DESCRIPTION
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
CLEANING DEVICE FOR FILTRATION MEMBRANE, WATER TREATMENT
DEVICE, AND CLEANING METHOD FOR FILTRATION MEMBRANE
MITSUBISHI ELECTRIC CORPORATION, a corporation organised and
existing under the Laws of Japan, whose address is 7-3,
Marunouchi 2-chome, Chiyoda-ku, Tokyo 100-8310, 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 cleaning device
for a filtration membrane, a water treatment device, and a
5 cleaning method for the filtration membrane.
BACKGROUND ART
[0002] As a method for separating and removing
contaminants from treatment-target water such as sewage or
10 industrial waste water, membrane filtration treatment using a
filtration membrane has been known. When the membrane
filtration treatment is continuously performed, contaminants
adhere on the surface and in the pores of the filtration
membrane and thus clogging occurs, whereby the filtration
15 performance gradually decreases. Accordingly, in order to
maintain the filtering performance, the filtration membrane
is cleaned using a cleaning liquid. Such a cleaning liquid
contains a chemical to enhance the cleaning effect.
For example, a water treatment device in Patent
20 Document 1 uses a cleaning liquid containing ozone. Ozone
has a high cleaning ability but is easily decomposed. Thus,
in the cleaning liquid remaining in a channel for supplying
the cleaning liquid to a filtration membrane, the ozone may
have been decomposed. In that case, the cleaning liquid in
25 which ozone has been decomposed is supplied to the filtration
3
membrane during the initial period of cleaning, and the
cleaning efficiency may be deteriorated. Accordingly, a
circulation channel for returning the cleaning liquid
remaining in the channel to a cleaning-liquid-reserving tank
5 is provided, and the cleaning liquid which remains in the
channel and in which ozone has been decomposed is replaced
with another cleaning liquid containing ozone, before
cleaning.
10 CITATION LIST
PATENT DOCUMENT
[0003] Patent Document 1: Japanese Laid-Open Patent
Publication No. 2003-251160
15 SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0004] For example, in the case where a sewage treatment
facility or a factory is renovated to introduce a water
treatment device, a space where the water treatment device
20 can be introduced may be limited in advance. In that case, a
cleaning-liquid-reserving tank may not be able to be
installed near a membrane-separation tank where membrane
filtration treatment is performed, and thus a channel from
the cleaning-liquid-reserving tank to the membrane-separation
25 tank may be elongated. In the conventional water treatment
4
device, the longer the channel is, the longer the time
required for supplying a cleaning liquid is. As a result, a
chemical contained in the cleaning liquid may be decomposed
while the cleaning liquid is being supplied, and the
5 concentration thereof may be less than a predetermined
concentration when the cleaning liquid is supplied to the
filtration membrane. Accordingly, in order to supply the
cleaning liquid to the filtration membrane before the
chemical has been decomposed, the conventional water
10 treatment device is devised to increase the supply flow speed.
However, the faster the supply flow speed is, the more the
usage amount of the cleaning liquid is.
[0005] The present disclosure has been made to solve the
above problem, and an object of the present disclosure is to
15 provide a cleaning device for a filtration membrane capable
of maintaining the chemical concentration in a cleaning
liquid and reducing the usage amount of the cleaning liquid.
SOLUTION TO THE PROBLEMS
20 [0006] A cleaning device for a filtration membrane
according to the present disclosure includes: a cleaningliquid-reserving tank that reserves therein a cleaning liquid
containing a chemical for cleaning the filtration membrane
and has an outlet and an inlet; a circulation channel
25 connecting the outlet and the inlet of the cleaning-liquid-
5
reserving tank and provided with a circulation pump for
circulating the cleaning liquid; a supply channel connected
to the circulation channel and provided with a supply pump
for supplying a part of the cleaning liquid circulating in
5 the circulation channel to the filtration membrane; and a
control unit that controls at least one of the circulation
pump and the supply pump such that a flow speed of the
cleaning liquid in the circulation channel becomes faster
than that in the supply channel.
10 [0007] A water treatment device according to the present
disclosure includes: a membrane-separation tank that has a
filtration membrane for performing membrane filtration
treatment on treatment-target water; a membrane-filtered
water tank that reserves therein membrane-filtered water on
15 which the membrane filtration treatment has been performed in
the membrane-separation tank; a cleaning-liquid-reserving
tank that reserves therein a cleaning liquid containing a
chemical for cleaning the filtration membrane and has an
outlet and an inlet; a circulation channel connecting the
20 outlet and the inlet of the cleaning-liquid-reserving tank
and provided with a circulation pump for circulating the
cleaning liquid; a supply channel connected to the
circulation channel and provided with a supply pump for
supplying a part of the cleaning liquid circulating in the
25 circulation channel to the filtration membrane; and a control
6
unit that controls at least one of the circulation pump and
the supply pump such that a flow speed of the cleaning liquid
in the circulation channel becomes faster than that in the
supply channel.
5 [0008] A cleaning method for a filtration membrane
includes: circulating a cleaning liquid in a circulation
channel connecting an outlet and an inlet of a cleaningliquid-reserving tank that reserves therein the cleaning
liquid; supplying a part of the cleaning liquid circulating
10 in the circulation channel to the filtration membrane, via a
supply channel for supplying the cleaning liquid from the
circulation channel to the filtration membrane; and making a
flow speed of the cleaning liquid in the circulation channel
faster than that in the supply channel.
15
EFFECT OF THE INVENTION
[0009] The present disclosure can provide a cleaning
device for a filtration membrane that includes a circulation
channel connecting an outlet and an inlet of a cleaning20 liquid-reserving tank, and a supply channel for supplying a
circulating cleaning liquid to a filtration membrane. In the
cleaning device for a filtration membrane, a flow speed of
the cleaning liquid in the circulation channel is made faster
than that in the supply channel, whereby the chemical
25 concentration in the cleaning liquid can be maintained and
7
the usage amount of the cleaning liquid can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] [FIG. 1] FIG. 1 is a schematic view of a water
5 treatment device according to embodiment 1.
[FIG. 2] FIG. 2 is a schematic view of a water
treatment device according to embodiment 2.
[FIG. 3] FIG. 3 is a schematic view of a water
treatment device according to embodiment 3.
10 [FIG. 4] FIG. 4 is a schematic view of the water
treatment device according to embodiment 3.
DESCRIPTION OF EMBODIMENTS
[0011] Embodiment 1
15 With reference to FIG. 1, a water treatment device
100 including a cleaning device for a filtration membrane 3
according to embodiment 1 will be described. FIG. 1 is a
schematic view of the water treatment device 100. The water
treatment device 100 includes: a membrane-separation tank 2
20 that has a filtration membrane 3 for performing membrane
filtration treatment on treatment-target water 1; a membranefiltered water tank 18 that reserves therein a membranefiltered water 19 on which the membrane filtration treatment
has been performed in the membrane-separation tank 2; a
25 cleaning-liquid-reserving tank 27 that reserves therein a
8
cleaning liquid 28 for cleaning the filtration membrane 3;
and a channel for discharging the membrane-filtered water 19
on which the membrane filtration treatment has been performed
by the filtration membrane 3 and supplying the cleaning
5 liquid 28.
[0012] In the membrane-separation tank 2, contaminants are
separated and removed by the filtration membrane 3, from the
treatment-target water 1 treated through the activated sludge
process, for example. The treatment-target water 1 is, for
10 example, water from waterworks, water from sewerage, sewage
secondary treated water, industrial wastewater, seawater,
human waste, or the like, and flows into the membraneseparation tank 2 via a treatment-target water channel 5. A
sludge-drawing channel 6 and a sludge-circulation channel 7
15 may be connected to the membrane-separation tank 2. The
sludge-drawing channel 6 is provided with a sludge-drawing
pump 9 for drawing sludge, and the sludge-circulation channel
7 is provided with a sludge-circulation pump 10 for
circulating sludge in the membrane-separation tank 2. In
20 addition, the membrane-separation tank 2 may have an aeration
device 8 at the bottom thereof. A membrane-surface aeration
blower 12 is connected to the aeration device 8 via an airsupply pipe 11.
[0013] The material of the filtration membrane 3 is not
25 limited, but is preferably a fluorine-based resin compound
9
having excellent resistance to strong oxidants such as ozone.
Other than that, for example, polyolefins such as
polyethylene, polypropylene, and polybutene; fluorine-based
resin compounds such as a tetrafluoroethylene-perfluoroalkyl
5 vinyl ether copolymer (PFA), a tetrafluoroethylenehexafluoropropylene copolymer (FEP), a tetrafluoroethyleneethylene copolymer (ETFE), polychlorotrifluoroethylene
(PCTFE), a chlorotrifluoroethylene-ethylene copolymer (ECTFE),
polyvinylidene fluoride (PVDF), and polytetrafluoroethylene
10 (PTFE); celluloses such as cellulose acetate and ethyl
cellulose; ceramic; or the like, may be used. In addition,
two or more types of the above substances may be used in
combination.
[0014] The type of the filtration membrane 3 is not
15 limited. For example, various filtration membranes 3, such
as a microfiltration (MF) membrane and an ultrafiltration
(UF) membrane, known in the technical field may be used.
[0015] An average pore diameter of the filtration membrane
3 is not limited, but is preferably not smaller than 0.001 μm
20 and not larger than 1 μm, and more preferably not smaller
than 0.01 μm and not larger than 0.1 μm. When the filtration
membrane 3 having an average pore diameter within this range
is used, not only contaminants adhered on the surface of the
filtration membrane 3 which comes in contact with the
25 treatment-target water 1 but also contaminants chemically
10
adhered on the surface of the filtration membrane 3 or in the
pores of the filtration membrane 3 which comes in contact
with the membrane-filtered water 19 can be efficiently
removed.
5 [0016] The shape of the filtration membrane 3 is not
limited. For example, the filtration membrane 3 may be
formed in a shape, such as a cylindrical shape or a flat
shape, known in the technical field. In addition, the
filtration membrane 3 of an immersion type, a casing type, a
10 monolith type, or the like may be used.
[0017] A water passage type of the filtration membrane 3
is not limited. For example, a dead-end filtration system or
a cross-flow filtration system may be used. The water
passage type may be: an external pressure filtration type in
15 which treatment-target water 1 flows outside a filtration
membrane 3, and filtered water flows inside the filtration
membrane 3; or an internal pressure filtration type in which
treatment-target water 1 flows inside a filtration membrane 3,
and filtered water flows outside the filtration membrane 3.
20 [0018] The membrane-filtered water 19 on which the
membrane filtration treatment has been performed in the
membrane-separation tank 2 is reserved in the membranefiltered water tank 18.
[0019] The water treatment device 100 includes a cleaning
25 device for cleaning the filtration membrane 3. The cleaning
11
device has the cleaning-liquid-reserving tank 27 that
reserves therein the cleaning liquid 28 containing a chemical
for cleaning the filtration membrane 3.
The type of the chemical is not limited as long as
5 the chemical does not deteriorate the material of the
filtration membrane 3 and is a substance that can decompose
organic matter or inorganic matter. Accordingly, a substance
known in the technical field may be used. Examples of the
chemical that can decompose organic matter include sodium
10 hypochlorite, hydrogen peroxide, sodium hydroxide, and ozone.
The above substances may be used singly, or two or more types
of the substances may be used in combination. When two or
more types of the chemicals that can decompose organic matter
are used in combination, a standard oxidation reduction
15 potential (25°C) of a first chemical is preferably lower than
2.0 V, which is measured using a hydrogen electrode, and the
standard oxidation reduction potential (25°C) of a second
chemical is preferably not lower than 2.0 V, which is
measured using the hydrogen electrode. For example, sodium
20 hypochlorite may be used as the first chemical, and ozone may
be used as the second chemical. Examples of the substance
that can decompose inorganic matter include an inorganic acid
such as hydrochloric acid, sulfuric acid, or nitric acid, and
an organic acid such as oxalic acid or citric acid. These
25 substances may also be used singly, or two or more types of
12
these substances may be used in combination. Two or more
types of the substances that can decompose organic matter and
the substances that can decompose inorganic matter may also
be used in combination. In that case, no limitation is
5 imposed as to which of the substances is used as the first
chemical or the second chemical. For example, when the
substance that can decompose organic matter is used as the
first chemical, the substance that can decompose inorganic
matter is used as the second chemical. When the substance
10 that can decompose inorganic matter is used as the first
chemical, the substance that can decompose organic matter is
used as the second chemical.
[0020] The chemical concentration in the cleaning liquid
28 is not limited. For example, when the substance that can
15 decompose organic matter is used, sodium hypochlorite
(effective chlorine concentration) is preferably not less
than 1.0 g/L and not greater 5.0 g/L, and sodium hydroxide is
preferably not less than 1.0 g/L and not greater than 4.0 g/L.
Ozone is preferably not less than 10 mg/L and not greater
20 than 40 mg/L, and more preferably not less than 20 mg/L and
not greater than 30 mg/L. When the substance that can
decompose inorganic matter is used, hydrochloric acid,
sulfuric acid, and nitric acid are each preferably not less
than 1.0 g/L and not greater than 10.0 g/L, oxalic acid is
25 preferably not less than 1.0 g/L and not greater than 2.0 g/L,
13
and citric acid is preferably not less than 1 g/L and not
greater than 10 g/L. If the chemical concentration is less
than the above range, it takes time to decompose contaminants
adhered to the filtration membrane 3, and the capacity of the
5 chemical tank is also increased according to increase of the
usage amount of the cleaning liquid 28. On the other hand,
if the chemical concentration is greater than the above range,
the usage amount of the chemical is increased, thus
increasing the cost needed for the chemical.
10 [0021] The channel is, for example, formed by piping or
the like. As shown in FIG. 1, the channel includes a
circulation channel 25, a supply channel 4, and a membranefiltered water channel 17. The circulation channel 25
connects an outlet 40 and an inlet 41 of the cleaning-liquid15 reserving tank 27, and is a channel for circulating the
cleaning liquid 28 reserved in the cleaning-liquid-reserving
tank 27. The supply channel 4 is a channel for supplying the
cleaning liquid 28 to the filtration membrane 3 of the
membrane-separation tank 2, and also a channel for supplying
20 the membrane-filtered water 19 on which the membrane
filtration treatment has been performed by the filtration
membrane 3 to the membrane-filtered water tank 18. The
membrane-filtered water channel 17 is a channel connecting
the membrane-filtered water tank 18 and the supply channel 4.
25 [0022] A switch unit 20 is provided to the supply channel
14
4 and connects the supply channel 4 and the membrane-filtered
water channel 17. A switch unit 21 is provided to the
circulation channel 25 and connects the circulation channel
25 and the supply channel 4.
5 The switch units 20, 21 are each a three-way valve
that can switch between the channel of the cleaning liquid 28
and the channel of the membrane-filtered water 19.
[0023] The circulation channel 25 includes a circulation
pump 22 and a circulation-flow-speed measurement unit 23. In
10 addition, the circulation channel 25 may also include a
cleaning-liquid-concentration measurement unit 24. The
circulation pump 22 causes the cleaning liquid 28 to return
to the cleaning-liquid-reserving tank 27 via the circulation
channel 25. The circulation-flow-speed measurement unit 23
15 is not limited as long as the circulation-flow-speed
measurement unit 23 can measure a flow speed of the cleaning
liquid 28 circulating in the circulation channel 25. For
example, an electromagnetic flow meter, a propeller flow
meter, an ultrasonic flow meter, or a radio flow meter may be
20 used.
[0024] The cleaning-liquid-concentration measurement unit
24 measures the chemical concentration in the cleaning liquid
28. For example, the cleaning-liquid-concentration
measurement unit 24 may be selected as appropriate from an
25 absorbance-type ozone concentration meter, an electrode-type
15
ozone concentration meter, and the like, according to the
chemical. The cleaning-liquid-concentration measurement unit
24 only has to be located on a downstream side of the
circulation pump 22, the circulation-flow-speed measurement
5 unit 23, and the switch unit 21, and is preferably at a
shorter distance from the inlet 41 of the cleaning-liquidreserving tank 27. When the cleaning-liquid-concentration
measurement unit 24 is disposed near the inlet 41 of the
cleaning-liquid-reserving tank 27, the chemical concentration
10 in the circulating cleaning liquid 28 returning to the
cleaning-liquid-reserving tank 27 can be measured.
Accordingly, the chemical concentration in the circulating
cleaning liquid 28 can be precisely grasped.
[0025] The supply channel 4 includes a supply pump 14 and
15 a supply-flow-speed measurement unit 15. In addition, the
supply channel 4 may also include a pressure gauge 13.
During the membrane filtration treatment, a membranefiltration pump 16, which is described below, provided to the
membrane-filtered water channel 17 causes the supply channel
20 4 to serve as a channel for supplying the membrane-filtered
water 19 to the membrane-filtered water tank 18. During
cleaning treatment of the filtration membrane 3, the supply
pump 14 provided to the supply channel 4 causes the supply
channel 4 to serve as a channel for supplying a part of the
25 cleaning liquid 28 circulating in the circulation channel 25
16
to the filtration membrane 3.
The supply-flow-speed measurement unit 15 measures
a flow speed of the cleaning liquid 28 in the supply channel
4. Similarly to the circulation-flow-speed measurement unit
5 23, the supply-flow-speed measurement unit 15 is not limited,
as long as the supply-flow-speed measurement unit 15 can
measure the flow speed of the cleaning liquid 28 circulating
in the circulation channel 25.
[0026] The membrane-filtered water channel 17 includes the
10 membrane-filtration pump 16. The membrane-filtration pump 16
causes the membrane-filtered water 19 separated through the
membrane-separation tank 2 during the membrane filtration
treatment, to flow into the membrane-filtered water tank 18
via the supply channel 4 and the membrane-filtered water
15 channel 17.
[0027] All the pumps and the switch units are connected to
a control unit 26. The measurement results of the supplyflow-speed measurement unit 15 and the circulation-flow-speed
measurement unit 23 are transmitted to the control unit 26.
20 The control unit 26 controls operation of all the pumps and
the switch units. A control method by the control unit 26
will be described in a water treatment method described below.
[0028] Next, the water treatment method using the water
treatment device 100 will be described. The water treatment
25 method is roughly classified into membrane filtration
17
treatment and cleaning treatment of the filtration membrane 3.
In the membrane filtration treatment, the treatment-target
water 1 is treated through the activated sludge process, and
then contaminants are separated and removed therefrom using
5 the filtration membrane 3. When the membrane filtration
treatment is continuously performed, the filtering
performance decreases. Specifically, as the filtration
membrane 3 is continuously used, clogging occurs owing to
adhesion of contaminants in pores of the filtration membrane
10 3, and on a surface of the filtration membrane 3 which comes
in contact with the treatment-target water 1 and a surface of
the filtration membrane 3 which comes in contact with the
filtered water. Consequently, the filtering performance
gradually decreases. In particular, if the filtration
15 membrane 3 is clogged, the pressure required during the
membrane filtration treatment is increased. Thus, a membrane
filtration flux and a membrane-filtered water amount per unit
time and unit membrane area decrease. Thus, the cleaning
treatment is periodically performed on the filtration
20 membrane 3 to maintain the performance of the filtration
membrane 3.
[0029] The membrane filtration treatment will be described.
Operations of the pumps and the switch units described below
are controlled by the control unit 26.
25 First, the circulation channel 25 side of the
18
switch unit 20 is closed, the membrane-separation tank 2 side
and the membrane-filtered water channel 17 side thereof are
opened, and the membrane-filtration pump 16 is activated.
Accordingly, the treatment-target water 1 is membrane
5 filtered by the filtration membrane 3, and the membranefiltered water 19 filtered by the filtration membrane 3 is
discharged to the membrane-filtered water tank 18 via the
supply channel 4 and the membrane-filtered water channel 17.
[0030] Next, the cleaning treatment of the filtration
10 membrane 3 will be described.
If the membrane filtration treatment is being
performed, the membrane-filtration pump 16 is stopped to end
the membrane filtration treatment. Then, the membranefiltered water channel 17 side of the switch unit 20 is
15 closed, and the membrane-separation tank 2 side and the
circulation channel 25 side thereof are opened. After the
filtration treatment ends, preliminary treatment may be
performed on the filtration membrane 3 before the cleaning
treatment of the filtration membrane 3 is started. For
20 example, exposure of the filtration membrane 3 to air for a
certain period facilitates removal of contaminants adhered on
a surface of the filtration membrane 3 which comes in contact
with the treatment-target water 1. In addition, a
preliminary cleaning liquid not containing a chemical may be
25 prepared to perform preliminary cleaning on the filtration
19
membrane 3. The preliminary cleaning facilitates removal of
contaminants adhered on the surface of the filtration
membrane 3 which comes in contact with the treatment-target
water 1.
5 [0031] Next, the cleaning liquid 28 is circulated. First,
the supply channel 4 side of the switch unit 21 is closed,
and the outlet 40 side and the inlet 41 side of the cleaningliquid-reserving tank 27 thereof are opened. Then, the
circulation pump 22 is activated to circulate the cleaning
10 liquid 28 containing a chemical from the cleaning-liquidreserving tank 27 via the circulation channel 25.
Accordingly, an old cleaning liquid 28 remaining in the
circulation channel 25 can be replaced with a new cleaning
liquid 28. Thus, even if the chemical contained in the old
15 cleaning liquid 28 remaining in the circulation channel 25
has been decomposed, cleaning efficiency in the initial
cleaning stage can be improved. The cleaning-liquidconcentration measurement unit 24 provided to the circulation
channel 25 measures the chemical concentration in the
20 cleaning liquid 28. Accordingly, whether or not the cleaning
liquid 28 has a predetermined chemical concentration is
checked. At this time, the measurement result of the
cleaning-liquid-concentration measurement unit 24 may be
transmitted to the control unit 26, so that, if the cleaning
25 liquid 28 has the predetermined chemical concentration, the
20
control unit 26 may perform control to start supplying the
cleaning liquid 28 to the filtration membrane 3 as described
below. Although not shown, the circulation channel 25 may
include, for example, a static mixer or the like for
5 uniformly mixing the cleaning liquid 28.
[0032] Next, the cleaning liquid 28 is supplied to the
filtration membrane 3. The switch unit 21 is opened for all
directions: the supply channel 4 side; and the outlet 40 side
and the inlet 41 side of the cleaning-liquid-reserving tank
10 27. Then, the supply pump 14 is activated to supply a part
of the cleaning liquid 28 circulating in the circulation
channel 25 to the filtration membrane 3 via the supply
channel 4, and reverse flow cleaning is performed on the
filtration membrane 3. The cleaning liquid 28 discharged
15 from the filtration membrane 3 after the reverse flow
cleaning is discharged to the membrane-separation tank 2, and
may be used as the treatment-target water 1 to undergo the
membrane filtration treatment. Alternatively, the cleaning
liquid 28 discharged from the filtration membrane 3 after the
20 reverse flow cleaning may be separately recovered as a
treated liquid. Each cleaning liquid 28, on which the
reverse cleaning treatment has been performed as described
below, is also treated as described above.
[0033] The circulation pump 22 and the supply pump 14 are
25 controlled by the control unit 26. At this time, the flow
21
speed of the cleaning liquid 28 in the circulation channel 25
is made faster than that in the supply channel 4. In
addition, the flow speed is adjusted such that a residence
time of the cleaning liquid 28 from the cleaning-liquid5 reserving tank 27 to the filtration membrane 3 becomes the
same as a residence time of the cleaning liquid 28 from the
cleaning-liquid-reserving tank 27 to the cleaning-liquidconcentration measurement unit 24. The flow speed may be
adjusted by controlling both the circulation pump 22 and the
10 supply pump 14 or one of the pumps.
[0034] With reference to FIG. 1, a method for adjusting
the flow speed by controlling the circulation pump 22 will be
described, for example. First, the flow speed of the
cleaning liquid 28 in the circulation channel 25 is made
15 faster than the flow speed of the cleaning liquid 28 in the
supply channel 4. At this time, the flow speed for supply
and the flow speed for circulation are measured using the
supply-flow-speed measurement unit 15 and the circulationflow-speed measurement unit 23, respectively. For example,
20 when a value of the supply-flow-speed measurement unit 15 is
high, an input to a motor of the circulation pump 22 is
increased so that a value of the circulation-flow-speed
measurement unit 23 becomes higher than the value of the
supply-flow-speed measurement unit 15. In the case of
25 controlling the supply pump 14, an input to a motor of the
22
supply pump 14 can be reduced so that the value of the
supply-flow-speed measurement unit 15 becomes lower than the
value of the circulation-flow-speed measurement unit 23. In
the case of controlling both the circulation pump 22 and the
5 supply pump 14, the inputs to the motors of the circulation
pump 22 and the supply pump 14 can be adjusted so that the
value of the circulation-flow-speed measurement unit 23
becomes higher than the value of the supply-flow-speed
measurement unit 15.
10 [0035] The circulation pump 22 is controlled such that the
residence time of the cleaning liquid 28 from the cleaningliquid-reserving tank 27 to the filtration membrane 3 becomes
the same as the residence time of the cleaning liquid 28 from
the cleaning-liquid-reserving tank 27 to the cleaning-liquid15 concentration measurement unit 24. Here, the supply channel
4 is formed as a shorter channel than the circulation channel
25. When the channels have the same pipe diameter, the
residence time of the cleaning liquid 28 can be obtained by
dividing the pipe length by the flow speed. Specifically,
20 the residence time of the cleaning liquid 28 from the
cleaning-liquid-reserving tank 27 to the cleaning-liquidconcentration measurement unit 24 can be obtained by dividing
the pipe length from the cleaning-liquid-reserving tank 27 to
the cleaning-liquid-concentration measurement unit 24 by the
25 flow speed obtained by the circulation-flow-speed measurement
23
unit 23. Alternatively, the pipe length from the cleaningliquid-reserving tank 27 to the switch unit 21 is divided by
the flow speed obtained by the circulation-flow-speed
measurement unit 23, and the pipe length from the switch unit
5 21 to the filtration membrane 3 is divided by the flow speed
obtained by the supply-flow-speed measurement unit 15. Then,
the residence time of the cleaning liquid 28 from the
cleaning-liquid-reserving tank 27 to the filtration membrane
3 can be obtained by adding up the above two quotients.
10 [0036] The control unit 26 controls the inputs to the
motors of the supply pump 14 and the circulation pump 22 such
that the residence time of the cleaning liquid 28 from the
cleaning-liquid-reserving tank 27 to the filtration membrane
3 becomes the same as the residence time of the cleaning
15 liquid 28 from the cleaning-liquid-reserving tank 27 to the
cleaning-liquid-concentration measurement unit 24. For
example, the case where the residence time of the cleaning
liquid 28 from the cleaning-liquid-reserving tank 27 to the
filtration membrane 3 is longer than the residence time of
20 the cleaning liquid 28 from the cleaning-liquid-reserving
tank 27 to the cleaning-liquid-concentration measurement unit
24 will be described. In the case of controlling the
circulation pump 22, the input to the motor of the
circulation pump 22 is increased. In the case of controlling
25 the supply pump 14, the input to the motor of the supply pump
24
14 is reduced. In the case of controlling the circulation
pump 22 and the supply pump 14, the input to the motor of the
circulation pump 22 is increased and the input to the motor
of the supply pump 14 is reduced.
5 Accordingly, the chemical concentration in the
cleaning liquid 28 to be supplied to the filtration membrane
3 can be estimated from a value of the cleaning-liquidconcentration measurement unit 24.
[0037] In the above, as a method for adjusting the flow
10 speed, an example in which the flow speed is adjusted using
values of the flow speed measured by the supply-flow-speed
measurement unit 15 and the flow speed measured by the
circulation-flow-speed measurement unit 23 has been described.
As another method, the supply-flow-speed measurement unit 15
15 and the circulation-flow-speed measurement unit 23 each
measure a flow rate, and the flow speed is calculated from
each measured flow rate. Specifically, when the channels
have the same pipe diameter, the flow speed can be obtained
by dividing the flow rate by a pipe cross-sectional area.
20 [0038] In addition, when the supply-flow-speed measurement
unit 15 and the circulation-flow-speed measurement unit 23
each measure the flow rate, the channels may have different
pipe diameters. For example, the supply channel 4 and the
circulation channel 25 may have different pipe diameters. In
25 that case, the residence time of the cleaning liquid 28 can
25
be obtained by dividing the flow rate per time by the
capacity of the pipe. The capacity of the pipe can be
obtained by multiplying the cross-sectional area and the
length of the pipe. Thus, the residence time of the cleaning
5 liquid 28 from the cleaning-liquid-reserving tank 27 to the
cleaning-liquid-concentration measurement unit 24 can be
obtained by dividing a value of the flow rate obtained by the
circulation-flow-speed measurement unit 23 by the capacity of
the pipe from the cleaning-liquid-reserving tank 27 to the
10 cleaning-liquid-concentration measurement unit 24.
Alternatively, the value of the flow speed obtained by the
circulation-flow-speed measurement unit 23 is divided by the
capacity of the pipe from the cleaning-liquid-reserving tank
27 to the switch unit 21, and the value of the flow speed
15 obtained by the supply-flow-speed measurement unit 15 is
divided by the capacity of the pipe from the switch unit 21
to the filtration membrane 3. Then, the residence time from
the cleaning-liquid-reserving tank 27 to the filtration
membrane 3 can be obtained by adding up the above two
20 quotients.
[0039] The cleaning time of the filtration membrane 3
taken when the cleaning liquid 28 containing a chemical is
used may be set as appropriate according to the amount of
contaminants adhered to the filtration membrane, etc. In
25 general, the cleaning time is preferably not longer than 90
26
minutes in the case of using sodium hypochlorite, is
preferably not longer than 60 minutes in the case of using
ozone water, and is preferably not shorter than 5 minutes and
not longer than 7 minutes in the case of using oxalic acid or
5 citric acid. If the cleaning time is elongated, the time
during which the filtration treatment of the treatment-target
water 1 is interrupted is also elongated, whereby the amount
of the membrane-filtered water decreases. Thus, a shorter
cleaning time is preferable.
10 [0040] The membrane-surface permeation flux, which is a
water amount supplied per membrane area, of the cleaning
liquid 28 containing a chemical is not limited. In general,
a flux at which the filtration membrane 3 can be filled to
ends thereof only has to be ensured. Specifically, the
15 membrane-surface permeation flux is preferably not greater
than 6 LMH (L/(m
2·h)) in the case of using sodium
hypochlorite, and is preferably not greater than 30 LMH
(L/(m
2·h)) in the case of using ozone water. If the
membrane-surface permeation flux is excessively high, as the
20 amount of the cleaning liquid 28 that is necessary is
increased, the cost for the chemical increases, the capacity
of the chemical tank also increases, or the filtration
membrane 3 is damaged. If the membrane-surface permeation
flux is excessively low, the cleaning liquid 28 does not fill
25 the filtration membrane to the ends thereof, and thus
27
contaminants adhered to the filtration membrane 3 cannot be
decomposed, or in the case of using ozone water as a chemical,
the ozone concentration decreases while the cleaning liquid
28 is being supplied.
5 [0041] As a cleaning method for the filtration membrane 3
according to the present embodiment, for example, the
cleaning method in which, after the cleaning liquid 28 is
caused to enter the filtration membrane 3, the cleaning
liquid 28 is retained in the membrane as it is, or the
10 filtration membrane 3 is immersed and retained in the
cleaning liquid 28, may be used.
[0042] After the cleaning treatment of the filtration
membrane 3 ends, the circulation pump 22 and the supply pump
14 are stopped. The circulation channel 25 side of a switch
15 unit 20 is closed, and the membrane-filtration pump 16 side
thereof is opened. Then, the membrane-filtration pump 16 is
activated to perform the filtration treatment of the
treatment-target water 1 again. Accordingly, the filtration
treatment of the treatment-target water 1 can be continuously
20 and efficiently performed.
[0043] The conventional cleaning device for the filtration
membrane 3 supplies the cleaning liquid 28 from the cleaningliquid-reserving tank 27 to the filtration membrane 3 at a
constant flow speed. Thus, when the channel from the
25 cleaning-liquid-reserving tank 27 to the filtration membrane
28
3 is long, a chemical in the cleaning liquid is being
decomposed while the cleaning liquid is being supplied, and
the concentration thereof decreases. On the other hand, if
the flow speed is made faster in order to supply the cleaning
5 liquid before the contained chemical has been decomposed, the
usage amount of the cleaning liquid increases.
[0044] The cleaning device for the filtration membrane 3
in the present embodiment includes the circulation channel 25
connecting the outlet 40 and the inlet 41 of the cleaning10 liquid-reserving tank 27, and the supply channel 4 for
supplying the circulating cleaning liquid 28 to the
filtration membrane 3. At least one of the circulation pump
22 and the supply pump 14 is controlled such that the flow
speed of the cleaning liquid 28 in the circulation channel 25
15 is made faster than that in the supply channel 4. The
circulation flow speed of the cleaning liquid 28 is made
faster than the supply flow speed to the filtration membrane
3, whereby the chemical concentration in the cleaning liquid
28 is prevented from decreasing while the cleaning liquid 28
20 is being supplied from the cleaning-liquid-reserving tank 27
to the filtration membrane 3. Accordingly, the chemical
concentration in the cleaning liquid 28 can be maintained.
Furthermore, the supply flow speed is slower than the
circulation flow speed, and thus the usage amount of the
25 cleaning liquid 28 can be reduced.
29
[0045] The water treatment device 100 according to the
present embodiment includes the cleaning device for the
filtration membrane 3 capable of maintaining the chemical
concentration in the cleaning liquid 28 and reducing the
5 usage amount of the cleaning liquid 28. Accordingly, the
cleaning-liquid-reserving tank 27 can be installed at a
remote location, thereby improving the degree of freedom of
design of the water treatment device 100. Furthermore, the
cleaning-liquid-reserving tank 27 can be installed separately,
10 thereby improving the degree of freedom of an installation
location of the water treatment device 100.
[0046] In the water treatment device 100, the membrane
filtration treatment and the cleaning treatment of the
filtration membrane 3 are repeated, and thus supply of the
15 cleaning liquid 28 and stop thereof are repeatedly performed.
Thus, while the supply of the cleaning liquid 28 is being
stopped, a chemical in the cleaning liquid 28 remaining in
the channel may be decomposed. The water treatment device
100 in the present embodiment circulates the cleaning liquid
20 28 before supplying the cleaning liquid 28 to the filtration
membrane 3. Accordingly, an old cleaning liquid 28 remaining
in the circulation channel 25 can be replaced with a new
cleaning liquid 28. Thus, even if the chemical in the old
cleaning liquid 28 remaining in the circulation channel 25
25 has been decomposed, cleaning efficiency in the initial
30
cleaning stage can be improved. In addition, the cleaningliquid-concentration measurement unit 24 provided to the
circulation channel 25 measures the chemical concentration in
the cleaning liquid 28. Accordingly, whether or not the
5 cleaning liquid 28 in the cleaning-liquid-reserving tank 27
has a predetermined chemical concentration is checked.
[0047] The residence time of the cleaning liquid 28 from
the cleaning-liquid-reserving tank 27 to the filtration
membrane 3 and the residence time of the cleaning liquid 28
10 from the cleaning-liquid-reserving tank 27 to the cleaningliquid-concentration measurement unit 24 are made the same.
Accordingly, the chemical concentration in the cleaning
liquid 28 to be supplied to the filtration membrane 3 can be
estimated from the value of the cleaning-liquid-concentration
15 measurement unit 24. Thus, with one cleaning-liquidconcentration measurement unit 24, whether or not the
cleaning liquid 28 in the cleaning-liquid-reserving tank 27
has a predetermined chemical concentration, and the
concentration in the cleaning liquid 28 to be supplied to the
20 filtration membrane 3 can be checked.
[0048] In the cleaning device for the filtration membrane
3 of the present embodiment, the case where the cleaning
liquid 28 containing one type of chemical is used has been
described. However, if the cleaning liquid 28 contains two
25 or more types of chemicals, a plurality of the cleaning-
31
liquid-reserving tanks 27 may be provided to perform the
cleaning treatment by the same method as above.
[0049] Embodiment 2
With reference to FIG. 2, a water treatment device
5 100 including a cleaning device for a filtration membrane 3
according to embodiment 2 will be described. FIG. 2 is a
schematic view of the water treatment device 100. Embodiment
2 shows an example of using, as a chemical in the cleaning
liquid 28, ozone which is a chemical that starts to be
10 decomposed immediately after the cleaning liquid is produced,
so that the concentration thereof is particularly difficult
to be maintained. The cleaning-liquid-reserving tank 27
stores therein ozone water as the cleaning liquid 28. The
other configurations are the same as in embodiment 1. The
15 same components as in embodiment 1 are denoted by the same
reference characters.
[0050] As shown in FIG. 2, the cleaning-liquid-reserving
tank 27 has an aeration device 31 at the bottom thereof, and
the aeration device 31 is connected to an ozone generator 29
20 via an ozone-supply pipe 30. The ozone material to be
supplied to the ozone generator 29 is not limited. For
example, liquid oxygen, or oxygen generated by pressure swing
adsorption (PSA) or pressure vacuum swing adsorption (PVSA)
may be used. Unnecessary ozone water is treated in exhaust25 ozone treatment equipment 33 via an exhaust-ozone pipe 32 and
32
is discharged to a treated-ozone pipe 34.
[0051] Next, a method for generating ozone water in the
cleaning-liquid-reserving tank 27 will be described. Other
water treatment methods are the same as in embodiment 1.
5 First, ozone gas generated by the ozone generator
29 is supplied from the aeration device 31 to the cleaningliquid-reserving tank 27 via the ozone-supply pipe 30.
Accordingly, ozone water is generated in the cleaning-liquidreserving tank 27. Then, the ozone water generated in the
10 cleaning-liquid-reserving tank 27 is supplied to the
filtration membrane 3 via the circulation channel 25 and the
supply channel 4, and reverse flow cleaning is performed on
the filtration membrane 3.
[0052] As in embodiment 1, the cleaning device for the
15 filtration membrane 3 in the present embodiment includes the
circulation channel 25 and the supply channel 4, and the flow
speed of the cleaning liquid 28 in the circulation channel 25
is made faster than that in the supply channel 4.
Accordingly, the chemical concentration in the cleaning
20 liquid 28 can be maintained and the usage amount of the
cleaning liquid 28 can be reduced.
[0053] The ozone gas generated by the ozone generator 29
is supplied from the aeration device 31 to the cleaningliquid-reserving tank 27 via the ozone-supply pipe 30,
25 whereby the ozone water can be generated in the cleaning-
33
liquid-reserving tank 27. Accordingly, even when ozone water
which can be easily decomposed is used as the cleaning liquid
28, the concentration in the ozone water reserved in the
cleaning-liquid-reserving tank 27 is easily maintained.
5 [0054] Although the case where the aeration device 31 is
used as ozone gas supply means has been described, other
supply means may be used as long as the device can generate
ozone water. For example, the ozone gas supply means of an
ejector type, a mechanical agitation type, a downward
10 injection type, or the like may be used.
[0055] Although the case where ozone is used as a chemical
has been described, a cleaning liquid 28 containing ozone and
another cleaning liquid 28 containing a chemical other than
ozone may be used in combination.
15 [0056] Embodiment 3
With reference to FIG. 3, a water treatment device
100 including a cleaning device for a filtration membrane 3
according to embodiment 3 will be described. FIG. 3 is a
schematic view of the water treatment device 100. The water
20 treatment device 100 in embodiment 3 includes a connecting
channel 37 connecting two positions of the circulation
channel 25 that are on the inlet 41 side of the cleaningliquid-reserving tank 27 from the circulation pump 22 and on
the outlet 40 side of the cleaning-liquid-reserving tank 27
25 from the cleaning-liquid-concentration measurement unit 24,
34
so as to form a shorter channel from the outlet 40 to the
inlet 41 of the cleaning-liquid-reserving tank 27 than the
circulation channel 25. The other configurations are the
same as in embodiment 1. The same components as in
5 embodiment 1 are denoted by the same reference characters.
[0057] For example, the circulation channel 25 includes: a
switch unit 38 between the switch unit 21, and the
circulation pump 22 and the circulation-flow-speed
measurement unit 23; and a switch unit 39 between the switch
10 unit 21 and the cleaning-liquid-concentration measurement
unit 24. The connecting channel 37 connected to the switch
unit 38 and the switch unit 39 is provided, and thus can form
a shorter channel from the outlet 40 to the inlet 41 of the
cleaning-liquid-reserving tank 27 than the circulation
15 channel 25.
[0058] Next, a water treatment method using the water
treatment device 100 will be described.
First, the cleaning liquid 28 is circulated via the
connecting channel 37, when the cleaning treatment of the
20 filtration membrane 3 is performed.
The switch unit 21 side of the switch unit 38 is
closed, and the circulation-flow-speed measurement unit 23
side and the switch unit 39 side thereof are opened. The
switch unit 21 side of the switch unit 39 is closed, and the
25 cleaning-liquid-concentration measurement unit 24 side and
35
the switch unit 38 side thereof are opened. Next, the
circulation pump 22 is activated to circulate the cleaning
liquid 28 through the outlet 40 of the cleaning-liquidreserving tank 27, the switch unit 38, the connecting channel
5 37, the switch unit 39, and the inlet 41 of the cleaningliquid-reserving tank 27 in this order. In this way, the
cleaning liquid 28 is supplied to the cleaning-liquidconcentration measurement unit 24 through a shorter channel
via the connecting channel 37 than the circulation channel 25.
10 Accordingly, whether or not the chemical concentration in the
cleaning liquid 28 to be supplied from the cleaning-liquidreserving tank 27 is a predetermined concentration can be
more precisely checked.
[0059] Next, circulation of the cleaning liquid 28 to be
15 supplied to the filtration membrane 3 will be described.
The switch unit 39 side of the switch unit 38 is
closed, and the circulation-flow-speed measurement unit 23
side and the switch unit 21 side thereof are opened. The
switch unit 38 side of the switch unit 39 is closed, and the
20 cleaning-liquid-concentration measurement unit 24 side and
the switch unit 21 side thereof are opened. The supply
channel 4 side of the switch unit 21 is closed, and the
switch unit 38 side and the switch unit 39 side thereof are
opened. Next, the circulation pump 22 is activated to
25 circulate the cleaning liquid 28 through the outlet 40 of the
36
cleaning-liquid-reserving tank 27, the switch unit 21, and
the inlet 41 of the cleaning-liquid-reserving tank 27 in this
order. Accordingly, an old cleaning liquid 28 remaining in
the circulation channel 25 can be replaced with a new
5 cleaning liquid 28. Thus, even if a chemical in the old
cleaning liquid 28 remaining in the circulation channel 25
has been decomposed, cleaning efficiency in the initial
cleaning stage can be improved. Other water treatment
methods are the same as in embodiment 1.
10 [0060] As in embodiment 1, the cleaning device for the
filtration membrane 3 in the present embodiment includes the
circulation channel 25 and the supply channel 4, and makes
the flow speed of the cleaning liquid 28 in the circulation
channel 25 faster than that in the supply channel 4.
15 Accordingly, the chemical concentration in the cleaning
liquid 28 can be maintained, and the usage amount of the
cleaning liquid 28 can be reduced.
[0061] It may be impossible to install the cleaningliquid-reserving tank 27 near the membrane-separation tank 2.
20 In that case, the channel from the cleaning-liquid-reserving
tank 27 to the filtration membrane 3 is elongated, and thus
the circulation channel 25 from the cleaning-liquid-reserving
tank 27 to the cleaning-liquid-concentration measurement unit
24 is also elongated. In such a water treatment device 100,
25 when the chemical concentration measured by the cleaning-
37
liquid-concentration measurement unit 24 is low, it is
impossible to determine whether or not the chemical
concentration in the cleaning liquid 28 supplied from the
cleaning-liquid-reserving tank 27 is low or the chemical
5 concentration has decreased while the cleaning liquid 28 is
being supplied to the filtration membrane 3. Regarding this
problem, in the present embodiment, the water treatment
device 100 includes the connecting channel 37 connecting two
positions of the circulation channel 25 that are on the inlet
10 41 side of the cleaning-liquid-reserving tank 27 from
circulation pump 22 and on the outlet 40 side of the
cleaning-liquid-reserving tank 27 from the cleaning-liquidconcentration measurement unit 24, so as to form a shorter
channel from the outlet 40 to the inlet 41 of the cleaning15 liquid-reserving tank 27 than the circulation channel 25,
whereby the problem can be solved. With this configuration,
the chemical concentration in the cleaning liquid 28 supplied
from the cleaning-liquid-reserving tank 27 and the chemical
concentration in the cleaning liquid 28 to be supplied to the
20 filtration membrane 3, can be checked separately.
[0062] The above-described configurations in embodiments
are merely examples and may be combined with another known
technique. In addition, each embodiment may be combined with
another embodiment, and the configuration thereof may be
25 partially omitted or changed without departing from the gist
38
of the present invention.
[0063] For example, embodiment 2 and embodiment 3 may be
combined. FIG. 4 is a schematic view of the water treatment
device 100. In the water treatment device 100 shown in FIG.
5 4, the ozone generator 29 is connected to the cleaningliquid-reserving tank 27 via the ozone-supply pipe 30. In
addition, the water treatment device 100 includes the
connecting channel 37 connecting two positions of the
circulation channel 25 that are on the inlet 41 side of the
10 cleaning-liquid-reserving tank 27 from the circulation pump
22 and on the outlet 40 side of the cleaning-liquid-reserving
tank 27 from the cleaning-liquid-concentration measurement
unit 24, so as to form a shorter channel from the outlet 40
to the inlet 41 of the cleaning-liquid-reserving tank 27 than
15 the circulation channel 25.
[0064] Also in such an embodiment, the circulation channel
25 and the supply channel 4 are provided, and the flow speed
of the cleaning liquid 28 in the circulation channel 25 is
made faster than that in the supply channel 4. Accordingly,
20 the chemical concentration in the cleaning liquid 28
containing ozone which can be easily decomposed can be
maintained, and the usage amount of the cleaning liquid 28
can be reduced.
[0065] Even when the cleaning liquid 28 contains ozone
25 which can be easily decomposed, the ozone concentration in
39
the cleaning liquid 28 supplied from the cleaning-liquidreserving tank 27, and the ozone concentration in the
cleaning liquid 28 to be supplied to the filtration membrane
3 can be separately checked.
5
DESCRIPTION OF THE REFERENCE CHARACTERS
[0066] 1 treatment-target water
2 membrane-separation tank
3 filtration membrane
10 4 supply channel
5 treatment-target water channel
6 sludge-drawing channel
7 sludge-circulation channel
8 aeration device
15 9 sludge-drawing pump
10 sludge-circulation pump
11 air-supply pipe
12 membrane-surface aeration blower
13 pressure gauge
20 14 supply pump
15 supply-flow-speed measurement unit
16 membrane-filtration pump
17 membrane-filtered water channel
18 membrane-filtered water tank
25 19 membrane-filtered water
40
20 switch unit
21 switch unit
22 circulation pump
23 circulation-flow-speed measurement unit
5 24 cleaning-liquid-concentration measurement unit
25 circulation channel
26 control unit
27 cleaning-liquid-reserving tank
28 cleaning liquid
10 29 ozone generator
30 ozone-supply pipe
31 aeration device
32 exhaust-ozone pipe
33 exhaust-ozone treatment equipment
15 34 treated-ozone pipe
36 switch unit
37 connecting channel
38 switch unit
39 switch unit
20 40 outlet
41 inlet
100 water treatment device
41
WE CLAIM:
[1] A cleaning device for a filtration membrane,
comprising:
a cleaning-liquid-reserving tank that reserves
5 therein a cleaning liquid containing a chemical for cleaning
the filtration membrane and has an outlet and an inlet;
a circulation channel connecting the outlet and the
inlet of the cleaning-liquid-reserving tank and provided with
a circulation pump for circulating the cleaning liquid;
10 a supply channel connected to the circulation
channel and provided with a supply pump for supplying a part
of the cleaning liquid circulating in the circulation channel
to the filtration membrane; and
a control unit that controls at least one of the
15 circulation pump and the supply pump such that a flow speed
of the cleaning liquid in the circulation channel becomes
faster than that in the supply channel.
[2] The cleaning device for the filtration membrane
20 according to claim 1, wherein the chemical contains at least
ozone.
[3] The cleaning device for the filtration membrane
according to claim 2, wherein the cleaning-liquid-reserving
25 tank has an aeration device connected to an ozone generator.
42
[4] The cleaning device for the filtration membrane
according to any one of claims 1 to 3, wherein
the circulation channel has a cleaning-liquidconcentration measurement unit that measures a chemical
5 concentration in the cleaning liquid, and
the control unit controls at least one of the
circulation pump and the supply pump, such that a residence
time of the cleaning liquid from the cleaning-liquidreserving tank to the filtration membrane becomes the same as
10 a residence time of the cleaning liquid from the cleaningliquid-reserving tank to the cleaning-liquid-concentration
measurement unit.
[5] The cleaning device for the filtration membrane
15 according to claim 4, further comprising
a connecting channel connecting two positions of
the circulation channel that are on the inlet side of the
cleaning-liquid-reserving tank from the circulation pump and
on the outlet side of the cleaning-liquid-reserving tank from
20 the cleaning-liquid-concentration measurement unit, so as to
form a shorter channel from the outlet to the inlet of the
cleaning-liquid-reserving tank than the circulation channel.
[6] A water treatment device comprising:
25 a membrane-separation tank that has a filtration
43
membrane for performing membrane filtration treatment on
treatment-target water;
a membrane-filtered water tank that reserves
therein membrane-filtered water on which the membrane
5 filtration treatment has been performed in the membraneseparation tank;
a cleaning-liquid-reserving tank that reserves
therein a cleaning liquid containing a chemical for cleaning
the filtration membrane and has an outlet and an inlet;
10 a circulation channel connecting the outlet and the
inlet of the cleaning-liquid-reserving tank and provided with
a circulation pump for circulating the cleaning liquid;
a supply channel connected to the circulation
channel and provided with a supply pump for supplying a part
15 of the cleaning liquid circulating in the circulation channel
to the filtration membrane; and
a control unit that controls at least one of the
circulation pump and the supply pump such that a flow speed
of the cleaning liquid in the circulation channel becomes
20 faster than that in the supply channel.
[7] A cleaning method for a filtration membrane,
comprising:
circulating a cleaning liquid in a circulation
25 channel connecting an outlet and an inlet of a cleaning-
44
liquid-reserving tank that reserves therein the cleaning
liquid;
supplying a part of the cleaning liquid circulating
in the circulation channel to the filtration membrane, via a
5 supply channel for supplying the cleaning liquid from the
circulation channel to the filtration membrane; and
making a flow speed of the cleaning liquid in the
circulation channel faster than that in the supply channel.
10 [8] The cleaning method for the filtration membrane
according to claim 7, further comprising:
measuring a chemical concentration in the cleaning
liquid by a cleaning-liquid-concentration measurement unit
provided to the circulation channel, and
15 performing control such that a residence time from
the cleaning-liquid-reserving tank to the filtration membrane
is the same as a residence time from the cleaning-liquidreserving tank to the cleaning-liquid-concentration
measurement unit.