Filtration system

Abstract

A filtration system (10B) comprises a batch recirculation loop comprising a pressurisation module (20) and a separation module (40), configured to allow liquid to be pressurised using the pressurisation module (20) while recirculating the liquid to the separation module (40), wherein the filtration system (10B) further comprises a feed arrangement (12) allowing it to supply feed liquid into the recirculation loop to allow feed liquid to mix with recirculated liquid, wherein the filtration system (10B) is further configured to allow it to operate in an open recirculation mode (10B) and in a closed recirculation mode, wherein, in the closed recirculation mode, no feed liquid is supplied into the recirculation loop while the pressurisation module pressurises liquid during recirculation, and wherein, in the open recirculation mode (12B), feed liquid is supplied into the recirculation loop during recirculation, and wherein the filtration system (10B) comprises a configuration allowing it to supply feed liquid to be mixed with recirculated liquid at a feed intake position (34) downstream of the pressurisation module (20) and upstream of or into the separation module (40).

Description

[0001] Filtration system

[0002] Field of the Invention

[0003] The present invention relates to a fluid separation system and method of operating a fluid separation system. More specifically, the present invention relates to system design and method of operating a fluid separation system to improve its performance. In examples, the invention relates to a membrane desalination system.

[0004] Background

[0005] Recent developments in water desalination and other membrane-based separation processes for the decontamination and / or purification of fluids have resulted in more energy efficient system designs, such as described in International Patent Publications W02020 / 039158A1 and WO2022 / 096895A2. Improved understanding of operating control processes and selection of components have led to the development of fluid separation systems that may operate successive cycles practically uninterrupted for prolonged periods of time, in the region of several months in line with cleaning cycles for the equipment used, e.g., for desalination membranes.

[0006] Such separation systems separate, by design, fluid into a “clean” (e.g., desalinated) permeate and a retentate with an increased concentration of the contaminant or component to be removed. A limit to the operation of such separation systems is posed by scaling or fouling processes due to the chemical interaction of high - intentionally enriched - concentrations of the component / contaminant to be removed with system components. For this reason, equipment maintenance may still be required in regular intervals, even if regular intervals may be several months apart.

[0007] The present disclosure provides additional design options for improved operation of such separation systems.

[0008] Summary of the Invention

[0009] In accordance with a first aspect of the invention, there is disclosed a filtration system as defined in claim 1 , the system comprising a batch recirculation loop comprising a pressurisation module and a separation module, configured to allow liquid to be pressurised using the pressurisation module while recirculating the liquid to the separation module. The filtration system further comprises a feed arrangement allowing it to supply feed liquid into the recirculation loop to allow feed liquid to mix with recirculated liquid. The filtration system is further configured to allow it to

[0010] Version 2025-10-16 operate in an open recirculation mode and in a closed recirculation mode, wherein, in the closed recirculation mode, no feed liquid is supplied into the recirculation loop while the pressurisation module pressurises liquid during recirculation.

[0011] By “filtration system”, a system is meant that uses filtration for the separation of components and / or contaminants from a liquid. A filtration system may be provided in the form of a membrane separation system. Filtration systems such as membrane separation systems may be used to generate a clean fluid such as water by reducing a load of a contaminant or component to be removed, such as salt and / or microparticles. As a simplification, herein, it is considered that a filtration system generates a permeate (cleaned fluid fraction) by separating it from a supply of liquid to be separated, whereby the component to be removed from the permeate remains within a retentate with correspondingly increased concentration. Herein, the fluid for separation may be referenced as “fresh fluid” or “fresh liquid” before it undergoes separation, and as “concentrated fluid” or “concentrated liquid” when part of the retentate.

[0012] In one example, the fresh fluid may be saline to be processed to generate clean water, resulting in an amount of higher-concentrated saline retentate. However, the invention is not necessarily limited to desalination and may, likewise, be used for the removal of microparticles such as microplastics, separation of foods, such as whey separation from milk, and other filtration processes.

[0013] Herein, the expression “clean” is used for fluid removed as permeate from a supply of fluid to be separated, wherein the degree of cleanliness to be achieved may be dependent on the type of fluid, application, regulatory requirements, and other parameters. In other applications, it may be the case that the enriched fraction of the retained component is a preferred product, and such applications may be covered by embodiments of the invention.

[0014] In the desalination example described herein, the separation process uses reverse osmosis (RO) via a selectively permeable membrane, that operates by pressurising saline on one side of a membrane of a membrane module, for production of desalinated water permeate on the other side of the membrane.

[0015] By “recirculation”, it will be understood that the system is configured with a loop in which retentate from the separation module is re-used in a filtration cycle, specifically by re-using retentate as feed to remain in the loop comprising the separation module and the pressurisation module. To this end, the pressurisation module may be used to modulate, and typically to maintain at a target level and / or to increase, the pressure levels that are required for effective membrane separation with the progressively higher-concentrated retentate in circulation.

[0016] Version 2025-10-16 As will be appreciated, fresh feed liquid may be supplied into the recirculation loop, and may need to be supplied from time to time when volume is removed from the recirculation loop.

[0017] Herein, a “closed recirculation” mode is understood as a configuration in which no new liquid is introduced into the recirculation loop while the retentate is being recirculated and pressurised using the pressurisation module. In a closed recirculation mode, feed liquid may be used to drive other components of the system. For instance, in a closed recirculation mode, the feed arrangement may be used to supply liquid as driving fluid to drive the pressurisation module, e.g. to displace or deform a moveable partition such as a piston or a diaphragm, while the driving fluid remains isolated from the recirculation loop. In some embodiments, feed liquid or a fraction thereof is used to move a piston of the pressurisation module. The closed recirculation mode may also be considered a batch mode.

[0018] The closed recirculation mode may utilise a variable volume loop, to account for a reduce volume of recirculating retentate owing to permeate production during recirculation cycles. Conveniently, the variable volume is provided by and / or operatively connected with the pressurisation module. In a practical example, the pressurisation module is provided by a piston arrangement comprising a chamber (in many embodiments, one of two chambers) whose chamber volume is reduced by actuation of the piston during pressurisation of the liquid in circulation.

[0019] The closed recirculation allows the system to operate while preventing dilution with fresh feed liquid, and therefore allows a reference membrane performance to be established. Furthermore, a closed recirculation allows the retentate concentration to be increased.

[0020] An “open recirculation” mode is understood as a configuration in which retentate is recirculated, and in addition fresh feed liquid is supplied into the recirculation loop.

[0021] The filtration system comprises a configuration allowing it to supply feed liquid to be mixed with recirculated liquid at a feed intake position downstream of the pressurisation module and upstream of or into the separation module.

[0022] The expressions upstream and downstream are understood to relate to a single recirculation cycle in which fluid passes through the separation module. The configuration may be such that the filtration system may switch between a configuration supplying feed liquid upstream of the pressurisation module and a configuration downstream of the pressurisation module. In that case, the filtration system may be operated to supply feed liquid upstream of the pressurisation module for some phases of its operation, and to supply feed liquid downstream of the pressurisation module for other phases of its operation. Alternatively, the filtration system may be operated to supply feed liquid only downstream of the pressurisation module.

[0023] Version 2025-10-16 In some embodiments, the system is further configured to allow it to supply feed liquid downstream of the pressurisation module, via the feed intake, during the open recirculation mode.

[0024] In the open recirculation mode, liquid may be supplied using the feed arrangement while the pressurisation module is inactive during recirculation. In that case, when the pressurisation module is kept inactive, it is therefore not used to increase the pressure in the recirculation loop during recirculation. The pressure may continue to be maintained, or increased, depending on the flow rate of the feed arrangement. In some embodiments, the feed liquid supply rate matches the permeate production rate, such that the liquid volume in circulation remains practically the same, when operated in that manner.

[0025] The fresh liquid may be supplied via, or from, a holding chamber, which may be a chamber of the pressurisation module.

[0026] Furthermore, a “mixed recirculation” mode is understood herein as a configuration in which fresh feed liquid is supplied into the recirculation loop to mix with retentate while this is being recirculated and pressurised using the pressurisation module. As will be appreciated, the fresh feed liquid is typically expected to dilute, or reduce the concentration, in the retentate, thereby reducing pressurisation requirements for a given filtration performance.

[0027] The pressurisation module is used to assist the pressurisation. The performance and degree of separation achieved within a predefined time window depends on relative component concentrations, pressure levels and flow rates. International Patent Publication W02020 / 039158A1 discloses a system and method for batch desalination with high energy efficiency, by using a pressurising chamber or charging module that can be supplied from two sides, during two phases of a batch desalination process. Herein, the pressurisation module is understood as a chamber for pressurising liquid for supply to the separation module, which may be operated by cycling through a phase of pressurisation and separation and another phase of purging and refilling.

[0028] In such a separation system, a supply of liquid to be separated may conveniently be provided via a common feed line to supply liquid into a recirculation loop, and / or to supply liquid into a pressurisation module. Furthermore, liquid held temporarily in one or more chambers of a pressurisation module may be used to feed the recirculation loop. In that manner, supply liquid for the recirculation loop may be provided from different sources: One source may be used during closed recirculation, when supply liquid is provided by retentate to be recirculated from the separation module, wherein the volume in circulation may decrease corresponding to the amount of, or rate of, permeate production. In that case, the liquid remaining in recirculation has a

[0029] Version 2025-10-16 gradually increasing concentration of the component to be separated. Another source is used during open recirculation and / or mixed recirculation, when supply liquid is provided from a feed line to replenish the volume in circulation. In that case, the fresh feed liquid will mix with retentate and usually contribute to a decreased and / or diluted concentration of the component to be separated. In this context, it will be appreciated fresh feed liquid may be supplied while permeate is removed. As such, the overall concentration (of the component to be separated) in recirculation may increase when feeding fresh feed liquid, depending on the amount of permeate that may be simultaneously removed, or depending on the rate of removal thereof, such the net effect of supplying fresh feed liquid for dilution may be a slower increase of net concentration than would otherwise be observed without fresh feed liquid.

[0030] Depending on the type of source, the inlet point for feeding liquid into the recirculation loop may differ. For feed liquid sourced from a chamber of the pressurisation module, the feeding arrangement may supply the chamber of the pressurisation module directly. For feed liquid sourced directly from the feeding arrangement, one or more intakes may bypass the pressurisation module. Different intake locations may be combined in one system.

[0031] In some embodiments, the system comprises a mixing section or mixing chamber located at or downstream of the fresh feed intake for supply feed liquid to mix with recirculated liquid.

[0032] In some embodiments, the mixing section or mixing chamber is provided by a chamber of the membrane module.

[0033] The mixing section or mixing chamber, as the case may be, may provide a portion at which the feed liquid is introduced into the recirculated liquid.

[0034] An appreciation underlying the development of the invention was that the use of an open recirculation loop and a closed recirculation loop may be coordinated, i.e. used in an alternating manner, to adapt to filtration demands. More specifically, the coordination may take into account the available volume in recirculation, and specifically the variable range of maximum volume and minimum volume of a variable volume recirculation loop, when operated in a closed recirculation mode.

[0035] By providing an operating mode in which the pressurisation module is not necessarily relied upon for pressurisation, the number of recirculation cycles can be effectively increased, or prolonged. The suggestion made in this disclosure is to use an open recirculation mode to enable such an operating mode.

[0036] Version 2025-10-16 A further appreciation underlying the development of embodiments was performance of the separation system can be improved by supplying feed liquid, during the open recirculation mode, such that it passes the membrane module before recirculating to the pressure module. In a simplified characterisation, the feed liquid is less concentrated and therefore provides favourable osmotic performance in the membrane compared to a recirculated volume liquid.

[0037] The system may comprise a mixing section or mixing chamber for the feed liquid. The mixing chamber may be a chamber or antechamber of the membrane module. The mixing chamber may allow the liquid in recirculation and the freshly supply liquid to mix, to provide improved flow characteristics, such as flow rate and pressure. The mixing chamber may enable a better degree of homogenisation of concentration levels.

[0038] A further appreciation underlying the development of embodiments was that a configuration using an open recirculation mode allows the pressurisation module to remain inactive, and therefore allows the pressurisation module to be set into a holding position that may be utilised for other purposes.

[0039] In some embodiments, the feed arrangement is operated to maintain fluid pressure in the recirculation loop while liquid is supplied.

[0040] In some embodiments, the feed arrangement is operated to increase fluid pressure in the recirculation loop while liquid is supplied.

[0041] The feed arrangement may be operated according to different parameters at different times to maintain and / or increase fluid pressure, and or to ensure a fluid pressure in the recirculation loop is maintained according to a predetermined pressure profile over time.

[0042] The expressions “maintain” or “increase” pressure will be understood as meaning that the system comprises a form of control feedback loop, with a suitable arrangement to determine pressure or a surrogate indication of pressure, and to modulate operation of pressurisation arrangements to reach or maintain a predetermined pressure.

[0043] It will be appreciated that, in the open recirculation mode, the pressure profile may be affected primarily, and practically only, by the feed arrangement, without having to take into account influences of the pressurisation module. Without wishing to be bound by theory, this is believed to facilitate maintaining a predetermined pressure profile, such as a constant pressure, or linearly increasing pressure, by control of pump parameters without reliance on the pressurisation module.

[0044] Version 2025-10-16 In some embodiments, the system is further configured to supply liquid only in an open recirculation mode, to avoid feeding the recirculation loop during closed loop pressurisation.

[0045] In some embodiments, the system is further configured to use the feed arrangement to pressurise the pressurisation module.

[0046] The feed liquid may be used to displace or deform an actuator of the pressurisation module.

[0047] In some embodiments, the system comprises a configuration allowing it to isolate from the recirculation loop fluid supplied to displace or deform a pressure-actuator from the recirculation loop.

[0048] The configuration may be provided in the form of a valve or other line-closing mechanism.

[0049] In some embodiments, the system is further configured to operate in a mixed recirculation mode, wherein, in the mixed recirculation mode, fluid is supplied using the feed arrangement while the pressurisation module is operated to contribute to fluid pressurisation during recirculation.

[0050] As mentioned above, the mixed recirculation mode may be used, for instance, to supply feed liquid into the recirculation loop to reduce the rate at which the recirculation loop needs to be pressurised due to permeate production, compared to a closed recirculation mode.

[0051] In some embodiments, the system comprises a configuration allowing it to derive an energy value representative of system parameters required to maintain the pressurisation module in a predetermined holding position, and to operate the system to maintain the pressurisation module in the predetermined holding position.

[0052] The energy value is, herein, understood as a metric measurable or otherwise determinable by sensors of the system, that allow the system to determine a position or holding position of the pressurisation module. To provide an illustrative example, the holding position of the pressurisation module may be a piston position along a piston barrel, and / or a diaphragm condition, or a bladder arrangement, within a travel range or within a deformation range, respectively. As will be appreciated, a predetermined holding position may be a holding position predetermined for a particular purpose, e.g. a home position, parking position or otherwise. For instance, a predetermined holding position may be a position in which a flow rate through the pressurisation module is maximised, minimised, or otherwise optimised. For instance, a holding position may be a piston position at which a pre-determined recirculation flow rate is maintained.

[0053] Version 2025-10-16 The energy value is a value measurable or otherwise derivable as a suitable input for the control of the holding position. To provide an illustrative example, the energy value may be a parameter indicating the performance, such as a pump rate or pump speed, respectively, or flow rate, of the feed arrangement. Parameters of the system, such as pump speed, or valve conditions to open or close flow channels, may be operated in response to the energy value.

[0054] In some embodiments, the energy value takes into account a pressure gradient in the recirculation loop.

[0055] By “pressure gradient”, it will be understood that the pressure level in the recirculation loop may change, specifically the pressure may increase, over time, due to increased concentration of the retentate. The rate of change may depend on how the pressurisation module is operated, e.g. may slow as the concentration increases.

[0056] An appreciation underlying the use of the pressure gradient as indication of an energy value was that the pressure gradient is indicative of an increase in concentration in the retentate, and may also be indicative of the rate of change of the increase in concentration.

[0057] In some embodiments, the energy value takes into account the energy demand of the feed arrangement.

[0058] An appreciation underlying the use of the feed arrangement driving energy, i.e. the energy demand of the feed arrangement, as indication of an energy value was that the power consumption, such as pump power consumption, is correlated with an increase in concentration in the retentate.

[0059] In some embodiments, the energy value takes into account the frequency of purge events to purge the recirculation loop.

[0060] As will be appreciated, systems operating in a batch recirculation loop are purged from time to time to remove highly concentrated liquid and to supply fresh feed liquid. The inventors appreciated that the need for purge events can be influenced at least to some extent by the amount of fresh supply liquid being introduced, e.g. by use of an open recirculation mode. In other words, the use of an open recirculation mode increases the time, or cycles, taken for the retentate concentration to increase, and therefore reduces the frequency (i.e. makes less often) the number of purge events required.

[0061] The number of purge events relative to the number of recirculation cycles may be taken into account when calculating an energy value.

[0062] Version 2025-10-16 In some embodiments, the pressurisation module comprises a displaceable actuator.

[0063] For instance, the pressurisation module may comprise a piston.

[0064] In some embodiments, the pressurisation module comprises a deformable actuator.

[0065] For instance, the pressurisation module may comprise a diaphragm.

[0066] In some embodiments, the system comprises a sensor arrangement configured to measure a separation value indicative of the concentration of the component to be separated, wherein the system is configured to switch to one of the open recirculation mode and the closed recirculation mode depending on the separation value.

[0067] The separation value may be a measure of the concentration of the component to be removed, or a suitable surrogate measure, in the permeate (e.g. measuring reduction of the component) and / or the retentate (e.g. measuring an increase of the component). Conversely, in an outlet for permeate, the separation value may be a measure indicative of the absence or low level of the component to be removed. The separation value may, therefore, be indicative of a decrease or increase of a component concentration below or above, respectively, a threshold value. For instance, a suitable indicator for salinity in a desalination system may be provided by a conductivity sensor. Other suitable indicators may be the flow volume, pressure levels, etc.

[0068] The sensor or sensors of the sensor arrangement may be located at a suitable position in the separation system. For instance, one or more sensors may be located in or downstream of the in at least one of the feed line, the recirculation line section from pressurisation module to separation module, the recirculation line section from separation module to pressurisation module, or other suitable locations.

[0069] In some embodiments, the system comprises a configuration allowing it to switch to the open recirculation mode when the separation value meets a predetermined threshold condition indicative of reduced separation performance.

[0070] In some embodiments, the system comprises a configuration allowing it to switch to the closed recirculation mode when the separation value meets a predetermined threshold condition indicative of reduced separation performance.

[0071] In some embodiments, at least one sensor of the sensor arrangement is arranged to obtain a measurement from the recirculation loop.

[0072] Version 2025-10-16 In some embodiments, at least one sensor of the sensor arrangement is arranged to obtain a measurement downstream of the separation module and upstream of the pressurisation module.

[0073] In some embodiments, at least one sensor of the sensor arrangement is arranged to obtain a measurement downstream of the pressurisation module and upstream of the separation module.

[0074] In some embodiments, at least one sensor of the sensor arrangement is arranged to obtain a measurement from a discharge port or purge line of the separation module.

[0075] In some embodiments, at least one sensor of the sensor arrangement is arranged to obtain a measurement from a permeate production line of the separation module.

[0076] In some embodiments, the filtration system is a membrane separation system.

[0077] The system may be a desalination system, or other liquid separation system such as a decontamination system for the removal of particles from liquids such as water, and from liquid foods such as milk, and other applications.

[0078] Description of the Figures

[0079] Exemplary embodiments of the invention will now be described with reference to the Figures, in which:

[0080] Figure 1 is a schematic illustration of an embodiment in one mode of operation;

[0081] Figure 2 is a schematic illustration of an embodiment in another mode of operation;

[0082] Figure 3 is a schematic illustration of an embodiment in yet another mode of operation;

[0083] Figure 4 is a flowchart of an operation cycle using different modes of Figures 1 to 3;

[0084] Figure 5 is a flowchart of another operation cycle using different modes of Figures 1 to 3;

[0085] Figure 6 is a graph illustrating the performance of different system configurations, and Figure 7 is a graph illustrating the performance of further different system configurations.

[0086] Description

[0087] Referring to Figures 1 to 3, a filtration system 10 such as, for example, a desalination system, comprises a separation module 40, here comprising a selectively permeable membrane, and a pressurisation module 20. The separation module 40 is configured to be provided with a feed of liquid to be separated into permeate and retentate. The separation element of the module 40 may be a membrane, porous structure or other separation body. Permeate is understood as a

[0088] Version 2025-10-16 fraction passing through the separation element, to leave the system 10 as product and expected to have a lower concentration of, or be practically free of, a component to be separated. Retentate is understood as a fraction held back by the membrane as retentate, and comprising a higher, or enriched, concentration of the component to be removed from the permeate.

[0089] The system 10 is configured to be operated in a batch recirculation mode, at least for some of its operation time, wherein retentate from the separation module 40 is retained in the system 10, to be recirculated to be re-supplied for further separation cycles. As permeate exits the system 10, the volume of retentate in circulation decreases while the concentration of retained component in the retentate increases, requiring higher separation pressures at the separation module 40. For instance, the separation pressures may need to maintain reverse osmosis conditions for continuously increasingly concentrated retentate.

[0090] The pressurisation module 20 allows the liquid in circulation to be pressurised, and to increase the pressure during operation of the system 10. The pressurisation module 20 comprises at least one variable volume chamber, and here two chambers 22, 24, separated by a moveable partition, here in the form of a piston 50. The piston 50 is only an example of a moveable partition, and other systems may use a diaphragm, bladder, or other suitable means to alter the volume of a chamber. The chamber 22 forms part of the recirculation loop and provides a mechanism to provide a variable volume. The chamber 24 is, here, part of the pressurisation module 20 and can be supplied with liquid to cause displacement of the piston 50, without however requiring liquid in the chamber 24 to be used to increase the fluid volume in recirculation. The piston 50 provides fluid isolation between the two chambers 22 and 24.

[0091] The system 10 comprises a first line 34 providing a fluid passage from a first variable chamber port 26 of the first chamber 22 to a first side of the separation module 40, and a second line 36 providing a fluid passage from a second variable chamber port 28 of the first chamber 22 to a second side of the separation module 40.

[0092] The separation module 40 may be of a design that may be supplied from two sides, e.g. may comprise a wound membrane of, practically, tubular shape comprising two opposite ends supplied by a first separation port 42 and a second separation port 44, wherein fluid may pass from one end to the other or in an opposite direction, and wherein permeate may pass radially (inwardly or outwardly) through the membrane or other separation structure, as the case may be. The separation module may further comprise a drainage port or purge line 56 for flushing the system, i.e. to remove fluid too highly concentrated for further separation cycles.

[0093] The system 10 may be operated in a flow direction in which fluid passes from the first chamber 22 through the first variable chamber port 26 via the first line 34 into the first separation port 42,

[0094] Version 2025-10-16 passes the membrane module 40, and exits via the second separation port 44 to recirculate via the second line 36 into the second variable chamber port 28 of the first chamber 22. The system 10 may also be operated in a reverse flow direction, for instance for flushing.

[0095] The second line 36 comprises, here, a recirculation pump 32, wherein a downstream portion 36A of the second line 36 is downstream of the recirculation pump 32, and an upstream portion 36B of the second line 36 is upstream of the recirculation pump 32. While only one recirculation pump 32 is illustrated in the Figures, a pump arrangement may comprise any number of suitable flow control means including one or more pumps.

[0096] The first line 34, the separation module 40, the second line 36 and the first chamber 22 make up the recirculation loop for batch recirculation of liquid, which can be operated for at least some time without requiring the recirculation loop to be provided with fresh supply liquid, as the piston 50 may be moved to adjust (reduce) the volume of the first chamber 22 as permeate is produced. As will be understood, the piston 50 has an effective travel range defined by the maximum size and the minimum size of the first chamber 22, and so the system requires refilling from time to time, for instance when the piston has reached the end of its travel range.

[0097] The system 10 comprises a feed arrangement, here comprising a first pump 12, supplying liquid to be separated into the system 10 via a feed line 14. Although not illustrated in the Figures, it will be appreciated that the first pump 12 is fed from an external supply such as a tank, basin, or other source. The feed line 14 supplies, in Figure 1 , the chamber 24 directly via a feed intake 15, although it will be appreciated that the feed line 14 may supply into a different intake point of the system 10. From the chamber 24, an offtake 52 allows liquid to be fed into the second line 36, here into the upstream portion 36B of the second line.

[0098] The offtake 52 may be provided in the form of a line-shutting mechanism such as a valve to allow the second line 36 to be isolated from the feed intake 15 and / or from the second chamber 24, respectively. As will be appreciated, the piston 50 may be actuated by a mechanism other than a supply feed, however the illustrated arrangement permits the fluid fed into the second line 36 to be used for, or to at least contribute to, a displacement of the piston 50 after a batch recirculation phase, when it is necessary to increase the volume of the first chamber 22. As will be appreciated from a comparison of Figures 1 , 2, and 3, the first chamber 22 has a smaller volume 22A when the second chamber 24 has a corresponding larger volume 24A (see Figure 1), and the first chamber 22 has a larger volume 22C when the second chamber 24 has a corresponding smaller volume 24C (see Figure 3). Likewise, the first chamber 22 may have an intermediate volume 22B when the second chamber 24 has a corresponding complementary volume 24B (see Figure 2). In the Figures, a movement of the piston 50 to the right-hand side, reducing the volume of the first chamber 22, corresponds to a reduced volume of the recirculation loop, and a movement of

[0099] Version 2025-10-16 the piston 50 to the left-hand side, reducing the volume of the second chamber 24, corresponds to an increase of the volume in the recirculation loop.

[0100] The feed arrangement 12 comprises a bypass line 16 that is illustrated in Figures 1 and 3 in a closed condition 16C, in which no liquid can pass through the bypass line 16, and in Figure 2 in an open condition 160, in which liquid can pass from the feed arrangement into the recirculation line. The bypass line 16 allows liquid to be supplied from the feed arrangement or other fluid source into a different inlet of the recirculation line, as illustrated in the Figures, by supplying fresh fluid downstream of the pressurisation module 20, here into, or through, a control valve 54 of the first line 34. As will be appreciated, the system 10 may therefore be supplied with feed liquid at multiple (here: two) inlet points, either to supply liquid into the second line 36 (here via the second chamber 24) or to supply liquid into the first line 34 (here by bypassing the second chamber 24). The effect is that the supply of feed liquid can be fed to support piston displacement of the piston 50 in two directions. Either, the feed liquid is supplied to support piston movement to reduce the volume of the first chamber 22, by supplying the second chamber 24, or feed liquid is supplied to support piston movement to increase the volume of the first chamber 22, by supplying the first line 34.

[0101] The illustrated arrangement also allows supply liquid may be used to be fed directly into the first separation port 42, here via an appropriate control and configuration of the control valve 54. As will be appreciated, other feed-in configurations may be used.

[0102] Furthermore, it will be understood that the feed intake 15, the offtake 52, and the control valve 54 are part of a flow control arrangement, comprising flow control mechanisms such as valves, to allow them to be operated to effect and / or block flow, as required. Furthermore, the first pump 12 and the recirculation pump 32 are also part of a flow control arrangement and may be operated to control flow and / or may be maintained inactive low, respectively, as may be required to adjust a position of the piston 50 as desired. The flow control arrangement may be used to hold the piston 50 at a desired position along the pressurisation chamber 20. For a given flow rate and / or flow setting, the piston 50 may take a holding position determined by relative flow rates and / or pressures (figuratively with reference to Figures 1 to 3, liquid may push the piston 50 to the left, or to the right, and a pressure from the left and from the right may provide an equilibrium for a holding position).

[0103] As will be appreciated, the system 10, specifically the flow control arrangement comprising the feed intake 15, the offtake 52, the control valve 54, the first pump 12 and the recirculation pump 32, as well as the drainage port or purge line 56, may be operated under the instructions of a controller arrangement (not shown) configured to actuate the different elements of the flow control arrangement. Embodiments of the invention may be characterised in the form of method steps

[0104] Version 2025-10-16 wherein different method steps may comprise operating the system in one of the modes and / or steps of actuating elements of the flow control arrangement to switch between modes. The controller arrangement may be provided in the form of a controller comprising a computer program comprising instructions to cause a computer to control the different embodiments of the invention and / or to carry out method steps. The computer program may be provided on a non-transitory storage medium.

[0105] The system 10 may be operated in one of several modes, wherein the modes may be defined by operating conditions of the flow control arrangement, specifically by open or shut conditions of valves and / or by flow control of pump arrangements and / or operation of pressurisation arrangements.

[0106] Figure 1 illustrates the system 10 in a purge / refill mode 10A, which may be the condition of the system prior to operation, or after completion of a batch recirculation phase. At this point, the piston 50 may be in the smallest-volume position 22A of the first chamber 22, however depending on the preceding operation the piston 50 may also be in another position, such as a service position, partway between the distal end points of the pressurisation module 20. The offtake 52 is open and the feed line 14 is used to supply fresh feed liquid via the feed intake 15, here also via the second chamber 24, and to supply feed liquid via the first chamber 22. Likewise, the drainage port or purge line 56 is open to allow liquid to exit the system 10. The first line 34 is initially maintained open by opening the control valve 54, to permit flushing with fresh supply via the first chamber 22 and the first line 34.

[0107] The flow control arrangement may be used to control the supply for, and to effectively flush, different parts of the system 10. For instance, the separation module 40 may be flushed from both sides, from the first separation port 42 or from the second separation port 44. Although not shown herein, one or more additional valves may be provided, for instance at the second separation port 44 or in the upstream portion 36B of the second line 36, to isolate parts of the system 10 while other parts of the system are flushed using fresh feed liquid. As will be appreciated, the system may be operated such that flushing is as effective as possible to avoid a waste of excess flushing liquid via the drainage port or purge line 56, however this is not necessarily a requirement of all embodiments of this invention.

[0108] The flushing phase may be effected by flow generated by the first pump 12 only, while the recirculation pump 32 remains inactive. For instance, the recirculation pump 32 may be, depending on the type of pump, in a bypass mode or may be operated as much as is necessary to permit flow and / or to avoid interfering with flow generated by the first pump 12. Alternatively, or in addition at different points in time, the recirculation pump 32 may be operated to assist the

[0109] Version 2025-10-16 first pump 12 to flush out retentate that may have remained in the recirculation loop from a preceding batch phase.

[0110] Once sufficiently flushed, the control valve 54 is closed to thereby cause feed liquid to displace the piston 50 to increase the volume of the first chamber 22. Depending on system design, another mechanism may be used to block fluid passage out of the first variable chamber port 26 and / or through the first line 34. At the end of the purge / refill mode 10A, the piston 50 has moved to increase the volume of the first chamber 22, thereby to maximise the volume of the recirculation loop, while also providing the first chamber 22 with fresh feed liquid.

[0111] Referring now to Figure 3, in a closed loop recirculation, the offtake 52 is closed, the bypass line 16 is in a closed condition 16C, and the feed line 14 is used to supply fresh feed liquid via the feed intake 15 merely to pressurise the pressurisation module. In other words, the recirculation loop is isolated from the feed arrangement 12. No feed liquid enters the recirculation loop comprising the first chamber 22, the first line 34, the separation module 40 and the second line 36. The first line 34 is open to permit passage from the first variable chamber port 26 to the first separation port 42. The drainage port or purge line 56 is closed, such that the only passage for liquid to exit the system 10 is by permeating via the separation module 40 to, or through, the production line 58. The system 10 may be operated by operating the piston 50 and optionally, by coordinated actuation of the recirculation pump 32, to maintain recirculation in a closed loop and to adjust the volume to compensate for permeate production via the production line 58.

[0112] The suggestion made in the present disclosure is to add an open recirculation mode, presented in Figure 2, in which fresh feed liquid is supplied while the pressurisation module 20 is maintained inactive so as not to contribute to pressurisation of the recirculation loop. The open recirculation mode is practically used after the purge / refill mode 10A and before the closed recirculation mode 10C. In Figure 2, the feed line 14 is operated in a manner bypassing the second chamber 24, here via the bypass line 16 which is in an open condition 160, into the first line 34, which in this example is fed via the control valve 54. It will be appreciated that flow paths via the feed intake 15 and / or the offtake 52 may be closed while the bypass line 16 is open. Thereby, the feed arrangement 14 supplies the recirculation line between the first chamber 22 and the separation module 40, such that fresh feed is supplied to be mixed with retentate after the pressurisation chamber and / or before entering the separation module 40. As an alternative to the layout illustrated in Figure 2, the feed line 14 may bypass the second chamber 24 by feeding into the second line 36, e.g. via the offtake 52. By maintaining a constant recirculation volume, it can be achieved that the piston 50 of the pressurisation arrangement is kept inactive.

[0113] Version 2025-10-16 The open recirculation mode achieves that the concentration of the component to be separated increases more slowly, compared to a closed recirculation mode of Figure 3, as fresh feed liquid is used to mix with, and to thereby practically dilute, retentate of increased concentration.

[0114] In tests of different system configurations, it was further discovered that the energy demand, or energy efficiency, may differ depending on the feed-in point for the supply of fresh feed liquid. In one configuration, herein a “pressure module first” supply, fresh feed liquid is supplied to, or mixed with, recirculated retentate in a region downstream of the separation module 40 and upstream of the first chamber 22, i.e. into the second line 36. Referring to Figures 1 or 2, the supply of fresh feed liquid may be fed via the valve 52, either through the second chamber 24 or via a bypass line from the feed line into the second line 36. In another configuration, herein a “membrane module first” supply, fresh feed liquid is supplied to, or mixed with, recirculated retentate in a region downstream of the first variable chamber port 26 and upstream of the membrane module 40. A feed-in point upstream of the membrane module may comprise an intake directly into the membrane module, e.g. into a chamber of the membrane module upstream of the membrane. Referring to Figure 2, the supply of fresh feed liquid may be fed via, or through, the valve 54, via the bypass line 16. The valve may be operated or configured such that fresh liquid is directed towards the separation module 40 and away from the pressurisation module 20. The fresh feed liquid may be supplied during recirculation and therefore comprises a general flow direction from the pressurisation module 20 to the separation module 40.

[0115] Figures 4 and 5 illustrate a control scheme 11 A, and 11 B, respectively, showing a cycle through the purge / refill mode 10A, followed by an open recirculation mode 10B and a closed recirculation mode 10C. As illustrated in Figure 4, operation of the system 10 may comprise a decision point 10D in which a determination is made whether or not an open loop recirculation mode 10B should follow the refill mode 10A. If, in point 10D, a decision is made to operate in the open loop recirculation mode 10B, the system proceeds to operate accordingly. If, in point 10D, a decision is made to avoid operation in the open loop recirculation mode 10B, then the system proceeds to operate in the closed recirculation mode 10C.

[0116] Without wishing to be bound by theory, it is believed that a practical advantage of a system configuration using the open recirculation mode 10B is that the overall volume of the pressurisation module can be reduced. In other words, fresh supply of feed liquid is not necessarily only possible via the refill mode as illustrated in the example of Figure 1 , limited by the maximum possible volume of the first chamber 22. In addition, fresh supply of feed liquid is enabled over time, or cycles, even for smaller pressurisation chamber volumes.

[0117] The effect is illustrated in Figure 6, which shows a bar chart 60 schematically illustrating the energy requirements E for operating a system 10, or variants thereof, in an open loop

[0118] Version 2025-10-16 configuration and in a closed loop configuration, for different vessel volumes V. For the purpose of Figure 6, other parameters such as flow rate and initial concentration are considered as being the same, for simplicity. Figure 6 illustrates seven vessel volumes increasing in size, Vei being a hypothetical reference system operating only in open recirculation mode (e.g. hypothetical vessel volume 0L and no closed recirculation mode). V62, Ves, V64, Ves, Vee, and Vs7 indicate incrementally larger vessel volumes. In the bar chart, numerals using the suffix -A correspond to white bar portions and illustrate the relative energy requirement for operating in an open recirculation mode 10B. Numerals using the suffix -B correspond to shaded bar portions and illustrate the relative energy requirement for operating in a closed recirculation mode 10C. A total energy requirement for a given cycle / configuration is the sum of both open recirculation and closed recirculation.

[0119] The chart 60 illustrates that the first bar 61 A has a relatively larger (here: largest) energy requirement, avoiding the use of a closed recirculation mode. When adding a closed recirculation mode, and with increasing vessel size, the energy requirement of the closed recirculation mode (indicated by shaded bar portions) increases, as can be appreciated from the need to operate the pressurisation module (e.g. the piston 50) to travel over a relatively larger range and / or to move larger fluid volumes. However, the overall energy requirement (open plus closed) decreases with an additional use of an open recirculation mode: The sum of open mode 62A and closed mode 62B for vessel size Vs2 is higher than the sum of open mode 63A and closed mode 63B for vessel size V63, and so on, and the sum of open mode 67A and closed mode 67B for the largest vessel size Vs? in graph 60 indicates the lowest energy requirement. This is believed to be a consequence of the reduced pressurisation requirement with a lower-concentration mix of retentate and fresh feed liquid.

[0120] A further interesting aspect is that the added benefit of further increased vessel sizes becomes less pronounced above a certain point, here indicated by an illustrative line 68. To provide illustrative examples, Vs2 may be 25L, Ves may be 50L, Vs4 may be 75L, Ves may be 100L, Vee may be 150L, and Vs7 may be 250L. There may be considerable cost differences for manufacturing, installing, maintaining and operating vessels of different size, e.g. when comparing a 100L vessel system with a 250L vessel system. In the illustrated example, for instance, a view may be taken that the energy saving from moving from Vs4 to Ves, or further from Ves to Vee, is progressively less pronounced, and based on energy saving consideration, a vessel volume increase beyond Vs4 may not (or may) merit the corresponding cost of a larger vessel volume. In this manner, data such as the data underlying the chart 60 of Figure 6 may allow a system designer to identify a suitable smallest vessel size that also allows energy-efficient operation. The position of the illustrative line 68 is exemplary and depending on application scenario a slightly lower energy requirement may be more important, as the case may be, than a smaller vessel size, or vice versa.

[0121] Version 2025-10-16 It is believed that the embodiments of the invention herein allow designing a vessel size by incorporating a corresponding coordinated use of closed loop recirculation and open loop recirculation. As will be appreciated, the relative duration or ratio of open vs closed loop may depend on different parameters such as type and concentration of the feed liquid, desired purity of the produced permeate, cleaning requirements and service intervals of different components of the system 10 such as pumps, valves, membranes etc. As such, the invention enables the use of the open recirculation mode and the closed recirculation mode in a ratio that optimises a desired metric, e.g. minimises combined energy requirement for a given vessel volume. However, other metrics may be used, such as flow rates, amount of fluid to be processed, and others.

[0122] The ratio of open recirculation mode to closed recirculation mode may be dynamically adjusted, for instance by adjusting a duration of open recirculation, flow rates during open and / or closed recirculation, pump performance and / or pressurisation speed and changes thereof. The adjustment may be based on an input value such as a sensor reading. For instance, one or more points in the recirculation loop, the drainage port or purge line 56, and / or production line 58 or other suitable location of the system may be provided with one or more sensors to measure a separation value indicative of the concentration of a component to be separated, such as a conductivity sensor that is configured to measure the saline concentration of the discharged saline. This allows the separation performance to be monitored. Other sensor types may be used, and sensors may be located at other appropriate locations of the system 10.

[0123] The inventors found that a further variation of performance can be achieved by controlling the supply point of fresh feed liquid into the recirculation loop. In relation to recirculated liquid, fresh feed liquid can be considered to be concentration-diluting liquid, and therefore serves to reduce the concentration of recirculated liquid, and therefore reduces separation energy demand. For practical purposes, a feed supply inlet may be an inlet supplying into, and through, a chamber of the pressurisation module (e.g. via feed intake 15 into the second chamber 24). An alternative suggestion made herein is to select a feed supply inlet such that fresh feed liquid is first passed through the membrane module, before recirculating into the pressurisation module. The fresh feed liquid may be supplied upstream of the membrane module. The supply upstream of the membrane module may be at one or more points between pressurisation module and membrane module. The fresh feed liquid may be supplied such that it may mix with recirculating liquid. For instance, the system may be arranged with a mixing chamber downstream of the pressurisation module and upstream of the membrane module. Alternatively, or in addition, a chamber or volume of the membrane module may suffice to provide a mixing chamber for mixing recirculated liquid and fresh feed liquid, to form a mixed liquid to pass the membranes of the membrane module. It will be appreciated that a mixed liquid can be considered a liquid diluted with fresh feed liquid.

[0124] Version 2025-10-16 The inventors found that there is a subtle, but demonstrable reduction in energy demand when fresh feed liquid is supplied to the membrane module first. The effect is illustrated in Figure 7, which shows a bar chart 70 schematically illustrating the energy requirements E for operating a system 10, or variants thereof, in an open loop configuration and in a closed loop configuration, for different vessel volumes V.

[0125] The axes of Figure 7 correspond to those of Figure 6, and each bar represents energy requirements for a given pressure vessel volume, incrementally increasing in size. V71 is a reference system operating only in open recirculation mode, the vessel volume being 0L, there being no closed recirculation mode. V72, V73, V74, V75, V76, and V77 indicate systems with pressurisation vessel, and incrementally larger vessel volumes. To provide illustrative examples, the vessel volume V72 may be 25L, V73 may be 50L, V74 may be 75L, V75 may be 100L, V76 may be 150L, and V77 may be 250L.

[0126] Similarly to Figure 6, the longer (white) bar portions of vessels sizes V71 to V77 illustrate the relative energy requirement for operation in an open recirculation mode 10B. The shorter (shaded) bar portions of vessel sizes V72 to V77 illustrate the relative energy requirement for operating in a closed recirculation mode. A total energy requirement for a given cycle / configuration is the sum of both open recirculation and closed recirculation. As such, a taller bar indicates a configuration with higher energy demand. In line with the description of Figure 6, the total energy demand decreases with increased volume of a pressure vessel, whereas larger vessels may permit more energy efficient operation yet may be more costly to install and maintain. Likewise, the benefit of reducing energy demand may become less pronounced at a certain level, here illustrated by an illustrative line 78, below which the energy reductions may no longer be (or may still be) proportionate to increased cost and logistics of operating a larger vessel. As mentioned above, the line 78 is illustrative and what amounts to an acceptable trade-off between vessel size and operational energy savings may depend on the application scenario.

[0127] For each volume V71 to V77 , Figure 7 illustrates a pair of bars, each bar corresponding to one of two supply modes. A first supply mode corresponds to a fresh feed liquid supply as “membrane module first” supply, and are indicated by numerals with a suffix “-M”. A second supply mode corresponds to a “pressure module first” supply, and are indicated by numerals with a suffix “-P”. Other parameters such as flow rate and initial concentration are considered as being the same, for simplicity.

[0128] The chart 70 illustrates that the first group of bars 71 P, 71 M has a relatively larger (here: largest) energy requirement, without the use of a closed recirculation mode. When including a closed recirculation mode, and with increasing vessel size, the energy requirement of the closed

[0129] Version 2025-10-16 recirculation mode (indicated by shaded bar portions) increases, due to the need to operate the pressurisation module (e.g. the piston 50) to travel over a relatively larger range and / or to move larger fluid volumes. However, the overall energy requirement (open plus closed) decreases with an additional use of an open recirculation mode. The behaviour corresponds to that illustrated in Figure 6.

[0130] An additional observation derivable from Figure 7 is that for each data pair for a given vessel volume V71 to V77, the “membrane module first” (suffix -M) supply requires less energy than the corresponding “pressure module first” (suffix -P) supply. For the vessel volume V71, a pressure first supply 71 P has a higher energy demand than a membrane first supply 71 M, for the vessel volume V72, a pressure first supply 72P has a higher energy demand than a membrane first supply 72M, for the vessel volume V73, a pressure first supply 73P has a higher energy demand than a membrane first supply 73M, for the vessel volume V74, a pressure first supply 74P has a higher energy demand than a membrane first supply 74M, for the vessel volume V75, a pressure first supply 75P has a higher energy demand than a membrane first supply 75M, for the vessel volume V76, a pressure first supply 76P has a higher energy demand than a membrane first supply 76M, and for the vessel volume V77, a pressure first supply 77P has a higher energy demand than a membrane first supply 77M. The energy requirements for the membrane-module first supply are about 5% lower than for the pressure-module first supply.

[0131] Without wishing to be bound by theory, it is believed that the reduced energy requirement is a consequence of the better osmotic pressure performance at the membrane achieved by supplying a reduced concentration. As will be appreciated, a reduction of a few percent, e.g. as is believed of around 5% energy requirement, may amount to a significant cost reduction when operating a system for prolonged periods of time.

[0132] The system 10 may switch operation between an open recirculation mode and a closed recirculation mode, and / or between an open recirculation mode, mixed recirculation mode and a closed recirculation mode depending on whether or not a predetermined end point is reached. For instance, the system may repeat open recirculation cycles, or a sequence of open and mixed recirculation cycles followed by closed recirculation mode after which the recirculation volume is minimised, and eventually requires resetting and / or replenishing via the feed arrangement. The open recirculation mode or open-and-mixed recirculation modes may be operated for a predetermined period of time, and / or with a predetermined volume of fluid, and / or until a concentration value measured by a sensor arrangement indicates sufficient permeate production performance and / or until a concentration value measured by a sensor arrangement indicates a change in concentration gradient. To this end, the system 10 may comprise a sensor arrangement configured to measure a separation value indicative of the concentration of the component to be separated, and to switch to a closed recirculation mode and / or to an open

[0133] Version 2025-10-16 recirculation mode and / or to a mixed recirculation mode in response to the separation value. Alternatively, or in addition, the system may use an energy value representative of system parameters required to maintain the pressurisation module in a predetermined holding position, in response to the energy value. In this manner, the pressurisation module may be held in a predetermined holding position during, or when switching between two or through three of, the open mode, closed mode, and / or mixed mode.

[0134] To operate a system in a membrane-first supply mode, to obtain the benefits indicated in Figure 7, the system may be configured such that fresh fluid feed that is supplied in the open recirculation mode is supplied to an intake downstream of the pressure module, and upstream of the membrane module or directly into the membrane module.

[0135] The fresh feed supply may be such that the fresh fluid feed is allowed to mix with recirculated liquid. To that end, the fresh feed supply may be upstream of a mixing chamber or mixing section.

[0136] Depending on the system design, the type of fluid to be separated, and / or the type of component to be separated from the fluid, different concentration indicators may be used. The threshold for determining the concentration may be an absolute threshold value or range, a relative threshold, or a rate of change. Alternatively, or in addition, to modulating the operation of the system based on separation values, the modes may be switched depending on timing, flow volumes, flow rates, and / or take into account multiple parameters. In some system configurations, the switching between modes may be based on pre-determined time intervals.

[0137] Herein, the invention has been described using the example of a desalination system using membrane separation to create a desalinated permeate from a supply of saline. It will be appreciated that the principle of the invention may also be applicable in other purification processes and / or downstream processes, such as ultrafiltration, nanofiltration, and microfiltration, specifically when components to be removed may be intentionally enriched, or retained in higher concentration, by recirculation during a batch or semi-batch operation, as may be expected, for instance, during reverse osmosis processes. The principles disclosed herein are believed to be applicable for solutions, suspensions, and combinations thereof, e.g. for processes separating salts from solution, as well as for processes separating suspended solids such as particles, proteins, microplastics etc from liquids such as water and / or liquid foods.

[0138] Whilst the principle of the invention has been illustrated using exemplary embodiments, it will be understood that the invention is not so limited, and that the invention may be embodied by other variants defined within the scope of the appended claims.

[0139] Version 2025-10-16

Claims

CLAIMS:

1. A filtration system comprising a batch recirculation loop comprising a pressurisation module and a separation module, configured to allow liquid to be pressurised using the pressurisation module while recirculating the liquid to the separation module, wherein the filtration system further comprises a feed arrangement allowing it to supply feed liquid into the recirculation loop to allow feed liquid to mix with recirculated liquid, wherein the filtration system is further configured to allow it to operate in an open recirculation mode and in a closed recirculation mode, wherein, in the closed recirculation mode, no feed liquid is supplied into the recirculation loop while the pressurisation module pressurises liquid during recirculation, and wherein, in the open recirculation mode, feed liquid is supplied into the recirculation loop during recirculation, and wherein the filtration system comprises a configuration allowing it to supply feed liquid to be mixed with recirculated liquid at a feed intake position downstream of the pressurisation module and upstream of or into the separation module.

2. The system according to claim 1 , further configured to allow it to supply feed liquid downstream of the pressurisation module, via the feed intake, during the open recirculation mode.

3. The system according to claim 1 or 2, wherein, in the open recirculation mode, liquid is supplied using the feed arrangement while the pressurisation module is inactive during recirculation.

4. The system according to any one of the preceding claims, comprising a mixing section or mixing chamber located at or downstream of the fresh feed intake for supply feed liquid to mix with recirculated liquid.

5. The system according to claim 4, wherein the mixing section or mixing chamber is provided by a chamber of the membrane module.

6. The system according to any one of the preceding claims, wherein the feed arrangement is operated to maintain fluid pressure in the recirculation loop while liquid is supplied.

7. The system according to any one of the preceding claims, wherein the feed arrangement is operated to increase fluid pressure in the recirculation loop while liquid is supplied.Version 2025-10-168. The system according to any one of the preceding claims, further configured to supply liquid only in an open recirculation mode, to avoid feeding the recirculation loop during closed loop pressurisation.

9. The system according to any one of the preceding claims, further configured to use the feed arrangement to pressurise the pressurisation module.

10. The system according to any one of the preceding claims, comprising a configuration allowing it to isolate from the recirculation loop liquid supplied to displace or deform a pressureactuator.11 . The system according to any one of the preceding claims, further configured to operate in a mixed recirculation mode, wherein, in the mixed recirculation mode, liquid is supplied using the feed arrangement while the pressurisation module is operated to contribute to fluid pressurisation during recirculation.

12. The system according to any one of the preceding claims, comprising a configuration allowing it to derive an energy value representative of system parameters required to maintain the pressurisation module in a predetermined holding position, and to operate the system to maintain the pressurisation module in the predetermined holding position.

13. The system according to claim 12, wherein the energy value takes into account a pressure gradient in the recirculation loop, an energy demand of the feed arrangement, and / or a frequency of purge events to purge the recirculation loop.

14. The system according to any one of the preceding claims, wherein at least one pressurisation module comprises a displaceable actuator, such as a piston, and / or wherein at least one pressurisation module comprises a deformable actuator, such as a diaphragm.

15. The system according to any one of the preceding claims, comprising a sensor arrangement configured to measure a separation value indicative of the concentration of the component to be separated, wherein the system is configured to switch to one of the open recirculation mode and the closed recirculation mode depending on the separation value.

16. The system according to claim 15, comprising a configuration allowing it to switch to the open recirculation mode when the separation value meets a predetermined threshold condition indicative of reduced separation performance.Version 2025-10-1617. The system according to claim 15 or 16, comprising a configuration allowing it to switch to the closed recirculation mode when the separation value meets a predetermined threshold condition indicative of reduced separation performance.

18. The system according to any one of claims 15 to 17, wherein at least one sensor of the sensor arrangement is arranged to obtain a measurement from the recirculation loop.

19. The system according to claim 18, wherein at least one sensor of the sensor arrangement is arranged to obtain a measurement downstream of the separation module and upstream of the pressurisation module.

20. The system according to claim 18 or 19, wherein at least one sensor of the sensor arrangement is arranged to obtain a measurement downstream of the pressurisation module and upstream of the separation module.21 . The system according to any one of claims 15 to 20, wherein at least one sensor of the sensor arrangement is arranged to obtain a measurement from a discharge port or purge line of the separation module.

22. The system according to any one of claims 15 to 21 , wherein at least one sensor of the sensor arrangement is arranged to obtain a measurement from a permeate production line of the separation module.

23. The system according to any one of the preceding claims, wherein the filtration system is a membrane separation system.Version 2025-10-16

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