JP2022144470A - Separation membrane module - Google Patents

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

The present invention relates to a separation membrane module used in membrane separation activated sludge treatment.

At present, the membrane separation activated sludge method is becoming 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 sedimentation tank of the normal activated sludge method, and the water to be treated in the biological reaction tank By maintaining a high biomass, the size of the bioreactor itself can be reduced, and the separation of sludge and treated water is performed by membrane filtration instead of gravity sedimentation, so suspended solids flow out to treated water. There are advantages such as being able to obtain clear treated water without any waste. Among them, the immersion type membrane separation activated sludge method in which the separation membrane module is immersed inside the aeration tank can use the aeration energy for both oxygen supply and membrane surface cleaning, so the separation membrane module is installed outside the aeration tank and the circulation pump is Compared to the membrane separation activated sludge process, which requires external circulation, this process requires less power and does not require a final sedimentation tank, saving space.

When performing membrane separation treatment by the membrane separation activated sludge method of the immersion type method, in order to wash the surface of the separation membrane, air bubbles are usually discharged from the air diffuser installed in the air diffuser (aeration block) below the separation membrane. is generated (aerated), and the gas-liquid mixed upward flow generated by the bubbles is applied to the separation membrane surface to wash the membrane surface. In general, the more air bubbles flowing on the separation membrane surface, the greater the shearing force acting on the sludge deposited on the separation membrane surface per unit time, and the more efficiently the separation membrane surface is washed. In addition, the larger the bubble size, the greater the shearing force, which is effective for cleaning. There is a problem that the In view of this, Patent Document 1 proposes a treatment method using a membrane-type fine-bubble air diffuser in which fine air diffusion slits are provided in a member made of rubber, urethane, or the like, as the air diffuser.

Further, Patent Document 2 discloses, as an immersion type separation membrane module, a separation membrane module in which a separation membrane cassette containing a plurality of separation membrane elements is housed in a housing, and an air diffuser is installed below. The separation membrane cassette is slidable so that maintenance, that is, removal or replacement of the failed membrane element or separation membrane cassette, can be easily performed when a failure occurs in some of the membrane elements that make up the separation membrane cassette. A structure that facilitates putting in and out of the housing is disclosed.
In addition, Patent Document 3 discloses a microbubble air diffuser configuration in which air diffuser slits of different sizes are arranged in the longitudinal direction of the air diffuser or a location for sealing the air diffuser slit is provided in order to make the diffused air uniform. ing.

JP 2010-82597 A Japanese Patent No. 6164216 JP 2012-24647 A

However, when the separation membrane module of the configuration described in Patent Document 2 is operated, the air discharged by the air diffuser is not only supplied to the separation membrane element to which air is originally intended to be supplied, but also to the gap area between the separation membrane cassettes and the housing. and the separation membrane cassette, the efficiency of cleaning the membrane surface with air is lowered, and the energy efficiency may be deteriorated.
It is conceivable to improve the above-described problem by installing a baffle plate for suppressing the inflow of air in the gap region. (near area) of the separation membrane cassette), and more air flows between the membranes at the ends than in the center of the separation membrane cassette, which causes uneven cleaning. However, the accumulated contaminants may spread to the ends of the separation membrane cassette, causing clogging of the flow path and possibly lowering the separation performance, which is not sufficient.
In addition, Patent Document 3 only describes an air diffuser structure that aims to make diffusion air uniform in the longitudinal direction. However, there is no description of a method for controlling diffuser air to a location (within the separation membrane cassette) where diffusion air is desired to flow and a location (within the gap between the separation membrane cassettes) where diffusion air is not desired to flow.
An object of the present invention is to allow the air supplied from the air diffuser to flow into the separation membrane cassette without waste even when there is a gap between the separation membrane cassettes, thereby improving the membrane surface cleaning power of the air and improving the separation performance. and to provide a separation membrane module capable of maximizing energy efficiency.

In order to solve such problems, the present invention has the following configurations.
(1) A separation membrane cassette in which a plurality of separation membrane elements provided with sheet-like separation membranes are arranged in parallel parallel to the membrane surface, and the plurality of separation membrane cassettes can be horizontally arranged with a gap and can be taken in and out. and a fine-bubble air diffusion pipe composed of a housing to be accommodated in the housing, and an elastic sheet formed with a large number of air diffusion slits that are arranged vertically below the housing and cover the central pipe and are opened and closed by expansion and contraction. and a block, wherein A is the vertically downward projected area of the separation membrane cassette, B is the vertically downward projected area of the gap, and formed on an elastic sheet existing within the vertically downward projected area A of the separation membrane cassette. When the total length of the air diffusion slits formed in the gap is N, and the total length of the air diffusion slits formed in the elastic sheet existing in the vertically downward projected area B of the gap is M, M × A ÷ (N × A separation membrane module, wherein B) is less than 0.8.
(2) The separation membrane module according to (1), wherein the air diffuser slit exists only within the vertical downward projection area of the separation membrane cassette.
(3) A plurality of the fine-bubble diffusers are arranged in a substantially straight line in the longitudinal direction to form a set of diffuser groups, and the ends of the fine-bubble diffusers of at least one set of diffuser groups are arranged. is disposed within the vertically downwardly projected area of the gap.

The separation membrane module of the present invention allows the air supplied from the microbubble diffuser to flow into the separation membrane cassette without waste, improving the ability of the air to clean the membrane surface, and maximizing separation performance and energy efficiency. can.

1 is a schematic perspective view showing one embodiment of a conventional separation membrane cassette used in the present invention; FIG. 1 is a schematic perspective view showing one embodiment of a conventional separation membrane module used in the present invention; FIG. 1 is a schematic perspective view showing one embodiment of an aeration block of the present invention; FIG. 1 (a) schematic perspective view and (b) schematic cross-sectional view showing one embodiment of the fine-bubble diffuser tube of the present invention Schematic side view showing one embodiment of the separation membrane module of the present invention. Schematic top view showing one embodiment of the arrangement of fine bubble air diffusers of the present invention. Schematic top view showing one embodiment of the arrangement of fine bubble air diffusers of the present invention. Schematic top view showing one embodiment of the arrangement of fine bubble air diffusers of the present invention. Schematic top view showing one embodiment of the arrangement of fine bubble air diffusers of the present invention. Schematic top view showing one embodiment of the arrangement of fine bubble air diffusers of the present invention. Schematic top view showing one embodiment of the arrangement of fine bubble air diffusers of the present invention. Schematic top view showing one embodiment of the arrangement of fine bubble air diffusers of the present invention. Graph showing the relationship between collection position and amount of collected air Schematic top view showing one embodiment of arrangement of conventional fine-bubble air diffusers

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 multiple separation membrane elements 15 . The separation membrane element is not particularly limited as long as it is an element having a flat membrane structure. That is, when the separation membranes are attached so that the permeation-side surfaces face each other, the water collecting portion is provided in a part of the peripheral portion of the membrane, and the peripheral portion other than the water collecting portion is sealed. By having a structure in which a resin portion is arranged on the permeate-side surface region of the separation membrane inside the sealed peripheral portion, and a part of the separation membranes on both sides are adhered with this resin portion, the membranes can be fixed together. Secure a permeate flow path. The water that has permeated the separation membrane passes through an internal water collection channel sandwiched between the flat membranes and is taken out of the separation membrane element system via a water collection nozzle 16 attached to the water collection portion.
The separation membrane cassette 14 is constructed by, for example, arranging a plurality of separation membrane elements parallel to the membrane surface so that the shafts 19 pass through the through holes provided at the four corners of the separation membrane element 15 . A clearance holding member (not shown) is provided between the adjacent separation membrane elements, and a space is provided between the separation membrane elements to secure a flow path for the water to be treated and the air. In addition, at both ends of the separation membrane cassette (both ends of the separation membrane elements arranged in parallel with the membrane surface), there are provided to prevent scratches caused by objects colliding with the membrane surface when housing in the housing, and to prevent the membrane elements from being damaged during operation. A membrane protection plate 18 is provided for regulating fluctuations in the distance between membrane elements due to rocking. The membrane protection plate 18 preferably has high rigidity and is less deformed against external forces such as loads applied during assembly and fluid forces acting during operation, but the material and structure are not particularly limited. The membrane protection plate 18 includes a plurality of separation membrane elements 15 and clearance holding members (not shown) arranged alternately so that the shafts 19 pass through the through holes provided at the four corners in the same manner as the separation membrane elements 15 . can be fixed by using fixing members 20 such as nuts at both ends of a shaft 19 which is threaded (not shown), and each member constituting the separation membrane cassette 14 can be integrated.
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. In the element block 8, the housing 21 is a structure that functions as a rack for storing the separation membrane cassettes 14 in parallel. An aeration block 12 is provided at the bottom of the housing 21, and the housing 21 has a bottom and top in the vertical direction (Z-axis direction) for allowing air and sludge to flow in the separation membrane cassette. having an opening; 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 on the front surface (side surface in the Y-axis direction) through which the separation membrane cassette can be put in and taken out. By adopting such a structure, each separation membrane cassette can be attached and detached from the housing, so maintenance and removal or replacement of the separation membrane element can be facilitated. In addition, when the separation membrane cassette is put in and taken out, it is preferable that the housing is provided with groove guides 22 (notch guides) for passing the end of the shaft 19 (see FIG. 1) or the fixing member 20 (see FIG. 1). . By doing so, it becomes possible to position the separation membrane cassette when suspending it, and the ease of assembly is improved. Furthermore, since it is possible to narrow the distance between the separation membrane cassette and the openings on the upper and lower sides, the filling rate of the separation membrane elements can be further increased. After the separation membrane cassette is installed, the side plates 34 are attached to the openings on the front and rear surfaces (side surfaces in the Y-axis direction) of the housing, and the side plates 33 are attached to the opening portions on both end surfaces (side surfaces in the X-axis direction) of the housing. is installed to close the opening, the air that has flowed into the element block from the aeration block 12 can be effectively utilized without escaping outside the element block, which is preferable in terms of membrane cleaning performance.
The housing 21 has a structure in which a plurality of separation membrane cassettes 14 can be stacked vertically or horizontally. Each separation membrane cassette is arranged at a position where it can be put in and taken out substantially horizontally through a plurality of openings with a gap therebetween. Although FIG. 2 shows an example in which three separation membrane cassettes are arranged in parallel in the horizontal direction in one stage in the vertical direction, the present invention is not particularly limited to this. It is possible to arbitrarily set the number of arrangement in the horizontal direction and the vertical direction. In particular, when stacking separation membrane cassettes in multiple stages in the vertical direction, space can be saved, and the membrane area per vertical unit area occupied by diffused air from the aeration block can be greatly increased. Therefore, energy can be saved.

FIG. 3 is a schematic perspective view showing one embodiment of the aeration block 12 used in the present invention. The structure of the frame 23 is not particularly limited. It has an opening for allowing air and sludge to flow in the side surface (in the X-axis and Y-axis directions). Further, the frame 23 is provided with a branch pipe 26 and a microbubble diffusion pipe 9 connected thereto. The microbubble air diffuser 9 may be arranged at a height that is included in the skirt portion 24 or may be arranged at a height that is included in the leg portion 25 . The branch pipe 26 and the fine bubble diffuser pipe 9 may be connected inside the frame 23 or may be connected outside. In FIG. 3, one branch pipe 26 is arranged on one side of the frame 23 However, for example, two branch pipes may be arranged so as to face each other from both sides of the frame, or may be arranged so as to line up on one side, and the arrangement and number thereof are not particularly limited.
Here, the structure and operation of the micro-bubble diffuser 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 microbubble diffuser tube 9 has a support tube 30 at its center, and an elastic sheet 29 is provided so as to cover the entire outer periphery of the support tube 30. Both ends of the elastic sheet 29 in the longitudinal direction are fastened by annular fasteners 31. is fixed. A plurality of air diffusion slits 35 are formed in the elastic sheet 29 . The length L of the diffusion slit in the longitudinal direction is preferably 0.1 to 10 mm, and more preferably 0.5 to 5 mm from the viewpoint of discharging fine bubbles. One end of the support tube 30 is connected to a connection tube 32, and a through channel 28 is provided near the connection end. Air supplied from the connection pipe 32 passes through the through-flow passage 28 and enters between the support pipe 30 and the elastic sheet 29 to inflate the elastic sheet 29 . Due to the expansion of the elastic sheet 29, the air diffusion slit 35 is opened, and the supplied air turns into microbubbles and is ejected into the liquid in the aeration tank. When the air supply is stopped, the elastic sheet 29 shrinks and the air diffuser slit 35 closes, so that the microorganism-containing liquid in the tank does not flow into the air diffuser pipe from the air diffuser slit when the fine bubbles are not released, and membrane filtration is performed. It is possible to prevent clogging of air diffuser slits and fouling of air diffuser pipes due to sludge in the microorganism-containing liquid during operation. Further, in the microbubble air diffuser of the present invention, the elastic sheet 29 can be provided with a region E in which the air diffuser slits 35 are not provided in order to control the air ejection position.

The material of the elastic sheet 29 is not particularly limited, and synthetic rubbers such as ethylene propylene diene rubber (EPDM), silicon rubber, urethane rubber, and other elastic materials can be appropriately selected and used. Among them, ethylene propylene diene rubber is preferable because of its excellent chemical resistance.

The materials of the connection pipe 32 and the support pipe 30 are not particularly limited as long as they are rigid enough not to be damaged by a load such as vibration caused by air diffusion. For example, metals such as stainless steel, acrylonitrile butadiene styrene resin (ABS resin), resins such as polyethylene, polypropylene, and polyvinyl chloride, composite materials such as fiber reinforced resin (FRP), and other materials can be preferably used. .
In addition, the size of the support tube 30 can be selected according to the size of the aeration block and the diffusion conditions, and the cross section viewed from the longitudinal direction may be circular, elliptical, or any other shape. .
FIG. 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, A is the vertically downward projected area of the separation membrane cassettes 14 arranged in parallel, and B is the vertically downward projected area of the gap between the separation membrane cassettes. 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. This includes the gap between That is, the projected area B is the vertical downward projected area including the gap between the membrane protective plates 18 and the gap between the membrane protective plate 18 and the side plate 33 .
6 to 12 are schematic top views showing embodiments of the arrangement of the fine bubble diffuser tubes 9 in the aeration block 12 used in the present invention.
In FIG. 6, a plurality of (two in FIG. 6) micro-bubble diffuser pipes 9 are connected to a branch pipe 26 arranged on one side of the frame 23 in the X-axis direction. Conventional fine-bubble air diffusers are often provided with diffusion slits 35 over the entire longitudinal direction of the elastic sheet. A region E without slits is provided, and 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 projection The ratio of the total length M per projected area of the air diffusion slits existing within the area B and the total length N per projected area of the air diffusion slits existing within the projected area A is smaller than 0.8 ( That is, (M/B)/(N/A)=M·A/(N·B)<0.8). As a result, unlike the conventional diffuser tube structure (that is, M·A/(N·B)=1) in which diffuser slits are provided over the entire longitudinal direction of the elastic sheet, the discharged air is The air can flow into the separation membrane cassette to which it is originally desired to supply air, instead of the gap between the cassettes or the gap between the side plate and the separation membrane cassette, improving the membrane surface cleaning efficiency and effectively utilizing energy. Here, the total length of air diffusion slits existing within the projected area is a value obtained by multiplying the number of air diffusion slits existing within the projected area by the length L of the air diffusion slits in the longitudinal direction. At this time, the air diffusion slit provided at the end of the annular fixture 31 (see FIG. 4) provided at the end of the elastic sheet is not included in the total length of the air diffusion slit because it does not discharge air. Only the diffuser slits that are diffused are counted in the total length of the diffuser slits.
Further, in FIG. 7, by providing a region E having no air diffusion slits over the entire projected area B, all of the air diffusion slits are present in the projected area A (that is, M A/(N ·B)=0), which is preferable to the configuration of FIG. 6 from the viewpoint of suppressing the air supply to the gap region between the separation membrane cassettes. However, if the region E without the air diffusion slit is made too large, the amount of air flowing into both ends of the separation membrane cassette in the X-axis direction (the range where the projected area A and the region E overlap) decreases. The length in the direction is preferably about the same as the length of the projected area B in the X-axis direction.
Also, as shown in FIG. 8, the branch pipe 26 on one side of the frame 23 in the X-axis direction is arranged so as to be within the projected area B, or the end of the diffuser pipe on the opposite side in the X-axis direction is shortened. By doing so, the number of diffusion slits existing within the projected area B may be reduced. By doing so, it is possible to reduce the length of the microbubble air diffuser to be installed while providing the same effect as providing the area E without the air diffusion slits in the elastic sheet, which is more preferable than FIG. 6 in terms of cost.
As shown in FIG. 9, both ends of one U-shaped microbubble air diffuser 9 may be connected to a branch pipe 26 arranged on one side of the frame 23 in the X-axis direction. 10, a plurality of linear diffuser pipes 9 (three in FIG. 10) are connected to two branch pipes 26 arranged to face each other in the X-axis direction of the frame 23, and both ends thereof are connected. It's okay to be there. Due to its structure (see FIG. 4), the fine bubble air diffuser has a tendency that the amount of air discharged from the diffuser slit on the upstream side in the longitudinal direction is large and the amount on the downstream side is small. Diffusion using two branch pipes is preferable from the viewpoint of reducing diffusion unevenness in the longitudinal direction of the fine bubble diffuser pipe, but on the other hand, as shown in FIG. It is preferable from the viewpoint of the manufacturing cost of the module. The arrangement of the branch pipes can be freely selected in consideration of air diffusion unevenness and manufacturing cost, the size of the aeration block, the required air diffusion flow rate, the routing of piping in the tank, and the like.
Further, as shown in FIG. 11, two branch pipes 26 arranged to face each other in the X-axis direction of the frame 23 each have a plurality of linear diffuser pipes 9 (three pipes each in FIG. 11). The air diffusers connected and facing each other are arranged so as to be aligned in a substantially straight line in the longitudinal direction to form a set of air diffuser groups. The space F between the tips of the diffuser tubes of at least one set of diffuser groups is arranged within the projected area B. Due to its structure (see FIG. 4), the fine bubble air diffuser tends to have a large amount of air discharged from the air diffusion slits on the upstream side in the longitudinal direction and a small amount on the downstream side. It is common to use air diffusers with the same length to unify the tendency. When arranged, the space F between the tips of the diffuser tubes was often positioned within the vertical downward projection area of the central separation membrane cassette. In contrast, in the embodiment of the present invention shown in FIG. 11, even if air diffusers with different lengths are used, the space F between the tips of the air diffusers is arranged within the projected area B, resulting in a central It is preferable from the viewpoint that the diffused air flowing into the separation membrane cassette can be increased and the amount of flowing air can be leveled between the separation membrane cassettes. Further, as shown in FIG. 12, a plurality of (three in FIG. 12) branch pipes 26 on one side of the frame 23 in the Y-axis direction are provided with linear microbubble air diffusers whose longitudinal direction is the X-axis direction. A plurality of (six in FIG. 12) each of the 9 may be arranged to form a set of air diffuser groups so as to be aligned in a substantially straight line in the longitudinal direction. Compared to the configuration of FIG. 11, the configuration of FIG. 12 has the disadvantages of more complicated piping arrangements and an increased number of required parts. There is an advantage in that the air to be applied can be made uniform.

An embodiment of the present invention will be described in detail below using the configurations shown in FIGS. 1 to 5 and 11. FIG. It should be noted that the present invention is by no means limited to the following examples.

(Comparative example 1)
50 membrane elements 15 (length 800 mm, width 480 mm, thickness approx. 1.8 mm), in which a composite flat membrane in which a polyvinylidene fluoride membrane is coated on a polyester non-woven fabric, are pasted are placed so that the gap between adjacent membrane elements is 6 mm. , and a membrane protection plate 18 was attached to prepare a separation membrane cassette 14 .
Next, as shown in FIG. 2, three separation membrane cassettes 14 were placed in the width direction (X-axis direction) and the height direction in a housing 21 having a height of about 835 mm, a width of about 1415 mm, and a depth of about 485 mm. The element block 8 was manufactured so that the element block 8 was arranged so as to form one stage (in the Z-axis direction), the side plate 33 and the side plate 34 were attached, and only the top and bottom were opened. At this time, the distance between the film protective plates in the X-axis direction was 81 mm, and the distance between the film protective plates and the side plates was 20.5 mm. In addition, two baffle plates 37 occupying about 97% of the opening area were installed at the two gaps between the film protective plates at heights of about 80 mm and 405 mm from the lower part of the housing.

Next, the element block 8 was placed on the aeration block 12 (height 460 mm×internal width 1415 mm×internal depth 485 mm, leg portion 25 height 240 mm).

As for the microbubble air diffuser 9, the outer diameter of the support tube 30 is Φ62 mm, and the total length in the longitudinal direction is 802 mm and 722 mm. From the two branch pipes 26 arranged to face each other, three straight diffuser pipes are connected so that the distance between the axes is 180 mm. The diffuser groups were formed so as to line up on a straight line, and the gaps between the ends of the diffuser tubes facing each other were arranged alternately. At this time, the distance between the ends of the air diffusion tubes facing each other in the space F is 42 mm, and all the spaces F are arranged within the vertically downward projected area (that is, within the projected area A) of the central separation membrane cassette of the three units. rice field. In addition, all air diffusion pipes were installed so that their central axes were located on one plane 337 mm below the upper end of the aeration block 12 . The elastic sheet 29 (see FIG. 4) of the microbubble diffuser tube 9 has a large number of diffuser slits 35 arranged in a zigzag pattern with a slit length L of 2 mm, a longitudinal interval of 2 mm, and a circumferential interval of 2.5 mm. Ethylene propylene diene rubber was used as the material. At this time, A≈0.588 m 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 installed in a tank, and water was added so that the water surface was located 500 mm above the upper end of the element block, and aeration was performed. The total aeration rate was set at 78 Nm ³ /min. Here, Nm ³ (Normal Lube)/min refers to the amount of air flowing per minute under standard conditions (pressure 1013 hPa, temperature 0° C., humidity 0%).
Air bubbles rising from the aeration block to the surface of the water are collected using a cylinder (inside diameter of 50 mm) immersed in water to a depth of 90 mm. FD-A10) was used for quantitative measurement. The measurement points were 13 points with a pitch of 110 mm symmetrical about the center in the width direction of the element block, and 5 points with a pitch of 90 mm after symmetrical about the center in the depth direction, for a total of 65 points. Measurement was taken at a sampling interval of 1 second and each point was measured for 15 seconds to obtain an average value.
FIG. 13 is a graph showing the amount of collected air, with the horizontal axis representing the coordinate in the width direction (X-axis direction) (0 at the center of the element block) and the vertical axis representing the amount of collected air. The plotted values are the average values of five measurements in the depth direction. Table 1 also shows the average value Q of the measurement values at the measurement points directly above the gap between the separation membrane cassettes (X = -220, 220 in total of 10 points) and the measurement points directly above the separation membrane cassettes (X = -220 , 220 (55 points in total)). As a result, P=1.41 and Q=1.33, both of which are equivalent values. Since a large amount of air is collected just above the space between the cassettes, it is considered that a large amount of air passes through the space between the cassettes, and it can be said that the air is not being effectively used accordingly.

(Example 1)
In Example 1, the total length in the longitudinal direction of the air diffuser 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 diffusers in all the air diffusion groups was set within the projected area B as shown in FIG. A separation membrane module was produced and measured in the same manner as in Comparative Example 1, except that they were arranged. At this time, M·A/(N·B)=0.79. As a result, the amount of air collected was as shown in FIG. 13, and as shown in Table 1, P=1.44 and Q=1.19. It has decreased by 10.6%. From this, it is considered that the amount of air flowing between the cassettes decreased and the amount of air flowing into the separation membrane cassette increased, resulting in an increase in air usage efficiency.
(Example 2)
Example 2 is the same as Example 1, except that the air diffusion slits vertically below the two gaps between the separation membrane cassettes are eliminated in the longitudinal direction by 81 mm, which is the same length as the distance in the X-axis direction of the gaps. A separation membrane module was prepared and measured. At this time, M·A/(N·B)=0.39. As a result, the amount of air collected was as shown in FIG. 13, and as shown in Table 1, P=1.48 and Q=0.93. It has decreased by 30.2%. From this, it is considered that the amount of air flowing between the cassettes decreased and the amount of air flowing into the separation membrane cassette increased, resulting in an increase in air usage efficiency.

8 element block 9 fine bubble diffuser 12 aeration block 13 separation membrane module 14 separation membrane cassette 15 separation membrane element 16 water collection nozzle 18 membrane protection plate 19 shaft 20 fixing member 21 housing 22 groove guide (notch guide)
23 Frame 24 Skirt 25 Leg 26 Branch pipe 28 Penetration channel 29 Elastic sheet 30 Support pipe 31 Annular fixture 32 Connection pipe 33 Side plate 34 Side plate 35 Air diffuser slit 37 Baffle plate A vertically downward projected area of separation membrane cassette B Vertical downward projected area of the gap between the separation membrane cassettes E Area without air diffusion slits in the elastic sheet F Space between the ends of a pair of air diffusion groups L Length of the air diffusion slits in the longitudinal direction M Within the projected area B Total length of existing air diffusion slits N Total length of air diffusion slits existing within projected area A P Average value of measurements at measurement points directly above the separation membrane cassette in the example Q Between the separation membrane cassettes in the example The average value of the measured values at the measurement point just above the gap of

Claims (3)

a separation membrane cassette in which a plurality of separation membrane elements each having a sheet-like separation membrane are arranged in parallel with the membrane surface;
a housing in which the plurality of separation membrane cassettes are horizontally arranged with a gap therebetween and accommodated so that they can be put in and taken out;
an aeration block that is arranged vertically below the housing and has a fine-bubble diffuser pipe composed of a central pipe and an elastic sheet formed with a large number of diffuser slits that open and close by expansion and contraction covering the central pipe;
and
A is the vertically downward projected area of the separation membrane cassette,
B, the vertically downward projected area of the gap;
N is the total length of the air diffusion slits formed in the elastic sheet existing within the vertically downward projected area A of the separation membrane cassette,
When the total length of the air diffusion slits formed in the elastic sheet existing within the vertically downward projected area B of the gap is M,
A separation membrane module, wherein M×A÷(N×B) is less than 0.8. 2. The separation membrane module according to claim 1, wherein said air diffusion slit exists only within a vertically downwardly projected area of said separation membrane cassette. A plurality of the fine-bubble air diffusers are arranged in a substantially straight line in the longitudinal direction to form a set of air diffuser groups,
3. The separation membrane module according to claim 1, wherein the space between the tips of the fine bubble diffuser tubes of at least one set of air diffuser groups is arranged within the vertical downward projection area of the gap.

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