Wastewater treatment methods

Abstract

To provide a method for treating wastewater containing nitrogen components, COD components, and hydrazones, which efficiently and effectively decomposes hydrazones prior to carrying out methods such as oxidative decomposition, thereby stably reducing the total nitrogen concentration and COD component concentration in the wastewater to below the discharge standard value. [Solution] The present invention relates to a method for treating wastewater containing nitrogen components, COD components, and hydrazones, comprising a pretreatment step of decomposing hydrazones in the wastewater by contacting the wastewater with a sponge metal catalyst. Here, it is preferable that the sponge metal catalyst mainly consists of one or more metal elements selected from nickel, cobalt, and copper.

Description

[Technical Field]

[0001] This invention relates to a method for efficiently decomposing and removing hydrazones from wastewater containing nitrogen components, COD components, and hydrazones using a sponge metal catalyst. [Background technology]

[0002] Hydrazine has a wide range of applications, including as a power fuel, a metal surface treatment agent, an antioxidant (deoxidizing agent), and a semiconductor cleaning agent. Furthermore, hydrazine is used as a starting material to produce functional materials such as foaming agents (organic foaming agents), thermosetting resin curing (crosslinking) agents, and pesticides.

[0003] In the production of hydrazine in this manner, a specific oxidizing agent such as chlorine (Cl2) or hydrogen peroxide (H2O2) is first reacted with excess ammonia (or a primary amine) in the presence of a ketone or aldehyde under reduced pressure in the gas phase to synthesize hydrazones (hereinafter also referred to as "hydrazones") or intermediate products (heterocyclic compounds) such as ketazine, aziridine, or oxadilane. Subsequently, these are separated from the reaction mixture by distillation, and hydrazine hydrate is obtained by hydrolysis. There are many known documents regarding methods for producing hydrazine using such ketones or aldehydes (see, for example, Patent Documents 1 and 2).

[0004] The wastewater discharged from the known hydrazine manufacturing process described above contains compounds of hydrazine with a small amount of highly reducing hydrazine and ketones or aldehydes. Specific examples include hydrazones (dimethylhydrazone) or ketazines (dimethylketazine), diaziridines (3,3-dimethyldiaziridine), and oxadilanes. It has been reported that isohydrazones can be obtained by reacting chlorine with excess ammonia in the presence of acetone or the like under reduced pressure in the gas phase (Non-Patent Literature 1). Although this compound matches the composition of hydrazone, its chemical properties differ from hydrazone, such as having a melting point approximately 70°C higher than that of hydrazone (40°C) and high solubility in water.

[0005] Wastewater discharged from the hydrazine manufacturing process, as well as from the manufacturing processes of organic foaming agents such as hydrazine derivatives (hydrazide compounds), contains at least hydrazones, and also contains nitrogen and COD components. Such wastewater is known to contain a wide variety of intermediate products with different structural formulas, including numerous unidentified organic nitrogen compounds (hydrazone derivatives), as well as high concentrations of salts such as sodium or ammonium chlorides and sulfates, and other organic compounds such as free acetone or free alcohols.

[0006] Because such wastewater has high concentrations of nitrogen and COD components, directly discharging it into rivers or the sea would cause significant environmental pollution. Therefore, wastewater containing nitrogen, COD, and hydrazones requires denitrification treatment or treatment to remove COD components.

[0007] Various methods have been proposed for denitrification and removal of COD components from wastewater. For example, there are biological treatment methods that utilize activated sludge or biofilm methods, which combine aerobic and anaerobic microorganisms.

[0008] However, when attempting to apply biological treatment to the wastewater described above, the wastewater has reducing properties and bioinhibitory properties due to its high salt concentration, which may kill the microorganisms, making biological treatment difficult as is. In order to make biological treatment possible, for example, the wastewater needs to be diluted to a concentration in which microorganisms can survive. However, diluting the wastewater leads to disadvantages such as an increase in the size of the treatment equipment due to the increase in liquid volume, and an increase in treatment equipment costs. In addition, the treatment performance of the equipment may become unstable due to fluctuations in the concentration of nitrogen and COD components, and it may not be able to meet the wastewater discharge standards. Furthermore, there is the problem of generating a large amount of secondary waste, such as excess activated sludge, as a result of treating nitrogen and COD components.

[0009] In addition to biological treatment, a chemical treatment method has also been proposed for removing nitrogen and COD components contained in wastewater. This method involves simultaneously adding an oxidizing agent such as hypochlorite, chlorine, or hydrogen peroxide along with a copper compound, and then heating and oxidizing the mixture while adjusting the pH with an acid or alkali agent (see, for example, Patent Documents 3 and 4).

[0010] However, as mentioned above, wastewater has a high COD load and is highly reducing, and it also forms high concentrations of salts and persistent organic nitrogen compounds (hydrazones) with chemically stable structures. Therefore, conventional oxidizing agent treatment methods result in slow decomposition rates and long reaction times. For practical purposes, heating to at least 80°C is necessary, which requires a lot of energy and poses a significant problem in terms of economic efficiency. Furthermore, persistent hydrazones have particularly low decomposition efficiency, requiring the addition of an excess amount of oxidizing agent beyond the required amount (equivalent) or the addition of reaction accelerators such as copper ions, making it difficult to efficiently reduce the concentrations of nitrogen and COD components in wastewater.

[0011] Furthermore, in wastewater containing persistent hydrazones, adding oxidizing agents such as chlorine generates self-reaction heat as the reaction progresses, producing a nitride (Acetone-X: 3,3-Dimethyl-diaza-cyclopropane) that readily explodes, posing a safety problem.

[0012] Chemical oxidative decomposition methods for reducing nitrogen and COD components in wastewater have the significant advantage of providing stable treatment performance even with daily fluctuations in salt concentration, nitrogen concentration, and COD load in the wastewater being treated. Another advantage is that the reaction equipment can be miniaturized. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] U.S. Patent No. 3,442,612 [Patent Document 2] German patent no. 1082889 [Patent Document 3] Japanese Patent Application Publication No. 49-79050 [Patent Document 4] Japanese Patent Application Publication No. 52-7148 [Non-patent literature]

[0014] [Non-Patent Document 1] H.J. Abendroth, G. Henrich, Agnew.chem. 71 283(1959) [Overview of the project] [Problems that the invention aims to solve]

[0015] This invention was proposed in view of the above circumstances, and aims to provide a method for treating wastewater containing nitrogen components, COD components, and hydrazones that can stably reduce the total nitrogen concentration and COD component concentration in the wastewater to below the discharge standard value. [Means for solving the problem]

[0016] In order to solve the above problems, the present inventor examined a pretreatment for effectively decomposing hydrazones in wastewater before performing methods such as oxidative decomposition treatment in the treatment of wastewater containing a nitrogen component, a COD component, and hydrazones. As a result, it was found that by performing a pretreatment of reducing and decomposing hydrazones by bringing the wastewater containing hydrazones into contact with a sponge metal catalyst, the total nitrogen concentration and the COD concentration in the wastewater can be stably reduced through subsequent steps such as oxidative decomposition treatment, and the present invention was thus completed.

[0017] (1) A first invention of the present invention is a method for treating wastewater containing a nitrogen component, a COD component, and hydrazones, which comprises a pretreatment step of reducing and decomposing hydrazones in the wastewater by bringing the wastewater into contact with a sponge metal catalyst.

[0018] (2) A second invention of the present invention is a method for treating wastewater according to the first invention, wherein the sponge metal catalyst contains, as a main component, one or more metal elements selected from nickel, cobalt, and copper.

[0019] (3) A third invention of the present invention is a method for treating wastewater according to the first or second invention, wherein in the pretreatment step, the pH of the wastewater is set under the condition of exceeding 9 and less than 14.

[0020] (4) A fourth invention of the present invention is a method for treating wastewater according to any one of the first to third inventions, further comprising an oxidative decomposition step of adding an oxidizing agent to the wastewater obtained through the pretreatment step (pretreatment wastewater after treatment) to oxidatively decompose nitrogen and COD contained in the pretreatment wastewater after treatment.

Advantages of the Invention

[0021] According to the present invention, hydrazones in wastewater can be efficiently and effectively decomposed, and the total nitrogen concentration and the COD concentration in the wastewater can be stably reduced to below the drainage standard value. [Brief explanation of the drawing]

[0022] [Figure 1] This is a process diagram showing an example of a wastewater treatment method. [Modes for carrying out the invention]

[0023] The following describes specific embodiments of the present invention (hereinafter referred to as "these embodiments"). It should be noted that the present invention is not limited in any way to the following embodiments, and can be modified as appropriate without altering the essence of the invention.

[0024] The wastewater treatment method according to this embodiment is a method for treating wastewater containing nitrogen components, COD components, and hydrazones. This treatment method is characterized by having a pretreatment step that efficiently and effectively decomposes hydrazones in the wastewater before carrying out known oxidative decomposition treatments or biological treatments.

[0025] Specifically, this wastewater treatment method includes a pretreatment step in which the wastewater to be treated is brought into contact with a sponge metal catalyst to decompose hydrazones in the wastewater.

[0026] Here, hydrazones refer to a group of organic nitrogen compounds produced by the dehydration condensation of a carbonyl compound with hydrazine or a hydrazine derivative. Furthermore, wastewater may contain hydrazine salts, hydrazide compounds, azo compounds, and synthetic intermediates of hydrazones and their heterocyclic hydrazine derivatives.

[0027] As will be explained in more detail later, by bringing wastewater into contact with a sponge metal catalyst in the pretreatment process, hydrazones in the wastewater can be decomposed into nitrogen (N2) gas and free carbonyl compounds. Then, by adding an oxidizing agent to the wastewater obtained after the pretreatment process and performing oxidative decomposition or biological treatment, it becomes possible to efficiently and effectively remove nitrogen and COD components that were originally present in the wastewater or that have become present in the wastewater as a result of the decomposition of hydrazones.

[0028] Figure 1 is a process diagram showing an example of a wastewater treatment method. The wastewater treatment method includes a pretreatment step S1 for decomposing hydrazones, an organic matter removal step S2 for volatilizing and removing organic matter, and an N / COD decomposition step S3 for decomposing and removing nitrogen and COD components.

[0029] [Pre-treatment process] The wastewater treatment method according to this embodiment includes a pretreatment step S1 for decomposing hydrazones in the wastewater. The pretreatment step S1 is a treatment performed prior to carrying out conventionally known treatments, such as oxidative decomposition treatment or biological treatment, on wastewater containing nitrogen components and COD components.

[0030] The pretreatment step S1 can be divided into an adjustment step S11, which adjusts the treatment conditions of the wastewater, and a hydrazone decomposition step S12, which decomposes hydrazones in the adjusted wastewater.

[0031] (Adjustment process S11) The adjustment step S11 is a process of adjusting the treatment conditions, such as the pH and temperature conditions, of the wastewater to be treated in order to optimize the hydrazone decomposition reaction in the hydrazone decomposition step S12, which will be described later. The adjustment step S11 is carried out by introducing the wastewater into equipment such as an adjustment tank.

[0032] The pH conditions for wastewater can be adjusted as appropriate depending on the type of hydrazones and other components present in the wastewater, but it is preferable to set it in the range of greater than 9 and less than 14. More preferably, it is preferable to adjust it in the range of pH 10 to 12.

[0033] The pH of wastewater can be adjusted using alkaline agents such as sodium hydroxide, sodium carbonate, and potassium hydroxide, or acidic agents such as sulfuric acid and hydrochloric acid.

[0034] While there are no particular limitations on the temperature conditions of the wastewater, generally, higher temperatures promote more efficient hydrolysis in the decomposition of persistent hydrazones. Therefore, higher temperatures are preferable for the decomposition of persistent hydrazones, but considering the energy costs for heating, equipment costs, and the material of the treatment tank (adjustment tank), a temperature range of approximately 40°C to 60°C is more preferable.

[0035] (Hydrazone decomposition process S12) The hydrazone decomposition step S12 is a treatment step for wastewater whose treatment conditions, such as pH and temperature, have been adjusted, and it is a step in which hydrazones contained in the wastewater are decomposed. Specifically, in the hydrazone decomposition step S12, hydrazones contained in the wastewater are decomposed by bringing the wastewater into contact with a sponge metal catalyst.

[0036] The hydrazone decomposition process S12 is carried out in equipment such as a hydrazone decomposition tower. This equipment is filled with a sponge metal catalyst that exhibits excellent low-temperature activity. By introducing wastewater into this equipment filled with the sponge metal catalyst, a reaction that decomposes hydrazones occurs within the equipment.

[0037] Sponge metal catalysts can be granular catalysts made by unfolding binary alloys of Ni-Al, Co-Al, or Cu-Al, which form a θ phase as an intermetallic compound (intermediate phase). Sponge metal catalysts are made by dissolving a portion of the aluminum from an alloy of aluminum with catalytic metals (main components) such as nickel (Ni), cobalt (Co), or copper (Cu). Sponge metal catalysts are also called "Raney catalysts."

[0038] Sponge metal catalysts are generally used as catalysts for the hydrogenation of organic compounds, but in the wastewater treatment method according to this embodiment, in the hydrazone decomposition step S12, the reactions shown in the following reaction formulas (Equation 1) and (Equation 2) are the main reactions, which hydrolyze or reductively decompose hydrazones in the wastewater into nitrogen (N2) gas and free carbonyl compounds.

[0039] [ka]

[0040] As mentioned above, the sponge metal catalyst can be a catalyst mainly composed of nickel, cobalt, or copper. Among these, nickel-based or cobalt-based catalysts are more preferable than copper-based catalysts because they exhibit superior hydrazone decomposition efficiency.

[0041] The method of contacting the wastewater with the sponge metal catalyst can be either batch or continuous; in either method, the wastewater and the sponge metal catalyst should be treated in such a way that they come into even contact.

[0042] Furthermore, in equipment such as hydrazone decomposition towers, it is preferable to provide a structure that allows for easy removal of nitrogen (N2) gas, hydrogen (H2) gas, and ammonia (NH3) gas, which are by-products of hydrazone decomposition, from the system. For example, in a hydrazone decomposition tower, if a column tower packed with a sponge metal catalyst is used and continuous processing is performed, wastewater should be introduced from the bottom of the column tower, and a piping line should be provided to extract the wastewater from the top, as well as a vent line from the very top of the tower above the extraction piping line to release gaseous components.

[0043] [Organic matter removal process] The organic matter removal step S1 is a process of volatilizing and removing organic matter contained in the wastewater from which hydrazones have been decomposed in the pretreatment step S1. Specifically, in the organic matter removal step S1, organic matter such as acetone (boiling point 56.5°C) or acetaldehyde (boiling point 20.2°C), which are decomposition products of hydrazones, and low-boiling point carbonyl compounds that are initially present in the wastewater, are volatilized, separated, and recovered.

[0044] The organic matter removal process S2 is carried out by introducing the wastewater that has undergone the pretreatment process S1 into equipment such as an organic matter volatilization tank. The equipment such as an organic matter volatilization tank can be any equipment that can volatilize, separate, and recover organic matter in the wastewater.

[0045] The method for volatilizing and separating organic matter is not particularly limited and can be performed, for example, by heating by direct steam injection, air bubbling, atmospheric pressure distillation, or under vacuum (e.g., by flash distillation). When volatilizing carbonyl compounds in wastewater, a higher temperature is generally preferable, but considering economic factors such as energy costs for heating, a temperature of around 50°C to 70°C is appropriate.

[0046] In this way, during the organic matter removal process S2, when organic matter such as carbonyl compounds is volatilized and separated from the wastewater, the wastewater from which the organic matter has been separated, and the concentrated carbonyl compounds that have been stripped from the cooling tower (e.g., condenser), are recovered. The recovered concentrated carbonyl compounds can be returned to the hydrazine production process or the hydrazine derivative compound production process.

[0047] [N / COD decomposition process] The N / COD decomposition step S3 is a step in which nitrogen and COD components are decomposed and removed from wastewater from which organic matter has been separated via the organic matter removal step S2. Specifically, in the N / COD decomposition step S3, known oxidative decomposition treatments or biological treatments are performed on the wastewater containing nitrogen and COD components.

[0048] Here, the wastewater supplied to the N / COD decomposition step S3 is the wastewater obtained through the pretreatment step S1 and the organic matter removal step S2, as described above. In particular, the persistent hydrazones contained in the wastewater are effectively decomposed in the pretreatment step S1. Therefore, even with known oxidative decomposition treatments, there is no risk of the reaction time being prolonged, and excessive energy consumption can be prevented, allowing for efficient decomposition of nitrogen and COD components. Furthermore, the generation of self-reaction heat by the oxidizing agent can be prevented, enabling safer treatment.

[0049] The N / COD decomposition process S3 is carried out by introducing wastewater from the organic matter removal process S2 into equipment such as an N / COD decomposition tank. The equipment such as the N / COD decomposition tank is equipped with a pH measuring device and an ORP measuring device. Furthermore, the equipment such as the N / COD decomposition tank is configured to allow for pH adjustment and ORP adjustment within the tank by directly supplying pH adjusting agents and oxidizing agents into the tank.

[0050] In the N / COD decomposition step S3, for example, as shown in the reaction equations (Equation 3) to (Equation 6) below, an oxidative decomposition reaction of COD derived from nitrogen components and organic matter takes place. Common oxidizing agents used in the oxidative decomposition reaction include sodium hypochlorite and chlorine.

[0051] The state in which hypochlorous acid has high oxidizing power is considered to be around pH 5, where the proportion of hypochlorous acid (HOCl) is highest. Below pH 5, as self-decomposition increases and the generation of chlorine gas increases, the efficiency of HOCl generation, which contributes to the oxidation reaction, decreases. Also, above pH 10, hypochlorite ions (OCl) are produced. - The proportion of hydrogen ions (H) tends to increase and the oxidizing power decreases. In other words, as the oxidative decomposition reaction of nitrogen and COD components proceeds, hydrogen ions (H) tend to increase. +As ) is released and the solution becomes acidic, it is preferable to adjust the pH to the optimal pH range of pH 5 to 10, preferably pH 7.5 to 8.5, by adding a pH adjusting agent. The pH adjusting agent is not particularly limited, and alkaline agents such as sodium hydroxide, sodium carbonate, and potassium hydroxide, or acidic agents such as sulfuric acid and hydrochloric acid can be used.

[0052] Thus, in the N / COD decomposition process S3, when the nitrogen and COD components are oxidatively decomposed, a chlorine-based oxidizing agent is supplied, for example. The oxidizing agent is the nitrogen component (e.g., NH4) remaining in the wastewater. 4+ It oxidizes and decomposes NH2NH2 into nitrogen (N2) gas, carbon dioxide (CO2) gas, etc., primarily through the reactions shown in the following reaction equations (Equation 3) and (Equation 4), and also oxidizes and decomposes high-boiling-point (BP) alcohols that are COD components, such as isopropyl alcohol (BP=82.4°C) or diacetone alcohol (DAA, BP=166°C), primarily through the reactions shown in the following reaction equations (Equation 5) and (Equation 6).

[0053] Specifically, in the case of oxidative decomposition reactions of nitrogen components, for example, the reactions shown in the following reaction equations (Equation 3) and (Equation 4) proceed as the main reactions. In reaction equation (Equation 3), ammonium is shown as an example of the nitrogen component to be oxidized and decomposed, and in reaction equation (Equation 4), hydrazine is shown. 2NH4 + + 3NaClO → N2↑ + 3NaCl + 3H2O + 2H + ...(Formula 3) NH2NH2+ Cl2(HOCl) → N2↑ + 2H2O + 2HCl ...(Formula 4)

[0054] Furthermore, in the case of oxidative decomposition reactions of COD components derived from organic matter, for example, the reactions shown in the following reaction equations (Equation 5) and (Equation 6) proceed as the main reactions. In reaction equation (Equation 5), isopropyl alcohol is shown as an example of the COD component to be oxidatively decomposed, and in reaction equation (Equation 6), diacetone alcohol is shown. C3H7OH + 6NaClO → 3CO2↑ + 6NaCl + H2O + 5H + ...(Formula 5) C6H 12 O2 + 6Cl2(HOCl) → 6CO2↑ + 12HCl + 2H2O + 8H + ...(Formula 6)

[0055] In the N / COD decomposition step S3, the endpoint of the reaction, where nitrogen and COD components in the wastewater have undergone oxidative decomposition, can be confirmed by measuring the oxidation-reduction potential (ORP) within the reaction system. For example, the ORP value that can confirm whether the total amount of reducing substances containing nitrogen and COD components derived from organic matter is in an oxidative decomposition state varies with pH and temperature, but in alkaline conditions, the potential is in the range of 550mV to 850mV, preferably in the range of 650mV to 750mV, with a silver / silver chloride electrode as the reference electrode.

[0056] Furthermore, the temperature conditions within the reaction system are not particularly limited and can be carried out at room temperature, for example. The reaction time can be approximately 5 to 60 minutes, preferably 10 to 20 minutes, at room temperature. If necessary, the reaction can also be carried out with appropriate heating.

[0057] Through this N / COD decomposition process S3, the concentrations of nitrogen and COD components in the final treated water discharged from the outlet of the N / COD decomposition tank and other equipment can be stably kept below the wastewater standard values. [Examples]

[0058] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0059] [Examples 1-3] In Examples 1 to 3, 18 L of wastewater containing an organic nitrogen compound group containing hydrazones, which is actual wastewater discharged from the manufacturing process of hydrazine (NN), was sampled into a poly-tank, and sulfuric acid (concentration 65%) or sodium hydroxide (concentration 20%) was quickly added to adjust the pH to 6. A part of the wastewater after pH adjustment was sampled, and the total nitrogen concentration (T-N), COD Mn concentration, organic nitrogen concentration (Org-N), hydrazine (hereinafter also referred to as "HH") concentration, etc. were analyzed.

[0060] Regarding the total nitrogen concentration (T-N), the summation method was adopted for quantification according to the factory wastewater test method (JIS0102). Also, for the COD Mn concentration, the potassium permanganate method was adopted according to the factory wastewater test method (JIS0102.17), and attention was paid to the silver masking method for chlorine in the wastewater to quantify the COD. Regarding the organic nitrogen concentration (Org-N), it was analyzed using a gas chromatograph analyzer (GC method) and a high-performance liquid chromatograph analyzer (HPLC method). Also, for the ammonia nitrogen concentration (NH4-N), nitrate nitrogen concentration (NO3-N), nitrite nitrogen concentration (NO2-N), and hydrazine concentration (HH), they were analyzed using an ion chromatograph analyzer (IC method).

[0061] The analysis results are shown in Table 1 below (the units of the analysis values in Table 1 are all "mg / L" except for the ORP value and iodine value). This wastewater is denoted as "Wastewater A".

[0062] Next, 800 ml each of Wastewater A was sampled into three glass beakers (capacity 1 L), heated to 60°C, and while mixing and stirring with a stirrer, sulfuric acid or sodium hydroxide was added to adjust the pH to 11.

[0063] Next, 10g each of three types of sponge metal catalysts, each primarily composed of nickel (Ni), cobalt (Co), or copper (Cu), were placed in a mesh basket and added to each solution. The wastewater and each sponge metal catalyst were then brought into contact for 60 minutes while being vigorously stirred. After that, the sponge metal catalysts were removed from each of the three solutions and degassed to remove any remaining hydrazone decomposition gases (N2) and free ketones (e.g., free acetone) from the solutions. The degassing treatment was carried out using a combination of air bubbling and stirring for 30 minutes while maintaining the solution temperature at 60°C.

[0064] Next, sulfuric acid or sodium hydroxide was added to each of the three degassed solutions to adjust the pH to a range of 6-8. Then, sodium hypochlorite solution (12% concentration) was sequentially added until the oxidation-reduction potential (ORP) value, using a silver / silver chloride electrode as the reference electrode, reached 850 mV. At the point when the ORP value of the solution reached 850 mV, the addition of sodium hypochlorite solution was stopped, and then a degassing treatment was performed to remove the decomposition gases (N2, CO2) remaining in the solution.

[0065] A portion of the solution obtained after degassing is taken to determine the total nitrogen concentration and COD. Mn The concentrations, organic nitrogen concentrations, and hydrazone concentrations were analyzed. The results of this analysis are shown in Table 2 below (all analytical values ​​in Table 2 are in "mg / L").

[0066] [Comparative Example 1] In Comparative Example 1, similar to Examples 1-3 described above, 800 ml of wastewater containing organic nitrogen compounds, including hydrazones, was placed in a glass beaker (capacity 1 L), and while being heated and maintained at 60°C, sulfuric acid or sodium hydroxide was added to adjust the pH to 11. Then, unlike in Examples 1-3, the wastewater A was vigorously stirred and mixed for 60 minutes without adding a sponge metal catalyst. Other conditions were the same as in Examples 1-3.

[0067] Subsequently, a portion of the treated solution was collected to determine the total nitrogen concentration and COD. MnThe concentrations, organic nitrogen concentrations, and hydrazone concentrations were analyzed. The results of this analysis are shown in Table 2 below.

[0068] [Examples 4-6] In Examples 4-6, 18 L of wastewater containing organic nitrogen compounds, including hydrazones, was collected in a poly tank from the manufacturing process of azodicarbonamide (ADCA), an organic blowing agent. Sulfuric acid (65% concentration) or sodium hydroxide (20% concentration) was quickly added to adjust the pH to 6. A portion of the wastewater after pH adjustment was then collected to determine the total nitrogen concentration and COD. Mn The concentration, organic nitrogen concentration, hydrazine concentration, etc., were analyzed in the same manner as in wastewater A of Examples 1 to 3.

[0069] The analysis results are shown in Table 1 below. The wastewater in question is referred to as "Wastewater B". A "-" in Table 1 indicates that the value was below the analytical limit.

[0070] Next, 800 ml each of wastewater B was collected in three glass beakers (1 L capacity), heated to 60°C, and sulfuric acid or sodium hydroxide was added while mixing and stirring with a stirrer to adjust the pH to 11.

[0071] Next, 10g each of three types of sponge metal catalysts, each primarily composed of nickel (Ni), cobalt (Co), or copper (Cu), were placed in a mesh basket and added to each solution. The wastewater and each sponge metal catalyst were then brought into contact for 60 minutes while being vigorously stirred. After that, the sponge metal catalysts were removed from each of the three solutions and degassed to remove any remaining hydrazone decomposition gases (N2) and free ketones (e.g., free acetone) from the solutions. The degassing treatment was carried out using a combination of air bubbling and stirring for 30 minutes while maintaining the solution temperature at 60°C.

[0072] Next, sulfuric acid or sodium hydroxide was added to each of the three degassed solutions to adjust the pH to a range of 6-8. Then, sodium hypochlorite solution (12% concentration) was sequentially added until the oxidation-reduction potential (ORP) value, using a silver / silver chloride electrode as the reference electrode, reached 850 mV. At the point when the ORP value of the solution reached 850 mV, the addition of sodium hypochlorite solution was stopped, and then a degassing treatment was performed to remove the decomposition gases (N2, CO2) remaining in the solution.

[0073] A portion of the solution obtained after degassing is taken to determine the total nitrogen concentration and COD. Mn The concentrations, including hydrazone concentrations, were analyzed. The results of this analysis are shown in Table 3 below (all analytical values ​​in Table 3 are in "mg / L").

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3]

[0077] As can be seen from the results shown in Tables 2 and 3 above, in Examples 1-3 (for wastewater A) and Examples 4-6 (for wastewater B), a pretreatment was performed by contacting a sponge metal catalyst with wastewater containing organic nitrogen compounds including hydrazones prior to oxidative decomposition using a sodium hypochlorite solution. As a result, the organic nitrogen compounds including hydrazones in the wastewater were reduced and decomposed, effectively lowering their concentration and stably reducing the total nitrogen concentration and COD concentration.

[0078] In particular, among the examples, it was found that in cases where nickel or cobalt was used as the metal species of the sponge metal catalyst, the total nitrogen concentration and COD concentration in the wastewater could be reduced to even lower levels, resulting in more effective treatment.

[0079] In contrast, in Comparative Example 1, where no pretreatment involving contact with a sponge metal catalyst was performed, the total nitrogen concentration and COD concentration in the wastewater could not be stably reduced even after subsequent oxidative decomposition treatment.

Claims

1. A method for treating wastewater containing nitrogen components, COD components, and hydrazones, The method includes a pretreatment step in which the wastewater is brought into contact with a sponge metal catalyst to decompose hydrazones in the wastewater. Methods for treating wastewater.

2. The aforementioned sponge metal catalyst mainly consists of one or more metal elements selected from nickel, cobalt, and copper. The wastewater treatment method according to claim 1.

3. In the aforementioned pretreatment step, the pH of the wastewater is set to be greater than 9 and less than 14. A method for treating wastewater according to claim 1 or 2.

4. The process further includes an oxidative decomposition step in which an oxidizing agent is added to the wastewater obtained through the aforementioned pretreatment step (post-pretreatment wastewater) to oxidatively decompose the nitrogen and COD components contained in the post-pretreatment wastewater. A method for treating wastewater according to claim 1 or 2.

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