JPH05329336A - Filtering method - Google Patents

Abstract

PURPOSE:To keep a high average filtering flux by shortening the time of one cycle and to stably perform cyclic backwashing filtering for a long period of time while suppressing the rise of filtering pressure, in a cyclic backwashing system for full-filtration, by changing a flow rate of a raw solution to a module at the time of the filling operation of the raw solution from that at the time of the filtering operation of the raw solution. CONSTITUTION:A raw solution containing suspended matter is introduced into a module 11 from the entrance and exit 22 on the primary side of a filter housing and transmitted through a precise filter membrane element 30 to be discharged from the entrance and exit on the secondary side of the housing. When a membrane generates clogging, backwashing is performed using a backwashing slution but, before backwashing, compressed gas is introduced into the module from gas inlets 25, 24 on the primary and secondary sides of the housing. In this case, the flow rate of the raw solution to the module at the time of the filling operation of the raw solution is changed from that at the time of the filtering operation of the raw solution. As mentioned above, the time of the filling operation of the raw solution is reduced by suppressing the flow rate of the raw solution and the time required in one cycle is shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a total filtration cycle backwash system, and more particularly to a total filtration using a microfiltration membrane cartridge filter in which backwash is periodically performed in order to maintain a high membrane permeation flux. It relates to a periodic backwash system. The whole filtration cycle backwash system of the present invention is applied to separation, purification, recovery, concentration, etc. of various polymers, microorganisms, yeasts, liquids containing or suspending fine particles, and particularly fine particles requiring filtration. It can be applied to all cases where it is necessary to separate the fine particles from a liquid containing, for example, various suspensions containing fine particles, fermentation liquid or culture liquid, and fine particles from pigment suspensions. It also applies when separating the.

[0002]

2. Description of the Related Art Conventionally, as a technique for separating a suspended substance from a liquid containing a suspended substance by using a membrane, for example, a reverse osmosis method using pressure as a driving force, an ultrafiltration method, a microfiltration method, a potential difference. There are an electrodialysis method using a driving force as a driving force, and a diffusion dialysis method using a concentration difference as a driving force. These methods are capable of continuous operation, can be separated, purified or concentrated without greatly changing the temperature and pH conditions during the separation operation, and can be separated over a wide range of particles, molecules, ions, etc., Economical because the processing capacity can be kept large even in a small plant, the energy required for the separation operation is small,
In addition, it is widely used because of the fact that it is possible to treat low-concentration liquids that are difficult with other separation methods. And, as the membrane used in these separation techniques, a polymer membrane mainly composed of organic polymers such as cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone, polyacrylonitrile, polyamide, polyimide, heat resistance, chemical resistance, etc. There are porous ceramic membranes, etc. that have excellent durability, and ultrafiltration membranes are mainly used for colloid filtration, and microfiltration for the filtration of fine particles of 0.05 to 10 μm. Uses a microfiltration membrane having suitable micropores. By the way, in recent years, with the progress of biotechnology, high purification, high performance, and high precision have been required, and the application fields of microfiltration or ultrafiltration technology are expanding. However,
In microfiltration or ultrafiltration, when separating fine particles using a membrane, a cake layer is generated on the membrane surface due to the effect of concentration polarization, and resistance to the flow of the permeated fluid is generated, and resistance due to clogging of the membrane is large. Then, there is a problem that the membrane permeation flux is drastically and remarkably reduced, which is the biggest cause of impeding the practical application of microfiltration or ultrafiltration. Further, the film used for it is easily contaminated, and it is necessary to take preventive measures against it.

As a filtration method, there is a so-called total filtration method in which all liquids to be filtered pass through a filter material (filter cloth, membrane, etc.) and a cake layer to separate fine particles contained in the liquid. In this conventional total filtration method, a high permeation flux is obtained at the stage where the liquid is passed and the suspended substances are captured and separated inside the filtration membrane, but at the stage when they are captured at the surface of the filtration membrane, the cake is obtained. When a layer is formed and a large amount of liquid is processed, or when the specific resistance of the formed cake layer is extremely high, the filtration resistance becomes large, and such a total filtration reduces the membrane permeation flux. On the other hand, in the field of wastewater treatment, filtration of fresh water, pool water, etc., it is known to perform backwashing in order to recover the filtration flux of a clogged filter.
However, this combined method of total filtration and backwash is a technology developed in the field of wastewater treatment in which the specific resistance of the cake layer is relatively small, and therefore, it is possible to remove fine particles with large specific resistance such as bacterial cell separation of the fermentation liquid. The filtration was ineffective as it was. Therefore, it has been considered to use a cross-flow type filtration method. In this cross-flow type filtration system, the raw liquid to be filtered flows in parallel to the membrane surface of the filtration membrane, the liquid permeates to the opposite side through the filtration membrane, and the flow of the raw liquid and the permeated liquid is orthogonal. This is why it is so called. In this cross-flow type filtration method, since the cake layer formed on the membrane surface is stripped off by the flow of the raw liquid parallel to the membrane, the membrane permeation flux is large compared to the conventional total filtration method, and a large amount of the raw liquid is obtained. Can be directly and continuously separated, purified, and concentrated, but when a membrane in the microfiltration region that removes particles with a large pure water permeation flux, that is, from 0.05 to 10 μm, is used, the membrane permeation flux rapidly increases. It is difficult to maintain a high membrane permeation flux at the initial stage of filtration, and as a result, when comparing the total filtration method with the total permeate amount, the improvement effect is small and it is not possible to obtain an economical permeation flux. Was enough.

As a method for increasing the permeation flux, the filtration is carried out by intermittently stopping the inflow of the raw liquid into the filtration membrane or by closing the valve on the permeate side of the filtration membrane in combination with the cross flow filtration method. By intermittently eliminating or reducing the pressure applied perpendicularly to the membrane surface of the membrane, or by applying pressure from the permeate side of the filtration membrane and flowing the liquid from the permeate side to the stock solution side,
An attempt to intermittently remove the cake layer and the adhering layer accumulated on the undiluted solution side of the filtration membrane has been attempted, which is called "backwashing". If the suspended substance left in the filtration system is left in the filtration system, the concentration of the suspension in the stock solution will gradually increase, and in some cases the viscosity of the stock solution will also increase. There was a problem that the permeation flux did not recover sufficiently even if it went. In addition, when backwashing is performed using a permeate, the amount of membrane permeation is substantially reduced by the amount of backwashing, so that there is a problem in that a backwash that can sufficiently restore the membrane permeation flux cannot be secured. On the other hand, as a method that does not reduce the activity of the bacterial cells, it has been attempted to reduce the cross-flow circulation flow rate to reduce the shearing force.However, if the shearing force is reduced, the effect of the cross-flow filtration method will be reduced. There is a problem that the permeation flux of the membrane is reduced if a measure that does not reduce the physical activity is taken. Further, when a pump having 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 pulsation of the pump is large and the effect of the cross-flow filtration system is reduced.

[0005]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention
Before the membrane permeation flux is significantly reduced or the filtration pressure is significantly increased, the pressure on the permeate side is made higher than the pressure on the raw solution side to backwash the fine particles trapped on the membrane surface and inside the membrane. By discharging out of the system, the membrane permeation flux is returned to an initial high level or the filtration pressure is returned to an initial low level. There is a whole filtration cycle backwash filtration method in which the average permeation flux is raised to a practically high level by repeating this. In order to maintain this whole backwash cycle backwashing stably for a long period of time, in order to prevent the captured fine particles from consolidating and irreversibly adhering to the membrane surface and reducing the backwashability, It is necessary to suppress the differential pressure or transmembrane flux within a certain range.
This is performed by controlling the amount of the undiluted solution delivered during filtration. However, in the whole filtration cycle backwash system, it is necessary to perform the undiluted solution filling operation before the filtration operation to fill the undiluted solution in the membrane module undiluted solution side, and suppressing the undiluted solution delivery amount requires a long time in the undiluted solution filling operation, The time required for one cycle becomes longer, and the higher the suspension concentration and the shorter the backwash cycle, the lower the average filtration flux.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and it is possible to maintain a practically high average membrane permeation flux while performing periodic backwashing. It is an object of the present invention to provide a novel whole filtration cycle backwash system capable of maintaining stable filtration over a long period of time. That is, the present invention is to filter a liquid containing a large amount of suspension using a microfiltration membrane, detect an increase in filtration pressure, or measure the pressure on the permeate side of the filtration membrane from the pressure on the stock solution side at regular intervals. Is also increased to perform periodic backwashing, and the suspension desorbed from the filtration membrane together with the backwashing liquid is discharged to the outside of the filtration system.
In a total filtration cycle backwash system consisting of pressure deliquoring operation, backwashing operation, and pressure deliquoring operation, the flow rate of the stock solution fed to the module is changed during the stock solution filling operation and the stock solution filtering operation. Full filtration cycle Backwash filtration method or filtration of a liquid containing a large amount of suspension using a microfiltration membrane to detect an increase in filtration pressure or to detect the pressure on the permeate side of the filtration membrane at regular intervals. In a whole filtration cycle backwash system in which the backwash is periodically carried out with the pressure higher than the stock solution side and the suspension desorbed from the filtration membrane together with the backwash solution is discharged out of the filtration system,
(1) Pore diameter anisotropy in the thickness direction of the film,
(2) The average pore diameter of the membrane surface on the primary side of filtration is 2 to 30 times the average diameter of the suspended particles in the stock solution to be removed,
(3) The average pore size of the densest layer existing inside the membrane or on the surface of the secondary membrane for filtration is 0.8 times or less than the average diameter of the suspended particles in the stock solution to be removed. Was achieved by a full filtration cycle backwash filtration method using a microfiltration membrane. Hereinafter, the present invention will be described in detail.

The backwashing method of the whole filtration cycle of the present invention removes fine particles which require filtration such as separation, purification, recovery and concentration of liquids containing or suspending various polymers, microorganisms, yeasts and particles. It can be applied to all cases where it is necessary to remove the fine particles from the liquid containing it, especially separation of enzymes, microorganisms, cells, etc. from fermentation liquid / culture liquid,
The effect is great when the filtration resistivity of the suspended matter is extremely large, such as concentration and recovery. The backwashing performed by the whole filtration cycle backwashing method of the present invention is more effective when performed with a liquid rather than gas, and a permeate can be used as the backwashing liquid when foreign matter from the outside of the system is avoided. In order to avoid a decrease in permeation amount by the amount of backflow of the permeated liquid, it is preferable to supply a cleaning liquid from the outside of the filtration system and perform backwashing with an appropriate backwashing amount. The backwash liquid supplied from outside the filtration system may be basically any liquid as long as it does not deteriorate the characteristics of the filtration membrane or the characteristics of the stock solution. If the stock solution is an aqueous solution, water is generally used as the backwash solution. If it is not desired to leave the backwash solution in the system after the backwash is finished, the liquid is removed by gas.

When performing constant pressure filtration, when the backwash is performed after the membrane permeation flux becomes extremely low as in the conventional "total filtration backwash technique", the recoverability of the membrane permeation flux after backwash is poor. Because,
Backwash is performed before reaching 1/50 of the initial permeation flux. A higher permeation flux can be obtained by backwashing preferably before reaching 1/10 of the permeation flux at the initial stage of filtration. When performing constant-flux filtration, if backwashing is performed after the pressure difference between the filtration membranes has become extremely high, the recoverability of the pressure difference between the filtration membranes after backwashing, that is, the cleaning property is deteriorated. Backwashing is preferably performed before the differential pressure reaches 1.0 kg / cm ² . More preferably, by performing backwashing before the differential pressure between filtration membranes reaches 0.3 kg / cm ² , the condition of permeation flux can be further increased. Since the backwash liquid has a high membrane permeation flux and a large amount of water is passed through the filtration membrane, the washing performance is higher.
The permeation flux of the backwash liquid is preferably 1 × 10 ⁻⁴ m ² / m ² / sec or more. Further, it is preferable that the amount of backwashing liquid is at least twice the volume of the primary side of the filter housing in order to recover the filtration capacity of the membrane. However, when the amount of the permeated liquid is small, the backwashing drainage amount becomes relatively large. Therefore, considering the balance between the filtration amount and the drainage amount, the backwashing amount of about twice the primary side capacity of the housing may be appropriate.

1 and 2 are a developed view of a general microfiltration membrane pleated type cartridge filter element and a sectional view of the same module. The microfiltration membrane 3 is fold-folded in a state of being sandwiched by the two liquid-permeable sheets 2 and 4, and is wound around a core 5 having a large number of core holes 33. An outer peripheral guard 1 is provided on the outer side thereof to protect the microfiltration membrane. Microfiltration membranes are sealed at both ends of the cylinder by end plates 6a and 6b.
The end plate contacts the seal portion of the filter housing (not shown) via the gasket 7. The filtered liquid is collected from the liquid collecting port 8 through the central through hole 32 formed by the core, and the secondary side inlet / outlet port 23 of the filter housing is collected.
Discharged from. FIG. 3 is a sectional view of a microfiltration membrane disc laminated cartridge filter element. In this element, microfiltration membranes (37) are installed on both sides of a disc-shaped membrane support (38), and such discs are laminated to form a cylindrical shape as a whole. The central part of the membrane support is concentrically punched into a donut shape, and when stacked, the punched central part forms a central through hole 32. Further, the support has a liquid passage means inside thereof, and the liquid that has permeated through the membrane is transmitted through the inside of the membrane support (38) to the central through hole 32.
And is discharged from the secondary side inlet / outlet 23.

The stock solution containing the suspension enters the module 11 from the stock solution tank 19 shown in FIG. The liquid that has permeated the microfiltration membrane element 30 is discharged from the secondary inlet / outlet port 23 and collected in the permeated liquid tank 15. When the membrane is clogged, the backwash liquid is usually supplied from the backwash tank 16 through the backwash pump 13 and the secondary inlet / outlet 23 to the element 30.
To the waste liquid port 18 through the primary inlet / outlet port 22 together with the suspended matter that has peeled off the filmy cake and accumulated. However, at this time, the undiluted solution and the permeated solution remaining in the module 11 are also discharged and the loss of the product increases, so that the primary side gas inlet 25 of the module before backwashing.
A pressurized gas is introduced from the secondary side gas inlet 24, and the liquid remaining in the module is pushed out to the stock solution tank 19 and the permeate tank 15. Further, the cleaning liquid is supplied from the cleaning liquid tank 14 through the pump 12 and the primary side inlet / outlet 22 to the module 11
The liquid remaining in the module, particularly in the membrane cartridge, is washed out and collected in the permeated liquid tank 15. This operation is called normal cleaning. However, by performing sufficient normal cleaning, it is backwashed and discharged. The production can be significantly reduced. A pipe 39 that bypasses the module 11 from the filtration pump 12 to the stock solution tank 19 is provided. By opening / closing the bypass 39, the amount of the stock solution supplied to the module 11 can be controlled while keeping the pump flow rate constant.

The microfiltration membrane which can be used in the present invention includes polyvinylidene fluoride, polyacrylonitrile, vinyl polymers such as polyvinyl chloride, polysulfones, polyether sulfones, aliphatic polyamides, cellulose esters, etc. The polymers may be used alone or in combination as a raw material. The production of the microfiltration membrane is carried out by dissolving the polymer in a good solvent, a mixed solvent of a good solvent and a non-solvent, or a mixture of plural kinds of solvents having different degrees of solubility to the polymer to prepare a membrane-forming stock solution, Is cast on a support or directly in a coagulating solution, washed and dried. In this case, examples of the solvent for dissolving the polymer include dichloromethane, acetone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, 2-pyrrolidone,
Examples thereof include N-methyl-2-pyrrolidone and sulfolane. Examples of the non-solvent added to the above solvent,
Examples thereof include cellosolves, alcohols such as methanol, ethanol and isopropanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, polyols such as polyethylene glycol, glycerin and ethyl glycol. The ratio of the non-solvent to the good solvent may be any range as long as the mixed solution can maintain a uniform state, but is 5 to 50.
Weight percent is preferred.

In addition, an inorganic electrolyte called an swelling agent, an organic electrolyte, a polymer electrolyte or the like may be added to control the porous structure. Examples of the electrolyte that can be used in the present invention include salt, sodium nitrate, potassium nitrate, sodium sulfate, zinc chloride, metal salts of inorganic acids such as magnesium bromide, sodium acetate, sodium formate, organic acid salts such as potassium butyrate, polystyrene sulfonic acid. Polymer electrolytes such as sodium, polyvinylpyrrolidone and polyvinylbenzyltrimethylammonium chloride, and ionic surfactants such as sodium dioctyl sulfosuccinate and sodium alkylmethyl taurate are used. Although some of these electrolytes show some effect when added alone to the polymer solution, particularly when these electrolytes are added as an aqueous solution, they may show particularly remarkable effects.
The addition amount of the electrolyte aqueous solution is not particularly limited as long as the addition does not lose the homogeneity of the solution, but it is usually 0.5% by volume to 10% by volume with respect to the solvent. The concentration of the electrolyte aqueous solution is not particularly limited, and the higher the concentration, the greater the effect, but the concentration usually used is 1% by weight to 60% by weight. The polymer concentration of the stock solution for film formation is 5 to 35% by weight, preferably 10 to 30% by weight. When it exceeds 35% by weight, the water permeability of the obtained microporous membrane becomes so small as to have no practical meaning, and when it is less than 5% by weight, a microfiltration membrane having sufficient separation ability cannot be obtained. ..

The stock solution for film formation prepared as described above is cast on a support, and the polymer solution film is immersed together with the support in a coagulating liquid immediately after casting or after a certain time. Water is most commonly used as the coagulation liquid, but an organic solvent that does not dissolve the polymer may be used, or two or more of these non-solvents may be mixed and used. The support may be arbitrarily selected from those which can be used as a support in the case of producing a microfiltration membrane, but it is preferable to use a non-woven fabric because the support need not be peeled off. The non-woven fabric that can be used in the present invention is generally made of polypropylene, polyester, etc., and is not limited by the material. After that, the casting film on which the polymer is precipitated in the coagulation bath is washed with water, washed with warm water, washed with a solvent, and dried. The microfiltration membrane 3 thus produced is pleated by a known method. As the protective sheets 2 and 4, non-woven fabric, filter paper, and / or a net-like body is used. In order to enhance the backwash effect, the amount of non-woven fabric applied is 18 g / m ² to 200 g / m ² , preferably 30 g / m ² to 100 g /
Often used are those made of synthetic fibers, such as polyester, polypropylene or nylon, of m ^{2 and} having a thickness of 0.1 mm to 1 mm. The reticulated body refers to a reticulated sheet in which monofilaments of synthetic polymer such as polyester, polypropylene or nylon are alternately knitted in a lattice shape, and the size of the stitches is preferably 12 mesh to 500 mesh. Particularly preferably, the mesh size is 25 to 250 mesh.

In order to align both ends of the fold-folded filter medium, the uneven portions of both ends are cut off with a cutter knife or the like, and the folds of the seam are rolled into a cylindrical shape and heat-sealed or an adhesive is used to apply liquid. Seal tightly. There are several methods for the end-sealing step depending on the material of the end plate, but all of them are carried out by known techniques known in the art. When using a thermosetting epoxy resin for the end plate, pour the liquid of the prepared epoxy resin adhesive into the potting mold and pre-cure it to increase the viscosity of the adhesive to an appropriate degree. Insert one end into this epoxy adhesive. Then, it is heated and completely cured. When the material of the end plate is a thermoplastic resin such as polypropylene or polyester, a method of inserting one end surface of the cylindrical filter medium into the resin immediately after the molten resin is poured into the mold is used. On the other hand, only the seal surface of the already molded end plate is melted with an infrared heater,
A method of welding one end surface of the cylindrical filter medium is also performed.

Filtration of a high suspension concentration liquid by the backwashing method of the whole filtration cycle is disclosed in JP-A-62-27006, JP-B-55-6406 and JP-B-1-43619. The use of such a film having anisotropy of pore diameter in the thickness direction is further effective in improving the product recovery rate in the liquid. This is because when the undiluted solution is filtered from the surface with a large pore size of such an anisotropic membrane to the surface with a small pore size, the suspension is not trapped only on the membrane surface but also enters and disperses inside the membrane. This is because the formation of a dense cake by the suspension is delayed because it is captured. For this reason, the filtration amount of the stock solution between the start of filtration and backwashing is more than doubled by using an anisotropic membrane rather than using an isotropic membrane having a uniform pore size in the thickness direction. Since the amount of product discharged in one backwash is the same regardless of the filtration amount, as a result, the product recovery rate is higher when the anisotropic membrane is used, and the product loss rate is higher than that of the isotropic membrane. Less than half. When the average pore size of the maximum pore size layer of the anisotropic membrane used is 2 to 30 times the particle size of the suspension to be removed (in the case of bacillus, its cylindrical diameter), the product recovery rate is particularly high, which is preferable. The most preferable range of the average pore size of the maximum pore size layer is 4 to 16 times the suspension particle size. The anisotropic film has a structure having a maximum pore size layer on one surface of the film and a densest layer on the opposite surface or inside the film. In the densest layer, the suspension particles in the stock solution must be completely removable. Therefore, the average pore size of the densest layer needs to be smaller than the average particle size of the suspension particles to be removed, and is preferably 0.8 times or less the average particle size of the suspension particles.

[0016]

EXAMPLES The present invention will be described in more detail with reference to specific examples of filtration, but the present invention is not limited to the examples as long as the gist of the invention is not exceeded. Example 1 The following experiment was carried out using a pleated cartridge module in which an anisotropic membrane made of polysulfone having an average pore size of 0.4 μm of the dense layer and an average pore size of the maximum pore layer of 3.8 μm was incorporated. A simulated fermentation broth containing 14% by volume of baker's yeast was used as the stock solution for filtration.
The stock solution was sent to the pleated cartridge module with an initial flow rate of 2 liters per minute by a filtration pump. It took 0.3 minutes to supply the stock solution. After the stock solution supply operation is completed, the bypass valve is opened, the stock solution feed amount to the pleated cartridge module is adjusted to 0.5 liter, and the solution is filtered for 4 minutes, and then 0.5 kg / cm ² on both the primary side and the secondary side of the membrane. A pressure dewatering operation was performed for 0.2 minutes by applying air pressure to collect the liquid remaining on the primary side into the stock solution tank and the liquid remaining on the secondary side into the permeate. Then, 1 liter of wash water was sent to the membrane holder by the backwash pump, and the backwash operation for washing and recovering the clogging of the membrane was performed for 0.5 minutes, and the backwash wash water was stored in the waste liquid tank. A pressure deliquoring operation was performed in which air pressure was applied to both sides of the membrane again to discharge and discard the backwash water remaining in the membrane holder. One cycle from the first filtration to the final drainage was completed, and the process was completed in a total of 5.2 minutes. Cyclic backwashing was repeated, but stable filtration could be realized without any increase in filtration pressure with time.
Moreover, the time required for one cycle was shortened. Figure 7 shows the filtration data
Shown in.

[0017]

[Table 1]

Comparative Example 1 A stock solution filling operation and a stock solution filtering operation were carried out with an initial filtration flow rate of 2 liters of a filtration pump, and the following operations were carried out in the same manner as in Example 1 to carry out periodic backwashing. Although the time required for one cycle was short, the filtration pressure increased with time, and the cycle backwash could not be continued. The filtration data is shown in FIG.

Comparative Example 2 A stock solution filling operation and a stock solution filtering operation were carried out at an initial filtration flow rate of 0.5 liter of a filtration pump, and the following operations were carried out in the same manner as in Example 1 to carry out periodic backwashing. The filtration pressure was not increased with time, and stable cycle backwash could be performed, but the required time for one cycle was 6.1 minutes, and the average filtration flow rate was low. Filtration data is shown in FIG.

[0020]

EFFECTS OF THE INVENTION A liquid containing a large amount of a suspension is filtered using a microfiltration membrane, and a rise in filtration pressure is detected or the pressure on the permeate side of the filtration membrane is set to be higher than that on the raw liquid side at regular intervals. In a whole filtration cycle backwashing system in which the suspension that has been desorbed from the filtration membrane together with the backwash solution is discharged to the outside of the filtration system after a large backwash is performed, one cycle of the operation procedure is mainly the stock solution filling operation, In a total filtration cycle backwash system consisting of stock solution filtration operation, pressurized dewatering operation, backwashing operation, and pressure dewatering operation, the flow rate of the undiluted solution to the module is changed between the undiluted solution filling operation and the undiluted solution filtration operation. As a result, the time required for one cycle can be shortened and a high average filtration flux can be maintained, and at the same time, the increase in filtration pressure can be suppressed and the cycle backwash filtration can be stably maintained for a long period of time.

[Brief description of drawings]

FIG. 1 is a view showing a structure of a general pleat type cartridge filter.

FIG. 2 is an overall view of a pleated cartridge filter module used in the present invention.

FIG. 3 is an overall view of a disc laminated cartridge filter module used in the present invention.

FIG. 4 is a filtration flow chart used in the present invention.

FIG. 5: Periodic backwash filtration experiment data of Comparative Example 1

FIG. 6 Periodic backwash filtration experiment data of Comparative Example 1

FIG. 7: Periodic backwash filtration experiment data of Example 1

[Explanation of symbols]

 1 Peripheral Guard 2 Protective Sheet 3 Filtration Membrane 4 Protective Sheet 5 Core 6 End Plate 7 Gasket 8 Liquid Collection Port 11 Filter Housing 12 Filtration Pump 13 Backwash Pump 14 Wash Solution Tank 15 Permeate Tank 16 Backwash Water Tank 17 Pressurized Gas Source 18 Waste Liquid Port 19 Undiluted Liquid Tank 22 Primary Side Inlet / Outlet 23 Secondary Side Inlet / Outlet 24 Secondary Side Pressurized Gas Inlet 25 Primary Side Pressurized Gas Inlet 26 Packing 27 Housing Head 28 Housing Ball 30 Filter Element 31 Pleated Part 32 Center Hole 33 Core Hole 35 Membrane Support Peripheral Protrusion 36 Membrane Support Perimeter Protrusion 37 Microfiltration Membrane 38 Membrane Support 39 Bypass Piping

Claims (2)

[Claims] 1. A liquid containing a large amount of a suspension is filtered using a microfiltration membrane, and an increase in filtration pressure is detected, or the pressure on the permeate side of the filtration membrane is set to be lower than the pressure on the stock solution side at regular intervals. The cycle is increased to perform periodic backwash, and the suspension desorbed from the filtration membrane together with the backwash solution is discharged to the outside of the filtration system. In a total filtration cycle backwash system consisting of liquid operation, backwashing operation, and pressure dewatering operation, total filtration characterized by changing the flow rate of the raw solution to the module during the stock solution filling operation and the stock solution filtering operation. Periodic backwash filtration method. 2. A liquid containing a large amount of a suspension is filtered using a microfiltration membrane, and an increase in filtration pressure is detected, or the pressure on the permeate side of the filtration membrane is set to be lower than the pressure on the stock solution side at regular intervals. In a total filtration cycle backwash system in which the suspension desorbed from the filtration membrane together with the backwash solution is discharged to the outside of the filtration system by increasing the size of the backwash solution periodically, and (1) the pore size varies in the thickness direction of the membrane. (2) the average pore size of the membrane surface on the primary side of filtration is 2 to 30 times the average diameter of the suspended particles in the stock solution to be removed, and (3) inside the membrane or All using a microfiltration membrane, characterized in that the average pore size of the densest layer present on the surface of the secondary membrane of the filtration is 0.8 times or less than the average diameter of the suspended particles in the stock solution to be removed. Filtration cycle backwash filtration method.