FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
FILTRATION MEMBRANE CLEANING APPARATUS, WATER TREATMENT
APPARATUS, AND FILTRATION MEMBRANE CLEANING METHOD
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION
ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS
IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED
2
DESCRIPTION
TECHNICAL FIELD
[0001] The present disclosure relates to a filtration
membrane cleaning apparatus, a water treatment apparatus, and
5 a filtration membrane cleaning method.
BACKGROUND ART
[0002] A membrane filtration process in which a filtration
membrane is used has been known as a method for separating
10 and removing contaminants from treatment-target water such as
sewage or wastewater from factories. When the membrane
filtration process is continuously executed, the contaminants
adhere on the surface of and in pores of the filtration
membrane so as to cause clogging, whereby the filtration
15 performance gradually decreases. In view of this drawback,
the filtration membrane is cleaned using ozonated water in
order to maintain the filtration performance.
For example, in a water treatment apparatus in
Patent Document 1, non-ozonated water containing no ozone is
20 sent to an ozonated water generation column, and ozone gas is
supplied to the non-ozonated water in the ozonated water
generation column so as to generate ozonated water, and a
filtration membrane is cleaned using the generated ozonated
water.
25
3
CITATION LIST
PATENT DOCUMENT
[0003] Patent Document 1: Japanese Laid-Open Patent
Publication No. 2003-251160
5
SUMMARY OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0004] However, the water treatment apparatus in Patent
Document 1 needs to be provided with the ozonated water
10 generation column for generating and storing the ozonated
water for cleaning the filtration membrane. Thus, the water
treatment apparatus in Patent Document 1 has problems in
terms of ensuring a space for installing the ozonated water
generation column and initial cost for the installation. In
15 view of these problems, a method that includes supplying
ozone gas into a pipe and dissolving the ozone gas in nonozonated water inside the pipe so as to generate ozonated
water inside the pipe is contemplated as a method for
generating ozonated water without installing any ozonated
20 water generation column. In the case of employing this
method, there is a concern that, when the distance from an
ozone gas supply unit to a filtration membrane is short or
when the supply speed of the ozonated water to the filtration
membrane is high, the ozonated water might be supplied to the
25 filtration membrane without increase, to a preset value, in
4
the concentration of ozone dissolved in the ozonated water.
Consequently, a problem arises in that the cleaning effect
for the filtration membrane decreases.
[0005] The present disclosure has been made to solve the
5 above problems, and an object of the present disclosure is to
provide a filtration membrane cleaning apparatus that can
suppress decrease in the cleaning effect for a filtration
membrane.
10 MEANS TO SOLVE THE PROBLEM
[0006] A filtration membrane cleaning apparatus according
to the present disclosure includes: an ozone gas supply unit
which supplies ozone gas; a non-ozonated water supply flow
path provided with a non-ozonated water supply pump which
15 supplies non-ozonated water as water containing no ozone; a
circulation flow path as a flow path inside which the ozone
gas supplied by the ozone gas supply unit is dissolved in the
non-ozonated water supplied from the non-ozonated water
supply flow path so as to generate ozonated water, the
20 circulation flow path being provided with a circulation pump
which circulates the generated ozonated water, the
circulation flow path being a flow path to which the ozone
gas supply unit and the non-ozonated water supply flow path
are connected; an ozonated water supply flow path connected
25 to the circulation flow path and provided with an ozonated
5
water supply pump which supplies, to a filtration membrane, a
part of the ozonated water being circulated through the
circulation flow path; and a control unit which controls the
non-ozonated water supply pump, the circulation pump, and the
5 ozonated water supply pump to simultaneously execute supply
of the non-ozonated water to the circulation flow path,
generation of the ozonated water inside the circulation flow
path, circulation of the ozonated water inside the
circulation flow path, and supply of the ozonated water to
10 the filtration membrane.
[0007] In addition, a water treatment apparatus according
to the present disclosure includes: a membrane separation
tank having a filtration membrane with which treatment-target
water is subjected to a membrane filtration process; a
15 membrane-filtered water tank which reserves membrane-filtered
water resulting from the membrane filtration process in the
membrane separation tank; an ozone gas supply unit which
supplies ozone gas; a non-ozonated water supply flow path
provided with a non-ozonated water supply pump which supplies
20 non-ozonated water as water containing no ozone; a
circulation flow path as a flow path inside which the ozone
gas supplied by the ozone gas supply unit is dissolved in the
non-ozonated water supplied from the non-ozonated water
supply flow path so as to generate ozonated water, the
25 circulation flow path being provided with a circulation pump
6
which circulates the generated ozonated water, the
circulation flow path being a flow path to which the ozone
gas supply unit and the non-ozonated water supply flow path
are connected; an ozonated water supply flow path connected
5 to the circulation flow path and provided with an ozonated
water supply pump which supplies, to the filtration membrane,
a part of the ozonated water being circulated through the
circulation flow path; and a control unit which controls the
non-ozonated water supply pump, the circulation pump, and the
10 ozonated water supply pump to simultaneously execute supply
of the non-ozonated water to the circulation flow path,
generation of the ozonated water inside the circulation flow
path, circulation of the ozonated water inside the
circulation flow path, and supply of the ozonated water to
15 the filtration membrane.
[0008] In addition, a filtration membrane cleaning method
according to the present disclosure includes: a step of
supplying non-ozonated water as water containing no ozone to
a circulation flow path; a step of dissolving ozone gas in
20 the non-ozonated water so as to generate ozonated water
inside the circulation flow path; a step of circulating the
ozonated water through the circulation flow path; and a step
of supplying, to a filtration membrane, a part of the
ozonated water being circulated through the circulation flow
25 path, wherein supply of the non-ozonated water to the
7
circulation flow path, generation of the ozonated water
inside the circulation flow path, circulation of the ozonated
water inside the circulation flow path, and supply of the
ozonated water to the filtration membrane are simultaneously
5 executed.
EFFECT OF THE INVENTION
[0009] The present disclosure is directed to a filtration
membrane cleaning apparatus for cleaning a filtration
10 membrane using ozonated water generated by dissolving ozone
gas in non-ozonated water. In the filtration membrane
cleaning apparatus, supply of the non-ozonated water to the
circulation flow path, generation of the ozonated water
inside the circulation flow path, circulation of the ozonated
15 water inside the circulation flow path, and supply of the
ozonated water to the filtration membrane are simultaneously
executed. Consequently, a filtration membrane cleaning
apparatus that can suppress decrease in the cleaning effect
for the filtration membrane is provided.
20
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] [FIG. 1] FIG. 1 is a schematic diagram of a water
treatment apparatus in embodiment 1.
[FIG. 2] FIG. 2 is a schematic diagram showing an
25 ozonated water generation unit and an ozone gas supply unit
8
in embodiment 1.
[FIG. 3] FIG. 3 is a flowchart showing a membrane
filtration process in embodiment 1.
[FIG. 4] FIG. 4 is a flowchart showing a
5 filtration membrane cleaning method in embodiment 1.
[FIG. 5] FIG. 5 is a schematic diagram of a water
treatment apparatus in a comparative example relative to
embodiment 1.
[FIG. 6] FIG. 6 is a schematic diagram of a water
10 treatment apparatus in embodiment 2.
[FIG. 7] FIG. 7 is a flowchart showing a
filtration membrane cleaning method in embodiment 2.
[FIG. 8] FIG. 8 is a schematic diagram of a water
treatment apparatus in embodiment 3.
15
DESCRIPTION OF EMBODIMENTS
[0011] Embodiment 1
A water treatment apparatus 100 including a
filtration membrane cleaning apparatus in embodiment 1 will
20 be described with reference to FIG. 1. FIG. 1 is a schematic
diagram of the water treatment apparatus 100 in embodiment 1.
The water treatment apparatus 100 includes: a membrane
separation tank 2 including a filtration membrane 3 with
which treatment-target water 1 is subjected to a membrane
25 filtration process; a membrane-filtered water tank 16 which
9
reserves membrane-filtered water 17 resulting from the
membrane filtration process in the membrane separation tank
2; a membrane filtration flow path 4; and a filtration
membrane cleaning apparatus.
5 [0012] In the membrane separation tank 2, for example,
contaminants are separated and removed, with the filtration
membrane 3, from the treatment-target water 1 treated through
an activated sludge process. The treatment-target water 1 is,
for example, water from waterworks, water from sewerage,
10 secondary treated sewage, industrial wastewater, seawater,
human waste, or the like, and is caused to flow into the
membrane separation tank 2 via a treatment-target water flow
path 5. A sludge draw-off flow path 10 may be connected to
the membrane separation tank 2. The sludge draw-off flow
15 path 10 is provided with a sludge draw-off pump 9 for drawing
off sludge. In addition, an aeration device 8 may be
disposed at a bottom portion of the membrane separation tank
2. A membrane surface aeration blower 6 is connected via an
air supply pipe 7 to the aeration device 8.
20 [0013] The material of the filtration membrane 3 is not
limited, but a fluorine-based resin compound having excellent
resistance to ozone which is a strong oxidizing agent is
preferable. Other examples of usable materials of the
filtration membrane 3 include: polyolefins such as
25 polyethylene, polypropylene, and polybutene; fluorine-based
10
resin compounds such as a tetrafluoroethylene-perfluoroalkyl
vinyl ether copolymer (PFA), a tetrafluoroethylenehexafluoropropylene copolymer (FEP), a tetrafluoroethyleneethylene copolymer (ETFE), polychlorotrifluoroethylene
5 (PCTFE), a chlorotrifluoroethylene-ethylene copolymer (ECTFE),
polyvinylidene fluoride (PVDF), and polytetrafluoroethylene
(PTFE); celluloses such as cellulose acetate and ethyl
cellulose; ceramic; and the like. Two or more types of the
above materials may be combined.
10 [0014] The type of the filtration membrane 3 is not
limited. For example, it is possible to use various
filtration membranes 3 publicly known in the relevant
technical field, such as microfiltration (MF) membranes and
ultrafiltration (UF) membranes.
15 [0015] The average pore diameter of the filtration
membrane 3 is not limited, but is preferably 0.001 μm or
larger and 1 μm or smaller and more preferably 0.01 μm or
larger and 0.1 μm or smaller. Use of a filtration membrane 3
having an average pore diameter that falls within this range
20 makes it possible to efficiently remove not only contaminants
having adhered on a surface, of the filtration membrane 3,
that is in contact with the treatment-target water 1 but also
contaminants having chemically adhered on a surface, of the
filtration membrane 3, that is in contact with the membrane25 filtered water 17 or contaminants having chemically adhered
11
in pores of the filtration membrane 3.
[0016] The shape of the filtration membrane 3 is not
limited. For example, the filtration membrane 3 may be
formed in shapes publicly known in the relevant technical
5 field, such as a cylindrical shape and a flat shape. Also,
the filtration membrane 3 may be of an immersion type, a
casing type, a monolith type, or the like.
[0017] The water passage system of the filtration membrane
3 is not limited. For example, the water passage system may
10 be a dead-end filtration system or a cross-flow filtration
system. It is possible to employ: an external pressure
filtration system in which the treatment-target water 1 is
caused to flow on the outer side of the filtration membrane 3,
and the membrane-filtered water 17 is caused to flow on the
15 inner side of the filtration membrane 3; or an internal
pressure filtration system in which the treatment-target
water 1 is caused to flow on the inner side of the filtration
membrane 3, and the membrane-filtered water 17 is caused to
flow on the outer side of the filtration membrane 3.
20 [0018] The membrane-filtered water tank 16 reserves the
membrane-filtered water 17 resulting from the membrane
filtration process in the membrane separation tank 2.
[0019] The membrane filtration flow path 4 is, for example,
a pipe and is a flow path that connects the filtration
25 membrane 3 and the membrane-filtered water tank 16 to each
12
other and through which the membrane-filtered water 17 is
sent to the membrane-filtered water tank 16. The membrane
filtration flow path 4 includes a membrane filtration pump 12,
membrane-filtered water flow rate measurement means 13, and a
5 pressure gauge 14. At the time of the membrane filtration
process, the membrane-filtered water 17 separated in the
membrane separation tank 2 is sent via a membrane-filtered
water flow path 15 to the membrane-filtered water tank 16 by
the membrane filtration pump 12. The membrane-filtered water
10 flow rate measurement means 13 measures the flow rate of the
membrane-filtered water 17 flowing through the membrane
filtration flow path 4.
[0020] Next, the filtration membrane cleaning apparatus
will be described. The filtration membrane cleaning
15 apparatus causes ozone gas to be dissolved in non-ozonated
water as water containing no ozone so as to generate ozonated
water 28 and cleans the filtration membrane 3 using the
generated ozonated water 28. The filtration membrane
cleaning apparatus includes a non-ozonated water supply flow
20 path 21, a circulation flow path 29, an ozone gas supply unit
23, an ozonated water supply flow path 35, and a control unit
37. The non-ozonated water supply flow path 21, the
circulation flow path 29, and the ozonated water supply flow
path 35 are formed of, for example, pipes or the like.
25 [0021] The non-ozonated water supply flow path 21 is a
13
flow path that connects the membrane-filtered water tank 16
and the circulation flow path 29 to each other and through
which the membrane-filtered water 17 reserved in the
membrane-filtered water tank 16 is supplied to the
5 circulation flow path 29. That is, in the present embodiment,
the non-ozonated water used for generating the ozonated water
28 is the membrane-filtered water 17 reserved in the
membrane-filtered water tank 16. The non-ozonated water
supply flow path 21 has a switch unit 18, a non-ozonated
10 water supply pump 19, and non-ozonated water supply flow rate
measurement means 20. The switch unit 18 opens/closes the
non-ozonated water supply flow path 21 according to an
instruction from the control unit 37. The non-ozonated water
supply pump 19 supplies the membrane-filtered water 17 as the
15 non-ozonated water from the membrane-filtered water tank 16
to the circulation flow path 29. The non-ozonated water
supply flow rate measurement means 20 measures the flow rate
of the non-ozonated water flowing through the non-ozonated
water supply flow path 21.
20 [0022] The circulation flow path 29 is a flow path inside
which ozonated water 28 is generated and through which the
generated ozonated water 28 is circulated. To the
circulation flow path 29, the ozone gas supply unit 23, the
non-ozonated water supply flow path 21, the ozonated water
25 supply flow path 35, an ozone gas removal unit 26, and an
14
overflow water flow path 27 are connected. The ozone gas
removal unit 26 is, for example, a pipe for discharging, from
the circulation flow path 29, ozone gas that has not been
dissolved in the ozonated water 28 inside the circulation
5 flow path 29. The overflow water flow path 27 is a flow path
for removing the ozonated water 28 from the circulation flow
path 29 when the amount of the ozonated water 28 being
circulated inside the circulation flow path 29 exceeds a
preset water amount. The overflow water flow path 27 is
10 provided, to the circulation flow path 29, at a water level
lower than the height of the ozone gas removal unit 26 in
order to prevent the ozonated water 28 from entering the
ozone gas removal unit 26.
[0023] The circulation flow path 29 further has a switch
15 unit 36, a circulation pump 30, circulation flow rate
measurement means 31, and dissolved ozone concentration
measurement means 32. The switch unit 36 is, for example, a
three-way valve that connects the circulation flow path 29
and the ozonated water supply flow path 35 to each other and
20 that can perform switching between flow paths for the
ozonated water 28 according to an instruction from the
control unit 37. The circulation pump 30 circulates the
ozonated water 28 through the circulation flow path 29. The
circulation flow rate measurement means 31 measures the flow
25 rate of the ozonated water 28 flowing through the circulation
15
flow path 29. The dissolved ozone concentration measurement
means 32 is, for example, an absorbance-type ozone
concentration meter or an electrode-type ozone concentration
meter that measures the concentration of the ozone dissolved
5 in the ozonated water 28 inside the circulation flow path 29.
The dissolved ozone concentration measurement means 32 is
preferably disposed between the switch unit 36 of the
circulation flow path 29 and a portion, of the circulation
flow path 29, to which the ozone gas supply unit 23 is
10 connected. The circulation flow path 29 may be provided with,
for example, a static mixer (not shown) which is means for
evenly mixing the ozonated water 28.
[0024] The ozone gas supply unit 23 generates ozone gas
and supplies the generated ozone gas to the circulation flow
15 path 29. An ozone raw material to be supplied to the ozone
gas supply unit 23 is not limited. For example, liquid
oxygen or oxygen that is generated through pressure swing
adsorption (PSA) or pressure vacuum swing adsorption (PVSA)
may be used.
20 [0025] FIG. 2 is a schematic diagram showing an ozonated
water generation unit 22 and the ozone gas supply unit 23 in
embodiment 1. FIG. 2 is an enlarged view showing the details
of the portion denoted by the reference character “22” in FIG.
1. The ozonated water generation unit 22 is a portion, of
25 the circulation flow path 29, to which the ozone gas supply
16
unit 23, the non-ozonated water supply flow path 21, the
ozone gas removal unit 26, and the overflow water flow path
27 are connected. The ozone gas supply unit 23 is connected
to the circulation flow path 29 and supplies ozone gas into
5 the circulation flow path 29. More specifically, the
ozonated water generation unit 22 of the circulation flow
path 29 includes an aeration device 25, and the ozone gas
supply unit 23 is connected via an ozone gas supply pipe 24
to the aeration device 25. Although FIG. 2 shows, as an
10 example, a case where the aeration device 25 is used as means
for supplying ozone gas from the ozone gas supply unit 23
into the circulation flow path 29, the ozone gas supply means
is not particularly limited as long as the means can cause
ozone gas to be dissolved in the non-ozonated water so as to
15 generate ozonated water 28 inside the circulation flow path
29. For example, ozone gas supply means of an ejector type,
a mechanical stirring type, and a downward injection type may
be used.
[0026] Through the circulation flow path 29, the ozonated
20 water 28 generated by dissolving the ozone gas in the nonozonated water supplied from the non-ozonated water supply
flow path 21 is circulated by the circulation pump 30. More
strictly speaking, the non-ozonated water supplied from the
non-ozonated water supply flow path 21 to the circulation
25 flow path 29 is mixed with the ozonated water 28 being
17
circulated through the circulation flow path 29, whereby
diluted ozonated water 28 is obtained. The ozone gas
supplied by the ozone gas supply unit 23 is dissolved in this
diluted ozonated water 28.
5 [0027] As described above, in the water treatment
apparatus 100 in the present embodiment, the ozone gas is
supplied from the ozone gas supply unit 23 into the
circulation flow path 29. Consequently, the water treatment
apparatus 100 in the present embodiment can generate the
10 ozonated water 28 inside the ozonated water generation unit
22 of the circulation flow path 29, and thus, does not need
to be provided with an ozonated water generation column
provided to a conventional water treatment apparatus.
[0028] The ozonated water generation column provided to
15 the conventional water treatment apparatus is a water tank
designed to be capable of reserving a necessary volume of
ozonated water 28 for cleaning the filtration membrane 3.
Meanwhile, the maximum capacity of the ozonated water
generation unit 22 in the present embodiment can be designed
20 to be smaller than the necessary volume of ozonated water 28
for cleaning the filtration membrane 3. For example, the
maximum capacity of the ozonated water generation unit 22 is
equal to or smaller than a quarter of the necessary volume of
ozonated water 28 for cleaning the filtration membrane 3.
25 [0029] In addition, the ozonated water generation unit 22
18
differs from the ozonated water generation column provided to
the conventional water treatment apparatus also in that: the
ozonated water generation unit 22 is a part of the
circulation flow path 29; and the generated ozonated water 28
5 is not reserved in the ozonated water generation unit 22 and
is circulated through the circulation flow path 29.
[0030] Furthermore, the overflow water flow path 27 is
connected to the ozonated water generation unit 22, whereas,
in general, the overflow water flow path 27 is not connected
10 to the ozonated water generation column provided to the
conventional water treatment apparatus.
[0031] With reference back to FIG. 1, the ozonated water
supply flow path 35 is a flow path that connects the
circulation flow path 29 and the filtration membrane 3 to
15 each other and through which a part of the ozonated water 28
being circulated through the circulation flow path 29 is
supplied to the filtration membrane 3. A part of the
ozonated water supply flow path 35 may be shared with the
membrane filtration flow path 4. FIG. 1 shows an example in
20 which the ozonated water supply flow path 35 and the membrane
filtration flow path 4 are connected to each other by a
switch unit 11, and a flow path from the switch unit 11 to
the filtration membrane 3 is shared. The switch unit 11 is,
for example, a three-way valve that can perform switching
25 between the flow path for the membrane-filtered water 17 and
19
the flow path for the ozonated water 28 according to an
instruction from the control unit 37. The ozonated water
supply flow path 35 includes an ozonated water supply pump 33
and ozonated water supply flow rate measurement means 34.
5 The ozonated water supply pump 33 sends the ozonated water 28
from the circulation flow path 29 via the ozonated water
supply flow path 35 to the filtration membrane 3. The
ozonated water supply flow rate measurement means 34 measures
the flow rate of the ozonated water 28 flowing through the
10 ozonated water supply flow path 35.
[0032] All the pumps and the switch units are connected to
the control unit 37. The control unit 37 controls operations
of all the pumps and the switch units. In addition,
measurement results obtained by all the flow rate measurement
15 means and the pressure gauge 14 are transmitted to the
control unit 37. In addition, The control unit 37 controls
an operation of the ozone gas supply unit 23. A method for
the control by the control unit 37 will be described in
relation to a water treatment method (described later).
20 [0033] Next, a water treatment method executed using the
water treatment apparatus 100 will be described. The water
treatment method is roughly divided into a membrane
filtration process and a cleaning process for the filtration
membrane 3. In the membrane filtration process, after the
25 treatment-target water 1 is treated through the activated
20
sludge process, contaminants are separated and removed
therefrom using the filtration membrane 3. When the membrane
filtration process is continuously executed, a problem arises
in that the filtration performance decreases. Specifically,
5 in association with continuous use of the filtration membrane
3, contaminants adhere: on the surface, of the filtration
membrane 3, that is in contact with the treatment-target
water 1; on the surface, of the filtration membrane 3, that
is in contact with the filtered water; and in pores of the
10 filtration membrane 3. Consequently, clogging occurs,
whereby the filtration performance gradually decreases. In
particular, when the filtration membrane 3 is clogged, a
higher pressure is necessary for the membrane filtration
process. Consequently, a membrane filtration flux and a
15 membrane-filtered water amount per unit time and unit
membrane area decrease. In view of this drawback, the water
treatment apparatus 100 periodically executes the cleaning
process for the filtration membrane 3 in order to maintain
the performance of the filtration membrane 3. Operations of
20 the pumps and the switch units described later are controlled
by the control unit 37.
[0034] Switching between the membrane filtration process
and the cleaning process for the filtration membrane 3 may be
set according to, for example, the time of the membrane
25 filtration process.
21
[0035] First, the membrane filtration process will be
described. FIG. 3 is a flowchart showing the membrane
filtration process in embodiment 1.
The control unit 37 causes the switch unit 11 to
5 close the circulation flow path 29 side thereof and open the
membrane separation tank 2 side and the membrane-filtered
water tank 16 side thereof (step S1). Then, the control unit
37 activates the membrane filtration pump 12 (step S2).
Consequently, the treatment-target water 1 is subjected to
10 membrane filtration with the filtration membrane 3, and the
membrane-filtered water 17 resulting from the filtration
executed with the filtration membrane 3 is sent via the
membrane filtration flow path 4 to the membrane-filtered
water tank 16. In addition, during the membrane filtration
15 process, the control unit 37 causes the membrane surface
aeration blower 6 to constantly operate, changes the
operating time of the sludge draw-off pump 9 according to the
concentration of sludge inside the membrane separation tank 2,
and causes the sludge draw-off pump 9 to draw off the sludge
20 inside the membrane separation tank 2.
[0036] Next, the cleaning process for the filtration
membrane 3 will be described. FIG. 4 is a flowchart showing
the filtration membrane cleaning method in embodiment 1. In
a case where the membrane filtration process is being
25 executed, the control unit 37 stops the membrane filtration
22
pump 12 and ends the membrane filtration process (step S3).
Then, the control unit 37 causes the switch unit 11 to close
the membrane-filtered water tank 16 side thereof and open the
membrane separation tank 2 side and the circulation flow path
5 29 side thereof (step S4).
[0037] Next, the control unit 37 causes preliminary
cleaning to be executed on the filtration membrane 3 (step
S5). Although preliminary cleaning for the filtration
membrane 3 is dispensable, preliminary cleaning can make it
10 easy to remove contaminants having adhered on the surface, of
the filtration membrane 3, that is in contact with the
treatment-target water 1. Specifically, the water treatment
apparatus 100 executes preliminary cleaning on the filtration
membrane 3 using a preliminary cleaning liquid containing no
15 chemical agent. For example, the control unit 37 causes the
switch unit 36 and the switch unit 18 to perform opening and
activates the non-ozonated water supply pump 19, the
circulation pump 30, and the ozonated water supply pump 33.
Consequently, the control unit 37 causes the membrane20 filtered water 17 to be sent to the filtration membrane 3 so
that preliminary cleaning can be executed. Alternatively,
the water treatment apparatus 100 may expose the filtration
membrane 3 to air for a certain time, to make it easy to
remove contaminants having adhered on the surface, of the
25 filtration membrane 3, that is in contact with the treatment-
23
target water 1.
[0038] Next, the control unit 37 causes the ozonated water
28 to be generated and circulated. First, the control unit
37 causes the switch unit 36 to close the ozonated water
5 supply flow path 35 side thereof and open the circulation
flow path 29 side thereof so as to circulate the ozonated
water 28 through the circulation flow path 29 (step S6). At
this time, ozonated water 28 generated when the previous time
of cleaning process for the filtration membrane 3 has been
10 executed remains inside the circulation flow path 29. Since
a time has elapsed from the previous time of cleaning process
for the filtration membrane 3, ozone in the ozonated water 28
remaining inside the circulation flow path 29 is decomposed,
whereby the concentration of the dissolved ozone has become
15 lower than the concentration obtained when the previous time
of cleaning process for the filtration membrane 3 has been
executed. In view of this, the control unit 37 activates the
circulation pump 30 and the ozone gas supply unit 23 (step
S7). Consequently, the control unit 37 causes the ozone gas
20 to be dissolved in the ozonated water 28 remaining inside the
circulation flow path 29 so as to generate ozonated water 28
in which the concentration is higher, and causes the
generated ozonated water 28 to be circulated inside the
circulation flow path 29. Then, the control unit 37
25 determines whether or not the value obtained by the dissolved
24
ozone concentration measurement means 32 has increased to a
preset value (step S8). When the control unit 37 determines
that the value obtained by the dissolved ozone concentration
measurement means 32 has not increased to the preset value,
5 the control unit 37 continues to cause the ozone gas supply
unit 23 to supply ozone gas and continues to cause the
ozonated water 28 to be circulated until the value obtained
by the dissolved ozone concentration measurement means 32
increases to the preset value.
10 [0039] The preset value for the dissolved ozone
concentration measurement means 32 may be set to be larger
than the concentration, of ozone dissolved in the ozonated
water 28, that is desired to be reached when the ozonated
water 28 is supplied to the filtration membrane 3 in
15 consideration of the fact that ozone is decomposed and the
concentration of the ozone dissolved in the ozonated water 28
decreases before the ozonated water 28 is supplied via the
ozonated water supply flow path 35 to the filtration membrane
3. The extent to which ozone is decomposed before the
20 ozonated water 28 is supplied via the ozonated water supply
flow path 35 to the filtration membrane 3 varies according to
the length of the ozonated water supply flow path 35 and the
supply flow rate, and thus, may be ascertained through an
experiment.
25 [0040] The preset value for the dissolved ozone
25
concentration measurement means 32 is preferably 10 mg/L or
higher and 50 mg/L or lower. When the concentration of the
ozone dissolved in the ozonated water 28 is lower than 10
mg/L, it takes time to decompose contaminants having adhered
5 to the filtration membrane 3, and a larger amount of the
ozonated water 28 is necessary, whereby the running cost for
cleaning the filtration membrane 3 increases. Meanwhile,
when the concentration of the ozone dissolved in the ozonated
water 28 is higher than 50 mg/L, the operating time of the
10 ozone gas supply unit 23 is lengthened, whereby higher
running cost is required for generating the ozonated water 28.
In addition, the time during which membrane filtration for
the treatment-target water 1 is stopped is also lengthened,
whereby the amount of the membrane-filtered water 17
15 decreases.
[0041] In a case where there is no ozonated water 28
remaining inside the circulation flow path 29, the control
unit 37 may control the switch unit 18 and the non-ozonated
water supply pump 19 to supply a preset amount of the non20 ozonated water to the circulation flow path 29.
[0042] The control unit 37 may cause execution of
generation and circulation of the ozonated water 28
simultaneously with the above membrane filtration process.
That is, steps S1 and S2 in FIG. 3 and steps S4 to S8 in FIG.
25 4 may be simultaneously executed. Consequently, the cleaning
26
process for the filtration membrane 3 can be swiftly started
after the membrane filtration process is ended.
[0043] Next, description will be given regarding a case
where supply of the ozonated water 28 to the filtration
5 membrane 3 is started so as to execute reverse cleaning on
the filtration membrane 3. The control unit 37 controls the
non-ozonated water supply pump 19, the circulation pump 30,
and the ozonated water supply pump 33 to simultaneously
execute supply of the non-ozonated water to the circulation
10 flow path 29, generation of the ozonated water 28 inside the
circulation flow path 29, circulation of the ozonated water
28 inside the circulation flow path 29, and supply of the
ozonated water 28 to the filtration membrane 3 (step S9).
The operation of the water treatment apparatus 100 will be
15 specifically described below.
[0044] First, the control unit 37 causes the switch unit
18 to perform opening, causes the switch unit 36 to perform
opening to all the directions, and causes the switch unit 11
to open the circulation flow path 29 side and the membrane
20 separation tank 2 side thereof and close the membranefiltered water tank 16 side thereof. Then, the control unit
37 activates the non-ozonated water supply pump 19 and the
ozonated water supply pump 33. Consequently, supply of the
non-ozonated water to the circulation flow path 29,
25 generation of the ozonated water 28 inside the circulation
27
flow path 29, circulation of the ozonated water 28 inside the
circulation flow path 29, and supply of the ozonated water 28
to the filtration membrane 3 are simultaneously executed, and
reverse cleaning of the filtration membrane 3 is started. As
5 described above, the control unit 37 also continuously causes
execution of generation and circulation of the ozonated water
28. Thus, the control unit 37 also drives the circulation
pump 30 in addition to the non-ozonated water supply pump 19
and the ozonated water supply pump 33.
10 [0045] Here, a method through which the control unit 37
controls the non-ozonated water supply pump 19, the ozonated
water supply pump 33, and the circulation pump 30 will be
described. The control unit 37 drives all of the nonozonated water supply pump 19, the ozonated water supply pump
15 33, and the circulation pump 30, and then controls each of
the pumps as follows.
[0046] First, at least one of the non-ozonated water
supply pump 19 and the ozonated water supply pump 33 is
controlled such that the flow rate of the non-ozonated water
20 to be supplied from the non-ozonated water supply flow path
21 to the circulation flow path 29 and the flow rate of the
ozonated water 28 to be supplied from the circulation flow
path 29 to the ozonated water supply flow path 35 become
equal to each other. That is, the control unit 37 controls
25 at least one of the non-ozonated water supply pump 19 and the
28
ozonated water supply pump 33 such that the value obtained by
the non-ozonated water supply flow rate measurement means 20
and the value obtained by the ozonated water supply flow rate
measurement means 34 become equal to each other. For example,
5 when the value obtained by the ozonated water supply flow
rate measurement means 34 becomes large, the control unit 37
controls the non-ozonated water supply pump 19 to increase
the output thereof such that the value obtained by the nonozonated water supply flow rate measurement means 20 also
10 becomes large. In contrast, when the value obtained by the
ozonated water supply flow rate measurement means 34 becomes
small, the control unit 37 controls the non-ozonated water
supply pump 19 to decrease the output thereof such that the
value obtained by the non-ozonated water supply flow rate
15 measurement means 20 also becomes small.
[0047] Then, the control unit 37 controls the circulation
pump 30 such that the flow rate of the ozonated water 28
inside the circulation flow path 29 becomes higher than the
flow rate of the ozonated water 28 to be supplied from the
20 circulation flow path 29 to the ozonated water supply flow
path 35. That is, the control unit 37 controls at least one
of the circulation pump 30 and the ozonated water supply pump
33 such that the value obtained by the circulation flow rate
measurement means 31 becomes larger than the value obtained
25 by the ozonated water supply flow rate measurement means 34.
29
For example, when the value obtained by the ozonated water
supply flow rate measurement means 34 becomes larger than the
value obtained by the circulation flow rate measurement means
31, the control unit 37 controls the circulation pump 30 to
5 increase the output thereof.
[0048] When, as a result of supplying the non-ozonated
water to the circulation flow path 29, the ozonated water 28
being circulated through the circulation flow path 29 is
diluted so that the value of the concentration of the
10 dissolved ozone inside the circulation flow path 29 measured
by the dissolved ozone concentration measurement means 32
becomes smaller than a preset threshold value, the control
unit 37 executes control as follows. The control unit 37
stops the non-ozonated water supply pump 19 and the ozonated
15 water supply pump 33, causes the switch unit 36 to close the
ozonated water supply flow path 35 side thereof, and causes
the switch unit 18 to perform closing. Meanwhile, the
control unit 37 keeps the circulation pump 30 activated.
Thus, when the value of the concentration of the dissolved
20 ozone measured by the dissolved ozone concentration
measurement means 32 is smaller than the preset threshold
value, the control unit 37 causes stoppage of supply of the
non-ozonated water to the circulation flow path 29 and
stoppage of supply of the ozonated water 28 to the filtration
25 membrane 3 and causes only execution of generation of the
30
ozonated water 28 inside the circulation flow path 29 and
execution of circulation of the ozonated water 28 inside the
circulation flow path 29. Consequently, the concentration of
the ozone dissolved in the ozonated water 28 being circulated
5 through the circulation flow path 29 gradually increases.
Thereafter, when the value obtained by the dissolved ozone
concentration measurement means 32 becomes equal to or larger
than the preset threshold value, the control unit 37 causes
the switch unit 36 to open the ozonated water supply flow
10 path 35 side thereof, causes the switch unit 18 to perform
opening, and activates the non-ozonated water supply pump 19
and the ozonated water supply pump 33. That is, the control
unit 37 causes supply of the non-ozonated water to the
circulation flow path 29, generation of the ozonated water 28
15 inside the circulation flow path 29, circulation of the
ozonated water 28 inside the circulation flow path 29, and
supply of the ozonated water 28 to the filtration membrane 3
to be simultaneously executed so as to restart reverse
cleaning of the filtration membrane 3. Consequently, the
20 concentration of the ozone dissolved in the ozonated water 28
can be kept at the preset threshold value or higher.
[0049] The time of the cleaning process for the filtration
membrane 3 using the ozonated water 28 is not particularly
limited and may be set as appropriate according to the amount
25 of the contaminants having adhered to the filtration membrane
31
3 or the like. In general, the time of the cleaning process
for the filtration membrane 3 is preferably 60 minutes or
shorter. The cleaning time is preferably short. The reasons
are as follows. When the cleaning time is long, the
5 operating time of the ozone gas supply unit 23 and the
operating times of the pumps are lengthened, whereby the
running cost increases. In addition, the time during which
membrane treatment for the treatment-target water 1 is
stopped is also lengthened, whereby the amount of the
10 membrane-filtered water 17 decreases.
[0050] A membrane-surface permeation flux which is the
amount of the ozonated water 28 to be supplied per filtration
membrane area is not particularly limited, and only a flux
that allows the filtration membrane 3 to be filled to ends
15 thereof has to be ensured. Specifically, the membranesurface permeation flux of the ozonated water 28 is
preferably 1 LMH (L/m2/h) or higher and 60 LMH or lower.
When the membrane-surface permeation flux of the ozonated
water 28 is higher than 60 LMH, the supply speed of the
20 ozonated water 28 is higher than the decomposition speed of
contaminants having adhered to the filtration membrane 3.
Thus, ozonated water 28 that has not reacted with the
contaminants flows outward of the filtration membrane 3. As
a result, the amount of the ozonated water 28 to be used
25 might increase more than necessary, and higher cost might be
32
required for cleaning the filtration membrane 3. Meanwhile,
when the membrane-surface permeation flux of the ozonated
water 28 is lower than 1 LMH, the filtration membrane 3 is
not filled with the ozonated water 28 to the ends thereof,
5 whereby the contaminants having adhered to the filtration
membrane 3 might become unable to be decomposed, or the
concentration might decrease during transport. As the
cleaning process for the filtration membrane 3 according to
the present embodiment, it is possible to employ: a cleaning
10 method that includes causing the ozonated water 28 to pass
through the inside of the filtration membrane 3 and
subsequently retaining, inside the filtration membrane 3, the
ozonated water 28 as is; a cleaning method that includes
immersing the filtration membrane 3 into the ozonated water
15 28 and retaining the filtration membrane 3; or the like.
[0051] The ozonated water 28 having come out from the
filtration membrane 3 after the cleaning process for the
filtration membrane 3 is discharged into the membrane
separation tank 2 and can be used as treatment-target water 1
20 to be subjected to the membrane filtration process.
Alternatively, ozonated water 28 having come out from the
filtration membrane 3 subsequently to reverse flow cleaning
may be separately collected and disposed of as a treated
liquid.
25 [0052] In the case of ending the cleaning process for the
33
filtration membrane 3, the control unit 37 stops the nonozonated water supply pump 19, the circulation pump 30, and
the ozonated water supply pump 33 (step S10). Then, the
control unit 37 causes the switch unit 11 to close the
5 circulation flow path 29 side thereof and causes the switch
unit 18 to perform closing (step S11). Consequently, supply
and circulation of the ozonated water 28 are stopped. Then,
the control unit 37 executes steps S1 and S2 shown in FIG. 3,
to restart the membrane filtration process for the treatment10 target water 1. Thus, the membrane filtration process for
the treatment-target water 1 can be executed continuously and
efficiently.
[0053] Advantageous effects of the water treatment
apparatus 100 in the present embodiment will be described in
15 comparison with the conventional water treatment apparatus
and a water treatment apparatus in a comparative example.
FIG. 5 is a schematic diagram of the water treatment
apparatus in the comparative example relative to embodiment 1.
In the conventional water treatment apparatus, it is
20 necessary to install an ozonated water generation column for
generating and reserving the ozonated water 28 for cleaning
the filtration membrane 3. Thus, the conventional water
treatment apparatus has problems in terms of ensuring a space
for installing the ozonated water generation column and
25 initial cost for the installation.
34
[0054] The water treatment apparatus in the comparative
example shown in FIG. 5 includes: a flow path that connects
the membrane-filtered water tank 16 and the filtration
membrane 3 to each other and through which the membrane5 filtered water 17 is supplied from the membrane-filtered
water tank 16 to the filtration membrane 3; and the ozone gas
supply unit 23 connected to the flow path. Inside the flow
path, ozonated water 28 is generated, and the generated
ozonated water 28 is supplied to the filtration membrane 3.
10 In the water treatment apparatus in the comparative example,
the ozonated water 28 is generated inside the flow path, and
thus it is unnecessary to install the ozonated water
generation column of the conventional water treatment
apparatus. However, there is the following concern regarding
15 the water treatment apparatus in the comparative example.
That is, for example, when the distance from the ozone gas
supply unit 23 to the filtration membrane 3 is short or when
the flow rate of the ozonated water 28 to be supplied to the
filtration membrane 3 is high, the ozonated water 28 might be
20 sent to the filtration membrane 3 before ozone gas supplied
from the ozone gas supply unit 23 into the flow path is
sufficiently dissolved in the membrane-filtered water 17.
Consequently, the ozonated water 28 might be supplied to the
filtration membrane 3 without increase, to the preset value,
25 in the concentration of the ozone dissolved in the ozonated
35
water 28. Thus, the water treatment apparatus in the
comparative example has a problem that the cleaning effect
for the filtration membrane 3 decreases.
[0055] Meanwhile, as shown in FIG. 1, the water treatment
5 apparatus 100 in the present embodiment includes: the
circulation flow path 29 as a flow path inside which the
ozone gas supplied by the ozone gas supply unit 23 is
dissolved in the non-ozonated water supplied from the nonozonated water supply flow path 21 so as to generate ozonated
10 water 28, the circulation flow path 29 being provided with
the circulation pump 30 which circulates the generated
ozonated water 28; and the control unit 37 which controls the
non-ozonated water supply pump 19, the circulation pump 30,
and the ozonated water supply pump 33 to simultaneously
15 execute supply of the non-ozonated water to the circulation
flow path 29, generation of the ozonated water 28 inside the
circulation flow path 29, circulation of the ozonated water
28 inside the circulation flow path 29, and supply of the
ozonated water 28 to the filtration membrane 3. Consequently,
20 the water treatment apparatus 100 in the present embodiment
does not need to be provided with the ozonated water
generation column provided to the conventional water
treatment apparatus. In addition, when the distance from the
ozone gas supply unit 23 to the filtration membrane 3 and the
25 flow rate of the ozonated water 28 to be supplied to the
36
filtration membrane 3 are each the same between the water
treatment apparatus 100 in the present embodiment and the
water treatment apparatus in the above comparative example,
the concentration of the ozone dissolved in the ozonated
5 water 28 can be more easily maintained in the water treatment
apparatus 100 in the present embodiment than in the water
treatment apparatus in the comparative example. Therefore,
the water treatment apparatus 100 in the present embodiment
can more significantly suppress decrease in the cleaning
10 effect for the filtration membrane 3 than the water treatment
apparatus in the comparative example.
[0056] Specifics are as follows. In the water treatment
apparatus 100 in the present embodiment, the ozone gas is
dissolved in the non-ozonated water so as to generate
15 ozonated water 28 inside the circulation flow path 29.
Furthermore, in the water treatment apparatus 100 in the
present embodiment, supply of the non-ozonated water to the
circulation flow path 29, generation of the ozonated water 28
inside the circulation flow path 29, circulation of the
20 ozonated water 28 inside the circulation flow path 29, and
supply of the ozonated water 28 to the filtration membrane 3
are simultaneously executed. Consequently, it is unnecessary
to reserve a necessary volume of ozonated water 28 for the
cleaning process for the filtration membrane 3. This can
25 make it unnecessary to install the ozonated water generation
37
column which is necessary for the conventional water
treatment apparatus.
[0057] Moreover, there is the following concern in a case
where, as in the water treatment apparatus in the above
5 comparative example, circulation of the ozonated water 28
inside the circulation flow path 29 and supply of the
ozonated water 28 to the filtration membrane 3 are not
simultaneously executed, with the same amount of ozone gas
being assumed to be supplied from the ozone gas supply unit
10 23 to the flow path. That is, depending on the distance from
the ozone gas supply unit 23 to the filtration membrane 3 and
the flow rate of the ozonated water 28 to be supplied to the
filtration membrane 3, the ozone gas might not be
sufficiently dissolved, and the ozonated water 28 might be
15 supplied to the filtration membrane 3 without increase, to
the preset value, in the concentration of the ozone dissolved
in the ozonated water 28. Meanwhile, in the water treatment
apparatus 100 in the present embodiment, supply of the nonozonated water to the circulation flow path 29, generation of
20 the ozonated water 28 inside the circulation flow path 29,
circulation of the ozonated water 28 inside the circulation
flow path 29, and supply of the ozonated water 28 to the
filtration membrane 3 are simultaneously executed. That is,
not the entire amount of the ozonated water 28 generated
25 inside the circulation flow path 29 is supplied to the
38
filtration membrane 3. Instead, a part of the ozonated water
28 generated inside the circulation flow path 29 is supplied
to the filtration membrane 3, and another part of the
generated ozonated water 28 is circulated through the
5 circulation flow path 29. Since a part of the generated
ozonated water 28 is circulated through the circulation flow
path 29 in this manner, the time required for supplying the
ozonated water 28 to the filtration membrane 3 is lengthened.
Consequently, the concentration of the ozone dissolved in the
10 ozonated water 28 is easily increased to the preset value.
Therefore, the water treatment apparatus 100 in the present
embodiment can more significantly suppress decrease in the
cleaning effect for the filtration membrane 3 than the water
treatment apparatus in the comparative example.
15 [0058] Meanwhile, when the flow rate of the non-ozonated
water to be supplied from the non-ozonated water supply flow
path 21 to the circulation flow path 29 is higher than the
flow rate of the ozonated water 28 to be supplied from the
circulation flow path 29 to the ozonated water supply flow
20 path 35, the concentration of the ozone dissolved in the
ozonated water 28 being circulated through the circulation
flow path 29 is less likely to increase. Also, the amount of
the ozonated water 28 to be discharged from the circulation
flow path 29 through the overflow water flow path 27
25 increases, whereby the ozonated water 28 is wastefully
39
consumed. In contrast, when the flow rate of the ozonated
water 28 to be supplied from the circulation flow path 29 to
the ozonated water supply flow path 35 is higher than the
flow rate of the non-ozonated water to be supplied from the
5 non-ozonated water supply flow path 21 to the circulation
flow path 29, there is a concern that the ozonated water 28
circulated inside the circulation flow path 29 might be
depleted and the circulation pump 30 might be operated in an
empty state. In view of these drawbacks, the control unit 37
10 controls at least one of the non-ozonated water supply pump
19 and the ozonated water supply pump 33 such that the flow
rate of the non-ozonated water to be supplied from the nonozonated water supply flow path 21 to the circulation flow
path 29 and the flow rate of the ozonated water 28 to be
15 supplied from the circulation flow path 29 to the ozonated
water supply flow path 35 become equal to each other.
Consequently, the flow rate of the non-ozonated water flowing
into the circulation flow path 29 and the flow rate of the
ozonated water 28 flowing out from the circulation flow path
20 29 become equal to each other, whereby the volume of the
ozonated water 28 being circulated through the circulation
flow path 29 can be kept at a fixed level.
[0059] Furthermore, the control unit 37 controls at least
one of the circulation pump 30 and the ozonated water supply
25 pump 33 such that the flow rate of the ozonated water 28
40
inside the circulation flow path 29 becomes higher than the
flow rate of the ozonated water 28 to be supplied from the
circulation flow path 29 to the ozonated water supply flow
path 35. Here, in the present embodiment, the flow rate of
5 the ozonated water 28 inside the circulation flow path 29 is
defined as x, and the flow rate of the ozonated water 28 to
be supplied from the circulation flow path 29 to the ozonated
water supply flow path 35 is defined as y. The expression
x>y is satisfied.
10 [0060] Here, it is assumed that the control unit 37 has
executed control such that both the flow rate of the ozonated
water 28 inside the circulation flow path 29 and the flow
rate of the ozonated water 28 to be supplied from the
circulation flow path 29 to the ozonated water supply flow
15 path 35 become x. In this case, since the flow rate of the
ozonated water 28 to be supplied to the ozonated water supply
flow path 35 is high, decrease in the concentration of the
ozone dissolved in the ozonated water 28 can be suppressed,
but a larger amount of the ozonated water 28 is used.
20 Meanwhile, in the water treatment apparatus 100 in the
present embodiment, the flow rate y of the ozonated water 28
to be supplied to the ozonated water supply flow path 35 is
lower than the flow rate x of the ozonated water 28 inside
the circulation flow path 29, whereby the amount of the
25 ozonated water 28 to be used can be decreased.
41
[0061] Next, it is assumed that the control unit 37 has
executed control such that both the flow rate of the ozonated
water 28 inside the circulation flow path 29 and the flow
rate of the ozonated water 28 to be supplied from the
5 circulation flow path 29 to the ozonated water supply flow
path 35 become y. In this case, since the flow rate of the
ozonated water 28 is low, the amount of the ozonated water 28
to be used can be decreased, but there is a concern that the
concentration of the ozone dissolved in the ozonated water 28
10 might decrease when the ozonated water is being supplied to
the filtration membrane 3. Meanwhile, in the water treatment
apparatus 100 in the present embodiment, the flow rate x of
the ozonated water 28 inside the circulation flow path 29 is
higher than the flow rate y of the ozonated water 28 to be
15 supplied from the circulation flow path 29 to the ozonated
water supply flow path 35, whereby decrease in the
concentration of the ozone dissolved in the ozonated water 28
can be suppressed.
[0062] In addition, when the value of the concentration of
20 the dissolved ozone measured by the dissolved ozone
concentration measurement means 32 is smaller than the preset
threshold value, the control unit 37 causes stoppage of
supply of the non-ozonated water to the circulation flow path
29 and stoppage of supply of the ozonated water 28 to the
25 filtration membrane 3 and causes only execution of generation
42
of the ozonated water 28 inside the circulation flow path 29
and execution of circulation of the ozonated water 28 inside
the circulation flow path 29. Then, when the value of the
concentration of the dissolved ozone measured by the
5 dissolved ozone concentration measurement means 32 becomes
equal to or larger than the preset threshold value, the
control unit 37 causes restart of supply of the non-ozonated
water to the circulation flow path 29 and restart of supply
of the ozonated water 28 to the filtration membrane 3.
10 Consequently, the concentration of the ozone dissolved in the
ozonated water 28 can be kept at the preset threshold value
or higher.
[0063] In addition, in a case where the pore diameter of
the filtration membrane 3 is very small, ozone gas having yet
15 to be dissolved in the ozonated water 28 is not transmitted
through the pores of the filtration membrane 3, whereby there
is a concern that the ozone gas having yet to be dissolved
might not be transmitted through the filtration membrane 3 so
as to cause gas lock inside the flow path. In view of this
20 drawback, the water treatment apparatus 100 in the present
embodiment includes the ozone gas removal unit 26 which is
connected to the circulation flow path 29 and which
discharges, from the circulation flow path 29, the ozone gas
that has not been dissolved inside the circulation flow path
25 29. Consequently, the ozone gas having yet to be dissolved
43
in the ozonated water 28 can be discharged from the
circulation flow path 29, whereby gas lock can be prevented.
[0064] Meanwhile, there is a concern regarding the water
treatment apparatus 100 that, when the non-ozonated water is
5 supplied to the circulation flow path 29 while the ozonated
water 28 is being supplied to the filtration membrane 3, the
timings of starting supply of the ozonated water 28 and
supply of the non-ozonated water might not necessarily
coincide with each other. For example, a case where supply
10 of the non-ozonated water to the circulation flow path 29 is
started earlier than supply of the ozonated water 28 to the
filtration membrane 3 is started, will be contemplated. In
this case, the water amount inside the circulation flow path
29 temporarily exceeds the maximum capacity of the
15 circulation flow path 29. Consequently, loads are applied to
the flow path, the pumps, and the switch units. In view of
this drawback, the water treatment apparatus 100 includes the
overflow water flow path 27 which is connected to the
circulation flow path 29 and through which the ozonated water
20 28 is removed from the circulation flow path 29 when the
amount of the ozonated water 28 being circulated inside the
circulation flow path 29 exceeds the preset water amount.
Consequently, when the water amount inside the circulation
flow path 29 temporarily exceeds the maximum capacity of the
25 circulation flow path 29, the ozonated water 28 being
44
circulated through the circulation flow path 29 can be
discharged from the circulation flow path 29. The overflow
water flow path 27 is provided, to the circulation flow path
29, at a water level lower than the height of the ozone gas
5 removal unit 26. Thus, when the water level of the ozonated
water 28 inside the circulation flow path 29 increases, the
ozonated water 28 can be prevented from entering the ozone
gas removal unit 26.
[0065] In addition, in the water treatment apparatus 100
10 in the present embodiment, the membrane-filtered water 17 is
used as the non-ozonated water. Consequently, it is
unnecessary to newly provide any water tank for reserving the
non-ozonated water.
[0066] Embodiment 2
15 A water treatment apparatus 100 including a
filtration membrane cleaning apparatus in embodiment 2 will
be described with reference to FIG. 6. FIG. 6 is a schematic
diagram of the water treatment apparatus 100 in embodiment 2.
In embodiment 1, an example in which the cleaning water for
20 cleaning the filtration membrane 3 is the ozonated water 28
has been described. Meanwhile, in the present embodiment, an
example in which at least two types of chemical solutions
which are the ozonated water 28 and cleaning water containing
a chemical agent other than ozone are each used as the
25 cleaning water for cleaning the filtration membrane 3, will
45
be described. The water treatment apparatus 100 including
the filtration membrane cleaning apparatus in the present
embodiment has a basic configuration which is the same as
that of the water treatment apparatus 100 including the
5 filtration membrane cleaning apparatus in embodiment 1. Thus,
only differences therebetween will be described. The same
constituents as those of the water treatment apparatus 100
including the filtration membrane cleaning apparatus in
embodiment 1 are denoted by the same reference characters.
10 [0067] Hereinafter, the ozonated water 28 is referred to
as first cleaning water 28, and the cleaning water containing
a chemical agent other than ozone is referred to as second
cleaning water 38. The chemical agent contained in the
second cleaning water 38 is not limited to one type of
15 chemical agent.
[0068] The water treatment apparatus 100 including the
filtration membrane cleaning apparatus in the present
embodiment includes a cleaning flow path 43 and a cleaning
water tank 39 which reserves the second cleaning water 38.
20 [0069] The cleaning flow path 43 is a flow path connecting
the filtration membrane 3 and the cleaning water tank 39 to
each other. FIG. 6 shows an example in which a flow path
that is a part of the cleaning flow path 43 and that extends
from the filtration membrane 3 to a switch unit 42 is shared
25 with the membrane filtration flow path 4 and the ozonated
46
water supply flow path 35. The cleaning flow path 43 has: a
cleaning pump 40 which supplies the second cleaning water 38
reserved in the cleaning water tank 39 to the filtration
membrane 3; and cleaning flow rate measurement means 41 for
5 measuring the flow rate of the second cleaning water 38
flowing through the cleaning flow path 43.
[0070] The type of the chemical agent for the second
cleaning water 38 reserved in the cleaning water tank 39 is
not particularly limited as long as the chemical agent is a
10 substance, other than ozone, capable of decomposing organic
matter or inorganic matter. As the chemical agent,
substances publicly known in the relevant technical field can
be used. Examples of the chemical agent capable of
decomposing organic matter include sodium hypochlorite,
15 hydrogen peroxide, sodium hydroxide, and the like. Among
these types of chemical agents, the chemical agent for the
second cleaning water 38 is preferably sodium hypochlorite
which is an inexpensive chemical agent and which allows the
concentration thereof to be easily maintained. These types
20 of chemical agents for the second cleaning water 38 may be
used singly, or two or more of these types of chemical agents
may be used in combination. In the case of combining two or
more of these types of chemical agents capable of decomposing
organic matter, a first chemical agent preferably has a
25 standard oxidation-reduction potential (25°C), measured using
47
a hydrogen electrode, of lower than 2.0 V, and a second
chemical agent preferably has a standard oxidation-reduction
potential (25°C), measured using a hydrogen electrode, of 2.0
V or higher. Specifically, it is preferable to use: cleaning
5 water that contains sodium hypochlorite as the first chemical
agent; and cleaning water that contains ozone as the second
chemical agent.
[0071] Examples of the substance capable of decomposing
inorganic matter include: inorganic acids such as
10 hydrochloric acid, sulfuric acid, and nitric acid; and
organic acids such as oxalic acid and citric acid. These
types of substances may also be used singly, or two or more
of these types of substances may also be used in combination.
Two or more types of substances capable of decomposing
15 organic matter and substances capable of decomposing
inorganic matter may be used in combination. In this case,
there is no limitation as to which substance is to be used as
a first chemical agent or as to which substance is to be used
as a second chemical agent. For example, in a case where a
20 substance capable of decomposing organic matter is used as
the first chemical agent, a substance capable of decomposing
inorganic matter is used as the second chemical agent.
Meanwhile, in a case where a substance capable of decomposing
inorganic matter is used as the first chemical agent, a
25 substance capable of decomposing organic matter may be used
48
as the second chemical agent.
[0072] The concentration of the chemical agent in the
second cleaning water 38 is not particularly limited. For
example, in the case of using a substance capable of
5 decomposing organic matter, the concentration of sodium
hypochlorite (effective chlorine concentration) is preferably
1.0 g/L or higher and 5.0 g/L or lower, and the concentration
of sodium hydroxide is preferably 1.0 g/L or higher and 4.0
g/L or lower. Meanwhile, in the case of using a substance
10 capable of decomposing inorganic matter, the concentration of
hydrochloric acid, sulfuric acid, or nitric acid is
preferably 1.0 g/L or higher and 10.0 g/L or lower, the
concentration of oxalic acid is preferably 1.0 g/L or higher
and 2.0 g/L or lower, and the concentration of citric acid is
15 preferably 1 g/L or higher and 10 g/L or lower. When the
concentration of any of the chemical agents is lower than the
lower limit of the above corresponding range, it takes time
to decompose contaminants having adhered to the filtration
membrane 3, and, in association with increase in the amount
20 of the cleaning water 28 to be used, the capacity of the
chemical agent tank also increases. Meanwhile, when the
concentration of any of the chemical agents is higher than
the upper limit of the above corresponding range, a larger
amount of the chemical agent is used, whereby higher cost is
25 required for the chemical agent.
49
[0073] The cleaning time for the filtration membrane 3
using the second cleaning water 38 is not particularly
limited and may be set as appropriate according to the amount
of the contaminants having adhered to the filtration membrane
5 3 or the like. In general, in the case of using sodium
hypochlorite, the cleaning time is preferably 90 minutes or
shorter, and, in the case of using oxalic acid or citric acid,
the cleaning time is preferably 5 minutes or longer and 7
minutes or shorter. The cleaning time for the filtration
10 membrane 3 using the second cleaning water 38 is preferably
short. The reason is as follows. When the cleaning time is
lengthened, the time during which membrane treatment for the
treatment-target water 1 is stopped is also lengthened,
whereby the amount of the membrane-filtered water decreases.
15 [0074] A membrane-surface permeation flux which is the
amount of the second cleaning water 38 to be supplied per
membrane area is not particularly limited. In general, only
a flux that allows the filtration membrane 3 to be filled to
the ends thereof has to be ensured. Specifically, in the
20 case of using sodium hypochlorite, the membrane-surface
permeation flux is preferably 6 LMH (L/m2/h) or lower. When
the membrane-surface permeation flux is excessively high,
higher cost is required for the chemical agent or the
capacity of the chemical agent tank increases in association
25 with increase in the necessary amount of the second cleaning
50
water 38. Meanwhile, when the membrane-surface permeation
flux is excessively low, the filtration membrane 3 is not
filled to the ends thereof with the second cleaning water 38,
whereby contaminants having adhered to the filtration
5 membrane 3 become unable to be decomposed.
[0075] All the pumps and the switch units are connected to
the control unit 37. In addition, measurement results
obtained by all the flow rate measurement means and the
pressure gauge 14 are transmitted to the control unit 37.
10 The control unit 37 controls operations of all the pumps and
the switch units. In addition, the control unit 37 controls
the operation of the ozone supply unit.
[0076] As a cleaning method for the filtration membrane 3
in the present embodiment, it is possible to employ: a
15 cleaning method that includes causing the second cleaning
water 38 to pass through the inside of the filtration
membrane 3 and subsequently retaining, inside the filtration
membrane 3, the second cleaning water 38 as is; a cleaning
method that includes immersing the filtration membrane 3 into
20 the second cleaning water 38 and retaining the filtration
membrane 3; or the like.
[0077] Next, a water treatment method executed using the
water treatment apparatus 100 in the present embodiment will
be described. Here, an example will be described in which
25 the cleaning process for the filtration membrane 3 is
51
executed using the second cleaning water 38 first, and then
the cleaning process for the filtration membrane 3 is
executed using the ozonated water 28 as the first cleaning
water 28. The methods for executing the membrane filtration
5 process and executing the cleaning process for the filtration
membrane 3 using the ozonated water 28 as the first cleaning
water 28 are the same as those in embodiment 1, and thus a
method for executing the cleaning process for the filtration
membrane 3 using the second cleaning water 38 will be
10 described. FIG. 7 is a flowchart showing a cleaning method
for the filtration membrane 3 in embodiment 2 and shows only
a cleaning method for the filtration membrane 3 using the
second cleaning water 38.
[0078] In a case where the membrane filtration process is
15 being executed, the control unit 37 stops the membrane
filtration pump 12 (step S20). Next, the control unit 37
causes the switch unit 42 to close the membrane-filtered
water flow path 15 side thereof and open the cleaning flow
path 43 side thereof (step S21). Then, the control unit 37
20 activates the cleaning pump 40 (step S22). Consequently, the
second cleaning water 38 is supplied via the cleaning flow
path 43 to the filtration membrane 3 so that a cleaning
process for the filtration membrane 3 is started. In the
case of ending the cleaning process for the filtration
25 membrane 3 using the second cleaning water 38, the control
52
unit 37 stops the cleaning pump 40 (step S23) and causes the
switch unit 42 to close the cleaning flow path 43 side
thereof (step S24). Consequently, supply of the second
cleaning water 38 is stopped.
5 [0079] In addition, the control unit 37 may cause
execution of generation and circulation of the ozonated water
28 as the first cleaning water 28 simultaneously with the
cleaning process for the filtration membrane 3 using the
above second cleaning water 38. Consequently, after the
10 cleaning process for the filtration membrane 3 using the
second cleaning water 38 is executed, the cleaning process
for the filtration membrane 3 using the ozonated water 28 as
the first cleaning water 28 can be swiftly started. Thus,
the control unit 37 causes execution of the cleaning process
15 for the filtration membrane 3 using the ozonated water 28
described in embodiment 1.
[0080] Similar to embodiment 1, the water treatment
apparatus 100 in the present embodiment includes: the
circulation flow path 29 as a flow path inside which the
20 ozone gas supplied by the ozone gas supply unit 23 is
dissolved in the non-ozonated water supplied from the nonozonated water supply flow path 21 so as to generate ozonated
water 28, the circulation flow path 29 being provided with
the circulation pump 30 which circulates the generated
25 ozonated water 28; and the control unit 37 which controls the
53
non-ozonated water supply pump 19, the circulation pump 30,
and the ozonated water supply pump 33 to simultaneously
execute supply of the non-ozonated water to the circulation
flow path 29, generation of the ozonated water 28 inside the
5 circulation flow path 29, circulation of the ozonated water
28 inside the circulation flow path 29, and supply of the
ozonated water 28 to the filtration membrane 3. Consequently,
the water treatment apparatus 100 in the present embodiment
does not need to be provided with the ozonated water
10 generation column provided to the conventional water
treatment apparatus. In addition, when the distance from the
ozone gas supply unit 23 to the filtration membrane 3 and the
flow rate of the ozonated water 28 to be supplied to the
filtration membrane 3 are each the same between the water
15 treatment apparatus 100 in the present embodiment and the
water treatment apparatus in the comparative example shown in
FIG. 5, the concentration of the ozone dissolved in the
ozonated water 28 can be more easily maintained in the water
treatment apparatus 100 in the present embodiment than in the
20 water treatment apparatus in the comparative example shown in
FIG. 5. Therefore, the water treatment apparatus 100 in the
present embodiment can more significantly suppress decrease
in the cleaning effect for the filtration membrane 3 than the
water treatment apparatus in the comparative example shown in
25 FIG. 5.
54
[0081] Moreover, the water treatment apparatus 100 in the
present embodiment further includes: the cleaning water tank
39 which reserves the second cleaning water 38 containing a
chemical agent other than ozone; and the cleaning flow path
5 43 which connects the filtration membrane 3 and the cleaning
water tank 39 to each other and which is provided with the
cleaning pump 40 which supplies, to the filtration membrane 3,
the second cleaning water 38 reserved in the cleaning water
tank 39. Consequently, the first cleaning water 28 as the
10 ozonated water 28 and the second cleaning water 38 can be
used in combination to execute the cleaning processes for the
filtration membrane 3.
[0082] The control unit 37 may cause execution of a
cleaning process for the filtration membrane 3 while the
15 second cleaning water 38 is being diluted with the membranefiltered water 17. Specifically, the control unit 37 causes
the switch unit 11 to close the membrane-filtered water flow
path 15 side thereof and open the filtration membrane 3 side
and the circulation flow path 29 side thereof. Then, the
20 control unit 37 causes the switch unit 42 to open the
cleaning flow path 43 side thereof and causes the switch unit
18 and the switch unit 36 to perform opening. Then, the
control unit 37 activates the non-ozonated water supply pump
19, the circulation pump 30, and the cleaning pump 40.
25 Consequently, the cleaning process for the filtration
55
membrane 3 can be executed while the second cleaning water 38
is being diluted with the membrane-filtered water 17. In
addition, the control unit 37 adjusts at least one of the
cleaning pump 40 and the non-ozonated water supply pump 19
5 according to the value obtained by the cleaning flow rate
measurement means 41 and the value obtained by the nonozonated water supply flow rate measurement means 20.
Consequently, the control unit 37 can adjust the
concentration and the flow rate of the diluted second
10 cleaning water 38 to be supplied to the filtration membrane 3.
[0083] Although an example in which the first cleaning
water 28 and the second cleaning water 38 are used in
combination to execute the cleaning processes for the
filtration membrane 3 has been described in the present
15 embodiment, the number of the types of the cleaning waters is
not limited to two. For example, the ozonated water 28
containing ozone, cleaning water containing the substance
capable of decomposing organic matter, and cleaning water
containing inorganic matter may be used in combination. When
20 the cleaning process for the filtration membrane 3 is
executed using the plurality of types of cleaning waters, the
order of use of these types of cleaning waters for executing
the cleaning processes for the filtration membrane 3 is not
particularly limited.
25 [0084] The flow path that is a part of the cleaning flow
56
path 43 and that extends from the filtration membrane 3 to
the switch unit 42 may be provided with means for evenly
mixing the second cleaning water 38 and the membrane-filtered
water 17, such as a static mixer, for example.
5 [0085] Embodiment 3
A water treatment apparatus 100 including a
filtration membrane cleaning apparatus in embodiment 3 will
be described with reference to FIG. 8. FIG. 8 is a schematic
diagram of the water treatment apparatus 100 in embodiment 3.
10 In each of embodiment 1 and embodiment 2, an example in which
the membrane-filtered water 17 is used as the non-ozonated
water has been described. Meanwhile, in the present
embodiment, an example in which clarified water 45 other than
the membrane-filtered water 17 is used as the non-ozonated
15 water will be described. The water treatment apparatus 100
including the filtration membrane cleaning apparatus in the
present embodiment has a basic configuration which is the
same as that of the water treatment apparatus 100 including
the filtration membrane cleaning apparatus in embodiment 1 or
20 embodiment 2. Thus, only differences therebetween will be
described. The same constituents as those of the water
treatment apparatuses 100 including the filtration membrane
cleaning apparatuses in embodiment 1 and embodiment 2 are
denoted by the same reference characters.
25 [0086] The water treatment apparatus 100 in the present
57
embodiment includes a clarified water tank 44 reserving the
clarified water 45 other than the membrane-filtered water 17.
The non-ozonated water supply flow path 21 connects the
clarified water tank 44 and the circulation flow path 29 to
5 each other. The clarified water 45 other than the membranefiltered water 17 only has to be clarified water that allows
obtainment of a minimum water quality required for generating
the ozonated water 28. For example, the clarified water 45
is at least one of tap water, industrial water, ion exchanged
10 water, pure water, and ultrapure water.
[0087] A method for the cleaning process for the
filtration membrane 3 in the present embodiment is the same
as that for the cleaning process for the filtration membrane
3 in embodiment 1 or embodiment 2, except that the clarified
15 water 45 is used as the non-ozonated water.
[0088] Similar to embodiment 1, the water treatment
apparatus 100 in the present embodiment includes: the
circulation flow path 29 as a flow path inside which the
ozone gas supplied by the ozone gas supply unit 23 is
20 dissolved in the non-ozonated water supplied from the nonozonated water supply flow path 21 so as to generate ozonated
water 28, the circulation flow path 29 being provided with
the circulation pump 30 which circulates the generated
ozonated water 28; and the control unit 37 which controls the
25 non-ozonated water supply pump 19, the circulation pump 30,
58
and the ozonated water supply pump 33 to simultaneously
execute supply of the non-ozonated water to the circulation
flow path 29, generation of the ozonated water 28 inside the
circulation flow path 29, circulation of the ozonated water
5 28 inside the circulation flow path 29, and supply of the
ozonated water 28 to the filtration membrane 3. Consequently,
the water treatment apparatus 100 in the present embodiment
does not need to be provided with the ozonated water
generation column provided to the conventional water
10 treatment apparatus. In addition, when the distance from the
ozone gas supply unit 23 to the filtration membrane 3 and the
flow rate of the ozonated water 28 to be supplied to the
filtration membrane 3 are each the same between the water
treatment apparatus 100 in the present embodiment and the
15 water treatment apparatus in the comparative example shown in
FIG. 5, the concentration of the ozone dissolved in the
ozonated water 28 can be more easily maintained in the water
treatment apparatus 100 in the present embodiment than in the
water treatment apparatus in the comparative example shown in
20 FIG. 5. Therefore, the water treatment apparatus 100 in the
present embodiment can more significantly suppress decrease
in the cleaning effect for the filtration membrane 3 than the
water treatment apparatus in the comparative example shown in
FIG. 5.
25 [0089] Meanwhile, the water quality of the membrane-
59
filtered water 17 might be influenced by the water quality of
the treatment-target water 1. Thus, when the membranefiltered water 17 is used as the non-ozonated water, the
ozone gas blown into the membrane-filtered water 17 and a
5 substance dissolved in the membrane-filtered water 17 might
react with each other so that the amount of the ozone capable
of being dissolved in the membrane-filtered water 17 might
decrease. Consequently, there are concerns that: a large
amount of ozone gas might be required for increasing the
10 concentration of ozone to be dissolved in the ozonated water
28; and it might take time to increase the concentration of
the dissolved ozone to the preset concentration.
[0090] Likewise, also in a case where the second cleaning
water 38 is diluted with the membrane-filtered water 17 in
15 embodiment 2, there is a concern that the chemical agent and
the substance dissolved in the membrane-filtered water 17
might react with each other so that the concentration of the
chemical agent dissolved in the membrane-filtered water 17
decreases, whereby the cleaning effect for the filtration
20 membrane 3 decreases.
[0091] In view of this drawback, in the water treatment
apparatus 100 in the present embodiment, the clarified water
45 other than the membrane-filtered water 17 is used as the
non-ozonated water. Specifically, the clarified water 45 is
25 at least one of tap water, industrial water, ion exchanged
60
water, pure water, and ultrapure water. Consequently,
generation of the ozonated water 28 and dilution of the
second cleaning water 38 can be executed more efficiently and
more stably than in a case where the membrane-filtered water
5 17 is used as the non-ozonated water.
[0092] The configurations described in the above
embodiments are merely examples and may be combined with
another known technique. In addition, the embodiments may be
combined with one another, and the configurations thereof may
10 be partially omitted or changed without departing from the
gist of the present disclosure.
DESCRIPTION OF THE REFERENCE CHARACTERS
[0093] 1 treatment-target water
15 2 membrane separation tank
3 filtration membrane
4 membrane filtration flow path
5 treatment-target water flow path
6 membrane surface aeration blower
20 7 air supply pipe
8 aeration device
9 sludge draw-off pump
10 sludge draw-off flow path
11 switch unit
25 12 membrane filtration pump
61
13 membrane-filtered water flow rate measurement
means
14 pressure gauge
15 membrane-filtered water flow path
5 16 membrane-filtered water tank
17 membrane-filtered water
18 switch unit
19 non-ozonated water supply pump
20 non-ozonated water supply flow rate measurement
10 means
21 non-ozonated water supply flow path
22 ozonated water generation unit
23 ozone gas supply unit
24 ozone gas supply pipe
15 25 aeration device
26 ozone gas removal unit
27 overflow water flow path
28 ozonated water (first cleaning water)
29 circulation flow path
20 30 circulation pump
31 circulation flow rate measurement means
32 dissolved ozone concentration measurement means
33 ozonated water supply pump
34 ozonated water supply flow rate measurement
25 means
62
35 ozonated water supply flow path
36 switch unit
37 control unit
38 second cleaning water
5 39 cleaning water tank
40 cleaning pump
41 cleaning flow rate measurement means
42 switch unit
43 cleaning flow path
10 44 clarified water tank
45 clarified water
100 water treatment apparatus

We Claim:
[Claim 1] A filtration membrane cleaning apparatus
comprising:
5 an ozone gas supply unit which supplies ozone gas;
a non-ozonated water supply flow path provided with
a non-ozonated water supply pump which supplies non-ozonated
water as water containing no ozone;
a circulation flow path as a flow path inside which
10 the ozone gas supplied by the ozone gas supply unit is
dissolved in the non-ozonated water supplied from the nonozonated water supply flow path so as to generate ozonated
water, the circulation flow path being provided with a
circulation pump which circulates the generated ozonated
15 water, the circulation flow path being a flow path to which
the ozone gas supply unit and the non-ozonated water supply
flow path are connected;
an ozonated water supply flow path connected to the
circulation flow path and provided with an ozonated water
20 supply pump which supplies, to a filtration membrane, a part
of the ozonated water being circulated through the
circulation flow path; and
a control unit which controls the non-ozonated
water supply pump, the circulation pump, and the ozonated
25 water supply pump to simultaneously execute supply of the
64
non-ozonated water to the circulation flow path, generation
of the ozonated water inside the circulation flow path,
circulation of the ozonated water inside the circulation flow
path, and supply of the ozonated water to the filtration
5 membrane.
[Claim 2] The filtration membrane cleaning apparatus
according to claim 1, wherein the control unit controls at
least one of the non-ozonated water supply pump and the
10 ozonated water supply pump such that a flow rate of the nonozonated water to be supplied from the non-ozonated water
supply flow path to the circulation flow path and a flow rate
of the ozonated water to be supplied from the circulation
flow path to the ozonated water supply flow path become equal
15 to each other.
[Claim 3] The filtration membrane cleaning apparatus
according to claim 1 or 2, wherein the control unit controls
at least one of the circulation pump and the ozonated water
20 supply pump such that a flow rate of the ozonated water
inside the circulation flow path becomes higher than a flow
rate of the ozonated water to be supplied from the
circulation flow path to the ozonated water supply flow path.
25 [Claim 4] The filtration membrane cleaning apparatus
65
according to any one of claims 1 to 3, wherein
the circulation flow path is further provided with
dissolved ozone concentration measurement means for measuring
a concentration of the ozone dissolved in the ozonated water
5 inside the circulation flow path, and
the control unit
causes, when the concentration of the dissolved
ozone is lower than a preset threshold value, stoppage of the
supply of the non-ozonated water to the circulation flow path
10 and stoppage of the supply of the ozonated water to the
filtration membrane, and execution of the generation of the
ozonated water inside the circulation flow path and execution
of the circulation of the ozonated water inside the
circulation flow path, and
15 causes, when the concentration of the dissolved
ozone becomes equal to or higher than the preset threshold
value, restart of the supply of the non-ozonated water to the
circulation flow path and restart of the supply of the
ozonated water to the filtration membrane.
20
[Claim 5] The filtration membrane cleaning apparatus
according to any one of claims 1 to 4, further comprising
an overflow water flow path which is connected to
the circulation flow path and through which the ozonated
25 water is removed from the circulation flow path when an
66
amount of the ozonated water being circulated inside the
circulation flow path exceeds a preset water amount.
[Claim 6] The filtration membrane cleaning apparatus
5 according to any one of claims 1 to 5, further comprising
an ozone gas removal unit which is connected to the
circulation flow path and which discharges, from the
circulation flow path, the ozone gas that has not been
dissolved inside the circulation flow path.
10
[Claim 7] The filtration membrane cleaning apparatus
according to any one of claims 1 to 6, further comprising:
a cleaning water tank which reserves cleaning water
containing a chemical agent other than the ozone; and
15 a cleaning flow path connecting the filtration
membrane and the cleaning water tank to each other and
provided with a cleaning pump which supplies, to the
filtration membrane, the cleaning water reserved in the
cleaning water tank.
20
[Claim 8] The filtration membrane cleaning apparatus
according to any one of claims 1 to 7, wherein the nonozonated water is at least one of membrane-filtered water,
tap water, industrial water, ion exchanged water, pure water,
25 and ultrapure water.
67
[Claim 9] A water treatment apparatus comprising:
a membrane separation tank having a filtration
membrane with which treatment-target water is subjected to a
5 membrane filtration process;
a membrane-filtered water tank which reserves
membrane-filtered water resulting from the membrane
filtration process in the membrane separation tank;
an ozone gas supply unit which supplies ozone gas;
10 a non-ozonated water supply flow path provided with
a non-ozonated water supply pump which supplies non-ozonated
water as water containing no ozone;
a circulation flow path as a flow path inside which
the ozone gas supplied by the ozone gas supply unit is
15 dissolved in the non-ozonated water supplied from the nonozonated water supply flow path so as to generate ozonated
water, the circulation flow path being provided with a
circulation pump which circulates the generated ozonated
water, the circulation flow path being a flow path to which
20 the ozone gas supply unit and the non-ozonated water supply
flow path are connected;
an ozonated water supply flow path connected to the
circulation flow path and provided with an ozonated water
supply pump which supplies, to the filtration membrane, a
25 part of the ozonated water being circulated through the
68
circulation flow path; and
a control unit which controls the non-ozonated
water supply pump, the circulation pump, and the ozonated
water supply pump to simultaneously execute supply of the
5 non-ozonated water to the circulation flow path, generation
of the ozonated water inside the circulation flow path,
circulation of the ozonated water inside the circulation flow
path, and supply of the ozonated water to the filtration
membrane.
10
[Claim 10] A filtration membrane cleaning method
comprising:
a step of supplying non-ozonated water as water
containing no ozone to a circulation flow path;
15 a step of dissolving ozone gas in the non-ozonated
water so as to generate ozonated water inside the circulation
flow path;
a step of circulating the ozonated water through
the circulation flow path; and
20 a step of supplying, to a filtration membrane, a
part of the ozonated water being circulated through the
circulation flow path, wherein
supply of the non-ozonated water to the circulation
flow path, generation of the ozonated water inside the
25 circulation flow path, circulation of the ozonated water
69
inside the circulation flow path, and supply of the ozonated
water to the filtration membrane are simultaneously executed.