Membrane separation device

Abstract

To provide a membrane separation apparatus with appropriate sieve residue capture means attached at an appropriate position, even when only the membrane separation apparatus is ordered.SOLUTION: A membrane separation apparatus 10 for filtration by immersion in treatment water, which is a mixture of organic wastewater and activated sludge, comprises a cylindrical membrane casing 11 opened at both top and bottom, a semipermeable membrane installed inside the membrane casing 11, and an air diffuser 12 installed below the semipermeable membrane, wherein the membrane separation apparatus is equipped with grid-shaped sieve residue capture means F below the air diffuser 12.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention includes a cylindrical membrane casing with openings at both the top and bottom, a semipermeable membrane installed inside the membrane casing, and an air diffuser installed below the semipermeable membrane. The present invention relates to a membrane separation device that is immersed in treated water, which is a mixture of organic wastewater and activated sludge, to separate permeate and turbidity components.

Background Art

[0002] Biological treatment using activated sludge is carried out to purify organic wastewater such as sewage, livestock wastewater, night soil, and wastewater generated in food factories. In recent years, the membrane separation activated sludge method, in which the above-mentioned membrane separation device is immersed in a biological treatment tank for solid-liquid separation, has attracted attention.

[0003] By the way, organic wastewater contains fibrous impurities such as pulp, hair, and thread waste. If these fibrous impurities entangle the semipermeable membrane, the flow of the treated water to the membrane surface may be inhibited, and appropriate membrane filtration performance may be impaired.

[0004] Therefore, in order to remove large impurities contained in organic wastewater, a slag removal device such as a bar screen is provided on the upstream side of the biological treatment tank. However, it has been difficult to completely remove fibrous impurities with such a slag removal device.

[0005] Patent Document 1 discloses a wastewater treatment device in which a membrane module for separating biologically treated wastewater into permeate and a retention liquid containing suspended components having a predetermined particle size or more is immersed in a treatment tank for biologically treating wastewater by microorganisms. This wastewater treatment device includes wastewater circulation means for circulating wastewater in the treatment tank, and impurity capturing means for capturing impurities in the wastewater is arranged upstream with respect to the circulating wastewater of the membrane module immersed in the treatment tank.

[0006] The above-mentioned wastewater circulation means is constituted by an aeration device arranged below the membrane module, and the impurity capturing means is arranged between the membrane module and the aeration device. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-47762 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, in the wastewater treatment apparatus described in Patent Document 1, the impurity capture means is positioned upstream of the membrane module, specifically below the membrane module, relative to the flow of wastewater circulating in the treatment tank by the wastewater circulation means. Furthermore, an aeration device, which functions as a wastewater circulation means, is positioned below the impurity capture means. As bubbles released from the aeration device pass through the impurity capture means and rise, there is a risk that the sieve residue captured by the impurity capture means will detach due to the rising bubbles. This detached sieve residue may then become entangled in the membrane module, potentially impairing the membrane filtration performance. Additionally, when a large amount of sieve residue is captured by the impurity capture means, the flow of bubbles released from the aeration device is obstructed by the impurity capture means, hindering proper wastewater circulation.

[0009] Incidentally, when a contractor receives an order for only the membrane separation unit, rather than the entire plant for purifying organic wastewater including the membrane separation unit, the contractor is required to install a means of capturing impurities on the membrane separation unit. However, contractors often neglect to install the impurities capture means, and even if an impurities capture means is installed, if it is inappropriate, the membrane filtration performance of the membrane module can be impaired in a short period of time.

[0010] In view of the above-mentioned problems, the object of the present invention is to provide a membrane separation device in which appropriate sieving residue capture means are attached in appropriate positions, even when only the membrane separation device is ordered. [Means for solving the problem]

[0011] In order to achieve the above object, the first characteristic configuration of the membrane separation device according to the present invention includes a cylindrical membrane casing that is open at both the top and bottom, a semi-permeable membrane provided inside the membrane casing, and an air diffuser installed below the semi-permeable membrane. It is a membrane separation device that is immersed in the water to be treated, which is a mixture of organic wastewater and activated sludge, and filtered. The point is that a lattice-like screen residue capturing means is provided below the air diffuser.

[0012] The upward flow generated in the water to be treated by the bubbles released from the air diffuser rises toward the semi-permeable membrane provided inside the membrane casing, and a circulating flow is formed in which the water to be treated flowing out from the upper opening of the membrane casing descends outside the membrane casing and flows into the air diffuser. When the water to be treated flowing into the air diffuser passes through the screen residue capturing means provided below the air diffuser, fibrous impurities floating in the water to be treated are appropriately captured by the lattice-like screen residue capturing means. Since the screen residue capturing means is installed below the air diffuser, the fibrous impurities captured by the screen residue capturing means will not be peeled off by the bubbles released from the air diffuser.

[0013] The second characteristic configuration is that, in addition to the first characteristic configuration described above, the semi-permeable membrane is joined to both sides of a membrane support provided in a plate-shaped membrane element, and the membrane elements are arranged at a predetermined interval M such that each membrane surface is in a vertical posture.

[0014] In the process where the upward flow of the water to be treated in which fibrous impurities are captured by the screen residue capturing means flows along the membrane surface of the membrane elements arranged at a predetermined interval M such that the membrane surface is in a vertical posture, the membrane surface is well purified. And even in a state where a large amount of screen residue is captured by the screen residue capturing means, the upward flow of the water to be treated generated by the bubbles released from the air diffuser is not obstructed by the screen residue capturing means.

[0015] The third characteristic configuration is that, in addition to the second characteristic configuration described above, the lattice width W of the screen residue capturing means is set such that M < W ≦ 5M with respect to the predetermined interval M.

[0016] By setting the grid width W of the screen residue capturing means within the range of M < W ≤ 5M with respect to the predetermined interval M of each membrane surface where the membrane elements are arranged, it becomes possible to reduce the flow resistance when the treated water passes through the screen residue capturing means and maintain a good circulating flow, while being able to appropriately capture fibrous impurities by the grid-like screen residue capturing means.

Advantages of the Invention

[0017] As described above, according to the present invention, even when only the membrane separation device is ordered, it has become possible to provide a membrane separation device with appropriate screen residue capturing means attached at an appropriate position.

Brief Description of the Drawings

[0018] [Figure 1] Explanation diagram of the membrane separation device [Figure 2] Explanation diagram of the membrane separation device and the membrane module [Figure 3] Explanation diagram of the membrane module [Figure 4] Explanation diagram of the membrane element [Figure 5] Explanation diagram of each part of the membrane module [Figure 6] (a) and (b) are explanatory diagrams of the screen residue capturing means

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the membrane separation device according to the present invention will be described. As shown in FIGS. 1 and 2, the membrane separation device 10 includes a cylindrical membrane casing 11 with a rectangular cross-section that is open at the top and bottom, a plurality of membrane modules 20 provided inside the membrane casing 11 and equipped with semipermeable membranes, and an air diffuser 12 installed below the membrane modules 20. It is immersed and arranged in a membrane separation tank filled with treated water, which is a mixture of organic wastewater and activated sludge, and is a device for solid-liquid separation and filtration of the treated water.

[0020] In the membrane casing 11, the membrane modules 20 are incorporated such that eight are arranged vertically and five are arranged horizontally in parallel. Below the lowermost membrane module 20, an air diffuser 12 having an air supply pipe for air diffusion is installed. By the diffused air supplied from the air supply pipe for air diffusion, an upward flow of the water to be treated in the membrane separation tank is generated between a plurality of membrane elements 21 arranged horizontally in a vertical posture in each membrane module 20, and the treated water that has permeated the membrane surface of each membrane element 21 is led out of the tank through the water collection pipe 13.

[0021] A treated water lead-out pipe (not shown) reaching the treatment water tank installed outside the membrane separation tank is connected to the water collection pipe 13, and a pump device is interposed in the middle of the pipeline. An air supply source such as a blower or a compressor is connected to the air supply pipe for air diffusion.

[0022] As shown in FIGS. 3, 4, and 5, each membrane module 20 is configured such that a plurality of membrane elements 21 are arranged in a space partitioned by a pair of front and rear water collection cases 22 and a pair of left and right cover members 23.

[0023] The membrane element 21 includes separation membranes 21b on both the front and back surfaces of a flat filter plate 21a as a membrane support. The separation membranes 21b are folded back at the upper side and the lower side of the filter plate 21a and arranged on both the front and back surfaces of the filter plate 21a.

[0024] The separation membranes 21b are wound around the periphery of the filter plate 21a, and the overlapping portions are adhered or welded to form an endless shape. The separation membranes 21b are adhered, welded, or pressed to the filter plate 21a at the lateral side portions of the membrane element 21 or in the vicinity thereof. For example, ultrasonic welding, thermal welding, adhesion with an adhesive, or pressing means using a pressing member is employed, and the adhered, welded, or pressed portion becomes the joint portion 21c.

[0025] The filter plate 21a is formed of an ABS resin or the like, and the separation membrane 21b is formed by coating and impregnating a non-woven fabric as a base material with a porous resin. That is, the separation membrane 21b functions as the semi-permeable membrane of the present invention. Note that the filter plate 21a is not limited to a material having rigidity such as an ABS resin, and may be configured using a flexible material such as a sheet-like non-woven fabric or a net.

[0026] The water collection case 22 and the cover member 23 are obtained by injection molding of ABS resin, polypropylene, or the like. The water collection case 22 is preferably configured to be translucent so that it is easy to confirm the inflow of sludge into the water collection case 22 due to damage to the separation membrane 21b or the like.

[0027] Multiple horizontal flow passages are formed through the interior of the filter plate 21a, running parallel to each other in the vertical direction. Multiple micropores communicating with the flow passages are formed on both the front and back surfaces of the filter plate 21a. The treated water that has permeated the separation membrane 21b flows through the flow passages via the micropores and flows out from both ends of the filter plate 21a.

[0028] A spacing holding portion 24 is provided in the lateral center of each membrane element 21 to maintain the spacing between each membrane element 21 at the aforementioned fixed interval.

[0029] The spacing section 24 is provided with multiple vertical slits arranged in parallel horizontally, and by inserting each membrane element 21 through each slit, each membrane element 21 is arranged in a vertical position at a fixed interval. The spacing section 24 is preferably made of an elastic material such as synthetic rubber so as to maintain the holding interval of each membrane element 21, absorb vibrations of the membrane elements 21 due to upward flow, and reduce wear of the separation membrane 21b due to contact.

[0030] In other words, the semipermeable membrane is bonded to both sides of a filter plate 21a, which serves as a membrane support provided on a plate-shaped membrane element 21, and the membrane elements 21 are arranged at predetermined intervals M such that each membrane surface is in a vertical orientation. The predetermined interval M is not particularly limited, but is set to about 5 to 10 mm, and in this embodiment to 6 mm.

[0031] Each membrane element 21 is arranged vertically at a fixed interval between them, with the separation membranes 21b of each membrane element 21 facing each other, by spacing-holding portions 24. A water collection case 22 is joined to the lateral side of each membrane element 21. The water collection case 22 is formed in a hollow shape with a water collection space inside, and connecting portions 25 and 26 that communicate with the water collection space are formed on the upper and lower surfaces, respectively.

[0032] Multiple slits 22a are formed on the opposing surfaces of the pair of water collection cases 22, at the same pitch as the slits provided in the spacing-holding section 24.

[0033] With the separation membrane 21b inserted through the slit 22a along with the filter plate 21a, resin is filled into the slit 22a to join each membrane element 21 to the water collection case 22. As a result, the treated water that has permeated through the separation membrane 21b is guided into each water collection case 22 through the flow channels formed in the filter plate 21a.

[0034] In Figure 2, a water collection pipe 13 is connected to the upper connection portion 25 of the top membrane module 20 on the left, and to the lower connection portion 26 of the bottom membrane module 20 on the right. The lower connection portion 26 of the top membrane module 20 on the left, and the upper connection portion 25 of the bottom membrane module 20 on the right are sealed with a sealing member (not shown). Note that in Figure 2, the upper connection portion 25 and the lower connection portion 26 are not shown, and the direction of treated water flow is indicated by a dashed arrow.

[0035] The system repeats a predetermined time cycle of a filtration operation, in which aeration is dispersed from the aeration device 12 while a pump device attached to the treated water outlet pipe is driven, and a relaxation operation, in which the pump device is stopped and aeration by the aeration device 12 is continued to clean the membrane surface.

[0036] As bubbles rise due to aeration by the aeration device 12, an upward flow of treated water is formed. The treated water that flows in from the bottom opening of the membrane casing 11 rises through the gaps between the membrane elements 21 within the membrane casing 11, flows out from the upper opening of the membrane casing 11, then flows downward along the side of the membrane casing 11, and then flows back into the bottom opening of the membrane casing 11, thus forming a circulating flow of treated water.

[0037] At this time, if fibrous impurities suspended in the water to be treated become entangled with the membrane elements 21, the impurities accumulating on the membrane elements 21 will clog the gaps between the membrane elements 21, obstructing the circulation flow of the water to be treated and reducing the filtration efficiency.

[0038] When this condition occurs, very complicated maintenance becomes necessary, which involves frequently lifting the membrane separation device 10 from the membrane separation tank and performing a cleaning process to remove impurities.

[0039] Therefore, the membrane separation apparatus 10 according to the present invention is equipped with a grid-shaped sieve sludge capture means F below the aeration device 12. As shown in Figure 2, the sieve sludge capture means F is attached to the membrane casing 11 below the aeration device 12 provided on the membrane casing 11, so as to cover the bottom opening.

[0040] As the water to be treated flows into the aeration device 12 and passes through the sieve capture means F located below the aeration device 12, fibrous impurities suspended in the water to be treated are appropriately captured by the grid-shaped sieve capture means F. Since the sieve capture means F is installed below the aeration device 12 and not above it, the fibrous impurities captured by the sieve capture means F are not detached by bubbles released from the aeration device 12.

[0041] The upward flow of the treated water in which fibrous impurities are captured by the screen residue capturing means F flows along the membrane surface of the membrane elements 21 arranged at a predetermined interval M so that the membrane surfaces are in a vertical position, and the membrane surfaces are purified well in the process. Then, even when the screen residue is captured by the screen residue capturing means F, the upward flow of the treated water generated by the bubbles discharged from the air diffuser 12 is not obstructed by the screen residue capturing means F.

[0042] As the screen residue capturing means F, expanded metal Fa, Tricar net (registered trademark) Fb, etc. can be preferably used. As shown in FIG. 6(a), the expanded metal Fa is a mesh-shaped metal plate obtained by expanding a metal plate of a predetermined thickness made of a non-ferrous metal such as a stainless steel plate, aluminum, copper, titanium, or an alloy thereof by an expand manufacturing machine while making cuts in a staggered pattern and forming the cuts into a rhombus or a tortoise shell shape. The Tricar net (registered trademark) Fb is a resin (polyethylene) square mesh net manufactured by continuous extrusion molding as shown in FIG. 6(b).

[0043] The grid width W of the screen residue capturing means F waspreferably set to M < W ≦ 5M with respect to the interval M between the membrane surfaces of the membrane elements 21 described above. In the present embodiment, the range is 6 mm < W ≦ 30 mm.

[0044] By setting the grid−width W of the screen residue capturing means F within the range of M < W ≦ 5M with respect to the predetermined interval M between the membrane surfaces of each membrane surface where the membrane elements 21 are arranged, while reducing the flow−through resistance when the treated water passes through the screen residue capturing means F and making it possible to maintain a good circulation flow, fibrous impurities can be appropriately captured by the grid−shaped screen residue capturing means F. Note that the grid width W refers to the wider width in the vertical and horizontal directions.

[0045] If the grid width W of the screen residue capturing means F satisfies W ≦ M, it will capture even short fibrous impurities that are less likely to cause blockage of the gaps between the membrane elements 21, and there is a risk that the slag removal ability of the screen residue capturing means F will decrease in a short period. If the grid width W of the screen residue capturing means F satisfies W ≧ 5M, there is a risk that long fibrous impurities that may cause blockage of the gaps between the membrane elements 21 will pass through the screen residue capturing means F. When the grid width W of the screen residue capturing means F is set within the range of M < W ≦ 5M, the slag removal ability of the screen residue capturing means F can be maintained for a relatively long period, and it is more preferable to set it within the range of 1.5M ≦ W ≦ 4.5M.

[0046] When the screen residue capturing means F captures a large amount of fibrous impurities and the capturing ability decreases, the membrane separation device can be lifted from the treatment tank, and the screen residue capturing means F can be cleaned or replaced.

[0047] In the above-described embodiment, as the membrane separation device 10, an example was described in which 8 membrane modules 20 were arranged in 5 columns vertically in a substantially rectangular parallelepiped membrane casing 11 with open top and bottom, but the number of arrangements of the membrane modules 20 is not particularly limited.

[0048] In the above-described embodiment, as the membrane separation device 10, a plurality of membrane modules 20 were arranged in a row in a substantially rectangular parallelepiped membrane casing 11 with open top and bottom, and each membrane module 20 was configured such that a plurality of membrane elements 21 were arranged in a space partitioned by a pair of front and rear water collection cases 22 and a pair of left and right cover members 23. However, without providing the membrane module 20, in a cylindrical membrane casing 11 with open top and bottom, a plurality of membrane elements 21 are arranged at a predetermined interval M such that each membrane surface is in a vertical posture, and each membrane element 21 is connected to a water collection pipe 13 via a tube. It is also possible to apply the present invention to a membrane separation device 10 in which an air diffuser 12 is installed below each membrane element 21. Also in this case, the above-described screen residue capturing means F may be installed below the air diffuser 12 in the vicinity of the lower opening of the membrane casing 11.

[0049] The embodiments described above are merely descriptions of one aspect of the present invention, and the present invention is not limited by this description. It goes without saying that the specific configuration of each part can be appropriately modified and designed within the scope that the effects of the present invention are achieved. [Explanation of symbols]

[0050] 10: Membrane separation device 11: Membrane casing 12: Air diffuser 20: Membrane Module 21: Membrane element 21b Separation membrane (semi-permeable membrane) F: Sieve residue capturing means

Claims

1. A membrane separation apparatus comprising a cylindrical membrane casing with openings at the top and bottom, a semipermeable membrane installed inside the membrane casing, and an aeration device installed below the semipermeable membrane, which filters treated water, a mixture of organic wastewater and activated sludge, by immersion in it. A membrane separation apparatus characterized by having a grid-like sieve residue capture means located below the aeration device.

2. The membrane separation apparatus according to claim 1, characterized in that the semipermeable membrane is bonded to both sides of a membrane support provided on a plate-shaped membrane element, and the membrane elements are arranged at predetermined intervals M such that each membrane surface is in a vertical position.

3. The membrane separation apparatus according to claim 2, characterized in that the grid width W of the sieve sludge capturing means is set to M < W ≤ 5M with respect to the predetermined interval M.

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