Cross-reference to Related Applications

[0001] The disclosures of related Australian Patent Application No. 2016903176, filed 12 August 2016, and Australian Patent Application No. 2017210503, filed 31 July 2017, both entitled "System and method for removing contaminants from water", are incorporated herein in their entirety by way of reference.

Technical Field

[0002] The present disclosure relates to a system and method for removing contaminants from water. The system and method have been developed for removing per- and poly-fluorinated alkyl substances (PFAS) from water. However, it will be appreciated that the system and method are not limited to this particular use, and may also be used for removing other contaminants from water or for removing PFAS or other contaminants from fluids other than water.

Background

[0003] PFAS are fluorosurfactants that have a variety of properties that make them useful in a wide range of industrial applications, such as water and stain repellents, aviation hydraulic fluid, metal coatings and fire-fighting foams.

[0004] It is only relatively recently that the presence of PFAS in the environment has been identified as representing a potentially significant ecological and health hazard, particularly due to the fact that PFAS are not known to degrade under normal environmental conditions and are bioaccumulative. PFAS can also transfer between different media, such as between soil and water, meaning that they are relatively mobile contaminants.

[0005] The chemical and material properties of PFAS makes remediation of sites contaminated by PFAS a significant challenge. [0006] Existing treatment systems using GAC (granular activated carbon) Adsorbers or WBA (weak base anion) resin have various disadvantages. A major disadvantage is that they require media change-outs or regeneration and therefore require a

duty/standby design to maintain continuous throughput. Alternatively, an extended shut down for a period of days is required in order to change media or regenerate the resin before restarting. In addition to downtime, extended shut-downs tend to promote microbiological fouling of media and a subsequent increase in uncertainty in predicting when breakthrough will occur. Other disadvantages include: blockages or deactivation due to microbiological growth on the media and to sedimentation; limited hydraulic capacity due to large pressure vessels being impractical; high cost of media; uncertainty of when media exhaustion and hence breakthrough will occur, leading to inefficient use of media and higher operating costs; and relatively high capital costs.

[0007] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

Summary

[0008] Throughout this specification:

• "comprise", or variations such as "comprises" or "comprising", will be

understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps;

• "powdered activated carbon" or "PAC" will be understood to mean activated carbon particles having a nominal diameter of 0.177 mm or less; and

• PAC described as having a "high adsorption capacity" or as being "highly

reactive" or "highly adsorbent" means PAC having an Iodine Number of > 1000 mg/g. [0009] Disclosed herein is a system for removing contaminants from water, comprising:

at least one treatment station for receiving contaminated water for treatment; a powdered activated carbon (PAC) delivery apparatus associated with the at least one treatment station for delivering PAC thereto;

a PAC recovery apparatus for recovering PAC in water from the at least one treatment station; and

a PAC recycling apparatus for recycling the PAC recovered by the PAC recovery apparatus to the at least one treatment station,

wherein the PAC delivery apparatus is configured to deliver the PAC to the at least one treatment station after water in the at least one treatment station has reacted with recovered PAC that has been recycled to the at least one treatment station by the PAC recycling apparatus.

[0010] The recovered and recycled PAC may be in a slurry form. Floccs in the recovered and recycled PAC may be broken up by a declumping mechanism prior to or upon the recovered and recycled PAC returning to the at least one treatment station. The declumping mechanism may comprise a recirculation pump through which the recovered and recycled PAC passes.

[0011] The at least one treatment station may comprise:

a primary treatment station for receiving contaminated water for treatment; and

a secondary treatment station downstream of the primary treatment station for receiving a supply of water from the primary treatment station,

wherein:

the PAC delivery apparatus is associated with the secondary treatment station for delivering the PAC to the secondary treatment station;

the PAC recovery apparatus is configured for recovering PAC in water from the secondary treatment station; and

the PAC recycling apparatus is configured for recycling the PAC recovered by the PAC recovery apparatus to the primary treatment station. [0012] The PAC delivery apparatus may deliver the PAC to a conduit through which the water flows from the primary treatment station to the secondary treatment station. The PAC delivery apparatus may deliver the PAC continuously or intermittently. The PAC delivery apparatus may be configured to vary the amount of PAC delivered or the rate of delivery of the PAC based on the flow rate of water undergoing treatment through the at least one treatment station. For example, more PAC may be delivered and/or the PAC may be delivered at a faster rate if the water undergoing treatment is flowing more quickly through the at least one treatment station.

[0013] The primary treatment station may comprise at least one tank. The primary treatment station may comprise an agitator for stirring the water in the primary treatment station.

[0014] The secondary treatment station may comprise at least one tank. The secondary treatment station may comprise an agitator for stirring the water in the secondary treatment station.

[0015] The PAC recovery apparatus may comprise a coagulant/flocculant delivery apparatus for delivering coagulant/flocculant to the water after the PAC delivery apparatus has delivered the PAC. For example, the coagulant/flocculent may be delivered to the secondary treatment station and/or to a PAC recovery station downstream of the secondary treatment station. The PAC recycling apparatus may comprise a conduit extending between the PAC recovery apparatus and an upstream end of the system to recycle PAC recovered by the PAC recovery apparatus to the upstream end of the system. For example, the conduit may extend between the PAC recovery apparatus and the primary treatment station to recycle PAC recovered by the PAC recovery apparatus to the primary treatment station.

[0016] The PAC recovery apparatus may comprise a settlement station downstream of the point of addition of the coagulant/flocculant. The settlement station may provide enhanced gravity separation, such as by utilising a lamella clarifier or centrifuge. [0017] The PAC recovery apparatus may comprise a filtration station downstream of the at least one treatment station. In embodiments including same, the filtration station may be downstream of the secondary treatment station or the PAC recovery station. The PAC recycling apparatus may comprise a conduit extending between the filtration station and the upstream end of the system to recycle PAC recovered by the filtration station to the upstream end of the system. For example, the conduit may extend between the filtration station and the primary treatment station to recycle PAC recovered by the filtration station to the primary treatment station.

[0018] The PAC recycling apparatus may comprise a conduit extending between the primary and secondary treatment stations to recycle PAC from the secondary treatment station to the primary treatment station.

[0019] The PAC recycling apparatus may comprise a pump for generating a fluid flow in any one or more of the conduits of the PAC recycling apparatus.

[0020] The PAC delivery apparatus may be configured to deliver virgin PAC (i.e., not recycled PAC) to the at least one treatment station.

[0021] The PAC may be formed from a coal-based material. The PAC may be of a grade selected to facilitate its efficient recovery by the PAC recovery apparatus. The PAC grade may specify the adsorption capacity, reaction kinetics, particle size and/or uniformity of particle size of the PAC. The PAC grade selected may have a high adsorption capacity, a fast reaction time, such as may be indicated by a pseudo second order adsorption rate constant of 0.01 to 8.06 g/mg/h for Perfluorooctane Sulfonate (PFOS) or 0.03 to 0.36 g/mg/h for Perfluorooctanoic acid (PFOA), and/or a particle size distribution of 60% finer than 45 μηι. The PAC may be formed from a coal-based material that is activated, for example by exposure to steam, at a temperature of greater than 1000°C (in order to produce a desired pore size).

[0022] A turbidity sensor may be provided for measuring the turbidity of water in the system at a point between an upstream end of the at least one treatment station and an upstream end of the PAC recovery station for validating that PAC has been delivered to the contaminated water and/or that the contaminated water has been effectively treated. The turbidity may be measured: after the recycled PAC has been mixed with incoming contaminated water but before PAC has been delivered by the PAC delivery apparatus; or in the treatment station to which the PAC delivery apparatus delivers the PAC. A turbidity sensor may be provided for measuring the turbidity of the water at the downstream end of the system to confirm the recovery of the PAC by the PAC recovery apparatus prior to the water being discharged from the system.

[0023] The quantity and/or rate of PAC delivered to the at least one treatment station by the PAC delivery apparatus may vary depending on the concentration and type of contaminant in the water being treated and the acceptable level of contaminant in the water output from the system. However, in an embodiment where the water being treated is contaminated with up to 5 μg/L of PFOS and a non-detect level of contaminant is required in the water output from the system, the quantity of PAC delivered to the at least one treatment station may be less than 0.002% by weight of the water in the at least one treatment station. The system may be configured to maintain its total PAC concentration (i.e., including recovered and recycled PAC, as well as PAC delivered by the PAC delivery apparatus) below approximately 3% by weight, or in some embodiments below approximately 1% by weight, of the water in the system, but the total PAC concentration could be maintained at a level lower or higher than these values in some embodiments. Excess PAC may be removed from the system intermittently or as required to maintain a maximum total PAC concentration and/or to prevent the water/PAC mixture carried by the system from becoming too thick. Excess PAC removed from the system may be transmitted to a dewatering apparatus, such as a geotube or a filter press. In embodiments comprising a primary treatment station and a secondary treatment station, the excess PAC may be removed from the primary treatment station.

[0024] A pH sensor may be provided for measuring a pH of water in the system. The pH sensor may be associated with the at least one treatment station. [0025] A chemical delivery apparatus may be provided for delivering a pH adjusting chemical to the system to adjust the pH of the water. The chemical delivery apparatus may deliver the pH adjusting chemical to an upstream end of the system. The chemical delivery apparatus may be configured to adjust the pH of the water to between 5 and 7.

[0026] The system may be configured to allow water in the at least one treatment station to react with the recycled PAC for up to around 5 minutes before the PAC delivery apparatus delivers PAC.

[0027] The contaminants removed by the system may comprise PFAS with or without co-contaminants, such as dissolved hydrocarbons and heavy metals.

[0028] Also disclosed herein is a system for removing contaminants from water, comprising:

at least one treatment station for receiving contaminated water for treatment; a decontaminant delivery apparatus associated with the at least one treatment station for delivering an indissoluble decontaminant thereto; and

a turbidity sensor for detecting turbidity of the water in the at least one treatment station to facilitate validating that the decontaminant delivery apparatus has delivered the decontaminant to the at least one treatment station and/or that the contaminated water has been effectively treated.

[0029] Also disclosed herein is a system for removing contaminants from water, comprising:

at least one treatment station for receiving contaminated water for treatment; a decontaminant delivery apparatus associated with the at least one treatment station for delivering an indissoluble decontaminant to the contaminated water;

a decontaminant recovery apparatus downstream of the delivery point of the decontaminant delivery apparatus for recovering decontaminant from the water; and a turbidity sensor for detecting turbidity of the water at the downstream end of the system to facilitate validating that the decontaminant recovery apparatus has recovered the decontaminant. [0030] In the system defined in paragraph [0028] and/or paragraph [0029], the decontaminant may be a decontaminant that adsorbs contaminants from the water.

[0031] Also disclosed herein is a system for removing PFAS from water, comprising: at least one treatment station for receiving water contaminated with PFAS for treatment;

a PAC delivery apparatus associated with the at least one treatment station for delivering PAC to the contaminated water for adsorption of PFAS from the water by the PAC; and

a PAC recovery apparatus downstream of the delivery point of the PAC delivery apparatus for recovering PAC from the water.

[0032] Also disclosed herein is a method of removing contaminants from water, comprising:

mixing recycled PAC with incoming contaminated water;

allowing the PAC to adsorb contaminants from the water;

delivering a further quantity of PAC to the water after the recycled PAC has adsorbed contaminants from the water and mixing the further quantity of PAC with the water;

allowing the further quantity of PAC to adsorb residual contaminants from the water;

recovering PAC from the water after the further quantity of PAC has adsorbed residual contaminants from the water; and

recycling the recovered PAC for mixing with the incoming contaminated water.

[0033] The PAC recovery may comprise any one or more of:

coagulation/flocculation, gravity separation and filtration.

[0034] The further quantity of PAC may comprise virgin PAC (i.e., not recycled PAC). [0035] The PAC may be of a grade selected to facilitate its efficient recovery by any one or more of: coagulation/flocculation, gravity separation and filtration.

[0036] The turbidity of the water may be measured to facilitate validating that the decontaminant has been delivered and/or that the contaminated water has been effectively treated. The turbidity may be measured: after the recycled PAC has been mixed with incoming contaminated water but before the further quantity of PAC is delivered; or after the further quantity of PAC is delivered, and ideally after the further quantity of PAC is mixed with the water, but before the recovery of PAC. The turbidity of the water may be measured after the recovery of PAC to confirm the recovery of the PAC prior to the water being discharged from the system.

[0037] Excess PAC may be removed from the water intermittently or as required to maintain the total concentration of PAC below 3%, or in some embodiments below 1%, by weight of the weight of water undergoing treatment and/or to prevent the water/PAC mixture from becoming too thick. Excess PAC removed from the water may be dewatered, such as by delivering the excess PAC to a geotube or a filter press.

[0038] The pH of the water may be measured. If required, the water may be treated to adjust its pH to between 5 and 7.

[0039] Also disclosed herein is a method of removing PFAS from water contaminated with PFAS, comprising:

delivering PAC into water contaminated with PFAS;

allowing the PAC to adsorb PFAS from the water; and

removing the PAC from the water.

[0040] Also disclosed herein is a method of removing contaminants from water, comprising:

delivering an indissoluble decontaminant to contaminated water; and detecting turbidity of the water to facilitate validating that the decontaminant has been delivered and/or that the contaminated water has been effectively treated. [0041] Also disclosed herein is a method of removing contaminants from water, comprising:

delivering an indissoluble decontaminant to contaminated water;

recovering the decontaminant from the water; and

detecting turbidity of the water after recovery of the decontaminant to facilitate validating that the decontaminant has been recovered.

[0042] In the method defined in paragraph [0040] and/or paragraph [0041], the decontaminant may adsorb contaminants from the water.

Brief Description of Drawing

[0043] An embodiment of the presently disclosed system will now be described, by way of example only, with reference to accompanying Figure 1.

Description of Embodiment

[0044] PAC is not routinely used for groundwater remediation purposes. Moreover, the use of PAC in treating water is counter-intuitive, as it involves turning the water pitch black during the treatment process. How to clarify the water after dosing it with PAC whilst achieving an acceptable cycle time and processing cost were obstacles identified by the present inventor.

[0045] Referring to Figure 1, there is provided a system 10 for removing

contaminants from water, and particularly for removing PFAS, such as PFOS, PFHxS and/or PFOA, with or without co-contaminants, such as dissolved hydrocarbons and heavy metals. The system 10 comprises a primary treatment station 12 for receiving contaminated water for treatment from an inlet 13. A secondary treatment station 14 is provided downstream of the primary treatment station 12 for receiving a supply of water from the primary treatment station. The primary and secondary treatment stations 12, 14 each comprise a tank with an agitator for mixing/stirring the contents of the tank. A PAC delivery apparatus 16 is associated with the secondary treatment station 14 for delivering virgin (i.e., not recycled) highly reactive PAC thereto, ideally by delivering the virgin PAC to a conduit through which water undergoing treatment passes from the primary treatment station 12 to the secondary treatment station 14. A PAC recovery apparatus 18 is provided for recovering PAC in water from the primary and secondary treatment stations 12, 14 and a PAC recycling apparatus recycles the recovered PAC to the primary treatment station 12.

[0046] In the illustrated embodiment, the PAC recovery apparatus 18 comprises a coagulant/flocculant delivery apparatus 20, such as a coagulant/flocculant reservoir, pump and delivery conduit extending between the coagulant/flocculant reservoir and a conduit through which water flows from the secondary treatment station 14 to a settlement station 22 for delivering coagulant/flocculant to the water flowing into the settlement station. In other embodiments (not shown), the settlement station 22 together with a mixing tank upstream thereof may form a PAC recovery station, and the coagulant/flocculant may instead be delivered to the mixing tank. In the illustrated embodiment, the settlement station 22 utilises a lamella clarifier or inclined plate settler to provide enhanced gravity separation. In other embodiments, the settlement station 22 may comprise a centrifuge. The PAC is recovered in slurry form.

[0047] The PAC recovery apparatus 18 comprises a filtration station 24 downstream of the settlement station 22. The filtration station 24 may comprise a media filter. A backwash apparatus may be associated with the filtration station 24 for periodic backwashing of filtration media in the filtration station 24.

[0048] The PAC recycling apparatus comprises conduits 26 extending from the base of each of the primary treatment station 12, the secondary treatment station 14 or PAC recovery station and settlement station 22 and from an outlet of filtration station 24 to the primary treatment station 12 to recycle PAC recovered from these system components to the primary treatment station 12. One or more pumps 28 are provided for generating fluid flow in the conduits 26. PAC recovered from the settlement station 22 passes through a recirculation circuit 27a and pump 27b to break up floccs in the PAC slurry before its delivery to the primary treatment station 12. [0049] A turbidity sensor 30 is provided for measuring the turbidity of the water in the secondary treatment station 14. The turbidity sensor measurements may be used to validate the presence and suspension of PAC in the secondary treatment station 14, wherein a higher turbidity confirms the presence and suspension of the PAC. A turbidity sensor 30' is also provided for measuring the turbidity of the water passing the filtration station 24 to validate removal of the PAC, and therefore of PFAS, from the water before it is discharged from the system 10.

[0050] The amount of PAC delivered by the PAC delivery apparatus 16 per unit of water being treated varies depending on the concentration and type of contaminant in the water being treated and the acceptable level of contaminant in the water output from the system 10. However, in an embodiment where the water being treated is contaminated with up to 5 μg/L of PFOS and a non-detect level of contaminant is required in the water output from the system, the amount of virgin PAC required to be delivered by apparatus 16 is less than 0.0013% by weight of the water in the secondary treatment station 14. The PAC delivery apparatus 16 is configured to vary the amount of PAC delivered (if delivered intermittently) or the rate of delivery of the PAC (if delivered continuously) based on the flow rate of water undergoing treatment through the secondary treatment station 14. For example, more PAC is delivered or the PAC is delivered at a faster rate if the water undergoing treatment is flowing more quickly through the secondary treatment station 14. The present inventor has found that this relatively low concentration of virgin PAC provides for fast and efficient PFAS adsorption.

[0051] The PAC used in the system 10 may be formed from a coal-based material that is activated, by exposure to steam, at a temperature of greater than 1000°C (in order to produce a desired pore size). The PAC has a high adsorption capacity, a fast reaction time, such as indicated by a pseudo second order adsorption rate constant of 0.01 to 8.06 g/mg/h for PFOS or 0.03 to 0.36 g/mg/h for PFOA, and a particle size distribution of 60% finer than 45 μιη. [0052] During operation, the total PAC concentration (i.e., including

recovered/recycled PAC as well as PAC delivered by the PAC delivery apparatus 16) in the system 10 tends to gradually increase, due to the addition of virgin PAC by the delivery apparatus 16. As such, excess PAC in the system 10 is removed from the primary treatment station 12 intermittently or as required in order to prevent the water/PAC mixture in the system 10 from becoming too thick. For example, the excess PAC removal may be configured to maintain the total concentration of PAC in the system 10 below 3% (or 1%) by weight of the water in the system. The excess PAC removed from the primary treatment station 12 is transmitted to a dewatering apparatus, such as a geotube 32.

[0053] A pH sensor 34 is associated with the primary treatment station 12 for measuring a pH of water entering the system 10. A chemical delivery apparatus 35 is associated with the primary treatment station 12 for delivering a pH adjusting chemical, such as an acid or base, to the primary treatment station to adjust, based on the pH measured by sensor 34, the pH of water in the primary treatment station to between 5 and 7.

[0054] The system 10 may be mobile for on-site operation at a contaminated site. For example, the system 10 may be arranged in a shipping container or other transportable housing. In larger scale operations, the system 10 may be static.

[0055] At startup of the system 10, contaminated water is delivered to the primary treatment station 12 and, for the initial cycle only, virgin PAC is delivered to the primary treatment station 12 by a PAC delivery apparatus 16'. The virgin PAC, or recycled PAC in subsequent cycles of the system 10, is stirred into the contaminated water using the agitator of the primary treatment station 12 to facilitate the PAC adsorbing PFAS from the water. The system 10 is configured such that the nominal residence time of water in the primary treatment station 12 is up to around 2 to 5 minutes before it passes to the secondary treatment station 14. Accordingly, the water is allowed to react with the PAC in the primary treatment station for around 2 to 5 minutes. [0056] The water/PAC suspension passes out of the primary treatment station 12 via an overflow weir 12a and is delivered by gravity to the secondary treatment station 14. The virgin PAC delivered to the secondary treatment station 14 is stirred into the water using the agitator of the secondary treatment station 14 to facilitate adsorption of residual PFAS. The system 10 is configured such that the nominal residence time of water in the secondary treatment station 14 is up to around 2 to 5 minutes before it passes to the settlement station 22. Accordingly, the water is allowed to react with the PAC in the secondary treatment station for around 2 to 5 minutes.

[0057] In the illustrated continuous treatment system 10, the agitators of the primary and secondary treatment stations 12, 14 operate continuously to facilitate maintaining the PAC in the primary and secondary treatment stations in substantially homogeneous suspension.

[0058] In the illustrated embodiment, the water/PAC suspension passes out of the secondary treatment station 14 via an overflow weir 14a and is delivered by gravity to the settlement station 22. Coagulant/flocculent is added to the water/PAC suspension between leaving the secondary treatment station 14 and arriving in the settlement station 22 by dosing the coagulant/flocculent into a conduit connecting the overflow weir 14a to the settlement station 22. In batch processing embodiments of the system, where the secondary treatment station 14 may also act as the settlement station, coagulant/flocculent is added to the water in the secondary treatment station after the PAC has been allowed to adsorb residual PFAS, and the agitator is then switched off or slowed down to facilitate the PAC forming floccs and settling towards the bottom of the secondary treatment station 14 for recovery and recycling into the primary treatment station 12. Water passes out of the settlement station 22 via an overflow weir 22a and is delivered to the filtration station 24 via a break tank 36.

[0059] It will be appreciated that the illustrated system 10 has numerous advantages over conventional PFAS decontamination processes. For example, the system 10 provides 'counter-current' flow of PAC and water being treated, which provides:

maximum PAC contact time with the water (to take advantage of the PFAS adsorption capacity of the PAC); and utilisation of the full loading capacity of the PAC. By dosing virgin PAC into the secondary treatment station 14, the virgin PAC can perform "polishing" of PFAS from the water therein without any significant reduction in the adsorption capacity of the virgin PAC, as most of the PFAS will have already been adsorbed by the recycled PAC used in the primary treatment station 12. As such, there is substantially no reduction in the PFAS adsorption performance of the virgin PAC upon its being recycled to the primary treatment station 12. Accordingly, the full loading capacity of the PAC can be utilised.

[0060] A further advantage is the simplicity of the system 10, which allows it to be established more quickly, from readily available equipment, and at a lower capital cost than conventional alternatives.

[0061] The system 10 provides an assurance that the contaminated water has been effectively treated by detecting turbidity, which is relatively easy to measure, as a proxy measure of treatment effectiveness. The detection of turbidity above a predetermined level indicates that PAC is suspended in the water and therefore that PFAS in the water has been adsorbed. Note that there is currently no commercially available online instrumentation for PFAS measurement. The certainty of treatment can be further increased by monitoring the virgin PAC delivery apparatus 16, wherein the system 10 is configured to validate effective treatment of the contaminated water if turbidity above a predetermined level is detected in the secondary treatment station 14 and the PAC delivery apparatus 16 indicates that virgin PAC has been delivered to the second treatment station 14. The system 10 may be configured to shut down and/or prevent discharge of water from the downstream end of the system, if ineffective treatment is indicated. Only a short contact time (such as <60 seconds) with virgin PAC, even at very low virgin PAC dose rates (e.g., if water flowing out of the primary treatment station 12 is contaminated with up to 5 μg/L of PFOS and a non-detect level of PFOS is required in the water output from the system 10, the amount of virgin PAC required to be delivered by apparatus 16 is less than 0.0013% by weight of the water in the secondary treatment station 14) is required to achieve a non-detect level of contamination. Use of PAC, which is indissoluble, to decontaminate the water, in combination with detecting turbidity downstream of the filtration station 24, also facilitates verifying that the water discharged from the system 10 is free from PAC (and PFAS adsorbed by the PAC), and thereby reduces the risk of PAC and PFAS being discharged from the system (i.e., low turbidity confirms that the PAC (and therefore the PFAS) has been filtered out prior to discharge).

[0062] The high-activity PAC used in the system 10 has the following specific characteristics that make it particularly suitable for the process:

very high specific surface area - leads to a high adsorption capacity for PFAS; highly activated by high temperature steam activation - leads to fast reaction kinetics and increased adsorption capacity;

45 μηι particle size - suitable for rapid particle settling for PAC recovery and recycle, and higher specific surface area for fast reaction kinetics;

coal-based PAC - has appropriate pore size for PFAS adsorption and appropriate specific gravity for efficient settling;

lower affinity for co-contaminants such as dissolved metals and metal cyanides relative to WBA resin - high reliability and specificity for PFAS;

high affinity for surface active and hydrophobic molecules - high selectivity for PFAS in co-contamination situations; and

suitable for adsorption of PFOS, PFOA, PFHxA, PFHxS, PFBS, PFBA, 6:2 FTS, 8:2 FTS and other PFAS molecules.

[0063] Significant savings can be achieved compared to conventional treatment methods as a result of recycling the PAC in the system 10. With on-site sampling of PFAS (and laboratory analysis), the system 10 allows a conservative dose rate of PAC to be used without incurring waste due to over-dosing. During operation of the system 10, the dose rate can be optimised based on routine analysis performed by the laboratory. It will be appreciated that the configuration of the system 10 ensures that it is not at risk of incurring a PFAS breakthrough due to a sample analysis delay at the laboratory. [0064] The system 10 facilitates continuous replacement of the PAC to maintain treatment effectiveness and is not impacted by microbiological or sediment load, i.e., as is the case in fixed bed adsorbers. As a result, the system 10 is suited to continuous operation.

[0065] The system 10 is capable of handling variability in the feedwater, including variation in PFAS concentration, total suspended solids (TSS), flowrate, and stop/start of an associated upstream water delivery system. Flow in the system 10 can also be stopped and restarted as often as required, without impacting the treated water quality.

[0066] The system 10 has relatively low capital and operating costs, and is made of locally available components. PAC and flocculation chemicals for the process are locally available and have a short lead time.

[0067] The system 10 is capable of treating co-contaminated water streams that are commonly encountered at the source zone of PFAS contamination.

[0068] The system 10 can treat both very high and very low concentrations of PFAS to achieve non-detect levels of PFOS, PFOA, PFHxA, PFHxS, PFBS, PFBA, 6:2 FTS, 8:2 FTS and other PFAS molecules.

[0069] Treated water output from the system 10 can be reinjected to an aquifer or disposed of as surface runoff. This is of particular advantage given that there is currently no on-line instrument for directly measuring PFAS, and very large volumes of water (millions of litres of water treated per day) are very expensive and impractical to store for the period of time required to get laboratory results to validate the water quality (typically, a turnaround time of around 3 days is the fastest laboratory analysis time available). When the system 10 is shutdown, such as when decontamination is completed or for system maintenance, any contaminated liquid/slurry resident in the system 10 may be drained or pumped to a dewatering station, such as to geotube 32, where it is dewatered, with the solids captured by the geotube 32 being safely retained therein. [0070] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiment(s), without departing from the broad general scope of the present disclosure. The present embodiment(s) is/are, therefore, to be considered in all respects as illustrative and not restrictive. Examples of possible variations and/or modifications include, but are not limited to:

• A single stage PFAS adsorption process, in which PAC is added, allowed to adsorb PFAS and recovered in a solid liquid separator, may be used instead of the illustrated two stage adsorber process, especially for low volume or low flowrate applications;

• A three or more stage PFAS adsorption process may be used;

• A single stage PAC adsorption process may be used and followed by a GAC adsorber or a WBA resin adsorber to polish the treated water;

• Instead of taking place in a series of tanks as described above, the PFAS

adsorption may be performed via inline mixing within pipework, wherein the recycled PAC is injected at an upstream point in the pipework and the virgin PAC is injected at a downstream location in the pipework; and/or

• Dewatering being performed using a filter press instead of geotube(s) 32.