Ultrafiltration system cleaning method and ultrafiltration system

Abstract

A method for cleaning an ultrafiltration system, wherein the ultrafiltration system comprises a plurality of modules having a primary side region and a secondary side region separated by a filter membrane and connected in parallel in the primary side region via a common discharge manifold, such a cleaning method comprises a backwashing process, and a discharge process of introducing gas into the plurality of modules via the discharge manifold after the backwashing process begins, and also comprises a process of forming a gas layer in the discharge manifold throughout the entire connection direction of the plurality of modules before the discharge process begins.

Description

Technical Field

[0001] The invention relates to a cleaning method of an ultrafiltration system and an ultrafiltration system. Background Art

[0002] Generally, as a method for separating and removing pollutants in water to be treated in various water treatment systems such as tap water treatment systems, sewage treatment systems, industrial water treatment systems, drainage treatment systems, and seawater desalination systems, a water treatment method using ultrafiltration is known.

[0003] Here, in the water treatment method using ultrafiltration, as the filtration continues, the dirty substances in the treated water adhere to the filter membrane and cause the filter membrane to become clogged, reducing the filtration performance. Therefore, the filter membrane needs to be regularly backwashed (hereinafter referred to as "backwashing") to eliminate the clogging.

[0004] Therefore, nowadays, in an ultrafiltration system that uses a filter membrane to filter treated water, backwash water is regularly passed from the secondary side (filtered water side) of the filter membrane to the primary side (treated water side), thereby backwashing the filter membrane. In addition, in the existing ultrafiltration system, the following operation (flushing operation) is performed: by circulating a flushing fluid such as compressed gas together with the backwash water from one side to the other in the primary side region, dirty substances accumulated on the side surface of the primary side region of the membrane are removed, thereby improving the cleaning effect. Here, in the ultrafiltration system, a structure in which multiple modules are connected in parallel is generally adopted (for example, refer to patent document 1). In an ultrafiltration system with such a structure, the flow difficulty of the flushing fluid deviates between the multiple modules connected in parallel, and as a result, the cleaning effect obtained deviates between the multiple modules.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 6362748 Summary of the invention

[0008] Problems to be solved by the invention

[0009] An object of the present invention is to obtain a sufficient and equal cleaning effect in an ultrafiltration system including a plurality of modules connected in parallel.

[0010] Solutions to Solve Problems

[0011] One scheme of the cleaning method of the ultrafiltration system is a cleaning method of the ultrafiltration system in which a plurality of modules including a primary side area and a secondary side area separated by a filter membrane are connected in parallel in the above-mentioned primary side area through a common discharge manifold, and is characterized in that it includes: a backwashing process of making backwash water flow relative to the above-mentioned multiple modules; and a discharge process of introducing gas into the above-mentioned multiple modules through the above-mentioned discharge manifold after the above-mentioned backwashing process starts, and includes a process of forming a gas layer in the above-mentioned discharge manifold throughout the entire connection direction of the above-mentioned multiple modules before the above-mentioned discharge process starts.

[0012] One scheme of an ultrafiltration system is an ultrafiltration system formed by connecting multiple modules including a primary side area and a secondary side area separated by a filter membrane in parallel in the primary side area through a common discharge manifold, characterized in that the above-mentioned discharge manifold is connected to the drain pipe via a taper, the cross-sectional area of ​​the end portion of the taper on the discharge manifold side is larger than the cross-sectional area of ​​the end portion of the taper on the drain pipe side, and the upper end position of the end portion of the taper on the discharge manifold side is located higher than the upper end position of the end portion of the taper on the drain pipe side in the vertical direction of the ultrafiltration system.

[0013] The effects of the invention are as follows.

[0014] According to the present invention, in an ultrafiltration system including a plurality of modules connected in parallel, a sufficient and uniform cleaning effect can be obtained in the plurality of modules. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 (a) to (d) are diagrams for explaining an example of the cleaning method of the ultrafiltration system of the present invention.

[0016] Figure 2 (a) to (e) are the continuation of Figure 1 Next, a diagram showing an example of the method for cleaning the ultrafiltration system of the present invention will be described.

[0017] Figure 3 (a) to (b) are diagrams for explaining an operation for forming a gas layer in another example of the cleaning method of the ultrafiltration system of the present invention.

[0018] Figure 4 (a) to (e) are diagrams for explaining an operation for forming a gas layer in another example of the cleaning method of the ultrafiltration system of the present invention.

[0019] Figure 5 (a) to (e) show an example of a schematic structure of the ultrafiltration system of the present invention, and illustrate an example of the cleaning method of the present invention when using such an ultrafiltration system.

[0020] Figure 6This is a schematic diagram illustrating an example of the shape of a special-shaped tapered pipe.

[0021] Figure 7 This is a diagram showing an example of a schematic configuration of an ultrafiltration system capable of implementing the cleaning method of the present invention. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the parts marked with the same reference numerals in each figure represent the same components.

[0023] The ultrafiltration system to which the ultrafiltration system cleaning method of the present invention can be applied is not particularly limited, and can be used to separate and remove pollutants in the treated water in various water treatments such as tap water treatment, sewage treatment, industrial water treatment, drainage treatment, and seawater desalination.

[0024] The inventors have conducted in-depth research on an ultrafiltration system having multiple modules connected in parallel, with the purpose of obtaining sufficient and equal cleaning effects in multiple modules. In addition, the inventors have focused on the following situation: when an ultrafiltration system consisting of multiple modules connected in parallel, including a primary side area and a secondary side area separated by a filter membrane, is backwashed, and when gas such as air is supplied to the primary side area, the raw water in the discharge header becomes a resistance to the supply of gas, which reduces the efficiency of the supply of gas. In more detail, the inventors have focused on the following situation: because the raw water in the discharge header becomes a resistance to the supply of gas, the amount of gas flowing to the module with smaller resistance (for example, the module near the supply port) is greater than the amount of gas flowing to other modules, and the resulting discharge effect is biased between modules. Therefore, the inventors have found that by forming a gas layer in the discharge header before supplying gas to the primary side area, the uniformity of the amount of gas flowing into the multiple modules can be improved, thereby completing the ultrafiltration system of this example.

[0025] (Brief structure of ultrafiltration system)

[0026] First, before explaining the cleaning method of the ultrafiltration system of this example, refer to Figure 7 The brief structure of an ultrafiltration system capable of implementing the cleaning method of this example is described. Figure 7 The ultrafiltration system 100 shown in the figure comprises: a plurality of modules 10, each of which includes a primary side region and a secondary side region separated by a filter membrane (not shown); and a common discharge header 20, which connects the plurality of modules 10 in parallel in the primary side region of the plurality of modules 10. Figure 7 The ultrafiltration system 100 shown includes: a treated water supply header 30 that supplies treated water from the primary side region to the plurality of modules 10; and a filtered water header 40 that discharges filtered water obtained by passing through the filtration membranes provided in the plurality of modules 10 to the outside of the system.

[0027] In addition, Figure 7 In the ultrafiltration system 100 shown in FIG. 1 , each of the plurality of modules 10 may include a membrane cap 11. Furthermore, the number of the plurality of modules 10 is not limited to the example shown in the figure ( Figure 7 In addition, the discharge header 20 shared by the plurality of modules 10 has a connection with each module 10 (in Figure 7 In the figure, the discharge manifold connection part 21 and the discharge valve 22 connected to the membrane cap 11 equipped for each module 10 are shown. In addition, although not shown in the figure, the discharge valve 22 can be provided in the following piping, which can function as an air supply pipe for conveying gas into the discharge manifold 20 and a drain pipe for discharging the treated water flowing into the discharge manifold 20. Furthermore, the treated water supply manifold 30 is provided with a treated water supply manifold connection part 31 and a treated water valve 32 connected to each module 10. Moreover, the filtered water manifold 40 is connected to each module 10 and is provided with a filtered water valve 41. In addition, the connection between the filtered water manifold 40 and each module 10 can be composed of a filtered water port not shown in the figure connected to the upper part of each module 10 in the vertical direction.

[0028] The plurality of modules 10 can also respectively have a plurality of submodules 12. The number of such submodules 12 is not limited to the illustrated example, and can be, for example, ten. Moreover, the submodule 12 can have a membrane element as a constituent element including a filter membrane not shown. The membrane element can have a small chamber with a diameter of several mm (for example, 2.5 mm) inside that serves as a fluid flow path. As the membrane element, there is no particular limitation, and a monomer module, a tubular module, a hollow fiber module, etc. can be used. Below, the case where the membrane element includes a monomer ceramic filter membrane is described.

[0029] also, Figure 7 The ultrafiltration system 100 shown in the figure can be in a state where all structural parts associated with the filtration process are filled with treated water or filtered water when the filtration process is in progress (i.e., the filtration process is being implemented). More specifically, the primary side region of the ultrafiltration system 100 is filled with treated water, and the secondary side region is filled with filtered water. The treated water transported from the treated water supply manifold 30 to the primary side region of the plurality of modules 10 seeps into the secondary side region through a filter membrane (not shown) and becomes filtered water, which is concentrated in the secondary side region, then transported to the filtered water manifold 40 and concentrated, and then discharged to the outside of the system. In addition, Figure 7 In the illustrated state, in the ultrafiltration system 100 , the discharge valve 22 is in a closed state, so that the treated water does not flow out from the discharge header 20 .

[0030] also, Figure 7In the embodiment, the treated water supply header 30 and the filtered water header 40 are shared by multiple modules 10 in the same manner as the discharge header 20. However, the ultrafiltration system capable of implementing the several cleaning methods exemplified below is not limited to Figure 7 In the manner shown, the treated water supply header 30 and the filtered water header 40 may not be connected to all the multiple modules 10 as shown in the figure, and each module 10 may be connected with an independent treated water supply pipe, filtered water pipe, and various valves that can be installed on the above-mentioned pipes.

[0031] and, Figure 7 In the embodiment, a discharge valve 22 is provided at one end of the discharge manifold 20, and such an end can function as an air supply port. However, the position of the discharge valve 22, that is, the position of the air supply port of the discharge manifold 20 is not particularly limited, and can be any position. For example, an air supply pipe (not shown) accompanied by the discharge valve 22 may be connected to the central part or other intermediate area instead of the end in the longitudinal direction of the discharge manifold 20.

[0032] Similarly, regarding the treated water supply header 30, a treated water conveying pipe (not shown) with a treated water valve 32 may be connected to the central portion or other intermediate region instead of the end portions in the longitudinal direction.

[0033] The relative positional relationship between the position of the air supply port of the discharge header 20 and the connection position of the treated water conveying pipe to the treated water supply header 30 is not particularly limited, and any positional relationship may be adopted.

[0034] Below, refer to Figure 1 to Figure 4 For those who have Figure 7 Various descriptions will be given of the cleaning methods of the ultrafiltration system that can be implemented by the ultrafiltration system with the simplified structure shown.

[0035] Also, for clarity, Figure 7 Some of the reference symbols shown are sometimes Figure 1 to Figure 4 Not shown.

[0036] (Ultrafiltration system cleaning method)

[0037] Here, Figure 1 (a)~(d) and Figure 2 (a) to (e) are diagrams illustrating an example of a method for cleaning an ultrafiltration system according to the present invention. Figure 1 (a)~(d) and Figure 2 In (a) to (e), the filtration process is shown in stages from the final stage ( Figure 1 (a)) to the end of the discharge process ( Figure 2 In addition, for the sake of clarity, Figure 1 and Figure 2 In Figure 1 (a) and Figure 2 (a) is indicated by symbols, Figure 1 (b) to (d) and Figure 2 Symbols are omitted in (b) to (e).

[0038] Figure 1 (a) is a diagram illustrating the ultrafiltration system 100 in a state where a filtration process is being performed. Figure 1 The ultrafiltration system 100 in the state shown in (a) is about to end the filtration process. Figure 1 As shown in (b), the treated water valve 32 and the filtered water valve 41 are closed, the discharge valve 22 is opened, the treated water is discharged from the discharge manifold 20, and a gas layer is formed in the discharge manifold 20 (a step of forming a gas layer by draining water). In this way, before the start of the following discharge process, by forming a gas layer in the discharge manifold 20 that covers the entire connection direction of the multiple modules 10, gas can be evenly introduced into the multiple modules 10 connected in parallel to each other, and in the above-mentioned multiple modules 10, the cleaning effect obtained by backwashing can be sufficient and equal. In addition, as Figure 1 As shown in (b), by forming a gas layer in the discharge manifold 20 after the filtration process is completed and before the backwashing process begins, a gas layer can be more reliably formed in the entire connection direction of multiple modules compared to the case where the gas layer is formed at a later time. As a result, the cleaning effect obtained by backwashing can be further reliably made sufficient and uniform.

[0039] In addition, Figure 1 (b) shows a situation in which the discharge manifold 20 is empty and the gas layer throughout the entire connection direction of the multiple modules 10 substantially extends throughout the entire area of ​​the discharge manifold 20. However, the cleaning method of this example is not limited to the illustrated method. Specifically, the gas layer only needs to extend throughout the entire connection direction of the multiple modules 10. For example, a treated water layer may remain in the area below the ultrafiltration system 100 in the vertical direction of the discharge manifold 20 and extend thereon. The water level of the treated water layer in the discharge manifold 20 can be reliably controlled, for example, by adjusting the time when the discharge valve 22 is in an open state manually or automatically using a timer. As a result, a gas layer of the desired volume can be reliably formed in the discharge manifold 20.

[0040] Figure 1(c) shows the state of the ultrafiltration system 100 shortly after the backwash process is started. In the backwash process, the filtered water valve 41 is opened, and the backwash water pressurized by the backwash pressurizing mechanism (not shown) is made to flow in the direction opposite to the filtering direction. In addition, the backwash water can be a part of the filtered water obtained in the filtering process that can be stored in a backwash water tank (not shown) or the like. In addition, the backwash pressurizing mechanism (not shown) is not particularly limited, and can be installed, for example, by a backwash pump or the like.

[0041] Here, in the backwashing process, shortly after the start, first, pressure is applied from the secondary side region to the primary side region for the purpose of removing the contaminants attached to the surface of the filter membrane in the module 10 facing the primary side region, and for this purpose, the discharge valve 22 and the treated water valve 32 are set to a closed state, and the pressurized backwashing water is reversed in the filtered water header 40 and flows into the plurality of modules 10. Figure 1 In the state shown in (c), by increasing the pressure in the ultrafiltration system 100, Figure 1 In the stage (b) shown in FIG. 1 , the gas layer formed in the discharge header 20 is temporarily compressed and its volume is reduced. Figure 1 The temporary condition in the backwash process shown in (c), that is, the filtered water valve 41 is opened but the discharge valve 22 and the treated water valve 32 are closed during the backwash process, and the state in which the ultrafiltration system 100 becomes high pressure due to the inflow of pressurized backwash water is called the backwash pressurization step.

[0042] Figure 1 (d) shows the following steps (backwash drainage outflow step): Figure 1 After the backwash pressurization step shown in (c), the treated water valve 32 is opened to allow the backwash water to flow out to the primary side area, and backwash drainage including the dirty substances stripped off in the backwash pressurization step is obtained. In the backwash drainage outflow step, the dirty substances stripped off from the filter membrane are washed away and removed. In addition, in the backwash drainage outflow step, since the pressure in the ultrafiltration system 100 is reduced, the treated water flowing into the discharge header 20 flows out from the discharge header 20 again, and the discharge header 20 can become empty again.

[0043] Figure 2(a) shows the state of the ultrafiltration system 100 shortly after the discharge process is started. When the discharge process is started, the discharge valve 22 is opened, and the compressed gas (for example, compressed air) in a pressurized state flows into the discharge manifold 20 through the discharge mechanism not shown in the figure. Here, in the discharge manifold 20, as described above, there is a gas layer (empty in the illustrated example) throughout the entire connection direction of the multiple modules 10. Therefore, when the compressed gas flows in the discharge manifold 20, the resistance is particularly small compared to the state of the discharge process included in the cleaning method according to the existing method in which the discharge manifold 20 is filled with treated water. Therefore, between the multiple modules 10, the compressed gas begins to flow in at approximately the same time, and the compressed gas is distributed to each module 10 approximately equally through the discharge process, and circulates in each module 10. Therefore, between the multiple modules 10, it is possible to effectively suppress the deviation of the cleaning effect obtained as a result of the backwash process.

[0044] Moreover, if Figure 2 As shown in (b), for example, in a monomer-type ceramic filter membrane whose vertical direction and length direction are consistent in the ultrafiltration system 100, the compressed gas flows from the upper side in the vertical direction toward the lower side in the vertical direction, and is mixed with water (treated water and / or backwash water) in the primary side region in the module 10 to form a gas-liquid mixed state, and can flow down. At this time, similarly, in the flow path of the compressed gas, the deviation of the resistance between the multiple modules 10 is also very small, so the same cleaning effect can be obtained in all modules.

[0045] Moreover, if Figure 2 As shown in (c) of FIG. 1 , the gas and water (treated water and / or backwash water) become a gas-liquid mixed state and flow from the plurality of modules 10 into the treated water supply header 30. Figure 2 As shown in (d) of FIG. 1 , the backwash wastewater is discharged from the treated water supply header 30. Figure 2 As shown in (e), after the filtered water valve 41 is closed and all the backwash wastewater is discharged from the treated water supply header 30, compressed gas is supplied from the discharge header 20 for a few seconds and discharged from the treated water supply header 30. After such a few seconds of gas supply, the discharge process is completed.

[0046] The above, according to the reference Figure 1-2 An example of a cleaning method is to make the cleaning effect obtained by backwashing sufficient and equal among a plurality of modules connected in parallel. Figure 3-4 Several other examples of cleaning methods are described.

[0047] Figure 3 (a) to (b) are diagrams for explaining the operation of forming a gas layer in another example of the cleaning method of the ultrafiltration system of the present invention. The cleaning method of this example is different from the reference in the following aspects: Figure 1-2 The cleaning method described is different: when a gas layer is formed in the discharge manifold 20, the discharge valve 22 is opened, and the water is not directly discharged from the discharge manifold 20, but the treated water valve 32 of the treated water supply manifold 30 is opened to discharge the treated water included in the primary side area of ​​the module 10 from the treated water supply manifold 30, thereby lowering the water level in the discharge manifold 20 and forming a gas layer. In addition, for the sake of clarity, only Figure 3 (a) is indicated by symbols, Figure 3 The symbols are omitted in (b).

[0048] like Figure 3 As shown in (a), after the filtration process is completed, the discharge valve 22 and the treated water valve 32 are opened to discharge the treated water from the treated water supply manifold 30 (a step of forming a gas layer by draining water). Figure 3 As shown in (b), the water level in the discharge manifold 20 is lowered (water level zero in the illustrated example), forming a gas layer throughout the entire connection direction of the multiple modules 10. At this time, by adjusting the time when the discharge valve 22 and the treated water valve 32 are opened, the water level in the discharge manifold 20 can be controlled to the desired water level. The control can be performed manually or by automatic control using a timer or the like. If a gas layer is formed by discharging the treated water retained in the discharge manifold 20, a gas layer can be further reliably formed throughout the entire connection direction of the multiple modules 10, and as a result, the cleaning effect obtained by backwashing can be further reliably equalized.

[0049] Moreover, the backwashing process after the formation of the gas layer can be compared with the reference Figure 1 (c)~ Figure 2 The same method as described in (e) is followed.

[0050] Figure 4 (a) to (e) are diagrams for explaining the operation for forming a gas layer in another example of the cleaning method of the ultrafiltration system of the present invention. The cleaning method of this example performs the operation for forming a gas layer in the filtration process, which is different from the reference Figure 1 to Figure 3 The various cleaning methods described are different. In addition, for the sake of clarity, only Figure 4 (a) is indicated by symbols, Figure 4 Symbols are omitted in (b) to (e).

[0051] Figure 4 The state shown in (a) indicates the state at the time of starting the filtration process. In the ultrafiltration system 100 in such a state, the treated water valve 32 and the discharge valve 22 are in an open state. Figure 4 (b)~

[0052] Figure 4 As shown in (c), a water filling operation is performed, that is, the treated water is allowed to flow from the primary side area into the plurality of modules 10 through the treated water valve 32 and the treated water supply header 30. Then, as shown in FIG. Figure 4 As shown in (c), before the treated water is about to reach the discharge manifold 20, or even if the treated water reaches the discharge manifold 20, the water filling operation is stopped at the timing when the gas layer throughout the entire connection direction of the multiple modules 10 becomes a state maintained in the discharge manifold 20. When the water filling operation is stopped, the discharge valve 22 is set to a closed state. In addition, it is also possible to stop the transportation of the treated water when the water filling operation is stopped and before closing the discharge valve 22, and then close the discharge valve 22. In this case, when the filtering process starts, it is necessary to start the transportation of the treated water again. If a gas layer is formed in the discharge manifold 20 by adjusting the stop timing of the water filling operation in the filtering process, there is no need to perform additional operations for forming the gas layer, so the cleaning method of the filtration system of the present invention can be made efficient.

[0053] After that, the filtered water valve 41 is opened to perform a filtering operation to make the filtered water flow out from the filtered water header 40. Figure 4 As shown in (d), the gas layer in the discharge header 20 will be compressed and the volume will decrease. Figure 4 When the backwashing process starts the backwashing drainage outflow step as shown in (e), the pressure in the ultrafiltration system 100 decreases and the discharge header 20 may become empty again. Figure 2 As shown in (a) to (e).

[0054] Above, refer to Figure 1 to Figure 4 and Figure 7 , for those who can Figure 7 Various cleaning methods implemented by the ultrafiltration system 100 of the structure briefly shown in FIG. Figure 5 (a) to (e) of the present invention describe an example of a schematic structure of the ultrafiltration system of the present invention and an example of the cleaning method of the present invention when using the ultrafiltration system.

[0055] exist Figure 5 In the ultrafiltration system 101 shown in (a), the discharge header 20 is connected to the pipe 50 that can function as a drain pipe and an air supply pipe via the special-shaped reducer 23 as a reducer of a predetermined shape, which is similar to the reference Figure 7The difference of the ultrafiltration system 100 described. The cross-sectional area of ​​the end of the special-shaped reducer 23 on the discharge manifold 20 side needs to be larger than the cross-sectional area of ​​the end of the special-shaped reducer 23 on the piping 50 side. In addition, the upper end position of the end of the special-shaped reducer 23 on the discharge manifold 20 side needs to be located higher than the upper end position of the end of the special-shaped reducer 23 on the piping 50 side in the vertical direction of the ultrafiltration system 101. If such a special-shaped special-shaped reducer 23 is connected to the discharge manifold 20, as long as the discharge valve 22 equipped with the piping 50 is in an open state, water will not stay in the portion (area) of the discharge manifold 20 that is higher than the upper end position of the special-shaped reducer 23 on the piping 50 side in the vertical direction, so that a gas layer can be formed well. Therefore, in the discharge manifold 20, a gas layer can be more reliably formed throughout the entire connection direction of multiple modules 10. Therefore, a sufficient and equal backwashing effect can be obtained between multiple modules connected in parallel. Figure 6 The shape of the special-shaped reducer 23 is described below.

[0056] Reference Figure 5 (b) to (e) briefly describe the conditions from the filtration process to the start of the backwash process using the ultrafiltration system 101 having the above structure. Figure 5 Reference symbols are omitted in (b) to (e).

[0057] Figure 5 The state shown in (b) indicates the state at the time of starting the filtration process. In the ultrafiltration system 101 in such a state, the treated water valve 32 and the discharge valve 22 are in an open state. Figure 5 (b)~ Figure 5 As shown in (c), a water filling operation is performed to allow treated water to flow from the primary side area into the plurality of modules 10 via the treated water valve 32 and the treated water supply header 30. Then, as shown in FIG. Figure 5 As shown in (c), even if the treated water reaches the discharge header 20, the gas layer throughout the entire connection direction of the plurality of modules 10 is maintained in the discharge header 20. This is because, as long as the discharge valve 22 is in an open state, the treated water will not stay in a portion (area) that is higher than the upper end position of the pipe 50 side of the special-shaped tapered pipe 23 in the vertical direction. In this way, according to the ultrafiltration system 101, it is possible to avoid the discharge header 20 being filled with treated water in terms of structure.

[0058] Then, if Figure 5 As shown in (d), when the filtration process starts, the discharge valve 22 is closed and the filtered water valve 41 is opened to allow the filtered water to flow out of the system. In addition, at this time, the gas layer in the discharge manifold 20 is compressed due to the increase in the internal pressure of the ultrafiltration system 101, and thus shrinks. Figure 5As shown in (e), by ending the filtration process and starting the backwash process, the internal pressure of the ultrafiltration system 101 decreases, and along with this, the pressure in the discharge header 20 decreases, the water level in the discharge header 20 decreases, and the discharge header 20 can become empty.

[0059] In addition, in the cleaning method using the ultrafiltration system 101, reference Figure 1 (b) or Figure 3 The operation for forming a gas layer described in (a), i.e., the "step of forming a gas layer by draining water" via the discharge manifold 20 or the treated water supply manifold 30. However, as described above, in the ultrafiltration system 101, it is structurally possible to avoid filling the discharge manifold 20 with treated water. Therefore, it is not necessary to implement the above-mentioned step of forming a gas layer by draining water and to stop the water filling operation before the discharge manifold 20 becomes full of water, so as to create a "state in which the gas layer throughout the entire connection direction of the plurality of modules 10 is maintained in the discharge manifold 20". In this way, according to the ultrafiltration system having a tapered tube having a predetermined shape, a gas layer can be easily formed without the need for special control.

[0060] Here, refer to Figure 6 , an example of the shape of the special-shaped tapered tube 23 is described. Figure 6 As shown in the schematic diagram of , the special-shaped tapered tube 23 has a small diameter portion 23a with a constant diameter and an eccentric tapered portion 23b. Moreover, the ratio of the diameter (inner diameter) D2 of the open end of the eccentric tapered portion 23b to the diameter (inner diameter) D1 of the small diameter portion 23a is D1:D2=1:2 to 1:4, preferably D1:D2=1:3. In addition, the ratio of the length L1 of the axial direction of the small diameter portion 23a to the length L2 of the eccentric tapered portion 23b is L1:L2=1:2 to 2:1, preferably L1:L2=4:3. In addition, the length L2 of the eccentric tapered portion 23b is not the length of the eccentric axial direction of the eccentric tapered portion 23b, but the length of the eccentric tapered portion 23b when measured in the axial direction of the small diameter portion 23a. In addition, the length L1 of the axial direction of the small diameter portion 23a is not particularly limited, and can be, for example, less than 10 cm. Furthermore, although not shown, the special-shaped tapered pipe 23 may have a flange or the like that can serve as a connection portion with other components.

[0061] Furthermore, when the special-shaped tapered pipe 23 is mounted in the ultrafiltration system 101, the upper end position of the eccentric tapered portion 23b is arranged in a manner that is higher than the upper end position of the small diameter portion 23a in the vertical direction of the ultrafiltration system 101. As a result, the area in the discharge header 20 located at a position higher than the upper end position of the small diameter portion 23a will not be filled with water as long as the discharge valve 22 is in an open state.

[0062] Industrial Applicability

[0063] According to the present invention, there is provided a method for cleaning an ultrafiltration system including a plurality of modules connected in parallel, and a sufficient and equal cleaning effect can be obtained in the plurality of modules.

[0064] Furthermore, according to the present invention, it is possible to provide an ultrafiltration system including a plurality of modules connected in parallel, wherein when backwashing is performed, a sufficient and equal cleaning effect can be obtained among the plurality of modules.

[0065] Explanation of symbols

[0066] 10—module, 11—membrane cap, 12—submodule, 20—discharge header, 21—discharge header connection portion, 22—discharge valve, 23—special-shaped tapered tube, 23a—small diameter portion, 23b—eccentric conical portion, 30—treated water supply header, 31—treated water supply header connection portion, 32—treated water valve, 40—filtered water header, 41—filtered water valve, 50—piping, 100, 101—ultrafiltration system.

Claims

1. A method for cleaning an ultrafiltration system, wherein the ultrafiltration system comprises a plurality of modules including a primary side region and a secondary side region separated by a filter membrane and connected in parallel in the primary side region through a common discharge header, wherein the method for cleaning the ultrafiltration system is characterized in that it comprises: a backwashing step of flowing backwash water relative to the plurality of modules; and a discharge step of introducing gas into the plurality of modules through the discharge header after the backwash step starts; Furthermore, the method includes forming a gas layer in the discharge header in the entire connection direction of the plurality of modules before the discharge step is started. The gas layer is formed by discharging the treated water held in the discharge header, or A filtering step is further included before the backwashing step. When the filtering step is started, when the plurality of modules are filled with water, the water filling operation is stopped before the discharge header is filled with water, thereby forming the gas layer.

2. The cleaning method of the ultrafiltration system according to claim 1, characterized in that: Before the backwashing step is started, the gas layer is formed.

3. An ultrafiltration system, used in the cleaning method of the ultrafiltration system according to claim 1, wherein a plurality of modules including a primary side region and a secondary side region separated by a filter membrane are connected in parallel in the primary side region through a common discharge header, characterized in that: The discharge header is connected to the drain pipe via a reducer. The cross-sectional area of ​​the discharge header side end of the above-mentioned reducer is larger than the cross-sectional area of ​​the drain pipe side end of the above-mentioned reducer, and the upper end position of the discharge header side end of the above-mentioned reducer is located higher than the upper end position of the drain pipe side end of the above-mentioned reducer in the vertical direction of the ultrafiltration system.

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