WO2007083723A1

WO2007083723A1 - Membrane filtration apparatus and its operating method

Info

Publication number: WO2007083723A1
Application number: PCT/JP2007/050747
Authority: WO
Inventors: Hiroaki Kubo; Sang-Hoon Park
Original assignee: Toray Industries, Inc.
Priority date: 2006-01-20
Filing date: 2007-01-19
Publication date: 2007-07-26
Also published as: JPWO2007083723A1; CN101370571A; AU2007206356A1; KR20080087899A

Abstract

This invention provides a membrane filtration apparatus that can realize stable membrane filtration operation at a high percentage operation recovery even for raw water having a relatively high level of turbidity. The membrane filtration apparatus comprises a dipping tank (1) having a raw water supply port in its upper part and a water discharge port in its lower part. A dipping-type hollow fiber membrane module (2) comprising a large number of hollow fiber membranes which have been bundled, is disposed within the dipping tank (1) so that the longitudinal direction of the hollow fiber membrane is a vertical direction. A diffuser tube (3) is disposed below the hollow fiber membrane module. The position of the raw water supply port is located above the hollow fiber membrane module. In a horizontal section of the dipping tank in which the hollow fiber membrane module has been disposed, the proportion of the sectional area of the hollow fiber membrane module to the sectional area within the dipping tank is 60% to 90%, the distance between the diffuser tube and the bottom face of the dipping tank is not less than 200 mm, and the position of the water discharge port is not less than 200 mm below the diffuser tube.

Description

Specification

Membrane filtration apparatus and method for operating the same

Technical field

The present invention relates to the structure of an apparatus for separating and filtering water with a hollow fiber membrane.

More specifically, the present invention relates to a membrane filtration treatment apparatus that enables stable membrane filtration with a high recovery rate even when raw water has high turbidity.

Background art

[0002] The membrane filtration method of filtering water with a separation membrane has features such as energy saving, space saving, labor saving, and improvement of water quality, and therefore is widely used in various fields. For example, membrane filtration using microfiltration membranes and ultrafiltration membranes has been applied to water purification manufacturing processes that produce industrial water and tap water from river water, groundwater and treated sewage water.

[0003] Further, since the hollow fiber membrane module can secure a large membrane area per unit volume, it is applied to many fluid treatment fields, for example, chemical purification, sterilization, turbidity, etc. by a microfiltration membrane.

[0004] In addition, the hollow fiber membrane module is roughly classified into a pressure type hollow fiber membrane module and an immersion type hollow fiber membrane module. The pressure-type hollow fiber membrane module is loaded with a number of hollow fiber membrane bundles in a pressure-resistant cylindrical case with no openings, and the ends of both ends of the membrane bundle and the inner walls of the cylindrical case are bonded and fixed. One end side or both ends are cut to open the inside of the hollow fiber membrane, and a filtrate collecting part is provided at the opening end to collect filtrate and supply the stock solution into the cylindrical case. This is a membrane module with a structure in which pressurized raw water is introduced into the module and filtered through the hollow fiber membrane surface. On the other hand, in the immersion type hollow fiber membrane module, both ends of the hollow fiber membrane bundle are bonded and fixed with an adhesive, and then one end side or both ends are cut to open the inside of the hollow fiber membrane. A membrane module that has a structure for collecting filtered water by providing a filtered water collecting section, and is a permeated water in which the membrane module is immersed in raw water in an immersion tank that is open to the atmosphere, and a filtering water collecting section is provided. This type employs a suction filtration system that suctions and filters the sides.

[0005] The pressure-type hollow fiber membrane module can set the filtration pressure higher than that of the immersion type. Therefore, the processing amount per membrane area can be increased. As a result, the number of membranes required for processing can be reduced, and the installation area can be reduced. On the other hand, the immersion type hollow fiber membrane module is used by immersing the hollow fiber membrane bundle in the treated raw water without providing a pressure-resistant cylindrical case around the hollow fiber membrane, so that it is clogged between the hollow fiber membranes. There is an advantage that turbidity can be easily discharged, that is, it is excellent in turbidity discharge performance and membrane filtration can be performed even with highly turbid raw water. In addition, since the filtration method is simple and there are few incidental pipes, there is an advantage that the equipment cost can be reduced.

[0006] As described above, the submerged membrane module has an advantage in that the pressure-resistant cylindrical case is clogged between the membranes. It has excellent turbidity discharge performance and can perform membrane filtration even with highly turbid raw water. Various contrivances have been made for the immersion tank filled with water and equipped with an immersion membrane module so that the turbidity can be discharged and membrane filtration can be performed on raw water with higher turbidity.

[0007] For example, in Patent Document 1, a plurality of membrane modules in which a plurality of tubular ceramic separation membranes are arranged in parallel are stacked in an immersion tank, and a diffuser tube is disposed below the plurality of membrane modules. An apparatus in which a sedimentation zone is formed in the lower region is disclosed. In this device, the membrane module is placed flat so that the longitudinal direction of the tubular separation membrane is horizontal, and when the suspended components are peeled off by surface scrubbing by air scrubbing and circulated in the tank, A sedimentation zone is provided to facilitate precipitation of components into the sedimentation zone and to reduce raw water turbidity near the membrane module.

[0008] Further, in Patent Document 2, a baffle plate is provided between the air diffuser and the bottom of the dipping tank in order to prevent the turbid components precipitated in the sedimentation zone from being sprinkled up again by air scrubbing. It is disclosed that it is installed! Speak.

[0009] In Patent Document 3, a flat membrane module is arranged inside an aeration tank (treatment tank) that performs activated sludge treatment, and an air diffuser is arranged below the aeration tank. It is disclosed that the tank area is set to be at least three times the membrane module area. By increasing the area inside the treatment tank in this way, it is possible to make the circulation flow in the tank easier to flow by the air supplied from the diffuser, and the effect of improving the discharge of turbidity clogged between the films is obtained. .

[0010] Among the submerged membrane modules, particularly in the submerged hollow fiber membrane module, a large number of hollow fiber membranes are bundled and arranged in the module, and the membrane surface per unit volume Since the product is made large, there is a demerit that turbid components are easily clogged between the membranes, and it is difficult to cope with raw water with high turbidity only by the conventional technology as described above. For this reason, the continuous air scrubbing method, in which air scrubbing is performed not only during the physical cleaning process but also during the filtration process, and most of the concentrated raw water in the immersion tank is periodically drained to remove the relatively pure raw water before concentration. Inflow methods (called the total drain method) and a combination of both methods have been generally adopted.

[0011] The continuous air scrubbing method is a method that is widely used mainly in the treatment of sewage wastewater.

The enormous running cost is a practical problem, and there is a problem of lack of certainty as a stable operation method for raw water with high turbidity.

[0012] On the other hand, the total drain method is a stable operation method for raw water with high turbidity because the concentration of the concentrated water in the tank rises and reaches the specified concentration, and then the entire amount is drained and filled again with the raw water before concentration. As a certain thing. However, if the total drainage method is adopted in a conventional device that maintains the high turbidity discharge characteristic, which is a feature of the immersion membrane module, by placing it in a wide immersion bath, Because most of the concentrated water is drained, there is a problem that the operation recovery rate is greatly reduced.

[0013] Here, it is possible to set the inner surface shape of the immersion tank to be approximately the same size as the membrane module shape. In this case, the operation recovery rate is greatly reduced even if the total drainage method is adopted. The problem to do is solved. However, if the shape of the membrane module and the inner shape of the immersion tank are similar and approximately the same size, there will be almost no functional difference from the pressurized module in which the hollow fiber membrane bundle is inserted into a pressure-resistant cylindrical case. In addition, the discharge of turbidity clogged between membranes is greatly reduced.

[0014] With respect to the membrane filtration processing apparatus in which the above-described submerged hollow fiber membrane module is arranged, improvement of turbidity discharge and improvement of operation recovery rate are contradictory matters, and both are favorable conditions. Was considered difficult.

Patent Document 1: Japanese Patent Laid-Open No. 2002-191946

Patent Document 2: JP-A-9-220441

Patent Document 3: Japanese Patent Application Laid-Open No. 8-267083

Disclosure of the invention Problems to be solved by the invention

[0015] In the present invention, a submerged hollow fiber membrane module that performs solid-liquid separation by suction filtration is disposed in a submerged tank, and a diffuser tube is disposed below the hollow fiber membrane module, thereby providing a hollow fiber membrane module. Membrane filtration device with raw water supply port located above the tank has a high ability to discharge turbidity clogged between the membranes, and the operation recovery rate is kept high even if the total drainage method is adopted. An object of the present invention is to provide a membrane filtration treatment apparatus that can perform a stable membrane filtration operation at a high recovery rate even for raw water with high turbidity.

Means for solving the problem

[0016] In order to achieve the above object, the membrane filtration apparatus of the present invention comprises a plurality of hollow fiber membranes bundled in an immersion tank provided with a raw water supply port at the top and a drain port at the bottom. The submerged hollow fiber membrane module is a membrane filtration treatment device in which the longitudinal direction of the hollow fiber membrane is in the vertical direction, and an aeration tube is arranged below the hollow fiber membrane module. The position of the supply port is above the hollow fiber membrane module, and the ratio of the cross-sectional area of the hollow fiber membrane module to the in-vessel cross-sectional area in the horizontal section where the hollow fiber membrane module is arranged is 60% to 90%. The distance force between the air diffuser and the bottom of the immersion tank is greater than or equal to OOmm, and the position of the drain outlet is 200mm or lower lower than the air diffuser.

[0017] Here, the ratio of the cross-sectional area of the hollow fiber membrane module to the cross-sectional area of the immersion tank in the horizontal cross section in which the hollow fiber membrane module is disposed is 70 to 80%, and the aeration tube and the bottom of the immersion tank Is preferably 200 to 700 mm.

[0018] Further, in the hollow fiber membrane module, a large number of hollow fiber membranes are bundled at least at the upper end portion and the lower end portion, and the upper end side of the hollow fiber membrane bundle is bundled and fixed with the end surface of the hollow fiber membrane being opened. A membrane module having a structure in which a water collecting part is provided on the open end surface of the hollow fiber membrane and the lower end side of the bundle of hollow fiber membranes is bundled in a plurality of small bundle units with the membrane end surface being non-opened. It is preferred to be Le! /.

[0019] Further, it is preferable that the drain outlet is installed on the bottom surface of the immersion tank.

[0020] In the operation method in which the raw water is subjected to membrane filtration with the membrane filtration device described above, it is effective to periodically take a method in which the water level in the immersion bath is lowered to a position 200 mm lower than the diffuser tube. It is. In addition, the above-mentioned membrane filtration treatment apparatus is used to treat raw water with membrane filtration It is also effective to periodically drain part of the water in the dipping bath as a drainage process.

The invention's effect

[0021] According to the present invention, it is possible to maintain a high drainage of turbidity clogged between the membranes, which is an advantage of the submerged hollow fiber membrane module, and to regularly or substantially remove all or most of the water in the immersion tank. Even if it drains, the operation recovery rate can be kept high. In addition, most of the suspended solids contained in the raw water settle in the vicinity of the bottom of the immersion tank without being membrane filtered and are present in a deposited or concentrated state. In contrast, it is possible to perform a stable membrane filtration operation with a high recovery rate.

Brief Description of Drawings

FIG. 1 is a schematic sectional view showing one embodiment of a membrane filtration device according to the present invention.

FIG. 2 is a schematic cross-sectional view of the horizontal cut surface taken along the horizontal line ZZ in FIG.

FIG. 3 is an enlarged schematic cross-sectional view showing one embodiment of the hollow fiber membrane module used in the present invention.

FIG. 4 is a schematic sectional view showing another embodiment of the membrane filtration apparatus according to the present invention.

FIG. 5 is a schematic cross-sectional view of the horizontal section cut along the horizontal line Z—Z in FIG.

FIG. 6 is a schematic cross-sectional view schematically showing the flow of water in the immersion tank during air scrubbing in the membrane filtration apparatus shown in FIG.

Explanation of symbols

[0023] 1: immersion tank, 1A: inner surface of immersion tank, 2: hollow fiber membrane module, 2B: outer surface of hollow fiber membrane module, 3: air diffuser, 4: air diffuser, 5: permeate pipe, 6: raw water Supply port, 7: Drain line, 8: Hollow fiber membrane, 9a, 9b: Adhesive fixing part, 10: Water collecting cap, 11: Air introduction cylinder, 12: Through hole, 13: Drain port

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] In the membrane filtration apparatus of the present invention, the raw water supply port is provided at the upper part and the drainage port is provided at the lower part. An immersion type hollow fiber membrane module in which a large number of hollow fiber membranes are bundled inside the immersion tank is arranged so that the longitudinal direction of the hollow fiber membrane is in the vertical direction, and below the hollow fiber membrane module. It is a membrane filtration processing apparatus which arrange | positions a diffuser tube. And, the position of the raw water supply port is above the hollow fiber membrane module, and the ratio of the hollow fiber membrane module cross-sectional area to the in-vessel cross-sectional area in the horizontal cross section where the hollow fiber membrane module is arranged is 60% to 90%. %, The distance force between the diffuser tube and the bottom of the immersion tank is more than OOmm, and the position of the drain is 200mm or more below the diffuser tube.

[0025] A membrane filtration apparatus according to the best embodiment of the present invention will be described below with reference to the drawings schematically. However, the scope of the present invention is not limited to these.

FIG. 1 is a schematic cross-sectional view showing one embodiment of a membrane filtration apparatus according to the present invention, and FIG. 2 is an upper view of the immersion tank and the hollow fiber membrane module cut along a horizontal line Z-Z in FIG. It is sectional drawing which shows the outline of the horizontal cut surface which also looked at force. FIG. 3 is an enlarged schematic cross-sectional view showing an embodiment of the hollow fiber membrane module in FIG. FIG. 4 is a schematic sectional view showing another embodiment of the membrane filtration apparatus according to the present invention. FIG. 5 is a cross-sectional view showing an outline of a horizontal cut surface when the immersion tank and the hollow fiber membrane module are cut along the horizontal line Z-Z in FIG. 4 and viewed from the upper side.

[0027] The immersion type hollow fiber membrane module 2 in the present invention has a hollow fiber membrane bundle in which a large number (for example, several hundred to several tens of thousands) of hollow fiber membranes ₈ are aligned and bundled, and both ends thereof are bonded and fixed. One end side 9a of the adhesive fixing part is bonded and fixed with the end face of the hollow fiber membrane open and a filtrate collecting part is provided, and the other end side 9b is the end face of the hollow fiber membrane. It is preferably a hollow fiber membrane module that is bonded and fixed in the closed state (the type illustrated in Fig. 1 and Fig. 3 etc.), but the end surfaces of the hollow fiber membranes are open at both ends of the adhesive fixing part. It may be a hollow fiber membrane module that is bonded and fixed with a filter water collecting part.

[0028] The hollow fiber membrane 8 is not particularly limited as long as it is a porous hollow fiber membrane having a desired filtration performance, but polyacrylonitrile, polyphenylenesulfone, polyphenylene sulfide sulfone, polyvinyl fluoride. -Polymer materials such as redene, polypropylene, polyethylene, polysulfone, polyvinyl alcohol, and cellulose acetate, and inorganic materials such as ceramic Group force At least one kind of force selected is preferred. From the viewpoint of membrane strength, a hollow fiber membrane having polyvinylidene fluoride strength is more preferred. The pore diameter on the surface of the hollow fiber membrane is not particularly limited, but can be conveniently selected so as to obtain a desired filtration performance within a range of 0.001 μm to 1 μm. Further, the outer diameter of the hollow fiber membrane 8 is not particularly limited, but the outer diameter is preferably in the range of 250 πι to 2000 / ζ πι because the hollow fiber membrane has high oscillating property and excellent detergency. .

[0029] Although there are no particular limitations on the adhesive used to bond and fix both ends of the hollow fiber membrane bundle with an adhesive, it is preferable to use a thermosetting resin such as epoxy resin or urethane resin.

[0030] Further, the adhesive fixing portions 9a and 9b respectively formed at both ends of the hollow fiber membrane bundle are connected via a large number of hollow fiber membrane portions existing therebetween, and the large number of hollow fibers. In the membrane part, the hollow fiber membranes are arranged in parallel, and the membrane filtration function is exhibited in this part. As shown in FIG. 3, the outer periphery of the parallel draw bundle in the multiple hollow fiber membrane portions may have a structure in which no reinforcing member is interposed, or a structure in which a reinforcing means is interposed (not shown). )! / ヽ. As a structure including the reinforcing means, for example, about 1 to 30 reinforcing stays (metal bars, etc.) are arranged on the outer periphery or inside of the aligned bundle of the hollow fiber membranes, and the adhesive fixing portions are connected to each other. There are also structures that are connected by a tape or a structure in which a perforated plate material such as a net is arranged so as to cover the outer periphery of the bundle of hollow fiber membranes between the adhesive fixing parts. Examples of the stage include a cylindrical rod-shaped body having a cross-sectional area of 3 to 700 mm ² .

[0031] In the hollow fiber membrane module of the present invention, an adhesive fixing portion 9a that is integrally bonded with the end surface of the hollow fiber membrane being opened is formed on the upper end side where a large number of hollow fiber membranes are bundled. A water collection portion by a water collection cap 10 is provided on the open end surface of the hollow fiber membrane.

[0032] The adhesive fixing portion 9b on the lower end side of the hollow fiber membrane bundle may have a structure in which an adhesive fixing portion is formed in which the membrane end surface is adhesively fixed with a plurality of small bundle units in a non-open state. Such a small bundle unit can further enhance the discharge of suspended solids from the module. The small bundle unit adhesive fixing portion formed on the lower end side of the hollow fiber membrane bundle is such that the small bundles that are bonded and fixed are not adhered to each other and independent, and there is a space between the small bundles. The number of small bundles formed on the lower end side of the hollow fiber membrane bundle is preferably 3-50 per membrane module. In addition, the number of hollow fiber membranes forming a small bundle is preferably 50 to 2000.

In the membrane filtration apparatus of the present invention, the ratio of the membrane module cross-sectional area to the in-vessel cross-sectional area of the immersion tank is the upper end of the membrane module 2 disposed in the immersion tank 1 as shown in FIG. 2 is a ratio (in percent) of the cross-sectional area of the outer surface 2B of the membrane module to the cross-sectional area of the inner surface 1A of the immersion tank in the horizontal section at the height from the bottom to the bottom. The upper end force of the membrane module 2 placed in the immersion tank 1 where the cross-sectional area of the membrane module 2 and the immersion tank 1 are not constant occupies the horizontal cross-sectional area of the immersion tank at the height to the lower end. If the ratio of the membrane module cross-sectional area changes, the maximum value should be within the range of 60% to 90%.

[0034] Note that the membrane module when the ratio of the cross-sectional area of the membrane module to the cross-sectional area in the tank of the immersion tank is defined from the one-end adhesive fixing part to the other-end adhesive fixing part, and the water collection attached to the front and rear thereof Do not include caps or air cylinders. In addition, the cross-sectional area of the membrane module outer surface 2B from the upper end to the lower end of the membrane module 2 refers to the area surrounded by the outer peripheral portion of the adhesive fixing portion 9a, 9b, and the hollow fiber membrane between the adhesive fixing portions. If is an exposed part, it refers to the circumscribed area that encloses all of the hollow fiber membranes present. In addition, when the outer peripheral part of the hollow fiber membrane bundle between the adhesive fixing parts is covered with a porous plate-like material such as a net, the area surrounded by the outer peripheral part of the net or the like is indicated.

[0035] When a plurality of hollow fiber membrane modules are arranged inside the immersion tank as shown in Fig. 4, the cross-sectional area of the inner surface 1A of the immersion tank is set as the denominator as shown in Fig. 5. And the ratio calculated using the sum of the cross-sectional areas of the outer surface 2B of each membrane module as a numerator.

[0036] In the present invention, a structure in which the air scrubbing air diffuser 3 is disposed below the membrane module 2 in order to discharge suspended substances accumulated in the hollow fiber membrane module out of the membrane module system. Any material is acceptable. The air diffuser 3 is formed with air diffuser holes 4 for diffusing compressed air supplied with a blower (not shown) equal force into the raw water in the immersion tank 1. The number does not matter.

[0037] In the present invention, the distance between the diffuser tube and the bottom of the immersion tank is the distance when the position of the diffuser hole 4 provided in the diffuser pipe 3 is expressed by the height distance of the bottom of the immersion tank. It is. Here, the position of the bottom surface of the immersion tank is the bottom surface when the bottom surface has a cone shape as shown in the figure. This is based on the substantially lowest position. In addition, when the height position of the diffuser hole 4 varies depending on the position of each diffuser hole, it indicates the distance to the diffuser hole at the lowest position of the immersion tank bottom surface force.

Next, the effect of the present invention will be described while describing the case of membrane filtration operation using a membrane filtration apparatus using the immersion type hollow fiber membrane module having the above-described configuration.

[0039] First, one to several hundred hollow fiber membrane modules 2 are arranged in the immersion tank 1, depending on conditions such as the amount of water treated and the immersion tank area. Here, raw water containing suspended solids is placed in the immersion tank 1 in advance, and when the upper end adhesive fixing part side that is bonded and fixed with the end face of the hollow fiber membrane opened is sucked with a pump or the like. The raw water containing suspended solids is solid-liquid separated (filtered) by the hollow fiber membrane 8, and the filtered water is sent from the water collection cap 10 to the water collection pipe (not shown) through the permeate pipe 5. If the raw water is aspirated and the filtered water is taken out of the immersion tank, the immersion tank water level drops, so the raw water is supplied into the immersion tank intermittently or regularly as necessary.

[0040] At this time, in the present invention, the raw water supply port 6 is installed above the membrane module, and the ratio of the membrane module cross-sectional area to the cross-sectional area in the bath of the immersion bath is set within a range of 60% to 90%. For this reason, most of the suspended solids in the raw water are placed in a downward flow accompanying the inflow of the raw water, and there is a gap between the membrane module 2 and the immersion tank 1 where a certain amount of space exists, or a gap between the multiple membrane modules arranged. Passes through and sinks to the bottom of the immersion bath. In the present invention, since the distance from the air diffuser 3 installed below the membrane module 2 to the bottom of the immersion tank is 200 mm or more, the suspended matter settled below the air diffuser wraps around the membrane filtration surface. Without being deposited in the lower part of the air duct, the suspended substance concentration in the vicinity of the hollow fiber membrane 8 can be lowered, and the membrane blockage by the suspended substance can be greatly relieved.

[0041] On the other hand, some suspended substances that have not settled down reach the vicinity of the membrane surface of the hollow fiber membrane 8, and adhere to the membrane surface and inside the membrane pores by membrane filtration. For this reason, when the filtration process for a predetermined time is completed, the filtered water or compressed air ^^ water cap 10 side force is also introduced in the direction toward the raw water side, and the washing operation (back flow) is performed to separate the suspended matter adhering to the inside of the membrane hole. Z) or from the air diffuser 4 of the air diffuser 3 installed below the hollow fiber membrane module 2 through the air introduction cylinder 11 at the lower part of the membrane module and the through hole 12 of the lower adhesive fixing part. Compressed air inside Supply to the hollow fiber membrane 8 to shake the hollow fiber membrane, peel off the suspended matter adhering to the surface of the hollow fiber membrane, and perform a washing operation (called air scrubbing) to discharge the suspended matter with the force between the hollow fiber membranes.

FIG. 6 shows the flow of water in the immersion tank when air scrubbing is performed in the membrane filtration apparatus shown in FIG. In the present invention, the membrane module is installed so that the ratio of the cross-sectional area of the membrane module 2 to the cross-sectional area of the immersion tank 1 in the tank is 60% to 90%, and the space in the tank is secured within a predetermined range. Therefore, it is possible to ensure high discharge of turbidity clogged between the hollow fiber membranes, which is an advantage of the submerged membrane module, and it is peeled off from the hollow fiber membranes by backwashing and air scrubbing. The suspended suspension is quickly discharged out of the membrane module, and the separated suspension floats in the immersion tank, and then the gap between the membrane module 2 and the immersion tank 1 inner wall or a plurality of membrane modules arranged. It sinks to the bottom of the immersion tank through the gap between them. At this time, a part of the suspension settles down to the suspended matter accumulation space below the diffuser, but a part of the suspension again moves to the vicinity of the surface of the hollow fiber membrane along the air flow. Move.

[0043] In the present invention, since the distance from the air diffuser 3 installed below the membrane module 2 to the bottom of the immersion bath is 200 mm or more, suspended substances are deposited and concentrated below the air diffuser. The water in the area is not disturbed even during air scrubbing. Therefore, the suspended matter that has moved into the region where it is difficult to be affected by air scrubbing below the diffuser tube moves to the vicinity of the hollow fiber membrane 8 where it does not move up again, and it does not get damaged.

[0044] As described above, in the membrane filtration apparatus of the present invention, suspended substances clogged between the hollow fiber membranes during air scrubbing can be easily discharged out of the module, and at least the suspended substances can be discharged. A part of the suspended matter can be allowed to settle down below the diffuser, and the force that has once settled down to the vicinity of the bottom surface of the immersion tank 1 and accumulated and concentrated does not reappear.

[0045] Then, the membrane filtration step, back-flow purification, and air scrubbing are repeatedly performed, and the suspended sediment that has accumulated and concentrated on the bottom surface of the immersion tank 1 is drained from the drainage line 7 to periodically increase the turbidity. It is possible to continue a stable membrane filtration operation even for the raw water.

[0046] However, in the immersion type hollow fiber membrane module, a large number of hollow fiber membranes are bundled and arranged in the module to increase the membrane area per unit volume, so that turbid components are clogged between the membranes. Since there is a problem that it is easy, even in the case of the membrane filtration processing apparatus of the present invention, Suspended substances that do not settle on the bottom of the immersion tank remain in the vicinity of the membrane surface of the hollow fiber membrane 8, and as the operation continues for a long period of time, the concentration of the suspended substance in the vicinity of the hollow fiber membrane gradually increases and eventually becomes stable. It becomes impossible to drive.

[0047] In order to solve this problem, it is necessary to perform an operation that can reduce the concentration of suspended solids in the vicinity of the hollow fiber membrane 8. For example, periodically drain almost all or all of the water with high suspended matter concentration in the immersion tank 1 and instead drain all the relatively clear raw water (raw water with relatively low suspended solids) into it. The law is done. In the case of conventional immersion-type hollow fiber membrane modules, the membrane module volume occupies the immersion tank volume is small, so when the total drainage method is used, the water recovery rate (referred to as the operation recovery rate) by the filtration treatment operation is greatly reduced. In the present invention, since the cross-sectional area of the membrane module 2 occupying the horizontal cross-sectional area of the immersion tank 1 is 60% to 90%, the operation recovery rate can be kept high even if the total drainage method is performed.

[0048] When the total amount drain method is periodically performed in the membrane filtration apparatus of the present invention, the water level in the immersion tank 1 is drained so that the water level in the immersion tank 1 is lowered by 200 mm from the air diffuser 3 to a position below. Yes, just drive. In the membrane filtration apparatus of the present invention, suspended substances staying at a position 200 mm below and below the air diffuser are not sprinkled again even after air scrubbing. It is not necessary to replace the water below the lower position. Therefore, when draining the entire amount regularly, drain the water in the bath so that the water level in the immersion bath is lowered to 200 mm below the diffuser tube, or below, so that it is the purpose of the drainage of the entire amount. The reduction of suspended solid concentration in the vicinity of the yarn membrane 8 can be sufficiently achieved.

[0049] Especially in the case of an immersion tank having a large space in the vertical direction below the hollow fiber membrane module, in order to reduce excess drainage and improve the operation recovery rate, 200mn from the air diffuser, which does not drain almost all or the whole volume! ~ 400mm low U, prefer the driving method to lower the water level to the position. If all the drainage is performed by the operation method described above, the operation recovery rate can be maintained high even in a membrane filtration apparatus using an immersion tank having a large space in the vertical direction below the hollow fiber membrane module 2.

[0050] Immediately before the total drainage is performed, the water level in the immersion tank is adjusted to obtain a hollow fiber membrane module. By making the amount of water in the tank above the level 2 as small as possible, the operation recovery rate can be maintained at a higher level. Further, by installing the air diffuser 3 at a position as close as possible to the lower end of the hollow fiber membrane module 2, it is possible to further reduce the amount of drainage when draining the entire amount, and to increase the operation recovery rate.

[0051] As described above, by using the membrane filtration treatment device specified in the present invention, it is possible to maintain a high discharge of turbidity clogged between the membranes, which is an advantage of the submerged membrane module, and periodically. Even if all or most of the water in the immersion tank is drained, the operation recovery rate can be maintained high. In addition, since many suspended solids in raw water are deposited and concentrated on the bottom of the immersion tank without membrane filtration, stable membrane filtration operation with high recovery rate is possible even for raw water with high turbidity. .

[0052] Furthermore, in order to greatly improve the operation recovery rate while maintaining excellent turbidity discharge, the ratio of the membrane module 2 cross-sectional area to the horizontal cross-sectional area of the immersion tank 1 is 70% to 80%. It is more preferable to set the distance between the air diffusing pipe 3 and the bottom of the immersion bath to 200 mm to 700 mm from the viewpoint of installation space and construction cost that are more preferable.

[0053] Further, when the sedimentation of suspended substances in the raw water is high, such as when a flocculant is added to the raw water, the amount of suspended substances floating near the hollow fiber membrane is reduced. By adopting an operation method that periodically drains a portion of the water in the immersion tank without implementing the above, stable operation with a high recovery rate can be achieved. However, also in this operation method, the higher the ratio of the membrane module 2 cross-sectional area to the horizontal cross-sectional area of the immersion tank 1, the lower the turbidity discharge performance, and the lower the cost, the larger the installation area of the apparatus. Therefore, even when this operation method is performed, it is effective to set the ratio of the cross-sectional area of the membrane module 2 to the horizontal cross-sectional area of the immersion tank 1 to 60 to 90%, and further to 70 to 80%. preferable. In addition, the distance between the diffuser 3 and the bottom of the immersion tank is effective to be 200 mm or more in order to prevent the suspended solids that have once settled from rising again. It is preferable to set it to 700mm!

Example

A hollow fiber membrane made of polyvinylidene fluoride with an outer diameter of 1.5 mm, an inner diameter of 0.9 mm, and a length of about 1000 mm is bundled with 3500 hollow fiber membrane bundles, with the upper end at the end of the hollow fiber membrane and the lower end. Was bonded and fixed with a urethane-based adhesive with the end face of the hollow fiber membrane closed, to produce a hollow fiber membrane module having a membrane area of 15 m ² . As shown in FIG. 3, this membrane module has a through hole 12 in the lower end adhesive fixing portion, the air introduction cylinder 11 on the lower side of the lower end adhesive fixing portion, and the upper side of the upper end adhesive fixing portion. The structure was equipped with a water cap 10. Further, a polyethylene mesh perforated plate was attached between the upper end adhesive fixing part and the lower end adhesive fixing part so as to surround the outer periphery of the hollow fiber membrane bundle (not shown).

[0055] One hollow fiber membrane module was placed vertically in the immersion bath shown in FIG. At this time, the membrane filtration experiment was conducted under the following conditions, with the ratio of the membrane module cross-sectional area occupying 75% of the horizontal cross-sectional area of the immersion tank and the distance between the diffuser tube and the bottom of the immersion tank being 300 mm. Went.

[0056] Lake water with turbidity of 2-50 was used as raw water, membrane filtration flow rate 0.5mZday, filtration process time 30 minutes later, membrane filtration water flow rate with sodium hypochlorite 10mg / L added 1. OmZday Back scrubbing for 30 seconds and air scrubbing with air flow lOOLZMin for 60 seconds were performed. Then, every time this filtration, backwashing, and air scrubbing was repeated 12 times, all the water in the immersion tank was drained, and the operation recovery rate was set to 98%.

[0057] These operations were carried out continuously for about 1 week. During the experimental period, no increase in transmembrane pressure difference was observed, and stable membrane filtration could be continued.

[0058] <Comparative Example 1>

Using the hollow fiber membrane module used in Example 1, the size is such that the ratio of the membrane module cross-sectional area to the horizontal cross-sectional area of the immersion tank is 95%, and the distance between the diffuser tube and the bottom of the immersion tank is 100 mm. A hollow fiber membrane module and the like were installed in different immersion tanks. In terms of operating conditions, only the number of times the entire amount of water in the immersion tank was drained was changed, and the membrane filtration flux, the operation recovery rate, etc. were set the same, and the same membrane filtration experiment as in Example 1 was conducted. .

[0059] As a result, the transmembrane pressure difference increased at a rate of 1. OkPaZday.

[0060] <Comparative Example 2>

Using the hollow fiber membrane module used in Example 1, the size of the membrane module cross-sectional area in the horizontal cross-sectional area of the immersion tank is 30%, and the distance between the air diffuser and the bottom of the immersion tank is 500 mm. A hollow fiber membrane module and the like were installed in different immersion tanks. Also in the operating conditions Regarding this, only the number of times the entire amount of water in the immersion tank was drained was changed, the membrane filtration flux, the operation recovery rate, etc. were set to be the same, and the same membrane filtration experiment as in Example 1 was performed.

[0061] As a result, the transmembrane pressure difference increased at a rate of 1. OkPaZday.

Industrial applicability

[0062] The membrane filtration apparatus using the submerged hollow fiber membrane module of the present invention can be applied not only to water treatment but also to sewage treatment and industrial wastewater treatment.

Claims

The scope of the claims

[1] An immersion type hollow fiber membrane module in which a plurality of hollow fiber membranes are bundled inside an immersion tank having a raw water supply port at the top and a drain port at the bottom. It is a membrane filtration processing device that is arranged so as to be in the vertical direction and has an aeration tube arranged below the hollow fiber membrane module, where the position of the raw water supply port is above the hollow fiber membrane module, The ratio of the cross-sectional area of the hollow fiber membrane module to the in-vessel cross-sectional area of the immersion tank in the horizontal cross-section where the thread membrane module is arranged is 60% to 90%, and the distance between the diffuser tube and the bottom of the immersion tank is 200 mm or more, In addition, the membrane filtration apparatus is characterized in that the position of the drain outlet is at least 200 mm lower than the air diffuser.

[2] The ratio of the cross-sectional area of the hollow fiber membrane module to the in-vessel cross-sectional area of the immersion tank in the horizontal cross section where the hollow fiber membrane module is disposed is 70 to 80%, and the distance between the aeration tube and the bottom of the immersion tank 2. The membrane filtration apparatus according to claim 1, wherein the force is ¾00 to 700 mm.

[3] In the hollow fiber membrane module, a large number of hollow fiber membranes are bundled at least at the upper end portion and the lower end portion, and the upper end side of the hollow fiber membrane bundle is bundled and fixed with the end surface of the hollow fiber membrane being opened. The membrane module has a structure in which a water collecting portion is provided on the end surface of the hollow fiber membrane, and the lower end side of the bundle of hollow fiber membranes is bundled in a plurality of small bundle units with the membrane end surface being in an unopened state. The membrane filtration apparatus according to claim 1, wherein:

[4] The membrane filtration apparatus according to claim 1, wherein the drain port is installed at the bottom of the immersion tank.

[5] In the operation of membrane filtration treatment of raw water with the membrane filtration treatment device according to any one of claims 1 to 4, the water level in the immersion bath is periodically lowered to a position below 200 mm lower than the diffuser tube. A method of operating a membrane filtration apparatus characterized by

[6] In the operation of performing membrane filtration treatment of raw water with the membrane filtration treatment device according to any one of claims 1 to 4, a part of the water in the immersion bath is periodically discharged to a drainage location. Operation method of membrane filtration processing equipment.