FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
AERATION AMOUNT CONTROL SYSTEM AND AERATION AMOUNT CONTROL
METHOD;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
TECHNICAL FIELD
[0001] The present invention relates to an aeration amount
control system and an aeration amount control method using a
5 separation membrane.
BACKGROUND ART
[0002] As a method for treating drained water containing
organic substances (hereinafter, referred to as “treatment
10 target water”), a membrane bioreactor (MBR) is used in which
organic substances in treatment target water are decomposed
using microorganisms and the treatment target water is
separated into solid and liquid by a separation membrane. In
filtering using the separation membrane, as the separation
15 membrane continues to be used, contaminants adhere to the
surface of the separation membrane and into the pores thereof
and thus clogging (fouling) may occur, whereby filtering
performance gradually deteriorates.
[0003] In the membrane bioreactor, an aeration device is
20 provided under the separation membrane in order to suppress
reduction in filtering performance due to fouling of the
separation membrane. The aeration device provided under the
separation membrane performs aeration with air or the like
toward the separation membrane, to peel the adhering
25 materials on the separation membrane surface by bubbles and
3
ascending flow of treatment target water. The energy cost
needed for aeration by the aeration device is estimated to
reach approximately half the whole operating cost of the
aeration amount control system. Accordingly, technology for
5 reducing the amount of aeration by the aeration device is
required.
[0004] Patent Document 1 proposes, as a membrane
separation device operation method, a method in which the
transmembrane pressure difference of the separation membrane
10 is measured and the aeration amount is controlled so that the
transmembrane pressure difference is kept at a predetermined
increase speed set in advance. Specifically, in the membrane
separation device operation method described in Patent
Document 1, a target value for the aeration amount is
15 increased at a constant rate on the basis of a difference
between a reference value and a measured value for the
transmembrane pressure difference.
CITATION LIST
20 PATENT DOCUMENT
[0005] Patent Document 1: Japanese Laid-Open Patent
Publication No. 2013-202472
SUMMARY OF THE INVENTION
25 PROBLEMS TO BE SOLVED BY THE INVENTION
4
[0006] However, in the membrane separation device
operation method described in Patent Document 1, while the
target value for the aeration amount is increased at a
predetermined constant rate, there is a possibility that the
5 aeration amount exceeds an aeration amount needed for
suppressing fouling. In the case where the increased target
value exceeds the aeration amount needed for suppressing
fouling, there is room for reduction in the energy cost
needed for aeration by the aeration device.
10 [0007] The present invention has been made to solve the
above problem, and an object of the present invention is to
obtain an aeration amount control system and an aeration
amount control method that enable reduction in operating cost
for the aeration amount control system.
15
SOLUTION TO THE PROBLEMS
[0008] An aeration amount control system according to the
present invention is an aeration amount control system for
performing aeration for a separation membrane in a membrane
20 separation tank storing treatment target water on the basis
of a target aeration amount, the aeration amount control
system including: a control device for determining a first
target aeration amount as the target aeration amount, and
after having determined the first target aeration amount,
25 determining a second target aeration amount as the target
5
aeration amount; an aeration device for performing the
aeration by supplying gas on the basis of the target aeration
amount determined by the control device; and a measurement
device for measuring a change amount of a transmembrane
5 pressure difference of the separation membrane with respect
to the gas supplied by the aeration device, wherein, if a
first change amount of the transmembrane pressure difference
of the separation membrane during the aeration performed on
the basis of the first target aeration amount by the aeration
10 device, calculated by the measurement device, is greater than
a second change amount of the transmembrane pressure
difference of the separation membrane during the aeration
performed on the basis of the second target aeration amount
by the aeration device, calculated by the measurement device,
15 the control device determines a value smaller than the second
target aeration amount, as a third target aeration amount.
[0009] An aeration amount control method according to the
present invention is an aeration amount control system for
performing aeration for a separation membrane in a membrane
20 separation tank storing treatment target water on the basis
of a target aeration amount, the aeration amount control
method including: an aeration amount determination step of
determining a first target aeration amount as the target
aeration amount, and after having determined the first target
25 aeration amount, determining a second target aeration amount
6
as the target aeration amount; an aeration step of performing
the aeration by supplying gas on the basis of the target
aeration amount determined in the aeration amount
determination step; and a change amount calculation step of
5 calculating a change amount of a transmembrane pressure
difference of the separation membrane with respect to the gas
supplied in the aeration step, wherein, if a first change
amount of the transmembrane pressure difference of the
separation membrane during the aeration performed on the
10 basis of the first target aeration amount, calculated by a
measurement device, is greater than a second change amount of
the transmembrane pressure difference of the separation
membrane during the aeration performed on the basis of the
second target aeration amount, calculated by the measurement
15 device, a value smaller than the second target aeration
amount is determined as a third target aeration amount.
EFFECT OF THE INVENTION
[0010] The aeration amount control system according to the
20 present invention enables reduction in energy cost needed for
aeration through increase/decrease of the target value for
the aeration amount, and thus can reduce the whole operating
cost of the aeration amount control system.
[0011] The aeration amount control method according to the
25 present invention enables reduction in energy cost needed for
7
aeration through increase/decrease of the target value for
the aeration amount, and thus can reduce the whole operating
cost of the aeration amount control system.
5 BRIEF DESCRIPTION OF THE DRAWINGS
[0012] [FIG. 1] FIG. 1 is a configuration diagram of an
aeration amount control system according to embodiment 1 of
the present invention.
[FIG. 2] FIG. 2 shows an example of the
10 configurations of a change amount calculation unit and a
control device of the aeration amount control system
according to embodiment 1 of the present invention.
[FIG. 3] FIG. 3 is a control flowchart in the
aeration amount control system according to embodiment 1 of
15 the present invention.
[FIG. 4] FIG. 4 is a graph illustrating the
relationship between a transmembrane pressure difference and
an aeration amount in the aeration amount control system
according to embodiment 1 of the present invention.
20 [FIG. 5] FIG. 5 is a control flowchart in the
aeration amount control system according to embodiment 1 of
the present invention.
[FIG. 6] FIG. 6 is a configuration diagram of an
aeration amount control system according to embodiment 2 of
25 the present invention.
8
[FIG. 7] FIG. 7 is a control flowchart in the
aeration amount control system according to embodiment 2 of
the present invention.
[FIG. 8] FIG. 8 is a configuration diagram of an
5 aeration amount control system according to embodiment 3 of
the present invention.
DESCRIPTION OF EMBODIMENTS
[0013] Hereinafter, embodiments of an aeration amount
10 control system and an aeration amount control method
according to the present disclosure will be described in
detail with reference to the accompanying drawings. It is
noted that the embodiments shown below are merely examples
and the present invention is not limited to these embodiments.
15 [0014] Embodiment 1
FIG. 1 is a configuration diagram of an aeration
amount control system 100 according to embodiment 1. As
shown in FIG. 1, the aeration amount control system 100
includes a membrane separation tank 2 into which treatment
20 target water 1 flows, a separation membrane 3 which is
provided so as to be immersed in the treatment target water 1
in the membrane separation tank 2 and filters the treatment
target water 1 in the membrane separation tank 2, a
filtration pump 4 for sucking treated water filtered by the
25 separation membrane 3, an aeration device 5 for performing
9
aeration for the treatment target water 1 toward the
separation membrane 3, a measurement device 6 for measuring a
change amount of the transmembrane pressure difference of the
separation membrane 3, and a control device 7 for controlling
5 the aeration amount of the aeration device 5.
[0015] The membrane separation tank 2 is configured such
that the treatment target water 1 flows into the membrane
separation tank 2, and a filtered water pipe (not shown) for
draining treated water via the separation membrane 3 is
10 connected to the membrane separation tank 2. The membrane
separation tank 2 is formed from a material that can receive
the treatment target water 1 and store the treatment target
water 1, and is formed from, for example, concrete, stainless,
or resin.
15 [0016] The separation membrane 3 separates the treatment
target water 1 into solid and liquid. The separation into
solid and liquid means that the treatment target water is
separated into contaminants and treated water. The
separation membrane 3 is provided so as to be immersed in the
20 treatment target water 1 in the membrane separation tank 2,
and is connected to the filtration pump 4 via the filtered
water pipe. The filtration pump 4 sucks the treatment target
water 1 in the membrane separation tank 2. The aeration
amount control system 100 removes contaminants in the
25 treatment target water by the separation membrane 3, to
10
obtain treated water.
[0017] The separation membrane 3 is formed from a material
such as a hollow fiber membrane or a flat membrane that can
separate solid and liquid from each other, and is formed from,
5 for example, a reverse osmosis (RO) membrane, a
nanofiltration (NF) membrane, an ultrafiltration (UF)
membrane, or a microfiltration (MF) membrane.
[0018] The aeration device 5 is provided under the
separation membrane 3, and includes an aeration pipe 51
10 having a plurality of aeration pores for performing aeration
for the treatment target water 1 toward the separation
membrane 3, and an air supply unit 52 for supplying gas to
the aeration pipe 51.
[0019] The aeration device 5 performs aeration with gas
15 such as air from the aeration pipe 51 provided under the
separation membrane 3, to peel adhering materials on the
surface of the separation membrane 3 by bubbles and ascending
flow of the treatment target water 1 caused by the bubbles,
thereby suppressing fouling of the separation membrane 3.
20 The aeration amount per membrane area of the separation
membrane 3 is controlled to be 0.01 to 10 (m3/hr/m2).
[0020] The air supply unit 52 is connected to the control
device 7, and supplies gas to the aeration pipe 51 on the
basis of output from the control device 7.
25 [0021] As the separation membrane 3 continues separation
11
into solid and liquid, it becomes impossible to completely
remove the contaminants adhered and deposited on the
separation membrane 3 through aeration by the aeration device
5. In order to remove the contaminants adhered and deposited
5 on the separation membrane 3 which cannot be completely
removed through aeration by the aeration device 5, reverse
washing by ozone water, sodium hypochlorite, or the like is
performed toward the separation membrane 3. The contaminants
adhered and deposited on the surface of the separation
10 membrane 3 and in the pores thereof are discharged through
the reverse washing. In addition, microorganisms adhered and
deposited on the surface of the separation membrane 3 and in
the pores thereof are sterilized through the reverse washing.
The separation membrane 3 is washed when the transmembrane
15 pressure difference reaches a predetermined value, e.g., 25
kPa.
[0022] The measurement device 6 measures a change amount
of the transmembrane pressure difference of the separation
membrane 3. The measurement device 6 is provided to the
20 filtered water pipe between the separation membrane 3 and the
filtration pump 4, and includes a pressure measurement unit
61 for measuring the transmembrane pressure difference of the
separation membrane 3, and a change amount calculation unit
62 for calculating the change amount of the transmembrane
25 pressure difference per unit time on the basis of the
12
transmembrane pressure difference measured by the pressure
measurement unit 61. The transmembrane pressure difference
is a pressure difference between the primary side, i.e., the
unpassed water side and the secondary side, i.e., the passed
5 water side of the separation membrane 3.
[0023] The measurement device 6 can recognize the degree
of fouling in the separation membrane 3 on the basis of the
transmembrane pressure difference value from the pressure
measurement unit 61. As the membrane filtration is continued,
10 the separation membrane 3 is gradually clogged and the
transmembrane pressure difference increases. The pressure
measurement unit 61 is an instrument capable of measuring the
transmembrane pressure difference, and may be a digital type
or an analog type. Further, the measurement device 6 is
15 provided with any storage medium such as a flexible disc, a
CD-ROM, or a memory card that can store the transmembrane
pressure difference measured by the pressure measurement unit
61.
[0024] The change amount calculation unit 62 calculates
20 the change amount of the transmembrane pressure difference
per unit time on the basis of the transmembrane pressure
difference measured by the pressure measurement unit 61, and
outputs the calculated change amount of the transmembrane
pressure difference per unit time to the control device 7.
25 In embodiment 1, the change amount of the transmembrane
13
pressure difference per unit time is calculated as a
transmembrane pressure difference increase speed. The
transmembrane pressure difference increase speed is a speed
at which the transmembrane pressure difference increases per
5 unit time. The change amount calculation unit 62 can be
implemented through software control by a CPU 1000a executing
a program stored in a memory 1001a as shown in FIG. 2(a), for
example. The pressure measurement unit 61 may be an
instrument that measures only the pressure in the filtered
10 water pipe, and the transmembrane pressure difference may be
calculated by the change amount calculation unit 62.
[0025] The control device 7 controls the aeration amount
of the aeration device 5. In addition, the control device 7
controls the aeration amount of the aeration device 5 on the
15 basis of the measurement value from the measurement device 6.
The control device 7 can be implemented through software
control by a CPU 1000b executing a program stored in a memory
1001b as shown in FIG. 2(b), for example.
[0026] The control device 7 includes a recording unit 71,
20 a change amount comparing unit 72, an aeration amount
calculation unit 73, and an aeration amount control unit 74.
[0027] The recording unit 71 is connected to the change
amount calculation unit 62 and the aeration amount control
unit 74. The recording unit 71 records, as aeration amount
25 information, the change amount of the transmembrane pressure
14
difference per unit time calculated by the change amount
calculation unit 62, and the aeration amount subjected to
aeration control by the aeration amount control unit 74 when
the change amount is calculated, in association with each
5 other.
[0028] The change amount comparing unit 72 compares a
first change amount which is the change amount of the
transmembrane pressure difference per unit time recorded in
the recording unit 71, and a second change amount which is
10 the change amount of the transmembrane pressure difference
per unit time calculated by the change amount calculation
unit 62 after calculation of the first change amount. The
change amount comparing unit 72 calculates an aeration amount
calculation command and outputs the calculated aeration
15 amount calculation command to the aeration amount calculation
unit 73. The aeration amount calculation command is
information which includes a result of comparison of the
change amounts by the change amount comparing unit 72 and
which is used for the aeration amount calculation unit 73 to
20 calculate the aeration amount.
[0029] The aeration amount calculation unit 73 calculates
a target aeration amount for the aeration device 5 on the
basis of the received aeration amount calculation command,
and outputs the target aeration amount to the aeration amount
25 control unit 74. As a result of comparison by the change
15
amount comparing unit 72, if the first change amount is
greater than the second change amount, the aeration amount
calculation unit 73 calculates, as the target aeration amount,
an aeration amount decreased by a predetermined amount or a
5 predetermined rate from the aeration amount recorded in
association with the second change amount in the recording
unit 71. It is desirable that the decrease amount of the
aeration amount is in a range of 0.01 to 5 (m3/hr/m2), and it
is desirable that the decrease rate of the aeration amount is
10 in a range of 10 to 50%. As a result of comparison by the
change amount comparing unit 72, if the first change amount
is smaller than the second change amount, the aeration amount
calculation unit 73 calculates, as the target aeration amount,
an aeration amount increased by a predetermined amount or a
15 predetermined rate from the aeration amount recorded in
association with the second change amount in the recording
unit 71. It is desirable that the increase amount or the
increase rate for the aeration amount is in the same range as
the decrease amount or the decrease rate for the aeration
20 amount. In addition, when a certain period has elapsed since
calculation of the target aeration amount and a timing for
calculating the next target aeration amount has come, the
aeration amount calculation unit 73 outputs, to the change
amount calculation unit 62, a change amount calculation
25 command for causing the change amount calculation unit 62 to
16
calculate the change amount of the transmembrane pressure
difference per unit time during the certain period from
calculation of the target aeration amount.
[0030] The aeration amount control unit 74 controls the
5 amount of gas to be supplied by the air supply unit 52, on
the basis of the aeration amount calculated by the aeration
amount calculation unit 73, to cause the aeration device 5 to
execute aeration. Examples of the control for the air supply
unit 52 by the aeration amount control unit 74 include
10 inverter control. In addition, the aeration amount control
unit 74 transmits the aeration amount at the time when the
change amount is calculated by the change amount calculation
unit 62, to the recording unit 71. The function of
transmitting the aeration amount to the recording unit 71 may
15 be imparted to the aeration amount calculation unit 73.
[0031] FIG. 3 is a control flowchart in the aeration
amount control system 100. The aeration amount control
system 100 method in the aeration amount control system 100
will be described with reference to the control flowchart
20 shown in FIG. 3.
[0032] While the aeration amount control system 100
executes the aeration amount control, the filtration pump 4
continuously sucks the treatment target water 1 in the
membrane separation tank 2. When the filtration process by
25 the aeration amount control system 100 is started, in
17
initialization step S1a, the control device 7 initializes n
to 1. Next, in aeration step S2a, the aeration amount
calculation unit 73 executes aeration at an aeration amount
Q1 set in advance as a first target aeration amount. As the
5 first target aeration amount Q1, an optional value is
employed from an appropriate range of the aeration amount
that enables suppression of fouling of the separation
membrane 3. For example, the first target aeration amount Q1
is set to the maximum flow amount of the aeration device 5.
10 [0033] In change amount calculation step S3a, when time T1
has elapsed since the start of aeration step S2a, the
aeration amount calculation unit 73 outputs a change amount
calculation command to the measurement device 6. The
measurement device 6 receives the change amount calculation
15 command and calculates a first transmembrane pressure
difference increase speed R1. The first transmembrane
pressure difference increase speed R1 is calculated on the
basis of the following Expression (1) using a transmembrane
pressure difference P1 measured at the start of aeration step
20 S2a by the pressure measurement unit 61, and a transmembrane
pressure difference P2 measured when the measurement device 6
receives the change amount calculation command.
R1 = (P2 - P1)/T1 ... (1)
The time T1 is a time needed for calculating the
25 transmembrane pressure difference increase speed, and may be
18
any period of one hour to one day or further one week. The
time T1 may not necessarily be a constant period, but may be
changed every time the change amount calculation step is
executed.
5 [0034] In recording step S4a, the recording unit 71
records the first transmembrane pressure difference increase
speed R1 and the first target aeration amount Q1 in
association with each other.
[0035] In change amount comparing step S5a, the change
10 amount comparing unit 72 compares a transmembrane pressure
difference increase speed Rn-1 which is the change amount of
the transmembrane pressure difference before decrease of the
aeration amount, calculated for the n = (n - 1)th time in
change amount calculation step S3a and recorded in the
15 recording unit 71, and a transmembrane pressure difference
increase speed Rn which is the change amount of the
transmembrane pressure difference after decrease of the
aeration amount, calculated for the nth time in change amount
calculation step S3a. That is, in the case of n = 2, in
20 change amount comparing step S5a, the change amount comparing
unit 72 compares the first transmembrane pressure difference
increase speed R1 and a second transmembrane pressure
difference increase speed R2. The change amount comparing
unit 72 calculates an aeration amount calculation command and
25 outputs the calculated aeration amount calculation command to
19
the aeration amount calculation unit 73. If the
transmembrane pressure difference increase speed Rn-1 is
greater than the transmembrane pressure difference increase
speed Rn, the process proceeds to aeration amount
5 determination step S6a, and if the transmembrane pressure
difference increase speed Rn-1 is smaller than the
transmembrane pressure difference increase speed Rn, the
process proceeds to aeration amount decrease step S8a.
In the case of n = 1, the transmembrane pressure
10 difference increase speed Rn-1 which is the change amount of
the transmembrane pressure difference before decrease of the
aeration amount, calculated for the n = (n - 1)th time, does
not exist. Therefore, the process proceeds to aeration
amount decrease step S8a.
15 [0036] In aeration amount determination step S6a, the
aeration amount calculation unit 73 calculates, as a target
aeration amount, an aeration amount increased by a
predetermined amount or a predetermined rate from the
aeration amount recorded in association with the
20 transmembrane pressure difference increase speed Rn in the
recording unit 71. That is, in the case of n = 2, in
aeration amount determination step S6a, the aeration amount
calculation unit 73 calculates a third target aeration amount
Q3 increased by a predetermined amount or a predetermined
25 rate from a second target aeration amount Q2.
20
[0037] In aeration step S7a, the aeration amount control
unit 74 executes aeration at the target aeration amount Qn.
[0038] In aeration amount decrease step S8a, the aeration
amount calculation unit 73 calculates a second target
5 aeration amount Q2 which is an aeration amount decreased by a
predetermined amount or a predetermined rate from the first
target aeration amount Q1. That is, in the case of n = 2,
the aeration amount calculation unit 73 calculates a third
target aeration amount Q3 decreased by a predetermined amount
10 or a predetermined rate from the second target aeration
amount Q2.
[0039] In addition step S9a, the control device 7
increments n by 1 to set n = n + 1, and then returns to
aeration step S2a.
15 [0040] Next, the relationship between the change amount
transmembrane pressure difference of the transmembrane
pressure difference per unit time and the aeration amount
will be described.
[0041] The present inventors have found out through
20 earnest study that there is a relationship as shown in FIG. 4
between the change amount of the transmembrane pressure
difference per unit time and the aeration amount.
[0042] FIG. 4 illustrates the relationship between the
transmembrane pressure difference and the aeration amount.
25 The vertical axis indicates the transmembrane pressure
21
difference (kPa), and the horizontal axis indicates the
filtration time (T). The lines in FIG. 4 correspond to
different aeration amounts, and Q2, Q3, and Q4 are the
aeration amounts sequentially decreased by a certain amount
5 or a certain rate from Q1. The magnitude order of the
aeration amounts is Q1 > Q2 > Q3 > Q4. As shown in FIG. 4,
the transmembrane pressure difference increase speed does not
greatly differ among Q1, Q2, and Q3, and sharply increases in
Q4. That is, as shown in FIG. 4, it has been found that,
10 when the aeration amount becomes small, the change amount of
the transmembrane pressure difference per unit time
(transmembrane pressure difference increase speed) sharply
increases. Hereinafter, the point at which the change amount
of the transmembrane pressure difference per unit time
15 (transmembrane pressure difference increase speed) sharply
increases is referred to as change point.
[0043] From FIG. 4, it has been found that executing
aeration at an aeration amount greater than the change point
merely achieves slight reduction of the transmembrane
20 pressure difference increase speed. That is, if aeration at
the change point is executed, the transmembrane pressure
difference increase speed is slightly increased as compared
to the case of executing aeration at an aeration amount
greater than the change point, but since the energy cost
25 needed for aeration is much greater than the operating cost
22
for washing or the like, the whole operating cost of the
aeration amount control system is reduced.
[0044] According to the control flowchart shown in FIG. 3,
in the aeration amount control system 100, if the first
5 transmembrane pressure difference increase speed R1 is
greater than the second transmembrane pressure difference
increase speed R2, a value smaller than the second target
aeration amount Q2 is calculated as the third target aeration
amount Q3, and if the first transmembrane pressure difference
10 increase speed R1 is smaller than the second transmembrane
pressure difference increase speed R2, a value greater than
the second target aeration amount Q2 is calculated as the
third target aeration amount Q3. That is, the aeration
amount control system 100 can execute aeration at the change
15 point through the control flowchart shown in FIG. 3. Thus,
the aeration amount control system 100 enables reduction in
the whole operating cost of the aeration amount control
system.
[0045] In the control method of the aeration amount
20 control system 100 shown in FIG. 3, in target aeration step
S7a, aeration is continued at the change point corresponding
to the target aeration amount calculated in aeration amount
determination step S6a. Operation from initialization step
S1a to target aeration step S7a shown in FIG. 3 is defined as
25 one change point detection operation. In the control method
23
of the aeration amount control system 100, it is preferable
to repeatedly execute this change point detection operation.
In the aeration amount control system 100, in the case of
executing the change point detection operation for the second
5 time, the target aeration amount Q1 set in advance may be
changed to the target aeration amount calculated in the
aeration amount determination step S6a, after the target
aeration step S7a, and the predetermined amount or the
predetermined rate by which the aeration amount is decreased
10 in aeration amount decrease step S8a may be made smaller than
that in the change point detection operation for the first
time, thus returning to initialization step S1a. In the
change point detection operation for the second time by the
aeration amount control system 100, since the predetermined
15 amount or the predetermined rate by which the aeration amount
is decreased in aeration amount decrease step S8a is made
smaller than that in the change point detection operation for
the first time, the change point can be detected more finely.
[0046] FIG. 5 is a control flowchart in the aeration
20 amount control system 100. A modification of the aeration
amount control method in the aeration amount control system
100 will be described with reference to the control flowchart
shown in FIG. 5. In the control flowchart shown in FIG. 3,
in change amount calculation step S3a, the transmembrane
25 pressure difference increase speed is calculated, whereas, in
24
the control flowchart shown in FIG. 5, in change amount
calculation step S3b, a transmembrane pressure difference
increase amount is calculated instead of the transmembrane
pressure difference increase speed.
5 [0047] When the filtration process by the aeration amount
control system 100 is started, in initialization step S1b,
the control device 7 initializes n to 1. Next, in aeration
step S2b, the aeration amount calculation unit 73 executes
aeration at an aeration amount Q1 set in advance as the first
10 target aeration amount. As the first target aeration amount
Q1, an optional value is employed from an appropriate range
of the aeration amount that enables suppression of fouling of
the separation membrane 3. For example, the aeration amount
Q1 is set to the maximum flow amount of the aeration device 5.
15 [0048] In change amount calculation step S3b, when time T
has elapsed since the start of aeration step S2b, the
aeration amount calculation unit 73 outputs a change amount
calculation command to the measurement device 6. The
measurement device 6 receives the change amount calculation
20 command and calculates a first transmembrane pressure
difference increase amount ΔP1. The first transmembrane
pressure difference increase amount ΔP1 is calculated on the
basis of the following Expression (2) using a transmembrane
pressure difference P1 measured at the start of aeration step
25 S2b by the pressure measurement unit 61, and a transmembrane
25
pressure difference P2 measured when the measurement device 6
receives the change amount calculation command.
ΔP1 = P2 - P1 ... (2)
[0049] In recording step S4b, the recording unit 71
5 records the first transmembrane pressure difference increase
amount ΔP1 and the first target aeration amount Q1 in
association with each other.
[0050] In change amount comparing step S5b, the change
amount comparing unit 72 compares a transmembrane pressure
10 difference increase amount ΔPn-1 which is the change amount of
the transmembrane pressure difference before decrease of the
aeration amount, calculated for the n = (n - 1)th time in
change amount calculation step S3b and recorded in the
recording unit 71, and a transmembrane pressure difference
15 increase amount ΔPn which is the change amount of the
transmembrane pressure difference after decrease of the
aeration amount, calculated for the nth time in change amount
calculation step S3b. That is, in change amount comparing
step S5b, in the case of n = 2, the change amount comparing
20 unit 72 compares the first transmembrane pressure difference
increase amount ΔP1 and a second transmembrane pressure
difference increase amount ΔP2. The change amount comparing
unit 72 calculates an aeration amount calculation command and
outputs the calculated aeration amount calculation command to
25 the aeration amount calculation unit 73. If the
26
transmembrane pressure difference increase amount ΔPn-1 is
greater than the transmembrane pressure difference increase
amount ΔPn, the process proceeds to aeration amount
determination step S6b, and if the transmembrane pressure
5 difference increase amount ΔPn-1 is smaller than the
transmembrane pressure difference increase amount ΔPn, the
process proceeds to aeration amount decrease step S8b.
In the case of n = 1, the transmembrane pressure
difference increase amount ΔPn-1 which is the change amount of
10 the transmembrane pressure difference before decrease of the
aeration amount, calculated for the n = (n - 1)th time, does
not exist. Therefore, the process proceeds to aeration
amount decrease step S8b.
[0051] In aeration amount determination step S6b, the
15 aeration amount calculation unit 73 calculates, as the target
aeration amount Qn, an aeration amount increased by a
predetermined amount or a predetermined rate from the
aeration amount recorded in association with the
transmembrane pressure difference increase amount ΔPn in the
20 recording unit 71. That is, in the case of n = 2, the
aeration amount calculation unit 73 calculates a third target
aeration amount Q3 increased by a predetermined amount or a
predetermined rate from the second target aeration amount Q2.
[0052] In target aeration step S7b, the aeration amount
25 control unit 74 executes aeration at the target aeration
27
amount Qn.
[0053] In aeration amount decrease step S8b, the aeration
amount calculation unit 73 calculates a second target
aeration amount Q2 which is an aeration amount decreased by a
5 predetermined amount or a predetermined rate from the first
target aeration amount Q1. That is, in the case of n = 2,
the aeration amount calculation unit 73 calculates a third
target aeration amount Q3 decreased by a predetermined amount
or a predetermined rate from the second target aeration
10 amount Q2.
[0054] In addition step S9b, the control device 7
increments n by 1 to set n = n + 1, and then returns to
aeration step S2b.
[0055] The aeration amount control system according to
15 embodiment 1 is an aeration amount control system for
performing aeration for a separation membrane in a membrane
separation tank storing treatment target water on the basis
of a target aeration amount, the aeration amount control
system including: a control device for determining a first
20 target aeration amount as the target aeration amount, and
after having determined the first target aeration amount,
determining a second target aeration amount as the target
aeration amount; an aeration device for performing aeration
by supplying gas on the basis of the target aeration amount
25 determined by the control device; and a measurement device
28
for measuring a change amount of a transmembrane pressure
difference of the separation membrane with respect to the gas
supplied by the aeration device, wherein, if a first change
amount of the transmembrane pressure difference of the
5 separation membrane during the aeration performed on the
basis of the first target aeration amount by the aeration
device, calculated by the measurement device, is greater than
a second change amount of the transmembrane pressure
difference of the separation membrane during aeration
10 performed on the basis of the second target aeration amount
by the aeration device, calculated by the measurement device,
the control device determines a value smaller than the second
target aeration amount, as a third target aeration amount.
[0056] With the above configuration, the aeration amount
15 control system 100 according to embodiment 1 enables
reduction in the energy cost needed for aeration through
increase/decrease of the target value for the aeration amount,
and thus can reduce the whole operating cost of the aeration
amount control system.
20 [0057] The aeration amount control method according to
embodiment 1 is performed in an aeration amount control
system for performing aeration for a separation membrane in a
membrane separation tank storing treatment target water on
the basis of a target aeration amount, the aeration amount
25 control method including: an aeration amount determination
29
step of determining a first target aeration amount as the
target aeration amount, and after having determined the first
target aeration amount, determining a second target aeration
amount as the target aeration amount; an aeration step of
5 performing the aeration by supplying gas on the basis of the
target aeration amount determined in the aeration amount
determination step; and a change amount calculation step of
calculating a change amount of a transmembrane pressure
difference of the separation membrane with respect to the gas
10 supplied in the aeration step, wherein, if a first change
amount of the transmembrane pressure difference of the
separation membrane during the aeration performed on the
basis of the first target aeration amount, calculated by the
measurement device, is greater than a second change amount of
15 the transmembrane pressure difference of the separation
membrane during the aeration performed on the basis of the
second target aeration amount, calculated by the measurement
device, a value smaller than the second target aeration
amount is determined as a third target aeration amount.
20 [0058] With the above configuration, the aeration amount
control method in the aeration amount control system 100
according to embodiment 1 enables reduction in the energy
cost needed for aeration through increase/decrease of the
target value for the aeration amount, and thus can reduce the
25 whole operating cost of the aeration amount control system.
30
[0059] Embodiment 2
The configuration of an aeration amount control
system 200 according to embodiment 2 of the present invention
will be described. It is noted that the same or
5 corresponding configurations as those in embodiment 1 will
not be described and only different configuration parts will
be described.
[0060] FIG. 6 is a configuration diagram of the aeration
amount control system 200. The aeration amount control
10 system 200 includes pluralities of separation membranes 3,
filtration pumps 4, aeration pipes 51, air supply units 52,
pressure measurement units 61, and change amount calculation
units 62. It is noted that units having the same function
are denoted by the same numerals followed by a, b. The other
15 configurations are the same as those in embodiment 1, and
therefore the same or corresponding parts are denoted by the
same reference characters and description thereof is omitted.
It is noted that the filtration system with reference
numerals followed by a is defined as filtration system a, and
20 the filtration system with reference numerals followed by b
is defined as filtration system b.
[0061] Change amount calculation units 62a, 62b calculate
the change amounts of the transmembrane pressure differences
per unit time in their respective systems at the same timing.
25 [0062] The recording unit 71 is connected to the change
31
amount calculation units 62a, 62b and the aeration amount
control unit 74. The recording unit 71 records the change
amount of the transmembrane pressure difference per unit time
calculated by the change amount calculation unit 62a and the
5 aeration amount in the filtration system a subjected to
aeration control by the aeration amount control unit 74 at
the time when the change amount of the transmembrane pressure
difference per unit time is calculated by the change amount
calculation unit 62a, in association with each other. In
10 addition, the recording unit 71 records the change amount of
the transmembrane pressure difference per unit time
calculated by the change amount calculation unit 62b and the
aeration amount in the filtration system b subjected to
aeration control by the aeration amount control unit 74 at
15 the time when the change amount of the transmembrane pressure
difference per unit time is calculated by the change amount
calculation unit 62b, in association with each other.
[0063] The change amount comparing unit 72 performs
comparison as to whether or not a first-system-a change
20 amount which is the change amount per unit time calculated in
the filtration system a is smaller than a threshold relative
to a first-system-b change amount which is the change amount
of the transmembrane pressure difference per unit time
calculated in the filtration system b at the same timing as
25 in the filtration system a. The change amount comparing unit
32
72 calculates an aeration amount calculation command and
outputs the calculated aeration amount calculation command to
the aeration amount calculation unit 73. The aeration amount
calculation command is information which includes a result of
5 comparison of the change amounts by the change amount
comparing unit 72 and which is used for the aeration amount
calculation unit 73 to calculate the aeration amount. The
threshold used for comparison by the change amount comparing
unit 72 is determined in accordance with the applied aeration
10 amount control system.
[0064] The aeration amount calculation unit 73 calculates
target aeration amounts for aeration devices 5a, 5b on the
basis of the received aeration amount calculation command,
and outputs the target aeration amounts to the aeration
15 amount control unit 74. If the comparison result from the
change amount comparing unit 72 is smaller than the threshold,
the aeration amount calculation unit 73 sets the target
aeration amount for the aeration device 5a, to an aeration
amount decreased by a predetermined amount or a predetermined
20 rate from the first-system-a change amount, and does not
change the aeration amount for the aeration device 5b. If
the comparison result from the change amount comparing unit
72 is equal to or greater than the threshold, the aeration
amount calculation unit 73 sets the target aeration amounts
25 for the aeration device 5a and the aeration device 5b, to an
33
aeration amount increased by a predetermined amount or a
predetermined rate from the first-system-a change amount.
[0065] The aeration amount control unit 74 controls supply
of air by air supply units 52a, 52b so that the aeration
5 amounts of the aeration devices 5a, 5b become the respective
target aeration amounts determined by the aeration amount
calculation unit 73.
[0066] FIG. 7 is a control flowchart in the aeration
amount control system 200. The aeration amount control
10 method in the aeration amount control system 200 will be
described with reference to the control flowchart shown in
FIG. 7.
[0067] When the filtration process by the aeration amount
control system 200 is started, in initialization step S1c,
15 the control device 7 initializes n to 1. Next, in aeration
step S2c, the control device 7 executes aeration at an
aeration amount Qa1 set in advance as the first-system-a
target aeration amount in the filtration system a, and
aeration at an aeration amount Qb set in advance as the
20 first-system-b target aeration amount in the filtration
system b. As the aeration amounts Qa1, Qb, optional values
are employed from an appropriate range of the aeration amount
that enables suppression of fouling of the separation
membrane 3. The aeration amount Qa1, Qb set in advance are
25 the same value, and, for example, are set to the maximum flow
34
amount of the aeration devices 5a, 5b.
[0068] When time T has elapsed since the start of aeration
step S2c, in change amount calculation step S3c, the change
amount calculation unit 62a calculates a first-system-a
5 transmembrane pressure difference increase speed Ra1, and the
change amount calculation unit 62b calculates a first-systemb
transmembrane pressure difference increase speed Rb1. The
first-system-a transmembrane pressure difference increase
speed Ra1 and the first-system-b transmembrane pressure
10 difference increase speed Rb1 are calculated in the
respective filtration systems on the basis of Expression (1).
[0069] In recording step S4c, the recording unit 71
records the aeration amount Qa1, the first-system-a
transmembrane pressure difference increase speed Ra1, and the
15 first-system-b transmembrane pressure difference increase
speed Rb1 in association with each other.
[0070] In change amount comparing step S5c, the change
amount comparing unit 72 determines whether or not the ratio
of a transmembrane pressure difference increase speed Ran
20 calculated for the nth time in the filtration system a
relative to a transmembrane pressure difference increase
speed Rbn calculated for the nth time in the filtration
system b in aeration amount calculation step S3c is equal to
or greater than a threshold. The change amount comparing
25 unit 72 calculates an aeration amount calculation command and
35
outputs the calculated aeration amount calculation command to
the aeration amount calculation unit 73. If the
transmembrane pressure difference increase speed Ran is equal
to or greater than the threshold relative to the
5 transmembrane pressure difference increase speed Rbn, the
process proceeds to aeration amount determination step S6c,
and if the transmembrane pressure difference increase speed
Ran is smaller than the threshold relative to the
transmembrane pressure difference increase speed Rbn, the
10 process proceeds to aeration amount decrease step S8c.
In the case of n = 1, since the aeration amounts
Qa1, Qb set in advance are the same value, the first-system-a
transmembrane pressure difference increase speed Ra1 and the
first-system-b transmembrane pressure difference increase
15 speed Rb1 are regarded as being not different from each other,
and thus the process proceeds to aeration amount decrease
step S8c.
[0071] In aeration amount determination step S6c, the
aeration amount calculation unit 73 calculates, as the target
20 aeration amount Qn for the filtration system a and the
filtration system b, an aeration amount increased by a
predetermined amount or a predetermined rate from the
aeration amount recorded in association with the
transmembrane pressure difference increase speed Ran in the
25 recording unit 71.
36
[0072] In aeration step S7c, the aeration amount control
unit 74 executes aeration at the target aeration amount Qn in
the filtration system a and the filtration system b.
[0073] In aeration amount decrease step S8c, the aeration
5 amount calculation unit 73 calculates, as the target aeration
amount for the filtration system a, a second target aeration
amount Q2 which is an aeration amount decreased by a
predetermined amount or a predetermined rate from the
aeration amount recorded in association with the
10 transmembrane pressure difference increase speed Ran in the
recording unit 71. That is, in the case of n = 2, the
aeration amount calculation unit 73 calculates a third target
aeration amount Q3 decreased by a predetermined amount or a
predetermined rate from the second target aeration amount Q2,
15 as the target aeration amount for the filtration system a.
[0074] In addition step S9c, the control device 7
increments n by 1 to set n = n + 1, and then returns to
aeration step S2c.
[0075] In the aeration amount control method in the
20 aeration amount control system 200 shown in FIG. 7, the
transmembrane pressure difference increase amount may be
calculated instead of the transmembrane pressure difference
increase speed. By applying the aeration amount control
method in the aeration amount control system 100 shown in FIG.
25 5 to the aeration amount control method in the aeration
37
amount control system 200 shown in FIG. 7, it is possible to
execute control on the basis of the transmembrane pressure
difference increase amount also in the aeration amount
control system 200.
5 [0076] The aeration amount control system according to
embodiment 2 is an aeration amount control system for
performing aeration for a plurality of separation membranes
in a membrane separation tank storing treatment target water
on the basis of a target aeration amount, the aeration amount
10 control system including: a control device for performing a
first target aeration amount as the target aeration amount;
an aeration device for performing aeration by supplying gas
on the basis of the target aeration amount determined by the
control device; and a measurement device for measuring change
15 amounts of transmembrane pressure differences of the
plurality of separation membranes with respect to the gas
supplied by the aeration device, wherein, if a difference of
respective first change amounts of the plurality of
separation membranes during the aeration performed on the
20 basis of the first target aeration amount by the aeration
device, calculated by the measurement device, is smaller than
a threshold, the control device determines a value smaller
than the first target aeration amount, as a second target
aeration amount.
25 [0077] With the above configuration, the aeration amount
38
control system 200 according to embodiment 2 can execute
control of the aeration amount using one of the plurality of
provided separation membranes. Therefore, the aeration
amount for the separation membrane other than the separation
5 membrane used for the control need not be changed, and while
fouling of the separation membrane other than the separation
membrane used for the control is suppressed, the energy cost
needed for aeration can be reduced through increase/decrease
of the target value for the aeration amount, whereby the
10 whole operating cost of the aeration amount control system
can be reduced.
[0078] Embodiment 3
The configuration of an aeration amount control
system 300 according to embodiment 3 of the present invention
15 will be described. It is noted that the same or
corresponding configurations as those in embodiment 1 will
not be described and only different configuration parts will
be described.
[0079] FIG. 8 is a configuration diagram of the aeration
20 amount control system 300. The aeration amount control
system 300 includes an information acquisition device 31
which acquires and stores treatment target water information.
The information acquisition device 31 includes a treatment
target water information acquisition unit 311 for acquiring
25 treatment target water information and a storage medium 312
39
for storing the treatment target water information.
[0080] The treatment target water information acquisition
unit 311 acquires, as treatment target water information, for
example, the water temperature of the treatment target water
5 1 in the membrane separation tank 2, the mixed liquor
suspended solid (MLSS) concentration, the turbidity of the
treatment target water 1, the suspended solid (SS)
concentration, the filtration flux of the separation membrane
3, the organic substance concentration in the treatment
10 target water 1, etc.
[0081] The water temperature of the treatment target water
1 in the membrane separation tank 2 is measured by providing
a water temperature sensor to the membrane separation tank 2.
The water temperature of the treatment target water 1 in the
15 membrane separation tank 2 may be measured by supplying the
treatment target water 1 to a water temperature sensor.
[0082] The turbidity, the MLSS concentration, and the SS
concentration of the treatment target water 1 are measured by
providing an MLSS concentration sensor, a turbidity meter,
20 etc., to the membrane separation tank 2. The turbidity, the
MLSS concentration, and the SS concentration of the treatment
target water 1 may be measured by supplying the treatment
target water 1 to an MLSS concentration sensor, a turbidity
meter, etc. The treatment target water 1 may be extracted
25 and the MLSS concentration, the SS concentration, the
40
turbidity, etc., thereof may be measured through manual
analysis.
[0083] The filtration flux of the separation membrane 3 is
measured by providing a flow rate sensor to the filtered
5 water pipe. The filtration flux can be measured by measuring
the filtered water amount per constant time to calculate the
flow rate and dividing the flow rate value by the membrane
area of the separation membrane 3.
[0084] The organic substance concentration, etc., in the
10 treatment target water 1 are measured by immersing an organic
substance concentration sensor such as a total organic carbon
concentration meter, an ultraviolet absorbance meter, or a
fluorescence intensity meter in the membrane separation tank
2. The organic substance concentration, etc., in the
15 treatment target water 1 may be measured by supplying the
treatment target water 1 in the membrane separation tank 2 to
such an organic substance concentration sensor. That is, the
organic substance in the water may be measured directly or
indirectly using a total organic carbon concentration meter,
20 an ultraviolet absorbance meter, a fluorescence intensity
meter, or the like.
[0085] The storage medium 312 stores the treatment target
water information acquired by the treatment target water
information acquisition unit 311 and the aeration amount
25 information recorded in the recording unit 71, in association
41
with each other.
[0086] As the water temperature is lowered, viscosity of
the water increases, and therefore the change amount of the
transmembrane pressure difference per unit time increases.
5 In addition, as the MLSS concentration, the SS concentration,
the turbidity, or the like increases, the separation membrane
3 becomes more likely to be clogged, and therefore the change
amount of the transmembrane pressure difference per unit time
increases. In addition, as the filtration flux increases,
10 the speed at which water passes through the separation
membrane 3 increases and the separation membrane 3 becomes
more likely to be clogged, and therefore the change amount of
the transmembrane pressure difference per unit time increases.
Organic substances which can cause clogging of the separation
15 membrane 3 can be accurately measured by measuring, as an
organic substance index for the treatment target water 1, for
example, ultraviolet (UV), total organic carbon (TOC),
chemical oxygen demand (COD), biochemical oxygen demand (BOD),
humic acid concentration, sugar concentration, protein
20 concentration, or the like.
[0087] Next, operation of the aeration amount control
system 300 according to embodiment 3 will be described. It
is noted that the same or corresponding configurations as
those in embodiment 1 will not be described and only
25 different configuration parts will be described.
42
[0088] In the aeration amount control system 300, the
storage medium 312 stores the treatment target water
information acquired by the treatment target water
information acquisition unit 311 and the aeration amount
5 information stored in the recording unit 71 in association
with each other, thereby generating a database.
[0089] In addition, the information acquisition device 31
may have a function of determining that the state of the
treatment target water 1 has greatly changed, and a function
10 of estimating an appropriate aeration amount at the time when
the state of the treatment target water 1 has greatly changed,
through checking against the treatment target water
information stored in the generated database, and setting the
estimated aeration amount as a target aeration amount.
15 [0090] In the case where the information acquisition
device 31 has the above functions, the aeration amount
control system 300 can perform operation of, when the state
of the treatment target water 1 in the membrane separation
tank 2 has greatly changed, checking the changed treatment
20 target water information against the treatment target water
information stored in the generated database, estimating an
appropriate aeration amount at the time when the state of the
treatment target water 1 has greatly changed, and setting the
estimated aeration amount as a target aeration amount.
25 [0091] Even in the case where data corresponding to the
43
state of the treatment target water 1 at the time when the
state of the treatment target water 1 has greatly changed is
not stored in the database, an appropriate aeration amount in
the state of the treatment target water 1 at the time when
5 the state of the treatment target water has greatly changed
can be estimated from data stored in the database. For
example, in the case where the database includes data
corresponding to water temperature of 10°C and water
temperature of 30°C and the water temperature of the
10 treatment target water 1 at the time when the state of the
treatment target water 1 has greatly changed is 20°C, an
appropriate aeration amount can be estimated as the average
value between the aeration amounts in the data corresponding
to water temperature of 10°C and water temperature of 30°C.
15 Further, it is possible to generate a more detailed
database by updating the database along with operation of the
aeration amount control system 300.
[0092] The aeration amount control system 300 according to
embodiment 3 includes a treatment target water information
20 acquisition unit for acquiring treatment target water
information about treatment target water in the membrane
separation tank, and a storage medium for storing the
treatment target water information, the target aeration
amount calculated by the control device, and a change amount
25 of a transmembrane pressure difference measured by the
44
measurement device, in association with each other.
[0093] With the above configuration, the aeration amount
control system 300 according to embodiment 3 can quickly
calculate a target aeration amount using data stored in the
5 database even when the state of the treatment target water 1
in the membrane separation tank 2 has greatly changed.
[0094] The present invention is not limited to the
configurations described in embodiments 1 to 3, and within
the scope of the present invention, the above embodiments may
10 be freely combined with each other or each embodiment may be
modified or simplified as appropriate.
[0095] While the embodiments of the present invention have
been described above, the embodiments disclosed herein are
illustrative in all aspects and are not intended to be
15 restrictive. The scope of right of the present invention is
indicated by the scope of claims and is intended to include
all modifications within the meaning and the scope equivalent
to the scope of claims.
20 DESCRIPTION OF THE REFERENCE CHARACTERS
[0096] 100, 200, 300 aeration amount control system
1 treatment target water
2 membrane separation tank
3 separation membrane
25 4 filtration pump
45
5 aeration device
6 measurement device
7 control device
31 information acquisition device
5 51 aeration pipe
52 air supply unit
61 pressure measurement unit
62 change amount calculation unit
71 recording unit
10 72 change amount comparing unit
73 aeration amount calculation unit
74 aeration amount control unit
311 treatment target water information acquisition
unit
15 312 storage medium
1000a, 1000b CPU
1001a, 1001b memory
46
We Claim
[1] An aeration amount control system for performing
aeration for a separation membrane in a membrane separation
tank storing treatment target water on the basis of a target
5 aeration amount, the aeration amount control system
comprising:
a control device for determining a first target
aeration amount as the target aeration amount, and after
having determined the first target aeration amount,
10 determining a second target aeration amount as the target
aeration amount;
an aeration device for performing the aeration by
supplying gas on the basis of the target aeration amount
determined by the control device; and
15 a measurement device for measuring a change amount
of a transmembrane pressure difference of the separation
membrane with respect to the gas supplied by the aeration
device, wherein
if a first change amount of the transmembrane
20 pressure difference of the separation membrane during the
aeration performed on the basis of the first target aeration
amount by the aeration device, calculated by the measurement
device, is greater than a second change amount of the
transmembrane pressure difference of the separation membrane
25 during the aeration performed on the basis of the second
47
target aeration amount by the aeration device, calculated by
the measurement device, the control device determines a value
smaller than the second target aeration amount, as a third
target aeration amount.
5
[2] The aeration amount control system according to
claim 1, wherein
if the first change amount is smaller than the
second change amount, the control device determines a value
10 greater than the second target aeration amount, as the third
target aeration amount.
[3] An aeration amount control system for performing
aeration for a plurality of separation membranes in a
15 membrane separation tank storing treatment target water on
the basis of a target aeration amount, the aeration amount
control system comprising:
a control device for performing a first target
aeration amount as the target aeration amount;
20 an aeration device for performing the aeration by
supplying gas on the basis of the target aeration amount
determined by the control device; and
a measurement device for measuring change amounts
of transmembrane pressure differences of the plurality of
25 separation membranes with respect to the gas supplied by the
48
aeration device, wherein
if a difference of respective first change amounts
of the plurality of separation membranes during the aeration
performed on the basis of the first target aeration amount by
5 the aeration device, calculated by the measurement device, is
smaller than a threshold, the control device determines a
value smaller than the first target aeration amount, as a
second target aeration amount.
10 [4] The aeration amount control system according to
claim 3, wherein
if the difference of the respective first change
amounts is equal to or greater than the threshold, the
control device determines a value greater than the first
15 target aeration amount, as the second target aeration amount.
[5] The aeration amount control system according to any
one of claims 1 to 4, further comprising an information
acquisition device including
20 a treatment target water information acquisition
unit for acquiring treatment target water information about
the treatment target water in the membrane separation tank,
and
a storage medium for storing the treatment target
25 water information, the target aeration amount calculated by
49
the control device, and the change amount of the
transmembrane pressure difference measured by the measurement
device, in association with each other.
5 [6] An aeration amount control method in an aeration
amount control system for performing aeration for a
separation membrane in a membrane separation tank storing
treatment target water on the basis of a target aeration
amount, the aeration amount control method comprising:
10 an aeration amount determination step of
determining a first target aeration amount as the target
aeration amount, and after having determined the first target
aeration amount, determining a second target aeration amount
as the target aeration amount;
15 an aeration step of performing the aeration by
supplying gas on the basis of the target aeration amount
determined in the aeration amount determination step; and
a change amount calculation step of calculating a
change amount of a transmembrane pressure difference of the
20 separation membrane with respect to the gas supplied in the
aeration step, wherein
if a first change amount of the transmembrane
pressure difference of the separation membrane during the
aeration performed on the basis of the first target aeration
25 amount, calculated by a measurement device, is greater than a
50
second change amount of the transmembrane pressure difference
of the separation membrane during the aeration performed on
the basis of the second target aeration amount, calculated by
the measurement device, a value smaller than the second
5 target aeration amount is determined as a third target
aeration amount.
[7] The aeration amount control method according to
claim 6, wherein
10 if the first change amount is smaller than the
second change amount, a value greater than the second target
aeration amount is determined as the third target aeration
amount.