Membrane separation apparatus

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 relates to a membrane separation device that comprises a cylindrical membrane casing that is open at the top and bottom, a semipermeable membrane installed inside the membrane casing, and an aeration device installed below the semipermeable membrane, and that is immersed in water to be treated, which is a mixture of organic wastewater and activated sludge, to separate the permeated liquid from turbid components. [Background technology]

[0002] Biological treatment using activated sludge is carried out to purify organic wastewater such as sewage, livestock wastewater, human waste, and wastewater from 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 to separate solid and liquid, has attracted attention.

[0003] Incidentally, organic wastewater contains fibrous impurities such as pulp, hair, and lint. If these fibrous impurities become entangled in the semipermeable membrane, the flow of the treated water onto the membrane surface may be impeded, and proper membrane filtration performance may be impaired.

[0004] Therefore, in order to remove large impurities contained in the organic wastewater, a sludge remover such as a bar screen is provided upstream of the biological treatment tank, but it is difficult to completely remove fibrous impurities using such a sludge remover.

[0005] Patent Document 1 proposes a wastewater treatment device in which a membrane module is immersed in a treatment tank in which the wastewater is biologically treated by microorganisms, and which separates the wastewater after biological treatment into a permeate and a retentate containing suspended components having a predetermined particle size or larger. The wastewater treatment device is equipped with a wastewater circulation means for circulating the wastewater within the treatment tank, and also proposes an impurity capture means for capturing impurities in the wastewater upstream of the circulating wastewater of the membrane module immersed in the treatment tank.

[0006] The wastewater circulating means described above is composed of an aeration device disposed below the membrane module, and the impurity capturing means is disposed between the membrane module and the aeration device. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-47762 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the wastewater treatment device described in Patent Document 1, the impurity capture means is disposed upstream of the membrane module with respect to the flow of wastewater circulated in the treatment tank by the wastewater circulation means, specifically below the membrane module, and further, an aeration device functioning as the wastewater circulation means is disposed below the impurity capture means, so that when the air bubbles released from the aeration device pass through the impurity capture means and rise, there is a risk that the sieve captured by the impurity capture means will peel off due to the rising of the air bubbles, and there is a risk that the peeled off sieve will become entangled with the membrane module, impairing the membrane filtration performance. In addition, when a large amount of sieve is captured by the impurity capture means, there is also a problem that the flow of the air bubbles released from the aeration device is obstructed by the impurity capture means, hindering good circulation of the wastewater.

[0009] By the way, when an order is placed for only a membrane separation device, rather than for an entire plant for purifying organic wastewater including the membrane separation device, the contractor must attach a contaminant capture means to the membrane separation device. However, contractors often neglect to attach the contaminant capture means, and even if the contaminant capture means is attached, if it is an inappropriate contaminant capture means, there is a problem that the membrane filtration performance of the membrane module is impaired in a short period of time.

[0010] In view of the above-mentioned problems, an object of the present invention is to provide a membrane separation device in which an appropriate sieve capturing means is attached at an appropriate position 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 semipermeable membrane provided inside the membrane casing, and an air diffuser installed below the semipermeable 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-shaped 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 semipermeable 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-shaped 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 semipermeable 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] 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, and the membrane surface is satisfactorily purified in the process. 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 to 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 water to be treated passes through the screen residue capturing means and maintain a good circulating flow, while also enabling the fibrous impurities to be appropriately captured 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 appropriate positions.

Brief Description of the Drawings

[0018] [Figure 1] Explanatory drawing of the membrane separation device [Diagram 2] Explanatory drawing of the membrane separation device and the membrane module [Diagram 3] Explanatory drawing of the membrane module [Figure 4] Explanatory drawing of the membrane element [Diagram 5] Explanatory drawing of each part of the membrane module [Figure 6] (a) and (b) are explanatory drawings 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 the water to be treated, which is a mixture of organic wastewater and activated sludge, and is a device for solid-liquid separation and filtration of the water to be treated.

[0020] The membrane modules 20 are assembled in a vertical arrangement of eight stages and a horizontal arrangement of five rows in the membrane casing 11. An aeration device 12 equipped with an aeration supply pipe is installed below the lowest membrane module 20, and the diffused air supplied from the aeration supply pipe generates an upward flow of the water to be treated in the membrane separation tank between the multiple membrane elements 21 arranged horizontally in a vertical position 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 a water collection pipe 13.

[0021] A treated water outlet pipe (not shown) leading to a treated water tank installed outside the membrane separation tank is connected to the water collection pipe 13, and a pump device is installed in the middle of the pipe. An air supply source such as a blower or compressor is connected to the aeration pipe.

[0022] As shown in Figures 3, 4 and 5, each membrane module 20 is configured by arranging a plurality of membrane elements 21 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 a flat filter plate 21a serving as a membrane support and a separation membrane 21b on both the front and back sides of the filter plate 21a. The separation membrane 21b is folded back at the upper and lower sides of the filter plate 21a and disposed on both the front and back sides of the filter plate 21a.

[0024] The separation membrane 21b is wound around the filter plate 21a, and the overlapping portion is bonded or welded to form an endless shape, and is bonded, welded, or pressed to the filter plate 21a at or near the lateral side portion of the membrane element 21. For example, ultrasonic welding, heat welding, bonding with an adhesive, or pressing means using a pressing member are used, and the bonded, welded, or pressed portion becomes the joint portion 21c.

[0025] The filter plate 21a is made of ABS resin or the like, and the separation membrane 21b is made by applying and impregnating a porous resin onto a nonwoven fabric base material. That is, the separation membrane 21b functions as the semipermeable membrane of the present invention. The filter plate 21a is not limited to a rigid material such as ABS resin, and may be made of a flexible material such as a sheet-like nonwoven fabric or a net.

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

[0027] Inside the filter plate 21a, a plurality of horizontal flow passages are formed in parallel in the vertical direction. A plurality of micropores communicating with the flow passages are formed on both the front and back sides of the filter plate 21a. The treated water that has permeated the separation membrane 21b flows through the flow passages from the micropores to flow out from both ends of the filter plate 21a.

[0028] A spacing maintaining portion 24 for maintaining the spacing between the membrane elements 21 at the above-mentioned constant spacing is provided at the lateral center of each membrane element 21.

[0029] The spacing retaining portion 24 is provided with a plurality of vertical slits arranged in parallel in the horizontal direction, and by inserting each membrane element 21 into each slit, the membrane elements 21 are arranged in a vertical position at the above-mentioned fixed intervals. The spacing retaining portion 24 is preferably formed of an elastic body such as synthetic rubber so as to be able to absorb vibration of the membrane elements 21 caused by the upward flow while maintaining the retaining intervals between the membrane elements 21, and to reduce wear of the separation membrane 21b due to contact.

[0030] That is, the semipermeable membranes are bonded to both sides of a filter plate 21a serving as a membrane support provided in a plate-like membrane element 21, and the membrane elements 21 are arranged at a predetermined interval M so that each membrane surface is in a vertical position. The predetermined interval M is not particularly limited, but is set to about 5 to 10 mm, and in this embodiment, it is set to 6 mm.

[0031] The membrane elements 21 are arranged in a vertical position at regular intervals so that the separation membranes 21b of each membrane element 21 face each other by the spacing retaining parts 24, and a water collection case 22 is joined to the lateral side parts of each membrane element 21. The water collection case 22 is formed in a hollow shape having a water collection space therein, and connecting parts 25, 26 that communicate with the water collection space are formed on the upper and lower surfaces, respectively.

[0032] A plurality of slits 22a are formed on the opposing surfaces of the pair of water collecting cases 22 at the same pitch as the respective slits provided in the spacing retaining portion 24.

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

[0034] 2, the upper connecting part 25 of the uppermost membrane module 20 on the left side and the lower connecting part 26 of the lowermost membrane module 20 on the right side are connected to the water collection pipes 13, and the lower connecting part 26 of the uppermost membrane module 20 on the left side and the upper connecting part 25 of the lowermost membrane module 20 on the right side are sealed with a sealing member (not shown). Note that the upper connecting part 25 and the lower connecting part 26 are omitted in Fig. 2, and the flow direction of the treated water is indicated by a dashed arrow.

[0035] A filtration operation in which the pump device attached to the treated water outlet pipe is driven while diffusing air from the aeration device 12, and a relaxation operation in which the pump device is stopped and the membrane surface is washed by continuing to diffuse air from the aeration device 12 are repeated in a predetermined time cycle.

[0036] The air diffused by the air diffuser 12 causes air bubbles to rise, forming an upward flow of the treated water, and the water to be treated flowing in through the bottom opening of the membrane casing 11 rises through the gaps between the membrane elements 21 inside the membrane casing 11, flows out from the top opening of the membrane casing 11, then flows downward along the side of the membrane casing 11, and further flows into the bottom opening of the membrane casing 11, forming a circulating flow of the water to be treated.

[0037] At this time, if fibrous impurities floating in the water to be treated become entangled with the membrane elements 21, the impurities accumulated on the membrane elements 21 will block the gaps between the membrane elements 21, hindering the circulating flow of the water to be treated and reducing the filtration efficiency.

[0038] When this state occurs, it becomes necessary to frequently pull the membrane separation device 10 out of the membrane separation tank and perform a cleaning process to remove the impurities, which is very troublesome maintenance.

[0039] Therefore, the membrane separation device 10 according to the present invention is provided with a lattice-shaped sieve capture means F below the air diffuser 12. As shown in Fig. 2, the sieve capture means F is attached to the membrane casing 11 below the air diffuser 12 provided in the membrane casing 11 so as to cover the bottom opening.

[0040] When the water to be treated flowing into the air diffuser 12 passes through the sieve capture means F provided below the air diffuser 12, fibrous impurities floating in the water to be treated are appropriately captured by the lattice-shaped sieve capture means F. Since the sieve capture means F is installed below the air diffuser 12, and not above the air diffuser 12, the fibrous impurities captured by the sieve capture means F are not peeled off by air bubbles released from the air diffuser 12.

[0041] In the process where 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 such that the membrane surface is in a vertical posture, the membrane surface is satisfactorily purified. And 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, trical 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 with a perforating machine while making cuts in a staggered pattern and forming the cuts into a rhombus or a tortoise shell shape. The trical net (registered trademark) Fb is a resin (polyethylene)-made 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 is preferably set such that M < W ≤ 5M with respect to the interval M between the membrane surfaces of the membrane elements 21 described above. In this embodiment, it is in the range of 6 mm < W ≤ 30 mm.

[0044] By setting the grid width W of the screen residue capturing means F in 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 resistance when the treated water passes through the screen residue capturing means F and enabling maintenance of 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 residue 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 in the range of M < W ≦ 5M, the residue 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 in the range of 1.5M ≦ W ≦ 4.5M.

[0046] When the screen residue capturing means F captures a large amount of fibrous impurities and its 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 the membrane modules 20 were arranged in 8 vertical rows and 5 horizontal columns 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, an example was described in which 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 above-described embodiment is an explanation of one aspect of the present invention, and the present invention is not limited to this description. It goes without saying that the specific configuration of each part can be appropriately modified and designed within the scope of the effect of the present invention. [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 device comprising a cylindrical membrane casing with upper and lower openings, a semipermeable membrane disposed inside the membrane casing, and an aeration device disposed below the semipermeable membrane, the membrane separation device being immersed in a to-be-treated water that is a mixture of organic wastewater and activated sludge and filtering the water, A membrane separation apparatus comprising a lattice-shaped sieve capturing means disposed below the air diffuser.

2. 2. The membrane separation apparatus according to claim 1, wherein the semipermeable membrane is bonded 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 so that each membrane surface is in a vertical position.

3. 3. The membrane separation apparatus according to claim 2, wherein the mesh width W of the sieve capturing means is set to satisfy M<W≦5M with respect to the predetermined interval M.

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