GB2043045A

GB2043045A - Process for treating ammonia- containing waste water

Info

Publication number: GB2043045A
Application number: GB7942262A
Authority: GB
Original assignee: Osaka Gas Co Ltd
Current assignee: Osaka Gas Co Ltd
Priority date: 1978-12-15
Filing date: 1979-12-07
Publication date: 1980-10-01
Also published as: GB2043045B; NL190699B; NL7909090A; DE2950710C2; DE2950710A1; FR2444008A1; FR2444008B1; NL190699C

Abstract

A process for treating NH3- containing waste water which comprises feeding at a pH of about 8.5 to about 11.5 the waste water to a reactor to subject the same to wet oxidation with an oxygen-containing gas in the presence of a catalyst while maintaining the waste water at a temperature of about 100 to about 370 DEG C and at pressure permitting the waste water to remain in the liquid phase, and supplying an alkali substance to the reactor.

Description

SPECIFICATION Process for treating waste water This invention relates to a process by which waste water containing ammonia or chemically oxidizable substances (hereinafter referred to as "COD components"), suspended solids, etc. in addition to ammonia is subjected to wet oxidation in the presence of a catalyst to convert these pollutants to nitrogen, carbon dioxide, water and the like and to thereby render the waste water harmless.

According to this invention, the ammonia contained in the waste water includes ammonium compounds which liberate ammonium ions when dissociated in water. The COD components include phenol, cyanides, thiocyanates, oils, thiosulfuric acid, sulfurous acid, sulfides, nitrous acid, etc.

For the control of water pollution, it is thought necessary in recent years to remove from water nitrogen components (particularly ammonia nitrogen) as well as COD components. The former serves as nutrients contributing chiefly to an abnormal growth of algae in rivers and lakes, occurrence of red tide in the sea, and occurrence of molds in reservoirs which renders municipal water musty. Thus more stringent regulations will be adopted against nitrogen pollutants.

In view of existing techniques for treating ammonia-containing waste water, Harada, one of the present inventors, et al. carried out extensive research to develop a process for treating waste water with ease and with economical feasibility which process is capable of removing ammonia or, ammonia and COD components at the same time irrespective of the concentration of ammonia, and found that the object was achievable by subjecting waste water to wet oxidation reaction in the presence of a specific catalyst and under specified conditions. Based on this finding, the invention of U.S. Patent No.

4,141,828 was accomplished. (The process disclosed therein will hereinafter be referred to as the process of the prior invention".) With the process of the prior invention, ammonia-containing waste water can be very effectively treated when subjected to wet oxidation at a pH of at least 9, but the subsequent research revealed that the process still involved some problems when treating some kinds of waste waters. When waste water with a pH of about 9 to about 1 1.5 is fed to the reactor, the progress of the reaction usually greatly reduces the the pH of the reaction system and consequently leads to a reduced harmful component decomposition efficiency, possibly necessitating an increased amount of catalyst and accelerating the consumption or degradation of the catalyst.Acid liquids will cause serious damage to the reactor, piping, heat exchanger, etc. and require neutralization of the effluent before discharge. Accordingly the inventors have made continued research and found that all the foregoing problems of the process of the prior invention can be overcome by feeding an alkali substance to the wet oxidation reactor at such a rate that at least about 80% of the waste water supplied to the reactor and positioned toward the water inlet of the reactor is maintained at a pH of at least about 8 at all times and that the liquid resulting from the wet oxidation has a pH of about 5 to about 8. This invention has been accomplished based on this novel finding.

Examples of the waste water to be treated by the present process are those which contain ammonia and which may further contain oxidizable organic and/or inorganic substances, such as gas liquor produced in cock oven plants, coal gasifying plants and coal liquefying plants, waste water from gas cleaning processes employed in these plants, oil-containing waste water, water from activated sludge process, sedimented activated sludge, waste water from chemical plants and oil refineries, municipal effluents, sewage, sewage sludge, etc. Waste water from high-temperature and/or highpressure systems can be advantageously treated by the present process at a reduced cost for heating and/or pressurizing the waste water.If the waste water contains an excess of suspended solids, the solids will adhere to the components of the treating apparatus, entailing a reduced efficiency such as a reduced heat transfer coefficient on the surface of the heat exchanger or a lower catalytic activity due to the deposition of solids on the surface of particles of the catalyst packed in the reactor. Accordingly, it is preferable to remove suspended solids partly or wholly from the waste water prior to the treatment depending on the concentration and composition of the solids. Alternatively, the waste water may be subjected to a non-catalytic wet oxydation process known as the Zimmermann process to partly or wholly decompose suspended solids prior to the present process and to prevent the poisoning of the catalyst used in the present process.The waste water to be treated by the present process has a pH of about 8.5 to about 1 1.5 so as to improve COD components and ammonia effectively. More preferable range of the pH is about 9 to about 11. It is therefore desirable to adjust the pH of the waste water before the reaction with an alkali such as sodium hydroxide, calcium hydroxide, sodium carbonate or the like depending on the kind of the waste water.

The alkali substance is introduced into the wet reaction system at the desired time and at a rate required to maintain at least about 80% of the waste water supplied to the reactor and positioned toward the water inlet of the reactor at a pH of at least about 8 at all times and to permit the treated liquid to retain a pH of about 5 to about 8 at all times. The same alkalis as used for the pH adjustment of the waste water are usable as such alkali substances.

Examples of useful active components of catalyst are iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten and compounds of these metals which are insoluble or sparingly soluble in water. These components are used singly, or at least two of them are conjointly usable. Examples of useful compounds which are insoluble or sparingly soluble in water are: (i) Oxides such as iron sesquioxide, tri-iron tetroxide, cobalt monoxide, nickel monoxide, ruthenium dioxide, rhodium sesquioxide, palladium monoxide, iridium dioxide, cupric oxide, tungsten dioxide, etc.

(ii) Chlorides such as ruthenium dichloride, platinum dichloride, etc.

(iii) Sulfides such as ruthenium sulfide, rhodium sulfide, etc.

These metals and compounds thereof are used as supported in the usual manner by a carrier such as titania, zirconia, alumina, silica, silica-alumina or active carbon, porous body of nickel, nickel-chromium, nickel-chromium-aluminum or nickel-chromium-iron, etc. Depending on the treating conditions, the waste water to be treated by the present process, when having a pld of higher than 1 1, could permit the carrier to dissolve out or cause conversion of part of the ammonia therein to nitrite nitrogen and/or nitrate nitrogen, possibly allowing the discharge of the nitrogen from the system along with the treated liquid. Titania and/or zirconia, if used as the carrier in such a case, will be prevented from dissolving out, while effectively inhibiting the conversion of ammonia.The amount of the active component to be supported by the carrier is about 0.05 to about 25%, preferably about 0.5 to about 3%, based on the weight of the carrier. The catalyst can be used in the form of globules, pellets, cylinders, crushed fragments, particles or in any other desired form. When the reactor is adapted for a fixed bed, the waste water is passed therethrough preferably at a space velocity of about 0.5 to about 10 h7 1. more preferably at about 1 to about 5 hut', based on an empty column. The grains or pieces of the supported catalyst useful for the fixed bed is usually about 3 to about 50 mm, preferably about 5 to about 25 mm in size.In the case of fluidized beds, it is preferable to use the supported catalyst as suspended in the waste water like a slurry in such an amount that it will form a fluidized bed within the reactor, namely in an amount of usually about 0.1 to about 20% by weight, more preferably about 0.5 to about 10% by weight, based on the resulting suspension. For the actual operation with the fluidized bed, it is preferable to feed the supported catalyst to the reactor as suspended in the waste water, separate the catalyst from the treated water resulting from the reaction by sedimentation, centrifuging or like suitable method and reuse the separated catalyst again. To facilitate the separation of the catalyst from the treated water, therefore, the supported catalyst useful for the fluidized bed is advantageously about 0.15 to about 0.5 mm in particuje cize.

Examples of useful oxygen-containing gases are air, oxygen-enriched air, oxygen, oxygencontaining waste gases, etc. By the oxygen-containing waste gases are meant those having a lower oxygen concentration than air and containing one or more of hydrogen cyanide, hydrogen sulfide, ammonia, sulfur dioxide, organic sulfur compounds, nitrogen oxides, hydrocarbons, etc., such as a waste gas from the regenerator of the redox desulfurization process. The use of such oxygen-containing waste gases is advantageous in that the harmful components of the gas can be rendered harmless along with those contained in the waste water. The feed rate of the oxygen-containing gas is determinable from the theoretical amount of oxygen required for the oxidation of the organic and/or inorganic substances in the waste water and for the decomposition of ammonia to nitrogen.Generally, the oxygen-containing gas is fed in an amount of about 1 to about 1.5 times, preferably about 1.05 to about 1.2 times, the theoretical amount of oxygen. If the absolute amount of oxygen is insufficient when the oxygencontaining waste gas is used, the gas is replenished with oxygen by supplying air, oxygen-enriched air or oxygen per se. The oxygen-containing gas may be fed to the reactor at a single level or in two or more levels via branched lines. For efficient use of oxygen, the gas flowing out from the reactor can be circulated for use when economical and advantageous to ihe operation.

The reaction is carried out at a temperature of usually about 100 to about 3700 C, preferably about 200 to about 3O00C. The higher the reaction temperature, the higher the efficiency of removal of ammonia, organic and/or inorganic substances and the shorter the residence time of the waste water within the reactor but the higher the equipment cost. Accordingly, the reaction temperature is determined in view of the kind of the waste water, the degree of treatment desired and operation and installation costs combined. The reaction pressure therefore needs only to be such that the waste water can at least retain its liquid phase at the predetermined temperature although higher temperatures result in more efficient removable of ammonia.

The wet oxidation step can be in combination with the following gas purifying step and/or reverse osmosis treatment for the treated water with great advantages.

Various processes have heretofore been proposed for purifying gases containing harmful components, such as hydrogen cyanide, hydrogen sulfide, ammonia, etc. For example, a process is known in which a gas containing such harmful components is brought into contact with water or an aqueous alkali solution to cause the harmful components to migrate into the solution for removal. The greatest drawback of this process is that it is cumbersome, difficult and economically very disadvantageous to treat the harmful components transferred to the solution. Accordingly it is now common practice to remove the harmful components individually from the gas. The latter process nevertheless is similarly disadvantageous from the viewpoint of operation and economy because the harmful components must be removed individually. The process has another drawback that the harmful components collected require a difficult treatment for disposal, or the products recovered from the harmful components are of low value for reuse due to the presence of impurities. However, when the liquid used for purging the gas and containing COD components, such as cyanides and sulfides, as well as ammonia is subjected to the wet oxidation treatment of the invention, the COD components and ammonia can be converted to nitrogen, carbon dioxide, water, etc. Thus the gas can be purified free of the drawbacks heretofore experienced with the prior art.

According to this invention, fuel gas, waste gas, etc. are purified by bringing the gas into contact with water or an aqueous solution of ammonia, caustic soda, caustic potash or like alkali, whereby hydrogen cyanide, hydrogen sulfide, ammonia and like harmful components are absorbed by the solution.

The liquid containing the harmful components is then subjected, singly or in combination with some other waste water, to the wet oxidation step described.

The waste water resulting from the wet oxidation treatment has a pH of about 5 to about 8, appears almost colorless and transparent, and can usually be discharged as it is. However, if it is desired to reuse the resulting water as industrial water, or if the water contains high concentrations of sodium sulfate and other substances derived from sulfur compounds, the effluent drawn off from the wet oxidation step in a pressurized state may be fed directly to a reverse osmosis unit, whereby the water can be separated into purified water and a concentrate with a high efficiency. The purified water can be reused, for example, as part of the washing liquid fot the gas purifying step, while sodium sulfate and like useful substances can be recovered from the concentrate easily.

This invention will be described below in greater detail with reference to the accompanying drawings, in which: Fig. 1 is a flow diagram illustrating one mode of the process of this invention in which a fixed bed is used; Fig. 2 is a flow diagram illustrating another mode of the present process in which a fluidized bed is used and the recovered catalyst is circulated for reuse; Fig. 3 is a flow diagram illustrating another mode of the present process which comprises in combination the step of purifying a gas containing ammonia and COD components such as hydrogen cyanide and hydrogen sulfide and the step of wet oxidation reaction and which employs a wet-type reactor including a fixed bed; Fig. 4 is a flow diagram illustrating another mode of the present progress similar to that shown in Fig. 3 and employing a wet-type reactor including a fluidized bed;; Fig. 5 is a flow diagram showing another mode of the present process which is similar to that shown in Fig. 3 and in which the purified water obtained from a reverse osmosis unit is circulated for use as part of gas purging water; and Fig. 6 is a flow diagram illustrating another mode of the present process similar to that shown in Fig. 4 and in which the purified water obtained from a reverse osmosis unit is circulated for use as part of gas purging water.

Throughout Figs. 1 to 6, like parts are referred to by like reference numerals.

With reference to Fig. 1, waste water is supplied from a tank 1 through a line 2 to a pump 3, by which the water is pressurized to a predetermined pressure level. The water is then led through a line 4, a heat exchanger 5 and a line 6, mixed with an oxygen-containing gas and admitted via a line 11 to a reactor 12 filled with a catalyst. As already described, the pH of the waste water is adjusted with an alkali depending on the kind of the waste water. The alkali can be added to the water at one or more portions of the tank 1, lines 2, 4, 6 and 11.

The oxygen-containing gas, pressurized by a compressor 7, is passed through a line 8, a humidifier 9 and a line 10, mixed with the waste water as stated above and fed to the reactor 12 through the line 11. It is preferable, but not critical, to use the humidifier which serves to prevent the evaporation of the water within the reactor to achieve an improved heat recovery efficiency. However, when an oxygencontaining waste gas is used as the oxygen source the humidifier is not used to prevent the transfer of harmful components from the waste gas to the treated water. For an improved liquid-gas contact efficiency and increased reaction efficiency in the reactor 12, it is advantageous to finely divide the gas bubbles in the stream of mixed water and gas.Methods of dividing such bubbles are disclosed for example in Japanese Patent Application Disclosures No. 49873/1 974 and No. 49874/1 974 incorporated by reference herein. The oxygen-containing gas may be added to the waste water at the outlet of the pump 3 or partially introduced directly into the reservoir 12 at a single level or as divided at two or more levels. When required, the waste water may be heated at the line 6 or at a lower portion of the reactor 12. However, when the required amount of heat can be provided by the heat of reaction, the waste water need not be heated. When heating is resorted to, the waste water, while flowing through the line 6, may be heated in an unillustrated oven or by heat exchange with a heat medium.

Alternatively, the water may be subjected to heat exchange with a heat medium at a lower portion of the reactor.

An alkali substance, which is usually in the form of an aqueous solution, is supplied from an alkali tank 21 via a line 22, a pump 23 and a line 24 to the reactor 12 at such a rate as to maintain at least about 80% of the waste water supplied to the reactor and positioned toward the reactor bottom at a pH of at least about 8 at all times and to permit the water run off from the reactor through a line 13 to retain a pH of about 5 to about 8. Since the pH of the waste water decreases as the water ascends the interior of the reactor 12 with the progress of the reaction, the pH of the water is measured by known means at a plurality of levels as positioned at a constant spacing over the distance of about 80% of the entire length of the reactor from its bottom, so that the alkali substance is supplied at the level where a reduction of the pH to about 8 has been detected.Depending on the reaction conditions, therefore, the line 24 may be branched into a plurality of lines for supplying the alkali substance at two or more levels with the progress of the reaction.

After the waste water has reacted with the oxygen in the gas under the specified conditions within the reactor 12, the resulting mixture is run offfrom an upper portion of the reactor 12 through a line 13 and conducted to a liquid-gas separation drum 14, in which the mixture is separated into a gas and a liquid.

The treated water flowing out from the separation drum 14 may be admitted to the humidifier 9 by way of a line 15, partly entrained in the oxygen-containing gas and sent to the reactor 12 through the lines 10 and 11. The remainder of the treated water drawn off from the humidifier 9 is passed through a line 16 to a cooler 17, cooled and decompressed to the atmospheric pressure and is released.

Alternatively, the treated water with an elevated pressure from the cooler 17 may be directly supplied to a reverse osmosis unit 25 to obtain purified water from a line 26 and a concentrate from a line 27.

The gas egressing from the separation drum 14 is sent through a line 19 to the heat exchanger 5, in which the gas gives heat.to the waste water, then decompressed to the atmospheric pressure and run off through a line 20. Alternatively, the liquid-gas mixture drawn off from the reactor 12 may be led directly to the heat exchanger 5 and thereafter separated into a gas and a liquid in the separation drum 14.

If the components of the concentrate from the line 27 is further decomposable, the concentrate may be led into the tank 1 and subjected to wet oxidation again.

With reference to Fig. 2, waste water is sent from a tank 1 into a mixer tank 34, in which the water is mixed with a catalyst from a container 32 through a line 33 into a slurry. The slurry is pressurized to a predetermined pressure level by a pump 3 and, in the same manner as in Fig. 1, is thereafter led through a line 4, a heat exchanger 5 and lines 6, 11 to a reactor 31 containing no catalyst. An oxygen-containing gas may usually be fed to the reactor in the same manner as in Fig. 1. To fluidize the slurry to a greater extent, part of the gas can be fed directly to the reactor 31 via at least one line branching from a line 10.

As in the embodiment of Fig. 1, an aqueous alkali solution is supplied from a tank 21 to the reactor 31 through a line 22, pump 23 and line 24 at a rate suitable to maintain at least about 80% of the waste water introduced to the reactor and positioned toward the waste water inlet of the reactor at a pH of at least about 8 at all times and to permit the treated water to retain a pH of about 5 to about 8.

The highly pressurized treated water containing the catalyst is sent through a line 13, liquid-gas separator 14, line 1 5, humidifier 9, line 1 6, cooler 1 7 and line 1 8 to a liquid-solid separtor 28 such as filter press. The separated liquid is drawn off from the system after decompression to the atmospheric pressure or, alternatively, directly introduced via a line 29 into a reverse osmosis unit 25, in which the liquid is separated into purified water flowirig out from a line 26 and condensate flowing out from a line 27. The catalyst recovered is returned through a line 30 to the container 32 and circulated for use.

When an oxygen-containing waste gas is used as the oxygen source, the humidifier 9 is not used as in the case of Fig. 1.

With reference to Fig. 3, fuel gas, waste gas or like gas containing ammonia and COD components, such as hydrogen cyanide and hydrogen sulfide, is fed through a line 35 to an absorbing tower 36 at a lower portion thereof and is purged with water or an aqueous alkali solution which is supplied from a tank 37 through a ine 38 and sprayed from the top of the tower 36. The waste water run off from the absorbing tower 36 and containing the ammonia and COD components is sent through a line 39 into a tank 1. The purified gas is drawn off from an upper portion of the tower 36 via a line 40.

The waste washing water may be mixed with some other waste water supplied through a line 41. The waste water is sent out from the tank 1 and subjected to wet oxidation in a reactor 12 of the fixed bed type in the same manner as in the embodiment of Fig. 1.

With the embodiment shown in Fig. 4, a gas containing ammonia and COD components, such as hydrogen cyanide and hydrogen sulfide, is first purified in the same manner as in Fig. 3, and the resulting waste water or a mixture thereof with some other waste water is subjected to wet oxidation in a reactor 31 of the fluidized bed type in the same manner as in Fig. 2. The catalyst is used in circulation as is the case with Fig. 2. The liquid phase from a ilquid-solid separator 28 may be drawn off from the system via a line 29 on decompression, or may be sent, without decompression, to an unillustrated reverse osmosis unit for separation into purified water and a concentrate.

With the embodiment shown in Fig. 5, waste water is first subjected to wet oxidation in a reactor 12 of the fixed bed type and then fed to a reverse osmosis unit 25. The purified water obtained is returned through a line 42 to a tank 37 for an absorbing liquid and reused as part of the absorbing liquid. In this case, the tank 37 is of course replenished with a quantity of water corresponding to the amount of the concentrate drawn offfrom the system through a line 27.

Fig. 6 shows another embodiment, in which the waste water treated in a wet oxidation reactor 31 of the fluidized bed type is fed to a liquid-solid separator 28, in which the liquid phase is separated from the catalyst. The catalyst is returned to a catalyst tank 32 via a line 30 and is thus circulated for use, while the liquid phase is fed, in a pressurized state, to a reverse osmosis unit 25 by way of a line 29 and is separated into purified water and a concentrate. The purified water is sent through a line 42 into an absorbing liquid tank 37 and is reused as part of the absorbing liquid.

In contrast with the present process, known processes require many steps and are costly. For example, the gas liquor produced in coke ovens in the manufacture of coke is usually treated by the successive steps of (1) removal of phenol, (2) pretreatment, (3) removal of ammonia by stripping, (4) treatment with activated sludge and (5) coagulating and sedimentation, which may further be followed by the steps of (6) oxidation with chemical, (7) adsorption with active carbon and (8) reverse osmosis, when required.The process of this invention consists essentially of a single step in which the gas liquor from the coke oven is fed directly to a reactor on pressurization without being cooled and catalytically oxidized with an oxygen-containing gas, whereby the ammonia and COD components (such as phenol, cyanides, thiocyanates, oils, thiosulfuric acid, sulfurous acid, sulfides, etc.) contained in the gas liquor can all be decomposed and rendered harmless. Thus the present process involves a greatly simplified operation which can be conducted at an exceedingly reduced overall cost (equipment cost and operation cost).

The process of this invention has overcome the problems encountered with the process of the prior invention when the waste water is fed at a pH of about 9 to about 11.5. The supply of an alkali substance mitigates the marked decrease of pH that takes place in the prior art within the reactor, thereby preventing the reduction of the decomposition efficiency, the degradation of the catalyst and the damage to the reactor, heat exchanger, piping system, etc. The present process has another advantage that whereas the process of the prior invention is unable to treat waste water at a pH of around 8.5 because of the low ammonia decomposition efficiency, the present process assures high efficiency in performing such treatment.

While high-temperature and high-pressure conditions employed for treating waste water at a pH of higher than 11 are likely to permit the carrier to dissolve out or give a large quantity of nitrite and/or nitrate nitrogen, the use of the titania and/or zirconia for the carrier precludes such objection.

The combination of the step of purifying a gas containing ammonia and COD components, such as hydrogen cyanide and hydrogen sulfide, and the step of treating waste water by wet oxidation greatly facilitates removal of such pollutants from the waste liquid resulting from the gas purifying step and heretofore considered difficult to treat.

Furthermore, the combination of the wet oxidation of waste water and a reverse osmosis process is economically very advantageous because the high pressure of the effluent from the wet oxidation step can be effectively utilized for the separation of the effluent into a concentrate and purified water, which may be used as industrial water as it is.

For a better understanding of this invention, examples will be given below.

EXAMPLE 1 The process of this invention is continuously practiced for 4,000 hours in the mode shown in Fig. 1.

A gas liquor (pH about 9.5) obtained from a coke oven is fed to a lower portion of a cylindrical stainless steel reactor at a space velocity of 0.99 hr1 (based on an empty column). The mass velocity of the liquor is 3.45 t/m2.hr. Air is introduced into the lower portion of the reactor at a space velocity of 50.8 her~1 (based on an empty column, under standard conditions). The reactor is filled with a catalyst in the form of pellets 5 mm in diameter and composed of 2.0% by weight of ruthenium supported on cz- alumina.The interior of the reactor is maintained at a temperature of 2750C and pressure of 75 kg/cm2 G, while supplying a 48% aqueous solution of caustic soda to the reactor at a rate required to maintain the portion of the water filling the reactor to 80% of the length thereof from its bottom at a pH of at least 8.5 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 7.5. The liquid-gas mixture resulting from the catalytic reaction is continuously drawn off from an upper portion of the reactor, and then led to a liquid-gas separator to separate into a liquid and gas, which are indirectly cooled and taken out of the system respectively.

The gas phase obtained 4,000 hours after the start of the operation is found to contain 2.5 ppm of ammonia and 0.03 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 1 shows the quality of the liquid phase and the amount of dissolved-out catalyst carrier as determined upon lapse of 4,000 hours after the start of the operation.

After the lapse of 4,000 hours, the reactor is divided vertically into two, and the inner surface thereof is checked for the unaided eye, but substantially no corrosion is found.

EXAMPLE 2 The sample procedure as in Example 1 is repeated except that the titania is used as the catalyst in niece of or-alumina.

The gas phase obtained 4,000 hours after the start of the operation is found to contain 0.5 ppm of ammonia and 0.01 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Substantially no corrosion is found on the inner surface of the reactor after lapse of 4,000 hours.

COMPARISON EXAMPLE 1 Waste water is continuously treated for 4,000 hours in the same manner as in Example 1 except that the 48% caustic soda solution is not supplied to the reactor.

The gas phase obtained 4,000 hours after the start of the operation is found to contain 5.0 ppm of ammonia and 0.6 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

After the lapse of 4,000 hours the reactor is divided vertically into two, and the inner surface thereof is checked for the unaided eye to find corrosion pits in various portions. A microscopic observation reveals that some of the pits have developed into transcrystalline cracks.

Table a

Example 1 Example 2 Comp. Ex. 1 Quality of Removal Quality of Removal Quality of Removal treated (%) treated (%) treated (%) water (ppm) water (ppm) water (ppm) COD 20.9 At least 15.0 At least 23.0 At least 99 99 99 Total NH3 1.9 " 1.5 " 48.0 98.3 TN * 10.4 " 5.0 " 45.0 98.4 TOD ** 48.0 " 29.5 " 175.4 98.9 TOC *** 25.0 98.3 20.0 98.8 41.0 97.1 pH 7.5 - 7.2 - 2.8 Concn. of 0.9 - None - 19.0 dissolved- detected out AI or TI SO, concn. 1500 - 1500 - 1340 . Total nitrogen .. Total oxygen demand ... Total organic carbon Based on the concentration of dissolved-out Al listed in Table 1, the ratio of the amount of the carrier dissolved out to the amount of the carrier originally used is 0.96% in Example 1, and 21.3% in Comparison Example 1.

EXAMPLE 3 The process of the invention is practiced in the mode shown in Fig. 1.

A gas liquor obtained from a coke oven and an effluent from a wet desulfurization process of the sulfur recovery type are mixed together in a ratio of 5:1, and the combined waste water is adjusted to a pH of about 10 with a caustic soda solution and then fed to a lower portion of a reactor at a space velocity of 1.73 hr1 (based on an empty column). The mass velocity of the water is 5.20 t/m2.hr. Air is introduced into the lower portion of the reactor at a space velocity of 244 hr1 (based on an empty column, under standard conditions). The reactor is filled with a catalyst in the form of balls about 10 mm in diameter and composed of 1.5% by weight of palladium supported on an alumina carrier.

The interior of the reactor is maintained at a temperature of 2650C and a pressure of 80 kg/cm2 G, while supplying a 48% aqueous solution of caustic soda to the reactor at a rate required to maintain the portion of the water filling the reactor to 80% of the length thereof from its bottom at a pH of at least about 8 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 8.0.

The liquid-gas mixture resulting from the catalytic wet oxidation reaction is continuously drawn off from an upper portion of the reactor, then led to a liquid-gas separator and separated into a liquid and gas, which are indirectly cooled and run off from the system respectively.

The gas phase is found to contain 1.5 ppm of ammonia and 0.04 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 2 shows the quality of the waste water mixture and the treated water.

EXAMPLE 4 Waste water is treated in the same manner as in Example 3 except that titania is used as the carrier in place of alumina.

The gas phase is found to contain nitrogen, oxygen, carbon dioxide, 0.8 ppm of ammonia and 0.02 ppm of nitrogen oxides but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 2 shows the quality of the treated water.

Table 2

Quality of Example 3 Example 4 combined waste water (ppm) Quality of Removal Quality of Removal treated (%) treated (%) water (ppm) water (ppm) COD 20,000 101 At least 48 At least 99 99 Total NH3 10,000 27 " 9 " Nitrite and 300 50 83.8 0.7 " nitrate nitrogen TOD 44,000 425 99.0 245 " TC " 2,000 250 88 150 92.5 TOC 1,500 94 93.7 20 98.7 TN 8,800 79 At least 9 At least Concn. of dis- - 1.4 - None solved-out Al detected or Tl . Total carbon COMPARISON EXAMPLE 2 The same waste water as treated in Example 3 is treated at the same temperature and pressure and with the same catalyst as used in Example 3 without supplying any caustic soda solution to the reactor to obtain treated water of the same quality as in Example 3. The waste water and air must then be fed at the following, greatly altered velocities.

Space velocity of waste water: 0.95 hr1 (based on an empty column) Mass velocity of waste water: 5.20 t/m2.hr (same as in Example 3) Space velocity of air: 133 hr1 (based on an empty column, under standard conditions) The amount of catalyst needed in Comparison Example 2 is found to be about 182, based on that used in Example 3 which is assumed to be 100. Thus Comparison Example 2 requires an exceedingly larger amount of catalyst than Example 3. This indicates that Comparison Example 2 is much more disadvantageous than Example 3.

The pH of the treated water is as low as about 2.8, while the concentration of dissolved-out Al is as high as 25 mg/l.

EXAMPLE 5 The process of this invention is practiced in the mode shown in Fig. 2 for treating a gas liquor obtained from a coke oven and containing phenol, ammonium thiocyanate, ammonium thiosulfate, ammonium nitrite, ammonium nitrate, ammonium carbonate and ammonia, as combined with waste water resulting from a coke oven gas purifying process and containing hydrogen cyanide, hydrogen sulfide, ammonia and a very small amount of naphthalene, in a ratio of 2 parts of the former to 1 part of the latter. A particulate catalyst 0.15 to 0.3 mm in particle size and comprising 5% by weight of ruthenium supported on a-alumina is admixed with the combined waste water to prepare a slurry containing 10% by weight of the catalyst.The slurry is adjusted to a pH of 10.5 with a calcium hydroxide solution and then fed to a cylindrical stainless steel reactor at a space velocity of 1.51 her~' (based on an empty column) and at a mass velocity of 4.53 t/m2.hr. Air is introduced to the reactor at a space velocity of 57.8 hr-' (based on an empty column, under standard conditions).

The interior of the reactor is maintained at a temperature of 2500C and pressure of 60 kg/cm2 G, while supplying a 48% aqueous solution of caustic soda to the reactor at a rate required to maintain the portion of the water filling the reactor to 80% of the length thereof from its bottom at a pH of at least 8.5 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 7.8. The liquid-gas mixture resulting from the catalytic wet oxidation reaction is continuously drawn off from an upper portion of the reactor, indirectly cooled and led into a liquid-gas separator, in which the mixture is separated into a liquid and a gas. The separated gas is decompressed to the atmospheric pressure and then released to the atmosphere. The liquid phase is decompressed to the atmospheric pressure, led to a liquid-solid separator and separated into the catalyst and treated water for the recovery of the catalyst. The separated gas phase is found to contain 3 ppm of ammonia and 0.05 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, whereas neither sulfur oxides nor hydrogen sulfide is detected.

Table 3 shows the quality of the combined waste water and the treated water.

EXAMPLE 6 Waste water is treated in the same manner as in Example 5 except that zirconia is used as the carrier in place of cr-alumina.

The gas phase is found to contain 2.1 ppm of ammonia and 0.08 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 3 shows the quality of the treated water.

Table 3

Quality of Example 5 Example 6 combined waste water (ppm) Quality of Removal Quality of Removal treated (%) treated (%) water (ppm) water (ppm) COD 3,500 10 At least 25 At least 99 99 Total NH3 4,000 4 At least 3.5 At least 99 99 Nitrate and 200 13 93.5 6.0 97.0 nitrite nitrogen TOD 12,700 25 At least 35 At least 99 99 TC 1,700 165 90.3 35 97.9 TOC 1,100 19 96.3 23 97.9 TN 3,500 18 At least 9.8 At least SO4 105 1046 - 1450 Concn. of dis- - 1.0 - None solved-out Al or detected or Zr EXAMPLES 7 to 20 Waste water is treated in the same manner as in Example 3 except that the catalyst listed in Table 4 is used in each example. Table 4 also shows the COD removal efficiency and ammonia removal efficiency achieved in each example, as well as the pH of the treated water and the concentration of dissolved-out carrier metal observed.

The gas phase is found to contain up to 5.0 ppm of ammonia and up to 1.0 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 4

Example Catalyst COD Ammonia pH of Concn. of removal removal treated dissolved (%) (%) water out carrier (ppm) 7 1.0% lr-Al203 99 At least 6.4 0.7 99 8 0.5% Pt-AI203 At least .. 7.2 1.0 99 9 1.0% Au-Al2o3 99 98 7.5 1.2 10 0.8% Pd-Al203 At least At least 6.0 0.7 99 99 11 1.0% Rh-Al-2O3 95 92 5.5 1.0 12 5.0% Fe AI20, 95 96 7.9 1.2 13 5.0% Ni-Al 203 90 97 5.2 1.9 14 5.0% W-Al2O3 90 92 6.3 1.2 15 5.0% Cu-Al2O3 98 92 6.5 1.0 16 5.0% Co- Al2O3 96 97 6.2 0.9 17 5.0% Fe2O3-Al2O3 90 94 6.9 1.1 x8 5.0% Fe304-Al203 89 90 6.9 1.1 19 2.0% Pd-Ni porous t least At least 7.9 0.6 carrier 99 99 20 2.0% Pt-Ni-Cr " " 7.7 0.4 porous carrier EXAMPLE 21 to 34 Waste water is treated in the same manner as in Example 3 except that the catalyst listed in Table 5 is used in each example. Table 5 also shows the COD removal efficiency and ammonia removal efficiency achieved in each example, as well as the pH of the treated water. No carrier metal is found to dissolve out.

The gas phase is found to contain up to 2.5 ppm of ammonia and up to 0.5 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 5

Example Catalyst COD Ammonia pH of COD Ammonia pri of removal removal treated (%) (%) water 21 1.0% Ir-TiO2 99 At least 6.2 99 22 0.3% Pt-TiO2 At least .. 7.1 99 23 1.0% Au-TiO2 99 98 7.2 24 0.5% Pd-TiO2 At least At least 6.9 99 99 25 1.0% Rh-ZrO2 95 93 6.9 26 5.0% Fe-TiO2 97 97 7.3 27 5.0% Ni-TiO2 92 98 6.2 28 5.0% W-'TiO2 91 93 6.3 29 5.0% Cu-TiO2 99 93 6.8 30 5.0% CoTiO2 97 98 6.3 31 5.0% Fe203-TiO2 92 95 6.9 32 5.0% Fe2o3-Tio2 92 91 7.1 33 2.0% Pd-TiO2 At least At least 7.2 99 99 34 2.0% Pt-TiO2 'S S 7.1 35 2.0% RuCl2-ZiO2 91 96 7.5 36 5.0% CoO-TiO2 91 95 7.5 EXAMPLES 37 to 41 The process of the invention is practiced in the mode shown in Fig. 1.

A gas liquor (pH 9.5) obtained from a coke oven is subjected to wet oxidation in the same manner as in Example 1 except that the liquor is adjusted to a pH of 10.5 with a caustic soda solution and then treated with use of the temperature, pressure and catalyst listed in Table 6 for each example.

Table 6 also shows the ammonia removal efficiency achieved in each example.

Table 6

Example mp. Pressure Ammonia removal efficiency (%) ( C) (kg/cm2G) 2%Pd-αAl2O3 1%Pt-αAl2O3 37 100 10 90 93 38 150 20 95 98 39 200 30 At least At least 99 99 40 250 45 " " 41 280 75 EXAMPLE 42 to 45 The process of the invention is practiced in the mode shown in Fig. 1.

A mixture (pH 8.2) of a gas liquor obtained from a coke oven and waste water resulting from a wet desulfurization process of the sulfur recovery type is first adjusted to the pH listed in Table 7 with a caustic soda solution, and is thereafter subjected to wet oxidation in the same manner as in Example 3.

Table 7 also shows the ammonia removal efficiency achieved in each example, as well as the pH of the treated water.

Table 7

Example pH of waste Ammonia removal pH of treated water mixture efficiency (%) water 42 8.5 95 7.5 43 9.0 At least 7.9 99 44 10.0 .. 7.5 45 11.0 It 7.8 EXAMPLE 46 The process of this invention is practiced in the same mode as shown in Fig. 1 except that the humidifier 9 is not used.

A gas liquor obtained from a coke oven is adjusted to a pH of 11.0 with a caustic soda solution and then fed to a lower portion of a reactor at a space velocity of 0.99 her~' (based on an empty column).

The mass velocity of the water is 3.45 t/m2hr. Air containing 2 g/Nm3 of hydrogen sulfide, 4 g/Nm3 of ammonia and 0.1 g/Nm3 of hydrogen cyanide is introduced into the lower portion of the reactor at a space velocity of 44.4 hr- (based on an empty column, under standard conditions). The reactor has charged therein a catalyst in the form of balls about 6 mm in diameter and composed of 2.0% by weight of palladium supported on alumina.

The interior of the reactor is maintained at a temperature of 2500C and pressure of 55 kg/cm2 G, while supplying a 48% aqueous solution of caustic soda to the reactor at a rate required to maintain the portion of the water filling the reactor to 80% of the length thereof from its bottom at a pH of at least 8.5 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 7.6. The liquid-gas mixture resulting from the catalytic reaction is continuously drawn off from an upper portion of the reactor and then led into a liquid-gas separator. The gas phase obtained 4,000 hours after the start of the operation is found to contain 3.5 ppm of ammonia and 0.05 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.Table 8 below shows the quality of treated water obtained 4,000 hours after the start of the treatment.

Table 8

Quality of Quality of gas liquor trated Removal (ppm) water (%) (ppm) COD 4,000 10 At least 99 Total NH3 5,000 2.5 At least 99 Nitrate and 60 0.8 98.7 nitrite nitrogen TOD 16,000 20 At least 99 TC 2,200 175 92.0 TOC 1,500 15 99 TN 4,700 4 At least 99 Concn. of dissolved: - 1.2 -our Al EXAMPLE 47 The process of this invention is practiced in the same mode as shown in Fig. 2 except that the humidifier 9 is not used.

With a gas liquor (pH 9.2) obtained from a coke oven is admixed a particulate catalyst 0.15 to 0.3 mm in particle size and comprising 5% by weight of ruthenium supported on titania to prepare a slurry, which is fed to a cylindrical stainless steel reactor at a space velocity of 1.51 her~1 (based on an empty column) and at a mass velocity of 4.53 t/m2.hr. Air containing 5 g/Nm3 of hydrogen sulfide is introduced to the reactor at a space velocity of 72.4 her~1 (based on an empty column, under standard conditions).

The interior of the reactor is maintained at a temperature of 2500C and pressure of 60 kg/cm2 G, while supplying an aqueous solution of caustic soda to the reactor at a rate required to maintain the water filling the reactor at a pH Oc at least 8.5 and to permit the water resulting from the wet oxidation to retain a pH of about 6.5. The liquid-gas mixture resulting from the catalytic wet oxidation reaction is continuously drawn off from an upper portion of the reactor, indirectly cooled and led into a liquid-gas separator, in which the mixture is separated into a liquid and a gas. The separated gas is decompressed to the atmospheric pressure and then released to the atmosphere. The liquid phase is decompressed to the atmospheric pressure,.led to a liquid-solid separator and separated into the catalyst and treated water for the recovery of the catalyst.The separated gas phase is found to contain 1.0 ppm of ammonia and 0.02 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, whereas neither sulfur oxides nor hydrogen sulfide is detected.

Table 9 shows the quality of the waste water and the treated water.

Table 9

Quality of Quality of gas liquor treated Removal (ppm) water (%) (ppm) COD 4,000 6.9 At least 99 Total NH3 5,000 0.3 At least 99 Nitrate and 300 0.3 At least nitrite nitrogen 99 TOD 16,000 20 At least 99 TC 2,200 120 94.5 TOC 1,500 15 99 TN 4,700 19 At least 99 EXAMPLE 48 First step An unpurified coke oven gas is introduced into an absorbing tower at its lower portion, while industrial water is sprayed from the top of the tower into contact with the gas under the conditions listed in Table 10. Table 11 shows the efficiency with which the harmful components of the gas are absorbed by the water. Table 12 shows the composition of the water at the outlet of the absorbing tower.

Table10 Space velocity of gas : 1231 her~1 Mass velocity of water : 64 t/mP.hr Space velocity of water : 10.5 he1 Temperature of the interior of tower: 400C Table 11

Charge Discharge Absorption (g/Nm ) (g/Nm ) efficiency (%) NH3 8.0 0.04 99.9 HCN 1.56 0.015 99.0 H2S 4.50 0.68 84.9 Table 12

Concentration tmg/i) NH3 933 HCN 181 H2S 448 Second step A mixture of one part by weight of the waste water from the first step, 1 part by weight of a gas liquor resulting from a coke oven and 0.1 part by weight of waste water from a wet desulfurization process of the sulfur recovery type is adjusted to a pH of about 10.5 with a caustic soda solution, and then introduced into the lowermost portion of a cylindrical reactor made of stainless steel at a space velocity of 0.74 hT1 (based on an empty column) and at a mass velocity of 2.59 t/m2.hr. Air is fed to a lower portion of the reactor at a space velocity of 51.4 hr1 (based on an empty column, under standard conditions). The reactor has charged therein a catalyst in the form of balls 5 mm in diameter and composed of 2.0% of ruthenium supported on a titania carrier.

The interior of the reactor is maintained at a temperature of 2500C and pressure of 45 kg/cm2 G, while supplying a 48% aqueous solution of caustic soda to the reactor at a rate required to maintain the portion of the water filling the reactor to 80% of the length thereof from its bottom at a pH of at least 8.5 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 7.2. The liquid-gas mixture resulting from the catalytic wet oxidation reaction is continuously drawn off from an upper portion of the reactor and led into a liquid-gas separator. The separated gas phase and liquid phase are indirectly cooled to about 300C individually. The gas phase is thereafter run off from the system, while the liquid phase, still in a pressurized state, is fed to the third step.

The gas phase is found to contain 0.5 ppm of ammonia and 0.03 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 13 shows the quality of the waste water mixture and the water resulting from the second step.

Table 13

Waste water mixture Water treated by 2nd (mg /I) step (mg/l) NH3 - 3873 2.5 HCN 110 trace H2S 297 trace COD 12850 84 TOC 1224 - 20 TOD 21142 106 TN 3267 5.0 SO4 1162 17960 Na+ 8700 1 8700 Third step The water from the second step is continuously passed, in the pressurized state (about 45 kg/cm2), through a reverse osmosis unit incorporating an acetate membrane with a desalination efficiency of 95 to 98%.

One hundred parts of the water fed to the reverse osmosis unit affords 70 parts of purified water and 30 parts of a concentrate. Replenishing industrial water is added to the purified water, and the mixture is used as the absorbing water for the first step. Sodium sulfate is recovered from the concentrate in the usual manner with a purity of at least 99%.

Table 14 shows the quality of the purified water and concentrate obtained from the water resulting from the second step and shown in the right column of Table 13.

Table 14

Purifiep-water Concentrate (m/l) (mail) NH3 0. t 8.1 HCN Trace Trace H2S 1 Trace Trace COD 1.5 276.5 TOC 4 57.3 TOD 5 342 TN 0.5 15.5 SO4- 260 59260 Na+ 350 28183 EXAMPLE 49 First step A coke oven gas is purified in the same manner as in the first step of Example 48. Table 15 shows the liquid-to-gas contact conditions, Table 1 6 the absorption efficiency achieved, and Table 17 the composition of the water at the outlet of the absorbing tower.

TABLE 15 Space velocity of gas: 611 hr1 Mass velocity of water: 4 t/m2.hr Space velocity of water: 1.0 hr-' Temperature of the interior of tower: 300C Table

Charge Discharge Absorption (g/Nm3) (g/Nm) efficiency (%) NH3 6.82 Trace At least 99 HCN 1.35 0.027 98 H28 5.00 0.80 84 . C10H8 1.23 0.21 82.9 Table 17

Concentration (mug /1) NH3 4092 HCN 794 H2S 2520 C10H8 612 Second step The waste water from the first step is first adjusted to a pH of about 9.5 with a caustic soda solution, and then introduced into the lowermost portion of a reactor at a space velocity of 1.4 hF1 (based on an empty column) and at a mass velocity of 3.45 t/m2.hr. Air is fed to a lower portion of the reactor at a space velocity of 67.4 hr-1 (based on an empty column, under standard conditions). The reactor has charged therein a catalyst in the form of balls 5 mm in diameter and composed of 2.0% of palladium supported on a titania carrier.

The interior of the reactor is maintained at a temperature of 2700C and pressure of 65 kg/cm2 G, while supplying a 48% aqueous solution of caustic soda to the reactor at a rate required to maintain the portion of the water filling the reactor to 80% of the length thereof from its bottom at a pH of at least 8.5 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 6.5. The liquid-gas mixture resulting from the catalytic wet oxidation reaction is continuously drawn off from an upper portion of the reactor and led into a liquid-gas separator. The separated gas phase and liquid phase are indirectly cooled approximately to room temperature respectively.

The gas phase is found to contain 0.2 ppm of ammonia and 0.01 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 18 shows the quality of the waste water before and after the wet oxidation treatment.

Table 18

Before treatment After treatment (mg/I) (mg/I) NH3 4092 4 HCN 794 Trace H2S 2520 5 C10H8 612 - Trace Na+ 3580 3580 SO4 None detected 7110 Third step The water from the second step is continuously passed, in the pressurized state (about 65 kg/cm2), through a reverse osmosis unit incorporating an acetate membrane with a desalination efficiency of 95 to 98%.

One hundred parts of the water fed to the reverse osmosis unit affords 85 parts of purified water and 15 parts of a concentrate. Replenishing industrial water is added to the purified water, and the mixture is used as the absorbing water for the first step. Sodium sulfate is recovered from the concentrate in the usual manner.

Table 1 9 shows the quality of the purified water and concentrate obtained from the water resulting from the second step and shown in the right column of Table 18.

Table 19

Purified water Concentrate (mg / I) (mg/I) NH3 0.06 26.3 HCN Trace Trace H23 0.05 33.1 C10H8 Trace Trace Na+ 72 23460.

804 - 70 47000 EXAMPLES 50 to 61 Waste water is treated in the same manner as in Example 48 except that the catalyst shown in Table 20 is used for each example. Table 20 gives the ammonia removal efficiency and COD removal efficiency achieved by the second step of each example.

The gas phase is found to contain up to 4.5 ppm of ammonia and up to 0.8 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 20

Example Catalyst Ammonia removal COD removal (%) (%) 50 1.0% % Ir-Al2O3 98 At least 99 51 0.3% Pt-TiO2 At least At least 99 99 52 l.0/o Au-AI203 92 99 53 0.8% Pd-TiO3 At least At least 99 99 54 1.5% Rh-AI2O, 93 95 55 5.0 h Fe.A1203 92 95 56 5.0% Ni-Al2O3 90 90 57 5.0% W-Al2O3 91 95 58 5.0% Cu-Al2O3 93 At least 99 59 5.0% % Co-Al2O3 98 60 2.0% Ru-Carbon At least 99 61 2.0% Ru-ZrO2 EXAMPLE 62 The process of this invention is practiced in the mode shown in Fig. 6.

First step An unpurified coke oven gas is introduced into a lower portion of an absorbing tower, while an aqueous solution of ammonia in a concentration of 1 g/liter is sprayed from the top of the tower.

Table 21 shows the liquid-gas contact conditions, Table 22 the absorption efficiency achieved, and Table 23 the composition of the water at the outlet of the absorbing tower.

TABLE 21 Space velocity of water: 662 hr1 Mass velocity of water: 10.6 t/m2.hr Space velocity of water: 2.6 hr- Temperature of the interior of tower: 250C Table 22

Charge Discharge Absorption (g/Nm ) (g/Nm ) efficiency (%) Nh3 7.50 0.83 89 HCN 1.53 0.05 97 H2S 4.73 0.04 At least C10H8 1.52 0.23 85 Table 23

Concentration - (mg /I) NH3 2667.5 HCN 370 H28 1173 C10H8 320 Second step A mixture of 1 part by weight of the waste water from the first step and 0.2 part by weight of a gas liquor resulting from a coke oven is adjusted to a pH of about 11. A particulate catalyst 0.15 to 0.3 mm in particle size and comprising 5% by weight of ruthenium supported on a titania carrier is admixed with the mixture to obtain a slurry containing the catalyst in a concentration of 10% by weight. The slurry is fed to a lower portion of a cylindrical stainless steel reactor at a space velocity of 1.51 hr-1 (based on an empty column) and at a mass velocity of 4.53 t/m2.hr. Air is introduced to the reactor at a space velocity of 62 hr1 (based on an empty column, under standard conditions).

The interior of the reactor is maintained at a temperature of 2500C and pressure of 60 kg/cm2 G, while supplying a 48% aqueous solution of caustic soda to the reactor at a rate required to maintain the portion of the water filling the reactor to 80% of the length thereof from its bottom at a pH of at least 8.5 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 6.5. The liquid-gas mixture resulting from the catalytic wet oxidation reaction is continuously drawn off from an upper portion of the reactor, indirectly cooled to 300 C and led into a liquid-gas separator, in which the mixture is separated into a liquid and a gas. The separated gas is decompressed to the atmospheric pressure and then released to the atmosphere.The liquid phase is introduced in a pressurized state (60 kg/cm2) into a liquid-solid separator, whereby it is separated into the catalyst and treated water for the recovery of the catalyst. The separated liquid phase is fed to the third step while being maintained at a controlled pressure of 50 kg/cm2.

The gas phase is found to contain 1.0 ppm of ammonia and 0.02 ppm of nitrogen oxides, the remainder being nitrogen, oxygen and carbon dioxide, but none of sulfur oxides, hydrogen sulfide and hydrogen cyanide are detected.

Table 24 shows the quality of the waste water mixture and the treated water.

Table 24

Waste water Water treated mixture by 2nd step (mg/I) (mg /I) NH3 2806 1.5 HCN 317 Trace H2S 1004 Trace COD 4125 8.5 TOC 727 12 TOD 8820 20 TN 2490 3.5 SO4-- 200 4995 Na+ 2400 2400 Table 24 indicates that the water resulting from the second step has been so cleaned that it can be discarded into the sea.

Third step The water resulting from the second step and separated from the catalyst is continuously passed, in the pressurized state (about 50 kg/cm2), through a reverse osmosis unit incorporating an acetate membrane with a desalination efficiency of 5 to 98%.

One hundred parts of the water fed to the reverse osmosis unit affords 85 parts of purified water and 15 parts of a concentrate. The purified water is usable as part of the absorbing water for the first step or as industrial water for some other applications. Sodium sulfate is recovered from the concentrate in the usual manner.

Table 25 shows the quality of the purified water and concentrate obtained from the liquid of the quality shown in the right column of Table 24.

Table 25

Purified water Concentrate (mg (mg/l) NH3 0.04 9.75 HCN Trace Trace H2S Trace Trace Na+ 56 15680 SO4-- 59 33000

Claims

1. A process for treating ammonia-containing waste water which comprises introducing at a pH of about 8.5 to about 11.5 the waste water to a reactor to subject the same to wet oxidation with an oxygen-containing gas in the presence of a catalyst while maintaining the waste water at a temperature of about 100 to about 3700C and at pressure permitting the waste water to remain in the liquid phase, the oxygen-containing gas containing oxygen in an amount of about 1 to about 1.5 times the theoretical amount required for decomposing the ammonia, organic substances and inorganic substances contained in the waste water, the catalyst being supported by a carrier and comprising at least one of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, tungsten and compounds thereof insoluble or sparingly soluble in water, and supplying an alkali substance to the reactor at a rate required to maintain at least about 80% of the waste water introduced to the reactor and positioned toward the water inlet of the reactor at a pH of at least about 8-at all times and to permit the water resulting from the wet oxidation to retain a pH of about 5 to about 8.

2. A process as defined in claim 1 wherein the ammonia-containing waste water is fed into the reactor at a pH of about 9 to about 11.

3. A process as defined in claim 1 wherein the active component of the catalyst comprises at least one of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten.

4. A process as defined in claim 1 wherein the active component of the catalyst comprises at least one of compounds insoluble or sparingly soluble in water or iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten.

5. A process as defined in claim 4 wherein the active component of the catalyst comprises at least one of oxides of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, copper and tungsten.

G. A process as defined in claim 5 wherein the active component of the catalyst comprises at least one of iron sesquioxide, tri-iron tetroxide, cobalt monoxide, nickel monoxide, ruthenium dioxide, rhodium sesquioxide, palladium monoxide, iridium dioxide, cupric oxide and tungsten dioxide.

7. A process as defined in claim 4 wherein the active component of the catalyst comprises at least one of ruthenium dichloride and platinum dichloride.

8. A process as defined in claim 4 wherein the active component of the catalyst comprises at least one of ruthenium sulfide and rhodium sulfide.

9. A process as defined in claim 1 wherein the carrier is at least one of titania, zirconia, alumina, silica, silica-alumina, active carbon, and porous bodies of nickel, nickel-chromium, nickel-chromiumaluminum and nickel-chromium-iron.

10. A process as defined in claim 9 wherein the carrier is at least one of titania and zirconia.

11. A process as defined in claim 9 wherein the carrier is at least one of alumina, silica, silicaalumina, active carbon, and porous bodies of nickel, nickel-chromium, nickel-chromium-aluminum and nickel-chromium-iron.

12. A process as defined in claim 1 wherein the wet oxidation of the waste water is carried out in a reactor of the fixed bed type.

13. A process as defined in claim 1 wherein the wet oxidation of the waste water is carried out in a reactor of the fluidized bed type.

14. A process as defined in claim 1 wherein the oxygen-containing gas is fed in an amount about 1.05 to about 1.2 times the required theoretical amount of oxygen.

15. A process as defined in claim 1 wherein the reaction is carried out at a temperature of about 200 to about 3000 C.

16. A process for treating waste water and a gas containing hydrogen cyanide, hydrogen sulfide and ammonia which comprises: (i) the first step of bringing an absorbing liquid comprising water or an aqueous alkali solution into contact with the gas to cause the absorbing liquid to remove the harmful components from the gas by absorption, and (ii) the second step of introducing at a pH of about 8.5 to about 11.5 the waste water from the first step, with or without other waste water combined therewith, to a reactor to subject the same to wet oxidation with an oxygen-containing gas in the presence of a catalyst while maintaining the waste water at a temperature of about 100 to about 3700C and at pressure permitting the waste water to remain in the liquid phase, the oxygen-containing gas containing oxygen in an amount of about 1 to about 1.5 times the theoretical amount required for decomposing the ammonia, organic substances and inorganic substances contained in the waste water, the catalyst being supported by a carrier and comprising at least one of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, tungsten and compounds thereof insoluble or sparingly soluble in water, and supplying an alkali substance to the reactor at a rate required to maintain at least about 80% of the waste water introduced to the reactor and positioned toward the water inlet of the reactor at a pH of at least about 8 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 5 to about 8.

17. A process as defined in claim 16 wherein the ammonia-containing waste water is fed into the reactor at a pH of about 9 to about 11.

18. A process as defined in claim 16 wherein the active component of the catalyst comprises at least one of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten.

19. A process as defined in claim 1 6 wherein the active component of the catalyst comprises at least one of compounds insoluble or sparingly soluble in water of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten.

20. A process as defined in claim 19 wherein the active component of the catalyst comprises at least one of oxides of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, copper and tungsten.

21. A process as defined in claim 20 wherein the active component of the catalyst comprises at least one of iron sesquioxide, tri-iron tetroxide, cobalt monoxide, nickel monoxide, ruthenium dioxide, rhodium sesquioxide, palladium monoxide, iridium dioxide, cupric oxide and tungsten dioxide.

22. A process as defined in claim 19 wherein the active component of the catalyst comprises at least one of ruthenium dichloride and platinum dichloride.

23. A process as defined in claim 19 wherein the active component of the catalyst comprises at least one of ruthenium sulfide and rhodium sulfide.

24. A process as defined in claim 16 wherein the carrier is at least one of titania, zirconia, alumina, silica, silica-alumina, active carbon, and porous bodies of nickel, nickel-chromium, nickel-chromium aluminum and nickel-chromium-iron.

25. A process as defined in claim 24 wherein the carrier is at least one of titania and zirconia.

26. A process as defined in claim 24 wherein the carrier is at least one of alumina, silica, silica alumina, active carbon, and porous bodies of nickel, nickel-chromium, nickel-chromium-aluminum and nickel-chromium-iron.

27. A process as defined in claim 1 6 wherein the wet oxidation of the waste water is carried out in a reactor of the fixed bed type.

28. A process as defined in claim 1 6 wherein the wet oxidation of the waste water is carried out in a reactor of the fluidized bed type.

29. A process as defined in claim 16 wherein the oxygen-containing gas is fed in an amount about

1.05 to about 1.2 times the required theoretical amount of oxygen.

30. A process as defined in claim 16 wherein the reaction is carried out at a temperature of about 200 to about 3000 C.

31. A process for treating ammonia-containing waste water which comprises: (i) the first step of introducing at a pH of about 8.5 to about 11.5 the waste water to a reactor to subject the same to wet oxidation with an oxygen-containing gas in the presence of a catalyst while maintaining the waste water at a temperature of about 100 to about 3700C and at pressure permitting the waste water to remain in the liquid phase, the oxygen-containing gas containing oxygen in an amount of about 1 to about 1.5 times the theoretical amount required for decomposing the ammonia, organic substances and inorganic substances contained in the waste water, the catalyst being supported by a carrier and comprising at least one of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, tungsten and compounds thereof insoluble or sparingly soluble in water, and supplying an alkali substance to the reactor at a rate required to maintain at least about 80% of the waste water introduced to the reactor and positioned toward the water inlet of the reactor at a pH of at least about 8 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 5 to about 8, and (ii) the second step of introducing the water in a pressurized state from the first step to a reverse osmosis unit to separate the water into purified water and a concentrate.

32. A process as defined in claim 31 wherein the ammonia-containing waste water is fed into the reactor at a pH of about 9 to about 11.

33. A process as defined in claim 31 wherein the active component of the catalyst comprises at least one of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten.

34. A process as defined in claim 31 wherein the active component of the catalyst comprises at least one of compounds insoluble or sparingly soluble in water of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten.

35. A process as defined in claim 34 wherein the active component of the catalyst comprises at least one of oxides of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, copper and tungsten.

36. A process as defined in claim 35 wherein the active component of the catalyst comprises at least one of iron sesquioxide, tri-iron tetroxide, cobalt monoxide, nickel monoxide, ruthenium dioxide, rhodium sesquioxide, palladium monoxide, iridium dioxide, cupric oxide and tungsten dioxide.

37. A process as defined in claim 34 wherein the active component of the catalyst comprises at least one of ruthenium dichloride and platinum dichloride.

38. A process as defined in claim 34 wherein the active component of the catalyst comprises at least one of ruthenium sulfide and rhodium sulfide.

39. A process as defined in claim 31 wherein the carrier is at least one of titania, zirconia, alumina, silica, silica-alumina, active carbon, and porous bodies of nickel, nickel-chromium, nickel-chromiumaluminum and nickel-chromium-iron.

40. A process as defined in claim 39 wherein the carrier is at least one of titania and zirconia.

41. A process as defined in claim 39 wherein the carrier is at least one of alumina, silica, silicaalumina, active carbon, and porous bodies of nickel, nickel-chromium, nickel-chromium-aluminum and nickel-chromium-iron.

42. A process as defined in claim 31 wherein the wet oxidation of the waste water is carried out in a reactor of the fixed bed type.

43. A process as defined in claim 31 wherein the wet oxidation of the waste water is carried out in a reactor of the fluidized bed type.

44. A process as defined in claim 31 wherein the oxygen-containing gas is fed in an amount about

1.05 to about 1.2 times the required theoretical amount of oxygen.

45. A process as defined in claim 31 wherein the reaction is carried out at a temperature of about 200 to 3000C.

46. A process for treating waste water and a gas containing hydrogen cyanide, hydrogen sulfide and ammonia which comprises: (i) the first step of bringing an absorbing liquid comprising water or an aqueous alkali solution into contact with the gas to cause the absorbing liquid to remove the harmful components from the gas by absorption, (ii) the second step of introducing at a pH of about 8.5 to about 11.5 the waste water from the first step, with or without other waste water combined therewith, to a reactor to subject the same to wel oxidation with an oxygen-containing gas in the presence of a catalyst while maintaining the waste water at a temperature of about 100 to about 3700C and at pressure permitting the waste water to remain in the liquid phase, the oxygen-containing gas containing oxygen in an amount of about 1 to about 1.5 times the theoretical amount required for decomposing the ammonia, organic substances and inorganic substances contained in the waste water, the catalyst being supported by a carrier and comprising at least one of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, tungsten and compounds thereof insoluble or sparingly soluble in water, and supplying an alkali substance to the reactor at a rate required to maintain at least about 80% of the waste water introduced to the reactor and positioned toward the water inlet of the reactor at a pH of at least about 8 at all times and to permit the water resulting from the wet oxidation to retain a pH of about 5 to about 8, and (iii) the third step of introducing the water in a pressurized state from the first step to a reverse osmosis unit to separate the water into purified water and a concentrate.

47. A process as defined in claim 46 wherein the ammonia-containing waste water is fed into the reactor at a pH of about 9 to about 11.

48. A process as defined in claim 46 wherein the active component of the catalyst comprises at least one of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten.

49. A process as defined in claim 46 wherein the active component of the catalyst comprises at least one of compounds insoluble or sparingly soluble in water of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten.

50. A process as defined in claim 49 wherein the active component of the catalyst comprises at least one of oxides of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, copper and tungsten.

51. A process as defined in claim 50 wherein the active component of the catalyst comprises at least one of iron sesquioxide, tri-iron tetroxide, cobalt monoxide, nickel monoxide, ruthenium dioxide, rhodium sesquioxide, palladium monoxide, iridium dioxide, cupric oxide and tungsten dioxide.

52. A process as defined in claim 49 wherein the active component of the catalyst comprises at least one of ruthenium dichloride and platinum dichloride.

53. A process as defined in claim 49 wherein the active component of the catalyst comprises at least one of ruthenium sulfide and rhodium sulfide.

54. A process as defined in claim 46 wherein the carrier is at least one of titania, zirconia, alumina, silica, silica-alumina, active carbon, and porous bodies of nickel, nickel-chromium, nickel-chromiumaluminum and nickel-chromium-iron.

55. A process as defined in claim 54 wherein the carrier is at least one of titania and zirconia.

56. A process as defined in claim 54 wherein the carrier is at least one of alumina, silica, silicaalumina, active carbon, and porous bodies of nickel, nickel-chromium, nickel-chromium-aluminum and nickel-chromium-iron.

57. A process as defined in claim 46 wherein the wet oxidation of the waste water is carried out in a reactor of the fixed bed type.

58. A process as defined in claim 46 wherein the wet oxidation of the waste water is carried out in a reactor of the fluidized bed type.

59. A process as defined in claim 46 wherein the oxygen-containing gas is fed in an amount about 1.05 to about 1.2 times the required theoretical amount of oxygen.

60. A process as defined in claim 46 wherein the reaction is carried out at a temperature of about 200 to about 3000 C.