Membrane type aeration device

Abstract

To provide a membrane type air diffuser capable of improving air diffusion unevenness.SOLUTION: A membrane type air diffuser 10 includes: a tube-like membrane 17 having a hollow insertion portion; a support 18 inserted into the insertion portion of the membrane 17; and a gas supply portion provided in a central portion of the membrane 17 in a longitudinal direction A, the membrane 17 including a bag-like portion 23 formed in a bag shape by two sheet members 21 and 22 on front and back, and the gas supply portion including a ventilation channel that communicates with an inside of the bag-like portion 23 of the membrane 17 from outside, wherein a plurality of slits 30 are formed in the sheet members 21 forming an outer peripheral surface of the bag-like portion 23 of the membrane 17 to release a gas supplied into the bag-like portion 23 through the ventilation channel of the gas supply portion to outside, and in a state in which the gas is released from the slits 30 to the outside, both ends C in the longitudinal direction A of the membrane 17 are positioned higher than the central portion.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a membrane type air diffuser that is installed below the liquid surface and emits air bubbles into the liquid. [Background technology]

[0002] Conventionally, as an example of this type of membrane type air diffuser, there is one that emits a large number of air bubbles 202 into water to be treated 201 in a tank 200, as shown in Fig. 23. This membrane type air diffuser 203 has a membrane 204 formed in a tubular shape, a support tube 205 inserted into the membrane 204, and an air supply unit 206.

[0003] An end of the membrane 204 is fixed watertightly to the support tube 205 with a fastener 207 such as a ring-shaped band. The support tube 205 is connected to an air supply pipe 208. The air supply unit 206 is provided in the center B in the longitudinal direction A of the support tube 205, and has an air passage 209 that communicates from the air supply pipe 208 to between the inner circumference of the membrane 204 and the outer circumference of the support tube 205.

[0004] A plurality of slits 211 are formed in the membrane 204 for releasing to the outside air 210 supplied from the air supply pipe 208 through the air passage 209 of the air supply section 206 between the inner circumference of the membrane 204 and the outer circumference of the support tube 205.

[0005] According to this, air 210 is supplied from the air supply pipe 208 through the air flow path 209 of the air supply section 206 to between the inner circumference of the membrane 204 and the outer circumference of the support tube 205, causing the membrane 204 to expand and the air 210 to be released into the treated water 201 as air bubbles 202 through the slits 211 of the membrane 204.

[0006] The above-mentioned membrane type aeration device 203 is described in, for example, Patent Document 1 below. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2005-81203 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the conventional type described above, the air 210 supplied from the air flow passage 209 of the air supply section 206 between the inner circumference of the membrane 204 and the outer circumference of the support tube 205 encounters flow resistance as it flows from the center B in the longitudinal direction A of the support tube 205 toward both ends C, and therefore the pressure loss at both ends C is greater than the pressure loss at the center B.

[0009] As a result, air 210 is more difficult to release from the slits 211 at both ends C of the membrane type air diffuser 203 than at the central portion B, which results in a problem of uneven air diffusion, such as a decrease in the amount of air bubbles 202 released from the slits 211.

[0010] An object of the present invention is to provide a membrane type air diffuser capable of improving uneven air diffusion. [Means for solving the problem]

[0011] In order to achieve the above object, the first invention is a membrane type air diffuser that is installed under the liquid surface and emits air bubbles into the liquid, The membrane has a tubular shape and a hollow insertion portion, a support inserted into the insertion portion of the membrane, and a gas supply portion provided in the center of the membrane in the longitudinal direction, The membrane has a bag-shaped portion formed of two sheet members on the front and back, the gas supply unit has an air passage communicating from the outside to the inside of the bag-shaped portion of the membrane; a sheet member constituting an outer peripheral surface of the bag-shaped portion of the membrane is formed with a plurality of slits for discharging to the outside the gas supplied into the bag-shaped portion through the ventilation flow path of the gas supply portion; When gas is released to the outside through the slits, both ends of the membrane in the longitudinal direction are positioned higher than the center.

[0012] According to this, by operating the membrane type air diffuser, gas is supplied into the bag-shaped part of the membrane through the ventilation passage of the gas supply part, the bag-shaped part of the membrane expands, and the gas in the bag-shaped part is released to the outside through the slits, thereby releasing a large number of air bubbles from the membrane type air diffuser into the liquid.

[0013] In this case, the gas supplied from the ventilation flow path of the gas supply section into the bag-shaped portion of the membrane encounters flow resistance as it flows from the center to both ends in the longitudinal direction of the membrane, and therefore the pressure loss at both ends of the membrane is greater than the pressure loss in the center.

[0014] In contrast, when gas is being released to the outside through the slits as described above, both ends of the membrane in the longitudinal direction are positioned higher than the center, so the depth from the liquid surface to both ends of the membrane is shallower than the depth from the liquid surface to the center of the membrane, and the liquid pressure applied to both ends of the membrane is smaller than the liquid pressure applied to the center of the membrane.

[0015] In this way, at both ends of the membrane in the longitudinal direction, the effect of increased pressure loss making it difficult to release bubbles and the effect of decreased liquid pressure making it easier to release bubbles are offset, thereby reducing the variation in the amount of bubbles released between the center and both ends in the longitudinal direction of the membrane, thereby improving uneven air diffusion in the membrane type air diffuser.

[0016] In the membrane type air diffuser according to the second invention, the membrane has a larger clearance between itself and the support at both ends in the longitudinal direction than at the center.

[0017] According to this, when the gas is discharged to the outside from the slit, the gas supplied into the bag-shaped portion of the membrane exerts a buoyant force on the membrane. Since there is a space between both ends of the membrane in the longitudinal direction and the support, the buoyant force acting on the membrane causes both ends of the membrane to rise above the center portion and to be positioned higher than the center portion.

[0018] In the membrane type air diffuser according to the third invention, the outer periphery of the support is shorter at both ends in the longitudinal direction than at the central portion.

[0019] This makes it possible to obtain a membrane type air diffuser that is configured so that there is more space between the support and both ends of the membrane in the longitudinal direction than there is between the support and the central portion.

[0020] In the membrane type air diffuser according to the fourth invention, the inner periphery of the membrane is longer at both ends in the longitudinal direction than at the central portion.

[0021] This makes it possible to obtain a membrane type air diffuser that is configured so that there is more space between the support and both ends of the membrane in the longitudinal direction than there is between the support and the central portion.

[0022] In the membrane type air diffuser of the fifth invention, the bottoms of both ends in the longitudinal direction of the support are located higher than the bottom of the central portion.

[0023] According to this, by inserting the support into the insertion portion of the membrane, both ends in the longitudinal direction of the membrane are positioned higher than the center portion. Effect of the Invention

[0024] As described above, according to the present invention, at both ends of the membrane in the longitudinal direction, the effect of increased pressure loss making it difficult to release bubbles and the effect of decreased liquid pressure making it easier to release bubbles are offset, thereby reducing the variation in the amount of bubbles released between the center and both ends in the longitudinal direction of the membrane, thereby improving uneven air diffusion in the membrane type air diffuser. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a perspective view of an air diffusion system according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a side view of a membrane type air diffuser provided in the air diffusion equipment according to the first embodiment. [Diagram 3] FIG. 2 is a cross-sectional view of an end portion of the membrane type air diffuser according to the first embodiment. [Figure 4] FIG. 2 is a perspective view of the membrane and the support tube of the membrane type air diffuser of the first embodiment. [Diagram 5] FIG. 2 is a partially cutaway plan view of the membrane of the membrane type air diffuser of the first embodiment. [Figure 6] FIG. 2 is a partially cutaway bottom view of the membrane of the membrane-type air diffuser of the first embodiment. [Figure 7] FIG. 4 is a cross-sectional view of a support tube of the membrane type air diffuser according to the first embodiment. [Figure 8] FIG. 2 is a cross-sectional view of the connecting portion between the membrane type air diffuser and the air supply pipe of the air diffusion equipment according to the first embodiment. [Figure 9] 9 is a view taken along the arrow XX in FIG. 8. [Figure 10] XX arrow view in FIG. 3. [Figure 11] FIG. 2 is a perspective view of a gas supply nozzle of the membrane type air diffuser according to the first embodiment. [Figure 12] 12 is a view taken along the arrow XX in FIG. 11. [Figure 13] 12 is a view taken along the arrow YY in FIG. 11. [Figure 14] FIG. [Figure 15] FIG. 13 is a disassembled view of the adapter, air supply pipe, and gas supply nozzle of the aeration equipment. [Figure 16] FIG. 2 is a diagram showing the steps of a method for manufacturing the membrane of the membrane-type air diffuser according to the first embodiment. [Figure 17] FIG. 2 is a diagram showing the steps of a method for manufacturing the membrane of the membrane-type air diffuser according to the first embodiment. [Figure 18] FIG. 11 is a cross-sectional view of a support tube of a membrane type air diffuser in a second embodiment of the present invention. [Figure 19] FIG. 2 is a cross-sectional view of an end portion of the membrane type air diffuser according to the first embodiment. [Figure 20] FIG. 11 is a partially cutaway side view of a membrane type air diffuser according to a third embodiment of the present invention. [Figure 21] FIG. 11 is a cross-sectional view of a support tube of a membrane type air diffuser in a fourth embodiment of the present invention. [Figure 22] FIG. [Figure 23] FIG. 1 is a diagram of a conventional membrane type air diffuser. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0027] (First embodiment) In the first embodiment, as shown in Fig. 1, reference numeral 1 denotes an aeration system provided in an aerobic tank (not shown) installed in, for example, a sewage treatment plant. The aeration system 1 is immersed below the surface of water to be treated 3 (an example of a liquid) consisting of activated sludge in the tank, and includes a plurality of membrane type aeration devices 10 that emit air bubbles 4 into the water to be treated 3, an air supply pipe 12 that supplies air 11 (an example of a gas for aeration) to each membrane type aeration device 10, an adapter 14 (see Fig. 8) that fixes the membrane type aeration device 10 to the air supply pipe 12, and a blower 15 that supplies air 11 to the air supply pipe 12 from outside the tank.

[0028] As shown in Figures 2 to 6, the membrane type air diffuser 10 has a membrane 17 formed in a tubular (cylindrical) shape with a hollow insertion portion 16 in the center, a support tube 18 (an example of a support) inserted horizontally into the insertion portion 16 of the membrane 17, and a gas supply nozzle 19 (an example of a gas supply portion) provided in the center of the membrane 17 in the longitudinal direction A.

[0029] The membrane 17 has a bag-shaped portion 23 formed into a bag shape by welding two front and back sheet members 21, 22. The front sheet member 21 and the back sheet member 22 are made of a soft elastic synthetic resin, and the front sheet member 21 forms the outer peripheral surface of the bag-shaped portion 23, while the back sheet member 22 forms the inner peripheral surface of the bag-shaped portion 23.

[0030] A circular first opening 24 is formed in the central portion and upper portion of the membrane 17 in the longitudinal direction A. The insertion portion 16 penetrates both ends of the membrane 17, and the insertion portion 16 and the upper portion of the membrane 17 communicate with each other via the first opening 24.

[0031] 8, 9 and 16, circular first through hole 26 and second through hole 27 are formed in the central and lower part of membrane 17 in the longitudinal direction A. Of these, first through hole 26 is formed in sheet member 21 on the front side. Second through hole 27 has a smaller diameter than first through hole 26 and is formed in sheet member 22 on the back side. The center of first through hole 26 and the center of second through hole 27 are coaxial.

[0032] 4 to 6, both sheet members 21, 22 are welded at welded portions 29. These welded portions 29 include end welded portions 29a formed around the entire periphery at both ends of membrane 17, a central welded portion 29b formed around first opening 24, and a longitudinal welded portion 29c formed between end welded portions 29a and central welded portion 29b.

[0033] A large number of slits 30 are formed in the sheet member 21 on the front side for discharging the air 11 supplied from the gas supply nozzle 19 into the bag-shaped portion 23 to the outside. As shown by the imaginary lines in Fig. 6, a non-formed region 31 where no slits 30 are formed is provided in the lower part of the sheet member 21 on the front side, and the slits 30 are formed in the region other than the non-formed region 31 and the welded portion 29.

[0034] In addition, in drawings such as Figure 2, the slit 30 is drawn in an oval shape to make it easier to see, but in reality, the slit 30 is a slit that is closed when air diffusion is not occurring and is slightly open when air diffusion is occurring.

[0035] 4 and 7, the support tube 18 is a straight circular tube made of resin with both ends open, and a circular second opening 33 is formed in the center and upper part in the longitudinal direction A of the support tube 18. As shown in Figures 8 and 9, when the support tube 18 is inserted into the insertion part 16 of the membrane 17, the position of the first opening 24 of the membrane 17 and the position of the second opening 33 of the support tube 18 coincide with each other.

[0036] 7, a bolt insertion hole 34 is formed in the lower part of the center in the longitudinal direction A of the support tube 18. As shown in Fig. 8 and Fig. 9, the position of the bolt insertion hole 34 of the support tube 18 and the center position of the second through hole 27 of the sheet member 22 on the back side of the membrane 17 coincide with each other.

[0037] 2, 6, 8, 9, 11 to 13, the gas supply nozzle 19 has a circular tubular portion 37, a flange portion 38, and a top plate portion 39. The tubular portion 37 is inserted into the first through-hole 26 (see FIG. 16) of the sheet member 21 on the front side of the membrane 17, and protrudes below the membrane 17. A pair of cutout portions 41 and an inlet 42 that opens into the air supply pipe 12 are formed at the lower end of the tubular portion 37.

[0038] The flange 38 is formed at the upper end of the tube portion 37 and projects outward in the radial direction of the tube portion 37, and enters the bag-shaped portion 23 of the membrane 17 as shown in Figures 8 and 9. A plurality of outlet ports 43 that open into the bag-shaped portion 23 are formed on the outer circumferential surface of the flange 38. A gas supply nozzle 19 is attached to the membrane 17 in the peripheral portion of the first through-hole 26 (see Figure 16) of the front-side sheet member 21 so that air 11 does not leak from the first through-hole 26 during air diffusion.

[0039] The top plate portion 39 is formed at the upper end of the cylindrical portion 37, and a bolt insertion hole 45 is formed in the top plate portion 39 so as to pass therethrough in the vertical direction.

[0040] An air flow passage 46 communicating with the inlet 42 and the outlet 43 is formed in the gas supply nozzle 19. As a result, the inside of the air supply pipe 12 and the inside of the bag-shaped portion 23 of the membrane 17 communicate with each other via the air flow passage 46 of the gas supply nozzle 19. In addition, a recess 47 curved in an arc shape along the outer circumferential surface of the support tube 18 is formed on the upper surface of the gas supply nozzle 19.

[0041] As shown in Figures 8 and 9, the membrane type air diffuser 10 is fixed to the air supply pipe 12 via an adapter 14. As shown in Figures 14 and 15, the adapter 14 has a rectangular parallelepiped adapter body 50 sandwiched between the membrane type air diffuser 10 and the air supply pipe 12, and a pair of support parts 55 that support the support pipe 18 of the membrane type air diffuser 10 from below via the membrane 17. The support parts 55 are provided at both ends of the adapter body 50 in the longitudinal direction A of the membrane type air diffuser 10.

[0042] The underside of the adapter body 50 is formed with a recess 52 curved in an arc shape along the outer circumferential surface of the air supply pipe 12, and an O-ring fitting portion 56. The adapter body 50 is also formed with a circular first fitting hole 53 penetrating in the up-down direction. The O-ring fitting portion 56 is formed to surround the periphery of the first fitting hole 53.

[0043] As shown in Fig. 1, the air supply pipe 12 is disposed below the membrane type air diffuser 10 and is perpendicular to the membrane type air diffuser 10 at the center in the longitudinal direction A of the membrane type air diffuser 10. As shown in Fig. 15, a plurality of circular second fitting holes 54 penetrating the air supply pipe 12 from the inside to the outside are formed at the upper end of the air supply pipe 12.

[0044] The position of the first fitting hole 53 of the adapter 14 coincides with the position of the second fitting hole 54 of the air supply pipe 12. As shown in Figures 8, 9 and 15, the cylindrical portion 37 of the gas supply nozzle 19 is fitted from above into the first fitting hole 53 of the adapter 14 and the second fitting hole 54 of the air supply pipe 12, and the lower end portion protrudes into the air supply pipe 12 through the second fitting hole 54.

[0045] In addition, an O-ring 62 (an example of a sealing member) that simultaneously seals between the underside of the adapter 14 and the outer peripheral surface of the air supply pipe 12, and between the inner peripheral surface of the first fitting hole 53 of the adapter 14 and the outer peripheral surface of the cylindrical portion 37 of the gas supply nozzle 19, is fitted into the O-ring fitting portion 56 and held by the adapter 14.

[0046] The air supply pipe 12, the adapter 14, the membrane 17, the support pipe 18 and the gas supply nozzle 19 are connected by a connecting member 51. The connecting member 51 has a T-head bolt 57 and a nut 58.

[0047] The T-head bolt 57 is inserted from below through the second insertion hole 54 of the air supply pipe 12, the bolt insertion hole 45 of the gas supply nozzle 19, the second through hole 27 of the sheet member 22 on the back side of the membrane 17, and the bolt insertion hole 34 of the support pipe 18, and protrudes into the support pipe 18.

[0048] Further, the head 57 a of the T-head bolt 57 is fitted into both notches 41 of the cylindrical portion 37 of the gas supply nozzle 19 from below, and engages with the inner circumferential surface of the upper end portion of the air supply pipe 12 .

[0049] Furthermore, the nut 58 is screwed onto the T-head bolt 57 inside the support tube 18 and engages with the inner peripheral surface of the support tube 18 .

[0050] The entire periphery of the second through hole 27 of the rear sheet member 22 is sandwiched between the outer circumferential surface of the support tube 18 and the top plate portion 39 of the gas supply nozzle 19. A cylindrical packing 60 made of an elastic material such as rubber is fitted into the bolt insertion hole 34 of the support tube 18. This prevents a portion of the air 11 supplied from the inside of the air supply pipe 12 through the ventilation flow path 46 of the gas supply nozzle 19 into the bag-shaped portion 23 of the membrane 17 from leaking into the support tube 18 from between the bolt insertion hole 34 and the T-head bolt 57.

[0051] The circumferential length of the inner circumferential surface of membrane 17 (hereinafter referred to as the inner circumferential length) is formed to be longer with some margin than the circumferential length of the outer circumferential surface of support tube 18 (hereinafter referred to as the outer circumferential length). As a result, when air 11 in air supply pipe 12 is not supplied into bag-shaped portion 23 of membrane 17 and bag-shaped portion 23 is contracted, the inner circumferential surface of membrane 17 (i.e., the inner circumferential surface of rear sheet member 22) does not contact the outer circumferential surface of support tube 18 without any gap over the entire circumference, but a gap with some margin is formed between the inner circumferential surface of membrane 17 and the outer circumferential surface of support tube 18.

[0052] Here, at both ends C of membrane 17 in the longitudinal direction A, there is a margin for membrane 17 to float up between the inner peripheral surface of membrane 17 and the outer peripheral surface of support tube 18, so when air 11 in air supply tube 12 is supplied into bag-shaped portion 23 of membrane 17, air 11 accumulates in the upper part of bag-shaped portion 23, and the upper part of membrane 17 floats up relative to support tube 18, as shown in Figures 3 and 8 to 10. As a result, when air 11 is released to the outside from slit 30 during aeration, both ends C of membrane 17 float up above center portion B, as shown by the imaginary lines in Figure 2, to a higher position.

[0053] In contrast, as shown in Figures 8 and 9, at the center B in the longitudinal direction A of the membrane 17, a gas supply nozzle 19 is attached to the membrane 17 and the membrane 17 is biased downward relative to the support tube 18, so that there is little room for the membrane 17 to float up between the inner surface of the membrane 17 and the outer surface of the support tube 18, and even if air 11 in the air supply pipe 12 is supplied into the bag-shaped portion 23 of the membrane 17, the upper part of the membrane 17 hardly floats up relative to the support tube 18.

[0054] The operation of the above configuration will be described below.

[0055] 1, 8 and 9, by driving the blower 15, air 11 is supplied from the blower 15 into the air supply pipe 12, and the air 11 in the air supply pipe 12 flows from the inlet 42 of the gas supply nozzle 19 through the air flow passage 46 and into the bag-shaped portion 23 of the membrane 17 through the outlet 43. This causes the bag-shaped portion 23 to expand, and the air 11 in the bag-shaped portion 23 is released to the outside through the slits 30 in the front sheet member 21, so that a large number of air bubbles 4 are released from the membrane type air diffuser 10 into the water 3 to be treated.

[0056] At this time, the air 11 supplied from the outlet 43 of the gas supply nozzle 19 into the bag-shaped portion 23 of the membrane 17 encounters flow resistance as it flows from the center B in the longitudinal direction A of the membrane 17 toward both ends C, and therefore the pressure loss at both ends C of the membrane 17 is greater than the pressure loss at the center B.

[0057] In contrast, in the state where air 11 is released to the outside from slits 30 as described above, buoyancy acts on membrane 17 due to air 11 supplied into bag-shaped portion 23 of membrane 17, and this buoyancy causes both ends C of membrane 17 to rise higher than central portion B, as shown by imaginary lines in Fig. 2. As a result, depth D1 from the water surface of the water 3 to both ends C of membrane 17 in the aerobic tank becomes shallower than depth D2 from the water surface to central portion B of membrane 17, and the water pressure applied to both ends C of membrane 17 becomes smaller than the water pressure applied to central portion B of membrane 17.

[0058] In this way, at both ends C of the membrane 17, the effect of increased pressure loss making it difficult to release the air bubbles 4 and the effect of decreased water pressure making it easier to release the air bubbles 4 are offset, thereby reducing the variation in the amount of air bubbles 4 released at the center B and both ends C of the membrane 17, thereby improving uneven air diffusion by the membrane type air diffuser 10.

[0059] 1, since the membrane type air diffuser 10 is perpendicular to the air supply pipe 12 at the center in the longitudinal direction A, the air 11 is supplied uniformly into the bag-shaped portion 23 from the center B of the membrane 17 toward both ends C through the air flow passage 46 of the gas supply nozzle 19. Therefore, a large number of air bubbles 4 are released uniformly from the membrane 17, without being released locally biased.

[0060] In addition, since the air intake pipe 12 is located below the membrane type aeration device 10, a large number of air bubbles 4 are released into the water 3 to be treated through the slits 30 of the membrane type aeration device 10 without being blocked by the air intake pipe 12.

[0061] A method for manufacturing the membrane 17 of the membrane type air diffuser 10 will be described below.

[0062] First, as shown in FIG. 16 , the tubular portion 37 of the gas supply nozzle 19 is inserted into the first through hole 26 of the front-side sheet member 21 in which a large number of slits 30 are formed, and the peripheral portion of the first through hole 26 is welded to the underside of the flange portion 38 of the gas supply nozzle 19, thereby attaching the gas supply nozzle 19 to the front-side sheet member 21.

[0063] 17, an outer periphery 65 (see FIG. 16) of the front sheet member 21 and an outer periphery 66 (see FIG. 16) of the back sheet member 22 are welded to form a rectangular membrane sheet 67 having a bag-shaped portion 23. The dotted portion in FIG. 17 is the welded portion 29 between the front sheet member 21 and the back sheet member 22.

[0064] Then, as shown in FIG. 17, opposing long sides 68 of membrane sheet 67 are joined together to form a tube, thereby forming membrane 17 having a bag-shaped portion 23 inside, an insertion portion 16 in the center, a first opening 24 at the top, and a gas supply nozzle 19 at the bottom, as shown in FIG. 4.

[0065] In the above first embodiment, a front sheet member 21 and a back sheet member 22 of approximately the same shape are used to form a tubular membrane 17, but the front sheet member 21 may be welded to the back sheet member 22 only in the necessary area to form a bag-shaped portion 23, or the back sheet member 22 may be welded to the front sheet member 21 only in the necessary area to form a bag-shaped portion 23. (Second embodiment) In the first embodiment described above, as shown in Fig. 7, the support tube 18 is a circular straight tube having a constant outer circumferential length, but in the second embodiment described below, as shown in Fig. 18, the outer circumferential length of the support tube 18 is formed so that it is shorter at both ends C than at the center B. In other words, the outer diameter E1 of the support tube 18 is smaller at both ends C than at the center B, and gradually decreases from the center B to both ends C.

[0066] According to this, as shown by the solid line in Figure 19, when the air diffusion is stopped and the bag-shaped portion 23 is reduced in size, the space 64 between the inner surface of the membrane 17 and the outer surface of the support tube 18 is wider at both ends C than at the central portion B, so that there is more space between the membrane 17 and the support tube 18 at both ends C than at the central portion B.

[0067] As a result, as shown by the imaginary lines in Figure 19, when the bag-shaped portion 23 is inflated and air 11 is released to the outside through the slits 30 during aeration, the buoyancy acting on the membrane 17 causes both ends C of the membrane 17 to rise higher than the central portion B. (Third embodiment) In the third embodiment, as shown by the solid line in Fig. 20, the inner periphery of the membrane 17 is formed so that it is longer at both ends C than at the central portion B. That is, the inner diameter E2 of the membrane 17 is larger at both ends C than at the central portion B, and gradually increases from the central portion B toward both ends C. The support tube 18 is a circular straight tube having a constant outer diameter.

[0068] According to this, when the air diffusion is stopped and the bag-shaped portion 23 is reduced in size, the space 64 between the inner surface of the membrane 17 and the outer surface of the support tube 18 is wider at both ends C than at the central portion B, so that there is more space between the membrane 17 and the support tube 18 at both ends C than at the central portion B.

[0069] As a result, as shown by the phantom lines in Figure 20, when the bag-shaped portion 23 is inflated and air 11 is released to the outside through the slits 30 during aeration, the buoyancy acting on the membrane 17 causes both ends C of the membrane 17 to rise higher than the central portion B. (Fourth embodiment) In the fourth embodiment, as shown in Fig. 21, the bottoms of both ends C of the support tube 18 are positioned higher than the bottom of the central part B. That is, both ends C of the support tube 18 are bent obliquely upward from the central part B, and by inserting the support tube 18 having such a shape into the insertion part 16 of the membrane 17, the bottoms of both ends C of the membrane 17 are positioned higher than the bottom of the central part B, as shown in Fig. 22.

[0070] In each of the above embodiments, air 11 is used as the gas for diffusion, but a gas other than air 11 may be used. [Explanation of symbols]

[0071] 3. Treated water (liquid) 4. Bubbles 10. Membrane type aeration device 11 Air (gas) 16 Insertion section 17 Membrane 18 Support tube (support body) 19 Gas supply nozzle (gas supply section) 21 Front sheet material 22 Back side sheet material 23 Pouch 30 Slit 46 Ventilation channel A Longitudinal direction B Central part C end

Claims

1. A membrane type aeration device that is installed below the liquid surface and releases air bubbles into the liquid, The membrane has a tubular shape and a hollow insertion portion, a support inserted into the insertion portion of the membrane, and a gas supply portion provided in the center of the membrane in the longitudinal direction, The membrane has a bag-shaped portion formed in a bag shape by two sheet members on the front and back, the gas supply unit has an air passage communicating from the outside to the inside of the bag-shaped portion of the membrane; a sheet member constituting an outer peripheral surface of the bag-shaped portion of the membrane is formed with a plurality of slits for discharging to the outside the gas supplied into the bag-shaped portion through the ventilation flow path of the gas supply portion; A membrane type air diffuser characterized in that, when gas is released to the outside through the slits, both ends in the longitudinal direction of the membrane are positioned higher than the center.

2. 2. The membrane type air diffuser according to claim 1, wherein the membrane has a greater clearance between itself and the support at both ends than at the center in the longitudinal direction.

3. 3. The membrane type air diffuser according to claim 1, wherein the outer periphery of the support is shorter at both ends in the longitudinal direction than at the center.

4. 4. The membrane type air diffuser according to claim 1, wherein the inner periphery of the membrane is longer at both ends than at a central portion in the longitudinal direction.

5. 2. The membrane type air diffuser according to claim 1, wherein the bottoms of both ends in the longitudinal direction of the support are positioned higher than the bottom of the central portion.

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