JP7122941B2 - Biopolymer removal equipment and water treatment system - Google Patents

Description

The present invention relates to biopolymer removal devices and water treatment systems.

In water treatment, when removing contaminants from water, it is sometimes required to remove biopolymers as contaminants. Membrane filtration technology is sometimes used to remove foreign substances from water.

Membrane filtration technology in water treatment is attracting attention from the viewpoint of high efficiency and energy saving compared to other separation methods because it does not involve phase transition, chemical change, or the like of the substance to be separated. Specifically, membrane filtration technology is being considered for use in fields such as seawater desalination, water supply, ultrapure water production, wastewater recovery, and membrane separation activated sludge (MBR).

However, in membrane filtration, as the filtration time increases, substances such as suspended solids and contaminants present in the supplied water adhere to the surface of the membrane and pores in the membrane, resulting in a decrease in water permeability. So-called membrane fouling occurs. As this membrane fouling progresses, the energy required per unit amount of treated water increases. On the other hand, the occurrence of membrane fouling also proves that the membrane has achieved solid-liquid separation. For these reasons, control of membrane fouling has become an important technical factor in membrane filtration technology, but dramatic improvements have not been made. Specifically, the running cost of membrane filtration has not improved dramatically in the last 30 years or so. It can also be said that this suggests that a technique for dealing with membrane fouling has not yet been established.

Membrane filtration methods for suppressing membrane fouling are roughly classified into physical cleaning and chemical cleaning. Physical washing includes, for example, so-called backwashing, in which permeated water is permeated in a direction opposite to the permeation direction of the membrane to physically wash the membrane. Membrane fouling that is removed by such physical cleaning is called reversible fouling, and membrane fouling that is not removed by physical cleaning is called irreversible fouling. As for chemical cleaning, for example, a method of cleaning a film using chemicals such as acids and alkalis can be mentioned as a general method. Chemical cleaning is cleaning performed to remove irreversible fouling. Control of this irreversible fouling is very important as a technique for suppressing membrane fouling.

Biopolymers have been reported to cause irreversible fouling in both microfiltration membranes in river water and reverse osmosis membranes in seawater desalination (e.g., Non-Patent Document 1 and Non-Patent Document 2). For this reason, irreversible fouling occurs when biopolymers are separated by membrane filtration. Biopolymers include organic substances composed of metabolites of microorganisms, such as polysaccharides and proteins, but it is difficult to specify detailed substances. For biopolymers, for example, a device called Liquid Chromatography-Organic Carbon Detection (LC-OCD: manufactured by DOC-Labor Dr. Huber), in which liquid chromatography using a size exclusion column is directly connected to an organic carbon detector, is used to determine the retention time. It is defined as the component with the shortest retention time detected around 30 minutes. The reason why biopolymers are exemplified as polysaccharides and proteins as described above is as follows. First, because the retention time of liquid chromatography by the size exclusion column is short, the component is a high-molecular-weight component and is hydrophilic. In addition, the LC-OCD is connected to a UV absorption detector, and no UV absorption at 254 nm is observed from the peak. Based on these findings, biopolymers are presumed to be organic substances composed of metabolites of microorganisms, such as polysaccharides and proteins, but it is difficult to identify detailed substances.

When attempting to separate biopolymers by membrane filtration, irreversible fouling occurs as described above. Therefore, as a method for suppressing such membrane fouling due to biopolymers, as shown in FIG. A method using a water treatment system and the like can be mentioned. That is, as the water supplied to the membrane filtration device 2, the water obtained by removing the biopolymer by adsorption using an adsorbent, the water obtained by removing the biopolymer by coagulation treatment, etc. A method of using water treated by the device 3 and the like can be mentioned. Thus, when the water from which the biopolymer has been removed by the pretreatment device 3 is supplied to the membrane filtration device 2 and filtered by the membrane filtration device 2, membrane fouling due to the biopolymer can be suppressed. FIG. 4 is a schematic diagram showing the configuration of a conventional water treatment system that suppresses membrane fouling due to biopolymers.

As a method for adsorbing and removing a biopolymer using an adsorbent, for example, a method using an adsorbent described in Patent Literature 1 and the like can be mentioned.

Patent Document 1 discloses an adsorbent containing a first polymer containing cationic groups, the adsorbent having a predetermined cationic group density and a predetermined cationic group content. A membrane fouling agent adsorbent having adsorption capacity for ring causing agents is described.

Examples of methods for removing biopolymers by flocculation include the methods described in Patent Documents 2 and 3.

Patent Document 2 describes a method for clarifying industrial water by adding a melamine-formaldehyde resin acid colloid solution to industrial water, flocculating it, and then filtering it.

Patent Document 3 describes a seawater treatment method in which a predetermined amount of a melamine-formaldehyde resin acid colloid solution is added to seawater, flocculation treatment is performed, filtration treatment is performed, and the obtained filtered water is treated with a reverse osmosis membrane. .

WO2015/178458 JP 2017-131871 A JP 2017-113681 A

Katsuki Kimura, Ken Tanaka, Yoshimasa Watanabe, WATER RESEARCH, 2014, 49, 434-443 Kazuhisa Takeuchi, Bull. Soc. Sea Water Sci. Jpn. 2009, 63, 367-371

According to Patent Document 1, biopolymers can be efficiently adsorbed and removed in the water to be treated, thereby preventing membrane fouling, especially physically irreversible membrane fouling in the membrane filtration process. is suppressed, and the water permeability of the filtration membrane can be maintained for a long period of time. Patent document 1 also describes regenerating an adsorbent that has adsorbed membrane fouling-causing substances in an adsorption step by bringing it into contact with a cleaning fluid.

However, in the method of using water obtained by adsorbing and removing biopolymers using an adsorbent as described in Patent Document 1 as water to be supplied to the membrane filtration device, before supplying to the membrane filtration, Since it is necessary to bring the adsorbent and the water to be treated into contact with each other, industrially, a relatively large adsorption tower is required. In addition, chemicals such as cleaning fluid are required for regeneration.

According to Patent Document 2, it is disclosed that treated water with high clarity can be obtained with a small amount of coagulant that enables direct filtration of coagulated treated water.

According to Patent Document 3, it is possible to prevent RO membrane contamination, a decrease in the amount of permeated water due to it, and membrane clogging, reduce the frequency of cleaning the membrane, and continue stable and efficient treatment. disclosed.

As water to be supplied to the membrane filtration device, in the method of using water obtained by removing biopolymers by coagulation treatment as described in Patent Document 2 and Patent Document 3, as described above, as a coagulant, After adding a melamine-formaldehyde resin acid colloid solution and performing flocculation treatment, filtration treatment or precipitation (pressure flotation) operation or the like is performed to clarify and remove the biopolymer.

However, in such a method, a melamine-formaldehyde resin acid colloidal solution is required as a flocculating agent. Either one of the facilities is required, and the facility becomes large. Moreover, drug cost will rise.

The present invention has been made in view of such circumstances, and is a biopolymer removal method that enables direct removal of biopolymers by membrane filtration over a long period of time without using special agents such as adsorbents and flocculants. It is an object to provide a device and a water treatment system comprising said biopolymer removal device.

As a result of various studies, the inventors of the present invention have found that the above object can be achieved by the present invention described below.

A biopolymer removal device according to an aspect of the present invention comprises a hollow fiber membrane having a molecular cutoff of 30,000 to 500,000 and a contact angle to water of 40 to 85°; and an acid cleaning unit for performing acid cleaning.

According to such a configuration, it is possible to provide a biopolymer removal apparatus capable of directly removing biopolymers by membrane filtration over a long period of time without using special agents such as adsorbents and flocculants.

This is believed to be due to the following.

First, hollow fiber membranes having a molecular weight cut off of 30,000 to 500,000 are considered to be able to remove biopolymers contained in the water to be treated by permeating the water to be treated. According to LC-OCD analysis, the biopolymer, which is the causative agent of membrane fouling, is considered to have a molecular weight of approximately 100,000 or more, although it varies depending on the type of substance. The inventors reasoned that biopolymers cause irreversible fouling in membrane filtration because they are smaller than the pores of the membranes used in water treatment. In other words, it was thought that this is because when biopolymer-containing water is treated with a membrane used in water treatment, it corresponds to the standard occlusion model or the complete occlusion model in the occlusion model of Hermans-Bredee et al. From this, it is considered that biopolymers can be directly removed by membrane filtration by using a hollow fiber membrane whose pore size is considered to be smaller than the effective size of biopolymers, in addition to the membranes used in water treatment.

It should be noted that the ease with which biopolymers pass through hollow fiber membranes differs depending on their structures and the like, even if they have the same molecular weight. Therefore, even if the molecular weight cut off of the hollow fiber membrane is smaller than the molecular weight of the biopolymer, it cannot be said that the hollow fiber membrane has a pore size smaller than that of the biopolymer. Therefore, regarding the relationship between the pore diameter of the hollow fiber membrane and the size of the biopolymer, it is preferable that the size of the biopolymer is not the molecular weight but the effective size. That is, the hollow fiber membrane is required to have a pore size smaller than the effective size of the biopolymer.

Hollow fiber membranes with a molecular weight cutoff of 30,000 to 500,000 are considered to be hollow fiber membranes with pore sizes smaller than the effective size of the biopolymer. Therefore, it is considered that biopolymers can be directly removed by membrane filtration by using such a hollow fiber membrane.

As described above, the hollow fiber membrane is not considered to correspond to the standard blockage model or the complete blockage model, and the biopolymer is unlikely to cause irreversible fouling and is likely to be removed from the hollow fiber membrane by washing. be done. Furthermore, since the hollow fiber membrane has a contact angle with water of 40 to 85°, it is considered that the biopolymer can be easily peeled off from the hollow fiber membrane while suppressing fouling other than fouling by the biopolymer. This also suggests that the biopolymer is easily removed from the hollow fiber membrane by washing. Furthermore, biopolymers, such as polysaccharides and proteins, can be hydrolyzed with acidic liquids. From this, it is considered that the biopolymer can be preferably removed from the hollow fiber membrane by periodically performing acid cleaning as cleaning of the hollow fiber membrane. From these facts, even if the biopolymer is removed by the hollow fiber membrane, the biopolymer does not cause irreversible fouling, and by periodically performing acid cleaning, the biopolymer is removed from the hollow fiber membrane. It is considered that it can be preferably removed. Therefore, it is believed that direct removal of biopolymers by hollow fiber membranes can be carried out over a long period of time.

From the above, it is considered that this biopolymer removal apparatus can directly remove biopolymers by membrane filtration over a long period of time without using special agents such as adsorbents and flocculants.

Further, in the biopolymer removal device, the hollow fiber membrane preferably has a folding endurance of 10,000 times or more according to the MIT test method under the condition of a load of 200 g/mm ² .

The hollow fiber membrane provided in the biopolymer removal device is periodically washed with an acid. Specifically, as will be described later, not only backwashing under acidic conditions but also rocking using air bubbles by supplying gas is periodically performed. According to such a configuration, the durability of the hollow fiber membrane against such acid washing is sufficiently high, and direct removal of the biopolymer by membrane filtration can be carried out over a longer period of time.

Further, in the biopolymer removal device, the hollow fiber membrane has a breaking strength after being immersed in 5% by mass sulfuric acid at a constant temperature of 60° C., and a ratio of the breaking strength before the immersion to the breaking strength is 80% or more. is preferred.

According to such a configuration, the hollow fiber membrane has sufficiently high durability against acid washing as described above, and the direct removal of the biopolymer by membrane filtration can be carried out over a longer period of time.

Moreover, in the biopolymer removal device, the hollow fiber membrane preferably contains polyvinylidene fluoride as a main component.

According to such a configuration, the hollow fiber membrane has sufficiently high durability against acid washing as described above, and the direct removal of the biopolymer by membrane filtration can be carried out over a longer period of time.

Further, in the biopolymer removal apparatus, the acid washing unit includes a backwashing unit for backwashing by allowing a backwashing fluid to permeate from the filtrate side of the hollow fiber membrane to the water to be treated side, and during the backwashing, the An acid addition unit that adds acid to the liquid that contacts the hollow fiber membranes, and a gas supply unit that supplies gas from the water-to-be-treated side of the hollow fiber membranes after the backwashing to rock the hollow fiber membranes. and the acid addition unit is added before or during the backwashing so that the pH of the liquid that has been in contact with the hollow fiber membranes during the backwashing after the backwashing is less than 5. , preferably an acid is added to the liquid.

According to such a configuration, it is possible to provide a biopolymer removal apparatus that can directly remove biopolymers by membrane filtration over a longer period of time.

This is believed to be due to the following. An acid is added to the liquid before or during the backwashing so that the pH of the liquid, which has been in contact with the hollow fiber membranes during the backwashing, after the backwashing is less than 5. Since backwashing is performed under such acidic conditions, it is thought that the biopolymer is easily peeled off from the hollow fiber membrane. In such a state that the biopolymer is easily peeled off from the hollow fiber membrane, gas is supplied from the water to be treated side of the hollow fiber membrane to rock the hollow fiber membrane, thereby removing the biopolymer from the hollow fiber membrane. It is considered that it can be preferably removed. Therefore, it is believed that the direct removal of biopolymers by hollow fiber membranes can be carried out over a longer period of time.

From the above, it is considered that this biopolymer removal device can directly remove biopolymers by membrane filtration over a longer period of time.

Further, in the biopolymer removal apparatus, the acid washing unit performs backwashing by allowing a backwashing fluid to permeate from the filtrate side of the hollow fiber membrane to the treated water side, and after the backwashing, a gas supply unit that supplies gas from the water to be treated side of the hollow fiber membranes to rock the hollow fiber membranes; and the acid addition unit is configured to supply the gas before or after supplying the gas so that the pH of the liquid that is in contact with the hollow fiber membrane when the gas is supplied is less than 5. Sometimes it is preferable to add an acid to the liquid.

According to such a configuration, it is possible to provide a biopolymer removal apparatus that can directly remove biopolymers by membrane filtration over a longer period of time.

This is believed to be due to the following. An acid is added to the liquid before or when the gas is supplied so that the pH of the liquid that is in contact with the hollow fiber membrane when the gas is supplied is less than 5. Under such acidic conditions, gas is supplied from the water-to-be-treated side of the hollow fiber membranes to cause the hollow fiber membranes to oscillate. From this, it is considered that the biopolymer can be preferably removed from the hollow fiber membrane because the hollow fiber membrane is rocked by the supply of the gas in a state where the biopolymer is easily separated from the hollow fiber membrane. Therefore, it is believed that the direct removal of biopolymers by hollow fiber membranes can be carried out over a longer period of time.

From the above, it is considered that this biopolymer removal device can directly remove biopolymers by membrane filtration over a longer period of time.

Further, in the biopolymer removal device, the biopolymer removal rate is preferably 40 to 100%.

According to such a configuration, it is possible to more preferably remove the biopolymer by membrane filtration. Since the biopolymer removal apparatus can suitably remove the biopolymer from the hollow fiber membrane that has suitably removed the biopolymer from the water to be treated, the biopolymer can be directly removed by membrane filtration. Removal can be carried out over a longer period of time.

Moreover, in the biopolymer removal device, it is preferably used for pretreating water supplied to the membrane filtration device.

According to such a configuration, the biopolymer removal device is used to pretreat the water supplied to the membrane filtration device, so that even if water treatment is performed by the membrane filtration device, the membrane filtration device In the provided membrane, fouling by biopolymers can be suppressed. That is, even if water treatment is performed with a membrane filtration device without using special agents such as adsorbents and flocculants, fouling due to biopolymers can be suppressed. Therefore, water treatment can be performed with the membrane filtration device while suppressing fouling due to the biopolymer.

A water treatment system according to another aspect of the present invention includes the biopolymer removal device and a membrane filtration device that performs membrane filtration on the water treated by the biopolymer removal device.

According to such a configuration, fouling due to biopolymers can be suppressed without using special agents such as adsorbents and flocculants, so water treatment can be suitably performed over a long period of time with the membrane filtration device.

According to the present invention, there is provided a biopolymer removal device capable of directly removing biopolymers by membrane filtration over a long period of time without using special agents such as adsorbents and flocculants, and the biopolymer removal device. A water treatment system can be provided.

FIG. 1 is a schematic diagram showing the configuration of a water treatment system comprising a biopolymer device according to an embodiment of the invention. FIG. 2 is a schematic diagram showing an example of a biopolymer removal device according to an embodiment of the present invention. FIG. 3 is a schematic diagram showing another example of the biopolymer removal device according to the embodiment of the present invention. FIG. 4 is a schematic diagram showing the configuration of a conventional water treatment system that suppresses membrane fouling due to biopolymers.

Embodiments according to the present invention will be described below, but the present invention is not limited to these.

The biopolymer removal apparatus according to the present embodiment comprises a hollow fiber membrane having a molecular weight cutoff of 30,000 to 500,000 and a contact angle to water of 40 to 85°, and a hollow fiber membrane which is periodically acidified. and an acid cleaning section for cleaning.

The biopolymer removal device is a device that removes biopolymers contained in the water to be treated by permeating the water to be treated through the hollow fiber membrane. Moreover, the biopolymer removal device 1 is preferably used to pretreat water supplied to the membrane filtration device 2, as shown in FIG. That is, as a water treatment system, as shown in FIG. 1, a water treatment system having the biopolymer removal device 1 in front of the membrane filtration device 2 is preferable. By doing so, fouling by the biopolymer can be suppressed in the membrane filtration device. Note that FIG. 1 is a schematic diagram showing the configuration of a water treatment system provided with a biopolymer device according to this embodiment.

The biopolymer is defined as a component with the shortest retention time detected around 30 minutes retention time by a device called LC-OCD, which directly connects liquid chromatography using a size exclusion column and an organic carbon detector. . Specifically, the biopolymer is a membrane provided in a membrane filtration device in a water treatment system, for example, after permeating the water to be treated through a reverse osmosis membrane or the like, among the fouling attached to the membrane, physical It is irreversible fouling that cannot be removed by regular washing, and includes substances of biological origin. In addition, the biopolymer is considered to be a high-molecular-weight component and hydrophilic, since the retention time of the biopolymer in liquid chromatography on the size exclusion column is short. In addition, the LC-OCD was connected to a UV absorption detector, and no UV absorption at 254 nm was observed from the peak, suggesting that the component does not have an unsaturated bond. For this reason, more specifically, the biopolymers include organic substances such as polysaccharides and proteins, which are composed of metabolites of aquatic microorganisms. On the other hand, the biopolymer is presumed to be an organic substance or the like composed of metabolites of microorganisms such as polysaccharides and proteins, but it is difficult to specify the detailed substance.

The water to be treated is not particularly limited as long as it contains the biopolymer. The water to be treated includes a wide range of raw water such as industrial water, river water, and seawater. Biopolymers in seawater are also called TEPs (Transparent Exopolymer Particles).

The hollow fiber membrane is not particularly limited as long as it has a molecular weight cutoff of 30,000 to 500,000 and a contact angle to water of 40 to 85°.

Preferably, the biopolymer does not clog the hollow fiber membrane so that the biopolymer does not cause irreversible fouling. For this purpose, the pore diameter of the hollow fiber membrane is preferably smaller than the effective size of the biopolymer. For this reason, the cutoff molecular weight of the hollow fiber membrane is, as described above, 30,000 to 500,000, preferably 30,000 to 400,000, and 50,000 to 400,000. It is more preferable to have The cut-off molecular weight refers to the molecular weight of the minimum polymer that can block passage through the hollow fiber membrane. Specifically, for example, the weight average molecular weight of the polymer at which the hollow fiber membrane has a rejection rate of 90%. be done. If the cutoff molecular weight of the hollow fiber membrane is too small, there is a tendency that sufficient water permeability cannot be ensured. Moreover, not only does it become impossible to ensure sufficient water permeation performance, but the strength of the hollow fiber membrane often becomes insufficient. In addition, when the cutoff molecular weight of the hollow fiber membrane is too large, the biopolymer removal performance tends to decrease. If the hollow fiber membrane does not sufficiently remove biopolymers, it will not function sufficiently as a biopolymer removal device.

Although the molecular weight of biopolymers is said to be approximately 100,000 or more, for example, proteins that exist in nature have a three-dimensional structure as a tertiary structure, so the molecular weight does not represent the size of the protein as it is. Not in. Even if they have the same molecular weight, for example, a linear protein and a globular protein formed into a globular shape by a tertiary structure differ in ease of permeation through a hollow fiber membrane. Linear proteins are more likely to permeate hollow fiber membranes than globular proteins, since linear chains are more likely to pass through the pores of hollow fiber membranes. For this reason, linear proteins appear smaller than globular proteins. In addition, the ease of removal by the hollow fiber membrane also varies depending on the amount of hydrophilic groups present on the surface of the protein. For these reasons, the pore diameter of the hollow fiber membrane is preferably smaller than the effective size of the biopolymer, and the molecular weight cut off of the hollow fiber membrane is not smaller than the molecular weight of the biopolymer. Performance cannot be guaranteed. Therefore, if the cut-off molecular weight of the hollow fiber membrane is within the above range, removal of the biopolymer by the hollow fiber membrane is preferably carried out.

The hollow fiber membrane has a contact angle with water of 40 to 85°, preferably 40 to 80°, more preferably 40 to 65°. The contact angle includes, for example, a static contact angle. Specifically, when a water droplet is dropped on the surface of the hollow fiber membrane, the water droplet surface is in contact with the surface of the hollow fiber membrane. The angle formed by the surface and the surface of the hollow fiber membrane can be mentioned. When the contact angle of the hollow fiber membrane to water is too small, the hydrophilicity of the hollow fiber membrane becomes too high, and the biopolymer itself has high hydrophilicity, so the biopolymer is peeled off from the hollow fiber membrane. tends to become weaker. Therefore, the biopolymer tends to be difficult to remove from the hollow fiber membrane by washing. Therefore, the differential pressure tends to increase in the hollow fiber membranes in the biopolymer removal device. Further, when the contact angle of the hollow fiber membrane with respect to water is too large, the hydrophilicity of the hollow fiber membrane becomes too low, and membrane clogging tends to occur easily due to hydrophobic components in water other than the biopolymer. . That is, even if biopolymer fouling can be suppressed, fouling other than biopolymer fouling tends to occur more easily. Therefore, the differential pressure tends to increase in the hollow fiber membranes in the biopolymer removal device. For these reasons, by setting the contact angle of the hollow fiber membrane to water within the above range, the biopolymer can be easily peeled off from the hollow fiber membrane while suppressing fouling other than fouling by the biopolymer. can be done. As a result, the biopolymer can be easily removed from the hollow fiber membrane by washing, the fouling due to the biopolymer can be suppressed, and fouling other than the fouling due to the biopolymer can be suppressed. Therefore, direct removal of biopolymers by hollow fiber membranes can be carried out over a long period of time.

The water contact angle of the surface of the hollow fiber membrane that comes into contact with the water to be treated may be within the above range. may Further, the contact angle of the hollow fiber membrane with respect to water is substantially the same regardless of the position of the hollow fiber membrane in the longitudinal direction. For this reason, the contact angle of the surface of the hollow fiber membrane that comes into contact with the water to be treated should be within the above range regardless of the position of the hollow fiber membrane in the longitudinal direction.

The material for the hollow fiber membrane is not particularly limited as long as it can be used as a material for the hollow fiber membrane. Moreover, it is preferable that the hollow fiber membrane contains a resin.

The resin contained in the hollow fiber membrane is not particularly limited as long as it can be used as a material for the hollow fiber membrane. Examples of the resin contained as a main component in the hollow fiber membrane include fluororesins such as polytetrafluoroethylene and polyvinylidene fluoride, acrylic resins, polyacrylonitrile, polystyrene, polyamide, polyacetal, polycarbonate, polyphenylene ether, polyphenylene sulfide, and polyethylene. Terephthalate, polyetherimide, polyamideimide, polychloroethylene, polyethylene, polypropylene, crystalline cellulose, polysulfone, polyphenylsulfone, polyethersulfone, acrylonitrile butadiene styrene (ABS) resin, acrylonitrile styrene (AS) resin, and copolymers thereof. As the resin contained as the main component, the exemplified resins may be used alone, or two or more of them may be used in combination. Among the resins exemplified above, the resin contained as the main component is preferably a fluororesin, and more preferably polyvinylidene fluoride. That is, the hollow fiber membrane preferably contains polyvinylidene fluoride as a main component. Here, the main component means that the proportion of the resin in the hollow fiber membrane is high. % or more, more preferably 90% by mass or more, and preferably less than 100% by mass. Resin contained as a main component contained in the hollow fiber membrane (for example, polyvinylidene fluoride) is a main component of the hollow fiber membrane, and specifically, it is preferably 85% by mass or more, and 90% by mass or more. and preferably less than 100% by mass.

The hollow fiber membrane may contain other components in addition to the resin that is the main component. Other components include hydrophilic resins and the like. For example, in order to adjust the contact angle of the hollow fiber membrane to water within the above range, the hollow fiber membrane may contain a hydrophilic resin as the other component. The hydrophilic resin is not particularly limited as long as it contains a hydrophilic group in its molecule. Examples of the hydrophilic resin include cellulose ester, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, polyvinylpyrrolidone, copolymer of vinylpyrrolidone and vinyl acetate, copolymer of vinylpyrrolidone and vinylcaprolactam, and poly Examples include acrylic acid esters. As the hydrophilic resin, the exemplified resins may be used alone, or two or more of them may be used in combination. Among the resins exemplified above, polyvinyl alcohol and polyvinylpyrrolidone are preferable as the hydrophilic resin because they are easy to handle.

The hollow fiber membrane preferably has a water permeability at a transmembrane pressure difference of 0.1 MPa of 100 to 10,000 L/m ² /hr, more preferably 100 to 8,000 L/m ² /hr, and 100 to 5,000 L. /m ² /hr is more preferred. If the water permeation rate is too small, there is a tendency that the advantage of downsizing the device by using the hollow fiber membrane (the advantage of reducing the installation space by the hollow fiber membrane type) tends to decrease. On the other hand, if the water permeability is too large, the fractionation properties tend to be lowered, and it may not be possible to secure the molecular weight cutoff within the above range in the hollow fiber membrane.

The breaking strength of the hollow fiber membrane is not particularly limited as long as it can be used as a hollow fiber membrane. Specifically, the tensile strength of the hollow fiber membrane is preferably 3 to 25 MPa, more preferably 3 to 20 MPa, even more preferably 3 to 15 MPa. As the breaking strength of the hollow fiber membrane, if the tensile strength is within the above range, it can be suitably used as a hollow fiber membrane. The tensile strength is obtained from the load when a hollow fiber membrane cut into a predetermined size is pulled at a predetermined speed and the hollow fiber membrane breaks.

Since the hollow fiber membrane is washed with an acid, it is preferable that the hollow fiber membrane has high acid resistance. Specifically, the hollow fiber membrane is a ratio of the breaking strength after immersion in 5% by mass sulfuric acid at a constant temperature of 60 ° C. to the breaking strength before the immersion (breaking strength after the immersion / before the immersion breaking strength×100: breaking strength retention) is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. In addition, the above tensile strength etc. are mentioned as the breaking strength here, for example. Moreover, the immersion time may be sufficient as long as the hollow fiber membrane is sufficiently damaged by the acid, specifically, for example, 30 days. If the breaking strength retention rate is too low, the hollow fiber membranes are more likely to be damaged by the acid cleaning, and the deterioration of the hollow fiber membranes tends to hinder long-term operation when periodic acid cleaning is carried out.

The hollow fiber membrane provided in the biopolymer removal device is periodically washed with an acid. Specifically, as will be described later, not only backwashing under acidic conditions but also rocking using air bubbles by supplying gas is periodically performed. Therefore, it is preferable that the hollow fiber membrane not only have the breaking strength and the breaking strength retention rate within the above ranges, but also be able to withstand these acid washings. Specifically, the hollow fiber membrane preferably has a folding endurance of 10,000 times or more according to the MIT test method under the condition of a load of 200 g/mm ² . That is, it is preferable that the hollow fiber membrane has durability such that the number of folds is 10,000 or more. The folding endurance is preferably 10,000 times or more, more preferably 20,000 times or more, and even more preferably 30,000 times or more. If the folding endurance number is too low, the durability against the acid washing, specifically against the rocking or the like, tends to be low, which tends to hinder long-term operation of the biopolymer device.

The MIT test method is a folding endurance test according to JIS P 8115 (2001), and is a method for evaluating the strength of a test piece against bending. In this embodiment, as the strength of the hollow fiber membrane, in addition to the breaking strength, the MIT test method is used to evaluate the durability against rocking and the like. In the MIT test method, the hollow fiber membrane is repeatedly folded under the condition of a load of 200 g/mm ² and the number of times of folding is measured when the hollow fiber membrane is cracked. Examples of the MIT test method include the MIT test method under conditions of a temperature of 60° C., a sample width of 15 mm, a load of 200 g/mm ² , a refraction angle of 135°, a refraction cycle of 175 cpm, and a refractive local index radius of 0.38 mm. be done.

The shape of the hollow fiber membrane is not particularly limited. The hollow fiber membrane has a hollow fiber shape, and one side in the longitudinal direction may be open and the other side may be open or closed. Examples of the shape of the hollow fiber membrane include a hollow fiber shape in which one side in the longitudinal direction is open and the other side is closed. In addition, the hollow fiber membrane is a filtration method in which the water to be treated (raw water) is allowed to flow inside the hollow fiber membrane and the filtered water is allowed to flow to the outside. An external pressure filtration type in which (raw water) is allowed to flow and filtered water is allowed to flow inside, but these are not particularly limited. The external pressure filtration system is preferable from the viewpoint that the surface area of the hollow fiber membrane can be increased.

The outer diameter of the hollow fiber membrane is preferably 0.5 to 3 mm, more preferably 0.7 to 2.5 mm, even more preferably 0.8 to 2 mm. With such an outer diameter, it is a suitable size for a hollow fiber membrane provided in a device that realizes a separation technique using a hollow fiber membrane.

The inner diameter of the hollow fiber membrane is preferably 0.4 to 2.5 mm, preferably 0.5 to 2 mm, more preferably 0.5 to 1.2 mm. If the inner diameter of the hollow fiber membrane is too small, the resistance of the permeated liquid (pipe pressure loss) increases, and the flow tends to be poor. On the other hand, if the inner diameter of the hollow fiber membrane is too large, the shape of the hollow fiber membrane cannot be maintained, and the membrane tends to be easily crushed or distorted.

When the outer diameter and inner diameter of the hollow fiber membrane are within the above ranges, the hollow fiber membrane has a suitable size as a hollow fiber membrane provided in a biopolymer removal device using a hollow fiber membrane, and the device can be miniaturized. I can plan.

The biopolymer removal device preferably has a biopolymer removal rate of 40 to 100%, more preferably 50 to 100%, and even more preferably 60 to 100%. In the biopolymer removal device, the biopolymer is removed by permeation through the hollow fiber membrane. It is preferably a hollow fiber membrane. If the biopolymer removal rate is too low, for example, when the water treated by the biopolymer removal device is used as the water supplied to the membrane filtration device, irreversible fouling due to the biopolymer occurs in the membrane filtration device. cannot be sufficiently suppressed, and the transmembrane pressure tends to increase. The biopolymer removal rate is based on the biopolymer concentration (A) in the water to be treated before passing through the hollow fiber membrane and the biopolymer concentration (B) in the filtered water after passing through the hollow fiber membrane. Calculated. The biopolymer removal rate is calculated by (1−B/A)×100(%).

The biopolymer removal device first includes the hollow fiber membrane. For example, the hollow fiber membranes may be modularized as follows and provided as this modularized product (hollow fiber membrane module). Specifically, a predetermined number of the hollow fiber membranes are bundled, cut into a predetermined length, and filled in a casing having a predetermined shape. It is fixed to the casing with resin to form a module. There are various structures of this module, such as a type in which both ends of the hollow fiber membrane are open and fixed, and a type in which one end of the hollow fiber membrane is open and fixed and the other end is sealed but not fixed. Structures are known, and in this embodiment, the hollow fiber membrane can be used in any module structure. In such a hollow fiber membrane module, since the hollow fiber membranes are sealed in the housing, the hollow fiber membranes are liquid-tightly fixed to the housing. Further, in the hollow fiber membrane module, the hollow fiber membranes and the housing may be directly bonded and sealed with a sealing agent, or the hollow fiber membranes may be attached to the cylindrical case with the sealing agent. Each of the hollow fiber membranes and the housing may be sealed by bonding and fixing the cylindrical case to the housing.

As described above, the biopolymer removal device includes not only the hollow fiber membranes but also an acid cleaning section that periodically acid-cleans the hollow fiber membranes.

The acid washing section is not particularly limited as long as it can periodically acid wash the hollow fiber membranes. After the water to be treated containing the biopolymer is permeated through the hollow fiber membrane, the biopolymer present on the hollow fiber membrane can be removed from the hollow fiber membrane by the acid washing.

This is believed to be due to the following. First, the hollow fiber membrane has a molecular weight cutoff of 30,000 to 500,000 and a contact angle to water of 40 to 85°. It is considered that the model does not apply, and biopolymers are unlikely to cause irreversible fouling. Furthermore, biopolymers are polysaccharides, proteins, etc., and are considered to be easily hydrolyzed in acidic liquids. From this, it is thought that after the water to be treated containing the biopolymer permeates the hollow fiber membrane, the biopolymer present on the hollow fiber membrane is easily peeled off from the hollow fiber membrane by the acid washing. be done. From this, it is considered that the biopolymer can be removed from the hollow fiber membrane by the acid washing.

The acid cleaning section is not particularly limited as long as it can perform the acid cleaning on the hollow fiber membrane. As the acid washing unit, for example, a backwashing unit that backwashes by allowing a backwashing fluid to permeate from the filtrate side of the hollow fiber membranes to the water to be treated side, and a backwashing unit that contacts the hollow fiber membranes during the backwashing. and a gas supply unit for supplying gas from the water-to-be-treated side of the hollow fiber membranes after the backwashing to rock the hollow fiber membranes. be done.

In the acid washing section, the acid addition section adds acid to the liquid that contacts the hollow fiber membranes during the backwashing, and the backwashing section transfers acid from the filtrate side of the hollow fiber membranes to the water to be treated side. The backwashing fluid is permeated and backwashed. Then, the acid adding section adds the Add acid to the liquid. By doing so, the hollow fiber membrane can be backwashed under the acidic conditions as described above.

The acid is not particularly limited, and examples thereof include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, oxalic acid, citric acid, hydrogen peroxide water, and hypochlorous acid aqueous solution.

By adding the acid, the liquid in contact with the hollow fiber membranes during the backwashing has a pH of less than 5 after the backwashing of the liquid that has been in contact with the hollow fiber membranes during the backwashing. is preferred, 4 or less is more preferred, and 3.5 or less is even more preferred. Hydrolysis of polysaccharides and proteins corresponding to biopolymers is promoted at a lower pH. For example, hydrolysis is promoted at a pH of 3 or less or 4 or less. Therefore, it is preferable that the pH of the liquid that has been in contact with the hollow fiber membranes during the backwashing is less than 5 after the backwashing. If the pH of the liquid in contact with the hollow fiber membranes during the backwashing is low after the backwashing, the pH of the liquid in contact with the hollow fiber membranes during the backwashing is low, and the pH of the liquid in contact with the hollow fiber membranes during the backwashing is low. If the pH of the liquid in contact with the hollow fiber membranes after the backwashing is high, the pH of the liquid in contact with the hollow fiber membranes during the backwashing is high. If the pH of the liquid that contacts the hollow fiber membranes during the backwashing is too high, the hydrolysis of the biopolymer is suppressed too much, and there is a tendency that the backwashing does not produce a sufficient cleaning effect. This pH does not have to be 3 or less or 4 or less, which promotes hydrolysis of the biopolymer, but if it is too high, e.g. Backwashing results in insufficient cleaning effect.

The acid cleaning section supplies gas from the side of the water to be treated of the hollow fiber membranes after the backwashing in the gas supply section to cause the hollow fiber membranes to oscillate. Since the biopolymer is in a state where it is easy to separate from the hollow fiber membrane by backwashing under acidic conditions as described above, gas is supplied from the water to be treated side of the hollow fiber membrane in this state. , the biopolymer can be preferably removed from the hollow fiber membrane by shaking the hollow fiber membrane.

The acid washing unit includes, for example, a backwashing unit that allows a backwashing fluid to permeate from the filtrate side of the hollow fiber membranes to the water to be treated side, and a backwashing unit that backwashes the hollow fiber membranes after the backwashing. A gas supply unit that supplies gas from the treated water side to rock the hollow fiber membranes, and an acid addition unit that adds acid to the liquid that comes into contact with the hollow fiber membranes when the gas is supplied. is mentioned.

The acid washing section adds acid to the liquid that contacts the hollow fiber membrane when the gas is supplied in the acid adding section, and the gas is supplied from the water to be treated side of the hollow fiber membrane in the gas supplying section. supply to cause the hollow fiber membranes to oscillate. Then, the acid adding section, before or at the time of supplying the gas, performs the above-described Add acid to the liquid. By doing so, the hollow fiber membranes can be rocked by the gas under the acidic conditions as described above.

The acid is not particularly limited, and examples thereof include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, oxalic acid, citric acid, hydrogen peroxide water, and hypochlorous acid aqueous solution.

By adding the acid, the liquid in contact with the hollow fiber membranes when the gas is supplied has a pH of less than 5, which is in contact with the hollow fiber membranes when the gas is supplied. It is preferably 4 or less, more preferably 3.5 or less. Hydrolysis of polysaccharides and proteins corresponding to biopolymers is promoted at a lower pH. For example, hydrolysis is promoted at a pH of 3 or less or 4 or less. Therefore, it is preferable that the pH of the liquid that is in contact with the hollow fiber membranes when the gas is supplied is less than 5. If the pH of the liquid that is in contact with the hollow fiber membranes when the gas is supplied is too high, hydrolysis of the biopolymer is suppressed too much, and even if the hollow fiber membranes are rocked by the supply of the gas, There is a tendency that sufficient cleaning effect is not exhibited. This pH does not have to be 3 or less or 4 or less, which promotes hydrolysis of the biopolymer, but if it is too high, e.g. This causes the hollow fiber membrane to oscillate, resulting in insufficient cleaning effect.

The acid cleaning section supplies gas from the side of the water to be treated of the hollow fiber membranes after the backwashing in the gas supply section to cause the hollow fiber membranes to oscillate. By supplying gas from the water-to-be-treated side of the hollow fiber membranes under the acidic conditions described above to agitate the hollow fiber membranes, the biopolymer can be preferably removed from the hollow fiber membranes.

After the acid cleaning, the biopolymer removal device includes a rinsing section that sprinkles water in order to return the liquid in contact with the hollow fiber membranes to near neutrality, and neutralizes the liquid in contact with the hollow fiber membranes. A neutralization processing unit may be provided.

Examples of the biopolymer removing device include the device shown in FIG. FIG. 2 is a schematic diagram showing an example of the biopolymer removal device 1 according to this embodiment.

The biopolymer removal apparatus 1 is an external pressure filtration type apparatus that supplies water to be treated (raw water) to the outer surface side of the hollow fiber membranes and extracts treated water (filtrate) from the inner surface side of the hollow fiber membranes. As shown in FIG. 2, the biopolymer removal device 1 includes a hollow fiber membrane module 31 provided with hollow fiber membranes housed in a housing, liquid feed pumps 11 to 13, an air compressor 32, and a chemical liquid tank. 33, a backwash water tank 34, piping connecting these, open/close valves 21 to 29 provided on the piping, and a control device 35.

The liquid-sending pumps 11 to 13 send fluids such as raw water into the pipes. The air compressor 32 supplies gas into the piping. The chemical liquid tank 33 stores an acid for performing the acid cleaning. The backwashing water tank 34 stores a backwashing fluid to be permeated from the filtrate side of the hollow fiber membrane to the treated water side during the backwashing. The on-off valves 21-29 regulate movement of the fluid in the pipe.

The control device 35 controls driving of the liquid-sending pumps 11-13 and the air compressor 32, and controls opening/closing operations of the opening/closing valves 21-29. The control device 35 is configured by, for example, a personal computer or the like. The control device 35 stores sequence information of each step (filling step, filtering step, backwashing step, bubbling step, draining step, etc.) sequentially executed in the biopolymer removal process (filtration process). and a control unit for controlling the driving of the air compressor 32 and controlling the opening/closing operations of the opening/closing valves 21 to 29 according to the sequence information.

A biopolymer removal operation by the biopolymer removal apparatus 1 and a cleaning method performed during the operation will be described.

First, referring to Table 1, a case where acid cleaning is not performed as cleaning will be described. Table 1 shows the relationship between each step, the drive state of the liquid feed pump, and the open/closed state of the open/close valve for the basic operating method of the biopolymer removal apparatus shown in FIG. "○" in Table 1 means that the corresponding liquid transfer pump is driven or the corresponding open/close valve is open.

First, the water filling process (before filtration) is performed. In this water filling step (before filtration), the control device 35 opens the opening/closing valves 21 and 23 from a state in which all the opening/closing valves of the biopolymer removal device 1 are closed, and the liquid feed pump 11 is driven. As a result, raw water is supplied to the hollow fiber membrane module 31, and the raw water is brought into contact with the hollow fiber membranes. Specifically, the housing of the hollow fiber membrane module is filled with raw water.

Next, a filtration step is performed. In this filtration process, the control device 35 opens the on-off valve 22 and closes the on-off valve 23 . As a result, the raw water permeates from the outer surface side to the inner surface side of the hollow fiber membranes provided in the hollow fiber membrane module 31 to obtain a filtrate.

Next, a backwash process is performed. In this backwashing step, the control device 35 opens the on-off valves 24 and 25, closes the on-off valves 21 and 22, drives the liquid feed pump 12, and stops the liquid feed pump 11. Let As a result, the backwashing fluid stored in the backwashing water tank 34 is supplied to the filtrate side of the hollow fiber membranes provided in the hollow fiber membrane module 31, and this backwashing fluid permeates to the treated water side. . In this way, the hollow fiber membranes provided in the hollow fiber membrane module 31 are backwashed.

Next, a depressurization step is performed. In this depressurization step, the control device 35 opens the open/close valve 27, closes the open/close valves 24 and 25, and stops the liquid feed pump 12. FIG. As a result, the air pressure inside the housing of the hollow fiber membrane module, which is increased by the backwashing process, can be lowered.

Next, a water filling step (after filtration) is performed. In this water filling step (after filtration), the control device 35 opens the opening/closing valves 21 and 23, closes the opening/closing valve 27, and drives the liquid feed pump 11. FIG. That is, the same process as the water filling process (before filtration) is performed. As a result, raw water is supplied to the hollow fiber membrane module 31, and the raw water is brought into contact with the hollow fiber membranes. Specifically, the housing of the hollow fiber membrane module is filled with raw water.

Next, a bubbling process is performed. In this bubbling process, the control device 35 opens the open/close valve 26 and closes the open/close valve 21 , stops the liquid feed pump 11 , and drives the air compressor 32 . As a result, the gas can be supplied from the water to be treated side to the hollow fiber membranes in contact with the undiluted solution, and the hollow fiber membranes can be oscillated.

Next, a drainage process is performed. In this draining process, the control device 35 opens the on-off valve 24, closes the on-off valve 26, and stops the air compressor 32. As shown in FIG. As a result, the water filled in the housing of the hollow fiber membrane module is drained.

Through the steps described above, the biopolymer removal apparatus performs the biopolymer removal operation and the cleaning performed during the operation when acid cleaning is not performed as cleaning.

Next, with reference to Table 2, the case where acid cleaning is performed as cleaning and the acid is added before the backwashing step will be described. Table 2 shows the relationship between each step, the drive state of the liquid feed pump, and the open/closed state of the open/close valve for the basic operating method of the biopolymer removal apparatus shown in FIG. "○" in Table 2 means that the corresponding liquid transfer pump is driven or the corresponding open/close valve is open.

First, the water filling process (before filtration) is performed. This water filling step (before filtration) is the same as the water filling step (before filtration) when acid washing is not performed as the washing.

Next, a filtration step is performed. This filtration step is also the same as the filtration step when acid washing is not performed as the washing.

Next, an acid addition step is performed. In this acid addition step, the control device 35 opens the opening/closing valves 23 and 29, closes the opening/closing valve 22, and drives the liquid feed pump 13. As shown in FIG. As a result, the acid stored in the chemical liquid tank 33 is added to the raw water, and the raw water to which the acid has been added is supplied to the hollow fiber membrane module 31 . Therefore, the undiluted solution in contact with the hollow fiber membranes is in a state in which an acid has been added.

Next, a backwash process is performed. In this backwashing step, the control device 35 opens the opening/closing valves 24 and 25 and closes the opening/closing valves 21, 23, and 29, drives the liquid feed pump 12, and , 13 are stopped. As a result, the backwashing fluid stored in the backwashing water tank 34 is supplied to the filtrate side of the hollow fiber membranes provided in the hollow fiber membrane module 31, and this backwashing fluid permeates to the treated water side. . In this way, the hollow fiber membranes provided in the hollow fiber membrane module 31 are backwashed. At this time, the hollow fiber membranes to be subjected to the backwashing step are in contact with raw water to which acid has been added from the side of the water to be treated of the hollow fiber membranes due to the acid addition step. Therefore, in this backwashing step, the hollow fiber membranes are backwashed in a state in which the liquid that has been in contact with the hollow fiber membranes during the backwashing is acidic, that is, has a pH of less than 5. Further, in the backwashing step, the pH of the liquid that has passed through the on-off valve 24 is measured, and acid is added in the acid addition step so that the pH becomes less than 5.

Next, a depressurization step, a water filling step (after filtration), a bubbling step, and a draining step are carried out. These depressurization process, water filling process (after filtration), bubbling process, and drainage process are the depressurization process, water filling process (after filtration), bubbling process, and It is the same as the drainage process, respectively.

According to the above-described steps, the biopolymer removal apparatus performs the biopolymer removal operation and during the operation when acid cleaning is performed as cleaning and acid is added before the backwashing step. Wash as required.

Next, referring to Table 3, the case where acid cleaning is performed as cleaning and the acid is added at the same time as the backwashing step will be described. Table 3 shows the relationship between each step, the drive state of the liquid feed pump, and the open/closed state of the open/close valve for the basic operating method of the biopolymer removal apparatus shown in FIG. "○" in Table 3 means that the corresponding liquid transfer pump is driven or the corresponding open/close valve is open.

First, the water filling process (before filtration) is performed. This water filling step (before filtration) is the same as the water filling step (before filtration) when acid washing is not performed as the washing.

Next, a filtration step is performed. This filtration step is also the same as the filtration step when acid washing is not performed as the washing.

Next, an acid addition step is performed. In this acid addition step, the control device 35 opens the opening/closing valves 23 and 28, closes the opening/closing valve 22, and drives the liquid feed pump 13. As shown in FIG. As a result, the acid stored in the chemical liquid tank 33 can be supplied to the backwash water tank 34 .

Next, a backwash process is performed. In this backwashing process, the control device 35 opens the on-off valves 24 and 25 and closes the on-off valve 28 , drives the liquid feed pump 12 , and stops the liquid feed pump 13 . As a result, the backwashing fluid stored in the backwashing water tank 34 is supplied to the filtrate side of the hollow fiber membranes provided in the hollow fiber membrane module 31, and this backwashing fluid permeates to the treated water side. . In this way, the hollow fiber membranes provided in the hollow fiber membrane module 31 are backwashed. An acid is added to the backwashing fluid by the acid addition step prior to the backwashing step. Therefore, in this backwashing step, the hollow fiber membranes are backwashed using a backwashing fluid to which acid has been added, so that the hollow fiber membranes are added with acid at the same time as the backwashing step. Become. Further, in the backwashing step, the pH of the liquid that has passed through the on-off valve 24 is measured, and acid is added in the acid addition step so that the pH becomes less than 5.

Next, a depressurization step, a water filling step (after filtration), a bubbling step, and a draining step are carried out. These depressurization process, water filling process (after filtration), bubbling process, and drainage process are the depressurization process, water filling process (after filtration), bubbling process, and It is the same as the drainage process, respectively.

According to the above-described steps, the biopolymer removal apparatus performs the biopolymer removal operation and during the operation when acid cleaning is performed as cleaning and acid is added at the same time as the backwashing step. Wash as required.

Next, with reference to Table 4, a case where acid cleaning is performed as cleaning and an acid is added before the bubbling step (gas supply step) will be described. Table 4 shows the relationship between each step, the drive state of the liquid feed pump, and the open/closed state of the open/close valve for the basic operating method of the biopolymer removal apparatus shown in FIG. "○" in Table 4 means that the corresponding liquid transfer pump is driven or the corresponding open/close valve is open.

First, the water filling process (before filtration) is performed. This water filling step (before filtration) is the same as the water filling step (before filtration) when acid washing is not performed as the washing.

Next, a filtration step is performed. This filtration step is also the same as the filtration step when acid washing is not performed as the washing.

Next, a backwash process is performed. This backwashing process is also the same as the backwashing process when acid washing is not performed as the washing.

Next, a depressurization step is performed. This depressurization step is also the same as the depressurization step when acid cleaning is not performed as the cleaning.

Next, an acid addition step is performed. This acid addition step also serves as the water filling step (after filtration) when acid washing is not performed as the washing. In this acid addition step, the control device 35 opens the opening/closing valves 21, 23, and 29, closes the opening/closing valve 27, and drives the liquid feed pumps 11, 13. As shown in FIG. As a result, the acid stored in the chemical tank 33 is added to the raw water, and the raw water to which the acid has been added is supplied to the hollow fiber membrane module 31, and the hollow fiber membranes are brought into contact with the raw water. Specifically, the housing of the hollow fiber membrane module is filled with acid-added raw water. Therefore, the undiluted solution in contact with the hollow fiber membranes is in a state in which an acid has been added.

Next, a bubbling process is performed. In this bubbling process, the control device 35 opens the opening/closing valve 26, closes the opening/closing valves 21 and 29, stops the liquid feed pump 12, and drives the air compressor 32. FIG. As a result, gas can be supplied from the water to be treated side to the hollow fiber membranes in contact with the undiluted solution to which the acid has been added, and the hollow fiber membranes can be oscillated. At this time, the hollow fiber membranes subjected to the bubbling step are in contact with the raw water to which the acid has been added by the acid addition step. Therefore, in this bubbling step, the hollow fiber membranes are bubbled while the liquid that is in contact with the hollow fiber membranes when the gas is supplied is acidic, that is, has a pH of less than 5. Also, the pH of this liquid is determined by measuring the pH of the liquid that has passed through the on-off valve 24 in the drainage process, and adding an acid in the acid addition process so that the pH becomes less than 5.

Next, a drainage process is performed. This draining process is the same as the draining process when acid cleaning is not performed as the cleaning.

According to the above-described steps, the biopolymer removal apparatus performs the biopolymer removal operation and during the operation when acid cleaning is performed as cleaning and acid is added before the bubbling step. Wash.

Examples of the biopolymer removal apparatus include the apparatus shown in FIG. 3 and the like, in addition to the apparatus shown in FIG. 2 as described above. FIG. 3 is a schematic diagram showing another example of the biopolymer removal device 1 according to this embodiment.

The biopolymer removal apparatus 1 is an external pressure filtration type apparatus that supplies water to be treated (raw water) to the outer surface side of the hollow fiber membranes and extracts treated water (filtrate) from the inner surface side of the hollow fiber membranes. As shown in FIG. 3, the biopolymer removal device 1 includes a hollow fiber membrane module 31 provided with hollow fiber membranes housed in a housing, liquid feed pumps 41 and 42, an air compressor 32, and a chemical liquid tank. 33, pipes connecting these, on-off valves 51 to 59 provided in the pipes, and a control device 35.

The liquid feed pumps 41 and 42 feed a fluid such as raw water into the pipe. The air compressor 32 supplies gas into the piping. The chemical liquid tank 33 stores an acid for performing the acid cleaning. The on-off valves 51-59 regulate movement of the fluid in the pipe.

The control device 35 controls driving of the liquid-sending pumps 41 and 42 and the air compressor 32, and controls opening/closing operations of the opening/closing valves 51-59. The control device 35 is configured by, for example, a personal computer or the like. The control device 35 stores sequence information of each step (filling step, filtering step, backwashing step, bubbling step, draining step, etc.) sequentially executed in the biopolymer removal process (filtration process). and a control unit for controlling the driving of the air compressor 32 and controlling the opening/closing operations of the opening/closing valves 51 to 59 according to the sequence information.

A biopolymer removal operation by the biopolymer removal apparatus 1 and a cleaning method performed during the operation will be described.

First, the case where acid cleaning is not performed as cleaning will be described with reference to Table 5. Table 5 shows the relationship between each step, the drive state of the liquid feed pump, and the open/closed state of the open/close valve for the basic operating method of the biopolymer removal apparatus shown in FIG. "○" in Table 5 means that the corresponding liquid transfer pump is driven or the corresponding open/close valve is open.

First, the water filling process (before filtration) is performed. In this water filling step (before filtration), the control device 35 opens the opening/closing valves 51 and 53 from a state in which all the opening/closing valves of the biopolymer removal device 1 are closed, and the liquid feed pump 41 is driven. As a result, raw water is supplied to the hollow fiber membrane module 31, and the raw water is brought into contact with the hollow fiber membranes. Specifically, the housing of the hollow fiber membrane module is filled with raw water.

Next, a filtration step is performed. In this filtering step, the control device 35 opens the on-off valve 52 and closes the on-off valve 53 . As a result, the raw water permeates from the outer surface side to the inner surface side of the hollow fiber membranes provided in the hollow fiber membrane module 31 to obtain a filtrate.

Next, a backwash process is performed. In this backwashing process, the control device 35 opens the opening/closing valves 54 and 55 and closes the opening/closing valves 51 and 52 , stops the liquid feed pump 41 , and drives the air compressor 32 . As a result, gas is supplied to the filtrate side of the hollow fiber membrane in contact with the stock solution, and part of the filtrate filtered by this filtration process (filtrate existing in the pipe) etc. is transferred to the water to be treated side. To Penetrate. In this way, the hollow fiber membranes provided in the hollow fiber membrane module 31 are backwashed.

Next, a depressurization step is performed. In this depressurization step, the control device 35 opens the open/close valve 57, closes the open/close valves 54 and 55, and stops the air compressor 32. As shown in FIG. As a result, the air pressure inside the housing of the hollow fiber membrane module, which is increased by the backwashing process, can be lowered.

Next, a water filling step (after filtration) is performed. In this water filling step (after filtration), the control device 35 opens the opening/closing valves 51 and 53 and closes the opening/closing valve 57, and further drives the liquid feed pump 41. FIG. That is, the same process as the water filling process (before filtration) is performed. As a result, raw water is supplied to the hollow fiber membrane module 31, and the raw water is brought into contact with the hollow fiber membranes. Specifically, the housing of the hollow fiber membrane module is filled with raw water.

Next, a bubbling process is performed. In this bubbling process, the control device 35 opens the open/close valve 56 and closes the open/close valve 51 , stops the liquid feed pump 41 , and drives the air compressor 32 . As a result, gas can be supplied from the water to be treated side to the hollow fiber membranes in contact with the undiluted solution, and the hollow fiber membranes can be oscillated.

Next, a drainage process is performed. In this drainage process, the control device 35 opens the opening/closing valve 54, closes the opening/closing valve 56, and stops the air compressor 32. As shown in FIG. As a result, the water filled in the housing of the hollow fiber membrane module is drained.

Through the steps described above, the biopolymer removal apparatus performs the biopolymer removal operation and the cleaning performed during the operation when acid cleaning is not performed as cleaning.

Next, with reference to Table 6, the case where acid cleaning is performed as cleaning and the acid is added before the backwashing step will be described. Table 6 shows the relationship between each step, the drive state of the liquid feed pump, and the open/closed state of the open/close valve for the basic operating method of the biopolymer removal apparatus shown in FIG. "○" in Table 6 means that the corresponding liquid transfer pump is driven or the corresponding open/close valve is open.

First, the water filling process (before filtration) is performed. This water filling step (before filtration) is the same as the water filling step (before filtration) when acid washing is not performed as the washing.

Next, a filtration step is performed. This filtration step is also the same as the filtration step when acid washing is not performed as the washing.

Next, an acid addition step is performed. In this acid addition step, the control device 35 opens the on-off valves 53 and 59, closes the on-off valve 52, and drives the liquid feed pump . As a result, the acid stored in the chemical liquid tank 33 is added to the raw water, and the raw water to which the acid has been added is supplied to the hollow fiber membrane module 31 . Therefore, the undiluted solution in contact with the hollow fiber membranes is in a state in which an acid has been added.

Next, a backwash process is performed. In this backwash process, the control device 35 opens the on-off valves 54 and 55, closes the on-off valves 51, 53 and 59, stops the liquid feed pumps 41 and 42, and turns off the air compressor 32. drive. As a result, the gas is supplied to the filtrate side of the hollow fiber membrane in contact with the stock solution, and part of the filtrate filtered in the filtration step permeates to the water to be treated side. In this way, the hollow fiber membranes provided in the hollow fiber membrane module 31 are backwashed. At this time, the hollow fiber membranes to be subjected to the backwashing step are in contact with raw water to which acid has been added from the side of the water to be treated of the hollow fiber membranes due to the acid addition step. Therefore, in this backwashing step, the hollow fiber membranes are backwashed in a state in which the liquid that has been in contact with the hollow fiber membranes during the backwashing is acidic, that is, has a pH of less than 5. Further, in the backwashing step, the pH of the liquid that has passed through the on-off valve 54 is measured, and acid is added in the acid adding step so that the pH becomes less than 5.

Next, a depressurization step, a water filling step (after filtration), a bubbling step, and a draining step are carried out. These depressurization process, water filling process (after filtration), bubbling process, and drainage process are the depressurization process, water filling process (after filtration), bubbling process, and It is the same as the drainage process, respectively.

According to the above-described steps, the biopolymer removal apparatus performs the biopolymer removal operation and during the operation when acid cleaning is performed as cleaning and acid is added before the backwashing step. Wash as required.

Next, with reference to Table 7, a case where acid cleaning is performed as cleaning and an acid is added at the same time as the backwashing step will be described. Table 7 shows the relationship between each step, the drive state of the liquid feed pump, and the open/closed state of the open/close valve for the basic operating method of the biopolymer removal apparatus shown in FIG. "○" in Table 7 means that the corresponding liquid transfer pump is driven or the corresponding open/close valve is open.

First, the water filling process (before filtration) is performed. This water filling step (before filtration) is the same as the water filling step (before filtration) when acid washing is not performed as the washing.

Next, a filtration step is performed. This filtration step is also the same as the filtration step when acid washing is not performed as the washing.

Next, an acid addition step is performed. In this acid addition step, the control device 35 opens the opening/closing valves 53 and 58, closes the opening/closing valves 51 and 52, and drives the liquid feed pump 42. As shown in FIG. As a result, the acid stored in the chemical liquid tank 33 can be supplied to a part of the filtrate (filtrate existing in the pipe) or the like filtered in the filtering step.

Next, a backwash process is performed. In this backwashing process, the control device 35 opens the opening/closing valves 54 and 55 and closes the opening/closing valves 53 and 58, stops the liquid feed pump 42, and drives the air compressor 32. As a result, the backwashing fluid stored in the backwashing water tank 34 is supplied to the filtrate side of the hollow fiber membranes provided in the hollow fiber membrane module 31, the gas is supplied, and the filtrate filtered by this filtration step is supplied. A part of (filtrate existing in the pipe) and the like permeate to the water to be treated side. In this way, the hollow fiber membranes provided in the hollow fiber membrane module 31 are backwashed. An acid is added to the filtrate used for the backwashing by the acid addition step before the backwashing step. Therefore, in this backwashing step, the hollow fiber membranes are backwashed using the acid-added filtrate, so that the hollow fiber membranes are added with acid at the same time as the backwashing step. Further, in the backwashing step, the pH of the liquid that has passed through the on-off valve 24 is measured, and acid is added in the acid addition step so that the pH becomes less than 5.

Next, a depressurization step, a water filling step (after filtration), a bubbling step, and a draining step are carried out. These depressurization process, water filling process (after filtration), bubbling process, and drainage process are the depressurization process, water filling process (after filtration), bubbling process, and It is the same as the drainage process, respectively.

According to the above-described steps, the biopolymer removal apparatus performs the biopolymer removal operation and during the operation when acid cleaning is performed as cleaning and acid is added at the same time as the backwashing step. Wash as required.

Next, referring to Table 8, a case where acid cleaning is performed as cleaning and an acid is added before the bubbling step (gas supply step) will be described. Table 8 shows the relationship between each step, the drive state of the liquid feed pump, and the open/closed state of the open/close valve for the basic operating method of the biopolymer removal apparatus shown in FIG. "○" in Table 8 means that the corresponding liquid transfer pump is driven or the corresponding open/close valve is open.

First, the water filling process (before filtration) is performed. This water filling step (before filtration) is the same as the water filling step (before filtration) when acid washing is not performed as the washing.

Next, a filtration step is performed. This filtration step is also the same as the filtration step when acid washing is not performed as the washing.

Next, a backwash process is performed. This backwashing process is also the same as the backwashing process when acid washing is not performed as the washing.

Next, a depressurization step is performed. This depressurization step is also the same as the depressurization step when acid cleaning is not performed as the cleaning.

Next, an acid addition step is performed. This acid addition step also serves as the water filling step (after filtration) when acid washing is not performed as the washing. In this acid addition step, the control device 35 opens the on-off valves 51, 53, 59, closes the on-off valve 57, and drives the liquid feed pumps 41, . As a result, the acid stored in the chemical tank 33 is added to the raw water, and the raw water to which the acid has been added is supplied to the hollow fiber membrane module 31, and the hollow fiber membranes are brought into contact with the raw water. Specifically, the housing of the hollow fiber membrane module is filled with acid-added raw water. Therefore, the undiluted solution in contact with the hollow fiber membranes is in a state in which an acid has been added.

Next, a bubbling process is performed. In this bubbling process, the control device 35 opens the open/close valve 56 and closes the open/close valves 51 and 59 , stops the liquid feed pumps 41 and 42 , and drives the air compressor 32 . As a result, gas can be supplied from the water to be treated side to the hollow fiber membranes in contact with the undiluted solution to which the acid has been added, and the hollow fiber membranes can be oscillated. At this time, the hollow fiber membranes subjected to the bubbling step are in contact with the raw water to which the acid has been added by the acid addition step. Therefore, in this bubbling step, the hollow fiber membranes are bubbled while the liquid that is in contact with the hollow fiber membranes when the gas is supplied is acidic, that is, has a pH of less than 5. Also, the pH of this liquid is determined by measuring the pH of the liquid that has passed through the on-off valve 54 in the drainage process, and adding acid in the acid addition process so that the pH becomes less than 5.

Next, a drainage process is performed. This draining process is the same as the draining process when acid cleaning is not performed as the cleaning.

According to the above-described steps, the biopolymer removal apparatus performs the biopolymer removal operation and during the operation when acid cleaning is performed as cleaning and acid is added before the bubbling step. Wash.

As described above, the biopolymer removal apparatus includes a water filling step of filling the periphery of the hollow fiber membrane with the water to be treated, a filtering step of filtering the water to be treated by the hollow fiber membrane, and a backwashing of the hollow fiber membrane. By performing a washing step, a bubbling step of supplying gas from the side of the water to be treated of the hollow fiber membrane to rock the hollow fiber membrane, and a draining step of draining the water to be treated from the periphery of the hollow fiber membrane. , removing the biopolymer and washing the hollow fiber membrane. In the biopolymer removal apparatus, the liquid feed pump, the air compressor, the chemical tank, the backwash water tank, the pipe, the opening/closing valve, and the control device are connected to the acid washing unit. Equivalent to. Further, the acid washing is the backwashing step and the bubbling step, and corresponds to the step of performing the backwashing step under the acidic conditions as described above. When the water filling step, the filtering step, the bubbling step, and the draining step are performed in order, the biopolymer removal apparatus includes the backwashing step and the bubbling step that result in such acid washing. Each time the filtration step is performed, it may be performed after the filtration step, or may be performed after the filtration step is performed a plurality of times. The number of times of the filtration step between performing the acid cleaning and then performing the acid cleaning is preferably 1 to 480 times, more preferably 1 to 192 times, and 1 to 48 times. is more preferred.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these.

[Examples 1 to 3 and Comparative Examples 1 to 3]
First, the hollow fiber membrane used in this example will be described.

The membrane used in this example is a hollow fiber membrane used in the external pressure filtration system, and as shown in Table 1, it is a hollow fiber membrane containing a resin and a hydrophilic resin as main components.

(Resin contained as main component)
PVDF: Polyvinylidene fluoride (Kynar741 manufactured by Arkema)
PSF: Polysulfone (Ultrason S3010 manufactured by BASF Japan Ltd.)
(Hydrophilic resin)
PVA: polyvinyl alcohol (PVA205 manufactured by Kuraray Co., Ltd.)
PVP: Polyvinylpyrrolidone (Sokalan K-90P manufactured by BASF Japan Co., Ltd.)
(Content rate of resin contained as main component)
The content of the resin contained as the main component in the hollow fiber membrane was calculated as follows.

First, after dissolving the hollow fiber membrane in a solvent such as dimethylformamide and dimethylacetamide, the weight of the remaining undissolved material was measured. Using this undissolved matter as a hydrophilic resin, the weight of the resin contained as the main component in the hollow fiber membrane was calculated. That is, the weight of the undissolved matter measured here is the content of the hydrophilic resin in the hollow fiber membrane, and the difference between the weight of the hollow fiber membrane and the weight of the undissolved matter (the weight of the hollow fiber membrane The weight-the weight of the undissolved matter) is the content of the resin contained as the main component in the hollow fiber membrane. From the content of the resin contained as the main component and the content of the hydrophilic resin, the content of the resin contained as the main component in the hollow fiber membrane was calculated.

As a result, the content of the resin contained as the main component in the hollow fiber membrane was 95% by mass in Examples 1 to 3 and Comparative Example 1, and 100% by mass in Comparative Examples 2 and 3. .

(Molecular weight cutoff)
The molecular weight cutoff of the hollow fiber membrane was measured by the following procedure.

A hollow fiber membrane to be measured was subjected to wet treatment such as immersing it in a 50% by mass ethanol aqueous solution for 15 minutes and then washing it with pure water for 15 minutes. A hollow fiber membrane module having an effective length of 20 cm was prepared by sealing one end of the wet-treated hollow fiber membrane.

A phosphate buffer solution was used as raw water to prepare a solution in which the marker protein was developed to a total organic carbon (TOC) of 500 mg/l. For the marker protein, for example, a protein with a known weight average molecular weight (Mw) as shown below was used. TOC is a concentration index of organic matter present in water. TOC is measured as the concentration of organic matter present in water, which is estimated from the amount of _CO2 generated by burning water, which is the measurement object, and is estimated from the detected amount of _CO2 .

Insulin (Mw: 5720)
Cytochrome C (Mw: 12500)
Ovalbumin (Mw: 43000)
Albumin (Mw: 67000)
Aldolase (Mw: 158000)
Apoferritin (Mw: 440000)
Thyroglobulin (Mw: 669000)
Blue dextran (Mw: 2000000)
Filtration is performed under conditions of a filtration pressure of 0.1 MPa and a temperature of 25° C., and the removal rate [(1−TOC of membrane filtered water/TOC of raw water)×100 from the TOC of the membrane filtered water and the TOC of the raw water. ] was calculated. The relationship between the obtained removal rate and the molecular weight of the marker protein was substituted into the following formula and fitted to create a fractionation curve, and the molecular weight (Mw) at 90% removal rate was defined as the molecular weight cutoff. .

R=100/(1−m×exp(−a×log(S)))
In the above formula, a and m are constants determined by the hollow fiber membrane, and are calculated based on at least two types of rejection measurements. A fractionation curve can be defined by determining a and m by substituting the experimental value of the inhibition rate for R and substituting the molecular weight of the marker protein used in the experiment for S.

Table 9 shows the fractional particle size of the resulting hollow fiber membrane.

(Contact angle with water)
The contact angle with water (water contact angle) was measured as follows.

A water droplet is dropped on the surface of the hollow fiber membrane and an image is taken at that moment. Then, the angle formed by the surface of the water droplet and the surface of the hollow fiber membrane was measured at the location where the surface of the water droplet was in contact with the surface of the hollow fiber membrane. This angle was taken as the contact angle of water on the surface of the hollow fiber. "Drop Master 700" manufactured by Kyowa Interface Science Co., Ltd. was used as a contact angle measurement device for water.

As a result, Table 9 shows the water contact angle (water contact angle) of the resulting hollow fiber membrane.

(Breaking strength of hollow fiber membrane)
The breaking strength of the hollow fiber membrane was measured as follows.

First, the hollow fiber membrane to be measured was cut into pieces having a length of 5 cm. Using an autograph (AG-Xplus manufactured by Shimadzu Corporation), the cut hollow fiber membrane was subjected to a tensile test in water at 25 ° C. at 100 mm / min, and the load when the hollow fiber membrane broke was measured. The tensile strength was obtained from the measured load. This tensile strength was taken as the breaking strength.

Table 9 shows the breaking strength of the resulting hollow fiber membrane.

(Hollow fiber membrane breaking strength retention after acid treatment)
A 5% by mass sulfuric acid aqueous solution was used as the chemical, and the obtained hollow fiber membrane was immersed in the chemical heated to 60° C. for 30 days. Then, the tensile strength of the hollow fiber membranes not immersed in the chemical solution and the tensile strength of the hollow fiber membranes after being immersed in the chemical solution for 30 days were measured in the same manner as for the breaking strength of the hollow fiber membranes. From this obtained value, the ratio of the breaking strength after immersion in 5% by mass of sulfuric acid at a constant temperature of 60 ° C. to the breaking strength before the immersion (breaking strength after the immersion / breaking strength before the immersion × 100: breaking strength retention) was calculated. In addition, this breaking strength retention is an index of chemical resistance. It can be seen that the higher the breaking strength retention, the higher the chemical resistance.

As a result, Table 9 shows the breaking strength retention of the obtained hollow fiber membranes.

(Inner diameter and outer diameter of hollow fiber membrane)
The inner diameter and outer diameter of the hollow fiber membrane were measured using a digital microscope VHX-5000 manufactured by Keyence Corporation.

Table 9 shows the inner and outer diameters of the resulting hollow fiber membranes.

(Folding number of hollow fiber membranes according to the MIT test method)
The folding endurance number of the hollow fiber membrane according to the MIT test method was measured as follows.

An MIT folding endurance tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used to measure the folding endurance number of the hollow fiber membrane according to the MIT test method. Specifically, from the outer diameter and inner diameter of the hollow fiber membrane, the area of the hollow fiber membrane (= (outer diameter / 2) ^ 2 × π - (inner diameter / 2) ^ 2 × π) is calculated, and the test piece A load of 200 g/mm ² was applied to the After that, bending was repeated until the bending angle reached 135°, and the hollow fiber membrane was broken. The number of times until breakage was taken as the number of folding endurance.

As a result, Table 9 shows the folding endurance number of the obtained hollow fiber membrane. The number of bends is up to 10,000 times, and if there is no breakage at that stage, the number of bend endurance is indicated as ">10,000".

(Water permeability of hollow fiber membrane)
The water permeability of the hollow fiber membrane was measured as follows.

A hollow fiber membrane to be measured was subjected to wet treatment such as immersing it in a 50% by mass ethanol aqueous solution for 15 minutes and then washing it with pure water for 15 minutes. Using a hollow fiber membrane module with an effective length of 20 cm in which one end of the hollow fiber membrane subjected to the wet treatment is sealed, using pure water as raw water, filtration pressure is 0.1 MPa, and filtration is performed at a temperature of 25 ° C. to measure the permeation rate per hour. From the measured water permeation rate, the water permeation rate per unit membrane area, unit time, and unit pressure was converted to obtain the water permeation rate (L/m ² /h: LMH) at a transmembrane pressure difference of 0.1 MPa.

As a result, Table 9 shows the water permeation rate of the resulting hollow fiber membrane at a transmembrane pressure difference of 0.1 MPa.

(Removal of biopolymer)
The biopolymer removal rate was measured when the hollow fiber membrane was used in the biopolymer removal device shown in FIG. 100 hollow fiber membranes having an effective length of 1 m were used.

First, the concentration of the biopolymer contained in the water to be treated (raw water) and the filtrate (treated water) was determined by Liquid Chromatography-Organic Carbon Detection (LC-OCD: LC-OCD Model 18 manufactured by DOC-Labor Dr. Huber). was measured using Specifically, the raw water and treated water were filtered with a 0.45 μm membrane filter to remove suspended solids, and then the LC-OCD was measured using an autosampler. When the TOC exceeded 5 ppm, it was diluted with pure water, adjusted to 5 ppm or less, and then subjected to an autosampler. In addition, the analysis was performed using ChromCALC, which is attached software, and the concentration of the component with the shortest retention time detected around the retention time of 30 minutes was defined as the biopolymer concentration.

As a result, Table 9 shows the biopolymer concentration in the raw water and the biopolymer concentration in the treated water.

(Biopolymer removal rate)
The biopolymer removal rate was calculated based on the raw water biopolymer concentration (A) and the treated water biopolymer concentration (B) obtained as described above. That is, the biopolymer removal rate was calculated by (1−B/A)×100(%).

As a result, Table 9 shows the biopolymer removal rate.

(Washing)
(Differential pressure rise speed)
Using the hollow fiber membrane in the biopolymer removal device shown in FIG. It was measured. 100 hollow fiber membranes having an effective length of 1 m were used. Specifically, while physically cleaning the biopolymer removal device at a membrane filtration flux of 3.0 m ³ /m ² /d, every 30 filtration steps, using sulfuric acid adjusted to pH 3, Filtration was carried out with backwashing and acid washing at the same time. The rate of increase in differential pressure accompanying this operation was measured.

As a result, Table 9 shows the rate of increase in differential pressure.

(Continuous operation time)
In addition, a membrane module was prepared by bundling 100 PSF hollow fiber membranes (effective length 1 m) with a molecular weight cutoff of 13,000 for water treated using this biopolymer removal device, and the water was treated at 3.0 m ³ /m ² /d, and the time required for the water permeability of this UF membrane to decrease by 10% was measured.

As a result, Table 9 shows the time required for the water permeability of this UF membrane to decrease by 10%.

As can be seen from Table 9, using a hollow fiber membrane having a molecular weight cut off of 30,000 to 500,000 and a contact angle to water of 40 to 85°, this hollow fiber membrane was periodically washed by an acid washing section. In the case of a biopolymer removal apparatus that performs organic pickling (Examples 1 to 3), the biopolymer removal rate is higher than in the case of not doing so (Comparative Examples 1 to 3), and even if the operation is continued The differential pressure rise rate was low, and by supplying the obtained treated water to the membrane filtration device in the latter stage, the decrease in the water permeability of the membrane was suppressed.

In the biopolymer removal device according to Comparative Example 1, the molecular weight cut off of the hollow fiber membrane exceeds 500,000, the biopolymer removal rate is low, and the obtained treated water is supplied to the subsequent membrane filtration device. However, the decrease in water permeability of the membrane could not be sufficiently suppressed.

In addition, in the biopolymer removal devices according to Comparative Examples 2 and 3, the hydrophilicity of the hollow fiber membranes was insufficient, and even if the hollow fiber membranes were washed with acid, the washing was not sufficiently performed, and the differential pressure increase rate was was high.

1 biopolymer removal device 2 filtration device 3 pretreatment device 11 to 13, 41, 42 liquid feed pump 21 to 29, 51 to 59 opening and closing valve 31 hollow fiber membrane module 32 air compressor 33 chemical tank 34 backwash water tank 35 control device

Claims (10)

a hollow fiber membrane having a cutoff molecular weight of 30,000 to 500,000 and a contact angle to water of 40 to 85°;
A biopolymer removing device, comprising: an acid washing unit for periodically acid washing the hollow fiber membranes. The biopolymer removal device according to claim 1, wherein the hollow fiber membrane has a folding endurance of 10,000 times or more according to the MIT test method under the condition of a load of 200 g/ ^mm2 . 3. The hollow fiber membrane according to claim 1, wherein the ratio of the breaking strength after immersion in 5% by mass sulfuric acid at a constant temperature of 60° C. to the breaking strength before the immersion is 80% or more. Biopolymer removal device. The biopolymer removal device according to any one of claims 1 to 3, wherein the hollow fiber membrane contains a resin and a hydrophilic resin as main components. The biopolymer removal device according to any one of claims 1 to 4 , wherein the hollow fiber membrane contains polyvinylidene fluoride as a main component. The acid cleaning unit
a backwashing unit for backwashing by allowing a backwashing fluid to permeate from the filtrate side of the hollow fiber membrane to the treated water side;
an acid addition unit that adds an acid to the liquid that contacts the hollow fiber membrane during the backwash;
a gas supply unit for supplying a gas from the water-to-be-treated side of the hollow fiber membrane after the backwashing to rock the hollow fiber membrane;
The acid-adding section adds a The biopolymer removal device according to any one of claims 1 to 5 , wherein an acid is added. The acid cleaning unit
a backwashing unit for backwashing by allowing a backwashing fluid to permeate from the filtrate side of the hollow fiber membrane to the treated water side;
a gas supply unit for supplying gas from the water-to-be-treated side of the hollow fiber membranes after the backwashing to cause the hollow fiber membranes to oscillate;
an acid addition unit that adds an acid to the liquid that contacts the hollow fiber membrane when the gas is supplied;
The acid adding section adds a The biopolymer removal device according to any one of claims 1 to 5 , wherein an acid is added. The biopolymer removal device according to any one of claims 1 to 7 , wherein the biopolymer removal rate is 40 to 100%. The biopolymer removal device according to any one of claims 1 to 8 , which is used for pretreating water supplied to a membrane filtration device. The biopolymer removal device according to any one of claims 1 to 9 ;
A water treatment system comprising a membrane filtration device for membrane filtration of water treated by the biopolymer removal device.

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