Improving chlorine resistance in continuous electrodeionization processing modules

Abstract

An electrochemical water treatment device is disclosed. The device includes a feed inlet fluidly connectable to a source of water containing dissolved silica and chlorine-containing compounds, and an electrochemical separation module fluidly connectable to the feed inlet. The electrochemical separation module includes a dilute compartment, a concentrate compartment, an ion exchange membrane disposed between the dilute compartment and the concentrate compartment, and a first electrode and a second electrode. A first portion of the volume of the dilute compartment includes a first ion exchange medium disposed proximate to the feed inlet. A second portion of the volume of the dilute compartment includes a second ion exchange medium disposed distal to the feed inlet. The first ion exchange medium has a greater tolerance to chlorine-containing compounds than the second ion exchange medium. A method for reducing the concentration of dissolved silica in water is disclosed. A method for facilitating the treatment of water containing dissolved silica is disclosed.

Description

[Technical Field]

[0001] Aspects and embodiments disclosed herein relate to an apparatus and method for removing contaminants, such as dissolved silica, from water containing chlorine-containing compounds that exhibit improved resistance to degradation from chlorine in the water. Summary of the Invention

[0002] According to one embodiment, an electrochemical water treatment device is provided. The electrochemical water treatment device may include a feed inlet fluidly connectable to a source of water containing dissolved silica and chlorine-containing compounds. The electrochemical water treatment device may further include an electrochemical separation module fluidly connectable to the feed inlet, the electrochemical separation module including a dilute compartment, a concentrate compartment, an ion exchange membrane disposed between the dilute compartment and the concentrate compartment, and a first electrode and a second electrode. A first portion of the volume of the dilute compartment may include a first ion exchange medium disposed proximate to the feed inlet. A second portion of the volume of the dilute compartment may include a second ion exchange medium disposed distal to the feed inlet. The first ion exchange medium may have a greater resistance to chlorine-containing compounds than the second ion exchange medium.

[0003] In a further embodiment, the electrochemical water treatment device may include a product outlet fluidly connected downstream of the dilution compartment of the electrochemical separation module.

[0004] In some embodiments, the first ion exchange medium may be more resistant to swelling due to absorption of chlorine-containing compounds compared to the second ion exchange medium.

[0005] In some embodiments, the first portion occupies about 10% to about 30% of the volume of the diluate compartment, and the second portion occupies about 70% to about 90% of the volume of the diluate compartment.

[0006] In certain embodiments, the first ion exchange medium may comprise a mixture of two or more ion exchange media. For example, the mixture of two or more ion exchange media may comprise a mixture of at least one cation exchange medium and at least one anion exchange medium. In certain embodiments, one of the at least one cation exchange medium and the at least one anion exchange medium has a water content of between about 40 and 50%, as does the at least one anion exchange medium.

[0007] In some embodiments, the first ion exchange medium can withstand chlorine-containing compounds present at concentrations of about 0.01 ppm to about 0.10 ppm for extended periods of time, such as days, weeks, or months.

[0008] In a further embodiment, the first ion exchange medium may include up to about 10% v / v of an adsorbent, such as a carbonaceous adsorbent.

[0009] In some embodiments, the second ion exchange medium may comprise an ion exchange medium suitable for removing dissolved silica from water from a water source. In certain embodiments, the second ion exchange medium may comprise a mixture of two or more ion exchange media. For example, the mixture of two or more ion exchange media may comprise a mixture of at least one cation exchange medium and at least one anion exchange medium. In certain embodiments, one of the at least one cation exchange medium and the at least one anion exchange medium has a water content of between about 50 and 60%, as does the at least one anion exchange medium.

[0010] In some embodiments, the at least one anion exchange medium of the first ion exchange medium may have a greater water content than the at least one anion exchange medium of the second ion exchange medium, while in other embodiments, the at least one cation exchange medium of the first ion exchange medium and the at least one cation exchange medium of the second ion exchange medium have approximately equal water contents.

[0011] In some embodiments, at least one of the first and second ion exchange media may be a microporous resin, a macroporous resin, or a cross-linked gel.

[0012] In some embodiments, the volume of the concentrating compartment may include a third ion exchange medium having a composition substantially similar to the first ion exchange medium.

[0013] In a further embodiment, the electrochemical separation module may include a plurality of dilute compartments and a plurality of concentrate compartments separated by an alternating series of cation exchange membranes and anion exchange membranes.

[0014] According to one embodiment, a method for reducing the concentration of dissolved silica in water is provided. The method may include directing a feed stream from a water source containing dissolved silica and chlorine-containing compounds to a feed inlet of an electrochemical separation module in an electrochemical water treatment device. The electrochemical separation module may include a dilute compartment, a concentrate compartment, an ion exchange membrane disposed between the dilute compartment and the concentrate compartment, and a first electrode and a second electrode. A first portion of the volume of the dilute compartment may include a first ion exchange medium disposed proximate to the feed inlet. A second portion of the volume of the dilute compartment may include a second ion exchange medium disposed distal to the feed inlet. The first ion exchange medium may have a greater tolerance to chlorine-containing compounds than the second ion exchange medium. The method may further include applying a voltage between the first electrode and the second electrode to produce a product stream having a reduced concentration of dissolved silica and a concentrate stream enriched in dissolved silica.

[0015] In some embodiments, directing the feed stream from the source of water to be treated may include directing water having a dissolved silica concentration of about 1 ppm.

[0016] In a further embodiment, the method includes discharging a product stream having a dissolved silica concentration of about 1 ppb.

[0017] According to one embodiment, a method for facilitating the treatment of water containing dissolved silica is provided. The method may include providing an electrochemical water treatment device connectable to a source of water containing dissolved silica and chlorine-containing compounds. The electrochemical separation module may include a feed inlet, a dilute compartment, a concentrate compartment, an ion exchange membrane disposed between the dilute compartment and the concentrate compartment, and a first electrode and a second electrode. A first portion of the volume of the dilute compartment may include a first ion exchange medium disposed proximate to the feed inlet. A second portion of the volume of the dilute compartment may include a second ion exchange medium disposed distal to the feed inlet. The first ion exchange medium may have a greater tolerance to chlorine-containing compounds than the second ion exchange medium. The method may further include providing instructions for directing wastewater from the water source to the feed inlet of the electrochemical separation module. The method may further include providing instructions for applying a voltage between the first electrode and the second electrode to produce a product stream having a reduced concentration of dissolved silica and a concentrate stream enriched in dissolved silica. [Brief explanation of the drawings]

[0018] The accompanying drawings are not drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by the same numeral. For clarity, not every component is labeled in every drawing. In the drawings, [Figure 1] FIG. 1 illustrates an electrochemical separation module according to one embodiment. [Figure 2] FIG. 2 illustrates a water treatment system incorporating the electrochemical separation module of FIG. 1, according to one embodiment. [Figure 3A] FIG. 3A illustrates the pressure drop across the dilute compartment of an electrochemical separation module with different ion exchange media configurations. [Figure 3B] FIG. 3B illustrates the pressure drop across the concentrating compartments of electrochemical separation modules with different ion exchange media configurations. [Figure 4]FIG. 4 illustrates the silica removal performance of electrochemical separation modules with different ion exchange media configurations. [Figure 5A] FIG. 5A illustrates the pressure drop across the dilute compartment for an electrochemical separation module having a different ion exchange media configuration than that shown in FIG. 3A. [Figure 5B] FIG. 5B illustrates the pressure drop across the concentrating compartment for an electrochemical separation module having a different ion exchange media configuration than that illustrated in FIG. 3B. [Figure 6] FIG. 6 illustrates the silica removal performance for electrochemical separation modules with different ion exchange media configurations; and [Figure 7] FIG. 7 illustrates the effluent resistivity of electrochemical separation modules with different ion exchange media configurations. DETAILED DESCRIPTION OF THE INVENTION

[0019] (Detailed explanation) Ion exchange is the reversible exchange of ions between a solid (e.g., an ion exchange resin) and a liquid (e.g., water). Ion exchange media function as "chemical sponges" and are therefore well-suited for the effective removal of contaminants from water and other liquids. Ion exchange technology is commonly used in water desalination and softening, wastewater reuse, and other water treatment processes. Ion exchange media are also used in a variety of specialized applications, such as chemical processing, pharmaceuticals, mining, and food and beverage processing.

[0020] Devices for purifying fluids using electric fields, i.e., electrochemical separation modules, can be used to treat water and other liquids containing dissolved ionic species. These modules contain concentrate and dilute (or deplete) compartments separated by ion-selective membranes. Electrochemical separation modules can be characterized by alternating electroactive, semipermeable anion- and cation-exchange membranes. The spaces between the membranes are configured to form liquid flow compartments with inlets and outlets. Application of an electric field via electrodes causes dissolved ions attracted to the opposing electrodes to migrate through the anion- and cation-exchange membranes. This typically results in the liquid in the dilute compartment being depleted of ions and the liquid in the concentrate compartment being enriched with the migrated ions.

[0021] As used herein, the phrases "separation module," "treatment device," "clarification device," or "apparatus" refer to any device that can be used to remove or reduce the concentration level of any undesirable species from a treated fluid. Examples of suitable treatment devices include, but are not limited to, ion exchange resin devices, reverse osmosis (RO), electrodeionization processes, electrodialysis, ultrafiltration, microfiltration, and capacitive deionization devices.

[0022] In certain non-limiting embodiments, the methods and devices disclosed herein comprise an electrochemical separation module. As used herein, the phrase "electrochemical separation module" refers to any number of electrically driven separation systems, non-limiting examples of which include, but are not limited to, electrodeionization treatment devices, electrodialysis devices, capacitive deionization treatment devices, and any combination thereof. Electrochemical water treatment devices can include any device that functions according to the principles of the systems and methods described herein, provided that they are not inconsistent with or contrary to their operation.

[0023] In certain embodiments, the electrochemical separation module may include an electrochemical deionization unit, non-limiting examples of which include electrodialysis (ED), electrodialysis reversal (EDR), electrodeionization (EDI), capacitive deionization, continuous electrodeionization (CEDI), and reversible continuous electrodeionization (RCEDI).

[0024] Electrodeionization (EDI) is a process that removes or at least reduces one or more ionized or ionizable species from water using one or more ion exchange media and an applied potential between electrodes to affect ion transport. The ion exchange media typically serve to alternately collect and expel ionic and / or ionizable species, and in some embodiments, facilitate the transport of ions, which may be continuous, via ionic or electronic exchange mechanisms. EDI devices can contain electrochemically active media with permanent or temporary charges and can be operated in batch, intermittent, continuous, and / or polarity-reversed modes. EDI devices can be operated to facilitate one or more electrochemical reactions specifically designed to achieve or enhance performance. Furthermore, such electrochemical devices may include ion exchange membranes, such as semipermeable or selectively permeable ion exchange or bipolar membranes. Continuous electrodeionization (CEDI) devices are EDI devices that operate in a manner that allows for continuous water purification while continuously recharging the ion exchange material. CEDI technologies can include processes such as continuous deionization, packed cell electrodialysis, and electrodialysis. Under controlled conditions of voltage and salinity, in CEDI systems, water molecules can split to produce hydrogen or hydronium ions or species and hydroxide or hydroxyl ions or species, regenerating the ion exchange media within the device and thereby facilitating the release of trapped species therefrom. In this way, the treated water stream can be continuously purified without the need for chemical recharging of the ion exchange media.

[0025] Electrodialysis (ED) devices operate on a similar principle to CEDI, except that ED devices typically do not contain an electroactive medium between the membrane and / or electrodes. Because of the lack of an electroactive medium, electrical resistance increases in feedwater with low salinity, which can hinder ED operation. Furthermore, because ED consumes a large amount of current when performed with feedwater with high salinity, ED devices have traditionally been most effective with feedwater with moderate salinity. In ED-based systems, the absence of an electroactive medium results in inefficient water splitting, and operation in such regions is generally avoided.

[0026] Capacitive deionization (CapDI) devices are used to remove ionic substances from a medium, such as hard water, by applying a voltage to a pair of electrodes with nanometer-sized pores to polarize the pair of electrodes. This allows the ionic substances to be adsorbed onto the surface of at least one of the electrodes. In a CapDI device, a low DC voltage is applied to the pair of electrodes, and a medium containing dissolved ions is passed between the two electrodes. Anions dissolved in the medium are adsorbed and concentrated on the positive electrode, and cations dissolved in the medium are adsorbed and concentrated on the negative electrode. When a current is applied in the opposite direction, for example, by electrically shorting the two electrodes, the concentrated ions are desorbed from the negative and positive electrodes. CapDI devices are energy-efficient because they do not use a high potential difference. Adsorption of ions to the electrodes can remove not only hardness components but also undesirable ions. CapDI devices have a relatively low environmental impact because they do not use chemicals to regenerate the electrodes.

[0027] CEDI and ED devices may include a separation module having multiple adjacent cells or compartments separated by selectively permeable membranes that allow the passage of either positively or negatively charged species, but typically not both. The dilution or depletion compartment is typically spaced apart from the concentrating or concentration compartment in such devices. One embodiment of an electrochemical separation module as used in a CEDI or ED device is shown in FIG. 1. In FIG. 1, electrochemical separation module 100 includes a dilution compartment 102, a concentration compartment 104, and an ion exchange membrane 106 separating the dilution compartment 102 and the concentration compartment 104. In some embodiments, only one of each component may be present, i.e., one dilution compartment 102, one concentration compartment 104, and one ion exchange membrane 106. As shown in FIG. 1 , the electrochemical separation module 100 may include multiple dilute compartments 102 and multiple concentrate compartments 104 separated by an alternating series of ion exchange membranes 106, such as alternating cation and anion exchange membranes. In other embodiments, there may be a greater number of dilute and concentrate compartments than are illustrated in FIG. 1 . The electrochemical separation module 100 is bounded by first and second electrodes 108a, 108b, which operate as anodes and cathodes, respectively. Within the dilute compartment 102, a first portion of the volume of the dilute compartment 102 contains a first ion exchange medium 110a. A second portion of the volume of the dilute compartment 102 contains a second ion exchange medium 110b, and the dashed line in FIG. 1 provides a visual aid for the interface between the two ion exchange media. The concentrate compartment 104 contains a third ion exchange medium 110c.

[0028] In CEDI and ED devices, a direct current (DC) electric field is typically applied across the cell from a voltage and current source applied to the electrodes (anode or positive electrode and cathode or negative electrode). The voltage and current sources (collectively, "power sources") can be powered by a variety of means, such as an alternating current (AC) source itself, or sources derived from solar, wind, or wave power. At the electrode / liquid interface, electrochemical half-cell reactions occur, initiating and / or promoting the movement of ions through the membranes and compartments. For example, in Figure 1, when a voltage is applied across the first and second electrodes, i.e., the cathode and anode, hydroxide and hydrogen ions can form in the water, causing ions present in the water to migrate to the electrode of opposite polarity.

[0029] In some embodiments, for electrodes contained within the electrolyte compartments, the specific electrochemical reactions occurring at the electrode / interface can be controlled to some extent by the concentration of salt within the compartment. For example, a sodium chloride-rich feed to the anolyte compartment tends to generate chlorine gas and hydrogen ions, while a similar feed to the catholyte compartment tends to generate hydrogen gas and hydroxide ions. Generally, hydrogen ions generated in the anolyte compartment associate with free anions, such as chloride ions, to maintain charge neutrality and produce a hydrochloric acid solution. Similarly, hydroxide ions generated in the catholyte compartment associate with free cations, such as sodium, to maintain charge neutrality and produce a sodium hydroxide solution. The reaction products of the electrode compartments, such as the chlorine gas and sodium hydroxide produced, can be utilized in the process for sterilization purposes, membrane cleaning and degassing purposes, and pH adjustment, as needed.

[0030] CEDI modules can be used downstream of RO membranes made of materials such as polyamide. Because these membranes have limited tolerance to free chlorine, such as residual chlorine from water disinfection processes, feedwater must be dechlorinated before treatment in the RO unit. However, in dechlorination systems using reducing agents such as sodium bisulfite, trace amounts of free chlorine or chloramines can reach the downstream CEDI module and cause system disruption. CEDI modules can be optimized for performance in specific treatment applications by selecting membranes and ion exchange media with specific physical and chemical properties. In some embodiments, such optimization can include selecting an ion exchange media with an appropriate amount of crosslinking for a particular application. CEDI modules may use ion exchange media with about 1% to about 10% by weight of divinylbenzene (DVB) as a polymeric crosslinker. As a non-limiting example, the ion exchange media used for the anion exchange process can have a DVB content of about 2% by weight. As another non-limiting example, the ion exchange media used for the cation exchange process can have a DVB content of about 8% by weight. The crosslinked weight percent is generally not specified for ion exchange media, but can be inferred from its water content in an approximately 1:1 relationship. Without wishing to be bound by any particular theory, the water content of an ion exchange resin is a measure of the amount of hydration water that fills the voids in the solid resin matrix, and as used herein, is considered to be the maximum weight percent of water that the ion exchange media can absorb and retain when exposed to water. Resins with high water content contain less dry matter, i.e., matrices made from polystyrene with divinylbenzene crosslinks that crosslink the polystyrene chains. While increased water content (and therefore less dry matter) may provide easier access for large ions to migrate in and out of the structure, increased water content also reduces the resin's physical strength and resistance to oxidative attack, both of which are generally provided by a crosslinked polymer structure.In some embodiments, an ion exchange medium can be considered to have a "high" degree of cross-linking if the water content of the ion exchange medium is between about 40% and about 50% by weight. A "low" cross-linked ion exchange medium may have a water content between about 50% and about 60% by weight.

[0031] Removal of dissolved silica from process water can be achieved by using high-moisture, low-crosslinked anion exchange media in the dilution compartment of electrically operated separation devices (e.g., ED, EDI, CEDI), which have increased susceptibility to oxidizing species such as free chlorine compared to low-moisture, high-crosslinked anion exchange media. During use, the ion exchange media closest to the inlet of the dilution compartment can be attacked by free chlorine in the feedwater, causing the ion exchange media to swell and potentially mechanically degrade or break down, resulting in blockage of water flow through the entire electrochemical separation module. These blockages can result in permanent damage requiring the entire electrochemical separation module to be rebuilt or replaced. Therefore, it would be desirable to include one or more ion exchange media within the electrochemical separation module that can treat water containing oxidizing ions and molecules without sustaining permanent damage or loss of treatment performance.

[0032] According to one embodiment, a water treatment system is provided that includes a feed inlet fluidly connected or connectable to a source of water containing dissolved silica and chlorine-containing compounds, and an electrochemical separation module fluidly connected or connectable to the feed inlet. The electrochemical separation module may include a dilute compartment, a concentrate compartment, an ion exchange membrane disposed between the dilute compartment and the concentrate compartment, and a first electrode and a second electrode. A first portion of the volume of the dilute compartment may include a first ion exchange medium disposed proximate to the feed inlet. A second portion of the volume of the dilute compartment may be disposed distal to the feed inlet. The second portion of the volume of the dilute compartment may include a second ion exchange medium that is more resistant to chlorine-containing compounds, such as being more resistant to swelling or crushing upon absorption or adsorption of chlorine-containing compounds than the second ion exchange medium. The water treatment system may further include a product outlet fluidly connected downstream of the electrochemical separation module. The product outlet may be configured to discharge treated water to a further downstream treatment stage or point of use.

[0033] One embodiment of a water treatment device incorporating the electrochemical separation module shown in Figure 1 is shown in Figure 2. As shown, a feed inlet 101, connected to or connectable to a source of water containing dissolved silica and chlorine-containing compounds to be treated (not shown), is positioned to distribute water from the water source to the dilution compartment 102 and concentration compartment 104 of the electrochemical separation module 100. As water flows through the depletion compartment 102 (shown by the arrow in Figure 2), ionic and other charged species are typically drawn to the concentration compartment 104 under the influence of an electric field, such as a DC field. Positively charged species are attracted toward a cathode, such as the second electrode 108b, located at one end of a stack of multiple depletion compartments 102 and concentration compartments 104, and negatively charged species are similarly attracted toward an anode, such as the first electrode 108a, located at the opposite end of the stack of compartments. The first and second electrodes 108a, 108b are typically contained within an electrolyte compartment (not shown), which may be partially isolated from fluid communication with the depletion compartment 102 and / or the concentration compartment 104. Once in the concentration compartment 104, the charged species may be captured by the barrier of the ion exchange membrane 106, which may at least partially define the concentration compartment 104. For example, anions may be prevented by the cation exchange membrane from migrating further toward the second electrode 108b and exiting the concentration compartment 104. The treated water in the dilution compartment 102 may be discharged through a product outlet 112 fluidly connected downstream of the electrochemical separation module 100. Once captured in the concentration compartment 104, the captured charged species may be removed in a concentrate stream and discharged to a waste outlet 114.

[0034] In some embodiments, the portion of the volume of the dilute compartment located proximate the feed inlet may include an ion exchange medium having a greater resistance to chlorine-containing compounds, such as a greater resistance to swelling or crushing, than the ion exchange medium in the portion of the dilute compartment distal to the feed inlet that is downstream of the portion proximate the feed inlet. A first portion of the volume of the dilute compartment may occupy about 10% to about 30% of the volume of the dilute compartment, such as the first portion of the dilute compartment 102 having the first ion exchange medium 110a shown in FIG. 1. The selection for the volume of the dilute compartment occupied by the first ion exchange medium may be determined by many factors, including, but not limited to, the inlet water quality, the desired treated water quality, the flow rate, and the residence time of the water in the electrochemical cell. For example, the first portion of the volume of the dilute compartment may occupy about 10% to about 30% of the volume of the dilute compartment, about 15% to about 25% of the volume of the dilute compartment, or about 20% of the volume of the dilute compartment, e.g., about 10%, about 15%, about 20%, about 25%, or about 30% of the volume of the dilute compartment. Without wishing to be bound by theory, by locating an ion exchange medium that is more resistant to swelling or other reactions from oxidizing species, such as chlorine-containing compounds, closer to the feed inlet, the water after contact with the first ion exchange medium may have a lower concentration of the chlorine-containing compounds and therefore may be less likely to swell or lose structural integrity to other ion exchange media present in the dilute compartment, such as in the second portion of the volume of the dilute compartment.

[0035] In some embodiments, the second portion of the volume of the diluate compartment, such as the second portion of the diluate compartment 102 having the second ion exchange medium 110b illustrated in Figure 1, may occupy about 70% to about 90% of the volume of the diluate compartment. For example, the second portion of the volume of the diluate compartment can occupy about 70% to about 90% of the volume of the diluate compartment, about 75% to about 85% of the volume of the diluate compartment, or about 80% of the volume of the diluate compartment, e.g., about 70%, about 75%, about 80%, about 85%, or about 90% of the volume of the diluate compartment.

[0036] In some embodiments of the water treatment system disclosed herein, one or both of the first and second ion exchange media may comprise a mixture of two or more ion exchange media. For example, one or both of the first and second ion exchange media may be a mixture of at least one cation exchange media and at least one anion exchange media. The specific type(s) and the specific amount (e.g., % w / w or % v / v) of each type of ion exchange media may be determined by the characteristics of the water to be treated, such as its chemical composition. In some embodiments, a binary mixture of cation and anion exchange media may be in equal amounts, e.g., 50% of each polar media in the mixture. Alternatively, the relative amounts of each polarity of ion exchange media may be determined, in part, by a balance between resistance to chemical attack and ion transport performance. For example, in water with a high concentration of oxidizing species, e.g., chlorine or chlorine-containing compounds, such as greater than about 0.02 ppm, the first ion exchange media may have a component media selected to be more resistant to chlorine-containing compounds than the corresponding component media in the second ion exchange media. As described herein, ion exchange media, i.e., cation exchange media or anion exchange media, having greater resistance to chlorine-containing compounds may have a higher crosslinking content and therefore a lower water content. In some embodiments, at least one of the at least one cation exchange media and the at least one anion exchange media may have a water content of between about 40 and 50%, for example, about 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%. Oxidizing species are generally anions in water, such as halide ions or peroxide ions. Therefore, the anion exchange resin of the first ion exchange media may have a water content of between about 40 and 50%, i.e., an increased amount of crosslinking, to resist absorption of oxidizing species present in water and subsequent swelling or damage.In some embodiments, the first ion exchange medium can resist swelling or structural damage in water having an oxidizing species concentration of about 0.01 ppm to about 0.10 ppm, such that no swelling or structural damage to the first ion exchange medium is detectable after prolonged exposure to such water, for example, over a period of multiple days or weeks. For example, the first ion exchange medium can resist structural damage in water having a concentration of oxidizing species of about 0.01 ppm to about 0.10 ppm, e.g., the first ion exchange medium can resist structural damage in water having a concentration of oxidizing species of about 0.01 ppm to about 0.10 ppm, about 0.02 ppm to about 0.09 ppm, about 0.03 ppm to about 0.08 ppm, about 0.04 ppm to about 0.07 ppm, or about 0.05 ppm, e.g., about 0.01 ppm, about 0.02 ppm, about 0.03 ppm, about 0.04 ppm, about 0.05 ppm, about 0.06 ppm, about 0.07 ppm, about 0.08 ppm, about 0.09 ppm, or about 0.10 ppm.

[0037] In some embodiments, the first ion exchange medium may further include an adsorbent to reduce the contaminant load of water from the water source entering the electrochemical separation module. The adsorbent may be any suitable adsorbent useful in water treatment, such as a carbonaceous adsorbent, e.g., activated carbon, zeolite, metal sponge, or other similar adsorbent. In some non-limiting embodiments, the adsorbent may be a fixed particle size beaded activated carbon adsorbent. For example, suitable carbonaceous adsorbents include, but are not limited to, A-BAC-MP (average particle size 0.5 mm) or A-BAC-LP (average particle size 0.6 mm), available from Kureha Corporation (Tokyo, Japan). Other suitable adsorbents are known in the art. The adsorbent may be present in the first ion exchange medium at up to about 10% v / v, for example, about 1% v / v, about 2% v / v, about 3% v / v, about 4% v / v, about 5% v / v, about 6% v / v, about 7% v / v, about 8% v / v, about 9% v / v, or about 10% v / v.

[0038] In some embodiments, the second ion exchange medium comprises an ion exchange medium suitable for removing silica from water from the water source. As described herein, the selection of an ion exchange medium for any portion of the dilute compartment may be determined by a balance between resistance to chlorine-containing compounds, such as resistance to swelling or structural damage associated with exposure to chlorine, and ion transport performance. As a specific example, transport of dissolved silica, a bulky cation, between compartments of an electrochemical separation module may be achieved using a cation exchange medium with a crosslink content of about 5 to 10%. In other embodiments, silica removal may not be a consideration for the ion exchange medium within a compartment of an electrochemical separation module. In this configuration, a highly crosslinked, i.e., lower water content, ion exchange medium may be used throughout the dilute compartment and in the concentrate compartment of the electrochemical separation module.

[0039] As described herein, the ion exchange medium, i.e., the cation exchange medium or the anion exchange medium, used in the second portion of the dilution compartment volume can have a lower crosslinking content and therefore a higher water content. In these embodiments, these types of ion exchange media may be better suited for ion transport rather than resistance to structural damage due to uptake or absorption of oxidizing species, such as chlorine-containing compounds. Water treatment using these types of ion exchange media may operate under conditions in which the concentration of chlorine-containing compounds is reduced by the first ion exchange medium in the first portion of the dilution compartment volume. In some embodiments of the second ion exchange medium in the second portion of the dilution compartment volume, at least one of the at least one cation exchange medium and the at least one anion exchange medium may have a water content of between about 50 and 60%, for example, about 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, or 60%. In certain embodiments, the at least one anion exchange medium has a water content of between about 50 and 60%. In the dilute compartment, at least one anion exchange medium of the first ion exchange medium may have a higher water content than at least one anion exchange medium of the second ion exchange medium. As disclosed herein, the relative water content and degree of cross-linking between the first and second ion exchange media in the dilute compartment may be determined based on the water quality of the feed water to the dilute compartment and the desired ion transport performance. Because most chlorine-containing compounds are anionic, the at least one cation exchange medium in each of the first and second ion exchange media is generally unaffected by chlorine-containing compounds. Therefore, the water content and degree of cross-linking of the cation exchange media in the first and second ion exchange media may be approximately equal. This relative ratio may be adjusted as needed to meet performance indicators, and the embodiments of the invention disclosed herein are not limited to having cation exchange media with equal water content in different portions of the dilute compartment volume.

[0040] In some embodiments of any electrochemical water treatment device disclosed herein, one or both of the first and second ion exchange media may be in any physical form suitable for the disclosed application. For example, one or both of the first and second ion exchange media may comprise a cross-linked gel medium, a microporous resin, or a macroporous resin. The choice of form may depend on the size of the electrochemical treatment module, the quality of the water being treated, and the desired quality of the treated water. As a non-limiting example, in a thin-cell electrochemical separation module, if the thickness of the dilute or concentrate compartment is 2.0 to 3.0 mm, it is possible to use a highly cross-linked, low-moisture (e.g., 40 to 50% moisture) ion exchange medium in the first portion of the dilute compartment under operating conditions that do not result in water splitting. A less cross-linked, higher-moisture (e.g., 50 to 60% moisture) ion exchange medium may be used in the second portion of the dilute compartment, where the majority of silica migration to the concentrate compartment may occur. As another non-limiting example, in thick-cell electrochemical separation modules having dilute and / or concentrate compartment thicknesses of approximately 10 mm, it has been observed that the ion exchange media in the first portion of the dilute compartment, including both Type I and Type II strong base anion resins and mixtures thereof, are susceptible to structural damage when exposed to oxidizing species in water. In this configuration, a highly crosslinked gel ion exchange media or macroporous ion exchange media would serve the purpose of controlling the conductivity, and therefore the ion transport performance, of the ion exchange media in the first portion of the dilute compartment without sacrificing the structural integrity of the ion exchange media.

[0041] In some embodiments of the electrochemical water treatment device disclosed herein, the volume of the concentrate compartment contains a third ion exchange medium having a composition substantially similar to that of the first ion exchange medium. The third ion exchange medium may be a mixture of two or more ion exchange media, such as a mixture of at least one cation exchange medium and at least one anion exchange medium as described herein. As used herein, "substantially similar" refers to the physical and chemical composition of two different ion exchange media characterized by at least one component of the ion exchange medium being identical and present in relative amounts within 10%. For example, the third ion exchange medium of the concentrate compartment may have the same combination of anion and cation exchange media as either the first or second ion exchange medium of the dilute compartment, but the mass or weight percentages of each component may be different. As a simplified example, the first ion exchange medium may contain 60% by weight of Medium A and 40% by weight of Medium B, and the third ion exchange medium may contain 50% by weight of Medium A and 50% by weight of Medium B. The relative ratios of ion exchange media present in the third ion exchange medium may be selected to balance the performance of the dilute compartment with the discharge of concentrate from the concentrate compartment and to reduce pressure drop through the dilute and concentrate compartments.

[0042] According to one embodiment, a method for reducing the concentration of dissolved silica in water is provided. The method may include directing a feed stream from a water source containing dissolved silica and chlorine-containing compounds to a feed inlet of an electrochemical separation module in an electrochemical water treatment device. The method may further include applying a voltage across a first electrode and a second electrode to produce a product stream having a reduced concentration of dissolved silica and a concentrated stream rich in dissolved silica. The electrochemical separation module may include a dilute compartment, a concentrate compartment, an ion exchange membrane disposed between the dilute compartment and the concentrate compartment, and a first electrode and a second electrode. A first portion of the volume of the dilute compartment may include a first ion exchange medium disposed proximate the feed inlet. A second portion of the volume of the dilute compartment may include a second ion exchange medium disposed distal to the feed inlet, the first ion exchange medium having a greater resistance to chlorine-containing compounds than the second ion exchange medium.

[0043] In some embodiments, directing the feed stream from the source of water to be treated comprises directing water having a dissolved silica concentration of about 1 ppm, hi some embodiments, discharging the product stream comprises discharging the product stream having a dissolved silica concentration of about 1 ppb.

[0044] According to one embodiment, a method for facilitating the treatment of water containing dissolved silica is provided. The method may include providing an electrochemical water treatment device connectable to a source of water containing dissolved silica and chlorine-containing compounds. The provided electrochemical separation module may include a feed inlet, a dilute compartment, a concentrate compartment, an ion exchange membrane disposed between the dilute compartment and the concentrate compartment, and a first electrode and a second electrode. A first portion of the volume of the dilute compartment may include a first ion exchange medium disposed proximate the feed inlet, and a second portion of the volume of the dilute compartment may include a second ion exchange medium disposed distal to the feed inlet. The first ion exchange medium may have a greater tolerance for chlorine-containing compounds than the second ion exchange medium. The method may further include providing instructions for directing wastewater from the water source to the feed inlet of the electrochemical separation module. The method may further include providing instructions for applying a voltage between the first electrode and the second electrode to produce a product stream having a reduced concentration of dissolved silica and a concentrate stream enriched in dissolved silica. [Example]

[0045] The function and advantages of these and other embodiments may be better understood from the following examples, which are intended to be exemplary in nature and are not to be construed as limiting the scope of the invention in any way.

[0046] The following examples refer to specific ion exchange media available from commercial suppliers. Exemplary cation exchange media suitable for use in the electrochemical separation modules of the present disclosure are C-211 UPS(Na), both strong acid cation exchange media available from Evoqua Water Technologies, LLC (Pittsburgh, PA). + The water content is 42 to 48%, the degree of cross-linking is 8%, and C-373(Na +Examples of anion exchange media suitable for use in the electrochemical separation modules of the present disclosure include, but are not limited to, DOWEX® MARATHON® A (Cl), both available from The Dow Chemical Company (Midland, MI). - in the form of 50 to 60% moisture content and DOWEX® MONOSPHERE® 550A (Cl - Examples of strong base anion exchange media include, but are not limited to, Type 1 strong base anion exchange media, such as resins in the form of 42-48% water content, and Type 2 strong base anion exchange media. These media types are exemplary only, and aspects and embodiments disclosed herein are not limited by any particular type and / or manufacturer of ion exchange media.

[0047] Example 1 Table 1 shows a comparison between different electrochemical separation module ion exchange media configurations (A to D) to evaluate resistance to media swelling and / or destruction due to chloride ion uptake and the impact on silica removal performance.

[0048] Ion exchange media configuration for electrochemical separation modules [Table 1]

[0049] Compared to Module A, Module B used a high cross-linked cation resin (C-373) but the same anion resin (MARATHON® A), so this configuration did not address the known problem of low cross-linked anion exchange media swelling or degradation due to chloride present in the feedwater to electrochemical separation modules. Module configurations C and D exhibited a delayed onset of increased pressure drop in the dilute compartment, as shown in Figures 3A and 3B. The delayed onset of pressure drop was attributed to the ion exchange media in Modules A and B swelling more quickly within the electrochemical separation module or losing its structural integrity and becoming disrupted to the point of forming blockages that restricted flow in and out of the module. Module C did not exhibit a loss of silica removal performance, while Module D exhibited a significant deterioration in silica removal performance, as shown in Figure 4.

[0050] Example 2 Table 2 shows a comparison between the ion exchange media configuration of module C from Table 1 and modifications of that ion exchange media configuration (module CD and concentrate) to evaluate resistance to media swelling or collapse due to chloride ion uptake, silica removal performance, and resulting water quality.

[0051] Ion exchange media configuration for electrochemical separation modules [Table 2]

[0052] As shown in Figures 5A and 5B, both module configurations C and CD had relatively stable pressure drop changes in the dilute compartment (Figure 5A) and concentrate compartment (Figure 5B) for approximately three months. This indicated that the ion exchange media was stable despite the presence of any oxidizing species in the feedwater to the electrochemical separation module. Module C contained the first portion of the concentrate compartment with high-crosslinked resin, approximately 20% of the compartment volume, and the remainder of the compartment volume contained low-crosslinked resin. Module CD contained the entire volume of the concentrate compartment filled with high-crosslinked resin. Module configuration CD was selected for further testing because it contained a larger proportion of more highly crosslinked ion exchange media in the concentrate compartment compared to module configuration D in Table 1, resulting in a lower pressure drop. As shown in Figures 6 and 7, module configurations C and CD performed approximately equally, as evidenced by a comparison of silica removal (Figure 6) and effluent resistivity (Figure 7).

[0053] The phraseology and terminology used herein are for purposes of description and should not be considered limiting. As used herein, the term "plurality" refers to two or more items or components. The terms "comprising," "including," "carrying," "having," "containing," and "involving," regardless of written description or claims, are open-ended terms, i.e., meaning "including but not limited to." Thus, the use of such terms is intended to encompass the subsequently listed items, and equivalents thereof, as well as additional items. Only the transitional phrases "consisting of" and "consisting essentially of" are closed or semi-closed transitional phrases, respectively, with respect to the claims. The use of ordinal numbers such as "first," "second," "third," etc. in the claims to modify claim elements does not, per se, imply any priority, precedence, or precedence of a claim element relative to other elements, or the chronological order in which acts of a method are performed, but is merely used as a label to distinguish a claim element having a certain name from other elements having the same name (but using ordinal numbers).

[0054] Having thus described several aspects of at least one embodiment, it should be understood that various changes, modifications, and improvements will readily occur to those skilled in the art. Any feature described in any embodiment may be included in, or substituted for, any feature of any other embodiment. Such changes, modifications, and improvements are intended to be part of this disclosure and within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

[0055] Those skilled in the art should understand that the parameters and configurations described herein are exemplary, and that the actual parameters and / or configurations will depend on the particular application in which the disclosed methods and materials are used. Those skilled in the art should be able to recognize or ascertain using no more than routine experimentation equivalents to the specific embodiments disclosed.

Claims

1. 1. An electrochemical water treatment device, comprising: a supply inlet fluidly connectable to a source of water containing dissolved silica and chlorine-containing compounds; and an electrochemical separation module fluidly connectable to the feed inlet, the electrochemical separation module including a dilution compartment, a concentration compartment, an ion exchange membrane disposed between the dilution compartment and the concentration compartment, and a first electrode and a second electrode; a first portion of the volume of the dilution compartment comprising a first ion exchange medium disposed proximate to the feed inlet, the first ion exchange medium comprising a mixture of at least one cation exchange medium and at least one anion exchange medium, the first ion exchange medium having a water content of between 40 and 50%; a second portion of the volume of the dilution compartment comprising a second ion exchange medium disposed distal to the feed inlet, the second ion exchange medium comprising an ion exchange medium suitable for removing dissolved silica from water from a source of water, the second ion exchange medium comprising a mixture of at least one cation exchange medium and at least one anion exchange medium, the second ion exchange medium having a water content of between 50 and 60%; the first ion exchange medium has a higher crosslink content than the second ion exchange medium, such that the first ion exchange medium has a greater resistance to chlorine-containing compounds than the second ion exchange medium; Electrochemical water treatment equipment.

2. 10. The apparatus of claim 1, further comprising a product outlet fluidly connected downstream of the dilution compartment of the electrochemical separation module.

3. 10. The device of claim 1, wherein the first ion exchange medium resists swelling due to absorption of chlorine-containing compounds to a greater extent than the second ion exchange medium.

4. 4. The device of claim 3, wherein the first portion occupies between 10% and 30% of the volume of the diluate compartment.

5. 5. The device of claim 4, wherein the second portion occupies between 70% and 90% of the volume of the diluate compartment.

6. 6. The device of any one of claims 1 to 5, wherein the first ion exchange medium is capable of withstanding chlorine-containing compounds present at concentrations of 0.01 ppm to 0.10 ppm for days, weeks, or months.

7. 10. The device of claim 1, wherein the first ion exchange medium further comprises up to 10% v / v of an adsorbent.

8. 8. The apparatus of claim 1, wherein the at least one anion exchange medium of the first ion exchange medium has a greater water content than the at least one anion exchange medium of the second ion exchange medium.

9. 8. The apparatus of claim 1, wherein the at least one cation exchange medium of the first ion exchange medium and the at least one cation exchange medium of the second ion exchange medium have equal water contents.

10. 10. The device of claim 1, wherein at least one of the first ion exchange medium and the second ion exchange medium comprises a microporous resin, a macroporous resin, or a cross-linked gel.

11. 11. The device of claim 1, wherein the volume of the concentrating compartment contains a third ion exchange medium having at least one component identical to the first ion exchange medium, and the weight percent or mass percent of the at least one component in the third ion exchange medium differs from the weight percent or mass percent of the at least one component in the first ion exchange medium by less than 10%.

12. 10. The device of claim 1, wherein the electrochemical separation module comprises a plurality of dilute compartments and a plurality of concentrate compartments separated by an alternating series of cation exchange membranes and anion exchange membranes.

13. 1. A method for reducing the concentration of dissolved silica in water, comprising: directing a feed stream from a source of water containing dissolved silica and chlorine-containing compounds to a feed inlet of an electrochemical separation module in an electrochemical water treatment device, the electrochemical separation module comprising: a dilution compartment, a concentration compartment, an ion exchange membrane disposed between the dilution compartment and the concentration compartment, and a first electrode and a second electrode; a first portion of the volume of the dilution compartment comprising a first ion exchange medium disposed proximate to the feed inlet, the first ion exchange medium comprising a mixture of at least one cation exchange medium and at least one anion exchange medium, the first ion exchange medium having a water content of between 40 and 50%; a second portion of the volume of the dilution compartment comprising a second ion exchange medium disposed distal to the feed inlet, the second ion exchange medium comprising an ion exchange medium suitable for removing dissolved silica from water from a source of water, the second ion exchange medium comprising a mixture of at least one cation exchange medium and at least one anion exchange medium, the second ion exchange medium having a water content of between 50 and 60%; the first ion exchange medium has a higher crosslink content than the second ion exchange medium, such that the first ion exchange medium has a greater resistance to chlorine-containing compounds than the second ion exchange medium; applying a voltage across the first electrode and the second electrode to produce a product stream having a reduced concentration of dissolved silica and a concentrate stream enriched in dissolved silica; A method comprising:

14. 14. The method of claim 13, wherein directing a feed stream from a source of water to be treated comprises directing water having a dissolved silica concentration of 1 ppm.

15. The method of claim 13, further comprising discharging a product stream having a dissolved silica concentration of 1 ppb.

16. 1. A method for facilitating the treatment of water containing dissolved silica, comprising: Providing an electrochemical water treatment device connectable to a source of water containing dissolved silica and chlorine-containing compounds, the electrochemical water treatment device comprising: an electrochemical separation module including a feed inlet, a dilution compartment, a concentration compartment, an ion exchange membrane disposed between the dilution compartment and the concentration compartment, and a first electrode and a second electrode; a first portion of the volume of the dilution compartment comprising a first ion exchange medium disposed proximate to the feed inlet, the first ion exchange medium comprising a mixture of at least one cation exchange medium and at least one anion exchange medium, the first ion exchange medium having a water content of between 40 and 50%; a second portion of the volume of the dilution compartment comprising a second ion exchange medium disposed distally from the feed inlet, the second ion exchange medium comprising an ion exchange medium suitable for removing dissolved silica from water from the water source, the second ion exchange medium comprising a mixture of at least one cation exchange medium and at least one anion exchange medium, the second ion exchange medium having a water content of between 50 and 60%; the first ion exchange medium has a higher crosslink content than the second ion exchange medium, such that the first ion exchange medium has a greater resistance to chlorine-containing compounds than the second ion exchange medium; providing instructions for directing wastewater from a water source to a feed inlet of an electrochemical separation module; providing instructions for applying a voltage between the first electrode and the second electrode to produce a product stream having a reduced concentration of dissolved silica and a concentrate stream enriched in dissolved silica; A method comprising:

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