JP7116618B2 - Hollow fiber membrane module - Google Patents

Description

The present invention relates to a hollow fiber membrane module.

BACKGROUND ART Conventionally, in the field of water treatment such as microfiltration and ultrafiltration, there has been known a separation technique using a hollow fiber membrane module in which a plurality of hollow fiber membranes are fixed in a bundle. Separation technology using hollow fiber membrane modules is often targeted for relatively clear raw water such as groundwater and subsoil water. However, in recent years, the scope of application of raw water has expanded, and the number of cases where it is applied to raw water with relatively large amounts of turbidity components and fluctuations in raw water quality, such as river surface water and industrial wastewater recovery, has increased. ing. Therefore, the hollow fiber membrane module is required to have a high turbidity resistance that can cope with them.

Usually, one end of the hollow fiber membrane bundle is open to obtain treated water, and the other end is sealed in some way. As a sealing method, various methods such as bending a U-shaped hollow fiber membrane and heat welding are known. In recent years, hollow fiber membrane modules of a both-ends-fixed type, in which sealed portions are collectively adhesively fixed with a resin to a container called a housing in which the hollow fiber membranes are placed, have become mainstream (Patent Document 1). However, with this structure, sufficient discharge capacity cannot be obtained when filtering raw water with a high concentration of turbidity. Therefore, there is a problem that turbidity components accumulate as filtration progresses, leading to clogging of the membrane, and there is a problem that it is not possible to deal with raw water with a high turbidity concentration.

In order to solve this problem, there is known a one-end free type hollow fiber membrane module in which one end of the hollow fiber membrane is open (Patent Documents 2 and 3). In Patent Literature 2, the ends of each hollow fiber membrane are sealed with an adhesive resin such as epoxy so that they are separated. It is described that this configuration can enhance the ability to discharge suspended matter. In addition, it is described that the hollow fiber membrane can be used as a sealing portion having high durability by permeating the resin with the hollow fiber membrane. On the other hand, Patent Literature 3 discloses a method for manufacturing a free portion that has fewer restrictions, can suppress seepage to the outside of the membrane, and can suppress apparatus costs.

JP 2006-247649 A JP-A-5-15746 JP 2017-070914 A

However, since the hollow fiber membrane modules disclosed in Patent Documents 2 and 3 use one-end free hollow fiber membrane bundles, the hollow fiber membranes may remain in contact with each other during filtration. In this case, there is a problem that not only the membrane effective utilization rate is lowered, but also the turbidity discharge performance is lowered.

Accordingly, the present invention has been made in view of the above-mentioned prior art, and an object thereof is to provide a hollow fiber membrane module capable of suppressing a decrease in membrane effective utilization rate and turbidity discharge performance. It is in.

In order to achieve the above object, the present invention provides a hollow fiber membrane having a plurality of hollow fiber membranes through which raw water permeates from the outside to the inside, and one end of each hollow fiber membrane is sealed with a sealing agent. and a fixing member that fixes the other ends of the plurality of hollow fiber membranes while the other ends are open. The hollow fiber membrane bundle is of a one-end free type in which the one end of the hollow fiber membrane is not fixed, and each of the plurality of hollow fiber membranes is provided with a protruding portion having a shape protruding from the outer surface of the hollow fiber membrane. The hollow fiber membrane provided with the protrusion is defined to have an elongation of 20% or more and less than 500% and an effective length of 0.3 m or more and 2.5 m or less, and the protrusion The part is arranged at a position in contact with the protruding part provided on the adjacent hollow fiber membrane.

In the hollow fiber membrane module according to the present invention, it is possible to prevent the hollow fiber membranes from being kept in contact with each other due to the protrusions coming into contact with each other. As a result, it is possible to prevent the water flow resistance of the hollow fiber membranes from increasing when the raw water permeates the hollow fiber membranes from the outside to the inside, and to prevent the membrane effective utilization rate from being lowered.

In addition, the projecting portion may always be in contact with the adjacent projecting portion. Alternatively, the protrusions may be arranged so as not to be in contact with the adjacent protrusions, while being in contact with the adjacent protrusions due to bending of the hollow fiber membrane or the like.

In the hollow fiber membrane module, the protrusion may be provided at the one end sealed with the sealant. In this aspect, it is possible to seal one end of the hollow fiber membrane with the sealant and form the protruding portion at the same time.

The error in effective length of the plurality of hollow fiber membranes may be less than 10%. In this aspect, it is possible to avoid a situation in which contact between adjacent protrusions is inhibited due to variations in the effective lengths of the hollow fiber membranes.

The protruding portion may be provided at an intermediate portion in the length direction of each of the plurality of hollow fiber membranes.

The protrusion may have a rounded shape. In this aspect, even if the protrusion contacts the hollow fiber membrane, it is possible to prevent the hollow fiber membrane from being damaged.

The hollow fiber membrane module may include a housing in which the hollow fiber membrane bundle is accommodated. That is, the hollow fiber membrane module may be an immersion type hollow fiber membrane module, or may have a structure in which a hollow fiber membrane bundle is accommodated therein to form a module.

A filling rate of the hollow fiber membrane bundle with respect to the volume of the internal space of the housing may be 20% or more and less than 65%. In this aspect, it is possible to effectively prevent the hollow fiber membranes from being kept in contact with each other while appropriately filling the space inside the housing with the hollow fiber membrane bundle. That is, if the filling rate is less than 20%, the ratio of contact between the hollow fiber membranes is reduced, but the membrane area of the hollow fiber membranes themselves is reduced, resulting in a decrease in filtration performance. On the other hand, when the filling rate is 65% or more, the number of contact points of the hollow fiber membranes increases regardless of the existence of the protrusions.

The width of the protrusion may be more than 1 time and less than 3 times the outer diameter of the hollow fiber membrane. In this aspect, the effect of the protruding portion can be effectively exhibited, and the gap between the hollow fiber membranes can be suppressed from becoming too wide, so that the hollow fiber membranes can be bent or broken during physical washing of the hollow fiber membranes. Problems can be prevented.

ADVANTAGE OF THE INVENTION According to this invention, the deterioration of a membrane effective utilization rate and turbidity discharge property can be suppressed.

It is a figure showing the whole hollow fiber membrane module composition concerning an embodiment. FIG. 4 is a diagram schematically showing hollow fiber membranes and protrusions provided in the hollow fiber membrane module; It is a figure for demonstrating the modification of the said protrusion part. FIG. 4 is a diagram showing a state in which hollow fiber membranes are maintained in contact with each other. It is a figure for demonstrating the modification of the said protrusion part. It is a figure for demonstrating the modification of the said protrusion part. It is a figure for demonstrating the modification of the said protrusion part. FIG. 10 is a diagram showing the overall configuration of a hollow fiber membrane module according to another embodiment;

EMBODIMENT OF THE INVENTION Hereinafter, it demonstrates in detail, referring drawings for the form for implementing this invention.

(overall structure)
As shown in FIG. 1, a hollow fiber membrane module 10 according to the present embodiment includes a hollow fiber membrane bundle 14 having a plurality of hollow fiber membranes 12, a housing 16 in which the hollow fiber membrane bundle 14 is accommodated, and a a fixed member 18 fixed to the .

The housing 16 has a sealed structure with a vertically elongated inner space. A fixing member 18 in the housing 16 partitions the internal space of the housing 16 into a storage space S1 in which the hollow fiber membrane bundle 14 is stored and an upper space S2 located above the storage space S1.

The upper end portion of the hollow fiber membrane 12 is fixed to the fixing member 18 . The upper end of the hollow fiber membrane 12 is open, and this opening communicates with the upper space S2 through a through hole 18a formed in the fixing member 18. As shown in FIG. On the other hand, the lower end of the hollow fiber membrane 12 is in a free state without being fixed anywhere.

A raw water pipe 22 connected to a pump 21 for supplying raw water and an air pipe 26 connected to a compressor 25 for supplying compressed air are connected to the lower end of the housing 16 . The raw water pipe 22 and the air pipe 26 are connected to each other to form one pipe, which is connected to the lower end of the housing 16 . The raw water pipe 22 and the air pipe 26 may be connected to the housing 16 separately.

By opening the on-off valve 22a provided in the raw water pipe 22, the raw water is introduced into the accommodation space S1. By opening the on-off valve 26a provided in the air pipe 26, compressed air for bubbling cleaning is introduced into the housing space S1. In the hollow fiber membrane module 10, the raw water introduced into the housing space S1 permeates from the outside to the inside of the hollow fiber membranes 12, thereby filtering the raw water. That is, the module 10 of the present embodiment is configured as an external pressure filtration type intermediate fiber membrane module in which pressure is applied to the hollow fiber membranes 12 from the outside. In addition, although the configuration in which the outer side of the hollow fiber membrane 12 is positively pressurized is employed in the present embodiment, the configuration is not limited to this. For example, a configuration may be adopted in which the inside of the hollow fiber membranes 12 is sucked, and as a result, the pressure on the outside becomes higher than the pressure on the inside, and the raw water permeates the hollow fiber membranes 12 from the outside to the inside.

A raw water discharge portion 28 is provided in the housing 16 so as to communicate with the accommodation space S1. A return pipe 29 for returning the raw water to the raw water supply destination is connected to the discharge portion 28 . Further, the housing 16 is provided with a filtered water discharge portion 31 so as to communicate with the upper space S2. A filtered water delivery pipe 32 is connected to the discharge portion 31 . A reverse pressure pipe 34 for performing reverse pressure washing is connected to the filtered water delivery pipe 32, and compressed air can be sent into the upper space S2 from a compressor 35 connected to the reverse pressure pipe 34.

(Hollow fiber membrane bundle)
The hollow fiber membrane bundle 14 has a plurality of hollow fiber membranes 12, and the plurality of hollow fiber membranes 12 are arranged in a bundle. The hollow fiber membrane bundle 14 preferably has a plurality of hollow fiber membranes 12 with an outer diameter in the range of 5 to 200 cm, more preferably 5 to 100 cm, and further preferably 5 to 50 cm. preferable.

The filling rate of the hollow fiber membrane bundle 14 in the housing 16 is preferably 20% or more and less than 65%, more preferably 20% or more and less than 60%, most preferably 20% or more, less than 55%. When the filling rate is less than 20%, a sufficient space is formed inside the housing 16, so that the ratio of contact between the hollow fiber membranes 12 is reduced, but the membrane area of the hollow fiber membrane bundle 14 is reduced. , the filtration performance is degraded. On the other hand, when the filling rate is 65% or more, the gap between the hollow fiber membranes 12 becomes small inside the housing 16, and it becomes difficult to obtain the effect of providing the projecting portion 40 described later. The filling rate is obtained by dividing (the cross-sectional area of the hollow fiber membranes 12×the number of hollow fiber membranes 12) by the cross-sectional area of the inner space of the housing 16 and multiplying the result by 100. The cross-sectional area of the inner space of the housing 16 is calculated by (1/2 the inner diameter of the housing 16)*(1/2 the inner diameter of the housing 16)*3.14.

(Hollow fiber membrane)
The material of the hollow fiber membrane 12 is not particularly limited, but in the case of the one-end free structure, it is preferable that the hollow fiber membrane 12 has a certain degree of flexibility in order to swing during physical cleaning. Specifically, the elongation of the hollow fiber membrane 12 is preferably 20% or more and less than 500%. More preferably 20% or more and less than 400%, most preferably 20% or more and less than 300%. If the elongation of the hollow fiber membrane 12 is smaller than this, sufficient strength cannot be maintained during shaking during physical cleaning, and problems such as breakage of the hollow fiber membrane 12 may occur. There is On the other hand, when it is 500% or more, the hollow fiber membranes 12 are too soft, and the effect of preventing the contact of the hollow fiber membranes 12 by the protruding portions 40 described later becomes difficult.

The effective length of the hollow fiber membrane 12 is preferably 0.3 m or more and 2.5 m or less, more preferably 0.3 m or more and 2.0 m or less, and most preferably 0.3 m or more and 1 m or less. .8 m or less. If the effective length is too short, the suspended matter can be sufficiently discharged without forming a gap in the hollow fiber membrane 12 . On the other hand, if the effective length is too long, there is a possibility that the effect of the projecting portion 40, which will be described later, cannot be effectively exhibited.

Although the outer diameter of the hollow fiber membrane 12 is not particularly limited, it is preferably 0.5 mm or more and less than 5.0 mm, more preferably 0.5 mm or more and less than 4.0 mm, and most preferably 0 mm. 0.5 mm or more and less than 3.0 mm.

(protrusion)
As shown in FIG. 2, one end of each hollow fiber membrane 12 is individually sealed with a sealant 38 . The sealant 38 uses a two-liquid mixed resin such as epoxy resin or urethane resin. A projecting portion 40 having a shape projecting from the outer surface of the hollow fiber membrane 12 is provided at one end of the hollow fiber membrane 12 by the resin forming the sealant 38 protruding to the outside of the hollow fiber membrane 12 . That is, the projecting portion 40 is provided integrally with the sealant 38 that closes the end portion of the tubular hollow fiber membrane 12 .

The width of the protrusion 40 is larger than the width of the hollow fiber membrane 12 . Specifically, the ratio of the maximum width (Dmax) of the protrusion 40 to the outer diameter (OD) of the hollow fiber membrane 12 is preferably greater than 1 and less than 3, more preferably 1. is greater than and less than 2.5 times, most preferably greater than 1 and less than 2 times. When the ratio Dmax/OD is 3 times or more, the width of one end of the hollow fiber membrane bundle 14 is too different from that of the other end, and problems such as bending or breaking of the hollow fiber membranes 12 occur during physical cleaning. can be.

The length (L) of the protrusion 40 in the longitudinal direction of the hollow fiber membrane 12 is preferably 0.05 cm or more and 15 cm or less, more preferably 0.1 cm or more and 10 cm or less, and most preferably , 0.1 cm or more and 5 cm or less. If the protruding portion 40 is too long, the effective length of the hollow fiber membrane 12 is shortened, resulting in a decrease in the processing flow rate. On the other hand, if the protruding portion 40 is too short, the anchoring effect of the resin sealant 38 forming the protruding portion 40 is reduced, resulting in a decrease in durability.

The projecting portion 40 is provided on each hollow fiber membrane 12 . As shown in FIG. 3, these projecting portions 40 are arranged at positions in contact with the projecting portions 40 provided on the adjacent hollow fiber membranes 12 . Since each projecting portion 40 is provided at the free end of each hollow fiber membrane 12, for example, if each end is located at a position equidistant from the fixing member 18, adjacent The projecting portions 40 are positioned so as to be able to contact each other. On the other hand, even if the respective ends are not exactly equidistant from the fixing member 18, if the variation in the effective length of the hollow fiber membranes 12 is within a predetermined range, the adjacent protrusions 40 will contact each other. It becomes possible. That is, as shown in FIG. 3, when viewed from the side, the projecting portion 40 provided on one hollow fiber membrane 12 and the projecting portion 40 provided on the adjacent hollow fiber membrane 12 are separated. If the two projecting portions 40 are arranged so as to have overlapping portions, the adjacent projecting portions 40 are positioned so as to be in contact with each other.

The error in the effective length of each hollow fiber membrane 12 is preferably less than 10%, more preferably less than 5%, and most preferably less than 2%.

In the hollow fiber membrane module 10 according to the present embodiment, when operated by the external pressure filtration method in which the processing liquid is passed from the outside to the inside of the hollow fiber membranes 12, from the outer peripheral side to the inner peripheral side of the hollow fiber membrane bundle 14 pressure towards. Therefore, if the hollow fiber membranes 12 are not provided with the protrusions 40, the contact area between the hollow fiber membranes 12 filled in the housing 16 increases as shown in FIG. In this case, particularly in the hollow fiber membranes 12 located inside the hollow fiber membrane bundle 14, it becomes difficult for water to pass through the portion where the hollow fiber membranes 12 are in contact with each other, and the water permeability tends to decrease. This can be confirmed by an evaluation test of pure water permeability. In particular, in the case of the hollow fiber membranes 12 having high pure water permeability, such a phenomenon occurs more remarkably because the resistance value of the contact portion between the hollow fiber membranes 12 becomes relatively large.

In addition, at the contact portion between the hollow fiber membranes 12, it is difficult for the turbidity components to be discharged during the physical backwashing, and the turbidity components tend to remain accumulated even after the backwashing. Therefore, even if the turbidity components can be separated from the hollow fiber membranes 12 by backwashing, if the gaps between the hollow fiber membranes 12 are insufficient, the turbidity components cannot be completely discharged and gradually accumulate. phenomenon occurs.

Therefore, by providing the hollow fiber membranes 12 with the protruding portions 40, it is possible to create gaps between the hollow fiber membranes 12 one by one, thereby not only improving the turbidity discharge performance but also It can facilitate water flow.

As described above, in the hollow fiber membrane module 10 according to the present embodiment, it is possible to prevent the hollow fiber membranes 12 from being kept in contact with each other due to the protrusions 40 coming into contact with each other. As a result, it is possible to prevent the water flow resistance of the hollow fiber membranes 12 from increasing when the raw water permeates the hollow fiber membranes from the outside to the inside, and to prevent the membrane effective utilization rate from being lowered. .

Further, in the present embodiment, since the protruding portion 40 is provided at the end portion of the hollow fiber membrane 12 that is sealed with the sealing agent 38, one end portion of the hollow fiber membrane 12 is sealed with the sealing agent 38. At the same time, it becomes possible to form the projecting portion 40 .

Here, in the example shown in FIG. 2, the projecting portion 40 is provided at the lower end portion of the hollow fiber membrane 12, which is the free end, but it is not limited to this. For example, as shown in FIG. 5 , the projecting portion 40 may be provided not at one end of the hollow fiber membrane 12 but at an intermediate portion in the length direction of the hollow fiber membrane 12 . In this case, the protrusion 40 is formed in a process separate from the process of sealing one end of the hollow fiber membrane 12 . Even in this case, each projecting portion 40 must be arranged at a position where they can contact each other.

The shape of the projecting portion 40 is not particularly limited, but a shape without corners is preferable. By doing so, even if the projecting portion 40 contacts the hollow fiber membrane 12, the hollow fiber membrane 12 can be prevented from being damaged.

For example, as shown in FIG. 2, protrusion 40 may be substantially spherical. Alternatively, the hollow fiber membrane 12 may be formed in an oblong shape elongated in the length direction. Further, as shown in FIG. 6, the protruding portion 40 includes a distal end side curved portion 40a having a curved outer surface, a tubular portion 40b extending substantially in the same width in the length direction of the hollow fiber membrane 12, and a curved portion. A configuration including a proximal side curved portion 40c having an outer surface may also be used. Further, as shown in FIG. 7, the projecting portion 40 includes a distal end side curved portion 40a having a curved outer surface, a tubular portion 40b extending in the length direction of the hollow fiber membrane 12 while changing the width, and a curved portion. It may be a configuration including a proximal side curved portion 40c having an outer surface of .

In the present embodiment, the hollow fiber membranes 12 are arranged so that the lower ends thereof are free, but the present invention is not limited to this. For example, the lower ends of the hollow fiber membranes 12 may be fixed to the fixing member 18, while the upper ends of the hollow fiber membranes 12 may be arranged in a free state where they are not fixed anywhere.

As shown in FIG. 8 , the hollow fiber membrane module 10 may be configured as an immersion type hollow fiber membrane module 10 . That is, the hollow fiber membrane module 10 has a fixing member 18, a hollow fiber membrane bundle 14, and a header 45, and is immersed in a raw water tank 47 in which raw water is stored. The hollow fiber membrane module 10 is configured such that the inside of the hollow fiber membranes 12 is sucked so as to have a negative pressure. As a result of this, the pressure on the outside is higher than the pressure on the inside. Therefore, filtered water flows into the header 45 as the raw water passes through the hollow fiber membranes 12 from the outside to the inside. A filtered water delivery pipe 32 is connected to the header 45 . An air pipe 26 for sending compressed air for bubbling cleaning is connected to the raw water tank 47 .

Examples are described below.

(Example 1)
A hollow fiber membrane module 10 as shown in FIG. 1 was produced using a hollow fiber membrane 12 having an elongation of 180%. The lower end of the hollow fiber membrane 12 is sealed with an epoxy resin, and the upper end of the hollow fiber membrane 12 is open. The effective length of the hollow fiber membranes 12 was 1 m, and the outer diameter of the hollow fiber membrane bundle 14 was 20 cm. The filling ratio of the hollow fiber membrane bundle 14 to the volume of the internal space of the housing 16 was 39%. The outer diameter (OD) of the hollow fiber membrane 12 was 1.25 mm, and the width (Dmax) of the protrusion 40 was 1.5 mm. Therefore, the ratio Dmax/OD of the width of the protrusion 40 to the outer diameter of the hollow fiber membrane 12 was 1.2. As a result, it was confirmed that a gap was formed between the hollow fiber membranes 12 . The error in the effective length of the hollow fiber membranes 12 was 2%.

(Example 2)
A hollow fiber membrane 12 having an effective length of 1.8 m and an outer diameter of 1.0 mm was used, and a protrusion 40 was formed on the hollow fiber membrane 12 so that the width Dmax was 2 mm. Dmax/OD at this time is 2.0.

The hollow fiber membranes 12 were used to make a hollow fiber membrane bundle 14 having an outer diameter of 20 cm and housed in a housing 16 . The filling rate of the hollow fiber membrane bundle 14 was 45% (Example 3)
A hollow fiber membrane 12 having an effective length of 0.3 m and an outer diameter of 2.0 mm was used, and a protrusion 40 was formed on the hollow fiber membrane 12 so that the width Dmax was 2.5 mm. Dmax/OD at this time is 1.25.

The hollow fiber membranes 12 were used to make a hollow fiber membrane bundle 14 having an outer diameter of 20 cm and housed in a housing 16 . The filling rate of the hollow fiber membrane bundle 14 was 26%.

(Comparative example 1)
For the hollow fiber membranes 12 having a width OD of 1.25 mm, the ends of the hollow fiber membranes 12 were sealed with a sealant 38 so that the width OD of the hollow fiber membrane bundle 14 was 1.25 mm. Since the sealant 38 does not protrude from the outer surface of the hollow fiber membrane 12, no protrusion 40 is formed. That is, Dmax/OD is 1.0. Other than that, the configuration is the same as that of the first embodiment.

(Comparative example 2)
In Comparative Example 2, as in Comparative Example 1, the ends of the hollow fiber membranes 12 were adjusted so that the width OD of the hollow fiber membrane bundle 14 was 1.25 mm for the hollow fiber membranes 12 having a width OD of 1.25 mm. The part was sealed with a sealant 38 . Since the sealant 38 does not protrude from the outer surface of the hollow fiber membrane 12, no protrusion 40 is formed. On the other hand, in Comparative Example 2, unlike Comparative Example 1, the filling rate of the hollow fiber membrane bundle 14 is set to 10%. Other than that, the configuration is the same as that of Comparative Example 1.

(Comparative Example 3)
It was difficult to produce a hollow fiber membrane bundle 14 with a Dmax/OD ratio of 3 times or more, and could not be evaluated.

(Comparative Example 4)
A hollow fiber membrane bundle 14 was produced using the hollow fiber membranes 12 having the same structure as in Example 1, and an attempt was made to increase the filling rate to 65% or more, but it was impossible to produce such a hollow fiber membrane module 10. could not.

(Evaluation method for each parameter)
The elongation of the hollow fiber membrane 12 was measured as follows. First, the hollow fiber membrane 12 to be measured was cut into pieces of 5 cm. A tensile test was performed on the cut hollow fiber membrane 12 using an autograph (AG-Xplus manufactured by Shimadzu Corporation) in water at 25° C. at a speed of 100 mm/min. Then, the length when the hollow fiber membrane 12 was broken was measured. Elongation (%) was defined as the percentage of the numerical value obtained by dividing the effective length of the hollow fiber membrane 12 when broken by the original length of the object to be measured.

The outer diameter of the hollow fiber membrane 12 was as follows. The hollow fiber membrane 12 is cut with a cutter knife, the cut cross section is observed with a microscope (VHX-6000 manufactured by Keyence Corporation), and the average outer diameter of the 20 hollow fiber membranes 12 is determined by the outer diameter of the hollow fiber membrane 12. defined as

The maximum outer diameter of the sealing portion, that is, the width of the protrusion 40 was measured using a digital vernier caliper. Thirty maximum sizes of the sealing portions (maximum width portions of the projecting portions 40) were measured, and the average value thereof was taken as the width (maximum outer diameter) of the projecting portions 40. FIG.

The effective length error was obtained by dividing the standard deviation of the effective lengths of all the hollow fiber membranes 12 of the hollow fiber membrane bundle 14 by the average value (synonymous with CV value).

(Effect evaluation method of turbidity discharge property)
Model water consisting of a suspension of ferric hydroxide and having an SS concentration of 300 mg/L is used as raw water, and a hollow fiber membrane module is used to perform an external pressure total filtration method at a flow rate of 150 LMH (L/m ² /h). Constant flow filtration was performed at rt for 30 minutes. After the filtration operation, back pressure cleaning was performed from the filtrate side of the hollow fiber membrane module with compressed air of 0.2 MPa, and then bubbling cleaning was performed from the bottom. The air flow rate for bubbling was 1700 NL/h. The turbidity discharge performance was evaluated by the ratio of the amount of SS discharged from the housing 16 by bubbling washing to the amount of SS supplied to the hollow fiber membrane module during the filtration operation.

(Method for evaluating effect of pure water permeability)
The pure water permeability obtained when a pressure of 100 kPa was applied to the hollow fiber membrane module with pure water was defined as the pure water permeability (m ³ /h/100 kPa).

(Module membrane effective utilization rate)
While the value obtained by multiplying the water permeability measured with one hollow fiber membrane 12 by the number of hollow fiber membranes 12 is regarded as the theoretical module water permeability, the module water permeability when actually measured with the hollow fiber membrane module. The value obtained by dividing the property by the theoretical module water permeability and multiplying by 100 was taken as the membrane effective utilization rate (%).

(Evaluation results)
As shown in Table 1, the hollow fiber membrane module 10 of Example 1 had a turbidity discharge property of 98%. Similarly, in Examples 2 and 3, the turbidity discharge properties were 97% and 99%, respectively. On the other hand, in Comparative Example 1, the turbidity discharge property was as low as 85%. As a result, it can be seen that the hollow fiber membrane 12 having the protruding portion 40 has improved turbidity discharge properties compared to the hollow fiber membrane 12 having no protruding portion 40 . That is, it is presumed that the formation of the protruding portions 40 suppresses the contact between the hollow fiber membranes 12, thereby improving the SS discharge performance by bubbling cleaning. Moreover, in terms of membrane effective utilization rate, Examples 1 to 3 were all higher than Comparative Examples 1 and 2. That is, it can be seen that due to the presence of the projecting portion 40, the module water permeability of the hollow fiber membrane bundle 14 is less likely to decrease from the theoretical module water permeability. That is, it can be seen that the presence of the protruding portion 40 suppresses an increase in the contact area between the hollow fiber membranes 12 and does not lower the water permeability performance. On the other hand, in Comparative Example 2, the turbidity discharge property is as high as 98%, but in Comparative Example 2, the filling rate is as low as 10%. It is presumed that the turbidity discharge is high due to the On the other hand, in Comparative Example 2, as in Comparative Example 1, the effective utilization rate is lower than in Examples 1-3. From this, it can be said that there is a possibility that the hollow fiber membranes are in contact with each other even if the filling rate is about 10%. The pure water permeability of the module is lower in Comparative Example 2 than in Examples 1-3. This is because in Comparative Example 2, the filling rate is low and the film area is small in the first place.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications and improvements are possible without departing from the spirit of the present invention.

REFERENCE SIGNS LIST 10 hollow fiber membrane module 12 hollow fiber membrane 14 hollow fiber membrane bundle 16 housing 18 fixing member 38 sealant 40 protrusion

Claims (9)

A hollow fiber membrane bundle having a plurality of hollow fiber membranes through which raw water permeates from the outside to the inside, one end of each hollow fiber membrane being sealed with a sealing agent;
a fixing member that fixes the other ends of the plurality of hollow fiber membranes while the other ends are open;
with
The hollow fiber membrane bundle is a one-end free type in which the one end of the hollow fiber membrane is not fixed,
Each of the plurality of hollow fiber membranes is provided with a protrusion having a shape protruding from the outer surface of the hollow fiber membrane, and the hollow fiber membrane provided with the protrusion has an elongation of 20% or more. is less than 500% and the effective length is specified to be 0.3 m or more and 2.5 m or less,
The hollow fiber membrane module, wherein the protruding portion is arranged at a position in contact with the protruding portion provided on the adjacent hollow fiber membrane. 2. The hollow fiber membrane module according to claim 1, wherein the protrusion is provided at the one end sealed with the sealant. 3. The hollow fiber membrane module according to claim 2, wherein the effective length error of the plurality of hollow fiber membranes is less than 10%. 2. The hollow fiber membrane module according to claim 1, wherein the protruding portion is provided at an intermediate portion in the length direction of each of the plurality of hollow fiber membranes. 5. The hollow fiber membrane module according to any one of claims 1 to 4, wherein the protrusion has a shape without corners. The hollow fiber membrane module according to any one of claims 1 to 5, further comprising a housing in which the hollow fiber membrane bundle is accommodated. 7. The hollow fiber membrane module according to claim 6, wherein the hollow fiber membrane bundle has a filling rate of 20% or more and less than 65% in the internal space of the housing. 8. The hollow fiber membrane module according to any one of claims 1 to 7, wherein the width of the protrusion is more than 1 time and less than 3 times the outer diameter of the hollow fiber membrane. 7. The hollow fiber membrane module according to claim 6, which is an external pressure filtration system in which pressure is applied to the hollow fiber membranes from the outside.

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