JP2011183364A - Flat membrane filtration apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat membrane filtration apparatus in which membrane surface cleaning effects of an upper stage membrane unit can be obtained effectively in the case of installing membrane units vertically in multistage. <P>SOLUTION: In the flat membrane filtration apparatus 10, a membrane unit 20, in which the membrane surfaces of a plurality of flat membrane elements 22 are arranged in parallel in a horizontal direction at a predetermined interval, is laminated in a treatment tank 12 vertically in multistage, and an aeration means 30 for diffusing air from a lower part of the membrane unit 20 between the flat membrane elements 22 is provided. A rectifying plate 50 is provided in a horizontal direction between the upper and lower membrane units 20. The rectifying plate 50 forms a plurality of openings 52 through which bubbles pass, and the distance between the openings 52 enlarges at a place, in which cross flows passing through the membrane unit 20 of the lower part gather. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a flat membrane filtration device, and more particularly to a flat membrane filtration device that separates a solid and a liquid by a membrane unit immersed in a treatment tank filled with water to be treated such as sewage and industrial wastewater and takes out the filtrate.

  There is an activated sludge treatment method that decomposes wastewater containing organic components with microorganisms in sewage and industrial wastewater. A membrane separation activated sludge method is known as one method of this activated sludge treatment method. The membrane separation activated sludge method uses a flat membrane filtration device for membrane separation of water to be treated and activated sludge after reaction treatment.

  The flat membrane filtration device is arranged in parallel with a plurality of membrane units immersed in a treatment tank filled with the water to be treated, and filtered water is obtained by suction-filtering the water to be treated from the inside of each membrane unit. Each membrane unit is vertically installed in the processing tank with a predetermined interval, and is provided with a diffuser for performing aeration below.

  The purpose of aeration is to obtain a cleaning effect that suppresses clogging of the membrane by removing solid matter such as sludge cake that accumulates on the membrane surface, and causes a swirl flow in the treatment tank to cause a water flow near the membrane surface. And agitation of the inside of the treatment tank, and supply of oxygen for aerobic treatment when the water to be treated in the treatment tank contains microorganisms such as activated sludge. Thereby, the filtration process by a membrane unit can be performed efficiently.

  In the conventional immersion flat membrane filtration device, there is a problem that the occupied area of the membrane units arranged in a plane in the treatment tank is widened, and the device is enlarged. Further, in this case, there is a problem that the power cost of air diffusion for maintaining the filtration performance of the membrane is large. To solve this problem, a cylindrical spacer is provided between the upper and lower membrane units so that the diffused air used in the lower stage can be used for the upper membrane unit without escaping to the outside of the membrane unit. It is disclosed in Document 1.

  According to Patent Document 1, the distance between the lower part of the membrane element of the upper membrane module and the upper part of the membrane element of the membrane module provided immediately below the upper membrane module is 50 cm or less, and is adjacent in the vertical direction. An immersion type membrane filtration device in which a current plate is provided between membrane modules is disclosed. FIG. 7 is an explanatory view of a current plate of a conventional flat membrane filtration device. As shown in FIG. 7A, the conventional rectifying plate 100 has a parallel rectifying plate configuration in which plate-like rectifying plate members 102 are arranged in parallel in the horizontal direction at appropriate intervals. Further, as shown in FIG. 7B, a partition member 104 is provided in a direction orthogonal to the rectifying plate member 102 of the rectifying plate 100 to form a lattice type rectifying plate.

  By providing the rectifying plate 100 between the upper and lower membrane modules, bubbles are prevented from concentrating to the center side, and the bubbles are allowed to enter the upper membrane module in a uniformly dispersed state. Contamination of the end portion of the upper membrane module due to concentration of can be prevented.

JP-A-11-57426

FIG. 8 is an explanatory view of the cross flow flow of the membrane unit. (1) is a single membrane unit, and (2) is a membrane unit laminated vertically.
As shown in FIG. 8 (1), the bubbles discharged from the air diffuser 200 are concentrated to the center as the arrow A rises. Therefore, it is difficult for the cross flow flow generated by the rising of the bubbles to occur on the side portion 204 of the membrane unit 202, the film surface cleaning effect by the cross flow flow is reduced, and the film surface is partially blocked. Occlusion of the membrane surface may reduce the effective membrane area and may cause an early increase in filtration pressure.

  As a result of the study by the present inventors, even when the membrane units 208 are installed in multiple stages in the vertical direction as shown in FIG. In this case, the bubbles were already concentrated in the central portion, and the special effect of reducing the distance between the upper and lower membrane units to 50 cm or less was not obtained.

  In addition, as described above, in the lower membrane unit 212, the bubbles are already concentrated in the central portion. Therefore, in the rectifying plate as described in Patent Document 1, the bubbles concentrated in the central portion are left as they are. It is considered that it is difficult to disperse bubbles that have only been supplied to the upper membrane unit 214 and concentrated in the center.

  Therefore, in order to solve the above-mentioned problems of the prior art, the flat membrane filtration device of the present invention is a flat membrane filtration device in which the membrane surface cleaning effect of the upper membrane unit can be effectively obtained when the membrane units are installed in multiple upper and lower stages. The purpose is to provide.

  In the flat membrane filtration device of the present invention, membrane units in which membrane surfaces of a plurality of flat membrane elements are arranged in parallel in a horizontal direction with a predetermined interval are stacked in multiple stages in a processing tank up and down, and from below the membrane unit In a flat membrane filtration apparatus having an air diffuser for diffusing between the flat membrane elements, a rectifying plate is provided horizontally between the upper and lower membrane units, and the rectifying plate has a plurality of openings through which bubbles pass. The opening is formed, and the interval between the openings is widened at the location where the crossflow flow that has passed through the lower membrane unit is concentrated.

In the process of passing through the lower membrane unit, it is inevitable that the crossflow flow generated by the air diffused by the air diffuser is concentrated in the center, but there are a plurality of rectifying plates formed between the upper and lower membrane units as in the above configuration. The cross flow flow bubbles concentrated in the center from the lower membrane unit can collide with the openings of the rectifying plate by widening the gap between adjacent openings where the cross flow flow is concentrated. . The impinging cross-flow bubbles are dispersed again and introduced into the upper membrane unit from the side opening. Therefore, the cleaning effect can be enhanced even with the upper layer side film unit having a stacked structure.
In this case, the rectifying plate is preferably a rectangular flat plate member in plan view.

According to the said structure, after making the bubble of the cross flow flow concentrated in the center which passed the lower stage membrane unit collide easily with a flat member, it can be disperse | distributed again. Further, since the rectifying plate has a flat plate shape, the thickness is small, and the rectifying plate can be attached at an arbitrary position between the upper and lower membrane units. Moreover, space saving in the vertical direction of the entire apparatus can be achieved.
In this case, the rectifying plate has the opening formed in a long hole shape along the laminating direction of the flat membrane element, and the interval between the adjacent openings is stepped from the center of the flat plate member to the side. It is good to make it narrow.

According to the above configuration, the air bubbles colliding at the center portion are laterally reduced by narrowing the interval between the openings on the side surfaces of the rectangular membrane unit in a plan view in a side where bubbles are difficult to hit by the crossflow flow. Move and pass easily. Therefore, the bubbles of the cross flow flow concentrated in the center can be effectively dispersed again.
In this case, in the rectifying plate, the interval between the openings is gradually reduced from the center of the flat plate member toward the four side surfaces.

According to the above configuration, the air bubbles colliding at the central portion move to the four corners by narrowing the interval between the four corner openings of the rectangular membrane unit in a plan view by the cross flow flow, that is, where the bubbles are difficult to hit. And pass easily. Therefore, the bubbles of the cross flow flow concentrated in the center can be effectively dispersed again.
In this case, the opening may be formed in a long hole shape along the laminating direction of the flat membrane elements, and a part of the long hole shape may be formed in a small diameter.

  According to the above configuration, the air bubbles colliding in the central portion are easily moved and passed by expanding the opening ratio of the side surface of the rectangular membrane unit in a side view where the bubbles are difficult to hit by the cross flow flow, that is, in plan view. Become. Therefore, the bubbles of the cross flow flow concentrated in the center can be effectively dispersed again.

  In conventional rectifying plates that are arranged side by side at appropriate intervals, the bubbles in the crossflow flow concentrated in the center pass through the rectifying plate as they are and are introduced into the upper membrane unit. However, according to the flat membrane filtration device of the present invention, since the interval between the openings at the location where the crossflow flow is concentrated is widened, the crossflow concentrated at the center The flow can be collided once and dispersed laterally and introduced uniformly into the upper membrane unit.

It is a figure which shows the structure outline of the flat membrane filtration apparatus of this invention. It is a top view of the baffle plate for flat membrane filtration apparatuses. It is explanatory drawing of the relationship between the total area ( _S1T ) between membranes, and the total area of a rectifying plate opening ( _S2T ), (1) is explanatory drawing of a film | membrane unit, (2) is explanatory drawing of a rectifying plate. . It is explanatory drawing of the modification 1 of the baffle plate for flat membrane filtration apparatuses, (1) is a top view, (2) is the figure which showed the attachment state of the flat membrane filtration apparatus. It is explanatory drawing of the modification 2 of the baffle plate for flat membrane filtration apparatuses, (1) is a top view, (2) is the figure which showed the attachment state of the flat membrane filtration apparatus. It is a graph which shows the relationship between filtration pressure and elapsed days. It is explanatory drawing of the baffle plate of the conventional flat membrane filtration apparatus. It is explanatory drawing of the crossflow flow of a membrane unit.

Embodiments of the flat membrane filtration device of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of a flat membrane filtration device of the present invention.
As shown in the figure, the flat membrane filtration apparatus 10 has a main basic configuration of a treatment tank 12 filled with water to be treated such as sewage and industrial waste water, a membrane unit 20, an air diffuser 30, and a rectifying plate 50. .

  The membrane unit 20 includes a plurality of flat membrane elements 22. The flat membrane element 22 is a flat membrane, and a membrane unit 20 is formed by arranging in parallel at a predetermined interval so that the membrane surfaces of the plurality of flat membrane elements 22 are parallel to each other. Yes.

  The flat membrane filtration apparatus 10 according to the embodiment has a multistage configuration of an upper membrane unit 24 and a lower membrane unit 26 in which two membrane units 20 are stacked in the vertical direction (vertical direction) of the treatment tank 12. Each of the upper membrane unit 24 and the lower membrane unit 26 is connected to a pipe 28, and a suction pump 29 is attached to the middle of the pipe 28. By operating the suction pump 29, filtered water can permeate from the membrane of the flat membrane element 22 constituting the membrane unit 20 and be discharged to the outside through the pipe 28. The upper and lower membrane units 24 and 26 may be covered with a casing (not shown) along the outer periphery (side surface), and an opening through which the crossflow flow passes may be formed on the upper and lower surfaces of the casing.

  A diffuser 30 is attached below the lower membrane unit 26. As an example, the air diffuser 30 may have a configuration in which a plurality of air diffusers are linearly arranged in parallel along the lower side of the flat membrane element 22 similarly to the flat membrane elements 22 arranged in parallel. The air diffuser 30 can supply cleaning air to the membrane unit 20 and prevent solid matter such as sludge from adhering to the membrane surface and blocking it. Further, the air diffuser 30 is configured such that an air diffuser 32 is provided below the pipe, and the amount of air diffused can be arbitrarily adjusted by a pump (not shown).

  The upper and lower membrane units 24 and 26 are arranged in the processing tank 12 with a predetermined interval between the upper and lower units, and a region to be a buffer region 40 for the crossflow flow is formed therebetween. The buffer region 40 is a region that prevents the crossflow flow that has passed through the lower membrane unit 26 from being directly introduced into the upper membrane unit 24. The distance (height) of the buffer region 40 can be set to be substantially the same distance as the distance from the bottom surface of the processing tank 12 to the lower end of the lower membrane unit 26, for example. The buffer region 40 is configured so that the crossflow flow that has passed through the lower membrane unit 26 does not flow out between the upper and lower membrane units 24 and 26. For example, the buffer region 40 may have a configuration in which spacers (not shown) surrounding four side surfaces are formed. Thereby, the inflow of the water from the side between the upper stage and lower stage membrane units 24 and 26, and the outflow to the exterior can be prevented. This spacer may be formed such that the upper end is connected to the lower end of the casing of the upper membrane unit 24 and the lower end is connected to the upper end of the casing of the lower membrane unit 26.

  A rectifying plate 50 for a flat membrane filtration device is attached to the buffer region 40. FIG. 2 is a plan view of a rectifying plate for a flat membrane filtration device. The rectifying plate 50 is a rectangular flat plate member having a size substantially the same as the region projected from the planar view of the membrane unit 20, and has a predetermined thickness.

  The flow straightening plate 50 for the flat membrane filtration device may have rigidity that can withstand the collision of the cross flow flow and the opening may be easily processed. For example, the material is made of stainless steel metal, plastic, or other synthetic resin. Can be used.

  The rectifying plate 50 has a plurality of openings 52 formed on the plate surface. The opening 52 is formed in the shape of a long hole along the stacking direction (arrow X in FIG. 1) of the flat membrane element 22 constituting the membrane unit 20. Further, the opening 52 is formed so that the opening ratio is increased toward the side from the center of the plate surface (the hole pitch is narrowed).

Since the rectifying plate 50 is attached in a cross-sectional direction intersecting with the crossflow flow rising between the upper and lower membrane units 24 and 26, the membrane unit 20 can be effectively cleaned if the crossflow flow is blocked. It is not preferable because it cannot be done. Therefore, the rectifying plate for a flat membrane filtration device of the present invention has an opening so as to satisfy the following relationship.
FIG. 3 is an explanatory diagram of the relationship between the total area between the films (S _1T ) and the total area of the rectifying plate openings (S _2T ), (1) is an explanatory diagram of the membrane unit, and (2) is an explanatory diagram of the rectifying plate. FIG.

First, the total inter-membrane area (S _1T ) of the membrane module 20 through which the crossflow flow passes can be expressed by the following equation.
S _1T = L1 × W1 × n1
Here, L1 is the length of the flat membrane element 22, W1 is the distance between the flat membrane elements 22, and n1 is the number of the flat membrane elements 22 (n = 1, 2, 3,...).

On the other hand, the total area (S _2T ) of the openings 52 of the rectifying plate 50 can be expressed by the following equation.
S _2T = L2 × W3 × n2
Here, L2 is the width of the opening 52, W3 is the length of the opening 52 (the length of the rectifying plate along the laminating direction of the flat membrane elements), and n2 is the number of the openings 52 (n = 1, 2, 3,...). Show.

In order to prevent the crossflow flow from being hindered by the installation of the rectifying plate 50, in this embodiment, the total area between the films (S _1T ) and the total area of the rectifying plate openings (S _2T ) are S _1T ≈S _2T.
It is set to satisfy the relationship. That is, if the total area (S _2T ) of the rectifying plate opening is set to be substantially the same as the total area (S _1T ) between the lower membrane units 26 through which the crossflow flows, the crossflow flow is hindered. There is no.

Further, as shown in FIG. 3B, the pitches (a, b, c, d, e, f...) Between the openings 52 of the rectifying plate 50 are set as follows.
a>b>c>d>e>f>...
That is, the pitches (a, b, c, d, e, f...) Between the openings 52 of the rectifying plate 50 from the central portion (dotted line in the figure) of the flat plate member that forms the rectifying plate 50 where bubbles are concentrated to the side. ) Is set to narrow in steps. As a result, the cross flow flow gathered at the center expands the area where it collides with the member at the center of the rectifying plate, and bubbles easily flow to the side.

Further, the width (L2) of the opening 52 of the rectifying plate 50 is expressed by the following equation in consideration of the problem of blocking the opening 52 due to the entanglement of the fiber contained in the water to be treated and the loss when the bubbles pass. Can do.
0.5W1 <L2 <1.5W1
Here, W1 indicates the distance between the flat membrane elements 22.

  According to such a flat membrane filtration device of the present invention, it is inevitable that the crossflow flow is concentrated in the center in the process of passing through the lower membrane unit 26, but the upper and lower membrane units 24 are configured as described above. , 26, a plurality of openings 52 are provided in the rectifying plate 50, and the interval between adjacent openings 52 where the crossflow flow is concentrated is widened, so that the crossflow flow concentrated in the center from the lower membrane unit 26 is Bubbles can collide. The collided airflows of the cross flow flow are dispersed again and introduced into the upper membrane unit 24 from the side openings 52. Therefore, the cleaning effect of the upper membrane unit 24 can be enhanced even with the membrane unit 20 having a structure in which the upper and lower layers are laminated.

  Further, the bubbles of the cross flow flow concentrated in the center that have passed through the lower membrane unit 26 can be easily collided and then dispersed again. Further, since the rectifying plate 50 has a flat plate shape, it is thin and can be attached at an arbitrary position between the upper and lower membrane units 24 and 26. Moreover, space saving in the vertical direction of the entire apparatus can be achieved.

  FIG. 4 is an explanatory view of a first modification of the rectifying plate for the flat membrane filtration device, (1) is a plan view, and (2) is a diagram showing an attached state of the flat membrane filtration device. As shown in the figure, the rectifying plate (rectifying plate 150) for the flat membrane filtration device of Modification 1 has the opening 152 along the stacking direction of the flat membrane elements 22 constituting the membrane unit 20 (arrow X in FIG. 1). It has a long hole shape. The opening 152 is formed so that a part thereof has a small diameter. Specifically, the diameter of the central portion (dotted line in the figure) of the opening 152 where the crossflow flow is likely to concentrate is made smaller and the diameter becomes larger toward the side (end). The openings 152 are formed so that the interval (pitch) between the openings gradually decreases from the center of the flat plate member to the side.

  According to the above configuration, the air bubbles colliding in the central portion are moved and passed by increasing the opening ratio of the side surface of the rectangular membrane unit 20 in a side view where the bubbles are difficult to hit by the crossflow flow, that is, in plan view. It becomes easy to do. Therefore, the bubbles of the cross flow flow concentrated in the center can be effectively dispersed again.

  FIG. 5 is an explanatory view of Modification 2 of the rectifying plate for the flat membrane filtration device, (1) is a plan view, and (2) is a diagram showing an attached state of the flat membrane filtration device. As shown in the figure, the flow straightening plate (flow straightening plate 250) for the flat membrane filtration device of Modification 2 has openings 252 formed in a lattice shape. Specifically, the rectifying plate 250 has a configuration in which two flat plate members are laminated. The two flat plate members include a flat plate member in which an opening A (solid line in FIG. 5 (1)) is formed in a long hole shape along the laminating direction (X direction) of the flat membrane element as shown in FIG. It is composed of a flat plate member in which an opening B (dotted line in FIG. 5 (1)) is formed in a long hole shape along a direction (Y direction) orthogonal to the stacking direction of the membrane elements. By laminating these two flat plate members, the portion where the opening in the X direction and the opening in the Y direction overlap (the hatched portion in FIG. 5A) becomes the opening 252 through which the crossflow flow passes. Each of the openings A and B is formed so that the pitch between the openings becomes narrower from the center of the flat plate member to the side. Such a rectifying plate 250 of Modification 2 has a configuration in which the distance between the openings 252 is gradually reduced from the center of the flat plate member toward the four side surfaces.

  According to the said structure, the space | interval between the opening of the corner | angular part which a bubble cannot hit easily, ie, planar view, is rectangular with the crossflow flow. That is, by making the aperture ratios at the four corners larger than the central portion of the rectifying plate 250, the bubbles collided at the central portion move to the four corners and pass easily. Therefore, the bubbles of the cross flow flow concentrated in the center can be effectively dispersed again.

  FIG. 6 is a graph showing the relationship between filtration pressure and elapsed days. The horizontal axis of the graph indicates the number of days (days) elapsed, and the vertical axis indicates the filtration pressure (kPa) of the suction pump 29 on the pipe 28 connected to the membrane unit 20. In the figure, the broken line indicates the case without the rectifying plate, and the solid line indicates the case with the rectifying plate. In the case of no rectifying plate, the filtration pressure tends to increase with the passage of days, and the filtration pressure increases to 17 kPa on the 50th day of operation.

On the other hand, when there is a rectifying plate, the filtration pressure slightly rises from about 6 kPa at the initial stage of operation. Thereafter, the filtration pressure is maintained at about 8 kPa even after 50 days have elapsed. Thus, in the case with the rectifying plate, the filtration pressure after 50 days can be suppressed to about half the value compared with the case without the rectifying plate.
Accordingly, the dispersion of the cross flow flow by the rectifying plate has a cleaning effect on the membrane element, and can effectively prevent an increase in the filtration pressure accompanying the blockage of the membrane surface.

  In the present embodiment, the configuration in which the membrane units 20 are stacked in two upper and lower stages has been described. The structure may be different.

DESCRIPTION OF SYMBOLS 10 ......... Membrane filtration apparatus, 12 ......... Treatment tank, 20 ......... Membrane unit, 22 ......... Flat membrane element, 24 ......... Upper membrane unit, 26 ......... Lower membrane unit, 28 ... ... Piping, 29 ......... Suction pump, 30 ......... Air diffuser, 32 ......... Air diffuser, 40 ......... Buffer area, 50, 150, 250 ......... Rectifying plate, 52, 152, 252 ... ... Opening, 100 ......... Rectifying plate, 102 ......... Rectifying plate member, 104 ......... Partition member, 200 ......... Air diffuser, 202 ......... Membrane unit, 204 ......... Side, 208 ......... Membrane unit, 210... Upper and lower membranes, 212... Lower membrane unit, 214.

Claims (5)

Membrane units in which the membrane surfaces of a plurality of flat membrane elements are arranged in parallel in a horizontal direction with a predetermined interval are stacked in a vertical direction in a processing tank, and diffused between the flat membrane elements from below the membrane units. In a flat membrane filtration device equipped with a diffuser,
A rectifying plate is provided in the horizontal direction between the upper and lower membrane units,
The rectifying plate forms a plurality of openings through which air bubbles pass, and a space between the openings is widened at a location where the crossflow flow that has passed through the lower membrane unit is concentrated.   The flat membrane filtration device according to claim 1, wherein the rectifying plate is a flat plate member that is rectangular in plan view.   In the rectifying plate, the opening is formed in a long hole shape along the laminating direction of the flat membrane element, and the interval between the adjacent openings is gradually reduced from the center of the flat plate member to the side. The flat membrane filtration device according to claim 2.   The flat membrane filtration device according to claim 2, wherein the rectifying plate narrows the interval of the openings stepwise from the center of the flat plate member toward four side surfaces.   The flat membrane filtration device according to claim 3, wherein the opening is formed in a long hole shape along a stacking direction of the flat membrane elements, and a part of the long hole shape is formed in a small diameter.

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