Membrane filtration apparatus and method for cleaning filtration membrane

Abstract

To provide a membrane filtration apparatus which can be backwashed without using a dedicated pump, and a method for washing a filtration membrane.SOLUTION: In a membrane filtration device 100, a membrane module is constituted of a plurality of membrane modules 1, 1', and the membrane modules 1, 1' are provided with filtration membranes 14, 14'. for filtering water to be treated, water to be treated inflow parts 11, 11' for allowing the water to be treated to flow in, treated water discharge parts 12, 12' for discharging treated water filtered by the filtration membranes 14, 14'., and impurity substance discharge parts for discharging impurity substances removed when cleaning the filtration membranes 14, 14'., which also serve as the water to be treated inflow parts 11, 11'. The treated water passed through one membrane module 1 is sent into the other membrane module 1' without being stored to wash the filter membrane of the other membrane module 1' and the treated water passed through the other membrane module 1' is sent into one membrane module 1 without being stored to wash the filter membrane of one membrane module 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a membrane filtration device for obtaining colorless, transparent treated water by filtering water containing impurities, and a method for cleaning the filtration membrane attached to the device. [Background technology]

[0002] In membrane filtration systems that turn polluted water into clear, colorless water, impurities accumulate on the filtration membrane during filtration. These accumulated impurities reduce the flow rate of water passing through the filtration membrane, lowering filtration efficiency and potentially damaging the filtration membrane. Therefore, when impurities accumulate on the filtration membrane, the impurities are removed by performing backwashing (hereinafter also referred to as backwashing), in which treated water is flowed in the opposite direction, flushing, bubbling, etc.

[0003] For example, Patent Document 1 discloses a technique for an external pressure type membrane filtration device that allows backwashing by passing filtered water from the inside to the outside of the hollow fiber membranes in a hollow fiber membrane module. In the backwashing described in Patent Document 1, "filtrate water in a filtrate water tank is introduced into the hollow fiber membrane module from a filtrate water inlet via a backwash valve, passes through the thick parts of the hollow fiber membranes from the inside of the hollow fiber membranes, and seeps into the space outside the hollow fiber membranes. During this process, suspended matter that has accumulated in the pores in the thick parts of the hollow fiber membranes is pushed out to the outside of the hollow fiber membranes, thereby cleaning the hollow fiber membranes." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-101418 Summary of the Invention [Problem to be solved by the invention]

[0005] However, backwashing requires a backwash pump to send the treated water stored in the tank in the opposite direction. Even with the technology described in Patent Document 1, a pump to send the filtered water in the opposite direction for backwashing is required, although the drawing in Patent Document 1 omits the liquid feed pump. In particular, when the piping distance from the storage tank to the membrane module is long, it may be necessary to select a backwash pump with a high discharge capacity, taking into consideration the pressure loss in the piping.

[0006] Pumps take up a lot of space in the entire membrane filtration system and are a high proportion of the cost. In addition, having a pump for filtration and a pump for backwashing increases the failure rate of the entire membrane filtration system, so there was a need for technology that did not require a dedicated pump for backwashing.

[0007] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a membrane filtration device and a method for cleaning a filtration membrane that can perform backwashing without using a dedicated pump. [Means for solving the problem]

[0008] The means adopted by the present inventors to solve the above problems will be described below. The membrane filtration device of the present invention is a membrane filtration device equipped with a membrane module for removing impurities from water to be treated that contains the impurities and obtaining treated water. In the present invention, impurities refer to substances contained in treated water that are unnecessary for the intended purpose (for example, drinking or hand washing) and should be removed, and examples thereof include suspended solids, ionic components, bacteria, viruses, and the like.

[0009] The basic configuration of the membrane filtration device is a configuration comprising a filtration membrane for filtering the water to be treated, a treated water inlet section into which the water to be treated flows, a treated water outlet section for discharging the treated water filtered by the filtration membrane, and an impurity outlet section for discharging impurities removed when the filtration membrane is cleaned. Here, the membrane module is composed of a plurality of membrane modules, and treated water that has passed through one membrane module is sent to the other membrane module without being stored therein, thereby enabling the filtration membrane of the other membrane module to be cleaned. Also, treated water that has passed through the other membrane module is sent to one membrane module without being stored therein, thereby enabling the filtration membrane of the one membrane module to be cleaned.

[0010] In a typical membrane filtration device, treated water that has passed through a membrane module is stored in a tank or the like and is used as drinking water as needed, while the treated water stored in the tank is used as backwash water when cleaning the filtration membrane. However, in the present invention, multiple membrane modules are provided, and treated water that has passed through one membrane module is sent directly to the other membrane module without being stored. This allows the treated water obtained by one membrane module or the other membrane module to be immediately sent to the other membrane module or one membrane module, so that the membrane modules can be backwashed while maintaining the necessary and sufficient water pressure without an extreme drop in water pressure.

[0011] As a means that can be adopted to solve the problem, it is possible to configure the system so that the filtration membrane in the other membrane module is alternately washed with treated water that has passed through one membrane module, and the filtration membrane in the one membrane module is alternately washed with treated water that has passed through the other membrane module.

[0012] In this configuration, by periodically switching the membrane module that performs the filtration, for example, it is possible to perform the filtration operation using one membrane module, and after the other membrane module has been washed with the treated water obtained thereby, switch to the other membrane module to perform the filtration operation, and then wash the one membrane module with the treated water obtained thereby. In this way, it is possible to alternately backwash one membrane module and the other membrane module.

[0013] As yet another means that can be adopted to solve the problem, the one membrane module and the second membrane module can be configured as follows. One membrane module is configured to include a first treated water inlet connected to a pump that sends out the treated water for filtration, a first treated water outlet that discharges the treated water to the outside, and a first impurity outlet that discharges impurities removed when the filtration membrane is cleaned to the outside. The other membrane module is configured to include a second treated water inlet connected to the pump, a second treated water outlet for discharging the treated water to the outside, and a second impurity outlet for discharging impurities removed during cleaning of the filtration membrane to the outside. The first treated water discharge section and the second treated water discharge section are then connected by a communication pipe.

[0014] Each membrane module is configured to have a treated water inlet, a treated water outlet, and an impurity outlet, and the treated water outlet is connected by a connecting pipe, which can be used both as a pipe for transporting treated water when it is used as drinking water through normal filtration operations, and as a pipe for transporting water for backwashing, thereby simplifying the configuration of the entire device.

[0015] As yet another means that can be adopted to solve the problem, the membrane filtration device can be configured to use an internal pressure filtration membrane. In this configuration, the first treated water discharge section includes a first upper treated water discharge section and a first lower treated water discharge section. Also, the second treated water discharge section includes a second upper treated water discharge section and a second lower treated water discharge section.

[0016] During cleaning of the filtration membranes, the treated water filtered by the one membrane module is not stored but can be sent to the second upper treated water discharge port or the second lower treated water discharge port of the other membrane module through the communicating pipe, and the treated water filtered by the other membrane module is not stored but can be sent to the first upper treated water discharge port or the first lower treated water discharge port of the one membrane module through the communicating pipe. Furthermore, the first treated water inlet also serves as the first impurity discharge section, and the second treated water inlet also serves as the second impurity discharge section.

[0017] In the internal pressure type, impurities accumulate on the inside of the filtration membrane. With the above-described configuration, treated water can be introduced as backwash water from the top or bottom of the membrane module through a connecting pipe, allowing the water to permeate from the outside to the inside of the filtration membrane. Furthermore, the impurities removed by washing can be discharged from the impurity discharge section, which also serves as the inlet for treated water. By using the inlet for treated water as the impurity discharge section, the structure of the membrane module can be simplified.

[0018] As yet another means that can be adopted to solve the problem, the membrane filtration device can be configured to use an external pressure type filtration membrane. In this configuration, the first impurity discharge section is configured to include a first upper impurity discharge section and a first lower impurity discharge section. Also, the second impurity discharge section is configured to include a second upper impurity discharge section and a second lower impurity discharge section. During cleaning of the filtration membranes, the treated water filtered by the one membrane module is not stored but can be sent to the second treated water discharge portion of the other membrane module through the communicating pipe, and the treated water filtered by the other membrane module is not stored but can be sent to the first treated water discharge portion of the one membrane module through the communicating pipe.

[0019] Furthermore, during cleaning of one of the membrane modules, impurities removed from the filtration membranes are discharged from either or both of the first upper impurity discharge section and the first lower impurity discharge section, and during cleaning of the other membrane module, impurities removed from the filtration membranes are discharged from either or both of the second upper impurity discharge section and the second lower impurity discharge section.

[0020] In the external pressure type, impurities accumulate on the outside of the filtration membrane. With the above-described configuration, treated water can be introduced as backwash water from the treated water discharge port of the membrane module through a connecting pipe, allowing it to permeate from the inside to the outside of the filtration membrane. Furthermore, impurities removed by washing can be discharged from the upper impurity discharge port or the lower impurity discharge port. For example, water in the membrane module can be discharged by draining it from the lower impurity discharge port. Furthermore, when bubbling or the like is used in combination, the water to be treated can be introduced from the treated water inlet port, and the impurities removed by bubbling or the like and the inflowing treated water can be discharged from the upper impurity discharge port.

[0021] Yet another means that can be employed to solve the problem is a method for cleaning the filtration membrane in a membrane filtration device for obtaining treated water from which impurities have been removed from water to be treated that contains the impurities. The basic configuration of the above-mentioned method for cleaning filtration membranes is such that the membrane filtration device is equipped with a plurality of membrane modules, and treated water filtered by one membrane module is used without being stored to clean the other membrane module, and treated water filtered by the other membrane module is used to clean the one membrane module without being stored.

[0022] By using the above method, the treated water obtained by one membrane module or the other membrane module can be immediately sent to the other membrane module or one membrane module, so that the other membrane module can be backwashed while maintaining the necessary and sufficient water pressure without an extreme drop in water pressure. [Effects of the Invention]

[0023] The membrane filtration device and the method for cleaning a filtration membrane of the present invention are provided with a plurality of membrane modules, and are configured so that treated water filtered by one membrane module or the other membrane module is used to clean the other membrane module or one membrane module without being stored, thereby eliminating the need for a dedicated pump for backwashing, resulting in effects such as reduced costs, simplification of the device, and a lower failure rate. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic diagram illustrating a membrane filtration device of the present invention. [Figure 2] 1 is a cross-sectional view showing a membrane module of the present invention. [Figure 3] FIG. 2 is an explanatory diagram showing the backwash mechanism of the present invention. [Figure 4] FIG. 2 is a schematic diagram showing a membrane filtration device according to a first modified example of the present invention. [Figure 5] FIG. 2 is a cross-sectional view showing a membrane module according to a first modified example of the present invention. [Figure 6] FIG. 10 is an explanatory diagram showing a backwashing mechanism in Modification 1 of the present invention. [Figure 7] FIG. 10 is a cross-sectional view showing a membrane module according to a second modification of the present invention. [Figure 8] FIG. 10 is an explanatory diagram showing a backwashing mechanism in Modification 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the following explanation, the figures are shown schematically to simplify the explanation. For example, the hollow fiber membranes 14·14... are actually bundled together in numbers of tens to hundreds, but in the figures they are simply shown as a few.

[0026] As shown in FIG. 1, the membrane filtration device 100 of the present invention includes a first membrane module 1, which is one of the membrane modules, a second membrane module 1', which is the other membrane module, a treated water tank 2 for storing the treated water, a pump 3 for sending the treated water to each of the membrane modules 1·1', a treated water tank 4 for storing the treated water, three-way valves 5·5'... for switching the water channels, manual valves 6·6'..., an intake and exhaust valve 7 for intake and exhaust, and flow gauges 8·8'.

[0027] Each membrane module 1, 1' is a so-called internal pressure membrane filtration module, a hollow fiber membrane module that performs filtration by the crossflow method. The first membrane module 1 is equipped with a first treated water inlet 11 for introducing the treated water, a first treated water outlet 12 for discharging the filtered treated water, and a first concentrated water outlet 13 for discharging concentrated water, the concentration of which has increased due to filtration, to the outside. Here, the first treated water outlet 12 is equipped with a first upper treated water outlet 121 located at the top and a first lower treated water outlet 122 located at the bottom. As will be described later, during cleaning of the filtration membrane, the first treated water inlet 11 also serves as the impurity outlet, and impurities can be discharged by switching the first treated water three-way valve 51.

[0028] The second membrane module 1', like the first membrane module 1, is equipped with a second treated water inlet 11', a second treated water outlet 12', and a second concentrated water outlet 13'. Here, the second treated water outlet 12' is equipped with a second upper treated water outlet 121' located at the top and a second lower treated water outlet 122' located at the bottom. Similarly, during cleaning of the filtration membrane, the second treated water inlet 11' also serves as an impurity outlet, and impurities can be discharged by switching the second treated water three-way valve 51'.

[0029] The water to be treated in the water to be treated tank 2 is pumped out by a pump 3. The discharge side of the pump 3 branches into a first water to be treated pipe L1 that is sent to one membrane module 1 and a second water to be treated pipe L1' that is sent to the other membrane module 1'. The first treated water pipe L1 branches via a first treated water three-way valve 51 into a first treated water inlet 11 and a first drain pipe L4. Similarly, the second treated water pipe L1' branches into a second treated water inlet 11' and a second drain pipe L4' via a second treated water three-way valve 51'.

[0030] The first treated water discharge section 12, which discharges treated water from which impurities have been removed by filtration, is composed of a first upper treated water discharge section 121 and a first lower treated water discharge section 122. A first treated water pipe L3 is connected to the first lower treated water discharge section 122, which is connected to the treated water tank 4 via a first treated water valve 61 and a first flow gauge 8. Similarly, the second treated water inlet section 12' is composed of a second upper treated water outlet section 121' and a second lower treated water outlet section 122'. A second treated water pipe L3' is connected to the second lower treated water outlet section 122', and is connected to the treated water tank 4 via a second treated water valve 61' and a second flow gauge 8'.

[0031] The first upper treated water discharge section 121 and the second upper treated water discharge section 121′ are connected by a communication pipe L2. An intake / exhaust valve 7 for intake and exhaust is connected to the middle of the communication pipe L2.

[0032] On the other hand, the first concentrated water discharge part 13 for discharging concentrated water in which the concentration of impurities has increased due to filtration is connected to the tank 2 for water to be treated and is configured to circulate as water to be treated. Similarly, the second concentrated water discharge part 13' is also connected to the tank 2 for water to be treated, and is configured to circulate as water to be treated.

[0033] Here, the configuration of the membrane modules 1 and 1' will be described. Note that the second membrane module 1' has the same configuration as the first membrane module 1, so the first membrane module 1 will be described as a representative. As shown in Figure 2, the first membrane module 1 of the present invention is configured by vertically arranging a plurality of first hollow fiber membranes 14, which are elongated cylindrical membranes, in a substantially cylindrical resin container 15. A first treated water inlet 11 is provided at the bottom of the container 15, and the treated water can flow into the first hollow fiber membranes 14 by a pump 3. The treated water flowing in from the first treated water inlet 11 passes through the first hollow fiber membranes 14, and is discharged via a first concentrated water discharge section 13.

[0034] The upper ends of the first hollow fiber membranes 14 are fixed to the upper end fixing wall 17, and the lower ends are fixed to the lower end fixing wall 18. That is, the insides of the first hollow fiber membranes 14 are connected to the first concentrated water discharge section 13, and the outsides are fixed so as to face the inside of the vessel 15. As a result, the interior of the vessel 15 is watertightly partitioned into a space outside the first hollow fiber membranes 14 and a space connected to the first concentrated water discharge section 13 and the first treated water inlet section 11.

[0035] Regarding the first hollow fiber membranes 14, 14..., the hollow fiber membranes are cylindrical filtration membranes that can be made of PVDF (polyvinylidene fluoride), polyethylene, polypropylene, etc. The diameter, length, total membrane area, and number of hollow fiber membranes can be selected appropriately depending on the scale of the device. Furthermore, the first hollow fiber membranes 14, 14... can be selected from microfiltration membranes (MF membranes), ultrafiltration membranes (UF membranes), and nanofiltration membranes (NF membranes) depending on the size of the impurities.

[0036] The first membrane module 1 of the present invention is a so-called internal pressure type cross-flow module, in which the water to be treated is passed from the inside to the outside of the first hollow fiber membranes 14 by flowing the water into the inside of the first hollow fiber membranes 14. As a result, the treated water from which turbidity has been removed passes to the outside of the first hollow fiber membranes 14. The treated water that has permeated to the outside of the first hollow fiber membranes 14 can be taken out from inside the container 15 via the first treated water discharge section 12. Generally, the treated water is taken out from the first upper treated water discharge section 121, but it may also be taken out from the first lower treated water discharge section 122, or from both.

[0037] Meanwhile, as the water to be treated passes through the first hollow fiber membranes 14 from the inside to the outside, impurities in the water to be treated adhere to the inner surface of the first hollow fiber membranes 14. At this time, the proportion of water in the water to be treated inside the first hollow fiber membranes 14 decreases, and the proportion of impurities increases accordingly. The water to be treated that does not pass through becomes concentrated water with an increased concentration of impurities, and is discharged from the first concentrated water discharge section 13.

[0038] During the filtration operation, the first three-way valve 51 for treated water is switched so as to communicate from the pump 3 to the first treated water inlet 11. This connection allows the treated water to be filtered by each of the membrane modules 1 and 1'. At this time, the treated water obtained by filtration is intended to be discharged from both the upper treated water discharge ports 121 and 121' and the lower treated water discharge ports 122 and 122', but because the upper treated water discharge ports 121 and 121' are connected by the connecting pipe L2, the pressure in the first upper treated water discharge port 121 and the second upper treated water discharge port 121' is balanced. Therefore, the treated water is discharged only from the lower treated water discharge ports 122 and 122' and passes through the first treated water pipe L3 and the second treated water pipe L3' to be stored in the treated water tank 4.

[0039] With the above-described mechanism, the first membrane module 1 can filter the water to be treated that contains impurities, thereby obtaining clean treated water from which the impurities have been removed. For filtration, the first membrane module 1 and the second membrane module 1' can be operated simultaneously, and filtration can be performed using the two membrane modules 1 and 1'. However, by installing a separate valve to restrict the discharge of treated water, filtration can also be performed by operating only one of the membrane modules.

[0040] Next, the backwashing method will be described with reference to FIG. When filtration is performed continuously, impurities accumulate on the hollow fiber membranes. In the embodiment shown in Figure 1, because the membrane module is an internal pressure type, impurities accumulate inside the first hollow fiber membranes 14·14... and the second hollow fiber membranes 14·14... In order to remove these accumulated impurities by backwashing, it is necessary to pass treated water through the hollow fiber membrane from the outside to the inside, and to use the water flow to peel off and remove the accumulated impurities.

[0041] Here, a specific backwashing procedure will be described. First, to wash the second membrane module 1', as shown in Figure 3(a), the second treated water three-way valve 51' is switched so that the treated water does not flow into the second membrane module 1' and the second treated water inlet 11' communicates with the second drain pipe L4'. Furthermore, each treated water valve 61 and 61' is closed.

[0042] When the pump 3 is operated in this state, the water to be treated flows into the first membrane module 1 and starts filtration. As described above, because the second water to be treated three-way valve 51' has been switched, the water to be treated does not flow into the second membrane module 1', and filtration is not performed in the second membrane module 1'. The treated water filtered by the first membrane module 1 passes through the communicating pipe L2 and flows into the second upper treated water discharge portion 121' of the second membrane module 1'.

[0043] The treated water that has flowed into the second upper treated water discharge section 121′ passes through the container 15 and permeates from the outside to the inside of the second hollow fiber membranes 14′, 14′.... Then, impurities that have accumulated on the inside of the second hollow fiber membranes 14′, 14′... are peeled off by the flow of the permeated treated water. At this time, because the first treated water valve 61 is closed, the treated water generated by filtration is not discharged into the treated water tank 4, but is used only as backwash water. Also, because the second treated water valve 61' is closed, the water containing the peeled impurities is not discharged into the treated water tank 4, but is discharged to the outside from the second treated water inlet portion 11' via the second drain pipe L4'.

[0044] In addition, since the second treated water three-way valve 51' is switched and the second treated water inlet 11' and the second drain pipe L4' are connected, the backwash water that has permeated the inside of the second filtration membranes 14'·14'... by backwashing is discharged to the outside via the second treated water inlet 11' and the second drain pipe L4'. At this time, since the communication pipe L2 is provided with the intake / exhaust valve 7, air flows in along with the drainage from the second drain pipe L4', which makes it easier to discharge the backwash water from the second drain pipe L4'.

[0045] In the above description, the treated water, which is the backwash water, is connected to flow in from the second upper treated water discharge port 121', but it may also be connected to flow in from the second lower treated water discharge port 122'. Also, it may be connected using an appropriate valve so that the water alternates between flowing into the second upper treated water discharge port 121' and flowing into the second lower treated water discharge port 122'.

[0046] Next, cleaning of the first membrane module 1 will be described with reference to FIG. 3(b). After cleaning of the second membrane module 1' is completed, as shown in FIG. 3(b), the first three-way treated water valve 51 is switched so that the treated water does not flow into the first membrane module 1 and the first treated water inlet 11 communicates with the first drain pipe L4. In addition, the second three-way treated water valve 51' is switched so that the treated water flows into the second treated water inlet 11' of the second membrane module 1'. At this time, the first treated water valve 61 and the second treated water valve 61' are kept closed.

[0047] When the pump 3 is operated in this state, the water to be treated flows into the second membrane module 1' and filtration begins. As described above, because the first three-way valve 51 for water to be treated has been switched, the water to be treated does not flow into the first membrane module 1, and filtration does not occur in the first membrane module 1. The treated water filtered by the second membrane module 1 flows into the first upper treated water discharge portion 121 of the first membrane module 1 through the communicating pipe L2.

[0048] The treated water that has flowed into the first upper treated water discharge section 121 passes through the container 15 and permeates from the outside to the inside of the first hollow fiber membranes 14. Then, impurities that have accumulated on the inside of the first hollow fiber membranes 14 are peeled off by the flow of the permeated treated water. At this time, because the second treated water valve 61' is closed, the treated water generated by filtration is not discharged into the treated water tank 4, but is used only as backwash water. Also, because the first treated water valve 61 is closed, the water containing the peeled impurities is not discharged into the treated water tank 4, but is discharged to the outside from the first treated water inlet portion 11 via the first drain pipe L4.

[0049] In addition, since the first treated water three-way valve 51 is switched and the first treated water inlet 11 and the first drain pipe L4 are connected, the backwash water that has permeated the inside of the first filtration membranes 14·14... by backwashing is discharged to the outside via the first treated water inlet 11 and the second drain pipe L4. At this time, since the communication pipe L2 is provided with the intake / exhaust valve 7, air flows in along with the drainage from the first drain pipe L4, which makes it easier to discharge the backwash water from the first drain pipe L4.

[0050] The backwash water is made to flow into either the first upper treated water discharge portion 121 or the first lower treated water discharge portion 122 in the same manner as in the case of FIG. 3(a).

[0051] As described above, after backwashing of the first membrane module 1 and the second membrane module 1′ is completed, The first three-way valve 51 for water to be treated and the second three-way valve 51' for water to be treated are switched to a state in which the water to be treated can flow into the first membrane module 1 and the second membrane module 1'. This allows the first membrane module 1 and the second membrane module 1' to be used again for filtration.

[0052] As described above, in the present invention, the filtration operation can be performed efficiently using the first membrane module 1 and the second membrane module 1'. If impurities accumulate on the hollow fiber membranes due to filtration, the treated water obtained by one membrane module can be used directly to backwash the other membrane module by switching the three-way valves 5 and 5' and the manual valves 6 and 6', without storing it in the treated water tank 4.

[0053] Furthermore, by switching the untreated water three-way valves 51, 51' and the treated water valves 61, 61' at predetermined time intervals, backwashing of one membrane module and backwashing of the other membrane module can be performed alternately. In these backwashing operations, there is no need to prepare a dedicated pump for backwashing; the water flow from the pump 3 used for the filtration operation can be used to backflow the treated water discharged from one membrane module into the other membrane module, cleaning it. As described above, the membrane filtration device of the present invention does not require a dedicated pump for backwashing, which not only reduces costs and simplifies the device but also reduces the failure rate.

[0054] "Variation 1" Next, a membrane filtration device 101 according to a modified example of the present invention will be described with reference to FIGS. As shown in Figure 4, the membrane filtration device 101 of this modified example includes a first membrane module 1 which is one of the membrane modules, a second membrane module 1' which is the other membrane module, a treated water tank 2 which stores the treated water, a pump 3 which sends the treated water to each membrane module 1·1', a treated water tank 4 which stores the treated water, three-way valves 5·5' and manual valves 6·6' which switch the water paths, an intake and exhaust valve 7 which performs intake and exhaust, flow gauges 8·8', check valves 9·9', and a compressor 10.

[0055] Each of the membrane modules 1 and 1' is a so-called external pressure membrane filtration module, a hollow fiber membrane module that performs filtration by the dead-end method. The first membrane module 1 is equipped with a first treated water inlet 11 for introducing the treated water, a first treated water outlet 12 for discharging the filtered treated water, a first concentrated water outlet 13 which is an impurity outlet for discharging concentrated water whose impurity concentration has been increased by filtration, and a first bottom wastewater drain 19. In addition, the second membrane module 1', like the first membrane module 1, is equipped with a second treated water inlet section 11', a second treated water outlet section 12', a second concentrated water outlet section 13' which is an impurity outlet section, and a second bottom wastewater drain 19'.

[0056] The water to be treated in the water to be treated tank 2 is pumped out by a pump 3. The discharge side of the pump 3 branches into a first water to be treated pipe L1 that is sent to one membrane module 1 and a second water to be treated pipe L1' that is sent to the other membrane module 1'. The first treated water pipe L1 is connected to the first treated water inlet portion 11 via a first treated water check valve 91 and a first treated water valve 63. Similarly, the second treated water pipe L1' is connected to a second treated water inlet 11' via a second treated water check valve 91' and a second treated water valve 63'.

[0057] A first treated water discharge unit 12, which discharges treated water from which impurities have been removed by filtration, is connected to the treated water tank 4 via a first treated water pipe L3. Similarly, the second treated water discharge part 12' is connected to the treated water tank 4 via a second treated water pipe L3'. Furthermore, the first treated water pipe L3 and the second treated water pipe L3' are connected by a communicating pipe L2 via a first communicating pipe three-way valve 53 and a second communicating pipe three-way valve 53'.

[0058] A first drain pipe L4 is connected to the first bottom discharge drain 19 via a first drain valve 64. Similarly, a second drain pipe L4' is connected to the second bottom discharge drain 19' via a second drain valve 64'.

[0059] Here, the configuration of the membrane modules 1 and 1' will be described. Note that the second membrane module 1' has the same configuration as the first membrane module 1, so the first membrane module 1 will be described as a representative. As shown in Figure 5, the first membrane module 1 of the present invention is configured by vertically arranging a plurality of first hollow fiber membranes 14, which are elongated cylindrical membranes, in a substantially cylindrical resin container 15. A first treated water inlet 11 is provided on the lower side of the container 15, and the treated water can flow into the container 15 by a pump 3. The treated water flowing in from the first treated water inlet 11 is stored in a first treatment tank 16, and the first hollow fiber membranes 14, which are arranged inside the treatment tank, are immersed in the inflowing treated water.

[0060] An upper end fixed wall 17 is provided at the upper end of the first treatment tank 16, and the inside of the container 15 is watertightly divided into the first treatment tank 16 and a space communicating with the first treated water discharge section 12. The lower ends of the first hollow fiber membranes 14, 14... are connected and fixed together with adjacent hollow fiber membranes by a first lower end fixing wall 18. However, the first lower end fixing wall 18 does not divide the first treatment tank 16 watertight, and the water to be treated flowing in from the first treated water inlet portion 11 can flow into the first treatment tank 16 through the opening in the first lower end fixing wall 18. The type of hollow fiber membrane is the same as that in the embodiment shown in FIG. 2, and therefore a description thereof will be omitted.

[0061] The lower ends of the first hollow fiber membranes 14 are closed, and the upper ends are open so as to communicate with the first treated water discharge section 12. The first membrane module 1 of the present invention is a so-called external pressure type, dead-end type membrane module, in which pressure is applied to the water to be treated that is in contact with the outside of the first hollow fiber membranes 14, causing the water to permeate from the outside to the inside of the first hollow fiber membranes 14. As a result, the treated water from which turbidity has been removed permeates the inside of the first hollow fiber membranes 14. The treated water that has permeated through the first hollow fiber membranes 14 rises toward the upper end because the lower end of the first hollow fiber membranes 14 is closed, allowing the treated water to be removed from the opening at the upper end via the first treated water discharge section 12.

[0062] Meanwhile, as the water to be treated passes through the first hollow fiber membranes 14 from the outside to the inside, impurities in the water adhere to the outer surface of the first hollow fiber membranes 14. At this time, the water content of the water to be treated outside the first hollow fiber membranes 14 decreases, and the impurities content increases accordingly. The water that does not pass through becomes concentrated water with an increased concentration of impurities. In addition, in the first concentrated water discharge section 13, the first concentrated water valve 62 is operated to discharge concentrated water appropriately, thereby adjusting the pressure so that the pressure in the first treatment tank 16 does not become excessively high due to the successive inflow of treated water.

[0063] During the filtration operation, the first treated water valve 63 and the second treated water valve 63' are open, and the first communicating pipe three-way valve 53 and the second communicating pipe three-way valve 53' are switched so that the treated water is sent to the first treated water pipe L3 and the second treated water pipe L3'. As a result, the treated water obtained by filtration passes through the first treated water pipe L3 and the second treated water pipe L3' and is stored in the treated water tank 4. At this time, the first drain valve 64 and the second drain valve 64' are kept closed.

[0064] With the above-described mechanism, the first membrane module 1 can filter the water to be treated that contains impurities, thereby obtaining clean treated water from which the impurities have been removed. In filtration, the first membrane module 1 and the second membrane module 1' can be operated simultaneously, and filtration can be performed using the two membrane modules 1 and 1'. However, filtration can also be performed by operating only one of the membrane modules.

[0065] Next, the backwashing method will be described with reference to FIG. When the filtration operation is performed continuously, impurities accumulate on the hollow fiber membranes. Since the configurations shown in Figures 4 to 6 are external pressure type membrane modules, impurities accumulate on the outside of the first hollow fiber membranes 14·14... and the second hollow fiber membranes 14′·14′... In order to remove these accumulated impurities by backwashing, it is necessary to pass treated water through the hollow fiber membrane from the inside to the outside, and to use the water flow to peel off and remove the accumulated impurities.

[0066] Here, a specific backwashing procedure will be described. First, for cleaning the second membrane module 1', as shown in Figure 6(a), the first communicating pipe three-way valve 53 and the second communicating pipe three-way valve 53' are switched to connect the first treated water discharge part 12 and the second treated water discharge part 12' via the communicating pipe L2. In addition, the second water to be treated valve 63' is closed to prevent the water to be treated from flowing into the second membrane module 1'.

[0067] When the pump 3 is operated in this state, the water to be treated flows into the first membrane module 1 and starts filtration. At this time, the second water to be treated valve 63' is closed, so the water to be treated does not flow into the second membrane module 1' and filtration does not occur in the second membrane module 1'. The treated water filtered by the first membrane module 1 is discharged from the first treated water discharge section 12, but because the first connecting pipe three-way valve 53 and the second connecting pipe three-way valve 53' are switched, the treated water passes through the connecting pipe L2 and flows into the second treated water discharge section 12' of the second membrane module 1'.

[0068] The treated water that has flowed into the second treated water discharge section 12' permeates from the inside to the outside of the second hollow fiber membranes 14', 14'.... At this time, impurities that have accumulated on the outside of the second hollow fiber membranes 14', 14'... are peeled off by the flow of the permeating treated water. The exfoliated impurities accumulate at the bottom of the container 15', and can be discharged from the second bottom drain 19' by opening the second drain valve 64'. Alternatively, backwashing may be performed after draining the water from the container 15. During backwashing, the second drain valve 64' is closed and the second drain pipe L4' is blocked to fill the container 15 with backwash water, and once the container 15 is filled with backwash water, the second drain valve 64' is switched again to open the second drain pipe L4' to drain the water. The intake / exhaust valve 7 is provided in the communication pipe L2, so that air can be introduced into the container 15 when draining water, and air can be expelled from the container 15 when pouring water.

[0069] Next, cleaning of the first membrane module 1 will be described with reference to Figure 6(b). After cleaning of the second membrane module 1' is completed, as shown in Figure 6(b), the first treated water valve 63 is closed and the second treated water valve 63' is opened so that the treated water flows into the second treated water inlet 11' of the second membrane module 1'. At this time, the two communicating pipe three-way valves 53 and 53' are left in place, and the first treated water outlet 12 and the second treated water outlet 12' are maintained connected by the communicating pipe L2. In addition, the concentrated water valves 62 and 62' and the drain valves 64 and 64' are closed.

[0070] When the pump 3 is operated in this state, the water to be treated flows into the second membrane module 1' and filtration begins. At this time, the first water to be treated valve 62 is closed, so the water to be treated does not flow into the first membrane module 1, and filtration does not occur in the first membrane module 1. The treated water filtered by the second membrane module 1' is discharged from the second treated water discharge section 12', but the treated water passes through the connecting pipe L2 and flows into the first treated water discharge section 12 of the first membrane module 1.

[0071] The treated water that has flowed into the first treated water discharge section 12 permeates from the inside to the outside of the first hollow fiber membranes 14. At this time, impurities that have accumulated on the outside of the first hollow fiber membranes 14 are peeled off by the flow of the permeating treated water. The exfoliated impurities accumulate at the bottom of the container 15, and can be discharged from the first bottom drain 19 by opening the first drain valve 64. Alternatively, backwashing may be performed after draining the water from the container 15. During backwashing, the first drain valve 64 is closed and the first drain pipe L4 is blocked to fill the container 15 with backwash water, and once the container 15 is filled with backwash water, the first drain valve 64 is switched again to open the first drain pipe L4 to drain the water. The intake / exhaust valve 7 is provided in the communication pipe L2, so that air can be introduced into the container 15 when draining water, and air can be expelled from the container 15 when pouring water.

[0072] As described above, after backwashing of the first membrane module 1 and the second membrane module 1' is completed, the first communicating pipe three-way valve 53 and the second communicating pipe three-way valve 53' are switched to connect the first treated water discharge section 12 to the first treated water piping L3, and connect the second treated water discharge section 12' to the second treated water piping L3'. In addition, the first treated water valve 63 and the second treated water valve 63' are opened to allow the treated water to flow into the first membrane module 1 and the second membrane module 1'. This allows the first membrane module 1 and the second membrane module 1' to be used again for filtration.

[0073] In cleaning the hollow fiber membranes, in addition to the backwashing described above, bubbling may be used in combination. This involves operating the compressor 10 to generate bubbles, and the bursting of the bubbles is used to remove impurities. For example, to perform bubbling in cleaning the second membrane module 1', the second bubble valve 65' can be opened to introduce bubbles from the second bottom discharge drain 19', or a bubble tube (not shown) can be introduced into the vessel 15 and then introduced from a position close to the second hollow fiber membranes 14', 14'.... When bubble tubes are used, they are preferably placed adjacent to three locations: the top, middle, and bottom of the second hollow fiber membranes 14', 14'..., and bubbles are sprayed sequentially starting from the top.

[0074] In the bubbling in the bubble tube described above, the second treated water valve 63' is opened to introduce the treated water, while the second concentrated water valve 62' is opened and the second drain valve 64' is closed. As a result, the inflowing treated water is not discharged from the second treated water discharge section 12' and the second bottom drain 19', but is instead discharged entirely from the second concentrated water discharge section 13'. It is also possible to configure the system so that the separated impurities are discharged to the outside by riding on the water flow at this time.

[0075] As described above, in the present invention, the filtration operation can be performed efficiently using the first membrane module 1 and the second membrane module 1'. If impurities accumulate on the hollow fiber membranes due to filtration, the treated water obtained by one membrane module can be used to backwash the other membrane module without being stored in the treated water tank 4 by switching the three-way valves 53 and 53' in the connecting pipes and the manual valves 6 and 6'.

[0076] Furthermore, by switching the communicating pipe three-way valves 53, 53' and the manual valves 6, 6' at predetermined intervals, backwashing of one membrane module and backwashing of the other membrane module can be performed alternately. In these backwashing operations, there is no need to prepare a dedicated pump for backwashing; the water flow from the pump 4 used for the filtration operation can be used to backflow the treated water discharged from one membrane module into the other membrane module, thereby cleaning it. As described above, the membrane filtration device of the present invention does not require a dedicated pump for backwashing, which not only reduces costs and simplifies the device but also reduces the failure rate.

[0077] "Variation 2" Next, a membrane filtration device 102 according to a modified example of the present invention will be described with reference to Figures 7 and 8. In the following description, the same parts will be denoted by the same reference numerals, and duplicated descriptions will be omitted.

[0078] This modification differs from the embodiment shown in FIG. 1 in that three membrane modules 1, 1', and 1'' are arranged in parallel. This modified example includes a first membrane module 1, a second membrane module 1', a third membrane module 1'', a treated water tank 2 for storing the water to be treated, a pump 3 for sending the water to be treated to each of the membrane modules 1, 1', and 1'', a treated water tank 4 for storing the treated water, three-way valves 5, 5', and 5'' for switching the water paths, manual valves 6, 6', and 6'', an intake and exhaust valve 7 for intake and exhaust, and flow gauges 8, 8', and 8''. The configuration of each membrane module 1, 1', 1'' is the same as that shown in FIG. 2, and therefore a description thereof will be omitted.

[0079] Regarding the backwashing method in this modified example, first, the cleaning of the third membrane module 1'' will be described. As shown in FIG. 8(a), the third water-to-be-treated three-way valve 51'' is switched to prevent the water to be treated from flowing into the third membrane module 1''.

[0080] When the pump 3 is operated in this state, the water to be treated flows into the first membrane module 1 and the second membrane module 1' and filtration begins. At this time, the third three-way valve 51'' for water to be treated has been switched, so the water to be treated does not flow into the third membrane module 1'', and filtration is not performed in the third membrane module 1''. The treated water filtered through the first membrane module 1 and the second membrane module 1' flows through the communicating pipe L2 into the third upper treated water discharge portion 121'' of the third membrane module 1''.

[0081] The treated water that has flowed into the third upper treated water discharge section 121'' passes through the container 15 and permeates from the outside to the inside of the third hollow fiber membranes 14''. As a result, impurities that have accumulated on the inside of the third hollow fiber membranes 14''. are peeled off by the flow of the permeated treated water. At this time, because the first treated water valve 61 and the second treated water valve 61' are closed, the treated water generated by filtration is not discharged into the treated water tank 4, but is used only as backwash water. Also, because the third treated water valve 61'' is closed, the water containing the peeled impurities is not discharged into the treated water tank 4, but is discharged to the outside from the third treated water inlet portion 11'' through the third drain pipe L4''.

[0082] Next, cleaning of the first membrane module 1 will be described with reference to FIG. 8(b). After cleaning of the third membrane module 1" is completed, as shown in FIG. 8(b), the first treated water three-way valve 51 is switched so that the treated water does not flow into the first membrane module 1 and the first treated water inlet 11 is connected to the first drain pipe L4. In addition, the second treated water three-way valve 51' and the third treated water three-way valve 51" are switched so that the treated water flows into the second treated water inlet 11' of the second membrane module 1' and the third treated water inlet 11" of the third membrane module 1". At this time, the first treated water valve 61, the second treated water valve 61', and the third treated water valve 61" are also kept closed.

[0083] When the pump 3 is operated in this state, the water to be treated flows into the second membrane module 1' and the third membrane module 1'', and filtration begins. At this time, the first three-way valve 51 for water to be treated has been switched, so the water to be treated does not flow into the first membrane module 1, and filtration does not occur in the first membrane module 1. The treated water filtered through the second membrane module 1' and the third membrane module 1'' flows into the first treated water discharge portion 12 of the first membrane module 1 through the communicating pipe L2.

[0084] The treated water that has flowed into the first treated water discharge section 12 permeates from the outside to the inside of the first hollow fiber membranes 14. Then, impurities that have accumulated on the inside of the first hollow fiber membranes 14 are peeled off by the flow of the permeated treated water. At this time, since the second treated water valve 61' and the third treated water valve 61'' are closed, the treated water generated by filtration is not discharged into the treated water tank 4, but is used only as backwash water. Also, since the first treated water valve 61 is closed, the water containing the peeled impurities is not discharged into the treated water tank 4, but is discharged to the outside from the first treated water inlet part 11 through the first drain pipe L4.

[0085] Next, the cleaning of the second membrane module 1' will be described with reference to FIG. 8(c). After the cleaning of the first membrane module 1 is completed, as shown in FIG. 8(c), the second treated water three-way valve 51' is switched so that the treated water does not flow into the second membrane module 1' and the second treated water inlet 11' communicates with the second drain pipe L4'. In addition, the first treated water three-way valve 51 and the third treated water three-way valve 51'' are switched so that the treated water flows into the first treated water inlet 11 of the first membrane module 1 and the third treated water inlet 11'' of the third membrane module 1''. At this time, the first treated water valve 61, the second treated water valve 61', and the third treated water valve 61'' are also kept closed.

[0086] When the pump 3 is operated in this state, the water to be treated flows into the first membrane module 1 and the third membrane module 1'', and filtration begins. At this time, the second three-way valve 51' for water to be treated is closed, so the water to be treated does not flow into the second membrane module 1', and filtration does not occur in the second membrane module 1'. The treated water filtered through the first membrane module 1 and the third membrane module 1'' flows through the communicating pipe L2 into the second treated water discharge portion 12' of the second membrane module 1'.

[0087] The treated water that has flowed into the second treated water discharge section 12' permeates from the outside to the inside of the second hollow fiber membranes 14', 14'.... Impurities that have accumulated on the inside of the second hollow fiber membranes 14', 14'... are then peeled off by the flow of the permeating treated water. At this time, because the first treated water valve 61 and the third treated water valve 61'' are closed, the treated water produced by filtration is not discharged into the treated water tank 4, but is used only as backwash water. Also, because the second treated water valve 61' is closed, the water containing the peeled impurities is not discharged into the treated water tank 4, but is discharged to the outside from the second treated water inlet section 11' through the second drain pipe L4'.

[0088] As described above, in this modified example, by using three membrane modules, two membrane modules produce treated water, which can be used to clean the remaining membrane module, so that sufficient treated water can be used for backwashing.

[0089] The present invention is not limited to the above embodiments. For example, in an internal pressure type membrane module, a compressor may be connected to the connecting pipe L2 so that air can be ejected during backwashing, and in an external pressure type membrane module, three or more membrane modules may be used. Furthermore, the three-way valves and manual valves may be replaced by solenoid valves or motor valves that are electronically controlled to open and close. [Explanation of symbols]

[0090] 100,101,102 Membrane filtration equipment 1. Membrane module 11 Treated water inlet 12 Treated water discharge section 121 Upper treated water discharge section 122 Lower treated water discharge section 13 Concentrated water discharge section 14 Hollow fiber membrane 15 Container 16 Treatment tank 17 Upper end fixed wall 18 Lower end fixed wall 19 Bottom drain 2. Treated water tank 3. Pump 4 Treated water tank 5 Three-way valve 51 Three-way valve for treated water 52 Treated water three-way valve 53 Connecting pipe three-way valve 6 Manual Valves 61 Treated water valve 62 Concentrated water valve 63 Treated water valve 64 Drain valve 65 Bubble valve 7 Intake and exhaust valves 8 Flow Gauge 9. Check valve 91 Treated water check valve 92 Compressor check valve 10 Compressor L1 Treated water piping L2 communication pipe L3 Treated water piping L4 drain pipe

Claims

1. A membrane filtration device including a membrane module for removing impurities from water to be treated containing the impurities, The membrane module is composed of a plurality of membrane modules, The membrane module includes a filtration membrane for filtering the water to be treated, a water to be treated inlet portion for introducing the water to be treated, a treated water discharge portion for discharging the treated water filtered by the filtration membrane, and an impurity discharge portion for discharging impurities removed during cleaning of the filtration membrane, The treated water that has passed through one membrane module is not stored but is sent to the other membrane module, thereby enabling cleaning of the filtration membrane of the other membrane module, A membrane filtration device characterized in that the treated water that has passed through the other membrane module is not stored but is sent into one of the membrane modules, thereby allowing the filtration membrane of the one membrane module to be cleaned.

2. 2. The membrane filtration device according to claim 1, wherein the filtration membrane in the other membrane module can be alternately washed with treated water that has passed through one of the membrane modules and the filtration membrane in the one membrane module can be alternately washed with treated water that has passed through the other membrane module.

3. the one membrane module includes a first treated water inlet connected to a pump that delivers the treated water, a first treated water outlet that discharges the treated water to the outside, and a first impurity outlet that discharges impurities removed during the cleaning to the outside; The other membrane module includes a second treated water inlet connected to the pump, a second treated water discharge portion that discharges treated water to the outside, and a second impurity discharge portion that discharges impurities removed during the cleaning to the outside, 3. The membrane filtration device according to claim 1, wherein the first treated water discharge section and the second treated water discharge section are connected by a communication pipe.

4. An internal pressure type membrane filtration device, the first treated water discharge section includes a first upper treated water discharge section and a first lower treated water discharge section; the second treated water discharge section includes a second upper treated water discharge section and a second lower treated water discharge section; during the cleaning, the treated water filtered by the one membrane module is not stored but can be sent to the second upper treated water discharge portion or the second lower treated water discharge portion of the other membrane module through the communicating pipe, the treated water filtered by the other membrane module is not stored but can be sent to the first upper treated water discharge portion or the first lower treated water discharge portion of the one membrane module through the communicating pipe, The first treated water inlet portion also serves as the first impurity discharge portion, 4. The membrane filtration device according to claim 3, wherein the second treated water inlet portion also serves as the second impurity discharge portion.

5. An external pressure type membrane filtration device, the first impurity discharge section includes a first upper impurity discharge section and a first lower impurity discharge section; the second impurity discharge section includes a second upper impurity discharge section and a second lower impurity discharge section; during the cleaning, the treated water filtered by the one membrane module is not stored but can be sent to the second treated water discharge portion of the other membrane module through the communicating pipe, the treated water filtered by the other membrane module is not stored but can be delivered to the first treated water discharge portion of the one membrane module through the communicating pipe, When cleaning one of the membrane modules, impurities removed from the filtration membrane are discharged from both or either of the first upper impurity discharge portion and the first lower impurity discharge portion, 4. The membrane filtration device according to claim 3, wherein, during cleaning of the other membrane module, impurities removed from the filtration membrane are discharged from both or either of the second upper impurity discharge section and the second lower impurity discharge section.

6. A method for cleaning a filtration membrane in a membrane filtration device for obtaining treated water from which impurities have been removed from water to be treated containing impurities, comprising: The membrane filtration device includes a plurality of membrane modules, The treated water filtered by one of the membrane modules is used to clean the other membrane module without storing it; A method for cleaning a filtration membrane, comprising cleaning one of the membrane modules using treated water filtered by the other membrane module without storing the treated water.

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