WO2025199176A1

WO2025199176A1 - Systems, devices, and methods for high-recovery electrodialysis for household desalination

Info

Publication number: WO2025199176A1
Application number: PCT/US2025/020478
Authority: WO
Inventors: JR. Michael S. BONO; Antonia FILINGERI; Melissa BREI; Benjamin M. JUDGE; Jonathan BESSETTE; Giuliana PERTUZ; Sophia Chen; Jeffrey D. COSTELLO; Soraya HONARPARVAR; V. Amos Greene WINTER
Original assignee: Massachusetts Institute of Technology
Current assignee: Massachusetts Institute of Technology
Priority date: 2024-03-18
Filing date: 2025-03-18
Publication date: 2025-09-25
Anticipated expiration: 2026-09-18

Abstract

The present disclosure is directed to systems, devices, and methods for electrodialysis-based home-scale water desalination. The system can include an electrodialysis (ED) stack that includes a separately disposed electrode rinse stream that is in a closed-loop configuration with the ED stack. The electrode rinse stream can flow from a separate rinse storage vessel and can, optionally, include an auxiliary pump dedicated to pumping the electrode rinse to the ED stack. The ED stack can include one or more compression molded spacers disposed between the electrodes and membranes thereof and endcapend caps on the periphery of the ED stack to reduce a volume of the system to allow for point of use operation. The system and its components can be packaged within dimensions of a reverse osmosis cabinet, which can provide for in-home installation and use.

Description

SYSTEMS, DEVICES, AND METHODS FOR HIGH-RECOVERY ELECTRODIALYSIS FOR HOUSEHOLD DESALINATION

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present disclosure claims priority to and the benefit of U.S. Provisional Application No. 63/566,879, entitled “High-Recovery, Reliable Electrodialysis for Household Desalination,” filed on March 18, 2024, the content of which is incorporated by reference herein in its entirety.

FIELD

[0002] The present disclosure relates to systems, devices, and methods for fluid desalination, and more particularly relates to systems, devices, and methods for compact electrodialysis desalination of household fluid purification having high recovery ratios.

BACKGROUND

[0003] Throughout much of the developing world, access to safe, reliable drinking water remains a challenge. For example, water scarcity has become a major problem in countries like India due to increased demand for drinking water. Electrodialysis removes charged ions from water by passing feed water tangentially through a stack of alternating cation exchange membranes and anion exchange membranes while an electric voltage is applied perpendicular to the membrane stack, resulting in alternating streams of water with concentrated and diluted ion contents such that the streams with the diluted ion content can be collected as the product of the desalination system. The purpose of this electrodialysis system is to meet the needs of home-scale, point-of-use (POU) desalination in settings such as India with brackish water supplies. In these settings, the current state of the art for desalination is reverse osmosis (RO), which operates by using a pressure difference to drive water through membranes resistant to ion transport. Indian homes currently rely on domestic reverse osmosis (RO) systems to desalinate groundwater to a salt content with total dissolved solids (TDS) that is suitable for drinking. About 13 million reverse osmosis (RO) units were sold in India in FY 2021. However, POU RO systems frequently only convert a small fraction of the provided feed water into desalinated product water, a ratio referred to as the recovery ratio of the desalination system. This leads to wasted water, a growing concern in settings such as India facing groundwater depletion. [0004] In order to ensure more efficient use of water, the Indian government has recently enacted a new standard mandating a recovery ratio of at least 40% for POU RO systems. Recently developed POU RO systems can meet this standard, but higher recovery and increasing water hardness due to groundwater depletion both pose challenges for maintaining the lifetime of RO membranes.

[0005] Compared to RO, electrodialysis offers the possibility of high recovery ratios and long membrane lifetimes. While ED appears to be a promising alternative for domestic groundwater desalination, they fail to meet the recovery ratios needed and suffer from needing large scale environments in which to work, thereby increasing cost and making them impractical for household and POU use.

[0006] Accordingly, there is a need for systems and methods for desalination technology that provides high recovery ratios and long system lifetime that are suitable for home-scale applications and usage.

SUMMARY

[0007] The present disclosure is directed to systems, devices, and methods for electrodialysis-based home-scale water desalination. Specifically, a desalination system of the present embodiments can include an electrodialysis stack that includes a separately disposed electrode rinse stream that is in a closed-loop configuration with the ED stack. The electrode rinse stream being separated from feed streams that are desalinated by the ED stack can allow for higher flow rates of the electrode rinse stream to flow therethrough so as not to be limited by the flow rate of the feed streams. The ED stack can include one or more compression molded spacers disposed between the electrodes and membranes thereof and end caps on the periphery of the ED stack to reduce a volume of the system to allow for point of use operation.

[0008] One exemplary embodiment of an electrodialysis (ED) system includes an ED stack, a pump, a feed stream, a valve manifold system, an electrode rinse stream, and a second pump. The ED stack includes a stack of alternating cation exchange membranes and anion exchange membranes, and one or more pairs of electrodes configured to exert an electric driving force to transport ions through the alternating cation exchange membranes and anion exchange membranes. The feed stream is in fluid communication with the pump to flow therethrough and is split into a diluate input stream and a concentrate input stream that enter the ED stack. The valve manifold system includes a set of valves and a reversal mechanism for flowing the diluate input stream and the concentrate input stream in alternating fluidic paths within the ED stack to produce a product output stream and a brine output stream, respectively. The electrode rinse stream is in fluid communication with the ED stack and is configured to flow into and out of physical contact with the one or more pairs of electrodes. The second pump is configured to flow the electrode rinse stream through the ED stack. The electrode rinse stream is in a closed-loop configuration with the ED stack and the second pump.

[0009] The feed stream, diluate input stream, and the concentrate input stream may not flow through any additional pump throughout their path through the ED system. The electrode rinse stream can include a sodium sulfate stream that is separate from both the concentrate input stream and the brine output stream. A flow rate of the diluate input stream can be greater than a flow rate of the concentrate input stream. In some embodiments, the flow rate of the concentrate input stream can be approximately in a range of about 4 Liters/hour to about 8 Liters/hour, and the flow rate of the diluate input stream can be approximately in a range of about 10 Liters/hour to about 20 Liters/hour. A flow rate of the electrode rinse stream can be configured to be tuned based on a voltage between the one or more pairs of electrodes and a current through the ED stack. A flow rate of the electrode rinse stream can be approximately in a range of about 10 Liters/hour to about 30 Liters/hour.

[0010] The closed-loop configuration can include an electrode rinse storage tank for storing the electrode rinse stream therein. The electrode rinse storage tank can include a two-port bag. In some embodiments, the ED stack can include two or more ED stages, with each stage of the two or more ED stages including a stage stack of alternating cation exchange membranes and anion exchange membranes in electrical communication with one or more pairs of electrodes of the stage of the two or more ED stages. The product output stream from each stage of the two or more ED stages, except a final stage of the two or more ED stages, can be in fluid communication with the diluate input stream for a downstream stage of the two or more ED stages. The brine output stream from each stage of the two or more ED stages, except the final stage of the two or more ED stages, can be in fluid communication with the concentrate input stream for a downstream stage of the two or more ED stages. The product output stream from the final stage can include a final product stream for the ED stack, and the brine output stream from the final stage can include a final brine stream for the ED stack. The voltage applied to each ED stage can be configured to be independently modulated. In some embodiments, the ED stack, the pump, the feed stream, the manifold system, and the electrode rinse stream can be configured to fit in an about 300 mm x about 280 mm x about 500 mm rectilinear envelope.

[0011] The system can include one or more flow spacers disposed between the stack of alternating cation exchange membranes and anion exchange membranes. The one or more flow spacers can include thermoplastic urethane (TPU). In some embodiments, the one or more flow spacers can include at least two layers of TPU. The one or more flow spacers can define a channel having a tortuous path through a first surface thereof.

[0012] The system can include a number of other components. For example, the system can include a pressure regulator disposed on the concentrate input stream upstream of the ED stack. In some embodiments, the system can include a pair of composite end caps disposed on opposite end of the ED stack, with each composite end cap having a core component in physical communication with one or more electrodes and one or more fluidic streams and a sheet metal component comprising regions parallel to and in physical communication with at least two adjacent surfaces of the core component. The sheet metal component may not be in direct physical communication with fluid or a source of electric voltage.

[0013] One exemplary method of manufacturing a flow spacer includes removing the region of a desired flow path from one or more layers of thermoplastic urethane (TPU), and positioning a first layer of thermoplastic urethane (TPU) in a stamp of an instrument configured to perform compression molding. The method includes positioning a mesh on the first layer of TPU, positioning a second layer of TPU on the mesh, and compression molding the first and second layers to the mesh to form the spacer, with the spacer having an imprint of the channel thereon. The stamp has raised edges on one or more sides of the stamp that define a channel to define a flow path in the spacer.

[0014] The method can further include cutting one or more TPU sheets using a laser instrument to form the first layer of TPU and the second layer of TPU.

[0015] One exemplary method of desalinating a system includes circulating at least a portion of a rinse stream from a storage tank through an electrodialysis (ED) stack that includes a stack of alternating cation exchange membranes and anion exchange membranes disposed between one or more pairs of electrodes that are configured to exert an electric driving force to transport ions through the alternating cation exchange membranes and anion exchange membranes, flowing at least a portion of the rinse stream exiting the ED stack back to the storage tank. The rinse stream is in a closed-loop configuration with the ED stack, and the rinse stream contacts the one or more pairs of electrodes when circulating through the ED stack.

[0016] The rinse stream can be circulated simultaneously with the ED stack separating a fluid from a salt content to form a product. The method can further include tuning a flow rate of the rinse stream based on a voltage between the one or more pairs of electrodes and a current through the ED stack. In some embodiments, the flow rate of the rinse stream can be approximately in a range of about 10 Liters/hour to about 30 Liters/hour.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] This disclosure will be more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0018] FIG. 1 is a schematic representation of a prior art circuit architecture of an electrodialysis (ED) stack;

[0019] FIG. 2A is a schematic representation of one embodiment of a circuit architecture in an ED system of the present embodiments;

[0020] FIG. 2B is a schematic representation of another embodiment of a circuit architecture in an ED system of the present embodiments having two electrical ED stages in series;

[0021] FIG. 3 is a schematic front view of one embodiment of the ED stack used in an ED system of the present embodiments;

[0022] FIG. 4 is a graph illustrating electrode flow rate as a function of current and voltage at the electrode compartments of the ED stack of FIG. 3;

[0023] FIG. 5A is a perspective view of one embodiment of a cabinet having the system of the present embodiments that includes a bag for storage of an electrode rinse;

[0024] FIG. 5B is a perspective view of the cabinet of FIG. 5A, with the cabinet oriented for a detailed view of the bag; [0025] FIG. 6 is a perspective view of the bag of FIGS. 5 A and 5B;

[0026] FIG. 7 is a schematic representation of a pair of prior art membranes of an electrodialysis stack having a spacer therebetween;

[0027] FIG. 8A is a schematic representation of a manufacturing method for a spacer of the present embodiments;

[0028] FIG. 8B is a schematic representation of the spacer of FIG. 8A following compression molding;

[0029] FIG. 9A is a perspective top view of a first surface of a machine molding stamp used to manufacture the spacer of FIG. 8A;

[0030] FIG. 9B is a perspective top view of a second surface of the stamp of FIG. 9A;

[0031] FIG. 9C is a detailed perspective view of the first surface of the stamp of FIG. 9 A;

[0032] FIG. 9D is a detailed perspective view of the second surface of FIG. 9B;

[0033] FIG. 10A is a perspective top view of the top surface of FIG. 8A before compression molding;

[0034] FIG. 10B is a perspective top view of the bottom surface of FIG. 8B before compression molding;

[0035] FIG. 11 is a perspective front view of a spacer of the ED stack of the present embodiments;

[0036] FIG. 12A is a perspective view of the spacer of FIG. 11 used in an ED stack with transparent end caps prior to filling with a dye;

[0037] FIG. 12B is a perspective view of the spacer of FIG. 12A the ED stack with the transparent end caps after filling with a dye;

[0038] FIG. 13 is a perspective view of the ED stack of the present embodiments between two end caps;

[0039] FIG. 14A is a schematic top view of one of the end caps of FIG. 13; [0040] FIG. 14B is a perspective schematic view of the end cap of FIG. 14A; and

[0041] FIG. 15 is a perspective schematic view of the end caps of the present embodiments connected to one another.

DETAILED DESCRIPTION

[0042] Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the systems, devices, related components (e.g., membranes, electrodes, end caps, etc.), and techniques disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the systems, devices, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure. Further, to the extent features, layers, sides, objects, steps, or the like are described as being “first,” “second,” third,” etc., and/or “lower,” “upper,” “middle,” etc., such numerical and/or location ordering/identification is generally arbitrary, and thus such numbering can be interchangeable unless indicated or otherwise understood by those skilled in the art to not be interchangeable.

[0043] To the extent that the instant disclosure includes various terms for components and/or processes of the disclosed systems, methods, and the like, one skilled in the art, in view of the claims, present disclosure, and knowledge of the skilled person, will understand such terms are merely examples of such components and/or processes, and other components, designs, processes, and/or actions are possible.

[0044] At least one novel aspect of the present disclosure lies in a compact fluid control system and components for a home-scale water desalination system that provides high recovery ratios and long system lifetime. The system of the present embodiments offers improvements in desalination performance due to: (i) use of a 2-port bag to store a separate electrode rinse stream; (ii) compression-molded flow spacers incorporating thermoplastic polyurethane; and (iii) compact composite end caps to seal the electrodialysis stack. The system can have a single pump flow fluid through an ED stack that includes a separate electrode rinse stream flowing a sodium sulfate solution to clean the electrodes thereof. The ED stack can include one or more custom end caps to facilitate entry and filtration of feed streams and exit streams to and from the stack. A compression molded spacer can be positioned between alternating cation exchange membranes and anion exchange membranes of the ED stack to facilitate improved ion exchange throughout the membranes.

[0045] ELECTRODIALYSIS STACK ARCHITECTURE

[0046] Existing electrodialysis (ED) stack architectures are wholly insufficient for point-of- use (POU) needs. For example, FIG. 1 illustrates a prior art desalination system 10. As shown, the desalination system 10 can include a feed stream 12 that flows through one or more flow dividers, e.g. , T/Y-Splits, to separate the feed stream 12 into a concentrate stream 12c and a diluate stream 12d. The system 10 includes a product tank P and a brine tank B that are in fluid communication with the diluate stream 12d and the concentrate stream 12c, respectively, to mix therewith. Once mixed, a product stream 12p and a brine stream 12b are formed, respectively, to be pumped through the system 10.

[0047] The system 10 includes separate pumps that are used for each of these streams. For example, as shown, each of the product stream 12p and the brine stream 12b is fed to a product pump 16p, and a brine pump 16b, respectively. Each of the product stream 12p and the brine stream 12b can be prefiltered and pass through a valve manifold system or reversal network 18. The valve manifold system 18 can include input solenoid valves and a reversal mechanism for flowing the input streams in opposite directions. For example, the valve manifold system 18 can include a matrix of valves that can be used to flip the product stream 12p and the brine stream 12b to eliminate buildup of scale. The matrix of valves can include a first set of valves 20, e.g., four solenoid valves, which are located upstream of an ED stack 22, with each stream being passed through the ED stack 22 before flowing through a second set of valves 24, e.g. , four solenoid valves, located downstream of the ED stack 22. An electrode rinse storage tank 26 is in communication with the ED stack 22 via an electrode rinse pump 28. Once the streams flow out of the second set of valves 24, the product stream 12p and the brine stream 12b can either be returned to the product tank P and the brine tank B, respectively, and/or exit the system as final product for collection and final brine for disposal via open/closed valves 30. [0048] The flows in the system 10 experience insufficient stack residence time, which can frequently necessitate batch operation or use of serial stacks for desired salt reduction from the concentrate stream 12c. Moreover, the system 10 is inefficient and requires frequent recycling of product and brine before a desired concentration of each is reached, and therefore uses a high number of pumps, tanks, and valves that increase size, cost, and complexity of the system. As a result, consumers that are accustomed to RO expect 90% salt reduction and a small footprint, which the system 10 cannot provide.

[0049] FIG. 2 illustrates an example system 100 of the present embodiments. The system 100 can use a single pump for product and brine pumping throughout to result in the final product and final brine streams. As shown, a feed stream 102 can enter a pump 106, e.g., main pump, where prefiltration can occur prior to splitting the feed stream into a product stream, or diluate stream, 102p and a brine stream, or concentrate stream, 102b. Each of the product stream 102p and the brine stream 102b can pass through a valve manifold system or reversal network 108 that can include input solenoid valves and a reversal mechanism for flowing the input streams in opposite directions. For example, the valve manifold system 108 can include a matrix of valves that can be used to flip the product stream 102p and the brine stream 102b to eliminate buildup of scale. The matrix of valves can include a first set of valves 120, e.g. , four solenoid valves, that are located upstream of an ED stack 122, with each stream being passed through the ED stack 122 before flowing through a second set of valves 124, e.g. , four solenoid valves, though the number of valves in a set can vary, located downstream of the ED stack 122. Moreover, each set of valves 120, 124 can include an equal number of solenoid valves, though in some embodiments, different numbers of valves can be used in each set 120, 124. Lastly, while some solenoid valves are shown open while others are closed, it will be appreciated that FIG. 2A illustrates a snapshot of the circuit architecture and in an alternate state, open valves can become closed and vice versa. The feed stream 102, the product stream 102p, and the brine stream 102b can flow through a network of paths, e.g., one or more fluid paths that are defined by a tube, a pipe, or the like, of any length that extends between the valves that form the matrix, and/or the valve manifold system 108 and the ED stack 122, and/or any components of the ED system 100 that are in fluid communication with one another. As shown, one or more of the product stream 102p or the brine stream 102b can flow through a pressure regulator 125 prior to flowing through the first set of valves 120. For the purposes of the present disclosure, a flow regulator and/or a pressure regulator can be understood to be anything that changes a given flow rate and/or pressure of a fluid running therethrough.

[0050] An electrode rinse storage tank 126 is in communication with the ED stack 122 via an electrode rinse pump 128 to flow an electrode rinse stream 130 therethrough. As shown, the electrode rinse vessel 126 can be disposed in a closed-loop configuration with the ED stack 122 via the electrode rinse pump to circulate the electrode rinse through the ED stack 122 without interfacing with either of the product stream 102p or the brine stream 102b. Once the streams flow out of the second set of valves 124, the product stream 102p and the brine stream 102b can exit the system as final product for collection and final brine for disposal.

[0051] In some embodiments, a system 100' having the ED stack 122 can include multiple ED stages in series, e.g. , two or more, such that the product and brine streams 102p, 102b exiting each ED stage can correspond to the diluate input stream and concentrate input stream, respectively, for the following stage, or a stage that is located downstream of the previous ED stage, and the product and brine streams exiting the final stage in series can correspond to the final product for collection and final brine for disposal. It will be appreciated that each ED stage can include a stage stack of alternating cation exchange membranes and anion exchange membranes in electrical communication with one or more pairs of electrodes of the stage of the two or more ED stages, and that the term “final stage” of the ED stages in series can refer to an ED stage that does not have a downstream ED stage relative to it. An ED stack with multiple stages can include multiple electrical stages, as shown in FIG. 2B, for two ED stages 122a, 122b, such that the voltages applied to each stage are independent of one another. Different voltages can be applied to the electrical stages, and these different voltages can be selected to increase the overall salt reduction that the ED system 100' can achieve.

[0052] It will be appreciated that, in some embodiments, the feed stream 102, the product stream 102p, and the brine stream 102b do not flow through a pump other than the main pump 104 throughout the ED system 100. Having one main pump 104 for the product and brine streams 102p, 102b that is separate from the electrode rinse pump 128, e.g., an auxiliary pump, can provide a reduced risk of electrode scaling due to solubility of the separate sodium sulfate electrode rinse that is introduced to the system 100 via the electrode rinse vessel 126 and electrode rinse pump 128. Moreover, a separate electrode rinse stream can avoid a number of potential shortcomings of recirculating brine for the electrode rinse stream, such as electrode scaling from insoluble salts and chloride oxidation to chlorine gas. In some embodiments, the main pump 104 and the electrode rinse pump 128 can be combined into one dual-head diaphragm pump.

[0053] FIG. 3 illustrates one embodiment of the ED stack 122 of the system 100 of the present embodiments. The ED stack 122 can include one or more membranes disposed between a pair of electrodes, e.g., cathode 129a, anode 129b, though a plurality of pairs of electrodes can be used in some embodiments. In some embodiments, the membranes can be arranged in pairs to filter one or more fluid streams, e.g., feed 102 received in the ED stack 122. The ED stack 122 can include ten cell pairs, though it will be appreciated that any number of membranes can be used in the ED stack and the ten used herein is merely exemplary. As shown, the ED stack 122 can include one or more cation exchange membranes (CEM) 131 and at least one anion exchange membrane (AEM) 133. In some embodiments, the ED stack can include one or more spacers, as discussed in greater detail below. The electrodes 129a, 129b can be made of one or more of platinum, copper, graphite, titanium, brass, platinum-coated titanium, and/or silver, among other materials known to those skilled in the art.

[0054] As shown, the CEM 131 and the AEM 133 can be arranged horizontally between the electrodes 129a, 129b to desalinate the feedwater, though other arrangements of the CEM 131 and the AEM 133 are possible as can be appreciated by one skilled in the art. One or more feed streams 102 can pass through the ED stack 122 where the electrodes 129a, 129b separate salt ions and heavy metal ions into cations and anions, and direct them into the product stream 102p and the brine stream 102b. The electrode rinse stream 130 can also pass through the ED stack 122, the stream 130 being used to clean the electrodes. The electrode rinse stream 130 can also provide a sufficient supply of one or more reactant components for one or more reactions occurring at the electrodes 129a, 129b in order to provide ionic current to the ED stack 122, and can also assist in the removal of one or more product components from one or more reactions occurring at the electrodes 129a, 129b in order to provide ionic current to the ED stack. The electrode rinse stream 130 can exit the outlet as contaminated electrode rinse stream 132 and be discarded to waste, though in some embodiments, the electrode rinse stream 132 can be recirculated through the ED stack for further rinsing. It will be appreciated that the electrode rinse stream 130 can be circulated through the ED stack 122 simultaneously with operation of the ED stack 122, e.g., while the system 100 is separating fluid in feed stream 102 from a salt content to form the product, for increased efficiency, though in some embodiments the electrode rinse stream 130 flows through the ED stack 122 during system downtime.

[0055] It will be appreciated that while the streams 102p, 102b, among others, are referred to as containing water throughout this specification, water is simply an example embodiment of each of the streams. For example, one or more of each of the streams 102p, 102b, can flow a different fluid therethrough, e.g., alcohol, slurries, and the like. It will also be appreciated that the electrode rinse stream can include sodium sulfate or another ion-rich solution for effective transduction of electric current to ionic current.

[0056] The electrode rinse solution 130 can be made up of recirculated brine or concentrate, as in prior art system, or a separate electrode rinse stream, as in the system 100. The high recovery of the system 100 of the present embodiments, e.g., about 70%, can be achieved by the pump 104 when the flow rate of the product stream 102p is significantly higher than the flow rate of the brine stream 102b. In some embodiments, the flow rate of the brine stream 102b can be approximately in a range of about 4 Liters/hour to 8 Liters/hour, and the flow rate of the product stream 102p can be approximately in a range of about 10 Liters/hour to about 20 Liters/hour. Therefore, while recirculated brine being used as the electrode rinse stream is limited to the brine flow rate, the separate electrode rinse stream 130 of the present embodiments can allow for a tunable electrode rinse solution flow rate from the electrode rinse vessel 126. Tunable flow rate of the separate electrode rinse stream 130 can minimize voltage drop between the electrodes 129a, 129b and increase stack current for more effective desalination, as shown in FIG. 4. In some embodiments, the electrode rinse pump 128 can maintain an electrode rinse flow rate in approximately a range of about 10 Liters/hour to about 30 Liters/hour.

[0057] The use of a single pump architecture in the system 100 can allow for storage in a compact cabinet 200, which can make the resulting ED system 100 more appropriate for consumers who have previously desalinated their water at the household level using RO units packaged in existing RO cabinets. The cabinet 200 can be sized to fit the components of the ED system 100 into an existing RO cabinet by replacing and/or repurposing some components of an RO cabinet, such as a Eureka Forbes Limited (EFL) Astor Cabinet and/or Royale Cabinet. Most conventional EFL cabinets, regardless of range, can be made to occupy an estimated 300 mm x 280 mm x 500 mm rectilinear envelope, though each product’s encasement can be spatially optimized based on its interior components. It will be appreciated that the cabinet 200 of the present embodiments can be sized to mimic the EFL cabinet, e.g., about 300 mm x about 280 mm x about 500 mm rectilinear envelope, to fit the desalination system 100 of the present embodiments.

[0058] As shown in FIGS. 5A-5B, the cabinet 200 can include the pump 104, the valve manifold system 108, the ED stack 122, prefiltration cartridge 135 for the feed stream 102, the electrode rinse pump 128, a prefiltration cartridge 136 for the electrode rinse stream 130, and the pressure regulator 125. A primary challenge in assembling the cabinet 200 can be inserting the ED stack 122 and the valve manifold system 108 as compactly as possible, while accommodating for both the components carried over from the RO unit, as well as the additional new support components. The weight of the ED stack 122 and the valve manifold system 108, e.g., solenoids, can provide a stable center of gravity, which can be accomplished by central placement of such components within the cabinet 200.

[0059] In some embodiments, the cabinet 200 can include a two-port bag 202 for storage of the electrode rinse solution 130. The bag 202 can be made up of ethylene vinyl acetate (EVA) and can be integrated with the electrode rinse stream 130 in a closed-loop configuration for storing sodium sulfate therein solution. It will be appreciated that the bag 202 can resemble a bag which is designed for intravenous administration of fluids. FIG. 6 illustrates the bag 202 in greater detail. As shown, the bag 202 can include an inlet 204 and an outlet 208 for allowing for the flow of the electrode rinse stream 130. For example, the inlet 204 can include a push-to-connect fitting 206 with a through- wall mount secured to a hole cut in a side of the hag 202. The inlet 204 can allow for flow of the electrode rinse stream 130 returning to the electrode rinse vessel 126 after circulation through electrodes 129a, 129b in the ED stack 122. The outlet 208 can include a push-to-connect adapter tubing 210 that connects to a drilled-out injection port that allows for the exit of the electrode rinse stream 130 from the electrode rinse vessel 126 being pumped by the electrode rinse pump 130 to the ED stack 122. That is, with respect to the schematic in FIG. 2, the electrode rinse stream 130 can exit the bag 202 via the push-to-connect adapter tubing 210 on the outlet 208 to the ED stack 122 and can return to the bag 202 through the inlet 204 via the push-to- connect fitting 206.

[0060] SPACERS [0061] In some embodiments, the cation exchange membrane (CEM) 131 and the anion exchange membrane (AEM) 133, respectively, can be separated by a spacer 134. In ED, the spacers 134 can ensure correct membrane separation and direct fluid flow. Conventionally, spacers were made with woven mesh to improve mixing and/or using UV-cured epoxy. A schematic of a prior art spacer is shown in FIG. 7.

[0062] The manufacturing process of the spacers 134 of the present embodiments can improve fluid flow and desalination efficiency through the ED stack 122. For example, the spacer 134 can be manufactured using a stamp 140 as shown in FIGS. 8A-8B in a compression molding process. More specifically, thermoplastic polyurethane (TPU) 142 can be used for scalable manufacturing of the spacers 134 by cutting TPU sheets using laser instruments. Before compression molding, a first TPU layer 142a can be positioned in the stamp 140, followed by a mesh 144 and a second layer of TPU 142b. It will be appreciated that the spacer can have three or more layers, and the number of layers in the figures is merely exemplary.

[0063] FIGS. 9A-9D illustrate the stamp 140 of FIGS. 8A-8B in greater detail. The stamp 140 can be made of aluminum and include a flat surface 148 on a first side 140a thereof and the raised edges 148 on a second side 140b to concentrate molding force along the flow path edges 146. The stamp 140 can include one or more of pins and/or holes 150 to ensure proper alignment. A height of the stamp edge 146 can be about 0.04 inches or about 0.01 millimeters. FIGS. 10A-10B illustrate the stamp 140 of FIG. 8A containing TPU 142 and mesh 144 before compression molding. As shown, the stamp 140 can produce a spacer 134 having a channel 138 therein, respectively, to allow for the exchange of ions while the feed water flows therethrough. As shown, the channel 138 can have a tortuous, or winding, path through the membrane to increase a time that the feedwater flows through the membrane, in turn increasing the desalination of the feed water stream 12. The compression molding process can produce a spacer 134 having a serpentine geometry that resembles that of the stamp 140 and a width of the channel 138 of about 0.015 meters and length of about 0.45 meters (about 0.15 meters per side), while the spacer thickness was about 750 pm. It will be appreciated that the compression molding method of the present embodiments differs from the conventional method of manufacture using melt deposition of ethylene-vinyl acetate (EVA), which can account for increased performance and lower failure rates. [0064] FIG. 11 illustrates the spacer 134 in greater detail. As shown, the spacer 134 resembles the shape of the stamp 140 with TPU compression-molded over the mesh 144 outside of the flow path and the mesh region 144 being free of TPU to provide an obstructed flow path through the channel 138. Moreover, slight additional compression in the TPU 142 can be seen at the edges 152 of the flow path where the stamp edges 146 exerted additional compression force on the spacer 134.

[0065] In one example, the TPU 142 can be a polyether TPU having an 83A-90A hardness and having a thickness of about 0.3 millimeters or 300 pm. The polyester mesh 144, e.g., about 500 pm thick, can be added thereto, as shown in FIG. 8A. The stamp 140 having raised edges 146 can be closed and heated at about 340 °F (171 °C) for about 5 minutes to about 1 1 minutes per side to produce the spacer 134 shown in FIG. 8B, with heating time varying based on the TPU grade used. In some embodiments, heating can be performed in a T-shirt press, e.g., from RoyalPress, though various heating devices can be used. Moreover, parchment paper can be added along the flat surfaces 148a, 148b. Then, the stamp 140 can be rapidly cooled with tap water before separating stamp sides and 148a, 148b and opened to remove the spacer 134. Internal and external leakage tests can be first carried out on each spacer 134 using a leakage test unit using tap water with food coloring to easily observe any possible leakage. The spacers can be tested all together in the same one-pass unit.

[0066] In some embodiments, the performance of the spacer 134 can be tested in a transparent test cell. For example, the end caps 160 can be designed from a transparent material to allow for testing of an individual spacer or multiple spacers in parallel. In the leakage test unit using tap water with food coloring to measure leaks mentioned above, transparent end caps can be used to visualize the spacer 134 before and after introduction of the dye, as shown in FIGS. 12A-12B.

[0067] DEMONSTRATED PERFORMANCE

[0068] The ED stack 122 of the present embodiments during laboratory testing with synthetic brine with total dissolved solids of about 900 mg/L was shown to yield consistent performance with an overall conductivity reduction of at least 48% during continuous desalination of about 1200 L of product water at an about 17 Liters/hour product delivery rate and a 70% recovery ratio. In some embodiments, the recovery ratio of the ED system of the present embodiments can be adjusted using an adjustable pressure regulator in a range of about 50% to about 90%.

[0069] In some embodiments, the system 100 can achieve a 15 Liters/hour product delivery rate and a recovery ratio of at least 70% while desalinating real brackish water with total dissolved solids of at least 800 mg/L to yield reductions of at least 50% in overall conductivity, sodium content, magnesium content, chloride content, and nitrate content. Reductions of at least 40% in sulfate content and total dissolved solids and a reduction of at least 30% in calcium content can also be achieved.

[0070] END CAPS

[0071] The end caps of the present embodiments can be optimized for an economical sheet metal process via 2D laser profiling, finishing, then final bending for stiffening ribs to promote efficient use of material to resist bending in critical, high weight-bearing areas. The end caps 160 can be added to the ED stack 122 to prevent leakage therefrom, to house the electrodes, and/or to route inlet and outlet flow paths, among other purposes. The end caps 160a, 160b can be sufficiently stiff, e.g. , by incorporating aluminum or steel components into the end caps, to provide compression to the stack membranes 131, 133, while also minimizing the amount of material to minimize end cap weight, volume, and cost. For example, the end caps 160a, 160b of the present embodiments can contain a polymer core, e.g. acrylonitrile butadiene styrene (ABS), that can be injection molded to be thin and light to reduce material cost, while being sufficiently stiff for appropriate load distributions and sealing.

[0072] One or more feed water streams 12 can pass through the ED stack 122 where the electrodes 129a, 129b separate salt ions and heavy metal ions into cations and anions, and direct them into the brine water stream 102b for disposal. The ED stack 122 disposed between the pair of end caps 160a, 160b is shown in FIG. 13. As shown, the end caps 160a, 160b can efficiently use sheet metal capabilities to stiffen edges and center of end cap using bends.

[0073] FIGS. 14A-14B illustrate the end caps 160a, 160b in greater detail. The overall volume of the end cap assembly can be reduced by extending one or more reverse bends 162 of the sheet metal component around a core 163 of the end cap 160, meeting priorities for compact consumer product packaging while still providing requisite stiffness for function. As shown, the sheet metal component can includes regions that are parallel to and in physical communication with at least two adjacent surfaces of the core 163. The core 163 can be fabricated from a material safe for water and electrical contact, e.g. a polymer such as acrylonitrile butadiene styrene (ABS), and the core material and geometry can be selected for compatibility with high-volume manufacturing approaches such as injection molding. Additional stiffness can be provided through the addition of low-profile ribs 164 that protrude away from the end cap core with minimal addition to the overall end cap envelope. The core can be in physical communication with one or more electrodes and one or more fluidic streams. Moreover, one or more cutouts 166 can be formed to allow access to ports, maintain stiffness, and have clearance 165 for a central electrode.

[0074] FIG. 15 illustrates the end caps 160a, 160b in an assembled state without the ED stack 122 therebetween, with an interior portion of the end cap 160b being shown in a translucent manner. As shown, tie rods 168 can be fastened against the sheet metal, or opened for clearance against the composite for even better corrosion resistance.

Alternatively, the end caps 160a, 160b can be bonded. Moreover, plumbing through the composite 164 can ensure water compatibility from corrosion of metal components. In some embodiments, the end caps can be welded in the comers for greater stiffness. The remaining holes for sheet metal can be mechanically fastened via mechanical fasteners 170 to the composite 164, but can also be bonded to improve two-part stiffness. Additional holes 172 can be formed on either side of the end cap 160a to support chiral composite parts that use one part sheet metal for both top and bottom end caps 160a, 160b. For example, additional holes or features can be added to work with both end caps (different as mirrors of each other) to have only one sheet metal part and less part differentiation to improve purchasing. It will be appreciated that the sheet metal component may not be in direct physical communication with fluid or a source of electric voltage.

[0075] Examples of the above-described embodiments can include the following:

1. An electrodialysis (ED) system, comprising: an ED stack that includes a stack of alternating cation exchange membranes and anion exchange membranes, and one or more pairs of electrodes configured to exert an electric driving force to transport ions through the alternating cation exchange membranes and anion exchange membranes; a pump; a feed stream that is in fluid communication with the pump to flow therethrough and is split into a diluate input stream and a concentrate input stream that enter the ED stack; a valve manifold system that includes a set of valves and a reversal mechanism for flowing the diluate input stream and the concentrate input stream in alternating fluidic paths within the ED stack to produce a product output stream and a brine output stream, respectively; an electrode rinse stream that is in fluid communication with the ED stack and is configured to flow into and out of physical contact with the one or more pairs of electrodes; and a second pump configured to flow the electrode rinse stream through the ED stack, wherein the electrode rinse stream is in a closed-loop configuration with the ED stack and the second pump.

2. The system of example 1 , wherein the feed stream, diluate input stream, and the concentrate input stream do not flow through any additional pump throughout their path through the ED system.

3. The system of example 1 or example 2, wherein the electrode rinse stream comprises a sodium sulfate stream that is separate from both the concentrate input stream and the brine output stream.

4. The system of any of examples 1 to 3, wherein the closed- loop configuration further comprises an electrode rinse storage tank for storing the electrode rinse stream therein.

5. The system of example 4, wherein the electrode rinse storage tank includes a two-port bag.

6. The system of any of examples 1 to 5, wherein the ED stack comprises two or more ED stages, wherein: each stage of the two or more ED stages includes a stage stack of alternating cation exchange membranes and anion exchange membranes in electrical communication with one or more pairs of electrodes of the stage of the two or more ED stages; the product output stream from each stage of the two or more ED stages, except a final stage of the two or more ED stages, is in fluid communication with the diluate input stream for a downstream stage of the two or more ED stages; the brine output stream from each stage of the two or more ED stages, except the final stage of the two or more ED stages, is in fluid communication with the concentrate input stream for a downstream stage of the two or more ED stages; the product output stream from the final stage comprises a final product stream for the ED stack; and the brine output stream from the final stage comprises a final brine stream for the ED stack.

7. The system of example 6, wherein the voltage applied to each ED stage is configured to be independently modulated.

8. The system of any of examples 1 to 7, wherein a flow rate of the diluate input stream is greater than a flow rate of the concentrate input stream.

9. The system of example 8, wherein the flow rate of the concentrate input stream is approximately in a range of about 4 Liters/hour to about 8 Liters/hour, and the flow rate of the diluate input stream is approximately in a range of about 10 Liters/hour to about 20 Liters/hour.

10. The system of any of examples 1 to 9, wherein a flow rate of the electrode rinse stream is configured to be tuned based on a voltage between the one or more pairs of electrodes and a current through the ED stack.

11. The system of any of examples 1 to 10, wherein the flow rate of the electrode rinse stream is approximately in a range of about 10 Liters/hour to about 30 Liters/hour.

12. The system any of examples 1 to 11, wherein the ED stack, the pump, the feed stream, the manifold system, and the electrode rinse stream are configured to fit in an about 300 mm x about 280 mm x about 500 mm rectilinear envelope.

13. The system of any of examples 1 to 12, further comprising one or more flow spacers disposed between the stack of alternating cation exchange membranes and anion exchange membranes. 14. The ED system of example 13, wherein the one or more flow spacers comprise thermoplastic urethane (TPU).

15. The ED system of example 14, wherein the one or more flow spacers comprise at least two layers of TPU.

16. The ED system of any of examples 13 to 15, wherein the one or more flow spacers define a channel having a tortuous path through a first surface thereof.

17. The system of any of examples 13 to 16, further comprising a pressure regulator disposed on the concentrate input stream upstream of the ED stack.

18. The system of any of examples 1 to 17, further comprising a pair of composite end caps disposed on opposite end of the ED stack, with each composite end cap comprising: a core component in physical communication with one or more electrodes and one or more fluidic streams; and a sheet metal component comprising regions parallel to and in physical communication with at least two adjacent surfaces of the core component, wherein the sheet metal component is not in direct physical communication with fluid or a source of electric voltage.

19. A method of manufacturing a flow spacer, comprising: removing the region of a desired flow path from one or more layers of thermoplastic urethane (TPU); positioning a first layer of thermoplastic urethane (TPU) in a stamp of an instrument configured to perform compression molding, the stamp having raised edges on one or more sides of the stamp that define a channel to define a flow path in the spacer; positioning a mesh on the first layer of TPU; positioning a second layer of TPU on the mesh; and compression molding the first and second layers to the mesh to form the spacer, the spacer having an imprint of the channel thereon.

20. The method of example 19, further comprising cutting one or more TPU sheets using a laser instrument to form the first layer of TPU and the second layer of TPU. 21. A method of desalinating a system, comprising: circulating at least a portion of a rinse stream from a storage tank through an electrodialysis (ED) stack that includes a stack of alternating cation exchange membranes and anion exchange membranes disposed between one or more pairs of electrodes that are configured to exert an electric driving force to transport ions through the alternating cation exchange membranes and anion exchange membranes; and flowing at least a portion of the rinse stream exiting the ED stack back to the storage tank, wherein the rinse stream is in a closed-loop configuration with the ED stack, and wherein the rinse stream contacts the one or more pairs of electrodes when circulating through the ED stack.

22. The method of example 21, wherein the rinse stream is circulated simultaneously with the ED stack separating a fluid from a salt content to form a product.

23. The method of example 21 or example 22, further comprising tuning a flow rate of the rinse stream based on a voltage between the one or more pairs of electrodes and a current through the ED stack.

24. The method of example 23, wherein the flow rate of the rinse stream is approximately in a range of about 10 Liters/hour to about 30 Liters/hour.

[0076] One skilled in the art will appreciate further features and advantages of the disclosures based on the provided for descriptions and embodiments. Accordingly, the inventions are not to be limited by what has been particularly shown and described. To the extent the present disclosure includes illustrations and descriptions that include prototypes, bench models, or schematic illustrations of set-ups, a person skilled in the art will recognize how to rely upon the present disclosure to integrate the techniques, systems, devices, and methods provided for into a product and/or production method, such as commercially viable ED systems across a variety of small, medium, and/or large scales. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

[0077] Some non-limiting claims that are supported by the contents of the present disclosure are provided below.

Claims

What is claimed is:

2. The system of claim 1 , wherein the feed stream, diluate input stream, and the concentrate input stream do not flow through any additional pump throughout their path through the ED system.

3. The system of claim 1, wherein the electrode rinse stream comprises a sodium sulfate stream that is separate from both the concentrate input stream and the brine output stream.

4. The system of claim 1 , wherein the closed-loop configuration further comprises an electrode rinse storage tank for storing the electrode rinse stream therein.

5. The system of claim 4, wherein the electrode rinse storage tank includes a two-port bag.

6. The system of claim 1, wherein the ED stack comprises two or more ED stages, wherein: each stage of the two or more ED stages includes a stage stack of alternating cation exchange membranes and anion exchange membranes in electrical communication with one or more pairs of electrodes of the stage of the two or more ED stages; the product output stream from each stage of the two or more ED stages, except a final stage of the two or more ED stages, is in fluid communication with the diluate input stream for a downstream stage of the two or more ED stages; the brine output stream from each stage of the two or more ED stages, except the final stage of the two or more ED stages, is in fluid communication with the concentrate input stream for a downstream stage of the two or more ED stages; the product output stream from the final stage comprises a final product stream for the ED stack; and the brine output stream from the final stage comprises a final brine stream for the ED stack.

7. The system of claim 6, wherein the voltage applied to each ED stage is configured to be independently modulated.

8. The system of claim 1, wherein a flow rate of the diluate input stream is greater than a flow rate of the concentrate input stream.

9. The system of claim 8, wherein the flow rate of the concentrate input stream is approximately in a range of about 4 Liters/hour to about 8 Liters/hour, and the flow rate of the diluate input stream is approximately in a range of about 10 Liters/hour to about 20 Liters/hour.

10. The system of claim 1, wherein a flow rate of the electrode rinse stream is configured to be tuned based on a voltage between the one or more pairs of electrodes and a current through the ED stack.

11. The system of claim 1 , wherein the flow rate of the electrode rinse stream is approximately in a range of about 10 Liters/hour to about 30 Liters/hour.

12. The system of claim 1, further comprising one or more flow spacers disposed between the stack of alternating cation exchange membranes and anion exchange membranes.

13. The ED system of claim 12, wherein the one or more flow spacers comprise thermoplastic urethane (TPU).

14. The system of claim 12, further comprising a pressure regulator disposed on the concentrate input stream upstream of the ED stack.

15. The system of claim 1, further comprising a pair of composite end caps disposed on opposite end of the ED stack, with each composite end cap comprising: a core component in physical communication with one or more electrodes and one or more fluidic streams; and a sheet metal component comprising regions parallel to and in physical communication with at least two adjacent surfaces of the core component, wherein the sheet metal component is not in direct physical communication with fluid or a source of electric voltage.

16. A method of manufacturing a flow spacer, comprising: removing the region of a desired flow path from one or more layers of thermoplastic urethane (TPU); positioning a first layer of thermoplastic urethane (TPU) in a stamp of an instrument configured to perform compression molding, the stamp having raised edges on one or more sides of the stamp that define a channel to define a flow path in the spacer; positioning a mesh on the first layer of TPU ; positioning a second layer of TPU on the mesh; and compression molding the first and second layers to the mesh to form the spacer, the spacer having an imprint of the channel thereon.

17. A method of desalinating a system, comprising: circulating at least a portion of a rinse stream from a storage tank through an electrodialysis (ED) stack that includes a stack of alternating cation exchange membranes and anion exchange membranes disposed between one or more pairs of electrodes that exert an electric driving force to transport ions through the alternating cation exchange membranes and anion exchange membranes; and flowing at least a portion of the rinse stream exiting the ED stack back to the storage tank, wherein the rinse stream is in a closed- loop configuration with the ED stack, and wherein the rinse stream contacts the one or more pairs of electrodes when circulating through the ED stack.

18. The method of claim 17, wherein the rinse stream is circulated simultaneously with the ED stack separating a fluid from a salt content to form a product.

19. The method of claim 17, further comprising tuning a flow rate of the rinse stream based on a voltage between the one or more pairs of electrodes and a current through the ED stack.

20. The method of claim 19, wherein the flow rate of the rinse stream is approximately in a range of about 10 Liters/hour to about 30 Liters/hour.