Determination of the permeability state of forward osmosis membranes using transmembrane pressure difference.

Abstract

A control device (10) and method for determining the permeability state of a forward osmosis (FO) membrane (2c) of a FO device (2) in a dialysate generator (1). The FO membrane (2c) separates a feed side (2a) and a draw side (2b) of the FO device (2). The FO device (2) has a feed inlet port (E) in fluid communication with the feed side (2a). in ) and the feed outlet port (E out ) and a draw inlet port (L ) in fluid communication with the draw side (2b). in ) and draw outlet port (L out ). The method includes providing (S1) a flow of pure water to the feed side (2a) and providing (S2) a flow of pure water to the draw side (2b). The method further includes monitoring (s3) one or more pressures indicative of a transmembrane pressure, TMP, between the feed side (2a) and the draw side (2b). The method further includes stopping (S4) the flow through one of the ports such that the TMP is maintained constant and of a non-zero magnitude, controlling (S5) the flow to or from one of the feed side (2a) and the draw side (2b) with the flow stopped based on the monitored one or more pressures, and determining (S7) a permeability state of the FO membrane based on a characteristic indicative of the flow.

Description

[Technical field]

[0001] The present disclosure relates to the field of dialysis and the permeability of forward osmosis membranes, and in particular to determining the permeability state of forward osmosis membranes located in dialysate generators. [Background technology]

[0002] Dialysis is commonly used to treat patients with kidney failure. There are several types of dialysis treatments, such as hemodialysis (HD), peritoneal dialysis (PD) and continuous renal replacement therapy (CRRT). Typically, a dialysate is used in the treatment, which is either delivered pre-made in a bag or produced at the time of use by mixing a concentrate with water.

[0003] Forward osmosis (FO) has emerged as an option for producing dialysate due to its potential to reduce water consumption. FO membranes are typically designed to be more or less selective for water molecules, which allows them to separate water from all other contaminants. However, undetected water permeability issues can alter the composition of the produced dialysate by allowing the transport of components other than water across the FO membrane.

[0004] Therefore, there is a need to detect such permeability problems so that the produced dialysate is not compromised. Summary of the Invention

[0005] The FO membrane of the present disclosure is used to prepare a dialysis solution. The FO membrane, in one embodiment, is more or less selective for water molecules, which allows the FO membrane to separate water from all other contaminants. The osmotic pressure difference between the feed (e.g., water or effluent from a dialysis treatment) and the draw (dialysis concentrate), separated by the FO membrane, is used to extract pure water from the feed to the dialysis concentrate, thereby diluting the dialysis concentrate. The diluted dialysis concentrate is then used to produce a dialysis solution. The system and method of the present disclosure detects permeability problems and allows the transport of components other than water across the FO membrane, thereby inhibiting changes in the composition of the produced dialysis solution.

[0006] It is therefore an object of the present disclosure to provide a simple and reliable method for determining the permeability state of a forward osmosis membrane.A further object is to provide a method for determining the permeability state of a forward osmosis membrane when the membrane is deployed for use in a dialysate generator.

[0007] These and other objects are achieved at least in part by the methods, the control devices and the dialysate generating devices according to the independent claims and by the embodiments according to the dependent claims.

[0008] According to one aspect, which may be combined with any other aspects and embodiments thereof, the present disclosure relates to a method for determining a permeability state of a forward osmosis (FO) membrane of a FO device in a dialysate generator. The FO membrane separates a feed side from a draw side of the FO device. The FO device includes a feed inlet port and a feed outlet port in fluid communication with the feed side, and a draw inlet port and a draw outlet port in fluid communication with the draw side. The method includes providing a flow of pure water to the feed side and providing a flow of pure water to the draw side. The method also includes monitoring one or more pressures indicative of a transmembrane pressure (TMP) between the feed side and the draw side. The method further includes stopping the flow through one of the ports, and controlling the flow to or from one of the feed side and the draw side with the stopped flow based on the monitored one or more pressures, such that the TMP is maintained constant and of a non-zero magnitude. The method further includes determining a permeability state of the FO membrane based on a characteristic indicative of the controlled flow.

[0009] The method provides a simple and reliable way to assess the permeability state of the FO membrane. For example, by controlling a pump to maintain the TMP, the flow provided by the pump reflects the flow of fluid transported between the two sides, which can reveal the permeability state of the membrane. In turn, the resulting outflow from the other side reflects the flow of fluid transported between the two sides. Because the method uses mechanical features already present in the dialysate generator, it is easy to implement and can be performed automatically without human intervention.

[0010] According to some embodiments, the method includes monitoring a characteristic indicative of the controlled flow, where the characteristic may be continuously observed, e.g., continuously measured.

[0011] According to some embodiments, controlling the flow includes controlling the flow with a pump, where a variety of flows can be provided.

[0012] According to some embodiments, the characteristic is the speed of the pump or the power provided to the pump. Thus, the permeability state can be assessed based on different characteristics.

[0013] According to some embodiments, the property is a rate of controlled flow into one of the feed side and the draw side with flow stopped, or the property is a rate of outflow from the other of the feed side and the draw side. Thus, the permeability state can be evaluated based on different properties.

[0014] According to some embodiments, determining the permeability state of the FO membrane includes determining whether the properties satisfy one or more criteria for an FO membrane having an acceptable permeability state, where the permeability state may be determined based on the properties of the FO membrane having an acceptable permeability state.

[0015] According to some embodiments, determining includes determining that the FO membrane has an acceptable permeability condition if the characteristic is within or at a predetermined interval that defines an FO membrane having an acceptable permeability condition, or determining that the FO membrane has a permeability error otherwise. Thus, the permeability condition may be evaluated based on a comparison of the characteristic to the predetermined interval relative to a characteristic of an FO membrane having an acceptable permeability condition.

[0016] According to some embodiments, the method includes performing the method both for controlling the flow such that the TMP is maintained positive and for controlling the TMP is maintained negative, and determining further includes, in each case, determining the permeability state of the FO membrane based on characteristics indicative of the controlled flow, where it is ensured that leaks causing only unidirectional flow are found.

[0017] According to a second aspect, which may be combined with any other aspect and its embodiments, the present disclosure relates to a controller for determining a permeability state of a forward osmosis (FO) membrane of a FO device in a dialysate generator. The FO membrane separates a feed side and a draw side of the FO device. The FO device comprises a feed inlet port and a feed outlet port in fluid communication with the feed side, and a draw inlet port and a draw outlet port in fluid communication with the draw side. The controller comprises a feed pump configured to provide a flow of pure water to the feed side, and a draw pump configured to provide a flow of pure water to the draw side. The controller further comprises one or more valves configured to control outflow from the feed side and the draw side, and one or more pressure sensors configured to sense a pressure indicative of a transmembrane pressure (TMP) between the feed side and the draw side. The controller is configured to monitor the one or more pressures indicative of the TMP. The controller is further configured to stop flow through one of the ports and control flow to one of the feed side and the draw side having the stopped flow based on the one or more pressures such that the TMP is maintained constant and at a non-zero magnitude. The controller is further configured to assess a permeability state of the FO membrane based on a characteristic indicative of the controlled flow.

[0018] According to some embodiments, the controller is configured to perform the methods according to any one of the embodiments described herein, either alone or in combination.

[0019] According to a third aspect, which may be combined with any other aspect and embodiments thereof, the present disclosure relates to a solution generator for generating a dialysis solution. The apparatus comprises a forward osmosis device comprising a FO membrane separating a feed side from a draw side of the FO device. The apparatus further comprises a controller according to the second aspect, and optionally any embodiment thereof.

[0020] According to a fourth aspect, the present disclosure relates to a computer program comprising instructions for causing a control device according to the second aspect to carry out a method according to the first aspect.

[0021] According to a fifth aspect, the present disclosure relates to a computer readable medium having stored thereon the computer program of the fourth aspect. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram of a FO device according to some embodiments of the present disclosure. [Diagram 2] FIG. 2 illustrates an example of a dialysate generating device according to some embodiments of the present disclosure. [Diagram 3] FIG. 3 shows a simplified portion of the dialysate generating apparatus of FIG. [Figure 4] 4A-4D are schematic diagrams of the FO device of FIG. 1 when flow through different ports is stopped and flow is restricted to the side of the stopped port. [Diagram 5] FIG. 5 illustrates a method for determining the permeability state of a FO membrane of a FO device according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] In the following description, a method for determining the permeability state of an FO membrane is described. The FO membrane is used in an FO device of a dialysate generator to generate dialysate, which is then used to generate dialysate that may be used in PD, HD, CRRT, or any other dialysis therapy that uses dialysate as a treatment or substitution fluid (e.g., to dilute blood after filtration).

[0024] In particular, FO membranes are used to extract water from patient effluent, tap water, or other water sources into a dialysis concentrate to produce dialysate. FO membranes can be compromised in permeability due to, for example, manufacturing errors, fouling, or wear. The compromised permeability can be due to leakage (solute transfer) or reduced water permeability. Undetected integrity problems can alter the composition of the produced dialysate by allowing transport of components other than water across the FO membrane. For example, leakage can allow transport of microorganisms from the feed side (effluent or tap water) to the draw side (mixed side), increasing the risk of peritonitis, for example, in PD. Furthermore, leakage can allow transport of solutes (electrolytes, glucose, urea, etc.) from the feed side (effluent or tap water) to the draw side (mixed side), thereby altering the composition of the produced dialysate. Degradation of water permeability can result in fewer water molecules being transported through the intended water channels in the FO membrane, preventing complete dilution of the concentrate.

[0025] Based on selectively stopping and controlling the flow to and / or from the FO device in a manner that maintains the transmembrane pressure (TMP) on the FO membrane constant as described in this disclosure, it has been found that it is possible to detect leaks and / or deterioration of permeability after the FO membrane is installed in the dialysate generator. To determine the permeability state of the FO membrane, the indicative characteristics of the resulting flow to maintain the TMP constant are investigated. The liquid flowing on the feed side and the draw side is pure water, therefore, has the same osmotic pressure and does not create any osmotic pressure difference between the two sides. Thereby, only the permeability is investigated. To detect leaks that allow only one-way movement, tests for leaks both from the feed side to the draw side and on the feed side to the draw side can be performed. Determining the permeability state here means determining whether the FO membrane has an acceptable permeability state or a permeability error, the permeability error being caused by a leak and / or a permeability deterioration.

[0026] In general, water transport through the intended water channel is driven by a solute concentration difference, e.g., between the feed side and the draw side. Solute movement (caused by leakage) is driven by the TMP, e.g., the pressure difference between the feed side and the draw side. However, transport through the intended water channel can also be driven by the TMP.

[0027] In some embodiments, the evaluation relies on the use of hardware already present in the device and concentrates typically used to generate dialysate. For example, a pressure sensor is already present to sense the pressure on the feed side. Pure water used in the method is already present to generate the dialysate.

[0028] Pure water is typically of water for injection (WFI) or water for dialysis (WFD) quality. WFI has a maximum of 500 ppg total organic carbon (TOC), a conductivity of less than 1.3 μS / cm at 25° C., and less than 0.25 EU / ml bacterial endotoxins. WFD has less than 100 CFU / ml colony forming units (CFU) and less than 0.25 EU / mL endotoxin units.

[0029] In the following, embodiments of the present disclosure will be described with reference to Figures 1 to 4. Figure 1 is a schematic diagram of a single FO device 2 according to some embodiments. The FO device 2 comprises a feed side 2a and a draw side 2b separated by a FO membrane 2c. The sides may also be referred to as compartments or chambers. In use, the FO membrane 2c separates the solution on the feed side 2a (called the feed solution) from the solution on the draw side 2b (called the draw solution). When producing a dialysate, there is an osmotic pressure difference between the fluids, and the draw solution on the draw side "draws" pure water from the feed solution on the feed side. Thus, water is extracted from the feed solution on the feed side 2a to the draw solution on the draw side 2b. As a result, in the FO process, the feed solution is dehydrated and the draw solution is diluted in the FO apparatus 2. The FO membrane 2c is designed to be more or less selective for osmotic water molecules, which allows the FO membrane 2c to separate water from all other contaminants. Thus, the FO membrane 2c is a water-permeable membrane. The FO membrane 2c typically has a pore size in the nanometer (nm) range, for example, 0.5 to 5 nm or less, depending on the solutes intended to be blocked. The FO device 2 typically includes a feed side 2a, a draw side 2b, and a cartridge that encloses the FO membrane 2c. The shape of the FO membrane 2c can be a flat sheet or a tubular or hollow fiber. The feed side 2a has an inlet port E through which the feed solution enters the feed side 2a. in and an outlet port E through which the feed solution is delivered from the feed side 2a. out The draw side 2b has an inlet port L through which the draw solution enters the draw side 2b. in and the outlet port L through which the draw solution is delivered from the draw side 2b. out The liquids on both sides typically flow countercurrently, but may alternatively flow cocurrently. The flow may be continuous. A suitable FO device for the FO device 2 is, for example, the Aquaporin TM , AsahiKASEI TM , Berghof TM , C.S.M. TM , FTSH2O TM , Koch Membrane SystemsTM , Porifera TM , Toyoboshi TM and Toray TM may be provided by

[0030] To generate the dialysis solution, the feed solution is, for example, the drain from a previous or current dialysis treatment or water. The draw solution is, for example, the dialysis concentrate, and water extracted from the feed solution dilutes the dialysis concentrate to a dialysis solution, which may also be called "diluted dialysis concentrate", "intermediate dialysis solution" or simply "dialysis solution". The dialysis concentrate is, for example, a concentrate that includes at least one of the following: NaCl, KCl, CaCl2, MgCl2, HAc, glucose, lactate, and bicarbonate. For example, the dialysis concentrate may include NaCl, CaCl2, MgCl2, and Na-lactate. To determine the permeability state of the FO membrane 2c, the feed solution and the draw solution are pure water.

[0031] FIG. 2 illustrates a dialysate generating apparatus 1 (hereinafter "apparatus 1") according to some embodiments of the present disclosure. Apparatus 1 includes a FO device 2 as described with reference to FIG. 1. Apparatus 1 also includes a flow path 20 including a number of liquid lines 20a-20n, hereinafter referred to as "lines". Apparatus 1 further includes a controller 30. Controller 30 includes a feed pump 3, a draw pump 5, and a diluent concentrate pump 6. The pumps are, for example, volumetric pumps (such as a piston pump) or non-volumetric pumps (e.g., a gear pump) with flow feedback from a flow sensor (not shown). Feed pump 3 is connected to an inlet connector P i The feed pump 3 is configured to pump effluent from a patient connected to the effluent container 35. The feed pump 3 is connected to the effluent container 35 or the inlet connector P iThe device 1 is configured to provide a flow of dialysis concentrate from the first side 2a to the first side 2a and from the first side 2a to a drain (not shown). The draw pump 5 is configured to provide a flow of dialysis concentrate from the dialysis concentrate container 31 to the second side 2b and further to pump the solution produced on the second side 2b to the dilute concentrate container 32. The pure water container 33 contains pure water. The liquid container 34 contains an osmotic agent or buffer solution, for example a glucose solution or a bicarbonate solution. The device 1 also comprises a conductivity sensor 7 configured to sense the conductivity of the solution produced from the second side 2b. The conductivity sensor 7 is typically configured to sense a conductivity in the range of 0.1 to 40 mS / cm. The conductivity sensor 7 may also include a temperature sensor (not shown) for compensating the sensed conductivity value. The device 1 further comprises one or more pressure sensors configured to sense a pressure indicative of the TMP of the FO device 2. For example, the device 1 comprises a first pressure sensor 8a arranged to sense the pressure of the feed side 2a. The device 1 may also comprise a second pressure sensor 8b arranged to sense the pressure of the draw side 2b. However, the device 1 may include additional pressure sensors for sensing pressures indicative of the TMP or other pressure sensors used to generate the dialysate. The diluent concentrate pump 6 is configured to provide a flow of liquid in the main line 20f. The controller 30 also comprises a valve arrangement 10 comprising a number of valves 10a-10p. In general, the valves connected to the lines can be configured to be open, where the flow of liquid in the line is permitted, and closed, where the flow of liquid in the line is stopped. The valves may be, for example, on / off valves, with an on state defining a state when the flow of liquid in the line is permitted and an off state defining a state when the flow of liquid in the line is stopped. The controller 30 further comprises a control unit 50 comprising at least one memory and at least one processor. The control device 30 is configured to control, via the control unit 50, the valves of the pump and valve arrangement 10 and the function of the mixing unit 9 to perform a number of different processes, such as diluting the dialysis concentrate into dialysis solution, supplying dialysis solution, and performing a cleaning process or a priming process.The controller 30 is also configured to receive a conductivity measurement from the conductivity sensor 7. The controller 30 is further configured to receive a pressure measurement from one or more pressure sensors, including first and second pressure sensors 8a, 8b. The controller 30 is further configured to determine a TMP of the FO device 2 based on the pressure measurements from the one or more pressure sensors. For example, the controller 30 may determine a hydrostatic pressure P at the feed side 2a. feed From the hydrostatic pressure P at the draw side 2b draw (TMP=ΔP=P feed -P draw 5. The control device 30 is further configured to determine a state of permeability of the FO membrane 2c in the device 1, defined by the method shown in FIG. 5. To that end, the at least one memory includes computer instructions for determining the state of permeability of the FO membrane 2c. When the instructions are executed by the at least one processor, the control device 30 performs a method for determining the state of permeability of the FO membrane 2c, which will be described below. The method may be executed by the control device 30 and stored as a computer program including computer instructions on the at least one memory.

[0032] First, however, the device 1 of FIG. 2 will be described in more detail. In FIG. 2, the inlet connector P i and feed inlet port E in A first effluent inlet line 20a is connected to an inlet connector P i and the feed inlet port E of the first side 2a in The inlet connector P ican be connected, for example, to a catheter of a PD patient or to a drainage line of an HD or CRRT device. A first drainage inlet valve 10a is connected to the first drainage inlet line 20a. A second drainage inlet line 20b is arranged between the first drainage inlet line 20a and the drainage container 35 to connect the first drainage inlet line 20a and the drainage container 35. A feed pump 3 is arranged to provide a flow of drainage in the second drainage inlet line 20b. A second drainage inlet valve 10b is connected to the second drainage inlet line 20b. A third drainage inlet line 20c is arranged between the first drainage inlet line 20a and the second drainage inlet line 20b to connect the first drainage inlet line 20a and the second drainage inlet line 20b. A third drainage inlet valve 10c is connected to the third drainage inlet line 20c. A fourth effluent inlet valve 10d is connected to the first effluent inlet line 20a between the junction of the second effluent inlet line 20b and the third effluent inlet line 20c. The effluent is supplied to the inlet connector P by opening the first effluent inlet valve 10a and the second effluent inlet valve 10b, closing the third effluent inlet valve 10c and the fourth effluent inlet valve 10d, and i The effluent can be collected in the effluent container 35 by pumping the effluent from the effluent container 35 to the feed side 2a with the feed pump 3. The effluent can then be pumped with the feed pump 3 from the effluent container 35 to the feed side 2a by opening the second effluent inlet valve 10b and the fourth effluent inlet valve 10d and closing the first effluent inlet valve 10a, the third effluent inlet valve 10c and the second water valve 10p. Alternatively, the effluent can be pumped from the effluent container 35 to the feed side 2a by opening the first effluent inlet valve 10a and the third effluent inlet valve 10c and closing the second effluent inlet valve 10b, the fourth effluent inlet valve 10d and the second water valve 10p through the first effluent inlet line 20a, the second effluent inlet line 20b and the third effluent inlet line 20c to the inlet connector P. i The discharge may be pumped directly to the first side 2a by means of a feed pump 3 pumping the discharged liquid from the first side 2a.

[0033] The effluent outlet line 20d is connected to the feed outlet port E of the first side 2a. outand a drain (not shown), and a feed outlet port E of the first side 2a out The drain 10f is connected to the effluent outlet line 20d. Thus, the FO device 2 has a feed inlet port E in fluid communication with the feed side 2a. in and feed outlet port E out Equipped with.

[0034] Further, the dialysis concentrate container 31 and the draw inlet port L of the draw side 2b in A dialysis concentrate line 20e is connected between the electrolyte container 31 and the draw inlet port L of the draw side 2b to connect the electrolyte container 31 and the draw inlet port L of the draw side 2b. in 3. A draw pump 5 is arranged to provide a flow to the dialysis concentrate line 20e. A main line 20f is arranged between the dialysis concentrate line 20e and the mixing unit 9 and connects the dialysis concentrate line 20e and the mixing unit 9. The mixing unit 9 includes liquid mixing functions such as a main pump that controls the flow rate obtained in the line 20m located downstream of the mixing unit 9, a liquid pump that provides a flow of osmotic agent or buffer from the liquid container 34, a conductivity sensor, a heater and a mixing chamber (these features are not explicitly shown). The main line 20f is connected to the dialysis concentrate line 20e between the dialysis concentrate container 31 and the draw pump 5. A dilute dialysis concentrate line 20g is arranged between the dilute dialysis concentrate container 32 and the main line 20f to connect the dilute dialysis concentrate container 32 and the main line 20f. A conductivity sensor 7 is connected to the diluted dialysis concentrate line 20g for sensing the conductivity of the liquid in the diluted dialysis concentrate line 20g and therefore the conductivity of the liquid in the dialysis concentrate container 32. A diluted dialysis concentrate valve 10g is connected to the diluted dialysis concentrate line 20g. A draw outlet port L of the draw side 2b out A first connection line 20h is connected to the draw outlet port L of the draw side 2b to connect the diluted dialysis concentrate line 20g to the out and the diluted dialysis concentrate line 20g. A first valve 10h is connected to the first connecting line 20h. Thus, the FO device 2 has a draw inlet port L in fluid communication with the draw side 2b. inand draw outlet port L out The first main valve 10i is connected to the main line 20f between the connection point of the main line 20f and the dialysis concentrate line 20e and the connection point of the diluted dialysis concentrate line 20g and the main line 20f. The concentrate valve 10e is connected to the dialysis concentrate line 20e between the dialysis concentrate container 31 and the draw pump 5. The dialysis concentrate can be pumped from the dialysis concentrate container 31 through the draw side 2b to the diluted dialysis concentrate container 32 by pumping with the draw pump 5, opening the concentrate valve 10e and the first connecting valve 10h, and closing the diluted dialysis concentrate valve 10g and the first main valve 10i. At the same time, the effluent can be pumped to the feed side 2a. Pure water is extracted by osmotic pressure from the effluent of the feed side 2a to the dialysis concentrate of the draw side 2b. The dialysis concentrate is thus diluted to form an intermediate dialysis solution, which is collected in the diluted dialysis concentrate container 32. This procedure can be called a FO session. Thus, the FO device 2 is configured to be used in a FO session to dilute dialysis concentrate in the process of producing dialysate.

[0035] A liquid line 20i is disposed between the liquid container 34 and the mixing unit 9 to connect the liquid container 34 and the mixing unit 9. A second main valve 10k is connected to the main line 20f between the dilution concentrate pump 6 and the mixing section 9. A first water line 20n is disposed between the pure water container 33 and the mixing unit 9 to connect the pure water container 33 and the mixing unit 9. A first water valve 10n is connected to the first water line 20n. A second main valve 10k is connected to the main line 20f between the dilution concentrate pump 6 and the mixing section 9. A first water line 20n is connected to the first water valve 10n. A second main valve 10k is connected to the main line 20f between the dilution concentrate pump 6 and the mixing section 9 to connect the pure water container 33 and the mixing unit 9. o To connect the mixing unit 9 and the outlet connector P, an outlet line of 20 m is provided. o The outlet connector P o can be connected, for example, to the catheter of a PD patient or to the dialysate line of an HD or CRRT machine. An outlet valve 10m is arranged in the outlet line 20m.

[0036] To mix the dialysis fluid, the diluted dialysis concentrate solution in the diluted dialysis concentrate container 32 is pumped into the mixing unit 9 by opening the diluted dialysis concentrate valve 10g, the second main valve 10k and the outlet valve 10m and pumping with the diluted concentrate pump 6. At the same time, the osmotic agent or buffer is pumped from the liquid container 34 to the mixing unit 9 through the liquid line 20i by pumping with a liquid pump (not shown). Pure water flows into the mixing unit 9 through the first water line 20n. The main pump (not shown) provides the desired flow rate of the resulting dialysis fluid in the line 20m downstream of the mixing unit 9. The conductivity sensor (not shown) of the mixing unit 9 measures the conductivity of the dialysis fluid obtained from the mixing unit 9. The diluted concentrate pump 6 and the liquid pump are controlled at specific speeds to achieve the desired predetermined concentration of the resulting dialysis fluid based on the conductivity of the produced fluid, the conductivity of the diluted dialysis concentrate solution and the flow rate of the produced fluid. In the mixing unit 9, the diluted dialysis concentrate solution, the osmotic agent / buffer and the pure water are mixed and optionally heated in a mixing chamber to form a dialysis solution. The dialysis solution is then delivered via an outlet line 20m to the outlet connector P o , and delivered to the desired destination (eg, a storage container or a dialysis machine).

[0037] The second water line 20p is disposed between the first water line 20n and the third discharge liquid line 20c. Thus, the second water line 20p connects the first water line 20n and the third discharge liquid line 20c. The second water line 20p connects to the first water line 20n between the pure water container 33 and the first water valve 10n. The second water line 20p further connects to the third discharge liquid line 20c between the third discharge liquid inlet valve 10c and the second discharge liquid line 20b. The second water valve 10p is connected to the second water line 20p. The third water line 20j is disposed between the first water line 20n and the main liquid line 20f. Thus, the third water line 20j connects the first water line 20n and the main liquid line 20f. The third water valve 10j is connected to the third water line 20j. The third water line 20j is connected to the first water line 20n between the pure water container 33 and the first water valve 10n. The third water line 20j is further connected to the main line 20f between the dilution concentrate pump 6 and the first main valve 10i. Thus, the pure water can be passed from the pure water container 33 to the feed side 2a and from the feed side 2a to the drain (not shown) via the second liquid line 20p, the third drain line 20c, the second drain line 20b and the first drain line 20a by opening the second water valve 10p and the fourth drain inlet valve 10d, closing the second drain inlet valve 10b, the first drain inlet valve 10a and the third drain inlet valve 10c, and pumping the pure water with the feed pump 3. Pure water can be passed simultaneously from the pure water container 33 to the draw side 2b and from the draw side 2b to the diluted dialysis concentrate container 32 via the third water line 20j, the main liquid line 20f, the dialysis concentrate line 20e, the connection line 20h and the diluted dialysis concentrate line 20g. Then the third water valve 10j, the first main valve 10i and the first connection valve 10h are opened and the concentrate valve 10e and the diluted dialysis concentrate valve 10g are closed. The pure water can then be pumped to the drain via the drain connection (not shown).

[0038] FIG. 3 shows a simplified version of a portion of the dialysate generating apparatus of FIG. 2, with some relevant parts (excluding the control unit 50) for carrying out the following method.

[0039] A method for determining the permeability state of an FO membrane will now be described with reference to the schematic diagrams of the FO apparatus in Figs. 4A-4D and the flow chart in Fig. 5. Figs. 4-4D show the FO device of Fig. 1 when the flow through different ports is stopped and the flow to the side of the stopped port is controlled. The ports through which the flow is stopped are shown with ports filled in black. The schematic diagrams show which flows are stopped in various embodiments of the method described below. The method is for example implemented by the control unit 50 of Fig. 2. The FO membrane is for example the FO membrane 2c of the FO device 2 in the apparatus 1 of Figs. 2 or 3. However, the method may be used in other apparatuses comprising an FO membrane for determining its permeability state. The method comprises providing S1 a flow of pure water to the feed side 2a. In other words, the method comprises passing pure water through the feed side 2a. Thus, the pure water is passed through the feed inlet port E. in Feed inlet port E is provided in From the first side 2a to the exit port E out 2, the supply S1 uses a feed pump 3 to pump pure water from a pure water container 33 to an inlet port E of the first side 2a. in and opening and closing appropriate valves. The operating point is typically well defined and thus providing S1 involves providing pure water at a constant, relatively high flow rate to the feed side 2a. In the case of PD, the flow rate provided by the feed pump 3 is, for example, 50 to 200 ml / min. In the case of HD, the flow rate provided by the feed pump 3 is, for example, 200 to 600 ml / min. The flow rate is either directly controlled in the feed pump 3 or is measured by a flow sensor (not shown) and used as feedback for flow rate control in the feed pump 3. The hydrostatic pressure P feedmay simply be the result of providing a certain flow rate, as described above. Alternatively, providing S1 may include providing the pure water with a hydrostatic pressure at the feed side 2a that is at or near atmospheric pressure, or different (higher or lower) than the hydrostatic pressure at the draw side 2b. The pressure is controlled, for example, using the feed pump 3 and / or the drain valve 10f. The pressure on the feed side may be measured using the first pressure sensor 8a and used as feedback for pressure control by the feed pump 3 and / or the drain valve 10f. The method also includes providing S2 a flow of pure water to the draw side 2b. Thus, the draw solution and the feed solution have the same osmotic pressure. As the flow is pure water, the flow has a very low osmotic pressure, much below 1 bar (14.5 psig). Providing S2 a flow of pure water to the draw side 2b may be performed while providing S1 a flow of pure water to the feed side 2a. In other words, the method includes passing pure water to the second side 2b. Therefore, pure water is drawn through the inlet port L in Draw inlet port L is provided in From the second side 2b through the draw outlet port L out 2, the pure water flows from the pure water container 33 to the draw inlet port L on the second side 2b using the draw pump 5. The operating point of the apparatus 1 is typically well defined while providing S2 a flow of pure water. For example, the operating point includes providing S2 a flow of pure water at a constant flow rate of the pure water provided to the draw side 2b. The flow rate provided by the draw pump 5 is typically the same as the flow rate used for the feed solution. In the example of FIG. 2, providing S2 is performed by using the draw pump 5 to pump pure water from the pure water container 33 to the draw inlet port L on the second side 2b. in This includes pumping pure water up to the draw side 2b. drawis typically at or near atmospheric pressure, e.g., 1013 hPa (about 1 bar, 14.5 psig). This is because the draw side 2b and the dilute concentrate vessel 32 are fluidly connected, meaning that they are also at approximately the same pressure, except for the residual hydrostatic pressure difference. Providing a flow of pure water to the draw side and the feed side S1, S2 is done at a flow rate that ensures that all solutes that may generate osmotic pressure are washed out, in order to have a good starting point for the following method steps, where the osmotic pressures on both sides (feed side and draw side) are equal. Thus, the osmotic pressure difference between the two sides is zero. Therefore, at this stage, it is not necessary to apply a constant hydrostatic pressure on either side.

[0040] After flow in both the feed side 2a and the draw side 2b is provided, the method steps may be repeatedly performed to determine the state of permeability from the feed side 2a to the draw side 2b or from the draw side 2b to the feed side 2a. For example, leaks in either direction may be detected. In general, by stopping flow through a port from one side, either the feed side 2a or the draw side 2b, and controlling flow to or from the same side with the stopped flow, and maintaining a constant TMP through the other port, the controlled inflow or outflow reflects the flow through the FO membrane 2c. Thus, in all embodiments, the method includes monitoring S3 one or more pressures indicative of the transmembrane pressure (TMP) between the feed side 2a and the draw side 2b. The TMP is calculated as ΔP=P feed -P draw The hydrostatic pressure at the draw side 2b can be kept near atmospheric pressure if the draw side is connected to a dilute concentrate vessel 32 or other vessels or liquid lines that are also connected to atmospheric pressure. Here, TMP is the hydrostatic pressure P feedThe monitoring S3 may thus include measuring the pressure of the feed side 2a, for example using a first pressure sensor 8a, and using the measured pressure of the feed side 2a as an estimate of the TMP. Alternatively, the monitoring S3 may include measuring the pressure of the feed side 2a (using a first pressure sensor 8a), measuring the pressure of the draw side 2b (using a second pressure sensor 8b), and using the measured pressure of the draw side 2b as an estimate of the TMP. feed -P draw and determining TMP as

[0041] Next, with reference to Figures 4A, 4B and 5, testing of water permeability by stopping and controlling the flow to / from the feed side 2a will be described. To carry out such a test, in a first embodiment, the method comprises: out Stopping the flow through the feed outlet port E out Stopping the flow through the filled outlet port E out In the example of FIGS. 2 and 3, the feed outlet port E is closed by closing the drain valve 10f. out In one embodiment, flow through the other ports is permitted, as shown by the lack of fill in FIG. 4A. Thus, the draw outlet port L out and draw inlet port L in The flow through the draw inlet port L is not stopped and typically remains at the same flow rate and pressure as during step S2. In an alternative embodiment, the flow through the draw inlet port L is stopped, for example, by stopping the pumping by the draw pump 5. in The flow through the feed inlet port E is also stopped based on the monitored pressure or pressures such that the TMP is maintained at a constant and non-zero magnitude. inThe method further includes controlling S5 the flow via either the inflow or outflow to the FO membrane 2c. The controlling S5 is performed, for example, by using the feed pump 3. Keeping the TMP constant means controlling the TMP so that a given TMP value is achieved by controlling the inflow or outflow to the feed side 2a. Having a non-zero TMP means that the hydrostatic pressures at the sides 2a, 2b are different and there is a TMP driving the water transport. The TMP can be either positive or negative. Depending on the positive or negative sign of the given TMP to which the TMP is to be controlled, either the inflow or outflow is controlled to keep the TMP constant at the given TMP. Since it is only the TMP that drives the water transport through the FO membrane 2c, the water transport can be made to proceed in different directions by changing the positive or negative sign of the TMP. Thus, if the TMP is positive, P feed P draw and the TMP is driving the transport of water from the feed side 2a to the draw side 2b. The predetermined TMP is, for example, 2 to 5 bar (29 to 72.5 psig), for example, 4 bar (58 psig). The only way that the feed side water can leave the feed side 2a is through the intended water channels in the FO membrane 2c, via leakage, and / or via water permeation through the FO membrane 2c to the draw side 2b. The pressure in the feed side 2a is then reduced and water is pumped into the feed side 2a to keep the TMP constant at the predetermined TMP. Thus, in some embodiments, the method includes adjusting the feed inlet port E based on one or more monitored pressures such that the TMP is maintained at a positive predetermined TMP. in Alternatively, TMP may be negative, which is equivalent to controlling the flow of P draw P feed, which means that the TMP is greater than the draw side 2b, driving the transport of water from the draw side 2b to the feed side 2a. The predetermined TMP is, for example, -0.5 to -2 bar (-7.3 to -29 psig), for example -1 bar (-14.5 psig). The water in the draw side 2a can exit from the draw side 2b to the feed side 2b through the FO membrane 2c via leakage and / or via water permeation through the intended water channels in the FO membrane 2c. However, the pressure in the feed side 2a then increases, and water is pumped out of the feed side 2a to keep the TMP constant. Thus, in some embodiments, the method comprises: increasing the feed inlet port E based on one or more monitored pressures such that the TMP is maintained at the negative predetermined TMP. in The TMP value used for the control is, for example, a predetermined TMP determined based on experiments and / or calculations. The predetermined TMP may also be determined by the manufacturer of the FO membrane as a specified maximum pressure difference between the feed side and the draw side of the FO membrane. draw typically remains at about atmospheric pressure. By controlling the inflow or outflow to feed side 2a to keep the TMP constant, the flow to or from feed side 2a reflects the net flow through leaks in the FO membrane 2c and / or water permeation through the membrane.

[0042] In one embodiment, the feed outlet port E out Stopping the flow through S4 and feed inlet port E in After a short period of stabilization, the feed inlet port E inThe inflow or outflow to the feed side 2a reveals whether there is a leak and / or a change in the membrane permeability. The inflow or outflow can be determined based on a characteristic indicative of the controlled inflow or outflow, respectively. According to some embodiments, the characteristic is the speed of the feed pump 3 or the power provided to the feed pump 3. In some embodiments, the characteristic is the flow rate of the controlled flow provided by the feed pump 2a. Such a characteristic is readily available as a control parameter in the control device 50 or other parameters used for the evaluation. The flow rate of the controlled flow may alternatively be measured using a flow sensor (not shown). The transport of water from the feed side 2a to the draw side 2b is determined by the draw inlet port L (provided with the draw pump 5). in Compared to the flow through the draw outlet port L out This is detected as an increase in flow through the draw outlet port L out The flow rate of the liquid from the draw inlet port L in The difference between the flow rate of liquid to the draw inlet port L and the flow rate of liquid to the draw inlet port L is, for example, equal to the controlled flow rate. in The same indication applies when the flow is stopped through the feed inlet port E, but there is no incoming flow at the draw side 2b. Therefore, the outflow from the draw side 2b is through the feed inlet port E. in In some embodiments, the characteristic is a flow rate out of draw side 2b. The method then includes measuring the outflow from draw side 2b with a flow sensor (not shown). Thus, the method may include monitoring S6 the characteristic indicative of the controlled flow.

[0043] The permeability of the FO membrane may then be determined based on one or more characteristics. Thus, the method further includes determining S7 a permeability state of the FO membrane based on the characteristic indicative of the controlled flow. The permeability state may be determined based on how well the characteristic meets permeability criteria for an FO membrane having an acceptable permeability state. Thus, in some embodiments, determining S7 includes determining whether the characteristic meets one or more criteria for an FO membrane having an acceptable permeability state. For example, the method may include evaluating a characteristic such as a slope or magnitude. For an FO membrane having an acceptable permeability state, the feed inlet port E in An expected flow rate of inflow or outflow from the FO membrane can be determined, which keeps the TMP constant at a given TMP and at the same operating conditions. An acceptable flow rate of an FO membrane having an acceptable permeability state can then be established as being within or in an interval around this determined flow rate. A controlled flow rate within or at the interval indicates that the FO membrane has an acceptable permeability state.

[0044] A controlled flow rate outside of an interval that is too high is indicative of a leak, and a flow rate outside of an interval that is too low indicates low permeability. The same is true for the flow from the draw side 2b. Thus, in some embodiments, the method includes determining that the FO membrane has an acceptable permeability state upon determining that the characteristic is within or at a predetermined interval that defines an FO membrane having an acceptable permeability state, or determining that the FO membrane has a permeability error otherwise. Thus, if the characteristic is within or at an interval that is acceptable for the characteristic, the method includes determining that the FO membrane has an acceptable permeability state and therefore has no permeability error. If the characteristic is outside the acceptable interval, the method includes determining that the FO membrane has a permeability error. Alternatively, the characteristic may be compared to an expected predetermined value of the same characteristic determined with an FO membrane having an acceptable permeability state under the same operating conditions. The results of the comparison reveal whether the FO membrane has an acceptable permeability state or not. Having the same operating conditions includes the same hydrostatic pressure and the same predetermined TMP. It may also include the same flow rate. The predetermined value to be assumed may be determined experimentally or may be determined based on calculations and / or assumptions.

[0045] Next, a second embodiment of the test for permeability by stopping and controlling the flow to / from the feed side 2a will be described. The first and second embodiments are almost identical, except for the features described below. To perform the test for permeability by stopping and controlling the flow to / from the feed side 2a according to the second embodiment, the method comprises: in Stopping the flow through the feed inlet port E in Stopping the flow through the filled inlet port E in 2 and 3, the feed pump 3 is stopped and the third and fourth effluent inlet valves 10c and 10d are closed to reduce the flow of the feed inlet port E. inFlow through the draw outlet port L can be stopped. Flow through the other ports is permitted, as shown by the lack of fill in FIG. 4B. Thus, the draw outlet port L out and draw inlet port L in In an alternative embodiment, the flow through the draw inlet port L in The flow through the feed outlet port E is also stopped based on the monitored pressure or pressures such that the TMP is maintained at a constant and non-zero magnitude. out The method further includes controlling S5 the flow via either the inflow or outflow to the feed inlet port E. The controlling S5 is performed, for example, using a drain pump (not shown) disposed in the effluent outlet line 20d. The drain pump may be used to maintain a certain hydrostatic pressure at the feed side 2a during the production of the dialysate, but may alternatively be used to pump liquid into the feed side 2a. The liquid is then pumped from a drain container (not shown) connected to the effluent outlet line 20d. The feed inlet port E in Stopping the flow through S4 and the feed outlet port E out After a short period of stabilization, the feed outlet port E out The inflow or outflow to the feed side 2a reveals whether there is a permeability error. The flow can be determined based on an indicative characteristic of the controlled flow. According to some embodiments, the characteristic is the speed of the drain pump or the power provided to the drain pump. In some embodiments, the characteristic is the controlled inflow or outflow flow rate provided by the drain pump. The remaining features are the same as described for the first embodiment of the method for testing permeability by stopping and controlling the flow to / from the feed side 2a.

[0046] Next, testing for permeability by stopping and controlling the flow to / from the draw side 2b is described. All the descriptions for testing for permeability by stopping and controlling the flow to / from the feed side 2a are also applicable to testing for permeability by stopping and controlling the flow to the draw side 2b, except for the variations indicated below. To perform testing for permeability by stopping and controlling the flow to / from the draw side 2b according to the third embodiment, the method includes: out Stopping the flow through the draw outlet port L out Stopping the flow through the filled outlet port L out In the example of FIGS. 2 and 3, the first connecting valve 10h is closed to close the draw outlet port L out Flow through the feed outlet port E can be stopped. Flow through the other ports is permitted, as shown by the lack of fill in FIG. 4C. Thus, the feed outlet port E out and feed inlet port E in The flow through the feed inlet port E is not stopped and typically remains at the same flow rate and pressure as during step S1. In an alternative embodiment, the flow through the feed inlet port E is stopped, for example by stopping the feed pump 3 and closing the third and fourth effluent inlet valves 10c and 10d. in The flow through the draw inlet port L is also stopped based on the monitored pressure or pressures such that the TMP is maintained at a constant and non-zero magnitude. inThe method further includes controlling S5 the flow via either inflow or outflow to the draw side 2b. The controlling S5 is performed, for example, with a draw pump 5. Keeping the TMP constant means controlling the TMP such that a predetermined TMP value is achieved by controlling the inflow or outflow to the draw side 2b. The only way for the pure water in the draw side 2b to exit from the draw side 2b to the feed side 2a is through a leak in the FO membrane 2c and / or via water permeation through the intended water channels in the FO membrane 2c. To allow any water transport from the draw side 2b to the feed side 2a through a leak, the TMP must be negative, and therefore the hydrostatic pressure P draw is the hydrostatic pressure P feed is greater than TMP=P feed -P draw The predetermined TMP is, for example, -0.5 to -2 bar (-7.3 to -29 psig), for example, -1 bar (-14.5 psig). feed Typically, P remains at about atmospheric pressure. For example, feed side 2a may be open for draining (and thus at atmospheric pressure) or P feed may be controlled to atmospheric pressure or any other desired pressure. When liquid is transported from the draw side 2b to the feed side 2a and is not allowed to flow into the draw side 2b, P draw Therefore, in some embodiments, the method further comprises adjusting the draw inlet port L based on one or more monitored pressures such that the TMP is maintained at a negative predetermined TMP. in Alternatively, TMP may be positive, which includes controlling the flow of P feed P draw, meaning that the TMP is driving the transport of water from the feed side 2a to the draw side 2b. The predetermined TMP is, for example, 2 to 5 bar (29 to 72.5 psig), for example, 4 bar (58 psig). The water in the feed side 2a can exit from the feed side 2a to the draw side 2a through the FO membrane 2c via leakage and / or via water permeation through the intended water channels in the FO membrane 2c. However, to maintain the TMP constant, the pressure in the draw side 2b must increase and water must be pumped out of the draw side 2b. Thus, in some embodiments, the method comprises adjusting the draw inlet port L based on one or more monitored pressures such that the TMP is maintained at a positive predetermined TMP. in By controlling the inflow or outflow to the draw side 2b to keep the TMP constant, the flow to the draw side 2b or from the feed side 2a reflects the net flow through the FO membrane 2c leaks and / or water permeation of the membrane.

[0047] In one embodiment, the draw outlet port L out Stop the flow through S4 and the draw inlet port L in After a short period of stabilization, the inlet port L in The inflow or outflow to the draw pump 5 reveals whether there is a leak and / or a change in the membrane permeability. The inflow or outflow can be determined based on an indicative characteristic of the controlled flow. According to some embodiments, the characteristic is the speed of the draw pump 5 or the power provided to the draw pump 5. According to some embodiments, the characteristic is the controlled flow rate provided by the draw pump 5. Such a characteristic is readily available as a control parameter stored in the control device 50 or other parameters used for the evaluation. The flow rate of the controlled flow may alternatively be measured using a flow sensor (not shown). The transport of water from the draw side 2b to the feed side 2a is performed by the feed inlet port E (provided with the feed pump 3). in Compared to the flow through the feed outlet port E outTherefore, the outflow from the feed side 2a is detected as an increase in the flow through the draw inlet port L. in More specifically, the feed outlet port E out The flow rate of the liquid from the feed inlet port E in The difference between the flow rate of liquid to the feed inlet port E and the flow rate of liquid to the feed inlet port E is, for example, equal to the controlled flow rate. in The same applies when the flow through the draw inlet port L is stopped, but there is no incoming flow at the feed side 2a. Therefore, the outflow from the feed side 2a is through the draw inlet port L. in In some embodiments, the characteristic is a flow rate out of the feed side 2a. The method then includes measuring the outflow from the feed side 2a with a flow sensor (not shown). The method may thus include monitoring S6 the characteristic indicative of the controlled flow. Monitoring S6 and determining S7 may be performed as described above, with the following modifications: For a FO membrane having an acceptable permeability state, the draw inlet port L in The expected flow rate of inflow or outflow from the feed side 2a can be determined, which keeps the TMP constant at the given TMP and at the same operating conditions. The acceptable flow rate of the FO membrane having an acceptable permeability state can then be established as being within or in an interval around this determined flow rate. A controlled flow rate within or at the interval indicates that the FO membrane has an acceptable permeability state. A controlled flow rate outside the interval that is too high is an indication of a leak, and a flow rate outside the interval that is too low indicates low permeability. The same is true for the flow from the feed side 2a.

[0048] Next, a fourth embodiment for testing water permeability by stopping and controlling the flow to / from the draw side 2b will be described. The third and fourth embodiments are almost the same, except for the features described below. To test water permeability by stopping and controlling the flow to / from the draw side 2b according to the fourth embodiment, the method includes: inStopping the flow through the draw inlet port L in Stopping flow through filled inlet port L in In the example of FIG. 2 and FIG. 3, by stopping the draw pump 5, the draw inlet port L in Flow through the feed outlet port E can be stopped. Flow through the other ports is permitted, as shown by the lack of fill in FIG. 4D. Thus, the feed outlet port E out and feed inlet port E in In an alternative embodiment, the flow through the feed inlet port E in The flow through the draw outlet port L is also stopped based on the monitored pressure or pressures such that the TMP is maintained at a constant and non-zero magnitude. out The method further includes controlling S5 the flow via either the inflow or outflow to the dilute concentrate pump 6. The controlling S5 is performed, for example, using the dilute concentrate pump 6 and another valve (not shown) connected to the dilute dialysis concentrate line 20g disposed between the dilute dialysis concentrate container 32 and the connection point of the first connection line 20h, the connection point of the first connection line 20h being closed.

[0049] In one embodiment, the draw inlet port L in Stop the flow through S4 and the draw outlet port L out After a short period of stabilization, the flow through the draw outlet port L is controlled S5. outThe inflow or outflow to the feed side 2a reveals whether there is a permeability error from the feed side 2a to the draw side 2b. The flow can be determined based on an indicative characteristic of the controlled flow. According to some embodiments, the characteristic is the speed of the dilute concentrate pump 6 or the power provided to the dilute concentrate pump 6. In some embodiments, the characteristic is the flow rate of the controlled flow provided by the dilute concentrate pump 6. Such a characteristic is readily available as a control parameter in the controller 50 or other parameters used for the determination. The flow rate of the controlled flow may alternatively be measured using a flow sensor (not shown). The remaining features are the same as the third embodiment of the method for testing permeability by stopping and controlling the flow to / from the draw side 2b.

[0050] According to some embodiments, the method includes determining the permeability state by testing the permeability from the feed side 2a to the draw side 2b and by testing the permeability from the draw side 2b to the feed side 2a. Such a method may include performing the method for both positive and negative TMP, thereby performing a more thorough leak test. Thus, in some embodiments, the method includes performing the method for both controlling the flow S5 such that the TMP is maintained positive and such that the TMP is maintained negative, and determining S7 further includes determining the permeability state of the FO membrane based on the indicative characteristics of the controlled flow in each case. The method may be performed using any of the embodiments described herein having a positive TMP and a negative TMP, respectively.

[0051] The result of the determination may be communicated to a user via a user interface (not shown) of the controller 10 and / or an alarm may be activated if a permeability error is detected. The user may then take appropriate action, such as replacing the FO device, to remedy the permeability error.

[0052] The present disclosure also relates to a controller 10 for determining the permeability state of a FO membrane 2c of a forward osmosis (FO) device 2 in a dialysate generator 1. The controller 10 comprises a feed pump 3 configured to provide a flow of pure water to a feed side 2a. The controller 10 comprises a draw pump 5 configured to provide a flow of pure water to a draw side 2b. The controller 10 further comprises one or more valves 10 configured to control the flow through one or more ports, and one or more pressure sensors 8a, 8b configured to sense one or more pressures indicative of a transmembrane pressure difference (TMP) between the feed side 2a and the draw side 2b. The controller 10 is further configured to monitor the one or more pressures indicative of the transmembrane pressure difference (TMP). The controller 10 is also configured to stop the flow through one of the ports and control the flow to or from one of the stopped feed side 2a and the draw side 2b based on the one or more pressures, so that the TMP is maintained constant and non-zero. The controller 10 is further configured to determine a permeability state of the FO membrane based on the characteristic indicative of the controlled flow. According to some embodiments, the controller 10 is configured to perform a method according to any one of the embodiments described herein, alone or in combination with other embodiments or portions thereof.

[0053] While the present invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method for determining the permeability state of an FO membrane (2c) of a forward osmosis, FO, device (2) in a dialysate generator (1), said FO membrane (2c) separating a feed side (2a) and a draw side (2b) of said FO device (2), said FO device (2) having a feed inlet port (E) in fluid communication with said feed side (2a), ｉｎ ) and the feed outlet port (E ｏｕｔ ) and a draw inlet port (L) in fluid communication with the draw side (2b). ｉｎ ) and the draw outlet port (L ｏｕｔ ), said method comprising: Providing a flow of pure water to the feed side (2a) (S1); providing a flow of pure water to the draw side (2b) (S2); monitoring (S3) one or more pressures indicative of the transmembrane pressure, TMP, between the feed side (2a) and the draw side (2b); Stopping flow through one of the feed inlet port (E in ), the feed outlet port (E out ), the draw inlet port (L in ), and the draw outlet port (L out ) (S4); controlling (S5) flow to or from one of the feed side (2a) and the draw side (2b) having stopped flow based on the one or more monitored pressures such that the TMP is maintained at a constant and non-zero magnitude; and determining (S7) the state of permeability of the FO membrane based on a characteristic indicative of the controlled flow.

2. 2. The method of claim 1, comprising monitoring (S6) the characteristic indicative of the controlled flow.

3. 2. The method of claim 1, wherein controlling the flow (S5) comprises controlling the flow of a pump (3, 5).

4. 4. The method according to claim 3, wherein the characteristic is the speed of the pump or the power provided to the pump (3, 5).

5. 2. The method of claim 1, wherein the characteristic is a flow rate of the controlled flow into the one of the feed side (2a) or the draw side (2b) with flow stopped, or the characteristic is a flow rate of outflow from the other of the feed side (2a) and the draw side (2b).

6. 2. The method of claim 1, wherein determining (S7) the state of water permeability of the FO membrane comprises determining whether the characteristic meets one or more criteria for an FO membrane having an acceptable water permeability state.

7. 7. The method of claim 6, comprising determining that the FO membrane has an acceptable permeability condition if the characteristic is determined to be within or at a predetermined interval defining an FO membrane having an acceptable permeability condition, or determining that the FO membrane otherwise has a permeability error.

8. 2. The method of claim 1, comprising performing the method for both controlling (S5) the flow so that the TMP is maintained positive and so that the TMP is maintained negative, and wherein the determining (S7) further comprises determining the state of permeability of the FO membrane based on the characteristic indicative of the controlled flow in each case.

9. 2. The method of claim 1, wherein controlling the flow (S5) comprises controlling the flow such that the TMP maintains a predetermined constant TMP.

10. A control device (10) for determining the permeability state of an FO membrane (2c) of a forward osmosis, FO, device (2) in a dialysate generator (1), said FO membrane (2c) separating a feed side (2a) and a draw side (2b) of said FO device (2), said FO device (2) having a feed inlet port (E) in fluid communication with said feed side (2a). ｉｎ ) and the feed outlet port (E ｏｕｔ ) and a draw inlet port (L) in fluid communication with the draw side (2b). ｉｎ ) and the draw outlet port (L ｏｕｔ ), and the control device (10) a feed pump (3) configured to provide a flow of pure water to the feed side (2a); a draw pump (5) configured to provide a flow of pure water to the draw side (2b); one or more valves (10) configured to control flow through one or more of the feed inlet port (E in ), the feed outlet port (E out ), the draw inlet port (L in ), and the draw outlet port (L out ); one or more pressure sensors (8a, 8b) configured to sense one or more pressures indicative of a transmembrane pressure, TMP, between the feed side (2a) and the draw side (2b); The control device (10) stopping flow through one of the feed inlet port (E in ), the feed outlet port (E out ), the draw inlet port (L in ), and the draw outlet port (L out ); monitoring one or more pressures indicative of said TMP; controlling flow to or from one of the feed side (2a) and the draw side (2b) having stopped flow based on the one or more pressures such that the TMP is maintained at a constant and non-zero magnitude; A control device configured to determine the state of permeability of the FO membrane based on a characteristic indicative of the controlled flow.

11. A control device (10) according to claim 10, configured to carry out the method according to any one of claims 2 to 9.

12. 11. A solution generator (1) for producing a dialysis solution, the solution generator (1) comprising a forward osmosis device (2) including a FO membrane (2c) separating a feed side (2a) and a draw side (2b) of the FO device (2), the solution generator further comprising a control device (10) according to claim 10.

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