1. A membrane separator comprising: a plurality of membrane elements arranged in parallel to form channels for a liquid to be treated between the membrane elements; and a water collecting case which keeps water-tight sides of the membrane elements along the channels for the liquid to be treated, and has therein a water collecting space with which permeate channels of the membrane elements communicate, wherein in the water collecting case, out of wall members arranged to surround the water collecting space, at least the wall member opposed to the sides of the membrane elements forms a projecting portion projecting to an outer side and recessed portions recessed to an inner side.

2. The membrane separator according to claim 1, wherein, in the water collecting case, the wall member opposed to the sides of the membrane elements forms the projecting portion projecting to the outer side, forms an expanded area in the water collecting space, and has a water collecting port opened so as to face the expanded area.

3. The membrane separator according to claim 1 or 2, wherein the water collecting case has ribs on the outer sides of the wall members surrounding the water collecting space, and the ribs are shaped so as to fit within an overall length dimension of the membrane separator along a direction in which the water collecting cases are arranged. 4 . A membrane cassette using the membrane separator according to any one of claims 1 to 3, wherein a plurality of the membrane separators are vertically stacked in multiple stages along a flowing direction of a liquid to be treated.

5. The membrane cassette according to claim 4, wherein the upper and lower membrane separators communicate with each other via water collecting ports that constitute coupling portions formed on wall surfaces opposed to each other of water collecting cases of the membrane separators. The wall member of a water collecting case forms a projecting portion projecting to the outer side and recessed portions recessed to the inner side.

Description
MEMBRANE SEPARATOR AND MEMBRANE CASSETTE
Technical Field
[0001]
The present invention relates to a membrane separator
and a membrane cassette used for filtration or
concentration in the water treatment of tap water,
wastewater and the like, and to the water collecting case
structure of the membrane separator and the membrane
cassette.
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.
[0003]
For example, in a membrane separator described in
Japanese Patent Application Laid-Open No. Hll-33370, two
flat membranes are stacked via a spacer, the two flat
membranes are welded or bonded end to end on both sides
of the two flat membranes to form a filtration membrane
member, and filtration water collecting portions provided
on the sides of the filtration membrane member
communicate with the inside of the filtration membrane
member.
[0004]
In a membrane separator described in Japanese Patent
No. 3815645, a separator unit is mounted with filtration
membranes on both surfaces of a water passing material
having a water passing function, the membrane ends of the
filtration membranes are joined to the water passing
material with joining members, hollow portions are formed
in the joining members, and suction pipes provided in the
hollow portions of the joining members communicate with
the channel of the water passing material.
[0005]
The conceptual model of such a membrane separator is
shown in FIGS. 18 to 19. A plurality of membrane elements
1 are arranged in parallel and channels 2 are formed
along the flowing direction of a liquid to be treated
between the membrane elements 1. The membrane elements 1
are formed by arranging filtration membranes on the
surfaces of membrane supporting members and have permeate
channels between the membrane supporting members and the
filtration membranes. Water collecting cases 3 arranged
on both sides of the membrane elements 1 have opening
portions communicating with water collecting spaces 4 in
the water collecting cases 3. The sides of the membrane
elements 1 inserted in the opening portions are held
water-tight by sealing materials. The permeate channels
of the membrane elements 1 communicate with the water
collecting spaces 4 of the water collecting cases 3.
Disclosure of the Invention
Problems to be Solved by the Invention
[0006]
In the membrane separator mentioned above, only the
membrane elements 1 and the water collecting cases 3 form
a module and other structural members are unnecessary.
Therefore, there are problems explained below.
[0007]
1. When the membrane separator is immersed in liquid
to be treated in a treatment tank, a configuration in
which a plurality of modules are stacked and arranged in
multiple stages is effective for increasing the number of
membrane elements 1 packed in the membrane separator.
[0008]
However, since only the membrane elements 1 and the
water collecting cases 3 form the module, the lower
membrane separator receives, through the water collecting
cases 3, the load of the upper membrane separator.
Therefore, the load applied to the water collecting cases
3 increases towards the lower membrane separator. The
water collecting cases 3 are required to have strength
enough to withstand the load.
[0009]
2. When the membrane separator is pulled out of the
treatment tank in maintenance or the like, the water
collecting cases 3 are filled with permeate. The weight
of the permeate in the water collecting cases 3 is
applied to the water collecting cases 3 besides their own
weight.
[0010]
3. When a filtration operation is performed, a
suction pressure as a driving pressure acts on the
insides of the water collecting cases 3. The internal
pressure is lower than the external pressure. During the
chemical cleaning of the membrane elements 1, since a
chemical is supplied from the water collecting cases 3
into the membrane elements 1, a supply pressure acts on
the insides of the water collecting cases 3. The internal
pressure is higher than the external pressure. Therefore,
deformation and breakage of the water collecting cases 3
may occur depending on pressures in use.
[0011]
However, since the water collecting cases 3 are
formed only of thin tabular wall members forming the
outer walls of the water collecting cases 3, and receive
the load, the internal pressure, and the external
pressure only through the peripheral wall members, the
withstand load of the water collecting cases 3 is
structurally small.
[0012]
As shown in FIG. 19, when ribs 5 are arranged inside
the water collecting cases 3 to reinforce the water
collecting cases 3, the ribs 5 constitute a factor that
prevents the flow of the permeate in the water collecting
spaces 4 of the water collecting cases 3. When the ribs 5
are arranged on the outside of the water collecting cases
3, the ribs 5 constitute a factor that prevents the flow
of the liquid to be treated in the treatment tank and the
external dimension of the membrane separator increases.
[0013]
In order to fill the membrane elements 1 with a
chemical, it is necessary to fill the water collecting
cases 3 with a chemical. When the water collecting spaces
4 of the water collecting cases 3 are unnecessarily large,
the amount of a chemical required during chemical
cleaning increases.
[0014]
The permeate simultaneously flows into the water
collecting spaces 4 of the water collecting cases 3 from
the respective membrane elements 1. Since the permeate in
the water collecting cases 3 flows through water
collecting ports 6 to the outside, the permeate flowing
in from the respective membrane elements 1 meets together
as it approaches the water collecting ports 6. In other
words, for the permeate flowing from the membrane
elements 1 distant from the water collecting ports 6
toward the water collecting ports 6, the permeate flowing
from the membrane elements 1 close to the water
collecting ports 6 into the water collecting spaces 4
acts as a channel resistance.
[0015]
This channel resistance increases as the distance of
the membrane elements 1 from the water collecting ports 6
increases, and constitutes a factor that prevents the
permeate from flowing into the water collecting spaces 4
from the membrane elements 1. Therefore, the flow rate of
the permeate flowing through the membrane elements 1
varies between the membrane elements 1.
[0016]
The present invention solves the problems and it is
an object of the present invention to provide a membrane
separator and a membrane cassette that can secure
sufficient strength in water collecting cases and realize
a smooth flow of permeate in water collecting spaces.
Means for Solving the Problems
[0017]
In order to attain the object, a membrane separator
according to the present invention includes: a plurality
of membrane elements arranged in parallel to form
channels for a liquid to be treated between the membrane
elements; and a water collecting case which keeps water-
tight the sides of the membrane elements along the
channels for the liquid to be treated, and has therein a
water collecting space with which the permeate channels
of the membrane elements communicate. In the water
collecting case, out of wall members arranged to surround
the water collecting space, at least the wall member
opposed to the sides of the membrane elements forms a
projecting portion projecting to the outer side and
recessed portions recessed to the inner side.
[0018]
In the membrane separator according to the present
invention, in the water collecting case, the wall member
opposed to the sides of the membrane elements forms the
projecting portion projecting to the outer side, forms an
expanded area in the water collecting space, and has a
water collecting port opened so as to face the expanded
area.
[0019]
In the membrane separator according to the present
invention, the water collecting case has ribs on the
outer sides of the wall members surrounding the water
collecting space, and the ribs are shaped so as to fit
within the overall length dimension of the membrane
separator along an inter-water collecting case direction.
[0020]
A membrane cassette according to the present
invention uses the membrane separator. A plurality of the
membrane separators are vertically stacked in multiple
stages along the flowing direction of a liquid to be
treated.
[0021]
In the membrane separation cassette according to the
present invention, the upper and lower membrane
separators communicate with each other via water
collecting ports that constitute coupling portions formed
on the wall surfaces opposed to each other of the water
collecting cases of the membrane separators.
Advantages of the Invention
[0022]
As explained above, in the present invention, since
out of the wall members arranged to surround the water
collecting space, at least the wall member opposed to the
sides of the membrane elements forms the projecting
portion projecting to the outer side and the recessed
portions recessed to the inner side, the buckling load of
the wall member increases. Therefore, in the present
invention, when a water collecting space having the same
capacity as that of the water collecting case in the
conventional configuration is provided, it is possible to
realize a water collecting case with increased strength.
[0023]
Since the wall member opposed to the sides of the
membrane elements forms the projecting portion projecting
to the outer side, forms the expanded area in the water
collecting space, and has the water collecting port
opened so as to face the expanded area, a channel around
the water collecting port is widened. Therefore, even if
permeate flowing in from the respective membrane elements
meets together and flows toward the water collecting port,
it is possible to suppress an increase in channel
resistance near the water collecting port and contribute
to the equalization of flow rate of the permeate flowing
through the respective membrane elements.
[0024]
Since the ribs are arranged outside the wall members
and within the overall length dimension of the membrane
separator along the direction in which the water
collecting cases are arranged, the ribs do not constitute
a factor that prevents the flow of the liquid to be
treated, the external dimension of the membrane separator
is not increased, and it is possible to increase the
strength of the water collecting case.
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 plan view of the membrane module in the
embodiment,-
FIG. 6 is a front view of the membrane module in the
embodiment,-
FIG. 7 is a plan view of a membrane module in another
embodiment of the present invention;
FIG. 8 is a side view of the membrane module in the
other embodiment of the present invention,-
FIG. 9 is a plan view of a membrane module in another
embodiment of the present invention;
FIG. 10 is a plan view of a membrane module in
another embodiment of the present invention,-
FIG. 11 is a front view of the membrane module in the
other embodiment of the present invention,-
FIG. 12 is a plan view of a membrane module in
another embodiment of the present invention,-
FIG. 13 is a front view of the membrane module in the
other embodiment of the present invention,-
FIG. 14 is a plan view of a water collecting case in
another embodiment of the present invention;
FIG. 15 is a plan view of a water collecting case in
another embodiment of the present invention;
FIG. 16 is a plan view of a water collecting case in
another embodiment of the present invention;
FIG. 17 is a plan view of a water collecting case in
another embodiment of the present invention;
FIG. 18 is a plan view showing a conventional
membrane module; and
FIG. 19 is a plan view showing the conventional
membrane module.
Best Mode for Carrying Out the Invention
[0026]
(First Embodiment)
Embodiments of the present invention are explained
below with reference to the accompanying drawings. In
FIGS. 1 to 6, a membrane cassette 11 of a membrane
separator includes a plurality of vertically-stacked
membrane modules 12. The membrane cassette 11 is immersed
and set in a 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. The
membrane separator can be formed of a single membrane
module.
[0027]
In the membrane module 12, a plurality of membrane
elements 13 are arranged in parallel at predetermined
intervals. Channels for a liquid to be treated are formed
in a vertical direction between the membrane elements 13.
Both sides of the membrane elements 13 along the flow of
the liquid to be treated are water-tightly sealed to
water collecting cases 14. Each of the water collecting
cases 14 is hollow-shaped and has a water collecting
space therein. However, the water collecting case 14 can
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 arrangement
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. 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 water collecting ports and communicate with water
collecting spaces 14a 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 to each other. The upper
coupling portions 23 of the water collecting cases 14 in
the upper membrane module 12 communicate with water
collecting pipes 26 via tubes 25.
[0031]
In this embodiment, the lower coupling portions 24 of
the lower membrane module 12 are closed by plugs (not
shown). However, it is possible to use a membrane module
having no lower coupling portions 24 as the lower
membrane module 12.
[0032]
Extraction of permeate only has to be performed from
at least one portion of the left and right upper coupling
portions 23 in the upper membrane module 12 and the left
and right lower coupling portions 24 in the lower
membrane module 12.
[0033]
As shown in FIG. 2, in each of the water collecting
cases 14, the plurality of membrane elements 13 are held
water-tight 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 possible to form
the opening portion 15 of the water collecting case 14 as
a plurality of slits instead of a single opening, insert
the membrane elements 13 in 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 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,
a permeate channel formed between the surfaces on the
front and back of the filtration plate 17 and the
filtration membrane 18 communicates with the water
collecting space 14a of the water collecting case 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 flexible material such as non-
woven fabric or a net is used for the membrane supporting
member.
[0034]
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 so as to include an end 19 on
the downstream side of the filtration plate 17 and an
upstream side reversed portion 2 9 folded so as to include
an end 2 7 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. One end located
on the outer side of the filtration membrane 18 extends
toward the downstream side and joins the ends of the
filtration membrane 18 to form a joined portion 30. The
joined portion 3 0 is formed by welding with ultrasound or
bonding with an adhesive.
[0035]
The membrane elements 13 having this structure are
arranged in parallel at predetermined intervals. The
plurality of membrane elements 13 are bound on the
filtration plate 17 by the sealing material (resin, etc.)
16 arranged between the membrane elements 13 and are
water-tightly sealed in the opening portion 15 of the
water collecting case 14 by the sealing material 16. The
sealing material 16 has only to ensure water-tightness
with the filtration membrane 18. It is not always
necessary to strongly press the filtration membrane 18
against the filtration plate 17.
[0036]
With 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 on four sides
of the filtration plate 17 by bonding or welding is
realized. However, in the membrane element 13, the
filtration plate 17 and the filtration membrane 18 can 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
the condition that the joining does not hinder the
permeate channel.
[0037]
As shown in FIG. 4, the sealing material 16 can be
formed for each of the membrane element 13. The edge side
portion of the filtration membrane 18 is bound by the
sealing material on the filtration plate 17 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.
[0038]
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 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.
[0039]
In the embodiment, the loop-shaped filtration
membrane 18 is formed by one membrane sheet. However, it
is possible to form the loop-shaped filtration membrane
18 with a plurality of membrane sheets. Further, the
filtration membrane 18 can be formed of a loop-shaped
seamless membrane sheet.
[0040]
In this embodiment, the membrane sheet is loop-shaped.
However, the filtration membrane 18 can be joined to the
filtration plate 17 at one of the upstream side end and
the downstream side end of the membrane element 13 or
both. This is on the condition that the inside of the
membrane element 13 is not over-pressurized during
chemical cleaning.
(Configuration of the water collecting case)
As shown in FIG. 5, in the water collecting case 14,
out of wall members 41 arranged to surround the water
collecting space 14a, at least the wall member 41 opposed
to the sides of the membrane elements 13 forms a
projecting portion 41a projecting to the outer side and
recessed portions 41b recessed to the inner side on both
sides of the projecting portion 41a. The projecting
portion 41a and the recessed portions 41b are desirably
formed to have curved surfaces and form a continuous
curved surface.
[0041]
In this way, since the wall member 41 forms the
projecting portion 41a projecting to the outer side and
the recessed portions 41b recessed to the inner side, the
buckling load of the wall member 41 increases. Therefore,
when the water collecting space 14a in this embodiment is
formed to have the same capacity as that of the water
collecting case in the conventional configuration, for
example, as shown in FIG. 5, even when the sectional area
and a width W of the water collecting space 14a are set
the same as the sectional area and width of the
conventional water collecting space, a water collecting
case with improved strength can be realized. The water
collecting case 14 is unlikely to be broken even if the
membrane modules 12 are stacked in multiple stages.
[0042]
The wall member 41 forms the projecting portion 41a
projecting to the outer side to form an expanded area 14b
in the water collecting space 14a. The upper coupling
portion 23 and the lower coupling portion 24 forming the
water collecting port are opened so as to face the
expanded area 14b.
[0043]
With this configuration, a channel around the upper
coupling portion 23 and the lower coupling portion 24
forming the water collecting port is widened. Therefore,
even if permeate flowing in from the respective membrane
elements 13 meets together and flows toward the upper
coupling portion 23 (the lower coupling portion 24), it
is possible to suppress an increase in channel resistance
near the upper coupling portion 23 (the lower coupling
portion 24) and contribute to the equalization of flow
rate of the permeate flowing through the respective
membrane elements 13.
[0044]
In this embodiment, the water collecting case 14
includes only the wall members 41. However, as shown in
FIGS. 7 and 8, it is possible to provide ribs 42 on the
outer side of the wall members 41 surrounding the water
collecting space 14a. In the ribs 42, longitudinal ribs
42a and lateral ribs 42b are arranged lengthwise and
crosswise. The ribs 42 are shaped so as to fit within the
overall length dimension of the membrane separator along
a direction in which the water collecting cases are
arranged.
[0045]
With this configuration, the ribs 42 do not
constitute a factor that prevents the flow of the liquid
to be treated, the external dimension of the membrane
separator is not increased, and it is possible to
increase the strength of the water collecting case 14.
[0046]
In the membrane module 12 according to the present
invention, the following operations and effects are
achieved.
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 bubbles of
the air. 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 the permeate flowing to
permeate through the filtration membranes 18.
[0047]
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.
[0048]
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.
[0049]
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 14a of the water collecting cases 14 through the
permeate channels between the filtration membranes 18 and
the filtration plates 17.
[0050]
At this point, even if the permeate flowing in from
the respective membrane elements 13 meets together and
flows toward the upper coupling portions 23 and the lower
coupling portions 24, it is possible to suppress an
increase in channel resistance near the upper coupling
portions 23 (the lower coupling portions 24) and
contribute to the equalization of flow rate of the
permeate flowing through the respective membrane elements
13.
[0051]
The permeate having flowed into the water collecting
cases 14 of the 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 2 5 and
the water collecting pipes 26.
[0052]
During this operation, the activated sludge mixture
is supplied as a cross flow to the channels among 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.
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.
[0053]
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.
[0054]
The filtration membrane 18 includes the reversed
portion 2 0 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.
[0055]
Further, since the swell of the reversed portion 20
is formed in the downstream area of the end 19 on the
downstream side of the filtration plate 17, the swell 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 of the reversed portion
20.
[0056]
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 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 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.
[0057]
However, when the ends of the filtration membrane 18
are joined in the joined portion 3 0 to form the loop-
shaped filtration membrane 18, there is no region where
the filtration membrane 18 and the filtration plate 17
are directly fixed. Therefore, for example, compared with
the case in which the membrane supporting member and the
filtration membrane are welded, it is possible to
suppress breakage of the filtration membrane 18 and apply
a high internal pressure in chemical cleaning.
[0058]
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 ends of both membrane sheets
are joined to form the joined portion 30. Therefore,
since a tensile stress 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, the sealing material
16 binds the filtration membrane 18 on the filtration
plate 17 from the outer side. Therefore, even if the
filtration membrane 18 receives an internal pressure and
swells to the outer side, a large strength can be secured.
[0059]
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.
[0060]
In the water collecting case 14, the wall member 41
continuously forms the projecting portion 41a and the
recesses 41b that form curved surfaces. Therefore, the
buckling load of the wall member 41 increases, the anti-
pressure strength against the internal and external
pressures increases, and the water collecting case 14 is
not broken even under the supply pressure of the chemical
and the driving pressure during the filtration operation.
Further, since the ribs 42 are provided, the anti-
pressure strength increases.
[0061]
As shown in FIG. 9, in the water collecting case 14,
the projecting portion 41a formed in the wall member 41
may be formed in a plurality of places. The recessed
portions 41b are formed on both sides of the projecting
portions 41a. However, the recessed portions 41b can be
formed only between the projecting portions 41a.
[0062]
As shown in FIGS. 10 and 11, the longitudinal ribs
42a and the lateral ribs 42b of the ribs 42 provided on
the outer side of the wall member 41 can be formed
shorter than the overall length dimension of the membrane
separator along the inter-water collecting case direction
In this case, as shown in FIGS. 12 and 13, the projecting
portion 41a formed in the wall member 41 may be formed in
a plurality of places. The recessed portions 41b are
formed on both sides of the projecting portions 41a.
[0063]
As shown in FIG. 14, in the water collecting case 14,
the projecting portion 41a formed in the wall member 41
can be formed in a rectangular shape in section. The
projecting corners of the projecting portion 41a and the
recessed corners of the recessed portions 41b are not
limited to right-angled corners and can be formed in a
chamfered shape or a curved surface shape.
[0064]
In this case, as shown in FIG. 15, the longitudinal
ribs 42a and the lateral ribs 42b of the ribs 42 can be
formed on the outer side of the wall member 41.
[0065]
As shown in FIG. 16, in the water collecting case 14,
the projecting portion 41a formed in the wall member 41
can be formed in a triangular shape in section. The
projecting corners of the projecting portion 41a and the
recessed corners of the recessed portions 41b are not
limited to right-angled corners and can be formed in a
chamfered shape or a curved surface shape.
[0066]
In this case, as shown in FIG. 17, the longitudinal
ribs 42a and the lateral ribs 42b of the ribs 42 can be
formed on the outer side of the wall member 41 and the
ribs 42 can be obliquely formed.
WE CLAIM:
1. A membrane separator comprising:
a plurality of membrane elements arranged in parallel
to form channels for a liquid to be treated between the
membrane elements; and
a water collecting case which keeps water-tight sides
of the membrane elements along the channels for the
liquid to be treated, and has therein a water collecting
space with which permeate channels of the membrane
elements communicate, wherein
in the water collecting case, out of wall members
arranged to surround the water collecting space, at least
the wall member opposed to the sides of the membrane
elements forms a projecting portion projecting to an
outer side and recessed portions recessed to an inner
side.
2. The membrane separator according to claim 1, wherein,
in the water collecting case, the wall member opposed to
the sides of the membrane elements forms the projecting
portion projecting to the outer side, forms an expanded
area in the water collecting space, and has a water
collecting port opened so as to face the expanded area.
3. The membrane separator according to claim 1 or 2,
wherein the water collecting case has ribs on the outer
sides of the wall members surrounding the water
collecting space, and the ribs are shaped so as to fit
within an overall length dimension of the membrane
separator along a direction in which the water collecting
cases are arranged.
4 . A membrane cassette using the membrane separator
according to any one of claims 1 to 3, wherein a
plurality of the membrane separators are vertically
stacked in multiple stages along a flowing direction of a
liquid to be treated.
5. The membrane cassette according to claim 4, wherein
the upper and lower membrane separators communicate with
each other via water collecting ports that constitute
coupling portions formed on wall surfaces opposed to each
other of water collecting cases of the membrane
separators.

The wall member of a water collecting case forms a projecting portion projecting to the outer side and recessed portions recessed to the inner side.