A system and method for selectively removing contaminants

Abstract

A system for selectively removing PFAS contaminants from an aqueous feed stream comprising at least one ion exchange column comprising a plurality of compartments for receiving at least one type of PFAS-selective ion exchange resin, the system configured to receive the aqueous feed stream, and form a PFAS-depleted effluent stream and PFAS-loaded ion exchange resins; and an ion exchange resin cleaning unit for recovering at least part of the PFAS-loaded ion exchange resin and forming PFAS-rich effluent streams.

Description

[0001] A SYSTEM AND METHOD FOR SELECTIVELY REMOVING CONTAMINANTS

[0002] TECHNICAL FIELD

[0003] The present invention relates to a system and a method of treating a contaminated aqueous feed stream, such as drinking water and wastewater, to selectively remove contaminants.

[0004] The present invention relates, in particular, to a system and method for selectively removing contaminants, such as per-fluoroalkyl and poly-fluoroalkyl substances (collectively termed “PF AS”), from contaminated water.

[0005] BACKGROUND ART

[0006] Per-fluoroalkyl and poly-fluoroalkyl substances (collectively “PF AS”) are a group of synthetic chemicals that are used to impart heat, stains, grease and water resistance to a range of products including cookware and packaging. However, human exposure to PFAS has been associated with negative health effects and perfluorooctanoic acid (PFOA), a type of PFAS, has been declared a Group 1 human carcinogen by the World Health Organisation (WHO).

[0007] PFAS are known as ‘forever chemicals’ as these chemicals are resistant to degradation in the environment and can accumulate within the human body. The general population is exposed to PFAS mainly via drinking water, and PFAS contamination has been found in surface and ground water commonly near landfills, sewage treatment plants and sites that use PFAS containing firefighting foams.

[0008] Given the potential health risks and nondegradable nature of PFAS, it has become increasingly important globally to regulate the levels of PFAS in drinking water to safe drinking limits. Many countries including Australia have set regulatory limits for specific PFAS contaminants such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).

[0009] Existing water treatment technologies for removing PFAS include activated carbon, membranes and ion exchange resins. Treatment of PF AS-contaminated water is costly and produces solid PF AS-containing waste (e.g. spent resin) which requires disposal or further treatment. It would be desirable to provide a system and method for removing contaminants, such as PFAS, from contaminated water, that alleviates at least one of the mentioned problems.

[0010] SUMMARY OF THE DISCLOSURE In one aspect of the present invention, there is provided a system for selectively removing a contaminant from an aqueous feed stream comprising at least one ion exchange column comprising a plurality of compartments for receiving at least one type of PFAS-selective ion exchange resin, the system configured to receive the aqueous feed stream and form a PFAS-depleted effluent stream and a PFAS-loaded ion exchange resin; and an ion exchange resin cleaning unit for recovering at least part of the PFAS-loaded ion exchange resin and forming a PFAS-rich effluent stream.

[0011] In this specification, the term “PF AS” refers to per-fluoroalkyl and poly-fluoroalkyl substances. Examples of PF AS include perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).

[0012] In this specification, the term “ion exchange resin” includes adsorbents of either or both organic and inorganic polymers.

[0013] Suitably, the aqueous feed stream is a contaminated water stream or wastewater stream.

[0014] The present invention was developed because of the Applicant’s motivation to improve existing systems for selectively removing PF AS contaminants from wastewater, particularly to reduce capital and operating costs related to resin disposal and recovery of chemicals along with a permanent destruction step.

[0015] This led to a realisation that reconfiguring the ion exchange column of the system may enable the system footprint to be reduced and the contaminant adsorption efficiency to improve.

[0016] In this respect, the Applicant developed an ion exchange column comprising a plurality of compartments for receiving at least one type of ion exchange resins.

[0017] Compartmentalisation of column

[0018] To enhance system efficiency, the Applicant configured the ion exchange column to compartmentalise the ion exchange resin, suitably by providing multiple beds of ion exchange resin. Without being bound by theory, it is believed that the compartmentalised column mimics a multi-column system with each compartment / ion exchange bed simulating one conventional column.

[0019] Each compartment may be separately replaceable as the resin contained within each compartment is exhausted with the PF AS compounds.

[0020] Each compartment in the column may comprise a mixture of the resins or a single type of resin.

[0021] Each compartment may contain one type of ion exchange resin. Each compartment may contain one type of PFAS-selective media.

[0022] Each compartment may contain a different mixture of ion exchange resins. Suitably, the ion exchange resins are substantially unmixed within each compartment.

[0023] Each compartment may contain the same mixture of ion exchange resins.

[0024] The ion exchange column may include a compartment containing a functionalised recoverable carbon adsorbent such as functionalized GAC (granular activated carbon).

[0025] The functionalised GAC containing compartment may precede the ion exchange resin compartments. Positioning the functionalised GAC-containing compartment at this location enables the GAC to adsorb hydrophobic PF AS and organics and protect the downstream ion exchange resin.

[0026] The column may include physical barriers such as trays, baffles and plates to separate the compartments. A suitable physical barrier is a perforated nozzle plate.

[0027] Alternatively, the different types of resins may be arranged in the column to form substantially separate layers or regions. In contrast, conventional ion exchange systems for PF AS removal typically comprise a series of columns with each containing one type of resin. One disadvantage of such systems is underutilisation of resin capacity during adsorption of the contaminant. This leads to frequent and premature resin replacement and significant waste disposal costs. Typical resin bed capacity utilisation of a conventional multi-column system was determined to be approximately 50% to 60%, leading to high treatment costs per unit volume of feed treated.

[0028] The reduced amount of resin used in ion exchange system of the present invention may maximise resin utilisation by increasing the likelihood that majority of the resin in each bed to reach or get close to saturation point.

[0029] In one embodiment, the system is configured to enable sequential flow of the aqueous feed stream through each compartment, suitably consisting of an ion exchange resin bed, of the ion exchange column. Suitably, each compartment consists of one type of ion exchange resin, wherein the compartments are fluidly connected in series.

[0030] Each ion exchange resin bed may contain at least one type of PFAS-selective ion exchange resin. Suitably, each ion exchange resin bed consists of one type of PFAS-selective ion exchange resin. The discrete beds may be configured to maximise utilisation (e.g. PFAS loading), for example by selection of the resin type and amount. This ensures that each resin bed operates efficiently near or at saturation, which in turn minimising waste and reducing overall treatment costs. At least one type of the ion exchange resin may be recoverable and reused in the column. This may reduce waste output from the system and reduce operational costs.

[0031] At least one ion exchange column may comprise two to three compartments.

[0032] Compartmentalisation of the column improves operation efficiency by enabling targeted re-use of the ion exchange resin. By compartmentalising the ion exchange resin, the present invention allows the spent resin to be cleaned in small batches. This minimises the chemical and waste footprint and potentially increases resin service life. The present invention also allows selective disposal of exhausted or spent resin as opposed to disposal of the entire bed or column.

[0033] In addition, the Applicant recognised that solids build-up and fouling in the column impede resin life span, but the current methods for chemical cleaning of the resin and re-use of cleaning solutions in conventional columns are limited or energy intensive. The PFAS loading profile in a single bed resin column shows that resin located at the front of the column adsorb a greater amount of PFAS than resin located towards the end of the column. Therefore, the Applicant realised that cleaning in zones and / or performing partial replacement of resin may be advantageous as they optimise resin adsorption. Without being bound by theory, it is believed that this is achieved by maximising the concentration gradient of the contaminant between the resin and the aqueous feed stream. The present invention may allow resins within the column to be interchangeable such that spent resin located at the top section of the column can be replaced with clean resin or resin having greater capacity from the bottom section of the column.

[0034] The system may also allow targeted cleaning of the compartments based on the fouling type, e.g. mineral scaling or organic fouling, to extend the lifespan of the resin media. The resins may be swapped or transferred between zones or compartments within the column.

[0035] The resin capacity and fouling may be monitored by measuring differential pressure and by PFAS breakthrough mapping in the ion exchange column. The interchanging of the compartments based on differential pressure or breakthrough criteria may be automated.

[0036] The system may comprise a plurality of ion exchange columns. Suitably, the plurality of ion exchange columns is arranged in parallel to receive the aqueous feed stream. Suitably, the plurality of ion exchange columns is arranged in series to receive the aqueous feed stream.

[0037] At least one column may be configured to provide an upflow lead-lag configuration with multiple compartments. Suitably, the lead-lag configuration involves a lead column arranged in series with a lag column. The lead and lag columns each comprise at least two compartments.

[0038] Types of ion exchange resin

[0039] The resin(s) may be selected based on a preference for selectivity, recoverability, or ease of desorption. This may depend on the composition of the aqueous feed stream.

[0040] The ion exchange resin may have either enhanced selectivity for short-chain PF AS or long-chain PF AS.

[0041] To further enhance the system efficiency, the ion exchange column may contain at least two types of ion exchange resin. Suitably, the ion exchange resins comprise a first resin type having enhanced selectivity for short-chain PF AS and a second type having enhanced selectivity for long-chain PFAS. Suitably, the resin comprises adsorption media having a customised functionality, morphology and particle size.

[0042] In this specification, short-chain PFAS includes a carbon chain length comprising up to 7 carbon atoms, suitably 4-7 carbon atoms. Suitably, short-chain PFAS comprises C4-C7 perfluoroalkylcarboxylic acids (PFCAs), for example perfluorobutanesulfonic acid (PFBS), perfluorobutanoic acid (PFBA), and fluorotelomer sulfonic acids (FTS).

[0043] In this specification, long-chain PFAS includes a carbon chain length comprising at least 8 carbon atoms, suitably 8-12 carbon atoms. Suitably, long-chain PFAS comprises C8-C12 PFCAs, for example perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).

[0044] The ion exchange column may contain a first type of ion exchange resin having high selectivity for short-chain PFAS, a second type of ion exchange resin having moderate selectivity for short-chain PFAS, and a third type of ion exchange resin having high selectivity for a long-chain PFAS. In this embodiment, the second type of ion exchange resin may have a lower selectivity for a short-chain PFAS compared to the first type of ion exchange resin and a lower selectively for a long-chain PFAS compared to the third type of ion exchange resin.

[0045] Suitable examples of resins may comprise tripropyl, tributyl, triethyl, trimethyl, diethyl amine, dimethyl amine, poly amine polystyrene and dimethylethanolamine functional groups. Other suitable examples of resins include acrylic based adsorbers.

[0046] Suitable examples of the first type of ion exchange resin include Strong Base Anionic Organic polymers, Quaternary Amines or Complex Amines or inorganic adsorbers.

[0047] Suitable examples of the second type of ion exchange resin include Strong Base Anionic functionalised polymers. Suitable examples of the third type of ion exchange resin include weak base anionic or strong base anionic or inorganic adsorbers.

[0048] The proportion of the different types of ion exchange resin is typically feed water quality driven.

[0049] Suitable ratios of the proportion of first to second type of ion exchange resin include 1:1, 1:1.5 or 1:2.

[0050] Suitable ratios of the proportion of the second to third type of ion exchange resin include 1:1, 1:1.5 or 1:2.

[0051] Suitable ratios of the proportion of the first to third type of ion exchange resin include 1:1, 1:1.5 or 1:2.

[0052] Integrating multiple types of ion exchange resins with varying PF AS selectivity into a single column may reduce the need to provide separate columns for each ion exchange resin type. This may reduce the overall footprint of the system compared to a conventional system that utilises separate columns for each resin type. This consolidation of different ion exchange resin types in a single column may also enhance operational efficiency and simplify maintenance of the column.

[0053] The ion exchange resins may comprise recoverable and / or single use type resins. Suitably, at least part of the ion exchange resin used are recoverable.

[0054] At least one type of ion exchange resin may have selectivity for a co-contaminant. The co-contaminant may comprise dissolved cationic or anionic contaminants. The cocontaminant may comprise heavy metals. Suitably examples of heavy metals include arsenic, cadmium, mercury, and lead ions. Suitable examples of dissolved anionic contaminants include nitrate and chromates.

[0055] Ion exchange resin cleaning unit

[0056] The ion exchange resin cleaning unit is configured to perform to clean and / or recover at least part of the ion exchange resin. This provides a closed loop system which may improve resin performance and longevity which in turn allows prolonged use and minimises resin replacement. It also contributes to reduced operational costs by optimising resin utilisation and reducing waste generation.

[0057] Recovery of the ion exchange resin may involve partial desorption of the PF AS contaminant from the resin.

[0058] Recovery of the ion exchange resin may involve stripping or elution.

[0059] The resin may be recovered by treating with a cleaning solution. This desorbs or releases the PF AS contaminant from the resin. The ion exchange resin cleaning unit may be configured to provide either internal / in-situ or external recovery configurations. Suitably, the ion exchange resin cleaning unit is part of the ion exchange column or is separate to the ion exchange column.

[0060] In embodiments where the ion exchange resin cleaning unit is separate to the ion exchange column, the ion exchange resin cleaning unit is configured to receive loaded or spent resin from the column for recovery.

[0061] In these embodiments, the ion exchange resin cleaning unit may include a cleaning solution inlet located at or near the top of the unit and a cleaning solution outlet located near the bottom of the unit. This enables downward flow of the cleaning solution in the unit.

[0062] In embodiments where the ion exchange resin cleaning unit forms part of the ion exchange column, the ion exchange resin cleaning unit may be configured to perform a backwashing step to flush at least part of the resin in the column with a cleaning solution. This avoids the need to remove the resin from the ion exchange column for cleaning or recovery.

[0063] The cleaning solution may alter the solution pH of one of more of the beds of resin. This may facilitate release of the PFAS contaminant from the resin.

[0064] The cleaning solution may be a solvent or chemical selected from brine, acids, or alkalis.

[0065] The cleaning solution may comprise an acid.

[0066] The cleaning solution may comprise a base.

[0067] The cleaning solution may be selected depending on the type of resin contaminant. In one suitable example, the cleaning solution comprises an organic or high pH solvent to target organic fouling in the resin. In another example, the cleaning solution comprises an acid to target mineral scaling in the resin.

[0068] In one embodiment, the ion exchange column may comprise a cleaning solution inlet for introducing a cleaning solution to recover at least part of the ion exchange resin. Suitably, the cleaning solution inlet is located at or near the top of the column and the cleaning solution outlet is located near the bottom of the column. This enables downward flow of the cleaning solution in the column.

[0069] The system may be configured to deliver a contaminated aqueous stream against gravity through the column and the cleaning solution with gravity through the loaded resin. The opposing flows of these streams may be beneficial by ensuring the polishing zone is restored with high efficiency by optimising chemical consumption and waste footprint. In this specification, the term “counter-current” is used to refer to the opposing flows of the contaminated aqueous feed stream and the cleaning solution.

[0070] Aqueous feed stream pre-treatment unit

[0071] To further improve efficiency, particularly to mitigate solids build-up and fouling, the system may include an aqueous feed stream pre-treatment unit for reducing the concentration of impurities in the aqueous feed stream before the aqueous feed stream is directed to the ion exchange column.

[0072] The filter may be configured to remove particulate and soluble impurities, such as total suspended solids (TSS), free chlorine and dissolved organic carbon compounds, from the aqueous feed stream before the aqueous feed stream is fed to the ion exchange column.

[0073] Suitably, the pre-treatment unit comprises a filter. More suitably, the filter is a granular activated carbon (GAC) filter.

[0074] The ion exchange resin cleaning and pre-treatment units may also help enhance resin performance and longevity.

[0075] Cleaning solution recovery unit

[0076] The system may include a cleaning solution recovery unit. Suitably, the recovery unit comprises a solid-liquid separator to separate the PF AS contaminant from the PFAS-rich effluent stream exiting the ion exchange resin cleaning unit and form a PFAS-rich waste stream and a recovered cleaning solution stream. Suitably, the solid-liquid separator includes a filter, more suitably a membrane filter (which may either be a polymeric or ceramic type), even more suitably a pH-stable membrane filter. Deploying a pH-stable membrane may improve the longevity and potentially efficiency of the membrane given that the PFAS-rich effluent stream is expected to be either acidic or alkaline.

[0077] The recovery unit comprises a plurality of solid-liquid separators that are arranged in series. Suitably, the recovery unit comprises a pair of solid-liquid separators that are arranged in series. In some embodiments, the recovery unit comprises an advanced membrane system including a ceramic membrane.

[0078] The cleaning solution recovery unit may be in fluid communication with a mixing tank for recycling the recovered cleaning solution. In the mixing tank, the recovered cleaning solution may be combined with fresh cleaning solution for treating more spent resin.

[0079] The cleaning solution recovery system may be selected based on the type and nature of resin used in the system.

[0080] PFAS contaminant concentrator The system may include a contaminant concentrator for concentrating the PF AS contaminant removed from the loaded resin. The contaminant concentrator may also be configured to destroy or render benign the PF AS contaminant before discharge into the environment. Suitably, the cleaning solution recovery unit is in fluid communication with contaminant concentrator to direct the PFAS-rich waste stream to the concentrator.

[0081] In another aspect, the present invention provides an ion exchange column for use with the previously described system.

[0082] In one embodiment, the present invention provides an ion exchange column for selectively removing a PFAS contaminant from an aqueous feed stream, wherein the ion exchange column is configured to compartmentalise at least one type of PFAS-selective ion exchange resins and receive the aqueous feed stream, and form a PFAS-depleted effluent stream and a PFAS-loaded ion exchange resin. Suitably, the PFAS-selective ion exchange resin is arranged in a multi-bed configuration in the column.

[0083] The ion exchange column may comprise at least two compartments, suitably three compartments, for receiving different types of ion exchange resins.

[0084] Each compartment may receive one type of ion exchange resin. Suitably, each type of ion exchange resin forms a bed of resin in the column.

[0085] The ion exchange column may comprise two types of ion exchange resins having different selectivity for PFAS, suitably three types of ion exchange resins having different selectivity for PFAS. In one embodiment, the ion exchange column may comprise a bed of a first type of ion exchange resin having high selectivity for short-chain PFAS, a bed of a second type of ion exchange resin having moderate selectivity for short-chain PFAS, and a bed of a third type of ion exchange resin having high selectivity for long-chain PFAS.

[0086] The ion exchange column may comprise a feed inlet for introducing a contaminated aqueous stream to the bottom of the ion exchange column.

[0087] The ion exchange column may comprise a treated aqueous stream outlet at the top of the ion exchange column.

[0088] The ion exchange column may be configured to allow the aqueous feed stream to follow sequentially through each compartment of resin.

[0089] Arranging the aqueous feed inlet at the bottom of the ion exchange column and the treated aqueous stream outlet at the top of the column generates upward flow of the aqueous feed stream through the column. Inducing fluid flow against gravity in this manner may reduce build-up of solids in the column and / or problems associated with pressure drop. The ion exchange column may be configured to locate the first type of ion exchange resin near the top of the ion exchange column, suitably, near the treated aqueous stream outlet.

[0090] The ion exchange column may be configured to locate the third type of ion exchange resin near the bottom of the ion exchange column, suitably near the aqueous feed inlet.

[0091] The ion exchange column may be configured to locate the second type of ion exchange resin between the first type of ion exchange resin and the third type of ion exchange resin.

[0092] The ion exchange column may be configured for sequential flow of the contaminated aqueous stream from a bed of the third type of ion exchange resin to a bed of the first type of ion exchange resin.

[0093] The ion exchange column may include at least one cleaning solution inlet for introducing cleaning solution to at least one of the resin beds.

[0094] The ion exchange column may comprise a cleaning solution inlet for introducing a cleaning solution to the first bed of ion exchange resin.

[0095] The ion exchange column may comprise a cleaning solution inlet for introducing a cleaning solution to the second bed of ion exchange resin.

[0096] The ion exchange column may comprise a cleaning solution inlet for introducing a cleaning solution to the third bed of ion exchange resin.

[0097] In another aspect of the present invention, there is provided a method of operating the previously described system for selectively removing a PF AS contaminant from an aqueous feed stream.

[0098] The method may include:

[0099] introducing an aqueous feed stream containing a PF AS contaminant to a system comprising at least one ion exchange column, the at least one ion exchange column comprising a plurality of compartments containing at least one type of PFAS-selective ion exchange resin, and forming a PFAS-depleted effluent stream and a PFAS-loaded ion exchange resin; and

[0100] recovering at least part of the PFAS-loaded ion exchange resin and forming a PFAS-rich waste stream from the PFAS-loaded ion exchange resin.

[0101] The method may include selecting an ion exchange resin having either enhanced selectivity for short-chain PF AS or long-chain PF AS. The method may include configuring the column to comprise at least two types of ion exchange resins, wherein the at least two types of ion exchange resins have different selectivity for the PF AS contaminant.

[0102] The method may include selecting at least one type of ion exchange resin to have enhanced selectivity for short-chain PF AS. Suitably, the method includes selecting at least one type of ion exchange resin to have enhanced selectivity for long-chain PFAS.

[0103] The method may include selecting an ion exchange resin that has enhanced selectivity for a co-contaminant such as heavy metals.

[0104] The method may include configuring the ion exchange column to contain a first type of ion exchange resin having high selectivity for short-chain PFAS, a second type of ion exchange resin having moderate selectivity for short-chain PFAS, and a third type of ion exchange resin having high selectivity for a long-chain PFAS.

[0105] The method may include selecting at least one type of ion exchange resin to be recoverable.

[0106] The method may include selecting the amount of each ion exchange resin for the column.

[0107] The method may include delivering the aqueous feed stream to the bottom of the column in a manner that enables the aqueous feed stream to flow upwards through the column.

[0108] The method may include configuring the ion exchange column to compartmentalise the at least two types of ion exchange resins. Suitably, the method includes loading each compartment of the column with one type of ion exchange resin.

[0109] In an embodiment wherein the different types of ion exchange resin are compartmentalised into discrete beds of resin, the method may include directing the aqueous feed stream to sequentially flow through each compartment of ion exchange resin.

[0110] The method may include flowing the aqueous feed stream sequentially through the compartments of ion exchange resin from the bottom of the ion exchange column to the top of the ion exchange column. Suitably, the method includes flowing the aqueous feed stream sequentially through the compartments of ion exchange resin from the bottom of the ion exchange column to the top of the ion exchange column, wherein at least one ion exchange resin having high selectivity for long-chain PFAS compounds is located near the bottom of the ion exchange column. More suitably, the method includes flowing the aqueous feed stream sequentially through the beds of ion exchange resin from the bottom of the ion exchange column to the top of the ion exchange column, wherein the at least one ion exchange resin having high selectivity for short-chain PFAS compounds is located near the top of the ion exchange column.

[0111] The method may include an ion exchange resin cleaning or recovery step to form recovered ion exchange resin for re-use in the column and a PFAS-rich waste stream.

[0112] The method may comprise introducing the cleaning solution to at least one of the beds of ion exchange resin in the ion exchange column.

[0113] The method may include cleaning or replacing the ion exchange resin loaded with the PFAS-containing contaminant. This step re-activates or recovers the at least one ion exchange resin for re-use in the column.

[0114] In one embodiment, the method comprises cleaning the loaded ion exchange resin internally in the ion exchange column.

[0115] The method may include contacting the ion exchange resin loaded with PFAS contaminant with a cleaning solution to unload the contaminant from the ion exchange resin. Suitably, the method includes delivering the cleaning solution to the top of the column, wherein the cleaning solution flows downwards with gravity through the column, and forms recovered ion exchange resin and a PFAS-rich effluent stream.

[0116] In this embodiment, the method may include a backwashing step. The backwashing step may involve in-situ flushing of the ion exchange resin in the column with a cleaning solution. Suitably, the method includes initiating the backwashing step after stopping the aqueous feed stream flow into the column.

[0117] In another embodiment, the method comprises cleaning the loaded ion exchange resin externally to the ion exchange column. The ion exchange resin cleaning or recovery step may include removing part of the ion exchange resin from the column before returning the reactivated or recovered ion exchange resin to the column. More suitably, the ion exchange resin cleaning or recovery step includes removing one ion exchange resin bed from the column before returning the re-activated or recovered ion exchange resin to the column.

[0118] The method may include monitoring the loading of the ion exchange resin in the column. Suitably, the method includes monitoring the PFAS contaminant concentration in an effluent stream of the column.

[0119] The method may include selecting an appropriate cleaning solution based on its pH. This enables the solution pH of the ion exchange resin in each compartment to be adjusted and control desorption of the PFAS contaminant. The method may include a pre-treatment step of separating suspended solids and / or organic compounds from the aqueous feed stream before introducing the contaminated aqueous feed stream to the ion exchange column. Suitably, the method includes filtering the aqueous feed stream to remove one or more of suspended solids, free halide ions such as chloride and / or organic carbon compounds from the aqueous feed stream before introducing the contaminated aqueous feed stream to the ion exchange column.

[0120] The method may include a cleaning solution recovery step. Suitably, the cleaning solution recovery step includes a solid-liquid separation step to separate the PF AS contaminant from the PFAS-rich effluent stream and form a PFAS-rich waste stream and a recovered cleaning solution stream.

[0121] The cleaning solution recovery step may include filtering the PFAS-rich effluent stream to remove the PFAS contaminant and form a PFAS-rich waste stream and a recovered cleaning solution stream.

[0122] The cleaning solution recovery step may include directing the recovered cleaning solution stream into a mixing tank for recycling back to the column. Suitably, the cleaning solution recovery step includes combining the recovered cleaning solution with fresh cleaning solution for treating more spent ion exchange resin.

[0123] The method may include concentrating the PFAS-rich waste stream from the ion exchange resin cleaning or recovery step to form a PFAS contaminant concentrate. Suitably, the concentrating step also includes destroying or rendering harmless the PFAS contaminant concentrate.

[0124] Implementing protocols for chemical cleaning and re-using cleaning solutions further improves operational efficiency and reduced chemical consumption. This sustainable approach lowers operational costs associated with ion exchange resin maintenance. The recovery and re-use of ion exchange resins and cleaning solutions may be achieved using membrane-based separation technologies. For example, suitable technologies include ceramic membrane, nanofiltration membrane, forwards osmosis membrane or disc tube reverse osmosis membrane.

[0125] In addition, a closed-loop hybrid system for selectively removing per- and polyfluoroalkyl substances (PFAS) from an aqueous stream is disclosed. The system may include at least one ion exchange column divided into multiple compartments containing one or more PFAS-selective resins or adsorbents, configured to receive an aqueous feed and discharge a PFAS-depleted effluent. A cleaning and reconditioning unit may be connected to the column to desorb PFAS from PFAS-loaded resins and recover the resins for re-use, forming a PFAS-rich effluent suitable for destruction or controlled disposal. Each compartment allows the resin to be cleaned or replaced on demand without interrupting operation. The system enables recovery and reuse of treatment chemicals and process streams, providing continuous operation with reduced chemical consumption, extended resin life, and minimal secondary waste generation.

[0126] Also disclosed herein is a system for selectively removing a contaminant from an aqueous feed stream comprising at least one ion exchange column comprising a plurality of compartments for receiving at least one type of PFAS-selective ion exchange resin which allows progressive replacement or selective disposal of exhausted or spent resin. This is opposed to the replacement or disposal of the entire resin bed or column.

[0127] BRIEF DESCRIPTION OF FIGURES

[0128] The invention is described below by way of example only with reference to the accompanying drawings, in which:

[0129] Figure l is a schematic flow diagram of a PF AS treatment system illustrating one example of a system for selectively removing PFAS from contaminated water.

[0130] Figure 2 is a process flow diagram illustrating another example of a PFAS treatment system for selectively removing PFAS from contaminated water.

[0131] DETAILED DESCRIPTION OF FIGURES

[0132] Figure 1 shows a system for selectively removing PFAS contaminant from a feed stream of contaminated water in accordance with the invention. The contaminant includes short-chain and long-chain PFAS.

[0133] The PFAS treatment system 10 includes an aqueous feed stream pre-treatment unit 13, a PFAS contaminant removal unit 15, an ion exchange resin cleaning unit 21, a cleaning solution recovery unit 23, and a PFAS contaminant concentrator 25.

[0134] In one exemplary operation, PFAS-contaminated feed water 11 is introduced to the pre-treatment unit 13 which includes a granular activated carbon (GAC) filter for removing total suspended solids (TSS), free chlorine, and total organic carbon (TOC) to produce a filtered PFAS-contaminated water stream 12. The filtered PFAS-contaminated water 12 is then fed to the PFAS removal system 15. The PFAS removal system 15 comprises a pair of ion exchange (IX) columns 17, 19 arranged in parallel. Each IX column 17, 19 includes a plurality individual compartments 1X1-3 containing beds of ion exchange resin of varying PFAS selectivity. Compartment 1X1 contains polymeric polystyrene-based selective anionic resins based on quaternary or complex amine or inorganic adsorbers, compartment 1X2 contains polymeric polystyrene-based selective strong base anionic resins based on quaternary amine and / or tertiary amines, and compartment 1X3 contains polymeric anionic resins based on secondary amines, weak base and strong base or complex amines or inorganic adsorbers.

[0135] Resins are typically selected based on the composition of the contaminated aqueous feed streams, such as drinking water and wastewater. For example, the resins may be selected based on a preference for selectivity, fouling resistance, or recoverability. Usually, the resins in the compartments (from IX3-IX1) are organised from left to right in the order of selectivity of long-chain PF AS to short-chain PFAS, i.e. low selectivity of short-chain PF AS & high capacity resins to high selectivity of short-chain PFAS resins.

[0136] The ion exchange resin in compartments 1X3 of both columns 17 and 19 has been selected to have high selectivity for long-chain PFAS and is generally more fouling resistant compared to the other types of resin in compartments 1X1 and 1X2. The ion exchange resin in 1X3 is also recoverable and possesses anti-fouling properties to make the resin easier to clean compared to the resins contained within IX 1 and 1X2. Ion exchange resin 1X2 has medium capacity and moderate selectivity for short-chain PFAS. Ion exchange resin 1X1 has the highest selectivity for short-chain PFAS and is a single use / polisher resin. The filtered PFAS-contaminated water 12 is fed into the bottom of each IX column 17, 19 and flows upwards against gravity through compartments 1X3, 1X2 and IX 1.

[0137] The compartment receiving the PF AS-contaminated feed water 11 first, in this example 1X3, may be used to perform an organic scavenging step to prevent fouling of resins in the other compartments.

[0138] Upward flow of the contaminated water reduces TSS build-up and pressure drop in the ion exchange column. As the filtered PF AS-contaminated water 12 flows through the column, the different types of PFAS contaminants are selectively adsorbed onto the different types of resins in each compartment. It was discovered that having one type of resin in each compartment enhances removal of the PFAS contaminants compared to each compartment containing a mixture of resins.

[0139] This forms a treated PFAS-depleted product stream 20 which exits the IX columns 17, 19 from the top of each of the column, and PFAS loaded / spent resin in the columns. In this embodiment, the spent resin is transferred to an external resin cleaning unit 21 which is in the form of a tank. In this tank, the spent resin is treated with a cleaning solution to recover the resin for re-use in the column and produce a PFAS-rich effluent stream which is stored in tank 22. The PFAS-rich effluent stream is subsequently transferred to a cleaning solution recovery unit 23 comprising a pair of solid-liquid separators 23 A and 23B arranged in series, wherein the effluent from separator 23A is the feed for separator 23B. The cleaning solution recovery unit 23 generates a recovered cleaning solution stream 26 and a PFAS-rich waste stream 28. Each solid-liquid separator includes a pH stable membrane for tolerating the cleaning solutions which are often either acidic or alkaline.

[0140] The recovered PFAS-free cleaning solution stream 26 is directed into a mixing tank 24 to be combined with fresh resin cleaning solution before being delivered to the resin cleaning vessel 21 to process more spent resin while the PFAS-rich waste stream 28 is sent to a PF AS concentrator 25 to concentrate the PF AS contaminant for disposal. In some embodiments, the PFAS concentrator 25 may be configured to destroy or render harmless the PFAS before being it is discharged to the environment.

[0141] Figure 2 shows a process flow diagram of another system for selectively removing PFAS from a feed stream 102 of contaminated water. The system 100 includes a multi -bed ion exchange column 105 comprising discrete beds of a short-chain polisher IX resin 107, a long-chain polisher IX resin 109, and a long-chain lead IX resin 110 that are arranged vertically along the column. A PFAS-containing feed water stream 102 is introduced at the bottom of column 105 and sequentially passed through the beds of IX resin 110, 109 then 107 to remove different forms of PFAS from the feed stream to form a treated water stream 111 and load the resin beds with PFAS contaminants. Treated water 111 exits from the top of column 105. Bypass line 120 is controlled by PFAS Quality Control (QC) sensor 122 to enable off specification treated water to be purged into by-pass tank 124, and potentially returned to the column 105 for reprocessing.

[0142] A key difference between the systems of Figures 1 and 2 is that the resin cleaning / recovery in Figure 1 is performed external to the ion exchange column while the resin cleaning / recovery in Figure 2 is performed in the ion exchange column.

[0143] In this respect, to recover the PFAS-containing loaded beds of resin, the PFAS feed 102 is stopped and an acid stream 101 is introduced to the column 105 at inlets above IX resin beds 109 and 110 and an alkali stream 103 is introduced to the column 105 at an inlet above IX resin bed 109 to backwash the loaded resins. The ability to selectively treat individual beds of resin using different cleaning solutions allow targeted processing of the resin beds. This is particularly beneficial when treating aqueous feed streams having varying types and concentrations of PFAS contaminants. It also avoids having to replace the entire mass of resin when only part of the resin has reached end of life.

[0144] The acid and alkali streams pass through the respective beds of loaded IX resin to recover the resins 107, 109 and 110 and form PFAS-rich backwash effluent streams which are stored in tanks 115 and 117, respectively. The PFAS-rich backwash solutions may be transferred to a cleaning solution recovery unit 113 where the PF AS is removed from solution and disposed of while the recovered acidic and alkali cleaning solutions are returned to the system. Impurity sensor 126 is used to monitor the composition of the PFAS-rich backwash solutions sent to the cleaning solution recovery unit 113.

[0145] Experimental Data of Removal Efficiency

[0146] The Applicant conducted three 50 kL batch trials using the PF AS treatment system of the present invention.

[0147] The trials were conducted under high Total Organic Carbon (TOC) conditions (e.g. >10 mg / L), and the results were analysed to assess ionic PF AS and Total Oxidizable Precursors (TOP A), the PF AS, oxidizable precursor, and fluorine removal efficiencies, and overall process stability. The TOPA results for the three batch trials are shown in Table 1. The various parameters in the table measures the following values:

[0148] • “Sum of PF AS (after oxidation)”: concentration of PFAS including oxidized precursors.

[0149] • “Sum of PFHxS + PFOS”: concentration of long-chain PFAS subset.

[0150] • “Sum of TOP C4-C14 carboxylates & C4-C8 sulfonates”: PFAS family after oxidation.

[0151] • “Sum of TOP C4-C14”: Fluorine as an indicator of the fluorine mass balance.

[0152] Table 1 - TOPA results

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[0157] The PF AS removal results for the three batch trials are shown in Table 2. The various parameters in the table measures the following values:

[0158] • “Sum of PF AS”: native PF AS before oxidation.

[0159] • “Sum of PFHxS + PFOS”: long-chain PF AS subset.

[0160] • “Sum of PF AS (WA DER List)”: PF AS group as per the list used by the Western Australian Department of Water and Environmental Regulation (DWER).

[0161] Table 2 - PFAS removal results

[0162]

[0163] Batch 1 - High precursor load

[0164] The influent contained 42.1 pg / L of oxidizable PFAS (with a fluorine equivalence of 26.7 pg F / L) and 10.5 pg / L of native PFAS. Less than 1% of this mass was long-chain PFAS, indicating dominance by short-chain precursors in the influent. The system achieved approximately 70% TOPA reduction and >99.9% ionic PFAS removal. The trial results for Batch 1 validate strong precursor capture even in high-TOC conditions.

[0165] Batch 2 - Moderate precursor load

[0166] The influent concentration decreased to 9.14 pg / L oxidizable PFAS and 12.5 pg / L native PFAS. The removal efficiency was approximately 52% for TOPA and >99.9% for native PFAS. This batch demonstrates stable operation and effective PFAS polishing under moderate loading conditions.

[0167] Batch 3 - Low precursor load The influent measured 4.36 pg / L oxidizable PF AS and 3.32 pg / L native PFAS, with a fluorine equivalence of 2.82 pg F / L. The removal efficiency was approximately 35% for TOPA and >99.9% ionic PFAS removal (<0.002 pg / L PFAS in the effluent). This indicates continued polishing capacity and stable bed performance across a range of PFAS amounts.

[0168] The removal efficiencies for the three batch trials are provided in Table 3.

[0169] Table 3 - PFAS and TOPA removal efficiency

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[0172] The results in Table 3 show that the system achieved consistently high PFAS and precursor removal across all three 50 kL batches. Batch 1 verified high precursor capture under complex, high-organic conditions which cause fouling or saturation of typical singlebed ion exchange resins, while Batches 2 and 3 confirmed process stability and achieved low effluent PFAS. Overall, the system achieved >99.9% ionic PFAS removal and up to 70% oxidizable PFAS reduction which shows improved hydrodynamic stability and fouling control using the compartmental multi-bed ion exchange column of the present invention.

[0173] In addition, as shown in Table 4, the present system consistently removed all monitored fluorotel omer sulfonic acids (FTS) (C4-C10) below detection limits across 50- 150 kL throughput. The removal efficiency exceeded 95% even at high loadings, confirming strong hydrophobic capture and minimal fouling impact. The data validates the robustness of the system and flow sequencing design for stable precursor (FTS) control when compared to the performance of single-bed configurations.

[0174] Table 4 - FTS removal efficiency

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[0178] Many modifications may be made to the embodiment without departing from the spirit and scope of the invention. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

CLAIMSThe claims defining the invention are as follows:

1. A system for selectively removing a contaminant from an aqueous feed stream comprising at least one ion exchange column comprising a plurality of compartments for receiving at least one type of PFAS-selective ion exchange resin, the system configured to receive the aqueous feed stream and form a PFAS-depleted effluent stream and a PFAS-loaded ion exchange resin; and an ion exchange resin cleaning unit for recovering at least part of the PFAS-loaded ion exchange resin and forming a PFAS-rich effluent stream.

2. The system according to claim 1, wherein each compartment contains one type of ion exchange resin.

3. The system according to either claim 1 or 2, wherein the at least one ion exchange column includes a physical barrier to separate the plurality of compartments.

4. The system according to any one of the preceding claims being configured to enable sequential flow of the aqueous feed stream through each compartment of the ion exchange column.

6. The system according to any one of the preceding claims, wherein the at least one type of PFAS-selective ion exchange resin has either enhanced selectivity for short-chain PFAS or long-chain PF AS.

7. The system according to any one of the preceding claims, wherein the at least one ion exchange column contains at least two types of PFAS-selective ion exchange resins.

8. The system according to any one of the preceding claims, wherein the ion exchange column contains a first type of ion exchange resin having high selectivity for shortchain PFAS, a second type of ion exchange resin having moderate selectivity for short-chain PFAS, and a third type of ion exchange resin having high selectivity for long-chain PFAS.

9. The system according to any one of the preceding claims, wherein the ion exchange resin cleaning unit is separate to the ion exchange column.

10. The system according to claim 9, wherein the ion exchange resin cleaning unit includes a cleaning solution inlet located at or near the top of the unit for introducing a cleaning solution and a cleaning solution outlet located near the bottom of the unit.

11. The system according to any one of claims 1 to 8, wherein the ion exchange resin cleaning unit is part of the ion exchange column.

12. The system according to claim 11, wherein the ion exchange column comprises a cleaning solution inlet located at or near the top of the column for introducing a cleaning solution and a cleaning solution outlet located near the bottom of the column.

13. The system according to either claim 11 or 12, wherein the ion exchange resin cleaning unit is configured to perform a backwashing step to flush at least part of the resin in the column with a cleaning solution.

14. The system according to claim 13, wherein the cleaning solution is a solvent or chemical selected from brine, an acid, or a base.

15. A method of operating a system for selectively removing a PF AS contaminant from an aqueous feed stream, the method including:introducing an aqueous feed stream containing a PF AS contaminant to a system comprising at least one ion exchange column, the at least one ion exchange column comprising a plurality of compartments containing at least one type of PFAS-selective ion exchange resin, and forming a PFAS-depleted effluent stream and a PFAS-loaded ion exchange resin; andrecovering at least part of the PFAS-loaded ion exchange resin and forming a PFAS-rich effluent stream from the PFAS-loaded ion exchange resin.

16. The method according to claim 15, including selecting the at least one type of PFAS-selective ion exchange resin to have either enhanced selectivity for short-chain PF AS or long-chain PF AS.

17. The method according to any one of claims 15 or 16, including configuring the ion exchange column to contain a first type of ion exchange resin having high selectivity for short-chain PF AS, a second type of ion exchange resin having moderate selectivity for shortchain PF AS, and a third type of ion exchange resin having high selectivity for a long-chain PF AS.

18. The method according to any one of claims 15 to 17, including delivering the aqueous feed stream to the bottom of the column in a manner that enables the aqueous feed stream to flow upwards through the column.

19. The method according to any one of claims 15 to 18, including configuring the ion exchange column to compartmentalise at least two types of ion exchange resins.

20. An ion exchange column for selectively removing a PF AS contaminant from an aqueous feed stream, wherein the ion exchange column is configured to compartmentalise at least one type of PFAS-selective ion exchange resin and receive the aqueous feed stream, and form a PFAS-depleted effluent stream and a PFAS-loaded ion exchange resin.

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