JP2008221178A - Cleaning method of hollow fiber membrane module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cleaning a hollow fiber membrane module capable of preventing twist and entanglement of hollow fiber membranes that may cause insufficient cleaning of its hollow fiber membrane element. <P>SOLUTION: The method for cleaning a hollow fiber membrane module for use in an external pressure filtration method whereby undiluted liquid is supplied to the outer surface side of the hollow fiber membranes and the filtrate is taken out of the inner surface side thereof is characterized by discharging liquid or gas disposed in the undiluted liquid side via an undiluted-liquid discharge port disposed below the hollow fiber membranes while the liquid or the gas is being discharged to the undiluted liquid side by applying pressure to the filtrate side of the hollow fiber membrane keeping the undiluted liquid side of the hollow fiber membrane filled with the liquid. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for cleaning a hollow fiber membrane module.

  In recent years, the development of separation technology using hollow fiber membranes has progressed, and it is widely used for various applications including water filtration. However, in the process of filtration with a hollow fiber membrane, solid matter such as suspended solids in a stock solution called SS adheres to the surface of the hollow fiber membrane or penetrates into the micropores, and the permeation flux decreases with time. . Therefore, in order to continue the filtration operation stably for a long time, it is indispensable to develop a method for cleaning the hollow fiber membrane that is effective at the same time as setting the filtration conditions.

  Conventionally, various methods have been studied as a method for cleaning a hollow fiber membrane module, and these can be roughly classified into a physical cleaning method and a chemical cleaning method. Physical cleaning methods include a method of forcibly removing adhering substances with a sponge ball, high-pressure water flow, etc., a liquid back-washing method in which liquid such as water and permeate is passed from the filtrate side to the stock solution side, and pressurized gas as filtrate. Gas back-washing method (for example, refer to Patent Documents 1 and 2) passing from the side to the stock solution side, pressurizing operation for introducing a gas having a pressure smaller than the pressure at which the gas is released from the stock solution side of the hollow fiber membrane from the filtrate side A wide variety of methods have been proposed, including a bubbling method in which bubbles are ejected to the stock solution side, an ultrasonic method, and an electrophoresis method. As a chemical cleaning method, a method of dissolving and removing deposits with a chemical solution such as an acid, an aqueous alkali solution, or a cleaning agent is known.

  Among these methods, the stock solution is supplied from the outer surface of the hollow fiber membrane, and the physical washing method of the external pressure filtration method in which the filtrate is taken out from the inner surface side of the hollow fiber membrane is a bubbling method in which bubbles are ejected to the stock solution side. Is widely adopted. Further, the bubbling method, the liquid backwashing method, the gas backwashing method, the pressurizing operation and the like may be performed in combination. In particular, the method of carrying out the bubbling after performing the pressurizing operation for introducing a gas having a pressure smaller than the pressure at which the gas is released from the raw solution side of the hollow fiber membrane from the filtrate side is a continuous filtration operation for a long period of time. This is an effective physical cleaning method that enables it (see, for example, Patent Document 3).

  However, when the hollow fiber membrane filtration apparatus is operated by using this cleaning method for the external pressure filtration method in which the stock solution is supplied from the outer surface of the hollow fiber membrane and the filtrate is taken out from the inner surface side of the hollow fiber membrane. It has been found that twists and entanglements occur in the hollow fiber membrane bundle over time, which gradually becomes severe, leading to a reduction in cleaning efficiency, and ultimately possibly reducing the filtration performance of the hollow fiber membrane. It has also been found that there is a possibility of causing membrane damage due to rubbing between hollow fiber membranes due to twisting and entanglement.

  The present inventors have already released the pressure after the pressurizing operation from the filtrate side, and then carried out bubbling, thereby reducing the performance of the hollow fiber membrane due to twisting and entanglement over time due to performing the above method. It was proposed that this can be prevented (see, for example, Patent Document 4). During the pressurizing operation from the filtrate side, the liquid or gas moving from the filtrate side to the stock solution side was discharged from the gas discharge port on the side surface of the filtration container.

Prior art documents related to the present invention include the following.
JP-A-53-108882 Japanese translation of PCT publication 1-500732 Japanese Patent Laid-Open No. 10-286441 JP 2001-29755 A

  However, this method is used when cleaning the external pressure filtration type hollow fiber membrane module in which the stock solution is supplied to the outer surface side of the hollow fiber membrane, that is, the raw water side, and the filtrate is taken out from the inner surface side of the hollow fiber membrane, that is, the filtration side. These liquids flowed out from the gas outlet on the side of the filtration container at once, but it was found that the twisted and entangled phenomenon occurred in the hollow fiber membrane due to the influence of the liquid flow in the module at this time. It was also found that the twists and entanglements expressed here cause the hollow fiber membranes to be rubbed against each other, and cause damage to the hollow fiber membranes.

  The present invention has been made to solve the above-described problems, and has reduced the poor cleaning of the hollow fiber membrane bundle and the hollow fiber membrane damage caused by the twisting and entanglement of the hollow fiber membranes that occur during the pressurizing operation from the filtrate side. It is providing the washing | cleaning method of a hollow fiber membrane module.

  The method for cleaning a hollow fiber membrane module of the present invention that solves the above problems is a hollow fiber used in an external pressure filtration system in which a stock solution is supplied from the outer surface of the hollow fiber membrane and the filtrate is taken out from the inner surface side of the hollow fiber membrane. A method for cleaning a thread membrane module, in which the liquid side of the hollow fiber membrane is filled with liquid and the liquid side or gas is discharged to the stock side by pressurizing the filtrate side of the hollow fiber membrane. This is a method for cleaning a hollow fiber membrane module in which liquid or gas is discharged from a stock solution discharge port provided at the bottom of the hollow fiber membrane.

  In the present invention, the valve opening for discharging from the stock solution outlet provided in the lower part of the hollow fiber membrane is preferably performed simultaneously with the introduction of the pressurized gas from the filtrate side, and the opening is completed when the injection of the pressurized gas is completed. It is preferable to continue to

  According to the method for cleaning a hollow fiber membrane module of the present invention, it becomes possible to reduce poor cleaning of the hollow fiber membrane due to twisting or entanglement of the hollow fiber membrane due to gas pressurization to the filtrate side of the hollow fiber membrane module. It is possible to reduce the load caused by the adhesion of SS to the membrane and to reduce membrane damage caused by rubbing between the hollow fiber membranes.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of an example of an external pressure type hollow fiber membrane module that can be used for performing the method for cleaning a hollow fiber membrane module of the present invention. In this hollow fiber membrane module, the filtration container 1 in which the hollow fiber membrane element 4 is housed is partitioned by a partition plate 2 so that the upper part is the filtrate side A and the lower part is the stock solution side B. The filtrate side A is provided with a filtrate outlet 5 and a pressurized gas introduction port 6, and the stock solution side B is provided with a stock solution introduction port 7, a gas discharge port 8, a gas introduction port 9 and a stock solution discharge port 10. .

  FIG. 2 shows a schematic configuration of a hollow fiber membrane module of the external pressure total filtration system using the hollow fiber membrane module shown in FIG. An example of a method for operating the hollow fiber membrane module to which the present invention is applied will be described with reference to FIG. From a state in which all the valves are closed, the gas discharge port valve 24 and the stock solution introduction port valve 21 are opened, the feed pump is operated to introduce the stock solution to the stock solution side E of the filtration container 25, and the stock solution is supplied from the gas discharge port valve 24. After overflowing, the filtrate outlet valve 23 is opened and the gas outlet valve 24 is closed to start filtration. As the filtration time elapses, the SS component adheres to the membrane surface of the hollow fiber membrane element 26 and the filtration capacity is lowered, so that the hollow fiber membrane module is subsequently washed by the method of the present invention. That is, after stopping the liquid feed pump, the stock solution inlet valve 21 and the filtrate outlet valve 23 opened in the filtration step are closed to stop the filtration, and then the pressurized gas inlet valve 22 is operated while the air compressor 29 is operated. At the same time as opening, not the gas outlet valve 24 but the stock solution outlet valve 27 is opened. The pressure of the pressurized gas necessary for the pressurized gas introduced to the filtrate side D of the hollow fiber membrane to pass through the hollow fiber membrane and escape to the stock solution side E (hereinafter, this pressure is referred to as “bubble point”). The pressurized gas is introduced into the filtrate side D of the filtration container 25 to perform the pressurizing step. By this pressurizing operation, the filtrate in the hollow fiber membrane and the liquid in the filtration container 25 pushed out to the stock solution side through the wall surface of the hollow fiber membrane are discharged from the stock solution outlet valve 27 to the outside. After performing the above pressurization process for a predetermined time, the pressurized gas inlet valve 22 and the stock solution outlet valve 27 are closed, and then the gas outlet valve 24 and the filtrate valve 23 are opened to release the pressure state on the filtrate side D. Then, after a predetermined time has elapsed, the filtrate valve 23 is closed to prevent gas and liquid from moving on the filtrate side D, the stock solution inlet valve 21 is opened, the liquid feed pump is operated, and the inside of the filtration container 25 is operated. Fill with stock solution. When the stock solution overflows from the gas discharge port valve 24, the liquid feed pump is stopped, the stock solution introduction port valve 21 is closed, and then the gas introduction port valve 28 is opened to perform bubbling cleaning for a predetermined time. After the above-described cleaning process is completed, the gas introduction valve 28 is closed, the stock solution outlet valve 27 is opened to discharge the drain, and the process returns to the filtration process.

  In the present invention, in the state where the stock solution outlet valve is opened at the time of pressurizing the filtrate side of the hollow fiber membrane module, gas movement should not ideally occur between the filtrate side and the stock solution side. Gas migration may occur due to poor sealing of the membrane partition plate, hollow fiber membrane leakage, or the like. At this time, the water surface of the filtration container undiluted solution side is lowered, and in some cases, all the liquid may be discharged. In this state, the bubbling washing effect of the subsequent process may be impaired, so the bubbling washing is performed. It is necessary to close the stock solution outlet valve immediately before opening, open the stock solution inlet valve and gas exhaust port valve, and fill the filtration container with the stock solution. The time during which the stock solution inlet valve is opened to fill the filtration container with the stock solution is preferably equal to the time set in the water filling step in the operation process.

In the present invention, the amount of gas supply when performing bubbling washing by introducing gas into the stock solution side of the hollow fiber membrane module after opening the pressurized state and then closing the filtrate side is not particularly limited. Since the membrane cleaning effect is high and the risk of membrane damage is small, it is preferably within the range of 10 to 500 NL / hr per 1 m ² of the effective membrane area of the hollow fiber membrane, and within the range of 20 to 300 NL / hr. It is more preferable. Further, the time for carrying out the bubbling cleaning is preferably within a range of 5 to 120 seconds, and more preferably within a range of 20 to 60 seconds.

  In the present invention, examples of the gas used when performing a pressurizing step for injecting a pressurized gas into the filtrate side of the hollow fiber membrane and a bubbling operation include air and nitrogen. As the pressure of the gas injected in the pressurizing step, it is necessary to set according to the material of the hollow fiber membrane, the pore diameter, the pressure at which the gas passes through the hollow fiber membrane, etc., for example, from a polysulfone resin hydrophilized Thus, when performing a pressurizing operation for injecting a gas having a pressure smaller than the bubble point using a hollow fiber membrane having an average pore diameter of 0.1 μm, the pressure may be within a range of 0.1 to 0.3 MPa. Preferably, the time for performing the pressurizing operation is preferably within a range of 1 to 60 seconds, and more preferably within a range of 5 to 30 seconds.

  The hollow fiber membrane used in the present invention includes polysulfone resin hydrophilized with polyvinyl alcohol resin, polysulfone resin to which hydrophilic polymer is added, polyvinyl alcohol resin, polyacrylonitrile resin, cellulose acetate. It is preferable in that it is made of a hydrophilic material such as a polyethylene resin or a hydrophilized polyethylene resin because it has high hydrophilicity and is excellent in the difficulty of SS component adhesion and exfoliation of the attached SS component. Hollow fiber membranes made of other materials can also be used. For example, polyolefin, polysulfone, polyethersulfone, ethylene-vinyl alcohol copolymer, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, polyperfluoroethylene, polymethacrylate, polyester, polyamide Hollow fiber membranes composed of organic polymer materials such as ceramics, hollow fiber membranes composed of inorganic materials such as ceramics can be selected according to the use conditions, desired filtration performance, etc. . Here, a polysulfone resin hydrophilized with a polyvinyl alcohol-based resin, a polysulfone-based resin to which a hydrophilic polymer is added, or a hollow fiber membrane made of a polyvinyl alcohol-based resin is not only excellent in the above-described hydrophilicity, Since it is excellent also in heat resistance, it is especially preferable. When an organic polymer material is used, it may be a copolymer obtained by copolymerizing other components in an amount of 30 mol% or less, or a blend of other materials in an amount of 30 wt% or less.

  When an organic polymer hollow fiber membrane is used, the method for producing the hollow fiber membrane is not particularly limited, and a method appropriately selected from known methods depending on the characteristics of the material and the desired hollow fiber membrane performance Can be adopted. Generally, a melt spinning method, a wet spinning method, a dry / wet spinning method, or the like is employed. From the viewpoint of water permeability, the hollow fiber membrane preferably has an asymmetric structure having a dense layer and a support layer. However, since a hollow fiber membrane generally produced by a melt spinning method has a symmetrical structure, wet spinning is preferable. It is preferable to produce by a phase change method such as a method or a dry-wet spinning method.

  The pore diameter of the hollow fiber membrane used in the present invention is not particularly limited, but it is preferably in the range of 0.001 to 5 μm because it has high water permeability and is less likely to reduce the filtration efficiency. Here, the pore diameter refers to the particle diameter of a reference material from which 90% is excluded when various reference substances with known particle diameters such as colloidal silica, emulsion, and latex are filtered through a hollow fiber membrane. The pore diameter is preferably uniform. With an ultrafiltration membrane, it is impossible to determine the pore size based on the particle size of the reference material as described above. However, when a similar measurement is performed using a protein with a known molecular weight, Those having a molecular weight of 3000 or more are preferred.

  From the viewpoint of the mechanical properties of the hollow fiber membrane and the membrane area as a module, the outer diameter of the hollow fiber membrane is preferably set in the range of 200 to 3000 μm, and more preferably in the range of 500 to 2000 μm. Similarly, the thickness of the hollow fiber membrane is preferably in the range of 50 to 700 μm, and more preferably in the range of 100 to 600 μm.

  In the present invention, the hollow fiber membrane is modularized and used for filtration. The form of the module can be appropriately selected according to the filtration method, filtration conditions, washing method, and the like, and a hollow fiber membrane module may be configured by mounting one or a plurality of hollow fiber membrane elements. As the form of the module, for example, several tens to hundreds of thousands of hollow fiber membranes are bundled into a U-shape in the module, and one end of the hollow fiber membrane bundle is collectively sealed with an appropriate sealing material , One end of the hollow fiber membrane bundle is fixed together, and the other end is a free state in which the hollow fiber membranes are not fixed to each other in a free state. And the like. Further, the shape of the hollow fiber membrane module is not particularly limited, and may be, for example, a cylindrical shape or a screen shape. In the cleaning method of the present invention, the hollow fiber membrane is twisted or entangled and the resulting damage to the hollow fiber membrane is small, a high membrane surface cleaning effect is exhibited, and the discharged SS can be discharged very easily. It is particularly preferable to use a one-end free type hollow fiber membrane module in which one end, particularly the lower end, of the yarn membrane bundle is free.

  In the present invention, the hollow fiber membrane is housed in one or a plurality of hollow fiber membrane elements, and the hollow fiber membrane elements are fixed in the housing, but the fixing method is not particularly limited. For example, the hollow fiber membrane element may be bonded to the housing, and the cartridge type hollow fiber membrane element may be fixed to the housing with a metal fitting or the like.

  The method for cleaning the hollow fiber membrane module of the present invention may include other steps such as a step of cleaning the surface of the hollow fiber membrane and the inside of the hollow fiber membrane module by repeating drain discharge and full water, and a flushing cleaning step, as required. It is also possible to add a process.

  The hollow fiber membrane can be washed with a chemical solution after filtration or back washing to dissolve and remove organic substances, inorganic substances, etc. adhering to the hollow fiber membrane. Here, as a chemical cleaning method, a method of treating with an alkali such as an aqueous sodium hydroxide solution to remove organic substances, inorganic materials, a method of treating with an acid such as an acid aqueous solution to remove metals, and a cleaning agent There are a method of treating with, a method of continuously carrying out a combination of these, and the hollow fiber membrane can be regenerated.

  A series of operations such as the filtration step, the gas pressurization step, the bubble washing step, and the chemical solution washing step described so far can be automatically performed by performing sequence control. For example, after filtration for a certain period of time, pressurization with gas and cleaning of the membrane surface with bubbles are performed once or several times, followed by water washing once or several times as necessary, and then chemical solution cleaning. This washing process can be performed automatically and continuously by sequence control, and the operation can be continued stably for a long period of time while alternately repeating the filtration and the washing process of the hollow fiber membrane and the filtration line. It is also possible to continue the operation stably for a long period of time by a so-called select switch method in which the filtration step and the washing step are continuously repeated by sequence control, and the back washing is manually performed when clogging becomes large.

  The cleaning method of the present invention is effective when the filtrate side of the hollow fiber membrane is pressurized with a gas having a pressure smaller than the puff point of the hollow fiber membrane in a state where the liquid side of the hollow fiber membrane is filled with liquid. Since it is expressed, stable filtration can be performed continuously for a long time with a higher permeation flux than ever before in a wide range of applications, including purification of river water, well water, lake water, etc. It is. For example, in the food industry, sterilization / iron removal / manganese removal of raw water, sterilization / fine particle removal of cleaning water, sterilization / fine particle removal of natural water, sterilization / purification of soy sauce, sterilization / purification of sake , Vinegar sterilization / purification, mirin purification, seasoning sterilization / purification, product recovery from brewing oil, sugar solution sterilization / fine particle removal / purification, honey purification, enzyme / protein purification / concentration, Purification of fermentation broth, recovery and purification of protein from cheese whey, production of high-protein milk by concentrating milk, recovery of protein from fishery processing wastewater, concentration of fish protein, recovery of meat protein from meat processing waste, pork Separation of red blood cells from blood, concentration and purification of albumin and globulin in blood, recovery and purification of physiologically active substances from soybean whey, recovery of protein from soybean juice, oil protein toxin removal and protein concentration, potato starch industrial wastewater from Used for applications such as protein recovery, natural pigment recovery and purification, various enzyme recovery and purification, clarification and sterilization of liquid beverages, concentration of citrus and apple peptin solutions, and purification of fermentation broth by recovery of bacterial cells and metabolites Yes, in the medical field, pretreatment of pure water and ultrapure water production equipment, cleaning water pyrogen removal, injection water production, dialysis water production, dialysate purification, vaccines, enzymes, viruses, nucleic acids, proteins It can be used for applications such as separation, concentration and purification of physiologically active substances such as hormone purification, artificial blood production, polysaccharide concentration and purification, hospital hand washing water sterilization, surgical instrument washing water sterilization, In the electronics industry, reverse osmosis membrane pretreatment, ultrapure water final filter, ultrapure water use point filter, ultrapure water unit built-in filter, cleaning water particulate removal, It can be used for applications such as polishing wastewater recovery and dicing wastewater recovery. In the chemical industry, paint concentration / recovery, oil agent separation / recovery, emulsion separation / recovery, colloid separation / recovery, fine powder It can be used for applications such as washing and purification, removal of washing water particulates, plating solution purification, and electrodialysis pretreatment. In the water treatment field, it removes MLSS from the waterworks, tertiary treatment of wastewater, and collection and reuse of wastewater. It can be used for applications such as purification of nuclear power generation wastewater and removal of bacteria. In the field of textile and dyeing processing, the closure of PVA desizing wastewater, recovery and reuse of textile processing oil, and the use of lanolin from hair washing wastewater. It can be used for purposes such as recovery and recovery of sericin from silk processing wastewater. In the steel and machining field, barrel polishing wastewater recovery, buffing wastewater recovery, rolling oil drainage treatment, water-soluble cutting Use for applications such as cutting oil drainage treatment, animal and vegetable oil processing wastewater treatment, removal of emulsion from degreasing washing wastewater, recovery of cleaning agent, removal of emulsion in rinse water, recovery of rinse water, and removal of ink from screen plate cleaning agent. Further, it can be used for applications such as steam drain recovery and purification of hot refrigerant water in an air conditioning system using a heat storage tank.

  Examples of the present invention will be described below, but the present invention is not limited thereby. From the results of the following examples, according to the present invention, twisting and entanglement of the hollow fiber membrane that is manifested in the hollow fiber membrane washing step can be suppressed, thereby reducing the reduction in the removal efficiency of the SS component adhering in the filtration step. It is clear that

Using a hollow fiber membrane module of “one end free” type having a membrane area of 7.0 m ^{2 made} of a hollow fiber membrane made of a polysulfone-based resin and having an average pore diameter of 0.02 μm and a bubble point of 0.5 MPa or more, A constant flow rate filtration was performed under the conditions of an external pressure total filtration method and a filtration rate of 0.58 m ³ / hr using a river surface water having a temperature of 19 to 27 ° C. and a turbidity of 0.88 to 3.30 degrees as raw water. The hollow fiber membrane is washed once every 30 minutes by sequence control, with the pressure of 10 MPa applied by introducing air at a pressure of 0.2 MPa to the filtrate side of the hollow fiber membrane module with the stock solution outlet valve opened. After that, close the stock outlet valve, open the filtrate outlet valve and gas outlet valve and release the pressurized state for 5 seconds, then close the filtrate outlet valve and press from the lower part of the hollow fiber membrane module on the stock side 0.1 MPa air was ejected at a flow rate of 0.6 Nm ³ / hr for 1 minute. The state of the hollow fiber membrane element after the filtrate-side gas introduction step is a state in which the hollow fiber membrane element is bundled without any twisting or entanglement, and the subsequent washing by air ejection (bubbling washing) from the lower part of the filtration container is efficiently performed. It was in a state that could be expected sufficiently. During the filtration operation, when the transmembrane pressure difference is measured periodically and the filtration time until the transmembrane pressure difference reaches 0.1 MPa is defined as the filtration life of the hollow fiber membrane module, the filtration life is 125 days. . rchukushi

Comparative Example In the example, when air having a pressure of 0.2 MPa was introduced into the filtrate side of the hollow fiber membrane module, the side gas outlet valve was opened instead of the raw water outlet valve at the lower part of the filtration container. After this step, the hollow fiber membrane element is twisted and entangled, and then rises in the step of ejecting air at a pressure of 0.1 MPa from the lower portion of the filtration container for 1 minute at a flow rate of 0.6 Nm ³ / hr. Air was hard to shake the twisted or entangled element. During the filtration operation, when the transmembrane pressure difference is measured periodically and the filtration time until the transmembrane pressure difference reaches 0.1 MPa is defined as the filtration life of the hollow fiber membrane module, the filtration life is 103 days. .

It is a figure which shows an example of the external pressure type | mold hollow fiber membrane module utilized for implementation of the washing | cleaning method of the hollow fiber membrane module of this invention. It is a figure which shows an example of the filtration apparatus which uses the external pressure type | mold hollow fiber membrane module of FIG.

Explanation of symbols

A, D: Filtrate side B, E ... Stock solution side 1, 25 ... Filtration container 2 ... Partition plate 4, 26 ... Hollow fiber membrane element 5 ... Filtrate outlet 6 ... Pressurized gas inlet 7 ... Stock solution inlet 8 ... Gas exhaust Outlet 9 ... Gas inlet 10 ... Stock solution outlet 21 ... Stock solution inlet valve 22 ... Pressurized gas inlet valve 23 ... Filtrate outlet valve 24 ... Gas outlet valve 27 ... Stock solution outlet valve 28 ... Gas inlet valve 29 ... Air Compressor

Claims (4)

A washing method for a hollow fiber membrane module used in an external pressure filtration system in which a stock solution is supplied to the outer surface side of the hollow fiber membrane and a filtrate is taken out from the inner surface side of the hollow fiber membrane, While the liquid is filled, pressurize the filtrate side of the hollow fiber membrane to discharge the liquid or gas to the stock solution side, while discharging the liquid or gas on the stock solution side from the stock solution outlet provided at the bottom of the hollow fiber membrane. A method for cleaning a hollow fiber membrane module.
2. The hollow fiber membrane according to claim 1, wherein when the filtrate side of the hollow fiber membrane is pressurized in a state where the liquid side of the hollow fiber membrane is filled with liquid, the hollow fiber membrane is pressurized with a gas having a pressure smaller than a puff point of the hollow fiber membrane. How to clean the module.
The method for cleaning a hollow fiber membrane module according to claim 1 or 2, wherein after the liquid or gas is discharged to the stock solution side, the pressurization on the filtrate side is released, and then the raw water side is filled with the raw water.
The hollow fiber membrane module is a single-end free-type hollow fiber membrane module in which the upper ends of the hollow fiber membrane bundle are fixed together and the lower ends are sealed one by one without fixing the hollow fiber membranes to each other. Item 4. The method for cleaning a hollow fiber membrane module according to any one of Items 1 to 3.

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