WO2013047466A1

WO2013047466A1 - Membrane module cleaning method

Info

Publication number: WO2013047466A1
Application number: PCT/JP2012/074470
Authority: WO
Inventors: 新谷　昌之; 池田　啓一; 智宏前田
Original assignee: 東レ株式会社
Priority date: 2011-09-29
Filing date: 2012-09-25
Publication date: 2013-04-04

Abstract

Provided is a membrane module cleaning method for cleaning a membrane module in which filtered water is obtained by membrane filtration of raw water using a filtration membrane, wherein a backwashing step for backwashing while backwashing drainage water is drained from below the membrane module and a recovery step for recovering at least some of the backwashing drainage water are conducted and followed by an air-washing step (A) for air-washing by filling the raw-water side of the membrane in the membrane module with at least some of the backwashing drainage water recovered in the recovery step, or an air-washing step (B) for air-washing while supplying the raw-water side of the membrane in the membrane module with at least some of the backwashing drainage water recovered in the recovery step.

Description

Membrane module cleaning method

The present invention relates to a method for cleaning a membrane module used for membrane filtration treatment of raw water.

The membrane separation method using a hollow fiber membrane has features such as energy saving, space saving, labor saving, and improvement of filtered water quality, and therefore is widely used in various fields. For example, microfiltration membranes and ultrafiltration membranes are applied to pretreatment in water purification processes for producing industrial water and tap water from river water, groundwater, and sewage treated water, and seawater desalination reverse osmosis membrane treatment processes. Furthermore, there is a method in which powdered activated carbon is added to raw water or the like for the purpose of removing soluble organic substances in the course of the membrane filtration treatment (Patent Document 1).

However, since the suspended substances in the raw water accumulate on the membrane surface due to the continuation of filtration, the permeation holes of the fluid formed in the membrane are blocked, and the filtration performance of the membrane gradually decreases.

Therefore, in order to maintain the filtration performance, air such as air (hereinafter simply referred to as air) is introduced into the raw water side of the filtration membrane as air bubbles, or the raw water from the filtered water side in the opposite direction to the filtration process. Back washing is generally performed in which filtered water or clarified water or the like is permeated to the side to remove suspended substances on the membrane surface.

Furthermore, in order to enhance the cleaning effect, empty reverse simultaneous cleaning in which empty cleaning and back cleaning are performed simultaneously is known (Patent Documents 2 and 3). However, when performing the above-described simultaneous reverse backwashing, since the backwash wastewater and air are mixed and discharged from the membrane module through the air vent pipe, a sufficient air flow rate is obtained due to the air vent pipe and the pressure loss of the module. And there is a problem that the backwash flow rate cannot be maintained.

In addition, when air washing is performed alone, the membrane surface may be crushed or the membrane surface may be roughened by vigorously rubbing the outer surface of the membrane through suspended substances separated from the membrane surface. There was a problem of scratching. In particular, in raw water containing high-hardness particles such as powdered activated carbon, the degree of membrane rubbing is remarkable, and until now, it has been an obstacle to adding powdered activated carbon to the raw water of the membrane module. On the other hand, when only backwashing is performed without performing air washing, suspended substances cannot be sufficiently separated from the membrane surface and accumulate in large quantities, resulting in a significant decrease in filtration performance. It was.

Also, a method has been proposed in which after the raw water in the membrane module is discharged once, backwash wastewater is discharged from the lower part of the membrane module, and backwashing is performed (Patent Documents 4 and 5). However, this method has a problem that a suspended substance that easily adheres to the membrane surface has insufficient peelability from the membrane, and the suspended substance accumulates in the membrane module.

On the other hand, methods for adding sodium hypochlorite to backwash water or using ozone-containing water for water used for backwashing have been proposed in order to enhance the cleaning effect (Patent Documents 3 and 6). Chlorine disinfectants have the effect of decomposing and removing organic substances such as humic substances and microorganism-derived proteins adhering to the membrane surface and membrane pores. However, when powdered activated carbon is contained in the raw water, those chemicals are consumed by the powdered activated carbon, and there is a problem that the effect of decomposing and removing the film-adhered organic matter is reduced.

JP10-309567A JP2007-289940A JP2001-079366A JP06-170364A JP 2794304B JP2001-187324A

Therefore, in order to solve the above problems of the prior art, after draining the raw water side of the membrane module out of the system, the backwash wastewater in the membrane module is discharged while performing backwashing, and then the membrane A method for cleaning a membrane module has been devised in which the raw water side in the module is filled with water and washed with air, and then the water on the raw water side in the membrane module is discharged out of the system.

According to this method, it is possible to reduce the amount of suspended substances in the membrane module at the time of air washing, and to suppress membrane abrasion and at the same time effectively wash the membrane module. In particular, it was found that even raw water containing high-hardness particles has a great effect of reducing membrane scratching and can be operated stably without deteriorating the water permeability of the membrane over a long period of time. In addition, when chemicals were used for the backwash water, it was possible to efficiently decompose and remove suspended substances adhering to the membrane surface.

However, in this cleaning method, since the water in the membrane module is discharged outside the system before and during the backwashing, it is necessary to supply water again for the airwashing. As compared with back washing or air washing alone, there is a problem that the water recovery rate is lowered.

The present invention can reduce the amount of suspended substances in the membrane module at the time of air washing without reducing the water recovery rate, reduce membrane abrasion, and at the same time, effectively wash the membrane module. The purpose is to provide. In addition, an object of the present invention is to provide a membrane module cleaning method capable of efficiently decomposing and removing suspended substances adhering to the membrane surface when chemicals are used for backwash water.

The method for cleaning the membrane module of the present invention for achieving the above object is as follows.

(1) A membrane module cleaning method for cleaning a membrane module that obtains filtered water by membrane filtration of the raw water with a filtration membrane, wherein backwashing is performed while discharging backwash drainage from the lower part of the membrane module. And collecting the raw water side of the membrane in the membrane module with at least a part of the backwash wastewater collected in the collection step, An air washing step A for performing washing or an air washing step B for carrying out air washing while supplying at least a part of the backwash waste water collected in the collection step to the raw water side of the membrane in the membrane module is performed. Cleaning method for membrane modules.

(2) A membrane module cleaning method for cleaning a membrane module that obtains filtered water by membrane filtration of the raw water with a filtration membrane, and performing backwashing while discharging backwash drainage from the lower part of the membrane module And a recovery step of recovering at least a part of the backwash wastewater, and a separation step of separating the backwash wastewater recovered in the recovery step into suspended substances and clarified water, An air washing step C in which the raw water side of the membrane is filled with the clarified water to perform air washing, or an air washing step in which air is washed while supplying the clarified water to the raw water side of the membrane in the membrane module. A method for cleaning a membrane module obtained by performing D.

(3) The membrane module cleaning method according to (2), wherein the separation method in the separation step is a precipitation separation method.

(4) The membrane module cleaning method according to any one of (1) to (3), wherein at least part of the water on the raw water side of the membrane in the membrane module is discharged before the backwashing step. .

(5) The membrane module cleaning method according to any one of (1) to (4), wherein a chemical is added to water used for backwashing in the backwashing step.

(6) The method for cleaning a membrane module according to (5), wherein the chemical is a chlorine-based disinfectant.

(7) The membrane module cleaning method according to (6), wherein a residual chlorine concentration of water used for the backwashing is in a range of 3 mg / L to 10 mg / L.

(8) The membrane module cleaning method according to any one of (1) to (7), wherein the raw water contains particles having a hardness higher than that of the filtration membrane.

According to the method for cleaning a membrane module of the present invention, it is possible to reduce the amount of suspended solids at the time of air washing without reducing the water recovery rate, and to effectively clean the membrane module while suppressing membrane abrasion. Can do. In addition, when chemicals are used, suspended substances attached to the membrane surface can be efficiently decomposed and removed.

FIG. 1 is an apparatus schematic flow diagram showing an example of a pressurized hollow fiber membrane filtration apparatus to which the first embodiment of the present invention is applied. FIG. 2 is a schematic apparatus flow diagram illustrating an example of a pressurized hollow fiber membrane filtration apparatus to which the second embodiment of the present invention is applied. FIG. 3 is an apparatus schematic flow diagram showing an example of a pressurized hollow fiber membrane filtration apparatus to which the third embodiment of the present invention is applied. FIG. 4 is an apparatus schematic flow diagram showing the pressurized hollow fiber membrane filtration apparatus used in Comparative Example 4.

Hereinafter, the present invention will be described in more detail with reference to the drawings. In addition, this invention is not limited to the following embodiment.

First embodiment:
FIG. 1 shows a pressurized hollow fiber membrane filtration apparatus to which the first embodiment of the present invention is applied. In FIG. 1, a pressurized hollow fiber membrane filtration device F1 includes a raw water tank 1, a membrane module 3 comprising a container in which a hollow fiber membrane HF is accommodated, a filtered water tank 4, a backwash wastewater recovery tank 6, an air blower 7, and A chemical reservoir 8 is provided.

The raw water tank 1 is provided with a pipeline PL1 for supplying the raw water RW to the raw water tank 1 from outside the system, and the raw water 1a is stored in the raw water tank 1. The raw water tank 1 and the raw water side space 3A of the membrane module 3 are connected by a pipe line PL2, and a raw water valve 10 and a raw water supply pump 2 are provided in the pipe line PL2. The filtered water side space 3B of the membrane module 3 and the filtered water tank 4 are connected by a pipe line PL3, and a filtered water valve 11 is provided in the pipe line PL3.

Pipe line PL4 is led out from filtered water tank 4, and its downstream end is connected to pipe line LP3 between membrane module 3 and filtered water valve 11. The line PL4 is provided with a backwash pump 5 and a backwash valve 12. The filtered water tank 4 stores filtered water 4a. The filtered water tank 4 has a pipe line PL5 for discharging filtered water (treated water) TW out of the system.

A pipe line PL6 derived from the raw water side space 3A of the membrane module 3 is provided below the membrane module 3, and a drain valve 15 is provided in the pipe line PL6. A branch line PL7 is provided between the membrane module 3 and the drain valve 15 and is branched from the pipe line PL6, and the downstream end thereof is connected to the backwash drainage recovery tank 6. A backwash drainage recovery valve 16 is provided in the pipe line PL7. In the backwash drainage recovery tank 6, backwash drainage 6a is stored.

The pipe PL8 is led out from the backwash drainage tank 8, and its downstream end is coupled to the pipe PL2 between the raw water valve 10 and the raw water supply pump 2, and the backwash drainage supply is supplied to the pipe PL8. A valve 17 is provided. The backwash drainage recovery tank 6 is provided with a pipe line PL9 for discharging the backwash wastewater to the outside of the system.

The pipe line PL10 is led out from the upper part of the raw water side space 3A of the membrane module 3, the downstream end thereof is opened to the outside of the system, and an air vent valve 13 is provided in the pipe line PL10.

The pipe line PL11 is led out from the air blower 7, and the downstream end thereof is coupled to the pipe line PL6 between the membrane module 3, the drain valve 15 and the backwash drainage recovery valve 16. An air supply valve 14 is provided in the pipe line PL11.

A pipe line PL12 is led out from the chemical liquid storage tank 8, and its downstream end is coupled to the pipe line PL4 between the backwash pump 5 and the backwash valve 12, and a chemical liquid supply pump 9 is provided in the pipe line PL12. It has been.

In FIG. 1 (pressurized hollow fiber membrane filtration device F1), raw water 1a stored in the raw water tank 1 is supplied to a raw water side space 3A of the hollow fiber membrane HF in the membrane module 3 by a raw water supply pump 2. The inside of the membrane module 3 includes a hollow fiber membrane HF whose opening end is fixed by an adhesive and an adhesive fixing portion FP on the raw water side space 3A of the hollow fiber membrane HF and the filtered water side of the hollow fiber membrane HF. It is divided into a space 3B.

In the membrane module 3, the raw water 1 a is filtered by the hollow fiber membrane HF, and the filtered water 4 a flows from the space 3 B on the filtrate side of the hollow fiber membrane HF through the pipe line PL 3, passes through the filtered water valve 11, and passes through the filtered water tank. 4 is transferred. At this time, the raw water valve 10 and the filtrate water valve 11 are open, and the backwash valve 12, the air vent valve 13, the air supply valve 14, the drain valve 15, the backwash drainage recovery valve 16, and the backwash drainage supply valve 17 are closed. It is. Part or all of the filtered water 4 a obtained by this filtration is stored in the filtered water tank 4.

The filtration process in the pressurization type hollow fiber membrane filtration device F1 supplies raw water 1a from the raw water tank 1 to the membrane module 3, and permeates the water from the raw water side of the hollow fiber membrane HF in the membrane module 3 to the filtered water side, and performs filtration. This is a step of transferring water to the filtered water tank 4.

The filtration time is appropriately set according to the quality of raw water, membrane filtration flux, etc. In the case of constant flow filtration, the predetermined membrane filtration differential pressure or filtered water volume [m ³ ], in the case of constant pressure filtration, Filtration may be continued until a predetermined filtration flow rate [m ³ / hr] or filtered water amount [m ³ ] is reached. The filtration flow rate indicates the amount of filtered water per unit time. The membrane filtration flux indicates the filtration flow rate per effective membrane area.

In the pressurized hollow fiber membrane filtration device F1, the membrane module cleaning method of the present invention is performed, for example, as follows. First, the raw water valve 10 and the filtrate water valve 11 are closed, the raw water supply pump 2 is stopped, and the filtration process is stopped. Next, with the backwash drainage recovery valve 16 closed, the air vent valve 13 and the drainage valve 15 of the membrane module 3 are opened, and the backwash pump 5 is operated, so that filtered water is discharged from the hollow fiber in the membrane module 3. The backwashing step is performed by allowing the membrane 3 to pass through the space 3B on the raw water side of the hollow fiber membrane in the membrane module 3 from the space 3B on the filtered water side of the membrane.

At this time, the backwash waste water on the raw water side flows from the membrane module 3 through the pipe line PL6 and is discharged out of the system through the drain valve 15. The backwash drainage immediately after the start of backwashing contains a large amount of suspended matter peeled from the hollow fiber membrane HF, but the suspended matter decreases as the backwash time elapses. When the amount of suspended substances is reduced, the recovery process is such that the backwash drainage 6a is recovered in the backwash drainage recovery tank 6 by closing the drainage valve 15 and opening the backwash drainage recovery valve 16. Done.

At the start of the backwash process, the backwashing is started with the air vent valve 13 and the backwash drainage recovery valve 16 open and the drainage valve 15 is closed, and the backwash drainage immediately after backwashing is recovered. Although it is possible to send water to the tank 6, since the recovered backwash wastewater contains a lot of suspended solids, the backwash wastewater immediately after the start of backwash is discharged outside the system by opening the drain valve 15. It is desirable to do.

In the backwashing step, the timing for switching backwash wastewater from draining out of the system to feeding water to the backwash wastewater collecting tank 6 is a method of automatically switching when the predetermined time has elapsed, the concentration of suspended solids There is a method of measuring when the value falls below a predetermined value. However, it is desirable to collect a sufficient amount of backwash wastewater to fill at least the raw water side of the membrane module 3.

In the backwashing step, the backwash flow rate [m ³ / hr] is preferably set lower than the flow rate of backwash wastewater discharged from the lower part of the membrane module 3 by its own weight. In this case, the water level of the membrane module 3 gradually decreases, and the surroundings on the raw water side in the membrane module 3 become a gas state. Conventional backwashing is performed in a state where the raw water side in the membrane module 3 is filled with water, and the backwash drainage is discharged out of the system through the air vent valve 13, so the water pressure is suspended. The peeling of the substance from the film surface was inhibited.

In contrast, in the present invention, the backwash wastewater is discharged from the lower part of the membrane module, so that the backwash wastewater is discharged from the lower part of the membrane module 3. For this reason, resistance due to water pressure is eliminated during backwashing or becomes extremely low, so that suspended substances are easily peeled off from the membrane surface and the cleaning effect is enhanced.

Before performing the backwashing step, at least a part of the raw water may be discharged by opening the air vent valve 13 and the drain valve 15. The water on the raw water side in the membrane module 3 may remain, but at least half of the membrane is above the water surface so as to be in contact with the gas. Preferably, until the water level becomes 1/3 or less of the length of the filtration membrane, more preferably, the entire membrane is above the water surface, and water is discharged so that the entire membrane is in contact with gas.

At this time, it is preferable that the raw water drained from the drain valve 15 is directly returned to the raw water tank 1 from the viewpoint of the water recovery rate. Further, the air drain valve 13 and the backwash drainage recovery valve 16 may be opened to collect the drained raw water in the backwash drainage recovery tank 6. In addition, the water recovery rate here shows the ratio of the filtrate water production amount with respect to the raw water amount supplied to the membrane module 3.

Furthermore, as a method for enhancing the cleaning effect, it is desirable to operate the chemical liquid supply pump 9 and add the chemicals in the chemical liquid storage tank 8 to the water used for backwashing (backwash water).

After carrying out the backwash process and the recovery process, the backwash drainage recovery valve 16 is closed, the backwash drainage supply valve 17 is opened, and the air vent valve 13 is left open, and the raw water supply pump 2 is opened. By operating, the raw water side in the membrane module 3 is filled with the collected backwash drainage, the air supply valve 14 is opened, and the air blower 7 is operated to supply air from below the membrane module 3, Perform an air wash.

The air washing may be performed after the raw water side in the membrane module 3 is filled with the collected backwash wastewater in advance, that is, the air washing step A, or the collected backwash wastewater on the raw water side in the membrane module 3. However, the washing step B is preferable because the washing effect is high.

In the air washing step A and the air washing step B, the water discharged from the upper portion of the membrane module 3, that is, the pipe PL10 via the air vent valve 13, is discharged to increase the water recovery rate. It is desirable to return to the water tank 1 or the backwash waste water collection tank 6.

Here, when a chemical is added to the backwash water, the chemical flows into the raw water tank 1 or the backwash drainage recovery tank 6. When returning to the raw water tank 1, Since it is diluted within 1, it usually has little effect on raw water. However, when a chemical is added at a high concentration, it is desirable to return to the raw water tank 1 after performing a chemical treatment such as a neutralization treatment. When returning to the backwash wastewater recovery tank 6, since chemicals can be reused, it is preferable to return to the backwash wastewater recovery tank 6 as it is without performing neutralization.

Thereafter, the air supply valve 14 is closed and the air blower 7 is stopped to complete the air washing process.

Next, by opening one of the drainage valve 15 or the backwash drainage recovery valve 16, water containing suspended substances separated from the membrane surface and membrane pores on the raw water side of the membrane module 3 (empty washing) The waste water) is discharged from the space 3A on the raw water side of the membrane module 3. Since the concentration of suspended solids is usually higher than that of raw water, it is preferable that the waste water is discharged out of the system from the drain valve 15. However, when the concentration of suspended solids is below the suspended solids concentration of raw water, In order to increase the water recovery rate, the washing waste water drained from the drain valve 15 is returned to the raw water tank 1 or the washing waste water is again returned to the back washing drain collection tank 6 via the back washing drain recovery valve 16. It is preferable to collect in

Here, as described above, chemicals can be added to the backwash water. However, when the chemicals are added at a high concentration, when the backwash water is collected in the raw water tank 1, chemical treatment such as neutralization treatment is performed. Is preferably returned to the raw water tank 1, and when backwash water is collected in the backwash wastewater collection tank 6, chemicals can be reused. It is preferable to send the washing waste water to the back washing waste water collecting tank 6 as it is.

After completion of the drainage, the drain valve 15 is closed, the raw water valve 10 is opened, the raw water supply pump 2 is operated, the raw water is supplied to the membrane module 3, and the raw water side of the membrane module 3 is filled. Here, the raw water discharged from the upper part of the membrane module 3, that is, the pipe PL10 through the air vent valve 13 and discharged from the pipe PL10, is supplied to the raw water tank 1 or the backwash drainage recovery tank 6 in order to increase the water recovery rate. It is desirable to send to.

However, when the raw water contains high-hardness particles, the raw water flows into the backwash drainage recovery tank 6 and causes the filter membrane to be rubbed by the subsequent washing process, so that it can be sent to the raw water tank 1 as much as possible. preferable. Thereafter, the air vent valve 13 is closed, the filtrate water valve 11 is opened, and the filtration process is started again.

According to the present invention, since most of the suspended solids can be removed by the backwashing step, it is possible to reduce the degree that the membrane is rubbed with the suspended solids and rubbed against the membrane during washing. Therefore, the present invention is particularly effective for washing the membrane module in membrane filtration when raw water contains high-hardness particles such as powdered activated carbon.

High hardness particles refer to particles having a hardness higher than the hardness of a filtration membrane used for filtration and washing. Examples of such high hardness particles include powdered activated carbon, metal powder, silt particles, sand, ceramic particles, and the like, and powdered activated carbon is preferably employed from the viewpoint of adsorption capability.

Here, for determining whether the hardness of the high hardness particles is higher than the hardness of the filtration membrane, the hardness is measured by a measuring method based on ISO145777-1 (instrumented indentation hardness), and the measured hardness is compared. Judgment. However, when the filtration membrane is hollow, the membrane is cut and measured to have a flat membrane shape.

In addition, as a conventional technique, a method of collecting backwash wastewater and returning it to the raw water tank is widely used. However, when the backwash wastewater containing the chemical is diluted in the raw water tank 1, the effect of the chemical disappears. Was. According to the present invention, since the backwash waste water containing the chemical can be used again in the next air washing step, a high cleaning effect can be obtained without eliminating the effect of the chemical.

It is preferable that the backwash drainage recovery tank 6 has a capacity necessary to collect at least a sufficient amount of backwash drainage to fill the space 3A on the raw water side of the membrane module 3. About the backwash waste water which overflowed the backwash waste water collection tank 6, in order to raise a water recovery rate, returning to the raw water tank 1 is desirable. Again, as described above, chemicals can be added to the backwash water. However, when chemicals are added at a high concentration, they can be returned to the raw water tank 1 after treatment with chemicals such as neutralization. desirable.

The cleaning method for the membrane module of the present invention may be performed every time after the filtration is completed, or may be sometimes performed in combination with another cleaning method. Moreover, the time for performing the backwashing step and the air washing step, and the ratio between them can be arbitrarily set, but the washing time for the backwashing step and the air washing step is about 30 seconds to 3 minutes. preferable. Furthermore, when the method for cleaning a membrane module of the present invention is repeated, it is preferable that the cleaning is performed 2 to 5 times.

When adding chemicals to backwashing water, it is not always necessary to add chemicals to backwashing water in each washing process, and it is recommended that chemicals be added to backwashing water every several cycles. It is effective to reduce the amount of use.

In addition, it is possible to further enhance the releasability of suspended substances by providing a step (immersion step) for holding the membrane module 3 in a state of being filled with water in at least one of the steps. Therefore, after performing the backwashing step and the recovery step, water is supplied into the membrane module 3 to provide an immersion step in which the inside of the membrane module 3 is filled with water, and then the empty washing step is performed. It is preferable.

In particular, by adding a chemical to the backwash water, water containing the chemical is retained in the membrane module 3, which is effective because the decomposition of the suspended substance by the chemical is promoted in the dipping process. At this time, it is not always necessary to provide an immersion process in each cleaning process, and it is effective to provide an immersion process every several cycles in order not to reduce the operating rate.

In addition, an organic or inorganic flocculant can be added to the raw water supplied to the raw water side of the membrane module 3 in the filtration step. By adding the flocculant, the effect of improving the releasability of the suspended substance can be obtained. Examples of organic flocculants include dimethylamine-based and polyacrylamide-based cationic polymer flocculants. On the other hand, polyaluminum chloride, polyaluminum sulfate, ferric chloride, polyiron, ferric sulfate, polysilica iron and the like can be used as the inorganic flocculant.

The membrane module 3 may be an external pressure type or an internal pressure type, but is preferably an external pressure type from the viewpoint of simplicity of pretreatment. Moreover, as a membrane filtration system, there is no problem even if it is a whole-volume filtration type module or a cross-flow filtration type module, but a whole-volume filtration type module is preferred from the viewpoint of low energy consumption. Furthermore, although it may be a pressurization type module or an immersion type module, a pressurization type module is preferable from the viewpoint that high flux filtration is possible.

The filtration membrane used in the membrane module 3 is not particularly limited as long as it is porous, but depending on the desired quality and amount of treated water, a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) is used. ), Or use both together. For example, when removing turbid components, Escherichia coli, Cryptosporidium, etc., either MF membrane or UF membrane may be used. However, when removing viruses, high molecular organic substances, etc., UF membrane is used. preferable.

As the shape of the filtration membrane, there are a hollow fiber membrane, a flat membrane, a tubular membrane and the like, and any of them may be used.

Filter membrane materials include polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetra Including at least one selected from the group consisting of fluoroethylene-perfluoroalkyl vinyl ether copolymers, and chlorotrifluoroethylene-ethylene copolymers, polyvinylidene fluoride, polysulfone, cellulose acetate, polyvinyl alcohol, and polyethersulfone. Further, from the viewpoint of film strength and chemical resistance, polyvinylidene fluoride (PVDF) is more preferable, and it has high hydrophilicity and excellent stain resistance. , Polyacrylonitrile is more preferable.

As a control method of the filtration operation, either constant flow filtration or constant pressure filtration may be used, but constant flow filtration is performed because a constant amount of treated water can be obtained and the entire control is easy. preferable.

The chemicals to be added to the backwash water can be selected after appropriately setting the concentration and holding time so that the membrane does not deteriorate, but sodium hypochlorite, chlorine dioxide, chloramine, hydrogen peroxide, ozone It is preferable to contain at least one of these because the cleaning effect on the organic matter is increased. In addition, it is preferable to contain at least one of hydrochloric acid, sulfuric acid, nitric acid, citric acid, oxalic acid and the like because the cleaning effect on aluminum, iron, manganese and the like is increased.

In particular, a chlorine-based disinfectant such as sodium hypochlorite is more preferable because of its immediate effect and low persistence.

When using a chlorine-based disinfectant, the residual chlorine concentration of water used for backwashing is preferably in the range of 3 mg / L to 10 mg / L. If it is less than 3 mg / L, the cleaning effect of the film may be reduced and the effect may be lost. On the other hand, when the concentration is higher than 10 mg / L, the amount of chemicals used may increase, and depending on the material of the filtration membrane, the filtration membrane may be deteriorated.

Here, the residual chlorine concentration is measured by a method based on the DPD (diethyl-p-phenylenediamine) absorptiometry described in “Water test method” 2001 edition (published by Japan Water Works Association).

The membrane module cleaning method of the present invention can also be used as a pretreatment of an RO membrane separation device that obtains fresh water by treating water to be treated such as seawater with an RO membrane or the like. At that time, if chemicals are added to the backwashing water in the backwashing process described above, the chemicals remaining in the membrane and on the membrane surface immediately after the start of the filtration process are contained in the membrane filtration water, affecting the subsequent RO membrane treatment. It is preferable to carry out a treatment such as neutralization as necessary.

For example, when an oxidizing agent such as sodium hypochlorite, chlorine dioxide, chloramine, hydrogen peroxide, or ozone is added to the backwash water, a reducing agent such as sodium sulfite, sodium bisulfite, or sodium thiosulfate is backwashed. What is necessary is just to supply the backwash waste_water | drain collect | recovered to the membrane module 3 after carrying out a reduction process by adding to the waste_water | drain collection | recovery tank 6. When acid such as hydrochloric acid, sulfuric acid, nitric acid, citric acid, or oxalic acid is added to the backwash water, an alkali such as sodium hydroxide or sodium hydrogen carbonate is added to the backwash waste water collecting tank 6 for neutralization. What is necessary is just to supply the backwash waste_water | drain collect | recovered to the membrane module 3 after processing.

However, since these treatments alone cannot remove chemicals remaining inside the filtration membrane, for example, when an oxidizing agent is added to the backwash water in the backwashing process described above, the cleaning method for the membrane module of the present invention is used. In addition, it is preferable to perform backwashing with water to which a reducing agent is added.

Second embodiment:
FIG. 2 shows a pressurized hollow fiber membrane filtration apparatus to which the second embodiment of the present invention is applied. FIG. 2 shows a pressurization type hollow fiber membrane filtration device F2, but the same reference numerals are given to components of the device that overlap with the pressurization type hollow fiber membrane filtration device F1 shown in FIG. In the description of the pressurization type hollow fiber membrane filtration device F2 shown in FIG. 2, the same description as that in the pressurization type hollow fiber membrane filtration device F1 shown in FIG. 1 is omitted.

The pressurization type hollow fiber membrane filtration device F2 shown in FIG. 2 is different from the pressurization type hollow fiber membrane filtration device F1 shown in FIG. 1 in that the backwash drainage is used instead of the backwash drainage recovery tank 6 shown in FIG. It is a point provided with the settling tank 18 for isolate | separating into the water containing a suspended solid, and clear water, and the clear water tank 19 for storing the obtained clear water.

2, the downstream end of the pipe PL7 having the backwash drainage recovery valve 16 is coupled to the settling tank 18. A pipe line PL <b> 21 is led out from the upper part of the settling tank 18, and its downstream end is connected to the clarified water tank 19. A pipe line PL22 is led out from the lower part of the settling tank 18, and its downstream end is open to the outside of the system. A suspended substance extraction valve 20 is provided in the pipe line PL22.

A pipe line PL23 is led out from the clarified water tank 19, and its downstream end is connected to the pipe line PL2 between the raw water valve 10 and the raw water supply pump 2. A clarified water supply valve 21 is provided in the pipe line PL23. A pipe line PL24 is led out from the upper part of the clarified water tank 19, and its downstream end is open to the outside of the system. The clarified water 19a exceeding the amount stored in the clarified water tank 19 is led out from the clarified water tank 19 by the pipe line PL24.

As separation means for separating backwash wastewater used in the sedimentation tank 18 into water containing suspended solids and clarified water, precipitation separation, coagulation sedimentation separation, pressurized flotation separation, centrifugation, sand filtration, UF / MF membrane separation, filter cloth separation, fibrous filter separation, cartridge filter separation, disk filter separation, filter press, belt press, vacuum dewatering, multiple disk dewatering, and the like can be selected. Suspended substances are usually suitable for precipitation separation because of their large specific gravity and high sedimentation properties. Also, precipitation separation is preferable from the viewpoint of equipment cost, processing cost, and the like.

In the pressurization type hollow fiber membrane filtration device F2 shown in FIG. 2, after finishing the filtration step, the drain valve 15 is closed, and the backwash valve 12, the air vent valve 13, and the backwash drainage recovery valve 16 are opened. In this state, the backwash pump 5 is operated to carry out the backwash process. In this backwashing step, it is preferable to send the total amount of backwash wastewater to the settling tank 18. Thereby, the amount of backwash drainage discharged out of the system can be reduced more than the pressurized hollow fiber membrane filtration device F1 (first embodiment) shown in FIG. 1, and the water recovery rate can be further increased.

As the backwash wastewater flows into the settling tank 18, the clear water in the settling tank 18 is pushed out into the clear water tank 19, so that the clear water tank 19 is filled with the clear water 19a.

After performing the backwashing step, the backwash drainage recovery valve 16 is closed, the clarified water supply valve 21 is opened, and the raw water supply pump 2 is operated while the air vent valve 13 remains open. The raw water side space 3A in the membrane module 3 is filled with the clarified water, the air supply valve 14 is opened, and the air blower 7 is operated so that air is supplied from below the membrane module 3 to perform air washing. .

The air washing may be performed after the raw water side space 3A in the membrane module 3 is filled with the clarified water in advance, that is, the air washing step C, or the clarified water is added to the raw water side space 3A in the membrane module 3. However, the washing step D is preferable because the washing effect is high.

In the air washing step C and the air washing step D, the clarified water that overflows and is discharged from the upper part of the membrane module 3, that is, the pipe PL10 through the air vent valve 13, is used to increase the water recovery rate. It is desirable to return to the raw water tank 1 or the sedimentation tank 18.

Here, as described above, chemicals can be added to the backwash water. However, when high-concentration chemicals are added, chemicals such as neutralization are performed when clear water is returned to the raw water tank 1. After that, it is preferable to return the clarified water to the raw water tank 1, and when the clarified water is returned to the precipitation tank 18, the chemicals can be reused. It is preferable to return to the tank 18.

Next, by opening one of the drainage valve 15 or the backwash drainage recovery valve 16, the flush wastewater is discharged. Since the washing waste water usually has a higher concentration of suspended solids than the raw water, it is preferable that the pressurized hollow fiber membrane filtration device F1 (first embodiment) shown in FIG. However, in the pressurized hollow fiber membrane filtration device F2 (second embodiment) shown in FIG. 2, the suspended solids can be separated by the settling tank 18, so that the water washing rate is increased in order to increase the water recovery rate. It is preferable to send the waste water to the settling tank 18.

In addition, when draining the waste water from the drain valve 15, the concentration of suspended substances in the waste water is equal to that of the raw water as in the pressurization type hollow fiber membrane filtration device F 1 shown in FIG. 1 (first embodiment). When the turbidity substance concentration is less than or equal to the turbid substance concentration, the washing waste water discharged from the drain valve 15 may be returned to the raw water tank 1 again.

Here, as described above, chemicals can be added to the backwash water, but when adding high-concentration chemicals, chemical treatment such as neutralization treatment is performed when the waste water is collected in the raw water tank 1. After washing, it is preferable to return the washing waste water to the raw water tank 1, and when collecting in the sedimentation tank 18, chemicals can be reused. It is preferable to send it to the sedimentation tank 18 as it is.

After completion of the drainage, the drainage valve 15 is closed, the raw water valve 10 is opened, the raw water supply pump 2 is operated, the raw water is supplied to the membrane module 3, and the space 3A on the raw water side of the membrane module 3 is filled. Here, the raw water discharged from the upper part of the membrane module 3, that is, the pipe PL10 through the air vent valve 13, is discharged to the raw water tank 1 or the sedimentation tank 18 in order to increase the water recovery rate. Is desirable.

However, when chemicals are added to the backwashing water in the backwashing process, if the raw water that overflows and is discharged is sent to the sedimentation tank 18, the chemical concentration in the sedimentation tank 18 will decrease, so it overflows and is discharged. The raw water to be used is preferably returned to the raw water tank 1.

Thereafter, the air vent valve 13 is closed, the filtrate water valve 11 is opened, and the filtration process is started again. During this filtration step, suspended substances in the backwash wastewater in the settling tank 18 are settled, and the backwash wastewater is separated into suspended substances and clarified water.

In the pressurized hollow fiber membrane filtration device F2 (second embodiment) shown in FIG. 2, the filtration time is preferably longer and more preferably 30 minutes or longer in order to sufficiently precipitate the suspended matter. preferable.

It should be noted that since suspended substances are accumulated at the bottom of the sedimentation tank 18, it is preferable to periodically open the suspended substance extraction valve 20 and appropriately discharge the suspended substances out of the system.

The clarified water overflowing the clarified water tank 19 is preferably returned to the raw water tank 1 in order to increase the water recovery rate. Here, as described above, a chemical can be added to the backwash water. However, when a chemical solution is added at a high concentration, after the chemical treatment such as neutralization is performed, the backwash water is supplied to the raw water tank 1. It is desirable to return to

In addition, when a treatment containing a chemical such as a flocculant such as a coagulation sedimentation treatment or pressurized flotation separation is performed as a separation means, the effect of the chemical added to the backwash water depends on the chemical added in the separation treatment. Since it may attenuate, it is desirable to add an additional chemical to the clarified water when supplying the clarified water in the air washing step.

Third embodiment:
FIG. 3 shows a pressurized hollow fiber membrane filtration device to which the third embodiment of the present invention is applied. FIG. 3 shows a pressurization type hollow fiber membrane filtration device F3, and the same reference numerals are given to components of the device that overlap with the pressurization type hollow fiber membrane filtration device F2 shown in FIG. In the description of the pressurization type hollow fiber membrane filtration device F3 shown in FIG. 3, the same description as that in the pressurization type hollow fiber membrane filtration device F2 shown in FIG. 2 is omitted.

3 is characterized in that powdered activated carbon is added to raw water. The pressurized hollow fiber membrane filtration device F3 (third embodiment) shown in FIG. 3 stores powdered activated carbon slurry in addition to the pressurized hollow fiber membrane filtration device F2 (second embodiment) shown in FIG. There are provided an activated carbon slurry storage tank 22, a slurry supply pump 23 for supplying powdered activated carbon to the raw water, and a stirrer 24 for mixing and stirring the raw water and powdered activated carbon.

3, the activated carbon slurry storage tank 22 and the raw water tank 1 are coupled by a pipe line PL31, and a slurry supply pump 23 is provided in the pipe line PL31. The raw water RW is supplied to the raw water tank 1 through the pipe line PL1. Inside the raw water tank 1, a stirrer 24 is provided.

The raw material of the powdered activated carbon may be any of woody materials such as coconut shells and sawdust, and coal-based materials such as peat, lignite and bituminous coal. Further, the smaller the particle size of the powdered activated carbon is, the larger the specific surface area and the higher the adsorption ability, which is preferable. However, as a matter of course, it is necessary to make it larger than the pore diameter of the membrane filter of the membrane module so as not to be mixed into the filtrate water.

The organic polymer resin filtration membrane described above can be preferably used in the membrane module cleaning method of the present invention because the hardness is lower than the hardness of the high hardness particles such as powdered activated carbon used here. .

Hereinafter, examples of the present invention and comparative examples will be described.

Evaluation method of membrane filtration differential pressure:
A pressure gauge is installed in each of the pipe line PL2 for supplying the raw water connected to the membrane module 3 to the membrane module 3 and the pipe line PL3 for leading the filtrate water from the membrane module 3, and the pressure gauge installed in the pipe line PL2. The pressure on the filtrate side of the membrane module detected by the pressure gauge installed in the pipe line PL3 was subtracted from the pressure on the raw water side of the membrane module detected by, and the membrane filtration differential pressure was calculated.

Test 1:
Using external pressure PVDF hollow fiber membrane module HFU-2008 (manufactured by Toray Industries, Inc.) (membrane area 11.5 m ² ), using river water as raw water, membrane filtration flux 1.5 m ³ / m ² / d, The membrane module is washed by the washing method of the present invention or the conventional washing method every 30 minutes for the filtration step, and the membrane module is operated for one month each, and the rate of increase in the membrane filtration differential pressure, and The water recovery rate was compared. The backwashing flux in the backwashing process was 1.7 m ³ / m ² / d, and the air flow rate in the air washing process was 14 L / min. The membrane filtration differential pressure in the initial stage of operation was 10 kPa. Table 1 shows the figure numbers of the membrane filtration devices used in each Example and each Comparative Example and the usage state of each process. In addition, Table 2 shows the open / close state of each valve in each step and the operation and stop states of each pump (including an air blower).

Using the pressurized hollow fiber membrane filtration device F1 shown in FIG. 1 having the backwash drainage recovery tank 6, the membrane module 3 was cleaned there. Every 30 minutes of filtration, backwash process BS1 (10 seconds), backwash process BS2 (50 seconds), backwash wastewater supply process (30 seconds), empty wash process (60 seconds), drainage process DS2 (15 seconds) The raw water supply step (30 seconds) was performed in this order.

Here, the backwashing process BS1 is a process including an operation of discharging the backwash drainage to the outside of the apparatus system through the drain valve 15 and the pipe line PL6. The backwash process BS2 is a process comprising an operation of supplying backwash wastewater to the backwash wastewater recovery tank 6 or the sedimentation tank 18 through the pipe PL7 via the backwash drainage recovery valve 16. It is a process including a wastewater recovery process. In the backwashing step BS1 and the backwashing step BS2, the water level on the raw water side of the membrane module gradually decreases, and finally, the water level on the raw water side of the membrane module at the end of the backwashing step BS2 is equal to the filtration membrane length. It became about 1/3.

The membrane filtration differential pressure after 1 month operation was 40 kPa, and it was able to operate stably. At this time, the water recovery rate was 96.1%.

Using the pressurized hollow fiber membrane filtration device F2 shown in FIG. 2 having the sedimentation tank 18 and the clarified water tank 19, the membrane module 3 was cleaned there. Every 30 minutes of filtration, backwash process BS2 (60 seconds), clarified water supply process (30 seconds), air washing process (60 seconds), drainage process DS2 (15 seconds), and raw water supply process (30 seconds) Were performed in this order. In the backwashing step BS2, the water level on the raw water side of the membrane module gradually decreases, and finally, the water level on the raw water side of the membrane module at the end of the backwashing step BS2 is about 1/3 of the filtration membrane length. became.

In Example 2, since the backwash process BS1 was not performed, the amount of backwash water discharged out of the apparatus system decreased, and the water recovery rate increased to 97.7%. The membrane filtration differential pressure after 1 month operation was 40 kPa, and it was possible to operate stably as in Example 1.

In the operation process in Example 2, the drainage process DS1 (15 seconds) was performed before the backwash process BS2. By performing the drainage process DS1 before the backwash process BS2, the raw water side of the membrane module was always filled with gas in the backwash process BS2.

The membrane filtration differential pressure after 1 month operation was 35 kPa, and compared with Examples 1 and 2, an increase in the membrane filtration differential pressure could be suppressed. It was confirmed that the cleaning effect is enhanced by performing the drainage process DS1 before the backwash process BS2. The water recovery rate was 97.7%, which was a high recovery rate as in Example 2.

Comparative Example 1

Except for not having the backwash drainage recovery tank 6, using the same apparatus as the pressurized hollow fiber membrane filtration apparatus F1 shown in FIG. The process BS3 (60 seconds), the air washing process (60 seconds), the drainage process (15 seconds), and the raw water supply process (30 seconds) were performed in this order.

Here, the backwashing step BS3 is a step consisting of an operation of draining out of the apparatus system through the air vent valve 13 and through the pipe line PL10. In the backwash process BS3, the water level on the raw water side of the membrane module was almost full.

The membrane filtration differential pressure after 1 month operation was 50 kPa, and the increase rate of the membrane filtration differential pressure was larger than in Examples 1 to 3. The water recovery rate was 94.8%, which was lower than those in Examples 1 to 3.

Comparative Example 2

As in Comparative Example 1, except for not having the backwash drainage recovery tank 6, using the same device as the pressurized hollow fiber membrane filtration device F1 shown in FIG. 60 seconds), the drainage process DS2 (15 seconds), and the raw water supply process (30 seconds) were performed in this order. The difference from Example 1 was that the air washing step was not performed, and the difference in the rate of increase in the membrane filtration differential pressure due to the presence or absence of the air washing step was examined.

The membrane filtration differential pressure after 1 month operation was 140 kPa, and a rapid increase in the membrane filtration differential pressure occurred compared to Example 1 having an air washing step after the back washing step. From this, it was confirmed that if there was no air washing step, the washing was insufficient and a rapid increase in the membrane filtration differential pressure occurred. The water recovery rate was 94.8%, which was lower than those in Examples 1 to 3.

Comparative Example 3

As in Comparative Example 1, except for not having the backwash drainage recovery tank 6, using the same device as the pressurized hollow fiber membrane filtration device F1 shown in FIG. 60 seconds), raw water supply step (30 seconds), air washing step (60 seconds), drainage step DS2 (15 seconds), and raw water supply step (30 seconds) were performed in this order. The difference from Example 1 is that there is no backwash wastewater recovery step, and the difference in the rate of increase in membrane filtration differential pressure and the water recovery rate due to the presence or absence of the backwash wastewater recovery step was investigated.

The membrane filtration differential pressure after 1 month operation was 40 kPa, and it was possible to operate stably as in Example 1. However, the water recovery rate was 93.2%, which was lower than that in Examples 1 to 3.

Table 3 shows the operation results in each Example and each Comparative Example in Test 1.

Test 2:
Using the same membrane module and raw water as in the case of Test 1, the filtration process and the washing of the membrane module were repeated in the same manner. In Test 2, the rate of increase in the membrane filtration differential pressure and the water recovery rate when sodium hypochlorite was added as a chemical to the backwash water were compared.

Table 4 shows the figure numbers of the membrane filtration devices used in the examples and comparative examples and the usage status of each process. Table 5 shows the open / close state of each valve in each step and the operation and stop states of each pump (including an air blower).

Using the pressurized hollow fiber membrane filtration device F2 shown in FIG. 2, sodium hypochlorite so that the residual chlorine concentration in the backwash water becomes 10 mg / L in the backwash step BS2 every 30 minutes of filtration. The membrane module was washed in the same manner as in Example 3 except that was added.

Just before the start of the air washing step, the water in the membrane module was collected and the residual chlorine concentration was measured. As a result, the residual chlorine concentration was 3 mg / L and had a bactericidal effect. As a result, in the operation for one month, the membrane filtration differential pressure did not increase from the start of operation, and could be operated stably. The water recovery rate was 97.7%.

Comparative Example 4

Using the pressurized hollow fiber membrane filtration device F4 shown in FIG. 4, sodium hypochlorite was added so that the residual chlorine concentration in the backwash water was 10 mg / L, as in Example 4. However, unlike Example 4, the clarified water 19a obtained by separating suspended substances from the collected backwash wastewater was returned to the raw water tank 1.

Therefore, the pressurized hollow fiber membrane filtration device F4 shown in FIG. 4 has a pipe line PL41 that is led out from the clarified water tank 19 and reaches the raw water tank 19, and a clarified water supply valve 21 is provided in the pipe line PL41. In this respect, it differs from the pressurized hollow fiber membrane filtration device F4 shown in FIG.

Immediately before the start of the air washing process, the water in the membrane module was collected and the residual chlorine concentration was measured. As a result, the residual chlorine concentration was 0 mg / L, and the effect of chlorine added to the backwash water was backwash water. Was completely deactivated by mixing with the raw water in the raw water tank. As a result, the membrane filtration differential pressure after one month of operation was 14 kPa, and the membrane filtration differential pressure increased by 4 kPa compared to when the operation was started. The water recovery rate was 97.7%.

Table 6 shows the operation results in Examples and Comparative Examples in Test 2. From this, compared with the conventional backwash wastewater recovery process for returning the backwash wastewater to the raw water tank, the backwash wastewater recovery process in the cleaning method of the present invention can suppress an increase in the membrane filtration differential pressure. confirmed.

Test 3:
Using the same membrane module and raw water as in the case of Test 1, the filtration process and the washing of the membrane module were repeated in the same manner. In Test 3, using the pressurized hollow fiber membrane filtration device F3 shown in FIG. 3, powdered activated carbon was added to the raw water tank so that the concentration of powdered activated carbon was 50 mg / L, and the membrane filtration differential pressure was increased. The speed, the water recovery rate, and the surface state of the filtration membrane were compared. Table 7 shows the figure numbers of the membrane filtration devices used in the examples and comparative examples and the usage status of each process. Table 8 shows the open / close state of each valve in each step and the operation and stop states of each pump (including an air blower).

Method for evaluating the surface condition of the filtration membrane:
Disassemble the membrane module, place the membrane in a water tank containing pure water, and continue to aerate with air until there is no change in the suspended solids concentration in the water tank. Then, the outer surface of the membrane was observed with an electron microscope at a magnification of 10,000 times.

Using the pressurized hollow fiber membrane filtration device F3 shown in FIG. 3, the membrane module was washed in the same manner as in Example 3 except that powdered activated carbon was added in the filtration step.

The membrane filtration differential pressure after 1 year operation was 52 kPa, and the operation could be performed stably. The water recovery rate was 97.7%. When the membrane module was disassembled and the membrane surface was observed with an electron microscope, it was confirmed that about 90% of the outer membrane surface was a smooth surface. That is, the degree of film rubbing was 10%.

Comparative Example 5

A membrane module similar to that in Example 1 except that the activated carbon fiber is added in the filtration step using the pressurized hollow fiber membrane filtration device F3 shown in FIG. Was washed.

The membrane filtration differential pressure after 1 year operation was 120 kPa, which was larger than that in Example 5. The water recovery rate was 94.8%. When the membrane module was disassembled and the membrane surface was observed with an electron microscope, only about 20% of the outer membrane surface was a smooth surface, and the other portions were not smooth, and many of the membrane pores were crushed. It was confirmed that it was rough or rough. That is, the degree of film rubbing was 80%.

Table 9 shows the operation results in Examples and Comparative Examples in Test 3.

According to the method for cleaning a membrane module of the present invention, it is possible to reduce the amount of suspended substances in the membrane module at the time of air washing without lowering the water recovery rate, and at the same time, effectively reduce the membrane abrasion and at the same time Can be cleaned. In addition, when chemicals are used for the backwash water, the suspended substances attached to the membrane surface can be efficiently decomposed and removed.

1: Raw water tank 1a: Raw water 2: Raw water supply pump 3: Membrane module 3A: Space on the raw water side of the membrane module (hollow fiber membrane) 3B: Space on the filtrate side of the membrane module (hollow fiber membrane) 4: Filtered water tank 4a : Filtered water 5: Backwash pump 6: Backwash drainage recovery tank 6a: Backwash drainage 7: Air blower 8: Chemical liquid storage tank 9: Chemical liquid supply pump 10: Raw water valve 11: Filtration water valve 12: Backwash valve 13: Air vent valve 14: Air supply valve 15: Drain valve 16: Backwash drainage recovery valve 17: Backwash drainage supply valve 18: Precipitation tank 19: Clarified water tank 19a: Clarified water 20: Suspended matter extraction valve 21: Clarified water supply Valve 22: Activated carbon slurry storage tank 23: Slurry supply pump 24: Stirrers F1, F2, F3, F4: Pressurized hollow fiber membrane filtration device FP: Adhesive fixing part HF: Hollow fiber membranes PL1, PL2, PL3, PL4, PL5, PL6 , PL7, PL8, PL , PL10, PL11, PL12, PL21, PL22, PL23, PL24, PL31, PL41: line RW: raw water TW: treated water (filtered water)

Claims

A membrane module washing method for washing a membrane module to obtain filtered water by membrane filtration of raw water through a filtration membrane, a backwashing step of performing backwashing while discharging backwash wastewater from the lower part of the membrane module, After performing the recovery step of recovering at least a part of the backwash wastewater, the raw water side of the membrane in the membrane module is filled with at least a part of the backwash wastewater recovered in the recovery step, and then air washing is performed. A membrane formed by performing an air washing step A or an air washing step B in which air washing is performed while supplying at least a part of the backwash drainage recovered in the recovery step to the raw water side of the membrane in the membrane module How to clean the module.
A membrane module washing method for washing a membrane module to obtain filtered water by membrane filtration of raw water through a filtration membrane, a backwashing step of performing backwashing while discharging backwash wastewater from the lower part of the membrane module, After performing a recovery step for recovering at least a part of the backwash wastewater and a separation step for separating the backwash wastewater recovered in the recovery step into suspended substances and clarified water, the raw water of the membrane in the membrane module An air washing step C for filling the clarified water with the clarified water and performing an air washing or an air washing step D for performing an air washing while supplying the clarified water to the raw water side of the membrane in the membrane module A method for cleaning a membrane module.
The method for cleaning a membrane module according to claim 2, wherein the separation method in the separation step is a precipitation separation method.
The method for cleaning a membrane module according to any one of claims 1 to 3, wherein at least a part of water on the raw water side of the membrane in the membrane module is discharged before the backwashing step.
The method for cleaning a membrane module according to any one of claims 1 to 4, wherein a chemical is added to water used for backwashing in the backwashing step.
The method for cleaning a membrane module according to claim 5, wherein the chemical is a chlorine-based disinfectant.
The method for cleaning a membrane module according to claim 6, wherein the residual chlorine concentration of water used for the backwashing is in the range of 3 mg / L to 10 mg / L.
The method for cleaning a membrane module according to any one of claims 1 to 7, wherein the raw water contains particles having a hardness higher than that of the filtration membrane.