EP4594258A2

EP4594258A2 - Systems and methods for the regeneration of ion exchange resins

Info

Publication number: EP4594258A2
Application number: EP23904562.8A
Authority: EP
Inventors: Thomas Mallmann; Savvas Hadjikyriacou
Original assignee: Evoqua Water Technologies LLC
Current assignee: Evoqua Water Technologies LLC
Priority date: 2022-12-14
Filing date: 2023-12-14
Publication date: 2025-08-06
Also published as: WO2024129944A3; AU2023398778A1; WO2024129944A2; CA3272032A1

Abstract

Systems for treating water containing PFAS are disclosed. Systems include a PFAS separation stage including a vessel and an ion exchange resin having an affinity for PFAS positioned within the vessel. Systems further include an ion exchange resin regeneration stage with a source of an ion exchange resin regeneration solution including a surfactant. The ion exchange resin regeneration stage is configured to dose spent ion exchange resin with a volume of the ion exchange resin regeneration solution to remove PFAS from the spent ion exchange resin and regenerate the ion exchange resin. Methods of treating water including PFAS with regeneration of a spent ion exchange resin are disclosed. Methods of facilitating regeneration of a spent ion exchange resin are also disclosed.

Description

SYSTEMS AND METHODS FOR THE REGENERATION OF ION EXCHANGE RESINS

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application Serial No. 63/432.614, filed on December 14, 2022 and titled “Efficient Regeneration of Spent Weak Base Anion Exchange Resins by the Combination of a Strong Base, a Surfactant and the Application of Heat,” the entire disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.

FIELD OF TECHNOLOGY

Aspects and embodiments disclosed herein are generally related to the removal and elimination of per- and polyfluoroalkyl substances (PF AS) from water using ion exchange resins.

BACKGROUND

There is rising concern about the presence of various contaminants in municipal wastewater, surface water, drinking water and groundwater. For example, perchlorate ions in water are of concern, as well as PF AS and PFAS precursors, along with a general concern with respect to total organic carbon (TOC).

PFAS are man-made chemicals used in numerous industries. PFAS molecules ty pically do not break down naturally. As a result, PFAS molecules accumulate in the environment and within the human body. PFAS molecules contaminate food products, commercial household and workplace products, municipal water, agricultural soil and irrigation water, and even drinking water. PFAS molecules have been shown to cause adverse health effects in humans and animals.

SUMMARY

In accordance with one or more aspects, there is provided a water treatment system for removing perfluoroalkyl and/or polyfluoroalkyl substances (PFAS). The system may include a PFAS separation stage for separating PFAS from the water to be treated. The PFAS separation stage may include a vessel having an inlet, an outlet, and ion exchange resin having an affinity for PFAS positioned within the vessel. The inlet of the vessel may be connectable to a source of contaminated w ater comprising a first concentration of PFAS. The system may include an ion exchange resin regeneration stage. The ion exchange resin regeneration stage may include a source of an ion exchange resin regeneration solution that includes a surfactant, e.g., a positively-charged surfactant, a nonionic surfactant, or a negatively-charged surfactant. The ion exchange resin regeneration stage may be configured to dose spent ion exchange resin with a volume of the ion exchange resin regeneration solution to remove PF AS from the spent ion exchange resin creating a PF AS concentrate and a regenerated ion exchange resin.

In some embodiments, the ion exchange resin regeneration stage further may be configured to separate the PF AS concentrate from the regenerated ion exchange resin. In some embodiments, the vessel discharges from the first outlet of the vessel a treated water having a second PF AS concentration lower than the first PF AS concentration.

In further embodiments, the system may include a control system constructed and arranged to regulate a feed of contaminated water into the PF AS separation stage and to regulate a volume of ion exchange resin regeneration solution for dosing the spent ion exchange resin.

In some embodiments, the surfactant is a positively-charged surfactant. In some embodiments, the positively-charged surfactant may be a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary sulfonium-based surfactant, or a tertiary oxonium-based surfactant. In certain embodiments, the positively-charged surfactant may be a quaternary ammonium-based surfactant. The quaternary ammonium- based surfactant may be an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen. For example, the 1-4 alkyl groups may include C1-C20 alkyl chains that are unsubstituted or substituted with one or more heteroatoms. In specific embodiments, the quaternary ammonium-based surfactant may be cetyltrimethylammonium chloride (CTAC). In some embodiments, the surfactant may be a negatively -charged surfactant. In some embodiments, the negatively-charged surfactant may be a sulfate surfactant. In some embodiments, the sulfate surfactant may include one or more alkyl groups on the sulfate ion. In some embodiments, the negatively-charged surfactant may be sodium dodecyl sulfate (SDS).

In some embodiments, a concentration of the surfactant, e.g., positively-charged surfactant, nonionic surfactant, or negatively-charged surfactant, in the ion exchange resin regeneration solution may be above the critical micelle concentration (CMC) of the surfactant, e.g., positively-charged surfactant or negatively-charged surfactant. For example, when the surfactant is positively-charged, the positively-charged surfactant may be a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary sulfonium-based surfactant, or a tertiary oxonium-based surfactant, e.g., an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen. The 1- 4 alkyl groups, e.g., one or more C1-C20 groups, e.g., one or more C8-C20 alkyl groups, may be used to increase solubility with the PF AS sorbed to the ion exchange resin to enhance or improve regeneration of the ion exchange resin.

In further embodiments, the ion exchange resin regeneration solution may include a base. The base may be one or more of NaOH, NH4OH, and N(CH2CH2CH3)4OH.

In some embodiments, the ion exchange resin may be an anion exchange resin. The anion exchange resin may be a weak base anion exchange resin. For example, the weak base anion exchange resin may be a macroporous styrenic matrix supporting amine, e.g., tertiary amine, functionalities.

In further embodiments, the system may include a PF AS concentration stage having an inlet fluidly connected to the outlet of the vessel. The PF AS concentration stage may be constructed and arranged to increase a PFAS concentration of the PF AS concentrate to a third PF AS concentration greater than the first PFAS concentration. In further embodiments, the system may include a PFAS destruction stage having an inlet fluidly connectable to an outlet of the PFAS concentration stage. The PFAS destruction stage may include one or more of electrochemical destruction, photochemical destruction, plasma destruction, and supercritical CO2 destruction.

In further embodiments, the system may include a PFAS polisher having an inlet fluidly connectable to the first outlet of the vessel.

In accordance with one or more aspects, there is provided a method of treating water containing PFAS. The method may include determining a concentration of PFAS in the water containing PFAS to be treated. The method may include introducing the water containing PFAS to a vessel having an ion exchange resin having an affinity for PFAS positioned within to promote removal of the PFAS and produce a product stream. The product stream may be treated water having a lower PFAS concentration than the water to be treated. The method further may include monitoring a PFAS breakthrough level of the product stream. The method additionally may include regenerating spent ion exchange resin using an ion exchange resin regeneration solution including a surfactant, e.g., a positively- charged surfactant, nonionic surfactant, or negatively-charged surfactant. The ion exchange resin regeneration solution may be dosed at a volume sufficient to remove PFAS from the spent ion exchange resin when the PF AS breakthrough level exceeds a predetermined threshold PF AS concentration.

In some embodiments, the PF AS may include one or more of perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorobutanesulfonic acid (PFBS), 4:2 fluorotelomer sulfonic acid (4:2 FTS), perfluorohexanoic acid (PFHxA), perfluoropentanesulfonic acid (PFPeS), perfluoroheptanoic acid (PFHpA), perfluorohexanesulfonic acid (PFHxS), 6:2 fluorotelomer sulfonic acid (6:2 FTS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonic acid (PFOS), and 8:2 fluorotelomer sulfonic acid (8:2 FTS).

In some embodiments, the ion exchange resin may be an anion exchange resin. In some embodiments, e.g.. the anion exchange resin, may be a weak base anion exchange resin. The weak base anion exchange resin may be a macroporous styrenic matrix supporting amine, e.g., tertiary amine, functionalities.

In some embodiments, the surfactant is a positively -charged surfactant. In some embodiments, the positively-charged surfactant may be a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary sulfomum-based surfactant, or a tertian- oxonium-based surfactant. In certain embodiments, the positively-charged surfactant may be a quaternary' ammonium-based surfactant. The quaternary' ammonium- based surfactant may be an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen. For example, the 1-4 alkyl groups may include C1-C20 alkyl chains that are unsubstituted or substituted with one or more heteroatoms. In specific embodiments, the quaternary ammonium-based surfactant may be cety ltrimethylammonium chloride (CTAC). In some embodiments, the surfactant may be a negatively -charged surfactant. In some embodiments, the negatively-charged surfactant may be a sulfate surfactant. In some embodiments, the sulfate surfactant may include one or more alkyl groups on the sulfate ion. In some embodiments, the negatively -charged surfactant may⁷ be sodium dodecyl sulfate (SDS).

In some embodiments, a concentration of the surfactant, e.g., a positively-charged surfactant, nonionic surfactant, or negatively-charged surfactant, in the ion exchange resin regeneration solution may be above the critical micelle concentration (CMC) of the surfactant, e.g., a positively-charged surfactant or negatively-charged surfactant. For example, the positively-charged surfactant may be a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary sulfonium-based surfactant, or a tertiary oxonium-based surfactant, e.g., an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen. The 1-4 alky l groups, e.g., one or more C1-C20 groups, e.g., one or more C8-C20 alkyd groups, may be used to increase solubility with the PF AS sorbed to the ion exchange resin to enhance or improve regeneration of the ion exchange resin.

In further embodiments, the ion exchange resin regeneration solution may include a base. The base may be one or more of NaOH, NH4OH, and N CFhCFfcCHs^OH.

In some embodiments, the predetermined threshold PF AS concentration may be 1 ng/L.

In some embodiments, regenerating the spent ion exchange resin may include mixing the ion exchange resin and the ion exchange resin regeneration solution to create a PFAS concentrate and a regenerated ion exchange resin.

In further embodiments, the method may include introducing the PFAS concentrate into a PFAS concentration stage to increase a PFAS concentration of the PFAS concentrate to a concentration greater than the PFAS concentrate prior to concentration.

In further embodiments, the method may include introducing an effluent of the PFAS concentration stage to a PFAS destruction stage to destroy the PFAS in the effluent of the PFAS concentration stage. The PFAS destruction stage may include one or more of electrochemical destruction, photochemical destruction, plasma destruction, and supercritical CO2 destruction.

In accordance with one or more aspects, there is provided a method of facilitating regeneration of a spent ion exchange resin containing PFAS. The method may include providing an ion exchange resin regeneration solution capable of removing PFAS from the spent ion exchange resin. The provided ion exchange resin regeneration solution may include a surfactant, e.g.. a positively-charged surfactant, nonionic surfactant, or negatively-charged surfactant. The method may include providing instructions for dosing the spent ion exchange resin with a volume of the ion exchange resin regeneration solution sufficient to remove PFAS from the spent ion exchange resin creating a PFAS concentrate and a regenerated ion exchange resin. The method further may include providing instructions for disposal of the PFAS concentrate.

In some embodiments, the surfactant is a positively-charged surfactant. In some embodiments, the positively-charged surfactant may be a quaternary ammonium-based surfactant, a quaternary' phosphonium-based surfactant, or a tertiary oxonium-based surfactant. In certain embodiments, the positively-charged surfactant may be a quaternary ammonium-based surfactant. The quaternary ammonium-based surfactant may be an ammonium-based surfactant comprising 1-4 alky l groups on the quaternary nitrogen. For example, the 1-4 alkyl groups may include C1-C20 alkyl chains that are unsubstituted or substituted with one or more heteroatoms. In specific embodiments, the quaternary ammonium-based surfactant may be CTAC. In some embodiments, the surfactant may be a negatively-charged surfactant. In some embodiments, the negatively-charged surfactant maybe a sulfate surfactant. In some embodiments, the sulfate surfactant may include one or more alkyl groups on the sulfate ion. In some embodiments, the negatively-charged surfactant may be sodium dodecyl sulfate (SDS).

In some embodiments, a concentration of the surfactant, e.g., positively-charged surfactant or negatively-charged surfactant, in the ion exchange resin regeneration solution may be above the critical micelle concentration (CMC) of the surfactant, e.g., positively- charged surfactant, nonionic surfactant, or negatively -charged surfactant. For example, the positively-charged surfactant may be a quaternary- ammonium-based surfactant, a quaternary- phosphonium-based surfactant, a tertiary- sulfonium-based surfactant, or a tertiary- oxonium- based surfactant, e.g., an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen. The 1-4 alkyl groups, e.g.. one or more C1-C20 groups, e.g.. one or more C8-C20 alkyl groups, may be used to increase solubility with the PFAS sorbed to the ion exchange resin to enhance or improve regeneration of the ion exchange resin.

In further embodiments, the ion exchange resin regeneration solution may include a base. The base may be one or more of NaOH, NH4OH. and N(CH2CH2CH3)4OH.

In further embodiments, the method may include providing instructions for increasing the temperature of the ion exchange resin regeneration solution when regenerating the ion exchange resin.

In some embodiments, the ion exchange resin may be an anion exchange resin. In some embodiments, e.g., the anion exchange resin, may be a weak base anion exchange resin. The weak base anion exchange resin may be a macroporous sty renic matrix supporting amine, e.g., tertiary- amine, functionalities.

The disclosure contemplates all combinations of any one or more of the foregoing aspects and/or embodiments, as well as combinations with any one or more of the embodiments set forth in the detailed description and any examples.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in the various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

FIG. 1 illustrates a schematic of a water treatment system for the removal of PF AS, according to an embodiment.

FIGS. 2A-2D illustrate the removal of PFAS species using different concentrations of base-containing ion exchange resin regeneration solutions.

FIG. 3 illustrates the removal of PFAS species using a surfactant-containing ion exchange resin regeneration solution for varied periods of regeneration time.

FIG. 4 illustrates the removal of PFAS species using different concentrations of sodium hydroxide-containing ion exchange resin regeneration solutions.

FIG. 5 illustrates the removal of PFAS species using different concentrations of sodium hydroxide and surfactant-containing ion exchange resin regeneration solutions

FIG. 6 illustrates the removal of PFAS by ion exchange resin. In FIG. 6, Effluent 1 is the removal on the first service cycle, and Effluents 2 and 3 are removal by the regenerated resin.

FIG. 7 illustrates the regeneration efficiency of the ion exchange resin after two service cycles.

FIG. 8 illustrates a comparison of the removal of select PFAS species using regeneration solutions including a cationic surfactant and an anionic surfactant.

DETAILED DESCRIPTION

In accordance with one or more embodiments, provided are systems and methods for the removal of PFAS from water using ion exchange chemistry. In further embodiments, provided by this disclosure are systems and methods for the regeneration of spent ion exchange resin, e.g., ion exchange resin containing sorbed PFAS compounds, by contacting the spent ion exchange resin with an ion exchange resin regeneration solution having a chemi stry that increases the solubility and/or miscibility of PFAS with water to remove the sorbed PFAS from the ion exchange resin.

The hydrophobicity of fluorocarbons and extreme electronegativity of fluorine give these and similar compounds unusual properties. Initially, many of these compounds w ere used as gases in the fabrication of integrated circuits. The ozone layer destroying properties of these molecules restricted their use and ultimately resulted in international treaties and treatment methods to prevent their release into the atmosphere. But other PFAS such as fluoro-surfactants have become increasingly popular. PFAS for include may comprise organic compounds consisting of fluorine, carbon and heteroatoms such as oxygen, nitrogen and sulfur and may themselves be comprised of surfactant chemistries that create properties which may even provide for water solubility or micelle formation in a polar media such as water. Presently thousands of PF AS chemistries are commonly in use as surface treatment/coatings in consumer products such as carpets, upholstery, stain resistant apparel, cookware, paper, packaging, and the like, and may also be found in chemicals used for chemical plating, electrolytes, lubricants, and the like, which may eventually end up in the water supply. Further, PFAS have been utilized as key ingredients in aqueous film forming foams (AFFFs). AFFFs have been the product of choice for firefighting at military and municipal fire training sites around the world. AFFFs have also been used extensively at oil and gas refineries for both fire training and firefighting exercises. AFFFs work by blanketing spilled oil/fuel, cooling the surface, and preventing re-ignition. PFAS in AFFFs have contaminated the groundwater at many of these sites and refineries, including more than 100 U.S. Air Force sites.

Although used in relatively small amounts, these compounds are readily released into the environment where their extreme hydrophobicity as well as negligible rates of natural decomposition result in environmental persistence and bioaccumulation. It appears as if even low levels of bioaccumulation may lead to serious health consequences, even for long term exposure to contaminant concentrations in the part-per-trillion range. The environmental effects of these compounds on plants and microbes are as yet largely unknown. Nevertheless, serious efforts to limit the environmental release of PFAS are now commencing - not only by potential restrictions in use of PFAS, but also in rendering harmless any solids, liquids, and gases that are already contaminated with PFAS.

The U.S. Environmental Protection Agency (EP A) has issued a Contaminant Candidate List (CCL 5) which lists PFAS as a broad class inclusive of any PFAS that fits the revised CCL 5 structural definition of per- and polyfluoroalkyl substances (PFAS), namely chemicals that contain at least one of the following three genera of structures:

R-(CF2)-CF(R')R", where both the CF2 and CF moieties are saturated carbons, and none of the R groups can be hydrogen.

R-CF2OCF2-R', where both the CF2 moieties are saturated carbons, and none of the R groups can be hydrogen.

CF3C(CF3)RR', where all the carbons are saturated, and none of the R groups can be hydrogen. The EPA's Comptox Database includes a CCL 5 PF AS list of over 10,000 PFAS substances that meet the Final CCL 5 PFAS definition. The EPA has committed to being proactive as emerging PFAS contaminants or contaminant groups continue to be identified and the term PFAS as used herein is intended to be all inclusive in this regard. Typical PFAS include, but are not limited to, perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA). perfluorobutanesulfonic acid (PFBS), 4:2 fluorotelomer sulfonic acid (4:2 FTS), perfluorohexanoic acid (PFHxA), perfluoropentanesulfonic acid (PFPeS), perfluoroheptanoic acid (PFHpA), perfluorohexanesulfonic acid (PFHxS), 6:2 fluorotelomer sulfonic acid (6:2 FTS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonic acid (PFOS), and 8:2 fluorotelomer sulfonic acid (8:2 FTS).

It may be desirable to have flexibility in terms of what type of approach is used for treating water containing PFAS. For example, the source and/or constituents of the process water to be treated may be a relevant factor. The properties of PFAS compounds may vary widely. Various federal, state and/or municipal regulations may also be factors. The U.S. Environmental Protection Agency (EPA) developed revised guidelines in May 2016 of a combined lifetime exposure of 70 parts per trillion (PPT) for PFOS and PFOA. In June 2022, this EPA guidance was tightened to a recommendation of 0.004 ppt lifetime exposure for PFOA and 0.02 ppt lifetime exposure for PFOS. Federal, state, and/or private bodies may also issue relevant regulations. Market conditions may also be a controlling factor. These factors may be variable and therefore a preferred water treatment approach may change over time.

Use of various adsorption media is one technique for treating water containing PFAS. Activated carbon and ion exchange resin are both examples of adsorption media that may be used to capture PFAS from water to be treated. Other adsorption media may also be implemented. Such techniques may be used alone or in conjunction.

Conventional activated carbon adsorption systems and methods to remove PFAS from water have shown to be effective on the longer alky l chain PFAS but have reduced bed lives when treating shorter alkyl chain compounds. Activated carbon treated with a surfactant can have increased bed life. Some conventional anion selective exchange resins have shown to be effective on the longer alkyl chain PFAS but have reduced bed lives when treating shorter alkyl chain compounds.

Membrane processes such as nanofiltration and reverse osmosis have been used for PFAS removal. Normal oxidative processes have heretofore been unsuccessful in oxidizing PFAS. Even ozone has been reported to be an ineffective oxidant. There have been reports of PF AS moieties being destroyed by combined oxidative technologies such as ozone plus UV or use of specialized anodes to selectively oxidize PFAS. Such techniques may be used in conjunction with the various embodiments disclosed herein.

In accordance with one or more embodiments, there is provided systems and methods of treating water containing PFAS. The water may contain at least 10 ppt PFAS, for example, at least 1 ppb PFAS. For example, the waste stream may contain at least 10 ppt - 1 ppb PFAS. at least 1 ppb - 10 ppm PFAS. at least 1 ppb - 10 ppb PFAS, at least 1 ppb - 1 ppm PFAS, or at least 1 ppm - 10 ppm PFAS.

In certain embodiments, the water to be treated may include PFAS wi th other organic contaminants. One issue with treating PFAS compounds in water is that the other organic contaminants compete with the various processes to remove PFAS. For example, if the level of PFAS is 80 ppb and the background total organic carbon (TOC) is 50 ppm, a conventional PFAS removal treatment, such as an activated carbon column, may exhaust very quickly. Thus, it may be important to remove TOC prior to treatment to remove PFAS.

Thus, in some embodiments, the systems and methods disclosed herein may be used to remove background TOC prior to treating the water for removal of PFAS. The methods may be useful for oxidizing target organic alkanes, alcohols, ketones, aldehydes, acids, or others in the water. In some embodiments, the water containing PFAS further may contain at least 1 ppm TOC. For example, the water containing PFAS may contain at least 1 ppm - 10 ppm TOC, at least 10 ppm - 50 ppm TOC, at least 50 ppm - 100 ppm TOC, or at least 100 ppm - 500 ppm TOC.

Ion exchange processes are used to remove undesired ions from water. A general ion exchange water treatment process includes the use of ion exchange, e.g., cation and anion, exchange resins. Ion exchange is the reversible interchange of ions between a solid, e.g., an ion exchange resin, and a liquid, e.g., water. Since ion exchange media act as “chemical sponges,” they are well suited for effective removal of contaminants from water and other liquids. Generally speaking, the ion exchange resin is contained in a treatment vessel through which the water to be treated is passed. As the water passes through and around the ion exchange resin, ions in the fluid to be processed are exchanged with ions found in the resin, thereby removing undesired ions from the fluid and exchanging them for less impactful ions, such as sodium ions, found in the resin. However, as ions are exchanged, the efficacy of the resin is reduced. Eventually, the resin becomes saturated with undesirable ions in which no further undesirable ions in the water to be treated can be exchanged for the less impactful ions found in the resin. Ion exchange resins may be regenerated by removing the undesirable ions from the resin and replacing these with the original ions on the resin, a process known as regeneration. During regeneration, a substance having a high concentration of the original ions found on the resin, such as a brine solution, is applied to the ion exchange resin.

Because this produces a new- balance of concentrations between the respective ions, the ion exchange resin now exchanges the undesirable ions captured during the service cycle for the less impactful ions applied during regeneration process. As a result of this process, the ability of the ion exchange resin to remove undesired ions from the water to be treated is restored. However, the regeneration process can be relatively lengthy, and during regeneration the treatment vessel being regenerated is off-line and is not treating water. Accordingly, it is desirable to utilize systems and methods that permit water treatment systems to be minimally impacted by the need to regenerate ion exchange resins.

Ion exchange resins come in many different forms and chemistries. Some ion exchange resins include a crosslinked polystyrene matrix. Ion exchange sites are introduced to the matrix after polymerization. The crosslinked polymer matrix ty pically has a relatively uniform distribution of ion exchange sites throughout the structure. Ion exchange resins may be anion exchange resins or cation exchange resins. Anion exchange resins have a positively charged matrix structure that attracts and adsorbs negatively charged ions or molecules. Anion exchange occurs when one anion in solution is taken up by the anion resin, while one anion in the anion resin is released to solution. Cation exchange resins have a negatively charged matrix structure that attracts and adsorbs positively charged ions or molecules. Cation exchange occurs when one cation in solution is taken up by the cation resin, while one cation in the cation resin is released to solution.

Anion exchange resins are an efficient class of sorbents for the removal of PF AS materials from water. They are divided into two main categories: strong base anion exchange resins and weak base anion exchange resins. The structural differences between the two classes of anion exchange resins define the ways they can be used as sorbents and the ways by which they can be regenerated. Strong base anion exchange resins, after being used for PF AS removal from water, can only be regenerated by the use of organic solvents, e.g., alcohols, e.g., methanol, ethanol, and/or isopropanol, that pose safety and environmental risks. In contrast, weak base anion exchange resins can be regenerated with aqueous alkali solutions, such as sodium hydroxide, which are more environmentally friendly and safer to handle for downstream processing.

Weak base anion exchange resins do not contain exchangeable ionic sites and function as acid adsorbers. These resins are capable of adsorbing strong acids with a high capacity and are readily regenerated with a caustic solution. They are particularly effective when used in combination with a strong base anion exchange resin because the combination provides an overall high operating capacity and regeneration efficiency. Weak base anion exchange resins are regenerated with the use of an aqueous solution of a strong inorganic base such as sodium hydroxide or a strong organic nitrogenous base, e.g., ammonium hydroxide or tetrabutylammonium hydroxide. While any inorganic base or organic base can be used to regenerate a weak base ion exchange resins that contain sorbed PF AS, strong bases are generally more efficient as disrupting the attractive static charge interactions between PF AS anion and the cationic sites of spent ion exchange resin, thus more effectively releasing from the PF AS from the spent ion exchange resin during regeneration. Weak base anion exchange resins are mostly of the macroporous styrenic type with high porosity and active sites for interaction with PF AS. Macroporous styrene resins can be functionalized with function groups that increase the affinity for or otherwise enhance sorption of PFAS compounds. For example, many commercial weak base anion exchange resins include amine functionalities, such as tertiary amines, for such a purpose. The amine functional group on the styrene ring should carry at least one hydrogen atom.

It is known that strong inorganic or organic bases can replace weak bases in their salt forms; an example of this is illustrated in Scheme 1. Use of a strong base, e.g., sodium hydroxide, as a regeneration solution for a spent weak base anion exchange resin containing sorbed PFAS will interrupt the ionic PFAS-N⁺ bond on the weak base anion exchange resin and give rise to a tertiary amine group on the styrene ring while releasing a PFAS-Na⁺ complex into the regeneration solution. The used regeneration solution contains an increased concentration of PFAS that can be disposed of at a later stage.

Scheme 1. Acid-base chemistry of a styrene-based weak base anion exchange resin. While the main chain of a styrene-based weak base anion exchange resin is hydrophobic by nature, the amine side chains, when protonated, are hydrophilic and have a larger exposure to water than the main chain. In general, resins, e.g., weak base anion exchange resins, are crosslinked and in the form of powder or beads.

One approach to increasing the effectiveness of an ion exchange resin regeneration solution is to incorporate a surfactant, e.g., a positively-charged surfactant or a negatively- charged surfactant, to promote direct interaction with the negative charge associated with PF AS. In some embodiments, the ion exchange resin regeneration solution may include with a surfactant, e.g., a positively-charged surfactant, nonionic surfactant, or a negatively -charged surfactant. In some embodiments, the surfactant may be approved for use in connection with consumable products such as drinking water. In some non-limiting embodiments, a positively charged surfactant may be a quaternary ammonium-based surfactant, e.g., N⁺(R)4, a quaternary⁷ phosphonium-based surfactant, e.g., P⁺(R)4, a tertiary⁷ sulfonium-based surfactant, e.g., S (R)w or a tertiary oxonium-based surfactant, e.g., O (R)v in any of these surfactants. R can be any alkyl group, e.g., any C1-C20 alkyl group either unsubstituted, e.g.. saturated or unsaturated, or be substituted with one or more heteroatoms, e.g., N, O, P, or S. For example, the positively-charged surfactant can be a quaternary ammonium-based surfactant having 1-4 alkyl groups on the quaternary⁷ nitrogen. The 1-4 alky l groups on the quaternary nitrogen can be any C1-C20 alkyl group, e.g.. any C8-C20 alkyl group. The alkyl groups on the quaternary⁷ nitrogen can be further be unsubstituted, e.g., saturated or unsaturated, or be substituted with one or more heteroatoms, e.g., N, O, P, or S. In some specific non-limiting embodiments, the positively charged surfactant in the ion exchange resin regeneration solution may be cetyltrimethylammonium chloride (CTAC). In some nonlimiting embodiments, the surfactant is a negatively-charged surfactant. For example, the negatively -charged surfactant can be a sulfate surfactant. Sulfate surfactants can one or more alkyl groups on the sulfate ion. In some embodiments, the negatively-charged surfactant is sodium dodecyl sulfate (SDS).

The use of surfactants, e.g., a positively-charged surfactants, nonionic surfactant, or a negatively-charged surfactants, in the ion exchange resin regeneration solution can play a synergistic role, optionally along with the presence of heat, to increase the number of interactions between the functional site on the ion exchange resin with the base. Without wishing to be bound by any particular theory, the surfactant can increase solubility of PF AS in the ion exchange resin regeneration solution, thus increasing the efficiency of removal from the ion exchange resin.

In some embodiments, a concentration of the surfactant, e.g., a positively-charged surfactant, nonionic surfactant, or a negatively-charged surfactant, in the ion exchange resin regeneration solution is above the critical micelle concentration (CMC) of the surfactant, e.g., a positively-charged surfactant, nonionic surfactant, or a negatively-charged surfactant. As used herein, the CMC of a surfactant is the concentration of a surfactant in a bulk phase above which aggregates of surfactant molecules, so-called micelles, start to form. For use in regenerating an ion exchange resin having sorbed PF AS, the formation of micelles in solution acts to ‘‘strip'’ the ion exchange resin of the PFAS by forming micelles around the PF AS molecules and increasing the solubility of PFAS in water, thus overcoming the hydrophobicity of the resin core. The formation of micelles of surfactant with the PFAS allows the ion exchange resin regeneration solution to contact all or substantially all active sites of the resin for functional group regeneration at a quantitative level. As a particular non-limiting example, surfactants including tetraalkylammonium salts have shown utility' as phase transfer catalysts in biphasic systems. Given the hydrophobicity of main chains of PFAS materials is evident that the compatibility' of tetraalkylammonium cation as a counterion for the PFAS anion will facilitate the transfer of PFAS into the water stream and its elution from the resin core or shell.

In accordance with one or more aspects, there is provided a water treatment system for removing PFAS. The water treatment system include a PFAS separation stage and an ion exchange resin regeneration stage. The PFAS separation stage includes a vessel having an inlet, an outlet, and ion exchange resin having an affinity⁷ for PFAS positioned within the vessel. The inlet of the vessel is connectable to a source of contaminated water comprising a first concentration of PFAS. The ion exchange resin regeneration stage includes a source of an ion exchange resin regeneration solution including a surfactant, e.g., a positively-charged surfactant, a nonionic surfactant, or a negatively-charged surfactant. The ion exchange resin regeneration stage configured to dose spent ion exchange resin with a volume of the ion exchange resin regeneration solution to remove PFAS from the spent ion exchange resin creating a PFAS concentrate and a regenerated ion exchange resin.

FIG. 1 presents a schematic of a w ater treatment system 100 in accordance with one or more embodiments. A source of contaminated water 110 containing a first concentration of PFAS is introduced to a PFAS separation stage that includes vessel 120a having an ion exchange resin having an affinity for PFAS 122 positioned within for treatment. Various pre- treatment and/or post-treatment unit operations may also be integrated into system 100. Product stream 130, which after treatment in vessel 120 has a second PFAS concentration that is lower than the first PFAS concentration, may be directed to a further unit operation for additional treatment, sent to a point of use, or otherwise discharged. Sensor 140 may measure a level of PFAS downstream vessel 120a. A controller 150 may receive input from sensor 140 in order to monitor PFAS levels, intermittently or continuously. The controller 150 may monitor for any identifiable breakthrough presence of PFAS in product stream 130. Monitoring may be in real-time or with lag, either onsite or remotely. For example, detecting an identifiable PFAS level may be indicative that a threshold or target level is approaching, indicating a loss of performance of the ion exchange resin 122 in vessel 120a. In some embodiments, the controller 150 may predict how many bed volumes remain before a predetermined PFAS breakthrough level is reached. A detected PFAS level may be compared to a threshold breakthrough level that may be considered unacceptable, such as may be dictated by a controlling regulatory body. Maintenance decisions may be made based on such comparison. Various operational parameters including input PFAS concentration, flow rate, media volume, and residence time may also be factored into the determination by the controller 150. Vessel 120a may be taken offline for preventative maintenance, such as ion exchange resin regeneration, in response to a predicted PFAS breakthrough. A source of ion exchange resin regeneration solution 120b fluidly coupled to vessel 120a is used to dose spent ion exchange resin with a volume of the ion exchange resin regeneration solution to remove PFAS from the spent ion exchange resin creating a PFAS concentrate and a regenerated ion exchange resin. Valve 160 between the vessel 120a and source of ion exchange resin regeneration solution 120b may be in communication with controller 150 to strategically direct the dosing of ion exchange resin regeneration solution to the vessel 120a and direct the regeneration process, such as how long the ion exchange resin regeneration solution is mixed with the spent ion exchange resin the temperature of the ion exchange resin regeneration solution. The ion exchange resin regeneration stage is further configured to separate the PFAS concentrate from the regenerated ion exchange resin, such as by removal of the PFAS concentrate from the vessel 120a and the addition of flushing or rinse water to remove any remaining PFAS concentrate from the vessel 120a via waste outlet 120c.

With continued reference to FIG. 1, the system 100 includes an optional PFAS concentration stage 170 having an inlet fluidly connected to a w aste outlet 120c of the vessel 120a; the dashed line box around select components in FIG. 1 indicates that the component(s) is/are optional. The PFAS concentration stage 170 is constructed and arranged to increase a PF AS concentration of the PFAS concentrate to a third PF AS concentration greater than the first PFAS concentration. The PFAS concentration stage 170 can be any suitable separation technology, such as electrolytic separation or a membrane separation technique, e.g., nanofiltration, that produces a treated water stream and a concentrated stream. The treated water stream from the PFAS concentration stage 170 can be used for any suitable purpose. The concentrated stream from PFAS concentration stage 170 having the third PFAS concentration can be directed to an optional PFAS destruction stage 180 having an inlet fluidly connectable to an outlet of the PFAS concentration stage 170. The PFAS destruction stage 180 can be any suitable PFAS destruction technique, including one or more of electrochemical destruction, photochemical destruction, plasma destruction, and supercritical CO2 destruction. This disclosure is in no way limited by the choice of downstream processing, e.g., PFAS concentration stage and/or PFAS destruction stage, of the PFAS concentrate resulting from the regeneration of the ion exchange resin. The system 100 can also include an optional PFAS polisher 190 that can be used to further treat the treated water stream 130 in the event that the treated water stream 130 does not meet one or more PFAS concentration requirements, such as a regulatory standard. The PFAS polisher 190 can be any suitable water treatment technique, including electrochemical separation, membrane separation, or an oxidative treatment process.

In accordance with one or more embodiments, a controller which is monitoring PFAS breakthrough levels may be in communication with a service provider, such as to schedule system maintenance, ion exchange resin replacement, and/or ion exchange resin regeneration.

In accordance with at least some embodiments, a controller may collect and/or report data pertaining to PFAS levels associated with a water treatment system. This data may be input to a service network.

In accordance with one or more aspects, there is provided a method of treating water containing PFAS. The method may include determining a concentration of PFAS in the water containing PFAS to be treated. The method may include introducing the water containing PFAS to a vessel having an ion exchange resin having an affinity for PFAS positioned within to promote removal of the PFAS and produce a product stream. The product stream may be treated water having a lower PFAS concentration than the water to be treated. The method further may include monitoring a PFAS breakthrough level of the product stream. The method additionally may include regenerating spent ion exchange resin using an ion exchange resin regeneration solution including a surfactant, e.g., a positively- charged surfactant, nonionic surfactant, or a negatively -charged surfactant. The ion exchange resin regeneration solution may be dosed at a volume sufficient to remove PF AS from the spent ion exchange resin when the PF AS breakthrough level exceeds a predetermined threshold PFAS concentration.

In some embodiments, the PFAS may include one or more of perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorobutanesulfonic acid (PFBS), 4:2 fluorotelomer sulfonic acid (4:2 FTS), perfluorohexanoic acid (PFHxA), perfluoropentanesulfonic acid (PFPeS), perfluoroheptanoic acid (PFHpA), perfluorohexanesulfonic acid (PFHxS), 6:2 fluorotelomer sulfonic acid (6:2 FTS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonic acid (PFOS), and 8:2 fluorotelomer sulfonic acid (8:2 FTS).

In some embodiments, the ion exchange resin may be an anion exchange resin. In some embodiments, e.g., the anion exchange resin, may be a weak base anion exchange resin. The weak base anion exchange resin may be a macroporous styrenic matrix supporting amine, e.g., tertiary amine, functionalities.

In some embodiments, the surfactant may be a positively-charged surfactant. In some embodiments, the positively-charged surfactant may be a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary sulfonium-based surfactant, or a tertiary' oxonium-based surfactant. In certain embodiments, the positively-charged surfactant may be a quaternary ammonium-based surfactant. The quaternary ammonium- based surfactant may be an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen. For example, the 1-4 alkyl groups may include C1-C20 alkyl chains that are unsubstituted or substituted with one or more heteroatoms. In specific embodiments, the quaternary ammonium-based surfactant may be CTAC. In some embodiments, the surfactant may be a negatively-charged surfactant. In some embodiments, the negatively-charged surfactant may be a sulfate surfactant. In some embodiments, the sulfate surfactant may include one or more alky l groups on the sulfate ion. In some embodiments, the negatively- charged surfactant may be sodium dodecyl sulfate (SDS).

In some embodiments, a concentration of the surfactant, e.g., a positively-charged surfactant, nonionic surfactant, or a negatively-charged surfactant, in the ion exchange resin regeneration solution may be above the critical micelle concentration (CMC) of the surfactant, e.g., a positively-charged surfactant, nonionic surfactant, or a negatively-charged surfactant. For example, when the surfactant is a positively-charged surfactant, the positively-charged surfactant may be a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary sulfonium-based surfactant, or a tertiary' oxonium- based surfactant, e.g., an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen. The 1-4 alkyl groups, e.g.. one or more C1-C20 groups, e.g., one or more C8-C20 alkyl groups, may be used to increase solubility with the PFAS sorbed to the ion exchange resin to enhance or improve regeneration of the ion exchange resin.

In some embodiments, the predetermined threshold PFAS concentration may be 1 ng/L.

In accordance with one or more aspects, there is provided a method of facilitating regeneration of a spent ion exchange resin containing PFAS. The method may include providing an ion exchange resin regeneration solution capable of removing PFAS from the spent ion exchange resin. The provided ion exchange resin regeneration solution may include a surfactant, e.g.. a positively-charged surfactant, nonionic surfactant, or a negatively -charged surfactant. The method may include providing instructions for dosing the spent ion exchange resin with a volume of the ion exchange resin regeneration solution sufficient to remove PFAS from the spent ion exchange resin creating a PFAS concentrate and a regenerated ion exchange resin. The method further may include providing instructions for disposal of the PFAS concentrate.

In some embodiments, the surfactant may be a positively-charged surfactant. In some embodiments, the positively-charged surfactant may be a quaternary ammonium-based surfactant, a quaternary' phosphonium-based surfactant, a tertiary sulfonium-based surfactant, or a tertiary’ oxonium-based surfactant. In certain embodiments, the positively-charged surfactant may be a quaternary ammonium-based surfactant. The quaternary ammonium- based surfactant may be an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen. For example, the 1-4 alkyl groups may include C1-C20 alkyl chains that are unsubstituted or substituted with one or more heteroatoms. In specific embodiments, the quaternary ammonium-based surfactant may be CTAC. In some embodiments, the surfactant may be a negatively-charged surfactant. In some embodiments, the negatively-charged surfactant may be a sulfate surfactant. In some embodiments, the sulfate surfactant may include one or more alkyl groups on the sulfate ion. In some embodiments, the negatively- charged surfactant may be sodium dodecyl sulfate (SDS).

In some embodiments, a concentration of the surfactant, e.g., a positively-charged surfactant, nonionic surfactant, or a negatively-charged surfactant, in the ion exchange resin regeneration solution may be above the critical micelle concentration (CMC) of the surfactant, e.g., a positively-charged surfactant, nonionic surfactant, or a negatively-charged surfactant. For example, when the surfactant is a positively-charged surfactant, the positively-charged surfactant may be a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertian- sulfonium-based surfactant, or a tertian- oxonium- based surfactant, e.g., an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen. The 1-4 alkyl groups, e g., one or more C1-C20 groups, e g., one or more C8-C20 alkyl groups, may be used to increase solubility with the PF AS sorbed to the ion exchange resin to enhance or improve regeneration of the ion exchange resin.

In some embodiments, the ion exchange resin may be an anion exchange resin. In some embodiments, e.g., the anion exchange resin, may be a weak base anion exchange resin. The weak base anion exchange resin may be a macroporous styrenic matrix supporting amine, e.g., tertiary- amine, functionalities.

EXAMPLES

The function and advantages of these and other embodiments can be better understood from the following examples. These examples are intended to be illustrative in nature and are not considered to be in any way limiting the scope of the invention. Example 1 - Composition and Concentration of Regeneration Solution

In this example, the effects of regeneration solution composition and component concentration on PF AS removal from an ion exchange resin were explored. In order to identify the proper regenerant for regeneration of an ion exchange resin, a number of organic and inorganic bases and cationic surfactants were evaluated. The experiments were carried out in a batch mode to facilitate the identification of the best regeneration solution composition for regenerating the PFAS loaded resin regeneration.

A weak base ion exchange resin, Lewatit MP62 (Aldrich, 62088-500G) in neutral form was first quatemized to be converted to its active form. Before quatemization, this weak base anion exchange resin had only ternary amine groups. When fully quatemized, this weak base anion exchange resin was capable of ion exchange. Quatemizing was performed by stirring the weak base resin into solution of HC1. Specifically, under stirring, 10 g of the weak base ion exchange resin was combined with 250 rnL of 1 M HC1. The weak base ion exchange resin was stirred overnight in order to ensure its complete conversion to the quaternary form. The next day, the pH of the stirring mixture was measured to ensure was still acidic, specifically below pH=4-5. The now activated weak base ion exchange resin was filtered under vacuum suction and isolated.

Next, the weak base ion exchange resin was loaded with PFAS by stirring it overnight in 2 L of a ground water sample that was contaminated with PFAS. During stirring the w eak base ion exchange resin into the contaminated water sample, the pH of the system was maintained acidic at pH=4.5-5.5. Following stirring with the contaminated water sample, the weak base ion exchange resin was isolated by suction filtration and left pumping under vacuum to remove as much water from the resin as possible. The PFAS loading of the resin was determined by analyzing the PFAS contaminants in the original water sample and measuring the PFAS contaminants in the now treated water sample after filtration and removal of the resin.

Aqueous solutions of four compositions to be used as weak base ion exchange resin regenerant solutions were prepared to test the efficacy of each for PFAS removal from the weak base ion exchange resin. The test regeneration solutions included: tetrabutylammonium hydroxide (N(CHsCH2CH2)4OH); ammonium hydroxide (NH4OH); sodium hydroxide (NaOH); and a mixture of NaOH and cetytrimethylammonium chloride (CTAC). Four different concentrations were run for each base as well as the combination of NaOH and CTAC: 0.10 M, 0.25 M, 0.50 M and 1.0 M. In the combination of NaOH and CTAC, the CTAC concentration was held constant at 0.25% w/v at every NaOH concentration and minimal direct interactions between the CTAC and the weak base anion exchange resin were expected as both are cationic. The volume of each test regeneration solution used to regenerate the weak base ion exchange resin was 100 mL.

The results for PF AS removal, expressed as a percentage from the known staring concentration of PF AS, from the weak base anion exchange resin across the range of regenerant solution concentrations and compositions are illustrated in FIGS. 2A-2D. The PF AS sample included a number of interrelated PF AS species, including perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorobutanesulfonic acid (PFBS), 4:2 fluorotelomer sulfonic acid (4:2 FTS), perfluorohexanoic acid (PFHxA), perfluoropentanesulfonic acid (PFPeS), perfluoroheptanoic acid (PFHpA), perfluorohexanesulfonic acid (PFHxS), 6:2 fluorotelomer sulfonic acid (6:2 FTS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonic acid (PFOS), and 8:2 fluorotelomer sulfonic acid (8:2 FTS). As illustrated, the most efficient regenerant for the removal of all PFAS compounds was the combination of NaOH and CTAC. As further illustrated, the three standalone bases, when used alone, had similar PFAS removal performance, and were particularly inefficient in removing the long alkyl chain PFAS compounds, i.e., PFHpS, PFOA PFNA, and PFOS. The three standalone bases showed higher efficiency for removing shorter alkyd chain PFAS compounds such as PFBA and PFBS but were on the whole less effective than the combination of NaOH and CTAC across all tested regenerant solution concentrations.

Having identified the combination NaOH and CTAC as an effective weak base anion exchange resin regeneration solution, the effects of CTAC concentration (in % w/v) and contact time with the PFAS -containing weak base anion exchange resin were explored. In this experiment, regeneration solutions containing 0. 15%. 0.25% and 0.35% w/v of CTAC in NaOH were mixed with PFAS-containing weak base anion exchange resin (Lewatit MP62 as described above) for 30, 60, and 120 minutes at a regeneration solution temperature of 60-65 °C. Also tested in this experiment was a regeneration solution containing 1 M NaOH and 46 mg of sodium chloride (NaCl). The salt was used to as a test to see if the addition of salt would cause the PFAS to be removed from the ion exchange resin. The results of this experiment are illustrated in FIG. 3. As illustrated, the combination of NaOH and CTAC demonstrated high efficiency for the removal of the long alkyd chain PFAS compounds relative to the shorter alkyl chain PFAS compounds. Of the three concentrations of CTAC studied, i.e., 0. 15%, 0.25%, and 0.35% w/v, 0.25% v/v CTAC in NaOH demonstrated the highest overall PFAS removal efficiency. The observed efficiency in PFAS removal at this concentration is consistent with expectations as this concentration is greater than the critical micelle concentration (CMC) of CT AC, which is 0. 1% w/v. It was believed that the formation and presence of CTAC micelles solubilized the PFAS compounds in the water which increased the removal efficiency from the weak base anion exchange resin. It was also observed that the regeneration solution containing 46 mg of NaCl was ineffective at removing PFAS from the ion exchange resin. It should be noted that 46 mg/L NaCl provided the same chloride concentration of 0.25% CTAC. These results demonstrate the cetyltrimethylammonium cation is the effective component of CTAC instead of chloride.

Example 2 - Effects of Base Concentration on PFAS Removal

In this example, the effects of base concentration on PFAS removal from an ion exchange resin were explored. As described herein, the combination of NaOH and CTAC showed the highest efficiency for PFAS removal across all metrics discussed in Example 1. This example evaluates NaOH concentration with a fixed amount of CTAC above the critical micelle concentration on the removal of PFAS from a weak base anion exchange resin. The experiments were carried out in a batch mode to identify the concentration of NaOH that, when paired with CTAC, provides the most efficient and effective removal of PFAS from a weak base anion exchange resin.

A weak base ion exchange resin, Lewatit MP62 (Aldrich, &62088-500G) in neutral form was first quatemized to be converted to its active form. Quatemizing was performed by stirring the w eak base resin into solution of HC1. Specifically, under stirring, 10 g of the weak base ion exchange resin was combined with 250 mL of 1 M HC1. The weak base ion exchange resin was stirred overnight in order to ensure its complete conversion to the quaternary form. The next day, the pH of the stirring mixture was measured to ensure the mixture was still acidic, specifically below pH=4-5. The weak base ion exchange resin was filtered under vacuum suction and isolated.

Next, the weak base ion exchange resin was loaded with PFAS by stirring it overnight in 2 L of a ground water sample that w as contaminated with PFAS. During stirring the weak base ion exchange resin into the contaminated water sample, the pH of the system was maintained acidic at pH=4.5-5.5. Following stirring with the contaminated water sample, the weak base ion exchange resin was isolated by suction filtration and left pumping under vacuum to remove as much water from the resin as possible. The PFAS loading of the resin was determined by analyzing the PFAS contaminants in the original water sample and measuring the PF AS contaminants in the now treated water sample after filtration and removal of the resin.

Selected results of PFAS removal as a function of base concentration are presented in FIGS. 4 and 5. FIG. 4 illustrates the efficiency of PFAS removal using various concentrations of NaOH as the regenerant solution and FIG. 5 illustrates the efficiency of PFAS removal using various concentrations of NaOH with a fixed amount of 0.2% w/v CTAC as the regenerant solution. As illustrated in FIG. 3, use of only NaOH as the regenerant solution was effective at removing smaller alkyl chain PFAS compounds such as PFBA, PFBS, 4:2 FTS, PFPeA, and PFHxA from the weak base anion exchange resin across all concentrations of NaOH but was less effective for removing long alkyl chain PFAS compounds. When the 0.2% w/v CTAC was added to the NaOH. as illustrated in FIG. 5, the removal of all PFAS compounds was highly efficient at all NaOH concentrations.

Rapid small-scale column tests (RSSCTs) w ere performed to monitor resin performance over several service/regeneration cycles, with the results illustrated in FIGS. 6 and 7. FIG. 6 illustrates PFAS breakthrough concentration curves for the initial service cycle (Influent 1 and Effluent 1) and two service cycles (Influent 2/3 and Effluent 2/3) following regeneration of the weak base anion exchange resin in the column with a regenerant solution including NaOH and CTAC. The RSSCT setup mimics a full treatment-scale platform using scaled down parameters such that performance of a full setup can be evaluated on the timescale of approximately one week. As illustrated in FIG. 6, the effluent curves indicated that PFAS removal performance was similar for the initial resin and following two regeneration cycles with a clear trend of earlier breakthrough following regeneration. FIG. 7 illustrates the mass balance for the PFAS removed by regeneration v. amount loaded for the two resin regeneration cycles. The first regeneration cycle did not have 100% removal of all PFAS compounds. Long-chain PFAS compounds were not removed efficiently. The second regeneration cycle had a better mass balance for PFAS removal under the same separation conditions as the first regeneration. It can be seen from FIG. 6 that after each service cycle, the efficiency of PFAS removal decreased and this was attributed to the lower solubility of the PFAS compounds in water. The lower solubility of the PFAS compounds in water was attributed to the gradual increase in concentration or the chemical equilibrium of the regenerant solution shifting tow ards the resin. It is knowor that high solute concentrations and equilibria phenomena can prevent quantitative resin regeneration. In addition to equilibrium constraints, chemisorption of contaminant species can interfere with resin regeneration. If a contaminant in the w ater to be treated reacts with a functional group on the resin, the contaminant can become chemically bonded to the sorbent, effectively reducing the sorption capacity of the sorbent permanently.

Example 3 - Comparison of PFAS Removal with Cationic and Anionic Surfactants

In this example, the effects of base concentration on PFAS removal from an ion exchange resin were explored. As described herein, the combination of NaOH and a cationic surfactant (CT AC) showed efficiency for PFAS removal across all metrics discussed in Example 1. This example evaluates an anionic surfactant, SDS, for removal of PFAS from a weak base anion exchange resin compared to the performance of the cationic surfactant.

The experiment was performed in accordance with Examples 1 and 2. Table 1 below provides the experimental conditions of this resin regeneration experiment.

Table 1. Experimental conditions for resin regeneration solutions

FIG. 8 illustrates the results of the regeneration experiment for selected PFAS species. In the experiments where the 0.25 g of the surfactant was used in the resign regeneration solution, first and second extractions were performed to explore a mass dependence on removal efficiency, i.e., surfactant consumption. The results in FIG. 8 showed that both cationic surfactants and anionic surfactants can be used for PFAS extraction from the resin when incorporated into a resin regeneration solution, with CT AC and SDS displaying comparable removal performance. It was observed that in some circumstances, SDS outperformed CTAC for PFAS removal. This disparity between SDS and CTAC was rationalized by comparing the structural characteristics each surfactant, i.e., the lipophilic and hydrophilic portions of the molecule, and their molar ratios in the resin regeneration solution. The phraseology and terminology' used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term "‘plurality” refers to two or more items or components. The terms “comprising,” “including,” “carrying,” “having,” “containing,” and “involving,” whether in the written description or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to.” Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Only the transitional phrases “consisting of ^? and “consisting essentially of,” are closed or semi-closed transitional phrases, respectively, with respect to the claims. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Having thus described several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Any feature described in any embodiment may be included in or substituted for any feature of any other embodiment. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be w ithin the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

Those skilled in the art should appreciate that the parameters and configurations described herein are exemplary and that actual parameters and/or configurations will depend on the specific application in which the disclosed methods and materials are used. Those skilled in the art should also recognize or be able to ascertain, using no more than routine experimentation, equivalents to the specific embodiments disclosed.

What is claimed is:

Claims

1. A water treatment system for removing perfluoroalkyl and/or polyfluoroalkyl substances (PF AS), comprising: a PF AS separation stage comprising: a vessel comprising an inlet, a first outlet, and ion exchange resin having an affinity for PF AS positioned within the vessel, the inlet of the vessel connectable to a source of contaminated water comprising a first concentration of PFAS, and an ion exchange resin regeneration stage comprising a source of an ion exchange resin regeneration solution comprising a surfactant, the ion exchange resin regeneration stage configured to dose spent ion exchange resin with a volume of the ion exchange resin regeneration solution to remove PFAS from the spent ion exchange resin creating a PFAS concentrate and a regenerated ion exchange resin.

2. The system of claim 1, wherein the ion exchange resin regeneration stage is further configured to separate the PFAS concentrate from the regenerated ion exchange resin.

3. The system of claim 1, w herein the vessel discharges from the first outlet of the vessel a treated water having a second PFAS concentration lower than the first PFAS concentration.

4. The system of claim 1 , further comprising a control system constructed and arranged to regulate a feed of contaminated water into the PFAS separation stage and to regulate a volume of ion exchange resin regeneration solution for dosing the spent ion exchange resin.

5. The system of claim 1, wherein the surfactant is a positively -charged surfactant, a nonionic surfactant, or a negatively -charged surfactant.

6. The system of claim 5, wherein the positively-charged surfactant is a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertian’ sulfonium-based surfactant, or a tertiary oxonium-based surfactant.

7. The system of claim 6, wherein the positively-charged surfactant is a quaternary ammonium-based surfactant.

8. The system of claim 7, wherein the quaternary' ammonium-based surfactant is an ammonium-based surfactant comprising 1-4 alkyl groups on the quaternary nitrogen.

9. The system of claim 8, wherein the quaternary ammonium-based surfactant is cetyltrimethylammonium chloride (CTAC).

10. The system of claim 1. wherein a concentration of the positively-charged surfactant in the ion exchange resin regeneration solution is above the critical micelle concentration (CMC) of the positively-charged surfactant.

11. The system of claim 10, wherein the positively-charged surfactant is a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary' sulfonium-based surfactant, or a tertiary' oxonium-based surfactant.

12. The system of claim 11, wherein the positively-charged surfactant comprises one or more alkyl groups to increase solubility with the PFAS sorbed to the ion exchange resin.

13. The system of claim 12, wherein the positively-charged surfactant comprises one or more one or more C8-C20 alkyl groups.

14. The system of claim 5, wherein the negatively-charged surfactant is a sulfate surfactant.

15. The system of claim 14, wherein the sulfate surfactant comprises one or more alkyl groups on the sulfate ion.

16. The system of claim 15, wherein the sulfate surfactant is sodium dodecyl sulfate (SDS).

17. The system of claim 1, wherein the ion exchange resin regeneration solution further comprises a base.

18. The system of claim 17, wherein the base is one or more of NaOH, NH4OH and N(CH₂CH₂CH3)4OH.

19. The system of claim 1, wherein the ion exchange resin comprises an anion exchange resin.

20. The system of claim 19, wherein the ion exchange resin comprises a weak base anion exchange resin.

21. The system of claim 20, wherein the weak base anion exchange resin comprises a macroporous styrenic matrix supporting amine functionalities.

22. The system of claim 1, further comprising a PF AS concentration stage having an inlet fluidly connected to a second outlet of the vessel and constructed and arranged to increase a PF AS concentration of the PFAS concentrate to a third PF AS concentration greater than the first PFAS concentration.

23. The system of claim 22, further comprising a PFAS destruction stage having an inlet fluidly connectable to an outlet of the PFAS concentration stage.

24. The system of claim 23, wherein the PFAS destruction stage comprises one or more of electrochemical destruction, photochemical destruction, plasma destruction, and supercritical CO2 destruction.

25. The system of claim 1, further comprising a PFAS polisher having an inlet fluidly connectable to the first outlet of the vessel.

26. A method of treating water containing perfluoroalkyl and/or polyfluoroalkyl substances (PFAS), comprising: determining a concentration of PFAS in the water containing PFAS to be treated; introducing the water containing PFAS to a vessel comprising an ion exchange resin having an affinity for PFAS to promote removal of the PFAS and produce a product stream comprising treated water having a lower PFAS concentration than the water to be treated; monitoring a PFAS breakthrough level of the product stream; and regenerating spent ion exchange resin using an ion exchange resin regeneration solution comprising a surfactant dosed at a volume sufficient to remove PFAS from the spent ion exchange resin when the PF AS breakthrough level exceeds a predetermined threshold PF AS concentration.

27. The method of claim 26, wherein the PFASs comprise one or more of perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorobutanesulfonic acid (PFBS), 4:2 fluorotelomer sulfonic acid (4:2 FTS), perfluorohexanoic acid (PFHxA), perfluoropentanesulfonic acid (PFPeS), perfluoroheptanoic acid (PFHpA), perfluorohexanesulfonic acid (PFHxS), 6:2 fluorotelomer sulfonic acid (6:2 FTS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonic acid (PFOS), and 8:2 fluorotelomer sulfonic acid (8:2 FTS).

28. The method of claim 27, wherein the ion exchange resin comprises an anion exchange resin.

29. The method of claim 28, wherein the ion exchange resin comprises a weak base anion exchange resin.

30. The method of claim 29, wherein the weak base anion exchange resin comprises a macroporous styrenic matrix supporting amine functionalities.

31. The method of claim 26, wherein the surfactant is a positively-charged surfactant, a nonionic surfactant, or a negatively -charged surfactant.

32. The method of claim 31, wherein the positively-charged surfactant is a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary sulfonium-based surfactant, or a tertiary oxonium-based surfactant.

33. The method of claim 32, wherein the positively -charged surfactant is a quaternary ammonium-based surfactant.

34. The method of claim 33, wherein the quaternary ammonium-based surfactant is an ammonium-based surfactant comprising 1-4 alky l groups on the quaternary nitrogen.

35. The method of claim 34, wherein the quaternary ammonium-based surfactant is cetyltrimethylammonium chloride (CTAC).

36. The method of claim 31, wherein the negatively-charged surfactant is a sulfate surfactant.

37. The method of claim 36, wherein the sulfate surfactant comprises one or more alkyl groups on the sulfate ion.

38. The method of claim 37, wherein the sulfate surfactant is sodium dodecyl sulfate (SDS).

39. The method of claim 26, wherein the surfactant is present in the ion exchange resin regeneration solution at a concentration greater than the critical micelle concentration of the surfactant.

40. The method of claim 39, wherein the surfactant is a positively charged surfactant comprising one or more of a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary sulfonium-based surfactant, or a tertiary' oxonium- based surfactant.

41. The method of claim 40. wherein the positively-charged surfactant comprises one or more alkyl groups to increase solubility with the PFAS sorbed to the ion exchange resin.

42. The method of claim 41, wherein the positively-charged surfactant comprises one or more one or more C8-C20 alkyl groups.

43. The method of claim 26, wherein the ion exchange resin regeneration solution further comprises a base.

44. The method of claim 43. wherein the base is one or more of NaOH. NH4OH and N(CH2CH₂CH₃)₄OH.

45. The method of claim 26, wherein the predetermined threshold PFAS concentration is 1 ng/L.

46. The method of claim 26, wherein regenerating the spent ion exchange resin comprises mixing the ion exchange resin and the ion exchange resin regeneration solution to create a PF AS concentrate and a regenerated ion exchange resin.

47. The method of claim 46, further comprising introducing the PF AS concentrate into a PF AS concentration stage to increase a PFAS concentration of the PF AS concentrate to a concentration greater than the PFAS concentrate prior to concentration.

48. The method of claim 47, further comprising introducing an effluent of the PFAS concentration stage to a PFAS destruction stage to destroy the PFAS in the effluent of the PFAS concentration stage.

49. The method of claim 48, wherein the PFAS destruction stage comprises one or more of electrochemical destruction, photochemical destruction, plasma destruction, and supercritical CO2 destruction.

50. A method of facilitating regeneration of a spent ion exchange resin containing perfluoroalkyl and/or polyfluoroalkyl substances (PFAS), comprising: providing an ion exchange resin regeneration solution capable of removing PFAS from the spent ion exchange resin, the ion exchange resin regeneration solution comprising a surfactant; providing instructions for dosing the spent ion exchange resin with a volume of the ion exchange resin regeneration solution sufficient to remove PFAS from the spent ion exchange resin creating a PFAS concentrate and a regenerated ion exchange resin; and providing instructions for disposal of the PFAS concentrate.

51. The method of claim 50, wherein the surfactant is a positively-charged surfactant, a nonionic surfactant, or a negatively-charged surfactant.

52. The method of claim 51, wherein the positively-charged surfactant is a quaternary ammonium-based surfactant, a quaternary phosphonium-based surfactant, a tertiary sulfonium-based surfactant, or a tertiary oxonium-based surfactant.

53. The method of claim 52, wherein the positively-charged surfactant is a quaternary' ammonium-based surfactant.

54. The method of claim 53, wherein the quaternary' ammonium-based surfactant is an ammonium-based surfactant comprising 1-4 alky l groups on the quaternary nitrogen.

55. The method of claim 54. wherein the quaternary ammonium-based surfactant is cetyltrimethylammonium chloride (CT AC).

56. The method of claim 51, wherein the negatively -charged surfactant is a sulfate surfactant.

57. The method of claim 56, wherein the sulfate surfactant comprises one or more alkyl groups on the sulfate ion.

58. The method of claim 57, wherein the sulfate surfactant is sodium dodecyl sulfate (SDS).

59. The method of claim 51, wherein a concentration of the positively-charged surfactant in the ion exchange resin regeneration solution is above the critical micelle concentration (CMC) of the positively-charged surfactant.

60. The system of claim 59, wherein the positively-charged surfactant is a quaternary ammonium-based surfactant, a quaternary' phosphonium-based surfactant, a tertiary' sulfonium-based surfactant, or a tertiary oxonium-based surfactant.

61. The method of claim 50, wherein the ion exchange resin regeneration solution further comprises a base.

62. The method of claim 61, wherein the base is one or more of NaOH, NH4OH and N(CH₂CH₂CH₃)4OH.

63. The method of claim 50, providing instructions for increasing the temperature of the ion exchange resin regeneration solution when regenerating the ion exchange resin.

64. The method of claim 50, wherein the ion exchange resin comprises an anion exchange resin.

65. The method of claim 65, wherein the ion exchange resin comprises a weak base anion exchange resin.

66. The method of claim 65. wherein the weak base anion exchange resin comprises a macroporous styrenic matrix supporting amine functionalities.