Separation Membrane Module

Abstract

To provide a separation membrane module with its separation membrane cassettes having a gap therebetween, capable of allowing air supplied from an air diffuser to wastelessly flow into the separation membrane cassettes.SOLUTION: The separation membrane module comprises a plurality of separation membrane cassettes constituted of a plurality of separation membrane elements each comprising a sheet-shaped separation membrane and disposed parallel to the membrane face, a housing extractably storing the plurality of separation membrane cassettes arranged in the horizontal direction with a gap therebetween, and an aeration block disposed perpendicularly below the housing and provided with a plurality of fine bubble diffusion pipes each constituted of a center pipe and an elastic sheet covering the center pipe and provided with a plurality of air diffusion slits opening / closing according to the expansion and shrinking of the elastic sheet, in which M×A÷(N×B) is smaller than 0.8 provided that A and B each respectively represent the projected areas of the separation membrane cassette and the gap projected perpendicularly therebelow, N represents the aggregate lengths of the air diffusion slits formed on the elastic sheet present in the projected area A projected perpendicularly therebelow, and M represents aggregate lengths of the air diffusion slits formed on the elastic sheet present in the projected area B projected perpendicularly therebelow.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a separation membrane module used in a membrane bioreactor. [Background technology]

[0002] Currently, the membrane separation activated sludge process is becoming more and more popular as a wastewater treatment method. This method is a treatment method in which a separation membrane such as a microfiltration membrane or an ultrafiltration membrane is used instead of the final settling tank of the normal activated sludge process to perform membrane separation treatment. It has the advantages of being able to reduce the size of the biological reactor itself by maintaining a high biomass in the water to be treated in the biological reactor, and being able to obtain clear treated water without discharging suspended matter into the treated water because the separation of the sludge and the treated water is performed by membrane filtration rather than by gravity settling. Among them, the immersion type membrane separation activated sludge process in which the separation membrane module is immersed inside the aeration tank requires less power than the external circulation type membrane separation activated sludge process in which the separation membrane module is installed outside the aeration tank and a circulation pump is required, and since the final settling tank is not required, space is saved, and together with the drop in the price of the membrane, it is becoming more and more popular.

[0003] When performing membrane separation treatment by the immersion type membrane separation activated sludge method, usually, in order to clean the surface of the separation membrane, air bubbles are generated (aeration) from an air diffuser arranged in an air diffuser (aeration block) below the separation membrane, and the gas-liquid mixed upward flow generated by the air bubbles acts on the surface of the separation membrane to clean the membrane surface. In general, the more air bubbles flowing on the separation membrane surface, the more the shear force per unit time acting on the accumulated sludge on the separation membrane surface can be increased, and the cleaning efficiency of the separation membrane surface can be improved. In addition, the larger the air bubble size, the more the shear force can be increased and the more effective the cleaning, but since the oxygen dissolution efficiency is low, the amount of air (aeration amount) required for biological treatment becomes large, and the air diffusion efficiency decreases. For this reason, Patent Document 1 presents a treatment method using a membrane type fine air bubble diffuser tube in which fine air diffusion slits are provided in a member such as rubber or urethane as an air diffuser tube.

[0004] Furthermore, Patent Document 2 discloses a submerged separation membrane module in which a separation membrane cassette containing a plurality of separation membrane elements is housed in a housing with an aeration device installed below, and discloses a structure that allows the separation membrane cassette to be easily slid in and out of the housing so that when a failure occurs in one of the membrane elements that make up the separation membrane cassette, maintenance can be easily performed, i.e., the failure of the membrane element or separation membrane cassette can be easily removed or replaced. Furthermore, Patent Document 3 discloses a fine bubble diffusing tube configuration in which diffusion slits of different sizes are arranged in the longitudinal direction of the diffusion tube and the diffusion slits are provided at places where they are sealed in order to make the diffused air uniform. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-82597 A [Patent Document 2] Patent No. 6164216 [Patent Document 3] JP 2012-24647 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a separation membrane module of the type described in Patent Document 2 is operated, the air discharged by the air diffuser is supplied not only to the separation membrane elements to which air is intended to be supplied, but also to the gap areas between the separation membrane cassettes and between the casing and the separation membrane cassette, which reduces the efficiency of membrane surface cleaning by air and can result in poor energy efficiency. One possible solution to the above-mentioned problems is to install a baffle plate in the gap area to suppress air inflow, but this is not sufficient because air that avoids the gap area tends to flow into the ends of the separation membrane cassette (near the gap area), which can result in uneven cleaning due to more air flowing between the membranes at the ends of the separation membrane cassette than between the center of the cassette, and if the flow in the gap area completely disappears, dirt will accumulate in the stagnation area and the accumulated dirt will spread to the ends of the separation membrane cassette, causing blockage of the flow path and a decrease in separation performance. Furthermore, Patent Document 3 merely describes an aeration pipe configuration that aims to uniformly distribute the diffused air in the longitudinal direction, and does not describe a method for controlling the diffused air to locations where it is desired for the diffused air to flow (inside the separation membrane cassettes) and locations where it is not desired for the diffused air to flow (inside the gaps between the separation membrane cassettes) when there is a gap between the separation membrane cassettes vertically above the aeration pipe. The object of the present invention is to provide a separation membrane module that can improve the membrane surface cleaning power of air by allowing air supplied from an air diffuser to flow into the separation membrane cassettes without waste, even when there are gaps between the separation membrane cassettes, thereby maximizing separation performance and energy efficiency. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention has the following configuration. (1) A separation membrane module comprising: a separation membrane cassette in which a plurality of separation membrane elements having a sheet-like separation membrane are arranged in parallel with their membrane surfaces; a housing in which a plurality of the separation membrane cassettes are arranged horizontally with gaps therebetween and accommodated so as to be removable and insertable; and an aeration block arranged vertically below the housing and equipped with a fine bubble diffusing tube composed of a central tube and an elastic sheet covering the central tube and formed with a number of air diffusion slits that open and close by expanding and contracting, wherein, when the vertically downward projected area of ​​the separation membrane cassette is A, the vertically downward projected area of ​​the gap is B, the total length of the air diffusion slits formed in the elastic sheet present within the vertically downward projected area A of the separation membrane cassette is N, and the total length of the air diffusion slits formed in the elastic sheet present within the vertically downward projected area B of the gap is M, then M×A÷(N×B) is smaller than 0.8. (2) The separation membrane module according to (1), wherein the air diffusion slit is present only within a vertically downward projected area of ​​the separation membrane cassette. (3) A plurality of the fine bubble diffusing tubes are arranged in a line in the longitudinal direction to form a set of air diffusion groups, and at least one of the sets of air diffusion groups Adjacent Tips of fine bubble diffusers Columnar formation between space And , The columnar space is defined as a space having one side of a cross-sectional shape perpendicular to the longitudinal direction of the tip as a bottom surface and the other side as an upper surface, and having a height equal to the shortest distance between the tips, and the vertical downward projection area of ​​the columnar space is The separation membrane module according to (1) or (2), which is disposed within a vertically downward projected area of ​​the gap. Effect of the Invention

[0008] The separation membrane module of the present invention allows air supplied from the fine bubble diffuser to flow into the separation membrane cassette without waste, improving the membrane surface cleaning power of the air, and maximizing separation performance and energy efficiency. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic perspective view showing one embodiment of a prior art separation membrane cassette used in the present invention. [Diagram 2] FIG. 1 is a schematic perspective view showing one embodiment of a conventional separation membrane module used in the present invention. [Diagram 3] FIG. 1 is a schematic perspective view showing one embodiment of an aeration block of the present invention. [Figure 4] FIG. 1A is a schematic perspective view showing one embodiment of a fine bubble diffusing tube according to the present invention; [Diagram 5] FIG. 1 is a schematic side view showing one embodiment of a separation membrane module of the present invention. [Figure 6] FIG. 1 is a schematic top view showing an embodiment of the arrangement of fine bubble diffusing tubes according to the present invention. [Figure 7] FIG. 1 is a schematic top view showing an embodiment of the arrangement of fine bubble diffusing tubes according to the present invention. [Figure 8] FIG. 1 is a schematic top view showing an embodiment of the arrangement of fine bubble diffusing tubes according to the present invention. [Figure 9] FIG. 1 is a schematic top view showing an embodiment of the arrangement of fine bubble diffusing tubes according to the present invention. [Figure 10] FIG. 1 is a schematic top view showing an embodiment of the arrangement of fine bubble diffusing tubes according to the present invention. [Figure 11] FIG. 1 is a schematic top view showing an embodiment of the arrangement of fine bubble diffusing tubes according to the present invention. [Figure 12] FIG. 1 is a schematic top view showing an embodiment of the arrangement of fine bubble diffusing tubes according to the present invention. [Figure 13] Graph showing the relationship between collection position and collected air volume [Figure 14] FIG. 1 is a schematic top view showing an embodiment of a conventional arrangement of fine bubble diffusing tubes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The separation membrane module of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic perspective view showing one embodiment of a conventional separation membrane cassette 14 used in the present invention. The separation membrane cassette 14 has a plurality of separation membrane elements 15. The separation membrane elements are not particularly limited as long as they are elements having a flat membrane structure, but the separation membrane element described in Patent Document 2 can be cited as a suitable example. That is, when the separation membranes are bonded together so that the permeation side surfaces face each other, a water collection section is provided on a part of the periphery of the membrane, and the periphery other than the water collection section is sealed. A resin section is disposed on the permeation side surface area of ​​the separation membrane inside the sealed periphery, and the resin section is used to bond parts of the separation membranes on both sides, thereby securing the fixation of the membranes and the permeate flow path. The water that has permeated the separation membrane passes through the internal water collection flow path sandwiched between the flat membranes and is taken out of the system of the separation membrane element via the water collection nozzle 16 attached to the water collection section. The separation membrane cassette 14 is constructed by arranging a plurality of separation membrane elements 15 in parallel with their membrane surfaces, for example, by passing shafts 19 through the through holes provided at the four corners of the separation membrane element 15. A clearance retaining member (not shown) is provided between adjacent separation membrane elements, and a space is provided between the separation membrane elements to ensure a flow path for the water to be treated and air. In addition, membrane protection plates 18 are provided at both ends of the separation membrane cassette (both ends of the separation membrane elements arranged in parallel with their membrane surfaces) to prevent damage caused by collision of objects with the membrane surfaces when the separation membrane cassette is housed in a housing and to regulate fluctuations in the distance between the membrane elements caused by the oscillation of the membrane elements during operation. The membrane protection plate 18 is preferably one that has high rigidity and is less deformed by external forces such as loads applied during assembly and fluid forces acting during operation, but the material and structure are not particularly limited. In addition, the membrane protection plate 18 can be fixed by passing a shaft 19 through a through hole provided at each of the four corners, in the same manner as the separation membrane elements 15, clamping the multiple alternately arranged separation membrane elements 15 and a clearance retaining member (not shown) from both ends, and using fixing members 20 such as nuts on both ends of the threaded shaft 19 (not shown), thereby integrating the various components that make up the separation membrane cassette 14. FIG. 2 is a schematic perspective view showing one embodiment of a conventional separation membrane module 13 used in the present invention. The separation membrane module 13 is composed of an element block 8 and an aeration block 12, and in the element block 8, a housing 21 is a structure that plays the role of a rack for accommodating separation membrane cassettes 14 in parallel. The aeration block 12 is disposed at the bottom of the housing 21, and the housing 21 has openings at the bottom and top in the vertical direction (Z-axis direction) to allow air and sludge to flow into the separation membrane cassette. The housing 21 may be connected to the aeration block 12 with bolts or the like, or may be placed on the top of the aeration block via a guide or the like. The element block 8 also has an opening at the front (Y-axis side) through which the separation membrane cassette can be inserted and removed. With this structure, each separation membrane cassette can be detached from the housing, making it easy to perform maintenance and remove or replace the separation membrane element. In addition, it is preferable to provide the housing with a groove guide 22 (notch guide) for passing the end of the shaft 19 (see FIG. 1) or the fixing member 20 (see FIG. 1) when inserting and removing the separation membrane cassette. This allows the separation membrane cassette to be positioned when suspended and improves assembly. Furthermore, it is possible to narrow the gap distance between the separation membrane cassette and the openings on the upper and lower sides, thereby further increasing the packing rate of the separation membrane elements. After the separation membrane cassette is installed, side plates 34 are installed on the openings on the front and rear sides of the housing (sides in the Y-axis direction) and side plates 33 are installed on the openings on both end faces of the housing (sides in the X-axis direction) to close the openings, which is preferable in terms of membrane cleaning performance because it allows the air that has flowed into the element block from the aeration block 12 to be effectively utilized without escaping outside the element block. The housing 21 has a structure that allows multiple separation membrane cassettes 14 to be stacked vertically or horizontally. Each separation membrane cassette is arranged with a gap between them at a position where it can be inserted and removed in a substantially horizontal direction through multiple openings. Although FIG. 2 shows an example in which three separation membrane cassettes arranged in parallel in the horizontal direction are arranged in one vertical row, the present invention is not limited to this example, and the number of cassettes arranged in the horizontal and vertical directions can be set arbitrarily according to the size of the immersion tank, the required processing capacity, and the like. In particular, when separation membrane cassettes are stacked in multiple rows in the vertical direction, it is possible to save space and to significantly increase the membrane area per unit vertical area occupied by the aeration air diffused from the aeration block, thereby saving energy.

[0011] FIG. 3 is a schematic perspective view showing one embodiment of the aeration block 12 used in the present invention. The frame 23 is composed of a skirt portion 24 and a leg portion 25, and the skirt portion 24 has openings at the lower and upper portions in the vertical direction (Z-axis direction), and the leg portion 25 has openings at the side portions in the horizontal direction (X-axis and Y-axis directions) for allowing air and sludge to flow. The frame 23 is also provided with a branch pipe 26 and a fine bubble diffusing tube 9 connected thereto. The fine bubble diffusing tube 9 may be disposed at a height that is contained within the skirt portion 24, or may be disposed at a height that is contained within the leg portion 25. The branch pipe 26 and the fine bubble diffusing tube 9 may be connected inside the frame 23 or may be connected outside. In FIG. 3, one branch pipe 26 is disposed on one side of the frame 23, but for example, two branch pipes may be disposed so as to face each other from both sides of the frame, or may be disposed side by side on one side, and the arrangement and number of the branch pipes are not particularly limited. Here, the structure and operation of the fine bubble diffusing tube 9 will be described with reference to the schematic perspective view of FIG. 4(a) and the schematic cross-sectional view of FIG. 4(b). The fine bubble diffusing tube 9 has a support tube 30 in the center, an elastic sheet 29 is provided so as to cover the entire outer circumference of the support tube 30, and both longitudinal ends of the elastic sheet 29 are fastened and fixed by an annular fastener 31. A plurality of air diffusion slits 35 are formed in the elastic sheet 29. The longitudinal length L of the air diffusion slit is preferably 0.1 to 10 mm, and a length of 0.5 to 5 mm is more preferable from the viewpoint of fine bubble discharge. One end of the support tube 30 is connected to a connecting tube 32, and a through flow passage 28 is provided near the connecting end. Air supplied from the connecting tube 32 passes through the through flow passage 28 and enters between the support tube 30 and the elastic sheet 29, causing the elastic sheet 29 to expand. The expansion of the elastic sheet 29 opens the air diffusion slit 35, and the supplied air becomes fine bubbles and is ejected into the liquid in the aeration tank. When the air supply is stopped, the elastic sheet 29 contracts and the air diffusion slits 35 are closed, so that the microorganism-containing liquid in the tank does not flow into the air diffusion tube through the air diffusion slits when fine bubbles are not being released, and this prevents the air diffusion slits from being blocked by sludge in the microorganism-containing liquid and the inside of the air diffusion tube from becoming dirty during membrane filtration operation. Furthermore, in the fine bubble diffusing tube of the present invention, an area E where the air diffusion slits 35 are not provided can be provided in the elastic sheet 29 in order to control the air discharge position.

[0012] There is no particular limitation on the material of the elastic sheet 29, and synthetic rubbers such as ethylene propylene diene rubber (EPDM), silicone rubber, and urethane rubber, as well as other elastic materials, may be appropriately selected and used. Among these, ethylene propylene diene rubber is preferable because of its excellent chemical resistance.

[0013] There are no particular limitations on the material of the connecting pipe 32 and the support pipe 30 as long as it is a material that has the rigidity to withstand loads such as vibrations caused by air diffusion. For example, metals such as stainless steel, resins such as acrylonitrile butadiene styrene resin (ABS resin), polyethylene, polypropylene, polyvinyl chloride, composite materials such as fiber reinforced plastic (FRP), and other materials can be preferably used. Furthermore, the size of the support tube 30 can be selected according to the size of the aeration block and the aeration conditions, and the cross section viewed from the longitudinal direction may be circular, elliptical, or another shape. 5 is a schematic side view showing one embodiment of the separation membrane module 13 used in the present invention. In the embodiment of the present invention, the vertically downward projected area of ​​the separation membrane cassettes 14 arranged in parallel is A, and the vertically downward projected area of ​​the gap between the separation membrane cassettes is B. Here, the gap between the separation membrane cassettes 14 arranged in parallel refers to the gap between the lower ends of the membrane protection plates 18 in the separation membrane cassettes 14 as shown in the figure, and also includes the gap between the membrane protection plate 18 and the side plate 33. In other words, the projected area B refers to the vertically downward projected area including the gap between the membrane protection plates 18 and the gap between the membrane protection plate 18 and the side plate 33. 6 to 12 are schematic top views showing embodiments of the arrangement of fine bubble diffusing tubes 9 in an aeration block 12 used in the present invention. In Fig. 6, a plurality of fine bubble diffusing tubes 9 (two in Fig. 6) are connected to a branch pipe 26 arranged on one side in the X-axis direction of the frame 23. In conventional fine bubble diffusing tubes, air diffusion slits 35 are often provided over the entire area in the longitudinal direction of the elastic sheet, but the fine bubble diffusing tube 9 of the present invention shown in Fig. 6 is characterized in that, when the total length of the air diffusion slits existing within the projected area A is N and the total length of the air diffusion slits existing within the projected area B is M, the ratio of the total length M per projected area of ​​the air diffusion slits existing within the projected area B to the total length N per projected area of ​​the air diffusion slits existing within the projected area A is smaller than 0.8 (i.e., (M / B) / (N / A)=M·A / (N·B)<0.8). As a result, in contrast to the conventional air diffusion pipe configuration in which air diffusion slits are provided over the entire longitudinal area of ​​the elastic sheet (i.e., M·A / (N·B)=1), the discharged air can be directed into the separation membrane cassette to which air is originally to be supplied, rather than into the gap area between the separation membrane cassettes or the gap area between the side plate and the separation membrane cassette, improving membrane surface cleaning efficiency and making effective use of energy. Here, the total length of the air diffusion slits present within the projected area refers to the product of the number of air diffusion slits present within the projected area and the longitudinal length L of the air diffusion slits. In this case, the air diffusion slits provided on the end side of the annular fixture 31 (see FIG. 4) provided at the end of the elastic sheet are not included in the total length of the air diffusion slits because they do not discharge air, and only the air diffusion slits that diffuse air are counted in the total length of the air diffusion slits. 7, by providing region E, which is entirely free of air diffusion slits within projected area B, all of the air diffusion slits are located within projected area A (i.e., M·A / (N·B)=0), which is preferable to the configuration in Fig. 6 from the viewpoint of suppressing air supply to the gap areas between the separation membrane cassettes. However, if region E, which is free of air diffusion slits, is made too large, the amount of air flowing into both ends in the X-axis direction of the separation membrane cassette (the area where projected area A and region E overlap) will decrease, so it is preferable that the length of region E in the X-axis direction be approximately the same as the length of projected area B in the X-axis direction. 8, the branch pipe 26 on one side of the frame 23 in the X-axis direction may be arranged so as to be within the projected area B, or the end of the diffuser tube on the opposite side in the X-axis direction may be shortened, thereby reducing the number of diffuser slits present within the projected area B. This provides the same effect as providing an area E in the elastic sheet with no diffuser slits, while reducing the length of the fine bubble diffuser tubes to be installed, making it more cost-effective than Fig. 6. As shown in FIG. 9, both ends of a single U-shaped fine bubble diffusing tube 9 may be connected to a branch pipe 26 arranged on one side of the frame body 23 in the X-axis direction, or, as shown in FIG. 10, a plurality of straight air diffusing tubes 9 (three in FIG. 10) may be connected to two branch pipes 26 arranged on both sides of the frame body 23 in the X-axis direction so as to face each other. Due to the configuration of the fine bubble diffusing tube (see FIG. 4), the air discharge amount of the air diffusing slit on the upstream side in the longitudinal direction tends to be large and the downstream side tends to be small. Therefore, it is preferable to diffuse air using two branch pipes from both sides in the X-axis direction as shown in FIG. 10 from the viewpoint of reducing unevenness in air diffusion in the longitudinal direction of the fine bubble diffusing tube, but it is preferable to diffuse air using one branch pipe from one side in the X-axis direction as shown in FIG. 9 from the viewpoint of manufacturing costs of the module. The arrangement of the branch pipes can be freely selected in consideration of unevenness in air diffusion and manufacturing costs, the size of the aeration block, the required air diffusion flow rate, the arrangement of piping in the tank, and the like. As shown in FIG. 11, a plurality of straight diffuser tubes 9 (three each in FIG. 11) are connected to two branch tubes 26 arranged to face each other on both sides of the X-axis direction of the frame body 23, and the opposing diffuser tubes are arranged to line up in a substantially straight line in the longitudinal direction to form a set of diffuser groups. The space F between the tips of the diffuser tubes of at least one set of diffuser groups is located within the projected area B. Due to the configuration of the fine bubble diffuser tube (see FIG. 4), the air discharge amount of the diffuser slit on the upstream side in the longitudinal direction tends to be large and the downstream side tends to be small. Therefore, when using multiple diffuser tubes, it is common to use diffuser tubes of the same length to unify the tendency. Therefore, in the conventional diffuser tube configuration, when the diffuser tubes are arranged facing each other for an odd number of separation membrane cassettes arranged in parallel, the space F between the tips of the diffuser tubes is often located within the vertically downward projected area of ​​the central separation membrane cassette. In contrast, in the embodiment of the present invention shown in Fig. 11, even if diffuser tubes of different lengths are used, the space F between the tips of the diffuser tubes is arranged within the projected area B, which is preferable from the viewpoint of increasing the amount of diffused air flowing into the central separation membrane cassette and leveling the amount of air flowing between the separation membrane cassettes. Also, as shown in Fig. 12, a plurality of (six in Fig. 12) linear fine bubble diffuser tubes 9 may be arranged in each of a plurality of (three in Fig. 12) branch tubes 26 on one side of the Y-axis direction of the frame 23 so that the longitudinal direction is the X-axis direction, forming a set of diffuser groups arranged in a substantially straight line in the longitudinal direction. The configuration of Fig. 12 has the disadvantage of more complicated piping arrangement and an increased number of required parts compared to the configuration of Fig. 11, but has the advantage of being able to uniform the air flowing into each separation membrane cassette when there are many separation membrane cassettes arranged in parallel. EXAMPLES

[0014] An embodiment of the present invention will be described in detail below using the configurations shown in Figures 1 to 5 and 11. Note that the present invention is not limited to the following embodiment.

[0015] Comparative Example 1 Fifty membrane elements 15 (length 800 mm, width 480 mm, thickness approximately 1.8 mm) each consisting of a composite flat membrane made of polyester nonwoven fabric coated with a polyvinylidene fluoride membrane were arranged in parallel with a gap of 6 mm between adjacent membrane elements, and a membrane protection plate 18 was attached to prepare a separation membrane cassette 14. Next, in a housing 21 having a height of about 835 mm, a width inside dimension of about 1415 mm, and a depth inside dimension of about 485 mm, three separation membrane cassettes 14 were arranged in the width direction (X-axis direction) and one in the height direction (Z-axis direction), as shown in FIG. 2, and a side plate 33 and a side plate 34 were attached, and an element block 8 was produced so that only the top and bottom were open. At this time, the distance in the X-axis direction between the gaps between the membrane protection plates was 81 mm, and the distance between the gaps between the membrane protection plates and the side plate was 20.5 mm. In addition, two baffle plates 37, which occupy about 97% of the opening area, were installed at height positions of about 80 mm and 405 mm from the bottom of the housing in two places between the membrane protection plates.

[0016] Next, the element block 8 was placed on the aeration block 12 (height 460 mm×inner width 1415 mm×inner depth 485 mm, height of the legs 25 240 mm).

[0017] The fine bubble diffusing tubes 9 were prepared in two types, three of each type, with the outer diameter of the support tube 30 being Φ62 mm and the total length in the longitudinal direction being 802 mm and 722 mm. As shown in FIG. 14, three straight diffusing tubes were connected from two branch tubes 26 arranged to face each other on both sides of the X-axis direction of the frame body 23 so that the distance between the axes was 180 mm, and the opposing diffusing tubes were arranged to form an air diffusion group so that they were aligned approximately on a straight line in the longitudinal direction, and the gaps between the tips of the opposing diffusing tubes were arranged alternately. In this case, the distance between the space F between the tips of the opposing diffusing tubes was 42 mm, and all of the spaces F were arranged within the vertically downward projected area of ​​the central separation membrane cassette of the three units (i.e., within the projected area A). In addition, all of the diffusing tubes were installed so that their central axes were located on a plane 337 mm below the top end of the aeration block 12. The elastic sheet 29 (see FIG. 4) of the fine bubble diffusing tube 9 has many diffusion slits 35 arranged at equal intervals in a staggered pattern with a slit length L of 2 mm, a longitudinal interval of 2 mm, and a circumferential interval of 2.5 mm. The material used is ethylene propylene diene rubber. 2 , B ≈ 0.098 m 2 , N ≒ 0.197 m, M ≒ 0.034 m, and M·A / (N·B) ≒ 1.04. The prepared separation membrane module was placed in a tank, and water was poured in so that the water surface was located 500 mm above the top end of the element block, and aeration was performed. The total amount of aeration was 78 Nm 3 / min. Here, Nm 3 (Normal Lube) / min refers to the amount of air flowing per minute under standard conditions (pressure 1013hPa, temperature 0℃, humidity 0%). Air bubbles rising from the aeration block to the water surface were collected using a cylinder (inner diameter 50 mm) submerged to a depth of 90 mm from the water surface, and the amount of air escaping from the top of the cylinder was quantitatively measured using a flow meter (Keyence, FD-A10) connected via a tube. Measurement points were 13 points symmetrical about the center of the element block widthwise with a pitch of 110 mm, and 5 points symmetrical about the center of the depthwise direction with a pitch of 90 mm, for a total of 65 points. Measurements were taken for 15 seconds at each point with a sampling interval of 1 second, and the average value was obtained. FIG. 13 is a graph showing the coordinate in the width direction (X-axis direction) (the center of the element block is 0) on the horizontal axis and the measured amount of trapped air on the vertical axis. The plotted values ​​are the average values ​​of the measurements at five points in the depth direction. Table 1 also shows the average value Q of the measurements at the measurement points directly above the gap between the separation membrane cassettes (a total of 10 points at X=-220, 220) and the average value P of the measurements at the measurement points directly above the separation membrane cassettes (a total of 55 points excluding X=-220, 220). As a result, P=1.41 and Q=1.33, both of which were equivalent values. Since the amount of trapped air directly above the cassettes is large, it is thought that a lot of air passed between the cassettes, and it can be said that the air is not being used effectively.

[0018] [Table 1]

[0019] Example 1 In Example 1, the total length of the air diffuser in the longitudinal direction was changed from 802 mm to 1004 mm and from 722 mm to 520 mm, and the space F between the tips of the air diffuser in all the air diffuser groups was arranged within the projected area B as shown in FIG. 11. Except for this, a separation membrane module was fabricated and measured in the same manner as in Comparative Example 1. In this case, M·A / (N·B)=0.79. As a result, the amount of captured air was as shown in FIG. 13, and as shown in Table 1, P=1.44, Q=1.19, and the amount of captured air directly above the space between the cassettes was reduced by 10.6% compared to Comparative Example 1. From this, it is considered that the air flowing between the cassettes was reduced, and the air flowing into the separation membrane cassette was increased, thereby improving the efficiency of air use. Example 2 In Example 2, a separation membrane module was prepared and measured in the same manner as in Example 1, except that the air diffusion slits located vertically below the two gaps between the separation membrane cassettes were removed in the longitudinal direction by 81 mm, which is the same length as the distance in the X-axis direction of the gaps. In this case, M·A / (N·B)=0.39. As a result, the amount of captured air was as shown in FIG. 13, and as shown in Table 1, P=1.48, Q=0.93, and the amount of captured air directly above the cassettes was reduced by 30.2% compared to Comparative Example 1. From this, it is considered that the amount of air flowing between the cassettes was reduced, and the amount of air flowing into the separation membrane cassettes was increased, resulting in an increase in the efficiency of air use. [Explanation of symbols]

[0020] 8 Element Blocks 9. Fine bubble diffuser 12 Aeration block 13 Separation Membrane Module 14 Separation membrane cassette 15 Separation membrane element 16 Water collecting nozzle 18 Membrane protection plate 19 Shaft 20 Fixing member 21 Case 22 Groove guide (notch guide) 23 Frame 24 Skirt Club 25 Legs 26 Branch Pipe 28 Through passage 29 Elastic Sheet 30 Support tube 31 Circular Fixture 32 Connecting pipe 33 Side plate 34 Side Panel 35 Air diffusion slit 37 Baffle Plate A Vertical downward projection area of ​​separation membrane cassette B Vertical downward projection area of ​​the gap between the separation membrane cassettes E Area without air diffusion slits in the elastic sheet F Space between the tips of a set of aeration groups L: The longitudinal length of the air diffusion slit M Total length of the air diffusion slits within the projected area B N Total length of the air diffusion slits within the projected area A P is the average value of the measured values ​​at the measurement point directly above the separation membrane cassette in the example. Q Average value of the measured values ​​at the measurement point directly above the gap between the separation membrane cassettes in the example

Claims

1. A separation membrane cassette in which a plurality of separation membrane elements each having a sheet-like separation membrane are arranged in parallel with their membrane surfaces in parallel; A housing in which a plurality of the separation membrane cassettes are arranged horizontally with gaps therebetween and accommodated in a removable manner; an aeration block disposed vertically below the housing and equipped with a fine bubble diffusing tube made of a central tube and an elastic sheet covering the central tube and having a large number of air diffusion slits formed therein that open and close by expanding and contracting; It is equipped with The vertical downward projection area of ​​the separation membrane cassette is A, The vertical downward projection area of ​​the gap is B, The total length of the air diffusion slits formed in the elastic sheet within the vertically downward projected area A of the separation membrane cassette is N, When the total length of the air diffusion slits formed in the elastic sheet within the vertically downward projected area B of the gap is M, M×A÷(N×B) is smaller than 0.

8. Separation membrane module.

2. The air diffusion slit is present only within a vertically downward projected area of ​​the separation membrane cassette. The separation membrane module according to claim 1 .

3. A plurality of the fine bubble diffusing tubes are arranged in a line in the longitudinal direction thereof to form a set of air diffusing groups, A columnar space is formed between the tips of adjacent fine bubble diffusing tubes of at least one diffuser group, The columnar space is defined as a space having one side of a cross-sectional shape perpendicular to the longitudinal direction of the tip as a bottom surface and the other side as a top surface, and having a height that is the shortest distance connecting the tips, The vertically downward projected area of ​​the columnar space is located within the vertically downward projected area of ​​the gap. The separation membrane module according to claim 1 or 2.

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