Method for treatment of waste water

A method for the treatment of waste water, which comprises wet oxidizing said waste water with a molecular oxygen-containing gas of an amount 1.0 to 1.5 times the amount thereof theoretically necessary for decomposing at least one substance selected from the group consisting of organic substances and inorganic substances present in said waste water to nitrogen, carbon dioxide, and water at a temperature not exceeding 370.degree. C. under a pressure enough for said waste water to retain a liquid phase in the presence of a solid catalyst comprising of a first catalytic component formed of titanium dioxide, a second catalytic component formed of the oxide of an element of lanthanide series, and a third catalytic component containing at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, tungsten, copper, silver, gold, platinum, palladium, rhodium, ruthenium, and iridium or a water-insoluble or sparingly water-soluble compound of said metal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method for the wet oxidation of a waste water 
containing a chemical oxygen-demanding substance (hereinafter referred to 
as "COD" component) in the presence of a catalyst. More particularly, it 
relates to a method for efficient detoxification of a waste water 
containing harmful oxidizable organic or inorganic substances, i.e. a COD 
component, by the catalytic wet oxidation of the waste water in the 
presence of molecular oxygen thereby effecting conversion of such organic 
substances into harmless substances such as carbon dioxide, water, and 
nitrogen. 
2. Description of the Prior Art 
In the methods for treatment of waste water, the biochemical method called 
as an "activated sludge method" and the wet oxidation method called as 
"Zimmermann method" have been popular. 
As universally known, the activated sludge method spends a long time in the 
decomposition of organic substances and requires the waste water to be 
diluted to a concentration fit for the growth of algae and bacteria and, 
therefore, has the disadvantage that the facilities for the activated 
sludge treatment demand a large floor area for their installation. Further 
in recent years, particularly in urban distriots, the disposal of excess 
sludge arising from the treatment calls for a huge expense. The Zimmermann 
method effects oxidative decomposition of organic substances contained in 
a high concentration in an aqueous solution by introducing air under a 
pressure in the range of 20 to 200 atmospheres at a temperature in the 
range of 200.degree. to 370.degree. C. into the aqueous solution. This 
method requires to use a large reaction vessel because the reaction 
proceeds at a low velocity and consumes a long time in the decomposition 
of organic substances and also requires this reaction vessel to be made of 
a material of high durability. The method, therefore, has an economic 
problem in terms of the cost of equipment and the cost of operation of 
this equipment. Methods which use various oxidizing catalysts for the 
purpose of heightening the reaction velocity in the treatment have been 
proposed. 
In the catalysts heretofore proposed for use in the method of catalytic wet 
oxidation, compounds of such noble metals as palladium and platinum 
(JP-A-49-44,556(1974)) and compounds of such heavy metals as cobalt and 
iron (JP-A-49-94,157(1974) have been popular. These catalysts have the 
aforementioned compounds deposited on spherical or cylindrical pieces of a 
carrier made of alumina, silica-alumina, silica gel, or activated carbon, 
for example. In the catalytic wet oxidation of a waste water, the waste 
water more often than not has the pH value thereof adjusted to a level 
exceeding 9 in advance of the treatment. Our study on these catalysts has 
revealed that, in the course of a protracted use, the catalysts suffer 
from loss of strength and reduction of size and, moreover, the carrier 
possibly succumbs to dissolution under the impact of the treatment. In the 
case of an alumina type catalyst, for example, the loss of strength tends 
to occur on account of exudation of alumina. 
Recently, a method using titania or zirconia as a carrier for the purpose 
of solving the problem of this nature has been proposed 
(JP-A-58-64,188(1983)). This invention discloses a catalyst having a 
compound of such a noble metal as palladium or platinum and a compound of 
such a heavy metal as iron or cobalt deposited on spherical or cylindrical 
pieces of carrier made of titania or zirconia. The catalyst according with 
this invention is indeed recognized to possess highly satisfactory 
strength as compared with the catalyst using the conventional carrier. The 
catalysts of this class invariably come in a particulate form. They are 
not fully satisfactory in catalytic activity or durability. The titania 
type catalysts, for example, are liable to undergo loss of strength due to 
crystal transformation. 
In some cases, the oxide of an element of the lanthanide series has been 
used as a catalyst. This catalyst, however, is not fully satisfactory in 
physical durability or moldability. 
Methods using the combinations of a cerium compound with such composite 
oxides as TiO.sub.2 -ZrO.sub.2, TiO.sub.2 -SiO.sub.2 -ZrO.sub.2, and 
TiO.sub.2 -ZnO for the purpose of further improving the conventional 
catalysts have been proposed (JP-A-63-158,189(1988) and 1-218,684(1989) to 
1-218,686(1989)). These catalysts are notably improved in durability and 
activity. They, however, prove at times to be inferior in initial activity 
to catalysts having catalytically active substances deposited exclusively 
on ceria. 
Incidentally, in the wet oxidation of a waste water, the water is required 
to be treated in a very large amount. More often than not, therefore, the 
method of using a fixed bed of catalyst in a flow system is adopted for 
the reaction. Further, the waste water frequently contains solid 
substances. In these cases, when the catalyst is in a particulate form, 
the fixed bed suffers from heavy pressure loss due to the passage of the 
waste water therethrough and consequently fails to give to the waste water 
the treatment at a high linear velocity and, therefore, requires to 
possess a large cross section for the flow of the waste water and give a 
proportionate addition to the floor area for the reaction vessel. In the 
case of the treatment of a waste water entrailing solid substances, the 
resistance offered by the fixed bed to the flowing waste water in 
consequence of the clogging of the bed with the solid substances is 
increased so much as to raise the running cost of the apparatus and render 
lasting operation of the apparatus impracticable. Specifically, in the 
treatment of waste water by the catalytic wet oxidation technique, since 
the reaction is carried out at an elevated temperature under a high 
pressure, the increase in the floor area to be occupied by the reaction 
vessel entails a fatal problem of boosting the cost of equipment. 
The fluidized bed method which fluidizes a powdery catalyst for the purpose 
of lowering the pressure loss caused by a catalyst bed has been proposed. 
This method has not yet found utility in any practical application, 
however, because it entails the disadvantage that the treatment requires 
use of a huge reaction vessel owing to the inevitable decrease in the 
concentration of the catalyst and the separation of the catalyst from the 
treated waste water is difficult. 
There is also a method which effects oxidative decomposition of organic 
substances in a waste water at normal room temperature under normal 
pressure by the use of ozone or hydrogen peroxide as an oxidizing agent. 
JP-A-58-55,088(1983), for example, discloses a method which effects 
oxidative decomposition of organic substances such as humic acid contained 
in a waste water at 20.degree. C. under normal pressure in the absence of 
a catalyst by the use of ozone and hydrogen peroxide. JP-A-58-37,039(1983) 
discloses a method which comprises adding a surfactant to a waste water 
containing an organic compound possessing an aromatic ring, mixing the 
resultant mixture with at least one member selected from among compounds 
of transition metals and alkaline earth metal compounds, and then bringing 
ozone into contact with the produced mixture at normal room temperature 
under a normal pressure and therefore effecting oxidative decomposition of 
the organic compound. Since the former method carries out the treatment in 
the absence of a catalyst, it is incapable of effectively treating a waste 
water having sparingly oxidizable substances suspended therein. Since the 
latter method uses the metallic ions of a transition metal or an alkaline 
earth metal as a catalyst, the treated waste water cannot be released in 
its unmodified form from the equipment and must be purged of the metallic 
ions in advance of the release and, therefore, has the disadvantage that 
the treatment requires an extra step for aftertreatment. Both these two 
methods have the disadvantage that since they treat the waste water at 
normal room temperature under normal pressure, the treatment consumes 
expensive ozone in a large amount, the reaction proceeds at a low 
velocity, the decomposition of organic substances occurs in a low ratio, 
and the ozone partially escapes the reaction and the unaltered ozone 
necessitates a treatment for detoxification. 
An object of this invention, therefore, is to provide a method for 
effecting efficient and lasting treatment of waste water. 
Another object of this invention is to provide a method for treating waste 
water efficiently at a high linear velocity. 
Yet another object of this invention is to provide a method for treating a 
waste water containing a solid substance stably at a high linear velocity 
for a long time. 
SUMMARY OF THE INVENTION 
These objects are accomplished by a method for the treatment of waste 
water, which comprises wet oxidizing waste water with a molecular 
oxygen-containing gas of an amount 1.0 to 1.5 times the theoretical amount 
thereof necessary for thoroughly decomposing at least one substance 
selected from the group of organic substances and inorganic substances 
present in said waste water into nitrogen, carbon dioxide, and water at a 
temperature of not higher than 370.degree. C. under a pressure enough for 
the waste water to retain a liquid phase in the presence of a solid 
catalyst comprising a first catalytic component formed of titanium 
dioxide, a second catalytic component formed of the oxide of an element of 
the lanthanide series, and a third catalytic component containing at least 
one metal selected from the group consisting of manganese, iron, cobalt, 
nickel, tungsten, copper, silver, gold, platinum, palladium, rhodium, 
ruthenium, and iridium or a water-insoluble or sparingly water-soluble 
compound of the metal. 
This invention further concerns a method for the treatment of waste water, 
wherein the catalyst is in the form of a monolithically constructed 
structure. This invention also concerns a method for the treatment of 
waste water, wherein the catalyst is in the form of honeycombs so shaped 
that the through holes thereof have an equivalent diameter in the range of 
2 to 20 mm, the cells thereof have a wall thickness in the range of 0.5 to 
3 mm, and the openings thereof account for a ratio in the range of 50 to 
80%. Further, this invention concerns a method for the treatment of waste 
water, wherein the simultaneous passage of the waste water and the 
oxygen-containing gas through the catalyst is effected in the presence of 
ozone and/or hydrogen peroxide. 
The catalyst contemplated by this invention is characterized by using 
titanium dioxide and the oxide of an element of lanthanide series as 
catalytic components. 
The oxides of elements of the lanthanide series exhibit a catalytical 
activity even in their simple forms. Since they have poor moldability, 
however, they cannot be easily molded in the shape of pellets or 
honeycombs. During their use in a long term reaction for the treatment, 
they are degraded in physical strength and this degradation forms a cause 
for deterioration of their catalytic activity. 
We have found that this problem can be solved by the combinations of 
titanium dioxide and the oxides of elements of the lanthanide series. 
These combinations are excellent in moldability and in physical stability 
as well, sparingly susceptible of degradation in strength and activity of 
catalyst, and capable of withstanding a long term use. 
When the powder obtained by coprecipitating the titanium compound and the 
lanthanide compound, impregnating, and intimately mixing the mixture as 
with a ball mill mixer, and calcining the resultant powder is used as a 
raw material for the catalyst, it produces a desirable effect of lending 
itself to improving the homogeneity of catalyst and to further enhancing 
the stability of strength and activity. 
The adoption of the technique of coprecipitation proves to be particularly 
advantageous among other conceivable techniques in the sense that the 
coprecipitation increases the BET (Brunauer-Emmet-Teller) specific surface 
area of the powder, fairly facilitates the molding of the powder in the 
shape of honeycombs, and widens the variety of catalyst shapes selectable 
to suit a given waste water. 
The catalyst of this invention is sparingly decomposable under the 
conditions of wet oxidation and, therefore, capable of exhibiting a high 
catalytic activity to acetic acid which often persists in a high 
concentration in varying waste water during the treatment. The catalyst of 
this invention, therefore, effects the treatment of acetic acid with high 
efficiency and manifests an outstanding effect in enhancing the efficiency 
of treatment of varying waste water at low temperatures. 
EXPLANATION OF THE PREFERRED EMBODIMENT 
The catalyst to be used in the present invention contains titanium dioxide 
as the first catalytic component, the oxide of an element of lanthanide 
series as the second catalytic component, and at least one metal selected 
from the group consisting of manganese, iron, cobalt, nickel, tungsten, 
copper, silver, gold, platinum, palladium, rhodium, ruthenium, and iridium 
or a water-insoluble or sparingly water-soluble compound of the metal as 
the third catalytic component. 
The BET surface area of the titanium dioxide as the first catalytic 
component of the catalyst to be used in the present invention is desired 
to exceed 10 m.sup.2 /g, preferably to fall in the range of 30 to 120 
m.sup.2 /g. 
At least one of the oxides of the elements of Lanthanide series such as 
lanthanum, cerium, praseodymium, neodymium, and samarium can be used as 
the second catalytic component serving the purpose of improving the 
stability of catalyst. Particularly, at least one of the oxides of 
lanthanum, cerium, and neodimium among other elements of lanthanide series 
proves to be desirable because it is effective in enhancing the stability 
of catalyst and the catalytic activity. 
As respect the proportions of the catalytic components of the catalyst to 
be used in this invention, the proportion of the first catalytic component 
is preferable to be in the range of 5 to 98% by weight as oxide, that of 
the second catalytic component in the range of 2 to 95% by weight as 
oxide, and that of the third component in the range of 0.05 to 25% by 
weight as metal or compound. Preferably, the amount of manganese, iron, 
cobalt, nickel, tungsten, copper, and silver among other elements to be 
used in the composition of the third catalytic component is in the range 
of 0 to 25% by weight as compound (oxide or sulfide, for example) and the 
amount of platinum, gold, palladium, rhodium, ruthenium, and iridium to be 
used is in the range of 0 to 10% by weight as metal (providing that the 
total amount of the two species of metals mentioned above is in the range 
of 0.05 to 25% by weight). More preferably, the proportion of the first 
catalytic component is in the range of 10 to 96% by weight as oxide, that 
of the second catalytic component in the range of 4 to 90% by weight as 
oxide, and that of the third catalytic component in the range of 0.1 to 9% 
by weight as metal or compound. Still more desirably, the proportion of 
the first catalytic component is in the range of 10 to 84% by weight as 
oxide, that of the second catalytic component in the range of 16 to 90% by 
weight as oxide, and that of the third catalytic component in the range of 
0.1 to 9% by weight as metal or compound. Preferably, the amount of 
manganese, iron, cobalt, nickel, tungsten, copper, and silver among other 
metals available for the composition of the third catalytic component is 
in the range of 0 to 9% by weight as compound and the amount of platinum, 
gold, palladium, rhodium, ruthenium, and iridium to be used is in the 
range of 0 to 5% by weight as metal (providing that the total amount of 
the two species of metals mentioned above is in the range of 0.1 to 9% by 
weight). Incidentally, the total amount of the first, second, and third 
catalytic components is 100% by weight. 
If the proportion of the third catalytic component deviates from the range 
mentioned above, the produced catalyst is deficient in oxidative activity. 
In the case of such a noble metal as platinum, palladium, or rhodium, the 
cost of raw material is unduly high and the produced catalyst is incapable 
of manifesting a sufficient effect proportionate to the cost. If the 
proportion of the first catalytic component and that of the second 
catalytic component deviate from the respective ranges mentioned above, 
the produced catalyst is deficient in resistance to hot water and 
undesirable in terms of catalyst life. 
The catalyst to be used in the present invention is preferable to be 
composed as defined above. The shape of this catalyst may be selected from 
among various shapes such as pellets, beads, rings, saddles, powder, 
random fragments, and integrally constructed structure such as honeycombs, 
for example. Among other shapes mentioned above, that of honeycombs proves 
to be particularly desirable. In this particular shape, the through holes 
have an equivalent diameter in the range of 2 to 20 mm, preferably 4 to 12 
mm. If this equivalent diameter is less than 2 mm, the through holes incur 
heavy pressure loss and, particularly when the waste water contains solid 
substances, tend to be clogged possibly to the extent of rendering a 
protracted use of the catalyst impracticable. If the equivalent diameter 
exceeds 20 mm, though the pressure loss is small and the possibility of 
clogging is low, the amount of the catalyst to be used for manifestation 
of a stated efficiency of treatment must be increased proportionately to 
the increase in the diameter. The diameter of the through holes is limited 
by the relation between the efficiency of treatment and the performance of 
the catalyst itself. 
The cells have a wall thickness in the range of 0.5 to 3 mm, preferably 0.5 
to 2 mm. If the wall thickness is less than 0.5 mm, the produced catalyst 
enjoys the advantage that it incurs only a small pressure loss and 
acquires a reduction in weight and yet suffers from the disadvantage that 
the catalyst loses mechanical strength. If the wall thickness exceeds 3 
mm, the catalyst has sufficient mechanical strength and yet suffers from 
the disadvantage that it experiences heavy pressure loss. 
For the same reason as given above, the ratio of openings is in the range 
of 50 to 80%, preferably 62 to 76%. 
With due respect to the true state of affairs mentioned above, the catalyst 
of the shape of honeycombs to be used particularly preferably in the 
present invention has through holes 2 to 20 mm in equivalent diameter and 
cells 0.5 to 3 mm in wall thickness and openings 50 to 80% in ratio. Even 
under such severe reaction conditions as a high reaction temperature in 
the range of 100.degree. to 370.degree. C. and a high reaction pressure 
enough for waste water to retain a liquid phase, the honeycomb-shaped 
catalyst fulfilling the requirements mentioned above possesses ample 
mechanical strength and a sufficiently large geometric surface area. It, 
therefore, excels in durability and allows waste water to be treated at a 
high linear velocity with low pressure loss. Even when the waste water 
contains solid substances, this catalyst is enabled to retain high 
activity over a long period without entailing the phenomenon of clogging. 
The cross-sectional shape of the through holes may be a rectangle, hexagon, 
or a corrugated circle on the condition that the equivalent diameter of 
the through holes is in the range mentioned above. 
In the present invention, it is preferable to use molecular oxygen and 
ozone and/or hydrogen peroxide as oxidizing agents because they enable 
such organic compounds as acetic acid which are held to be rather 
insusceptible of oxidation to be decomposed with high efficiency and allow 
the reaction to proceed at relatively low temperature and pressure. 
Further, since the catalyst of this invention possesses an ability to 
decompose ozone to oxygen, it is characterized by possessing the advantage 
of substantially decomposing the waste ozone and preventing the waste 
ozone from leaking into the ambient air. 
The amount of the ozone to be used is sufficient in the range of 0.001 to 
1.2 mols, preferably 0.003 to 0.6 mol, per mol of the amount of oxygen 
theoretically necessary for effecting thorough decomposition of the 
organic and inorganic substances present in the waste water into nigrogen, 
carbon dioxide, and water. The amount of hydrogen peroxide to be used is 
sufficient in the range of 0.01 to 1.8 mols, preferably 0.003 to 0.2 mol, 
per mol of the aforementioned theoretical amount of oxygen. When ozone 
and/or hydrogen peroxide is used in combination with molecular oxygen, 
though the reaction temperature varies with the behavior of the waste 
water, the amount of the oxidizing agent to be used, and so on, it is 
lower than when molecular oxygen alone is used. In case where the reaction 
temperature falls in the range of 200.degree. to 300.degree. C. when the 
molecular oxygen is used, it falls approximately in the range of 
100.degree. to 250.degree. C. when the oxidizing agent is additionally 
used. 
The starting raw material for the titanium to be used in the first 
catalytic component of the present invention may be selected from among 
such inorganic titanium compounds as titanium chloride, titanium sulfate, 
titanium hydroxide, titanium dioxide, and titania sol and such organic 
titanium compounds as titanium oxalate and tetraisopropyl titanate. 
The starting materials for elements of lanthanide series usable for the 
second catalytic component of this invention include oxides, hydroxides, 
and inorganic salts, for example. The starting raw materials for cerium 
are cerium acetate, cerium nitrate, cerium sulfate, cerium oxide, and 
ceria sol, for example. The addition of this starting material to the 
titanium dioxide can be favorably attained by the following methods. 
(1) A method which comprises dissolving a salt of a lanthanide series 
element in a solution of a titanium salt, adding ammonia to the resultant 
solution thereby inducing precipitation, washing the precipitate, drying 
it, and calcining the dried precipitate at a temperature in the range of 
300.degree. to 900.degree. C. 
(2) A method which comprises suspending a finely powdered oxide of a 
lanthanum series element in a solution of a titanium salt, adding ammonia 
to the resultant solution thereby inducing precipitation, washing the 
precipitate, drying it, and calcining the dried precipitate at a 
temperature in the range of 300.degree. to 900.degree. C. 
(3) A method which comprises impregnating uncalcined TiO.sub.2 with a salt 
solution of a lanthanide series element, drying the impregnated titanium 
dioxide, and calcining the dried titanium dioxide at a temperature in the 
range of 300.degree. to 900.degree. C. 
(4) A method which comprises adding a finely powdered oxide of a lanthanide 
series element to uncalcined TiO.sub.2, subjecting the resultant mixture 
to wet or dry pulverization and mixture in a ball mill, drying the 
pulverized mixture, and calcining the mixture at a temperature in the 
range of 300.degree. to 900.degree. C. 
(5) A method which comprises impregnating precalcined TiO.sub.2 with a salt 
solution of a lanthanide series element, drying the pregnated titanium 
dioxide, and calcining the dried titanium dioxide at a temperature in the 
range of 300.degree. to 900.degree. C. Optionally, in the impregnation, 
the aforementioned salt solution may be used in the form of a mixed 
solution with a salt solution of the third catalytic component. 
In the methods mentioned above, those of (1) to (4) probe to be preferable. 
In these four desirable methods, the method of (1) proves to be 
particularly preferable. 
The starting materials which are effectively usable for the composition of 
the third catalytic component include oxides, hydroxides, inorganic salts, 
and organic salts, for example. They are suitably selected from among 
ammonium salts, oxalates, nitrates, sulfates, and halides, for example. 
The production of a catalyst by the addition of manganese, iron, nickel, 
cobalt, tungsten, copper, silver, gold, platinum, palladium rhodium, 
ruthenium, and/or iridium to the first and second catalytic components is 
accomplished by causing an aqueous solution of salts of these metals to be 
deposited by means of impregnation on a molded structure of the first and 
second catalytic components, drying the impregnated structure, and 
calcining the dried structure. 
Otherwise, the production may be attained by a procedure which comprises 
impregnating a carrier formed of the first catalytic component with an 
aqueous solution of the mixture of metal salts respectively of the second 
catalytic component and the third catalytic component, drying the 
impregnated aggregate, and calcining the dried aggregate. 
Still otherwise, the production may be accomplished by a procedure which 
comprises adding an aqueous solution of the aforementioned metal salts in 
combination with a molding agent to a powder formed of the first and 
second catalytic components and kneading and molding the resultant 
mixture. 
When the catalyst to be used in the present invention is produced by 
calcining, at a temperature in the range of 600.degree. to 900.degree. C., 
a powdered or molded aggregate formed of the first and second catalytic 
components, it enjoys a still greater improvement in physical durability 
under the reaction conditions. 
In accordance with the present invention, the supernatant and the 
sedimented activated sludge resulting from the treatment with activated 
sludge, the waste water from fermentation, the waste water from the 
process of polymerization of organic compounds, the cyan-containing waste 
water, the phenol-containing waste water, the oil-containing waste water, 
the waste water from other chemical plants, the industrial effluents from 
food plants, and the waste waters containing such oxidizable organic or 
inorganic substances as excrements, sewage, and sewer sludge can be 
treated by wet oxidation. When the honeycomb-shaped catalyst is used in 
the present invention, the treatment can be continued stably for a long 
time even on a waste water containing solid substances in a concentration 
of 0.1 g/liter. 
As respects the reaction conditions in the present invention, the reaction 
temperature is not higher than 370.degree. C., and is generally in the 
range of 100.degree. to 370.degree. C., preferably 160.degree. to 
300.degree. C. The pressure of the reaction system is only required to be 
enough for the waste water inside the reaction column to retain a liquid 
phase, namely a pressure approximately in the range of 1 to 230 
kg/m.sup.2. The molecular oxygen-containing gas to be fed to the reaction 
system is used in an amount 1 to 1.5 times the amount of oxygen necessary 
for the oxidative decomposition. The amount of the catalyst to be used is 
approximately in the range of 5 to 99% of the inner volume of the reaction 
column. The waste water is fed in combination with the molecular 
oxygen-containing gas to the catalyst bed at such a rate that the 
residence time for oxidation is in the range of 2 to 120 minutes, 
preferably 4 to 60 minutes. 
The molecular oxygen-containing gases which are effectively usable in this 
invention include air, the mixed gas of oxygen and air, and a gas 
generally called as an oxygen-enriched air, for example. Though the pH 
value of the reaction system may be on the acid side or on the alkali 
side, it is desired to be not more than 9, preferably not more than 7. 
Concerning the reaction conditions to be adopted where ozone and/or 
hydrogen peroxide is used as an oxidizing agent in combination with 
molecular oxygen, the reaction temperature is in the range of 100.degree. 
to 250.degree. C., the reaction pressure is to be enough for the waste 
water to retain a liquid phase within the reaction tower, specifically a 
pressure in the range of 1 to 200 kg/cm.sup.2, and the residence time is 
in the range of 3 to 120 minutes, preferably 5 to 60 minutes. The amount 
of ozone to be used is in the range of 0.001 to 1.2 mols, preferably 0.003 
to 0.6 mol, per mol of the aforementioned theoretical amount of oxygen. 
Then, the amount of hydrogen peroxide to be used is in the range of 0.001 
to 1.8 mols, preferably 0.003 to 0.2 mol, per mol of the theoretical 
amount of oxygen.

Now, the present invention will be described more specifically below with 
reference to working examples and controls. This invention is not limited 
to these examples. 
EXAMPLE 1 
An oxide containing titanium and cerium was prepared by the following 
method. As the source for titanium, a sulfuric acid aqueous solution of 
titanyl sulfate of the following composition was used. 
______________________________________ 
TiOSO.sub.4 (reduced to TiO.sub.2) 
250 g/liter 
Total H.sub.2 SO.sub.4 
1,100 g/liter 
______________________________________ 
A solution of 9.6 kg of cerous nitrate [Ce(NO.sub.3).sub.3.6H.sub.2 O] in 
100 liters of water and 4.7 liters of the aforementioned sulfuric acid 
aqueous solution of titanyl sulfate added thereto were vigorously mixed. 
The resultant mixture was kept at a temperature of about 30.degree. C. and 
thoroughly stirred and aqua ammonia was gradually added dropwise thereto 
until the pH value reached 8. Then, the produced mixture was left standing 
in the ensuant state for 15 hours. The gel consequently obtained was 
separated by filtration, washed with water, dried at 200.degree. C. for 10 
hours, then calcined in the open air at 650.degree. C. for 3 hours, and 
further pulverized, to obtain a powder. This powder was found to have a 
composition of TiO.sub.2 :CeO.sub.2 =4:6 (molar ratio) [23.6:76.4 (weight 
ratio)] and a BET specific surface area of 50 m.sup.2 /g. In a kneader, 4 
kg of the powder mentioned above, 1.4 kg of water, and 120 g of starch 
were thoroughly kneaded. The resultant mixture was kneaded during 
simultaneous addition thereto of a suitable amount of water, extrusion 
molding the kneaded mixture into a honeycomb die having an aperture 
diameter (equivalent diameter of through holes) of 4 mm, a cell wall 
thickness of 0.7 mm, and an opening ratio of 72%, dried at 120.degree. C. 
for six hours, and calcined at 500.degree. C. for six hours. 
The molded structure consequently obtained was impregnated with an aqueous 
platinic chloride solution, dried at 120.degree. C. for six hours, and 
then calcined at 400.degree. C. for six hours. The finished catalyst had 
Pt carried in a ratio of 0.4% by weight. The composition of this catalyst 
was TiO.sub.2 :CeO.sub.2 :Pt=23.5:76.1:0.4 (weight ratio). 
EXAMPLE 2 
A powder of dry titanium dioxide was obtained by following the procedure of 
Example 1, except that the use of cerous nitrate and the step of 
calcination were omitted. This powder had a water content of 5% by weight. 
3.4 kg of the powder was mixed with a solution of 4.4 kg of cerous nitrate 
in 10 liters of water. The mixture was dried at 80.degree. C. for 12 hours 
and then at 120.degree. C. for six hours, calcined in the open air at 
500.degree. C. for five hours, and pulverized, to obtain a powder. The 
powder was found to have a composition of TiO.sub.2 :CeO.sub.2 =8:2 (molar 
ratio) (64.9:35.1 (weight ratio)) and a BET specific surface area of 90 
m.sup.2 /g. 
In a kneader, 4 kg of the powder, 1.5 kg of water, and 40 g of starch were 
thoroughly kneaded. The resultant mixture was extrusion molded into 
cylindrical pellets 5 mm in diameter and 6 mm in length, dried at 
120.degree. C. for six hours, and calcined at 700.degree. C. for three 
hours. 
Then, a catalyst having Ru carried in a ratio of 1.5% by weight was 
obtained by following the procedure of Example 1, except that an aqueous 
ruthenium nitrate solution was used in the place of the aqueous platinic 
chloride solution. The composition of this catalyst was TiO.sub.2 
:CeO.sub.2 :Ru=64.0:34.5:1.5 (weight ratio). 
EXAMPLE 3 
A mixture obtained by adding to 3.9 kg of a commercially available anatase 
type titanium dioxide powder (BET specific surface area 70 m.sup.2 /g) a 
solution of 2.4 kg of cerous nitrate in 5 liters of water was dried at 
80.degree. C. for 12 hours and at 120.degree. C. for six hours and then 
pulverized and mixed in a ball mill for four hours. The produced mixed 
powder was calcined in the open air at 700.degree. C. for three hours and 
pulverized, to obtain a powder. The powder was found to have a composition 
of TiO.sub.2 :CeO.sub.2 =9:1 (molar ratio) (80.7:19.3 (weight ratio)) and 
a BET specific surface area of 40 m.sup.2 /g. 
A honeycomb-shaped catalyst having an aperture diameter (equivalent 
diameter) of 6 mm, a cell thickness of 1 mm, an opening ratio of 73%, and 
a Pt deposition ratio of 0.6% by weight was obtained by following the 
procedure of Example 1. The composition of this catalyst was TiO.sub.2 
:CeO.sub.2 :Pt=80.2:19.2:0.6 (weight ratio). 
EXAMPLE 4 
Waste water treatment by the wet oxidation technique was carried out by the 
following procedure severally using the catalysts obtained in Examples 1 
to 3. A reaction tube made of stainless steel was packed with a given 
catalyst and a preheated mixture of waste water with air of an oxygen 
concentration of 21% was continuously introduced for 4,000 hours into the 
reaction tube via the lower part thereof. The waste water samples taken at 
the inlet and the outlet of the reaction tube were analyzed for COD (Cr) 
to determine the ratio of removal in the initial stage of treatment and 
after 4,000 hours' treatment. The catalyst was tested for strength in the 
initial stage of reaction and after 4,000 hours' reaction to determine the 
strength ratio of the catalyst. The waste water subjected to the treatment 
had a COD (Cr) of 20 g/liter and a pH of 6. The reaction was carried out 
at a reaction temperature of 230.degree. C. under a reaction pressure of 
50 kg/cm.sup.2, with the waste water introduced at a space velocity of 1.2 
hr.sup.-1 (based on empty tower) and the air at a space velocity of 100 
hr.sup.-1 (based on empty tower under standard conditions) into the 
reaction tube. The results of the treatment are shown in Table 1. 
TABLE 1 
______________________________________ 
COD removal ratio (%) 
Catalyst strength ratio 
Initial After 4,000 After 4,000 hrs' 
Catalyst stage hrs' reaction 
reaction/initial stage 
______________________________________ 
Example 1 
99 99 0.96 
Example 2 
98 98 0.95 
Example 3 
98 97 0.92 
______________________________________ 
Control 1 
1.2 kg of water and 40 g of starch were added to 4 kg of a commercially 
avilable cerium oxide powder, and kneaded thoroughly by a kneader. The 
mixture was extruded into a cylindrical pellet having 5 mm of diameter and 
6 mm of length and calcined at 120.degree. C. for 6 hours and at 
700.degree. C. for 3 hours. A catalyst having a Pt deposition ratio of 
0.6% by weight was obtained by following the procedure of Example 1, 
except that the cylindrical pellets were used instead. When this catalyst 
was used in the reaction under the conditions of Example 4, though the COD 
removal ratio was 99% in the initial stage of treatment, the catalyst 
strength decreased and powders of the catalyst generated, and the 
efficiency of treatment likewise declined with the elapse of time. After 
400 hours' treatment, amount of the catalyst decreased and the reaction 
proceeded sparingly. 
EXAMPLE 5 
Waste water treatment was carried out for 500 hours at a reaction 
temperature of 200.degree. C. under a reaction pressure of 45 kg/cm.sup.2, 
except that a mixed gas containing oxygen in a concentration of 18% and 
ozone in a concentration of 1% was used in the place of air having an 
oxygen concentration of 21% and the catalyst obtained in Example 1 was 
used instread. In this treatment, the COD removal ratio was found to be 
97%. 
EXAMPLE 6 
Waste water treatment was carried out for 500 hours by following the 
procedure of Example 5, except that an aqueous 3% hydrogen peroxide 
solution was supplied at a space velocity of 0.05 hr.sup.-1 (based on 
empty column) in combination with the mixed gas and the catalyst obtained 
in Example 1 was used instead. The COD removal ratio was found to be 98%. 
EXAMPLE 7 
A powder of a composition of TiO.sub.2 :La.sub.2 O.sub.3 - 78.3:21.7 
(weight ratio) was obtained by following the procedure of Example 1, 
except that 702 g of lanthanum nitrate (La(NO.sub.3).sub.3.6H.sub.2 O) and 
3.8 liters of a sulfuric acid solution of titanyl sulfate was used 
instead. Pellets of the same shape as in Example 2 were obtained by 
processing the powder in accordance with the procedure of Example 2 and 
then subjected to deposition of rhodium by impregnation. The composition 
of the produced catalyst was TiO.sub.2 :La.sub.2 O.sub.3 :Rh 
=77.3:21.5:1.2 (weight ratio). 
EXAMPLE 8 
In 40 liters of water, 1.95 kg of titanium tetrachloride (TiCl.sub.4) was 
dissolved during simultaneous elimination of heat. In the resultant 
solution, 80 g of finely powdered neodymium oxide (Nd.sub.2 O.sub.3) was 
dispersed and kept thoroughly stirred and, at the same time, adjusted to 
pH 9 by gradual dropwise addition thereto of aqua ammonia. The resultant 
mixture was left standing for 15 hours. The gel consequently formed 
therein was separated by filtration, washed with water, dried at 
180.degree. C. for five hours, and then calcined in the open air at 
800.degree. C. for two hours. The powder obtained after the subsequent 
step of pulverization had a BET specific surface area of 8 m.sup.2 /g. 
Same shape of a pelletized catalyst having a composition of TiO.sub.2 
:Nd.sub.2 O.sub.3 : MnO.sub.2 =82:8:10 (weight ratio) was obtained by 
following the procedure of Example 2, except that manganese nitrate was 
added to the powder. 
Control 2 
Same shape of a pelletized catalyst having a composition of TiO.sub.2 
:MnO.sub.2 =90:10 (weight ratio) was obtained by following the procedure 
of Example 8, except that a commercially avilable titanium dioxide powder 
(BET specific surface area 140 m.sup.2 /g) was used instead. 
EXAMPLE 9 
Waste water treatment of the wet oxidation technique was carried out by the 
following procedure severally using the catalysts obtained in the examples 
and the controls cited above. A reaction tube made of stainless steel was 
packed with 1 liter of a given catalyst (catalyst bed length 2 m) and a 
preheated mixture of waste water with air of an oxygen concentration of 
21% was continuously introduced for 4,000 hours into the reaction tube 
through the lower part thereof. The waste water samples taken at the inlet 
part and the outlet part of the reaction tube were tested for COD (Cr) to 
determine the removal ratio in the initial stage of reaction and after 
4,000 hours' reaction. The catalyst strength was tested in the initial 
stage of reaction and after 4,000 hours' reaction to determine the 
catalyst strength ratio. The waste water subjected to the treatment 
contained 12,000 ppm of acetic acid and 1,000 ppm of ammonia. The 
treatment was carried out at a reaction temperature of 230.degree. C. 
under a reaction pressure of 50 kg/cm.sup.2, with the waste water 
introduced at a space velocity of 1.2 hr.sup.-1 (based on empty tower) and 
the air at a space velocity of 60 hr.sup.-1 (based on empty column under 
standard conditions) into the reaction tube. The results obtained are 
shown in Table 2. 
TABLE 2 
______________________________________ 
Acetic acid NH.sub.3 Catalyst 
removal ratio (%) 
removal ratio (%) 
strength ratio 
After After After 4,000 
Initial 4,000 hrs' 
Initial 
4,000 hrs' 
hrs' reaction/ 
Catalyst 
stage reaction stage reaction 
Initial stage 
______________________________________ 
Example 1 
99 99 99 99 0.96 
Example 2 
98 98 99 99 0.95 
Example 7 
98 98 99 99 0.97 
Example 8 
92 90 94 91 0.95 
Control 2 
71 58 63 51 0.87 
______________________________________