JP4840285B2 - Cleaning method for submerged membrane module - Google Patents

Description

  The present invention relates to a method for cleaning a submerged membrane module. More specifically, a method for cleaning a submerged membrane module used in a water purification process in a water supply, an industrial water production field such as industrial water, food, and medical process water, and a sewage treatment field such as sewage and industrial wastewater with a chemical solution It is about.

  Membrane separation technology using separation membranes such as hollow fiber membranes is used for drinking water production in the waterworks, industrial water, industrial ultrapure water, industrial water production such as food and medicine, municipal sewage purification and industrial wastewater treatment. It is used in a wide range of fields such as wastewater treatment. Moreover, the separation membrane module used for membrane separation is classified into a pressure type and an immersion type regardless of the processing field.

  The immersion type separation membrane module is immersed in the immersion tank and performs filtration through the separation membrane using the suction pressure or the pressure due to the water head difference as the driving force. The membrane filtration water is removed from the treated water in the immersion tank. It is used as an obtained immersion membrane separation means. In many cases, the immersion module does not cover the outer side of the separation membrane with a case in order to bring the primary surface of the separation membrane into contact with the water to be treated in the immersion tank. Even when covered with a case, it is covered with a case provided with many holes through which water to be treated can flow.

  In such membrane separation means, when water to be treated is filtered, water in the water to be treated is taken out as permeated water through the separation membrane, and impurities remain on the surface of the separation membrane and in the porous part. The clogging of the membrane or the blockage of the flow path between the separation membranes may proceed, and the original amount of permeated water may not be obtained.

  Therefore, reverse flow cleaning that peels and removes the impurity layer (cake layer) that has adhered and accumulated on the surface of the separation membrane by causing the permeate to flow backward from the secondary side to the primary side of the separation membrane periodically during the membrane filtration operation. Or air that blows air continuously or intermittently from the bottom of the separation membrane module, or peels or removes impurities accumulated between the separation membrane surface or between the separation membranes by shearing force of bubbles Perform physical cleaning as represented by cleaning.

  However, if the membrane filtration operation lasts for a long time, impurities that cannot be removed even by the above-mentioned physical cleaning adhere to and accumulate on the separation membrane surface and between separation membranes, so chemical cleaning that uses chemicals to dissolve and remove these impurities is necessary. It becomes. The chemical cleaning includes a chemical cleaning process in which impurities attached and accumulated on the separation membrane are dissolved or removed by a chemical solution, and a rinsing process in which the chemical solution in the separation membrane module is washed away.

  About the chemical cleaning method of the immersion type membrane module, generally, the immersion type membrane module is taken out of the immersion tank, the immersion type membrane module is transferred to a separate chemical cleaning tank, and the immersion type membrane module is placed in this tank. A technique of soaking for a certain time is taken. However, when chemical cleaning is performed by this method, not only a large amount of chemical solution is used, but also a special cleaning facility called a chemical solution cleaning tank is required, and a process and means for transferring a submerged membrane module are required. Not suitable for large-scale submerged membrane filtration facilities. Therefore, it is desired to perform chemical cleaning of the submerged membrane module online while being installed in the immersion tank.

  As a method of cleaning the membrane module online, a chemical solution is passed from the chemical solution storage tank to the primary side from the secondary side of the separation membrane module, and in the middle of the pipe connecting the chemical solution storage tank and the separation membrane module. A chemical cleaning method has been proposed in which a chemical solution is filtered with an installed filter and then supplied again to the secondary side of the separation membrane module to circulate the chemical solution (see Patent Document 1). This method is suitable for a pressure-type membrane module in which the inside of the membrane module is a closed space and pipes are connected to the upper and lower portions. However, when applied to an apparatus in which an immersion membrane module is installed in the immersion tank, the entire inner wall surface in the wide immersion tank will be contaminated with the chemical solution, and in the rinse process before the filtration process restarts, the immersion tank It is necessary to use a large amount of rinsing water in order to rinse the entire large inner wall surface of the inside, which is not suitable for on-line chemical cleaning of the submerged membrane module.

  Therefore, as a technology that can reduce the amount of chemical cleaning waste water when online chemical cleaning is performed with the immersion membrane module installed in the immersion bath, the treated water in the immersion bath is discharged out of the bath, When a part of the membrane of the module is exposed on the surface of the water, a chemical cleaning method has been proposed in which injection of a chemical solution is started to the secondary side of the membrane and leached to the primary side (patent) Reference 2). In this method, when a part of the membrane of the submerged membrane module is exposed on the water surface, the chemical solution supplied from the secondary side of the membrane and leached to the primary side is diluted with the water to be treated in the immersion tank. The chemical injected into the secondary side of the membrane is preferentially leached from the membrane portion exposed on the water surface to the primary side of the membrane, so that most of the chemical solution leached on the membrane surface is covered. It is described that it is held on the membrane surface without coming into contact with the treated water and then flows down.

  However, in the method of Patent Document 2, although the relationship between the speed of discharging the water to be treated in the immersion tank and the speed of injecting the chemical solution from the secondary side of the membrane is important, these speeds are clearly specified. In addition, the conditions for preventing the discharged water to be treated from coming into contact with the chemical solution leached to the primary side of the membrane are not clear. Furthermore, in Patent Document 2, the chemical liquid injected and held on the secondary side of the membrane is then discharged to the primary side of the membrane by washing the permeated water back from the secondary side of the membrane. Then, it is discharged out of the tank. When the chemical solution is discharged from the secondary side of the membrane by such a technique, the inner wall surface of the immersion bath is contaminated with the chemical solution being discharged, and the chemical solution attached to the inner wall surface of the immersion bath is cleaned before the filtration process is resumed. It needs to be removed and requires a lot of rinse water.

  Further, as a chemical cleaning technique other than the above, after draining the water to be treated in the immersion tank, the chemical solution is intermittently passed through the secondary side of the immersion membrane module a plurality of times. The amount of the chemical solution to be passed is larger than the minimum flow rate sufficient to ooze the entire outer surface of the submerged membrane module, and the amount of the chemical solution to be passed after the second time is set to 2 to 2 of the minimum flow rate. A chemical cleaning method characterized by a factor of 5 has been proposed (see Patent Document 3). However, in Patent Document 3, since the chemical liquid passed from the secondary side of the immersion membrane module flows directly into the immersion tank, the wide inner wall surface in the immersion tank is the chemical liquid as in Patent Documents 1 and 2. It will be contaminated, and it is necessary to wash and remove the chemical solution adhering to the wide inner wall surface in the immersion tank by water washing or the like before resuming the filtration process, which requires a large amount of rinse water.

JP 2006-281022 JP 2006-255567 A Japanese Patent No. 3582001

  The purpose of the present invention is to perform chemical cleaning of the submerged membrane module on-line with the membrane module installed in the immersion tank, and to suppress the amount of chemical used for chemical cleaning to a small amount. Further, it is possible to provide a cleaning method for a submerged membrane module that can clean a chemical without contaminating the inside of the immersion tank with a chemical solution, and a submerged membrane filtration suitable for performing this chemical cleaning method To provide an apparatus.

The present invention for achieving the above object is specified by the following items.
(1) A method for cleaning a submerged membrane module installed in a dipping tank for storing the water to be treated, and after draining all of the water to be treated in the dipping tank, the permeated water collection of the submerged membrane module is performed. When the chemical solution is passed from the outlet and the secondary side in the submerged membrane module is filled with the chemical solution, the chemical solution is stopped and held for a predetermined time. While maintaining the chemical solution, water is supplied into the immersion tank, air is blown out from below the immersion type membrane module to perform air cleaning, and then all the water in the immersion tank is discharged. A method for cleaning a submerged membrane module, characterized in that the submerged membrane module is supplied into the immersion tank.
(2) In the method for cleaning a submerged membrane module according to (1), by supplying water to be treated into the immersion tank and storing it, starting suction on the secondary side in the submerged membrane module A method for cleaning a submerged membrane module, characterized in that the remaining chemical solution on the secondary side is discharged.
(3) In the method for cleaning an immersion type membrane module according to (1) or (2), when the chemical solution is passed through the permeate outlet of the immersion type membrane module, the chemical solution is discharged from the secondary side in the immersion type membrane module. A method for cleaning a submerged membrane module, wherein the remaining permeated water is discharged out of the immersion tank.
(4) In the method for cleaning a submerged membrane module according to any one of (1) to (3), after all the water in the immersion tank has been discharged after air cleaning, the water to be treated supplied into the immersion tank among initial predetermined amount or a predetermined time, the washing method of the submerged membrane module, characterized in that the discharged without accumulating in the dipping bath.

(5) In the method for cleaning an immersion membrane module according to any one of (1) to (4), the chemical solution supplied to the secondary side in the immersion membrane module is sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, citric acid. A method for cleaning a submerged membrane module, which is a chemical solution containing at least one selected from the group consisting of acid, ascorbic acid, sodium hydroxide, sodium hypochlorite, hydrogen peroxide, and a surfactant .

  According to the method of the present invention, chemical cleaning of a submerged membrane module can be performed online while the membrane module is installed in the immersion tank, and the amount of chemical used for chemical cleaning can be reduced to a small amount. Can be suppressed. Furthermore, the membrane can be chemically cleaned without contaminating the immersion tank with a chemical solution. Further, since the amount of the chemical solution used is small, it is possible to reduce the amount of rinsing water used for rinsing after chemical cleaning.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the scope of the present invention is not limited to these.
FIG. 1 is a schematic cross-sectional view showing an embodiment of a submerged membrane module according to the present invention.

  The submerged membrane module in the present invention refers to a module in which a single or a plurality of separation membranes are disposed inside, and the outer periphery of the separation membrane is exposed. Examples of the shape of the separation membrane include a hollow fiber membrane, a tubular membrane, and a flat membrane. Here, the hollow fiber membrane means a tubular separation membrane having a diameter of less than 2 mm, and the tubular membrane means a tubular membrane having a diameter of 2 mm or more. In the present invention, any shape of separation membrane may be used, but when the liquid for chemical cleaning is sealed on the permeate side (secondary side), the sealed liquid can be easily held, Since it is easy to ensure the membrane area, a tubular hollow fiber membrane or a tubular membrane is preferable. That is, in the case of a flat membrane, the pressure from the liquid held on the permeate side tends to cause separation of the membrane from the support, but in the case of a tubular hollow fiber membrane or tubular membrane, the retained liquid This is because the pressure from is applied uniformly in all directions of the film and peeling of the film is difficult to cause.

  Further, as shown in FIG. 1, the submerged membrane module 1 using hollow fiber membranes is typically several hundred to tens of thousands of hollow fiber membranes 2 (hollow fiber membranes are schematically shown by lines). A membrane module structure in which both ends of a bundle of hollow fiber membranes bundled together is bonded and fixed. One end side (the upper side in FIG. 1) of the adhesive fixing portion 3 is adhesively fixed with the end surface of the hollow fiber membrane being opened. The other one end (lower side in FIG. 1) of the adhesive fixing portion 3 'is adhesively fixed with the end surface of the hollow fiber membrane closed.

  The hollow fiber membrane 2 is not particularly limited as long as it is a hollow fiber-like separation membrane having a porous membrane surface. Polyacrylonitrile, polyphenylsulfone, polyphenylene sulfide sulfone, polyvinylidene fluoride, polypropylene, polyethylene, polysulfone, polyvinyl It is preferably a hollow fiber membrane made of at least one selected from the group consisting of organic materials such as alcohol and cellulose acetate, and inorganic materials such as ceramics, and more preferably a polyvinylidene fluoride hollow fiber membrane from the viewpoint of membrane strength. preferable. The pore diameter on the surface of the hollow fiber membrane is not particularly limited, but may be appropriately selected within the range of 0.001 μm to 1 μm. Also, the outer diameter of the hollow fiber membrane 2 is not particularly limited, but is preferably in the range of 250 μm to 2000 μm because the hollow fiber membrane has high oscillating property and excellent detergency.

  Moreover, although it does not specifically limit about the adhesive agent in adhering and fixing the both ends of a hollow fiber membrane bundle with an adhesive agent, It is preferable to use thermosetting resins, such as an epoxy resin and a urethane resin.

Further, the adhesive fixing portions 3 and the adhesive fixing portions 3 ′ formed at both ends of the hollow fiber membrane bundle are connected via a large number of hollow fiber membranes 2 existing therebetween, and the large number of hollow fibers. In the membrane 2, the hollow fiber membranes are arranged in parallel, and the membrane filtration function is exhibited in the hollow fiber membrane 2 portion. The parallel alignment bundles in the multiple hollow fiber membrane portions may have a structure in which no reinforcing member is interposed, or may have a structure in which a reinforcing means is interposed. As a structure with the reinforcing means interposed, for example, about 1 to 30 preferably cylindrical stays (metal rods, etc.) having a cross-sectional area of 3 to 700 mm ² are arranged on the outer periphery or inside of the aligned bundle of hollow fibers. In addition, a structure in which the adhesive fixing portions are connected by a stay, or a structure in which a porous plate-like material such as a net is arranged so as to cover the outer periphery of the bundle of hollow fiber membranes between the adhesive fixing portions.

  FIG. 2 is a diagram showing an outline of a submerged membrane filtration apparatus in which a submerged membrane module is disposed in a submerged tank. The water to be treated is continuously or intermittently flowed as raw water 6 into the immersion tank 5 from the raw water supply port. The inflow raw water (treated water) is phase-separated in the immersion tank 5 into a liquid phase 5a and a settled sludge phase 5b made of settled suspended matter. The immersion type membrane module 1 is immersed in the immersion tank 5, and the separation membrane in the immersion type membrane module 1, the permeated water pipe 7, and the suction pump 8 disposed on the downstream side of the permeated water pipe Through the filtration valve 9, the water to be treated in the liquid phase 5a is subjected to membrane filtration, and permeated water (membrane filtered water) is taken out (filtration step). At this time, the on-off valve 19 in the middle of the piping is in an open state. In this filtration step, the immersion tank 5 is left stationary, so that suspended substances settle out of the liquid phase 5a and the concentration of suspended substances in the liquid phase 5a is reduced, so that the immersion membrane module 1 is separated. Suspended material load on the membrane is reduced.

  After performing the filtration process alone for a predetermined time, the suction pump 8 is stopped, the filtration valve 9 is closed, and the filtration process is stopped. Subsequently, the backwash valve 12 is opened, and backwash water is sent to the submerged membrane module 1 through the backwash water pipe 10 by the backwash pump 11 to perform backwashing of the hollow fiber membrane (backwash process). At the same time, the air washing valve 15 is opened, and the air supplied from the blower 13 is sent into the liquid phase 5a through the air washing air pipe 14 and the air diffuser 16 installed in the lower part of the submerged membrane module 1. The air bubbles are diffused into the submerged membrane module 1 to clean the hollow fiber membrane with air (air washing step). By the backwashing and air washing, the hollow fiber membrane in the submerged membrane module 1 is swung, and the suspended substances accumulated on the surface of the hollow fiber membrane and the flow path between the hollow fiber membranes are peeled off and removed. At this time, suspended substances accumulated on the surface of the hollow fiber membrane and the flow path between the hollow fiber membranes flow back into the liquid phase 5a, and further, suspended substances that have settled in the liquid phase 5a or have settled once rise up. The suspended solid concentration in the liquid phase 5a increases.

  On the other hand, at the time before performing the back washing process and the air washing process, the time for performing the filtration process alone, that is, the settling time of the suspended substance in the liquid phase 5a after the immersion tank 5 is in a stationary state. It is the longest, the amount of suspended matter in the sedimented sludge phase 5b is maximized, the concentration of the suspended suspended matter is most advanced, and the suspended matter concentration is the highest. Therefore, at this time, the discharge valve 18 provided at the bottom of the immersion tank 5 is opened, and the suspended suspended matter in the settled sludge phase 5b is taken out as sludge and discharged outside the immersion tank via the discharge pipe 17 (discharge). Mud process). Therefore, a mud discharge process is performed as a pre-process of a backwashing process and an air washing process as a process following a filtration process.

  Here, the stationary state means, for example, that the circulation flow in the vertical direction mainly in the immersion tank is caused by the gas-liquid mixed phase flow generated by the air diffuser from the air diffuser installed below the immersion type separation membrane module. Furthermore, it means a state where there is little turbulence or drift in the water flow mainly due to the inflow of the inflow water into the immersion tank, and the sedimentation inhibition of suspended substances by the water flow is small. For example, it means a state where the average flow velocity of the water flow in the immersion bath is 0.4 m / min or less and the average flow velocity of the water flow in the immersion bath is 80 mm / min or less.

  As a situation where the chemical cleaning of the submerged membrane module 1 is necessary, it may be after a long-term filtration operation. In order to perform such chemical cleaning of the submerged membrane module in a state where the membrane module is installed in the submerged tank, that is, on the submerged membrane filtration device, additional equipment such as piping shown in FIG. 3 is required. Become. That is, the chemical liquid supply pipe 20, the chemical liquid supply valve 21, the chemical liquid supply pump 22, the chemical liquid disposal valve 23, the chemical liquid disposal pipe 24, and the chemical liquid disposal suction pump 25 are connected to or installed in the submerged membrane filtration apparatus shown in FIG. .

  The procedure of the chemical cleaning method for the submerged membrane module is as follows. First, the discharge valve 18 is opened to discharge all the water to be treated in the immersion tank 5 (FIG. 4), and then the on-off valve 19 and the chemical solution supply valve 21 are opened. Then, the chemical solution is supplied to the secondary side of the submerged membrane module 1 by the chemical solution supply pump 22 (FIG. 5). At this time, since the permeated water remaining in the secondary side of the submerged membrane module and the pipe on the downstream side thereof is discharged to the primary side, the remaining permeated water is discharged out of the immersion tank. When the discharge of the remaining permeate is finished, the discharge valve 18 is closed (FIG. 6). The amount of residual permeated water discharged from the secondary side to the primary side can be known from the volume on the secondary side in the submerged membrane module and the volume in the piping. What is necessary is just to set the time until the discharge valve 18 is closed by obtaining the time until the discharge is completed from conditions such as the amount of remaining permeated water and the chemical solution supply flow rate. At this time, the discharged permeated water may be discharged because only a small amount of the supplied chemical solution is mixed. The supply of the chemical solution continues thereafter, and when the secondary side of the submerged membrane module is filled with the chemical solution, the on-off valve 19 and the chemical solution supply valve 21 are closed, and then the chemical solution supply pump 22 is stopped, and in this state Hold for a predetermined time (FIG. 7). This makes it possible to dissolve or detach suspended substances attached to the inside and outside surfaces of the membrane. The amount of the chemical solution supplied to the submerged membrane module 1 is sufficient to allow the chemical solution to ooze out to the outer surface of the membrane, so that it depends on the volume on the secondary side of the submerged membrane module 1 and the volume in the chemical solution supply pipe. Just decide. Further, for the on-off valve 19 and the chemical solution supply valve 21 that are closed after the chemical solution is supplied, the chemical solution having a predetermined chemical solution supply amount that is determined according to the volume on the secondary side of the submerged membrane module 1 and the volume in the chemical solution supply pipe. It is set to be automatically closed when is supplied. Further, the time for holding the chemical solution is preferably 5 minutes to 120 minutes, more preferably 30 minutes to 60 minutes.

  After holding the chemical solution on the secondary side of the submerged membrane module 1 for a certain period of time, the submerged module 1 is submerged in the immersion tank 5 while the chemical solution is held (water to be treated or permeated water is used). (FIG. 8). When the submerged membrane module 1 is filled with water, the supply of water is stopped, the flush valve 15 is opened, and air cleaning is performed with air supplied from the blower 13 via the air diffuser 16 (FIG. 9). ). This air cleaning makes it possible to peel off and remove suspended substances dissolved by the chemical solution and separated from the membrane. Subsequently, the air washing valve 15 is closed, then the blower 13 is stopped, and after the air washing is finished, the discharge valve 18 is opened, and the entire amount of water in the immersion tank is discharged (FIG. 4). At this time, there is no problem even if the discharged water is discharged because the chemical liquid held on the secondary side of the submerged membrane module 1 is hardly mixed. After the discharge of the entire amount of water is completed, the water to be treated is supplied to the dipping tank 5 with the discharge valve 18 kept open. The water to be treated immediately after the supply is discharged out of the immersion tank (FIG. 10). This makes it possible to completely discharge suspended substances remaining in the discharge pipe 17 when the above-mentioned total amount of water is discharged, and to further dilute the chemical solution mixed in a small amount in the discharged water. It becomes possible. The time for discharging the water to be treated is preferably about 1 minute. When about 1 minute has passed since the discharge of the water to be treated, the discharge valve 18 is closed, and the supplied water to be treated is stored in the immersion tank 5 (FIG. 8).

  When the entire submerged membrane module 1 is submerged in the water to be treated supplied to the immersion tank 5, the supply of the water to be treated is stopped, the on-off valve 19 is opened, and the switching valve 23 is opened to the chemical waste pipe side. The liquid remaining on the secondary side of the submerged membrane module 1 is discharged to a waste liquid tank (not shown) by the chemical liquid disposal suction pump 25, and the permeated water is contaminated with the chemical liquid when supplying the chemical liquid. The washing water is also discharged into the waste liquid tank (FIG. 11). Thus, the chemical solution on the secondary side of the membrane module can be discharged without contaminating the immersion tank with the chemical solution. Further, at this time, the amount of permeated water discharged to the waste liquid tank is preferably 5 to 10 times the amount of the chemical solution supplied at the time of chemical cleaning in order to sufficiently clean the secondary side in the submerged membrane module 1 and the inside of the pipe. At this time, the amount of permeated water discharged to the waste liquid tank is much smaller than the amount of rinsing water used in conventional chemical cleaning, and the rinsing water for washing the remaining chemical liquid can be greatly reduced.

  When the cleaning (rinsing) of the submerged membrane module 1 and the remaining chemical solution in the pipe is completed, the switching valve 23 is opened with respect to the permeate pipe side, and the filtration valve 9 of the permeate pipe 7 is opened. Then, the membrane filtration step for obtaining the permeated water by the suction pump 8 is resumed (FIG. 12). Simultaneously with this switching, the chemical liquid disposal suction pump 25 is stopped. In addition, regarding the operation to switch the switching valve 23 from the state opened to the chemical waste pipe side to the state opened to the permeate pipe side, a pH meter, a residual chlorine meter, etc. installed in the chemical waste pipe Automatically measures the pH and residual chlorine concentration of the waste liquid flowing through the pipe, and when the pH becomes neutral or the residual chlorine concentration falls below the reference value, the residual chemical solution in the pipe is washed. It may be determined that it has been removed and switched automatically.

  As the switching valve 23 for switching the pipe from which the chemical liquid or water discharged from the membrane module secondary side flows out from the chemical liquid disposal pipe 24 to the permeate pipe 7, a three-way switching valve may be used. Other switching means may be used as long as such a switching function can be exhibited.

The invention is explained in more detail using the following examples. In the following examples and comparative examples, 3500 polyvinylidene fluoride hollow fiber membranes having an outer diameter of 1.5 mm and a nominal pore diameter of 0.05 μm are accommodated, the upper adhesive end side is open, and the lower adhesive end side is sealed. A cylindrical immersed hollow fiber membrane module (length 1 m, effective membrane area 15 m ² ) having the structure shown in FIG. 1 was used. In this hollow fiber membrane module, both ends of a hollow fiber membrane bundle consisting of 3500 hollow fiber membranes are fixed with an adhesive, a part of one end side of the adhesive fixing part is cut to open the inside of the hollow fiber membrane, It was produced by placing a module cap with a permeate outlet on the adhesive end.

[Example 1]
In the apparatus in which the above immersion membrane module was installed in the immersion membrane filtration apparatus shown in FIG. 3, Lake Biwa water was supplied as raw water, and a membrane filtration operation was performed for one month. As a result, after one month, the permeated water amount of the submerged membrane module decreased to 24.4% in terms of the initial value ratio.

Therefore, chemical cleaning of the submerged membrane module with reduced permeated water amount was performed according to the following procedure.
First, the discharge valve 18 is opened to discharge all of the water to be treated in the immersion tank 5, and then the on-off valve 19 and the chemical solution supply valve 21 are opened, and 1N hydrochloric acid is submerged by the chemical solution supply pump 22. To the secondary side. The total amount of hydrochloric acid supplied at this time was 4 L. This amount substantially corresponds to the total volume in the pipe connected to the submerged membrane module and on the secondary side of the submerged membrane module. Further, the discharge valve 18 was closed when the first 4 L of water was discharged from the start of supplying the chemical solution.

  When 4 L of hydrochloric acid was supplied, the on-off valve 19 and the chemical solution supply valve 21 were closed, and then the chemical solution supply pump 22 was stopped and held in that state for 60 minutes. Subsequently, the water to be treated is supplied to the immersion tank 5 until the immersion membrane module is submerged, the air washing valve 15 is opened, and air washing is performed with air supplied from the blower 13 through the air diffuser 16. For a minute. After completion of the air cleaning, the discharge valve 18 was opened, the entire amount of the water to be treated in the immersion tank 5 was discharged, and the supply of the water to be treated to the immersion tank 5 was started with the discharge valve 18 being opened. When the water to be treated is supplied for 1 minute, the discharge valve 18 is closed, and the water to be treated is continuously supplied to the immersion tank 5. When the immersion membrane module is submerged, the supply of the water to be treated is stopped and the on-off valve 19 is opened. The switching valve 23 was opened with respect to the waste liquid tank side, and 40 L of suction was performed by the chemical liquid disposal suction pump 25 to discharge the hydrochloric acid remaining on the secondary side.

  After chemical cleaning with hydrochloric acid was completed in this way, chemical cleaning with 3,000 mg / L sodium hypochlorite was performed by the same method as described above.

  After all chemical cleaning was completed, membrane filtration was resumed and the amount of permeated water in the submerged membrane module was measured. As a result, the initial value ratio was recovered to 94.7%.

[Comparative Example 1]
As in the case of Example 1, the submerged membrane filtration apparatus shown in FIG. 3 is installed with the submerged membrane module, and Lake Biwa water is supplied as raw water and subjected to a membrane filtration operation for one month. The chemical cleaning was performed by the following procedure for the submerged membrane module in which the permeated water amount decreased to 24.4% of the initial value ratio after the elapse of the month.

  First, the on-off valve 19 and the chemical solution supply valve 21 were opened, and 1N hydrochloric acid was supplied to the secondary side of the submerged membrane module by the chemical solution supply pump 22. The amount of hydrochloric acid supplied at this time was 10 L.

  At the time when 10 L of hydrochloric acid was supplied, the on-off valve 19 and the chemical liquid supply valve 21 were closed, and then the chemical liquid supply pump 22 was stopped and held in that state for 60 minutes.

  Subsequently, the air washing valve 15 was opened, and air washing was performed for 1 minute with air supplied from the blower 13 via the air diffuser 16. After the air cleaning is completed, the discharge valve 18 is opened and all the water to be treated in the immersion tank 5 is discharged. Then, the open / close valve 19 and the backwash valve 12 are opened, and the backwash pump 11 backwashes the submerged membrane module ( Rinse). When backwashing was performed for 150 L, the discharge valve 18 was closed, and backwash water was supplied until the submerged membrane module in the immersion tank 5 was submerged.

  In the above chemical cleaning with hydrochloric acid, the amount of hydrochloric acid supplied to the secondary side is 10 L and the amount of rinse water is 150 L. The amount of hydrochloric acid is 2.5 times that of Example 1, and the rinse water is about 4 times that of Example 1. Double the amount was used. Moreover, in Comparative Example 1, since an excessive amount of hydrochloric acid was supplied to the total volume on the secondary side of the submerged membrane module in the pipe connected to the submerged membrane module, hydrochloric acid was the primary of the submerged membrane module. Since the remaining chemical solution was discharged to the outside through the immersion tank, the immersion tank was contaminated by the chemical solution, and a large amount of rinse water was used to clean (rinse) this chemical solution contamination. Was necessary.

  After completion of chemical cleaning with hydrochloric acid as described above, chemical cleaning with 3,000 mg / L sodium hypochlorite was performed in the same manner as described above.

  In the above chemical cleaning with sodium hypochlorite, as in the case of hydrochloric acid cleaning, the immersion tank was contaminated with a chemical solution, and it was necessary to use a large amount of rinse water.

  After all chemical cleaning was completed, membrane filtration was resumed and the amount of permeated water of the submerged membrane module was measured. As a result, the initial value ratio was recovered to 94.4%.

[Comparative Example 2]
2 is a device in which the immersion membrane module is installed in the immersion membrane filtration device shown in FIG. 2, and Lake Biwa water is supplied as raw water, and the membrane filtration operation is performed for one month. The chemical cleaning was carried out by the following procedure for the submerged membrane module reduced to 24.8% of the ratio.

  First, the discharge valve 18 was opened, and all the water to be treated in the immersion tank 5 was discharged. Next, 1N hydrochloric acid was supplied to the immersion tank 5 until the immersion membrane module was immersed in hydrochloric acid, and the state was maintained for 60 minutes. The amount of hydrochloric acid supplied at this time was 65 L. Then, the air washing valve 15 was opened and air washing was performed for 1 minute with the air supplied from the blower 13 through the air diffuser 16. After air cleaning, the discharge valve 18 is opened, all the hydrochloric acid in the immersion tank 5 is discharged, the open / close valve 19 and the backwash valve 12 are opened, and the backwash pump 11 performs backwashing (rinsing) of the immersion type membrane module. It was. At this time, backwashing for 150 L of backwashing water was performed.

  In the above chemical cleaning with hydrochloric acid, 65 L of hydrochloric acid and 150 L of rinsing water to be supplied to the dipping bath are used, and the amount of hydrochloric acid used is about 16 times that of Example 1, and the rinsing water is about 4 times that of Example 1. Amount used. In Comparative Example 2, since a large amount of hydrochloric acid was supplied into the immersion tank and washed with hydrochloric acid, a wide area in the immersion tank was contaminated with the chemical solution, and a large amount of rinse water is required to clean (rinse) this chemical solution contamination. Met.

  After chemical cleaning with hydrochloric acid was completed, chemical cleaning with 3,000 mg / L sodium hypochlorite was performed in the same manner as described above.

  In the above chemical cleaning with sodium hypochlorite, a large amount of chemical solution is required as in the case of hydrochloric acid cleaning, and a large amount of rinse water is used to clean the contamination in the immersion tank due to the chemical solution. Was necessary.

  When the amount of permeated water of the submerged membrane module was measured after all the chemical cleaning was completed, the initial value ratio recovered to 95.1%.

  The method of the present invention can be applied to chemical cleaning of an immersion type membrane module installed in an immersion tank as it is. Submerged membrane filtration devices equipped with a submerged membrane module are used in, for example, drinking water production in waterworks, industrial water, industrial ultrapure water, food and medical industrial water production fields, municipal sewage purification, and industrial wastewater treatment. It can be used in the wastewater treatment field, but is not limited to these applications.

It is a schematic sectional drawing which shows one embodiment of an immersion type membrane module. It is the schematic which shows one embodiment of the immersion type membrane filtration apparatus which does not provide the chemical cleaning equipment. It is the schematic which shows one embodiment of the immersion type membrane filtration apparatus by this invention. It is the schematic which shows one process at the time of carrying out chemical cleaning of the membrane module in the immersion type membrane filtration apparatus shown in FIG. It is the schematic which shows another 1 process (chemical | medical solution supply process I) at the time of carrying out chemical cleaning of the membrane module in the immersion type membrane filtration apparatus shown in FIG. It is the schematic which shows another 1 process (chemical | medical solution supply process II) at the time of carrying out chemical cleaning of the membrane module in the immersion type membrane filtration apparatus shown in FIG. It is the schematic which shows another 1 process (chemical | medical solution holding process) at the time of carrying out chemical cleaning of the membrane module in the immersion type membrane filtration apparatus shown in FIG. It is the schematic which shows another 1 process (water supply process before air washing | cleaning) at the time of carrying out chemical cleaning of the membrane module in the immersion type membrane filtration apparatus shown in FIG. It is the schematic which shows another 1 process (air washing process) at the time of carrying out chemical cleaning of the membrane module in the immersion type membrane filtration apparatus shown in FIG. It is the schematic which shows another 1 process (processed water supply process) at the time of carrying out chemical cleaning of the membrane module in the immersion type membrane filtration apparatus shown in FIG. It is the schematic which shows another 1 process (chemical | medical solution discharge | emission process) at the time of carrying out chemical cleaning of the membrane module in the immersion type membrane filtration apparatus shown in FIG. It is the schematic which shows the process in which the membrane filtration by a membrane module is performed in the immersion type membrane filtration apparatus shown in FIG.

Explanation of symbols

1: Submerged membrane module 2: Hollow fiber membrane 3, 3 ': Adhesive fixing part 4: Secondary side of membrane 5: Immersion tank 5a: Liquid phase 5b: Sedimented sludge phase 6: Inflow raw water 7: Permeate pipe 8: Suction pump 9: Filtration valve 10: Backwash water pipe 11: Backwash pump 12: Backwash valve 13: Blower 14: Air washing air pipe 15: Air washing valve 16: Air diffuser 17: Discharge pipe 18: Drain valve 19 : On-off valve 20: Chemical liquid supply pipe 21: Chemical liquid supply valve 22: Chemical liquid supply pump 23: Switching valve 24: Chemical liquid disposal pipe 25: Suction pump for chemical liquid disposal

Claims (5)

  A method for cleaning a submerged membrane module installed in a dipping tank for storing the water to be treated, and after discharging the whole amount of water to be treated in the dipping tank, a chemical solution from the permeate outlet of the submerged membrane module When the secondary side in the submerged membrane module is filled with the chemical solution, the chemical solution is stopped and held for a predetermined time, and then the chemical solution is held on the secondary side in the membrane module. As it is, water is supplied into the immersion tank, air is blown out from below the immersion membrane module to perform air cleaning, and then all the water in the immersion tank is discharged, and then the water to be treated is immersed in the immersion tank. A method for cleaning a submerged membrane module, characterized by being supplied into the inside.   The method for cleaning an immersion type membrane module according to claim 1, wherein after the water to be treated is supplied and stored in the immersion tank, the secondary side in the immersion type membrane module is started by starting suction. A method for cleaning a submerged membrane module, wherein the remaining chemical solution on the side is discharged.   3. The method for cleaning an immersion type membrane module according to claim 1 or 2, wherein the remaining permeated water discharged from the secondary side in the immersion type membrane module when a chemical solution is passed through the permeate outlet of the immersion type membrane module. Is discharged out of the immersion tank. A method for cleaning a submerged membrane module. The method for cleaning an immersion type membrane module according to any one of claims 1 to 3, wherein after the entire amount of water in the immersion tank is discharged after air cleaning, the initial portion of the water to be treated supplied into the immersion tank. quantitative or a predetermined time, washing method of submerged membrane module, characterized in that the discharged without accumulating in the dipping bath.   In the washing | cleaning method of the immersion type membrane module in any one of Claims 1-4, the chemical | medical solution supplied to the secondary side in an immersion type membrane module is a sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, a citric acid, ascorbic acid, A method for cleaning an immersion membrane module, which is a chemical solution containing at least one selected from the group consisting of sodium hydroxide, sodium hypochlorite, hydrogen peroxide, and a surfactant.

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