JP2008030004A - Electric deionizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric deionizer which can be operated stably for a long period of time without generating scale even when a hardness component is contained in the water to be treated. <P>SOLUTION: The electric deionizer is obtained by alternately arraying a plurality of anion exchange membranes 13 and a plurality of cation exchange membranes 14 between a cathode 12 and an anode 11 to alternately form concentration chambers 15 and demineralization chambers 16. A bipolar membrane 20 is arranged in each of concentration chambers 15 to divide each concentration chamber 15 into a cathode-side divided chamber 15A and an anode-side divided chamber 15B. Mixed resins 21A, 21B of an anion exchange resin with a cation exchange resin are packed in the concentration chamber 15. The mixed resin 21A to be packed in the cathode-side divided chamber 15A has a high mixing ratio of the cation exchange resin and the mixed resin 21B to be packed in the anode-side divided chamber 15B has a high mixing ratio of the anion exchange resin. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrodeionization apparatus in which a plurality of anion exchange membranes and cation exchange membranes are alternately arranged between a cathode and an anode to alternately form a concentration chamber and a desalting chamber. The present invention relates to an electrodeionization apparatus that can be stably and efficiently operated for a long period of time by preventing the generation of scale in the concentration chamber by improving the configuration of the concentration chamber.

  Conventionally, for the production of deionized water used in various industries such as semiconductor manufacturing factory, liquid crystal manufacturing factory, pharmaceutical industry, food industry, electric power industry, etc. A plurality of anion exchange membranes (A membranes) 13 and cation exchange membranes (C membranes) 14 are alternately arranged between (anode 11 and cathode 12) to alternately form concentration chambers 15 and desalting chambers 16, An electrodeionization apparatus in which the anion exchanger and the cation exchanger made of ion exchange resin, ion exchange fiber, graft exchanger, or the like are mixed or filled in multiple layers in the desalting chamber 16 is widely used (see Patent Documents 1 to 3). ). In FIG. 5, 17 is an anode chamber and 18 is a cathode chamber.

The electrodeionization device generates H ⁺ ions and OH ⁻ ions by water dissociation and continuously regenerates the ion exchanger filled in the desalting chamber, enabling efficient desalting treatment. Thus, it does not require a regeneration treatment using chemicals such as the ion exchange resin apparatus that has been widely used so far, and complete continuous water sampling is possible, and an excellent effect that high-purity water is obtained is exhibited.

However, when tap water that has been turbidized, dechlorinated, and softened from river water, groundwater, etc. at a water purification plant or the like is used directly as the water to be treated in an electrodeionization device or when the calcium concentration of the water to be treated is high (1 ) Since scale generation in the concentrating chamber and (2) deterioration of treated water conductivity due to increased CO ₂ load occur, tap water is not directly passed as treated water in the electrodeionization device. .

Among the problems (1) and (2), the increase in the CO ₂ load in (2) can be solved by using a relatively inexpensive decarboxylation device as a pretreatment device for the electrodeionization device.

  However, in order to prevent scale in the concentration chamber of (1), it is necessary to install a softening device or the like to completely remove the hardness component in the water, but in the case of using the softening device The regeneration is necessary, and the advantage of using the regeneration-free electrodeionization apparatus is lost.

In order to solve such problems, a reverse osmosis membrane device (RO membrane device), a decarboxylation tower, etc. have been conventionally used as a pretreatment device for an electrodeionization device in order to reduce hardness components and CO ₂ concentration. The installation method is used.

  However, since the RO membrane device is operated at a high pressure of 1 to 2 MPa, expensive equipment is required and the operating cost is increased. In addition, even when an RO membrane device is used as a pretreatment device for an electrodeionization device, calcium carbonate scale is generated in the concentration chamber of the electrodeionization device due to slight leakage of calcium from the RO membrane. There was also a problem that stable operation could not be performed. Thus, two stages of RO membrane devices are arranged in series to further remove calcium and the like, but this is not practical in terms of costs. For this reason, if treatment can be performed with a single-stage RO membrane device under normal water supply conditions, a pure water production system must be designed with a single-stage RO membrane device. In addition, there is a concern that scale cannot be generated in the concentration chamber because it cannot cope with the deterioration of water supply conditions such as an increase in the concentration of carbonic acid and the breakthrough of the RO membrane device.

  In such an electrodeionization apparatus, a mechanism for generating scale will be described with reference to FIG.

Calcium carbonate is the most problematic factor for generating scale in electrodeionization equipment. In the electrodeionization apparatus, the water to be treated is generally branched and used as the supply water for the concentration chamber. In the concentration chamber 15, calcium ions (Ca ²⁺ ) are ion-exchanged and permeated from the desalting chamber 16 on the cation exchange membrane 14 side, and approach the surface of the anion exchange membrane 13 by electrical action. On the other hand, hydrogen carbonate ions (HCO ₃ ⁻ ) permeate from the desalting chamber 16 on the anion exchange membrane 13 side. In the concentration chamber 15, when either calcium ion (Ca ²⁺ ) or hydrogen carbonate ion (HCO ₃ ⁻ ) is increased, calcium carbonate (CaCO ₃ ) is formed by the following reactions (1) and (2). Is done.
HCO ₃ ⁻ + OH ⁻ → CO ₃ ²⁻ + H ₂ O (1)
Ca ²⁺ + CO ₃ ²⁻ → CaCO ₃ (2)

  When scale occurs in the concentration chamber 15 in this manner, the electrical resistance increases and the voltage value cannot be kept constant, so that stable processing performance cannot be maintained. Moreover, since the above reaction is an irreversible reaction, if the reaction proceeds, there may be a situation where the module is finally replaced if the module is washed or further left standing.

In general, the saturation condition of calcium carbonate is represented by the following formula.
log [Ca ²⁺ ] + log [HCO ₃ ⁻ ] + pHs = log (Ks / K ₂ )
Ks: solubility product of calcium carbonate K ₂ : second dissociation constant of carbonic acid pHs: saturation pH of calcium carbonate

The difference between the pH in the actual aqueous solution and the saturated pH (pHs) of calcium carbonate is called the Langeria index (LSI),
LSI = pH-pHs> 0
Then, calcium carbonate is deposited.

Also in the concentration chamber 15 of the electrodeionization apparatus, OH ⁻ ions generated by water dissociation in the demineralization chamber 16 permeate from the anion exchange membrane 13 side, so that it is locally alkaline. Therefore, the LSI on the surface of the anion exchange membrane 13 becomes positive (> 0), so that calcium carbonate scale is deposited in the vicinity of the anion exchange membrane 13 in the concentration chamber 15. In addition, calcium hydroxide may be formed.

Therefore, the present applicant has previously proposed an electrodeionization apparatus having a bipolar membrane in the concentration chamber (see Patent Document 4) as a solution to such a scale problem in the concentration chamber.
Japanese Patent No. 1782943 Japanese Patent No. 2751090 Japanese Patent No. 2699256 JP 2001-198577 A

  However, in the electrodeionization apparatus described in Patent Document 4, the electrolytic voltage may increase depending on the quality of the raw water flowing into the electrodeionization apparatus and the operating conditions, which may hinder the operation. It was. Therefore, as a result of various investigations on the cause of the voltage increase, it was found that the movement of hydroxide ions and hydrogen ions generated by water divergence at the bipolar membrane interface is rate-limiting and the electrolytic resistance increases. It was.

  The present invention solves the above-mentioned conventional problems and provides an electrodeionization apparatus that can be stably operated for a long period of time without generating a scale even if hardness components are contained in the water to be treated. Objective.

  In order to solve the above problems, the present invention provides a plurality of anion exchange membranes and cation exchange membranes alternately arranged between a cathode and an anode to alternately form a concentration chamber and a desalting chamber, Electrodeionization in which a concentration chamber is filled with a mixed resin in which an anion exchange resin and a cation exchange resin are mixed and a bipolar membrane is provided in the concentration chamber to form a cathode side compartment and an anode side compartment in the concentration chamber In the apparatus, the cathode side compartment is filled with a mixed resin having a high mixing ratio of a cation exchange resin, and the anode side compartment is filled with a mixed resin having a high mixing ratio of an anion exchange resin. An electrodeionization apparatus is provided (claim 1).

According to the above invention (invention 1), when a bipolar membrane is disposed in the concentration chamber, hydrogen carbonate ions permeated from the desalting chamber on the anion exchange membrane side into the concentration chamber and calcium ions permeated from the cation exchange membrane side. Are blocked by a bipolar membrane, so that calcium carbonate is not formed in the concentration chamber. Thereby, generation | occurrence | production of the calcium carbonate scale in a concentration chamber can be prevented. Further, OH ⁻ ions generated by water dissociation in the desalting chamber permeating from the anion exchange membrane side are also blocked by the bipolar membrane, so that calcium hydroxide is not formed in the concentration chamber. In each compartment partitioned by the bipolar membrane provided in the concentrating chamber, the cathode compartment has a high mixing ratio of the cation exchange resin so that hydrogen generated by water separation at the bipolar membrane interface is generated. The movement of ions is promoted, and bonds with hydroxide ions that have permeated through the anion exchange membrane easily occur. On the other hand, by increasing the mixing ratio of the anion exchange resin in the anode compartment, the movement of hydroxide ions generated by water detachment at the bipolar membrane interface is promoted, so the hydrogen permeated through the cation exchange membrane. It becomes easier to bond with ions. As a result, current easily flows, voltage increase is suppressed, and stable treated water quality can be obtained.

  In the said invention (invention 1), the mixing ratio of the cation exchange resin of the mixed resin with which the said cathode side compartment is filled is more than 50 to 90 volume%, and the anion exchange with which the said anode side compartment is filled The mixing ratio of the resin is preferably more than 50 to 90% by volume (claim 2).

  According to the above invention (invention 2), in the compartment on the cathode side, the movement of hydrogen ions generated by water detachment at the bipolar membrane interface is promoted, and the bond with the hydroxide ions that have permeated the anion exchange membrane is achieved. It tends to happen. On the other hand, in the compartment on the anode side, the movement of hydroxide ions generated by water detachment at the bipolar membrane interface is promoted, so that it becomes easier to bond with hydrogen ions that have permeated the cation exchange membrane. By these, it becomes easier to flow an electric current, a voltage rise is suppressed, and the stable treated water quality is obtained.

  In the above inventions (Inventions 1 and 2), the bipolar membrane is preferably provided such that the anion exchange layer surface is located on the anode side and the cation exchange layer surface is located on the cathode side (Invention 3). .

According to the above invention (invention 3), the hydrogen carbonate ions permeating from the desalting chamber on the anion exchange membrane side into the concentration chamber and the calcium ions permeating from the cation exchange membrane side are blocked, and the anion exchange membrane OH generated by dissociation of water in the desalting compartment coming transmitted from the side ^- ions can also be blocked by a bipolar membrane.

  Moreover, in the said invention (Invention 1-3), it can be set as the structure filled with the ion exchanger in the said desalination chamber (Invention 4). According to this invention (invention 4), the quality of deionized water obtained in the demineralization chamber can be further improved.

  Furthermore, in the said invention (invention 1-4), it can be set as the structure which provided the flow path which supplies a part of effluent of the said desalination chamber to the inflow side of the said concentration chamber (invention 5). . According to this invention (invention 5), even when water having a high calcium concentration such as tap water is treated, a part of deionized water is introduced into the concentrating chamber, so that the circulating water in the concentrating chamber can be obtained. Can be diluted with deionized water to reduce the calcium concentration, thereby further preventing the generation of scale.

  According to the electrodeionization apparatus of the present invention, by arranging the bipolar membrane in the concentration chamber, hydrogen carbonate ions, hydroxide ions, and calcium ions do not associate in the concentration chamber. The formation of calcium hydroxide can be suppressed, and even if a hardness component is contained in the water to be treated, the electrodeionization apparatus can be stably operated for a long time without generating scale in the concentration chamber. Furthermore, since the hydroxide ions and hydrogen ions generated by water divergence at the boundary surface of the bipolar membrane are moved quickly, the increase in electrolytic resistance can be suppressed, stable operation can be performed for a long time, and power consumption can be reduced. Reduction can be achieved. Further, depending on the quality of the water to be treated, the RO membrane device required as a pretreatment device can be omitted, and the equipment cost and the treatment cost can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an electrodeionization apparatus according to an embodiment of the present invention, and FIGS. 2 and 3 are enlarged sectional views of a concentration chamber of the electrodeionization apparatus according to the embodiment. 1-3, the same code | symbol is attached | subjected to the structure same as the conventional electrodeionization apparatus shown in FIG.5 and FIG.6.

  In the electrodeionization apparatus according to the present embodiment, the bipolar membrane 20 is provided in the concentration chamber 15 to partition the concentration chamber 15, and the cathode-side partition chamber 15 </ b> A and the anode-side partition chamber 15 </ b> B are formed in the concentration chamber 15. Then, the configuration is the same as that of the conventional electrodeionization apparatus shown in FIG. 5 except that the concentration chamber 15 is filled with mixed resins 21A and 21B of anion exchange resin and cation exchange resin.

  The bipolar membrane 20 is installed in the concentration chamber 15 so that the anion exchange layer 20B side of the bipolar membrane 20 is located on the anode 11 side and the cation exchange layer 20A side of the bipolar membrane 20 is located on the cathode 12 side.

  The bipolar membrane 20 used in the present invention is not particularly limited as long as it has an anion exchange layer and a cation exchange layer and has high water electrolysis efficiency. In some cases, an anion exchange membrane and a cation exchange membrane can be used in an overlapping manner.

  In such an electrodeionization apparatus, the mixed resin 21A filled in the cathode side compartment 15A has a high mixing ratio of the cation exchange resin, and thus hydrogen generated by water separation at the interface of the bipolar membrane 20 is obtained. Ion migration is promoted. On the other hand, the mixed resin 21B filled in the anode side compartment 15B has a high mixing ratio of the anion exchange resin, thereby promoting the movement of hydroxide ions generated by water separation at the interface of the bipolar membrane 20. Is done. As a result, the current easily flows. The reason why such an effect is obtained will be described later.

  Specifically, the mixing ratio of the mixed resin filled in the concentration chamber 15 is such that the mixing ratio of the cation exchange resin is more than 50 to 90% by volume (the mixing ratio of the anion exchange resin is 10 to 50 in the cathode side compartment 15A. Less than volume%). When the mixing ratio of the cation exchange resin is 50% by volume or less, the effect of promoting the movement of hydrogen ions generated in the cathode-side compartment 15A due to water separation at the interface of the bipolar membrane 20 is not sufficient. On the other hand, if it exceeds 90% by volume, not only the effect is not obtained, but also the mobility of the anion is lowered.

  Further, in the anode side compartment 15B, it is preferable that the mixing ratio of the anion exchange resin is more than 50 to 90% by volume (the mixing ratio of the cation exchange resin is less than 10 to 50% by volume). When the mixing ratio of the anion exchange resin is 50% by volume or less, the effect of promoting the movement of hydroxide ions generated by water separation at the interface of the bipolar membrane 20 in the anode-side compartment 15B is not sufficient. On the other hand, even if it exceeds 90 volume%, the improvement of the effect beyond it is not acquired, but the mobility of the cation which exists slightly falls.

Next, the operation of the electrodeionization apparatus having such a configuration will be described.
As shown in FIG. 3, since the bipolar membrane 20 is provided in the concentration chamber 15, the bicarbonate ions and hydroxide ions that have permeated into the concentration chamber 15 from the desalting chamber 16 on the anion exchange membrane 13 side are In addition, calcium ions and hydrogen ions that have not been able to permeate the bipolar membrane 20 and have been permeated from the cation exchange membrane 14 side cannot permeate the bipolar membrane 20. For this reason, generation | occurrence | production of the calcium carbonate scale in a concentration chamber can be prevented. For convenience of explanation, the mixed resin 21A and the mixed resin 21B are omitted in FIGS.

  At this time, in the bipolar film 20, water dissociation occurs when a voltage equal to or higher than the theoretical water electrolysis voltage (0.83 V) is applied, so that a current flows. For this reason, installing the bipolar membrane 20 in the concentration chamber 15 does not impair the deionization performance of the electrodeionization apparatus.

  However, as it is, the electrolysis voltage increases, which is not preferable in terms of power consumption and stable operation. This is because the movement of hydroxide ions and hydrogen ions generated by the water divergence at the interface of the bipolar film 20 becomes the rate-determining rate and the electrolytic resistance increases. Therefore, in this embodiment, by filling the cathode side compartment 15A with the mixed resin 21A having a high mixing ratio of the cation exchange resin, the mobility of hydrogen ions as cations is improved, and the anion exchange membrane (A membrane). Bonding with the hydroxide ions that have passed through 13 is likely to occur. Further, since the anode side compartment 15B is filled with the mixed resin 21B having a high ratio of the anion exchange resin, the mobility of hydroxide ions as anions is improved and the cation exchange membrane (C membrane) 14 is permeated. In addition, it becomes easier to bond with hydrogen ions. As a result, when the concentration chamber 15 is viewed as a whole, current easily flows and treated water (deionized water) with stable water quality is obtained.

  However, even when the bipolar membrane 20 is disposed in the concentrating chamber 15, a scale may be generated when water with a high calcium concentration such as tap water is processed. It is preferable to introduce a part of deionized water obtained from the desalting chamber 16 into the concentration chamber 15 and dilute the concentration chamber circulating water with deionized water to reduce the calcium concentration.

  In the electrodeionization apparatus of the present invention, a cathode side compartment 15A and an anode side compartment 15B are formed in the concentrating chamber 15, and mixed resins 21A and 21B of anion exchange resin and cation exchange resin are placed in the concentrating chamber 15. Although it is filled, the deionized water obtained in the demineralization chamber 16 is mixed or filled with anion exchangers and cation exchangers made of ion exchange fibers or graft exchangers. It is preferable at the point which improves water quality. Further, the anode chamber 17 and the cathode chamber 18 may be filled with an ion exchanger.

  In the electrodeionization apparatus according to the present embodiment, as described above, the provision of the bipolar membrane 20 in the concentration chamber 15 can effectively prevent the occurrence of calcium carbonate scale in the concentration chamber 15, Even in this case, when water having a high calcium concentration such as tap water is treated, scale may be generated. Therefore, in this case, as shown in FIG. 4, a part of the deionized water obtained from the desalting chamber 16 is introduced into the concentration chamber 15, and the circulating water in the concentration chamber 15 is diluted with deionized water. It is preferable to reduce the calcium concentration. Similarly, it is preferable to use deionized water for the water in the anode chamber 17 and the cathode chamber 18.

  Further, only the water to be treated introduced into the concentrating chamber 15 may be softened. In this case, a softening device is required, but the treatment cost is higher than when all the water to be treated is softened. Is greatly reduced.

EXAMPLES Hereinafter, although a comparative example and an Example are given and this invention is demonstrated in detail, this invention is not limited to the following Example.
In addition, the test apparatus used by the following comparative examples and Examples arrange | positions the following apparatus in series in order of the activated carbon apparatus and the electrodeionization apparatus.
Activated carbon device: “Crycol KW10-30”, Electrodeionization device manufactured by Kurita Kogyo Co., Ltd .: “Critenon SH type”, Treated water volume by Kurita Kogyo Co., Ltd .: 100 L / hr

Moreover, the following were prepared as to-be-processed water (city water) for a test.
Water to be treated: Concentration of feed water Ca 28ppm (CaCO ₃ conversion)
Water supply CO ₂ concentration 29ppm (CaCO ₃ conversion)

[Comparative Example 1]
The following ion exchange resin is used to fill the ion exchange membrane and demineralization chamber of the electrodeionization apparatus. The treated water has a current value of 6.5 A, a water recovery rate of 80%, an inlet conductivity of 170 μS / cm, and a concentration. Water was passed under the condition of an initial chamber flow rate of 25 L / hr, and the change over time in the applied voltage was measured after 1 week, 1 month, 2 months, and 3 months after the obtained treated water. The results are shown in Table 1, and the applied voltage in the initial state is also shown.
In addition, the to-be-processed water was used as the makeup water and the electrode chamber water.
Anion exchange membrane: “Aciplex A501SB”, manufactured by Asahi Kasei Kogyo Co., Ltd. Cation exchange membrane: “Aciplex K501SB”, manufactured by Asahi Kasei Kogyo Co., Ltd. Ion exchange resin: Anion exchange resin (manufactured by Mitsubishi Chemical Corporation, “SA10A”) and cation exchange resin ( Mitsubishi Chemical Co., Ltd. “SK1B”) mixed at a volume mixing ratio of 6: 4.

[Comparative Example 2]
A bipolar membrane was provided in the concentration chamber of the electrodeionization apparatus used in Comparative Example 1 to assemble the electrodeionization apparatus shown in FIG. 1, and a water flow test was conducted in the same manner except that this electrodeionization apparatus was used. It was. The results are shown in Table 1.
As the bipolar film, CMS (trade name) manufactured by Astom Co., Ltd. was used.

[Example 1]
In the electrodeionization apparatus of Comparative Example 2, the cathode side compartment 15A partitioned by the bipolar membrane is filled with a mixed resin of anion exchange resin: cation exchange resin = 1: 9, and the anode side compartment 15B is filled with an anion exchange resin: An electrodeionization apparatus was assembled in the same manner except that the mixed resin of cation exchange resin = 9: 1 was filled, and a water passage test was conducted in the same manner except that this electrodeionization apparatus was used. The results are shown in Table 1. The anion exchange resin and the cation exchange resin are the same as those filled in the desalting chamber in Comparative Example 1.

[Example 2]
In Example 1, as shown in FIG. 4, instead of the water to be treated, a part (20%) of deionized water obtained from the desalting chamber was supplied as make-up chamber circulating water makeup water and electrode chamber water. In the same manner, the test was conducted under the water flow conditions shown in Table 1. The results are shown in Table 1.

  As shown in Table 1, in the electrodeionization apparatus of Comparative Example 1, the differential pressure on the concentration chamber side increased in one week, and operation became impossible. In Comparative Example 2, the electrolysis voltage increased one week after the start of water flow. On the other hand, in the electrodeionization apparatuses of Examples 1 and 2, there was little increase in voltage and it was possible to operate stably for 3 months. Moreover, the water quality of the treated water (deionized water) obtained was also favorable.

It is a schematic block diagram which shows the electrodeionization apparatus which concerns on one Embodiment of this invention. It is typical sectional drawing which shows the concentration chamber in the electrodeionization apparatus which concerns on the same embodiment. It is sectional drawing which shows the flow of the ion of the concentration chamber in the electrodeionization apparatus which concerns on the same embodiment. It is a systematic diagram which shows the electrodeionization apparatus which concerns on one Embodiment of this invention. It is typical sectional drawing which shows the conventional electrodeionization apparatus. It is sectional drawing which shows the flow of the ion of the concentration chamber in the conventional electrodeionization apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Ion exchanger 11 ... Anode 12 ... Cathode 13 ... Anion exchange membrane 14 ... Cation exchange membrane 15 ... Concentration chamber 15A ... Cathode side compartment 15B ... Anode side compartment 16 ... Desalination chamber 17 ... Anode chamber 18 ... Cathode chamber 20: Bipolar membrane 21A: Mixed resin (mixing ratio of cation exchange resin exceeds 50% by volume)
21B ... Mixed resin (mixing ratio of anion exchange resin exceeds 50% by volume)

Claims (5)

A plurality of anion exchange membranes and cation exchange membranes are alternately arranged between the cathode and the anode to alternately form a concentration chamber and a desalting chamber, and an anion exchange resin and a cation exchange resin are formed in the concentration chamber. An electrodeionization apparatus in which a mixed membrane is filled and a bipolar membrane is provided in the concentration chamber to form a cathode side compartment and an anode side compartment in the concentration chamber,
The cathode compartment is filled with a mixed resin having a high cation exchange resin mixing ratio, and the anode compartment is filled with a mixed resin having a high anion exchange resin mixing ratio. Electrodeionizer.   The mixing ratio of the cation exchange resin in the mixed resin filled in the cathode side compartment is more than 50 to 90% by volume, and the mixing ratio of the anion exchange resin filled in the anode side compartment is more than 50 to 90. The electrodeionization apparatus according to claim 1, wherein the electrodeionization apparatus is in volume%.   3. The electrodeionization apparatus according to claim 1, wherein the bipolar membrane is provided such that the anion exchange layer surface is located on the anode side and the cation exchange layer surface is located on the cathode side.   The electrodeionization apparatus according to any one of claims 1 to 3, wherein the demineralization chamber is filled with an ion exchanger. The electrodeionization apparatus according to any one of claims 1 to 4, further comprising a flow path for supplying a part of the effluent of the demineralization chamber to the inflow side of the concentration chamber.

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