Pre-acidification method for maintaining a stable effluent PH in water treatment systems containing weak basic anion exchange resins

Abstract

A method for maintaining stable effluent pH in a water treatment system containing weak base anion exchange resin by adding a weak base anion exchange resin to a column, passing an acid solution through the weak base anion exchange resin to acidify the resin, and passing water in need of treatment through the acidified resin, The pH of the effluent water after passing through the acidified resin can be maintained within 2.0 pH units of pH of the water in need of treatment prior to it passing through the acidified resin.

Description

[0001] PRE-ACIDIFICATION METHOD FOR MAINTAINING A STABLE EFFLUENT PH IN WATER TREATMENT SYSTEMS CONTAINING WEAK BASIC ANION EXCHANGE RESINS

[0002] BACKGROUND

[0003] Fluorochemicals have been used in a wide variety of applications including the water-proofing of materials, as protective coatings for metals, as fire-fighting foams for electrical and grease fires, for semi-conductor etching, and as lubricants. Reasons for such widespread use of fluorochemicals include their favorable physical properties which include chemical inertness, low coefficients of friction, and low polarizabilities (i.e., fluorophilicity). Per- and polyfluoroalkyl substances (PFAS) refer to a large group of fluorinated aliphatic chemicals, for which there is currently a focus due to the widespread contamination of water around the world with an array of these substances.

[0004] PFAS contain carbon-fluorine bonds, which are some of the strongest bonds in organic chemistry. Consequently, the substances are virtually non-biodegradable - an advantage when they are in use, but quite the opposite if they make their way into the environment. Compounds in this class namely accumulate in the bodies of living organisms once ingested. Their durability means that even traces must be removed from wastewater and that contaminated groundwater must be cleaned up. This involves adhering to national and regional limits measured in parts per trillion (ppt), some of which are extremely low.

[0005] Anion exchange resins (AER) are one of the few effective technologies for removing PFAS during the water treatment process. Ion exchange is a process in which ions are exchanged between a solution and an ion exchanger, typically an insoluble solid or gel which may be treated to include functional groups. Anion exchangers are used for negatively charged anions. Cation exchangers are used for positively charged cations. Ion exchange can be a reversible process in that the ion exchanger can be regenerated or loaded by washing the ion exchange resin with an excess of the ions to be exchanged (e.g., chloride ions, sodium ions, hydrogen ions and hydroxide ions etc.). A number of anion exchange resins have been marketed for their high selectivity for PFAS, e.g. AMBERLITE™ PSR 2 Plus, DOWEX™ PSR-2, AMBERLITE™ PSR 3, Lewatit® TP 108, Lewatit® TP 108 DW, Lewatit® MonoPlus TP 109, Lewatit® K 6362, Purofine® PFA694E, SIR-110-MP-HP, SIR-110-HP, SEPLITE® LSI106, Calres® 2301, Calres® 2309, Calres® 2304, Sorbix® LC3 and use of such products is increasing. Many of these are strong basic anion exchange resins (SBA) having quaternary ammonium groups. More recently, interest has increased in weak basic anion exchange resins (WBA), which have primary, secondary and / or tertiary amine functional groups and become deprotonated above a specific pH (i.e., nonionic). The pH dependent behavior of WBA, such as Lewatit® MP 62 WS, can be leveraged to control the extent of contaminant desorption. WBAs have greater capacity, are more resistant to oxidative attacks, less susceptible to organic fouling and are easier to regenerate. WBAs have greater amenability to aqueous-only regeneration than SBA counterparts.

[0006] WBA in the free-base form contain uncharged amine groups that require pretreatment with solutions of strong acids to effectively bind to perfluoroalkyl acids (PFAA), such as perfluorooctane sulfonate (PFOS). However, such pre-acidification often renders effluent water very acidic at the beginning of operation (“start-up”). This acidic start-up effluent needs to be discarded, otherwise it will cause corrosion of the distribution system and health concerns.

[0007] There is a need and desire for effective pre-acidification methods to avoid significant reduction in effluent pH in water treatment systems comprising WBA., preferably WBA in-situ in a column or vessel in a co-current flow pattern. It is desirable to find a process that is economically feasible, easy and convenient or a process that uses a simple low cost materials.

[0008] It is an objective of the present disclosure to provide an effective pre-acidification method to avoid significant effluent pH reduction in a water treatment system comprising a WBA, preferably WBA in-situ in a column or vessel in a co-current flow pattern.

[0009] SUMMARY OF THE INVENTION

[0010] The foregoing objectives are achieved by provision of a method for maintaining stable effluent pH in a water treatment system containing weak base anion exchange resin by adding a weak base anion exchange resin to a column; passing an acid solution through the weak base anion exchange resin, such as at 1-15 BV / hr to acidify the resin, preferably to at least 1% but less than 75% total capacity of the resin; and passing water in need of treatment through the acidified resin. pH of the effluent water after passing through the acidified resin is maintained within 2.0 pH units, preferably within 1.5 pH units, of pH of the water in need of treatment prior to it passing through the acidified resin. The resin may be styrenic and comprise amino functional groups in free base form.

[0011] In certain embodiments, the resin contains, consist essentially of, or consists of tertiary amino groups. In some embodiments, the resin has less than 10% strong basic sites, preferably less than 5% strong basic sites, more preferably less than 0.5% strong basic sites, most preferably less than 0.1% strong basic sites, based on total available functional sites of the resin.

[0012] In certain embodiments, the resin is prepared by a phthalimide process.

[0013] In some embodiments, the resin has a mean bead size of about 0.40 to 1.25 mm.

[0014] The water in need of treatment may be municipal water, drinking water, surface water, or ground water and is often drinking water. In certain of those embodiments, the water in need of treatment contains per- and polyfluoroalkyl substances (PFAS).

[0015] In certain embodiments, the acid solution is prepared from hydrochloric or sulfuric acid.

[0016] In some embodiments, the column has co-current operation.

[0017] By comparison, resins pre-acidified in a mixing tank (e.g. in a manufacturing plant) with different amounts of acids, or by mixing a pre-acidified resin with a non-acidified resin to reach certain acidification levels, which are then loaded into a column, are not able to stabilize effluent water pH like the in-situ methods described herein. Advantageously, using existing resin product and conducting acidification in-situ in a column or vessel during start-up avoids the need for adding additional resin products to a water treatment system and provides flexibility to resin users with different acidification requirements.

[0018] The methods according to the present invention may be used in a system for removing PFAS from water.

[0019] The preceding summary is not intended to restrict in any way the scope of the claimed invention. In addition, it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

[0020] DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing effluent pH as a function of rinse water bed volumes in accordance with Example 1.

[0021] FIG. 2 is a graph showing effluent pH as a function of rinse water bed volumes in accordance with Example 2. FIG. 3 is a graph showing effluent pH as a function of rinse water bed volumes in accordance with Example 3.

[0022] FIG. 4 is a graph showing effluent pH as a function of rinse water bed volumes in accordance with Example 4.

[0023] DETAILED DESCRIPTION

[0024] The present disclosure discloses a method of pre-acidifying a WBA resin in a water treatment system. The method involves adding a WBA resin to a column, passing an acid solution through the WBA resin to acidify the resin, and passing water in need of treatment through the acidified resin. The method can maintain pH of the effluent within 2 pH units of the pH of the water in need of treatment prior to it passing through the column. The method is convenient for use with a water treatment system for removal of PFAS.

[0025] As used herein, “resin” refers to an ion exchange resin.

[0026] As used herein “weak base anion exchange resin” or “WBA” means a resin that has a primary, secondary or tertiary amine functional group, which acts as a weak base.

[0027] As used herein “strong basic sites” refers to functional groups on a resin backbone that act as a strong base, including but not limited to quaternary ammonium groups, such as trimethylamine and dimethylethanolammonium.

[0028] As used herein “column” refers to a vessel equipped with an inlet flow distributor and an outlet collector or drain support.

[0029] As used herein “total capacity” refers to an indicator for the total available functional groups on a resin.

[0030] As used herein “operating capacity” refers to achievable exchange capacity during the operation of a particular resin under distinct and defined conditions.

[0031] As used herein “effluent” refers to the solution collected at the outlet of a column.

[0032] As used herein “bed volumes” means the volume of water passing through the resin bed divided by the volume of the resin in the column. Bed volumes may be abbreviated herein as “BV.” As used herein, “PFAS" refers to per- and polyfluoroalkyl substances. PFAS 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), Perfluorooctane sulfonate (PFOS), Perfluorononanoic acid (PFNA), 8:2 Fluorotelomer sulfonate (8:2 FTS).

[0033] As used herein, “co-current operation” or “co-current flow” refers to a configuration in which there is the same direction of flow between the acidification and operation processes.

[0034] As used herein, “regeneration” refers to the transfer of an ion exchanger in the initial ionic form prior to the next cycle of use. A “regenerant" refers to the reagent applied to an ion exchanger in order to perform regeneration.

[0035] As used herein, “eluting” or “elution” refers to the extraction of a targeted (desirable) ion from an ion exchange material. It may also be referred to as recovery, stripping, or desorption.

[0036] As used herein, “eluent” is the solvent or solution pumped through an exchange material to transfer previously sorbed species. It may also be referred to as mobile phase.

[0037] Examples of anion exchange materials suitable for the present invention include: weak base cross-linked anion exchange resins with or without certain fractions of strong basic sites. Such resins can be made, e.g., according to the phthalimide processes disclosed in US 5,464,875; US 7,053,129; and US 20070259046, or by known chloromethylation processes. Preferably, the resin will contain less than 10% strong basic sites, preferably less than 5% strong basic sites, more preferably less than 0.5% strong basic sites, most preferably less than 0.1% strong basic sites, based on total available functional sites of the resin. In certain embodiments, the resins my consist essentially of or consist entirely of weak basic sites, such as a resin prepared by amidoalkylation of a bead polymer with phthalimide or a phthalimide derivative ( “phthalimide process”). In some preferred embodiments, WBA is made using a phthalimide process.

[0038] The structure of the anion exchange resins can be either gel or macro porous. The gel type resins often have higher capacity, while the macro porous type is usually fouling resistant and chemically / mechanically stronger. The anion exchange resins can be styrenic or acrylic polymers, such as polystyrene / divinylbenzene or polyacrylate, having a variety of amine exchange groups selected from primary, secondary or tertiary functional groups, and may have a fraction of quaternary amine group as well.

[0039] Preferably, the WBA has a high total and operating capacity, such as greater than 1.2 equivalent per liter. In certain embodiments, the capacity is about 1.7 equivalent per liter or higher.

[0040] In certain embodiments, the WBA has a mean bead size of about 0.40 to 1.25 mm. In certain preferred embodiments, the WBA is styrenic, macropourous with tertiary amino groups in free base form, such as those prepared using a phthalimide process.

[0041] Commercially available resins suitable for use herein include Lanxess’s Lewatit® MP 62 WS, Lewatit® MP 62, Lewatit® MonoPlus MP 64, Lewatit® MonoPlus MP 68, Lewatit® A 365, Lewatit® A 8072, Lewatit® A 8072+, Lewatit® A 8073, Lewatit® S 4228, Lewatit® S 4268, Lewatit® S 4328, Lewatit® S 4468, Lewatit® S 4528, Lewatit® S 5221, Lewatit® S 5228 and Lewatit® S 5328, Puroiite's Purolite® AIOOPIus, Purolite® A103Plus, Purolite® A133, Purolite® A111, Purolite® A110, Purolite® A848, or Purolite® A830, Dupont’s Amberlite™ HPR6700, Amberlite™ HPR7000, Amberlite™ HPR9500, Amberlite™ HPR9600, or Amberlite™ HPR9700, Mitsubishi’s DIAION™ WA10, DIAION™ WA20, DIAION™ WA21J, DIAION™ WA30, or DIAION™ WA55, Relite™ JA300, Relite™ JA310, Relite™ JA450, or Relite™ JA830, and SunResin’s SEPLITE® MA939, SEPLITE® MA940, SEPLITE® MA943, SEPLITE® Monojet™ MA9400, SEPLITE® MA950, SEPLITE® LSF930A, SEPLITE® LSF930B, SEPLITE® LSF973, SEPLITE® LSF9300 or SEPLITE® Monojet™ LSF9730.

[0042] Typically, the acidification of the resin is carried out by pouring or pumping an acid solution over the loaded exchange resin held in a column. Suitable acid solutions can be prepared from inorganic acids and organic acids. Examples of inorganic acids are: hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, sulfurous acid, sulfamic acid. Organic acids include citric acid, acetic acid, formic acid, malic acid, lactic acid, oxalic acid, tartaric acid, malonic acid, butyric acid, glycolic acid and gluconic acid. These acids could be available in their existing forms, or could be generated in-situ by other chemicals. As an example a metal salt, such as ferric chloride or aluminum chloride, could hydrolyze in water and generate hydrochloric acid in situ.

[0043] The column dimensions will be selected based on the water flow rate, ion exchange resin utilized and desired throughputs but generally for a commercial scale has a diameter less than 15 feet, such as less than 12 feet or less than 10 feet and is often greater than 1 foot. In certain laboratory scale embodiments exemplified herein, the column diameter is less than 1 foot, such as from about 1 to about 2 inches in diameter.

[0044] The acidification of the resin is based on the total capacity of the resin selected and is performed from at least 1% up to 100%. The resin may be acidified from about 2.5%, from about 5%, from about 10%, from about 15%, or from about 20%, up to about 99%, or up to about 95%, or up to about 90%, or up to about 85%, or up to about 80%, or up to about 75%, or up to about 70%, or up to about 65%, or up to about 60%, or up to about 55%, or up to about 50%, or any range of such values. The maximum acidification level will depend on the feed water chemistry and the particular resin selected. By way of example, a WBA resin used in the method disclosed herein may be acidified from about 5 to about 95%, from about 10 to about 90%, from about 15 to about 85%, or from about 20 to about 80% of total capacity. In certain embodiments, the resin is acidified to at least 1 % but less than 75% of total capacity. In some embodiments, the resin is acidified to no greater than 50% total capacity, more preferably from about 5%, or from about 10%, or from about 20% to no greater than 50% of total resin capacity.

[0045] The acidification is typically practiced at room temperature, e.g. at a temperature of 15 to 30°C. However, the method may also be carried out at a higher temperature for example at a temperature between 30 and 80°C. Optionally, a rinse may thereafter occur with water, e.g., demineralized water at a rate of 1-20 BV / hour.

[0046] After acidification, and optional rinse, the water in need of treatment is eluted through the column. In certain embodiments, the water for treatment is passed through the column at 5-30 BV / hour. Upon exiting the column, the effluent will have a pH that is within 2.0 units, preferably 1.5 units, of pH of the water prior to passing it through the acidified resin.

[0047] In certain advantageous embodiments, the water in need of treatment may contain PFAS, which may become bound to the resin, and the PFAS can be recovered from the resin with a regenerant solution. The amount of regenerant solution that is needed to recover PFAS from the anion exchange resin depends on the amount and nature of the PFAS that are adsorbed on the anion exchange resin as well as on the composition of the regenerant solution. It has been found that generally an aqueous solution regenerant is successful for WBA. The total amount of regeneration solution and its composition is typically determined on basis of the amount of ion exchange material to be regenerated and the actual loading of the adsorbed species. One should generally apply a large excess of the regeneration liquid. It is preferred that the regenerant be used in an amount of at least 1.1 times, especially 2 to 10 times, the quantity (equivalent) of the functional sites on the exchange material to be treated. The excess regeneration liquid can easily be drained from the regenerated particles after the regeneration process is finished. The drained liquid can be weighed and analyzed to determine the actual amount and composition of the drained regeneration liquid. The composition and amount of the drained regeneration liquid can then be adjusted by adding appropriate amounts of its components so that the drained regeneration liquid may be re-used. Reuse of the regeneration liquid will create less waste, is environmentally friendly, and reduces the costs. EXAMPLES

[0048] Materials

[0049] Lewatit® MP 62 WS from Lanxess Corporation. Sulfuric acid (95-98% active), hydrochloric acid (36.7% active), sodium chloride, sodium sulfate, sodium nitrate and sodium bicarbonate were purchased from Thermo Fisher Scientific.

[0050] Three waters were used: demineralized water, well water and synthetic water. The demineralized water was produced with mixed bed ion exchange resins. The well water was from a private well, had the following properties.

[0051] Well Water

[0052] Concentration(ppm)

[0053] Total hardness as CaCOa 121.5

[0054] Chloride 1.0

[0055] Sulfate 3.0

[0056] Nitrate 0.9

[0057] Alkalinity as CaCOs 113.7

[0058] pH 7.45

[0059] Synthetic water was prepared by adding 3.3 grams sodium chloride, 0.592 grams sodium sulfate, 0.1 grams sodium nitrate and 1.9 grams of sodium bicarbonate to 19994.1 grams of demineralized water. The final synthetic solution has the following targeted ionic species concentrations:

[0060] Synthetic Water

[0061] Concentration(ppm)

[0062] Sodium 96.7

[0063] Chloride 100

[0064] Sulfate 20.0

[0065] Nitrate 2.0

[0066] Bicarbonate 70

[0067] pH 7.8

[0068] Comparative Example 1 - Ex-situ Batch Acidification with H2SO4

[0069] Test procedure

[0070] (a). First, prepared an 8% H2SO4 stock solution by adding 82.9 grams of H2SO4 (95-98%) to 917.1 grams of demineralized water. Mixed well. (b). Then, prepared H2SO4 solutions at 25% and 50% acidification strength based on 300ml resin:

[0071] Acidification, Resin, Resin Eq. 8% Demin. Total % mL capacity, H2SO4 to H2SO4, Water, Acidification eq treat resin g g Solution, g 25 300 0.51 0.1275 78.1 300 378.1 50 300 0.51 0.255 156.2 300 456.2 (c). Added 300 ml dilution water to a 1000ml glass beaker, added the required amount of H2SO4 solutions. Mixed well.

[0072] (d). Added 300 ml MP62 WS resin to the beaker in step (c), mixed for 1 hour.

[0073] (e). Transferred 190 ml acidified resin to a 2 inch diameter glass column, rinsed with demineralized water. Samples for effluent pH measurements were taken at different accumulated bed volumes.

[0074] (f). Rinsed with the synthetic water, monitored effluent pH at different accumulated bed volumes.

[0075] Tables 1-25 and 1-50 and FIG. 1 show the effluent pH as a function of rinse water bed volumes for 25% and 50% acidified resins. After 125 bed volumes, the effluent pHs were still acidic. Table 1-25

[0076]

[0077] Table 1-50

[0078]

[0079] Comparative Example 2 - Ex-situ Batch Acidification with H2SO4 and Well Water Rinse The procedure from Comparative Example 1 was repeated except targeting 20% acidification with H2SO4, and the treated resin was rinsed with well water (no demineralized water or synthetic water rinse after acidification).

[0080] Table 2-20 and FIG. 2 show the effluent pH as a function of rinse water bed volumes. After 98 bed volumes, the effluent pH was still acidic. Table 2-20

[0081]

[0082] Comparative Example 3 - Ex-situ Batch Acidification with HCI and Well Water Rinse The procedure from Comparative Example 2 was repeated except the 20% acidification was achieved with HCI by mixing 100% acidified beads with untreated beads as follows:

[0083] a). Added 420 g 5% HCI to a 1000 mb beaker, then added 300 mb MP 62 WS resin to the beaker, mixed for 1 hour, rinsed the resin with 600 mb demineralized water five times.

[0084] (b). Transferred 25.8 mb 100% acidified resin in 100 ml well water to a 500 ml glass beaker. (c). Transferred 103.2 mb untreated MP 62 WS resin in 200 mb well water to the above beaker. Mixed for 2 minutes. The mixed beads provided an average 20% acidification.

[0085] (d). Transferred the mixture prepared in step (c) to a 2 inch diameter glass column, then started rinsing with well water and monitored the effluent pH.

[0086] Table 3-20 and FIG. 3 show the effluent pH as a function of rinse water bed volumes. After 98 bed volumes of rinse with well water, the effluent pH was still acidic. Table 3-20

[0087]

[0088] Example 4 - Inventive

[0089] Procedure

[0090] HCI Solutions: Prepared HCI solutions for acidifying the MP 62 WS resin by first preparing 5% HCI stock solution by adding 117 mL HCI (36.7%) to a -liter volumetric flask, then adding demineralized water to the 1 liter mark. Shook the flask to let it mix thoroughly. Prepared HCI solutions with different acidification strengths were prepared using the stock solution according to the below:

[0091] Acidification, Resin, Resin Eq. HCI to 5% HCI, Demin. Total % mL capacity, treat resin g Water, Acidification eq g Solution, g 0 500 0.85 0 0 0 0

[0092] 20 500 0.85 0.17 124.1 500 624.1 50 500 0.85 0.425 310.3 313.9 624.1 75 500 0.85 0.6375 465.4 158.7 624.1 100 500 0.85 0.85 620.5 3.6 624.1

[0093] Column acidification test: The acidification test was performed in a plastic column (1 inch diameter, and 34 inches long) with co-current flow. (a). Measured 500 mL fresh MP 62 WS resin in 600 L well water with a graduated cylinder. Transfer the mixture to the column. Let the resin settle, then drained the water to just above the resin bed.

[0094] (b). Obtained the appropriate amounts of HCI acidification solutions (624.1 g) targeting for 20%, 50%, 75% and 100% acidification levels respectively. Passed the acid solution through the column at 54 ml / min.

[0095] (c). After passing every 100 mL effluent, collected about 40 mL sample to measure pH. (d). After the acidification solution passed through, started feeding the well water from the top of the column at 108 mL / min.

[0096] (e). Collected 40 mL effluent to measure pH at the 0.31, 0.93, 1.86, 3.41, 6.2, 11.32, 21.24, 40.78 and 79.53 accumulated bed volumes. For 75% acidification, samples with 102.91 and 126.29 accumulated bed volumes were also taken for pH measurement.

[0097] Tables 4-Acidificaiton and 4-Rinse and FIG. 4 show the effluent pH as a function of rinse water bed volumes. At acidification over 50%, the effluent pH was acidic. In the case of 75% and 100% acidification levels, pH was less than 3 at up to 80 accumulated bed volumes of rinse. Theoretically, 100% acidification should provide a near neutral effluent pH, because all the HCI acid will be adsorbed by the resin in the column. It seemed that some acids were pushed off the resin by well water.

[0098] Table 4-Acidification

[0099]

[0100] Table 4-Water Treatment

[0101]

[0102] The pH of the raw well water was 7.45. The pH of effluent when the column was not pre-acidified increased more than 2 units. Effluent pH was kept within about 2 units of raw well water at 20% and 50% acidification for up to 80 bed volumes. It is expected that the methods disclosed herein are able to stabilize pH for even greater bed volumes, such as 100, 500, 1000, 5,000 or more bed volume.

[0103] The foregoing examples, are specific to a particular WBA and are not meant to limit the acidification step encompassed by invention. The level of maximum level acidification for a resin to maintain stable pH for effluent will vary depending on the raw pH of the water in need of treatment and the percentage of strong basic sites on the resin. Various ranges of pre-acidification of a WBA are embodied within the scope of the present disclosure.

Claims

What is claimed is:

1. A method for maintaining stable effluent pH in a water treatment system containing weak base anion exchange resin comprising the steps of:adding a weak base anion exchange resin to a column;passing an acid solution through the weak base anion exchange resin to acidify the resin, preferably to at least 1% but less than 75% total capacity of the resin; andpassing water in need of treatment through the acidified resin,wherein pH of the effluent water after passing through the acidified resin is within 2.0 pH units of pH of the water in need of treatment prior to it passing through the acidified resin.

2. The method according to claim 1, wherein the resin is styrenic.

3. The method according to claims 1 or 2, wherein the resin comprises amino functional groups in free base form.

4. The method according to any of the preceding claims, wherein the resin contains tertiary amino groups.

5. The method according to any of the preceding claims, wherein the resin has less than 10% strong basic sites, preferably less than 5% strong basic sites, more preferably less than 0.5% strong basic sites, most preferably less than 0.1% strong basic sites, based on total available functional sites of the resin.

6. The method according to any of the preceding claims, wherein the resin is prepared by a phthalimide process.

7. The method according to any of the preceding claims, wherein the resin has a mean bead size of about 0.40 to 1.25 mm.

8. The method according to any of the preceding claims, wherein the water in need of treatment is municipal water, drinking water, surface water, or ground water.

9. The method according to claim 8, wherein the water in need of treatment is drinking water.

10. The method according to claim 9, wherein the water in need of treatment contains per-and polyfluoroalkyl substances (PFAS).

11. The method according to any of the preceding claims, wherein the acid solution is prepared from hydrochloric or sulfuric acid.

12. The method according to any of the preceding claims, wherein the step of passing an acid solution is performed at 1-15 BV / hr.

13. The method according to any of the preceding claims, wherein the column has co-current operation.

14. The method according to any of the preceding claims, wherein pH is maintained within 1.5 units after passing 11 bed volumes of the water in need of treatment.

15. The method according to any of the preceding claims, wherein the resin is acidified to at least about 20% up to about 50% of the total capacity of the resin.

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