WO2006126833A1

WO2006126833A1 - Immersed hollow fiber membrane module

Info

Publication number: WO2006126833A1
Application number: PCT/KR2006/001951
Authority: WO
Inventors: Sang Hoon Kim; Hang Duk Rho; Sung Su Bae; Tae Jeong Kim; Tae Duog Lee; Sung Du Leem
Original assignee: Sk Chemicals Co., Ltd.
Priority date: 2005-05-25
Filing date: 2006-05-24
Publication date: 2006-11-30
Also published as: KR20060122024A; KR101214439B1

Abstract

The present invention relates to an immersed hollow fiber membrane module. More particularly, the present invention relates to an immersed hollow- fiber membrane module into which a guide for protecting and supporting the hollow fiber membrane and a new type of air diffuser to prevent entanglement and damage of the hollow fiber membrane and minimize fouling of the hollow fiber membrane.

Description

IMMERSED HOLLOW FIBER MEMBRANE MODULE

Technical Field

The present invention relates to an immersed hollow fiber membrane

module, particularly to an immersed hollow fiber membrane module into which a

guide for protecting and supporting the hollow fiber membrane and a new type of

air diffuser to prevent entanglement and damage of the hollow fiber membrane and

minimize fouling of the hollow fiber membrane.

Background Art

Since its first introduction for water purification and treatment of sewage

and wastewater in the 1960s, the use of a separation membrane has been increased

by leaps and bounds. Till now, the separation membrane has been mainly used for

advanced treatment, or treatment of primarily treated wastewater to further

improve the quality of water.

Although the conventional method provides relatively good quality of water,

it has disadvantages that there is required an additional facility for a separation

membrane process, thus increasing costs for installation, operation and maintenance.

To solve this problem, Kazuo Yamamoto et al. conducted the first successful experimentation of treating wastewater by immersing hollow fiber membrane

directly in the aeration tank based ("Direct Solid-Liquid Separation Using Hollow

Fiber Membrane in an Activated Sludge Aeration Tank") in 1989, and this resulted

in the rapid development in the membrane bioreactor (MBR) process.

The MBR process offers are considered very advantageous as set forth below.

First, the concentration (MLSS) of the activated sludge can be maintained at a

relatively higher level (8,000-15,000 ppm) than that of the conventional activated

sludge process, and thus sewage can be treated with less retention time, thereby

reducing the space required for sewage treatment. Second, stable sewage treatment

is possible even when the activated sludge does not sediment well, which may occur

in such bacterial process as the standard activated sludge process, because of organic

shock loading, bulking, foaming, etc.

However, the MBR process is prone to contamination of the separation

membrane, or membrane fouling.

Sewage treatment using separation membrane is mostly driven by pressure

difference. Membrane fouling resulting from the accumulation of activated sludge

or other membrane fouling materials on the surface or in the pores of the membrane

reduces effective membrane surface area and, thereby, reduces treatment capacity.

Many researchers have made extensive efforts to develop materials for separation membrane which are resistant to membrane fouling. Also, studies have

been also made on the method to induce a cross flow on the membrane surface.

Researches on the separation membrane materials have been mainly focused

on modifying the membrane surface to have hydrophilic property using surfactants,

plasma, etc. Also, researches on physical solutions using air flow on the membrane

surface, especially by inducing a cross flow to sweep off the sludge cake

accumulated on the membrane surface or preventing the accumulation, have been

performed.

The conventional hollow fiber membrane modules for solving the membrane

fouling problem are as follows.

The hollow fiber membrane modules of Mitsubishi Rayon and Zenon are of

the type with the treated water collectors positioned at both ends. In these modules,

the water treated by the separation membrane is collected at the collectors and

transferred to the treatment tank by pumps.

In this type of modules, the movement of the hollow fiber membrane is

restricted because its both ends are fastened to the treated water collectors.

Consequently, despite the cross flow of treated water by air supply (supplied to the

hollow fiber membrane surface) or the physical shaking by air supply (vibration),

the sludge accumulated on the hollow fiber membrane is not removed easily. Especially, the hollow fiber membrane modules of the two companies have

two locations where decompression occurs first (i.e., the locations where the

pressure difference is largest) and strong sludge accumulation there cannot be

prevented.

The module of Zenon also has a problem that the activated sludge carried

upward by the air supplied at the bottom does not completely escape from the top

collector but is accumulated therein, resulting in an interrupted flow and

accumulation of sludge. In addition, because the air diffuser is equipped at the

bottom of the module, air is not directly transferred to the hollow fiber membrane

module, resulting in increased air loss. As a result, the energy required for

maintaining the air supply accounts for 30 to 70 % of total power consumption.

Such inefficient air supply triggers propagation of membrane fouling

(especially by sludge cake) to the region with larger pressure difference, or to the

less contaminated region. Consequently, the entire hollow fiber membrane is

contaminated, thereby reducing the cycle of maintenance cleaning and the durability

of the hollow fiber membrane.

The conventional hollow fiber membrane modules with the treated water

collector positioned at one end to solve the membrane fouling problem (the other

end is free end) are as follows. Although the use may be said to be different, a similar module with the

collector positioned at one end was disclosed in "Use of Sealed-End Hollow Fibers

for Bubbleless Membrane Aeration: Experimental Studies" by T. Ahmed et al. in

1992.

In addition, modules almost identical to that of the above paper are disclosed

in JP 11128692 by filed Toray and in JP 10202270 filed by Kuraray.

These modules are quite differently from the modules with the collectors

positioned at both ends in operation type, productivity and durability. As is often

found in the Toray's module, the sealed part at one end of the hollow fiber

membrane tends to be cut off during operation. Besides the durability problem,

membrane fouling is hardly reduced because of lack of air supply.

The most frequently occurring problem of the module with only one end of

the hollow fiber membrane fastened is that the hollow fiber membrane becomes

entangled as it falls or abnormal treated water flow happens because of a

non-uniform air flow. Physical stress is focused on the entangled region, resulting

in cutting off at the entangled part or at the interface with a binder.

The hollow fiber membrane (separation membrane) may not fall during the

operation of inside the aeration tank, but it may fall easily as the hollow fiber

membrane module is taken out of the aeration tank for maintenance or other purposes. And, the hollow fiber membrane may get entangled when the air

diffuser is inclined during the operation. In that case, there occurs water pressure

difference in the air diffuser. Less air is supplied at the region with higher water

pressure, while more air is supplied at the region with lower water pressure,

resulting in flow from the higher air supply region to the lower air supply region,

which makes the hollow fiber membrane entangled.

Also, if the hollow fiber membrane module is inclined, a regularly patterned

flow cannot be induced because the supplied air reaches different regions of the

module. The resultant abnormal flow causes counterflow in the module, thereby

resulting in entanglement of the hollow fiber membrane. Physical stress is focused

on the entangled region, resulting in cutting off at the entangled part or at the

interface with a binder.

Disclosure of the Invention

The present invention was come up with in order to solve the

afore-mentioned problems. An object of the present invention is to provide an

immersed hollow fiber membrane module in which a guide for protecting the

hollow fiber membrane is used to prevent tilting or entanglement of the hollow fiber

membrane and an air diffuser with new structure is provided at the guide, so that contamination of the hollow fiber membrane surface can be minimized with a small

amount of air.

In order to attain the above goal, the present invention provides an

immersed hollow fiber membrane module comprising: a hollow fiber membrane

bundle, wherein the top end is sealed as a free end and the bottom end is open; a

bottom collector which comprises an upper block to which the bottom end of the

hollow fiber membrane bundle is fastened by a binder and a lower block at which

the treated water discharged from the hollow fiber membrane is collected; an air

diffuser which is formed on the upper block; an air supply pipe which is vertically

connected to the air diffuser; a treated water discharge pipe which is vertically

connected to the inside of the lower block; and a guide which encloses and protects

the entire hollow fiber membrane bundle wherein the bottom end of the guide is

engaged with the top surface of the upper block.

Preferably, the guide is squared and has a wastewater inlet which penetrates

the lower part of the guide from the front to the back.

The upper block of the bottom collector is squared and has a fastening means,

at which the hollow fiber membrane bundle is bound and fastened by a guider, on

the top; a united hole, through which the treated water discharge pipe passes, at one

end; and a united protrusion, by which the lower block is engaged, at the bottom. The lower block of the bottom collector is also squared and has an engaging

groove, in which the engaging protrusion is seated, on the top; a collection passage

for the treated water discharged from the open bottom end of the hollow fiber

membrane bundle, inside the engaging groove; and a united hole, through which

the treated water discharge pipe passes, at one end.

Preferably, the air diffuser comprises: an air inlet which is formed on one end

of the upper block (at the opposite side of the engagement hole), so that the bottom

end of the air supply pipe can be inserted; air supply lines which are connected with

the air inlet and are formed along the edge of the fastening means by which the

hollow fiber membrane bundle is fastened; and a plurality of air nozzles formed at

the air supply lines with equal spacing, with an angle of 45° to 65° to the hollow

fiber membrane, as injection holes.

Several of such immersed hollow fiber membrane modules are installed

inside a cassette of a SKID frame depending on the capacity of the aeration tank.

Preferably, on each end of the cassette are attached an air supply main pipe,

which is connected to the air supply pipe of each of the immersed hollow fiber

membrane modules, and a final discharge pipe, which is connected to each of the

treated water discharge pipe.

Hereinafter, the embodiments of the present invention will be described in detail with reference to accompanying drawings.

Fig. 1 and Fig. 2 are perspective views of the immersed hollow fiber

membrane module according to the present invention and Fig. 3 is a perspective

view illustrating the state in which several hollow fiber membrane modules are

installed inside a cassette.

The subject matter of the present invention is that a squared guide for

protecting the hollow fiber membrane bundle is used to prevent tilting,

entanglement and damage of the hollow fiber membrane and that a new type of air

diffuser is equipped at the bottom collector in order to minimize contamination of

the hollow fiber membrane surface with a small amount of air.

The immersed hollow fiber membrane module of the present invention

comprises a hollow fiber membrane (10), a bottom collector (12), a guide (14) for

protecting the hollow fiber membrane, an air diffuser, etc.

As seen in Fig. 1, the top end of the individual hollow fiber membrane (10) is

sealed as free end and the bottom end is in the form of open tube. The bottom end

of the hollow fiber membrane bundle is fastened to the bottom collector (12) by a

binder (16: adhesive).

In another embodiment, as seen in Fig. 2, the entire top end of the hollow

fiber membrane bundle (10) may be sealed by a sealant (adhesive). The squared guide (14) is fixed on the bottom collector (12). The hollow-

fiber membrane bundle (10) is accommodated inside the guide (14) to prevent the

hollow fiber membrane (10) from being tilted, entangled and damaged.

That is, when external force (e.g., flow of air or wastewater) is applied to the

hollow fiber membrane (10), the squared guide (14) prevents the hollow fiber

membrane (10) from being tilted, entangled and damaged by supporting the hollow

fiber membrane (10).

The guide (14) has a wastewater inlet (18) which penetrates the lower part of

the guide (14) from the front to the back.

The construction of a bottom collector having an air diffuser is as follows.

Fig. 4 and Fig. 5 show perspective views of the collector of the immersed

hollow fiber membrane module in accordance with the present invention showing

the separated state. And, Fig. 6 is a perspective view showing the assembled state.

The bottom collector (12) comprises an upper block (20), to which the bottom

end of a hollow fiber membrane bundle (10) is fastened by a binder (16), and a lower

block (22), at which the treated water discharged from the bottom end of the hollow

fiber membrane (10) is collected.

The upper block (20) of the bottom collector (12) is a squared block and has a

fastening means (24), at which the hollow fiber membrane bundle (10) is bound and fastened by the binder (16), on the top, an engagement hole (28), through which a

treated water discharge pipe (30) passes, at one end, and an engaging protrusion (32),

by which the lower block (22) is engaged, at the bottom.

The fastening means (24) has a stair-shaped leak bump (58) at the inner

circumference for preventing leakage caused by contraction of the binder (16).

After the bottom end of the hollow fiber membrane bundle (10) is bonded

and fastened to the fastening means (24) of the upper block (20) by molding with an

adhesive, the bottom end of the hollow fiber membrane bundle (10) protruding out

of the fastening means (24) is cut off along with the binder. As a result, the bottom

end of the hollow fiber membrane bundle (10) is aligned parallel to the engaging

protrusion (32) and becomes opened.

The upper block (20) is also equipped with an air diffuser. An air inlet (34)

is formed on one end of the upper block (20) [at the opposite side of the engagement

hole (28)]. A pair of air supply lines (36) are formed along the edge of the fastening

means (24) by which the hollow fiber membrane bundle (10) is fastened. And a

plurality of air nozzles are formed at the air supply lines with equal spacing,

resulting in an air supply passage.

The air nozzles (38) are formed with an angle of from 45° to 65° with

reference to the hollow fiber membrane bundle (10), as injection holes. The air inlet (34) of the upper block (20) is engaged with the bottom end of an

air supply pipe (40) and the engagement hole (28) at the opposite side is engaged

with the bottom end of a treated water discharge pipe (30). The air supply pipe (40)

and the treated water discharge pipe (30) are set upright and stretch to the top end

of the guide (14), as accommodated in the guide (14).

The lower block (22) of the bottom collector (12) is squared and matches the

bottom of the upper block (20). The lower block (22) has an engaging groove (42),

in which an engaging protrusion (32) formed at the bottom of the upper block (20) is

seated, on the top; a collection passage (44) for the treated water discharged from the

open bottom end of the hollow fiber membrane bundle (10), inside the engaging

groove (42); and an insertion hole (46), through which the treated water discharge

pipe (30) passes, at one end.

The upper block (20) and the lower block (22) are assembled as follows. The

engaging protrusion (32) of the upper block (20) is inserted into the engaging groove

(42) of the lower block (22) and bolts (48) are inserted into a plurality of bolt holes

formed along the edge of the upper block (20) and the lower block (22). The bottom

end of the hollow fiber membrane bundle (10) is cut off, so that it is aligned parallel

to the engaging protrusion (32) and becomes open and connected to the treated

water collection passage (44) of the lower block (22). A rubber seal (50) is equipped on top of the lower block (22) at which it

engages with the upper block (20), i.e., along the outer circumference of the

engaging groove (42), in order to prevent the treated water collected at the collection

passage (44) of the lower block (22) from being leaked.

Several of such immersed hollow fiber membrane modules are installed

inside a cassette (52), or a framework, depending on the capacity of the aeration tank,

as seen in Fig. 3.

On each end of the cassette (52) are attached an air supply main pipe (54),

which is connected to the air supply pipe (40) of each of the immersed hollow fiber

membrane modules, and a final discharge pipe (56), which is connected to each of

the treated water discharge pipe (30).

Of course, the air supply main pipe (54) is connected to an air supply means

(not shown) and the final discharge pipe (56) is connected to a container for

collecting or post-treating the treated water.

The immersed hollow fiber membrane module of the present invention is

operated as follows.

First, a cassette (52) in which several immersed hollow fiber membrane

modules are installed is immersed in an aeration tank (not shown) containing

wastewater. Then, the wastewater in the aeration tank flows toward the hollow fiber

membrane bundle (10) through the inlet (18) of the guide (14). At the same time,

the wastewater is passed through the hollow fiber membrane (10) by external

pressure, while being filtered.

The hollow fiber membrane (10) may be, for example, a tube having an outer

diameter ranging from 0.2 to 4.2 mm and an inner diameter ranging from 0.05 to 4.1

mm made of polysulfone, sulfonated polysulfone, polyethersulfone, polyvinylidene

fluoride, etc. It has numerous micropore size that are hardly discernible with eyes.

That is, the wastewater is filtered while it passes from the outside to the

inside of the hollow fiber membrane (10).

The filtered treated water flows down inside the hollow fiber membrane (10)

and is collected at the treated water collection passage (44) of the lower block (22) of

the bottom collector (12).

Subsequently, the treated water collected at the treated water collection

passage (44) of the lower block (22) is discharged through the treated water

discharge pipe (30) inserted in the insertion hole (46) of the lower block (22), as seen

in Fig. 9. Then, the treated water flows into the facility for post-treatment or

collection through a final discharge pipe (56), which is formed from the combination

of the treated water discharge pipe (30) of each hollow fiber membrane module. As the wastewater is filtered, the surface of the hollow fiber membrane is

contaminated by impurities (dirt, cake, clog), particularly by sludge cake. The air

diffuser removes the impurities to prevent membrane fouling.

Removal of impurities by the air diffuser may be carried out as follows.

Air may be sprayed on the surface of the hollow fiber membrane (10) to

detach sludge cake or other impurities. Especially, by inducing cross flow of

wastewater with the sprayed air, accumulation of sludge cake on the membrane

surface can be prevented.

First, air is supplied to the air supply pipe (40) of each hollow fiber

membrane module through the air supply main pipe (54) equipped on one end of

the cassette (14) (see Fig. 7).

Subsequently, the air is supplied to the pair of air supply lines (36) through

the air inlet (34) of the upper block (20). Finally, it is sprayed through the air

nozzles (38: injection holes formed at an angle of about 45° to 65° to the hollow

fiber membrane) formed on the air supply lines (36) with equal spacing (see Fig. 8).

Since air is sprayed uniformly at the front and back of the bottom end of the

hollow fiber membrane bundle (10), impurities can be removed easily with a small

amount of air.

As a result, bubbles formed in the wastewater by the air sprayed through the air nozzles (38) offer the effect of scrubbing and vibration as they rise, thereby

removing sludge cake or other impurities accumulated on the surface of the hollow

fiber membrane (10).

As seen in Fig. 10, the wastewater is filtered in the horizontal direction

[perpendicular to the hollow fiber membrane (10)], while the air and the bubbles rise

upward.

More particularly, the filtering direction of the wastewater and the rising

direction of the bubbles are perpendicular to each other and, thus, induce cross flow.

The cross flow removes impurities as they are accumulated on the surface of the

hollow fiber membrane (10) and, thus, minimizes membrane fouling.

In conventional methods, an abnormal flow of wastewater or a non-uniform

flow of air causes falling or entanglement of the hollow fiber membrane, thereby

resulting in the cutting off of the hollow fiber membrane. In contrast, the present

invention is free from such problem because the hollow fiber membrane bundle (10)

is installed in the squared guide (14).

That is, even when physical stress caused by abnormal flow is accumulated

on the hollow fiber membrane (10), the squared guide (14) supports the hollow fiber

membrane (10) and prevents it from falling or being entangled. Brief Description of the Drawings

Fig. 1 is a perspective view of the immersed hollow fiber membrane module

according to the present invention.

Fig. 2 is a perspective view of the immersed hollow fiber membrane module

according to another embodiment of the present invention.

Fig. 3 is a perspective view illustrating the state in which several of the

hollow fiber membrane modules shown in Fig. 1 are installed inside a cassette.

Fig. 4 and Fig. 5 are perspective views of the collector of the immersed

hollow fiber membrane module in accordance with the present invention showing

the separated state.

Fig. 6 is a perspective view of the collector of the immersed hollow fiber

membrane module in accordance with the present invention showing the assembled

state.

Fig. 7 is a cross-sectional view of Fig. 6 along the line A-A.

Fig. 8 is a cross-sectional view of Fig. 6 along the line B-B.

Fig. 9 is a cross-sectional view of Fig. 6 along the line C-C.

Fig. 10 is a schematic diagram for illustrating the process by which the cross

flow of wastewater is induced by the action of the air diffuser of the immersed

hollow fiber membrane module in accordance with the present invention. Fig. 11 is a graph showing the membrane resistance of the immersed hollow

fiber membrane module with or without a guide.

Best Mode for Carrying Out the Invention

Practical and preferred embodiments of the present invention are illustrated

as shown in the following examples. However, it will be appreciated that those

skilled in the art may, in consideration of this disclosure, make modifications or

improvements within the spirit and scope of the present invention.

As can be seen in the result of Experimental Examples 1 and 2 below, the

immersed hollow fiber membrane module of the present invention experienced little

damage of the hollow fiber membrane and used 1/3 of air compared with the

conventional methods. Thus, 30 to 70 % of energy saving can be attained with

regard to operation and maintenance.

Experimental Example 1

An experiment was performed to compare air consumption by the immersed

hollow fiber membrane module in accordance with present invention and the

conventional hollow fiber membrane module.

At an activated-sludge concentration (MLSS: mixed liquor suspended solids) of 8,000, the modules of the present invention, M company and Z company were

operated at a fixed flux (throughput) of 25 LMH (L/m²/hr). The surface area of

each hollow fiber membrane was 1 m².

Operation scheme is as follows: constant-flow operation using inverter;

normal washing for 14 minutes and reverse washing for 1 minute. The optimum

air amount was determined by varying air flow until there was no change in

pressure and flow rate.

As seen in Table 1 below, the amount of air required to prevent membrane

fouling was 0.08 Nm³/min-module for the present invention, about 1/3 that of the

conventional methods.

Table 1

Experimental Example 2

Maintenance cost of the immersed hollow fiber membrane module of the

present invention was compared with those of M company and Z company at an

MBR sewage works.

Power consumption by the hollow fiber membrane module for air supply accounted for 30 % or more of the total power consumption, which means that air

supply takes up quite a large portion of the management cost.

As seen in Table 2 below, the present invention reduced about 40 % of

management cost.

Table 2

Maintenance cost per ton (unit: won/m³)

Experimental Example 3

Membrane fouling of the immersed hollow fiber membrane module of the

present invention was measured with or without the squared guide. The result is

shown in Fig. 11.

As seen in Fig. 11, the membrane resistance differed as much as double

depending on the presence of the guide. When there was no guide, membrane

fouling was accelerated because of air loss, thereby increasing the membrane

resistance. To conclude, the guide used in the immersed hollow fiber membrane module

of the present invention prevents tilting and entanglement of the hollow fiber

membrane while minimizing air loss. As a result, the membrane resistance

constant of the hollow fiber membrane remains at a level almost same as that of the

initial one and thus membrane fouling can be minimized.

Industrial Applicability

As apparent from the foregoing description, the immersed hollow fiber

membrane module in accordance with the present invention offers the following

advantageous effects.

1) With the air supplied from the air diffuser inside the bottom collector,

impurities (dirt, cake, clog) can be easily removed from the hollow fiber membrane.

Therefore, the problems of entanglement and cutting off of the hollow fiber

membrane and membrane fouling can be resolved.

2) The air supplied from the air diffuser induces cross flow inside the guide,

which prevents the air from leaking outward while offering quick flow inside the

guide. Therefore, accumulation of impurities on the surface of the hollow fiber

membrane can be prevented effectively.

3) Although the tope end of the hollow fiber membrane is sealed as free end, the protective and supporting action of the guide prevents the hollow fiber

membrane from tilting or being entangled.

4) Several of the squared hollow fiber membrane modules of the present

invention can be installed to cope with large capacity. The small spacing between

each module saves installation space as compared with the conventional immersed

modules.

5) Damage of membrane can be checked during operation. That is, damage

of the hollow fiber membrane can be checked from air pressure difference and visual

inspection.

6) The immersed hollow fiber membrane module of the present invention

can reduce air consumption to about 1/3, compared with the conventional

immersed hollow fiber membrane modules, and saves operation and maintenance

cost by 30 to 70 %.

Those skilled in the art will appreciate that the concepts and specific

embodiments disclosed in the foregoing description may be readily utilized as a

basis for modifying or designing other embodiments for carrying out the same

purposes of the present invention. Those skilled in the art will also appreciate that

such equivalent embodiments do not depart from the spirit and scope of the present

invention as set forth in the appended claims.

Claims

1. An immersed hollow fiber membrane module comprising:

(a) a hollow fiber membrane bundle, wherein the top end is sealed as a free

end and the bottom end is open;

(b) a bottom collector which comprises an upper block to which the bottom

end of the hollow fiber membrane bundle is fastened by a binder and a lower block

at which the treated water discharged from the hollow fiber membrane is collected;

(c) an air diffuser which is formed on the upper block;

(d) an air supply pipe which is vertically connected to the air diffuser;

(e) a treated water discharge pipe which is vertically connected to the inside

of the lower block; and

(f) a guide which encloses and protects the entire hollow fiber membrane

bundle wherein the bottom end of guide is engaged with the top surface of the

upper block.

2. The immersed hollow fiber membrane module as set forth in Claim 1,

wherein the guide is squared and has a wastewater inlet which penetrates the lower

part of the guide from the front to the back.

3. The immersed hollow fiber membrane module as set forth in Claim 1,

wherein the upper block of the bottom collector is squared and has (a) a fastening

means, at which the hollow fiber membrane bundle is bound and fastened by a

binder, on the top; (b) an engagement hole, through which the treated water

discharge pipe passes, at one end; and (c) an engaging protrusion, by which the

lower block is engaged, at the bottom.

4. The immersed hollow fiber membrane module as set forth in Claim 1,

wherein the lower block of the bottom collector is also squared and has (a) an

engaging groove, in which the engaging protrusion is seated, on the top; (b) a

collection passage for the treated water discharged from the open bottom end of the

hollow fiber membrane bundle, inside the engaging groove; and (c) an insertion hole,

through which the treated water discharge pipe passes, at one end.

5. The immersed hollow fiber membrane module as set forth in Claim 1,

wherein the air diffuser comprises:

(a) an air inlet which is formed on one end of the upper block (at the opposite

side of the engagement hole), so that the bottom end of the air supply pipe can be

inserted; (b) air supply lines which are connected with the air inlet and are formed

along the edge of the fastening means by which the hollow fiber membrane bundle

is fastened; and

(c) a plurality of air nozzles formed at the air supply lines with equal spacing,

with an angle of 45° to 65° to the hollow fiber membrane, as injection holes.

6. The immersed hollow fiber membrane module as set forth in any of

Claims 1 to 5, which is installed inside a cassette of a frame, depending on the

capacity of the aeration tank, along with other such immersed hollow fiber

membrane modules.

7. The immersed hollow fiber membrane module as set forth in Claims 6,

wherein on each end of the cassette are attached an air supply main pipe, which is

connected to the air supply pipe of each of the immersed hollow fiber membrane

modules, and a final discharge pipe, which is connected to each of the treated water

discharge pipe.