Membrane separation device

A membrane separation device is provided with membrane modules comprising multiple membrane elements, a frame body accommodating the membrane modules stacked in multiple stages, a stopper for closing an end portion of the frame body to prevent the membrane modules accommodated in the frame from being released, and elastic members which, arranged in a state of elastic deformation in the vertical direction in the frame with the end portion of the frame being closed, suppress vertical vibration of the membrane modules accommodated in the frame, whereby making it possible to avoid vibration of the membrane modules inside the frame body even if the volume of the membrane modules accommodated in the frame body varies.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a membrane separation device using activated sludge process suitable for water treatment, such as sewage treatment and wastewater treatment.

2. Description of the Related Art

Conventionally, in sewage treatment and wastewater treatment employing the activated sludge process, a membrane separation device of submerge type is used for solid-liquid separation which is necessary in the treatment process.

International Patent Publication No. WO2009/118785 discloses a pair of liquid collection unit, a plurality of membrane elements which are arranged between the pair of liquid collection units, and a membrane module having such a structure that filtered liquid which has passed through the membrane elements is collected in the liquid collection units.

The membrane modules are stacked in multiple stages and connected to the liquid collection units which are arranged adjacent thereto in a vertical direction such that filtered liquid is flow through between the liquid collection units.

A frame body accommodating the stacked membrane modules having multiple stages is used in order to maintain the orientation and connection state of each of the membrane modules and integrally install the membrane modules when the stacked membrane modules having the multiple stages are submerged into a biological treatment tank and the like and solid-liquid separation operations are performed.

It is preferable that the membrane modules, including the liquid collection units, are made of a resin to reduce the weight, while the frame body is made of a metal in many cases so as to provide a sufficient strength so as to hold each of the membrane modules in a stable position when it is disposed and submerged in the biological treatment tank and the like, as well to allow the membrane modules accommodated in the frame body to be integrally submerged into or taken out from the biological treatment tank and the like. Accordingly, the membrane modules and the frame body are made of different materials having different thermal expansion coefficients, and thus it is necessary to set the size of the frame body considering the variations in the ambient temperature.

In addition, when such a membrane separation device is submerged into the biological treatment tank, the volume of the membrane modules made of resin might be increased by absorbing water in the tank, and thus it is also necessary to set the volume of the metal frame body considering the expansion of the volume of the membrane module in advance.

Furthermore, when such a membrane separation device is transported by loading in a bulk container and if such a container transportation occurs under tropical regions right on the equator, for example, the temperature inside the container rises significantly, thereby causing such a phenomenon in which resin casings constituting the liquid collection units of the membrane modules expand under a high temperature and then shrink into a size smaller than the original size when the temperature returns to a room temperature, whereby the volume of the membrane modules tends to become smaller than the volume of the metal frame body.

Therefore, it is possible to set the size of the frame body considering the shrinking effect as described above, by performing a so-called annealing such that the membrane modules are exposed to a high temperature environment in advance so as to remove the molding distortion of the resin casings and the like. However, it is not practical since the manufacturing cost would increase remarkably, if the manufacture process should include such a process for exposing all of the membrane modules to a high temperature environment.

In such a situation, if the membrane separation device in which the volume of the membrane modules stacked in multiple stages in a frame body is smaller than that of the frame body is submerged and disposed in a biological treatment tank, and then a filtering operation is performed by aeration using a diffuser device provided below the membrane separation device, the membrane modules vibrate in a vertical direction within the frame body due to a upward flow caused by the aeration. The resulting wear and tear would cause problems of a considerably shortened life of the membrane modules.

SUMMARY OF THE INVENTION

In the view of the problems as described above, an objective of the present invention is to provide a membrane separation device which can avoid vibration of the membrane modules inside the frame body even if the volume of the membrane modules accommodated in the frame body varies.

In order to achieve the above-mentioned objective, the first characteristic structure of the membrane separation device in accordance with one embodiment of the present invention is that it includes a plurality of membrane modules each including a plurality of membrane elements, a frame body accommodating the membrane modules by stacking the membrane modules in multiple stages, a closing member closing an end portion of the frame body so as to prevent the membrane modules accommodated in the frame body from being released, and an elastic member disposed in the frame body such that the elastic member is elastically deformed in a vertical direction in a state where the end portion of the frame body is closed.

Since the membrane modules stacked in multiple stages are accommodated in the frame body, and the elastic member is disposed in the frame body such that the elastic member is elastically deformed in a vertical direction when the end portion of the frame body is closed, even if the dimensions of the membrane modules of the multiple stages are made smaller in advance than the dimensions of the frame body, or the membrane modules shrink after manufacturing thereof, vibration of the membrane modules in the vertical direction within the frame body can be effectively suppressed by the elastic member, thereby making it possible to stably operate the membrane modules for a long period of time.

It should be noted that the elastic member is not limited to a specific material or shape so long as the elastic member can prevent vibration of the membrane modules in the vertical direction. For example, the elastic member can appropriately employ a spring made of a metal of plastic, an elastically deformable resin member or natural rubber member, and the like.

The second characteristic structure in accordance with one embodiment of the present invention is that the elastic member is disposed between the membrane modules, in addition to the first characteristic structure as described above.

According to the above-described structure, not only the vibration of the entire membrane modules inside the frame body is suppressed, but also abrasion caused between the membrane modules is reliably prevented by the elastic member even if a slight vibration occurs, thereby making it possible to stably operate all of the membrane modules for a long period of time.

The third characteristic structure in accordance with one embodiment of the present invention is that it is further provided with a coupling portion configured to couple and fix the adjacent membrane modules each other in the vertical direction, and a coupling margin of the coupling portion and a thickness of the elastic member are set such that a coupling state of the coupling portion is maintained regardless of an extent of elastic deformation of the elastic member, in addition to the second characteristic structure as described above.

The stacking position of the membrane modules stacked in the multiple stages in the frame body is stably maintained by the coupling portion configured to couple and fix the adjacent membrane modules each other in the vertical direction. Since the coupling margin of the coupling portion and the thickness of the elastic member are set such that the coupling state of the coupling portion is maintained regardless of the extent of the elastic deformation of the elastic member which is disposed between the membrane modules, it is possible to reliably avoid such an undesirable situation that the coupling of the coupling portion in the frame body releases and the stacking position of the membrane modules breaks. For example, even if each of the membrane modules shrinks and becomes smaller than its original dimensions under the certain circumstances as described above, it is possible to appropriately suppress the vibration, as well as reliably avoiding such an undesirable situation in which the stacked position of the membrane modules brakes. It is further preferable if the coupling margin of the coupling portion and the thickness of the elastic member are set such that the coupling state of the coupling portion is also maintained when the elastic member is in an uncompressed state without elastic deformation.

The fourth characteristic structure in accordance with one embodiment of the present invention is that each membrane module includes a plurality of membrane elements, each including a membrane support body in a form of a flat panel or sheet and a separation membrane arranged on a front surface and a rear surface of the support body, the plurality of membrane elements being arranged in a longitudinal position such that the separation membranes thereof face one another with a fixed distance provided therebetween; a liquid collection unit is provided in a traverse direction side portion of each of the membrane elements, where the liquid collection portion is configured to collect filtered liquid which has permeated from each of the membrane elements; the coupling portion includes an opening and an insertion portion, where the opening is in communication with the liquid collection unit of each of the adjacent membrane modules such that the filtered liquid flows therethrough, and the insertion portion is configured to engage with an inner wall of the opening and fit therein in a liquid-tight state; and a length of the insertion portion to maintain the liquid-tight state defines the coupling margin, in addition to any one of the above-mentioned first to third characteristic structures.

According to such structures described above, the stacked membrane modules are coupled to each other in the vertical direction by opposing surfaces of the liquid collection unit thereof so as to maintain the stacking position via the coupling portion, while the filtered liquid collected in each of the collection units can flow through the coupling portions which are coupled in the liquid-tight state. In addition, since the length of the insertion portion that maintains the liquid-tight state defines the coupling margin, the vibration is appropriately suppressed and the liquid-tight state is also appropriately maintained, even if each of the membrane modules shrinks and becomes smaller than its original dimensions under certain circumstances.

The fifth characteristic structure in accordance with one embodiment of the present invention is that the elastic member which is formed of a rubber sheet configured to elastically deform in a thickness direction thereof is disposed between opposing surfaces of the vertically adjacent membrane modules, where the elastic member includes convex portions having a thickness greater than the thickness of the elastic member or concave portions or holes having a thickness smaller than the thickness of the elastic member, in addition to any one of the above-mentioned second to fourth characteristic structures.

In order to place the elastic member having a sheet-like shape between the adjacent membrane modules and to maintain the elastic body in a elastically deformed state, it is necessary to press the membrane modules with a rather large force, and thus it is necessary for the closing member which closes the frame body and the end portion of thereof to have a sufficient strength. This may limit the degree of freedom in designing the frame body, and a required thickness of the rubber sheet may disadvantageously increase the material cost thereof. However, by employing the structures described above, the rubber sheet which is provided with the thicker convex portions or the thinner concave portions or hole portions elastically and partially deforms between the opposing surfaces of the vertically adjacent membrane modules so as to suppress the vibration, and thus the required pressing force onto the membrane modules to suppress the vibration can be reduced without extremely increasing the strength of the closing member which closes the frame body and the end portion thereof, as well as the material cost for the rubber sheet can be reduced.

As described above, according to the present invention, it became possible to provide a membrane separation device in which vibration of the membrane modules in the frame body can be avoided even when the volume of the membrane modules accommodated in the frame body varies.

DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Hereafter, the membrane separation device in accordance with the present invention is described. As shown inFIG. 1andFIG. 2, a membrane separation device10includes five rows of membrane module groups laterally arranged in a frame body11and submerged into liquid to be treated in a biological treatment tank, where membrane modules20are longitudinally arranged to form an eight-stage stack in each membrane module group.

The frame body11is formed of a metal and includes a lower frame11, a side frame11b, an upper frame11c, and the like, since it is necessary for the frame body11to have a sufficient strength such that each of the membrane modules20is held in a stable position when the membrane modules20are arranged and submerged in the biological treatment tank, as well as the membrane modules20accommodated therein are integrally submerged into or taken out of the biological treatment tank.

The membrane modules20are made of a resin and the like. Because the volume of the membrane modules20will increase by absorbing water in the biological treatment tank, the frame body11is manufactured to have dimensions that take into account the expansion of the volume of the membrane modules20.

A diffuser air supply pipe12is provided under the membrane module20at the bottom of the stack in the biological treatment tank, and diffusion air supplied by the diffuser air supply pipe20causes an upward flow of the liquid to be treated between a plurality of membrane elements21which are in a longitudinal position and laterally arranged in a horizontal direction in each of the membrane module20. The treated liquid which has been filtered through the membrane surface of each membrane element21is led to the outside of the tank via a liquid collection pipe13.

The liquid collection pipe13is in communication with a treated liquid delivery pipe (not shown) which leads to a treated liquid tank which is disposed outside the biological treatment tank, and a pumping apparatus is installed in a middle of the pipeline. The diffuser air supply pipe12is in communication with an air supply source such as a blower or a compressor.

The upper frame11cis provided with a stopper (closing member)14which closes an upper end portion of the frame body11such that the membrane module groups accommodated therein are not released from the upper end portion of the frame body11. The stopper14is made of a metal similar to the frame11and formed in a flat plate shape, and is fastened with bolts to the upper frame11cwhich is disposed on the front and rear sides of each top-stage membrane module20of each of the membrane module groups which are laterally arranged in five rows.

An elastic member15is disposed between the membrane modules20which are stacked in the frame body11. The top-stage membrane modules20is pressed with a large force by the stopper14, and the elastic body15arranged between the membrane modules20is in an elastically deformed state, that is, in this case, in a compressed state, thereby suppressing vibration in a vertical direction of the membrane modules20accommodated in the frame body11due to the upward flow caused by aeration of the diffuser device12.

The membrane modules20are explained below. As shown inFIG. 3A, each membrane module20includes a pair of front and rear liquid collection units22, a pair of right and left cover members23, and a plurality of membrane elements21. The plurality of membrane elements21are arranged in a longitudinal position with a fixed distance therebetween and disposed in a space defined by the pair of front and rear liquid collection units22and the pair of right and left cover members23such that membrane surfaces are facing one another.

As shown inFIG. 3B, each membrane element21is formed of a filter plate21ain a form of a flat panel as a membrane support body, and a separation membrane21b, where the separation membrane21bis disposed on both sides of the filer plate21a.

The liquid collection unit22is hollowed out such that the treated liquid which has been filtered through the separation membrane21bis guided to the inside of the liquid collection unit22through liquid collection passages formed in the filter plate21a.

A filter plate21ais formed of ABS resin and the like, and the separation membrane21bis formed by applying and impregnating a porous resin into a non-woven fabric as a base material. The filter plate21ais not limited to a rigid material such as ABS resin, but may be formed using a flexible material such as a sheet-shaped non-woven fabric or a net.

The collection units22and the cover members23are obtained by injection molding of ABS resin, polypropylene, or the like. It is preferable that the collection units22are made of a transparent or translucent material such that it may be easy to check if the sludge flows into the collection units22due to damages to the separation membrane21band the like.

Each of the liquid collection units22has a coupling portion24provided between and connecting and fixing the membrane modules20which are adjacent in the vertical direction.

The coupling portion24includes an opening26which is in communication with the respective liquid collection units22of the vertically adjacent membrane modules20such that the filtered liquid flows therethrough between the liquid collection units22, and an insertion portion25which is engaged with an inner wall of the opening26and fitted therein in a liquid-tight state.

As shown inFIG. 4, the insertion portion25is liquid-tightly engaged with the opening26which is formed in the liquid collection unit22of the membrane module20stacked immediately thereabove, thereby providing communication between the adjacent liquid collection units22in the vertical direction. Consequently, the membrane modules20stacked inside the frame body11are coupled to one another at respective opposite surfaces of the corresponding liquid collection units22adjacent in the vertical direction and stably held in their position via the coupling portions24, while the filtered liquid which is collected from the membrane element21of each membrane module20into the collection unit22is allowed to flow through the coupling portions24which are coupled in a liquid-tight state. The filtered liquid passing through the coupling portions24is led out to the collection pipe13which is disposed in the vicinity of the upper frame11cand inside the lower frame11a.

The elastic member15is explained below. As shown inFIG. 3C, the elastic member15is formed of a rubber sheet which is elastically deformable in a thickness direction thereof and formed to have a size similar to that of an upper surface of the liquid collection unit22.

Convex portions15awhich have a thickness greater than that of the rubber sheet are formed on the surface of the rubber sheet in a dispersed manner, and a cut-out portion having a U-shape is formed in a center portion of the rubber sheet such that the insertion portion25is inserted therein when the rubber sheet is disposed between the opposing surfaces of the liquid collection units22of the membrane modules20adjacent in the vertical direction.

The elastic member15is disposed between the opposing surfaces of the liquid collection unit22of the membrane modules20adjacent in the vertical direction. The coupling margin of the coupling portion24and the thickness of the elastic member15are set such that the insertion portion25remains inserted in the opening26in a liquid-tight state such that the coupling state of the coupling portion24is maintained regardless of the extent of the elastic deformation of the elastic member15.

For example, the coupling margin of the coupling portion24and the thickness of the elastic member15are set such that the insertion portion25remains inserted in the opening26in a liquid-tight state such that the coupling state of the coupling portion24is maintained, whether the stopper14is fastened with the bolts so as to press the top-stage membrane module20with a large force such that the elastic member15is in an elastically deformed state as shown inFIG. 5A, or the elastic member15is in a non-compressed state without elastic deformation, as shown inFIG. 5B, as the total height of the eight stacked membrane modules20becomes too smaller than the accommodation height of the frame body11due to the shrinking of the membrane modules such that tightening the bolts cannot make the stopper14press the top membrane module20with a sufficiently large force.

In addition, a packing such as an O-shaped ring27is disposed on an outer periphery of the insertion portion25such that the packing is in pressure contact with the inner peripheral surface of the opening26. However, the structure to form the liquid-tight state is not limited to this specific structure.

The coupling margin of the coupling portion24is defined by the length of the insertion portion25to maintain the liquid-tight state even when the elastic member15is in a non-compressed state, and the thickness of the elastic member15is defined by the weight of the membrane module20, the material and dimensions of the rubber sheet, the number and size of the convex portions15a, and the like.

The elastic member15may have, instead of the convex portions15aformed on the surface of the rubber sheet, concave portions or holes which have a thickness smaller than the thickness of the rubber sheet and formed on the rubber sheet in a distributed manner. In addition, it is possible to form convex portions, concave portions, and holes in combination.

Furthermore, the elastic member15may be formed of, instead of a rubber sheet, a plurality of cylindrical rubber members corresponding to the convex portions15awhich are arranged in a distributed manner.

In order to place the elastic member15having a sheet-like shape between the adjacent membrane modules20and to maintain the elastic member15in a elastically deformed state, it is necessary to press the membrane modules20with a rather large force, and thus it is necessary for the stopper14which closes the frame body11and the end portion thereof to have a sufficient strength. This may limit the degree of freedom in designing the frame body11, and the required thickness of the rubber sheet may disadvantageously increase the material cost.

However, the rubber sheet which is provided with the thicker convex portions or the thinner concave portions or holes formed thereon in a distributed manner partially and elastically deforms between the opposing surfaces of the membrane modules20adjacent in the vertical direction so as to suppress the vibration, and thus it is possible to reduce the required pressing force onto the membrane modules20to suppress the vibration without extremely increasing the strength of the stopper14which closes the frame body and the end portion thereof, while the material cost for the rubber sheet can also be reduced.

As described above, since the elastic member15is disposed, in an elastically deformed state, between the membrane modules20which are stacked in a state in which the upper end portion of the frame body11is closed by the stopper14, even if the height of the group of the membrane modules is formed in advance to be smaller than the accommodation height from the lower frame11ato the stopper14provided on the upper frame11c, or even if the membrane modules shrink after manufacturing thereof, the vibration in the vertical direction of the membrane modules20within the frame body member11is effectively suppressed by the elastic member15such that the membrane modules20can be stably operated for a long pried of time.

Furthermore, not only the vibration of the entire membrane modules20inside the frame body11is suppressed, but also, if a slight vibration occurs, abrasion caused between the membrane modules20is reliably prevented by providing the elastic member15between the membrane modules20, and thus it possible to stably operate all of the membrane modules20for a long period of time.

Furthermore, when the membrane separation device is transported by loading in a bulk container and the like, more specifically, when such container transportation occurs in tropical regions right on the equator, for example, the temperature inside the container rises significantly, thereby causing such a phenomenon in which the membrane modules20constituting the liquid collection units of the membrane modules expand under such a high temperature, and then shrink into a size smaller than the original size when the temperature returns to a room temperature, resulting in a smaller volume than the volume of the metal frame body. Even in such a case, vibration of the membrane modules20is properly suppressed during operation of the membrane separation device10so as to reliably avoid an undesirable situation such as collapsing of the stacking position of the membrane modules20due to release of the coupling state of the coupling portions24inside the frame body11.

The membrane separation device according to another embodiment of the present invention is described below. In the embodiment described above, the elastic member15is made of a rubber sheet in a flat plate shape and disposed between the membrane modules20. However, the shape and the location of the elastic member are not limited to these. For example, an elastic member of a block shape may be disposed between the top-stage membrane module20and the stopper14, or between the bottom-stage membrane module20and the lower frame11a. Any structure can be used so long as it can prevent vibrations of the membrane modules20within the frame body11during the operation of the membrane separation device.

In addition, the elastic member is not limited to a specific material or shape so long as it can prevent vibration of the membrane modules in the vertical direction, and may be a spring such as a coil spring made of a resin or metal or a leaf spring. The elastic member may also employ other elastically deformable materials such as synthetic rubber or natural rubber.

Each embodiment described above is an example of the present invention, and thus the present invention is not limited by the description. A design of the specific structure of each part is appropriately changed so long as the function and effects of the present invention can be achieved.