JP2002166140A - Tubular filtration membrane for immersion type membrane filtration system - Google Patents

Abstract

(57) [Problem] To provide a tubular filtration membrane for a submerged membrane filtration system, in which cake components formed by depositing filtration components can be removed to extend the life. SOLUTION: The tubular filtration membrane 11 for the immersion type membrane filtration system comprises:
A filtration membrane layer 20 formed in a cylindrical shape, and a support membrane layer 21 disposed on the outer peripheral surface of the filtration membrane layer 20 and having liquid permeability for imparting shape retention to the filtration membrane layer 20 are provided. ,
The crushing pressure is set to at least 20 kPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtration membrane, and more particularly to a tubular filtration membrane used for a submerged membrane filtration system.

[0002]

2. Description of the Related Art A plurality of tubular support-microfiltration composite membranes (hereinafter, referred to as tubular filtration membranes) each having a microfiltration membrane disposed on the inner surface are bundled and housed in a cylindrical container, and bundled at both ends. A fixed membrane module (hereinafter, referred to as a tubular filtration membrane module) has been conventionally used in a cross-flow filtration system similar to ultrafiltration, as described in Japanese Patent Publication No. 56-35483. .

[0003] When a cake layer formed on the membrane surface has a relatively high filtration resistance and a liquid containing a filtration component is filtered, it is known that backwashing with a filtrate is effective as a method of extending the life. In order to recover the filtration performance, it is empirically necessary to backwash at a pressure higher than the filtration pressure. However, in conventional tubular filtration membrane modules that are not intended for backwashing, backwashing has never been attempted,
Further, according to the confirmation by the present inventors, the tubular filtration membrane cannot actually withstand a backwash pressure higher than the filtration pressure, and the tubular filtration membrane is crushed.

In recent years, a cross-flow filtration system using a buoyancy of air bubbles by immersing in a liquid to be treated (for example,
See 129094. This filtration system is commonly called an immersion membrane filtration system, and the membrane module used for this is commonly called an immersion membrane module. ) Has been used in various fields as an energy-saving precision filtration system for high-contamination liquids. In this field, hollow fiber membrane modules and flat membrane modules are exclusively used (see, for example, the Japan Environmental Improvement Education Center, a research report on the practical application of a small domestic wastewater treatment system incorporating a membrane treatment method, Heisei 1992). -1995 fiscal year)), for a tubular filtration membrane module, an application relating to a special utilization form in which a liquid to be treated is taken out of a storage tank and immersion-type membrane filtration is performed using piping and a membrane module having a special structure ( Japanese Patent Application Laid-Open Nos. 9-47639 and 9-99223), but there is no specific description about the tubular filtration membrane itself, as well as filtration characteristics compared with other membrane forms, and incorporation into a module. There is no description of the filtration characteristics as compared with other module forms at the time, and there is no report example actually used.

[0005] A method of using a microfiltration module for immersing in a liquid to be treated and filtering it by suction or head difference is also disclosed.
It has attracted attention as an energy-saving, low-cost filtration method that replaces the conventional sand filtration method. Also in this field, hollow fiber membrane modules and flat membrane modules are exclusively used.

Hereinafter, this filtration system and the above-mentioned immersion type membrane filtration system are both referred to as an immersion type membrane filtration system in this specification, and the membrane module used for this is referred to as an immersion type membrane module. The membrane filtration method is a method of filtering while naturally circulating the liquid to be treated using the buoyancy of air bubbles, and supplying and circulating the liquid to be treated to the membrane module using a mechanical circulating means such as a pump. Although it is clearly distinguished from the ultrafiltration method), the conventional tubular filtration membrane withstands the backwashing pressure, although the filtration pressure used in the immersion type membrane filtration method is at most about 20 kPa. Can not do.

On the other hand, the hollow fiber membrane module has a sufficiently high pressure to withstand backwashing, but has a large pressure loss in the hollow fiber membrane because a relatively thin hollow fiber membrane having an inner diameter of several hundred μm is used. Backwashing is not always effective. Exceptionally, there is a backwash method that uses the pressure resistance of the hollow fiber membrane to blow out air from the direction opposite to the filtration at a pressure of several hundred kPa or higher, which is higher than the bubble point. However, there is a problem that not only a special structure that can withstand this pressure is required but also energy consumption is large. Also, the flat membrane module does not originally have strength enough to withstand backwashing, and therefore requires extreme care when chemically cleaning the membrane by flowing a chemical from the direction opposite to the filtration.

[0008] Therefore, in particular, in the field of adopting the immersion type membrane filtration system, a membrane module which can save energy and can effectively use backwashing has not yet been developed.

Although a tubular filtration membrane having an inner diameter much larger than that of a hollow fiber membrane has the potential of effectively utilizing backwashing, as described above, a conventional tubular filtration membrane has a lower backwashing pressure. Not only can not withstand, when a large number of tubular filtration membranes tightly bundled into a large tubular filtration membrane module, the gap between the tubular filtration membranes is small, the filtration flow rate is large,
In fields that replace sand filtration, resistance to the filtrate cannot be ignored.

[0010] An object of the present invention is to provide a tubular filtration membrane for a submerged membrane filtration system capable of removing cake components formed by depositing filtration components and extending the life. Another object of the present invention is to realize a tubular filtration membrane for a submerged membrane filtration system that has a small resistance to a filtrate even when it is bundled in a large amount and densely.

[0011]

The filtration membrane of the present invention is a tubular filtration membrane used in a submerged membrane filtration system, and is disposed on a cylindrical filtration membrane layer and an outer peripheral surface of the filtration membrane layer. And a liquid-permeable support membrane layer for imparting shape retention to the filtration membrane layer, and a crushing pressure of at least 20 k
Pa is set.

[0012] The tubular filtration membrane further includes, for example, a liquid-permeable reinforcing layer disposed on the outer peripheral surface of the support membrane layer. The tubular filtration membrane has, for example, an inner diameter of 3-1.
It is set to 5 mm. Furthermore, this tubular filtration membrane has, for example, a ratio (A / B) of the wall thickness (A) to the outer diameter (B) of 0.5.
03 to 0.1 is set.

The support film layer and the reinforcing layer are formed using, for example, a polyester resin-based nonwoven fabric.

[0014] Further, in this tubular filtration membrane, for example, a projection having a height of 0.02 to 0.2 mm is partially formed on the outer peripheral surface. The projection is formed, for example, in a spiral shape around the axis of the filtration membrane layer.

Further, the filtration membrane layer used in the tubular filtration membrane is, for example, a layer made of a microfiltration membrane.

[0016]

The tubular filtration membrane for immersion type membrane filtration of the present invention is characterized in that when the liquid to be treated is passed from the inside to the outside of the cylindrically formed filtration membrane layer, the filtration contained in the liquid to be treated is separated. The components are captured by the filtration membrane layer, and the liquid to be treated from which the filtration components have been removed can be discharged to the outside from the support membrane layer side. By such a filtration step, a filter component is deposited on the inner peripheral surface of the filtration membrane layer to form a cake layer, and the cake layer applies a pressure from the outside to the inside of the tubular filtration membrane of the present invention. In addition, backwashing can remove from the filtration membrane layer. At this time, since the crushing pressure of the tubular filtration membrane of the present invention is set to at least 20 kPa, it can withstand the pressure applied at the time of backwashing, and can be used for the immersion-type membrane filtration system while maintaining its shape. .

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic configuration of a submerged membrane filtration apparatus employing a tubular filtration membrane for submerged membrane filtration according to the present invention. In the figure, an immersion type membrane filtration device 1 includes a tubular filtration membrane module 2 and a storage tank 3 capable of storing the tubular filtration membrane module 2 therein and capable of storing a liquid to be treated therein.
And an air supply device 4 arranged in the storage tank 3, and a bubble guide tube 5 for sending all bubbles generated from the air supply device 4 to the tubular filtration membrane module 2.

As shown in FIG. 2 (longitudinal sectional view of the tubular filtration membrane module 2), the tubular filtration membrane module 2 includes a cylindrical storage container 10 and a plurality of tubular filtration containers filled in the storage container 10. And a membrane 11 (an embodiment of a tubular filtration membrane for immersion membrane filtration according to the present invention). Storage container 10
Is a member made of, for example, a resin, and has a discharge port 12 for discharging the liquid to be treated (filtrate) after the filtration process on its side surface.
Are formed. In addition, on the inner peripheral surface of the storage container 10, a spacer 13 protrudes toward the center at upper and lower portions thereof. The spacer 13 is for providing a gap between the tubular filtration membrane 11 and the inner peripheral surface of the storage container 10. 2, the thickness of the tubular filtration membrane 11, the gap between the tubular filtration membranes 11, the gap between the tubular filtration membrane 11 and the inner peripheral surface of the storage container 10, and the like are emphasized for easy understanding.

The tubular filtration membrane 11 is an elongated cylindrical member as shown in FIG. 3, and is prevented from being in close contact with each other in the storage container 10 by a projection 22 described later (that is, provided with an interval therebetween). Many of them are densely filled in parallel with each other along the opening direction of the storage container 10. The upper end and the lower end of each of the tubular filtration membranes 11 are integrally held in the storage container 10 while maintaining the open state by the holding portions 10a formed using a resin material such as urethane resin. And fixed. As a result, both ends of the storage container 10 are liquid-tightly closed by the holding portions 10a. The details of the tubular filtration membrane 11 and the method of manufacturing the tubular filtration membrane module 2 will be further described later.

The storage tank 3 is formed in a container shape having an opening at the top. The tubular filtration membrane module 2 is arranged in such a storage tank 3 at an interval from the bottom surface of the storage tank 3 using a support (not shown). The outlet 12 of the tubular filtration membrane module 2 thus installed
Is connected to a discharge path 12a such as a hose, and the discharge path 12a is led to the outside of the storage tank 3.

The air supply device 4 is arranged below the tubular filtration membrane module 2, that is, near the bottom of the storage tank 3, and is an air ejection port for ejecting air bubbles toward the tubular filtration membrane module 2 ( (Not shown).

Next, the details of the tubular filtration membrane 11 will be described. The tubular filtration membrane 11 is formed in a cylindrical shape as shown in FIG. 3, and as shown in FIG. 4 (a cross-sectional end view taken along the line IV-IV in FIG. 3), in order from the inner peripheral surface to the outer peripheral surface. It has a two-layer structure including a filtration membrane layer 20 and a support membrane layer 21.

The type of the filtration membrane layer 20 can be appropriately selected according to the type of the filtration component to be removed from the liquid to be treated, and is not particularly limited. For example, it is necessary to remove fine particles such as microorganisms. If there is, a microfiltration membrane is used. The microfiltration membrane is defined as, for example, “a membrane used for separating fine particles and microorganisms of about 0.01 to several μm by filtration” in JIS K 3802. Here, a practical filtration pressure of 20 kPa or less is used. It is preferable to use a porous membrane that can be filtered and has many micropores having a pore size larger than 0.04 μm. Incidentally, the type of such a microfiltration membrane is not particularly limited, and various known types, for example, an organic polymer membrane such as a cellulose membrane or a polyolefin-based resin membrane can be used.

The support membrane layer 21 is for imparting shape retention to the above-mentioned filtration membrane layer 20 and for setting the filtration membrane layer 20 to a cylindrical shape. Various materials can be used for such a support membrane layer 21 as long as it is a porous material having liquid permeability. Usually, however, stiffness, excellent strength, excellent chemical resistance, and high heat resistance are used. It is preferable to use a nonwoven fabric made of a polypropylene resin or a polyester resin having properties and economy, and it is particularly preferable to use a nonwoven fabric made of a polyester resin.

As shown in FIG. 3, the tubular filtration membrane 11 is continuously formed in a spiral shape around the axis of the filtration membrane layer 20 on the outer peripheral surface, that is, the outer peripheral surface of the support membrane layer 21. It has a projection 22. The projections 22 prevent the tubular filtration membranes 11 from adhering to each other in the tubular filtration membrane module 2 and increase the fluidity of the liquid to be treated (filtrate) that has passed through the tubular filtration membrane 11 in the storage container 10. It is for.

For example, when the height of the projections 22 is set to 0.05 mm, the effective length of the tubular filtration membrane 11 is, for example, 70 c
m, between two adjacent tubular filtration membranes 11
An area of at least 0.005 × 70 = 0.35 cm ² is secured. Therefore, if a large number of such gaps exist between the tubular filtration membranes 11, the resistance to the flow of the filtrate in the storage container 10 will be significantly reduced, and the fluidity of the filtrate will be significantly increased.

Usually, the inner diameter (X in FIG. 4) of the tubular filtration membrane 11 as described above is preferably set to 3 to 15 mm, more preferably 5 to 10 mm. When the inner diameter is less than 3 mm, when filtering the liquid to be treated, in particular, the highly polluted liquid to be treated, the tubular filtration membrane 11 is likely to be clogged by various filtration components and impurities contained in the liquid to be treated. This may make it difficult to continue the filtration treatment stably for a long period of time. Conversely, when the inner diameter exceeds 15 mm, the number of tubular filtration membranes 11 that can be filled in the storage container 10 having a limited volume is reduced, and thus the filtration area per unit volume of the tubular filtration membrane module 2 is reduced. Becomes smaller. As a result, the filtration flow rate is reduced, and it may be difficult to perform an efficient filtration of the liquid to be treated.

The tubular filtration membrane 11 preferably has a ratio (A / B) of the thickness (A) to the outer diameter (B) of 0.03 to 0.1. The tubular filtration membrane 1 referred to here
1 is the thickness (height) of the protrusion 22 described above.
Contains. When this ratio is less than 0.03, when pressure is applied to the tubular filtration membrane 11 from the outside, the tubular filtration membrane 11 is easily crushed. As a result, the tubular filtration membrane 1 is removed in order to eliminate a cake layer composed of a filtration component and the like deposited on the inner peripheral surface of the tubular filtration membrane 11 in the process of filtering the liquid to be treated.
When pressure is applied from the outside to 1 to perform the backwashing operation, the tubular filtration membrane 11 is crushed, and it becomes substantially difficult to backwash the tubular filtration membrane 11. Conversely, this ratio is 0.
If the number exceeds 1, the number of the tubular filtration membranes 11 that can be filled in the storage container 10 having a limited capacity will be reduced, or the surface area of the filtration membrane layer 20 will be reduced. The filtration area per unit volume becomes smaller. As a result, the filtration flow rate is reduced, and it may be difficult to perform an efficient filtration of the liquid to be treated.

Since the above-mentioned tubular filtration membrane 11 has the above-described ratio between the wall thickness and the outer diameter, the crushing pressure is the upper limit of the filtration pressure normally set in the immersion type membrane filtration system. It can be set to 20 kPa or more, that is, at least 20 kPa. In addition, the "crush pressure" mentioned here means that when the pressure is applied from the outside (that is, the support membrane layer 21 side) of the tubular filtration membrane 11 to the inside, the tubular filtration membrane 11 starts to be crushed. Refers to pressure.

Incidentally, since the crushing pressure of the tubular filtration membrane 11 is proportional to the cube of the ratio of the wall thickness to the outer diameter (for example, Fujio Oguri, "Handbook of Mechanical Design Charts", 9-2, Kyoritsu Shuppan Co., Ltd. ), The larger the ratio is set, the larger the ratio becomes.

The crushing pressure of the tubular filtration membrane 11 is also proportional to the longitudinal elastic modulus of the tubular filtration membrane 11 (for example, see Fujio Oguri, Handbook of Mechanical Design Charts, 9-2, Kyoritsu Shuppan Co., Ltd.) As a method for setting the crushing pressure of the tubular filtration membrane 11 as described above, a method of setting the longitudinal elastic modulus of the tubular filtration membrane 11 to be large can be considered. However, in order to set the longitudinal elastic modulus to be large, as a fiber constituting the nonwoven fabric for the support film layer 21, a special polymer fiber having a higher strength than a polypropylene resin fiber or a polyester resin fiber is used, or It is necessary to make the nonwoven fabric more dense, which is not only disadvantageous in terms of economy, but also increases the resistance (pressure loss) to the flow of the filtrate. Therefore, for the tubular filtration membrane 11, in order to reduce the pressure loss of the liquid to be treated and to achieve the above-mentioned crushing pressure economically, the ratio between the wall thickness and the outer diameter is set in the above range. Preferably, a method is employed.

The height of the projection 22 is usually 0.02
It is preferably set to 0.2 mm. Protrusion 22
If the height is less than 0.02 mm, the tubular filtration membranes 11 tend to adhere to each other, and as a result, it may be difficult to increase the fluidity of the filtrate. On the other hand, if it exceeds 0.2 mm, the number of the tubular filtration membranes 11 that can be filled in the storage container 10 of the tubular filtration membrane module 2 will decrease, so that the filtration area per unit volume of the tubular filtration membrane module 2 will be reduced. Becomes smaller. As a result, the filtration flow rate is reduced, which may hinder efficient filtration of the liquid to be treated. Here, the height of the protrusion 22 refers to the amount of protrusion from the surface of the support film layer 21.

The height of the projections 22 can be appropriately selected according to the type of the liquid to be treated. For example, when the liquid to be treated has a relatively small filtration flow rate, such as activated sludge liquid, it is preferable to set the projection 22 to a low level from the viewpoint of securing a filtration area. On the other hand, when the liquid to be treated has a relatively large filtration flow rate, such as river water, the projections 22 are preferably set higher from the viewpoint of increasing the fluidity of the filtrate.

Next, an example of a method for manufacturing the above-mentioned tubular filtration membrane 11 will be described with reference to FIG. First, the support membrane layer 2
1. A long and strip-shaped (tape-shaped) composite membrane 23 in which the filtration membrane layer 20 is integrally laminated on 1 is prepared. Then, as shown in FIG. 5, the composite film 23 is spirally wound around a separately prepared columnar mandrel 24 while overlapping both end portions 23a in the width direction such that the support film layer 21 side is the front side. Put on. In this state, when the both end portions 23a which are superimposed on each other are adhered by an adhesive or an ultrasonic welding method, a target tubular filtration membrane 11 can be obtained. In addition, the manufacturing method of such a tubular filtration membrane 11 is described in, for example,
It is already known in US Pat.

In the manufacturing process of such a tubular filtration membrane 11, both ends 23a of the superposed composite membrane 23 form the spiral projection 22 described above. here,
By appropriately adjusting the degree of overlap and the bonding method of the composite film 23,
The height of the projection 22 can be set in the above range.

Next, a method for manufacturing the above-mentioned tubular filtration membrane module 2 will be described with reference to FIGS. First,
A number of tubular filtration membranes 11 are bundled to form a tubular filtration membrane group 11a. On the other hand, a storage container 10 is prepared, and as shown in FIG. 6, a tubular filtration membrane group 11a is inserted into the storage container 10 to combine the storage container 10 with the tubular filtration membrane group 11a.
0 is formed. In this combination 30, the tubular filtration membrane group 1
1a is set so that both ends protrude from both ends of the storage container 10. Both ends of the tubular filtration membrane 11 constituting the tubular filtration membrane group 11a are closed by, for example, heat sealing.

Next, as shown in FIG. 7, one end of the combination 30 is immersed in a mold 31 containing an uncured resin 31a such as an uncured urethane resin. Here, the uncured resin 31a is filled between the tubular filtration membranes 11 constituting the tubular filtration membrane group 11a, and reaches the inner peripheral surface of the storage container 10 uniformly. It will be completely closed. After the resin 31a is completely cured in this state, the mold 31 is removed and the combined body 30 is removed.
The same operation is carried out for the other end of. This allows
The tubular filtration membrane group 11 is held and fixed to the storage container 10.

Next, when the cured resin projecting from both ends of the storage container 10 and the tubular filtration membrane 11 are cut off, the remaining resin portion forms the holding portion 10a, and the intended tubular filtration membrane module 2 is obtained. Can be In this tubular filtration membrane module 2, both ends of the storage container 10, except for both end portions of each tubular filtration membrane 11, are cured resin, that is, the holding unit 1.
0a results in a liquid-tight closure.

As a material for forming the holding portion 10a, other thermosetting resins such as an epoxy resin or a hot melt adhesive, in addition to the urethane resin described above, can be used.

Next, with reference to FIG. 1, the operation of the above-mentioned tubular filtration membrane 11 will be explained while explaining the operation of filtering the liquid to be treated using the above-mentioned immersion type membrane filtration apparatus 1. First, a liquid to be treated containing a filtering component such as a microgel, a colloid component, or a microorganism is supplied and stored in the storage tank 3. The stored liquid to be treated is ejected from the air outlet of the air supply device 4 and is accompanied by air bubbles rising in the liquid to be treated, as shown by arrows in FIG. It passes through the inside of the film 11 from the lower side to the upper side. At this time, the liquid to be treated passes through the tubular filtration membrane 11 from the inside to the outside and is filtered, and the filtration component contained in the treatment liquid is collected by the filtration membrane layer 20 of the tubular filtration membrane 11, Removed from the liquid to be treated. The liquid to be treated (filtrate) from which the components to be filtered have been removed passes through the gap between the tubular filtration membranes 11 and passes through the outlet 1
2 and is continuously discharged to the outside via the discharge path 12a. By such a series of filtration treatments, the liquid to be treated in the storage tank 3 naturally circulates through the tubular filtration membrane module 2 from the lower side to the upper side as shown by arrows in FIG. .

In the above-described filtration process, the filtration components contained in the liquid to be treated are gradually deposited on the inner peripheral surface of the tubular filtration membrane 11, ie, the surface of the filtration membrane layer 20, to form a cake layer. Then, the filtration performance of the tubular filtration membrane 11 is reduced. In this case, the tubular filtration membrane 11 can remove the cake layer by the backwashing operation, and can recover the filtration performance.
More specifically, storage container 1 of tubular filtration membrane module 2
By increasing the pressure within 0, a pressure greater than the filtration pressure is applied from the outside to the inside of the tubular filtration membrane 11, whereby the cake layer can be eliminated. At this time, the tubular filtration membrane 11
Since the crushing pressure is set to at least 20 kPa as described above, the crushing pressure is not crushed by the pressing force during the backwashing operation, the shape is maintained even after the backwashing process, and the above It can be applied to the filtration process. Therefore, since the cake layer of the tubular filtration membrane 11 can be appropriately removed by the backwashing operation, the service life can be extended as compared with the conventional tubular filtration membrane.

Further, since the tubular filtration membrane 11 has the projections 22 on the outer peripheral surface as described above, it does not easily adhere to the adjacent tubular filtration membrane 11 in the tubular filtration membrane module 2, and the tubular filtration membrane 11 An effective gap for allowing the filtrate to flow can be formed therebetween. As a result, the tubular filtration membrane module 2 including the tubular filtration membrane 11 can increase the fluidity of the filtrate in the storage container 10,
The filtrate is easily discharged from the discharge port 12 without delay.

By the way, the above-mentioned tubular filtration membrane module 2
The membrane area A of a filtration membrane module in which a large number of tubular membranes such as the tubular filtration membrane 11 and the hollow fiber membrane according to the present embodiment are held and fixed at both ends of a cylindrical storage container, The inner diameter of the membrane is di, the number is N, the length of the storage container is L, and the length of the holding and fixing portion (corresponding to the total length of the upper and lower holding portions 10a in FIG. 2 in the vertical direction) is l. Then, it is given by the following equation (1).

[0044]

(Equation 1)

The maximum number of tubular membranes that can be stored in the storage container is as follows: the outer diameter of the tubular film is d ₀ , the cross-sectional area of the holding and fixing portion (the area of the cross section perpendicular to the axis of the storage container) is S,
When the filling rate is ε, it is given by the following equation (2).

[0046]

(Equation 2)

From the above, the membrane area per unit volume of the module, which is an index of the structural compactness of the filtration membrane module, is given by the following equation (3). Where δ
Is the thickness of the tubular membrane.

[0048]

(Equation 3)

When a hollow fiber membrane is used as the tubular membrane, the filling rate of the hollow fiber membrane in the storage container is usually at most 0 in order to prevent a large resistance to the flow of the filtrate. It is about 3. on the other hand,
Since the tubular filtration membrane according to the present embodiment has a larger tubular shape than the hollow fiber membrane and has a stronger stiffness, all the tubular filtration membranes are filled in a parallel bundle close to each other in the storage container. Can be. The filling rate at this time is about 0.9 in the closest packed state.

The following equation (4), which is obtained by multiplying the above equation (3) by the flux j which is the filtration flow rate per unit membrane area, shows the filtration flow rate per unit volume of the filtration membrane module. It is an index of compactness.

[0051]

(Equation 4)

Although there are differences depending on the structure of the filtration membrane module and the liquid to be treated, when the tubular filtration membrane according to the above-described embodiment is used, the filling factor is about 3 times that when the hollow fiber membrane is used.
In this case, the flux is about twice as large as that using a hollow fiber membrane due to a small pressure loss. On the other hand, the outer diameter of the tubular filtration membrane according to the above-described embodiment is 10 to 20 times that of the hollow fiber membrane. Therefore, the above equation (4)
4εj / d ₀ in the module using the tubular filtration membrane and the module using the hollow fiber membrane are almost the same, and the ratio between the wall thickness and the outer diameter of the tubular filtration membrane is substantially the same as that of the tubular filtration membrane module. Compactness is determined. The ratio between the wall thickness and the outer diameter of a commercially available hollow fiber membrane is larger than 0.1. Therefore, if the ratio between the wall thickness and the outer diameter of the tubular filtration membrane is 0.1 or less, the filtration flow rate per unit volume of the tubular filtration membrane module is superior to that of the module using the hollow fiber membrane. . Therefore, even when the tubular filtration membrane module using the tubular filtration membrane according to the above-described embodiment is configured to have the same size as the module using the hollow fiber membrane, the module using the hollow fiber membrane is used. Thus, the filtration flow rate per unit volume of the module can be increased. From such a viewpoint, the ratio between the wall thickness and the outer diameter of the tubular filtration membrane 11 is set to 0.1.
It is preferable to set it to 03 to 0.1.

[Other Embodiments] (1) In the above-described embodiment, the spiral projections 22 are provided on the outer peripheral surface of the tubular filtration membrane 11, but there are cases where such projections 22 are not provided. Also, the tubular filtration membrane of the present invention can be backwashed similarly to the tubular filtration membrane 11 according to the above-described embodiment.

In the above-described embodiment, the projections 22 are provided in a continuous spiral shape, but the shape of the projections 22 is not limited to this. That is, the protrusions 22 need only be partially provided on the outer peripheral surface of the support film layer 21, and may be provided in various forms such as intermittent spiral shapes and dot shapes.

(2) In the above-described embodiment, the tubular filtration membrane 11 is formed in a two-layer structure including the filtration membrane layer 20 and the support membrane layer 21. When the above-described required value is set by appropriately setting the ratio to the outer diameter, as shown in FIG. 8, a reinforcing layer 25 having more liquid permeability is arranged on the outer peripheral surface of the support film layer 21. Is also good.

The reinforcing layer 25 used here is not particularly limited as long as it has liquid permeability, but is usually the same nonwoven fabric as the one constituting the support film layer 21, especially a polyester resin-based nonwoven fabric. Non-woven fabric is preferably used. In addition, the tubular filtration membrane 11 provided with such a reinforcing layer 25 is
Usually, it can be manufactured by using a composite membrane in which a reinforcing layer 25 is further laminated on the support membrane layer 21 side of the composite membrane 23 used for manufacturing the tubular filtration membrane 11. In the case of manufacturing such a composite membrane, the reinforcing layer 25
Usually, it is preferable to bond the surface of the support film layer 21 with a hot melt adhesive or a thermosetting adhesive interspersed. By doing so, the composite membrane can suppress an increase in filtration resistance due to the reinforcing layer 25, and has the same filtration resistance as that of the tubular filtration membrane 11 according to the above-described embodiment, that is, a filter liquid having a high permeability. Can be achieved.

When the tubular filtration membrane 11 has such a reinforcing layer 25, the thickness and outer diameter of the tubular filtration membrane 11 are calculated including the reinforcing layer 25. When the projections 22 are formed on the surface of the tubular filtration membrane 11, the projections 22 need to be formed on the surface of the reinforcing layer 25.

[0058]

Comparative Example 1 14 parts by weight of heat-resistant polyvinyl chloride was dissolved in 56 parts by weight of tetrahydrofuran as a solvent, and 30 parts by weight of isopropyl alcohol was further added thereto. The synthetic resin solution obtained in this manner is coated with a porous material having a thickness of 0.1 mm.
After being impregnated into a 12 mm polyester resin-based nonwoven fabric, it was dried. As a result, a composite membrane having a thickness of 0.15 mm, in which a filtration membrane layer made of a polyvinyl chloride resin film having a large number of micropores having an average pore diameter of 0.4 μm and a support membrane layer made of a polyester resin nonwoven fabric are laminated. I got

The obtained composite membrane was cut into a tape having a width of 2 cm, and the composite membrane tape was spirally wound around a cylindrical mandrel so that both ends in the width direction were overlapped. Then, the overlapped portion is ultrasonically welded to a length of about 70c.
m, an inner diameter of 5 mm, and a ratio of the thickness to the outer diameter of 0.028, to produce a tubular filtration membrane having a smooth outer peripheral surface.

One end of the obtained tubular filtration membrane was sealed and sufficiently wet with water, and then the other end was connected to a vacuum pump. When the inside of the tubular filtration membrane was gradually decompressed while observing the appearance of the tubular filtration membrane, it was suddenly crushed at -17 kPa.

Further, a transparent plastic pipe having an inner diameter of 28 mm and a total length of 50 cm, having a filtrate outlet on the side face, was prepared as a storage container. And in this storage container,
The obtained 19 tubular filtration membranes were bundled and inserted, and the tubular filtration membranes were fixed at both ends of the storage container using urethane resin. Then, the tubular filtration membrane projecting from both ends of the storage container was cut to produce a tubular filtration membrane module.

The thus obtained tubular filtration membrane module was immersed in a water tank to filter water with a difference in head, and then taken out of the water tank. Then, a compressor was connected to the outlet of the storage container, and air was gradually supplied into the storage container while observing the appearance of the tubular filtration membrane.
At pressure a, all tubular filtration membranes collapsed.

Example 1 A hot-melt adhesive was interspersed on the nonwoven fabric side of the composite film prepared in Comparative Example 1, and the same nonwoven fabric as the nonwoven fabric was bonded and laminated as a reinforcing layer. The composite membrane thus obtained is formed in a tubular shape in the same manner as in Comparative Example 1, and has a reinforcing layer of a continuous spiral nonwoven fabric on the outer peripheral surface.
m, an inner diameter of 5 mm, a wall thickness of 0.3 mm, and a ratio of the wall thickness to the outer diameter of 0.054 was produced as a tubular filtration membrane. When the crushing pressure of this tubular filtration membrane was measured in the same manner as in Comparative Example 1, it was about 80 kPa.

Example 2 A tubular filtration membrane similar to that of Example 1 was produced except that the inner diameter was set to 7 mm and the ratio of the thickness to the outer diameter was set to 0.039.
When the crushing pressure of this tubular filtration membrane was measured in the same manner as in Comparative Example 1, it was about 30 kPa.

Example 3 Using the tubular filtration membrane obtained in Example 1, a tubular filtration membrane module having a membrane area of about 0.13 m ² was produced in the same manner as in Comparative Example 1. A plastic pipe having the same inner diameter as the storage container of the module was connected to the lower part of the tubular filtration membrane module as a bubble guide tube. And
This is immersed in the liquid to be treated, and bubbles are generated at a flow rate of 15 L / min per 1 m ^{2 of the} membrane area from a nozzle having a diameter of 4 mm arranged at a position 20 cm below the lower surface of the tubular filtration membrane module.
Filtration of the liquid to be treated was started at a pressure of a head difference of 60 cm (about 6 kPa).

As the liquid to be treated, a transparent aqueous solution having a carboxymethylcellulose concentration of 3,000 ppm was used. The viscosity of this aqueous solution was 7 mPa · s at 25 ° C., but the viscosity of the filtrate was about 1.3 mPa · s, so it is considered that the carboxymethyl cellulose was suspended in the state of a microgel in the liquid to be treated. .

In the above-described filtration step, the filtration flow rate was initially 30 mL / min, but gradually decreased to 17 mL / min after 2 hours, and thereafter became substantially constant. Three hours after the start of the filtration, the filtration was suspended, and only the bubbles were continuously sent for 10 minutes, and then the filtration was started again. Then, the initial filtration flow rate was restored to 20 mL / min, but after about 10 minutes, the initial filtration flow was again 17 mL / min. Down to

Next, a compressor was connected to the filtrate outlet (inner diameter 6 mm, length 1.5 m) of the tubular filtration membrane module, and an air pressure of 40 kPa was applied to the storage container. As a result, the tubular filtration membrane was backwashed using the filtrate collected in the outlet and the storage container. The time required for the backwash was about 20 seconds. After that, when the filtration was started again, the initial filtration flow rate was recovered to 27 mL / min, and 17 mL /
Minutes. From the above results, it can be seen that the tubular filtration membrane of this example can effectively remove the cake layer of carboxymethylcellulose deposited on the inner peripheral surface by performing the backwashing operation, and by appropriately repeating the backwashing. It can be seen that the life can be extended.

Example 4 In the manufacturing process of the tubular filtration membrane of Example 1, the energy at the time of ultrasonic welding was adjusted, and the height of the spiral projection by the welded portion was set to 0.1 mm. The ratio of wall thickness to outer diameter was 0.069). In addition, the composite membrane used in Comparative Example 1 was formed in a cylindrical shape, and the length and the inner diameter were set to be the same, and a smooth tubular filtration membrane having no protrusion on the surface (the ratio of the wall thickness to the outer diameter was 0.1 mm). 028).

A tubular filtration membrane module 2 as shown in FIG. 2 was manufactured using the obtained tubular filtration membrane with projections and the smooth filtration membrane. Here, in the storage container 10,
JIS K 6741-1975 Nominal -250 (Nominal pressure 500 kPa , An inner diameter of about 250 mm) was used, and a discharge port 12 was formed by welding a rigid polyvinyl chloride socket having a nominal size of -50 to the pipe. The total length of the module 2 is set to 28 cm, and the storage container 10
At the lower end of the flange 40, as shown in FIG.
Was attached. In addition, in the storage container 10, the thickness of the spacer 13 was set to 8 mm. The tubular filtration membrane was set so that the effective length was about 20 cm. further,
The number of filled tubular filtration membranes was set to 1,400 for the module 2 using the tubular filtration membrane with protrusions, and set to 1,500 for the module 2 using the smooth tubular filtration membrane. The filling factor of the tubular filtration membrane is 0.86 for each module 2. The effective membrane area is
About 4.4 in module 2 using a tubular filtration membrane with projections
m ² , about 4 for module 2 using a smooth tubular filtration membrane.
7 m ² .

Next, as shown in FIG. 9, an overflow port 41a is provided at the upper part, and
About 70 cm in diameter and about 150 c in height with 1b above
m water tank 41 was prepared. Then, the tubular filtration membrane module 2 was installed in the water tank 41, and a filtration flow rate measuring device was assembled. Here, a leg 42 having a height of about 10 cm was attached to the flange 40 of the tubular filtration membrane module 2, and the leg 42 was set so that the tubular module 2 did not directly contact the bottom surface of the water tank 41. Further, a hose 43 was connected to the discharge port 12, and one end of the hose 43 was disposed outside the water tank 41.

The water overflowing from the overflow port 41a is supplied into the water tank 41 through the supply line 41b while supplying tap water filtered with an ultrafiltration membrane having a molecular weight cut off of 30,000 as water to be treated at a rate of 10 L / min. And the filtrate from the hose 43 were collected in a bucket and set in the water tank 41 by a circulation pump. When the filtration flow rate was measured with the head difference P set to 60 cm, the flow rate was 30 L / min in the module 2 using the tubular filtration membrane with projections, while it was 24 L / min in the module 2 using the smooth tubular filtration membrane. Minutes. This indicates that the tubular filtration membrane having the projections can increase the filtration flow rate.

[0073]

According to the tubular filtration membrane for immersion type membrane filtration of the present invention, since the crushing pressure is set to at least 20 kPa, the cake layer formed by depositing the filtration component can be removed by back washing. Yes, it is possible to extend the life.

[Brief description of the drawings]

FIG. 1 is a schematic view of an immersion type membrane filtration device using a tubular filtration membrane for an immersion type membrane filtration system according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a tubular filtration membrane module used in the immersion type membrane filtration device.

FIG. 3 is a perspective view of the tubular filtration membrane for the immersion type membrane filtration system.

FIG. 4 is a cross-sectional end view taken along the line IV-IV of FIG. 3;

FIG. 5 is a view showing a manufacturing process of the tubular filtration membrane for the immersion type membrane filtration system.

FIG. 6 is a view showing one manufacturing process of the tubular filtration membrane module.

FIG. 7 is a view showing another manufacturing process of the tubular filtration membrane module.

FIG. 8 is a view corresponding to FIG. 4 of a tubular filtration membrane for a submerged membrane filtration system according to another embodiment.

FIG. 9 is a schematic diagram of a filtration flow rate measuring device used in Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Tubular filtration membrane 20 Filtration membrane layer 21 Support membrane layer 22 Projection 25 Reinforcement layer

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Naoki Murakami 2-3-1, Furube-cho, Takatsuki-shi, Osaka F-term in Yuasa Corporation (reference) 4D006 GA07 HA22 JA04A JB09 KC03 KC14 MA02 MA08 MA09 MA31 MA33 MB16 MC11 MC22 PB24 PB70

Claims (8)

[Claims] 1. A tubular filtration membrane used in a submerged membrane filtration system, comprising: a filtration membrane layer formed in a cylindrical shape; and a filtration membrane layer disposed on an outer peripheral surface of the filtration membrane layer. A tubular filtration membrane for a submerged membrane filtration system, comprising: a liquid-permeable support membrane layer for imparting shape retention; and a crush pressure set to at least 20 kPa. 2. The tubular filtration membrane for a submerged membrane filtration system according to claim 1, further comprising a liquid-permeable reinforcing layer disposed on an outer peripheral surface of the support membrane layer. 3. The tubular filtration membrane for a submerged membrane filtration system according to claim 1, wherein the inner diameter is set to 3 to 15 mm. 4. The ratio (A / B) between the thickness (A) and the outer diameter (B).
The tubular filtration membrane for a submerged membrane filtration system according to claim 1, wherein is set to 0.03 to 0.1. 5. The tubular filtration membrane for a submerged membrane filtration system according to claim 1, wherein the support membrane layer and the reinforcing layer are formed using a polyester resin-based nonwoven fabric. 6. The immersion type membrane filtration system tube according to claim 1, wherein projections having a height of 0.02 to 0.2 mm are partially formed on the outer peripheral surface. Filtration membrane. 7. The tubular filtration membrane for a submerged membrane filtration system according to claim 6, wherein the projection is formed in a spiral shape around the axis of the filtration membrane layer. 8. The tubular filtration membrane for a submerged membrane filtration system according to claim 1, wherein the filtration membrane layer is a layer made of a microfiltration membrane.