energy inputs (SEI) for the removal of PFBA under air + methane, air, and nitrogen. The inset shows the temperatures developed in each case as a function of time. In all cases the air / N2 flow rate was 40 L / min, the CH4 flow 4931-7710-2166.1 - 5 -104889.001015 / 22-2414 rate was 2 L / min, and 650 g of spiked sand were treated. Data represent the average ± one standard deviation of triplicate samples.

[0033] FIG.21. Defluorination extents observed in four different runs using air + methane, air, and nitrogen. The base gas (air or nitrogen) was fed at 40L / min and the methane flow rate was 2 L / min. The defluorination was calculated based on the fluoride extracted from the solids and the total fluorine expected from the initial concentration of the six parent PFAS. Data represent the average ± one standard deviation of triplicate samples.

[0034] FIG.22. Fluorine mass balance in the treatment with A. air (40L / min) + CH4 (2.5L / min) at 250 W and B. air alone (40L / min) at 700 W. Panel C. shows the defluorination extent—the parent PFAS on the solids and PFAS in the impingers are considered in the mass balance. Data represent the average ± one standard deviation of triplicate samples.

[0035] FIG.23. Schematic of the GAP liquid treatment system.

[0036] FIG.24. Schematic illustrating the placement and trapping / neutralizing effect of grounded mesh when added to the GAP liquid treatment system.

[0037] FIG.25. Mass (a) parent compound removed and (b) fluoride produced as a function of specific energy input (SEI) for hydrated electron (e-aq) scavenging experiments conducted with PFOA in air GAP discharge. Experiments were conducted with 0, 1, 10, and 100 mM scavenger (nitrate). PFAS and fluoride analyses were conducted on single samples at each time point from a single experimental run. A linear regression, conducted in R, is displayed for each experimental run. Results are displayed as a function of SEI to account for differing plasma powers across runs. Results as a function of treatment time could be found in FIG.6.

[0038] FIG.26. Mass (a) parent compound removed and (b) fluoride produced as a function of specific energy input for reactive oxygen and nitrogen species (RONS) scavenging experiments conducted with PFOA in air GAP discharge. Experiments were conducted with 1% (w / v) scavengers (methanol, NAC, and sucrose). PFAS and fluoride analyses were conducted on single samples at each time point from a single experimental run. A linear regression, conducted in R, is displayed for each experimental run. Results are displayed as a function of SEI to account for differing plasma powers across runs. Results as a function of treatment time could be found in FIG.7.

[0039] FIG.27. PFAS and fluoride results from gas-phase charged particle trapping / neutralizing experiments. Mass (a) parent compound removed and (b) fluoride 4931-7710-2166.1 - 6 -104889.001015 / 22-2414 produced as a function of specific energy input for experiments conducted with 6:2 FTS, PFOA, and PFOS in air GAP discharge. PFAS and fluoride analyses were conducted on triplicate and duplicate samples, respectively, at each time point from a single experimental run. Average PFAS and fluoride results with error bars representing standard deviation for each time point are shown. Results are displayed as a function of SEI to account for differing plasma powers across runs. Results as a function of treatment time could be found in FIG.8.

[0040] FIG.28. Dominant degradation products include fluoride and unquantified fluorine during treatment of (a, b) 6:2 FTS, (c, d) PFOA, and (e, f) PFOS in air GAP discharge. PFAS and fluoride results were taken from control experiments conducted alongside experiments trapping / neutralizing gas-phase charged particles. PFAS and fluoride analyses were conducted on triplicate and duplicate samples, respectively, at each time point from a single experimental run. Average results for each time point are shown.

[0041] FIG.29. Schematic of PFAS degradation pathways during GAP treatment. Hypothesized dominant pathways (thermal mineralization driven by gas-phase charged particles, H / F exchange driven by e- and / or e-aq, and fragmentation via charge transfer from gas-phase charged particles) are indicated by a green outline. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0042] The present disclosure may be understood more readily by reference to the following detailed description of desired embodiments and the examples included therein.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0044] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0045] As used in the specification and in the claims, the term "comprising" can include the embodiments "consisting of" and "consisting essentially of.” The terms 4931-7710-2166.1 - 7 -104889.001015 / 22-2414 “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients / steps and permit the presence of other ingredients / steps. However, such description should be construed as also describing compositions or processes as "consisting of" and "consisting essentially of" the enumerated ingredients / steps, which allows the presence of only the named ingredients / steps, along with any impurities that might result therefrom, and excludes other ingredients / steps.

[0046] As used herein, the terms “about” and “at or about” mean that the amount or value in question can be the value designated some other value approximately or about the same. It is generally understood, as used herein, that it is the nominal value indicated ±10% variation unless otherwise indicated or inferred. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about” or “approximate” whether or not expressly stated to be such. It is understood that where “about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0047] Unless indicated to the contrary, the numerical values should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0048] All ranges disclosed herein are inclusive of the recited endpoint and independently of the endpoints. The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value; they are sufficiently imprecise to include values approximating these ranges and / or values.

[0049] As used herein, approximating language can be applied to modify any quantitative representation that can vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value specified, in some cases. In at least 4931-7710-2166.1 - 8 -104889.001015 / 22-2414 some instances, the approximating language can correspond to the precision of an instrument for measuring the value. The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4.” The term “about” can refer to plus or minus 10% of the indicated number. For example, “about 10%” can indicate a range of 9% to 11%, and “about 1” can mean from 0.9-1.1. Other meanings of “about” can be apparent from the context, such as rounding off, so, for example “about 1” can also mean from 0.5 to 1.4.

[0050] Further, the term “comprising” should be understood as having its open- ended meaning of “including,” but the term also includes the closed meaning of the term “consisting.” For example, a composition that comprises components A and B can be a composition that includes A, B, and other components, but can also be a composition made of A and B only. Any documents cited herein are incorporated by reference in their entireties for any and all purposes.

[0051] Any embodiment or aspect provided herein is illustrative only and does not limit the scope of the present disclosure or the appended claims. Any part or parts of any one or more embodiments or aspects can be combined with any part or parts of any one or more other embodiments or aspects.

[0052] Per- and polyfluoroalkyl substances (PFAS) have been widely used in multiple industries due to the properties conferred by the recalcitrant C-F bonds in the hydrophobic tails and, for some PFAS, the hydrophilicity of the acidic (carboxylic, sulfonic) heads. The same properties that make these substances attractive (e.g., chemical inertness, water / oil repellent) have led to significant bioaccumulation (in all trophic levels) and pervasive contamination of soil, groundwater, and surface water worldwide. Given the recalcitrance, bioaccumulative potential, and toxicity of PFAS, it is imperative to develop cost-effective technologies that remove and mineralize these contaminants.

[0053] PFAS destruction technologies developed to date are applied to aqueous matrices (e.g., non-thermal plasma, supercritical water oxidation (SCWO), hydrothermal alkaline treatment (HALT), electrochemical oxidation, and UV-generated hydrated electron; there are only a few alternatives for the direct treatment of PFAS-laden solids, including thermal desorption, smoldering, and ball milling – HALT has been shown to treat contaminated solids, but an aqueous medium is needed to carry out the reaction. 4931-7710-2166.1 - 9 -104889.001015 / 22-2414

[0054] To harness the effectiveness of the techniques developed for aqueous matrices, one approach relies on the desorption of PFAS from contaminated solids (e.g., through soil washing or foam fractionation) followed by treatment of the PFAS-laden solution. Despite the relatively good mass removals, these approaches remain, in many instances, time intensive and / or cost prohibitive; there is a need for technologies that can cost-effectively treat PFAS-contaminated solids.

[0055] Dry thermal processes such as smoldering and combustion have been proven to degrade PFAS in solid matrices – PFAS mass removals typically exceed 99% within a few hours of treatment, but high temperatures are needed (>1000°C) to modulate gaseous perfluorocarbon emissions. The high operational costs and the generation of unknown byproducts represent barriers in the widespread adoption and deployment of thermal-based technologies.

[0056] One alternative to treat PFAS-laden solids is the use of non-equilibrium plasma, which has been shown to be effective at degrading PFAS in aqueous matrices. In non-equilibrium plasma discharges, electrons in the feed gas are excited and their temperature is much higher than that of the rest of the gas (hence the name). Irrespective of the type of discharge (e.g., dielectric barrier discharge (DBD) or gliding arc plasmatron (GAP)), non-equilibrium plasma produces a reactive environment that may degrade PFAS through a combination of heat, ultraviolet and visible (UV-Vis) radiation, and reaction with free electrons and reactive species (e.g., reactive oxygen and nitrogen species, RONS). This highly reactive environment and its tunability (by controlling the power and the feed gas type), make non-equilibrium plasma an attractive candidate to efficiently degrade recalcitrant contaminants such as PFAS. To date, only one study has evaluated the applicability of non- thermal plasma to directly treat (i.e., no use of an aqueous environment) PFAS-laden solids.

[0057] In this disclosure, a plasma-based technology is provided to treat PFAS- laden solid, as illustrated by treatment of sand. A GAP reactor was used to generate plasma discharges and treat the solids in a fluidized bed configuration, enabling potential scalability of the treatment process. The effect of feed gas (air, nitrogen, and argon) and temperature (heat released from the plasma discharge) on PFAS removal are discussed. The potential mechanism(s) and measured degradation products are presented. The results from this study demonstrate that plasma-based technologies are a suitable approach for the treatment of PFAS-laden solids. 4931-7710-2166.1 - 10 -104889.001015 / 22-2414

[0058] Materials and Methods

[0059] Chemicals

[0060] Perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), potassium perfluorobutanesulfonate (PFBS), potassium perfluorohexanesulfonate (PFHxS), potassium perfluorooctanesulfonate (PFOS), acetic acid (Glacial, Reagent Plus, ≥99%), ammonium acetate (≥99%), ammonium chloride, disodium ethylenediaminetetraacetate dihydrate (EDTA), LC / MS grade methanol (OmniSolv®), and aluminum phthalocyanine chloride (AlPc-Cl) were purchased from Sigma-Aldrich (Allentown, PA, USA).

[0061] Sodium 1H,1H,2H,2H-perfluorooctanesulfonate (6:2 fluorotelomer sulfonate, 6:2FTS) was obtained from Toronto Research Chemicals. A standard mix of 24 native PFAS (PFAC-24PAR) and a mix of 19 mass-labeled PFAS (MPFAC-24ES) were obtained from Wellington Laboratories (Guelph, ON, Canada). Ammonium hydroxide, optima LC / MS grade water, sodium fluoride (NaF, >99%), and reagent alcohol (HPLC grade) were purchased from ThermoFisher Scientific (Fairlawn, NJ, USA).

[0062] Sample Preparation

[0063] All PFAS-laden solids in this study consisted of laboratory spiked sand. All- purpose sand (Quikrete®) was sieved to obtain a relatively homogeneous particle size (0.450 mm < particle size < 1 mm). Sieved solids and methanol were mixed at a 1:1 ratio (i.e., 1 mL of methanol per 1 gram of sand) in a high-density polyethylene (HDPE) bottle and spiked with a mix of PFBA, PFOA, PFBS, PFHxS, PFOS, and 6:2FTS each at a nominal concentration of 3-5 µg / g.

[0064] Thorough mixing of the slurry was performed for 15 min in an orbital shaker at 280 RPM. The bottle was then placed in a fume hood for at least 3 days to remove the methanol through evaporation. Complete evaporation was ensured by mixing the contents periodically and confirmed visually.

[0065] PFAS Extraction and Analysis

[0066] PFAS were extracted. Briefly, 1 g of sample was spiked with 2 ng of extraction standard (ES; MPFAC-24ES) and mixed with 8 mL of 1% (v / v) ammonium hydroxide in methanol in a 50 mL polypropylene (PP) vial. The resulting slurry was vortexed for 30 seconds, sonicated at 30°C for 15 minutes, and centrifuged for 20 minutes at 3000 RPM. The supernatant was collected in a new 50 mL PP centrifuge vial. 4931-7710-2166.1 - 11 -104889.001015 / 22-2414

[0067] The extraction procedure was repeated three more times, and the supernatants were pooled in the same 50 mL centrifuge vial. The pooled extract was evaporated to dryness in a water bath (60°C) under a gentle stream of nitrogen. The resulting dry sample was reconstituted in 1 mL of 1% acetic acid in methanol. The reconstituted solution was vortexed for 10 seconds, and then sonicated for 10 minutes (at 30°C) to ensure dissolution. Half of the volume of the clean sample (0.5 mL) was transferred to a new 2 mL centrifuge vial containing 0.5 mL of LC / MS grade water.

[0068] Aliquots (50 µL) were drawn for PFAS analysis, and the rest archived at 4°C. Extracts exceeding the PFAS quantitation range (e.g., for spiked, untreated samples) were further diluted with a water-methanol (50:50) solution containing ES at 1 µg / L prior to analysis.

[0069] Separation and detection of PFAS analytes was achieved using an Exion LC coupled with a X500R QTOF mass spectrometer (Sciex, USA) (LC-QToF-MS). A Gemini C- 18 column (3 mm × 50 mm, 3 μm; Phenomenex, USA) and guard column were used and maintained at 40 °C. A delay column (Luna C-18, 30 x 5 mm, 5 μm; Phenomenex, USA) was installed to modulate PFAS background contamination at the quantification windows. The analytes were eluted using 10 mM ammonium acetate in LC / MS grade water (Solvent A) and 10 mM ammonium acetate in LC / MS grade methanol (Solvent B) at a flow rate of 500 μL / min with the following gradient (A% / B%): 99 / 1 (0 min), 99 / 1 (0.25 min), 50 / 50 (0.50 min), 1 / 99 (4.50 min), 1 / 99 (8.50 min), 99 / 1 (10 min), 99 / 1 (13 min). The total run time was 13 minutes, and the injection volume 10 μL.

[0070] The mass spectrometer was operated in negative electrospray ionization (ESI−). Mass-labeled extraction standards were utilized to quantify PFAS analytes with scheduled high resolution multiple reaction monitoring (scheduled MRMHR) via isotope dilution. The electrospray ionization capillary voltage was -4.5 kV with source temperature of 500 °C. The mass transitions, declustering potentials, and collision energies can be found elsewhere. PFAS analytes and paired ES, their typical recoveries, and quality assurance and control elements can be found, for example, at Table S1.

[0071] Fluoride Extraction and Analysis

[0072] Fluoride was extracted from (un)treated solids by mixing 1 g of sand with 3 mL of 10 mM sodium hydroxide (in water) in a 15 mL PP vial. The slurry was vortexed for 30 seconds, sonicated at 30°C for 15 minutes, and centrifuged at 4000 RPM for 20 minutes. 4931-7710-2166.1 - 12 -104889.001015 / 22-2414 The supernatant was collected in a new 15 mL PP vial, and the extraction procedure was repeated once more.

[0073] A portion (1.8 mL) of the resulting pooled extract was mixed with 0.2 mL of total ionic strength adjustor buffer III (TISAB III, made in house) in a 2 mL PP centrifuge vial; TISAB III was needed to achieve close-to-complete fluoride recoveries in spike- recovery experiments (FIG.6). The contents were vortexed for 10 seconds and then centrifuged at 13000 RPM for 30 min to remove fine particles. The clean supernatant (1 mL) was transferred to a new 2 mL PP centrifuge vial and used for fluoride analysis. Spiked controls (with sodium fluoride) were included in each batch; results were considered valid if recoveries were within 80-120% of the expected values. All aqueous samples and standards received the same amount of TISAB III (10%). Selected extracts and aqueous samples with fluoride levels at or below the level of quantification (LOQ, typically ~10µM) were concentrated through evaporation and re-analyzed after adding TISAB III.

[0074] Fluoride was measured following a spectrophotometric method. To a 2 mL PP centrifuge vial containing 1850 µL of reagent alcohol, 50 µL of the sensor (135 µM AlPc- Cl in reagent alcohol) and 50 µL of the prepared samples (solid extracts or aqueous samples with TISAB III) were added. The contents were vortexed for 5 seconds, poured into 1 cm quartz cuvettes, and the absorbance was measured in an Agilent 8453 UV-visible spectroscopy system. As shown, the absorbance at ~672nm decreases with increasing concentration of fluoride (FIG.7).

[0075] Gliding Arc Plasmatron (GAP) and Degradation Experiments

[0076] A fluidized bed GAP reactor (FB-GAP) was built by adapting a stainless- steel pipe (reactor body; length: 35.5 cm; diameter: 3.6 cm), in which the contaminated solids were loaded and treated, to the outlet of a plasmatron (FIG.8) – the upward gas flow ensured the fluidization of the solids.

[0077] Gas (air, nitrogen, or argon) was fed at variable flow rates (typically 40 L / min) tangentially to the cylindrical plasmatron body, creating a gas vortex that was ionized due to the electrodes’ voltage difference. The plasma arc rotated and stretched, gliding on the high voltage and ground electrodes, as a function of gas flow rate, current, and breakdown voltage of the gas. The column of packed solids inside the reactor body (typically 650 g) was physically separated from the plasmatron by a 450 µm stainless-steel mesh; therefore, only reactive species and heat released from the plasmatron were expected to interact with the 4931-7710-2166.1 - 13 -104889.001015 / 22-2414 contaminated solids. The temperature within the reactor was tracked using a stainless-steel thermocouple probe, which was located 5 cm above the plasmatron (FIG.8). While a vertical temperature gradient may have developed inside the reactor, no other temperature measurements were collected; it was assumed that the temperature was relatively homogeneous thanks to the fluidization of the treated solids.

[0078] To avoid clogging the plasmatron, solids were loaded while air was flowing through the reactor. The initial and final reaction times were operationally defined and corresponded to the times when the power source (to generate the plasma discharge) was turned on and off, respectively. In the open FB-GAP reactor (FIG.8) solid samples were collected from the center of the column with a long handheld stainless-steel spoon every 10 minutes, for up to 60 minutes. All solid samples were extracted and analyzed in triplicates. In selected runs, methane was fed as the auxiliary gas (at variable flow rates 1 – 3 L / min) and experiments were run.

[0079] As an attempt to measure semi-volatile PFAS and HF, the FB-GAP was sealed (FIG.9), and the off gas passed through four base traps (500 mL of 0.1 M NaOH) in series. Only the initial and final solid samples were collected, which were extracted and analyzed as described above. An aliquot of the base trap solutions (0.5 mL) was mixed with an equal volume of 1% acetic acid in methanol (spiked with 1 ng ES) and centrifuged at 13000 RPM for 30 min to remove fine particles. The clean supernatant (0.7 mL) was transferred to a new 2 mL PP centrifuge vial and used for PFAS analysis. Fluoride measurements were directly performed with the base trap solutions after adding TISAB III as described in section 2.4. Calibration curves and spike-recovery tests with and without NaOH added confirmed a negligible effect of pH on the spectrophotometric response (data not shown).

[0080] Other example reactors are shown in FIGs.15 and 16. As shown in FIG.15, a reactor can include a plasma generator, which can include a high voltage electrode, a ground electrode, and an inlet to receive a feed, which feed can be, for example, plasma air and / or methane. An influent stream – which can be, for example, aqueous PFAS – can introduce a material to the reactor, where the material is contacted with plasma generated by the plasma generator. A cap or other covering can be present; such a cap or covering can be water-cooled, as shown in FIG.15. Cooling water can be flowed in and out of the cap, as shown in FIG.15. A condensate can form on a surface of the cap, as shown. Although not 4931-7710-2166.1 - 14 -104889.001015 / 22-2414 shown in FIG.15, the condensate can be collected, for example for further processing. A reactor can be configured to include a recirculation line; as shown, a recirculation pump can be present to effect recirculation of material from the top of the reactor to the bottom of the reactor. An effluent can be drawn from the reactor; as shown, this can be accomplished by an effluent stream.

[0081] FIG.16 provides an alternate reactor. As shown, a reactor can be configured for condensate trapping as well as for including influent / effluent streams. As shown, a reactor can include can include a plasma generator, which can include a high voltage electrode, a ground electrode, and an inlet to receive a feed, which feed can be, for example, plasma air and / or methane.

[0082] An influent stream – which can be, for example, aqueous PFAS – can introduce a material to the reactor, where the material is contacted with plasma generated by the plasma generator. A reactor can include a condenser region adapted to receive condensation; such a region can receive material from the reactor and promote condensation of that material. As shown, condensate can form within the condenser; condensate can be collected for further processing. The condenser region can contain water from the condensation; the condenser region can also include an effluent stream, as shown in FIG.11.

[0083] Without being bound to any particular theory or embodiment, a system according to the present disclosure can include a first reactor configured to contact a PFAS- laden solid material – such a particulate or beads – with a plasma-activated carrier fluid. Such a plasma-activated carrier fluid can be produced at the first reactor. Such contact can effect desorption of the PFAS from the solid material, and the desorbed PFAS can accumulate in the carrier fluid.

[0084] The solid material can be collected for further use or processing. The carrier fluid – now comprising at least some of the PFAS that desorbed from the PFAS-laden solid material – can then be further processed. Such further processing can include, for example, contacting the carrier fluid with a plasma-activated fluid. Such contacting can take place in an second reactor, which second reactor generates the plasma-activated fluid that contacts the PFAS-laden carrier fluid.

[0085] The contacting can, as described elsewhere herein, give rise to degradation of the PFAS present in the carrier fluid. Such degradation can include, for example, 4931-7710-2166.1 - 15 -104889.001015 / 22-2414 mineralization. The products resulting from contacting the PFAS-containing carrier fluid with the plasma-activated fluid can be collected for further processing.

[0086] Furnace Tests

[0087] A Fisher Isotemp 650 / 750 series programmable muffle furnace was used to conduct experiments in which thermolysis was expected to be the only degradative process. Solids (3.5 g) were loaded into ceramic crucibles – without lid – and left to react at variable temperatures for determined periods. The temperature was either varied during the run – if a temperature profile observed in GAP experiments was being matched – or fixed if only a set temperature was being evaluated.

[0088] Results and Discussion

[0089] PFAS Degradation and Mechanism

[0090] The FB-GAP reactor achieved almost complete mass removals of PFBA, PFOA, 6:2FTS, PFBS, PFHxS, and PFOS after an hour of treatment at a fixed power of 630 W (FIG.1A). Around 5% of the perfluoroalkyl sulfonic acids (PFSA) remained on the sand, implying that PFSA are more recalcitrant than perfluoroalkyl carboxylic acids (PFCA). The fluorotelomer sulfonate, however, exhibited a similar degradation profile as that of PFCAs (FIG.1A), suggesting that the presence of CH2 units in the chain renders the molecule more amenable to degradation. Without being bound to any particular theory or embodiment, given the similarities in the degradation profiles of short and long chain PFAS (e.g., PFBS and PFOS), it can be concluded that the main degradation processes at play are not chain dependent.

[0091] As discussed in the introduction, it is expected that plasma discharges lead to PFAS degradation through UV radiation, heat, and / or via reaction with RONS. To test whether heat was the main PFAS removal process, the temperature profile observed in the FB-GAP reactor was reproduced in a muffle furnace and samples were collected at different time points (FIG.1b). Without being bound to any particular theory or embodiment, the similarity in the PFAS degradation extents indicates that thermolysis was the main process responsible for the observed mass removals. The higher recalcitrance of PFSA, the chain length independent degradation, and the onset degradation temperatures (PFCA and 6:2FTS exhibited appreciable mass removals at temperatures > 130°C and PFSA at temperatures > 350°C) are consistent with observations in thermal degradation studies, which further confirms that thermolysis was the main driver for PFAS degradation in the FB-GAP reactor. 4931-7710-2166.1 - 16 -104889.001015 / 22-2414

[0092] Effect of Gas and Power Input

[0093] The degradation of PFAS under different gases and power inputs was explored. Mass removals for all six parent PFAS for all conditions tested are presented in FIG.10. As illustrated with PFOS, decreasing the power input from 630 W to 480 W resulted in no mass removal (FIG.2). Without being bound to any particular theory or embodiment, this may be a result of the low temperatures developed at 480 W – while at 630 W the system reaches ~400 °C within 60 minutes (FIG.1), the temperature does not surpass 150 °C in the same period at 480 W (FIG.2B).

[0094] Without being bound to any particular theory or embodiment, generally increasing the power of the plasma source led to higher temperatures, which in turn accelerated the PFAS mass removals. At 660W, the mass removals were faster than at 630W, consistent with the slightly higher temperature developed in the system (FIG.2). Under this condition, faster removals were observed for all PFAS and the recalcitrance of PFSA was more obvious (FIG.10C). The final temperature under nitrogen at 780W was not higher than the attained under air, but the 350°C threshold for PFSA degradation was reached much sooner. This resulted in faster PFOS removal with >99% degradation within 30 minutes. Under moisture-free nitrogen, little to no RONS are expected, therefore, the observed degradation can -- without being bound to any particular theory or embodiment – be ascribed to thermolysis. This is another line of evidence supporting thermal degradation as the main degradative mechanism in the FB-GAP.

[0095] Because the degradation / defluorination of PFAS in water via non- equilibrium plasma is more energy efficient under argon than under air, argon was tested as the feed gas in the fluidized bed reactor. No PFAS transformation occurred within 60 minutes of treatment (FIG.2), suggesting that dissociative electron attachment – electron transfer may be a principal mechanism under argon discharges – does not readily occur in a dry gaseous environment. Besides the potential contribution of reactive species, the temperature developed with argon marginally surpassed that in the test with air at 480W; the low breakdown voltage of argon impeded attaining higher powers and consequently, higher temperatures.

[0096] As an attempt to promote the role of reactive species, water mist was introduced to the plasmatron through the gas inlet. It was hypothesized that the mist would promote the formation of RONS and increase their half-life, which would in turn accelerate 4931-7710-2166.1 - 17 -104889.001015 / 22-2414 the degradation of PFAS in the GAP reactor. The addition of mist under nitrogen gas at two different power settings did not improve the performance. Further experimentation with air and larger quantities of mist did not yield different results (data not shown).

[0097] Although the temperature was variable in each of the runs, constantly increasing as a function of time (FIG.2B), the kinetics of PFAS mass removals were relatively constant after a specific onset (FIG.11). In the experiment with air at 630W, up to 50% PFBA had been removed at 20 minutes (FIG.1); however, only thereafter did the removal occurred at a seemingly constant observed rate constant (kObs), which are derived from the slope of the semilogarithmic plots – eq.1, FIG.11. ^^ ln௧^^ൌ െ^^ை^^ ∗ ^^ (1)^where Ctis the

[0098] Both PFCA exhibited a similar kObs (0.16-0.17 min-1), which was ~30% higher than the observed for 6:2FTS. It is interesting that the apparent kObswere constant for some of the run despite exhibiting a temperature increase from 270 °C at 20 min to 395 °C at 50 min. The kObsafter the onset at 30 minutes (at ~350 °C) were the same for all three PFSA (0.08 min-1), twice slower than the observed for PFCA. As previously discussed with FIG.2, the kinetics were faster for the run with nitrogen; the kObswere approximately 2.5-fold faster for the PFCA, PFSA, and the fluorotelomer sulfonate when compared to the air treatment (FIG.11). The relative reactivity between these PFAS classes was maintained in the N2run (i.e., the fluorotelomer and the sulfonic acids were ~30% and ~2-fold slower than the PFCA), demonstrating that the observed rates are likely caused by the same degradative mechanism, thermolysis. The onset was 10 minutes (350°C) for all PFAS, and the temperature variations were lower than in the air run (350-420°C), hence explaining the relatively constant mass removals. The seemingly invariable concentrations – towards the end of the reaction – in FIGs.11C and 11D reflect mass removals >99.98% and 99.9%, respectively. At such degradation extents (and low PFAS concentrations) further removal may be limited or cross- contamination may occur.

[0099] Despite the artifacts potentially introduced by the variable temperatures, our PFOA kObs match the first order rates previously reported (0.15 min-1at 250°C and 0.3-0.4 min-1at 300-400°C). 4931-7710-2166.1 - 18 -104889.001015 / 22-2414

[0100] Plasma Assisted Combustion

[0101] Given the role of temperature in the removal of PFAS, methane was fed as an auxiliary gas to attain higher temperatures at lower power inputs in a shorter period through combustion. An advantage of using plasma for the combustion process is that lean fuel mixtures can be used (i.e., plasma-assisted combustion). Click or tap here to enter text.This translates into higher temperatures at lower energy inputs and, potentially, lower treatment costs. Although different methane flow rates were tested (all with 40L air / min), one representative case is discussed below. In general, methane flow rates ≤ 1 L / min resulted in no appreciable combustion and > 2 but ≤ 3 L / min exhibited increasing temperatures and faster heating.

[0102] Although the removal rates seem slower than the obtained under nitrogen (FIGs.12 and 10), the specific energy input (SEI, the electrical energy used to treat a given mass of contaminated solid, eq.2) was significantly lower when methane was used as an auxiliary gas. The SEI required to remove >95% of PFBA in the FB-GAP with 2 L / min of methane (0.36 kJ / g) was ca.4 times lower than the observed in the N2 run at 780 W (1.40 kJ / g), whose SEI was in turn 1.5 lower than that in the treatment under air at 630W (2.08 kJ / g, FIG.3). The better SEI stems from the higher temperatures attained with the addition of methane, which can reach up to ~900 °C within one hour of treatment – twice as high as the generated with power inputs 3 to 4 times greater (FIG.3). After considering the electricity and methane used (see Section S4.2.), the use of methane translates to treatment cost savings of ~ 30%. The costs could be further reduced through optimization, which highlights the scalability and economic viability of this approach. ^^^^^^^^^^ ^^^^^^ ∗ ^^^^^^^^^sec^^^^^^^ ൌ(2) ^^^^^^^^^^^^^^ ^^^^^^^^ ^^^^^^

[0103]

[0104] While thermal desorption may be a potential PFAS mass removal process in the FB-GAP system, the detection of shorter chain PFAS suggest that parent compound degradation is occurring (FIG.13). Although thermal degradation is non-specific, i.e., different bonds in a molecule are randomly broken, the formation of shorter chain perfluoroalkyl acids support the hypothesis that the first step in the thermal destruction of PFSA and PFCA is the scission of the bond between the alpha carbon and the headgroup (i.e., desulfonation or decarboxylation). Note, however, that the shorter chain PFAS account for 4931-7710-2166.1 - 19 -104889.001015 / 22-2414 <1% mol / mol of the parent PFAS; therefore, it is not clear whether this thermal degradation pathway is dominant. The measured short chain PFAS were even lower for the nitrogen run, representing <0.1% of the parent compounds on a per mole basis: PFPeA 7.3 ng / g, PFHxA 10.6 ng / g, and PFHpS 5.39 ng / g. Because the measured products only accounted for a small fraction of the PFAS degraded, the remaining products were likely more volatile and escaped the system through the off-gas, were not amenable to the analytical tools used (e.g., trifluoroacetic acid (TFA)), and / or were further mineralized (i.e., fluoride formation).

[0105] The fluoride extracted from the treated solids increased as a function of time and accounted for up to ~15% and ~20% of the total fluorine (from the parent PFAS in the untreated sand, Eq.3) in the air (660W) and nitrogen (780W) runs, respectively (FIG.4). The higher temperatures and faster PFAS degradation observed under N2 were likely the main drivers for the slightly larger defluorination. The detection of fluoride and the measurable defluorination further demonstrate that the observed mass removals were partly due to mineralization of the parent PFAS, not simply thermal desorption. The relatively low defluorination extents may be explained by 1) the formation of volatile PFAS lost to the off- gas, 2) the formation of non-volatile, more recalcitrant intermediates not amenable to the analytical techniques used, or 3) a combination of both. ^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^%^ ൌ^^^^^^^^ ^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^ ^^^^^^^^^^(3)is used as an auxiliary gas (FIG.4), but it decreases to <5% at temperatures > 450°C. Since no apparent decrement in fluoride is observed for runs with no fuel added (see Air 660 W and Nitrogen 780 W, FIG.4), the higher temperatures reached through methane combustion likely decrease the fluoride yields through 1) HF losses (i.e., volatilization) and / or 2) reaction of fluorine with silicon – sand is mostly SiO2– and F is either lost to the gas phase (e.g., as silicon tetrafluoride, SiF4) or irreversibly bound to the solids. If HF is formed, it is expected to be recovered in the base traps (discussed in the next section). Potential side reactions of fluorine, on the other hand, could lead to compounds that are beyond our analytical methods and incomplete mass balances.

[0107] To test the effect of the treatment temperature on the recovery of fluoride, sand spiked with sodium fluoride was added to porcelain crucibles, dried at 105°C, and subsequently treated at 450°C and 800°C for 30 minutes in a muffle furnace. As observed in 4931-7710-2166.1 - 20 -104889.001015 / 22-2414 the experiments with PFAS, the amount of fluoride recovered from sand decreased as the temperature increased (FIG.14). Note that even at 450° the fluoride recovery was ~50%.

[0108] Products in the off-gas

[0109] Since most of the PFAS mineralization products are likely volatilized at the temperatures reached in the FB-GAP, the reactor was modified to allow for sampling of the off-gas. The top part of the reactor was sealed, and the gaseous stream was passed through four 500 mL base traps (0.1 M NaOH) connected in series, all immersed in ice baths (FIG.9). The discussion in is focused on the products measured in the base traps because the PFAS and fluoride concentrations measured in the solids – at the end of the run – are negligible.

[0110] The first base trap collected a significant number of fine particles as illustrated by the brown-reddish color. Although sand was sieved to > 0.425 mm, fines may have been associated with bigger grains. Moreover, the combined effect of fluidization (mechanical motion) and high temperatures may have increased the number of fine particles. Not only solid particles were collected; ca.50 mL of water were also retrieved in the first trap. This excess water likely resulted from the combustion of methane, which then condensed in the trap. Inside the reactor, this water may increase the defluorination extents through a combination of processes, including the hydrolysis of acyl fluorides – proposed to be a main product during PFAS thermal degradation.

[0111] The six PFAS initially present in the contaminated sand were detected in the base traps at concentrations that account for only up to 0.3% of the total fluorine. Although this indicates thermal desorption is a potential pathway, its contribution to the total PFAS mass removal is negligible – note that a fraction of the measured PFAS may have resulted from their desorption from transported solids (i.e., collected fines). The concentration of these six parent PFAS is only evident in the first two traps, and carboxylic acids seem to be more easily desorbed / transported than their homologous sulfonic acids, consistent with their comparatively lower boiling points. Shorter chain PFAS were also detected (e.g., PFPeA, PFHxA, and PFHpA), suggesting that PFAS are indeed transformed; however, their concentrations were lower than the observed for the parent PFAS. Fluoride was only detected in the first base trap, consistent with the relatively low volatility of HF (when compared to PFAS). The measured fluoride accounted for up to ~45% of the fluorine initially present in the sand as the sum of all six parent PFAS. These results (1) show that PFAS are mineralized in the FB-GAP, and (2) the fluoride yields are higher than the obtained 4931-7710-2166.1 - 21 -104889.001015 / 22-2414 during the smoldering combustion of PFAS-spiked soils (note that fluoride recoveries were high for GAC).

[0112] To assess sample processing contamination and evaluate the extraction recoveries, each batch of processed samples included a method blank (MB) and two ongoing precision and recovery standards (OPR) as detailed in Method 1633 by the EPA.1Sand was used as the matrix for these QA / QC. MB and OPR were processed as the rest of the samples except the MB did not receive native PFAS, the low-level OPR (LLOPR) was spiked with native standard at 2x the LOQ, and the OPR was spiked to attain a concentration at the mid- point of the calibration range (5µg / L). Each analytical sequence included doubled blanks (DB; no ES) and instrumental blanks (IB; ES added) consisting of methanol and water (50% / 50%). DB were injected every six samples, whereas IB were injected at the beginning of the analytical sequence and following high concentration samples to detect potential carryover. The accuracy of the calibration curve, which spanned from 10 ng / L to 50 µg / L, was verified via an initial calibration verification (ICV). A continuous calibration verification (CCV) was included every twelve samples and at the end of the analytical sequence. The native PFAS and ES recoveries were considered valid if within 70-130% and 60-140% of the expected values, respectively – these criteria were met as exemplified with OPR (Table S1). Table S1. Native PFAS, corresponding extraction standards (ES), and typical recoveries. Native PFAS Abbreviation Recovery Mass-Labeled PFAS Extraction Recovery ES analyte (%)aStandard (ES) (%)a2 5 8 3 3 1 5 7 8 334931-7710-2166.1 - 22 -104889.001015 / 22-2414

[0113] Fluoride Analysis

[0114] TISAB III Solution

[0115] A TISAB III (concentrated) solution was prepared in house by mixing (w / w %) ammonium chloride (26%), ammonium acetate (5%), disodium EDTA (2%), and water (67%) in a polypropylene (PP) bottle. To ensure complete dissolution of the salts, the contents were heated in a water bath at 60°C for 10 min and the pH was adjusted to 8.0 using 2 M sodium hydroxide. The addition of TISAB III improved the fluoride recoveries in spike- recovery experiments (FIG.6).

[0116] A schematic of the GAP reactor used in this study is presented in FIG.8. Click or tap here to enter text.

[0117] Energy Costs

[0118] Electricity Costs Assuming an average cost of $0.16 per kWh for electricity, and considering the specific energy input (SEI; kJ / kg) required to remove > 95% of PFBA from PFAS-laden solids (650g sand) ^ No CH4addition (under nitrogen at 780 W) ^ $62 per metric ton ^^^^ $0.16 1 ^^^^ℎ $0.062 1400 ∗ ∗ ൌ Eq.1 ^^^^ ^^^^ ^^^^^ No CH4 addition (under air at 630 W) ^ $93 per metric ton ^^^^ $0.16 1 ^^^^ℎ $0.093 2081 ∗ ∗ ൌ Eq.2 ^^^^ ^^^^ ^^^^^ CH4addition (under air at 200 W) ^ $16 per metric ton ^^^^ $0.16 1 ^^^^ℎ $0.016 363 ∗ ∗ ൌ Eq.3 ^^^^ ^^^^ℎ 3600 ^^^^ ^^^^

[0119] Methane combustion

[0120] Methane:Air Stoichiometric Ratio Methane undergoes complete combustion according to Eq.4 ^^^^ସ ^ 2^^ଶ → ^^^^ଶ ^ 2^^ଶ^^ Eq. 4

[0121] If air is used instead of pure oxygen, one liter of methane will burn completely with 9.524 L of air (Eq.5), yielding Eq.6. The moles of gas are calculated at standard temperature and pressure conditions (273 K, 1 atm). 4931-7710-2166.1 - 23 -104889.001015 / 22-2414 1 ^^^^^^ ^^^^ 2 ^^^^^^ ^^ 22.4 ^^ ^^ 1 ^^ ^ ^^ସ^^^^^ 1 ^^ ^^ଶ ଶସ∗ ∗ ∗ 22.4 ^^ ^^^^ସ1 ^^^^^^ ^^^^ସ1 ^^^^^^ ^^∗ଶ0.21 ^^ ^^ଶEq.5 ൌ9.524 ^^ ^^^^^^^^^^ସ ^ 2^^ଶ ^ 7.524^^ଶ → ^^^^ଶ ^ 2^^ଶ^^ ^ 7.524^^ଶ Eq. 6

[0122] Therefore, the stoichiometric air to fuel ratio is ଽ.ହଶସ ^ ^^^ ^ ^ ^ுర. If 15% is considered as the optimal excess air for complete combustion, the final air to fuel ratio (AF) is 9.524 ^^ ^^^^^^ 10.95 ^^ ^^^^^^ ^^^^^^^^௨^௧^^^ ൌ1 ^^ ^^^^∗ 1.15 ൌEq.7 ସ 1 ^^ ^^^^ସ

[0123] Methane:Air RatioAssisted combustion The air to methane ratio used in the plasma-assisted combustion process presented in the main text is 40 ^^ ^^^^^^ 20 ^^ ^^^^^^ ^^^^^^^^^^ ^^^^^௧^ௗ ൌൌ Eq.8 2 ^^ 1 ^^ The equivalent ratio combustion compared^^^^ ൌ Eq. 910.95ൌ 1.826

[0124] Cost for

[0125] The plasma-assisted combustion process in the fluidized bed GAP reactor removes > 95% of PFBA from PFAS-laden sand within 20 min. During this period, the temperature rises from 25°C to ~440 °C. Considering that the cost of methane per therm (i.e., 100 ft3) is $1.40, and the methane flow rate is 2 L / min, the cost for methane consumption is $30 per metric ton treated. ^^ ^^^^ $1.40 1 ^^^^ଷ1 $0. 2ସ030 ∗ଷ∗ 68 ^^∗ 20 ^^^^^^ ∗ൌ ^^^^^^ 100 ^^^^ 28.31 0.65 ^^^^ ^^^^^^^^ ^^^^Eq. 9

[0126] Therefore, the use of plasma-assisted combustion decreased the treatments costs from $65 (N2 run at 780W) to $46 per ton of PFAS-laden sand ^ ~30% savings.

[0127] The extensive use and recalcitrance of per- andsubstances (PFAS) have caused soil and water contamination across the globe. Most PFAS destruction technologies are applied to aqueous matrices; there is a need for technologies that can effectively treat PFAS-contaminated solids. In this study, a fluidized bed gliding arc (non- thermal) plasma reactor (FB-GAP) was used to treat PFAS-laden sand under different gas discharges. Argon plasma did not degrade PFAS, suggesting there is no dissociative electron attachment in dry gas. Similar parent compound degradation and defluorination extents were 4931-7710-2166.1 - 24 -104889.001015 / 22-2414 observed under air- and nitrogen-discharges, implying that thermolysis was the main PFAS degradation process. The use of methane as an auxiliary gas increased maximum temperatures and reduced treatment costs through plasma-assisted combustion of a lean fuel mix. The fluorine mass balance was ~20% after accounting for fluoride and targeted PFAS in treated solids and aqueous base traps for the effluent gas. The difference (~80%) likely resulted from irreversible reactions with SiO2 or formation of volatile organofluorine compounds.

[0128] Environmental Implications

[0129] The gliding arc plasmatron (GAP), a type of non-thermal plasma discharge, offers a scalable, energy-efficient solution for treating PFAS-contaminated solids. Unlike traditional thermal-based technologies, the potential for effluent gas recirculation within the GAP system may eliminate products of incomplete combustion (PIC) generated from the treated solids. Moreover, integrating plasma-assisted combustion into a fluidized bed configuration reduces treatment costs, making GAP a more sustainable and economically viable approach to PFAS remediation.

[0130] 1. Introduction

[0131] Per- and polyfluoroalkyl substances (PFAS) have been widely used in multiple industries due to the properties conferred by the recalcitrant C-F bonds and, for some PFAS, the hydrophilicity of the acidic (carboxylic, sulfonic) headgroups. The same properties that make these substances useful (e.g., chemical inertness, water / oil repellency) are responsible for the observed bioaccumulation (of some PFAS) and pervasive contamination of soil, groundwater, and surface water worldwide. Given the recalcitrance, bioaccumulative potential, and toxicity of PFAS, it is imperative to develop cost-effective technologies that remove and mineralize these contaminants.

[0132] Most PFAS destruction technologies are applied to aqueous matrices, including non-thermal plasma, supercritical water oxidation (SCWO), hydrothermal alkaline treatment (HALT), electrochemical oxidation, and UV-generated hydrated electrons. There are only a few alternatives for the direct treatment of dry PFAS-laden solids, including thermal desorption or destruction (e.g., incineration, smoldering, reactivation) and ball milling. Informed by the more mature aqueous PFAS treatment methodologies, many solids treatment approaches rely on the desorption of PFAS from contaminated solids (e.g., through soil washing or foam fractionation) followed by treatment of the PFAS-laden solution. 4931-7710-2166.1 - 25 -104889.001015 / 22-2414 Despite the relatively good mass removals, these approaches remain, in many instances, time intensive and / or cost prohibitive. Therefore, there is a need for technologies that can cost- effectively treat PFAS-contaminated solids.

[0133] Dry thermal processes such as smoldering and combustion have been proven to remove parent PFAS from solid matrices. PFAS mass removals typically exceed 99% within a few hours of treatment, but high temperatures are needed (>1000°C) to reduce gaseous perfluorocarbon emissions (i.e., achieve complete mineralization). The high operational costs and the generation of products of incomplete combustion (PIC) represent barriers in the widespread adoption and deployment of thermal-based technologies.

[0134] A promising alternative to treat PFAS-laden solids is the use of non- equilibrium plasma, which has been shown to be effective at degrading PFAS in aqueous matrices. In non-equilibrium plasma discharges, electrons in the feed gas are excited and their temperature is much higher than that of the rest of the gas (i.e., “non-equilibrium”). Irrespective of the type of discharge (e.g., dielectric barrier discharge (DBD) or gliding arc plasmatron (GAP)), non-equilibrium plasmas create a reactive environment that may degrade PFAS through a combination of heat, ultraviolet and visible (UV-Vis) radiation, and reaction with free electrons and reactive species (e.g., reactive oxygen and nitrogen species, RONS). This highly reactive environment is tunable by controlling the power and the feed gas type, making non-equilibrium plasma an attractive candidate for the efficient degradation of recalcitrant contaminants such as PFAS.

[0135] In this study, a GAP reactor was used to generate plasma discharges and treat PFAS-laden sand in a fluidized bed configuration—a scalable treatment process. The effect of feed gas (air, nitrogen, and argon), auxiliary gas (methane), and temperature (heat released from the plasma discharge) on PFAS removal is discussed. The potential mechanism(s) and measured degradation products are presented. The results from this study demonstrate that non-equilibrium plasma technologies are a promising alternative for the treatment of PFAS-laden solids.

[0136] 2. Materials and Methods

[0137] 2.1. Chemicals

[0138] Perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), potassium perfluorobutanesulfonate (PFBS), potassium perfluorohexanesulfonate (PFHxS), potassium perfluorooctanesulfonate (PFOS), acetic acid (Glacial, Reagent Plus, ≥99%), ammonium 4931-7710-2166.1 - 26 -104889.001015 / 22-2414 acetate (≥99%), ammonium chloride, disodium ethylenediaminetetraacetate dihydrate (EDTA), LC / MS grade methanol (OmniSolv®), and aluminum phthalocyanine chloride (AlPc-Cl) were purchased from Sigma-Aldrich (Allentown, PA, USA). Sodium 1H,1H,2H,2H-perfluorooctanesulfonate (6:2 fluorotelomer sulfonate, 6:2FTS) was obtained from Toronto Research Chemicals. A standard mix of 24 native PFAS (PFAC-24PAR) and a mix of 19 mass-labeled PFAS (MPFAC-24ES; extraction standard [ES]) were obtained from Wellington Laboratories (Guelph, ON, Canada). Ammonium hydroxide, optima LC / MS grade water, sodium fluoride (NaF, >99%), and reagent alcohol (HPLC grade) were purchased from ThermoFisher Scientific (Fairlawn, NJ, USA).

[0139] 2.2. Sample Preparation

[0140] All PFAS-laden solids in this study consisted of laboratory spiked sand. All-purpose sand (Quikrete®) was dry sieved to obtain a relatively homogeneous particle size (0.450 mm < particle size < 1 mm). Sieved solids and methanol were mixed at a ratio of 1 mL of methanol per 1 gram of sand in a high-density polyethylene (HDPE) bottle and spiked with a mix of PFBA, PFOA, PFBS, PFHxS, PFOS, and 6:2FTS, each at a nominal concentration of 3-5 µg / g. Thorough mixing of the slurry was performed for 15 min in an orbital shaker at 280 RPM. The bottle was then placed in a fume hood for at least 3 days to remove the methanol through evaporation. Complete evaporation was ensured by mixing the contents periodically and confirmed visually.

[0141] 2.3. Gliding Arc Plasmatron (GAP) and Degradation Experiments

[0142] A fluidized bed GAP reactor (FB-GAP) was built by adapting a stainless- steel pipe (reactor body; length: 35.5 cm; diameter: 3.6 cm), in which the contaminated solids were loaded and treated, to the outlet of a plasmatron (FIG.6); the upward gas flow ensured the fluidization of the solids. Gas (air, nitrogen, or argon) was fed at variable flow rates (typically 40 L / min) tangentially to the cylindrical plasmatron body, creating a gas vortex that was ionized due to the electrodes’ voltage difference. The plasma arc rotated and stretched, gliding on the high voltage and ground electrodes, as a function of gas flow rate, current, and breakdown voltage of the gas. The column of solids inside the reactor body (typically 650 g) was physically separated from the plasmatron by a 450 µm stainless-steel grounded mesh; therefore, only reactive species and heat released from the plasmatron were expected to interact with the contaminated solids. The thin mesh used in this study was not anticipated to interfere. The temperature within the reactor was tracked using a stainless-steel thermocouple 4931-7710-2166.1 - 27 -104889.001015 / 22-2414 probe which was located 5 cm above the plasmatron (FIG.6). Although a vertical temperature gradient may have developed inside the reactor, no other temperature measurements were collected; it was assumed that the temperature was relatively homogeneous due to the fluidization of the treated solids.

[0143] 2.4. Furnace Tests

[0144] A Fisher isotemp 650 / 750 series programmable muffle furnace was used to conduct experiments in which thermolysis was expected to be the only degradative process. Solids (3.5 g) were loaded into ceramic crucibles – without lid – and left to react at variable temperatures for determined periods. The temperature was either varied during the run – if a temperature profile observed in GAP experiments was being matched – or fixed if only a set temperature was being evaluated.

[0145] 2.5. PFAS Extraction and Analysis

[0146] PFAS were extracted from solids using a procedure for anionic PFAS. Briefly, 1 g of sample was spiked with 2 ng of ES and mixed with 8 mL of 1% (v / v) ammonium hydroxide in methanol in a 50 mL PP vial. The resulting slurry was vortexed for 30 seconds, sonicated at 30°C for 15 minutes, and centrifuged for 20 minutes at 3000 RPM. The supernatant was collected in a new 50 mL PP centrifuge vial. The extraction procedure was repeated three more times, and the supernatants were pooled in the same 50 mL centrifuge vial. The pooled extract was evaporated to dryness in a water bath (60°C) under a gentle stream of nitrogen. The resulting dry sample was reconstituted in 1 mL of 1% acetic acid in methanol. The reconstituted solution was vortexed for 10 seconds, and half of the volume of the clean sample (0.5 mL) was transferred to a new 2 mL centrifuge vial containing 0.5 mL of LC / MS grade water. Aliquots (50 µL) were transferred for PFAS analysis, and the rest archived at 4°C. Extracts exceeding the PFAS quantitation range (e.g., for spiked, untreated samples) were further diluted with a water-methanol (50:50) solution containing ES at 1 µg / L prior to analysis.

[0147] Separation and detection of PFAS analytes was achieved using an Exion LC coupled with a X500R QTOF mass spectrometer (Sciex, USA; LC-QToF-MS). A Gemini C-18 column (3 mm × 50 mm, 3 μm; Phenomenex, USA) and guard column were used and maintained at 40 °C. A delay column (Luna C-18, 30 x 5 mm, 5 μm; Phenomenex, USA) was installed to reduce PFAS background contamination in the quantification windows. The analytes were eluted using 10 mM ammonium acetate in LC / MS grade water (Solvent A) and 4931-7710-2166.1 - 28 -104889.001015 / 22-2414 10 mM ammonium acetate in LC / MS grade methanol (Solvent B) at a flow rate of 500 μL / min with the following gradient (A% / B%): 99 / 1 (0 min), 99 / 1 (0.25 min), 50 / 50 (0.50 min), 1 / 99 (4.50 min), 1 / 99 (8.50 min), 99 / 1 (10 min), 99 / 1 (13 min). The total run time was 13 minutes, using a 10 μL sample injection volume. The mass spectrometer was operated in negative electrospray ionization (ESI−). Mass-labeled extraction standards were utilized to quantify PFAS analytes (i.e., isotope dilution) with scheduled high resolution multiple reaction monitoring. The electrospray ionization capillary voltage was -4.5 kV with source temperature of 500 °C. PFAS analytes and paired ES, their typical recoveries, and quality assurance and control elements can be found in the supplementary information (Section S2, Table S1).

[0148] 2.6. Fluoride Extraction and Analysis

[0149] Fluoride was extracted from (un)treated solids by mixing 1 g of sand with 3 mL of 10 mM sodium hydroxide (in water) in a 15 mL PP vial. The slurry was vortexed for 30 seconds, sonicated at 30°C for 15 minutes, and centrifuged at 4000 RPM for 20 minutes. The supernatant was collected in a new 15 mL PP vial, and the extraction procedure was repeated once more. A portion (1.8 mL) of the resulting pooled extract was mixed with 0.2 mL of TISAB III (made in house – Supplementary information Section S3) in a 2 mL PP centrifuge vial. TISAB III was needed to achieve nearly-complete fluoride recoveries in spike-recovery experiments (FIG.8). The contents were vortexed for 10 seconds and then centrifuged at 13000 RPM for 30 min to remove fine particles. The clean supernatant (1 mL) was transferred to a new 2 mL PP centrifuge vial and used for fluoride analysis. Spiked controls (with sodium fluoride) were included in each batch; results were considered valid if recoveries were within 80-120% of the expected values. Selected extracts and aqueous samples with fluoride concentrations at or below the level of quantification (LOQ, typically ~10 µM) were concentrated through evaporation and re-analyzed.

[0150] 2.7. Data Analysis

[0151] 2.7.1. Kinetics of Mass Removal – First Order Rates

[0152] In selected cases, the kinetics of parent PFAS degradation / removal were analyzed via a first order model (Eq.1) ^^ ^^^^^^^^∗ ^^ (1)4931-7710-2166.1 - 29 -104889.001015 / 22-2414

[0153] where ^^௧is the concentration of PFAS at a given time ^^, ^^^is the initial PFAS concentration at time zero, and ^^ை^^is the observed first order rate constant.

[0154] 2.7.2. Specific Energy Input (SEI)

[0155] To compare the energy efficiency of different treatment conditions, the specific energy input (i.e., the energy used per mass of contaminated solid) was calculated using Eq.2. The time used for the calculation was the point at which a mass removal ≥ 90% (i.e., ≥ one order of magnitude) was attained for a selected parent PFAS. Note that this equation is analogous to the electrical energy per order of magnitude (EE / O) calculation typically used for aqueous systems. ^^^^^^^^^^ ^^^^^^ ∗ ^^^ ^ ^^^^^^^ ^^^^^ / ^^^ ൌ ^^^^^ ^^^^^^(2) ^^^^^^^^^^^^^^ ^^^^^^^^ ^^^^

[0156] 2.7.3. Defluorination

[0157] The fluoride measured in the aqueous extracts (^^^^^^^^^^^^^^^^^^ௌ) and the base traps (^^^^^^^^^^^^^^^^^^^்) was compared to the total fluorine expected from the parent PFAS to determine the extent of defluorination (Eq.3) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^%^ ^^^^^^^^^^^^^^^^^^^^ ∗ ^^^^^^^^ ^^^^^^^^^^^^^^^^^^ ^ ^^^^^^^^^^^^^^^^^^^^^^ ∗ ^^^^^^(3)a on the contaminated solid (µmol / g sand) and ^^^்is the volume in the base traps.

[0159] 3. Results and Discussion

[0160] A discussion of PFAS mass removals and associated mechanisms is presented in Sections 3.1 and 3.2. Information on measured degradation products and the implications on PFAS fate and transport is presented in Section 3.3.

[0161] 3.1.Parent PFAS Mass Removals and Mechanism

[0162] The FB-GAP reactor achieved nearly complete mass removals of the parent PFAS PFBA, PFOA, 6:2FTS, PFBS, PFHxS, and PFOS after an hour of treatment at a fixed power of 630 W under air (FIG.17). Around 5% of the perfluoroalkyl sulfonic acids (PFSA) remained on the sand, suggesting that PFSA are more recalcitrant than perfluoroalkyl carboxylic acids (PFCA). The fluorotelomer sulfonate, however, exhibited a similar degradation profile as that of PFCAs (FIG.17), suggesting that the presence of CH2 units in 4931-7710-2166.1 - 30 -104889.001015 / 22-2414 the chain renders the molecule more amenable to degradation. Given the similarities in the degradation profiles of short and long chain PFAS (e.g., PFBS and PFOS), it can be concluded that the main mass removal processes are not chain-length dependent.

[0163] Since the degradation / defluorination of PFAS in water via non-equilibrium plasma is more energy efficient under argon than under air, argon was tested as the feed gas in the fluidized bed reactor. No PFAS transformation occurred within 60 minutes of solids treatment (FIG.18). In aqueous system, dissociative electron attachment-electron transfer is believed to be the main PFAS degradation mechanism under argon discharges, therefore the full recovery of parent compounds from the solids suggests that this degradation mechanism does not readily occur in a dry gaseous environment. Besides the potential contribution of reactive species, the temperature developed with argon marginally surpassed that in the test with air at 480W (FIG.18); the low breakdown voltage of argon impeded attaining higher powers and consequently, higher temperatures.

[0164] As illustrated with PFOS, decreasing the power input from 630 W to 480 W resulted in no mass removal (FIG.18). This was likely a result of the low temperatures developed at 480 W—while at 630 W the system reaches ~400 °C within 60 minutes, the temperature does not surpass 150 °C in the same period at 480 W (FIG.18B). Mass removals for all six parent PFAS for all conditions tested are presented in FIG.10. Congruently, increasing the power of the plasma source led to higher temperatures, which in turn accelerated the PFAS mass removals (comparison of orange, blue, and purple data sets [FIG. 18]) and made more obvious the recalcitrance of PFSA (FIG.10C). Although the final temperature developed under nitrogen at 780 W was similar to the temperature attained under air at 660 W, relatively high temperatures were attained in a shorter period (350°C within 10 minutes). This resulted in faster PFOS removal, with >99% of the PFAS mass removed within 30 minutes. Under moisture-free nitrogen, little to no RONS are expected; therefore, the observed mass removals can be fully ascribed to thermal processes (i.e., thermolysis and / or thermal desorption). Information on measured degradation products is presented in Section 3.3.

[0165] Plasma discharges may degrade PFAS through UV radiation, heat, and / or via reaction with RONS; however, the conclusions derived from the data shown in FIG.18 suggest that thermal processes alone may be responsible for the observed parent compound removals. To test whether heat was the main PFAS removal process, the temperature profile 4931-7710-2166.1 - 31 -104889.001015 / 22-2414 observed in the FB-GAP reactor under air at 630 W (FIGs.17 and 18) was reproduced in a muffle furnace and spiked sand was directly treated in ceramic crucibles (samples were collected at different time points [FIG.19]). The similarity in the PFAS concentration profiles indicates that thermolysis (i.e., degradation due to heat) was the main process responsible for the observed mass removals. PFCA and 6:2FTS exhibited appreciable mass removals at temperatures > 130°C, while PFSA required temperatures > 350°C. The higher recalcitrance of PFSA, the chain length independent degradation, and the onset degradation temperatures are consistent with previous observations, further supporting that thermolysis was the main driver for PFAS mass removals in the FB-GAP reactor.

[0166] Although the temperature was variable in each of the runs, constantly increasing as a function of time (FIG.18B), the kinetics of PFAS mass removals were relatively constant after a specific onset (FIG.11). In the experiment with air at 630W, up to 50% PFBA was removed at 20 minutes (FIG.17); however, only thereafter did the removal occurred at a seemingly constant observed first-order rate constant (kObs), which is derived from the slope of the semilogarithmic plots (Eq.1, FIG.11). Only the data with a constant slope was considered for this analysis as discussed below and presented in FIG.11.

[0167] Both carboxylic acids exhibited a similar kObs (0.16-0.17 min-1), which was ~30% higher than the rate constant observed for 6:2FTS. It is interesting that the apparent kObs were constant for most of the run regardless of the temperature increase from 270 °C at 20 min to 395 °C at 50 min. The kObsafter the onset at 30 minutes (at ~350 °C) were the same for all three PFSA (0.08 min-1), approximately half of the PFCA values (FIG.11A-B). As previously discussed with FIG.18, the kinetics were faster for the run with nitrogen; the kObswere approximately 2.5-fold faster for the PFCA, PFSA, and the FTS when compared to the air treatment (FIG.11). Under nitrogen, the onset for PFAS mass removals was 10 minutes (350°C), and the temperature variations were lower than in the air run (350-420°C), hence explaining the relatively constant mass removals. The relative reactivity among the PFAS classes investigated was also consistent in the N2 run (i.e., the fluorotelomer sulfonate and the sulfonic acids were ~30% and ~50% less reactive than the PFCA), demonstrating that the observed rates are likely driven by the same mass removal process (thermal desorption and / or thermolysis). The seemingly invariable, low concentrations – towards the end of the reaction – in FIGs.11C and 11D reflect mass removals >99.98% and 99.9%, respectively. At such 4931-7710-2166.1 - 32 -104889.001015 / 22-2414 degradation extents (and low PFAS concentrations) further removal may be limited or cross- contamination may occur.

[0168] Despite any artifacts potentially introduced by the variable temperatures, our PFOA kObs matched the first order rate constants previously reported in a thermal degradation study (0.15 min-1at 250°C and 0.3-0.4 min-1at 300-400°C), Click or tap here to enter text.further indicating that thermal processes were likely responsible for the observed PFAS mass removals in the FB-GAP reactor. The degradation of PFOA exhibited similar kinetics irrespective of the matrix being treated (technical salt alone or in the presence of GAC; soil; or sand (this study).

[0169] 3.2.Plasma Assisted Combustion

[0170] Given the role of temperature in the removal of PFAS, methane was fed as an auxiliary gas to attain higher temperatures through combustion. An advantage of using plasma for the combustion process is that lean fuel mixtures can be used (i.e., plasma-assisted combustion). This allows attaining higher temperatures faster and at lower energy inputs, potentially lowering treatment costs. Although different methane flow rates were tested (all ≤ 3 L CH4 / min with 40 L air / min), only one representative case is discussed below. In general, methane flow rates ≤ 1 L / min resulted in no appreciable combustion and > 2 but ≤ 3 L / min exhibited faster heating and increased final temperatures.

[0171] Although the PFAS removal rates were slower when methane was used as an auxiliary gas (e.g., compared to the nitrogen run; FIGs.12 and 10d), the SEI (electrical energy used to treat a given mass of contaminated solid, Eq.2) was significantly lower. The SEI required to remove >95% of PFBA in the FB-GAP with 2 L / min of methane (0.36 kJ / g) was ca.4 times lower than the observed in the N2 run at 780 W (1.40 kJ / g), whose SEI was in turn 1.5 lower than that in the treatment under air at 630W (2.08 kJ / g, FIG.20). The improved SEI stems from the higher temperatures attained with the addition of methane, reaching up to ~900 °C within one hour of treatment – twice as high as the generated with power inputs 3 to 4 times greater (inset FIG.20). The lower SEIs, achieved with methane as an auxiliary gas, translate to treatment cost savings of ~ 30% after considering the electricity and methane used (see Section S4.2.). The costs could be further reduced through optimization, highlighting the scalability and economic viability of this treatment approach.

[0172] In this study, a mass removal of 3µg / g was be used as an arbitrarily defined limit (>90% mass removal in our work) for comparison purposes. For the air, N2, and air + 4931-7710-2166.1 - 33 -104889.001015 / 22-2414 CH4runs, the SEI at 3µg / g of PFOA removed were 1.90, 0.81, and 0.18 kJ / g, respectively (FIG.13), all lower than the SEI in others’ work (2.23 kJ / g at the same mass removal extent). These numbers highlight the highly energy-efficient nature of the FB-GAP reactor, especially when methane is used as an auxiliary gas. Note that the SEI are normalized by the amount of treated material in a given period of time, which produces significantly lower specific energy inputs for the FB-GAP. This is unlikely to change the conclusion on the superiority of the FB-GAP system as the corona discharge system is harder to scale up.

[0173] 3.3. Degradation products

[0174] While thermal desorption may be a potential PFAS mass removal process in the FB-GAP system, the detection of shorter chain PFAS suggest that parent compound degradation may be occurring (FIG.14a). Note that the PFAS solutions used to prepare the contaminated solids were made with technical salts and acids that may contain shorter chain perfluoroalkyl acids as impurities (e.g., PFBA, PFPeA, PFHxA, and PFHpA in PFOA and PFHpS (up to 8%) in PFOS-K). Click or tap here to enter text.Unfortunately, the concentration of these shorter chain acids was not determined for the untreated solids because dilutions were made prior to analysis to quantify the parent PFAS only. Thus, the potential contribution from impurities in the technical salts / acids to the presence of these compounds at later points in the treatment cannot be ruled out.

[0175] Although thermal degradation is non-specific (i.e., different bonds in a molecule are randomly broken), the potential formation of shorter chain perfluoroalkyl acids support the hypothesis that the first step in the thermal destruction of PFSA and PFCA is the scission of the bond between the alpha carbon and the headgroup (i.e., desulfonation or decarboxylation). However, the shorter chain PFAS accounted for <1.5% mol / mol of the parent PFAS. The measured short chain PFAS were even lower for the nitrogen run, likely because of the faster mass removals, representing <0.2% of the sum of the parent compounds on a per mole basis (FIG.14b). Since the measured perfluoroalkyl acids only accounted for a small fraction of the PFAS degraded, the remaining products were likely 1) more volatile and escaped the system through the effluent gas (off-gas hereafter), 2) not amenable to the analytical methods / tools used (e.g., trifluoroacetic acid (TFA)), and / or 3) further mineralized (i.e., fluoride formation).

[0176] The fluoride extracted from the treated solids increased as a function of time and accounted for up to ~15% and ~20% of the total fluorine initially present in the sand 4931-7710-2166.1 - 34 -104889.001015 / 22-2414 (calculated from the parent PFAS in the untreated sand, Eq.3) in the air (630 and 660W) and nitrogen (780W) runs, respectively (FIG.21). The higher temperatures and faster PFAS degradation observed under N2were likely the main drivers for the slightly larger defluorination. The measurable defluorination further demonstrates that the observed PFAS mass removals were caused, in part, by mineralization of the parent PFAS, not simply by thermal desorption. These relatively low defluorination extents may be explained by the three reasons stated above and / or potential reactions between fluorine radicals and the steel reactor or the silicates in the treated solids.

[0177] The defluorination extent reaches a similar maximum of ~17% when methane is used as an auxiliary gas (FIG.21), but it decreases to <5% at temperatures > 450°C. Since no apparent decrement in fluoride was observed for runs with no fuel added (see Air 660 W and Nitrogen 780 W, FIG.21), the higher temperatures reached through methane combustion likely decrease the fluoride yields through 1) HF losses (i.e., volatilization) and / or 2) reaction of fluorine with silicon—sand is mostly SiO2—leading to fluorine losses to the gas phase (e.g., as silicon tetrafluoride, SiF4) or through irreversible binding to the solids. If HF is formed, it is expected to be recovered in the base traps (discussed below in Section 3.3.1.). Potential side reactions of fluorine, on the other hand, could lead to compounds that are beyond the analytical methods employed in this study, creating a gap in the mass balances.

[0178] To test the effect of the treatment temperature on the recovery of fluoride, sand spiked with sodium fluoride was added to porcelain crucibles, dried at 105°C, and subsequently treated at 450°C and 800°C for 30 minutes in a muffle furnace (FIG.15). As observed in the experiments with PFAS, the amount of fluoride recovered from NaF-spiked sand decreased as the temperature increased. Note that even at 450° the fluoride recovery was ~50%. Therefore, our observations suggest that the most likely cause for the observed fluorine losses in the FB-GAP is the reaction with silicon in sand. Since a major product of the reaction between quartz (SiO2) and fluorine is SiF4 and its hydrolysis may not yield 100% F-, the fluoride recovery in aqueous traps that receive the off-gas may not be complete.

[0179] 3.3.1. Products in the effluent gas of the FB-GAP reactor

[0180] The reactor was modified to allow for sampling of the effluent gas as most of the PFAS mineralization products are likely volatilized at the temperatures reached in the FB-GAP, especially when methane is used as an auxiliary gas. The top part of the reactor was 4931-7710-2166.1 - 35 -104889.001015 / 22-2414 sealed, and the gaseous stream was passed through four 500 mL base traps (0.1 M NaOH) connected in series, all immersed in an ice bath (FIG.7). In this configuration, the FB-GAP was operated with and without methane to understand the effect of higher temperature on the product distribution. In both cases, the PFAS mass removals from the solids were greater than 99%, thus, only the transformation products / defluorination extents are discussed below.

[0181] The first base trap collected fine particles as qualitatively evidenced through a brown-reddish coloration (not shown). Although sand was sieved to > 0.425 mm, fine particles may have been associated with bigger grains (no wet sieving or washing of the sand was conducted). Moreover, the combined effect of fluidization (mechanical motion) and high temperatures may have eroded some of the particles and created finer grains. In addition to the accumulation of solids, ca.35 mL of water were retrieved in the first trap in the treatment with methane as an auxiliary gas. This excess water likely resulted from the combustion of methane, which then condensed in the trap. The presence of water vapor throughout the reaction may contribute to the mineralization of PFAS, for instance, through the hydrolysis of perfluorinated acyl fluorides (RCOF), proposed to be a main thermal degradation product of PFAS.

[0182] The six PFAS initially present in the contaminated sand—and to a lower extent, shorter-chain compounds—were detected in the base traps at concentrations that account for up to 0.60% and 0.16% of the total fluorine initially present in treatments with and without methane, respectively (FIG.16). Although this indicates thermal desorption is a potential PFAS mass removal pathway in the FB-GAP reactor, its contribution to the total mass loss is negligible. The concentration of the six parent PFAS was significant only in the first base trap, suggesting there is limited transport of fluorinated alkyl acids through the gas phase upon hydration. The concentrations were 3 to 5 times higher in the treatment with methane, which achieved temperatures 100-200 °C higher (FIG.16c). The higher temperatures and the presence of water vapor may have facilitated the transport of PFAS through the off-gas. Carboxylic acids seem to be more easily desorbed / transported than the analogous sulfonic acids (FIG.16), consistent with their comparatively lower boiling points. Shorter chain PFAS were also detected (e.g., PFPeA, PFHxA, and PFHpA) albeit at lower concentrations, suggesting that the parent PFAS are transformed with and without methane. Note that a fraction of these PFAS may have resulted from thermal desorption of short-chain impurities (from the technical salts / acids used). 4931-7710-2166.1 - 36 -104889.001015 / 22-2414

[0183] In the absence of methane, the pH of all four base traps was < 4 likely as a result of the formation of nitrogen (di)oxide in the air plasma discharge with subsequent accumulation of nitric acid upon dissolution of these gases. Even with methane a pH drop was observed (from ~12.7 to ~8.5), but it was less pronounced than in the case with air only—CO2from methane combustion likely buffered the solution in the base traps through the formation of (bi)carbonate. A potential issue arising from the low pH in the run without methane is that part of the fluoride may be lost as HF (pKa= 3.2). Therefore, the defluorination extents presented below may be conservative estimates.

[0184] Fluoride was only detected in the first base trap and accounted for up to 17% and 2% of the total fluorine in the methane and air only runs (FIG.22). The amount of fluoride on the solids had the opposite trend (i.e., higher for the run without methane) and was consistent with the results presented in FIG.21 despite the differences in absolute temperature developed in the reactor (FIGs.18 and 16). This resulted in a total defluorination—and, effectively, a fluorine mass balance—of 22% and 16% for the runs with and without methane, respectively (FIG.22). The similarity in the defluorination extents may suggest that the fluorine that is “lost” from the solids in the presence of methane (as observed in FIG.21), irrespective of its chemical form (e.g., SiF4 or HF), is trapped in the impingers.

[0185] The gap in the fluorine mass balance could be a consequence of potential irreversible reactions between fluorine and SiO2 (as described above) and / or the formation of gaseous products during the thermal degradation of PFAS (e.g., perfluorocarbons) that are not measurable by LC-QTOF-MS with ESI. While there is limited information on the PFAS degradation products during combustion reactions (i.e., thermal treatment under oxygen), The preponderance of acyl fluorides is decreased when PFAS are pyrolyzed, but similar degradation products are observed: short and long chain (un)saturated perfluorocarbons, and in the presence of salts in the solid matrices, chlorinated and brominated perfluorocarbons. Our findings on treating PFAS-contaminated water reveal that direct exposure to the GAP discharge results in near-complete mineralization (defluorination) through a process that is not purely thermal.

[0186] 4. Conclusions

[0187] The results from this study demonstrate that non-thermal plasma can be a viable treatment technology for dry PFAS-laden solids. While temperature was found to be the main driver for the PFAS mass removals from contaminated solids, plasma-assisted 4931-7710-2166.1 - 37 -104889.001015 / 22-2414 combustion via the FB-GAP may be more advantageous than regular thermal processes because 1) it is a scalable process that reduces treatment costs through the combustion of lean-fuel mixtures, and 2) any volatile organofluorine compounds may be further treated via recirculation of the off-gas through the highly reactive plasma discharges, potentially enabling complete PFAS mineralization. The latter may help to avoid expensive post- treatment / afterburner controls (treatment at >1000°C) and reduce the reliance on granular activated carbon (or other sorbents) to capture volatile products.

[0188] Appendix A. Supplementary data

[0189] The supplementary data including information on the reactors, QA / QCs, fluoride analyses, PFAS degradation profiles, first order kinetics, cost calculations, shorter chain PFAS, fluoride controls, and PFAS in the base traps (impingers) can be found in the online version of the article.

[0190] Additional Disclosure

[0191] Minimal research exists on the species that play a role in gliding arc plasma treatment of PFAS-contaminated water. This study reports that hydrated electrons and gas- phase charged particles are significant and identifies potential dominant degradation pathways.

[0192] Per- and polyfluoroalkyl substances (PFAS) are a diverse group of manmade organofluorine compounds that have garnered increasing attention from regulatory bodies, researchers, and the general public due to their potential for bioaccumulation and toxicity. The typical chemical structure of PFAS includes a perfluorinated carbon moiety (- CF3or -CF2-) and a hydrophilic head group (e.g. -COOH), which gives the compounds unique chemical and physical properties including hydrophobicity, oleophobicity, thermal stability, and surfactancy. These properties make PFAS useful for a variety of applications such as cookware, food packaging, paints, lubricants, and fire-fighting foams; since their initial production in the U.S. in the 1940s, PFAS have been used for such applications widely and without restraint. Simultaneously, PFAS have accumulated in environmental matrices and within the bodies of living things, as their unique properties also make them recalcitrant to conventional treatment methods and natural attenuation. Researchers have linked PFAS to a number of negative health effects including altered immune and thyroid function, adverse reproductive and developmental effects, liver and kidney disease, and cancer. 4931-7710-2166.1 - 38 -104889.001015 / 22-2414

[0193] Researchers and regulatory bodies have placed much emphasis on analysis and treatment of PFAS-contaminated drinking water, as its consumption is one main route of human exposure. Major sources of PFAS in drinking water include leaching from sites that use aqueous film forming foams (AFFF, a PFAS-containing firefighting foam), discharge from fluoropolymer manufacturing plants, and effluent from water treatment plants. In April 2024, the U.S. Environmental Protection Agency established legally enforceable Maximum Contaminant Levels (MCLs) ranging from 4.0–10.0 ng / L for six different PFAS in drinking water; PFOA, PFOS, PFHxS, PFNA, HFPO-DA (GenX chemicals), and PFBS were chosen based on historical use and potential for bioaccumulation and toxicity. Similarly, the EU issued a Drinking Water Directive in 2020 which set a threshold of 0.5 µg / L for total PFAS and set limits for a variety of individual PFAS to 0.1 µg / L. Meanwhile, PFAS concentrations in source water can be significantly higher than these desired values, and current treatment trains employed in drinking water facilities are generally not effective in reducing PFAS. In a study conducted on twenty-five different paired source and treated drinking water samples in the U.S., total quantifiable PFAS levels in source waters ranged from <1–1,102 ng / L, and it was determined that in twenty-four of these samples PFAS concentrations did not decrease post-treatment.

[0194] To accommodate PFAS-related drinking water regulations and better protect communities from exposure, researchers are assessing a variety of technologies for the treatment of PFAS-contaminated water. While several removal methods, including granular activated carbon (GAC) and ion exchange (IX) resin, have shown great promise for this application, they have limitations; mainly, any waste they produce (e.g. spent GAC or resin, regenerant solutions) still contains PFAS that have the potential to leach back into the environment. Thus, destructive technologies, which intend to mineralize PFAS in water, are also being studied. A few promising destructive technologies for this application include advanced reduction processes (ARPs), photocatalytic processes, supercritical water oxidation (SCWO), sonolysis, electrochemical oxidation (EO), activated persulfate oxidation, and non- equilibrium plasma.

[0195] Knowledge of degradation products is of particular importance in this case, as PFAS are known to degrade into shorter chain PFAS, which is undesirable because these are still recalcitrant and have potential for bioaccumulation and toxicity. Despite differences in how the aforementioned destructive technologies approach PFAS degradation, many 4931-7710-2166.1 - 39 -104889.001015 / 22-2414 follow similar pathways. Generally, these could be divided into four categories. First, (1) decarboxylation-hydroxylation-elimination-hydrolysis (DHEH, also referred to as chain- shortening), involves cleavage of the headgroup (via oxidation or reduction) to form an unstable perfluoroalkyl radical, followed by reaction with water to hydroxylate the radical, HF elimination, then finally hydrolysis to form a new PFAS compound one chain-length shorter than the original. Second, (2) hydrodefluorination (H / F exchange) in which a C–F bond is cleaved (via reduction) to form an unstable radical, which reacts with water to form a C–H bond in its place. Third, (3) hydroxydefluorination (OH / F exchange) in which a C–F bond is cleaved (via reduction) to form an unstable radical, which reacts with a hydroxyl radical (•OH) to form a C–OH bond in its place. Fourth, and less commonly proposed, (4) thermal mechanisms (e.g. cleavage of the headgroup via unimolecular bond scission followed by pyrolysis, or HF elimination to form perfluoroacyl fluoride compounds and volatile organofluorine compounds, perfluoroalkanes and / or olefins)

[0196] Non-equilibrium plasma is a neutral ionized gas composed of free electrons, ions, and photons, formed at relatively low pressures (e.g. atmospheric), which prevents its free electrons and gas molecules from colliding with enough frequency to reach thermodynamic equilibrium. Thus, while their free electrons reach high temperatures characteristic of strictly thermal plasmas, their other components remain close to room temperature. When applied to water, these discharges can create a rich reactive environment of heat, gas-phase charged particles (e.g. free electrons e-, Ar+, O2+, •O2-), UV, hydrated electrons (e-aq), and reactive oxygen and nitrogen species (RONS, e.g. •OH, •NO), all of which can contribute to PFAS degradation and participate in the mechanisms described above.

[0197] The mechanisms for PFAS degradation via non-equilibrium plasma discharges are not currently well understood, and the dominant pathway likely varies across discharge types investigated (e.g. streamer vs. gliding arc), how they are applied (e.g. above the water surface vs. submerged), and the plasma gas used (e.g. argon vs. air). However, a few studies have gathered evidence to support potential pathways and the key reactive species that might facilitate them. Generally, the aqueous reactive species e-aqand •OH have been deemed relevant to PFAS degradation by several types of non-equilibrium plasma discharges. Pathways including direct attack of the perfluoroalkyl tail at the plasma-water 4931-7710-2166.1 - 40 -104889.001015 / 22-2414 interface, DHEH, H / F, and OH / F exchange have been hypothesized, and the importance of gas-phase charged particles including Ar+and e- have been suggested.

[0198] GAP discharge is unique compared to other discharges studied for this application as it exhibits both thermal and non-thermal properties; the temperature of the gas in GAP discharge (300–1000 K) is elevated compared to other strictly non-equilibrium plasma discharges (300 K). Based on experiments, one can hypothesize that RONS play a significant role in PFAS degradation during treatment with GAP discharge, as PFAS degraded more quickly in air than in nitrogen or oxygen alone. But the specific species that partake in PFAS degradation in water during GAP treatment have not been probed.

[0199] In this work, both the aqueous and gas-phase plasma species that participate in PFAS degradation during GAP treatment of contaminated water were studied using aqueous phase scavengers and a grounded metal mesh, respectively.

[0200] Materials and methods

[0201] GAP liquid treatment system

[0202] A schematic of the GAP liquid treatment system used for this work is shown in FIG.23.

[0203] PFAS solution preparation

[0204] In all experiments, PFAS solutions were prepared by adding 100 mg of 6:2 FTS (CAS 27619-97-2, 98% purity, manufactured by SynQuest Labs, Alachua, FL, USA), PFOA (CAS 335-67-1, 96% purity, manufactured by Sigma-Aldrich, St. Louis, MO, USA), or PFOS (PFOSK was used, CAS 2795-39-3, 98% purity, manufactured by Sigma-Aldrich, St. Louis, MO, USA) to 1 L of distilled water in a polypropylene Erlenmeyer flask. To dissolve PFAS, solutions were placed on a stirring hot plate for 2 hours.

[0205] Mechanistic studies in the bulk liquid

[0206] Scavenging hydrated electrons. To explore the role that hydrated electrons (e-aq) play in PFAS degradation in the GAP liquid treatment system, sodium nitrate (NaNO3) was used as a scavenger. PFOA solutions spiked with 0, 1, 10, and 100 mM NaNO3 were treated. All experiments were conducted in air plasma. The calculated average plasma powers from each experiment are summarized in Table 1. Addition of NaNO3slightly decreased the breakdown voltage, which resulted in lower average plasma powers with increasing NaNO3 concentration. 4931-7710-2166.1 - 41 -104889.001015 / 22-2414

[0207] Table 1. Average plasma power in experiments exploring the role of hydrated electrons during PFAS degradation in the GAP liquid treatment system. Sodium nitrate concentration (mM) Average plasma power (W) 0 300treatment. At each time point, one sample was collected for PFAS analysis, and one sample was collected for fluoride analysis.

[0209] Scavenging reactive oxygen and nitrogen species. To explore the role that aqueous reactive oxygen and nitrogen species (RONS) play in PFAS degradation in the GAP liquid treatment system, methanol, n-acetyl cysteine (NAC), and sucrose were used as scavengers. PFOA solutions spiked with 1% methanol, NAC, and sucrose (separately) were treated. All experiments were conducted in air plasma. These scavengers did not influence breakdown voltage; thus, calculated average plasma power, 300 W, was consistent throughout experiments. Samples were collected at 0 (no plasma), 20, 40, and 60 minutes of treatment. At each time point, one sample was collected for PFAS analysis, and one sample was collected for fluoride analysis.

[0210] Mechanistic studies in the gas phase

[0211] Trapping / neutralizing gas-phase charged particles. To explore the role that gas-phase charged particles play in PFAS degradation in the GAP liquid treatment system, a grounded metal mesh was placed between the plasma source and the PFAS-contaminated liquid. This mesh traps and neutralizes gas-phase charged particles (i.e. free electrons and ions) but allows neutral particles to pass through to interact with the liquid. A schematic of the placement of the mesh and its trapping / neutralizing effect is shown in FIG.24. All experiments were conducted in air plasma. To ensure the mesh did not significantly affect the temperature of the plasma gas, the reactor was deconstructed and temperature of the gas exiting the gliding arc chamber was measured with a thermocouple. Plasma gas temperature was around 400 °C with and without mesh, thus mesh did not significantly affect gas temperature.

[0212] 6:2 FTS, PFOA, and PFOS solutions (separately) were treated with and without grounded mesh. The calculated average plasma powers from each experiment are 4931-7710-2166.1 - 42 -104889.001015 / 22-2414 summarized in Table 2. Average plasma power was calculated by multiplying the supplied current, which was held constant throughout each experiment, by the average voltage of the arc, which was measured using a multimeter. Grounded mesh slightly decreased breakdown voltage, which resulted in lower average plasma powers in mesh experiments.

[0213] Table 2. Average plasma power in experiments exploring the role of gas- phase charged particles during PFAS degradation in the GAP liquid treatment system. Parent compound Mesh / No mesh Average plasma power (W) 6:2 FTS Mesh 20020, 40, and 60 minutes of treatment. At each time point, triplicate samples were collected for PFAS analysis, and duplicate samples were collected for fluoride analysis.

[0215] Throughout these experiments, samples were collected at 0 (no plasma), 20, 40, and 60 minutes of treatment. At each time point, triplicate samples were collected for PFAS analysis, and duplicate samples were collected for fluoride analysis.

[0216] Analytical methods

[0217] Fluoride analysis via ion selective electrode (ISE). Fluoride analysis was conducted using a fluoride ion selective electrode (ORIONTMIonplus Sure-Flow Solid State Combination Fluoride Electrode, Thermo Fisher Scientific, Waltham, MA, USA). Calibration of the electrode ranged from 0.5 mg / L to 10.0 mg / L. The fluoride electrode filling solution used was manufactured by Thermo Fisher Scientific. Standards (0.5, 1.0, 2.0, 5.0, and 10.0 mg / L) manufactured by LabChem (Zelienople, PA, USA) were used for calibration. As recommended by the electrode manufacturer, samples were diluted with equal volume TISAB II, manufactured by LabChem, prior to analysis. All measurements were taken at room temperature.

[0218] PFAS analysis via HPLC-QTOF-MS. PFAS were quantified using HPLC- QTOF-MS (SCIEX x500r QTOF system, Framingham, MA, USA). To account for potential formation of quantifiable degradation products (e.g. shorter chain PFAS), samples were analyzed for a suite of 24 PFAS, outlined in Table S1. 4931-7710-2166.1 - 43 -104889.001015 / 22-2414

[0219] Data analysis. Mass of parent compound (i.e.6:2 FTS, PFOA, or PFOS) removed and mass of fluoride produced were calculated by multiplying measured concentrations by the total volume in the reactor. For experiments trapping / neutralizing gas- phase charged particles, in which triplicate samples were taken for PFAS analysis and duplicate samples were taken for fluoride analysis, results were averaged, and the standard deviation was calculated at each time point for data presentation.

[0220] Because in some cases average plasma power varied between experiments, results were presented as a function of specific energy input (SEI, kJ / L) rather than time. SEI was calculated using Equation 1. Results presented as a function of time could be found in the Supporting Materials (FIGs.6–8). Plasma Power (kW) × Time (s) Specific Energy Input (kJ / L) = (Equation 1) Initial Volume (L)

[0221] To analyze degradation products, moles of each product were calculated from the measured concentrations. Total fluorine was calculated based on the quantifiable PFAS and fluoride in the initial sample. Unquantified fluorine was then calculated at each time point by subtracting the moles of quantified fluorine (from PFAS and fluoride analysis results) from the total fluorine.

[0222] Results and discussion

[0223] Non-equilibrium plasma discharges in contact with water generate a diverse reactive environment of heat, gas-phase charged particles (e.g. e-, Ar+, O2+, •O2-), UV, hydrated electrons (e-aq), and reactive oxygen and nitrogen species (RONS, e.g. •OH, •NO). Most mechanistic studies on PFAS degradation in water via non-equilibrium plasma discharges focus on aqueous reactive species, typically employing scavenger or probing experiments to investigate which species play a significant role and assessing these results alongside degradation products to draw conclusions about mechanism. As discussed below, this work began with similar tactics. There is interest in the gas phase, specifically which gas-phase species generated by plasma might interact with PFAS at locations in the reactive environment where temperature is expected to be elevated compared to the bulk liquid.

[0224] Hydrated electrons might contribute to PFAS degradation but not mineralization

[0225] It has been purported that hydrated electrons (e-aq) play a significant role in PFAS degradation in water during treatment with argon and air plasma streamers over the surface of water. These can partake in a variety of PFAS degradation pathways including 4931-7710-2166.1 - 44 -104889.001015 / 22-2414 DHEH, H / F exchange, and OH / F exchange. To investigate the role of e-aqin PFAS degradation via air GAP discharge, experiments were conducted treating 100 mg / L PFOA solutions spiked with 0, 1, 10, and 100 mM sodium nitrate.

[0226] Results from e-aq scavenging experiments are shown in FIG.25. Increased e-aqscavenger concentration correlated with decreased mass of PFOA removed (FIG.25a) but did not inhibit fluoride production (FIG.25b). Using fluoride production as a metric for PFOA mineralization, these results suggest that there is a degradation pathway that does not result in significant mineralization, driven in part by e-aq at the plasma-water interface and / or in the bulk liquid. Discussed in more detail in later sections, no quantifiable shorter chain PFAS were formed in these experiments, suggesting that this pathway is not DHEH. However, H / F and / or OH / F exchange pathways are possible.

[0227] Reactive oxygen and nitrogen species appear to be inconsequential to PFAS degradation

[0228] Based on studies in various plasma gases (N2, O2, and air), one can hypothesize that RONS (e.g. •OH, •NO), rather than ROS or RNS alone, play a role in PFAS degradation in water during treatment with GAP discharge. Another group that used air plasma streamers over the surface of water determined that •OH played a significant role in PFOA degradation in their system, and one can hypothesize that, like e-aq, •OH might help to decrease the activation energy for thermal degradation of PFAS in water. Although it has been suggested that •OH are incapable of initiating PFAS degradation, they could partake in other steps of a variety of PFAS degradation pathways including DHEH and OH / F exchange. To investigate the role of RONS in PFAS degradation via air GAP discharge, experiments were conducted treating 100 mg / L PFOA solutions spiked with 1% w / v methanol, N-acetyl cysteine (NAC), and sucrose. These scavengers were not intended to be targeting specific RONS, but RONS in general, as specificity of RONS scavengers has been met with skepticism.

[0229] Results from RONS scavenging experiments are shown in FIG.26. For all scavengers tested, mass of PFOA removed (FIG.26a) and fluoride produced (FIG.26b) were not significantly affected, suggesting that RONS at the plasma-water interface and / or in the bulk liquid are inconsequential to PFAS degradation in water via air GAP discharge. Combined with results from e-aqscavenging experiments, which eliminated DHEH as a possible dominant PFAS degradation pathway during treatment with air GAP discharge due 4931-7710-2166.1 - 45 -104889.001015 / 22-2414 to reduced formation of shorter chain PFAS, RONS scavenging experiment results eliminate the likelihood of PFAS degradation by OH / F exchange as RONS are expected to participate in this pathway. H / F exchange via e-aqat the plasma-water interface and / or in the bulk liquid remains as a possible dominant pathway for PFAS degradation via air GAP discharge, and there appears to be some other pathway resulting in PFAS mineralization, which is explored further in the following sections.

[0230] Although the scavengers tested have been used to scavenge RONS, it is possible that scavenging was unsuccessful in the GAP liquid treatment system. Unsuccessful scavenging of RONS might be due to instability of the scavengers in higher temperature regions of the GAP liquid treatment system (e.g. at the plasma-water interface). Further, while concentrations used in this study were significantly higher than the PFOA concentrations used (1% w / v versus 0.01% w / v) and thus were expected to be sufficient for scavenging, it is possible that the amount of RONS generated overpowered the amount of scavenger used and thus the scavengers were degraded by the plasma. However, if this was the case, we would expect to see at least an initial effect on PFOA degradation; shown in FIG.7b, samples taken after 10 minutes of treatment and analyzed for fluoride fit linearly with the data taken at subsequent time points, suggesting no initial hindrance of PFOA degradation by RONS scavengers.

[0231] Synergies of gas-phase charged particles and thermal energy produced by GAP on PFAS mineralization

[0232] As discussed above, results from experiments scavenging reactive species in the aqueous phase (e-aqand RONS) suggest that these species do not play a significant role in PFOA mineralization via air GAP discharge. Considering the seemingly inconsequential effect that aqueous reactive species have on PFAS mineralization during this treatment along with the hypothesis that heat drives mineralization, experiments were designed to explore the role that gas-phase charged particles and gas-phase neutral particles, which exist in a higher- temperature region of the GAP liquid treatment system than aqueous species, play. A grounded mesh, which captures gas-phase free electrons, neutralizes gas-phase ions, and allows neutral particles to pass through to the bulk solution, was placed in the GAP liquid treatment system just past the source of plasma discharge.

[0233] PFAS and fluoride results from these experiments and their controls are shown in FIG.27. Trapping / neutralizing gas-phase charged particles with grounded mesh 4931-7710-2166.1 - 46 -104889.001015 / 22-2414 significantly decreased the mass of parent compound removed (FIG.27a) and completely inhibited fluoride production (FIG.27b) for all PFAS tested (6:2 FTS, PFOA, and PFOS). Using fluoride production as a metric for PFAS mineralization, these results suggest that gas- phase charged particles are essential to PFAS mineralization in water, while neutral particles do not play a role. Other non-equilibrium plasma studies have also suggested that gas-phase charged particles, including Ar+and e- may play a role in PFAS degradation in water.

[0234] Based on the thermal characteristics of GAP, prior evidence that temperature plays a significant role in PFAS mineralization via GAP and the distribution of observed degradation products during treatment discussed in the following section, we hypothesize that gas-phase charged particles react with PFAS in the gas phase and at the plasma-water interface; initiating a thermal mineralization reaction, while also potentially causing fragmentation and / or H / F exchange. Though plasma diagnostics were not conducted in these experiments, air plasma is expected to produce a variety of gas-phase ions such as O+, O2+, N2+, H2O+, H+, O3-, and O2-. Using PFOA as an example, based on its ionization potential, if charge exchange were to occur several of these gas-phase ions that might be present in air GAP discharge have significantly higher ionization potentials and would provide the molecule with ample energy to initiate a reaction.

[0235] In the GAP liquid treatment system, the estimated average air discharge temperature at the powers used in this work is typically around 300 °C, calculated using an energy balance. When this air comes into contact with water, the temperature dissipates throughout the bulk, warming but not boiling it. The temperature at the plasma-water interface and in the bulk is not expected to be high enough for thermal degradation. Purely thermal destructive techniques for PFAS treatment typically run at much higher temperatures; for example, incineration and smoldering combustion of PFAS-contaminated matrices are typically conducted at temperatures greater than 900 °C. Further, while some other non- equilibrium discharges produce high temperature filaments that might come into contact with water at the surface and participate in thermal degradation of PFAS, we do not expect direct contact between the arc (the filament in GAP discharge) and water in the GAP liquid treatment system because of the high plasma gas flow rate. Thus, thermal degradation via direct contact with high temperature filaments is not expected in the GAP liquid treatment system. However, based on evidence that temperature plays a role in PFAS mineralization during GAP treatment in combination with results from this work in which 4931-7710-2166.1 - 47 -104889.001015 / 22-2414 trapping / neutralizing gas-phase charged particles completely halted mineralization, we hypothesize that these particles react with PFAS via charge transfer, excitation, and / or ionization to create a less stable intermediate that thermally degrades at the temperatures provided by GAP. This hypothesized process in which gas-phase plasma species have a catalytic effect is similar to plasma-assisted combustion processes.

[0236] Finally, although results from experiments scavenging reactive species in the aqueous phase suggest that aqueous reactive species do not play a role in PFAS mineralization during GAP treatment, it is possible that gas-phase charged particles generate aqueous reactive species conducive to mineralization that were not scavenged by experiments conducted here. In this case, gas-phase charged particles would still play a significant role in initiating PFAS mineralization via GAP discharge, but indirectly; for example, gas-phase charged particles can react with water molecules to form •OH.

[0237] Degradation products support hypothesized mechanisms

[0238] Knowledge of the degradation products formed during treatment of PFAS- contaminated water could provide support for hypothesized mechanisms and insight into which are dominant. For example, formation of shorter chain PFAS compounds is typically used as an indicator for the DHEH (chain-shortening) pathway. A fluorine mass balance analysis of degradation products quantifiable by the methods used in this work was conducted on samples from the gas-phase charged particle trapping / neutralizing control experiments (i.e. air GAP discharge with no grounded mesh present). Degradation of parent compound (6:2 FTS, PFOA, or PFOS) along with production of fluoride (F-) and other shorter chain FTS, PFCA, and PFSA compounds (listed in Table S1) were tracked, and unquantified fluorine was calculated based on these results.

[0239] FIG.28 shows the dominant degradation products formed in these experiments which, for all PFAS tested, were fluoride, indicative of mineralization, and unquantified fluorine. Based on our hypothesis that heat, assisted by gas-phase charged particles, drives PFAS mineralization during GAP treatment, we suspect that the fluoride produced is, at least in part, a product of this mechanism. Unquantified fluorine could be indicative of various PFAS degradation pathways. First, unquantified fluorine might be partially hydrogenated PFAS, products of H / F exchange that are unquantifiable by methods used in this work. Without being bound to any particular theory or embodiment, based on results from gas-phase charged particle trapping / neutralizing experiments, H / F exchange 4931-7710-2166.1 - 48 -104889.001015 / 22-2414 during GAP treatment might be driven by e- at the plasma-water. Further, based on results from e-aq scavenging experiments, H / F exchange during GAP treatment might also be driven by e-aqat the plasma-water interface and / or in the bulk liquid. Unquantified fluorine could also be fragments created from reactions between PFAS and gas-phase charged particles via charge transfer, and supported by results from gas-phase charged particle trapping / neutralizing experiments in this work. A schematic of hypothesized pathways is shown in FIG.29.

[0240] Non-dominant degradation products, all of which are shorter-chain PFAS, formed in these experiments are shown in FIG.9. These results indicate that DHEH (chain- shortening) is present but not a dominant pathway for PFAS degradation in water during GAP treatment. This pathway might be driven by e- at the plasma-water interface or by aqueous reactive species (e.g. e-aq, •OH) as described in other non-equilibrium plasma work. DHEH and OH / F exchange, both pathways proposed in other non-equilibrium plasma work that do not appear dominant during GAP treatment of PFAS-contaminated water, are shown with the hypothesized dominant pathways in FIG.29.

[0241] Implications

[0242] As explained, several pathways are provided by which PFAS degrade during GAP treatment of contaminated water: (1) thermal mineralization driven by gas-phase charged particles, (2) H / F exchange driven by free electrons (e-) at the plasma-water interface or e-aqat the plasma-water interface / in the bulk liquid, and (3) fragmentation via charge transfer from gas-phase charged particles.

[0243] Abbreviations

[0244] PFAS: Per- and polyfluoroalkyl substances

[0245] 6:2 FTS: 1H,1H,2H,2H-Perfluorooctanesulfonic acid

[0246] PFOA: Perfluorooctanoic acid

[0247] PFOS: Perfluorooctanesulfonic acid (potassium salt)

[0248] GAP: Gliding arc plasma

[0249] e-: Free electrons

[0250] e-aq: Hydrated electrons

[0251] •OH: Hydroxyl radicals

[0252] RONS: Reactive oxygen and nitrogen species

[0253] Aspects 4931-7710-2166.1 - 49 -104889.001015 / 22-2414

[0254] The following Aspects are illustrative only and do not limit the scope of the present disclosure or the appended claims. Any part or parts of any one or more Aspects can be combined with any part or parts of any one or more other Aspects.

[0255] Aspect 1. A method for treating a PFAS-laden solid material, comprising: treating a feed fluid with a gliding-arc plasma (GAP) to give rise to a plasma-activated fluid; fluidizing the PFAS-laden solid material; and contacting the PFAS-laden solid material and the plasma-activated fluid in a reaction zone under conditions sufficient to at least partly mineralize at least some of the PFAS so as to give rise to (i) a treated solid material having a reduced PFAS load and (ii) at least one degradation product, the PFAS-laden solid material optionally comprising any one or more of sand, soil, sediment, absorbent media, particulate activated carbon, and ion exchange resin.

[0256] The plasma-activated fluid can be a gas. The plasma-activated fluid can also be a liquid.

[0257] Aspect 2. The method of Aspect 1, further comprising collecting the treated solid material. Such treated solid material can have reduced or even zero loading of PFAS.

[0258] Aspect 3. The method of any one of Aspects 1-2, further comprising collecting at least one degradation product.

[0259] Aspect 4. The method of any one of Aspects 1-3, wherein the feed fluid comprises any one or more of air, argon, dinitrogen, and oxygen.

[0260] Aspect 5. The method of Aspect 4, wherein the feed fluid comprises an auxiliary fluid.

[0261] Aspect 6. The method of Aspect 5, wherein the auxiliary fluid comprises a hydrocarbon, the hydrocarbon optionally comprising at least one of methane, acetylene, benzene, diesel, gasoline, light oil, and heavy oil.

[0262] Aspect 7. The method of any one of Aspects 1-6, wherein the reaction zone is at a temperature of from about 50 to about 2000ºC. The reaction zone can be at a temperature of, for example, from about 50 to about 2000ºC, or from about 200 to about 1500 ºC, or even from about 350 to about 1000ºC. In some embodiments, the reaction zone is at less than about 1000 ºC.

[0263] Aspect 8. The method of any one of Aspects 1-7, wherein a PFAS comprises a per- or polyfluorinated substance. 4931-7710-2166.1 - 50 -104889.001015 / 22-2414

[0264] Aspect 9. The method of Aspect 8, wherein a PFAS comprises any one or more of perfluorooctanoic acid (PFOA), perfluorobutanoic acid (PFBA),perfluorooctanesulfonic acid (PFOS), perfluorobutanesulfonic acid (PFBS), hexafluoropropylene oxide-dimer acid (HFPO–DA or GenX), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluorodecanoic acid (PFDA), perfluorohexanoic acid (PFHxA), and perfluorobutanoic acid (PFBA). It should be understood that the foregoing is not an exhaustive list of PFAS; other example PFAS are found at, for example, https: / / setac.onlinelibrary.wiley.com / doi / full / 10.1002 / ieam.4450.

[0265] Aspect 10. The method of any one of Aspects 1-9, wherein the PFAS- laden solid material comprises ion-exchange resin beads.

[0266] Aspect 11. The method of any one of Aspects 1-10, wherein the method is performed so as to reduce a loading of a PFAS of the PFAS-laden solid material by at least about 50% within 30 minutes.

[0267] Aspect 12. A method for treating a PFAS-laden solid material, comprising: treating a feed fluid with a gliding-arc plasma (GAP) to give rise to a plasma-activated fluid; and contacting the PFAS-laden solid material and the plasma-activated fluid in a reaction zone under conditions sufficient to at least partly mineralize at least some of the PFAS so as to give rise to treated solid material having a reduced PFAS load and to degradation products.

[0268] Aspect 13. The method of Aspect 12, further comprising giving rise to relative motion between the plasma-activated fluid and the PFAS-laden material. This can be accomplished by, for example retaining the PFAS-laden material and flowing the plasma- activated fluid through the PFAS-laden material. The plasma-activated fluid can also be mixed with the PFAS-laden material.

[0269] Aspect 14. The method of any one of Aspects 12-13, further comprising contacting the PFAS-laden solid material with an auxiliary fluid. Such an auxiliary fluid can, for example liberate at least some of PFAS from the PFAS-laden solid material.

[0270] Aspect 15. The method of Aspect 14, wherein the contacting the PFAS- laden solid material with an auxiliary fluid is prior to contacting the PFAS-laden solid material and the plasma-activated fluid.

[0271] Aspect 16. The method of Aspect 14, wherein the contacting the PFAS- laden solid material with an auxiliary fluid is concurrent with contacting the PFAS-laden solid material and the plasma-activated fluid. 4931-7710-2166.1 - 51 -104889.001015 / 22-2414

[0272] Aspect 17. The method of Aspect 14, wherein the auxiliary fluid comprises at least one of an alcohol and a salt.

[0273] Aspect 18. The method of Aspect 17, wherein the alcohol comprises methanol.

[0274] Aspect 19. The method of any one of Aspects 12-18, wherein the feed fluid comprises an auxiliary fluid.

[0275] Aspect 20. The method of Aspect 19, wherein the auxiliary fluid comprises a hydrocarbon.

[0276] Aspect 21. The method of any one of Aspects 12-20, wherein the PFAS- laden solid material comprises an adsorbent, the adsorbent optionally comprising ion- exchange resin beads. It should be understood that ion-exchange resins beads are a non- limiting, example adsorbent, and other adsorbents – such as activated carbon – are suitable.

[0277] Aspect 22. The method of any one of Aspects 12-21, wherein the reaction zone is at a temperature of from about 50 to about 2000ºC. The reaction zone can be at a temperature of, for example, from about 50 to about 2000ºC, or from about 200 to about 1500 ºC, or even from about 350 to about 1000ºC.

[0278] Aspect 23. The method of any one of Aspects 12-22, wherein a PFAS comprises a per- or polyfluorinated substance.

[0279] Aspect 24. The method of Aspect 23, wherein a PFAS comprises any one or more of perfluorooctanoic acid (PFOA), perfluorobutanoic acid (PFBA),perfluorooctanesulfonic acid (PFOS), perfluorobutanesulfonic acid (PFBS), hexafluoropropylene oxide-dimer acid (HFPO–DA or GenX), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluorodecanoic acid (PFDA), perfluorohexanoic acid (PFHxA), and perfluorobutanoic acid (PFBA).

[0280] Aspect 25. A remediation system, comprising: a gliding-arc plasma (GAP) reactor, the GAP reactor configured to receive a PFAS-laden solid material therein, the GAP reactor configured to fluidize the PFAS-laden solid material, the GAP reactor configured to output a fluid comprising degradation products resulting from contact between the PFAS- laden solid material and a plasma-activated fluid within the reactor, the GAP reactor comprising an inlet to receive a feed fluid, and the GAP reactor configured to form the plasma-activated fluid from the feed fluid. 4931-7710-2166.1 - 52 -104889.001015 / 22-2414

[0281] Aspect 26. The remediation system of Aspect 25, further comprising a temperature control train configured to maintain a temperature within the GAP reactor during contact between the PFAS-laden solid material and the GAP.

[0282] Aspect 27. The remediation system of any one of Aspects 25-26, further comprising a supply of the feed fluid.

[0283] Aspect 28. The remediation system of Aspect 26, wherein the feed fluid comprises air. The feed fluid can also comprise, for example, a hydrocarbon.

[0284] Aspect 29. The remediation system of any one of Aspects 25-28, wherein the reactor further comprises an inlet configured to receive an auxiliary fluid.

[0285] Aspect 30. The remediation system of Aspect 29, further comprising a supply of the auxiliary fluid, the auxiliary fluid optionally comprising at least one hydrocarbon, the hydrocarbon optionally comprising methane.

[0286] Aspect 31. A remediation system, comprising: a gliding-arc plasma (GAP) reactor, the GAP reactor configured to receive a PFAS-laden solid material therein, the GAP reactor configured to form a plasma-activated fluid from a GAP and a feed fluid, the GAP reactor configured to effect contact between the plasma-activated fluid and the PFAS-laden solid material, the GAP reactor configured to output a fluid comprising degradation products resulting from contact between the PFAS-laden solid material and the plasma-activated fluid within the reactor. GAP-treated gas can, for example, be feed gas or products of plasma assisted combustion of feed gas and auxiliary gas (hydrocarbons).

[0287] Aspect 32. The remediation system of Aspect 31, further comprising a retention chamber configured to contain the PFAS-laden solid material therein during contact between the PFAS-laden solid material therein and the plasma-activated fluid.

[0288] Aspect 33. A remediation system, comprising: a pre-treatment zone, the pre-treatment zone configured to contact a PFAS-laden solid material and a carrier fluid under conditions to remove PFAS from the PFAS-laden solid material and into the carrier fluid to give rise to PFAS-laden carrier fluid; and a remediation zone, the remediation zone configured to contact to PFAS-laden carrier fluid and a plasma-activated fluid so as to degrade fluorinate in the PFAS-laden carrier fluid.

[0289] Aspect 34. The remediation system of Aspect 33, wherein the PFAS-laden solid material comprises an adsorbent, the adsorbent optionally comprising ion-exchange resin beads. It should be understood that ion-exchange resins beads are a non-limiting, 4931-7710-2166.1 - 53 -104889.001015 / 22-2414 example adsorbent, and other adsorbents – such as activated carbon – are suitable. It should also be understood that the disclosed technology is not limited to treating ion-exchange resin beads, as other PFAS-laden solid materials can be used in conjunction with the disclosed technology. It should also be understood that degradation can include mineralization, and some degradation can be expected in the pre-treatment zone. The remediation zone will further degrade / mineralize the PFAS in the carrier fluid.

[0290] Aspect 35. The remediation system of any one of Aspects 33-34, wherein a fluorinate comprises any one or more of perfluorooctanoic acid (PFOA), perfluorobutanoic acid (PFBA),perfluorooctanesulfonic acid (PFOS), perfluorobutaesulfonic acid (PFBS), hexafluoropropylene oxide-dimer acid (HFPO–DA or GenX), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluorodecanoic acid (PFDA), perfluorohexanoic acid (PFHxA), and perfluorobutanoic acid (PFBA).

[0291] Aspect 36. A method, comprising: contacting a PFAS-laden solid material with at least one of a first plasma and a first plasma-activated carrier fluid, the contacting being performed such that PFAS accumulates in a carrier fluid to give rise to a PFAS-laden carrier fluid and a plasma-treated solid material; optionally collecting plasma-treated solid material; contacting the PFAS-laden carrier fluid with at least one of a second plasma and a second plasma-activated carrier fluid, the contacting being performed so as to at least partially degrade PFAS accumulated in the PFAS-laden carrier fluid.

[0292] Aspect 37. The method of Aspect 36, wherein the first plasma-activated carrier fluid is formed at a first reactor. In some embodiments, the first plasma is formed at the first reactor.

[0293] Aspect 38. The method of Aspect 36, wherein the second plasma-activated carrier fluid is formed at a second reactor. In some embodiments, the second plasma is formed at the second reactor.

[0294] Aspect 39. The method of any of Aspects 36-38, wherein contacting the PFAS-laden carrier fluid with a second plasma-activated carrier fluid is performed under conditions sufficient to mineralize PFAS accumulated in the PFAS-laden carrier fluid.

[0295] Aspect 40. A system, comprising: a first reactor, the first reactor configured to receive a PFAS-laden solid material and contact the PFAS-laden solid material with at least one of a first plasma and a first plasma-activated carrier fluid such that PFAS accumulate in a carrier fluid so as to give rise to a PFAS-laden carrier fluid and a plasma- 4931-7710-2166.1 - 54 -104889.001015 / 22-2414 treated solid material; and a second reactor, the second reactor being configured to receive the PFAS-laden carrier fluid and contact the PFAS-laden carrier fluid with at least one of a second plasma and a second plasma-activated carrier fluid so as to at least partially degrade PFAS accumulated in the PFAS-laden carrier fluid and give rise to PFAS degradation products.

[0296] An example such process is depicted in non-limiting FIG.5. As shown, a first reactor can contact PFAS-laden solid material with at least one of a first plasma and a first plasma-activated carrier fluid such that PFAS accumulates in a carrier fluid; this can be accomplished by the PFAS desorbing from the solid material. The first plasma or first plasma-activated carrier fluid can be formed in the first reactor, for example when the first reactor is a gliding-arc plasma or other plasma-forming reactor. This is not a requirement, though, as the first plasma-activated carrier fluid can be created elsewhere and then communicated to the first reactor for contact with the PFAS-laden solid material. Solid material with reduced PFAS content can be collected from the first reactor. Such collected material can be further treated and then recycled back into service. Ion exchange resin is one such solid material; as explained elsewhere herein, the solid material can be an adsorbent, such as activated carbon or an ion exchange resin.

[0297] PFAS-laden carrier fluid can be communicated to a second reactor, where the PFAS-laden carrier fluid can be contacted with at least one of a second plasma and a second plasma-activated carrier fluid, the result of which can be degradation of the PFAS into degradation products. These degradation products can be collected. The at least one of a plasma and a second plasma-activated carrier fluid can be formed in the second reactor. This, however, is not a requirement, as the at least one of a plasma and a second plasma-activated carrier fluid can also be formed elsewhere and then communicated to the second reactor. In some embodiments, the second reactor forms the second plasma, for example when the second reactor is a gliding-arc plasma or other plasma-forming reactor.

[0298] Carrier fluid that has been treated in the second reactor can optionally be recycled for further processing, for example to be plasma treated or otherwise treated and then used in the first reactor. Carrier fluid can also be treated and then disposed of, depending on the user’s needs.

[0299] It should be understood that PFAS-laden solid material can be contacted with a plasma in the first reactor and then PFAS-laden carrier fluid (resulting from the 4931-7710-2166.1 - 55 -104889.001015 / 22-2414 foregoing contact) can be contacted with a plasma and / or a plasma-activated carrier fluid in the second reactor. It should be also understood that PFAS-laden solid material can be contacted with a plasma-activated carrier fluid in the first reactor and then PFAS-laden carrier fluid (resulting from the foregoing contact) can be contacted with a plasma and / or a plasma-activated carrier fluid in the second reactor.

[0300] Aspect 41. The system of Aspect 40, wherein the system is configured to collect plasma-treated solid material.

[0301] Aspect 42. The system of any one of Aspects 40-41, wherein the system is configured to collect PFAS degradation products.

[0302] Aspect 43. The system of any one of Aspects 40-42, wherein at least one of the first reactor and the second reactor is a gliding arc plasma (GAP) reactor.

[0303] Aspect 44. The system of any one of Aspects 40-43, wherein at least one of the first reactor and the second reactor comprises a heat exchanger, the heat exchanger optionally being water-cooled.

[0304] Aspect 45. The system of any one of Aspects 40-44, wherein the second reactor is configured to collect a condensate resulting from contacting the PFAS-laden carrier fluid and the at least one of a second plasma and a second plasma-activated carrier fluid.

[0305] Aspect 46. The system of any one of claims 40-45, further comprising a source of a first plasma.

[0306] Aspect 47. The system of any one of claims 40-46, further comprising a source of a first plasma-activated carrier fluid.

[0307] Aspect 48. The system of any one of claims 40-47, further comprising a source of a second plasma.

[0308] Aspect 49. The system of any one of claims 40-48, further comprising a source of a second plasma-activated carrier fluid. 4931-7710-2166.1 - 56 -

Claims

104889.001015 / 22-2414 What is Claimed:

1. A method for treating a PFAS-laden solid material, comprising: treating a feed fluid with a gliding-arc plasma (GAP) to give rise to a plasma- activated fluid; fluidizing the PFAS-laden solid material; and contacting the PFAS-laden solid material and the plasma-activated fluid in a reaction zone under conditions sufficient to at least partly mineralize at least some of the PFAS so as to give rise to (i) a treated solid material having a reduced PFAS load and (ii) at least one degradation product, the PFAS-laden solid material optionally comprising any one or more of sand, soil, sediment, absorbent media, particulate activated carbon, and ion exchange resin.

2. The method of claim 1, further comprising collecting the treated solid material.

3. The method of any one of claims 1-2, further comprising collecting at least one degradation product.

4. The method of any one of claims 1-2, wherein the feed fluid comprises any one or more of air, argon, dinitrogen, and oxygen.

5. The method of claim 4, wherein the feed fluid comprises an auxiliary fluid.

6. The method of claim 5, wherein the auxiliary fluid comprises a hydrocarbon, the hydrocarbon optionally comprising at least one of methane, acetylene, benzene, diesel, gasoline, light oil, and heavy oil.

7. The method of any one of claims 1-2, wherein the reaction zone is at a temperature of from about 50 to about 2000ºC, optionally at less than about 1000 ºC.

8. The method of any one of claims 1-2, wherein a PFAS comprises a per- or polyfluorinated substance. 4931-7710-2166.1 - 57 -104889.001015 / 22-2414 9. The method of claim 8, wherein a PFAS comprises any one or more of perfluorooctanoic acid (PFOA), perfluorobutanoic acid (PFBA),perfluorooctanesulfonic acid (PFOS), perfluorobutanesulfonic acid (PFBS), hexafluoropropylene oxide-dimer acid (HFPO–DA or GenX), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluorodecanoic acid (PFDA), perfluorohexanoic acid (PFHxA), and perfluorobutanoic acid (PFBA).

10. The method of any one of claims 1-2, wherein the PFAS-laden solid material comprises ion-exchange resin beads.

11. The method of any one of claims 1-2, wherein the method is performed so as to reduce loading of a PFAS of the PFAS-laden solid material by at least about 50% within 30 minutes.

12. A method for treating a PFAS-laden solid material, comprising: treating a feed fluid with a gliding-arc plasma(GAP) to give rise to a plasma-activated fluid; and contacting the PFAS-laden solid material and the plasma-activated fluid in a reaction zone under conditions sufficient to at least partly mineralize at least some of the PFAS so as to give rise to treated solid material having a reduced PFAS load and to degradation products.

13. The method of claim 12, further comprising giving rise to relative motion between the plasma-activated fluid and the PFAS-laden solid material.

14. The method of any one of claims 12-13, further comprising contacting the PFAS- laden solid material with an auxiliary fluid.

15. The method of claim 14, wherein the contacting the PFAS-laden solid material with an auxiliary fluid is prior to contacting the PFAS-laden solid material and the plasma- activated fluid. 4931-7710-2166.1 - 58 -104889.001015 / 22-2414 16. The method of claim 14, wherein the contacting the PFAS-laden solid material with an auxiliary fluid is concurrent with contacting the PFAS-laden solid material and the plasma-activated fluid.

17. The method of claim 14, wherein the auxiliary fluid comprises at least one of an alcohol and a salt.

18. The method of claim 17, wherein the alcohol comprises methanol.

19. The method of any one of claims 12-13, wherein the feed fluid comprises an auxiliary fluid.

20. The method of claim 19, wherein the auxiliary fluid comprises a hydrocarbon.

21. The method of any one of claims 12-13, wherein the PFAS-laden solid material comprises ion-exchange resin beads.

22. The method of any one of claims 12-13, wherein the reaction zone is at a temperature of from about 50 to about 2000ºC.

23. The method of any one of claims 12-13, wherein a PFAS comprises a per- or polyfluorinated substance.

24. The method of claim 23, wherein a PFAS comprises any one or more of perfluorooctanoic acid (PFOA), perfluorobutanoic acid (PFBA),perfluorooctanesulfonic acid (PFOS), perfluorobutanesulfonic acid (PFBS), hexafluoropropylene oxide-dimer acid (HFPO–DA or GenX), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluorodecanoic acid (PFDA), perfluorohexanoic acid (PFHxA), and perfluorobutanoic acid (PFBA).

25. A remediation system, comprising: a gliding-arc plasma (GAP) reactor, the GAP reactor configured to receive a PFAS-laden solid material therein, the GAP reactor configured to fluidize the PFAS-laden solid material, 4931-7710-2166.1 - 59 -104889.001015 / 22-2414 the GAP reactor configured to output a fluid comprising degradation products resulting from contact between the PFAS-laden solid material and a plasma- activated fluid within the reactor, the GAP reactor comprising an inlet to receive a feed fluid, and the GAP reactor configured to form the plasma-activated fluid from the feed fluid.

26. The remediation system of claim 25, further comprising a temperature control train configured to maintain a temperature within the GAP reactor during contact between the PFAS-laden solid material and the GAP.

27. The remediation system of any one of claims 25-26, further comprising a supply of the feed fluid.

28. The remediation system of claim 26, wherein the feed fluid comprises air.

29. The remediation system of any one of claims 25-26, wherein the reactor further comprises an inlet configured to receive an auxiliary fluid.

30. The remediation system of claim 29, further comprising a supply of the auxiliary fluid, the auxiliary fluid optionally comprising at least one hydrocarbon, the hydrocarbon optionally comprising methane.

31. A remediation system, comprising: a gliding-arc plasma (GAP) reactor, the GAP reactor configured to receive a PFAS-laden solid material therein, the GAP reactor configured to form a plasma-activated fluid from a GAP and a feed fluid, the GAP reactor configured to effect contact between the plasma-activated fluid and the PFAS-laden solid material, 4931-7710-2166.1 - 60 -104889.001015 / 22-2414 the GAP reactor configured to output a fluid comprising degradation products resulting from contact between the PFAS-laden solid material and the plasma- activated fluid within the reactor.

32. The remediation system of claim 31, further comprising a retention chamber configured to contain the PFAS-laden solid material therein during contact between the PFAS-laden solid material therein and the plasma-activated fluid.

33. A remediation system, comprising: a pre-treatment zone, the pre-treatment zone configured to contact a PFAS-laden solid material and a carrier fluid under conditions to remove PFAS from the PFAS-laden solid material and into the carrier fluid to give rise to PFAS-laden carrier fluid; and a remediation zone, the remediation zone configured to contact to PFAS-laden carrier fluid and a plasma-activated fluid so as to degrade fluorinate in the PFAS-laden carrier fluid.

34. The remediation system of claim 33, wherein the PFAS-laden solid material comprises ion-exchange resin beads.

35. The remediation system of any one of claims 33-34, wherein a fluorinate comprises any one or more of perfluorooctanoic acid (PFOA), perfluorobutanoic acid (PFBA),perfluorooctanesulfonic acid (PFOS), perfluorobutanesulfonic acid (PFBS), hexafluoropropylene oxide-dimer acid (HFPO–DA or GenX), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluorodecanoic acid (PFDA), perfluorohexanoic acid (PFHxA), and perfluorobutanoic acid (PFBA).

36. A method, comprising: contacting a PFAS-laden solid material with at least one of a first plasma and a first plasma-activated carrier fluid, the contacting being performed such that PFAS accumulates in a carrier fluid to give rise to a PFAS-laden carrier fluid and a plasma-treated solid material; optionally collecting plasma-treated solid material; 4931-7710-2166.1 - 61 -104889.001015 / 22-2414 contacting the PFAS-laden carrier fluid with at least one of a second plasma and a second plasma-activated carrier fluid, the contacting being performed so as to at least partially degrade PFAS accumulated in the PFAS-laden carrier fluid.

37. The method of claim 36, wherein the first plasma-activated carrier fluid is formed at a first reactor.

38. The method of claim 36, wherein the at least one of a plasma and a second plasma- activated carrier fluid is formed at a second reactor.

39. The method of any of claims 36-38, wherein contacting the PFAS-laden carrier fluid with the at least one of a plasma and a second plasma-activated carrier fluid is performed under conditions sufficient to mineralize PFAS accumulated in the PFAS- laden carrier fluid.

40. A system, comprising: a first reactor, the first reactor configured to receive a PFAS-laden solid material and contact the PFAS-laden solid material with at least one of a first plasma and a first plasma-activated carrier fluid such that PFAS accumulate in a carrier fluid so as to give rise to a PFAS-laden carrier fluid and a plasma-treated solid material; and a second reactor, the second reactor being configured to receive the PFAS-laden carrier fluid and contact the PFAS-laden carrier fluid with at least one of a second plasma and a second plasma-activated carrier fluid so as to at least partially degrade PFAS accumulated in the PFAS-laden carrier fluid and give rise to PFAS degradation products.

41. The system of claim 40, wherein the system is configured to collect plasma-treated solid material. 4931-7710-2166.1 - 62 -104889.001015 / 22-2414 42. The system of any one of claims 40-41, wherein the system is configured to collect PFAS degradation products.

43. The system of any one of claims 40-41, wherein at least one of the first reactor and the second reactor is a gliding arc plasma (GAP) reactor.

44. The system of any one of claims 40-41, wherein at least one of the first reactor and the second reactor comprises a heat exchanger, the heat exchanger optionally being water-cooled.

45. The system of any one of claims 40-41, wherein the second reactor is configured to collect a condensate resulting from contacting the PFAS-laden carrier fluid and the at least one of a second plasma and a second plasma-activated carrier fluid.

46. The system of any one of claims 40-41, further comprising a source of a first plasma.

47. The system of any one of claims 40-41, further comprising a source of a first plasma- activated carrier fluid.

48. The system of any one of claims 40-41, further comprising a source of a second plasma.

49. The system of any one of claims 40-41, further comprising a source of a second plasma-activated carrier fluid. 4931-7710-2166.1 - 63 -

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