JPH04265129A - Filtration system - Google Patents

Abstract

PURPOSE:To increase a filtration flux when filtering a feed fluid containing suspended material using a filter membrane in a dead-end type filtration system by making a washing liquid flow parallel to the filter membrane also on the feed fluid side and entraining gas along in the flow of the washing liquid. CONSTITUTION:Back washing is performed with pressure on the permeated liquid side being higher than that on the feed fluid side, and simultaneously, a washing liquid 24 is also made to flow in the parallel direction to a filter membrane 22 on the feed fluid side till a discharge outlet so that suspended material 23 desorbed and the back washing liquid may easily be discharged. If the suspended material 23 is hard to desorb, gas is entrained along in the flow of the washing liquid 24 to disturb the surface of the filter membrane 22. Thereby, in a dead-end type filtration system performing back washing periodically, a high membrane permeating flux is obtained. Thus, the separation, recovery, purification, concentration, etc., of every suspended component from liquid containing various suspended materials are effectively and economically carried out.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dead-end filtration method, and more particularly to a new dead-end filtration method in which backwashing is carried out periodically to maintain a high membrane permeation flux. The dead-end filtration method of the present invention is applied to the separation, purification, recovery, concentration, etc. of fluids containing or suspending various polymers, microorganisms, yeast, and fine particles, and is particularly applicable to the separation, purification, recovery, and concentration of fluids containing or suspending various polymers, microorganisms, yeast, and fine particles. It can be applied in any case where it is necessary to separate fine particles from a fluid containing them, such as in various suspensions containing fine particles, fermentation liquids or culture liquids, as well as suspensions of pigments, etc. It is also applied when separating and removing crud from condensate in nuclear power generation. However, with the rapid development of biotechnology in recent years, the production of biochemical substances through cultivation, fermentation, enzymatic reactions, etc. has become popular in many fields such as pharmaceuticals, foods, and chemical products. Although the added value of these produced substances increases by refining them, the current situation is that a lot of cost is incurred in this refining operation. The dead-end filtration method of the present invention is particularly effective in these fields, for example, when using exoenzyme-producing bacteria that perform high-density culture by continuously removing reaction inhibitors from the culture solution. It has a wide variety of applications, including continuous recovery of enzymes, recovery of enzymes from a solution obtained by crushing intracellular enzyme-producing bacteria, and removal of biocatalysts from culture solutions obtained in a batch process.

0002

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

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

0004

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

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

[0006]

[Means for Solving the Problems] The present invention has been made to solve the problems of the prior art described above, and has a practical high membrane permeation flux, and is capable of transporting bacterial cells, etc. The object of the present invention is to provide a novel dead-end filtration method that reduces activity loss. That is, the present invention uses a precision filtration membrane to supply and filter a raw fluid consisting of a fluid containing suspended matter, thereby separating the fluid and suspended matter, and reducing the pressure on the permeate fluid side of the filtration membrane to the raw fluid side. In the dead-end filtration system, backwashing is carried out periodically at a pressure greater than It is characterized by flowing cleaning liquid. The present invention will be explained in detail below. The dead-end filtration method of the present invention is suitable for separating, purifying, recovering, and concentrating fluids containing or suspending various polymers, microorganisms, yeast, and particulates from fluids containing fine particles that require filtration. It can be applied in any case where it is necessary to separate fine particles, but especially in cases where the specific filtration resistance of suspended substances is extremely high, such as in the separation, concentration, and recovery of enzymes, microorganisms, and cells from fermentation liquids and culture liquids. is effective.

The filtration method of the present invention is characterized by backwashing by making the pressure on the permeate side higher than the pressure on the raw fluid side, and at the same time, flowing the cleaning liquid on the raw fluid side in a direction parallel to the filtration membrane. was accompanied by gas. One of the reasons why the suspended solids deposited on the filtration membrane during backwashing is not sufficiently desorbed and the permeation flux is not sufficiently recovered is that the suspended solids and backwash liquid desorbed during backwashing do not reach the outlet. The problem is that the liquid remains in the filter without being absorbed. In the present invention, in order to easily discharge the desorbed suspended solids and backwash liquid, the cleaning liquid is also flowed on the raw fluid side in a direction parallel to the filtration membrane until it reaches the discharge port, and when the suspended solids are difficult to desorb. This is most effective when gas is entrained in the cleaning liquid to disturb the surface of the filtration membrane. The cleaning liquid on the raw fluid side is preferably the same as the backwashing liquid used for backwashing, but if you want to avoid contamination with foreign matter from outside the system, use the permeate as the backwashing liquid, and use the raw fluid itself as the cleaning liquid on the raw fluid side. be able to. In addition, in order to avoid a decrease in the permeation amount by the amount of backflow of the permeate, it is preferable to supply a cleaning liquid from outside the filtration system and perform backwashing with an amount of backwash liquid as required. Basically, any cleaning liquid supplied from outside the filtration system may be used as long as it does not degrade the properties of the filtration membrane or change the properties of the raw fluid, but if the raw fluid is an aqueous solution, sterile water is generally used. It is preferable. Further, if it is desired not to leave the backwash liquid in the filtration system after the backwash is completed, it is preferable to perform dehydration using gas. If backwashing is performed after the membrane permeation flux becomes extremely low, the recovery of the membrane permeation flux after backwashing will deteriorate. This is due to suspended solids penetrating deeply into the filtration membrane, the accumulated suspended solids becoming compacted, or the suspended solids strongly bonding to the filtration membrane when filtration is performed for a long time. This is because the turbid substances cannot be completely removed. For this reason, when performing constant pressure filtration, it is preferable to perform backwashing before the permeation flow rate reaches 1/100 of the initial filtration flow rate, and to obtain an even higher permeation flow rate, backwashing should be performed before reaching 1/10 of the permeation flow rate at the initial stage of filtration. is preferred. In addition, when performing constant-speed filtration, if backwashing is performed after the pressure difference between the filtration membranes becomes extremely high, the recovery of the pressure difference between the filtration membranes after backwashing, that is, the cleaning performance of the filtration membranes, will deteriorate. It is preferable to perform backwashing before reaching 100 times the initial pressure difference between the filtration membranes, and more preferably perform backwashing before reaching 10 times the initial pressure difference between the filtration membranes. Therefore, the time from the start of filtration to backwashing is short, and if the specific resistance of the suspended solids is large, it is preferable to perform backwashing after filtration is performed for 0.5 minutes or more and up to 3 minutes. In addition, cleaning performance will be higher if a large amount of backwash liquid is passed through the filtration membrane at a high permeation flow rate, but if the permeation flux of backwash liquid is increased and backwash is performed for a long time, Not only will the amount be enormous, but the ratio of backwashing time to filtration time will increase, effectively lowering the average permeation flux, so the permeation flow rate should be 1 x 10-4 m3/m2/se within the range where the permeation flux can be sufficiently recovered.
c or more, and the time is preferably 1 second or more and 30 seconds or less.

The filtration membrane used must have a pore size that can block suspended solids, and precision filtration membranes usually have a pore size of 0.
Those having a pore size of 0.05 to 10 μm are used. The total filtration amount when these microfiltration membranes are used for filtration in a short time of 0.5 to 3 minutes is significantly influenced by the structure of the filtration membrane. In other words, when suspended substances are blocked on the surface of a filtration membrane, the blocked suspended substances create a very large filtration resistance and the permeation flux rapidly decreases, resulting in a low total filtration amount.
A so-called anisotropic membrane has a structure in which the pore size changes continuously or discontinuously in the membrane thickness direction, and the pore size on one surface of the filtration membrane is different from the pore size on the other surface. By using it toward the raw fluid side, suspended matter can be blocked inside the filtration membrane, making it possible to obtain a large total filtration amount. Furthermore, when the filtration membrane has a composite structure in which a porous membrane and a nonwoven fabric or a mesh body are integrated, the same effect can be obtained by making the nonwoven fabric or mesh body side the undiluted solution side.

Next, the dead-end filtration system of the present invention will be explained based on the drawings. Figure 1 shows the state of suspended matter that accumulates on the filtration membrane when performing conventional dead-end filtration.The amount of suspended matter that accumulates increases over time, and the permeation flux eventually reaches zero. approach. Figure 2 shows the state of suspended solids deposited on the filtration membrane when cross-flow filtration is performed.At the beginning of filtration, the suspended solids gradually increase, but the suspended solids accumulate due to the shear force of the raw fluid. The amount of substance takes a constant value, and the permeation flux eventually approaches a constant value. FIG. 3 shows the flow of the dead-end filtration method of the present invention. After filtration has been carried out for a certain period of time, sterilized water is flowed back from the permeate side to the raw fluid side, and sterile water is also flowed parallel to the filtration membrane on the raw fluid side to be discharged together with the suspended solids that have been desorbed from the filtration membrane. , perform the filtration again. By repeating this cycle, it becomes possible to continuously maintain a high permeation flux without increasing the concentration of suspended solids in the raw fluid. Figure 4
shows the fluid state of suspended solids on the filter membrane surface during backwashing and washing in the filtration method of the present invention.

0010

[Examples] The present invention will be explained in more detail with reference to specific examples below, but the present invention is not limited to the examples unless it goes beyond the gist of the invention. Example 1 Escherichia coli (IFO3301) was cultured with shaking 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 filtration stock solution. The culture conditions were a temperature of 37°C, p.
It was H7.0. This stock solution was subjected to dead-end filtration using a precision filtration membrane with a nominal pore size of 0.2 μm, which periodically performs backwashing according to the present invention. The filter used has an effective membrane area of 10
0cm2, the experimental conditions were a pressure difference of 0.5×105 Pa,
The liquid temperature is 25℃, and the backwash flux is 1 x 10-3 m3/m.
2/sec, backwashing time was 3 seconds, and the backwashing liquid was sterilized water. FIG. 5 shows the results of the present invention together with a comparative example in which no cleaning water was flowed to the raw fluid side. In the filtration method of the present invention, the permeation flux was well recovered by backwashing.

[0011]

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

[Brief explanation of the drawing]

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

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

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

FIG. 4 shows the flow state of suspended solids during backwashing in the filtration method of the present invention.

FIG. 5 shows changes over time in permeation flux when E. coli culture solution is filtered using the filtration method of the present invention.

[Explanation of symbols]

1 Flow of raw fluid in dead-end filtration 2 Flow of permeate in dead-end filtration 3 Movement direction of suspended solids in dead-end filtration 4 Suspended solids deposited on the filtration membrane 5 Filter membrane 6 Raw material in cross-flow filtration Fluid flow 7 Flow of permeate in cross-flow filtration 8 Movement direction of suspended solids in cross-flow filtration 9 Suspended solids deposited on the filtration membrane 10 Filtration membrane 11 Raw fluid inlet 12 Permeate outlet 13 Backwash liquid Inlet 14 Drainage outlet 15 Filter 16 Filtration membrane 17 Gas inlet 18 Hydrophobic porous membrane 19 Pump 20 Sterilization filter 21 Solenoid valve 22 Filtration membrane 23 Suspended solids 24 Washing liquid

Claims (2)

[Claims] Claim 1: Using a precision filtration membrane, a raw fluid consisting of a fluid containing suspended matter is supplied and filtered to separate the fluid and suspended matter, and the pressure on the permeate fluid side of the filtration membrane is reduced to the raw fluid side. In the dead-end filtration system, backwashing is carried out periodically at a pressure greater than A dead-end filtration method characterized by flowing cleaning liquid. 2. The dead-end filtration method according to claim 1, wherein the cleaning liquid flowing to the raw fluid side contains gas.