U.S. patent application number 11/672574 was filed with the patent office on 2007-06-07 for ceramic filter and method for purifying water.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Manabu ISOMURA, Makoto Itoh, Kenji Mutoh, Minoru Ohta, Tomonori Takahashi.
Application Number | 20070125704 11/672574 |
Document ID | / |
Family ID | 26624945 |
Filed Date | 2007-06-07 |
United States Patent
Application |
20070125704 |
Kind Code |
A1 |
ISOMURA; Manabu ; et
al. |
June 7, 2007 |
CERAMIC FILTER AND METHOD FOR PURIFYING WATER
Abstract
A ceramic filter is provided including a substrate, a separation
layer comprising titania and having an average pore size in a range
of 0.08 to 1 .mu.m and a thickness in a range of 5 to 20 .mu.m, and
an intermediate layer formed between the substrate and the
separation layer. The intermediate layer includes aggregate
particles that are bonded together with glass frits, and aggregate
particles of the intermediate layer are smaller than aggregate
particles of the substrate and larger than aggregate particles of
the separation layer.
Inventors: |
ISOMURA; Manabu;
(Tsushima-City, JP) ; Takahashi; Tomonori;
(Chita-City, JP) ; Mutoh; Kenji; (Motosu-Gun,
JP) ; Ohta; Minoru; (Okazaki-City, JP) ; Itoh;
Makoto; (Handa-City, JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Assignee: |
NGK Insulators, Ltd.
Nagoya-City
JP
|
Family ID: |
26624945 |
Appl. No.: |
11/672574 |
Filed: |
February 8, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10309321 |
Dec 2, 2002 |
|
|
|
11672574 |
Feb 8, 2007 |
|
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Current U.S.
Class: |
210/510.1 ;
210/767 |
Current CPC
Class: |
C02F 1/444 20130101;
B01D 2325/04 20130101; C04B 2111/00801 20130101; C04B 2111/2092
20130101; B01D 69/12 20130101; B01D 2325/28 20130101; C04B 41/89
20130101; B01D 67/0046 20130101; C04B 38/0054 20130101; C04B 41/52
20130101; C04B 41/009 20130101; B01D 71/024 20130101; B01D 39/2068
20130101; C04B 38/0054 20130101; C04B 35/46 20130101; C04B 41/52
20130101; C04B 41/0072 20130101; C04B 41/4539 20130101; C04B
41/5022 20130101; C04B 41/5031 20130101; C04B 41/52 20130101; C04B
41/0072 20130101; C04B 41/4539 20130101; C04B 41/5041 20130101;
C04B 41/009 20130101; C04B 35/10 20130101; C04B 41/009 20130101;
C04B 38/00 20130101; C04B 41/009 20130101; C04B 38/0054
20130101 |
Class at
Publication: |
210/510.1 ;
210/767 |
International
Class: |
B01D 24/00 20060101
B01D024/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 7, 2001 |
JP |
2001-374769 |
Nov 6, 2002 |
JP |
2002-322032 |
Claims
1. A ceramic filter, comprising: a substrate; a separation layer
comprising titania and having an average pore size in a range of
0.08 to 1 .mu.m and a thickness in a range of 5 to 20 .mu.m; and an
intermediate layer formed between said substrate and said
separation layer, said intermediate layer comprising aggregate
particles bonded together with glass frits, said aggregate
particles of said intermediate layer being smaller than an average
pore size of said substrate and larger than aggregate particles of
said separation layer.
2. The ceramic filter according to claim 1, wherein said glass
frits have an average particle size, in terms of volume definition,
that is equal to or smaller than 2/3 of the average particle size
of said aggregate particles of said intermediate layer and contain
10% by volume or less of particles having a size that is equal to
or larger than 3/2 of the average particle size of said aggregate
particles of said intermediate layer.
3. A method for purifying raw water, comprising the steps of:
providing a ceramic filter comprising a substrate, a separation
layer comprising titania and having an average pore size in a range
of 0.08 to 1 .mu.m and a thickness in a range of 5 to 20 .mu.m, and
an intermediate layer formed between said substrate and said
separation layer, said intermediate layer comprising aggregate
particles bonded together with glass frits, wherein said aggregate
particles of said intermediate layer are smaller than an average
pore size of said substrate and larger than aggregate particles of
said separation layer; and passing raw water through said ceramic
filter.
4. The method according to claim 3, further comprising a step of
adding a coagulant to said raw water to cause partial or complete
coagulation of impurities in said raw water before said raw water
is passed through said ceramic filter; and wherein said glass frits
have an average particle size, in terms of volume definition, that
is equal to or smaller than 2/3 of the average particle size of
said aggregate particles of said intermediate layer and contain 10%
by volume or less of particles having a size that is equal to or
larger than 3/2 of the average particle size of said aggregate
particles of said intermediate layer.
5. The method according to claim 3, wherein said raw water is
passed through said ceramic filter in a dead-end filtration
manner.
6. The method according to claim 4, wherein said raw water is
passed through said ceramic filter in a dead-end filtration manner.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/309,321, filed Dec. 2, 2002, the entirety
of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a ceramic filter used for
water purification or the like and a method for purifying water
using the same.
BACKGROUND OF THE INVENTION
[0003] Ceramic filters have a separation layer, which controls the
pore size of the filter, formed on a surface of a substrate formed
from a ceramic porous body or a surface of an intermediate layer
formed on the substrate. Since such ceramic filters have a high
physical strength, endurance, corrosion resistance and the like,
they are used for removing suspended matters, bacteria or dust
particles from liquid or gas in a wide variety of fields including
water treatment, exhaust gas treatment, and medical, pharmacy or
food industry field.
[0004] A known ceramic filter is formed by bonding alumina
particles having a diameter of 12 .mu.m on a support (substrate)
made of cordierite with glass frits, bonding alumina particles
having a diameter of 1.5 .mu.m thereon with glass frits, firing the
product at 1179.degree. C., and to promote self-sintering of
alumina particles having a diameter of 0.3 .mu.m at 1179.degree. C.
(see U.S. Pat. No. 4,983,423 and U.S. Pat. No. 510,652).
[0005] U.S. Pat. No. 5,415,775 also discloses an embodiment of a
filter having a support (substrate) and a separation layer formed
thereon, the separation layer being made of titania and having a
thickness of 25 .mu.m and a pore size of 0.2 .mu.m. However, when
serving as a filter for water purification, for example, ceramic
filters with an alumina separation layer are inferior to ceramic
filters with a titania separation layer in fouling characteristic.
To treat raw water with high turbidity, the raw water needs to be
subjected to a pretreatment, such as coagulation, before
filtration. However, even if fouling is reduced by any
pretreatment, the filter with the separation layer of alumina still
suffers significant fouling.
[0006] As for the filters with a titania separation layer, if the
average pore size is below 0.08 .mu.m, or if the film thickness is
above 20 .mu.m, a satisfactory fouling characteristic cannot be
provided. In water purification, in particular, the filters still
suffer significant fouling if dead-end filtration is adopted for
the raw water with high turbidity. In addition, if the average pore
size of the separation layer is above 1 .mu.m, or if the thickness
thereof is below 5 .mu.m, the filter provides inadequate bacteria
removal. Furthermore, if the separation layer formed on the
intermediate layer is fired without adding any sintering aid to the
aggregate particles, or if the intermediate layer is fired with a
sintering aid other than glass frit added, the filter has a large
maximum pore size and cannot provide high bacteria removal.
[0007] The present invention has been devised in view of such
circumstances. An object thereof is to provide a ceramic filter
having both good fouling characteristics and high bacteria removal
capability, and that can be used suitably for water purification or
the like, and a method for purifying water using the filter.
SUMMARY OF THE INVENTION
[0008] According to a first aspect of the present invention, a
ceramic filter is provided, comprising: a separation layer made of
titania having an average pore size of 0.08 to 1 .mu.m and a
thickness of 5 to 20 .mu.m.
[0009] According to a second aspect of the present invention, a
ceramic filter is provided, comprising: a substrate, a separation
layer, and an intermediate layer formed between the substrate and
the separation layer. The intermediate layer comprises aggregate
particles that are smaller than aggregate particles forming the
substrate and that are larger than the aggregate particles forming
the separation layer. The intermediate layer is formed by bonding
aggregate particles together with glass frits, and the separation
layer is made of titania having an average pore size of 0.08 to 1
.mu.m and a thickness of 5 to 20 .mu.m.
[0010] According to a third aspect of the present invention, a
method for purifying water is provided, comprising the steps of:
providing a ceramic filter comprising a substrate, a separation
layer, and an intermediate layer formed between the substrate and
the separation layer, the intermediate layer comprising aggregate
particles that are smaller than aggregate particles forming the
substrate and that are larger than aggregate particles forming the
separation layer, wherein the intermediate layer is formed by
bonding the aggregate particles together with glass frits, and
wherein the separation layer is made of titania having an average
pore size of 0.08 to 1 .mu.m and a thickness of 5 to 20 .mu.m, and
passing raw water through the ceramic filter.
[0011] In the invention, the term "separation layer of titania"
indicates a separation layer containing 95% by weight or more of
TiO.sub.2.
DETAILED DESCRIPTION OF THE INVENTION
[0012] A ceramic filter according to a first aspect of the present
invention includes a separation layer of titania, which has an
average pore size of 0.08 to 1 .mu.m, preferably 0.1 to 0.6 .mu.m,
and a thickness of 5 to 20 .mu.m, preferably 10 to 15 .mu.m.
Compared to an alumina separation layer or the like, the titania
separation layer has a good fouling characteristic, so that it is
easy to clean contaminations off the separation layer, and good
filtration performance can be maintained for a long time. The
ceramic filter according to the present invention is significantly
superior to the conventional ceramic filters, in particular, if it
is used for water purification applications involving pretreatment
of raw water, such as coagulation, or dead-end filtration.
[0013] If the average pore size is below 0.08 .mu.m or the
thickness is above 20 .mu.m, however, the fouling characteristic
deteriorates, or if the average pore size is above 1 .mu.m or the
thickness is below 5 .mu.m, the bacteria removal capability
deteriorates. Thus, according to the present invention, the average
pore size and the thickness of the separation layer are limited to
the ranges described above to provide both good fouling
characteristic and high bacteria removal capability.
[0014] A second aspect of the invention is a preferred embodiment
of the present invention, and includes a ceramic filter with a
titania separation layer, and which also includes an intermediate
layer provided between the substrate and the separation layer. The
intermediate layer comprises aggregate particles that are smaller
than those of the substrate and larger than those of the separation
layer.
[0015] The aggregate particles of the intermediate layer are bonded
together with glass frits. Forming such an intermediate layer on
the porous support substrate and depositing the separation layer on
a surface of the intermediate layer provides a filter that is
subject to suffering less membrane defects and that has a better
bacteria removal capability than those filters having a separation
layer deposited directly on a surface of the substrate, or on a
surface of an intermediate layer that is fired without adding any
sintering aids to the aggregate particles, or that is fired with an
added sintering aid other than glass frit.
[0016] If the intermediate layer is too thick, the permeability
thereof is reduced. Therefore, the thickness thereof is preferably
equal to or less than 200 .mu.m. The intermediate layer is formed
by filtered-depositing a slurry containing aggregate particles and
glass frits on the substrate. The filter can have a further
improved bacteria removal capability if the glass frits have an
average particle size, in terms of volume definition, equal to or
smaller than two-thirds of that of the aggregate particles of the
intermediate layer and contains 10% by volume or less of coarse
particles having a size equal to or larger than three-seconds of
the average particle size of the aggregate particles.
[0017] The average particle size of the glass frits is preferably
defined as described above because if the average particle size of
the glass frits is too large, the amount of the glass frits
required for strength development is excessively increased and
membrane defects are also increased. The fraction of the coarse
particles in the glass frits is preferably defined as described
above because if a large number of coarse particles are contained,
membrane defects are increased.
[0018] A third aspect of the invention is a method for purifying
water, in which raw water is passed through the ceramic filter
according to the first or second aspects of the invention. By using
a filter having both good fouling characteristics and a high
bacteria removal capability, as described above, water purification
can be conducted adequately for a long time.
[0019] In water purification in water works, the raw water to be
processed may be filtered without any pretreatment, or may be
filtered after a pretreatment, such as coagulation. If the raw
water is clear and causes less fouling, it is filtered without a
pretreatment in many cases, or if the raw water has a high
turbidity, coagulation is to be performed before filtration.
[0020] The filtration methods include dead-end filtration and
cross-flow filtration. In cross-flow filtration, in which fouling
matters are removed by the stream of the raw water, fouling does
not tend to occur. However, in the dead-end filtration, fouling
matters tend to accumulate, so that fouling occurs easily.
[0021] As described above, the titania separation layer has a good
fouling characteristic compared to an alumina separation layer.
Therefore, the ceramic filter according to the present invention is
particularly effective when used for water purification under
conditions where fouling is likely to occur, for example, in the
case where the raw water has a high turbidity and is passed through
the ceramic filter after coagulation, in part or whole, of
impurities in the raw water, or where the raw water is passed
through the ceramic filter in a dead-end filtration manner.
[0022] Now, the present invention will be described in more detail
with reference to examples. However, the present invention should
not be limited to these examples.
Production of Intermediate Body
Substrate:
[0023] A substrate containing alumina as an aggregate and having an
average pore size of 20 .mu.m and a membrane area of 0.4 m.sup.2
was used. The substrate had an outer diameter of 30 mm and a length
of 1000 mm and had 55 holes longitudinally penetrating
therethrough. The substrate was immersed in water to impregnate the
substrate pores with water. To increase the impregnation rate, the
pressure in the container containing the substrate was
decreased.
Intermediate Layer Slurry 1:
[0024] As an aggregate, alumina particles were obtained by grinding
an alumina raw material into pieces having an average particle size
of 3 .mu.m with a ball mill. The ground alumina was mixed with
water with a water to alumina ratio of 80 to 20. Furthermore,
kaolin having an average particle size of 1 .mu.m was added thereto
as a sintering aid with an alumina to kaolin ratio of 100 to 10. In
addition, a dispersing agent was added in an amount of 1% with
respect to the total amount of alumina and kaolin, and Welan gum
was added as an organic binder by the percentage of 0.1% to water.
In this way, an intermediate layer slurry 1 was prepared.
Intermediate Layer Slurry 2:
[0025] As an aggregate, alumina particles were obtained by grinding
an alumina raw material into pieces having an average an particle
size of 3 .mu.m with a ball mill. Ground glass frits having an
average particle size of 1 .mu.m, which is one-third of that of the
aggregate particles, were also used. The glass frits contained 90%
of particles having a diameter equal to or smaller than the average
particle size of the aggregate particles (3 .mu.m). The ground
alumina was mixed with water with a water to alumina ratio of 80 to
20. Furthermore, the glass frits were added thereto with an alumina
to glass frit ratio of 100 to 14. In addition, a dispersing agent
was added in an amount of 1% with respect to the total amount of
alumina and glass frit, and Welan gum was added as an organic
binder by the percentage of 0.1% to water. In this way, an
intermediate layer slurry 2 was prepared.
[0026] The particle size distribution was measured with SALD-2000
manufactured by Shimadzu Corporation. A measurement sample used was
prepared by adding 1% by weight of a polycarboxylic acid dispersing
agent to the powder and diluting the same with water to provide an
adequately scattered light intensity. The relative index of
refraction of alumina with respect to water was 1.7+0.0i, the
relative index of refraction of the glass frit with respect to
water was 1.5+0.0i, and the relative index of refraction of titania
with respect to water was 2.6+0.0i. The particle size distribution
was expressed in terms of volume definition.
Deposition of Intermediate Layer:
[0027] The surfaces of the substrate on the inner and outer wall
sides were separated, the intermediate slurry was applied to the
inner wall side and the pressure on the outer wall side was reduced
to a vacuum using a vacuum pump, thereby filtered-depositing an
intermediate layer. The thickness of the membrane deposited on the
inner wall side was controlled based on the amount of the filtrate
on the outer wall side. The intermediate layer was controlled to
have a thickness of 150 .mu.m.
Firing the Intermediate Layer:
[0028] The intermediate layer slurry deposited on the substrate was
fired in an air atmospheric electric furnace. The intermediate
layer slurry 1 containing no glass frit was fired at 1400.degree.
C. for 5 hours. The intermediate layer slurry 2 containing glass
frits was fired at 1000.degree. C. for 5 hours. Hereinafter, the
intermediate layer formed from the intermediate layer slurry 1 will
be referred to as an intermediate layer 1, and the intermediate
layer formed from the intermediate layer slurry 2 will be referred
to as an intermediate layer 2.
Production of Separation Layer
Separation Layer Slurry 1:
[0029] As an aggregate, alumina particles having an average
particle size of 0.3 .mu.m were used. The alumina particles were
mixed with water with a water to alumina ratio of 97 to 3.
Furthermore, a dispersing agent was added in an amount of 1% with
respect to alumina, and Welan gum and PVA were added as organic
binders by the percentages of 0.08% and 0.1% to water,
respectively. In this way, a separation layer slurry 1 was
prepared.
Separation Layer Slurry 2:
[0030] As an aggregate, titania particles having an average
particle size of 0.5 .mu.m were used. The titania particles were
mixed with water with a water to titania ratio of 97 to 3.
Furthermore, a dispersing agent was added in an amount of 1% with
respect to titania, and Welan gum and PVA were added as organic
binders by the percentages of 0.08% and 0.1% to water,
respectively. In this way, a separation layer slurry 2 was
prepared.
Deposition of Separation Layer:
[0031] Membranes of the separation layer slurry 1 and the
separation layer slurry 2 were deposited on the intermediate layer
described above. The inner and outer wall side surfaces of the
substrate having the intermediate layer formed thereon were
separated, the slurries were applied to the inner wall side, and
the pressure on the outer wall side was reduced to a vacuum using a
vacuum pump, thereby filtered-depositing a separation layer. The
thickness of the membrane deposited on the inner wall side was
controlled based on the amount of the filtrate on the outer wall
side.
Firing of Separation Layer:
[0032] The separation layer slurry deposited on the intermediate
layer was fired in an air atmospheric electric furnace. The
separation layer slurry 1 containing the alumina particles as an
aggregate was fired at 1300.degree. C. for 5 hours. The separation
layer slurry 2 containing the titania particles as an aggregate was
fired at 1000.degree. C. for 5 hours. Hereinafter, the separation
layer of alumina formed from the separation layer slurry 1 will be
referred to as a separation layer 1, and the separation layer of
titania formed from the separation layer slurry 2 will be referred
to as a separation layer 2.
Sealing of the Substrate:
[0033] Both ends of the substrate having the intermediate layer and
the separation layer formed thereon were cut off, and then the
substrate was sealed at both ends with epoxy resin.
Evaluation of Filter Performance
EXAMPLE 1
[0034] In terms of the fouling characteristics, separation layers
of different membrane properties were compared with each other. In
this comparison, the fouling characteristics were examined for the
filter having the separation layer 1 of alumina formed on the
intermediate layer 1 and the filter having the separation layer 2
of titania formed on the intermediate layer 1 (the separation
layers of both the filters have an average pore size of 0.12 .mu.m
and a thickness of 10 .mu.m). The fouling characteristics were
evaluated as described below. The results of the evaluation are
shown in Table 1. For the filter having the separation layer 2 of
titania, the pressure increase per day was about 2 kPa/day or less
after 14 days of filtration with a filtration flow rate of 2
m.sup.3m.sup.-2day.sup.-1. On the other hand, the filter having the
separation layer 1 of alumina exhibited a pressure increase that
was about twice as high.
Method for Evaluating Fouling Characteristic:
[0035] A constant flow rate filtration of river water was conducted
in a housing having an inner wall and an outer wall that were
separated in which the substrates with the respective membranes
were placed. As a pretreatment, depending on the turbidity, 10 to
30 ppm of polyaluminum chloride had been added to the river water
for coagulation. The direction of filtration was from the inner
wall side to the outer wall side, and the filtration was conducted
in the dead-end filtration manner. The filtration flow rate was
constant at 2 m.sup.3m.sup.-2day.sup.-1. Generally, as filtration
proceeds, contaminations accumulate on the inner wall surface and
the pressure thereon increases. To avoid the pressure increase, a
high pressure water of 5 kg/cm was applied from the outer wall side
to the inner wall side and back flushed to clean the contaminations
off the membrane every 6 hours. Operation continued for two weeks
under these conditions, and a pressure variation during the
operation was observed. The pressure increased with the time of
operation and decreased after the back flushing. However, even
after the back flushing, an initial pressure could not be restored,
and the pressure gradually increased. For each of the samples, a
difference between pressures at the start of the operation and at
the end of the operation was measured every day to determine a
pressure increase rate per day, and the pressure increase rates per
day of the samples were compared with each other. A membrane having
a lower pressure increase rate is less susceptible to contamination
and has a better fouling characteristic. TABLE-US-00001 TABLE 1
Average Thickness Of Fouling Intermediate Separation Pore Size
Separation Characteistic Layer Layer (.mu.m) Layer (.mu.m)
(kPa/day) Intermediate Separation 0.12 10 4.1 Layer 1 Layer 1
(Alumina) Separation 0.12 10 2.0 Layer 2 (Titania)
EXAMPLE 2
[0036] The relationship between the thickness of the titania
separation layer and the fouling characteristic and disinfection
capability was evaluated. For filters with a separation layer 2 of
titania formed on the intermediate layer 2 having a different
thickness, the fouling characteristic and the disinfection
capability were examined. Evaluation of the bacteria removal
capability (bacteria removal performance) was conducted in
conformity to AMST-001, the Performance Examination of Membrane
Module for Water Supply by Association of Membrane Separation
Technology of Japan, and JIS-K3823. The results were as shown in
Table 2. It was confirmed that, as for the fouling characteristic,
when the thickness of the separation layer of titania was equal to
or less than 15 .mu.m, operation was possible with a pressure
increase rate equal to or less than 2 kPa/day, if the thickness was
more than 20 .mu.m, the pressure increase rate significantly
increased and exceeded 3 kPa/day. As for the bacteria removal
capability, if the thickness of the separation layer of titania was
more than 10 .mu.m, the bacteria removal performance exceeded 5.
When the thickness was equal to 5 .mu.m, the bacteria removal
performance, which is a reference value, was 4, which is a limit
value defined by AMST-001. TABLE-US-00002 TABLE 2 Thickness Average
Of Fouling Bacteria Pore Separation Charac- Removal Intermediate
Separation Size Layer teristic Perfor- Layer Layer (.mu.m) (.mu.m)
(kPa/day) mance Intermediate Separation 0.12 5 1.6 4 Layer 2 Layer
2 0.12 10 1.8 6 (Bonded With (Titania) 0.12 15 1.9 6 Glass Frits)
0.12 20 2.3 6 0.12 25 3.1 6 0.12 30 3.5 6
EXAMPLE 3
[0037] Separation layers 3 to 8 were formed in the same manner as
the separation layer 2 using titania particles having different
particle sizes from that of the titania particles used for the
separation layer slurry 2. For filters having the separation layers
2 to 8, respectively, formed on the intermediate layer 2 (the
thickness of any separation layer was 10 .mu.m), the fouling
characteristic and the bacteria removal capability were examined.
Pore sizes of the separation layers 2 to 8 were measured by an air
flow method. Then, the average pore size of the separation layer 2
was 0.12 .mu.m, the average pore size of the separation layer 3 was
0.06 .mu.m, the average pore size of the separation layer 4 was
0.08 .mu.m, the average pore size of the separation layer 5 was
0.22 .mu.m, the average pore size of the separation layer 6 was
0.61 .mu.m, the average pore size of the separation layer 7 was
0.98 .mu.m, and the average pore size of the separation layer 8 was
1.92 .mu.m. The results were as shown in Table 3. As for the
fouling characteristic, the filter having the separation layer 3
which has an average pore size smaller than 0.08 .mu.m exhibited
more than twice as high as the pressure increase for the filter
having the separation layer 2. Besides, the filter having the
separation layer 8 which has an average pore size larger than 1
.mu.m exhibited a bacteria removal performance below 4.
TABLE-US-00003 TABLE 3 Thickness Average Of Fouling Bacteria Pore
Separation Charac- Removal Intermediate Separation Size Layer
teristic Perfor- Layer Layer (.mu.m) (.mu.m) (kPa/day) mance
Intermediate Separation 0.12 10 1.8 6 Layer 2 Layer 2 (Bonded With
Separation 0.06 10 5.2 6 Glass Frits) Layer 3 Separation 0.08 10
2.2 6 Layer 4 Separation 0.22 10 1.5 6 Layer 5 Separation 0.61 10
1.3 6 Layer 6 Separation 0.98 10 1.2 4 Layer 7 Separation 1.92 10
1.1 3 Layer 8
EXAMPLE 4
[0038] For filters having the separation layer 2 of titania having
a thickness of 10 .mu.m formed on the intermediate layer 1 fired at
1400.degree. C. using kaolin as a sintering aid and the
intermediate layer 2 containing the aggregate particles bonded with
glass frits and fired at 1000.degree. C., respectively, the fouling
characteristic and a maximum pore size were measured and the
bacteria removal capability was evaluated. The results were as
shown in Table 4. Compared to the filter having the separation
layer formed on the intermediate layer 1, the filter having the
separation layer formed on the intermediate layer 2 had a small
maximum pore size and a high disinfection capability. The results
show that the combination of the intermediate layer having the
aggregate particles bonded with the glass frits and the separation
layer of titania provides high bacteria removal capability and good
fouling characteristic. TABLE-US-00004 TABLE 4 Thickness Of Average
Separation Fouling Maximum Bacteria Intermediate Separation Pore
Size Layer Characteristic Pore Size Removal Layer Layer (.mu.m)
(.mu.m) (kPa/day) (.mu.m) Performance Intermediate Separation 0.12
10 2.0 3.6 4.5 Layer 1 Layer 2 Intermediate Separation 0.12 10 1.8
2.2 6 Layer 2 Layer 2
EXAMPLE 5
[0039] Intermediate layers were formed in the same manner as the
intermediate layer 2 using, as an aggregate for the intermediate
layers, alumina particles obtained by grinding an alumina raw
material into pieces having an average particle size of 3 .mu.m
with a ball mill, and as glass frits, various types of glass frits
having an average particle sizes and coarse particle ratios shown
in Table 5. Then, the separation layer 2 was formed on the
intermediate layers to provide ceramic filters, which were then
evaluated in terms of maximum pore size and bacteria removal
capability.
[0040] The particle size distribution was measured with SALD-2000
manufactured by Shimadzu Corporation. A measurement sample used was
prepared by adding 1% by weight of a polycarboxylic acid dispersing
agent to the powder and diluting the same with water to provide an
adequate scattered light intensity. A relative index of refraction
of alumina with respect to water was 1.7+0.0i, a relative index of
refraction of the glass frit with respect to water was 1.5+0.0i,
and a relative index of refraction of titania with respect to water
was 2.6+0.0i. The particle size distribution was expressed in terms
of volume definition.
[0041] The results were as shown in table 5. If glass frits having
an average particle size larger than two-thirds of the average
particle size of the aggregate particles of the intermediate layer
are used, or if the volume ratio of coarse particles having a
particle size equal to or larger than one-and-a-half
(three-seconds) of the average particle size of the aggregate
particles is higher than 10%, an increased maximum pore size and a
reduced bacteria removal performance are provided. TABLE-US-00005
TABLE 5 Ratio Of Average Average Particle Size Of Particle Coarse
Glass Frits To Size Of Particle Maximum Bacteria Aggregate Glass
Frits Ratio* Pore Size Removal Particles (.mu.m) (%) (.mu.m)
Performance 1/1 3 15 3.1 5 2/3 2 10 2.5 6 1/3 1 1 2.2 6 2/3 2 15
3.0 5 2/5 2 1 2.4 6 *Volume ratio of glass frits particles having
particle size equal to or larger than two-thirds of average
particle size of aggregate particles
[0042] As described above, the ceramic filter according to the
present invention has both good fouling characteristic and high
bacteria removal capability and can be suitably used for water
purification or the like. Besides, according to the method for
purifying water of the invention, since the ceramic filter having
both good fouling characteristic and high bacteria removal
capability is used, water purification can be conducted adequately
for a long time. The ceramic filter according to the invention is
particularly effectively used for water purification under a
condition where fouling is easy to occur, for example, in the case
where the raw water has a high turbidity and coagulation of part or
whole of impurities in the raw water is conducted as a pretreatment
before filtration or where the dead-end filtration is adopted.
* * * * *