Membrane filtration apparatus and method for cleaning filtration membranes

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 and transparent treated water by filtration from treated water containing impurities, and a method for cleaning a filtration membrane attached to the device.

Background Art

[0002] In a membrane filtration device for making polluted water into colorless and transparent water, impurities accumulate on the filtration membrane by filtration. The accumulated impurities reduce the flow rate of water passing through the filtration membrane and the filtration efficiency. There is also a possibility of damaging the filtration membrane. Therefore, when impurities accumulate on the filtration membrane, reverse cleaning (hereinafter also referred to as reverse washing) in which the treated water is made to flow in the reverse direction, flushing, bubbling, etc. are performed to remove the impurities accumulated on the filtration membrane.

[0003] For example, in Patent Document 1, a technique of a membrane filtration device capable of reverse washing in which filtered water is passed from the inside to the outside of the hollow fiber membrane in a hollow fiber membrane module in an outside pressure type membrane filtration device is shown. In the reverse washing described in Patent Document 1, "filtered water in the filtered water tank is introduced into the hollow fiber membrane module from the filtration water outlet through the reverse washing valve, passes through the wall thickness portion of the hollow fiber membrane from the inside of the hollow membrane, and leaches into the outside space of the hollow fiber membrane. In this process, the suspended substances deposited in the pores of the wall thickness portion of the hollow fiber membrane are pushed out to the outside of the hollow fiber membrane, thereby cleaning the hollow fiber membrane."

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in order to perform backwashing, a backwash pump is required to send the treated water stored in the tank in the reverse direction. Even with the technology described in Patent Document 1, although the liquid transfer pump is omitted in the drawings of Patent Document 1, a pump is still required to send the filtered water in the reverse direction for backwashing. 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 account the pressure loss in the piping.

[0006] Pumps pose a significant space and cost issue for the entire membrane filtration system. Furthermore, the existence of separate pumps for filtration and backwashing increases the overall failure rate of the membrane filtration system. Therefore, a technology that does not require a dedicated pump for backwashing was desired.

[0007] This invention has been made in view of the above-mentioned problems, and its objective is to provide a membrane filtration apparatus 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 employed by the inventors to solve the above problems are described below. The present invention is a membrane filtration apparatus comprising a membrane module for obtaining treated water from which impurities have been removed from water to be treated that contains impurities. In this invention, impurities are substances contained in the treated water that are unnecessary for its intended purpose (e.g., drinking water or handwashing water) and should be removed. Examples include suspended solids, ionic components, bacteria, viruses, and the like.

[0009] The basic configuration of the above membrane filtration apparatus comprises a filtration membrane for filtering the water to be treated, a water to be treated inlet for receiving the water to be treated, a treated water outlet for discharging the treated water filtered by the filtration membrane, and an impurity discharge outlet for discharging impurities removed during the cleaning of the filtration membrane. Here, the membrane module is composed of multiple membrane modules, and the treated water that has passed through one membrane module is not stored but is sent into the other membrane module, thereby enabling the cleaning of the filtration membrane of the other membrane module. Furthermore, the treated water that has passed through the other membrane module is not stored but is sent into the first membrane module, thereby enabling the cleaning of the filtration membrane of the first membrane module.

[0010] In typical membrane filtration systems, treated water that has passed through the membrane module is stored in a tank or similar container and used as drinking water as needed. However, when cleaning the filtration membrane, the treated water stored in the tank is used as backwash water. In contrast, the present invention is configured to have multiple membrane modules, and to send the treated water that has passed through one membrane module directly to another membrane module without storage. This allows the treated water obtained from one membrane module or the other membrane module to be immediately sent to the other membrane module or the one membrane module, enabling backwashing of the membrane modules while maintaining sufficient water pressure without a drastic drop in water pressure.

[0011] As a means to solve the problem, it is also possible to configure the system to alternately wash the filtration membrane in the other membrane module with treated water that has passed through one membrane module, and then wash the filtration membrane in the first membrane module with treated water that has passed through the other membrane module.

[0012] In this configuration, by periodically switching the membrane modules that perform filtration, for example, one membrane module can perform filtration, and after the other membrane module has been washed with the treated water obtained, the system can be switched to perform filtration with the other membrane module, and the first membrane module can be washed with the treated water obtained. In this way, backwashing can be performed alternately on one membrane module and the other membrane module.

[0013] Another possible means for solving the problem is to configure the first membrane module and the second membrane module as follows. One membrane module is configured to include a first water to be treated inlet connected to a pump that sends out the water to be treated for filtration, a first treated water discharge section that discharges the treated water to the outside, and a first impurity discharge section that discharges impurities removed during cleaning of the filtration membrane 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 treated water to the outside, and a second impurity discharge outlet for discharging impurities removed during cleaning of the filtration membrane to the outside. Then, the first treated water discharge section and the second treated water discharge section are connected by a connecting pipe.

[0014] Each membrane module is configured to include a treated water inlet, a treated water outlet, and an impurity outlet. By connecting the treated water outlets with connecting pipes, the piping used for supplying treated water for drinking purposes through normal filtration can be used for both supplying water for backwashing and other purposes, thus simplifying the overall configuration of the device.

[0015] Another possible solution to the problem is to use a membrane filtration system with an internal pressure type filtration membrane. In this configuration, the first treated water discharge section is provided with a first upper treated water discharge section and a first lower treated water discharge section. The second treated water discharge section is provided with a second upper treated water discharge section and a second lower treated water discharge section.

[0016] Furthermore, during cleaning of the filtration membrane, the treated water filtered by one membrane module is not stored but can be supplied via the connecting pipe to the second upper treated water discharge section or the second lower treated water discharge section of the other membrane module. Similarly, the treated water filtered by the other membrane module is not stored but can be supplied via the connecting pipe to the first upper treated water discharge section or the first lower treated water discharge section of the one membrane module. Furthermore, the first water to be treated inlet also serves as the first impurity discharge outlet, and the second water to be treated inlet also serves as the second impurity discharge outlet.

[0017] In an internal pressure system, impurities accumulate on the inside of the filtration membrane. With the above configuration, treated water can be introduced as backwash water from the top or bottom of the membrane module via a connecting pipe and permeated from the outside to the inside of the filtration membrane. Furthermore, the washed and detached impurities can be discharged from the impurity discharge section, which also serves as the treated water inlet. By combining the treated water inlet with the impurity discharge section, the structure of the membrane module can be simplified.

[0018] Another possible solution to the problem is to use a membrane filtration system with an external pressure type filtration membrane. In this configuration, the first impurity discharge section is equipped with a first upper impurity discharge section and a first lower impurity discharge section. The second impurity discharge section is equipped with a second upper impurity discharge section and a second lower impurity discharge section. Furthermore, during cleaning of the filtration membrane, the treated water filtered by one membrane module is not stored but can be sent to the second treated water discharge section of the other membrane module via the connecting pipe. Similarly, the treated water filtered by the other membrane module is not stored but can be sent to the first treated water discharge section of the one membrane module via the connecting pipe.

[0019] Furthermore, when cleaning the one membrane module, the impurities removed from the filtration membrane are configured to be discharged from either or both of the first upper impurity discharge part and the first lower impurity discharge part. Also, when cleaning the other membrane module, the impurities removed from the filtration membrane are configured to be discharged from either or both of the second upper impurity discharge part and the second lower impurity discharge part.

[0020] In the case of the outside pressure type, impurities accumulate on the outside of the filtration membrane. By adopting the above configuration, through the communication pipe, the treated water can flow in as reverse washing water from the treated water discharge part of the membrane module and permeate from the inside to the outside of the filtration membrane. Also, the impurities peeled off by cleaning can be discharged from the upper impurity discharge part or the lower impurity discharge part. For example, the water in the membrane module can be discharged by draining it from the lower impurity discharge part. Also, when using bubbling or the like in combination, the water to be treated is made to flow in from the water to be treated inflow part, and the impurities peeled off by bubbling or the like and the inflowing water to be treated can also be discharged from the upper impurity discharge part.

[0021] As yet another means that can be adopted to solve the problem, a cleaning method for the filtration membrane in a membrane filtration device for obtaining treated water from which the impurities have been removed from the water to be treated containing the impurities can be adopted. The basic configuration of the cleaning method for the filtration membrane is such that the membrane filtration device includes a plurality of membrane modules, and the other membrane module is cleaned without storing the treated water filtered by one membrane module, and the one membrane module is cleaned without storing the treated water filtered by the other membrane module.

[0022] By adopting 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 the one membrane module, so that the reverse washing of the other membrane module can be performed while maintaining a necessary and sufficient water pressure without extremely reducing the water pressure.

Advantages of the Invention

[0023] In the membrane filtration device and the method for cleaning the filtration membrane of the present invention, which include a plurality of membrane modules, the treated water filtered by one of the membrane modules or the other membrane module is used without being stored to clean the other membrane module or the one membrane module. As a result, a dedicated pump for backwashing is not required, and effects such as cost reduction, simplification of the device, and reduction of the failure rate are achieved.

Brief Description of the Drawings

[0024] [Figure 1] FIG. 1 is a schematic diagram showing the membrane filtration device of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing the membrane module of the present invention. [Figure 3] FIG. 3 is an explanatory diagram showing the backwashing mechanism of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing the membrane filtration device in Modification 1 of the present invention. [Figure 5] FIG. 5 is a cross-sectional view showing the membrane module in Modification 1 of the present invention. [Figure 6] FIG. 6 is an explanatory diagram showing the backwashing mechanism in Modification 1 of the present invention. [Figure 7] FIG. 7 is a cross-sectional view showing the membrane module in Modification 2 of the present invention. [Figure 8] FIG. 8 is an explanatory diagram showing the backwashing mechanism in Modification 2 of the present invention.

Embodiments for Carrying Out the Invention

[0025] Embodiments for carrying out the present invention will be described below based on FIGS. 1 to 3. In the following description, the drawings are schematically shown for the sake of simplicity of explanation. For example, the hollow fiber membranes 14, 14,... are actually used by bundling dozens to hundreds of them, but are shown simplified as several in the drawings.

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

[0027] Each membrane module 1·1' is a so-called internal pressure type membrane filtration module, and is a hollow fiber membrane module that performs filtration using a cross-flow method. The first membrane module 1 is equipped with a first water to be treated inlet 11 for introducing water to be treated, a first treated water discharge 12 for discharging filtered treated water, and a first concentrated water discharge 13 for discharging concentrated water, in which the concentration of impurities has increased due to filtration, to the outside. Here, the first treated water discharge 12 is equipped with a first upper treated water discharge 121 located at the top and a first lower treated water discharge 122 located at the bottom. As will be described later, when cleaning the filtration membrane, the first water to be treated inlet 11 also serves as an impurity discharge bay, and impurities can be discharged by switching the first water to be treated 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 discharge section, 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 sent out by the pump 3. The discharge side of the pump 3 branches into a first water to be treated pipe L1 that supplies water to one membrane module 1, and a second water to be treated pipe L1' that supplies water to the other membrane module 1'. The first water to be treated pipe L1 branches off to the first water to be treated inlet 11 and the first drain pipe L4 via the first water to be treated three-way valve 51. Similarly, the second water to be treated pipe L1' branches off to the second water to be treated inlet 11' and the second drain pipe L4' via the second water to be treated three-way valve 51'.

[0030] The first treated water discharge section 12, which discharges treated water from which impurities have been removed by filtration, consists of a first upper treated water discharge section 121 and a first lower treated water discharge section 122. The first lower treated water discharge section 122 is connected to the first treated water piping L3, 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 12' consists of a second upper treated water outlet 121' and a second lower treated water outlet 122'. The second lower treated water outlet 122' is connected to a second treated water pipe L3', which 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 connecting pipe L2. An intake / exhaust valve 7 for intake and exhaust is connected to the middle section of the connecting pipe L2.

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

[0033] Here, we will explain the configuration of membrane module 1·1'. Note that the configuration of the second membrane module 1' is the same as that of the first membrane module 1, so we will explain the first membrane module 1 as a representative example. As shown in Figure 2, the first membrane module 1 in the present invention is constructed by arranging a plurality of elongated cylindrical membranes, the first hollow fiber membranes 14, 14…, vertically within a substantially cylindrical resin container 15. The container 15 is provided with a first water to be treated inlet 11 at the bottom, allowing water to be treated to flow into the first hollow fiber membranes 14, 14… by a pump 3. The water to be treated that flows in from the first water to be treated inlet 11 passes through the first hollow fiber membranes 14, 14… and is discharged via the first concentrated water discharge section 13.

[0034] The first hollow fiber membranes 14, 14... have their upper ends fixed to the upper end fixing wall 17 and their lower ends fixed to the lower end fixing wall 18. That is, the inside of the first hollow fiber membranes 14, 14... communicates with the first concentrated water discharge section 13, and the outside is fixed so as to face the inside of the container 15. As a result, the inside of the container 15 is watertightly divided into the space outside the first hollow fiber membranes 14, 14... and the space communicating with the first concentrated water discharge section 13 and the first treated water inlet section 11.

[0035] Regarding the first hollow fiber membrane 14·14…, the hollow fiber membrane is a cylindrical filtration membrane, and can be made of PVDF (polyvinylidene fluoride), polyethylene, polypropylene, etc. The diameter, length, total membrane area, and number of hollow fiber membranes can be appropriately selected according to the scale of the apparatus. Furthermore, depending on the size of the impurities, the first hollow fiber membrane 14·14… can be selected and used as a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), or a nanofiltration membrane (NF membrane).

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

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

[0038] During filtration, the first water treatment three-way valve 51 is switched to communicate with the pump 3 and the first water treatment inlet 11. This connection allows the water to be filtered by each membrane module 1·1'. At this time, the treated water obtained by filtration is intended to be discharged from either the upper treated water discharge sections 121 and 121' and the lower treated water discharge sections 122 and 122'. However, since the upper treated water discharge sections 121 and 121' are connected by a connecting pipe L2, the pressures of the first upper treated water discharge section 121 and the second upper treated water discharge section 121' are balanced. Therefore, the treated water is discharged only from the lower treated water discharge sections 122 and 122' and is stored in the treated water tank 4 through the first treated water piping L3 and the second treated water piping L3'.

[0039] Through the mechanism described above, the first membrane module 1 filters the water to be treated, which contains impurities, and clean treated water from which the impurities have been removed can be obtained. In filtration, the first membrane module 1 and the second membrane module 1' can be operated simultaneously, allowing filtration to be performed by both membrane modules 1 and 1'. However, by providing 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, we will explain the backwashing method based on Figure 3. If the filtration operation is performed continuously, impurities will accumulate on the hollow fiber membrane. In the configuration shown in Figure 1, since it is an internal pressure type membrane module, impurities will accumulate on the inside of the first hollow fiber membrane 14·14… and the second hollow fiber membrane 14'·14'…. To remove these accumulated impurities by backwashing, it is necessary to allow treated water to permeate the hollow fiber membrane from the outside to the inside, and for the accumulated impurities to be detached and removed by the water flow.

[0041] Here, we will explain the specific backwashing procedure. First, for cleaning 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 61·61' is kept closed.

[0042] If pump 3 is operated in this state, the water to be treated will flow into the first membrane module 1 and filtration will begin. As described above, since the second water to be treated three-way valve 51' is switched, the water to be treated will not flow into the second membrane module 1', and filtration will not be performed in the second membrane module 1'. The treated water filtered by the first membrane module 1 flows through the connecting pipe L2 into the second upper treated water discharge section 121' of the second membrane module 1'.

[0043] The treated water that flows 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 had accumulated on the inside of the second hollow fiber membranes 14'·14'… are detached by the flow of the permeated treated water. In this state, with the first treated water valve 61 closed, the treated water produced by filtration is not discharged into the treated water tank 4, but is used only as backwash water. Also, with the second treated water valve 61' closed, the water containing the detached impurities is not discharged into the treated water tank 4, but is discharged to the outside through the second treated water inlet 11' and the second drain pipe L4'.

[0044] Furthermore, when the second water treatment three-way valve 51' is switched on, and the second water treatment inlet 11' and the second drain pipe L4' are connected, the backwash water that has permeated through the inside of the second filtration membrane 14'·14'… due to backwashing is discharged to the outside via the second water treatment inlet 11' and the second drain pipe L4'. At this time, because the connecting pipe L2 is equipped with an intake / exhaust valve 7, air flows in along with the drainage from the second drain pipe L4'. This makes it easier to discharge the backwash water from the second drain pipe L4'.

[0045] In the above description, the treated water, which is backwash water, is connected to flow in from the second upper treated water discharge section 121', but it may also be connected to flow in from the second lower treated water discharge section 122'. Alternatively, an appropriate valve may be used to connect the water so that it flows alternately into the second upper treated water discharge section 121' and the second lower treated water discharge section 122'.

[0046] Next, the cleaning of the first membrane module 1 will be explained based on Figure 3(b). Once the cleaning of the second membrane module 1' is complete, as shown in Figure 3(b), the first treated water valve 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 communicates with the first drain pipe L4. Also, the second treated water three-way 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' remain closed.

[0047] If pump 3 is operated in this state, the water to be treated will flow into the second membrane module 1' and filtration will begin. As described above, since the first water to be treated three-way valve 51 is switched, the water to be treated will not flow into the first membrane module 1, and filtration will not be performed in the first membrane module 1. The treated water filtered by the second membrane module 1 flows through the connecting pipe L2 into the first upper treated water discharge section 121 of the first membrane module 1.

[0048] The treated water that flows 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, 14.... Then, impurities that had accumulated on the inside of the first hollow fiber membranes 14, 14... are detached by the flow of the permeated treated water. In this state, with the second treated water valve 61' closed, the treated water produced by filtration is not discharged into the treated water tank 4, but is used only as backwash water. Also, with the first treated water valve 61 closed, the water containing the detached impurities is not discharged into the treated water tank 4, but is discharged to the outside through the first treated water inlet 11 and the first drain pipe L4.

[0049] Furthermore, when the first water treatment three-way valve 51 is switched on, and the first water treatment inlet 11 and the first drain pipe L4 are connected, the backwash water that has permeated through to the inside of the first filtration membranes 14, 14... due to backwashing is discharged to the outside via the first water treatment inlet 11 and the second drain pipe L4. At this time, because the connecting pipe L2 is equipped with an intake / exhaust valve 7, air flows in along with the drainage from the first drain pipe L4. This makes it easier to discharge backwash water from the first drain pipe L4.

[0050] The method for directing the backwash water into either the first upper treated water discharge section 121 or the first lower treated water discharge section 122 is the same as in the case shown in Figure 3(a).

[0051] As described above, once the first membrane module 1 and the second membrane module 1' have been backwashed, The first three-way valve 51 for the water to be treated and the second three-way valve 51' for the water to be treated are switched to allow the water to be treated to flow into the first membrane module 1 and the second membrane module 1'. This allows the filtration operation to be performed again using the first membrane module 1 and the second membrane module 1'.

[0052] As described above, in the present invention, filtration can be efficiently performed using the first membrane module 1 and the second membrane module 1'. Furthermore, if impurities accumulate on the hollow fiber membrane due to filtration, the treated water obtained from one membrane module can be used directly for backwashing the other membrane module without being stored in the treated water tank 4 by switching the three-way valves 5·5' and the manual valves 6·6'.

[0053] Furthermore, by switching each of the three-way valves 51 and 51' for the water to be treated and each of the treatment water valves 61 and 61' at predetermined intervals, it is possible to alternately backwash one membrane module and backwash the other membrane module. In these backwashing operations, there is no need to prepare a dedicated pump for backwashing; the water flow from 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 for cleaning. Thus, with the membrane filtration apparatus of the present invention, a dedicated pump for backwashing is not required, which reduces costs, simplifies the apparatus, and lowers the failure rate.

[0054] "Differentiation Example 1" Next, a modified example of the present invention, a membrane filtration apparatus 101, will be described with reference to Figures 4 to 6. As shown in Figure 4, the modified membrane filtration apparatus 101 comprises a first membrane module 1, which is one membrane module, a second membrane module 1', a treated water tank 2 for storing treated water, a pump 3 for supplying treated water to each membrane module 1 and 1', a treated water tank 4 for storing treated water, three-way valves 5 and 5' and manual valves 6 and 6' for switching water channels, intake and exhaust valves 7 for intake and exhaust, flow gauges 8 and 8', check valves 9 and 9', and a compressor 10.

[0055] Each membrane module 1·1' is a so-called external pressure type membrane filtration module, and is a hollow fiber membrane module that performs filtration using a dead-end method. The first membrane module 1 includes a first water to be treated inlet 11 for introducing water to be treated, a first treated water discharge 12 for discharging filtered treated water, and an impurity discharge 13 and a first concentrated water discharge 19 for discharging concentrated water in which the concentration of impurities has increased due to filtration. Furthermore, the second membrane module 1', like the first membrane module 1, is equipped with a second water to be treated inlet 11', a second treated water discharge section 12', and a second concentrated water discharge section 13' and a second bottom drain 19', which are impurity discharge sections.

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

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

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

[0059] Here, we will explain the configuration of membrane module 1·1'. Note that the configuration of the second membrane module 1' is the same as that of the first membrane module 1, so we will explain the first membrane module 1 as a representative example. As shown in Figure 5, the first membrane module 1 in the present invention is constructed by arranging a plurality of elongated cylindrical membranes, the first hollow fiber membranes 14, 14..., in the vertical direction inside a substantially cylindrical resin container 15. The container 15 is provided with a first water to be treated inlet 11 on its lower side, allowing water to be treated to flow into the container 15 by a pump 3. The water to be treated that flows in from the first water to be treated inlet 11 is stored in the first treatment tank 16, and the first hollow fiber membranes 14, 14... arranged inside the treatment tank are immersed in the incoming water.

[0060] An upper end fixing wall 17 is provided at the upper end of the first treatment tank 16, and the inside of the container 15 is watertightly partitioned into the first treatment tank 16 and a space communicating with the first treated water discharge section 12. Furthermore, the lower ends of the first hollow fiber membranes 14, 14... are connected and fixed together with the adjacent hollow fiber membranes by the first lower end fixing wall 18. However, the first lower end fixing wall 18 does not watertightly partition the first treatment tank 16, and the water to be treated that flows in from the first water to be treated inlet 11 can pass through the opening in the first lower end fixing wall 18 and flow into the first treatment tank 16. The type of hollow fiber membrane is the same as that shown in Figure 2, so we will omit further explanation.

[0061] The first hollow fiber membranes 14·14… have their lower ends closed and their upper ends open to communicate with the first treated water discharge section 12. The first membrane module 1 in this invention is a so-called external pressure type and dead-end type membrane module, and by applying pressure to the water to be treated that is in contact with the outside of the first hollow fiber membranes 14·14…, the water to be treated is permeated from the outside to the inside of the first hollow fiber membranes 14·14…. As a result, treated water from which turbidity has been removed permeates to the inside of the first hollow fiber membranes 14·14…. The treated water that permeates through the first hollow fiber membranes 14·14… rises towards the upper end because the lower end of the first hollow fiber membranes 14·14… is closed. As a result, the treated water can be extracted from the opening at the upper end via the first treated water discharge section 12.

[0062] On the other hand, when the water to be treated permeates from the outside to the inside of the first hollow fiber membrane 14·14…, impurities in the water to be treated adhere to the outer surface of the first hollow fiber membrane 14·14…. At this time, the water content of the water to be treated outside the first hollow fiber membrane 14·14… decreases, and the proportion of impurities increases accordingly. The water that does not permeate becomes concentrated water with an increased concentration of impurities. Furthermore, in the first concentrated water discharge section 13, the pressure can be adjusted so that the pressure inside the first treatment tank 16 does not become excessively high due to the sequentially flowing treated water by operating the first concentrated water valve 62 to discharge concentrated water as needed.

[0063] During the filtration operation, the first treated water valve 63 and the second treated water valve 63' are open, and the first three-way connecting pipe valve 53 and the second three-way connecting pipe 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 is stored in the treated water tank 4 through the first treated water pipe L3 and the second treated water pipe L3'. At this time, the first drain valve 64 and the second drain valve 64' are kept closed.

[0064] Through the mechanism described above, the first membrane module 1 filters the water to be treated, which contains impurities, and clean treated water from which the impurities have been removed can be obtained. In filtration, the first membrane module 1 and the second membrane module 1' are operated simultaneously, allowing filtration to be performed using both membrane modules 1 and 1'. Alternatively, filtration can be performed by operating only one of the membrane modules.

[0065] Next, the backwashing method will be explained based on Figure 6. When filtration is performed continuously, impurities accumulate on the hollow fiber membrane. In the configurations shown in Figures 4 to 6, since it is an external pressure type membrane module, impurities accumulate on the outside of the first hollow fiber membrane 14·14… and the second hollow fiber membrane 14'·14'…. To remove these accumulated impurities by backwashing, it is necessary to allow treated water to permeate from the inside to the outside of the hollow fiber membrane, and for the accumulated impurities to be detached and removed by the water flow.

[0066] Here, we will explain the specific backwashing procedure. First, for cleaning the second membrane module 1', as shown in Figure 6(a), the first three-way valve 53 and the second three-way valve 53' are switched so that the first treated water discharge section 12 and the second treated water discharge section 12' are connected by the connecting pipe L2. Furthermore, 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 pump 3 is operated in this state, the water to be treated flows into the first membrane module 1 and filtration begins. At this time, since the second water to be treated valve 63' is closed, 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. However, due to the switching of the first three-way valve 53 and the second three-way valve 53' of the connecting pipe, the treated water flows through the connecting pipe L2 into the second treated water discharge section 12' of the second membrane module 1'.

[0068] The treated water that flows into the second treated water discharge section 12' permeates from the inside to the outside of the second hollow fiber membrane 14'·14'…. At this time, impurities that had accumulated on the outside of the second hollow fiber membrane 14'·14'… are detached by the flow of the permeated treated water. Since the detached impurities accumulate at the bottom of container 15', they can be discharged from the second bottom drain 19' by opening the second drain valve 64'. Alternatively, backwashing may be performed after draining the container 15 in advance. During backwashing, the second drain valve 64' is closed to block the second drain pipe L4', filling the container 15 with backwash water. Once the container 15 is filled with backwash water, the second drain valve 64' is switched back to open the second drain pipe L4' and drain the water. The intake and exhaust valve 7 is provided in the connecting pipe L2, which allows air to flow into the container 15 when draining water and to discharge air from the container 15 when filling water.

[0069] Next, the cleaning of the first membrane module 1 will be explained based on Figure 6(b). Once the cleaning of the second membrane module 1' is complete, 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 connecting pipe three-way valves 53 and 53' are left as they are, maintaining the state in which the first treated water discharge section 12 and the second treated water discharge section 12' are connected by the connecting pipe L2. Also, the respective concentrated water valves 62 and 62' and the respective drain valves 64 and 64' are kept closed.

[0070] When 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, since the first water to be treated valve 62 is closed, no water to be treated flows into the first membrane module 1, and no filtration is performed 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 flows through the connecting pipe L2 into the first treated water discharge section 12 of the first membrane module 1.

[0071] The treated water that flows into the first treated water discharge section 12 permeates from the inside to the outside of the first hollow fiber membranes 14·14…. At this time, impurities that had accumulated on the outside of the first hollow fiber membranes 14·14… are detached by the flow of the permeating treated water. Since the detached impurities accumulate at the bottom of the container 15, they can be discharged from the first bottom drain 19 by opening the first drain valve 64. Alternatively, backwashing may be performed after draining the container 15 in advance. During backwashing, the first drain valve 64 is closed to block the first drain pipe L4, filling the container 15 with backwash water. Once the container 15 is filled with backwash water, the first drain valve 64 is switched back to open the first drain pipe L4 and drain the water. The intake and exhaust valve 7 is provided in the connecting pipe L2, which allows air to flow into the container 15 when draining water and to discharge air from the container 15 when filling water.

[0072] As described above, once the first membrane module 1 and the second membrane module 1' have been backwashed, the first three-way connecting valve 53 and the second three-way connecting valve 53' are switched so that the first treated water discharge section 12 and the first treated water piping L3 are connected, and the second treated water discharge section 12' and the second treated water piping L3' are connected. Furthermore, 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 filtration operation to be performed again using the first membrane module 1 and the second membrane module 1'.

[0073] In cleaning the hollow fiber membrane, in addition to the backwashing described above, bubbling may also be used by operating the compressor 10 to generate bubbles and using the bursting of these bubbles to remove impurities. For example, to perform bubbling when cleaning the second membrane module 1', the second bubble valve 65' can be opened to introduce bubbles from the second bottom drain 19', or a bubble tube (not shown) can be introduced into the container 15 and bubbles can be introduced from a position close to the second hollow fiber membranes 14', 14'.... When using bubble tubes, it is preferable to place them adjacent to the top, middle, and bottom of the second hollow fiber membranes 14', 14'... and switch between them sequentially from the top to eject bubbles.

[0074] In the bubbling process in the aforementioned bubble tube, 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 incoming treated water is not discharged from the second treated water discharge section 12' or the second bottom drain 19', but is entirely discharged from the second concentrated water discharge section 13'. The system can also be configured to discharge the detached impurities to the outside with the water flow at this time.

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

[0076] Furthermore, by switching the three-way valves 53 and 53' of each connecting pipe and the manual valves 6 and 6' at predetermined intervals, it is possible to alternately backwash one membrane module and backwash the other membrane module. In these backwashing operations, there is no need to prepare a dedicated pump for backwashing; the water flow from 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 for cleaning. Thus, with the membrane filtration apparatus of the present invention, a dedicated pump for backwashing is not required, which reduces costs, simplifies the apparatus, and lowers the failure rate.

[0077] "Differentiation Example 2" Next, a modified membrane filtration apparatus 102 according to the present invention will be described with reference to Figures 7 and 8. In the following description, the same parts will be referred to by the same reference numerals, and redundant explanations will be omitted.

[0078] In this modified version, the difference from the configuration in Figure 1 is that there are three membrane modules 1·1'·1'' arranged in parallel. In this modified configuration, the system includes a first membrane module 1, a second membrane module 1', a third membrane module 1'', a treated water tank 2 for storing treated water, a pump 3 for supplying treated water to each membrane module 1·1'·1'', a treated water tank 4 for storing treated water, three-way valves 5·5'·5'' for switching water channels, manual valves 6·6'·6'', intake / exhaust valves 7 for intake and exhaust, and flow gauges 8·8'·8''. Note that the configuration of each membrane module 1·1'·1'' is the same as in Figure 2, so we will omit the explanation.

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

[0080] When 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, because the third water to be treated three-way valve 51'' is switched, the water to be treated does not flow into the third membrane module 1'', and filtration does not occur in the third membrane module 1''. The treated water filtered by the first membrane module 1 and the second membrane module 1' flows through the connecting pipe L2 into the third upper treated water discharge section 121'' of the third membrane module 1''.

[0081] The treated water flowing 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 membrane 14''·14''…. As a result, impurities that had accumulated on the inside of the third hollow fiber membrane 14''·14''… are detached by the flow of the permeated treated water. At this time, with the first treated water valve 61 and the second treated water valve 61' closed, the treated water produced by filtration is not discharged into the treated water tank 4 and is used only as backwash water. Also, with the third treated water valve 61'' closed, the water containing the detached impurities is not discharged into the treated water tank 4 but is discharged to the outside through the third treated water inlet 11'' and the third drain pipe L4''.

[0082] Next, the cleaning of the first membrane module 1 will be explained based on Figure 8(b). Once the cleaning of the third membrane module 1'' is complete, as shown in Figure 8(b), the first treated water valve 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 communicates with the first drain pipe L4. Also, 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 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, since the first water to be treated three-way valve 51 is 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' and the third membrane module 1'' flows through the connecting pipe L2 into the first treated water discharge section 12 of the first membrane module 1.

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

[0085] Next, the cleaning of the second membrane module 1' will be explained based on Figure 8(c). Once the cleaning of the first membrane module 1 is complete, as shown in Figure 8(c), the second treated water valve 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'. Also, 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 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, since the second water to be treated three-way valve 51' is closed, 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 and the third membrane module 1'' flows through the connecting pipe L2 into the second treated water discharge section 12' of the second membrane module 1'.

[0087] The treated water that flows into the second treated water discharge section 12' permeates from the outside to the inside of the second hollow fiber membrane 14'·14'…. Then, impurities that had accumulated on the inside of the second hollow fiber membrane 14'·14'… are detached by the flow of the permeated treated water. At this time, with the first treated water valve 61 and the third treated water valve 61'' closed, the treated water produced by filtration is not discharged into the treated water tank 4 and is used only as backwash water. Also, with the second treated water valve 61' closed, the water containing the detached impurities is not discharged into the treated water tank 4 but is discharged to the outside through the second treated water inlet 11' and the second drain pipe L4'.

[0088] As described above, in this modified configuration, by using three membrane modules, two membrane modules can generate treated water, and the remaining membrane module can be washed with this treated water, thus allowing sufficient treated water to be used for backwashing.

[0089] The present invention is not limited to the embodiments described above. For example, in an internal pressure type membrane module, a compressor may be connected to the communication pipe L2 to allow air to be ejected during backwashing. In an external pressure type membrane module, three or more membrane modules may be used. Furthermore, valves that were previously three-way valves or manual valves may be opened and closed electronically using solenoid valves or motor valves. [Explanation of Symbols]

[0090] 100, 101, 102 Membrane filtration system 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 Processing tanks 17 Upper end fixed wall 18 Lower end fixed wall 19 Bottom drain 2. Water tank to be treated 3 pumps 4. Treated water tank 5. Three-way valve 51 Three-way valve for treated water 52 Treated water three-way valve 53. Three-way valve for connecting pipes 6 Manual valves 61 Treatment water valve 62 Concentrated water valve 63. Water valve to be treated 64 Drain valve 65 Bubble valve 7. Intake and exhaust valves 8 flow gauges 9. Check valve 91 Check valve for treated water 92 Compressor Check Valve 10 Compressors L1 Water treatment piping L2 communication pipe L3 treated water piping L4 drain pipe

Claims

1. An internal pressure type membrane filtration apparatus comprising a membrane module for obtaining treated water from which impurities have been removed from water to be treated that contains impurities, The aforementioned membrane module is composed of a plurality of membrane modules, One membrane module comprises a filtration membrane for filtering the water to be treated, a first water to be treated inlet connected to a pump for supplying the water to be treated and allowing the water to flow in, a first treated water discharge outlet for discharging the water filtered by the filtration membrane to the outside, and a first impurity discharge outlet for discharging the impurities removed during cleaning of the filtration membrane to the outside. The other membrane module comprises a filtration membrane for filtering the water to be treated, a second water to be treated inlet connected to the pump for introducing the water to be treated, a second treated water discharge outlet for discharging the water filtered by the filtration membrane to the outside, and a second impurity discharge outlet for discharging the impurities removed during cleaning of the filtration membrane to the outside. The first treated water discharge section is provided with a first upper treated water discharge section and a first lower treated water discharge section. The second treated water discharge section is equipped with a second upper treated water discharge section and a second lower treated water discharge section. The first treated water discharge section and the second treated water discharge section are connected by a connecting pipe. During the aforementioned cleaning process, the treated water filtered by one membrane module is not stored but is configured to be sent via the connecting pipe to the second upper treated water discharge section or the second lower treated water discharge section of the other membrane module. The treated water filtered by the other membrane module is not stored but is configured to be sent by the connecting pipe to the first upper treated water discharge section or the first lower treated water discharge section of the first membrane module. The first water to be treated inlet also serves as the first impurity discharge outlet. The second water inlet for treatment also serves as the second impurity discharge section, The treated water that has passed through one membrane module is not stored but is sent into the other membrane module, thereby enabling the cleaning of the filtration membrane of the other membrane module. A membrane filtration apparatus characterized in that the treated water that has passed through the other membrane module is not stored but is sent into the first membrane module, thereby enabling the filtration membrane of the first membrane module to be washed.

2. An external pressure type membrane filtration apparatus comprising a membrane module for obtaining treated water from which impurities have been removed from water to be treated that contains impurities, The aforementioned membrane module is composed of a plurality of membrane modules, One membrane module comprises a filtration membrane for filtering the water to be treated, a first water to be treated inlet connected to a pump for supplying the water to be treated and allowing the water to flow in, a first treated water discharge outlet for discharging the water filtered by the filtration membrane to the outside, and a first impurity discharge outlet for discharging the impurities removed during cleaning of the filtration membrane to the outside. The other membrane module comprises a filtration membrane for filtering the water to be treated, a second water to be treated inlet connected to the pump for introducing the water to be treated, a second treated water discharge outlet for discharging the water filtered by the filtration membrane to the outside, and a second impurity discharge outlet for discharging the impurities removed during cleaning of the filtration membrane to the outside. The first impurity discharge section is provided with a first upper impurity discharge section and a first lower impurity discharge section. The second impurity discharge section is provided with a second upper impurity discharge section and a second lower impurity discharge section. The first treated water discharge section and the second treated water discharge section are connected by a connecting pipe. During the aforementioned cleaning process, the treated water filtered by one membrane module is not stored but is configured to be sent to the second treated water discharge section of the other membrane module via the connecting pipe. The treated water filtered by the other membrane module is not stored but is configured to be sent to the first treated water discharge section of the first membrane module via the connecting pipe. During cleaning of one of the membrane modules, the impurities removed from the filtration membrane are discharged from both or either of the first upper impurity discharge section and the first lower impurity discharge section. During the cleaning of the other membrane module, the impurities removed from the filtration membrane are discharged from both or either the second upper impurity discharge section and the second lower impurity discharge section. The treated water that has passed through one membrane module is not stored but is sent into the other membrane module, thereby enabling the cleaning of the filtration membrane of the other membrane module. A membrane filtration apparatus characterized in that the treated water that has passed through the other membrane module is not stored but is sent into the first membrane module, thereby enabling the filtration membrane of the first membrane module to be washed.

3. A method for cleaning a filter membrane in a membrane filtration apparatus for obtaining treated water from which impurities have been removed from water to be treated that contains impurities, Using the membrane filtration apparatus according to claim 1 or claim 2, The treated water filtered by one membrane module is used to wash the other membrane module without being stored. A method for cleaning a filtration membrane, characterized by cleaning the first membrane module using treated water filtered by the other membrane module without storing it.

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