FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
WATER TREATMENT DEVICE AND WATER TREATMENT 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.
2
DESCRIPTION
5 TECHNICAL FIELD
[0001] The present disclosure relates to a water treatment
device and a water treatment method.
BACKGROUND ART
10 [0002] In water and sewage treatments and waste water
treatment, a membrane filtration method in which treatment
target water is filtered by a filtration membrane to obtain
clarified filtered water is widely adopted. The filtration
membrane used in the method is an organic material membrane
15 or an inorganic material membrane whose surface has
innumerable fine holes having a pore diameter of about 0.1
micrometers, for example. With this membrane, suspended
substances in the treatment target water can be removed.
[0003] In the membrane filtration method, while filtered
20 water having an extremely high quality can be obtained as
treated water by a filtration membrane having a fine
structure as described above, there is a problem that pores
of the filtration membrane are clogged by substances such as
suspended substances. Meanwhile, in general, “backwashing”
25 in which a chemical solution that contains filtered water,
3
ozone, or hypochlorous acid is passed through the filtration
membrane in a direction opposite to the filtration direction
of the treatment target water, to remove clogging of the
filtration membrane pores, is performed. For example, Patent
5 Documents 1 and 2 disclose filtration membrane backwashing
methods that use ozone water which is water having ozone
dissolved therein.
CITATION LIST
10 PATENT DOCUMENT
[0004] Patent Document 1: Japanese Laid-Open Patent
Publication No. 2001-300576
Patent Document 2: Japanese Laid-Open Patent
Publication No. 2014-128790
15
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0005] For example, when a filtration membrane is cleaned
by ozone water, ozone water that contains ozone by a
20 concentration necessary for cleaning needs to be generated
every time cleaning is performed. This is due to instability
of ozone. That is, even when ozone water having a target
ozone concentration is generated, ozone is decomposed with a
lapse of time when supply of ozone gas is stopped, whereby
25 the ozone concentration is decreased and the effect as a
4
cleaning agent is impaired. Therefore, different from
filtration membrane cleaning by a cleaning agent, such as
sodium hypochlorite, that has a relatively slow decomposition
speed and thus can be preserved, even when a filtration
5 membrane needs to be cleaned, cleaning cannot be immediately
started, and excessive fouling (clogging of pores) is caused
at the filtration membrane.
[0006] Further, the dissolved ozone concentration is
easily influenced by characteristics of a liquid serving as a
10 solvent for ozone gas, and the dissolving speed of ozone and
the final dissolved ozone concentration change at each
generation. Therefore, the cleaning effect varies, a
cleaning effect as expected cannot be obtained in an ozone
water cleaning step of injecting ozone water to the
15 filtration membrane, and cleaning is immediately required
again, whereby the cleaning frequency may be increased.
[0007] The present disclosure has been made in order to
solve the problem as described above. An object of the
present disclosure is to provide a water treatment device and
20 a water treatment method that eliminate uncertainness due to
characteristics of ozone in ozone water generation and
cleaning, that start ozone water generation at an appropriate
timing, and that attain a stable and sufficient ozone water
cleaning effect.
25
5
SOLUTION TO THE PROBLEMS
[0008] A water treatment device disclosed in the present
disclosure is for performing a membrane filtration step of
filtering treatment target water by a filtration membrane to
5 obtain treated water, and an ozone water cleaning step of
cleaning the filtration membrane by ozone water, and
includes:
a calculation unit for calculating a trans-membrane
pressure value from a difference in pressure measured before
10 and after the filtration membrane; and
a control unit for instructing start of generation
of the ozone water when the calculated trans-membrane
pressure value or an estimation value calculated on the basis
of the trans-membrane pressure value has become equal to a
15 reference value or has exceeded the reference value.
EFFECT OF THE INVENTION
[0009] According to the water treatment device disclosed
in the present disclosure, uncertainness due to
20 characteristics of ozone in ozone water generation and
cleaning can be eliminated, ozone water generation can be
started at an appropriate timing, and stable and sufficient
ozone water cleaning effects can be obtained.
25 BRIEF DESCRIPTION OF THE DRAWINGS
6
[0010] [FIG. 1] FIG. 1 is a diagram describing an example
of the configuration of a water treatment device in
embodiment 1.
[FIG. 2] FIG. 2 is a flowchart describing
5 operation of the water treatment device in embodiment 1.
[FIG. 3] FIG. 3 is a diagram describing start and
completion of an ozone water cleaning step in embodiment 1.
[FIG. 4] FIG. 4 is another diagram describing
start and completion of the ozone water cleaning step in
10 embodiment 1.
[FIG. 5] FIG. 5 is another diagram describing
start and completion of the ozone water cleaning step in
embodiment 1.
[FIG. 6] FIG. 6 is a diagram describing an example
15 of the configuration of a water treatment device in
embodiment 2.
[FIG. 7] FIG. 7 is a flowchart describing
operation of the water treatment device in embodiment 2.
[FIG. 8] FIG. 8 is a diagram showing an example of
20 hardware forming a calculation unit, a control unit, a
setting unit, and trans-membrane pressure change speed
calculation means shown in embodiments 1 and 2.
DESCRIPTION OF EMBODIMENTS
25 [0011] Hereinafter, preferred embodiments of a water
7
treatment device according to the present disclosure will be
described with reference to the drawings. The same
components and corresponding parts are denoted by the same
reference characters, and detailed descriptions thereof will
5 be omitted. In the subsequent embodiments as well, redundant
descriptions of components denoted by the same reference
characters will be omitted.
[0012] Embodiment 1
FIG. 1 shows an example of the configuration of a
10 water treatment device according to embodiment 1. The water
treatment device shown in FIG. 1 includes a storage tank 2
which stores a filtration membrane 1. The storage tank 2 is
filled with treatment target water 4, and the filtration
membrane 1 is immersed in the treatment target water 4. In
15 addition, a treatment target water pipe 19 which supplies the
treatment target water 4 to the storage tank 2 is provided.
A filtered water pipe 15 is connected to the filtration
membrane 1. Further, a pressure gauge 9 is installed on the
filtered water pipe 15. Pressure information obtained by the
20 pressure gauge 9 is transmitted to a calculation unit 10, to
be converted into a trans-membrane pressure.
[0013] A filtration pump 13 is connected to the filtered
water pipe 15, and allows filtered water obtained through the
filtration membrane 1 to be sent to a filtered water tank 14.
25 Further, the filtered water pipe 15 is connected to an ozone
8
water supply pipe 7. The ozone water supply pipe 7 supplies,
to the filtration membrane 1, ozone water discharged via an
ozone water supply pump 6 from an ozone water generation
device 3. The ozone water generation device 3 is composed
5 of: an ozone gas generator 12 which generates ozone gas; an
ozone water tank 5 which causes the generated ozone gas to
come into contact with a liquid stored therein, to generate
ozone water; and an ozone water concentration meter 8 which
measures the dissolved ozone concentration in the ozone water
10 tank 5.
[0014] The filtered water pipe 15 and the ozone water
supply pipe 7 have valves 16, 17 installed thereon, and
supply of filtered water or ozone water is switched by
opening/closing of these valves. Further, a control unit 11
15 which can receive operation parameters of devices set at a
setting unit 18, a calculation result calculated by the
calculation unit 10, and information from other apparatuses,
and can transmit an instruction to each apparatus, is
provided.
20 [0015] Next, a series of operations of water treatment
performed by the water treatment device shown in FIG. 1 will
be described with reference to a flowchart in FIG. 2.
[Membrane filtration step]
In a membrane filtration step (step S1), receiving
25 of the treatment target water 4 into the storage tank 2 and
9
filtration of the treatment target water 4 by the filtration
membrane 1 are performed. The treatment target water 4
supplied from the treatment target water pipe 19 is stored in
the storage tank 2. The valve 17 is opened (at this time,
5 the valve 16 is closed) and the filtration pump 13 is
operated to perform suction, whereby filtration of the
treatment target water 4 by the filtration membrane 1 is
performed. Filtered water obtained through filtration is
transferred to the filtered water tank 14.
10 [0016] In association with the filtration, fouling of the
filtration membrane 1, i.e., clogging of pores, advances.
When fouling advances, the difference in pressure (transmembrane pressure: TMP) before and after the filtration
membrane 1 increases. An excessive increase in the TMP
15 causes a failure of the device, such as damage of the
filtration membrane 1, and it is preferable to understand the
degree of fouling by always monitoring the TMP. In the water
treatment device of the present embodiment, in the
calculation unit 10, pressure information obtained by the
20 pressure gauge 9 is subjected to a predetermined process, to
be converted into a TMP, and the TMP is recorded. Here, the
predetermined process is a process of obtaining the
difference between the pressure acting on the primary side of
the filtration membrane 1 and the pressure acting on the
25 secondary side of the filtration membrane 1. Here, as the
10
pressure acting on the primary side of the filtration
membrane 1, the water pressure caused by the water level of
the storage tank 2 is adopted, and as the pressure acting on
the secondary side, the sum of the water pressure caused by
5 the mounting height of the pressure gauge 9 and the
measurement value by the pressure gauge 9 is adopted.
[0017] The treatment target water 4 is not limited in
particular, and may be, for example, natural water collected
from rivers, lakes and marshes, oceans, or the like, or
10 sewage, industrial drainage, or the like. In a case of
operation as a membrane separation bioreactor, activated
sludge may be stored in the storage tank 2, the treatment
target water 4 may be introduced to the storage tank 2, and
the mixed liquid may be filtered by the filtration membrane
15 1.
[0018] Filtration may be performed continuously or
intermittently. For example, filtration may be stopped every
time a predetermined period elapses, backwash may be
conducted by, for example, causing filtered water to
20 reversely flow, and then, filtration may be resumed, for
example. The shape of the filtration membrane 1 may be of a
hollow fiber type or a flat membrane type. As a material of
the filtration membrane 1, an inorganic material such as a
ceramic, or a fluorocarbon resin-based organic material such
25 as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene
11
(PTFE) can be used, for example. In either case, the
filtration membrane 1 to be used is not limited as long as
the filtration membrane 1 has a pore diameter that allows the
treatment target water 4 to be filtered to have a target
5 water quality, and has a structure or a material having a
sufficient ozone tolerance.
[0019] [Ozone water generation step]
As described above, fouling of the filtration
membrane 1 advances in association with filtration, and the
10 TMP increases. There is a limitation for the TMP that can be
provided to the filtration membrane 1, and when filtration is
continued at a TMP not less than the limitation, the
filtration membrane 1 may be damaged. Even in a case of a
TMP within the limitation, when filtration is continued while
15 a high TMP is maintained, reduction of the TMP by cleaning
may become difficult. Therefore, it is preferable to perform
ozone water cleaning when a limit value Pmax of the TMP
inputted in advance to the setting unit 18 has been reached.
For example, Pmax is preferably set to 10 to 50 kPa.
20 [0020] Meanwhile, when the filtration membrane 1 is
cleaned by ozone water, ozone water necessary for filtration
needs to be generated as necessary. This is due to
characteristics of ozone. That is, since the half-life is
extremely short, ozone water necessary for one time cannot be
25 kept for a long period. If ozone water is to be kept, it is
12
necessary to continuously supply ozone gas even while ozone
water is not necessary. This is not efficient. Therefore,
in order to start cleaning at the time point when Pmax is
reached, it is necessary, from the viewpoint of efficiency,
5 to start generation of ozone water a predetermined time
period before the determined Pmax is reached.
[0021] The water treatment device shown in the present
embodiment has measures for solving such a problem. That is,
the calculation unit 10 sequentially calculates a TMP from a
10 measurement value obtained by the pressure gauge 9 during
execution of the membrane filtration step, and the calculated
TMP is transmitted to the control unit 11. Accordingly, the
TMP acting on the filtration membrane 1 is always monitored.
Further, the control unit 11 sequentially compares the TMP
15 with Pmax inputted in advance to the setting unit 18 and Psub
being a TMP lower by a certain value than Pmax (step S2), and
when the control unit 11 has detected that Psub has been
reached, i.e., the TMP has become equal to or has exceeded
Psub, ozone water generation is started (step S3). Psub is
20 preferably set in the setting unit 18 such that the time
period in which the TMP reaches Pmax from Psub is not less than
the time period in which ozone water generation can be
completed. Since the time period taken for ozone water
generation is about 10 to 120 minutes, Psub is preferably set
25 to a value lower by 5 to 20 kPa than Pmax, for example.
13
[0022] As described above, in the membrane filtration
step, when the TMP has reached Psub, the ozone water
generation step is started, and the ozone gas generator 12
operates to start supply of ozone gas to the ozone water tank
5 5. A liquid that can serve as a solvent for ozone is stored
in advance in the ozone water tank 5, and this liquid is
brought into contact with ozone gas, whereby ozone water is
generated. As this liquid, for example, tap water,
industrial water, pure water, or ultrapure water may be used,
10 or a part of filtered water stored in the filtered water tank
14 may be transferred to be used. During ozone water
generation in the ozone water tank 5, an acidic chemical such
as hydrochloric acid or sulfuric acid, or a radical scavenger
(e.g., carbonic acid gas) may be injected to the liquid in
15 the ozone water tank 5 simultaneously with or before supply
of ozone gas. When such an operation is further performed,
decomposition of ozone can be suppressed, and ozone water
having a high concentration can be obtained in a shorter
time.
20 [0023] While the ozone water generation step is executed,
the membrane filtration step is continued. That is, in the
membrane filtration step, the filtration pump 13 operates and
the treatment target water 4 is filtered through the
filtration membrane 1. However, operation of apparatuses
25 related to ozone water generation and operation of
14
apparatuses related to membrane filtration are independent
from each other. Therefore, except when the TMP has reached
Pmax, i.e., the TMP has become equal to or has exceeded Pmax,
it is not always necessary to stop these apparatuses for
5 ozone water generation and to pause the membrane filtration
step. This is one aspect of the effects of the present
embodiment. Since ozone water generation is started before
the limit value Pmax of the trans-membrane pressure of the
membrane that requires cleaning is reached, the time period
10 in which the filtration is stopped can be shortened to an
extreme extent. When Pmax is reached before ozone water
generation is completed, the filtration step is stopped as
described above, or operation can be continued with the
amount of filtered water (filtration flux) reduced until
15 ozone water generation is completed.
[0024] The ozone water concentration during ozone water
generation is always monitored by the ozone water
concentration meter 8, and is transmitted to the calculation
unit 10. The concentration information received by the
20 calculation unit 10 is transmitted to the control unit 11,
and when the control unit 11 has determined that the ozone
water concentration during monitoring has reached a
predetermined concentration Ctarget set in advance in the
setting unit 18, an ozone water cleaning step is started.
25 [0025] [Ozone water cleaning step]
15
After the control unit 11 has determined that the
dissolved ozone concentration in ozone water has reached the
predetermined concentration Ctarget, i.e., has become equal to
or has exceeded Ctarget, the membrane filtration step is
5 stopped (step S4). Meanwhile, while supply of ozone gas to
the ozone water tank 5 by the ozone gas generator 12 is
continued, supply of ozone water to the filtration membrane 1
is started. That is, instructions are transmitted from the
control unit 11, whereby the filtration pump 13 is stopped,
10 the valve 17 is closed, and the valve 16 is opened. Further,
the ozone water supply pump 6 operates, and ozone water
stored in the ozone water tank 5 is supplied to the
filtration membrane 1 through the ozone water supply pipe 7.
The supplied ozone water, while passing through the
15 filtration membrane from the secondary side to the primary
side thereof, chemically decomposes or physically separates
the fouling-causing substances (e.g., organic components such
as biofilm) that are clogging the filtration membrane pores.
[0026] In operation of the water treatment device, it is
20 necessary that the cleaning effect intended by an operation
manager can always be stably obtained. However, much of the
cleaning mechanism of a water treatment filtration membrane
by ozone water has not been clarified, and management of the
cleaning effect has been difficult. In addition, management
25 of the cleaning effect has been made more difficult by the
16
fact that the ozone water concentration obtained as a result
of ozone water generation changes due to characteristics of
the liquid serving as a solvent for ozone gas.
[0027] Regarding this, the inventors conducted thorough
5 studies and found the following. That is, in ozone water
cleaning of a water treatment filtration membrane, there can
be a correlation between the cleaning effect, i.e., the TMP
reduction effect, and a CT value obtained as the product of
the concentration of ozone water used in cleaning and the
10 cleaning time period. That is, ozone water cleaning was
performed on a filtration membrane that had been fouled, to
an extent to show a predetermined TMP, through filtration of
water having dissolved therein an organic matter such as
sugar or protein. Then, even in a case where an ozone water
15 concentration C changed every time, when the ozone water
cleaning time period was adjusted such that the CT value
being the product of the ozone water concentration C and a
cleaning time period T using the ozone water becomes
constant, the reduction amounts of the TMP were at similar
20 levels after respective cleanings in which the ozone water
concentration C changed. Therefore, it is considered that
the ozone water cleaning effect can be managed when the
cleaning time period is managed while understanding change in
the ozone water concentration obtained as a result of ozone
25 water generation.
17
[0028] In the water treatment device shown in the present
embodiment, the concentration of ozone water stored in the
ozone water tank 5 in the ozone water generation step is
measured by the ozone water concentration meter 8. The
5 measurement value is sequentially transmitted to the
calculation unit 10, and the calculated present ozone water
concentration information is transmitted to the control unit
11. The control unit 11 compares the present ozone water
concentration transmitted from the control unit with an ozone
10 water concentration Ctarget set in advance in the setting unit
18. As shown in FIG. 3, when it has been determined that
Ctarget has been reached, an ozone water cleaning step is
started (step S5).
[0029] With respect to the ozone water concentration after
15 the ozone water cleaning step is started, operation may be
performed such that the ozone water concentration becomes
Ctarget on average by, for example, adjusting the concentration
or flow rate of ozone gas supplied to the ozone water tank 5
by changing output of the ozone gas generator 12. In this
20 case, the control unit 11 having received a measurement value
from the ozone water concentration meter 8 via the
calculation unit 10 increases or decreases the concentration
or flow rate of ozone gas to be discharged from the ozone gas
generator 12, in accordance with divergence between the
25 present ozone water concentration and the target value Ctarget.
18
In this manner, the ozone gas generator 12 is controlled by
the control unit 11 such that the ozone water concentration
during execution of the ozone water cleaning step becomes
Ctarget on average. Further, the control unit 11 calculates a
5 necessary cleaning time period α1 from the ozone water
concentration Ctarget and the target CT value CTtarget
predetermined in the setting unit 18, and executes the ozone
water cleaning step for the necessary cleaning time period
α1.
10 [0030] The ozone water concentration may be allowed to be
as is without changing the concentration and flow rate of
ozone gas and other conditions. In this case, the control
unit 11 sequentially obtains the measurement value from the
ozone water concentration meter 8 and records the measurement
15 value as the ozone water concentration via the calculation
unit 10. The product of the recorded ozone water
concentration and an elapsed time of the ozone water cleaning
step is accumulated, and when the accumulated value has
reached CTtarget (step S6), i.e., at a time point when the
20 accumulated value has become equal to or has exceeded CTtarget,
the ozone water cleaning step may be completed (step S7).
For example, the following formula may be introduced in the
calculation unit 10, and a calculation result may be
sequentially compared or judged with respect to CTtarget.
25 [0031] CTpresent = Σ(Cpresent×Δt)
19
Here,
CTpresent represents a present accumulated CT value.
Cpresent represents a present ozone water
concentration.
5 Δt represents an elapsed time from the previous
CTpresent calculation.
[0032] When the ozone water concentration in the ozone
water cleaning step is allowed to be as is, an average ozone
water concentration Cave at each time point from the start of
10 the ozone water cleaning step may be sequentially calculated
as shown in FIG. 4, and CTtarget may be compared with a ∫Cave·dt
value obtained as the product of this calculated value and an
execution time period of the ozone water cleaning step at the
same time point, whereby the completion point of the ozone
15 water cleaning step may be determined (step S6).
[0033] In the present embodiment, the ozone water
concentration is used as a start condition for the ozone
water cleaning step. That is, when the ozone water
concentration Ctarget set in advance has been reached, the
20 ozone water cleaning step is started. However, for example,
as shown in FIG. 5, without determining Ctarget, operation may
be performed such that, when a predetermined time period β
has elapsed in the ozone water generation step, the ozone
water cleaning step may be compulsorily started. At this
25 time, although the ozone water concentration at the start of
20
the ozone water cleaning step is not necessarily constant,
the cleaning effect itself by ozone water can be managed by
the CT value. Therefore, the execution time period of the
ozone water cleaning step may be adjusted in accordance with
5 CTtarget and the ozone water concentration sequentially
measured.
[0034] After completion of the ozone water cleaning step,
ozone gas supply from the ozone gas generator 12 and ozone
water supply by the ozone water supply pump 6 are stopped,
10 the valve 16 is closed, and the filtration step is resumed
(step S8).
[0035] As described above, according to the present
embodiment, in association with start of the ozone water
generation step, ozone water having a high concentration can
15 be obtained in a shorter time. In addition, since the
cleaning time period is managed while change in the ozone
water concentration is understood, the ozone water cleaning
effect can be managed. Due to these remarkable effects,
uncertainness due to characteristics of ozone in ozone water
20 generation and cleaning can be eliminated, ozone water
generation can be started at an appropriate timing, and
stable and sufficient ozone water cleaning effects can be
obtained.
[0036] Embodiment 2
25 In the water treatment device that filters the
21
treatment target water 4 by a filtration membrane to obtain
treated water, fouling of the filtration membrane advances as
described above. However, the fouling speed, i.e., the
trans-membrane pressure change speed, is not necessarily
5 constant, and changes depending on the filtration condition
such as characteristics of the treatment target water at each
time. Therefore, when the start timing of ozone water
generation is also determined in accordance with the transmembrane pressure change speed, more efficient operation can
10 be performed.
[0037] In the water treatment device shown in embodiment
1, comparison between Psub and TMP at each time point is
performed in the control unit 11, whereby the start timing of
the ozone water generation step is determined. However, in
15 the present embodiment, as shown in FIG. 6, since transmembrane pressure change speed calculation means 110 is added
to the control unit 11, the start timing of the ozone water
generation step can be more appropriately determined.
[0038] That is, in the present embodiment, during
20 execution of the membrane filtration step, the TMP is
calculated by the calculation unit 10 from the measurement
value at the pressure gauge 9, and is sequentially recorded
in the control unit 11. That is, the control unit 11
sequentially records a present trans-membrane pressure Pn and
25 a trans-membrane pressure Pn-1 that is a trans-membrane
22
pressure a predetermined time period T1 before the present
time and that has been predetermined in the setting unit 18,
and calculates an average trans-membrane pressure change
speed v from Pn-1 to Pn on the basis of the difference between
5 Pn and Pn-1, and T1.
[0039] Further, the control unit 11 sequentially
calculates ΔP being the product of a time period T2
predetermined in the setting unit 18 and the average transmembrane pressure change speed v, and a value Pn+x obtained by
10 adding Pn to ΔP. The control unit 11 sequentially compares
the value Pn+x with Pmax also set in advance in the setting
unit 18, and when having determined that Pn+x has reached Pmax
(step S9), starts the ozone water generation step (step S3).
[0040] Pn+x is an estimation trans-membrane pressure after
15 the time period T2 from the present time. T1 needs to be a
time period appropriate for predicting a trans-membrane
pressure in a near future from the present time on the basis
of a trans-membrane pressure increase speed near the present
time, and is preferably set between 10 minutes to 240
20 minutes. In a case where T1 is shorter than 10 minutes, v is
calculated to be excessively large or small, under great
influence of change in the trans-membrane pressure due to
some variation in the filtration flow rate in the filtration
step.
25 [0041] Meanwhile, in a case where T1 is longer than 240
23
minutes, when the trans-membrane pressure suddenly increases
or decreases due to some reason while the trans-membrane
pressure reaches Pn from Pn-1, calculation of v and Pn+x cannot
be appropriately performed under influence thereof.
5 [0042] As for T2, a time period required for a necessary
ozone water concentration Ctarget to be reached from the start
of ozone water generation is preferably inputted, and T2 is
10 to 120 minutes. That is, after a lapse of a time period
required for ozone water generation from the present time,
10 when it has been determined that the trans-membrane pressure
can reach a value not less than Pmax determined as the limit
trans-membrane pressure, the ozone water generation step is
immediately started.
[0043] Even in a case where the trans-membrane pressure
15 change speed changes every second as described, a local
trans-membrane pressure change speed is sequentially
calculated and recorded, whereby a future trans-membrane
pressure can be estimated, and by using this, the start
timing of ozone water generation can be appropriately
20 determined.
[0044] FIG. 8 shows an example of hardware forming the
calculation unit 10, the control unit 11, the setting unit
18, and the trans-membrane pressure change speed calculation
means 110. The hardware is composed of a processor 100 and a
25 storage device 200, and although not shown, the storage
24
device 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, a hard disk as
an auxiliary storage device may be provided. By executing a
5 program inputted from the storage device 200, the processor
100 performs calculations and controls described with
reference to FIG. 2 and FIG. 7, for example. In this case, a
program for calculation and control is inputted to the
processor 100 from the auxiliary storage device via the
10 volatile storage device. The processor 100 may output data
such as a calculation result to the volatile storage device
of the storage device 200, or may store data in the auxiliary
storage device via the volatile storage device. A plurality
of the processors 100 may be mounted, and the calculation
15 unit 10, the control unit 11, and the setting unit 18 may be
implemented by a single processor 100.
[0045] Although the present disclosure is described above
in terms of various exemplary embodiments and
implementations, it should be understood that the various
20 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
25 disclosure. It is therefore understood that numerous
25
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
5 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.
10 DESCRIPTION OF THE REFERENCE CHARACTERS
[0046] 1 filtration membrane
2 storage tank
3 ozone water generation device
4 treatment target water
15 5 ozone water tank
6 ozone water supply pump
7 ozone water supply pipe
8 ozone water concentration meter
9 pressure gauge
20 10 calculation unit
11 control unit
12 ozone gas generator
13 filtration pump
14 filtered water tank
25 15 filtered water pipe
26
16, 17 valve
18 setting unit
19 treatment target water pipe
27
We Claim :
[1] A water treatment device for performing a membrane
filtration step of filtering treatment target water by a
filtration membrane to obtain treated water, and an ozone
5 water cleaning step of cleaning the filtration membrane by
ozone water, the water treatment device comprising:
a calculation unit for calculating a trans-membrane
pressure value from a difference in pressure measured before
and after the filtration membrane; and
10 a control unit for instructing start of generation
of the ozone water when the calculated trans-membrane
pressure value or an estimation value calculated on the basis
of the trans-membrane pressure value has become equal to a
reference value or has exceeded the reference value.
15
[2] The water treatment device according to claim 1,
wherein
when the trans-membrane pressure value and the
reference value are compared with each other, the reference
20 value is set to a second value lower by a certain value than
a first value at which reduction of the trans-membrane
pressure value by the ozone water cleaning step becomes
difficult.
25 [3] The water treatment device according to claim 2,
28
wherein
the certain value is set such that a time period in
which the trans-membrane pressure value reaches the first
value from the second value is longer than a time period from
5 the start of generation of the ozone water to completion of
the generation of the ozone water.
[4] The water treatment device according to claim 2,
wherein
10 when the calculated trans-membrane pressure value
has become equal to the first value at which reduction of the
trans-membrane pressure value by the ozone water cleaning
step becomes difficult, or has exceeded the first value, the
membrane filtration step is stopped.
15
[5] The water treatment device according to claim 1,
wherein
when the estimation value and the reference value
are compared with each other, the reference value is a limit
20 value at which reduction of the trans-membrane pressure value
by the ozone water cleaning step becomes difficult.
[6] The water treatment device according to claim 5,
wherein
25 the estimation value is a value obtained by
29
calculating a trans-membrane pressure change speed from a
difference between a trans-membrane pressure value calculated
by the calculation unit and a trans-membrane pressure value a
predetermined time period before with respect to the
5 calculated trans-membrane pressure value, and then
calculating a trans-membrane pressure value after a
predetermined time period on the basis of the trans-membrane
pressure change speed.
10 [7] The water treatment device according to claim 5,
wherein
when the calculated trans-membrane pressure value
has become equal to the limit value at which reduction of the
trans-membrane pressure value by the ozone water cleaning
15 step becomes difficult, or has exceeded the limit value, the
filtration membrane step is stopped.
[8] The water treatment device according to any one of
claims 1 to 7, wherein
20 after a concentration of the generated ozone water
has reached a predetermined target concentration, the ozone
water cleaning step is started.
[9] The water treatment device according to claim 8,
25 wherein
30
when an integrated value of the concentration of
the ozone water and an elapsed time of the ozone water
cleaning step has become a set value, the ozone water
cleaning step is ended.
5
[10] The water treatment device according to claim 8,
wherein
the control unit adjusts a concentration and a flow
rate of ozone gas of an ozone gas generator such that the
10 concentration of the ozone water in the ozone water cleaning
step becomes the target concentration on average.
[11] A water treatment method having a membrane
filtration step of filtering treatment target water by a
15 filtration membrane to obtain treated water, and an ozone
water cleaning step of cleaning the filtration membrane by
ozone water, the water treatment method comprising:
calculating a trans-membrane pressure value from a
difference in pressure measured before and after the
20 filtration membrane;
starting generation of the ozone water when the
trans-membrane pressure value has become equal to a reference
value set to be lower by a certain value than a limit value
at which reduction of the trans-membrane pressure value by
25 the ozone water cleaning step becomes difficult, or has
31
exceeded the reference value;
after a concentration of the generated ozone water
has reached a predetermined target concentration, stopping
the filtration membrane step and starting the ozone water
5 cleaning step; and
ending the ozone water cleaning step when an
integrated value of the concentration of the ozone water and
an elapsed time of the ozone water cleaning step has become a
set value.
10
[12] A water treatment method having a membrane
filtration step of filtering treatment target water by a
filtration membrane to obtain treated water, and an ozone
water cleaning step of cleaning the filtration membrane by
15 ozone water, the water treatment method comprising:
calculating a trans-membrane pressure value from a
difference in pressure measured before and after the
filtration membrane;
starting generation of the ozone water when an
20 estimation value of a trans-membrane pressure value after a
certain time period and calculated on the basis of the
calculated trans-membrane pressure value has become equal to
a limit value at which reduction of the trans-membrane
pressure value by the ozone water cleaning step becomes
25 difficult, or has exceeded the limit value;
32
after a concentration of the generated ozone water
has reached a predetermined target concentration, stopping
the filtration membrane step and starting the ozone water
cleaning step; and
5 ending the ozone water cleaning step when an
integrated value of the concentration of the ozone water and
an elapsed time of the ozone water cleaning step has become a
set value.