1. A membrane element comprising: a membrane supporting member arranged along a flowing direction of a liquid to be treated; and a filtration membrane formed of a flat sheet membrane that is arranged to cover both front and back surfaces of the membrane supporting member and is loop-shaped to have a reversed portion folded so as to include ends on an upstream side and a downstream side of the membrane supporting member.

2. The membrane element according to claim 1, wherein the filtration membrane includes at least one joined portion, the joined portion is formed by arranging ends of the filtration membrane to be stacked on top of each other on the surfaces or end faces of the membrane supporting member and joining a back surface at one end onto a front surface at the other end of the filtration membrane, and the end facing the downstream side, out of the ends of the filtration membrane stacked in the joined portion is arranged on an outer side.

3. A membrane module comprising: at least one membrane element;and at least one water collecting case, wherein the membrane element comprises: a membrane supporting member arranged along a flowing direction of a luquid to be treated; a filtration membraneformed of a flat sheet membrane that is arranged to cover both front and back surfaces of the membrance supporting member and is loop-shaped to have a reversed portion folded so as to include ends on an upstream side and a downstream side of the membrane supporting member; and the water collecting case includes an opening portion communicating with a water collecting space therein and keeps water-tight sides of the membrane element inserted in the opening portion.

4. The membrane element according to claim 1, further comprising: a sealing material formed water-tightly on an edge side portion of the filtration membrane on both sides of the membrane supporting member along the flowing direction of the liquid to be treated. By forming a filtration membrane in a loop shape, it is possible to apply a high internal pressure and perform reverse liquid cleaning at a high internal pressure in chemical cleaning. A membrane element and a membrane module in which breakage and peeling are unlikely to occur on a filtration membrane even if aeration is performed in a state in which a filtration operation is stopped or even if a high internal pressure is applied in chemical cleaning.

Description
MEMBRANE ELEMENT AND MEMBRANE MODULE
Technical Field
[0001]
The present invention relates to a membrane element
and a membrane module used for filtration or
concentration in the water treatment of tap water,
wastewater, and the like.
Background Art
[0002]
As a conventional membrane separator, for example, a
submerged membrane filtration apparatus having a
plurality of membrane elements arranged in parallel at
appropriate intervals is known. As the membrane element,
for example, there is a membrane element shown in FIGS. 9
and 10. In FIGS. 9 and 10, in the membrane element,
filtration membranes 2 formed of an organic membrane are
arranged to cover the surfaces of a rectangular flat
filtration plate 1, which is a membrane supporting member,
and the filtration membranes 2 are jointed to the
filtration plate 1 in the peripheral edges of the
filtration membranes 2. The filtration plate 1 has a
water collecting port 3. As the membrane supporting
member, the filtration plate 1 of resin is described as
an example. However, in some case, a membrane supporting
member made of a flexible material such as a non-woven
fabric or a net may be used.
[0003]
The membrane element receives a driving pressure and
filters water to be treated with the filtration membrane
2. The membrane element is used for gravity filtration
using a head pressure in a tank as the driving pressure
or suction filtration giving a negative pressure as the
driving pressure to the inner side of the filtration
membrane 2.
[0004]
As a method of joining the filtration plate 1 and the
filtration membranes 2 in such a membrane element, for
example, welding and bonding are performed. The welding
is a method of melting the resin of the filtration plate
1 using ultrasound to form a welded portion 4 and joining
the filtration plate 1 and the filtration membranes 2 in
the welded portion 4.
[0005]
As the method of joining the filtration plate 1 and
filtration membranes 2, for example, there is a method
described in Japanese Patent No. 3010979. In the method,
a filtration membrane is arranged on the surface of a
filtration plate, ultrasonic vibrations from above the
filtration membrane are applied along the peripheral edge
of the filtration membrane, and the filtration membrane
is welded to the filtration plate with the frictional
heat of ultrasonic vibrations.
[0006]
According to a method described in Japanese Patent
Application Laid-Open No. Hll-33370, two flat membranes
are stacked via a spacer and the two flat membranes are
welded or bonded end to end on both sides of the flat
membranes to form a filtration membrane body.
[0007]
According to a method described in Japanese Patent No.
3815645, a separator unit is obtained by attaching
filtration membranes via spacers on both surfaces of a
member having a water passing function and forming a
hollow portion in a joining member for joining membrane
ends .
Disclosure of the Invention
Problems to be Solved by the Invention
[0008]
When the above-described membrane separator is used,
the membrane separator is immersed in an activated sludge
mixture in an aeration tank, and air for aeration is
diffused from an air diffuser. In this state, a driving
pressure is applied to the membrane element to filter the
activated sludge mixture and permeate having permeated
through the filtration membrane is led to the outside of
the tank as treated water.
[0009]
At this point, upflow is caused by the air-lift
action of air bubbles of the air for aeration diffused
from the air diffuser. The membrane surface of filtration
membrane of the membrane element is aerated and cleaned
by this upflow. Thus a decrease in separating function
due to fouling is suppressed and the membrane separator
is prevented from being nonfunctional.
[0010]
In this way, in the membrane separator, the process
of aerating and cleaning is necessary to prevent fouling.
In this case, it has been known that a cleaning effect is
improved if aeration is performed in a state in which a
filtration operation is stopped.
[0011]
However, as shown in FIG. 11, if the membrane
separator is left in the state in which the filtration
operation is stopped, permeate accumulates in the inside
of the membrane element, i.e., between the filtration
plate 1 and the filtration membranes 2, and the
filtration membranes 2 slightly swell.
[0012]
As shown in FIG. 12, when only the aeration is
performed in the state in which the filtration operation
is stopped, the permeate having accumulated between the
filtration plate 1 and the filtration membranes 2 is
pushed upward by upflow. As a result, as shown in FIG. 8,
the filtration membrane 2 is folded in the welded portion
4 to form a swell 5 near the upper part of the membrane
element. This swell 5 acts as a resistance against the
upflow, and vibrations and stresses occur on the
filtration membrane 2. Therefore, the filtration membrane
2 is likely to peel off in the welded portion 4 or be
broken near the welded portion 4.
[0013]
When fouling occurs, chemical cleaning for removing
the fouling becomes necessary. This chemical cleaning is
performed by supplying a chemical from the water
collecting port 3 to a permeate channel between the
filtration plate 1 and the filtration membranes 2. When
an internal pressure in the permeate channel between the
filtration plate 1 and the filtration membranes 2
increases with the supply pressure of the chemical, the
filtration membranes 2 swell outward and exert a peeling
action on the joined portions of the filtration plate 1
and the filtration membranes 2.
[0014]
Therefore, as explained above, since a tensile force
acts in a direction in which the filtration membrane 2 is
peeled from the joined surface with the filtration plate
1, disadvantageously, breakage and peeling are likely to
occur on the filtration membrane 2 in the welded portion
4 and a high internal pressure cannot be applied in the
chemical cleaning.
[0015]
The present invention solves the problems and it is
an object of the present invention to provide a membrane
element and a membrane module in which breakage and
peeling are unlikely to occur on a filtration membrane
even if aeration is performed in a state in which a
filtration operation is stopped or even if a high
internal pressure is applied in chemical cleaning.
Means for Solving the Problems
[0016]
In order to attain the object, a membrane element
according to the present invention includes: a membrane
supporting member arranged along the flowing direction of
a liquid to be treated; a filtration membrane formed of a
flat membrane that is arranged to cover the principal
planes on the front and back of the membrane supporting
member and is loop-shaped to have a reversed portion
folded so as to include the ends on the upstream side and
the downstream side of the membrane supporting member;
and a sealing material formed water-tightly on the edge
side portion of the filtration membrane on both sides of
the membrane supporting member along the flowing
direction of the liquid to be treated.
[0017]
In the membrane element of the present invention, the
filtration membrane has at least one joined portion. The
joined portion is formed by arranging the ends of the
filtration membrane to be stacked on top of each other on
the principal planes or the end faces of the membrane
supporting member and joining the surface at one end onto
the surface at the other end of the filtration membrane.
[0018]
In the membrane element of the present invention, the
end facing the downstream side, out of the ends of the
filtration membranes stacked in the joined portion is
arranged on the outer side.
[0019]
A membrane module of the present invention includes:
at least one membrane element; and at least one water
collecting case. The membrane element includes: a
membrane supporting member arranged along the flowing
direction of a liquid to be treated; a filtration
membrane formed of a flat membrane that is arranged to
cover the principal planes on the front and back of the
membrane supporting member and is loop-shaped to have a
reversed portion folded so as to include the ends on the
upstream side and the downstream side of the membrane
supporting member; and a sealing material formed water-
tightly on the edge side portion of the filtration
membrane on both sides of the membrane supporting member
along the flowing direction of the liquid to be treated.
The water collecting case has an opening portion
communicating with an inner water collecting space
therein and keeps water-tight the sides of the membrane
element inserted in the opening portion.
Advantages of the Invention
[0020]
As explained above, in the present invention, opening
edges on both sides of the loop-shaped filtration
membrane are held on the membrane supporting member by-
forming the sealing material water-tightly on the edge
side portion of the filtration membrane on both sides of
the membrane supporting member along the flowing
direction of the liquid to be treated. Therefore, there
is no region where the filtration membrane and the
membrane supporting member are directly fixed. The
sealing material does not always need to strongly press
the filtration membrane against the filtration plate.
However, in the membrane element, the filtration plate
and the filtration membrane can also be directly joined
in an area where the membrane surface of the filtration
membrane does not come into contact with the liquid to be
treated, for example, an area corresponding to the
sealing material or an area located in the water
collecting case. This is on the condition that the
joining does not hinder a permeate channel.
[0021]
The filtration membrane may be formed in a loop shape
by joining the ends of one or a plurality of membrane
sheets. The filtration membrane can also be formed of a
membrane sheet that is seamless and formed in a loop
shape.
[0022]
With this configuration, when a chemical is supplied
at a predetermined pressure to the permeate channel
between the membrane supporting member and the filtration
membrane in chemical cleaning, the filtration membrane
receives an internal pressure and swells to the outer
side. In this state, a tensile stress acts along the
membrane surface of the filtration membrane. However,
since there is no region where the filtration membrane
and the membrane supporting member are directly fixed,
compared with the case in which the membrane supporting
member and the filtration membrane are welded as in the
prior art, it is possible to suppress breakage of the
filtration membrane and apply a high internal pressure in
chemical cleaning.
[0023]
On both sides of the membrane element along the
flowing direction of the liquid to be treated, the
sealing material is water-tightly formed on the
filtration membrane. Therefore, even if the filtration
membrane receives an internal pressure and swells to the
outer side, the filtration membrane can secure a large
strength.
[0024]
When air is diffused from below the membrane element
in a state in which a filtration operation is stopped,
permeate present between the membrane supporting member
and the filtration membrane is pushed to the downstream
side of the flow of the liquid to be treated and is
collected in the reversed portion. The filtration
membrane flexibly swells in the reversed portion to allow
the permeate to move. Further, since the swell of the
reversed portion occurs in the downstream area of the end
on the downstream side of the membrane supporting member,
the swell of the reversed portion does not serve as a
resistance against the flow of the liquid to be treated
along the membrane supporting member. Vibrations and
stresses do not occur in the filtration membrane because
of the swell of the reversed portion. Therefore, it is
possible to suppress a load acting on the filtration
membrane and prevent the filtration membrane from
breaking. Since the end arranged on the outer side faces
the downstream side and is not opposed to the flow of the
liquid to be treated, it is possible to suppress peeling
of the joined portion of the filtration membrane.
Brief Description of the Drawings
[0025]
FIG. 1 is a perspective view showing a membrane
cassette in an embodiment of the present invention;
FIG. 2 is a sectional view showing a main part in a
membrane module of the membrane cassette;
FIG. 3 is a perspective view showing a membrane
element in the embodiment of the present invention;
FIG. 4 is a front view showing the membrane element;
FIG. 5 is a perspective view showing a membrane
element in another embodiment of the present invention;
FIG. 6 is a perspective view showing a membrane
element in a third embodiment of the present invention;
FIG. 7 is a schematic diagram showing an action of a
membrane element of the present invention;
FIG. 8 is a schematic diagram showing an action of a
conventional membrane element;
FIG. 9 is a disassembled perspective view showing the
configuration of the conventional membrane element;
FIG. 10 is a perspective view showing the
conventional membrane element;
FIG. 11 is a side view showing the conventional
membrane element; and
FIG. 12 is a side view showing the conventional
membrane element.
Best Mode for Carrying Out the Invention
[0026]
(First Embodiment)
An embodiment of the present invention is explained
below with reference to the accompanying drawings. In
FIGS. 1 to 4, a membrane cassette 11 forming a membrane
separator includes a plurality of membrane modules 12
arranged in a vertically parallel multistage fashion. The
membrane cassette 11 is set and immersed in liquid to be
treated in a treatment tank (not shown) . In the membrane
cassette 11, an air diffuser lla is arranged below the
lower membrane module 12.
[0027]
In the membrane module 12, a plurality of membrane
elements 13 are arranged in parallel at predetermined
intervals. Both sides in the lateral direction of each of
the membrane elements 13 are water-tightly sealed to
water collecting cases 14. Longitudinal channels are
formed between the membrane element 13 . Each of the water
collecting cases 14 is hollow-shaped and has a water
collecting space therein. Although the water collecting
case 14 is formed like a square box, the water collecting
case 14 may be in a shape other than a square. However,
the water collecting case 14 can also be provided only on
one side of the membrane element 13. In this case, the
other side of the membrane element 13 is sealed by resin
or the like explained later.
[0028]
In this embodiment, a configuration in which the
membrane elements 13 are arranged in the up-to-down
direction is explained. However, the arranging direction
of the membrane elements 13 is not limited to the up-to-
down direction. The membrane elements 13 only have to be
arranged along the flowing direction of the liquid to be
treated. Therefore, as explained later, it is also
possible to arrange the membrane elements 13 in the
horizontal direction or obliquely.
[0029]
The membrane module 12 includes upper coupling
portions 23 provided on the upper end faces of the water
collecting cases 14 and lower coupling portions 24
provided on the lower end faces thereof. The upper
coupling portions 23 and the lower coupling portions 24
form channels and communicate with the water collecting
spaces of the water collecting cases 14.
[0030]
The lower coupling portions 24 of the upper membrane
module 12 and the upper coupling portions 23 of the lower
membrane module 12 are coupled. The upper coupling
portions 23 of the water collecting cases 14 of the upper
membrane module 12 communicate with water collecting
pipes 26 via tubes 25.
[0031]
However, the lower coupling portions 24 of the lower
membrane module 12 can also communicate with the water
collecting pipes 26 via the tubes 25. Further, the lower
coupling portions 24 or the upper coupling portions 23
can also communicate with the water collecting pipes 26
not via the tubes 25 but directly.
[0032]
In this embodiment, the lower coupling portions 24 of
the lower membrane module 12 are closed by plugs (not
shown). However, it is also possible to use a membrane
module having no lower coupling portions 24 as the lower
membrane module 12.
[0033]
Extraction of permeate only has to be performed from
at least one of the left and right upper coupling
portions 2 3 of the upper, membrane module 12 and the left
and right lower coupling portions 24 of the lower
membrane module 12.
[0034]
As shown in FIG. 2, the plurality of membrane
elements 13 are water-tightly held by each of the water
collecting cases 14 via a sealing material (resin, etc.)
16 potted in an opening portion 15. However, the water
collecting case 14 is not limited to the configuration
shown in FIG. 2. There are various structures for water-
tightly joining the membrane elements 13 to the water
collecting case 14. For example, it is also possible to
form a plurality of slits instead of the single opening
portion 15 of the water collecting case 14, insert the
membrane elements 13 into the slits, and pot the sealing
material 16 of resin or the like in the slits.
Alternatively, it is also possible to arrange a seal
material such as rubber around the membrane elements 13.
(Configuration of the membrane element)
As shown in FIGS. 3 and 4, the membrane element 13
includes a filtration plate 17 made of resin, which forms
a membrane supporting member, and a filtration membrane
18 made of a flat sheet membrane (an organic membrane)
arranged to cover the surfaces on the front and back of
the filtration plate 17. In each of the membrane elements
13, permeate channels formed between the surfaces on the
front and back of the filtration plate 17 and the
filtration membrane 18 communicate with the water
collecting spaces of the water collecting cases 14. In
this embodiment, the filtration plate 17 made of resin is
explained as an example of the membrane supporting member.
However, in some case, a membrane supporting member of a
flexible material such as non-woven fabric or a net is
used.
[0035]
The upper end side of the membrane element 13 is
located on the downstream side in the flowing direction
of the liquid to be treated. The lower end side of the
membrane element 13 is located on the upstream side in
the flowing direction of the liquid to be treated. The
filtration membrane 18 includes a downstream side
reversed portion 20 folded to include an end 19 on the
downstream side of the filtration plate 17 and an
upstream side reversed portion 29 folded to include an
end 27 on the upstream side thereof. The ends of the
filtration membrane 18 overlap each other on the surfaces
or end faces of the filtration plate 17. The back surface
at one end is joined onto the front surface at the other
end and the one end facing towards the downstream side is
located on the outer side to form a joined portion 30.
The joined portion 3 0 is formed by welding with
ultrasound or bonding with an adhesive.
[0036]
The membrane elements 13 having this structure are
arranged in parallel at predetermined intervals. The
plurality of membrane elements 13 are water-tightly
sealed into the opening portion 15 of the water
collecting case 14 by the sealing material (resin, etc.)
16 arranged between the membrane elements 13.
[0037]
In this configuration, the membrane element 13 has a
structure in which the filtration plate 17 and the
filtration membrane 18 are not directly fixed and joined.
A structure in which the filtration membrane 18 and the
filtration plate 17 are not directly fixed by bonding or
welding on four sides of the filtration plate 17 is
realized.
[0038]
However, in the membrane element 13, the filtration
plate 17 and the filtration membrane 18 can also be
directly joined in an area where the membrane surface of
the filtration membrane 18 does not come into contact
with the liquid to be treated, for example, an area
corresponding to the sealing material 16 or an area
located inside the water collecting case 14. This is on
condition that the joining does not hinder the permeate
channel.
[0039]
As shown in FIG. 4, the sealing material 16 can be
formed for each of the membrane elements 13. The edge
side portion of the filtration membrane 18 is held by the
sealing material 16 for each of the membrane elements 13
on both sides of the filtration plate 17 along the
flowing direction of the liquid to be treated. Thereafter,
it is possible to arrange the membrane elements 13 having
this structure in parallel at predetermined intervals and
bind the plurality of membrane elements 13 with the
sealing material (resin, etc.) 16 arranged between the
membrane elements 13. Further, as explained above, it is
also possible to arrange a seal material such as a rubber
material on the filtration membrane 18 and join the
filtration membrane 18 to the filtration plate 17.
[0040]
In the embodiment, the loop-shaped filtration
membrane 18 is formed by one membrane sheet. However, as
shown in FIG. 5, it is also possible to form the loop-
shaped filtration membrane 18 with a plurality of
membrane sheets.
[0041]
In FIG. 5, one out of two membrane sheets forming the
filtration membrane 18 forms the downstream side reversed
portion 2 0 folded to include the upper end edge 19 of the
filtration plate 17. The other membrane sheet forms the
upstream side reversed portion 29 folded to include the
end 27 on the upstream side. The ends of both membrane
sheets are stacked on top of each other on the surfaces
of the filtration plate 17 and the ends of both membrane
sheets are joined to form two joined portions 30. The
joined portions 30 are formed by welding with ultrasound
or bonding with an adhesive.
[0042]
Further, the filtration membrane 18 can also be
formed of a seamless loop-shaped membrane sheet.
[0043]
Regardless of which of the membrane elements 13 is
used, the following operations and effects are realized
in the membrane module 12 of the present invention.
Normal operation
Air is diffused as a gas for aeration from the air
diffuser lla arranged below the lower membrane module 12.
Upflow of air-liquid mixtures is caused inside the
membrane cassette 11 by the air-lift action of air
bubbles. The liquid to be treated in a treatment tank
(not shown) is supplied between the membrane elements 13
by this upflow. A flow of the liquid to be treated along
the membrane surfaces of the membrane elements 13 is
formed. The liquid to be treated is supplied as a cross
flow with respect to the flow of permeate flowing to
permeate through the filtration membrane 18.
[0044]
In this embodiment, the liquid to be treated is
supplied as the cross flow by the upflow caused by the
air-lift action. Therefore, the membrane elements 13 are
arranged in the up-to-down direction. However, when the
liquid to be treated is supplied as the cross flow
between the membrane elements 13 by a power unit such as
a pump, the membrane elements 13 can also be arranged in
the horizontal or oblique direction.
[0045]
There are various systems for applying a driving
pressure to the membrane elements 13. In this embodiment,
an activated sludge mixture in the tank is gravity-
filtrated by the membrane elements 13 with a water head
in the tank as a driving pressure. Alternatively, a
suction pressure is applied to the membrane module 12 of
the membrane cassette 11 as a driving pressure through
the water collecting pipes 26 and the tubes 25 by a
suction pump to suck and filter the activated sludge
mixture.
[0046]
The permeate having received the driving pressure and
permeated through the filtration membranes 18 of the
membrane elements 13 flows into the water collecting
spaces of the water collecting cases 14 through the
permeate channels between the filtration membranes 18 and
the filtration plates 17. The permeate having flowed into
the water collecting cases 14 of the lower membrane
module 12 flows into the water collecting cases 14 of the
upper membrane module 12 from the lower coupling portions
24 through the upper coupling portions 23. The permeate
having flowed into the water collecting cases 14 of the
upper membrane module 12 is led out to the outside of the
tank as treated water from the upper coupling portions 23
through the tubes 25 and the water collecting pipes 26.
[0047]
During this operation, the activated sludge mixture
is supplied as a cross flow to the channels between the
membrane elements 13 by upflow. The membrane surfaces of
the membrane elements 13 are aerated and cleaned by the
upflow. Thus a decrease in separating function due to
fouling is suppressed and the membrane separator is
prevented from being nonfunctional. In this case, since
the ends arranged on the outer side face the downstream
side and are not opposed to the flow of the liquid to be
treated, peeling of the filtration membrane joined
portions can be suppressed.
Aeration and cleaning operation
In the case of the gravity filtration, valves (not
shown) provided in the water collecting pipes 26 are
closed. In the case of the suction filtration, the
suction pump is stopped to stop the filtration operation.
When the air diffuser lla is operated to perform the
aeration and cleaning in this state, an excellent
cleaning effect can be obtained.
[0048]
At this point, the upflow pushes the permeate in each
of the membrane elements 13 to the upper downstream side
between the filtration plate 17 and the filtration
membrane 18. However, as shown in FIG. 7, the filtration
membrane 18 includes the reversed portion 20 folded to
include the end 19 on the downstream side of the
filtration plate 17. Therefore, the permeate pushed to
the upper downstream side between the filtration plate 17
and the filtration membrane 18 is collected in the
reversed portion 20. The filtration membrane 18 flexibly
swells in the reversed portion 20 to allow the permeate
to move. Further, since a swell 20a of the reversed
portion 2 0 is formed in the downstream area of the end 19
on the downstream side of the filtration plate 17, the
swell 20a of the reversed portion 20 does not act as a
resistance against the upflow flowing along the
filtration plate 17. Vibrations and stresses do not occur
in the filtration membrane 18 because of the swell 20a of
the reversed portion 20.
[0049]
Therefore, a load acting on the filtration membrane
18 is suppressed to prevent the filtration membrane 18
from being broken because the reversed portion 20
flexibly swells to allow the permeate to move and the
swell 20a does not act as a resistance against the upflow.
Chemical cleaning
During chemical cleaning, a chemical is supplied to
each of the membrane modules 12 of the membrane cassette
11 through the water collecting pipes 26 and the tubes 25.
The chemical is supplied at a predetermined pressure to
the permeate channel between the filtration plate 17 and
the filtration membrane 18. At this point, the filtration
membrane 18 receives an internal pressure and swells to
the outer side. In this state, a tensile stress acts on
the filtration membrane 18 along the membrane surface.
[0050]
However, instead of fixing the filtration membrane 18
and the filtration plate 17, when the ends of the
filtration membrane 18 are joined in the joined portion
3 0 to form the loop-shaped filtration membrane 18,
naturally, the filtration membrane 18 does not peel from
the filtration plate 17 unlike in the prior art. Since
only a tensile stress acts on the joined portion 30, the
joined portion 30 can sufficiently withstand the tensile
stress. It is possible to apply a high internal pressure
to the joined portion 30 in chemical cleaning.
[0051]
Compared with the case in which the filtration plate
17 and the filtration membrane 18 are welded as in the
prior art, in this embodiment, the ends of both membrane
sheets are stacked on top of each other on the surfaces
of the filtration plate 17 and the surface at one end is
joined to the surface at the other end to form the joined
portion 30. Therefore, since the tensile force acting on
the filtration membrane 18 acts as a shearing force in
the joined portion 30, a large joining strength can be
secured. Further, on both sides along the flowing
direction of the liquid to be treated of the membrane
element 13, since the sealing material 16 is water-
tightly formed on the filtration membrane 18, even if the
filtration membrane 18 receives an internal pressure and
swells to the outside, a large strength can be secured.
[0052]
For example, in the conventional configuration, i.e.,
in the case in which the filtration membrane was welded
and joined to the filtration plate, when the internal
pressure was equal to or higher than 4 0 kPa, breakage of
a welded portion was observed. However, in the
configuration of the present invention, even under a
condition in which the internal pressure was 10 0 kPa,
breakage in the joined portion 3 0 did not occur and the
anti-pressure strength was improved.
[0053]
Therefore, it is possible to perform, while
suppressing breakage of the filtration membrane 18 in
chemical cleaning, reverse liquid cleaning for feeding a
chemical in a short time under a high pressure and
causing the chemical to permeate from the inner side to
the outer side under a high internal pressure.
WE CLAIM:
1. A membrane element comprising: a membrane supporting member arranged
along a flowing direction of a liquid to be treated; and a filtration membrane
formed of a flat sheet membrane that is arranged to cover both front and back
surfaces of the membrane supporting member and is loop-shaped to have a
reversed portion folded so as to include ends on an upstream side and a
downstream side of the membrane supporting member.
2. The membrane element according to claim 1, wherein the filtration membrane
includes at least one joined portion, the joined portion is formed by arranging
ends of the filtration membrane to be stacked on top of each other on the
surfaces or end faces of the membrane supporting member and joining a back
surface at one end onto a front surface at the other end of the filtration
membrane, and the end facing the downstream side, out of the ends of the
filtration membrane stacked in the joined portion is arranged on an outer side.
3. A membrane module comprising: at least one membrane element;and at least
one water collecting case, wherein the membrane element comprises: a
membrane supporting member arranged along a flowing direction of a luquid to
be treated; a filtration membraneformed of a flat sheet membrane that is
arranged to cover both front and back surfaces of the membrance supporting
member and is loop-shaped to have a reversed portion folded so as to include
ends on an upstream side and a downstream side of the membrane supporting
member; and the water collecting case includes an opening portion
communicating with a water collecting space therein and keeps water-tight sides
of the membrane element inserted in the opening portion.
4. The membrane element according to claim 1, further comprising: a sealing
material formed water-tightly on an edge side portion of the filtration
membrane on both sides of the membrane supporting member along the flowing
direction of the liquid to be treated.

By forming a filtration membrane in a loop shape, it
is possible to apply a high internal pressure and perform
reverse liquid cleaning at a high internal pressure in
chemical cleaning. A membrane element and a membrane
module in which breakage and peeling are unlikely to
occur on a filtration membrane even if aeration is
performed in a state in which a filtration operation is
stopped or even if a high internal pressure is applied in
chemical cleaning.