CN1306943A

CN1306943A - Waste water treating method and catalyst washing regeneration method

Info

Publication number: CN1306943A
Application number: CN 00100415
Authority: CN
Inventors: 原田吉明; 二川道夫; 山崎健一
Original assignee: Osaka Gas Co Ltd
Current assignee: Osaka Gas Co Ltd
Priority date: 2000-01-31
Filing date: 2000-01-31
Publication date: 2001-08-08
Anticipated expiration: 2020-01-31
Also published as: CN100528362C; CN100381371C; CN1781606A

Abstract

The waste water treating process includes two steps. In the first step of wet oxidation treatment, at 100 deg.c over temperature and at least one part of waste water in liquid pressure and in the presence of carried catalyst and oxygen exceeding theoretic amount, waste water containing nitrogen compound and/or organic matter and/or inorganic matter are decomposed into nitrogen and/or CO2 and water. In the second step of gas-liquid separation, at least part of separated high temperature liquid phase is mixed circularly with waste water before wet oxidation treatment.

Description

Method for treating waste water and method for washing and regenerating catalyst

The present invention relates to a method for treating wastewater containing at least one nitrogen-containing compound, an organic substance, and an inorganic substance (hereinafter, this is simply referred to as wastewater).

In addition, the invention also relates to a washing regeneration method of the catalyst used in the wet oxidation treatment of the wastewater. According to the method for washing and regenerating a catalyst of the present invention, it is possible to simultaneously wash and remove metal components adhering to a heat exchanger, a gas-liquid separator, a cooler, various pipes, and the like in a wet oxidation facility for wastewater.

A method for wet oxidation treatment of wastewater containing at least one nitrogen-containing compound, an organic substance, and an inorganic substance (hereinafter collectively referred to as "dirty component") is known.

For example, Japanese patent publication No. 59-29317 filed by the present applicant discloses a method for decomposing ammonia, organic substances and inorganic substances in wastewater by wet-oxidizing the wastewater in the presence of a supported catalyst.

As demonstrated by the results shown in the examples, the process generally provides the best wastewater treatment. However, in this method, when the concentration of the contaminated components in the wastewater is high (for example, when the TOD value is 65000mg/l or more), a large amount of air (oxygen) is used and the wastewater is treated under high-temperature and high-pressure conditions, and a large amount of water is evaporated in the heat exchanger, the heater, and the reaction tower and transferred to the gas phase. Therefore, in order to cope with the temperature decrease due to the latent heat of evaporation, it is necessary to increase the heat transfer area of the heat exchanger or to externally heat the reaction mixture with an external heater or the like, and it is difficult to continue the reaction while maintaining a good liquid phase state, and the removal rate of the fouling components is decreased. Further, when the concentration of the contaminated components in the wastewater is high or when the activity of the catalyst is reduced by the adhesion of the metal components in the wastewater to the surface of the catalyst, the treatment cannot be performed satisfactorily.

Further, as conventional techniques relating to the wet oxidation treatment method, for example, Japanese patent laid-open Nos. 53-20663, 54-42851, 55-152591, 62-132589, 3-777691 and 4-104898 are proposed.

In the wet oxidation method of these waste waters, at least one selected from the group consisting of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and water-insoluble or water-insoluble compounds of these metals is usually used in a state of being supported on a carrier of a metal oxide such as silica, alumina, titania, zirconia, etc., having various shapes such as a sphere, a granule, a cylinder, a chip, a honeycomb, etc., a carrier of a composite metal oxide containing at least one of these metal oxides, an activated carbon carrier, etc. Since such a supported catalyst (hereinafter, referred to simply as a waste water oxidation catalyst) is used in a large amount in the treatment of waste water, it is necessary to regenerate and reuse the catalyst whose activity is lowered with the lapse of treatment time. The present inventors have found that when a wastewater oxidation catalyst is subjected to a two-step treatment in advance, i.e., an acid washing treatment with an acidic aqueous solution and a liquid-phase reduction treatment or a gas-phase reduction treatment with an alkaline aqueous solution, the activity of the catalyst is remarkably restored (refer to Japanese patent publication No. Hei 3-66018, and hereinafter this method is referred to as "the prior application method").

This previously filed method can produce excellent catalyst regeneration effects, but since two-step treatments of acid washing treatment and reduction treatment must be carried out, it is expected that the same excellent effects can be achieved with a simpler treatment operation in terms of practical use.

Accordingly, a main object of the present invention is to provide a novel technique by which, in wet oxidation of wastewater containing at least one nitrogen-containing compound, an organic substance and an inorganic substance, even when the wastewater is treated under high-temperature and high-pressure conditions using a relatively large amount of air (oxygen), the reaction can be continued while maintaining a good liquid phase state without increasing the heat transfer area of a heat exchanger or heating the wastewater externally using a heater or the like.

It is another object of the present invention to provide a novel technique for effectively and economically treating wastewater having a high concentration of a fouling component by suppressing adhesion of a metal component to a catalyst surface.

Further, a main object of the present invention is to provide a novel method for regenerating a catalyst for wastewater treatment, which can exhibit a high catalyst regeneration effect by a simple treatment operation.

FIG. 1 is a flow chart showing an embodiment of the present invention.

Fig. 2 is a flowchart showing another embodiment of the present invention.

The invention provides a wastewater treatment method and a catalyst washing regeneration method,

1. a method for treating wastewater (hereinafter referred to as "treatment method 1") characterized by comprising the following two steps:

(1) wet oxidation treatment of a wastewater containing at least one of a nitrogen-containing compound, an organic substance and an inorganic substance in the wastewater in the presence of a supported catalyst and in the presence of oxygen in an amount of at least the theoretical amount of oxygen necessary for decomposing the nitrogen-containing compound and/or the organic substance and/or the inorganic substance in the wastewater into nitrogen and/or carbon dioxide and water while maintaining a temperature of at least 100 ℃ and a pressure at which at least a part of the wastewater is maintained in a liquid phase;

(2) at least a part of the high-temperature liquid phase obtained by gas-liquid separation after wet oxidation treatment is circularly mixed with the wastewater before wet oxidation treatment.

2. The method for treating wastewater according to claim 1, wherein the catalytically active component in the step (1) is at least one selected from the group consisting of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and water-insoluble or hardly soluble compounds of these metals.

3. The method for treating waste water according to claim 1, wherein the linear velocity of the liquid in the column (the amount of the liquid introduced into the column/the cross-sectional area of the column) in the step (1) is 0.1 to 1.0 cm/sec.

4. The method for treating wastewater according to claim 1, wherein the oxygen source in the step (1) is air, oxygen-enriched air, high-purity oxygen, ozone and H₂O₂At least one of (1).

5. The method for treating wastewater according to claim 1, wherein the circulation amount of the high-temperature liquid phase in the step (2) is 0.1 to 15 times that of the wastewater.

6. A method for treating wastewater (hereinafter referred to as "second treatment method") characterized by comprising the following five steps:

(1) wet oxidation treatment of a wastewater containing at least one nitrogen-containing compound, organic substance and inorganic substance in the presence of a supported catalyst in the presence of a high-purity oxygen-containing gas (oxygen concentration of 80% or more) having a theoretical oxygen amount or more necessary for decomposing the nitrogen-containing compound and/or organic substance and/or inorganic substance in the wastewater into nitrogen and/or carbon dioxide and water while maintaining a temperature of 100 ℃ or more and a pressure of a liquid phase of at least a part of the wastewater,

(2) at least one part of high-temperature liquid phase obtained by first gas-liquid separation after wet oxidation treatment is circularly mixed with the wastewater before wet oxidation treatment,

(3) after heat exchange is carried out between the high-temperature gas-liquid phase obtained by the first gas-liquid separation and the wastewater before wet oxidation treatment, the gas-liquid phase is cooled for the second gas-liquid separation,

(4) subjecting the liquid phase obtained by the second gas-liquid separation to a biological treatment, and

(5) the excess sludge produced in the biological treatment is mixed with the above-mentioned waste water in a circulating manner.

7. The method for treating wastewater as described in claim 6, wherein the oxygen concentration in the high-purity oxygen-containing gas in the step (1) is 80% or more.

8. The method for treating wastewater according to claim 6, wherein the catalytically active component in the step (1) is at least one selected from the group consisting of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and water-insoluble or hardly soluble compounds of these metals.

9. The method for treating waste water as described in claim 6, wherein the linear velocity of the liquid in the column (the amount of the liquid introduced into the column/the cross-sectional area of the column) in the step (1) is 0.1 to 1.0 cm/sec.

10. The method for treating wastewater according to claim 6, wherein the oxygen source in the step (1) is air rich in oxygen, high purity oxygen, ozone and H₂O₂At least one of (1).

11. The method for treating wastewater according to claim 6, wherein the circulation amount of the high-temperature liquid phase in the step (2) is 0.1 to 15 times that of the wastewater.

12. The method for treating wastewater as described in claim 6, wherein the biological treatment method in the step (4) is an activated sludge treatment method and/or a biological denitrification method.

13. A method for washing and regenerating a catalyst, characterized in that a method for washing and regenerating a supported catalyst for wet oxidation of wastewater, which comprises using at least one of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, and tungsten, and water-insoluble or hardly-soluble compounds of these metals as a catalyst active ingredient, comprises the steps of: an acidic aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more.

14. The catalyst washing regeneration method is characterized in that iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten and the water insolubility of the metalsOr even at least one of the sparingly soluble compounds as a catalyst active ingredient, comprising the steps of: an alkaline aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more.

15. A method for washing and regenerating a catalyst, characterized in that a method for washing and regenerating a supported catalyst for wet oxidation of wastewater, which comprises using at least one of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, and tungsten, and water-insoluble or hardly-soluble compounds of these metals as a catalyst active ingredient, comprises the steps of: (1) an acidic aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more; (2) an alkaline aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more.

16. A method for washing and regenerating a catalyst, characterized in that a method for washing and regenerating a supported catalyst for wet oxidation of wastewater, which comprises using at least one of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, and tungsten, and water-insoluble or hardly-soluble compounds of these metals as a catalyst active ingredient, comprises the steps of: (1) an alkaline aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and heating at a temperature of room temperature or moreContacting the catalyst with a wash solution at a temperature; (2) an acidic aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more.

17. And (3) a catalyst washing regeneration method for carrying out wet oxidation treatment on the catalyst washing waste liquid generated in at least one method of 13-16 and the wastewater.

18. The method for washing and regenerating a catalyst as described in 17, wherein the catalyst washing liquid is subjected to coagulation and precipitation treatment to remove metal components in the liquid, and then subjected to wet oxidation treatment together with the wastewater. I, invention relating to waste water treatment method

The wastewater to be treated in the present invention is not particularly limited as long as it contains at least one nitrogen-containing compound, an organic substance and an inorganic substance.

As the nitrogen-containing compound contained in the waste water, for example, NH₄-N (nitrogen in the form of ammonium, the same applies hereinafter), NO₂-N、NO₃N, organic nitrogen (including amines), inorganic nitrogen (including CN, SCN), etc.

Examples of the organic substances contained in the wastewater include organic substances (phenols, alcohols, carboxylic acids, etc.), organic chlorine compounds (trichloroethylene, tetrachloroethylene, dioxin, etc.), suspended substances (derived from organic solid wastes, sludge generated in various biological treatment steps, kitchen waste, municipal waste, biomass, etc.).

The inorganic substances contained in the wastewater are, for example, generally inorganic substances (e.g., S)₂O₃ ^2-、SO₃ ^2-、SCN^-、CN^-Etc.).

The wastewater to be treated by the present invention includes, for example, wastewater containing 1 of the above nitrogen-containing compounds, organic substances and inorganic substances alone, and wastewater containing two or more of these substances at the same time.

Such wastewater is, for example, coal gas liquid produced from coal-processing coke oven plant, coal gasification plant, coal liquefaction plant, etc., wastewater produced by gas generation in these plants, wastewater produced from wet desulfurization tower and wet decyanation tower, photographic wastewater, printing wastewater, pesticide wastewater, dyeing wastewater, wastewater from semiconductor manufacturing plant, petrochemical plant wastewater, petroleum refining plant wastewater, pharmaceutical plant wastewater, paper mill wastewater, chemical plant wastewater, domestic wastewater containing kitchen waste, paper, plastics, etc., wastewater produced by feces and urine, thermal decomposition of municipal waste, sludge produced by biological treatment (anaerobic treatment, aerobic treatment) of industrial wastewater, sewage sludge, wastewater produced by oil conversion of sewage sludge, wastewater containing organic chlorine compounds, various cyanide-containing wastewater discharged from electroplating industry, wastewater for steel soft nitriding treatment, wastewater produced by steel soft nitriding treatment, and the like, A cyanide solution for surface treatment such as liquid carbon impregnation treatment and chemical conversion treatment, and a cyanide waste solution discharged during these surface treatments. For example, the cyanide-containing wastewater may contain various organic and inorganic substances (organic acids such as formic acid and acetic acid), various nitrogen-containing compounds such as ammonia (hereinafter, all nitrogen-containing compounds including cyanogen and ammonia are collectively referred to as "nitrogen-containing compounds" unless otherwise specified), and organic chlorine compounds such as trichloroethylene.

The present invention is also useful for the treatment of wastewater or sludge containing one or more metal components such as Mg, Al, Si, P, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Cd.

The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a flow chart showing an embodiment of the method of treatment 1.

FIG. 2 is a flow chart showing an embodiment of the method of treatment 2.

In the treatment method 1, the wastewater is pumped up from a raw water tank to a predetermined pressure, mixed with an oxygen-containing gas pressurized by a compressor, heated to a predetermined temperature by a heat exchanger (simply referred to as "heat exchanger" in fig. 1), and supplied to a reaction column.

In the 2 nd treatment method, the wastewater is pumped up from the raw water tank to a predetermined pressure, mixed with the high-purity oxygen-containing gas pressurized by the compressor, heated to a predetermined temperature by a heat exchanger (simply referred to as "heat exchanger" in fig. 2), and then supplied to the reaction column.

The reaction column is packed with a catalyst supported by a carrier.

Examples of the catalytically active component include iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, and tungsten, and water-insoluble or hardly soluble compounds of these metals. More specifically, examples of such compounds include oxides (cobalt oxide, iron oxide, etc.), chlorides (ruthenium dichloride, platinum dichloride, etc.), sulfides (ruthenium sulfide, rhodium sulfide, etc.), and the like. These metals and compounds thereof may be used alone or in combination of two or more, or may be mixed with a metal (e.g., La, Ce, Te, etc.) as a third component to form a composite catalyst. These catalytically active components can be used in a state supported on a known metal oxide support or metal support according to a conventional method.

The metal oxide support and the metal support are not particularly limited, and those used as known catalyst supports can be used. Examples of the metal oxide support include alumina, silica, zirconia, titania, composite metal oxides containing these metal oxides (alumina-silica, alumina-silica zirconia, titania-zirconia, and the like), and metal oxide supports containing these metal oxides or composite metal oxides as a main component, and examples of the metal support include iron, aluminum, and the like. Among these carriers, zirconia, titania and titania-zirconia, which are excellent in durability, are more preferable.

The shape of the supported catalyst is not particularly limited, and examples thereof include spheres, granules, cylinders, chips, powders, and honeycombs. When the supported catalyst is filled, the volume of the reaction tower is preferably such that the space velocity of the liquid is 0.5 to 10hr in the case of a fixed bed^-1More preferably 1 to 5hr^-1. When the supported catalyst is in the form of spheres, granules, cylinders, chips, powders, etc., the size of the supported catalyst used in the fixed bed is usually 3 to 50mm, more preferably 5 to 25 mm. In the case of using the honeycomb carrier with a catalyst supported thereon, the honeycomb structure may have any shape such as a quadrangle, a hexagon, or a circle with an openingThe substance of (1). The area per unit volume and the aperture ratio are not particularly limited, but the area per unit volume is usually 200 to 800m²/m³And a substance having an aperture ratio of 40 to 80%. Examples of the material for the honeycomb structure include the same metal oxides and metals as described aboveMore preferred are zirconia, titania and titania-zirconia having excellent durability.

The amount of the catalyst active ingredient supported on the carrier is usually 0.05 to 25% by weight, more preferably 0.3 to 3% by weight.

In the heat exchanger, a high-temperature gas-liquid phase obtained by a gas-liquid separator described below is circulated to recover heat. When the reaction temperature cannot be maintained or must be raised to a predetermined temperature during the reaction in winter or the like, the reaction mixture may be heated by a heater (not shown) or steam may be supplied from a steam generator (not shown). In order to raise the temperature in the reaction column to a predetermined temperature during the operation, steam may be directly introduced into the reaction column to raise the temperature, or a heater (not shown) may be provided between the heat exchanger and the reaction column to raise the temperature.

The temperature in the reaction column is 100 ℃ or higher, more preferably 150 ℃ or higher. The higher the reaction temperature is, the higher the decomposition clearance of the fouling components becomes and the retention time of the wastewater in the reaction column becomes short, but on the other hand, it is preferable to determine the reaction temperature by comprehensively considering the concentration of the fouling components in the wastewater, the degree of treatment required, the running cost, the construction cost, and the like, because the facility cost increases.

The pressure during the reaction is preferably a pressure at which the wastewater to be treated can be kept in a liquid phase at the reaction temperature or higher. Here, "pressure capable of maintaining a liquid phase" means that the pressure of a liquid phase can be substantially maintained in a reaction column when the amount of liquid (wastewater), the amount of water vapor, and the amount of gas (the amount of gas in the column other than water vapor) are at equilibrium under the conditions of a predetermined reaction temperature and the amount of oxygen-containing gas introduced in the embodiment of fig. 1 and the amount of high-concentration oxygen-containing gas introduced with the oxygen concentration of 80% or more in the embodiment of fig. 2, and the amount of water vapor is 60% or less (more preferably 50% or less).

In the treatment method 2, the biological treatment of the treated water after the wet oxidation treatment significantly increases the reaction pressure, and thus, it is not necessary to perform the ultra-high oxidation treatment. The concentration of the wastewater to be treated may vary depending on the type of wastewater, the concentration of the contaminated component, etc., and may be, for exampleIn the range of 10 to 20kg/cm²Is subjected to wet oxidation treatment at a relatively low pressure.

In the treatment method 1, the amount of oxygen supplied to the reaction column is not less than the theoretical amount of oxygen necessary for decomposing the nitrogen-containing compound, the organic substance and the inorganic substance into harmless products, more preferably 1 to 3 times the theoretical amount of oxygen, and particularly preferably 1.05 to 1.2 times the theoretical amount of oxygen. As the oxygen source, there can be used air, oxygen-enriched air (oxygen-enriched air obtained by using a selective oxygen permeable membrane, air-oxygen mixture, oxygen-enriched air obtained by treating air with a PSA apparatus, etc.), oxygen, and a substance (O) capable of generating oxygen under the conditions of wastewater treatment₃、H₂O₂Etc.).

In the second treatment method, the amount of oxygen supplied to the reaction column is not less than the theoretical oxygen amount necessary for decomposing the nitrogen-containing compound, the organic substance and the inorganic substance into harmless products, more preferably 1.05 to 3 times the theoretical oxygen amount, and particularly preferably 1.1 to 1.2 times the theoretical oxygen amount. As the oxygen source, a gas having a high oxygen concentration and an oxygen concentration of 80% or more, for example, oxygen-enriched air (oxygen-enriched air obtained by using a selective oxygen permeable membrane, air-oxygen mixture, oxygen-enriched air obtained by treating air with a PSA apparatus, or the like), high-purity oxygen, and a substance (O) capable of generating high-concentration oxygen under wastewater treatment conditions can be used₃、H₂O₂Etc.).

In the treatment methods 1 and 2, an oxygen-containing off-gas containing one or two or more kinds of impurities such as hydrogen cyanide, hydrogen sulfide, ammonia, sulfur oxide, nitrogen oxide, hydrocarbon, etc. may be used as the oxygen source. According to the present invention, impurities in these oxygen sources may also be decomposed together with the components to be treated in the wastewater.

In the present invention, the "theoretical oxygen amount" means that nitrogen-containing compounds, organic substances and inorganic substances (components to be treated) in wastewater are decomposed into harmless products (N)₂、H₂O and CO₂) The amount of oxygen necessary for the reaction. The theoretical oxygen amount can be easily obtained by analyzing the component to be treated in the wastewater to be treated and calculating the oxygen amount necessary for decomposition. In practical terms, it can be based on experience and trialExperiments show that several parameters are used to find out the relation formula which can be used for calculating the theoretical oxygen amount and can be approximated with high precision. Such a relational expression is described in, for example, Japanese patent publication No. 58-27999.

The treated liquid obtained from the reaction tower is separated into a gas phase and a liquid phase by a first gas-liquid separator. As described above, a part of the separated gas phase and liquid phase is used as a heat source for wastewater in the heat exchanger, and then sent to the cooler and further sent to the second gas-liquid separator to be separated into a gas phase (discharge gas) and a liquid phase (treated water).

In the present invention, at least a part of the high-temperature and high-pressure liquid phase obtained in the first gas-liquid separator 1 is circulated back to the reaction column through a liquid circulation line and a circulation pump (this circulation operation is referred to as "thermal recycling") to be mixed with the wastewater. The amount of the liquid to be circulated can be appropriately determined depending on the properties of the wastewater (the type of the component to be treated, the concentration thereof, etc.), the degree of activity reduction of the catalyst filled in the reactor, etc., and is usually 0.1 to 15 times, more preferably 1 to 10 times the amount of the wastewater. Since the fixed bed is formed in the reaction column and the washing of the catalyst is carried out, the linear velocity of the liquid in the column is usually 0.1 to 1.0cm/sec, more preferably 0.2 to 0.9 cm/sec.

The liquid phase and the gas phase other than the circulating liquid are cooled by the cooler through the heat exchanger by the first gas-liquid separator 1, and then separated into the exhaust gas and the treated water in the second gas-liquid separator.

The treated water obtained from the 2 nd gas-liquid separator may be biologically treated by a conventional method (an activated sludge treatment method, a biological denitrification method, etc.) according to the required water quality standard. Excess sludge produced by such biological processes may be subjected to wet oxidation treatment by the method of the present invention.

For example, NH remains in the treated water₄N, the biological treatment of the treated water is carried out by nitrification by nitrifying bacteria under aerobic conditions and denitrification by denitrifying bacteria under anaerobic conditions, as described below. (1) (2)

In addition, (NO) remains in the treated water₂+NO₃) when-N is present, NO can be substituted₂Carrying out nitration reaction and denitrification reaction to generate NO₃。

Since this biological treatment method is a known technique, it is not limited in the present invention, and it is usually carried out at a pH of 7.5 to 8 and a temperature of 30 ℃.

In addition, the excess sludge produced by the biological treatment method can be recycled to the raw water tank, and the wet oxidation treatment method of the invention is adopted to treat the excess sludge together with the wastewater.

In addition, the regeneration treatment liquid of the reaction tower used in the present invention, in which the catalyst is packed, may be subjected to a wet oxidation treatment together with the wastewater after removing the metal components in the liquid by coagulation-precipitation treatment, if necessary. The regeneration of the catalyst is not particularly limited, and for example, the catalyst can be regenerated by a washing treatment using a gas-liquid mixed phase of an acidic aqueous solution and air and/or a gas-liquid mixed phase of an alkaline aqueous solution and air. Examples of the acidic aqueous solution include an aqueous nitric acid solution and an aqueous ascorbic acid solution, and examples of the basic aqueous solution include an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution.

According to the present invention, when a wastewater containing at least one nitrogen-containing compound, an organic substance and an inorganic substance (a contaminated component) is subjected to wet oxidation treatment, a part of a high-temperature liquid phase obtained by gas-liquid separation after the wet oxidation treatment is thermally recycled to maintain a liquid linear velocity in a column, and therefore, even when a large amount of air (oxygen) or an oxygen-containing gas is used and the treatment is performed under high-temperature and high-pressure conditions, external heating is not required, and a good liquid phase state can be maintained to continue the reaction.

Further, according to the present invention, since the amount of the metal component adhering to the surface of the catalyst can be reduced and the liquid film resistance on the surface of the catalyst can be reduced, the activity and durability of the catalyst can be improved, and the wastewater can be effectively treated without being limited by the concentration of the fouling component.

Further, according to the present invention, since each step can be continuously performed and the process flow is very simple, the process cost (equipment cost, transportation cost, etc.) is remarkably reduced and the process management becomes easy.

Furthermore, according to the treatment method 2 of the present invention, the concentration is 10kg/cm²(0.98MPa) or lessAfter wet oxidation treatment is carried out for a short time under a relatively mild pressure, COD remaining in the treated water can be decomposed by an activated sludge method, and NH remaining in the treated water can be decomposed by biological denitrification treatment₄-N and/or (NO)₂+NO₃)-N。

Further, according to the treatment method 2, when a gas having a high oxygen content concentration (for example, pure oxygen) is used, it is 10kg/cm²Under a relatively low pressure condition of (0.98MPa) or less, the wastewater treatment can be carried out in units of time.

Further, according to the treatment method 1, when the wastewater treatment is performed under subcritical, critical or supercritical conditions using a gas containing oxygen, the operation can be completed in units of seconds. II, invention relating to catalyst washing and regenerating method

When wet oxidation treatment is generally performed on wastewater at a high temperature of 100 ℃ or higher, if a catalyst is used, the catalyst activity gradually decreases due to chemical attack of the catalyst metal caused by precipitation, and decomposition products of the contaminated components in the wastewater, and microscopic changes in chemical and physical properties of the surface of the catalyst metal. In particular, the change in the chemical and physical properties of the metal surface of the catalyst is difficult to grasp unlike precipitation, erosion and the like which are easily observed by a microscope or the like, and it is not clear what substance adversely affects the catalytic activity. However, it is presumed that such changes in the chemical and physical properties of the catalyst surface are caused by the catalyst activity suppressing factors equivalent to or more serious than the corrosion phenomenon of the catalyst surface and the like. The activity of the catalyst washed in a gas-liquid mixed phase by the method of the present invention can be recovered to the same level as or higher than that of the catalyst treated by the method of the prior application. In particular, depending on the type of wastewater to be treated, the composition of the catalyst, and the like, the activity of the catalyst can be recovered almost to the same level as that of a new catalyst when the regeneration treatment is carried out under optimum conditions.

The wastewater oxidation catalyst washed and regenerated by the method of the present invention contains at least one catalyst active component selected from the group consisting of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, tungsten, and water-insoluble or hardly-soluble compounds of these metals. Examples of the water-insoluble or hardly water-soluble compound include (i) oxides such as iron oxide, iron tetraoxide, cobalt monoxide, nickel monoxide, ruthenium dioxide, rhodium oxide, palladium monoxide, iridium dioxide, copper oxide, and tungsten dioxide, (ii) chlorides such as ruthenium chloride and platinum chloride, and (iii) sulfides such as ruthenium sulfide and rhodium sulfide.

The washing liquid for catalyst regeneration according to the present invention includes various modes, and the various modes are described in detail below.

The 1 st mode of the present invention is a method for washing a waste water oxidation catalyst having a reduced catalytic activity with an acidic aqueous solution under aeration with air.

As the acidic aqueous solution, an aqueous nitric acid solution, an aqueous ascorbic acid solution, or the like is preferably used. The concentration of the acidic aqueous solution varies depending on the degree of activity reduction of the wastewater oxidation catalyst, and is usually 1% by weight or more, and more preferably 5 to 10% by weight.

The amount of air introduced was 1m relative to the washing liquid³/hr is 10Nm³More than hr, preferably 10 to 100Nm³/hr。

The conditions for washing the wastewater oxidation catalyst in a gas-liquid mixed phase state may be determined depending on the degree of reduction of the catalyst activity, the type of the catalyst, the degree of restoration of the catalyst activity, the type and concentration of the washing liquid, and the like, and are not particularly limited, and the washing is usually carried out at a temperature of room temperature =20 ℃ or higher (more preferably 40 to 90 ℃) for 15 minutes or longer (more preferably 30 to 180 minutes). The pressure during washing may be atmospheric pressure, and it is not necessary to pressurize it, but it may be carried out under pressurized conditions.

The washing treatment of the wastewater oxidation catalyst may be performed by introducing air and a washing liquid in a state where the operation of the reaction tower in which the wastewater wet oxidation is performed is stopped. Particularly, when 2 or more reaction towers for wet oxidation treatment of waste water are used, the regeneration treatment of the waste water oxidation catalyst in several reaction towers can be alternately performed without stopping the waste water treatment.

Alternatively, the catalyst may be taken out of the reaction column and charged into a separate treatment tank for treatment.

The catalyst after completion of washing may be washed with water if necessary, and then reused. In addition, when the catalyst activity is not sufficiently recovered after 1 washing, the same washing regeneration treatment may be performed a plurality of times.

In the second mode of the present invention, the waste water oxidation catalyst having a lowered catalytic activity is washed with an aqueous alkali solution under the condition of introducing air.

The alkaline aqueous solution is preferably an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution or the like. Among them, an aqueous sodium hydroxide solution is more preferable. The concentration of the alkaline aqueous solution varies depending on the degree of activity reduction of the wastewater oxidation catalyst, and is usually 1% by weight or more, and more preferably 5 to 10% by weight.

In the case of washing with an alkaline aqueous solution, the amount of air introduced, washing conditions, washing method, washing with water if necessary, drying, repeated washing, and the like are the same as in the case of washing with an acidic aqueous solution.

In the 3 rd embodiment of the present invention, the wastewater oxidation catalyst having a decreased catalytic activity is washed with an acidic aqueous solution under an air-introduced condition, and then washed with an alkaline aqueous solution under an air-introduced condition. In the 2-step washing method, the amount of air introduced during washing with an alkaline aqueous solution and during washing with an acidic aqueous solution, washing conditions, washing method, repeated washing with water, drying, washing, and the like as necessary are the same as in the above-mentioned 1 st embodiment and 2 nd embodiment, respectively.

In the 4 th mode of the present invention, the wastewater oxidation catalyst having a lowered catalytic activity is washed with an alkaline aqueous solution under an air-introduced condition, and then washed with an acidic aqueous solution under an air-introduced condition. In the 2-step washing method, the amount of air introduced during washing with an alkaline aqueous solution and during washing with an acidic aqueous solution, washing conditions, washing method, repeated washing with water, drying, washing, and the like as necessary are the same as in the above-mentioned 1 st embodiment and 2 nd embodiment, respectively.

The waste washing liquid produced in the above embodiments 1 to 4 may be subjected to solid-liquid separation by, for example, coagulation-precipitation treatment, and then subjected to a known wet oxidation treatment together with the waste water (for example, the above-mentioned "method for wet contact oxidation treatment of waste water" proposed by the present inventors). In this case, the cross treatment may be performed as long as it involves a liquid phase derived from the wastewater.

According to the present invention, the following remarkable effects can be achieved.

(a) Since the factor of the catalyst activity reduction can be largely eliminated by a simple operation, the activity of the wastewater oxidation catalyst can be recovered to a reusable degree.

(b) The optimum regeneration treatment conditions are selected according to the catalyst, and the activity of the regenerated catalyst can be restored to the degree equivalent to that of the new catalyst.

(c) Since the use and regeneration of the catalyst can be repeated, the overall life of the catalyst can be significantly increased.

(d) Since the cost of the catalyst required for wastewater treatment is reduced, the wastewater treatment cost can be reduced.

(e) In particular, when 2 or more reactors for wet oxidation treatment of wastewater are used, the wastewater treatment is not stopped, and the wastewater oxidation catalyst deteriorated in several reactors can be alternately regenerated, so that the labor for removing and refilling the catalyst is not required.

(f) Since the metal components adhering to the heat exchanger, the gas-liquid separator, the cooler, various pipes, and the like in the wet wastewater oxidation facility can be simultaneously washed and removed, the effects of preventing the clogging of these devices, preventing the decrease in the thermal conductivity, and the like can be achieved.

The features of the present invention will be further described with reference to examples and comparative examples.

Examples 1A to 2A and comparative examples 1A to 2A

Coal gas liquids (containing nitrogen compounds, organic substances and inorganic substances) produced in coke oven plants having the properties shown in Table 1 were treated by the treatment method 1 according to the flow shown in FIG. 1.

TABLE 1

pH	9.5
pH	9.5	COD	6500mg/l
NH₄-N	2600mg/l	COD	6500mg/l
NH₄-N	2600mg/l	T-N	2900mg/l

Example 1A: supplying gas liquid to the reaction tower at a tower speed of 4hr^-1The linear velocity of the liquid in the column was 0.71cm/sec and the mass velocity was 25.5m (based on the empty column volume)³/m²Hr while supplying air at a superficial velocity of 80.4hr^-1(conversion to standard state). The air supply amount corresponds to 1.1 times the theoretical oxygen amount. Further, the reaction column was packed with a spherical catalyst (diameter: about 5mm) comprising titanium oxide as a carrier and ruthenium in an amount of 2% by weight of the carrier while maintaining the temperature at 250 ℃ and the pressure at 70kg/cm²G.

The treated liquid obtained from the reaction column was introduced into the 1 st gas-liquid separator to carry out gas-liquid separation, and a part of the obtained liquid phase (the same amount as the supplied gas-liquid) was thermally recycled to the reaction column, while the gas-liquid phase obtained from the 1 st gas-liquid separator was thermally recovered by a heat exchanger, cooled by a cooler, and separated into an effluent gas and treated water by the 2 nd gas-liquid separator.

The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 2.

In example 1A, after 8000 hours of operation, COD and NH in the treated water₄-N is less than 10 mg/l.

Example 2A: the wet oxidation treatment of the coal gas liquid was performed in the same manner as in example 1A except that the amount of the heat recycling liquid was changed to 1/2. However, since the amount of heat recycle liquid was halved, the air column velocity in the column related to coal gas liquid was 3hr^-1The linear velocity of the liquid in the column was 0.53cm/sec and the mass velocity was 19.1m (based on the empty column volume)³/m²·hr。

Comparative example 1A: the wet oxidation treatment of coal gas liquid was carried out in the same manner as in example 1A, except that the thermal recycle was not carried out. However, due to the omission of heat recycle, the gas-liquid related tower internal air velocity was 2hr^-1The linear velocity of the liquid in the column was 0.35cm/sec and the mass velocity was 12.7m (based on the empty column volume)³/m²·hr。

Comparative example 2A: the wet oxidation treatment of the coal gas liquid was carried out in the same manner as in example 1A, except that the diameter of the reaction column was changed. However, due to the change in the diameter of the reaction column, the gas-liquid related internal column velocity was 2hr^-1The linear velocity of the liquid in the column was 0.088cm/sec and the mass velocity was 3.2m (based on the empty column volume)³/m²Hr. The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 2.

TABLE 2

	COD(mg/l)	NH₄-N(mg/l)
	COD(mg/l)	NH₄-N(mg/l)	Example 1A	1.8	＜1
Example 2A	5.5	＜1	Example 1A	1.8	＜1
Example 2A	5.5	＜1	Comparative example 1A	11	＜1
Comparative example 2A	26	2.5	Comparative example 1A	11	＜1

From the results shown in Table 2, it was found that the linear velocity of the liquid in the column was increased by the heat recirculation, the liquid film resistance on the catalyst surface was reduced, and the adhesion of the metal component to the catalyst surface was suppressed, whereby the catalyst activity was maintained high for a long period of time, and the quality of the treated water was improved.

The time required for the water quality treatment was 450 hours in example 1A, 340 hours in example 2A, and 200 hours in comparative example 1A, in the same manner as in example 2A.

In addition, in any of examples 1A to 2A and comparative examples 1A to 2A, in the dischargeNo NO was detected in the gas (gaseous phase)_x、SO_xAnd NH₄-N。

Examples 3A to 12A

The gas-liquid treatment was carried out in the same manner as in example 1A, except that the combination of the catalyst component and the carrier was changed. The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 3.

TABLE 3

	Catalyst and process for preparing same	COD(mg/l)	NH4-N(mg/l)
	Catalyst and process for preparing same	COD(mg/l)	NH4-N(mg/l)	Example 3A	1％Ir-TiO₂	2.9	＜1
Example 4A	0.5％Pt-TiO₂	2.1	＜1	Example 3A	1％Ir-TiO₂	2.9	＜1
Example 4A	0.5％Pt-TiO₂	2.1	＜1	Example 5A	1％Au-TiO₂	3.0	＜1
Example 6A	0.5％Pd-TiO₂	1.9	＜1	Example 5A	1％Au-TiO₂	3.0	＜1
Example 6A	0.5％Pd-TiO₂	1.9	＜1	Example 7A	1％Rh-TiO₂	1.9	＜1
Example 8A	5％Fe-TiO₂	4.5	2.5	Example 7A	1％Rh-TiO₂	1.9	＜1
Example 8A	5％Fe-TiO₂	4.5	2.5	Example 9A	5％Ni-TiO₂	4.0	1.5
Example 10A	5％W-TiO₂	7.8	4.9	Example 9A	5％Ni-TiO₂	4.0	1.5
Example 10A	5％W-TiO₂	7.8	4.9	Example 11A	5％Cu-TiO₂	2.1	4.0
Example 12A	5％Co-ZrO₂	2.1	＜1	Example 11A	5％Cu-TiO₂	2.1	4.0

Example 13A

According to the flow shown in fig. 1, the coal gas washing tower waste water generated in the coal gasification process was introduced into a tower packed with an ion exchange resin according to the treatment method 1, and after ammonia components were adsorbed and removed, the waste water containing ammonia after being desorbed with an aqueous sulfuric acid solution was treated (pH =6.6, COD =1.9mg/l, NH4-N =2100mg/l, T-N =2100 mg/l).

That is, the above waste water was supplied to a reaction tower at a tower internal space velocity of 8hr^-1The linear velocity of the liquid in the column was 0.88cm/sec and the mass velocity was 31.8m (based on the empty column volume)³/m²Hr, supplying oxygen-enriched air (oxygen concentration of 90%) as oxygen-containing gas at the same time, and superficial velocity of 13.4hr^-1(conversion to standard state). The amount of the oxygen-containing gas supplied is equivalent toAt 1.5 times the theoretical oxygen amount. Further, the reaction column was packed with a spherical catalyst (diameter: about 1.5mm) comprising titanium oxide as a carrier and ruthenium in an amount of 2.3% by weight of the carrier while maintaining a temperature of 200 ℃ and a pressure of 20kg/cm²·G。

The treated liquid obtained from the reaction tower was introduced into the 1 st gas-liquid separator, subjected to gas-liquid separation, a part of the obtained liquid phase (the same amount as the supplied wastewater) was thermally recycled to the reaction tower, the gas phase for heating wastewater was cooled by a cooler, and then separated into a discharge gas and treated water by the 2 nd gas-liquid separator.

The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 4.

Example 14A

The temperature at the time of the reaction except for (i) was 170 ℃ and the pressure was 9.9kg/cm²G, (ii) the liquid-empty-column velocity (based on the empty-column volume) in the reaction column was 4hr^-1(i.e., catalyst loading)2 times that of example 13A), (iii) adding 48% NaOH to the wastewater beforehand to adjust its pH to 9.7, and (iv) superficial velocity of oxygen-containing gas was 6.7hr^-1Except that, the same method as in example 13A was used to treat the wastewater containing ammonia. The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 4.

Example 15A

Except that (i) the empty tower velocity (based on empty tower volume) of liquid in the reaction tower is 2hr^-1(i.e., the amount of catalyst charged was 2 times that of example 14) and (ii) the superficial velocity of the oxygen-containing gas (based on the superficial volume) was 3.4hr^-1Except that, the same method as in example 13A was used to treat the wastewater containing ammonia. The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 4.

In this example, decomposed NH was added to a position 2/3 below the catalyst-packed site of the reaction column₄-N = 1.1 times the theoretical amount of H required of 120mg/l₂O₂Almost the same results as in example 14A were obtained.

Example 16A

Ammonia-containing wastewater was treated in the same manner as in example 15A, except that 48% NaOH was previously added to the wastewater to adjust the pH to 11.5. The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 4.

TABLE 4

	COD (mg/l)	NH₄-N (mg/l)	(NO₂+NO₃)-N (mg/l)	T-N (mg/l)
	COD (mg/l)	NH₄-N (mg/l)	(NO₂+NO₃)-N (mg/l)	T-N (mg/l)	Example 13A	1.0	＜1	＜1	＜1
Example 14A	1.2	＜1	＜5	＜5	Example 13A	1.0	＜1	＜1	＜1
Example 14A	1.2	＜1	＜5	＜5	Example 15A	1.6	120	＜5	120
Example 16A	1.1	＜1	150	150	Example 15A	1.6	120	＜5	120

Example 17A

Except that the treatment temperature and the treatment pressure of the ammonia-containing wastewater are respectively set to exceed the critical temperature (374 ℃) and the critical pressure (220 kg/cm)²) 380 ℃ and 230kg/cm²The liquid-void velocity (based on void volume) in the reaction column was 240hr^-1(namely, the catalyst loading was 1/62.5 of example 13A), and the ammonia-containing wastewater was treated in the same manner as in example 13A. The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 5.

Comparative example 3A

Ammonia-containing wastewater was treated in the same manner as in example 17A, except that the treatment temperature of the ammonia-containing wastewater was 630 ℃ and that no catalyst was used. The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 5.

TABLE 5

	COD (mg/l)	NH₄-N (mg/l)	(NO₂+NO₃)-N (mg/l)	T-N (mg/l)
	COD (mg/l)	NH₄-N (mg/l)	(NO₂+NO₃)-N (mg/l)	T-N (mg/l)	Example 17A	1.0	＜1	＜1	＜1
Comparative example 3A	1.9	110	25	135	Example 17A	1.0	＜1	＜1	＜1

Example 18A

The organic matter-containing wastewater from a petrochemical plant (pH =2.6, COD =28100mg/l, TOD =101800mg/l, TOC =36500mg/l, NH) was treated by the treatment method 1 according to the scheme shown in FIG. 1₄-N is less than 1mg/l, T-N is less than 1 mg/l). The organic substances in the wastewater are acetic acid, acrylic acid, formaldehyde, formic acid and the like.

That is, the above-mentioned waste water was supplied to a reaction column at a tower internal space velocity of 2.9hr^-1The linear velocity of the liquid in the column was 0.71cm/sec and the liquid mass velocity was 25.5m (based on the empty column volume)³/m²Hr while supplying air as oxygen-containing gas at a superficial velocity of 553hr^-1(conversion to standard state). The air supply amount corresponds to 1.5 times the theoretical oxygen amount. Further, the reaction column was packed with a spherical catalyst (diameter: about 5mm) comprising titanium oxide as a carrier and ruthenium in an amount of 1.5% by weight of the carrier while maintaining a temperature of 270 ℃ and a pressure of 90kg/cm²·G。

The treated liquid obtained from the reaction tower was introduced into the 1 st gas-liquid separator to be subjected to gas-liquid separation, a part of the obtained liquid phase (the same amount as the supplied gas-liquid) was thermally recycled to the reaction tower, the gas phase for heating the wastewater was cooled by a cooler, and then the gas phase was separated into a discharge gas and treated water by the 2 nd gas-liquid separator.

In this example, a pressure of 24kg/cm can be recovered at the outlet of the reactor²Steam of 0.84 ton/hr.

Comparative example 4A

Wet oxidation treatment of wastewater was carried out in the same manner as in example 18A, except that thermal recycling was not carried out. However, due to the omission of heat recycle, the tower velocity in relation to the waste water was 1.5hr^-1The linear velocity of the liquid in the column was 0.35cm/sec and the mass velocity was 12.7m (based on the empty column volume)³/m²·hr。

The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 6.

TABLE 6

	COD (mg/l)	TOC (mg/l)	NH₄-N (mg/l)	T-N (mg/l)
	COD (mg/l)	TOC (mg/l)	NH₄-N (mg/l)	T-N (mg/l)	Example 18A	＜3	＜5	＜1	＜1
Comparative example 4A	28.1	12	＜1	＜1	Example 18A	＜3	＜5	＜1	＜1

The time required for example 18A to achieve the same water quality as comparative example 4A was 350 hours.

In addition, in both of example 18A and comparative example 4A, NO was detected in the exhaust gas (gas phase)_x、SO_xAnd NH₄-N。

In example 18A, the COD and TOD of the treated water were not more than 10mg/l even after 8000 hours of operation.

Examples 1B to 2B and comparative examples 1B to 2B

Coal gas liquids (containing nitrogen-containing compounds, organic substances and inorganic substances) produced in coke oven plants having the properties described in Table 7 were treated by the method of the present invention according to the flow chart shown in FIG. 2.

TABLE 7

Example 1B: supplying gas liquid to the reaction tower at a tower speed of 8hr^-1The linear velocity of the liquid in the column was 0.71cm/sec and the mass velocity was 25.5m (based on the empty column volume)³/m²Hr, while supplying high-purity oxygen-containing gas (gas obtained by compressing air and increasing oxygen concentration with PSA device) with oxygen concentration of 92.5%, and superficial velocity of 24.9hr^-1(according to standard form)State conversion). The gas supply amount corresponds to 1.5 times the theoretical oxygen amount. Further, the reaction column was packed with a spherical catalyst (diameter: about 5mm) comprising titanium oxide as a carrier and ruthenium in an amount of 2% by weight of the carrier while maintaining a temperature of 250 ℃ and a pressure of 46kg/cm²·G。

Then, the obtained treated water is subjected to biological denitrification treatment. The biological denitrification treatment was carried out by adding methanol in an amount of 2.5 times the mole number of the remaining ammonia to the treated water, and successively carrying out the nitrification reaction by nitrifying bacteria and the denitrification reaction by denitrifying bacteria at 30 ℃ and pH 7.2.

The compositions of the wet oxidation treated water and the denitrified water (parenthesized values) obtained 100 hours after the start of the reaction are shown in Table 8.

In example 1B, after 8000 hours of operation, COD and NH in the denitrified water₄-N is less than 10 mg/l.

Example 2B: the wet oxidation treatment of the coal gas liquid was performed in the same manner as in example 1B, except that the amount of the heat recycling liquid was changed to 1/2. But due to the halving of the amount of hot recycle liquid, withThe gas-liquid related tower internal air speed is 6hr^-1The linear velocity of the liquid in the column was 0.53cm/sec and the mass velocity was 19.1m (based on the empty column volume)³/m²·hr。

The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 8.

Comparative example 1B: the wet oxidation treatment of coal gas liquid was carried out in the same manner as in example 1B, except that the thermal recycle was not carried out. However, due to the omission of heat recycle, the gas-liquid related tower internal air velocity was 4hr^-1(based on the empty column volume) and the linear velocity of the liquid in the column is0.35cm/sec, and a mass velocity of 12.7m³/m²·hr。

Comparative example 2B: the wet oxidation treatment of the coal gas liquid was carried out in the same manner as in example 1B, except that the diameter of the reaction column was changed. However, due to the change of the diameter of the reaction column, the gas-liquid related internal column velocity was 4hr^-1The linear velocity of the liquid in the column was 0.088cm/sec and the mass velocity was 3.2m (based on the empty column volume)³/m²·hr。

TABLE 8

	COD (mg/l)	NH₄-N (mg/l)	(NO₂+NO₃)-N (mg/l)	T-N (mg/l)
	COD (mg/l)	NH₄-N (mg/l)	(NO₂+NO₃)-N (mg/l)	T-N (mg/l)	Example 1B	4.0 (3.0)	＜1 (＜1)	45 (＜10)	45 (＜10)
Example 2B	8.2 (7.0)	＜1.2 (＜1)	50 (＜10)	52 (＜10)	Example 1B	4.0 (3.0)	＜1 (＜1)	45 (＜10)	45 (＜10)
Example 2B	8.2 (7.0)	＜1.2 (＜1)	50 (＜10)	52 (＜10)	Comparative example 1B	14.0 (13.0)	＜2.1 (＜1)	63 (＜10)	65 (＜10)
Comparative example 2B	35.1 (30.5)	9.1 (＜1)	120 (＜10)	130 (＜10)	Comparative example 1B	14.0 (13.0)	＜2.1 (＜1)	63 (＜10)	65 (＜10)

From the results shown in Table 8, it was found that the linear velocity of the liquid in the column was increased by the heat recirculation, the liquid film resistance on the catalyst surface was reduced, and the adhesion of the metal components derived from the waste water to the catalyst surface was suppressed, whereby the high catalyst activity was maintained for a long period of time, and the quality of the treated water after wet oxidation was improved. Furthermore, the same treated water is subjected to biological denitrification treatment, thereby further improving the water quality.

In addition, in any of examples 1B to 2B and comparative examples 1B to 2B, the discharge was performedNo NO was detected in the gas (gaseous phase)_x、SO_xAnd NH₄-N。

The water quality was treated in the same manner as in example 2B, 470 hours for example 1B, 365 hours for example 2B, and 230 hours for comparative example 1B.

Examples 3B to 12B

The gas-liquid treatment was carried out in the same manner as in example 1B, except that the combination of the catalyst component and the carrier was changed.

The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 9.

TABLE 9

	Catalyst and process for preparing same	COD(mg/l)	NH₄-N(mg/l)
	Catalyst and process for preparing same	COD(mg/l)	NH₄-N(mg/l)	Example 3B	1％Ir-TiO₂	4.1	＜10
Example 4B	0.5％Pt-TiO₂	3.9	＜10	Example 3B	1％Ir-TiO₂	4.1	＜10
Example 4B	0.5％Pt-TiO₂	3.9	＜10	Example 5B	1％Au-TiO₂	3.9	＜10
Example 6B	0.5％Pd-TiO₂	1.9	＜10	Example 5B	1％Au-TiO₂	3.9	＜10
Example 6B	0.5％Pd-TiO₂	1.9	＜10	Example 7B	1％Rh-TiO₂	2.0	＜10
Example 8B	5％Fe-TiO₂	9.4	＜10	Example 7B	1％Rh-TiO₂	2.0	＜10
Example 8B	5％Fe-TiO₂	9.4	＜10	Example 9B	5％Ni-TiO₂	8.9	＜10
Example 10B	5％W-TiO₂	9.4	＜10	Example 9B	5％Ni-TiO₂	8.9	＜10
Example 10B	5％W-TiO₂	9.4	＜10	Example 11B	5％Cu-TiO₂	4.3	＜10
Example 12B	5％Co-ZrO₂	2.9	＜10	Example 11B	5％Cu-TiO₂	4.3	＜10

Example 13B

According to the flow shown in FIG. 2, the coal gas washing tower waste water generated in the coal gasification process was introduced into a tower filled with an ion exchange resin according to the 2 nd treatment method, and after the ammonia component was removed by adsorption, the waste water containing ammonia (pH =6.6, COD =1.9mg/l, NH) after being desorbed with an aqueous sulfuric acid solution was treated (pH =6.6, COD =1.9 mg/l)₄-N=2100mg/l,(NO₂+NO₃)-N=ND,T-N=2100mg/l)。

That is, the above waste water was supplied to a reaction tower at a tower internal space velocity of 10hr^-1The linear velocity of the liquid in the column was 0.88cm/sec and the mass velocity was 31.8m (based on the empty column volume)³/m²Hr, supplying oxygen-enriched air (oxygen concentration of 95%) as oxygen-containing gas at the same time, and superficial velocity of 15.9hr^-1(conversion to standard state). The amount of oxygen-containing gas supplied was 1.5 times the theoretical amount of oxygen. Further, the reaction column was packed with a spherical catalyst (diameter: about 1.5mm) comprising titanium oxide as a carrier and ruthenium in an amount of 2.3% by weight of the carrier while maintaining a temperature of 200 ℃ and a pressure of 20kg/cm²·G。

The treated liquid obtained from the reaction tower was introduced into the 1 st gas-liquid separator to be subjected to gas-liquid separation, and a part of the obtained liquid phase (the same amount as the supplied gas-liquid) was thermally recycled to the reaction tower, while the gas phase for heating the wastewater was cooled by a cooler, and then separated into a discharge gas and treated water by the 2 nd gas-liquid separator.

Then, the obtained wet oxidation treated water was subjected to biological denitrification treatment in the same manner as in example 1B.

The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 10.

Example 14B

In addition to (i) reactionAt a temperature of 170 ℃ and a pressure of 9.9kg/cm²G, (ii) the liquid-empty-column velocity (based on the empty-column volume) in the reaction column was 5hr^-1(i.e., the amount of catalyst charged was 2 times that of example 13B), (iii) 48% NaOH was previously added to the wastewater to adjust the pH to 9.7, and (iv) the superficial velocity of the oxygen-containing gas was 7.95hr^-1Except that the ammonia-containing wastewater was treated by wet oxidation and then subjected to biological denitrification in the same manner as in example 13B.

Example 15B

The same procedure as in example 14B was repeated except that 48% NaOH was previously added to the wastewater to adjust the pH to 11.5, to thereby subject the ammonia-containing wastewater to wet oxidation treatment and then to biological denitrification treatment. The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 10.

Watch 10

	COD (mg/l)	NH₄-N (mg/l)	(NO₂+NO₃)-N (mg/l)	T-N (mg/l)
	COD (mg/l)	NH₄-N (mg/l)	(NO₂+NO₃)-N (mg/l)	T-N (mg/l)	Example 13B	1.1 (1.0)	＜1 (＜1)	＜1 (＜1)	＜1 (＜10)
Example 14B	1.9 (1.6)	＜12.5 (＜10)	＜1 (＜1)	120 (＜10)	Example 13B	1.1 (1.0)	＜1 (＜1)	＜1 (＜1)	＜1 (＜10)
Example 14B	1.9 (1.6)	＜12.5 (＜10)	＜1 (＜1)	120 (＜10)	Example 15B	1.9 (1.3)	4.5 (＜1)	165 (＜10)	150 (＜10)

Comparative example 3B

Except that the treatment temperature and the treatment pressure of the ammonia-containing wastewater are respectively set to exceed the critical temperature (374 ℃) and the critical pressure (220 kg/cm)²) 380 ℃ and 230kg/cm²The liquid-void velocity (based on void volume) in the reaction column was 240hr^-1(namely, the catalyst loading was 1/62.5 of example 14B), and the ammonia-containing wastewater was subjected to only wet oxidation treatment in the same manner as in example 13B. The quality of treated water and the properties of the exhaust gas were almost the same as those in example 13B.

Example 16B

The organic matter-containing wastewater from the petrochemical plant (pH =2.6, COD =28100mg/l, TOD =101800mg/l, TOC =36500mg/l, NH) was treated by the treatment method 2 according to the scheme shown in FIG. 2₄-N < 1mg/l or less, T-N < 1mg/l or less). The organic substances in the wastewater are acetic acid, acrylic acid, formaldehyde, formic acid and the like.

That is, the above-mentioned waste water was supplied to a reaction column at a tower internal space velocity of 2.9hr^-1The linear velocity of the liquid in the column was 0.71cm/sec and the liquid mass velocity was 0.71cm/sec (based on the empty column volume)25.5m³/m²Hr, while supplying oxygen-enriched air (oxygen concentration: 92.5%) as oxygen-containing gas at superficial velocity of 116hr^-1(conversion to standard state). The oxygen-rich gas was supplied in an amount corresponding to 1.2 times the theoretical oxygen amount. In addition, the reaction column was packed with a spherical catalyst (about 5mm in diameter) comprising titanium oxide as a carrier and platinum in an amount of 1.5% by weight as a carrier while maintaining the sameHolding temperature of 270 ℃ and pressure of 67kg/cm²。

Then, the obtained wet oxidation treatment water was treated by an activated sludge method (temperature about 30 ℃ C., pH 7.4).

The composition of the treated water obtained 100 hours after the start of the reaction is shown in Table 11.

In this example, a recovery pressure of 24kg/cm was obtained at the outlet of the reactor at a rate of 0.84ton/hr²The steam of (2).

Comparative example 4B

Wet oxidation treatment of wastewater was carried out in the same manner as in example 16B, except that thermal recycling was not carried out. However, due to the omission of heat recycle, the tower velocity in relation to the waste water was 1.5hr^-1The linear velocity of the liquid in the column was 0.35cm/sec and the mass velocity was 12.7m (based on the empty column volume)³/m²·hr。

TABLE 11

	COD (mg/l)	TOC (mg/l)	NH₄-N (mg/l)	T-N (mg/l)
	COD (mg/l)	TOC (mg/l)	NH₄-N (mg/l)	T-N (mg/l)	Example 16B	＜3 (1.8)	＜5 (＜5)	＜1 (＜1)	＜1 (＜1)
Comparative example 4B	275 (＜13)	＜15 (＜10)	＜1 (＜1)	1 (＜1)	Example 16B	＜3 (1.8)	＜5 (＜5)	＜1 (＜1)	＜1 (＜1)

From the results shown in Table 11, it was found that the linear velocity of the liquid in the column was increased by the heat recirculation, the liquid film resistance on the catalyst surface was reduced, and the adhesion of the metal components derived from the waste water to the catalyst surface was suppressed, whereby the high catalyst activity was maintained for a long period of time, and the water quality of the wet oxidation post-treatment water was improved. Furthermore, the same treated water is biologically treated, and the water quality can be further improved.

In addition, in both of example 16B and comparative example 4B, NO was detected in the exhaust gas (gas phase)_x、SO_xAnd NH₄-N。

In example 16B, after 8000 hours of operation, the COD and TOD in the treated water were less than 10 mg/l.

Examples 1C to 8C

(1) Wet oxidation treatment of wastewater

First, wet oxidation treatment was performed on coal gas liquid (COD6000ppm, total ammonia amount 3000ppm, total nitrogen amount 4000ppm) generated in a coke oven.

That is, an aqueous sodium hydroxide solution was added to the gas liquid to adjust the pH to about 10 at a space velocity of 1.0hr^-1The lower part of the cylindrical reactor was supplied (based on the empty column). The mass velocity of the liquid was 8.0m³/m²·hr。

On the other hand, the space velocity in the lower part of the reaction column was 65hr^-1(based on the empty tower as a reference,standard state) supply air.

The reaction column was packed with a spherical waste water oxidation catalyst (diameter about 5mm) having a composition described in the following table 12. In Table 12, 1% Ir-TiO₂Means a catalyst in which iridium is supported on a titania carrier in an amount of 1% by weight.

The coal gas liquid used initially contained 15ppm in total of iron, calcium, and magnesium, and compounds containing these elements were added in advance to make the total amount 2500ppm in order to make the effect of the present invention more clear.

In the wet oxidation treatment of gas liquid, the inside of the reaction towerMaintaining the temperature at 250 deg.C and the pressure at 70kg/cm²G, adding an aqueous sodium hydroxide solution to the reaction mixture to adjust the pH of the treatment solution after the wet oxidation treatment to about 7.5, and continuing the reaction for 5000 hours. As a result, the activity index of the catalyst was lowered as shown in Table 12. Precipitates on the catalyst surface were analyzed to confirm the presence of sulfur, ash (silica, iron oxide, magnesium oxide, and others), and carbon, hydrocarbons, and the like were not detected.

(2) Regeneration washing treatment of catalyst

Then, the wastewater oxidation catalyst having a decreased activity is subjected to regeneration treatment by the following various methods.

Method-1: a10% aqueous nitric acid solution (80 ℃) was introduced into a reaction column packed with a wastewater oxidation catalyst under atmospheric pressure, and after washing for 1 hour, the reaction column was washed with water for 1 hour. The introduction conditions of the aqueous nitric acid solution and water are the same as those of the wastewater during wastewater treatment.

Method-2: air and a 10% aqueous nitric acid solution (80 ℃) were introduced into a reaction column filled with a wastewater oxidation catalyst under atmospheric pressure, and after washing for 1 hour, washing was carried out with water for 1 hour. The conditions for introducing the aqueous nitric acid solution and the air are respectively the same as those for introducing the wastewater and the air in the wastewater treatment. I.e. 1m relative to the aqueous nitric acid solution³Hr, air inlet volume of 65Nm³/hr。

In addition, the conditions for introducing water in washing with water are the same as those for introducing wastewater in wastewater treatment.

Method-3: a10% aqueous solution of sodium hydroxide (80 ℃) was introduced into a reaction column packed with a wastewater oxidation catalyst under atmospheric pressure, and after washing for 1 hour, the column was washed with water for 1 hour. The introduction conditions of the aqueous sodium hydroxide solution and water were the same as those of the wastewater during the wastewater treatment.

Method-4: air and a 10% aqueous solution of sodium hydroxide (80 ℃) were introduced into a reaction column packed with the wastewater oxidation catalyst under atmospheric pressure, and after washing for 1 hour, washing was carried out with water for 1 hour. The conditions for introducing the aqueous sodium hydroxide solution and air were the same as those for introducing the wastewater and air during the wastewater treatment. I.e., 1m relative to the aqueous sodium hydroxide solution³Hr, air inlet volume of 65Nm³/hr。

TABLE 12

Fruit of Chinese wolfberry Applying (a) to Example (b)	Catalyst composition	Before regeneration Index of activity	Method 1 Index of activity	Method 2 Index of activity	Method 3 Index of activity	Method 4 Index of activity
Fruit of Chinese wolfberry Applying (a) to Example (b)	Catalyst composition	Before regeneration Index of activity	Method 1 Index of activity	Method 2 Index of activity	Method 3 Index of activity	Method 4 Index of activity	1C	1％Ir-TiO₂	65	73	93	83	98
2C	1％Pt-TiO₂	67	74	93	84	99	1C	1％Ir-TiO₂	65	73	93	83	98
2C	1％Pt-TiO₂	67	74	93	84	99	3C	1％Au-AlO₂	54	69	88	74	94
4C	5％Ni-AlO₂	54	68	87	73	95	3C	1％Au-AlO₂	54	69	88	74	94
4C	5％Ni-AlO₂	54	68	87	73	95	5C	5％W-AlO₂	66	69	88	72	96
6C	2% Pd-activated carbon	67	71	94	87	99	5C	5％W-AlO₂	66	69	88	72	96
6C	2% Pd-activated carbon	67	71	94	87	99	7C	1% Pt-activated carbon	63	69	92	79	99
8C	2％Ru-TiO₂	69	84	97	93	100	7C	1% Pt-activated carbon	63	69	92	79	99

In table 12, "activity index" means the removal rate of ammonia when wet oxidation treatment of wastewater is performed using a regenerated catalyst under the same conditions when the removal rate of ammonia is 100% in the case of wet oxidation treatment of wastewater using a fresh catalyst. It was confirmed that the regenerated catalyst exhibited an increase in activity index for removal of COD as well as for removal of ammonia.

The results shown in Table 12 show the excellent effects of the present invention in the washing/regeneration treatment of the wastewater oxidation catalyst with an acidic aqueous solution or a basic aqueous solution under aeration.

Comparative example 1C

The same catalyst as in example 1C was used to perform wet oxidation treatment on the gas liquid under the same conditions as in example 1.

Then, catalyst regeneration was performed by the method-1 and the method-2 in example 1C using a 2N sulfuric acid aqueous solution as a washing liquid of the catalyst. The results are shown in Table 13.

Watch 13

Comparative example	Catalyst composition	Before regeneration Index of activity	Method 1 Index of activity	Method 2 Index of activity
Comparative example	Catalyst composition	Before regeneration Index of activity	Method 1 Index of activity	Method 2 Index of activity	1C	1％Ir-TiO₂	65	66	67

From the results shown in Table 13, it was found that the effect of regenerating the catalyst was not sufficiently obtained when an aqueous sulfuric acid solution was used as the washing liquid.

Comparative example 2C

The same catalyst as in example 2C was used to perform wet oxidation treatment on the gas liquid under the same conditions as in example 2C.

The catalyst was then washed and regenerated using 10% aqueous nitric acid using method-1 and method-2 of example 2C. However, in method-2, 1m was used relative to the washing solution³The air inlet rate is 5 Nm/hr³And/hr. The results are shown in Table 14.

TABLE 14

Comparative example	Catalyst composition	Before regeneration Index of activity	Method 1 Index of activity	Method 2 Index of activity
Comparative example	Catalyst composition	Before regeneration Index of activity	Method 1 Index of activity	Method 2 Index of activity	2C	1％Pt-TiO₂	67	74	77

From the results shown in Table 14, it was found that when the gas-liquid mixed phase was washed with the aqueous nitric acid solution and air, if the amount of air introduced was too small, the effect of regenerating the catalyst was not sufficiently obtained.

Example 9C

(1) Wet oxidation treatment of wastewater

First, a waste liquid (ph10.6) containing cyanide complex ions having a composition shown in table 15 was subjected to wet oxidation treatment using a 1 st reaction tower in which no catalyst was packed and a 2 nd reaction tower in which a catalyst was packed.

Watch 15

Composition (I)	Concentration (mg/l)
Composition (I)	Concentration (mg/l)	total-CN	10000
COD_Mn	15000	total-CN	10000
COD_Mn	15000	TOC	5000
TOD	30240	TOC	5000
TOD	30240	Total of-N	8000
NH₃-N	2615	Total of-N	8000
NH₃-N	2615	Na	25000
K	15000	Na	25000
K	15000	Fe	2000
Zn	145	Fe	2000
Zn	145	P	240
Al	1.3	P	240
Al	1.3	Cu	5.4

That is, at a space velocity of 1.0hr^-1(based on empty tower) and a mass velocity of 14.15m³/m²Hr supplying the waste liquid to the lower part of the 1 st-order reaction column, and allowing the space velocity in the lower part of the 1 st-order reaction column to reach 3.4hr^-1(toEmpty tower as a reference, standard condition) supply air. The amount of air supplied corresponds to the theoretical amount of oxygen (82.5 Nm)³0.0103 times of kl).

When the waste liquid is decomposed, the waste liquid and air are introduced into the heat exchanger at the inlet side thereof, the temperature of the gas-liquid mixture on the outlet side of the heat exchanger (= the temperature of the gas-liquid mixture on the inlet side of the first reaction column) is set to 150 ℃, and a part of the treatment liquid discharged from the 2 nd reaction column and the treatment liquid discharged from the first reaction column are mixed by a pump in a circulating manner, thereby adjusting the temperature. Further, in the first reaction column, steam was supplied to maintain the temperature of 220 ℃ and the pressure of 30kg/cm in the column². In addition, a tray-type reaction column was installed at a distance of 70cm from the first-time reaction column.

In the liquid (pH10.6) after the treatment in the 1 st reaction column, when the metal component in the initial waste liquid becomes sludge, it is discharged from the lower part of the reaction column and the lower part of the solid-liquid separator (membrane press). The composition of the 1 st treatment liquid obtained by the solid-liquid separator is shown in Table 16.

TABLE 16

Composition (I)	Concentration (mg/l)
Composition (I)	Concentration (mg/l)	total-CN	0.1
COD_Mn	1445	total-CN	0.1
COD_Mn	1445	TOC	5000
TOD	25300	TOC	5000
TOD	25300	Total of-N	6690
NH₃-N	6900	Total of-N	6690
NH₃-N	6900	Na	20900
K	12540	Na	20900
K	12540	Fe	47
Zn	20	Fe	47
Zn	20	P	145
Al	＜0.5	P	145
Al	＜0.5	Cu	3.5

Then, 0.62ml of sulfuric acid corresponding to the alkali metal content (Na0.909mol/l + K0.332mol/1=1.231mol/l)1/2 in the first treatment liquid was added from a sulfuric acid storage tank to the first treatment liquid, and then the space velocity was 0.75/hr (based on the empty column) and the mass velocity was 14.15m³/m²Hr, the reaction mixture was fed to a second reaction column packed with a catalyst, and air was fed at a space velocity of 90.4/hr (in a standard state based on the empty column). The air supply amount corresponds to 1.1 times the theoretical oxygen amount. In addition, a spherical catalyst (with the diameter of 4-6 mm) is filled in the second reaction tower, and the spherical catalyst takes titanium oxide as a carrier and carries ruthenium with the weight of 2% of the carrier. The composition of the treated liquid (pH3.1) obtained from the second reaction column is shown in Table 17.

TABLE 17

Composition (I)	Concentration (mg/l)
Composition (I)	Concentration (mg/l)	total-CN	＜0.01
COD_Mn	＜1	total-CN	＜0.01
COD_Mn	＜1	TOC	＜5
TOD	＜5	TOC	＜5
TOD	＜5	Total of-N	40
NH₃-N	＜1	Total of-N	40
NH₃-N	＜1	Na	20900
K	12540	Na	20900
K	12540	Fe	1.0
Zn	0.3	Fe	1.0
Zn	0.3	P	0.3
Al	＜0.5	P	0.3
Al	＜0.5	Cu	0.3

(2) Regeneration washing treatment of catalyst

Then, the wastewater oxidation catalyst, the activity of which was decreased after the second treatment for 16000 hours, was subjected to regeneration treatment by the following various methods.

Method-1: a10% ascorbic acid aqueous solution (60 ℃) was introduced into a reaction column packed with a wastewater oxidation catalyst under atmospheric pressure, and after washing for 5 hours, the reaction column was washed with water for 1 hour. The conditions for introducing the ascorbic acid aqueous solution and water are the same as those for introducing the wastewater in the wastewater treatment.

Method-2: air and a 10% aqueous ascorbic acid solution (60 ℃) were introduced into a reaction column packed with the wastewater oxidation catalyst under atmospheric pressure, and after washing for 5 hours, washing was carried out with water for 1 hour. The conditions for introducing the ascorbic acid aqueous solution and air are respectively the same as those for introducing the wastewater and air in the wastewater treatment. I.e., 1m relative to the ascorbic acid aqueous solution³Hr, air inlet amount of 120Nm³/hr。

Method-3: a10% aqueous nitric acid solution (60 ℃) was introduced into a reaction column packed with a wastewater oxidation catalyst under atmospheric pressure, and after washing for 5 hours, the reaction column was washed with water for 1 hour. The introduction conditions of the aqueous nitric acid solution and water are the same as those of the wastewater during wastewater treatment.

Method-4: air and a 10% aqueous nitric acid solution (60 ℃) were introduced into a reaction column filled with a wastewater oxidation catalyst under atmospheric pressure, and after washing for 5 hours, washing was carried out with water for 1 hour. The introduction conditions of the aqueous nitric acid solution and air are respectively the same as those of the wastewater and air during wastewater treatment. I.e. 1m relative to the aqueous nitric acid solution³Hr, air inlet amount of 120Nm³/hr。

Method-5: a10% ascorbic acid aqueous solution (60 ℃) was introduced into a reaction column packed with a catalyst for oxidation with wastewater under atmospheric pressure, and washed for 5 hours. Then, air and a 10% nitric acid aqueous solution were introduced under atmospheric pressure, and after washing for 5 hours, the mixture was washed with water for 1 hour. The conditions for introducing the aqueous ascorbic acid solution and the aqueous nitric acid solution were the same as those for introducing the wastewater in the wastewater treatment, and the amount of introduced air was 1/2 in the wastewater treatment. I.e. 1m relative to the aqueous nitric acid solution³Hr, emptyThe gas introduction amount is 60Nm³/hr。

The regeneration state of the catalyst after various methods is shown in Table 18.

Watch 18

Activity before regenerationIndex of refraction	69
Activity before regenerationIndex of refraction	69	Method-1 Activity index after treatment	84
Method-2 Activity index after treatment	97	Method-1 Activity index after treatment	84
Method-2 Activity index after treatment	97	Method-3 Activity index after treatment	89
Method-4 Activity index after treatment	92	Method-3 Activity index after treatment	89
Method-4 Activity index after treatment	92	Method-5 Activity index after treatment	100

From the results in Table 18, it can be seen that the excellent effects of the present invention are exhibited when the waste water oxidation catalyst is subjected to washing regeneration treatment with an acidic aqueous solution under aeration conditions.

In addition, after the heat exchanger and the piping in the wet oxidation facility for wastewater, which is deteriorated in the treatment performance due to the adhesion of the metal components, are treated by the above-mentioned method-5, the total thermal conductivity of the heat exchanger, which is lowered by about 80% as compared with the initial state, is recoveredTo the initial state, and increased by about 1.5kg/cm compared with the initial state²The pressure loss in the pipe is restored to the initial state.

Claims

1. The wastewater treatment method is characterized by comprising the following two steps:

(1) wet oxidation treatment of a wastewater containing at least one nitrogen-containing compound, organic substance and inorganic substance in the presence of a supported catalyst and in the presence of oxygen which is higher than the theoretical oxygen amount necessary for decomposing the nitrogen-containing compound and/or organic substance and/or inorganic substance in the wastewater into nitrogen and/or carbon dioxide and water while maintaining a temperature of 100 ℃ or higher and a pressure at which at least a part of the wastewater is maintained in a liquid phase,

2. A method for treating waste water according to claim 1, wherein the catalyst active ingredient in the step (1) is at least one selected from the group consisting of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and water-insoluble or hardly soluble compounds of these metals.

3. The method of treating waste water according to claim 1, wherein the linear velocity of the liquid in the column (the amount of liquid introduced into the column/the cross-sectional area of the column) in the step (1) is 0.1 to 1.0 cm/sec.

4. The method for treating waste water according to claim 1, wherein the oxygen source in the step (1) is air, oxygen-enriched air, high-purity oxygen, ozone and H₂O₂At least one of (1).

5. The method of treating waste water according to claim 1, wherein the circulating amount of the high-temperature liquid phase in the step (2) is 0.1 to 15 times that of the waste water.

6. The wastewater treatment method is characterized by comprising the following five steps:

7. A method for treating wastewater according to claim 6, wherein the oxygen concentration in the high-purity oxygen-containing gas in the step (1) is 80% or more.

8. A method for treating waste water according to claim 6, wherein the catalyst active ingredient in the step (1) is at least one selected from the group consisting of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and water-insoluble or hardly soluble compounds of these metals.

9. The method of treating waste water according to claim 6, wherein the linear velocity of the liquid in the column (the amount of liquid introduced into the column/the cross-sectional area of the column) in the step (1) is 0.1 to 1.0 cm/sec.

10. The method for treating waste water according to claim 6, wherein the oxygen source in the step (1) is air, oxygen-enriched air, high-purity oxygen, ozone and H₂O₂At least one of (1).

11. The method of treating waste water according to claim 6, wherein the circulating amount of the high-temperature liquid phase in the step (2) is 0.1 to 15 times that of the waste water.

12. The wastewater treatment method according to claim 6, wherein the biological treatment method in the step (4) is an activated sludge treatment method and/or a biological denitrification method.

13. A method for washing and regenerating a catalyst, characterized in that a method for washing and regenerating a supported catalyst for wet oxidation of wastewater, which comprises at least one of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, and tungsten, and water-insoluble or hardly-soluble compounds of these metals as a catalyst active ingredient, comprises the steps of: using an acidic aqueous solution as the washing liquid, andin washing solution 1m³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more.

14. A method for washing and regenerating a catalyst, characterized in that a method for washing and regenerating a supported catalyst for wet oxidation of wastewater, which comprises at least one of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, and tungsten, and water-insoluble or hardly-soluble compounds of these metals as a catalyst active ingredient, comprises the steps of: an alkaline aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more.

15. A method for washing and regenerating a catalyst, characterized in that a method for washing and regenerating a supported catalyst for wet oxidation of wastewater, which comprises at least one of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, and tungsten, and water-insoluble or hardly-soluble compounds of these metals as a catalyst active ingredient, comprises the steps of: (1) using acidic aqueous solutions asWashing liquid, and for washing liquid 1m³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more; (2) an alkaline aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more.

16. A method for washing and regenerating a catalyst, characterized in that a method for washing and regenerating a supported catalyst for wet oxidation of wastewater, which comprises at least one of iron, cobalt, nickel, magnesium, ruthenium, rhodium, palladium, iridium, platinum, copper, gold, and tungsten, and water-insoluble or hardly-soluble compounds of these metals as a catalyst active ingredient, comprises the steps of: (1) an alkaline aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more; (2) an acidic aqueous solution was used as a washing solution, and 1m for the washing solution³/hr at 10Nm³Introducing air at a ratio of/hr or more, and contacting the catalyst with the washing solution at a temperature of room temperature or more.

17. A method for washing and regenerating a catalyst, which comprises subjecting a waste liquid from washing the catalyst produced by at least one of the methods of claims 13 to 16 to wet oxidation treatment together with wastewater.

18. The method for washing and regenerating a catalyst according to claim 17, wherein the catalyst washing liquid is subjected to a coagulation-precipitation treatment to remove metal components in the liquid, and then subjected to a wet oxidation treatment together with the wastewater.