JPH1066985A - Treatment of nitrogen compound-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the residual nitrogen in a treated water to sufficiently low concentration by volatilizing the treated water after nitrogen compounds in nitrogen compounds-containing waste water is decomposed into ammonia and then oxidation-decomposing the ammonia in the flow-out water and the waste gas to convert the nitrogen oxides to harmless gaseous nitrogen. SOLUTION: The nitrogen compounds-containing waste water is heated in the presence of a catalyst to decompose the nitrogen compounds to ammonia by heating in nitrogen compounds decomposition process as a 1st process. The treated water containing the produced ammonia is volatilized in an alkaline region in an ammonia valatilizing process as a 2nd process to transfer almost all of ammonia to a gas phase. A small quantity of ammonia remaining in a water flowing-out from the valatilizing process is oxidation-decomposed in the presence of a catalyst with the addition of an oxidizing agent in a liquid ammonia decomposition process as a 3rd process. The gas discharged from the volatilizing process containing ammonia is converted to the harmless gaseous nitrogen by oxidizing ammonia with oxygen in air in a gas phase ammonia decomposition process as a 4th process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating wastewater containing nitrogen compounds. More specifically, the present invention efficiently and economically treats wastewater containing a high concentration of a nitrogen compound that produces ammonia by thermal decomposition or oxidative decomposition of urea, hydrazine, monoethanolamine, etc. The present invention relates to a method for treating wastewater containing nitrogen compounds, which can prevent discharge of harmful substances into the wastewater.

[0002]

2. Description of the Related Art When released into water, nitrogen compounds cause eutrophication. When released into the atmosphere as nitrogen oxides, they are not only harmful to health but also involved in photochemical reactions. And contribute to a secondary compound pollution phenomenon called smog. For this reason, the wastewater containing the nitrogen compound must be subjected to the denitrification treatment, and the volatilization of the nitrogen compound into the air during the treatment step must be prevented. Methods for treating nitrogen in wastewater include biological treatment, nitrification and denitrification, discontinuous point chlorine, ion exchange resin, electrodialysis,
There is an ammonia stripping method and the like. The wastewater containing urea may be diluted and discharged, or may be subjected to biological treatment. However, the biological treatment method has a problem that the decomposition time is long and the installation area of the treatment apparatus is large. It is known that a wastewater containing hydrazine is subjected to an oxidation treatment by aeration in the presence of copper ions, but the treatment takes about one day due to a low reaction rate. For wastewater containing monoethanolamine, a decomposition method utilizing a catalytic reaction has been proposed, but has not yet been put to practical use. It is known that urea is hydrolyzed by heating an aqueous solution to produce ammonia, and converted to nitrogen when reacted with nitrous acid, as shown by the following formula. CO (NH ₂ ) ₂ + H ₂ O → CO ₂ + 2NH ₃ CO (NH ₂ ) ₂ + 2HNO ₂ → 2N ₂ + CO ₂ + 3H ₂ O When hydrazine is heated in the presence of air, hydrazine is reduced to about 1
It is known that ammonia and nitrogen generate and decompose at 80 ° C. Further, it has been confirmed that monoethanolamine is decomposed by heating to produce ammonia. However, there is no known method for utilizing these reactions for wastewater treatment. The reaction between urea and nitrous acid requires a large amount of nitrous acid when urea is contained in a high concentration, and cannot be used economically for wastewater treatment. Wastewater containing a high concentration of nitrogen compounds cannot obtain sufficient treated water quality only by heat treatment. Further, even if the nitrogen compound is converted to ammonia, the nitrogen content in the wastewater does not decrease, so that further treatment is required.

[0003]

SUMMARY OF THE INVENTION In the treatment of wastewater containing a high concentration of nitrogen compounds, the present invention reduces the cost of an oxidizing agent required for the decomposition treatment of nitrogen compounds and reduces harmful nitrogen compounds into the atmosphere. It is an object of the present invention to provide a method for treating nitrogen compound-containing wastewater, which can convert nitrogen compounds into harmless nitrogen gas without discharging, and can reduce residual nitrogen in treated water to a sufficiently low concentration. Things.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have heated wastewater containing nitrogen compounds to decompose nitrogen compounds into ammonia, and vaporized ammonia by volatilization. It has been found that nitrogen compounds in wastewater can be efficiently decomposed to harmless nitrogen gas by transferring to the gas phase and oxidizing it to form nitrogen gas and oxidizing and decomposing ammonia remaining in the water phase. Thus, the present invention has been completed. That is, the present invention provides: (1) (1) a nitrogen compound decomposition step of heat-treating a nitrogen compound-containing wastewater in the presence of a catalyst to decompose nitrogen compounds into ammonia; (3) A liquid phase in which an oxidizing agent is added to the effluent from the ammonia volatilization step, and ammonia is oxidatively decomposed in the presence of a catalyst. Ammonia decomposition step, and
(4) A method for treating nitrogen compound-containing wastewater, comprising: a gas phase ammonia decomposition step of oxidatively decomposing ammonia by contacting an exhaust gas from an ammonia volatilization step with a catalyst. Further, as a preferred embodiment of the present invention, (2) in the nitrogen compound decomposition step, a titania catalyst or a noble metal-supported titania catalyst packed tower is used, and
(1) The method for treating wastewater containing nitrogen compounds according to (1), wherein the treatment is carried out at a temperature of SV = 0.1 to 10 hr ^-1.
The method for treating nitrogen compound-containing wastewater according to item (1), wherein air stripping is performed at a temperature of 0 ° C. or more and a gas-liquid ratio (G / L) of 1,000 to 5,000 times. , Water temperature 8
The method for treating nitrogen compound-containing wastewater according to item (1), wherein the steam is stripped at a temperature of 0 ° C. or more and a steam amount / treatment solution amount ratio of 5 to 20%. (5) In the liquid phase ammonia decomposition step, Addition of sodium nitrite or hydrogen peroxide (1)
(6) In the liquid phase ammonia decomposition step, a noble metal-supported titania catalyst packed column is used at 100 to 180 ° C, SV =
(1) The method for treating wastewater containing a nitrogen compound according to (1), wherein the wastewater is treated at 0.1 to 20 hr ^-1 . SV
(1) The method for treating wastewater containing nitrogen compounds according to (1), wherein the treatment is performed at 10,000 to 50,000 hr ^-1 , and (8) the vanadium-
Using a titania-based reduction catalyst packed tower, 250 to 450 ° C,
SV = 3,000~20,000hr ^-1 at the (1) reduction treatment the NO _x which byproduct processing method of a nitride wastewater according to claim, and the like.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention can be applied to wastewater containing a nitrogen compound such as urea, hydrazine and monoethanolamine which decomposes upon heating to produce ammonia. FIG. 1 is a process flow diagram of the present invention.
In the first nitrogen compound decomposition step, the nitrogen compound-containing wastewater is heated in the presence of a catalyst to decompose the nitrogen compound into ammonia. It is considered that urea, hydrazine, and monoethanolamine each react as shown in the following formula to generate ammonia. CO (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂ 3N ₂ H ₄ → 4NH ₃ + N ₂ 2N ₂ H ₄ → 2NH ₃ + H ₂ + N ₂ H ₂ NCH ₂ CH ₂ OH + H ₂ O → NH ₃ + HOCH ₂ CH
Examples of the catalyst used for the decomposition of ₂ OH nitrogen compounds include, for example, porous granular catalysts such as titania, silica alumina, and alumina, and catalysts in which noble metals such as platinum, ruthenium, and palladium are supported on these granular materials. Can be. Among these, a titania catalyst and a noble metal-supported titania catalyst are particularly preferable because of high stability of performance in a decomposition reaction of a nitrogen compound into ammonia. The reaction temperature in the nitrogen compound decomposition step is preferably from 80 to 200C, more preferably from 140 to 175C. If the reaction temperature is lower than 80 ° C., the reaction may be slow, a long time may be required for the treatment, or the decomposition rate to ammonia may not be sufficiently increased. When the reaction temperature exceeds 200 ° C,
A reactor with high pressure resistance is required. The reaction format is
It is preferable to pass water through the catalyst packed tower, and the treatment speed is S
V = 0.1 to 10 ^- and is preferably ^1, SV = 1
More preferably, it is ５5 hr ⁻¹ . If the reaction is carried out under the above conditions, it is usually unnecessary to make the SV less than 0.1 hr ^-1, and if the SV is too small, the reactor becomes large.
If the SV exceeds 10 hr ^-1 , the decomposition of the nitrogen compound into ammonia may not proceed sufficiently. In the nitrogen compound decomposition step, usually 90% or more of the nitrogen content is converted to ammonia. Depending on the setting of reaction conditions, a conversion of 99% or more can be achieved.

[0006] The treated water containing a nitrogen compound decomposing step containing ammonia generated by decomposition of the nitrogen compound is then sent to the ammonia volatilization step of the second step, where it is volatilized in an alkaline region to transfer most of the ammonia to the gas phase. .
Ammonia in water

Embedded image The equilibrium shifts to the right by increasing the pH or increasing the temperature, and ammonia can be volatilized by raising the pH or increasing the temperature. In the method of the present invention, any of an air stripping method and a vapor stripping method can be used for volatilization of ammonia. The air stripping method is a method in which the pH of water containing ammonia nitrogen is increased to bring the pH into contact with air, and ammonia is volatilized using the air as a carrier gas. The pH of water is preferably 7 or more, more preferably 9 or more, and 10 or more.
More preferably, it is the above. If the pH of the water is about 7, almost no ammonia can be volatilized at room temperature, so the water must be heated, but if the pH is 9 or more, the ammonia can be easily volatilized, Then, even at room temperature, 80% or more of ammonia can be volatilized. The water temperature is preferably 20 ° C. or higher. If the water temperature is lower than 20 ° C., the amount of air required for volatilization of ammonia increases, and it may take a long time. The amount of air blown is 1,000 gas-liquid ratio (G / L).
It is preferably from 0 to 5,000 times. Gas-liquid ratio is 1.0
If it is less than 00 times, the volatilization of ammonia may be insufficient. A gas-liquid ratio of 5,000 times is sufficient and usually does not need to exceed 5,000 times.
In the air stripping method, since oxygen is contained in the gas, it serves as an oxygen source when processing the ammonia-containing gas in the subsequent stage, and is thus preferable.

The steam stripping method is a method in which water containing ammonia nitrogen is preheated, steam is blown, and ammonia is volatilized using steam as a carrier gas. Steam stripping can be performed neutrally,
Preferably, the pH of the water is 7 or higher. If the pH of the water is less than 7, it is difficult to vaporize ammonia efficiently even by steam stripping. Water temperature is 80 ℃
It is preferable that it is above. When the water temperature is lower than 80 ° C., the amount of water vapor condensed increases, and the effect of the steam stripping method may not be sufficiently exerted.
The amount of steam to be blown is 5 to 20% in the ratio of steam amount / treatment liquid amount.
It is preferred that If the ratio of the amount of steam / the amount of the processing solution is less than 5%, the volatilization of ammonia may be insufficient. It is sufficient that the ratio of the amount of steam / the amount of the processing liquid is 20%, and usually the ratio of the amount of steam / the amount of the processing liquid does not need to exceed 20%. The vapor stripping method has a smaller amount of radiated gas than the air stripping method and can obtain a high-concentration ammonia-containing gas. 90% by air stripping or steam stripping
The above-mentioned ammonia can be volatilized and transferred to the gas phase.

Since a small amount of ammonia still remains in the water flowing out of the ammonia volatilization step, an oxidizing agent is added to oxidize and decompose ammonia in the presence of a catalyst in the liquid phase ammonia decomposition step of the third step. The oxidizing agent to be added is not particularly limited, and examples thereof include sodium nitrite, hydrogen peroxide, and sodium hypochlorite. Ammonia reacts with these oxidizing agents according to the following formula to form harmless nitrogen gas. NH ₃ + NaNO ₂ → N ₂ + H ₂ O + NaOH 2NH ₃ + 3H ₂ O ₂ → N ₂ + 6H ₂ O The added amount of the oxidizing agent is an amount corresponding to the reaction equivalent calculated from the above formula or the like or a slightly excessive amount. Is preferred. Examples of the catalyst to be used include a catalyst in which a noble metal such as platinum, ruthenium, and palladium is supported on a porous granular catalyst such as titania, silica alumina, and alumina. Among them, a noble metal-supported titania catalyst is particularly preferable because of its high decomposition rate of ammonia. The reaction temperature in the liquid phase ammonia decomposition step is 100 to 1
The temperature is preferably 80 ° C, more preferably 140 to 175 ° C. If the reaction temperature is lower than 100 ° C., the reaction may be slow, a long time may be required for the treatment, or the decomposition rate of ammonia may not be sufficiently increased. When the reaction temperature exceeds 180 ° C., a reactor having a high pressure resistance is required. As for the reaction mode, it is preferable to pass water through a catalyst packed column. Processing speed is preferably SV = 0.1 to 20 ^-1, more preferably SV = 1~10hr ^-1. If the reaction is carried out under the above conditions, the SV is usually set at 0.
It is not necessary to set the reaction time to less than ¹ hr ^-1, and if the SV is too small, the reactor becomes large. When SV exceeds 20hr ^-1
The decomposition of ammonia may not proceed sufficiently. In the liquid phase ammonia decomposition step, usually 98% or more of ammonia is converted to nitrogen gas and removed.

The ammonia-containing gas discharged from the ammonia stripping step is mixed with air in the case of the air stripping method as it is, or in the case of the steam stripping method, by mixing air to supply oxygen. Send to ammonia decomposition process. In the gas-phase ammonia decomposition step, as shown in the following equation, ammonia is oxidized by oxygen in the air to form harmless nitrogen gas. 4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O As a catalyst used for the gas phase oxidative decomposition of ammonia, for example, a catalyst in which a noble metal such as platinum, ruthenium, or palladium is supported on a porous granular catalyst such as titania, silica alumina, or alumina And the like. Among these, a platinum-supported catalyst is particularly preferred because of its high decomposition rate of ammonia. The reaction temperature of the gas phase ammonia decomposition step is
The temperature is preferably from 200 to 400 ° C. Reaction temperature 2
If the temperature is lower than 00 ° C., the reaction may be slow, a long time may be required for the treatment, or the decomposition rate of ammonia may not be sufficiently increased. When the reaction temperature exceeds 400 ° C., heat-resistant materials are required for the equipment, and the energy consumption increases. In the reaction mode, it is preferable to vent the catalyst into the packed column, and the superficial velocity is SV = 10,000 to 50,000 hr ^-1.
It is preferred that If the SV is less than 10,000 hr ^-1 , the size of the reaction apparatus increases. SV is 50,000hr
^If it exceeds ^-1 , the oxidative decomposition of ammonia may not proceed sufficiently.

During the gas phase oxidative decomposition reaction of ammonia, NO _x may be by-produced due to a side reaction represented by the following formula. 4NH ₃ + 5O ₂ → 4NO + 6H ₂ O By-product NO _x can be reduced to harmless nitrogen gas by ammonia remaining in the processing gas or by adding a gas containing ammonia as shown in the following formula. . The catalyst used in the reduction reaction with ammonia _{4NO + 4NH 3 + O 2 →} 4N 2 + 6H 2 O NO x, for example, vanadium - titania catalyst, copper and the like loaded with zeolite catalyst to. The reaction temperature of the reduction reaction with ammonia of the NO _x is, 250-45
Preferably it is 0 ° C. When the reaction temperature is lower than 250 ° C., the reaction is slow and requires a long time for the treatment.
_Ox may not be sufficiently removed. Reaction temperature 4
If the temperature exceeds 50 ° C., heat-resistant materials are required for the equipment, and the energy consumption increases. In the reaction mode, it is preferable to vent to the catalyst packed column, and the superficial velocity is SV = 3.0.
It is preferably from 00 to 20,000 hr ^-1 . If the SV is less than 3,000 hr ^-1 , the size of the reaction apparatus increases.
If the SV exceeds 20,000 hr ⁻¹ , the reduction reaction of NO _x with ammonia may not proceed sufficiently. According to the method for treating nitrogen compound-containing waste water of the present invention, most of the generated ammonia is transferred to the gas phase by volatilization treatment, and is converted to nitrogen gas by oxidative decomposition by oxygen in the air.
The required amount of the oxidizing agent can be greatly reduced as compared with the conventional method in which the oxidizing agent is added and oxidatively decomposed in the liquid phase. Further, since the amount of ammonia to be processed in the liquid phase is reduced, the load of the liquid phase processing whose reaction rate is lower than that in the case of the gas phase processing is reduced, the liquid phase processing equipment is downsized, and The total nitrogen concentration can be sufficiently reduced.

[0011]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Example 1 Water containing 10,000 mg / liter of monoethanolamine was prepared, and a column packed with 50 ml of a titania catalyst having an average particle size of 1.5 mm and supporting 0.5% by weight of platinum was prepared under the condition of pH 10.2. At 170 ° C., 50 ml / hr or S
The solution was passed at a flow rate of V1 hr ^-1 . The concentration of ammonia nitrogen in the treated water was 2,260 mg / liter, and the nitrogen component of monoethanolamine was almost completely converted to ammonia nitrogen. 1,000 ml of treated water, pH 1
After being adjusted to 0, the mixture was put into a volatilization treatment tower filled with glass beads having a diameter of 3 mm in an acrylic resin column having an inner diameter of 50 mm and a height of 1,500 mm. Treated for 1 hour. The concentration of ammonia nitrogen remaining in the water after treatment is 136mg
/ Liter. Sodium nitrite was added to the treated water so that the molar ratio of nitrite nitrogen to ammonia nitrogen was 1.0, and the pH was adjusted to 6.5.
50% by weight of a titania catalyst having an average particle size of 1.5 mm carrying
l at 165 ° C at 200 ml / h
r, that is, the liquid was passed through at a flow rate of SV 4 hr ^-1 . The concentration of ammoniacal nitrogen in the treated water was 5 mg / l or less, and the total nitrogen concentration was 10 mg / l or less. Further, the average concentration of ammonia in the volatilized gas generated in the above volatilization treatment was 1,130 ppm (volume ratio). 150 ml of an oxidation catalyst in which 0.5% by weight of platinum is supported on γ-alumina
The filled stainless steel reactor having an inner diameter of 50 mm was directly connected to a stainless steel reactor filled with 500 ml of a vanadium-titania-based reduction catalyst, and the above-mentioned volatile gas was heated to 330 ° C. (SV) 20,000
0 hr ^-1 , superficial velocity (SV) 6,000 hr with respect to the reduction catalyst
^It was passed at a flow rate of ^-1 . Ammonia concentration in processing gas is 1pp
m (volume ratio) or less, NO _X concentration was 17 ppm (by volume). Example 2 Water containing 10,000 mg / liter of hydrazine was prepared, and a column packed with 50 ml of a titania catalyst having an average particle size of 1.5 mm and supporting 0.5 wt% of platinum at pH 10 was placed at 95 ° C. The solution was passed at a flow rate of 50 ml / hr, that is, SV ¹ hr ^-1 . The concentration of ammoniacal nitrogen in the treated water was 5,830 mg / liter. Treated water 1,00
After adjusting 0 ml to pH 10, the inner diameter is 50 mm, the height is 1,
A 500 mm acrylic resin column was charged into a volatilization tower filled with glass beads having a diameter of 3 mm, and air was blown from the lower portion of the column with an air diffuser at a rate of 50 Nl / min to be treated for 1 hour. The concentration of ammoniacal nitrogen remaining in the water after the treatment was 804 mg / l. Sodium nitrite was added to the treated water so that the molar ratio of nitrite nitrogen to ammonia nitrogen was 1.0, and the pH was adjusted to 6.5. The solution was passed through a column packed with 50 ml of a titania catalyst having a diameter of 1.5 mm at 165 ° C. at a flow rate of 100 ml / hr, that is, an SV of 4 hr ⁻¹ . The concentration of ammoniacal nitrogen in the treated water was 5 mg / l or less, and the total nitrogen concentration was 10 mg / l or less. Further, the average concentration of ammonia in the volatile gas generated in the above-mentioned volatile treatment was 2,680 ppm (volume ratio). A stainless steel reactor having an inner diameter of 50 mm filled with 150 ml of an oxidation catalyst having 0.5 wt% of platinum supported on γ-alumina and a stainless steel reactor charged with 500 ml of a vanadium-titania-based reduction catalyst were directly connected to each other, and the above-mentioned volatilization was performed. After heating the gas to 330 ° C., the gas was passed through the oxidation catalyst at a superficial velocity (SV) of 20,000 hr ⁻¹ and the reduction catalyst at a superficial velocity (SV) of 6,000 hr ⁻¹ . Ammonia concentration in the process gas is below 1 ppm (volume ratio), NO _X concentration 1
It was 5 ppm (by volume).

[0012]

According to the method of the present invention, most of the generated ammonia is transferred to the gas phase by volatilization, and is oxidized and decomposed by oxygen in the air to be converted into nitrogen gas. The required amount of the oxidizing agent can be greatly reduced as compared with the method of oxidative decomposition by adding an oxidizing agent.
In addition, since the amount of ammonia to be treated in the liquid phase is reduced, the load of the liquid phase treatment whose reaction rate is lower than in the case of the gas phase treatment is reduced, the liquid phase treatment equipment is downsized, and Can be sufficiently reduced.

[Brief description of the drawings]

FIG. 1 is a process flow diagram of the present invention.

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location C02F 1/58 CDV C02F 1/58 ZABP ZAB B01D 53/36 ZABE

Claims (1)

[Claims] (1) a nitrogen compound-decomposing step of heat-treating a nitrogen-compound-containing wastewater in the presence of a catalyst to decompose nitrogen compounds into ammonia; and (2) a nitrogen compound-decomposing step in which the treated water is volatilized in an alkaline region. An ammonia volatilization step of treating and transferring most of the ammonia to a gaseous phase, (3) a liquid phase ammonia decomposition step of adding an oxidizing agent to the effluent from the ammonia volatilization step and oxidatively decomposing ammonia in the presence of a catalyst; And (4) a gas-phase ammonia decomposition step of oxidizing and decomposing ammonia by contacting an exhaust gas from the ammonia volatilization step with a catalyst.