Membrane separation device

Abstract

A membrane separation device 10 that is immersed into water to be treated, which is a mixed liquid of organic wastewater and activated sludge, so as to filter the water to be treated comprises: a cylindrical membrane casing 11 having an open top and bottom; a semi-permeable membrane provided inside the membrane casing 11; an air diffusion device 12 installed below the semi-permeable membrane; and a lattice-like sieve residue capturing means F disposed below the air diffusion device 12. The semi-permeable membrane is joined to both surfaces of a membrane support body provided to a plate-like membrane elements. The membrane elements are arranged at prescribed intervals M such that each membrane surface is orientated vertically, and the lattice width W of the sieve residue capturing means F is set to satisfy M<W≤5M with respect to the prescribed interval M.

Description

membrane separation equipment

[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 permeate from turbid components.

[0002] Biological treatment using activated sludge is carried out to purify organic wastewater such as sewage, livestock wastewater, human waste, 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 to separate solids and liquids, has been attracting attention.

[0003] However, 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 water to be treated onto the membrane surface may be obstructed, potentially impairing the proper membrane filtration performance.

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

[0005] Patent Document 1 proposes a wastewater treatment device in which a membrane module is immersed in a treatment tank that biologically treats the wastewater using microorganisms, and which separates the wastewater after biological treatment into a permeate and a retentate containing suspended components of a predetermined particle size or larger.The wastewater treatment device is characterized in that it is equipped with a wastewater circulation means that circulates the wastewater within the treatment tank, and also has an impurity capture means that captures impurities in the wastewater upstream of the membrane module immersed in the treatment tank, based on the circulating wastewater.

[0006] The wastewater circulation 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.

[0007] Japanese Patent Application Publication No. 9-47762

[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. Therefore, when the air 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 peel off due to the rising of the air bubbles, and there is a risk that the peeled sieve residue will become entangled in the membrane module, impairing the membrane filtration performance. Furthermore, when a large amount of sieve residue is captured by the impurity capture means, there is also the 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 in the treatment tank.

[0009] However, when an order is placed for only the membrane separation device, rather than for the entire plant for purifying organic wastewater including the membrane separation device, the contractor must install impurity capture means in the membrane separation device. However, there are many cases where contractors neglect to install the impurity capture means, and even if the impurity capture means is installed, if it is inappropriate, the membrane filtration performance of the membrane module will be 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 an order is received for only the membrane separation device.

[0011] In order to achieve the above-mentioned object, a first characteristic configuration of the membrane separation device according to the present invention is that it is 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 is immersed in the water to be treated, which is a mixture of organic wastewater and activated sludge, to filter the water, and is equipped with a lattice-shaped sieve capture means below the aeration device.

[0012] The air bubbles released from the diffuser cause an upward flow in the water to rise toward the semipermeable membrane installed inside the membrane casing, and the water to be treated flowing out from the upper opening of the membrane casing flows down the outside of the membrane casing and into the diffuser, forming a circulating flow. When the water to be treated flowing into the diffuser passes through a sieve capture means provided below the diffuser, fibrous impurities floating in the water to be treated are properly captured by the lattice-shaped sieve capture means. Because the sieve capture means is installed below the diffuser, the fibrous impurities captured by the sieve capture means are not peeled off by the air bubbles released from the diffuser.

[0013] The second characteristic configuration of the present invention is that, in addition to the first characteristic configuration described above, the semipermeable membranes are bonded to both surfaces of membrane supports provided on plate-shaped membrane elements, and the membrane elements are arranged at a predetermined interval M so that each membrane surface is in a vertical position.

[0014] The upward flow of the water to be treated, from which fibrous impurities have been captured by the sieve capture means, flows along the membrane surfaces of the membrane elements arranged at a predetermined interval M so that the membrane surfaces are in a vertical position, thereby effectively cleaning the contaminated membrane surfaces. Furthermore, even when a large amount of sieve is captured by the sieve capture means, the upward flow of the water to be treated, which is generated by the air bubbles released from the air diffuser, is not obstructed by the sieve capture means disposed below the air diffuser.

[0015] The third characteristic feature of the present invention is that, in addition to the second characteristic feature described above, the grid width W of the sieve capturing means is set to satisfy M<W≦5M with respect to the predetermined interval M.

[0016] By setting the grid width W of the sieve capture means in the range of M < W ≦ 5M with respect to the predetermined spacing M between each membrane surface on which the membrane elements are arranged, it becomes possible to reduce the flow resistance when the treated water passes through the sieve capture means and maintain a good circulation flow, while also making it possible to properly capture fibrous impurities with the lattice-shaped sieve capture means.

[0017] As described above, according to the present invention, even when an order is received for only a membrane separation device, it is possible to provide a membrane separation device in which an appropriate sieve capturing means is attached at an appropriate position.

[0018] Fig. 1 is an explanatory diagram of a membrane separation device. Fig. 2 is an explanatory diagram of a membrane separation device and a membrane module. Fig. 3 is an explanatory diagram of a membrane module. Fig. 4 is an explanatory diagram of a membrane element. Fig. 5 is an explanatory diagram of each part of a membrane module. Figs. 6(a) and 6(b) are explanatory diagrams of a sieve capturing means.

[0019] A membrane separation apparatus according to the present invention will now be described. As shown in Figures 1 and 2, the membrane separation apparatus 10 comprises a cylindrical membrane casing 11 with a rectangular cross section that is open at the top and bottom, a plurality of membrane modules 20 that are installed inside the membrane casing 11 and that are equipped with semipermeable membranes, and an aeration device 12 that is installed below the membrane modules 20. The membrane separation apparatus 10 is immersed in a membrane separation tank that is filled with water to be treated, which is a mixture of organic wastewater and activated sludge, and performs solid-liquid separation and filtration of the water to be treated.

[0020] The membrane modules 20 are assembled in a vertical arrangement of eight columns 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. 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 discharged outside the tank through a water collection pipe 13.

[0021] A treated water outlet pipe (not shown) that leads treated water 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 pipe. An air supply source such as a blower or compressor is connected to the aeration air supply pipe.

[0022] As shown in Figures 3, 4 and 5, each membrane module 20 is composed of a plurality of membrane elements 21 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 a flat filter plate 21a serving as a membrane support, and a separation membrane 21b on both the front and back surfaces of the filter plate 21a. The separation membrane 21b is folded back at the upper and lower edge portions of the filter plate 21a and disposed on both the front and back surfaces 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 edge of the membrane element 21. For example, ultrasonic welding, heat welding, bonding with an adhesive, or pressing means using a pressing member may be used, and the bonded, welded, or pressed portion becomes the joint 21c.

[0025] The filter plate 21a is made of ABS resin or the like, and the separation membrane 21b is made by coating and impregnating a nonwoven fabric base material with a porous resin. That is, the separation membrane 21b functions as the semipermeable membrane of the present invention. Note that the filter plate 21a is not limited to being made of a rigid material such as ABS resin, but may also be made of a flexible material such as a sheet-like nonwoven fabric or 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 if sludge has flowed into the water collection case 22 due to damage to the separation membrane 21b, etc.

[0027] The filter plate 21a has a plurality of horizontal flow passages formed in parallel in the vertical direction inside the filter plate 21a. The filter plate 21a has a plurality of micropores formed on both sides thereof that communicate with the flow passages. The treated water that has permeated the separation membrane 21b flows through the micropores and the flow passages and then flows 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 constant spacing is provided at the center of each membrane element 21 in the lateral direction.

[0029] The spacing member 24 has 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 member 24 is preferably formed of an elastic material 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 spacing between the membrane elements 21 and to reduce wear of the separation membranes 21b due to contact.

[0030] That is, the semipermeable membranes are bonded to both surfaces of filter plates 21a serving as membrane supports provided in plate-like membrane elements 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 preferably about 5 to 10 mm, and is set to 6 mm in this embodiment.

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

[0032] A plurality of slits 22 a 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 portion 24 .

[0033] With the separation membranes 21b inserted into the slits 22a together with the filter plates 21a, the slits 22a are 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 membranes 21b is guided into each water collection case 22 through the flow passages formed in the filter plates 21a.

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

[0035] A filtration operation in which a pump device attached to the treated water outlet pipe is driven while aeration is performed from the aeration device 12, 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 are repeated in a predetermined time cycle.

[0036] The air diffused by the air diffuser 12 causes bubbles to rise, forming an upward flow of the treated water, and the treated water flowing in through the bottom opening of the membrane casing 11 rises through the gaps between the membrane elements 21 within the membrane casing 11, flows out through 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 treated water.

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

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

[0039] Therefore, the membrane separation apparatus 10 according to the present invention is provided with a lattice-shaped sieve capture means F below the air diffuser 12. As shown in Figure 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 properly 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 will not be peeled off by the air bubbles released from the air diffuser 12.

[0041] The membrane surfaces are effectively purified as the upward flow of the water to be treated, from which fibrous impurities have been captured by the sieve capture means F, flows along the membrane surfaces of the membrane elements 21, which are arranged at predetermined intervals M so that the membrane surfaces are in a vertical position. Even when the sieve is captured by the sieve capture means F, the upward flow of the water to be treated, which is generated by the air bubbles released from the air diffuser 12, is not obstructed by the sieve capture means F.

[0042] As the sieve capture means F, Expand Metal Fa, Trical Net (registered trademark) Fb, etc. can be suitably used. As shown in Fig. 6(a), Expand Metal Fa is a mesh-like metal plate made by expanding a metal plate of a predetermined thickness made of stainless steel, non-ferrous metal such as aluminum, copper, or titanium, or an alloy thereof, while making staggered cuts in an expanding machine, and then forming the cuts into a diamond or tortoiseshell shape. As shown in Fig. 6(b), Trical Net (registered trademark) Fb is a square mesh net made of resin (polyethylene) manufactured by continuous extrusion molding.

[0043] The grid width W of the sieve capturing means F is preferably set to M<W≦5M, where M is the predetermined interval between the membrane surfaces of the membrane elements 21. In this embodiment, the range is 6 mm<W≦30 mm.

[0044] By setting the grid width W of the sieve capture means F in the range of M<W≦5M with respect to the predetermined spacing M between each membrane surface at which the membrane elements 21 are arranged, it becomes possible to reduce the flow resistance when the water to be treated passes through the sieve capture means F, thereby maintaining a good circulation flow, while also making it possible to properly capture fibrous impurities with the lattice-shaped sieve capture means F. The grid width W refers to the wider width of the length and width.

[0045] If the grid width W of the sieve capture means F is W≦M, even short fibrous impurities that are unlikely to cause clogging of the gaps between the membrane elements 21 will be captured, and there is a risk that the debris removal ability of the sieve capture means F will decrease in a short period of time, and if the grid width W of the sieve capture means F is W≧5M, there is a risk that long fibrous impurities that are likely to cause clogging of the gaps between the membrane elements 21 will slip through the sieve capture means F. If the grid width W of the sieve capture means F is set in the range M<W≦5M, the debris removal ability of the sieve capture means F can be maintained for a relatively long period of time, and it is more preferable to set it in the range of 1.5M≦W≦4.5M.

[0046] If the sieve capture means F captures a large amount of fibrous impurities and its capture capacity decreases, the membrane separation device 10 can be pulled out of the treatment tank and the sieve capture means F can be cleaned or replaced.

[0047] In the above-described embodiment, an example of the membrane separation device 10 has been described in which the membrane modules 20 are arranged in eight vertical rows and five horizontal rows in the membrane casing 11, which is an approximately rectangular parallelepiped and has openings at the top and bottom. However, the number of membrane modules 20 arranged is not particularly limited.

[0048] In the above-described embodiment, the membrane separation apparatus 10 is described as being configured such that a plurality of membrane modules 20 are arranged in a row in a substantially rectangular membrane casing 11 that is open at the top and bottom, and each membrane module 20 has a plurality of membrane elements 21 disposed within a space defined by a pair of front and rear water collection cases 22 and a pair of left and right cover members 23. The present invention can also be applied to other membrane separation apparatuses 10 that do not include membrane modules 20, but instead have a cylindrical membrane casing 11 that is open at the top and bottom, and a plurality of membrane elements 21 arranged at a predetermined interval M with their membrane surfaces in a vertical position, and each membrane element 21 is connected to a water collection pipe 13 via a tube that guides treated water, with an air diffuser 12 installed below each membrane element 21. In this case, too, the above-described sieve capture means F may be installed below the air diffuser 12 near 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 effects of the present invention.

[0050] 10: Membrane separation device 11: Membrane casing 12: Aeration device 20: Membrane module 21: Membrane element 21b: Separation membrane (semipermeable membrane) F: Sieve capture means

Claims

1. A membrane separation device comprising a cylindrical membrane casing open at the top and bottom, a semipermeable membrane installed inside the membrane casing, and an aeration device installed below the semipermeable membrane, and which is immersed in the treated water, which is a mixture of organic wastewater and activated sludge, and which filters the water, characterized in that a lattice-shaped sieve capture means is provided 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 a predetermined interval M so that each membrane surface is in a vertical position.

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

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