JPH05329339A - Filtering apparatus - Google Patents

Abstract

PURPOSE:To enhance transmission flux by cyclically backwashing a filter membrane in such a state that the pressure on the transmitted fluid side of the filter membrane is made higher than that on the raw fluid side of the filter membrane and discharging a backwashing solution and a desorbed suspended substance out of a filtering system. CONSTITUTION:In a dead end type filtering system wherein a raw fluid containing a suspended substance is supplied to a filter membrane to be filtered to separate the suspended substance from the fluid, the pressure on the transmitted fluid side of the filter membrane 16 is made higher than that on the raw fluid side thereof to cyclically perform backwashing. The filter membrane is backwashed and a backwashing solution (sterilized water) and the suspended substance desorbed from the filter membrane 16 are discharged out of the filtering system. Thereafter, the sterilized water remaining in the filtering system is discharged by gas and filtration is again performed. By this constitution, transmission flux is restored and, since backwashing is cyclically performed, the transmission flux can be held to a high value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dead end type filtration method, and more particularly to a new dead end type filtration method in which backwash is periodically performed to maintain a large membrane permeation flux. The dead end type filtration method of the present invention is applied to separation, purification, recovery, concentration, etc. of various macromolecules, microorganisms, yeasts, fluids 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 the fluid containing the fine particles, for example, various suspensions containing fine particles, a fermentation solution or a culture solution, and fine particles from a suspension of a pigment. It is also applied when separating, and the gas is purified by separating and removing the particles from the suspended gas containing the particles, for example, sterilized nitrogen gas to be filled into ampules for medical use, gas for positive pressure to ultrapure water production equipment. It is also applicable to the production of dust-free, aseptic gas to be filled as, or air-conditioned positive dust-free in the 1C production line, aseptic air, etc.

[0002]

2. Description of the Related Art Conventionally, as a technique for separating a suspended substance from a raw fluid 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, There are an electrodialysis method using a potential difference as a driving force, a diffusion dialysis method using a concentration difference as a driving force, and the like. 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., It is economical because it can keep the processing capacity of a small plant large, the energy required for the separation operation is small, and it is possible to process a low concentration raw fluid that is difficult with other separation methods. There is. And as the membrane used in these separation techniques, cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone,
There are polymer membranes mainly composed of organic polymers such as polyacrylonitrile, polyamide, polyimide, etc. and porous ceramic membranes with excellent durability such as heat resistance and chemical resistance. In some cases, an ultrafiltration membrane is used, and in microfiltration intended for the filtration of fine particles, a microfiltration membrane having suitable micropores is used. 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 generated due to the effect of concentration polarization, which causes resistance to the flow of the permeated fluid, and resistance due to clogging of the membrane increases. Therefore, 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 filtering method, there is a so-called dead end type filtering method in which all the fluid to be filtered passes through a filter material (filter cloth, membrane, etc.) and a cake layer to separate fine particles contained in the fluid. .. In this conventional dead-end type filtration method, a high permeation flux is obtained at the stage where the fluid passes and the suspended substances are trapped inside the filtration membrane and separated, but at the stage where they are trapped at the surface of the filtration membrane. In that case, a cake layer is formed, and when a large amount of raw fluid is processed or when the specific resistance of the formed cake layer is extremely high, the filtration resistance becomes large.When such dead end filtration is performed, the membrane permeation flux becomes small. Become. For this reason, it was considered to use a cross flow type filtration system. In this cross-flow type filtration system, the raw fluid to be filtered flows in parallel to the membrane surface of the filtration membrane, the fluid permeates to the opposite side through the filtration membrane, and the flow of the raw fluid and the permeated fluid are orthogonal to each other. This is why it is so called. 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 that the membrane permeation flux is large compared to the conventional dead end type filtration method, and a large amount of The raw fluid can be directly and continuously separated, purified, and concentrated, but when an ultrafiltration membrane or a microfiltration membrane with a high pure water permeation flux, that is, a high molecular weight cutoff, is used, the membrane permeation flux is suddenly increased. It is difficult to maintain a high membrane permeation flux at the initial stage of filtration, and as a result, comparing the dead-end type filtration system with the total permeate flow rate, the effect is small and it is not possible to obtain an economical permeation flux. Was enough.

[0004]

As described above, the cross-flow type filtration system is in principle an advanced separation technique, but the biggest problem is the membrane permeation flux, which is a conventional dead-end type filtration system. However, there is a problem in that even if this cross-flow method is used as a microfiltration method, a sufficiently high membrane permeation flux cannot be obtained even though it is slightly large. In addition, even if you look at a concrete example of separation of suspended solids and fluid that has been performed conventionally, for example, when separating bacterial cells from a fermentation broth, the conventional centrifugation method and diatomaceous earth filtration are used. Even if a cross-flow filtration method is used instead of the method, the membrane permeation flux decreases as the filtration time elapses due to the cake layer formed on the membrane surface and clogging, as well as shearing when circulating the raw fluid. There was a problem that the activity of the cells was lost due to the force.

As a method for increasing the permeation flux, the filtration is carried out by intermittently stopping the inflow of the raw fluid into the filtration membrane or closing the valve on the permeation fluid side of the filtration membrane in combination with the cross flow filtration method. The pressure perpendicular to the membrane surface of the membrane is intermittently eliminated or reduced, and pressure is applied from the permeate side of the filtration membrane to flow the fluid from the permeate side to the raw fluid side. An attempt to intermittently remove the cake layer and the adhering layer accumulated on the membrane surface of the so-called “backwashing” has been made, but even when these backwashing is performed, the suspended substances desorbed from the filtration membrane are removed. If left in the filtration system, the concentration of suspended solids in the raw fluid will gradually increase, and in some cases the viscosity of the raw fluid will also increase, so the membrane permeation flux will gradually decrease and even if backwashing is performed. There was a problem that the permeation flux was not fully recovered.
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. 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 pulsation of the pump is large and the effect of the cross flow filtration system is small.

[0006]

The present invention has been made in order to solve the above-mentioned problems in the prior art, and has a practically high membrane permeation flux, such as bacterial cells. It is an object of the present invention to provide a novel dead-end type filtration method that reduces the decrease in activity. That is, according to the present invention, in a dead end type filtration system in which a raw fluid composed of a fluid containing a suspended substance is supplied and filtered to separate the fluid and the suspended substance, the pressure on the permeable fluid side of the filtration membrane is set to The filtration method is characterized in that the backwash is periodically performed at a pressure higher than the pressure, and the backwash solution that has passed to the raw fluid side and the suspended substance desorbed from the filtration membrane are discharged to the outside of the filtration system. Hereinafter, the present invention will be described in detail. A feature of the present invention is that the conventional dead end type filtration system is subjected to periodic backwashing, and the suspended substances desorbed from the filtration membrane by the backwashing are discharged to the outside of the filtration system. In conventional dead-end filtration, when backwashing is performed, suspended substances desorbed from the filtration membrane gradually accumulate in the filter, and even if backwashing is gradually performed, the permeation flux cannot be sufficiently recovered. In the present invention, periodic backwash can be performed by discharging the suspended substance desorbed from the filtration membrane together with the backwash liquid to the outside of the system. Further, by using the dead end type filtration method, the filtration system is simplified, and the shearing force when circulating the raw fluid as in the cross flow type filtration method is eliminated, and it becomes possible to prevent the activity of the bacterial cells from being lowered.

It is more effective to carry out backwashing with a liquid rather than gas, and although a permeate may be used as the backwashing liquid, not only the amount of permeation is reduced by the amount of backflow of the permeate, but also the permeation flow through the membrane When the amount of backwash liquid equivalent to the amount of permeated liquid is required to fully recover the bundle, there is a danger that virtually no permeated liquid will be obtained, so it is necessary to supply the cleaning liquid from outside the filtration system. It is preferable to carry out backwashing with an appropriate backwashing liquid amount. The washing liquid supplied from outside the filtration system can be basically anything as long as it does not deteriorate the characteristics of the filtration membrane or change the characteristics of the raw fluid, but if the raw fluid is an aqueous solution, generally use sterile water. Preferably. Further, if it is not desired to leave the backwash solution in the filtration system after the backwashing, it is preferable to perform dehydration with gas. When constant pressure filtration is performed, if backwashing is performed after the membrane permeation flux becomes extremely low, the recoverability of the membrane permeation flux after backwashing deteriorates, reaching 1/50 of the permeation flux at the initial stage of filtration. Backwash before. Preferably one of the permeation fluxes at the beginning of filtration
Higher permeate flux is obtained by backwashing before reaching / 10. Further, when performing constant-rate filtration, if the backwashing is performed after the pressure difference between the filtration membranes becomes extremely high, the recoverability of the pressure difference between the filtration membranes after the backwashing, that is, the cleaning property deteriorates.
Backwash is performed before reaching 50 times the differential pressure between filtration membranes at the initial stage of filtration. Preferably, backwashing is performed before reaching 10 times the differential pressure between filtration membranes at the initial stage of filtration, whereby the condition of permeation flux can be further increased. The backwashing liquid has a high membrane permeation flux and a large amount of water is passed through the filtration membrane to enhance the cleaning property, but the permeation flux of the backwashing liquid is 1 × 10 ⁻⁴ m ³ / m ² / sec or more. The backwash time is preferably 1 second or more.

Next, the dead end type filtration system of the present invention will be described with reference to the drawings. Fig. 1 shows the state of suspended solids deposited on the filtration membrane during the conventional dead end filtration. The amount of suspended solids deposited increases with time, and finally the permeation flux becomes zero. Approach. Fig. 2 shows the state of suspended solids deposited on the filtration membrane during cross-flow filtration. Suspended solids gradually increase at the beginning of filtration, but the suspension builds up due to the shearing force of the original fluid. The amount of substance takes a constant value, and the permeation flux finally approaches a constant value. Figure 3
Shows a flow of the dead end type filtration system of the present invention. After filtration for a certain period of time, sterilized water is caused to flow from the permeated fluid side to the raw fluid side and discharged together with the suspended substances desorbed from the filtration membrane. After that, sterile water remaining in the filtration system is discharged by gas, and filtration is performed again. By repeating this cycle, it is possible to maintain a high permeation flux without increasing the concentration of suspended matter in the raw fluid.

[0009]

The present invention will be described in more detail with reference to specific examples below, but the present invention is not limited to the examples as long as the gist of the invention is not exceeded. Example 1 Escherichia coli (IFO3301) was dispersed in 0.9 wt% physiological saline at a content rate of 1 dryg / l as a suspension, and a microfiltration membrane having a nominal pore diameter of 0.2 μm was used. Dead end type filtration was carried out in which backwashing was periodically performed. The filter used had an effective membrane area of 100 cm ² , the experimental conditions were a pressure difference of 0.5 × 10 ⁴ Pa, a liquid temperature of 25 ° C., a filtration time of 120 seconds, and a backwash flux of 1 × 10 ⁻³ m ³ / m.
^The backwash was performed at a rate of ² / sec and a backwash time of 3 seconds, and the backwash solution was sterilized water. Fig. 4 shows a cross flow type filtration method and back washing using the permeated liquid as a back washing liquid (advance time 120 seconds, back washing time 3 seconds) and the case of performing the conventional dead end type filtration. The results obtained by the filtration method of the present invention are shown together with the comparative examples. The permeation flux when performing conventional dead-end filtration approaches zero with time, and in cross-flow filtration with backwashing, the permeation flux is not sufficiently recovered by backwashing and the permeation flux gradually decreases. There is. On the other hand, the permeation flux remained high in the dead end type filtration of the present invention in which backwashing was periodically performed.

Example 2 20 ppm of tannic acid was dissolved in commercially available beer, and a protein aggregate was used as a suspension, and a backwash of the present invention was carried out periodically using a microfiltration membrane having a nominal pore size of 2.0 μm. The dead end type filtration was performed. The filter used had an effective membrane area of 100 cm ² and the experimental conditions were a pressure difference of 0.5 ×.
It was performed at 10 ⁴ Pa, a liquid temperature of 25 ° C., a filtration time of 60 seconds, a backwash flux of 5 × 10 ⁻³ m ³ / m ² / sec, and a backwash time of 4 seconds, and sterile water was used as the backwash solution. FIG. 5 shows a comparison between a comparative example in which the permeated liquid was used as the backwash liquid in the cross-flow type filtration method and backwashing was performed (operating time: 60 seconds, backwashing time: 3 seconds), and a conventional dead end type filtration was performed. The results obtained by the filtration method of the present invention are shown together with examples. The permeation flux when performing conventional dead-end filtration approaches zero with time, and in cross-flow filtration with backwashing, the permeation flux is not sufficiently recovered by backwashing and the permeation flux gradually decreases. There is. On the other hand, the permeation flux was maintained at a high value in the dead end type filtration of the present invention in which backwashing was periodically performed.

Example 3 20 ppm of tannic acid was dissolved in commercially available beer and the protein aggregated was used as a suspension, and the backwashing of the present invention was carried out periodically using a microfiltration membrane having a nominal pore size of 2.0 μm. The dead end type filtration was performed. The filter used had an effective membrane area of 100 cm ² and the experimental conditions were a pressure difference of 0.5 ×.
10 ⁴ Pa, liquid temperature 25 ° C., backwash flux 5 × 10
^-3 m ³ / m ² / sec, backwash time was 4 seconds, and sterilized water was used as the backwash solution. 1/5 when backwashing is performed when the permeation flux reaches 1/10 of the permeation flux immediately after the start of filtration.
FIG. 6 shows a comparison of the amount of permeated liquid in the case of backwashing when reaching 0, 1/100. 1/5 if 1/10
A permeated liquid amount about 3 times that of 0 was obtained, and at 1/100, the permeated flux was not sufficiently recovered, so the increase in the permeated liquid amount gradually slowed down.

Example 4 20 ppm of tannic acid was dissolved in commercially available beer and the protein aggregated was used as a suspension, and the backwashing of the present invention was carried out periodically using a microfiltration membrane with a nominal pore size of 2.0 μm. The dead end type filtration was performed. The filter used had an effective membrane area of 100 cm ² and the experimental conditions were a pressure difference of 0.5 ×.
It was 10 ⁴ Pa, the liquid temperature was 25 ° C., the filtration time was 60 seconds, and sterile water was used as the backwash liquid. The amount of permeated liquid was compared when the backwash amount was constant at 200 ml and the membrane permeation flux of the backwash liquid was changed, and the results are shown in FIG. 7. Membrane permeation flux of backwash liquid is 1 ×
At 10 ⁻⁴ m ³ / m ² / sec or less, the permeation flux was not sufficiently recovered by backwashing, and the increase in the amount of permeate was gradually delayed.

[0013]

INDUSTRIAL APPLICABILITY According to the present invention, a high membrane permeation flux can be obtained in a dead end type filtration system in which backwashing is periodically carried out, whereby liquids containing various suspending substances can be separated from each suspension component. Separation, recovery, purification, concentration, etc. are performed extremely efficiently and economically. Further, the process can be continued and the device can be downsized, and the selectivity of the membrane can be used to continuously and selectively separate only the target substance, which can be applied to bioreactors such as yeast and cells. It can be applied and has various effects such as easier operation management than the conventional technology.

[Brief description of drawings]

FIG. 1 shows a deposition state of suspended matter in a conventional dead end type filtration.

FIG. 2 shows the state of deposition of suspended matter in conventional cross-flow filtration.

FIG. 3 shows a flow of a dead end type filtration system of the present invention in which backwashing is periodically performed.

FIG. 4 is a comparison of changes in permeation flux when performing dead-end filtration in which the backwashing of the present invention is carried out cyclically using Escherichia coli dispersion, cross-flow filtration accompanied by backwashing, and conventional dead-end filtration. Is shown.

FIG. 5: Comparison of changes in permeation flux when dead-end type filtration in which the backwashing of the present invention is carried out periodically using protein-aggregated beer, cross-flow filtration with backwashing, and conventional dead-end filtration is performed. Is shown.

FIG. 6 shows a difference in permeation amount given by permeation flux up to backwashing using the filtration system of the present invention.

FIG. 7 shows the influence on the amount of permeated liquid due to the difference in permeation flux of the backwash liquid when the filtration system of the present invention is used.

[Explanation of symbols]

 1 Flow of raw fluid for dead-end filtration 2 Flow of permeate for dead-end filtration 3 Movement direction of suspended solids for dead-end filtration 4 Suspended solids deposited on filtration membrane 5 Filtration membrane 6 Cross-flow filtration raw material Flow of fluid 7 Flow of permeate in cross-flow filtration 8 Direction of movement of suspended matter in cross-flow filtration 9 Suspended substance deposited on filter membrane 10 Filter membrane 11 Raw fluid inlet 12 Permeate outlet 13 Backwash liquid Inlet 14 Drainage outlet 15 Filter 16 Filter membrane 17 Gas inlet 18 Pressure gauge 19 Pump 20 Sterilizing filter 21 Solenoid valve

Claims (8)

[Claims] 1. A dead-end type filtration system for separating a fluid and a suspended substance by supplying a raw fluid consisting of a fluid containing a suspended substance and filtering the same by using a filter membrane. The method of filtration is characterized in that the backwashing is periodically performed by increasing the pressure of the above to be higher than the pressure of the raw fluid side. 2. The backwash solution that has passed from the permeate side of the filtration membrane to the raw fluid side and the suspended substance desorbed from the filtration membrane are discharged to the outside of the filtration system. Filtration method. 3. The filtration method according to claim 1, wherein sterile water is used as the backwash solution. 4. The filtration method according to claim 1, wherein dehydration is performed using gas after the backwashing. 5. A raw fluid consisting of a fluid containing solid particles is supplied using a filtration membrane and filtered at a constant pressure to separate the fluid and solid particles, and the pressure on the permeable fluid side of the filtration membrane is adjusted to the raw fluid. In a dead-end type filtration system in which backwash is periodically performed at a pressure higher than that on the side, backwash is performed before the membrane permeation flux reaches 1/50 of the membrane permeation flux at the initial stage of filtration. Filtration method. 6. The membrane permeation flux of the backwash solution is 1 × 10 ⁻⁴ m
The filtration method according to claim 5, wherein the filtration method is ³ / m ² / sec or more. 7. A raw fluid consisting of a fluid containing solid particles is supplied using a filtration membrane and filtered at a constant flow rate to separate the fluid and the solid particles, and the pressure on the permeable fluid side of the filtration membrane is adjusted to the raw fluid side. In the dead end type filtration system in which backwashing is performed periodically by increasing the pressure higher than the pressure of, the pressure difference between the filtration membranes at the start of filtration is set to 0.1 Kg / cm ² or less, and the pressure difference between the filtration membranes at the start of filtration is A filtration method comprising performing backwashing before reaching 50 times the transmembrane pressure difference. 8. The membrane permeation flux of the backwash solution is 1 × 10 ⁻⁴ m
The filtration method according to claim 7, wherein the filtration method is ³ / m ² / sec or more.