JP2006231181A - Membrane filtration method of clean water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane filtration method of clean water preventing membrane blocking due to substances with strong affinity with a membrane material, such as organic matter like humin contained in raw water or soluble silica. <P>SOLUTION: In this membrane filtration method, a material constituting a filtration membrane 3 and homogeneous particles are added to clean raw water to form a homogeneous particle layer 5 on the surface of the filtration membrane; and substances with strong affinity with the membrane material, such as organic matter like humin contained in raw water or soluble silica are adsorbed on the homogeneous particle layer 5 to perform membrane filtration. Adsorption of these substances to the membrane surface is greatly reduced, and the homogeneous particle layer 5 is easily peeled off from the membrane surface by a normal back-washing operation, thus reducing the frequency of chemical washing. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a clarified water membrane filtration method for obtaining purified water from relatively clean raw water such as groundwater, underground water, well water, spring water, and the like.

  Conventionally, a membrane filtration method has been widely used as a method for obtaining purified water used in many facilities such as water and sewage, pharmaceuticals, and food. The membrane filtration method is a solid-liquid separation technology that can remove suspended substances in raw water using a filtration membrane. However, if there are many suspended substances in raw water, PAC (polyaluminum chloride) or A method has been adopted in which a flocculant such as ferric chloride is added to increase the particle size of the suspended substance to facilitate membrane filtration and backwashing.

  On the other hand, when the raw water is relatively clean clear water such as groundwater, underground water, well water, spring water, etc., membrane filtration treatment without agglomeration without using a flocculant is desired. However, when clarified water is subjected to membrane filtration without agglomeration, stable operation may be difficult due to membrane clogging. In such a case, since the membrane differential pressure cannot be recovered by a normal back washing operation, the frequency of chemical cleaning of the filtration membrane is increased, the maintenance management becomes complicated, and the membrane filtration cost may increase.

  This is because groundwater and the like have already been subjected to natural filtration treatment, and the particle size of suspended substances in the raw water is small, and the pores on the membrane surface are likely to be clogged, and organic substances such as humic substances and soluble silica This is considered to be due to the fact that the material in the raw water, which has a strong affinity with the membrane material such as, adsorbs to the membrane surface and does not easily peel off by normal backwashing.

In Patent Document 1, in a water treatment method of a total amount filtration method using a membrane module for water filtration, a coating layer made of inorganic particles having good detachability with respect to the filtration membrane is formed on the surface of the filtration membrane. A method for removing the ring material together with the coating layer by backwashing is disclosed. However, since the substance in the raw water having a strong affinity with the membrane material permeates the coating layer and is adsorbed on the filtration membrane, this method cannot sufficiently prevent the membrane clogging described above.
JP 2004-130197 A

  The present invention solves the above-mentioned conventional problems, prevents clogging of the membrane by substances having a strong affinity with organic materials such as humic substances and soluble silica contained in raw water, and for chemical cleaning. This is to provide a clarified water membrane filtration method capable of reducing the number of times and facilitating maintenance and reducing the operation cost.

  The membrane filtration method of the clear water of the present invention made in order to solve the above problems is to add particles of the same quality as the material constituting the filtration membrane to the clear raw water to form a homogeneous particle layer on the surface of the filtration membrane, Membrane filtration is performed while adsorbing a substance having a high affinity with the membrane surface material contained in the raw water to the homogeneous particle layer. In addition, it is preferable that the particle diameter of homogeneous particle | grains shall be 2 times or more of the membrane pore diameter of a filtration membrane. Further, a method of filtering while adding a certain amount of homogeneous particles to raw water, or a method of starting filtration after forming a homogeneous particle layer on the filtration membrane surface in advance every backwashing can be taken.

  In the clarified water membrane filtration method of the present invention, a layer of particles having the same quality as the material constituting the filtration membrane is formed on the surface of the filtration membrane, and a substance having a high affinity with the membrane surface material contained in the raw water is used as the homogeneous particles. Since membrane filtration is performed while adsorbing to the layer, adsorption of the same substance to the membrane surface is greatly reduced. Further, since this homogeneous particle layer can be easily peeled off from the film surface by a normal back washing operation, it is possible to reduce the number of times of chemical washing, facilitate maintenance, and reduce operating costs.

Hereinafter, preferred embodiments of the present invention will be described.
FIG. 1 is a block diagram illustrating a raw water treatment facility for carrying out the present invention, wherein 1 is a raw water tank in which raw water which is relatively clean clear water such as groundwater, underground water, well water, spring water, etc. is stored. Reference numeral 2 denotes a membrane module for subjecting raw water to membrane filtration. The material of the filtration membrane 3 is not particularly limited, and is a ceramic membrane such as alumina, titania, mullite, zirconia, silica, spinel or a mixture thereof, or a polymer such as PVDF (polyvinyldenfluoride) or CA (cellulose acetate). A membrane is used. Various membrane structures such as a flat membrane, a monolith membrane, and a hollow fiber membrane can be used.

  The raw water is driven into the membrane module 2 by the pump 4, and dead-end filtration is performed in this embodiment. In the present invention, the clarified water is used as raw water, but a flocculant is not used, but particles having the same quality as the material constituting the filtration membrane 3 (homogeneous particles) are added to the raw water to form a homogeneous particle layer 5 on the surface of the filtration membrane 3. To do. The addition position may be any position as long as it is a previous stage of the membrane module 2 as indicated by a broken line in FIG.

  When the material of the filter membrane 3 is an alumina ceramic membrane, alumina particles are added as homogeneous particles, and when the filter membrane 3 is a titania ceramic membrane, titania particles are added. Similarly, when the filtration membrane 3 is a PVDF polymer membrane, PVDF particles are added. However, when the material of the filtration membrane 3 is a ceramic membrane such as alumina, titania, mullite, zirconia, silica, spinel or a mixture thereof, the inventor has a higher affinity between the materials than the polymer material. It has been found that the homogeneous particles to be added need not be completely the same as the material of the filtration membrane 3 because of the high price. For example, when the material of the filtration membrane 3 is titania, ceramic particles such as alumina, mullite, zirconia, silica, spinel, or a mixture thereof can be used as homogeneous particles as well as titania.

  The particle size of the homogeneous particles added to the raw water is preferably at least twice the membrane pore size of the filtration membrane 3. This is to facilitate peeling from the film surface by backwashing operation. If the particle size of the homogeneous particles is equal to or less than the membrane pore diameter of the filtration membrane 3, the homogeneous particles enter the pores of the filtration membrane 3 and cause membrane clogging. Further, the filtration may be started after adding a certain amount of homogeneous particles to the raw water, or after forming a homogeneous particle layer in advance for each backwash.

  Thus, if homogeneous particles are added to raw water to form the homogeneous particle layer 5 on the surface of the filtration membrane 3, organic substances such as humic substances having high affinity with the membrane surface material contained in the raw water, soluble silica, etc. Is adsorbed by the homogeneous particle layer 5 and the amount of adsorption to the surface of the filtration membrane 3 decreases. For this reason, fouling substances are less likely to be formed on the membrane surface than in the prior art, and even when the membrane differential pressure rises, as shown in FIG. If washing is performed, the homogeneous particle layer 5 can be easily peeled off from the surface of the filtration membrane 3, and an excellent backwashing effect can be obtained. Further, the backwashing does not necessarily require the use of the backwashing pump 7. For example, as shown in FIG. 2, pressurized water or pressurized air may be driven into the membrane module 2 by pressurized backwashing.

In addition, the procedure of pressure backwashing is as follows, for example.
In the case of backwashing with water (1) V3 is closed and V4 is opened, and filtered water is stored in the backwashing water tank 8. Or V6 is opened and filtered water is stored in the backwash water tank 8 from the treated water tank 6 by the pump 8.
(2) Next, V7 is opened and the inside of the backwash water tank 8 is pressurized with compressed air.
(3) Open V2 and backwash.
In the case of air backwashing (1) V8 is opened and the secondary side of the membrane module 2 is pressurized with compressed air.
(2) Open V2 and backwash.
The above-described backwashing method itself is the same as before, and the present invention is not particularly limited by the backwashing method as long as it is a backwashing method capable of peeling the same particle layer to be formed. Further, the frequency of backwashing is the same as in the prior art. For example, it may be performed every predetermined time or every time the membrane differential pressure reaches a predetermined value.

Membrane filtration experiments were conducted using three types of ceramic membranes with the underground water as raw water and the membrane materials of alumina, titania and zirconia, respectively, and polymer membranes with PVDF as PVDF. The ceramic membrane used was a monolith membrane manufactured by the applicant company, and the polymer membrane used was a commercially available hollow fiber membrane.
The membrane area is all 0.4 m ² and the pore diameter is 0.1 μm. However, only membranes made of alumina and PVDF were used as the membrane material, and membranes having a pore diameter of 1 μm were also tested.
Various kinds of particles were added to the raw water under the conditions shown in Table 1, and changes in membrane pressure difference were observed for 1 week while repeating backwashing every 3 hours at an operating flux of 8 m ³ / (m ² · day). . The differential pressure increase rate per day is shown in Table 1.

Hereinafter, the present invention will be described in detail with reference to the test results of the differential pressure increase rate attached to Table 1. Experiments 1 to 6 are conventional filtration conditions in which particles are not added, and this was used as a comparative example.
Experiments 7 to 14 are conditions under which raw water is filtered while adding a certain amount of particles of the same material as the filter membrane material. Among these, in Experiments 7 to 12, the increase rate of the membrane differential pressure was reduced as compared with Experiments 1 to 6, and there was a clogging suppression effect that is an effect of the present invention. However, in Experiments 13 and 14, clogging progressed. This is because, in Experiments 7 to 12, the particle diameter of the added particles is 2 to 5 times the membrane pore diameter, and in Experiments 13 and 14, it is 1.5 times the particle diameter of the added particles. This is probably because the particles themselves were clogged in the pores. Therefore, the particle size of the homogeneous particles to be added needs to be at least 1.5 times the membrane pore size, desirably 2 times or more.

  Experiments 15 to 18 are conditions in which a filter membrane material is an alumina ceramic membrane and filtered while adding a certain amount of titania, mullite, and zirconia as ceramic particles and CA as polymer particles to raw water. In Experiment 18, a membrane having a membrane pore size of 1.0 μm was used. Among these, Experiments 15, 16, and 18 show that the increase speed of the membrane differential pressure is reduced compared with Experiments 1 to 6 regardless of the difference in the membrane pore diameter, and there is an effect of suppressing clogging that is an effect of the present invention. It was. However, in Experiment 17, no effect was seen. This is because, in Experiments 15, 16, and 18, the material of the added particles is ceramic, and the affinity between the materials is higher than that of the polymer, so that the fouling substance in the groundwater that clogs the alumina filter membrane is removed. This is because it can be adsorbed by a particle layer of another ceramic material such as titania. On the other hand, in Experiment 17, it was presumed that the CA particles were unable to adsorb the fouling substance in the groundwater that would block the alumina filtration membrane, and thus it was estimated that no effect was seen.

  Experiments 19 to 22 were conducted by using ceramic membranes with titania and zirconia as the filter membrane material, and adding alumina, zirconia, spinel, and ceramic particles in which 50% of titania and alumina were mixed on a weight basis to the raw water for filtration. It is a condition. In Experiments 19 to 22, the rate of increase in the membrane differential pressure was reduced as compared with Experiments 1 to 6, and there was a clogging suppression effect that is an effect of the present invention. As shown in Experiments 15, 16, and 18, when the material of the filtration membrane is a ceramic membrane such as alumina, titania, mullite, zirconia, silica, spinel, or a mixture thereof, the affinity between the materials is high. It was found that the homogenous particles added need not be exactly the same as the material of the filtration membrane because it is higher than the molecular material.

  Experiments 23 to 25 are conditions in which a filtration membrane material is a PVDF polymer membrane and filtered while adding a certain amount of alumina and CA particles to raw water. In Experiments 23 to 25, the rate of increase in the membrane differential pressure was increased as compared with Experiments 1 to 6. It turns out that it needs to be added.

Membrane filtration experiments were carried out using well water as raw water and three types of ceramic membranes, each of which is made of alumina, titania and silica, and a polymer membrane whose filtration membrane is CA. The ceramic membrane used was a monolith membrane manufactured by the applicant company, and the polymer membrane used was a commercially available hollow fiber membrane.
The membrane area is all 0.4 m ² and the pore diameter is 0.1 μm. However, a membrane having a pore diameter of 1 μm was also tested only for membranes made of titania and CA.

In Example 2, a particle layer of each material was formed in advance for each backwash so that the particle layer thickness shown in Table 2 was obtained, and then actual operation (filtration) was started. Specifically, the same particle layer was formed by filtering a solution containing high-concentration particles (added to the raw water) with a high flux until a predetermined layer thickness was obtained for each backwash. A change in membrane differential pressure was observed for 1 week while repeating backwashing every 3 hours at an operating flux of 8 m ³ / (m ² · day). The differential pressure increase rate per day is shown in Table 2.

Hereinafter, the present invention will be described in detail with reference to the test results of the differential pressure increase rate added in Table 2. Experiments 1 to 6 are conventional filtration conditions in which particles are not added, and this was used as a comparative example.
Experiments 7 to 9 are experiments carried out under the condition that filtration is started after a particle layer of the same material is formed 5 μm to 50 μm at each backwashing on a ceramic membrane whose material of the filtration membrane is alumina, titania or silica. . From this, the effect of suppressing the increase in the film differential pressure was observed regardless of the difference in the particle layer thickness. However, although it does not affect the effect of suppressing the increase in the differential pressure of the membrane, in reality, if a too thick particle layer is formed, the pressure loss increases, and if an indentation pressure is required, the cost increases. It is not desirable to form an excess particle layer that exceeds.

  Experiments 10 and 11 are experiments carried out under the conditions in which filtration is started after a CA and alumina particle layer is formed for each backwashing on a ceramic membrane made of titania. In Experiment 10, the effect of suppressing the increase in the membrane differential pressure was not observed, but in Experiment 11, the effect of suppressing the increase in the differential pressure was observed. From this, in the case of the ceramic membrane as shown in Example 1, since the affinity between the materials is higher than that of the polymer material, the added homogeneous particles need to be completely the same as the material of the filtration membrane. It was judged that it was not.

  Experiments 12 and 13 were conducted using a membrane having a pore diameter of 1.0 μm. From this, it is clear that even if the membrane pore diameter is increased, the effect of suppressing the increase in the membrane differential pressure is observed when the homogeneous particle layer is formed.

  As shown in the data of the above-described examples, according to the method of the present invention, membrane filtration is performed in a state where a homogeneous particle layer is formed on the surface of the filtration membrane by adding the same quality particles as the material constituting the filtration membrane to the raw water. Backwashing can prevent an increase in membrane differential pressure, and continuous use over a long period of time is possible. Therefore, according to the present invention, there is an advantage that the number of times of chemical cleaning can be reduced, maintenance can be facilitated, and operation cost can be reduced.

It is explanatory drawing which shows embodiment of this invention. It is explanatory drawing which shows other embodiment of this invention.

Explanation of symbols

1 Raw Water Tank 2 Membrane Module 3 Filtration Membrane 4 Pump 5 Homogeneous Particle Layer 6 Treated Water Tank 7 Backwash Pump 8 Backwash Water Tank

Claims (4)

  Particles of the same quality as the material constituting the filtration membrane are added to clear raw water to form a homogeneous particle layer on the surface of the filtration membrane, and substances having high affinity with the membrane surface material contained in the raw water are adsorbed to this homogeneous particle layer. A membrane filtration method for clarified water, characterized in that membrane filtration is performed.   The membrane filtration method for clarified water according to claim 1, wherein the particle size of the homogeneous particles is at least twice the membrane pore size of the filtration membrane.   2. The membrane filtration method for clarified water according to claim 1, wherein filtration is performed while adding a certain amount of homogeneous particles to raw water. The method for filtering membranes of clarified water according to claim 1, wherein filtration is started after forming a homogeneous particle layer on the surface of the filtration membrane in advance for each backwashing.

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