JPH04317730A - Composite filtration membrane - Google Patents

Abstract

PURPOSE:To conduct an efficient separation, recovery, purification and concn. of suspended substances by supplying the raw fluid containing the suspended substances to a composite laminate membrane having nonwoven fabric and woven fabric or glass fiber having a specific fiber size laminated on a precision filtration membrane in order to filter the raw fluid therethrough. CONSTITUTION:The nonwoven fabric and woven fabric or glass fiber having a fiber size of 0.5-5 times the diameter of hole in the surface of a precision filtration membrane are laminated on this membrane to form a composite laminate membrane. The raw fluid containing suspended substances such as high molecules, microorganisms, yeast, fine particles, etc., is supplied from a raw fluid inlet 11, introduced into a filter 15 by a pump 19 and the filtration is performed through a precision filtration membrane 16 for a predetermined time. Back washing water is supplied into the filter from a back washing water inlet 13 and the sterile water produced by a sterilization filter 20 is passed through the precision filtration membrane 16 in order to desorb the suspended substances therefrom. The suspended substances, together with the sterile water, is thereafter discharged from a liq. discharge opening 14 through a solenoid valve 21. A gas is supplied from a gas inlet 17 into the filter to carry out the sterile water remaining therein and then the refiltration is performed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a precision filtration membrane, and particularly to a composite membrane that has a high ability to trap suspended solids and has good backwashing ability in order to maintain a large membrane permeation flux. . The composite filtration membrane of the present invention can be used to separate fluids containing or suspending various polymers, microorganisms, yeast, and fine particles.
It can be applied in purification, recovery, concentration, etc., and in particular in any case where it is necessary to separate fine particles from a fluid containing fine particles that requires filtration, such as in various suspensions containing fine particles. Separating fine particles from liquids, fermentation liquids, culture liquids, pigment suspensions, etc.
It is also applied when separating and removing crud from condensate in nuclear power generation. However, with the rapid development of biotechnology in recent years, the production of biochemical substances through cultivation, fermentation, enzymatic reactions, etc. has become popular in many fields such as pharmaceuticals, foods, and chemical products. Although the added value of these produced substances increases by refining them, the current situation is that a lot of cost is incurred in this refining operation. The dead-end filtration method of the present invention is particularly effective in these fields, for example, when using exoenzyme-producing bacteria that perform high-density culture by continuously removing reaction inhibitors from the culture solution. It has a wide variety of applications, including continuous recovery of enzymes, recovery of enzymes from a solution obtained by crushing intracellular enzyme-producing bacteria, and removal of biocatalysts from culture solutions obtained in a batch process.

0002

BACKGROUND ART Conventionally, techniques for separating suspended solids from a raw fluid containing suspended solids using a membrane include, for example, reverse osmosis, ultrafiltration, microfiltration, which uses pressure as a driving force, There are electrodialysis methods that use a potential difference as a driving force, and diffusion dialysis methods that use a concentration difference as a driving force. These methods can be operated continuously, can separate, purify, or concentrate without significantly changing temperature or pH conditions during the separation operation, and can separate a wide range of particles, molecules, ions, etc. It is economical because it can maintain a large processing capacity in a small plant, requires little energy for separation operations, and can process low-concentration raw fluids that are difficult to use with other separation methods, so it has been widely implemented. There is. The membranes used in these separation techniques include cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone,
There are polymer membranes mainly made of organic polymers such as polyacrylonitrile, polyamide, polyimide, etc., and porous ceramic membranes with excellent durability such as heat resistance and chemical resistance, and are mainly used for colloid filtration. For microfiltration, ultrafiltration membranes are used, and microfiltration membranes with suitable pores are used for precision filtration, which targets the filtration of fine particles. As mentioned above, with the advancement of biotechnology, higher purity, higher performance, and higher precision are required, and continuous operation is now possible in place of the conventional centrifugation and diatomaceous earth filtration. There is no need to add filter aids or flocculants.The separation efficiency is independent of the difference in specific gravity between the bacterial cells and the suspension, and a clear filtrate is produced regardless of the physical properties of the culture solution or the type of bacterial cells. It is possible to obtain high concentration culture and improve production efficiency, it is possible to have a completely closed system and there is no leakage of bacteria, it is possible to wash the bacteria after concentration, it is easy to scale up and it is highly economical, etc. , the field of application of microfiltration or ultrafiltration technology is expanding. However, despite the many advantages of filtration membranes, when microparticles are separated using microfiltration or ultrafiltration membranes, a cake layer is generated due to the influence of concentration polarization, which creates resistance to the flow of the permeate fluid. There is a problem in that the resistance due to membrane clogging increases and the membrane permeation flux rapidly and significantly decreases, and this has been the biggest cause of hindering the practical application of precision filtration or ultrafiltration. Furthermore, the membrane used therein is easily contaminated, and measures to prevent this are required.

[0003] As a filtration method, there is a so-called dead-end filtration method in which all the fluid to be filtered passes through a filter medium (filter cloth, membrane, etc.) and a cake layer to separate fine particles contained in the fluid. . In this conventional dead-end filtration system, a high permeation flux is obtained when the fluid passes through and the suspended solids are trapped inside the filtration membrane and separated, but when the suspended solids are trapped on the surface of the filtration membrane, When a large amount of raw fluid is processed or when the specific resistance of the formed cake layer is extremely high, the filtration resistance becomes large, and when such dead-end filtration is performed, the membrane permeation flux is small. Become. For this reason, a cross-flow type filtration system was considered. In this cross-flow filtration system, the raw fluid to be filtered is passed parallel to the membrane surface of the filtration membrane, the fluid passes through the filtration membrane to the opposite side, and the flow of the raw fluid and the permeated fluid are perpendicular to each other. This is why it is called this way. In this cross-flow filtration method, the cake layer formed on the membrane surface is stripped off by the flow of the raw fluid parallel to the filtration membrane, so the membrane permeation flux is larger than in the conventional dead-end filtration method, and a large amount of It is possible to directly and continuously separate, purify, and concentrate raw fluids. However, in order to remove microbial cells and polymer products from culture fluids and fermentation fluids, which have extremely high filtration specific resistance for suspended solids, ultrafiltration membranes with high pure water permeation flux, or high molecular weight cutoff, and precision filters are used. When using a filtration membrane, the membrane permeation flux decreases rapidly and it is difficult to maintain a high membrane permeation flux at the beginning of filtration.As a result, when comparing the dead-end filtration method and the total permeate volume, was small and insufficient to obtain an economical permeation flux.

0004

[Problems to be Solved by the Invention] As mentioned above, the cross-flow filtration system is an advanced separation technology in principle, but the biggest problem, the membrane permeation flux, is lower than that of the conventional dead-end filtration system. However, even if this cross-flow method is adopted as a precision filtration method, a sufficiently high membrane permeation flux cannot be obtained. Also, looking at specific examples of conventional separation of suspended solids and fluids,
For example, when separating bacterial cells from a fermentation liquid, even if a cross-flow filtration method is used instead of the conventional centrifugation method or diatomaceous earth filtration method, a cake layer or clogging may occur on the membrane surface. Therefore, there is a problem that not only the membrane permeation flux decreases as the filtration time passes, but also the activity of the bacterial cells is lost due to the shear force when circulating the raw fluid.

Conventional methods for increasing permeation flux include intermittently stopping the flow of raw fluid into the filtration membrane, or closing the valve on the permeate side of the filtration membrane. By intermittently eliminating or reducing the pressure applied to the filtration membrane, or by applying pressure from the permeate side of the filtration membrane and flowing fluid from the permeate side to the raw fluid side, deposits can be removed on the membrane surface on the raw fluid side of the filtration membrane. Attempts have been made to intermittently remove the cake layer and adhering layer, but if the filtration specific resistance of suspended solids is small, backwashing can easily remove suspended solids that have accumulated on the filtration membrane. However, in the case of polymeric components and bacterial cells that have a high filtration specific resistance of suspended solids and strong adhesion to the filtration membrane, they cannot be sufficiently removed from the filtration membrane even if backwashing is performed, and the membrane permeation flow rate decreases. There were problems such as insufficient recovery. In addition, if the suspended solids desorbed from the filtration membrane during backwashing are left in the filtration system, the concentration of suspended solids in the raw fluid will gradually increase, and in some cases, the viscosity of the raw fluid will also increase. Therefore, there was a problem that the membrane permeation flux gradually decreased and the permeation flux did not recover sufficiently even if backwashing was performed. On the other hand, in the case of cross-flow filtration, the method of not reducing the activity of bacterial cells is to reduce the circulation flow rate and reduce the shearing force, but since reducing the shearing force reduces the effectiveness of the cross-flow filtration method. However, if measures were taken that did not actually reduce bacterial cell activity, there was a problem that the membrane permeation flux would decrease. Furthermore, when a pump with a small shearing force such as a diaphragm pump is used to reduce the crushing of bacterial cells by the pump, there is a problem that the pump pulsates so much that the effect of the cross-flow filtration system is reduced.

[0006]

[Means for Solving the Problems] The present invention has been made to solve the problems of the prior art described above, and has a practical high membrane permeation flux, and is capable of transporting bacterial cells, etc. The object of the present invention is to provide a novel filtration membrane that reduces the decrease in activity. That is, the present invention uses a precision filtration membrane to supply and filter a raw fluid consisting of a fluid containing suspended matter, thereby separating the fluid and suspended matter, and reducing the pressure on the permeate fluid side of the filtration membrane to the raw fluid side. In the dead-end filtration method, backwashing is performed periodically at a pressure greater than It is a composite filtration membrane with cloth or glass fiber, and the microfiltration membrane surface pore diameter on the surface where the fiber thickness of nonwoven fabric, woven fabric, or glass fiber comes into contact is 0.
This is achieved by having a thickness of 5 times or more and 5 times or less. The present invention will be explained in detail below. The composite filtration membrane used in the dead-end filtration method of the present invention can be made of various polymers,
It can be applied in any case where it is necessary to separate fine particles from a fluid containing microorganisms, yeast, or particles that require filtration, such as the separation, purification, recovery, and concentration of fluids containing or suspending microorganisms, yeast, and particles. However, it is particularly effective in cases where the filtration specific resistance of suspended substances is extremely high, such as when separating, concentrating, and recovering enzymes, microorganisms, and cells from fermentation liquids and culture liquids.

The filtration membrane used in the filtration method of the present invention must have a pore size that can block suspended solids, and precision filtration membranes usually have a pore size of 0.05 to 10 μm. The total filtration amount when these microfiltration membranes are used for filtration in a short time of 0.5 to 3 minutes is significantly influenced by the structure of the filtration membrane. There are two types of filtration membranes: so-called isotropic membranes, in which the pore diameters of the micropores existing inside the membrane do not substantially change, and pore diameters on both surfaces of the membrane do not substantially change, and pore diameters that are continuous in the membrane thickness direction. Alternatively, it is classified as having a structure called an anisotropic membrane, in which the pore size on one surface of the membrane is different from the pore size on the other surface. Among these, isotropic membranes are described in JP-A No. 58-98015, but during filtration, the entire membrane exhibits a large resistance to the flow of fluid, and only a small flow rate can be obtained (i.e., (only a small flow rate can be obtained per unit time, per unit time, and per unit pressure difference), and it also has drawbacks such as easy clogging, short filtration life, and lack of blocking resistance. On the other hand, the anisotropic film is
As described in No. 051, JP-A No. 63-139930, the membrane has a layer with a small pore size called a dense layer on one surface of the membrane or inside the membrane, and has relatively large pores or extremely large voids. from the inside of the membrane to the other surface. Suspended solids are trapped on the filtration membrane surface when an isotropic membrane is used or when the raw fluid is supplied to the smaller pore side of the anisotropic membrane, whereas when the raw fluid is supplied to the larger pore side of the anisotropic membrane. When fed, suspended solids are trapped inside the filter membrane. In other words, when suspended solids are blocked on the surface of a filtration membrane, the blocked suspended solids create a very large filtration resistance and the permeation flux decreases rapidly, resulting in a lower total filtration rate. A so-called anisotropic membrane has a structure in which the pore diameter changes continuously or discontinuously in the membrane thickness direction, and the pore diameter on one surface of the filtration membrane is different from the pore diameter on the other surface.The side with the larger surface pore diameter is the raw fluid side. By using it for this purpose, suspended solids can be blocked inside the filtration membrane, making it possible to obtain a large total filtration amount. The average pore diameters on the membrane surface and inside the membrane shown here were calculated from photographs taken with an electron microscope.

The composite filtration membrane of the present invention has a composite structure in which a precision filtration membrane and a nonwoven fabric, woven fabric, or glass fiber are integrated, and by placing the nonwoven fabric side on the raw solution side, the ability to trap suspended substances and Improves cleaning performance through backwashing. In particular, when the particle size distribution of the suspended solids is wide, the effect is great because large suspended solids are trapped inside the nonwoven fabric and small suspended solids are trapped inside the porous filtration membrane. These nonwoven fabrics, woven fabrics, or glass fibers have different suspended solid blocking performance depending on the thickness, porosity, and thickness of the fibers forming them. That is, the thinner the fiber thickness and the lower the porosity, the more fine suspended solids can be blocked, and the thicker the thickness, the more suspended solids can be blocked. The thickness of the fibers has a correlation with the surface pore size of the filtration membrane with which the nonwoven fabric or the like comes into contact. That is, it is preferable that the substantial pore diameter of the nonwoven fabric or the like is approximately the same as or slightly larger than the surface pore diameter of the filtration membrane with which the nonwoven fabric or the like is in contact. The thickness of the fibers of the nonwoven fabric or the like is 0.5 times or more and 5 times or less the pore size on the surface of the filtration membrane so that the pore size becomes substantially continuous at the interface between the filtration membrane and the nonwoven fabric. That is, when the average pore diameter on the surface of the filtration membrane is 2 μm, the fiber thickness of the nonwoven fabric is preferably 1 μm or more and 5 μm or less. If the porosity of the nonwoven fabric is extremely low, the filtration resistance will increase, and if it is too high, it will not block suspended solids, so it is usually preferably 50% or more and 90% or less, and more preferably 60% or more and 75% or less. . Furthermore, if the thickness of the nonwoven fabric is too small, the effect of trapping suspended substances cannot be obtained, so it is preferable that the thickness is 1/2 or more of the thickness of the filtration membrane. Although the material of the nonwoven fabric is not particularly limited, polyester, polypropylene, polyamide, stainless steel, etc. are generally used. In addition, when backwashing is performed periodically, there are problems such as a large load on the filtration membrane during backwashing and cracks in the filtration membrane when the strength of the filtration membrane is weak. By integrating with the filtration membrane, it becomes possible to dramatically increase the strength of the filtration membrane. The method of integrating the filtration membrane and nonwoven fabric, etc. is as follows.
Melting bonding may be performed in dots or lines with an adhesive or by heat sealing, but when forming a filtration membrane as in Japanese Patent Publication No. 45-13931, it is also possible to directly cast the membrane-forming stock solution onto a nonwoven fabric etc. and filter it. A porous structure may be formed with the membrane partially penetrating a nonwoven fabric or the like.

Backwashing performed in the dead-end filtration of the present invention is more effective when carried out with a liquid than with a gas, and a permeated liquid can be used as the backwashing liquid if foreign matter contamination from outside the system is to be avoided. In addition, in order to avoid a decrease in the permeation amount by the amount of backflow of the permeate, it is preferable to supply a cleaning liquid from outside the filtration system and perform backwashing with an amount of backwash liquid as required. Basically, any cleaning liquid supplied from outside the filtration system may be used as long as it does not degrade the properties of the filtration membrane or change the properties of the raw fluid, but if the raw fluid is an aqueous solution, sterile water is generally used. It is preferable. Further, if it is desired not to leave the backwash liquid in the filtration system after the backwash is completed, it is preferable to perform dehydration using gas. If backwashing is performed after the membrane permeation flux becomes extremely low, the recovery of the membrane permeation flux after backwashing will deteriorate. This is due to suspended solids penetrating deeply into the filtration membrane, the accumulated suspended solids becoming compacted, or the suspended solids strongly bonding to the filtration membrane when filtration is performed for a long time. This is because the turbid substances cannot be completely removed. Therefore, when performing constant pressure filtration, 1 of the permeation flow rate at the initial stage of filtration
It is preferable to perform backwashing before reaching 1/100, and in order to obtain an even higher permeation flow rate, it is preferable to perform backwashing before reaching 1/10. In addition, when performing constant-speed filtration, if backwashing is performed after the pressure difference between the filtration membranes becomes extremely high, the recovery of the pressure difference between the filtration membranes after backwashing, that is, the cleaning performance of the filtration membranes, will deteriorate. It is preferable to carry out backwashing before the pressure difference between the filtration membranes reaches 100 times the initial pressure difference between the membranes, more preferably 1
Perform backwashing before reaching 0 times. Therefore, the time from the start of filtration to backwashing is short, and if the specific resistance of the suspended solids is large, it is preferable to perform backwashing after filtration is performed for 0.5 minutes or more and up to 3 minutes. In addition, cleaning performance will be higher if a large amount of backwash liquid is passed through the filtration membrane at a high permeation flow rate, but if the permeation flux of backwash liquid is increased and backwash is performed for a long time, Not only will the amount be enormous, but the ratio of backwashing time to filtration time will increase, effectively lowering the average permeation flux, so the permeation flow rate should be 1 x 10-4 m as long as the permeation flux can be recovered sufficiently.
3/m2/sec or more, and the time is 1 second or more 30
Preferably within seconds.

Next, the dead-end filtration system of the present invention will be explained based on the drawings. Figure 1 shows the state of suspended matter that accumulates on the filtration membrane when performing conventional dead-end filtration.The amount of suspended matter that accumulates increases over time, and the permeation flux eventually reaches zero. approach. Figure 2 shows the state of suspended solids deposited on the filtration membrane when cross-flow filtration is performed.At the beginning of filtration, the suspended solids gradually increase, but the suspended solids accumulate due to the shear force of the raw fluid. The amount of substance takes a constant value, and the permeation flux eventually approaches a constant value. FIG. 3 shows the flow of the dead-end filtration method of the present invention. After filtration is performed for a certain period of time, sterilized water is passed from the permeate side to the raw fluid side and discharged together with the suspended solids desorbed from the filtration membrane. Thereafter, the sterilized water remaining in the filtration system is discharged using gas, and filtration is performed again. By repeating this cycle, it becomes possible to maintain a high permeation flux without increasing the concentration of suspended solids in the raw fluid. Figure 4 shows a cross section of the filtration membrane when the side with the smaller pore size of the anisotropic membrane is placed on the stock solution side and suspended matter is blocked on the filtration membrane surface, and Figure 5 shows the side with the smaller anisotropic pore size on the stock solution side. This shows a cross section of the filtration membrane when it is turned to the side. Figure 6 shows a composite membrane of the invention. In the composite membrane structure of the present invention, suspended solids are blocked inside the nonwoven fabric and the filtration membrane, so that there is no significant filtration resistance, resulting in a high filtration rate.

[0011]

[Examples] The present invention will be explained in more detail with reference to specific examples below, but the present invention is not limited to the examples unless it goes beyond the gist of the invention. Example 1 Dead-end filtration in which backwashing of the present invention is periodically performed was performed using a suspension of protein aggregates obtained by dissolving 20 ppm of tannic acid in commercially available beer. The anisotropic membrane is polysulfone (P3500 manufactured by Amoco) 1
A film-forming stock solution prepared by dissolving 5 parts of polyvinylpyrrolidone, 15 parts of polyvinylpyrrolidone, and 3 parts of water in 70 parts of N-methylpyrrolidone was applied to a polypropylene nonwoven fabric with a fiber thickness of approximately 4 μm, a porosity of 70%, and a thickness of 150 μm. It was cast at 180 μm through a casting coater, and air adjusted to 25° C. and 45% relative humidity was applied to the surface of the liquid film at 2 m/sec for 5 seconds.
Thereafter, it was immediately immersed in a coagulation bath filled with water. The obtained filtration membrane is an anisotropic precision filtration membrane having an internal dense layer with an average pore diameter of 1.5 μm, and the average pore diameter on the side in contact with the nonwoven fabric is 5 μm, and periodic backwashing is performed with the nonwoven fabric side as the stock solution side. Filtered. The filter used has an effective membrane area of 1
00cm2, and the experimental conditions were a pressure difference of 0.5×105P.
a, liquid temperature 2°C, filtration time 60 seconds, backwash flux 5x
Backwashing was carried out at a rate of 10-3 m3/m2/sec and a time of 4 seconds, and sterilized water was used as the backwashing liquid. Figure 7 shows a case where the composite membrane of the present invention is used, an anisotropic membrane prepared by the above method without using a nonwoven fabric, with the side with larger pores on the undiluted solution side, and cases where the side with smaller pores is on the undiluted solution side. The graph shows the change in total filtration amount over time. Dead-end filtration using the composite membrane of the present invention with periodic backwashing showed a high filtration rate.

Example 2 A composite membrane in which an anisotropic microfiltration membrane with a dense layer average pore diameter of 1.5 μm was formed on various nonwoven fabrics by the method of Example 1 using the suspension of Example 1 as the filtration stock solution. Dead-end filtration with periodic backwashing was carried out. The fiber thickness of the nonwoven fabric is 2 μm, 4 μm, 20 μm, and 30 μm, respectively, the porosity is about 70%, and the thickness is 150 μm. The filter used had an effective membrane area of 100 cm2, the experimental conditions were a pressure difference of 0.5 x 105 Pa, a liquid temperature of 2°C, a filtration time of 60 seconds, and a backwash flux of 5 x 10-3 m3/m2/se.
c. Backwashing was carried out for 4 seconds, and sterile water was used as the backwashing liquid. FIG. 8 shows the results of the total filtration amount after 5 hours of filtration operation when the above composite membrane was used with the nonwoven fabric side as the stock solution side. As a result, a high filtration rate was obtained when the thickness of the nonwoven fabric fibers was 0.5 to 5 times the average pore diameter of the filtration membrane of 5 μm in contact with the nonwoven fabric, that is, 2.5 μm to 25 μm.

Example 3 Using the suspension of Example 1 as a filtration stock solution, anisotropic precision filtration membranes with a dense layer average pore diameter of 1.5 μm and a thickness of 180 μm were formed on nonwoven fabrics of different thicknesses by the method of Example 1. Dead-end filtration with periodic backwashing was carried out using the composite membrane. The thickness of the nonwoven fabric is 80 μm, 120 μm, and 2
00 μm and 300 μm, the fiber thickness is 4 μm, and the porosity is about 70%. The filter used has an effective membrane area of 100 cm.
2, the experimental conditions were a pressure difference of 0.5 x 105 Pa, a liquid temperature of 2°C, a filtration time of 60 seconds, and a backwash flux of 5 x 10-3.
The backwashing was performed at a rate of m3/m2/sec and a time of 4 seconds, and sterilized water was used as the backwashing liquid. FIG. 9 shows the total filtration amount after 5 hours of filtration operation when each composite membrane was used. As a result,
A high filtration rate was obtained when the thickness of the nonwoven fabric was 1/2 or more of the thickness of the filtration membrane, 180 μm, that is, 90 μm or more.

[0014]

Effects of the Invention According to the present invention, a high membrane permeation flux can be obtained in a dead-end filtration system in which backwashing is performed periodically using a composite membrane. Separation, recovery, purification, concentration, etc. of each suspended component are performed extremely efficiently and economically. Furthermore, it is possible to make the process continuous and downsize the equipment, and by utilizing the selectivity of the membrane, it is possible to continuously and selectively separate only the target substance, and it is possible to separate only the target substance continuously and selectively, and it is possible to use the membrane to selectively separate only the target substance. It can be applied and has various effects such as easier operation management than conventional technology.

[Brief explanation of the drawing]

FIG. 1 shows the state of accumulation of suspended solids in conventional dead-end filtration.

FIG. 2 shows the state of accumulation of suspended solids in conventional cross-flow filtration.

FIG. 3 shows a flowchart of a dead-end filtration system in which backwashing is performed periodically according to the present invention.

FIG. 4 shows a cross-sectional state of the anisotropic membrane when suspended substances are blocked on the surface of the filtration membrane from the side with the smaller pore size.

FIG. 5 shows a cross-sectional state of the anisotropic membrane when suspended substances are blocked from the side with larger pores.

FIG. 6 shows a cross-sectional state of the composite membrane of the present invention when suspended substances are blocked from the nonwoven fabric side.

FIG. 7 shows the total filtration amount when protein-agglomerated beer was used for dead-end filtration with periodic backwashing using the composite membrane of the present invention.

FIG. 8 shows the total filtration amount when protein-agglomerated beer was used in dead-end filtration in which backwashing was performed periodically using composite membranes with different thicknesses of nonwoven fibers.

FIG. 9 shows the total filtration amount when protein-agglomerated beer was used in dead-end filtration in which backwashing was performed periodically using composite membranes with different thicknesses of nonwoven fabrics.

[Explanation of symbols]

1 Flow of raw fluid in dead-end filtration 2 Flow of permeate in dead-end filtration 3 Movement direction of suspended solids in dead-end filtration 4 Suspended solids deposited on the filtration membrane 5 Filter membrane 6 Raw material in cross-flow filtration Fluid flow 7 Flow of permeate in cross-flow filtration 8 Movement direction of suspended solids in cross-flow filtration 9 Suspended solids deposited on the filtration membrane 10 Filtration membrane 11 Raw fluid inlet 12 Permeate outlet 13 Backwash liquid Inlet 14 Drainage outlet 15 Filter 16 Filtration membrane 17 Gas inlet 18 Pressure gauge 19 Pump 20 Sterilization filter 21 Solenoid valve 22 Filtration membrane cross section 23 Suspended solids 24 Filtration membrane cross section 25 Suspended solids 26 Filtration membrane cross section 27 Nonwoven fabric cross section 28 Suspension Turbid substance 29 Composite filtration membrane of the present invention

Claims (6)

[Claims] Claim 1: A filtration method in which a raw fluid consisting of a fluid containing suspended matter is supplied and filtered using a precision filtration membrane to separate the fluid from the suspended matter, wherein the filtration membrane is a combination of the precision filtration membrane and a nonwoven fabric. , a laminated composite membrane with woven fabric or glass fiber, characterized in that the fiber thickness of the nonwoven fabric, woven fabric, or glass fiber is 0.5 times or more and 5 times or less the pore diameter of the surface of the filtration membrane on the contacting surface. Composite filtration membrane. 2. The filtration membrane is periodically backwashed by making the pressure on the permeate side of the filtration membrane higher than the pressure on the raw fluid side,
2. The composite filtration membrane according to claim 1, wherein the composite filtration membrane is used in a dead-end filtration system in which suspended solids desorbed from the filtration membrane are discharged from the filtration system together with the backwash liquid. 3. The composite filtration membrane according to claim 1, wherein the thickness of the nonwoven fabric, woven fabric, or glass fiber is 1/2 or more of the thickness of the microfiltration membrane. 4. The composite filtration membrane according to claim 1, wherein a part of the microfiltration membrane is impregnated with nonwoven fabric, woven fabric, or glass fiber. 5. The microfiltration membrane has an anisotropic structure in which the pore diameter changes continuously or discontinuously in the membrane thickness direction, and the pore diameter on one surface of the microfiltration membrane is different from the pore diameter on the other surface, 2. The composite filtration membrane according to claim 1, wherein a nonwoven fabric, woven fabric, or glass fiber is present on the side with larger surface pores. 6. The composite filtration membrane according to claim 1, wherein the nonwoven fabric, woven fabric, or glass fiber side of the composite filtration membrane faces the raw fluid side.