{Technical Field}
The present invention relates to a regeneration method
for a filtration apparatus, a filtration apparatus, and a
water treatment apparatus. The present invention particularly
relates to a regeneration method for a filtration 5 apparatus, a
filtration apparatus, and a water treatment apparatus that are
used in a water treatment apparatus of a seawater desalination
plant, a water treatment plant, and the like.
{Background Art}
10 In recent years, as the seawater desalination market has
been expanding due to global water shortage, seawater
desalination plants are being constructed. As a technology for
seawater desalination, there is known a method for producing
fresh water by removing salt in seawater with a reverse
15 osmosis membrane (RO membrane). A filtration apparatus using
an RO membrane performs removal of suspended matters as a
pretreatment.
In order to remove suspended matters, in general, a
flocculant is continuously injected into the seawater to
20 flocculate the suspended matters. As the flocculant, iron salt
is used. This metal reacts with an alkaline component in the
water to generate metal hydroxide.
The metal hydroxide acts as a binder, and collision and
contact of suspended matters in the seawater cause
25 conglomeration, generating flocs. An injection amount of the
3
flocculant is increased and decreased in accordance with an
amount of suspended matters in the seawater. For example, when
iron salt is used as the flocculant, the iron salt is injected
so as to be 1 to10 ppm as iron in the seawater.
Other methods for separating suspended 5 matters include
filter filtration, centrifugation, and filtration using a
solid filter material. A method using a solid filter material
is advantageous in that it is inexpensive as compared with
filter filtration or centrifugation, and easy to maintain.
10 For the solid filter material, those sized to have a diameter
of 300 to 2500 μm are typically used. When suspended matters
to be removed are small, the flocculant is added to water to
be treated to form flocs thereby to increase the size of an
object to be removed, and then the filtration is performed.
15 Here again, the flocculant is continuously injected to the
water to be treated (see PTL 1).
Continuous injection of the flocculant causes growth of
the flocs, which makes it easier to capture the flocs with a
downstream filter. However, the filter itself must be washed
20 regularly to discharge flocs that have been deposited inside,
to outside of the system. The flocs deposited in the filter
are discharged from inside of the filter by backwashing.
{Citation List}
{Patent Literature}
25 {PTL 1} Japanese Unexamined Patent Application, Publication
4
No. 2000-202460
{Summary of Invention}
{Technical Problem}
Washing-waste water discharged from backwashing has a
high turbidity, and adversely affects the environment 5 nvironment if
discharged as it is. Therefore, the washing-waste water is
subject to solid-liquid separation with a dehydrator or the
like, and a remaining solid content is disposed as sludge
outside the system. Treatment of the sludge requires a sludge
10 treatment facility. The method of continuously injecting a
flocculant has a high environmental load.
When a large amount of a flocculant is used in filtration
using a solid filter material, flocs are captured at a filter
layer, and a differential pressure of the filter layer is
15 increased. An increase in the differential pressure makes it
difficult for the water to be treated to pass, deteriorating
removal efficiency. In order to reduce the differential
pressure, the filter layer must be backwashed. The filter
immediately after backwashing has a low removal rate (capture
20 rate) of suspended matters, and requires long time (e.g., five
hours or more) until the water quality of filtrate becomes
stable, causing deterioration of water quality of the
filtrate.
Although various mechanisms are considered as a
25 suspended-matter removal mechanism by filtration using a solid
5
filter material, for example, screening, removal by an
interception effect of sedimentation or the like in a stagnant
pool in a void or a gap, or adhesion/adsorption
(electrostatic, intermolecular force, or cohesion), they have
not been fully elucidated at present. Thus, there 5 are problems
in improvement of a removal rate, and in stabilization of load
fluctuation or water quality of filtrate at starting.
The present invention has been made in view of the above
circumstances, and it is an object of the present invention to
10 provide a regeneration method for a filtration apparatus, a
filtration apparatus, and a water treatment apparatus that
shorten a time required until stabilization of water quality
of filtrate after backwashing, and stably provide filtrate
satisfying a desired water quality standard.
15 {Solution to Problem}
The inventors, as a result of intensive study, have
obtained new knowledge that suspended matters of 0.1 to 10 μm
are not easily removed by a conventional filtration method
using a solid filter material. Based on this, the inventors
20 have invented a water treatment apparatus, a filtration
apparatus, and a regeneration method for a filtration
apparatus, for removing suspended matters of 0.1 to 10 μm.
The present invention provides a regeneration method for
a filtration apparatus that has a filter layer formed by
25 filling a solid filter material formed with a protrusion on a
6
surface, and passes water to be treated containing suspended
matters through the filter layer to perform filtration of the
suspended matters. The regeneration method for a filtration
apparatus includes a step of backwashing the filter layer by
passing washing liquid through the filter layer in 5 a direction
opposite to a passing direction of the water to be treated
such that the protrusion is retained on a surface of the solid
filter material.
The filter layer formed by filling the solid filter
10 material formed with the protrusion on the surface causes a
microscopic change in a flow of the water to be treated with
the protrusion, to capture suspended matters having a size of
0.1 μm or more to 10 μm or less. This makes it possible to
improve water quality of filtrate even when the water to be
15 treated includes many suspended matters having a size of 0.1
μm or more to 10 μm or less. A fluctuation of water quality of
the water to be treated is allowed, and the water quality of
the filtrate can be stabilized.
When the protrusion is formed on the surface of the solid
20 filter material by a protrusion element, the protrusion can be
stably added in a short time. The filter layer formed by
filling the solid filter material added with the protrusion
can stably remove (capture) suspended matters at a high
removal rate (capture rate) from an initial stage of the step
25 of removing suspended matters from the water to be treated.
7
This can shorten a starting time of the filtration apparatus
as compared with a conventional one.
Washing the filter layer while retaining the protrusion
on the surface of the solid filter material enables
regeneration of the filter layer capable 5 of capturing
suspended matters with the protrusion, even after backwashing.
This can provide filtrate with desired water quality after
backwashing. It is not necessary to retain 100% of the
protrusion, and it is sufficient to retain the protrusion to
10 an extent allowing filtrate with desired water quality to be
obtained after backwashing.
In one aspect of the invention above, in the step of
backwashing the filter layer, it is preferable to control a
passing speed of the washing liquid so as to suppress a
15 developing rate of the solid filter material to retain the
protrusion on the surface of the solid filter material.
By suppressing the developing rate, movement of the solid
filter material can be restrained such that the protrusion is
not stripped off, and the protrusion can be retained on the
20 surface of the solid filter material.
In one aspect of the invention above, the washing liquid
is passed through the filter layer without a step of air
washing that backwashes the filter layer by introducing air.
Not performing the air washing that washes the filter
25 layer by introducing air enables washing with the movement of
8
the solid filter material restrained. This allows the
protrusion to be retained on the surface of the solid filter
material.
In one aspect of the invention above, in the step of
backwashing the filter layer, a developing rate of 5 the filter
layer is obtained, and the developing rate of the filter layer
is made to be more than 0% to less than 30%, preferably more
than 0% to 5% or less.
Liquid washing at the developing rate of 30% or less
10 allows the protrusion to be retained on the surface of the
solid filter material, while providing a backwashing effect.
A filter layer subjected to liquid washing at the developing
rate of 5% or less can provide filtrate with water quality of
a value equal or close to that before the backwashing, from
15 immediately after the backwashing.
In one aspect of the invention above, it is preferable to
include a step of collecting backwash filtrate generated by
the backwashing, and a step of passing the backwash filtrate
through the filter layer toward a passing direction of the
20 water to be treated, and reforming a protrusion on the surface
of the solid filter material.
The backwash filtrate contains suspended matters that
have been stripped off from the solid filter material by the
backwashing, or a protrusion element and suspended matters. A
25 suspended-matter concentration of the backwash filtrate is
9
higher than a suspended-matter concentration of water to be
treated. Collecting the backwash filtrate to pass thorough the
filter layer allows a protrusion to be reformed. This can
shorten a time required until stabilization of water quality
of filtrate after backwashing. Since suspended matters, or 5 a
protrusion element and suspended matters are collected to be
reused, an amount of the protrusion element to be newly used
can be reduced, enabling suppression of treatment cost.
The present invention provides a regeneration method for
10 a filtration apparatus that has a filter layer formed by
filling a solid filter material formed with a protrusion on a
surface, and passes water to be treated containing suspended
matters through the filter layer to perform filtration of the
suspended matters. The regeneration method for a filtration
15 apparatus includes the steps of backwashing the filter layer
by passing washing liquid through the filter layer in a
direction opposite to a passing direction of the water to be
treated; collecting backwash filtrate generated by the
backwashing; and passing the backwash filtrate through the
20 filter layer toward the passing direction of the water to be
treated, and reforming a protrusion to a surface of the solid
filter material.
In the invention above, the washing liquid is passed
through the solid filter material, thereby a filtering part is
25 washed, and the protrusion added to the surface of the solid
10
filter material is stripped off. The backwash filtrate
contains suspended matters that have been stripped off from
the solid filter material by the backwashing, or a protrusion
element and suspended matters. Collecting the backwash
filtrate to pass thorough the filter layer allows 5 a protrusion
to be reformed. This can shorten a time required until
stabilization of water quality of filtrate after backwashing.
Since a protrusion element, or a protrusion element and
suspended matters are collected to be reused, an amount of the
10 protrusion element to be newly used can be reduced, enabling
suppression of treatment cost.
In one aspect of the invention above, it is preferable to
include the steps of adding a protrusion to the surface of the
solid filter material by feeding a protrusion element to the
15 filter layer toward a passing direction of the water to be
treated during passing of the water to be treated; and after
feeding of the protrusion element in the step of adding a
protrusion, determining whether or not a protrusion satisfying
a preset standard has been added to the surface of the solid
20 filter material, and when it is determined that the protrusion
has been added, reducing a feeding amount of the protrusion
element as compared with when adding the protrusion.
When the protrusion is stripped off due to the
backwashing or the passing of the water to be treated, a
25 removal rate of suspended matters at the filter layer is
11
lowered. Additionally, when an amount of suspended matters in
the water to be treated is increased during the passing, the
removal rate of suspended matters at the filter layer is also
lowered. According to one aspect of the invention above,
feeding the protrusion element to the filter layer 5 causes a
protrusion to be quickly added to the surface of the solid
filter material and the filter layer to be regenerated. In the
regenerated filter layer, a microscopic change is caused in a
flow of the water to be treated by the protrusion, allowing
10 suspended matters having a size of 0.1 μm or more to 10 μm or
less to be captured. This realizes the filter layer capable
of improving water quality of filtrate even when the water to
be treated includes many suspended matters having a size of
0.1 μm or more to 10 μm or less.
15 In one aspect of the invention above, a step of measuring
a differential pressure between a first side of the filter
layer and a second side of the filter layer may be included,
to feed the protrusion element within a range where the
measured differential pressure is less than a predetermined
20 value, in the step of adding the protrusion.
Excessively forming the protrusion to narrow a passage of
water to be treated allows an interception effect to be
enhanced, as with when a solid filter material with a small
diameter is used. However, according to one aspect of the
25 invention above, the filter layer is regenerated to be capable
12
of capturing suspended matters having a size of 0.1 μm or more
to 10 μm or less with a protrusion, without narrowing of the
passage to an extent allowing the enhancement of the
interception effect. Keeping the differential pressure in the
filter layer, which is generated by adding of the 5 e protrusion,
at less than the predetermined value, enables a lower initial
differential pressure, and a longer backwashing interval.
In one aspect of the invention above, there may be
included a step of directly or indirectly measuring an amount
10 of a protrusion element contained in filtrate that has come
out from the filter layer in the step of adding the
protrusion, and it may be determined that the protrusion has
been added to the surface of the solid filter material when
the measured amount of the protrusion element becomes equal to
15 or less than a preset threshold value.
When the protrusion element is fed to the filter layer,
the protrusion element adheres to the surface of the solid
filter material to form a protrusion. In the step of adding
the projection, a decrease in an amount of the protrusion
20 element contained in the filtrate serves as an index
indicating that the protrusion element has adhered to the
surface of the solid filter material. Thus, according to the
aspect described above, it is possible to add a protrusion
required to capture suspended matters having a size of 0.1 μm
25 or more to 10 μm or less.
13
In one aspect of the invention above, a total feeding
amount of the protrusion element to the filter layer in the
step of adding the protrusion may be counted, and it may be
determined that the protrusion has been added to the surface
of the solid filter material when the counted 5 total feeding
amount reaches a preset threshold value.
Presetting a total feeding amount of the protrusion
element to the filter layer allows desired protrusion to be
easily added.
10 In one aspect of the invention above, there is included a
step of passing the water to be treated through the filter
layer and inspecting water quality of the filtrate that has
come out from the filter layer. When an inspection value of
the filtrate exceeds a preset threshold value, it is
15 determined that the protrusion satisfying a preset standard
has not been added to the surface of the solid filter
material, and the step of adding the protrusion is performed.
When the inspection value of the filtrate is equal to or less
than the preset threshold value, it is determined that the
20 protrusion satisfying the preset standard has been added to
the surface of the solid filter material, and the feeding
amount of the protrusion element is reduced as compared with
when adding the protrusion,.
When the protrusion is stripped off, the stripped
25 protrusion also becomes a suspended matter, deteriorating
14
water quality. Additionally, when the protrusion is stripped
off, a removal rate of the suspended matters in the filter
layer is also lowered, deteriorating water quality of the
filtrate. According to the aspect described above, since the
protrusion is added (regenerated) in accordance with the 5 water
quality of the filtrate, the water quality of the filtrate can
be more stable.
The present invention provides a filtration apparatus
including a filter layer formed by filling a solid filter
10 material formed with a protrusion on a surface; a washingliquid
feeding part that passes washing liquid through the
filter layer in a direction opposite to a passing direction of
the water to be treated to perform backwashing; and a
backwashing control part that controls a passing speed of the
15 washing liquid so as to restrain movement of the solid filter
material to retain the protrusion on the surface of the solid
filter material.
In one aspect of the invention above, the backwashing
control part preferably obtains a developing rate of the
20 filter layer, and controls the passing speed of the washing
liquid such that the developing rate of the filter layer
becomes more than 0% to less than 30%, preferably more than 0%
to 5% or less.
In one aspect of the invention above, it is preferable to
25 include a collecting part that collects backwash filtrate
15
generated by the backwashing, and a protrusion-reforming part
that passes the collected backwash filtrate through the filter
layer toward a passing direction of the water to be treated,
and reforms the protrusion on the surface of the solid filter
5 material.
The present invention provides a filtration apparatus
including a filter layer formed by filling a solid filter
material formed with a protrusion on a surface; a washingliquid
feeding part that passes washing liquid through the
10 filter layer in a direction opposite to a passing direction of
the water to be treated to perform backwashing; a collecting
part that collects backwash filtrate generated by the
backwashing; and a protrusion-reforming part that passes the
collected backwash filtrate through the filter layer toward a
15 passing direction of the water to be treated, and reforms the
protrusion on the surface of the solid filter material.
The present invention provides a water treatment
apparatus including a filtration apparatus described above; a
water-to-be-treated feeding part that feeds water to be
20 treated to a first side of the filter layer to pass the water
to be treated through the filter layer; a protrusion-element
feeding part that feeds a protrusion element to the first side
of the filter layer; a determination part that, based on a
preset standard, determines whether or not a protrusion has
25 been added to a surface of the solid filter material; and a
16
protrusion-forming control part that, when the determination
part determines that the protrusion has been added, controls
the protrusion-element feeding part to reduce a feeding amount
of the protrusion element as compared with when it is
5 determined that the protrusion has not been added.
{Advantageous Effects of Invention}
A regeneration method for a filtration apparatus, a
filtration apparatus, and a water treatment apparatus
according to the present invention shorten a time required
10 until stabilization of water quality of filtrate after
backwashing, and stably provide filtrate satisfying a desired
water quality standard. Moreover, according to the present
invention, feeding a protrusion element enables restoration
(regeneration) of removal performance without an increase in a
15 differential pressure.
{Brief Description of Drawings}
Fig. 1 is a schematic block diagram of a water treatment
apparatus according to a first embodiment.
Fig. 2 is a schematic view explaining a biofilm.
20 Fig. 3 is a schematic block diagram of a water treatment
apparatus according to Modified Example 1.
Fig. 4 is a schematic block diagram of a water treatment
apparatus according to Modified Example 2.
Fig. 5 is a schematic view explaining a passage width d0.
17
Fig. 6 is a graph showing a simulation result in Study 1.
Fig. 7 is a schematic view explaining a flow of water to
be treated.
Fig. 8 is a view showing a simulation result in Study 2.
Fig. 5 9 is a view showing a simulation result in Study 2.
Fig. 10 is a view showing a simulation result in Study 2.
Fig. 11 is a graph showing a simulation result in Study 3.
Fig. 12 is a graph showing a measurement result of a
differential pressure of a filter layer in Study 4.
10 Fig. 13 is a graph showing a measurement result of an SDI
of Tests A and B in Study 4.
Fig. 14 is a graph showing a measurement result of a
differential pressure of a filtering part (filter layer) in
Study 5.
15 Fig. 15 is a graph showing a measurement result of an SDI
of filtrate that has come out from the filtering part (filter
layer) in Study 5.
Fig. 16 is a graph showing a measurement result of
differential pressures of a coarse-particle separation part
20 and a filtering part (filter layer) in Study 6.
Fig. 17 is a graph showing a measurement result of an SDI
of filtrate that has come out from the filtering part (filter
layer) in Studies 6, 7, and 8.
Fig. 18 is a graph showing a measurement result of
25 differential pressures of a coarse-particle separation part
18
and a filtering part (filter layer) in Study 7.
Fig. 19 is a graph showing a measurement result of
differential pressures of a coarse-particle separation part
and a filtering part (filter layer) in Study 8.
Fig. 20 is a graph showing a calculation result 5 of a
relation between a washing speed and a developing rate in
Study 9.
Fig. 21 is a graph showing a relation between a washing
speed and a differential pressure of Test A in Study 9.
10 Fig. 22 is a graph showing a relation between a washing
speed and a differential pressure of Test B in Study 9.
Fig. 23 is a graph showing a relation between a washing
speed and an SDI immediately before next washing in Study 9.
Fig. 24 is a graph showing a relation between a washing
15 speed and an SDI 30 minutes after washing in Study 9.
{Description of Embodiments}
{First Embodiment}
Fig. 1 is a schematic block diagram of a water treatment
apparatus including a filtration apparatus according to the
20 embodiment. The water treatment apparatus includes a filtering
part 2 (filtration apparatus), a water-to-be-treated feeding
part 3, a protrusion-element feeding part 4, a water-quality
inspection part 5, a determination part 6, and a protrusionforming
control part 7.
25 The filtering part 2 has at least one filter layer 2a, a
19
first opening 2b, a second opening 2c, a third opening 2d, a
fourth opening 2e, a washing-liquid feeding part 8, and a
backwashing control part 9. The first opening 2b and the
fourth opening 2e are provided on a first side of the filter
layer 2a. The second opening 2c and the third opening 2d 5 are
provided on a second side of the filter layer. The first
opening 2b and the second opening 2c are inflow/outflow ports
for water to be treated. The third opening 2d and the fourth
opening 2e are inflow/outflow ports for washing liquid. The
10 first opening 2b is connected with a first passage 10. The
second opening 2c is connected with a second passage 11. The
third opening 2d is connected with a third passage 12. The
fourth opening 2e is connected with a fourth passage 13.
The filter layer 2a is formed by filling a solid filter
15 material in the filtering part. A filling amount of the solid
filter material is appropriately set. One filter layer 2a is
formed by a solid filter material made of one kind of
material. A plurality of the filter layers 2a may be laminated
in the filtering part. For example, a sand filter layer filled
20 with sand and an anthracite filter layer formed by filling
anthracite may be laminated. Solid filter materials made of
different materials have different surface conditions.
Combination of filter layers formed by different materials
enables removal of suspended-matters with a wide range of
25 sizes.
20
A solid filter material to be used is granular or
fibrous. For example, the solid filter material is made of
sand, anthracite, crushed activated carbon, fiber bundle, and
the like. Since crushed activated carbon has an effect of
removing chlorine, using crushed activated carbon as the 5 solid
filter material enables removal of chlorine contained in water
to be treated, in the filtering part. This can prevent
deterioration in an RO membrane, even when the RO membrane is
provided at a subsequent stage.
10 An average particle diameter of the solid filter material
is selected from 300 μm or more to 2500 μm or less. A
definition of "the average particle diameter of the solid
filter material" is based on AWWA B100-01 and JIS8801.
On a surface of a solid filter material, a protrusion is
15 formed. The protrusion may be formed by adhesion of at least
either suspended matters or a protrusion element, to the
surface of the solid filter material. The suspended matters
may be contained in water to be treated or the like, and
adhere to the surface of the solid filter material to form a
20 protrusion when the water to be treated is passed through the
filter layer.
The protrusion element is made of iron chloride, iron
sulfate, polyaluminum chloride (PAC), aluminum sulfate,
mineral, high-molecular polymer (cationic high-molecular
25 polymer, anionic high-molecular polymer, and nonionic high21
molecular polymer), inorganic pigment, and the like. The
mineral is, for example, kaolin. For the cationic highmolecular
polymer, polyacrylic ester-based, polymethacrylic
acid ester-based, and polyacrylamide-based are suitable. As
the anionic high-molecular polymer, polyacrylamide-5 based and
polyacrylic acid-based are preferable. As the nonionic highmolecular
polymer, polyacrylic ester-based, polymethacrylic
acid ester-based, and polyacrylamide-based are preferable.
The inorganic pigment is, for example, calcium carbonate,
10 talc, and titanium oxide.
For example, iron chloride becomes iron hydroxide in the
water, and a microfloc of the iron hydroxide adheres to the
surface of the solid filter material, to form a protrusion.
The microfloc may involve minute particles in the water. For
15 example, kaolin physically adheres to the surface of the solid
filter material, to form a protrusion. For example, highmolecular
polymer acts as an adhesive for bonding particles
contained in the water to the solid filter material, and
adheres to the surface of the solid filter material along with
20 the particles, to form a protrusion.
The protrusion element that constitutes the protrusion
may be one or more kinds. For example, when kaolin and highmolecular
polymer are fed to the filter layer, the kaolin
physically adheres to the surface of the solid filter
25 material, and particles contained in the water and the kaolin
22
adhere to the surface of the solid filter material through an
adhesive effect of the high-molecular polymer, to form a
protrusion.
The washing-liquid feeding part 8 can feed washing liquid
to the second side of the filtering part 2, to pass th5 e
washing liquid through the filter layer 2a in a direction
opposite to the passing direction of the water to be treated.
In this embodiment, the washing-liquid feeding part 8 is
configured by a washing-liquid tank 8a and a third feeding
10 means 8b. The washing-liquid feeding part 8 is connected to
the third opening 2d via the third passage 12. The washingliquid
tank 8a is a container that stores washing liquid. The
stored washing liquid is seawater (water to be treated) or
water to be primarily treated that has passed the filter layer
15 2a. When an RO desalination apparatus or an electrodialyzer
is provided at a subsequent stage of the filtering part 2, the
stored washing liquid is concentrated water (brine) that has
been separated at the filter layer 2a, or the like. The third
feeding means 8b is a pump capable of adjusting a feeding
20 speed, or the like. The third feeding means 8b can feed the
washing liquid stored in the washing-liquid tank 8a to the
filtering part 2 via the third passage 12.
The backwashing control part 9 controls a passing speed
of the washing liquid so as to suppress a developing rate of a
25 solid filter material to retain a protrusion on the surface of
23
the solid filter material. This passing speed provides a
desired backwashing effect.
"The protrusion is retained on the surface of the solid
filter material" is not limited to that all the protrusions
are retained on the surface of the solid filter material5 .
When a preset standard amount of the protrusion can be
retained, the filter layer after backwashing can provide
suspended-matter removal performance equal to that before
backwashing. When a part of the protrusion is retained, the
10 filter layer after backwashing can provide suspended-matter
removal performance higher than that of the filter layer
completely stripped of the protrusion. An amount of the
protrusion that should be retained (standard amount) is
confirmed through a preliminary test or the like in advance.
15 It is preferable to retain the protrusion to an extent
allowing an SDI of filtrate that has come out from the filter
layer after backwashing to be a value equal or close to an SDI
of filtrate that has come out from the filter layer before
backwashing.
20 The "desired washing effect" means that a differential
pressure of the filter layer has returned to an initial
differential pressure when the water to be treated is passed
through the filter layer after backwashing. Whether the
desired washing effect can be obtained or not by passing the
25 washing liquid at the passing speed above is confirmed through
24
a preliminary test or the like in advance.
In this embodiment, the backwashing control part 9 can
obtain a developing rate of the filter layer, and control a
passing speed of the washing liquid such that the developing
rate becomes equal to or less than a predetermined 5 ed developing
rate. The developing rate can be calculated from an
experimental formula based on a particle diameter of sand,
density of sand, water temperature, or the like. The
developing rate may be obtained by a sensor capable of
10 detecting movement of the solid filter material, provided
inside the filtering part. The "developing rate" is a ratio of
a moving distance to a length of the filter layer when the
solid filter material receives a flow of the washing liquid to
move in the flow direction of the washing liquid. When the
15 length of the filter layer before passing of the washing
liquid is L1, and the length of the filter layer in passing of
the washing liquid is L2, the developing rate can be
calculated from the formula (L2-L1)/L1×100. In order to
suppress energy consumption of power, it is preferable that
20 the developing rate is more than 0% to less than 30%,
preferably more than 0% to 5% or less.
The water-to-be-treated feeding part 3 can feed water to
be treated to the first side of the filtering part 2, to pass
the water to be treated through the filter layer 2a. In this
25 embodiment, the water-to-be-treated feeding part 3 is
25
configured by a water-to-be-treated tank 3a and a first
feeding means 3b. The water-to-be-treated feeding part 3 is
connected to the first opening 2b of the filtering part 2 via
the first passage 7. The water-to-be-treated tank 3a is a
container that stores the water to be treated. 5 . The stored
water to be treated is seawater, dirty water, industrial
wastewater, or the like. The first feeding means 3b is a pump
or the like. The first feeding means 3b can feed the water to
be treated stored in the water-to-be-treated tank 3a, to
10 filtering part 2 via the first passage 7.
The protrusion-element feeding part 4 can feed a
protrusion element to the first side of the filtering part 2.
In this embodiment, the protrusion-element feeding part 4 is
configured by a protrusion element tank 4a and a second
15 feeding means 4b. The protrusion-element feeding part 4 is
connected to the first opening 2b of the filtering part 2 via
the first passage 7, at a downstream side of the water-to-betreated
feeding part 3. The protrusion element tank 4a is a
container that stores the protrusion element. The second
20 feeding means 4b is a pump or the like. The second feeding
means 4b can feed the protrusion element stored in the
protrusion element tank 4a, to the filtering part 2 via the
first passage 7.
It should be noted that the protrusion-element feeding
25 part 4 can also serve as a collecting part 14 and a
26
protrusion-reforming part 15 described later. In this case,
the collecting part 14 and the protrusion-reforming part 15
are not required to be provided separately.
The filtering part 2 preferably includes the collecting
part 14 and the protrusion-5 reforming part 15.
The collecting part 14 can collect and store backwash
filtrate (washing liquid that has passed the filter layer)
generated by backwashing. The collecting part 14 is connected
to the fourth opening 2e via the fourth passage 13.
10 The protrusion-reforming part 15 can pass the collected
backwash filtrate through the filter layer toward a passing
direction of the water to be treated. The protrusion-reforming
part 15 is, for example, a pump connected to the collecting
part 14. The protrusion-reforming part 15 is connected to the
15 first opening 2b of the filtering part 2 via the first passage
10.
After backwashing, when the protrusion is stripped off
and suspended-matter removal performance of the filter layer
is degraded, the protrusion element needs to be fed to form a
20 protrusion on the surface of the solid filter material. The
backwash filtrate contains the protrusion element of the
protrusion that has been stripped off by backwashing. Passing
this backwash filtrate through the filter layer allows the
protrusion element to adhere again to the surface of the solid
25 filter material to reform a protrusion. By utilizing
27
backwashing liquid for reforming of the protrusion, necessity
of further addition of the protrusion element can be
eliminated, or an amount of the protrusion element to be
further added can be reduced. This can suppress processing
5 cost.
The water-quality inspection part 5 inspects water
quality of filtrate that has come out from the second side of
the filtering part. The water-quality inspection part 5 is,
for example, an SDI (Silt Density Index) measuring device, a
10 turbidimeter, a TOC meter, an SS meter, a UV meter, a COD
meter, and the like. In Fig. 1, the water-quality inspection
part 5 is connected to the second passage 11 and the
determination part 6. The water-quality inspection part 5 can
inspect the water quality of the filtrate discharged from the
15 filtering part 2 to the second passage 11, and output an
inspection result to the determination part 6.
The determination part 6 can determine, based on a preset
standard, whether or not a protrusion has been added to a
surface of a solid filter material. In this embodiment, the
20 "standard" is a threshold value provided for an inspection
value that is obtained by the water-quality inspection part 5.
The determination part 6 can determine that a protrusion
satisfying a preset standard has not been added (hereinafter
abbreviated as a protrusion has not been added) when the
25 inspection value obtained from the water-quality inspection
28
part 5 exceeds a preset threshold value, and determine that
the protrusion satisfying the preset standard has been added
(hereinafter abbreviated as a protrusion has been added) when
the inspection value becomes equal to or less than the
threshold value. The threshold value is appropriately 5 set in
accordance with an item of water quality to be inspected. The
determination part 6 may be incorporated into the protrusionforming
control part 7.
It should be noted that, in this embodiment, the
10 determination part 6 may include a counting means (not shown)
that counts a total feeding amount of the protrusion element.
For example, the counting means is connected to a second
feeding means 4b. For example, the counting means can receive
a power-supply ON/OFF signal of the second feeding means 4b,
15 and count a total feeding amount of the protrusion element
based on a time when the power supply of the second feeding
means 4b is ON, and a concentration of the protrusion element
in the protrusion forming liquid. The determination part 6 can
determine, when the counted total feeding amount of the
20 protrusion element reaches a preset threshold value, that a
standard amount of the protrusion has been added to the
surface of the solid filter material. The determination part 6
may be incorporated into the second feeding means 4b or the
protrusion-forming control part 7. When the determination part
25 6 includes the counting means, the determination part 6 is
29
configured capable of determining whether or not a protrusion
has been added based on information of at least either the
counting means or the water-quality inspection part 5.
The protrusion-forming control part 7 can control a
feeding amount of the protrusion element from the 5 protrusionelement
feeding part 4 such that the protrusion element is fed
so as to add a protrusion to the surface of the solid filter
material when the determination part 6 determines that the
protrusion has not been formed, and the feeding amount of the
10 protrusion element is reduced when it is determined the
protrusion has been added. The feeding amount of the
protrusion element required for adding a protrusion to the
surface of the solid filter material has been appropriately
set in accordance with a kind of the protrusion element.
15 "Reduce the feeding amount of the protrusion element" means
decreasing the feeding amount of the protrusion element as
compared with when adding the protrusion.
When protrusion elements, such as iron chloride and highmolecular
polymer, capable of providing a flocculation effect
20 are used, the feeding amount of the protrusion element is set
to be reduced to an amount with which at least a flocculation
effect cannot be expected. "Reduce the feeding amount of the
protrusion element" includes stopping of the feeding amount of
the protrusion element.
25 The backwashing control part and the protrusion-forming
30
control part are, for example, configured by a CPU (Central
Processing Unit), a RAM (Random Access Memory), a ROM (Read
Only Memory), a computer-readable storage medium, and the
like. Then, a series of processing for achieving various
functions is, as an example, stored in a form of a program 5 am in
a storage medium or the like, and the CPU reads the program
into the RAM or the like to execute information processing and
arithmetic processing, thereby to achieve the various
functions. It should be noted that, the program may be applied
10 with a form such as a form that is previously installed in a
ROM or another storage medium, a form provided in a state
being stored in a computer-readable storage medium, or a form
that is delivered via a wired or wireless communication means.
The computer-readable storage medium is a magnetic disk, a
15 magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor
memory, or the like.
The water treatment apparatus 1 includes an SBS adding
part 16 that adds sodium hydrogen sulfite (SBS) to water to be
treated on an upstream side of the filtering part 2. The SBS
20 adding part 16 is connected to the first passage 10 that is on
an upstream side of the filtering part 2. Water to be treated,
such as seawater or treated waste water, contains an oxidizing
agent such as a hypochlorous acid. Such an oxidizing agent
sterilizes microorganisms, which causes delay in biofilm
25 formation. The SBS adding part prevents delay in biofilm
31
formation by adding SBS to the water to be treated to
neutralize the oxidizing agent.
The water treatment apparatus 1 may include, at a
downstream side of the filtering part 2, a reverse-osmosismembrane
treatment part 17, an electrodialysis 5 part (not
shown), an evaporator (not shown) or the like. The reverseosmosis-
membrane treatment part 17 is, for example, a reverseosmosis-
membrane treatment apparatus having a plurality of
reverse-osmosis-membrane elements in a container. The reverse10
osmosis-membrane treatment apparatus can divide the water to
be treated (filtrate) that has passed through the filtering
part 2, into fresh water and concentrated water containing
ions, salt or the like, with a reverse osmosis membrane (RO
membrane).
15 Next, there is described a method for removing suspended
matters with the water treatment apparatus 1, and a
regeneration method of a filtering part when a regeneration of
the filtering part is required while the water treatment
apparatus 1 is removing the suspended matters. The suspended20
matter removing method according to the embodiment includes
the following steps (S1) to (S6):
(S1) A step of adding a protrusion
(S2) A step of determining whether or not a protrusion
has been added
25 (S3) A step of reducing a feeding amount of the
32
protrusion element as compared with when adding a protrusion
(S4) A step of passing water to be treated containing
suspended matters, through the filter layer having a solid
filter material formed with the protrusion
(5 S5) A step of forming a biofilm
(S6) A step of backwashing the filter layer (step of
regenerating the filtering part)
In the step of adding a protrusion (S1), the protrusion
element is fed to the filter layer 2a to add a protrusion to
10 the surface of the solid filter material.
The protrusion element is made of iron chloride, iron
sulfate, polyaluminum chloride (PAC), aluminum sulfate,
mineral, high-molecular polymer (cationic high-molecular
polymer, anionic high-molecular polymer, and nonionic high15
molecular polymer), inorganic pigment, and the like. The
mineral is, for example, kaolin. For the cationic highmolecular
polymer, polyacrylic ester-based, polymethacrylic
acid ester-based, and polyacrylamide-based are suitable. As
the anionic high-molecular polymer, polyacrylamide-based and
20 polyacrylic acid-based are preferable. As the nonionic highmolecular
polymer, polyacrylic ester-based, polymethacrylic
acid ester-based, and polyacrylamide-based are preferable.
The inorganic pigment is, for example, calcium carbonate,
talc, and titanium oxide. The protrusion element may be
25 powder or liquid. In this embodiment, the protrusion element
33
is stored in a protrusion element tank in a solution state
prepared at a predetermined concentration (protrusion forming
liquid).
The protrusion element adheres to the surface of the
solid filter material to form a protrusion itself, 5 or bonds
particles in water to the solid filter material. For example,
iron chloride becomes iron hydroxide in the water, and a
microfloc of the iron hydroxide adheres to the surface of the
solid filter material, to form a protrusion. The microfloc may
10 involve minute particles in the water. For example, kaolin
physically adheres to the surface of the solid filter
material, to form a protrusion. For example, high-molecular
polymer acts as an adhesive for bonding particles contained in
the water to the solid filter material, and adheres to the
15 surface of the solid filter material along with the particles,
to form a protrusion.
The protrusion element that is fed to the filter layer
may be one or more kinds. For example, when kaolin and highmolecular
polymer are fed to the filter layer, the kaolin
20 physically adheres to the surface of the solid filter
material, and particles contained in the water and the kaolin
adhere to the surface of the solid filter material through an
adhesive effect of the high-molecular polymer, to form a
protrusion.
25 The protrusion element may be powder or suspension
34
containing minute particles. In this embodiment, the
protrusion element is fed in a solution state containing the
protrusion element (protrusion forming liquid). A solvent of
the protrusion forming liquid is industrial water, seawater,
clear water or the like. When the protrusion element is 5 made
of high-molecular polymer, the protrusion forming liquid is
preferably prepared with solution containing particles (e.g.
seawater).
A concentration of the protrusion element in the
10 protrusion forming liquid is set such that a predetermined
amount of the protrusion element is fed when the protrusion
forming liquid is passed through the filter layer 2a. The
feeding amount of the protrusion element may be appropriately
set in accordance with a kind of the protrusion element and a
15 component of the water to be treated.
A protrusion is added by passing the protrusion forming
liquid through from the first side to the second side of the
filter layer 2a. This allows a protrusion to be added to the
surface of the solid filter material. A filtering speed of the
20 protrusion forming liquid is preferably same as a filtering
speed of the water to be treated. The filtering speed can be
adjusted by the first feeding means 3b or the second feeding
means 4b. When the filtering speed is adjusted by the first
feeding means 3b, the water to be treated is passed through
25 the filter layer 2a, in parallel with the step of adding a
35
protrusion (S1).
Next, it is determined whether or not a protrusion has
been added to the surface of the solid filter material (S2).
Based on a preset standard, it is determined whether or not a
protrusion has been added to the surface of the 5 solid filter
material. In this embodiment, water quality of filtrate that
has come out from the filter layer 2a is inspected, and it is
determined whether or not a protrusion has been added based on
the obtained inspection value.
10 Water-quality inspection is performed with an SDI
measuring device, a turbidimeter, a TOC meter, an SS meter, a
UV meter, a COD meter and the like. The threshold value is
set in accordance with an inspection method. For example, when
the inspection method is an SDI, the threshold value may be
15 SDI<4 or the like.
When the inspection value of the filtrate is equal to or
less than a preset threshold value, it is determined that a
protrusion has been added to the surface of the solid filter
material, and a feeding amount of the protrusion element is
20 reduced as compared with when the protrusion is added (S3).
The extent of the reduction of the feeding amount of the
protrusion element may be appropriately set in accordance with
a kind of the protrusion element. When there is used a
protrusion application that can provide a flocculation effect
25 in accordance with a feeding amount, the feeding amount of the
36
protrusion element after being reduced is an amount of a
degree in which the flocculation effect cannot be expected
even if added to the water to be treated. For example, when
the protrusion element is made of iron chloride, it is reduced
to about less than 0.5 ppm as iron (Fe) with respect 5 to an
amount of solution to be passed through the filter layer 2a.
In the step (S3), the feeding amount of the protrusion element
may be set to be zero, by stopping the feeding of the
protrusion element.
10 Water to be treated containing suspended matters is
passed through the filter layer 2a (S4), with the feeding
amount of the protrusion element reduced (or stopped). Here,
a protrusion has been added to the surface of the solid filter
material filled in the filter layer 2a.
15 In the step of forming a biofilm (S5), solution
containing microorganisms is fed to the filter layer 2a.
Passing the solution containing microorganisms from the first
side to the second side of the filter layer 2a causes a
biofilm to be formed on the surface of the solid filter
20 material. If the water to be treated contains microorganisms,
the water to be treated may be fed to the filter layer 2a. In
this case, a period while the water to be treated is being
passed through the filter layer 2a is equivalent to performing
the step of forming a biofilm (S5). When the water to be
25 treated is passed through the filter layer 2a, suspended
37
matters contained in the water to be treated may adhere to a
protrusion to form an effective protrusion themselves.
When water to be treated contains chlorine (Cl), it is
preferable to add SBS to the water to be treated, and then
pass through the filter layer 2a. An addition amount of 5 the
SBS is determined depending on the residual chlorine. This can
eliminate an inhibiting factor for biofilm formation.
The step of adding a protrusion (S1) can be performed in
an initial step of suspended-matter removal, or when a
10 protrusion once added to the surface of the solid filter
material is stripped off during treatment, or when a component
of the water to be treated fluctuates and water quality of the
filtrate is degraded. The water quality is continuously
inspected during passing of solution, such as a protrusion
15 element or water to be treated, through the filter layer 2a.
When an inspection value of the filtrate exceeds a preset
threshold value, it is determined that a protrusion has not
been formed on the surface of the solid filter material, and
the protrusion element in an amount to add a protrusion is fed
20 to the filter layer 2a. When the inspection value of the
filtrate is equal to or less than a preset threshold value, it
is determined that a protrusion has been added to the surface
of the solid filter material, and a feeding amount of the
protrusion element is reduced as compared with when the
25 protrusion is added.
38
When the protrusion element is fed to the filter layer
filled with the solid filter material, the protrusion element
comes into contact with the solid filter material to add a
protrusion to the surface of the solid filter material. At a
removal of suspended matters from the water to 5 be treated,
passing the protrusion element through the filter layer at an
early stage allows the protrusion to be added to the surface
of the solid filter material in a short time.
The filter layer formed by filling the solid filter
10 material added with the protrusion can stably remove suspended
matters at a high removal rate from an initial stage of the
step of removing suspended matters from the water to be
treated. This can shorten a starting time of the filtration
apparatus as compared with conventional ones. Additionally,
15 since the filter layer filled with the solid filter material
added with the protrusion can capture suspended matters of 0.1
μm or more to 10 μm or less, it is possible to improve the
water quality of the filtrate even when the water to be
treated includes many suspended matters having a size of 0.1
20 μm or more to 10 μm or less. Namely, it makes it possible to
cope with fluctuation in water quality of the water to be
treated. Adding a protrusion to the surface of the solid
filter material of 300 μm or more to 2500 μm or less provides
a suspended-matter removal effect more than an interception
25 effect.
39
Reducing the feeding amount of the protrusion element
enables suppression of sludge generation. This suppresses an
increase in a differential pressure in the filter layer, which
can prolong a backwashing interval and eliminate necessity of
5 a sludge treatment facility.
Even when the feeding of the protrusion element is
stopped, water quality of the filtrate in the step (S4) can be
stabilized until the protrusion is stripped off, as long as
the protrusion has once been added to the surface of the solid
10 filter material. The protrusion can be replenished by
continuing the feeding of the protrusion element, even though
the amount is small. Therefore, even if the protrusion is
stripped off, stability of the water quality of the filtrate
can be maintained. Moreover, when the feeding of the
15 protrusion element is stopped, an amount of protrusion-element
usage can be lowered, enabling reduction of treatment cost.
Feeding solution containing microorganisms (e.g.,
seawater) to the filter layer causes the microorganisms to
adhere to the solid filter material S to form a biofilm BF on
20 the surface of the solid filter material. As the solution
containing microorganisms continuously flows, the biofilm BF
grows around the previously-formed biofilm BF as a core.
Since the biofilm BF grows while securing a passage F of the
water to be treated such that oxygen and nutrition are
25 supplied to the previously-formed biofilm BF, the protrusion
40
is presumed to become as shown in Fig. 2 (see Costerton, J.W.;
Lewandowski, Z.; Caldwell, D.E.; Korber, D.R.; Lappin-Scott,
H.M. "Microbial Biofilms", Annual Reviews of Microbiology 49,
pp. 711-745 (1995)).
The protrusion element is derived from other 5 her than
microorganisms. Feeding the protrusion element allows a
protrusion to be added to the surface of the solid filter
material in a short time, earlier than forming the biofilm.
It is considered that feeding of solution containing
10 microorganisms to such a solid filter material causes
microorganisms to adhere to a protrusion to form the biofilm,
and to grow around the protrusion as a core. The biofilm that
has adhered to the protrusion becomes a part of the protrusion
itself. As the protrusion becomes larger, the protrusion can
15 be easily adhered by suspended matters having a size of 0.1 μm
or more to 10 μm or less. In this embodiment, since the
protrusion can be made larger by forming of the biofilm even
after the feeding amount of the protrusion element is reduced,
the water quality of the filtrate can be stabilized for a
20 longer time.
Since the water quality of the filtrate is inspected
during passing of the water to be treated, a protrusion can be
added again to the surface of the solid filter material when
the water quality of the filtrate is degraded. The water
25 quality of the filtrate can be more stable since it is
41
possible to adjust an amount of the protrusion to be added so
as to provide a desired water quality when the protrusion is
stripped off to degrade suspended-matter removal performance,
or when an amount of suspended matters contained in the water
5 to be treated is increased.
Although, in the step of adding a protrusion (S1) in the
embodiment, a protrusion is added after the solid filter
material fills the filtering part, a similar effect can be
obtained by forming the filter layer by filling the filtering
10 part with the solid filter material, that has been added with
a protrusion in another container.
After a predetermined time of operation, or when a
differential pressure of the filter layer exceeds a certain
value, or the like, the step of backwashing the filter layer
15 (S6) is performed.
In the step of backwashing the filter layer (S6), washing
liquid is passed through the filter layer in a direction
opposite to a passing direction of the water to be treated.
At this time, the washing liquid is fed to the second side of
20 the filter layer such that the protrusion is retained on the
surface of the solid filter material. The washing liquid is
passed at a speed that can provide a desired washing effect
and can suppress a developing rate of the solid filter
material.
25 The step of backwashing (S6) is performed only by washing
42
liquid, while air washing that washes the filter layer by
introducing air is not performed. The air washing is a washing
method that makes larger movement of the solid filter material
than that of backwashing using washing liquid, and mixes the
solid filter material in the filter layer. Not performing 5 erforming the
air washing enables suppression of the movement of the solid
filter material.
In the step of backwashing the filter layer (S6), for
example, it is preferable to obtain the developing rate of the
10 filter layer and perform control such that the washing liquid
is passed at a speed causing the developing rate of the filter
layer to become more than 0% to less than 30%, preferably more
than 0% to 5% or less.
By performing backwashing such that the protrusion is
15 retained on the surface of the solid filter material to
regenerate the filter layer, the filtrate satisfying a desired
water quality standard can be stably obtained from immediately
after the backwashing.
It is not necessary to completely retain the biofilm, and
20 it is sufficient to retain the biofilm that constitutes the
protrusion satisfying a preset standard. For example, it is
sufficient to retain a biofilm having a size such as that
shown on the left side of the figure in Fig. 2, while a
biofilm of about 200 μm on the right-most side of the figure
25 in Fig. 2 may be stripped off without being retained.
43
The regeneration method for a filtration apparatus
according to the embodiment may include a step of collecting
washing liquid (backwash filtrate) that has passed the filter
layer, and a step of passing the collected backwash filtrate
through the filter layer and reforming a protrusion 5 on a
surface of the solid filter material.
The collected backwash filtrate is temporarily stored in
a container. After an end of the backwashing, the collected
backwash filtrate is passed through the filter layer, and the
10 protrusion is reformed on the surface of the solid filter
material. The container that stores the backwash filtrate may
be the protrusion element tank of the protrusion-element
feeding part. In this case, as with the step (S2) above, it is
determined whether or not a standard amount of the protrusion
15 has been retained (added), and the step (S1) or (S3) above is
performed.
The steps of collecting the backwash filtrate and
utilizing the collected wash filtrate for reforming protrusion
are especially effective when many protrusions are stripped
20 off from the surface of the solid filter material. For
example, it is effective when the developing rate is 30% or
more.
It should be noted that, collecting and utilizing the
backwash filtrate for reforming a protrusion are also
25 effective even when backwashing is performed by washing liquid
44
without consideration of retaining of a protrusion, or when
backwashing is performed by air washing.
{Modified Example 1}
Fig. 3 is a schematic block diagram of a water treatment
apparatus 21. The water treatment apparatus 21 has 5 a same
configuration as that of the first embodiment except for
including a coarse-particle separation part 22.
The coarse-particle separation part 22 is provided
between a water-to-be-treated feeding part 3 and a filtering
10 part 2, in a preceding stage of a protrusion-element feeding
part 4. The coarse-particle separation part 22 mainly
separates suspended matters larger than 10 μm contained in
water to be treated. The coarse-particle separation part 22
is a sand filtration apparatus, a floatation-separation
15 apparatus, or the like. When the coarse-particle separation
part 22 is a sand filtration apparatus, the water to be
treated may be passed without addition of a flocculant. When
the coarse-particle separation part 22 is a floatationseparation
apparatus, solid-liquid separation is performed by
20 bonding/floating SS (sludge or floating matter) with a large
amount of bubbles (micro-air) generated from water to be
treated mixed with saturated pressurized water.
In this embodiment, by passing water to be treated
through the coarse-particle separation part 22, suspended
25 matters larger than 10 μm is mainly separated from the water
45
to be treated, to make it water to be primarily treated.
Then, the water to be primarily treated is guided to the
filter layer, and suspended matters having a size of 0.1 μm or
more to 10 μm or less are removed.
The protrusion element can be fed to the filter 5 layer 2a,
at a same time as the guiding of the water to be primarily
treated to the filter layer. The protrusion element may be fed
to the filter layer 2a before the guiding of the water to be
primarily treated to the filter layer 2a. In either case, a
10 protrusion satisfying a preset standard is added to the
surface of the solid filter material in accordance with the
first embodiment, and then the feeding amount of the
protrusion element is reduced (or stopped).
According to the embodiment, by separating the rough
15 removal of suspended matters with a large particle diameter in
the water to be treated, and the removal of suspended matters
with a medium particle diameter of 0.1 μm or more to 10 μm or
less, an increase in a differential pressure due to clogging
or the like in the filter layer can be suppressed. This makes
20 it possible to stabilize the water quality of the filtrate of
the filter layer, and to reduce a backwashing frequency of the
filter layer.
{Modified Example 2}
Modified Example 2 is different from the first embodiment
25 in that the water treatment apparatus includes a differential46
pressure measurement part. Fig. 4 is a schematic block diagram
of a water treatment apparatus 31 according to Modified
Example 2. Since a configuration for regenerating a filtering
part is same as that of the first embodiment, illustration and
explanation of configurations regarding backwashing, such as 5 a
washing-liquid feeding part 8, a backwashing control part 9
and a protrusion-reforming part 15, are omitted.
The water treatment apparatus 31 includes a filtering
part 2 (filtration apparatus), a water-to-be-treated feeding
10 part 3, a protrusion-element feeding part 4, a water-quality
inspection part 5, a determination part 36, a protrusionforming
control part 37, and a differential-pressure
measurement part 32.
The differential-pressure measurement part 32 can measure
15 a differential pressure between a first side (first opening
side) and a second side (second opening side) of a filter
layer 2a (the filtering part 2). In this embodiment, the
differential-pressure measurement part 32 is connected to the
first side and the second side of the filtering part 2. The
20 differential-pressure measurement part 32 is, for example, a
water pressure meter. The water pressure meter detects
pressures on the first side and the second side of the
filtering part 2, to measure the differential pressure.
The determination part 36 can determine, based on a
25 preset standard, whether or not a protrusion has been added to
47
a surface of a solid filter material. In this embodiment, the
determination part 36 includes a protrusion-element-amount
measurement means (not shown) that directly or indirectly
measures an amount of the protrusion element contained in the
filtrate that has come out from the second 5 side (second
opening side) of the filtering part 2. The protrusion-elementamount
measurement means may be sufficient if it can directly
or indirectly measure the amount of the protrusion element.
For example, when the protrusion element is made of iron
10 chloride, a water-quality analyzer capable of monitoring an
iron concentration can be used as the protrusion-elementamount
measurement means, to directly measure the protrusion
element. For example, using an SDI measuring device as the
protrusion-element-amount measurement means enables indirect
15 measurement of the protrusion element. For example, when the
protrusion element is made of kaolin, using a turbidimeter as
the protrusion-element-amount measurement means enables
indirect measurement of the protrusion element.
When the protrusion element is indirectly measured, the
20 protrusion-element-amount measurement means can also serve as
the water-quality inspection means. In this embodiment, the
protrusion-element-amount measurement means is an SDI
measuring device, which also serves as the water-quality
inspection means.
25 The determination part 36 can determine that a protrusion
48
has been added to the surface of the solid filter material
when a measured value of the protrusion-element-amount
measurement means becomes equal to or less than a preset
threshold value. The determination part 36 may also determine
that a protrusion has been added to the surface of 5 the solid
filter material, when it is confirmed that the measured value
becomes equal to or less than a preset threshold value and has
been maintained in the state for a certain time. The
determination part 36 may be incorporated into the protrusion10
forming control part 37.
The protrusion-forming control part 37 is connected to
the differential-pressure measurement part 32, the
determination part 36, and a second feeding means 4b. The
protrusion-forming control part 37 can control a feeding
15 amount of the protrusion element from the protrusion-element
feeding part 4 such that a differential pressure measured by
the differential-pressure measurement part 32 becomes less
than a predetermined value. The protrusion-forming control
part 37 receives a differential pressure value measured by the
20 differential-pressure measurement part 32, and automatically
controls the feeding amount of the protrusion element from the
protrusion-element feeding part 4 such that the differential
pressure is maintained at less than the predetermined value.
The protrusion-forming control part 37 can control the
25 protrusion-element feeding part 4 to feed the protrusion
49
element to add a protrusion to the surface of the solid filter
material when the determination part 36 determines that a
standard amount of the protrusion has not been added, and to
reduce the feeding amount of the protrusion element when the
determination part 36 determines that a protrusion 5 has been
added.
The water treatment apparatus 31 may include, at a
downstream side of the filtering part 2, a reverse-osmosismembrane
treatment part 17, an electrodialysis part (not
10 shown), an evaporator (not shown) or the like.
The suspended-matter removing method according to the
embodiment includes the following steps (S11) to (S16):
(S11) A step of adding a protrusion
(S12) A step of measuring a differential pressure between
15 a first side of a filter layer and a second side of the filter
layer
(S13) A step of reducing a feeding amount of the
protrusion element as compared with when adding a protrusion
(S14) A step of passing water to be treated containing
20 suspended matters, through the filter layer having a solid
filter material added with the protrusion
(S15) A step of forming a biofilm
(S16) A step of backwashing the filter layer
In the step of adding a protrusion (S11), the protrusion
25 element is fed to the filter layer 2a to add a protrusion to
50
the surface of the solid filter material. A procedure for
feeding the protrusion element to the filter layer 2a is same
as that of the first embodiment.
In this embodiment, while the protrusion element is being
fed to the filter layer 2a, the differential pressure 5 between
the first side and the second side of the filter layer 2a is
measured (S12). In the step of adding a protrusion (S11), the
protrusion element is fed to the filter layer 2a in a range
that the differential pressure measured at (S12) is less than
10 a predetermined value. When the measured differential pressure
becomes equal to or more than the predetermined value, the
feeding of the protrusion element is immediately stopped. The
"predetermined value" may be set based on an allowable
pressure of the filtering part, or may previously be set by
15 performing a preliminary test or the like. In the preliminary
test, the differential pressure of the filter layer is
measured, and water quality of filtrate is inspected, for
example, by passing the protrusion forming liquid containing
the protrusion element with an optional concentration through
20 the filter layer. The differential pressure of the filter
layer when an inspection value of the filtrate becomes a
desired value may be set to be a predetermined value.
In the step (S13), an amount of the protrusion element
contained in the filtrate that has come out from the filter
25 layer 2a in the step of adding a protrusion (S11), is directly
51
or indirectly measured. When the measured amount of the
protrusion element becomes equal to or less than a preset
threshold value, it is determined that a protrusion has been
added to the surface of the solid filter material. When it is
determined that the protrusion has been added, the 5 feeding
amount of the protrusion element is reduced (or stopped), as
with the step (S3) in the first embodiment.
Water to be treated containing suspended matters is
passed through the filter layer 2a (S14), with the feeding
10 amount of the protrusion element reduced (or stopped), as with
the step (S4) in the first embodiment.
In the step of passing the water to be treated containing
suspended matters (S14), it is preferable to inspect the water
quality of the filtrate that has come out from the filter
15 layer, as with the step (S4) in the first embodiment.
The step of forming a biofilm (S15) and the step of
backwashing the filter layer (S16) may be performed as with
the step (5) and the step (S6) in the first embodiment.
According to the embodiment, measuring the differential
20 pressure between the first side and the second side of the
filter layer enables reliable suppression of an increase in
the differential pressure due to formation of a protrusion.
According to the embodiment, measuring the amount of the
protrusion element in the filtrate that comes out when the
25 protrusion element is fed enables confirmation that the
52
protrusion element has not come out to the filtrate. Thereby,
in an indirect way, it can be confirmed that a protrusion has
been formed on the surface of the solid filter material.
Next, there is described a basis of a suspended-matter
removing effect of a filter layer formed by filling a 5 solid
filter material formed with a protrusion on a surface due to
an adhesion of a protrusion element.
(Study 1)
A study was made, through a simulation, regarding a
10 relationship between a capture rate and a size of suspended
matters captured in a filter layer (captured-particle
diameter) at a time when water to be treated containing
suspended matters is passed through a filter layer formed by
filling a solid filter material. A balance equation in the
15 filtration, in consideration of diffusion by Brownian motion
and an interception effect, was made for execution of the
simulation. A passage width d0 is equivalent to a diameter of
a small circle that is in a region surrounded by three solid
filter materials in contact with each other, and is in contact
20 with the three solid filter materials (see Fig. 5). Diffusion
of suspended matters due to turbulence of a flow generated by
unevenness on a surface is not considered. The solid filter
materials had a spherical shape, and particle diameters of
100μm, 300μm (a minimum diameter of sand used industrially for
25 sand filtration), and 1200μm (a maximum diameter of sand used
53
industrially for sand filtration). A filtering speed was 25
m/h (equivalent to cross-sectional porosity of 50% of a sand
filter column at a superficial velocity 12.5 m/h). In this
simulation, the passage width d0 was same as the particle
5 diameter of the solid filter material.
A simulation result is shown in Fig. 6. In this figure,
the horizontal axis is the captured-particle diameter (μm),
and the vertical axis is the capture rate (%). According to
Fig. 6, as the solid filter material is smaller, the capture
10 rate of suspended matters having a size about 10 μm became
higher. However, it was confirmed that suspended matters
having a size of 0.1 μm to 5 μm can be hardly captured, even
when there was used a solid filter material having a size of a
minimum diameter of sand used industrially for sand
15 filtration.
A result of (Study 1) above shows that filtration using
the solid filter material can hardly remove suspended matters
of 0.1 μm or more to 10 μm or less. This result suggests that,
conventionally, as water to be treated contained more
20 suspended matters of 0.1 μm or more to 10 μm or less, water
quality of the filtrate was further degraded, even when a same
solid filter material was used for the filtration.
Thus, the inventors have concluded that, it is possible
to cope with load fluctuation and stabilize the water quality
25 of the filtrate, by removing suspended matters having a size
54
of 0.1 μm or more to 10 μm or less. In conventional filtration
using a solid filter material, the reason why suspended
matters having a size of 0.1 μm or more to 10 μm or less are
not removed is considered as follows.
Fig. 7 shows a schematic view of a flow of water 5 to be
treated when the water to be treated is passed through the
filter layer formed by filling a solid filter material. In
this figure, a symbol S represents a solid filter material,
and lines F extending in a vertical direction in the figure
10 represent stream lines of the water to be treated. The water
to be treated flowing in the filter layer is typically in a
laminar flow state as shown in Fig. 7. It is known that, in
the laminar flow state, a flow rate of the water to be treated
becomes lower as closer to a surface of the solid filter
15 material, and there is a region where the flow rate becomes
substantially zero (blocking-layer region) on the surface of
the solid filter material.
When the water to be treated is passed through the filter
layer formed by filling the solid filter material, coarse
20 suspended matters contained in the water to be treated cannot
be passed through a gap of the solid filter material, and are
captured. Even among suspended matters having a size capable
of being passed through a gap of the solid filter material of
the solid filter material, relatively larger suspended matters
25 may come out from the laminar flow by the law of inertia, and
55
collide with the solid filter material to be captured. In the
suspended matters contained in the water to be treated, fine
suspended matters (colloidal particles with a diameter of less
than 0.1 μm) may be captured by the solid filter material due
5 to diffusion by Brownian motion.
Whereas, among the suspended matters contained in the
water to be treated, medium sized suspended matters (particles
with a diameter of 0.1 μm or more to 10 μm or less) cannot
come out of the laminar flow by the law of inertia or the
10 like, and are passed through the filter layer with the laminar
flow.
Based on the consideration above, a study was made
regarding a method for intentionally removing medium sized
suspended matters (particles with a particle diameter of 0.1
15 μm or more to 10 μm or less) from the laminar flow.
(Study 2)
A study was made, through a simulation, regarding a
behavior of suspended matters when water to be treated
containing suspended matters is passed through a filter layer
20 formed by filling a solid filter material added with a
protrusion. The simulation was performed by using the Lattice
Boltzmann Method (method for analyzing a fluid flow by using
the molecular kinetic theory, and movement of suspended
matters by using a motion equation). Diffusion by Brownian
25 motion is not considered. A passage width d0 was 600 μm, which
56
was equivalent to a diameter of the solid filter material, a
length of the passage was 1.5 mm, and a flow rate was 25 m/h
(equivalent to cross-sectional porosity of 50% of a sand
filter column at a superficial velocity 12.5 m/h). It was
assumed that there was a protrusion with a height of 60 5 μm and
a width of 60 μm on a surface of the solid filter material,
and particle diameters of suspended matters were 1 μm
(suspended matter S1) and 5 μm (suspended matter S2). In this
condition, there is no interception effect from the sizes of
10 suspended matters, the size of protrusion, and the passage
width.
A simulation result is shown in Figs. 8 to 10. In Figs. 8
to 10, a vertical direction in the figure is a passage width
d0, and the water to be treated flows from left to right in
15 the figure. Fig. 8 is a view showing a flow of suspended
matters. Fig. 9 is a view illustrating a state of protrusions
in an early stage of passing of the water to be treated, and
Fig. 10 is a view illustrating a state of protrusions in a
late stage of passing of the water to be treated.
20 According to Fig. 8, it could be confirmed that a
presence of protrusions C caused a microscopic change in a
flow direction of suspended matters M. Accordingly, it was
confirmed that medium sized suspended matters came out of a
laminar flow, and the medium sized suspended matters out of
25 the laminar flow became easy to enter a blocking region, so
57
that a capture rate of the medium sized suspended matters
could be increased.
According to Figs. 9 and 10, it was confirmed that the
suspended matters M adhered to the protrusions C when the
water to be treated was passed through the filter layer 5 formed
by filling the solid filter material formed with a protrusion
on a surface. A position where the suspended matters M adhered
was a corner facing an upstream side of a passing direction of
the water to be treated. It was confirmed that suspended
10 matters adhered to protrusions in the early stage of passing
water (Fig. 9), and other suspended matters adhered around the
suspended matters, that had adhered to the protrusions in the
early stage of passing water, as a core, in the late stage of
passing water (Fig. 10), so that the protrusions grown.
15 Although not illustrated, when the water to be treated
was passed through a filter layer filled with a solid filter
material not formed with a protrusion on a surface, no
suspended matter adhered to the surface of the solid filter
material.
20 A result of (Study 2) above suggests that, by feeding the
protrusion element to the filter layer to add a standard
amount of the protrusion, suspended matters contained in water
to be treated adhere to the protrusion, and thereby the
protrusion can be grown, even when the feeding amount of the
25 protrusion element is reduced or stopped afterward.
58
(Study 3)
A study was made, by using the Lattice Boltzmann Method,
regarding a minimum size of a protrusion required for adhesion
of suspended matters of 0.45 μm (an average pore diameter of a
filter for an SDI measurement) to 10 μm in seawater, on 5 a
surface of the solid filter material. Diffusion by Brownian
motion is not considered. The protrusion is rectangular, and
a vertical length from the surface of the solid filter
material to the highest portion of the protrusion was defined
10 as a height. Particle diameters of suspended matters were 0.45
μm, 2 μm, 5 μm, and 10 μm, and a calculation was performed for
each of the particle diameters. A passage width d0 was 600 μm,
which was equivalent to a diameter of the solid filter
material, a length of the passage was 1200 μm, and a flow rate
15 was 0.006 m/s (a value equivalent to cross-sectional porosity
of 50% of a sand filter column at a superficial velocity 10.8
m/h). A simulation result is shown in Fig. 11. In this
figure, the horizontal axis is the captured-particle diameter
(μm), and the vertical axis is the height of a protrusion
20 (μm).
According to Fig. 11, as a size of the protrusion is
larger, small suspended matters could be captured more.
Placing a rectangular body (protrusion) of 4 μm enabled
removal of suspended matters of 10 μm. According to Fig. 11,
25 removal of suspended matters of 0.45 μm required a rectangle
59
(protrusion) with a height of 40 μm.
(Study 4)

Protrusion forming liquid containing a protrusion element
was passed through a filter layer formed by filling a 5 solid
filter material for three hours, to add a protrusion to a
surface of the solid filter material. Then, passing of the
protrusion forming liquid was stopped, and in that state,
water to be treated was passed through the filter layer for
10 three hours. A filtering speed was 10 m/h.
A filter column (column diameter 5 cm) was formed in a
three-layered structure of an anthracite filter layer, a sand
filter layer, and a gravel filter layer. The anthracite filter
layer, the sand filter layer, and the gravel filter layer are
15 sequentially arranged from an upstream side of the passing
direction of the water to be treated. The anthracite filter
layer is a filter layer formed by filling anthracite with an
average particle diameter of 700 μm. A length of the
anthracite filter layer is 200 mm. The sand filter layer is a
20 filter layer formed by filling sand with an average particle
diameter of 475 μm. A length of the sand filter layer is 500
mm. The gravel filter layer is a filter layer formed by
filling gravel with an average particle diameter of 2000 μm.
A length of the gravel filter layer is 100 mm.
25 The protrusion element was made of iron chloride (FeCl3:
60
Wako Pure Chemical Industries, Ltd.). Iron chloride reacts
with an alkaline component in water to generate iron
hydroxide, as formula (1) below. This iron hydroxide was
presumed to adhere to the filter material to form a
5 protrusion.
FeCl3 + 3HCO3
- = Fe(OH)3 + 3CO2 + 3Cl- ∙∙∙ (1)
Seawater was used as the water to be treated. An SDI of
the seawater before passing was 6.14. Protrusion forming
liquid containing the protrusion element was prepared, and the
10 protrusion forming liquid was passed through the filter layer
along with the water to be treated. A concentration of the
protrusion element in the protrusion forming liquid was set so
as to cause an Fe-concentration of 1 ppm with respect to an
amount of passing water.
15 During the passing of the water to be treated, a
differential pressure of the filter layer was measured by a
differential-pressure measuring device. Additionally, an Feconcentration
and an SDI of liquid (filtrate) that has passed
the filter layer were continuously measured. The Fe20
concentration was measured by a 2,4,6-tris-2-pyridyl-1,3,5-
triazine absorptiometric method (abbreviated as TPTZ
absorptiometric method) described in JIS B8224.
The SDI is obtained by the following formula (2) based on
a time required for filtration/collection at 206 kPa, by using
25 a filter with a diameter of 47 mm and an average pore diameter
61
of 0.45 μm.
SDITm = (1 - Δt1/Δt2) × 100/Tm ∙∙∙ (2)
Δt1: A time (sec) required for filtration/collection of
initial 500 ml.
Δt2: A time (sec) required for filtration/5 collection of
500 ml after Tm minutes.
Tm: A time from the t1 filtration/collection starting
time to the t2 filtration/collection starting time (normally
15 minutes).
10 An upper limit of the SDI index is 6.67. Since the SDI
is decreased, it is suggested that a ratio of suspended-matter
particles larger than 0.45 μm is decreased.

For comparison, only seawater was passed without passing
15 of the protrusion forming liquid through the filter layer, and
the measurement was performed as with Test A.
Fig. 12 shows a measurement result of a differential
pressure of the filter layer. In this figure, the horizontal
axis is an elapsed time (h), and the vertical axis is the
20 differential pressure (kPa) of the filter layer. According to
Fig. 12, by passing the protrusion forming liquid containing
iron hydroxide, the differential pressure of the filter layer
was slightly increased in Test A, but an increase in the
differential pressure was not observed after the passing of
25 the protrusion forming liquid was stopped. In Test B (a case
62
without passing of protrusion forming liquid), a change in a
differential pressure of the filter layer was hardly observed
within the same period of time.
Fig. 13 shows a measurement result of an SDI of Tests A
and B. In this figure, the horizontal axis is an 5 elapsed time
(h), and the vertical axis is the SDI (-).
According to Fig. 13, the SDI of the filtrate was
decreased to about 4 after two to three hours of passing in
Test A. Even after the passing of the protrusion forming
10 liquid was stopped, the SDI of the filtrate was maintained at
about 4.
Although not shown in Fig. 13, an Fe-concentration of the
filtrate reached 1 μg/L (detection lower limit) after two
hours of the passing in Test A. This shows that the iron
15 hydroxide contained in the protrusion forming liquid remains
in the filter layer. After the passing of the protrusion
forming liquid was stopped, the Fe-concentration of the
filtrate was maintained at 1 μg/L. Accordingly, it could be
confirmed that the iron hydroxide remaining in the filter
20 layer was not stripped off by subsequent water passing.
It was confirmed that, it is possible to add a protrusion
required to stabilize water quality of the filtrate to the
surface of the solid filter material, by passing the
protrusion forming liquid for three hours so as to cause an
25 Fe-concentration of 1 ppm with respect to the water to be
63
treated. It is presumed that a suspended-matter removal
ability can be maintained unless iron hydroxide comes out from
the filter layer.
According to Fig. 13, the SDI of the filtrate remained
high at 5.21 when only the water to be treated 5 d was passed
through without passing of the protrusion forming liquid, as
with Test B. In Test B, it is presumed that, although
suspended matters were removed with mainly an interception
effect and diffusion by Brownian motion, medium suspended
10 matters (0.1 μm to 10 μm) could not be removed, preventing a
sufficient decrease of the SDI. It is presumed that the SDI
was kept high because medium suspended matters have not been
removed.
A result of this Study shows that, after passing of the
15 protrusion forming liquid through the filter layer, the water
quality of the filtrate can be improved quickly in two to
three hours. Even after the passing of the protrusion forming
liquid was stopped, the water quality of the filtrate was
stable.
20 In sand filtration using a typical flocculant, the
flocculant is continuously added. The flocculant and sludge
formed by suspended matters contained in the water to be
treated cause clogging of a filter layer, increasing a
differential pressure along with the continuation of the
25 filtration. Thus, in general, the filter layer must be washed
64
in a washing speed in which a developing rate of air washing
(washing by collision between filter materials, using air
bubbling) and the filter water becomes 30%. Whereas, in the
present filtration method, which injects protrusion forming
liquid to add a protrusion to a surface of a 5 solid filter
material, it is only capturing suspended matters contained in
water to be treated, reducing a washing frequency of a solidfilter-
material layer without increasing a differential
pressure.
10 (Study 5)
A suspended-mater removal test was performed by using a
water treatment apparatus provided with a coarse-particle
separation part (column diameter 5 cm) and a filtering part
(column diameter 5 cm).
15 A sand filtration apparatus was used as the coarseparticle
separation part. The sand filtration apparatus has a
sand filter layer (length 1200 mm) formed by filling sand with
an average particle diameter of 350 μm, and a gravel filter
layer (length 100 mm) formed by filling gravel with an average
20 particle diameter of 2000 μm. The sand filter layer is on an
upstream side of the gravel filter layer in a passing
direction of water to be treated.
The filtering part has a filter layer. The filter layer
is configured by an anthracite filter layer (length 200 mm)
25 formed by filling anthracite with an average particle diameter
65
of 700 μm, a sand filter layer (length 1000 mm) formed by
filling sand with an average particle diameter of 350 μm, and
a gravel filter layer (length 100 mm) formed by filling gravel
with an average particle diameter of 2000 μm. The anthracite
filter layer, the sand filter layer, and the gravel 5 ravel filter
layer are arranged in this order from the upstream side in the
passing direction of the water to be treated.
Water to be treated was passed through the coarseparticle
separation part by a water-to-be-treated feeding
10 part. Then, filtrate (primarily treated water) that had come
out from the coarse-particle separation part was passed
through the filtering part. The primarily treated water before
entering the filtering part was added with protrusion forming
liquid, and the protrusion forming liquid and the primarily
15 treated water were passed in same time. After three hours from
the start of passing, the passing of the protrusion forming
liquid was stopped. The water to be primarily treated
continued to be passed for three hours even after the passing
of the protrusion forming liquid was stopped.
20 Differential pressures of the coarse-particle separation
part and the filtering part were measured by a differentialpressure
measuring device, during the passing of the water to
be treated and the primarily treated water. Additionally, an
SDI of liquid (filtrate) that had passed the filtering part
25 was continuously measured. A filtering speed was 10 m/h.
66
The protrusion element was made of iron chloride (FeCl3),
and the protrusion forming liquid was fed so as to cause an
Fe-concentration of 1 ppm with respect to the primarily
treated water. An SDI of seawater before passing is 6.28.
Fig. 14 shows a measurement result of 5 differential
pressures of the coarse-particle separation part and the
filtering part (filter layer). In this figure, the horizontal
axis is an elapsed time (h), and the vertical axis is the
differential pressure (kPa). According to Fig. 14, during the
10 passing of the water to be treated, a change in the
differential pressure of the filtering part was hardly
observed at the coarse-particle separation part. According to
Fig. 14, while the differential pressure of the filtering part
was slightly increased during the passing of the protrusion
15 forming liquid, an increase in the differential pressure was
not observed during the passing of only the primarily treated
water after the passing of the protrusion forming liquid was
stopped.
Fig. 15 shows an SDI measurement result of the filtrate
20 that has come out from the filtering part. In this figure, the
horizontal axis is an elapsed time (h), and the vertical axis
is the SDI (-). According to Fig. 15, although the SDI of
seawater before passing was 6 or more, the SDI of the filtrate
of the filtering part was decreased to less than 4 after two
25 to three hours of passing of the protrusion forming liquid.
67
The SDI of the filtrate of the filtering part could be
maintained at less than 4, even after the passing of the
protrusion forming liquid was stopped. While a standard of a
turbidity concentration required for feed water to an RO
(reverse osmosis) membrane is generally SDI<4, the filtrate 5 of
two to three hours of passing satisfied the water quality
standard.
Based on the results of Studies 1 to 3, it is presumed
that the coarse-particle separation part mainly captures
10 suspended matters smaller than 0.1 μm, and suspended matters
larger than 10 μm. Since the SID has been decreased by the
passing the primarily treated water from which coarse
particles are removed through the filtering part (filtering
layer), the filter layer seems to capture medium sized
15 suspended matters of 0.1 μm or more to 10 μm or less.
(Study 6)
A suspended-mater removal test was performed by using a
water treatment apparatus provided with a coarse-particle
separation part (column diameter 5 cm) and a filtering part
20 (column diameter 5 cm). A sand filtration apparatus was used
as the coarse-particle separation part. The sand filtration
apparatus has a sand filter layer (length 800 mm) formed by
filling sand with an average particle diameter of 350 μm, and
a gravel filter layer (length 100 mm) formed by filling gravel
25 with an average particle diameter of 2000 μm. The sand filter
68
layer is on an upstream side of the gravel filter layer in a
passing direction of water to be treated.
The filtering part has a filter layer. The filter layer
is configured by an anthracite filter layer (length 200 mm)
formed by filling anthracite with an average particle 5 ticle diameter
of 700 μm, a sand filter layer (length 600 mm) formed by
filling sand with an average particle diameter of 350 μm, and
a gravel filter layer (length 100 mm) formed by filling gravel
with an average particle diameter of 2000 μm. The anthracite
10 filter layer, the sand filter layer, and the gravel filter
layer are arranged in this order from the upstream side in the
passing direction of the water to be treated.
Water to be treated was passed through the coarseparticle
separation part by a water-to-be-treated feeding
15 part. Then, filtrate (primarily treated water) that had come
out from the coarse-particle separation part was passed
through the filtering part. The primarily treated water before
entering the filtering part was added with protrusion forming
liquid, and the protrusion forming liquid and the primarily
20 treated water were passed in same time. After three hours from
the start of passing, the passing of the protrusion forming
liquid was stopped. The primarily treated water continued to
be passed through for three hours even after the passing of
the protrusion forming liquid was stopped.
25 Differential pressures of the coarse-particle separation
69
part and the filtering part were measured by a differentialpressure
measuring device, during the passing of the water to
be treated and the primarily treated water. Additionally, an
SDI of liquid (filtrate) that had passed the filtering part
was continuously measured. A 5 filtering speed was 10 m/h.
The protrusion element was made of kaolin. As the kaolin,
powder with an average particle diameter of 10 to 15 μm was
used (made by Takehara Kagaku Kogyo Co., Ltd.). The protrusion
forming liquid was fed to cause a kaolin concentration of 2
10 ppm with respect to the primarily treated water. An SDI of
seawater before passing is 5.2.
Fig. 16 shows a measurement result of differential
pressures of the coarse-particle separation part and the
filtering part (filter layer). In this figure, the horizontal
15 axis is an elapsed time (h), and the vertical axis is the
differential pressure (kPa). According to Fig. 16, during the
passing of the water to be treated, a change in differential
pressures of the coarse-particle separation part and the
filtering part was hardly observed.
20 Fig. 17 shows an SDI measurement result of the filtrate
that has come out from the filtering part. In this figure, the
horizontal axis is an elapsed time (h), and the vertical axis
is the SDI (-). According to The Fig. 17, after the passing of
the protrusion forming liquid through the filter layer, the
25 SDI of the filtrate quickly fell to below 4. It is presumed
70
that the kaolin is captured to form a protrusion, and the
protrusion removes medium sized suspended matters. Here, it
was confirmed that an increase in differential pressures of
the coarse-particle separation part and the filtering part was
5 small.
As an index that indicates a performance of a filter
column, an L/D is used. The L/D is obtained by dividing a
layer thickness L by a particle diameter D. The L/D is a value
proportional to a total area of the filter material per unit
10 filtration area, and as this value is larger, a surface area
of the filter material per unit filtration area is larger.
The L/D of this testing apparatus was 4385. The L was
calculated from an input amount of kaolin, and the L/D
calculated by using a particle diameter of 12.5 μm (an
15 arithmetic average of an average particle diameter) was 0.4.
Thus, it is found that SDI<4 can be satisfied without an
increase of the surface area.
(Study 7)
Protrusion forming liquid containing high-molecular
20 polymer as a protrusion element was fed to primarily treated
water, and a differential pressure of a filtering part and an
SDI of filtrate of the filtering part were measured, as with
(Study 6) above. A filtering speed was 10 m/h.
A solid filter material and a filter layer are same as
25 those in (Study 6) above. As the high-molecular polymer,
71
there was used Himoloc Q707 (polyamide based, molecular weight
(estimate) = 70,000, specific gravity = 1.15) made by HYMO
CORPORATION. The protrusion forming liquid was fed so as to
cause a high-molecular polymer concentration of 0.5 ppm with
respect to the primarily treated water. The water 5 to be
treated is Seawater. An SDI of the seawater before passing
was 5.2.
Fig. 18 shows a measurement result of differential
pressures of a coarse-particle separation part and the
10 filtering part (filter layer). In this figure, the horizontal
axis is an elapsed time (h), and the vertical axis is the
differential pressure (kPa) of the filter layer. According to
Fig. 18, during the passing of the water to be treated, a
change in differential pressures of the coarse-particle
15 separation part and the filtering part was hardly observed.
Fig. 17 shows an SDI measurement result of the filtrate
that has come out from the filtering part. According to Fig.
17, although the SDI of seawater was 5.2, the SDI of the
filtrate of the filtering part was decreased to less than 4
20 after two to three hours of passing of the protrusion forming
liquid. The SDI of the filtrate of the filtering part could
be maintained at less than 4, even after the passing of the
protrusion forming liquid was stopped. It was considered that
the high-molecular polymer had utilized suspended matters in
25 the seawater to form a protrusion on the surface of the solid
72
filter material, causing a decrease in the SDI. Here, it was
confirmed that an increase in differential pressures of the
coarse-particle separation part and the filtering part was
small.
(5 Study 8)
Protrusion forming liquid containing kaolin and highmolecular
polymer as a protrusion element was fed to primarily
treated water, and a differential pressure of the filtering
part and an SDI of the filtrate of the filtering part were
10 measured, as with (Study 6) above. A filtering speed was 10
m/h.
A solid filter material and a filter layer are same as
those in (Study 6) above. As the kaolin, powder with an
average particle diameter of 10 to 15 μm was used (made by
15 Takehara Kagaku Kogyo Co., Ltd.). As the high-molecular
polymer, there was used Himoloc Q707 (polyamide based,
molecular weight (estimate) = 70,000, specific gravity = 1.15)
made by HYMO CORPORATION. The protrusion forming liquid was
fed so as to cause kaolin of 2 ppm and high-molecular polymer
20 of 0.5 ppm with respect to the primarily treated water. The
water to be treated is Seawater. An SDI of the seawater before
passing was 5.6.
Fig. 19 shows a measurement result of the differential
pressures of the coarse-particle separation part and the
25 filtering part (filter layer). In this figure, the horizontal
73
axis is an elapsed time (h), and the vertical axis is the
differential pressure (kPa) of the filter layer. According to
Fig. 19, during the passing of the water to be treated, a
change in the differential pressure of the filtering part was
hardly observed at the coarse-particle separation 5 part.
According to Fig. 19, during the passing of the protrusion
forming liquid, the differential pressure of the filtering
part was not increased, and even after the passing of the
protrusion forming liquid was stopped, the differential
10 pressure of the filtering part was not increased.
Fig. 17 shows an SDI measurement result of the filtrate
that has come out from the filtering part. According to Fig.
17, although the SDI of the seawater before passing was 5.6 or
more, the SDI of the filtrate of the filtering part was
15 decreased to less than 4 after two to three hours of passing
of the protrusion forming liquid. The SDI of the filtrate of
the filtering part could be maintained at less than 4, even
after the passing of the protrusion forming liquid was
stopped. It was presumed that the kaolin and the high20
molecular polymer formed a protrusion on the surface of the
solid filter material, causing a decrease the SDI.
(Study 9)
Filtration was performed by passing seawater that has
been primarily filtered at a constant filtering speed, through
25 a filter layer formed by filling a solid filter material.
74
Then, the filtered water was passed at a predetermined speed
for ten minutes from a direction opposite to the filtration
direction at every 48 hours. A filtering speed was 12 m/h. A
washing speed was 20 m/h.
A filter column (column diameter 30 cm) was formed in 5 a
one-layered structure of a sand filter layer. The sand filter
layer is a filter layer formed by filling sand with an average
particle diameter of 450 μm. A length of the sand filter layer
is 600 mm.
10 Fig. 20 shows a calculation result of a relation between
a washing speed and a developing rate. In this figure, the
horizontal axis is washing (m/h), and the vertical axis is the
developing rate (%). According to Fig. 20, when an average
particle diameter was 450 μm, temperature was 25°C, and a salt
15 concentration = 35 g/kg, washing of the filter layer in this
test at a washing speed of 20 m/h caused the developing rate
of sand to become about 3%. Washing at 40 m/h or more caused
the developing rate to become 30%, which is generally used for
a sand filter layer using a flocculant.
20 During the passing of the seawater that had been
primarily filtered, a differential pressure of the filter
layer was measured by a differential pressure meter.
Additionally, an SDI after 30 minutes from the end of washing,
and an SDI immediately before next washing were measured.
25 For comparison, the washing speed was changed to a
75
predetermined speed, and influence of washing speed on the
differential pressure and on the SDI after washing was
verified. In this test, the developing rates (washing speeds)
were a developing rate 0% (15 m/h), a developing rate 3.3% (20
m/h), a developing rate 15% (30 m/h), and a developing 5 veloping rate
26% (40 m/h).
Figs. 21 and 22 show a relation between a washing speed
and a differential pressure. Fig. 21 is a graph showing when
the washing was performed at the washing speed 20 m/h (Test
10 A). Fig. 22 is a graph showing when the washing was performed
at the washing speeds 20 m/h, 15 m/h, 30 m/h, and 40 m/h (Test
B). In Figs. 21 and 22, the horizontal axis is a date when
the study was made, and the vertical axis is the differential
pressure of the filter layer. Both of the initial differential
15 pressures of filter column are 5 kPa. When washing was
performed at the washing speeds that were set in the Tests A
and B, the differential pressure after washing became 5 kPa,
which was equal to the initial differential pressure, at all
the washing speeds. It was confirmed that, although suspended
20 matters had been captured through the filtration, and the
differential pressure had been increased, the washing stripped
the suspended matters that had increased the differential
pressure, and reset the differential pressure.
Fig. 23 shows a relation between a washing speed and an
25 SDI immediately before the next washing (46 to 47 h after
76
washing). In this figure, the horizontal axis is a date when
the study was made, and the vertical axis is the SDI (-) of
the filtrate of the water to be treated. According to Fig. 23,
in the measurement of the SDI immediately before the next
washing, even when the developing rate was changed from 0% 5 to
26% (from 15 m/h to 40 m/h in washing speed) with respect to
the developing rate 3.3% (washing speed 20 m/h), no difference
was observed in the SDI. It was confirmed that the washing
speed had no influence on the SDI of the filtrate.
10 Fig. 24 shows a relation between a washing speed and an
SDI after 30 minutes from washing. In this figure, the
horizontal axis is a date (time) when the study was made, and
the vertical axis is the SDI (-) of the filtrate of the water
to be treated. As regards the water quality 30 minutes after
15 washing, the SDI is higher when the washing has been performed
at a developing rate 0% (washing speed 15 m/h) than when the
washing has been performed at a developing rate 3.3% (washing
speed 20 m/h). It could be confirmed that the decrease in the
SDI after washing was faster at the developing rate 3.3%
20 (washing speed is 20 m/h). It is presumed that backwashing at
20 m/h that causes filter sand to develop is desirable to
shorten a rise time after washing.
In sand filtration using a flocculant, in order to strip
off sludge that is derived from the flocculant and has adhered
25 to sand filter, washing is strongly performed by air washing
77
at a washing speed to cause a developing rate of about 30%.
This test result has shown that a washing effect can be
obtained even by gentle washing with a reduced developing
rate. It has been found that a washing effect can be obtained
even by washing that reduces a developing rate of a 5 filter
layer and appropriately strips off a biofilm without
performing air washing, rather than a strong washing that
increases the developing rate and strips off all the biofilm
formed on a solid filter material layer by performing air
10 washing.
Washing with a reduced developing rate without performing
air washing is considered to be able to reduce power.
{Reference Signs List}
15 1, 21 water treatment apparatus
2 filtering part (filtration apparatus)
2a filter layer
2b first opening
2c second opening
20 2d third opening
2e fourth opening
3 water-to-be-treated feeding part
3a water-to-be-treated tank
3b first feeding means
25 4 protrusion-element feeding part
78
4a protrusion element tank
4b second feeding means
5 water-quality inspection part
6 determination part
7 protrusion-5 forming control part
8 washing-liquid feeding part
9 backwashing control part
10 first passage
11 second passage
10 12 third passage
13 fourth passage
14 collecting part
15 protrusion-reforming part
16 SBS adding part
15 17 reverse-osmosis-membrane treatment part
22 coarse-particle separation part

We Claim:
1. A regeneration method for a filtration apparatus that has
a filter layer formed by filling a solid filter material
formed with a protrusion on a surface, and passes water to
be treated containing suspended matters through the 5 filter
layer to perform filtration of the suspended matters, the
regeneration method for a filtration apparatus comprising:
a step of backwashing the filter layer by passing
washing liquid through the filter layer in a direction
10 opposite to a passing direction of the water to be treated
such that the protrusion is retained on the surface of the
solid filter material.
2. The regeneration method for a filtration apparatus
according to claim 1, wherein, in the step of backwashing
15 the filter layer, a passing speed of the washing liquid is
controlled so as to suppress a developing rate of the
solid filter material to retain the protrusion on the
surface of the solid filter material.
3. The regeneration method for a filtration apparatus
20 according to claim 2, wherein the washing liquid is passed
through the filter layer without a step of air washing
that backwashes the filter layer by introducing air.
4. The regeneration method for a filtration apparatus
80
according to any of claims 1 to 3, wherein, in the step of
backwashing the filter layer, a developing rate of the
filter layer is obtained and the developing rate of the
filter layer is made to become more than 0% to less than
5 30%.
5. The regeneration method for a filtration apparatus
according to any of claims 1 to 4, further comprising the
steps of:
collecting backwash filtrate generated by the
10 backwashing; and
passing the backwash filtrate through the filter layer
toward the passing direction of the water to be treated,
and reforming a protrusion on the surface of the solid
filter material.
15 6. A regeneration method for a filtration apparatus that has
a filter layer formed by filling a solid filter material
formed with a protrusion on a surface, and passes water to
be treated containing suspended matters through the filter
layer to perform filtration of the suspended matters, the
20 regeneration method for a filtration apparatus comprising
the steps of:
backwashing the filter layer by passing washing liquid
through the filter layer in a direction opposite to a
passing direction of the water to be treated;
81
collecting backwash filtrate generated by the
backwashing; and
passing the backwash filtrate through the filter layer
toward the passing direction of the water to be treated,
and reforming a protrusion on the surface of the 5 solid
filter material.
7. The regeneration method for a filtration apparatus
according to any of claims 1 to 6, further comprising the
steps of:
10 adding a protrusion to the surface of the solid filter
material by feeding a protrusion element to the filter
layer toward the passing direction of the water to be
treated during passing of the water to be treated; and
after feeding of the protrusion element in the step of
15 adding a protrusion, determining whether or not a
protrusion satisfying a preset standard has been added to
the surface of the solid filter material, and when it is
determined that the protrusion has been added, reducing a
feeding amount of the protrusion element as compared with
20 when adding the protrusion.
8. The regeneration method for a filtration apparatus
according to claim 7, further comprising a step of
measuring a differential pressure between a first side of
the filter layer and a second side of the filter layer,
82
wherein
the protrusion element is fed within a range where the
measured differential pressure is less than a
predetermined value, in the step of adding a protrusion.
9. The regeneration method for a filtration 5 apparatus
according to claim 7 or 8, further comprising a step of
directly or indirectly measuring an amount of the
protrusion element contained in filtrate that has come out
from the filter layer in the step of adding a protrusion,
10 wherein it is determined that the protrusion has been
added to the surface of the solid filter material when the
measured amount of the protrusion element becomes equal to
or less than a preset threshold value.
10. The regeneration method for a filtration apparatus
15 according to claim 7, wherein
a total feeding amount of the protrusion element to
the filter layer in the step of adding a protrusion is
counted, and it is determined that the protrusion has been
added to the surface of the solid filter material when the
20 counted total feeding amount reaches a preset threshold
value.
11. The regeneration method for a filtration apparatus
according to any of claims 7 to 10, further comprising a
step of passing the water to be treated through the filter
83
layer and inspecting water quality of the filtrate that
has come out from the filter layer, wherein
when an inspection value of the filtrate exceeds a
preset threshold value, it is determined that the
protrusion satisfying the preset standard has 5 not been
added to the surface of the solid filter material, and the
step of adding a protrusion is performed; and
when the inspection value of the filtrate is equal to
or less than the preset threshold value, it is determined
10 that the protrusion satisfying the preset standard has
been added to the surface of the solid filter material,
and the feeding amount of the protrusion element is
reduced as compared with when the protrusion is added.
12. A filtration apparatus comprising:
15 a filter layer formed by filling a solid filter
material formed with a protrusion on a surface;
a washing-liquid feeding part that passes washing
liquid through the filter layer in a direction opposite to
a passing direction of the water to be treated to perform
20 backwashing; and
a backwashing control part that controls a passing
speed of the washing liquid so as to restrain movement of
the solid filter material to retain the protrusion on the
surface of the solid filter material.
25
84
13. The filtration apparatus according to claim 12, wherein
the backwashing control part obtains a developing rate of
the filter layer, and controls the passing speed of the
washing liquid such that the developing rate of the filter
layer 5 becomes more than 0% to less than 30%.
14. The filtration apparatus according to claim 12 or 13,
further comprising:
a collecting part that collects backwash filtrate
generated by the backwashing; and
10 a protrusion-reforming part that passes the collected
backwash filtrate through the filter layer toward the
passing direction of the water to be treated, and reforms
the protrusion on the surface of the solid filter
material.
15 15. A filtration apparatus comprising:
a filter layer formed by filling a solid filter
material formed with a protrusion;
a washing-liquid feeding part that passes washing
liquid through the filter layer in a direction opposite to
20 a passing direction of the water to be treated to perform
backwashing;
a collecting part that collects backwash filtrate
generated by the backwashing; and
a protrusion-reforming part that passes the collected
85
backwash filtrate through the filter layer toward the
passing direction of the water to be treated, and reforms
the protrusion on the surface of the solid filter
material.
16. 5 A water treatment apparatus comprising:
a filtration apparatus according to any of claims 12
to 15;
a water-to-be-treated feeding part that feeds water to
be treated to a first side of a filter layer to pass the
10 water to be treated through the filter layer;
a protrusion-element feeding part that feeds a
protrusion element to the first side of the filter layer;
a determination part that, based on a preset standard,
determines whether or not a protrusion has been added to a
15 surface of a solid filter material; and
a protrusion-forming control part that, when the
determination part determines that a protrusion has been
added, controls the protrusion-element feeding part to
reduce a feeding amount of the protrusion element as
20 compared with when the protrusion is added, more than when
it is determined that the protrusion has not been added.