Additive in water treatment

Abstract

A method of increasing the removal of short chain PFAS from a treated wastewater is described, The method comprising the steps of: forming or obtaining the treated wastewater, treated for the removal of PFAS; adding an effective amount of a cationic polymer to the treated wastewater; subjecting the treated wastewater and cationic polymer to foam fractionation to form a foam and a further treated wastewater; and optionally removing the foam from the further treated wastewater.

Description

[0001] Additive in water treatment

[0002] This document claims priority from AU2024903519 filed on 29 October 2024 entitled Additive in water treatment; and PCT / AU2024 / 050938 filed on 31 August 2024 entitled An improved method of water treatment, the contents of each of which are hereby incorporated by reference in their entirety.

[0003] Technical field

[0004] The present invention relates to the removal of Per- and polyfluoroalkyl substances (PFAS) from wastewater. In embodiments, the wastewater is leachate.

[0005] Background

[0006] Per- and polyfluoroalkyl substances (PFAS) are hazardous and toxic chemical that are resistant to thermal, microbial and chemical degradation. PFAS has oleophobic and hydrophobic properties that result in it being used in industrial products such as paper, leather, lubricants, cement, metal cleaners, floor polishes, cosmetics and in foam-based fire extinguishers. Most of these products end up in landfill sites at the end of their life cycle. Hence, PFAS contamination is ubiquitous in many if not all landfill leachates.

[0007] Landfill leachate is primarily generated from rainwater percolation through putrescible waste disposed into landfill sites. It is a complex solution often rich in organic compounds and nutrients (mostly nitrogen compounds) with little consistency from site to site.

[0008] The magnitude of PFAS in landfill leachate issue is a significant environmental concern. For example, in the United States there are currently more than 2,000 active landfill sites across the nation. In 2013, the total volume of leachate generated in the United States was estimated to be 61 .1 million m3, with 79% of the volume coming from landfills in wet climates (>75 cm / yr precipitation) that contain 47% of United States solid waste. The mass of measured PFAS compounds from U.S. landfill leachate transferred to wastewater treatment plants was estimated to be between 563 and 638 kg for 2013.

[0009] Due to the complexity of leachate matrix, including high concentrations of organic and nitrogenous compounds, PFAS removal via traditional adsorption-based technologies, is significantly compromised. Granular Activated Carbon (GAC) and ion exchange (IX) systems are proven to remove PFAS from most water sources, but fouling is a prominent issue when applied to landfill leachate due to high levels of co-contaminants such as TSS, TOC, COD, NH3, colour, total N and other inorganic chemicals. The high rates and volume of the waste generated also make these options unviable.

[0010] Membrane based filtration, reverse osmosis (RO) and nanofiltration (NF), are also proven effective to remove PFAS. However, both methods are prone to organic and inorganic fouling and produce large volumes of concentrated waste, which can be difficult to manage and usually requires further volume reduction via high energy solutions such as thermal evaporation.

[0011] Destructive technologies like electro-oxidation, super critical water oxidation and thermal destruction appear to be attractive alternatives, but the high flow rates (200 - 1 ,000 kL / d) and co-contamination species within the leachate chemistry make them impractical and costly in terms of both capital and energy consumption. Hence, treating PFAS-contaminated leachate is a balance between capital, removal effectiveness, maintenance requirements, waste-stream production, and associated waste disposal costs.

[0012] Foam fractionation can avoid the pitfalls inherent to other technologies due to its fundamental principles of operation. Foam fractionation (or more accurately bubble fractionation) is a separation process that exploits the differences in surface properties of substances to selectively remove them from a liquid solution. The foam forms within the contaminated water because of the naturally occurring or artificially added surfactants within the water column when air is rigorously introduced. The foam collected collapses as a liquid, known as foamate, which is typically a small fraction of the feed volume. It does not have the same clogging and fouling issues of media-based systems and does not require the level of pre- treatment required for traditional methods such as adsorption, RO / NF. The foamate (concentrate stream) produced is relatively very small and more suitable for management via destruction or other technologies.

[0013] It would be desirable to provide improved foam fractionation systems and methods that more efficiently remove PFAS from wastewater such as leachate, or at least which provides a useful alternative.

[0014] Summary of invention

[0015] Herein described is a method of increasing the removal of total short chain PFAS from leachate, the method comprising the steps of: adding an effective amount of a cationic polymer to the leachate; subjecting the leachate and cationic polymer to a first foam fractionation to form a foam and a treated leachate; removing the foam from the treated leachate.

[0016] Without wishing to be bound by theory, it is thought that the cationic polymer assists in attracting the hydrophilic heads of the PFAS molecules. Short chain PFAS molecules have weaker adsorption tendencies at the I iquid / ai r interface, but the concentrated PFAS molecules, adsorbed to the cationic polymer, can assist in increasing the adsorption tendency.

[0017] In one embodiment, wastewater has been pre-treated (is a second, third or other multiple stage of foam fractionation). In another embodiment, treated wastewater once treated by the cationic polymer is subject to a process to remove total short chain PFAS.

[0018] Thus, in one aspect there is provided a method of increasing the removal of total short chain PFAS from wastewater, the method comprising the steps of: step 1 : adding an effective amount of a cationic polymer to the wastewater; subjecting the wastewater and cationic polymer to a first foam fractionation process to form a foam and a treated wastewater; step 2: subjecting the treated wastewater to a second foam fractionation process, comprising adding at least one short-chain PFAS removal compound, wherein a decreased amount of short-chain PFAS removal compound is required in step 2 when preceded by step 1 , compared to the same step 2 when not preceded by step 1 .

[0019] It has been surprisingly found that when an effective amount of a cationic polymer is added to wastewater such as leachate, total PFAS can be removed during the foam fractionation process in an amount greater than if the cationic polymer were not added. In an embodiment, following treatment in the first stage with cationic polymer, less short-chain PFAS removal agents are required in subsequent foam fractionation passes but at lower chemical dosages compared to the same stages without being subject to the cationic polymer in the first stage. In an embodiment the amount of short short-chain PFAS removal compound in step 2 is decreased by at least about 80, 75, 50, 40, 30, 25 or 10 % when the process in step 2 is preceded by step 1 .

[0020] Without wishing to be bound by theory, it is thought that the cationic polymer removes organic acids, organic carbon and COD (OA / OC / COD) in the first step, which means that the short-chain PFAS removal compound(s) added in the second step is / are able to more readily act on the short-chain PFAS compounds without competition from the other organics. Organic acids represent specific low- molecular-weight compounds that indicate microbial activity, and very high molecular weight compounds (humic and fulvic acids) that are inherently resistant to biological activity; organic carbon quantifies the total amount of carbon contained in organic matter; and chemical oxygen demand measures the total oxygen required to oxidise all organic and some inorganic substances. The present cationic polymer can decrease the levels of OA / OC / COD with the goal of reducing the amount of short-chain PFAS removal compounds in the next stage(s).

[0021] The short-chain PFAS removal compound is selected from compounds capable of adsorbing or binding short-chain per- and polyfluoroalkyl substances. Suitable compounds include activated carbon in granular or powdered form; ion-exchange strong base anion exchange resins; modified clays including modified bentonite to include PFAS attracting functional groups such as organo-bentonite; layered double hydroxides; zeolites; metal-based adsorbents including alumina, iron oxides and metal-doped biochars; carbon-based nanomaterials including carbon nanotubes and graphene oxide; cyclodextrin polymers; and molecularly imprinted polymers.

[0022] In leachate specifically, the presence of other anionic species in the liquid can affect the role of the cationic polymer. Accordingly, the amount of cationic polymer added can be important in order for it to be effective. In an embodiment, the amount of cationic polymer added is in excess of 100 mg / L. In an embodiment, the amount of cationic polymer added is in excess of 150 mg / L.

[0023] In another aspect there is provided a method of increasing the removal of short chain PFAS from a treated wastewater, the method comprising the steps of: forming or obtaining the treated wastewater, treated for the removal of

[0024] PFAS; adding an effective amount of a cationic polymer to the treated wastewater; subjecting the treated wastewater and cationic polymer to foam fractionation to form a foam and a further treated wastewater; removing the foam from the further treated wastewater.

[0025] In an embodiment, the wastewater is leachate. Accordingly, the treated wastewater feed in this aspect can be a treated leachate.

[0026] It has been found that treated wastewater, treated for the removal of PFAS, typically has long chain PFAS removed but short chain PFAS molecules remain. The inventors have found that in some embodiments once long chain PFAS have been removed, the effective amount of cationic polymer added to the foam fractionation process is surprisingly efficacious at removing total short chain PFAS molecules in a subsequent treatment stage.

[0027] Thus, in an embodiment, the treated wastewater is one that has been subject to a treatment such as foam fractionation that removes substantially only or at least some long chain PFAS. Such treatments are typically cationic polymer free.

[0028] Accordingly, in this aspect of the present invention, the treated wastewater is the liquid stream from a typical foam fractionation process.

[0029] The following description applies to all aspects of the invention, unless the context makes clear otherwise.

[0030] Long chain PFAS are those with an alkyl chain carbon number greater than 7, such as C8, C9, C10 (https: / / pfas-1.itrcweb.orq / 2-2-chemistry-terminoloqy-and- acronyms / ). Short chain PFAS compounds, such as those with a carboxylate group attached (PFCAs), are those with an alkyl chain carbon number less than or equal to 7 such as C7, C6, C5, C4. C7 is borderline and is considered long chain by some and short chain by others. Short chain PFAS compounds with a sulphonate group attached (PFSAs) are those with a carbon number less than 6 such as C5, C4. Figure 11 sets out the carbon number for PFAS molecules.

[0031] Although PFAS compounds are surfactants by design, their concentrations are typically very low (ug / L), and as such, addition of a co-surfactant is sometimes or often required to enhance the foaming process. The hydrophobicity imparted by the PFAS moieties (carbon chain length) dictates the attachment affinity towards the air-water interface, so the PFAS compounds with long chain structures have a strong efficacy for adsorption to the foam. The hydrophobic carbon tail of the PFAS is collected at the air-liquid interfaces along with a small quantity of interstitial liquid (illustrated in Figure 1).

[0032] The present inventors have found that when a wastewater is treated by active aeration for PFAS removal, typically, long chain PFAS molecules are removed first. However, most short chain PFAS molecules remain. Short-chain PFAS molecules have higher mobility, water solubility and lower surface activity. They therefore have weaker adsorption tendencies i.e. lower partitioning coefficient. As a result, their separation from water sources by hydrophobic adsorption is inherently less favourable. To date, the removal of short chain PFAS by foam fractionation remains challenging.

[0033] The present cationic polymeric additive represents an environmentally sustainable approach to improving total short chain PFAS removal which in embodiments is commercially desirable. By total short chain PFAS removal it is meant that the overall sum of short chain PFAS is decreased. The short chain PFAS removal is undertaken in a wastewater in which either the long-chain PFAS content has been decreased or from which organic acids, organic carbon and COD (OA / OC / COD) has been decreased.

[0034] Per- and polyfluoroalkyl substances (PFAS) refer to organic compounds that contain one or more fluorine atoms. The present invention is not limited to any one or more particular PFAS compounds.

[0035] PFAS typically include fluorinated alkyl chains ranging from C2 to C18. This term encompasses perfluorinated carboxylic acids (PFCA) and perfluorinated sulfonic acids (PFSA). Within the PFAS category are long chain compounds such as perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) alongside other short- and long-chain PFAS. PFOA and PFOS are well-known examples of PFCA and PFSA, respectively.

[0036] Due to their acidic protons, PFAS generally have a pKa below 7 (as observed in sulfonic and carboxylic acids), causing them to exist in an anionic or deprotonated state in wastewater (e.g., landfill leachate). Any mention of PFAS in their acidic or protonated forms includes their anionic counterparts (e.g., references to sulfonic and carboxylic acids also imply the presence of sulfonates and carboxylates). Common PFAS found in wastewater include those categorised as PFSA, PFCA, and FTSA, as listed below, which are often present in their anionic or deprotonated forms.

[0037] PFSA (Perfluorosulfonic Acids)

[0038] • PFBS - Perfluorobutane sulfonic acid (C4)

[0039] • PFPeS - Perfluoropentane sulfonic acid (C5)

[0040] • PFHxS - Perfluorohexane sulfonic acid (C6)

[0041] • PFHpS - Perfluoroheptane sulfonic acid (C7)

[0042] • PFOS - Perfluorooctane sulfonic acid (C8)

[0043] • PFNS - Perfluorononane sulfonic acid (C9) • PFDS - Perfluorodecane sulfonic acid (C10)

[0044] • PFDoS - Perfluorododecane sulfonic acid (C12)

[0045] PFCA - Perfluorocarboxylic acid

[0046] • PFBA - Perfluorobutanoic acid (C4)

[0047] • PFPeA - Perfluoropentanoic acid (C5)

[0048] • PFHxA - Perfluorohexanoic acid (C6)

[0049] • PFHpA - Perfluoroheptanoic acid (C7)

[0050] • PFOA - Perfluorooctanoic acid (C8)

[0051] • PFNA - Perfluorononanoic acid (C9)

[0052] • PFDA - Perfluorodecanoic acid (C10)

[0053] • PFUnDA - Perfluoroundecanoic acid (C11 )

[0054] • PFDoDA - Perfluorododecanoic acid (C12)

[0055] • PFT rDA - Perfluorotridecanoic acid (C13)

[0056] • PFTDA - Perfluorotetradecanoic acid (C14)

[0057] FTSA (Fluorotelomer Sulfonic Acids)

[0058] • 4:2 FTSA - 4:2 Fluorotelomer sulfonic acid (C4)

[0059] • 6:2 FTSA - 6:2 Fluorotelomer sulfonic acid (C6)

[0060] • 8:2 FTSA - 8:2 Fluorotelomer sulfonic acid (C8)

[0061] FTCA (Fluorotelomer Carboxilic Acids)

[0062] • 4:2 FTCA - 4:2 Fluorotelomer carboxylic acid (C4)

[0063] • 6:2 FTCA - 6:2 Fluorotelomer carboxylic acid (C6)

[0064] • 8:2 FTCA - 8:2 Fluorotelomer carboxylic acid (C8)

[0065] The above list is exemplary only. There are thousands of PFAS compounds, most likely about 3000+. Some PFAS compounds are regulated. Regulations change over time, and new PFAS compounds are emerging all the time. GenX is a trade name for a technology that is used to make high performance fluoropolymers (e.g., some nonstick coatings) without the use of perfluorooctanoic acid (PFOA). Hexafluoropropylene oxide-dimer acid (HFPO) dimer acid and its ammonium salt are the major chemicals associated with the GenX technology. The focus of the present process is on the removal of PFAS to reduce the likelihood of the regulated compounds requiring treatment in resultant waste e.g. sludge and to do so cost effectively.

[0066] The processes of the invention can be performed on any liquid. The liquid can be water. The water can be wastewater. The waste in the wastewater can be PFAS. Thus, by wastewater it is meant any contaminated liquid comprising PFAS. In some embodiments, the contaminated liquid can be a raw leachate or a treated leachate. The contaminated liquid can be municipal water. The contaminated liquid can be surface water. The contaminated liquid can be groundwater. The liquid to be treated can be held in a holding tank before delivery to the first vessel.

[0067] Leachate is a type of polluted water that is particularly difficult to treat due to the high levels of different contaminants. Leachate is water that runs off from e.g. landfill and it can be contaminated by the materials in the landfill. Leachate can be harmful to the health of the surrounding flora and fauna. The Total Organic Carbon (TOC) content of the leachate can be in the range of from about 200 to 25,000 mg / L. This is high compared to e.g. groundwater which usually has TOC levels in the range of from about 1 to 5 mg / L. The leachate may also have, for example, high levels of Total Dissolved Solids (TDS), heavy metals, nutrients (including Total Nitrogen (TN) which includes Total Kjeldahl Nitrogen (TKN) which can include ammonia) and sometimes oils and grease.

[0068] Leachate can comprise contaminants including one or more of (but not limited to): materials that contribute to TOC, materials that contribute to TDS, oil(s), heavy metal(s), ammonia. The level of TOC can be at least about 3500, 4000, 5000, 6000, 7000, 8000 or 9000 mg / L. The level of TDS can be at least about 2,000 mg / L, 8000 mg / L or 14,000 mg / L. The level of TKN can be at least about 400, 800, 1600, or 2500 mg / L although in many instances it can be higher.

[0069] In embodiments, the wastewater treated by the method of the invention is leachate that has TOC contamination levels higher than about 4, 5 or 6 mg / L. In an embodiment, the wastewater has TOC contamination higher than about 5 mg / L. The wastewater can be leachate, or it can be another type of wastewater as described herein.

[0070] A cationic polymer is a polymer that contains at least one cationic component. Without being limited to theory, these cationic polymers can act as flocculants or coagulants, facilitating the formation of flocs from individual small particles of matter. In this context the polymer binds with the PFAS by adsorbing them onto the polymer through mechanisms such as bridging or charge neutralisation. Such polymers may also be designated as “cationic polymer flocculants” or “cationic polymer coagulants.” The cationic polymer should be soluble in water.

[0071] Various cationic monomer components, such as ammonium, sulfonium and phosphonium quaternaries, can be used to synthesise the cationic polymers. Alternatively, neutral variations can be protonated post-polymerisation. The term therefore also encompasses amphoteric polymers that possess both cationic and anionic components, as long as the overall balance of charge remains cationic.

[0072] The cationic polymer is not a cationic surfactant that is non-polymeric. Cetyltrimethylammonium bromide (CTAB, linear chain C19H42BrN) is a non- polymeric cationic surfactant. CTAB can enhance short chain PFAS removal via the role of charge attraction of the hydrophilic head groups (illustrated in Figure 2). The addition of cetyltrimethylammonium bromide (CTAB) as the co-surfactant can result in enhanced short chain PFAS removal from synthetic and groundwater sources. However, it has been found that the presence of co-contaminants in landfill leachate can significantly impact the collection mechanism by which short chain PFAS can be removed and in many cases involving leachate CTAB is not efficacious.

[0073] Other pollutants in landfill leachate can interfere with the effectiveness of CTAB by reacting with it or competing for the same adsorption sites, reducing its availability to interact with PFAS. These pollutants can also change how CTAB behaves in solution, such as altering surface tension or preventing the formation of micelles that trap PFAS. Additionally, contaminants might block adsorption sites or dilute the CTAB, making it less effective overall. In some cases, the pollutants may form complexes with PFAS or CTAB, making it more difficult to remove PFAS from the leachate.

[0074] Furthermore, CTAB exhibits high toxicity to human and marine environments.

[0075] CTAB is classified as a toxic chemical with human exposure limit between 0.05 and 0.4 mg / kg body weight per day and approximately 0.03 mg / L for aquatic environments. As a result, it should be avoided where possible in any process where discharge to sewers or the environment are possible, and there can be no guarantee that the CTAB deports wholly to the foamate with no residual in the treated leachate which is released.

[0076] Cationic polymers on the other hand offer several advantages over cationic surfactants in removing contaminants like PFAS from wastewater such as landfill leachate. With higher molecular weights, cationic polymers can create larger aggregates or flocs, enhancing the removal of suspended particles. They can function as bridging agents, effectively connecting smaller particles and facilitating flocculation, which leads to larger aggregates that settle more easily. Additionally, cationic polymers can neutralise the negative charges of a broader range of particles, reducing repulsive forces and improving overall removal efficiency. They also tend to have longer retention times in treatment systems, allowing for more interaction with PFAS. Unlike cationic surfactants, which can create significant foam that interferes with separation, cationic polymers typically do not produce significant foam, making them easier to work with in foam fractionation. Furthermore, cationic polymers may provide a more stable performance across various conditions, such as not changing pH and salinity, resulting in consistent results in PFAS removal.

[0077] The molecular weight of the cationic polymer can vary. Some cationic polymers can be effective at lower molecular weight, for example as low as 1 ,000 g / mol in weight-average molecular weight. But in general, the cationic polymers will have higher molecular weights, e.g., up to 50,000,000 g / mol in weight-average molecular weight.

[0078] Suitable cationic polymers include those that comprise at least one of a polyacrylamide, a polyacrylic acid, a polydiallyldimethyl ammonium, or a polyamine. Polydiallyldimethylammonium chloride (PolyDADMAC) is a type of cationic polymer formed from the polymerisation of diallyldimethylammonium chloride (DADMAC). It can be used in a water treatment processes, including flocculation and coagulation, due to its ability to interact with negatively charged particles, enhancing their removal from water. In an embodiment, the cationic polymer is PolyDADMAC. In addition, the PolyDADMAC exposure limit to humans is 1 ,000 mg / kg body weight per day, in contrast to CTAB.

[0079] The wastewater to be treated can be contacted with the cationic polymer. This contact can be prior to foam fractionation. The contact of the wastewater with the polymer can be during foam fractionation. The wastewater that has been contacted with the polymer can be subject to aeration. Air can be bubbled through the wastewater to form bubbles which rise to form a foam on the surface of the waste water. The foam comprises the injected air / gas and at least some of the PFAS components as well as the cationic polymer. At least some of the foam can be removed off the surface of the wastewater, effectively removing at least some of the PFAS component from the wastewater to form a lower PFAS component content.

[0080] The amount of the cationic polymer should be effective to remove organics and or short chain PFAS. In an untreated wastewater, the amount of organic acid removed should be considered. In a treated wastewater, the sum total of short chain PFAS removal should be considered, rather than the removal of any one particular short chain PFAS molecule. In one or all embodiments, the effective amount is at least about 100 mg / L of the cationic polymer, preferably at least about 150 mg / L, more preferably at least about 200 mg / L.

[0081] In embodiments, the cationic polymer additive demonstrates a significant increase in short chain PFAS removal from leachate at concentrations greater than about 100 mg / L. Below this level, the positive charged sites in the polymer could have been passivated by the relatively high concentration of anions, alkalinity, and other negatively charged organic compounds in the leachate (including tannins, humics and fulvics). In embodiments, the cationic polymer additive demonstrates a significant increase in organic acid and organic carbon (COD decrease) removal from leachate at concentrations greater than about 150 mg / L. Below this level, the positive charged sites in the polymer could have been passivated by the relatively high concentration of anions, alkalinity, and other negatively charged organic compounds in the leachate (including tannins, humics and fulvics).

[0082] In an embodiment, there is more than one stage of foam fractionation undertaken a series of vessels. A first vessel can be followed by a second vessel and so on. The first vessel can be a foam fractionator. The second vessel can also be a foam fractionator. A foam fractionator, also known as a foam separator, is a device used in various industrial processes to remove organic compounds, proteins, and or other dissolved or suspended particles from a liquid (usually water). The primary purpose of a foam fractionator is to improve water quality by removing or at least reducing the concentration of pollutants and contaminants. While a foam fractionator can be used it should be understood that any vessel into which there can be a flow of liquid, and in which froth or foam can be created, is in scope.

[0083] The applicant / patentees own W02025043303 - THE CONTROL OF CONTINUOUS WATER TREATMENT filed 31 August 2024 describes a multistage foam fractionation process. The contents of W02025043303 as published is incorporated by reference in its entirety. Where there is any discrepancy between the inventions described, the present specification and invention description takes precedence.

[0084] Each vessel can be configured to receive incoming liquid for treatment. The vessel can have one or more inlets to receive the liquid to be treated. The first vessel can receive incoming liquid from a holding tank or supply reservoir of wastewater for treatment. The holding tank can be filled, for example, by pumping raw leachate through a mechanical control valve to control the volumetric flow to the supply reservoir. The level in the supply reservoir can be monitored by a submersible / pressure level transmitter. The cationic polymer can be added to the leachate in the holding tank, to the first vessel and or into the pipe joining the two.

[0085] The liquid to be treated can be pumped from the supply reservoir to the first vessel at a steady flow rate by a first feed pump. The liquid can be pumped into the top or near the top of the first vessel. Air can be injected into the bottom or near the bottom of the first vessel. The air can be injected, and bubbles formed via any means including fine bubble diffusers to generate air bubbles, venturi and or airstones.

[0086] The second vessel can receive incoming liquid from the first vessel through an inlet. The liquid to be treated is treated liquid. The treated liquid can be pumped to the second vessel at a steady flow rate. The liquid can be pumped into the top or near the top of the second vessel. Air can be injected as with the first vessel into the bottom or near the bottom of the second vessel.

[0087] In an embodiment there are one or more first vessels operating in parallel. The first foam collected from each first vessel can be treated separately or combined. The first treated liquid from each first vessel can be treated separately or combined. In an embodiment there are one or more second vessels operating in parallel. The second foam collected from each second vessel can be treated separately or combined. The second treated liquid from each second vessel can be treated separately or combined. If there is a third vessel the same description applies.

[0088] In some embodiments, the cationic polymer is added to the first vessel. The liquid from the first is sent to the second vessel. In some embodiments, the cationic polymer is added to the second vessel (or to a pipe connecting the first vessel with the second vessel), so the treated liquid is mixed with the cationic polymer once in the second vessel. This can be done in addition to adding the cationic polymer to the first vessel. In an embodiment, the cationic polymer is only added to the second vessel in the continuous foam fractionation series.

[0089] In an embodiment of the process there is one or more third vessels configured to receive incoming second treated liquid (further treated liquid) from the second vessel. The second treated liquid from the second vessel can be pumped using a third vessel feed pump, optionally at a steady flow rate, into the top or near the top of the third vessel for further treatment. The one or more third vessels can generate a third treated liquid and a third foam. In some embodiments, the cationic polymer is added to the third vessel (or to a pipe connecting the second vessel with the third vessel), so the treated liquid is mixed with the cationic polymer once in the third vessel. This can be done in addition to adding the cationic polymer to the first and or the second vessel. In an embodiment, the cationic polymer is only added to the third vessel in the continuous foam fractionation series. In other embodiments, the cationic polymer flows into the third vessel with the cationic polymer therein.

[0090] The foam can be removed from a process step. The foam can be removed by any means including vacuum, scraping, passive or other. In an embodiment, each vessel can comprise a hood. In the base of the hood can be an upward facing cone, which causes the foam to rise through the cone and be trapped at the top of the vessel in the hood and which thereby assists in the build-up of pressure within the vessel. Each hood can have an opening therein which allows for the exit of foam. This exiting of the foam can be under pressure.

[0091] Brief Description of the Figures

[0092] Embodiments of the invention will now be described with reference to the accompanying drawings which are not drawn to scale and which are exemplary only and in which:

[0093] Figure 1 is a schematic showing how the hydrophobic carbon tail of the PFAS is collected at the air-liquid interfaces along with a small quantity of interstitial liquid.

[0094] Figure 2 is background art showing how CTAB can enhance short chain PFAS removal via the role of charge attraction of the hydrophilic head groups.

[0095] Figure 3 is Table 1 showing the chemical parameters of a leachate.

[0096] Figure 4 is a schematic of a single stage foam fractionation process. Figure 5 is a schematic of a multistage continuous foam fractionation process.

[0097] Figure 6 is Table 2 showing the results of the CTAB trial.

[0098] Figure 7 is Table 3 showing a control experiment without cationic polymer additive.

[0099] Figure 8 is Table 4 showing the PFAS concentrations in the Raw Leachate, and the impact of the various PDM doses (PDM is a cationic polymer, and is PolyDADMAC).

[0100] Figure 9 is Table 5 showing the PFAS concentrations in the Treated Leachate at various dose rates of the PDM additive.

[0101] Figure 10 is Table 6 showing the PFAS concentrations in the Treated Leachate with and without PDM additive

[0102] Figure 11 shows a table of PFAS molecule carbon counts.

[0103] Figure 12a-d are Tables 7 to 11 showing the percentage removal of PFAS from FF1 , FF2 and FF3 at various dose rates (0 ppm (Table 7), 100 ppm (Table 8), 125 ppm (Table 9), 150 ppm (Table 10), 175ppm (Table ”)).

[0104] Figure 13 is a graph showing removal of short chain PFAS at various dose rates.

[0105] Figure 14 is a table showing the colour observations of an experiment.

[0106] Examples of Embodiments of the Invention

[0107] Embodiments of the invention will now be described with reference to the following examples which are exemplary only. This present study involved two assessments: the addition of CTAB to landfill leachate (comparative example), and also the addition of a polymer reagent (PDM). PDM is Polydiallyldimethylammonium chloride (PolyDADMAC).

[0108] PDM polymer is a cationic polyelectrolyte and exhibits a high charge density, which would potentially encourage electrostatic adsorption of short chain PFAS compounds.

[0109] The leachate source was an Australian landfill leachate treatment operation. The characteristic of the leachate is outlined in Table 1 of Figure 3. The data of the Table of Figure 3 is typical of the site from which it was collected, and the chemical parameters present are typical of landfill leachate in general, with high salinity, alkalinity, organics and ammonia. The colour was a dark amber brown, due to the strong presence of humic and fulvic acids. The odour was very strong and acrid, as expected from putrescible waste. Other landfill sites have similar matrices but vary on the overall concentration of chemical compounds, including salinity and odour.

[0110] In these tests, the source leachate was pumped from a storage tank to a foam fractionation process. The system schematic is shown in Figure 4. Leachate was pumped into the foam fractionation (FF) unit at a defined flow rate, while regulated airflow was introduced from the bottom to produce fine air bubbles. The bubbles moved upwards and coalesced to produce a foam layer due to the presence of background surfactants within the leachate matrix. PFAS compounds were removed via adsorption onto the foam that was created. The PFAS-containing foam continued to flow upwards through a hood where it collapsed and was removed as a liquid (foamate). The PFAS depleted treated leachate was discharged from the fractionator and entered a second storage vessel (not shown). The treated leachate in this vessel was again passed through a foam fractionator unit to affect a second pass treatment. The raw leachate and the treated leachate from the second pass were sampled and analysed for the interpretation of the data.

[0111] Example 1: CTAB

[0112] Leachates can vary in concentration and are complex compared to many industrial wastewaters, so to ensure abundant co-surfactant charge was available, and not deactivated or passivated, high dose rates were applied (7 mg / L).

[0113] Foam fractionation (FF) trials were conducted using a bench scale foam fractionator (XFLOW model 6 - 2.5 Protein Skimmers). A peristaltic pump (Master Flex L / S series) was used for the liquid phase (leachate) delivery to the fractionation column. The liquid feed flowrate was measured by a rotameter (Dwyer Instrument Inc).

[0114] For all trials, the liquid flowrate was pre-set to create a hydraulic retention time of 30 minutes per pass. The air flow was adjusted to a pre-determined airflow rate. The trials were performed without addition of the co-surfactant. No primary surfactant was required because the leachate contained background surfactants in its matrix.

[0115] Results

[0116] The trial results are shown in Table 2 of Figure 6. Only compounds with Feed concentrations above the LoR (limit or reporting) are shown.

[0117] The results showed approximately 20% of PFBS (C4) removal with and without addition of CTAB. The removal of PFPeA (C5) was moderate at 4% without CTAB and 11 % with CTAB. This observation could be within procedural uncertainty. The removal of PFHxA (C6) also showed no improvement with the addition of CTAB.

[0118] A reason for the lack of improvement of short chain PFAS removal using CTAB is likely because the wastewater is leachate. Landfill leachate is a very complex solution containing very high TDS, TOC, COD, nitrogen compounds that render conventional PFAS treatment systems, such as IX resin and activated carbon, uneconomic and impractical. RO and NF effectively remove PFAS but require extensive pre-treatment and create large volumes of waste that requires additional treatment. Foam Fractionation is the only process that is both cost effective and efficient at removing regulated long chain PFAS compounds, such as PFOA, PFOS, PFHpA and PFHxS. The removal of short chain PFAS however remains challenging due to the reduced affinity for attachment of PFAS to the bubbles. This study confirmed that at the doses trialled, CTAB offers no benefit of enhanced removal because the anionic compounds in the leachate matrix (including tannic, humic and fulvic acids) deactivated the positively charged amine groups on the CTAB. This impacted the capacity to bind the negatively charged short chain PFAS head group, and act as a collector.

[0119] In addition to CTAB addition being ineffective, the compound is highly undesirable as a reagent due to its toxicity to human, marine and aquatic life. There can be no guarantee that CTAB does not exceed the toxic exposure levels in the treated leachate that is released to sewer or environment. There are no specific analyses for CTAB in treated leachate so this risk is enhanced by not knowing the concentrations in the discharged stream.

[0120] Example 2 - Pilot scale - PDM

[0121] The trial utilised a 3-fractionator pilot system constructed from transparent polycarbonate, with dimensions of 400 mm in diameter and a maximum internal volume of 100 L. These pilot vessels allowed for clear observation of leachate treatment dynamics, including agitation, aeration, bubble size, foam generation, and liquid level within the vessel.

[0122] Due to the complex chemical nature of the landfill leachate four PDM doses were assessed to ensure passivation and deactivation of the charged sites did not occur. These were 50, 100, 150 and 200 mg / L. No surfactant addition was required because the leachate naturally had background surfactants within its matrix.

[0123] Two tests were conducted at pilot scale.

[0124] 1 . Raw Leachate,

[0125] 2. T reated Leachate from the primary separation stage of a full scale facility, from which long chain PFAS was significantly or completely depleted.

[0126] The feed was pumped to create a hydraulic retention time of 30 minutes per pass.

[0127] T reated leachate from foam fractionator FF1 , after the first pass, was gravitationally transferred to foam fractionator FF2 for the second pass. Similarly treated leachate from FF2, after the second pass, was gravitationally transferred to foam fractionator FF3 for the third pass. Air was introduced via a diffuser into the base of each fractionator to create fine bubbles.

[0128] Foamate was collected from each foam fractionator via gravity removal from the foamate collection hood into a designated collection tank. A schematic of the pilot process is shown in Figure 5.

[0129] Raw leachate

[0130] Each dose of PDM was injected into the Raw Leachate Feed line prior to entry into FF1 : 50, 100, 150 and 200 mg / L.

[0131] Treated leachate (subject to one foam fractionation process)

[0132] T reated leachate was fed to FF1 . Only one dose of PDM was injected into the Treated Leachate Feed line prior to entry into FF1 (150 mg / L). This was selected on the basis of the Raw Leachate test results.

[0133] The Treated Leachate predominantly contained short chain PFAS (e.g. PFBS, PFPeA, PFHxA), representing approximately 90% of the total PFAS concentration in the feed used in the test.

[0134] Feed leachate (raw or primary treated) and the third pass treated leachate, were collected for analysis after 3 x hydraulic retention times had passed. PFAS analyses were performed by a NATA accredited laboratory using a modified version of LC-MS draft Method USA EPA 1633.

[0135] Results - Raw Leachate

[0136] Table 3 of Figure 7 is a control experiment without cationic polymer additive. The results show long chain PFAS removal. However, total short chain PFAS (C4-C6) concentration is not significantly reduced.

[0137] Without reagent addition:

[0138] • PFBS (C4) was depleted by only 20%.

[0139] • PFPeA (C5), zero 0% removal was observed.

[0140] • PFHxA (C6), the removal was approximately 7%. Table 4 of Figure 8 shows the PFAS concentrations in the Raw Leachate used in this test, and the impact of the various PDM doses. Only compounds with detected levels in the Raw Leachate are shown.

[0141] • For PFBS (C4) at higher dose rates of 150 and 200 mg / L, a significant depletion from raw leachate was observed, at 64 and 71% respectively.

[0142] • At all dose rates of PDM, the removal of PFPeA (C5) from raw leachate was approximately 70%.

[0143] • For PFHxA (C6), at the dose rates of 50 and 100 mg / L the removal from raw leachate was negligible, approximately 4%, but at the higher doses of 150 and 200 mg / L the removal increased significantly to approximately 80%.

[0144] Results - Treated Leachate

[0145] Table 5 of Figure 9 shows the PFAS concentrations in the Treated Leachate with and without additive (150 ug / L).

[0146] • PFBS (C4) was depleted by 3% in the un-dosed samples, and 75% with the additive.

[0147] • PFHpA (C4) was completely depleted with and without the addition of PDM.

[0148] • PFPeA (C5) had 3% removal without the addition of PDM; but with the additive, 83% removal was shown.

[0149] • For PFHxA (C6) the removal was approximately 12% in the un-dosed samples. With the additive, 83% was observed.

[0150] The polymer PDM did facilitate significant removal of short chain compounds, notably PFBS, PFHpA and PFHxA. Other short chain compounds could not be assessed because they were not detected in the feed solutions.

[0151] Further trials

[0152] The results of further trials are shown in Table 6 of Figure 10.

[0153] The analytical results indicate that the addition of PDM significantly enhanced the removal of PFBS. As shown in table 6, PFBS removal in the effluent without PDM addition (0 ppm) was only 8%. However, with a dosage of 150 ppm PDM, the removal efficiency improved substantially to 87%. The results for 50 ppm PDM also demonstrated a notable reduction. At a dosage of 200 ppm PDM, the detection limit of the current analytical method prevented precise quantification of the actual removal. Nevertheless, based on the detection limit, more than 80% PFBS removal was achieved.

[0154] All results show an increase in PFBA concentration in the treated leachate (effluent). This unusual result could be due to:

[0155] - Oxidisation of other PFAS into PFBA

[0156] - Analytical errors, such as matrix effects or interference from other substances in the leachate.

[0157] - Short-chain PFAS like PFBA have different partitioning behaviours compared to long-chain PFAS. PFBA's lower surface activity and higher solubility in water mean it is less likely to be removed effectively, leading to an apparent increase in its concentration as other compounds are removed.

[0158] A reduction in PFPeA was observed only in samples treated with 150 ppm and 200 ppm PDM. The PFPeA removal efficiency for these samples was 6% and 38%, respectively. Interestingly, when the PDM was added to the raw leachate, the removal was >65%.

[0159] The analytical results indicate that the addition of PDM significantly enhanced the removal of PFHxA. As shown in table 6, PFHxA removal in the effluent without PDM addition was 48%. However, with a dosage of 150 ppm and 200 ppm PDM, the removal efficiency improved to 68% and 94% respectively. In the pilot trials we achieved around 70-75% removal.

[0160] The results indicate that a PDM dosage of 150 ppm or higher can be effective in removing short-chain PFAS compounds.

[0161] PDM and Organic Acid (OA) Removal

[0162] These further experiments were undertaken to assess the effectiveness of PolyDADMAC (PDM) in removing organic acids, organic carbon and COD (OA / OC / COD) from landfill leachate and to evaluate whether this removal can improve the downstream removal of short-chain PFAS with lower doses of additives. The experiments involve using PDM as a reagent for neutralizing organic acids in the first stage of a foam fractionation system (FF1). This approach is intended to enable the use of alternative, potentially more effective, short-chain PFAS removal agents in subsequent foam fractionation passes (FF2 and FF3), but at lower chemical dosages.

[0163] Initial bench-scale tests used fulvic acid as a surrogate for total organic carbon (TOC) and chemical oxygen demand (COD) in ultra-pure water. However, colorimetric and COD analysis using UV / Vis spectrometry proved unreliable for quantifying treatment effects. Visual observation of treated samples by eye were more effective than colour analysis by UV-Vis for acknowledging colour change or depletion. These qualitative assessments indicated that noticeable colour reduction occurred between doses of 100 mg / L and 150 mg / L of PDM

[0164] To validate these qualitative observations, a pilot trial was undertaken to assess the impact of PDM dosing at five concentrations (0, 100, 125, 150, and 175 mg / L) introduced into the FF1 feed. The system consisted of three fractionators constructed from transparent polycarbonate, each with a diameter of 400 mm and a maximum internal volume of 100 L (see Figure 1). While FF2 and FF3 were cylindrical in design, FF1 employed a rectangular foam fractionator that had previously been validated to perform equivalently to its cylindrical counterparts in earlier comparative studies. The actual hydraulic retention time (HRT) for each fractionator was 24 minutes. Leachate was fed into FF1 , where polymer was dosed inline at one of the five concentrations. For each dose rate, samples were taken from the outlet of FF1 , FF2, and FF3 after steady-state conditions were achieved, and after two HRT cycles to ensure process stability.

[0165] The operating conditions were established for each foam fractionator during the initial stages of the pilot trial. These conditions were standardised and maintained throughout the tests to minimise variability and ensure consistent comparison across dosing scenarios. The five concentrations were recorded as five tests (Tests 1-5). Colour test results

[0166] As shown in Table 13 or Figure 14, no colour reduction was recorded in Test 1 , where no PDM was added. In contrast, Tests 2 and 3 indicate that PDM contributed to an increase in colour, with readings nearly doubling at a dose rate of 125 mg / L. However, in Tests 4 and 5, a reduction in colour was observed in the FF3 treated leachate (TL), aligning with visual observations made during the trial. These results suggest that higher PDM dosing (>150 mg / L) may enhance removal of colour-causing organics, particularly in later stages of foam fractionation.

[0167] Results

[0168] The PFAS removal for the five Tests 1-5 are shown in Figure 12. Table 7 of Figure 12a shows the results for Test 1 (0 ppm). Table 8 of Figure 12b shows the results for Test 2 (100 ppm). Table 9 of Figure 12c shows the results for Test 3 (125 ppm). Table 10 of Figure 12d shows the results for Test 4 (150 ppm). Table 11 of Figure 12e shows the results for Test 5 (175 ppm).

[0169] The results indicate that a PDM dose of 150 mg / L corresponds to a notable improvement in short chain PFAS removal efficiency. This observation aligns with findings from the colour test, where 150 mg / L appeared to be the point at which significant removal of organic acids occurred. This suggests that the reduction in organic acids at this dose may enhance PFAS removal performance.

[0170] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

[0171] 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

CLAIMS1 . A method of increasing the removal of short chain PFAS from a treated wastewater, the method comprising the steps of: forming or obtaining the treated wastewater, treated for the removal of PFAS; adding an effective amount of a cationic polymer to the treated wastewater; subjecting the treated wastewater and cationic polymer to foam fractionation to form a foam and a further treated wastewater; and optionally removing the foam from the further treated wastewater.

2. The method of claim 1 , wherein the wastewater is leachate.

3. The method of claim 1 or 2, wherein the method includes the step of subjecting wastewater to foam fractionation to form the treated wastewater (in the absence of cationic polymer).

4. The method of any one of claims 1 to 3, wherein the method is applied to a continuous multistage foam fractionation process by addition of the cationic polymer prior to a second stage of foam fractionation.

5. The method of any one of claims 1 to 4, wherein the cationic polymer is added to the treated wastewater from the first foam fractionator prior to entry into a second vessel.

6. The method of claim 5, wherein the cationic polymer is added directly into the second vessel.

7. A method of increasing the removal of total short chain PFAS from wastewater, the method comprising the steps of: step 1 : adding an effective amount of a cationic polymer to the wastewater; subjecting the wastewater and cationic polymer to a first foam fractionationprocess to form a foam and a treated wastewater; and step 2: subjecting the treated wastewater to a second foam fractionation process, comprising adding at least one short-chain PFAS removal compound, wherein a decreased amount of short-chain PFAS removal compound is required in step 2 when preceded by step 1 , compared to the same step 2 when not preceded by step 1 .

8. The method of claim 7, wherein the wastewater is leachate.

9. The method of claim 7 or 8, wherein the short-chain PFAS removal compound is bentonite.

10. The method of any one of claims 1 to 9, wherein the cationic polymer includes at least one of a polyacrylamide, a polyacrylic acid, a polydiallyldimethyl ammonium, or a polyamine.

11. The method of claim 10, wherein the cationic polymer is Polydiallyldimethylammonium chloride (PolyDADMAC).

12. The method of any one of claims 1 to 11 , wherein the effective amount is at least about 50, 100, 150 or 200 mg / L.

13. The method of claim 12, wherein the effective amount is more than about 100 mg / L.

14. The method of claim 12, wherein the effective amount is more than about 150 mg / L.

15. The method of any one of the preceding claims, wherein the foam is removed and is subject to further processing.

16. The method of any one of the preceding claims wherein: long chain PFAS are those with a carbon number greater than 7, such as C7, C8, C9, C10;short chain PFAS compounds with a carboxylate group attached (PFCAs) are those with a carbon number less than or equal to 7 such as C7, C6, C5, C4; and short chain PFAS compounds with a sulphonate group attached (PFSAs) are those with a carbon number less than 6 such as C5, C4.

17. Wastewater when treated by the method of any one of the preceding claims. l ' l

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