JPH08323372A - Treatment of wastewater containing nitrate - Google Patents

Abstract

(57) [PROBLEMS] To provide a method for treating nitrogen components in wastewater containing nitrate radicals with high efficiency and stably for a long period of time. SOLUTION: Processing is performed according to a process consisting of the following steps (1) and (2). (1) A step of bringing the nitrate-containing wastewater into contact with a reducing solid catalyst in the presence of a reducing substance to wet-reduce the nitrate radical in the wastewater to ammonia nitrogen.
(2) A step of bringing the treated water from the step (1) into contact with an oxidation catalyst to oxidatively decompose the ammonia nitrogen component, the organic substance and the inorganic substance in the treated water.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for treating wastewater containing nitrate radicals. More specifically, the present invention is a chemical plant facility, a food processing facility, a metal processing facility, a leather manufacturing facility, a pharmaceutical manufacturing facility, a textile industry facility, a paper pulp industry facility, a dyestuff dye industry facility, an electronic industry facility, a photographic processing facility,
Treats wastewater containing nitrate radicals discharged from various industrial facilities such as human waste and sewage treatment facilities, and removes nitrate radicals in the wastewater along with organic and inorganic substances such as nitrogen, carbon dioxide,
The present invention relates to a method of converting water into water or the like to render wastewater harmless, particularly a method of performing advanced treatment of nitrogen components.

[0002]

2. Description of the Related Art In sea areas, lakes, rivers, etc., the generation of red tides and musty odorous substances due to eutrophication has long been a problem, but the cause is nitrogen contained in wastewater discharged into these areas. , Nutrients such as phosphorus are the cause. For this reason, in recent years, following the enforcement of the stricter regulation of the third total amount regulation, chemical oxygen demand substances (C
Not only OD components), but also wastewater regulations related to nitrogen components have been implemented, and qualitative improvement in wastewater treatment is required from the viewpoint of environmental protection.

Conventionally, as a method for removing nitrogen components,
Methods such as denitrification treatment by living organisms, ion exchange method, and oxidative denitrification with oxidants such as hypochlorous acid and ozone are used.

The biological denitrification is a method of nitrifying ammonia nitrogen into nitrate nitrogen and then anaerobically treating the nitrate nitrogen to produce nitrogen gas, but it requires a long treatment time. In addition, there is a problem that the device scale is inevitably increased. In addition, it is difficult to maintain proper treatment conditions in order to carry out a microbial reaction, and it is not suitable for wastewater containing a high concentration of nitrogen, wastewater discharged irregularly, or wastewater with a large concentration change. is there.

The ion exchange method requires frequent regeneration of the ion exchange base material and significantly impairs the durability of the ion exchange base material in waste water containing a large amount of ions other than nitrogen-containing ions. There is a problem.

Further, the denitrification method using hypochlorous acid has a risk of producing organic chlorine, which has been a problem in recent years, and the denitrification method using ozone not only requires the presence of bromine ions as a catalyst but also All of these methods have a problem that a large amount of oxidant is required and the cost is increased.

[0007]

SUMMARY OF THE INVENTION Therefore, the present invention has an object of accurately solving the above-mentioned problems of the prior art, and when treating the wastewater containing nitrate radicals, the nitrogen component in the wastewater is increased. It is an object of the present invention to provide an efficient and stable treatment method for a long period of time.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, by treating the wastewater by a process including a wet reduction treatment step and a wet oxidation treatment step shown below, The inventors have found that the nitrogen component therein can be treated with high efficiency and stably for a long period of time, and have completed the present invention based on this finding.

That is, the present invention is a method for treating nitrate-containing wastewater, which comprises treating the nitrate-containing wastewater by the following procedure.

(1) The nitrate-containing wastewater is supplied in the presence of a reducing substance at a temperature of 120 to 370 ° C. and under a pressure at which the wastewater holds a liquid phase, without substantially supplying oxygen.
A step of wet-reducing nitrate radicals in wastewater to ammonia nitrogen by contacting with a reducing solid catalyst. (2) The treated water discharged in the step (1) is 120 to 370.
At a temperature of ℃, and the pressure at which the wastewater holds the liquid phase,
A step of wet-oxidizing and decomposing the ammonia nitrogen component, the organic substance and the inorganic substance in the treated water by contacting with a solid catalyst for oxidation while supplying oxygen.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The "nitrate" in the present invention means nitrate ion and nitrite ion. Therefore,
The nitrate-containing wastewater of the present invention means wastewater containing nitrate ions and / or nitrite ions, usually nitrate ions, or nitrate ions and nitrite ions. The nitrogen atoms constituting these nitrate ions and nitrite ions are collectively referred to as nitrate nitrogen (sometimes referred to as "NO ₃ -N"), and the nitrate-containing wastewater of the present invention contains nitrate nitrogen. It can also be called drainage. Ammonia nitrogen is a general term for nitrogen atoms constituting molecular ammonia (NH ₃ ) and ammonium ion (NH ₄ ⁺ ) and may be represented as “NH ₃ —N”.

Specific examples of nitrate-containing wastewater include chemical plant equipment, food processing equipment, metal processing equipment, leather manufacturing equipment, pharmaceutical manufacturing equipment, textile industry equipment, paper pulp industry equipment, dyeing dye industry equipment, electronic industry equipment. , Photo processing equipment,
Examples include various wastewater containing nitrate radicals discharged from various industrial equipment such as human waste / sewage treatment equipment.

There is no particular limitation on the concentration of nitrate radicals in the wastewater when treated by the method of the present invention, and it can be appropriately determined according to the type of wastewater discharged from various industrial facilities, the scale of the treatment equipment, and the like. it can. Usually, as nitrate nitrogen, 50
~ 50,000 mg / l, preferably 100-20,0
It is recommended to set it to 00 mg / 1. If the concentration of nitrate radicals is too low, the treatment cost will increase and it will be economically disadvantageous.

The nitrate radical-containing wastewater may contain COD components, nitrogen compounds, sulfur compounds, organic halogen compounds, inorganic salts and the like. In the present invention, these are collectively referred to as “organic substances and inorganic substances”, including the undecomposed reducing substances described later.

The present invention will be described in detail below.

Step (1) In the step (1), the nitrate-containing wastewater is substantially treated in the presence of a reducing substance at a temperature of 120 to 370 ° C. and under a pressure at which the wastewater holds a liquid phase. Wet-reduce the nitrate radicals in the wastewater to ammonia nitrogen by bringing them into contact with a solid reducing catalyst without supplying oxygen to them.

The reaction mechanism in the step (1) will be explained by taking the case of using methanol as a reducing substance as an example, and the following reaction is considered to occur. 3HNO ₃ + 4CH ₃ OH + 3H ⁺ → 3NH ₄ ⁺ + 4CO ₂ + 5H ₂ O ··· (1) 6HNO ₃ + 5CH ₃ OH → 3N ₂ + 5CO ₂ + 13H ₂ O ·· (2) Therefore, it is discharged after the reduction treatment in step (1). In addition to ammonia nitrogen, the treated water may contain nitrogen gas and undecomposed reducing substances. In the present invention, since the wet reduction is carried out using the solid catalyst for reduction described later, the reaction shown in (1) above is likely to occur, and the conversion of nitrate radicals into ammoniacal nitrogen can be carried out efficiently. it can.

The reducing substance used in the step (1) is not particularly limited as long as it has the ability to reduce nitrate radicals by depriving the nitrate radicals of oxygen atoms, and does not generate secondary pollutants after the treatment. None, any compound can be used. Typical examples of the reducing substance include lower alcohols having 1 to 5 carbon atoms such as methanol, ethanol, isopropanol, butanol; organic acids such as formic acid, acetic acid, oxalic acid, propionic acid; formaldehyde, acetaldehyde, propylaldehyde, butyraldehyde. Such as lower aldehydes having 1 to 5 carbon atoms; saccharides such as sucrose, glucose, fructose and maltose; lower ketones such as acetone and methyl ethyl ketone; inorganic sulfur compounds such as sodium thiosulfate and sodium sulfide;
Nitrogen compounds such as ammonia, hydrazine, amides, amines and amino acids; phenols and the like can be mentioned. Of these, lower alcohols, lower aldehydes, saccharides and ammonia, particularly methanol and ammonia, are preferably used in view of handleability, economy, and ease of post-treatment. The reducing substance may be used alone or in combination of two or more kinds. The reducing substance may be added as it is, or the reducing substance contained in the waste water as a COD component may be used. That is, when the wastewater to be treated originally contains the above-mentioned reducing substances as COD components,
The reducing substance can be supplied by using this reducing substance or by mixing the wastewater containing the above-mentioned reducing substance as a COD component discharged from another treatment facility with the wastewater to be treated.

The amount of the reducing substance used is 0.5 ≦ reducing substance / nitrate (molar ratio) ≦ 10, preferably 1 ≦ reducing substance / nitrate (molar ratio) ≦ 7 in the waste water. Is good. If the reducing substance / nitrate (molar ratio) is less than 0.5, the reduction is insufficient and the nitrate cannot be sufficiently converted to ammonia nitrogen. Then, in order to sufficiently convert the nitrate radicals to ammonia nitrogen, it is sufficient that the reducing substances are present at a reducing substance / nitrate radical ratio (molar ratio) of 10 or less, and more reducing substances are present in the wastewater. However, no further improvement in the reduction of nitrate radicals to ammonia nitrogen is observed, which is economically disadvantageous. The nitrate radical concentration is the concentration of nitrate ions and / or nitrite ions as described above.

As the solid reducing catalyst used in the step (1), any solid catalyst capable of reducing nitrate nitrogen to ammonia nitrogen in the presence of the reducing substance can be used. For example, a metal and / or at least one element selected from titanium, silicon, aluminum, zirconium, manganese, iron, cobalt, nickel, cerium, tungsten, copper, silver, gold, platinum, palladium, rhodium, ruthenium and iridium. Mention may be made of compounds, or catalysts containing these and activated carbon or carbon compounds.

In particular, a solid catalyst containing the following catalyst A component and catalyst B component is preferably used. Here, the catalyst A component is an oxide of at least one element selected from iron, titanium and zirconium, a carbon compound or activated carbon, and the catalyst B component is manganese, cobalt, nickel, cerium, tungsten, copper. , A metal and / or a compound of at least one element selected from silver, gold, platinum, palladium, rhodium, ruthenium and iridium.

The above carbon compound means a molded product of an organic polymer compound such as a chelate resin.

Specific examples of the catalyst component A include binary oxides such as titanium oxide, iron oxide, zirconium oxide, titanium oxide-zirconium oxide and titanium oxide-iron oxide (composite oxides). In addition to (including oxides), chelating resins and activated carbon can be mentioned. Catalyst A
The proportion of the components in the solid catalyst is 30 to 99.95% by weight.
Is preferable, and the durability of the reducing solid catalyst is improved by using the catalyst A component in an amount of 30% by weight or more. Among the components of catalyst A, activated carbon is particularly preferably used, and by using activated carbon, a solid catalyst for reduction having excellent activity can be obtained.

Specific examples of the component B of the catalyst include metals, oxides and complex oxides of the above elements.
The proportion of the catalyst B component in the solid catalyst is 0.05 to 70% by weight.
It is preferable that the content be 0.05% by weight or more, so that the nitrate radical can be sufficiently converted to ammonia nitrogen. Among the above elements,
In the case of silver, gold, platinum, palladium, rhodium, ruthenium and iridium (hereinafter referred to as "B-1 component"), the ratio (total amount) of the metal and / or compound is 0.05 of the solid catalyst for reduction. It is preferable to be 10% by weight. Even if it is used in a proportion of more than 10% by weight, no corresponding improvement in the reduction performance is observed, and since it is an expensive raw material, the cost of the solid reducing catalyst is increased, which is economically disadvantageous. . In addition, in the case of manganese, cobalt, nickel, cerium, tungsten and copper (hereinafter referred to as "B-2 component"), the ratio (total amount) of the metal and / or compound is 0.0 of the solid catalyst.
It is preferable to be 5 to 70% by weight. Of course, within the total amount of 0.05 to 70% by weight, the B-1 component and the B-2 component are used in combination in the ranges of 0.05 to 10% by weight and 0.05 to 70% by weight, respectively. You can also

The solid catalyst for reduction contains B as the catalyst B component.
The case of containing the -1 component is particularly effective because the catalyst activity is high. In particular, among the B-1 components, when the metal and / or the compound of at least one element selected from platinum, palladium, rhodium, ruthenium and iridium is contained, it is preferable because the catalytic activity is high. B-
Among the two components, manganese, cobalt, nickel and copper are preferably used. When a chelate resin is used as the catalyst A component, it is preferable that the catalyst B component is an ion, and the ion is fixed by forming a complex compound using the chelate component of the chelate resin as a ligand.

Among the solid catalysts for reduction, particularly preferable examples include palladium / activated carbon and palladium / titanium oxide.

The shape of the reducing solid catalyst is not particularly limited, and may be, for example, granular, spherical, pellet-shaped, or ring-shaped, or may be an integral structure such as honeycomb-shaped. When treating the wastewater containing the suspension, a honeycomb-shaped one is preferably used because clogging of the catalyst layer may occur due to solids or precipitates.

In the case of a granular catalyst, the average particle size thereof is usually 1 to 10 mm, preferably 2 to 7 mm. If the average particle size is less than 1 mm, the pressure loss may increase. On the other hand, the average particle size is 10 mm
If it exceeds, a sufficient geometric area cannot be obtained, the contact area may be reduced, and a sufficient reducing ability may not be obtained. In the case of a pellet catalyst, the average diameter is usually
It is 1 to 10 mm, particularly preferably 3 to 8 mm, and the average length is usually 2 to 15 mm, and particularly preferably 3 to 10 mm. Average diameter is 1
If it is less than mm or the average length is less than 2 mm, pressure loss may increase, while if the average diameter exceeds 10 mm or the average length exceeds 15 mm, sufficient geometric surface area can be obtained. In some cases, the contact efficiency may decrease and a sufficient reducing ability may not be obtained. In the case of a honeycomb catalyst, the equivalent diameter of the through hole is usually 2 to 20 mm, the cell wall thickness is 0.1 to 3 mm, and the opening ratio is 50 to 90%. It is preferable that the cell wall thickness is 155 mm, the cell wall thickness is 0.5 to 3 mm, and the aperture ratio is 50 to 90%. When the equivalent diameter of the through hole is less than 2 mm, the pressure loss becomes large, while when it exceeds 20 mm, the pressure loss becomes small, but the contact rate may decrease and the catalytic activity may decrease. If the cell wall thickness is less than 0.1 mm, the pressure loss will be small and the catalyst can be made lighter, but the mechanical strength of the catalyst may decrease, while if it exceeds 3 mm, the mechanical strength may be reduced. Is sufficient, the effective contact area of the catalyst becomes smaller than the amount of the catalyst, and it is impossible to expect the activity according to the amount of the catalyst. Regarding the aperture ratio, for the same reason as above, 5
It is better to set it to 0 to 90%.

The method for preparing the solid reducing catalyst is not particularly limited and can be prepared by a conventionally known method. For example, a commercially available titania pellet as the catalyst A component may be impregnated and supported with palladium metal as the catalyst B component. It can also be prepared by coprecipitating or kneading the compounds of the respective catalyst components.

In the reduction treatment in the step (1), the temperature of the waste water is 120 to 370 ° C., preferably 150 to 300 ° C., and at this temperature, the waste water is under a pressure to maintain the liquid phase and oxygen is substantially contained. Carry out under conditions not supplied.

When the temperature of the waste water is less than 120 ° C, the treatment efficiency is insufficient, while the critical temperature of water is 370 ° C,
If it exceeds this, the waste water cannot be retained in the liquid phase. In addition,
When the temperature of the waste water exceeds 370 ° C., it is necessary to install a treatment device that can withstand such conditions, which causes a problem of increased cost of the treatment device.

The pressure at the time of the reduction treatment may be any pressure as long as it can maintain the wastewater in the liquid phase at the above-mentioned wastewater temperature and can be appropriately determined.

In the present invention, “substantially without supply of oxygen” means that oxygen is not actively supplied to the wastewater to be treated, and a small amount of oxygen is dissolved in the wastewater to be treated. It also includes cases where Supplying oxygen to the wastewater to be treated is not preferable because oxygen reoxidizes ammonia nitrogen generated by the reduction of nitrate radicals or the reducing substance is oxidized, and the effect can be sufficiently exhibited.

The pH of the waste water is not particularly limited,
Considering the material of the processing device, it is preferable to adjust the range of 2 to 12.

Regarding the supply rate of the wastewater, it is preferable that the space velocity of the wastewater with respect to the reducing solid catalyst is 0.1 to 20 hr ^-1 , preferably 0.3 to 10 hr ^-1 .
If it is less than 0.1 hr ^-1 , the processing equipment becomes too large and inefficient, while if it exceeds 20 hr ^-1 , the reduction efficiency is lowered.

The apparatus for carrying out the step (1) may be of a single-tube type or a multi-tube type. Further, the apparatus according to the present invention is preferably provided with a pressure accumulator for stabilizing the system pressure and preventing pulsating flow. This pressure accumulator can be installed between the drainage booster pump and the reaction tower and / or between the reaction tower and the pressure control valve. When precise pressure control is unnecessary, wastewater can be treated without supplying gas.

Step (2) In the step (2), the treated water discharged in the step (1) is treated as 12
At a temperature of 0 to 370 ° C. and at a pressure at which the waste water maintains a liquid phase, while supplying oxygen, the waste water is brought into contact with the solid catalyst for oxidation to contact with ammonia nitrogen components, organic substances and inorganic substances in the treated water. Wet oxidatively decomposes material.

In the treated water discharged from the step (1),
Ammonium ion (NH ₄ ⁺ ) and ammonia (NH ₃ )
And exist in an equilibrium state (collectively referred to as “ammonia nitrogen component”), and in addition, organic and inorganic substances originally contained in the nitrate-containing wastewater, and in some cases, undecomposed reducing substances exist. In the step (2), the ammonia nitrogen component, the organic substance and the inorganic substance are oxidatively decomposed or burned by a solid catalyst for oxidation while supplying oxygen to be converted into nitrogen, carbon dioxide, water and the like to be rendered harmless. .

The oxygen used for the above-mentioned oxidative decomposition or combustion may be oxygen alone or an oxygen-containing gas, but normally, inexpensive air is used except for special cases such as downsizing of the apparatus. Oxygen is the amount of 1 necessary for decomposing ammonia nitrogen components, organic substances and inorganic substances in treated water into nitrogen, carbon dioxide, water, etc.
It is recommended to supply ~ 5 times the amount. Particularly, considering the cost, it is preferable to supply 1.6 to 3 times the required amount of oxygen. When the amount of oxygen used is less than 1 time, the surface of the catalyst is always in a state of being deficient in oxygen, that is, a reducing atmosphere, and the efficiency of oxidative decomposition or combustion decreases. On the other hand, when the amount of oxygen used exceeds five times, the demerit due to the increase of gas hold-up in the reaction tower exceeds the efficiency of reaction rate improvement, and the treatment efficiency tends to decrease.

Examples of the solid catalyst for oxidation used in the step (2) include titanium, silicon, aluminum, zirconium, manganese, iron, cobalt, nickel, cerium, tungsten, copper, silver, gold, platinum, palladium, rhodium and ruthenium. And those containing a metal and / or compound of at least one element selected from iridium and iridium can be used. Examples of the compound containing the above element include oxides thereof or multi-component oxides (including complex oxides).

The shape of the oxidation solid catalyst is not particularly limited, and various shapes as described for the reduction solid catalyst used in the step (1) can be used.

The reaction temperature is 120 to 370 ° C., preferably 140 to 170 ° C. When the reaction temperature is too low, the treatment efficiency is insufficient, while the critical temperature of water is 370 ° C. and above this. The treated water cannot be retained in the liquid phase.
When the temperature of the treated water exceeds 370 ° C., it is necessary to provide a treatment device that withstands such conditions, which causes a problem of increased cost of the treatment device.

The pressure at the time of treatment may be any pressure as long as it can maintain the treated water in the liquid phase at the temperature of the treated water in the above range and can be appropriately determined.

Regarding the supply rate of the treated water, the space velocity of the treated water with respect to the solid catalyst for oxidation is 0.1 to 20 hr ^-1 ,
It is preferably 0.3 to 10 hr ⁻¹ . If it is less than 0.1 hr ⁻¹ , the processing apparatus becomes too large and inefficient, while if it exceeds 20 hr ⁻¹ , the efficiency is lowered.

The apparatus for carrying out the step (2) may be of a single-tube type or a multi-tube type.

Next, one specific example of the present invention is shown in FIG.
The processing method of the present invention will be described in detail based on this flow schematic diagram.

The nitrate-containing wastewater to be treated is introduced from the line 1, the reducing substance such as methanol is supplied to the nitrate-containing wastewater from the line 2 by the pump 4, and after mixing, the wastewater is heated by the booster pump 3. Supply to the exchanger 5. After the wastewater is heated to the reaction start temperature by the treated water from the wet reduction reaction tower 6 in this heat exchanger 5, it is supplied from the bottom to the wet reduction reaction tower 6 filled with the solid catalyst for reduction, and the wastewater is discharged here. The nitrates in the product are reduced to ammonia nitrogen. The treated water after the reduction treatment is discharged from the line 7, cooled by the heat exchanger 5, decompressed by the pressure control valve 8, and the treated water containing ammonia nitrogen, undecomposed methanol and the like is introduced into the treated water tank 9. To do. Here, a harmless gas such as nitrogen gas in the treated water is discharged into the atmosphere through the line 10.
The treated water may be directly introduced into the next wet oxidation reaction tower 15 without separating the nitrogen gas and the like in the treated water tank 9 (see FIG. 2).

The treated water is boosted by the booster pump 11, while the air supplied from the air supply line 13 is boosted by the compressor 12, then mixed with the treated water and supplied to the heat exchanger 14. Here, the treated water is heated to the reaction start temperature by the treated water from the wet oxidation reaction tower 15 and then supplied to the wet oxidation reaction tower 15 filled with the solid catalyst for wet oxidation, where the ammonia in the treated water is supplied. Nitrogen components, organic substances and inorganic substances are oxidatively decomposed into nitrogen, carbon dioxide, water and the like. The treated wastewater is discharged from the line 16, cooled by the heat exchanger 14, decompressed by the pressure control valve 17, and then introduced into the treated water tank 18, where a harmless gas is discharged from the line 19 and Harmless treated water is discharged from line 20.

[0049]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 As the nitrate-containing wastewater, wastewater containing 2% by weight of sodium nitrate and 3% by weight of ethanol was used, and this was treated according to the schematic flow chart shown in FIG. The reducing substance (ethanol) / nitrate (molar ratio) in this waste water was 2.77.

<Step (1)> The above waste water was introduced into the wet reduction reactor 6, the reaction temperature (waste water temperature) was 270 ° C., the reaction pressure was 85 kg / cm ² G, and the space velocity for the catalyst was ¹ hr ^−1.
Wet reduction treatment was performed under the conditions of. As the solid catalyst for reduction, an oxide of titanium and iron (Ti
O ₂ : Fe ₂ O ₃ (weight ratio) = 10: 90 (99.4% by weight) and platinum as a catalyst B component (0.6% by weight)
The catalyst in the form of pellets was used.

<Step (2)> The treated water from the wet reduction reactor 6 is introduced into the wet oxidation reactor 15, and the reaction temperature is set to 160.
C, reaction pressure 9 kg / cm ² G, space velocity 2 hr ^{−1 to} the catalyst, and the amount of oxygen required to decompose the ammonia nitrogen component in the treated water and undecomposed ethanol into nitrogen, carbon dioxide, water, etc. The wet oxidation treatment was carried out while introducing an amount of air corresponding to 2.5 times. As the oxidation catalyst, a pellet-shaped catalyst containing titanium, iron and platinum was used.

As a result, the ammonia nitrogen concentration in the treated water discharged from the wet oxidation reactor 15 was 4 mg / l or less, and the nitrate nitrogen concentration was 10 mg / l or less.

Example 2 As the nitrate-containing wastewater, wastewater containing 5% by weight of ammonium nitrate was used, and methanol was added to this wastewater so as to be 4% by weight, and according to the schematic flow chart shown in FIG. Processed. The reducing substance (ammonia + methanol) / nitrate (molar ratio) in this waste water was 3.

<Step (1)> The above waste water is introduced into the wet reduction reactor 6, the reaction temperature is 250 ° C., the reaction pressure is 70 kg / c.
The wet reduction treatment was carried out under the conditions of m ² G and a space velocity of 1 hr ⁻¹ with respect to the catalyst. As the reducing solid catalyst, titanium oxide (99% by weight) as the catalyst A component and the catalyst B are used.
A catalyst consisting of palladium (1% by weight) as a component was used.

<Step (2)> The treated water from the wet reduction reactor 6 is introduced into the wet oxidation reactor 15, and the reaction temperature is set to 160.
℃, reaction pressure 9kg / cm ² G, space velocity 2hr ^{-1 to} the catalyst, and the amount of oxygen required to decompose ammonia nitrogen component and undecomposed methanol in the treated water into nitrogen, carbon dioxide, water, etc. The wet oxidation treatment was carried out while introducing an amount of air corresponding to 2.5 times. The same catalyst as used in Example 1 was used as the oxidation catalyst.

As a result, the ammonia nitrogen concentration in the treated water discharged from the wet oxidation reactor 15 was 4 mg / l or less, and the nitrate nitrogen concentration was 20 mg / l or less.

Example 3 As the nitrate-containing wastewater, wastewater containing 6% by weight of ammonium nitrate was used, and methanol was added to this wastewater so as to be 1.8% by weight, and the flow diagram shown in FIG. Therefore treated. The reducing substance (ammonia + ethanol) / nitrate (molar ratio) in this wastewater is 1.75.
Met.

<Step (1)> The above waste water is introduced into the wet reduction reactor 6, the reaction temperature (waste water temperature) is 250 ° C., the reaction pressure is 70 kg / cm ² G, and the space velocity for the catalyst is ¹ hr ^−1.
Wet reduction treatment was performed under the conditions of. As the reducing solid catalyst, a catalyst composed of activated carbon as the catalyst A component and palladium (2% by weight) as the catalyst B component was used.

<Step (2)> The treated water from the wet reduction reactor 6 is introduced into the wet oxidation reactor 15, and the reaction temperature is set to 160.
C, reaction pressure 9 kg / cm ² G, space velocity 2 hr ^{−1 to} the catalyst, and the amount of oxygen required to decompose the ammonia nitrogen component in the treated water and undecomposed ethanol into nitrogen, carbon dioxide, water, etc. The wet oxidation treatment was performed while introducing an amount of air corresponding to twice the above. As the oxidation catalyst, a pellet-shaped catalyst containing titanium, iron, cerium and platinum was used.

As a result, the ammonia nitrogen concentration in the treated water discharged from the wet oxidation reactor 15 was 4 mg / l or less, and the nitrate nitrogen concentration was 10 mg / l or less.

[0062]

According to the treatment method of the present invention, nitrate radicals in waste water can be treated with high efficiency and long-term stability.

In particular, when the catalyst comprising the catalyst A component and the catalyst B component is used as the solid reducing catalyst in the step (1), the nitrogen component can be highly treated and the catalyst is excellent in durability. Therefore, it shows stable activity over a long period of time.

[Brief description of drawings]

FIG. 1 is a schematic flow chart showing one of the processing methods of the present invention.

FIG. 2 is a schematic flow chart showing another example of the processing method of the present invention. (1) Wastewater supply line (2) Reducing substance supply line (3) Booster pump (4) Reducing substance supply pump (5) Heat exchanger (6) Wet reduction reactor (7) Line (8) Valve (9) Treatment Water tank (10) Exhaust gas treatment line (11) Booster pump (12) Compressor (13) Air supply line (14) Heat exchanger (15) Wet oxidation reactor (16) Line (17) Valve (18) Treated water tank (19) Treated gas line (20) Treated water discharge line

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukihiro Yoneda 1 992, Nishikioki, Kamahama, Aboshi-ku, Himeji-shi, Hyogo 1

Claims (6)

[Claims] 1. A method for treating nitrate-containing wastewater, which comprises treating the nitrate-containing wastewater according to the following procedure. (1) Nitrate-containing wastewater in the presence of reducing substances
At a temperature of 370 ° C. and under a pressure at which the wastewater maintains a liquid phase, the nitrate radicals in the wastewater are wet-reduced to ammonia nitrogen by contacting the solid catalyst for reduction without substantially supplying oxygen. The process of doing. (2) The treated water discharged in the step (1) is 120 to 370.
At a temperature of ℃, and the pressure at which the wastewater holds the liquid phase,
A step of wet-oxidizing and decomposing the ammonia nitrogen component, the organic substance and the inorganic substance in the treated water by contacting with a solid catalyst for oxidation while supplying oxygen. 2. The reducing solid catalyst used in step (1) is titanium, silicon, aluminum, zirconium, manganese, iron, cobalt, nickel, cerium, tungsten, copper, silver, gold, platinum, palladium, rhodium, The metal and / or compound of at least one element selected from ruthenium and iridium, or those containing activated carbon or carbon compound.
The described method. 3. The reducing solid catalyst used in step (1) is, as the catalyst A component, an oxide, a carbon compound or activated carbon composed of at least one element selected from iron, titanium and zirconium, and a catalyst B. As components, manganese, cobalt, nickel, cerium, tungsten,
The method according to claim 1, which contains a metal and / or compound of at least one element selected from copper, silver, gold, platinum, palladium, rhodium, ruthenium and iridium. 4. The solid catalyst for oxidation used in step (2) is titanium, silicon, aluminum, zirconium, manganese, iron, cobalt, nickel, cerium, tungsten, copper, silver, gold, platinum, palladium, rhodium, The method according to any one of claims 1 to 3, which contains a metal and / or a compound of at least one element selected from ruthenium and iridium. 5. The reducing substance is at least one selected from lower alcohols having 1 to 5 carbon atoms, lower aldehydes having 1 to 5 carbon atoms, sugars and ammonia.
4. The method according to any one of 4 above. 6. The reducing substance is added to 0.5 in the step (1).
The method according to claim 1 or 5, wherein the reducing agent / nitrate (molar ratio) is present at a ratio of ≦ 10.