Determining 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 more particularly 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, including hemodialysis (HD), peritoneal dialysis (PD), and continuous renal replacement therapy (CRRT). Typically, a dialysate is used in the treatment, which is either delivered pre-formed in a bag or generated 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 for reducing water consumption. FO membranes are typically designed to be more or less selective for water molecules, allowing 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 disclosed FO membrane is used to prepare dialysate. In one embodiment, the FO membrane is more or less selective for water molecules, allowing it 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 into the dialysis concentrate, thereby diluting the dialysis concentrate. The diluted dialysis concentrate is then used to produce dialysate. The disclosed system and method detect permeability problems and allow transport of components other than water across the FO membrane, thereby preventing changes in the composition of the produced dialysate.

[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, control devices and 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 the 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 stream of pure water to the feed side and providing a stream 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 flow through one of the ports to maintain the TMP at a constant, non-zero magnitude, and controlling 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. The method further includes determining the 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 an FO membrane. For example, by controlling a pump to maintain TMP, the flow provided by the pump reflects the flow of fluid transported between the two sides and 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 using 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 flow of a controlled flow into one of the feed side and the draw side with the flow stopped, or the property is a rate of flow of an 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 determined to be 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 can 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 to control the flow so that the TMP is maintained positive and to control the flow so that the TMP is maintained negative, and determining further includes, in each case, determining the permeability state of the FO membrane based on the characteristics indicative of the controlled flow, thereby ensuring that leaks that cause only unidirectional flow are found.

[0017] According to a second aspect, which can be combined with any other aspect and its embodiments, the present disclosure relates to a controller for determining the 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 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 controller includes 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 includes 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 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, so that the TMP is maintained at a constant and non-zero magnitude. The controller is further configured to assess the permeability state of the FO membrane based on the characteristic indicative of the controlled flow.

[0018] According to some embodiments, the controller is configured to perform the method 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 dialysate. 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 perform 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 explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram of a FO device according to some embodiments of the present disclosure. [Figure 2] FIG. 2 illustrates an example of a dialysate generator according to some embodiments of the present disclosure. [Figure 3] FIG. 3 shows a simplified portion of the dialysate generator 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. [Figure 5] FIG. 5 illustrates a method for determining the permeability state of the FO membrane of a FO device according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0023] The following description describes a method for determining the permeability state of an FO membrane. The FO membrane is used in an FO device in a dialysate generator to generate dialysate, which is then used to generate dialysate. The dialysate 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] Specifically, 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 become impaired in permeability due to, for example, manufacturing errors, fouling, or wear. Impaired permeability can be due to leaks (solute transport) or reduced hydraulic conductivity. 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, leaks 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, leaks 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. Deterioration in hydraulic conductivity can result in fewer water molecules being transported through the intended water channels in the FO membrane, preventing complete dilution of the concentrate.

[0025] As described herein, it has been discovered that by selectively stopping and controlling flow into and / or out of an FO device in a manner that maintains a constant transmembrane pressure (TMP) across the FO membrane, it is possible to detect leaks and / or deterioration in permeability after the FO membrane is installed in a dialysate generator. To determine the permeability state of the FO membrane, the resulting flow characteristics for maintaining a constant TMP are investigated. The liquid flowing on the feed side and the draw side is pure water, therefore, has the same osmotic pressure, and no osmotic pressure difference occurs between the two sides. This allows only permeability to be investigated. To detect leaks that allow only unidirectional movement, leak tests can be performed both from the feed side to the draw side and from the feed side to the draw side. Determining the permeability state here means determining whether the FO membrane has an acceptable permeability state or a permeability error, where a permeability error is caused by a leak and / or permeability degradation.

[0026] Generally, water transport through the intended water channel is driven by a solute concentration difference, e.g., the concentration difference between the feed side and the draw side. Solute migration (caused by leaks) 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. The purified 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] Embodiments of the present disclosure will now be described with reference to FIGS. 1 to 4. FIG. 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 an FO membrane 2c. The sides may also be referred to as compartments or chambers. During use, the FO membrane 2c separates a solution on the feed side 2a (called the feed solution) from a solution on the draw side 2b (called the draw solution). When producing dialysate, an osmotic pressure difference exists 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 FO apparatus 2 dehydrates the feed solution and dilutes the draw solution. The FO membrane 2c is designed to be more or less selective for osmotic water molecules, allowing it 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, e.g., 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 surrounding the FO membrane 2c. The FO membrane 2c can be in the form of 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. Suitable FO devices for the FO device 2 include, for example, Aquaporin TM , AsahiKASEI TM , Berghof TM , CSM TM , FTSH2O TM , Koch Membrane SystemsTM , Porifera TM , Toyobo TM and Toray TM may be provided by

[0030] To produce a dialysis solution, the feed solution is, for example, the effluent from a previous or current dialysis treatment or water. The draw solution is, for example, a dialysis concentrate, and water extracted from the feed solution dilutes the dialysis concentrate into a dialysis solution, which may also be referred to as a "diluted dialysis concentrate," "intermediate dialysis solution," or simply "dialysis solution." The dialysis concentrate is, for example, a concentrate containing at least one of NaCl, KCl, CaCl, MgCl, HAc, glucose, lactate, and bicarbonate. For example, the dialysis concentrate may contain NaCl, CaCl, MgCl, 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 plurality 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 dilute concentrate pump 6. The pumps may be, for example, volumetric pumps (such as piston pumps) or non-volumetric pumps (e.g., gear pumps) 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 the patient connected to the effluent container 35. The feed pump 3 is connected to the effluent container 35 or the inlet connector P iThe apparatus 1 is configured to provide a flow of dialysis concentrate from the first side 2a to the first side 2a and a flow of effluent 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 to pump the solution produced on the second side 2b to the diluted concentrate container 32. The pure water container 33 contains pure water. The liquid container 34 contains an osmotic agent or buffer solution, such as a glucose solution or a bicarbonate solution. The apparatus 1 also includes a conductivity sensor 7 configured to sense the conductivity of the solution produced on 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 apparatus 1 further includes one or more pressure sensors configured to sense a pressure indicative of the TMP of the FO device 2. For example, the apparatus 1 includes a first pressure sensor 8a arranged to sense the pressure of the feed side 2a. The apparatus 1 may also include a second pressure sensor 8b arranged to sense the pressure of the draw side 2b. However, the apparatus 1 may include additional pressure sensors for sensing pressures indicative of the TMP or other pressure sensors used to generate the dialysate. The dilute concentrate pump 6 is configured to provide a flow of fluid to the main line 20f. The controller 30 also includes a valve assembly 10 including a plurality of valves 10a-10p. Generally, the valves connected to the lines can be configured to be open, allowing fluid flow through the line, or closed, stopping fluid flow through the line. The valves may be, for example, on / off valves, with an on state defining a state when fluid flow through the line is allowed and an off state defining a state when fluid flow through the line is stopped. The controller 30 further includes a control unit 50 including at least one memory and at least one processor. The control device 30 is configured to control the function of the valves of the pump and valve device 10 and the mixing unit 9 by the control unit 50 to perform several 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 conductivity measurements from the conductivity sensor 7. The controller 30 is further configured to receive pressure measurements from one or more pressure sensors, including first and second pressure sensors 8a, 8b. The controller 30 is further configured to determine the 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 the hydrostatic pressure P at the feed side 2a. feed From the hydrostatic pressure P on the draw side 2b draw is configured to determine TMP as TMP = ΔP = P feed -P draw 5. The controller 30 is further configured to determine the permeability state of the FO membrane 2c in the apparatus 1, as defined by the method shown in FIG. 5. To that end, the at least one memory includes computer instructions for determining the permeability state of the FO membrane 2c. When the instructions are executed by the at least one processor, the controller 30 performs a method for determining the permeability state of the FO membrane 2c, as described below. The method may be executed by the controller 30 and stored as a computer program including computer instructions on the at least one memory.

[0032] First, however, the device 1 of Figure 2 will be described in more detail. In Figure 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 to, for example, a catheter of a PD patient or 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 and the first effluent inlet line 20a. 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. i The effluent can be collected in the effluent container 35 by pumping the effluent from the effluent container 35 into the container 35 using the feed pump 3. The effluent can then be pumped by 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 by the feed pump 3 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 and into the inlet connector P i The discharged liquid may be pumped directly to the first side 2a by a feed pump 3 from the first side 2a.

[0033] The effluent outlet line 20d is connected to the feed outlet port E on the first side 2a. outand a drain (not shown), and the feed outlet port E of the first side 2a out The drain 10f is connected to the drain. 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] Furthermore, 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 in A draw pump 5 is disposed to provide flow to the dialysis concentrate line 20e. A main line 20f is disposed between the dialysis concentrate line 20e and the mixing unit 9, connecting the dialysis concentrate line 20e and the mixing unit 9. The mixing unit 9 includes a main pump that controls the flow rate available in line 20m downstream of the mixing unit 9, a liquid pump that provides the 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 diluted dialysis concentrate line 20g is disposed between the diluted dialysis concentrate container 32 and the main line 20f to connect the diluted dialysis concentrate container 32 and the main line 20f. A conductivity sensor 7 is connected to the diluted dialysis concentrate line 20g to sense 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 on the draw side 2b out A first connecting 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 diluted dialysis concentrate line 20g. A first valve 10h is connected to first connecting line 20h. Thus, FO device 2 has a draw inlet port L that is in fluid communication with draw side 2b. inand draw outlet port L out The system includes a first main valve 10i connected to the main line 20f between the connection point between the main line 20f and the dialysis concentrate line 20e and the connection point between 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 to the diluted dialysis concentrate container 32 via the draw side 2b by using the draw pump 5 to pump the concentrate. The concentrate valve 10e and the first connecting valve 10h are opened, and the diluted dialysis concentrate valve 10g and the first main valve 10i are closed. At the same time, the effluent can be pumped to the feed side 2a. Pure water is extracted from the effluent on the feed side 2a to the dialysis concentrate on the draw side 2b by osmotic pressure. 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 an FO session to dilute dialysis concentrate in the process of producing dialysate.

[0035] To connect the liquid container 34 and the mixing unit 9, a liquid line 20i is arranged between the liquid container 34 and the mixing unit 9. A second main valve 10k is connected to the main line 20f between the diluted concentrate pump 6 and the mixing section 9. To connect the pure water container 33 and the mixing unit 9, a first water line 20n is arranged between the pure water container 33 and the mixing unit 9. A first water valve 10n is connected to the first water line 20n. The mixing unit 9 and the outlet connector P o To connect the mixing unit 9 and the outlet connector P, a 20m outlet line is o The outlet connector P o may 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 dialysate, 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 using the diluted concentrate pump 6. Simultaneously, an osmotic agent or buffer is pumped from the liquid container 34 to the mixing unit 9 through the liquid line 20i by pumping using 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 dialysate in line 20m downstream of the mixing unit 9. A conductivity sensor (not shown) in the mixing unit 9 measures the conductivity of the dialysis liquid obtained from the mixing unit 9. The diluted concentrate pump 6 and the liquid pump are controlled to specific speeds to achieve a desired predetermined concentration of the resulting dialysate based on the conductivity of the produced liquid, the conductivity of the diluted dialysis concentrate solution, and the flow rate of the produced liquid. In the mixing unit 9, the diluted dialysis concentrate solution, osmotic agent / buffer and pure water are mixed and optionally heated in the mixing chamber to form the dialysate. The dialysate is then delivered via the outlet line 20m to the outlet connector P o , and delivered to the desired destination (e.g., a storage container or a dialysis machine).

[0037] The second water line 20p is arranged between the first water line 20n and the third discharge liquid line 20c. Therefore, the second water line 20p connects the first water line 20n and the third discharge liquid line 20c. The second water line 20p is connected to the first water line 20n between the pure water container 33 and the first water valve 10n. The second water line 20p is further connected 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 arranged between the first water line 20n and the main liquid line 20f. Therefore, 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 diluted concentrate pump 6 and the first main valve 10i. Thus, pure water can be passed from the pure water container 33 to the feed side 2a and from the feed side 2a to a drain (not shown) via the second liquid line 20p, the third liquid line 20c, the second liquid line 20b, and the first liquid line 20a by opening the second water valve 10p and the fourth liquid inlet valve 10d, closing the second liquid inlet valve 10b, the first liquid inlet valve 10a, and the third liquid inlet valve 10c, and pumping pure water with the feed pump 3. Pure water can be simultaneously passed 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 connecting line 20h, and the diluted dialysis concentrate line 20g. Then, the third water valve 10j, the first main valve 10i, and the first connecting 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 part 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 flowchart in FIG. 5. FIGS. 4-4D show the FO device of FIG. 1 when flow through different ports is stopped and flow toward the stopped ports is restricted. Ports through which flow is stopped are indicated by solid black ports. The schematic diagrams show which flows are stopped in various embodiments of the method described below. This method is implemented, for example, 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 FIG. 2 or 3. However, the method may be used in other apparatuses that include an FO membrane for determining its permeability state. The method includes providing a flow of pure water S1 to the feed side 2a. In other words, the method includes 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 in From the first side 2a to the outlet 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 on the first side 2a. in and opening and closing appropriate valves. The operating point is typically well-defined, and therefore 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 controlled directly by 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 on the feed side 2a is feedmay simply be the result of providing a certain flow rate, as described above. Alternatively, providing S1 may include providing pure water with a hydrostatic pressure on the feed side 2a that is at or near atmospheric pressure, or that is different (higher or lower) than the hydrostatic pressure on 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 stream of pure water to the draw side 2b. Thus, the draw solution and the feed solution have the same osmotic pressure. Because the stream is pure water, the stream has a very low osmotic pressure, well below 1 bar (14.5 psig). Providing S2 a stream of pure water to the draw side 2b may be performed while providing S1 a stream of pure water to the feed side 2a. In other words, the method includes passing pure water through the second side 2b. Therefore, pure water is drawn through the inlet port L in Draw inlet port L in From the second side 2b through the draw outlet port L out 2, the pure water flows to the FO device 2, where it exits the FO device 2. The operating point of the apparatus 1 is typically well-defined while providing S2 the pure water flow. For example, the operating point includes providing S2 the pure water flow at a constant flow rate of 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 hydrostatic pressure P drawis typically at or near atmospheric pressure, e.g., 1013 hPa (approximately 1 bar, 14.5 psig). This is because the draw side 2b and the diluted concentrate container 32 are fluidly connected, meaning they are also at approximately the same pressure, except for the potential hydrostatic pressure difference. Providing pure water flow to the draw side and the feed side S1, S2 is done at a flow rate that ensures that all solutes that could generate osmotic pressure are washed away, in order to obtain a good starting point for the following method steps, where the osmotic pressure on both sides (feed side and draw side) is equal. Therefore, the osmotic pressure difference between the two sides is zero. Therefore, there is no need to apply a constant hydrostatic pressure to either side at this stage.

[0040] After flow on both the feed side 2a and the draw side 2b is provided, method steps can be performed repeatedly 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 can be detected. Generally, by stopping flow through a port from one side, either the feed side 2a or the draw side 2b, 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. TMP is determined by the formula 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 the dilute concentrate vessel 32 or other vessels or liquid lines that are also connected to atmospheric pressure. Here, TMP is the hydrostatic pressure P feedThus, monitoring S3 may include measuring the pressure on feed side 2a, for example using first pressure sensor 8a, and using the measured pressure on feed side 2a as an estimate of TMP. Alternatively, monitoring S3 may include measuring the pressure on feed side 2a (using first pressure sensor 8a) and measuring the pressure on draw side 2b (using second pressure sensor 8b), and using P feed -P draw and determining TMP as:

[0041] 4A, 4B and 5, testing the water permeability by stopping and controlling the flow to / from the feed side 2a will now be described. To perform such a test, in a first embodiment, the method comprises: out Stopping flow through the feed outlet port E out Stopping the flow through the filled outlet port E out 4A. In the example of FIGS. 2 and 3, closing drain valve 10f allows the feed outlet port E out In one embodiment, flow through other ports is allowed, as indicated 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 remains unstopped, typically remaining 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 so that the TMP is maintained at a constant, non-zero magnitude. inThe method further includes controlling (S5) the flow through either the inflow or outflow to the FO membrane 2c. Controlling (S5) is performed, for example, using the feed pump 3. Maintaining a constant TMP means controlling the TMP so that a predetermined 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 on the sides 2a and 2b are different, and there is a TMP that drives the water transport. The TMP can be either positive or negative. Depending on the positive or negative sign of the predetermined TMP to which the TMP is to be controlled, either the inflow or outflow is controlled to maintain the TMP constant at the predetermined TMP. Since only the TMP drives the water transport through the FO membrane 2c, changing the positive or negative sign of the TMP can cause the water transport to proceed in different directions. Thus, when the TMP is positive, P feed HA P draw The TMP is greater than 2 bar (29 to 72.5 psig), driving the transport of water from feed side 2a to draw side 2b. The predetermined TMP is, for example, 2 to 5 bar (29 to 72.5 psig), e.g., 4 bar (58 psig). The only way feed-side water can exit feed side 2a is through the intended water channels in FO membrane 2c, via leaks, and / or via water permeation through FO membrane 2c to draw side 2b. The pressure in feed side 2a is then reduced, and water is pumped into feed side 2a, maintaining the TMP constant at the predetermined TMP. Thus, in some embodiments, the method includes controlling the pressure of feed inlet port E based on one or more monitored pressures so 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 predetermined TMP, 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), e.g., -1 bar (-14.5 psig). Water in the draw side 2a can exit from the draw side 2b to the feed side 2b through the FO membrane 2c via leaks and / or 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 maintain the TMP constant. Thus, in some embodiments, the method includes adjusting the feed inlet port E based on one or more monitored pressures so that the TMP is maintained at a 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 maintain a constant TMP, 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 flow through S4 and feed inlet port E in After a short stabilization period, the feed inlet port E inThe inflow or outflow to the feed pump 3 reveals whether there is a leak and / or a change in 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 stream provided by the feed pump 2a. Such a characteristic is readily available as a control parameter in the controller 50 or other parameter used for the evaluation. The flow rate of the controlled stream 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 initiated 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 liquid flow rate 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 equal to the controlled flow rate. in The same point applies if the flow also includes stopping of the flow 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 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 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 the 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 The 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. The acceptable flow rate of an FO membrane having an acceptable permeability state can then be established as being within or within 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 a too-high interval is indicative of a leak, while a flow rate outside a too-low interval indicates low permeability. The same is true for flow from the draw side 2b. Thus, in some embodiments, the method includes determining that the FO membrane has an acceptable permeability state if the characteristic is determined to be within or at a predetermined interval defining an FO membrane having an acceptable permeability state; otherwise, determining that the FO membrane has a permeability error. Thus, if the characteristic is within or at an acceptable interval for the characteristic, the method includes determining that the FO membrane has an acceptable permeability state and, therefore, 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 for the same characteristic determined using 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. 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 used 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 substantially the same, 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 includes: in Stopping flow through feed inlet port E in Stopping flow through 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, thereby reducing the flow rate of the feed inlet port E. inFlow through the draw outlet port L can be stopped. Flow through the other ports is allowed, as indicated by the lack of fill in Figure 4B. Therefore, out and draw inlet port L in In an alternative embodiment, the flow through the draw inlet port L in The method also stops flow through the feed outlet port E based on one or more monitored pressures so that the TMP is maintained at a constant, non-zero magnitude. out The method further includes controlling S5 the flow via either the inflow or outflow to the feed inlet port E. 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. in Stopping the flow through S4 and feed outlet port E out After a short stabilization period, 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 rate provided by the drain pump. The remaining features are the same as those described for the first embodiment of the method for testing permeability by stopping and controlling flow to / from the feed side 2a.

[0046] Next, testing for permeability by stopping and controlling flow to / from the draw side 2b will be described. All descriptions for testing for permeability by stopping and controlling flow to / from the feed side 2a are also applicable to testing for permeability by stopping and controlling flow to the draw side 2b, except for the variations noted below. To test for permeability by stopping and controlling flow to / from the draw side 2b according to the third embodiment, the method includes: out Stopping flow through the draw outlet port L out Stopping flow through the filled outlet port L out In the example of FIGS. 2 and 3, by closing the first connecting valve 10h, the draw outlet port L out Flow through the feed outlet port E can be stopped. Flow through the other ports is allowed, as indicated by the lack of fill in Figure 4C. 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 one or more monitored pressures so that the TMP is maintained at a constant and non-zero magnitude. inThe process further includes controlling S5 the flow via either inflow or outflow to draw side 2b. Controlling S5 is performed, for example, using draw pump 5. Maintaining the TMP constant means controlling the TMP so that a predetermined TMP value is achieved by controlling the inflow or outflow to draw side 2b. The only way for pure water in draw side 2b to exit draw side 2b to feed side 2a is through a leak in FO membrane 2c and / or via water permeation through intended water channels in FO membrane 2c. To allow any water transport from draw side 2b to feed side 2a through a leak, 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), e.g., -1 bar (-14.5 psig). feed Typically, P remains at about atmospheric pressure. For example, feed side 2a may be open to drain (and thus 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 so that the TMP is maintained at a predetermined negative TMP. in Alternatively, TMP may be positive, which means that P feed HA P draw, meaning that the TMP is driving the transport of water from feed side 2a to draw side 2b. The predetermined TMP is, for example, 2 to 5 bar (29 to 72.5 psig), e.g., 4 bar (58 psig). Water in feed side 2a can exit from feed side 2a to draw side 2a through FO membrane 2c via leaks and / or water permeation through intended water channels in FO membrane 2c. However, to maintain a constant TMP, the pressure in draw side 2b must increase, and water must be pumped out of draw side 2b. Thus, in some embodiments, the method adjusts draw inlet port L based on one or more monitored pressures so that the TMP is maintained at a positive predetermined TMP. in By controlling the inflow or outflow to the draw side 2b to maintain a constant TMP, the flow to the draw side 2b or from the feed side 2a reflects the net flow through leaks in the FO membrane 2c and / or water permeation through the membrane.

[0047] In one embodiment, the draw outlet port L out Stopping flow through S4 and draw inlet port L in After a short period of stabilization, the flow of the liquid into the draw inlet port L is controlled by S5. 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 controller 50 or other parameter used for 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 via 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 liquid flow rate from the feed inlet port E in The difference between the flow rate of the liquid to the feed inlet port E and the flow rate of the 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 feed side 2a 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 , indicating a controlled flow to the draw inlet port L. Thus, 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). Thus, the method may include monitoring S6 the characteristic indicative of the controlled flow. Monitoring S6 and determining S7 may be performed as described above, with the following modification: For an 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 a given TMP and at the same operating conditions. The 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. 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 permeability by stopping and controlling flow to / from the draw side 2b will be described. The third and fourth embodiments are substantially the same, except for the features described below. To test permeability by stopping and controlling flow to / from the draw side 2b according to the fourth embodiment, the method involves: inStopping flow through the draw inlet port L in Stopping flow through the filled inlet port L in 4D. In the example of FIGS. 2 and 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 allowed, as indicated by the lack of fill in Figure 4D. Therefore, out and feed inlet port E in In an alternative embodiment, the flow through the feed inlet port E in The method also stops flow through the draw outlet port L based on one or more monitored pressures so that the TMP is maintained at a constant, non-zero magnitude. out The method further includes controlling S5 the flow via either the inflow or outflow to the diluted dialysis concentrate pump 6. Controlling S5 may be performed, for example, using the diluted dialysis concentrate pump 6 and another valve (not shown) connected to the diluted dialysis concentrate line 20g disposed between the diluted 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 by S5. outThe flow in or out of 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 parameter 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 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 a positive TMP and a negative TMP, thereby providing a more thorough leak test. Thus, in some embodiments, the method includes performing the method for both controlling the flow S5 so that the TMP is maintained positive and so 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, each having a positive TMP and a negative TMP.

[0051] The results 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 can then take appropriate action, such as replacing the FO device, to correct the permeability error.

[0052] The present disclosure also relates to a controller 10 for determining the permeability state of a forward osmosis (FO) membrane 2c of a FO device 2 in a dialysate generator 1. The controller 10 includes a feed pump 3 configured to provide a flow of pure water to a feed side 2a. The controller 10 includes a draw pump 5 configured to provide a flow of pure water to a draw side 2b. The controller 10 further includes one or more valves 10 configured to control 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 (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 TMP. The controller 10 is also configured to stop flow through one of the ports and control flow to or from one of the stopped feed side 2a and draw side 2b based on the one or more pressures, so that the TMP is maintained at a constant, non-zero magnitude. The controller 10 is further configured to determine the permeability state of the FO membrane based on the characteristics 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. 1. A method of operating a dialysate generator (1) for determining the permeability state of an FO membrane (2c) of a forward osmosis (FO) device (2) in the dialysate generator (1), the FO membrane (2c) separating a feed side (2a) and a draw side (2b) of the FO device (2), the FO device (2) having 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 ) and the operating method comprises: 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 transmembrane pressure, TMP, between the feed side (2a) and the draw side (2b); 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 ) stopping the flow through one of the controlling (S5) flow to or from one of the feed side (2 a) and the draw side (2 b) with stopped flow based on the monitored one or more pressures so 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 characteristics indicative of the controlled flow.

2. 2. The method of claim 1, further 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. A method according to claim 3, wherein said 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 controlled flow rate of the flow into the one of the feed side (2 a) or the draw side (2 b) with flow stopped, or the characteristic is a flow rate of outflow from the other of the feed side (2 a) and the draw side (2 b).

6. 2. The method of claim 1, wherein determining the state of the FO membrane's permeability (S7) includes determining whether the characteristic meets one or more criteria for an FO membrane having an acceptable 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 otherwise determining that the FO membrane has a permeability error.

8. 10. The method of claim 1, comprising performing the method for both controlling the flow (S5) so that the TMP is maintained positive and controlling the flow (S6) so that the TMP is maintained negative, and wherein the determining (S7) further comprises determining the state of the water 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 to maintain a predetermined constant TMP.

10. A control device (10) for determining the permeability state of a FO membrane (2c) of a forward osmosis (FO) device (2) in a dialysate generator (1), the FO membrane (2c) separating a feed side (2a) and a draw side (2b) of the FO device (2), the FO device (2) having 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 ), and the control device (10) a feed pump (3) configured to provide a flow of pure water to said feed side (2a); a draw pump (5) configured to provide a flow of pure water to the draw side (2b); 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 valves (10) configured to control flow through one or more of the 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) 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 ) to stop the flow through one of the monitoring one or more pressures indicative of said TMP; controlling flow to or from one of the feed side (2 a) and the draw side (2 b) with stopped flow based on the one or more pressures so 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 of operation 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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