JPH1177067A - Treatment of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To safely, inexpensively, simply, stably and continuously treatwaste water while preventing the formation of scale in an apparatus by oxidizing and decomposing a COD component and/or a nitrogen-containing component contained in waste water by adding a solid catalyst and a chelating agent. SOLUTION: When a COD component and/or a nitrogen-containing component, for example, an ammonium salt, hydrazine, nitrite, nitrogen oxide or the like contained in discharge water are subjected to oxidation/decomposition treatment, a solid catalyst and a chelating agent are added. As the chelating agent, one compd. selected from ethylenediaminetetracetate, trans-1,2- cyclohexanediaminetetracetate, glycoletherdiaminetetraacetate or the like, salts formed from these compds. and an alkali metal hydroxide and salts formed from ethylenediamine or triethanolamine and ethylenediamine or triethanolamine and an acid is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing CO contained in wastewater.
The present invention relates to a wastewater treatment method for detoxifying a wastewater by oxidizing and decomposing a D component and / or a nitrogen-containing component in the presence of a solid catalyst, and is particularly selected from the group consisting of aluminum, alkaline earth metals and heavy metals. It is useful in a method of treating wastewater containing a water-soluble salt and / or oxide of at least one metal with a solid catalyst.

More specifically, the present invention relates to chemical plants, plating industrial equipment, leather manufacturing equipment, metal industrial equipment, metal mining equipment, power generation equipment, food manufacturing equipment, pharmaceutical manufacturing equipment, textile industrial equipment, pulp and paper industrial equipment, Industrial wastewater represented by dyeing dye industrial equipment, electronic industrial equipment, mechanical industrial equipment, printing plate making equipment, glass manufacturing equipment, photo processing equipment, etc.
Contacting the solid catalyst with a solid catalyst at a temperature of 370 ° C. or less and a pressure at which the wastewater retains a liquid phase, comprising a scale-forming substance that is a water-soluble salt and / or oxide of aluminum, alkaline earth metal or heavy metal. Also, the present invention relates to a method for treating wastewater, in which substances contained in the wastewater are converted into nitrogen, carbon dioxide, water and ash to detoxify the wastewater.

[0003]

2. Description of the Related Art As a method of treating wastewater in the presence of a solid catalyst, a method of decomposing or removing a COD component or a nitrogen-containing component of wastewater using oxygen, ozone, hydrogen peroxide or the like as an oxidizing agent, methanol, hydrogen or the like is used. A method of reducing and removing nitrate in wastewater as a reducing agent has been proposed. As one example, a catalytic wet oxidation method using oxygen in an oxygen-containing gas as an oxidizing agent uses a specific solid catalyst, and wet-oxidizes the wastewater while supplying the oxygen-containing gas under a pressure at which the wastewater maintains a liquid phase. It is a method of processing. According to this method, the COD component and the nitrogen-containing component in the wastewater can be decomposed into water, carbon dioxide gas, nitrogen gas, inorganic salts, ash, or lower molecular weight organic substances, and the wastewater can be easily purified. Therefore, in many cases, it is possible to directly discharge treated water into rivers and the like, and even when a further purification treatment step by post-treatment is required, this post-treatment step is performed when the catalytic wet oxidation treatment method is not adopted. It can be very small compared to.

[0004] This catalytic wet oxidation treatment is also effective in treating components related to iodine consumption.
The iodine consumption can be easily reduced even at a relatively low temperature of 0 ° C. or less.

[0005]

However, in the above-mentioned various methods for treating wastewater in the presence of a solid catalyst, water-soluble salts and / or oxides of aluminum, alkaline earth metals or heavy metals are contained in the wastewater. When a scale-forming substance is contained, they are deposited as scales in a heat exchanger, a catalytic reaction tower, or the like, and may cause clogging of the device, and development of a method that does not generate scale in the device has been desired. .

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found that a scale-forming substance which is a water-soluble salt and / or oxide of aluminum, an alkaline earth metal or a heavy metal is obtained. For wastewater containing ５００500 mg / L, when the wastewater is subjected to treatment using a solid catalyst such as catalytic wet oxidation treatment, the formation of scale in the apparatus is prevented by adding a chelating agent to the wastewater, thereby ensuring safety. It has been found that continuous, inexpensive, simple and stable wastewater treatment can be performed. The present invention has been completed based on this finding.

[0007] The present invention is specified as follows.

(1) A method for treating wastewater, comprising oxidizing and decomposing a COD component and / or a nitrogen-containing component contained in the wastewater in the presence of a solid catalyst and a chelating agent to render the wastewater harmless.

(2) The wastewater contains at least one water-soluble salt (and / or oxide) of a metal selected from the group consisting of aluminum, silicon, alkaline earth metals and heavy metals. The method for treating wastewater as described.

(3) The chelating agent comprises the following (A) to (D)
The method for treating wastewater according to (1) or (2), which is at least one of the compounds classified as (1).

(A) Ethylenediaminetetraacetic acid (EDT)
A), trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA), glycol etherdiaminetetraacetic acid (GEDTA or EGTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), oxalic acid, maleic acid, phthalic acid At least one compound selected from the group consisting of, citric acid, succinic acid, salicylic acid, sulfosalicylic acid, β-mercaptopropionic acid, thioglycolic acid and dimercaptosuccinic acid.

(B) A salt formed from at least one compound selected from (A) and an alkali metal hydroxide.

(C) Ethylenediamine or triethanolamine.

(D) A salt formed from ethylenediamine or triethanolamine and an acid.

(4) The content of the water-soluble salt and / or oxide of at least one metal selected from the group consisting of aluminum, alkaline earth metals and heavy metals in the wastewater is 1% as the total concentration of metal ions. The method for treating wastewater according to any one of (1) to (3), which is in a range of from 500 mg / L to 500 mg / L.

(5) The total molar concentration of the chelating agent is 0.5 to 50 times the total molar concentration of at least one metal ion selected from the group consisting of aluminum, alkaline earth metals and heavy metals in the wastewater. The method for treating wastewater according to any one of (1) to (4), wherein a chelating agent is added to the wastewater.

(6) The temperature at the time of wastewater treatment is 40 to 200 ° C.
The method for treating wastewater according to any one of (1) to (5).

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The nitrogen-containing component according to the present invention is
For example, it is a general term for compounds containing a nitrogen atom such as ammonia, ammonium salt, hydrazine, hydrazinium salt, nitric acid, nitrate, nitrite, nitrite, and nitric oxide.

The alkaline earth metal according to the present invention includes beryllium, magnesium, calcium, strontium,
Barium and radium.

The heavy metals according to the present invention include transition metals of the fourth to sixth periods in the long-period periodic table of elements such as chromium, manganese, iron, cobalt, nickel, copper, zinc, cadmium, mercury, gallium, and indium. , Thallium, tin,
Lead, antimony, bismuth, lanthanoid, actinoid.

The scale-forming substance according to the present invention is a water-soluble salt of at least one metal selected from the group consisting of aluminum, alkaline earth metals and heavy metals, and / or
Or, it is a generic term for oxide.

The content of the scale-forming substance according to the present invention is 1 to 500 mg / L, preferably 2 to 200 mg / L, more preferably 5 to 100 mg / L as the total concentration of metal ions. When the amount is less than 1 mg / L, a scale is not often generated even without using this method.
When the amount exceeds 500 mg / L, not only the cost of adding the chelating agent increases, but also a step of treating the substance remaining after the wastewater treatment using the solid catalyst is required.

The chelating agent according to the present invention is particularly a compound that coordinates with a metal ion as a polydentate ligand or a salt containing an ion that coordinates with a metal ion as a polydentate ligand. Although not limited, for example, at least one of the compounds classified into the following (A) to (G) can be employed.

(A) Ethylenediaminetetraacetic acid (EDT)
A), trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA), glycol etherdiaminetetraacetic acid (GEDTA or EGTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), oxalic acid, maleic acid, phthalic acid At least one compound selected from the group consisting of, citric acid, succinic acid, salicylic acid, sulfosalicylic acid, β-mercaptopropionic acid, thioglycolic acid and dimercaptosuccinic acid.

(B) A salt formed from at least one compound selected from (A) and an alkali metal hydroxide.
For example, ethylenediaminetetraacetic acid tetrasodium tetrahydrate can be mentioned.

(C) Ethylenediamine or triethanolamine.

(D) A salt formed from ethylenediamine or triethanolamine and an acid. Here, the acid is a substance that is soluble in water and shows acidity, and examples thereof include sulfuric acid, hydrochloric acid, and acetic acid.

(E) Crown ether.

(F) Polymer chelating agents such as salts of polyacrylic acid with alkali metals or salts of acrylic acid / maleic acid copolymer with alkali metals.

(G) Urea, 2,3-dimercaptopropanol, unithiol, aminoethylmercaptan, thiourea, thiocarbazide, orthophenanthroline or acetylacetone.

The chelating agent according to the present invention includes:
At least one of the compounds classified into (A) to (D)
It is preferable to adopt a type.

Although one molecule of hydrazine has two nitrogen atoms which can be a coordination site, hydrazine is not included in the chelating substance here because it is easily decomposed by wastewater treatment using a solid catalyst.

When the chelating agent according to the present invention is contained in waste water, it can also be used. Further, the addition of the chelating agent may be performed in a drainage tank, or by mixing the chelating agent solution with the wastewater at an arbitrary position in a pipe from the drainage tank of the processing apparatus to the heat exchanger.

The concentration of the chelating agent according to the present invention is not particularly limited. For example, the above (A) to (E) and (G)
In the chelating agent, the total molar concentration of the chelating agent is preferably 0.5 to 50 times the total molar concentration of the metal ions of the scale-forming substance contained in the wastewater, and 0.8 to 50 times.
It is more preferably 20 times, more preferably 1.0 to 10 times. When the ratio is less than 0.5 times, the effect of suppressing the formation of scale becomes small, and when the ratio exceeds 50 times, the cost of chelating agent addition only increases. In the polymer chelating agent (F), the number of coordination sites of the polymer chelating agent dissolved per unit volume of the drainage is 1 to 100 times the number of moles of the metal ion of the scale-forming substance. Preferably, it is 2 to 40 times. When the ratio is less than 1 time, the effect of suppressing scale formation is small, and when the ratio is more than 100 times, the cost of chelating agent addition only increases.

The substance to be treated contained in the wastewater according to the present invention is not particularly limited as long as it is a COD component and / or a nitrogen-containing component, but hydrazine, ammonia, sulfide, sulfite, thiosulfate, Cyanates, cyanates, thiocyanates and the like are preferable because they can be easily processed at a relatively low temperature.

Before adding the chelating agent, the wastewater according to the present invention can be subjected to pH adjustment and solid-liquid separation as required to reduce dissolved scale components in advance. By doing so, the amount of the chelating agent added can be reduced, and the processing cost can be reduced.

When the solution containing the scale-forming substance is subjected to wastewater treatment using a solid catalyst in the absence of a chelating substance, the scale is converted into a stable oxide or salt which is insoluble or hardly soluble in water at a high temperature. Generate. However, in the presence of the chelating agent, the chelating agent chelates with the cations constituting the scale-forming substance to form a stable complex that is stably dissolved in water. Therefore, it is difficult to generate scale in the processing apparatus.

The temperature during the wastewater treatment according to the present invention is 40 to
200 ° C. is preferred, and more preferably 80 to 170 ° C. If the temperature of the wastewater treatment exceeds 200 ° C., the chelating agent is partially decomposed, and the effect of adding the chelating agent cannot be sufficiently obtained, which is not preferable. When the temperature is lower than 40 ° C., the treatment reaction does not substantially proceed, and in most cases, no scale is generated in the treatment device without adding a chelating agent.
Not preferred.

With respect to the pressure during the wastewater treatment according to the present invention, the pressure at which the wastewater retains the liquid phase at the treatment temperature is set. When the temperature at the time of the wastewater treatment is less than 100 ° C., the treatment can be performed at atmospheric pressure without particularly adjusting the pressure.

The solid catalyst according to the present invention may be any catalyst as long as it has durability and activity under wet reaction conditions. For example, titanium, silicon, zirconium, manganese, iron ,cobalt,
Nickel, tungsten, cerium, copper, silver, gold, platinum, palladium, rhodium, ruthenium, and a solid catalyst containing a water-insoluble or hardly soluble compound of at least one element selected from the group consisting of iridium. Can be used.

The solid catalyst according to the present invention preferably has the composition specified as described above.
Various things such as a granular form, a pellet form, and an integrated structure such as a honeycomb can be adopted.

The inflow velocity of the wastewater during the wastewater treatment according to the present invention is preferably in the range of 0.1 to 20 hr ^{-1 in} space velocity (LHSV) with respect to the solid catalyst.
More preferably, it is in the range of 0.5 to 5 hr ^-1 .
If the LHSV is less than 0.1 hr ^-1 , the processing efficiency does not increase with respect to the catalyst amount, but the processing cost increases, which is not preferable. When the LHSV exceeds 20 hr ^-1 , the treatment of wastewater becomes insufficient, which is not preferable.

[0043]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

(Catalyst Preparation Example) Ferric nitrate was dissolved in water, zirconyl nitrate and palladium nitrate were added, and an aqueous solution of sodium hydroxide was added to adjust the pH to 9, which was filtered and washed to obtain a cake. After drying and calcining at 700 ° C., it is pulverized to obtain an iron-zirconium-palladium oxide powder (weight ratio Fe ₂ O ₃ : ZrO ₂ : PdO = 60: 39.5:
0.5).

The thus obtained oxide powder is added with starch,
After adding water and mixing well, the mixture was shaped into a pellet (cylindrical, average diameter 5 mm, length 6 mm), dried, and calcined at 400 ° C. for 4 hours to obtain a completed catalyst.

Example 1 According to the flow as shown in FIG. 1, a hydrazine-containing wastewater containing a scale component shown below and containing about 30,000 to 50,000 mg / L of iodine is described below. Processed. Calcium ion 10 to 20 mg / L Magnesium ion 10 to 20 mg / L Iron (III) ion 2 to 5 mg / L TOC 50 to 100 mg / L The drainage tank 4 regularly receives wastewater having the above composition. 500 mg of ethylenediaminetetraacetic acid tetrahydrate was added to 1 L of the wastewater received each time.

The drainage of the drainage tank 4 is 9 kg /
The pressure was increased to cm ² G and supplied into the apparatus at a flow rate of 0.5 L / hr. Further, after the pressure of the air supplied from the line 10 was increased by the compressor 6, the air was mixed into the drainage in the line 11. The air supply was set to an amount corresponding to twice the oxygen demand determined by the following equation, and controlled by a mass flow controller.

Oxygen demand = Iodine consumption × Molecular weight of oxygen / (2 × Molecular weight of iodine) This gas-liquid mixture was heated to 120 ° C. by the heat exchanger 2 and the heater 14 installed in the pipe 12, and then wet-oxidized. Introduced into tower 1. The wet oxidation tower 1 is filled with 1 liter of the solid catalyst obtained in the catalyst preparation example, the wastewater is treated in the wet oxidation tower 1, the treated water is cooled in the heat exchanger 2 through the line 13, and the gas-liquid It was introduced into the separator 5. In the gas-liquid separator 5, the liquid level is detected by a liquid level controller (LC), the liquid level control valve 7 is operated to maintain a constant liquid level, and the pressure is detected by a pressure controller (PC). The pressure control valve 8 was operated to maintain a constant pressure.

A continuous processing test was performed for about 10,000 hours by the above method. The obtained treated water was sampled every 24 hours, and the concentration of metal ions such as calcium and the amount of iodine consumed were analyzed.

The concentration of metal ions in the obtained treated water is:
The results were as follows, and no significant concentration difference was observed before and after the wet oxidation treatment. Calcium ion 10 to 20 mg / L Magnesium ion 10 to 20 mg / L Iron (III) ion 2 to 5 mg / L The iodine consumption was always 200 mg / L or less.

After the test for 10,000 hours, the reaction was stopped and the inside of the apparatus was inspected.
No scale formation was observed inside the wet oxidation tower 1.

(Example 2) In the same manner as in Example 1, except that 20 to 30 mg of oxalic acid per 1 L of effluent was added to effluent in the same manner as in Example 1 in place of ethylenediaminetetraacetic acid tetrahydrate, as oxalate ions. Test.

The obtained treated water was sampled every 24 hours and analyzed for iodine consumption.
/ L or less.

After the test for 10,000 hours, the reaction was stopped, and the inside of the apparatus was inspected. As a result, formation of a slight scale on the inner wall of the heat exchanger 2 was recognized. This scale could be easily removed by washing with nitric acid.

(Example 3) The wastewater to be treated had the following composition. Instead of ethylenediaminetetraacetic acid tetrahydrate, 40 mg of ethylenediamine was added per liter of wastewater, the wastewater treatment temperature was set to 140 ° C, and the air supply amount The test was performed in the same manner as in Example 1 except that the amount was twice as much as the theoretical oxygen demand required for converting ammonia to nitrogen. NH ₃ 300 to 400 mg / L Calcium ion 5 to 10 mg / L Magnesium ion 5 to 10 mg / L The obtained treated water was sampled every 24 hours, and the respective concentrations of calcium ion, magnesium ion and ammonia were analyzed.

The concentrations of the respective components in the obtained treated water are as follows, and no significant difference was observed between calcium ions and magnesium ions before and after the wet oxidation treatment. NH ₃ 0.5 to 2 mg / L Calcium ion 5 to 10 mg / L Magnesium ion 5 to 10 mg / L After the test for 10,000 hours, the reaction was stopped, and the inside of the device was inspected. No scale was found in the pipe 12 or inside the wet oxidation tower 1.

(Example 4) The wastewater to be treated had the following composition, the amount of ethylenediaminetetraacetic acid tetrahydrate added was 400 mg per liter of wastewater, and the wastewater treatment temperature was 1
The test was performed in the same manner as in Example 1 except that the temperature was set to 40 ° C. and the amount of air supply was set to 1.5 times the required amount obtained from the following TOD. Na ₂ S 8% NaSH 3% Na ₂ CO ₃ 3% Aluminum 20 mg / L (TOD 100,000 mg / L) The obtained treated water was sampled every 24 hours to analyze the aluminum concentration and sulfide ion concentration. . As a result, the concentration of aluminum is 18 to 22 mg / L,
The average was 20 mg / L. Further, the sulfide ion concentration was 0.1 mg / L or less.

(Comparative Example) A test was conducted in the same manner as in Example 1 except that no chelating agent was added to the waste water.

Although the treated water iodine consumption was 200 mg / L or less, the pressure loss gradually increased, and the treated water iodine consumption was 900 m / hour after approximately 1,000 hours of operation.
g / L. Thereafter, the apparatus was stopped and the inside of the reactor was inspected. As a result, formation of a strong scale was confirmed on the inner wall of the heat exchanger 2 and the inside of the solid catalyst layer of the wet oxidation tower 1.

[0060]

According to the present invention, when treating wastewater containing scale-forming substances using a solid catalyst, it is possible to prevent the formation of scale in the apparatus by adding a chelating agent to the wastewater, and to maintain the apparatus. This facilitates safe, inexpensive, simple, and stable long-term continuous wastewater treatment.

[Brief description of the drawings]

FIG. 1 shows a flow of an example of a processing apparatus according to the present invention.

[Explanation of Codes] Wet oxidation tower 2. Heat exchanger 3. Drainage feed pump 4. Drain tank 5. Gas-liquid separator 6. Air compressor 7. Liquid level control valve 8. Pressure control valve 9. Mass flow controller 10. Air line 11. Line 12. Line 13. Line 14． heater

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C02F 1/58 C02F 1/58 J 1/62 1/62 Z C09K 3/00 108 C09K 3/00 108C 108B

Claims (6)

[Claims] 1. A wastewater treatment method comprising oxidizing and decomposing a COD component and / or a nitrogen-containing component contained in a wastewater in the presence of a solid catalyst and a chelating agent to detoxify the wastewater. 2. The wastewater treatment according to claim 1, wherein the wastewater contains a water-soluble salt and / or oxide of at least one metal selected from the group consisting of aluminum, alkaline earth metals and heavy metals. Method. 3. The method for treating wastewater according to claim 1, wherein the chelating agent is at least one of the compounds classified into the following (A) to (D). (A) Ethylenediaminetetraacetic acid (EDTA), trans-1,2-cyclohexanediaminetetraacetic acid (CyDT
A), glycol ether diamine tetraacetic acid (GEDTA)
Or EGTA), diethylenetriaminepentaacetic acid (DT
PA), nitrilotriacetic acid (NTA), oxalic acid, maleic acid, phthalic acid, citric acid, succinic acid, salicylic acid, sulfosalicylic acid, β-mercaptopropionic acid, thioglycolic acid, and dimercaptosuccinic acid At least one compound. (B) A salt formed from at least one compound selected from (A) and an alkali metal hydroxide. (C) Ethylenediamine or triethanolamine. (D) A salt formed from ethylenediamine or triethanolamine and an acid. 4. The content of water-soluble salts and / or oxides of at least one metal selected from the group consisting of aluminum, alkaline earth metals and heavy metals in the wastewater is 1 to 3 as the total concentration of metal ions. The method for treating wastewater according to any one of claims 1 to 3, wherein the amount is in the range of 500 mg / L. 5. The total molar concentration of the chelating agent is 0.5 to 50 times the total molar concentration of at least one metal ion selected from the group consisting of aluminum, alkaline earth metals and heavy metals in the waste water. 5. The method for treating wastewater according to claim 1, wherein a chelating agent is added as described above. 6. The method for treating wastewater according to claim 1, wherein the temperature during wastewater treatment is 40 to 200 ° C.