Field
The present invention relates to a filter medium, a
process for producing the filter medium, a filtration
5 device, a method for operating the filtration device, and a
filtration system, and more specifically, relates to a
filter medium, a process for producing the filter medium, a
filtration device, a method for operating the filtration
device, and a filtration system, which are capable of
10 efficiently removing suspended substances in water to be
treated.
Background
Hitherto, fillers for water purifiers using fibrous
activated carbon have been proposed (see, for example,
15 Patent Literature 1). In this filler for water purifier, a
fibrous activated carbon is used having a specific surface
area of 1,300 m2/g or more as well as setting the
cumulative pore volume occupied by pores having a pore
radius of 0.9 nm or more and 1.6 nm or less to be in a
20 predetermined range. Accordingly, the filler for water
purifier is possible to efficiently remove trihalomethane
present in tap water at an extremely low concentration of
about several ppb.
Citation List
25 Patent Literature
Patent Literature 1: JP 3122205 B1
Summary
Technical Problem
Incidentally, in a desalination apparatus to
30 desalinate seawater by a reverse osmosis membrane
3
filtration device, a filtration device (pretreatment
device) such as a dual media filter (DMF) that filters
seawater to be supplied to the reverse osmosis membrane
filtration device to decrease the concentration of
5 suspended substances is used in order to prevent
contamination of the reverse osmosis membrane. In such a
filtration device, filtration of seawater causes clogging
of filter medium such as activated carbon and the pressure
loss increases, and it is thus required to periodically
10 conduct backwashing after operation for a predetermined
period to remove dirt from the filter medium.
However, general activated carbon to be used as a
filter medium in a conventional filtration device has a
specific surface area of 1000 m2/g or more and also a great
15 number of fine pores having a diameter of about several nm.
Thus there is no significant difference between the pore
size of activated carbon and the molecular size of
suspended substances such as organic substances contained
in seawater. For this reason, it is difficult to promptly
20 remove the suspended substances adsorbed to the activated
carbon in the conventional filter medium even if
backwashing is conducted, and the filtration device cannot
be necessarily efficiently operated in some cases.
The present invention has been achieved in view of
25 such circumstances, and an object thereof is to provide a
filter medium, a process for producing the filter medium, a
filtration device, a method for operating the filtration
device, and a filtration system, which are capable of
promptly regenerating the adsorption power by backwashing
30 and realizing efficient operation of the filtration device.
Solution to Problem
In a filter medium of this invention, a cumulative
4
pore volume of pores having a pore radius of 2 nm or less
is 25% or less with respect to a cumulative pore volume of
pores having a pore radius of 50 nm or less.
According to this configuration, the micropores having
a pore 5 radius of 0.8 nm or more and 2 nm or less and the
submicropores having a pore radius of 0.8 nm or less, which
make it difficult to desorb the adsorbed suspended
substances from the filter medium at the time of
backwashing, are decreased. It is thus possible to promptly
10 desorb the suspended substances from the filter medium at
the time of backwashing. This makes it possible to realize
a filter medium capable of more promptly regenerating the
adsorption power by backwashing and realizing more
efficient operation of a filtration device.
15 The filter medium of this invention is preferable to
comprises a carbon-based material By this configuration,
the filter medium has a lower specific gravity than the
filter sand that is generally used in the sand filter layer
of the filtration device and it is thus easy to provide a
20 filter layer on the sand filter layer. In addition, the
affinity of the filter medium for organic substances is
improved, and it is thus possible to efficiently remove the
suspended substances due to the organic substances in the
water to be treated.
25 In the filter medium of this invention, the carbonbased
material is preferable to contain activated carbon.
By this configuration, the filter medium has a lower
specific gravity than the filter sand that is generally
used in the sand filter layer of the filtration device and
30 it is thus easier to provide a filter layer on the sand
filter layer. In addition, the affinity of the filter
medium for organic substances is improved, and it is thus
5
possible to efficiently remove the suspended substances due
to the organic substances in the water to be treated.
A process for producing filter medium of this
invention is a process for producing the filter medium and
5 a carbon-based material is activated by water vapor.
A process for producing filter medium of this
invention is a process for producing the filter medium and
a carbon-based material is activated by a carbonic acid gas.
According to these processes, micropores having a pore
10 radius of 0.8 nm or more and 2 nm or less in the carbonbased
material are appropriately destroyed by an activation
treatment with water vapor or a carbonic acid gas. It is
thus possible to set the cumulative pore volume of pores
having a pore radius of 2 nm or less to be 25% or less with
15 respect to the cumulative pore volume of pores having a
pore radius of 50 nm or less. This makes it possible for
the method of manufacturing a filter medium to realize a
filter medium capable of promptly desorbing the suspended
substances from the filter medium at the time of
20 backwashing as well as efficiently adsorbing the suspended
substances in the water to be treated.
In the process for producing filter medium of this
invention, it is preferable that the activation treatment
is conducted with water vapor under a condition having a
25 surface temperature of the carbon-based material of 750C
or higher. By this method, the method of manufacturing a
filter medium can appropriately destroy micropores having a
pore radius of 2 nm or less in the carbon-based material,
and it is thus easy to set the cumulative pore volume of
30 pores having a pore radius of 2 nm or less to be 25% or
less with respect to the cumulative pore volume of pores
having a pore radius of 50 nm or less of the filter medium.
6
In the process for producing filter medium of this
invention, it is preferable that the activation treatment
is conducted with the carbonic acid gas under a condition
having a surface temperature of the carbon-based material
5 of 850C or higher. By this method, the method of
manufacturing a filter medium can appropriately destroy
micropores having a pore radius of 2 nm or less in the
carbon-based material, and it is thus easy to set the
cumulative pore volume of pores having a pore radius of 2
10 nm or less to be 25% or less with respect to the cumulative
pore volume of pores having a pore radius of 50 nm or less
of the filter medium.
In the process for producing filter medium of this
invention, it is preferable that the activation treatment
15 is conducted until a mass decrease of the carbon-based
material reaches 50% or more. By this method, the
destruction of micropores having a pore radius of 2 nm or
less in the carbon-based material is conducted in an
appropriate range, and it is thus easy to set the
20 cumulative pore volume of pores having a pore radius of 2
nm or less to be 25% or less with respect to the cumulative
pore volume of pores having a pore radius of 50 nm or less
of the filter medium.
A filtration device of this invention comprises the
25 filter medium or the filter medium obtained by the process
for producing the filter medium.
According to this filtration device, a filter medium
in which the cumulative pore volume of pores having a pore
radius of 2 nm or less is 25% or less with respect to the
30 cumulative pore volume of pores having a pore radius of 50
nm or less is equipped, and it is thus possible to
efficiently desorb the suspended substances retained in the
7
filter medium from the filter medium at the time of
backwashing as well as to efficiently remove the suspended
substances contained in the water to be treated. Hence,
the filtration device can realize a filtration device
5 capable of promptly regenerating the adsorption power by
backwashing and realizing efficient operation.
A method for operating filtration device of this
invention is a method for operating the filtration device,
and the method comprises: a filtering step of filtering
10 water to be treated through the filter medium to decrease
suspended substances in the water to be treated; and a
washing step of washing the filter medium by backwashing
when an amount of suspended substances in water to be
treated filtered through the filter medium reaches one
15 third of a total amount adsorbed to the filter medium.
According to this method for operating the filtration
device, it is possible to conduct backwashing under a
condition having a sufficient margin with respect to the
adsorption capacity of the filter medium and thus to
20 prevent the adsorption of the suspended substances in the
water to be treated to micropores having a pore radius of 2
nm or less from which it is difficult to desorb the
suspended substances in the filter medium. This makes it
possible to promptly desorb the suspended substances
25 adsorbed to the filter medium from the filter medium at the
time of backwashing, and it is thus possible to realize a
method of operating a filtration device capable of promptly
regenerating the adsorption power by backwashing and
realizing efficient operation.
30 A method for operating filtration device of this
invention is a method for operating the filtration device,
and the method comprises: a concentration of suspended
8
substances measuring step of measuring a first
concentration of suspended substances in the water to be
treated and measuring a second concentration of suspended
substances in filtered water, the filtered water is
5 obtained by filtering the water to be treated through the
filter medium; and a filter medium washing step of
conducting a calculation of a difference value between a
first time integrated value of the first concentration of
suspended substances measured and a second time integrated
10 value of the second concentration of suspended substances
measured and conducting a backwashing of the filter medium
when the difference value calculated is equal to or less
than a predetermined value.
According to this method for operating the filtration
15 device, the filter medium is backwashed when the
performance of the filter medium is deteriorated and the
second concentration of suspended substances in the
filtered water with respect to the first concentration of
suspended substances in the water to be treated is equal to
20 or higher than a predetermined value, and it is thus
possible to appropriately wash the filter medium according
to a change in the second concentration of suspended
substances in the filtered water. This makes it possible
to promptly desorb the suspended substances adsorbed to the
25 filter medium from the filter medium at the time of
backwashing, and it is thus possible to realize a method of
operating a filtration device capable of promptly
regenerating the adsorption power by backwashing and
realizing efficient operation.
30 A filtration system of this invention comprises: a
water to be treated filtering unit equipped with the
filtration device according to claim 9 that filters water
9
to be treated supplied through a water to be treated line
to obtain filtered water; and a salt enriching unit that
filters the filtered water through a separation membrane to
obtain permeated water and enriched water.
5 According to this filtration system, a filtration
device in which the micropores having a pore radius of 0.8
nm or more and 2 nm or less and the submicropores having a
pore radius of 0.8 nm or less, which make it difficult to
desorb the adsorbed suspended substances from the filter
10 medium at the time of backwashing are decreased is equipped
and it is thus possible to promptly desorb the suspended
substances from the filter medium at the time of
backwashing. This makes it possible to more promptly
regenerate the adsorption power of the filter medium of the
15 filtration device by backwashing and to realize more
efficient operation of the filtration system.
Advantageous Effects of Invention
According to the present invention, it is possible to
realize a filter medium, a process for producing filter
20 medium, a filtration device, a method for operating the
filtration device, and a filtration system, which are
capable of promptly regenerating the adsorption power by
backwashing and realizing efficient operation of the
filtration device.
25 Brief Description of Drawings
FIG. 1 is an outline diagram of a water treatment
apparatus according to an embodiment of the present
invention.
FIG. 2 is a schematic cross-sectional diagram
30 illustrating an example of a dual media filtration device
according to an embodiment of the present invention.
10
FIG. 3 is a schematic diagram of a general filter
medium using activated carbon.
FIG. 4 is a schematic diagram of a filter medium
according to an embodiment of the present invention.
5 FIG. 5A is a diagram illustrating the relationship
between the filtration time through a general filter medium
using activated carbon and the concentration of suspended
substances in filtered water.
FIG. 5B is a diagram illustrating the relationship
10 between the filtration time through a filter medium
according to an embodiment of the present invention and the
concentration of suspended substances in filtered water.
FIG. 6 is a diagram illustrating the relationship
between the cumulative pore volume and the pore radius of a
15 filter medium according to an embodiment of the present
invention.
FIG. 7 is a schematic cross-sectional diagram
illustrating another example of a dual media filtration
device according to an embodiment of the present invention.
20 FIG. 8 is a flow diagram of a method of operating a
filtration device according to an embodiment of the present
invention.
FIG. 9 is a schematic diagram of a filtration system
according to an embodiment of the present invention.
25 Description of Embodiments
Hereinafter, embodiments of the present invention will
be described in detail with reference to the accompanying
drawings. Incidentally, the present invention is not
limited to the following embodiments and can be implemented
30 with appropriate modifications. In addition, the
respective following embodiments can be implemented in
appropriate combination.
11
First, the outline of a water treatment apparatus
equipped with a filtration device according to an
embodiment of the present invention will be briefly
described. FIG. 1 is an outline diagram of a water
5 treatment apparatus according to an embodiment of the
present invention. As illustrated in FIG. 1, a water
treatment apparatus 1 according to the present embodiment
is a water treatment apparatus in which filtered water W2
obtained by filtering water to be treated W1 through a
10 water to be treated filtering unit 11 as a dual media
filtration device. In the water treatment apparatus 1, the
filtered water W2 obtained is filtrated through a reverse
osmosis membrane 12a of a reverse osmosis membrane
filtering unit 12 to obtain permeated water W3 and enriched
15 water W4. The water to be treated W1 is not particularly
limited, and for example, it is possible to use seawater,
river water, lake water, groundwater, municipal sewage,
brackish water, industrial water, industrial wastewater,
and water obtained by subjecting these water to treatments
20 such as aggregation, precipitation, filtration, adsorption,
and a biological treatment.
The water treatment apparatus 1 according to the
present embodiment is equipped with: the water to be
treated filtering unit 11 to which the water to be treated
25 W1 is supplied through a water to be treated line L1; the
reverse osmosis membrane filtering unit 12 provided to a
filtered water line L2 of the subsequent stage of the water
to be treated filtering unit 11; and an energy recovery
unit 13 provided to an enriched water line L3 of the
30 subsequent stage of the reverse osmosis membrane filtering
unit 12.
The water to be treated W1 is supplied through the
12
water to be treated line L1 to the water to be treated
filtering unit 11 by a liquid sending pump 14. The water
to be treated filtering unit 11 filters the water to be
treated W1 to obtain the filtered water W2 from which the
5 suspended substances in the water to be treated W1 is
removed. As the water to be treated filtering unit 11, for
example, it is possible to use a dual media filter (DMF) in
which a first filter layer 24 (not illustrated in FIG. 1,
see FIG. 2) and a second filter layer 25 (not illustrated
10 in FIG. 1, see FIG. 2) are layered. The first filter layer
24 contains a filter medium according to the present
embodiment, and the second filter layer 25 contains silica
sand having a relatively smaller particle size with
respective to the filter medium according to the present
15 embodiment.
In the water to be treated filtering unit 11, the pH
of the filtered water W2 is adjusted with an acid such as
H2SO4 or HCl so as to have a predetermined value (for
example, pH 7.2 or lower) if necessary. By adjusting the
20 pH as described above, it is possible to decrease the
malfunction such as contamination (fouling) of the reverse
osmosis membrane 12a of the reverse osmosis membrane
filtering unit 12 due to the suspended substances in the
water to be treated W1.
25 The pressurized filtered water W2 is supplied to the
reverse osmosis membrane filtering unit 12 through the
filtered water line L2 by a high pressure pump 15. The
reverse osmosis membrane filtering unit 12 is equipped with
the reverse osmosis membrane 12a which permeates the
30 filtered water W2 supplied from the water to be treated
filtering unit 11 to obtain the permeated water W3 and the
enriched water W4 in which salts and the like in the
13
filtered water W2 are enriched. The reverse osmosis
membrane filtering unit 12 discharges the permeated water
W3 through a permeated water line L4 as well as discharges
the enriched water W4 through the enriched water line L3.
5 A filter member such as a micro cartridge filter may
be further provided between the water to be treated
filtering unit 11 and the reverse osmosis membrane
filtering unit 12. By allowing the filtered water W2 to
pass through the filter member, it is possible to remove
10 fine particles which affect contamination of the reverse
osmosis membrane 12a of the reverse osmosis membrane
filtering unit 12.
The energy recovery unit 13 recovers the energy of the
high-pressure enriched water W4 pressurized by the high
15 pressure pump 15. The energy recovered by the energy
recovery unit 13 is used, for example, as the energy for
driving the high pressure pump 15 and the energy for
transducing the pressure of the filtered water W2 to a high
pressure. This makes it possible for the water treatment
20 apparatus 1 to improve the energy efficiency of the entire
water treatment apparatus 1.
As the energy recovery unit 13, for example, it is
possible to use a Pelton Wheel type energy recovery device,
a Turbochager type energy recovery device, a PX (Pressure
25 Exchanger) type energy recovery device, and a DWEER
(DualWorkEnergy Exchanger) type energy recovery device.
[0036] Next, the water to be treated filtering unit 11
according to the present embodiment will be described in
detail with reference to FIG. 2. FIG. 2 is a schematic
30 cross-sectional diagram of the water to be treated
filtering unit 11 according to the present embodiment. As
illustrated in FIG. 2, this water to be treated filtering
14
unit 11 is a gravity filtration device. This water to be
treated filtering unit 11 includes, for example, a
rectangular parallelepiped-shaped filter tank 21. A
perforated block 22 as a filter bed is provided at the
lower 5 portion of the filter tank 21. A ground layer 23 is
provided on the perforated block 22 by gravel covered in
layers. A first filter layer 24 is provided on the ground
layer 23 by sand covered in layers. A second filter layer
25 is provided on the first filter layer 24 by a filter
10 media covered in layers. The second filter layer 25 is
configured to include the filter medium according to the
present embodiment. This filter medium has a relatively
lower specific gravity than the sand constituting the first
filter layer 24, and the particle size of the filter medium
15 is relatively larger than the sand.
At the upper portion of the filter tank 21, a water to
be treated supply pipe 26 is provided above the second
filter layer 25. Seawater as the water to be treated W1 is
supplied into the filter tank 21 through the water to be
20 treated supply pipe 26. Incidentally, a flocculant such as
ferric chloride is added to this seawater. This water to
be treated supply pipe 26 is provided with a flow
regulating valve V1 which opens and closes the water to be
treated supply pipe 26 to adjust the flow rate of the water
25 to be treated W1. At the lower portion of the filter tank
21, a filtered water effluence pipe 27 is provided below
the perforated block 22. This filtered water effluence
pipe 27 is provided with a flow regulating valve V2 capable
of adjusting the flow rate of the filtered water W2 by
30 opening and closing the filtered water effluence pipe 27.
In addition, a washing water supply pipe 28 is provided
below the perforated block 22 at the lower portion of the
15
filter tank 21. This washing water supply pipe 28 is
provided with a liquid sending pump 29 which sends washing
water W5 into the filter tank 21.
In addition, a drainage gutter 30 that is
5 substantially U-shaped in cross-sectional view and extends
in a substantially horizontal direction is provided above
the second filter layer 25. This drainage gutter 30 is
supported by the filter tank 21 via a beam member (not
illustrated). Both ends having an aperture of the drainage
10 gutter 30 are connected to a drainage port (not
illustrated) formed on the wall of the filter tank 21. In
addition, the position of the upper surface in the vertical
direction of the drainage gutter 30 is positioned below the
upper end of the filter tank 21. A filter medium effluence
15 preventing net 31 which prevents effluence of the filter
medium is provided around the drainage gutter 30. This
filter medium effluence preventing net 31 is supported by
the filter tank 21 by a support member (not illustrated).
In this water to be treated filtering unit 11, the
20 water to be treated W1 supplied into the filter tank 21
through the water to be treated supply pipe 26 sequentially
passes through the second filter layer 25, the first filter
layer 24, the ground layer 23, and the perforated block 22
as a downward flow, so that the suspended substances in the
25 water to be treated W1 are adsorbed and removed by the
second filter layer 25 and the first filter layer 24 and
the filtrated water W2 is thus obtained. This filtered
water W2 is discharged out of the filter tank 21 through
the filtered water effluence pipe 27.
30 Moreover, after the operation for a predetermined
period, the washing water W5 is supplied into the filter
tank 21 through the washing water supply pipe 28 provided
16
at the lower portion of the filter tank 21 by the liquid
sending pump 29, and the first filter layer 24 and the
second filter layer 25 are backwashed. This washing water
W5 sequentially passes through the perforated block 22, the
5 ground layer 23, the first filter layer 24, and the second
filter layer 25 as an upward flow. By this, the suspended
substances adsorbed to the first filter layer 24 and the
second filter layer 25 are desorbed from the first filter
layer 24 and the second filter layer 25 and removed as
10 wastewater by the washing water W5, and the first filter
layer 24 and the second filter layer 25 are thus
regenerated. The wastewater containing the suspended
substances is discharged via the drainage gutter 30
installed at the upper portion of the filter tank 21.
15 Incidentally, the first filter layer 24 and the second
filter layer 25 are backwashed as it is judged that the
first filter layer 24 and the second filter layer 25 have
reached the adsorption equilibrium of the suspended
substances in a case in which the concentration of
20 suspended substances in the filtered water W2 reaches a
predetermined concentration or higher (for example, 2 mg/kg
as TOC (Total Organic Carbon)).
Next, the filter medium according to the present
embodiment will be described in detail. The filter medium
25 according to the present embodiment is one which
constitutes the second filter layer 25 described above, and
in which the cumulative pore volume of pores having a pore
radius of 2 nm or less is 25% or less with respect to the
cumulative pore volume of pores having a pore radius of 50
30 nm or less. Incidentally, in the present invention, the
pore radius and the pore volume are values measured by the
nitrogen adsorption method in conformity with JIS Z 8831-2:
17
2010 and JIS Z 8831-2: 2010.
Here, the filter medium will be described in detail
with reference to FIGS. 3 and 4. FIG. 3 is a schematic
diagram of a general filter medium using activated carbon,
5 and FIG. 4 is a schematic diagram of the filter medium
according to the present embodiment. As illustrated in FIG.
3, a macropore 101 having a pore radius of 50 nm or more is
formed on the surface of a general filter medium 100 using
activated carbon. In this macropore 101, a plurality of
10 mesopores 102 having a pore radius of 2 nm or more and 50
nm or less are formed. In the plurality of these mesopores
102, a large number of micropores 103 having a pore radius
of 0.8 nm or more and 2 nm or less are formed. In the
plurality of micropores 103, submicropores (not
15 illustrated) having a pore radius of 0.8 nm or less are
formed. In the filter medium 100, the micropores 103
accounts for 25% or more and 75% or less in the total pore
volume, and the magnitude of the specific surface area
becomes 1000 m2/g or more by this. Accordingly, the filter
20 medium 100 has an excellent adsorption capacity to the
suspended substances in the water to be treated W1.
However, the molecular radius of the macromolecule such as
a polysaccharide which is the suspended substances in the
water to be treated W1 is equivalent to the inner diameter
25 of the micropore 103. The suspended substances adsorbed to
the inside of the micropore 103 maintain a state of being
adsorbed to the filter medium 100 even if washing water
passes through at the time of backwashing of the filtration
device and are not easily desorbed from the filter medium
30 100 in some cases. Furthermore, the macromolecule adsorbed
in the pores deteriorates the adsorptivity of the filter
medium since it gradually elutes over a long period of time
18
in some cases.
On the other hand, as illustrated in FIG. 4, in a
filter medium 200 according to the present embodiment, a
part of the micropores 103 of the filter medium 200 is
5 destroyed by an activation treatment or the like. The
cumulative pore volume of pores having a pore radius of 2
nm or less is thus 25% or less with respect to the
cumulative pore volume of pores having a pore radius of 50
nm or less. This makes it possible to decrease the amount
10 of suspended substances adsorbed to the deep inside of the
micropore 103 while securing the adsorption capacity to the
suspended substances by the plurality of mesopores 102 and
the appropriate number of micropores 103. It is thus
possible to promptly desorb the suspended substances at the
15 time of backwashing in the filter medium 200.
Next, the relationship between the operation time of
the filtration device and the concentration of suspended
substances in the filtered water W2 will be described with
reference to FIGS. 5A and 5B. FIG. 5A is a diagram
20 illustrating the relationship between the filtration time
through a general filter medium using activated carbon and
the concentration of suspended substances in the filtered
water W2. FIG. 5B is a diagram illustrating the
relationship between the filtration time through the filter
25 medium according to the present embodiment and the
concentration of suspended substances in the filtered water
W2.
As illustrated in FIG. 5A, in the general filter
medium using activated carbon having a specific surface
30 area of 1000 m2/g or more, the cumulative pore volume of
pores having a pore radius of 2 nm or less exceeds 25% with
respect to the cumulative pore volume of pores having a
19
pore radius of 50 nm or less. For this reason, in the case
of using a general filter medium, the operation time t1
until the first backwashing of the filter medium 100 after
the start of operation is long, but the operation times t2
5 to t4 until the second backwashing to the fourth
backwashing of the filter medium 100 are greatly shortened.
It is considered that this result is because a relatively
long operation time t1 can be secured until the first
backwashing since the suspended substances are adsorbed to
10 a large number of micropores 103 inside the filter medium
100 until the first backwashing after the start of
operation. On the other hand, it is considered that this
result is because the suspended substances once adsorbed to
the micropore 103 are desorbed from the filter medium 100
15 only to a certain extent even by backwashing and a large
number of micropores 103 are clogged by the suspended
substances and the operation times t2 to t4 until the
second backwashing to the fourth backwashing are thus
shortened.
20 On the contrary, as illustrated in FIG. 5B, in the
filter medium 200 according to the present embodiment, the
operation time t1 until the first backwashing of the filter
medium 200 after the start of operation is shorter as
compared to the general filter medium 100 using activated
25 carbon. On the other hand, the operation times t2 to t4
until the second backwashing to the fourth backwashing of
the filter medium 200 are substantially constant to be the
same as the operation time t1, the total operation time t1
to t4 until the first backwashing to the fourth backwashing
30 is longer as compared to the case of the filter medium 100.
It is considered that this result is because the ratio of
the micropores 103 from which it is difficult to desorb the
20
adsorbed suspended substances is appropriately decreased
and the cumulative pore volume of pores having a pore
radius of 2 nm or less is 25% or less with respect to the
cumulative pore volume of pores having a pore radius of 50
5 nm or less in the filter medium 200 according to the
present embodiment. Thus the suspended substances adsorbed
to the filter medium 200 are efficiently desorbed by
backwashing and the filter medium 200 can be efficiently
regenerated.
10 As described above, according to the filter medium 200
of the present embodiment, the cumulative pore volume of
pores having a pore radius of 2 nm or less is 25% or less
with respect to the cumulative pore volume of pores having
a pore radius of 50 nm or less. Thus the pore radius of
15 pores of the filter medium 200 is appropriately greater
with respect to the molecular size of the suspended
substances such as organic substances contained in the
water to be treated W1. It is possible to appropriately
prevent the adsorption of suspended substances to the fine
20 pores of the filter medium 200 and to efficiently desorb
the suspended substances retained in the filter medium 200
from the filter medium 200 at the time of backwashing.
This makes it possible to promptly desorb the suspended
substances adsorbed to this filter medium 200 at the time
25 of backwashing without impairing the adsorption efficiency
to the suspended substances in the water to be treated W1,
and it is thus possible to regenerate the filter medium 200
in a short time and to efficiently operate the filtration
device.
30 The specific surface area of the filter medium 200
according to the present embodiment is preferably 100 m2/g
or more, since the adsorption capacity to the suspended
21
substances contained in the water to be treated W1 is
improved. This increases the time until the filter medium
200 breaks through as compared to a case in which the
specific surface area of the filter medium 200 is less than
5 100 m2/g, and thus it is possible to increase the operation
time until the backwashing and the operation efficiency of
the filtration device is improved. In addition, according
to the filter medium 200, the specific surface area is
preferably 150 m2/g or more and more preferably 200 m2/g or
10 more from the viewpoint of even further improving the
adsorption capacity to the suspended substances described
above. The specific surface area is preferably 800 m2/g or
less, more preferably 500 m2/g or less, and still more
preferably 400 m2/g or less from the viewpoint of even more
15 efficiently desorbing the suspended substances at the time
of backwashing. In consideration of the facts described
above, the specific surface area of the filter medium 200
is preferably 100 m2/g or more and 800 m2/g or less, more
preferably 150 m2/g or more and 500 m2/g or less, and still
20 more preferably 200 m2/g or more and 400 m2/g or less.
Next, the relationship between the cumulative pore
volume and the pore radius of the filter medium 200
measured by the method of JIS Z 8831-3: 2010 will be
described with reference to FIG. 6. Incidentally, the
25 cumulative pore volume is the cumulative volume of the
entire pores belonging to the filter medium 200 in a
measurable range. FIG. 6 is a diagram illustrating the
relationship between the cumulative pore volume and the
pore radius of the filter medium 200 according to the
30 present embodiment. Incidentally, in FIG. 6, the
horizontal axis indicates the pore radius (nm) of the
filter medium 200 and the vertical axis indicates the
22
cumulative pore volume (%) of the filter medium 200. As
illustrated in FIG. 6, in the present embodiment, the
specific surface area is set to 100 m2/g or more and 800
m2/g or less by appropriately removing the micropores 103
5 having a pore radius of 2 nm or less by an activation
treatment or the like. Thus the cumulative pore volume of
pores having a pore radius of 2 nm or less is smaller than
that of general activated carbon and can be set to be 25%
or less with respect to the cumulative pore volume of pores
10 having a pore radius of 50 nm or less. This decreases the
micropores 103 having a pore radius of 0.8 nm or more and 2
nm or less and the submicropores having a pore radius of
0.8 nm or less from which it is difficult to desorb the
adsorbed suspended substances from the filter medium at the
15 time of backwashing, and it is thus possible to promptly
desorb the suspended substances from the filter medium at
the time of backwashing. As a result, it is possible to
realize a filter medium capable of more promptly
regenerating the adsorption power by backwashing and
20 realizing more efficient operation of the filtration device.
In the filter medium according to the present
embodiment, the cumulative pore volume of pores having a
pore radius of 2 nm or less is preferably 25% or less, more
preferably 10% or less, and still more preferably 1% or
25 less with respect to the cumulative pore volume of pores
having a pore radius of 50 nm or less from the viewpoint of
even further improving the effect described above.
Here, the cumulative pore volume will be described.
In general, the saturated vapor pressure in the pores of
30 the filter medium decreases depending on the curvature of
the surface of the filter medium by the function of the
surface tension, and thus the adsorption capacity increases
23
as the specific surface area increases and the number of
curved surfaces increases. In addition, the saturated
vapor pressure P0
r in the pores having a pore radius r is
represented by the Kelvin equation of the following Formula
5 (1). In general, the adsorption capacity increases as p/p0
increases, and thus the adsorption capacity increases as p0
decreases.


)cos
2
ln( / ) ( 0 0 RTr
V
p P r m   Formula (1)
(In Formula (1), p0 represents the saturated vapor
10 pressure of the liquid plane surface. Vm represents the
surface molar volume of the liquid.  represents the
surface tension of the liquid. R represents the gas
constant. T represents the absolute temperature. 
represents the contact angle between the liquid and the
15 pore wall.)
The cumulative pore volume is determined from the pore
radius distribution. The pore radius distribution can be
determined by comparing the adsorption isotherms by the tplot
method or the s-plot method which conforms to JIS Z
20 8831-3: 2010. In these methods, the nitrogen adsorption
isotherm representing the relationship between the
adsorption capacity and the pressure is measured and
compared with the standard sample to determine the pore
radius distribution. Moreover, the adsorption capacity
25 increases by the presence of pores, and thus the pore
radius distribution is determined by determining the volume
of the pores from an increase in adsorption capacity
corresponding to the pore radius.
As the filter medium 200, various kinds of filter
30 media can be used in the range of achieving the effect of
the present invention. As the filter medium 200, for
24
example, it is possible to use various kinds of ceramics
such as alumina, various kinds of carbon-based materials
such as coal, charcoal, coal coke, petroleum coke, pitch
coke, activated carbon using these, and particulate
5 activated carbon obtained by granulating carbon black with
a thermosetting resin such as pitch/tar binder/phenol,
activated alumina, activated clay, silica gel, zeolite, and
the like.
In the present embodiment, the filter medium 200 is
10 preferably formed of at least one kind of a carbon-based
material or activated carbon and more preferably formed of
activated carbon. By this, the filter medium 200 has a
lower specific gravity than the filter sand used in the
first filter layer 24 of the water to be treated filtering
15 unit 11, and it is thus easy to provide the second filter
layer 25 containing the filter medium 200 on the first
filter layer 24. In addition, a carbon-based material and
activated carbon exhibit high affinity for organic
substances, and it is thus possible to efficiently remove
20 the suspended substances due to the organic substances in
the water to be treated W1.
Next, a process for producing the filter medium 200
according to the present embodiment will be described. In
the process for producing the filter medium 200 according
25 to the present embodiment, the filter medium 200 in which
the cumulative pore volume of pores having a pore radius of
2 nm or less is 25% or less with respect to the cumulative
pore volume of pores having a pore radius of 50 nm or less
is manufactured by activating the various kinds of carbon30
based materials described above with water vapor and/or a
carbonic acid gas. According to this process, it is
possible to decrease the specific surface area of the
25
carbon-based material by appropriately destroying the
micropores 103 having a pore radius of 2 nm or less in the
carbon-based material by an activation treatment with at
least either of water vapor or a carbonic acid gas. It is
5 thus possible to set the cumulative pore volume of pores
having a pore radius of 2 nm or less to be 25% or less with
respect to the cumulative pore volume of pores having a
pore radius of 50 nm or less. This makes it possible to
manufacture the filter medium 200 capable of promptly
10 desorbing the suspended substances from the filter medium
at the time of backwashing as well as efficiently adsorbing
suspended substances in the water to be treated W1.
[0056] As the condition for the activation treatment in
a case in which the activation treatment is conducted with
15 water vapor, a condition is preferable in which the surface
temperature of the carbon-based material is 750C or higher
and 850C or lower and the time is 12 hours or longer and
72 hours or shorter, that is longer than that for a general
activation treatment of activated carbon. In addition, in
20 a case in which the activation treatment is conducted with
a carbonic acid gas, a condition is preferable in which the
surface temperature of the carbon-based material is 850C
or higher and 950C or lower and the time is 12 hours or
longer and 72 hours or shorter, that is longer than that
25 for a general activation treatment of activated carbon By
appropriately destroying the micropores having a pore
radius of 2 nm or less in the carbon-based material by
activating the carbon-based material under such a condition,
it is possible to obtain the filter medium 200 in which the
30 cumulative pore volume of pores having a pore radius of 2
nm or less is 25% or less with respect to the cumulative
pore volume of pores having a pore radius of 50 nm or less.
26
In addition as the condition for the activation
treatment., it is preferable to conduct the activation
treatment until the mass decrease of the carbon-based
material caused by gasification and wear reaches 50% or
5 more under the condition of temperature and time described
above. By this, the destruction of the micropores 103
having a pore radius of 2 nm or less in the carbon-based
material is conducted in an appropriate range. It is thus
possible to easily obtain the filter medium 200 in which
10 the cumulative pore volume of pores having a pore radius of
2 nm or less is 25% or less with respect to the cumulative
pore volume of pores having a pore radius of 50 nm or less.
In addition, the mass decrease by the activation treatment
is more preferably 75% or more and still more preferably
15 80% or more from the viewpoint of even more easily
manufacturing the filter medium 200 in which the cumulative
pore volume of pores having a pore radius of 2 nm or less
is 25% or less with respect to the cumulative pore volume
of pores having a pore radius of 50 nm or less.
20 As described above, according to the filter medium 200
of the present embodiment, the cumulative pore volume of
pores having a pore radius of 2 nm or less is 25% or less
with respect to the cumulative pore volume of pores having
a pore radius of 50 nm or less. It is thus possible to
25 efficiently desorb the suspended substances retained in the
filter medium from the filter medium at the time of
backwashing as well as to efficiently remove the suspended
substances contained in the water to be treated W1. Hence,
it is possible to realize the filter medium 200 capable of
30 promptly regenerating the adsorption power by backwashing
and realizing efficient operation of the filtration device.
Moreover, by using this filter medium 200, it is possible
27
to efficiently operate the filtration device by only
applying the filter medium 200 without greatly changing the
structure of the filtration device main body.
Incidentally, in the embodiment described above, an
5 example in which the filter medium 200 according to the
present embodiment is applied to the water to be treated
filtering unit 11 has been described, but the present
invention is not limited to the water to be treated
filtering unit 11 and can be applied to various kinds of
10 filtration devices.
Next, a method of operating a filtration device
according to the present embodiment will be described. The
method of operating a filtration device according to the
present embodiment includes: a filtering step of filtering
15 the water to be treated through the filter medium to
decrease the suspended substances in the water to be
treated; and a washing step of backwashing the filter
medium when the amount of suspended substances in the water
to be treated filtered through the filter medium reaches
20 one third or more of the total amount adsorbed to the
filter medium. In other words, in the method of operating
a filtration device according to the present embodiment,
the total amount adsorbed to the filter medium with respect
to the concentration of suspended substances in the water
25 to be treated is adjusted so as to be three-fold or more
the integrated amount of suspended substances which pass
through the filter medium during the operation period
between the backwashing intervals of the filtration device.
Incidentally, in the method of operating a filtration
30 device according to the present embodiment, it is not
necessarily required to use the filter medium 200 according
to the embodiment described above as the filter medium, and
28
various kinds of filter media can be used.
According to this method of operating a filtration
device, it is possible to conduct backwashing under a
condition having a sufficient margin with respect to the
5 adsorption capacity of the filter medium and thus to
prevent excessive adsorption of the suspended substances
into pores of the filter medium. In addition, the
filtration device is operated in a range having a
sufficient margin in the adsorption capacity of the filter
10 medium, and it is thus possible to prevent permeation of
the suspended substances in the water to be treated through
the filtration device even if there are suspended
substances which are not desorbed from the inside of the
pores of the filter medium by backwashing. Furthermore,
15 there is a margin in the adsorption capacity of filter
medium and it is thus possible to prevent permeation of the
suspended substances in the water to be treated through the
filtration device even in a case in which it is not
possible to completely remove the suspended substances from
20 the filter medium by one time of backwashing. This makes
it possible to promptly desorb the suspended substances
adsorbed to the filter medium from the filter medium at the
time of backwashing, and it is thus possible to realize a
method of operating a filtration device capable of promptly
25 regenerating the adsorption power by backwashing and
realizing efficient operation.
In the method of operating a filtration device
according to the present embodiment, the total amount
adsorbed to the filter medium with respect to the
30 concentration of suspended substances in the water to be
treated is set to be preferably five-fold or more and still
more preferably 10—fold or more the integrated amount of
29
suspended substances which pass through the filter medium
during the operation period between the backwashing
intervals of the filtration device from the viewpoint of
even further improving the effect described above.
5 In addition, in the method of operating a dual media
filtration device according to the present embodiment, for
example, the kind and used amount of filter medium are
determined so that the following relational expression is
satisfied.
10 Amount adsorbed to filter medium per unit mass in
concentration of suspended substances in water to be
treated (mg/kg)  used amount (kg) of filter medium =
{concentration of suspended substances in water to be
treated (mg/kg) - concentration of suspended substances in
15 filtered water (mg/kg)}  operation time of filtration
device between backwashing treatments (h)  flow rate of
water to be treated permeating through filter medium (m3/h)
 1000  3 (or 5 or 10)
FIG. 7 is a diagram illustrating another example of
20 the filtration device according to the present embodiment.
As illustrated in FIG. 7, this filtration device 210 is
equipped with: a turbidity meter for water to be treated
(device for measuring concentration of suspended substances
in water to be treated) 211 that is provided to the water
25 to be treated supply pipe 26; a turbidity meter for
filtered water (device for measuring concentration of
suspended substances in filtered water) 212 that is
provided to the filtered water effluence pipe 27; and a
control unit 213 which calculates the amount of suspended
30 substances in the water to be treated W1 measured by the
turbidity meter for water to be treated 211 and the amount
of suspended substances in the filtered water W2 measured
30
by the turbidity meter for filtered water 212 and controls
the operation of the filtration device 210 based on the
result of calculation in addition to the configuration of
the filtration tank 21 illustrated in FIG. 2.
5 The turbidity meter for water to be treated 211 is
provided on the upstream side to the filter medium 200 in
the flow path of the water to be treated W1. The turbidity
meter for water to be treated 211 measures the
concentration of suspended substances in the water to be
10 treated W1 before being filtered through the filter medium
200. The turbidity meter for filtered water 212 is
provided on the downstream side to the filter medium 200 in
the flow path of the water to be treated W1. The turbidity
meter for filtered water 212 measures the concentration of
15 the filtered water W2 that is the water to be treated W1
after being filtered through the filter medium. The
turbidity meter for water to be treated 211 and the
turbidity meter for filtered water 212 are not particularly
limited as long as they can measure the concentration of
20 the water to be treated W1 or the filtered water W2.
The control unit 213 is realized, for example, by
utilizing a general purpose or dedicated computer such as a
CPU (Central Processing Unit), a ROM (Read Only Memory), or
a RAM (Random Access Memory) and a program operating on the
25 computer. The control unit 213 calculates the time
integrated value (cumulative value per predetermined time)
of the concentration of suspended substances in the water
to be treated W1 measured by the turbidity meter for water
to be treated 211. In addition, the control unit 213
30 calculates the time integrated value (cumulative value per
predetermined time) per predetermined time of the
concentration of suspended substances in the filtered water
31
W2 measured by the turbidity meter for filtered water 212.
The control unit 213 calculates a difference value between
the time integrated value per predetermined time of the
concentration of suspended substances in the water to be
5 treated W1 calculated and the time integrated value per
predetermined time of the concentration of suspended
substances in the filtered water W2 calculated. The
control unit 213 determines whether or not the difference
value calculated is equal to or less than a predetermined
10 threshold value. Furthermore, the control unit 213
continues the normal operation of the filtration device 210
in a case in which the difference value calculated is equal
to or less than the predetermined threshold value. In
addition, in a case in which the difference value
15 calculated exceeds the predetermined threshold value, the
control unit 213 closes the flow regulating valve V1 of the
water to be treated supply pipe 26 and the flow regulating
valve V2 of the filtered water effluence pipe 27 and then
supplies the washing water W5 into the filtration device
20 210 through the washing water supply pipe 28 by driving the
liquid sending pump 29 to conduct backwashing of the filter
medium 200. In addition, after backwashing of the
filtration device 210, the control unit 213 erases the time
integrated value per predetermined time of the
25 concentration of suspended substances in the water to be
treated W1 calculated and the time integrated value per
predetermined time of the concentration of suspended
substances in the filtered water W2 calculated. Thereafter,
the control unit 213 calculates the time integrated value
30 per predetermined time (integrated value) of the
concentration of suspended substances in the water to be
treated W1 measured by the turbidity meter for water to be
32
treated 211 and the time integrated value per predetermined
time (integrated value) of the concentration of suspended
substances in the filtered water W2 measured by the
turbidity meter for filtered water 212 again.
5 Next, the method for operating the filtration device
210 will be described in detail with reference to FIG. 8.
FIG. 8 is a flow diagram of the method for operating the
filtration device 210 according to the present embodiment.
As illustrated in FIG. 8, the method for operating the
10 filtration device 210 according to the present embodiment
includes: a concentration of suspended substances measuring
step of respectively measuring the first concentration of
suspended substances in the water to be treated W1 and the
second concentration of suspended substances in the
15 filtered water W2 obtained as the water to be treated W1 is
filtered through the filter medium; and a filter medium
washing step of conducting backwashing of the filter medium
based on the difference value between the first time
integrated value (cumulative value) of the first
20 concentration of suspended substances in the water to be
treated W1 measured and the second time integrated value
(cumulative value) of the second concentration of suspended
substances in the filtered water W2 measured.
In the concentration of suspended substances measuring
25 step, the turbidity meter for water to be treated 211
measures the first concentration of suspended substances in
the water to be treated W1 (step ST111). In addition, in
the concentration of suspended substances measuring step,
the turbidity meter for filtered water 212 measures the
30 second concentration of suspended substances in the
filtered water W2 (step ST112).
After the start of operation of the filtration device
33
210, in the amount of suspended substances evaluating step,
the control unit 213 calculates the first time integrated
value per predetermined time of the first concentration of
suspended substances in the water to be treated W1 measured
5 by the turbidity meter for water to be treated 211 (step
ST121). Next, the control unit 213 calculates the second
time integrated value per predetermined time of the second
concentration of suspended substances in the filtered water
W2 measured by the turbidity meter for filtered water 212
10 (step ST122). Subsequently, the control unit 213
calculates the difference value between the first time
integrated value per predetermined time of the first
concentration of suspended substances in the water to be
treated W1 calculated and the second time integrated value
15 per predetermined time of the second concentration of
suspended substances in the filtered water W2 calculated
(step ST123) and determines whether or not the difference
value calculated is equal to or less than a predetermined
threshold value (step ST124). Thereafter, the control unit
20 213 continues the normal operation of the filtration device
210 (step ST125) in a case in which the difference value
calculated is equal to or less than the predetermined
threshold value (step ST124: Yes). In addition, in a case
in which the difference value calculated exceeds the
25 predetermined threshold value (step ST124: No), the control
unit 213 closes the flow regulating valve V1 of the water
to be treated supply pipe 26 and the flow regulating valve
V2 of the filtered water effluence pipe 27 and then
supplies the washing water W5 into the filtration device
30 210 through the washing water supply pipe 28 by driving the
liquid sending pump 29 to conduct backwashing of the filter
medium 200 (step ST126). Next, after backwashing of the
34
filtration device 210, the control unit 213 erases the
first time integrated value per predetermined time of the
first concentration of suspended substances in the water to
be treated W1 calculated and the second time integrated
5 value per predetermined time of the second concentration of
suspended substances in the filtered water W2 calculated
(step ST127). Thereafter, the control unit 213 calculates
the first time integrated value per predetermined time of
the first concentration of suspended substances in the
10 water to be treated W1 measured by the turbidity meter for
water to be treated 211 and the second time integrated
value per predetermined time of the second concentration of
suspended substances in the filtered water W2 measured by
the turbidity meter for filtered water 212 again (steps
15 ST111, ST112, ST121, and ST122).
In addition, in the method of operating a filtration
device according to the present embodiment, the kind and
used amount of the filter medium are determined so that the
first concentration of suspended substances to be measured
20 by the turbidity meter for water to be treated 211 provided
on the upstream side of the filter medium and the second
concentration of suspended substances to be measured by the
turbidity meter for filtered water 212 provided on the
downstream side of the filter medium satisfy the following
25 relational expression.
Amount adsorbed to filter medium per unit mass in
first concentration of suspended substances in water to be
treated W1 (mg/kg)  used amount (kg) of filter medium =
{first time integrated value of first concentration of
30 suspended substances in water to be treated W1 (mg/kgh) -
second time integrated value of second concentration of
suspended substances in filtered water W2 (mg/kgh)}  flow
35
rate of water to be treated W1 permeating through filter
medium (m3/h)
As described above, according to the method for
operating the filtration device 210 according to the
5 present embodiment, it is possible to accurately ascertain
the amount of suspended substances adsorbed to the filter
medium based on the difference value between the first time
integrated value of the first concentration of suspended
substances to be measured by the turbidity meter for water
10 to be treated 211 provided on the upstream side of the
filter medium and the second time integrated value of the
second concentration of suspended substances to be measured
by the turbidity meter for filtered water 212 provided on
the downstream side of the filter medium. It is thus to
15 sufficiently set the operation time of the filtration
device 210 required until the backwashing. This makes it
possible for the method for operating the filtration device
210 to prevent the deterioration in performance of the
filtration device 210 due to poor washing of the suspended
20 substances adsorbed to the filter medium at the time of
backwashing caused in a case in which the operation time of
the filtration device 210 is too long. In addition, the
method for operating the filtration device 210 can also
prevent a decrease in the rate of operation of the
25 filtration device 210 due to an increase in the number of
backwashing caused in a case in which the operation time of
the filtration device 210 is too short.
Incidentally, in the embodiment described above, the
turbidity meter for water to be treated 211 and the
30 turbidity meter for filtered water 212 are used, but it is
also possible to use a concentration meter for organic
substances such as a TOC (total organic carbon) meter
36
instead of a turbidity meter. It is possible to operate
the filtration device 210 in the same manner as the above
by taking the concentration of suspended substances as the
concentration of organic substances in the case of using a
5 concentration meter for organic substances.
Next, the filtration system according to the present
embodiment will be described with reference to FIG. 9. FIG.
9 is a schematic diagram of a filtration system 300
according to the present embodiment. As illustrated in FIG.
10 9, the filtration system 300 according to the present
embodiment is equipped with: a filtration device 301 to
which a water to be treated line L10 is connected; and a
salt enriching unit 302 provided at the subsequent stage of
the filtration device 301. A filtered water line L11 is
15 provided between the filtration device 301 and the salt
enriching unit 302.
The water to be treated line L10 supplies the water to
be treated W1 of raw water such as seawater to the
filtration device 301. The filtration device 301 filters
20 the water to be treated W1 supplied through the water to be
treated line L10 to obtain the filtered water W2. In
addition, the filtration device 301 supplies the filtered
water W2 to the salt enriching unit 302 via the filtered
water line L11. The salt enriching unit 302 permeates the
25 filtered water W2 through a separation membrane 302a to
obtain the permeated water W3 in which the salts in the
filtered water W2 are removed and the enriched water W4 in
which the salts in the filtered water W2 are enriched. In
addition, the salt enriching unit 302 discharges the
30 enriched water W4 via the enriched water discharge line L13
as well as supplies the permeated water W3 to the various
kinds of devices (not illustrated) at the subsequent stages
37
via the permeated water line L12. The separation membrane
302a is not particularly limited as long as the permeated
water W3 and the enriched water W4 can be obtained from the
filtered water W2.
5 The filtration device 301 is equipped with a first
filter layer 301b and a second filter layer 301c layered in
a filtration device main body 301a. The first filter layer
301b is provided on a top portion 301d side of the
filtration device main body 301a and is configured to
10 include the filter medium 200 described above. The second
filter layer 301c is provided on a bottom portion 301e side
of the filtration device main body 301a and is configured
to include a particulate filter medium such as silica sand.
The inorganic impurities in the water to be treated W1 are
15 removed by these first filter layer 301b and second filter
layer 301c, and it is thus possible to measure and
ascertain the concentration of suspended substances in the
water to be treated W1 based on the organic substance-based
impurities by a water quality evaluating unit 303 to be
20 described later.
In addition, the filtration system 300 according to
the present embodiment is equipped with: the water quality
evaluating unit 303 which evaluates the quality of the
filtered water W2 flowing through the filtered water line
25 L11; a flocculant supply unit 304 which supplies a
flocculant 304a to the water to be treated line L10 via a
flocculant supply line L21; and a control unit 305 which
controls the amount of flocculant to be supplied from the
flocculant supply unit 304 based on the evaluation result
30 of water quality of the filtered water W2 by the water
quality evaluating unit 303.
The water quality evaluating unit 303 measures and
38
monitors the concentration of suspended substances such as
organic substances in the water to be treated W1. The
control unit 305 determines whether or not the
concentration of suspended substances in the water to be
5 treated W1 measured by the water quality evaluating unit
303 is equal to or higher than a predetermined threshold
value. Thereafter, the control unit 305 supplies the
flocculant 304a from the flocculant supply unit 304 to the
water to be treated line L10 by operating a chemical supply
10 pump 306 provided to the flocculant supply line L21 in a
case in which the concentration of suspended substances in
the water to be treated W1 is equal to or higher than the
predetermined threshold value. In addition, the control
unit 305 stops supply of the flocculant 304a from the
15 flocculant supply unit 304 to the water to be treated line
L10 by stopping the chemical supply pump 306 in a case in
which the concentration of suspended substances in the
water to be treated W1 is less than the predetermined
threshold value.
20 As described above, according to the filtration system
300 of the present embodiment, the filtration device 301 in
which the micropores having a pore radius of 0.8 nm or more
and 2 nm or less and the submicropores having a pore radius
of 0.8 nm or less, which make it difficult to desorb the
25 adsorbed suspended substances from the filter medium 200 at
the time of backwashing are decreased is equipped and it is
thus possible to promptly desorb the suspended substances
from the filter medium 200 at the time of backwashing.
This makes it possible to more promptly regenerate the
30 adsorption power of the filter medium of the filtration
device 310 by backwashing and to realize more efficient
operation of the filtration system.
39
Reference Signs List
1 WATER TREATMENT APPARATUS
11 DUAL MEDIA FILTRATION DEVICE
12 REVERSE OSMOSIS MEMBRANE FILTERING UNIT
5 12a REVERSE OSMOSIS MEMBRANE
13 ENERGY RECOVERY UNIT
14 PUMP
15 HIGH PRESSURE PUMP
21, 210, and 301 FILTRATION DEVICE
10 22 PERFORATED BLOCK
23 GROUND LAYER
24 FIRST FILTER LAYER
25 SECOND FILTER LAYER
26 WATER TO BE TREATED SUPPLY PIPE
15 27 FILTERED WATER EFFLUENCE PIPE
28 WASHING WATER SUPPLY PIPE
29 LIQUID SENDING PUMP
30 DRAINAGE GUTTER
31 FILTER MEDIUM EFFLUENCE PREVENTING NET
20 100 and 200 FILTER MEDIUM
101 MACROPORE
102 MESOPORE
103 MICROPORE
211 TURBIDITY METER FOR WATER TO BE TREATED (DEVICE

We Claim:
1. A filter medium, wherein a cumulative pore volume of
pores having a pore radius of 2 nm or less is 25% or
5 less with respect to a cumulative pore volume of pores
having a pore radius of 50 nm or less.
2. The filter medium according to claim 1, comprising a
carbon-based material.
10
3. The filter medium according to claim 2, wherein the
carbon-based material contains activated carbon.
4. A process for producing the filter medium according to
15 any one of claims 1 to 3, wherein a carbon-based
material is activated by water vapor.
5. A process for producing the filter medium according to
any one of claims 1 to 3, wherein a carbon-based
20 material is activated by a carbonic acid gas.
6. The process for producing the filter medium according
to claim 4, wherein the activation treatment is
conducted with water vapor under a condition having a
25 surface temperature of the carbon-based material of
750C or higher.
7. The process for producing the filter medium according
to claim 5, wherein the activation treatment is
30 conducted with the carbonic acid gas under a condition
having a surface temperature of the carbon-based
material of 850C or higher.
42
8. The process for producing the filter medium according
to any one of claims 4 to 7, wherein the activation
treatment is conducted until a mass decrease of the
5 carbon-based material reaches 50% or more.
9. A filtration device comprising the filter medium
according to any one of claims 1 to 3 or the filter
medium obtained by the process for producing the filter
10 medium according to any one of claims 4 to 8.
10. A method for operating the filtration device according
to claim 9, the method comprising:
a filtering step of filtering water to be treated
15 through the filter medium to decrease suspended
substances in the water to be treated; and
a washing step of washing the filter medium by
backwashing when an amount of suspended substances in
water to be treated filtered through the filter medium
20 reaches one third of a total amount adsorbed to the
filter medium.
11. A method for operating the filtration device according
to claim 9, the method comprising:
25 a concentration of suspended substances measuring
step of measuring a first concentration of suspended
substances in the water to be treated and measuring a
second concentration of suspended substances in
filtered water, the filtered water is obtained by
30 filtering the water to be treated through the filter
medium; and
a filter medium washing step of conducting a
43
calculation of a difference value between a first time
integrated value of the first concentration of
suspended substances measured and a second time
integrated value of the second concentration of
5 suspended substances measured and conducting a
backwashing of the filter medium when the difference
value calculated is equal to or less than a
predetermined value.
10 12. A filtration system comprising:
a water to be treated filtering unit equipped
with the filtration device according to claim 9 that
filters water to be treated supplied through a water to
be treated line to obtain filtered water; and
15 a salt enriching unit that filters the filtered
water through a separation membrane to obtain permeated
water and enriched water.