JP2008119680A - Membrane separation element and membrane separation module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane separation element having excellent durability in use constituted of a separation membrane of remarkably improved durability including strength and resistance to bending in the vicinity of its fixed part without sacrificing its excellent characteristics such as its excellent separation function. <P>SOLUTION: The membrane separation element is constituted of a pair of flat separation membranes 1 each disposed on either side of a holder 7 with each of the flat separation membranes 1 attached to the holder 7 on its outer peripheral edge. A composite separation membrane constituted of a base layer 2 and a porous layer 4 having a separation function is employed in the above flat separation membranes 1. The base layer 2 of the composite separation membrane is comprised of a peripheral thick-walled part 2A having a thickness 1.1 to 3 times greater than that of its central part with the peripheral thick-walled part 2A disposed in the vicinity of and attached to the outer peripheral edge of the holder 7 and the ratio of the surface area of the peripheral thick-walled part 2A of the base layer 2 relative to the permeation surface area of the separation membrane 1 being not lower than 1% and not higher than 30%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a membrane particularly suitable for purification of sewage (cooking, washing, baths, toilets, other domestic wastewater generated from other living environments) and wastewater generated from production factories, restaurants, fishery processing factories, food processing plants, etc. The present invention relates to a separation element and a membrane separation module.

  In recent years, separation membranes in the form of flat membranes and hollow fiber membranes that have come to be used for purification of sewage and wastewater include membrane separation elements in which separation membranes are arranged, and membrane separation modules in which a plurality of the elements are arranged Used for water purification treatment.

  There are various types and forms of separation membranes disposed in such membrane separation elements, but a polyvinylidene fluoride resin solution containing a surfactant is applied to the surface of a substrate such as a woven fabric or a non-woven fabric. After applying or impregnating the base material, the polyvinylidene fluoride resin is solidified, and a porous polyvinylidene fluoride resin layer is formed on the surface of the base material layer. A separation membrane is known (see Patent Document 1).

  In this composite separation membrane, the porous polyvinylidene fluoride resin layer acts as a separation functional layer, but in such a flat membrane, an effective membrane per unit volume compared to other forms of separation membrane, for example, a hollow fiber membrane. Since it is difficult to increase the area, it is required to increase the water permeation amount while maintaining the pore diameter according to the filtration target. However, if the porosity is increased to increase the water permeation amount, the pore size becomes too large or the surface cracks and the blocking rate decreases. On the other hand, if the pores are made small in order to increase the blocking rate, the water permeability will be lowered this time. In other words, the improvement in the rejection rate and the improvement in water permeability are in a contradictory relationship, and it is difficult to make a good balance between the two.

  In addition, in the separation membrane for sewage wastewater, it is used to prevent inorganic substances such as sand, sludge, and other solids from violently colliding with the membrane surface, supplying oxygen to activated sludge, and preventing clogging. Since bubbles caused by aeration operations collide violently with the film surface, it is required to have a film strength that can sufficiently withstand such an impact. This film strength is mainly borne by the base material layer, and a nonwoven fabric is generally used for the base material layer. However, the strength of the base material layer is still not sufficient, and further enhancement is required. In particular, when the density of the base material is increased in order to increase the strength of the separation membrane, the resin of the separation functional layer and the base material are not entangled, and a trouble that the base material layer and the separation functional layer are separated during the membrane filtration operation is likely to occur.

  In addition, in the membrane separation element, the outer peripheral edge of the separation membrane is fixed to the support base frame with a hot melt adhesive or the like, so when used in an environment where significant impact or vibration is applied to the membrane surface, During the filtration operation, the vicinity of the fixed portion of the separation membrane is easily broken by fatigue. For example, during membrane filtration operation, inorganic substances such as sand, sludge, and other solids in the water to be treated collide with the membrane surface violently, or supply oxygen to activated sludge and clogging prevention. When a significant impact or vibration is applied to the membrane surface due to the aerating operation of air bubbles and the membrane surface, the separation membrane is locally fatigued and broken in the vicinity of the fixed part between the support base frame and the separation membrane. It becomes easy to cause breakage of the film and leakage of the liquid. In particular, when the density of the base material is lowered in order to prevent separation between the separation functional layer and the base material layer, local fatigue of the separation membrane in the vicinity of the fixing portion tends to increase.

Further, in Patent Document 2, as a physical joining method between the separation membrane and the supporting base frame, local heating or ultrasonic wave or high frequency irradiation is performed on the overlapped joining portion to melt the resin material at the joining interface. In addition, Patent Document 3 discloses a submerged membrane cartridge and a manufacturing method in which a resin filter plate and a surface of the filter plate are disposed along the peripheral edge of the filter plate. A filtration membrane is fused to form a water-stopping portion and a fixed portion at a plurality of melting margins that protrude from the surface of the filter plate and are molded along the peripheral edge of the filter plate. Thus, a method of intermittently fixing the periphery of the filtration membrane to the filter plate at the water stop portion has been proposed. The local heating and ultrasonic or high-frequency irradiation used in this physical bonding method are liable to damage the bonded part due to the heat or vibration generated by the heating or irradiation, and the damaged part is the starting point. There is a problem that there is a high possibility of tearing and leaking.
JP 2003-135939 A Japanese Patent Laid-Open No. 7-24271 JP 2006-7222 A

  The present invention solves the above-mentioned problems of the prior art, and does not hinder the characteristics of the separation membrane having an excellent separation membrane function, and the membrane durability such as folding resistance and strength in the vicinity of the fixing portion of the separation membrane. It is an object of the present invention to provide a membrane separation element that is remarkably improved in performance and that makes it difficult for the separation membrane and the element support to peel off and has excellent durability during use.

(1) A membrane separation element in which flat separation membranes are arranged on both sides of a support, and the support and the separation membrane are fixed at the outer periphery, and the substrate layer and porous separation are used as the separation membrane. A composite separation membrane composed of a functional layer is used, and on the periphery side in the vicinity of the fixed outer periphery, the substrate layer thickness is 1.1 to 3 times the substrate layer thickness at the center of the separation membrane. A membrane separation element, wherein a base layer thick portion is provided, and an area ratio of the base layer thick portion is 1% or more and 30% or less with respect to a permeation area of the separation membrane.
(2) A composite separation membrane in which a layer in which a resin and a substrate constituting the porous separation functional layer are mixed is used as a separation membrane between the base material layer and the porous separation functional layer of the composite separation membrane. The membrane separation element according to (1), wherein the base material layer is made of a nonwoven fabric or a woven or knitted fabric.
(3) Grooves are provided in the bonding part of the support, the ratio of the groove to the bonding part is 10% or more and 50 or less, and the depth of the groove is 1% or more and 40% or less of the thickness of the support plate. The membrane separation element (4) according to claim 1 or 2, wherein the permeate that has permeated through the separation membrane is formed with a concavo-convex on the surface of the support, and the element is formed. The membrane separation element according to any one of (1) to (3), wherein a permeate outlet communicating with the permeate flow path is provided.
(5) A membrane separation module in which a plurality of the membrane separation elements according to any one of (1) to (4) are housed in a housing or fixed in an arrayed state.

  In the membrane separation element of the present invention, the membrane strength in the vicinity where the separation membrane is fixed to the support can be sufficiently increased. Therefore, the membrane separation treatment is performed by the immersion type using the membrane separation element and the membrane separation module. In addition, minerals such as sand, sludge, and other solids contained in the water to be treated collide violently with the membrane surface, and air bubbles caused by aeration operations to prevent oxygen supply to the activated sludge and clogging are severe. Even if it collides, local fatigue of the separation membrane in the vicinity of the fixing portion between the support base frame and the separation membrane can be sufficiently suppressed, and the strength of the separation membrane is sufficiently high. Film tearing can be greatly suppressed. Therefore, durability at the time of use of the separation membrane in the membrane separation element is improved, and long-term operation is facilitated.

  The separation membrane used in the membrane separation element of the present invention is a composite separation membrane comprising a base material layer and a porous separation functional layer, and in particular, a composite separation in which a porous separation functional layer comprising a polyvinylidene fluoride resin is formed. It is preferable to use a membrane. Here, between the base material layer and the porous separation functional layer, it is preferable that a layer in which the resin constituting the porous separation functional layer and the base material are mixed is interposed. As a result, a high peel resistance of 10,000 or more in MIT folding resistance can be obtained. Such a MIT folding resistance level can sufficiently prevent the separation membrane from being broken.

  In the composite separation membrane in which the porous separation functional layer is formed on the base material layer, the base material layer has a function of supporting the porous separation functional layer and giving strength to the separation membrane. The material constituting the base material layer is not particularly limited, such as an organic base material and an inorganic base material, but an organic base material is preferable from the viewpoint of easy weight reduction. Examples of the organic substrate include woven and knitted fabrics and nonwoven fabrics made of organic fibers such as cellulose fibers, cellulose triacetate fibers, polyester fibers, polypropylene fibers, and polyethylene fibers. Among these, a nonwoven fabric whose density is relatively easy to control is particularly preferable.

  The separation membrane disposed in the membrane separation element of the present invention has a base material layer thickness 1.1 to 3 times the base material layer thickness of the central portion of the separation membrane on the peripheral side in the vicinity of the fixed outer peripheral edge. The base material layer thick part having a thickness is provided, and the area ratio of the base material layer thick part is 1% or more and 30% or less with respect to the permeation area of the separation membrane. FIG. 1 shows a cross section of an embodiment of the membrane separation element in which the separation membrane is disposed on both sides of the support and the outer peripheral edge is fixed. FIG. 2 shows the planar shape of the separation membrane as viewed from the line II in FIG. FIG. 3 is a perspective view of the membrane separation element showing a state in which the permeate outlet 9 is provided in the membrane separation element of FIG. 1 and the separation membrane is partially broken.

  The membrane separation element of the present invention will be described with reference to FIG. 1 showing one embodiment thereof. In this figure, the composite separation membrane 1 is composed of a base material layer 2, a porous separation functional layer 4, and a mixed layer 3 interposed therebetween. The peripheral side of the base material layer 2 is a base material layer thick portion 2A.

  Here, the thickness of the base layer central portion 2C may be equal to the normal thickness of the base layer in the composite separation membrane. If the thickness of the central part 2C of the base material layer is too thin, it will be difficult to maintain the strength as a separation membrane, and if it is extremely thick, the water permeability will be lowered, so a range of 0.01 mm to 1 mm is generally preferred. Most preferably, the range is 0.05 mm to 0.5 mm.

  Moreover, in order to make the thickness of the base material layer thick part 2A on the peripheral side of the base material thicker than the center part 2C, a means such as attaching the base material may be taken, and there is no particular limitation. Since the base material to be pasted may have a lower water permeability when a base material having a higher density than that of the central part 2C is pasted, a base material having the same or lower density as that of the central part 2C is pasted. It is preferable. The surface on which the substrate is attached is not particularly limited, but the element side of the support is preferred.

  The thickness of the base material layer thick portion 2A on the peripheral side of the base material layer needs to be thicker than the thickness of the base material layer central portion 2C, and is 0.01 mm or more thicker than the thickness of the base material layer central portion 2C. It is preferable. If the base material layer thick portion 2A is too thin, it is difficult to sufficiently prevent the tear due to local fatigue. Conversely, if it is extremely thick, it becomes difficult to bond. Generally, a range of 0.02 mm to 3 mm is preferable. Most preferably, it is the range of 0.07 mm-2 mm.

  In addition, the area ratio of the base layer thick portion 2A on the peripheral side of the base layer is in the range of 1% to 30% with respect to the permeation area of the separation membrane. Preferably, it is in the range of 5% to 26%. The area ratio of the base material layer thick part 2A here is a value obtained from the following formula from the total membrane area of the permeation surface of the separation membrane and the membrane area of the base material layer thick part.

Area ratio of base material layer thick part = ((total film area of transmission surface−film area of base material layer thick part) ÷ total film area of transmission surface) × 100 (%)
Note that the total membrane area of the permeation surface of the separation membrane is the total area of the membrane that is on the inner side of the membrane excluding the fixed portion at the outer peripheral edge and is permeable to liquid.

Further, the base material layer thick part 2A on the peripheral side in the vicinity of the fixed outer peripheral edge and the base material layer central part 2C have a thickness ratio in a range of 1.1 to 3 times that of the central part. . Preferably it is the range of 1.2 times-2.5 times. The thickness ratio here is a value obtained from the thickness of the base layer thick part 2A and the thickness of the center part 2C by the following equation.
Thickness ratio = thickness of base material layer thick part ÷ thickness of base material layer center The density of the base material layer is 0.7 g / cm ³ or less, preferably 0.6 g / cm ³ or less. . This density range is suitable for accepting a film-forming stock solution and forming a composite layer of a base material layer and a porous layer in the manufacturing process described later. However, when the density is extremely low, the strength as a separation membrane is lowered, and thus it is preferably 0.3 g / cm ³ or more. The density here is an apparent density, which can be obtained from the area, thickness and weight of the substrate by the following formula.

Apparent density = weight of substrate / (area of substrate × thickness)
On the other hand, if the thickness of the porous separation functional layer is too thin, defects such as cracks may occur, and the filtration performance may deteriorate. If the thickness is too thick, the water permeability may decrease, so it is usually 0.001 to 0.5 mm. The thickness is preferably selected in the range of 0.05 to 0.2 mm.

  Furthermore, in the composite separation membrane in which the porous separation functional layer is formed on the base material layer, a part of the polyvinylidene fluoride resin composition constituting the porous separation functional layer enters the base material, and the porous separation It is preferable that the layer in which the resin constituting the functional layer and the base material are mixed is interposed between the porous separation functional layer and the base material layer. By inserting the polyvinylidene fluoride-based blend resin inside the base material surface side, the porous separation functional layer is firmly fixed to the base material layer by the so-called anchor effect, and the porous separation functional layer is peeled off from the base material layer. Can be prevented. The porous separation functional layer may be present on one side with respect to the base material layer, or may be present on both sides. The porous separation functional layer may have a symmetric structure or an asymmetric structure with respect to the base material layer. Further, when the porous separation functional layer is present on both sides with respect to the base material layer, the porous separation functional layers on both sides may be continuous through the base material layer, or discontinuous It does not matter.

  Next, a method for producing a separation membrane used in the present invention will be described. This separation membrane has, for example, a porous separation function in which a membrane-forming stock solution containing, for example, a polyvinylidene fluoride resin and a pore-opening agent is adhered to one or both surfaces of a substrate and solidified in a coagulating solution containing a non-solvent. It can be manufactured by forming a layer. At this time, the means for attaching the film-forming stock solution to the surface of the substrate may be application of the film-forming stock solution, or the substrate may be immersed in the film-forming stock solution. When applying the film-forming stock solution to the substrate, it may be applied on one side of the substrate or on both sides. It is also possible to join both layers after forming only the porous separation functional layer separately from the substrate.

  In coagulating the membrane-forming stock solution, only the membrane-forming stock solution for forming a porous separation functional layer on the substrate may be brought into contact with the coagulating solution, or the membrane-forming stock solution for forming a porous separation functional layer. The film may be immersed in the coagulating liquid together with the base material. In order to bring only the membrane-forming solution film for forming the porous separation functional layer into contact with the coagulation liquid, for example, a method of bringing the membrane-forming solution film formed on the substrate into contact with the surface of the coagulation bath so that it is on the lower side. Also, the substrate is brought into contact with a smooth plate such as a glass plate or a metal plate and pasted so that the coagulation bath does not wrap around the substrate side. There is a method of immersion. In the latter method, the base material may be attached to the plate and then the film of the film forming stock solution may be formed, or the film of the film forming raw solution may be formed on the base material and then attached to the plate.

  In addition to the polyvinylidene fluoride resin described above, a pore-opening agent or a solvent for dissolving them may be added to the film-forming stock solution as necessary.

  In the case of adding a pore-opening agent having an action of promoting porous formation to the film-forming stock solution, the pore-opening agent may be any one that can be extracted by the coagulation liquid, and preferably has high solubility in the coagulation liquid. For example, polyoxyalkylenes such as polyethylene glycol and polypropylene glycol, aqueous polymer such as polyvinyl alcohol, polyvinyl butyral, and poracrylic acid, and glycerin can be used.

  In the present invention, as the pore opening agent, a surfactant containing a polyoxyalkylene structure, a fatty acid ester structure or a hydroxyl group can be used. Use of a surfactant makes it easy to obtain the target pore structure.

The polyoxyalkylene _{structure, - (CH 2 CH 2 O} ) n -, - (CH 2 CH 2 (CH 3) O) n -, - (CH 2 CH 2 CH 2 O) n -, - (CH 2 CH ₂ CH ₂ CH ₂ O) _n — and the like can be mentioned, but — (CH ₂ CH ₂ O) _n — so-called polyoxyethylene is particularly preferable from the viewpoint of hydrophilicity.

  Examples of the fatty acid ester structure include fatty acids having a long-chain aliphatic group. The long-chain aliphatic group may be linear or branched, and examples of the fatty acid include stearic acid, oleic acid, lauric acid, and palmitic acid. Moreover, fatty acid ester derived from fats and oils, such as beef tallow, palm oil, coconut oil, etc. are also mentioned.

  Examples of the surfactant having a hydroxyl group include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, glycerin, sorbitol, glucose, and sucrose.

  The surfactant used as the pore-opening agent in the present invention preferably contains two or more of a polyoxyalkylene structure, a fatty acid ester structure and a hydroxyl group.

  Of these, surfactants containing all of the polyoxyalkylene structure, fatty acid ester structure and hydroxyl group are particularly preferably used. For example, polyoxyethylene sorbitan fatty acid ester includes polyoxyethylene sorbitan monostearate, polyoxyethylene palm Oil fatty acid sorbitan, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene fatty acid ester, polyethylene glycol monostearate, polyethylene glycol monooleate, polyethylene glycol monolaurate Can be mentioned. These surfactants are particularly preferable because they not only improve the dispersibility of the inorganic fine particles, but also have the characteristics that even if they remain in the porous layer and are dried, the water permeability and blocking properties are not lowered.

  When a solvent for dissolving a polyvinylidene fluoride resin, other organic resin, a pore-opening agent, or the like is used in the film forming stock solution, N-methylpyrrolidone (NMP), N, N- Dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetone, methyl ethyl ketone and the like can be used. Of these, NMP, DMAc, DMF, and DMSO, which are highly soluble in polyvinylidene fluoride resins, can be preferably used.

  In addition, a non-solvent can also be added to the film-forming stock solution. The non-solvent does not dissolve the polyvinylidene fluoride resin or other organic resins, and acts to control the size of the pores by controlling the solidification rate of the polyvinylidene fluoride resin and other organic resins. To do. As the non-solvent, water and alcohols such as methanol and ethanol can be used. Of these, water and methanol are preferred from the viewpoint of ease of wastewater treatment and price. These may be mixed.

  In the composition of the film-forming stock solution, the polyvinylidene fluoride resin is 5 to 30% by weight, the pore-opening agent is 0.1 to 15% by weight, the solvent is 45 to 94.8% by weight, and the non-solvent is It is preferably within the range of 0.1% by weight to 10% by weight. Among them, when the amount of the polyvinylidene fluoride-based resin is extremely small, the strength of the porous layer is lowered, and when it is too large, the water permeability may be lowered. Therefore, the range of 8% by weight to 20% by weight is more preferable. If the amount of the pore-opening agent is too small, the water permeability may decrease, and if the amount is too large, the strength of the porous layer may decrease. In addition, if it is extremely large, it may remain excessively in the polyvinylidene fluoride resin and elute during use, and the quality of the permeated water may deteriorate or the water permeability may change. Therefore, a more preferable range is 0.5 wt% to 10 wt%. Furthermore, if the amount of the solvent is too small, the stock solution is likely to be gelled, and if the amount is too large, the strength of the porous layer is lowered. If the amount of non-solvent is too large, gelation of the stock solution tends to occur, and if it is extremely small, control of the size of pores and macrovoids becomes difficult. Therefore, it is more preferably 0.5 wt% to 5 wt%.

  On the other hand, as the coagulation bath, a non-solvent or a mixed solution containing a non-solvent and a solvent can be used. When a non-solvent is used for the film-forming stock solution, the non-solvent in the coagulation bath is preferably at least 80% by weight of the coagulation bath. If the amount is too small, the solidification rate of the polyvinylidene fluoride-based resin is slowed and the pore diameter is increased. More preferably, it is in the range of 85% by weight to 100% by weight. On the other hand, when a non-solvent is not used for the film-forming stock solution, it is preferable to reduce the content of the non-solvent in the coagulation bath, compared to the case where a non-solvent is also used for the film-forming stock solution. preferable. When the amount of the non-solvent is large, the solidification rate of the polyvinylidene fluoride resin increases, and the surface of the porous layer becomes dense and the water permeability may decrease. More preferably, the range is from 60% to 99% by weight. By adjusting the content of the non-solvent in the coagulation bath, the pore size on the surface of the porous layer and the size of the macrovoids can be controlled. If the temperature of the coagulation bath is too high, the coagulation rate will be too fast. Conversely, if the temperature is too low, the coagulation rate will be too slow, so it is usually selected in the range of 15 ° C to 80 ° C. preferable. More preferably, it is the range of 20 to 60 degreeC.

  In addition, the separation membrane used in the present invention may be any of a nanofiltration membrane, an ultrafiltration membrane, and a microfiltration membrane, and one or more appropriate membranes are selected and combined depending on the size of the separation symmetric substance. However, an ultrafiltration membrane and a microfiltration membrane are particularly preferable for treating sewage wastewater. Further, it is more preferable that the rejection of fine particles having an average particle size of 0.088 μm is 90% or more. If this rejection rate is not satisfied, in the treatment of sewage wastewater, bacterial cells and sludge may leak, clogging by bacterial cells and sludge may occur, filtration differential pressure may increase, and the service life may become extremely short. To do.

  Here, the blocking rate is the temperature of 25 ° C. of raw water in which polystyrene latex fine particles (nominal particle size 0.088 μm, standard deviation 0.0062 μm) manufactured by Ceradyne are dispersed in reverse osmosis membrane permeated water to a concentration of 10 ppm. From the absorbance of ultraviolet light having a wavelength of 202 nm obtained by allowing the separation membrane to permeate under a pressure of 10 kPa and obtaining the raw water and the permeated water, respectively, the following equation is used.

Blocking rate (%) = [(absorbance of stock solution−absorbance of permeated water) / absorbance of raw water] × 100
Further, the MIT folding resistance test of the separation membrane is measured using an MIT folding resistance test apparatus (No. 530-S, Toyo Seiki Seisakusho Co., Ltd.) according to the JIS P8115 MIT folding resistance test.
The separation membrane is cut into a size of 15 mm wide × 110 mm long, a load of 2 kg is applied, the bending angle is 135 ± 2 °, the rotation speed is 175 cpm, and the number of times until it breaks is measured. .

  The adhesion strength between the separation membrane and the element support plate is measured using “TENSILON” (TENSILON / UTM-4L TOYOMSURING INSTRUMENTS CO., LTD) according to JIS K6854 180 degree peel test. A separation membrane sample having a width of 25 mm obtained by laminating a separation membrane with an element support plate with a hot melt fixing agent is used to measure the peel strength at a peel rate of 200 mm / min.

  In the membrane separation element of the present invention, the flat membrane-like composite separation membrane is disposed on both sides of the support, and the support and the separation membrane are fixed at the outer periphery, and are surrounded by the support and the separation membrane. A flow path through which the membrane permeate flows is formed in the space. The permeate flows from the flow path to the permeate outlet and is taken out of the element. In order to form the flow path in the space surrounded by the support and the separation membrane in a predetermined direction, it is preferable to form irregularities on the support surface. For example, in the support body 7 shown in FIGS. 1 and 4, a projection 6 for forming a flow path is provided.

  This membrane separation element is a membrane separation module having a structure in which a plurality of the membrane separation elements are housed in a housing, or a membrane separation module having a structure in which a plurality of membrane separation elements are fixed in an arrayed state. It is immersed in the tank in which the liquid is stored and used for membrane filtration. These membrane separation elements and membrane separation modules are provided with a liquid collecting means for collecting the permeated liquid that has permeated through the separation membrane, and used as a liquid processing apparatus for the treatment of sewage wastewater.

  Although the form of the membrane separation element of this invention is not specifically limited, An example of the form of the membrane separation element which can be used suitably for a sewage wastewater use etc. was shown to FIGS. This will be described below with reference to these drawings.

  The membrane separation element shown in FIGS. 1 to 4 has a flat membrane-like separation membrane 1 arranged on both sides of a rigid support body (consisting of an outer peripheral base material frame portion and a flow path plate portion therein) 7. Do it. The flat membrane-like separation membrane 1 is a composite separation having a layer structure in which a layer 3 in which a resin constituting a porous separation functional layer and a base material are mixed is interposed between the porous separation functional layer 4 and the base material layer 2. It is a membrane.

  In this form of membrane separation element, the separation membrane 11 is disposed on both sides of the support 7 in order to increase the amount of water permeation. The support 7 has protrusions 6 formed on both surfaces of the flow path plate portion on the center side. Further, a groove 7A is formed on the separation membrane fixing portion surface of the support 7 in order to increase the fixing strength of the fixing portion between the composite separation membrane and the element support.

  The composite separation membrane 1 eliminates impurities in the liquid (liquid to be treated) stored in the immersed bath without allowing permeation during membrane filtration. The permeate passing through the composite separation membrane 1 from the outside to the inside of the element flows between the support and the composite separation membrane 1. The protrusions 6 on the surface of the support are for allowing the permeated water filtered by the separation membrane 1 to flow efficiently in a predetermined direction. The permeate flowing between the support 7 and the composite separation membrane flows toward the permeate outlet 9 provided on the upper side surface of the element, and is taken out to the outside. In order to connect the flow path in the element to the permeate outlet 9, communication openings 10 are provided in the vicinity of the permeate outlet 9 on both the front and back surfaces of the base material frame of the support.

  The support body 7 is composed of an outer peripheral base frame portion and a flow path plate portion therein, and has a structure in which a plurality of irregularities (projections 6 and the like) for forming a flow path are formed on both surfaces of the flow path plate portion. Is. The protrusions 6 are formed with a plurality of grooves arranged in parallel at regular intervals so that the distance to the permeate outlet 9 and the channel resistance are made uniform and the water to be treated flows evenly with respect to the membrane surface. It is preferable to provide in.

  At this time, the protrusions 6 are preferably provided so that the ratio of the total area of the protrusions to the area of the filtration membrane is in the range of 0.15 to 0.35. When this ratio is less than 0.15, the contact area of the projections with respect to the filtration membrane is reduced, and as a result, the frictional force between the filtration membrane and the projection per projection increases, and the filtration membrane may be damaged due to wear. is there. On the other hand, if it exceeds 0.35, the influence of impeding the permeability of the liquid from the filtration membrane becomes large at the portion where the filtration membrane and the protrusion are in close contact. More preferably, it is the range of 0.2-0.3.

  On the other hand, if the height of the protrusion is too low, a sufficient space cannot be formed between the support and the filtration membrane due to a pressure difference between the stock solution side and the permeation side during use. Accordingly, the height of the protrusion is preferably at least 0.35 mm. On the other hand, in view of making the thickness of the filtration membrane element compact and increasing the area of the packed filtration membrane as the membrane separation device, it is preferable that the height of the protrusion is low.

  Furthermore, it is preferable that the element is provided with a groove on a fixing surface where the element support and the separation membrane are fixed at the outer peripheral portion.

  In the fixing surface of the element support, the groove 7A on the surface of the separation membrane fixing portion of the support 7 is preferably provided so that the ratio of the groove to the fixing portion is in the range of 10% to 40%. If this ratio is too small, there is a possibility that the fixing effect is not changed from the case where the groove is not provided. Preferably, it is in the range of 20% to 30%.

  On the other hand, when the depth of the groove is too deep, the strength of the support plate is remarkably lowered, causing damage. Therefore, the depth of the groove is preferably 25% of the thickness of the support plate.

  The shape of the groove is not particularly limited, but examples thereof include a vertically square groove, an inclined V-shaped groove, a semicircular groove, a polygonal concave shape, and a circular concave shape. It is done.

  The number of grooves is preferably 1 to 10. If the number of grooves is too large, the strength of the element support member is lowered. More preferably, it is two.

The position of the groove may be the same position on the fixing surfaces on both sides of the element support member, or may be different. You may arrange | position continuously in a peripheral part, may arrange | position discontinuously, and may combine.
In addition, the size of the shape of the polygonal dent or the shape of the circular dent is preferably 1% to 50% of the width of the fixing surface. A size of 15% is preferable.
The shaping positions may be the same or different in the fixing surfaces on both sides of the element support member.

  Moreover, as a material of the support body 7, the material with the rigidity whose tensile strength in D638 of ASTM test method is about 15 MPa or more is preferable. For example, metals such as stainless steel, acrylonitrile-butadiene-styrene copolymer (ABS resin), resins such as polyethylene, polypropylene and polyvinyl chloride, composite materials such as fiber reinforced resin (FRP), and other materials are preferably used. can do.

  Moreover, in the membrane separation element of this invention, as shown in FIG. 1, it is preferable to adhere the peripheral part (base material frame) of the support body 7 and the separation membrane 1 by adhesion | attachment using a hot-melt-adhesive. Here, “adhering” means fixing both members in contact with each other, and it is preferable to bond them separately using a resin or the like, but even if the separation membrane itself is welded, various other types are also possible. It may be fixed by a method.

  In the membrane separation element configured as described above, the permeated water filtered by the separation membrane 1 passes through the opening 10 for the permeate to pass through both sides of the base material frame of the support, and the base material It passes through the permeate outlet 9 provided on the side of the frame and is taken out of the element. In order to take out the permeate, a suction pipe is connected to the permeate outlet 9.

  Subsequently, a method of housing a plurality of the membrane separation elements in a housing to form a membrane separation module and immersing the membrane separation module in water to be treated for water treatment will be described with reference to FIG. A plurality of membrane separation elements are housed in a housing so as to be parallel to each other and between the membrane surfaces of the separation membrane 1, and a membrane separation module is assembled. This membrane separation module is used so as to be immersed in water to be treated such as organic waste water stored in the water tank 14 to be treated. Inside the membrane separation module 13, there are a plurality of membrane separation elements loaded in the vertical direction, and below that there is provided an air diffuser 15 for supplying the gas from the blower 12 to the membrane surface of the separation membrane, In addition, a pump 16 for sucking permeate is provided downstream of the membrane separation module 13.

  In the water treatment apparatus configured as described above, water to be treated such as sewage wastewater passes through the separation membrane 1 of the membrane separation element by the suction force of the pump 16. At this time, suspended substances such as microbial particles and inorganic particles contained in the water to be treated are removed by filtration. Then, the permeated water that has passed through the separation membrane 1 flows through the flow path formed by the protrusion 6 of the support, passes through the opening 10 that communicates the back and front surfaces of the base material frame, and is permeated in the base material frame. The solution is taken out of the water tank 14 through the liquid outlet 9. On the other hand, the air diffuser 15 generates air bubbles in parallel with the filtration, and the upward flow generated by the air lift action of the air bubbles flows in parallel to the membrane surface of the membrane separation element 8 and is deposited on the membrane surface. Acts to disengage.

  The liquid to be treated is not limited to sewage wastewater, but can be used for water purification, clean water treatment, wastewater treatment, industrial water production, etc. in the water treatment field, river water, lake water, groundwater Seawater, sewage, drainage, etc. can be treated water.

  The water permeability and blocking rate of the separation membranes in the examples and comparative examples were measured as follows.

[Water permeability of separation membrane]
The separation membrane is cut into a circle with a diameter of 50 mm, set in a cylindrical filter holder, and the reverse osmosis membrane permeated water is preliminarily permeated for 5 minutes at a head height of 1 m at 25 ° C. The water permeability is measured by collecting for 5 minutes.

[Separation rate of separation membrane]
A calibration curve of the concentration is obtained using latex particles (polystyrene latex fine particles manufactured by Ceradyne, nominal particle size 0.088 μm, standard deviation 0.0062 μm). That is, a separation membrane (circular with a diameter of 43 mm) is set in a holder for measuring a fine particle rejection rate (UHP-43K, manufactured by Advantech Toyo Co., Ltd.), raw water prepared to have a latex particle concentration of about 10 ppm, and an evaluation pressure of 10 kPa is added. 25 cc of permeated water is collected after preliminary permeation of 25 cc while stirring the raw water at a nitrogen pressure. The latex particle concentration of each of the raw water and the permeated water is measured with a spectrophotometer (U-3200, manufactured by Hitachi, Ltd.) as an absorbance value of ultraviolet rays having a wavelength of 202 nm. From the absorbance ratio (concentration ratio), the rejection rate is obtained by the following formula.
Blocking rate (%) = [(absorbance of raw water−absorbance of permeated water) / absorbance of raw water] × 100
[MIT folding resistance test of separation membrane]
In accordance with the JIS P8115 MIT folding resistance test, the measurement is performed using an MIT folding resistance test apparatus (Toyo Seiki Seisakusho No. 530-S type). That is, the separation membrane is cut into a size of 15 mm width × 110 mm length, a load of 2 kg is applied, bending is performed under the conditions of a bending angle of 135 ± 2 ° on the left and right, and a rotational speed of 175 cpm, and the number of times until it breaks is obtained. It was.

[Fixing strength test]
According to JIS K6854 180 degree peel test, measurement is performed using “TENSILON” (TENSILON / UTM-4L TOYOMSURING INSTRUMENTS CO., LTD). That is, a separation membrane sample having a width of 25 mm, in which a separation membrane was bonded to the element support plate with a hot melt adhesive, was pulled at a peeling rate of 200 mm / min, and the strength until peeling was determined.

<Example 1>
Polyvinylidene fluoride (PVDF / Kureha Chemical Co., Ltd., KF # 850) was used as a resin component for the film-forming stock solution. Moreover, monostearic acid polyoxyethylene sorbitan was used as a pore opening agent, N, N-dimethylformamide (DMF) was used as a solvent, and H ₂ O was used as a non-solvent. These were sufficiently stirred at a temperature of 95 ° C. to prepare a film-forming stock solution having the following composition.

Polyvinylidene fluoride (PVDF): 17.0% by weight
Polyoxyethylene sorbitan monostearate: 8.0% by weight
N, N-dimethylformamide (DMF): 72.0% by weight
H ₂ O: 3.0% by weight
As a substrate, a rectangular polyester fiber nonwoven fabric having a density of 0.42 g / cm ^{3 and a} size of 50 cm width × 150 cm length and a central portion of a rectangular polyester fiber nonwoven fabric of size 50 cm width × 150 cm length 40 cm width × 140 cm length ( A non-woven fabric with a rectangular shape is stacked on top of each other, passed through a heater roll heated to 180 ° C., and two non-woven fabrics are attached at a nip pressure of 180 kg / cm to produce a base material with a thin central part and a thickness difference. did.

  Next, after the film-forming stock solution is cooled to 30 ° C., it is applied to the smooth surface side of the substrate having a thickness difference, and immediately after the application, it is immersed in pure water at 20 ° C. for 5 minutes. The composite separation membrane was manufactured by immersing in hot water for 2 minutes to wash away N, N-dimethylformamide as a solvent and polyoxyethylene sorbitan monostearate as a pore-opening agent.

Next, with respect to the composite separation membrane, when the blocking rate of latex fine particles having an average particle size of 0.088 μm was measured at the thick part of the base material layer on the peripheral side of the base material, it was a high value of 99.4%. The water permeability was 40.1 × 10 ⁻⁹ m ³ / m ² · s · Pa. The rejection of 0.088 μm latex fine particles in the center of the separation membrane was 99.1%, which was the same level as the peripheral edge. Moreover, the amount of water permeation was 44.5 × 10 ⁻⁹ m ³ / m ² · s · Pa, which was higher than the thickness of the base layer on the peripheral side.

  Further, when the number of times until the rupture of the separation membrane was measured with an MIT folding resistance test apparatus, the number of ruptures at the thickened portion of the base material layer on the peripheral side was 130,981 times compared to 30,500 at the center portion. It was much higher than the central part and satisfied the desired level of folding resistance.

  Further, from the obtained composite separation membrane, the membrane separation element shown in FIG. 1 (excluding the support groove 7A) and FIG. 4 was produced. In the obtained membrane separation element, the area ratio of the thick part of the base material layer on the peripheral side was 25.3%. Moreover, when the strength until peeling with a tensile tester was measured, it was 1520 N / 5 mm, which satisfies the desired level of peeling resistance. When this membrane separation element was used in a submerged membrane separation method as shown in FIG. 5 and tested for 3 months with activated sludge, no damage to the separation membrane was observed in the vicinity of the bonded portion. The results are shown in Table 1.

<Example 2>
The composite separation membrane obtained in the same manner as in Example 1 was fixed to an element provided with a groove having a groove ratio of 28% and a groove depth of 1.5 mm with respect to the fixing portion of the element support member. The membrane separation element shown in FIG. 4 was produced. In the obtained membrane separation element, the area ratio of the thick part of the base material layer on the peripheral side was 25.3%. Further, when the strength until peeling with a tensile tester was measured, the separation membrane was not peeled off from the element support member, and the separation membrane was broken, which was very satisfactory. When this membrane separation element was used in a submerged membrane separation method as shown in FIG. 5 and tested for 3 months with activated sludge, no damage to the separation membrane was observed in the vicinity of the bonded portion. The results are shown in Table 1.

<Comparative example>
As in the case of the conventional membrane separation element, the base material (density 0.42 g / cm ³ , size 50 cm width × 150 cm length, thickness 0.3 mm, polyester, thickness is substantially uniform, and there is no thickness difference between the peripheral portion and the central portion. A composite separation membrane was produced in the same manner as in Example 1 using a fiber nonwoven fabric.

When the blocking rate of latex fine particles having an average particle size of 0.088 μm of the obtained composite separation membrane was measured, it was a high value of 99.3%. Further, the water permeability was 43.8 × 10 ⁻⁹ m ³ / m ² · s · Pa. Moreover, when the number of times until the rupture of the separation membrane was measured with an MIT folding resistance test apparatus, it was 31,221 times, which was the same level as the central portion of Example 1.

  Further, a membrane separation element was produced in the same manner as in Example 1. When the fixing strength was measured with a tensile tester, it was 440 N / 5 mm, which was less than half that of Example 1. When an actual liquid test using activated sludge was performed, cracks were found in the separation membrane near the bonded area.

It is sectional drawing which shows typically one embodiment of the membrane separation element concerning this invention. It is a figure which shows typically the planar shape of the separation membrane which was seen by the line II of FIG. It is a figure which shows typically the planar shape of the membrane separation element seen by the arrow of line DD of FIG. It is a perspective view which shows one embodiment of the membrane separation element which concerns on this invention. It is a figure which shows the general | schematic flow of the method of performing a waste liquid process using the membrane separation module which concerns on this invention.

Explanation of symbols

1: Composite separation membrane 2: Base material layer 2A: Peripheral base material layer thick part 2C: Base material layer central part 3: Mixed layer 4: Porous separation functional layer 5: Adhesive layer 6: Protrusion 7: Support 7A: Support groove 8: Membrane separation element 9: Permeate outlet 10: Opening for communication 11: Separation membrane 12: Blower 13: Membrane separation module 14: Water tank 15: Air diffuser 16: pump

Claims (5)

  A membrane separation element in which flat separation membranes are disposed on both sides of a support, and the support and the separation membrane are fixed at the outer periphery, and as the separation membrane, a base material layer and a porous separation functional layer, A base material layer having a base material layer thickness 1.1 to 3 times the base material layer thickness of the central part of the separation membrane is provided on the peripheral side in the vicinity of the fixed outer peripheral edge. A membrane separation element, characterized in that a thick portion is provided and an area ratio of the base layer thick portion is 1% or more and 30% or less with respect to a permeation area of the separation membrane.   A composite separation membrane in which a layer in which a resin and a substrate constituting the porous separation functional layer are intervened between the base material layer and the porous separation functional layer of the composite separation membrane is used as a separation membrane, and The membrane separation element according to claim 1, wherein the base material layer comprises a nonwoven fabric or a woven or knitted fabric.   A groove is provided in the fixing portion of the support, the ratio of the groove to the fixing portion is 1% or more and 50% or less, and the depth of the groove is 1% or more and 40% or less of the thickness of the support plate. The membrane separation element according to claim 1 or 2, characterized in that   In order to form a flow path of the permeate that has passed through the separation membrane, an unevenness is formed on the surface of the support, and a permeate outlet that communicates with the flow path of the permeate in the element is provided. The membrane separation element according to claim 1.   A membrane separation module in which a plurality of membrane separation elements according to any one of claims 1 to 4 are accommodated in a housing or fixed in an arrayed state.

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