JP6960791B2 - Cleaning method of hollow fiber membrane filtration device and hollow fiber membrane filtration device - Google Patents

Description

The present invention relates to a method for cleaning a hollow fiber membrane filtration device and a hollow fiber membrane filtration device.

Conventionally, it is known to use a hollow fiber membrane in which a large number of pores are formed in a water treatment for removing impurities in water. In filtration using a hollow fiber membrane, substances larger than the pores (ions, fine particles, etc.) are separated from the raw water by allowing the raw water (water before filtration) to permeate the membrane due to the pressure difference between the inside and outside of the membrane. .. Since this method does not involve a phase change or a chemical change of the substance to be separated, it is promising from the viewpoint of high efficiency and energy saving as compared with other separation methods.

However, in filtration using a hollow fiber membrane, suspended solids called SS (Suspended Solids) contained in raw water may adhere to the surface of the membrane and invade the pores of the membrane. As a result, the permeation flow velocity of the raw water decreases with the passage of filtration time (fouling phenomenon). Therefore, in order to continue the filtration by the hollow fiber membrane stably for a long period of time, it is necessary to remove the suspended solids adhering to the membrane surface by regularly cleaning the hollow fiber membrane.

In Patent Documents 1 and 2, as one of the methods for cleaning the hollow fiber membrane, reverse pressure cleaning is performed to remove suspended solids adhering to the surface of the hollow fiber membrane by flowing filtered water in the direction opposite to the filtration direction. (Hereinafter, also referred to as "backwash") is described. In Patent Document 1, a gas having a pressure smaller than the pressure at which the gas is released from the outer surface side of the hollow fiber membrane is introduced into the inner surface side of the hollow fiber membrane, and the liquid on the inner surface side is discharged within 20 seconds. The method is described. Further, Patent Document 2 describes a method of discharging the raw water on the primary side of the membrane in the hollow fiber membrane module and then pushing out the filtered water from the secondary side of the membrane toward the primary side of the membrane by a pressurized gas.

Japanese Patent No. 3887072 Japanese Unexamined Patent Publication No. 2015-155076

In the back pressure cleaning in Patent Documents 1 and 2, air compressed by the air compressor is introduced into the region on the inner surface side of the hollow fiber membrane, and the compressed air causes filtered water from the inner surface side to the outer surface side of the membrane. Is pushed out. Here, the compressed air may contain fine particles, moisture, oil taken out from the air compressor, microorganisms such as bacteria, and various pollutants such as viruses. Therefore, if compressed air is introduced into the hollow fiber membrane as it is as in Patent Documents 1 and 2, the region on the inner surface side of the membrane may be contaminated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a hollow fiber membrane filtration device capable of cleaning a hollow fiber membrane while suppressing contamination of a region on the inner surface side of the hollow fiber membrane. It is to provide a cleaning method and a hollow fiber membrane filtration apparatus.

The method for cleaning the hollow fiber membrane filtration device according to one aspect of the present invention is a method for cleaning the surface of the hollow fiber membrane in the hollow fiber membrane filtration device that filters raw water by the hollow fiber membrane. This method, by passing raw water from the outer surface toward the inner surface side of the hollow fiber membrane of the hollow fiber membrane in the hollow fiber membrane, a filtration step of taking out the filtered water from the inner surface side, the A separation means arranged in a gas introduction path that guides a gas toward the inner surface side region of the hollow thread film, and is a contaminant of at least one of fine particles, water, oil, microorganisms, and viruses contained in the gas. by the gas which has passed through the separating means which can separate from the gas, and a backwash step of extruding the filtered water toward the outer surface side from the inner surface side of the hollow fiber membrane, after the back washing step, the gas By operating the depressurization valve provided in the depressurization path branched from the portion on the hollow thread film side of the separation means in the introduction path, the pressure in the region on the inner surface side of the hollow thread film is made higher than the atmospheric pressure. The depressurization step comprises a depressurization step of releasing gas from the inner surface side region while maintaining a large pressure, and the depressurization step is performed before the pressure in the inner surface side region of the hollow yarn film becomes equal to atmospheric pressure. It ends in.

In this cleaning method, the suspended solids adhering to the outer surface of the hollow fiber membrane during the filtration step are removed by pushing out the filtered water from the inner surface side to the outer surface side of the hollow fiber membrane in the backwashing step. Can be done. Here, in the gas used for extruding the filtered water, pollutants such as fine particles, water, oil, microorganisms and viruses are separated by passing through the separation means. Therefore, it is possible to prevent these contaminants from being mixed into the inner surface side region of the hollow fiber membrane during the backwashing step. Therefore, according to the cleaning method of the hollow fiber membrane filtration device of the present invention, it is possible to clean the hollow fiber membrane while suppressing contamination of the region on the inner surface side of the hollow fiber membrane.
Further, since the pressure in the region on the inner surface side of the hollow fiber membrane can be maintained at a positive pressure with respect to the atmospheric pressure in the depressurization step, the pressure is directed toward the region on the inner surface side of the hollow fiber membrane in the depressurization step. It is possible to prevent the outside air from flowing in. As a result, contamination of the region on the inner surface side of the hollow fiber membrane can be more reliably prevented.

In the cleaning method of the hollow fiber membrane filtration device, in the backwashing step, air taken in from the outside is used as the gas, and the separation accuracy is 0.01 μm or more and 1.0 μm or less, and the contamination contained in the air. An air filter capable of separating substances may be used as the separation means.

It is particularly preferable in terms of cost to use outside air for extruding the filtered water in the backwashing step. However, since a large amount of pollutants are present in the outside air, it is necessary to remove the pollutants in advance when the outside air is used in the backwashing step. Here, it has been clarified by the studies by the present inventors that pollutants in the outside air are effectively removed by passing through an air filter having a separation accuracy of 1.0 μm or less. Therefore, by using this air filter as a separation means, it is possible to prevent contaminants from being mixed into the region on the inner surface side of the hollow fiber membrane even when outside air is used in the backwashing step. Further, by using an air filter having a separation accuracy of 0.01 μm or more, the pressure loss of air when passing through the air filter can be reduced.

In the method for cleaning the hollow fiber membrane filtration device, the filtered water may be extruded by a gas adjusted to a pressure of 0.05 MPa or more and less than 0.5 MPa in the backwashing step.

By adjusting the gas pressure during the backwashing step to 0.05 MPa or more, the cleaning effect of the outer surface of the hollow fiber membrane can be enhanced. However, even if the pressure of the gas is increased to 0.5 MPa or more, the improvement of the cleaning effect is small. Therefore, from the viewpoint of energy efficiency, it is preferable that the gas pressure during the backwashing step is adjusted to less than 0.5 MPa.

In the method for cleaning the hollow fiber membrane filtration device, the hollow fiber membrane whose inner surface is hydrophilic until the contact angle of water becomes less than 90 ° may be used.

When the inner surface of the hollow fiber membrane is hydrophobic, the inner surface dries when gas is introduced into the inner surface side of the hollow fiber membrane in the backwashing step. As a result, when the filtration step is restarted, it becomes difficult to allow the raw water to permeate from the outer surface side to the inner surface side of the hollow fiber membrane. On the other hand, by using the hollow fiber membrane having a hydrophilic inner surface as described above, it is possible to prevent the inner surface of the hollow fiber membrane from drying during the backwashing step.

The hollow thread film filtering device according to another aspect of the present invention includes a hollow thread film, a housing for accommodating the hollow thread film, a raw water supply means for supplying raw water into the housing, and an inner surface side of the hollow thread film. It is arranged in the gas introduction path that guides the gas toward the region and the gas introduction path, and at least one of pollutants such as fine particles, water, oil, microorganisms and viruses contained in the gas can be separated from the gas. A separation means, a depressurization path for releasing a gas in a region on the inner surface side of the hollow yarn film by branching from a portion on the hollow yarn film side of the separation means in the gas introduction path, and a depressurization path. A pressure release valve provided in the pressure release path, a pressure detection unit that detects pressure in the inner surface side region of the hollow thread film, and a pressure detection unit that detects pressure in the pressure release step after the backwashing step. A control unit that controls the depressurization valve is provided so that the pressure to be pressed is held at a pressure higher than the atmospheric pressure, and the control unit has a pressure detected by the pressure detecting unit equal to the atmospheric pressure. The pressure release valve is controlled to be closed before the pressure is reduced.

In this hollow fiber membrane filtration device, filtered water can be obtained by supplying raw water into the housing and allowing the raw water to permeate from the outer surface side to the inner surface side of the hollow fiber membrane. Then, by guiding the gas toward the region on the inner surface side of the hollow fiber membrane through the gas introduction path, the filtered water can be pushed out from the inner surface side to the outer surface side of the hollow fiber membrane by this gas. This makes it possible to remove suspended solids adhering to the outer surface of the hollow fiber membrane during filtration. Moreover, since a separation means capable of separating contaminants such as fine particles, water, oil, microorganisms or viruses from the gas is arranged in the gas introduction path, the gas after passing through the separation means is passed through the inner surface of the hollow fiber membrane. Can lead to the area on the side. Therefore, it is possible to prevent these contaminants from being mixed into the region on the inner surface side of the hollow fiber membrane.
Further, since the pressure in the region on the inner surface side of the hollow fiber membrane can be maintained at a positive pressure with respect to the atmospheric pressure, it is possible to prevent the outside air from flowing toward the region on the inner surface side of the hollow fiber membrane. As a result, contamination of the region on the inner surface side of the hollow fiber membrane can be more reliably prevented. Moreover, by automatically controlling the pressure relief valve by the control unit, the pressure adjustment as described above can be easily performed.

In the hollow fiber membrane filtration device, the gas introduction path may be provided with an air intake port for taking in air from the outside. The separation means may include an air filter having a separation accuracy of 0.01 μm or more and 1.0 μm or less and capable of separating the pollutants contained in the air.

According to this configuration, outside air can be used to extrude the filtered water, which is preferable in terms of cost. Moreover, by using the outside air after passing through the air filter, it is possible to prevent contaminants from being mixed into the region on the inner surface side of the hollow fiber membrane.

The hollow fiber membrane filtration device may be configured to guide a gas adjusted to a pressure of 0.05 MPa or more and less than 0.5 MPa toward the region on the inner surface side of the hollow fiber membrane.

According to this configuration, the filtered water can be pushed out from the inner surface side to the outer surface side of the hollow fiber membrane by the gas adjusted to the pressure of 0.05 MPa or more and less than 0.5 MPa. This pressure range is preferable from the viewpoint of the cleaning effect and energy efficiency of the hollow fiber membrane in the back pressure cleaning as described above.

In the hollow fiber membrane filtration device, the inner surface of the hollow fiber membrane may be hydrophilized until the contact angle of water is less than 90 °.

According to this configuration, even when a gas is introduced into the region on the inner surface side of the hollow fiber membrane in the back pressure cleaning, it is possible to prevent the inner surface from drying.

In the hollow fiber membrane filtration device, the separation means may be configured to be capable of separating at least one of water and oil contained in the gas from the gas. The valve arranged after the separation means may be configured to be driveable by the gas passing through the separation means.

According to this configuration, the gas from which water and oil have been removed by passing through the separating means can be effectively used as a driving source for the valve.

As is clear from the above description, according to the present invention, a method for cleaning a hollow fiber membrane filtration device capable of cleaning a hollow fiber membrane while suppressing contamination of a region on the inner surface side of the hollow fiber membrane, and a hollow fiber membrane. A filament membrane filtration device can be provided.

It is a figure which shows typically the structure of the hollow fiber membrane filtration apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows typically the cross section of the upper end side along the longitudinal direction of a hollow fiber membrane. It is a figure which shows the operating state of a pump, and the open / closed state of a valve in each step of the cleaning method of the hollow fiber membrane filtration device which concerns on Embodiment 1 of this invention. It is a figure which shows typically the structure of the hollow fiber membrane filtration apparatus which concerns on Embodiment 2 of this invention. It is a figure which shows typically the structure of the hollow fiber membrane filtration apparatus which concerns on Embodiment 3 of this invention. It is a figure which shows typically the partial structure of the hollow fiber membrane filtration apparatus which concerns on Embodiment 4 of this invention.

Hereinafter, the hollow fiber membrane filtration device and the cleaning method thereof according to the embodiment of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
<Hollow fiber membrane filtration device>
First, the configuration of the hollow fiber membrane filtration device 1 according to the first embodiment of the present invention will be described mainly with reference to FIG. FIG. 1 schematically shows the main components of the hollow fiber membrane filtration device 1. As shown in FIG. 1, the hollow fiber membrane filtration device 1 includes a hollow fiber membrane module 10, a raw water supply means 20, a gas introduction path 30, a separation means 40, a compressor 50, and a receiver tank 60. Mainly prepared.

The hollow fiber membrane module 10 is an external pressure filtration type module, and mainly has a hollow fiber membrane bundle 12 having a plurality of bundle-shaped hollow fiber membranes 11 and a housing 13 for accommodating the hollow fiber membrane bundle 12. ing. The hollow fiber membrane module 10 is a filtration type module of either an external pressure total amount filtration type or an external pressure circulation filtration type, depending on the purpose of filtration and the required performance. From the viewpoint of membrane life, an external pressure circulation filtration type module capable of cleaning the membrane surface at the same time as the filtration treatment is preferable. On the other hand, from the viewpoint of equipment simplicity, installation cost, and operating cost, an external pressure total filtration type module is preferable.

The hollow fiber membrane bundle 12 is fixed to the housing 13 by the fixing member 14 with the upper end 11A of each hollow fiber membrane 11 open, and is sealed with resin or the like with the lower end 11B of each hollow fiber membrane 11 not fixed. It is a one-sided free type. The space inside the housing 13 is partitioned by a fixing member 14 into a raw water side space S1 through which raw water flows and a filtered water side space S2 through which filtered water flows.

The upper end 11A of each hollow fiber membrane 11 penetrates the fixing member 14 and opens into the filtered water side space S2. As a result, the portion of the hollow fiber membrane 11 on the inner surface side communicates with the filtered water side space S2. The hollow fiber membrane bundle is not limited to the one-end free type, and may be a double-ended fixed type in which the upper end 11A and the lower end 11B of each hollow fiber membrane 11 are fixed. However, according to the one-end free type hollow fiber membrane bundle 12, the hollow fiber membrane 11 can be easily swung by air bubbles when gas is introduced into the filled raw water side space S1 for bubbling cleaning. Therefore, it is preferable.

Various materials can be used for the hollow fiber membrane 11, and the material is not particularly limited. For example, the hollow yarn film 11 is made of polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinylfluoride, tetrafluoroethylene-hexafluoropropylene copolymer, etc. Selected from the group consisting of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride (PVDF), polysulfone, cellulose acetate, polyvinyl alcohol and polyethersulfone. It is preferable to include at least one type. In particular, from the viewpoint of film strength and chemical resistance, the hollow fiber membrane 11 preferably contains PVDF.

FIG. 2 shows a cross section (longitudinal cross section on the upper end 11A side) when the hollow fiber membrane 11 is cut along the longitudinal direction. As shown in FIG. 2, the hollow fiber membrane 11 is a hollow cylindrical filtration membrane, and has an outer surface 11B (cylindrical outer surface) and an inner surface 11C (cylindrical inner surface). In a state where the hollow fiber membrane 11 is housed in the housing 13 (FIG. 1), the outer surface 11B faces the raw water side space S1. Further, a large number of pores (not shown) are formed on the membrane wall of the hollow fiber membrane 11.

According to the hollow fiber membrane 11, impurities in the raw water are separated by allowing the raw water (water before filtration) supplied to the raw water side space S1 of the housing 13 to permeate from the outer surface 11B side toward the inner surface 11C side. Then, the filtered water 100 can be taken out from the region (hollow portion 11D) on the inner surface 11C side. The filtered water 100 flows out to the filtered water side space S2 (FIG. 1) through the opening of the upper end 11A of the hollow fiber membrane 11, and then flows out of the housing 13.

The separation accuracy of the hollow fiber membrane 11 is such that microorganisms such as bacteria in raw water can be separated. Specifically, the separation accuracy of the hollow fiber membrane 11 is 10.0 μm or less, preferably less than 5.0 μm, more preferably less than 2.0 μm, and less than 0.5 μm. It is more preferably less than 0.2 μm.

The inner surface 11C of the hollow fiber membrane 11 is made hydrophilic by, for example, applying a hydrophilic resin dissolved in water. That is, the contact angle of water on the inner surface 11C is less than 90 °. This makes it possible to prevent the inner surface 11C from drying when a gas such as compressed air is introduced into the hollow portion 11D. The contact angle of water on the inner surface 11C is preferably less than 85 °, more preferably less than 80 °. Further, as the hydrophilic resin, for example, polyvinylpyrrolidone, cellulose ester, ethylene-vinyl alcohol, polyvinyl alcohol and the like can be used, but it is particularly preferable to use polyvinyl alcohol having high hydrophilicity.

The contact angle of water on the inner surface 11C can be measured as follows. First, the hollow fiber membrane 11 is cut along the longitudinal direction. Next, a water droplet is dropped on the inner surface 11C of the hollow fiber membrane 11, and an image at that moment is taken. The angle formed by the water droplet surface and the inner surface 11C at the place where the water droplet surface is in contact with the inner surface 11C of the hollow fiber membrane 11 is the contact angle of water on the inner surface 11C. As the measuring device, "Drop Master 700" manufactured by Kyowa Interface Science Co., Ltd. can be used.

In the present invention, only the inner surface 11C of the hollow fiber membrane 11 may be hydrophilized as described above, and the outer surface 11B may not be hydrophilized, and the outer surface 11B and the inner surface 11B of the hollow fiber membrane 11 may not be hydrophilized. The surface 11C may be hydrophilized. Further, neither the outer surface 11B nor the inner surface 11C of the hollow fiber membrane 11 may be hydrophilized.

The housing 13 is made of, for example, a cylindrical container. A filtered water outlet 13A for flowing out the filtered water from the filtered water side space S2 to the outside of the housing 13 is provided in the upper part of the housing 13. A gas discharge port 13B for discharging gas from the raw water side space S1 to the outside of the housing 13 is provided directly below the fixing member 14 on the side portion of the housing 13. A gas discharge path 92 is connected to the gas discharge port 13B. At the lower part of the housing 13, a raw water inlet / outlet 13C for allowing the raw water to flow into the raw water side space S1 or to flow the raw water out of the housing 13 from the raw water side space S1 is provided.

The raw water supply means 20 supplies raw water into the housing 13 (raw water side space S1), and mainly includes a liquid feed pump 21, a raw water pipe 22, and a raw water valve 23. As shown in FIG. 1, one end (downstream end) of the raw water pipe 22 is connected to the raw water inlet / outlet 13C of the housing 13, and the other end (upstream end) of the raw water pipe 22 is connected to a water source (not shown). A liquid feed pump 21 is arranged on the other end side of the raw water pipe 22. The raw water valve 23 switches the flow and cutoff of raw water in the pipe, and is arranged on the downstream side in the flow direction of the raw water with respect to the liquid feed pump 21. The on / off of the operation of the liquid feed pump 21 and the opening / closing of the raw water valve 23 are controlled by a control device (not shown). As a result, raw water can be supplied to the raw water side space S1 of the housing 13 through the raw water pipe 22. Further, as shown in FIG. 1, a drain path 94 for discharging raw water is connected to a portion of the raw water pipe 22 on the downstream side of the raw water valve 23.

The gas introduction path 30 is a path for guiding the air (gas) taken in from the outside of the hollow fiber membrane filtration device 1 toward the region (hollow fiber portion 11D, FIG. 2) on the inner surface 11C side of the hollow fiber membrane 11. be. As shown in FIG. 1, one end (downstream end) of the gas introduction path 30 is connected to the filtered water outlet 13A of the housing 13, and the other end (upstream end) of the gas introduction path 30 is air from the outside into the path. An air intake port 30A for taking in (outside air) is provided. The air taken into the path from the air intake port 30A flows into the filtered water side space S2 of the housing 13 through the gas introduction path 30, and then the hollow fiber membrane 11 is hollow through the opening of the upper end 11A of the hollow fiber membrane 11. It flows into the part 11D. That is, the filtered water outlet 13A also functions as an air inlet into the housing 13.

As shown in FIG. 1, the compressor 50, the receiver tank 60, the separation means 40, and the gas introduction valve 31 are arranged in this order from the upstream side to the downstream side of the gas introduction path 30.

The compressor 50 is, for example, a refueling type air compressor, which compresses the air taken into the gas introduction path 30 from the air intake port 30A and discharges the compressed air to the downstream side. The compressor 50 compresses the air so that the dew point is -60 ° C or higher and lower than 0 ° C. The dew point of the compressed air is preferably −50 ° C. or higher and lower than 0 ° C., and more preferably −40 ° C. or higher and lower than 0 ° C. The dew point of compressed air can be measured using a dew point meter (TK-100) manufactured by Tekne Corporation. The compressor 50 is not limited to the refueling type, and may be a non-refueling type.

The receiver tank 60 temporarily stores the compressed air sent from the compressor 50, and is arranged after the compressor 50. A regulator (pressure reducing valve) for pressure adjustment is arranged at the outlet of the receiver tank 60. With this pressure reducing valve, the pressure of the compressed air introduced into the hollow portion 11D of the hollow fiber membrane 11 through the gas introduction path 30 can be adjusted. In the present embodiment, compressed air adjusted to a pressure of 0.05 MPa or more and less than 0.5 MPa can be guided toward the hollow portion 11D of the hollow fiber membrane 11. The receiver tank 60 is not an essential component in the hollow fiber membrane filtration device of the present invention, and may be omitted. Further, in the present invention, the pressure of compressed air is not limited to the above range.

The gas introduction valve 31 switches between the flow and cutoff of compressed air in the gas introduction path 30, and is arranged after the separation means 40. Further, the gas introduction valve 31 is, for example, an electric on-off valve, and like the raw water valve 23, the opening degree is controlled by a control device (not shown).

In the hollow fiber membrane filtration device 1, reverse pressure cleaning is performed to clean the outer surface 11B of the hollow fiber membrane 11 by flowing filtered water through the hollow fiber membrane 11 in the direction opposite to the filtration direction as follows. be able to. First, after temporarily suspending the filtration of raw water by the hollow fiber membrane 11, air (outside air) is taken into the gas introduction path 30 from the air intake port 30A, and this air is compressed by the compressor 50. This compressed air is stored in the receiver tank 60. Then, the compressed air flowing out of the receiver tank 60 is introduced into the filtered water side space S2 of the housing 13 through the gas introduction path 30. As a result, as shown in FIG. 2, the liquid surface of the filtered water 100 in the hollow portion 11D of the hollow fiber membrane 11 is pressurized by compressed air, and the filtered water 100 is directed from the inner surface 11C side to the outer surface 11B side. Can be extruded. As a result, the suspended solids adhering to the outer surface 11B during filtration can be removed from the outer surface 11B by the water pressure of the filtered water.

Here, since the compressed air used for the above-mentioned back pressure cleaning is outside air, it may contain fine particles such as dust, microorganisms such as bacteria, and viruses. Further, when the refueling type compressor 50 is used as in the present embodiment, the oil taken out from the compressor 50 to the downstream side may be mixed in the compressed air. Therefore, during back pressure cleaning, these pollutants may be mixed into the hollow portion 11D of the hollow fiber membrane 11 due to the introduction of compressed air, and in this case, it becomes difficult to obtain clean filtered water.

Therefore, in the hollow fiber membrane filtration device 1 according to the present embodiment, a separation means 40 capable of separating pollutants such as fine particles, microorganisms and viruses contained in the compressed air from the compressed air is arranged in the gas introduction path 30. There is. As a result, these pollutants can be separated in advance when the compressed air passes through the separating means 40, so that it is possible to prevent the hollow portion 11D of the hollow fiber membrane 11 from being contaminated.

In the present embodiment, the separation means 40 is composed of an air filter 41. As shown in FIG. 1, the air filter 41 is arranged between the receiver tank 60 and the gas introduction valve 31 in the gas introduction path 30.

The air filter 41 is configured to be capable of separating at least fine particles (dust) contained in compressed air, and is preferably configured to be capable of separating even smaller microorganisms (mold, spores, bacteria, etc.) than the fine particles. It is more preferable that the virus is configured to be separable even to a virus smaller than a microorganism. The separation accuracy of the air filter 41 is 10.0 μm or less, preferably less than 5.0 μm, more preferably 1.0 μm or less, and even more preferably 0.1 μm or less. As described in Examples described later, bacteria can be effectively separated from compressed air by using an air filter 41 having a separation accuracy of 1.0 μm or less.

On the other hand, if the separation accuracy of the air filter 41 is too high, the pressure loss when the compressed air passes through the air filter 41 becomes large, which causes a decrease in energy efficiency. Therefore, the separation accuracy of the air filter 41 is preferably 0.01 μm or more, more preferably 0.02 μm or more, and further preferably 0.05 μm or more.

The air filter 41 may be configured so that oil can also be separated. Specifically, the element of the air filter 41 may be able to capture the oil mist that may be contained in the compressed air. As described above, since the compressor 50 is a refueling type, oil mist may be mixed in the air discharged from the compressor 50, but this can be separated by the air filter 41. Therefore, in addition to the fine particles, microorganisms and viruses, it is possible to prevent oil from being mixed into the hollow portion 11D of the hollow fiber membrane 11. When the compressor 50 is an oil-free type, the air filter 41 does not have to have the function of the oil separator as described above.

The hollow fiber membrane filtration device 1 further includes a filtered water path 80 for taking out the filtered water to the outside of the device, and a filtered water valve 81 provided in the filtered water path 80. As shown in FIG. 1, one end (upstream end) of the filtered water path 80 is connected to a portion P1 on the downstream side of the gas introduction valve 31 in the gas introduction path 30. The filtered water flows out of the housing 13 from the filtered water outlet 13A, then flows into the filtered water path 80 from the site P1, and is then taken out of the device.

The hollow fiber membrane filtration device 1 further includes a pressure release path 70, a pressure release valve 71 provided in the pressure release path 70, a pressure detection unit 72, and a control unit 73 that controls the opening and closing of the pressure release valve 71. I have.

The depressurization path 70 is a path for venting air (gas) in the hollow portion 11D of the hollow fiber membrane 11 to the outside. As shown in FIG. 1, one end (upstream end) of the depressurization path 70 is connected to a portion P2 between the gas introduction valve 31 and the portion P1 in the gas introduction path 30, and the other end of the depressurization path 70 (upper end). The downstream end) is open to the atmosphere. The depressurization valve 71 is, for example, an electric valve, and switches between air flow and shutoff in the depressurization path 70.

When the pressure release valve 71 is opened while the pressure in the hollow portion 11D of the hollow fiber membrane 11 is higher than the atmospheric pressure and the gas introduction valve 31 is closed, the air in the hollow portion 11D flows into the pressure release path 70 due to the pressure difference. After that, it is discharged to the outside of the device. In this way, the air in the hollow portion 11D of the hollow fiber membrane 11 can be evacuated to the outside through the pressure release path 70.

The pressure detection unit 72 is a sensor that detects the pressure in the hollow portion 11D of the hollow fiber membrane 11, and is provided on the upstream side of the filtered water valve 81 in the filtered water path 80 in the present embodiment. The pressure detection unit 72 may be provided at a position where the pressure in the space communicating with the hollow portion 11D of the hollow fiber membrane 11 can be detected, and is provided, for example, on the downstream side of the portion P1 in the gas introduction path 30. Is also possible.

The control unit 73 controls the opening and closing of the pressure release valve 71 so that the pressure detected by the pressure detection unit 72 (the pressure in the hollow portion 11D of the hollow fiber membrane 11) is held at a pressure higher than the atmospheric pressure. Specifically, information on the pressure detected by the pressure detection unit 72 is sent to the control unit 73. Then, the control unit 73 controls to close the pressure release valve 71 before the pressure detected by the pressure detection unit 72 becomes equal to the atmospheric pressure.

In the present invention, the control unit 73 that automatically controls the opening and closing of the pressure relief valve 71 is not essential, and the opening and closing of the pressure relief valve 71 may be manually controlled after omitting the control unit 73.

The hollow fiber membrane filtration device 1 further includes a bubbling path 90 and a bubbling valve 91 provided in the bubbling path 90. As shown in FIG. 1, one end (upstream end) of the bubbling path 90 is connected to a portion P3 between the receiver tank 60 and the air filter 41 in the gas introduction path 30, and the other end of the bubbling path 90 (upper end). The downstream end) is connected to a portion P4 on the downstream side of the raw water valve 23 in the raw water pipe 22. As a result, the compressed air flowing through the gas introduction path 30 can flow into the bubbling path 90 at the portion P3. Then, this compressed air can be supplied into the housing 13 (raw water side space S1) through the bubbling path 90 and the downstream portion of the raw water pipe 22. By sending compressed air in this way while the raw water side space S1 is filled with water, air bubbles can be generated in the raw water side space S1 and the hollow fiber membrane 11 can be bubbling-cleaned.

In the present embodiment, the case where the gas introduction valve 31 and the pressure release valve 71 arranged after the air filter 41 are electric valves has been described, but these valves are driven by the compressed air that has passed through the air filter 41. It may be a possible air-driven valve. Since the compressed air that has passed through the air filter 41 is separated from the oil, it can be effectively used as a drive source for the valve.

<How to clean the hollow fiber membrane filtration device>
Next, a method for cleaning the hollow fiber membrane filtration device according to the first embodiment of the present invention will be described. In the method for cleaning the hollow fiber membrane filtration device according to the present embodiment, the outer surface 11B of the hollow fiber membrane 11 is cleaned in the hollow fiber membrane filtration device 1 (FIG. 1) described above. FIG. 3 shows an operating state of the liquid feed pump 21 and an open / closed state of each valve in each step of the method for cleaning the hollow fiber membrane filtration device according to the present embodiment. In FIG. 3, the circles mean the pump on state or the valve open state, and the blanks mean the pump off state or the valve closed state.

First, a water filling process is carried out. In this step, the raw water valve 23 and the gas discharge valve 93 are opened and the liquid feed pump 21 is operated in a state where all the valves of the hollow fiber membrane filtration device 1 are closed. As a result, the raw water sent by the liquid feed pump 21 is supplied into the housing 13 (raw water side space S1) through the raw water pipe 22.

Next, a filtration step is carried out. In this step, after the raw water overflows from the gas discharge port 13B, the filtered water valve 81 is opened and the gas discharge valve 93 is closed while the liquid feed pump 21 is operating. The raw water supplied to the raw water side space S1 permeates the membrane wall from the outer surface 11B side of the hollow fiber membrane 11 toward the inner surface 11C side. As a result, impurities (bacteria and the like) in the raw water are separated, and the filtered water 100 is taken out from the inner surface 11C side. The filtered water 100 flows out of the housing 13 through the filtered water outlet 13A and is taken out of the device through the filtered water path 80.

In the above filtration step, suspended solids in the raw water may adhere to the outer surface 11B of the hollow fiber membrane 11 as the filtration time elapses, and the pores of the membrane may be blocked. As a result, the permeation flow velocity of the raw water decreases, and the filtration capacity of the hollow fiber membrane 11 decreases. Therefore, after a certain period of time has elapsed from the start of filtration, the backwashing step and the bubbling step described below are carried out. As a result, the suspended solids adhering to the outer surface 11B of the hollow fiber membrane 11 are removed, and the filtration capacity of the hollow fiber membrane 11 can be restored.

First, a backwash process is carried out. In this step, the gas introduction valve 31 and the drain valve 95 are opened, respectively. First, air (outside air) is taken into the gas introduction path 30 through the air intake port 30A, and this air is compressed by the compressor 50. This compressed air is stored in the receiver tank 60. Then, the compressed air flowing out of the receiver tank 60 passes through the air filter 41 and is guided to the filtered water side space S2 of the housing 13. As shown in FIG. 2, the filtered water 100 remaining in the hollow portion 11D of the hollow fiber membrane 11 after the filtering step is pressurized by the compressed air. As a result, the filtered water 100 is pushed out from the inner surface 11C side of the hollow fiber membrane 11 toward the outer surface 11B side by the compressed air. As a result, the adhesive force of the suspended solid to the outer surface 11B is weakened, and the suspended solid floats from the outer surface 11B.

Here, as described above, these are pushed out by the compressed air that has passed through the air filter 41 (separation means 40) capable of separating pollutants such as fine particles, oil, microorganisms or viruses contained in the compressed air. It is possible to prevent contaminants from being mixed into the hollow portion 11D of the hollow fiber membrane 11. As a result, it is possible to prevent the hollow portion 11D of the hollow fiber membrane 11 from being contaminated during the backwashing step, so that clean filtered water can be obtained even when the filtering step is restarted after the backwashing step. ..

In the backwashing step, the filtered water is pushed out by the compressed air adjusted to a pressure (gauge pressure) of 0.05 MPa or more and less than 0.5 MPa by a regulator arranged at the outlet of the receiver tank 60. By increasing the pressure of the compressed air to 0.05 MPa or more, the pressing force of the filtered water increases and the cleaning effect of the hollow fiber membrane 11 increases, but even if the pressure is increased to 0.5 MPa or more, the cleaning effect tends to saturate. .. Therefore, from the viewpoint of achieving both the cleaning effect and the energy efficiency of the hollow fiber membrane 11, the pressure of the compressed air is preferably adjusted to 0.05 MPa or more and less than 0.5 MPa, and is adjusted to 0.1 MPa or more and less than 0.5 MPa. It is more preferable that the pressure is adjusted to 0.1 MPa or more and less than 0.3 MPa. However, in the present invention, the pressure of the compressed air during the backwashing step is not limited to the above range.

Further, in the backwashing step, all the filtered water remaining in the hollow portion 11D of the hollow fiber membrane 11 is pushed out to the outer surface 11B side (raw water side space S1), so that air is blown to the entire hollow portion 11D at the end of the backwashing step. It becomes full. Here, when the inner surface 11C of the hollow fiber membrane 11 has hydrophobicity, the inner surface 11C dries, and when the filtration process is restarted, the raw water permeates from the outer surface 11B side to the inner surface 11C side. It becomes difficult to make it. On the other hand, in the present embodiment, by using the hollow fiber membrane 11 in which the inner surface 11C is hydrophilized until the contact angle of water becomes less than 90 °, the inner surface 11C is dried at the end of the backwashing step. Can be prevented. Therefore, even when the filtration step is restarted after the backwashing step, the problem that the raw water does not permeate the hollow fiber membrane 11 does not occur.

Next, a depressurization step is carried out. In this step, the inside of the hollow portion 11D is depressurized by removing the air introduced into the hollow portion 11D of the hollow fiber membrane 11 to the outside in the backwashing step. Specifically, by opening the pressure release valve 71 with the gas introduction valve 31 closed, the air in the hollow portion 11D flows out of the housing 13 and flows into the pressure release path 70 from the portion P2, and the device It is discharged to the outside.

Here, in the depressurization step, air is evacuated from the hollow portion 11D while maintaining the pressure in the hollow portion 11D detected by the pressure detection unit 72 at a pressure higher than the atmospheric pressure. Specifically, at the start of the depressurization step, the air introduced in the backwashing step fills the hollow portion 11D, so that the pressure in the hollow portion 11D is higher than the atmospheric pressure. Then, while monitoring the pressure in the hollow portion 11D by the pressure detecting unit 72, the air in the hollow portion 11D is evacuated, and the depressurizing valve 71 is closed before the detected pressure reaches (equals to) the atmospheric pressure to perform the depressurizing step. To finish. That is, even at the end of the depressurization step, the pressure in the hollow portion 11D is maintained to be higher than the atmospheric pressure. By keeping the pressure in the hollow portion 11D positive with respect to the atmospheric pressure in this way, the outside air containing contaminants (fine particles, microorganisms, viruses, etc.) is hollowed out in the hollow fiber membrane 11 through the pressure release path 70. It is possible to prevent the flow into the portion 11D.

Further, as described above, the state where the pressure in the hollow portion 11D is larger than the atmospheric pressure is maintained until the next filtration step is restarted. Here, if the pressure in the hollow portion 11D is too large with respect to the atmospheric pressure, the filtered water will be violently ejected by the air pressure when the next filtration step is restarted, which is not preferable. Further, it is not preferable from the viewpoint of film durability that the inner surface 11C side of the hollow fiber membrane 11 is in an excessively high pressure state until the next filtration step is restarted. Therefore, at the end of the depressurization step, the difference between the pressure of the hollow portion 11D and the atmospheric pressure is preferably adjusted to less than 50 kPa, more preferably less than 30 kPa, and adjusted to less than 10 kPa. Is even more preferable.

In the present embodiment, the case where the opening / closing of the pressure relief valve 71 is automatically controlled by the control unit 73 has been described, but the present invention is not limited to this, and the opening / closing of the pressure relief valve 71 is manually controlled without using the control unit 73. It is also possible.

Next, a bubbling step is carried out. In this step, the bubbling valve 91 and the gas discharge valve 93 are opened in a state where the raw water side space S1 of the housing 13 is filled with raw water. As a result, compressed air is supplied to the lower part of the raw water side space S1 through the bubbling path 90 and the downstream portion of the raw water pipe 22. Then, a bubble flow that rises along the longitudinal direction of the hollow fiber membrane 11 is generated, which causes the hollow fiber membrane 11 to be shaken. As a result, the suspended solid whose adhesion to the outer surface 11B is weakened in the backwashing step is peeled off from the film.

Next, a drainage process is carried out. In this step, the bubbling valve 91 is closed and the drain valve 95 is opened. As a result, the raw water containing the suspended solids peeled off from the outer surface 11B of the hollow fiber membrane 11 in the bubbling step is discharged from the raw water inlet / outlet 13C to the outside of the housing 13. After the outer surface 11B of the hollow fiber membrane 11 is washed as described above, the water filling step and the filtration step described above are restarted.

Here, the features of the hollow fiber membrane filtration device 1 and the cleaning method thereof according to the first embodiment described as described above, and their actions and effects are listed.

The method for cleaning the hollow fiber membrane filtration device according to the first embodiment is a method for cleaning the outer surface 11B of the hollow fiber membrane 11 in the hollow fiber membrane filtration device 1 for filtering raw water by the hollow fiber membrane 11. In this method, raw water is permeated from the outer surface 11B side to the inner surface 11C side of the hollow fiber membrane 11, so that the filtered water is taken out from the inner surface 11C side, and the fine particles and oil contained in the compressed air. A backwashing step in which filtered water is pushed from the inner surface 11C side to the outer surface 11B side of the hollow fiber membrane 11 by compressed air that has passed through a separating means 40 capable of separating contaminants such as microorganisms or viruses from the compressed air. It has.

The hollow fiber membrane filtration device 1 according to the first embodiment includes a hollow fiber membrane 11, a housing 13 for accommodating the hollow fiber membrane 11, a raw water supply means 20 for supplying raw water into the housing 13, and a hollow fiber membrane 11. The gas introduction path 30 that guides the compressed air toward the region on the surface 11C side (hollow fiber portion 11D) and the gas introduction path 30 are arranged, and pollutants such as fine particles, oil, microorganisms, or viruses contained in the compressed air are introduced. It includes a separating means 40 that can be separated from the compressed air.

According to this feature, the suspended solids adhering to the outer surface 11B of the hollow fiber membrane 11 are removed by pushing out the filtered water from the inner surface 11C side of the hollow fiber membrane 11 toward the outer surface 11B side. be able to. Then, by passing the compressed air used for extruding the filtered water through the separating means 40, pollutants such as fine particles, oils, microorganisms and viruses can be separated from the compressed air in advance. Therefore, it is possible to prevent these contaminants from being mixed into the region on the inner surface 11C side of the hollow fiber membrane 11 during back pressure cleaning.

In the cleaning method of the hollow fiber membrane filtration device, air taken in from the outside is used in the backwashing step, and the contaminants contained in the air can be separated with a separation accuracy of 0.01 μm or more and 1.0 μm or less. The air filter 41 is used as the separating means 40. In the hollow fiber membrane filtration device 1, the gas introduction path 30 is provided with an air intake port 30A for taking in air from the outside. The separation means 40 includes an air filter 41 having a separation accuracy of 0.01 μm or more and 1.0 μm or less and capable of separating the pollutants contained in air.

Cost reduction can be achieved by using outside air to extrude the filtered water. Moreover, by using the air filter 41 capable of separating the pollutants contained in the outside air, it is possible to prevent the pollutants from being mixed into the region on the inner surface 11C side of the hollow fiber membrane 11.

In the cleaning method of the hollow fiber membrane filtration device, the filtered water is pushed out by compressed air adjusted to a pressure (gauge pressure) of 0.05 MPa or more and less than 0.5 MPa in the backwashing step. The hollow fiber membrane filtration device 1 is configured to guide compressed air adjusted to a pressure of 0.05 MPa or more and less than 0.5 MPa toward a region on the inner surface 11C side of the hollow fiber membrane 11. This pressure range is preferable from the viewpoint of cleaning effect and energy efficiency of the hollow fiber membrane 11 in back pressure cleaning.

In the method for cleaning the hollow fiber membrane filtration device, the hollow fiber membrane 11 whose inner surface 11C is hydrophilized until the contact angle of water becomes less than 90 ° is used. In the hollow fiber membrane filtration device 1, the inner surface 11C of the hollow fiber membrane 11 is hydrophilized until the contact angle of water is less than 90 °. Thereby, even when air is introduced into the region on the inner surface 11C side of the hollow fiber membrane 11 in the back pressure cleaning, it is possible to prevent the inner surface 11C from drying.

In the cleaning method of the hollow fiber membrane filtration device, after the backwashing step, gas is removed from the region on the inner surface 11C side while maintaining the pressure in the region on the inner surface 11C side of the hollow fiber membrane 11 at a pressure higher than the atmospheric pressure. It is equipped with a depressurization process. The hollow thread film filtering device 1 includes a pressure release path 70 for removing air in a region on the inner surface 11C side of the hollow thread film 11 to the outside, a pressure release valve 71 provided in the pressure release path 70, and a hollow. The pressure detecting unit 72 that detects the pressure in the region on the inner surface 11C side of the thread film 11 and the pressure release valve 71 are controlled so that the pressure detected by the pressure detecting unit 72 is held at a pressure larger than the atmospheric pressure. A control unit 73 and a control unit 73 are provided.

As a result, the pressure in the region on the inner surface 11C side of the hollow fiber membrane 11 can be maintained at a positive pressure with respect to the atmospheric pressure, so that the outside air does not flow toward the region on the inner surface 11C side of the hollow fiber membrane 11. Can be prevented. As a result, contamination of the region on the inner surface 11C side of the hollow fiber membrane 11 can be more reliably prevented.

In the hollow fiber membrane filtration device 1, the separation means 40 is configured to be able to separate the oil contained in the compressed air from the compressed air. The gas introduction valve 31 and the pressure release valve 71, which are arranged after the separation means 40, may be configured to be driveable by the compressed air that has passed through the separation means 40. As a result, the compressed air from which the oil has been separated by passing through the separation means 40 can be effectively used as a drive source for these valves.

(Embodiment 2)
Next, the hollow fiber membrane filtration device 1A according to the second embodiment of the present invention will be described with reference to FIG. The hollow fiber membrane filtration device 1A according to the second embodiment basically has the same configuration as the hollow fiber membrane filtration device 1 according to the first embodiment, but the air filter 41 is arranged in front of the compressor 50. It is different in that it is. Hereinafter, only the points different from the first embodiment will be described.

As shown in FIG. 4, in the second embodiment, the air filter 41 is arranged on the upstream side of the compressor 50 in the gas introduction path 30. Therefore, the air after the contaminants have been separated by the air filter 41 can be compressed by the compressor 50, and the compressed air can be guided toward the hollow fiber membrane module 10. Further, the upstream end of the bubbling path 90 is directly connected to the outlet of the receiver tank 60 instead of the gas introduction path 30. In this hollow fiber membrane filtration device 1A, it is possible to carry out the cleaning method according to the process flow of FIG. 3 in the same manner as in the first embodiment.

In the second embodiment, since the air filter 41 is arranged in front of the compressor 50, it is possible to send clean air after the pollutants have been separated by the air filter 41 to the compressor 50, and the compressor 50 pollution can be prevented. Further, since the air discharged from the compressor 50 can be directly guided to the hollow fiber membrane module 10 without passing through the air filter 41, the pressure loss of the compressed air can be further reduced.

(Embodiment 3)
Next, the hollow fiber membrane filtration device 1B according to the third embodiment of the present invention will be described with reference to FIG. The hollow fiber membrane filtration device 1B according to the third embodiment basically has the same configuration as the hollow fiber membrane filtration device 1 according to the first embodiment, but the air filter 41 is also provided on the raw water side of the hollow fiber membrane module 10. It differs in that it is configured to guide the compressed air that has passed through. Hereinafter, only the points different from the first embodiment will be described.

As shown in FIG. 5, in the hollow fiber membrane filtration device 1B according to the third embodiment, the upstream end of the bubbling path 90 is directly connected to the outlet of the air filter 41. In this hollow fiber membrane filtration device 1B, the cleaning method according to the process flow of FIG. 3 can be carried out in the same manner as in the first embodiment.

In the third embodiment, the compressed air that has passed through the air filter 41 can also be supplied to the raw water side of the hollow fiber membrane module 10. Therefore, it is possible to prevent the space on the raw water side of the hollow fiber membrane module 10 from being contaminated during the bubbling cleaning. From the viewpoint of suppressing clogging of the air filter 41 and prolonging the filter life, only the compressed air leading to the filtered water side of the hollow fiber membrane module 10 is passed through the air filter 41 as in the first embodiment. Is preferable.

(Embodiment 4)
Next, the hollow fiber membrane filtration device according to the fourth embodiment of the present invention will be described with reference to FIG. The hollow fiber membrane filtration device according to the fourth embodiment basically has the same configuration as the hollow fiber membrane filtration device 1 according to the first embodiment, but the separation means 40 includes not only the air filter 41 but also the air filter 41. It differs in that it is composed of a mist separator 42 and a mist separator 42. Hereinafter, only the points different from the first embodiment will be described.

FIG. 6 shows only the configuration in the vicinity of the separation means 40 in the hollow fiber membrane filtration device of the fourth embodiment. The separation means 40 includes an air filter 41 and a mist separator 42. The air filter 41 is the same as that described in the first embodiment.

The mist separator 42 dries the compressed air by separating the moisture contained in the compressed air. As shown in FIG. 6, the mist separator 42 is arranged between the receiver tank 60 and the air filter 41 in the gas introduction path 30. The mist separator 42 can separate the mist-like water droplets contained in the compressed air from the compressed air, and for example, a mist separator 42 that separates the mist-like water droplets from the compressed air by centrifugation can be used.

In the fourth embodiment, the air filter 41 not only suppresses the mixing of fine particles, oil, microorganisms and viruses into the hollow portion 11D of the hollow fiber membrane 11, but also causes the contaminated water to be mixed into the hollow portion 11D. Can be suppressed by the mist separator 42. This makes it possible to more reliably prevent contamination of the hollow portion 11D. Moreover, by arranging the mist separator 42 in front of the air filter 41, it is possible to prevent the moisture contained in the compressed air from adhering to the air filter 41 and causing clogging of the filter. Further, the separation means 40 (air filter 41 and mist separator 42) in the fourth embodiment can be arranged in the front stage of the compressor 50 as in the second embodiment.

Further, similarly to the above, the gas introduction valve 31 and the pressure release valve 71 (FIG. 1) arranged after the separation means 40 may be air-driven valves that can be driven by the compressed air that has passed through the separation means 40. As a result, compressed air in which moisture and oil are separated can be used as a driving source for the valve.

(Other embodiments)
In the first embodiment, the case where outside air is used to extrude the filtered water has been described for the purpose of cost reduction, but the present invention is not limited to this, and for example, a gas stored in a tank (air or a gas other than air) may be used. It is possible. In this case, a tank is provided on the upstream end side of the gas introduction path 30.

In the above-described first to fourth embodiments, the case where only one air filter 41 is provided has been described, but a plurality of air filters 41 may be provided. Further, a plurality of air filters 41 may be arranged in series or in parallel depending on the purpose.

In the third embodiment, the air filter 41 may be omitted, and the separation means 40 may be configured only by the mist separator 42.

Hereinafter, the present invention will be described in more detail based on Examples. However, the present invention is not limited to the following examples, and it is possible to carry out the present invention with appropriate modifications within a range that can be adapted to the gist of the preceding and following description, and all of them are the techniques of the present invention. It is included in the target range.

(Example 1)
A hollow fiber membrane module 10 (FIG. 1) was produced using a hollow fiber membrane made of PVDF (manufactured by Kuraray Co., Ltd.). Then, the hollow fiber membrane filtration device 1 (FIG. 1) was assembled using the hollow fiber membrane module 10.

The separation accuracy of the hollow fiber membrane was 0.02 μm. The hollow fiber membrane was hydrophilized with polyvinyl alcohol, and the contact angle of the inner surface was 65 °. As the hollow fiber membrane bundle, one free at one end was used. As the air filter, a mist separator AFM30 (filtration accuracy (separation accuracy) of 0.3 μm) manufactured by SMC Corporation was used.

First, the raw water was supplied to the raw water side space of the housing, and the raw water was allowed to permeate from the outer surface to the inner surface of the hollow fiber membrane. Next, the compressed air that passed through the air filter pushed the filtered water from the inner surface of the hollow fiber membrane toward the outer surface. At this time, the pressure of the compressed air was 0.2 MPa, and the dew point of the compressed air was −5 ° C.

Next, the air inside the hollow portion of the hollow fiber membrane was evacuated. At this time, the depressurization was completed in a state where the pressure in the hollow portion of the membrane was 5 kPa higher than the atmospheric pressure. Next, compressed air was supplied to the filled raw water side space, and the hollow fiber membrane was washed with air bubbles. Finally, the raw water in the raw water side space was discharged from the housing.

The cycle consisting of the above steps was repeated over about 2 weeks. During that time, general bacteria in the filtered water were measured every day. Bacteria were measured according to the method specified by the Minister of Health, Labor and Welfare based on the provisions of the Ministerial Ordinance on Water Quality Standards.

(Example 2)
This is the same as in Example 1 except that the separation accuracy of the air filter is set to 1.0 μm.

(Example 3)
The same as in Example 1 except that the separation accuracy of the hollow fiber membrane is 2.0 μm, the contact angle of the inner surface of the hollow fiber membrane is 60 °, and the separation accuracy of the air filter is 0.1 μm.

(Example 4)
Same as Example 1 except that the contact angle of the inner surface of the hollow fiber membrane is 45 °, the separation accuracy of the air filter is 1.0 μm, and the difference between the pressure in the hollow portion of the membrane and the atmospheric pressure is 10 kPa. Is.

(Example 5)
This is the same as in Example 1 except that the difference between the pressure in the hollow portion of the membrane and the atmospheric pressure is set to 0 kPa.

(Example 6)
This is the same as in Example 3 except that the difference between the pressure in the hollow portion of the membrane and the atmospheric pressure is set to 0 kPa.

(Example 7)
This is the same as in Example 1 except that the separation accuracy of the air filter is set to 10 μm.

(Example 8)
This is the same as in Example 1 except that the separation accuracy of the hollow fiber membrane is set to 10 μm.

(Comparative Example 1)
The same as in Example 1 except that the air filter was not used.

The conditions of Examples 1 to 8 and Comparative Example 1 and the measurement results of bacteria are shown in Table 1 below.

As shown in Table 1, the number of times of detection of bacteria in Comparative Example 1 was larger than that in Examples 1 to 8. From this result, it was found that using the compressed air that has passed through the air filter to extrude the filtered water effectively contributes to the prevention of bacterial contamination in the hollow portion of the hollow fiber membrane. In particular, Example 1 in which the separation accuracy of the air filter is 0.01 to 1.0 μm, the separation accuracy of the hollow fiber membrane is 2.0 μm or less, and the difference between the pressure in the hollow portion of the membrane and the atmospheric pressure exceeds 0 kPa. In ~ 4, the number of times of detection of bacteria was 0, and particularly good results were obtained.

It should be understood that the embodiments and examples disclosed this time are exemplary in all respects and are not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1,1A, 1B Hollow fiber membrane filtration device 10 Hollow fiber membrane module 11 Hollow fiber membrane 11B Outer surface 11C Inner surface 11D Hollow part 13 Housing 20 Raw water supply means 30 Gas introduction path 30A Air intake port 31 Gas introduction valve 40 Separation means 41 Air filter 42 Mist separator 70 Depressurization path 71 Depressurization valve 72 Pressure detection unit 73 Control unit 100 Filtered water

Claims (9)

A method of cleaning the surface of the hollow fiber membrane in a hollow fiber membrane filtration device that filters raw water with a hollow fiber membrane.
A filtration step of extracting filtered water from the inner surface side by allowing raw water to permeate the hollow fiber membrane from the outer surface side of the hollow fiber membrane toward the inner surface side of the hollow fiber membrane.
A separation means arranged in a gas introduction path that guides a gas toward the inner surface side region of the hollow fiber membrane , and contaminates at least one of fine particles, water, oil, microorganisms, and viruses contained in the gas. by the gas which has passed through the separating means which can separate the material from the gas, and a backwash step of extruding the filtered water toward the outer surface side from the inner surface side of the hollow fiber membrane,
After the backwashing step, the inner surface side of the hollow fiber membrane is operated by operating a pressure relief valve provided in the pressure release path branched from the portion on the hollow fiber membrane side of the separation means in the gas introduction path. It is provided with a depressurization step of removing gas from the region on the inner surface side while maintaining the pressure in the region of the above at a pressure higher than the atmospheric pressure.
The depressurization step, the pressure in the inner surface side area of the hollow fiber membrane is characterized that you finished before equal to the atmospheric pressure, the cleaning method of the hollow fiber membrane filtration system. In the backwashing step, the air filter taken in from the outside is used as the gas, and an air filter having a separation accuracy of 0.01 μm or more and 1.0 μm or less and capable of separating the pollutants contained in the air is used as the separation means. The method for cleaning a hollow fiber membrane filtration device according to claim 1, wherein the hollow fiber membrane filtration device is used. The method for cleaning a hollow fiber membrane filtration device according to claim 1 or 2, wherein in the backwashing step, the filtered water is extruded by a gas adjusted to a pressure of 0.05 MPa or more and less than 0.5 MPa. The hollow fiber membrane filtration device according to any one of claims 1 to 3, wherein the hollow fiber membrane whose inner surface is hydrophilic until the contact angle of water becomes less than 90 ° is used. Cleaning method. Hollow fiber membrane and
A housing for accommodating the hollow fiber membrane and
A raw water supply means for supplying raw water into the housing,
A gas introduction path that guides gas toward the region on the inner surface side of the hollow fiber membrane, and
A separating means that is arranged in the gas introduction path and can separate at least one of pollutants such as fine particles, water, oil, microorganisms and viruses contained in the gas from the gas.
A depressurization path for releasing gas in the region on the inner surface side of the hollow fiber membrane by branching from a portion on the hollow fiber membrane side of the separation means in the gas introduction path.
A pressure relief valve provided in the pressure relief path and
A pressure detection unit that detects pressure in the region on the inner surface side of the hollow fiber membrane, and
A control unit that controls the pressure release valve is provided so that the pressure detected by the pressure detection unit is held at a pressure higher than the atmospheric pressure in the pressure release step after the backwashing step .
The hollow fiber membrane filtration device is characterized in that the control unit controls to close the pressure release valve before the pressure detected by the pressure detection unit becomes equal to the atmospheric pressure. The gas introduction path is provided with an air intake port for taking in air from the outside.
The hollow fiber membrane according to claim 5 , wherein the separation means includes an air filter having a separation accuracy of 0.01 μm or more and 1.0 μm or less and capable of separating the pollutants contained in the air. Filtration device. The fifth or sixth aspect of the present invention, wherein the gas adjusted to a pressure of 0.05 MPa or more and less than 0.5 MPa is configured to be guided toward the region on the inner surface side of the hollow fiber membrane. Hollow fiber membrane filtration device. The hollow fiber membrane filtration device according to any one of claims 5 to 7 , wherein the inner surface of the hollow fiber membrane is hydrophilized until the contact angle of water becomes less than 90 °. .. The separation means is configured so that at least one of water and oil contained in the gas can be separated from the gas.
The hollow fiber membrane according to any one of claims 5 to 8 , wherein the valve arranged after the separation means is configured to be driveable by a gas passing through the separation means. Filtration device.

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