JP2015160185A - membrane bioreactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane bioreactor using a microporous membrane which has higher permeability while keeping a particle blocking rate.SOLUTION: The microporous membrane used in the membrane bioreactor of the present application, is a microporous membrane being an asymmetric membrane, and comprises a surface layer in which micropores are formed and a support layer which supports the surface layer and in which pores larger than the micropores are formed. A raw material of the microporous membrane is a vinylidene fluoride resin. The surface layer has a plurality of spheroids, and a plurality of linear binding materials 2 extend in the three-dimensional direction from each of the spheroids 1, and the adjacent spheroids 1 are connected to each other by the linear binding materials 2, and form a three-dimensional network structure with the spheroids 1 as an intersection. In the membrane bioreactor of the present application, clogging of the microporous membrane to active sludge is largely suppressed by using the microporous membrane having the three-dimensional network structure, and running cost is reduced, and a cleaning and replacement frequency of the membrane can be reduced.

Description

  The present invention relates to a membrane bioreactor.

  The membrane bioreactor is an apparatus used for wastewater treatment technology also called membrane separation activated sludge method. In the conventional sedimentation tank type activated sludge method, the sludge and the treated water are separated using a sedimentation tank. In the membrane bioreactor, the sludge and the treated water are separated by membrane filtration. The membrane bioreactor is superior to the sedimentation tank type activated sludge method in that it does not require a sedimentation tank and the like, so that the equipment can be downsized and the quality of treated water is high. On the other hand, however, there are problems such as regenerating and replacing clogged microporous membranes, or pumping used for membrane filtration and aeration to clean the membrane surface, which requires energy and increases running costs. It was.

  As a method for solving this problem, Patent Document 1 discloses that fine particles made of polyvinyl alcohol gel or the like are put in activated sludge, and the solid matter is peeled off by contact with the membrane surface by a liquid flow, thereby reducing operating energy. A method has been proposed. However, this method is effective only at the point where the fine particles are in contact, and it is necessary to add a considerable amount of fine particles in order to obtain a sufficient effect to prevent clogging. Further, depending on the type of foreign matter adhering to the film, sufficient peeling cannot be expected with the degree of contact of fine particles.

  As another method, Patent Document 2 proposes a method of performing membrane cleaning in-line using alkaline water and acidic water produced by a diaphragm electrolyzer. However, cleaning with such a chemical solution is expensive, and depending on the chemical solution used, there is a possibility of affecting the biota in the activated sludge.

  As another method, Patent Document 3 proposes a method of suppressing generation and growth of an adhesive substance by applying zeolite carrying antibacterial metal ions to the surface of a filtration membrane. However, this method cannot be expected to be effective for adhesive substances that are not derived from bacteria, or there is a concern that the effect may be reduced over time due to detachment of zeolite or dissolution of antibacterial metal ions in water.

JP 63-214177 A JP 10-005784 A JP 2002-224541 A

  An object of the present invention is to reduce membrane exchange frequency and operating energy by preventing clogging of a microporous membrane used in a membrane bioreactor.

  The present inventors have intensively studied to solve the above problems. As a result, it was found that clogging of the microporous membrane against activated sludge can be greatly suppressed by optimizing the configuration of the microporous membrane used in the membrane bioreactor, especially the surface geometric structure, and the present invention was completed. I let you.

  The membrane bioreactor according to the first aspect of the present invention uses a microporous membrane as a separation membrane. This separation membrane has a surface layer, and this surface layer has a plurality of spherical bodies 1, and a plurality of linear binders 2 extend from each spherical body 1 in a three-dimensional direction. Are connected to each other by a linear bonding material 2 to form a three-dimensional network structure with the spherical body 1 as an intersection. FIG. 1 shows an example of the three-dimensional network structure of the present application. FIG. 1 is a scanning electron microscope (SEM) photograph of the surface layer surface.

  The membrane bioreactor according to the second aspect of the present invention is the membrane bioreactor according to the first aspect of the present invention, wherein the spherical particles of the microporous membrane have a width of ± 10% of the average particle diameter. In the range of 45% or more.

  The membrane bioreactor according to the third aspect of the present invention is the membrane bioreactor according to the first aspect or the second aspect of the present invention described above, wherein the length of the binder of the microporous membrane is ±± It has a frequency distribution of 35% or more in a range of 30% width.

  The membrane bioreactor according to the fourth aspect of the present invention is the membrane bioreactor according to any one of the first to third aspects of the present invention, wherein the spherical body of the microporous membrane is 0. It has an average particle size of 0.05 to 0.5 μm.

  The membrane bioreactor according to the fifth aspect of the present invention is the membrane bioreactor according to any one of the first to fourth aspects of the present invention, wherein the microporous membrane having a support layer is separated from the membrane bioreactor. It is said. The support layer is a layer that is made of the same material as the surface layer and reinforces the surface layer from deformation. The support layer is generally a layer containing macrovoids. “Macrovoid” refers to a huge cavity having a minimum size of several μm and a maximum size approximately equal to the thickness of the support layer. The surface layer has a thickness of 0.5 to 10 μm, and the support layer has a thickness of 20 to 500 μm.

  The membrane bioreactor according to the sixth aspect of the present invention is the membrane bioreactor according to any one of the first to fifth aspects of the present invention, wherein the microporous membrane supports the support layer. A material layer is provided. The material of the base material layer is made of a material different from that of the support layer.

  The membrane bioreactor according to the seventh aspect of the present invention is the membrane bioreactor according to any one of the first to sixth aspects of the present invention, wherein the material of the microporous membrane is polyvinylidene fluoride. Resin.

  The membrane bioreactor according to the eighth aspect of the present invention is the same as the membrane bioreactor according to the seventh aspect of the present invention, except that the polyvinylidene fluoride resin constituting the microporous membrane is good as shown in FIG. A graph of a solution dissolved in a solvent, in which the horizontal axis indicates the shear rate and the vertical axis indicates the reciprocal of the solution viscosity, is a curve including an arc having a convex on the upper side. That is, it suffices if a part of the graph includes an arc having a convex on the upper side.

The membrane bioreactor according to the ninth aspect of the present invention is the membrane bioreactor according to any one of the seventh aspect to the eighth aspect of the present invention, as shown in FIG. An area having a shear rate of 40 per second or less in a graph of a solution of 10 parts by weight of vinylidene resin, 10 parts by weight of polyethylene glycol, and 80 parts by weight of dimethylacetamide, with the horizontal axis being the shear rate and the vertical axis being the reciprocal of the solution viscosity. It can be approximated by a quadratic function, and the quadratic coefficient of the quadratic function is smaller than 10 ⁻⁸ .

  The membrane bioreactor according to the tenth aspect of the present invention is the membrane bioreactor according to the seventh aspect or the ninth aspect of the present invention, wherein the polyvinylidene fluoride resin has a weight average molecular weight (Mw) of 60 10,000 to 1.2 million.

  The membrane bioreactor of the present invention has a three-dimensional network structure in which a surface layer has a plurality of spherical bodies, the spherical bodies and a linear binding material that connects the spherical bodies to each other, and the spherical bodies are intersections. Since the microporous membrane formed with is used, it is difficult to clog activated sludge and the like. Therefore, compared with a conventional membrane bioreactor using a general microporous membrane, the running cost can be reduced, and furthermore, membrane cleaning and replacement can be reduced.

It is a surface photograph of the surface layer which the microporous film which concerns on 1st Embodiment has. It is a photograph of the conventional PVDF filtration membrane. It is the surface photograph of the surface layer which the microporous film of Example 1 has, and is a photograph used for the measurement of the particle size of the spherical body and the length of the linear binder. It is a flowchart which shows the manufacturing method of the microporous film which concerns on 2nd Embodiment. (A) is a cross-sectional photograph of the microporous membrane of Example 1. FIG. (B) is an enlarged photograph of a cross-sectional portion of the surface layer. 4 is a graph showing the relationship between the reciprocal of the solution viscosity of the raw material liquid of Example 1 and the shear rate. It is a schematic diagram which shows sectional drawing (left) of an asymmetric membrane, and sectional drawing (right) of a symmetrical membrane. (Source: JPO Homepage / 2005 Standard Technology Collection Water Treatment Technology / 1-6-2-1 Symmetric Membrane and Asymmetric Membrane) It is a schematic diagram which shows the structural example of a membrane bioreactor. It is a figure which shows the fouling resistance of Example 1 and Comparative Example 1.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same or similar reference numerals, and redundant description is omitted. Further, the present invention is not limited to the following embodiments.

  The membrane bioreactor according to the first embodiment of the present invention will be described. FIG. 1 is a part of a photograph of the surface (surface layer side) of a microporous membrane used in the membrane bioreactor according to the first embodiment taken with a scanning electron microscope (SEM). As shown in FIG. 1, the surface layer has a plurality of spherical bodies 1, and a plurality of linear binders 2 extend from each spherical body 1 in a three-dimensional direction. They are connected by a linear binder 2 to form a three-dimensional network structure with the spherical body 1 as an intersection, and the generated voids are holes. Therefore, a hole is easily formed in the surface layer, and the hole is not easily deformed.

  Even if the surface of the microporous membrane used in the conventional membrane bioreactor has the “spherical body” or the “binding material” in the present invention, it has only one of them. For example, a microporous membrane having only a portion corresponding to the “binding material” in the present invention is difficult to maintain a strength sufficient to be used as a filtration membrane even if it is uniformly bonded. In order to prevent this, if the portion corresponding to the “binding material” is thickened, it becomes a surface rather than a linear shape, and it is difficult to make the holes fine. FIG. 2 is a scanning electron micrograph of a conventional microporous membrane (made of polyvinylidene fluoride) having such a structure as an example. The microporous membrane according to the first embodiment is higher than the conventional microporous membrane having the same average flow pore diameter due to the spherical bodies 1 possessed by the surface layer and the linear binder 2 connecting them. It has permeability. Here, the “average flow pore size” is a value obtained by ASTM F316-86, and when a microporous membrane is used as a filtration membrane, it greatly affects the blocking particle size. On the contrary, a microporous membrane having only a portion corresponding to a “spherical body” is a filtration membrane having a structure in which a sphere is in contact with the sphere. The pores of such a filtration membrane are only the gaps between the spheres, and the water permeability becomes extremely poor. Several membranes with a structure in which spheres and spheres are partially connected by a linear substance have been reported, but such membranes are not suitable for filtration membranes because their pore sizes and shapes are not uniform. . That is, the three-dimensional network structure of the present invention appears only when both the spherical body and the binder are present. For this reason, the effect of the present invention cannot be obtained with a microporous membrane used in a conventional membrane bioreactor.

  The difference between the microporous membrane used in the membrane bioreactor according to the first embodiment of the present invention and the microporous membrane used in the conventional membrane bioreactor does not stop there. When the microporous membrane has a structure like the microporous membrane used in the membrane bioreactor according to the first embodiment of the present invention, the spherical bodies are arranged on the membrane surface almost on the same plane. Large unevenness does not occur. Furthermore, as shown in FIG. 1, the spherical bodies 1 are almost uniform in size and are uniformly dispersed. Therefore, a surface layer in which the shape and size of the gap generated between the spherical body 1 and the spherical body 1 are uniform is formed. The space between the spheres 1 is delimited by a linear binder 2 that bridges the adjacent spheres 1, and the resulting holes are egg-shaped or almost egg-shaped with no dents on the outer periphery curve. Thus, a microporous membrane having a uniform pore shape is obtained. For this reason, particles and viscous objects contained in the activated sludge of the membrane bioreactor are difficult to enter the membrane, and as a result, the microporous membrane is not easily clogged.

  The average particle diameter of the spherical body of the surface layer of the microporous membrane used in the membrane bioreactor according to the first embodiment of the present invention is 0.05 to 0.5 μm. Preferably it is 0.1-0.4 micrometer, More preferably, it is 0.2-0.3 micrometer. The particle size of the spherical body is determined by taking a photograph using a scanning electron microscope (SEM) or the like at a magnification at which the spherical body can be clearly confirmed on the surface layer side surface of the microporous film. It can be determined by measuring the particle size and averaging the number. Specifically, it is as described in the examples. The “particle diameter” is the diameter of a perfect circle when the outer periphery of the spherical body is surrounded by a perfect circle having the maximum diameter that does not include the surrounding holes. In order to make the shape of the pores of the surface layer more uniform, the shape of each spherical body is preferably close to a perfect sphere. The preferred size of the spherical body varies depending on the size of the fine particles that need to be prevented from permeating. In the case of a membrane bioreactor, both high quality of treated water and permeability can be achieved when the spherical body takes the above range.

  It is preferable that the size of the spherical body has little variation. For this reason, the particle size of the spherical body preferably has a frequency distribution of 45% or more, more preferably 50% or more in the range of ± 10% of the average particle size in the frequency distribution. More preferably, it is 55% or more, More preferably, it is 60% or more. When the frequency of 45% or more is distributed in the range of the width of ± 10% of the average particle diameter, the spherical body of the surface layer has a more uniform shape and size, and the pore diameter between the spherical body and the spherical body Can form uniform (aligned) voids.

  The spherical bodies are preferably dispersed uniformly on the surface of the surface layer. Therefore, the distance between the spherical body and the nearest spherical body (distance between the centers of the spherical bodies) has a frequency distribution of 50% or more in the range of ± 30% of the average distance in the frequency distribution. It is preferable. More preferably, it is 70% or more, More preferably, it is 75% or more. If the frequency distribution is 50% or more in the range of ± 30% width of the average distance, the spherical bodies are more uniformly dispersed on the surface of the surface layer. In this case as well, the pore size is between the spherical bodies and the spherical bodies. Can form uniform (aligned) voids.

  The average length of the linear binding material included in the surface layer of the microporous membrane used in the membrane bioreactor according to the first embodiment of the present invention is 0.05 to 0.5 μm. Preferably it is 0.1-0.4 micrometer, More preferably, it is 0.2-0.3 micrometer. Most of the lengths of the linear binders are close to the average length, and the length is uniform. Further, the average length varies depending on the produced microporous membrane, and the value has a width as described above. Therefore, various microporous membranes having different pore sizes formed in the surface layer and different average flow pore diameters can be obtained.

The average length of the linear binder is taken with a scanning electron microscope (SEM) or the like at a magnification at which the linear binder can clearly confirm the surface layer side surface of the microporous film, and at least 100 or more. The length of an arbitrary linear binding material can be measured and the number averaged. Specifically, it is as described in the examples. The “length of the linear binding material” is a distance between the perfect circles when the outer periphery of the spherical body is surrounded by a perfect circle having a maximum diameter that does not include the surrounding holes.

  The length of the linear binder preferably has a frequency distribution of 30% or more, more preferably 50% or more in the range of ± 30% of the average length in the frequency distribution. More preferably, it is 55% or more, More preferably, it is 60% or more. When the frequency of 30% or more is distributed in the range of the average length ± 30%, the spherical bodies in the surface layer are more uniformly dispersed, and the pore diameter is uniform (aligned) between the spherical bodies and the spherical bodies. A void can be formed.

  The ratio of the average particle diameter of the spherical body to the average length of the linear binder is preferably between 3: 1 and 1: 3. When the average particle diameter of the spherical body is smaller than three times the average length of the linear binder, the opening on the surface layer surface of the microporous membrane becomes large, and a high permeation amount can be obtained more remarkably. In addition, if the average particle size of the spheres is larger than one third of the average length of the binder, the number of binders that can be connected to one sphere increases, so there is little dropout of the filter media and high pressure resistance. Features can be obtained more prominently.

  The average pore diameter of the microporous membrane used in the membrane bioreactor according to the first embodiment of the present invention is 0.05 to 8 μm, preferably 0.05 to 0.5 μm, more preferably 0. 0.07 to 0.25 μm, and further 0.1 to 0.25 μm. That is, when a microporous membrane is used as a filtration membrane, a substance having a diameter of about 0.05 to 8 μm or more can be separated according to the average flow pore size. The average flow hole diameter is a value based on the bubble point method (ASTM F316-86).

The microporous membrane used in the membrane bioreactor according to the first embodiment of the present invention has a pure water permeation flux of 1.5 × 10 ⁻⁹ m ³ / m ² / Pa / s or more, preferably 30 * 10 < ^-9 > m < ³ > / m < ² > / Pa / s or more, More preferably, it is 60 * 10 < ^-9 > m < ³ > / m < ² > / Pa / s or more. When the pure water permeation flux is 1.5 × 10 ⁻⁹ m ³ / m ² / Pa / s or more, sufficient water permeability of the membrane is obtained, and higher filtration pressure is obtained when water permeability is not sufficiently obtained. Etc., and the problem of increased operating costs can be avoided. In addition, as shown in Example 1, the pure water permeation flux allows water to flow at the filtration pressure in the microporous membrane, measures the flow rate per unit time, and divides the flow rate by the effective filtration area and the filtration pressure. Can be sought.

  The polymer used as the material of the microporous membrane used in the membrane bioreactor according to the first embodiment of the present invention includes a polyvinylidene fluoride resin (containing a main component (containing 50% by weight or more)). Are preferred. Examples of the polyvinylidene fluoride resin include a resin containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer. A plurality of types of vinylidene fluoride homopolymers having different physical properties (viscosity, molecular weight, etc.) may be contained. Alternatively, a plurality of types of vinylidene fluoride copolymers may be contained. The vinylidene fluoride copolymer is not particularly limited as long as it is a polymer having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and other fluorine-based monomers, for example, Examples thereof include a copolymer of at least one fluorine-based monomer selected from vinyl fluoride, tetrafluoroethylene, propylene hexafluoride, and ethylene trifluoride chloride and vinylidene fluoride. Particularly preferred is a vinylidene fluoride homopolymer (polyvinylidene fluoride). In addition, it does not necessarily need to be a pure polyvinylidene fluoride resin, and in order to give other characteristics (for example, antibacterial property), you may mix other polymers in the range which does not prevent the effect of this invention.

  Since the polyvinylidene fluoride resin is a fluororesin, it is mechanically, thermally and chemically stable. Other typical fluororesins include polytetrafluoroethylene (PTFE) or so-called tetrafluorinated resins such as tetrafluoroethylene-based copolymer resins (tetrafluoroethylene / perfluoroalkoxyethylene copolymers, etc.). Although there is a resin, the tetrafluoride-based resin has a weak intermolecular entanglement, and therefore the pores are likely to be deformed by the filtration pressure when the mechanical strength is low and a microporous membrane is formed. In addition, there is a drawback that the holes are more likely to be deformed when used at high temperatures. In these respects, the polyvinylidene fluoride resin is superior. In addition, the polyvinylidene fluoride resin has an advantage that it is easier to process than other fluororesins (for example, PTFE), and is easy to perform secondary processing (for example, cutting or adhesion to other materials) after processing.

  Of the polyvinylidene fluoride-based resins, a resin having the following characteristics is particularly preferable. That is, in a solution in which a polyvinylidene fluoride resin is dissolved in a good solvent, a part of the graph in which the reciprocal of the solution viscosity (unit cP) is the vertical axis and the shear rate (unit 1 / s) is the horizontal axis is a quadratic function. As shown in FIG. 6, in the low shear rate region (40 / s or less), it is preferable that the polyvinylidene fluoride resin is a curve in which the quadratic function includes an arc having a convex on the upper side. This indicates that there is a point where the viscosity of the solution rapidly increases in the low shear rate region.

For example, in a solution of 10 parts by weight of a polyvinylidene fluoride resin, 10 parts by weight of polyethylene glycol, and 80 parts by weight of dimethylacetamide, the quadratic coefficient of the quadratic function indicated by a part of the graph of the reciprocal of the solution viscosity and the shear rate is 10 A polyvinylidene fluoride resin that is smaller than ⁻⁸ is preferable.

The surface layer of the microporous membrane used in the membrane bioreactor of the present invention is induced when the raw material liquid comes into contact with a non-solvent and the solvent in the raw material liquid replaces the non-solvent. When the polyvinylidene fluoride resin having the above-described characteristics is used, the viscosity of the raw material liquid changes rapidly as the substitution proceeds, so that it is considered that a three-dimensional network structure composed of a spherical body and a linear binder is developed. . In fact, it has been confirmed by Examples that the three-dimensional network structure of the present application is expressed from a raw material liquid of polyvinylidene fluoride resin having a second order coefficient smaller than 10 ⁻⁸ .

Furthermore, the weight average molecular weight of the polyvinylidene fluoride resin is 600,000 to 1,200,000, preferably 600,000 to 1,000,000, more preferably 700,000 to 950,000, and even more preferably 790,000 to 900,000. is there. The higher the weight-average molecular weight of the polyvinylidene fluoride resin, the easier it is to form spherical bodies and linear binders, so that a microporous film having a surface layer having a three-dimensional network structure can be easily obtained. Therefore, the selection range of a good solvent and a poor solvent, which will be described later, is widened, and it becomes easier to further increase the permeability and membrane strength of the microporous membrane. Also, it is preferable to prevent the weight average molecular weight from being too high, since the viscosity of the raw material liquid can be suppressed, it becomes easy to apply uniformly, and a mixed portion of the support layer and the base material layer can be more easily formed.
In order not to impede the effects of the present invention, polyvinylidene fluoride having a weight average molecular weight outside this range may be mixed in order to increase the adhesion to other materials and the film strength.

  Here, the “good solvent” is defined as a liquid capable of dissolving a necessary amount of polyvinylidene fluoride resin under a temperature condition for applying the raw material liquid. The “non-solvent” is defined as a solvent that does not dissolve or swell the polyvinylidene fluoride resin under a temperature condition that replaces the good solvent in the coating film with a non-solvent. The “poor solvent” is defined as a solvent that cannot dissolve the required amount of the polyvinylidene fluoride-based resin, but can dissolve less than that amount, or swells.

  Good solvents include N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide, N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, phosphorus Examples include lower alkyl ketones such as trimethyl acid, esters, amides, and the like. These good solvents may be used as a mixture, and may contain a poor solvent and a non-solvent as long as the effects of the present invention are not impaired. When film formation is performed at room temperature, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, and N, N-dimethylformamide are preferable.

  Non-solvents include water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, low molecular weight polyethylene glycol and other aliphatic hydrocarbons, aromatic hydrocarbons, chlorine Hydrocarbons or other chlorinated organic liquids. The non-solvent needs to be dissolved in a good solvent and is preferably mixed with the good solvent in a free ratio. A good solvent or a poor solvent may be intentionally added to the non-solvent.

  Since the substitution rate of the good solvent and the non-solvent affects the expression of the three-dimensional network structure of the present invention, the combination thereof is also important. As the combination, NMP / water, DMAc / water, DMF / water, and the like are preferable from the viewpoint of easy expression of a three-dimensional network structure, and a combination of DMAc / water is particularly preferable.

  In addition to the polyvinylidene fluoride resin as a raw material and its good solvent, it is preferable to add a porosifying agent that promotes porosity to the raw material liquid for film formation. The porous agent is not limited as long as it does not inhibit dissolution of the polyvinylidene fluoride resin in a good solvent, dissolves in a non-solvent, and promotes the microporous membrane to become porous. . Examples include organic high-molecular substances or low-molecular substances, such as water-soluble polymers such as polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone, and polyacrylic acid, and sorbitan fatty acid esters. Low ethylene oxide, such as ester of polyhydric alcohol such as (mono, triester, etc.), ethylene oxide low molar adduct of sorbitan fatty acid ester, ethylene oxide low molar adduct of nonylphenol, pluronic ethylene oxide low molar adduct Mole adducts, polyoxyethylene alkyl esters, alkylamine salts, surfactants such as sodium polyacrylate, polyhydric alcohols such as glycerin, tetraethylene glycol, triethylene glycol, etc. Mention may be made of the recall class. These may be used alone or in a mixture of two or more.

These porous agents preferably have a weight average molecular weight of 50,000 or less, more preferably 30,000 or less, and still more preferably 10,000 or less. When the weight average molecular weight is 50,000 or less, it can be uniformly dissolved in the polyvinylidene fluoride resin solution. This porous agent remains in the porous resin for a relatively long time compared to the good solvent when the good solvent is extracted in a non-solvent and structural aggregation occurs. Therefore, it greatly affects the film structure. As a porous agent when water is used as a non-solvent, it is easy to exert these functions, and since it easily develops a three-dimensional network structure composed of a spherical body and a linear binder, The liquid is preferable. More preferred are polyethylene glycol and polyvinyl pyrrolidone, and particularly preferred is polyethylene glycol. More preferably, the weight average molecular weight is 200 to 1,000. When the weight average molecular weight is 200 to 1000, the structure is particularly easily developed. Moreover, by setting the weight average molecular weight to 1000 or less, it becomes easy to remove the porous agent after the structure is developed.

  When a porosifying agent is used, since the porosizing agent is extracted after the structural aggregation accompanying the good solvent extraction is moderated, the obtained porous resin has high porosity. The resulting structure depends on the type of porous agent, molecular weight, added amount, and the like. If the amount of the porous agent added is small, such an effect is difficult to obtain, but if the amount added is large, the macrovoids generated in the support layer may increase and the film strength may be lowered. Therefore, it is preferable to add the porous agent in an amount of 0.1 to 2 times, more preferably 0.5 to 1.5 times the weight of the polyvinylidene fluoride resin.

  The production method of the microporous membrane used in the membrane bioreactor according to the second embodiment of the present invention is as follows. FIG. 4 shows a rough flow of the manufacturing method.

(1) Raw material liquid preparation step (S01):
First, a raw material solution is prepared by dissolving a polymer that is a material of a microporous membrane in a solvent that is a good solvent for the polymer. Specifically, for example, polyvinylidene fluoride as a material of 5 to 20 parts by weight and polyethylene glycol as a porosizing agent in an amount of 0.1 to 2 times the material weight are 70 to 90 parts by weight. After dissolving in dimethylacetamide (DMAc) at normal temperature to 100 ° C., it is returned to normal temperature to make a raw material liquid.

(2) Porous process (S02):
Next, a non-woven fabric as a base material layer is placed on a smooth coating table such as a glass plate or a stainless steel plate, and the raw material liquid is applied thereon. In addition, you may apply | coat directly on them, using a glass plate etc. as a support body, without placing a nonwoven fabric etc., In that case, it becomes a microporous film without a base material layer. Moreover, it is preferable to apply | coat so that the thickness after film forming may be 10-500 micrometers. Immediately after coating, or after standing for a certain period of time, it is immersed in a non-solvent for the polymer of the material for 3 minutes to 12 hours. When providing the leaving time after application | coating, about 5 to 60 second is preferable. If the standing time is taken longer, the average flow hole diameter becomes larger, but if it is taken too long, pinholes are generated and the effects of the present invention may not be sufficiently obtained. A good solvent and a non-solvent are mixed, and the solubility of the polymer in the good solvent is lowered due to the mixing of the non-solvent, and the polymer is precipitated to cause porosity (non-solvent induced phase separation method (NIPS)).
Specifically, for example, a polyester nonwoven fabric is placed on a glass plate, and the raw material liquid is applied. For the application, a baker applicator, a bar coater, a T die, or the like can be used. After soaking in a non-solvent, the glass plate as a coating stage is removed to obtain a microporous film.

(3) Cleaning / drying step (S03):
Finally, the obtained microporous membrane is washed by changing water several times. In general, DMAc is less likely to evaporate than water, and therefore, if the cleaning is incomplete, the solvent (DMAc) is concentrated and the created pore structure may be dissolved again. In order to reduce the amount of drainage and increase the washing speed, warm water may be used for washing, or an ultrasonic washing machine may be used. After washing, the microporous membrane may be dried. Drying may be natural drying, a hot-air dryer or a far-infrared dryer may be used to increase the drying speed, and pintenter drying is used to prevent shrinkage and undulation of the microporous membrane during drying. It is good also as a machine.

As in the porosification step (S02), a base material layer may be provided during film formation. When the base material layer is provided, shrinkage of the polymer is suppressed at the time of immersion, so that a surface layer having sufficient voids can be obtained as compared with the case where the base material layer is not provided. Alternatively, the raw material liquid can be prevented from inadvertently flowing out during the application of the raw material liquid. This is particularly effective in the case of a raw material liquid having a low viscosity. Furthermore, the base material layer functions as a reinforcing material at the time of filtration, so that the membrane can more withstand the filtration pressure. As the base material layer, non-woven fabrics, woven fabrics, porous boards, etc. obtained by paper making, carding, spunbonding, melt blowing, etc. can be used, and the materials include polyester, polyolefin, ceramic, cellulose, etc. Can be used. Of these, a polyester nonwoven fabric is preferred because of its excellent balance of flexibility, lightness, strength, heat resistance, and the like. In the case of using a nonwoven fabric, the basis weight is preferably in the range of 15~150g / ^{m 2,} more preferably in the range of 30~70g / ^{m 2.} When the basis weight exceeds 15 g / m ² , the effect of providing the base material layer is sufficiently obtained. On the other hand, when the basis weight is less than 150 g / m ² , post-processing such as bending and heat bonding becomes easy.

  As described above, since the microporous membrane used in the membrane bioreactor of the present invention has a three-dimensional network structure with a homogeneous spherical body and a linear binder, the pore size and pore diameter of the surface layer are uniform. Therefore, high permeability (for example, high water permeability and high liquid permeability) can be realized. That is, since the size and shape of the pores are more uniform, a membrane with a narrower pore size distribution is obtained, and unprecedented permeability can be obtained while maintaining the particle blocking rate. Furthermore, since a polyvinylidene fluoride resin is used as the film material, it can have excellent chemical resistance and high heat resistance (˜120 ° C.). The microporous membrane of the present invention may be a flat membrane or a hollow fiber membrane. When the microporous membrane used in the membrane bioreactor of the present invention is a flat membrane, there is an advantage that the clogging of the membrane can be easily cleaned as compared with a general flat membrane. In addition, when the microporous membrane of the present invention is a hollow fiber membrane, there is an advantage that the effect of backwashing can be easily obtained as compared with a general hollow fiber membrane.

  A membrane bioreactor is obtained by incorporating the microporous membrane made as described above in a liquid-tight manner in the pipe connecting the activated sludge tank and the suction pump so that clear filtered water can be obtained from the suction pump. . Although there is no particular limitation on the method of assembling, it is preferable to use a cartridge that can be easily attached and detached in order to improve maintainability. For example, when a flat membrane-like microporous membrane is used, the cartridge is shaped by providing a cavity inside the flat plate, providing a hole connecting one side of the flat plate and the cavity, There may be used a plurality of holes that connect the two, and a microporous film adhered on both surfaces of the flat plate in a liquid-tight manner. A configuration example of the membrane bioreactor is shown in FIG. The activated sludge 4 is put in the activated sludge tank 3. Several membrane bioreactor cartridges are connected to form a membrane bioreactor unit 5 and placed in the activated sludge tank 3. In this example, two membrane bioreactor units 5 are inserted. A suction pump 6 and a flow meter 7 are connected to each membrane bioreactor unit 5. A pressure gauge 8 is connected between the membrane bioreactor unit 5 and the suction pump 6 to read the differential pressure of the membrane. Then, sewage is introduced into the activated sludge tank 3 using the sewage supply pump 9.

  Hereinafter, the present invention will be described in more detail with reference to examples and the like. However, the scope of the present invention is not limited by these descriptions.

[Used materials]
The reagent grade 1 manufactured by Wako Pure Chemical Industries, Ltd. was used for polyethylene glycol 600 (weight average molecular weight 600), and the reagent special grade manufactured by Wako Pure Chemical Industries, Ltd. was used as it was for dimethylacetamide.
As the polyvinylidene fluoride, Arkema polyvinylidene fluoride “Kyner HSV900” (weight average molecular weight 800,000, number average molecular weight 540,000) was used.
H1007 (weight per unit area: 70 g / m ² ) manufactured by Japan Vilene was used for the polyester nonwoven fabric as the base material layer.
A glass plate having a size of 50 cm × 120 cm was used.
As the water, ultrapure water having a specific resistance value of 18 MΩ · cm or more manufactured by “DirectQ UV” (trade name) manufactured by Millipore was used.

〔Evaluation method〕
The physical property values of the microporous membranes obtained in Examples and Comparative Examples were measured by the following methods.
1) Average molecular weight of polymer The number average molecular weight and weight average molecular weight were determined by dissolving the polymer in dimethylformamide (DMF), using Shodex Asahipak KF-805L as a column, and using gel permeation chromatography (GPC) method with DMF as a developing agent. It was determined by measuring and converting to polystyrene.

2) Thickness of surface layer and thickness of support layer As shown in FIG. 7, a cross section of the obtained microporous film was photographed with a scanning electron microscope (SEM), and this photograph was image-analyzed. The length of the surface layer was defined as “surface layer thickness”, and the value obtained by subtracting the thickness of the surface layer from the total thickness of the microporous membrane was defined as “support layer thickness”.

3) Average flow hole diameter The average flow hole diameter was determined according to ASTM F316-86 using "Capillary Flow Porometer CFP-1200AEX" manufactured by PMI.

4) Pure water permeation flux The obtained microporous membrane was cut to a diameter of 25 mm, set in a filter sheet holder having an effective filtration area of 3.5 cm ² , and pressurized with a filtration pressure of 50 kPa to allow 5 mL of ultrapure water to pass through. The time required for passing water was measured. The flux was determined by the following formula (1).
Flux (10 ⁻⁹ m ³ / m ² / Pa / sec) = Water flow rate (m ³ ) ÷ Effective filtration area (m ² ) ÷ Filtration pressure (Pa) ÷ Time (sec) (1)

5) Number of spherical bodies, average particle diameter, frequency distribution The surface layer surface of the microporous membrane was photographed with a scanning electron microscope at a magnification of 20,000 times. Then, as shown in FIG. 3, for a spherical body having a central portion in a vertical 4 μm × horizontal 6 μm region in the center of the photograph, the outer circumference of the spherical body is a perfect circle or ellipse having the maximum diameter that does not include the surrounding holes. The diameter of the perfect circle or ellipse (the average of the major axis and the minor axis in the case of an ellipse) was taken as the particle size of the spherical body. However, since the number of the linear binding materials to be connected is 3 or less is difficult to distinguish from the linear binding materials, it was not regarded as a spherical body. And the average value of the diameter of all the spherical bodies contained in this area | region was made into the average particle diameter. Further, the number distribution of particles within a range of ± 10% of the average particle diameter was counted from all the spherical bodies, and the number was divided by the total number of particles of the spherical body to obtain a frequency distribution.

6) Center-to-center distance between spherical bodies, frequency distribution The center-to-center distance between the circle drawn in 5) and another circle closest to the circle was determined. The average value of the distance between the centers was defined as the average distance. Further, among the distances between the centers, those included in the range of ± 30% of the average distance were counted, and the number was divided by the total number of particles of the spherical body to obtain the frequency distribution.

7) Number of binders, average length, frequency distribution As shown in FIG. 7, all the binders between the spheres included in the region (when two spheres are connected by a plurality of binders) The number and length of only one of them were measured, and the number and average length of all binders were determined. Moreover, the frequency distribution was calculated | required by counting the number of the binders included in the range of the width | variety of +/- 30% of the average length among them, and dividing the number by the number of all the binders.

8) Second-order coefficient Using a Brookfield B-type rotational viscometer DV-II + Pro, the solution viscosity at 25 ° C. was measured while changing the shear rate, and the shear rate relative to the reciprocal of the solution viscosity (unit cP) (unit 1 / s ) With a quadratic function (Y = aX ² + bX + c), a secondary coefficient (a, unit (1 / s) ⁻² ) was obtained.

9) Thickness of surface layer and support layer A cross section of the microporous membrane was photographed with a scanning electron microscope at a magnification of 1000 times. The image was analyzed and the thicknesses of the surface layer and the support layer were determined.

10) Fouling resistance of membrane bioreactor Operate the suction pump of the membrane bioreactor so that the flux is 0.9 m ³ / m ² / day, read the pressure gauge of the membrane bioreactor, and read the differential pressure of the membrane Was recorded.

[Example 1]
[Preparation process of raw material liquid]
10 parts by weight of polyvinylidene fluoride “Kyner HSV900 (weight average molecular weight 800,000)” and 10 parts by weight of polyethylene glycol were mixed with 80 parts by weight of dimethylacetamide and dissolved at 90 ° C. It was returned to room temperature to obtain a raw material solution.
[Porosification process]
A unitika spunbonded nonwoven fabric as a base material layer was placed on a glass plate, and a raw material solution was applied thereon with a thickness of 200 μm using a bar coater. Immediately after the application, the membrane was put in ultrapure water to make the membrane porous. The ultrapure water was replaced several times for cleaning, and the membrane was taken out of the water and dried to obtain a microporous membrane.

[Processing into cartridge shape]
A plate made of ABS resin with a width of 50 centimeters, a length of 100 centimeters, and a thickness of 5 millimeters, with a cavity inside, is provided with several holes that connect the surface of both sides of the flat plate and the cavity, and the flat plate On both surfaces, a microporous membrane was liquid-tightly attached so that the total effective filtration area on both surfaces was 0.8 square meters. And the hole which connects one side of a flat plate and a cavity part was provided, and the tube was connected to the one side of that side, and the cartridge was produced. A membrane bioreactor unit in which 10 cartridges were placed vertically was prepared so that 10 tubes of the cartridge could be connected together to a suction pump.

[Comparative Example 1]
A membrane bioreactor unit was produced in the same manner as in Example 1 except that the membrane used in Kubota's liquid intermediate membrane 510 was used as the microporous membrane.

[Membrane bioreactor]
An activated sludge tank of 3 cubic meters is put into an activated sludge tank in a stainless steel container having a width of 2 m, a depth of 1 m, and a depth of 2 m. Each unit was connected to a suction pump and aerated from the lower part of each unit to form a membrane bioreactor.

FIG. 6 shows a graph when the inverse of the solution viscosity (unit cP) and the shear rate (unit 1 / s) are correlated with a quadratic function for the raw material liquid of Example 1. The raw material liquid of Example 1 in which the three-dimensional network structure of the present application was expressed drawn a curve including a clear arc having a convex on the upper side in a low shear rate region. That is, the viscosity rapidly increased in a region where the shear rate was 40 / s or less. Specifically, the three-dimensional network structure of the present application was manifested in a film made from a raw material liquid having a secondary coefficient a smaller than 10 ⁻⁸ .

  “◯” in Table 1 indicates that a three-dimensional network structure having a spherical body was developed. “X” indicates that there is no three-dimensional network structure having a spherical body.

表３に球状体の粒径の度数分布表を示す。粒径は、幅０．０５μｍ（０．１５〜０．２０μｍ）内に集中しており、球状体が均一の粒径を有していることがわかる。

Table 2 shows the characteristics of the particle size of the spherical body of Example 1. The surface layer of the microporous membrane of Example 1 has a spherical average particle size of 0.190 μm. Further, 112 spheres corresponding to 62% of the spheres have a particle diameter within a range of ± 10% of the average particle diameter.

Table 3 shows a frequency distribution table of the particle diameters of the spherical bodies. The particle size is concentrated within a width of 0.05 μm (0.15 to 0.20 μm), and it can be seen that the spherical body has a uniform particle size.

表５に線状の結合材の長さの度数分布表を示す。度数分布は、０．２０〜０．２５μｍの範囲がピークとなるように増加減少しており、結合材の長さが特定の範囲に集中しているのがわかる。

表６に実施例１について、球状体の平均粒径、球状体間の中心間距離の平均距離、結合材の平均長を示す。

Table 4 shows the characteristics of the linear bonding material of Example 1. In the surface layer of the microporous membrane of Example 1, the average length of the linear binder is 0.219 μm. Furthermore, the length of 259 binders, which is 61% of the binder, is in the range of ± 30% of the average length.

Table 5 shows a frequency distribution table of the lengths of the linear binders. The frequency distribution increases and decreases so that the range of 0.20 to 0.25 μm peaks, and it can be seen that the length of the binder is concentrated in a specific range.

Table 6 shows the average particle diameter of the spheres, the average distance between the centers of the spheres, and the average length of the binder for Example 1.

FIG. 9 compares the fouling resistance of Example 1 and Comparative Example 1. The horizontal axis in FIG. 9 is the elapsed time, and the vertical axis is the film differential pressure. The smaller the change in the film differential pressure over time, the higher the fouling resistance. The differential pressure after the lapse of 50 days is -3 kilopascal in Example 1 and -12 kilopascal in Comparative Example 1, indicating that the Example has higher fouling resistance.

  The use of nouns and similar directives used in connection with the description of the invention (especially in connection with the claims below) is not specifically pointed out herein or clearly contradicted by context. , And construed to cover both singular and plural. The phrases “comprising”, “having”, “including” and “including” are to be interpreted as open-ended terms (ie, including but not limited to) unless otherwise specified. The use of numerical ranges in this specification is intended only to serve as a shorthand for referring individually to each value falling within that range, unless otherwise indicated herein. Each value is incorporated into the specification as if it were individually listed herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. Any examples or exemplary phrases used herein (eg, “etc.”) are intended only to better describe the invention, unless otherwise stated, and to limit the scope of the invention. is not. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

  In the present specification, preferred embodiments of the present invention are described, including the best mode known to the inventors for carrying out the invention. Variations of these preferred embodiments will become apparent to those skilled in the art after reading the above description. The present inventor expects skilled workers to apply such modifications as appropriate, and intends to implement the present invention in a manner other than that specifically described herein. . Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

1 Spherical body 2 Linear binder

Claims (10)

A membrane bioreactor using a microporous membrane as a separation membrane,
The microporous membrane is
Comprising a surface layer formed with micropores;
The surface layer has a plurality of spherical bodies, and a plurality of linear binders extend from each of the spherical bodies in a three-dimensional direction,
The adjacent spherical bodies are connected to each other by the linear binder, and form a three-dimensional network structure with the spherical bodies as intersections.
Membrane bioreactor.
The membrane bioreactor according to claim 1, wherein the spherical body has a frequency distribution of 45% or more in a range of ± 10% of the average particle diameter.
The membrane bioreactor according to claim 1 or 2, wherein the length of the binding material has a frequency distribution of 35% or more in a range of ± 30% of the average length.
The membrane bioreactor according to any one of claims 1 to 3, wherein the spherical body has an average particle diameter of 0.05 to 0.5 µm.
The microporous membrane includes a surface layer and a support layer in which pores larger than the micropores of the surface layer are formed;
The support layer is made of the same material as the surface layer,
The surface layer has a thickness of 0.5 to 10 μm,
The thickness of the support layer is 20 to 500 μm.
The membrane bioreactor according to any one of claims 1 to 4.
The membrane bioreactor according to claim 1, wherein the microporous membrane includes a base material layer that supports the support layer, and the base material layer is made of a material different from that of the support layer.
The membrane bioreactor according to any one of claims 1 to 6, wherein a material of the microporous membrane is a polyvinylidene fluoride resin.
The solution in which the polyvinylidene fluoride-based resin is dissolved in a good solvent is a curve including an arc having a convex on the upper side, with the horizontal axis representing the shear rate and the vertical axis representing the reciprocal of the solution viscosity.
The membrane bioreactor according to claim 7.
A solution of 10 parts by weight of the polyvinylidene fluoride resin, 10 parts by weight of polyethylene glycol, and 80 parts by weight of dimethylacetamide has a shear rate of 40 per second or less in a graph in which the horizontal axis is the shear rate and the vertical axis is the reciprocal of the solution viscosity. Can be approximated by a quadratic function,
The quadratic coefficient of the quadratic function is less than 10 ⁻⁸ ,
The membrane bioreactor according to claim 7 or 8.
  The membrane bioreactor according to claims 7 to 9, wherein the polyvinylidene fluoride resin has a weight average molecular weight (Mw) of 600,000 to 1,200,000.

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