JPH04271815A - Filtering method - Google Patents

Abstract

PURPOSE:To offer a method for effectively filtering and removing fine particles from the various suspended solution such as fermentative liquid, and filtration device using this method. CONSTITUTION:1. In the total periodical back washing system, which executes filtration while eliminating collected cake on the surface of filter medium by repeated periodical back washing, a pleat cartridge type filter elements is used in which a sandwiched filter film with plural protective sheets is folded to make pleat, round up into cylindrical shape and its jointed part are sealed liquid hermetically, and both ends of the cylinder except liquid drainage hole of filtrate are also liquid sealed hermetically. 2. This filtering method is characterized by using 25-250 mesh net type body sheets or an unwoven cloth having 30-100g/m<2> unite weight as protective sheet of the primary side. By using such special pleat cartridge type filter element applying in the total filtration periodical back washing system, the back washing is repeated periodically while collected cake on the surface of the filter medium is removed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a total filtration periodic backwashing system, and particularly to a total filtration periodic backwashing system using a microfiltration membrane cartridge filter in which backwashing is performed periodically to maintain a large membrane permeation flux. It relates to a filtration periodic backwashing system. The total filtration periodic backwashing system of the present invention is applied to the separation, purification, recovery, and concentration of fluids containing or suspending various polymers, microorganisms, yeast, and fine particles, and is particularly applicable to fine particles that require filtration. It can be applied in any case where it is necessary to separate fine particles from a fluid containing fine particles, such as from various suspensions containing fine particles, fermentation liquids or culture liquids, as well as suspensions of pigments, etc. It is also applied to the separation of fine particles, and is also used to purify gas by separating and removing fine particles from suspended gas containing fine particles, for example, sterilizing nitrogen gas to be filled into pharmaceutical ampoules, and positive application to ultrapure water production equipment. It is also applied to the production of dust-free, sterile gas filled as pressurized gas, or dust-free, sterile air for air conditioning in IC manufacturing lines.

0002

[Prior Art] Conventionally, techniques for separating suspended solids from a raw fluid containing suspended solids using a membrane include, for example, reverse osmosis, ultrafiltration, precision filtration, etc. using 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 even small plants can maintain large processing capacity, and the energy required for separation operations is small.
Moreover, it is widely practiced because it is possible to treat low-concentration raw fluids that are difficult to use with other separation methods. The membranes used in these separation techniques include polymer membranes mainly made of organic polymers such as cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone, polyacrylonitrile, polyamide, and polyimide, as well as those with heat resistance, chemical resistance, etc. There are porous ceramic membranes with excellent durability.Ultrafiltration membranes are used mainly for filtering colloids, and precision filtration is used for filtering fine particles of 0.05 to 10μm. In this case, a microfiltration membrane with suitable micropores is used. By the way, in recent years, with the progress of biotechnology, higher purity, higher performance,
As higher precision is required, the fields of application of precision filtration or ultrafiltration technology are expanding. However, when separating fine particles using a membrane in microfiltration or ultrafiltration, a cake layer is formed due to the influence of concentration polarization, creating resistance to the flow of the permeate fluid, and the resistance increases due to membrane clogging. However, there is a problem in that the membrane permeation flux rapidly and significantly decreases, and this has been the biggest cause of hindering the practical application of microfiltration 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 total 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 total filtration method, a high permeation flux is obtained when the fluid passes through and the suspended solids are captured and separated inside the filtration membrane, but when the suspended solids are trapped on the surface of the filtration membrane, a high permeate flux is obtained. When a layer is formed and a large amount of raw fluid is processed, or when the specific resistance of the formed cake layer is extremely high, filtration resistance becomes large, and when such total filtration is performed, the membrane permeation flux becomes small. On the other hand, in fields such as wastewater treatment, water production, and pool water filtration, it is known that backwashing is performed to restore the filtration flux of a clogged filter. However, this method that combines total filtration and backwashing is a technology developed in the field of wastewater treatment, where the resistivity of the cake layer is relatively small, so it is difficult to remove microscopic particles with high resistivity, such as when separating bacterial cells from fermentation liquid. Filtration had no effect as it was. For this reason, a cross-flow filtration method 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 type filtration method, the cake layer formed on the membrane surface is stripped off by the flow of the raw fluid parallel to the membrane, so the membrane permeation flux is larger than in the conventional total filtration method, and a large amount of raw fluid is It is possible to separate, purify, and concentrate directly and continuously. However, when using a membrane with a large pure water permeation flux, that is, in the precision filtration range that removes particles of 0.05 to 10 μm, the membrane permeation flux decreases rapidly. It is difficult to maintain a high membrane permeation flux at the beginning of filtration due to the decrease in membrane permeation flux, and as a result, when comparing all filtration methods and total permeate volume, the improvement effect is small and is insufficient to obtain an economical permeation flux. That was enough.

0004

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

[0005] As a method of increasing the permeation flux, the flow of raw fluid into the filtration membrane is intermittently stopped by using the cross-flow filtration method, or by closing the valve on the permeate side of the filtration membrane. By intermittently eliminating or reducing the pressure applied perpendicular to the membrane surface of the membrane, or by applying pressure from the permeate side of the filtration membrane and causing the fluid to flow from the permeate side to the raw fluid side, the raw fluid side of the filtration membrane can be Attempts have been made to intermittently remove the cake layer and adhesion layer deposited on the membrane surface, but when backwashing is performed, the suspended solids desorbed from the filtration membrane are also removed. If left in the filtration system, the concentration of suspended matter in the raw fluid will gradually increase, and in some cases, the viscosity of the raw fluid will also increase, so the membrane permeation flux will gradually decrease, even if backwashing is performed. There were problems such as insufficient recovery of permeation flux. Furthermore, when backwashing is performed using the permeated liquid, the amount of membrane permeation is reduced by the amount of backwashing, so there is a problem that it is not possible to secure enough backwash liquid to sufficiently recover the membrane permeation flux. On the other hand, as a method to not reduce the activity of bacterial cells, reducing the shearing force by lowering the cross-flow circulation flow rate is used, but reducing the shearing force reduces the effectiveness of the cross-flow filtration method, so If measures were taken not to reduce body activity, there was a problem that the membrane permeation flux would decrease. In addition, 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 objective is to provide a novel total filtration periodic backwashing system that reduces activity loss. In other words, in a total filtration periodic backwashing system that performs filtration while removing cake trapped on the surface of the filter medium by periodically repeating backwashing, the filter element used therein is sandwiched with a filtration membrane between multiple protective sheets. Filtration using a pleated cartridge-type filter element, which is folded into pleats and rolled into a cylindrical shape, and the seam is sealed liquid-tight, leaving an outlet for the filtrate at both ends of the cylinder, and the rest is sealed liquid-tight. The above objectives have been achieved by the method.

The present invention will be explained in detail below. One feature of the present invention is that all prior art filtration methods are subjected to periodic backwashing, and the suspended solids desorbed from the filtration membrane are discharged from the filtration system by the backwashing. In conventional total filtration, when backwashing is performed, suspended solids desorbed from the filtration membrane gradually accumulate in the filter, and the permeation flux cannot be recovered sufficiently even with backwashing. In the present invention, the periodic backwashing effect becomes significant by discharging the suspended solids desorbed from the filtration membrane to the outside of the system along with the backwashing liquid. In addition, by using a total filtration periodic backwashing system, the filtration system becomes simple, and unlike cross-flow filtration systems, there is no shearing force when circulating the raw fluid, making it possible to prevent a decrease in bacterial activity. . Furthermore, in the cross-flow filtration system, the cake removal effect due to the shear force generated when the raw fluid flows over the membrane surface was hardly observed in pleated cartridge filters compared to hollow fiber membranes and flat membrane modules; Not only does the cyclic backwashing system have the same effectiveness as hollow fiber and flat membrane modules, but the use of pleated cartridge filters makes it possible to create modules with larger areas at a lower cost than hollow fiber or flat membrane modules. The advantage arises that it can be formed.

Backwashing is more effective when carried out with a liquid than with a gas.Although permeate may be used as the backwash liquid, not only does the amount of permeate decrease by the amount of permeate that is reversed, but the membrane permeation flow is If the amount of backwashing liquid equivalent to the amount of permeated liquid is required to fully recover the bundle, there is a risk that virtually no permeated liquid will be obtained, so cleaning liquid should be supplied from outside the filtration system to meet the needs. It is preferable to perform backwashing with a corresponding amount of backwashing liquid. Basically, any cleaning liquid supplied from outside the filtration system can 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. Furthermore, if it is not desired to leave the backwash liquid in the filtration system after the backwash is completed, it is preferable to perform dehydration using gas. When performing constant pressure filtration, if backwashing is performed after the membrane permeation flux becomes extremely low, as in the conventional "total filtration backwashing technology," the recovery of the membrane permeation flux after backwashing will be poor. Backwashing is performed before the permeation flux reaches 1/50 of the initial filtration 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. In addition, when performing constant-speed filtration, if backwashing is performed after the filtration transmembrane pressure difference becomes extremely high, the recovery of the filtration transmembrane pressure difference after backwashing, that is, the cleaning performance, will deteriorate, so It is preferable to perform backwashing before the pressure reaches 50 times the transmembrane differential pressure. More preferably, by performing backwashing before reaching 10 times the filtration transmembrane pressure difference at the initial stage of filtration, the permeation flux conditions can be further increased. The cleaning performance will be higher if a large amount of backwash liquid is passed through the filtration membrane with a high membrane permeation flux.
The permeation flux of backwash liquid is 1 x 10-4 m3/m2/se
It is preferable that it is more than c. Further, the backwashing time is preferably 1 second or more, and particularly preferably from 2 seconds to 10 seconds in terms of economic efficiency.

FIGS. 1 and 2 are an exploded view of a general microfiltration membrane cartridge filter element and an overall view of the module. The precision filtration membrane 3 consists of two liquid-permeable sheets 2
, folded in a sandwiched state by 4,
It is wound around the core 5 having a large number of core holes 33. There is a peripheral guard 1 on the outside, which protects the microfiltration membrane. End plates 6a are provided at both ends of the cylinder.
6b seals the microfiltration membrane. The end plate is connected to the filter housing (
(not shown). The filtered liquid passes through the central through hole 32 formed by the core, is collected from the liquid collection port 8, and is discharged from the secondary side inlet/outlet 23 of the filter housing. FIG. 3 shows the flow of the total filtration periodic backwashing system 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. After that, 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. In order to prevent the backwash liquid from being mixed with the filtrate, the backwash liquid remaining in the housing and the filter element is removed before restarting filtration after backwashing is completed. For this purpose, as shown in FIG. 2, the upper and lower parts of the filter housing are provided with ports that communicate with both ends of the central through hole 32 formed by the core of the filter element, a secondary side inlet/outlet 23, and a pressurized gas inlet 24. A pressurized gas is introduced into the secondary side of the filter element so that residual backwash liquid can be discharged from the secondary side inlet/outlet.

Microfiltration membranes that can be used in the present invention include known membranes such as vinyl polymers such as polyvinylidene fluoride, polyacrylonitrile, and polyvinyl chloride, polysulfones, polyethersulfones, aliphatic polyamides, and cellulose esters. Polymers can be used alone or in combination as raw materials. To produce a precision filtration membrane, the above polymer is dissolved in a good solvent, a mixed solvent of a good solvent and a non-solvent, or a mixture of multiple types of solvents with different degrees of solubility for the polymer to prepare a membrane-forming stock solution. This is then cast onto a support or directly into a coagulation solution, washed and dried. In this case, examples of solvents that dissolve the polymer include dichloromethane, acetone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, 2-pyrrolidone, N-methyl-2-pyrrolidone, and sulfolane. Examples of nonsolvents added to the above solvent include cellosolves, alcohols such as methanol, ethanol, and isopropanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, polyethylene glycol, glycerin, and ethyl glycol. Examples include polyols. The ratio of the non-solvent to the good solvent may be in any range as long as the mixed liquid can maintain a homogeneous state, but it should be between 5 and 5.
0% by weight is preferred.

[0011] Furthermore, an inorganic electrolyte, an organic electrolyte, a polymer electrolyte, etc. called a swelling agent may be added to control the porous structure. Electrolytes that can be used in the present invention include common salt, metal salts of inorganic acids such as sodium nitrate, potassium nitrate, sodium sulfate, zinc chloride, and magnesium bromide, organic acid salts such as sodium acetate, sodium formate, and 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 alkylmethyltaurate are used. Although some of these electrolytes exhibit some effect even when added alone to a polymer solution, when these electrolytes are added as an aqueous solution, particularly remarkable effects may be exhibited. The amount of the aqueous electrolyte solution to be added is not particularly limited as long as the addition does not cause loss of uniformity of the solution, but is usually from 0.5% by volume to 10% by volume based on the solvent. Further, there is no particular restriction on the concentration of the electrolyte aqueous solution, 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 as a membrane forming stock solution is 5 to 35% by weight, preferably 10 to 30% by weight.
It is. When it exceeds 35% by weight, the water permeability of the resulting microporous membrane becomes so small that it has no practical meaning;
When it is smaller than , a microfiltration membrane with sufficient separation ability cannot be obtained.

The membrane-forming stock solution prepared as described above is cast onto a support, and the polymer solution membrane together with the support is immersed in a coagulating solution immediately after casting or after a certain period of time. Water is most commonly used as the coagulating liquid, but organic solvents that do not dissolve the polymer may also be used, or two or more of these non-solvents may be mixed. The support can be arbitrarily selected from those that can be used as a support in the production of microfiltration membranes, but it is particularly preferable to use a nonwoven fabric since there is no need to peel off the support. The nonwoven fabric that can be used in the present invention is generally made of polypropylene, polyester, etc., and is not subject to any material limitations. The cast film on which the polymer has been precipitated in the coagulation bath is then washed with water, hot water, solvent, etc., and then dried.

The microfiltration membrane 3 thus produced is folded by a known method. As the protective sheets 2 and 4, nonwoven fabrics, filter paper, and/or net-like bodies are used. In order to enhance the backwashing effect, the amount of nonwoven fabric fitted is 18g/
m2 to 200g/m2, preferably 30g/m2
from 100g/m2, thickness from 0.1mm to 1m
Synthetic fibers such as polyester, polypropylene or nylon are often used. A net is a net-like sheet made of synthetic polymer monofilaments such as polyester, polypropylene, or nylon that are woven alternately in a lattice pattern, and the mesh size is 1.
2 mesh to 500 mesh is suitable. Particularly preferably, the mesh is from 25 mesh to 250 mesh.

[0014] In order to align both ends of the pleated filter medium, use a cutter knife or the like to cut off the uneven parts at both ends, roll it into a cylindrical shape, and seal the pleats at the seams using heat sealing or 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 performed using conventionally known techniques. When using a thermosetting epoxy resin for the end plate, pour the prepared epoxy resin adhesive liquid into the potting mold, pre-cure it and increase the viscosity of the adhesive to an appropriate level, then insert it into the cylindrical filter media. Insert one end into this epoxy adhesive. Then heat it to harden it completely. When the material of the end plate is a thermoplastic resin such as polypropylene or polyester, one end surface of the cylindrical filter medium is inserted into the resin immediately after the hot melted resin is poured into the mold. On the other hand, only the sealing surface of the already molded end plate is melted using an infrared heater.
A method of welding one end surface of a cylindrical filter medium is also used.

[0015]

[Examples] The present invention will be explained in more detail by referring to specific examples of filtration, but the present invention is not limited to the examples unless it goes beyond the gist of the invention. Example 1 A polysulfone microfiltration membrane with an average pore diameter of 1.4 μm was used as the filtration membrane, a 100-mesh polyester network was used as the primary protective sheet, and a plating amount of 100 g/m2 was applied to the secondary protective sheet.
, 300 μm thick polyester nonwoven fabrics were folded into a pleat shape with a pleat height of 10 mm, rolled to have an outer diameter of 70 mm, both ends were brought together, and heat sealed. Both ends of the cylinder thus created are inserted into polypropylene end plates, only the surface of which is melted by an infrared heater, and sealed. In this way, a pleated cartridge filter with a cylindrical length of about 25 cm and a filtration membrane area of about 0.6 m2 was manufactured. Using this filter, 20 ppm of tannic acid was dissolved in commercially available beer, and protein was aggregated as a suspension. The filtration flux was 5 kl/m2/h, the backwash flux was 10 kl/m2/h, and the filtration time was When periodic backwash filtration was carried out under the conditions of 54 seconds and 4 seconds of backwash time, 10 kl/m2 of filtrate was obtained by the time the filtration pressure reached 3 kg/cm2. On the other hand, when normal total filtration is performed using the same filter, only 2 filtrate is obtained by the time the filtration pressure reaches 3 kg/cm2.
When the same liquid was filtered again after backwashing, only 60 liters could be filtered and the filtration pressure rose to 3 kg/cm2.

Example 2 A polysulfone microfiltration membrane with an average pore diameter of 0.45 μm was used as the filtration membrane, and a polyester nonwoven fabric with a plating amount of 50 g/m2 and a thickness of 200 μm was used as the primary and secondary protective sheets. Fold it into pleats to a length of 10 mm, roll it up to an outer diameter of 70 mm, bring both ends together, and heat seal. Both ends of the cylinder thus created are inserted into polypropylene end plates, only the surface of which is melted by an infrared heater, and sealed. The length of the cylinder made in this way is about 25 cm, and the filtration membrane area is about 0.
．． The following filtration experiment was conducted using a 7 m2 pleated cartridge filter. Escherichia coli (IFO3301
) was permeabilized for 18 hours using a culture solution containing 10 g/l of glucose, 5 g/l of polypeptone, 5 g/l of yeast extract, and 5 g/l of sodium chloride to obtain a filtered stock solution. The culture conditions were a temperature of 37°C and a pH of 7.0. Using this culture solution, periodic backwash filtration was performed under the conditions of filtration flux of 0.5 kl/m2/h, backwash flux of 2 kl/m2/h, filtration time of 54 seconds, and backwash time of 4 seconds. However, by the time the filtration pressure reached 5 kg/cm2, it was 1000 liters/m2.
Two filtrates were obtained. On the other hand, when normal full filtration is performed using the same filter, the filtrate obtained by the time the filtration pressure reaches 5 kg/cm2 is only 50 liters/m2, and even after backwashing, there is no practical filtrate flow. No recovery of the bundle was observed.

[0017]

[Effect of the invention] By performing total filtration while repeating periodic backwashing using a pleated cartridge filter, more than 10 times more highly suspended liquid can be filtered compared to conventional total filtration. Yes, and only 7cm in diameter.
Large amounts of highly suspended liquids can be filtered with a small element of 25 cm in length.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the structure of a general pleated cartridge filter.

FIG. 2 is an overall view of the pleated cartridge filter module.

FIG. 3: Filtration flow diagram.

[Explanation of symbols]

1. Outer circumference guard 2 Protective sheet 3 Filtration membrane 4 Protective sheet 5 Core 6 End plate 7 Gasket 8 Gathering entrance 11 Filter housing 12 Filtration pump 13 Backwash pump 22 Primary side entrance 23 Secondary side entrance 24 Pressurized gas inlet 25 Air bleed 26 Packing 27 Housing head 28 Housing ball 30 Filter element 31 Pleated part 32 Central hole 33 Core hole

Claims (4)

[Claims] Claim 1: In a total filtration periodic backwashing system that performs filtration while removing cake trapped on the surface of the filter medium by periodically repeating backwashing, the filter element used therein is provided with a plurality of protective membranes. A pleated cartridge-type filter element that is sandwiched between sheets, pleated and rolled into a cylindrical shape, and the seam is sealed liquid-tightly, leaving a filtrate outlet at both ends of the cylinder, and the rest of the cylinder is sealed liquid-tightly. A filtration method using 2. The filtration method according to claim 1, wherein a pleated cartridge type filter element is used, wherein a mesh sheet of 25 mesh to 250 mesh is used as the primary side protective sheet. [Claim 3] The amount of plating as the primary side protective sheet is 3.
The filtration method according to claim 1 or 2, using a pleated cartridge type filter element characterized by using a nonwoven fabric of 0 to 100 g/m2. 4. The filtration method according to claim 1, wherein a filter housing is used, wherein the filter housing has ports that communicate with both ends of a central through hole formed by the core of the pleated cartridge type filter element.