JP7088493B2 - How to clean the hollow fiber membrane - Google Patents

Description

The present invention relates to a method for cleaning a hollow fiber membrane used when purifying the waste liquid discharged from the cultivation of agricultural products by nutrient solution for reuse in cultivation.

Conventionally, in order to circulate and use the nutrient solution in hydroponic cultivation, various germs and the like have propagated in the nutrient solution after use, and it is necessary to remove these germs and the like in order to prevent diseases of agricultural products. be. In addition, since a large amount of organic substances such as fertilizers are present in the nutrient solution after use, sufficient sterilization effect cannot be obtained even by irradiation with ultraviolet rays or addition of silver ions, and sterilization by a filtration device using a hollow fiber membrane is used. Is being considered. However, it is known that the hollow fiber membrane is clogged by long-term use, and especially in the drainage after use for hydroponic cultivation, there are many organic substances such as fertilizers as well as germs as described above. Because it was included, it was more likely to be clogged.

Generally, for cleaning the hollow fiber membrane, backflow cleaning in which a liquid or gas flows back from the permeated water side to the raw water side, a method of flushing the membrane surface on the raw water side, and the like are known.

For example, Patent Document 1 describes a cleaning method in a water purification system, in which a mixed aqueous solution containing citric acid and a detergent is used to flush the surface of a separation membrane such as a hollow fiber membrane on the raw water side from the permeate water side. A cleaning method in which one or both of the backflow cleanings are performed on the raw water side is disclosed.

JP-A-2007-869

However, the cleaning method disclosed in Patent Document 1 is used in a separation membrane for obtaining purified water from river water, and is for removing a poorly water-soluble substance adhering to the raw water side of the separation membrane. By being used in hydroponic cultivation, sufficient cleaning and sterilizing effects can be obtained for hollow fiber membranes that have been filtered from the drainage of nutrients that contain not only germs but also organic substances such as fertilizers. In the backflow cleaning, there is a problem that the pores of the hollow fiber membrane are widened and the life is shortened.

Therefore, in the present invention, the hollow fiber membrane is filtered even for the hollow fiber membrane obtained by filtering the waste liquid of the nutrient solution containing a large amount of organic substances such as fertilizer as well as various germs by being used in the nutrient solution cultivation. It is an object of the present invention to provide a method for cleaning a hollow fiber membrane capable of eliminating clogging or the like that causes a decrease in capacity.

[1] That is, the method for cleaning the hollow thread film in the present invention is a method for cleaning the hollow thread film carried out by a filtering device that filters the drainage of nutrient solution cultivation with the hollow thread film, and is the same as the above-mentioned drainage. A flashing step in which the raw water side of the hollow thread film to be abutted is poured by the drainage liquid at a flow rate higher than that at the time of filtration, and the cleaning liquid heated to 25 to 45 ° C. is filtered at 0.1 to 1.0 MPa. 2 . Between the cleaning liquid tank in which the cleaning liquid is stored and the filtering device, the cleaning liquid heated to 25 to 45 ° C. after the soaking step of keeping the temperature at 1 to 1.0 MP a and allowing it to stand still. The flushing step by the drainage is more than a series of steps of the heating and pressurizing impregnation step, the soaking step, and the circulation step by the cleaning liquid. It is a method for cleaning a hollow thread film, which is carried out in a short cycle.

[2] The method for cleaning a hollow fiber membrane according to the above [1], wherein the cleaning liquid is an alkaline cleaning liquid or a chlorine-based cleaning liquid.

As described above, according to the present invention, the hollow fiber membrane obtained by filtering the drainage of the nutrient solution containing a large amount of organic substances such as fertilizer as well as various germs by being used in the hydroponic cultivation can be obtained. It is possible to eliminate clogging and the like that cause a decrease in the filtration capacity of the material.

It is a block diagram which shows the outline of the apparatus which uses the cleaning method of this invention. It is a figure which shows the opening and closing of a valve for carrying out the cleaning method of this invention. It is a graph which shows the filtration amount of the hollow fiber membrane when the cleaning method of this invention is used.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. Since the embodiments described below are preferable specific examples for carrying out the present invention, various technical restrictions are made, but the present invention is particularly limited in the following description. Unless otherwise stated, it is not limited to these forms. In addition, the description indicating the numerical range includes the upper limit and the lower limit.

FIG. 1 shows a schematic diagram of an apparatus or the like used for hydroponic cultivation, and a drain tank 3 for storing drainage discharged after cultivating agricultural products in a nutrient solution medium (not shown) and a drain tank. To clean the filtration device 1 that filters the waste liquid sent from the liquid 3, the filtration tank 4 that stores the filtrate that is filtered by the filtration device 1 and is supplied to the nutrient solution medium again, and the filtration device 1. It is provided with a cleaning liquid tank 2 in which the cleaning liquid of the above is stored, and is also provided with a pipe for connecting those facilities and valves SV1 to SV9 for allowing or preventing the passage of the pipe.

(Filtration device)
The filtration device 1 is a device for filtering the waste liquid discharged after cultivating agricultural products, and is provided with a hollow fiber membrane 11 inside, and the hollow fiber membrane 11 is substantially used for filtration. Will be. In FIG. 1, two hollow fiber membranes 11 are arranged in series, but in another embodiment, one hollow fiber membrane 11 may be arranged or two hollow fiber membranes 11 may be arranged in parallel. Three or more units may be arranged in series or in parallel.

(Hollow fiber membrane)
The hollow fiber membrane 11 has an elongated tubular structure having a plurality of fine holes on the side surface. In the filtration device 1, as shown in FIG. 1, a plurality of hollow fiber membranes 11 are arranged side by side and modularized. Generally, the outer wall side of the hollow fiber membrane is the raw water side, and the filtered water is permeated to the inner wall side. However, in the hollow fiber membrane adopted in the present invention, the inner wall of the hollow fiber membrane 11 is the raw water side and is nourished. As for the drainage of the liquid, the one that passes through the inside of the hollow fiber membrane 11 and permeates the hollow fiber membrane 11 becomes filtered water, and the one that is discharged from the hollow fiber membrane 11 without being filtered becomes concentrated water.

Here, as the material of the hollow thread film 11, a polysulfone resin treated to be hydrophilic with a polyvinyl alcohol resin, a polyvinylidene fluoride resin, a polysulfone resin injected with a hydrophilic polymer, a vinylidene fluoride resin, and the like. Hydrophilic materials such as polyvinyl alcohol-based resin, polyacrylonitrile-based resin, cellulose acetate-based resin, and hydrophilized polyethylene-based resin make it difficult for organic substances contained in the drainage of nutrient solution to adhere and make them peelable. Although it is preferable in that it is excellent, a hollow thread film made of another material can also be used. For example, it is composed of organic polymer-based materials such as polyolefin-based, polysulfone-based, polyethersulfone-based, cellulose acetate-based, polyvinylidene fluoride-based, polyperfluoroethylene-based, polymethacrylic acid ester-based, polyester-based, and polyamide-based materials. Hollow fiber membranes, hollow fiber membranes made of inorganic materials such as ceramics, and the like can be selected according to usage conditions, desired filtration performance, and the like.

When an organic polymer-based 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 according to the characteristics of the material and the desired hollow fiber membrane performance. Can be selected. Generally, a melt spinning method, a wet spinning method, a dry wet spinning method and the like are adopted. Further, from the viewpoint of water permeability, the hollow fiber membrane preferably has an inclined structure having a dense layer and a support layer, but since the hollow fiber produced by the melt spinning method generally has a symmetrical structure, a dry-wet spinning method is used. It is preferable to manufacture by a phase conversion method such as.

The pore size of the hollow fiber membrane 11 used in the present embodiment is not particularly limited, but it is in the range of 0.001 to 5 microns because it has high water permeability and there is little possibility that the filtration efficiency is lowered. preferable. The pore size referred to here refers to the particle size of a reference substance such as colloidal silica, of which 90% of which is excluded when the hollow fiber membrane 11 filters various reference substances having a known particle size. The pore diameter is preferably uniform.

(Cleaning liquid tank)
The cleaning liquid tank 2 is a tank for storing a cleaning liquid for cleaning the hollow fiber membrane 11. As shown in FIG. 1, the cleaning liquid stored in the cleaning liquid tank 2 is sent to the filtration device 1 by the liquid feeding pump P2. A heater H is provided in the lower portion of the cleaning liquid tank 2, and the cleaning liquid stored in the cleaning liquid tank 2 can be heated to a predetermined temperature. Regarding the control of the heater H, the temperature control device C connected to the heater H is connected to a control device (not shown) and operates according to the type of cleaning to heat or heat the cleaning liquid to the heater H. Not done or controlled.

Further, a liquid level sensor S1 is provided inside the cleaning liquid tank 2 so as to be in contact with the cleaning liquid, and when the amount of storage in the cleaning liquid tank 2 becomes larger or less than a predetermined amount, it becomes a control device (not shown). You can be notified.

The cleaning liquid tank 2 is connected to the chemical tank 21 by a pipe, and the chemical tank 21 stores a chemical stock solution for cleaning such as an alkaline chemical or a chlorine-based chemical. Chemicals such as alkaline chemicals or chlorine-based chemicals are supplied from the chemical tank 21 to the cleaning liquid tank 2, and water supplied from the water supply device WS passes through the second valve SV2, the filtration device 1, each pipe, and the like. Further, by passing through at least one of the fourth valve SV4 or the ninth valve SV9 and the eighth valve SV8 and each pipe, the pipes and the filtering device 1 are washed with water and supplied to the cleaning liquid tank 2, the inside of the cleaning liquid tank 2 The chemical is diluted with to adjust an alkaline cleaning solution or a chlorine-based cleaning solution. The alkaline cleaning liquid is a cleaning liquid having an alkaline pH of 9 to 14 at 25 ° C., and the chlorine-based cleaning liquid is a cleaning liquid containing a chlorine compound such as sodium hypochlorite.

(Drainage tank)
The drainage tank 3 is a tank for storing the drainage liquid discharged after cultivating a crop in a nutrient solution medium (not shown), and is connected to the nutrient solution medium by a pipe. The drainage in the drainage tank 3 is discharged from the drainage tank 3 to the pipe leading to the filtration device 1 by the liquid feed pump P1. The discharged effluent passes through the filter F1, the filter F2, and the filter F3 in order, and various impurities contained in the effluent are stepwise removed. Specifically, the filters F1, the filter F2, and the filter F3 have smaller voids in order in the range of 0.1 to 100 μm, and impurities having a large diameter that do not dissolve in the effluent are removed in order. The filter F1, the filter F2, and the filter F3 are each physically replaceable, and when a pressure difference of a predetermined value or more occurs in the pressure gauges G1 and G2 after being used for a certain period of time, the filter F1 and the filter F2 are used. , It is determined that the filter F3 is clogged, and the filter F1, the filter F2, and the filter F3 can be replaced with new ones. Then, the drainage liquid that has passed through the filter F1, the filter F2, and the filter F3 passes through the first valve SV1 and is sent to the filtration device 1.

Then, to the drainage tank 3, the concentrated liquid concentrated in the filtration device 1 without penetrating the hollow fiber membrane 11 passes through the ninth valve SV9, and at least one of the sixth valve SV6 or the seventh valve SV7 is pressed. Piping is connected so that it can pass through and come back. In this way, the concentrated liquid returned to the drainage tank 3 can be sent to the filtration device 1 again, and the amount of liquid to be discarded can be reduced. In addition, the concentrated liquid that cannot be reused due to an increase in the concentration of unnecessary components dissolved in the drainage due to being sent to the filtration device 1 multiple times is drained to the outside of the system through the fifth valve SV5. You can also do it.

Further, a liquid level sensor S2 is provided inside the drainage tank 3 so as to be in contact with the drainage, and is not shown when the amount of storage in the drainage tank 3 becomes larger or less than a predetermined amount. The control device can be notified.

(Filtration tank)
The filtration tank 4 is a tank for storing the filtrate filtered by the filtration device 1. The filtrate filtered by the filtration device 1 passes through the third valve SV3, passes through the flow meter FM, and is stored in the filtration tank 4. Then, the filtrate stored in the filtration tank 4 can be sent to a nutrient solution medium (not shown), crops can be cultivated again, and the drainage can be circulated and used.

Further, a liquid level sensor S3 is provided inside the filtration tank 4 so as to be in contact with the drainage liquid, and when the amount of storage in the filtration tank 4 becomes larger or less than a predetermined amount, a control device (not shown) is not shown. Can be notified to.

(How to clean the hollow fiber membrane)
The method for cleaning the hollow fiber membrane 11 is carried out by combining a flushing step, a heating / pressurizing impregnation step, a soaking step, a circulation step and the like.

(Flushing process)
The flushing step is a step in which the raw water side of the hollow fiber membrane 11 in contact with the drainage liquid is flushed with the drainage liquid at a flow rate higher than that at the time of filtration. For example, in the case of the hollow fiber membrane 11 that filters from the inner wall side to the outer wall side, the inner wall side of the hollow fiber membrane 11 is the raw water side. Specifically, as shown in FIGS. 1 and 2, the second valve SV2, the third valve SV3, with the first valve SV1, the ninth valve SV9, the sixth valve SV6, and the seventh valve SV7 open. With the fourth valve SV4, the fifth valve SV5, and the eighth valve SV8 closed, the drainage from the drainage tank 3 is discharged by the operation of the liquid feed pump P1, and the hollow fiber membrane 11 in the filtration device 1 is discharged. This is a step of passing liquid through the raw water side of the above water at a higher flow rate than when filtering, and returning to the drainage tank 3. In this way, by flowing the raw water side of the hollow fiber membrane 11 using the drainage liquid, impurities such as organic fine particles staying around the fine pores of the hollow fiber membrane 11 can be physically removed. The first valve SV1 to the ninth valve SV9 are solenoid valves, and a predetermined program is executed according to an instruction in a control device (not shown) connected to them, and the opening and closing of those valves is controlled. In this case, it is possible to manage the normal operating state by making it possible to remotely monitor the open / closed state of each valve.

(Heating and pressurizing impregnation process)
The heating / pressurizing impregnation step is a step of sending the cleaning liquid heated to 25 to 45 ° C. to the filtration device 1 at 0.1 to 1.0 MPa. Specifically, as shown in FIGS. 1 and 2, with the fourth valve SV4 and the eighth valve SV8 open, the first valve SV1, the second valve SV2, the third valve SV3, and the fifth valve SV5, With the sixth valve SV6, the seventh valve SV7, and the ninth valve SV9 closed, the cleaning liquid heated to 25 to 45 ° C. by the heater H is discharged from the cleaning liquid tank 2 by the operation of the liquid feed pump P2. This is a cleaning step in which a liquid is passed from the raw water side of the hollow fiber membrane 11 in the filtration device 1 to the filtration side, that is, in the direction of filtering through the fine pores of the hollow fiber membrane 11 at a water pressure of 0.1 to 1.0 MPa. .. In this way, by passing the fine pores of the hollow fiber membrane 11 in the filtration device 1 using the cleaning liquid heated to a predetermined temperature, the organic fine particles clogged in the fine pores of the hollow fiber membrane 11 Impurities such as these can be sufficiently impregnated with the cleaning liquid for cleaning.

The temperature of the cleaning liquid is preferably heated to 25 to 45 ° C, more preferably 30 to 40 ° C. When the temperature of the cleaning liquid is within this range, impurities such as organic fine particles clogged in the fine pores of the hollow fiber membrane 11 can be sufficiently dissolved or decomposed, and components such as chlorine compounds dissolved in the cleaning liquid can be sufficiently dissolved or decomposed. It can be volatilized to reduce the cleaning effect and prevent adverse effects on the working environment. On the other hand, the alkaline compound is hard to volatilize, but the same cleaning effect can be obtained by heating in the above temperature range.

The pressure for sending the cleaning liquid to the filtration device 1 is preferably 0.1 to 1.0 MPa, preferably 0.15 to 0.5 MPa so that the pressure becomes higher within the allowable pressure of the hollow fiber membrane. Is even more preferable. When the pressure for sending the cleaning liquid to the filtration device 1 is within this range, the fine pores of the hollow fiber membrane 11 in the filtration device 1 can be passed through, and the hollow fiber membrane 11 is clogged in the fine pores. Impurities such as organic fine particles can be sufficiently impregnated with the cleaning liquid for cleaning.

(Pickling process)
The soaking step is a step of keeping the cleaning liquid at 0.1 to 1.0 MPa and allowing it to stand in the liquid feeding path. Specifically, at the time of cleaning in the heating / pressurizing impregnation step, the cleaning liquid heated to 25 to 45 ° C. by the heater H is discharged from the cleaning liquid tank 2 by the operation of the liquid feed pump P2, and then 0.1 to After passing the liquid from the raw water side of the hollow fiber membrane 11 in the filtration device 1 to the filtration side, that is, in the direction of filtering the fine pores of the hollow fiber membrane 11 with a water pressure of 1.0 MPa, it is shown in FIGS. 1 and 2. As described above, the ninth valve SV9 is open, the first valve SV1, the second valve SV2, the third valve SV3, the fourth valve SV4, the fifth valve SV5, the sixth valve SV6, the seventh valve SV7, and the eighth valve. This is a step in which the SV 8 is closed, the pressurized state is maintained for about 2 to 4 hours, and the hollow fiber membrane 11 in the filtration device 1 is immersed in a cleaning liquid. By keeping the cleaning liquid heated to a predetermined temperature at a predetermined pressure in this way, impurities such as organic fine particles adhering to the fine pores of the hollow fiber membrane 11 in the filtration device 1 are chemically dissolved or dissolved. It can be disassembled and removed.

The temperature of the cleaning liquid is preferably heated to 25 to 45 ° C, more preferably 30 to 40 ° C. When the temperature of the cleaning liquid is within this range, impurities such as organic fine particles adhering to the fine pores of the hollow fiber membrane 11 can be sufficiently dissolved or decomposed, and components such as chlorine compounds dissolved in the cleaning liquid can be sufficiently dissolved or decomposed. It can be volatilized to reduce the cleaning effect and prevent adverse effects on the working environment.

Further, the pressure of the cleaning liquid is preferably kept at 0.1 to 1.0 MPa so as to be higher within the allowable pressure of the hollow fiber membrane, and more preferably 0.15 to 0.5 MPa. When the pressure for sending the cleaning liquid to the filtration device 1 is within this range, the hollow fiber membrane 11 in the filtration device 1 can be immersed in the fine pores and adheres to the fine pores of the hollow fiber membrane 11. The cleaning liquid can be sufficiently impregnated with impurities such as organic fine particles, and can be dissolved or decomposed.

(Circulation process)
The circulation step is a step of sending the cleaning liquid heated to 25 to 45 ° C. so as to circulate between the cleaning liquid tank 2 in which the cleaning liquid is stored and the filtration device 1. Specifically, as shown in FIGS. 1 and 2, the first valve SV1, the second valve SV2, and the third valve SV3 are in a state where the fourth valve SV4, the eighth valve SV8, and the ninth valve SV9 are open. With the fifth valve SV5, the sixth valve SV6, and the seventh valve SV7 closed, the cleaning liquid heated to 25 to 45 ° C. by the heater H is discharged from the cleaning liquid tank 2 by the operation of the liquid feed pump P2. , The direction of filtering from the raw water side of the hollow fiber membrane 11 in the filtration device 1 to the filtration side, that is, through the fine pores of the hollow fiber membrane 11, and the concentration side from the raw water side, that is, the hollow fiber membrane 11 does not filter. This is a step of repeating the step of passing the liquid in the direction of the ninth valve SV9 and returning to the cleaning liquid tank 2 for a predetermined time. In this way, by circulating and passing the liquid through the filtration device 1 from the cleaning liquid tank 2 using the cleaning liquid heated to a predetermined temperature, the hollow fiber membrane 11 may be clogged or adhered to the inside of the fine holes and the wall surface. Impurities such as organic fine particles can be chemically dissolved or decomposed to remove them. Further, the temperature of the cleaning liquid is preferably 25 to 45 ° C., more preferably 30 to 40 ° C., as in the heating / pressurizing impregnation step.

By repeating these steps regularly, it is possible to eliminate clogging that causes a decrease in the filtration capacity of the hollow fiber membrane 11, and it is possible to maintain the filtration amount of the hollow fiber membrane 11 within a certain range. can. Further, the degree of contamination of the hollow fiber membrane 11 differs depending on the type of the crop to be cultivated in the time interval or the washing cycle in which the steps such as the heating and pressurizing impregnation step are carried out. It can be set arbitrarily according to.

In this way, by a cleaning method that combines these flushing steps, heating and pressurizing impregnation steps, soaking steps, circulation steps, etc., clogging that causes a decrease in the filtration capacity of the hollow fiber membrane 11 can be eliminated. The filtration amount of the hollow fiber membrane 11 can be maintained within a certain range. Further, in addition to these steps, it is also possible to combine a step of supplying water such as tap water from the water supply device WS and washing the hollow fiber membrane 11 in the filtration device 1 with water.

In addition, the operation of opening and closing each valve and the implementation of each process in a remote place physically separated from the place where the filtration device 1, the cleaning liquid tank 2, the drainage tank 3, the filtration tank 4, and each valve are provided. And management such as monitoring of the implementation status of those processes can be performed. For example, a control device (not shown) may be installed in a remote location from the filtration device 1 or the like to operate the control device, or a control device (not shown) may be installed in a place where the filtration device 1 or the like is provided. It can also be installed and managed by operating an information terminal that is connected to the control device by wire or wirelessly at a remote location. In this way, by performing management even in a remote location, the operator does not need to be at the actual site, and a plurality of systems including the filtration device 1 installed in a plurality of locations are centrally managed. It has the effect of being able to do it.

<Example 1>
Hydroponic cultivation of agricultural products was carried out in an agricultural greenhouse, and the hollow fiber membrane 11 in the filtration device 1 was washed using the drainage liquid and the washing liquid as follows. That is, a flushing step is carried out in a 10-minute cycle, and a heating / pressurizing impregnation step is carried out in which a cleaning liquid heated to 35 ° C. is sent to the filtration device 1 at 0.2 MPa in a 3-day cycle. After impregnation, it was soaked and washed for 2 hours, and then circulated and washed for 20 minutes.

<Comparative Example 1>
The hollow fiber membrane 11 in the filtration device 1 was washed in the same manner as in Example 1 except that the heating / pressurizing impregnation step and the circulation step were not performed.

<Comparative Example 2>
The hollow fiber membrane 11 in the filtration device 1 was washed in the same manner as in Example 1 except that the heating / pressurizing impregnation step was not performed.

In Examples 1 and Comparative Examples 1 and 2, a graph showing the number of days of use on the horizontal axis and the filtration flow rate of the hollow fiber membrane 11 on the vertical axis is shown in FIG.

As shown in FIG. 3, in Example 1, the filtration flow rate of the hollow fiber membrane 11 can maintain the target flow rate of 5 L / min even after about 80 days have passed, and the hollow fiber membrane 11 is hollow. It was found that clogging and the like that cause a decrease in the filtration capacity of the filament membrane 11 could be eliminated. On the other hand, in Comparative Example 1 and Comparative Example 2, the filtration flow rate of the hollow fiber membrane 11 fell below the target flow rate of 5 L / min within a few days to 10 days, and did not recover to the target flow rate thereafter.

1 ... Filtration device 11 ... Hollow fiber membrane 2 ... Cleaning liquid tank 21 ... Chemical tank 3 ... Drainage tank 4 ... Filtration tanks P1 to P3 ... Liquid feed pumps SV1 to SV9 ... 1st valve to 9th valve H ... Heater C ... Temperature control devices F1 to F3 ... Filters S1 to S3 ... Liquid level sensors G1, G2 ... Pressure gauge FM ... Flow meter WS ・ ・ ・ Water supply device

Claims (2)

This is a method for cleaning hollow fiber membranes, which is carried out by a filtration device that filters the waste liquid of nutrient solution cultivation with a hollow fiber membrane.
A flushing step in which the raw water side of the hollow fiber membrane in contact with the drainage liquid is flushed with the drainage liquid at a flow rate higher than that at the time of filtration.
The cleaning liquid heated to 25 to 45 ° C. is sent to the filtration device at 0.1 to 1.0 MPa, and the liquid is passed from the raw water side to the filtration side through the hollow fiber membrane to clean the hollow fiber membrane. Heating and pressure impregnation process and
After the heating and pressurizing impregnation step, the cleaning liquid is kept at 0.1 to 1.0 MPa and allowed to stand, and the soaking step.
It is provided with a circulation step of sending the cleaning liquid heated to 25 to 45 ° C. after the soaking step so as to circulate between the cleaning liquid tank in which the cleaning liquid is stored and the filtration device.
The hollow fiber is characterized in that the flushing step by the drainage is carried out in a shorter cycle than the series of steps by the washing liquid in the heating and pressurizing impregnation step, the soaking step and the circulation step. How to clean the membrane. The method for cleaning a hollow fiber membrane according to claim 1, wherein the cleaning liquid is an alkaline cleaning liquid or a chlorine-based cleaning liquid.

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