CN1678535A

CN1678535A - Method of treating waste water containing high level nitrate-nitrogen

Info

Publication number: CN1678535A
Application number: CNA03820133XA
Authority: CN
Inventors: 村木务; 塙正治; 长谷胜典; 石崎真; 柴山治雄
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2002-08-29
Filing date: 2003-08-27
Publication date: 2005-10-05
Also published as: AU2003264341A1; KR100659996B1; KR20050059112A; JPWO2004020347A1; WO2004020347A1

Abstract

A method of chemical treatment for waste water containing nitrate-nitrogen, in which waste water containing nitrate-nitrogen can be treated under atmospheric pressure and in which high level nitrate-nitrogen can be effectively treated. This method is characterized by comprising adding hydrazine or a salt thereof to waste water to be treated, reducing the nitrate-nitrogen to nitrite-nitrogen in the presence of sponge copper catalyst and thereafter bringing the water to be treated containing the nitrite-nitrogen into contact with at least one amide so as to carry out quantitative and chemical reduction to nitrogen through diazotizing reaction.

Description

Method for treating discharge water containing high concentration of nitrate nitrogen

Technical Field

The present invention relates to a method for treating waste liquids, such as nitric acid or nitrite, used in the chemical industry for the production of inorganic pigments or dyes, or for treating effluent water from metal product production plants, especially effluent water containing high concentrations of nitrate nitrogen.

Background

As the emission source of the nitrogen-containing compound at a high concentration, there can be mentioned nitric acid and nitrite used in the chemical industry for producing inorganic pigments or dyes, and nitric acid, nitrous acid and salts thereof and ammonia used in the metal product and semiconductor manufacturing industries. When discharged in closed waters such as inland sea, bay or lake, the discharged water containing such nitrogen compounds causes eutrophication and a severely polluted environment. Therefore, the discharged water containing the nitrogen-containing compound must be subjected to denitrification treatment.

As typical denitrification methods in the discharged water, there can be mentioned biological methods utilizing denitrification capability of microorganisms, physicochemical methods such as ion exchange method, reverse osmosis method or electrodialysis method, and chemical methods in which hydrogen gas is dissolved under pressure in the discharged water to be treated so as to reduce nitrate nitrogen in the presence of a catalyst.

However, the above-mentioned denitrification method has some problems as described below.

That is, although the biological process utilizing the denitrification capability of microorganisms is the cheapest in operation cost and the most widely used, it is difficult to use it for the effluent water containing nitrate nitrogen up to about 10 g/l or more because of the low reaction speed, and the treatment capability of the apparatus becomes unstable due to fluctuation of the nitrate nitrogen concentration in the effluent water to be treated, resulting in failure to meet the quality standard of the effluent water. In addition, there is a problem in that secondary waste such as excessive activated sludge is generated as a result of the denitrification process.

In the physicochemical method, the processor can be made small, and assured processing can be expected; however, since the method described separates and concentrates nitrate nitrogen of the discharged water, there is ultimately a problem that it is necessary to separately treat the nitrate nitrogen-concentrated liquid.

On the other hand, in the chemical method, since clean hydrogen is used to reduce nitrate nitrogen or nitrite nitrogen, the reaction speed is higher and the processor can be made smaller compared to the biological method. However, due to the chemical nature of hydrogen, its solubility in water is low; therefore, like the biological method, there is a problem that the method is not sufficient for treating the discharged water containing a high concentration of nitrate nitrogen.

Disclosure of the invention

The present invention has been made in view of the above problems of the prior art, and provides a method of treating discharged water containing high concentration of nitrate nitrogen, with which a treater can be made small, a detoxification process can be completed in a short time, stable treatment can be performed regardlessof fluctuations in the nitrate nitrogen concentration load or the volume of discharged water during a day, and the amount of secondary waste generated is small.

The present invention relates to a method for treating discharge water containing nitrate nitrogen at a high concentration, comprising a first reduction step in which nitrate nitrogen is reduced to nitrite nitrogen using hydrazine or a salt thereof as a reducing agent in the presence of a sponge copper catalyst, and a second reduction step in which nitrite nitrogen contained in water after the treatment in the first reduction step is contacted with at least one amide so as to be converted into nitrogen gas. The pH of the solution treated in the first reduction step is set to 8 to 14, and the pH of the solution treated in the second reduction step is set to 3.5 or less. Further, the at least one amide is selected from amide sulfuric acid, urea, and mixtures thereof.

That is, the present invention is a method in which the discharged water containing a high concentration of nitrates is treated in a two-step reduction process of a first reduction step and a second reduction step. In the first and second reduction steps, nitrate nitrogen or nitrite nitrogen is completely processed into nitrogen and carbon dioxide or acid anions.

Best mode for carrying out the invention

The invention relates to a chemical compoundA method for chemically treating nitrate nitrogen contained in discharge water to be treated. The method comprises a first reduction step in which hydrazine or a salt thereof is added to the effluent water to be treated and nitrate nitrogen is converted to nitrite nitrogen using a sponge copper catalyst, and a second reduction step in which the water to be treated containing nitrite nitrogen obtained in the first reduction step is contacted with at least one amide and a diazotization reaction is usedShould, quantitatively and chemically reduce to nitrogen (N)₂). The method of contacting the catalyst with the effluent water to be treated may be a batch system or a continuous system.

The sponge copper catalyst used in the present invention is a catalyst prepared by eluting aluminum from an alloy of copper and aluminum. Sponge copper catalysts are commonly used for the hydrogenation of organic compounds. However, in the first reduction step of the present invention, nitrate nitrogen is reduced to nitrite nitrogen in the presence of hydrazine due to a reaction according to the following [ equation 1]as a main reaction.

[ equation 1]

In the present invention, the pH of the discharged water to be treated in the first reduction step is set to 8 to 14. This is because the reaction rate of reducing nitrate nitrogen often decreases when the pH of the discharged water to be treated is low. Therefore, it is preferable to control the pH of the discharged water to be treated so as to be 8 or more. On the other hand, when the pH of the discharged water to be treated is more than 14, it is economically disadvantageous because more alkali is required for control.

In addition, the amide suitable for use in the second reduction step of the present invention is at least one amide, and hydrolysis proceeds to produce an environmentally friendly product. The choice of amide depends on the type of end product. Generally preferred at least one amide includes amide sulfuric acid, urea, and mixtures thereof, selected from the amide chemicals most preferably used for reducing nitrite to nitrogen and acid anions or carbon dioxide. Depending on the concentration of nitrite at the beginning of its conversion reaction to nitrogen, the pH may vary from about 0.5 to 6; but the control of the pH required to maintain the optimum pH range of the amide used is carried out. Preferably, the pH is controlled to be in the range of 0.5 to 3.5.

In the second reduction step, nitrite nitrogen is reduced to nitrogen gas in the presence of nitrite and at least one amide due to the reaction [ equation 2]below as the main reaction.

For example, in the case of amidosulfuric acid, [ equation 2]is

In the case of urea, [ equation 2]is

In the second reduction step, the pH of the discharged water to be treated is set to 3.5 or less. This is because nitrate nitrogen is often not sufficiently reduced when the pH of the effluent water to be treated is raised. Therefore, it is desirable to control the pH of the discharged water to be treated to 3.5 or less.

In the method of treating nitrate containing discharged water of the present invention, the discharged water may be treated under normal pressure. Thus, the treater using the method of the present invention does not require equipment for pressurizing the discharge water, and the method can be economically performed, and the treater is small in size and easy to control.

Examples

In examples 1 and 2, experiments were conducted in which nitrate nitrogen was converted to nitrite nitrogen in an aqueous solution in order to confirm the utility of the first reduction step of the present invention. In examples 3-5, a series of experiments were conducted in order to demonstrate the utility of the second reduction step of the present invention, i.e., a reduction process inwhich at least one amide selected from the group consisting of amidosulfuric acid, urea, and mixtures thereof, is used to reduce nitrite nitrogen to nitrogen.

Example 1

7.5 ml of hydrazine hydrate reagent (20 mol/l) and 20 g of sponge copper catalyst were added to 200 ml of a 1 mol/l (14 g/l as N) sodium nitrate solution, followed by stirring for 6 hours while the solution was maintained at 50 ℃ and atmospheric pressure and the pH of the sodium nitrate solution was 12.5. Thereafter, the remaining nitrate ions and nitrite ions in the solution were analyzed. The results are shown in Table 1 and compared with the case without addition of catalyst.

From the results of table 1, it was found that nitrate nitrogen was hardly decomposed when no catalyst was added, whereas in the case of the present invention where a sponge copper catalyst was added, the reduction reaction of nitrate nitrogen was promoted and the concentration of residual nitrate nitrogen was reduced to 0.001 mol/l or less. Further, when ammonia generated in the side reaction part remains in the solution, the entire nitrogen-containing component may not be sufficiently removed. However, when a sponge copper catalyst was used, the concentration of residual ammonia was 0.02 mol/liter.

TABLE 1

	Catalyst with copper	Without copper catalyst
	Catalyst with copper	Without copper catalyst	Concentration of residual nitrate nitrogen (mol/l)	＜0.001 (< 0.01 g/l as N)	0.95 (13 g/l as N)
Concentration of residual nitrite nitrogen (mol/l)	0.95 (13 g/l as N)	＜0.002 (< 0.03 g/l as N)	Concentration of residual nitrate nitrogen (mol/l)	＜0.001 (< 0.01 g/l as N)	0.95 (13 g/l as N)

Example 2

7.5 ml of hydrazine hydrate reagent (20 mol/l) and 20 g of sponge copper catalyst were added to 200 ml of a 1 mol/l (14 g/l as N) sodium nitrate solution, followed by stirring for 6 hours while the solution was maintained at 50 ℃ and atmospheric pressure and the pH of the sodium nitrate solution was 8.0. Thereafter, the remaining nitrate ions and nitrite ions in the solution were analyzed. The results are shown in Table 2.

From the results of table 2, it was found that, although the reduction reaction of nitrate nitrogen to nitrite nitrogen was performed because the pH was lower than that of example 1, the reaction rate became lower.

TABLE 2

	Copper catalyst
	Copper catalyst	Concentration of residual nitrate Nitrogen (mol/l)	0.48(6.7 g/l as N)
Concentration of residual nitrite Nitrogen (mol/l)	0.45(6.3 g/l as N)	Concentration of residual nitrate Nitrogen (mol/l)	0.48(6.7 g/l as N)

Example 3

200 ml of a 1 mol/l amide sulfuric acid solution was added to a reactor equipped with a stirrer, sulfuric acid was added to maintain the pH at 1, and 200 ml of a 1 mol/l sodium nitrite solution was poured in at a flow rate of 4 ml/min. After completion of the reaction, nitrite ions, nitrate ions and ammonium ions in the solution were measured by an IC analyzer (ion chromatograph analyzer), and the results are shown in table 3.

From the results of Table 3, it was found that when the amidosulfuric acid solution and the nitrite ion-containing solution were contacted, nitrite nitrogen was converted into nitrogen gas, and thus the concentration of nitrite nitrogen in the residual solution was decreased to less than 0.002 mol/liter.

TABLE 3

Concentration of residual nitrite nitrogen (mol/l)

＜0.002 (< 0.03 g/l as N)

Example 4

In analogy toexample 3, 200 ml of a 1 mol/l amide sulfuric acid solution were added to a reactor with stirrer, the pH was maintained at 3.5 by adding sulfuric acid and 200 ml of a 1 mol/l sodium nitrite solution were poured in at a flow rate of 4 ml/min. After completion of the reaction, nitrite ions, nitrate ions and ammonium ions in the solution were measured by an IC analyzer (ion chromatograph analyzer), and the results are shown in table 4.

From the results of Table 4, it was found that when the amidosulfuric acid solution and the nitrite ion-containing solution were contacted, the concentration of nitrite nitrogen in the solution decreased; however, the concentration of nitrite nitrogen remaining in the solution was higher than in example 3.

TABLE 4

Concentration of residual nitrite nitrogen (mol/l)

0.2 (2.8 g/l as N)

Example 5

In analogy to example 3, 100 ml of a 1 mol/l urea solution were introduced into a reactor with stirrer, the pH was maintained at 1 by addition of sulfuric acid and 200 ml of a 1 mol/l sodium nitrite solution were poured in at a flow rate of 4 ml/min. After completion of the reaction, nitrite ions, nitrate ions and ammonium ions in the solution were measured by an IC analyzer (ion chromatograph analyzer), and the results are shown in Table 5.

From the results of Table 5, it was found that when the urea solution and the nitrite ion-containing solution were contacted, nitrite nitrogen in the solution was converted into nitrogen gas, and the concentration of nitrite nitrogen remaining in the solution was decreased to 0.002 mol/liter.

TABLE 5

Concentration of residual nitrite nitrogen (mol/l)

0.02 (0.28 g/l as N)

In the above examples, hydrazine hydrate was used as hydrazine in the case of the first reduction step of nitrate nitrogen in aqueous solution to nitrite nitrogen, while amide sulfuric acid and urea reagents were used as amides in the case of the second reduction step of nitrite nitrogen to nitrogen. However, in all of the above cases, the present invention is not limited thereto.

Industrial applicability

According to the present invention, since nitrate nitrogen and nitrite nitrogen contained in the discharged water can be chemically treated at normal pressure, the discharged liquid can be economically treated with a small suitable apparatus. In addition, since a high concentration of nitrate nitrogen of 10 g/l or more can be effectively treated, the industrial value of the method is extremely large.

Claims

1. A method for treating an effluent containing a high concentration of nitrate nitrogen, said method comprising a first reduction step in which nitrate nitrogen is reduced to nitrite nitrogen using hydrazine or a salt thereof as a reducing agent in the presence of a sponge copper catalyst, and a second reduction step in which nitrite nitrogen contained in the water treated in the first reduction step is contacted with at least one amide so as to be converted into nitrogen gas.

2. The method for treating an effluent containing a high concentration of nitrate nitrogen according to claim 1, wherein the pH of the water to be treated in the first reduction step is set to 8 to 14.

3. The method of treating a discharged water containing a high concentration of nitrate nitrogen according to claim 1 or 2, wherein the pH of the water to be treated in the second reduction step is set to 3.5 or less.

4. A method of treating a discharge water containing a high concentration of nitrate nitrogen according to any one of claims 1 to 3, wherein the at least one amide is selected from the group consisting of amidosulfuric acid, urea, and mixtures thereof.