Technical Field
The present invention relates to a suspended-matter
removing method and a suspended-matter removing apparatus.
The present invention particularly relates to a suspendedmatter
removing method utilizing a biofilm and a 5 suspendedmatter
removing apparatus utilizing a biofilm that are used
in a seawater desalination plant and a water treatment plant.
Background Art
In recent years, as the seawater desalination market
10 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 osmosis membrane (RO membrane). A filtration
15 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
flocculate the suspended matters. As the flocculant, iron
20 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
conglomeration, generating flocs. An injection amount of
25 the flocculant is increased and decreased in accordance with
3
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 0.5 to10 ppm as iron in the seawater.
Other methods for separating suspended matters include
filter filtration, centrifugation, and filtration 5 n 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. For the solid filter material, those sized to
10 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. Here again, the flocculant is continuously
15 injected to the water to be treated.
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 regularly to discharge flocs that have been deposited
20 inside, to outside of the system. The flocs deposited in
the filter are discharged from inside of the filter by
backwashing.
As a method using a solid filter material, there is
also known a method that utilizes a biofilm to separate
25 suspended matters with a filter filled with a solid filter
4
material without using a flocculant, as disclosed in NPL 1.
Citation List
Non Patent Literature
NPL 1 Kazuhisa Takeuchi et al., "The study of environmentally
friendly pretreatment system", Desalination and 5 Water
Treatment, Volume 51, Issue 7-9, February 2013, pages 1874-
1880
Summary of Invention
Technical Problem
10 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 increased. An increase in the differential pressure
makes it difficult for the water to be treated to pass,
15 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 rate) of suspended matters, and requires long
time (e.g., five hours or more) until the water quality of
20 filtrate becomes stable, causing deterioration of water
quality of the filtrate.
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
25 layer is increased. An increase in the differential pressure
5
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.
However, the filter layer immediately after backwashing has
a low removal rate (capture rate) of suspended 5 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
10 suspended-matter removal mechanism by filtration using a
solid 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
15 have not been fully elucidated at present. Thus, there are
problems in improvement of a removal rate, and in
stabilization of load fluctuation or water quality of
filtrate at starting.
When paying attention to the suspended-matter removal
20 by interception among the removal mechanisms, a passage
becomes smaller as a particle diameter of the solid filter
material is smaller, enabling removal of smaller suspended
matters. Moreover, using a smaller solid filter material
increases a specific surface area of the solid filter
25 material, which can increase a removal rate of fine suspended
6
matters that can be captured on a surface of the solid filter
material by Brownian luck.
However, when a small solid filter material is used, a
pressure loss of the filter is large, and power of a water
feed pump rises, increasing an operation amount. 5 Moreover,
since an operation pressure is high, a container that stores
the solid filter material is required to have a higher
pressure resistance, increasing cost for the apparatus. In
other words, making a solid filter material smaller to
10 improve a removal rate is in a trade-off relation with the
cost.
An apparatus that utilizes a biofilm to remove
(separate) suspended matters, as in NPL 1, requires about
two weeks to one month until the biofilm grows to provide a
15 removal effect. Moreover, a suspended-matter removing
apparatus utilizing a biofilm has a problem that, when
operation of the apparatus is stopped, removal performance
temporarily drops, and a time (e.g., five hours or more) is
required for recovery. Further, there is also a problem that
20 a suspended-matter removing apparatus utilizing a biofilm
cannot follow a rapid change of a suspended-matter
concentration in water to be treated.
The present invention has been made in view of the
above circumstances, and it is an object of the present
25 invention to provide a suspended-matter removing method
7
utilizing a biofilm and a suspended-matter removing apparatus
utilizing a biofilm that require no sludge treatment
facility, and inexpensively provide filtrate satisfying a
desired water quality standard. It is also an object of the
present invention to provide a suspended-5 matter removing
method utilizing a biofilm and a suspended-matter removing
apparatus utilizing a biofilm that can provide filtrate
satisfying a desired water quality standard sooner than a
conventional one at starting or at restarting after operation
10 stop, and also follow a load fluctuation of water to be
treated.
Solution to Problem
The inventors, as a result of intensive study, have
obtained new knowledge that suspended matters of 0.1 to 10
15 μm are not easily removed by a conventional filtration method
using a solid filter material. Based on this, the inventors
have invented a suspended-matter removing method utilizing a
biofilm and a suspended-matter removing apparatus utilizing
a biofilm for removing suspended matters of 0.1 to 10 μm or
20 less.
The present invention provides a suspended-matter
removing method utilizing a biofilm, including the steps of
feeding a protrusion element to a filter layer formed by
filling a solid filter material, to add a protrusion to a
25 surface of the solid filter material; determining whether or
8
not a protrusion satisfying a preset standard has been added
to the surface of the solid filter material; 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; forming a biofilm on the 5 e surface
of the solid filter material; and passing water to be treated
including suspended matters through the filter layer having
the solid filter material added with the protrusion in a
state which the feeding amount of the protrusion element is
10 reduced.
In the invention above, the protrusion is added to the
surface of the solid filter material thereby to cause a
microscopic change in a flow of the water to be treated in
the filter layer, causing suspended matters having a size of
15 0.1 μm or more to 10 μm or less to be captured. This makes
it possible to improve 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. A
fluctuation of water quality (load fluctuation) of the water
20 to be treated is allowed, and the water quality of the
filtrate can be stabilized.
In the invention above, since the protrusion element
is fed to the filter layer so as to add a protrusion to the
surface of the solid filter material, the protrusion can be
25 stably added in a short time. The filter layer formed by
9
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
of removing suspended matters from the water to be treated.
This can shorten a starting time of the 5 filtration apparatus
as compared with a conventional one.
In the invention above, suspended matters are removed
from the water to be treated with the feeding amount of the
protrusion element reduced, which can reduce sludge10
generation amount as compared with when the protrusion
element is continuously fed. This suppresses an increase in
a differential pressure in the filter layer, allowing a
backwashing interval to be prolonged.
In the invention above, forming the biofilm allows
15 growth of the protrusion even after the feeding amount of
the protrusion element is reduced. This can maintain
suspended-matter removal performance at the filter layer and
stabilize water quality of the filtrate.
In one aspect of the invention above, it is preferable
20 to stop feeding of the protrusion element in the step of
reducing the feeding amount of the protrusion element.
Stopping the feeding of the protrusion element enables
suppression of sludge generation, eliminating necessity of a
sludge treatment facility.
25 In one aspect of the invention above, there may be
10
further included a step of passing the water to be treated
through the filter layer in parallel with the step of adding
the protrusion. This makes it possible to add a protrusion
as required while filtering the water to be treated.
In one aspect of the invention above, it is 5 preferable
to include a step of 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 determined that the protrusion satisfying a preset
10 standard has not been formed on 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 protrusion satisfying the preset standard
15 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.
Since the protrusion element forms a protrusion by
adhering to the surface of the solid filter material, the
20 protrusion may be stripped off. Moreover, a protrusion that
has been adhered by a biofilm to grow is stripped of the
biofilm when microorganisms are killed. When the protrusion
or the biofilm is stripped off, a removal performance of the
filter layer is also lowered, deteriorating water quality of
25 the filtrate. According to the aspect described above, since
11
the protrusion is added in accordance with the water quality
of the filtrate, the water quality of the filtrate can be
more stable.
In one aspect of the invention above, a step of
measuring a differential pressure between a first 5 t 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 value, in the step of adding the protrusion.
10 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
invention above, the filter layer is regenerated to be
15 capable of capturing suspended matters having a size of 0.1
μm or more to 10 μm or less with a protrusion, without
narrowing 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
20 the 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
25 of a protrusion element contained in filtrate that has come
12
out from the filter layer in the step of adding the
protrusion, and it can be determined that the protrusion
satisfying a preset standard 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 5 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
10 the projection, a decrease in an amount of the protrusion
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
15 protrusion required to capture suspended matters having a
size of 0.1 μm or more to 10 μm or less.
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 can be
20 determined that the protrusion satisfying a preset standard
has been added to the surface of the solid filter material
when the counted total feeding amount reaches a preset
threshold value.
Presetting a total feeding amount of the protrusion
25 element to the filter layer allows desired protrusion to be
13
easily added.
In one aspect of the invention above, in the step of
passing the water to be treated, it is preferable to pass
the water to be treated through a coarse-particle separation
part to make it to be water to be primarily treated by 5 mainly
separating suspended matters larger than 10 μm contained in
the water to be treated, and then pass the water to be
primarily treated through the filter layer to remove
suspended matters having a size of 0.1 μm or more to 10 μm
10 or less.
Water to be treated containing many suspended matters
with a large particle diameter may cause clogging in an early
stage, due to an interception effect. According to the
aspect described above, since the coarse-particle separation
15 part roughly removes suspended matters having a large
particle diameter, a filtering part can remove suspended
matters having a size of 0.1 μm or more to 10 μm or less with
less influence of suspended matters having a large particle
diameter. Thus, the water quality of the filtrate that has
20 come out from the filtering part can be stabilized, the
differential pressure in the filter layer becomes less likely
to be generated, and a backwashing interval can be prolonged.
When water to be treated contains an oxidizing agent
such as chlorine, in one aspect of the invention above, it
25 is preferable to add sodium hydrogen sulfite to the water to
14
be treated, and then pass the water to be treated through
the filter layer.
This can remove residual chlorine in the water to be
treated, enabling elimination of an inhibiting factor for
5 biofilm formation.
In one aspect of the invention above, a height of the
protrusion is preferably 4 μm or more. This allows the
protrusion to capture suspended matters having a size of 10
μm or less. When the height of the protrusion is too low, a
10 microscopic flow becomes less likely to be generated, and
suspended-matter particles also become less likely to adhere.
In one aspect of the invention above, an average
particle diameter of the solid filter material is preferably
300 μm or more to 2500 μm or less. This can realize the
15 filter layer capable of providing an interception effect
while suppressing the differential pressure of the filter
layer in an initial state.
In one aspect of the invention above, the protrusion
element can be made of kaolin. In one aspect of the invention
20 above, the protrusion element can be made of iron chloride.
In one aspect of the invention above, the protrusion element
can be made of high-molecular polymer.
Making the protrusion element of the above-described
materials makes it possible to inexpensively form a
25 protrusion on the surface of the solid filter material.
15
Making the protrusion element of the above-described
materials realizes the filter layer that can capture
suspended-matter particles having a size of 0.1 μm or more
to 10 μm or less, while hardly increasing the differential
5 pressure of the filter layer.
In one aspect of the invention above, in the step of
reducing the feeding amount of the protrusion element, the
feeding amount of the protrusion element is preferably
reduced such that content of the protrusion element is less
10 than 0.5 ppm as iron (Fe) in solution that passes the filter
layer.
Reducing feeding of the protrusion element enables
suppression of sludge generation. Whereas, even though the
amount is small, continuation of the feeding of the
15 protrusion element allows a protrusion to be additionally
formed even when the protrusion is stripped off, or water
quality of the water to be treated is deteriorated, and
therefore the water quality of the filtrate can be
stabilized.
20 In one aspect of the invention above, it is preferable
to include a step 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
such that the protrusion is retained on the surface of the
25 solid filter material.
16
Washing the filter layer while retaining the protrusion
on the surface of the solid filter material enables
regeneration of the filter layer capable of capturing
suspended matters with the protrusion, even after
backwashing. This can provide filtrate with desired 5 ired water
quality after backwashing as compared with a conventional
one. It is not necessary to retain 100% of the protrusion,
and it is sufficient to retain the protrusion to an extent
allowing filtrate with desired water quality to be obtained
10 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
developing rate of the solid filter material to retain the
15 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 surface of the solid filter material.
20 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
17
of 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%.
Liquid washing at the developing rate being 30% or less
allows the protrusion to be retained on the surface of the
10 solid filter material, while providing a backwashing effect.
A filter layer subjected to liquid washing at the developing
rate being 5% or less can provide filtrate with water quality
of a value equal or close to that before the backwashing,
from immediately after the backwashing.
15 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 water to be treated and reforming a protrusion on the
20 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 suspended-matter concentration of the backwash filtrate is
25 higher than a suspended-matter concentration of water to be
18
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 a protrusion element and suspended matters 5 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 suspended-matter
10 removing apparatus utilizing a biofilm, including a filtering
part having a filter layer formed by filling a solid filter
material; a water-to-be-treated feeding part that feeds water
to be treated to a first side of the filtering part to pass
the water to be treated through the filter layer; a
15 protrusion-element feeding part that feeds a protrusion
element to the first side of the filtering part; a waterquality
inspection part that inspects water quality of
filtrate that has come out from a second side of the filtering
part; a determination part that, based on a preset standard,
20 determines whether or not a protrusion has been added to the
surface of the solid filter material; and a control part that
controls the protrusion-element feeding part to feed the
protrusion element to the filtering part so as to add a
protrusion to the surface of the solid filter material when
25 the determination part determines that the protrusion has
19
not been formed, and to reduce a feeding amount of the
protrusion element as compared with when it is determined
that the protrusion has not been formed, when the
determination part determines that the protrusion has been
5 added.
In one aspect of the invention above, the control part
may also control the protrusion-element feeding part to stop
feeding of the protrusion element when the determination part
determines that the protrusion has been added.
10 In one aspect of the invention above, it is preferable
to include an SBS adding part that is connected to an upstream
side of the filtering part and adds sodium hydrogen sulfite
to the water to be treated before being passed through the
filtering part.
15 Advantageous Effects of Invention
A suspended-matter removing method utilizing a biofilm
and a suspended-matter removing apparatus utilizing a biofilm
according to the present invention perform filtration of
water to be treated with a filter layer formed by filling a
20 solid filter material added with a protrusion, thereby to
inexpensively provide filtrate satisfying a water quality
standard without necessity of a sludge treatment facility.
The suspended-matter removing method utilizing a biofilm and
the suspended-matter removing apparatus utilizing a biofilm
25 can also provide filtrate satisfying a desired water quality
20
standard sooner than a conventional one at starting or at
restarting after operation stop, and also follow a load
fluctuation of water to be treated. Moreover, according to
the present invention, feeding a protrusion element enables
restoration of removal performance without an increase 5 crease in a
differential pressure.
Brief Description of Drawings
Fig. 1 is a schematic block diagram of a suspended-matter
removing apparatus according to a first embodiment.
10 Fig. 2 is a diagram explaining a backwashing means.
Fig. 3 is a schematic view explaining a biofilm.
Fig. 4 is a schematic block diagram of a suspended-matter
removing apparatus according to Modified Example of a second
embodiment.
15 Fig. 5 is a schematic block diagram of a suspended-matter
removing apparatus according to Modified Example of a third
embodiment.
Fig. 6 is a schematic view explaining a passage width d0.
Fig. 7 is a graph showing a simulation result in Study
20 1.
Fig. 8 is a schematic view explaining a flow of water to
be treated.
Fig. 9 is a view showing a simulation result in Study 2.
Fig. 10 is a view showing a simulation result in Study
25 2.
21
Fig. 11 is a view showing a simulation result in Study
2.
Fig. 12 is a graph showing a simulation result in Study
3.
Fig. 13 is a graph showing a measurement result of 5 a
differential pressure of a filter layer in Study 4.
Fig. 14 is a graph showing a measurement result of an
SDI of Tests A and B in Study 4.
Fig. 15 is a graph showing a measurement result of a
10 differential pressure of a filtering part (filter layer) in
Study 5.
Fig. 16 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.
15 Fig. 17 is a graph showing a measurement result of
differential pressures of a coarse-particle separation part
and a filtering part (filter layer) in Study 6.
Fig. 18 is a graph showing a measurement result of an
SDI of filtrate that has come out from the filtering part
20 (filter layer) in Studies 6, 7, and 8.
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 7.
Fig. 20 is a graph showing a measurement result of
25 differential pressures of a coarse-particle separation part
22
and a filtering part (filter layer) in Study 8.
Fig. 21 is a graph showing a calculation result of a
relation between a washing speed and a developing rate in
Study 9.
Fig. 22 is a graph showing a relation between a 5 washing
speed and a differential pressure of Test A in Study 9.
Fig. 23 is a graph showing a relation between a washing
speed and a differential pressure of Test B in Study 9.
Fig. 24 is a graph showing a relation between a washing
10 speed and an SDI immediately before next washing in Study 9.
Fig. 25 is a graph showing a relation between a washing
speed and an SDI 30 minutes after washing in Study 9.
Description of Embodiments
One embodiment of a suspended-matter removing method
15 and a suspended-matter removing apparatus according to the
present invention is now described below with reference to
drawings.
{First Embodiment}
Fig. 1 is a schematic block diagram of a suspended20
matter removing apparatus according to the embodiment. The
suspended-matter removing apparatus 1 includes a filtering
part 2, a water-to-be-treated feeding part 3, a protrusionelement
feeding part 4, a water-quality inspection part 5, a
determination part 6, and a protrusion-forming control part
25 7 (control part).
23
The filtering part 2 has at least one filter layer 2a,
a first opening 2b provided on a first side of the filter
layer 2a, and a second opening 2c provided on a second side
of the filter layer. The first opening 2b and the second
opening 2c are inflow/outflow ports for liquid, of 5 the
filtering part 2. The first opening 2b is connected with a
first passage 7. The second opening 2c is connected with a
second passage 8.
The filter layer 2a is formed by filling a solid filter
10 material in the filtering part. A filling rate 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
15 layer filled with sand and a crushed-carbon filter layer
formed by filling crushed carbon 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
20 with a wide range of sizes.
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
25 of removing chlorine, using crushed activated carbon as the
24
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.
An average particle diameter of the solid 5 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.
The water-to-be-treated feeding part 3 can feed water
10 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 embodiment, the water-to-be-treated feeding part 3
is configured by a water-to-be-treated tank 3a and a first
feeding means 3b. The water-to-be-treated feeding part 3 is
15 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. The stored
water to be treated is seawater, dirty water, industrial
wastewater, or the like. The first feeding means 3b is a
20 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 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
25 2. In this embodiment, the protrusion-element feeding part
25
4 is configured by a protrusion element tank 4a and a second
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 waterto-
be-treated feeding part 3. The protrusion element 5 ement tank
4a is a container that stores the protrusion element. The
second 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
10 the first passage 7.
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
26
is stored in the protrusion element tank in a solution state
prepared at a predetermined concentration (protrusion
forming liquid).
For example, iron chloride becomes iron hydroxide in
the water, and a microfloc of the iron hydroxide adheres 5 to
the surface of the solid filter material, to form a
protrusion. The microfloc may involve minute particles in
the water. For example, kaolin physically adheres to the
surface of the solid filter material, to form a protrusion.
10 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 surface of the solid filter
material along with the particles, to form a protrusion.
The protrusion element that is fed to the filter layer
15 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
material, and particles contained in the water and the kaolin
adhere to the surface of the solid filter material through
20 an adhesive effect of the high-molecular polymer, to form a
protrusion.
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
25 is, for example, an SDI (Silt Density Index) measuring
27
device, a 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 9 and
the determination part 6. The water-quality inspection part
5 can inspect the water quality of the 5 filtrate discharged
from the filtering part 2 to the second passage 9, 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
10 to a surface of a solid filter material. In this embodiment,
the "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
15 added (hereinafter abbreviated as a protrusion has not been
added) when the inspection value obtained from the waterquality
inspection part 5 exceeds a preset threshold value,
and determine that the protrusion satisfying the preset
standard has been added (hereinafter abbreviated as a
20 protrusion has been added) when the inspection value becomes
equal to or less than the threshold value. The threshold
value is appropriately set in accordance with an item of
water quality to be inspected. The determination part 6 may
be incorporated into the protrusion-forming control part 7.
25 It should be noted that, in this embodiment, the
28
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 5 feeding
means 4b, 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
10 part 6 can determine that, when the counted total feeding
amount of the protrusion element reaches a preset threshold
value, 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
15 or the protrusion-forming control part 7. When the
determination part 6 includes the counting means, the
determination part 6 is configured capable of determining
whether or not a protrusion has been added based on
information of at least either the counting means or the
20 water-quality inspection part 5.
The protrusion-forming control part 7 can control a
feeding amount of the protrusion element from the protrusionelement
feeding part 4 such that the protrusion element is
fed so as to add a protrusion to the surface of the solid
25 filter material when the determination part 6 determines that
29
the protrusion has not been formed, and the feeding amount
of the 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 5 appropriately
set in accordance with a kind of the protrusion element.
"Reduce the feeding amount of the protrusion element" means
decreasing the feeding amount of the protrusion element as
compared with when adding the protrusion.
10 When protrusion elements, such as iron chloride and
high-molecular polymer, capable of providing a flocculation
effect 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
15 amount of the protrusion element" includes stopping of the
feeding amount of the protrusion element.
The suspended-matter removing apparatus 1 preferably
includes an SBS adding part 10 that adds sodium hydrogen
sulfite (SBS) to water to be treated on an upstream side of
20 the filtering part 2. The SBS adding part 10 is connected
to the first passage 8 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
25 microorganisms, which causes delay in biofilm formation. The
30
SBS adding part prevents delay in biofilm formation by adding
SBS to the water to be treated to neutralize the oxidizing
agent.
The suspended-matter removing apparatus 1 may include,
at a downstream side of the filtering part 2, a 5 reverseosmosis-
membrane treatment part 11, an electrodialysis part
(not shown), an evaporator (not shown) or the like. The
reverse-osmosis-membrane treatment part 11 is, for example,
a reverse-osmosis-membrane treatment apparatus having a
10 plurality of reverse-osmosis-membrane elements in a
container. The reverse-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
15 reverse osmosis membrane (RO membrane).
The suspended-matter removing apparatus 1 preferably
includes a backwashing means for backwashing the filter layer
2a, as shown in Fig. 2. Fig. 2 is a diagram for explaining
a configuration of the backwashing means. The backwashing
20 means includes a washing-liquid feeding part 12 and a
backwashing control part 13. The filtering part 2 has a
third opening 2d and a fourth opening 2e. The fourth opening
2e is provided on the first side of the filter layer 2a. The
third opening 2d is provided on the second side of the filter
25 layer. The third opening 2d and the fourth opening 2e are
31
inflow/outflow ports for washing liquid. The third opening
2d is connected with a third passage 14. The fourth opening
2e is connected with a fourth passage 18.
The washing-liquid feeding part 12 can feed washing
liquid to the second side of the filtering part 2, to 5 pass
the washing liquid through the filter layer 2a in a direction
opposite to the passing direction of the water to be treated.
In Fig. 2, the washing-liquid feeding part 12 is configured
by a washing-liquid tank 12a and a third feeding means 12b.
10 The washing-liquid feeding part 12 is connected to the third
opening 2d via the third passage 14. The washing-liquid tank
12a 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 2a.
15 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 12b is a pump capable of adjusting a
20 feeding speed, or the like. The third feeding means 12b can
feed the washing liquid stored in the washing-liquid tank
12a to the filtering part 2 via the third passage 14.
The backwashing control part 13 controls a passing
speed of the washing liquid so as to suppress a developing
25 rate of a solid filter material to retain a protrusion on
32
the surface of 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 5 material.
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
33
through a preliminary test or the like in advance.
In Fig. 2, the backwashing control part 13 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 5 predetermined 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.
15 When a length of the filter layer before the passing the
washing liquid is L1, and a 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
20 that the developing rate is more than 0% to less than 30%,
preferably more than 0% to 5% or less.
The backwashing means preferably includes the
collecting part 16 and the protrusion-reforming part 17.
The collecting part 16 can collect and store backwash
25 filtrate (washing liquid that has passed the filter layer)
34
generated by backwashing. The collecting part 16 is connected
to the fourth opening 2e via the fourth passage 18.
The protrusion-reforming part 17 can pass the collected
backwash filtrate through the filter layer toward a passing
direction of the water to be treated. The 5 protrusionreforming
part 17 is, for example, a pump connected to the
collecting part 16. The protrusion-reforming part 17 is
connected to the first opening 2b of the filtering part 2
via the first passage 8.
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 protrusion on the surface of the solid filter material.
The backwash filtrate contains the protrusion element of the
15 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 filter material to reform a protrusion. By
utilizing backwashing liquid for reforming the protrusion,
20 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
cost.
The protrusion-forming control part 7 and backwashing
25 control part 13 are, for example, configured by a CPU
35
(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 in a storage medium or the like, and the CPU 5 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 with a form such as a form that is previously
10 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 magneto-optical disk, a CD-ROM, a DVD15
ROM, a semiconductor memory, or the like.
Next, a suspended-matter removing method according to
the embodiment is described. The suspended-matter removing
method according to the embodiment includes the following
steps (S1) to (S6):
20 (S1) A step of adding a protrusion
(S2) A step of determining whether or not a protrusion has
been added
(S3) A step of reducing a feeding amount of the protrusion
element as compared with when adding a protrusion
25 (S4) A step of passing water to be treated containing
36
suspended matters, through the filter layer having a solid
filter material formed with the protrusion
(S5) A step of forming a biofilm
(S6) A step of backwashing the filter layer
In the step of adding a protrusion (S1), a 5 protrusion
element is fed to the filter layer 2a, to add a protrusion
to the surface of the solid filter material.
The protrusion element is made of iron chloride, iron
sulfate, polyaluminum chloride (PAC), aluminum sulfate,
10 mineral, high-molecular polymer (cationic high-molecular
polymer, anionic high-molecular polymer, and nonionic highmolecular
polymer), inorganic pigment, and the like. The
mineral is, for example, kaolin. For the cationic highmolecular
polymer, polyacrylic ester-based, polymethacrylic
15 acid ester-based, and polyacrylamide-based are suitable. As
the anionic high-molecular polymer, polyacrylamide-based and
polyacrylic acid-based are preferable. As the nonionic highmolecular
polymer, polyacrylic ester-based, polymethacrylic
acid ester-based, and polyacrylamide-based are preferable.
20 The inorganic pigment is, for example, calcium carbonate,
talc, and titanium oxide.
The protrusion element adheres to the surface of the
solid filter material to form a protrusion itself, or bonds
particles in water to the solid filter material. For example,
25 iron chloride becomes iron hydroxide in the water, and a
37
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
example, kaolin physically adheres to the surface of the
solid filter material, to form a protrusion. For 5 example,
high-molecular 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 the particles, to form a protrusion.
10 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
physically adheres to the surface of the solid filter
material, and particles contained in the water and the kaolin
15 adhere to the surface of the solid filter material through
an adhesive effect of the high-molecular polymer, to form a
protrusion.
The protrusion element may be powder or suspension
containing minute particles. In this embodiment, the
20 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 made of high-molecular polymer, the protrusion
25 forming liquid is preferably prepared with solution
38
containing particles (e.g. seawater).
A concentration of the protrusion element in the
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. 5 The
feeding amount of the protrusion element may be appropriately
set in accordance with a kind of the protrusion element and
a component of the water to be treated.
A protrusion is added by passing the protrusion forming
10 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 protrusion forming liquid is preferably same as a
filtering speed of the water to be treated. The filtering
15 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 the filter layer 2a, in parallel with the step
of adding a protrusion (S1).
20 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 solid
filter material. In this embodiment, water quality of
25 filtrate that has come out from the filter layer 2a is
39
inspected, and it is determined whether or not a protrusion
satisfying a preset standard has been added based on the
obtained inspection value. These are hereinafter abbreviated
as a protrusion has been added, and a protrusion has not been
5 added.
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,
10 when the inspection method is an SDI, the threshold value
may be 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
15 filter material, and a feeding amount of the protrusion
element is 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
20 is used a protrusion application that can provide a
flocculation effect in accordance with a feeding amount, the
feeding amount of the 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.
25 For example, when the protrusion element is made of iron
40
chloride, it is reduced to about less than 0.5 ppm as iron
(Fe) with respect 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
5 stopping the feeding of the protrusion element.
Water to be treated containing suspended matters is
passed through the filter layer 2a (S3), with the feeding
amount of the protrusion element reduced (or stopped). Here,
a protrusion has been added to the surface of the solid
10 filter material filled in the filter layer 2a.
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
15 biofilm to be formed on the surface of the solid filter
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
20 performing the step of forming a biofilm (S5). When the
water to be treated is passed through the filter layer 2a,
suspended matters contained in the water to be treated may
adhere to a protrusion to form an effective protrusion
themselves.
25 When water to be treated contains chlorine (Cl), it is
41
preferable to add SBS to the water to be treated, and then
pass through the filter layer 2a. An addition amount of the
SBS is determined depending on the residual chlorine. The
SBS is preferably added such that oxidation-reduction
potential (ORP) becomes a predetermined value. For 5 example,
the SBS is added such that the ORP becomes 200 mV or less.
This can eliminate an inhibiting factor for biofilm
formation.
In this embodiment, the step of adding a protrusion
10 (S1) can be performed in an initial step of suspended-matter
removal, or when a 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
15 quality is continuously inspected during passing of solution,
such as a protrusion 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
20 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 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
25 added to the surface of the solid filter material, and a
42
feeding amount of the protrusion element is reduced as
compared with when the protrusion is added.
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 5 a
protrusion to the surface of the solid filter material. At
a removal of suspended matters from the water to be treated,
passing the protrusion element through the filter layer at
an early stage allows the protrusion to be added to the
10 surface of the solid filter material in a short time.
The filter layer formed by filling the solid filter
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
15 water to be treated. This can shorten a starting time of
the suspended-matter removing apparatus as compared with
conventional ones. Additionally, since the filter layer
filled with the solid filter material added with the
protrusion can capture suspended matters of 0.1 μm or more
20 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 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.
25 Adding a protrusion to the surface of the solid filter
43
material of 300 μm or more to 2500 μm or less provides a
suspended-matter removal effect more than an interception
effect.
Reducing the feeding amount of the protrusion element
enables suppression of sludge generation. This 5 suppresses
an increase in a differential pressure in the filter layer,
which can prolong a backwashing interval and eliminate
necessity of a sludge treatment facility.
Even when the feeding of the protrusion element is
10 stopped, water quality of the filtrate in the step (S3) can
be stabilized until the protrusion is stripped off, as long
as the protrusion has once been added to the surface of the
solid filter material. The protrusion can be replenished by
continuing the feeding of the protrusion element, even though
15 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
protrusion element is stopped, an amount of protrusionelement
usage can be lowered, enabling reduction of treatment
20 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 the surface of the solid filter material. As the solution
25 containing microorganisms continuously flows, the biofilm BF
44
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
supplied to the previously-formed biofilm BF, the protrusion
is presumed to be as shown in Fig. 3 (see Costerton, J.5 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, in this embodiment, is derived
10 from other 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 microorganisms to such a solid filter
15 material causes microorganisms to adhere to a protrusion to
form the biofilm, and 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 be easily adhered by suspended matters
20 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 the biofilm even after the feeding amount of the
protrusion element is reduced, the water quality of the
filtrate can be stabilized for a longer time.
25 Since the water quality of the filtrate is inspected
45
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 quality of the filtrate can be more stable since it is
possible to adjust an amount of the protrusion to be adde5 d
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 to be treated is increased.
10 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
part with the solid filter material, that has been added with
15 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
(S6) is performed.
20 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 the filter layer such that the protrusion is
25 retained on the surface of the solid filter material. The
46
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.
The step of backwashing (S6) is performed only by
washing liquid, while air washing that washes the 5 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
10 layer. Not performing 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 filter layer and perform control such that the washing
15 liquid is passed at a speed at which the developing rate of
the filter layer becomes more than 0% to less than 30%,
preferably more than 0% to 5% or less.
By performing backwashing such that the protrusion is
retained on the surface of the solid filter material to
20 regenerate the filter layer, the filtrate satisfying a
desired water quality standard can be stably obtained from
immediately after the backwashing.
It is more preferable that the step of backwashing the
filter layer (S6) is performed such that the biofilm formed
25 in (S5) above is retained. As regards "a biofilm is
47
retained", it is not necessary to retain all the biofilms,
and 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. 3, 5 , while a
biofilm of about 200 μm on the right-most side of the figure
in Fig. 3 may be stripped off without being retained.
{Second Embodiment}
Fig. 4 is a schematic block diagram of a suspended10
matter removing apparatus 21. The suspended-matter removing
apparatus 21 has 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
15 between a water-to-be-treated feeding part 3 and a filtering
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
20 is a sand filtration apparatus, a floatation-separation
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 floatation25
separation apparatus, solid-liquid separation is performed
48
by 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, 5 suspended
matters larger than 10 μm is mainly separated from the water
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
10 or more to 10 μm or less are removed.
The protrusion element can be fed to the filter layer
2a, at a same time as guiding the water to be primarily
treated to the filter layer. The protrusion element may be
fed to the filter layer 2a before guiding the water to be
15 primarily treated to the filter layer 2a. In either case, a
protrusion 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).
20 According to the embodiment, by separating the rough
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
25 clogging or the like in the filter layer can be suppressed.
49
This makes it possible to stabilize the water quality of the
filtrate of the filter layer, and reduce a backwashing
frequency of the filter layer.
{Third Embodiment}
The third embodiment is different from the 5 first
embodiment in that the suspended-matter removing apparatus
includes a differential-pressure measurement part. Same
reference numerals are given to configurations that are
identical to those in the first embodiment, and description
10 thereof is omitted
Fig. 5 is a schematic block diagram of a suspendedmatter
removing apparatus according to the embodiment. The
suspended-matter removing apparatus 31 includes a filtering
part 2 (filtration apparatus), a water-to-be-treated feeding
15 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
20 measure 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
25 2. The differential-pressure measurement part 32 is, for
50
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
preset standard, whether or not a protrusion has 5 been added
to a surface of a solid filter material. In this embodiment,
the determination part 36 includes a protrusion-elementamount
measurement means (not shown) that directly or
indirectly measures an amount of the protrusion element
10 contained in the filtrate that has come out from the second
side (second opening side) of the filtering part 2. The
protrusion-element-amount measurement means may be
sufficient if it can directly or indirectly measure the
amount of the protrusion element. For example, when the
15 protrusion element is made of iron chloride, a water-quality
analyzer capable of monitoring an iron concentration can be
used as the protrusion-element-amount measurement means, to
directly measure the protrusion element. For example, using
an SDI measuring device as the protrusion-element-amount
20 measurement means enables indirect measurement of the
protrusion element. For example, when the protrusion element
is made of kaolin, using a turbidimeter as the protrusionelement-
amount measurement means enables indirect
measurement of the protrusion element.
25 When the protrusion element is indirectly measured, the
51
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
5 inspection means.
The determination part 36 can determine that a
protrusion that is preset and satisfies a standard has been
added to the surface of the solid filter material, when a
measured value of the protrusion-element-amount measurement
10 means becomes equal to or less than a preset threshold value.
The determination part 36 may also determine that a
protrusion that is preset and satisfies a standard has been
added to the surface of the solid filter material, when it
is confirmed that the measured value becomes equal to or less
15 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 protrusion-forming control part 37.
The protrusion-forming control part 37 is connected to
the differential-pressure measurement part 32, the
20 determination part 36, and a second feeding means 4b. The
protrusion-forming control part 37 can control a feeding
amount of the protrusion element from the protrusion-element
feeding part 4 such that the differential pressure measured
by the differential-pressure measurement part 32 becomes less
25 than a predetermined value. The protrusion-forming control
52
part 37 receives a differential pressure value measured by
the 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 5 the
predetermined value.
The protrusion-forming control part 37 can control the
protrusion-element feeding part 4 to feed the protrusion
element to add a protrusion to the surface of the solid
10 filter material when the determination part 36 determines
that a protrusion has not been added, and to reduce the
feeding amount of the protrusion element when the
determination part 36 determines that a protrusion has been
added.
15 The water treatment apparatus 31 may include, at a
downstream side of the filtering part 2, a reverse-osmosismembrane
treatment part 11, an electrodialysis part (not
shown), an evaporator (not shown) or the like. The water
treatment apparatus 31 may include a backwashing means (not
20 shown) for backwashing the filter layer 2a.
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 a
25 first side of a filter layer and a second side of the filter
53
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
suspended matters, through the filter layer having a 5 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
10 protrusion element is fed to the filter layer 2a to add a
protrusion to 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
15 being fed to the filter layer 2a, the differential pressure
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)
20 is less than 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
25 may previously be set by performing a preliminary test or
54
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 the filter layer. 5 r. 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
10 contained in the filtrate that has come out from the filter
layer 2a in the step of adding a protrusion (S11), is directly
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
15 added to the surface of the solid filter material. When it
is determined that the protrusion has been added, the 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
20 passed through the filter layer 2a (S14), with the feeding
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
25 inspect the water quality of the filtrate that has come out
55
from the filter 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
5 (5) and (S6) in the first embodiment.
According to the embodiment, measuring the differential
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.
10 According to the embodiment, measuring the amount of
the protrusion element in the filtrate that comes out when
the protrusion element is fed enables confirmation that the
protrusion element has not come out to the filtrate.
Thereby, in an indirect way, it can be confirmed that a
15 protrusion has been formed on the surface of the solid filter
material.
Next, a basis for the present invention and a working
effect are described.
(Study 1)
20 A study was made, through a simulation, regarding a
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
25 filling a solid filter material. A balance equation in the
56
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 5 in
contact with the three solid filter materials (see Fig. 6).
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
10 diameters of 100μm, 300μm (a minimum diameter of sand used
industrially for sand filtration), and 1200μm (a maximum
diameter of sand used 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
15 velocity 12.5 m/h). In this simulation, the passage width
d0 was same as the particle diameter of the solid filter
material.
A simulation result is shown in Fig. 7. In this figure,
the horizontal axis is the captured-particle diameter (μm),
20 and the vertical axis is the capture rate (%). According to
Fig. 5, as the solid filter material is smaller, the capture
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
25 when there was used a solid filter material having a size of
57
a minimum diameter of sand used industrially for sand
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 5 t suggests
that, conventionally, as water to be treated contained more
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.
10 Thus, the inventors have concluded that, it is possible
to cope with load fluctuation and stabilize the water quality
of the filtrate, by removing suspended matters having a size
of 0.1 μm or more to 10 μm or less. In conventional filtration
using a solid filter material, the reason why suspended
15 matters having a size of 0.1 μm or more to 10 μm or less are
not removed is considered as follows.
Fig. 8 shows a schematic view of a flow of water to be
treated when the water to be treated is passed through the
filter layer formed by filling a solid filter material. In
20 this figure, a symbol S represents a solid filter material,
and lines F extending in a vertical direction in the figure
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. 8. It is known that, in
25 the laminar flow state, a flow rate of the water to be treated
58
becomes lower as closer to a surface of the solid filter
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 5 the
filter layer formed by filling the solid filter material,
coarse 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
10 capable of being passed through a gap of the solid filter
material of the solid filter material, relatively larger
suspended matters may come out from the laminar flow by the
law of inertia, and collide with the solid filter material
to be captured. In the suspended matters contained in the
15 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 to diffusion by Brownian
motion.
Whereas, among the suspended matters contained in the
20 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 like, and are passed through the filter layer
with the laminar flow.
25 Based on the consideration above, a study was made
59
regarding a method for intentionally removing medium sized
suspended matters (particles with a particle diameter of 0.1
μm or more to 10 μm or less) from the laminar flow.
(Study 2)
A study was made, through a simulation, regarding 5 a
behavior of suspended matters when water to be treated
containing suspended matters is passed through a filter layer
formed by filling a solid filter material added with a
protrusion. The simulation was performed by using the
10 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 motion is not considered. A passage width d0 was
600 μm, which was equivalent to a diameter of the solid
15 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 μm and a width of 60 μm on a surface of the
20 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 suspended matters, the size of
protrusion, and the passage width.
25 A simulation result is shown in Figs. 9 to 11. In
60
Figs. 9 to 11, a vertical direction in the figure is a passage
width d0, and the water to be treated flows from left to
right in the figure. Fig. 9 is a view showing a flow of
suspended matters. Fig. 10 is a view illustrating a state
of protrusions in an early stage of passing of the water 5 to
be treated, and Fig. 11 is a view illustrating a state of
protrusions in a late stage of passing of the water to be
treated.
According to Fig. 9, it could be confirmed that a
10 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
the laminar flow became easy to enter a blocking region, so
15 that a capture rate of the medium sized suspended matters
could be increased.
According to Figs. 10 and 11, 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
20 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 matters adhered to protrusions in
25 the early stage of passing water (Fig. 10), and other
61
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.
11), so that the protrusions grown.
Although not illustrated, when the water to be 5 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.
10 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
15 the protrusion element is reduced or stopped afterward.
(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
20 diameter of a filter for an SDI measurement) to 10 μm in
seawater, on 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
25 of the protrusion was defined as a height. Particle
62
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 5 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. 12. In this figure,
the horizontal axis is the captured-particle diameter (μm),
10 and the vertical axis is the height of a protrusion (μm).
According to Fig. 12, 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.
15 12, removal of suspended matters of 0.45 μm required a
rectangle (protrusion) with a height of 40 μm.
(Study 4)

Protrusion forming liquid containing a protrusion
20 element was passed through a filter layer formed by filling
a 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
25 three hours. A filtering speed was 10 m/h.
63
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 sequentially arranged from an upstream side 5 de 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
10 is a 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.
15 The protrusion element was made of iron chloride
(FeCl3: 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
20 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
25 the protrusion forming liquid was passed through the filter
64
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.
During the passing of the water to be treated, 5 , a
differential pressure of the filter layer was measured by a
differential-pressure measuring device. Additionally, an
Fe-concentration and an SDI of liquid (filtrate) that has
passed the filter layer were continuously measured. The Fe10
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
15 using a filter with a diameter of 47 mm and an average pore
diameter of 0.45 μm.
SDITm = (1 - Δt1/Δt2) × 100/Tm ∙∙∙ (2)
Δt1: A time (sec) required for filtration/collection of
initial 500 ml.
20 Δt2: A time (sec) required for filtration/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).
25 An upper limit of the SDI index is 6.67. Since the SDI
65
is decreased, it is suggested that a ratio of suspendedmatter
particles larger than 0.45 μm is decreased.

For comparison, only seawater was passed without
passing of the protrusion forming liquid through 5 the filter
layer, and the measurement was performed as with Test A.
Fig. 13 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
10 differential pressure (kPa) of the filter layer. According
to Fig. 13, 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
15 the passing of the protrusion forming liquid was stopped.
In Test B (a case 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. 14 shows a measurement result of an SDI of Tests
20 A and B. In this figure, the horizontal axis is an elapsed
time (h), and the vertical axis is the SDI (-).
According to Fig. 14, 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
25 liquid was stopped, the SDI of the filtrate was maintained
66
at about 4.
Although not shown in Fig. 14, 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
hydroxide contained in the protrusion forming liquid 5 d 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
10 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
15 to cause an Fe-concentration of 1 ppm with respect to the
water to be 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. 14, the SDI of the filtrate remained
20 high at 5.21 when only the water to be treated 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
25 matters (0.1 μm to 10 μm) could not be removed, preventing a
67
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
protrusion forming liquid through the filter layer, 5 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.
10 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
15 filtration. Thus, in general, the filter layer must be washed
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
20 liquid to add a protrusion to a surface of a solid filter
material, it is only capturing suspended matters contained
in water to be treated, reducing a washing frequency of a
solid-filter-material layer without increasing a
differential pressure.
25 (Study 5)
68
A suspended-mater removal test was performed by using
a suspended-matter removing apparatus provided with a coarseparticle
separation part (column diameter 5 cm) and a
filtering part (column diameter 5 cm).
A sand filtration apparatus was used as the coarse5 -
particle 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
10 an average 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)
15 formed by filling anthracite with an average particle
diameter 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.
20 The anthracite 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 coarse25
particle separation part by a water-to-be-treated feeding
69
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 5 d and the
primarily 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
10 after the passing of the protrusion forming liquid was
stopped.
Differential pressures of the coarse-particle
separation part and the filtering part were measured by a
differential-pressure measuring device, during the passing
15 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 filtering
speed was 10 m/h.
The protrusion element was made of iron chloride
20 (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. 15 shows a measurement result of differential
25 pressures of the coarse-particle separation part and the
70
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. 15, during
the passing of the water to be treated, a change in the
differential pressure of the filtering part was 5 hardly
observed at the coarse-particle separation part. According
to Fig. 15, while the differential pressure of the filtering
part was slightly increased during the passing of the
protrusion forming liquid, an increase in the differential
10 pressure was not observed during the passing of only the
primarily treated water after the passing of the protrusion
forming liquid was stopped.
Fig. 16 shows an SDI measurement result of the filtrate
that has come out from the filtering part. In this figure,
15 the horizontal axis is an elapsed time (h), and the vertical
axis is the SDI (-). According to Fig. 16, 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 to three hours of passing of the protrusion forming
20 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. While a standard of
a turbidity concentration required for feed water to an RO
(reverse osmosis) membrane is generally SDI<4, the filtrate
25 of two to three hours of passing satisfied the water quality
71
standard.
Based on the results of Studies 1 to 3, it is presumed
that the coarse-particle separation part mainly captures
suspended matters smaller than 0.1 μm, and suspended matters
larger than 10 μm. Since the SID has been decreased 5 sed 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
suspended matters of 0.1 μm or more to 10 μm or less.
10 (Study 6)
A suspended-mater removal test was performed by using
a suspended-matter removing apparatus provided with a coarseparticle
separation part (column diameter 5 cm) and a
filtering part (column diameter 5 cm). A sand filtration
15 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 with an average particle
20 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
72
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 filter layer, the sand filter layer, 5 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 coarse10
particle separation part by a water-to-be-treated feeding
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
15 forming liquid, and the protrusion forming liquid and the
primarily 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
20 after the passing of the protrusion forming liquid was
stopped.
Differential pressures of the coarse-particle
separation part and the filtering part were measured by a
differential-pressure measuring device, during the passing
25 of the water to be treated and the primarily treated water.
73
Additionally, an SDI of liquid (filtrate) that had passed
the filtering part was continuously measured. A 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 5
μm was used (made by Takehara Kagaku Kogyo Co., Ltd.). The
protrusion forming liquid was fed to cause a kaolin
concentration of 2 ppm with respect to the primarily treated
water. An SDI of seawater before passing is 5.2.
10 Fig. 17 shows a measurement result of 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. 17, during
15 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.
Fig. 18 shows an SDI measurement result of the filtrate
that has come out from the filtering part. In this figure,
20 the horizontal axis is an elapsed time (h), and the vertical
axis is the SDI (-). According to The Fig. 18, after the
passing of the protrusion forming liquid through the filter
layer, the SDI of the filtrate quickly fell to below 4. It
is presumed that the kaolin is captured to form a protrusion,
25 and the protrusion removes medium sized suspended matters.
74
Here, it was confirmed that an increase in differential
pressures of the coarse-particle separation part and the
filtering part was small.
As an index that indicates a performance of a filter
column, an L/D is used. The L/D is obtained by dividing 5 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 filtration area, and as this value is larger, a
surface area of the filter material per unit filtration area
10 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
arithmetic average of an average particle diameter) was 0.4.
Thus, it is found that SDI<4 can be satisfied without an
15 increase of the surface area.
(Study 7)
Protrusion forming liquid containing high-molecular
polymer as a protrusion element was fed to primarily treated
water, and a differential pressure of a filtering part and
20 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
those in (Study 6) above. As the high-molecular polymer,
there was used Himoloc Q707 (polyamide based, molecular
25 weight (estimate) = 70,000, specific gravity = 1.15) made by
75
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
to be treated is Seawater. An SDI of the seawater before
5 passing was 5.2.
Fig. 19 shows a measurement result of differential
pressures of a 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
10 differential pressure (kPa) of the filter layer. According
to Fig. 19, 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.
Fig. 18 shows an SDI measurement result of the filtrate
15 that has come out from the filtering part. According to Fig.
18, although the SDI of seawater was 5.2, the SDI of the
filtrate of the filtering part was 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
20 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 the seawater to form a protrusion on the surface
of the solid filter material, causing a decrease in the SDI.
25 Here, it was confirmed that an increase in differential
76
pressures of the coarse-particle separation part and the
filtering part was small.
(Study 8)
Protrusion forming liquid containing kaolin and highmolecular
polymer as a protrusion element was fed 5 to
primarily treated water, and a differential pressure of the
filtering part and an SDI of the filtrate of the filtering
part were measured, as with (Study 6) above. A filtering
speed was 10 m/h.
10 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
Takehara Kagaku Kogyo Co., Ltd.). As the high-molecular
polymer, there was used Himoloc Q707 (polyamide based,
15 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 highmolecular
polymer of 0.5 ppm with respect to the primarily
treated water. The water to be treated is Seawater. An SDI
20 of the seawater before passing was 5.6.
Fig. 20 shows a measurement result of the 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
25 differential pressure (kPa) of the filter layer. According
77
to Fig. 20, 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 part.
According to Fig. 20, during the passing of the protrusion
forming liquid, the differential pressure of the 5 filtering
part was not increased, and even after the passing of the
protrusion forming liquid was stopped, the differential
pressure of the filtering part was not increased.
Fig. 18 shows an SDI measurement result of the filtrate
10 that has come out from the filtering part. According to Fig.
18, although the SDI of the seawater before passing was 5.6
or more, the SDI of the filtrate of the filtering part was
decreased to less than 4 after two to three hours of passing
of the protrusion forming liquid. The SDI of the filtrate
15 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 highmolecular
polymer formed a protrusion on the surface of the
solid filter material, causing a decrease the SDI.
20 (Study 9)
Filtration was performed by passing seawater that has
been primarily filtered at a constant filtering speed,
through a filter layer formed by filling a solid filter
material. Then, the filtered water was passed at a
25 predetermined speed for ten minutes from a direction opposite
78
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
a one-layered structure of a sand filter layer. The sand
filter layer is a filter layer formed by filling sand 5 with
an average particle diameter of 450 μm. A length of the sand
filter layer is 600 mm.
Fig. 21 shows a calculation result of a relation
between a washing speed and a developing rate. In this
10 figure, the horizontal axis is washing (m/h), and the
vertical axis is the developing rate (%). According to Fig.
21, when an average particle diameter was 450 μm, temperature
was 25°C, and a salt concentration = 35 g/kg, washing of the
filter layer in this test at a washing speed of 20 m/h caused
15 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.
During the passing of the seawater that had been
20 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
79
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 5 a developing
rate 26% (40 m/h).
Figs. 22 and 23 show a relation between a washing speed
and a differential pressure. Fig. 22 is a graph showing when
the washing was performed at the washing speed 20 m/h (Test
10 A). Fig. 23 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. 22 and 23, 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
15 initial differential 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
20 confirmed that, although suspended 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.
25 Fig. 24 shows a relation between a washing speed and
80
an SDI immediately before the next washing (46 to 47 h after
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.
24, in the measurement of the SDI immediately before the 5 next
washing, even when the developing rate was changed from 0%
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
10 the washing speed had no influence on the SDI of the filtrate.
Fig. 25 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
15 water to be treated. As regards the water quality 30 minutes
after 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
20 decrease in the SDI after washing was faster at the
developing rate 3.3% (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
25 strip off sludge that is derived from the flocculant and has
81
adhered to sand filter, washing is strongly performed by air
washing 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 5 developing
rate. It has been found that a washing effect can be obtained
even by washing that reduces a developing rate of a filter
layer and appropriately strips off a biofilm without
performing air washing, rather than a strong washing that
10 increases the developing rate and strips off all the biofilm
formed on a solid filter material layer by performing air
washing.
Washing with a reduced developing rate without
performing air washing is considered to be able to reduce
15 power.
Reference Signs List
1, 21 suspended-matter removing apparatus
2 filtering part
2a filter layer
20 2b first opening
2c second opening
3 water-to-be-treated feeding part
3a water-to-be-treated tank
3b first feeding means
25 4 protrusion-element feeding part
82
4a protrusion element tank
4b second feeding means
5 water-quality inspection part
6 determination part
7 protrusion-5 forming control part (control part)
8 first passage
9 second passage
10 SBS adding part
11 reverse-osmosis-membrane treatment part
10 22 coarse-particle separation part

We Claim:
1. A suspended-matter removing method utilizing a biofilm,
comprising the steps of:
By feeding a protrusion element to a filter layer
formed by filling a solid filter material, adding 5 a
protrusion to a surface of the solid filter material;
determining whether or not a protrusion
satisfying a preset standard has been added to the
surface of the solid filter material;
10 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;
forming a biofilm on the surface of the solid
filter material; and
15 passing water to be treated including suspended
matters through the filter layer having the solid filter
material added with the protrusion in a state in which
the feeding amount of the protrusion element is reduced.
20 2. The suspended-matter removing method according to claim
1, wherein the feeding of the protrusion element is
stopped, in the step of reducing the feeding amount of
the protrusion element.
25 3. The suspended-matter removing method according to claim
84
1 or 2, further comprising a step of passing the water
to be treated through the filter layer in parallel with
the step of adding a protrusion.
4. The suspended-matter removing method according to 5 o any
of claims 1 to 3, further comprising a step of inspecting
water quality of the filtrate that has come out from
the filter layer, wherein
when an inspection value of the filtrate exceeds
10 a preset threshold value, it is determined that the
protrusion satisfying the preset standard has not been
formed on 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
15 equal to or less than the preset threshold value, it is
determined 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
20 protrusion is added.
5. The suspended-matter removing method according to any
of claims 1 to 4, further comprising a step of measuring
a differential pressure between a first side of the
25 filter layer and a second side of the filter layer,
85
wherein
the protrusion element is fed within a range in
which the measured differential pressure is less than a
predetermined value, in the step of adding a protrusion.
5
6. The suspended-matter removing method according to any
of claims 1 to 5, further comprising a step of directly
or indirectly measuring an amount of the protrusion
element contained in filtrate that has come out from
10 the filter layer in the step of adding the protrusion,
wherein it is determined that the protrusion satisfying
the preset standard 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
15 preset threshold value.
7. The suspended-matter removing method according to any
of claims 1 to 3, wherein a total feeding amount of the
protrusion element to the filter layer in the step of
20 adding a protrusion is counted, and it is determined
that the protrusion satisfying the preset standard has
been added to the surface of the solid filter material
when the counted total feeding amount reaches a preset
threshold value.
25
86
8. The suspended-matter removing method according to claims
1 to 7, wherein
in the step of passing the water to be treated,
the water to be treated is passed through a coarseparticle
separation part to make the water to be 5 treated
into water to be primarily treated by mainly separating
suspended matters larger than 10 μm contained in the
water to be treated, and
then the water to be primarily treated is passed
10 through the filter layer to removed suspended matters
having a size of 0.1 μm or more to 10 μm or less.
9. The suspended-matter removing method according to any
of claims 1 to 8, wherein sodium hydrogen sulfite is
15 added to the water to be treated, and then the water to
be treated is passed through the filter layer.
10. The suspended-matter removing method according to any
of claims 1 to 9, wherein a height of the protrusion is
20 4 μm or more.
11. The suspended-matter removing method according to any
of claims 1 to 10, wherein an average particle diameter
of the solid filter material is 300 μm or more to 2500
25 μm or less.
87
12. The suspended-matter removing method according to any
of claims 1 to 11, wherein the protrusion element is
made of kaolin.
5
13. The suspended-matter removing method according to any
of claims 1 to 11, wherein the protrusion element is
made of iron chloride.
10 14. The suspended-matter removing method according to claim
13, wherein, in the step of reducing the feeding amount
of the protrusion element, the feeding amount of the
protrusion element is reduced such that content of the
protrusion element becomes less than 0.5 ppm as iron in
15 solution that passes the filter layer.
15. The suspended-matter removing method according to any
of claims 1 to 14, wherein the protrusion element is
made of high-molecular polymer.
20
16. The suspended-matter removing method according to any
of claims 1 to 15, further comprising a step of
backwashing the filter layer by passing washing liquid
through the filter layer in a direction opposite to a
25 passing direction of the water to be treated such that
88
the protrusion is retained on the surface of the solid
filter material.
17. The suspended-matter removing method according to claim
16, wherein, in the step of backwashing 5 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.
10
18. The suspended-matter removing method according to claim
17, wherein the washing liquid is passed through the
filter layer without a step of air washing that
backwashes the filter layer by introducing air.
15
19. The suspended-matter removing method according to any
of claims 16 to 18, 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
20 is made to become more than 0% less than 30%.
20. The suspended-matter removing method according to any
of claims 16 to 19, further comprising the steps of:
collecting backwash filtrate generated by the
25 backwashing; and
89
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.
5
21. The suspended-matter removing method according to any
of claims 1 to 15, further comprising the steps of:
backwashing the filter layer by passing washing
liquid to the filter layer in a direction opposite to a
10 passing direction of the water to be treated;
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
15 treated, and reforming a protrusion on the surface of
the solid filter material.
22. A suspended-matter removing apparatus utilizing a
biofilm, comprising:
20 a filtering part having a filter layer formed by
filling a solid filter material;
a water-to-be-treated feeding part that feeds
water to be treated to a first side of the filtering
part to pass the water to be treated through the filter
25 layer;
90
a protrusion-element feeding part that feeds a
protrusion element to the first side of the filtering
part;
a water-quality inspection part that inspects
water quality of filtrate that has come out from a 5 second
side of the filtering part;
a determination part that, based on a preset
standard, determines whether or not a protrusion has
been added to the surface of the solid filter material;
10 and
a control part that, when the determination part
determines that the protrusion has not been formed,
controls the protrusion-element feeding part to feed
the protrusion element to the filtering part so as to
15 add a protrusion to the surface of the solid filter
material, and 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
20 it is determined that the protrusion has not been
formed.
23. The suspended-matter removing apparatus according to
claim 22, wherein the control part controls the
25 protrusion-element feeding part to stop feeding of the
91