In situ electro-osmosis removal of PFAS from impacted soils

Abstract

Methods, Apparatus and systems are described for removing PFAS and PFAS components from contaminated soil via electroosmotic flow. Designs and experiment testing revealed surprising results leading to conditions, methods, and configurations for the superior removal of PFAS from soil.

Description

[0001] In situ Electro-osmosis Removal of PFAS from Impacted Soils

[0002] RELATED APPLICATIONS

[0003] This application claims the priority benefit of U.S. Provisional Patent Application Ser. No. 63 / 584,759 filed 22 September 2023.

[0004] FIELD OF THE INVENTION

[0005] The present invention is directed to the removal of perfluoroalkylated substances (PFAS) from PFAS-containing soils.

[0006] INTRODUCTION

[0007] Recent studies have demonstrated that PFAS presents adverse human health effects and has the potential to bioaccumulate. In October 2021, EPA released a Strategic Roadmap providing a description of upcoming federal regulatory activities related to PFAS. According to the Roadmap, many of the EPA programs will be updated with increased regulation of select PFAS. A few of the key proposed actions include: (a) to establish a national primary drinking water regulation for PFOA and PFOS that would set enforceable limits, (b) publish health advisories for GenX and PFBS, and (c) designate PFOA and PFOS as CERCLA hazardous substances while evaluating other PFAS (US EPA, 2021). Due to the long-term usage of AFFF at the fire training sites resulted in many heavily impacted sites with high PFAS source strengths, which potentially leach high concentrations of PFAS to the downgradient groundwater and surface waters. By effectively tackling the PFAS at the source zone will limit the migration of PFAS to the groundwater. There is a significant need to treat PFAS-impacted solids that are source zones, IDW and soil generated as part of soil removal actions. Limited viable cost- effective treatment technologies are currently available for the in-situ treatment of PFAS- impacted solid matrices.

[0008] Per- and polyfluoroalkyl substances (PFAS), including perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), and hundreds of other similar compounds, have been widely used in the United States in a multitude of applications. There are significant concerns associated with these compounds due to widespread contamination coupled with uncertainties about risks to human health and the environment. PFAS are molecules having chains of carbon atoms surrounded by fluorine atoms. The C-F bond is very stable enabling the compounds to persist in the natural environment. Some PFAS include hydrogen, oxygen, sulfur, phosphorus, and / or nitrogen atoms. One example is PFOS:

[0009] Table 1 Definition of PFAS grouping, acronyms and Chemical Abstract Services Registry Number (CAS RN).

[0010] Due to the repeated use of AFFF for firefighting and fire training operations at many of the civilian and Department of Defense’s (DoD) sites, a number of PFAS source zone soils have been identified at many of these sites. A large number of AFFF -impacted sites requiring investigation, monitoring, and interim remedial activities produce a large volume of solid and liquid investigation-derived waste (IDW). The treatment and disposal of PFAS-impacted source soils and IDW present unique challenges as treatment technologies and best practices for handling and disposition are currently evolving. There is a significant need to treat PFAS- impacted solids that are source zones, investigation-derived waste (IDW), and generated as part of soil removal actions. Limited viable technologies are currently available for the in-situ treatment of PFAS-impacted solid matrices.

[0011] In the United States, current technologies that are being applied to solve the PFAS removal from soil include low-temperature thermal desorption and soil washing technology. However, these technologies are energy intensive when compared to electro-osmosis technology, which needs less energy than these technologies.

[0012] Electro-osmosis has been historically applied for the remediation of soils, sediments, and sewage sludge contaminated with both inorganic, and various neutral, cationic, and anionic organic contaminants including PFAS and petroleum hydrocarbons. The principle of electroosmotic remediation relies on the application of a low-intensity voltage through a soil core placed between electrodes (cathode and anode). The electric field mobilizes charged species, causing ions and water to move toward the electrodes from the soil. This mechanism is responsible for the transportation and removal of free ions such as H+, OH- (generated by water electrolysis on the electrodes), cations (metals,), anions (chloride, cyanide, fluoride, nitrate, and ionizable organic contaminants, such as PFAS. The technology was also applied for the removal of total petroleum hydrocarbons from soils, which are the common co-contaminants at the AFFF- impacted sites.

[0013] The application of electro-osmosis for the removal of contaminants from soil is a Battelle-patented technology (US 5,098,538). The basic mechanism of electro-osmosis is the transport of water (PFAS contaminated) through porous media under the influence of an applied electric potential. The electro-osmosis phenomenon even drives the PFAS trapped in the air- water / air-soil interfaces of the pore-water and soil pores. The concentrated PFAS collected mainly at the anode and cathode (in the form of leachate) could be further destroyed using PFAS destruction technologies. The use of GAC ion exchange media or membrane (IX) in front of the anode would drive PFAS being collected in these materials, which results in easy removal of PFAS concentrated on GAC or IX media, without the need to dig and haul the PFAS concentrated soil. The electro-osmosis followed by the destruction of collected PFAS concentrate, could be applied as a treatment train approach as an in-situ application for removal of PFAS in soil media. The use of granular activated carbon (GAC) / anion exchange membrane near the anode where the PFAS is driven during electro-osmosis will serve as the easy and complete removal of PFAS from the soil, followed by desorption of GAC / anion exchange material to collect the PFAS concentrate followed by destruction using SCWO process (PFAS Annihilator™).

[0014] Electro-osmosis has been demonstrated to effectively treat heavy metals and other organic contaminants including PFAS. PI Dr. Satya Chauhan and the Battelle team have developed the electro-osmosis technology for the removal of heavy metals from soils, and sludge matrices (US 5,098,538). Recently, under Battelle internal research and development project tested the viability of the electro-osmosis technology for the treatment of PFAS-spiked soils and AFFF-impacted field soils. The results have shown that the electro-osmotic movement of PFAS from the soil resulted in the >99% enrichment of PFAS near the anode, while in the control where no voltage was applied, there was no electro-osmotic movement of PFAS was observed. In contrast, all the cationic ions moved towards the cathode and collected as leachate. Further, the use of GAC or IX in front of the anode would drive PFAS collected in the sorbent material. The sorbent material can be removed and desorbed following the GAC or IX regeneration. The complete destruction of PFAS recovered from GAC or IX along with the leachate collected will be treated using SCWO. SCWO technology has been demonstrated under a project funded by the U.S. EPA to treat AFFF. A mobile demonstration system capable of treating up to 500 gallons per day (gpd) has been constructed and is ready to mobilize to sites.

[0015] Our objective is to apply electro-osmosis technology for the in-situ removal of PFAS at AFFF-impacted unsaturated source zone soils.

[0016] Advantages:

[0017] (a) Application of electro-osmosis for in-situ PFAS removal near AFFF-impacted source zones, IDW, PFAS-impacted sediments, etc.

[0018] (b) Introduction a granular activated carbon / anion exchange membrane / anion exchange sorbent material to collect PFAS near the anode.

[0019] (c) Treatment train approach - enables integration of electro-osmosis with Battelle's GAC Regeneration technology to collect PFAS followed by destruction using SCWO.

[0020] (d) Applicability for in situ treatment of source soils and other solid media

[0021] Successful application of electro-osmosis technology for AFFF-impacted soil will provide a cost-effective, energy-efficient in situ treatment option for the clean-up of PFAS in source zone soils. Restoration of aquifers without proper treatment of source areas (and hence limiting PFAS movement to groundwater plumes), is unlikely to provide a long-term solution to the remediation of the impacted sites. Hence, the elimination of the ongoing PFAS source to groundwater plumes will reduce the ultimate groundwater treatment cost. Overall, the life-cycle cost advantage of this treatment approach over other current approaches is the removal of the long-term source of PFAS contamination to groundwater.

[0022] SUMMARY OF THE INVENTION

[0023] Application of an electric field results in the movement of PFAS molecules from cathode to anode due to the negatively charged tails of surfactants, which results in depletion of PFAS near cathode with reductions of PFAS up to >99%. This migration of PFAS would result in the need to dig out the minimum amount of PFAS-contaminated soil that requires disposal. GAC / Anion exchange membranes positioned in front of the anode, however, would collect and trap PFAS molecules in these membranes. PFAS-concentrated GAC / Anion exchange membranes can be easily removed, eliminating the need to dig out and haul the PFAS-concentrated soil away for disposal. In one aspect, the invention provides a method for removing PFAS from soil, comprising: positioning PFAS-contaminated soil between a cathode and anode; applying a voltage between the cathode and the anode; and collecting PFAS from an adsorbent positioned at the anode. In an alternative method, overflow from the anode is used instead of, or in addition to, the adsorbent.

[0024] In another aspect, the invention provides a method for removing PFAS from soil, comprising: positioning PFAS-contaminated soil between a cathode and anode; applying a voltage between the cathode and the anode; and wherein the method is characterizable by trends observed in any of the data herein. For example, the ratio of (short chain carboxylates / long chain carboxylates) is greater in the effluent (leachate) from the cathode than the overflow from the anode (or in the sorption membrane, if present).

[0025] In a further aspect, the invention provides a method for removing PFAS from soil, comprising: positioning PFAS-contaminated soil between a cathode and anode; applying a voltage between the cathode and the anode; and wherein the method is characterizable by trends observed in any of the data herein. For example, the ratio of (short chain carboxylates / long chain carboxylates) is greater in the effluent (leachate) from the cathode than the overflow from the anode (or in the sorption membrane, if present).

[0026] In another aspect, the invention provides a method or system for removing PFAS from soil, comprising: a cathode and anode disposed a distance apart from each other in contaminated soil; wherein the soil is contaminated with PFAS; a voltage is (or can be) applied between the cathode and anode; wherein a sorbent media is disposed between the anode and cathode; typically, the anode and cathode are at least 15 or at least 20 cm apart and the sorbent media membrane is disposed within 5 cm of the anode, preferably within 2 cm.

[0027] In further aspects, the invention comprises methods of removing PFAS or methods of making the systems comprising drilling at least 2 first wells for anodes and drilling at least two wells for cathodes. The invention also provides methods of partitioning PFAS components from PFAS-contaminated soil. Selectively separating PFAS components is advantageous since components such as PFOS is more costly and difficult to destroy than other components; thus enabling more efficient PFAS destruction.

[0028] In any of its aspects, the invention may be further characterized by one or any combination of the following: further comprising removing leachate at the cathode; wherein the soil has a zeta potential between -30 and 10, or between -30 and 0, or between -30 and -10; wherein the voltage is at least 30 V / in; or at least 50 V / in; or at least 100 V / in; wherein the voltage is applied for at least 30 minutes, or at least 1 hour, or at least 10 hours, or at least 50 hours; further comprising adding an acid at the cathode; wherein the acid comprises acetic acid, HC1, or citric acid; wherein the distance between the cathode and the anode is in the range of 0.1 to 0.4m, or 0.1 to 0.3m; wherein the voltage applied between anode and cathode is at least 50 or at least 60 V and up to 400, or 300, or 200 V; further comprising adding an electrolyte to the soil; wherein the electrolyte has a salt concentration of at least 0.001 M, or at least 0.005 M, or at least 0.01 M, or in a range of 0.001 to 0.1 M; wherein the electrolyte comprises a cation selected from Na, K, NH4, Mg, Ca, or combinations thereof; wherein the electrolyte comprises an anion comprising Cl, Br, acetate, citrate, lactate, or combinations thereof; wherein a leachate flowing toward the cathode comprises a higher mass ratio of short chain PFSA / long chain PFSA or long chain PFCA / short chain than the comparable ratio in the adsorbent; removing contaminated sorbent (usually GAC), replacing sorbent with fresh or regenerated sorbent; wherein the soil comprises at least 10 ppt PFSA, or at least 1 ppb, or at least 1 ppm PFAS; comprising adding deionized water to the soil; comprising operating at a voltage wherein the mass ratio of short chain PFCA / long chain PFCA in the adsorbent is the same or higher than the comparable ratio in the soil prior to treatment; wherein the mass ratio of short chain PFCA, long chain PFCA, short chain PFSA, long chain PFSA, and / or intermediates in the absorbent are within 20% or within 10% of the same ratio in the soil (for example, the mass ratio of short chain PFCA / long chain PFCA in the adsorbent is within 20% of the same ratio in the soil prior to treatment); the system comprising, in sequence in a direction, at least one supply well, at least two anodes, at least two cathodes, and at least one extraction well; wherein an electrolyte or deionized water is supplied to the soil through the supply well; wherein he sorbent at the anode can be, for example, GAC / IX resin / IX membrane; wherein a wire mesh encases the anode well to a depth of 2 to 4 m and can be used to secure the sorbent in place; wherein the electrode rods are 0.7m to 2m in length and constructed from materials such as: titanium coated with IrO2 / Ta2Os, platinum coated with titanium, aluminum, graphite, or stainless steel (the choice of the electrode will depend on the electrolyte media (carbonaceous backfill, fresh water, seawater, etc.)).

[0029] Multiple extraction wells will be added near the cathode to collect all leachate generated by electroosmotic flow. The sorbent media can be granulated activated carbon (GAC), anion exchange resin, or cation exchange resin materials or membranes. Sorbent media is preferably granulated activated carbon (GAC). Sometimes, the electrodes are spaced apart by no more than 1 m.

[0030] The invention includes any of the apparatus, methods, systems (apparatus plus fluids and, optionally conditions, or data described herein. The method, system, or apparatus may be further characterized by ±10% or ±20% or ±30% of any of the properties and / or measurements described herein. The invention is further elucidated in the examples below. In some preferred embodiments, the invention may be further characterized by any selected descriptions from the examples, for example, within ±30%, ±20% (or within ±10%) of any of the values in any of the examples, tables or figures. “All ranges are inclusive and combinable. For example, when a range of “1 to 5’ is recited, the recited range should be construed as including ranges “1 to 4”, “1 to 3”, “1-2”, “1-2 & 4-5”, “1-3 & 5”, “2-5”, any of 1, 2, 3, 4, or 5 individually, and the like.”

[0031] As is standard patent terminology, the term “comprising” means “including” and does not exclude additional components. Any of the inventive aspects described in conjunction with the term “comprising” also include narrower embodiments in which the term “comprising” is replaced by the narrower terms “consisting essentially of’ or “consisting of.”

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1: Schematic of Electro-osmotic Technology

[0034] Figure 2: Bench scale PFAS-EO experimental design and the post treated dewatered soil cake. Figure 3: Schematic of fluid flow through and layers of a soil cake.

[0035] Figure 4A: PF AS removal monitored in experiments conducted at 60V and different holding times (left-to-right in each layer) - 6 hours, 27 hours and 48 hours.

[0036] Figure 4B: Removal of Cations (Na, Mg, Ca, left-to-right in each layer) monitored in experiments conducted at 60V and different holding times - 6 hours, 27 hours, and 48 hours. Figure 5A Total PFAS measured (nmole) in electro-osmotic treatment by varying the treatment times. Figure 5B. Percent PFAS distribution measured in experiments applying 30V using 0.0 IM NaCl for 24 hr, 48 hr and 336 hr in Soil Layer 1 (near anode), Layer 2, Layer 3 (near cathode) and Leachate. Layer 1-2-3 -Leachate shown top-to-bottom in each bar.

[0037] Figure 6: Current (Amp) and Temperatures (°C) Recorded in experiments at different voltages and holding times using 0.0 IM NaCl as Electrolyte.

[0038] Figure 7: Proposed Field Scale PFAS-EO Treatment Layout. Figure 8: Lab testing device.

[0039] Figure 9. 2D Baseline Model.

[0040] Figure 10. Estimated maximum voltage and optimal flow velocity.

[0041] Figure 11. Model predicting Optimal Voltage and Flow Velocity.

[0042] Figure 12. Baseline model showing estimated time to flow from one electrode to the other. Figure 13. Horizontal Plot of Electric Field Between Electrodes for Various Electrode Spacings. Figure 14. The Average Electric Field Between the Electrodes vs Electrode Spacing.

[0043] Figure 15. Required Voltage (Minimum and Upper) vs Electrode Spacing.

[0044] Figure 16. Scale Factor for Required Voltage vs Electrode Configuration for Constant Electrode Spacing.

[0045] Figure 17. Horizontal Plot of Electric Field Between Electrodes for Various Electrode Configurations.

[0046] Fig. 18 shows movement of PFAS using deionized water under the influence of a lower voltage (VI) and a higher voltage (V2).

[0047] Figure 19A depicts the basic schematic of the setup. Figure 19B and Figure 19C depict the distribution of PFAS in each section based on mass. Figure 19D shows the concentration of PFAS in the effluent on a mass basis.

[0048] Fig. 20 shows the mass balance of total PFAS after the experiment.

[0049] Fig. 21 schematically illustrates the construction of an electrode disposed in the ground. The illustration is not to scale.

[0050] RESULTS AND DISCUSSION

[0051] PFAS Electro-osmosis (PFAS-EO) Experiments. For all the proof-of-concept experiments, voltage is applied on soil core (10 - 60 Volts / sq. inch) for different durations. The soil core is kept moist for an uninterrupted current flow. We explored using deionized (DI) water, and 0.0 IN NaCl solution as the water supplied to the unit to keep it moist for different time intervals. Figure 2 shows the apparatus used in the testing and the post treated dewatered soil cake. A schematic of the experimental flow for the tests is shown in Fig. 3. Under the influence of electric field, as the PFAS moves towards anode, the cations (metals) and other cocontaminant move towards cathode (Figure 3: Schematic of fluid flow through and layers of a soil cake. Figure -7 A and Figure 3 : Schematic of fluid flow through and layers of a soil cake. Figure -7B) Figure 3: Schematic of fluid flow through and layers of a soil cake. Figure 4B show the depletion of cations in soil and enrichment in the leachate.

[0052] PFAS Targeted Analysis. PFAS targeted analysis for all samples was performed at Battelle Environmental Analytical Laboratory. All the samples are analyzed for the targeted list of 24 PFAS analytes (Table 1) using liquid chromatography -tandem mass spectroscopy (LC-MS / MS).

[0053] Proof of Concept Results Using PFAS Spiked Field Soil

[0054] A total of seven experiments were conducted. Test 1 was the equipment shakedown test using field soil 1. Test 2-6 were conducted using PFOA and PFOS mix spiked soil. The soil used for Tests 2-6 was also a field soil 2 which had negligible amounts of PFAS concentrations, hence spiked with PFOA and PFOS. Test 7 was conducted with a different field soil 3 with high concentrations of PFAS. Prior to performing the experiments, pH, zeta potential and ionic conductivity of all the soils were measured (Table 2).

[0055] Below are the observations derived from data collected from these experiments.

[0056] • There was a reverse trend of water moving to cathode and the PFAS moving to anode. For negative zeta potential of soil movement of water under electro-osmosis with water clearly moved from anode to cathode in Tests 2-6 (Table 2). The data clearly shows the trend of increasing moisture content from layer 1 (close to anode) to layer 3 (close to cathode), except for control Test 3 where similar moisture content or no change was observed in the absence of voltage.

[0057] • Movement of PFAS from cathode to anode due to negatively charged tails of surfactants, which resulted in depletion of PFAS near cathode with % reductions up to 98% in layer 3.

[0058] • The PFAS removal increased with voltage gradient as well as time.

[0059] • Test 2 vs. 4 suggests that dewatering of cake due to electro-osmosis is nearly complete @50V / in and 30 minutes. Also, PFAS removal from Layer 1 is nearly complete, but the removed PFAS may not have fully migrated out of Layer 2 as PFAS gain by Layer 1 still at halfway point.

[0060] • Test 7 was a different soil (Soil 3), voltages above 10V raised the cake temperature too much and too fast, up to 52 °C. so 10V was applied for Ih, <10mL leachate collected. Even with low voltage application, Test 7 shows up to 31% concentration of PFAS near anode. • PFAS was detected in the leachate of all the test conditions. Other than Test 2, the leachate PFAS mass percentage remained below 1% in all the spiked soil electro-osmosis conditions. The PFAS leached out of the soil in aqueous leachate might be the PFAS present in the dissolved form in the soil moisture. • Total mass balance of the PFAS: The results of all the experiments converted into mass basis to understand the mass distribution in different fractions of soil, and the leachate (Table 3). For Test 1, control soil data is missing (need to analyze). Although the data for layer 2 was not analyzed, considering the increasing concentration trend from layer 1 to 3, overall mass balance of the PFAS recovery in all the spiked soil experiments seems to be good (Table 3). Other than test 7 conditions, where low voltage (10 V) was used, concentration of PFAS in layer 1 was observed in all experiments (>46%).

[0061] Table 2 Electro-osmosis experimental conditions and percent moisture content variation in all the tests conducted.

[0062] Table 3 Mass balance of PFAS in each fraction of soil and leachate in electro-osmosis experiments conducted.

[0063] Further experiments were conducted with unspiked field Soil 4 with Zeta potential -14.3 at conditions 60V for 6 hours, 27 hours, and 48 hours. Under the influence of electric field, as the PFAS moves towards anode, the cations (metals) and other co-contaminant move towards cathode (Fig. 4A and Fig. 4B). Figure 3: Schematic of fluid flow through and layers of a soil cake.

[0064] Figure - / B show the depletion of cations in soil and enrichment in the leachate. Under testing conditions 60V, 27 hrs, showed better PFAS removal (Figure 3: Schematic of fluid flow through and layers of a soil cake.

[0065] Figure 4 A) and cations removal (Figure 3: Schematic of fluid flow through and layers of a soil cake.

[0066] Figure 4B) and mass balance.

[0067] Comparison of Mass distribution of PFAS in AFFF -impacted field soils using sorbent material and without using sorbent: All these tests were conducted using unspiked soil 5 (zeta potential -20.4). Mass distribution of PFAS analytes in different soil fractions was compared with experiments using sorbent material (granular activated carbon) and using no sorbent. The classification of different chain length PFAS was performed as short chain perfluorinated carboxylates (PFCAs) (C4-C7); long chain PFCAs (C8-C14); short chain perfluorinated sulfonates (PFSAs) (C4-C6); long chain PFSAs (C7-C10); and Intermediates (N-EtFOSAA, N- MeFOSAA, FOSA, 4:2 FTS, 6:2 FTS, and 8:2 FTS). There is a clear chain length and class dependent distribution observed in experiments, where O.OlM NaCl was supplied as the electrolyte solution as seen below in Experiment 15, Experiment 17, and Experiment 21 comparing the variation in holding time (Fig. 5A and 5B). For shorter chain PFCAs, a clear trend of migration towards anode was observed, while for the longer chain PFCAs, these were predominantly measured in leachate collected (Table 4). In contrast, shorter chain PFSAs were predominantly (70-91%) detected in leachate, while the longer chain PFSAs were predominantly (41-75%) found migrating towards anode (layer 1, sorbent, and overflow). This is the surprising trend observed, typically shorter chain length PFCAs tend to breakthrough faster and expected to be found in the leachate under normal conditions, while the sulfonates tend sorb on to the soil. However, the reverse trend of shorter chain carboxylates migrating to anode and found predominantly in overflow, while shorter chain sulfonates migrating to cathode and found predominantly in leachates.

[0068] Table 4 Experimental conditions and mass balance

[0069] Comparing the PFAS Distribution in Conditions using Electrolyte and DI water: In Experiment 21, >80 % of short chain PFCAs and long chain PFSAs (57%) was moved towards anode (layer 1, sorbent, and overflow), while the longer chain PFCAs, shorter chain PFSAs, and Intermediates seem to be predominantly found in leachate (Table 5). This trend is more evident in the figures comparing time trend comparison of 30V with 0.01M NaCl for 24 hr, 48 hr, and 336 hr (Figure 5A and 5B). Whereas comparing these results with Experiment 22, where DI water was supplied as the electrolyte solution, there seems to be almost equal distribution of different PFAS classes measured towards anode and cathode (Table 5). Table 5 Comparison of Percent PFAS distribution measured in experiments applying 30V for 336 hr using O.OlM NaCl and DI water as electrolytes. NA indicates no overflow No Electrolyte and No Sorbent: In the experiment where no sorbent was used (60V, 24 hr), electric field was applied to the soil core without using any electrolyte. Soil was dewatered and collected as leachate. Hence, the results cannot be directly compared with other experiments where electrolyte was used. In this experiment, both short and long chain PFCAs and short chain PFSAs were predominantly (79-81%) moved towards the anode, while the long chain PFSAs and the intermediates were distributed mainly across layer 1 and layer 2 indicating the progression towards anode, if allowed for longer duration, might have moved completely towards anode). These results clearly indicate the effect of electro-osmotic migration of PFAS towards anode.

[0070] Intermediates NA NA 34.72% NA 47.24% 6.22% 11.83% Table 6. Percent PFAS distribution measured in experiment applying 60V for 24 hr without using any electrolyte and sorbent near anode. Effect of Treatment Duration: Figure 5 A and 5B shows results of the experiments, where the applied electric field Voltage and the electrolyte and varying the duration of the treatment. Results indicate that as the duration of the treatment increases, PFAS migration towards the anode increases. Hence, applying moderate voltages - longer duration electro-osmosis treatments are recommended to keep the technology cost-effective.

[0071] Current and Temperature Changes with Time: For all the experiments, current and the Temperature were monitored. While using the 0.01 M NaCl as electrolyte, it was observed that a black layer was formed, which is the result of oxidized organic matter. However, no such layer formation was observed in experiments where DI water was used as the electrolyte. This black layer formation increased the current and the temperature under the tested conditions, which was sooner (<12 min) in conditions tested at higher Voltages (60 V) compared to lower voltages (30 V) (15 - 16.4 min) (Figure 6). Increase in current and temperatures were also higher under the conditions tested at higher voltages (Figure 6). These results also suggest testing at lower voltages for longer durations seems feasible under field conditions.

[0072] Application of Electro-osmosis to in situ Field Scale Treatment of PFAS in Soils

[0073] An in-situ electro-osmotic removal of PFAS from an AFFF-impacted source zone vadose zone soil can be conducted at a selected site. For example, the treatment can be performed with 20 x 20 feet (6 x 6 m) dimensions at the source zone (Figure 7). Electrode wells will be installed with depth up to 10 ft at the pre-determined distances for the anodes and the cathodes. The primary material for sorbing the collected PFAS at the anode will be GAC / IX resin / IX membrane. A wire mesh can encase the anode well to a certain depth and will be used to secure all the GAC in place. Multiple extraction wells will be added near the cathode to collect all leachate generated by electroosmotic flow (Figure ). Spacing of the electrode and number of electrodes will vary based on flow velocity calculations. Prior to the application of electric field, the soil will be saturated with anolyte from the anode side using the peristaltic pumps more details can be found in subsequent sections. Once the soil is saturated, an electric field will be applied based on the conditions and duration determined from the treatability testing. Different holding times 3 - 6 months will be evaluated at 30V and 60V. During the 3-6 month holding period, groundwater samples will be extracted and sampled periodically for PFAS via the extraction wells. At the end of the 3-6 month holding period PFAS will be analyzed in the soil, GW, and sorbent. Further to prevent movement of the TOC near the electrodes, a stainless-steel mesh filter can be installed surrounding the electrodes. Pre- and post-treatment soil samples collected at different depths and the leachate samples can be analyzed for PFAS Targeted analysis (Table 1) and the suspect screening analysis can be performed, along with anions, cations and total petroleum hydrocarbons. PFAS collected in post treated solid and liquid matrices will be further completely treated using destruction technologies.

[0074] As shown in Fig. 7, supply wells can be placed left (upstream) of anodes that are surrounded by sorbent (typically GAC). In the figure, soil sampling is conducted at numerous sites, and temperature probes can be used if temperature is monitored. Downstream is an array of cathodes. The number of anodes and cathodes can be selected depending on the area to be treated. For example, at least 3 anodes and an array of at least 3 cathodes. Similarly, multiple supply wells and extraction wells can be used; for example, at least 3 of each. Downstream (placed right) of the cathodes are extraction wells for leachate.

[0075] In situ Field Scale Treatment Design

[0076] Electrode wells. In the contaminated area, multiple, for example at least 6, electrode wells can be installed using hollow-stem auger drilling. Each well can have a casing, for example, a 4-inch PVC casing and 0.01-inch slotted wire mesh. A wire mesh can be placed 4 ft from the end of the well (distance may vary based on the geology of the site). To filter out contaminants, sorbent materials such as GAC / IX resin / IX membrane will surround the wire mesh, preferably from the bottom of the borehole up to 1 / 2 foot above the screened interval. The top of the remaining well can be sealed with bentonite chips and hydrated for at least an hour. Finally, a mixture of cement and bentonite powder can be added to fill the remaining space up to the bottom of the well vault.

[0077] A hollow-stem auger drill can be used to install the electrode wells. Each electrode can be constructed with a 4-inch (10 cm) diameter PVC casing and 0.01-inch slotted screen. The screened interval can be between 19 and 23 feet below the ground surface across the clay unit. A schematic of the electrode well setup is shown in Figure 21. As part of the electrokinetic process, pH changes occur across the electrode due to the movement of ions produced from the decomposition of water. It's desirable to control pH, especially at the cathode, to prevent contaminant precipitation and ensure that electroosmotic flow is not inhibited during remediation. Weak acids like acetic acid, hydrochloric acid, and citric acid can be used at the cathode to neutralize OH- ions produced during electrolysis of the fluids. Organic acids such as acetic acid and citric acid are preferred because they have good acid / base buffer capacity, are biodegradable and environmentally friendly, prevent the formation of insoluble salts, and reduce the energy expenditure of the process by increasing or maintaining the electrical conductivity of the system.

[0078] From Fig. 21, starting at the surface, there is a well vault surrounding the well head, optional features to protect from freezing, typically a gravel base, a separator, a seal between the well-casing and borehead well, polymer tubing, a sand filter pack, a polymer well screen. For anodes, a sorbent such as granular activated carbon (GAC) is disposed between the screen and the electrode wire.

[0079] Supply wells. We can install multiple, preferably at least 3, supply wells in the contaminated area using hollow-stem auger drilling. Each supply well can have a 4-inch diameter PVC casing and a 0.01-inch slotted screen. The construction process can be like the electrode wells but with the replacement of a medium sand filter instead of GAC packed around the screen from the bottom of the borehole up to the top of the screen. The well can then be topped by a fine sand filter pack up to 1 / 2 foot above the screened interval.

[0080] Monitoring wells / Extraction Wells. Within the treatment area, multiple monitoring wells can be installed using hollow-stem auger drilling. These wells will be double-casing wells, with each having a 6-inch PVC surface casing installed to approximately 13 feet below ground surface (bgs) and then grouted in place.

[0081] First, a drill can be made through the bottom of a 6-inch casing to create a 2-inch diameter monitoring well. Next, we can install a 0.01-inch slotted screen section at a depth of 10ft bgs. To ensure proper filtration, we can add a medium (20 / 30) sand filter pack around the screen section from the bottom of the borehole up to 1 / 2 ft above the screened interval. A 2-foot- thick bentonite seal can then be placed above the sand pack by adding bentonite chips and hydrating for one hour. Finally, we can fill the remaining annulus with cement and bentonite powder grout up to the bottom of the well vault. Electrodes and Power Supply. Multiple wells, such as at least six electrode wells can be used during the PFAS-EO system, with, for example, three electrode wells serving as anodes and the other three serving as cathodes. The electrodes are made of 3 / 4-inch diameter rods. The rods will be around 4ft and can be constructed from materials such as: titanium coated with IrO2 / Ta2O5, platinum coated with titanium, Aluminum, Graphite, or Stainless steel. The choice of the electrode will depend on the electrolyte media (carbonaceous backfdl, fresh water, seawater, etc). The electrode geometry will vary depending on the site conditions and the electroosmotic flow. The PFAS-EO system may utilize a 24 / 240 DC power supply that accepts input power from a 3- phase alternate current (AC) of 240 V. The power supply may have a capacity of 6kW and can output 0 to 250 V and 0 to 24A. The power supply can operate in constant current mode, with the voltage varying in response to changes in soil conductivity.

[0082] Electrolyte. To improve soil conditions, it may be necessary to use an electrolyte solution. This solution can be made, for example, by adding 60% (w / w) potassium lactate to 250-gallon totes or by creating a 0.01 M NaCl solution. Once the solution is prepared, it should be transferred to the supply and electrode wells through the supply system. To neutralize the pH and prevent corrosion from water hydrolysis, a buffer solution is also created by adding anhydrous potassium carbonate powder (99%) to 250-gallon totes for transfer to the supply wells. To administer the amendment supply, feed pumps are used and controlled by a timer that injects short-duration pulses. Each pulse injects a specific amount of the solution into each well. The electrolyte solution may employ any salt suitable for the soil conditions. Examples may include, for example, salts of Na, K, NH4, Ca, or Mg (or combinations thereof) along with a suitable counterion such as Cl, Br, acetate (or combinations thereof).

[0083] Flow Velocity Calculations

[0084] To calculate the electroosmotic flow velocity for several electrode systems, electrodes are placed in a 5-gallon aquarium tank based on the pilot scale design (Fig. 8). Soil properties were pre-defined. Electric field calculations were combined with basic electroosmosis equations to estimate flow velocity.

[0085] A series of models were built and analyzed to estimate electroosmotic flow velocity for several cases. There is a minimum voltage difference for which this flow can begin. In all cases examined, this voltage difference is below 100V. There is an upper limit to the voltage difference at which maximum flow velocity is achieved. In all cases, this voltage difference is above 100V

[0086] Baseline Model

[0087] A parametric 2D electrostatic (ES) model is used (see Fig. 9).

[0088] Baseline setup:

[0089] Soil’s relative permittivity is sr=10

[0090] Glass wall 10 mm thick, 8r=5

[0091] - Anode / cathode at +1 / 2 Volt (AV = 1 V)

[0092] Results are linear with voltage and are given in a per voltage difference

[0093] ES calculation variables include: anode / cathode spacing electrode spacing and size

[0094] - tank size soil permeability and electrical conductivity glass thickness and permeability

[0095] Electroosmotic flow calculations include: zeta potentials porosity of ground viscosity permittivity

[0096] Initial Calculation: Inputs to Model Permittivity free space

[0097] Calculation of Electrostatic Field (Baseline Model) Map of X-Component of Electric Field in Soil

[0098] The electric field (x-component) was mapped within the container. The electric field is given in V / m per voltage difference between the anode / cathode. The results are linear with voltage difference.

[0099] Flow Velocity vs Electrode Voltage Difference

[0100] The model predicts no maximum flow rate and assumes a linear increase in flow with the electric force after the F-function maximizes. This assumption is likely invalid as a critical velocity is likely reached due to other factors. A gradation factor is used to calculate this maximum flow velocity (Figure 10). This factor assumes an asymptotic value above the curve’s knee to estimate maximum velocity.

[0101] Minimum & Upper Voltage Requirements for Flow

[0102] The minimum voltage for electroosmotic flow to begin would be -100V. Flow is marginal with a flow velocity of ~lE-6m / s. Roughly the same for a porosity of 50 and 75%. Increasing voltage after this value will increase flow velocity roughly linearly. The estimated maximum voltage beyond which little increase in flow is obtained would be -400V (Figure 13). For a porosity of 50 and 75%, flow velocity achieves about 0.8E-5 and 1.1 E-5 m / s, respectively (Figure 11).

[0103] Time Estimate for Electroosmotic Flow to Span the Distance Between the Electrodes

[0104] Figure 12 shows the estimated time for flow from one electrode to the other for the baseline model. Calculation is simply the electrode spacing divided by the flow speed. The time to cover the electrode span significantly decreases with higher voltage. The take-away is one can initiate electroosmotic flow at the minimum lower voltage, but significantly faster flow will occur at the upper limit. Variation in Electrode Spacing Between Cathode / Anode

[0105] The required voltage difference between the electrodes for variations on electrode spacings between the anode / cathode were examined.

[0106] Spacing variations examined:

[0107] Baseline

[0108] 80% baseline (electrodes 20% closer)

[0109] 60% baseline (40% closer)

[0110] 50% baseline (50% closer)

[0111] Calculations make use of the fact that for a given electric field generated and set up, the same curves as previously presented are still valid.

[0112] Figure 15 shows the minimum and upper limit to the required voltage as a function of electrode spacing. As electrode spacing decreases, less voltage is required to generate the required electric field to initiate electroosmotic flow. One can initiate electroosmotic flow at a smaller voltage difference if the electrodes are closer together.

[0113] Variation in Electrode Configuration

[0114] The required voltage difference between the electrodes for variations in electrode configurations were examined.

[0115] Configurations examined:

[0116] Nominal

[0117] - More Electrodes

[0118] Bigger Electrodes

[0119] Using bigger electrodes reduces the required voltage by 4% (Figure 16).

[0120] Overall, comparing all these configurations shows very little difference in electric field (Figure 17).

[0121] Chain length and functional group dependent mass distribution of PFAS was observed when using 0.0 IM NaCl as the electrolyte solution (above), while no such chain length or functional group distribution is observed when DI water is used as electrolyte (Table 6). Shorter chain PFSAs were found migrating towards cathode, and predominantly (70-91%) detected in leachate, while the longer chain PFSAs were predominantly (41-75%) found migrating towards anode (layer 1, sorbent, and overflow). However, reverse trend was observed with PFCAs, shorter chain PFCAs migrated towards anode and found predominantly in overflow, while shorter chain sulfonates migrated towards cathode and found predominantly in leachates. This is the surprising trend observed, typically shorter chain length PFCAs tend to breakthrough faster and expected to be found in the leachate under normal conditions, while the PFSAs tend sorb on to the soil.

[0122] Such opposite distribution of chain lengths between different functional groups was not observed when no electrolyte was used. In an experiment conducted at 60V, 24 hours, where no electrolyte solution was used, both short and long chain PFCAs and short chain PFSAs were predominantly (79-81%) moved towards the anode due to electro-osmosis, while the long chain PFSAs and the intermediates were distributed mainly across layer 1 and layer 2 indicating the progression towards anode, if allowed for longer duration, might have moved completely towards anode.

[0123] Examples - no electrolyte

[0124] An electric field was applied to an AFFF-impacted soil at two voltages. Experiments with higher voltage showed a general trend of higher PFAS concentration at the anode (location 1) and depletion at the cathode (location 4) indicating electroosmotic movement of PFAS towards anode in the soil studied (Figure 18). Electroosmotic movement of PFAS was predominant in Perfluoroalkyl sulfonates (PFSAs) compared to perfluoroalkyl carboxylates (PFCAs). Both PFSAs and PFCAs concentrate at the anode under the influence of electric field indicating electroosmotic movement of PFAS. Overall, higher voltage showed increased electroosmotic movement of total PFAS compared to lower voltage. However, it was surprising to observe this trend more clearly with PFSAs, while PFCAs did not show much dependence in changes in voltages. This can be explained due to the hydrophobicity of PFSAs compared to the PFCAs, and hence PFSAs movement in the soil towards anode is driven by the electroosmosis process - higher concentration at higher voltages. Similar trend of voltage dependence on the concentration of intermediates was also observed, as all the intermediates (4:2 FTS, 6:2 FTS, 8:2 FTS, NEtFOSAA, NMeFOSAA, PFOSA) are also sulfonates. There was no trend observed for shorter chain PFCAs (PFBA, PFPeA, PFHxA, PFHpA [C4-C7 chain lengths]) as these analytes were present at the detection limits, while the longer chain PFCAs (PFOA, PFNA, PFDA, PFUnA, PFDoA, PFTrDA, PFTeDA [C8-C14 chain lengths]) did not show much difference in overall concentration at anode at different voltages. However, electroosmotic flow of longer chain PFCAs was slow at lower voltage as indicated by higher concentration at cathode for VI compared to lower concentration (depletion) at V2 during the duration of the experiment. The trend of higher electroosmotic flow of PFAS towards anode at higher voltage (V2) compared to the lower voltage (VI) is also observed from the higher PFAS concentration in GAC (located surrounding anode) at V2 compared to VI.

[0125] Battelle tested the viability of electro-osmosis technology for the treatment of PFAS AFFF-impacted field soils. Figure 19A depicts the basic schematic of the setup. The cube represents the PFAS-contaminated soil, divided into four sub-sections: Locations 4, 3, 2, and 1. L4 is closest to the cathode, while LI is closest to the anode. The blue arrow indicates the groundwater flow. The anode and the cathode are made of conductive graphite and are positioned at opposite ends of the setup. The anode electrodes are surrounded by a well filled with clean granular activated carbon (GAC) to collect PFAS moving toward the anode. The GAC can be removed, and the liquid can be continuously pumped out of the system. Next to the cathode, there is an effluent collection bucket for continuously collecting the water electro-osmotically moved toward the cathode. When an electrical field is applied across the anode and the cathode, clean water should move toward the cathode, and PFAS contaminated water should electrokinetically move to the anode. Figure 19B and Figure 19C depict the distribution of PFAS in each section based on mass. For the first Voltage (VI at 40 V), 27.02% of the PFAS was collected in locations 1 and 2, as well as in the GACs. With the second voltage (V2 at 60 V), V2, which is greater than VI, approximately 70% of the PFAS was trapped in locations 1 and 2, and the GACs, indicating better PFAS removal at higher voltage. These tests were conducted over a period of 6 days. It is anticipated that extending the operation time and making finer adjustments in voltage between the cathode and anode could result in improved PFAS removal.

[0126] In Figure 19D, the concentration of PFAS in the effluent is shown on a mass basis. This is because during the process of electroosmosis, more liquid is pulled toward the cathode. As a result, at higher voltages (orange bar), we would expect to see more liquid being collected at the effluent side. Because PFAS concentrations are very low, any changes in the amount of liquid leaving can cause a significant dilution in our PFAS concentration. However, in this case, data is plotted on a mass basis. Therefore, the decrease in the amount of PFAS at the effluent and increasing PFAS concentrations towards anode at higher voltage indicates the effectiveness of the electro-osmotic process.

[0127] The mass balance of total PFAS after the experiment showed 105% recovery compared to the initial PFAS mass (Figure 20) indicating that no degradation of PFAS on the anode occurred, consistent with previous studies. Short chain PFCAs are analytes with chain lengths C4- C7 and long chain PFCAs are analytes with chain lengths C8- C14. Short chain PFSAs are analytes with chain lengths C4- C5 and long chain PFSAs are analytes with chain lengths C6- CIO.

[0128] References:

[0129] DoD (2019). Consolidated Quality Systems Manual for Environmental Laboratories, version 5.3. Per- and Polyfluoroalkyl Substances (PFAS) Using Aqueous Chromatography Tandem Mass Spectrometry (LC / MS / MS) With Isotope Dilution or Internal Standard Quantification in Matrices Other Than Drinking Water Table B-15. Available at https: / / denix.osd -version- 5 -3 ■■filial / , accessed December 23, 2020.

[0130] SERDP / ESTCP. (2020). Requirements for SERDP & ESTC P Projects Addressing PFAS- Related Issues. Available at https: / / www.serdp-estcp.org / Investigator-Resources / ESTCP- Resources / Demonstration-Plans / Requirements-for-PFAS-Projects, accessed December 23, 2020.

[0131] U.S. EPA (2019). Method 533: Determination of Per- and Polyfluoroalkyl Substances in Drinking Water by Isotope Dilution Anion Exchange Solid Phase Extraction and Aqueous Chromatography / Tandem Mass Spectrometry. (815-B- 19-020). Available at substances- accessed December 23, 2020.

[0132] U.S. EPA (2020). Method 537.1: Determination of Selected Per- and Polyfluorinated

[0133] Alkyl Substances in Drinking Water by Solid Phase Extraction and Aqueous

[0134] Chromatography / Tandem Mass Spectrometry (LC / MS / MS), Rev 2. (600-R-20-006). Available at

Claims

What is claimed:

1. A method for removing PFAS from soil, comprising: positioning PFAS-contaminated soil between a cathode and anode; applying a voltage between the cathode and the anode; and collecting PFAS from an adsorbent positioned at the anode.

2. The method of claim 1 further comprising removing leachate at the cathode.

3. The method of any of the above claims wherein the soil has a zeta potential between -30 and 10, or between -30 and 0, or between -30 and -10.

4. The method of any of the above claims wherein the voltage is at least 30 V / in; or at least 50 V / in; or at least 100 V / in.

5. The method of any of the above claims wherein the voltage is applied for at least 30 minutes, or at least 1 hour, or at least 10 hours, or at least 50 hours.

6. The method of any of the above claims further comprising adding an acid at the cathode.

7. The method of claim 6 wherein the acid comprises acetic acid, HC1, or citric acid.

8. The method of any of the above claims wherein the distance between the cathode and the anode is in the range of 0.1 to 0.4m, or 0.1 to 0.3m.

9. The method of any of the above claims wherein the voltage applied between anode and cathode is at least 50 or at least 60 V and up to 400, or 300, or 200 V.

10. The method of any of the above claims further comprising adding an electrolyte to the soil.11 . The method of claim 10 wherein the electrolyte has a salt concentration of at least 0.001 M, or at least 0.005 M, or at least 0.01 M, or in a range of 0.001 to 0.1 M.

12. The method of either of claims 10-11 wherein the electrolyte comprises a cation selected from Na, K, NH4, Mg, Ca, or combinations thereof.

13. The method of any of claims 10-12 wherein the electrolyte comprises an anion comprising Cl, Br, acetate, citrate, lactate, or combinations thereof.

14. The method of any of claims 10-14 wherein a leachate flowing toward the cathode comprises a higher mass ratio of short chain PFSA / long chain PFSA or long chain PFCA / short chain than the comparable ratio in the adsorbent.

15. The method of any of claims 1-9 comprising adding deionized water to the soil.

16. The method of claim 15 comprising operating at a voltage wherein the mass ratio of short chain PFCA / long chain PFCA in the adsorbent is the same or higher than the comparable ratio in the soil prior to treatment.

17. The method of claim 15 wherein the mass ratio of short chain PFCA, long chain PFCA, short chain PFSA, long chain PFSA, and / or intermediates in the absorbent are within 20% or within 10% of the same ratio in the soil. For example, the mass ratio of short chain PFCA / long chain PFCA in the adsorbent is within 20% of the same ratio in the soil prior to treatment.

18. A method and system for removing PFAS from soil, comprising: a cathode and anode disposed a distance apart from each other in contaminated soil; wherein the soil is contaminated with PFAS; a voltage is (or can be) applied between the cathode and anode; wherein a sorbent media is disposed between the anode and cathode; typically, the anode and cathode are at least 15 or at least 20 cm apart and the sorbent media membrane is disposed within 5 cm of the anode, preferably within 2 cm.

19. The system of claim 18 comprising, in sequence in a direction, at least one supply well, at least two anodes, at least two cathodes, and at least one extraction well.

20. The system of any of claims 18-19 wherein an electrolyte or deionized water is supplied to the soil through the supply well.T1

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