Field
The present invention relates to a water-quality
evaluation method, for example, when treatment target water
such as seawater is filtered.
5
Background
As a method for evaluating quality of a fine particle
or a turbidity component in seawater supplied to a seawater
desalination plant for performing a desalination treatment
10 of seawater using a reverse osmosis membrane device, a silt
density index (SDI) value defined in ASTM D4189 to evaluate
the contamination degree of seawater which is treatment
target water, a fouling index (FI) value defined in JIS K
3802, or the like is used.
15 In addition, as a method for evaluating quality of
seawater when seawater contains a water-soluble polymer
(for example, a neutral polysaccharide) in addition to a
fine particles or a turbidity component, a soluble fouling
factor (SFF) indicating a residual index of a water-soluble
20 polymer contained in treatment target water has been
proposed (refer to Patent Literature 1).
Citation List
Patent Literature
25 Patent Literature 1: Japanese Laid-open Patent
Publication No. 2012-213676 A
Summary
Technical Problem
30 However, in measurement of SFF used as an index of a
concentration of a water-soluble polymer such as a
polysaccharide, seawater is directly filtered. Therefore,
there is also an influence of a fine particle or a
3
turbidity component coexisting in seawater
disadvantageously.
A water-soluble polymer such as a polysaccharide
increases viscosity when being dissolved in seawater,
5 thereby increases time for passing through a filtration
membrane, and increases SFF. A fine particle or a turbidity
component coexisting in seawater is trapped by a filtration
membrane during a filtration treatment, causes clogging of
the filtration membrane, and thereby changes filtration
10 time, resulting in variation of a SFF value
disadvantageously.
Therefore, when a fine particle or a turbidity
component coexists in seawater, an SFF value varies, and
therefore emergence of a water-quality evaluation method
15 capable of measuring an SFF value influenced only by a
water-soluble polymer such as a polysaccharide by
eliminating an influence of the fine particle or the
turbidity component has been desired.
In view of the above problem, an object of the present
20 invention is to provide a water-quality evaluation method
capable of determining an SFF value influenced only by a
water-soluble polymer such as a polysaccharide by
eliminating an influence of a fine particle or a turbidity
component, for example, when treatment target water such as
25 seawater is evaluated.
Solution to Problem
A first invention of a present invention for solving
the above-described object is a water-quality evaluation
30 method of a treatment target water for evaluating waterquality
of treatment target water. The water-quality
evaluation method includes a fine particle removing step
for filtering the treatment target water through a first
4
filtration membrane, and collecting a fine particle or a
turbidity component contained in the treatment target water
to obtain filtered water, a clarified water filterability
measurement step for measuring filterability of clarified
5 water by causing the clarified water to pass through a
second filtration membrane different from the first
filtration membrane, a filtered water filterability
measurement step for measuring filterability of the
filtered water by filtering the filtered water through the
10 second filtration membrane used in the clarified water
filterability measurement step, and a contamination degree
evaluation step for evaluating the contamination degree of
the treatment target water based on the measured
filterability of the clarified water and the measured
15 filterability of the filtered water.
According to the present invention, a fine particle or
a turbidity component contained in treatment target water
is removed in advance, and then an index of the
contamination degree influenced only by a water-soluble
20 polymer can be measured by eliminating an influence of the
fine particle or the turbidity component.
A second invention is the water-quality evaluation
method in the first invention, in which when the clarified
water filterability measurement step and the filtered water
25 filterability measurement step are repeated a plurality of
times, the contamination degree of the treatment target
water is evaluated based on filterability of clarified
water measured in the last step and measured filterability
of filtered water.
30 According to the present invention, when the clarified
water filterability measurement step and the filtered water
filterability measurement step are repeated a plurality of
times, evaluation which has eliminated an influence of a
5
fine particle or a turbidity component as much as possible
can be performed by evaluating the contamination degree of
treatment target water based on filterability of clarified
water measured in the last step and filterability of
5 filtered water measured in the last step.
A third invention is the water-quality evaluation
method in the first or second invention, in which when the
clarified water filterability measurement step and the
filtered water filterability measurement step are repeated
10 a plurality of times, an evaluation value of the
contamination degree in each step is determined, an
evaluation value of the contamination degree previously
determined and an evaluation value of the contamination
degree determined this time are compared, and a case where
15 a difference between the compared evaluation values of the
contamination degrees is a predetermined value or less is
used as evaluation of the contamination degree.
According to the present invention, the clarified
water filterability measurement step and the filtered water
20 filterability measurement step are performed a plurality of
times, each of the contamination degrees is determined, and
a case where a difference in evaluation of the
contamination degree therebetween is equal to or smaller
than a predetermined value can be recognized as true
25 evaluation of the contamination degree.
A fourth invention is the water-quality evaluation
method in the second or third invention, in which when the
clarified water filterability measurement step and the
filtered water filterability measurement step are repeated
30 a plurality of times, the second filtration membrane is
changed each time.
According to the present invention, when a clarified
water filterability measurement step and a filtered water
6
filterability measurement step are repeated a plurality of
times, evaluation which has eliminated an influence of a
fine particle or a turbidity component as much as possible
can be performed by evaluating the contamination degree of
5 treatment target water based on filterability of clarified
water measured in the last step and filterability of
filtered water measured in the last step while the second
filtration membrane is changed each time to eliminate an
influence of a fine particle or a turbidity component.
10 A fifth invention is the water-quality evaluation
method in any one of the first to fourth inventions, in
which the fine particle removing step is performed a
plurality of times.
According to the present invention, a fine particle or
15 a turbidity component is removed repeatedly, and therefore
a collecting efficiency of a fine particle or a turbidity
component can be improved before the contamination degree
of treatment target water is evaluated.
A sixth invention is the water-quality evaluation
20 method in any one of the first to fifth inventions, in
which in the fine particle removing step, a fine particle
or a turbidity component is collected by a filtration
membrane having a larger opening than the second filtration
membrane, and then a fine particle or a turbidity component
25 is further collected by a first filtration membrane having
the same opening as the second filtration membrane.
According to the present invention, by removing a
relatively large fine particle or turbidity component
present in treatment target water in advance, clogging of a
30 filtration membrane can be suppressed when a fine particle
or a turbidity component for evaluation of the
contamination degree is removed subsequently, filtration
time can be reduced, and rapid measurement is possible.
7
A seventh invention is the water-quality evaluation
method in any one of the first to sixth inventions, in
which the treatment target water is supplied to a membrane
separation device with a separation membrane.
5 According to the present invention, it is possible to
accurately determine the contamination degree caused by a
water-soluble polymer of treatment target water supplied to
a membrane separation device with a separation membrane.
Advantageous Effects of Invention
10 According to the present invention, a fine particle or
a turbidity component contained in treatment target water
is removed in advance, and then an index of the
contamination degree influenced only by a water-soluble
polymer (for example, a polysaccharide derived from
15 microbial metabolism) can be measured by eliminating an
influence of the fine particle or the turbidity component.
Brief Description of Drawings
FIG. 1 is a schematic diagram of an evaluation process
20 using a filtration device for performing a water-quality
evaluation method according to Example 1.
FIG. 2 is a process diagram of the water-quality
evaluation method in Example 1.
FIG. 3 exemplifies a test result indicating that there
25 is no change in a concentration of an organic substance
before and after filtration using artificial seawater to
which a polysaccharide has been added simulatively.
FIG. 4 is a schematic diagram of an evaluation process
using a filtration device for performing a water-quality
30 evaluation method according to Example 2.
FIG. 5 is a schematic diagram of an evaluation process
using a filtration device for performing a water-quality
evaluation method according to Example 3.
8
FIG. 6 is a schematic diagram of an evaluation process
using a filtration device for performing a water-quality
evaluation method according to Example 4.
FIG. 7 is a process diagram of the water-quality
5 evaluation method in Example 4.
FIG. 8 is a process diagram of another water-quality
evaluation method in Example 4.
FIG. 9 is a schematic diagram of an evaluation process
using a filtration device for performing a water-quality
10 evaluation method according to Example 5.
FIG. 10 is a process diagram of the water-quality
evaluation method in Example 5.
FIG. 11 is a schematic diagram of a filtration
treatment system for performing a water treatment of
15 treatment target water according to Example 6 with a
membrane separation device.
FIG. 12 is a flow diagram of evaluation for evaluating
water-quality of treatment target water.
20 Description of Embodiments
Hereinafter, preferred Examples of the present
invention will be described in detail with reference to the
attached drawings. Incidentally, the present invention is
not limited by the Examples, but when there is a plurality
25 of Examples, combination of the Examples is also included
in the present invention.
Example 1
FIG. 1 is a schematic diagram of an evaluation process
using a filtration device for performing a water-quality
30 evaluation method according to Example 1.
The filtration device illustrated in FIG. 1 is used
for performing the water-quality evaluation method,
includes a filter 21 provided with filtration membranes (a
9
first filtration membrane 13A and a second filtration
membrane 13B) and a filtration tank 22 to receive a
filtrate, and performs reduced pressure filtration using a
pressure reducing device (not illustrated) (also in the
5 following description of the filtration device, a pressure
reducing device will be omitted similarly).
For example, each of the first filtration membrane 13A
and the second filtration membrane 13B uses a
microfiltration membrane (MF membrane) as a cellulose
10 filter, and preferably uses, for example, a membrane filter
having a diameter of 47 mm and a pore diameter of 0.45 μm.
For example, as a use amount of each of treatment
target water and clarified water (for example, ion exchange
water) used for filtration, 500 ml is used. Each of
15 treatment target water and clarified water is caused to
pass through a filtration membrane, and filtration time
therefor (T0, T1) is measured.
In water-quality evaluation, a reduced pressure
condition of a filtration device is under a reduced
20 pressure of -67 kPa (-500 mmHg). Time (second) required
for 500 ml of treatment target water to pass through a MF
membrane having a diameter of 47 mm (a real filtering
surface has a diameter of 35 mm) is measured, and is used
as measurement time of filterability.
25 For example, the treatment target water in the present
invention is raw water to be subjected to a water treatment
with a membrane separation device using a separation
membrane such as an ultrafiltration membrane (UF membrane),
a nanofiltration membrane (NF membrane), or a reverse
30 osmosis membrane (RO membrane). Examples thereof include
sea water, mine drainage, and cooling tower drainage. The
treatment target water in the present invention means water
containing at least a fine particle or a turbidity
10
component, or a water-soluble polymer. Incidentally, the
treatment target water may contain either a fine particle
or a turbidity component singly, or may contain both
thereof.
5 Here, the water-soluble polymer also includes a
polymer derived from metabolism of a microorganism or the
like, and examples thereof include a neutral
polysaccharide. The neutral polysaccharide has a molecular
weight of 10,000 or more, for example. However, the
10 neutral polysaccharide may have a molecular weight of more
than one million or ten million, for example. In addition,
a polymer component having a molecular weight of 10,000 or
less may be contained.
A water-quality evaluation method according to the
15 present Example using this filtration device will be
described with reference to FIG. 1. As illustrated in FIG.
1, the water-quality evaluation method according to the
present Example is a water-quality evaluation method of a
treatment target water for evaluating water-quality of
20 treatment target water 12 containing at least a fine
particle or turbidity component 11 and a water-soluble
polymer, and evaluates the contamination degree (T1/T0) of
the treatment target water 12 based on a fine particle
removing step for filtering the treatment target water 12
25 through a first filtration membrane 13A, and collecting the
fine particle or turbidity component 11 contained in the
treatment target water 12 to obtain filtered water 14, a
clarified water filterability measurement step for
measuring filterability (clarified water filtration time:
30 T0) of clarified water 15 by causing the clarified water 15
to pass through a (another new) second filtration membrane
13B different from the first filtration membrane 13A used
in the fine particle removing step, a filtered water
11
filterability measurement step for measuring filterability
(filtered water filtration time: T1) of the filtered water
14 by filtering the filtered water 14 through the second
filtration membrane 13B used in the clarified water
5 filterability measurement step, the measured filterability
(clarified water filtration time: T0) of the clarified
water 15, and the measured filterability (filtered water
filtration time: T1) of the filtered water 14.
Incidentally, the first filtration membrane 13A and the
10 second filtration membrane 13B collect both a fine
particles and a turbidity component when the treatment
target water 12 contains both the fine particle and the
turbidity component.
FIG. 2 is a process diagram of the water-quality
15 evaluation method according to the present Example.
As illustrated in FIG. 2, the water-quality evaluation
method includes a first step (S1) to a fourth step (S4).

A fine particle removing step in the first step (S1)
20 is a step for introducing the treatment target water 12
into the filter 21, filtering the treatment target water 12
through the first filtration membrane 13A disposed in the
filter 21, and collecting the fine particle or turbidity
component 11 contained in the treatment target water 12 to
25 obtain the filtered water 14. Here, the filtered water 14
after termination of the first step is stored separately.

A clarified water filterability measurement step in
the second step (S2) is a step for disposing the other new
30 second filtration membrane 13B different from the first
filtration membrane 13A used in the first step (S1) in the
filter 21, then causing the clarified water 15 to pass
through the filter 21, and measuring filterability of the
12
clarified water 15.
Filterability of the clarified water 15 is measured by
measuring clarified water filtration time (T0) required for
the clarified water 15 to pass through the second
5 filtration membrane 13B.

A filtered water filterability measurement step in the
third step (S3) is a step for performing a filtration
treatment by causing the filtered water 14 obtained in the
10 first step to pass through the filter 21 provided with the
second filtration membrane 13B left in a state used in the
clarified water filterability measurement step in the
second step (S2), and measuring filterability of the
filtered water 14. Incidentally, in FIG. 1, the filtered
15 water 14 is moved as indicated by a one-dot chain line, but
in an actual operation, the filtered water 14 stored
separately is introduced into the filter 21 (similar also
in a filtered water filterability measurement step in the
following Examples).
20 Filterability of the filtered water 14 is measured by
measuring filtered water filtration time (T1) required for
the filtered water 14 to pass through the second filtration
membrane 13B.

25 A contamination degree evaluation step in the fourth
step (S4) is a step for evaluating the contamination degree
(T1/T0) of the treatment target water 12 based on the
measured filterability (clarified water filtration time:
T0) of the clarified water 15 and the measured
30 filterability (filtered water filtration time: T1) of the
filtered water 14.
Here, the contamination degree is also referred to as
a soluble fouling factor (SFF) representing a residual
13
index of a water-soluble polymer contained in the treatment
target water 12 (refer to Patent Literature 1).
When evaluation of the contamination degree is
measured, the first filtration membrane 13A and the second
5 filtration membrane 13B are switched from each other, the
treatment target water 12 is sequentially caused to pass
through the first filtration membrane 13A and the second
filtration membrane 13B which are different filtration
membranes from each other, and the contamination degree is
10 measured based on the filtration time (T1) required for the
filtered water 14 to pass through the second filtration
membrane 13B.
According to the present Example, in the fine particle
removing step in the first step (S1), the fine particle or
15 turbidity component 11 in the treatment target water 12 is
collected by the first filtration membrane 13A, and the
filtered water 14 does not contain a fine particle or a
turbidity component having an influence on filterability.
On the other hand, the polysaccharide in the treatment
20 target water 12 is water-soluble, and therefore it has been
confirmed that the concentration thereof does not change
before and after passage in the filtration in the first
step (S1) (FIG. 3).
FIG. 3 exemplifies a test result indicating that there
25 is no change in a concentration of an organic substance
before and after filtration using artificial seawater to
which a polysaccharide has been added simulatively. Here,
as indicated in Table 1, as simulative treatment target
water in the present test example, water obtained by adding
30 1 mg/L guar gum as a polysaccharide to artificial seawater
containing sodium chloride as a main component was used.
At that time, the temperature was set to 25°C, and the pH
was set to 6.5. As a filtration membrane, a cellulose
14
filter MF membrane (membrane filter having a diameter of 47
mm and a pore diameter of 0.45 μm) was used, and a reduced
pressure condition was set to -67 kPa (-500 mmHg).
Table 1
Base Artificial seawater
Guar gum 1 mg/L
Temperature 25°C (adjusted)
pH 0.5
5
As illustrated in FIG. 3, change in total organic
carbon (TOC) was a minimum determination limit or less
before and after the filtration, and no significant change
was observed.
10 Therefore, by causing the filtered water 14 to pass
through the second filtration membrane 13B different from
the first filtration membrane 13A which has removed the
fine particle or turbidity component 11, in the first time,
the fine particle or turbidity component 11 which can be
15 collected by the first filtration membrane 13A is
collected, and in the second time, measurement for
evaluating the contamination degree is performed. An
influence of the fine particle or turbidity component 11 is
thereby eliminated, and filterability influenced only by a
20 polysaccharide is evaluated.
As a result, an index (SFF value) of the contamination
degree influenced only by a water-soluble polymer
(polysaccharide) can be measured by eliminating an
influence of the fine particle or turbidity component 11
25 contained in the treatment target water 12.
Incidentally, the fine particle or turbidity component
11 not collected by the first filtration membrane 13A has
little influence on filterability, and therefore in many
cases, there is no influence on evaluation of SFF even when
15
the fine particle or turbidity component 11 is not
collected in the filtration in the first step (S1).
As a result, according to the present Example, it is
possible to accurately determine the contamination degree
5 caused by a water-soluble polymer of treatment target water
supplied to a membrane separation device, for example, with
an RO membrane.
In the present Example, for example, when the
concentration of a fine particle or a turbidity component
10 in the treatment target water 12 is low, approximate
evaluation can be performed even when the same filtration
membrane is used without switching the first filtration
membrane 13A and the second filtration membrane 13B from
each other.
15 Example 2
FIG. 4 is a schematic diagram of an evaluation process
using a filtration device for performing a water-quality
evaluation method according to Example 2.
In the present Example, after a filtration operation
20 is further performed by repeating filtration using the
first filtration membrane 13A twice or more in the first
step (S1) in Example 1, in a similar manner to Example 1,
an operation of the second step (S2) is performed, then
filtration time of the second filtration membrane 13B is
25 measured in the third step (S3), and the contamination
degree of the treatment target water 12 is evaluated.
The filtration operation using the first filtration
membrane 13A in the first step (S1) is performed in order
to remove the fine particle or turbidity component 11.
30 Therefore, a collection efficiency of the fine particle or
turbidity component 11 is improved by causing the treatment
target water 12 to pass through the first filtration
membrane 13A twice or more before the contamination degree
16
of the treatment target water 12 is evaluated.
In the present Example, only an operation in the first
step is repeated, and therefore the switching number of the
filtration membrane is similar to Example 1. Therefore,
5 measurement can be performed in a short time efficiently
while an influence of the fine particle or turbidity
component 11 is eliminated as much as possible.
Example 3
FIG. 5 is a schematic diagram of an evaluation process
10 using a filtration device for performing a water-quality
evaluation method according to Example 3.
In the present Example, in Example 1, in the first
step (S1), removal of a fine particle or a turbidity
component is performed twice, that is, "fine particle
15 removal 1-1" and "fine particle removal 1-2" are performed.
A fine particle or a turbidity component is removed
using a first filtration membrane 13A1 having a large
opening in the first "fine particle removal 1-1", and using
a first filtration membrane 13A2 having the same opening
20 (pore diameter 0.45 μm) as used in the second step in the
second "fine particle removal 1-2". After a filtration
operation of the treatment target water 12 is performed
twice in the first step (S1), in a similar manner to
Example 1, an operation of the second step (S2) is
25 performed, then filtration time of the second filtration
membrane 13B is measured in the third step (S3), and the
contamination degree of the treatment target water is
evaluated.
Here, the first filtration membrane 13A1 having a
30 large opening (pore diameter) has a larger opening (a
larger pore diameter) than the second filtration membrane
13B used for evaluating the contamination degree. When a
membrane filter having a pore diameter of 0.45 μm is used
17
as the second filtration membrane 13B, the pore diameter of
the filtration membrane having a large opening is 0.45 μm
or more, for example from 0.5 μm to 3 μm, preferably from
0.6 μm to 2 μm, and more preferably from 0.7 μm to 1 μm.
5 Incidentally, a too large opening reduces the trapping
amount of the fine particle or turbidity component 11 which
can be trapped, and in contrast, a too small opening
generates a pressure loss to increase filtration time.
Therefore, the above range is preferable. Incidentally,
10 examples of the filtration membrane having a large opening
include a wire mesh and a mesh filter.
However, an optimal value of the pore diameter of the
filtration membrane having a large opening changes also
according to the particle diameter of a coexisting fine
15 particle or turbidity component, a particle diameter
distribution thereof, and the content thereof in seawater.
Therefore, the pore diameter of the first filtration
membrane 13A is suitably from 5 μm to 10 μm or more in some
cases. In addition, treatment target water may be caused
20 to pass through a plurality of filtration membranes having
different pore diameters sequentially in the descending
order of the pore diameter.
According to the present Example, by removing a
relatively large fine particle or turbidity component 11
25 present in the treatment target water 12 in advance,
clogging of a filtration membrane can be suppressed when
the fine particle or turbidity component 11 is removed in
the first step (S1), filtration time can be reduced in the
first step (S1), and therefore rapid measurement is
30 possible.
Example 4
FIG. 6 is a schematic diagram of an evaluation process
using a filtration device for performing a water-quality
18
evaluation method according to Example 4.
In the present Example, when the clarified water
filterability measurement step and the filtered water
filterability measurement step are repeated a plurality of
5 times using a different filtration membrane (second
filtration membrane 13B or third filtration membrane 13C)
each time in Example 1, the contamination degree (T21/T20)
of the treatment target water 12 is evaluated based on
filterability of the clarified water 15 (clarified water
10 filtration time: T20) measured in the last step (n-th time
(the second time in the present Example)) and measured
filterability of a second filtered water 14B (filtered
water filtration time: T21).
In the present Example, when there is an influence of
15 filterability due to presence of the fine particle or
turbidity component 11, the second filtration membrane 13B
and the third filtration membrane 13C are switched from
each other each time, and filtration is performed a
plurality of times (two times in the present Example).
20 Evaluation which has eliminated an influence of the fine
particle or turbidity component 11 as much as possible can
be performed by evaluating the contamination degree
(T21/T20) of the treatment target water 12 based on
filterability (clarified water filtration time: T20) of the
25 second clarified water 15 in the last step (the second time
in the present Example) and measured filterability
(filtered water filtration time: T21) of the second
filtered water 14B while an influence of the fine particle
or turbidity component 11 is eliminated a plurality of
30 times.
FIG. 7 is a process diagram of the water-quality
evaluation method according to the present Example.
As illustrated in FIG. 7, the water-quality evaluation
19
method includes a first step (S11) to a seventh step (S17).

A fine particle removing step in the first step (S11)
is a step for introducing the treatment target water 12
5 into the filter 21, filtering the treatment target water 12
through the first filtration membrane 13A disposed in the
filter 21, and collecting the fine particle or turbidity
component 11 contained in the treatment target water 12 to
obtain first filtered water 14A. Here, the first filtered
10 water 14A after termination of the first step is stored
separately.

A first clarified water filterability measurement step
in the second step (S12) is a step for disposing the other
15 new second filtration membrane 13B different from the first
filtration membrane 13A used in the first step (S11) in the
filter 21, then causing the clarified water 15 to pass
through the filter 21, and measuring filterability of the
clarified water 15.
20 Filterability of the clarified water 15 is measured by
measuring clarified water filtration time (T10) required
for the clarified water 15 to pass through the second
filtration membrane 13B.

25 A first filtered water filterability measurement step
in the third step (S13) is a step for performing a
filtration treatment by causing the first filtered water
14A obtained in the first step to pass through the filter
21 provided with the second filtration membrane 13B left in
30 a state used in the first clarified water filterability
measurement step (S12) in the second step (S12), and
measuring filterability of the first filtered water 14A.
Filterability of the first filtered water 14A is
20
measured by measuring filtered water filtration time (T11)
required for the first filtered water 14A to pass through
the second filtration membrane 13B.

5 A first contamination degree evaluation step in the
fourth step (S14) is a step for evaluating the
contamination degree (T11/T10) of the treatment target water
12 based on the measured filterability (clarified water
filtration time: T10) of the clarified water 15 and the
10 measured filterability (filtered water filtration time:
T11) of the first filtered water 14A.

A second clarified water filterability measurement
step in the fifth step (S15) is a step for disposing the
15 other new third filtration membrane 13C different from the
second filtration membrane 13B used in the fourth step
(S14) in the filter 21, then causing the clarified water 15
to pass through the filter 21, and measuring filterability
of the clarified water 15.
20 Filterability of the clarified water 15 is measured by
measuring clarified water filtration time (T20) required
for the clarified water 15 to pass through the third
filtration membrane 13C.

25 A second filtered water filterability measurement step
in the sixth step (S16) is a step for performing a
filtration treatment by causing the second filtered water
14B obtained in the third step (S13) to pass through the
filter 21 provided with the third filtration membrane 13C
30 left in a state used in the second clarified water
filterability measurement step in the fifth step (S15), and
measuring filterability of the second filtered water 14B.
Filterability of the second filtered water 14B is
21
measured by measuring filtered water filtration time (T21)
required for the second filtered water 14B to pass through
the third filtration membrane 13C.

5 A second contamination degree evaluation step in the
seventh step (S17) is a step for evaluating the
contamination degree (T21/T20) of the treatment target water
12 based on the measured filterability (clarified water
filtration time: T20) of the clarified water 15 measured in
10 the fifth step (S15) and the measured filterability
(filtered water filtration time: T21) of the second
filtered water 14B.
Incidentally, when there is no influence of a fine
particle or a turbidity component in treatment target
15 water, a first evaluation value (T11/T10) of the
contamination degree of the treatment target water 12 in
the fourth step (S14) and a second evaluation value
(T21/T20) of the contamination degree of the treatment
target water 12 in the seventh step (S17) are predetermined
20 values which are the same as or very close to each other.
However, when there is an influence of a fine particle or a
turbidity component in filtration, the influence of the
fine particle or the turbidity component is eliminated by
increasing the number of filtration.
25 Therefore, for example, evaluation which has
eliminated an influence of the fine particle or turbidity
component 11 as much as possible can be performed by
evaluating the contamination degree (T1×n/T0×n) of the
treatment target water 12 based on filterability (clarified
30 water filtration time: T0×n) of the clarified water 15 in
the last step (the n-th time in the present Example) and
measured filterability (filtered water filtration time:
T1×n) of the n-th filtered water 14n while an influence of
22
the fine particle or turbidity component 11 is eliminated
by switching the second filtration membrane 13B, the third
filtration membrane 13C, and a subsequent filtration
membrane from one another each time and performing
5 filtration a plurality of times.
FIG. 8 is a process diagram of another water-quality
evaluation method in Example 4.
In addition, as illustrated in FIG. 8, the first
evaluation value (T11/T10) of the contamination degree of
10 the treatment target water 12 in the fourth step (S14) and
the second evaluation value (T21/T20) of the contamination
degree of the treatment target water 12 in the seventh step
(S17) are compared, and when it is determined that a
difference therebetween is a predetermined reference value
15 or less (Yes), it is determined that these evaluation
values are true evaluation values which have eliminated an
influence of a fine particle or a turbidity component, and
an operation is terminated.
On the other hand, when it is determined that the
20 difference is more than the predetermined reference value
(No), it is determined that an influence of a fine particle
or a turbidity component still remains, and an operation is
continued.
Specifically, the following steps are further
25 performed.

A third clarified water filterability measurement step
in the eighth step (S18) is a step for disposing another
new fourth filtration membrane 13D different from the third
30 filtration membrane 13C used in the seventh step (S17) in
the filter 21, then causing the clarified water 15 to pass
through the filter 21, and measuring filterability of the
clarified water 15.
23
Filterability of the clarified water 15 is measured by
measuring clarified water filtration time (T30) required
for the clarified water 15 to pass through the fourth
filtration membrane 13D.
5
A third filtered water filterability measurement step
in the ninth step is a step for performing a filtration
treatment by causing third filtered water 14C obtained in
the sixth step (S16) to pass through the filter 21 provided
10 with the fourth filtration membrane 13D left in a state
used in the third clarified water filterability measurement
step in the eighth step (S18), and measuring filterability
of the third filtered water 14C.
Filterability of the third filtered water 14C is
15 measured by measuring filtered water filtration time (T31)
required for the third filtered water 14C to pass through
the fourth filtration membrane 13D.

A third contamination degree evaluation step in the
20 tenth step (S20) is a step for evaluating the contamination
degree (T31/T30) of the treatment target water 12 based on
the measured filterability (clarified water filtration
time: T30) of the clarified water 15 measured in the eighth
step (S18) and the measured filterability (filtered water
25 filtration time: T31) of the third filtered water 14C.
In addition, as illustrated in FIG. 8, the second
evaluation value (T21/T20) of the contamination degree in
the seventh step (S17) and the third evaluation value
(T31/T30) of the contamination degree in the tenth step
30 (S20) are compared, and when it is determined that a
difference therebetween is a predetermined reference value
or less (Yes), it is determined that these evaluation
values are true evaluation values which have eliminated an
24
influence of a fine particle or a turbidity component, and
an operation is terminated.
On the other hand, when it is determined that the
difference is more than the predetermined reference value
5 (No), it is determined that an influence of a fine particle
or a turbidity component still remains, and filtration
operations similar to the eighth to tenth steps are further
continued.
As described above, in the present Example, the
10 clarified water filterability measurement step and the
filtered water filterability measurement step are performed
repeatedly a plurality of times using different filtration
membranes, and an evaluation value of the contamination
degree in each step is determined. An evaluation value of
15 the contamination degree previously determined and an
evaluation value of the contamination degree determined
this time are compared, and when a difference between the
compared contamination degrees is a predetermined reference
value, these evaluation values can be true evaluation
20 values of the contamination degree.
Here, the predetermined value of the difference is 0.1
seconds at a minimum when a measurement error or the like
is considered. It is preferable to set a higher value.
In the present Example, at least two different
25 filtration membranes are used and are switched from one
another each time. However, the present invention is not
limiter thereto, but includes a case where filtration is
performed while a filtration membrane is not necessarily
changed completely each time, and is not changed in the
30 middle.
Example 5
FIG. 9 is a schematic diagram of an evaluation process
using a filtration device for performing a water-quality
25
evaluation method according to Example 5. FIG. 10 is a
process diagram of a water-quality evaluation method in
Example 5.
As illustrated in FIG. 9, the water-quality evaluation
5 method includes a first step (S21) to a ninth step (S29).

An initial clarified water filterability measurement
step in the first step (S21) in the present Example is a
step for causing the clarified water 15 to pass through the
10 filter 21 provided with the first filtration membrane 13A,
and measuring filterability of the clarified water 15.
Filterability of the clarified water 15 is measured by
measuring clarified water filtration time (T00) required
for the clarified water 15 to pass through the first
15 filtration membrane 13A.

An initial filtered water filterability measurement
step in the second step (S22) is a step for performing a
filtration treatment by causing the treatment target water
20 12 containing the fine particle or turbidity component 11
to pass through the filter 21 provided with the first
filtration membrane 13A left in a state used in an initial
clarified water filterability measurement step (S21) in the
first step (S21) to obtain the first filtered water 14A,
25 and measuring initial filterability of the treatment target
water 12.
In the present Example, in the second step (S22), a
fine particle removing step for removing the fine particle
or turbidity component 11 in the treatment target water 12
30 is performed.
Filterability of the treatment target water 12 is
measured by measuring treatment target water filtration
time (T01) required for the treatment target water 12 to
26
pass through the first filtration membrane 13A.

An initial contamination degree evaluation step in the
third step (S23) is a step for evaluating the contamination
5 degree (T01/T00) of the treatment target water 12 based on
the measured filterability (clarified water filtration
time: T00) of the clarified water 15 and the measured
filterability (treatment target water filtration time: T01)
of the treatment target water 12.
10
A first clarified water filterability measurement step
in the fourth step (S24) is a step for disposing the other
new second filtration membrane 13B different from the first
filtration membrane 13A used in the third step (S23) in the
15 filter 21, then causing the clarified water 15 to pass
through the filter 21, and measuring filterability of the
clarified water 15.
Filterability of the clarified water 15 is measured by
measuring clarified water filtration time (T10) required
20 for the clarified water 15 to pass through the second
filtration membrane 13B.

A first filtered water filterability measurement step
in the fifth step (S25) is a step for performing a
25 filtration treatment by causing the first filtered water
14A obtained in the second step (S22) to pass through the
filter 21 provided with the second filtration membrane 13B
left in a state used in the clarified water filterability
measurement step in the fourth step (S24), and measuring
30 filterability of the first filtered water 14A.
Filterability of the first filtered water 14A is
measured by measuring filtered water filtration time (T11)
required for the first filtered water 14A to pass through
27
the second filtration membrane 13B.

A first contamination degree evaluation step in the
sixth step (S26) is a step for evaluating the contamination
5 degree (T11/T10) of the treatment target water 12 based on
the measured filterability (clarified water filtration
time: T10) of the clarified water 15 measured in the fourth
step (S24) and the measured filterability (filtered water
filtration time: T11) of the first filtered water 14A.
10 Incidentally, when there is no influence of a fine
particle or a turbidity component in treatment target
water, an initial evaluation value (T01/T00) of the
contamination degree of the treatment target water 12 in
the third step (S23) and a first evaluation value (T11/T10)
15 of the contamination degree of the treatment target water
12 in the sixth step (S26) are predetermined values which
are the same as or very close to each other. When the
difference is a predetermined reference value (Yes), a
filtration step for removing a fine particle or a turbidity
20 component is terminated.
On the other hand, when it is determined that the
difference is more than the predetermined value (No), it is
determined that an influence of the fine particle or
turbidity component 11 still remains, and an operation is
25 continued.
Specifically, the following steps are further
performed.

A second clarified water filterability measurement
30 step in the seventh step (S27) is a step for disposing the
other new third filtration membrane 13C different from the
second filtration membrane 13B used in the sixth step (S26)
in the filter 21, then causing the clarified water 15 to
28
pass through the filter 21, and measuring filterability of
the clarified water 15.
Filterability of the clarified water 15 is measured by
measuring clarified water filtration time (T20) required
5 for the clarified water 15 to pass through the third
filtration membrane 13C.

A second filtered water filterability measurement step
in the eighth step (S28) is a step for performing a
10 filtration treatment by causing the second filtered water
14B obtained in the fifth step (S25) to pass through the
filter 21 provided with the third filtration membrane 13C
left in a state used in the second clarified water
filterability measurement step in the seventh step (S27),
15 and measuring filterability of the second filtered water
14B.
Filterability of the second filtered water 14B is
measured by measuring filtered water filtration time (T21)
required for the second filtered water 14B to pass through
20 the third filtration membrane 13C.

A second contamination degree evaluation step in the
ninth step (S29) is a step for evaluating the contamination
degree (T21/T20) of the treatment target water 12 based on
25 the measured filterability (clarified water filtration
time: T20) of the clarified water 15 measured in the
seventh step (S27) and the measured filterability (filtered
water filtration time: T21) of the second filtered water
14B.
30 In addition, as illustrated in FIG. 10, the first
evaluation value (T11/T10) of the contamination degree in
the sixth step (S26) and the second evaluation value
(T21/T20) of the contamination degree in the ninth step
29
(S29) are compared, and when it is determined that a
difference therebetween is a predetermined reference value
or less (Yes), it is determined that these evaluation
values are true evaluation values which have eliminated an
5 influence of a fine particle or a turbidity component, and
an operation is terminated.
On the other hand, when it is determined that the
difference is more than the predetermined reference value
(No), it is determined that an influence of a fine particle
10 or a turbidity component still remains, and filtration
operations similar to the seventh to ninth steps are
further continued.
In the present Example, by determining an initial
value before performing a treatment for removing a fine
15 particle in the treatment target water 12 containing the
fine particle or turbidity component 11 unlike Examples 3
and 4, the evaluation number of the contamination degree is
increased, and evaluation can be performed based on an
initial value of the treatment target water 12 as a value
20 to be compared.
As a result, when the treatment target water 12 having
a small influence of the fine particle or turbidity
component 11 is treated, the contamination degree can be
evaluated even in an early stage without exchange of a
25 filtration membrane a plurality of times.
Example 6
FIG 11 is a schematic diagram of a filtration
treatment system for performing a water treatment of
treatment target water according to Example 6 with a
30 membrane separation device. Hereinafter, in the present
Example, a desalination treatment system exemplifying a
desalination device provided with a separation membrane for
concentrating salt as a membrane separation device will be
30
described.
As illustrated in FIG. 11, a desalination treatment
system 100 according to the present Example includes a
treatment target water line L10 for supplying the treatment
5 target water 12 as raw water (for example, seawater), a
filtration device 102 for filtering impurities in the
treatment target water 12, disposed in the treatment target
water supply line L10, a salt concentration device 123
provided with a separation membrane 123a for separating the
10 filtered treatment target water 12 into permeate 121 and
concentrated water 122 having salt concentrated, disposed
on a downstream side of the filtration device 102, a waterquality
evaluation device 125 for monitoring presence of an
organic substance in the treatment target water 12,
15 disposed on a downstream side of the filtration device 102,
and a control device 133 for determining whether the
concentration of the organic substance in the treatment
target water 12 is a predetermined reference value
(threshold) or more using a result of monitoring by the
20 water-quality evaluation device 125, and adding (or further
adding) an aggregating agent 132 from an aggregating agent
tank 131 to the treatment target water line L10 for
supplying the treatment target water 12 when the
concentration of the organic substance is more than the
25 reference value (threshold). Incidentally, the aggregating
agent 132 is supplied from the aggregating agent tank 131
through an aggregating agent supply line L21 connected to
the treatment target water line L10 with a chemical agent
injection pump 134.
30 Here, when the organic substance monitoring device 125
in an outlet side of the filtration device 102 is disposed,
filtering layers 102a and 102b in the filtration device 102
trap inorganic impurities, and therefore a ratio of organic
31
impurities can be determined.
The filtration device 102 uses a carbon material such
as anthracite as the filtering layer 102a on an upper layer
side, and uses a granular filtering material such as silica
5 sand as the filtering layer 102b on a lower layer. The
filtering layers 102a and 102b are stacked in a filtration
device main body 102c. The treatment target water 12 is
introduced from a top 102d side, and is caused to pass
through the filtering layers 102a and 102b to trap a
10 suspension in the treatment target water 12.
The water-quality evaluation device 125 performs any
one of the water-quality evaluation methods in Examples 1
to 4 described above. When the control device 133
determines that a value obtained as a result of the water15
quality evaluation is more than a predetermined reference
value, the aggregating agent 132 is introduced from the
aggregating agent tank 131 to the treatment target water
supply line L10 through the aggregating agent supply line
L21 with the chemical agent injection pump 134, and the
20 aggregating agent 132 is supplied to the treatment target
water 12 to promote aggregation of aggregates.
FIG 12 is a flow diagram of evaluation for evaluating
water-quality of treatment target water.
As illustrated in FIG. 12, water-quality of the
25 treatment target water 12 is evaluated using the waterquality
evaluation device 125 (S31). As a result of the
evaluation, it is determined whether the concentration of
an organic substance in the treatment target water 12 is
more than a reference value (threshold) (S32). As a result
30 of the determination in step S32, when the concentration is
more than a reference value (threshold) (Yes), the control
device 133 makes determination, gives an instruction to the
chemical agent injection pump 134, and adds (or further
32
adds) the aggregating agent 132 from the aggregating agent
tank 131 to the treatment target water 12 (S33). On the
other hand, when the concentration is not more than the
reference value (No), the operation is continued (S34).
5 In this way, according to the present Example, as a
result of measurement using the water-quality evaluation
device 125, only when it is determined that the
concentration of an organic substance in the treatment
target water 12 is more than a predetermined reference
10 value, the control device 131 gives an instruction to the
chemical agent injection pump 134, and adds (or further
adds) the aggregating agent 132 to the treatment target
water 12. The use amount of the aggregating agent 132 when
the aggregating agent 132 is added (or further added) can
15 be reduced.
Thereafter, this water-quality evaluation is repeated
after an elapse of a predetermined time or as necessary.
Reference Signs List
20 11 FINE PARTICLE OR TURBIDITY COMPONENT
12 TREATMENT TARGET WATER
13A to 13C FIRST TO THIRD FILTRATION MEMBRANES
14A to 14C FIRST TO THIRD FILTERED WATER
15 CLARIFIED WATER
25 21 FILTER
22 FILTRATION TANK

We Claim:
1. A water-quality evaluation method of a treatment target
water for evaluating water-quality of treatment target
5 water, comprising:
a fine particle removing step for filtering the
treatment target water through a first filtration
membrane, and collecting a fine particle or a turbidity
component contained in the treatment target water to
10 obtain filtered water;
a clarified water filterability measurement step
for measuring filterability of clarified water by
causing the clarified water to pass through a second
filtration membrane different from the first filtration
15 membrane;
a filtered water filterability measurement step for
measuring filterability of the filtered water by
filtering the filtered water through the second
filtration membrane used in the clarified water
20 filterability measurement step; and
a contamination degree evaluation step for
evaluating the contamination degree of the treatment
target water based on the measured filterability of the
clarified water and the measured filterability of the
25 filtered water.
2. The water-quality evaluation method according to claim
1, wherein
when the clarified water filterability measurement
30 step and the filtered water filterability measurement
step are repeated a plurality of times, the
contamination degree of the treatment target water is
evaluated based on filterability of clarified water
34
measured in the last step and measured filterability of
filtered water.
3. The water-quality evaluation method according to claim
5 1 or 2, wherein
when the clarified water filterability measurement
step and the filtered water filterability measurement
step are repeated a plurality of times, an evaluation
value of the contamination degree in each step is
10 determined, an evaluation value of the contamination
degree previously determined and an evaluation value of
the contamination degree determined this time are
compared, and a case where a difference between the
compared evaluation values of the contamination degrees
15 is a predetermined value or less is used as evaluation
of the contamination degree.
4. The water-quality evaluation method according to claim
2 or 3, wherein
20 when the clarified water filterability measurement
step and the filtered water filterability measurement
step are repeated a plurality of times, the second
filtration membrane is changed each time.
25 5. The water-quality evaluation method according to any
one of claims 1 to 4, wherein the fine particle
removing step is performed a plurality of times.
6. The water-quality evaluation method according to any
30 one of claims 1 to 5, wherein
in the fine particle removing step, a fine particle
or a turbidity component is collected by a filtration
membrane having a larger opening than the second
35
filtration membrane, and then a fine particle or a
turbidity component is further collected by a first
filtration membrane having the same opening as the
second filtration membrane.
5
7. The water-quality evaluation method according to any
one of claims 1 to 6, wherein the treatment target
water is supplied to a membrane separation device with
a separation membrane.