Generation of treatment fluid for use in dialysis

Abstract

An arrangement for providing a treatment fluid for use in dialysis therapy comprises a first system (10), which is operable to process source water into product water for medical use and provide a flow of product water in a circulation path (13), and a second system (20), which is operable to generate the treatment fluid by mixing the product water with one or more concentrates. The second system comprises a main path (21), which is fluidly connected to a tapping junction (CP) on the circulation path for obtaining a diverted flow of product water, and a supply sub-system (23, 24), which is operable to supply the concentrate(s) into the main path at one or more dosing points (DP, DP') for mixing with the product water. A variable restrictor (43) in the circulation path or in the main path upstream of the dosing point(s) is adjusted, by a control device (41), to maintain a target fluid pressure at a predefined location in the second system.

Description

[0001] GENERATION OF TREATMENT FLUID FOR USE IN DIALYSIS

[0002] Technical Field

[0003] The present disclosure relates generally to dialysis, and in particular to arrangements for generating treatment fluid for use in dialysis.

[0004] Background Art

[0005] Dialysis is a therapy that replaces the normal blood-filtering function of the kidneys. It is used when the kidneys are not working well, which is known as kidney failure and includes acute kidney injury (AKI) and chronic kidney disease (CKD). Dialysis involves removal of water from the blood of the patient suffering from kidney failure, as well as exchange of solutes with the blood. One example of dialysis therapy is peritoneal dialysis (PD), in which a treatment fluid is infused into the peritoneal cavity of the patient to interface with the blood of the patient through the peritoneal membrane. Another example of dialysis therapy is extracorporeal (EC) blood therapy, in which blood is circulated outside of the patient and interfaced with one or more treatment fluids. Modalities of extracorporeal blood therapy include hemodialysis (HD), hemofiltration (HF) and hemodiafiltration (HDF).

[0006] Treatment fluids used in PD and HD are commonly known as dialysis fluids. In HF, the treatment fluid is known as replacement fluid, since it is infused into the blood of the patient to replace fluid removed during therapy. In HDF, both dialysis fluid and replacement fluid are used.

[0007] Dialysis therapy is typically automated and performed under control of a dialysis machine. In PD, the machine is known as a cycler, which is connected in fluid communication with the peritoneal cavity and is operated to control the flow of fresh dialysis fluid into the peritoneal cavity and the flow of spent dialysis fluid from the peritoneal cavity. In EC blood therapy, there are two main categories of machines: "chronic machines" for treatment of patient suffering from CKD, and "acute machines" for treatment of patients suffering from AKI.

[0008] Over time, dialysis therapy consumes large quantities of treatment fluid. In some modalities of dialysis therapy, pre-made treatment fluid is delivered in prefilled bags to the point of care. For example, conventional automated PD is performed by use of prefilled bags. AKI machines are configured to use prefilled bags of treatment fluid, by staff installing a prefilled bag before treatment, and replacing the prefilled bag as required. On the other hand, CKD machines have integrated capability to generate treatment fluid by mixing one or more concentrates with purified water of well-defined quality. Recently, PD machines with integrated capability of fluid generation have been proposed.

[0009] There is a general desire to advance generation of treatment fluid for all types of dialysis therapy. Another desire is to enable generation of treatment fluid even if purified water is not available.

[0010] Since the treatment fluid is a medical fluid, it is desirable for an arrangement for providing treatment fluid to be operationally stable in the sense that the treatment fluid is generated with a consistent and accurate composition.

[0011] It may also be desirable that an arrangement for providing treatment fluid is made up of re-usable or permanent components and fluid lines as far as possible. This will both minimize the environmental impact, by reducing the amount of components and fluid lines that go to waste, as well as reduce the need for manual intervention by the user to prepare the arrangement for fluid generation. The provision of re-usable components results in a need to implement a technique of disinfecting the arrangement, or at least its re-usable components and fluid lines. Here, it is desirable for the arrangement to be operationally stable in the sense that the disinfection is reliable and results in an adequate disinfection of relevant components and fluid lines.

[0012] Summary

[0013] It is an objective to at least partly overcome one or more limitations of the prior art.

[0014] One objective is to provide a technique of ensuring the operational stability of an arrangement for providing a treatment fluid for use in dialysis therapy.

[0015] Another objective is to provide such a technique that is capable of ensuring operational stability of the arrangement when it is operated to generate treatment fluid and / or if it is operated for disinfection.

[0016] One or more of these objectives, as well as further objectives that may appear from the description below, are at least partly achieved by an arrangement for providing a treatment fluid for use in dialysis therapy, a method and a computer-readable medium according to the independent claims, embodiments thereof being defined by the dependent claims.

[0017] The present disclosure proposes a combination of a first system for generating product water for medical use from source water, and a second system for generating treatment fluid by mixing product water from the first system with at least one concentrate. The first system is operable to circulate product water in a circulation path within the first system, and the second system is operable to divert or tap off a flow of product water from the circulation path into a main fluid path for mixing with the respective concentrate at one or more dosing points. The combination of first and second system may generate treatment fluid for any type of dialysis therapy and even if purified water is not readily available. To ensure operational stability of the combination of first and second systems, a variable restrictor is arranged in the circulation path or in the main fluid path upstream of the dosing point(s). The variable restrictor is dynamically adjusted to maintain a target fluid pressure at a predefined location in the second system. The variable restrictor may be adjusted to achieve a consistent pressure at the dosing point(s), which will improve the ability of the second system to generate the treatment fluid with a consistent and accurate composition. Alternatively or additionally, the variable restrictor may be adjusted, during heat disinfection of the second system, to achieve an elevated fluid pressure in a heater, which is active during the heat disinfection, so as to counteract boiling within the heater. This will improve the operational stability of the second system when it is operated for heat disinfection.

[0018] Still other objectives, aspects, embodiments and technical effects, as well as features and advantages may appear from the following detailed description, from the attached claims as well as from the drawings.

[0019] Brief Description of the Drawings

[0020] FIG. 1 is a block diagram of an example dialysis system configured for generation of PD fluid.

[0021] FIG. 2A is a block diagram of an example arrangement for treatment fluid production, and FIG. 2B is a flow chart of an example method of operating the arrangement in FIG. 2A.

[0022] FIG. 3 is a flow chart of an example method of operating an arrangement for treatment fluid production for stability in fluid generation and / or heat disinfection.

[0023] FIG. 4A is a block diagram of an example arrangement for treatment fluid production comprising a mechanical pressure regulator, and FIG. 4B is a block diagram of an example arrangement for treatment fluid production with electric feedback pressure control.

[0024] FIG. 5 is a section view of an example mechanical pressure regulator for use in the arrangement of FIG. 4A.

[0025] FIGS 6A-6B shows two example configurations for dosing concentrates in a fluid preparation system (FPS).

[0026] FIG. 7 is a block diagram of an example FPS.

[0027] FIG. 8A-8B are block diagrams of an example water purification system (WPS). FIG. 9A is a block diagram of an example combination of a WPS and an FPS in an arrangement for treatment fluid production, FIG. 9B illustrates the arrangement of FIG. 9A with the FPS in production mode, and FIG. 9C is a flow chart of an example procedure that may be performed in the WPS during the production mode.

[0028] FIG. 10A is a flow chart of an example method of operating a WPS during heat disinfection, and FIG. 10B illustrates the arrangement of FIG. 9A during heat disinfection of the WPS.

[0029] FIG. 11 A is a flow chart of an example method of operating an FPS in a singlepass state of a heat disinfection mode, and FIG. 1 IB illustrates the arrangement of FIG. 9A with the FPS in a single-pass state during heat disinfection.

[0030] FIG. 12A is a flow chart of an example method of operating an FPS in a multipass state of a heat disinfection mode, and FIG. 1 IB illustrates the arrangement of FIG. 9A with the FPS in a multi-pass state during heat disinfection.

[0031] FIG. 13A is a block diagram of an example combination of a WPS and an FPS, and FIG. 13B illustrates a flow path established during heat disinfection.

[0032] FIG. 14 is a block diagram of an example control system.

[0033] Detailed Description of Example Embodiments

[0034] Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments are shown. Indeed, the subject of the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure may satisfy applicable legal requirements.

[0035] Also, it will be understood that, where possible, any of the advantages, features, functions, devices, and / or operational aspects of any of the embodiments described and / or contemplated herein may be included in any of the other embodiments described and / or contemplated herein, and / or vice versa. In addition, where possible, any terms expressed in the singular form herein are meant to also include the plural form and / or vice versa, unless explicitly stated otherwise. As used herein, "at least one" shall mean "one or more" and these phrases are intended to be interchangeable. Accordingly, the terms "a" and / or "an" shall mean "at least one" or "one or more", even though the phrase "one or more" or "at least one" is also used herein. As used herein, except where the context requires otherwise owing to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, that is, to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments. As used herein, the terms "multiple", "plural" and "plurality" are intended to imply provision of two or more elements. The term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0036] It will furthermore be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing the scope of the present disclosure.

[0037] Like reference signs refer to like elements throughout.

[0038] Well-known functions or constructions may not be described in detail for brevity and / or clarity. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0039] As used herein, "dialysis therapy" or "dialysis" refers to any therapy that replaces or supplements the renal function of a patient by use of a treatment fluid. Dialysis therapy includes, without limitation, extracorporeal (EC) blood therapy and peritoneal dialysis (PD) therapy.

[0040] As used herein, "product water" refers to water that has a purity suitable for medical use. In some embodiments, the product water meets criteria of so-called "water for dialysis" "water for injection", or "ultrapure water". For example, criteria for "water for dialysis" or "dialysis water" may be defined in accordance with ANSI / AAMI / ISO 23500-3:2019.

[0041] As used herein, "treatment fluid" refers to any fluid that is consumed as a result of dialysis therapy. Treatment fluid includes, without limitation, dialysis fluid for infusion into the peritoneal cavity during PD therapy, dialysis fluid for supply to a dialyzer during EC blood therapy, and replacement fluid and substitution fluid for infusion into blood during EC blood therapy.

[0042] As used herein, "heat disinfection" refers to a technique of deactivating bacteria and viruses by subjecting them to a fluid at a required temperature for a required time period. The fluid may be water, optionally in combination with a cleaning agent ("disinfectant"). Non-limiting examples of disinfectants that are used for disinfection of dialysis systems include acetic acid, citric acid, peracetic acid, sodium hypochlorite, and sodium metabisulfite.

[0043] As used herein, "A0 concept" refers to an established technique of quantifying the effect of heat disinfection on deactivation of microorganisms. An A0 value may be calculated according to: A0 T is the fluid temperature (in °C), z is a bacteria coefficient, and At is the exposure time at the fluid temperature. By use of this equation, a value of the microbial deactivation may be calculated, by summation or integration, during heat-up, holding, and cooling of any moist heat disinfection process. For example, a condition for sufficient heat disinfection may be that the AO value is at least 500, 600, 700, 800 or 900. Generally, the fluid temperature needs to exceed 65°C to be effective.

[0044] FIG. 1 is a generic overview of a dialysis system 1 for PD therapy. The dialysis system 1 is fluidly connected to the peritoneal cavity PC of a patient P. As indicated by a double-ended arrow, the dialysis system 1 is operable to convey fresh dialysis fluid into PC and to receive spent dialysis fluid from PC on a fluid path 2. The fluid path 2 may be defined by tubing that connects to an implanted catheter (not shown) in fluid communication with the peritoneal cavity PC. A drain line 3 is connected to the dialysis system 1 for conveying the spent dialysis fluid to a drain 4, for example a floor drain, a toilet, a sink, a bag, or a container. PD therapy is typically implemented as daily treatment sessions, each comprising a number of fluid exchange cycles. The respective fluid exchange cycle may include a fill phase, a dwell phase and a drain phase, performed in sequence. In the fill phase, fresh dialysis fluid is supplied to PC on fluid path 2. In the dwell phase, the dialysis fluid resides in PC. In the drain phase, spent dialysis fluid is extracted from PC on fluid path 2.

[0045] In the illustrated example, the dialysis system 1 includes a water purification system 10 ("WPS", or "first system"), which is operable to generate product water by purification processing of source water, for example tap water, a fluid preparation system 20 ("FPS", or "second system"), which is operable to generate a treatment fluid by mixing the product water with one or more liquid concentrates, and a therapy system 30, which is operable to control the flows of fresh and spent treatment fluid in relation to the peritoneal cavity. The product water is purified water that is produced to meet criteria for medical use, for example so-called "water for dialysis" "water for injection", or "ultrapure water". The WPS 10, the FPS 20, and the therapy system 30 may be implemented as a single machine or as two or more separate machines. The source water is received by the WPS 10 from a source 5 on a water supply line 6.

[0046] The liquid concentrate is a consumable that is supplied from a container or bag ("concentrate container"), which is connected for fluid communication with the FPS 20. In the example of FIG. 1, a liquid concentrate Cl is held in a concentrate container 7, which is removably connected to the FPS 20 of the dialysis system 1. The container 7 is thus a disposable unit that is regularly disconnected and replaced with a new container full of concentrate Cl. For example, the container 7 may be replaced when the remaining amount of concentrate Cl is deemed insufficient, or when a predefined time has elapsed since the container 7 was installed for use by the FPS 20. The container 7 may be attached directly to the FPS 20 or via a disposable tubing 8, as shown.

[0047] FIG. 2A is a more detailed block diagram of an example dialysis system 1, comprising a combination of a WPS 10 and an FPS 20 ("WPS-FPS arrangement"), and a therapy system 30.

[0048] The WPS 10 comprises a purification sub-system 11, which is operable to generate product water (PW) from source water (SW). The purification sub-system 11 may include any conventional equipment for water purification. Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from the water. The purification sub-system 11 may be configured to operate by membrane filtration or ion exchange, or a combination thereof. One commonly used membrane filtration technique for water purification is reverse osmosis (RO), in which an RO membrane is used to separate ions, molecules and larger particles from water. Ion exchangers (IEX) are also commonly used for water purification. Simply put, an ion exchanger operates to remove ionic impurities from water by replacing the respective ionic impurity with another ionic substance. Typical ion exchangers are ion-exchange resins (functionalized porous or gel polymer), zeolites, montmorillonite, clay, or soil humus. Electrodeionization (EDI) is also used for water purification. In principle any conventional or future water purification technique may be implemented in the purification sub-system 11.

[0049] In the WPS 10, a feed line 12 extends from a water port 12a to the purification sub- system 11. A tubing 6 extends from a SW source (not shown) and has a terminal connector 6a, which is connected to the port 12a. The WPS 10 further defines a circulation path 13. The purification sub-system 11 is connected to the circulation path 13 so that PW generated by the purification sub-system 11 is circulated back to the purification sub-system 11 on the circulation path 13. A drain line 14 extends from the purification sub-system 11 to a drain port 14a on the WPS 10, and a terminal connector 15a on a disposable tubing 15 is connected to the drain port 14a. The disposable tubing 15 is arranged to extend to a drain 4.

[0050] The FPS 20 comprises a main fluid path ("main path") 21 that extends through the FPS 20 to an output port Pl for treatment fluid (TF). The main path 21 is fluidly connected to the WPS 10 at a connection or tapping point ("tapping junction") CP on the circulation path 13. When the WPS 10 is operated to circulate product water in the circulation path 13, the FPS 20 is operable to divert a flow of product water (PW) from the circulation path 13 into the main path 21 via the tapping point CP.

[0051] In the example of FIG. 2A, the treatment fluid is generated by mixing the product water with a concentrate provided by a supply arrangement or sub-system in the FPS 20. The supply arrangement includes a supply line 23, which extends from an inlet port P2 for concentrate to a dosing point DP in the main path 21, and a supply pump ("concentrate pump") 24 in the supply line 23. A concentrate container 7 is connected to the inlet port P2, here by a terminal connector 8 a on a fluid line 8 connected to the container 7. The FPS 20 further comprises a processing sub-system 22, which is located in the main path 21 downstream of the dosing point DP. The processing sub-system 22 may comprise various components for ensuring or improving mixing, for verifying the composition of the resulting treatment fluid, for removal of potential contaminants, etc. These components may include one or more of a fluid pump, a mixing chamber, a bubble trap, sensor(s), filter(s), etc. It is to be noted that the FPS 20 may be configured to generate treatment fluid in batches or on the fly. Here, "on the fly" (or "online" or "on demand") implies that the treatment fluid is generated at a flow rate determined by the therapy system 30.

[0052] Although a single container 7 is shown in FIGS 1 and 2A, the treatment fluid may be generated by mixing product water with any number of concentrates. Each such concentrate may be supplied from a respective container, which is releasably connected to a respective inlet port on the FPS 20.

[0053] In FIG. 2A, the FPS 20 comprises additional ports P3, P4. The port P3 is a return port for spent treatment fluid from the therapy system 30. A drain line 25 extends from the return port P3 to a drain port P4. A tubing 3 is connected by a terminal connector 3a to the drain port P4 and extends to the drain 4. A functional unit 26 is arranged in the drain line 25 to operate on the spent treatment fluid. The functional unit 26 may, for example, include one or more of a drain pump, sensor(s), a bubble trap, etc. As shown, the processing sub-system 22 may be connected to the drain line 25 by connecting line 26', to allow the processing sub-system 22 to direct fluid to drain, for example during start-up of the FPS 20.

[0054] In the illustrated example, the FPS 20 further includes a heating device ("heater") 27. The heater 27 may be an electrical heater or any other type of device capable of heating a passing fluid. The heater 27 may be used to heat the treatment to a target temperature suitable for dialysis therapy. The heater 27 may also be used in heat disinfection of the FPS 20.

[0055] In FIG. 2A, a terminal connector 31a on a disposable tubing 31 is releasably connected to the outlet port Pl on the FPS 20 to direct treatment fluid to the therapy system 30. Further, a terminal connector 32a on a disposable tubing 32 is releasably connected to the return port P3 on the FPS 20 to direct spent treatment fluid to the FPS 20 from the therapy system 30. The therapy system 30 may be configured to perform PD therapy or EC blood therapy by use of treatment from the FPS 30. The therapy system 30 may be configured to accumulate a supply of TF for use during on-going or up-coming dialysis therapy, or use the TF as it is produced by the FPS ("on-demand"). Techniques and machines for performing PD therapy and EC blood therapy are well- known in the art and will not be further described.

[0056] In some embodiments, the WPS 10 and the FPS 20 are included in separate machines. In such embodiments, the main path 21 may be releasably connected to a PW outlet port (not shown) on the WPS 10, where the PW outlet port is fluidly connected to the tapping point CP. In other embodiments, the WPS 10 and the FPS 20 are integrated in a single machine and the main path 21 is permanently connected to the WPS 10.

[0057] FIG. 2B is a flow chart of an example method Ml of operating the combination of WPS 10 and FPS 20 for production of treatment fluid TF. The corresponding operation is shown in FIG. 2A, where thicker lines indicate passage of fluid and arrows indicate flow direction. In step S10, the circulation path 13 is established in the WPS 10. Step S10 may involve operating a plurality valves ("valve arrangement") in the fluid circuit of the WPS 10. In step Si l, the WPS 10 is operated to generate product water PW from source water SW and to circulate the product water PW in the circulation path 13. In step S12, the FPS 20 is operated to divert a flow of PW from the circulation path 13 into the main path 21, for example by operating one or more fluid pumps in the processing sub-system 22. In step S13, the FPS 20 is operated to mix the product water PW with one or more concentrates to produce the treatment fluid TF. In FIG. 2A, the one or more concentrates is represented by Cl and the supply pump 24 is operated to generate a controlled flow of concentrate Cl from the container 7 along the supply path 23 to the dosing point DP on the main path 21. The mixing occurs in the main path 21 and the processing sub-system 22. In FIG. 2A, the resulting TF is supplied via the main path 21 to the outlet port Pl for receipt by the therapy system 30. As noted, the temperature of TF may be controlled by use of the heater 27.

[0058] The present disclosure aims at ensuring the operational stability of a combination of a WPS 10 and an FPS 20. For example, it has been found that the composition of the treatment fluid varies with the fluid pressure at the dosing point DP. Further investigations have revealed that the flow rate of concentrate generated by the supply pump 24 will change with the counterpressure at the dosing point DP, even if the supply pump 24 is controlled to operate at a constant pump speed. If this problem is ignored, the treatment fluid may not meet regulatory protocols. The counterpressure may vary as a result of temporal variations in the fluid pressure in the circulation path 13 of the WPS 10. Such pressure variations may be inherent to the operation of the WPS 10. It has also been found that the fluid pressure at the dosing point DP varies with the TF production rate, i.e., the flow rate of treatment fluid along the main path 21 to the outlet port Pl. For example, in some tests, a change of TF production rate from 100 ml / min to 300 ml / min resulted in a pressure change at the dosing point DP of 130 mmHg, which is turn resulted in a TF composition error of approximately ±1%. The problem of composition error is addressed by the present disclosure.

[0059] In some embodiments, the FPS 20 includes durable fluid paths. As used herein, "durable" implies that the fluid paths are permanently installed. A durable fluid path needs to be intermittently disinfected to counteract microbial growth, for example by heat disinfection. During heat disinfection, fluid is heated by the heater 27, which is located downstream of the dosing point DP, and the heated fluid is distributed in the FPS 20. The Applicant has found that at some operating conditions of the FPS 20, boiling may occur in the heater 27, in particular for the combination of low pressure in the heater and high target temperature at the heater outlet. Boiling will result in uncontrolled release of gas from the fluid, for example air. The released gas, as it is conveyed within the FPS 20 together with the heated fluid, may interfere with the temperature control of the heater 27. If gas is present together with liquid in a temperature sensor, the measured temperature of the liquid may be significantly offset from the ground truth. Irrespective of origin, the temperature of the heated fluid is seen to fluctuate if boiling occurs in the heater 27. The temperature fluctuations may cause a safety system to shut down the FPS 20. It is also possible that the boiling results in an uncontrolled pressure increase within the fluid circuit if the fluid circuit is not open to atmospheric pressure. The increased pressure may damage components in the FPS 20, such as filters or sensors, resulting in reduced and / or unpredictable performance of the FPS 20, or even complete malfunction. The increased pressure may also cause fluid lines to burst and / or connectors to be detached. The problem of gas release during heat disinfection is addressed by the present disclosure.

[0060] Generally, the solution to either or both of these problems involves arranging a variable restrictor in the circulation path 13 of the WPS 10 or in the main path 21 of the FPS 20 upstream of the dosing point DP, and adjusting the variable restrictor so as to maintain a target fluid pressure at a predefined location in the FPS 20. To address the problem of composition error, the predefined location is at the dosing point DP. To address the problem of gas release during heat disinfection, the predefined location is in the heater 27.

[0061] FIG. 3 is a flow chart of an example method M2 of operating a combination of a WPS and an FPS to address the above-identified problems. In step S20, a pressureindicating signal that is indicative of fluid pressure at a predefined location in the FPS 20 is obtained. As described further below, the pressure-indicating signal may be hydraulic or electric, depending on implementation. Step S21 is provided to address the problem of composition error and involves adjusting the above-mentioned variable restrictor to maintain a target pressure at the dosing point DP while the FPS 20 is operated to generate treatment fluid, for example according to the method Ml in FIG. 2B. Step S22 is provided to address the problem of gas release during heat disinfection and involves adjusting the above-mentioned variable restrictor to maintain a target pressure in the heater 27 so as to counteract or prevent boiling in the heater 27 while the FPS 20 is being heat disinfected.

[0062] In some embodiments, the method M2 only involves steps S20 and S21 to address the composition error, whereas step S22 is omitted and the problem of gas release is ignored or solved by other means.

[0063] In some embodiments, the method M2 only involves steps S20 and S22 to address the gas release during heat disinfection, whereas step S22 is omitted and the problem of composition error is ignored or solved by other means.

[0064] The FPS 20 may be seen to be operable in a production mode and a heat disinfection mode. In some embodiments, the method M2 is performed in both the production mode and the heat disinfection mode, with the method M2 involving steps S20 and S21 in the production mode, and steps S20 and S22 in the heat disinfection mode.

[0065] In some embodiments, the target pressure is defined as an absolute pressure, which is the total pressure relative to a perfect vacuum (absolute zero pressure). The term "ambient total pressure" is used herein to indicate the atmospheric pressure given as absolute pressure at a relevant location. In other embodiments, the target pressure is given as gauge pressure, which is a pressure differential relative to the prevailing atmospheric pressure. Gauge pressure is also known as overpressure in the art.

[0066] It is realized that the target pressure differs between steps S21 and S22. The target pressure in step S21 ("first target pressure") corresponds to the counterpressure for the supply pump 24 when supplying concentrate into the main path 21. In some embodiments, the first target pressure is set at or slightly above atmospheric pressure. For example, given as gauge pressure (pressure above atmospheric pressure), the first target pressure may be set in the range of 0-20 mmHg. As explained above, it is desirable to minimize variations in the counterpressure. In practice, some pressure variations may remain when step S21 is performed. However, step S21 will reduce the variations in counterpressure compared to when step S21 is not performed. In some embodiments, the variations in counterpressure are reduced by at least 50%. For example, tests show that the above-mentioned pressure change at the dosing point DP of 130 mmHg when changing the TF production rate from 100 ml / min to 300 ml / min may be suppressed to 12 mmHg with a mechanical pressure regulator (below), and to effectively zero with an electrical pressure controller (below) . The first target pressure may be fixed or variable. For example, the first target pressure may be set to a predefined or measured value each time the WPS 10 and the FPS 20 are started.

[0067] The target pressure in step S22 ("second target pressure") corresponds to the fluid pressure in the heater 27. To counteract boiling, the second target pressure may be set as high as possible. The upper limit of the second target pressure may be given by the ability of components in the FPS 20, and optionally the WPS 10, to withstand pressure. In any event, the second target pressure is higher than the first target pressure of step S21. In some embodiments, the second target pressure is at least 50 mmHg or 100 mmHg in gauge pressure. In some embodiments, the upper limit of the second target pressure is in the range of 200-500 mmHg. The second target pressure may be fixed or variable. For example, the second target pressure may be set to a predefined value at start of the heat disinfection and may be increased if there are signs of boiling in the heater 27, for example if the pressure in the processing sub-system 22 exceeds a limit or if gases are accumulated at an increased rate in a mixing chamber, a bubble trap or a filter within the processing sub-system 22. Here, it is assumed that the FPS 20 implements a mechanism for expelling the accumulated gases as needed. The increased rate of gas accumulation may be detected based on how often this mechanism is activated.

[0068] The elevated pressure in the heater 27 of the FPS 20 may have the additional benefit of compressing the gases that are accumulated within the FPS 20, to thereby enable less frequent activation of the mechanism for expelling accumulated gases.

[0069] If the second target pressure is given in terms of gauge pressure, it may be beneficial to determine the second target pressure in view of the atmospheric pressure at the location of the WPS-FPS arrangement (FIG. 2A). The atmospheric pressure changes with altitude. For example, while water boils at 100°C at sea level (nominal atmospheric pressure 760 mmHg), boiling occurs already at 92°C at 2640 meters above sea level (nominal atmospheric pressure 561 mmHg). Thus, while a gauge pressure of 50-100 mmHg may be sufficient to prevent boiling in the heater at sea level, it may not be sufficient when the WPS-FPS arrangement is installed at higher altitude. Thus, in some embodiments, the atmospheric pressure is measured by an auxiliary pressure sensor, and the second target pressure is set based on the measured atmospheric pressure to correspond to a total pressure that prevents or at least mitigates the risk of boiling in the heater. The second target pressure may be set by use of a predefined calculation function or a predefined look-up table. The second target pressure may be determined at any time before heat disinfection. For example, the second target pressure may be determined at first installation of the WPS-FPS arrangement, or whenever the WPS-FPS arrangement is started. The dynamic adjustment of the second target pressure based on the atmospheric pressure has the further advantage of reducing the power consumption as well as mitigating the stress on components of the WPS-FPS arrangement, compared to when the WPS-FPS arrangement is operated with a fixed second target pressure (gauge pressure) that is set to prevent boiling at all possible altitudes.

[0070] FIG. 4A is a block diagram of a WPS-FPS arrangement that is operable to perform the method M2 in accordance with a first example. The WPS-FPS arrangement in FIG. 4A is similar to the WPS-FPS arrangement in FIG. 2A and will not be described in detail. The method M2 is enabled by a pressure controller 40 in the form of a mechanical pressure regulator 40, which is arranged in the main path 21 upstream of the dosing point DP. The pressure regulator 40 is a unitary component with an internal mechanism that is arranged to be actuated by a hydraulic signal representing the outlet or downstream pressure of the component, to stabilize the outlet pressure to a preset value.

[0071] An example of a mechanical pressure regulator 40 is schematically shown in cross-section in FIG. 5. The regulator 40 comprises a main body 140 that defines an inlet channel 141, an outlet channel 142 and a connecting chamber 143 between the inlet and outlet channels 141, 142. The channels 141, 142 and the chamber 143 define a passageway through the main body 140. The main body 140 further defines a guide channel 144 and a top chamber 145. A unitary valve member is arranged for movement inside the main body 140. In the illustrated example, the valve member defines a piston with a crown 150, an actuator plate 151, and a stem 152 that connects the crown 150 to the actuator plate 151. In a variant, not shown, the valve member is a diaphragm. In FIG. 5, the valve member is arranged with the actuator plate 152 in the top chamber 145, the stem 151 in the guide channel 144 and the crown 150 in the connecting chamber 143. As shown by a double-ended arrow, the valve member is movable along the guide channel 144. Thereby, the crown 150 is moveable relative to a seat 143a that is defined at the interface between the inlet channel 141 and the connecting chamber 143. A spring 153 is arranged in the top chamber 145 between the actuator plate 152 and a pressure definition element 154. The axial distance between pressure definition element 154 and the bottom of the top chamber 145 sets the outlet pressure of the regulator 40. In some embodiments, the axial distance is adjustable. For example, the element 154 may be in threaded engagement with the main body 140, so that a rotation of the element 154 changes the distance. The main body 140 further defines a pressure transfer channel 147 which is fluidly connected to the outlet channel 142 and extends to an actuator space 146 in the top chamber 145 beneath the actuator plate 152. As the inlet pressure changes, the position of the crown 150 is automatically adjusted based on the outlet pressure given by the hydraulic pressure that is transferred via the channel 147 to the actuator space 146, so as to maintain a predefined outlet pressure. The regulator 40 may thus be seen to be operated based on a hydraulic signal and includes a control system 41 and a variable restrictor 43. The control system 41 comprises the top chamber 145, the actuator plate 153, the spring 153 and the pressure definition element 154. The variable restrictor 43 comprises the crown 50 and the seat 143a.

[0072] Reverting to FIG. 4 A, the regulator 40 may be configured to generate the first target pressure at the dosing point DP in accordance with step S21. Assuming that the regulator 40 is switchable between different outlet pressures, for example by adjustment of the above-mentioned axial distance, the regulator 40 may also be used for generating the second target pressure at the heater 27 in accordance with step S22. Here, the regulator 40 may be configured to generate an outlet pressure that is known to result in the second target pressure in the heater 27. Since the regulator 40 is only capable of generating an outlet pressure that is lower than the inlet pressure, the WPS 10 is likely to be operated with an elevated and fixed fluid pressure in the circulation path 13 during both fluid production and heat disinfection. The elevated and fixed fluid pressure in the circulation path 13 may be achieved by installing a fixed restrictor (not shown) downstream of the tapping point CP in the WPS. The example in FIG. 4A may lead to waste of energy, if the elevated fluid pressure is present in the circulation path 13 at all times even if it is not needed during fluid production.

[0073] FIG. 4B is a block diagram of a WPS-FPS arrangement that is operable to perform the method M2 in accordance with a second example. The WPS-FPS arrangement in FIG. 4B is similar to the WPS-FPS arrangement in FIG. 2A and will not be described in detail. The method M2 is enabled by an electrical pressure controller 40, which comprises a control system 41, a pressure sensor 42, and a variable restrictor 43. The variable restrictor 43 is arranged in the circulation path 13 of the WPS 10. In the illustrated example, the pressure sensor 42 is arranged in the main path 21 at the dosing point DP. The control system 41 is arranged to receive a sensor signal SSI from the pressure sensor 21 and generate a control signal CS1 for electrical adjustment of the flow resistance of the variable restrictor 43. The flow resistance corresponds to a pressure drop over the restrictor 43. The variable restrictor 43 may be any type of motorized restrictor, such as a needle valve, diaphragm valve, multi-stage orifice plate valve, globe valve, ball valve, etc. The control system 41 is configured to adjust the variable restrictor 43 by feedback control based on SSI achieve a predefined pressure at the pressure sensor 42. Any type of feedback control algorithm may be used in the control system 41, including but not limited to a P, PI or PID algorithm. The control system 41 may be configured to perform the method M2 of FIG. 3. For example, the control system 41 may perform steps S20 and S21 to maintain the first target pressure at the dosing point DP. In the illustrated example, the pressure at the pressure sensor 42 is effectively identical to the pressure at the dosing point DP. Alternatively or additionally, the control system 41 may perform steps S20 and S22 to maintain the second target pressure in the heater 27. In the illustrated example, the variable restrictor 43 is adjusted to generate a pressure at the pressure sensor 42 that is known to result in the second target pressure in the heater 27. In an alternative, the second target pressure may be generated based on SSI from a pressure sensor located closer to or on the heater 27. Generally, the pressure sensor 42 may be at any location along the main path 21 or even in the circulation path 13 as long as the measured pressure can be related to the pressure at the predefined location. Any such pressure sensor 42 will provide a signal SSI that is indicative of the pressure at the predefined location. The pressure sensor 42 may be configured to measure either gauge pressure or absolute pressure. A pressure sensor for gauge pressure is configured to measure pressure as a differential to the prevailing atmospheric pressure at the location of the pressure sensor. Such a pressure sensor is typically less costly than a pressure sensor for absolute pressure. In some embodiments, the control system 41 operates on SSI from different pressure sensors when performing step S21 and step S22, respectively. If only one pressure sensor 42 is used, it may be preferable for the pressure sensor 42 to be located close to the dosing point DP to achieve high accuracy and stability of the first target pressure.

[0074] As shown in FIG. 4B, the control system 41 may be arranged to receive a further sensor signal SS2 that includes a value indicative of the prevailing ("local") atmospheric pressure. If the signal SSI represents gauge pressure, the control system 41 may be configured to determine the second target pressure based on SS2, as described hereinabove. In the illustrated example, SS2 is obtained from a sensor 44. In some embodiments, the sensor 44 is a pressure sensor that provides the ambient total pressure at the location of the WPS-FPS arrangement. Alternatively, the sensor 44 may be an altitude sensor that provides the altitude at the location of the WPS-FPS arrangement, or a position sensor (for example a GPS sensor) that provides geographic coordinates of the WPS-FPS arrangement. The skilled person understands that a geographic location may be used for determining an altitude, which may be converted into a nominal atmospheric pressure. In other alternatives, SS2 is given by input data entered by a technician or other user, for example via a keyboard, touch screen, etc. (cf. feedback device 84 in FIG. 14). The input data may be given as ambient total pressure, altitude, geographic location, etc. The location of the variable resistor 43 in the circulation path 13 provides a number of advantages. If the control system 41 is configured to perform step S21 during fluid production and step S22 during heat disinfection, the fluid pressure in the circulation path 13 will only be elevated when needed during heat disinfection. During fluid production, a lower pressure is established in the circulation path 13. This will reduce the power consumption compared to the first example in FIG. 4A. Further, additional functionality is enabled by arranging the variable restrictor in the circulation path 13. One additional function is a safety function that will be described below with reference to FIG. 9C. Another additional function is an ability to selectively adjust the flow resistance in the circulation path 13 during heat disinfection of the WPS 10, as will be described below with reference to FIG. 10A.

[0075] In some embodiments, as shown in FIG. 4B, the variable restrictor 43 is located downstream of the tapping point CP in the circulation path 13. This may facilitate attainment of a stable fluid pressure at the tapping point CP and thus at the pressure sensor 42.

[0076] In a variant, not shown, the mechanical pressure regulator 40 of FIG. 4A is installed in the circulation path 13, for example upstream of the tapping point CP. In this variant, the regulator 40 is operable to generate a first or a second outlet pressure at the tapping point CP, with the first outlet pressure being known to result in the first target pressure at the dosing point DP, and the second outlet pressure being known to result in the second target pressure in the heater 27. However, such a variant is likely to be less robust and less accurate.

[0077] In another variant, not shown, the variable restrictor 43 is arranged in the main path 21 upstream of the dosing point DP. However, like the example in FIG. 4A, the WPS 10 is likely to be operated with an elevated and fixed fluid pressure in the circulation path 13 at all times, which results in waste of energy.

[0078] The control system 41 may perform other functions in addition to operating the variable restrictor 43. As shown in FIG. 4B, the control system 41 may receive one or more additional input signals [SSx] and generate one of more additional control signals [CSx], for example for operating the WPS 10 and / or the FPS 20.

[0079] As noted above, the FPS may include more than one dosing point, for example if the product water is mixed with two or more concentrates to produce the treatment fluid. FIG. 6A shows part of an FPS 20 with two dosing points DP, DP'. A first supply line 23 extends to a first dosing point DP on the main fluid line 21, and a second supply line 23' extends to a second dosing point DP' on the main fluid line 21. A first supply pump 24 in the first supply line 23 is operable to generate a flow rate Qc| of a first concentrate into the main path 21. A second supply pump 24' in the second supply line 23' is operable to generate a flow rate Qc2 of a second concentrate into the main path 21. A main pump 25 is arranged in the main path 21, downstream of the dosing points DP, DP', to generate a flow rate QTP of treatment fluid. When the pumps 24, 24', 25 are operating, product water is diverted from the WPS 10 (not shown) at a flow rate QpW=QTF ‘ Qcl ‘ QC2- By relatively adjusting the speeds of the supply pumps 24, 24' to the speed of the main pump 25, treatment fluid of a target composition is generated at flow rate QTP. AS shown, the pressure sensor 42 may be arranged between the dosing points DP, DP' in the main path 21. This may improve the accuracy of the fluid pressure at the respective dosing point DP, DP'.

[0080] FIG. 6B shows a variant in which the supply lines 23, 23' are merged into a common supply line 23" downstream of the supply pumps 24, 24'. The common supply line 23" extends to a dosing point DP in the main path 21. FIG. 6B shows that a single dosing point may be used even if the treatment fluid is formed by mixing product water with plural concentrates. The pressure sensor 42 may be arranged upstream of the dosing point DP, as shown, or downstream thereof.

[0081] The proposed technique will now be further described with reference to a detailed example of an FPS 20 in FIG. 7 and a WPS 10 in FIGS 8A-8B.

[0082] Turning first to the FPS 20 in FIG. 7, the main path 21 of the FPS 20 is fluidly connected to the circulation path 13 of the WPS 10 at the tapping point CP. The main path 21 extends through the FPS 20. An on / off valve VI is arranged in the main path 21 to control the admission of product water. The main path 21 extends through two dosing points DP, DP'. A pressure sensor 42 is arranged in the main path 21 between the dosing points DP, DP'. A first mixing chamber 28a is arranged in the main path 21 downstream of the dosing points DP, DP'. The first mixing chamber 28a may be a high-swirl chamber configured to even out any large concentration / density differences that may be caused by the entry of concentrates. Downstream of the mixing chamber 28a, a heater 27 and a second mixing chamber 28b are arranged in sequence. Thus, in the illustrated example, the FPS 20 includes two mixing chambers in sequence, which has been found to promote efficient mixing of product water and concentrates. In an alternative, a single mixing chamber is used. Temperature sensors SI, S2 are arranged in the main path 21 to sense the fluid temperature upstream and downstream of the heater 9. During TF production, the heater 9 may be operated by feedback control, based on a signal from the sensor S2, to control the downstream fluid temperature to a predefined temperature, for example 37°C. A 3-way valve V2 is arranged in the main path 21 downstream of the mixing chamber 28b. The valve V2 is connected to a gas removal line 29, which is connected to a top portion of the mixing chamber 28b. The valve V2 is operable to selectively connect the gas removal line 29 to the main path 21, for example to release gas accumulated in the mixing chamber 28b during production of treatment fluid, via a drain line (not shown, cf. 26' in FIG. 2) that extends from the main path 21 to drain. The mixing chamber 28b may be seen to implement a bubble trap. A main pump 25 is arranged in the main path 21 downstream of the valve V2. The main pump 25 sets the flow rate of TF along the main path 21 during TF production, as described with reference to FIGS 6A-6B. Downstream of the main pump 25, a pressure sensor S3, a conductivity sensor S4, and a temperature sensor S5 are arranged in the main path 21. The conductivity sensor S4 may be used to provide conductivity feedback when treatment fluid is generated, as well as during phases when the mixture of product water and concentrates is not delivered through the outlet port Pl (cf. FIG. 2A), for example during composition stabilization before start of TF production. The signal from temperature sensor S5 may be used for temperature compensation of the signal from the conductivity sensor S4, as is well-known in the art. Although not shown in FIG. 7, the FPS 20 may include additional components downstream of the sensors S3-S5, for example one or more filtration units.

[0083] The FPS is arranged within a casing 20a, which is configured to expose two ports P2, P2' for connection to the concentrate containers 7, 7'. The containers 7, 7' contain a respective concentrate that forms part of the treatment fluid. In the example of PD fluid, one of the concentrates may contain an osmotic agent, such as glucose, and the other concentrate may contain a plurality of different electrolytes. In the example of treatment fluid for use in EC blood therapy, one of the concentrates may be a B concentrate and the other concentrate may be an A concentrate, as is well known in the art. In the illustrated example, the ports P2, P2' are releasably connected to terminal connectors 8a, 8a' on tubing 8, 8' in fluid communication with the containers 7, 7'. Supply lines 23, 23' extend from the ports P2, P2' to the main path 21. Supply pumps 24, 24' in the input lines 23, 23' are operable to pump the respective concentrate into the main path 21 at dosing points DP, DP'.

[0084] Turning now to FIGS 8A-8B, a main fluid path ("main path") 1 extends through the WPS 10. In the illustrated example, a tank or reservoir 200 is arranged in the main path 1. The tank 200 is arranged to receive source water, which may have passed a prefiltration sub-system (not shown) that may be configured to remove chemical compounds of chlorine, absorb organic compounds, toxic substances and pesticides, and filter out particles. The tank 200 comprises a level sensor 201, which is configured to indicate at least one fluid level in the tank 200, via a level signal LI. The level sensor 201 may thus signal when the water reaches one or more discrete levels, or indicate the fluid level along a continuous scale. The level signal LI allows a control system to control the level of water in the tank 200. The tank 200 comprises a plurality of ports 202-206. A first inlet port 202 for source water is defined in the top portion of the tank 200. An outlet port 203 is defined in the bottom portion of the tank 200. By ports 202, 203, the tank 200 is included in the main path 1. A second inlet port 204 is defined in the top portion and connected to a first return line 415, which is fluidly connected to receive product water that is recirculated in the WPS 10. A third inlet port 205 is defined in the top portion of the tank 200 and connected to a second return line 405, which is fluidly connected to receive retentate ("reject water") from a second subsystem 400 (below). In some embodiments, at least one of the inlet ports 202, 204, 205 is connected to a spray nozzle (not shown) inside the tank 200 to disperse the incoming water. The inlet ports 204, 205 may be merged into a common port. A gas outlet or vent 206 is defined in the top portion of the tank 200. The vent 206 allows gases to escape from the tank 200 and also allows air to enter the tank as needed. The water is thus held in the tank 200 at atmospheric pressure. The provision of the vent 206, and thus atmospheric pressure in the tank 200, is advantageous for several reasons. It will allow for removal of air and other gases that may be released from the water in the tank 200. Further, since water is recirculated back to the tank 200, it allows for continuous removal of gases in the fluid circuit of the WPS 10. Further, during start-up of the WPS 10, gases may be present in the fluid circuit and need to be vented. Further, removal of gases from the fluid circuit is relevant whenever the fluid circuit has been opened during service and maintenance.

[0085] FIG. 8A also shows a first sub-system 300 in the WPS 10 in accordance with an example. In the flow direction along the main path 1, the first sub-system 300 comprises a UV irradiation device 301, a feed pump 302, a pressure sensor 303, a first reverse osmosis (RO) unit 304, a temperature sensor 309, a conductivity sensor 310, a heater 311, a flow switch 312, and a temperature sensor 313. It is to be understood that while each of these components serve a specific function in the context of the illustrated example, all components need not be included as shown.

[0086] The pressure sensor 303 is configured to provide a measurement signal PPI representing hydraulic pressure (water pressure). The sensors 309, 310 provide a respective measurement signal T2, C2 representing water temperature and water conductivity, respectively. The signals PPI, T2, C2 may be used by a control system for controlling the operation of the WPS 10.

[0087] The heater 311 is operable to heat the water. In some embodiments, the heater 311 is a flow-through electrical heater. In some embodiments, a control system operates the heater 311 by feedforward control based on the signal T2 and / or the signal T3 to achieve a target temperature of the water entering a second sub- system 400 (below). In other embodiments, the control system operates the heater 311 by feedback control based on a measurement signal T4 from a temperature sensor 414 in the second subsystem 400 (FIG. 8B).

[0088] The flow switch 312 is included as a safety measure to prevent that the heater 311 is activated when the flow rate of water through the heater 311 is too low, since this may cause irreparable damage to the heater 311. Thus, the flow switch 312 is configured to autonomously disable the heater 311 when the flow rate of water through the flow switch 312 is below a preset threshold value.

[0089] The UV irradiation device 301 is included to reduce microbial activity in the passing water. By installing the device 301 upstream of the RO unit 304, the microbial load entering the RO unit 304 and other downstream components will be reduced. This will extend the life of the RO unit 304. The device 301 may comprise a processing chamber for receiving incoming water, and at least one UV source in the processing chamber. The UV source is operable to generate UV radiation so as to irradiate at least part of the processing chamber. The UV radiation thereby interacts with the fluid within the processing chamber. In some embodiments, the UV irradiation device 301 is configured to additionally remove chlorine from the passing water. This may be achieved by increasing the irradiating power of the UV source and / or by confining the emitted UV radiation to wavelengths of high absorptivity for chlorine in the water, such as dichloramine and monochloramine. Generally, a UV irradiation device 301 configured to perform dechlorination may be installed anywhere in the main path 1 upstream of the first RO unit 304.

[0090] The RO unit 304 is of conventional structure and comprises a semi-permeable filter or membrane 304'. The RO membrane 304' is commonly comprised of a thin-film, cross-linked composite polymer and is able to withstand relatively high fluid pressure. For example, the RO membrane 304' may be a spirally wound membrane or flat sheet membrane. The membrane 304' separates the body of the RO unit 304 into a feed side or chamber 304a and a permeate side or chamber 304b. The RO unit 304 comprises one or more inlet ports and one or more outlet ports on the feed side 304a, and one or more outlet ports on the permeate side 304b. The RO unit 304 operates by cross-flow filtration, which is achieved by causing the water to flow along the membrane 304'. Permeate passes through the membrane 304', while reject water exits the RO unit 304 through the outlet port(s) on the feed side 304a. The fluid pressure on the feed side 304a needs to be sufficient to overcome the osmotic pressure created by solutes dissolved in the water. Thereby, filtered water is forced across the membrane 304' to form a permeate stream through the outlet port(s) on the permeate side 304b, while dissolved solutes are excluded and discharged with the reject water in a more highly concentrated state. The feed-side fluid pressure may be in the range of 5-50 bar, and is typically 5-15 bar.

[0091] The fluid pressure on the feed side 304a of the RO unit 304 is defined by the feed pump 302, also known as booster pump. The fluid pressure on the feed side 304a may be monitored via the measurement signal PPI. A drain line 305 is connected to receive the reject water from the RO unit 304. The drain line 305 extends from the outlet port(s) on the feed side 304a to a drain 4. With reference to FIG. 2A, the drain line 305 corresponds to lines 14, 15. An adjustable flow restriction device ("flow restrictor") 306 is arranged in the drain line 2A and operated to maintain a desired fluid pressure on the feed side 304a.

[0092] In the example of FIG. 8A, a connecting line 307 is arranged to fluidly connect the drain line 305, at a location upstream of the flow restrictor 306, to the main path 1, at a location intermediate the feed pump 302 and the RO unit 304. Thereby, a water recirculation path or loop is defined between the outlet and inlet ports on the feed side 304a of the RO unit 304. The recirculation path may be used to maintain a high rate of water flow on the feed side 304a, thereby reducing the amount of water that otherwise would be discarded to drain. An auxiliary pump ("recirculation pump") 308 is arranged within the recirculation path to increase the fluid flow velocity or flow rate along the RO membrane 304' sufficiently to inhibit a locally increased concentration close to the membrane surface. Such locally increased concentration may result in fouling of the RO membrane 304', depending on the hardness of the incoming water to the RO unit 304. The term "fouling" includes the build-up of all kinds of layers on the surface of the RO membrane 304', including biofouling and scaling.

[0093] In a variant, the recirculation pump 308 and the connecting line 307 are omitted. In another variant, the recirculation pump 308 is omitted, and the connecting line 307 is arranged to fluidly connect the drain line 305 to the main path 1, at a location upstream of the feed pump 302, to define a recirculation path. Thereby, the suction created by the operating feed pump 302 will cause recirculation of water through the connecting line 307. A flow restrictor may be arranged in the connecting line 307 for adjustment of the recirculated flow.

[0094] The RO unit 304 may be a disposable ("sacrificial") component, which is removably installed in the WPS 10. To this end, the main path 1 and the drain line 305 may be provided with terminal connectors for releasable attachment to the inlet and outlet ports of the RO unit 304.

[0095] A return line 314 is fluidly connected to the main path 1 downstream of the heater 311, at junction JI. The return line 314 is connected, at junction J2, to the first return line 415. An on / off valve 315 is arranged in the return line 314. Further, the variable restrictor 43 used by the method M2 is arranged in the first return line 415. The variable restrictor 43 is responsive to the control signal CS1 from the control system 41 (FIG. 4B).

[0096] In the example of FIG. 8 A, a bypass line 316 is connected to the main path 1 upstream and downstream of the RO unit 304. A first on / off valve 317 is arranged in the main path 1 upstream of the RO unit 304, intermediate the RO unit 304 and the junction of the bypass line 316 to the main path 1. A second on / off valve 318 is arranged in the main path 1 downstream of the RO unit 304, intermediate the RO unit 304 and the junction of the bypass line 316 to the main path 1. A third on / off valve 319 is arranged in the bypass line 316. The bypass line 316 and the valves 317-319 define a bypass arrangement. When the WPS 10 is operated to produce product water, valve 319 is closed and valves 317, 318 are open. When the WPS 10 is heat disinfected, as described further below, valves 317, 318 are closed and valve 319 is open to direct heated fluid through the bypass line 316 instead of through the RO unit 304. Both valves 317, 318 are closed to seal off the RO unit 304 from the heated fluid. One reason for the bypass arrangement is that when using a disposable RO unit, which is replaced when consumed, it is possible to refrain from heat disinfecting the RO unit 304. Thereby, the RO unit 304 need not be configured to withstand the high temperatures used in heat disinfection, which is likely to lower the cost of the RO unit 304.

[0097] FIG. 8B depicts a second sub-system 400 in the WPS 10 in accordance with an example. In FIG. 8B, the main path 1 continues from encircled A in FIG. 8A and extends to junction J3. In the flow direction along the main path 1, the second subsystem 400 comprises an on / off valve 401, a pressure sensor 402, a pump 403, a pressure sensor 409, a second RO unit 404, a flow meter 410, an on / off valve 411, a UV irradiation device 412, a conductivity sensor 413, and a temperature sensor 414. It is to be understood that while each of these components serve a specific function in the context of the illustrated example, all components need not be included as shown.

[0098] The valve 401 is operable to selectively open and close the main path 1 to control admission of water into the second sub-system 400. The sensors 402, 409, 410, 413 and 414 provide measurement signals PP2, PP2', Fl, C3, T4 representing water pressure, water pressure, water flow rate, water conductivity and water temperature, respectively. The signals PP2, PP2', Fl, C3, T4 may be used by a control system for controlling the operation of the WPS 10.

[0099] The RO unit 404 is configured to perform water filtration by reverse osmosis, similar to the RO unit 304. In the illustrated example, the RO unit 404 is permanently installed in the second sub-system 400. In other words, it is not installed to facilitate replacement by a user of the WPS 10. The RO unit 404 may differ from the RO unit 304 in terms of performance, cost, etc. However, principally, the RO unit 404 comprises an RO membrane 404', a feed side 404a, a permeate side 404b, inlet port(s) and outlet port(s) on the feed side 404a, and outlet port(s) on the permeate side 404b. Similar to the first sub-system 300, a feed pump 403 is arranged in the main path 1 to define the fluid pressure on the feed side 404a of the RO unit 404. A drain line 405 is connected to receive the reject water from the RO unit 404. In contrast to the first sub-system 300, the drain line 405 does not extend to drain, but to the inlet port 205 on the tank 200, as shown by encircled C in FIGS 8A-8B. Thus, reject water from the RO unit 404 is recirculated back to the tank 200. An adjustable flow restriction device ("flow restrictor") 406 is arranged in the drain line 405 to maintain a desired fluid pressure on the feed side 404a of the RO unit 404. A connecting line 407 is arranged to fluidly connect the drain line 405, at a location upstream of the flow restrictor 406, to the main line 1, at a location intermediate the feed pump 403 and the RO unit 404. Thereby, like in the first sub-system 300, a water recirculation path or loop is defined between the outlet and inlet ports on the feed side 404a of the RO unit 404. An auxiliary pump ("recirculation pump") 408 is arranged within the recirculation path.

[0100] The UV irradiation device 412 may be similar to the UV irradiation device 301 in the first sub-system 300. The UV irradiation device 412 is installed to further mitigate microbial activity. It is realized that the device 412 need not be configured to remove chlorine in the incoming water, which should be effectively free of chlorine at this location in the WPS 10. By placing the UV irradiation device 412 in the main path 1 downstream of the RO unit 404, the device 412 is arranged to operate on water with the lowest content of suspended solids within the WPS 10. This will improve the efficiency of the device 412, since suspended solids are known to be a limitation parameter for water treatment by UV irradiation due to the absorption of the light by the solids and potential shielding of pathogens from the light.

[0101] The return line 415 is fluidly connected to the main path 1 downstream of the RO unit 404, at junction J3. In FIG. 8B, the return line 415 extends to encircled B and is continued from encircled B in FIG. 8 A. The return line 415 is arranged to enable continuous production of product water during operation of the WPS 10, by allowing excess product water to be circulated back to the tank 200. As shown, a one-way valve 416 may be arranged in the return line 415.

[0102] It may be noted that the purification sub-system 11 in FIG. 2A corresponds to the first and second sub-systems 300, 400 in FIGS 8A-8B, and that the circulation path 13 corresponds to the return line 415 and the tank 200.

[0103] The WPS 10 in FIGS 8A-8B is merely given as an example. In some embodiments, the purification sub-system 11 includes only one of the RO units 304, 404. In other embodiments, the purification sub-system 11 is based on another purification technique than reverse osmosis.

[0104] FIG. 9A is a block diagram of an example combination of a WPS and an FPS. Compared to FIGS 7 and 8A-8B, some components are omitted, mainly to simplify the presentation. For example, the drain and connecting lines for the respective RO unit 304, 404 in the WPS, mixing chambers in the FPS, as well as several sensors are omitted. Further, the supply arrangement is configured for dosing a single concentrate at a single dosing point DP. Some components have been added, including a pressure sensor 413' in the main path 1 downstream of the second RO unit 404 of the WPS, as well as fluid lines 29a, 29b, valves V3, V4, V5 and a functional block 22' in the FPS. Specifically, a drain line 29a extends from the main path 21 in the FPS 20 to drain 4, and a connecting line 29b extends between the drain line 29a and the main path 21 upstream of the dosing point DP. A first on / off valve V3 is arranged in the connecting line 29b, a second on / off valve V4 is arranged in the drain line 29a downstream of its junction to the connecting line 29b, and a third on / off valve ("outlet valve") V5 is arranged in the main path 21 downstream of its junction to the drain line 29a. The pressure sensor 413' is arranged to provide a measurement signal PP3. The functional block 22' represents any components located downstream of the main pump 25, for example including one or more filtration units.

[0105] From the foregoing, it is understood that FIG. 9A is an example of a WPS-FPS arrangement, in which the WPS 10 comprises a purification sub-system 11 that is configured to generate product water from source water. The WPS 10 is operable to define a circulation path, which in this example corresponds to the return line 415 and the tank 200. The circulation path comprises an inlet 202 for the source water, and the purification sub-system 11 is connected to the circulation path intermediate the inlet 202 and the tapping junction CP. This allows the WPS 10 to be operated to continuously circulate product water in the circulation path, while being replenished with source water whenever required.

[0106] In the example of FIG. 9A, the purification sub-system comprises RO units 304, 404 that are arranged in series on a flow path through the purification sub-system 11 during generation of product water so that the flow path extends through the feed chamber 304a, 404a, the semi-permeable membrane 304', 404' and the permeate chamber 304b, 404b of the respective RO unit 304, 40.

[0107] In the illustrated example, the tank 200 is included in the circulation path and includes the inlet 202 for source water. The provision of the tank 200 serves to decouple the operation of the purification sub-system 11 from the supply of source water and from the operation of a pre-filtration sub-system, if present. This decoupling facilitates the design and / or operation of the purification sub-system 11. Further, in some embodiments, the amount of water in the tank 200 is controlled to define an air gap at the top of the tank 200. This is achieved by controlling the fluid level in the tank 200, based on the level sensor 201, to not rise above a predefined maximum level in the tank 200. By providing an air gap and arranging the first inlet port 202 above the predefined maximum level, water is prevented from flowing back from the tank 200 towards the water supply (5 in FIG. 1). Likewise, the air gap prevents backflow into other inlet ports if these are installed above the predefined maximum level. The air gap also serves as a barrier to microorganisms in relation to the inlet ports. Another technical advantage of the tank 200 is an ability to allow for thermal expansion of the water in the WPS 10. This may be particularly relevant when the WPS 10 is configured to be intermittently cleaned (sanitized) by heat disinfection.

[0108] In the illustrated example, the pressure sensor 42 is arranged intermediate the dosing point DP and the heater 27 in the FPS 20, and the variable restrictor 43 is arranged in the circulation path of the WPS 10.

[0109] Operations of the WPS-FPS arrangement of FIG. 9A are illustrated in FIGS 9B, 10B, 1 IB and 12B. In these drawings, open valves and operating fluid pumps are indicated by filled symbols, fluid lines through which fluid is flowing are indicated by thicker lines, and flow directions are indicated by thick solid arrows.

[0110] FIG. 9B shows the WPS-FPS arrangement of FIG. 9A during production of treatment fluid in accordance with the method Ml in FIG. 2B. Thus, the valves in the WPS 10 are set to define the circulation path to extend from the purification sub-system 11 via the return line 415 and the tank 200 back to the purification sub-system 11. The pumps 302, 403 are operated to circulate water on the circulation path. During the circulation, product water is output from the purification sub-system 11 and passes the tapping point CP. Dashed arrows in FIG. 9B indicate that reject water from the first RO unit 304 is directed to drain (cf. drain line 305 in FIG. 8A) and that reject water from the second RO unit 404 is directed back to the tank 200 (cf. drain line 405 in FIG. 8B). The FPS 20 is in the production mode. The main pump 25 is operated to divert product water from the tapping point CP into the main path 21, and the supply pump 24 is operated to supply concentrate along the supply line 23 to the dosing point DP, resulting in treatment fluid being pumped out of the FPS 20 via the outlet valve V5. While the FPS 20 is in the production mode, the variable restrictor 43 may be adjusted by the control system 41 (FIG. 4B), via the control signal CS1, to maintain a predefined target pressure ("first target pressure") at the dosing point DP, in accordance with steps S20, S21 of the method M2 (FIG. 3). The control system 41 may generate the control signal CS1 based on the signal SSI from the pressure sensor 42. Reverting to the FPS 20 in FIG. 7, the main path 1 extends through flush ports on the pumps 24, 24', 25. The flush port may be provided to enable circulation at seal rings helping to maintain proper temperature, eliminate debris buildup at seal faces, cool the seal faces for more efficient performance and for longer life expectancy of the pump. It is realized the first target pressure at the dosing point DP also affects the pressure at the flush ports. For some fluid pumps, the pressure at the flush ports should preferably be negative or close to atmospheric to avoid leakage to the surroundings. Thus, for an FPS 20 with such fluid pumps, the first target pressure may be set to achieve a suitable pressure at the flush ports.

[0111] FIG. 9C is a flow chart of an example method M3 that may additionally be performed by the control system 41 while the WPS 10 is operated to circulate product water in the circulation path in accordance with FIG. 9B. The method M3 is provided to ensure continued production of product water by the WPS 10 while safeguarding the second RO unit 404. In step S30, the fluid pressure on the permeate side 404b of the RO unit 404 is monitored based on the pressure signal PP3 from the sensor 413'. In step S31, the monitored pressure is evaluated in relation to a pressure limit. If the monitored pressure is below the pressure limit, no action is taken and the method returns to step S30. If the monitored pressure exceeds the pressure limit, step S32 is performed to open the variable restrictor 43 to decrease the fluid pressure on the permeate side 404b. Suitably, the variable restrictor 43 is opened such that the fluid pressure on the permeate side is well below the pressure limit. If step S32 fails to lower the fluids pressure below the pressure limit, the operation of the WPS 10 is stopped and the operator is alerted.

[0112] For some configurations of the WPS, the method M3 may alternatively or additionally be performed for the first RO unit 304. The method M3 may also be performed during heat disinfection of the WPS (below).

[0113] FIG. 10A is a flow chart of an example method M4 of operating the WPS 10 to perform a heat disinfection. FIG. 10B shows the WPS-FPS arrangement of FIG. 9A while the WPS 10 is being heat disinfected. In step S40, the circulation path is established in the WPS 10. In FIG. 10B, step S40 involves operating valves in the WPS 10 to define the circulation path through the return line 415 and the tank 200. As indicated by a dashed box in FIG. 10A, step S40 may involve a step S40a of operating the purification sub-system 11 to bypass the RO unit 304. Step S40a may be performed when the RO unit 304 is a sacrificial device. As used herein, "sacrificial" implies that the device has a limited life and is intended to be discarded and replaced with a new device, when a predefined end of life has been reached or when an in situ test indicates that its performance has deteriorated to warrant a replacement In the example of FIG. 10B, step S40a involves closing valves 317, 318 and opening valve 319. In step S41, the variable restrictor 43 is adjusted to be more open than in FIG. 9B when the WPS 10 is operated to provide product water for use by the FPS 20 in production mode. In some embodiments, the variable restrictor 43 is fully open in step S41. In step S42, the WPS 10 is operated to generate and transfer heated fluid in a heat disinfection path within the WPS 10. In the example of FIG. 10B, the heated fluid is product water that is heated by the heater 311 and the heat disinfection path includes the return path 415, the tank 200 and the main path 1 downstream of the tank 200 except for the RO unit 304 which is bypassed. In step S42, the product water is pumped along the heat disinfection path by the pumps 302, 403. The heat disinfection in step S42 may be performed in accordance with the A0 concept. This means that the heat disinfection is performed to achieve a predefined A0 value, which is a function of fluid temperature and exposure time. The fluid temperature is given at the coldest location in the heat disinfection path. In the example of FIG. 10B, the coldest location is likely to be immediately upstream of the heater 311. For example, the A0 value may be calculated based on the signal T2 from the temperature sensor 309 (FIG. 8A).

[0114] From FIG. 10B, it should be realized that opening the variable restrictor 43 in accordance with step S41 results in a reduced flow resistance, and thus a reduced pressure drop, in the heat disinfection path. This will reduce the power consumption of the WPS 10 for a given flow rate of the heated fluid. In some embodiments, the flow resistance of the variable restrictor 43 may be reduced to a minimum by step S41. In other words, the variable restrictor 43 is fully opened. One reason for this is to increase the fluid flow through the RO unit 404 during heat disinfection. The fluid flow through the RO unit 404 depends on the pressure difference over the RO unit 404. Thus, the fluid flow will increase with decreasing pressure downstream of the RO unit 404. A maximum fluid flow may be achieved by fully opening the variable restrictor 43 in FIG. 10B. Further, by fully opening the variable restrictor 43, the required power to pump the heated fluid is minimized.

[0115] All fluid lines that are being heat disinfected by the method M3 are durable. It is to be understood that the WPS 10 may include further durable fluid lines and associated component(s) that need to be heat disinfected, for example return line 314, valve 315, return line 405 (FIG. 8B), restrictor 406 (FIG. 8B), connecting line 407 (FIG. 8B), pump 408 (FIG. 8B). To the extent that such a further disposable fluid line and associated component(s) cannot be heat disinfected during the stage shown in FIG. 10B, the valves in the WPS 10 may be set to define a second heat disinfection path that includes the further disposable fluid line, whereupon step S42 is performed for the second heat disinfection path. Here, step S41 may be performed if the variable restrictor 43 is included in the second heat disinfection path. In FIG. 10B, a second heat disinfection path may be defined to include the return line 314 by the valve 401 being closed and the pump 403 being stopped.

[0116] In a variant of FIG. 10B, the first disinfection path is defined to also include at least the return line 314 and the valve 315. Thus, the circulation path is established in step S40 to direct heated fluid through the tank 120 not only via the return line 415 but also via the return line 314. This will speed up the heat disinfection of the WPS by reducing the number of heat disinfection paths to be established. With such a first disinfection path, another benefit of step S41 is to increase the flow rate through the RO unit 404 and into the return line 415. Opening the variable restrictor 43 decreases the pressure drop at the tapping point CP caused by the flow through the return line 314 and hence changes the relation between the flow rates in the return lines 314, 415.

[0117] As noted above, the FPS 20 may be operable in a heat disinfection mode, in which a fluid circuit within the FPS 20 is heat disinfected. Depending on the configuration of the fluid circuit, the FPS 20 may be operated in a plurality of different disinfection states in the heat disinfection mode. The disinfection states are defined to expose different parts of the fluid circuit to heated fluid. The use of different disinfection states is motivated when it is difficult or undesirable to simultaneously expose all relevant fluid paths in the fluid circuit to the heated fluid. For example, the use of different disinfection states may be implemented to limit the power consumption during heat disinfection. The plurality of disinfection states may include one or more states in which the FPS 20 is operated to drive heated fluid through the fluid circuit to drain. This type of disinfection state is denoted "single-pass state" herein. The plurality of disinfection states may further include one or more states in which the FPS 20 is operated to circulate heated fluid within the fluid circuit. This type of disinfection state is denoted "multi-pass state" herein. Generally, a single-pass state results in significantly higher power consumption, since the heated fluid will be directed to drain, and thus discarded, during an exposure time period required to achieve a sufficient disinfection of the related fluid paths. It is realized that the power may be significantly reduced by performing the heat disinfection of the FPS 20 through a combination of single-pass and multi-pass states.

[0118] FIG. 11 A is a flow chart of an example method M5 of operating a WPS-FPS arrangement for heat disinfection of the FPS 20 in a single-pass state. FIG. 1 IB shows the WPS-FPS arrangement of FIG. 9A with the FPS 20 in such a single-pass state. In step S50, the circulation path is established in the WPS 10. In FIG. 1 IB, step S50 involves operating valves in the WPS 10 to define the circulation path through the return line 415 and the tank 200. In step S51, the WPS 10 is operated to circulate product water on the circulation path. In FIG. 11B, step S51 involves operating the pumps 302, 403. In step S52, the FPS 20 is operated to divert product water from the circulation path and direct the product water along a single-pass path through the FPS 20 to drain. The single-pass path includes the heater 27. In FIG. 1 IB, step S52 results in valves VI, V4 being open, valves V3, V5 being closed, and pump 25 operating to pump product water through the FPS 20. In step S54, the heater 27 is operated to heat the passing product water to achieve a target temperature (heat disinfection temperature) at a selected location in the drain line 29a. The duration of step S54 may be determined by an A0 value given as a function of fluid temperature measured by a sensor (not shown) in the drain line 29a. Alternatively, the fluid temperature in the drain line 29a may be estimated based on the fluid flow rate and a temperature measured by a temperature sensor in the main path 21 (cf. S5 in FIG. 7).

[0119] The method M5 additionally includes a step S53 of adjusting the variable restrictor 43 in the WPS 10 to counteract boiling in the heater 27, in accordance with steps S20, S22 of the method M2 (FIG. 3).

[0120] Depending on the configuration of the FPS 20, the heat disinfection mode may include one or more additional single-pass states, each of which being performed in accordance with the method M5.

[0121] FIG. 12A is a flow chart of an example method M6 of operating a WPS-FPS arrangement for heat disinfection of the FPS 20 in a multi-pass state. FIG. 12B shows the WPS-FPS arrangement of FIG. 9A with the FPS 20 in such a multi-pass state. In a multi-pass state, the FPS 20 does not receive product water from the WPS 10. Instead, existing product water in the FPS 20 is circulated and heated within the FPS 20. However, in the method M6, the WPS 10 is used for controlling the fluid pressure in the FPS 20.

[0122] In step S60, the circulation path is established in the WPS 10 such that there is an open fluid connection to the FPS 20. This open fluid connection is used for transferring fluid pressure from the WPS 10 to the FPS 20. Step S60 may result in the same circulation path as step S40 (cf. FIG. 10B) or S50 (cf. FIG. 1 IB). However, as indicated by dashed boxes in FIG. 12A, the flow path through the purification sub-system 11 may be modified to bypass the first RO unit 304 (step S60a) and / or the second RO unit 404 (step S60b). This is possible since no product water needs to be transferred to the FPS 20 in the multi-pass state. In FIG. 12B, the first RO unit 304 is bypassed by valves 317, 318 being closed and valve 319 being open. In FIG. 12B, the second RO unit 404 is bypassed by valve 315 being open and valve 401 being closed. By bypassing the first RO unit 304 and / or the second RO unit 404, the flow resistance in the WPS 10 is reduced, lowering the power consumption of the WPS 10. In step S61, the WPS 10 is operated to circulate product water on the circulation path. In FIG. 12B, step S61 involves operating the pump 302. In step S62, the FPS 20 is operated to establish a disinfection path. The disinfection path is a closed path that includes the heater 27. In FIG. 12B, step S62 results in valves VI, V3 being open and valves V4, V5 being closed. In step S63, the FPS 20 is operated to circulate pre-existing product water within the FPS 20 along the disinfection path. In FIG. 12B, step S63 involves operating the pump 25. In step S65, the heater 27 is operated to heat the passing product water. The heat disinfection in step S65 may be performed in accordance with the A0 concept, and the duration of step S65 may be determined by an A0 value given as a function of fluid temperature at a coldest location in the disinfection path, for example immediately upstream of the heater 27. For example, the A0 value may be calculated based on a signal from the temperature sensor SI (FIG. 7).

[0123] The method M6 additionally includes a step S64 of adjusting the variable restrictor 43 in the WPS 10 to counteract boiling in the heater 27, in accordance with steps S20, S22 of the method M2 (FIG. 3). In the example of FIG. 12B, an adjustment of the variable restrictor 43 will change the pressure in the return line 415 upstream of the variable restrictor 43, and this pressure will be transferred via the return line 415 to the tapping point CP, and from the tapping point into the FPS 20 via the main path 21. Experiments indicate that pressure may be transferred into the FPS 20 even if the oneway valve 416 (FIG. 8B) is installed in the return line 415. This is believed to be due to an expansion of the fluid that is circulated in the FPS 20, causing one-way valve 416 to be slightly opened. In an alternative, the WPS 10 may include a bypass arrangement that allows the one-way-valve 416 to be bypassed during the method M6.

[0124] Depending on the configuration of the FPS 20, the heat disinfection mode may include one or more additional multi-pass states, each of which being performed in accordance with the method M6.

[0125] FIG. 13A shows an example WPS 10, which is configured to allow the FPS 20 to be separately disinfected from the WPS 10. FIG. 13A is provided to give an overall understanding of how a WPS 10 may be configured to provide this function. Many alternatives are readily apparent to the skilled person. In FIG. 13 A, the main path 1 extends to and through the tank 200. As noted above, the tank 200 may be vented so that atmospheric pressure prevails in the tank 200. The main path 1 further extends from the bottom portion of the tank 200 to the inlet of the purification sub-system 11, which is configured to process incoming water for purification, for example in accordance with any example set forth herein. The circulation path 13 extends from the outlet of the purification sub-system 11 to the top portion of the tank 200. Thus, the circulation path 13 directs processed ("purified") water from the purification sub-system 11 back to the tank 200. A fluid pump (not shown) is arranged to pump water from the tank 200 to and through the purification sub-system 11, and to pump the purified water from the purification sub-system 11 via the circulation path 13 back to the tank 200. Thereby, the WPS 10 is operable to continuously supply purified water on the circulation path 13. The purified water is equal to the above-mentioned product water, PW. The FPS 20 is fluidly connected to the WPS 10 on two connecting paths 21, 21', which extend to a respective connection point CP, CP' on the circulation path 13. In the illustrated example, the main path 21 of the FPS 20 is connected to the circulation path 13 at connection point CP, and a secondary line 21' extends from the FPS 20 to connection point CP'. A path segment 13a of the circulation path 13 extends between the connection points CP, CP'. A variable restrictor 43 is arranged in the circulation path 13 to enable one or more of the functions described with reference to FIG. 3. In the illustrated example, as indicated by dashed lines, the circulation path 34 may optionally include an on / off valve 43', 43" downstream and / or upstream of the connection points CP, CP'.

[0126] FIG. 13B shows the system of FIG. 13A during heat disinfection of the FPS 20. As indicated by thicker lines, the FPS 20 is operated to generate a throughflow of heated fluid from the secondary line 21' to the main path 21' via the path segment 13a. The flow of heated fluid may instead be reversed. The disinfection state in FIG. 13B provides a simple and effective way of ensuring that the FPS 20 is disinfected all the way to its fluid connection to the WPS 10. The disinfection state of FIG. 13B is also denoted "interface disinfection state" herein. It may be preferable to perform the interface disinfection state as a multi-pass state, to economize with fluid and heating power. In some embodiments, the interface disinfection state is the final or concluding disinfection state of the heat disinfection mode of the FPS 20. In other words, the heat disinfection of the FPS 20 is concluded by disinfecting all fluid paths that extend between the FPS 20 and the WPS 10. After the heat disinfection state, the FPS 20 will not obtain product water, PW, from the WPS 10 until it is again time for the FPS 20 to generate treatment fluid, TF (cf. FIG. 2A). This will ensure the microbial integrity of the FPS 20 between sessions for production of treatment fluid.

[0127] In some embodiments, as shown in FIG. 13B, the WPS 10 is operated to stop the flow of PW in the circulation path 13 while the FPS 20 is in the interface disinfection state. This will minimize risk that the heated fluid enters the WPS 10 during the interface disinfection state.

[0128] The Applicant has also found that it may be beneficial to block fluid transport from CP, CP' into the WPS 10 during the interface disinfection state. Experiments indicate that the heated fluid may form vapor as it flows into and through the path segment 13a between the connection points CP, CP'. If this vapor is diverted into the WPS 10, the amount of fluid in the FPS 20 will decrease over time. This may disrupt the heating of the fluid in the FPS 20. The risk that vapor is diverted into the WPS 10 is elevated when the tank 200 is held at atmospheric pressure. To mitigate this risk and to ensure consistent and well-controlled heat disinfection of the FPS 20, the WPS 10 may be configured to selectively block fluid transport from the connection points CP, CP' to the tank 200 during the interface disinfection state. Experiments indicate that such blocking of fluid transport significantly reduces the duration of the interface heat disinfection, for example from 60-100 minutes without blocking to 10-12 minutes with blocking.

[0129] In some embodiments, the purification sub-system 11 inherently blocks or significantly impedes vapor transport, and the fluid transport need only be blocked downstream of the connection points CP, CP'. This may be achieved by closing the variable restrictor 43. For example, a restricting element of the variable restrictor 43 may be actively moved to close the flow path through the variable restrictor 43 and thereby close the circulation path 13. Alternatively or additionally, the on / off valve 43' may be provided and actively operated ("energized") to close the circulation path 13 in the interface disinfection state. If necessary, the on / off valve 43" may be provided and actively operated to close the circulation path 13 in the interface disinfection state.

[0130] It is realized that, during the interface disinfection state, the variable restrictor 43 cannot and will not be used for achieving a target fluid pressure within the heater 27 of the FPS 20 (cf. step S22 in FIG. 3).

[0131] The technique of blocking fluid transport during the interface disinfection state is equally applicable when the WPS 10 is configured without a variable restrictor in the circulation path 13, for example as shown in FIG. 4A. In such configurations, the fluid transport may be blocked by providing and operating one or more of the on / off valves 43', 43".

[0132] The technique of closing the circulation path 13 in the interface disinfection state has a number of technical advantages. The disinfection time may be significantly reduced, which allows for quicker turnaround times in the disinfection cycle, thereby improving overall operational efficiency. The disinfection process is rendered reliable and consistent to ensure that the disinfection is achieved every time. By preventing vapor escape, water loss during the disinfection process is minimized. Temperature fluctuations that might compromise the disinfection process are mitigated. The impact of varying environmental conditions and atmospheric pressures on the disinfection process is mitigated, so that disinfection remains effective regardless of external factors. The operational reliability of the WPS and the FPS is improved, reducing the likelihood of unexpected downtime or failures. The reduction in disinfection time and water loss translates to cost savings in both energy and water usage. Last but not least, the technique helps ensure compliance with health and safety regulations regarding water quality.

[0133] FIG. 14 is a block diagram of an example device 80, which may correspond to the control system 41 in FIG. 4B. The functionality of the device 80 may be defined by a combination of software and hardware circuitry, or exclusively by specific hardware circuitry. In FIG. 14, the device 80 comprises processor circuitry 81, which may be or include a central processing unit (CPU), graphics processing unit (GPU), microcontroller, microprocessor, ASIC, FPGA, or any other specific or general processing device. The device 80 may operate by executing instructions stored in a computer memory, such as memory 82. The instructions when executed by the processor circuitry 81 may cause the device 80 to perform any of the methods, procedures and functions described herein, or part thereof. The memory 82 may comprise one or more of a buffer, flash memory, hard drive, removable media, volatile memory, non-volatile memory, random access memory (RAM), or another suitable data storage device. Such a memory 82 is considered a non-transitory computer-readable medium. The instructions may be supplied to the device 80 on a computer-readable medium, which may be a tangible (non-transitory) product (for example magnetic medium, optical disk, read-only memory, flash memory, etc.) or a propagating signal. The device 80 includes an I / O interface 83a, which may include any conventional communication interface for wired or wireless communication. As shown, the device 80 is arranged to receive input signals [SS] and to output control signals [CS]. For example, the input signals may be obtained from the pressure sensor 42, and optionally, from sensors in the WPS 10 and / or the FPS 20. The control signals may be provided to the variable restrictor 43, and optionally, to pumps, heaters and valves in the WPS 10 and / or FPS 20. The device 80 may comprise a further interface 83b for connection to a feedback device 84 for user interaction. The feedback device 84 may include one or more of a display, a touch screen, a speaker, one or more signaling lamps, a keyboard / keypad, a microphone, a computer mouse, a projector, a camera, etc.

[0134] While the subject of the present disclosure has been described in connection with what is presently considered to be the most practical embodiments, it is to be understood that the subject of the present disclosure is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and the scope of the appended claims. Further, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

[0135] In the following, clauses are recited to summarize some aspects and embodiments as disclosed in the foregoing.

[0136] Cl. An arrangement for providing a treatment fluid for use in dialysis therapy, said arrangement comprising: a first system, which comprises a purification sub-system and is operable to process source water by the purification sub-system to produce product water for medical use and provide a flow of product water in a circulation path within the first system; a second system which is operable to generate the treatment fluid by mixing the product water with one or more concentrates; wherein the second system comprises: a main fluid path, which is fluidly connected to a tapping junction on the circulation path for obtaining a diverted flow of product water; and a supply arrangement, which is fluidly connected to the main fluid path at one or more dosing points and is operable to supply the one or more concentrates into the main fluid path for mixing with the diverted flow of product water; wherein the arrangement further comprises: a variable restrictor, which is arranged in the circulation path or in the main fluid path upstream of the one or more dosing points; and a control system, which is configured to adjust the variable restrictor so as to maintain a target fluid pressure at a predefined location in the second system.

[0137] C2. The arrangement of Cl, wherein the variable restrictor and the control system are embodied by a mechanical pressure regulator, which is arranged in fluid communication with the main fluid path at the predefined location.

[0138] C3. The arrangement of Cl, which further comprises a pressure sensor, which is configured to provide a measurement signal indicative of fluid pressure at the predefined location, and wherein the control system is configured to adjust the variable restrictor, by feedback control based on the measurement signal, to maintain the target fluid pressure at the predefined location.

[0139] C4. The arrangement of C3, wherein the pressure sensor is arranged in the main fluid path at the one or more dosing points.

[0140] C5. The arrangement of C4, wherein the variable restrictor is arranged in the circulation path of the first system downstream of the tapping junction.

[0141] C6. The arrangement of any preceding clause, wherein the predefined location is at the one or more dosing points, and wherein the control system is configured to maintain the target fluid pressure while the second system is operated to generate the treatment fluid. C7. The arrangement of any one of C1-C5, wherein the predefined location is within a heating device in the second system, wherein the control system is configured to maintain the target fluid pressure within the heating device while the second system is operated to perform a heat disinfection of fluid paths within the second system by use of the heating device.

[0142] C8. The arrangement of C7, wherein the heating device is arranged in the main fluid path downstream of the one or more dosing points, wherein the second system, during said heat disinfection, is configured to heat, by the heating device, product water obtained from the first system and to distribute the thus-heated product water in the second system, wherein the control system, during said heat disinfection, is configured to adjust the variable restrictor to achieve the target fluid pressure within the heating device, said target fluid pressure being set to counteract boiling of the product water in the heating device.

[0143] C9. The arrangement of C7 or C8, wherein the control system is configured to obtain a value indicative of the atmospheric pressure at the location of the arrangement, and determine the target fluid pressure as a function of said value.

[0144] CIO. The arrangement of C9, wherein the control system is configured to obtain said value from a sensor.

[0145] Cl l. The arrangement of CIO, which includes the sensor, which is arranged to measure total ambient pressure at the location of the arrangement.

[0146] C12. The arrangement of any one of C9-C11, wherein the control system is configured to set the target fluid pressure as a pressure differential relative to the atmospheric pressure.

[0147] C13. The arrangement of any one of C7-C12, wherein said heat disinfection comprises at least one single-pass state, wherein the second system, in the at least one single-pass state, is configured to pump product water from the first system along the main fluid path, through the second system including the heating device, to a drain, wherein the first system is configured to provide the flow of product water in the circulation path when the second system is in the single-pass state, and wherein the control system is configured to adjust the variable restrictor to achieve the target fluid pressure within the heating device when the second system is in the single-pass state.

[0148] C14. The arrangement of C7-C13, wherein said heat disinfection comprises at least one multi-pass state, wherein the second system, in the at least one multi-pass state, is configured to circulate existing product water in the second system through the heating device on a disinfection path within the second system, wherein the first system is configured to provide the flow of product water in the circulation path when the second system is in the at least one multi-pass state, wherein the second system is configured to transfer a fluid pressure, which is generated by the first system at the tapping junction, from the tapping junction to the disinfection path via the main fluid path when the second system is in the at least one multi-pass state, and wherein the control system is configured to adjust the variable restrictor to achieve the target fluid pressure within the heating device when the second system is in the at least one multipass state.

[0149] C15. The arrangement of Cl 4, wherein the variable restrictor is arranged in the circulation path, wherein first system comprises a first reverse osmosis, RO, unit and a second RO unit, which each comprises a feed chamber and a permeate chamber separated by a semi-permeable membrane, wherein the first system is configured, when the second system is operated to generate the treatment fluid, to define a flow path through the feed chamber, the semi-permeable membrane and the permeate chamber of the first and second RO units, respectively, wherein the first RO unit is arranged upstream of the second RO unit in the flow path, and wherein the first system is configured, when the second system is in the at least one multi-pass state, to modify the flow path to bypass at least one of the first RO unit or the second RO unit.

[0150] Cl 6. The arrangement of any one of Cl -Cl 4, wherein the first system comprises a purification sub-system, which is configured to generate the product water from the source water, wherein the circulation path comprises an inlet for the source water, and wherein the purification arrangement is connected to the circulation path intermediate the inlet and the tapping junction.

[0151] C17. The arrangement of C16, wherein the first system comprises a reservoir, which is included in the circulation path and comprises the inlet for the source water.

[0152] C18. The arrangement of C17, wherein the reservoir is at atmospheric pressure when the first system is operated to provide the flow of product water in the circulation path.

[0153] Cl 9. The arrangement of any one of C16-C18, wherein the second system (20) comprises a secondary connecting line (21'), which is fluidly connected to a further tapping junction (CP') on the circulation path (13), and wherein the control system (41) is configured to operate the second system (20) to perform a heat disinfection by generating a throughflow of a heated fluid in the circulation path (13) between the tapping junction (CP) and the further tapping junction (CP'), via the main line (21) and the secondary connecting line (21').

[0154] C20. The arrangement of Cl 9, wherein the control system (41) is configured to, while the second system (20) is operated to generate the throughflow of heated fluid, cause the first system (10) to stop the flow of the product water in the circulation path (13). C21. The arrangement of C19 or C20, wherein the control system (41) is configured to, while the second system (20) is operated to generate the throughflow of heated fluid, cause the first system (10) to block fluid transport in the circulation path (13).

[0155] C22. The arrangement of C19 in combination with C17 or Cl 8, wherein the control system (41) is configured to, while the second system (20) is operated to generate the throughflow of heated fluid, cause the first system (10) to block fluid transport along the circulation path (34) to the reservoir (200).

[0156] C23. The arrangement of any one of C16-C22, wherein the variable restrictor is arranged in the circulation path, wherein the purification sub-system comprises a reverse osmosis, RO, unit, which comprises a feed chamber and a permeate chamber separated by a semi-permeable membrane, wherein the first system is configured to define a flow path through the feed chamber, the semi-permeable membrane and the permeate chamber, wherein the first system further comprises a sensor configured to generate a first signal indicative of fluid pressure in the permeate chamber, and wherein the control system is configured to, when the second system is operated to generate the treatment fluid, monitor the first signal for detection that the fluid pressure in the permeate chamber exceeds a limit and, in response to said detection, adjust the variable restrictor to decrease the fluid pressure in the permeate chamber.

[0157] C24. The arrangement of any one of C16-C22, wherein the variable restrictor is arranged in the circulation path, wherein the purification sub-system comprises a further heating device, wherein the first system is further operable to perform a further heat disinfection, in which the flow of product water is provided in the circulation path and heated by the further heating device, wherein the control system, during the further heat disinfection, is configured to reduce a flow resistance of the variable restrictor compared to when the first system is operated to provide the flow of product water in the circulation path for use by the second system to generate the treatment fluid.

[0158] C25. The arrangement of C24, wherein the control system is configured, during the further heat disinfection, to reduce the flow resistance of the variable restrictor to a minimum.

[0159] C26. The arrangement of C24 or C25, wherein the purification sub-system comprises a first reverse osmosis, RO, unit and a second reverse osmosis, RO, unit, which each comprises a feed chamber and a permeate chamber separated by a semi- permeable membrane, wherein the first system is configured, when the second system is operated to generate the treatment fluid, to define a flow path through the feed chamber, the semi-permeable membrane and the permeate chamber of the first and second RO units, respectively, wherein the first RO unit is arranged upstream of the second RO unit in the flow path, and wherein the first system is configured, during the further heat disinfection, to modify the flow path to bypass the first RO unit.

[0160] C27. The arrangement of C26, wherein the first system further comprises a reservoir, which is included in the circulation path and comprises an inlet for the source water, and wherein the purification sub-system further comprises: a first drain line extending from a retentate outlet of the feed chamber of the first RO unit to a drain; a first flow restriction device in the first drain line to define a flow resistance at the retentate outlet of the feed chamber of the first RO unit; a second drain line extending from a retentate outlet of the feed chamber of the second RO unit to the reservoir; and a second flow restriction device in the second drain line to define a flow resistance at the retentate outlet of the feed chamber of the second RO unit.

[0161] C28. The arrangement of any one of C26 or C27, wherein the first RO unit is a sacrificial component which is removably installed in the first system.

[0162] C29. The arrangement of C28, wherein the second RO unit is permanently installed in the first system.

[0163] C30. The arrangement of C23, wherein the purification sub-system further comprises: a feed pump arranged upstream of the RO unit to supply pressurized water to a water inlet of the feed chamber of the RO unit; a drain line extending from a retentate outlet of the feed chamber of the RO unit; a flow restriction device in the drain line to define a flow resistance at the retentate outlet; a connecting line, which is arranged to define a recirculation path from the retentate outlet of the feed chamber of the RO unit to the water inlet of the feed chamber of the RO unit; and an auxiliary pump in the recirculation path.

[0164] C31. The arrangement of any preceding clause, wherein the second system is operable in at least two operating modes, and wherein the target fluid pressure and the predefined location differ between the at least two operating modes.

[0165] C32. The arrangement of C31, wherein the at least two operating modes comprises a fluid generation mode, in which the second system is configured to generate the treatment fluid, and a heat disinfection mode, in which the second system is configured to perform a heat disinfection of one or more fluid paths within the second system.

[0166] C33. A method operating an arrangement for providing a treatment fluid for use in dialysis therapy, said method comprising: operating a first system to process source water by purification into product water for medical use and provide a flow of product water in a circulation path; operating a second system to obtain a diverted flow of product water from the circulation path along a main fluid path; and operating the second system to generate the treatment fluid by supplying one or more concentrates into the main fluid path for mixing with the diverted flow of product water; said method further comprising, during an operating mode of the second system, adjusting a variable restrictor, which is arranged in the circulation path or upstream of the one or more dosing points in the main fluid path, so as to maintain a target fluid pressure at a predefined location in the second system.

[0167] C34. The method of C33, wherein the second system, in the operating mode, is configured to generate the treatment fluid, and wherein the predefined location is at the one or more dosing points.

[0168] C35. The method of C33, wherein the second system, in the operating mode, is configured to perform a heat disinfection of one or more fluid paths within the second system by use of a heating device, and wherein the predefined location is within the heating device. C36. A computer-readable medium comprising computer instructions which, when executed by processor circuitry, is configured to cause the processor circuitry to perform the method of any one of C33-C35.

Claims

CLAIMS1. An arrangement for providing a treatment fluid for use in dialysis therapy, said arrangement comprising: a first system (10), which comprises a purification sub-system (11) and is operable to process source water by the purification sub-system (11) to produce product water for medical use and provide a flow of product water in a circulation path (13) within the first system (10), a second system (20) which is operable to generate the treatment fluid by mixing the product water with one or more concentrates, wherein the second system (20) comprises: a main fluid path (21), which is fluidly connected to a tapping junction (CP) on the circulation path (13) for obtaining a diverted flow of product water, and a supply arrangement (23, 24), which is fluidly connected to the main fluid path (21) at one or more dosing points (DP, DP') and is operable to supply the one or more concentrates into the main fluid path (21) for mixing with the diverted flow of product water, wherein the arrangement further comprises: a variable restrictor (43), which is arranged in the circulation path (13) or in the main fluid path (21) upstream of the one or more dosing points (DP, DP'), and a control system (41), which is configured to adjust the variable restrictor (43) so as to maintain a target fluid pressure at a predefined location in the second system (20).

2. The arrangement of claim 1, wherein the variable restrictor (43) and the control system (41) are embodied by a mechanical pressure regulator, which is arranged in fluid communication with the main fluid path (21) at the predefined location.

3. The arrangement of claim 1, which further comprises a pressure sensor (42), which is configured to provide a measurement signal indicative of fluid pressure at the predefined location, and wherein the control system (41) is configured to adjust the variable restrictor (43), by feedback control based on the measurement signal, to maintain the target fluid pressure at the predefined location.

4. The arrangement of claim 3, wherein the pressure sensor (42) is arranged in the main fluid path (21) at the one or more dosing points (DP, DP').

5. The arrangement of claim 4, wherein the variable restrictor (43) is arranged in the circulation path (13) of the first system (10) downstream of the tapping junction (CP).

6. The arrangement of any preceding claim, wherein the predefined location is at the one or more dosing points (DP, DP'), and wherein the control system (41) is configured to maintain the target fluid pressure while the second system (20) is operated to generate the treatment fluid.

7. The arrangement of any one of claims 1-5, wherein the predefined location is within a heating device (27) in the second system (20), wherein the control system (41) is configured to maintain the target fluid pressure within the heating device (27) while the second system (20) is operated to perform a heat disinfection of fluid paths within the second system (20) by use of the heating device (27).

8. The arrangement of claim 7, wherein the heating device (27) is arranged in the main fluid path (21) downstream of the one or more dosing points (DP, DP'), wherein the second system (20), during said heat disinfection, is configured to heat, by the heating device (27), product water obtained from the first system (10) and to distribute the thus-heated product water in the second system (20), wherein the control system (41), during said heat disinfection, is configured to adjust the variable restrictor (43) to achieve the target fluid pressure within the heating device (27), said target fluid pressure being set to counteract boiling of the product water in the heating device (27).

9. The arrangement of claim 7 or 8, wherein the control system (41) is configured to obtain a value indicative of the atmospheric pressure at the location of the arrangement, and determine the target fluid pressure as a function of said value.

10. The arrangement of claim 9, wherein the control system (41) is configured to obtain said value from a sensor (44).

11. The arrangement of claim 10, which includes the sensor (44), wherein the sensor (44) is arranged to measure total ambient pressure at the location of the arrangement.

12. The arrangement of any one of claims 9-11, wherein the control system (41) is configured to set the target fluid pressure as a pressure differential relative to the atmospheric pressure.

13. The arrangement of any one of claims 7-12, wherein said heat disinfection comprises at least one single-pass state, wherein the second system (20), in the at least one single-pass state, is configured to pump product water from the first system (10) along the main fluid path (21), through the second system (20) including the heating device (27), to a drain (4), wherein the first system (10) is configured to provide the flow of product water in the circulation path (13) when the second system (20) is in the single-pass state, and wherein the control system (41) is configured to adjust the variable restrictor (43) to achieve the target fluid pressure within the heating device (27) when the second system (20) is in the single-pass state.

14. The arrangement of any one of claims 7-13, wherein said heat disinfection comprises at least one multi-pass state, wherein the second system (20), in the at least one multi-pass state, is configured to circulate existing product water in the second system (20) through the heating device (27) on a disinfection path (29') within the second system (20), wherein the first system (10) is configured to provide the flow of product water in the circulation path (13) when the second system (20) is in the at least one multi-pass state, wherein the second system (20) is configured to transfer a fluid pressure, which is generated by the first system (10) at the tapping junction (CP), from the tapping junction (CP) to the disinfection path (29') via the main fluid path (21) when the second system (20) is in the at least one multi-pass state, and wherein the control system (41) is configured to adjust the variable restrictor (43) to achieve the target fluid pressure within the heating device (27) when the second system (20) is in the at least one multi-pass state.

15. The arrangement of claim 14, wherein the variable restrictor (43) is arranged in the circulation path (13), wherein first system (10) comprises a first reverse osmosis, RO, unit (304) and a second RO unit (404), which each comprises a feed chamber (304a; 404a) and a permeate chamber (304b; 404b) separated by a semi-permeable membrane (304'; 404'), wherein the first system (10) is configured, when the second system (20) is operated to generate the treatment fluid, to define a flow path through the feed chamber (304a; 404a), the semi-permeable membrane (304'; 404') and the permeate chamber (304b; 404b) of the first and second RO units (304, 404), respectively, wherein the first RO unit (304) is arranged upstream of the second RO unit(404) in the flow path, and wherein the first system (10) is configured, when the second system (20) is in the at least one multi-pass state, to modify the flow path to bypass at least one of the first RO unit (304) or the second RO unit (404).

16. The arrangement of any one of claims 1-14, wherein the first system (10) comprises a purification sub-system (11), which is configured to generate the product water from the source water, wherein the circulation path (13) comprises an inlet (202) for the source water, and wherein the purification arrangement (11) is connected to the circulation path (13) intermediate the inlet (202) and the tapping junction (CP).

17. The arrangement of claim 16, wherein the first system (10) comprises a reservoir (200), which is included in the circulation path (13) and comprises the inlet (202) for the source water.

18. The arrangement of claim 17, wherein the reservoir (200) is at atmospheric pressure when the first system (41) is operated to provide the flow of product water in the circulation path (13).

19. The arrangement of any one of claims 16-18, wherein the second system (20) comprises a secondary connecting line (2T), which is fluidly connected to a further tapping junction (CP') on the circulation path (13), and wherein the control system (41) is configured to operate the second system (20) to perform a heat disinfection by generating a throughflow of a heated fluid in the circulation path (13) between the tapping junction (CP) and the further tapping junction (CP'), via the main line (21) and the secondary connecting line (21').

20. The arrangement of claim 19, wherein the control system (41) is configured to, while the second system (20) is operated to generate the throughflow of heated fluid, cause the first system (10) to stop the flow of the product water in the circulation path (13).

21. The arrangement of claim 19 or 20, wherein the control system (41) is configured to, while the second system (20) is operated to generate the throughflow of heated fluid, cause the first system (10) to block fluid transport in the circulation path22. The arrangement of claim 19 in combination with claim 17 or 18, wherein the control system (41) is configured to, while the second system (20) is operated to generate the throughflow of heated fluid, cause the first system (10) to block fluid transport along the circulation path (34) to the reservoir (200).

23. The arrangement of any one of claims 16-22, wherein the variable restrictor (43) is arranged in the circulation path (13), wherein the purification sub-system (11) comprises a reverse osmosis, RO, unit (404), which comprises a feed chamber (404a) and a permeate chamber (404b) separated by a semi-permeable membrane (404'), wherein the first system (10) is configured to define a flow path through the feed chamber (404a), the semi-permeable membrane (404') and the permeate chamber (404b), wherein the first system (10) further comprises a sensor (413') configured to generate a first signal indicative of fluid pressure in the permeate chamber (404b), and wherein the control system (41) is configured to, when the second system (20) is operated to generate the treatment fluid, monitor the first signal for detection that the fluid pressure in the permeate chamber (404b) exceeds a limit and, in response to said detection, adjust the variable restrictor (43) to decrease the fluid pressure in the permeate chamber (404b).

24. The arrangement of any one of claims 16-22, wherein the variable restrictor (43) is arranged in the circulation path (13), wherein the purification sub-system (11) comprises a further heating device (311), wherein the first system (10) is further operable to perform a further heat disinfection, in which the flow of product water is provided in the circulation path (13) and heated by the further heating device (311), wherein the control system (41), during the further heat disinfection, is configured to reduce a flow resistance of the variable restrictor (43) compared to when the first system (10) is operated to provide the flow of product water in the circulation path (13) for use by the second system (20) to generate the treatment fluid.

25. The arrangement of claim 24, wherein the control system (41) is configured, during the further heat disinfection, to reduce the flow resistance of the variable restrictor (43) to a minimum.

26. The arrangement of claim 24 or 25, wherein the purification sub-system (11) comprises a first reverse osmosis, RO, unit (304) and a second reverse osmosis, RO, unit (404), which each comprises a feed chamber (304a; 404a) and a permeate chamber (304b; 404b) separated by a semi-permeable membrane (304'; 404'), wherein the first system (10) is configured, when the second system (20) is operated to generate thetreatment fluid, to define a flow path through the feed chamber (304a; 404a), the semi- permeable membrane (304'; 404') and the permeate chamber (304b; 404b) of the first and second RO units (304; 404), respectively, wherein the first RO unit (304) is arranged upstream of the second RO unit (404) in the flow path, and wherein the first system (10) is configured, during the further heat disinfection, to modify the flow path to bypass the first RO unit (304).

27. The arrangement of claim 26, wherein the first system (10) further comprises a reservoir (200), which is included in the circulation path (13) and comprises an inlet (202) for the source water, and wherein the purification sub-system (11) further comprises: a first drain line (305) extending from a retentate outlet of the feed chamber (304a) of the first RO unit (304) to a drain (4); a first flow restriction device (306) in the first drain line (305) to define a flow resistance at the retentate outlet of the feed chamber (304a) of the first RO unit (304); a second drain line (405) extending from a retentate outlet of the feed chamber (404a) of the second RO unit (404) to the reservoir (200); and a second flow restriction device (406) in the second drain line (405) to define a flow resistance at the retentate outlet of the feed chamber (404a) of the second RO unit (404).

28. The arrangement of claim 26 or 27, wherein the first RO unit (304) is a sacrificial component which is removably installed in the first system (10).

29. The arrangement of claim 28, wherein the second RO unit (404) is permanently installed in the first system (10).

30. The arrangement of claim 23, wherein the purification sub-system (11) further comprises: a feed pump (302; 403) arranged upstream of the RO unit (304; 404) to supply pressurized water to a water inlet of the feed chamber (304a; 404a) of the RO unit (304; 404); a drain line (305; 405) extending from a retentate outlet of the feed chamber (303a, 404a) of the RO unit (304; 404); a flow restriction device (306; 406) in the drain line (305; 405) to define a flow resistance at the retentate outlet; a connecting line (307; 407), which is arranged to define a recirculation path from the retentate outlet of the feed chamber (304a; 404a) of the RO unit (304; 404) to the water inlet of the feed chamber (304a; 404a) of the RO unit (304; 404); and an auxiliary pump (308; 408) in the recirculation path.

31. The arrangement of any preceding claim, wherein the second system (20) is operable in at least two operating modes, and wherein the target fluid pressure and the predefined location differ between the at least two operating modes.

32. The arrangement of claim 31, wherein the at least two operating modes comprises a fluid generation mode, in which the second system (20) is configured to generate the treatment fluid, and a heat disinfection mode, in which the second system (20) is configured to perform a heat disinfection of one or more fluid paths within the second system (20).

33. A method operating an arrangement for providing a treatment fluid for use in dialysis therapy, said method comprising: operating (Si l) a first system to process source water by purification into product water for medical use and provide a flow of product water in a circulation path; operating (S12) a second system to obtain a diverted flow of product water from the circulation path along a main fluid path; and operating (SI 3) the second system to generate the treatment fluid by supplying one or more concentrates into the main fluid path for mixing with the diverted flow of product water; said method further comprising, during an operating mode of the second system, adjusting (S21; S22) a variable restrictor, which is arranged in the circulation path or upstream of the one or more dosing points in the main fluid path, so as to maintain a target fluid pressure at a predefined location in the second system.

34. The method of claim 33, wherein the second system, in the operating mode, is configured to generate the treatment fluid, and wherein the predefined location is at the one or more dosing points.

35. The method of claim 33, wherein the second system, in the operating mode, is configured to perform a heat disinfection of one or more fluid paths within the second system by use of a heating device, and wherein the predefined location is within the heating device.

36. A computer-readable medium comprising computer instructions which, when executed by processor circuitry (81), is configured to cause the processor circuitry (81) to perform the method of any one of claims 33-35.

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