JP2000117272A - Waste water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new technique in which even in the case the relatively large quantity of oxygen is used to make treatment under high temperature/high pressure conditions, without outer heating needed and with a liquid phase state maintained well, reaction can be continued when performing wet oxidation of waste water containing at least one (polluted component) of nitrogen compounds, organic materials and inorganic materials. SOLUTION: This treatment is provided with a process in which waste water containing at least one of nitrogen compounds, organic material, and inorganic material is subjected to wet oxidizing treatment while it is kept at temperature of 100 deg.C or more and at pressure at which at least part of the waste water is maintained in the liquid phase, in the presence of a deposited catalyst, and in the presence of the theoretical quantity or more of oxygen required for decomposing the nitrogen compounds and/or organic material and/or inorganic material in the waste water into nitrogen and/or carbon dioxide and water and a process in which at least part of the high temperature liquid phase obtained by gas-liquid separation after the wet oxidizing treatment is circulated and mixed with the waste water before the wet oxidizing treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wastewater containing at least one of a nitrogen compound, an organic substance and an inorganic substance.
(In the following, these are sometimes simply called wastewater.)
Regarding the processing method.

[0002]

BACKGROUND ART Nitrogen compounds, organic substances and inorganic substances
(Hereinafter, these may be simply referred to as "polluting components")
A method for wet-oxidizing wastewater containing at least one of the following is known.

[0003] For example, Japanese Patent Publication No. 59-29317 by the present applicant discloses a method of decomposing ammonia, organic substances and inorganic substances in wastewater by subjecting the wastewater to wet oxidation in the presence of a supported catalyst. Is disclosed.

[0004] As apparent from the results shown in the examples, this method can generally exhibit an extremely excellent wastewater treatment effect. However, in this method, when the concentration of pollutants in the wastewater is high (for example, when the TOD value is
(65,000 mg / l or more), by using a relatively large amount of air (oxygen) and treating under high temperature and high pressure conditions, a large amount of water evaporates in the reaction tower, Move to For this reason, external heating is required to cope with the temperature decrease due to the latent heat of evaporation, and it is difficult to maintain the liquid phase in a good state and to continue the reaction, which may reduce the pollutant removal rate. Further, when the concentration of the pollutant component in the wastewater is high or when the metal component in the wastewater adheres to the surface of the catalyst and its activity is reduced, the treatment may not be performed well.

[0005]

Accordingly, the present invention provides at least one of a nitrogen compound, an organic substance and an inorganic substance.
When performing wet oxidation of wastewater containing seeds, using a relatively large amount of air (oxygen) and performing treatment under high temperature and high pressure conditions, external heating is not required and the liquid phase state is good. The main object of the present invention is to provide a new technology that can maintain the reaction and continue the reaction.

Another object of the present invention is to provide a new technique capable of effectively treating wastewater having a high concentration of pollutant components by suppressing the adhesion of metal components to the catalyst surface.

[0007]

The present inventor has conducted intensive studies in view of the state of the art as described above, and as a result, has found that a part of the high-temperature liquid phase obtained by the gas-liquid separation device after the wet oxidation treatment is obtained. It has been found that when circulating in a wet oxidation reaction tower, the above problems can be achieved.

That is, the present invention provides the following wastewater treatment method; (1) nitrogen compound, while maintaining wastewater containing at least one of organic substances and inorganic substances at a temperature of 100 ° C. or more and a pressure at which at least a part of the wastewater maintains a liquid phase, in the presence of a supported catalyst; Wet oxidation treatment in the presence of oxygen in excess of the theoretical amount of oxygen required to decompose nitrogen compounds and / or organic and / or inorganic substances into wastewater into nitrogen and / or carbon dioxide and water; and
(2) A method for treating wastewater, comprising a step of circulating and mixing at least a part of a high-temperature liquid phase obtained by gas-liquid separation after wet oxidation with wastewater before wet oxidation.

II. The catalytically active component in the step (1) is
Item 1. The above item 1 which is at least one selected from the group consisting of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and compounds of these metals insoluble or hardly soluble in water. Wastewater treatment method.

III. 2. The method for treating wastewater according to claim 1, wherein the liquid linear velocity in the column (column liquid entering amount / column sectional area) in the step (1) is 0.1 to 1.0 cm / sec.

IV. The oxygen source in step (1) is at least one of air, oxygen-enriched air, pure oxygen, ozone and H ₂ O ₂ .
Item 2. The method for treating wastewater according to Item 1, which is a seed.

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

[0013]

DETAILED DESCRIPTION OF THE INVENTION The wastewater to be treated by the present invention is:
There is no particular limitation as long as it contains at least one of a nitrogen compound, an organic substance, and an inorganic substance.

The nitrogen compounds contained in the wastewater include:
NH ₄ —N (means ammonium nitrogen; the same applies hereinafter), NO ₂
-N, NO ₃ -N, organic nitrogen (including amines), inorganic nitrogen
(Including CNs and SCNs).

The organic substances contained in the wastewater include:
Common organic substances (phenols, alcohols,
Carboxylic acids), organic chlorine compounds (trichloroethylene, tetrachloroethylene, dioxins, etc.),
Suspended substances (derived from organic solid waste, sludge generated from various biological treatment processes, kitchen waste, municipal waste, biomass, and the like).

The inorganic substances contained in the wastewater include:
Common inorganic materials ^{_{(e.g., S 2 O 3 2-, SO}} 3 2-, SCN -, CN
^-, etc.) and the like.

As the various wastewaters to be treated by the present invention, wastewater containing one of the above-mentioned nitrogen compounds, organic substances and inorganic substances alone, and those containing two or more of these together Wastewater.

Examples of such wastewater include gas liquids generated in a coal processing coke oven plant, a coal gasification plant, a coal liquefaction plant, etc .; wastewater generated by gas generation in these plants; Wastewater, photographic wastewater, printing wastewater from desulfurization tower and wet de-cyanation tower,
Agrochemical-related wastewater, dyeing wastewater, semiconductor manufacturing plant wastewater, petrochemical plant wastewater, petroleum refinery plant wastewater, pharmaceutical plant wastewater, paper mill wastewater, chemical plant wastewater, kitchen waste, paper, plastics, etc. Wastewater, pharmaceutical factory wastewater,
Wastewater generated by coal liquefaction or gasification, wastewater generated by thermal decomposition of municipal waste, sludge generated by biological treatment (anaerobic treatment, aerobic treatment) of industrial wastewater, sewage sludge, oil of sewage sludge Wastewater generated by chemical conversion, wastewater containing organochlorine compounds, various wastewater containing cyanide discharged from the plating industry, cyanide liquid used for surface treatment such as soft nitriding treatment, liquid carburizing treatment, chemical conversion treatment of iron and steel, etc. And the like, cyan waste liquid discharged from the surface treatment step. For example, the above-mentioned waste water containing cyanide further contains various organic and inorganic substances (such as organic acids such as formic acid and acetic acid) and various nitrogen compounds such as ammonia (hereinafter, unless otherwise required, contains cyan and ammonia. All nitrogen compounds may be collectively referred to as simply "nitrogen compounds"), or may contain an organic chlorine compound such as trichloroethylene.

The present invention further relates to Mg, Al, Si, P, Ca, T
It is also useful for treating wastewater or sludge containing one or more metal components such as i, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Cd.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a flow sheet showing the outline of the present invention.

The wastewater is pressurized from a raw water tank to a predetermined pressure by a pump, mixed with an oxygen-containing gas pressurized by a compressor, and then mixed with a heat exchanger (abbreviated as "heat exchange" in FIG. 1). ), The mixture is heated to a predetermined temperature, and then supplied to the reaction tower.

The reaction tower is filled with a catalyst supported on a carrier.

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

As the metal oxide carrier and the metal carrier,
There is no particular limitation, and those used as known catalyst carriers can be used. As the metal oxide carrier, alumina, silica, zirconia, titania, composite metal oxides containing these metal oxides (alumina-silica,
Alumina-silica-zirconia, titania-zirconia, etc.), metal oxide-based carriers containing these metal oxides or composite metal oxides as main components, and the like. Examples of the metal carrier include iron and aluminum. Among these carriers, zirconia, titania and titania-zirconia having excellent durability are more preferable.

The shape of the supported catalyst is also not particularly limited, and examples thereof include a sphere, a pellet, a column, a fragment, a powder, and a honeycomb. In the case of using a fixed bed, the reaction tower volume in the case of filling and using such a supported catalyst is set so that the space velocity of the liquid is about 0.5 to 10 hr ^-1 , more preferably about ¹ to 5 hr ^-1 . Is good. The size of the supported catalyst used in the fixed bed is spherical, pellet-like, cylindrical, crushed, in the case of powder, etc., usually about 3 to 50 mm, more preferably 5 to 25 mm.
mm. When the catalyst is supported on a honeycomb-shaped carrier and used, a honeycomb structure having an opening having an arbitrary shape such as a square, a hexagon or a circle is used. The area per unit volume, the aperture ratio, etc. are not particularly limited, but are usually 200 per area per unit volume.
Use a material with an aperture ratio of about 800 to about 800 m ² / m ³ . Examples of the material of the honeycomb structure include the same metal oxides and metals as described above, and zirconia, titania, and titania-zirconia having excellent durability are more preferable.

The amount of the catalytically active component carried on the carrier is usually about 0.05 to 25% by weight, more preferably about 0.3 to 3% by weight.

In the heat exchanger, heat is recovered by circulating a high-temperature gas-liquid phase from a gas-liquid separator described later. When a predetermined reaction temperature cannot be maintained during the reaction in winter or when the temperature needs to be raised to a predetermined temperature, heating is performed by a heater (not shown), or a steam generator (not shown). (Not shown), it is also possible to supply steam to the reaction tower. Also, in order to bring the temperature inside the reaction tower to a predetermined temperature at startup, the steam is directly sent to the reaction tower to raise the temperature, or a heater (not shown) is provided between the heat exchanger and the reaction tower. And the temperature can be raised.

The temperature in the reaction tower is usually about 100 ° C. or more, more preferably about 150 ° C. or more. The higher the temperature during the reaction, the higher the decomposition removal rate of the pollutant components and the shorter the residence time of the wastewater in the reaction tower, but on the other hand, the equipment cost increases. The concentration may be determined in consideration of the concentration, the required processing degree, the operation cost, the construction cost, and the like.

The pressure during the reaction may be any pressure at which the wastewater to be treated can maintain a liquid phase at the reaction temperature. Here, the `` pressure at which the liquid phase can be maintained '' refers to the amount of liquid (wastewater), the amount of water vapor, and the amount of gas (steam Excluding the gas in the column), the pressure at which the amount of water vapor is 60% or less (more preferably 50% or less) and the inside of the reaction column is substantially maintained in a liquid phase.

The amount of oxygen supplied to the reaction tower is not less than the theoretical amount of oxygen necessary to decompose nitrogen compounds, organic substances and inorganic substances into harmless products, and is more preferably 1% of the theoretical amount of oxygen. The amount is about 1.0 to 1.2 times the theoretical oxygen amount. As the oxygen source, air, oxygen-enriched air (oxygen-enriched air obtained using a selective oxygen permeable membrane, air-oxygen mixture, air is PSA
It is possible to use oxygen-enriched air obtained by processing in an apparatus), oxygen, and substances capable of generating oxygen under wastewater treatment conditions (O ₃ , H ₂ O _2, etc.). As the oxygen source, an oxygen-containing waste gas containing one or more of hydrogen cyanide, hydrogen sulfide, ammonia, sulfur oxides, organic sulfur compounds, nitrogen oxides, and hydrocarbons as impurities may be used. According to the present invention, the impurities in these oxygen sources are also decomposed together with the components to be treated in the wastewater.

In the present invention, the term "theoretical oxygen amount" means "a nitrogen compound, an organic substance and an inorganic substance (component to be treated) in wastewater are harmless products (N ₂ , H ₂ O and CO 2). ₂ ) The amount of oxygen required to decompose to ₂ ). The theoretical oxygen amount can be easily determined by analyzing the components to be treated in the wastewater to be treated and calculating the oxygen amount required for their decomposition. Practically, based on experience and experiments, it is possible to find a relational expression that approximately calculates the theoretical oxygen amount with high accuracy using several parameters. An example of such a relational expression is described in Japanese Patent Publication No. 58-27999.

The treated liquid 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 heating source of wastewater in a heat exchanger, and then sent to a cooler.
Gas (liquid) and liquid phase (treated water)
And separated.

In the present invention, at least a part of the high-temperature and high-pressure liquid phase obtained in the first gas-liquid separator is circulated to the reaction tower via a liquid circulation line and a circulation pump (this circulation operation is referred to as “ Hot recycle)) and mix it into wastewater. The circulation amount of the liquid is appropriately determined according to the nature of the wastewater (the type and concentration of the components to be treated and the concentration thereof), the degree of reduction in the activity of the catalyst filled in the reactor, and the like.
It is in the range of about 15 times, more preferably about 1 to 10 times. The liquid linear velocity in the tower is usually 0.1 to 1.0 cm / s in order to perform catalyst washing while forming a fixed bed in the reaction tower.
ec, more preferably about 0.2 to 0.9 cm / sec.

The liquid phase other than the circulating liquid is cooled by a cooler from a first gas-liquid separator via a heat exchanger, and then separated into exhaust gas and treated water in a second gas-liquid separator. You.

The treated water obtained by the second gas-liquid separator is further subjected to a conventional biological treatment method (activated sludge treatment method, biological denitrification method, etc.) according to the required water quality standards. Can be offered. Excess sludge generated by such a biological treatment method can be subjected to wet oxidation treatment according to the method of the present invention.

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

[0038]

According to the present invention, when performing wet oxidation of wastewater containing at least one of nitrogen compounds, organic substances and inorganic substances (pollutant components), it is obtained by gas-liquid separation after wet oxidation treatment. A part of the high-temperature liquid phase is hot-recycled to maintain the liquid linear velocity in the tower, so that even when a relatively large amount of air (oxygen) is used and processing is performed under high-temperature and high-pressure conditions, external heating can be performed. And the reaction can be continued while maintaining a good liquid phase state.

Further, according to the present invention, the amount of metal component adhering to the catalyst surface can be reduced and the liquid film resistance of the catalyst surface can be reduced, so that the catalyst activity and durability can be improved. Without being restricted by the concentration of pollutants, wastewater can be treated efficiently.Also, according to the present invention, a high-concentration oxygen-containing gas (e.g., pure oxygen)
In the case of using, wastewater treatment can be performed in a unit of time under a relatively low pressure condition of 10 kg / cm ² (0.98 MPa) or less.

When the wastewater treatment is performed under subcritical, critical or supercritical conditions using air, the operation can be completed in a time period of seconds.

Further, according to the method of the present invention, since each step is continuously performed and the processing flow is extremely simple, the processing cost (equipment cost, operation cost, etc.) is remarkably reduced, and the step management becomes easy. .

[0042]

EXAMPLES Examples and comparative examples are shown below to further clarify the features of the present invention.

EXAMPLES 1-2 AND COMPARATIVE EXAMPLES 1-2 According to the flow shown in FIG. 1, according to the method of the present invention, gas liquids (nitrogen-containing compounds, organic substances and inorganic substances) generated in a coke oven plant having the properties shown in Table 1 are obtained. (Including active substances).

[0044]

[Table 1]

(1) Example 1: The gas liquid was introduced into the tower at an overhead tower speed of 4 hr ^-1.
(Superficial volume basis), while supplying the reactor tower in the liquid linear velocity 0.71 cm / sec and mass velocity 25.5m ³ / m ² · hr, the superficial velocity 80.4Hr ^-1 air simultaneously (calculated as the standard state) Supplied with The air supply amount was an amount corresponding to 1.1 times the theoretical oxygen amount. The reaction column was filled with a spherical catalyst (diameter of about 5 mm) in which 2% of the weight of the carrier was supported on a titania carrier, and the temperature was maintained at 250 ° C. and the pressure was 70 kg / cm ² · G.

The treatment liquid from the reaction tower is led to the first gas-liquid separator, where gas-liquid separation is performed, and a part of the obtained liquid phase (the same amount as the supplied gas liquid) is hot recycled to the reaction tower. At the same time, the gas-liquid phase from the first gas-liquid separator was heat-recovered by a heat exchanger, then cooled by a cooler, and then separated into exhaust gas and treated water by a second gas-liquid separator.

Table 2 shows the composition of the treated water obtained 100 hours after the start of the reaction. In the first embodiment,
Even after 8000 hours of operation, COD and NH ₄ -N in the treated water remain 10
It was less than mg / l.

(2) Example 2: The wet oxidation treatment of the gas liquid was performed according to the method of Example 1 except that the amount of the hot recycled liquid was halved. However, since the amount of hot recycle liquid was halved, the tower speed in the tower was 3h
r ^-1 (based on empty tower volume), liquid linear velocity in the tower was 0.53 cm / sec, and mass velocity was 19.1 m ³ / m ² · hr.

Table 2 shows the composition of the treated water obtained 100 hours after the start of the reaction.

(3) Comparative Example 1 A wet oxidation treatment of a gas liquid was performed according to the method of Example 1 except that hot recycling was not performed. However, by omitting the hot recycling, the superficial velocity in the tower was 2 hr ^-1 (based on the superficial volume), the liquid linear velocity in the tower was 0.35 cm / sec, and the mass velocity was 12.7 m in relation to the gas liquid.
³ / m ² · hr.

Table 2 shows the composition of the treated water obtained 100 hours after the start of the reaction.

(4) Comparative Example 2: The gas liquid was subjected to wet oxidation treatment in accordance with the method of Comparative Example 1 except that the diameter of the reaction tower was changed.
However, due to the change in the diameter of the reaction tower, the superficial velocity in the tower is 2 hr ^-1 (based on the superficial volume) and the liquid linear velocity in the tower is 0.088 cm in relation to the gas liquid.
/ sec and a mass velocity of 3.2 m ³ / m ² · hr.

Table 2 shows the composition of the treated water obtained 100 hours after the start of the reaction.

[0054]

[Table 2]

As is clear from the results shown in Table 2, by performing the hot recycling, the liquid linear velocity in the tower is increased, the liquid film resistance on the catalyst surface is reduced, and the metal component derived from wastewater is reduced. Since the adhesion to the catalyst surface is suppressed,
A high degree of catalytic activity is maintained for a long time, and the quality of treated water is improved.

The time required to reach the treated water quality equivalent to that of Comparative Example 2 was 450 hours in Example 1, and 3 hours in Example 2.
40 hours, and 200 hours in Comparative Example 1.

In each of Examples 1 and 2 and Comparative Examples 1 and 2, NO _x , SO _x and NH ₄ -N were not detected from the exhaust gas (gas phase).

Examples 3 to 12 Gas liquid treatment was performed in the same manner as in Example 1 except that the combination of the catalyst component and the carrier was changed. From the start of the reaction
Table 3 shows the composition of the treated water obtained after 100 hours.

[0059]

[Table 3]

Example 13 According to the flow shown in FIG. 1, according to the method of the present invention, wastewater from a gas washing tower in a coal gasification step is passed through an ion-exchange resin packed tower to adsorb and remove ammonia components, and then desorbed with an aqueous sulfuric acid solution. Ammonia-containing wastewater (pH = 6.6, COD = 1.9 mg /
l, NH ₄ -N = 2100 mg / l, TN = 2100 mg / l).

That is, the above-mentioned wastewater was emptied at a tower speed of 8 hours.
^-1 (superficial volume basis), while supplying the reactor tower in the liquid linear velocity 0.88 cm / sec and mass velocity ^{31.8m 3 3 / m 2 · hr} , oxygen-enriched air (oxygen concentration 90 as the oxygen-containing gas %) Superficial tower speed 13.4hr
Supplied at ^-1 (standard conversion). The oxygen-containing gas supply rate is
The amount was equivalent to 1.5 times the theoretical oxygen amount. The reaction tower was filled with a spherical catalyst (diameter of about 1.5 mm) in which 2.3% by weight of ruthenium was supported on a titania carrier, and the temperature was maintained at 200 ° C. and the pressure was 20 kg / cm ² · G.

The treatment liquid from the reaction tower is led to a first gas-liquid separator, where gas-liquid separation is performed, and a part of the obtained liquid phase (the same amount as the amount of waste water supplied) is hot recycled to the reaction tower. ,
After cooling the gas phase used for heating the wastewater with a cooler,
Was separated into exhaust gas and treated water by the gas-liquid separator of No. 1.

Table 4 shows the composition of the treated water obtained 100 hours after the start of the reaction.

Example 14 (a) The temperature during the reaction was 170 ° C., the pressure was 9.9 kg / cm ² · G, and (b) the liquid superficial velocity in the reaction tower (based on the superficial volume) was 4 hours.
^-1 (i.e., the catalyst loading was twice that of Example 13), (c) the pH was adjusted to 9.7 by adding 48% NaOH to wastewater in advance, and (e) oxygen-containing gas Sky tower speed of 6.7
Ammonia-containing wastewater was treated in the same manner as in Example 13 except that hr- ¹ was used. Table 4 shows the composition of the treated water obtained 100 hours after the start of the reaction.

Example 15 (A) The liquid superficial velocity in the reaction column (based on the superficial volume) was set to 2 hr ^-1 (that is, the amount of catalyst charged was twice that of Example 14), and
(B) Ammonia-containing wastewater was treated in the same manner as in Example 13 except that the superficial velocity (based on superficial volume) of the oxygen-containing gas was 3.4 hr ^-1 . Table 4 shows the composition of the treated water obtained 100 hours after the start of the reaction.

In this example, 1.1 times the theoretical amount of H ₂ O ₂ required to decompose NH ₄ —N = 120 mg / l was added to the position 2/3 from the lower part of the catalyst packed portion of the reaction tower. As a result, substantially the same results as in Example 14 could be obtained.

Example 16 (a) Ammonia-containing wastewater was treated in the same manner as in Example 15 except that 48% NaOH was previously added to the wastewater to adjust its pH to 11.5. Table 4 shows the composition of the treated water obtained 100 hours after the start of the reaction.

[0068]

[Table 4]

Example 17 The treatment temperature and the treatment pressure of the ammonia-containing wastewater were set to 380 ° C. and 230 kg / cm ² which exceeded the critical temperature (374 ° C.) and the critical pressure (220 kg / cm ² ) of water, respectively. Ammonia-containing wastewater was treated in the same manner as in Example 13 except that the inner liquid superficial velocity (based on the superficial volume) was 240 hr ^-1 (that is, the catalyst loading was 1 / 62.5 of Example 13). Table 5 shows the composition of the treated water obtained 100 hours after the start of the reaction.

Comparative Example 3 Ammonia-containing wastewater was treated in the same manner as in Example 17 except that the treatment temperature of the ammonia-containing wastewater was 630 ° C. and no catalyst was used. Table 5 shows the composition of the treated water obtained 100 hours after the start of the reaction.

[0071]

[Table 5]

Example 18 According to the flow shown in FIG. 1, according to the method of the present invention, wastewater containing an organic substance from a petrochemical plant (pH = 2.6, COD = 28100 mg / l,
TOD = 101 800 mg / l, TOC = 36500 mg / l, NH ₄ -N = 1 mg / l, T-
N = 1 mg / l). Organics in the wastewater were acetic acid, acrylic acid, formaldehyde, formic acid and the like.

That is, the above wastewater is supplied to the column with a liquid superficial velocity of 2.9 h.
r ^-1 (based on empty tower volume), while supplying liquid to the reaction tower at a liquid linear velocity of 0.71 cm / sec and a liquid mass velocity of 25.5.8 m ³ / m ²・ hr, air as an oxygen-containing gas was introduced at an empty tower velocity of 553 hr. ^-1 (standard condition conversion)
Supplied with The air supply amount was an amount corresponding to 1.5 times the theoretical oxygen amount. In the reaction tower, a spherical catalyst (1.5 mm in diameter) in which 1.5% of platinum by weight of a carrier was supported on a titania carrier was used.
5mm), temperature 270 ° C and pressure 90kg / cm
^It was kept at ² · G.

The treatment liquid from the reaction tower is led to a first gas-liquid separator, where gas-liquid separation is performed, and a part of the obtained liquid phase (the same amount as the amount of waste water supplied) is hot-recycled to the reaction tower. ,
After cooling the gas phase used for heating the wastewater with a cooler,
Was separated into exhaust gas and treated water by the gas-liquid separator of No. 1.

In the present example, at the outlet of the reactor, steam at a pressure of 24 kg / cm ² could be recovered at 0.84 ton / hr.

Table 6 shows the composition of the treated water obtained 100 hours after the start of the reaction.

Comparative Example 4 A wet oxidation treatment of wastewater was performed according to the method of Example 18 except that hot recycling was not performed. However, due to the omission of hot recycling, the superficial tower velocity in the tower was 1.5 hr ^-1 (based on the superficial tower volume) and the liquid linear velocity in the tower was 0.35 cm /
The sec and the mass velocity were set to 12.7 m ³ / m ² · hr.

Table 6 shows the composition of the treated water obtained 100 hours after the start of the reaction.

[0079]

[Table 6]

The time required to reach the treated water quality equivalent to that of Comparative Example 4 was 350 hours in Example 18.

In each of Example 18 and Comparative Example 4, NOx, SOx and NH
_4- N was not detected.

Further, in Example 18, the COD and TOD in the treated water were less than 10 mg / l even after the operation for 8000 hours.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an outline of the present invention.

Continuation of front page (72) Inventor Kenichi Yamazaki 4-1-2, Hirano-cho, Chuo-ku, Osaka City, Osaka Prefecture F-term in Osaka Gas Co., Ltd. 4D050 AA12 AB06 AB07 AB11 AB14 AB15 AB16 AB17 AB19 AB34 AB35 AB40 BB01 BB02 BB09 BC01 BC02 BC06 BD02 BD06 CA06 4G069 AA03 BC31A BC31B BC33A BC33B BC60A BC60B BC66A BC66B BC67A BC67B BC68A BC68B BC70A BC70B BC71A BC71B BC72A BC72B BC74A BC74B BC75A BC75B CA05 CA07 DA06

Claims (5)

[Claims] (1) A supported catalyst while maintaining a wastewater containing at least one of a nitrogen compound, an organic substance and an inorganic substance at a temperature of 100 ° C. or more and a pressure at which at least a part of the wastewater maintains a liquid phase. Wet oxidation in the presence of oxygen and in the presence of oxygen in excess of the stoichiometric amount of oxygen required to decompose nitrogen compounds and / or organic and / or inorganic substances in wastewater to nitrogen and / or carbon dioxide and water Processing,
And (2) a method for treating wastewater, comprising a step of circulating and mixing at least a part of a high-temperature liquid phase obtained by gas-liquid separation after wet oxidation with wastewater before wet oxidation. 2. The catalytically active component in the step (1) comprises iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and compounds of these metals which are insoluble or hardly soluble in water. The method for treating wastewater according to claim 1, wherein the method is at least one selected from the group. 3. The liquid linear velocity in the column in step (1) (the amount of liquid entering the column /
2. The method for treating wastewater according to claim 1, wherein the cross-sectional area of the tower 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 at least one of air, oxygen-enriched air, pure oxygen, ozone and H ₂ O ₂ . 5. The method for treating wastewater according to claim 1, wherein the circulation amount of the high-temperature liquid phase in step (2) is 0.1 to 15 times the amount of wastewater.