JP2002336854A - Immersion type membrane filtration apparatus for septic tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an immersion type membrane filtration apparatus which can be installed in a septic tank having a limited whose internal space volume and in which the liquid that is stored in the septic tank and treated by aerobic activated sludge can be filtered efficiently. SOLUTION: This immersion type membrane filtration apparatus 3 filters an aerobic activated sludge processed liquid in a septic tank 2 by the immersion type membrane filtration method, and is provided with a tubular filtration membrane module 4 arranged in the septic tank 2 so that a plurality of tubular filtration membranes are housed in a cylindrical housing vessel 10 having a filtrate discharging port 12 and each of the tubular filtration membranes is held by both ends and opened to the vertical direction an air jetting unit 6 arranged below the module 4 and supplying air bubbles toward the module 4, a filtrate discharging unit 8 for discharging the filtrate from the port 12 of the vessel 10 to the outside of the tank 2, and a backwashing unit 9 for making the filtrate in the unit 8 flow backward into the vessel 10 through the port 12 while pressurizing the filtrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an immersion type membrane filtration apparatus, and more particularly, to an immersion type filtration apparatus for filtering an aerobic activated sludge treatment liquid stored in a septic tank by an immersion type membrane filtration method to obtain a filtrate. It relates to a membrane filtration device.

[0002]

2. Description of the Related Art In recent years, a cross-flow filtration system in which a membrane module is immersed in a liquid to be treated and filtered while utilizing the buoyancy of air bubbles (for example, Japanese Patent Application Laid-Open No. 61-12909)
See No. 4 publication. Hereinafter, this filtration method is called an immersion type membrane filtration method, and the membrane module used for this is called an immersion type membrane module. In addition, the immersion type membrane filtration method is a method in which the liquid to be treated is naturally circulated by utilizing the buoyancy of air bubbles while the liquid to be treated is naturally circulated. It is clearly distinguished from the ultrafiltration method of supplying and circulating. ) 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). ~ Heisei 7
For the tubular filtration membrane module, an application concerning a special use form in which the liquid to be treated is taken out of the storage tank and immersion-type membrane filtration is performed using piping and a membrane module having a special structure (Japanese Patent Application Laid-Open No. Hei 9 (1997)). -47639 and JP-A-9-99223), but there is no description about the performance comparison with the hollow fiber membrane module or the flat membrane module, and no report examples actually used. Therefore, the properties of the tubular filtration membrane module itself are almost unknown.

[0003] The immersion type membrane filtration system has already been applied to various fields, but as an effective water purification means in Japan, as described in the above literature,
Over the years, public institutions have been actively pursuing research and development. In addition, public and private research institutes continue to make active presentations in conference presentations, such as the collection of lectures on sewerage research and the annual meeting of the Society for Water Environment.

[0004] About ten years have passed since the immersion type membrane filtration system was put into practical use, and there is a view that it has now been established as a reliable unit separation operation. In the meantime, although the management technology has advanced remarkably, As can be seen from the above-mentioned documents, there has been no significant progress in the cost, compactness, energy efficiency, etc. of membrane modules, especially in terms of hardware.
Further improvement is strongly desired. However, it is difficult to expect remarkable progress with respect to hollow fiber membrane modules and flat membrane modules that have been intensively researched and developed.

On the other hand, no particular attention has been paid to the application of the tubular filtration membrane module, which is almost unknown, to the immersion type membrane filtration system, and no publication has been made in the above-mentioned literatures. It is speculated by the present inventors that the difference in filtration performance with respect to the flat membrane module is not clear, and that many applications to which the immersion type membrane filtration method is applied involve a large amount of impurities. It is conceivable that the tubular filtration membrane itself was expected to be clogged by these for inclusion.

However, when scientifically inferring the characteristics of a tubular filtration membrane module, many advantages are found over hollow fiber membrane modules and flat membrane modules. For example: All air flow can be used to increase the cross flow parallel flow. 2. Since the passage between the bubble and the liquid to be treated is cylindrical, the mass transfer coefficient is larger than that of other module forms, and the flux (filtration flow rate per unit membrane area) is large in principle. 3. Since the film itself constitutes a passage between the bubble and the liquid to be treated, the module structure becomes compact. 4. Since the inner diameter is much larger than that of the hollow fiber membrane, the pressure loss is small and the backwashing effect is large. And so on. Nowadays, as the technology for effectively removing contaminants has progressed for a long time, the possibility of realizing these advantages is increasing.

However, in the tubular filtration membrane module, unlike other types of membrane modules, air bubbles pushed into one tubular filtration membrane cannot move to another tubular filtration membrane. Alternatively, in a tubular filtration membrane having a small flow rate, the filtration performance is reduced. Therefore, in order for the immersion type membrane filtration device using the tubular filtration membrane module to exhibit the above advantages, it is necessary to supply air bubbles to all the tubular filtration membranes as uniformly as possible.
However, the above-mentioned publications (JP-A-9-47639 and JP-A-9-99223) do not describe the importance of uniformly distributing bubbles in such a tubular filtration membrane module and how to realize it. It is not mentioned, and according to the drawing, there are even obstacles in the passage of the bubbles.

When the liquid to be treated is an activated sludge liquid from domestic wastewater, the water quality fluctuates greatly. When a large amount of the liquid to be treated suddenly flows in, the quality of the treated water is reduced and the liquid is separated from the bacterial cell flocks. It is generally difficult to efficiently carry out the filtration process using a submerged membrane filtration device because the clogging of the membrane is accelerated due to the secretion of high-molecular-weight microorganisms that occur (for example, Shinichiro Hamaya et al., 37th Sewer Research Conference Lectures, 7-90, 2000, etc.). In this connection,
In recent years, attempts have been made actively to improve the efficiency of immersion type membrane filtration by introducing microbial carriers into activated sludge so that the quality of the treated water does not easily decrease even when the liquid to be treated flows in abruptly. (Eg, Shoji Tadokoro, Monthly Domestic Wastewater, Feb. 1999, 28, 199)
9, and Kuniko Baba et al., The 37th Sewer Research Conference Lecture Book, 7-53, 2000), but the conventional immersion type membrane filtration device has not always been able to carry out efficient filtration treatment.

In Japan, millions of single septic tanks are used as domestic wastewater treatment facilities. However, since the single septic tank has a small capacity, water quality fluctuation and water quantity fluctuation are large, and purification capacity is high. It is said to be a source of pollution for rivers and lakes due to its low level. For this reason, it is necessary to replace a single septic tank with a merged septic tank with a large capacity or to improve the sewerage facilities, but since these require enormous costs and secure land, they are actually implemented. It is difficult. Therefore, it is socially beneficial if the purification capacity of the existing single septic tank can be increased to the level of the combined septic tank.

[0010] An object of the present invention is to provide a submerged membrane filter that can be disposed in a septic tank having a limited internal space volume and that can efficiently filter an aerobic activated sludge treatment liquid stored in the septic tank. It is to implement the device.

[0011]

The immersion type membrane filtration device for a septic tank according to the present invention is a method for filtering aerobic activated sludge treatment liquid stored in a septic tank by an immersion type membrane filtration method to obtain a filtrate. A plurality of tubular filtration membranes having a function of filtering an aerobic activated sludge treatment liquid on the inner surface thereof are housed in a cylindrical storage container having a filtrate outlet, and are held at both ends thereof. A tubular filtration membrane module arranged in a septic tank such that the filtration membrane is opened in the vertical direction, and an air ejection device arranged below the tubular filtration membrane module for supplying air bubbles to the tubular filtration membrane module. A filtrate discharge device that has a filtrate discharge path extending from the discharge port of the storage container and discharges the filtrate to the outside of the septic tank, and adds the filtrate in the filtrate discharge path to the storage container through the discharge port. Backflow while pressing And a backwashing device for.

Here, the tubular filtration membrane has, for example, a microfiltration membrane layer formed in a cylindrical shape, and a nonwoven fabric layer arranged on the outer peripheral surface of the microfiltration membrane layer. The tubular filtration membrane has, for example, an inner diameter of 3 to 15 mm.

The immersion type membrane filtration device for a septic tank is
For example, further comprising a packing layer, including a packing, disposed between the tubular filtration membrane module and the air ejection device, for guiding air bubbles from the air ejection device toward the tubular filtration membrane module while dispersing them. Have. In this case, the filler has, for example, an outer diameter of 5 to 50 mm and a length of 5 to 50 m.
m porous hollow cylinder. The hollow cylinder is, for example, a microorganism carrier.

Further, the backwashing device used in the immersion type membrane filtration device for a septic tank includes, for example, an air generating device and an air container for supplying air pressure from the air generating device to the filtrate in the filtrate discharging path. And an air supply device for adding air to the discharge port direction. This backwashing device
For example, the apparatus further includes a reverse flow rate setting device for setting the amount of the filtrate to be back-flowed into the storage container to at least 200 ml per 1 m ² of the membrane area of the tubular filtration membrane stored in the storage container.

Further, a filtrate discharge device used in the immersion type membrane filtration device for a septic tank includes, for example, a storage tank for storing a filtrate from a filtrate discharge path in the septic tank, and a storage tank for storing the filtrate outside the septic tank. And a pressurizing device for pressurizing the inside of the storage tank and sending out the filtrate stored in the storage tank to the final filtrate discharge path.

Further, the tubular filtration membrane module used in the immersion type membrane filtration device for a septic tank includes, for example, a cylindrical water collecting pipe having a liquid passage hole and an outer cylinder arranged at intervals on the outer periphery of the water collecting pipe. A tubular storage container provided with a plurality of tubular filtration membranes disposed between a water collecting pipe and an outer cylinder, each of which has a cylindrical shape and has an aerobic activated sludge treatment liquid filtering function on an inner surface. It has a filtration membrane group and holding portions provided at both ends of the storage container for holding both ends in the longitudinal direction of the tubular filtration membrane group, and the water collecting pipe has the above-mentioned outlet.

The septic tank is, for example, a single septic tank.

[0018]

FIG. 1 shows a schematic configuration of a domestic wastewater treatment system employing a immersion type membrane filtration device for a septic tank according to an embodiment of the present invention. In the figure, a domestic wastewater treatment system 1 mainly includes a septic tank 2 and a submerged membrane filtration device 3 (an embodiment of the present invention).

The septic tank 2 is a so-called five-person tank, which is a single septic tank (a household small-sized septic tank) whose production is currently prohibited by law. Is divided into The preliminary filtration tank 501 is provided with an inflow port 503 for general living wastewater and a manhole 504, and is supplied with anaerobic activated sludge for biologically purifying the general living wastewater. Therefore, the general wastewater is denitrified in the preliminary filtration tank 501. Further, in the preliminary filtration tank 501, a filter medium layer 505 for removing suspended matter contained in the general wastewater is disposed. A passage 506 connecting the preliminary filtration tank 501 and the aeration tank 502 is disposed near the filter medium layer 505, and the general wastewater that has been denitrified in the preliminary filtration tank 501 passes through the passage 506 through the aeration tank. It is set to be able to be supplied in 502. This aeration tank 5
In 02, aerobic activated sludge is introduced, and the general wastewater is biologically de-BOD-treated to become an aerobic activated sludge treatment liquid (hereinafter, referred to as a liquid to be treated). In addition, aeration tank 5
An air lift pump 507 is arranged from 02 to the preliminary filtration tank 501. This air lift pump 507
Removes the anaerobic activated sludge in the aeration tank 502 from the pre-filtration tank 50
1, and uses air from an air generator 509 described later as a pressure source. The aeration tank 502 is provided with a manhole 508.

The fluctuation of the water level of the general wastewater flowing into the septic tank 2 usually depends on L1 (lower limit) and L1 shown in FIG.
2 (upper limit). By the way, in many households equipped with such a septic tank 2, about 60 to 70% of the daily drainage is drained intensively during the period from dinner to when the bath is drained. If the water level does not drop sufficiently when such a large amount of wastewater is concentrated, the wastewater flowing from the inflow port 503 overflows from the manholes 504 and 508 in an almost untreated state. for that reason,
A float sensor (not shown) for notifying that the water level in the septic tank 2 has reached the upper limit (L2) is arranged.

The immersion type membrane filtration device 3 mainly includes an aeration tank 5
02, and mainly includes a tubular filtration membrane module 4, a support device 5, an air ejection device 6, a packing layer 7, a filtrate discharge device 8, and a backwash device 9.

As shown in FIG. 2 (longitudinal sectional view of the tubular filtration membrane module 4), the tubular filtration membrane module 4 includes a cylindrical storage container 10 and a tubular filtration membrane group 11 filled in the storage container 10. And the main. The storage container 10 is, for example, a member made of resin, and a discharge port 12 for discharging the liquid to be treated (filtrate) after the filtration treatment is formed on a side surface thereof. Further, on the inner peripheral surface of the storage container 10, a tubular filtration membrane group 11 and the storage container 1
Spacer 13 for providing a gap between the inner peripheral surface and the inner peripheral surface
Project toward the center.

The spacer 13 is set such that the inner peripheral surface side of the storage container 10 is thin and the center side of the storage container 10 is thick.
It is formed in a substantially wedge shape, and is shown in FIGS. 3 (a view corresponding to a cross section taken along the line III-III in FIG. 2 of the tubular filtration membrane module 4), FIGS. V
(V sectional view), the storage container 10 has a plurality of slits 13a formed at substantially equal intervals in the circumferential direction. The spacers 13 provided at the upper part and the lower part of the storage container 10 respectively correspond to the storage container 1.
The amount of protrusion from the inner peripheral surface of 0 is set to be the same.

Each of the spacers 13 is a spacer 1
The cross-sectional area inside the storage container 10 in a cross section perpendicular to the axial direction of the storage container 10 at the portion having the cross section 3 (a cross section at the center in the vertical direction of the spacer 13, that is, a cross section taken along the line aa in FIG. 3-10% of the cross-sectional area in the area corresponding to the shaded area)
It is preferable that the setting is made such that This ratio is 3
%, The inner peripheral surface of the storage container 10, in particular, the outlet 1
As a result, it is difficult to form a gap between the liquid 2 and the tubular filtration membrane group 11, and as a result, in the storage container 10, the fluidity of the liquid to be treated (filtrate) that has been filtered through the later-described tubular filtration membrane 11 a is reduced. And the filtration flow rate may decrease. On the other hand, when this ratio exceeds 10%, the ratio occupied by the tubular filtration membrane group 11 in the storage container 10 becomes small, so that the filtration efficiency of the liquid to be treated may decrease.

The tubular filtration membrane group 11 is a group including a large number of tubular filtration membranes 11a formed in an elongated cylindrical shape. Each of the tubular filtration membranes 11a is prevented from sticking to each other by a projection 22 described later. While closely (that is, while providing an interval), they are densely gathered parallel to each other along the opening direction of the storage container 10. The upper end portion and the lower end portion of such a tubular filtration membrane group 11 are formed in a storage container 10 while maintaining the open state of each tubular filtration membrane 11a by a holding portion 10a formed using a resin material such as urethane resin. It is held together and fixed to the body. As a result, both ends of the storage container 10 are liquid-tightly closed by the holding portions 10a.

The tubular filtration membrane 11a constituting the above-mentioned tubular filtration membrane group 11 is formed in a cylindrical shape as shown in FIG. 6, and as shown in FIG. 7 (a sectional view taken along the line VII-VII in FIG. 6). , The filtration membrane layer 20 in order from the inner peripheral surface side to the outer peripheral surface side.
And a support film 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. 6, the tubular filtration membrane 11a 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 11a from adhering to each other in the tubular filtration membrane group 11, and the liquid to be treated (filtrate) that has been filtered through each tubular filtration membrane 11a in the storage container 10. The purpose is to increase the fluidity of the product.

For example, when the height of the projection 22 is set to 0.05 mm, the effective length of the tubular filtration membrane 11a is, for example, 70 mm.
cm, an area of at least 0.005 × 70 = 0.35 cm ² is secured between two adjacent tubular filtration membranes 11a. Therefore, if a large number of such gaps exist in the tubular filtration membrane group 11, the storage container 1
Within zero, the resistance to the flow of the filtrate will be significantly reduced and the fluidity of the filtrate will be significantly increased.

The tubular filtration membrane 11a as described above is usually
The inner diameter (X in FIG. 7) 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 11a is formed by various filtration components and impurities contained in the liquid to be treated.
May be easily clogged, and it may be difficult to stably continue the filtration treatment for a long period of time. Conversely, when the inner diameter exceeds 15 mm, the number of the tubular filtration membranes 11a included in the tubular filtration membrane group 11 that can be filled in the storage container 10 having a limited volume is reduced, so that the tubular filtration membrane module is reduced. The filtration area (effective membrane area) per unit volume of No. 4 becomes small.
As a result, the filtration flow rate is reduced, so that it may be difficult to efficiently perform the filtration of the liquid to be treated while reducing the size of the tubular filtration membrane module 4.

It is preferable that the ratio (A / B) of the wall thickness (A) to the outer diameter (B) of the tubular filtration membrane 11a is set to 0.025 to 0.1, and 0.03 to 0.13. More preferably, it is set to 0.1. The wall thickness and the outer diameter of the tubular filtration membrane 11a include the thickness (height) of the projection 22 described above. When this ratio is less than 0.025, when pressure is applied to the tubular filtration membrane 11a from the outside, the tubular filtration membrane 11a is easily crushed. As a result, 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 11a in the filtration step of the liquid to be treated, backwashing is performed by applying pressure to the tubular filtration membrane 11a from the outside. When the operation is performed, the tubular filtration membrane 11a is crushed, and it becomes substantially difficult to backwash the tubular filtration membrane 11a. In order to achieve a pressure resistance of 20 kPa or more, it is preferable to set this ratio to 0.03 or more. On the other hand, when this ratio exceeds 0.1, the filtration area (effective membrane area) per unit volume of the tubular filtration membrane module 4 becomes small. As a result, the filtration flow rate is reduced, so that it may be difficult to efficiently perform the filtration of the liquid to be treated while reducing the size of the tubular filtration membrane module 4.

The above-mentioned tubular filtration membrane 11a has a high crushing pressure because the ratio between the wall thickness and the outer diameter is defined as described above. In particular, when this ratio is 0.03 or more, the tubular filtration membrane 1
The crushing pressure of 1a can be set to 20 kPa or more, which is the upper limit of the filtration pressure normally set in the immersion type membrane filtration method, that is, at least 20 kPa. Note that the “crush pressure” here refers to the time when the tubular filtration membrane 11a starts to be crushed when pressure is applied from the outside (that is, the support membrane layer 21 side) to the inside of the tubular filtration membrane 11a. Refers to pressure.

Incidentally, since the crushing pressure of the tubular filtration membrane 11a 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 height of the projection 22 is usually 0.02
It is preferably set to 0.2 mm. Protrusion 22
Is less than 0.02 mm, the tubular filtration membrane group 11
In this case, the tubular filtration membranes 11a 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, when it exceeds 0.2 mm, the tubular filtration membrane group 1
The number of the tubular filtration membranes 11a included in 1, that is, the number of the tubular filtration membranes 11a that can be filled in the storage container 10 of the tubular filtration membrane module 4 is reduced. Filter area becomes smaller. As a result, the filtration flow rate is reduced, so that it may be difficult to efficiently perform the filtration of the liquid to be treated while reducing the size of the tubular filtration membrane module 4. Here, the height of the protrusion 22 refers to the amount of protrusion from the surface of the support film layer 21.

Incidentally, since the liquid to be treated is an aerobic activated sludge treatment liquid having a relatively small filtration flow rate, the height of the projections 22 is preferably set to be low from the viewpoint of securing a filtration area. If the height of the projections 22 is within the above range, even if the tubular filtration membrane module 4 is large, having a membrane area of about 100 m ² , most of the liquid to be treated is subjected to the tubular filtration by the projections 22. The gap formed between the membranes 11a hardly becomes a large resistance to the flow of the filtrate.

Next, an example of a method for manufacturing the above-mentioned tubular filtration membrane 11a will be described with reference to FIG. First, an elongated strip-shaped (tape-shaped) composite membrane 23 in which the filtration membrane layer 20 is integrally laminated on the support membrane layer 21 is prepared. Then, as shown in FIG. 8, this composite film 23 is spirally wound on a separately prepared cylindrical mandrel 24 while overlapping both ends 23a in the width direction such that the support film layer 21 side is on the front side. Put on. In this state, when the both end portions 23a overlapped with each other by an adhesive or an ultrasonic welding method, a target tubular filtration membrane 11a can be obtained. In addition, the manufacturing method of such a tubular filtration membrane 11a is already known, for example, in Japanese Patent Publication No. 56-35483.

In the manufacturing process of such a tubular filtration membrane 11a, both ends 23a of the superposed composite membrane 23 are
The above-mentioned spiral projection 22 will be formed. Here, the height of the projections 22 can be set in the above range by appropriately adjusting the degree of overlap of the composite films 23 and the bonding method.

Next, a method for manufacturing the above-mentioned tubular filtration membrane module 4 will be described with reference to FIGS. The tubular filtration membrane module 4 requires a great deal of care in handling the flat membrane and the hollow fiber membrane, and is easily manufactured by a simpler process than a flat membrane module or a hollow fiber membrane module requiring many manufacturing steps. be able to. First, a number of tubular filtration membranes 11a are bundled to form a tubular filtration membrane group 11. Also, a storage container 10 is prepared, and as shown in FIG.
The tubular filtration membrane group 11 is inserted into the storage container 10 to form a combined body 30 of the storage container 10 and the tubular filtration membrane group 11. In this combination 30, both ends of the tubular filtration membrane group 11 are set to protrude from both ends of the storage container 10.
Further, both ends of the tubular filtration membrane 11a constituting the tubular filtration membrane group 11 are closed by, for example, heat sealing.

Next, as shown in FIG. 10, 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 11a constituting the tubular filtration membrane group 11, and the spacer 13
Through the slit 13a provided in the storage container 10 to uniformly reach the inner peripheral surface of the storage container 10, and the opening of the storage container 10 is completely closed. After the resin 31a is completely cured in this state, the mold 31 is removed and the combination 30
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 hardened resin projecting from both ends of the storage container 10 and the tubular filtration membrane 11a are cut off, the remaining resin portion forms the holding portion 10a, and the intended tubular filtration membrane module 4 is obtained. Can be In this tubular filtration membrane module 4, both ends of the storage container 10 are liquid-tightly closed by the cured resin, that is, the holding portion 10a, except for both ends of each tubular filtration membrane 11a. Since the spacer 13 of the storage container 10 is formed in a wedge shape as described above, the holding portion 10a is easily fixed strongly to the inner peripheral surface of the storage container 10, and the tubular filtration membrane group 11 is To be stably held and fixed.

As a material for forming the holding portion 10a, other thermosetting resin such as epoxy resin or hot melt adhesive can be used in addition to the urethane resin as described above. However, when the large tubular filtration membrane module 4 is manufactured, the amount of the resin material used needs to be set to a large amount. It is preferable to use a material that is slow and has a relatively small elastic modulus. In addition, the hot melt adhesive can be collected and reused from the material cut off in the above-described manufacturing process. Also in this point, the tubular filtration membrane module 4 is advantageous as compared with the hollow fiber membrane module in which the use of the hot melt adhesive is difficult due to the relatively high viscosity of the hot melt adhesive.

In FIG. 2 and the like relating to the tubular filtration membrane module 4, for convenience of understanding, the thickness of the tubular filtration membrane 11a,
The gap between the tubular filtration membranes 11a and the gap between the tubular filtration membrane 11a and the inner peripheral surface of the storage container 10 are emphasized. Also,
In order to make the drawing easier to understand, FIG.
The number of “a” is expressed as a small number, and FIG. 3 shows only a part of the tubular filtration membrane 11a.

The support device 5 is provided in the aeration tank 502
This is for supporting the tubular filtration membrane module 4 in an upright state, and mainly includes a guide tube 5a and support legs 5b as shown in FIG. The guide tube 5a is formed in a tubular shape having substantially the same shape as the storage container 10 of the tubular filtration membrane module 4, and has a flange portion 5c at a lower end portion. On the other hand, the support leg 5b is for supporting the guide cylinder 5a, and extends from the flange portion 5c to the bottom of the aeration tank 502. The tubular filtration membrane module 4 is configured such that the tubular filtration membrane 11a is opened in the vertical direction,
Is placed on top.

The air jetting device 6 supplies air for enhancing the activity of the aerobic activated sludge to the liquid to be treated in the aeration tank 502 and supplies air bubbles to the tubular filtration membrane module 4. And is horizontally arranged below the guide tube 5a as shown in FIG. As shown in FIG. 12 (a bottom view of the air ejection device 6, that is, a view taken in the direction of arrow XII in FIG. 11), the air ejection device 6 uses a cross-shaped or T-shaped joint 6c to connect a plurality of pipes 6a. It has a plurality of (seven in this example) air ejection holes 6d opening toward the bottom of the aeration tank 502 in a hexagonal lattice pattern state. As shown in FIG. 1, a first air supply path 511 extending from an air generator 509 such as an air compressor disposed outside the septic tank 2 and having a first solenoid valve 510 is connected to the air ejection device 6. ing. Each of the air ejection holes 6d is set so that the air supplied from the first air supply path 511 to the air ejection device 6 can be made into a foam (air bubble) and ejected into the liquid to be treated.

As shown in FIG. 11, the packing layer 7 is formed so that a space 512 is formed between the packing layer 7 and the tubular filtration membrane module 4 in the guide cylinder 5a of the support device 5 described above. It is arranged below. The thickness of the space 512 (D _{1 in} FIG. 11) is usually 5 to 20 cm.
Is preferably set to.

The filler layer 7 is composed of a pair of nets 513 and 513 horizontally arranged at intervals in the guide cylinder 5a, and a filler 514 filled between the nets 513 and 513.
And Each net-like body 513 is, for example, a wire mesh or a metal punching panel.
It is for holding within a. The filler 514 disperses the air bubbles ejected from the air ejection device 6, and
This is for capturing various impurities, particularly fibrous impurities, contained in the liquid to be treated. The type of the filler 514 is not particularly limited, and various types can be used depending on the characteristics of the liquid to be treated and the types of impurities contained in the liquid to be treated.

However, the filling 514 is set so that the air bubbles supplied from the air jetting device 6 are set to such a size that the function of filtering the liquid to be treated by the tubular filtration membrane module 4 can be sufficiently achieved. It is preferable that the liquid does not hinder the smooth circulation of the liquid to be treated in the aeration tank 502. As such a filler 514, usually,
What has a simple shape and a small bulk density, for example, various Raschig rings for gas-liquid contact or hollow cylindrical materials (pipe-like materials) are used. In addition, as a hollow cylindrical material, the outer diameter is 5-50 mm (preferably 5-15 mm) and the length is 5-50 mm (preferably 5-15 mm). It is preferable to use a porous body.

As such a hollow cylindrical material, various types are commercially available and can be used, but those having a function as a microorganism carrier may be used. Examples of the hollow cylindrical material having a function as a microbial carrier are described in, for example, "Biostage" (trade name of Tsutsunaka Sheet Waterproofing Co., Ltd.), Kuniko Baba et al., 37th Sewer Research Conference, 7-53, 2000. In addition, one having both an outer diameter and a length of about 10 mm can be mentioned.
In addition, two or more kinds of hollow cylindrical materials may be appropriately used in combination.

As will be described in detail later, the packing layer 7 controls the total flow rate of the air bubbles supplied from the air blowing device 6 to at least half of the tubular filtration membranes 11a included in the tubular filtration membrane module 4. The air bubbles are preferably set to be dispersible so that air bubbles of at least 30% of the average value of the air flow rate per one tubular filtration membrane 11a divided by the total number of the tubular filtration membranes 11a can be distributed. Such conditions usually include the inner diameter of the tubular filtration membrane 11a, the number of air bubble ejection holes 6d in the air ejection device 6, the size of the filler 514,
It can be achieved by appropriately setting or adjusting the characteristics (particularly, viscosity) of the liquid to be treated, the thickness of the filler layer 7, the thickness of the space 512, and the like. However, in the application of the immersion type membrane filtration device 3, the viscosity of the liquid to be treated is 1 to 50.
In consideration of the range of mPa · s, it is sufficient to consider fibrous substances as impurities contained in the liquid to be treated,
On the other hand, the total amount of air bubbles generated from the air ejection device 6 is realistically 5 to 15 l / min per 1 m ² of the membrane area of the tubular filtration membrane 11a. Is a sectional area 100c perpendicular to the axial direction of the guide cylinder 5a.
Since about 1 piece per m ² is practical, the thickness of the filling layer 7 (D _{2 in} FIG. 1) is usually adjusted by the filling 5
By setting the dimension (length) of the fourteen to five to fifty times, the above-described condition can be achieved.

The filtrate discharge device 8 is for discharging the liquid to be treated (filtrate) filtered in the tubular filtration membrane module 4 to the outside of the purification tank 2. As shown in FIG. The apparatus mainly includes a discharge path 515, a storage tank 516, and a final filtrate discharge path 517. The filtrate discharge path 515 includes a first discharge path 515 a extending from the discharge port 12 of the tubular filtration membrane module 4 and a second discharge path 51 connected to the first discharge path 515 a via a part of the backwashing device 9.
5b (see FIG. 11).

The storage tank 516 is for temporarily storing the filtrate from the filtrate discharge path 515. The storage tank 516 has a built-in float valve (not shown) at the bottom, and has a gas-liquid flow passage 518 extending from the upper part to the outside of the purification tank 2. The gas-liquid flow passage 518 is
The tip is open outside the septic tank 2, and
An atmosphere release valve 519 is provided outside the septic tank 2. A second discharge path 515b is connected to the gas-liquid flow path 518 at a height slightly lower than the upper end of the tubular filtration membrane module 4 in the aeration tank 502 (see FIG. 11). Outside the septic tank 2
A second air supply path 520 branched from the first air supply path 511 is connected to the storage tank 516 side of the atmosphere release valve 519. The second air supply path 520 is connected to the second solenoid valve 521
have. The second air supply passage 520 and the gas-liquid flow passage 518 communicating with the air generator 509 are provided with a storage tank 516.
A pressurizing device for pressurizing the inside is configured.

The final filtrate discharge path 517 is connected to the storage tank 51.
6 is connected to a float valve built in the bottom portion and extends outside the septic tank 2.

The backwashing device 9 is provided in the middle of the filtrate discharge path 515, that is, the first discharge path 515a and the second discharge path 515.
15b is provided with a fixed quantity float valve 40 (an example of a reverse flow rate setting device) provided between the fixed flow rate valve 15 and the fixed flow rate setting device 15b. Quantitative float valve 40
As shown in FIG. 13, the apparatus mainly includes a float valve portion 41 and a liquid amount setting pipe. Float valve part 41
Has a float receiver 43 and a float 44 as shown in FIG. The float receiver 43 is a cylindrical member in which a filtrate passage 43a is formed in the axial direction, and has a tapered portion 43b that expands outward at the upper end of the passage 43a. The lower end of the passage 43a is formed in a net shape having an opening 43c in the center.
On the other hand, the float 44 is formed in a spherical shape that can float in the filtrate and can close the passage 43a when it comes into contact with the above-mentioned tapered portion 43b, and has a polyester resin filament 45 extending downward. Have been. The filament 45 passes through the float receiver 4 through the opening 43c.
3 and has a floating stopper 46 at the lower end.

As shown in FIG. 13, the lower end of the float receiver 43 of the float valve section 41 is connected to the distal end of the first discharge path 515a of the filtrate discharge path 515 using a socket 47. The liquid amount setting pipe 42 is for adjusting the volume of the filtrate present in the fixed quantity float valve 40, is connected to the float valve section 41 using a socket 48, and is connected to the float valve section 41 using a socket 49. 2 discharge path 515b. As a result, the quantitative float valve 40 is connected to the air generator 509 through the gas-liquid flow passage 518 and the second air supply passage 520. Therefore, the second air supply passage 520 and the gas-liquid flow passage 518 constitute an air supply device for adding the air from the air generator 509 to the filtrate discharge passage 515.

In the immersion type membrane filtration device 3 as described above, the open-to-atmosphere valve 519 and the second solenoid valve 521 automatically open and close in conjunction with the opening and closing operation of the first solenoid valve 510 which operates according to a timer (not shown). It is set as follows. More specifically, when the first solenoid valve 510 is in the open state, the atmosphere release valve 519 is in the open state and the second solenoid valve 521 is in the open state.
Is closed, and when the first solenoid valve 510 is closed, the first solenoid valve 510 is set so that the atmosphere opening valve 519 is closed and the second solenoid valve 521 is opened.
The atmosphere release valve 519 and the second solenoid valve 521 are linked.

Each member constituting the immersion type membrane filtration device 3 including the tubular filtration membrane module 4 is set to have a maximum diameter smaller than the inner diameter of the manhole 508. It is set so that it can be stored inside.

Next, with reference to FIG. 1, a description will be given of the treatment of general wastewater by the above-mentioned domestic wastewater treatment system 1. The general wastewater flowing into the septic tank 2 from the inflow port 503 is stored in the preliminary filtration tank 501. This preliminary filtration tank 5
In 01, the general living wastewater is denitrified, and various impurities contained in the general living wastewater are removed from the preliminary filtration tank 50.
Settle to the bottom of 1. In addition, suspended matter contained in the general wastewater is removed when the suspended matter passes through the filter medium layer 505. The general wastewater pre-filtered in this way is
Move into the aeration tank 502 through the passage 506 and remove the BOD
It is processed to become a liquid to be treated.

In the immersion type membrane filtration device 3, when the first solenoid valve 510 is set to the open state, the air from the air generator 509 is supplied to the air ejection device 6 through the first air supply path 511. . The air supplied to the air ejection device 6 is ejected from the air ejection holes 6d as air bubbles,
The liquid to be treated stored in the aeration tank 502 is stirred. As a result, the aerobic activated sludge in the liquid to be treated is activated, and the liquid to be treated is purified by the aerobic activated sludge.

The air bubbles ejected from the air ejection holes 6d rise in the liquid to be treated while being guided by the guide cylinder 5a, and pass through the filling layer 7. At this time, the air bubbles flow inside and on the surface of the filler 514 and disperse while changing the direction one after another in the filler layer 7 together with the liquid to be treated. Then, the air bubbles that have passed through the filler layer 7 rise while meandering in the space 512 and while increasing the meandering range, and are substantially evenly distributed with respect to each of the tubular filtration membranes 11a included in the tubular filtration membrane module 4. Will be supplied.

The liquid to be treated stored in the aeration tank 502 is
Due to the buoyancy of the air bubbles supplied to the tubular filtration membrane module 4 as described above, as shown by arrows in FIG.
It passes through each tubular filtration membrane 11a from the lower side to the upper side. At this time, since the atmosphere release valve 519 is set to the open state, the liquid to be treated is the water level in the aeration tank 502 (range L1 to L2 in FIG. 1), the second discharge path 515b, and the gas-liquid flow path. 518 is passed through the tubular filtration membrane 11a from the inside to the outside due to the pressure (head difference P: FIG. 1 shows the head difference when the water level is L2) due to the difference from the height position of the connection portion with the filter 518. And, the filtration component contained in the liquid to be treated,
It is collected by the filtration membrane layer 20 of the tubular filtration membrane 11a and is removed from the liquid to be treated. The liquid to be treated (filtrate) from which the filtration component has been removed passes through the gap between the tubular filtration membranes 11a,
The first discharge path 5 of the filtrate discharge path 515 from the discharge port 12
It is discharged into 15a. The filtrate discharged into the first discharge path 515a passes through the quantitative float valve 40 and the second discharge path 515b, and is continuously stored in the storage tank 516 via the gas-liquid flow path 518.

At this time, in the fixed quantity float valve 40, the float 44 floats together with the floating stopper 46 by the filtrate passing therethrough to set the passage 43a in an open state, and the floating stopper 46 contacts the lower end of the passage 43a. Because they are in contact with each other, they are prevented from separating from the float receiver 43 by a certain distance or more.

By the above-mentioned filtration treatment, the aeration tank 50
The liquid to be treated in 2 passes through the tubular filtration membrane module 4 from the lower side to the upper side as shown by arrows in FIGS. 1 and 11 and naturally circulates. At this time, the tubular filtration membrane 1
1a has the projections 22 on the outer peripheral surface as described above, so that it hardly adheres to the adjacent tubular filtration membranes 11a in the tubular filtration membrane module 4 and allows the filtrate to flow between the tubular filtration membranes 11a. Effective gap can be formed. Therefore, the tubular filtration membrane module 4 provided with the tubular filtration membrane 11a can increase the fluidity of the filtrate in the storage container 10 and easily discharge the filtrate from the outlet 12 without any delay.

Various impurities such as fibrous substances (eg, lint and hair) contained in the liquid to be treated are captured by the filler 514 when the liquid to be treated passes through the filler layer 7. You. As a result, in the liquid to be treated flowing through the packing layer 7 toward the tubular filtration membrane module 4, impurities are effectively removed.
The tubular filtration membrane 11a hardly causes blockage due to clogging of impurities, and can stably filter the liquid to be treated.

In the above-described filtration process, when the timer is operated and the first solenoid valve 510 is closed, the air release valve 519 is closed and the second solenoid valve 521 is set to the open state in conjunction therewith. Is done. As a result, the air from the air generator 509 is pressed into the storage tank 516 via the second air supply path 520 and the gas-liquid flow path 518. Thereby, the inside of the storage tank 516 is pressurized, and the filtrate stored therein is pushed out into the final filtrate discharge path 517 through a float valve (not shown) by this air pressure, and is discharged to the outside of the purification tank 2. When the entire amount of the filtrate in the storage tank 516 is pushed into the final filtrate discharge path 517, the float valve in the storage tank 516 is closed, and the storage tank 5 is closed.
Reference numeral 16 is set to a state in which the filtrate can be stored again.

By the way, in the above-mentioned filtration step, the filtration components contained in the liquid to be treated are separated by the tubular filtration membrane 11.
The cake layer is gradually deposited on the inner peripheral surface of a, that is, the surface of the filtration membrane layer 20 to form a cake layer, thereby reducing the filtration performance of the tubular filtration membrane 11a. In this case, the cake filtration layer can be removed from the tubular filtration membrane 11a by the backwashing operation using the backwashing device 9 to recover the filtration performance. Such a backwash operation
It is carried out simultaneously with the step of draining the filtrate from the storage tank 516 as described above. Specifically, in the filtrate drainage step as described above, the second
Part of the air supplied into the gas-liquid flow path 518 through the air supply path 520 flows through the second discharge path 515b and reaches the fixed quantity float valve 40 of the backwashing device 9. The air that has reached the fixed quantity float valve 40 applies air pressure in the direction of the outlet 12 to the filtrate in the fixed quantity float valve 40, and pushes out the filtrate in the direction of the first discharge path 515a. As a result, the filtrate in the second discharge path 515b, the fixed amount float valve 40, and the first discharge path 515a flows back from the discharge port 12 into the tubular filtration membrane module 4, and the second discharge path 5
It passes through each tubular filtration membrane 11a from the outside to the inside at a pressure corresponding to the air pressure of the air supplied into 15b. As a result, the deposited layer (cake layer) of the filtration component deposited on the inner peripheral surface of each tubular filtration membrane 11a is removed and washed.

In the above-described backwashing step, when the filtrate in the liquid amount setting pipe 42 is pushed out of the fixed amount float valve 40, the float 44 is moved by its own weight to the float receiver 4.
No. 3 abuts against the tapered portion 43b to close the passage 43a. Therefore, the tubular filtration membrane module 4
The amount of the filtrate flowing back into the inside is substantially the same as the quantitative float valve 4.
It is limited to the amount defined by 0 and the volume of the first discharge path 515a. Therefore, the amount of the filtrate used for backwashing can be arbitrarily set by adjusting the volume of the quantitative float valve 40, particularly the volume of the liquid amount setting pipe 42.

In the above-described backwashing step, the air pressure of the air supplied into the second discharge path 515b is set to at least the above-mentioned filtration pressure based on the head difference P, that is, the above-mentioned filtration pressure based on the head difference P. It is preferable to set. When the air pressure is lower than the filtration pressure, the cleaning of the tubular filtration membrane 11a may be insufficient, and the filtration performance of the tubular filtration membrane 11a may not be easily recovered.

Incidentally, the tubular filtration membrane 11a has a high crushing pressure as described above (for example, at least a crushing pressure of 2).
(Because it is set to 0 kPa), it is not crushed by the pressing force at the time of the above-mentioned backwashing operation, the shape is maintained even after the backwashing process, and it is continuously applied to the above-mentioned filtration step. be able to. That is, the immersion type membrane filtration device 3 can continue the filtration treatment after the backwashing step as described above.

After completion of the above-mentioned drainage step and backwashing step,
When the timer operates and the first solenoid valve 510 is opened, the air release valve 519 is set to the open state and the second solenoid valve 521 is set to the closed state in conjunction with the operation. Thereby, in the domestic wastewater treatment system 1, the above-described filtration step is performed again. Therefore, in the domestic wastewater treatment system 1, the filtration step and the drainage step are repeatedly performed, and in the drainage step, the backwashing of the tubular filtration membrane 11a is simultaneously performed. Even if it does not, the tubular filtration membrane 11
The filtration performance a, in particular, the high flux characteristics can be maintained satisfactorily for a long time, and the filtration of the liquid to be treated can be efficiently continued for a long period of time.

The immersion type membrane filtration device 3 uses the air generation device 509 as an air generation source for the air jetting device 6, the filtrate discharge device 8 and the backwashing device 9, so that the overall configuration is small. In addition, the filtration step, the drainage step, and the backwashing step can be performed economically.

In the above-mentioned filtration step, the inflow port 5
When the water level of the liquid to be treated in the septic tank 2 reaches near the lower limit (L1) in FIG. 1, the water head difference P decreases and the immersion type membrane filtration device 3 The filtration process will automatically stop.

Incidentally, the above-mentioned domestic wastewater treatment system 1
When the dimensional conditions and operating conditions of each part are set as follows, an average of about 0.9 L / min (about 1,300
The filtration flow rate of L), that is, the filtration capacity, can be achieved in the immersion type membrane filtration device 3. Regarding the septic tank 2 A capacity between the lower limit (L1 in FIG. 1) and the upper limit (L2 in FIG. 1) of the water level: 350 L. ◎ Regarding the tubular filtration membrane module 4 Storage container 10: Nominal length of 36 cm -300-hard vinyl chloride pipe (JIS K6741-1975 thickness =
9.2 mm, approximate inner diameter = 298 mm, nominal pressure = 500
kPa, weight per meter = 14 kg). Discharge port 12: Nominal 13-Uses a socket with hard vinyl chloride screws. The thickness of the spacer 13: 9.2 mm. Tubular filtration membrane 11a: Nominal pore size of filtration membrane layer 20 = 0.4μ
m, inner diameter = 7 mm, outer diameter = 7.7 mm. The number of filled tubular filtration membranes 11a: 1100. Length of each holding part 10a: about 3 cm. Effective membrane area of the tubular filtration membrane module 4: about 7 m ² . Height from the bottom of the aeration tank 502 to the upper end of the tubular filtration membrane module 4: 75 cm. Regarding the filling layer 7 The thickness of the filling layer 7 (D _{2 in} FIG. 11): about 15 cm. Knitted body 513: Thickness 1 with many holes of 5 mm in diameter
mm stainless steel perforated panel. Filler 514: outer diameter 8 mm, length 10 mm, thickness 1.5
mm polypropylene hollow cylindrical foam. Usage (volume) of the filling 514: about 2% of the volume of the aeration tank 502. The thickness of the space 512 (D _{1 in} FIG. 11): about 10 cm. Distance from the bottom surface of the filler layer 7 to the bottom of the guide cylinder 5a (D _{3 in} FIG. 11): 5 cm. Height from the bottom of aeration tank 502 to the bottom of packing layer 7:
About 15cm. ◎ About the air blowing device 6 Pipe 6a: Nominal 13-Use a rigid vinyl chloride tube. Diameter of air ejection hole 6d: 5 mm. The interval between the air ejection holes 6d: about 9.5 cm. The position of the air outlet 6d: about 5c from the bottom of the aeration tank 502
m above. ◎ Filtrate discharge device 8 Storage tank 516: A stainless steel pipe with a nominal diameter of 200 is used. Storage tank 516 capacity: about 20L. ◎ About backwashing device 9 Amount of filtrate for backwashing per one time flowing backward from the quantitative float valve 40: about 2 L ◎ About air generating device 509 Discharge pressure: 20 to 40 kPa. Discharge rate: 70 to 100 L / min. Power consumption: 80-100W. ◎ About operation conditions of immersion type membrane filtration device 3 Filtration process 18 minutes-repetition operation of backwashing and draining process 2 minutes.

As will be described later, the tubular filtration membrane module 4 used in the above-mentioned immersion type membrane filtration device 3 has a larger filtration flow rate, particularly a higher flux, than the conventional flat membrane module and hollow fiber membrane module. It can be configured smaller than a hollow fiber membrane module.
Therefore, the immersion type membrane filtration device 3 can be incorporated into a small septic tank such as a single septic tank, and the above-mentioned domestic wastewater treatment system 1 can be easily realized using an existing single septic tank. That is, when this immersion type membrane filtration device 3 is incorporated into an existing single septic tank, its purification ability can be increased to the level of a combined septic tank. In addition, since the tubular filtration membrane module 4 has a large flux as described above, a required filtration flow rate can be ensured even when the head difference P is small.

Since the tubular filtration membrane module 4 has a simpler structure than a conventional membrane module, it can be used, for example, by periodically turning it upside down. By doing so, it is possible to avoid that impurities passing through the packing layer 7 block the lower end portion of the tubular filtration membrane 11a,
The tubular filtration membrane module 4 can be used stably for a longer period.

Next, the compactness and economical efficiency of the above-mentioned tubular filtration membrane module 4 will be explained while comparing the conventional filtration membrane module with the conventional filtration membrane module. The relationship between the distribution state of the supplied air bubbles and the filtration characteristics will also be described. Further, effective backwash conditions of the tubular filtration membrane module 4 by the backwash device 9 will be described.

Analytical analysis of the characteristics of the tubular filtration membrane module
Measurement research report on the practical use of conventional small domestic wastewater treatment system was introduced the "film processing method described in the Japan Environment Improvement Education Center issue cited in the technology: 1992 -
As seen in the 1995 edition, the flux is greater for flat membrane modules than for hollow fiber membrane modules. For this reason, a module using a flat membrane as a conventional module was compared for analysis.

For reference, an outline of a module using a flat membrane (hereinafter, referred to as a flat membrane module) will be described with reference to FIG. In the figure, a flat membrane module 50 mainly includes a storage container 51 and a number of membrane plates 52 arranged in the storage container 51. The storage container 51 is, for example, a rectangular tubular member whose upper and lower parts are open. On the other hand, as shown in FIG. 16, the membrane plate 52 has a rectangular frame 53 and a gap 5 in the frame 53.
4a is provided mainly with a pair of filtration membranes 54, 54 facing each other. This filtration membrane is, for example, a microfiltration membrane. An outlet 53a for the filtrate is formed in the upper part of the frame 53 so as to communicate with the gap 54a. Each membrane plate 52
Is normally connected to a discharge pipe 55 as shown in FIG. The outline of the flat membrane module is described in, for example, Research Committee for Advanced Treatment Septic Tanks Using Membrane Separation Technology, etc., Ministry of Construction, “Water and Wastewater” Vol. 40, N
o. 3, 45 (1998).

When immersion type membrane filtration is carried out using such a flat membrane module 50, the membrane plate 5 is put together with air bubbles.
The liquid to be treated flowing between the two flows from the outside to the inside of the filtration membrane 54 and is filtered. Then, the filtrate at that time passes through the gap 5
4a, and is discharged into the discharge pipe 55 via the discharge port 53a.

Table 1 summarizes the main characteristics of the tubular filtration membrane module 4 used in the present embodiment and the flat membrane module 50 as described above. Here, in order to prevent unnecessary complexity, the length L of the membrane is common to both modules. For the same reason, the installation area of the module indicates the thickness of the storage container 10 for the tubular filtration membrane module 4 and the area occupied by the membrane portion excluding the frame 53 for the flat membrane module 50.

[0081]

[Table 1]

The viscosity of most of the actual liquids (liquids to be treated) to which the immersion type membrane filtration method is applied is several mPa · s or more, and both the flat membrane module 50 and the tubular filtration membrane module 4 The flow of the liquid to be treated can be regarded as laminar flow. In cross-flow filtration in which the parallel flow is laminar, the filtration flow rate of the tubular filtration membrane module 4 with respect to the flat membrane module 50 is represented by the following equation (1) (for example,
Nakagaki, Shimizu, "Film Processing Technology Dai-kei", Vol. 1-Chapter 3, Fuji Techno System Co., Ltd. (1991)).

[0083]

(Equation 1)

Where J, M and u are the filtration flow rate, the membrane area and the linear velocity of the parallel flow, respectively.
And P indicate values of the tubular filtration membrane module 4 and the flat membrane module 50, respectively. Parallel flow is assumed to consist of a mixture of bubbles and liquid, but moving at the same speed. d is the distance between the membrane plate 52 of the flat membrane module 50, also, I d _i is the tubular filtration membrane module 4
2 shows the inner diameter of the tubular filtration membrane 11a.

Here, the indices a and c are 1/3 for both laminar flows. Therefore, substituting these values gives
The following equation (2) is obtained.

[0086]

(Equation 2)

Here, in the tubular filtration membrane module 4, all the tubular filtration membranes 11 a and the flat membrane module 5
At 0, assuming that the bubbles are evenly distributed between all the membrane plates 52, the linear velocities of the parallel flows in each module are expressed by the following equations (3) and (4), respectively.
Is led.

[0088]

(Equation 3)

Here, q _a is the air flow rate per one flow path, and the air flow rate per one tubular filtration membrane 11a in the tubular filtration membrane module 4 and the air flow rate per one tubular filtration membrane 11a in the tubular filtration membrane module 50. It means the flow rate of air per interval of one membrane plate 52 having a width w. Therefore, u
_a is the converted linear velocity. ρ _f and μ _f are the density and viscosity of the liquid to be treated, respectively. σ is a dimensionless pressure loss coefficient, which is 32 for the tubular filtration membrane module 4 and 12 for the flat membrane module 50. g is the gravitational acceleration.

The converted linear velocity is the air flow rate per unit film area,
Alternatively, the total air flow rate per module can be converted as shown in Table 2 below using numerical values representing the shape of each module.

[0091]

[Table 2]

From Tables 1 and 2, the linear velocity ratio between the tubular filtration membrane module 4 and the flat membrane module 50 is expressed by the following equation (5).

[0093]

(Equation 4)

Using the equations (2) and (5), the capabilities of the tubular filtration membrane module 4 and the flat membrane module 50 can be compared from various viewpoints. However, to simplify without losing reality, Then, the density ρ _f of the liquid to be treated is set to 1,000 kg / m ³ and the length L of the film is set to 1 m as conditions common to both modules. For the flat membrane module 50, the thickness t of the membrane plate 52 is set to 5 mm, and for the tubular filtration membrane module 4, the ratio (d ₀ ) between the outer diameter (d ₀ ) and the inner diameter (d _i ) of the tubular filtration membrane 11a is set. ₀ / d _i) 1.2,
Filling ratio ε 0.8 (approximately 0.9 in the closest packed state)
Set to each. The air flow rate is 1 unit per unit membrane area which is used as a standard in the flat membrane module 50.
5 L / min / m ² is used as a comparison standard.

[0095] Table 3 The following, a viscosity mu _f of the liquid to be treated 10m
When set to Pa · s, membrane plate 52 spacing d and the tubular filtration membrane 11a of the inner diameter d _i and the same west also,
The calculation results when the total membrane area and the total air flow rate are the same for both modules are shown.

[0096]

[Table 3]

[0097] Further, Table 4 The following shows the calculation results of changing only the viscosity mu _f of the liquid to be treated 100 mPa · s under the same conditions.

[0098]

[Table 4]

As shown in Tables 3 and 4, with respect to the liquid to be treated in a wide viscosity range, the tubular filtration membrane module 4 has a filtration flow rate of about half the installation area of the flat membrane module 50. Is larger than the flat membrane module 50.

As another example, the viscosity μ _{f of the} liquid to be treated is
The when set to 10 mPa · s, membrane plate 52 spacing d and the tubular filtration membrane 11a of the inner diameter d _i and the same west also, for both modules, calculated in the case of a module footprint and the total air flow to the same Table 5 shows the results.

[0101]

[Table 5]

Table 5 shows that, for the same module installation area and the same total air flow rate, the tubular filtration membrane module 4 has a filtration flow rate more than twice that of the flat membrane module 50. Further, Tables 3 to 5 show that the flux obtained by dividing the filtration flow rate by the membrane area is large, and that the tubular filtration membrane module 4 is superior in principle to the flat membrane module 50.

As is clear from the above analysis examples, if air bubbles are evenly distributed to all the tubular filtration membranes 11a, the tubular filtration membrane module 4
It can be said that it has excellent performance in principle compared to the hollow fiber membrane module. Therefore, next, the validity of these analysis results is verified using a model liquid.

Test method for verifying the validity of analysis results
The following tests were examined to verify the validity of the analysis results above the method . The details of the test method and the results will be described later, but here, the logical background of the test method for verifying the validity of the analysis result will be described.

When a specific actual liquid (liquid to be treated) is used, a specific result reflecting the specific properties is inevitably derived, and the general characteristics of the tubular filtration membrane module 4 may not always be revealed. . On the other hand, in principle and scientific evaluation methods using model liquids controlled to a certain characteristic, there is concern about separation from the actual liquid, but dissolved components are irreversibly adsorbed on the membrane, As long as the cake layer formed by the deposition of the filtration component on the film does not exhibit peculiar behavior, and if the basic hydrodynamic properties of the actual liquid can be approximated as a Newtonian fluid like the model liquid, The results obtained here are considered to be essentially the same for actual liquids, even if it is necessary to add special measures for each type of actual liquid.

The present inventors set the following requirements as properties to be possessed by the model liquid. 1. Clear characteristics and easy measurement. 2. The characteristics do not change within the time required for the test. 3. It must be readily available and can be re-tested by a third party. 4. Not exhibit specific chemisorption on the membrane. 5. It is difficult to filter.

A suspension of latex or clay mineral that has been widely used as an evaluation solution for microfiltration membranes for a long time is required.
Does not satisfy As a result of examining various liquids other than these, the present inventors have found that an aqueous suspension of carboxymethylcellulose almost satisfies all the requirements of 1 to 5.

Carboxymethylcellulose is considered to be a typical water-soluble polymer, and its aqueous solution is transparent.
When the filtration is carried out at a constant speed with a microfiltration membrane, the filtration pressure increases immediately. Further, since the viscosity of the filtrate is close to that of water, it is considered that carboxymethyl cellulose in the aqueous solution is not dissolved in water in a molecular state but is suspended in water in a state of a microgel.

It is known that when activated sludge is filtered by a submerged membrane filtration method, the filtration resistance is increased. The cause is not a sludge but a secreted water-soluble macromolecular substance. (For example, Shinichiro Hamatani et al., The 37th Annual Meeting of the Japan Sewage Works Conference, 7-90, 2000), it is suggested that a fine aqueous gel suspension of carboxymethylcellulose is suitable. It is considered to have the quality as a filtration model liquid.

When it is desired to greatly change the viscosity of the aqueous carboxymethylcellulose suspension, polyethylene oxide having a relatively high molecular weight is added. Unlike carboxymethylcellulose, polyethylene oxide is almost completely dissolved in water in a molecular state, and the viscosity of a solution obtained by filtering an aqueous solution thereof through a microfiltration membrane is not different from that of the original aqueous solution. Therefore, it is considered that the use of an aqueous suspension of carboxymethylcellulose or a liquid whose viscosity has been adjusted by adding polyethylene oxide thereto can objectively verify the above-described analysis prediction without losing generality. Therefore, in this test, an aqueous suspension of carboxymethylcellulose was used as a model liquid (test liquid).

Verification Test of Validity of Analysis Result Next, in order to verify the validity of the analysis result, the result of verifying the analysis prediction with the model liquid will be described.

First, 14 parts by weight of a heat-resistant polyvinyl chloride resin 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 thus obtained was impregnated into a 0.12 mm thick polyester resin-based nonwoven fabric, which was a porous body, and then dried. As a result, 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-based nonwoven fabric were laminated, and the thickness was 0.15 m.
m composite membrane was obtained. Further, a hot melt adhesive was scattered on the support film layer side of the composite film, and a polyester resin nonwoven fabric having a thickness of 0.15 mm was further laminated as a reinforcing layer.
A reinforced composite membrane was manufactured separately.

The obtained reinforced composite film was cut into a tape having a width of 2 cm, and the reinforced composite film tape was overlapped at both ends in the width direction as described above, and the reinforcing layer side was turned to the front side. As described above, spiral winding was performed on a cylindrical mandrel so that a spiral projection was formed on the surface. Then, the overlapped portion is ultrasonically welded to a length of about 70c.
m, inner diameter 7 mm, wall thickness 0.3 mm, projection height 0.05
mm, an outer diameter of 7.7 mm including the projections, and a ratio of wall thickness to outer diameter of 0.045 was produced.

Using the composite membrane (without a reinforcing layer) obtained as described above, the flat membrane module 50 as described above was used.
It was created. Further, the tubular filtration membrane module 4 as described above was prepared using the tubular filtration membrane obtained as described above. Table 6 shows the specifications of each module. In addition,
In the tubular filtration membrane module 4, a plastic pipe having an inner diameter of 28 mm was used as the storage container 10. On the other hand, in the flat membrane module 50, a spacer having the same width and a thickness of 7 mm as the frame 53 constituting the membrane plate 52 is used, the interval between the membrane plates 52 is set to 7 mm, and the flow rate of bubbles and the liquid to be treated is set. The road width was set to 4 cm, the same as the film width. The reason that each module is set to such a small size is that the above equation (5) is used.
Since it is assumed that the air bubbles are evenly distributed between all the tubular filtration membranes 11a and all the membrane plates 52, the distribution of the air bubbles is made uniform.

[0115]

[Table 6]

Next, using the created module, FIG.
The test immersion type membrane filtration system 600 shown in FIG. In the figure, a test immersion type membrane filtration system 600 is shown.
A storage tank 601, a tubular filtration membrane module 4 or a flat membrane module 50 disposed in the storage tank 601, a cylindrical support base 602 for supporting the module 4 (50) in the storage tank 601, An air ejection pipe 603 located 30 cm below the bottom surface of the module 4 (50) in the support base 602 is mainly provided. Module 4 (5
0) outlet 12 or outlet pipe 55 (in FIG. 17,
(Not shown) is connected to a filtrate discharge path (not shown).

As a storage tank 601, a transparent container having a diameter of 25 cm and a depth of 170 cm was used, and immersion membrane filtration was performed on the model liquid stored in the storage tank 601. At this time, the temperature of the model liquid was adjusted to 26 ± 1 ° C. The aqueous solutions shown in Table 7 were used as model liquids. In Table 7, CM
C means carboxymethylcellulose and PEO means polyethylene oxide. The viscosities shown in Table 7 are values at 26 ± 1 ° C.

[0118]

[Table 7]

First, the viscosity of the filtrate was measured and the CMC
And PEO permeability were confirmed. The viscosity of the solution containing only CMC was about 1.5 mPa · s or less (the limit of the reading accuracy of the viscometer), while the viscosity of the mixed solution of CMC and PEO was a viscosity corresponding to the concentration of PEO. . From these results, it was determined that most of CMC was suspended in water in the form of a microgel and thus did not pass through the membrane, and that PEO was dissolved in water in the molecular state and passed through the membrane.

The time required for the filtration flow rate to reach a constant value was such that the air flow rate was small, and the model liquid concentration tended to increase as the concentration increased, but was generally about 3 hours.
This steady value is used for the following filtration flow rates. In addition, the filtration flow rate was measured using a 20 ml measuring cylinder and a stopwatch. Capacitance measurement error is ± 0.1
ml.

If the only component removed from the model liquid by filtration is CMC, the well-known cross-flow filtration flux equation (6) is used to obtain C _g , C _b (C _{b g} is the gelling concentration, C _b is the CMC concentration in model solution) is determined only by CMC concentration, also, the diffusion coefficient D should generally inversely proportional to the viscosity of the mixture.

[0122]

(Equation 5)

Therefore, the flux of the mixed solution having a constant CMC concentration should be as shown in the following equation (7). Here, α and β are constants.

[0124]

(Equation 6)

FIG. 18 shows the relationship between the filtration flow rate and the viscosity of the model liquid measured by using the tubular filtration membrane module 4 and setting the air flow rate to 1.5 L / min and the head difference to 60 cm. Show. In the figure, the slope of the straight line is a theoretical value when the diffusion coefficient D is inversely proportional to the viscosity.
Although it is smaller than 0.67, it shows good linearity (if the diffusion coefficient D is proportional to the viscosity to the power of -1.25, the theoretical value and the measured value match).

In a region where the reduced linear velocity of air corresponds to the air flow rate used in the actual immersion type membrane filtration method, the above equation (5) is used.
Is approximately 1, the linear velocity u in the above equation (7) is proportional to the reduced linear velocity of air, that is, the flow rate of air. Therefore, from the above equations (2), (5) and (7), in reality, the filtration flow rate is 1/3 of the air flow rate.
Expected to be proportional to the power. Therefore, the head difference was set to 60 cm using a mixture of 0.9% CMC and PEO,
The relationship between the air flow rate and the filtration flow rate was confirmed while changing the air flow rate. The results are shown in FIG. In FIG. 19, the slope 0.33 of the straight line is equal to ３ of the analysis predicted value.

Next, with respect to the flat membrane module 50, the.
Using a mixed solution of 9% CMC and PEO, the head difference is 60c
m, and the relationship between the air flow rate and the filtration flow rate was confirmed while changing the air flow rate. The results are shown in FIG. FIG.
As in the case of the tubular filtration membrane module 4, the above equation (7)
Is satisfied.

Finally, using the results of these measurements, the above equations (2) and (5) are verified. From the specifications of both modules, if the air flow rate is common, these equations are as shown in the following equations (2-1) and (5-1), respectively.

[0129]

(Equation 7)

Here, the density of the liquid to be treated is 1,000 kg.
/ M ^3, viscosity as 8 mPa · s, are shown in Table 8 the results of calculating the filtered flow ratio. The measured values in Table 8 are as follows:
It was determined from the data in FIGS. 19 and 20.

[0131]

[Table 8]

In the flat membrane module 50 used for the test, since there are three flow paths for two membrane plates 52, it is considered that the linear velocity is smaller than the analytical formula of n >> 1. Then, it can be said that the analysis value and the measured value of the filtration flow rate are in very good agreement.

The interval d between the membrane plates 52 and the tubular filtration membrane 11
a inner diameter d _i and the same west also, when a module footprint and the total air flow to the same for both modules, the results shown in Table 5 is also logically proved possible to obtain. In addition, as long as the dissolved components in the liquid to be treated are not irreversibly adsorbed on the membrane or the cake layer does not behave unusually, the results obtained for all real liquids that can be approximated as laminar flow are as follows. Holds. In practice, a relatively well-controlled immersion type membrane filtration test of activated sludge (for example, Okawa Ron et al., 37th Edition)
In the sewer research presentation, 7-94, 2000), the filtration flow rate is almost proportional to the 1/3 power of the total air flow rate. Although it is difficult to read, it can be generally determined that the filtration flow rate is proportional to the 1/3 power of the total air flow rate).

As described above, it has been found that the tubular filtration membrane module 4 used in the present embodiment is much more compact than the conventional membrane module, that is, the flat membrane module 50.

In consideration of the results of the above verification test, the tubular filtration membrane module 4 used in the present embodiment is considered.
, The filtration flow rate per unit volume based on the outer dimensions is more than twice that of a flat membrane module and a hollow fiber membrane module used under the same air flow rate. In the immersion type membrane filtration method, since the energy cost required for the filtration process increases as the air flow rate used at that time increases, the tubular filtration membrane module 4 is compared with the conventional flat membrane module or hollow fiber membrane module. In that case, it can be seen that the economic efficiency is much better.

In connection with the downsizing of the tubular filtration membrane module,
Means to Achieve the compactness of the tubular filtration membrane module 4 used in the present embodiment is described in JP-A-9-47639 and JP-A-9-99223 cited in the description of the prior art. It is preferable that the tubular filtration membrane 11a be packed as densely as possible without carrying any elements other than the tubular filtration membrane group 11 into the storage container 10 as in the module.

The effective membrane area per unit volume of the tubular filtration membrane module 4, which is an index of the compactness of the module 4, is expressed by the following equation (8).

[0138]

(Equation 8)

Here, 1 is the total length of the holding portion 10a (corresponding to the total length of the upper and lower holding portions 10a in FIG. 2 in the vertical direction), and δ is the wall thickness of the tubular filtration membrane 11a. S is the internal cross-sectional area of the storage container 10 perpendicular to the axial direction, that is, the module installation area in Table 1 described above.

In the holding section 10a and the flat membrane module 50, the frame 53 of the membrane plate 52 needs to have the same length in all module forms in order to fix the filtration membrane. The term L / (L + 1) in 8) can be considered to be almost unchanged by the type of module. Then, the tubular filtration membrane module 4
The effective membrane area per unit volume of the container
The ratio is proportional to the ratio of the inner diameter to the outer diameter (inner diameter / outer diameter) and inversely proportional to the outer diameter.

Here, the filling rate is, as shown in Table 1,
For the internal cross-sectional area perpendicular to the axial direction of the storage container 10,
It is defined by the ratio of the area occupied by the tubular filtration membrane 11a. More specifically, the filling factor (ε) in the tubular filtration membrane module 4 used in the present embodiment is represented by the following equation (9).

[0142]

(Equation 9)

Here, in the tubular filtration membrane module 4 used in the present embodiment, the filling rate of the tubular filtration membrane 11a is 0.9 which is almost equal to the closest packed state, based on the inside of the spacer 13. It can be set, but based on the inside of the storage container 10 including the spacer 13,
It becomes a value smaller than 0.9.

As described above, the spacer 13 is provided at the outlet 1
2 and a gap between the tubular filtration membrane group 11 and the outlet 12
This is for reducing the resistance of the flow of the filtrate toward the container, but the ratio of the area occupied by the spacer 13 in the internal cross-sectional area perpendicular to the axial direction of the storage container 10 is sufficiently 3 to 10% as described above. It is. Therefore, in consideration of this point, in order to achieve the compactness of the tubular filtration membrane module 4, it is preferable to set the filling factor of the tubular filtration membrane 11a to at least 0.70 or more, and to set it to 0.75 or more. Would be more preferable.

[0145] The tubular filtration membrane 11a is formed by the above formula (2).
As shown in the above, as the inner diameter increases, not only does the filtration flow rate decrease, but also the outer diameter necessarily increases, and as can be seen from the above equation (8), the effective membrane area per unit volume of the module also increases. Become smaller. Therefore, from such a viewpoint, the inner diameter of the tubular filtration membrane 11a is preferably set to 15 mm or less, more preferably 10 mm or less.

As can be seen from the above equation (8), in order to obtain the tubular filtration membrane module 4 having a large effective membrane area per unit volume, the ratio of the wall thickness to the outer diameter of the tubular filtration membrane 11a is required. Small ones are preferred. Therefore, from such a viewpoint, the ratio of the tubular filtration membrane 11a is preferably set to 0.1 or less as described above.

[0147] As indicated by the verification test and analysis of the design described above of the layer of packing, very well coincide with the verification test results using the analytical prediction and model solution,
It can be seen that the tubular filtration membrane module 4 is particularly excellent in compactness as compared with the conventional membrane module. However, in order to exhibit such excellent characteristics, it is necessary to appropriately set the distribution of the air bubbles supplied from the air ejection device 6 to the tubular filtration membrane module 4. Hereinafter, this point will be described.

As described above, the filtration flow rate is 1/3 of the air flow rate.
It is proportional to the power. Therefore, it is possible to accurately predict the relationship between the distribution state of air bubbles and the filtration flow rate. The tubular filtration membrane module 4 in which the total number of the tubular filtration membranes 11a is N
In the case where the air bubbles are uniformly distributed to all the tubular filtration membranes 11a, the filtration flow rate J _N in the tubular filtration membrane module 4 is given by the following equation (10). Wherein the effective membrane area of M _N is tubular filtration membrane module 4, j _N filtration flow rate of one of the tubular filtration membranes 11a, Q is the total air flow rate, k, k'is a constant. Note that the total air flow Q
More specifically, per unit time (one minute), the tubular filtration membrane module 4
Means the total flow of air supplied to the

[0149]

(Equation 10)

On the other hand, the air per one tubular filtration membrane is obtained by dividing the total average value (the total flow rate of the air bubbles supplied from the air blowing device 6) by the total number of the tubular filtration membranes into the n tubular filtration membranes 11a. Assuming that the air flows by φ at the average value of the flow rates, that is, the Q / N) ratio, the air flow rate per one of the remaining (N−n) pieces is represented by the following equation (11).

[0151]

[Equation 11]

Therefore, the filtration flow rate of the tubular filtration membrane module 4 is represented by the following equation (12).

[0153]

(Equation 12)

Thus, the following equation (13) is obtained. In the equation, r = n / N, which means the ratio of the tubular filtration membrane 11a having a small air flow rate.

[0155]

(Equation 13)

FIG. 21 shows how the filtration flow rate of the tubular filtration membrane module 4 depends on φ and r using equation (13). In the figure, the numerical value of the curve is φ
As shown in the figure, the total flow rate of the air bubbles supplied from the air bubble supply device 6 is supplied to the tubular filtration membranes 11a of 1/2 or more (that is, at least half). If at least 30% of the air flows through the average value of the air flow rate per one of the tubular filtration membranes 11a divided by the total number (hereinafter referred to as "the total average value", hereinafter referred to as the total average value), all It is possible to secure a filtration flow rate of 90% or more when the air bubbles are evenly distributed to the tubular filtration membrane 11a.

Therefore, what is important as a design target of the supporting device 5 is to set the packing layer 7 so that air bubbles of at least 30% of the total average value can be distributed to at least half of the tubular filtration membranes 11a. is there. Such conditions can be achieved by configuring the filler layer 7 as described above.

In the above immersion type membrane filtration device 3, when a porous hollow cylindrical material having a function as a microorganism carrier as described above is used as the packing 514, the liquid to be treated is Since the surface area of 514 is large, it comes into efficient contact with the surface and the inside. And then,
Various cells contained in the liquid to be treated are filled 514.
It is efficiently carried on. As a result, the cells contained in the liquid to be treated are removed when passing through the packing layer 7, so that the tubular filtration membrane 11a also effectively suppresses such blockage due to the clogging of the cells. Will be done. Therefore, in the domestic wastewater treatment system 1 using the immersion-type membrane filtration device 3 including such a packing material 514, a large amount of the liquid to be treated rapidly flows into the septic tank 2, whereby the water quality of the liquid to be treated is greatly increased. (That is, the sludge concentration decreases), the filtration process can be stably continued.

Setting of Backwashing Conditions As described above, the tubular filtration membrane module 4 used in the immersion type membrane filtration device 3 is more efficient and economical while making it more compact than a hollow fiber membrane module or a flat membrane module. It is suitable for performing immersion type membrane filtration. Therefore, if the backwash conditions of the tubular filtration membrane module 4 by the backwash device 9 can be appropriately set, the immersion type membrane filtration device 3 extends the life while maintaining the high flux property of the tubular filtration membrane 11a. And more efficient and economical immersion membrane filtration can be performed. Therefore, the present inventors cite the following factors relating to backwashing, and try to set effective backwashing conditions by analyzing the relationship between these factors and the recovery rate of the tubular filtration membrane 11a by backwashing. Was.

1. 1. Pressure loss inside the tubular filtration membrane 11a of the backwash liquid 2. Micropore diameter of filtration membrane layer 20 constituting tubular filtration membrane 11a 3. Filtration pressure history before backwashing 4. Separate components contained in the liquid to be treated Filtration mechanism 6. 6. Backwash pressure Backwash volume

However, the filtration method was quantitative filtration or constant-pressure filtration, and a filtrate was used as the backwash liquid in consideration of reality. In addition, as a model liquid of the aerobic activated sludge treatment liquid, carboxymethyl cellulose (CMC) suspension water was used,
In addition, colloidal silica having various average particle diameters was used as a model liquid such as river water.

As described above, the suspension of CMC is transparent, and it appears that CMC is dissolved in a molecular state.
The viscosity of the filtrate is almost equal to that of water, and it is considered that CMC is actually suspended in a gel state. In addition, the suspension of CMC has a high rate of increase in filtration resistance in total filtration, and the clogging component is said to be a secretion of the molecular weight of bacterial cells (for example, Shinichiro Hamaya, et al., Lecture at the 37th Sewer Research Conference) , 7-90, 2000) was considered suitable for a model liquid of activated sludge liquid. Polyethylene oxide (PEO) was used for adjusting the viscosity of this suspension. Since the PEO aqueous solution has the same filtrate viscosity as the original aqueous solution after the filtration treatment, it is considered that PEO passes through the microfiltration membrane. Further, the viscosity of the filtrate of the mixture of CMC and PEO also corresponds to the PEO concentration, and it is considered that PEO passes through the microfiltration membrane even in such a mixture.

On the other hand, many suspended components of natural water, such as river water, are considered to be fine mineral powder, and kaolin powder is also used as an evaluation substance for domestic water purifiers. In addition to its low filtration resistance, it is extremely easy to backwash and is considered to be unsuitable as an evaluation substance for a long-term immersion type membrane filtration system. Therefore, colloidal silica having at least a soft surface and being more difficult to filter was used as a model liquid such as river water.

To examine the relationship between the above factors and the recovery rate, the above-mentioned domestic wastewater treatment system 1 was constructed. At this time, the tubular filtration membrane 11a is formed using a composite membrane 23 in which a filtration membrane layer 20 composed of a microfiltration membrane having a nominal pore diameter of 0.4 μm is integrally laminated on a support membrane layer 21 composed of a nonwoven fabric made of polyester resin. The inner diameter is 7mm and the crushing pressure is 3
The one with 3 kPa was used. Further, as the tubular filtration membrane module 4, a storage container 10 made of a vinyl chloride pipe having an inner diameter of 28 mm and a length of 70 cm was filled with seven tubular filtration membranes 11 a as described above. Note that both ends of the tubular filtration membrane 11a were fixed to the storage container 10 using a urethane resin so that the effective length was about 65 cm (effective membrane area = about 0.1 m ² ). Further, the tubular filtration membrane module 4 was disposed on a guide cylinder 5a formed of a 35-cm-long vinyl chloride pipe, which was disposed on a support leg 5b having a length of 10-cm. Further, the air ejection device 6
Was horizontally arranged at a position about 30 cm below the lower part of the tubular filtration membrane module 4.

Using the domestic wastewater treatment system 1 set as described above, the test liquid (CMC) stored in the septic tank 2 was used.
/PEO=0.1% by weight / 0.8% by weight of mixed solution: viscosity = 8 cps), but head difference P = 60 cm (6 kPa)
, And the change with time of the filtration flow rate was examined. The filtration flow rate was measured using a measuring cylinder and a stopwatch. The flow rate of air supplied from the first air supply path 511 to the air ejection device 6 was set at 1.5 L / min.

FIG. 22 shows the results of the above-mentioned constant pressure filtration test. In FIG. 22, the solid line indicates the filtration flow rate when the constant-pressure filtration is continued. On the other hand, the alternate long and short dash line changes the filtration time, sets the amount of backwashing liquid defined by the quantitative float valve 40 to 25 ml, and sets the backwash pressure (air pressure) to 20 k.
The filtration flow rate immediately after backwashing for 30 seconds while setting to Pa is shown collectively. The backwash time was set to 30 seconds. FIG.
Thus, when the above test solution was subjected to constant pressure filtration, the filtration time was 2 hours.
When the time exceeds 0 minutes, it can be seen that even if the backwashing operation is performed, the original filtration flow rate is not recovered.

Next, using the domestic wastewater treatment system 1 set as described above, a test liquid (having an average particle diameter of 0.5 μm) was used.
m, concentration of “c” ppm colloidal silica suspension shown in FIG.
The relationship between the backwash cycle and the filtration pressure was investigated. here,
Outside the septic tank 2, a flow meter, a digital pressure gauge, and a quantitative tube pump are connected in this order to the terminal portion of the final filtrate discharge path 517 of the filtrate discharge device 8, and the suction force of the quantitative tube pump is adjusted. The filtration flow rate was adjusted. The test liquid was stirred in the aeration tank 502 of the septic tank 2 so that the colloidal silica suspension used as the test liquid did not precipitate.

After performing a quantitative filtration for 9 minutes by setting the filtration flow rate by the quantitative tube pump to “F” L / min, the amount of the backwash liquid was set to 25 ml, the backwash pressure (air pressure) was set to 30 kPa, and the backwash was performed for 30 seconds. FIG. 23 shows the results obtained when the filtration-backwash cycle (filtration cycle) was repeated. In FIG. 23, the filtration cycles without “c” or “F” are the same as the filtration conditions of the previous cycle.
The five cycles 17 to 21 are a filtration mode in which filtration is performed for 8 minutes and aeration (supply of air bubbles from the air ejection device 6) is performed for 2 minutes, that is, a filtration mode in which a backwash operation is not performed.

Unlike the case of constant pressure filtration using a CMC / PEO mixed solution as a test solution, in this quantitative filtration using a colloidal silica suspension as a test solution, continuous filtration-backwashing was performed under relatively wide filtration conditions. The cycle was repeated. From FIG. 23, it can be seen that the filtration pressure after backwashing has recovered to the filtration pressure at the start of each filtration cycle. Also, it can be seen that the filtration pressure, which was not recovered only by aeration, has been effectively recovered by backwashing.

FIGS. 22 and 23 show typical examples of the results of the constant pressure filtration test and the quantitative filtration test, respectively. Similar tests were carried out by variously combining the above factors. To summarize the results, the following 1 to 1
Six things turned out. However, in the quantitative filtration test, the recovery rate R was defined by the following equation (14), and in the constant pressure filtration test, the recovery rate R was defined by the following equation (15).

[0171]

[Equation 14]

In the equation (14), P _f indicates the filtration pressure before back washing, P _i indicates the filtration pressure immediately after back washing, and P _i-1 indicates the filtration pressure immediately after the start of filtration. In the formula (15), J _f is filtered flow before backwashing, J _i is filtered flow rate immediately after backwashing, J _i-1 denotes the filtration flow rate immediately after the start of filtration. Equations (14) and (1)
In 5), when R = 1, the filtration pressure has completely recovered.

1. Tubular filtration membrane 11a having an inner diameter of 3 mm or more
Then, the pressure loss of the backwash liquid (filtrate) can be ignored. 2. The filtration pressure history before backwashing has a great effect on the recovery rate. If the pressure exceeds a specific pressure (recovery limit pressure), the filtration pressure does not completely recover and irreversible clogging occurs. 3. The recovery rate depends on the filtration membrane layer 20 in the tubular filtration membrane 11a.
It is considered that the relationship with the membrane structure is stronger than the pore diameter of the micropores (recovery limit pressure is considerably different depending on the membrane structure), but complete recovery was possible if the filtration pressure history was equal to or less than the recovery limit pressure. 4. It is a necessary condition for complete recovery that the filtration mechanism is within the range of the cake filtration mechanism (the filtration pressure in quantitative filtration is proportional to the integrated filtration amount). 5. Under the conditions satisfying the necessary conditions for complete recovery according to the above 2 to 4, in the suspension of colloidal silica, a: the backwash amount of the filtrate was increased by 1 m ² of the membrane area of the tubular filtration membrane 11 a.
When it was set to about 200 ml or more per unit, it completely recovered. b: When the backwash pressure was set to be equal to or higher than the maximum filtration pressure, it completely recovered. c: Regardless of the filtration amount, the filtration pressure history is below the recovery limit pressure,
When the filtration mechanism was in the range of the cake filtration mechanism, it completely recovered. 6. Under the conditions satisfying the conditions for complete recovery according to the above 2 to 4, the CMC / PEO suspension did not completely recover after a certain amount of filtration. b: Under a certain filtration amount, when the backwashing amount of the filtrate was set to about 200 ml or more in terms of the membrane area of the tubular filtration membrane per 1 m ² , it was completely recovered at a backwashing pressure of the maximum filtration pressure or more. .

When the filtered amount of the CMC / PEO suspension exceeds a specific value, the reason why the CMC / PEO suspension is not completely recovered by backwashing is that the CMC gel accumulates on the membrane surface and the membrane is in close contact with each other. If so, it is considered that a continuous film, which is weak but mutually bonded, is formed, and the film is not easily broken by the backwashing. In other words, in such a case, it is considered that complete recovery is not achieved unless backwashing is performed before a complete film of suspended particles is formed, that is, before the filtration amount exceeds a certain value. On the other hand, since the colloidal silica does not form such a film, it is considered that the colloidal silica recovers regardless of the filtration amount. However, in any of the test liquids, the suspended particles pushed into the micropores at a pressure higher than a specific value related to the membrane structure do not detach even if the backwash pressure / backwash liquid volume is increased. That is, when filtration is performed with a filtration pressure equal to or higher than a specific value, backwashing becomes substantially difficult.

According to the above, preferable backwashing conditions are
Set the backwash pressure at or above the maximum filtration pressure during filtration
Or the amount of backwashing of the filtrate is determined on the membrane surface of the tubular filtration membrane 11a.
Product 1m ^TwoThe minimum required amount is about 200 ml or more.
Can be cited. Therefore,
In the immersion type membrane filtration device 3 described above, the quantitative float valve 4
0 is reverse in the tubular filtration membrane module 4 in the backwashing step.
The amount of the filtrate to be flowed is the tubular shape stored in the storage container 10.
1m of membrane area of filtration membrane 11a^TwoAt least 200m per
It is preferable that the volume be set to 1.

[Other Embodiments] (1) In the above embodiment, the case where the tubular filtration membrane module 4 in which the filtrate outlet 12 is provided on the side surface of the storage container 10 is described. The tubular filtration membrane module that can be used in the immersion type membrane filtration device of the present invention is not limited to this.

Referring to FIGS. 24 and 25, another tubular filtration membrane module 200 that can be used in the immersion type membrane filtration device of the present invention will be described. This tubular filtration membrane module 200 has a structure shown in FIGS. 24 (longitudinal sectional view of the tubular filtration membrane module 200) and FIG.
As shown in FIG. 24 (a diagram corresponding to a cross section taken along line XXV-XXV), the apparatus mainly includes a cylindrical storage container 210 and a tubular filtration membrane group 211 filled in the storage container 210.
The storage container 210 is a member made of, for example, a resin, and has a cylindrical water collecting pipe 212 and a cylindrical outer pipe arranged concentrically with an interval (space) provided around the axis of the water collecting pipe 212 at the outside thereof. A cylinder 213 is mainly provided. Water collecting pipe 212
Is closed at the lower end in the figure, and is open at the upper end in the figure to form a discharge port 212a. Further, the water collecting pipe 212 has a plurality of liquid passage holes 212b on a wall surface.

The group of tubular filtration membranes 211 is a group including a large number of tubular filtration membranes 211a formed in an elongated cylindrical shape.
Each of the tubular filtration membranes 211a is connected to the water collecting pipe 21 of the storage container 210.
In the space formed between the outer tube 213 and the outer cylinder 213, the water collecting pipe 2
Filled in parallel with 12. The upper end and the lower end of such a group of tubular filtration membranes 211 are placed in the storage container 210 while maintaining the open state of each tubular filtration membrane 211a by the holding portions 210a formed using a resin material such as urethane resin. It is held together and fixed to the body. As a result, both ends of the storage container 210 are liquid-tightly closed by the holding portion 210a. The tubular filtration membrane 211a is formed similarly to the tubular filtration membrane 11a described in the above embodiment.

In FIG. 24 and the like, the thickness of the tubular filtration membrane 211a, the gap between the tubular filtration membranes 211a, and the like are emphasized for easy understanding. Also, to make the drawings easier to understand,
In FIG. 24, the number of tubular filtration membranes 211a is expressed in a small number, and in FIG. 25, only a part of the tubular filtration membrane 211a is shown.

Such a tubular filtration membrane module 200
Are the water collecting pipe 212 and the outer cylinder 213 in the storage container 210.
The water collection pipe 212 with respect to a cross-sectional area perpendicular to the axial direction (S ′: an area of a portion shown by a hatched line in FIG. 25)
It is preferable that the ratio (d _s / S ′) of the outer diameter (d _s ) is set to be 0.3 to ¹ m ⁻¹ . Further, it is preferable that the filling rate represented by the following equation (16) is set to be at least 0.8. Note that in equation (16),
N is the tubular filtration membrane 211a included in the tubular filtration membrane group 211
The number of, d ₀ is the outer diameter of the tubular filtration membrane 211a, S 'is the cross-sectional area.

[0181]

(Equation 15)

This tubular filtration membrane module 200 is
When the rate is set as described above, the hollow fiber membrane or
Per unit volume compared to conventional module using flat membrane
Film area is large, resulting in cost
It is easy to make impact. In addition, this tubular filtration membrane module
In the immersion type membrane filtration method using the
Of immersion type membrane filtration system using air and supply of air bubbles
If the volume is set to the same level, the unit
The filtration flow rate per product is better than with a conventional module.
More. That is, this tubular filtration membrane module 2
00 is the tubular filtration membrane described in the above embodiment.
Same as module 4 compared to conventional filtration membrane module
Excellent compactness and economy. In particular,
Ratio (d _s/ S ') within the above range, the filtration
Energy efficiency drop due to pressure loss during operation
To increase the economics of submerged membrane filtration.
Can be. Therefore, this tubular membrane filtration module 20
0 is the tubular filtration membrane module used in the above embodiment.
As with fuel 4, energy required to supply air bubbles
Reduction, resulting in the economy of immersion membrane filtration
Can be enhanced.

The tubular filtration membrane module 2 as described above
When the liquid to be treated is filtered in the same manner as in the above-described embodiment using 00, the liquid to be treated stored in the storage tank 2 is ejected from the air ejection holes 6d of the air ejection device 6. With the air bubbles, as shown by arrows in FIG. 24, the air bubbles pass through the inside of each tubular filtration membrane 211a of the tubular filtration membrane module 200 from the lower side to the upper side. At this time, the liquid to be treated passes through the tubular filtration membrane 211a from the inside to the outside, and is filtered.
It is collected by the filtration membrane layer 20 of 1a and removed from the liquid to be treated. Liquid to be treated (filtrate) from which filtered components have been removed
Passes through the gap between the tubular filtration membranes 211a, and
2b flows into the water collecting pipe 212. The filtrate that has flowed into the water collection pipe 212 is discharged from the outlet 212 a to the storage container 210.
Is continuously discharged to the outside. By such a series of filtration treatments, the liquid to be treated in the aeration tank 502 naturally circulates through the tubular filtration membrane module 200 from the lower side to the upper side in the same manner as indicated by the arrow in FIG. become. When such a tubular filtration membrane module 200 is used, the first discharge path 515a of the filtrate discharge device 8 is connected to the outlet 212
Connect to a.

The tubular filtration membrane module 200 as described above
Can be manufactured, for example, through the following steps. First, using a fixing device 230 as shown in FIG.
The storage container 210 is formed. Fixing device 23 used here
Reference numeral 0 denotes an outer cylinder holding portion 231 for holding the outer tube 213 and a water collecting tube holding portion for holding the water collection tube 212. 232.

The outer cylinder holding part 231 has a receiving part 233 for storing one end of the outer cylinder 213 and a pressing plate 234 for fixing the outer cylinder 213 to the receiving part 233. The receiving portion 233 has a circular concave portion 233a capable of storing the end of the outer cylinder 213, and a hole 233b is formed in the center of the concave portion 233a. Further, the concave portion 233a is set so that the inner diameter on the opening side is increased in the middle in the depth direction, and the step portion 233c is formed at such a changed portion of the inner diameter. Further, a groove 235 is formed on the periphery of the opening of the concave portion 233a, and an annular rubber elastic body 235a is arranged in the groove 235. On the other hand, the holding plate 234 has the outer cylinder 21 at the center.
3 is a member provided with an insertion hole 234a into which the receiving portion 233 can be inserted, and the planar shape is set to be substantially the same as the receiving portion 233.

On the other hand, the water collecting pipe holding portion 232 is
36, a positioning member 237, a presser 238, and a nut 239. The shaft 236 is connected to the water collecting pipe 212.
It is a rod-shaped member that can be inserted into the inside and penetrates the hole 233b of the receiving part 233, and has a spiral part 236a at one end and a head 236b at the other end. The positioning member 237 includes an insertion portion 2 that can be inserted into the water collecting pipe 212.
37a and a substantially columnar member integrally having a projecting portion 237b projecting from the water collecting pipe 212 with the insertion portion 237a inserted into the water collecting pipe 212, and the shaft 236 penetrates the central portion thereof. Hole 237c for the
Are formed. The protrusion amount of the protrusion 237b is set to be the same as the distance from the lower part of the recess 233a of the receiving part 233 to the step part 233c. The holding member 238 is a disk-shaped member that can be inserted into the inside of the water collecting pipe 212, and has an insertion hole 238a for inserting the shaft 236 at the center. The nut 239 can be attached to the spiral portion 236a of the shaft 236.

Using the fixing device 230 described above, the storage container 2
When forming 10, the outer cylinder 213 is first held by the outer cylinder holding portion 231. Here, one end of the outer cylinder 213 is inserted into the concave portion 233a of the receiving portion 233, and the step portion 233c is formed.
Contact. Then, the insertion hole 234a of the holding plate 234
With the outer cylinder 213 inserted therein, the pressing plate 234 is fixed while being pressed against the rubber elastic body 235a.
As a result, the outer cylinder 213 is held with one end inserted into the recess 233a.

Next, the water collecting pipe 212 is arranged inside the outer cylinder 213 by using the water collecting pipe holding part 232. Here, first, a tubular rubber elastic body 237d is attached to the tip of the insertion portion 237a of the positioning member 237, and the insertion portion 237a is inserted into the water collecting pipe 212 in this state. Water collection pipe 2
The presser 238 is inserted into the side 12 from a side different from the side where the positioning member 237 is inserted. And the shaft 23
6 is inserted into the insertion hole 238 a of the holding member 238 and the through hole 237 c of the positioning member 237 so that the head 236 b thereof comes into contact with the holding member 238. In this state, the spiral portion 236 a of the shaft 236 is
The water collecting pipe 212 is inserted into the outer cylinder 213 so as to protrude from 3b, and a nut 239 is attached to the spiral part 236a.
Accordingly, the fixing device 230 is configured such that the water collecting pipe 212 is
The two are held in a state of being arranged concentrically within 13 to form the storage container 210.

Next, the group of tubular filtration membranes 211 is filled in the storage container 210 formed as described above. Here, as shown in FIG. 26, a large number of tubular filtration membranes 211a
Are inserted in a space formed between the outer cylinder 213 and the water collecting pipe 212. At this time, the length of each tubular filtration membrane 211 a is set to be longer than that of the storage container 210, and both ends of the tubular filtration membrane group 211 are set to protrude from the storage container 210. Both ends of each tubular filtration membrane 211a are closed by heat sealing.

Next, a tubular filtration membrane group 21 was formed using a resin material.
1 is fixed to the storage container 210. Here, first, a mold 240 as shown in FIG. 27 is prepared. The mold 240 has a cavity 241. The cavity 240 has a central portion 242 into which the tubular filtration membrane group 211 can be inserted, and an outer cylinder of the storage container 210 formed continuously around the central portion 242. 213 into which the outer tube 213 can be inserted. An uncured resin material 244 (for example, an uncured urethane resin) is injected into the center 242 of the mold 240.

On the other hand, in the storage container 210 formed by the fixing device 230, the opening side of the water collecting pipe 212 is closed using the cap 245 (FIG. 26). And FIG.
As shown in FIG. 7, the tubular filtration membrane group 211 protruding from the storage container 210 is gradually immersed in the resin material 244 injected into the center portion 242 of the cavity 241, and
3 is held in the outer tube insertion portion 243. This state is maintained until the resin material 244 is cured.
Is completely cured, and then the mold 240 is removed. Thereby, one end side of the tubular filtration membrane group 211 is
0 is fixed to one end. Thereafter, the cured resin material 24 protruding from the storage container 210
4 and the tubular filtration membrane group 211 are cut off, and the cap 245 is removed.

Next, the storage container 210 is once separated from the fixing device 230, the storage container 210 is turned in the opposite direction, and is fixed again by the fixing device 230. In this state, when the above-described operation on the mold 240 is repeated, the other end of the tubular filtration membrane group 211 is also fixed to the other end of the storage container 210, and the intended tubular filtration membrane module 200 is obtained. . At this time, the opening of the water collecting pipe 212 is
If not closed at 45, the resin material 244 flows into the water collecting pipe 212, which closes one end of the water collecting pipe 212. The manufactured tubular filtration membrane module 200
, Both ends of the storage container 210 are
Except for both ends of 11a, a holding portion 210a made of the cured resin material 244 is formed, and the holding portion 210a is closed in a liquid-tight manner.

As the resin material 244 used in the above-described manufacturing process, similarly to the case of the tubular filtration membrane module 4 used in the above embodiment, in addition to the urethane resin, another thermosetting resin such as an epoxy resin is used. A conductive resin or a hot melt adhesive can also be used. Further, in the above-described manufacturing process, in order to enhance the adhesiveness between the storage container 210 and the resin material 244, the use of an adhesion auxiliary agent on the inner peripheral surface of the outer cylinder 213 and the outer peripheral surface of the water collection pipe 212 is previously performed. Or a surface treatment by corona discharge treatment, or a groove for enhancing the anchor effect of the resin material 244 may be added.

(2) In the above embodiment, the storage container 10 of the tubular filtration membrane module 4 is formed in a cylindrical shape. However, the storage container 10 is not particularly limited as long as it is cylindrical. The present invention can be carried out in the same manner even when it is formed in a rectangular cylindrical shape. 28 and 29 (FIG. 2)
8 (XXIX-XXIX cross section), an example of the tubular filtration membrane module 4 in which the storage container 10 is formed in a rectangular tube shape is shown.
In this tubular filtration membrane module 4, the storage container 10
Has a filtrate outlet 12 on the side surface as in the case of the above-described embodiment, but the spacer 13 is formed only on the surface where the outlet 12 is formed. Therefore, the tubular filtration membrane group 11 is filled so as to be in close contact with the inner surface of the storage container 10 except for the surface on which the spacer 13 is formed. Such a tubular filtration membrane module 4
Also in the above, since a gap is formed by the spacer 13 between the tubular filtration membrane group 11 and the discharge port 12, the filtrate from the tubular filtration membrane 11a is smoothly discharged from the discharge port 12.

When the tubular filtration membrane module 4 provided with such a rectangular tubular storage container 10 is used for the immersion type membrane filtration device 3, the guide cylinder 5a of the support device 5 is formed in the same shape as the tubular filtration membrane module 4. It is necessary to form it into a rectangular cylindrical shape corresponding to the above.

(3) In the above-described embodiment, the spiral projections 22 are provided on the outer peripheral surfaces of the tubular filtration membranes 11a and 211a. Modules 4, 200 can be backwashed.

Further, in the above-described embodiment, the projections 22 are provided in the tubular filtration membranes 11a and 211a 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.

(4) In the above embodiment, the tubular filtration membranes 11a and 211a are formed of the filtration membrane layer 20 and the support membrane layer 21.
Although formed in a layered structure, when the crushing pressure of the tubular filtration membrane 11a is set to the above-mentioned required value by appropriately setting the ratio of the wall thickness to the outer diameter, as shown in FIG. A reinforcing layer 25 having liquid permeability may be further arranged on the outer peripheral surface of the film layer 21.

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 11a provided with such a reinforcing layer 25,
211a is the support membrane layer 21 of the composite membrane 23 described above, which is usually used to manufacture the tubular filtration membranes 11a, 211a.
It can be manufactured by using a composite film in which a reinforcing layer 25 is further laminated on the side. In the case of manufacturing such a composite film, it is usually preferable that the reinforcing layer 25 is bonded to the surface of the support film layer 21 by scattering a hot melt adhesive or a thermosetting adhesive. By doing so, the composite membrane can suppress an increase in filtration resistance due to the reinforcing layer 25, and can improve the tubular filtration membranes 11a and 211 according to the above-described embodiment.
The same filtration resistance as that of a, that is, the permeability of the filtrate can be achieved.

When the tubular filtration membranes 11a, 211a have such a reinforcing layer 25, the tubular filtration membranes 11a, 211a,
The thickness and outer diameter of 211a are calculated including this reinforcing layer 25. When the projections 22 are formed on the surfaces of the tubular filtration membranes 11a and 211a, the projections 22 need to be formed on the surface of the reinforcing layer 25.

The tubular filtration membrane used in the above-described verification test on the tubular filtration membrane module has such a reinforcing layer 25. (5) In the above embodiment, the case where the immersion type membrane filtration device 3 of the present invention is applied to a small septic tank has been described.
The immersion type membrane filtration device 3 can also be applied to a larger septic tank, for example, a septic tank for treating large-scale domestic wastewater or industrial wastewater using aerobic activated sludge.

[0202]

The immersion type membrane filtration device for a septic tank according to the present invention comprises:
It is a compact combination of a tubular filtration membrane module with an air ejection device, filtrate discharge device and backwashing device. The aerobic activated sludge treatment liquid stored in the septic tank can be efficiently filtered.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a domestic wastewater treatment system employing a submerged membrane filtration device according to an embodiment of the present invention.

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

FIG. 3 is a cross-sectional view of the tubular filtration membrane module taken along the line III- in FIG.
FIG.

FIG. 4 is a view taken in the direction of the arrow IV in FIG. 3;

FIG. 5 is a sectional view taken along line VV of FIG. 4;

FIG. 6 is a perspective view of a tubular filtration membrane used in the tubular filtration membrane module.

FIG. 7 is a sectional end view taken along the line VII-VII in FIG. 6;

FIG. 8 is a view showing a manufacturing process of the tubular filtration membrane.

FIG. 9 is a view showing one manufacturing process of the tubular filtration membrane module.

FIG. 10 is a diagram showing another manufacturing process of the tubular filtration membrane module.

FIG. 11 is a partial detailed cross-sectional view of the immersion type membrane filtration device.

FIG. 12 is a bottom view of an air ejection device used in the immersion type membrane filtration device.

FIG. 13 is a front view of a quantitative float valve employed in the immersion type membrane filtration device.

FIG. 14 is a cross-sectional view of a float valve portion constituting the fixed quantity float valve.

FIG. 15 is a partial cross-sectional front view of an example of the flat membrane module.

FIG. 16 is a partially cutaway perspective view of a membrane plate used in the flat membrane module.

FIG. 17 is a schematic diagram of a test submerged membrane filtration system used to test the properties of the tubular filtration membrane module.

FIG. 18 is a graph showing the relationship between the viscosity of the model liquid used in the verification test and the filtration flow rate.

FIG. 19 is a graph showing a result of examining a relationship between an air flow rate and a filtration flow rate in a tubular filtration membrane module, which was performed in a verification test.

FIG. 20 is a graph showing a result of examining a relationship between an air flow rate and a filtration flow rate in a flat membrane module, which was performed in a verification test.

FIG. 21 is a graph showing the relationship between the ratio of the tubular filtration membrane having a small air flow rate and the filtration flow rate in the tubular filtration membrane module.

FIG. 22 is a graph showing the results of a constant pressure filtration test.

FIG. 23 is a graph showing the results of a quantitative filtration test.

FIG. 24 is a longitudinal sectional view of another type of tubular filtration membrane module usable in the immersion type membrane filtration device.

FIG. 25 is a view corresponding to a section taken along line XXV-XXV of FIG. 24, of the tubular filtration membrane module of the other embodiment.

FIG. 26 is a view showing one manufacturing process of the tubular filtration membrane module of the other embodiment.

FIG. 27 is a diagram showing another manufacturing process of the tubular filtration membrane module of the other embodiment.

FIG. 28 is a longitudinal sectional view of a tubular filtration membrane module of still another form usable in the immersion type membrane filtration device.

FIG. 29 is a view of the tubular filtration membrane module according to still another embodiment, corresponding to a section taken along XXIX-XXIX in FIG. 28.

FIG. 30 is a view corresponding to FIG. 7 of a modified example of the tubular filtration membrane.

[Explanation of symbols]

 2 Septic tank 3 Immersion type membrane filtration device 4,200 Tubular filtration membrane module 6 Air ejection device 7 Packing layer 8 Filtrate discharge device 9 Backwash device 10,210 Storage container 12,212a Outlet 10a, 210a Holding portion 11,211 Tubular filtration membrane group 11a, 211a Tubular filtration membrane 20 Filtration membrane layer 21 Support membrane layer 40 Quantitative float valve 212 Water collecting pipe 212b Liquid passage hole 509 Air generator 514 Filler 515 Filtrate discharge path 516 Storage tank 517 Final filtrate discharge path 518 gas-liquid flow path 520 second air supply path

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 69/10 B01D 69/10 C02F 3/00 C02F 3/00 B 3/06 3/06 3/12 ZAB 3/12 ZABS (72) Inventor Naoki Murakami 2-3-1, Furube-cho, Takatsuki-shi, Osaka F-term in Yuasa Corporation (Reference) 4D003 AA01 AB02 BA01 CA02 CA07 DA09 EA15 EA19 EA30 4D006 GA07 HA27 HA93 JA02A JA19A JA25A JA70A JB04 JB06 KA01 KA44 KB14 KB22 KB25 KC03 KC13 KE01R MA02 MA09 MA31 MA33 MA34 MC11 MC22 MC48 PA01 PB08 PB24 PC62 PC65 4D027 AA03 AA11 AA16 AB06 AB11 AB16 BA03 4D028 BB02 BC17 BC28 BD11 BD17

Claims (11)

[Claims] An apparatus for obtaining a filtrate by subjecting an aerobic activated sludge treatment liquid stored in a septic tank to a filtration treatment by a submerged membrane filtration method, wherein an inner surface of the aerobic activated sludge treatment liquid is filtered. A plurality of tubular filtration membranes having a function are accommodated in a cylindrical storage container having an outlet for the filtrate and held at both ends, and the inside of the septic tank is opened so that the tubular filtration membrane is opened vertically. A tubular filtration membrane module disposed in the air filtration device for supplying air bubbles toward the tubular filtration membrane module disposed below the tubular filtration membrane module; and a filtrate discharge extending from the discharge port. A filtrate discharge device having a path and discharging the filtrate to the outside of the septic tank; and causing the filtrate in the filtrate discharge path to flow backward while being pressurized into the storage container through the discharge port. Immersion type membrane filtration device for a septic tank, comprising: 2. The septic tank according to claim 1, wherein the tubular filtration membrane includes a microfiltration membrane layer formed in a cylindrical shape, and a nonwoven fabric layer disposed on an outer peripheral surface of the microfiltration membrane layer. Immersion type membrane filtration equipment. 3. The immersion type membrane filtration device for a septic tank according to claim 1, wherein the tubular filtration membrane has an inner diameter of 3 to 15 mm. 4. A filling device disposed between the tubular filtration membrane module and the air ejection device for dispersing and guiding the air bubbles from the air ejection device toward the tubular filtration membrane module. The immersion type membrane filtration device for a septic tank according to claim 1, further comprising a packing layer containing a substance. 5. The immersion type membrane filtration device for a septic tank according to claim 4, wherein the packing is a porous hollow cylindrical material having an outer diameter of 5 to 50 mm and a length of 5 to 50 mm. 6. The immersion type membrane filtration device for a septic tank according to claim 5, wherein the hollow cylindrical material is a microorganism carrier. 7. The backwashing device according to claim 1, wherein the backwashing device includes an air generating device and an air supply device for applying air pressure by air from the air generating device to the filtrate in the filtrate discharging path in a direction toward the discharge port. Claims 1, 2, 3,
The immersion type membrane filtration device for a septic tank according to 4, 5, or 6. 8. The backwashing device according to claim 1, wherein the amount of the filtrate to flow back into the storage container is at least 200 m per 1 m ² of the membrane area of the tubular filtration membrane stored in the storage container.
The immersion type membrane filtration device for a septic tank according to claim 7, further comprising a reverse flow rate setting device for setting the value to l. 9. A filtrate discharge device, comprising: a storage tank for storing the filtrate from the filtrate discharge path in the septic tank; and a final filtrate discharge path extending from the storage tank to outside the septic tank. And a pressurizing device for pressurizing the inside of the storage tank and sending out the filtrate stored in the storage tank to the final filtrate discharge path. 9. The immersion type membrane filtration device for a septic tank according to 5, 6, 7, or 8. 10. The tubular filtration membrane module, comprising: a cylindrical storage container having a cylindrical water collecting pipe having a liquid passage hole; and an outer cylinder arranged at an outer periphery of the water collecting pipe at an interval. A tubular filtration membrane group including a plurality of tubular filtration membranes disposed between a water pipe and the outer cylinder, the plurality of tubular filtration membranes being formed in a cylindrical shape and having a function of filtering the aerobic activated sludge treatment liquid on the inner surface, and the storage container A holding portion provided at both ends of the tubular filtration membrane group for holding both ends in the longitudinal direction of the tubular filtration membrane group, wherein the water collecting pipe has the discharge port. 4,
The immersion type membrane filtration device for a septic tank according to 5, 6, 7, 8 or 9. 11. The submerged membrane filtration device for a septic tank according to claim 1, wherein the septic tank is a single septic tank.