JP5530862B2 - Membrane element - Google Patents

Description

  The present invention relates to a flat membrane element used for solid-liquid filtration separation in wastewater treatment or the like.

  2. Description of the Related Art A membrane filtration apparatus in which a plurality of flat plate membrane elements are immersed in a treatment tank is known for removing suspended substances from industrial wastewater and separating activated sludge in organic wastewater treatment. By setting the inside of the membrane element to suction negative pressure, the water to be treated passes through the filtration membrane from the outside to the inside of the membrane element, the suspended matter is captured by the filtration membrane, and the membrane permeated water is externally supplied from the membrane element water collection port. To be taken out. The membrane surface deposit captured by the filtration membrane is separated from the membrane surface by the flow of treated water parallel to the membrane, which is generated by bubbles from the air diffuser provided below the membrane element. Further, the filtration membrane is cleaned regularly or irregularly by backwashing in which a fluid flows from the inside of the membrane element to the outside.

  A membrane element is often used in which filtration membranes are disposed on both sides of a rectangular flat plate made of resin through spacers such as a fiber sheet serving as a flow path for permeated water and the periphery is sealed.

  Patent Document 1 discloses a membrane element that uses a hollow structure filter plate with micropores on its surface and provides a support material inside the hollow structure to reduce the weight while ensuring the rigidity of the filter plate. Has been. By using the hollow space as the permeate flow path, the membrane permeate flows from the flow path secured by the spacer through the micropores on the surface of the filter plate to the internal flow path, thereby increasing the permeate flow rate. There is also disclosed a membrane element in which a micro groove for guiding membrane permeated water is formed on the entire surface of the filter plate and the spacer is removed.

  Patent Document 2 discloses a membrane element that uses a filter plate having a hollow structure having a micropore on the surface and has a support material, and that excludes a spacer, as in Patent Document 1. Further, a membrane element that can be backwashed by directly attaching a filtration membrane around the micropores to the filter plate is disclosed.

  In Patent Document 3, a filter plate having grooves formed on the surface to serve as a flow path for membrane permeated water is used. By joining the filter membrane and the filter plate not only at the peripheral part but also at the central part, the element becomes large. However, there has been disclosed a membrane element that does not break due to excessive swelling of the filtration membrane during backwashing.

JP-A-7-194947 Japanese Patent Laid-Open No. 8-10587 JP 2008-49239 A JP 2006-231139 A

  However, even if a hollow structure filter plate with micropores on the surface is used, the flow path formed by spacers such as fiber sheets has a small flow path cross section, so that the membrane permeated water flows to the micropores. Resistance was large and there was a limit to increase in permeate flow rate. When the spacer was not used, the filtration membrane was brought into close contact with the surface of the filter plate due to the negative suction pressure. As a result, the cross section of the flow path was further reduced, and the effect of increasing the amount of water flow was small. On the other hand, even if an attempt is made to provide a large number of holes on the surface of the filter plate, there is a problem that the rigidity of the filter plate is lowered when the interval between the holes is reduced. Moreover, in the method of forming a running water groove on the surface of the filter plate, there is a problem that the groove portion becomes a fold and the filter plate is easily bent.

  Accordingly, an object of the present invention is to provide a membrane element that is lightweight, has sufficient rigidity, and has a large permeate flow rate.

The membrane element of the present invention is a membrane element having a filtration membrane and a filter plate that supports the filtration membrane,
The surface of the filter plate has a network structure of substantially the entire portion covered with the filtration membrane,
Inside the filter plate, a running water space is formed inside the mesh structure ,
In the flowing water space, a support material that vertically supports the surface having the mesh structure is provided with an interval between the support materials,
The filtration membrane is joined to the portion of the filter plate where the support material is located,
In the flowing water space, in addition to the support material to which the filtration membrane is bonded, a support material that vertically supports the surface having the mesh structure and is not bonded to the filtration membrane is provided between the support materials. characterized in that was.

  According to the membrane element having the above configuration, the filter plate is hollow and the surface has a network structure, so that the weight is reduced. The membrane permeated water that has passed through the filter membrane quickly passes through the network structure to the flowing water space inside the filter plate. Therefore, the amount of running water can be increased.

  As an embodiment of the present invention, it is preferable that the opening of the mesh structure is formed so as to gradually decrease from the outer surface of the filter plate toward the inside along the thickness direction of the filter plate. Alternatively, the mesh structure is integrally formed, and the opening of the mesh structure is formed so as to have a portion that gradually decreases from the outer surface of the filter plate toward the inside along the thickness direction of the filter plate. It is preferable. If it does in this way, the rigidity of a filter plate can be enlarged more, maintaining the aperture ratio in the filter plate surface which influences the flow volume of permeated water large.

  As another embodiment of the present invention, the opening ratio of the network structure is preferably 50% or more on the outer surface of the filter plate. Further, it is preferable that the opening of the mesh structure has a width of 0.2 mm or more in a portion having the smallest cross-sectional area. Furthermore, it is preferable that the opening shape of the mesh structure has a width of 15 mm or less on the outer surface of the filter plate.

In embodiments of the present invention, wherein the flowing water space, spaced a support you support surface vertically with the network structure, the filtration membrane to the location part of the support of the filter plate surface Are joined . Moreover, it is preferable that the space | interval of the junction part of the said filtration membrane and a support material is 60 mm or more and 150 mm or less. If it does in this way, it can be set as the membrane element which has the intensity | strength which can be backwashed even if it is large sized, maintaining the effect of this invention that it is lightweight, is rigid, and there is much flowing water. Furthermore, since the amount of flowing water during backwashing is large due to the stitch structure of the present invention, the membrane surface can be effectively washed.

In embodiments of the present invention, the filtration membrane in addition to the support member joined, between said support member, providing a supporting member in which the filtration membrane is not bonded. The support material to which the filter membrane is not joined improves the strength of the filter plate during suction filtration.By optimizing the design with the mesh structure of the filter plate, etc., a lighter membrane element and can do.

  As another embodiment of the present invention, the filter plate is preferably produced by joining two parts by injection molding. Since the mesh structure portion and the peripheral edge portion of the filter plate are integrally formed, the strength of the filter plate is improved, and particularly the strength at the time of backwashing in which pressure is applied from the inside is improved. Moreover, the freedom degree of shape design can be increased.

  As described above, according to the present invention, it is possible to provide a membrane element that is lightweight, has sufficient rigidity, and has a large permeate flow rate. Further, by increasing the mesh opening ratio on the outer surface of the filter plate, it is possible to increase the permeate flow rate without arranging a spacer. Further, by providing a filter membrane fixing support material and joining the filter membrane to the filter plate even at the central portion of the filter plate, it is possible to obtain a membrane element having strength that can be backwashed even if it is large. Moreover, the intensity | strength of a filter plate can be improved by joining two components by injection molding and forming a filter plate.

The perspective view of the membrane element which concerns on this invention Sectional view of the membrane element according to the present invention Sectional drawing of the mesh structure portion of the filter plate according to the present invention Cross-sectional view showing the dent of the filtration membrane

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view of a membrane element according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, and the scale is not accurate because the thickness direction is enlarged for convenience of explanation. The filtration membrane 1 is arranged on both surfaces of the flat filter plate 2. The filter plate 2 has a hollow structure. The surface on which the filtration membrane 1 is disposed has a substantially uniform network structure (21). The center part of the filter plate sandwiched between the mesh structure surfaces 21 on both sides of the filter plate 2 forms a flowing water space 26 having a substantially constant thickness, and supports 22 and 23 (hereinafter “ribs”) that support the mesh structure surface vertically. Called). There is no opening in the end face 25. The filter membrane 1 is welded to the filter plate peripheral edge 24 so as to cover all the openings of the mesh structure surface 21 of the filter plate (31). As a result, the treatment liquid always passes through the filtration membrane 1 and enters the element from the outside. The permeated water is collected outside through a water collection port 4 provided in a part of the filter plate. Further, the filtration membrane 1 is welded to the filter plate at a position opposite to the ribs 22 even in the central portion of the filter plate other than the filter plate peripheral portion 24 (32). This prevents the filtration membrane from swelling more than necessary during backwashing and preventing damage.

  As the filtration membrane in this embodiment, a non-woven fabric made of synthetic resin was used as a base material, and a polymer membrane layer having a large number of micropores having an average pore diameter of 0.4 μm on both surfaces was used. From the definition of JIS K 3802, it is called a microfiltration membrane. The kind of filtration membrane is not limited to this, and various membranes of a flat membrane type can be used including an ultrafiltration membrane for separating smaller solids.

  The filter plate 2 in the present embodiment has a substantially rectangular shape, and the size is 500 mm × 1000 mm × thickness 6 mm. The shape of the filter plate for carrying out the present invention may be rectangular, circular, or other various shapes, but it needs to be at least flat. There is no particular limitation on the size of the filter plate, but it is preferable that the filter plate is large as a product for which effects such as light weight and high rigidity according to the present invention are particularly desired. When the filter plate shape is rectangular, the short side is preferably 400 mm or more.

  The filter plate 2 in this embodiment was produced using ABS resin. Various materials can be used for the filter plate as long as the structure of the present invention can be realized, but it is preferable to use a thermoplastic resin because of its low specific gravity and good moldability. It is more preferable to use a thermoplastic resin having a low point. Moreover, it is preferable to use a resin that can be welded at a low temperature even when the filter plate and the filter membrane are joined by a thermal welding method to be described later. Examples of such resins include PVC resin and ABS resin.

  The filter plate 2 in the present embodiment is produced by injection-molding two parts divided in half in the thickness direction, and bonding the entire periphery of the filter plate peripheral portion 24 and a filtration membrane fixing rib 22 described later with an adhesive. (27, 28). Various known methods can be adopted as the forming method. As shown in Patent Documents 1 and 2, it is possible to join the hollow body component and the component that closes the open end thereof. However, it is preferable that the mesh structure surface 22 and the peripheral edge portion 24 can be integrally formed because the strength of the filter plate during backwashing, in which pressure is applied from the inside of the element, is dramatically improved. For example, injection molding, press molding, vacuum molding, and the like can be given. In particular, it is particularly preferable to use an injection molding method capable of integrally molding the mesh structure surface 21, the peripheral edge portion 24, the ribs 22 and 23, the water collection port 4, and other peripheral structure for fixing the membrane element.

  In order to increase the effective use area of the filtration membrane 1, the surface of the filter plate 2 has a network structure 21 in substantially the entire portion covered with the filtration membrane 1. Here, “substantially the whole” means that the inside of the portion where the filtration membrane and the filter plate of the peripheral portion 24 are joined (filtration membrane—filter plate peripheral portion joining line 31), and the filtration membrane in consideration of the joining position accuracy in the manufacturing process. When the filtration membrane fixing rib 22 is further provided except for the vicinity of the filter plate peripheral edge joining line 31, it means that the joining portion (filtration membrane-filtration membrane fixing rib joining line 32) and the vicinity thereof are excluded. .

  In this embodiment, the shape of the mesh opening is a square, and this is arranged in a lattice form having an angle of 45 degrees with the side of the outer periphery of the filter plate at a cycle of 2.5 mm. However, the shape and arrangement are not limited to this. The shape can be a square, a rectangle, various polygons, a circle, a long hole, etc. The array can be a lattice, a staggered, a turtle shell, etc., and the angle of the array can be set freely it can.

  Moreover, it is preferable that the mesh openings are uniformly distributed over the entire mesh structure surface 21 so that the filtration membrane deposit (cake) is uniformly deposited.

  FIG. 3 is a cross-sectional view perpendicular to the length direction of a portion (hereinafter referred to as “beam 53”) corresponding to the yarn forming the mesh of the mesh structure portion 21 in the present embodiment. The openings 54 gradually decrease from the filter plate outer surface 51 toward the inside along the thickness direction of the filter plate 2, and have a width of 1 mm at the mesh structure / running water interface 52. On the other hand, the cross section of the beam 53 draws an arc having a radius of curvature of 0.5 mm in the vicinity of the outer surface 51 of the filter plate, gradually becomes thicker toward the inside, and has a width of 1.5 mm at the network structure / running water interface 52. It has become.

  The larger the mesh opening ratio, the larger the permeate flow rate, but the rigidity of the filter plate 2 becomes smaller. Here, the flow rate of the permeated water greatly affects the area ratio (hereinafter referred to as “outer surface opening ratio”) of the openings 54 (hereinafter referred to as “outer surface openings 55”) in the outer surface 51 of the filter plate in contact with the filtration membrane 1. is there. That is, when a spacer is disposed between the filtration membrane 1 and the filter plate surface 51, the membrane permeated water reaches the outer surface opening 55 through the flowing water path formed by the spacer, and passes through the opening 54 to enter the inside of the filter plate. It is guided to the flowing water space 26. When the spacer is not arranged, it passes between the filter membrane 1 and the filter plate surface 51 that are in close contact with each other by suction negative pressure, reaches the outer surface opening 55, and is guided to the running water space 26 inside the filter plate through the opening 54. In this path, the flowing water resistance is large in the portion where the membrane permeated water reaches the outer surface opening 55. If the outer surface opening ratio is large, the distance until the permeated water that has passed through the filtration membrane 1 reaches the outer surface opening 55 becomes shorter on average, the flowing water resistance decreases, and the permeated water flow rate increases. Once the permeate reaches the opening 54, the effect of the size of the opening on the permeate flow rate is small. Therefore, in order to increase the permeate flow rate, the outer surface opening ratio only needs to be large.

  On the other hand, since the rigidity of the filter plate 2 depends on the cross-sectional shape and cross-sectional area of the beam 53, even if the outer surface opening ratio is increased, the decrease in rigidity is suppressed by reducing the opening on the inner side of the filter plate. be able to. That is, a high permeate flow rate and high rigidity can be achieved at a higher level. Specifically, the individual openings 54 may be large on the outer surface and smaller on the inner side, and the sectional area may gradually change along the thickness direction of the filter plate.

In FIG. 3, the cross-sectional area of the opening (the area of the cross section parallel to the surface of the filter plate) is the largest at the outer surface 51 of the filter plate and the smallest at the network structure / running water interface 52. Since the mesh structure surface is pushed to the inside of the filter plate by the filtration membrane during suction filtration, it is reasonable in terms of strength design that the opening cross-sectional area is minimized on the innermost side of the mesh structure surface.
But the opening cross-sectional area in this invention may become the minimum between the filter-plate outer surface 51 and the mesh structure-run water space interface 52. FIG. However, in that case, in order to achieve both the permeate flow rate and the rigidity at a high level, the opening 54 has a portion that gradually decreases from the outer surface of the filter plate toward the inside along the thickness direction of the filter plate. It is necessary to be. Further, in order to improve the flatness of the outer surface 51 of the filter plate, the beam portion is not integrally structured by a wire mesh joined so as to intersect vertically and horizontally, but is integrally formed by injection molding or the like. Need to be.

When considering the size and opening ratio of the opening on the outer surface 51 of the filter plate, there is a problem of how to define the boundary between the opening and the other portion. Even if the cross-sectional shape of the beam 53 is substantially triangular and the filtration membrane 1 is supported at the apex, the beam and the filtration membrane are actually in contact with each other with a certain finite width. Further, it is considered that the peripheral edge (edge) of the opening on the outer surface of the filter plate is usually chamfered so that the filter membrane is not damaged.
Here, in consideration of the fact that the resistance when the membrane permeate flows is remarkably lowered if there is a slight gap, the periphery (edge) of the outer surface opening 55 is chamfered (C machining, R machining). Therefore, it is appropriate to consider that the chamfered portion is included in the opening 54. For example, in FIG. 3, it is appropriate to consider that the region immediately adjacent to the left and right on the top of the beam cross section belongs to the opening, and the outer surface opening ratio can be regarded as 100%.

In addition, when the outer surface opening edge is R-processed, the filtration membrane is actually recessed during suction filtration, and a portion where the filtration membrane and the filter plate are in close contact with each other is formed. As shown in FIG. 4, assuming that the cross-sectional shape of the recessed filtration membrane forms an arc, the width (X) of the contact portion is obtained from the opening width (L in FIG. 4) and the dent amount (D). Can do. Table 1 shows the calculation results.
Large membrane elements are often used at a negative pressure of about −20 kPa (transmembrane differential pressure), but the design pressure is designed to withstand a negative pressure of about −90 kPa (intermembrane differential pressure). The transmembrane pressure difference is defined as the pressure inside the membrane element based on the pressure outside the membrane element through the membrane. When the pressure is applied toward the inside of the membrane, it is called negative pressure, and when it is pressurized toward the outside of the membrane, it is called positive pressure. When used in an open system under atmospheric pressure, the transmembrane pressure difference is also referred to as internal pressure (gauge pressure). In the filtration membrane used in the present embodiment, when the one side of the square of the outer surface opening is in the range of 2.5 to 4 mm, the dent amount when sucked at -90 kPa (transmembrane differential pressure) is 2 to 2 of the length of one side. 4%. Using the results in Table 1, for example, when the side is 2.5 mm, the dent amount is 3%, and the radius of curvature of R processing is 0.5 mm, the outer surface opening ratio excluding the close contact portion is about 91%. . Moreover, since the influence of the thickness of a filtration membrane, etc. will become small if an opening becomes large, the amount of dents will become large and will be 5 to 10%. In this case, the contact width is increased, but the opening itself is also increased, so the influence on the aperture ratio is still small.
Considering that the membrane element is actually used with a smaller negative pressure, it can be considered that the portion subjected to the R processing is included in the opening 54 as described above.

  When perforations having a constant cross-sectional area are provided, for example, even if holes having a radius r are closely packed and spaced apart from each other, the aperture ratio is about 40%, and achieving a larger aperture ratio is a point of strength. It ’s difficult. According to the present invention, since an outer surface opening ratio larger than that can be realized, the outer surface opening ratio is preferably 50% or more and 80% or more in order to increase the permeate flow rate. It is particularly preferred.

  The thickness of the mesh structure portion 21 in the present embodiment is 1.5 mm. The thickness of the mesh structure portion can be determined in consideration of the strength of the material, the cross-sectional shape of the beam, the installation interval of the gap holding ribs 23 to be described later, but if it is too thin, the rigidity of the filter plate becomes insufficient. It is preferably 1 mm or more, and more preferably 1.2 mm or more. Conversely, if it is too thick, the weight of the filter plate increases. Since a general filter plate is a resin plate having a thickness of 6 to 8 mm, in order to enjoy the effect of weight reduction, the thickness of the network structure portion is preferably 4 mm or less, and more preferably 3 mm or less. preferable.

  In the conventional method of forming micro grooves on the surface of the filter plate, there is a problem that the groove portion is broken and the filter plate is easily bent. In the mesh structure, since the beams extend vertically and horizontally, the thickness of the mesh structure surface 21 is uniform throughout, and there is no such problem. This also helps to increase the rigidity of the filter plate.

  If the outer surface opening 55 is too large, the inside of the membrane element is sucked to give a negative pressure, and when the filtration membrane 1 is drawn into the opening 54, there is a possibility that the portion that contacts the edge of the filtration membrane opening is damaged. The given negative pressure acts on the entire opening on the outer surface of the filtration membrane, and balances with the reaction force from the filter plate and the tensile stress in the filtration membrane at the edge of the opening. This is because the greater the ratio, the greater the force applied to the filtration membrane.

As described above, the large membrane element is designed to withstand a negative pressure of about −90 kPa (transmembrane differential pressure). Therefore, the presence or absence of damage to the filtration membrane after suction with a negative pressure of −90 kPa (transmembrane pressure difference) was confirmed by experiments. In the mesh structure in the present embodiment, as described above, the outer surface opening is a square with a side of 2.5 mm, and the beam is R-processed with a radius of curvature of 0.5 mm at the contact portion with the filter membrane. In this case, damage to the filtration membrane could not be confirmed. Next, when the cross-sectional shape and size of the beam were not changed and the opening was a square with a side of 4 mm, traces pressed against the beam were observed on the filter membrane surface, but damage to the filter membrane could not be confirmed. There wasn't.
In an experiment in which a positive pressure was applied to the element to be described later, the filtration membrane fixed with a parallel line having an interval of 115 mm was not damaged at all even when a pressure of 12 kPa (transmembrane differential pressure) was applied from the inside. According to a simple approximate calculation, even if a negative pressure of −90 kPa (transmembrane pressure difference) is applied, if the width of the outer surface opening is smaller than 115 × 12/90 = about 15.3 mm, the filtration membrane is damaged. It is thought that it will not receive.
From the above, the outer surface opening preferably has a width of less than 15 mm, more preferably 4 mm or less.

  As described above, it is reasonable that the preferable range of the size of the outer surface opening 55 is defined by the width of the opening shape. Here, the width of the shape means the length of one side in a square, the length of a short side in a rectangle, the diameter in a circle, the short diameter in an ellipse, and the width in a long hole. Further, when the width is not uniquely determined, it is possible to define the dimension that defines the maximum dent amount into the opening of the filtration membrane as the width here. For example, in a triangle, it is the diameter of an inscribed circle, and is generally the diameter of the largest inscribed circle in the opening shape.

  If the minimum cross-sectional area of the opening is too small, processing problems will occur. For example, there is a problem that the hole is blocked by the wraparound of the resin during injection molding. Therefore, when the opening shape is a square, the length of one side is preferably 0.2 mm or more, and more preferably 0.5 mm or more. This is because the probability of occurrence of blockage of the hole is sufficiently small if it is 0.2 mm or more, and the probability is negligibly small if it is 0.5 mm or more. In addition, a preferable range can be defined by the width of the opening shape as well as the amount of dent of the filtration membrane in the outer surface opening for the wraparound of the resin at the time of injection molding. That is, the length of the short side in a rectangle, the diameter in a circle, the short diameter in an ellipse, and the width in a long hole.If the width is not uniquely determined by convention, it is the diameter of an inscribed circle in a triangle. The diameter of the largest circle inscribed in the opening shape.

  Inside the two mesh structure surfaces 21 of the filter plate 2, a running water space 26 surrounded by the two mesh structure surfaces 21 and the filter plate peripheral edge portion 24 is formed. In the present embodiment, the size is 450 mm × 950 mm × thickness 3 mm.

  In the flowing water space 26 inside the filter plate, the rib that vertically supports the mesh structure surface realizes two functions. A gap holding function for holding the space between the mesh structure surfaces 21 at the time of suction filtration and a filtration membrane fixing function for joining the filtration membrane 1 to prevent the filtration membrane 1 from bulging outside during backwashing.

  The rib for fixing the filtration membrane (hereinafter referred to as “filtration membrane fixing rib 22”) joins the two mesh structure surfaces 21, and the filtration membrane is joined on the surface of the filter plate (32). In the present embodiment, the filtration membrane fixing rib 22 having a width of 7 mm and a length of 910 mm parallel to the long side of the flowing water space 26 is 3 mm at an interval of 115 mm so that the short side direction of the flowing water space is substantially divided into four equal parts. Book provided. In the present embodiment, since a part obtained by dividing the filter plate in half in the thickness direction is injection-molded, the filtration membrane fixing rib is also divided in two in the thickness direction. The ribs divided into these two parts were joined with an adhesive (28). The portion of the mesh structure surface 21 where the filtration membrane fixing ribs 22 are located was eliminated, the surface thereof was formed smoothly, and the filtration membrane 1 was joined by thermal welding (32).

  Here, the size of the filtration membrane fixing rib 22 is not limited to the present embodiment, but if the width is too wide, there is a problem that a region having no opening increases on the surface of the filter plate. There is a possibility that the adhesive surface 28 of the rib may be broken by being pulled by the filtration membrane 1 to which internal pressure is applied. In addition, according to the heat welding method described later, the width of the filtration membrane-filtration membrane fixing rib joining line 32 is about 2 mm. Therefore, the width of the filtration membrane fixing rib is desirably 3 mm or more. As a result, the width of the filtration membrane fixing rib is preferably in the range of 3 to 12 mm, and more preferably in the range of 5 to 8 mm.

  The arrangement shape of the filtration membrane fixing rib 22 is not particularly limited, but it is easy to make it straight.

  When the interval between the filter plate peripheral edge 31 and the filtration membrane fixing rib 22 to which the filtration membrane 1 is fixed, and the interval between the filtration membrane fixing ribs 22 (referred to collectively as the “filtration membrane fixing interval 29”) are too wide, The filtration membrane 1 swells excessively during backwashing, causing inconvenience that the filtration membranes of adjacent membrane elements come into contact with each other, and there is a high probability that the filtration membrane will be damaged due to the force applied to the filtration membrane-filter plate junction. This is not preferable. Moreover, since the part which does not contribute to passage of permeate increases when a space | interval is too narrow, it is unpreferable.

  For the membrane element according to the present embodiment (the filtration membrane fixing interval is 115 mm), pressure is applied from the inside, and the swelling of the filtration membrane (maximum value of the distance from the filter plate surface 51. Usually, the filtration membrane fixing interval 29 Observed in the center part), the situation such as breakage was observed. First, when tap water is injected from the water collection port 4 and pressure is applied, the bulge of the filtration membrane becomes 8 mm at an internal pressure of 10 kPa, and water leaks through the filtration membrane, so the internal pressure can be increased beyond this. There wasn't. Next, the filter membrane surface was treated so that air did not pass through it, and air was injected from the water collection port to apply pressure. As the internal pressure was increased, the swelling of the filtration membrane gradually increased. The amount of swelling of the filtration membrane was 8 mm at 10 kPa, 10 mm at 12 kPa, and 13 mm at 18 kPa, and no further swelling occurred. Among these, when the pressurization exceeded 12 kPa, wrinkles remained in a part of the filtration membrane even when the pressure was returned to zero. Although damage to the filtration membrane could not be confirmed, the possibility that local irreversible elongation occurred in the nonwoven fabric that is the base material of the filtration membrane cannot be denied. When pressurization was continued, the filter plate started to deform at a pressure of 25 kPa, and the filter plate skeleton was damaged at 32 kPa. Therefore, in this embodiment, the membrane-filter plate bonding strength did not become a problem.

  Furthermore, the inventors have discovered that the filtration membrane deposited layer deposited on the filtration membrane surface is easily peeled off when the filtration membrane 1 swells during backwashing. That is, when the filtration membrane 1 swells and extends outward, a displacement occurs between the filtration membrane deposition layer and the filtration membrane surface, and the filtration membrane deposit layer is detached from the filtration membrane surface by the shearing force. According to the experiment with the membrane element according to the present embodiment (the filtration membrane fixing interval is 115 mm), the filtration membrane swell was detached when the bulge of the filtration membrane was 3 mm or more. The amount of swelling from which the deposited layer separates depends greatly on the properties of the deposited layer, but it is considered that the swelling of the filtration membrane is preferably 5 mm or more.

  As described above, there is an optimum range for the swelling of the filtration membrane during backwashing, the upper limit is determined by the amount of swelling and the filtration membrane is not damaged, and the lower limit is determined by whether the filtration membrane deposited layer can be detached. . In order not to damage the filtration membrane, the pressure during backwashing is 25 kPa or less, preferably 18 kPa or less, more preferably 12 kPa or less. Considering the distance between adjacent membrane elements, the membrane bulge amount is preferably 13 mm or less. In order to set the bulging amount to 5 to 13 mm at an internal pressure of 12 kPa, the filtration membrane fixing interval 29 may be set to 60 to 150 mm or less. The swelling of the filtration membrane depends on the physical properties of the filter membrane base material as well as the pressure during backwashing, but the filtration membrane fixing interval 29 is greatly influenced within practical conditions. If the filtration membrane fixing interval is more preferably in the range of 80 to 130 mm, an almost optimal filtration membrane bulge can be obtained.

  In this embodiment, both ends of the filtration membrane fixing rib 22 are separated from the filtration membrane-filter plate peripheral joint line 31 by 20 mm, but the present invention is not limited to this. The distance between the end of the filtration membrane-filtration membrane fixing rib joining line 32 (hereinafter referred to as "filtration membrane-rib joining end 33") and the filtration membrane-filter plate peripheral joining line 31 prevents damage to the filtration membrane during backwashing. For this purpose, it is preferably smaller than the filtration membrane fixing interval 29. Further, if the filtration membrane swells during backwashing, stress concentrates on the filtration membrane-rib joint end 33, so the distance between the filtration membrane-rib joint end 33 and the filtration membrane-filter plate peripheral joint line 31 is 50 mm or less. Is more preferable.

  One end or both ends of the filtration membrane fixing rib 22 may be connected to the filter plate peripheral portion 24, or the filtration membrane-filtration membrane fixing rib joining line 32 and the filtration membrane-filter plate peripheral joining line 31 may be connected. However, when both ends of the filtration membrane fixing rib 22 are connected to the filter plate peripheral edge portion 24, the water collection port 4 is provided for each of the plurality of flowing water spaces 26 or a part of the filtration membrane fixing rib 22 is provided. It is necessary to provide a water passage that connects the flowing water spaces 26 divided into two.

The rib for holding the gap (hereinafter referred to as “gap holding rib 23”) only needs to hold the gap during suction filtration.
In the present embodiment, linear gap holding ribs 23 having a width of 5 mm and a length of 910 mm are provided at a total of four locations in the middle of the filter plate peripheral edge 24 and the filtration membrane fixing ribs 22 and between the filtration membrane fixing ribs 22. Provided. The distance between the filtration membrane fixing rib and the gap retaining rib was about 55 mm.
In this embodiment, since the part obtained by dividing the filter plate in half in the thickness direction is injection-molded, the gap holding rib is also divided in two in the thickness direction. Unlike the filtration membrane fixing rib 22, the rib divided into these two parts was not particularly bonded. Therefore, the two mesh structure surfaces 21 are not joined to each other via the gap holding ribs 23. In addition, the opening 54 is closed at the portion where the gap retaining rib 23 is present, but the outer surface of the filter plate is not formed smoothly, and the shape of the mesh structure surface is left as it is. This is for the convenience of manufacturing the injection mold and is not limited to this.

  The arrangement | positioning shape of the space | gap holding rib 23 is not specifically limited. It may be linear as in this embodiment, or small island-shaped ribs can be appropriately isolated and arranged. The space | interval arrangement | positioning space | interval of the space | gap holding rib 23 should just not contact two mesh-structure surfaces 21 which oppose at the time of suction filtration (a filter plate is crushed). The preferred arrangement interval depends on the bending rigidity of the mesh structure surface 21 and the bending rigidity strongly depends on the thickness of the surface and the like. It is desirable to design. In addition, since the filtration membrane fixing rib 22 also has a gap holding function, there is a case where the gap holding rib 23 may not be provided in addition to the filtration membrane fixing rib.

  As a method for joining the filtration membrane 1 and the filter plate 2, known methods such as a method of fixing using an adhesive and a method of welding using ultrasonic waves can be used. However, since stress concentrates at the joint between the filtration membrane 1 and the filter plate 2 during backwashing, it is preferable to use a heat welding method using a hot plate, in which the strength reduction of the base material of the filtration membrane 1 is small.

  On the outer periphery of the filter plate 2, there are provided a water collection port 4 for discharging permeate to the outside of the membrane element, a hole for a fixing tool when assembling a module by arranging a plurality of membrane elements in parallel. Such peripheral members can also be manufactured integrally by injection molding.

DESCRIPTION OF SYMBOLS 1 Filtration membrane 2 Filter plate 21 Mesh structure part 22 Filtration membrane fixing rib 23 Space | gap holding rib 24 Filter plate peripheral part 25 Filter plate end surface 26 Flowing water space 27 Filter plate peripheral part adhesion surface 28 Filtration membrane fixing rib adhesion surface 29 Filtration membrane fixing space | interval 31 Filtration Membrane-Filter Plate Perimeter Bonding Line 32 Filtration Membrane-Filtration Membrane Fixed Rib Bonding Line 33 Filtration Membrane-Rib Junction End 4 Water Collection Port 51 Filter Plate Outer Surface 52 Mesh Structure Surface-Water Flow Space Boundary Surface 53 Opening 55 Outer surface opening 56 Inner opening

Claims (8)

A membrane element having a filtration membrane and a filter plate supporting the filtration membrane,
The surface of the filter plate has a network structure of substantially the entire portion covered with the filtration membrane,
Inside the filter plate, a running water space is formed inside the mesh structure ,
In the flowing water space, a support material that vertically supports the surface having the mesh structure is provided with an interval between the support materials,
The filtration membrane is joined to the portion of the filter plate where the support material is located,
In the flowing water space, in addition to the support material to which the filtration membrane is bonded, a support material that vertically supports the surface having the mesh structure and is not bonded to the filtration membrane is provided between the support materials. A membrane element characterized by that. 2. The membrane element according to claim 1, wherein the opening of the mesh structure gradually decreases from the outer surface of the filter plate toward the inside along the thickness direction of the filter plate. The network structure is integrally formed,
The membrane element according to claim 1 or 2, wherein the opening of the mesh structure has a portion that gradually decreases from the outer surface of the filter plate toward the inside along the thickness direction of the filter plate. The membrane element according to claim 2 or 3, wherein an opening ratio of the network structure is 50% or more on the outer surface of the filter plate. The membrane element according to any one of claims 2 to 4, wherein the opening of the mesh structure has a width of 0.2 mm or more in a portion having the smallest cross-sectional area. The membrane element according to any one of claims 2 to 5, wherein the opening of the mesh structure has a width of 15 mm or less on the outer surface of the filter plate. The membrane element according to any one of claims 1 to 6, wherein an interval between the support materials to which the filtration membrane is bonded is 60 mm or more and 150 mm or less. The membrane element according to any one of claims 1 to 7 , wherein the filter plate is manufactured by joining two parts by injection molding.

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