JPH1110148A - Water purifying process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare efficiently water of high safety containing only a small amount of impurities and microbes by forming round or ellipse holes on both faces of a membrane with a polyacrylonitrile hollow fiber filter membrane with small diameter layers of the membrane formed only inside the membrane and filtering. SOLUTION: When the purification of water in which pathogenic microbes contained in tap water are removed, a polyacrylonitrile hollow fiber filter membrane with round or ellipse holes on both faces of a membrane having small diameter layers of the membrane formed only inside the membrane is used. At that time, the membrane with round or ellipse holes formed on both faces is used to make the fouling of the membrane hard to generate. For the purpose of improving the permeability of the membrane, the average pare diameter is set as approximately 1 μm or more to 50 μm or less on the in-membrane surfaces and approximately 0.05 μm or more to 10 μm or less on the out- membrane surface. Also it is preferable to set the inner diameter of the polyacrylonitrile hollow fiber filter membrane is set as approximately 0.5 mm-5 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water purification method for efficiently obtaining highly safe water free from impurities and free from pathogenic microorganisms.

[0002]

2. Description of the Related Art In recent years, the problem of pathogenic microorganisms contained in tap water has been highlighted. Cryptosporidium and other "microorganisms that do not die from chlorine" can be countermeasured by: 1) reducing the turbidity of purified water to 0.1 degrees or less in conventional treatments such as coagulated sedimentation sand filtration; Sterilization, and 3) membrane filtration. However, in the case of 1), there is a problem that the installation space for equipment such as a sand filtration facility is large, and in the case of 2), a sufficient maintenance system is required, and it is difficult to use small-scale water supply.

On the other hand, in the case of 3), turbidity or the like is directly filtered without using a chemical such as a flocculant, so that the amount of sludge can be reduced, the chemical injection control is not required, and the installation space is small. There is a feature that it can be completed, automatic operation can be performed, completely removes pathogenic microorganisms because anything larger than the pores of the membrane can never pass, and a high level of sanitary treated water can be secured. Some of them have been put into practical use (for example, Water Works, April 1996, pp. 86-89).

[0004] As the material of the membrane, cellulose-based, polyamide-based, polyacrylonitrile-based, polycarbonate-based, polysulfone-based resins and the like are used. Among them, polyacrylonitrile-based resins are excellent in hydrophilicity and water permeability of the membrane. In addition, there is an advantage that the mechanical strength characteristics are also good. In addition, results in river water treatment using hollow fiber ultrafiltration membrane modules made of polyacrylonitrile-based materials are also increasing (Ikuo Matsuo, New Membrane Technology Symposium '97 SESSION1, Abstracts of Lectures, pages 1-2-1 to 1--1) 2-8, The Membrane Society of Japan).

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a water purification method for efficiently obtaining highly safe water free of impurities and free of pathogenic microorganisms.

[0006]

The present invention has solved the above-mentioned problems. That is, the present invention is characterized in that (1) filtration is performed using a polyacrylonitrile-based hollow fiber filtration membrane having circular or elliptical pores on both surfaces of the membrane and having a minimum pore size layer of the membrane only inside the membrane. (2) The average pore diameter of the pores on the inner surface of the membrane is 1 μm.
(3) water purification method according to the above (1), wherein the average pore size of pores on the outer surface of the membrane is 0.
(1) or (2), wherein the inner diameter of the polyacrylonitrile-based hollow fiber filtration membrane is 0.5 mm to 5 mm. 1) to (3) water purification methods,
(5) having a circular or elliptical hole on both surfaces of the membrane,
A method for purifying water by supplying raw water from the outer surface side of a filtration membrane to a module incorporating a polyacrylonitrile-based hollow fiber filtration membrane having a minimum pore size layer only inside the membrane, and (6) natural water The present invention relates to the purification method of the above (1) or (5), which is water.

Hereinafter, the present invention will be described in detail. The present invention is characterized by using a polyacrylonitrile-based hollow fiber filtration membrane having circular or elliptical pores on both surfaces of the membrane and having a minimum pore size layer only in the interior of the membrane.
By using a film in which the holes on both surfaces are circular or elliptical, fouling (clogging) of the film can be suppressed.

The size of the circular or elliptical pores on both surfaces of the membrane is such that the average pore diameter on the inner surface of the membrane is 1 μm or more and 50 μm or less, preferably 5 μm or more and 30 μm or less in order to improve the water permeability of the membrane. The average pore diameter on the outer surface of the membrane is preferably from 0.05 μm to 10 μm, and more preferably from 0.1 μm to 5 μm. As for the average pore diameter on both surfaces of the membrane in the present invention, the average pore diameter was determined by observing the membrane surface with an electron microscope and analyzing the image. The average pore size is represented by the following equation.

[0009]

(Equation 1)

Furthermore, since the membrane used in the present invention has a minimum pore size layer inside the membrane, the outer surface of the membrane acts as a kind of pre-filter for the minimum pore size layer which controls the separation function of the membrane,
Shows fouling resistance to sludge and microorganisms. Further, since the pores other than the minimum pore diameter layer are large, they exhibit high water permeability. The minimum pore diameter layer of the membrane referred to in the present invention is a layer that has small voids or pores of the polymer constituting the membrane in a cross section in the film thickness direction when viewed microscopically, and contributes to the fractionation performance of the membrane. The average pore size of the pores present in the minimum pore size layer (hereinafter, referred to as the average pore size of the minimum pore size layer) is 0.01 μm or more and 1 μm or less. The average pore size of the smallest pore size layer is 0.01
If it is less than μm, the water permeability of the membrane tends to decrease, and if it is more than 1 μm, the ability to remove fine particles tends to decrease. The average pore size of the preferred minimum pore size layer is 0.01
It is not less than μm and not more than 0.5 μm. In addition, the thickness of the minimum pore size layer is arbitrary, but if too thick, water permeability is reduced,
It is usually at most 30 μm, preferably at most 10 μm. The average pore size of the minimum pore size layer referred to in the present invention is ASTM.
The average pore diameter measured by the air flow method described in F316-86.

The acrylonitrile-based polymer used in the hollow fiber filtration membrane includes at least 70% by weight, preferably 85% to 100% by weight of acrylonitrile;
One or more vinyl compounds copolymerizable with acrylonitrile contain 30% by weight or less, preferably 0% by weight or less.
It is an acrylonitrile homopolymer or an acrylonitrile-based copolymer in an amount of from 15% by weight to 15% by weight. The intrinsic viscosity of the acrylonitrile polymer is 0.4 or more and 2.0
Less than is preferred. If the intrinsic viscosity is less than 0.4, the strength of the film tends to be low, and if it is 2.0 or more, the solubility tends to be poor.

The vinyl compound is not particularly limited as long as it is a known compound having copolymerizability with acrylonitrile. Preferred copolymerization components include acrylic acid, methyl acrylate, ethyl acrylate and itacone. Acid, vinyl acetate, sodium acrylsulfonate, sodium methallylsulfonate, sodium p (para) -styrenesulfonate, hydroxyethyl methacrylate,
Examples thereof include ethyl triethyl ammonium methacrylate, ethyl trimethyl ammonium methacrylate, and vinylpyrrolidone.

The fiber diameter of the hollow fiber filtration membrane used in the present invention is not particularly limited, but the inner diameter is 0.5 mm or more and 5 m or more.
m or less is preferable. If the inner diameter is too small, the pressure loss of the liquid flowing through the hollow fiber filtration membrane tube (supply water when filtering from the inner surface side of the membrane, or membrane filtration water when filtering from the outer surface side) increases. That is, when filtering from the inner surface side of the membrane, the supply water pressure in the hollow fiber membrane tube decreases, and the substantial filtration pressure (the differential pressure between the inner surface of the membrane and the outer surface of the membrane) decreases,
When filtering from the outer surface side, the pressure of the membrane filtration water flowing into the hollow fiber membrane tube increases, and the substantial filtration pressure of the membrane decreases. Therefore, even if filtration is performed from either side, if the inner diameter is small, the substantial filtration pressure applied to the membrane is reduced due to pressure loss, and the amount of filtered water obtained is reduced. It is difficult to get it efficiently. On the other hand, if the inner diameter is too large, the membrane area that can be filled per unit volume decreases, and the amount of filtered water per module decreases, so that it is also difficult to achieve the above object of the present invention.

The polyacrylonitrile-based hollow fiber filtration membrane used in the present invention comprises, for example, a stock solution prepared by dissolving an acrylonitrile-based polymer in a specific organic solvent, and a high-concentration aqueous solution of a solvent dissolving the acrylonitrile-based polymer. It can be manufactured by discharging from a double annular nozzle together with the internal liquid, passing through an air gap, and coagulating in a coagulation bath (for example, Japanese Patent Application No. 9-131391).
issue).

When actually performing filtration, it is usually performed using a module in which a number of hollow fiber membranes are bundled and inserted into a case. Whether the filtration is performed by supplying raw water to the outer surface side of the membrane and performing filtration to the inner surface side, or by supplying raw water to the inner surface side of the membrane and performing filtration to the outer surface side, depends on the state of filtration. It is determined as appropriate. When the raw water contains a large amount of film contaminants such as turbid substances, a method of filtering from the outer surface side of the membrane is more preferable because the load of the film contaminants per unit membrane area is smaller. Since the outer surface area of the hollow fiber membrane is larger than the inner surface area, if the same water quality liquid is filtered by the same amount, it is better when the liquid is filtered from the outer surface of the membrane.
This is effective in reducing the membrane contaminant load per unit membrane area, maintaining a high level of filtered water in the membrane, and efficiently obtaining highly safe water.

In the case where raw water is supplied to the hollow fiber membrane module from the outer surface side of the membrane to perform a filtration operation, Japanese Patent Application Laid-Open No.
-Backwashing, as disclosed in
It is more preferable to carry out the filtration operation by incorporating air washing or the like in order to maintain the amount of filtered water at a high level and to “obtain highly safe water efficiently” which is the object of the present invention. Raw water to be washed by filtration, which is an object of the present invention, is not particularly limited, and examples thereof include natural waters such as river water, lake water, groundwater, and seawater. In addition, these natural waters are coagulated and sedimented,
Using water purified by an existing purification method such as a coagulation filtration method or a pressure flotation method, or water sterilized by a strong sterilizing agent such as ozone as raw water, and using the present invention to further improve the water quality. Can also. The purified water obtained by the present invention can be used for drinking water, industrial water and the like.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. Each measuring method is as follows. In addition, the hollow fiber membrane and the planar membrane used as the measurement samples were all completely impregnated with water.

The amount of water permeation of the hollow fiber membrane is determined by permeating ultrafiltration water at 25 ° C. from the inner surface to the outer surface of the hollow fiber membrane sample having a length of 50 mm, and the amount is liter / hr · m ² · a.
tm. However, the effective film area was converted to the inner surface.
The intrinsic viscosity of the acrylonitrile polymer is determined by Journa
l of Polymer Science (A-1)
According to the measuring method described in Vol. 6, 147 to 157 (1968), measurement was carried out at 30 ° C. using N, N-dimethylformamide as a solvent.

[0019]

Example 1 A copolymer consisting of 91.5% by weight of acrylonitrile, 8.0% by weight of methyl acrylate and 0.5% by weight of sodium methallylsulfonate having an intrinsic viscosity [η] = 16% by weight, And 12% by weight of polyvinylpyrrolidone having a weight average molecular weight of 9,000 (K17, manufactured by BASF)
Was dissolved in a mixed solvent of 54% by weight of N-methyl-2-pyrrolidone and 18% by weight of γ-butyrolactone to obtain a homogeneous solution. This solution was maintained at 60 ° C., and a spinneret (double annular nozzle 0.5 mm−) was prepared together with an internal solution composed of a mixed solution of 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of water.
0.7 mm-1.3 mm), and a 20 mm air gap was immersed in a coagulation bath made of water at 80 ° C. to complete the coagulation. At this time, the area from the spinneret to the coagulation bath is surrounded by a cylindrical tube, and the humidity of the air gap in the tube is 100%.
The temperature was controlled at 60 ° C. The spinning speed was fixed at 10 m / min.

The obtained hollow fiber membrane had a structure having a minimum pore diameter layer inside the membrane, and the pores on both surfaces of the membrane were circular. The average pore size of the minimum pore size layer was 0.05 μm, the average pore size on the outer surface was 0.6 μm, and the average pore size on the inner surface was 10 μm. In addition, the membrane performance was such that inner / outer diameter = 0.
8 / 1.2 (mm), the water permeability of the membrane is 2500 liters /
hr · m ² · atm.

Using this hollow fiber membrane, the effective membrane area = 0.
A 15 m ² module was created. In this module,
River surface water having a turbidity of 3 was supplied from the outer surface of the membrane at 20 ° C. at an average filtration pressure of 0.15 kgf / cm ² . Supply water 1
0% was discharged out of the module as concentrated water. Also,
The module was operated by applying a backwashing operation (filtration pressure: 0.4 kgf / cm ² ) for filtering the membrane filtered water from the inner surface of the membrane for 1 minute every 60 minutes of filtration. The permeability of the membrane filtration water is 550
It was stabilized at liter / hr · m ² · atm (the film area was converted to the film inner surface). At this time, Pseu
domonasDiminuta was present at 30 cells / ml, but was not present in the filtrate.

[0022]

Comparative Example 1 Using the polymer and spinneret used in Example 1,
According to Example 1 of JP-B-52-150072, the inner / outer diameter is 0.8 / 1.4 (mm), and the water permeability of the membrane is 200.
1 / hr · m ² · atm was obtained. The resulting hollow fiber membrane had a structure in which the minimum pore size layers were present on both surfaces of the membrane, and the pores on both surfaces of the membrane were non-circular. Using the hollow fiber membrane, a module having an effective membrane area of 0.15 m ² was prepared. In this module, river surface water having a turbidity of 3 is applied from the outer surface side of the membrane at 20 ° C., average filtration pressure = 0.15 kgf / cm.
Supplied at ² . 10% of the feed water was discharged out of the module as concentrated water. In addition, a backwashing operation of filtering the membrane filtered water from the inner surface of the membrane for 1 minute every 60 minutes of filtration (filtration pressure:
0.4 kgf / cm ² ) was added to operate the module. The permeation rate of the membrane filtration water is 100 liter / hr · m ²
• Stable at atm (film area is converted to film inner surface).

[0023]

According to the present invention, highly safe water free from impurities and free from pathogenic microorganisms can be efficiently obtained.

Claims (1)

[Claims] 1. A water filtration method using a polyacrylonitrile-based hollow fiber filtration membrane having circular or elliptical pores on both surfaces of the membrane and having a minimum pore size layer of the membrane only inside the membrane. Purification method.