WO2025153463A1

WO2025153463A1 - Apparatus for generation of product water for medical use

Info

Publication number: WO2025153463A1
Application number: PCT/EP2025/050746
Authority: WO
Inventors: Vishnu SHYAM; Carl-Henry Örndal; Cristina SCRET; Andreas Winquist; Henrik Lindgren; Robert HALLSTRÖM; Sverre KNUTSEN
Original assignee: Gambro Lundia AB
Current assignee: Gambro Lundia AB
Priority date: 2024-01-16
Filing date: 2025-01-14
Publication date: 2025-07-24
Anticipated expiration: 2026-07-16

Abstract

A water generation apparatus comprises first and second systems (300, 400) arranged in sequence along a main flow path (1). The first system is configured to process incoming water into processed water with reduced water hardness. The processed water is generated by a reverse osmosis, RO, unit (304) in the first system, which receives the incoming water from a feed pump (302). The second system is configured to generate product water for medical use from the processed water. A return flow path (8) extends from a location intermediate the first and second systems to a feed side of the RO unit. A start-up procedure is performed by the apparatus, by operating a valve arrangement (314, 401) to close the main flow path between the first and second systems and open the return flow path, start and operate the feed pump for a time period, and operate the valve arrangement to open the main flow path after the time period.

Description

APPARATUS FOR GENERATION OF PRODUCT WATER FOR MEDICAE

USE

Technical Field

The present disclosure relates to techniques for generation of product water for medical use.

Background Art

Many medical applications or uses require access to water of high purity. One such medical application is dialysis treatment. Medical fluids used in dialysis treatment include dialysis fluids and replacement fluids. Dialysis treatment consumes large quantities of medical fluid. In some modalities of dialysis treatment, pre-made medical fluid is delivered in prefilled bags to the point of care. For example, this is standard practice in extracorporeal blood treatment of patients with AKI (Acute Kidney Injury) and in peritoneal dialysis. On the other hand, dialysis machines for extracorporeal blood treatment of patients with CKD (Chronic Kidney Disease), for example by hemodialysis, hemofiltration and hemodiafiltration, are conventionally configured to produce the required medical fluid on demand by mixing one of more concentrates with water. In this context, the water is typically produced centrally in a dialysis clinic by use of expensive equipment for production of high-purity water.

The transportation of prefilled bags of pre-made medical fluid is undesirable from an environmental perspective. The prefilled bags are also bulky and heavy to handle and require significant storage space. It is therefore desired that more modalities of dialysis treatment shall use medical fluid that is locally produced on-demand.

On-demand production of medical fluid for dialysis treatment requires access to water of adequate quality. The water used when generating medical fluid must meet strict requirements set by standards or guidelines. The water purity requirements for the production of medical fluid for dialysis are far more stringent than those required for drinking, bathing, cooking and other domestic purposes. Equipment for purification of tap water also needs to be capable of handling varying types of impurities and varying levels of impurities in the tap water. For example, municipal tap water often includes residual disinfectant chemicals, such as chlorine and chloramines. Further, water hardness may vary considerably between different regions and water sources. Water distribution systems may be a source of lead, copper, or zinc contamination due to corrosion of pipes. Furthermore, homes using well water may have to contend with varying amounts of nitrates, arsenic, and other organic compounds. One commonly used technique for water purification is reverse osmosis (RO), in which an RO membrane is used to separate ions, molecules and particles from water. Ion exchangers (IEX) are also commonly used for water purification purposes.

While equipment for producing high-purity water from tap water is commercially available, existing equipment is expensive, bulky and noisy and therefore mainly useful in a centralized setting, for example in a hospital or clinic, where the produced water may be produced in a secluded area and distributed to a large number of dialysis machines. To enable dialysis treatment outside of such centralized settings, for example in the home of the patient, or where otherwise central distribution of high-purity water is not possible, there is a need for water purification equipment that is suitable for use at a smaller scale. For example, a small-scale water purification equipment may produce water for use by or for a single or a few dialysis machines. The water purification equipment should ideally have low structural complexity and be inexpensive in terms of both production cost and operating cost. It may also be desirable for the level of noise during operation to be low. The water purification equipment should preferably be compact and easy to maintain. It may be desirable to implement the water purification device as a stand-alone device, which is portable for flexible use. It is also generally desirable for the equipment to be efficient in terms of power consumption as well as water consumption.

Summary

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

A further objective is to provide a technique of generating product water for medical use in a robust and well-controlled way.

Another objective is to provide such a technique which is efficient in terms of water consumption.

One or more of these objectives, as well as further objectives that may appear from the description below, are at least partly achieved by an apparatus for generation of product water for medical use, a computer-implemented method, and a computer- readable medium according to the independent claims, embodiments thereof being defined by the dependent claims.

A first aspect of the present disclosure is an apparatus for generation of product water for medical use. The apparatus comprises: a main flow path extending from a main water inlet to a main water outlet; a first system arranged in the main flow path and configured to process incoming water for reduction of water hardness, resulting in processed water with reduced water hardness; and a second system arranged in the main flow path intermediate the first system and the main water outlet, wherein the second system is configured to receive the processed water from the first system and further process the processed water into said product water. The first system comprises a reverse osmosis, RO, unit for use in processing of the incoming water, the main flow path comprises a feed line extending to a water inlet on a feed side of the RO unit, and the first system comprises a feed pump arranged in the feed line to pressurize the incoming water at the water inlet of the RO unit. The apparatus further comprises a return flow path, which is arranged to fluidly connect the main flow path, at a location intermediate the first and second systems, to a feed side of the RO unit, and a valve arrangement, which is operable to selectively direct the processed water from the first system on the main flow path to the second system, or on the return flow path to the feed side of the RO unit. The apparatus is configured to perform a start-up procedure, in which the valve arrangement is operated to close the main flow path and open the return flow path, the feed pump is started and operated for a time period, and the valve arrangement is operated to open the main flow path after the time period, and optionally close the return flow path.

A second aspect of the present disclosure is a computer-implemented method of operating an apparatus for generation of product water for medical use. The apparatus comprises: a main flow path extending from a main water inlet to a main water outlet; a first system arranged in the main flow path and configured to process incoming water for reduction of water hardness, resulting in processed water with reduced hardness; and a second system arranged in the main flow path intermediate the first system and the main water outlet, wherein the second system is configured to receive the processed water from the first system and further process the processed water into said product water. The first system comprises a first reverse osmosis, RO, unit for use in processing of the incoming water, wherein the apparatus comprises a return flow path, which is arranged to fluidly connect the main flow path, at a location intermediate the first and second systems, to a feed side of the RO unit, and a valve arrangement, which is operable to selectively direct the processed water from the first system on the main flow path to the second system, or on the return flow path to the feed side of the RO unit. The main flow path comprises a feed line extending to a water inlet on the feed side of the RO unit, and the first system comprises a feed pump arranged in the feed line to pressurize the incoming water at the water inlet of the RO unit. The method comprises: operating the valve arrangement to close the main flow path and open the return flow path; starting the feed pump and operating the feed pump for a time period, and operating the valve arrangement to open the main flow path after the time period. A third aspect of the present disclosure is a computer-readable medium comprising program instructions, which when executed by a processor causes the processor to perform the method of the second aspect.

These aspects provide a technique of starting the apparatus for generating product water in a safe, robust and well-controlled way. The processed water that is generated by the first system is recirculated, on the return flow path, back to the RO unit of the first system during start-up. The recirculation allows the first system to be started separately from the second system with minimum waste of water. For example, the valve arrangement may be selectively switched to direct the processed water from the first system to the second system at a time point when the RO unit in the first system is known or deemed to produce processed water of adequate quality. The sequential startup of the first and second systems, which are fluidly connected in series on the main flow path, is likely to shorten the time required for the apparatus to reach steady-state operation. Further, the recirculation mitigates or eliminates the risk that the second system receives processed water of inferior quality, for example in terms of water hardness, during start-up. This is likely to prolong the life of the second system and/or limit the need for maintenance of the same.

In the following, various embodiments of the first aspect are defined. These embodiments provide at least some of the technical effects and advantages described in the foregoing, as well as additional technical effects and advantages as readily understood by the skilled person, for example in view of the following detailed description.

In some embodiments, the return flow path extends to a location on the main flow path upstream of the feed pump.

In some embodiments, the apparatus further comprises a sensor, which is arranged in the main flow path intermediate the first system and the valve arrangement, said sensor being configured to generate a sensor signal representing a composition-related parameter of the processed water, wherein the apparatus is configured to determine said time period based on the sensor signal.

In some embodiments, the composition-related parameter corresponds to electrical conductivity.

In some embodiments, the first system further comprises a drain line extending from a retentate outlet on a feed side of the RO unit, wherein a flow restriction device is arranged in the drain line to define a flow resistance at the retentate outlet on the feed side of the RO unit.

In some embodiments, the flow restriction device is operable to change the flow resistance based on a control signal. In some embodiments, the first system comprises a connecting line, which is arranged in fluid communication with the drain line and the feed line to define a recirculation path from the retentate outlet on the feed side of the RO unit to a water inlet on the feed side of the RO unit, and an auxiliary pump, which is arranged in the recirculation path to provide an added flow rate along the second flow path.

In some embodiments, the auxiliary pump is arranged in the connecting line.

In some embodiments, the RO unit defines a permeate side, which is separated from the feed side by a semi-permeable membrane, wherein the RO unit comprises the water inlet on the feed side and a permeate outlet on the permeate side, wherein the main flow path comprises a first flow path from the water inlet, through the semi- permeable membrane to the permeate outlet, wherein the RO unit further comprises the retentate outlet on the feed side to define a second flow path on the feed side from the water inlet to the retentate outlet along the semi-permeable membrane.

In some embodiments, the apparatus further comprises a reservoir, which is arranged in the main flow path upstream of the first system and configured to hold said incoming water for the first system at atmospheric pressure.

In some embodiments, the reservoir comprises a water inlet port, which is connected for fluid communication with the main water inlet, wherein the reservoir is configured to define an air gap above a predefined top level of the incoming water inside the reservoir.

In some embodiments, the reservoir comprises a level sensor for signaling at least one fluid level in the reservoir, so as to enable a control device to control an inflow of water through the water inlet port to maintain said air gap in the reservoir.

In some embodiments, the apparatus further comprises a vent in a side wall of the reservoir, wherein the vent is configured to release both gases and water from the reservoir.

In some embodiments, the return flow path extends to a return port on the reservoir.

In some embodiments, the apparatus further comprises a recirculation path, which extends from a first location in the main path downstream of the second system, to a second location in the main path upstream of the first system and/or to a third location in the main flow path intermediate the first system and the second system, to provide for recirculation of the product water generated by the second system.

In some embodiments, the first system comprises a drain line for directing reject water from the RO unit to a drain, and the apparatus further comprises a heat transfer device, which is configured to transfer heat between a first locus in the drain line and a second locus in the main flow path upstream of the RO unit. In some embodiments, the heat transfer device comprises at least one of a heat exchanger or a heat pump.

In some embodiments, the apparatus further comprises a control device, which is configured to operate the heat pump to achieve a target temperature of the incoming water at the RO unit.

In some embodiments, the control device is configured to operate the heat pump to transfer heat from the first locus to the second locus.

In some embodiments, the control device is configured to selectively reverse the heat pump to transfer heat from the second locus to the first locus.

In some embodiments, the control device is configured to selectively reverse the heat pump based on a signal indicative of the temperature and/or hardness of the incoming water to the first system.

In some embodiments, the heat pump is a thermoelectric heat pump.

In some embodiments, the second locus is upstream of the sensor that is configured to generate the sensor signal representing a composition-related parameter.

In some embodiments, the control device is configured to operate the heat pump to achieve a target temperature of the processed water at the sensor that is configured to generate the sensor signal representing a composition-related parameter.

In some embodiments, the RO unit is a sacrificial component which is removably installed in the first system.

In some embodiments, the RO unit has a target lifetime that allows for generation of 20,000-100,000 L of said processed water, and preferably 40,000-70,000 L of said processed water.

In some embodiments, the target lifetime is defined for the incoming water to the RO unit having a hardness of 450 ppm and/or a conductivity of 2000 pS/cm, and for the processed water being generated at a flow rate of 1 L/min.

In some embodiments, the apparatus is configured to generate the product water at a point of care, and the apparatus is configured to provide for replacement of the first RO unit by a non-trained user at the point of care.

In some embodiments, the apparatus further comprises a monitoring device, which is configured to determine, based on an output signal of a sensor in the apparatus, a performance parameter that is indicative of a flow resistance through the RO unit and evaluate the performance parameter for detection of a need for replacement of the RO unit.

In some embodiments, the sensor comprises at least one of a pressure sensor in the main flow path upstream of the RO unit, a flow meter in the main flow path downstream of the RO unit, or a power sensor for measuring a power consumption of the feed pump.

In some embodiments, the second system comprises a second RO unit for use in processing of the processed water from the first system.

In some embodiments, the second RO unit is permanently installed in the second system.

In some embodiments, a retentate outlet of the second RO unit is connected for fluid communication with the main flow path at a location upstream of the first system, to provide for recirculation of retentate water from the second RO unit into the main flow path.

In some embodiments, the apparatus further comprises a pre-processing system, which is arranged in the main flow path and configured to receive source water from the main water inlet and at least remove particles from the source water to provide pre- processed water, wherein the first system is fluidly connected to receive the pre- processed water from the pre-processing system.

In some embodiments, the pre-processing system is further configured to remove chlorine from the source water.

In some embodiments, the apparatus further comprises at least one radiation source arranged in the main flow path upstream of the RO unit, said radiation source being operable to emit UV radiation for removal of chlorine in the incoming water to the RO unit.

Any embodiment of the first aspect may be adapted as an embodiment of the second aspect.

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

Brief Description of the Drawings

FIG. 1 is a schematic diagram of an example water purification apparatus (WPA).

FIGS 2A-2C are block diagrams of systems included in an example WPA, and FIG. 2D is a view of an example reserve osmosis (RO) unit for use in a WPA.

FIGS 3A-3D are flow charts of example methods of operating the WPA in FIGS 2A-2C.

FIG. 4A is a block diagram of an example WPA configured in accordance with a first concept, and FIG. 4B is a flow chart of an example method of operating the WPA in FIG. 4A. FIG. 5 is a block diagram of an example sub-assembly of a WPA configured in accordance with a second concept.

FIG. 6 is a block diagram of an example WPA configured in accordance with a third concept.

FIG. 7 is a block diagram of an example WPA configured in accordance with a fourth concept.

FIG. 8A is a block diagram of an example WPA configured in accordance with a fifth concept, and FIG. 8B is a flow chart of an example method of operating the WPA in FIG. 8A.

FIG. 9A is a block diagram of an example WPA configured in accordance with a sixth concept, and FIG. 9B is a flow chart of an example method performed in relation to the WPA in FIG. 9A.

FIG. 10A is a block diagram of an example WPA configured in accordance with a seventh concept, and FIG. 1 OB is a flow chart of an example method of operating the WPA in FIG. 10A.

FIG. 11 is a block diagram of an example WPA according to a variation.

FIG. 12 is a block diagram of an example WPA configured in accordance with a variant of the first concept.

FIGS 13A is a block diagram of an example WPA with a heat transfer device, and FIG. 13B depicts an example heat transfer device.

Detailed Description of Example Embodiments

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

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

It will furthermore be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing the scope of the present disclosure. As used herein, the terms "multiple", "plural" and "plurality" are intended to imply provision of two or more elements. The term "and/or" includes any and all combinations of one or more of the associated listed elements.

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

The present disclosure relates to a technique of generating water for use in medical treatment of a human or animal body. As used herein, a medical treatment is an attempted remediation of a health problem and includes any therapy that brings the water into contact with the body, including the blood in the body. The present disclosure may be relevant to current or future therapies in which the water is mixed with one or more concentrates to form a medical fluid that is allowed to interact with the blood of the patient. Such therapies include dialysis therapy, plasmapheresis, apheresis, extracorporeal membrane oxygenation, assisted blood circulation, extracorporeal liver support/dialysis, etc. It is foreseen that this "on-demand generation" of medical fluid will become increasingly common in the future. On-demand generation allows the medical fluid to be generated in the amounts needed and also allows the composition of the medical fluid to be adjusted. The present disclosure may be particularly relevant to on-demand generation of medical fluid on a small scale, for use by a single or a few dialysis machines. Thus, the technique described herein may be utilized at bedside in the home of a patient or in a clinic to enable on-demand generation of medical fluid.

As noted, the water purification technique is applicable to dialysis therapy. As used herein, "dialysis therapy" refers to any therapy that replaces or supplements the renal function of a patient by use of dialysis fluid. Dialysis therapy includes, without limitation, extracorporeal (EC) blood therapy and peritoneal dialysis (PD) therapy. Examples of EC blood therapy include hemodialysis (HD), hemofiltration (HF) and hemodiafiltration (HDF).

FIG. 1 is a schematic overview of a water purification apparatus, WPA, in accordance with some embodiments. The apparatus comprises a water inlet 1' for input of source water, SWA, from a water source 10, and a water outlet 1" for output of purified water, PWA. The source water may be of any quality. In some embodiments, the source water is tap water (drinking water) or some form of pre-processed tap water. The water inlet T may comprise a connector for engagement with a corresponding connector associated with the water source 10. Eikewise, the water outlet 1" may comprise a connector for engagement with a corresponding connector associated with a receiving device (not shown). The receiving device may be any device configured to generate a medical fluid by mixing the purified water with one or more concentrates. In some embodiments, the receiving device is a dialysis machine or a stand-alone apparatus for generation of medical fluid for use in dialysis therapy. In some embodiments, the WPA is integrated with the receiving device. For example, the WPA and the receiving device may be included in the same flow path.

The WPA is operable to process the source water, SWA, into product water, PWA, which is of sufficient quality for use in the intended medical treatment, at least in terms of impurities. Thus, the WPA is configured to perform a purification processing of SWA to produce PWA. As used herein, "purification" refers to removal of impurities such as undesirable chemicals, biological contaminants, suspended solids, and gases. It does not imply that the purified water is sterile or substantially free of microbial activity, although this may be the case. In a non-limiting example, applicable to so- called "water for dialysis" or "dialysis water", PWA fulfils at minimum, the following maximum allowable levels of toxic chemicals with known toxicity in dialysis settings: aluminum 0.01 ppm, copper 0.1 ppm, fluoride 0.2 ppm, lead 0.005 ppm, nitrate (as N) 2 ppm, sulfate 100 ppm, zinc 0.1 ppm, and total chlorine 0.1 ppm. In some embodiments, PWA (or the medical fluid that is produced from PWA) is subjected to further processing for removal of microorganisms, endotoxins, etc. Such processing may involve any conventional technique for sterilization, including filtration by one or more ultrafilters. However, in some embodiments, PWA is generated by the WPA to fulfil all requirements of "water for dialysis" or "dialysis water", for example in accordance with ANSI/AAMI/ISO 23500-3:2019.

The WPA comprises a main flow path 1 ("main path") that extends from the water inlet T to the water outlet 1". In the example of FIG. 1, a pre-processing system 100 is arranged in the main path 1 to receive and process the source water, SWA. The preprocessing system 100, which is optional, may be configured to at least process SWA for removal of particles. In some embodiments, the pre-processing system 100 is configured to remove particles with a nominal size of 1 pm or more, i.e., to pass particles with a nominal size below 1 pm. In some embodiments, the system 100 is additionally configured to reduce one or more contaminants such as volatile organic compounds (VOCs), and trihalomethanes (THMs) that may be present in SWA. In some embodiments, the system 100 is further configured to effectively remove chlorine from SWA. As used herein, "effectively remove" implies that the total amount of chlorine in the dechlorinated water is 0.1 mg/L (0.1 ppm) or less. The water that is produced by the pre-processing system 100 is referred to as "pre-processed water" herein. In some embodiments, the pre-processed water may be termed "dechlorinated water". Chlorine may be present in free forms and/or combined forms in water. The free forms may include dissolved hypochlorite ions, hypochlorous acid and chlorine gas. The combined forms may include chloramines that kill bacteria and oxidize organic matter. Examples of such chloramines include monochloramine, dichloramine and trichloramine. The total amount of chlorine is given by the sum of the free and combined forms of chlorine.

As will be exemplified further below, the dechlorination may alternatively or additionally be performed by UV irradiation of the water within the WPA.

In the example of FIG. 1, a reservoir or tank 200 is arranged downstream of the pre-processing system 100 to collect the pre-processed water.

A first purification system 300 ("first system" or "first main system", PSI) is arranged downstream of the tank 200 to receive and process incoming water. The first system 300 is configured to at least reduce the water hardness of the incoming water. This process is commonly denoted "water softening" and involves removal of at least calcium and magnesium. The water that is produced by the first system 300 is referred to as "processed water" or "softened water" herein. Water hardness is the amount of polyvalent cations and is usually attributed to the sum of dissolved calcium plus magnesium in the water. Hardness may be classified as carbonate or non-carbonate hardness, depending upon the presence of counter anions in the water. Hardness classification may be given as equivalence units of mgCaCOs/L. The first system 300 may also be configured to reduce minerals and/or TDS (Total Dissolved Solids) of the incoming water

One function of the first system 300 is to reduce water hardness so as to mitigate or even prevent scaling of downstream components in the WPA, such as the second purification system 400 (below). In some embodiments, the first system 300 is configured to generate processed water with a water hardness of less than 60 ppm (mgCaCC /L), and preferably less than 30, 20 or 10 ppm (mgCaCOs/L). In some embodiments, the first system 300 is configured to reduce the water hardness of incoming water by at least 90% and preferably by at least 95%, in terms of equivalence units of mgCaCOs/L.

In some embodiments, the system 300 is configured to process the incoming water by reverse osmosis (RO) to reduce water hardness. This means that the system 300 comprises at least one RO unit for use in processing the source water, SWA. The RO unit comprises an RO filter which is arranged to separate ions, molecules and particles from the incoming water. Specifically, the RO unit is configured to perform cross-flow filtration (also known as tangential flow filtration) where the majority of the incoming water ("feed water") travels tangentially across the surface of the RO filter, rather than through the RO filter. The filtered water that passes the RO filter is denoted "permeate" or "permeate water", and the non-filtered water is denoted "retentate" or "reject water". An example of an RO unit will be described below with reference to FIG. 2D. The skilled person understands that RO is a non- selective technique and that processing by RO will not only reduce water hardness but also remove impurities that are unrelated to water hardness. Such impurities may include various inorganic and organic compounds.

A second purification system 400 ("second system" or "second main system", PS2) is arranged downstream of the first system 300 and configured to perform a final processing of the processed water to generate the purified water, PWA. The second system 400 may thus be configured to remove remaining impurities not removed by the system 300 so that PWA has a required purity. Alternatively or additionally, the second system 400 may be configured to reduce the microbial load of the processed water from the first system 300.

The system 400 may implement any suitable purification technique, for example membrane filtration, ion exchange, electrodeionization (EDI), or any combination thereof. The membrane filtration may involve reverse osmosis (RO). Thus, in some embodiments, the system 400 comprises at least one RO unit for use in processing incoming water. In some embodiments, the system 400 comprises at least one ion exchanger (IEX), instead of or in addition to the RO unit(s). As known in the art, an ion exchanger is operable to remove ionic impurities from water by replacing the respective ionic impurity with another ionic substance. Specifically, negative ions are replaced by OH’ and positive ions are replaced by H⁺, with OH’ and H⁺ being joined to form a water molecule. Typical ion exchangers are ion-exchange resins (functionalized porous or gel polymer), zeolites, montmorillonite, clay, or soil humus.

The operation of the WPA is controlled through control signals, which are generated and output by a control device 500. The control signals are collectively represented as [CS] in FIG. 1 and are supplied to operable components (not shown) in the WPA, such as pumps, valves, heaters, flow restrictors, etc. The control device 500 is configured to generate the control signals based on measurement signals, collectively represented as [MS]. The measurement signals represent current values of various status parameters of the WPA, such as pressure, temperature, flow rate, chemical composition, conductivity, etc. At least some of the measurement signals may be given by sensors (not shown) in the WPA. The control device 500 comprises a combination of processing circuitry 501 and memory 502. The memory 502 may store program instructions for execution by the processing circuitry 501 to implement the operation of the control device 500. The program instructions may be supplied to the control device 500 on a computer-readable medium, which may be a tangible (non-transitory) product (for example, magnetic medium, optical disk, read-only memory, flash memory, etc.) or a propagating signal. The processing circuitry 501 may comprise a generic processor, for example a microprocessor, microcontroller, CPU, DSP (digital signal processor), GPU (graphics processing unit), etc., or a specialized processor, such as an ASIC (application specific integrated circuit) or an FPGA (field programmable gate array), or any combination thereof. The memory 502 may include volatile and/or non-volatile memory such as read only memory (ROM), random access memory (RAM) or flash memory.

As shown, the control device 500 may be connected to a human-machine interface (HMI) device 503. The term HMI device is intended to include any and all devices that are capable of performing guided human-machine interaction comprising display of information or instructions and receipt of input data. For example, the HMI device 503 may comprise a combination of a display device and data entry hardware. The data entry hardware may include one or more of a keyboard, keypad, computer mouse, control buttons, touch panel, microphone and voice control functionality, camera and gesture control functionality, etc. In one implementation, the HMI device 503 is or comprises a touch- sensitive display, also known as touch screen. Alternatively or additionally, the HMI device 503 may comprise a speaker or a projector to provide information or instructions to a user.

The provision of the pre-processing system 100 in the WPA may extend the useful life of the systems 300, 400 and/or reduce the need for maintenance, by reducing the amount of particles/solids and contaminants in the water to be processed by these systems. Further, as noted above, the pre-processing system 100 may be configured to produce dechlorinated water. Chlorine is strongly oxidizing, and elevated levels of chlorine in the incoming water to an RO unit are known to cause irreversible damage to its RO filter. Therefore, it may be desirable to ensure that the feed water to the RO unit(s) in the system 300 is sufficiently dechlorinated, by the pre-processing system 100 and/or by subjecting the water to UV radiation elsewhere in the WPA. It may also be noted that ion exchangers are equally likely to be irreversibly damaged by chlorine.

The provision of the tank 200 serves to decouple the operation of the systems 300, 400 from the supply of source water, SWA, and from the operation of the preprocessing system 100, if present. This may facilitate the design and/or operation of the systems 300, 400. Further technical advantages of the tank 200 are discussed below with reference to FIG. 2A.

In some implementations, depending on the quality of the source water and the required performance of the WPA, the pre-processing system 100 and/or the tank 200 may be omitted.

In some embodiments, the second system 400 mainly serves the function of reducing the microbial load of the processed water from the first system 300. Thus, in some embodiments, a main part of the chemical substances ("impurities") present in SWA is removed by the first system 300, whereas the second system 400 has the main function of reducing the microbial load of the processed water from the first system 300 such that the PWA that is output by the WPA meets applicable requirements. As noted above, when the first system 300 involves a non-selective purification technique such as RO, most chemical compounds will be affected by the purification, not only water hardness. This separation of functionality between the first and second systems 300, 400 is advantageous in that it enables separate optimization of the respective system 300, 400.

By connecting the systems 300, 400 in series, the first system 300 is more exposed to impurities than the second system 400. This will extend the operative life of the second system 400 and may also allow the second system 400 to include more advanced/sensitive purification equipment, if desired. The first system 300, on the other hand, may need additional consideration to ensure proper operation of the WPA over time. As noted above, the first system 300 may comprise one or more RO units. In some embodiments, the first system 300 may be configured to perform automated cleaning, disinfection or sanitization of the RO filter in the respective included RO unit. The cleaning may, for example, involve flushing the RO filter with water, which may or may not be heated, for example up to about 45°C. In some embodiments, described in more detail below with reference to FIG. 4A, at least one RO unit in the first system 300 is configured as a sacrificial or disposable component, which is removably installed in the first system 300. Thereby, the RO unit may be replaced as needed, for example when the RO filter is deemed to be clogged by impurities, for example as a result of scaling, and/or at regular service intervals. The use of a disposable RO unit may appear to increase the operating cost of the WPA. However, by using a disposable RO unit as proposed herein, a conventional water softener is not required in the WPA. Many conventional water softeners are bulky and costly, and may require supervision and periodic maintenance. Thus, in practice, the proposed technique of using a disposable RO unit results in cost savings. Further, by the provision of the second system 400, the RO unit(s) in the first system 300 need not be high-end products, i.e., highly qualified products with high purification performance. Instead, relatively simple and cheap low- end RO units may be used, for example commercially available under- the- sink RO units. At present, the cost ratio between high-end and low-end RO units on the market is at least a factor of 5-10. Thus, the replacement of RO units may have a marginal impact on the operating cost of the WPA. Further, the replacement of RO unit (s) in the first system 300 may lower the demands on the purification performance of the second system 400, enabling reductions in the production cost of the WPA.

FIGS 2A-2C depicts a WPA in accordance with a detailed implementation example. The WPA is separated into subsets in FIGS 2A-2C, where the fluid connections between the different subsets are indicated by encircled letters A-G. Methods of operating the WPA will be described with reference to FIGS 3A-3D. The methods may be performed by the control device 500 in FIG. 1. The WPA described with reference to FIGS 2-3 embodies various inventive concepts that provide distinct technical advantages. In addition to being briefly presented in relation to FIGS 2-3, some of these concepts will be presented and discussed in detail further below with reference to FIGS 4-10.

FIG. 2A is a block diagram of an upstream portion of the WPA, including a preprocessing system 100 and a tank 200. The source water SWA is received at A, and the main path 1 extends from A to C. It is assumed that SWA is sufficiently pressurized to flow along the main path 1 through the pre-processing system 100 into the tank 200. In the flow direction along the main path 1, the pre-processing system 100 comprises a one-way valve 101, an inlet valve 102, a filtration device 103, a flow restrictor 104, a temperature sensor 105, and a composition sensor 106. The filtration device 103 is configured to perform both removal of particles and dechlorination. In one embodiment, the filtration device comprises activated carbon (AC) filters 103 A, 103B, which are connected in series. Each AC filter 103 A, 103B is formed by a container that holds activated carbon, also known as active carbon or activated charcoal. The activated carbon has been processed (activated) to have small, low-volume pores that increase the surface area available for adsorption and/or chemical reactions. The activated carbon forms a bed inside the container. The bed of activated carbon is arranged to remove chlorine from the incoming water, and to absorb toxic substances and pesticides. In an example embodiment, the bed of activated carbon is arranged to remove free and combined forms of chlorine. In a further example embodiment, the bed of activated carbon is also arranged to reduce organic compounds (TOC, total organic carbon) including pesticides of the incoming water. The bed of activated carbon also inherently filters out particles from the incoming water.

The flow restrictor 104 is included to create a backing pressure in the main path 1 so as to limit the flow rate of water through the filtration device 103. The inlet valve 102 ("main inlet valve") may be operable via a control signal VC1 to selectively open and close the main path 1 to control admission of SWA into the WPA. Alternatively, the inlet valve 102 may be a flow control valve which is operable to admit SWA into the main flow path 1 at variable flow rate.

The one-way valve 101 is included to prevent flow reversal in the main path 1 and thus backflow through the filtration device 103. The temperature sensor 105 is configured to provide a measurement signal T1 indicative of the temperature of SWA. The composition sensor 106 is configured to provide signal Cl. As used herein, a composition sensor is configured to provide a measurement signal indicative of the amount of at least one substance in the water. For example, the composition sensor may be a conductivity sensor (or equivalently, a resistivity sensor), or a concentration sensor, for example an ion-selective sensor. The signals Tl, Cl may be used by the control device 500 in controlling the operation of the WPA.

The tank 200 is arranged to receive and collect the pre-processed water from the system 100. The tank 200 comprises a level sensor 201, which is configured to indicate at least one fluid level in the tank 200, via a measurement signal LI. The level sensor 201 may thus signal when the water reaches one or more discrete levels, or indicate the fluid level along a continuous scale. The measurement signal LI allows the control device 500 to control the level of water in the tank 200. The tank 200 comprises a plurality of ports 202-206. A first inlet port 202 for pre-processed water is defined in the top portion of the tank 200. The first inlet port 202 is thus connected to the main path 1. An outlet port 203 is defined in the bottom portion of the tank 200 and connected to the main path 1. The tank 200 is thus fluidly connected to the first system 300 through the outlet port 203. A second inlet port 204 is defined in the top portion and connected to a first return line 8, which is fluidly connected to receive water that has been processed by the first system 300 and the second system 400, respectively (cf. FIGS 2B-2C). A third inlet port 205 is defined in the top portion of the tank 200 and connected to a second return line 2B, which is fluidly connected to receive retentate ("reject water") from the second processing system 400. In some embodiments, at least one of the inlet ports 202, 204, 205 is connected to a spray nozzle (not shown) inside the tank 200 to disperse the incoming water. The inlet ports 204, 205 may be merged into a common port. A gas outlet or vent 206 is defined in the side portion of the tank 200. The vent 206 allows gases to escape from the tank 200, as indicated by a dashed arrow. The water is thus held in the tank 200 at atmospheric pressure.

In some embodiments, the amount of water in the tank 200 is controlled to define an air gap 207 at the top of the tank 200, by ensuring that the fluid level in the tank 200 does not rise above a predefined maximum level in the tank 200. The control device 500 may be configured to control the fluid level in the tank by controlling the inlet valve 102. Depending on the type of level sensor 201, the fluid level in the tank 200 may or may not be allowed to vary during operation of the WPA. Arranging the first inlet port 202 above the predefined maximum level will minimize the risk that water flows back from the tank 200 towards the pre-processing system 100, which might disrupt the operation of the filtration device 103. Likewise, the air gap 207 prevents backflow into the inlet ports 204, 205 if these are installed above the predefined maximum level. The air gap 207 also serves as a barrier to microorganisms in relation to the inlet ports 204 and 205. Activated carbon beds are known to act as a nutrient-rich environment for microorganisms and thus the pre-processing system 100 may be a key point of ingress for microorganisms into the WPA. The air gap 207 will mitigate microbial contamination of the return lines 8, 2B. Another technical advantage of the tank 200 is its ability to be used as a flow rate watchdog, via the signal LI. Depending on implementation, the control device 500 may be configured to detect if the fluid level cannot be maintained at the predefined maximum level in the tank 200, if the fluid level is unable to reach a predefined operative level in the tank, or if the fluid level reaches a predefined lower level in the tank 200. This may indicate a malfunction of the preprocessing system 100 or the water source 10 and may cause the control device 500 to stop the operation of the WPA. Another technical advantage of the tank 200 is an ability to allow for thermal expansion of the water in the WPA. This may be particularly relevant when the WPA is configured to be intermittently cleaned (sanitized) by heat disinfection. The provision of the vent 206, and thus atmospheric pressure in the tank 200, is advantageous for several reasons. It will allow for removal of air and other gases that may be released from the water in the tank 200. Further, since water is recirculated back to the tank 200 from the first and second systems 300, 400, it allows for continuous removal of gases in the entire hydraulic circuit of the WPA, including the RO units in the systems 300, 400 (below). Further, during start-up of the WPA, gases may be present in the hydraulic circuit and need to be vented. Further, removal of gases from the hydraulic circuit is relevant whenever the hydraulic circuit has been opened during service and maintenance, for example when an RO unit is replaced with a new one. Another advantage of having atmospheric pressure in the tank 200 is that it facilitates the recirculation of water from the first and second systems 300, 400 through the return lines 8, 2B.

In the illustrated example of FIG. 2A, the vent 206 is arranged in the side wall of the tank 200, at a location spaced from the top of the tank 200, to define an overflow or spillway for water. The vent 206 is thus configured to not only allow gases to escape the tank 200 but also water. Thereby, the vent 206 is arranged to define a maximum attainable fluid level in the tank 200, ensuring the air gap at the top of the tank 200. Should the control of the water level in the tank 200 fail for some reason, excess water will flow through the vent 206 and the air gap 207 will be maintained.

FIG. 2B is a block diagram of the first system 300 in the WPA in accordance with an example. In FIG. 2B, the main path 1 extends from C to E. In the flow direction along the main path 1, the first system 300 comprises a UV irradiation device 301, a feed pump 302, a pressure sensor 303, an RO unit 304, a temperature sensor 310, a composition sensor 311, a flow switch 312, and a heater 313. It is to be understood that while each of these components serve a specific function in the context of the illustrated example, all components need not be included as shown. For example, any one of components 301-303, 310-313 may be omitted or placed elsewhere in other examples of the first system 300.

The pressure sensor 303 is configured to provide a measurement signal Pl representing hydraulic pressure (water pressure). The sensors 310, 311 provide a respective measurement signal T2, C2 representing water temperature and water composition, respectively. The signals Pl, T2, C2 may be used by the control device 500 in controlling the operation of the WPA.

The heater 313 is operable to heat the water. In some embodiments, the heater 313 is a flow-through heater. In some embodiments, the control device 500 operates the heater 313 by feedforward control based on the signal T1 and/or the signal T2 to achieve a target temperature of the water entering the second system 400. In other embodiments, the control device 500 operates the heater 313 by feedback control based on a measurement signal T3 from a temperature sensor 411 (below) in the second system 400.

The flow switch 312 is included as a safety measure to prevent that the heater 313 is activated when the flow rate of water through the heater 313 is too low, since this may cause irreparable damage to the heater 313. Thus, the flow switch 312 is configured to autonomously disable the heater 313 when the flow rate of water through the flow switch 312 is below a preset threshold value.

The UV irradiation device 301 is included to reduce microbial activity in the passing water. By installing the device 301 upstream of the RO unit 304, the microbial load entering the RO unit 304 and other downstream components will be reduced. This will extend the life of the first system 300. The device 301 may comprise a processing chamber for receiving incoming water, and at least one UV source in the processing chamber. The UV source is operable to generate UV radiation so as to irradiate at least part of the processing chamber. The UV radiation thereby interacts with the fluid within the processing chamber. The flow of water through the processing chamber may be intermittent or continuous. In some embodiments, the UV irradiation device 301 is configured to additionally remove chlorine from the passing water. This may be achieved by increasing the irradiating power of the UV source and/or by confining the emitted UV radiation to wavelengths of high absorptivity for chlorine in the water, such as dichloramine and monochloramine. The UV irradiation device 301 may thus be installed to supplement the pre-processing system 100, or even replace the dechlorination functionality of the pre-processing system 100. Generally, a UV irradiation device 301 configured to perform dechlorination may be installed anywhere in the main path 1 upstream of the first RO unit 304.

The RO unit 304 is of conventional structure and comprises a semi-permeable filter or membrane 304'. The RO membrane 304' is commonly comprised of a thin-film, cross-linked composite polymer, and is able to withstand relatively high fluid pressure. For example, the RO membrane 304' may be a spirally wound membrane or flat sheet membrane. An enlarged view of the RO unit 304 is shown in FIG. 2D. The membrane 304' separates the body of the RO unit 304 into a feed side or chamber 304" and a permeate side or chamber 304'". The RO unit 304 comprises one or more inlet ports 304A' (one shown) and one or more outlet ports 304C' (one shown) on the feed side 304", and one or more outlet ports 304B' on the permeate side 304'". It is to be understood that the specific arrangement of the RO membrane 304' and the ports 304A', 304B', 304C' in FIG. 2D is merely given as a non-limiting example. As noted above, the RO unit 304 operates by cross-flow filtration. Such filtration is achieved by causing the water to flow along the membrane 304'. In FIG. 2D, this is achieved by proper location of inlet and outlet ports 304A', 304C' on the feed side 304". Permeate passes through the membrane 304', while reject water exits the RO unit 304 through the outlet port(s) 304C'. The fluid pressure on the feed side 304" needs to be sufficient to overcome the osmotic pressure created by solutes dissolved in the water. Thereby, filtered water is forced across the membrane 304' to form a permeate stream through the outlet port(s) 304B', while dissolved solutes are excluded and discharged with the reject water in a more highly concentrated state. The feed-side fluid pressure may be in the range of 5-50 bar, and is typically 5-15 bar. On a general level, as indicated by dot-dashed arrows in FIG. 2D, the RO unit 304 may be seen to define a first flow path FP1, which extends from the inlet port(s) 304A' through the membrane 304' to the outlet port(s) 304B', and a second flow path FP2, which extends on the feed side 304" from the inlet port(s) 304A' to the outlet port(s) 304C along the membrane 304'. It is realized that FP1 is part of the main path 1 through the WPA.

Reverting to FIG. 2B, the fluid pressure on the feed side of the RO unit 304 is defined by the feed pump 302, also known as a booster pump. The pumping rate or speed of the feed pump 302 is set by a control signal PCI. The fluid pressure on the feed side may be monitored via the measurement signal Pl of the pressure sensor 303, which is arranged intermediate the feed pump 302 and the RO unit 304. A drain line 2A is connected to receive the reject water from the RO unit 304. The drain line 2A extends from the outlet port(s) on the feed side of the RO unit 304 to a drain 309 or a receptable for reject water. A flow restriction device ("flow restrictor") 306 is arranged in the drain line 2A to maintain a desired fluid pressure on the feed side of the RO unit 304. The flow restrictor 306 may be fixed or adjustable. For example, the flow restrictor 306 may comprise a small orifice, a needle valve or other variable orifice valve. In the illustrated example, a bypass line 4A is connected to extend between locations on the drain line 2A upstream and downstream of the flow restrictor 306. The bypass line 4A comprises a drain valve 307, which is operable to selectively close and open the bypass line 4A subject to a control signal VC2. Downstream of the flow restrictor 306 and the bypass line 4, a further drain valve 308 is arranged in the drain line 2A. The further drain valve 308 is operable to selectively close and open the drain line 2A subject to a control signal VC3. By opening the drain valves 307, 308, the entire volume of reject water is allowed to flow into the drain line 2A and out of the WPA into the drain 309. This bypass state may be advantageous in purging reject water upon initial use of the RO unit 304, for example when the RO unit 304 has been replaced for a new one. Additionally, the bypass state may facilitate a draining operation in which most or all of the water in the WPA is expelled from the WPA into the drain 309. In some embodiments, the flow restrictor 306 is motorized and capable of adjusting its flow resistance in response to a control signal (cf. FC1 in FIG. 5). With such a motorized flow restrictor 306, valves 307, 308 and bypass line 4A may be omitted.

In the example of FIG. 2B, a connecting line 3A is arranged to fluidly connect the drain line 2A, at a location upstream of the flow restrictor 306, to the main path 1, at a location intermediate the feed pump 302 and the RO unit 304. Thereby, a water recirculation path or loop is defined between the outlet and inlet ports on the feed side of the RO unit 304. The recirculation path may be used to maintain a high rate of water flow on the feed side of RO unit 304, thereby reducing the amount of water that otherwise would be discarded to drain. An auxiliary pump ("recirculation pump") 305 is arranged within the recirculation path to increase the fluid flow velocity or flow rate along the RO membrane 304' sufficiently to inhibit a locally increased concentration close to the membrane surface. Such locally increased concentration may result in fouling of the RO membrane 304', depending on the hardness of the incoming water to the RO unit 304. The term "fouling" includes the build-up of all kinds of layers on the surface of the RO membrane 304', including biofouling and scaling. The pumping rate or speed of the recirculation pump 305 is set by a control signal PC2.

In a variant, the recirculation pump 305 and the connecting line 3A are omitted. In another variant, the recirculation pump 305 is omitted, and the connecting line 3A is arranged to fluidly connected to the drain line 2A to the main path 1, at a location upstream of the feed pump 302, to define a recirculation path. Thereby, the suction created by the operating feed pump 302 will cause recirculation of water through the connecting line 3A. A flow restrictor may be arranged in the connecting line 3A for adjustment of the recirculated flow.

While it is possible to omit the recirculation pump 305 and the connecting line 3A, it is believed that the combination of the feed pump 302 and the recirculation pump 305 results in increased performance, less noise and lower power consumption. If only the feed pump 305 is present in the RO unit 304, this pump needs to have a greater capacity to create both the desired pressure and recirculated flow. If the feed pump 302 is supplemented by the recirculation pump 305, both pumps can have lower capacity, meaning less noise and lower cost in total as two lower capacity pumps are cheaper than one higher capacity pump. It may also be noted that the two pumps 302, 305 serve different purposes, which are difficult to accommodate by a single pump, namely boosting pressure versus boosting flow velocity. In the illustrated example, the recirculation pump 305 is located in the connecting line 3A, which is believed to be beneficial compared to having the recirculation pump 305 in the main path 1. The pressure sensor 303 may be located outside the recirculation path, as shown, or within the recirculation path.

In the illustrated example, the RO unit 304 is removably installed in the WPA. To this end, the main path 1 is provided with terminal connectors 304A, 304B for releasable attachment to the inlet and outlet ports 304A', 304B' of the RO unit 304, and the drain line 2A is provided with a terminal connector 304C for releasable attachment to the outlet port 304C of the RO unit 304.

A return line 8 is fluidly connected to the main path 1 downstream of the heater 313. As indicated by B, the return line 8 extends to the inlet port 204 on the tank 200 and thus serves to recirculate processed water to the tank 200. A control valve 314 ("return path valve") is arranged in the return line 8. The control valve 314 is operable to selectively close and open the return line 8 subject to a control signal VC4. Even if the fluid pressure is significantly lower on the permeate side compared to the feed side, the water that leaves the first system 300 is likely pressurized above atmospheric pressure. Therefore, as shown, a flow restrictor 315 may be arranged in the return line 8, to cause a pressure drop in the return line 8 and enable a controlled flow of water into the tank 200 from the first system 300. As indicated by F in FIG. 2B, a further return line 5 from the second system 400 is fluidly connected to or merged with the return line 8. Thus, the flow restrictor 315 also enables a controlled flow of water into the tank 200 from the second system 400.

FIG. 2C is a block diagram of the second system 400 in the WPA in accordance with an example. In FIG. 2C, the main path 1 extends from E to G. In the flow direction along the main path 1, the second system 400 comprises an inlet valve 401, a pressure sensor 402, a pump 403, an RO unit 404, a flow meter 408, a UV irradiation device 409, a composition sensor 410, a temperature sensor 411 and an outlet valve 412. It is to be understood that while each of these components serve a specific function in the context of the illustrated example, all components need not be included as shown. For example, any one of components 401-403, 408-412 may be omitted or placed elsewhere in other examples of the second system 400.

The inlet valve 401 is operable via a control signal VC5 to selectively open and close the main path 1 to control admission of water into the second system 400. The outlet valve 412 ("main outlet valve") is operable via a control signal VC6 to selectively open and close the main path 1 to control output of purified water from the second system 400.

The sensors 402, 408, 410 and 411 provide measurement signals P2, Fl, C3, T3 representing water pressure, water flow rate, water temperature and water composition, respectively. The signals P2, Fl, C3, T3 may be used by the control device 500 in controlling the operation of the WPA.

The RO unit 404 is configured to perform water filtration by reverse osmosis, similar to the RO unit 304. In the illustrated example, the RO unit 404 is permanently installed in the second system 404. In other words, it is not installed to facilitate replacement by a user of the WPA. As noted above, the RO unit 404 may differ from the RO unit 304 in terms of performance, cost, etc. However, principally, the RO unit 404 has the configuration shown in FIG. 2D, comprising an RO membrane 404', a feed side 404", a permeate side 404"', inlet port(s) 404A' and outlet port(s) 404C' on the feed side 404", and outlet port(s) 404B' on the permeate side 404'". The foregoing description of FIG. 2D with reference to the RO unit 304 is equally applicable to the RO unit 404. Similar to the first system 300, a feed pump 403 ("booster pump") is arranged in the main path 1 to define the fluid pressure on the feed side of the RO unit 404. The pumping rate or speed of the feed pump 403 is set by a control signal PC3. A drain line 2B is connected to receive the reject water from the RO unit 404. In contrast to the first system 300, the drain line 2B does not extend to drain, but to the inlet port 205 on the tank 200. Thus, reject water from the RO unit 404 is recirculated back to the tank 200. A flow restriction device ("flow restrictor") 406 is arranged in the drain line 2B to maintain a desired fluid pressure on the feed side of the RO unit 404. The flow restrictor 406 may be fixed or adjustable. In the illustrated example, a bypass line 4B is connected to extend between locations on the drain line 2B upstream and downstream of the flow restrictor 406. The bypass line 4B comprises a control valve 407, which is operable to selectively close and open the bypass line 4B subject to a control signal VC7. Like the flow restrictor 306 in FIG. 2B, the flow restrictor 406 may be motorized. With such a motorized flow restriction mechanism, valve 407 and bypass line 4B may be omitted. A connecting line 3B is arranged to fluidly connect the drain line 2B, at a location upstream of the flow restrictor 406, to the main line 1, at a location intermediate the feed pump 403 and the RO unit 404. Thereby, like in the first system 300, a water recirculation path or loop is defined between the outlet and inlet ports on the feed side of the RO unit 404. An auxiliary pump ("recirculation pump") 405 is arranged within the recirculation path. The pumping rate or speed of the auxiliary pump 405 is set by a control signal PC4.

The UV irradiation device 409 may be similar to the UV irradiation device 301 in the first system 300. The UV irradiation device 409 is installed to further mitigate microbial activity. It is realized that the device 409 need not be configured to remove chlorine in the incoming water, which should be effectively free of chlorine at this location in the WPA. By placing the UV irradiation device 409 in the main path 1 downstream of the RO unit 404, the device 409 is arranged to operate on water with the lowest content of suspended solids within the WPA. This will improve the efficiency of the device 409, since suspended solids are known to be a limitation parameter for water treatment by UV irradiation due to the absorption of the light by the solids and potential shielding of pathogens from the light.

The return line 5 is fluidly connected to the main path 1 intermediate the RO unit 404 and the outlet valve 412. The return line 5 is arranged to enable continuous production of product water, PWA, during operation of the WPA, by allowing excess PWA to be recirculated back to the tank 200 through the return lines 5, 8. As shown, a one-way valve 413 may be arranged in the return line 5 to prevent processed water from flowing from the first system 300 along the return line 5 to the second system 400 to potentially mix with the purified water PWA. In an alternative example, the return line 5 is separate from the return line 8 and extend to the tank 200. In such an alternative example, a flow restrictor may be arranged in the return line 5, similar to the flow restrictor 315 in FIG. 2B, to generate a net positive pressure in the main flow path 1 at the outlet from the second system 400. In the specific example of FIG. 2C, the return line 5 is fluidly connected to the main path 1 downstream of the sensors 408, 410, 411.

FIG. 3 A is a flow chart of a first method Ml for operating the WPA in FIGS 2A- 2C. The purpose of the first method Ml is to fill the first system 300 (PSI) with water and may be performed whenever PS 1 is empty of water or may contain pockets of air, for example when a new RO unit 304 has been installed. The first method Ml may be seen to involve a "priming" of PSI. During the first method Ml, the inlet valve 401 of the second system 400 (PS2) is typically closed so that only PSI is "primed" in the first method Ml. In step Si l, the UV irradiation device 301 is activated by a control signal (not shown in FIG. 2B). In step S12, the main inlet valve 102 is opened (by control signal VC1) and all pumps are stopped (if active). When the valve 102 is open, source water SWA will flow through the pre-processing system 100 and pre-processed water will enter the tank 200. In step S13, the control of the fluid level in the tank 200 is started. This level control involves ensuring, based on the signal LI from the level sensor 201, that the air gap 207 is maintained in the tank 200, and optionally that the tank 200 is not depleted of water. In one example, if a maximum fluid level is reached in the tank 200 during the method Ml, the inlet valve 102 is closed, otherwise the inlet valve 102 is kept open. In step S14, the drain valves 307, 308 in PSI are opened (by control signals VC2, VC3). In step S15, the feed pump 302 in PSI is started and run at speed SMI 1 (by control signal PCI). Thereby, a desired fluid pressure is generated on the feed side of the RO unit 304. Permeate starts to flow through the membrane 304' and into the main path 1 downstream of the RO unit 304, and reject water starts to flow from the RO unit 304 into the drain line 2A and to the drain 309. In step SI 6, the recirculation pump 305 in PSI is started and run at speed SRI 1 (by control signal PC2). Thereby, part of the reject water is recirculated back into the feed side of the RO unit 304. In step S17, the current operating state of the WPA is maintained for a flushing period. The duration of the flushing period may be experimentally determined to result in adequate filling of the hydraulic circuit of PSI. Possibly, the tank 200 is filled to its maximum fluid level during the flushing period. In step SI 8, after the flushing period, the UV irradiation device 301 is deactivated. In step S18, the pumps 302, 305 may also be deactivated. In a non-limiting example, SMI 1 is set to result in a flow rate of 1000 ml/min, SRI 1 is set to result in a flow rate of 3000 ml/min, and the flushing period is 1 - 10 minutes. FIG. 3B is a flow chart of a second method M2 for operating the WPA in FIGS 2A-2C. The purpose of the second method M2 is to start up the first system 300 (PSI) for production of processed water of suitable quality. In step S21, the drain valves 307, 308 in PSI are opened (by control signals VC2, VC3). In step S22, the UV irradiation device 301 is activated. In step S23, the level control in the tank 200 is started. In step S24, the return path valve 314 is opened (by control signal VC4) and the inlet valve 401 of the second system 400 (PS2) is closed (by control signal VC5). In step S25, the feed pump 302 in PSI is started and run at speed SM12. In step S26, the recirculation pump 305 in PSI is started and run at speed SR12. The speeds SM12, SR12 may be predefined to correspond to an optimum working point of PS 1. In a non-limiting example, SMI 2 is set to result in a flow rate of 1500 ml/min, and SR 12 is set to result in a flow rate of 4500 ml/min. In step S27, the upstream drain valve 307 is closed (by control signal VC2). In step S28, the operating state of PSI is maintained for a stabilization period. The duration of the stabilization period may be experimentally determined to result in stable operation of the RO unit 304. In a non-limiting example, the stabilization period is 1-5 minutes. After step S28, the second method M2 transitions to the third method M3.

FIG. 3C is a flow chart of the third method M3. The purpose of the third method M3 is to start up the second system 400 (PS2), and thereby the WPA, for production of purified water PWA of suitable quality. In step S31, the inlet valve 401 of PS2 is opened (by control signal VC5) and the UV irradiation device 409 is activated. In step S32, the control device 500 initiates a first control mode to control the feed pump 403 in PS2 (via control signal PC3) to achieve a first target flow rate TFla at the flow meter 408, as given by the signal Fl. The target flow rate TFla may but need not be equal to the production flow rate of the purified water when the WPA is operative. In a nonlimiting example, TFla is 500 ml/min. The first control mode involves feedback control. In step S33, the recirculation pump 405 in PS2 is set to run at speed SR21. The speed SR21 may be predefined to correspond to an optimum working point of PS2. In a non-limiting example, SR21 is set to result in a flow rate of 2500 ml/min. In step S34, after a waiting period, the return path valve 314 is closed (via control signal VC4) to define an effectively stiff or non-compliant hydraulic path between the feed pump 302 in PS 1 and the flow meter 408 in PS2. The waiting period may be experimentally determined and may, for example, be 1-5 minutes. In step S35, the control device 500 is switched from the first control mode to a second control mode, in which the feed pump 403 in PS2 in controlled (via control signal PC3) to achieve a target pressure TP2 at the pressure sensor 402, as given by the signal P2. In a non-limiting example, TP2 is in the range of 0.5-1 bar. Low TP2 tends to increase the risk of cavitation in the feed pump 403, and high TP2 results in high power consumption. The second control mode involves feedback control. In step S36, the control device 500 initiates a third control mode, which is executed in parallel with the second control mode. The third control mode involves controlling the feed pump 302 in PS 1 to achieve a second target flow rate TFlb at the flow meter 408, as given by the signal Fl. The target flow rate TFlb is equal to the production flow rate of PWA when the WPA is operative. Typically, TFlb is in the range of 200-1500 ml/min. In a non-limiting example, TFlb is 500 ml/min. The third control mode involves feedback control. After step S36, the WPA operates to produce purified water at a fixed flow rate. In step S37, the temperature of the purified water is adjusted, if necessary, by use of the heater 313 (via control signal HC). The temperature adjustment may be performed by feedback control, based on the signal T3 from sensor 411. For example, the water temperature may be controlled to fall within a predefined temperature range or to meet a predefined target value. In step S38, adjustment of the recovery rate of one or both of the RO units 304, 404 may be performed, either manually or automatically. As used herein, "recovery rate" refers to the ratio of permeate flow to feed water flow, and indicates the overall operation efficiency of an RO unit. The adjustment in step S38 may involve changing the flow resistance in the drain line 2A, 2B, for example by manipulation of the respective flow restrictor 306, 406. In step S39, the performance of the RO units 304, 404 is checked by evaluation of one or more operating parameters. The operating parameters may include one or more of composition, temperature, or flow rate of the purified water PWA, given by signal C3, T3, and Fl, respectively. Also the pressure of the PWA may be monitored by a pressure sensor (not shown) downstream of the RO unit 404 in the second system 400. If at least one operating parameter is found to deviate from a preset value or range, step S39A proceeds to step S39C, in which an operational error is signaled to the user, for example on the HMI device (503 in FIG. 1). If no deviation is found, step S39A proceeds to step S39B in which the main outlet valve 412 is opened or at least enabled for opening. When enabled for opening, the control device 500 will respond to a command from a downstream receiving device to open the valve 412. In a non-limiting example, with the composition being given by conductivity, step S39A may require the conductivity of PWA to be below 20 p S/cm.

It is realized that the recirculation pumps 305, 405 are run at fixed speeds during operation of the WPA, whereas the feed pumps 302, 403 are separately controlled by the control device 500. The feed pump 302 in PSI is controlled to achieve the target flow rate TFlb of purified water PWA, and the feed pump 403 in PS2 is controlled to achieve the target pressure TP2 at the inlet of the feed pump 403. This control approach has been found to result in stable operation of the WPA. Further, cavitation in the feed pump 403 is actively prevented.

During operation of the WPA, the control device 500 may be configured to monitor a performance parameter of the replaceable RO unit 304, to identify a current or future need to replace the RO unit 304. The performance parameter may be directly or indirectly representative of the flow resistance of the membrane 304' in the RO unit 304. One example performance parameter is given by the pressure measured by the pressure sensor 303. Another example performance parameter is given by the power consumption of the feed pump 302, for example given by a drive current or drive voltage supplied to the feed pump 302. Yet another performance parameter may be given by a flow rate measured by a flow meter (not shown) arranged in the main path 1 downstream of the RO unit 304 in PS 1.

FIG. 3D is a flow chart of a fourth method M4. The purpose of the fourth method M4 is to terminate the operation of the WPA in a well-controlled way. In step S41, the main outlet valve 412 is closed and/or disabled for opening. In step S42, the feed pumps 302, 403 are stopped. In step S43, the recirculation pumps 305, 405 are stopped. Step S43 may be performed with a time delay to step S42. In a non-limiting example, the time delay may be 1-5 minutes. In step S44, the inlet valve 401 of PS2 is closed. In step S45, the UV irradiation devices 301, 409 are deactivated.

The implementation example that has been described hereinabove with reference to FIGS 1-3 embodies a number of fundamental concepts. These concepts will be individually described below with reference to FIGS 4-12. Each concept provides its own specific technical advantages and may be implemented in a WPA, alone or in combination with one or more other concepts. As will be understood from the following description, as well as from the foregoing description of FIGS 1-3, distinct synergies are also attained by combining concepts in a WPA.

As indicated by dashed lines in FIGS 4A, 6, 7, 8A, 9A, 10A, 11 and 12, a preprocessing system 100 may be arranged upstream of the first system 300, for example to perform dechlorination of the source water, SWA. The pre-processing system 100 may have any functionality as described above with reference to FIGS 1 and 2A.

FIG. 4A is a block diagram of an example WPA that embodies a first concept. In the first concept, the WPA comprises a main flow path 1 that extends from a main water inlet 1' for source water, SWA, to a main water outlet 1" for product water, PWA. A first system 300 is arranged in the main path 1 and configured to process incoming water for reduction of water hardness, resulting in processed water with reduced water hardness. The first system 300 comprises a first RO unit 304 for use in processing of the incoming water. A second system 400 is arranged in the main path 1 intermediate the first system 300 and the water outlet 1". The second system 400 is configured to receive the processed water from the first system 300 and further process the processed water into PWA. The second system 400 comprises a second RO unit 404 for use in processing of the processed water from the first system 300. A specific feature of the first concept is that the first RO unit 304 is a sacrificial component which is removably installed in the first system 300.

Thus, according to the first aspect, the WPA comprises two RO units 304, 404, which are arranged in sequence so that the downstream (second) RO unit 404 receives and processes (purifies) the processed water (permeate) from the upstream (first) RO unit 304, which is a sacrificial/disposable component.

The respective RO unit 304, 404 may be configured in accordance with FIG. 2D.

As used herein, "sacrificial component" implies that the component has a limited life and is intended to be discarded, and replaced with a new component, when its end of life has been reached. Thus, in the first concept, the RO unit 304 is a disposable.

Generally, the RO unit 304 is arranged in the WPA to be accessible for replacement by a non-trained user. A non-trained user is distinct from a service technician or the like, who has received extensive training on how to perform maintenance, service and overhaul of WPAs, typically by dismantling or disassembling the apparatus. The non-trained user may be a patient or a caretaker. Through the replacement-friendly design of the WPA, the replacement of the RO unit 304 can, and typically is, performed locally at the site where the WPA is installed for use. In other words, the replacement is performed at the point of care. As used herein, "point of care" is the site where medical care is received, for example in the home of the patient or in a clinic or hospital.

In FIG. 4A, the RO unit 304 is removably installed by way of releasable connectors 304A, 304B, 304C, which are connected to the respective port on the RO unit 304 (cf. 304A', 304B', 304C' in FIG. 2D). The releasable connectors 304A-304C may be of any suitable type for quick release, such as screw fitting, bayonet fitting, snap fitting, luer fitting, etc. The WPA may be configured to simplify replacement of the RO unit 304 by providing easy access for a user to the RO unit 304 and the connectors 304A-304C. For example, the WPA may comprise a housing with a dedicated door or hatch, which when opened provides the user free access to the RO unit 304. Further, the WPA may be configured to present step-by-step instructions to the non-trained user on the HMI device (503 in FIG. 1) on how to remove the RO unit 304 from the WPA and install a new RO unit 304 in its place.

One technical advantage of configuring the first RO unit 304 as a sacrificial component is that the WPA may be deliberately operated, during regular operation, to sacrifice the RO unit 304 so as to protect the downstream second RO unit 404 in the second system 400. For example, as discussed with reference to the WPA in FIGS 1-3, the first RO unit 304 may be operated to reduce the water hardness of the incoming water such that the resulting processed water is sufficiently soft to mitigate scaling of the second system 400. This means that the substances that contribute to water hardness are captured by the RO membrane 304' of the first RO unit 304, resulting in a relatively fast degradation of the RO membrane 304'. This degradation is likely to be at least partly irreversible, i.e. persists even if the RO membrane 304' is subjected to a cleaning procedure.

Another advantage of using a sacrificial RO unit 304 is that the need to configure the WPA to perform regular cleaning of the RO unit 304 may be reduced or even obviated. Thus, the structure of the WPA may be simplified.

Further, by replacing the RO unit 304, based on a suitable criterion, the need for service and maintenance of the WPA as a whole may be reduced. The criterion for replacement may be given by the time since the last replacement, the effective operational time since the last replacement, or be based on measured quality of the product water PWA or a measured performance parameter for the RO unit 304, for example as discussed below with reference to FIGS 9A-9B.

The first RO unit 304 may be configured to have a predefined target lifetime when installed in the WPA. This means that the first RO unit 304 should not have to be replaced within the target lifetime. For example, the target lifetime may be given in terms of the amount of processed water that can be generated by the RO unit 304, i.e. in terms of the total production of purified water by the first RO unit 304. In some embodiments, the target lifetime is at least 20,000 L or 25,000 L, and not more than 90,000 L or 100,000 L. For a target lifetime in this range, the RO unit 304 is sufficiently simple, and thereby cheap, to allow for a reasonable operational cost of the WPA. The target lifetime also allows the WPA to be operated for a reasonable time before the RO unit 304 needs to be replaced. Assuming that PD therapy consumes 50 L PWA per day, calculations indicate that a target lifetime of 25,000 L may correspond to approximately 6 months of PD therapy. The period of use is proportional to the target lifetime, so a doubling of the target lifetime results in a doubling of the period of use. In another example, CRRT (Continuous Renal Replacement Therapy) is assumed to consume 500 L PWA per day. By analogy with the foregoing example, a target lifetime of 25,000 L may correspond to approximately 18 days of CRRT therapy.

In some embodiments, the target lifetime is in the range of 40,000 L to 70,000 L.

It is realized that the target lifetime is defined for a nominal or standard operating condition of the RO unit 304. In some embodiments, the nominal operating condition involves incoming water with a hardness of 450 ppm (mgCaCO3/L) and/or a conductivity of 2,000 pS/cm, and a flow rate of the processed water of 1 L/min. The target lifetime may be defined to ensure that the permeate water from the RO unit 304 fulfils one or more water quality parameters during the target lifetime, for example in term of water hardness, conductivity, or microbial load, or any combination thereof. For example, the target lifetime may be defined so that the processed water has a hardness of less than 30 ppm (mgCaCO3/L) and/or a conductivity of less than 50 pS/cm.

In some embodiments, the WPA is configured to operate the replaceable RO unit 304 without heat disinfection of the RO membrane 304' during the target lifetime. For example, the RO unit 304 may be configured for a maximum fluid temperature of 40°C, 50°C, or 60°C. Thus, the RO unit 304 need not be configured to withstand temperatures above the maximum fluid temperature. Such a RO unit is much cheaper, for example by a factor 5-10, than an RO unit that is configured to withstand higher temperatures.

In some embodiments, the WPA is configured to operate the replaceable RO unit 304 without cleaning, disinfection or sanitization of the RO membrane 304' by a cleaning agent and/or by application of heat during the target lifetime. As used herein, "cleaning" is performed to remove deposits, "sanitization" is performed to remove bacteria, and "disinfection" is performed to remove both bacteria and viruses.

In the example of FIG. 4A, the second RO unit 404 is permanently installed in the second system 400. This allows for the use of a high-end RO unit 404 in the second system 400. The use of a high-end RO unit 404, with high-end performance, relaxes the requirements on the first RO unit 404. Thus, there is a symbiosis between the RO units 304, 404, where the first RO unit 304 provides for use of a second RO unit 404 of high performance and quality, and this type of second RO unit 404 provides for use of a simpler first RO unit 304, which is a sacrificial component.

The WPA may be configured to perform a cleaning, sanitization or disinfection of the RO membrane 404' of the second RO unit 404 by use of a cleaning agent and/or by application of heat.

As understood from FIGS 1-3, the WPA may comprise additional components. For example, as shown in FIG. 4A, a feed pump 302 may be arranged in the main path 1 upstream of the first RO unit 304 to increase the pressure of the incoming water to the RO unit 304. Although not shown in FIG. 4A, a corresponding feed pump (cf. 403 in FIG. 2B) may be arranged in the second system 400 upstream of the second RO unit 404.

FIG. 4B is a flow chart of an example method M5 of operating a WPA for replacement of the first RO unit 304. The method M5 may be performed by the control device 500 in FIG. 1. In the method M5, the user is instructed to remove the RO unit 304 from the WPA when a criterion for replacement is fulfilled, for example as exemplified hereinabove. The user may be instructed on the HMI device (503 in FIG. 1). The method M5 comprises a step S51 of instructing the user to disconnect and remove the RO unit 304 from the first system 300 (denoted PSI in FIG. 4B). In step S52, the user is instructed to install a new RO unit 304 in the first system 300. The completion of step S52, hence installation of a new RO unit 304, may be automatically detected by the control device 500 and/or confirmed by user input via the HMI device. Automatic detection of installation may use any form of detection system to detect disconnection of an RO unit followed by connection of an RO unit, for example by computer vision, or by use of electrical contacts in the connectors 304A-304C and in the ports 304A'-304C' of the RO unit 304. Further, after detection of installation, a test may be performed to verify one or more properties of the RO unit 304, for example as described below with reference to FIGS 9A-9B. The WPA is thereby ready to be started, for example in accordance with the methods Ml, M2 or M3 (FIGS 3A-3B), or a combination thereof. In step S53, the WPA is operated to generate PWA with required properties, for example a conductivity of less than 20 p S/cm. As noted above, the PWA may fulfil all or part of the requirements of "water for dialysis".

FIG. 5 is a block diagram of a first RO unit 304 that embodies a second concept. In the second concept, the main flow path 1 comprises a feed line 1A that extends to the water inlet 304A' on the feed side 304" of the RO unit 304, which may or may not be a sacrificial component. The first system 300 comprises a feed pump 302 arranged in the feed line 1A to pressurize the incoming water at the water inlet 304A'. The first system 300 further comprises a drain line 2A that extends from the retentate outlet 304C' on the feed side 304" of the RO unit 304. A flow restriction device 306 is arranged in the drain line 2A to define a flow resistance at the retentate outlet 304C' on the feed side 304" of the RO unit 304. The flow restriction device 306 is included to maintain a desired fluid pressure on the feed side 304" of the RO unit 304. The restriction device 304 may be configured with a fixed flow resistance or to enable the flow resistance to be varied. In some embodiments, the restriction device 306 is a variable orifice valve. In some embodiments, the restriction device 306 is operable to change the flow resistance based on a control signal. In some embodiments, the restriction device 306 is motorized and electrically controllable by a control signal, which is generated by the control device 500 (FIG. 1) and represented as FC1 in FIG. 5. In some embodiments, as shown, the restriction device 306 is supplemented by a bypass path 4A containing an on/off valve 307. The bypass path 4A is connected to the drain line 2A on both sides of the restriction device 306. The purpose of the on/off valve 307 is to enable a high flow rate through the feed side 304", for example during priming, if such a high flow rate is not supported by the restriction device 306. Thus, the on/off valve 307 may be selectively opened, subject to a control signal (cf. VC2 in FIG. 2B).

In some embodiments, as shown in FIG. 5, the first system 300 further comprises a connecting line 3A, which is arranged in fluid communication with the drain line 2A and the feed line 1A to define a recirculation path from the retentate outlet 304C' to the water inlet 304A'. An auxiliary pump ("recirculation pump") 305 is arranged in the recirculation path to provide an added flow rate on a flow path along the RO membrane 304' on the feed side 304" of the RO unit 304 (cf. FP2 in FIG. 2D). The provision of the recirculation loop reduces the amount of water that is discarded to drain. Other advantages and features of the recirculation path and the recirculation pump 305 have been discussed with reference to FIG. 2B and will not be repeated. In the illustrated example, the recirculation pump 305 is arranged in the connecting line 3A.

It is to be noted that the degree of flow resistance by the restriction device 306, through its impact on the fluid pressure on the feed side 304", affects the flow rate of processed water from the RO unit 304. The recirculation pump 305, on the other hand, has little or no influence on the fluid pressure on the feed side 304", but rather affects the flow rate of water through the feed side 304".

Although the second concept is illustrated for the first RO unit 304 in FIG. 5, it is equally applicable to the second RO unit 404.

FIG. 6 is a block diagram of an example WPA that embodies a third concept. In the third concept, the WPA comprises a main flow path 1 that extends from a main water inlet 1' for source water, SWA, to a main water outlet 1" for product water, PWA. A first system 300 is arranged in the main path 1 and configured to process incoming water for reduction of water hardness, resulting in processed water with reduced water hardness. The first system 300 comprises a first RO unit 304 for use in processing of the incoming water. A second system 400 is arranged in the main path 1 intermediate the first system 300 and the water outlet 1". The second system 400 is configured to receive the processed water from the first system 300 and further process the processed water into PWA. The second system 400 may use any suitable water processing technique, such as reverse osmosis and/or ion exchange. A specific feature of the third concept is a recirculation path 5 that is arranged to provide for recirculation of the product water, PWA, which is generated by the second system 400, back to the first system 300 and/or the second system 400. In the illustrated example, the flow of PWA along the main path 1, and in the recirculation path 5, is generated by the feed pump 302 in the first system 300. By recirculating PWA, it is possible to operate the WPA to continuously generate PWA at a predefined flow rate, even if a downstream device (not shown) obtains PWA from the WPA at a lower flow rate and/or intermittently. The continuous operation will ensure a consistent quality of the generated PWA. By contrast, should the PWA generation rate of the WPA need to be modified according to the needs of the downstream device, the quality of the generated WPA may vary as a result of transient effects. This may be mitigated by discarding the initial PWA that is generated whenever the PWA generation rate is modified. However, this may lead to significant waste of water, as well as longer response times of the WPA.

In the illustrated example, the WPA comprises an outlet valve 412 that is selectively opened by the control device 500 (FIG. 1) to provide PWA to the downstream device. The outlet valve 412 may instead be part of and controlled by the downstream device.

In some embodiments, as indicated by a solid arrow in FIG. 6, the recirculation path 5 extends from a first location in the main path 1 downstream of the second system 400, to a second location in the main path 1 upstream of the first system 300. Thus, the recirculated PWA is included in the incoming water to the first system 300, which may limit the effect of the recirculated PWA on the operation of the second system 400. As understood from the implementation example in FIGS 1-3, it may be beneficial to recirculate excess PWA via a tank (200 in FIG. 2A) arranged in the main path 1 upstream of the first system 300. This will further decouple the operation of the first and second systems 300, 400 from the recirculation of excess PWA.

In some embodiments, as indicated by reference numeral 6 in FIG. 6, the recirculation path instead extends from the first location to a third location in the main path 1 intermediate the first and second systems 300, 400. A tank (not shown) may be arranged in the main path 1 intermediate the first and second systems 300, 400 to receive the recirculated PWA. The tank may also receive the processed water from the first system 300.

In some embodiments, the recirculation path extends from the first location to both the second location and the third location.

As shown in FIG. 6, the recirculation path may include a flow restriction device 315. One purpose of the restriction device 315 is to ensure a desired fluid pressure at the water outlet 1". This is relevant whenever the pressure at the second or third locations at the end of the recirculation path is significantly lower than the desired fluid pressure at the outlet 1". In the example of FIGS 1-3, the recirculation path extends to a tank 200 at atmospheric pressure, and the restriction device 315 is arranged to establish a higher fluid pressure at the outlet 1". The restriction device 315 may also serve to provide a more controlled flow in the recirculation path. The restriction device 315 may be configured with a fixed flow resistance or to enable the flow resistance to be varied. FIG. 7 is a block diagram an example WPA that embodies a fourth concept. In the illustrated example, the components along the main flow path 1 may be the same as in the first concept (FIG. 4) and will not be described again. It may be noted that the first RO unit 300 may, but need not, be a sacrificial component. In the illustrated example, a tank 200 is arranged upstream of the first system 300 to receive SWA, optionally after pre-processing by system 100. A specific feature of the fourth concept is that the drain path 2B from the second RO unit 404 is fluidly connected to the main path 1 at a location upstream of the first system 300, so that reject water ("retentate") from the second RO unit 400 is returned for processing by the first and second systems 300, 400. This will increase the efficiency of WPA, by reducing the amount of reject water that is expelled to drain. The underlying rationale is that the reject water from the second RO unit 404 contains relatively small amounts of impurities, since the major part of impurities are removed by the first system 300. Recycling the reject water from the second system 400 will therefore have little negative impact on the operation of the first system 300. For example, since the second system 400 operates on water that has been softened by the first system 300, the recycling of reject water from the second system 400 will not increase scaling of the RO membrane 304'. Thus, the life of the RO membrane 304' is largely unaffected by the recycling. It is to be noted that, in the example of FIG. 7, the reject water from the first system 300 is not recycled. The drain line 2A from the first system 300 may extend to a drain. In a variant, part of the reject water from the first system 300 is also recycled, for example as described with reference to the example in FIG. 5.

As seen in FIG. 7, the drain line 2B may include a flow restriction device 406, which corresponds to the flow restriction device 306 in FIG. 5 and is included to maintain a desired fluid pressure on the feed side of the RO unit 404.

By connecting the drain line 2B to the tank 200, as shown, the operation of the first and second systems 300, 400 is decoupled from the recirculation of reject water. Further, recirculation into the tank 200 may facilitate mixing of the reject water into the SWA. However, the drain line 2B may extend to another location in the main path 1 upstream of the first system 300, for example as indicated by a dashed arrow 7. Further, the tank 200 may be omitted.

FIG. 8A is a block diagram of an example WPA that embodies a fifth concept. In the illustrated example, the components along the main flow path 1 may be the same as in the third concept (FIG. 6) and will not be described again. A specific feature of the fifth concept is that the main path 1, at a location intermediate the first system 300 and the second system 400, is connected for fluid communication with the main flow path 1 at a location upstream of first system 300. This allows for processed water, which is generated by the first system 300, to be recirculated back to the first system 300. This recirculation may be employed during start-up of the WPA to allow the first system 300 to be started separately from the second system 400. This will result in a controlled start procedure for the WPA. For example, time to reach steady-state operation of the WPA may be minimized. Further, the first system 300 may generate processed water of inferior quality during start-up, and the recirculation will prevent the second system 400 from being exposed to such processed water. This will, for example, reduce the risk for scaling in the second system 400.

The fifth concept may be particularly useful when the first RO unit 304 is a sacrificial component, to ensure that a newly installed first RO unit 304 is properly filled with water ("primed") and is operated to generate processed water of proper quality before the processed water is admitted into the second system 400.

In the illustrated example, a return flow path 8 is arranged to fluidly connect the main path 1, at a juncture intermediate the first and second systems 300, 400, to the feed side (304" in Fig. 2D) of the RO unit 304. A combination of on/off valves 314, 401 forms a valve arrangement that is switchable between directing the processed water from the first system 300 on the main path 1 to the second system 400, or directing the processed water on the return path 8 to the feed side of the RO unit 304. In the illustrated example, valve 314 is arranged in the return path 8, and valve 401 is arranged in the main path 1 downstream of the juncture of the return path 8. The valves 314, 401 may be operated by control signals from a control device (500 in FIG. 5). It is realized that other implementations of the valve arrangement are conceivable, for example as a unitary three-way valve.

In the illustrated example, a sensor 311 is arranged in the main path 1 intermediate the first system 300 and the juncture of the return path 8. The sensor 311 is configured to generate a sensor signal C2 for a parameter that represents the operation of the first system 300, such as pressure, temperature, flow rate, etc. In some embodiments, the sensor signal C2 represents a composition-related parameter of the processed water. In some embodiments, the composition-related parameter corresponds to electrical conductivity.

In the illustrated example, a feed pump 302 is arranged in main path 1 upstream of the first RO unit 304. The return path 8 extends to a location on the main path 1 upstream of the feed pump 302, so that the suction created by the feed pump 302 drives the recirculation of processed water.

Although not shown in FIG. 8A, a tank may be arranged in the main path 1 upstream of the first system 300 receive the processed water from the return path 8. The tank may also be arranged to receive SWA, optionally after pre-processing by system 100.

FIG. 8B is flow chart of an example method M6 for starting the WPA in FIG. 8A. The method M6 may be performed by the control device 500 in FIG. 1. In step S61, the valves 314, 401 are operated to close the main path 1 between the first and second systems 300, 400 (denoted PSI and PS2 in FIG. 8B), and open the return path 8. In step S62, the feed pump 302 is started and operated at a first predefined operating point, OP1. Thereby, processed water is generated at a fixed flow rate and recirculated back to the inlet of the RO unit 304. In step S63, a value of one or more status parameters for the first system 300 is determined based on the sensor signal C2. In step S64, the value from step S63 is evaluated in relation to a predefined criterion that defines an acceptable property of the processed water. For example, step S64 may verify that a measured conductivity is below a predefined conductivity limit. If the evaluation in step S64 is affirmative, the method proceeds to step S65, in which the valves 314, 401 are operated to open the main path 1 and close the return path 8. Thus, the flow of processed water is switched towards the second system 400. In step S66, the second system 400 is started and operated at a second predefined operating point, OP2. If the evaluation in step S64 is negative, the method proceeds to step S67 to check if a maximum time has passed since step S62. If not, the method proceeds to step S63, optionally after a waiting time in step S68. If maximum time has passed, the start-up procedure may be terminated and an error signal may be generated in step S69 to alert the operator that the start-up procedure has failed.

By steps S63, S64, S67 and S68, the processed water from the first system 300 is switched towards the second system 400 when the feed pump 302 has been operated for a time period. In the example of FIG. 8B, the time period is given by measurements. In a variant, the time period is predefined.

In a variant, the valve arrangement may be controlled to open both the main path 1 and the return path 8 in step S65, so that processed water is provided both to the second system 400 and recirculated back to the first system 300.

FIG. 9A is a block diagram of an example WPA that embodies a sixth concept. In the illustrated example, the components along the main flow path 1 may be the same as in the third concept (FIG. 6) and will not be described again. The first RO unit 304 is a sacrificial component configured for replacement, as indicated by connectors 304A- 304C. A specific feature of the sixth concept is a monitoring device 510, which is configured to determine a performance parameter that is indicative of a flow resistance through the first RO unit 304 and evaluate the performance parameter for detection of a need for replacement of the first RO unit 304. The flow resistance is representative of a degree of fouling of the RO membrane 304'. The monitoring device 510 may be included in the control device 500 (FIG. 1) or a separate device. As shown, the WPA may include a pressure sensor 303, which is arranged in the main path 1 upstream of the RO unit 304 to generate a pressure signal Pl indicative of the fluid pressure on the feed side of the RO unit 304. For example, for a constant flow rate of water through the RO unit 304, the fluid pressure on the feed side will increase with increasing flow resistance through the RO unit 304. Alternatively or additionally, the WPA may include a flow meter 320, which is arranged in the main path 1 intermediate the first and second systems 300, 400 to generate a flow signal F2 indicative of the flow rate of processed water from the first system 300. The flow rate of processed water from the first system 300 will decrease with increased flow resistance through the RO unit 304. Likewise, an increased flow resistance through the RO unit 304 will cause the power consumption of the feed pump 302 to increase. The power consumption may be represented by signal El, which may represent a drive current or drive voltage of the feed pump 302. The signal El is generated by a power sensor 321, which may be co-located with the pump 302, as shown, or be included in the monitoring device 510. The power sensor 321 may be arranged to measure the electrical drive current that is supplied to a motor in the pump 302 during operation of the pump 302 or the electrical drive voltage that is applied to the motor during operation of the pump 302. As indicated in FIG. 9A, the monitoring device 510 may be configured to operate on at least one of the signals El, Pl, F2 to evaluate the status of the RO membrane 304' and output a filter status signal, FSS.

FIG. 9B is flow chart of an example method M7 of operating the monitoring device 510 in FIG. 9A. The method M7 may be performed continuously or intermittently during operation of the WPA. In step S71, measurement data indicative of at least one of feed side pressure (signal Pl), downstream flow rate (signal F2) or feed pump power (signal El) is obtained. In step S72, the measurement data is evaluated in relation to a predefined criterion. For example, one or more performance parameters may be determined from the measurement data and compared to a respective acceptable range. The acceptable range may be defined to ensure proper operation of the RO unit 304. Outside the acceptable range there may be an increased risk for damage to or failure of the RO membrane 304', elevated power consumption and noise of the feed pump 302, etc. In examples of step S72, the feed side pressure or feed pump power may be compared to a maximum allowable limit, or downstream flow rate may be compared to a minimum allowable limit. If the respective performance parameter is within the acceptable range, the method returns to step S71 (by step S73), optionally after a waiting period in step S74. Otherwise, step S75 is performed to indicate a need to replace the RO unit 304 via the signal FSS.

As an alternative or supplement to the method M7, a need to replace the RO unit 304 may be signaled when the RO unit 304 has been installed for a predefined time period, has been in use for a predefined time period, or has been operated to generate a predefined amount of processed water.

FIG. 10A is a block diagram of an example WPA that embodies a seventh concept. In the seventh concept, the WPA comprises a main flow path 1 that extends from a main water inlet 1' for source water, SWA, to a main water outlet 1" for product water, PWA. A first system 300 is arranged in the main path 1 and configured to process incoming water for reduction of water hardness, resulting in processed water with reduced water hardness. The first system 300 comprises a first RO unit 304 for use in processing of the incoming water, and a first feed pump 302 for feeding the incoming water to the first RO unit 304. The first RO unit 300 may, but need not, be a sacrificial component. A second system 400 is arranged in the main path 1 intermediate the first system 300 and the water outlet 1". The second system 400 is configured to receive the processed water from the first system 300 and further process the processed water into PWA. The second system 400 comprises a second RO unit 404 for use in processing of the processed water from the first system 300, and a second feed pump 403 for feeding the processed water to the second RO unit 404. A flow meter 408 is arranged to provide a sensor signal Fl indicative of the flow rate of PWA as generated by the second system 400. A pressure sensor 402 is arranged to provide a sensor signal P2 indicative of the inlet pressure of the processed water at the second feed pump 403. A specific feature of the seventh concept is a first controller 511, which is configured to generate a first control signal PCI for the first feed pump 302 based on the sensor signal Fl, and a second controller 512, which is configured to generate a second control signal PC3 for the second feed pump 403 based on the sensor signal P2. The first and second controllers 511, 512 may be included in the control device 500 of FIG. 1. The provision of the first and second controllers 511, 512 has been found to provide a simple and stable control of the WPA, by providing separate control of the first feed pump 302 and the second feed pump 403. In other words, the first and second controllers 511, 512 operate independently of each other, in the sense that they operate on different input variables and control different pumps.

The first feed pump 302 is controlled by the first controller 511 to achieve a well- defined flow rate of product water PWA from the second system 400. The second controller 512 is arranged to achieve an adequate inlet pressure of the second feed pump 403 to ensure proper operation of the second feed pump 403. There is a risk for cavitation in the feed pump 402 if its inlet pressure is too low. As the inlet pressure of the second feed pump 403 is increased, the power consumption of the WPA is rapidly increased through increased power consumption of the first system 300 to achieve the increased inlet pressure of the second feed pump 403. Further, an excessive inlet pressure of the second feed pump 403 may cause uncontrolled pressure pulsations in the hydraulic system of the WPA.

In some embodiments, as indicated in FIG. 10A, the first controller 511 is configured to generate the first control signal PCI to achieve a target flow rate, TFlb, of PWA at the flow meter 408. In some embodiments, TFlb is in the range of 100-2000 ml/min, for example in the range of 200-1500 ml/min.

In some embodiments, as indicated in FIG. 10A, the second controller 512 is configured to generate the first control signal PCI to achieve a target inlet pressure, TP2, of the processed water at the second feed pump 403. The Applicant has found that TP2 > 0 bar (atmospheric pressure) mitigates the risk of cavitation. The Applicant has further found that TP2 < 1 bar results in an acceptable power consumption and mitigates occurrence of uncontrolled pressure pulsations. It is currently believed that preferable performance is achieved with TP2 in the range of 0.1-0.9 bar.

In the example of FIG. 10A, the flow meter 408 is arranged in the main path 1 intermediate the second RO unit 404 and the water outlet 1". Should the seventh concept be combined with the recirculation of the third concept (FIG. 6), the flow meter 408 is arranged upstream of the recirculation line, i.e., between the second system 400 and the juncture of line 5 in FIG. 6, to monitor the total flow of PWA generated by the second system 400. The flow meter 408 may be based on any conventional measurement technique, such as mechanical, pressure based, variable area based, optical, electromagnetic, ultrasonic, Coriolis based, thermal mass based, or vortex based.

In the example of FIG. 10A, the pressure sensor 402 is arranged in the main path 1 upstream of the second feed pump 403. The pressure sensor may be of conventional construction to operate, for example, by resistive, capacitive, inductive, magnetic or optical sensing, and using one or more diaphragms, bellows, Bourdon tubes, piezoelectrical components, semiconductor components, strain gauges, resonant wires, accelerometers, etc.

The Applicant has found that the performance of the control according to the seventh concept is improved if the hydraulic system between the feed pump 302 and the flow meter 408 is "stiff" when the WPA is operated to generate PWA. In this context, "stiff" implies that that there is no compliance in this hydraulic system. In other words, the hydraulic system is configured so that a predefined change in flow rate by the feed pump 302 causes a deterministic change in flow rate at the flow meter 408, assuming that the flow resistance through the RO unit 304 remains the same. Such a hydraulic system is provided in the example of FIG. 10A, assuming that all fluid lines are nonyielding at relevant operation conditions. The skilled person understands that even if reject water is diverted from the RO units 304, 404 on drain lines 2A, 2B, the hydraulic system is still "stiff" under steady-state operation of the WPA.

FIG. 10B is a flow chart of an example method M8 of controlling the WPA in FIG. 10A. The method M8 may be performed by the control device 500 in FIG. 1. In step S81, a target flow rate, TF1, for the PWA that is generated by the WPA is obtained. In step S82, a target pressure, TP2, at the inlet of the second feed pump 403 is obtained. The target values TF1, TP2 may be retrieved from memory (502 in FIG. 1) and/or entered by an operator on an input interface of the WPA, for example the HMI device 503 in FIG. 1. The method M8 starts two control routines, which are performed independently of each other. In one routine, steps S83 and S84 are repeatedly performed. In step S83, a measured value of the flow rate of PWA from the second system 400 is obtained from the measurement signal Fl. In step S84, a control signal (PCI in FIG. 10A) for the first feed pump 302 is generated to match the measured value to the target value, TF1. Step S84 may be based on any suitable control algorithm, including feedback control using P, PI or PID control, or feed forward control. In the other routine, steps S85 and S86 are repeatedly performed. In step S85, a measured value of the inlet pressure to the second feed pump 403 is obtained from the measurement signal P2. In step S86, a control signal (PC3 in FIG. 10A) for the second feed pump 403 is generated to match the measured value to the target value, TP2. Step S86 may be based on any suitable control algorithm, including feedback control using P, PI or PID control, or feed forward control.

FIG. 11 is a block diagram of an example WPA that embodies an alternative to the seventh concept. Compared to the WPA in FIG. 10A, the WPA in FIG. 11 includes a flow meter 408', which is arranged between the first and second systems 300, 400 to measure the flow rate of processed water from the first system 300 into the second system 400. A first controller 511' is configured to generate a control signal PCI for the first feed pump 302 based on a signal F2 from the flow meter 408', to achieve a target flow rate TF2 of processed water into the second system 400. A second controller 512' is configured to generate a control signal PC3 for the second feed pump 403 based on the signal Fl from the flow meter 408, to achieve a target flow rate TF1 of PWA from the second system 400.

While the controllers 511', 512' in FIG. 11 are operable to control the WPA to produce the target flow rate TF1 of PWA, the control is sensitive to disturbances. One reason for this is that the control is separated into two consecutive control routines; one control routine for the first system 300, and one control routine for the second system 400. Disturbances in the first system 300 will thereby have a direct impact on the control of the second system 400. Compared to the seventh concept (FIGS 10A-10B), the control is less stable in FIG. 11. In the seventh concept, one control routine operates both systems 300, 400 jointly to generate PWA at the target flow rate, and another control routine ensures proper operation of the second feed pump 403. This ensures stable operation of both systems 300, 400 even if one of the systems 300, 400 is subject to disturbances. Another disadvantage of the control in FIG. 11 is that the risk for cavitation at the second feed pump 403 is not addressed. This risk may increase over time, with increasing fouling of the RO membrane 304' if such fouling reduces the inlet pressure of the second feed pump 403. Cavitation may potentially destroy the pump 403. The risk for cavitation is minimized in the seventh concept.

FIG. 12 is a block diagram of a variant of the first concept in FIG. 4A. Compared to FIG. 4A, both RO units 304, 404 are configured as sacrificial components. Thus, like the first RO unit 304, the second RO unit 404 is removably installed by way of releasable connectors 404A, 404B, 404C, which are connected to the respective port of the RO unit 404 (cf. 404A', 404B', 404C in FIG. 2D). The use of disposable RO units in both systems 300, 400 may enable simplification of the WPA.

The Applicant currently believes that the variant in FIG. 12 is particularly useful when the use of the WPA is likely to be discontinued for longer time periods, for example for several days, one or more weeks, or even one or more months. Such discontinuous operation is likely to occur when the WPA is used for generating PWA in intensive care. For example, the PWA may be supplied to a mixing unit that generates treatment fluid for a dialysis machine used in intensive care to treat a patient suffering from acute kidney injury, AKI, by dialysis therapy, for example PD or CRRT (Continuous Renal Replacement Therapy). An intensive care unit (ICU) may see this type of patient relatively seldom. Approximately 5%-30% of the patients in ICU may require dialysis therapy. In between uses, the WPA, the mixing unit, and the dialysis machine may be stowed away. In some embodiments, two or more of the WPA, the mixing unit and the dialysis machine are combined into a unitary machine.

The underlying rationale of having only disposable RO units 304, 404 in the WPA is to improve patient safety and decrease the start-up time of the WPA after storage. In some embodiments, the control device 500 is configured to instruct the user to replace both RO units 304, 404. For example, such an instruction may be provided whenever the WPA is started after storage. In some embodiments, the replacement instruction is automatically provided by the control device 500 when the storage time exceeds a predefined time limit, for example 2-7 days. It is also conceivable that a replacement instruction is provided whenever the total time of use or the total time of installation of the RO units 304, 404 exceeds a predefined limit, or the RO units 304, 404 have been operated to generate a predefined amount of product water.

In some embodiments, the target life of the respective RO unit 304, 404 may be smaller than when only the first RO unit 304 is disposable (FIG. 4). This may reduce the cost of the RO units 304, 404 even further and is enabled by the fact that the WPA is likely to only be used for a relatively short time between storages.

It is to be understood that the WPA, for replacement of the RO units 304, 404, may be operated by analogy with the method M5 in FIG. 4B. Thus, the user may be instructed to disconnect and remove the RO units 304, 404 (step S51), whereupon the WPA may be operated to perform a cleaning, sanitization or disinfection of the hydraulic system of the first and second systems 300, 400 (step S53). When this operation is completed, the user is instructed to install new RO units 304, 404 in the WPA. The WPA is thereby ready to be started, for example in accordance with the methods Ml -M3 in FIGS 3A-3C. It is realized that the second system 400 may be primed by a method similar to the method Ml for priming the first system 300.

In view of growing environmental concerns, it is desirable to reduce the consumption of electrical power by the WPA. This objective may be achieved by the example WPA in FIG. 13 A, which shows a simplified version of the first system 300. The second system 400 is not shown in FIG. 13A but may be configured in correspondence with FIG. 2C and fluidly connected to the first system 300 at points D, E and F. The pre-processing system 100 is optional and indicated by dashed lines. The following description will focus on added components compared to the WPA in FIGS 2A-2C.

When the WPA is running to generate product water, the heater 313 is operated to heat the passing water to achieve a target temperature of the water that enters the second system 400. The target temperature may be set to achieve a predefined temperature of the product water that is generated by the second system 400, or by operational requirements of the second system 200. In some embodiments, the target temperature is in the range of 25-37°C. While the WPA is operated to generate the product water, the water in the tank 200 will be at an elevated temperature, as a result of the recirculation of fluid in the WPA. In the example of FIG. 13 A, the product water at elevated temperature is returned to the first system 300 through return line 5, and conveyed to the tank by return line 8. Further, reject water at elevated temperature is returned to the tank 200 from the RO unit 404 via drain line 2B. Like the water in the tank 200, the reject water in the drain line 2A from the RO unit 304 will be at an elevated temperature.

During production of product water, the tank 200 will be replenished by admission of SWA, optionally pre-processed by the system 100. The temperature of the SWA is typically well below the target temperature. It is not uncommon for tap water to be in the range of 5-15°C. This means that the water temperature in the tank 200 will be lowered whenever the tank 200 is replenished. If it were not for the replenishment, the heater 313 would only need to compensate for heat losses in the WPA. However, the replenishment by cold SWA causes a significant increase in the power consumption of the heater 313.

In FIG. 13 A, this problem is addressed by the addition of a heat transfer device (HTD) 50, which is arranged to transfer energy (heat) Hl from a first location ("locus") HL1 in the drain line 2A to a second location ("locus") in the main path 1 upstream of the heater 313. FIG. 13A shows two examples of the second location: a location HL2 upstream of the tank 200, or a location HL3 downstream of the tank 200. By the HTD 50, heat that would otherwise be passed to the drain 309 is recovered and used to heat the water upstream of the heater 313. This reduces the power consumption of the heater 313. It may be preferable for HL2 to be the second location for the heat transfer since the temperature difference is larger between HL1 and HL2 than between HL1 and HL3, A larger temperature difference translates to a better heat transfer efficiency. As noted above, the flow rate of SWA into the tank 200 may vary over time, and may even be intermittent. Under such conditions, it may be preferable for HL3 to be the second location for the heat transfer, since the varying flow at HL2 may give a reduced heat transfer efficiency. However, depending on the temperatures and flow rates in the WPA, the heat transfer capacity may be better between HL1 and HL2 even if the inflow of SWA varies over time.

In some embodiments, and as shown in FIG. 13 A, the second location HL2/HL3 is upstream of the RO unit 304. This will raise the temperature of the water entering the RO unit 304, which in turn will increase the filtration performance of the RO unit 304. It is well-known that fluid temperature is a key factor for the performance of the RO membrane (304' in FIG. 2D). Generally, permeate flow increases with increasing water temperature. However, the salt rejection ratio of the RO unit 304 decreases with increasing water temperature. For many RO units, the optimum temperature is in the range of 20-30°C, typically at or close to 25°C. By the HTD 50, the water temperature may be increased to increase the flow rate of permeate water. This means that the flow rate of reject water is decreased, resulting in a further reduced energy loss to drain 309. In some embodiments, and as shown in FIG. 13 A, the second location HL2/HL3 is upstream of one or more sensors in the main path 1. Sensors have a rated temperature range, in which they are calibrated for use. Thus, for a sensor upstream of the heater 313, the HTD 50 may allow for the sensor to have a relatively narrow temperature range. This may reduce the cost of the sensor and/or improve its performance. In the example of FIG. 13 A, the sensor 311 is arranged upstream of the heater 313. As described above with reference to FIG. 8 A, the signal C2 from the sensor 311 may be used during start-up of the WPA, to determine when to open the main path 1 and close the return path 8. As noted above, the sensor 311 may be configured to measure a composition-related parameter. In some embodiments, the sensor 311 is a conductivity sensor. Such sensors are known to be strongly temperature-dependent, so it is beneficial to have a limited operating range in terms of water temperature. The composition sensor 311 may also be used for monitoring the operation and performance of the RO unit 304 during production of product water. In some embodiments, the WPA comprises two conductivity sensors, one upstream and one downstream of the RO unit 304, to allow for calculation of the salt rejection ratio, as is known in the art. It may be beneficial for the HTD 50 to be located upstream of both of these conductivity sensors.

In some embodiments, the HTD 50 is a heat exchanger, which is fluidly interposed in the main path 1 and the drain line 2A. As used herein, "fluidly interposed" implies that the heat exchanger is inserted into a fluid line to pass a fluid flowing along the fluid line. A schematic view of a heat exchanger 50 is shown in FIG. 13B. The heat exchanger 50 defines at least one first fluid channel 50A, which is fluidly interposed in the drain line 2A, and at least one second fluid channel 50B, which is fluidly interposed in the main path 1. A heat exchanger is a passive device which is designed to transfer a nominal amount of heat Hl, for a given fluid and a given flow rate, from the fluid in the first fluid channel(s) 50A to the fluid in the second fluid channel(s) 50B, or vice versa. As explained hereinabove, the transfer of heat Hl reduces the power consumption of the heater 313. The heat exchanger 50 may be of any type, such as a plate heat exchanger, a tube heat exchanger or a spiral heat exchanger, and may be arranged in counter flow configuration or parallel flow configuration.

It may be desirable for the temperature of the water entering the RO unit 304 and/or the sensor(s) 311 to be well-controlled. To this end, the HTD 50 may be or include a heat pump, which is operable to transfer thermal energy (heat) between HL1 and HL2/HL3. The heat pump 50 is an active device, which is electrically operable to control the amount of heat Hl that is transferred. Also the direction of transfer by the heat pump 50 is controllable. The amount of heat Hl is "controlled" in the sense that it is selectively adjustable. The heat pump 50 may be controlled by a control device (500 in FIG. 1), for example to achieve a target temperature at a selected location between HL2/HL3 and the heater 313. In FIG. 13 A, the control device may use the signal T2 from the temperature sensor 310 to operate the heat pump 50 to achieve a controlled water temperature at the sensor 311. Alternatively, if a temperature sensor is located in the main path 1 upstream of the RO unit 304, the heat pump 50 may be controlled to achieve a controlled water temperature at the inlet of the RO unit 304.

In a variant, the heat pump 50 and the heater 313 are jointly controlled to achieve a target temperature in the main path 1 downstream of the heater 313.

It is even possible to omit the heater 313, if the heat pump 50 has a sufficiently large heat transfer capability.

Another technical advantage of using a heat pump 50 lies in its ability of reversing the direction of energy transfer. In the example of FIG. 13 A, reversing the direction of energy transfer means that the heat Hl is transferred from HL2/HL3 to HL1. Thereby, the temperature of the water entering the RO unit 304 may be decreased by the heat pump 50. The directional reversal expands the utility of the WPA, for example by allowing for a wider range of SWA temperatures. For example, the direction of the heat pump 50 may be switched when the SWA temperature exceeds a predefined limit, which may set in view of the above-mentioned optimum temperature of the RO unit 304. The SWA temperature may be given by an output signal 52 of a sensor 51 in the main path 1 upstream of the tank 200. Another reason for decreasing the temperature of the water entering the RO unit 304 may be to mitigate scaling in the first system 300. If the WPA is operated in a region with high water hardness, scaling of the RO membrane may become significant, resulting in a need for more frequent replacement of the RO unit 304 or use of descaling procedures. Scaling increases with increasing water temperature. Thus, in regions with high water hardness, the heat pump 50 may be operated to decrease the water temperature in the RO unit 303 to a target temperature below the optimum temperature for the RO unit. In some embodiments, the water hardness is inferred from the output signal 52 of the sensor 51, which may be an online water hardness meter, a conductivity sensor, etc.

In some embodiments, the heat pump 50 is a conventional heat pump that operates to transfer thermal energy using a refrigeration cycle. Such a heat pump is powerefficient.

In some embodiments, the heat pump 50 is a thermoelectric heat pump, also known as a Peltier device or a Peltier heat pump. Generally, a thermoelectric heat pump is a solid-state device that transfers heat from one side of the device to the other, with consumption of electrical energy, depending on the direction of the current. Compared to a conventional heat pump, a thermoelectric heat pump has the advantages of being small and silent, operating without moving parts, having long operative life, and requiring little or no service and maintenance.

FIG. 13A is merely given as a non-limiting example. The HTD 50 may be provided in any WPA described herein, for example in accordance with any of the first to seventh concepts and any associated embodiment, variant or example.

In the specific context of FIG. 13 A, the WPA may be defined as an apparatus for generation of product water for medical use, with the apparatus comprising: a main flow path extending from a main water inlet to a main water outlet; a first system, which is arranged in the main flow path and configured to process incoming water for reduction of water hardness, resulting in processed water with reduced hardness, the first system comprising a first RO unit, a first feed pump for feeding the incoming water to the first RO unit, and a drain line for directing reject water from the RO unit to a drain; a second system, which is arranged in the main flow path intermediate the first system and the main water outlet, wherein the second system is configured to receive the processed water from the first system and further process the processed water into said product water; a reservoir, which is arranged in the main flow path upstream of the first system and configured to hold said incoming water for the first system; a recirculation path, which extends to the reservoir from a first location in the main flow path downstream of the second system; and a heat transfer device, which is configured to transfer heat between a first locus in the drain line and a second locus in the main flow path upstream of the RO unit.

In some embodiments, the second locus is upstream of the reservoir.

In some embodiments, the second locus is intermediate the reservoir and the RO unit.

In some embodiments, the heat transfer device comprises at least one of a heat exchanger or a heat pump.

In some embodiments, the WPA further comprises a control device, which is configured to operate the heat pump to achieve a target temperature of the incoming water at the RO unit.

In some embodiments, the control device is configured to selectively reverse the heat pump to transfer heat from the second locus to the first locus. In some embodiments, the control device is configured to selectively reverse the heat pump based on a signal indicative of the temperature and/or hardness of the incoming water to the third system.

In some embodiments, the heat pump is a thermoelectric heat pump.

In some embodiments, the further comprises an electrical heater in the main flow path, and the second locus is upstream of the electrical heater.

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

Further, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, parallel processing may be advantageous.

Claims

1. An apparatus for generation of product water for medical use, comprising: a main flow path (1) extending from a main water inlet (1') to a main water outlet (1"), a first system (300) arranged in the main flow path (1) and configured to process incoming water for reduction of water hardness, resulting in processed water with reduced water hardness, and a second system (400) arranged in the main flow path (1) intermediate the first system (300) and the main water outlet (1"), wherein the second system (400) is configured to receive the processed water from the first system (300) and further process the processed water into said product water, wherein the first system (300) comprises a reverse osmosis, RO, unit (304) for use in processing of the incoming water, wherein the main flow path (1) comprises a feed line (1A) extending to a water inlet (304A') on a feed side (304") of the RO unit (304), and wherein the first system (300) comprises a feed pump (302) arranged in the feed line (1A) to pressurize the incoming water at the water inlet (304A') of the RO unit (304), wherein the apparatus comprises a return flow path (8), which is arranged to fluidly connect the main flow path (1), at a location intermediate the first and second systems (300, 400), to a feed side (304") of the RO unit (304), and a valve arrangement (314, 401), which is operable to selectively direct the processed water from the first system (300) on the main flow path (1) to the second system (400), or on the return flow path (8) to the feed side (304") of the RO unit (304), and wherein the apparatus is configured to perform a start-up procedure, in which the valve arrangement (314, 401) is operated to close the main flow path (1) and open the return flow path (8), the feed pump (302) is started and operated for a time period, and the valve arrangement (314, 401) is operated to open the main flow path (1) after the time period, and optionally close the return flow path (8).

2. The apparatus of claim 1, wherein the return flow path (8) extends to a location on the main flow path (1) upstream of the feed pump (302).

3. The apparatus of claim 1 or 2, further comprising a sensor (311), which is arranged in the main flow path (1) intermediate the first system (300) and the valve arrangement (314, 401), said sensor (311) being configured to generate a sensor signal (C2) representing a composition-related parameter of the processed water, wherein the apparatus is configured to determine said time period based on the sensor signal (C2).

4. The apparatus of claim 3, wherein the composition-related parameter corresponds to electrical conductivity.

5. The apparatus of any preceding claim, wherein the first system (300) further comprises a drain line (2A) extending from a retentate outlet (304C) on a feed side (304") of the RO unit (304), wherein a flow restriction device (306) is arranged in the drain line (2A) to define a flow resistance at the retentate outlet (304C) on the feed side (304") of the RO unit (304).

6. The apparatus of claim 5, wherein the flow restriction device (306) is operable to change the flow resistance based on a control signal.

7. The apparatus of claim 5 or 6, wherein the first system (300) comprises a connecting line (3A), which is arranged in fluid communication with the drain line (2A) and the feed line (1A) to define a recirculation path from the retentate outlet (304C) on the feed side (304") of the RO unit (304) to a water inlet (304A') on the feed side (304") of the RO unit (304), and an auxiliary pump (305), which is arranged in the recirculation path to provide an added flow rate along the second flow path (FP2).

8. The apparatus of claim 7, wherein the auxiliary pump (305) is arranged in the connecting line (3A).

9. The apparatus of claim 7 or 8, wherein the RO unit (304) defines a permeate side (304"'), which is separated from the feed side (304") by a semi-permeable membrane (304'), wherein the RO unit (304) comprises the water inlet (304A') on the feed side (304") and a permeate outlet (304B') on the permeate side (304'"), wherein the main flow path (1) comprises a first flow path (FP1) from the water inlet (304A'), through the semi-permeable membrane (304') to the permeate outlet (304B'), wherein the RO unit (304) further comprises the retentate outlet (304C) on the feed side (304") to define a second flow path (FP2) on the feed side (304") from the water inlet (304A') to the retentate outlet (304C) along the semi-permeable membrane (304’).

10. The apparatus of any preceding claim, further comprising a reservoir (200), which is arranged in the main flow path (1) upstream of the first system (300) and configured to hold said incoming water for the first system (300) at atmospheric pressure.

11. The apparatus of claim 10, wherein the reservoir (200) comprises a water inlet port (202), which is connected for fluid communication with the main water inlet (T), wherein the reservoir (200) is configured to define an air gap (207) above a predefined top level of the incoming water inside the reservoir (200).

12. The apparatus of claim 11, wherein the reservoir (200) comprises a level sensor (201) for signaling at least one fluid level in the reservoir (200), so as to enable a control device (500) to control an inflow of water through the water inlet port (202) to maintain said air gap (207) in the reservoir (200).

13. The apparatus of any one of claims 10-12, further comprising a vent (206) in a side wall of the reservoir (200), wherein the vent (206) is configured to release both gases and water from the reservoir (200).

14. The apparatus of any one of claims 10-13, wherein the return flow path (8) extends to a return port (204) on the reservoir (200).

15. The apparatus of any preceding claim, further comprising a recirculation path (5, 6), which extends from a first location in the main path (1) downstream of the second system (400), to a second location in the main path (1) upstream of the first system (300) and/or to a third location in the main flow path (1) intermediate the first system (300) and the second system (400), to provide for recirculation of the product water generated by the second system (400).

16. The apparatus of any one of claims 1-4 or 10-15, wherein the first system (300) comprises a drain line (2A) for directing reject water from the RO unit (304) to a drain (309), wherein the apparatus further comprises a heat transfer device (50), which is configured to transfer heat between a first locus (HL1) in the drain line (2A) and a second locus (HL2; HL3) in the main flow path (1) upstream of the RO unit (304).

17. The apparatus of claim 16, wherein the heat transfer device (50) comprises at least one of a heat exchanger or a heat pump.

18. The apparatus of claim 17, further comprising a control device (500), which is configured to operate the heat pump to achieve a target temperature of the incoming water at the RO unit (304).

19. The apparatus of claim 18, wherein the control device (500) is configured to operate the heat pump (50) to transfer heat from the first locus (HL1) to the second locus (HL2; HL3).

20. The apparatus of claim 19, wherein the control device (500) is configured to selectively reverse the heat pump (50) to transfer heat from the second locus (HL2; HL3) to the first locus (HL1).

21. The apparatus of claim 20, wherein the control device (500) is configured to selectively reverse the heat pump (50) based on a signal (52) indicative of the temperature and/or hardness of the incoming water to the first system (300).

22. The apparatus of any one of claims 18-21 in combination with claim 3 or 4, wherein the second locus (HL2; HL3) is upstream of the sensor (311) that is configured to generate the sensor signal (C2) representing a composition-related parameter.

23. The apparatus of claim 22, wherein the control device (500) is configured to operate the heat pump to achieve a target temperature of the processed water at the sensor (311) that is configured to generate the sensor signal (C2) representing a composition-related parameter.

24. The apparatus of any one of claims 17-23, wherein the heat pump is a thermoelectric heat pump.

25. The apparatus of any preceding claim, wherein the RO unit (304) is a sacrificial component which is removably installed in the first system (300).

26. The apparatus of claim 25, wherein the RO unit (304) has a target lifetime that allows for generation of 20,000-100,000 L of said processed water, and preferably 40,000-70,000 L of said processed water.

27. The apparatus of claim 25 or 26, wherein the target lifetime is defined for the incoming water to the RO unit (304) having a hardness of 450 ppm and/or a conductivity of 2000 pS/cm, and for the processed water being generated at a flow rate of 1 L/min.

28. The apparatus of any one of claims 25-27, which is configured to generate the product water at a point of care, wherein the apparatus is configured to provide for replacement of the first RO unit (304) by a non-trained user at the point of care.

29. The apparatus of any preceding claim, further comprising a monitoring device (500'), which is configured to determine, based on an output signal of a sensor (302, 320, 321) in the apparatus, a performance parameter that is indicative of a flow resistance through the RO unit (304) and evaluate the performance parameter for detection of a need for replacement of the RO unit (304).

30. The apparatus of claim 29, wherein the sensor (302, 320, 321) comprises at least one of a pressure sensor (303) in the main flow path upstream (1) of the RO unit (304), a flow meter (320) in the main flow path (1) downstream of the RO unit (304), or a power sensor (321) for measuring a power consumption of the feed pump (302).

31. The apparatus of any preceding claim, wherein the second system (400) comprises a second RO unit (404) for use in processing of the processed water from the first system (300).

32. The apparatus of claim 31, wherein the second RO unit (404) is permanently installed in the second system (400).

33. The apparatus of claim 31 or 32, wherein a retentate outlet (404C) of the second RO unit (404) is connected for fluid communication with the main flow path (1) at a location upstream of the first system (300), to provide for recirculation of retentate water from the second RO unit (404) into the main flow path (1).

34. The apparatus of any preceding claim, further comprising a pre-processing system (100), which is arranged in the main flow path (1) and configured to receive source water from the main water inlet (T) and at least remove particles from the source water to provide pre-processed water, wherein the first system (300) is fluidly connected to receive the pre-processed water from the pre-processing system (100).

35. The apparatus of claim 34, wherein the pre-processing system (100) is further configured to remove chlorine from the source water.

36. The apparatus of any preceding claim, further comprising at least one radiation source (301) arranged in the main flow path (1) upstream of the RO unit (304), said radiation source (301) being operable to emit UV radiation for removal of chlorine in the incoming water to the RO unit (304).

37. A computer-implemented method of operating an apparatus for generation of product water for medical use, said apparatus comprising a main flow path (1) extending from a main water inlet (T) to a main water outlet (1"); a first system (300) arranged in the main flow path (1) and configured to process incoming water for reduction of water hardness, resulting in processed water with reduced hardness; and a second system (400) arranged in the main flow path (1) intermediate the first system (300) and the main water outlet (1"), wherein the second system (400) is configured to receive the processed water from the first system (300) and further process the processed water into said product water, wherein the first system (300) comprises a reverse osmosis, RO, unit (304) for use in processing of the incoming water, wherein the apparatus comprises a return flow path (8), which is arranged to fluidly connect the main flow path (1), at a location intermediate the first and second systems (300, 400), to a feed side (304") of the RO unit (304), and a valve arrangement (314, 401), which is operable to selectively direct the processed water from the first system (300) on the main flow path (1) to the second system (400), or on the return flow path (8) to the feed side (304") of the RO unit (304), wherein the main flow path (1) comprises a feed line (1A) extending to a water inlet (304A') on the feed side (304") of the RO unit (304), and wherein the first system (300) comprises a feed pump (302) arranged in the feed line (1A) to pressurize the incoming water at the water inlet (304A') of the RO unit (304), said method comprising: operating (S61) the valve arrangement to close the main flow path and open the return flow path, starting (S62) the feed pump and operating the feed pump for a time period, and operating (S65) the valve arrangement to open the main flow path after the time period.

38. A computer-readable medium comprising program instructions, which when executed by a processor (501) causes the processor (501) to perform the method according to claim 37.