Sustainable System and Method for Removing and Concentrating Per- and Polyfluoroalkyl Substances (PFAS) from Water

Abstract

A sustainable system for removing and concentrating per- and polyfluoroalkyl substances (PFAS) from water. The system includes an anion exchange vessel having a selected anion exchange resin therein configured to remove PFAS from the water. A line coupled to the vessel introduces a flow of water contaminated with PFAS such that the PFAS bind to the selected anion exchange resin and are thereby removed from the water. A regenerant solution line is coupled to the anion exchange vessel to introduce an optimized regenerant solution to the anion exchange vessel to remove the PFAS from the anion exchange resin, thereby regenerating the anion exchange resin and generating a spent regenerate solution comprised of the removed PFAS and the optimized regenerant solution. A separation and recovery subsystem recovers the optimized regenerant solution for reuse and separates and concentrates the removed PFAS.

Claims

1. A system for reducing an amount of a toxic spent regenerant solution produced by a system which removes per- and polyfluoroalkyl substances (PFAS) from contaminated water, the system comprising: a concentration subsystem configured to separate and concentrate the PFAS in the contaminated water to produce the toxic spent regenerant solution; and a separation and recovery subsystem configured to receive the toxic spent regenerant solution, the separation and recovery subsystem including at least one of a distillation subsystem, an evaporation subsystem, or a membrane separation subsystem, at least one of the distillation subsystem, the evaporation subsystem, or the membrane separation subsystem configured to concentrate the PFAS, water, and salt in the toxic spent regenerant solution to reduce the amount of toxic spent regenerant solution.

2. The system of claim 1 in which the concentration subsystem includes an anion exchange vessel including an anion exchange resin therein configured to receive a flow of the contaminated water such that the PFAS in the contaminated water bind to the anion exchange resin to remove PFAS from the contaminated water and configured to receive a regenerant solution comprising a mixture of a salt, a solvent and water to regenerate the anion exchange resin and produce the toxic spent regenerant solution.

3. A method for reducing an amount of a toxic spent regenerant solution produced by a method which removes per- and polyfluoroalkyl substances (PFAS) from contaminated water, the method comprising: separating and concentrating the PFAS in the contaminated water to produce the toxic spent regenerant solution; and subjecting the toxic spent regenerant solution to a separation and recovery process including at least one of a distillation process, an evaporation process, or a membrane separation process, at least one of the distillation process, the evaporation process, or the membrane separation process configured to concentrate the PFAS, water, and salt in the toxic spent regenerant solution to reduce the amount of toxic spent regenerant solution.

4. The method of claim 3 in which the separating and concentrating the PFAS includes introducing a regenerant solution comprising a mixture of a salt, a solvent, and water to an anion exchange resin to remove the PFAS from the anion exchange resin to regenerate the anion exchange resin and generate the toxic spent regenerant solution.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0019] Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

[0020] FIG. 1 shows an example of a typical PFAS with a hydrophobic non-ionic tail and an anionic head;

[0021] FIG. 2 shows a three-dimensional view depicting the complex three-dimensional structure of a typical anion exchange resin bead showing examples of positively charged exchange sites of the resin bead binding to negatively charged hydrophilic heads of PFAS molecules, and the hydrophobic carbon-fluorine tails of the PFAS adsorbing to the hydrophobic backbone of the resin bead;

[0022] FIG. 3 is a schematic block diagram showing the primary embodiments of one embodiment of sustainable system and method for removing and concentrating PFAS from water; and

[0023] FIG. 4 is a block diagram showing the primary steps of one embodiment of the sustainable method for removing and concentrating PFAS from water.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

[0025] As discussed in the Background section, anion exchange resins are highly effective at removing PFAS from water because of the multiple removal methods involved. The molecular structure of most PFAS compounds can be broken into two functional units including the hydrophobic non-ionic “tail,” comprised of the fluorinated carbon chain and the hydrophilic anionic “head,” having a negative charge. FIG. 1 shows an example of a typical PFAS 10 with hydrophobic non-ionic tail 12 and hydrophilic anionic head 14, in this example, a sulfonate group, although anionic head 14 may be a carboxylate group or similar type group.

[0026] Anion exchange resins are essentially adsorbents with anion exchange functionality. The resin beads are typically composed of neutral copolymers (plastics) that have positively charged exchange sites. FIG. 2 shows an example of the complex three-dimensional structure of a typical onion exchange resin bead 16 with positively charged exchange sites exemplarily indicated at 18. Anion exchange resins tend to be effective at removing PFAS from water because they take advantage of the unique properties of both the anion exchange resin bead and the perfluorinated contaminants, or PFAS, using a dual mechanism of adsorption and anion exchange. For example, hydrophobic carbon-fluorine tail 12, FIGS. 1 and 2, of PFAS 10 adsorbs to the hydrophobic backbone on anion exchange resin 16, FIG. 2, comprised of cross-linked polystyrene polymer chains, exemplarily indicated at 20 and divinylbenzene cross-links exemplarily indicated at 22. The negatively-charged hydrophilic heads 24 (sulfonate groups) or 26 (carboxylate groups) of PFAS 10 are attracted to positively-charged anion exchange sites 18 on anion exchange resin bead 16. The negatively charged heads 24, 26 of PFAS 10 displaces exchangeable inorganic counter ion 38, e.g., a chloride ion which is provided on anion exchange bead 18 when it is manufactured. The hydrophobic, uncharged carbon-fluorine tails 12 are adsorbed to the uncharged hydrophobic backbone comprised of polystyrene polymer chain 20 and divinylbenzene crosslink 22 via Van der Waals forces as shown.

[0027] Depending on the specific properties of both resin bead 16 and the PFAS 10, this dual mechanism of removal may be highly effective at removing PFAS from water and certain anion exchange resins have very high removal capacity for PFAS from water.

[0028] While the dual mechanism of PFAS removal discussed above may be highly effective at removing PFAS from water because the adsorption of the hydrophobic tails of the PFAS to the hydrophobic backbone of the anion resin exchange bead, it also makes resin regeneration and reuse more difficult. A high concentration of a brine or base solution, e.g., a solution of a salt, such as NaCl, and water, or a solution of a base, such as NaOH and water, may be used to effectively displace the anionic head of the PFAS from the anion exchange site of the anion exchange resin bead, but the hydrophobic carbon-fluorine tail tends to stay adsorbed to the resin backbone. Similarly, an organic solvent, e.g., methanol or ethanol, may be used to effectively desorb the hydrophobic tail from the backbone, but then the anionic head of the PFAS stays attached to the resin anion exchange site. Research to date has demonstrated that effective regeneration techniques must overcome both mechanisms of attraction. Solutions combining organic solvents and a suit or base, such as NaCl or NaOH, have shown the most successful results to date, e.g., as disclosed in Deng et al., 2010, and Chularueangaksorn et al., 2013, discussed in the Background section. Other research has focused on using combinations of ammonium salts, including ammonium hydroxide and ammonium chloride, e.g., as disclosed by Conte et al., Polyfluorinated Organic Micropollutants Removal from Water by Ion Exchange and Adsorption, Chemical Engineering Transactions, Vol. 43 (2015), incorporated by reference herein.

[0029] There is shown in FIG. 3, one embodiment of sustainable system 100 for removing and concentrating PFAS from water. System 100 includes anion exchange vessel 102 including a selected anion exchange resin therein, exemplarily indicated at 104, configured to remove PFAS from flow of water 106 contaminated with PFAS. System 100 also includes line 108 which is configured to introduce flow of water 108 contaminated with PFAS into anion exchange vessel 102 such that the PFAS binds to selected union exchange resin 104 and are removed from the water to provide flow of treated water 116. In one example, selected anion exchange resin 104 is preferably configured to be small, e.g., about 0.5 mm to about 1 mm diameter beads made of an organic polymer substrate or similar material which is preferably porous and provides a high surface area. Exemplary selected anion exchange resins may include Dow® AMBERLITE™, IRA958 Cl, DOWEX™ PSR-2, Dow® XUS-43568.00, and similar type anion exchange resins.

[0030] System 100 also includes regenerant solution line 110 coupled to anion exchange vessel 102 configured to introduce optimized regenerant solution 112 into anion exchange vessel 102 to remove the PFAS from anion exchange resin 104 to regenerate anion exchange resin 104 and generate spent regenerant solution 120 in line 122 comprised of removed PFAS and optimized regenerant solution. In one example, optimized regenerant solution 112 is made in regenerant solution make-up tank 114 coupled to regenerant solution line 110 as shown. In one design optimized regenerant solution 112 preferably includes a mixture of a salt or base, e.g., sodium chloride (NaCl) or sodium hydroxide (NaOH), a solvent and water. In one example, the solvent may include an alcohol or similar type solvent. In one example, optimized regenerant solution 112 includes about 50% to about 90% methanol by volume, about 10% to about 50% water by volume, and about 1% to about 5% salt or base by weight. In another example, optimized regenerant solution includes about 70% methanol by volume, about 28% water by volume, and about 2% salt or base by weight. As discussed above, preferably, selected anion exchange resin 104 and regenerant solution 112 removes PFAS from water by a dual mechanism including desorption and ion exchange. For ion exchange removal of PFAS from selected anion exchange resin 104, the anion of the salt or base, e.g., chloride of the NaCl or the hydroxide group of NaOH of optimized regenerant solution 112 displaces the hydrophilic heads 24 or 26, FIG. 2, of PFAS 10 on exchange sites 18 of anion exchange resin 16 due to the high concentration of the anions in optimized regenerant solution 112. For desorption, the solvent, e.g., an alcohol, such as methanol, ethanol or similar type alcohol of the optimized regenerant solution 112 displaces hydrophobic carbon tails 12 of the PFAS 112 bonded to the backbone of anion exchange resin 16 due to the high concentration of the solvent in optimized regenerant solution 112. The result is system 100 and efficiency removes both large and small chain PFAS from water.

[0031] In one example, the PFAS removed by anion exchange resin 14 may include Perfluorobutyric acid (PFBA), Perfluoropentanoic acid (PFPeA), Perfluorobutane sulfonate (PFBS), Perfluorohexanoic acid (PFHxA), Perfluoroheptanoic acid (PFHpA), Perfluorohexane sulfonate (PFHxS), 6:2 Fluorotelomer sulfonate (6:2 FTS), Perfluorooctanoic acid (PFOA), Perfluoroheptane sulfonate (PFHpS), Perfluorooctance sulfonate (PFOS), Perfluorononanoic acid (PFNA), 8:2 Fluorotelomer sulfonate (8:2 FTS).

[0032] System 100 also includes the separation and recovery system 124 coupled to line 122 which recovers optimized regenerant solution 120 for reuse as reclaimed regenerant solution 126 by line 128 coupled to line 110 and preferably to regenerant solution makeup tank 114. In one design, separation and recovery subsystem 124 provides reclaimed solvent 132 by line 128 as shown and solution 136 of concentrated PFAS, salt or base, and water by line 138 which is coupled to line 128 as shown. The PFAS in solution 136 is removed (discussed below) to provide solution 152 of concentrated salt or base and water output by line 138 coupled to line 128. Thus, reclaimed regenerant solution 126 preferably includes reclaimed solvent 132 and reclaimed salt or base and water.

[0033] In one design, separation and recovery subsystem 124 may include evaporation subsystem 130. In this example, spent regenerant solution 120 is subjected to evaporation by evaporation subsystem 130 to produce reclaimed solvent 132 output to line 128 and solution 136 of concentrated desorbed PFAS, salt or base and water. Condenser 140 may be utilized to condense reclaimed solvent 132. In another example, separation and recovery subsystem 124 may include one or more of a distillation subsystem 142 and/or a membrane separation subsystem 144 which similarly produce reclaimed solvent 132 for reuse by lines 128 and 110 and solution 136 of concentrated PFAS, salt or base, and water.

[0034] In one example, separation and recovery subsystem 124 may further include solvent purification subsystem 141 coupled to line 128 which removes carryover PFAS from separation and recovery subsystem 124 and provides purified reclaimed solvent 144 in line 128 for reuse as regenerant solution 112 via regenerant solution makeup tank 114 and regenerant solution line 110. In one example, solvent purification subsystem 141 is a smalt vessel, e.g., vessel 160 shown in caption 162 as shown having anion exchange resin 104 therein which removes carryover PFAS in line 134 to create concentrated PFAS in the vessel. When vessel 160 becomes saturated with PFAS, it can be removed and taken off-site for destruction.

[0035] Separation and recovery subsystem 122 may also include super-loading recovery subsystem 150 coupled to line 138 output by separation and recovery subsystem 124 having solution 136 of concentrated PFAS, salt or base, and water. Superloading recovery subsystem 150 creates ultra concentrated PFAS waste product adsorbed to anion exchange resin 104 and concentrated salt or base or caustic water solution 152 purified for reuse. Super-loading recovery subsystem 150 preferably provides solution 152 of concentrated salt or base and water coupled to line 128 for reuse as regenerant solution 112 via regenerant solution makeup tank 114 and regenerant solution line 112. In one example, superloading and recovery subsystem 150 is a small vessel, e.g., vessel 170 in caption 172 as shown having anion exchange resin therein which provides ultra-concentrated PFAS on anion exchange resin 104 and outputs solution 152 of concentrated salt or base and water. When vessel 170 becomes saturated with PFAS, it can be removed and taken off-site for destruction. The small size and high concentration of PFAS reduces costs associated with removal of PFAS from water.

[0036] System 100 also preferably includes sample lap 156 or 158 as shown for testing the level of PFAS in treated water 116. When PFAS are detected in treated water 116, it means anion exchange resin 104 in vessel 102 has been saturated with PFAS attached to anion exchange resin 104 and anion exchange resin 104 need to be regenerated.

[0037] The sustainable method for removing concentrated per- and polyfluoroalkyl substances (PFAS) from one embodiment of this invention may include selecting an anion exchange resin configured to move PFAS and provide clean, treated water, step 200, FIG. 4. The selected anion exchange resin is then added to an anion exchange vessel, step 202. A flow of water contaminated with PFAS is introduced to the anion exchange vessel such that the PFAS bind to the selected anion exchange resin and are thereby removed from the water, step 204. An optimized regenerant solution is introduced to the anion exchange vessel to desorb PFAS from the union exchange resin thereby regenerating the anion exchange resin and generating a spent regenerant solution comprised of desorbed PFCs and the optimized regenerant solution, step 206. The spent regenerant solution is then subjected to a separation and recovery process to recover the optimized regenerant solution for reuse and separate and concentrate the removed PFAS.

[0038] The result is that system 100, and the method thereof for removing and concentrating PFAS from water, efficiently and effectively removes PFAS from water, regenerates the anion exchange resin and then concentrates, or ultra concentrates, the desorbed PFAS with a solvent purification subsystem and/or on super loading recovery subsystem in small vessels that can be inexpensively disposed of. Thus, system 100 and the method thereof provides a sustainable system and method for concentrating and removing PFAS from water and regenerating the selected anion exchange resin, which significantly reduces the cost to remove PFAS from water because it generates less toxic waste than conventional and known methods for removing PFAS. The separated and concentrated or ultra-concentrated PFAS is easier and less expensive to handle and transport. System 100 and the method thereof efficiently reclaims the solvent, salt or base, and water from the spent regenerant solution which further reduces cost.

[0039] Although specific features of the invention are shown in some drawings and not in others, this is for convenience only, as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims.

[0040] In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons