JPH10165772A - Reverse osmosis membrane module and liquid separation method - Google Patents

Abstract

(57) [Problem] To provide a reverse osmosis membrane module and a fluid separation method capable of preventing generation of silica scale and operating at a high recovery rate. SOLUTION: A membrane body 6 includes a raw water spacer 12 and a permeated water spacer 14 on both sides of a reverse osmosis membrane 13. A raw water side electrode 11 is stacked outside the raw water spacer 12, and a permeated water side electrode 15 is stacked outside the permeated water spacer 14.
The raw water side electrode 11 and the permeated water side electrode 15 are connected to an external DC power supply 9 via conductors 7, 8 and connection terminals 7a, 8a formed on the housings 4a, 4b, respectively. During the filtration process, a DC voltage is applied so that the raw water side electrode 11 becomes a cathode and the permeated water side electrode 15 becomes an anode.
At the time of washing, the polarity of the DC voltage applied to the raw water side electrode 11 and the permeated water side electrode 15 is switched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reverse osmosis membrane module and a liquid separation method using a reverse osmosis membrane.

[0002]

2. Description of the Related Art In various industrial fields, such as the electronics industry, the medical industry, and the food industry, a reverse osmosis (RO) method is used for producing pure water, purified water, or drinking water. The reverse osmosis method is more widely used in the desalination treatment of water than the electrodialysis method and the ion exchange method, and is an indispensable technique particularly in pure water production.

However, when desalination is performed using a reverse osmosis device equipped with a reverse osmosis membrane (RO membrane) module,
Depending on the quality of the raw water (undiluted solution), scaling occurs in which insoluble inorganic components are precipitated on the membrane surface of the reverse osmosis membrane, which may significantly reduce membrane performance. As the scale (precipitates of insoluble inorganic components), calcium salts and silica (for example, silicic acid, silica gel, and the like) are generally used as the substance for producing scale.

Therefore, in order to prevent scaling,
Conventionally, various methods have been adopted. For example, for calcium salts, adding acid to raw water, adding a scale inhibitor to raw water, softening with a cation exchange resin, or performing intermittent physical cleaning such as flushing Cleaning the surface is performed. On the other hand, a lime softening method or the like is used for silica.

[0005]

However, when the lime softening method is applied to this silica, the equipment cost increases,
For equipment other than a large plant, the cost is high and it is not realistic. For this reason, in order to actually prevent the scaling of silica, the reverse osmosis membrane device is operated at a low recovery rate, thereby suppressing the occurrence of scaling.

That is, when the dissolved silica is in a supersaturated state, it starts to polymerize, grows into a colloid, and eventually aggregates and precipitates. When this phenomenon occurs on the surface of the reverse osmosis membrane, silica scale is generated on the surface of the reverse osmosis membrane. Normal temperature (2
0 to 25 ° C.), the solubility of silica is about 120 m
g / L (liter). In the reverse osmosis membrane device, the operation is performed while controlling the recovery rate so that the silica concentration in the concentrated water (concentrate) on the concentration side of the reverse osmosis membrane does not exceed the solubility. I have. For example, when the silica concentration in the raw water is 50 mg / L, the silica concentration in the concentrated water does not exceed the solubility if the recovery is 58%, but it is usually operated at a recovery of 40% or less in consideration of safety. Have been. However, when the operation is performed at such a low recovery rate, the amount of waste water is increased, and the running cost is increased.

[0007] As described above, there is no effective preventive measure especially for silica among the scale-forming substances, and it is necessary to operate at a low recovery rate. In particular, in Japan, there are many areas such as the Kyushu area where groundwater contains a large amount of silica. Therefore, when operating a reverse osmosis membrane device or reverse osmosis membrane plant using groundwater as raw water in such an area, the generation of silica scale is prevented,
It is important to increase the recovery rate and reduce the running cost.

An object of the present invention is to provide a reverse osmosis membrane apparatus and a treatment method using a reverse osmosis membrane capable of preventing generation of silica scale and capable of operating at a high recovery rate.

[0009]

Means for Solving the Problems and Effects of the Invention The present inventor has confirmed by experiments that applying a DC voltage via a reverse osmosis membrane can suppress the formation of silica scale on the surface of the reverse osmosis membrane. . Although the mechanism of the scale suppression according to the present invention has not been clarified, it is inferred as follows.

In the reverse osmosis membrane module according to the present invention, a first electrode connected to one pole of a DC power supply is provided on a raw solution flow path side of a permeable membrane that separates a raw solution flow path and a permeate flow path in a housing. And a second electrode connected to the other pole of the DC power supply is arranged on the permeate flow path side.

In the reverse osmosis membrane module according to the present invention, a DC electric field is generated around the permeable membrane by applying a DC voltage between the first electrode and the second electrode;
This can prevent scale from being generated on the film surface of the permeable film body.

In particular, it is preferable that the first electrode is connected to the negative electrode of the DC power supply, and the second electrode is connected to the positive electrode of the DC power supply. In this case, the first electrode disposed on the stock solution flow channel side serves as a cathode, and hydroxide ions (OH ⁻ ) generated by electrolysis of water on the stock solution flow channel side suppress the polymerization of silica ions or silica monomers and become permeable. It is considered that silica scale is prevented from being formed on the film surface of the film body.

In addition, like the silica, calcium ions, which are scale-producing substances, are electrodeposited on the surface of the first electrode serving as a cathode, and hardly adhere to the permeable membrane. Thereby, it is also possible to prevent the generation of calcium scale on the membrane surface of the permeable membrane.

A switching means for switching the polarity of a DC voltage applied between the first and second electrodes by a DC power supply may be provided. In this case, the first
When the polarity of the DC voltage is switched so that the first electrode becomes the anode, the metal substance electrodeposited on the surface of the first electrode when the first electrode is the cathode is ionized again and detaches from the first electrode surface.
Thereby, the surface of the electrode can be cleaned. Also,
Active oxygen is generated from the first electrode when the first electrode becomes an anode. The active oxygen decomposes contaminants such as organic substances attached to the membrane surface of the permeable membrane by its own oxidizing power. Thereby, the effect of cleaning the membrane surface of the permeable membrane can be further obtained.

In particular, the first and second electrodes are preferably made of an inert material. This prevents corrosion of the first and second electrodes due to the reaction with the stock solution and the permeate. In addition, it is preferable to be made of a non-electrolytic corrosion metal material. This prevents corrosion of the first and second electrodes due to energization.

Further, the first and second electrodes are preferably formed in a mesh. Accordingly, a DC voltage can be applied to the entire permeable membrane on both the stock solution side and the permeate solution side without obstructing the flow of the stock solution and the permeate solution in the stock solution flow channel and the permeate solution flow channel.

Preferably, the first and second electrodes are made of platinum or carbon or an alloy of platinum and carbon. Further, the permeable membrane is preferably made of a flat or spiral reverse osmosis membrane, and the first and second electrodes are preferably arranged to face each other along the surface of the reverse osmosis membrane.
This makes it possible to generate a DC electric field over the entire surface of the reverse osmosis membrane, thereby preventing the generation of scale.

In the liquid separation method according to the present invention, the first electrode is disposed on the side of the raw liquid flow path partitioned by the permeable membrane, and the second electrode is disposed on the side of the permeate liquid flow path. The transmission process is performed while applying a DC voltage between the two electrodes.

In particular, when a DC voltage is applied so that the first electrode becomes a cathode, hydroxide ions (OH ⁻ ) generated by electrolysis of water in the stock solution flow path are converted to silica ions or silica monomers. It is considered that the formation of silica scale is prevented by suppressing the formation of silica. In addition, calcium ions are electrodeposited on the surface of the first electrode, not on the permeable membrane, thereby preventing the formation of calcium scale on the membrane surface of the permeable membrane.

It is preferable that the transmission process is performed while switching the polarity of the DC voltage applied between the first and second electrodes. When a DC voltage is applied so that the first electrode becomes a cathode, the formation of silica scale or calcium scale on the membrane surface of the permeable membrane is suppressed, while metal ions are deposited on the first electrode surface. Electrodeposit. Therefore,
When a DC voltage is applied so that the first electrode becomes an anode,
The metal substance electrodeposited on the surface of the first electrode is ionized, and the metal substance can be removed from the surface of the first electrode.

Active oxygen is generated from the first electrode serving as the anode, and the oxidizing power of the first electrode can decompose contaminants attached to the surface of the permeable membrane. As described above, during the normal permeation processing, the permeation processing is performed while suppressing the generation of scale while applying a DC voltage so that the first electrode on the undiluted flow path side becomes a cathode, and then the first processing is performed at appropriate intervals.
Then, the polarity of the DC power supply connected to the second electrode is inverted, and the first electrode is cleaned. By such a processing method, even when the silica concentration on the stock solution flow path side is concentrated to the solubility or higher, it is possible to perform the permeation treatment at a high recovery rate without generating silica scale on the membrane surface of the permeable membrane. it can.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a reverse osmosis membrane module according to the present invention will be described with reference to the drawings. FIG. 1 is a partial sectional view of a reverse osmosis membrane module according to the present invention.

The reverse osmosis membrane module 10 shown in FIG. 1 has a flat membrane thin-layer flow type module structure formed by housing a flat membrane member 6 inside a pair of housings 4a and 4b. I have. On one housing 4a, a raw water inlet 1 and a concentrated water outlet 2 communicating with the raw water flow path of the membrane 6 are formed. In the other housing 4b, a permeated water outlet 3 communicating with the permeated water flow path of the membrane 6 is formed. The area where the film body 6 is housed is sealed with the O-ring 5 from the outside.

FIG. 2 is an enlarged sectional view of the film body 6. The membrane body 6 includes a reverse osmosis membrane 13 and raw water spacers 12 and permeated water spacers 14 superposed on both sides thereof.
The raw water spacer 12 forms a raw water flow path, and the permeated water spacer 14 forms a permeated water flow path.

Further, a raw water side electrode 11 is arranged outside the raw water spacer 12, and a permeated water side electrode 15 is arranged outside the permeated water spacer 14. The raw water side electrode 11 and the permeated water side electrode 15 are each a flat membrane type reverse osmosis membrane 1.
3 is formed by a net-like member extending in a plane shape facing the surface of the third member. The raw water side electrode 11 and the permeated water side electrode 1
5 is made of an inert material having a non-electrolytic corrosion property, for example, platinum, carbon, or an alloy thereof. A conductor 7 is connected to the raw water side electrode 11, and the conductor 7 passes through a passage formed in the housing 4a and is connected to a connection terminal 7a exposed on the surface of the housing 4a.
In addition, a conductor 8 is connected to the permeated water side electrode 15, and the conductor 8 is connected to a connection terminal 8a exposed on the surface of the housing 4b through a passage formed in the housing 4b.

The raw water introduced from the raw water inlet 1 flows through a raw water flow path constituted by a raw water spacer 12,
Part of the raw water permeates through the reverse osmosis membrane 13 to become permeated water, and is guided to the permeated water channel formed by the permeated water spacer 14. Further, the permeated water is guided to the outside through the permeated water outlet 3. On the other hand, raw water (concentrated water) in which solutes in raw water are concentrated
Is discharged from the concentrated water outlet 2 to the outside.

The connection terminals 7 a and 8 a provided on the housings 4 a and 4 b are connected to an external DC power supply 9 via conductors 16 and 17 and a switch 19. This allows
A DC voltage is applied between the raw water side electrode 11 and the permeated water side electrode 15. At the time of a normal filtration process, the raw water side electrode 11 is connected to the DC power supply 9 so that the raw water side electrode 11 becomes a cathode and the permeate water side electrode 15 becomes an anode.

As a result, a DC electric field is generated in the raw water flow path or the permeated water flow path between the raw water side electrode 11 and the permeated water side electrode 15. Then, the water in the raw water is electrolyzed by the DC electric field, and the hydroxide ion (OH ⁻ ) generated thereby suppresses the polymerization of the silica monomer. For this reason, generation of silica scale on the surface of the reverse osmosis membrane 13 can be suppressed.

On the other hand, raw water contains metal ions such as calcium, magnesium and iron. In particular, calcium ions are substances that produce scale, like silica.
As described above, when the raw water electrode 11 is set as a cathode, these metal ions are electrodeposited on the surface of the raw water electrode 11 which is a cathode, thereby causing calcium to cause scaling on the reverse osmosis membrane 13 surface. Is prevented.

If a DC voltage is applied so that the raw water electrode 11 always serves as a cathode and the treatment is continued, electrodeposition of metal ions such as calcium and magnesium on the surface of the raw water electrode 11 proceeds. For this reason, the polarity of the voltage applied to the raw water side electrode 11 and the permeate water side electrode 15 is switched intermittently by the switch 19, and the metal deposit on the surface of the raw water side electrode 11 is ionized and removed. Thereby, the raw water side electrode 11
Surface cleaning can be performed.

While the raw water electrode 11 is set as the anode, active oxygen is generated from the raw water electrode 11.
The oxidizing power of the active oxygen decomposes contaminants such as organic substances adhered to the surface of the reverse osmosis membrane 13 and cleans the surface.

FIG. 3 is a configuration diagram of a reverse osmosis membrane device using the reverse osmosis membrane module of FIG. The reverse osmosis membrane device includes a raw water tank 22, a pump 23, a pre-filter 24, a reverse osmosis membrane module 10, a DC power supply 9, and pipes 21, 25, 2
6, 27 are provided. Raw water is stored in a raw water tank 22 through a pipe 21, and then supplied from a tank 22 to a pre-filter 24 by a pump 23. The pre-filter 24 is composed of a cartridge filter having a nominal pore size of 1 to 30 μm, and removes fine particles that may block the flow path of the reverse osmosis membrane disposed downstream.

The raw water from which fine particles have been removed by the prefilter 24 is supplied to the reverse osmosis membrane module 10. In the reverse osmosis membrane module 10, the direct current power supply 9 supplies the raw water side electrode 1.
The filtration process is performed in a state where a DC voltage is applied to the electrode 1 and the permeated water side electrode 15. Then, the permeated water is guided to a predetermined place through the pipe 27. Further, a part of the concentrated water is returned to the raw water tank 22 through the pipe 25, and the rest is discharged out of the system through the pipe 26.

In this reverse osmosis membrane device, filtration is performed with a DC voltage applied from a DC power supply 9 so that the electrode on the raw water flow path side of the reverse osmosis membrane module 10 becomes a cathode. From 9, the polarity of the DC voltage applied to the reverse osmosis membrane module 10 is switched to remove electrodeposits on the raw water side electrode surface, and the membrane separation process is performed while repeating such an operation.

The reverse osmosis membrane module according to the present invention is not limited to a flat membrane thin-layer flow type, but may be a spiral type.

[0036]

EXAMPLES Here, a filtration test was conducted under the following conditions using a reverse osmosis membrane apparatus using the flat membrane thin-layer flow type reverse osmosis membrane module of the present invention.

[0037]

[Table 1]

As a comparative example, a filtration test was performed on the flat membrane laminar flow type reverse osmosis membrane module shown in FIG. 1 without applying a DC voltage under the following conditions.

[0039]

[Table 2]

FIG. 4 shows the test results. As a result of operating the example and the comparative example at a recovery rate of 85%, in the comparative example, the dissolved silica concentration in the concentrated water was twice the solubility of 250%.
３００300 mg / L, and silica scale was formed on the membrane surface. As a result, the flux (Flux) retention decreased rapidly as the operation time elapsed.

On the other hand, in the example, the concentration of dissolved silica in the concentrated water is 250 to 300 mg, which is twice the solubility.
/ L, almost no formation of silica scale was observed, so that the flow rate retention was slightly reduced and stable.

According to the above test results, when the filtration treatment is performed by the reverse osmosis membrane module in a state where a DC electric field is applied, even if the concentration of the silica in the concentrated water exceeds the solubility, the reverse osmosis is performed. It was found that the formation of silica scale on the film surface of the film was suppressed. Thereby, it became possible to perform the filtration treatment of the reverse osmosis membrane module at a high recovery rate.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a reverse osmosis membrane module according to the present invention.

FIG. 2 is a partially enlarged view of the reverse osmosis membrane module of FIG.

FIG. 3 is a configuration diagram of a reverse osmosis membrane device using the reverse osmosis membrane module of FIG. 1;

FIG. 4 is a graph showing a change over time in a flux performance of a reverse osmosis membrane module according to an example of the present invention and a comparative example.

[Description of Signs] 1 Raw water inlet 2 Concentrated water outlet 3 Permeated water outlet 6 Membrane 7, 8, 16, 17 Conducting wire 7a, 8a Connection terminal 9 DC power supply 10 Reverse osmosis membrane module 11 Raw water side electrode 12 Raw water spacer 13 Reverse osmosis Membrane 14 Permeated water spacer 15 Permeated water side electrode 19 Switch

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 1/44 C02F 1/44 C

Claims (10)

[Claims] 1. A first electrode connected to one pole of a DC power supply is disposed on a side of the raw liquid flow path of a permeable membrane that separates a raw liquid flow path and a permeated liquid flow path in a housing, and the first electrode is connected to the first liquid flow path. A reverse osmosis membrane module, wherein a second electrode connected to the other pole of the DC power supply is disposed on the liquid flow path side. 2. The reverse osmosis membrane module according to claim 1, wherein the first electrode is connected to a negative electrode of the DC power supply, and the second electrode is connected to a positive electrode of the DC power supply. 3. The first and second DC power supplies are connected to each other.
3. The reverse osmosis membrane module according to claim 1, further comprising a switching unit for switching the polarity of the DC voltage applied between the electrodes. 4. The reverse osmosis membrane module according to claim 1, wherein said first and second electrodes are made of an inert material. 5. The method according to claim 1, wherein said first and second electrodes are made of a non-electrolytic corrosion metal material.
The reverse osmosis membrane module according to any one of the above. 6. The reverse osmosis membrane module according to claim 1, wherein the first and second electrodes are formed in a net shape. 7. The reverse osmosis membrane module according to claim 4, wherein the first and second electrodes are made of platinum, carbon, or an alloy of platinum and carbon. 8. The method according to claim 1, wherein the permeable membrane comprises a flat membrane type or a spiral type reverse osmosis membrane, and the first and second electrodes are arranged to face each other along the surface of the reverse osmosis membrane. The reverse osmosis membrane module according to any one of claims 1 to 7, wherein: 9. A first electrode is disposed on the side of the undiluted liquid flow path partitioned by the permeable membrane, and a second electrode is disposed on the side of the permeated liquid flow path, and a direct current is provided between the first and second electrodes. A liquid separation method comprising performing a permeation treatment while applying a voltage. 10. The liquid separation method according to claim 9, wherein the permeation processing is performed while switching the polarity of the DC voltage applied between the first and second electrodes.