WO2012035692A1

WO2012035692A1 - Water separation membrane module

Info

Publication number: WO2012035692A1
Application number: PCT/JP2011/003994
Authority: WO
Inventors: 敬子中野; 牛房　信之; 泰子小島
Original assignee: 株式会社日立製作所
Priority date: 2010-09-16
Filing date: 2011-07-13
Publication date: 2012-03-22
Also published as: JP2012061419A

Abstract

In spiral-structured water treatment separation modules, organic material is adsorbed at a membrane surface, occluding a polymer mesh structure and reducing the amount of water permeation. The problem is that the adsorbed organic material develops into a gel clump and becomes clogged in the narrow portions of the gap between the membrane and a spacer, thus greatly degrading the amount of water that permeates through the module. To address this problem, in this water separation module, which is provided with a central pipe, a plurality of water separation membranes (11) that are attached to the central pipe and are provided in a spiral manner to the periphery of the central pipe in a manner so as to overlap each other, and a spacer (12) that is between the plurality of water separation membranes on the side at which untreated water flows in, concavities and convexities having a size that does not interfere with the mesh shape of the spacer (12) and having a size that can establish water flow paths are applied to the surface of the water separation membranes (9, 11), and thereby clogging of the narrow portions of the gap between the membranes (11) and the spacer (12) can be suppressed.

Description

Water separation membrane module

The present invention relates to a water separation membrane module structure.

A reverse osmosis membrane is used in advanced treatment of water purification. A semi-permeable membrane is used on the surface of the reverse osmosis membrane, and the material of the semi-permeable membrane is roughly classified into cellulose acetate type and aromatic polyamide type. Among these, aromatic polyamide-based reverse osmosis membranes are widely used for industrial use because of their high water permeability and electrolyte removal performance. As the structure, a composite semipermeable membrane structure in which an aromatic polyamide membrane is formed on a microporous support is often used, and the thickness of the aromatic polyamide portion is generally 200 to 300 nm. As a membrane for supporting the semipermeable membrane, a porous polysulfone membrane and a nonwoven fabric are combined to form a planar reverse osmosis membrane.

Reverse osmosis membranes are used to remove organic substances and electrolytes that dissolve in water during seawater desalination, pure water production used in the manufacture of precision electronic equipment such as semiconductors, advanced water treatment, and sewage / wastewater regeneration.

Of these uses, when used for sewage regeneration treatment, water is generally supplied to the reverse osmosis membrane through the following treatment process. First, coarse impurities, waste, etc. contained in sewage are removed through a sieve called a screen. Next, a fine suspension such as sand is added to the flocculant if necessary, and then submerged in a sedimentation basin for separation. The supernatant water still contains suspended solids, dissolved organic matter, etc., and is decomposed using microorganisms. Microbial colonies and metabolites are sludge. Sludge and water are separated by settling in a sedimentation basin or passing through a microfiltration membrane. The sewage primary treated water treated in this way contains almost no suspended solids, and has been purified to such a quality that it can be discharged into the river at this stage or reused depending on the application, such as greening spray water. In Japan, at this stage, it is discharged into rivers and water is recycled using natural purification. However, since there are not enough rivers and lakes necessary for natural purification in the Middle East, inland areas, islands, etc., there is an increasing demand for further purification of sewage primary treated water and reuse it as drinking water or industrial water. The reverse osmosis membrane is used in this final treatment to remove electrolytes and dissolved organic substances in the sewage primary treated water.

Many reverse osmosis membranes used for sewage regeneration treatment are folded into a shape called a spiral in order to increase the membrane surface area in the module. A bag-like reverse osmosis membrane is fixed to the center core, and it is rolled up like an umbrella and stored in a cylinder. The main module is a cylindrical shape with a diameter of 4 inches, 8 inches, etc. and a length of 1 m. Between the membranes, a mesh called a spacer, which is a plastic fiber with a thickness of 1 mm or less, woven with a mesh with a spacing of 2 to 3 mm is inserted to secure a water flow path. However, since the spacer lattice portion is pressed against the membrane, the spacer and the membrane are in contact with each other, and the fiber portion has a small gap between the membrane and the water flow path.

In addition to reverse osmosis membranes, ultrafiltration membranes and nanofilter membranes may be formed with the same spiral structure.

Japanese Patent Laid-Open No. 10-329441 JP-A-9-29252

Reverse osmosis membranes are a type of separation membrane, but there are two methods for water filtration using separation membranes. One is a total filtration system, which is a system that allows the entire amount of supplied water to pass through the membrane. Components that cannot pass through the membrane are deposited on the membrane surface. The other is a cross-flow filtration method, in which water flows parallel to the membrane surface, part of the permeate passes through the membrane to the permeate, and the rest is taken out from the module as concentrated water with the concentration of the lysate increased. . The latter cross-flow filtration method is used for filtration through reverse osmosis membranes. This method reduces the increase in operating load due to the deposition of dissolved material on the membrane surface and the increase in concentration. However, the cross-flow filtration method also has a problem that the dissolved matter is adsorbed on the membrane surface and the amount of permeated water deteriorates with time.

The adsorbed material on the membrane surface includes organic fouling that adsorbs organic matter in addition to the scale in which the electrolyte is deposited at a high concentration near the membrane surface, biofouling in which microorganisms in the water grow. Clean water or cleaning liquid is periodically flowed over the membrane surface and the adsorbed material is removed by shearing force. However, when organic matter is adsorbed, it cannot be completely removed by shearing force, and it gradually accumulates to remove water. The amount of transmission decreases. The power (pressure) is increased to obtain a constant permeation amount, but this leads to an increase in the power cost of the pump. In addition, since the reverse osmosis membrane gradually deteriorates due to the cleaning liquid, the ion rejection rate decreases. As these progress, it is necessary to replace the reverse osmosis membrane module. When replacing the reverse osmosis membrane module, it is necessary to stop the operation for a long time, and since the reverse osmosis membrane module cannot be recycled, it is necessary to replace it with a new reverse osmosis membrane module. This increases the running cost per unit of water, such as product costs and waste disposal costs.

Organic fouling has several stages. First, organic substances having affinity with the reverse osmosis membrane surface material are adsorbed on the membrane surface. As the amount of adsorption increases, it fills the gaps in the polymer network structure of the reverse osmosis membrane, making it difficult for water molecules to permeate. In addition, the adsorbed organic substances are entangled and grow into a gel-like lump. These gel-like lumps accumulate on the part where the film and the spacer are in contact with each other, such as the lattice part of the spacer or the fiber part of the spacer, or the gap is narrowed, and the channel is blocked.

This phenomenon of organic fouling is likely to occur upstream of the reverse osmosis membrane module. When the blockage of the flow path occurs upstream, water is not supplied to the downstream side of the module even though the membrane is in good condition. Since the original performance of the membrane cannot be exhibited, cleaning and membrane replacement are required.

As a method for solving this, for example, in Patent Document 1, the surface area of the reverse osmosis membrane is increased by forming pleats with a spacing of about 1 to 10 μm in the semipermeable membrane on the surface of the reverse osmosis membrane, A method is described in which it is easily adsorbed to a concave portion having a low flow velocity, and the convex portion is difficult to adsorb, thereby preventing a decrease in water permeability.

However, although the initial adsorption of organic substances is suppressed, the gel-like lump grows more than the interval between the pleats on the surface of the reverse osmosis membrane. It will occur.

In addition, a method for widening the flow path is described in Patent Document 2, but in this case as well, the crossing portion of the spacer and the fiber portion are in contact with the surface of the reverse osmosis membrane. Cannot be prevented.

In order to solve the above-mentioned problem of organic fouling, particularly the problem of gel block being blocked, the area of the contact portion between the spacer and the membrane where the blockage is most likely to occur and the area where the gap is narrow is reduced. By sufficiently supplying the water to be treated to the downstream side of the module, the organic fouling is suppressed to the adsorption stage and the deterioration of the water permeation amount is prevented.

Specifically, unevenness is formed on the surface of the reverse osmosis membrane so that the contact with the spacer is a contact with a small area.

According to the present invention, in a spiral-type water separation membrane module, the channel blockage due to organic matter fouling is suppressed, and the membrane can be used effectively over a long period of time. Module replacement frequency can be reduced.

It is the figure explaining the combination of one spacer and membrane in the water separation membrane module concerning one Example of this invention. It is the figure which showed the cross section of the combination of one spacer and membrane of the water separation membrane module concerning one Example of this invention. It is a block diagram of each member in the membrane module concerning one Example of this invention. It is a schematic diagram of a spiral structure water separation membrane module. It is the schematic of a water separation membrane module. It is the figure which showed the cross section of the combination of one spacer and film | membrane of the conventional membrane module. It is the figure which showed the uneven | corrugated shaped type | mold concerning one Example of this invention. It is a schematic diagram of the laboratory instrument concerning one Example of this invention.

Embodiments according to the present invention will be described below with reference to the drawings.

FIG. 4A is a diagram of the reverse osmosis membrane module 4 according to one embodiment of the present invention, and FIG. 4B is a schematic diagram thereof. A hollow central pipe 15 is provided at the center of the module 4, and a plurality of water separation membranes (reverse osmosis membranes) 11 are attached to the central pipe 15. A set of two water separation membranes 11 are wound around the central pipe 15 in a spiral shape and overlap each other. The end of the water separation membrane 11 on the outer side of the spiral is formed into a bag shape by sealing the two water separation membranes 11, and the end of the inner side of the spiral is attached to the central pipe 15 by bonding. The inside of the 11 bags communicates with a hollow water channel in the central pipe 15 so that the water in the bag is collected in the central pipe 15. A spacer 12 is installed between adjacent bags. In some cases, a water-conditioning mesh 13 is placed inside the bag. The bag of the water separation membrane 11 is wound around the central pipe 15 while being overlapped with the spacer 12 and the mesh 13, and the outer cylindrical portion of the cylinder is hardened with a pressure resistant resin.

As shown in FIG. 4B, the water to be treated that has entered the water separation membrane module 4 is separated into two by the water separation membrane 11. Since the water separation membrane 11 is difficult to pass the dissolved component, it is separated into the permeated water having a small dissolved amount permeated through the membrane 11 and the concentrated water in which the dissolved component is concentrated, and is discharged out of the module 4.

In FIG. 4A, the water to be treated for reverse osmosis membrane enters the module from the side of the cylindrical reverse osmosis membrane module, is outside the bag of the water separation membrane 11, and the spacer 12 is It is led to the arranged area. Only water molecules and components that do not need to be removed by the water separation membrane 11 from the water to be treated pass through the membrane 11 to be purified to become permeated water and enter the inside of the bag of the membrane 11. The permeated water inside the bag passes through the region where the water conditioning mesh 13 is disposed, is collected in a water channel in the central pipe 15, and is guided to the outside of the reverse osmotic pressure module. In the water to be treated, components that have passed through the membrane 11 pass through the module and are concentrated, and flow out from the peripheral part of the module as concentrated water. Contrary to FIG. 4, the spiral-structured membrane module is also of a type in which treated water is introduced into the bag of the water separation membrane 11, the treated water is passed through the central pipe, and the permeated water flows out from the peripheral part. is there. In this case, the spacer 12 is disposed inside the bag of the membrane 11 and the water conditioning mesh 13 is disposed outside the bag.

FIG. 3 shows a diagram of the water separation membrane 11, the spacer 12, and the mesh 13. The spacer 12 is overlapped so as to contact the treated water side 8 of the water separation membrane 11, and the water conditioning mesh 13 is overlapped on the permeate side 9 of the water separation membrane 11 so that water can permeate uniformly. A membrane module having a similar spiral structure is formed. The water separation membrane 11 has unevenness on the surface, and the surface having the unevenness is arranged facing the spacer side.

1 is a plan view of the combination of the water separation membrane 11 and the spacer 12, and FIG. 2 is a sectional view thereof. In order to suppress clogging between the spacer and the water separation membrane due to organic fouling, in particular, a gel-like lump, unevenness is provided on the surface of the water separation membrane 11. In FIG. 1, 1 indicated by a black dot is an apex of unevenness of the film, and a portion indicated by a dotted line indicates the fiber 2 of the spacer 12. Since the unevenness 1 is narrower than the width of the spacer fiber 2, the film 11 contacts the fiber 2 at the apex of the unevenness regardless of the spacer hole. That is, as shown in the cross-sectional view of FIG. 2, the film 11 and the fiber 2 of the spacer are in contact with each other at a point, and the distance 3 between the film 11 and the fiber 2 is secured.

Since the unevenness 1 on the film surface is as small as about 0.1 mm, the density of the film when the spiral structure is formed does not change greatly. A membrane module having the same membrane area as the conventional one can be formed by reducing the spacer thickness by about 0.2 mm as required.

Conventionally, as shown in FIG. 5, the distance between the fiber 2 of the spacer and the film 11 is constant. Particularly, the lattice point portion of the spacer is in contact with the film when the spiral structure is formed, so the distance is narrow. Organic matter accumulates here and it is easy to block.

The distance between the irregularities on the film surface should be 1/10 or less so as not to interfere with the mesh structure of 2 to 3 mm spacing of the spacers. And the interval so that the least common multiple of the film surface irregularities is as large as possible. Considering the ease of production, etc., it is preferably formed in the range of 100 to 500 μm.

In addition, since the gel-like lump of organic matter may grow to several tens of μm, the depth of the unevenness is desirably 100 μm or more from the viewpoint of securing the flow path.

A reverse osmosis membrane using an aromatic polyamide as a semipermeable membrane is generally formed by first forming a polysulfone membrane as a support membrane, and an organic solvent solution of a dicarboxylic acid or tricarboxylic acid as a raw material for the polyamide membrane on the surface thereof. An aqueous solution of diamine or triamine is sequentially applied to form a film by interfacial polymerization. The uneven shape on the reverse osmosis membrane surface can be formed by several methods.

One is a method in which irregularities are formed on the surface of the polysulfone membrane, and the semipermeable membrane is formed in an irregular shape. After forming the polysulfone membrane, it gives vibration during solvent drying when embossing and forming a porous membrane, sprays polysulfone fine particles on the surface during solvent drying, forms a smooth polysulfone membrane, and prints a polysulfone solution in a dot pattern Such a method is conceivable.

The second is a method of forming surface irregularities after forming a reverse osmosis membrane, such as embossing or folding the membrane to wrinkle the surface.

On the other hand, unevenness is not necessary on the permeate side (water conditioning mesh side) of the water separation membrane 11. This is because in the permeated water, the concentration of dissolved matter is small and clogging is unlikely to occur. Further, when there is no unevenness on the permeate side, it is easier to create a bag by bonding and sealing the film 11. In other words, the surface of the water separation membrane 11 has a rougher surface (the unevenness is larger) on the surface to be treated and the concentrated water side than the surface on the permeated water side.

Hereinafter, the effects of the present embodiment were verified by experiments.
(Experiment 1)
An acrylic mold in which the quadrangular pyramids (vertices are cut off) shown in FIG. 6 was prepared. One side of the quadrangular pyramid is 0.1 mm and the depth is 0.15 mm.

A flat membrane reverse osmosis membrane (LFC3 made by Nitto Denko) is cut to a size of 100 x 25 mm, wetted with pure water and placed on a mold with the semipermeable membrane facing the acrylic side, and silicon rubber from the nonwoven fabric side. Rubbing with a squeegee, the unevenness of the acrylic mold was transferred to the film. As a result, an uneven shape having a difference between the peak and the bottom of about 100 μm was formed on the surface of the film. Here, the NFC LFC3 manufactured by Nitto Denko is classified as a nanofilter membrane, but is treated here as a kind of reverse osmosis membrane, and hereinafter referred to as a reverse osmosis membrane.

A simple module for evaluation was produced using this membrane. A spacer (fiber spacing 2.5 mm, fiber diameter 0.5 mm) taken out from a commercially available spiral-type reverse osmosis membrane module was cut into 100 mm × 25 mm, and a cell composed of three acrylic plates 16 as shown in FIG. The eight reverse osmosis membranes 11 and the four spacers 12 are alternately stacked so that the semipermeable membrane surface is on the spacer side, and the upper and lower sides are sandwiched between Viton sheets 17, and a load of 5 kg is applied to the whole.

After the biological treatment, water to be treated filtered through a 0.1 μm pore microfiltration membrane was pressurized to 0.05 MPa with nitrogen and passed through the cell, and the time required for 500 ml to pass through was measured. At this pressure, water molecules do not pass through the semipermeable membrane by reverse osmosis, and water passes between the semipermeable membrane and the semipermeable membrane.

Similarly, without forming irregularities on the reverse osmosis membrane, it was put in a cell with the configuration of FIG. 7, the treated water was passed through under pressure of 0.05 MPa, and the time required for 500 ml to pass was measured. The measured average values were almost the same, indicating that the resistance on the semipermeable membrane side of the membrane module immediately after the start of use did not change.

(Experiment 2)
Prepare a sample water in which 0.2 g of polystyrene (standard product with a molecular weight of 1,000 to 4,000,000 for size exclusion chromatography) is dispersed in 1 L of water, and flow it through the simple module prepared in Experiment 1 at a pressure of 0.05 MPa. The possibility of blockage of the flow path was examined. Since polystyrene is insoluble in water, it was considered to be an accelerated test simulating a lump that grew like a gel. In order to save sample water, 1 L is flowed through a simple module and collected, and the collected liquid is pressurized again and flowed repeatedly.

When measuring the time required for 100 ml of water to pass by 30%, it can be about 5 times longer when the surface is uneven, compared to when the surface is not uneven. I understood.

(Experiment 3)
In order to investigate whether the performance as a reverse osmosis membrane has changed, we conducted a filtration experiment on a reverse osmosis membrane with irregularities and investigated the water permeation rate. Although the reverse osmosis membrane module is a cross-flow type, in this example, the reverse osmosis membrane was cut into a 47 mmφ circular shape and set in a pressure filter of the total volume filtration type. The treated water to be filtered was pure water, and the speed at which 100 ml permeated through pressurization to 0.3 MPa was measured. As a result, it took about 20 minutes, and it was confirmed that even if it was uneven, it was equivalent to a normal reverse osmosis membrane and there was no problem in practical use.

DESCRIPTION OF SYMBOLS 1 ... The peak part of the unevenness | corrugation on the surface of a water separation membrane, 2 ... Spacer fiber, 3 ... Space | interval (space) of a water separation membrane and a spacer, 4 ... Water separation membrane module, 8 ... Water separation membrane surface to be treated (semi-permeable membrane surface), 9... Water separation membrane surface on the permeated water side, 11... Water separation membrane, 12. Water mesh, 14 ... sealing part, 15 ... center pipe, 16 ... acrylic plate, 17 ... Viton sheet.

Claims

In a water separation membrane module that separates treated water into permeate and concentrated water using a water separation membrane,
A central pipe,
A plurality of water separation membranes attached to the central pipe and spirally installed around the central pipe so that each overlaps;
A spacer provided between the plurality of water separation membranes and provided on the side into which the untreated water flows,
The water separation membrane module is characterized in that irregularities are formed on a surface of the water separation membrane on the spacer side.
In claim 1,
The spacer is made of fiber and has a mesh shape,
The water separation membrane module is characterized in that the interval between the irregularities is smaller than the width of the fiber forming the spacer.
In claim 1 or claim 2,
The water separation membrane module according to claim 1, wherein the depth of the irregularities is 1 to 200 μm.
In any one of Claims 1 thru | or 3,
A water separation membrane module, characterized in that the density of the convex portions of the irregularities formed on the surface of the water separation membrane on the treated water side is 400 to 1000 / cm2.