JPH08309370A - Treatment of nitrate radical-containing waste water - Google Patents

Abstract

PURPOSE: To stably treat a nitrogen component in waste water with high efficiency over a long period of time by bringing nitrate radicals in waste water into contact with a reducing solid catalyst at specific temp. to reduce the same to ammonia nitrogen and stripping ammonia from treated water to oxidize and decompose the same by an oxidizing catalyst. CONSTITUTION: Nitrate radical-containing waste water is introduced from a line 1 and a reducing substance is supplied from a line 2 by a pump 4 to be mixed with the waste water and this waste water is supplied to a heat exchanger 5 by a pressure raising pump 3. Further, the waste water is raised in temp. by the primary treated water from a wet reducing reaction column 6 to be supplied to the wet reducing reaction column 6 and nitrate radicals in waste water are reduced to ammonia nitrogen at 120-370 deg.C. The primary treated water is introduced into the top of a diffusion column 16 by a pump 13 while air heated by a heat exchanger 20 is supplied to the lower part of the diffusion column 16 through a line 21 to strip ammonia from the primary treated water. The exhaust gas from the diffusion column 16 is introduced into an exhaust gas combustion device 26 packed with an oxidizing catalyst and ammonia gas is converted to harmless gas.

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,
A method of treating wastewater containing nitrate radicals discharged from various industrial facilities such as human waste and sewage treatment facilities and converting the nitrate radicals in the wastewater into gases such as nitrogen and carbon dioxide to render the wastewater harmless, especially nitrogen The present invention relates to a method for performing advanced processing of 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 As a result of intensive research to solve the above problems, the present inventors have found that a reduction treatment step, a stripping step and an exhaust gas combustion step, or a reduction treatment step, a stripping step and The present invention has been completed based on this finding, by treating wastewater by a process including an exhaust gas absorption step, it is possible to treat nitrogen components in wastewater with high efficiency and stably for a long period of time.

That is, one of the present invention (hereinafter, referred to as "first invention") is a method for treating nitrate-containing wastewater, characterized by treating the nitrate-containing wastewater by 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) A step of stripping the ammonia nitrogen component from the primary treated water by blowing a gas into the primary treated water discharged in the step (1).

(3) A step of oxidatively decomposing the ammonia stripped in the step (2) with an oxidation catalyst.

Another invention (hereinafter, referred to as "second 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 the wastewater to ammonia nitrogen by contacting with a reducing solid catalyst.

(2) A step of stripping the ammonia nitrogen component from the primary treated water by blowing a gas into the primary treated water discharged in step (1).

(3) A step of absorbing the ammonia stripped in the step (2) with an absorbent.

[0015]

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 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. Usually, as nitrate nitrogen, 50 to 50,000
0 mg / l, preferably 100-20,000 mg / 1
It is good to do. 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.

Hereinafter, the first invention will be described in the steps (1) and (2).
A detailed description will be given in the order of and (3).

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 the 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, reduction in step (1) The treated water discharged after the treatment (referred to as "primary treated water" in the present invention) may contain nitrogen gas, undecomposed reducing substances, etc. in addition to ammonia nitrogen. In the present invention,
Since the wet reduction is performed using the solid catalyst for reduction described below, the reaction shown in (1) above is likely to occur, and the conversion of nitrate radicals into ammoniacal nitrogen can be efficiently performed.

The reducing substance used in the above (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 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-mentioned 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 solid catalyst is improved by using the catalyst A component in a proportion of 30% by weight or more. Among the catalyst A components, activated carbon is particularly preferably used, and by using activated carbon, a solid catalyst having excellent activity can be obtained.

Specific examples of the catalyst B component include metals, oxides and complex oxides of the above-mentioned 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 to 10 of the solid catalyst. It is good to set it as the weight%. 10
Even if it is used in a proportion exceeding 5% by weight, no corresponding improvement in reduction performance is observed, and since it is an expensive raw material, the cost of the solid catalyst increases, which is economically disadvantageous. Other than that, manganese, cobalt, nickel,
In the case of cerium, tungsten and copper (hereinafter referred to as "B-2 component"), the ratio (total amount) of the metal and / or compound is 0.05 to 70% by weight of the solid catalyst.
It is good to do. 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, a granular shape, a spherical shape, a pellet shape, or a ring shape, or an integral structure such as a honeycomb shape. 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, its average particle diameter is usually 1 to 10 mm, and particularly 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 300 ° 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 the reduction treatment may be any pressure as long as it can hold 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 into 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 cannot be sufficiently exerted.

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 waste water, it is preferable that the space velocity of the waste water with respect to the solid catalyst is 0.1 to 20 hr ^-1 , preferably 0.3 to 10 hr ^-1 . 0.1
When it is less than hr ⁻¹ , the processing apparatus becomes too large and it is inefficient, while when it exceeds 20 hr ⁻¹ , the reduction efficiency decreases.

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 ammonia nitrogen component (NH ₃ + NH ₄ ⁺ ) is stripped from the primary treated water by blowing gas into the treated water from the step (1). In particular,
The primary treated water containing ammonia nitrogen discharged from the step (1) is introduced into the stripping tower, and by blowing gas into the primary treated water, the ammonia nitrogen component is stripped from the primary treated water, A gas containing ammonia is discharged from the top of the stripping tower and treated water (in the present invention, referred to as "secondary treated water") is discharged from the bottom of the tower. When a part of the reducing substance used in the step (1) remains undecomposed in the primary treated water, the undecomposing reducing substance is stripped together with the ammonia nitrogen component. Prior to the stripping in step (2), nitrogen gas contained in the primary treated water may be separated in advance. In the following description, the gas containing ammonia and the like discharged from the step (2) is referred to as “exhaust gas”.

The gas used for the above stripping is not particularly limited, and a gas generally used for this type of stripping operation, such as air or steam, can be used. In addition, a gas discharged in the step (3) described later or a gas discharged from another facility can be used. These may be used alone or in appropriate combination. Further, the gas may be heated by heat exchange or the like before being introduced into the stripping tower, and it is preferable to introduce a high temperature gas in order to efficiently perform stripping.

Regarding the processing conditions in step (2),
When the properties of the wastewater and a part of the reducing substance used remain undecomposed, it can be appropriately determined in consideration of the type and amount used. Regarding the treatment temperature, the temperature of the primary treated water is preferably kept at 30 ° C. or higher, preferably 50 ° C. or higher, more preferably 70 ° C. or higher. Therefore, it is preferable that the temperature of the gas is heated to about the same as the processing temperature. If the treatment temperature is lower than 30 ° C, stripping is not sufficiently performed, which is not preferable. Further, the gas supply conditions are not particularly limited, and the gas may be supplied under the conditions generally used for this type of stripping operation.

In step (2), the pH of the secondary treated water
Is 6 to 14, preferably 10 to 14, and more preferably 1
It is preferable to add an alkaline substance to the primary treated water in advance so that the amount becomes 2 to 14, and to introduce this into the stripping tower. this is,
As shown in the following equation, regarding ammonia nitrogen in the primary treated water, ammonium ions and ammonia are in an equilibrium state, and when the pH or temperature of the primary treated water is increased, the proportion of ammonia increases and stripping occurs. This is because it becomes easier.

[0044]

Embedded image

Examples of the above-mentioned alkaline substance include hydroxides of alkali metals or alkaline earth metals, and specifically, sodium hydroxide, potassium hydroxide,
An aqueous solution of calcium hydroxide or the like is used. Of these, sodium hydroxide aqueous solution is preferably used in terms of price and solubility.

The secondary treated water discharged from the step (2) is 1
It can be recycled to the next treated water. In particular,
Part or all of the secondary treated water discharged from the bottom of the stripping tower is recycled and mixed with the primary treated water, and this is introduced to the top of the stripping tower. This recycling ratio can be appropriately determined according to the properties of the wastewater to be treated, the treatment status, and the like. By recycling in this way, advanced treatment of wastewater becomes possible.

Step (3) In step (3), if ammonia stripped in step (2) or undecomposed reducing substance is present, ammonia and undecomposed reducing substance are oxidatively decomposed by an oxidation catalyst. . Specifically, ammonia discharged from the step (2) or an exhaust gas containing ammonia and an undecomposed reducing substance is introduced into an exhaust gas combustor, where ammonia or ammonia and undecomposed in the presence of an oxidation catalyst. It is detoxified by oxidizing and decomposing or burning the reducing substance of and converting it into nitrogen gas, carbon dioxide gas and the like.

The oxygen used for the oxidative decomposition or combustion may be either oxygen alone or an oxygen-containing gas, but air is usually used. The amount of oxygen used, specifically, ammonia discharged from the top of the stripping column, or the ratio of exhaust gas containing ammonia and undecomposed reducing substance to oxygen, is not particularly limited and can be appropriately determined.
However, when the amount of oxygen is too large for ammonia or the like, side reactions represented by the formulas (2) and (3) are likely to occur in addition to the target reaction represented by the formula (1) below, and nitrogen oxidation is likely to occur. Things (NOx) are generated.

4NH ₃ + 3O ₂ → 2N ₂ + 5H ₂ O (1) 4NH ₃ + 5O ₂ → 4NO + 6H ₂ O ... (2) 4NH ₃ + 7O ₂ → 4NO ₂ + 6H ₂ O (3) As described above, since the amount of NOx produced tends to increase as the amount of oxygen used in the exhaust gas increases, ammonia in the exhaust gas from step (2), or ammonia and undecomposed reducing substances Is measured and the amount of oxygen or air supplied to the exhaust gas combustor is adjusted so that the reactions represented by the above formulas (2) and (3) do not occur, and NOx
It is better to suppress the generation of.

The gas detoxified by the exhaust gas combustion in the step (3) can be released to the atmosphere or can be returned to the step (2) and used as a stripping gas.

There is no particular limitation on the oxidation catalyst used in the step (3), and an oxidation catalyst generally used for oxidative decomposition or combustion of this kind of exhaust gas can be used. For example, as the catalyst A component, at least one oxide selected from titanium, silicon and zirconia, and as the catalyst B component, at least one metal or oxide selected from vanadium, tungsten and molybdenum,
As the catalyst component C, a catalyst containing at least one metal or oxide selected from platinum, palladium, rhodium, ruthenium, iridium, chromium, manganese, iron and copper can be used. As the catalyst A component, a binary complex oxide containing titanium and silicon, a binary complex oxide containing titanium and zirconia, and a ternary complex oxide containing titanium, silicon and zirconia are preferably used.

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

The treatment temperature for oxidative decomposition or combustion of the exhaust gas in the step (3) is in the range of 25 to 700 ° C., preferably 100 to 500 ° C. in order to decompose ammonia gas and the like efficiently. Good. 25
Decomposition efficiency is low below ℃, while N above 700 ℃
This is not preferable because the production of Ox increases.

The space velocity of the exhaust gas with respect to the oxidation catalyst is not particularly limited and may be appropriately determined depending on the composition of the exhaust gas and the characteristics of the oxidation catalyst, but it is 100 to 100,000 hours.
It is preferable to adjust r ⁻¹ , particularly in the range of 200 to 50,000 hr ⁻¹ . If it is less than 100 hr ^-1, the processing device is inefficient too large, whereas 100,000 ^-1
If it exceeds, the decomposition efficiency decreases.

The exhaust gas supplied to the exhaust gas combustor mainly contains ammonia, undecomposed reducing substances, etc., but contains components contained in the wastewater to be treated, such as COD components. May be. Alternatively, the gas may be mixed with a gas containing ammonia generated from other equipment for processing.

Next, one specific example of the first invention is shown in FIG. 1, and the processing method of the first invention will be described in detail with reference to this flow schematic diagram.

The nitrate-containing wastewater to be treated is introduced from the line 1, the reducing substance, for example, 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. Waste water is sent from the wet reduction reaction tower 6 to this heat exchanger 5
After the temperature is raised to the reaction start temperature by the secondary treatment water, it is supplied from the bottom to the wet reduction reaction tower 6 filled with the solid catalyst for reduction, where the nitrate radical in the waste water is reduced to ammonia nitrogen. The primary waste water after the reduction treatment is discharged from the line 7, cooled by the heat exchanger 5, and then decompressed by the pressure control valve 8 to perform the primary treatment of the primary treated water containing ammonia nitrogen, undecomposed methanol and the like. It is introduced into the water tank 9. Here, a harmless gas such as nitrogen gas in the primary treated water is discharged from the line 10 to the atmosphere. It should be noted that the primary treated water is directly separated in the primary treated water tank 9 without separating nitrogen gas and the like, and the diffusion tower 1
6 may be introduced (see FIG. 2).

If necessary, an alkaline substance is supplied from the line 11 to adjust the pH of the primary treated water, and then the primary treated water is introduced into the top of the stripping column 16 by the pump 13. The secondary treated water from the bottom of the stripping tower 16 may be recycled to the top of the stripping tower 16 by adjusting, for example, a valve 18 if necessary. From the lower part of the stripping tower 16, heated by the heat exchanger 20 via the line 21, for example, air is supplied, and gas-liquid contact is performed to make ammonia gas or ammonia gas and undecomposed from the primary treated water. Methanol is stripped, and the ammonia gas or the exhaust gas containing the ammonia gas and undecomposed methanol is discharged from the top of the stripping tower 16. On the other hand, the secondary treated water from which exhaust gas has been stripped is pumped from the bottom of the diffusion tower 16 to the pump
Discharge by 7. The exhaust gas from the stripping tower 16 is mixed with the air from the line 22 and then heat-exchanged with the processing gas from the exhaust gas combustor 26 in the heat exchanger 25 to raise the temperature to the reaction start temperature, and then filled with the oxidation catalyst. Exhaust gas combustor 2
Introduce to 6. Here, ammonia gas, or ammonia gas and undecomposed methanol are converted into harmless gases such as nitrogen gas and carbon dioxide gas. And this nitrogen gas,
The processing gas such as carbon dioxide gas is transferred to the heat exchanger 25,
After being used to raise the temperature of the exhaust gas from the stripping tower 16, the heat is further exchanged with the air from the line 21 in the heat exchanger 20 and then discharged to the atmosphere.

The path shown by the broken line in FIG. 1 is a path that is particularly used at the start of operation, and air is supplied to the preheating furnace 24 until the high-temperature processing gas is supplied to the heat exchanger 25. Then, the temperature is raised and the temperature is supplied to the exhaust gas combustor 26. Further, it is not necessary to supply all of the processing gas discharged from the exhaust gas combustor 26 to the heat exchanger 25, and it may be directly supplied to the heat exchanger 20 by operating the valve 27. Further, a part of the processing gas after the heat exchange in the heat exchanger 25 can be released to the atmosphere by operating the valve 28.

Next, the second invention will be described. The steps (1) and (2) are the same as the step (1) of the first invention.
And (2).

In the second invention, the exhaust gas from the step (2) is absorbed and removed using an absorbent. As the absorbent, any one can be used as long as it can absorb an ammonia gas and, in some cases, an undecomposed reducing substance. Conventionally known absorbents and absorption methods generally used for removing ammonia from a gas containing ammonia gas can be used. Representative examples of the absorbent include water, acidic aqueous solutions, alkaline aqueous solutions, and adsorbents such as activated carbon and zeolite. These may be used alone or in combination of two or more kinds. For example, when an acidic aqueous solution and an alkaline aqueous solution are combined, when NOx is by-produced, this NOx can also be efficiently absorbed and removed together with ammonia.

[0062]

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

Example 1 Wastewater containing 2% by weight of sodium nitrate and 3% by weight of ethanol was used as the wastewater containing nitrate radicals, and this was treated according to the schematic flow chart shown in FIG. The reducing substance (ethanol) / nitrate (molar ratio) in this wastewater is 2.8 /
It was 1.

<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.
The reduction treatment was performed under the conditions of. As the solid catalyst for reduction, an oxide of titanium and iron (TiO 2) as a component of catalyst A is used.
_A catalyst comprising ₂ : Fe ₂ O ₃ (weight ratio) = 10: 90 (99.4% by weight) and platinum (0.6% by weight) as a catalyst B component was used.

<Step (2)> The primary treated water discharged from the wet reduction reactor 6 was adjusted to pH 12 by adding an aqueous sodium hydroxide solution and then supplied to the upper part of the stripping tower 16.
On the other hand, air was supplied from the lower part of the stripping tower 16 to strip ammonia components and the like. The treatment conditions in the stripping tower 16 are as follows: treatment temperature (temperature of primary treated water) 50 ° C., liquid gas ratio L / G (= liquid supply amount / gas supply amount) 1.0 kg /
It was Nm ³ .

<Step (3)> The exhaust gas (gas containing ammonia gas) discharged from the wet reduction reactor 6 is mixed with air to adjust the ammonia concentration in the exhaust gas to 5,000 pp.
After adjusting to m, it is introduced into the exhaust gas combustor 25, where the reaction temperature is 350 ° C. and the space velocity of gas relative to the catalyst is 5,000
The treatment was carried out under the condition of ⁰ hr ^-1 . A honeycomb-shaped oxidation catalyst containing a binary composite oxide containing titanium and zirconium and vanadium, tungsten and palladium was used as the oxidation catalyst.

As a result, the ammonia nitrogen concentration in the treated water (secondary treated water) discharged from the stripping tower 16 was 10 mg.
/ L or less, nitrate nitrogen concentration is 20 mg / l or less,
Further, the ammonia concentration in the treated gas discharged from the exhaust gas combustor 26 was 10 ppm, and the nitrogen oxide concentration was 4 ppm.

Example 2 Wastewater containing 5% by weight of sodium nitrate was used as the nitrate-containing wastewater, and 4% methanol was used as a reducing substance in this wastewater.
It was added so as to be in a weight% and treated according to the schematic flow chart shown in FIG. The reducing substance (ammonia + methanol) / nitrate (molar ratio) in this waste water was 3/1.

<Step (1)> The above waste water was introduced into the wet reduction reactor 6, the reaction temperature (waste water temperature) was 250 ° C., the reaction pressure was 70 kg / cm ² G, and the space velocity for the catalyst was ¹ hr ^−1.
The reduction treatment was performed under the conditions of. As a solid catalyst for reduction, titanium oxide (99% by weight) as a catalyst A component
A catalyst composed of palladium (1% by weight) as the catalyst B component was used.

<Step (2)> Stripping was performed under the same conditions as in Example 1.

<Step (3)> The exhaust gas (gas containing ammonia gas) discharged from the wet reduction reactor 6 is mixed with ammonia and air discharged from other equipment to adjust the ammonia concentration to 1% by volume. The same procedure as in Example 1 was carried out except that the oxidative decomposition was carried out.

As a result, the ammonia nitrogen concentration in the treated water (secondary treated water) discharged from the stripping tower 16 was 10 mg.
/ L or less, nitrate nitrogen concentration is 50 mg / l or less,
Further, the ammonia concentration in the treated gas discharged from the exhaust gas combustor 26 was 10 ppm, and the nitrogen oxide concentration was 4 ppm.

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 + methanol) / nitrate (molar ratio) in this wastewater is 1.75.
It was / 1.

<Step (1)> The above waste water was introduced into the wet reduction reactor 6, the reaction temperature (waste water temperature) was 250 ° C., the reaction pressure was 70 kg / cm ² G, and the space velocity for the catalyst was ¹ hr ^−1.
The reduction treatment was performed under the conditions of. As the reducing solid catalyst, a catalyst composed of activated carbon (98% by weight) as the catalyst A component and palladium (2% by weight) as the catalyst B component was used.

<Step (2)> Stripping was performed under the same conditions as in Example 1.

<Step (3)> Oxidative decomposition was carried out under the same conditions as in Example 1.

As a result, the ammonia nitrogen concentration in the treated water (secondary treated water) discharged from the stripping tower 16 was 10 mg.
/ L or less, nitrate nitrogen concentration is 20 mg / l or less,
Further, the ammonia concentration in the treated gas discharged from the exhaust gas combustor 26 was 10 ppm, and the nitrogen oxide concentration was 4 ppm.

[0078]

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 composed of 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 flow system diagram showing an example of a processing method of the present invention.

FIG. 2 is a flow system diagram showing another example of the processing method of the present invention. (1) Waste water supply line (2) Reductant supply line (3) Booster pump (4) Reductant supply pump (5) Heat exchanger (6) Wet reduction reactor (7) Line (8) Pressure control valve (9) ) Primary treated water tank (10) Line (11) Alkaline substance supply line (12) Alkaline substance supply pump (13) Primary treated water supply pump (16) Dispersion tower (17) Primary treated water discharge pump (18) Valve (20) Heat exchanger (21) Air supply line (22) Air supply line (23) Treated gas discharge line (24) Preheating furnace (25) Heat exchanger (26) Exhaust gas combustor (27) Treated water discharge line

Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C02F 1/20 ZAB B01D 53/36 ZABE 1/58 ZAB B01J 23/64 103M (72) Inventor Yukihiro Yoneda Hyogo prefecture 1 992 Nishioki, Okihama, Aboshi-ku, Himeji City

Claims (9)

[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) A step of stripping the ammonia nitrogen component from the primary treated water by blowing a gas into the primary treated water discharged in the step (1). (3) A step of oxidatively decomposing the ammonia stripped in the step (2) with an oxidation catalyst. 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 method according to claim 1, wherein 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. 5. The reducing substance is present in a ratio of 0.5 ≦ reducing substance / nitrate (molar ratio) ≦ 10.
The described method. 6. The method according to claim 1, wherein in the step (2), the gas after the oxidative decomposition in the step (3) is used as the gas blown into the primary treated water. 7. The step after stripping in step (2)
The method according to claim 1, wherein an alkaline substance is added in advance to the primary treated water so that the pH of the secondary treated water becomes 6 to 14. 8. The method of claim 1 wherein the secondary treated water from step (2) is recycled to the primary treated water from step 1. 9. 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., under a pressure at which the wastewater retains a liquid phase, and without substantially supplying oxygen, it is contacted with a reducing solid catalyst to wet the nitrate radical in the wastewater into ammonia nitrogen. The process of reducing. (2) A step of stripping ammonia nitrogen components from the primary treated water by blowing gas into the primary treated water from the step (1). (3) A step of absorbing the ammonia stripped in the step (2) with an absorbent.