Fixing carrier for activated sludge in sewage or waste water treatment

A fixing carrier for fixing an activated sludge employed in a sewage or waste-water treatment in which PA1 a clay, containing kaolinite minerals, of from 10 to 40 parts by weight and a foaming agent of from 5 to 20 parts by weight are blended with a granulated blast furnace slag of from 60 to 90 parts by weight in the presence of water to prepare a wet mixture which is kneaded and shaped into a shaped mixture; and PA1 said shaped mixture is baked at a baking temperature of less than 950.degree. C. at maximum, with the proviso that each of a heat-up time required of said shaped mixture to reach said baking temperature for producing a baked product and a heat-down time required of said baked product to reach a temperature of up to 100.degree. C. is about one hour.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a fixing carrier for fixing an activated 
sludge employed in a biochemical treatment of waste waters such as sewage 
or industrial waste waters containing organic matters. 
2. Description of the Prior Art 
Hitherto, in order to remove the organic matters from the waste water, a 
biochemical treatment of the waste water employing microorganisms has been 
employed. As this treatment, an activated-sludge treatment process is 
generally conducted: an activated sludge (an aggregation of 
microorganisms) is suspended and aerated in an aeration tank of a 
waste-water treatment apparatus so that pollutants contained in the waste 
water are decomposed and removed. However, such activated-sludge treatment 
process has problems that pollutant loading per unit of aeration-tank 
volume is too small and that a large amount of excess sludge is produced. 
These problems are resolved by a prior art described in Japanese Laid-Open 
Patent Publication No. 60-150893 relating to a fixing carrier for the 
activated sludge (microorganisms) employed in the biochemical treatment of 
waste water, which carrier is constructed of inorganic-foam pellets having 
a mean-particle diameter of nothing smaller than 2 mm and a specific 
gravity of up to 1.5. The pellets are prepared as follows: first, a 
foaming agent and a glass-forming agent are blended with expansible 
minerals, non-expansible minerals or refractories to prepare a mixture 
which is then powdered and shaped; and the pelleted mixture is baked into 
the above inorganic-foam pellets. In addition, in order to resolve the 
above problems, another proposal is made, in which crushed stones are 
employed as the fixing carrier for the activated sludge employed in the 
activated-sludge treatment process. Further another proposal is also made 
in a published document Yousui Haisui Handbook (2) (Handbook (2) of Water 
and Waste Water) "published by Sangyo Yousui Chosa Kai (A Board of 
Investigation of Industrial Waste Water)" on Nov. 30, 1974, pp. 823-824, 
FIGS. 3 and 4. This proposal relates to an activated-sludge treatment 
process in which a honeycomb-like fixed-bed type carrier made of plastics 
serves as a carrier for the activated sludge and is disposed in a 
biochemical-reaction tank of a waste-water treatment apparatus. 
However, the above-mentioned prior art and proposals suffer from many 
problems. 
For example, as for the inorganic-foam pellets disclosed in the Japanese 
Laid-Open Patent Publication No. 60-150893, a complex-production process 
thereof makes it difficult to provide such pellets at low cost. In 
addition, in the biochemical treatment of the waste water, foams or pores 
in the pellet are filled with water to increase apparent specific gravity 
of the pellet. This deteriorates a flow properties of the pellet to cause 
the pellet so to be deposited in a dead space of the aeration tank or 
reactor. As a result, in such dead space, the activated sludge fixed to 
the pellets dies from lack of oxygen, accumulates to make the space 
anaerobic and rots to produce a harmful gases, for example such as 
hydrogen sulfide and the like. The hydrogen sulfide and like harmful gases 
deteriorate the functions of the activated sludge, so that a treatment 
performance of the aeration tank employing the above inorganic-foam 
pellets becomes remarkably poor. On the other hand, in case that the 
inorganic material is foamed to have an apparent specific gravity of up to 
1.5, the pellet is greatly occupied by volume of the foams or pores while 
poor in its sturctural strength, which leads to breakdown of the pellet in 
its use for a long period of time. 
In case that the crushed stone is employed as the fixing carrier for the 
activated sludge, the crushed stone is poor in both surface area to weight 
ratio and surface area to volume ratio. For example, as for a crushed 
stone having a diameter of 50 mm, its surface area to volume ratio is only 
90 m.sup.2 /m.sup.3. In this case, due to a lack of an effective surface 
area for fixing the activated sludge (microorganisms), it is impossible to 
retain a sufficient amount of the activated sludge (microorganisms) in the 
biochemical-reaction tank so that a treatment efficiency of waste water by 
sue of such biochemical-reaction tank is remarkably low. Further, a 
porosity of the crushed stone is about 35%. Since this value is very 
small, voids or pores of the crushed stone are immediately clogged with 
the activated sludge having proliferated. In order to prevent the voids or 
pores of the crushed stone from being clogged with the proliferated 
activated sludge, it is necessary to frequently conduct a washing 
operation of the crushed stone serving as the fixing carrier for the 
activated sludge. Incidentally, the crushed stone has a defect that the 
porosity of the crushed stone decreases as the surface area of the same 
increases. In case that the honeycomb-like fixed-bed type carrier made of 
plastics and the like is employed as the fixing carrier for the activated 
sludge, the honeycomb construction of such carrier is readily clogged with 
the proliferated activated sludge. In addition, such honeycomb 
construction has a problem in that it is difficult to realize a steady 
activated sludge layer therein: the activated sludge once fixed to the 
honeycomb construction readily drops out of the construction to 
deteriorate a quality of a treated water. 
As described above, since the conventional fixing carrier for the activated 
sludge employed in the sewage or waste-water treatment process has many 
problems, it is difficult to employ such conventional fixing carrier in a 
large-scale treatment of sewage and other waste water, for example such 
as: ammonia liquors discharged from coke ovens of ironworks; waste water 
discharged from coal-gasification or liquefaction plants; waste water 
produced in the petroleum-refining process; waste water discharged from 
food-processing plants; waste water discharged from fermentation plants of 
alcohol and the like; and like waste waters. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to resolve the above problems by 
providing a novel fixing carrier for fixing the activated sludge 
(microoranisms) sludge employed in the sewage or waste-water treatment. 
In order to accomplish the above object, various materials have been 
reviewed as to a raw materials of the fixing carrier for the activated 
sludge (microorganisms). The inventors of the present application found 
that of these materials, a granulated blast furnace is the most excellent 
as raw materials. The granulated blast furnace slag is produced by 
obtaining a slag as a by-product when pig iron is produced in the blast 
furnace of ironworks, and subsequently by chilling the slag suddenly by 
use of a highly-pressurized water. Consequently, on the basis of the above 
finding, in Japanese Patent Application Nos. 61-184934 (filed: Aug. 6, 
1986) and 61-184935 (filed: Aug. 6, 1986), inventors of the present 
application have proposed a fixed-bed type activated-sludge treatment 
process which is characterized by a ceramic carrier for fixing the 
activated sludge in the aeration tank, a principal component of which 
ceramic carrier is the granulated blast furnace slag. These Japanese 
Patent Applications corresponds to the pending U.S. patent application 
(Masahiro FUJII et al.) filed on Aug. 6, 1987. 
The inventors of the present application continued their researches and 
found an improved ceramic material having a pore size suitable for fixing 
the activated sludge employed in the biochemical treatment of the sewage 
or industrial waste water. 
The reasons why the inventors of the present aplication employ the 
granulated blast furnace slag as a principal component of the fixing 
carrier for the activated sludge (microorganisms) employed in the sewage 
or waste-water treatment are as follows: 
(1) since the granulated blast furnace slag is a by-product in the 
ironworks, it costs little and its composition is stable; 
(2) A finely-powdered granulated blast furnace slag serves well as the 
fixing carrier for the activated sludge, so that a ceramic material a 
principal component of which is made of the granulated blast furnace slag 
is excellent in fixing performance as to the activated sludge, and 
(3) Since the granulated blast furnace slag contains CaO by an amount of 
from 42 to 45% by weight, the ceramic material containing the granulated 
blast furnace slag as its principal component can be produced at the 
baking temperature lower than that of a ceramic material containing 
alumina or silica as its principal component. 
As describd above, the granulated blast furnace slag is excellent as a raw 
material of the fixing carrier for the activated sludge (microorganisms). 
However, it is not possible to obtain a ceramic material suitable for 
fixing the activated sludge by the use of the granulated blast furnace 
slag only, so suitable additives such as a binder, a foaming agent and the 
like must be blended with the granulated blast furnace slag for obtaining 
the ceramic material suitable for fixing the activated sludge. 
As for the binder, the inventors of the present application found that 
clays were materials adapted to be formed as the binder, among which clays 
a clay containing kaolinite minerals is provided with a large affinity to 
the granulated blast furnace slag while excellent in molding and 
processing. In addition, the inventors of the present application also 
found that properties of the foaming agent exerted a powerful influence on 
a formation process of fine pores of the ceramic material, which fine 
pores exert a powerful influence on the fixing performance of the ceramic 
material as to the activated sludge. 
On the basis of the above findings, the inventors of the present 
application made the present invention as to the fixing carrier for the 
activated sludge employed in the sewage or waste-water treatment, which 
carrier costs little and is excellent in both structural strength and 
fixing performance as to the activated sludge (microorganisms). In 
addition, in preparation, the raw materials of the fixing carrier is also 
excellent in formability. 
The gist of the present invention resides in the following: 
A fixing carrier for fixing an activated sludge (microorganisms) employed 
in a sewage or waste-water treatment, characterized in that: 
a clay, containing kaolinite minerals, of from 10 to 40 parts by weight and 
a foaming agent of from 5 to 20 parts by weight are blended with a 
granulated blast furnace slag of from 60 to 90 parts by weight in the 
presence of water to prepare a wet mixture which is kneaded and shaped 
into a shaped mixture; and 
said shaped mixture is baked at a baking temperature of less than 
950.degree. C. at maximum, with the proviso that a heating time required 
so that the shaped mixture may reach the baking temperature for producing 
a baked product is about one hour and that a cooling time required so that 
the heated, shaped mixture may reach a temperature of up to 100.degree. C. 
is also about one hour.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to the present invention, an improved fixing carrier for fixing 
the activated sludge (microorganisms) is prepared as follows: first, a 
clay containing kaolinite minerals and a foaming agent are blended with 
the granulated blast furnace slag in the presence of water to prepare a 
wet mixture which is shaped into a shaped mixture having a predetermined 
form such as a ring-like form or a saddle-like form, and then the thus 
shaped mixture is baked into a final product, i.e., the improved fixing 
carrier of the present invention. 
Now, will be described hereinbelow a process for producing the fixing 
carrier of the present invention for fixing the activated sludge 
(microorganisms) employed in the sewage or waste-water treatment. 
First, the clay and the foaming agent are blended with the granulated blast 
furnace slag which is a principal component of the fixing carrier of the 
present invention. The obtained mixture is shaped in the presence of water 
into the shaped mixture having the predetermined form such as the 
ring-like form or the saddle-like form. In this case, a grain size of the 
granulated blast furnace slag is preferably within a range of from about 
20 to about 200 .mu.m. When the grain size of the granulated blast furnace 
slag is less than 20 .mu.m, the density of the fixing carrier becomes too 
excessive at the time of baking so that the fixing carrier impairs its 
adherability for the activated sludge. On the other hand, when the grain 
size of the granulated blast furnace slag is over 200 .mu.m, the baked 
final product or fixing carrier has an excess porosity to deteriorate in 
its structural strength. 
As for the clays, clays containing the kaolinite minerals, for example such 
as Kibushi clay and Kaerume clay and the like are preferable. Namely, 
among the various clays, the clays containing the kaolinite minerals have 
a large affinity to the granulated blast furnace slag while since they are 
excellent in molding and processing, they are easily shaped into various 
forms. In addition, when the clay containing the kaolinite minerals is 
used, it is hard that the cracking and the like develop in the shaped form 
of the fixing carrier in the baking process. 
As for the foaming agent, there is a combustible material, for example such 
as thermoplastic-resin, sawdust, rice bran, walnut-shell flour, coke dust 
and the like. However, in order to improve the fixing performance of the 
fixing carrier for the activated sludge, it is preferable to employ a 
foaming agent such as calcium carbonate, sodium carbonate, potassium 
carbonate and like carbonate: the foaming agent is pyrolytically 
decomposed at a temperature of from 750.degree. to 900.degree. C. which is 
lower than the baking temperature of the ceramic material by an amount of 
from 50.degree. to 200.degree. C., so that gasses are produced. 
Any of the above carbonates is pyrolytically decomposed at a temperature of 
from 750.degree. to 900.degree. C. to produce a carbon-dioxide gas which 
forms numerous fine pores in the ceramic material during its 
melting/baking operation. Consequently, after completion of the baking 
operation, the numerous pores having a pore size suitable for fixing the 
activated sludge are formed in the surface of the thus baked ceramic 
material or fixing carrier of the present invention. 
In this case, since the conventional combustible foaming agent burns at a 
temperature of from 400.degree. to 600.degree. C., there is a fear that a 
part of formed pores are closed if the baking temperature reaches 
950.degree. C. In contrast with this, since the foaming agent of the 
present invention made of carbonates forms the pores at a temperature of 
from 750.degree. to 900.degree. C., there is no fear that the thus formed 
pores are closed, even when the baking temperature reaches 950.degree. C. 
In blending of the clay containing the kaolinite minerals and the foaming 
agent with the granulated blast furnace slag, in order to ensure an ease 
of sintering and a suitable porosity together with a sufficient structural 
strength of the ceramic material, it is preferable to blend a 10 to 40 
parts by weight of the clay and a 5 to 20 parts by weight of the foaming 
agent with a 60 to 90 parts by weight of the granulated blast furnace 
slag. Particularly, in this case, when the clay is less than 10 parts by 
weight, it is hard for the clay to serve as an effective inorganic binder, 
which makes it impossible to obtain a fixing carrier having a sufficient 
strength. On the other hand, when the clay is over 40 parts by weight, it 
is hard for the clay to be rapidly baked. Incidentally, when the foaming 
agent is over 20 parts by weight, it is impossible to obtain a final 
product having a sufficient strength. 
In preparation of the fixing carrier of the present invention for the 
activated sludge (microorganisms), the clay and the foaming agent 
described above are blended with the granulated blast furnace slag having 
the above grain size and kneaded in the presence of water to prepare the 
wet mixture which is shaped into the shaped mixture having the 
predetermined form such as the ring-like form, saddle-like form and the 
like through an extrusion-molding process or a pressure-molding process. 
The thus shaped mixture is then baked at a suitable baking temperature, 
for example, at a baking temperature of 950.degree. C. or 900.degree. C. 
at maximum, provided that each of a heat-up time required of the shaped 
mixture to reach the baking temperature for producing a baked final 
product and a heat-down time required of the thus produced final product 
to reach a temperature of up to 100.degree. C. is about one hour. The thus 
produced baked product having the granulated blast furnace slag and the 
clay as its principal components constitutes a most suitable fixing 
carrier for fixing the activated sludge (microorganisms) employed in the 
sewage or waste-water treatment. 
Incidentally, in addition to the granulated blast furnace slag, as a raw 
material of the fixing carrier for the activated sludge (mcroorganisms) 
employed in the sewage or waste-water treatment, it is also employed any 
other suitable slag such as an air-cooled blast furnace slag which 
originates in the blast furnace of the iron-works, a converter slag which 
originates in the converter and the like. 
According to the present invention, the principal component of the fixing 
carrier for the activated sludge (microorganisms) employed in the sewage 
or waste-water treatment is made of a pig-iron slag and a steel slag both 
produced in the ironworks, and more particularly made of the granulated 
blast furnace slag. Since any of the above slags contains components such 
as calcium components, magnesium components, iron components, phosphorus 
components and like components which are nutrients for the microorganisms, 
these slags are excellent in affinity to the activated sludge 
(microorganisms). In addition, the fixing carriers of the present 
invention having a predetermined form are randomly loaded in the aeration 
tank to form an aggregation of the fixing carriers for the activated 
sludge in the aeration tank so that the porosity of such fixing carriers 
is large making it possible to retain activated sludge is retained also in 
gaps formed between the fixing carriers of such aggregation, whereby it is 
possible to keep the activated sludge at a high-concentration level in the 
aeration tank. Incidentally, in case that these gaps are clogged with the 
activated sludge (microorganisms), it is possible to easily remove the 
excess sludge (microorganisms), from these gaps through a rinsing 
operation. 
Hereinbelow will be described examples of the fixing carrier of the present 
invention. 
EXAMPLE 1 
The following raw materials were mixed with each other in a dry condition 
by use of a raw-material kneader to prepare a dry mixture: 
a 70 parts by weight of the granulated blast furnace slag; 
a 30 parts by weight of the Kibushi clay; and 
a 10 parts by weight of the foaming agent (sawdust). 
The thus obtained dry mixture was kneaded in the presence of water to 
prepare a wet mixture which was shaped into a shaped mixture having a 
ring-like form having an outer diameter of 25 mm, a height of 25 mm and a 
radial thickness of 3 mm by use of a vacuum-type extrusion molding 
machine. Then, the thus shaped mixture was dried and thereafter received 
in a conveyor-type electric furnace so as to be heated to a temperature of 
900.degree. C. therein and then cooled. In this case, it was conducted to 
heat the shaped mixture to the temperature of 900.degree. C. by taking 
about one hour and subsequently it was conducted to cool the heated, 
shaped mixture from the temperature of 900.degree. C. to the temperature 
of not more than 100.degree. C. by taking about one hour. The thus 
produced ring-like fixing carrier for the activated sludge had a total 
surface area of 284 m.sup.2 /fixing carrier m.sup.3, a specific surface of 
1.24 m.sup.2 /g, a pore diameter of up to 100 .mu.m, a crushing strength 
of from 10 to 40 Kgf, a bulk specific gravity of 0.36, a porosity of an 
aggregation of the fixing carriers having been disorderly loaded in the 
aeration tank being 70%. 
EXAMPLE 2 
The following raw materials were mixed with each other in the same manner 
as that of the Example 1 to prepare a dry mixture: 
a 80 parts by weight of the granulated blast furnace slag; 
a 20 parts by weight of the Kaerume clay; and 
a 15 parts by weight of the foaming agent (calcium carbonate). 
The thus prepared dry mixture was kneaded in the presence of water to 
prepare a wet mixture which was shaped into a shaped mixture having a 
U-shaped form by use of a vacuum-type extrusion molding machine. Then, the 
U-shaped mixture was reshaped into a saddle-shaped form which is like a 
saddle to be put on a horse and that has an outer diameter (D) of a size 
of 3/8 inch (9.525 mm) through a roll-type forming machine, as shown by 
FIGS. 1(a)-1(c). After that, the thus reshaped mixture was placed on a 
netted conveyor of the electric furnace. In the electric furnace, it was 
conducted to heat the shaped mixture to the temperature of 950.degree. C. 
by taking about one hour and subsequently it was conducted to cool the 
heated, shaped mixture from the temperature of 950.degree. C. to the 
temperature of not more than 100.degree. C. by taking about one hour. The 
thus produced, saddle-shaped fixing carrier for the activated sludge had a 
total surface area of 787 m.sup.2 /m.sup.3, a specific surface of 0.67 
m.sup.2 /g , a pore diameter of up to 100 .mu.m, a crushing strength of 
from 10 to 14 Kgf, a bulk specific gravity of 0.32, and a porosity of an 
aggregation of the fixing carriers having been disorderly loaded in the 
aeration tank being 77%. 
EXAMPLE 3 
A cassette having a capacity of 20 liters, filled with the ring-like fixing 
carriers of the Example 1 of the present invention or the saddle-shaped 
fixing carriers of the Example 2 of the present invention, was set in a 
biochemical-reaction tank having a capacity of 40 liters, in which tank 
received an activated-sludge mixture liquid having an activated-sludge 
concentration of about 2500 mg/liter taken from an aeration tank of an 
activated-sludge treatment plant for a sewage. Then, the activated-sludge 
mixture liquid was subjected to an aeration operation in the 
biochemical-reaction tank. As a result, the activated sludge was fixed to 
the interior of the cassette after 10 to 15 hours from the beginning of 
such aeration operation. After that, an artificial sewage having a mean 
BOD.sub.5 concentration of 128 mg/liter was biochemically treated with the 
use of the above cassette for a treatment time of 16 hours, 12 hours, 8 
hours and 6 hours, respectively. Incidentally, in this case, a sludge 
thickener tank was eliminated so that a return operation of the activated 
sludge was not conducted. 
As a result, in any of the above fixing carriers of the Examples 1 and 2 of 
the present invention and in any of the above treatment times, it was 
possible to obtain a well-treated water having a BOD level of up to 5 
mg/liter, a COD level of from 5 to 15 mg/liter, and a suspended-solid 
concentration of from 5 to 15 mg/liter. In this case, the activated sludge 
substantially did not drop out of the cassette filled with the fixing 
carriers of the present invention, which clarifies the fact that the 
activated sludge is steadily fixed to the fixing carriers of the present 
invention. 
The fixing carrier of the present invention enables the treatment time of 
the waste water to be cut about 1/2 to about 1/3, so as to remarkably 
improve the treatment efficiency of the waste water. 
As described above, since the fixing carrier of the present invention 
employs the slags originating in the ironworks as its principal component, 
the raw material thereof costs little. In addition, of these slags, each 
of the blast furnace slag and the converter slag contains CaO at a high 
concentration so that the fixing carrier of the present invention 
containing such slag is lower in baking temperature than the other 
analogous baked product, which enables the fixing carrier of the present 
invention to be rapidly baked so that a baking operation thereof costs 
little. In addition, since the fixing carrier of the present invention 
employs the clay containing the kaolinite minerals as its binder, the 
fixing carrier of the present invention is excellent in molding and 
processing in its preparation while provided with a large resistance to 
cracking at the time of baking, which leads to a sufficient structural 
strength. Further, since the fixing carrier of the present invention 
contains the nutrients for the activated sludge (microorganisms), for 
example such as calcium, magnesium, iron, phosphorus and the like, it has 
a large affinity to the activated sludge (microorganisms). 
Further, the fixing carrier of the present invention has the ring-like form 
or a saddle-shaped form so that its surface area is large, which leads to 
a sufficient amount of gaps formed between the fixing carriers of the 
present invention loaded in the aeration tank. As a result, a large amount 
of the activated sludge can be retained in such gaps to make it possible 
to save the biochemical-reaction tank of the waste-water treatment 
apparatus in volume to an amount of from about 1/2 to 1/3. In addition, 
since the activated sludge can be retained in the gaps between fixing 
carriers, it is possible to substantially prevent the excess sludge from 
flowing out of the biochemical-reaction tank, so that it is also possible 
to simplify the sludge thickener tank in its construction.