Method and Apparatus to Separate Per-and Polyfluoroalkyl Substances (PFAS) from Water Using Colloidal Gas Aphrons (CGAs)

Abstract

A method for the decontamination of water containing one or more PFAS, having the steps of generating colloidal gas aphrons (CGAs) by mixing a gas, water, and one or more surfactants together with high shear forces, introducing the CGAs and a PFAS-containing water in an enclosed space where the CGAs move upwards through the water due to their inherent buoyancy, allowing the plurality of CGAs to extract PFAS from the water, and separating the PFAS-containing CGAs from the surface of the water in the enclosed space for further treatment or disposal, leaving the water with lower PFAS concentrations in the vessel. The aphrons may be anionic or cationic and created by mixing speeds or surfactant concentration, and treatment may be with gas bubbles to remove PFAS from water gas bubbles or destruction of PFAS by plasma reactor or deployed in situ through wells into geologic ground formations.

Claims

1. A method for the decontamination of water containing one or more PFAS, comprising the steps of: generating colloidal gas aphrons (CGAs) by mixing under high shear forces gas, water, and one or more surfactants together; introducing the CGAs and a PFAS-containing water in a plasma reactor where the CGAs move upwards through the water due to their inherent buoyancy; sorbing the PFAS to the CGAs to extract PFAS from the water; and separating the PFAS-containing CGAs from the surface of the water in the plasma reactor for further treatment or disposal.

2. The method as claimed in claim 1 where a surfactant or surfactants with the same charge (either anionic or cationic) are used.

3. The method as claimed in claim 1 where at least two surfactants with different charges (anionic and cationic) are used.

4. The method as claimed in claim 1 where the properties of the CGAs are adjusted by at least one of the following: shear forces; mixing speed; or surfactant concentration.

5. The method as claimed in claim 1 where gas bubbles and CGAs are introduced into the PFAS-containing water to remove contaminants.

6. The method as claimed in claim 1 where the enclosed space for further treatment or disposal is a batch system.

7. The method as claimed in claim 1 where the enclosed space is a continuous reactor.

8. (canceled)

9. The method as claimed in claim 8 further where the CGAs are decanted from the enclosed space.

10. The method as claimed in claim 1 where the PFAS treatment technology uses gas bubbles to remove PFAS from water.

11. The method as claimed in claim 1 where the water contains one PFAS.

12. The method as claimed in claim 1 where the water contains a plurality of PFAS.

13. The method as claimed in claim 1 where one or more of the PFAS are anionic.

14. The method as claimed in claim 1 where one or more of the PFAS are cationic.

15. The method as claimed in claim 1 where one or more of the PFAS are zwitterionic.

16. The method as claimed in claim 1 where one or more of the PFAS are long-chained.

17. The method as claimed in claim 1 where one or more of the PFAS are short-chained.

18. The method as claimed in claim 1 where one or more of the PFAS are PFAAs.

19. The method as claimed in claim 1 where one or more of the PFAS are precursors.

20. The method as claimed in claim 1 where the plurality of CGAs extract PFAS from the water due to both electrostatic and hydrophobic processes.

21. The method as claimed in claim 1 where the CGAs are pumped from the enclosed space.

22. The method as claimed in claim 1 where the CGAs are decanted from the enclosed space.

23. The method as claimed in claim 1 are CGAs are directly treated or disposed of.

24. The method as claimed in claim 1 where the CGAs are allowed to revert naturally to liquid form prior to transportation to treatment or disposal.

25. The method as claimed in claim 1 where the CGAs are facilitated to revert to liquid form prior to transportation to treatment or disposal.

26. The method as claimed in claim 1 where baffles are placed in the enclosed space to change the flow direction in the vessel to facilitate the separation of the aphrons from the vessel,

27. A method for the decontamination of water containing one or more PFAS contaminants, comprising the steps of: generating colloidal gas aphrons (CGAs) using a gas, water, and electrostatically charged surfactant where the water contains PFAS; injecting the CGAs through a screened well or open tube and into the formation through a porous material in a trench, the one or more PFAS contaminants accumulating on the plurality of CGAs; sorbing the PFAS to the CGAs from electrostatic and hydrophobic partitioning to remove PFAS from the bulk liquid; treating the CGAs with a plasma reactor; and disposing of the PFAS-containing CGAs.

28. The method as claimed in claim 27 where the plasma reactor comprises a vessel.

29. The method for the decontamination of an aquifer containing one or more PFAS contaminants, comprising the steps of: generating colloidal gas aphrons (CGAs) by mixing a gas, water, and at least one surfactant with high shear forces; injecting the CGAs through an open tube a screened well into geologic formation through a natural aquifer material, the one or more PFAS contaminants accumulating on the plurality of CGAs; generating a layer of CGAs and high-concentration PFAS on a top surface of a water table in the geologic formation; and extracting the groundwater near the water table or too of the confined aquifer that contains the concentrated PFAS for treatment due to both electrostatic and hydrophobic processes.

30. The method as claimed in claim 29 wherein the aquifer material is comprised of one or more of the following: gravel, sand, silt, clay, or fractured geologic media, or some combination thereof.

31. The method as claimed in claim 29 further comprising the step of extracting the concentrated PFAS and CGAs.

32. The method of claim 29 further comprising the step of allowing the concentrated PFAS to be retained in a subsurface of the geologic formation.

33. The method of claim 29 further comprising a porous material in a trench.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.

[0026] FIG. 1 provides an excerpt from the prior art in which dyes are demonstrated to be proxies for PFAS.

[0027] FIG. 2 illustrates an apparatus for proof-of-concept experiments where CGAs are generated using a spinning disc configuration and pumped through a column containing contaminated water.

[0028] FIG. 3 illustrates the unique multi-layered structure of CGAs (air, water, and electrostatically-charged surfactant) formed during proof-of-concept experiments as observed via a microscope/camera assembly.

[0029] FIG. 4 illustrates the results of the experiments where CGAs were pumped through dye solutions.

[0030] FIGS. 5A and 58 are graphs that show the results of experiments where CGAs were pumped through liquid solution containing six different PFAAs: trifluoromethanesulfonic acid (referred to as triflate in its deprotonated form), TFA, PFBA, PFBS, PFOA, and PFOS.

[0031] FIG. 6 illustrates control experiments comparing the removal of a short-chain PFAS (PFBA) by CGAs to the effect of removal by gas bubbling alone (N2) and gas bubbling (N2) in the presence of CTAB in the bulk solution.

[0032] FIG. 7 illustrates the model of PFAS contaminated water being treated ex-situ using a separation column, and CGAs being pumped at the bottom of the column, with the CGA-high concentration PFAS layer then skimmed or pumped for further treatment or disposal.

[0033] FIG. 8 shows a baffle in a separation column to increase contact time between CGAs and the influent stream according to a preferred embodiment of the invention.

[0034] FIG. 9 shows the addition of a distribution plate for CGAs to enable more uniform delivery according to a preferred embodiment.

[0035] FIG. 10 shows a preferred embodiment where both gas bubbles and CGAs are used for either treatment or for separation.

[0036] FIG. 11 illustrates a model of an in-situ application using another preferred embodiment, where CGAs are injected directly in the aquifer.

[0037] FIG. 12 illustrates the conceptual model of an in-situ application using yet another preferred embodiment, where CGAs are injected in man-made trenches.

DETAILED DESCRIPTION OF THE INVENTION

[0038] Detailed descriptions of the preferred embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for later filed claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner.

[0039] A proof-of-concept laboratory experiment was performed to visually and quantitatively evaluate the removal of a PFAS surrogate from an artificial contaminated water system. PFAS are a diverse class of chemicals, and their analysis is complicated, expensive and time consuming. Prior art such as Sörengård, M., Östblom, E., Köhler, S., Ahrens, L., 2020, Adsorption behavior of per- and polyfluoroalkyl substances (PFASs) to 44 inorganic and organic sorbents and use of dyes as proxies for PFAS sorption, Journal of Environmental Chemical Engineering 8, 103744, https://doi.org/10.1016/j.jece.2020.103744 (2020) further described below and in FIG. 1, have previously demonstrated that dyes can be successfully used as proxies to assess PFAS sorption where methylene blue (MB) correlates well with adsorption of shorter chain PFAS (such as perfluorobutanoic acid) via predominantly electrostatic forces, and rose bengal (RB) correlates well with adsorption of longer chain PFAS (such as perfluorooctanesulfonate) via predominantly hydrophobic forces (Sörengård et al., 2020). Therefore, for proof-of-concept purposes MB and RB were used to assess the efficacy of CGAs in removing short-chain and long-chain PFAS. The key mechanisms of contaminant removal by CGAs are via both electrostatic and hydrophobic interactions, so optimal removal is achieved when the contaminant and the CGAs are oppositely charged, or hydrophobic. MB and RB are cationic and anionic, respectively. Consequently, CGAs were made using anionic (sodium dodecylbenzenesulfonate (NaDBS)) and cationic (cetrimonium bromide (CTAB)) surfactants for MB and RB experiments, respectively.

[0040] FIG. 1 illustrates the adsorption behavior of per- and polyfluoroalkyl substances (PFASs) to 44 inorganic and organic sorbents and use of dyes as proxies for PFAS sorption with the x axis being hydrophobic sorption and the y axis being electrostatic sorption for a number of PFAS compounds, including PFSA, PFCA, FTSA, FOSA. Further depicted is methylene blue (MB) which correlates well with adsorption of shorter chain PFAS (such as perfluorobutanoic acid) via predominantly electrostatic forces, and rose bengal (RB) which correlates well with adsorption of longer chain PFAS (such as perfluorooctanesulfonate).

[0041] In accordance with a preferred embodiment of the invention, the setup for experiments is shown in FIG. 2 and further described below. Bulk surfactant solution 100 in Beaker 114 is depicted schematically comprising CGAs made of a surfactant 102, liquid 104 and gas 106. The CGAs were generated using a spinning disc configuration having motor 108 connected via shaft 110 to disc 112. A rotary tool such as motor 108 is capable of approximately 5,000 to 35,000 revolutions per minute (rpm) and was connected to a 3D-printed shaft 110 with a 2.5-in. diameter disc 112 attached to the tool. Following the method of Longe (1989) and others, CGAs were produced in a 5-L beaker 114 which had four baffles 115 to enable adequate air induction and ensure that the entire fluid passed through the spinning disc zone where maximum shearing takes place. Beaker 114 was filled with 1-L surfactant solution 116 prepared above its critical micelle concentration (CMC). The concentration of CTAB and NaSDS solutions used in the experiments were 380 parts per million (ppm) (CMC .sup.˜330 ppm) and 700 ppm (CMC .sup.˜540 ppm), respectively. To produce CGAs, the spinning disc was lowered approximately 1-2 in. below the surface of the surfactant solution and the spinning disc was rotated at 12,500 rpm for 1 min to generate a cloudy fluid containing CGAs.

[0042] Peristaltic pump 120 transported the CGAs at a rate of 40 ml/min from beaker 114 in direction 118 to the bottom of a 2-L, 21-in. tall vertical separation column 122 containing 1.5-1 of MB or RB dye solutions 117 (PFAS surrogate solutions). The MB and RB concentrations used were 20 ppm and 5 ppm, respectively. CGAs accumulating at the air/water interface were continuously removed in direction 124 from column 122.

[0043] The experiments were performed in batch mode. The CGAs were continuously removed from the batch separation column during the experiment. Surfactant solution 100 in Beaker 114 is depicted schematically comprising CGAs made of a surfactant 102, liquid 104 and gas 106.

[0044] CGAs, with their unique multi-layered structure were successfully generated during the experiments which was confirmed using microscopy as shown diagrammatically in FIG. 3. Scan 140 shows a number of CGAs 145 in bulk water 148 with each CGA having air 142 in the center, surrounded by water layer 144, surrounded in turn with electrostatically charged surfactant layer 146 The CGAs were generated using a spinning disc configuration at 12.500 RPMs and imaged using light microscopy.

[0045] Dye concentrations were measured in the bulk liquid using a spectrophotometer. First, a calibration curve was created by creating known specific concentrations of dye and recording their resulting absorbance. For RB, wavelength was set at 550 nm, and for MB, wavelength was at 663 nm.

[0046] Dye solution was obtained from the separation column in the bulk liquid every minute and was filled in a cuvette for measurement. Resulting absorbances were recorded and dye concentrations were calculated using individual calibration curves.

[0047] FIG. 4 is a graph showing the results of dye removal that was observed during CGA sparging experiments. Removal in percentage is shown on the y axis for each of two solutions with methylene blue (MB) 150 shown in diagonal cross hatching and rose bengal (RB) 152 shown in rectangular cross hatching. CGS were introduced into 1.5 L dye solutions at a rate of 40 ml/minute. Overall, 81% MB and 91% RB removal in 6 to 8 minutes was observed, during CGA batch removal test as shown in FIG. 4, which demonstrates that CGAs can be used to remove both short- and long-chain PFAS, and anionic and cationic PFAS.

[0048] During some dye tests, the removal rates were initially high for the first several minutes, but then dropped as the test continued. This was later determined to be caused by leaving some of the CGAs at the top of the water layer in the separation column (e.g., the CGA removal step was inefficient during the test), and having these CGAs naturally collapse back to a liquid phase and thereby released the dye back into the water phase. This reduction in performance can be easily avoided in future laboratory tests or field applications by employing a more efficient CGA removal step.

[0049] A second set of experiments were conducted with liquid solutions containing analytical grade PFAS purchased from Sigma-Aldrich. PFAS were measured in the collected samples by targeted analysis using Liquid Chromatography with tandem mass spectrometry (LC-MS-MS).

[0050] Experiments were first conducted with liquid solutions containing ultra-short (triflate, TFA), short-chain (PFBA, PFBA), and long-chain (PFOA, PFOS) PFAS with a treatment time of 10 minutes using CGAs generated with CTAB (cationic surfactant).

[0051] The percentage removals were as follows: 60-90% for ultra-short chain, 91-95% for short-chain, and 0-88% for long-chain PFAS. PFOA removal was 90% and no reduction in PFOS was observed (Kulkarni et al., 2022). Figure SA shows results of this experiment with the y axis being normalized concentration, and the x axis being time with data for triflate (TFA), short-chain (PFBA, PFBS), and long-chain (PFOA, PFOS) PFAS. FIG. 5B shows results of this experiment with the y axis being PFAS removal as a percentage and the x axis being time. The removal of ultra-short chain (triflate, TFA), short-chain (PFBA, PFBS), and long-chain (PFOA, PFOS) PFAS with a treatment time of 10 minutes using CGAs were as follows: 60-90% for ultra-short chain, 91-95% for short-chain, and 0-88% for long-chain PFAS. PFOA removal was 90% and no reduction in PFOS was observed

[0052] Further control experiments were conducted comparing the removal of a short-chain PFAS (PFBA) by CGAs to the removal by gas bubbling alone (N.sub.2) and gas bubbling (N2) in the presence of CTAB in the bulk solution.

[0053] As shown in FIG. 6, a graph is depicted with the x axis being time in minutes and the y axis being PFBA/Normalized Concentration. The graph shows results for CGAs, N2 Bubbles and NS Bubbles plus CTAB. As shown, removal via CGAs was significantly higher (90% for CGAs vs. 11% for nitrogen bubbling in a CTAB solution vs. 0% of nitrogen bubbling alone) with 10 minutes of treatment. Additionally, CGAs provided faster kinetics than nitrogen bubbling, with or without CTAB in bulk solution, for the removal of PFBA (short-chain PFAS) (Kulkarni et al., 2022).

[0054] In a preferred embodiment separation system 200 shown in FIG. 7, PFAS-containing water 217 is pumped in direction 218 into separation column 220 as influent water. Separately CGAs are generated and introduced into the bottom of separation column 220, containing PFAS impacted water, via direction 216 from pump 214 which in turn draws CGA solution 208 in direction 212 generated through spinning action of disc 206 being turned by shaft 204 connected to motor 202. Baffles 210 are position within beaker 211 to facilitate generation of CGAs.

[0055] PFAS sorb on the CGAs due to electrostatic and hydrophobic processes. The CGAs with the attached PFAS move upwards in separation column 220 because of the inherent buoyancy of the CGAs. Subsequently, a CGA layer 222 containing higher PFAS concentrations is created at the top of separation column 220 that is then removed from separation column 220 in direction 226 by pumping or skimming and into receiving vessel 228. Once in receiving vessel 228, the removed CGAs then collapse naturally in a few minutes (based on the scientific literature, the typical half-life before a CGA collapses is .sup.˜4 minutes) to form a liquid with concentrated PFAS. This low-volume, high concentration liquid is delivered in direction 229 and treated by existing ex-situ treatment technologies 230 (e.g., destructive technologies), disposed safely in engineered depositories or landfills, or managed in some other way. Effluent water 224 is driven out of column 220.

[0056] FIG. 8 shows baffle 248 in separation column 240 according to a preferred embodiment of the invention. Baffle 248 can be added to separation column 240 to improve the separation and recovery of CGAs from effluent water by increasing the contact time between influent stream 244 and CGA mixture. CGAs are introduced into separation column 240 via input stream 246 with PFAS-contaminated water influent stream 244 being introduced in separation column 240. PFAS and CGAs collect in upper portion 242 of separator column 250 as they move in direction 250. Effluent water 252 flows off the top of separation column 240. CGAs are pumped out of separation column 240 via stream 254.

[0057] FIG. 9 shows the addition of perforated distribution plate 266 that can be added to separation column 260 with influent stream 262 and introduction of CGAs 268 through stream 264 through plate 266 through which the CGA mixture flows to enable more uniform delivery and distribution of CGAs according to a preferred embodiment. Effluent water flows through output 270 while collapsed CGAs and concentrated PFAS flow through output 272.

[0058] FIG. 10 shows a system for separation in an existing gas/liquid PFAS treatment process. CGAs 286 are introduced via stream 284 into tank 280 with gas 294 being introduced via port 288. Influent water is introduced via stream 282 and CGAs can be used together with conventional gas bubbles for either direct treatment (such as a plasma reactor) or for separation (foam fractionation) 296. Effluent stream then flows out stream 292.

[0059] In an in-situ application shown in FIG. 11, CGAs 304 are injected via well 302 within and/or under PFAS plume 316 directly in aquifer 311 lying below ground 300. In this application well 302 is drilled in the formation 307 (either vertical or horizontal) and CGAs 304 are directed down well 302 and out well screen 306 near the bottom of well 302. When a CGA is introduced in a groundwater treatment zone 310, PFAS will collect at the outer surface via electrostatic and hydrophobic partitioning processes and be drawn upwards by the buoyancy of the injected CGA. The CGA injection results in lower PFAS concentrations in the deeper portions of the injection zone, remediating this portion of aquifer 311. The CGA-injection will also create higher PFAS concentrations 313 near the top of aquifer 311, making it easier to remove the PFAS by skimming the low volume of groundwater containing higher concentrations of PFAS and/or by direct removal of the CGAs using shallow extraction wells. Concentrated CGAs/PFAS 312 move in direction 314 through shallow well 315 where they can be skimmed for further treatment or disposal.

[0060] In yet another embodiment shown in FIG. 12, in situ trench removal 320 utilizes CGA injection 322 that can be conducted through porous media 324 in man-made trenches 325 using gravel or sand or other materials drilled through ground 330 into aquifer 316. Under its natural horizontal flow gradient in direction 308, groundwater will flow through one side of trench 325 and out the opposite side. Injection of CGAs via well 326 in trench 325 through screen 327 serves to concentrate PFAS at the surface of the water via direction 328 to the surface, thereby facilitating the removal or treatment of the high concentration, lower volume of contaminated groundwater or CGA-PFAS layer.

[0061] While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the later issued claims.