WO2016033319A1

WO2016033319A1 - Electrochemically regenerated water decationization method and apparatus

Info

Publication number: WO2016033319A1
Application number: PCT/US2015/047167
Authority: WO
Inventors: David Francis RATH; Lyle KIRMAN; Kevin J.R. ELLIOTT; Shabnaz OOZEER
Original assignee: Tangent Company Llc
Priority date: 2014-08-27
Filing date: 2015-08-27
Publication date: 2016-03-03

Abstract

An apparatus and method for the purification of water in using electrochemical decationization is disclosed, which is characterized in that a bipolar membrane and a cation exchange membrane are installed, and chloride source is added to concentrate flow so as to form soluble chlorine salt, thereby preventing scale formation in device.

Description

ELECTRO CHEMICALLY REGENERATED WATER DECATIONIZATION

METHOD AND APPARATUS

FIELD OF THE INVENTION

[0001] The invention relates to the field of water purification methods and apparatus.

BACKGROUND OF THE INVENTION

[0002] Most if not all conventional electrodeionization (EDI) systems require extensive pre-treatment including softening and reverse osmosis (RO) to remove hardness and excessive total dissolved solids (TDS). EDI systems are also limited in their ability to treat influent waters with high concentrations of hardness and silica, as well as waters with high levels of organics, such as in tertiary waste water applications, where anion resins and membranes can foul. In addition, conventional systems are typically designed for continuous flow, and thus have extremely limited capacity of regenerated resin and essentially no usable stored capacity. A further drawback of conventional water softening using ion exchange resins is that the hardness in the NaCl regeneration produces brine waste consisting mainly of NaCl, CaCl₂, MgCl₂ and the like. Increasing environmental restrictions on discharge of brine wastes and salt-brine regenerated softeners makes removal of hardness from potable water without significant production of brine waste desirable. SUMMARY OF THE INVENTION

[0003] The method and apparatus of the invention are intended to purify water using electro-decationization (EDC). Advantageously, the invention provides a robust system that can do so without the need for any pre-treatment other than filtration to remove suspended solids. In residential applications, the apparatus and method of the invention can easily process water with a hardness concentration on the order of 340 mg/L or higher without deleteriously forming scale in the EDC cell portion of the system or generating significant brine waste. To reduce or eliminate hardness, the invention takes advantage of the solubility of chloride salts of hardness ions for an electrochemical decationizing process, in which the hardness ions in the feed water are prevented from precipitating by electrochemically exchanging them into a concentrate stream containing chloride as the principal counter-ion, whereby the solubilized hardness ions can be discharged out of the system as a concentrated stream of dissolved hardness ions. Chloride as a counter ion allows high concentrations of hardness ions to remain soluble for high recovery rates without scaling. Hardness can be removed by a small bleed stream or, in certain embodiments, hardness can be intentionally precipitated as a hydroxide external to the decationization cells in a specialized cell designed for this purpose. Further, by circulating low pH concentrate through the concentrate and cathode chambers of the EDC unit, any scale that does form in them can be easily removed simply by turning off or reducing the DC current to the EDC unit and continuing to recirculate the low pH concentrate through these chambers. This low pH concentrate is used to continually neutralize hydroxyl produced on the anode side of the bipolar junction as well as the cathode, preventing hydroxide scaling from occurring.

[0004] In addition, the method and apparatus of this invention employs a relatively large stored capacity in regenerated ion exchange resins. This capacity is achieved by employing a large volume of ion exchange resins and efficiently regenerating the resin continuously. Because most of this regeneration occurs during periods of no product water flow, the cell possesses stored capacity for on demand decationization during periods of normal to peak flows and usage. Moreover, as a result of the chromatographic effect of ion distribution in the ion exchange chambers used to retain hardness, the inventors have determined that the ionic voltage drop specific to each ion species contributing to hardness can be utilized to control and optimize cell regeneration. Efficient regeneration is achieved by directing the hydrogen regeneration ions through the more resistant calcium and magnesium ion loaded portions of the bed by directing the influent flow (loading) through the individual resin columns from opposite ends. With the efficient implementation of stored capacity, a much higher influent concentration of dissolved solids can be treated, provided that the total mass per day of dissolved solids in the feed does not exceed the capacity of the resins that are regenerated in a day. In a typical residential application, the method and apparatus described herein can process over 1,000 liters per day of water with a total hardness concentration on the order of 340 mg/L as CaC0₃ or more. Even higher daily loading of TDS or higher peak flow rates can be accommodated simply by adding more decationization cells to the EDC portion of the system for other applications.

[0005] As a result of the foregoing features, the apparatus and method of the invention can find application in treating hard water with high silica concentration in association with hardness without scaling the concentrating chambers of the EDC device; hardness removal in waters with high organics such as tertiary waste water applications where anion resins and membranes could foul; pretreatment for reverse osmosis (RO) systems to increase recovery without acid injection or integrated treatment of concentrate recycle; domestic water softening; boiler feed self-regenerating decationization that can remove hardness independent of anionic chemistry; commercial dishwashers or any other application where traditional chemically regenerated softeners are used; and in the oil and gas industry where produced water is used such that removal of hardness without the use of trucked-in chemicals or the subsequent requirement to truck out the regenerant waste would be a great advantage.

[0006] Pursuant to the foregoing, in one aspect of the invention there is provided a water treatment apparatus comprising a cathode chamber comprising an electrode operative as a cathode; an anode chamber comprising an electrode operative as an anode; at least one decationization cell interposed between said cathode and anode chambers. The decationization cell comprises a first cation exchange chamber proximal said cathode chamber and comprising a cation exchange medium bounded on a first side proximal said cathode chamber by a cation exchange membrane and on a second side distal said cathode chamber by a bipolar interface; a second cation exchange chamber proximal said anode chamber and comprising a cation exchange medium bounded on a first side proximal said anode chamber by a cation exchange membrane or a bipolar interface and on a second side distal said anode chamber by a cation exchange membrane; and, a concentrate chamber interposed between said first cation exchange chamber and said second cation exchange chamber, said cathode chamber and said concentrate chamber being coupled to a concentrate stream flow path allowing concentrate to enter and exit said cathode and concentrate chambers. The apparatus further comprises a concentrate reservoir coupled to said concentrate flow path, and a chloride source in functional communication with said concentrate reservoir or concentrate flow path to maintain a concentration of chloride in said concentrate stream wherein said chloride is the principal counter-ion for calcium, magnesium and sodium therein.

[0007] In one aspect of the invention said cation exchange chambers have inlets and outlets coupled and configured such that water will flow through said first cation exchange chamber in a direction substantially opposite the flow of water through said second cation exchange chamber. In another aspect, the apparatus comprises a plurality of said decationization cells interposed between said cathode chamber and said anode chamber, in some embodiments wherein a plurality of adjacent cation exchange chambers have inlets and outlets coupled and configured such that water will flow through one said adjacent cation exchange chamber in a direction substantially opposite the flow of water through the other said adjacent cation exchange chamber. In some embodiments the chloride source is a hydrochloric acid reservoir, and in still further embodiments the apparatus will comprise a controller adapted to control the chemistry of concentrate in said concentrate flow path to contain chloride as the principal counter-ion for calcium, magnesium and sodium therein.

[0008] In another aspect of the invention, the apparatus of claim 1, wherein said concentrate stream flow path is coupled to a concentrate conditioning unit comprising a scale precipitation chamber adapted to precipitate and accumulate scale for periodic disposal from the apparatus in fluid communication with at least a portion of said concentrate stream and containing at least one electrode operative at least as a cathode; an acidification chamber adjacent said scale precipitation chamber and separated therefrom by a cation exchange membrane, said acidification chamber having an inlet and an outlet coupled to said concentrate stream flow path; and, an anode chamber adjacent said acidification chamber and on a side distal said scale precipitation chamber and containing at least one electrode operative at least as an anode.

[0009] In a further aspect of the invention there is provided a method of decationizing water comprising introducing an influent water into a decationization cell interposed between cathode and anode chambers, said decationization cell as described above, maintaining said concentrate stream in said concentrate chamber to contain chloride as the principal counter-ion for calcium, magnesium and sodium therein, energizing said electrodes to concentrate in said concentrate chamber cations exchanged into said cation exchange media; and, removing concentrate from said decationization cell. In some embodiments said chemistry is maintained by adding hydrochloric acid. In one aspect the method comprises at least periodically monitoring the resistance across said decationization cell and reducing a voltage across said cell after said resistance indicates said cation exchange media is substantially regenerated to an H+ form.

[0010] In another aspect of the invention the method further comprises electrochemically treating said concentrate removed from said decationization cell to precipitate cations therein as hydroxyl salts. In embodiment thereof, the concentrate is introduced into a concentrate conditioning unit comprising a scale precipitation chamber adapted to precipitate and accumulate scale for periodic disposal from said unit in fluid communication with at least a portion of said concentrate stream and containing at least one electrode operative at least as a cathode; an acidification chamber adjacent said scale precipitation chamber and separated therefrom by a cation exchange membrane, said acidification chamber having an inlet and an outlet coupled to said concentrate stream flow path; and, an anode chamber adjacent said acidification chamber and on a side distal said scale precipitation chamber and containing at least one electrode operative at least as an anode; and, energizing said electrodes in said concentrate conditioning unit to precipitate cations therein as hydroxyl salts in said scale precipitation chamber. [0011] A fuller understanding of these and other aspects of the invention will be had from the following description of the invention, detailed description of preferred embodiments and the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Fig. 1 is a schematic representation showing the principal components of an apparatus according to the invention incorporating a decationization unit according to the invention.

[0013] Fig. 2 is a schematic representation of the functional components of a decationization cell according to the invention.

[0014] Fig. 3 is a schematic representation illustrating the advantageous chemistries employed in a decationization cell according to the invention.

DESCRIPTION OF THE INVENTION

[0015] The limiting factor for recovery rates for most waters will be calcium. However, as shown in Table 1 , the solubility limit for calcium chloride, as well as other chloride salts of hardness ions, is high. The process of the invention takes advantage of the high solubility of Ca²⁺, Mg²⁺, Ba²⁺ etc. in combination with CI^" as the counter ion.

Table 1: Solubility of chloride salts

Source: Handbook of Chemistry and Physics, CRC Press, Ann Arbor, MI.

[0016] Essentially, the process removes hardness and lowers total dissolved solids by electrochemically forming highly soluble chloride salts of hardness ions and removing them from the system as a concentrated bleed stream of dissolved salt species such as those in Table 1. As will be apparent to one of ordinary skill in the art from Fig. 3, configuring the decationization cell to have adjacent cation exchange chambers suitably bounded by cation exchange membranes and, in the case of the chamber proximal the cathode, a bipolar

2__|_ membrane bounding the concentrate chamber distal the cathode, cations such as Ca and

2__|_

Mg that are exchanged from the influent water into the cation exchange resin are then exchanged through the cation exchange membranes into the concentrate chambers as a result of displacement by H regenerant being produced at the anode and bipolar interface. The hydrogen ions and hydroxide ions released into the water, respectively, in the cathode chamber resin and concentrate chambers react substantially according to the neutralization reaction, H⁺ + OH^" = H₂0. By maintaining the concentrate stream to provide CI^" as essentially the sole counter ion, highly soluble chloride salts are readily formed to ensure that the hardness ions remain dissolved and are transported out of the system.

[0017] A cell according to the invention can advantageously employ fewer components than most standard EDI cells because anion exchange membranes, resins and resin plates will not be required. Moreover, because anions are not treated, the process is less affected by organics or complicated anionic chemistries. To that end, the electrodecationization (EDC) unit is comprised of one or more decationization cells. Each cell is comprised of a pair of cation exchange chambers 2a/2b and interposed between a pair of electrode chambers 8a/12. As seen in Fig. 2, in its simplest configuration comprising a single decationization cell 11 between electrodes 13/15, a first of said cation exchange chambers 2a proximal the electrode chamber operating as the cathode chamber is bounded by a cation exchange membrane 7 on a first side proximal said cathode chamber 8a and by a bipolar interface 14 on a second side distal said cathode chamber. The second of said cation exchange chambers 2b, proximal the electrode chamber operating as the anode chamber 12, is bounded by a cation exchange membrane 7 or a bipolar interface on a first side proximal said anode chamber 12 and by a cation exchange membrane 7 on a second side distal said anode chamber.

[0018] One or more additional said decationization cells can be disposed between said electrode chambers to provide additional capacity. Depending on the capacity needs of the device, the EDC unit can include any desired number of decationization cells. Similarly, the apparatus can be configured to include additional cation exchange chambers appended to one or more of said decationization cells such that the EDC will include an odd number of cation exchange chambers between the electrodes. In operation, cation exchange media in the ion exchange chambers are constantly being regenerated by hydrogen ions generated at the anode and at the bipolar interfaces proximal the cathode chamber as a result of DC current generated between the electrodes, including during periods of no or limited product water use. Because the ion exchange media are constantly regenerating, even during periods of no water use, ion exchange capacity is stored for periods of peak demand.

[0019] Suitable bipolar interfaces for use in accordance with the invention will be apparent to those of ordinary skill in the art in view of the instant disclosure. Bipolar membranes are preferred, and are commercially available from, for example, Astom Corporation of Japan under the tradename Neosepta, and from Fumatech Gmbh of Germany under the tradename Fumasep. Other methods for forming a bipolar interface include producing interfaces or surfaces where anion ion exchange resins are in contact with a cation exchange membrane, where cation exchange resins are in contact with an anion exchange membrane, or where anion resins are in contact with cation resins as in EDI units with mixed bed resins.

[0020] Suitable cation exchange membranes for use in the invention may either be heterogeneous, where ground up ion exchange resins mixed with a polymeric binder and reinforcing fabric are made into sheets, or they may be homogeneous, where they are monomers or novolac resins that are already functionalized and cast into sheet form, either with or without a reinforcing fabric. Any ion exchange membrane with strong acid functionality and, if present, a reinforcing fabric that is compatible with the pH extremes it may encounter in service will work in this device. The preferred cation exchange membranes for this device are membranes with very low water permeability, strong acid functionality and a reinforcing fabric such as those made by Mega Corporation in the Czech Republic or Membranes International in the United States, those made by Astom Corporation in Japan under the tradename Neosepta, and membranes made by Fumatech GmbH in Germany under the tradename Fumasep. Those of ordinary skill in the art will be able to select and implement suitable cation and anion exchange membranes for use in accordance with the invention in view of the instant disclosure.

[0021] Suitable cation exchange media for use in the cation exchange chambers of the decationization cell according to the invention include any strong acid cation exchange media, particularly polymers of styrene and divinyl benzene that are functionalized with sulfonic acid groups. These include cation exchange resins such as C-100, C-150 and SST60 manufactured by the Purolite company and their corresponding resins made by the Dow Chemical Company, Lanxess and others that will be apparent to those skilled in the art in view of this disclosure. Other polymers may also be used if they are also functionalized with sulfonic acid groups.

[0022] In the cathode chamber of the EDC unit, the electrode operative as a cathode may be any material that is corrosion resistant to brine, and is not damaged by hydrogen gas evolution or an elevated pH environment. This includes various grades of stainless steel such as 316 and 317, Hastelloys, Alloy 20, nickel and nickel alloys, as well as monel. In the anode chamber of the EDC unit, the at least one electrode operative as an anode may be any material that is dimensionally and chemically stable in the solutions to which it will be exposed. This includes platinum, and titanium coated with a catalytic coating of iridium oxide, ruthenium oxide, or mixed metal oxides. These and other materials suitable for use as electrodes in accordance with the invention will be apparent to those of ordinary skill in the art in view of the instant disclosure.

[0023] As will be apparent to one of ordinary skill in the art in view of the instant disclosure, the method and apparatus according to the invention have broad potential application. Although illustrated below in association with a typical residential application, one of ordinary skill in the art will be able to adapt the invention to other applications in view of the instant disclosure. One of ordinary skill in the art will be able to configure the apparatus to achieve sufficient stored ion removal capacity to meet any desired daily demands in view of the instant disclosure.

[0024] In carrying out the methods of the invention, raw feed water is introduced into the EDC unit. The raw feed water is filtered to remove particulate material suspended in the feed. Suitable pre-filters for use in accordance with the apparatus of the invention are typically simple cartridge filter housings with a 1 -5 micron cartridge and sized for peak flow rates on the order of 25 L/min. Advantageously, beyond the noted pre-filter to remove suspended solids, the raw feed water need not be pre -treated to remove ions prior to introduction into the EDC. As water moves through the cation exchange chamber cations are exchanged into the resin to produce decationized (softened) product water and, as a result of displacement by H⁺ regenerant produced at the anode and bipolar membrane, then transported through the cation exchange membranes into the concentrate chambers for subsequent processing or removal. [0025] As described in more detail below, the cathode chamber is in fluid communication with a concentrate stream flow path, whereby cations entering the cathode chamber from an adjacent cation exchange chamber of the decationization cell are transported out of the cathode chamber of the EDC unit for disposal or further treatment or conditioning in accordance with the invention, and whereby acidified or conditioned concentrate flows into the cathode chamber to maintain a non-scaling condition in the chamber and on the localized high pH surfaces therein.

[0026] As also described in more detail below, the anode chamber in preferred configurations of the EDC unit according to the invention is separated from an adjacent cation exchange chamber of a decationization cell by an interface adapted to prevent transport of chloride ions into the anode chamber and enable the transport of hydrogen ions generated in the anode chamber into the cation exchange chamber for purposes of regeneration thereof. A cation exchange membrane is preferred for this purpose, though a bipolar membrane also will suitably perform this function. In this configuration, the anode chamber is coupled to a source of deionized water, as shown via flow path 6, or an anolyte source from which deionized water or a non-chloride ion containing anolyte solution is circulated through the anode chamber. In the case of the former, the flow of deionized water can be discharged to a drain via flow path 6 as shown, or as makeup to the concentrate reservoir as described in U.S. Patent Application Serial No. 13/364,540, filed February 2, 2012, incorporated herein by reference. This arrangement also allows the apparatus to employ a high chloride strength concentrate stream in the concentrate stream flow paths through the EDC unit without generation of chlorine gas and its deleterious effects, advantageously providing an ample supply of chloride ions for the formation of soluble chloride salts.

[0027] As seen in the drawings, in the methods and apparatus of the invention the ions removed from the feed water in the cation exchange chambers of the EDC unit to the concentrate chambers is either transported out of the system via a suitable valve to drain, or can optionally be treated in a concentrate conditioner (CC) unit, where hardness ions can be precipitated and removed from the concentrate stream at a controlled location and the concentrate stream acidified for recirculation back to the EDC unit to clean the surfaces of the EDC unit where precipitates will tend to form. Such a CC unit utilizes the lower solubility characteristics of hardness -hydroxyl combinations, as seen in Table 2, which can be generated in the cathode compartment thereof, making them filterable or otherwise removable from the system through settling or filtration. Concurrently H⁺ is generated for acidification of the bulk brine recirculation through the concentrate chambers. Suitable CC configurations comprise a scale precipitation chamber adapted to precipitate and accumulate scale for periodic disposal from the apparatus in fluid communication with at least a portion of said concentrate stream and containing at least one electrode operative at least as a cathode; an acidification chamber adjacent said scale precipitation chamber and separated therefrom by a cation exchange membrane, said acidification chamber having an inlet and an outlet coupled to said concentrate stream flow path; and, an anode chamber adjacent said acidification chamber and on a side distal said scale precipitation chamber and containing at least one electrode operative at least as an anode, and are described in detail in U.S. Patent Application Serial No. 13/364,540, filed February 2, 2012, incorporated herein by reference in its entirety. Table 2: Solubility of Hydroxyl salts

Solubility at 25°C

Source: CRC Handbook of Chemistry & Physics

[0028] Chloride as the counter-ion can be provided by a recirculating brine concentrate stream augmented as needed by a source of chloride ion, such as sodium, potassium, calcium or magnesium chloride or, preferably, HC1 from an HC1 reservoir, which advantageously provides both acidity and chloride. Of course, while the method and apparatus of the invention contemplate chloride as the sole counter-ion, herein it is referred to as the principal counter-ion to allow for the possibility that some other counter-ion might be present in the concentrate in small and immaterial amounts as a result of membranes and seals not being 100% effective.

[0029] A chloride source, such as a hydrochloric acid reservoir, can be coupled to the concentrate flow path to ensure an adequate source of chloride counter-ion to maintain the solubility of the hardness ions in the concentrate chambers. In some embodiments the concentrate reservoir, which is coupled to the hydrochloric acid reservoir or other chloride source noted above, is coupled to one or more other sources of water capable of modifying the make-up of the concentrate stream cycling through the EDC unit and, if present, to the CC unit. In some such embodiments it can be coupled via suitable valves and, if needed, pumps to one or more of a CC unit, raw feed water from the feed water flow path into the EDC unit, deionized water that has been circulated through the anode chamber, or water shunted from the concentrate stream flow path of the EDC unit. Each of these water sources or combinations thereof can be used to adjust the chemistry of the concentrate in the concentrate reservoir and hence, the makeup of the concentrate stream throughout the system. As will be apparent to one of ordinary skill in the art, in the absence of precipitation of hardness ions in a CC, the makeup of the concentrate to ensure adequate chloride can be determined by the amount of required H⁺ according to the following equation:

EQ_H+ = EQIN x VDAY + 10^A(-pHcoNc) V_WASTE

Where:

EQ_IN ⁼ cations in influent water, in equivalents per litre

V_DA_Y = volume of water to treat, in litres per day

EQ_H+ = hydrogen ion required to neutralize OH- production in the EDC, in equivalents per day

pHcoNC ⁼ pH of the concentrate

[0030] As can be seen, for every equivalent of cations removed, an equal number of equivalents of acid plus the amount of acid lost in the blowdown volume must be added, which also gives the number of equivalents of chloride ion.

[0031] Under optimal conditions, the salt needed to replenish an EDC cell is only as much as is needed to replace the salt lost in the process of removing solids from the concentrate stream, such as via a drain or in a CC. Typically, this could be as low as 0.4 L of concentrate per 1 ,000 L of treated water in residential applications. If the salt concentration is on the order of 8.68 g/L, the salt loss/replenishment is about 3.5 grams per 1 ,000 L of treated water. By contrast, in a typical salt regenerated softener, treating water with on the order of 256.5 mg/L of hardness as calcium carbonate would use about 540-900 grams of salt and generate 150 to 250 L of waste water. Thus, it will be apparent that the EDC of the invention uses much less salt and water than a conventional softener.

[0032] As indicated above, an advantage of the inventive method and apparatus derives in part from its use of stored ion exchange capacity produced by the relatively low power, essentially continuous regeneration of the ion exchange media in the unit. To that end, the unit is configured to have a sufficient volume of ion exchange media to accommodate the ion exchange requirements at anticipated peak flows, and then to continuously regenerate that media, particularly during periods of nominal or no flow. In configuring such a system to have sufficient stored capacity for a particular application the following factors should be taken into account:

1. TDS and hardness concentration of the water to be treated as CaC0₃;

2. The maximum volume of water to be treated per day;

3. The maximum anticipated flow rate;

4. Operating capacity per liter of the ion exchange resins used in the system, which is substantially less than the total capacity, typically on the order of 70%;

5. An efficiency factor that is defined as the fraction of the DC current that regenerates exhausted ion exchange resin instead of just moving hydrogen ions through the resin, and the effective current of the system, which is determined by multiplying applied current times the number of bipolar junctions plus 1 (for the anode regenerant). From this and the efficiency factor, one can derive the coulombs per day of effective regeneration, which in turn can be used to derive the capacity regenerated per day or vise versa; and,

6. Percent recovery defined as a percentage of the feed water that becomes product water. [0033] Items 1, 2, 4 and 6 determine the minimum total volume of resin that the EDC portion of the system needs to contain, i.e., sufficient operating capacity when fully regenerated to purify all of the water used in a 24 hour period. Item 3 determines the cross- sectional area and depth of cation exchange resin required in the EDC portion of the system to avoid excessive pressure drop. Typically, systems are designed to have a pressure drop of less than 10 psi at peak flow. Item 5 determines the amperage that must be applied to the EDC portion of the system, and item 6 defines the total volume of water that must be treated to result in the desired daily total volume. With these considerations, the capacity regenerated in a day can be tuned for the specific needs of the end user to optimize the power consumption versus the performance of the unit. Other factors relevant to optimizing such a device, such as the temperature limits of the ion exchange membranes or other components, and other practical component limitations will be apparent to one of ordinary skill in the art in view of the instant disclosure. Thus, one of ordinary skill in the art will be able to make the necessary calculations to optimize the stored capacity for any particular cell according to the invention in view of the foregoing considerations and instant disclosure.

[0034] Because the effectiveness of the process will depend on the ionic form of the resin (Ca, Na, H etc.), being able to monitor the chromatographic distribution of ions in real time is important to optimizing the function of the apparatus for practical applications. In general, Ca and Mg hardness are preferentially retained in a cation exchange column and sodium ions could be allowed to pass. Knowing the relationship between the electrical resistance across the cell and the ionic loading of the resin when fully regenerated and loaded, the efficiency of hardness removed per coulomb of current applied can be optimized. As shown in Table 4 below, these differentiations are quite distinct and provide for a useful control strategy.

[0035] Because, based on applicant's experimentation, the electrical resistance of Ca form resin is 10.47 times greater than H form resin, and the Na form resin is 7.61 times greater than H form resin, the primary ionic loading can be inferred by monitoring the electrical resistance across the cell. When primarily in the Ca and Mg form, a controller can increase the voltage in order to drive a fixed current and produce the target ionic flux rate. As the ionic form of the resin converts to H and Na, the voltage required to drive the same fixed current will decline. A controller sensing this lower voltage requirement can lower the voltage further to drive a small maintenance current, saving power while providing a means to monitor resin bed condition.

[0036] For example, an EDC with 2 decationizing cells between the electrodes has a normal operating current density of 13 mA per square centimeter with H+ form ion exchange resin, with an operating voltage of 10 to 15 volts. When water is treated, the ion exchange resin will exchange from H+ to Ca++, Na+ etc. When the resin is loaded, the voltage will increase to a maximum range of 50 to 60 V in order to maintain 13 mA/cm2. During periods of low or no water treatment, the resin will gradually regenerate to the H+ form and the voltage will decrease. When the voltage decreases to approximately 24V, the hydrogen ion produced at the bipolar membrane is no longer used efficiently and the controller can, after a programmable time delay, reduce the current to a maintenance current of 2 mA/cm2, providing cathodic protection for the cathode preventing chloride corrosion and retaining contaminant ions in the concentrate chambers. This maintenance current will require approximately 5V, reducing the power required when the system is in a regenerated state. Once the voltage required to drive the maintenance current rises to approximately 10V, the controller can, after a second programmable time delay, restore the full regeneration current of 13 mA/cm2 and contaminants are removed from the resin at the maximum rate of the system.

Table 4

Notes: 1) Electrodes @ 3.5cm separation with 13mA/cm2 flux

[0037] For the cation exchange resin to be regenerated into the H+ form, the hydrogen ions generated at the bipolar membrane must displace the contaminant calcium ions (for example) and the calcium ion must cross the cation membrane into the waste (concentrate) stream. Since the cation exchange resin in the H+ form has a much lower voltage drop and therefore resistance than the calcium form resin, the ionic current of H+ ions will tend to flow across the H+ charged resin beads and not displace the calcium, resulting in poor regeneration efficiency. Thus, in addition to the foregoing, efficiencies can be gained by placing cation cells in pairs with alternating flow paths so that calcium form resin is paired with H+ form in the adjacent cell. This helps to balance the ionic resistance resulting in more evenly displaced calcium ions. The baffle design described in US Patent No. 8,337,686, incorporated herein by reference, could also be used to increase efficiency.

[0038] Another embodiment utilizing the chromatographic distribution of ions and their respective voltage drops would employ multiple electrodes at different stations (zones) along the length of the cells. For example, current would be reduced at the zone where the voltage drop is low (which indicates resin regenerated into the desired H+ form) and current increased at the higher voltage drop zone where exhausted or partially exhausted resin requires more regeneration. This arrangement could perhaps be used to ensure regeneration does not displace Na+ ions, for example, allowing them to leak from the cation resin chamber into the product water where this is deemed desirable.

[0039] These and other embodiments and a fuller understanding of the invention will be had from the following non-limiting detailed description of preferred embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] As shown in Fig. 1, in perhaps one of its simplest configurations, an apparatus for removing cations in accordance with the invention comprises an electro-decationization (EDC) unit 1 for removing cationic species from a raw feed water entering the EDC unit via flow paths 4a and 4b, which is then made available for use via product water flow path 10, and a brine, or concentrate reservoir 5 for maintaining and, if appropriate, facilitating the adjustment of the makeup of the concentrate stream for circulation through the EDC unit, as shown with the aid of pump 50. Also appended to the EDC unit 1 is chloride source 20 for acidifying the concentrate stream and for providing a source of chloride counter-ions if needed. In some embodiments the chloride source 20 can be a simple reservoir containing a source of chloride ions such as NaCl, KC1, CaCl₂ or the like. Preferably, chloride source 20 is a hydrochloric acid reservoir coupled to concentrate flow path 9a so as to provide a source of chloride counter-ions and acidity. [0041] In some embodiments, particularly when an HC1 reservoir is not employed, it will be advantageous to include a concentrate conditioner (CC) unit 23 to condition the concentrate stream pH and manage hardness precipitation. Suitable CC configurations comprise a scale precipitation chamber adapted to precipitate and accumulate scale for periodic disposal from the apparatus in fluid communication with at least a portion of said concentrate stream and containing at least one electrode operative at least as a cathode; an acidification chamber adjacent said scale precipitation chamber and separated there from by a cation exchange membrane, said acidification chamber having an inlet and an outlet coupled to said concentrate stream flow path; and, an anode chamber adjacent said acidification chamber and on a side distal said scale precipitation chamber and containing at least one electrode operative at least as an anode, and are described in U.S. Patent Application Serial No. 13/364,540, filed February 2, 2012, incorporated herein by reference. For most effective cleaning in a short time interval, the pH of the acidified concentrate conveyed to the concentrate chambers 8, 8a via flow path 9b should be maintained below a pH value of 6, preferable below a pH value of 5, and more preferably below pH4. This can be readily accomplished by including various sensors, such as pH sensors and conductivity sensors, in acidified concentrate stream flow path 9b, and associated circuitry. By monitoring the data from these sensors, flow and amperage can be adjusted to modify the make-up and pH of the concentrate stream if the pH exceeds the desired level.

[0042] With reference to Fig. 1 , after filtering to remove suspended solids, the water to be treated (or raw water) is conveyed to an EDC unit 1 through raw water flow paths 4a and 4b. As shown in Fig 1, the EDC unit 1 includes a pair of decationization cells 11 comprised of two cation exchange resin chambers 2a and 2b, through which the raw water is passed. These cation exchange resin chambers are separated by a concentrate compartment 8 and, respectively, contain cation exchange media to remove some or all of the cations carried by the raw water, thereby producing decationized product water.

[0043] The cation exchange chamber proximal the cathode chamber 8a of the decationization unit is bounded on the side proximal the cathode chamber by a cation exchange membrane 7, which allows the passage of cations from the cation exchange resin into the cathode compartment 8a, and on a side distal the cathode chamber by a bipolar membrane 14. As shown in Fig. 2, the cathode chamber 8a is also a concentrate compartment which, like concentrate compartment(s) 8, is coupled to concentrate flow path 9a out of the EDC unit and concentrate flow path 9b into the EDC unit.

[0044] As shown, the cation exchange chamber proximal the anode chamber of the decationization unit is bounded on each side by cation exchange membranes 7. In the embodiment shown, the anode chamber is coupled to a source of deionized water (not shown) via DI water flow path 6.

[0045] The net result of the foregoing configuration is that cationic impurities taken up by the cation resin are moved through the cation exchange resin contained in the cation exchange chambers 2a, 2b, then through the cation exchange membranes 7, into the concentrate compartments 8, 8a, where they are transferred out of the EDC cells as a highly concentrated stream of solubilized cations via concentrate stream flow path 9a which, in turn, can be eliminated from the system via a suitable valve to drain 90.

[0046] Referring to Figures 1 and 2, raw water is communicated to the inlets of the cation exchange resin chambers 2a and 2b via raw feed water flow paths 4a and 4b, respectively. If desired, raw water conduit 4a and/or 4b can include a conductivity sensors in order for the system to get an initial measurement of the conductivity and, hence, approximate concentration of electrolytes in the feed water, or other sensors useful to evaluate the condition of the feed water as will be apparent to those of ordinary skill in the art in view of the instant disclosure. In order to balance the flow of current through the decationization cells 11 , the raw feed water is divided into flow paths 4a and 4b which are respectively coupled to inlets located at opposite ends of cation exchange chambers 2a, 2b. In this way, raw feed water from flow path 4a will flow through cation exchange chamber 2a in a direction opposite that of raw feed water entering cation exchange chamber 2b via flow path 4b. The purpose of this flow pattern is to make the flow of electric current through the resin chambers and membranes more uniform, since there are significant differences in the conductivities of ion exchange resins in various ionic forms, the Na+ form being more conductive than the Ca++ form for strong acid cation exchange resins as described above. With the flow paths as described and as shown in Figs. 1 and 2, the electrical current distribution is more uniform at all levels of exhaustion or regeneration.

[0047] As will be apparent, raw feed water flow paths 4a and 4b can be divided and coupled to additional alternately opposing cation exchange chamber inlets of additional decationization cells to produce additional stored capacity to the EDC unit. Thus, although as shown the raw feed water is divided into two flow paths 4a, 4b in order that water will flow through adjacent cation exchange resin chambers in opposite directions, it will be apparent to those of ordinary skill in the art that the raw water flow path can be divided into additional flow paths in order to facilitate counter-current flow through additional decationization cells 11. Other methods of producing a more uniform current flow, such as baffle arrangements and the like as described in U.S. Serial No. 12/445,848 (Published International Application Serial No. PCT/US08/05195) incorporated herein by reference, also can be employed in accordance with the present invention.

[0048] The substantially decationized water, i.e. softened or product water, is conveyed from the cation exchange chambers to product water flow path 10 where it can be distributed to, for example, a faucet for use or to a storage tank (not shown). In order to maintain desired qualities of the product water, product water flow path 10 can include various sensors, such as pH sensors and/or conductivity sensors as would be apparent to those skilled in the art in view of the instant disclosure, to determine the pH and level of demineralization of the product water. As illustrated in Fig. 3, upon regeneration of the cation exchange resins with hydrogen ions generated at the anode and at the bipolar membranes 14, sodium, calcium and magnesium ions exchange through cation exchange membranes 7 into the concentrated solution as ions solubilized by chloride as the principal counter-ion that can be removed from the concentrate chambers via concentrate flow path 9a.

[0049] In the embodiments shown, the anode compartment 12 is separated from the adjacent cation exchange chamber 2b by a cation exchange membrane 7, and is coupled to a source of deionized water that can be flowed through the anode chamber via DI water flow path 6. The deionized water can be eliminated from the system via drain 91 or, if desired, connected via suitable valves to the concentrate reservoir to assist in controlling the makeup of the concentrate stream. Alternatively, the anode chamber 12 may be supplied with a non-chloride ion containing anolyte solution from a reservoir. In either embodiment, the cation exchange membrane 7 is an effective barrier to the transport of any anions, and chloride ion in particular, from the adjacent cation exchange chamber 2b to the anode chamber 12. In certain embodiments, a bipolar membrane can also be used. Because the circulating deionized water or anolyte solution will contain substantially no chloride ion, the electrode reaction on anode 15 consists almost exclusively of oxygen evolution (with concomitant stoichiometric production of hydrogen ions), and, advantageously, does not involve significant evolution of chlorine, thereby avoiding undesirable oxidation of components. These and other suitable anode chamber configurations suitable for use in the invention are described in detail in U.S. Patent Application Serial No. 13/364,540, filed February 2, 2012, incorporated herein by reference.

[0050] As seen in Figure 1, the concentrate compartments 8, 8a also have inlets that are coupled to an acidified concentrate flow path 9b in turn coupled to a concentrate reservoir 5 and chloride reservoir 20. Concentrate reservoir 5 can be connected to various makeup sources, such as deionized water from the anode chamber, raw water or product water in order to adjust the composition of the concentrate. As shown, concentrate reservoir 5 is charged with makeup water via makeup water source 51. As described above, chloride reservoir 20 and any optional CC unit are coupled to the EDC unit 1 and concentrate reservoir 5 via concentrate flow path 9a/9b. Reservoir 20 is likewise used to modify the make-up of concentrate flowing through concentrate flow path and into the concentrate reservoir 5 to provide a low-pH electrolyte solution concentrated in H+ and chloride ions as needed to ensure that the chemistry of the concentrate flowing through compartments 8, 8a readily forms soluble chloride salts with the hardness ions removed from the raw water stream by the cation exchange chambers. In preferred embodiments the apparatus also includes a CC unit 23. The ready availability of chloride counter-ions maintains the solubility of hardness ions that will remain dissolved in the concentrate stream and can be carried out of the system via drain 90, and the acidic pH also neutralizes OH^" produced on the anode side of the bipolar membranes 14, as well as on the cathode 13.

[0051] As will be apparent to those of ordinary skill in the art in view of the foregoing, the various chambers and membranes of the EDC unit can be configured in a plate and frame configuration or an annular configuration wherein the compartments are configured concentrically as is known in the art and as disclosed in, for example, U.S. Serial No. 12/445,848 (Published International Application Serial No. PCT/US08/05195) incorporated herein by reference.

Claims

What is claimed is:

1. A water treatment apparatus comprising:

a) a cathode chamber comprising an electrode operative as a cathode;

b) an anode chamber comprising an electrode operative as an anode;

c) at least one decationization cell interposed between said cathode and anode chambers comprising:

i) a first cation exchange chamber proximal said cathode chamber and comprising a cation exchange medium bounded on a first side proximal said cathode chamber by a cation exchange membrane and on a second side distal said cathode chamber by a bipolar interface;

ii) a second cation exchange chamber proximal said anode chamber and comprising a cation exchange medium bounded on a first side proximal said anode chamber by a cation exchange membrane or a bipolar interface and on a second side distal said anode chamber by a cation exchange membrane; and,

iii) a concentrate chamber interposed between said first cation exchange chamber and said second cation exchange chamber;

d) said cathode chamber and said concentrate chamber being coupled to a concentrate stream flow path allowing concentrate to enter and exit said cathode and concentrate chambers;

e) a concentrate reservoir coupled to said concentrate flow path; and,

f) a chloride source in functional communication with said concentrate reservoir or concentrate flow path to maintain a concentration of chloride in said concentrate stream wherein said chloride is the principal counter-ion for calcium, magnesium and sodium therein.

2. The apparatus of claim 1, wherein said cation exchange chambers have inlets and outlets coupled and configured such that water will flow through said first cation exchange chamber in a direction substantially opposite the flow of water through said second cation exchange chamber.

3. The apparatus of claim 1 comprising a plurality of said decationization cells interposed between said cathode chamber and said anode chamber.

4. The apparatus of claim 1 comprising a plurality of said decationization cells interposed between said cathode chamber and said anode chamber, wherein a plurality of adjacent cation exchange chambers have inlets and outlets coupled and configured such that water will flow through one said adjacent cation exchange chamber in a direction substantially opposite the flow of water through the other said adjacent cation exchange chamber.

5. The apparatus of claim 1, wherein said chloride source is a hydrochloric acid reservoir.

6. The apparatus of claim 1, wherein said concentrate stream flow path is coupled to a concentrate conditioning unit comprising:

i) a scale precipitation chamber adapted to precipitate and accumulate scale for periodic disposal from the apparatus in fluid communication with at least a portion of said concentrate stream and containing at least one electrode operative at least as a cathode; ii) an acidification chamber adjacent said scale precipitation chamber and separated therefrom by a cation exchange membrane, said acidification chamber having an inlet and an outlet coupled to said concentrate stream flow path; and,

iii) an anode chamber adjacent said acidification chamber and on a side distal said scale precipitation chamber and containing at least one electrode operative at least as an anode.

7. The apparatus of claim 1, further comprising a controller adapted to control the chemistry of concentrate in said concentrate flow path to contain chloride as the principal counter-ion for calcium, magnesium and sodium therein.

8. A method of decationizing water comprising:

a) introducing an influent water into a decationization cell interposed between cathode and anode chambers, said decationization cell comprising:

ii) a second cation exchange chamber proximal said anode chamber and comprising a cation exchange medium bounded on a first side proximal said anode chamber by a cation exchange membrane or a bipolar interface and on a second side distal said anode chamber by a cation exchange membrane; and, iii) a concentrate chamber interposed between said first cation exchange chamber and said second cation exchange chamber; and,

b) maintaining said concentrate stream in said concentrate chamber to contain chloride as the principal counter-ion for calcium, magnesium and sodium therein,

c) energizing said electrodes to concentrate in said concentrate chamber cations exchanged into said cation exchange media; and,

d) removing concentrate from said decationization cell.

9. The method of claim 8, further comprising maintaining the chemistry of said concentrate in said concentrate chamber to comprise chloride as the principal counter-ion for calcium, magnesium and sodium therein by adding hydrochloric acid to said concentrate.

10. The method of claim 8, further comprising at least periodically monitoring the resistance across said decationization cell and reducing a voltage across said cell after said resistance indicates said cation exchange media is substantially regenerated to an H⁺ form.

11. The method of claim 8, further comprising electrochemically treating said concentrate removed from said decationization cell to precipitate cations therein as hydroxyl salts.

12. The method of claim 9, further comprising electrochemically treating said concentrate removed from said decationization cell by introducing said concentrate into a concentrate conditioning unit comprising: i) a scale precipitation chamber adapted to precipitate and accumulate scale for periodic disposal from said unit in fluid communication with at least a portion of said concentrate stream and containing at least one electrode operative at least as a cathode; ii) an acidification chamber adjacent said scale precipitation chamber and separated therefrom by a cation exchange membrane, said acidification chamber having an inlet and an outlet coupled to said concentrate stream flow path; and,

iii) an anode chamber adjacent said acidification chamber and on a side distal said scale precipitation chamber and containing at least one electrode operative at least as an anode; and,

energizing said electrodes in said concentrate conditioning unit to precipitate cations therein as hydroxyl salts in said scale precipitation chamber.