JP2000015062A - Membrane filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the leakage of microorganisms such as pathogenic protozoans even when hollow fiber membranes are broken by incorporating a filter of a filter medium whose hole diameter is greater than the pore diameter of the filter membrane of a filter membrane module in the after stage of the module. SOLUTION: Membrane filter raw water is supplied to a filter membrane module 2 by a raw water pump 1, passes through a filter 3 of a filter medium whose hole diameter is greater than the pore diameter of the filter membrane of the module 2, and is taken out as filtrate. In the normal operation of the filter 3, valves 7, 8 are closed, and the filtrate is taken out from a valve 11. In case of the breakage of the filter membrane of the module 2 to cause the accumulation of pathogenic protozoans on the surface of the filter medium. valves 9. 11 are closed, and hot water is supplied from a hot water-washing circulation tank 4 to the filter 3 through valves 8. 10 to be circulated through the valve 7. In this way, the pathogenic protozoans are exterminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a membrane filtration device for a water purification process. More particularly, the present invention relates to a membrane filtration device used for water purification treatment of industrial water or tap water, and particularly to a membrane filtration device used for water purification treatment of tap water.

[0002]

2. Description of the Related Art Membrane separation is a technology that has become widespread while expanding its application fields because it has features such as energy saving, space saving, labor saving and improvement of product quality.
Membrane separation methods include methods such as reverse osmosis, ultrafiltration, microfiltration, gas separation, blood purification, and pervaporation. In addition, the form of the separation membrane includes a hollow fiber membrane, a flat membrane, a tubular membrane, and the like, which are properly used depending on the properties and characteristics of each of the above-mentioned separation objects.

Hitherto, in the field of microfiltration, small disc filters and flat membrane pleated cartridge filters which have been used for the purpose of separating and filtering relatively small volume aqueous solutions and relatively clear aqueous solutions have been used. I have. In the field of ultrafiltration, flat membrane filtration devices and tubular or hollow fiber membrane modules have been used in the production of ultrapure water, food, and soft drinks.

In recent years, studies have been made to apply such microfiltration or ultrafiltration hollow fiber membranes to a water purification process for producing industrial water or tap water from river water or groundwater. The technology of microfiltration and ultrafiltration has begun to be applied to such fields that are used for a long time even for raw water that is often used.

A membrane module using a porous membrane, particularly a hollow fiber membrane, can have a very large filtration area per unit volume and a simple sealing mechanism for separating a stock solution to be treated and a membrane permeate. It has various advantages such as excellent water quality and easy operation management.

In particular, in the field of tap water purification processing, attention is paid to the fact that the water quality is superior to the conventional coagulation sedimentation / sand filtration method, and that automation is easy and labor saving can be achieved.
It is being actively introduced. Furthermore, even for tap water contaminated with pathogenic protozoa having strong resistance to chlorine disinfection such as Cryptosporidium and Giardia, attention has been paid to technology that can reliably remove pathogenic protozoa, and such raw water Recommended as a processing method.

However, when used for such a purpose, in a membrane filtration device using a polymer membrane, particularly a hollow fiber membrane module, there is a possibility that the hollow fiber membrane is broken and raw water is mixed into the membrane filtration water. I do. Evaluation items of normal water quality, for example,
For turbidity, even if a few hollow fiber membranes break, there is almost no problem.However, in the case of Cryptosporidium, a very small number of hollow fiber membranes break, especially due to their strong infectivity. It is said that there may be problems. For this reason, when introducing a membrane filtration device for the purpose of reliably removing pathogenic protozoa such as Cryptosporidium and Giardia, improvement of the reliability of the membrane filtration device is considered to be an important issue.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the conventional hollow fiber membrane type module, such as a pathogenic protozoan represented by cryptosporidium even if the hollow fiber membrane breaks. It is an object of the present invention to provide a filtration membrane device and a method for producing water for industrial use or tap water in which no microorganisms leak.

[0009]

The present invention has the following construction to attain the above object. That is,
In a membrane filtration device for a water purification process, a filter device made of a filtration material having a pore size larger than the pore size of the filtration membrane used in the filtration membrane module is incorporated at the subsequent stage of the filtration membrane module, and the membrane filtrate is filtered by the filter device. It is characterized by being configured to be filtered, and has the following preferred embodiments. (1) A means for washing the filter device installed at the subsequent stage of the filtration membrane module with hot water is provided. (2) A means for washing the filter device installed at the subsequent stage of the filtration membrane module with hot water of 60 ° C. or higher is provided. (3) A hot water washing line and a subsequent hot water circulation tank are attached to a filter device installed at a stage subsequent to the filtration membrane module so that hot water washing can be performed. (4) A hot water washing line and a hot water circulating tank attached to a filter device installed at the subsequent stage of the filtration membrane module can be used for both hot water washing and chemical cleaning of the filtration membrane. (5) The filtration material used in the filter device installed downstream of the filtration membrane module is made of an inorganic porous material. (6) The filtration material used for the filter device installed at the subsequent stage of the filtration membrane module is made of a sintered metal porous material. (7) The filtration material used for the filter device installed downstream of the filtration membrane module is made of a porous ceramic material. (8) The filtration material used for the filter device installed at the subsequent stage of the filtration membrane module is made of a vitreous porous material. (9) The filtration material used in the filter device installed at the subsequent stage of the filtration membrane module is made of an organic polymer membrane having heat resistance of 50 ° C. or more. (10) The pore size of the filtration material used in the filter device installed downstream of the filtration membrane module is 0.03 μm or more and 4.0 μm or less. (11) The pore size of the filtration material used in the filter device installed downstream of the filtration membrane module is 0.05 μm or more and 2.0 μm or less. (12) The pore size of the filtration material used in the filter device installed downstream of the filtration membrane module is 0.01 μm or more and 1.0 μm or less.

Further, in the present invention, filtered water obtained by passing raw water through a filtration membrane module is passed through a filter device made of a filter material having a pore diameter larger than that of a filtration membrane used in the filtration membrane module. It is intended to provide a method for producing industrial water or tap water by supplying raw water to the filtration membrane module, and extracting water permeated from any of the filter devices. A method for producing water is provided.

[0011]

FIG. 1 shows an example of an embodiment of the present invention. Membrane filtration raw water is supplied to the filtration membrane module 2 by the raw water pump 1, and the membrane filtration water passes through the filter device 3 made of a filter material having a pore diameter larger than the pore diameter of the filtration membrane used in the filtration membrane module 2, and is filtered water. Is taken out as Reference numeral 4 denotes a circulation tank for hot water washing of the filter device 3, which is provided with a heater 6 for heating. Reference numeral 5 denotes a circulation pump for heating and cleaning. During the normal filtration operation, the valves 7 and 8 are closed and the filtered water is supplied to the valve 11.
If the filtration membrane of the filtration membrane module breaks and pathogenic protozoa such as cryptosporidium are captured and deposited on the filter material surface of the filter device, the valves 9 and 11 are closed. Hot water is supplied from the hot-water washing circulation tank 4 to the filter device via the valves 8 and 10 and circulated through the valve 7. Hot water temperature is 50 ℃
Or more, preferably 60 ° C. or more, more preferably 70 ° C.
All that is required is the above. Higher temperatures can reduce the infectivity of pathogenic protozoa with shorter circulation flushes. 6
30 minutes or more at 0 ° C, 5 minutes or more at 65 ° C, 7
At 0 ° C., 2 minutes or more is considered sufficient. Of course, equipment such as a hot water washing line and a hot water circulation tank are attached to the membrane filtration device from the beginning, or as a transportable unit, close to the filtration membrane module only during hot water washing. It may be installed and connected to the filtered water line for cleaning as in FIG. In addition, the effect of killing and disinfecting pathogenic protozoa remains the same regardless of whether the circulation direction of the hot water is the reverse washing method reverse to the filtration water transmission direction or the same as the filtration water transmission direction. Therefore, any one may be used. However, in general, if the filtration membrane is broken, what is deposited on the filter device includes not only the pathogenic protozoa but also general turbid substances. Therefore, backwashing is preferable. Further, when the filter device is clogged with turbidity or the like and the pressure of the filter device rises, the clogged substance is dissolved and removed by chemical cleaning to recover the filtration pressure of the filter device. Usually, washing is performed with an aqueous solution of a mineral acid such as hydrochloric acid or sulfuric acid, an aqueous solution of an alkali such as caustic soda or potassium hydroxide, and / or an aqueous solution of sodium hypochlorite. For this reason, it is preferable that the apparatus for hot water cleaning can also be used for chemical cleaning. At this time, the chemical solution may be heated to perform the hot water cleaning and the chemical cleaning at the same time.

[0012] Pathogenic protozoa such as Cryptosporidium have a strong resistance to ordinary sterilization methods such as chlorine addition, and are very infectious, so that high removal rates are expected for membrane filtration devices. I have. Although it depends on the amount of Cryptosporidium in the raw water, it is generally considered that 10 ^-6.5 or more is required. However, the filtration accuracy of the filtration membrane and the filter material is a matter of probability, and when trapped and deposited on the surface of the filter material, a higher removal rate is required, but there is a practical limit. Generally, pathogenic microorganisms can be killed by heat, but pathogenic protozoa such as cryptosporidium lose their infectivity with relatively low hot water (Isao Kimata and Motohiro Iseki: What is cryptosporidium?) Protozoa like that, Environmental Technology, Vol. 26, No. 9,
(Pages 3-8, 1997), it is considered that it is advisable to appropriately wash the filter device with hot water to kill the pathogenic protozoa trapped and deposited on the surface of the filter material, and to keep the number at or below a certain number.

The pore diameters of the filtration membrane and the filter material are expressed in terms of the average pore diameter as the diameter of particles exhibiting a 90% to 95% rejection ratio, as long as they are in a magnitude relationship based on the results measured in principle by the same method and standard. There is no problem with the pore size or the maximum pore size. An average pore diameter or a so-called nominal pore diameter may be used as long as the size relationship between pores can be clearly understood, such as a combination of an ultrafiltration membrane and a microfiltration filter. In the case where the filtration accuracy is not represented by the pore size as in the case of an ultrafiltration membrane, even if the filtration precision is represented by the molecular weight cut off, the pore size is not limited as long as the pore size is smaller than that of the subsequent filter material.

As the filtration membrane module, an external pressure total filtration type membrane module, a membrane module in which a membrane element is loaded in a tank type container, an external pressure circulation (cross flow) type membrane module, and an internal pressure circulation (cross flow) type It is apparent from the configuration of the present invention that the present invention is not restricted at all in applying the present invention to the type membrane module. Further, whether the filtration membrane module is an ultrafiltration membrane or a microfiltration membrane can be applied without any problem as long as the pore size is smaller than that of the subsequent filter material.

As a filter material constituting the filter device, an inorganic porous material, an organic polymer porous material, or an organic-inorganic composite porous material is used. Any material can be used as the filter material, as long as it has a predetermined filtration accuracy, permeation speed and durability.

As the inorganic porous material, a sintered metal filter material, a ceramic filter material, a glass porous material and the like are used.

The sintered metal filter material includes a material obtained by sintering stainless steel fibers and a material obtained by sintering stainless steel particles. From the viewpoint of the pore size range of the filter material and the characteristics relating to water permeability, that is, filtration differential pressure, SUS304 is particularly preferred. Or a 316 sintered metal fiber microfiltration membrane is particularly preferably used. As the ceramic filter material, a ceramic monolithic or tubular precision filter or ultrafiltration filter can be used.

As the organic polymer porous material, any material having a heat resistance of 50 ° C., preferably 60 ° C., more preferably 70 ° C. or more can be used. Examples of such an organic polymer porous material include ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, Microfiltration membrane, ultrafiltration membrane, sintered porous filter material made of tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, polysulfone and polyethersulfone, etc. Can be used.

The filter material has a pore diameter of 0.03 μm or more and 4.0 μm or less, preferably 0.05 μm or less.
μm or more and 2.0 μm or less, more preferably 0.1 μm
A filter material having an average pore size in the range of not less than 1.0 μm and not more than 1.0 μm is used. One of the conditions to determine the pore size is to remove the turbid matter or microorganisms that may be mixed in the event that the filter membrane breaks and cannot be disinfected or killed by chlorine sterilization, etc. Can be assured. Another is that the use of a filter device allows the use of a membrane filtration system without significant increase in filtration pressure differential over a long period of time. That is, the water permeability of the filter material is 1,000 L / (m ² · h) / (100 k
Pa) or more, preferably 10,000 L / (m ^{2 ·} h) /
(100 kPa) or more is used. The higher the upper limit of the water permeability, the smaller the pressure loss due to the filter device may be.However, there is actually a trade-off relationship with the filtration accuracy of the filter material. So, about 150,000
^{0L / (m 2 · h)} / (100kPa) or less, with respect to a more preferred filtration accuracy of about 50,000L / (m ² ·
h) / (100 kPa). As a result of examining the filtering material and the filtering accuracy from the above viewpoints, it was found that the above-mentioned pore size range can be preferably used.

[0020]

EXAMPLES The present invention will be described in further detail with reference to examples.

The effect of the present invention was confirmed by the following method. That is, it is said that an experiment using Cryptosporidium is very difficult, and therefore, it is usually sufficient to evaluate the removability of predetermined particles. Usually, there are two types of Cryptosporidium which are problematic in human infection, and have an ellipsoidal shape. Small size, (4.5-5.4)-(4.2-5.0) μm,
It is reported to be (6.6 to 7.9) to (5.3 to 6.5) μm in a large type, and can be evaluated by the removability of polystyrene beads of 4 to 6 μm. (Yasushi Inada: Reliability of Alternative Indicators for Cryptosporidium Removal Evaluation, Journal of Japan Water Works Association, Vol. 66, No. 11, page 95-
97 (1997) [Sylvana Y. Li, James A. Goodrich e
t al., "ReliabilityofSurrogates for Determining Cry
ptospordium Removal ", J.AWWA, vol.89, No.5, pp.90-99
(May 1997) abstract]). However, it is not practical to evaluate a removal rate of 10 ⁻⁶ to 10 ^{−7 with} a polystyrene bead for a membrane module of a practical scale, since an extremely large amount of test water is required. Therefore, here, the fine particles present in the raw water were measured and evaluated. Also, compared to the conventional coagulated sedimentation sand filtration method, turbidity was controlled as 0.1 or less as a provisional guideline for Cryptosporidium, and turbidity was compared for reference.

Example 1 Outer diameter 680 μm, inner diameter 400 μm, average pore diameter 0.01
A filtration membrane module in which 7 filtration membrane elements each having a membrane area of 12 m ^{2 each} consisting of 3,500 μm polyacrylonitrile porous hollow fiber membranes are loaded in a stainless steel tank, and a filtration area 0 having a rejection of 95% for particles having a diameter of 0.6 μm. .34m
^A membrane filtration system was configured so that the flow shown in FIG. 1 was achieved by using a filter device equipped with ^two SUS316 sintered stainless steel fiber filters. 70 hollow fiber membranes of one of the hollow fiber membrane elements loaded in this tank type filtration membrane module were cut to obtain a turbidity of 5.
Raw water containing 6.2 × 10 ⁸ particles / ml of 2, 4 μm or more was entirely filtered at a flow rate of 60 l / min, and turbidity and fine particles in the filtered water taken out from the filter device were measured.
As a result, the turbidity was 0.01 or less, and the number of particles of 4 μm or more was 10 / ml or less. The number of particles is the same as the filtered water obtained by filtering the same raw water with a membrane module in which the hollow fiber membrane has not been cut, and the removal rate of particles slightly smaller than Cryptosporidium is 10 ⁻⁸ , It was equivalent.

Further, the membrane filtration water was stored in a circulating tank for washing with hot water, heated to adjust hot water at 85 ° C., and the filter device was backwashed and circulated. ° C had been reached. In the case of Cryptosporidium, it is said that it loses its infectivity at 72.4 ° C. for 1 minute.
It can be disinfected.

The filtration pressure difference of the entire membrane filtration apparatus, that is, of the membrane filtration system, is 10
The increase was not more than kPa, and almost no increase in the filtration pressure difference was observed.

Comparative Example The turbidity of filtered water and the number of particles were measured by using the apparatus of Example 1 and operating without loading the filter material into the filter apparatus. As a result, the turbidity was 0.035, and the number of particles having a particle size of 4 μm or more was detected as 4.0 × 10 ⁶ particles / ml. From this result, it can be seen that cutting 70 hollow fiber membranes reduces the particle removal rate by membrane filtration to about 1/100. Depending on the number of protozoa in the raw water, the possibility of infection may increase.

[0026]

As described above, according to the present invention, a membrane filtration device used in the field of a water purification treatment process and the like can be used for sterilizing chlorine such as cryptosporidium even if the filtration membrane is broken. The resistant pathogenic protozoa and foreign substances can be reliably removed, and if necessary, pathogenic protozoa such as cryptosporidium captured on the filter material can be easily killed and disinfected.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing one embodiment of the device of the present invention.

[Explanation of symbols]

 1: Raw water supply pump 2: Filtration membrane module 3: Filter device 4: Hot water circulation tank 5: Hot water circulation pump 6: Heater 7: Hot water circulation line valve 8: Hot water circulation line valve 9: Membrane filtration water line valve 10: Membrane filtered water line Narbu 11: Membrane filtered water line Narbu

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C02F 1/44 C02F 1/44 HF term (Reference) 4D006 GA06 GA07 HA06 HA19 KA52 KA55 KA57 KB14 KC03 KC15 MA01 MA02 MA06 MA22 MB15 MC02 MC03 MC04 MC39 PB02 PB06 PB24 4D064 DB01 DC05

Claims (10)

[Claims] 1. A filter device comprising a filtration material having a pore size larger than the pore size of the filtration membrane used in the filtration membrane module is incorporated at the subsequent stage of the filtration membrane module, and the filtrate of the membrane filtration module is filtered by the filter device. A membrane filtration device configured to be filtered. 2. The membrane filtration device according to claim 1, wherein the filter device installed downstream of the filtration membrane module has a means capable of washing with hot water. 3. The membrane filtration device according to claim 1, wherein the filter device installed downstream of the filtration membrane module is provided with a unit capable of hot water washing with hot water of 60 ° C. or higher. 4. A hot water washing line, which is attached to a filter device installed at a stage subsequent to the filtration membrane module, and a hot water circulation tank is provided following the hot water washing line. Membrane filtration equipment. 5. A hot water washing line and a hot water circulating tank attached to a filter device installed at a stage subsequent to the filtration membrane module can be used for both hot water washing and chemical cleaning of the filtration membrane. The membrane filtration device according to claim 4. 6. The membrane filtration device according to claim 1, wherein the filtration material used for the filter device installed downstream of the filtration membrane module is made of an inorganic porous material. 7. A filter material used in a filter device installed at a stage subsequent to the filtration membrane module is made of a porous material selected from sintered metals, ceramics, and vitreous materials. The membrane filtration device according to item 1. 8. A filter material used for a filter device installed at a stage subsequent to the filtration membrane module, comprising an organic polymer membrane having a heat resistance of 50 ° C. or more.
The membrane filtration device according to any one of claims 1 to 5. 9. The filter material according to claim 1, wherein the pore size of the filtration material used in the filter device installed downstream of the filtration membrane module is 0.03 μm or more and 4.0 μm or less.
The membrane filtration device according to any one of the above. 10. A method for producing water for industrial or tap water, wherein raw water is passed through a filtration membrane of the membrane filtration device according to any one of claims 1 to 9, and water permeated from a filter member is taken out.