FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
MEMBRANE CLEANING DEVICE AND 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 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

DESCRIPTION
TECHNICAL FIELD
5 [0001] The present disclosure relates to a membrane
cleaning device and a membrane cleaning method for cleaning,
with ozone water, a separation membrane for filtrating
treatment target water.

BACKGROUND ART
[0002] As a method for treating drained water (hereinafter,
referred to as treatment target water) containing organic
substances, there has been known a membrane bioreactor
(hereinafter, referred to as MBR) in which organic substances
in treatment target water are decomposed using activated
sludge containing microorganisms and solid-liquid separation
is performed through filtration using a separation membrane.
As the separation membrane of the MBR continues to be used,
contaminants adhere to the surface or the pores of the
separation membrane and thus clogging occurs, whereby
filtration performance gradually deteriorates. Therefore,
for a membrane separation tank for performing filtration, a
membrane cleaning device for cleaning the separation membrane
with ozone water is provided together.
[0003] Conventionally, for the membrane cleaning device as
described above, it is required that ozone water is
efficiently generated to reduce the cost needed for
generating ozone water, and technology therefor is being
developed. For example, Patent Document 1 discloses, as a
method for cleaning the separation membrane of the MBR, a
method in which ozone gas is supplied to dissolution water in
which an acid is added, thereby generating ozone water.
Ozone water is self-decomposed under an alkaline condition,
but is comparatively stable under an acidic condition. If
the dissolution water is set at pH 5 or lower in advance, it
is possible to generate ozone water using a less ozone supply
amount.
[0004] Further, Patent Document 2 discloses a water
treatment method in which, after an oxidation treatment step
of performing an oxidation treatment on treatment target
water by adding ozone to the treatment target water, the
treatment target water having undergone the oxidation
treatment is subjected to reverse osmosis membrane treatment,
wherein the oxidation treatment step includes an alkaline
oxidation treatment step of performing oxidation treatment
under an alkaline condition and an acidic oxidation treatment
step of performing oxidation treatment under an acidic to
neutral condition. As in this conventional example, the
alkaline oxidation treatment step is performed first, whereby
efficiency of oxidation treatment for organic substances by
ozone is enhanced, and organic substances in the dissolution
water are decomposed so that the molecular weights thereof
are reduced. By thereafter performing the acidic oxidation
treatment step, it is possible to generate ozone water using
a less ozone supply amount.
CITATION LIST
PATENT DOCUMENT
[0005] Patent Document 1: WO2016/031331
Patent Document 2: Japanese Laid-Open Patent
Publication No. 2005-324118

SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0006] In the case of using MBR treatment water as
dissolution water for dissolving ozone gas, organic
substances contained in the MBR treatment water react with
ozone, so that ozone is ineffectively consumed. Therefore,
it is necessary to efficiently decompose organic substances
in the dissolution water. Hydroxyl radicals generated by
self-decomposition of ozone have greater oxidizing power than
ozone and are highly reactive with organic substances.
However, in a method of generating ozone water under an
acidic condition, the generation amount of hydroxyl radicals
is small.
[0007] Therefore, in the case of using MBR treatment water
as dissolution water in the method disclosed in Patent
Document 1, it takes an enormous amount of time to decompose
organic substances in the dissolution water, and thus the
treatment time until reaching a dissolved ozone concentration
required for membrane cleaning is prolonged. On the other
hand, in the method of generating ozone water under an
alkaline condition as in Patent Document 2, selfdecomposition
of ozone is promoted and the generation amount
of hydroxyl radicals can be increased. Thus, it is possible
to efficiently decompose organic substances in the
dissolution water.
[0008] However, in the case of using MBR treatment water
as dissolution water, the organic substance concentration in
the MBR treatment water varies depending on the operation
status of the MBR, and thus the amount of ozone required for
decomposing organic substances also varies. Therefore, in
the case where ozone gas is supplied at a constant
concentration and a constant flow rate to the dissolution
water, the treatment time required for decomposing organic
substances varies. In Patent Document 2, the treatment time
is determined irrespective of the organic substance
concentration in the dissolution water, and thus the
treatment time is not optimized. That is, even when the
organic substance concentration in the dissolution water is
low, the treatment time cannot be shortened, so that a longer
treatment time than necessary is taken.
[0009] The present disclosure has been made to solve the
above problems, and an object of the present disclosure is to
provide a membrane cleaning device and a membrane cleaning
method capable of efficiently generating ozone water to be
used for membrane cleaning, thereby reducing the cost needed
for generating ozone water.

SOLUTION TO THE PROBLEMS
[0010] A membrane cleaning device according to the present
disclosure is a membrane cleaning device for cleaning, with
ozone water, a separation membrane for filtering treatment
target water, the membrane cleaning device including: an
ozone water generation unit which stores treated water
filtered through the separation membrane as dissolution water,
and dissolves ozone gas in the dissolution water, to generate
ozone water; ozone gas supply means for supplying ozone gas
to the ozone water generation unit; and pH adjustment means
for adjusting pH of the dissolution water stored in the ozone
water generation unit, on the basis of an organic substance
concentration in the dissolution water.
[0011] A membrane cleaning method according to the present
disclosure is a membrane cleaning method for cleaning, with
ozone water, a separation membrane for filtering treatment
target water, the membrane cleaning method including: an
ozone water generation process of using treated water
filtered through the separation membrane as dissolution water
and dissolving ozone gas in the dissolution water, to
generate ozone water, wherein the ozone water generation
process includes a first process of dissolving ozone gas in
the dissolution water under a neutral or alkaline condition,
and a second process of dissolving ozone gas in the
dissolution water under an acidic condition after the first
process, and whether to shift from the first process to the
second process is determined on the basis of an organic
substance concentration in the dissolution water, and whether
to start feeding the ozone water to the separation membrane
is determined on the basis of a dissolved ozone concentration
in the dissolution water.

EFFECT OF THE INVENTION
[0012] The membrane cleaning device according to the
present disclosure includes the pH adjustment means for
adjusting the pH of the dissolution water on the basis of the
organic substance concentration in the dissolution water.
Thus, a treatment time needed for decomposing organic
substances in the dissolution water is estimated from the
measured value of the organic substance concentration, and
during this period, ozone water is generated under a pH
condition suitable for decomposition of organic substances,
and thereafter, the pH can be adjusted so as to reach a pH
condition suitable for increasing the dissolved ozone
concentration. Therefore, irrespective of variation in the
organic substance concentration in the dissolution water,
ozone water can be efficiently generated, and the cost needed
for generating ozone water can be reduced.
[0013] In the membrane cleaning method according to the
present disclosure, whether to shift from the first process
to the second process is determined on the basis of the
organic substance concentration in the dissolution water,
whereby the treatment time in the first process can be
optimized without excess/deficiency, and when the organic
substance concentration in the dissolution water is low, the
treatment time in the first process can be shortened. In
addition, whether to start feeding ozone water to the
separation membrane is determined on the basis of the
dissolved ozone concentration in the dissolution water,
whereby the treatment time in the second process can be
optimized without excess/deficiency. Therefore, irrespective
of variation in the organic substance concentration in the
dissolution water, ozone water can be efficiently generated,
and the cost needed for generating ozone water can be reduced.
Objects, features, aspects, and effects of the
present disclosure other than the above will become more
apparent from the following detailed description with
reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0014] [FIG. 1] FIG. 1 is a diagram showing the entire
configuration of a membrane cleaning device according to
embodiment 1.
[FIG. 2] FIG. 2 is a diagram showing the
configuration of process shift determination means of the
membrane cleaning device according to embodiment 1.
[FIG. 3] FIG. 3 is a diagram showing the
configuration of pH adjustment means of the membrane cleaning
device according to embodiment 1.
[FIG. 4] FIG. 4 is a diagram showing the
configuration of feeding start determination means of the
membrane cleaning device according to embodiment 1.
[FIG. 5] FIG. 5 is a diagram showing an example of
a connection part between an ozone water feeding pipe and a
filtered water pipe in the membrane cleaning device according
to embodiment 1.
[FIG. 6] FIG. 6 is a diagram showing another
example of the connection part between the ozone water
feeding pipe and the filtered water pipe in the membrane
cleaning device according to embodiment 1.
[FIG. 7] FIG. 7 is a flowchart illustrating a
membrane cleaning start procedure in the membrane cleaning
device according to embodiment 1.
[FIG. 8] FIG. 8 is a diagram showing the entire
configuration of a membrane cleaning device according to
embodiment 2.
[FIG. 9] FIG. 9 is a diagram showing the
configuration of process shift determination means of the
membrane cleaning device according to embodiment 2.
[FIG. 10] FIG. 10 is a flowchart illustrating a
membrane cleaning start procedure in the membrane cleaning
device according to embodiment 2.
[FIG. 11] FIG. 11 is a diagram showing the entire
configuration of a membrane cleaning device according to
embodiment 3.
[FIG. 12] FIG. 12 is a flowchart illustrating a
membrane cleaning start procedure in the membrane cleaning
device according to embodiment 3.
[FIG. 13] FIG. 13 is a hardware configuration
diagram implementing a part of the function of the process
shift determination means, the pH adjustment means, or the
feeding start determination means in the membrane cleaning
device according to embodiment 1.

DESCRIPTION OF EMBODIMENTS
[0015] Embodiment 1
Hereinafter, a membrane cleaning device and a
membrane cleaning method according to embodiment 1 of the
present disclosure will be described with reference to the
drawings. FIG. 1 shows the entire configuration of the
membrane cleaning device according to embodiment 1. FIG. 2,
FIG. 3, and FIG. 4 respectively show the configurations of
process shift determination means, pH adjustment means, and
feeding start determination means of the membrane cleaning
device according to embodiment 1. In the drawings, the same
or corresponding parts are denoted by the same reference
characters.
[0016] The entire configuration of the membrane cleaning
device according to embodiment 1 will be briefly described
with reference to FIG. 1. The membrane cleaning device is
for cleaning a separation membrane 2 which separates
treatment target water W1 containing activated sludge into
activated sludge and treated water W2, in a water treatment
system using MBR, for example. In the following description,
the membrane cleaning device for cleaning the separation
membrane 2 of the MBR will be described. However, a membrane
to be cleaned by the membrane cleaning device according to
the present disclosure is not limited to the separation
membrane 2 of the MBR, and activated sludge does not
necessarily need to be contained in the treatment target
water W1.
[0017] As shown in FIG. 1, a membrane separation tank 1
stores, as treatment target water W1, inflow water W which
flows therein from an aeration tank (not shown) for
performing organism treatment using activated sludge. The
separation membrane 2 is provided in the membrane separation
tank 1 and immersed in the treatment target water W1. The
treatment target water W1 contains activated sludge, and is
separated into activated sludge and treated water W2 through
filtration by the separation membrane 2.
[0018] As the separation membrane 2 continues to be used,
contaminants adhere to the surface or the pores thereof and
thus clogging occurs. Therefore, it is necessary to clean
the separation membrane 2 by the membrane cleaning device.
The separation membrane 2 is connected to a filtered water
pipe 3a and a filtration pump 4. Treated water W2 filtered
through the separation membrane 2 is sucked by the filtration
pump 4, to flow through the filtered water pipe 3a, and then
is stored in a treated water tank 5.
[0019] The materials of the membrane separation tank 1 and
the treated water tank 5 are not particularly limited, and
may be made from concrete, stainless steel, or resin, for
example. As the separation membrane 2, there are various
types such as reverse osmosis membrane (RO membrane),
nanofiltration membrane (NF membrane), ultrafiltration
membrane (UF membrane), and microfiltration membrane (MF
membrane) which are different in pore size, and an
appropriate one is selected from these. As the material of
the separation membrane 2, a fluorine-based resin compound
such as polytetrafluoroethylene resin (PTFE) or
polyvinylidene fluoride resin (PVDF) is highly resistant to
ozone water and thus is preferable. It is noted that the
separation membrane 2 may be a hollow fiber membrane or a
flat membrane.
[0020] The treated water W2 stored in the treated water
tank is discharged to outside of the system through a
treated water discharge pipe 3b, but partially flows through
a dissolution water pipe 3c, to be stored as dissolution
water W3 in an ozone water generation unit 6. The treated
water discharge pipe 3b and the dissolution water pipe 3c may
be each provided with one or both of a pump and a valve, as
appropriate.
[0021] The ozone water generation unit 6 performs an ozone
water generation process of using the treated water W2 as the
dissolution water W3 and dissolving ozone gas in the
dissolution water W3 to generate ozone water W4. The ozone
water generation process includes a first process of
dissolving ozone gas in the dissolution water W3 under a
neutral or alkaline condition, and a second process of
dissolving ozone gas in the dissolution water W3 under an
acidic condition after the first process. The dissolution
water W3 stored in the ozone water generation unit 6
increases in the dissolved ozone concentration through the
ozone water generation process, to become ozone water W4
having a predetermined dissolved ozone concentration. In the
following description, the dissolution water W3 that has
reached the predetermined dissolved ozone concentration so
that the dissolution water W3 can be used for membrane
cleaning is referred to as "ozone water W4".
[0022] As the material of the ozone water generation unit
6, for example, stainless steel or a fluorine-based resin
compound is highly resistant to ozone and thus is preferable.
The surface of the container of the ozone water generation
unit 6 may be coated with a fluorine-based resin compound.
[0023] The ozone water generation unit 6 is connected via
an ozone gas pipe 3d to an ozonizer 61 which is ozone gas
supply means. The ozonizer 61 generates ozone gas using, as
a raw material, for example, liquid oxygen or oxygen
generated by pressure swing adsorption (PSA) or pressure
vacuum swing adsorption (PVSA), and supplies the ozone gas to
the ozone water generation unit 6. The ozone gas generated
by the ozonizer 61 flows through the ozone gas pipe 3d to the
ozone water generation unit 6. In the ozone water generation
unit 6, ozone gas can be dissolved in the dissolution water
W3 by a method such as ejector method, aeration method, or
dissolution membrane method.
[0024] The ozone water generation unit 6 is connected to
an exhaust ozone gas decomposition portion 62 via an exhaust
ozone gas pipe 3e. In the exhaust ozone gas decomposition
portion 62, a catalyst such as activated carbon or manganese
oxide for decomposing ozone gas into oxygen is provided. The
exhaust ozone gas discharged from the ozone water generation
unit 6 is decomposed into oxygen through contact with the
catalyst in the exhaust ozone gas decomposition portion 62,
and then discharged to outside of the system.
[0025] The process shift determination means 7 determines
whether to shift from the first process to the second process
on the basis of the organic substance concentration in the
dissolution water W3. The pH adjustment means 8 adjusts the
pH of the dissolution water W3 stored in the ozone water
generation unit 6 on the basis of the organic substance
concentration in the dissolution water W3. The feeding start
determination means 10 determines whether to start feeding
ozone water to the separation membrane 2 on the basis of the
dissolved ozone concentration in the dissolution water W3.
[0026] The ozone water feeding unit 11 is formed of an
automatic valve of electromagnetic type or air type, a pump,
and the like, and feeds the ozone water W4 generated by the
ozone water generation unit 6 to the separation membrane 2,
on the basis of a result of determination by the feeding
start determination means 10. The ozone water W4 fed by the
ozone water feeding unit 11 flows to the separation membrane
2 via an ozone water feeding pipe 3g and the filtered water
pipe 3a, to clean the separation membrane 2. That is, the
membrane cleaning using the ozone water W4 is reverse flow
cleaning in which the ozone water W4 flows through the
separation membrane 2 in a direction opposite to the
direction in which the treatment target water W1 is filtered.
[0027] Next, functions of the process shift determination
means 7 and the feeding start determination means 10 will be
described. As described above, the ozone water generation
process in the ozone water generation unit 6 includes the
first process of dissolving ozone gas in the dissolution
water W3 under a neutral or alkaline condition, and the
second process of dissolving ozone gas in the dissolution
water W3 under an acidic condition. The treatment time in
the first process is determined by the process shift
determination means 7, and the treatment time in the second
process is determined by the feeding start determination
means 10.
[0028] The self-decomposition speed of ozone becomes
faster as the pH becomes higher, and hydroxyl radicals
generated in the process of self-decomposition of ozone has
higher oxidizing power than ozone. Therefore, in the first
process of dissolving ozone gas in the dissolution water W3
under a neutral or alkaline condition, efficiency of
oxidation treatment on organic substances by the dissolved
ozone is enhanced, whereby decomposition of organic
substances in the dissolution water W3 can be promoted.
[0029] Preferably, the pH setting value in the first
process is in a range from pH 7 to pH 10. If the pH is lower
than 7, self-decomposition of ozone is inhibited and thus
decomposition of organic substances cannot be promoted. If
the pH is higher than 10, a large amount of an alkali to be
added to the dissolution water W3 and a large amount of an
acid to be added to the dissolution water W3 at the time of
shifting to the second process are needed, and further, a
large amount of ion components flows into the membrane
separation tank 1 when membrane cleaning is performed, and
thus influences treatment for the treatment target water W1.
Therefore, setting the pH to higher than 10 is not preferable.
[0030] On the other hand, the self-decomposition speed of
ozone is more inhibited as the pH is lowered. Therefore, in
the second process of dissolving ozone gas in the dissolution
water W3 under an acidic condition, self-decomposition of
ozone is inhibited as compared to the first process, whereby
the dissolved ozone concentration can be increased.
Preferably, the pH setting value in the second process is in
a range from pH 2 to pH 6. In pH 2, the self-decomposition
of ozone is inhibited almost perfectly. If the pH is lower
than 2, a large amount of an acid to be added to the
dissolution water W3 at the time of shifting to the second
process is needed, and further, a large amount of ion
components flows into the membrane separation tank 1 when
membrane cleaning is performed, and thus influences treatment
for the treatment target water W1. Therefore, setting the pH
to lower than 2 is not preferable. In addition, if the pH is
higher than 6, the dissolved ozone concentration decreases
through self-decomposition of ozone. Therefore, setting the
pH to higher than 6 is not preferable.
[0031] The organic substance concentration in the treated
water W2 varies depending on the MBR operation conditions
such as solid retention time (SRT) in the membrane separation
device and the dissolved oxygen concentration in the
treatment target water W1. Therefore, in the membrane
cleaning device that uses the treated water W2 as the
dissolution water W3, the amount of ozone gas needed for
decomposing organic substances in the dissolution water W3
varies depending on the MBR operation conditions. In
addition, in the case where a constant amount of ozone gas is
supplied from the ozonizer 61 to the ozone water generation
unit 6, the treatment time in the first process needed for
decomposing organic substances in the dissolution water W3
varies depending on the MBR operation conditions. Therefore,
the process shift determination means 7 estimates the
treatment time in the first process needed for decomposing
organic substances in the dissolution water W3, on the basis
of the organic substance concentration in the dissolution
water W3, to determine whether to shift to the second process,
whereby the treatment time in the first process can be
optimized without excess/deficiency.
[0032] In addition, the treatment time in the second
process needed for generating the ozone water W4 having the
predetermined dissolved ozone concentration also varies
depending on variation in the composition and the
concentration of dissolved components and the dissolved ozone
concentration in the dissolution water W3 at the time of
shifting to the second process. The predetermined dissolved
ozone concentration is a dissolved ozone concentration that
enables cleaning of contaminants adhered to the separation
membrane 2, and specifically, is set in a range from 5 mg/L
to 80 mg/L. Therefore, the feeding start determination means
determines whether to start feeding ozone water to the
separation membrane 2, on the basis of the dissolved ozone
concentration in the dissolution water W3, whereby the
treatment time in the second process can be optimized without
excess/deficiency.
[0033] Specific configurations of the process shift
determination means 7, the pH adjustment means 8, and the
feeding start determination means 10 according to embodiment
25 1 will be described with reference to FIG. 2, FIG. 3, and FIG.
4. As shown in FIG. 2, the process shift determination means
7 includes an organic substance sensor 71, a memory (second
memory) 72, and a comparison unit (second comparison unit) 73.
The organic substance sensor 71 and the comparison unit 73,
the memory 72 and the comparison unit 73, and the comparison
unit 73 and the pH adjustment means 8, are respectively
connected via a signal line 9c, a signal line 9d, and a
signal line 9a. The organic substance sensor 71 continuously
or regularly measures the organic substance concentration in
the dissolution water W3 stored in the ozone water generation
unit 6, in the ozone water generation process (in particular,
first process). The organic substance concentration can be
measured using the absorbance for ultraviolet at 254 nm
(UV254), total organic carbon (TOC), fluorescence intensity,
or the like which is an index for organic substances.
[0034] The memory 72 stores a threshold for organic
substance concentration for shifting from the first process
to the second process. The comparison unit 73 acquires a
measured value from the organic substance sensor 71 via the
signal line 9c, and acquires the threshold stored in the
memory 72 via the signal line 9d. Further, the comparison
unit 73 compares the measured value from the organic
substance sensor 71 with the threshold, and controls the pH
adjustment means 8 so that the ozone water generation unit 6
shifts from the first process to the second process when the
measured value becomes equal to or smaller than the threshold.
Specifically, when the measured value from the organic
substance sensor 71 becomes equal to or smaller than the
threshold, the comparison unit 73 transmits a process shift
signal to the pH adjustment means 8 via the signal line 9a.
[0035] The threshold for organic substance concentration
can be calculated using the following Expression (1) in which
an ozone water generation time including the first process
and the second process is calculated using, as parameters,
the organic substance concentration and a threshold for
dissolved ozone concentration for starting cleaning. The
organic substance concentration that minimizes the ozone
water generation time calculated using Expression (1) can be
used as the threshold for organic substance concentration for
shifting from the first process to the second process.
[Ozone water generation time] = f(organic substance
concentration, threshold for dissolved ozone concentration
for starting cleaning) ... (1)
[0036] As shown in FIG. 3, the pH adjustment means 8
includes a pH sensor 81, a memory (fifth memory) 82, a pH
adjustment control unit 83, and a pH adjustment unit 84. The
pH sensor 81 and the pH adjustment control unit 83, the
memory 82 and the pH adjustment control unit 83, the pH
adjustment control unit 83 and the pH adjustment unit 84, and
the pH adjustment control unit 83 and the process shift
determination means 7, are respectively connected via signal
lines 9e, 9f, 9g, 9a. The pH adjustment unit 84 and the
ozone water generation unit 6 are connected to each other via
an acid/alkali supply pipe 3f.
[0037] The pH sensor 81 continuously measures the pH of
the dissolution water W3 stored in the ozone water generation
unit 6, during the ozone water generation process. The
memory 82 stores respective pH setting values for the
dissolution water W3 for the first process and the second
process. The pH adjustment control unit 83 controls the pH
adjustment unit 84 so that the pH of the dissolution water W3
becomes the pH setting value stored in the memory 82 in the
first process or the second process. The pH adjustment unit
84 stores an acid and an alkali, and supplies the acid or the
alkali to the ozone water generation unit 6 on the basis of a
signal transmitted via the signal line 9g from the pH
adjustment control unit 83, to adjust the pH of the
dissolution water W3.
[0038] Before the first process is started, the pH
adjustment control unit 83 acquires a measured value from the
pH sensor 81 via the signal line 9e, and acquires a pH
setting value for the first process from the memory 82 via
the signal line 9f. The pH adjustment control unit 83
transmits a signal to the pH adjustment unit 84 so as to add
an acid if the measured value from the pH sensor 81 is higher
than the pH setting value, and add an alkali if the measured
value is lower than the pH setting value.
[0039] In addition, when the pH adjustment control unit 83
has received a process shift signal from the process shift
determination means 7, the pH adjustment control unit 83
acquires the pH setting value for the second process from the
memory 82, and transmits a signal to the pH adjustment unit
84 to perform control so that the pH of the dissolution water
W3 becomes the pH setting value for the second process. It
is noted that, since the process shift determination means 7
transmits a process shift signal on the basis of the organic
substance concentration in the dissolution water W3, it can
be said that the pH adjustment means 8 adjusts the pH of the
dissolution water W3 on the basis of the organic substance
concentration in the dissolution water W3 stored in the ozone
water generation unit 6.
[0040] In shifting from the first process to the second
process, the pH adjustment unit 84 adds an acid to the
dissolution water W3 in the ozone water generation unit 6.
It is noted that the acid/alkali supply pipe 3f may include a
plurality of pipes, and may be provided with one or both of a
pump and a valve as appropriate. The acid to be added to the
dissolution water W3 is, for example, an aqueous solution of
sulfuric acid, nitric acid, hydrochloric acid, or carbonic
acid, or carbon dioxide gas, and the alkali is, for example,
sodium hydroxide or sodium carbonate.
[0041] As shown in FIG. 4, the feeding start determination
means 10 includes a dissolved ozone sensor 101, a memory
(first memory) 102, and a comparison unit (first comparison
unit) 103. The dissolved ozone sensor 101 and the comparison
unit 103, the memory 102 and the comparison unit 103, and the
comparison unit 103 and the ozone water feeding unit 11, are
respectively connected via signal lines 9h, 9i, 9b.
[0042] The dissolved ozone sensor 101 measures the
dissolved ozone concentration in the dissolution water W3 in
the ozone water generation unit 6 during the ozone water
generation process. For measurement of the dissolved ozone
concentration, using ultraviolet absorbance allows continuous
measurement to be easily performed, and thus is preferable.
The memory 102 stores a threshold for dissolved ozone
concentration for starting feeding ozone water to the
separation membrane 2. Preferably, the threshold for
dissolved ozone concentration is 5 mg/L to 80 mg/L.
[0043] The comparison unit 103 compares a measured value
from the dissolved ozone sensor 101 with the threshold
acquired from the memory 102 via the signal line 9i, and
transmits a feeding start signal to the ozone water feeding
unit 11 via the signal line 9b when the measured value
becomes equal to or greater than the threshold. The ozone
water feeding unit 11 feeds the ozone water W4 generated in
the ozone water generation unit 6 to the separation membrane
2 via the ozone water feeding pipe 3g. Thus, cleaning of the
separation membrane 2 by the membrane cleaning device is
started.
[0044] As shown in FIG. 5 and FIG. 6, the ozone water
feeding pipe 3g is connected to the filtered water pipe 3a.
In an example shown in FIG. 5, the ozone water feeding pipe
3g, the filtered water pipe 3a, and the separation membrane 2
are connected via a three-way valve 12. In an example shown
in FIG. 6, the ozone water feeding pipe 3g and the filtered
water pipe 3a are respectively provided with switch valves
13a, 13b. The ozone water feeding pipe 3g may be provided
with a pump as appropriate.
[0045] It is noted that, of the functions of the process
shift determination means 7, the pH adjustment means 8, or
the feeding start determination means 10, a function executed
by software is implemented by a processing circuit 20
including a processor 21 and a memory 22 as shown in FIG. 13.
For example, the function of the comparison unit 73 of the
process shift determination means 7, the pH adjustment
control unit 83 of the pH adjustment means 8, or the
comparison unit 103 of the feeding start determination means
is implemented by the processor 21 such as a CPU. The
memory 22 includes a volatile storage device such as a random
access memory, and a nonvolatile auxiliary storage device
such as a flash memory. Instead of a flash memory, an
auxiliary storage device of a hard disk may be provided. The
processor 21 executes a program inputted from the memory 22.
In this case, the program is inputted from the auxiliary
storage device to the processor 21 via the volatile storage
device.
[0046] The procedure for starting membrane cleaning in the
membrane cleaning device according to embodiment 1 will be
described with reference to a flowchart shown in FIG. 7.
First, in step S1, the dissolution water W3 is supplied to
the ozone water generation unit 6. Specifically, the treated
water W2 stored in the treated water tank 5 is fed to the
ozone water generation unit 6 via the dissolution water pipe
3c, and is stored as the dissolution water W3.
[0047] Next, in step S2, the first process is performed.
Specifically, the pH adjustment means 8 performs adjustment
so that the pH of the dissolution water W3 stored in the
ozone water generation unit 6 becomes the pH setting value
for the first process stored in the memory 82 of the pH
adjustment means 8. In addition, ozone gas generated by the
ozonizer 61 is supplied to the ozone water generation unit 6
so that the ozone gas is dissolved in the dissolution water
W3.
[0048] Subsequently, in step S3, whether or not the
organic substance concentration in the dissolution water W3
in the ozone water generation unit 6 is equal to or smaller
than the threshold, is determined. Specifically, the value
of the organic substance concentration measured by the
organic substance sensor 71 is compared with the threshold
for organic substance concentration stored in the memory 72.
In step S3, if the measured value of the organic substance
concentration is greater than the threshold (NO), the process
returns to step S2, to continue the first process. The pH
setting value for the dissolution water W3 in the ozone water
generation unit 6 is kept at the pH setting value for the
first process.
[0049] In step S3, if the measured value of the organic
substance concentration is equal to or smaller than the
threshold (YES), the process proceeds to step S4, to perform
the second process of the ozone water generation process.
Specifically, the process shift determination means 7
transmits a process shift signal to the pH adjustment means 8
via the signal line 9a. When having received the process
shift signal, the pH adjustment means 8 performs adjustment
so that the dissolution water W3 becomes the pH setting value
for the second process stored in the memory 82. At this time,
supply of ozone gas is continued.
[0050] Next, in step S5, whether or not the dissolved
ozone concentration in the dissolution water W3 is equal to
or greater than the threshold, is determined. Specifically,
the feeding start determination means 10 compares the value
of the dissolved ozone concentration measured by the
dissolved ozone sensor 101 with the threshold for dissolved
ozone concentration stored in the memory 102. In step S5, if
the measured value of the dissolved ozone concentration is
smaller than the threshold (NO), the process returns to step
S4, to continue the second process.
[0051] In step S5, if the measured value of the dissolved
ozone concentration in the dissolution water W3 is equal to
or greater than the threshold (YES), the process proceeds to
step S6 and the ozone water feeding unit 11 starts feeding
the ozone water W4. Specifically, the feeding start
determination means 10 transmits a feeding start signal to
the ozone water feeding unit 11 via the signal line 9b. When
having received the feeding start signal, the ozone water
feeding unit 11 feeds the ozone water W4 generated in the
ozone water generation unit 6 to the separation membrane 2
via the ozone water feeding pipe 3g, to start cleaning of the
separation membrane 2. During the cleaning, supply of ozone
gas may be continued, or as long as the predetermined
dissolved ozone concentration can be maintained, supply of
ozone gas may be stopped.
[0052] As described above, according to embodiment 1, in
the membrane cleaning device in which the treated water W2
filtered through the separation membrane 2 is used as the
dissolution water W3 and ozone gas is dissolved in the
dissolution water W3 to generate the ozone water W4, the pH
of the dissolution water W3 stored in the ozone water
generation unit 6 is adjusted on the basis of the organic
substance concentration in the dissolution water W3.
Therefore, even if the organic substance concentration varies
depending on the MBR operation conditions, the treatment time
needed for decomposing organic substances can be estimated
from the measured value of the organic substance
concentration. Therefore, during the treatment time needed
for decomposing organic substances, ozone water can be
generated under the pH condition suitable for decomposition
of organic substances, and thereafter, the pH can be adjusted
to reach the pH condition suitable for increasing the
dissolved ozone concentration.
[0053] In addition, in the ozone water generation unit 6,
the first process of dissolving ozone gas in dissolution
water under a neutral or alkaline condition, and the second
process of dissolving ozone gas in the dissolution water
under an acidic condition, are performed, and whether to
shift from the first process to the second process is
determined on the basis of the organic substance
concentration in the dissolution water W3. Therefore, the
treatment time in the first process can be optimized without
excess/deficiency, and when the organic substance
concentration in the dissolution water W3 is low, the
treatment time in the first process can be shortened.
[0054] In addition, whether to start feeding ozone water
to the separation membrane 2 is determined on the basis of
the dissolved ozone concentration in the dissolution water W3.
Therefore, the treatment time in the second process can be
optimized without excess/deficiency. Thus, according to
embodiment 1, the ozone water W4 can be efficiently generated
irrespective of variation in the organic substance
concentration in the dissolution water W3 depending on the
MBR operation conditions, whereby the cost needed for
generating ozone water can be reduced.
[0055] Embodiment 2
FIG. 8 shows the entire configuration of a membrane
cleaning device according to embodiment 2 of the present
disclosure, and FIG. 9 shows the configuration of process
shift determination means of the membrane cleaning device
according to embodiment 2. The membrane cleaning device
according to embodiment 2 is different from the membrane
cleaning device according to the above embodiment 1 only in
the configuration of the process shift determination means.
The other configurations are the same and therefore the
description thereof is omitted here.
[0056] The membrane cleaning device according to
embodiment 2 includes process shift determination means 7A.
As shown in FIG. 9, the process shift determination means 7A
includes an organic substance sensor 74, an ozone gas sensor
75, a memory (third memory) 72A, and a comparison unit (third
comparison unit) 73A. The organic substance sensor 74 and
the comparison unit 73A, the ozone gas sensor 75 and the
comparison unit 73A, and the memory 72A and the comparison
unit 73A, are respectively connected via signal lines 9k, 9m,
9n.
[0057] The organic substance sensor 74 measures an initial
value of the organic substance concentration in the
dissolution water W3 to be supplied to the ozone water
generation unit 6, before start of the ozone water generation
process. The organic substance sensor 74 is favorably
provided at the dissolution water pipe 3c or the ozone water
generation unit 6, but the provided position thereof is not
particularly limited. Before start of the ozone water
generation process, the dissolution water W3 may be sampled
and the organic substance concentration thereof may be
measured. The organic substance concentration can be
measured using UV254, TOC, fluorescence intensity, or the
like which is an index for organic substances.
[0058] The ozone gas sensor 75 is provided to the ozone
gas pipe 3d and measures an ozone gas amount (hereinafter,
referred to as ozone supply amount) supplied to the ozone
water generation unit 6. The ozone supply amount is
calculated from the cumulative value of the ozone gas
concentration and the flow rate. The ozone supply amount
needed until shifting from the first process to the second
process differs depending on the initial value of the organic
substance concentration in the dissolution water W3. That is,
if the initial value of the organic substance concentration
in the dissolution water W3 is great, the ozone supply amount
needed until shifting from the first process to the second
process is also increased.
[0059] The memory 72A stores a threshold for ozone supply
amount needed until shifting from the first process to the
second process, the threshold being set so as to correspond
to the initial value of the organic substance concentration
in the dissolution water W3. The comparison unit 73A
acquires, from the memory 72A, the threshold for ozone supply
amount corresponding to the organic substance concentration
acquired from the organic substance sensor 74, and compares
the measured value of the ozone supply amount acquired from
the ozone gas sensor 75 with the threshold. When the
measured value becomes equal to or greater than the threshold,
the comparison unit 73A transmits a process shift signal to
the pH adjustment means 8 via the signal line 9a.
[0060] The organic substances in the dissolution water W3
react with ozone and thus decrease. Therefore, the organic
substance concentration in the dissolution water W3 during
the ozone water generation process can be estimated using, as
parameters, the initial value of the organic substance
concentration in the dissolution water W3 and the ozone
supply amount. The threshold for ozone supply amount can be
calculated using the following Expression (2) in which the
organic substance concentration in the dissolution water W3
is calculated using, as parameters, the initial value of the
organic substance concentration in the dissolution water W3
and the ozone supply amount. The ozone supply amount when
the organic substance concentration calculated using
Expression (2) becomes the threshold for organic substance
concentration calculated by an organic substance
concentration threshold calculation method (e.g.,
Expression(1)), is calculated, and the calculated ozone
supply amount is used as the threshold for ozone supply
amount.
[Organic substance concentration] = f(initial value
of organic substance concentration, ozone supply amount) ...
(2)
[0061] The membrane cleaning start procedure in the
membrane cleaning device according to embodiment 2 will be
described with reference to a flowchart shown in FIG. 10. It
is noted that the description of the same procedure as in the
flowchart shown in FIG. 7 in the above embodiment 1 will not
be repeated. First, in step S11, the dissolution water W3 is
supplied to the ozone water generation unit 6. Next, in step
S12, the initial value of the organic substance concentration
in the dissolution water W3 is measured by the organic
substance sensor 74. Subsequently, in step S13, the
threshold for ozone supply amount for process shifting is
determined. Specifically, the comparison unit 73A of the
process shift determination means 7A acquires, from the
memory 72A, the threshold for ozone supply amount
corresponding to the initial value of the organic substance
concentration measured by the organic substance sensor 74.
[0062] Next, in step S14, the first process is performed.
Subsequently, in step S15, whether or not the ozone supply
amount supplied to the dissolution water W3 in the ozone
water generation unit 6 is equal to or greater than the
threshold, is determined. Specifically, the comparison unit
73A of the process shift determination means 7A compares the
value of the ozone supply amount measured by the ozone gas
sensor 75 with the threshold determined in step S13. In step
S15, if the measured value of the ozone supply amount is
smaller than the threshold (NO), the process returns to step
S14, to continue the first process. In step S15, if the
measured value of the ozone supply amount is equal to or
greater than the threshold (YES), the process proceeds to
step S16, to perform the second process. The subsequent
process from step S16 is the same as the subsequent process
from step S4 in the flowchart in FIG. 7.
[0063] In the membrane cleaning device according to
embodiment 2, the threshold for ozone supply amount
corresponding to the initial value of the organic substance
concentration in the dissolution water W3 is determined, and
when the measured value of the ozone supply amount becomes
equal to or greater than the threshold, shift from the first
process to the second process is performed. Thus, the same
effects as in the above embodiment 1 are obtained.
[0064] Embodiment 3
FIG. 11 shows the entire configuration of a
membrane cleaning device according to embodiment 3 of the
present disclosure. The membrane cleaning device according
to embodiment 3 is different from the membrane cleaning
device according to the above embodiment 1 only in the
configuration of the process shift determination means. The
other configurations are the same and therefore the
description thereof is omitted here.
[0065] The membrane cleaning device according to
embodiment 3 includes process shift determination means 7B.
As shown in FIG. 11, the process shift determination means 7B
includes a dissolved ozone sensor 76, an ozone gas sensor 75,
a memory (fourth memory) 72B, and a comparison unit (fourth
comparison unit) 73B. The dissolved ozone sensor 76 and the
25 comparison unit 73B, the ozone gas sensor 75 and the
comparison unit 73B, the memory 72B and the comparison unit
73B, and the comparison unit 73B and the pH adjustment means
8, are respectively connected via signal lines 9p, 9m, 9n, 9a.
[0066] The dissolved ozone sensor 76 continuously measures
the dissolved ozone concentration in the dissolution water W3
stored in the ozone water generation unit 6, during the ozone
water generation process. It is noted that the dissolved
ozone sensor 101 (see FIG. 4) of the feeding start
determination means 10 may be shared as the dissolved ozone
sensor 76 of the process shift determination means 7B. As in
the above embodiment 2, the ozone gas sensor 75 is provided
to the ozone gas pipe 3d and measures the ozone supply amount
from the cumulative value of the ozone gas concentration and
the flow rate.
[0067] The memory 72B stores a threshold for dissolved
ozone concentration needed until shifting from the first
process to the second process, the threshold being set so as
to correspond to the ozone supply amount supplied to the
dissolution water W3. The comparison unit 73B compares the
measured value obtained by the dissolved ozone sensor 76 with
the threshold stored in the memory 72B, and when the measured
value of the dissolved ozone concentration becomes equal to
or greater than the threshold, the comparison unit 73B
transmits a process shift signal to the pH adjustment means 8
via the signal line 9a.
[0068] Ozone supplied to the dissolution water W3 is
partially dissolved in the dissolution water W3 to become
dissolved ozone, and reacts with organic substances in the
dissolution water W3 and thus is consumed. Therefore, the
organic substances in the dissolution water W3, dissolved
ozone, and supplied ozone gas are in an equilibrium condition.
For example, if the concentration of organic substances which
consume ozone decreases, the dissolved ozone concentration
increases. That is, the organic substance concentration in
the dissolution water W3 can be estimated using the dissolved
ozone concentration and the ozone supply amount as parameters.
The comparison unit 73B of the process shift determination
means 7B estimates the organic substance concentration in the
dissolution water W3 using the dissolved ozone concentration
in the dissolution water W3 and the ozone supply amount as
parameters, and determines whether to shift from the first
process to the second process, on the basis of the estimated
organic substance concentration in the dissolution water W3.
[0069] The threshold for dissolved ozone concentration can
be calculated using the following Expression (3) in which the
organic substance concentration in the dissolution water W3
is calculated using the dissolved ozone concentration and the
ozone supply amount as parameters. The dissolved ozone
concentration when the organic substance concentration
calculated using Expression (3) becomes the threshold for
organic substance concentration calculated by an organic
substance concentration threshold calculation method (e.g.,
Expression (1)), is calculated, and the calculated dissolved
ozone concentration is used as the threshold for dissolved
ozone concentration.
[Organic substance concentration] = f(dissolved
ozone concentration, ozone supply amount) ... (3)
[0070] A membrane cleaning start procedure in the membrane
cleaning device according to embodiment 3 will be described
with reference to a flowchart shown in FIG. 12. It is noted
that the description of the same procedure as in the
flowchart shown in FIG. 7 in the above embodiment 1 will not
be repeated. First, in step S21, the dissolution water W3 is
supplied to the ozone water generation unit 6. Next, in step
S22, the first process is performed, and subsequently, in
step S23, the ozone supply amount is measured by the ozone
gas sensor 75.
[0071] Next, in step S24, the threshold for dissolved
ozone concentration for process shifting is determined.
Specifically, the comparison unit 73B of the process shift
determination means 7B acquires, from the memory 72B, the
threshold for dissolved ozone concentration corresponding to
the ozone supply amount measured by the ozone gas sensor 75.
Subsequently, in step S25, whether or not the dissolved ozone
concentration in the dissolution water W3 in the ozone water
generation unit 6 is equal to or greater than the threshold,
is determined. Specifically, the comparison unit 73B of the
process shift determination means 7B compares the value of
the dissolved ozone concentration measured by the dissolved
ozone sensor 76 with the threshold determined in step S24.
[0072] In step S25, if the measured value of the dissolved
ozone concentration is smaller than the threshold (NO), the
process returns to step S22, to continue the first process.
In step S25, if the measured value of the dissolved ozone
concentration is equal to or greater than the threshold (YES),
the process proceeds to step S26, to perform the second
process. The subsequent process from step S26 is the same as
the subsequent process from step S4 in the flowchart in FIG.
[0073] In embodiment 3, the threshold for dissolved ozone
concentration corresponding to the ozone supply amount
supplied to the dissolution water W3 is determined, and when
the measured value of the dissolved ozone concentration
becomes equal to or greater than the threshold, shift from
the first process to the second process is performed. Thus,
the same effects as in the above embodiment 1 are obtained.
[0074] Although the disclosure is described above in terms
of various exemplary embodiments and implementations, it
should be understood that the various features, aspects, and
functionality described in one or more of the individual
embodiments are not limited in their applicability to the
particular embodiment with which they are described, but
instead can be applied, alone or in various combinations to
one or more of the embodiments of the disclosure. It is
therefore understood that numerous modifications which have
not been exemplified can be devised without departing from
the scope of the present disclosure. For example, at least
one of the constituent components may be modified, added, or
eliminated. At least one of the constituent components
mentioned in at least one of the preferred embodiments may be
selected and combined with the constituent components
mentioned in another preferred embodiment.

DESCRIPTION OF THE REFERENCE CHARACTERS
[0075] 1 membrane separation tank
2 separation membrane
3a filtered water pipe
3b treated water discharge pipe
3c dissolution water pipe
20 3d ozone gas pipe
3e exhaust ozone gas pipe
3f acid/alkali supply pipe
3g ozone water feeding pipe
4 filtration pump
25 5 treated water tank
4 1
6 ozone water generation unit
7, 7A, 7B process shift determination means
8 pH adjustment means
9a, 9b, 9c, 9d, 9e, 9f, 9g, 9h, 9i, 9k, 9m, 9n, 9p
5 signal line
10 feeding start determination means
11 ozone water feeding unit
12 three-way valve
13a, 13b switch valve
10 20 processing circuit
21 processor
61 ozonizer
62 exhaust ozone gas decomposition portion
71, 74 organic substance sensor
15 22, 72, 72A, 72B, 82, 102 memory
73, 73A, 73B, 103 comparison unit
75 ozone gas sensor
76, 101 dissolved ozone sensor
81 pH sensor
20 83 pH adjustment control unit
84 pH adjustment unit

We Claim :
[1] A membrane cleaning device for cleaning, with ozone
water, a separation membrane for filtering treatment target
water, the membrane cleaning device comprising:
an ozone water generation unit which stores treated
water filtered through the separation membrane as dissolution
water, and dissolves ozone gas in the dissolution water, to
generate ozone water;
ozone gas supply means for supplying ozone gas to
the ozone water generation unit; and
pH adjustment means for adjusting pH of the
dissolution water stored in the ozone water generation unit,
on the basis of an organic substance concentration in the
dissolution water.
[2] The membrane cleaning device according to claim 1,
further comprising:
feeding start determination means for determining
whether to start feeding the ozone water from the ozone water
generation unit to the separation membrane, on the basis of a
dissolved ozone concentration in the dissolution water; and
an ozone water feeding unit for feeding the ozone
water generated in the ozone water generation unit to the
separation membrane on the basis of a result of determination
by the feeding start determination means.
[3] The membrane cleaning device according to claim 2,
wherein
the feeding start determination means includes
a dissolved ozone sensor to measure the
dissolved ozone concentration in the dissolution water in the
ozone water generation unit,
a first memory to store a threshold for the
dissolved ozone concentration for starting feeding the ozone
water, and a first comparison unit to compare a measured
value by the dissolved ozone sensor with the threshold stored
in the first memory, and to cause the ozone water feeding
unit to feed the ozone water when the measured value becomes
equal to or greater than the threshold.
[4] The membrane cleaning device according to any one
of claims 1 to 3, wherein
the ozone water generation unit performs a first
process of dissolving ozone gas in the dissolution water
under a neutral or alkaline condition, and a second process
of dissolving ozone gas in the dissolution water under an
acidic condition after the first process.
[5] The membrane cleaning device according to claim 4,
further comprising process shift determination means for
determining whether to shift from the first process to the
second process, on the basis of the organic substance
concentration in the dissolution water.
[6] The membrane cleaning device according to claim 5,
Wherein the process shift determination means includes
an organic substance sensor to measure the
organic substance concentration in the dissolution water in
the ozone water generation unit in the first process,
a second memory to store a threshold for the
organic substance concentration for shifting from the first
process to the second process, and
a second comparison unit to compare a measured
value by the organic substance sensor with the threshold
stored in the second memory, and to control the pH adjustment
means so as to shift from the first process to the second
process when the measured value becomes equal to or smaller
than the threshold.
[7] The membrane cleaning device according to claim 5,
wherein
the process shift determination means includes
an organic substance sensor to measure an
initial value of the organic substance concentration in the
dissolution water in the ozone water generation unit,
an ozone gas sensor to measure an ozone gas
amount supplied to the ozone water generation unit,
a third memory to store a threshold for an
ozone gas amount needed until shifting from the first process
to the second process, the threshold being set so as to
correspond to the initial value of the organic substance
concentration in the dissolution water, and
a third comparison unit to acquire, from the
third memory, the threshold corresponding to the initial
value of the organic substance concentration measured by the
organic substance sensor, to compare a measured value by the
ozone gas sensor with the threshold, and to control the pH
adjustment means so as to shift from the first process to the
second process when the measured value becomes equal to or
greater than the threshold.
[8] The membrane cleaning device according to claim 5,
Wherein the process shift determination means includes
a dissolved ozone sensor to measure the
dissolved ozone concentration in the dissolution water in the
ozone water generation unit in the first process,
an ozone gas sensor to measure an ozone gas
amount supplied to the ozone water generation unit,
a fourth memory to store a threshold for the
dissolved ozone concentration for shifting from the first
process to the second process, the threshold being set so as
to correspond to the ozone gas amount supplied to the ozone
water generation unit, and
a fourth comparison unit to acquire, from the
fourth memory, the threshold corresponding to the ozone gas
amount measured by the ozone gas sensor, to compare a
measured value by the dissolved ozone sensor with the
threshold, and to control the pH adjustment means so as to
shift from the first process to the second process when the
measured value becomes equal to or greater than the threshold,
and the fourth comparison unit estimates the organic substance concentration in the dissolution water, using, as
parameters, the dissolved ozone concentration in the dissolution water and the ozone gas amount supplied to the
ozone water generation unit, and determines whether to shift from the first process to the second process, on the basis of
the estimated organic substance concentration in the
dissolution water.
[9] The membrane cleaning device according to any one of claims 4 to 8, wherein
the pH adjustment means includes
a pH sensor to measure pH of the dissolution
water stored in the ozone water generation unit,
a pH adjustment unit to supply an acid or an
alkali to the ozone water generation unit, to adjust pH of
the dissolution water,
a fifth memory to store respective pH setting
values of the dissolution water for the first process and the
second process, and
a pH adjustment control unit to control the pH
adjustment unit so that pH of the dissolution water becomes
the corresponding pH setting value stored in the fifth memory
in each of the first process and the second process.
[10] The membrane cleaning device according to any one
of claims 1 to 9, wherein
the separation membrane is a separation membrane
that makes separation into activated sludge and the treated
water.
[11] A membrane cleaning method for cleaning, with ozone
water, a separation membrane for filtering treatment target
water, the membrane cleaning method comprising:
an ozone water generation process of using treated
water filtered through the separation membrane as dissolution water and dissolving generate ozone water, the ozone process of dissolving under a neutral or of dissolving ozone gas acidic condition after whether to shift from second process is determined on substance concentration to start feeding the is determined on the in the dissolution water