JPH0679146A - Filtration method - Google Patents

Abstract

PURPOSE:To reduce a backwash drained water quantity significantly by backwashing a combination of liquid and gas, when a liquid containing a large amount of suspension is filtered using a micro-filter membrane with an anisotropic pore structure, then a periodic backwashing process is performed and the suspension desorbed from the filter membrane is discharged to an area outside a filtration system together with a backwash liquid. CONSTITUTION:A total filtration periodic backwash system filters liquid containing a large amount of suspension using a micro-filter membrane 3 with an anisotropic pore structure, then backwashes the liquid by detecting an increase in filtering pressure or making the charged liquid side pressure of the filter membrane 3 higher than the feedstock liquid side pressure every specified time, in a periodic backwash fashion, and discharges the suspension desorbed from the filter membrane 3 to an area outside a filtration system together with a backwash liquid. In this system, a combination of liquid and gas is backwashed. Consequently, microparticles can be removed by filtration efficiently from various suspensions such as a fermentation liquid.

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, a total filtration using a microfiltration membrane cartridge filter that periodically performs backwash 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 any case where it is necessary to separate the fine particles from a liquid containing, for example, various suspensions containing the fine particles, a fermentation solution or a culture solution, and fine particles from a suspension of a pigment. It also applies when separating.

[0002]

2. Description of the Related Art Conventionally, as a technique for separating a suspended substance from a liquid containing a suspended substance 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 that uses the driving force as the driving force, a diffusion dialysis method that uses the concentration difference as the driving force, and the like. These methods are capable of continuous operation, can be separated, purified or concentrated without significantly 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 for 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 fine filtration for the filtration of fine particles of 0.05 to 10 μm. Uses a microfiltration membrane having micropores suitable for that. 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 fine particles are separated using a membrane, a cake layer is created due to the effect of concentration polarization, which creates a resistance to the flow of the permeated fluid, and the resistance due to clogging of the membrane increases. There is a problem that the permeation flux is drastically and remarkably reduced, and this 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 the liquid to be filtered passes through a filter medium (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 passes and the suspended substances are trapped inside the filtration membrane to be separated, but at the stage where they are trapped at the surface of the filtration membrane, cake is obtained. When a layer is formed and a large amount of liquid is treated, 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 fields such as wastewater treatment and fresh water / pool water filtration, it is known to perform backwashing 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 not effective as it was. For this reason, it was considered to use a cross flow type filtration method. In this cross-flow type filtration method, 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 this raw liquid and the permeated liquid are orthogonal to each other. This is why it is called. In this cross-flow type filtration method, the cake layer formed on the membrane surface is stripped off by the flow of the original liquid parallel to the membrane, so the membrane permeation flux is large compared to the conventional total filtration method, and a large amount of the original liquid is obtained. Can be directly and continuously separated, purified, and concentrated, but when a membrane in the microfiltration area 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 flow rate, 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, so the membrane permeation flux will gradually decrease and backwash There was a problem that the permeation flux was not fully recovered 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, 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, if a pump with a small shearing force such as a diaphragm pump is used to reduce the crushing of bacterial cells in the pump, there is a problem that the pulsation of the pump is large and the effect of the cross-flow filtration system is small.

[0005]

In the full filtration cycle backwashing method, the pressure on the permeate side is set higher than the pressure on the stock solution side before the decrease of the membrane permeation flux becomes noticeable or before the increase of the filtration pressure becomes noticeable. Then, by backwashing and discharging the fine particles captured on the membrane surface and inside the membrane to the outside of the system, the membrane permeation flux returns to the initial high level or the filtration pressure returns to the initial low level. By repeating this, the average permeation flux can be obtained at a practically high level. The present inventor has (1) the pore size anisotropy in the thickness direction of the membrane in this total filtration cycle backwashing method, and (2) the average pore size of the membrane surface on the primary side of the filtration in the stock solution to be removed. It is 2 to 30 times the average diameter of the suspended particles, and (3) the average pore diameter of the densest layer present inside the membrane or on the surface of the secondary side membrane of the filtration has 0.8 times or less of the average diameter, a higher average permeation flux can be obtained by using a microfiltration membrane characterized by
It was discovered that the backwashing frequency is low and therefore the practicality of this total filtration cycle backwashing method is increased. However, the suspension concentration is 1-20
In the application of removing cells and medium-derived particles from a high-concentration fermented solution that reaches as high as vol%, the backwashing frequency will inevitably increase, and therefore the backwashing wastewater amount will increase and the treatment will be very expensive. That caused the problem.

[0006]

The present invention has been made in order to solve the above-mentioned problems in the prior art, and has a practically high average membrane permeation flux for a long time. It is an object of the present invention to provide a novel whole filtration cycle backwash system that can be maintained stably. That is, a liquid containing a large amount of suspension is filtered using a microfiltration membrane, and the pressure on the permeate side of the filtration membrane is made larger than the pressure on the raw solution side at regular intervals to perform backwashing periodically. It has been found that the above problems can be solved by backwashing by combining a liquid and a gas in a total filtration cycle backwashing system in which the suspension desorbed from the filtration membrane together with the backwash solution is discharged to the outside of the filtration system.

The whole filtration cycle backwashing method of the present invention removes fine particles requiring 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 the fermentation liquid / culture liquid,
The effect is great when the filtration resistance of suspended solids such as concentration and recovery is extremely large. The backwash performed by the whole filtration cycle backwash method of the present invention is basically performed with a liquid. A permeate can be used as the backwash liquid when foreign matter from the outside of the system is avoided.
Further, in order to avoid a decrease in the permeation amount by the amount of backflow of the permeated liquid, it is preferable to supply the cleaning liquid from the outside of the filtration system and carry out the backwashing with the required 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 completed, the liquid is removed by gas.

After backwashing with the liquid is completed, filtration is performed for a certain period of time and liquid backwashing is performed again. During this time, backwashing is performed several times by using gas. The gas pressure should be 0.5 to 1 kg / cm ² higher than the bubble point of the membrane. Further, the cleaning liquid is constantly circulated on the primary side of the membrane while being circulated, and the cake separated from the membrane surface by jetting gas is always dispersed and removed in the liquid. If the liquid containing the suspension used in the previous backwash is used as it is, the effective backwash can be achieved with a small amount of the backwash liquid.

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 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 module (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 module is collected.
Emitted from. FIG. 3 is a sectional view of a microfiltration membrane disc laminated cartridge filter element. This element has microfiltration membranes (37) 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-passing means inside, and the liquid that has permeated the membrane is transmitted through the inside of the membrane support (38) and the central through hole 32.
And discharged from the secondary inlet / outlet 23.

The stock solution containing the suspension enters the module 11 from the stock solution tank 14 shown in FIG. 4 through the filter pump 12 and the filter module primary inlet 22. The liquid that has passed through the microfiltration membrane element 30 is discharged from the secondary outlet 23 and collected in the permeated liquid tank 15. When the membrane is clogged, the backwash liquid is normally sent from the backwash tank 16 to the element 30 via the backwash pump 13 and the secondary outlet 23, and the film-like cake is peeled off and deposited suspension is deposited. Then, the liquid is discharged to the waste liquid port 18 through the primary side inlet 22. In backwashing with gas, the cleaning liquid is sent from the cleaning liquid tank 19 to the module 11 via the pump 12, returned from the primary side outlet 25 of the module to the tank 19, and circulated, while introducing pressurized gas from the gas inlet 24 and permeating the membrane. The gas is discharged from the primary outlet 25 together with the cleaning liquid.

The microfiltration membrane that 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 above-mentioned 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 coagulation solution, washed and dried. In this case, examples of the solvent that dissolves the polymer include dichloromethane, acetone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, 2-pyrrolidone, N-methyl-2-pyrrolidone, and sulfolane. Examples of non-solvents added to the above solvent include cellosolves, alcohols such as methanol, ethanol and isopropanol, acetone, ketones such as methyl ethyl ketone, tetrahydrofuran, ethers such as dioxane, polyethylene glycol, glycerin, ethyl glycol such as ethyl glycol. Examples thereof include polyols. 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.
50% by weight 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 sodium chloride, 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, and 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 uniformity of the solution is not lost by the addition, 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. Polymer concentration as a film forming stock solution is 5 to 35% by weight, preferably 10 to 30% by weight
Is. When it exceeds 35% by weight, the water permeability of the obtained microporous membrane becomes so small as to have no practical meaning, and it becomes 5% by weight.
When it is smaller than that, 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 together with the support is immersed in the 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 can be arbitrarily selected from those which can be used as a support in the case of producing a microfiltration membrane, but when a non-woven fabric is used, the support need not be peeled off, which is preferable. 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. The amount of non-woven fabric attached is 18 g / m ² to enhance the backwash effect.
To 200 g / m ² , preferably 30 g / m ² to 10
Often made of synthetic fibers such as polyester, polypropylene or nylon with a weight of 0 g / m ² and 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 the folds of the seam are heat-sealed or liquid-bonded with an adhesive. Seal tightly. There are several methods for the end sealing process depending on the material of the end plate, but all of them are carried out by the conventionally known publicly known technique. When using a thermosetting epoxy resin for the end plate, pour the liquid epoxy resin adhesive compounded 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 a cylindrical filter medium is also performed.

Filtration of a liquid having a high suspension concentration 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 the pore size in the thickness direction is further effective in improving the product recovery rate in the liquid. This is because when the stock solution is filtered from the large pore surface of such an anisotropic membrane to the small pore surface, 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 due to the suspension is delayed because it is captured. Therefore, the filtration amount of the stock solution from the start of filtration to the backwashing is more than doubled by using the anisotropic membrane rather than using the 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, the result is that 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 diameter of the maximum pore diameter layer of the anisotropic membrane used is 2 to 30 times the particle diameter of the suspension to be removed (in the case of bacillus, its cylindrical diameter), the product recovery rate becomes 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 A device as shown in FIG. 4 incorporating a pleated cartridge module having about 0.34 square meters of polysulfone anisotropic membrane with a dense layer having an average pore size of 0.4 .mu.m and a maximum layer having an average pore size of 3.8 .mu.m. The following experiment was conducted using A simulated fermentation liquid in which 14% by volume of baker's yeast was dispersed was used as the stock solution for filtration. Filtration pump flow rate 0.2 per minute
It was filtered for 2.5 minutes while feeding the stock solution to the module in liters, then backwashed with pressurized air for 0.5 minutes.
When this was repeated 4 times and further filtered for 2.5 minutes, the filtration pressure exceeded 0.4 kg / cm ² , so backwashing was carried out here with water for 0.5 minutes. Then, even if the filtration was further performed for 2.5 minutes, the filtration pressure rose only to about 0.1 kg / cm ² , and the filtration could be continued under the same conditions thereafter. The data of the pressure change over time are shown in FIG.

COMPARATIVE EXAMPLE 1 A pleated cartridge module having about 0.34 square meters of polysulfone anisotropic membrane having a dense layer having an average pore size of 0.4 μm and a maximum layer having an average pore size of 3.8 μm is shown in FIG. The following experiment was conducted using the apparatus as described above. A simulated fermentation liquid in which 14% by volume of baker's yeast was dispersed was used as the stock solution for filtration. Filtration pump flow rate 0.2 per minute
While feeding the stock solution to the module in liters, it was filtered for 2.5 minutes and then backwashed with water for 0.5 minutes. This was repeated many times, but the filtration pressure increased only to about 0.1 kg / cm ² , and the filtration could be continued under the same conditions thereafter. The data of the pressure change with time are shown in FIG. As a matter of course, the amount of backwashing wastewater reached 5 times that of Example 1.

[0018]

EFFECT OF THE INVENTION A liquid containing a large amount of suspension is filtered using a microfiltration membrane, and the pressure on the permeate side of the filtration membrane is made larger than the pressure on the raw solution side at regular intervals to periodically backwash. The total amount of backwashing wastewater is significantly reduced by backwashing a combination of liquid and gas in a full filtration cycle backwash system that discharges the suspension desorbed from the filtration membrane together with the backwash solution to the outside of the filtration system. Was achieved.

[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 is a graph showing changes in pressure over time in a backwashing experiment of the entire filtration cycle of Example 1.

FIG. 6 is a graph showing changes in pressure over time in a backwashing experiment of the entire filtration cycle of Comparative 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 Module 12 Filtration Pump 13 Backwash Pump 14 Stock Solution Tank 15 Permeate Tank 16 Backwash Water Tank 17 Pressurized Gas Source 18 Waste Liquid Port 19 Cleaning Liquid Tank 22 Primary Side Inlet 23 Secondary Side Inlet / Outlet 24 Secondary Side Pressurized Gas Inlet 25 Primary Side Outlet 26 Packing 27 Module Head 28 Module Ball 30 Filter Element 31 Pleated Part 32 Center Through Hole 33 Core Hole 35 Membrane Support Peripheral protrusion 36 Membrane support Peripheral protrusion 37 Microfiltration membrane 38 Membrane support

Claims (3)

[Claims] 1. A liquid containing a large amount of a suspension is filtered using a microfiltration membrane, and the pressure on the permeate side of the filtration membrane is made higher than the pressure on the raw solution side at regular intervals to periodically backwash. In the whole filtration cycle backwash system for discharging the suspension desorbed from the filtration membrane together with the washing solution to the outside of the filtration system, backwashing is performed by combining liquid and gas, and the whole filtration cycle backwash filtration method. . 2. A microfiltration membrane is used in the form of a pleated cartridge filter element.
The full filtration cycle backwash filtration method according to claim 1. 3. The full filtration cycle backwash filtration method according to claim 2, wherein backwash with a gas is performed while circulating wash water on the primary side of the filtration membrane.