JP6561448B2 - Method and apparatus for electrodeionization treatment of vanadium-containing water - Google Patents

Description

  The present invention relates to a method and an apparatus for electrodeionization treatment of vanadium-containing water, and in particular, prevents an increase in the differential pressure in the concentration chamber of the electrodeionization apparatus when treating vanadium-containing water with the electrodeionization apparatus. The present invention relates to a processing method and a processing apparatus capable of stable operation.

  As a system to produce pure water by treating industrial water, city water, natural water, various industrial wastewater, etc., raw water is treated with a reverse osmosis membrane (RO membrane) device and then treated with an electrodeionization device. The apparatus is well known (for example, Patent Document 1).

FIG. 1 is a system diagram showing an example of a conventional pure water production apparatus using an RO membrane apparatus and an electrodeionization apparatus.
The raw water is turbidized by the membrane pretreatment device 2 through the raw water tank 1, then filtered by the activated carbon tower 3, and then passed through the filtration water tank 4, followed by the RO membrane device 5, the membrane deaeration device 6, and the electricity. Water is sequentially passed through the deionizer 7 for processing.

  Thus, in the pure water manufacturing apparatus which deionizes by combining the RO membrane device 5 and the electrodeionization device 7, the ORP (oxidation reduction potential) of the activated carbon filtrate introduced into the RO membrane device 5 is 350 mV or more. The ORP is lowered by adding a reducing agent to the filtered water tank 4. This is to prevent oxidative degradation of the RO membrane and the subsequent electrodeionization device due to the oxidizing substance. When the ORP of the water supply of the RO membrane device 5 is less than 350 mV, no reducing agent is added.

  On the other hand, vanadium is used as a catalyst, and is contained in ash such as coal and petroleum, and also in certain natural waters. Conventionally, vanadium in raw water is known to oxidize and degrade cation exchange resins (for example, Patent Documents 2 to 4), but there is no recognition of the influence on anion exchange resins.

  In addition, in the electrodeionization device, a deaeration device is provided in front of the electrodeionization device as a DO reduction means for reducing the dissolved oxygen (DO) in the concentrating chamber and improving the quality of the treated water. A sulfite is added to the water supply of the apparatus (for example, Patent Documents 5 to 7).

JP 2004-57935 A Japanese Patent No. 4721554 Japanese Patent No. 3963100 Japanese Patent No. 3963101 JP 2003-117557 A JP 2001-212468 A Japanese Patent Laid-Open No. 2003-1260

  As described above, conventionally, when raw water is processed by the RO membrane device and the electrodeionization device, when the ORP of the RO membrane device is 350 mV or higher, a reducing agent is added to the RO membrane device to lower the ORP. Control is performed, but such control is not performed when the ORP is lower than 350 mV.

  However, according to the study of the present inventor, when the raw water contains a large amount of vanadium, for example, when the vanadium contains 5 ppb or more, even if the ORP of the RO membrane device is 350 mV or less, for example, 330 mV, it is operated for a long time. It has been found that there is a problem that the differential pressure rises due to the blockage of the concentration chamber of the electrodeionization apparatus by continuing the process. In this case, normally, it was necessary to replace the module once every five years with a frequency of once every two years.

  The present invention provides an electrodeionization treatment method and a treatment apparatus for vanadium-containing water that can prevent the blockage of the concentration chamber of the electrodeionization apparatus when the vanadium-containing water is treated with the electrodeionization apparatus and can perform stable operation over a long period of time. The purpose is to provide.

As a result of intensive studies to solve the above problems, the present inventors adjusted the ORP of vanadium-containing water introduced into the electrodeionization device to 300 mV or less when the vanadium-containing water is processed by the electrodeionization device. As a result, it was found that the blockage of the concentration chamber can be suppressed.
That is, the gist of the present invention is as follows.

[1] In the method of treating vanadium-containing water with an electrodeionization device, the electrodeionization device is an electrodeionization device in which a concentration chamber is filled with an anion exchange resin, and is introduced into the electrodeionization device. An electrodeionization method for vanadium-containing water, wherein the ORP of vanadium-containing water is adjusted to 300 mV or less.

[2] The electrodeionization method for vanadium-containing water according to [1], wherein ORP is adjusted by adding a reducing agent to the vanadium-containing water.

[3] The electrodeionization treatment of vanadium-containing water according to [2], wherein the reducing agent is one or more selected from the group consisting of bisulfite, sulfite, and hydrogen gas. Method.

[4] The method according to [2] or [3], wherein the vanadium-containing water is treated with a reverse osmosis membrane device and then treated with the electrodeionization device, and the reduced water is permeated through the reverse osmosis membrane device. A method for electrodeionization treatment of vanadium-containing water, wherein the agent is treated with the electrodeionization apparatus after the agent is added.

[5] In an apparatus for treating vanadium-containing water with an electrodeionization apparatus, the electrodeionization apparatus is an electrodeionization apparatus in which a concentration chamber is filled with an anion exchange resin, and is introduced into the electrodeionization apparatus. An apparatus for treating vanadium-containing water, comprising ORP adjusting means for adjusting the ORP of vanadium-containing water to 300 mV or less.

[6] The treatment apparatus for vanadium-containing water according to [5], wherein the ORP adjusting means is a reducing agent adding means for adding a reducing agent to the vanadium-containing water.

[7] The treatment apparatus for vanadium-containing water according to [6], wherein the reducing agent is one or more selected from the group consisting of bisulfite, sulfite, and hydrogen gas.

[8] In [6] or [7], the apparatus includes a reverse osmosis membrane device for treating the vanadium-containing water and the electrodeionization device for treating the permeated water of the reverse osmosis membrane device, and adding the reducing agent An apparatus for treating vanadium-containing water, wherein a reducing agent is added to the permeated water of the reverse osmosis membrane device by means.

  ADVANTAGE OF THE INVENTION According to this invention, when processing vanadium containing water with an electrodeionization apparatus, obstruction | occlusion of the concentration chamber of an electrodeionization apparatus can be prevented, and stable operation can be performed over a long period of time.

It is a systematic diagram which shows an example of the pure water manufacturing apparatus using RO membrane apparatus and an electrodeionization apparatus.

  Embodiments of the electrodeionization treatment method and treatment apparatus for vanadium-containing water of the present invention will be described in detail below.

When vanadium-containing water is treated with an electrodeionization apparatus, the reason why the pressure difference in the concentration chamber increases with time is as follows.
The vanadium derived from raw water is removed by the RO membrane, for example, when the RO membrane device is provided in front of the electrodeionization device, and the vanadium concentration of the permeated water of the RO membrane device (water supply of the electrodeionization device) is the lower limit of analysis. Less than 1 ppb. However, the vanadium concentration does not become zero, and there is about 0.5 ppb depending on the RO membrane removal performance. Conventionally, it has not been recognized that anion exchange resins undergo oxidative degradation in the presence of such a small amount of vanadium.
However, since vanadium in the feed water of the electrodeionization apparatus exists in the form of vanadic acid (anion species) in the water, it moves electrically in the electrodeionization apparatus and flows into the concentration chamber. A part of the vanadium in the concentration chamber is contained and discharged in the concentrated water, but most of the vanadium is adsorbed and accumulated in the anion exchange resin in the concentration chamber.
For example, as a result of verification by the present inventor, it was found that 1 mg of vanadium is adsorbed per 1 L of anion exchange resin in the concentrating chamber when the water supply with vanadium concentration <1 ppb is treated for about 2 years with an electrodeionization apparatus.
For this reason, even if the vanadium concentration of the feed water is low, the anion exchange resin in the concentration chamber of the electrodeionization device has a locally high vanadium concentration, and the ORP of the feed water is about 330 mV. The vanadium oxidation catalyst function causes the anion exchange resin to oxidize and deteriorate, leading to resin crushing, and increases the differential pressure in the concentration chamber.

Therefore, in the present invention, the ORP of the water supply of the electrodeionization apparatus is adjusted to be 300 mV or less. When the ORP of the feed water is 300 mV or less, the oxidizing substances in the feed water are reduced, and the oxidative deterioration of the anion exchange resin in the concentration chamber using vanadium as a catalyst and the resulting resin crushing are suppressed.
As a result, an increase in the differential pressure in the concentration chamber of the electrodeionization apparatus is suppressed, and long-term stable operation is possible.

  The raw water to be treated in the present invention contains vanadium and includes natural water, well water, city water, industrial water, various factory effluents and the like containing vanadium. Although there is no restriction | limiting in particular about the vanadium density | concentration of raw | natural water, For example, when processing raw | natural water with a RO membrane apparatus and an electrodeionization apparatus sequentially, raw | natural water which becomes 1-40ppb as vanadium density | concentration of the feed water of RO membrane apparatus is mentioned. . For example, in the apparatus shown in FIG. 1, the vanadium concentration of raw water is usually about 5 to 30 ppb.

  When such raw water is processed by an apparatus equipped with an RO membrane device upstream of the electrodeionization device as shown in FIG. 1, the vanadium concentration of the RO membrane permeated water obtained is usually less than 1 ppb, which is the lower limit of analysis. As described above, even water with a vanadium concentration <1 ppb does not contain vanadium at all, but contains about 0.5 ppb vanadium. Even when water containing such a very small amount of vanadium is used as water supply for the electrodeionization apparatus, if the ORP is not adjusted according to the present invention, the electrodeionization is performed as in Comparative Example 1 described later. Blocking of the concentration chamber of the device occurs.

  In the present invention, the raw water is such that if the ORP is not adjusted, the ORP of the water supply of the electrodeionization apparatus is higher than 300 mV, for example, 330 to 350 mV.

  As described above, when processing is conventionally performed with an RO membrane device and an electrodeionization device, the ORP of the RO membrane device is adjusted to 350 mV or less in order to prevent oxidative deterioration of the RO membrane device and the electrodeionization device. However, when the water that has become ORP 330 to 350 mV by this adjustment is processed with the RO membrane device and the electrodeionization device, the ORP of the water supply of the electrodeionization device also becomes about 330 to 350 mV, as described above. Oxidative deterioration of the anion exchange resin in the concentrated chamber occurs.

The ORP is preferably adjusted by adding a reducing agent. As the reducing agent, bisulfite such as sodium bisulfite, sulfite such as sodium sulfite, one kind of conventionally known reducing agents such as hydrogen gas, or 2 More than seeds can be used.
Among these, when hydrogen gas is used, there is no problem of increase in the salt concentration of the feed water of the electrodeionization device which affects the specific resistance and the removal rate of silica and boron, and the treated water quality is maintained or improved by suppressing the salt load. Can be made.

When adding a reducing agent for the adjustment of ORP, the reducing agent may be added at the entrance of the electrodeionization apparatus. When the RO membrane apparatus is provided in the front stage of the electrodeionization apparatus, It may be added at the inlet or may be added to the outlet of the RO membrane device (permeated water of the RO membrane device).
Moreover, you may add a reducing agent to the liquid feeding line which supplies a part of treated water from the demineralization chamber of an electrodeionization apparatus to a concentration chamber.

  When a reducing agent such as bisulfite is added at the entrance of the RO membrane device, the reducing agent such as bisulfite is removed by the RO membrane device, so it does not load the electrodeionization device. When added to the permeate, it can be a load on the electrodeionization device. However, as in the examples described later, since the necessary amount of reducing agent for reducing ORP by about 50 to 100 mV is relatively small, the salt load of the electrodeionization apparatus is not greatly increased. Therefore, it is preferable to add a reducing agent to the permeated water of the RO membrane device from the viewpoint of reducing the amount of reducing agent used.

  In addition, since the added reducing agent can efficiently react with an oxidizing substance in water and reduce it, the RO membrane device 5, the membrane deaerator 6 and the electrodeionization device 7 as shown in FIG. In the case of sequential treatment, it is preferable to add a reducing agent to the permeated water of the RO membrane device 5 because the contact efficiency between the reducing agent and the oxidizing substance in water is improved by the stirring action of the membrane deaerator 6.

In the present invention, the ORP of water supplied to the electrodeionization device (water introduced into the electrodeionization device) may be 300 mV or less, and is usually adjusted to about 200 to 300 mV, preferably about 230 to 280 mV. If the ORP of the feed water of the electrodeionization apparatus is higher than the above upper limit, oxidative deterioration of the anion exchange resin in the concentration chamber of the electrodeionization apparatus cannot be prevented. If the ORP is excessively lowered, the amount of reducing agent such as bisulfite added is increased, which increases the load on the RO membrane device or the electrodeionization device, which is not preferable.
In addition, DO in the water supply of an electrodeionization apparatus is about 0.1-1 ppm normally, and if it is less than 1 ppm, the oxidative degradation of the electrodeionization apparatus by DO will be suppressed. In the range of the DO, the DO in the water supply is sufficiently reduced, and there is almost no influence of the ORP due to the DO removal.

In the present invention, the oxidative degradation of the anion exchange resin in the concentration chamber of the electrodeionization apparatus is prevented. Therefore, the electrodeionization apparatus used in the present invention is one in which the anion exchange resin is filled in the concentration chamber. is there. Usually, the concentration chamber is filled with a cation exchange resin as a mixed resin together with an anion exchange resin. In addition, an anion exchange resin and a cation exchange resin may be laminated and filled.
An ion exchanger may be filled instead of the ion exchange resin.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
In the following examples and comparative examples, the following were used as the RO membrane device, membrane deaeration device, and electrodeionization device.

<RO membrane device>
Nitto Denko "KROA-2032" 8 inches, 12 pieces <Membrane deaerator>
Hoechst “Lixel X-50” 10 inches, 1 piece <Electrical deionization equipment>
Kurita Kogyo Co., Ltd. “KCDI-UPz-100H” throughput 10m ³ / hr, 1 unit

[Example 1]
Treated with city water having a vanadium concentration of 19 ppb and an ORP of about 330 mV as raw water, the water was sequentially passed through an RO membrane device, a membrane deaerator, and an electrodeionization device.
The permeated water of the RO membrane device had a vanadium concentration of less than 1 ppb, an ORP of about 330 mV, and the vanadium concentration of the concentrated water was 76 ppb. Sodium bisulfite was added to the permeated water of this RO membrane device, and the membrane was deaerated with a membrane deaerator to obtain deaerated water with a vanadium concentration <1 ppb, DO <1 ppm, and an ORP of about 260 mV.
In the electrodeionization apparatus, treated water and concentrated water having a vanadium concentration <1 ppb were obtained using deaerated treated water having an ORP of about 260 mV as feed water.
Although this treatment was continued for one year, the differential pressure in the concentration chamber of the electrodeionization apparatus was 0.06 MPa at the start of operation, and the differential pressure after one year was 0.08 MPa. Little increase was observed.

[Comparative Example 1]
In Example 1, the same treatment was performed except that sodium bisulfite was not added to the permeated water of the RO membrane device. As a result, the differential pressure in the concentration chamber of the electrodeionization device was 0 in one year of operation. The pressure rose to 30 MPa, making it difficult to continue operation.
In Comparative Example 1, after the operation for one year, the concentration chamber of the electrodeionization apparatus was examined, and it was confirmed that the concentration chamber was closed because the anion exchange resin was oxidatively deteriorated and crushed. It was.

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Membrane-type pretreatment device 3 Activated carbon tower 4 Filtration water tank 5 RO membrane device 6 Membrane deaeration device 7 Electrodeionization device

Claims (4)

In the method of treating vanadium-containing water with a reverse osmosis membrane device and then treating with an electrodeionization device, the electrodeionization device is an electrodeionization device in which the concentration chamber is filled with an anion exchange resin,
A method for electrodeionization treatment of vanadium-containing water, wherein the ORP of the vanadium-containing water introduced into the electrodeionization device is adjusted to 300 mV or less by adding a reducing agent to the permeate of the reverse osmosis membrane device. . 2. The method for electrodeionization treatment of vanadium-containing water according to claim 1 , wherein the reducing agent is one or more selected from the group consisting of bisulfite, sulfite, and hydrogen gas. A reverse osmosis membrane apparatus for treating vanadium-containing water, in the device for chromatic and electrodeionization apparatus which processes the permeate from the inverse osmosis unit, electric deionizer, the anion exchange resin is filled in the concentrating compartment Comprising an ORP adjusting means for adjusting the ORP of the vanadium-containing water introduced into the electrodeionization apparatus to 300 mV or less ,
The ORP adjustment means, said reverse osmosis membrane vanadium-containing water treatment apparatus characterized by the reducing agent adding means der Rukoto adding a reducing agent to permeate the device. 4. The apparatus for treating vanadium-containing water according to claim 3 , wherein the reducing agent is one or more selected from the group consisting of bisulfite, sulfite, and hydrogen gas.

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