JP2003053160A - Cleaning method for separating membrane and membrane filtrater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which is capable of efficiently cleaning a separating membrane and membrane filter which is capable of efficiently cleaning the separating membrane. SOLUTION: If the separating membrane is cleaned by water for back washing stored in an accumulation tank disposed on a secondary side after the raw water on the primary side of the separating membrane is drained, the separating membrane can be efficiently cleaned. The effect is higher if pressurized gas is supplied into the accumulation tank and the separating membrane is back washed after the pressure is increased. The cleaning can be cost effectively and efficiently performed if the filtrate water of the separating membrane is used as the water for back washing and the volume of the water for back washing is set at 0.1 to 10 L per 1 m<2> of the area of the separating membrane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separation membrane washing method and a membrane filtration device for solid-liquid separation.

[0002]

2. Description of the Related Art Filtration of water using a membrane filtration device has been used for various purposes because it has excellent separation performance and can perform a large amount of continuous treatment with a compact device configuration. The separation membrane includes a microfiltration membrane, an ultrafiltration membrane, a reverse osmosis membrane, etc., which are appropriately selected and used according to the substance to be separated. For example, microfiltration membranes are 10 μm or less, especially 1 μm
The following fine particles and microorganisms can be efficiently removed. In order to increase the membrane area and facilitate handling, the microfiltration membrane is a hollow fiber membrane module in which a hollow fiber membrane is formed into a cylindrical shape or a screen shape, or a pleated type in which a flat membrane is folded into a pleated shape and formed into a cylindrical shape. It is used as a membrane module, a flat membrane module having a flat membrane formed in a screen shape, and the like.

[0003] When filtration is performed using these separation membranes, suspended substances in water, bacteria and the like are separated and removed in the fine pores of the membrane, and clear filtered water is obtained. However, when filtration is continuously performed for a long period of time, there is a problem that the fine pores are closed and the amount of filtered water is reduced and the filtration pressure is increased.

[0004] Therefore, in order to prevent early clogging of the separation membrane due to the substance clogging the membrane surface in water, backwashing in which filtered water is reversely passed from the secondary side to the primary side of the separation membrane, and the same gas is passed. Reverse aeration, conversely, gas is supplied to the membrane surface of the separation membrane, scrubbing cleaning that moves the membrane and cleaning that combines these are regularly performed, and the membrane surface blocking substance attached to the primary side of the membrane The operation of recovering the filtration performance by peeling off is carried out.

[0005]

However, in this method, reverse water flow is carried out in the state where raw water is present on the primary side of the separation membrane, so that the raw water present on the primary side of the separation membrane is subjected to load during reverse flow. In some cases, the permeation flux may be reduced, or the separated membrane surface blocking substance may be difficult to remove from the vicinity of the separation membrane.
As a result, the filtration performance may not be recovered sufficiently.

[0006] As a method for solving these problems, JP-A-5-18
No. 4885 discloses that when performing reverse flow washing of an ultrafiltration mesoporous tubular membrane, the concentrate compartment on the primary side of the membrane module is emptied and then the liquid in the permeate compartment on the secondary side of the membrane module is primary. A method of sending to the side is disclosed. In this method, the raw water on the primary side of the membrane is drained and then backwashed, and the washing effect can be enhanced as compared with the case where raw water is present.

[0007] However, in JP-A-5-184885, a backwash pump is used as a means for backwashing, and in backwashing with a pump, it is necessary to separately provide a pump that is used only during backwashing. Also becomes a problem. Furthermore, in order to effectively perform backwashing, it is necessary to apply high pressure and high flow rate to the membrane immediately after backwashing, but the pump has the characteristic that the pressure and flow rate obtained gradually increase after starting. For,
In some cases, a sufficient backwashing effect could not be obtained at the beginning of startup.

[0008] As a method for solving these problems, Japanese Unexamined Patent Publication No.
Japanese Laid-Open Patent Publication No. 187627 discloses a filter device and a cleaning method for backwashing, in which filtered water is stored in a pressure tank branched from a filtered water passage. In this filtration device, filtered water is sent into the pressure tank by valve operation, the pressure of the filtered water is increased by compressing the gas in the tank, and at the end of the storage, the discharge valve on the primary side of the membrane is opened, and the filtered water in the pressure tank is opened. The reverse flow of water to the membrane module. In this filtering device, the pressure of the filtered water stored in the pressure tank serves as the driving force for the reverse water flow, and the backwash pump is not used. Also,
In backwashing with a pressure tank, the pressure in the pressure tank can be instantly applied to the membrane module immediately after the start of backwashing.

[0009] However, in the above-described invention, the discharge valve on the membrane primary side is opened at the same time as the end of the storage of the filtered water in the pressure tank, and the filtered water in the pressure tank is passed back through the membrane module. In this case, since the raw water on the primary side of the membrane is washed without being drained, there was a problem that a sufficient washing effect was not obtained. The present invention has been made to solve the above problems, and provides a method capable of effectively cleaning a separation membrane and a membrane filtration device capable of efficiently cleaning the separation membrane.

[0010]

[Means for Solving the Problems] That is, the first gist of the present invention is a method for backwashing a separation membrane, which comprises discharging the raw water from the primary side of the separation membrane to the secondary side of the separation membrane. A method for cleaning a separation membrane, which comprises backwashing with backwashing water stored in an allocated pressure storage tank. Further, it is preferable to store the backwash water in the pressure accumulating tank, supply pressurized gas to the pressure accumulating tank, raise the pressure, and then perform the backwash, because the cleaning effect is high. It is preferable that the backwash water is the filtered water of the separation membrane, since a separate water source is not required. The amount of backwash water used for backwashing is 0.1 to 10 per 1 m ² of membrane area of the separation membrane.
It is preferable for it to be L because it can be effectively washed.

[0011] A second aspect of the present invention is a filtration device having a separation membrane, which communicates with the separation membrane, raw water supply means for supplying raw water to the separation membrane, and the primary side of the separation membrane. , A raw water conduit with a water valve device, a drain pipe with a drain valve device,
It comprises a vent valve device, a filtered water conduit provided with a discharge valve device communicating with the secondary side of the separation membrane, and an accumulator tank provided with a backwash valve device branched to the filtered water conduit. A filtration device, which is characterized by: Also, in the accumulator tank,
It is preferable to provide the air supply valve device and the exhaust valve device because the backwash pressure can be increased. It is preferable that the separation membrane is a microfiltration membrane because the washing effect is high.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the separation membrane cleaning method of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a conceptual diagram showing a flow of a method for cleaning a separation membrane and a filtration device of the present invention. The filtration device is a membrane module 10, raw water supply means 1, water supply valve device 2, raw water conduit 3, drain valve device 4, drain pipe 5, discharge valve device 6, filtered water conduit 7, backwash valve device 8,
The pressure storage tank 9 is generally configured. Membrane module 10
The U-shaped hollow fiber membrane 12 is fixed in the housing 11 in an open state at the end face of the potting portion 13. Further, the housing 11 is provided with a ventilation valve device 14.

Raw water is supplied to the membrane primary side of the membrane module 10 via the raw water conduit 3 and the water supply valve device 2 by the raw water supply means 1, and the gas on the membrane primary side is discharged from the ventilation valve device 14 to the outside of the membrane module 10. Is discharged. Raw water permeates from the outer surface side to the inner surface side of the hollow fiber membrane 12, and the filtered water is taken out of the apparatus through the filtered water conduit 7 and the discharge valve device 6. For example, filtration is performed for a certain period of time by constant flow rate filtration, and backwashing is performed when the filtration differential pressure increases due to blockage of the membrane surface. Here, backwash means that water is reversely passed through the membrane module 10 from the secondary side of the separation membrane toward the primary side.

[0014] When performing backwash, first, the discharge valve device 6 is closed, and the backwash valve device 8 is opened to store the filtered water in the pressure accumulating tank 9, and at the same time, the pressure inside the tank is increased. The amount of filtered water in the accumulator tank 9 is monitored by a liquid level sensor, and when a fixed amount of water is stored, the backwash valve device 8 is closed, the raw water supply means 1 is stopped, and the water supply valve device 2 is closed. Then, when the drain valve device 4 is opened, the membrane module 1
Gas outside of 0 is introduced to the membrane primary side through the vent valve device 14. Thereby, the raw water on the primary side of the membrane module 10 is drained through the drain pipe 5 and the drain valve device 4.

When the backwash valve device 8 is opened after the drainage is finished, the filtered water stored in the pressure accumulating tank 9 flows into the membrane module 10 through the filtered water conduit 7 and the inner surface side of the hollow fiber membrane 12 Permeate to the outer surface side. As a result, the membrane surface blocking substance deposited on the outer surface of the hollow fiber membrane is peeled off and discharged to the outside of the membrane module 10 via the drain pipe 5 and the drain valve device 4. The amount of filtered water in the accumulator tank 9 decreases with the progress of backwashing,
The water level sensor detects the decrease in the liquid level, the backwash valve device 8 is closed, and the backwash is completed. After the backwash is finished, the filtration operation is restarted. In this example, the storage level in the accumulator tank 9 is detected by the water level sensor, but the storage level may be controlled by another method such as a float switch.

[0016] The method for draining the raw water on the primary side of the separation membrane is not particularly limited as long as the raw water can be drained. For example, the membrane module 10 is higher than the drain pipe 5 and the drain valve device 4. By arranging as described above, the raw water can be drained by falling by its own weight by opening the ventilation valve device 14. The vent valve device 14 can be used without particular limitation as long as it has a function of introducing gas at the time of backwashing and discharging gas at the start of filtration, and an air vent is preferably used. When it takes a long time to introduce and discharge the gas only with the air vent, an electromagnetic valve, an air valve or the like may be separately provided and the air vent may be used as an auxiliary.

[0017] The time required for the drainage of the primary side of the membrane module before backwashing is 1 second to 5 minutes, more preferably 5 seconds to 3 minutes. By setting the time from 1 second to 5 minutes, drainage can be performed without significantly reducing the operating time of the device. Further, as a method of shortening the drainage time, it is also possible to connect the ventilation valve device 14 to a pressurized gas source (not shown) and forcibly drain the drainage.

The pressure accumulating tank 9 of the present invention can be used without particular limitation as long as it has airtightness and pressure resistance. In order to enable backwashing under high pressure, it is preferable that the pressure accumulating tank 9 has higher pressure resistance, but in order to achieve high pressure resistance, it is necessary to increase the tank thickness or provide a reinforcing material. Occurs, the size increases and the weight also increases,
A preferable value is 600 kPa, more preferably 500
kPa can be mentioned.

[0019] The capacity of the pressure resistant tank 9 can be appropriately selected according to the amount of water required for backwashing. The backwash water driving force is the pressure of the backwash water stored in the accumulator tank 9. When the pressure is low, the effect of backwash is small, and when the pressure is high, the effect is large, but when it is too high, the pressure resistance of the membrane module increases. May cause problems. The pressure in the accumulator tank 9 is preferably 10 to 600 kPa, more preferably 100 to 500 kPa.
Can be mentioned.

[0020] The amount of backwash water used for backwashing is preferably 0.1 to 10 L per 1 m ² of membrane area of the separation membrane.
If the amount of water for backwashing is less than 0.1 L, the effect of backwashing is low, and if it exceeds 10 L, the recovery rate of filtered water is low.

[0021] The backwash frequency may be appropriately selected depending on the raw water quality, and may be once every several minutes to several hours.

The backwash water can be used without particular limitation as long as it does not contaminate the secondary side of the membrane module, but filtered water of the membrane module 10 is preferably used.
By storing the filtered water of the membrane module 10 in the accumulator tank 9, it is not necessary to separately prepare backwash water.

[0023] The raw water supply means 1 of the present invention means the membrane module 1
0 can be used without particular limitation as long as the required amount of raw water can be supplied to 0 and the required amount of filtered water can be stored in the pressure accumulating tank 9. For example, various pumps can be exemplified.

[0024] The water supply valve device 2, the drainage valve device 4, the discharge valve device 6,
The valve device such as the backwash valve device 8 can be used without particular limitation as long as it has a function of switching for blocking and passing liquid, and examples thereof include an electromagnetic valve and an air valve. Raw water conduit 3, drain pipe 5, filtered water conduit 7
Etc. are not particularly limited as long as they have a pressure resistance suitable for the backwash pressure to be set, and for example, a commonly used metal pipe or the like can be used.

[0025] Fig. 2 is a conceptual diagram showing another flow of the method for cleaning a membrane module and the filtration device of the present invention. The filter device includes an air supply valve device 15 and an exhaust valve device 16 in the accumulator tank 9.
Is provided.

To carry out backwashing, as in the case of FIG. 1, backwashing water is stored in the pressure accumulating tank 9, and when the storage is completed, the backwashing valve device 8 is closed, and then the drainage valve device 4 is opened. The gas outside the membrane module 10 is introduced into the membrane primary side through the ventilation valve device 14. Thereby, the raw water on the primary side of the membrane module 10 is drained. At that time, by opening the air supply valve device 15 and supplying the pressurized gas into the pressure accumulating tank 9 for a certain period of time, the pressure in the pressure accumulating tank 9 can be raised to a desired pressure. After the pressure rises, the air supply valve device 8 is closed and the supply of the pressurized gas is terminated. By increasing the pressure in the accumulator tank 9, the backwash effect can be improved.

[0027] The amount of filtered water in the accumulator 9 decreases as the backwash progresses, the water level sensor detects a drop in the liquid level, and the backwash valve device 8 closes to complete the backwash. Since there is residual pressure in the accumulator tank 9 at that time, the residual pressure is released by opening the exhaust valve device 15.

When using pressurized air for backwashing, a source of pressurized gas is separately required, but for example, a part of the pressurized gas for valve control can be used. Further, in the above-mentioned example, the example in which the pressurized gas is supplied into the pressure accumulating tank 9 only before the backwash valve device 8 is opened and the reverse liquid flow is started has been shown. The pressurized gas may be supplied while the valve washing device 8 is open and the backwashing is being performed. In this case, even if the backwashing progresses and the amount of the backwashing water in the accumulator tank 9 decreases, the pressure does not drop, so that the washing effect is improved.

[0029] Fig. 3 is a conceptual diagram showing another flow of the method for cleaning a membrane module and the filtration device of the present invention. In this example, an air diffuser 17 is provided below the membrane module 10. When backwashing is performed, water for backwashing is stored in the pressure accumulating tank 9 as in FIG. 1, and when the storage is completed, the backwash valve device 8 is closed. Next, air from the blower is introduced into the membrane module 10 from the air diffuser 17, and the hollow fiber membrane 12
Scrubbing cleaning is performed. The scrubbing air is exhausted from the ventilation valve device 14 to the outside of the membrane module 10. After completion of the scrubbing cleaning, backwashing is performed in the same manner as in the example of FIG.

[0030] The filtration device of the present invention is suitably used when performing pressurized total filtration. In the case of performing total filtration under pressure, a microfiltration membrane is preferably used as the separation membrane because the membrane surface is likely to be clogged when the fractional pore size of the separation membrane becomes small.

[0031] The membrane module is not particularly limited in its structure as long as the membrane is a microfiltration membrane. For example, a hollow fiber membrane module in which a hollow fiber membrane is formed in a cylindrical shape or a screen shape, or a flat membrane in a pleated shape. It can be applied to a pleated type membrane module formed in a folded cylinder shape, a flat type membrane module in which a flat membrane is formed in a screen shape, and the like. Further, in the above-mentioned example, the structure in which one end of the hollow fiber membrane is potted is illustrated as the membrane module, but the structure in which both ends are potted may be used.

[0032] The pore size of the microfiltration membrane is not particularly limited as long as it has a pore diameter of about 0.01 to 10 µm, and its form, structure, size, material, etc. can be applied to known microfiltration membranes. it can. For example, as the material of the hollow fiber membrane, polyolefin, polysulfone, polyvinyl alcohol, cellulose, polyacrylonitrile, polyamide,
Examples thereof include polyimide, polytetrafluoroethylene, polyvinylidene fluoride and the like. Further, when a hydrophobic hollow fiber membrane is used for filtering water, it can be used after being hydrophilized.

Hereinafter, the present invention will be specifically described with reference to examples.

<Example 1> 1. As a filtering device, a filtering device having the structure shown in FIG. 2 was produced. The accumulator tank capacity is 20 L (pressure resistance 500 kPa), an air-driven valve that serves as a backwash valve device is installed at the inlet of the accumulator tank, and after the water storage in the accumulator tank is completed, the valve is closed to drain the raw water on the primary side of the separation membrane. I made it possible.
Furthermore, an air supply valve device was provided to enable pressurization. The membrane module also includes a hydrophilic polyethylene porous hollow fiber membrane:
EX410TS (manufactured by Mitsubishi Rayon Co., Ltd., average pore size: 0.
A cylindrical microfiltration module (membrane area 8 m ² ) prepared by using 1 μm, inner diameter 270 μm, outer diameter 410 μm) was used.

[0035] 2. Filtration test A filtration test was carried out using the prepared filtration device. Well water was used as raw water for the filtration test, and after filtration was performed for 60 minutes at a filtration flux of 3 m / d, backwashing was repeated for 1 month using a pressure accumulator tank pressurized to 300 kPa.
The filtration pressure difference at the end of the test was measured. The amount of backwash water used for backwashing was 1 L per 1 m ² of the membrane area of the membrane module. The test conditions and results are shown in Table 1.

<Example 2> A filtration test was performed in the same manner as in Example 1 except that the filtration device produced in Example 1 was used and pressurized gas was not supplied to the accumulator tank. The test conditions and results are shown in Table 1.

<Comparative Example 1> A filtration apparatus having the same structure as that of Example 1 is used except that the backwash valve device is not provided, and the raw water on the primary side of the membrane module is not drained before backwashing. A filtration test was carried out as in Example 1. The test conditions and results are shown in Table 1. In addition, after the completion of water storage in the pressure storage tank, the raw water supply means was stopped and the drain valve device was opened to perform backwashing. Here, in order to make the pressure in the accumulator tank at the start of backwashing the same as in Example 1, pressurized air was supplied to the accumulator tank during the water storage to 300 kPa.

[0038]

【table 1】

[0039] From the results shown in Table 1, it can be seen that in Examples 1 and 2, the increase in the filtration differential pressure was smaller than that in Comparative Example 1, and the backwashing was effectively performed.

[0040]

According to the membrane module cleaning method and the membrane filtration of the present invention, the raw water on the primary side of the membrane module is drained and then backwashed with the backwash water stored in the pressure accumulating tank, thereby performing reverse water flow. In the state where the raw water existing on the primary side of the membrane, which is the load at the time, is removed, the pressure in the accumulator tank is instantly applied to the membrane module immediately after the start of backwashing, so that the backwashing property can be improved. .

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a flow of a method for cleaning a membrane module and a filtration device of the present invention.

FIG. 2 is a conceptual diagram showing another flow of the method for cleaning a membrane module and the filtration device of the present invention.

FIG. 3 is a conceptual diagram showing another flow of the method for cleaning a membrane module and the filtration device of the present invention.

[Explanation of symbols]

1 Raw water supply means 2 Water supply valve device 3 Raw water conduit 4 Drain valve device 5 drainage pipe 6 Discharge valve device 7 Filtered water conduit 8 Backwash valve device 9 Accumulation tank 10 membrane module 11 housing 12 Hollow fiber membrane 13 potting section 14 Ventilation valve device 15 Air supply valve device 16 Exhaust valve device 17 Air diffuser

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4D006 GA07 HA03 HA19 HA41 HA71                       JA20A JA53A JA55A JA63A                       JA67A JA70A KA12 KC02                       KC03 KC13 KC14 KE01R                       KE06R KE21P MA01 MA03                       MC11 MC22 MC29 MC30 MC33                       MC39 MC54 MC58 MC62 PA01                       PB05

Claims (7)

[Claims] 1. A method for backwashing a separation membrane, which comprises draining raw water on the primary side of the separation membrane and then backwashing with backwash water stored in a pressure storage tank disposed on the secondary side of the separation membrane. A method for cleaning a separation membrane, comprising: 2. The separation membrane according to claim 1, wherein backwash water is stored in the accumulator tank, pressurized gas is supplied to the accumulator tank, and the backwash is performed after increasing the pressure. Cleaning method. 3. The method for cleaning a separation membrane according to claim 1, wherein the backwash water is filtered water for the separation membrane. 4. The method for cleaning a separation membrane according to claim 1, wherein the amount of backwash water used for backwashing is 0.1 to 10 L per 1 m ² of the membrane area of the separation membrane. 5. A filtration apparatus having a separation membrane, comprising a separation membrane, a raw water supply means for supplying raw water to the separation membrane, and a raw water conduit provided with a water supply valve device communicating with the primary side of the separation membrane. A drainage pipe provided with a drainage valve device, a ventilation valve device, a filtered water conduit provided with a discharge valve device communicating with the secondary side of the separation membrane, and a backwash valve provided by branching to the filtered water conduit A filtration device comprising a pressure accumulating tank equipped with the device. 6. The filtration device according to claim 5, wherein the pressure accumulation tank is provided with an air supply valve device and an exhaust valve device. 7. The filtration device according to claim 5, wherein the separation membrane is a microfiltration membrane.