JPH08309360A - Method and apparatus for treating waste water containing oxidizable substance - Google Patents

Abstract

PURPOSE: To efficiently treat an oxidizable substance by guiding an aq. electrode soln. from an anode chamber to a cathode chamber when the oxidizable substance in waste water is subjected to oxidation treatment and injecting oxygen into the cathode chamber to keep the concn. of nitric acid in the cathode chamber constant. CONSTITUTION: The waste water in a waste water tank 17 passes through a second washing column 28, the anode soln. circulating tank 22 of a silver recovery device and the anode soln. circulating tank 15 of a nitric acid recovery device to reach the anode soln. circulating tank 4 of an oxidative decomposition device. An anode soln. is guided to an anode chamber 1 by circulating piping 41 to be returned to the anode soln. circulating tank 4. Monovalent silver ions in the anode soln. guided to the anode chamber 1 are converted to divalent silver ions. The greater part of the oxidizable substance contained in the waste water supplied to the anode soln. circulating tank 4 is oxidized and decomposed in the anode chamber 1 and the remainder thereof is oxidized and decomposed in the anode soln. circulating tank 4. Nitric acid in a cathode soln. is reduced to nitrous acid in a cathode chamber 2. Oxygen is supplied to the cathode chamber 2 through piping 47 in order to regenerate nitrous acid formed in the cathode chamber to nitric acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater containing an oxidizable substance and an apparatus for treating the same, and in particular, the concentration of the oxidizable substance as a chemical oxygen demand (COD)
TECHNICAL FIELD The present invention relates to a wastewater treatment method suitable for treatment for reducing COD in industrial wastewater containing an oxidizable substance that varies at 3 g / liter or less, and a treatment apparatus therefor.

[0002]

2. Description of the Related Art The degree of water pollution that does not relate to a specific harmful substance in the drainage standards for sea areas and lakes is specified by COD in Japan's Law Concerning Prevention of Water Pollution. COD is a Japanese Industrial Standard Factory Drainage Test Method K010
2 The measuring method is defined as “oxygen consumption (COD) by potassium permanganate at 100 ° C.”.
Oxygen consumption is the amount of oxygen consumed by the oxidizable substances in the wastewater, mainly organic substances, and is the amount of oxygen consumed after a certain excess amount of potassium permanganate is added to the test water and heated for a certain period of time. This is a method of obtaining the amount of oxygen consumed from the amount of potassium manganate.

JP-A-64-30689 describes a waste treatment method. In this treatment method, waste is treated by an electrolytic cell having an anode chamber and a cathode chamber separated by a porous diaphragm or a cation exchange membrane. The anode chamber liquid in the anode chamber is nitric acid (4 to 12 gmol / liter) containing silver nitrate (0.1 to 1 gmol / liter), and the cathode chamber liquid in the cathode chamber is nitric acid (6 to 16 gmol / liter). . The waste is supplied into the anode chamber and is oxidatively decomposed by radicals produced by the action of water and silver ions in the divalent valence state produced by the potential difference on the anode.

Further, in the waste treatment system shown in FIG. 2 of JP-A-64-30689, nitric acid is reduced in the catholyte to produce nitrous acid as a reverse reaction of the oxidation reaction on the anode. Therefore, a boiler that promotes the decomposition of nitrous acid into nitric acid, nitric oxide, and water, a packed tower that oxidizes and absorbs nitric oxide into nitric acid vapor with air or oxygen, and the gas from the packed tower is washed with concentrated nitric acid. And a scrubbing tower for removing nitric oxide.

[0005]

The waste treatment method described in Japanese Unexamined Patent Publication No. Sho 64-30689 is applied to the treatment of wastes composed of non-silicone organic substances or wastes containing substances that can be decomposed by oxidation. Applicable.

In addition, "D. F. Steel, Electro Chemistry and West Deposition,
Chemistry in Britain, October 1991, 9
15-918 "(Reference 1), the waste treatment method disclosed in JP-A-64-30689 can be applied to oxidative decomposition treatment of phenol present in wastewater at a concentration of 5.6% to 100%. It is shown. However, if the concentration is less than 5.6%, it is necessary to concentrate the wastewater or mix it with wastewater having a high phenol concentration to raise the phenol concentration to 5.6% or more.

When 100 kg of phenol is completely electrolytically oxidatively decomposed into carbon dioxide gas and water, water accompanying hydrogen ions transferred from the anode chamber to the cathode chamber through the cation exchange membrane and the cation exchange membrane are used to generate electricity. Since the total amount of water flowing from the anode chamber to the cathode chamber due to dynamic osmotic pressure reaches 1700 liters, if 100 kg of phenol is present in 1700 liters of water and 5.6%, the amount of electrode liquid in the anode chamber is There is no excess or deficiency. However, if water is insufficient and the amount of electrolyte in the anode chamber decreases, water may be added, but conversely, if water becomes excessive and the amount of electrolyte in the anode chamber becomes excessive. This excess amount of electrolytic solution is extracted from the anode chamber, and the nitric acid concentration and silver nitrate concentration in the electrolytic solution in the anode chamber decrease. In order to avoid such a problem, it is necessary to raise the phenol concentration to 5.6% or more as described above.

The phenol concentration in this case is equivalent to COD of 133 g / liter, and is disclosed in JP-A-64-30689.
A preferable limit of applying the method of the publication to treatment of wastewater containing an oxidizable substance is that COD is 133 g / liter or more regardless of the type of the oxidizable substance.

It is possible to concentrate the wastewater having a low COD to a COD of 133 g / liter or more. However, it is necessary to evaporate and remove a large amount of water until the COD reaches the above value, as the degree of water pollution is lower. Therefore, it is difficult to continuously treat wastewater having a COD of less than 133 g / liter.

When the wastewater contains a metal compound together with the oxidizable substance, the wastewater is concentrated and the conventional method is applied.
Metal compounds accumulate in the anode and cathode electrolytes,
Eventually, the insoluble metal compound may precipitate to make it difficult to continue the oxidative decomposition treatment.

An object of the present invention is to treat effluent having a COD of less than 133 g / liter, which can suppress a decrease in nitric acid concentration in the cathode chamber due to water flowing in through a porous membrane or a cation exchange membrane. It is an object to provide a method for treating wastewater containing a substance and a treatment apparatus therefor.

Another object of the present invention is to provide a method for treating wastewater containing an oxidizable substance and a treatment apparatus for the same, by which nitric acid can be continuously recovered and easily added to the wastewater.

Another object of the present invention is to provide a method for treating wastewater containing an oxidizable substance which can easily recover silver contained in an aqueous electrolytic solution and can easily add silver to the wastewater to be treated, and the treatment thereof. To provide a device.

Another object of the present invention is to provide a method for treating wastewater containing an oxidizable substance and a treatment apparatus therefor, which makes it possible to regenerate the aqueous electrolytic solution in the first cathode chamber of the oxidative decomposition apparatus with a simple apparatus. To do.

Another object of the present invention is to provide a method for treating wastewater containing an oxidizable substance capable of reducing nitrogen oxide contained in the gas released to the outside.

Another object of the present invention is to provide a method for treating waste water containing an oxidizable substance capable of efficiently regenerating an aqueous electrolytic solution in the first cathode chamber.

Another object of the present invention is to provide a method for treating wastewater containing an oxidizable substance, which can make the treatment apparatus compact.

Another object of the present invention is to provide a method for treating wastewater containing an oxidizable substance and a treatment apparatus therefor capable of continuously recovering silver and reducing the power consumption required therefor. is there.

Another object of the present invention is to provide a method for treating waste water containing an oxidizable substance, which can prevent accumulation of polyvalent anions other than monovalent anions in the treatment apparatus.

[0020]

To achieve the above object, the present invention is characterized by an electrolytic oxidative decomposition means having a first anode chamber and a first cathode chamber separated by a porous membrane or a cation exchange membrane. To the first aqueous electrolytic solution containing nitric acid and silver ions, which is introduced into the first anode chamber, is added waste water containing an oxidizable substance and having a chemical oxygen consumption of less than 133 g / liter;
The oxidizable substance is oxidized and treated by the action of divalent silver ions contained in the first aqueous electrolyte solution, and the excess first aqueous electrolyte solution in the first anode chamber is replaced with the first aqueous electrolyte solution. To lead to the cathode chamber.

A second aspect of the present invention that achieves the above-mentioned other object is that the second aqueous electrolytic solution flowing out from the first cathode chamber is isolated by an anion exchange membrane. Leading to the second liquid chamber of the nitric acid recovery means, and moving the nitrate ions in the second aqueous electrolytic solution from the second liquid chamber to the first liquid chamber through the anion exchange membrane to form nitric acid. Is added to the wastewater introduced to the first anode chamber.

A third aspect of the present invention which achieves the above-mentioned other object is that the first electrode chamber and the second electrode chamber of the silver deposition electrolysis means have a first electrode chamber and a second electrode chamber separated by an anion exchange membrane. The second aqueous electrolytic solution discharged from the second liquid chamber of the nitric acid recovery means is introduced into the electrode chamber of the second electrode chamber where the electrode serving as the cathode is present, and the monovalent solution contained in the second aqueous electrolytic solution is introduced. And depositing the silver ions as metallic silver on the electrode, and guiding the waste water to be supplied to the first anode chamber to the electrode chamber in which the electrode serving as the anode exists among the first electrode chamber and the second electrode chamber. The purpose is to elute metallic silver adhering to the latter electrode into the drainage.

The features of the inventions of claims 4 and 8 for achieving the above-mentioned other object are to inject air, oxygen or ozone into the second aqueous electrolytic solution of the first cathode chamber.

According to a fifth aspect of the invention for achieving the above-mentioned other object, the first aqueous electrolytic solution introduced to the first cathode chamber is
Before the nitric acid is added, the nitric oxide-containing gas discharged from the first cathode chamber is brought into contact with the gas.

[0025] A sixth aspect of the present invention which achieves the above-mentioned other object is that the air, oxygen or ozone is passed through an air chamber formed between air-permeable cathodes arranged in the first cathode chamber. Injecting into the second aqueous electrolytic solution.

In order to achieve the above-mentioned other object, the invention of claim 7 is characterized in that the nitric acid recovery means is an electrodialysis means, and the second aqueous electrolytic solution is the second chamber. The nitric acid ion moved into the second anode chamber of the electrodialysis means, which is the first chamber, is converted to nitric acid by introducing the catholyte into the cathode chamber and performing electrodialysis.

According to a ninth aspect of the present invention which achieves the above-mentioned other object, the polarities of the electrodes arranged in the first electrode chamber and the second electrode chamber are switched, and the first electrode chamber and the second electrode chamber are made to correspond to the polarities. 2 The electrode chamber for separately guiding the aqueous electrolyte and the drainage is to be switched.

A feature of the fourteenth aspect of the present invention for achieving the above-mentioned other object is that the anion exchange membrane is an anion exchange membrane that selectively permeates monovalent anions.

[0029]

According to the first aspect of the present invention, a wastewater containing an oxidizable substance and having a chemical oxygen consumption of less than 133 g / liter is first.
Is discharged from the first anode chamber by guiding it to the anode chamber,
Since the first aqueous electrolytic solution containing nitric acid is introduced into the first cathode chamber, it is possible to suppress a decrease in nitric acid concentration in the first cathode chamber due to water flowing through the cation exchange membrane. The suppression of the decrease in nitric acid concentration can eliminate the necessity of supplying new nitric acid from the outside of the system to the first cathode chamber, and can improve the degree of inhibition of oxidative decomposition of the oxidizable substance due to the decrease in nitric acid concentration.

According to the invention of claim 2, the following effects are obtained in addition to the effects produced by the invention of claim 1. Nitric acid ions contained in the second aqueous electrolytic solution discharged from the first cathode chamber of the electrolytic oxidative decomposition means are moved to the first liquid chamber by dialysis through the anion exchange membrane in the nitric acid recovery means to form nitric acid. Therefore, the nitrate ions contained in the second aqueous electrolytic solution introduced into the second liquid chamber can be continuously moved into the wastewater introduced into the first liquid chamber. This is equivalent to continuously recovering the nitric acid contained in the second aqueous electrolytic solution in the second liquid chamber into the waste water containing the oxidizable substance in the first liquid chamber. Thus, the nitric acid contained in the second aqueous electrolytic solution can be continuously recovered and easily added to the waste water. COD containing oxidizable substances
In the case of treating wastewater having an amount of less than 133 g / liter by supplying it to the first anode chamber of the electrolytic oxidative decomposition means to oxidize the oxidizable substance by the action of divalent silver ions,
Nitric acid can be substantially continuously recovered and reused from the aqueous electrolytic solution. Therefore, COD is 133g including oxidizable substances.
The electrolytic oxidative decomposition utilizing the action of divalent silver ions can be applied to the treatment of the oxidizable substance contained in the waste water of less than 1 / liter, and the oxidizable substance can be efficiently treated. . The nitric acid contained in the second aqueous electrolytic solution discharged to the external environment can be significantly reduced.

According to the invention of claim 3, in addition to the function and effect produced by the invention of claim 2, a first electrode chamber of a silver deposition electrolysis means having a first electrode chamber and a second electrode chamber separated by an anion exchange membrane, and The second aqueous electrolytic solution discharged from the second liquid chamber of the nitric acid recovery means is introduced into the electrode chamber of the second electrode chamber in which the cathode electrode exists, and monovalent silver ions contained in the second aqueous electrolytic solution are introduced. Is deposited as metallic silver on the electrode, the silver contained in the second aqueous electrolytic solution can be easily recovered. This leads to a significant reduction in the amount of silver contained in the second aqueous electrolytic solution discharged to the external environment. Of the first electrode chamber and the second electrode chamber, the drainage supplied to the first anode chamber is guided to the electrode chamber in which the electrode serving as the anode exists, and the metallic silver adhering to the latter electrode is eluted into the drainage. Therefore, silver can be easily added to the wastewater to be treated. Since both silver deposition and elution are performed, the power consumption of the silver deposition electrolysis means can be very small.

Since each of the inventions of claim 4 and claim 8 has the function and effect produced by the invention of claim 2, air, oxygen or ozone is injected into the second aqueous electrolytic solution in the first cathode chamber.
The nitrous acid produced in the first cathode chamber can be converted to nitric acid. In particular, the second aqueous electrolytic solution in the first cathode chamber can be regenerated by a simple device for injecting air, oxygen or ozone into the first cathode chamber. It should be noted that the eighth aspect of the invention also brings about an operational effect obtained by the seventh aspect of the invention described later. Further, the invention of claim 4 subordinate to claim 3 also produces the action and effect produced by the invention of claim 3.

According to a fifth aspect of the present invention, in addition to the function and effect of the fourth aspect of the invention, the first aqueous electrolytic solution introduced into the first cathode chamber is brought into contact with the gas containing nitrogen oxide discharged from the first cathode chamber. Therefore, the nitric oxide is absorbed by the first aqueous electrolytic solution, and as a result, the nitric oxide contained in the gas released to the outside can be reduced. The nitric oxide absorbed by the first aqueous electrolytic solution becomes nitric acid and is supplied to the first cathode chamber.

According to the invention of claim 6, in addition to the effect produced by the invention of claim 2, air, oxygen or ozone is passed through an air chamber formed between air-permeable cathodes arranged in the first cathode chamber. Since the gas is injected into the second aqueous electrolytic solution, the gas can be efficiently diffused into the second aqueous electrolytic solution. Therefore, the reaction of air, oxygen or ozone with nitrous acid contained in the second aqueous electrolytic solution is actively performed, and the amount of change from nitrous acid to nitric acid increases. Thus, the second aqueous electrolytic solution can be efficiently regenerated in the first cathode chamber.

According to the invention of claim 7, in addition to the effect produced by the invention of claim 2, nitric acid is recovered by electrodialysis, so that the area of the anion exchange membrane can be reduced.
Therefore, the nitric acid recovery means is downsized, and the wastewater treatment device containing the oxidizable substance is compact.

According to a ninth aspect of the present invention, in addition to the function and effect produced by the third aspect of the invention, the polarities of the electrodes arranged in the first electrode chamber and the second electrode chamber are switched, and the second electrode is provided in accordance with the polarity. By switching the electrode chambers that separately guide the aqueous electrolytic solution and the wastewater, the removal of monovalent silver ions contained in the second aqueous electrolytic solution and the elution of silver into the wastewater guided to the first anode chamber can be performed. It can be performed continuously. In addition, since silver is deposited and eluted simultaneously, the power consumption of the silver deposition electrolysis means can be very small.

In the fourteenth aspect of the invention, in addition to the function and effect of the third aspect of the invention, since the anion exchange membrane that selectively permeates monovalent anions is used as the anion exchange membrane, the second aqueous electrolysis is performed. The polyvalent anions other than the monovalent anions contained in the liquid are not taken into the wastewater guided to the first anode chamber, and the accumulation in the processing device can be prevented.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus for treating waste water containing an oxidizable substance, which is a preferred embodiment of the present invention, will be described with reference to FIG.

This embodiment comprises a silver recovery device, a nitric acid recovery device and an oxidative decomposition device.

The silver recovery device comprises a silver deposition / elution electrolytic bath 31,
An anolyte circulation tank 22 and a catholyte circulation tank 23 are provided. The silver deposition / elution electrolysis cell 31 has an anion exchange membrane 21 selectively permeable to monovalent anions inside, and has electrode chambers 19 and 20 separated by this membrane. Anolyte circulation tank 22
To the electrode chamber 19 by the circulation pipe 34 and the circulation pipe 5
3 is connected to the electrode chambers 20 respectively. The catholyte circulation tank 23 is connected to the electrode chamber 20 by a circulation pipe 35 and to the electrode chamber 19 by a circulation pipe 54, respectively.
The anolyte circulation tank 22 is connected to the second cleaning tower 28 by a pipe 33. The catholyte circulation tank 23 is connected to the neutralizer 11 by a pipe 50.

The detailed structure of the silver recovery device will be described with reference to FIG. The on-off valve 55A is located at the inlet side of the electrode chamber 19 of the circulation pipe 34, and the on-off valve 55B is located at the electrode chamber 1 of the circulation pipe 34.
9, an opening / closing valve 56A is provided at the inlet side of the electrode chamber 19 of the circulation pipe 54, and an opening / closing valve 56B is provided at the circulation pipe 5
No. 4 electrode chamber 19 is provided at the outlet side portion. Further, the opening / closing valve 58A is located at the inlet side portion of the electrode chamber 20 of the circulation pipe 35, the opening / closing valve 58B is located at the outlet side portion of the electrode chamber 20 of the circulation pipe 35, and the opening / closing valve 57A is located at the electrode chamber 20 of the circulation pipe 53.
And an on-off valve 57B are provided at the outlet side portion of the electrode chamber 20 of the circulation pipe 53, respectively. Electrode chamber 1
The electrode 59 provided inside 9 is connected to the changeover switch 63. The electrode 60 provided in the electrode chamber 20 is connected to the changeover switch 64. Terminals 63A and 64B are power sources 62
Connected to the positive electrode of. Terminals 63B and 64A are power sources 62
Connected to the cathode. On-off valves 55A, 55B, 56A,
56B, 57A, 57B, 58A and 58B, and the changeover switches 63 and 64 are controlled by the controller 61.

The nitric acid recovery device comprises a nitric acid electrodialysis tank 30, an anolyte circulation tank 15 and a catholyte circulation tank 16. The nitric acid electrodialysis tank 30 has a monovalent anion selective permeable anion exchange membrane 14 installed therein, and has an anode chamber 12 and a cathode chamber 13 separated by this membrane. The anolyte circulation tank 15 is connected to the anode chamber 12 by a circulation pipe 37, and the catholyte circulation tank 16 is connected to the cathode chamber 13 by a circulation pipe 38. The anolyte circulation tank 15 is connected to the anolyte circulation tank 22 of the silver recovery device by a pipe 36. Catholyte circulation tank 16
Is connected to the catholyte circulation tank 23 of the silver recovery device by a pipe 39. The oxidative decomposition apparatus includes an electrolytic oxidative decomposition tank 29, an anolyte circulation tank 4 and a catholyte circulation tank 5. The electrolytic oxidative decomposition tank 29 has a cation exchange membrane 3 made of a fluorinated ethylene polymer therein, and has an anode chamber 1 and a cathode chamber 2 separated by the membrane. The anolyte circulation tank 4 is connected to the anode chamber 1 through a circulation pipe 41, and is connected to the anolyte circulation tank 15 of the nitric acid recovery device through a pipe 40. The catholyte circulation tank 5 is connected to the cathode chamber 2 by a circulation pipe 42, and a pipe 43
Is connected to the catholyte circulation tank 16 of the nitric acid recovery device. The anolyte circulation tank 4 is connected to the first washing tower 27 by a pipe 26. The catholyte circulation tank 16 is also connected to the first cleaning tower 2 through the pipe 48.
Connected to 7. The anolyte circulation tank 4 is further connected to the exhaust gas treatment device 7 via a duct 44. Exhaust gas treatment device 7
Is connected to an exhaust stack (not shown) by a duct 46. The duct 65 connected to the catholyte circulation tank 5 is connected to the first cleaning tower 27.

The drain tank 17 is connected to the second washing tower 28 by a pipe 24. First washing tower 27 and second washing tower 28
Are connected by a duct 67. The duct 45 connects the second cleaning tower 28 and the exhaust gas treatment device 7. The exhaust gas treatment device 7 is connected to the neutralization device 11 via a pipe 49.

FIG. 3 shows an electrolytic oxidative decomposition tank 29A which is another structural example of the electrolytic oxidative decomposition tank 29. Electrolytic oxidation decomposition tank 29
A has a plurality of cation exchange membranes (or porous diaphragms) 3 provided therein, and forms an anode chamber 1 and a cathode chamber 2 separated by the cation exchange membranes 3. Anode 6 is anode chamber 1
Placed inside. Two porous cathodes 8 in each cathode chamber 2
Placed inside. An air chamber 9 is formed in the cathode chamber 2 between a pair of porous cathodes 8. In the configuration of FIG. 1, an electrolytic oxidative decomposition tank 29A may be used instead of the electrolytic oxidative decomposition tank 29A.

Another example of the structure of the nitric acid electrodialysis tank 30 is shown in FIG. The nitric acid electrodialysis tank 30A of FIG. 4 is provided with a plurality of anion exchange membranes 14 therein, and an anode chamber 12 in which an anode is arranged and a cathode chamber 13 in which a cathode is arranged are alternately provided. Figure 5
Still another configuration example of the nitric acid electrodialysis tank 30 is shown. This nitric acid electrodialysis tank 30B has an anion exchange membrane 14 inside,
Bipolar ion exchange membranes 10 in which a cation exchange membrane and an anion exchange membrane are combined are alternately arranged. Between the anion exchange membrane 14 and the bipolar ion exchange membrane 10,
Anode chamber 12 receiving hydrogen ions from the cation exchange membrane surface of the bipolar exchange membrane and cathode chamber 13 receiving hydroxide ions from the anion exchange membrane surface of the bipolar exchange membrane.
Are arranged alternately. In FIG. 1, nitric acid electrodialysis tank 3
Instead of 0, a nitric acid electrodialysis tank 30A or a nitric acid electrodialysis tank 30B may be used.

The treatment of wastewater containing an oxidizable substance using the wastewater treatment apparatus of this embodiment described above will be described below.

Wastewater containing organic matter which is an oxidizable substance to be treated (COD is smaller than 133 g / liter)
Is supplied to the drain tank 17. This wastewater reaches the anolyte circulation tank 4 of the oxidative decomposition apparatus through the second washing tower 28, the anolyte circulation tank 22 of the silver recovery apparatus and the anolyte circulation tank 15 of the nitric acid recovery apparatus. In the second washing tower 28, the first washing tower 2
Nitric oxide contained in the gas discharged from 7 is absorbed by the waste water. The gas from which the nitric oxide has been removed is guided to the exhaust gas treatment device 7 through the duct 45 and treated. The gas is discharged from the exhaust gas treatment device 7 to the duct 46 and exhausted to the outside from an exhaust stack (not shown). The silver and nitric acid recovered in the anolyte circulation tank 22 and the nitric acid recovered in the anolyte circulation tank 15 are added to the waste water, respectively. The amount of nitric acid added in the anolyte circulation tank 22 is
It is significantly smaller than the amount of nitric acid added in the anolyte circulation tank 15, and is at least equivalent to the amount of silver ions eluted from the anode of the silver deposition / dissolution electrolytic tank 31. Silver reacts with nitric acid to form silver nitrate.

The anolyte is an aqueous solution of nitric acid (4 to 12 g mol / l) containing silver nitrate (0.1 to 1 g mol / l). The silver ions and nitric acid contained in the anolyte are those recovered by the silver recovery device and the nitric acid recovery device, and are provided by waste water. This anolyte is guided to the anode chamber 1 by the circulation pipe 41 and returned to the anolyte circulation tank 4. By the way, the catholyte introduced from the catholyte circulation tank 5 into the cathode chamber 2 through the circulation pipe 42 is nitric acid (6 to 16 gmol / liter).
Is an aqueous solution of. The anolyte and catholyte are electrolytes. The anode in the anode chamber 1 and the cathode in the cathode chamber 2 are connected to a DC power source, and a voltage is applied between these electrodes.

Monovalent silver ions in the anolyte introduced into the anode chamber 1 are converted into silver ions in a divalent valence state (divalent silver ions) on the anode by the action of positive potential difference. It
Radicals (secondary oxidizing species) are generated by the action of this divalent silver ion and the water in the waste water. Due to the reverse action of this, divalent silver ions are converted into monovalent silver ions. Most of the oxidizable substance contained in the waste water supplied to the anolyte circulation tank 4 is oxidatively decomposed by radicals in the anode chamber 1 and the rest in the anolyte circulation tank 4. The temperature of the anolyte is 50 ° C. or higher, preferably 50 ° C. to 90 ° C., in order to accelerate the decomposition of the oxidizable substance. Since divalent silver ions are continuously generated on the anode as described above, the oxidizable substance is also decomposed continuously. Gases such as carbon dioxide gas and halogen generated by the oxidative decomposition are guided to the anolyte circulation tank 4 along with the anolyte, and further the duct 44.
Is guided to the exhaust gas treatment device 7. The halogen gas is absorbed and removed by the absorbing liquid in the exhaust gas treatment device 7. The absorbing liquid that has absorbed the halogen gas is sent to the neutralizing device 11 through the pipe 49. The remaining gas is discharged from the exhaust gas treatment device 7 to the duct 46 and discharged from the exhaust stack into the outside atmosphere.

Further, the hydrogen ions generated near the anode are
It moves from the anode chamber 1 to the cathode chamber 2 through the cation exchange membrane 3 to carry the charges. At the same time, water moves through the cation exchange membrane 3 from the anode compartment 1 to the cathode compartment 2 either as hydronium ions combined with hydrogen ions or simply by electroosmotic pressure. 133g of COD in wastewater to be treated
In the case of less than / liter, the ratio P of the amount of water moving to the cathode chamber 2 through the cation exchange membrane 3 with respect to the amount of waste water supplied to the anolyte circulation tank 4 is represented by (Equation 1). C is the chemical oxygen demand (COD g / liter) of the wastewater.

P = C / 133 (Equation 1) In the cathode chamber 2, nitric acid in the catholyte is reduced to nitrous acid by the action of the negative potential difference. The nitric acid concentration in the catholyte decreases due to its conversion to nitrous acid and the migration of water through the cation exchange membrane 3 to the cathode chamber 2.

As described above, in the cathode chamber 2 of the electrolytic oxidative decomposition tank 29, a reduction reaction of nitric acid to nitrous acid occurs as a reverse reaction of the oxidation reaction in the anode chamber 1. Anolyte circulation tank 4
When the concentration of the non-oxidizing substance in the wastewater supplied to the exhaust gas is 100 g / liter as COD, when the non-oxidizing substance is completely oxidatively decomposed in the anode chamber 1 and the anolyte circulation tank 4, the cathode chamber electrolyte solution In theory 6.25 gmol / l nitric acid is reduced to nitrous acid. Nitrous acid is unstable in a nitric acid solution and decomposes into nitric acid and 3HNO ₂ ⇒ HNO ₃ + 2NO + H ₂ O nitric oxide by the following heterogeneous reaction. COD is 100 g /
In the case of 1 liter, when the supplied non-oxidizing substance is completely oxidatively decomposed and the decomposition of nitrous acid is completely performed by the above reaction, theoretically 4.17 g mol / l of nitric acid is oxidized in the catholyte. It becomes nitrogen and is lost.

Oxygen (or air) is supplied to the cathode chamber 2 through a pipe 47 in order to regenerate the nitric acid generated in the cathode chamber 2 into nitric acid by oxidation. Ozone may be used instead of oxygen, or oxygen (or air) and ozone may be used in combination. The nitrous acid generated in the cathode chamber 2 is oxidized by oxygen to become nitric acid. The nitric oxide slightly generated by the above reaction is introduced into the first cleaning tower 27 through the duct 65 together with unreacted oxygen (or air).

When the electrolytic oxidative decomposition tank 29A of FIG. 3 is used, air or oxygen, or air or oxygen containing ozone is supplied to the air chamber 9 to efficiently diffuse the gas into the cathode chamber 2. be able to. For this reason,
The reaction between nitrous acid and its gas can be activated and nitric acid can be produced more efficiently.

Further, the COD in the waste water to be treated is 133
When it is less than g / liter, the anolyte in the anode chamber 1 of the oxidative decomposition apparatus based on (Equation 2) becomes excessive and is discharged from the anode chamber 1 and the anolyte circulation tank 4. This excess anolyte contains silver nitrate and nitric acid.

R = 1− (C / 133) (Equation 2) where R is the ratio of the excess anolyte liquid amount to the wastewater supply amount.

The nitric acid concentration must be 4 gmol / liter or more in order to prevent the deposition of silver on the cathode of the electrolytic oxidative decomposition tank 29, and the practical maximum nitric acid concentration is 1
6 g mol / l. When the concentration of the non-oxidizing substance in the waste water is 100 g / liter in COD, the nitric acid concentration of the anolyte solution is 4 times that of the anolyte solution in order to make the nitric acid concentration of the catholyte solution in the electrolytic oxidative decomposition tank 29 4 gmol / l. 16 g mol / l is required.

The excess anolyte discharged from the anolyte circulation tank 4 is sent to the first cleaning tower 27 through the pipe 43.
Further, the anolyte is passed through the pipe 26 and the catholyte circulation tank 5
Be led to. For this reason, the catholyte circulation tank 5 is filled with the anolyte.
Since the nitric acid having a high concentration supplied to the cathode chamber 2 reaches the cathode chamber 2, the degree of decrease in the nitric acid concentration in the cathode chamber is reduced. The nitric acid concentration in the cathode chamber 2 is maintained at a predetermined value by supplying the anolyte to the catholyte circulation tank 5, oxidizing nitrous acid by injecting oxygen, and oxidizing nitric oxide. Therefore, it is possible to prevent the difficulty in continuing the electrolytic oxidative decomposition of the oxidizable substance due to the decrease in the nitric acid concentration.

The nitric oxide introduced into the first cleaning tower 27 is oxidized in the gas phase in the first cleaning tower 27 and converted into nitrogen dioxide. This nitrogen dioxide is absorbed by this anolyte when it comes into contact with the anolyte in the first cleaning tower 27, and becomes nitric acid. Nitric oxide that has not been absorbed by the anolyte in the first cleaning tower 27 is guided to the second cleaning tower 28 through the duct 67 together with the gas, and is absorbed by the waste water supplied from the drain tank 17. This absorbed nitric oxide also becomes nitric acid in the wastewater. The gas released from the second cleaning tower 28 is the exhaust gas treatment device 7
Sent to By providing the first cleaning tower 27 and the second cleaning tower 28, the concentration of nitric oxide in the exhaust gas discharged to the outside can be significantly reduced.

Excessive catholyte from the catholyte circulation tank 5 of the oxidative decomposition apparatus is led to the catholyte circulation tank 16 of the nitric acid recovery apparatus through the pipe 43. The amount of excess catholyte (excess catholyte) discharged from the catholyte circulation tank 5 is substantially equal to the amount of waste water supplied to the anolyte circulation tank 4, and the excess catholyte is discharged from the anolyte circulation tank 4. Is equal to the sum of the amount of anolyte solution and the amount of water that has reached the cathode chamber 2 from the anode chamber 1 through the cation exchange membrane 3.

The treatment of the discharged excess catholyte, specifically the recovery of nitric acid and silver from this catholyte is carried out by a nitric acid recovery device and a silver recovery device. The recovered nitric acid and silver nitrate are supplied to the anode chamber 1 again. Therefore, the anode chamber 1
The nitric acid concentration and the silver concentration therein are maintained at predetermined values, and the electrolytic oxidative decomposition of the oxidizable substance can be continued in a good state.

The excess catholyte supplied to the catholyte circulation tank 16 is introduced into the cathode chamber 13 through the catholyte circulation pipe 38. The nitric acid contained in this catholyte is dissociated into nitrate ions and hydrogen ions. Anode inside the anode chamber 12 and cathode chamber 13
The cathode inside is connected to a DC power supply, and a voltage is applied between these electrodes. Therefore, the nitrate ions in the cathode chamber 13 selectively pass through the anion exchange membrane 14 and reach the anode chamber 12. In the anode chamber 12, nitrate ions combine with hydrogen ions generated at the anode to form nitric acid. The anolyte containing nitric acid is introduced into the anolyte circulation tank 15 and supplied to the wastewater that has reached the anolyte circulation tank 15. On the other hand, in the cathode chamber 13, the hydrogen ions dissociated from nitric acid are combined with hydroxide ions generated at the cathode to be neutralized into water.

Since the nitric acid recovery apparatus including the nitric acid electrodialysis tank 30 produces nitric acid in the anode chamber using the nitrate ions separated from the catholyte by electrodialysis, the nitric acid is substantially continuously separated from the catholyte. And, the nitric acid can be continuously and easily supplied to the wastewater to be treated. The driving force of the electrodialysis means used in the nitric acid recovery device is the potential difference across the ion exchange membrane and the movement of nitrate ions permeating through the ion exchange membrane accelerated by this, which is the difference between the cathode chamber and the anode chamber. The nitrate ion can be dialyzed even if the chemical concentration gradient of the nitrate ion is reversed. By using the nitric acid electrodialysis cell of FIGS. 4 and 5, nitrate ions can be removed from a large amount of excess catholyte in a short time. The nitric acid recovery device recovers nitric acid by electrodialysis.
The amount of energy consumed is significantly smaller than in the case of recovering nitric acid by evaporating the waste liquid discharged to the outside with the configuration shown in Fig. 1 of 689 publication.

When the waste water to be treated contains a compound such as sulfur or phosphorus, the excess catholyte contains, in addition to nitrate ions, polyvalent anions such as sulfate ions and phosphate ions. Since the nitric acid recovery apparatus used in this example is provided with the monovalent anion selective permeable anion exchange membrane 14, these polyvalent anions are not recovered and the catholyte and the catholyte of the silver recovery apparatus are not recovered. It is discharged to the circulation tank 23. Therefore, an increase in the concentration of polyvalent anions in the wastewater supplied to the oxidative decomposition apparatus is prevented, so that it is possible to prevent the generation of precipitates due to the accumulation of polyvalent anions in the oxidative decomposition apparatus. This effect is
This is even more remarkable because the polyvalent anion is not recovered even by the silver recovery device.

The above-mentioned nitric acid recovery device substantially quantitatively separates the nitric acid contained in the excess catholyte in the catholyte circulation tank 16 that is discharged to the outside and transfers it to the waste water before it is supplied to the oxidative decomposition device. Thus, it has a function of keeping the nitric acid concentration in the anolyte in the oxidative decomposition apparatus at a predetermined value. By arranging a plurality of nitric acid recovery devices of FIG. 1 in parallel and connecting each anolyte circulation tank in series and each other's catholyte circulation tank in series, the nitrate ions in the excess anolyte are sequentially separated. The concentration of nitric acid in the waste water before being supplied to the oxidative decomposition apparatus can be further increased.

The nitric acid electrodialysis tank 30 can use a combination of a bipolar membrane and an anion exchange membrane instead of a general combination of an electrode and an anion exchange membrane.

Most of the nitric acid is removed in the nitric acid recovery apparatus, and the excess catholyte containing silver nitrate is supplied from the catholyte circulation tank 16 to the catholyte circulation tank 23 of the silver recovery apparatus. Controller 6
By the first control signal output from 1, the opening / closing valve 55A,
55B, 58A and 58B are opened, and open / close valves 56A, 5A
6B, 57A and 57B are closed. The changeover switch 63 is connected to the terminal 63A and the changeover switch 64 is connected to the terminal 64A by the first control signal. Therefore, the electrode 59 becomes the anode and the electrode 60 becomes the cathode,
A voltage is applied between these electrodes.

The silver deposition / elution electrolytic bath 31 of the silver recovery device is
The silver ions (existing as silver nitrate) contained in the excess catholyte discharged from the catholyte circulation tank 16 of the nitric acid recovery device in which nitric acid has been removed to some extent by the negative potential difference
It is to be deposited as metallic silver on top. In order to deposit metallic silver on a platinum cathode in an aqueous silver nitrate solution having a concentration of 1 gmol / liter, a negative potential difference of 0.80 V or more between the anode and the anode is sufficient. Even if the nitric acid concentration is 1 gmol / l, the reduction reaction to nitrous acid does not occur unless the negative potential difference reaches 0.94 V, so that the precipitation of silver ions as metallic silver on the cathode occurs preferentially. However, in order to deposit metallic silver on the cathode and remove it from the aqueous solution until the silver ion concentration in the aqueous silver nitrate solution becomes 1 mg mol / liter, a negative potential difference of 0.98 V or more is theoretically required. Since nitric acid is not reduced to nitrous acid at a negative potential difference of 0.94 V, the nitric acid concentration must be lower than 1 mg mol / liter in order to prevent silver ion precipitation preferentially.

In the silver recovery apparatus used in this embodiment, most of the nitric acid-removed catholyte in the catholyte circulation tank 23 is introduced into the electrode chamber 20, drainage is introduced into the electrode chamber 19, and 1 V is applied between the electrodes. Processing is performed by applying the above potential difference. The silver ions constituting the silver nitrate contained in the catholyte do not pass through the anion exchange membrane 21 and are deposited as metallic silver on the electrode 60 which is the cathode.
At the same time, the nitrate ions forming the silver nitrate dissociate from the nitric acid, and pass through the anion exchange membrane 21 together with the slightly remaining nitrate ions to combine with hydrogen ions generated in the electrode chamber 19 to form nitric acid. This nitric acid is mixed with the wastewater flowing into the anolyte circulation tank 22. The nitrate ion and silver ion are removed, and the concentration of silver ion in the excess catholyte discharged from the catholyte circulation tank 23 to the pipe 50 is reduced to about 1 mg mol / liter. The catholyte is guided to the neutralizer 11 by the pipe 50 and neutralized, and then discharged to the outside by the discharge pipe 51. Both silver ions and nitrate ions that constitute silver nitrate are removed from the excess catholyte supplied to the catholyte circulation bath 23 by the silver deposition / elution electrolytic bath 31.

The excess catholyte supplied to the catholyte circulation tank 23 contains polyvalent anions that are not recovered by the nitric acid recovery device. However, since the silver recovery device has the anion exchange membrane 21 that is selectively permeable to monovalent anions, it is possible to prevent polyvalent anions from being recovered in waste water. The polyvalent anions are discharged from the catholyte circulation tank 23 into the pipe 50 together with the catholyte.

The controller 61 outputs the second control signal when a preset time has elapsed. By the time the first control signal is output and the second control signal is output, silver having a predetermined thickness is deposited on the electrode 60. Based on the second control signal,
The on-off valves 55A, 55B, 58A and 58B are closed, and the on-off valves 56A, 56B, 57A and 57B are opened. At the same time, the changeover switch 63 is connected to the terminal 63B and the changeover switch 64 is connected to the terminal 64B. Contrary to the above, the electrode 59 becomes the cathode and the electrode 60 becomes the anode, and the excess catholyte is introduced into the electrode chamber 19 and the drainage is introduced into the electrode chamber 20. Metallic silver is deposited on the electrode 59 and nitrate ions move from the electrode chamber 19 to the electrode chamber 20. The metallic silver deposited on the electrode 60 becomes monovalent silver ions and is eluted into the waste water in the electrode chamber 20. The silver ions eventually combine with nitrate ions to become silver nitrate. The recovered silver and nitric acid are supplied to the anolyte circulation layer 4 of the oxidative decomposition apparatus and reused. In this example, silver can be continuously recovered in the waste water from the excess catholyte discharged to the outside. Since the controller 61 alternately outputs the first control signal and the second control signal, it is possible to deposit metallic silver on the electrodes 59 and 60 alternately.

In this example, metal silver was deposited on the electrodes (removal of silver from the catholyte) in an electrode chamber having a silver recovery device,
Since the metallic silver deposited on the electrodes in the other electrode chambers is simultaneously eluted into the wastewater, the potential difference required for the electrode reaction is extremely small, and the required electrical energy depends on the low ion concentration in the excess catholyte. It becomes a low value due to a slight potential difference caused by the ionic conductivity of the ions. Further, since the potential difference required for the electrode reaction may be low, even if the concentration of silver ions in the excess catholyte is reduced, nitric acid is not reduced and metallic silver is deposited on the cathode. In the present embodiment, the silver ions and the nitrate ions constituting the silver nitrate can be simultaneously removed from the catholyte. The dissolution rate of silver in the wastewater containing the oxidizable substance before the treatment, that is, the amount of silver supplied to the anode chamber 1 of the oxidative decomposition apparatus per unit time is determined by the silver recovery apparatus from the excess catholyte. Is kept substantially equal to the amount of.

The rate of silver electrolytic deposition is governed by the mass transfer rate. Therefore, the lower the silver concentration in the excess catholyte, the lower the silver deposition rate. The adoption of a three-dimensional electrode having a large surface area makes it possible to increase the deposition rate of silver. 1 are arranged in parallel, the respective anolyte circulation tanks are connected in series, and the respective catholyte circulation tanks are also connected in series. By sequentially separating the silver ions that make up silver nitrate,
The silver in the catholyte can be continuously removed to a low concentration.

In this embodiment, the electrodes for depositing silver and the electrodes for eluting the deposited silver are changed over to the changeover switches 63, 64.
It is set by switching the polarity of each electrode by the operation of. However, it is also possible to move the electrodes instead of switching the polarities. That is, by moving the electrode 60 on which silver is deposited to the electrode chamber 19 and the electrode 59 after elution of the attached silver is moved to the electrode chamber 20, the silver deposited on the electrode 60 is eluted and the silver is deposited on the electrode 59. Can be made.
At this time, the electrode in the electrode chamber 19 is always kept at the anode, and the electrode in the electrode chamber 20 is kept always at the anode. Although it is necessary to stop the process in the silver recovery device when the electrode is moved, silver recovery can be continuously performed by switching to the process in the spare silver recovery device.

In this example, the C of the wastewater containing the oxidizable substance was
Even when the OD is less than 133 g / liter, the COD of water discharged from the apparatus of this embodiment to the outside can be significantly reduced by oxidizing and decomposing the oxidizable substance by the radicals generated based on divalent silver. Furthermore, in the processing,
Since this embodiment has a nitric acid recovery device and a silver recovery device, nitric acid and silver ions can be continuously recovered from the excess anolyte discharged from the anolyte circulation tank 4 of the oxidative decomposition device and can be supplied to the waste water. Their concentration in the anolyte of the decomposer can be kept substantially constant. Further, the respective concentrations of nitric acid and silver contained in the excess anolyte discharged to the outside can be significantly reduced.

In this embodiment, the area of the anion exchange membrane 14 installed in the nitric acid electrodialysis tank 30 of the nitric acid recovery device is remarkably larger than that of the anion exchange membrane installed in the diffusion dialysis tank of Embodiment 3. Can be made smaller. This makes it possible to make the treatment device for wastewater containing oxidizable substances compact.

(Specific Example 1) The apparatus for treating wastewater containing an oxidizable substance, which is the object of this example, is the apparatus shown in FIG.
One nitric acid recovery device and two silver recovery devices are provided in parallel. In this waste water treatment device, the anolyte circulation tank 22 of the second silver recovery device, the first
Anolyte circulation tank 22 of silver recovery device, anolyte circulation tank 15 of second nitric acid recovery device, and anolyte circulation tank 1 of first nitric acid recovery device
5 connected in series, the catholyte circulation tank 16 of the first nitric acid recovery device, the catholyte circulation tank 16 of the second nitric acid recovery device, the catholyte circulation tank 23 of the first silver recovery device, and the anode of the second silver recovery device. The liquid circulation tank 22 is connected in series. The anolyte circulation tank 4 of the oxidative decomposition apparatus is connected to the anolyte circulation tank 15 of the first nitric acid recovery apparatus, and the catholyte circulation tank 5 of the oxidative decomposition apparatus is connected to the catholyte circulation tank 16 of the first nitric acid recovery apparatus. . As the electrolytic oxidation decomposition tank, the electrolytic oxidation decomposition tank 29A of FIG. 3 is used. Table 1 shows the examination results in the case of treating the wastewater containing 100 g / liter of COD as the oxidizable substance by the wastewater treatment apparatus having the above configuration. The nitric acid concentration in the waste water supplied to the anolyte circulation tank 4 of the oxidative decomposition apparatus was 4 gmol / liter, and the silver nitrate concentration was 0.2 gmol / liter. In this example, shown in Table 1.

[0078]

[Table 1]

As described above, 752 liters of 1 m ³ of waste water supplied to each anode chamber 1 of the oxidative decomposition apparatus was introduced into the cathode chamber 2 through the cation exchange membrane 3 in the process of oxidative decomposition. The remaining 248 liters becomes excess anolyte and is introduced into the cathode chamber 2 through the first washing tower 27 and the catholyte circulation tank 5 to act as catholyte.

The theoretical amount of nitrous acid produced in the catholyte (electrolyte) in the cathode chamber 2 is 6250 gmol. The theoretical amount of oxygen required to oxidize this nitrous acid to nitric acid is 3125 gmol. Oxygen equivalent to 1.5 times this amount of oxygen is used as 113 m ³ of oxygen gas, and the electrolytic oxidation decomposition tank 2
9A was supplied to each air chamber 9 and was diffused in the catholyte in each cathode chamber 2. As a result, a total of 38 m ³ of oxygen and a total of 1 m ³
The gas containing nitric oxide is supplied from each cathode chamber 2 to the first cleaning tower 27 through the catholyte circulation tank 5. This gas is
In the first cleaning tower 27, countercurrently contacted with 248 liters of excess anolyte having a nitric acid concentration of 16 gmol / liter and a silver nitrate concentration of 0.8 gmol / liter discharged from the anolyte circulation tank 4, and contained. Nitric oxide content decreased to 0.02%. This gas was brought into countercurrent contact with the waste water containing the oxidizable substance in the second washing tower 28, and dropped until nitrogen oxide was not detected.

Nitric acid concentration 1 flowing out from the first washing tower 27
248 liters of excess anolyte having a concentration of 6.2 gmol / liter and a silver nitrate concentration of 0.8 gmol / liter flows into each cathode chamber 2 as a catholyte. The catholyte in each cathodic chamber 2 merges to form an excess catholyte of 1 m ³ at a nitric acid concentration of 4 gmol / liter and a silver nitrate concentration of 0.2 gmol / liter. I was led to 13.
Here, the concentration of nitric acid in the excess catholyte is lowered to 0.8 gmol / liter by electrodialysis. The excess catholyte discharged from the catholyte circulation tank 16 of the first nitric acid recovery device contains nitric acid 0.8 g mol / l and silver 21.6 g / l. The nitric acid concentration was 0.16 g mol / liter and the silver concentration was 21.6 g / liter. This excess catholyte is
In the electrode chamber 20 where the electrode 60, which is the cathode at the present time, is present, the nitric acid concentration is 0.01 gmol / liter, and metallic silver is deposited on the electrode 60, so that the silver concentration is 1.1 g / l.
Furthermore, in the electrode chamber 20 of the second silver recovery device in which the electrode 60, which is the cathode at present, is present, the nitric acid concentration is 0.005 g mol / liter and the silver concentration is 0.1 g.
/ Liter. Excess catholyte containing nitric acid at a concentration of 0.005 g mol / l and silver at a concentration of 0.1 g / l discharged from the catholyte circulation tank 23 of the second silver recovery device is introduced to the neutralizer 11. .

On the other hand, from the second washing tower 28, the electrode chamber 1 of the second silver recovery device, in which the electrode 59, which is currently the anode, is present.
9, the supplied wastewater containing the oxidizable substance has a nitric acid concentration of 0.03 gmol / liter due to nitrate ions guided from the electrode chamber 20 through the anion exchange membrane 21 by electrodialysis, and the metal The silver concentration is 1.1 g / liter due to silver ions ionized by the potential difference from the electrode 59 to which silver is attached. This drainage is the electrode chamber 1 of the first silver recovery device in which the electrode 59, which is currently the anode, is present.
Guided to 9. Here, the wastewater has a nitric acid concentration of 0.16 g.
Mol / liter, silver concentration becomes 21.6 g / liter. The nitric acid concentration increases as the wastewater passes through the respective anode chambers of the second nitric acid recovery device and the first nitric acid recovery device, and the nitric acid concentration of the wastewater reaching the anolyte circulation tank 4 of the oxidative decomposition device is 4 gmol / liter. Is. This waste water is concentrated in the anode chamber 1 by losing water to a nitric acid concentration of 16 g mol / liter and a silver concentration of 86.4 g / liter.

1 m supplied to the anode chamber 1 of the oxidative decomposition apparatus
^As COD contained in the waste water of ³ , 100 g / liter of the oxidizable substance is oxidatively decomposed, and the COD of the excess anolyte discharged from the anolyte circulation tank 4 is lowered to 400 mg / liter. Further, this COD is diluted with water that has passed through the cation exchange membrane 3 in the cathode chamber 2 to become 100 mg / liter. The COD of the excess catholyte discharged from the catholyte circulation tank 23 of the second silver recovery device is 100 mg / liter. The metal species contained in 1 m ³ of wastewater to be treated have the same concentration as the catholyte circulation tank 23 of the second silver recovery device.
Emitted from.

(Specific Example 2) The apparatus for treating wastewater containing an oxidizable substance, which is the object of this example, has the same structure as in Specific Example 1. With this treatment device, the oxidizable substance is converted into COD of 50
Table 2 shows the examination results when treating wastewater containing g / liter.
Shown in In this example, as shown in Table 2, oxidation

[0085]

[Table 2]

1 m ³ supplied to each anode chamber 1 of the decomposer
376 liters of water of the waste water was introduced into the cathode chamber 2 through the cation exchange membrane 3 in the process of oxidative decomposition. The remaining 6
24 liters become excess anolyte and the first washing tower 27
Also, it is introduced into the cathode chamber 2 through the catholyte circulation tank 5 and acts as a catholyte.

In the catholyte in the cathode chamber 2, theoretically 3125
g mol nitrous acid is produced. In order to oxidize this nitrous acid to nitric acid, theoretically 1563 gmol of oxygen is required.
Oxygen equivalent to 1.5 times this oxygen amount (oxygen gas 56 m ³ ).
Through the air chambers 9 to the cathode chambers 2 of the electrolytic oxidative decomposition tank 29A.
Of the catholyte. A gas containing a total of 19 m ³ of oxygen and a total of 0.5 m ³ of nitric oxide is supplied from each cathode chamber 2 to the first cleaning tower 27 via the catholyte circulation tank 5, and has a nitric acid concentration of 6.4 g mol / liter and After countercurrent contact with 624 liters of excess anolyte having a silver nitrate concentration of 0.32 gmol / liter, the content of nitric oxide was reduced to 0.02%. This nitric oxide is removed in the second washing tower 28.

Concentration of nitric acid flowing out from the first washing tower 27 6.
624 liters of anolyte having a silver nitrate concentration of 5 gmol / liter and a silver nitrate concentration of 0.32 gmol / liter flow into each cathode chamber 2. The excess catholyte flowing out from the catholyte circulation tank 5 has a nitric acid concentration of 4 gmol / liter, a silver nitrate concentration of 0.2 gmol / liter, and a volume of 1 m ³ . This excess catholyte has a nitric acid concentration of 0.1 in the cathode chamber 13 of the first nitric acid recovery device.
Cathode chamber 1 of the second nitric acid recovery device to 8 g mol / liter
Within 3, the nitric acid concentration drops to 0.16 gmol / l. The silver concentration in the excess catholyte is unchanged at 21.6 g / l. The excess catholyte is used in the first silver recovery device in the electrode chamber 20 in which the electrode 60, which is the cathode at the present time, is present, the nitric acid concentration is 0.03 g mol / liter, the silver concentration is 1.1 g / liter, and the second The concentration of nitric acid is 0.005 in the electrode chamber 20 of the silver recovery device where the electrode 60, which is currently the cathode, is present.
The g mol / l and silver concentration dropped to 0.1 g / l.

On the other hand, from the second washing tower 28, the electrode chamber 1 of the second silver recovery device in which the electrode 59, which is currently the anode, is present.
In Example 9, the nitric acid concentration in the waste water becomes 0.03 g mol / liter and the silver concentration becomes 1.1 g / liter. This drainage is
The nitric acid concentration was 0.16 g mol / liter, the silver concentration was 21.6 g / liter, and the nitric acid concentration was the second nitric acid recovery device in the electrode chamber 19 of the first silver recovery device where the electrode 59, which is currently the anode, is present. In the anode chamber 12 of the above, the amount was 0.8 gmol / liter, and in the anode chamber 12 of the first nitric acid recovery apparatus, it was 4 gmol / liter. The waste water loses water in the anode chamber 1 and is concentrated to have a nitric acid concentration of 6.4 g mol / liter and a silver concentration of 34.6 g / liter.

The oxidizable substance was oxidatively decomposed in the anode chamber 1 of the oxidative decomposition apparatus, and the COD of the excess anolyte was lowered to 80 mg / liter. Further, this COD is diluted with water to 50 mg / liter in the cathode chamber 2 of the oxidative decomposition apparatus. The COD of the excess catholyte discharged from the catholyte circulation tank 23 of the second silver recovery device is 50 mg / liter. The metal chemical species contained in the waste water of 1 m ³ to be treated are discharged from the catholyte circulation tank 23 of the second silver recovery device in the same concentration.

(Specific Example 3) The apparatus for treating waste water containing an oxidizable substance, which is the object of this example, has the same configuration as in Specific Example 1. With this processing equipment, the oxidizable substance is converted into COD of 10
Table 3 shows the examination results when treating wastewater containing g / liter.
Shown in In this example, as shown in Table 3, oxidation

[0092]

[Table 3]

1 m ³ supplied to each anode chamber 1 of the decomposer
75 liters of the waste water was introduced into the cathode chamber 2 through the cation exchange membrane 3 in the process of oxidative decomposition. 92 remaining
5 liters become excess anolyte and are introduced into the cathode chamber 2 through the first washing tower 27 and the catholyte circulation tank 5 to act as catholyte.

Theoretically 625 g in the catholyte in the cathode chamber 2.
Molar nitrous acid is produced. To oxidize this nitrous acid to nitric acid, theoretically 313 g mol of oxygen is required. Oxygen equivalent to 1.5 times this oxygen amount (oxygen gas 10.5 m ³ ).
Through the air chambers 9 to the cathode chambers 2 of the electrolytic oxidative decomposition tank 29A.
Of the catholyte. A gas containing a total of 3.5 m ³ of oxygen and a total of 0.1 m ³ of nitric oxide is supplied from each cathode chamber 2 to the first cleaning tower 27 via the catholyte circulation tank 5, and the nitric acid concentration is 4.3 g mol / mol. Liter and silver nitrate concentration 0.22 gmol /
In countercurrent contact with 925 liters of excess anolyte, the nitric oxide content dropped to 0.02%. This nitric oxide is removed in the second washing tower 28.

Concentration of nitric acid flowing out from the first washing tower 27 4.
An anolyte solution of 925 liters having a silver nitrate concentration of 3 gmol / liter and a silver nitrate concentration of 0.22 gmol / liter flows into each cathode chamber 2. The excess catholyte flowing out from the catholyte circulation tank 5 has a nitric acid concentration of 4 gmol / liter and a silver nitrate concentration of 0.2 gmol / liter and a volume of 1 m ³ . This excess catholyte has a nitric acid concentration of 0.1 in the cathode chamber 13 of the first nitric acid recovery device.
Cathode chamber 1 of the second nitric acid recovery device to 8 g mol / liter
Within 3, the nitric acid concentration drops to 0.16 gmol / l. The silver concentration in the excess catholyte is unchanged at 21.6 g / l. The excess catholyte is used in the first silver recovery device in the electrode chamber 20 where the electrode 60, which is the cathode at the present time, is present, the nitric acid concentration is 0.03 g mol / liter, the silver concentration is 1.1 g / liter, and the second The concentration of nitric acid is 0.005 in the electrode chamber 20 of the silver recovery device where the electrode 60, which is currently the cathode, is present.
The g mol / l and silver concentration dropped to 0.1 g / l.

On the other hand, from the second washing tower 28, the electrode chamber 1 of the second silver recovery device in which the electrode 59, which is currently the anode, is present.
In Example 9, the nitric acid concentration in the waste water becomes 0.03 g mol / liter and the silver concentration becomes 1.1 g / liter. This drainage is
The nitric acid concentration was 0.16 g mol / liter, the silver concentration was 21.6 g / liter, and the nitric acid concentration was the second nitric acid recovery device in the electrode chamber 19 of the first silver recovery device where the electrode 59, which is currently the anode, is present. In the anode chamber 12 of the above, the amount was 0.8 gmol / liter, and in the anode chamber 12 of the first nitric acid recovery apparatus, it was 4 gmol / liter. The waste water loses water in the anode chamber 1 and is concentrated to have a nitric acid concentration of 4.3 g mol / liter and a silver concentration of 23.4 g / liter.

The oxidizable substance was oxidatively decomposed in the anode chamber 1 of the oxidative decomposition apparatus, and the COD of the excess anolyte solution was reduced to 11 mg / liter. Further, this COD is diluted with water to 10 mg / liter in the cathode chamber 2 of the oxidative decomposition apparatus. The COD of the excess catholyte discharged from the catholyte circulation tank 23 of the second silver recovery device is 10 mg / liter. The metal chemical species contained in the waste water of 1 m ³ to be treated are discharged from the catholyte circulation tank 23 of the second silver recovery device in the same concentration.

As is clear from the first to third embodiments described above, the embodiment shown in FIG. 1 also has the following effects.

The higher the concentration of the oxidizable substance in the waste water, the higher the concentrations of nitric acid and silver nitrate in the anolyte in the anode chamber 19 of the oxidative decomposition apparatus, which is convenient for the progress of the oxidative decomposition reaction. For this reason, it becomes possible to reduce the concentration of the oxidizable substance after the oxidative decomposition treatment, regardless of the concentration of the oxidizable substance in the raw wastewater to be treated in the same treatment time.

The nitric acid concentration and silver nitrate concentration of the electrolyte solution (anolyte solution) supplied to the anode chamber 1 of the oxidative decomposition apparatus and the electrolyte solution (catholyte solution) flowing out of the cathode chamber 2 of the oxidative decomposition apparatus are the same as those of the raw wastewater to be treated. It is maintained at a predetermined value regardless of the concentration of the oxidizable substance. Therefore, the operating conditions of each nitric acid recovery device and silver recovery device are kept constant regardless of the concentration of the oxidizable substance in the raw wastewater to be treated.

Further, the higher the concentration of the oxidizable substance in the raw waste water to be treated, the greater the amount of nitrogen oxide in the gas flowing out from the cathode chamber 2 of the oxidative decomposition apparatus. However, the first washing tower 27
Since the nitric acid concentration of the excess anolyte for cleaning the gas therein is increased, the performance of removing the nitric oxide in the gas by the excess anolyte is improved. Excess anolyte with a high nitric acid concentration removes more nitric oxide from the gas.

As a result, the operating conditions that need to be adjusted depending on the concentration of the oxidizable substance in the raw waste water to be treated are the load current amount of the electrolytic oxidative decomposition tank and the blowing amount of oxygen or air.

In the above embodiment, the amount of silver supplied to the electrode chamber, which is the cathode chamber of the silver deposition / elution electrolytic cell 31, is 21.6 kg / m ³ per unit amount of raw waste water to be treated.
1m ² as the surface area of the metal cathode of the silver deposition / elution electrolytic bath 31
Assuming a uniform deposition of up to 5 kg per unit, a cathode surface area of 4.32 m ² is required for every 1 m ³ of throughput of one polarity / electrode solution switching batch.

(Specific Example 4) The amount of energy required to treat the wastewater containing the oxidizable substance and the wastewater containing the oxidizable substance in the embodiment of FIG.
Table 4 shows the results for each COD of the raw wastewater, comparing the amount of energy required in the case of treating by the conventional method according to Document 1 above after concentrating to 3 g / liter.

[0105]

[Table 4]

The electric power required for electrolytic oxidative decomposition in the oxidative decomposition apparatus and the latent heat of vaporization required for regeneration of the catholyte are the same in the treatment according to the embodiment of FIG. 1 and the treatment according to the conventional method. The difference between the electric power required for dialysis of nitric acid and the deposition / elution of silver in the embodiment of FIG. 1 and the latent heat of vaporization for the concentration of wastewater in the conventional method becomes larger as the COD of the raw wastewater is lower. In the range of COD in the embodiment of FIG. 1, the required energy amount in the process according to the embodiment of FIG. 1 is 19 to 56% of the required energy amount in the process according to the conventional method.

[0107]

According to the first aspect of the present invention, it is possible to suppress the decrease in the nitric acid concentration in the first cathode chamber due to the water flowing in through the porous membrane or the cation exchange membrane. The suppression of the decrease in nitric acid concentration can eliminate the necessity of supplying new nitric acid from the outside of the system to the first cathode chamber, and can improve the degree of inhibition of oxidative decomposition of the oxidizable substance due to the decrease in nitric acid concentration.

According to the invention of claim 2, the effect of the invention of claim 1 is obtained, and the nitric acid contained in the second aqueous electrolytic solution is continuously recovered so that nitric acid can be easily added to the waste water. . Further, the nitric acid contained in the second aqueous electrolytic solution discharged to the external environment can be significantly reduced.

According to the invention of claim 3, in addition to the effect of the invention of claim 2, silver contained in the aqueous electrolytic solution can be easily recovered and silver can be easily added to the waste water to be treated. By recovering silver, the amount of silver contained in the second aqueous electrolytic solution discharged to the external environment can be significantly reduced. Furthermore, since silver is deposited and eluted together, the consumption of electric power in the silver deposition electrolysis means can be very small.

Each of the inventions of claims 4 and 8 obtains the effect of the invention of claim 2, and is a simple device for injecting air, oxygen or ozone into the first cathode chamber, which is generated in the first cathode chamber. The generated nitrous acid can be converted to nitric acid, and the second aqueous electrolytic solution in the first cathode chamber can be regenerated. The invention of claim 8 also produces the effect obtained in claim 7 described later. The invention of claim 4 subordinate to claim 3 produces the effect obtained by claim 3.

According to the invention of claim 5, while obtaining the effect of the invention of claim 4, nitric oxide is absorbed in the first aqueous electrolytic solution,
As a result, the amount of nitric oxide contained in the gas released to the outside can be reduced. The nitric oxide absorbed by the first aqueous electrolytic solution becomes nitric acid and is supplied to the first cathode chamber.

The invention of claim 6 obtains the effect of the invention of claim 4 and can activate the reaction of air, oxygen or ozone with nitrous acid contained in the second aqueous electrolytic solution in the first cathode chamber. , The second aqueous electrolytic solution in the first cathode chamber can be efficiently regenerated.

According to the invention of claim 7, the effect of the invention of claim 2 is obtained, and the nitric acid recovery means is downsized by reducing the area of the anion exchange membrane. It becomes compact.

The invention of claim 9 obtains the effect of the invention of claim 3, removes monovalent silver ions contained in the second aqueous electrolytic solution, and removes silver into the waste water introduced to the first anode chamber. Can be continuously eluted. In addition, since silver is deposited and eluted simultaneously, the power consumption of the silver deposition electrolysis means can be very small.

The invention of claim 14 obtains the effect of the invention of claim 11 or claim 12, and in addition to the monovalent anions contained in the second aqueous electrolytic solution, the polyvalent anions are contained in the first anode chamber. It is prevented from being taken into the guided wastewater and can be prevented from accumulating in the treatment equipment.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a wastewater treatment apparatus containing an oxidizable substance, which is a preferred embodiment of the present invention.

FIG. 2 is a detailed configuration diagram of the silver recovery device of FIG.

3 is a configuration diagram of another embodiment of the electrolytic oxidative decomposition tank of FIG.

FIG. 4 is a configuration diagram of another embodiment of the nitric acid electrodialysis tank of FIG. 1.

5 is a configuration diagram of another embodiment of the nitric acid electrodialysis tank of FIG. 1. FIG.

[Explanation of symbols]

1, 12 ... Anode chamber, 2, 13 ... Cathode chamber, 3 ... Cation exchange membrane, 4, 15, 22 ... Anolyte circulation tank, 5, 16, 23
... Catholyte circulation tank, 7 ... Exhaust gas treatment device, 14, 21 ... Anion exchange membrane, 19, 20 ... Electrode chamber, 26, 47, 48
... Piping, 27 ... First cleaning tower, 28 ... Second cleaning tower, 29 ...
Electrolytic oxidative decomposition tank, 30 ... Nitric acid electrodialysis tank, 31 ... Silver deposition / elution electrolytic tank, 59, 60 ... Electrode, 61 ... Controller, 62
... power supply, 63, 64 ... changeover switch.

Claims (15)

[Claims] 1. A first aqueous solution containing nitric acid and silver ions introduced into the first anode chamber of an electrolytic oxidative decomposition means having a first anode chamber and a first cathode chamber separated by a porous membrane or a cation exchange membrane. Wastewater containing an oxidizable substance is added to the electrolytic solution, and the oxidizable substance is treated by being oxidized by the action of divalent silver ions contained in the first aqueous electrolytic solution, and is treated as the first aqueous electrolytic solution. In the method for treating wastewater containing an oxidizable substance that regenerates the contained monovalent silver ions into the divalent silver ions in the first anode chamber by the action of a positive potential difference, the chemical oxygen consumption is less than 133 g / liter. The waste water is added to the first aqueous electrolytic solution and is oxidized by the action of the divalent silver ions to be treated, and the excess first aqueous electrolytic solution in the first anode chamber is added to the first aqueous electrolytic solution. Oxidizable substance characterized by being guided to the cathode chamber Wastewater treatment method including. 2. A second aqueous electrolytic solution flowing out from the first cathode chamber is introduced to the second liquid chamber of a nitric acid recovery means having a first liquid chamber and a second liquid chamber separated by an anion exchange membrane. The nitric acid ions in the second aqueous electrolytic solution are moved from the second liquid chamber to the first liquid chamber through the anion exchange membrane to form nitric acid, and the nitric acid is introduced into the drainage which is guided to the first anode chamber. A method for treating wastewater containing an oxidizable substance according to claim 1, which is added. 3. An electrode in which a cathode electrode of the first electrode chamber and the second electrode chamber of the silver recovery electrolysis means has a first electrode chamber and a second electrode chamber separated by an anion exchange membrane. The second aqueous electrolytic solution discharged from the second liquid chamber of the nitric acid recovery means into the chamber, and monovalent silver ions contained in the second aqueous electrolytic solution are deposited on the electrode as metallic silver, Of the first electrode chamber and the second electrode chamber, the drainage to be supplied to the first anode chamber is guided to the electrode chamber in which an electrode serving as an anode is present, and metallic silver adhering to the latter electrode is drained. The method for treating wastewater containing an oxidizable substance according to claim 2, wherein the wastewater is eluted into the inside. 4. The method according to claim 1, wherein air, oxygen or ozone is injected into the second aqueous electrolytic solution in the first cathode chamber.
Alternatively, the method for treating wastewater containing the oxidizable substance according to claim 3. 5. The treatment of wastewater containing an oxidizable substance according to claim 4, wherein the first aqueous electrolytic solution guided to the first cathode chamber is brought into contact with a gas containing nitrogen oxide discharged from the first cathode chamber. Method. 6. The air, oxygen or ozone is added to the first
The method for treating wastewater containing an oxidizable substance according to claim 4, wherein the water is injected into the second aqueous electrolytic solution through an air chamber formed between air-permeable cathodes arranged in the cathode chamber. 7. The nitric acid recovery means is an electrodialysis means,
The second aqueous electrolytic solution was introduced into the second cathode chamber of the electrodialysis means, which was the second chamber, and electrodialysis was performed to move the second aqueous electrolyte solution in the second anode chamber of the electrodialysis means, which was the first chamber. The method for treating wastewater containing an oxidizable substance according to claim 2, wherein the nitrate ion is nitric acid. 8. The method for treating wastewater containing an oxidizable substance according to claim 7, wherein air, oxygen or ozone is injected into the second aqueous electrolytic solution in the first cathode chamber. 9. The electrode for switching the polarities of the electrodes arranged in the first electrode chamber and the second electrode chamber and separately guiding the second aqueous electrolytic solution and the drainage corresponding to the polarities. The method for treating wastewater containing an oxidizable substance according to claim 3, wherein the chamber is also switched. 10. A porous membrane or a cation exchange membrane, and a first anode separated by the cation exchange membrane and having an anode.
A first cathode chamber in which an anode chamber and a cathode are arranged is provided, and a divalent divalent metal that oxidizes the oxidizable substance is used to oxidize the monovalent silver ion in the first aqueous electrolytic solution containing nitric acid and monovalent silver ions. Electrolytic oxidative decomposition means having means for generating a potential difference at the anode for regeneration into silver ions; and a first conduit for guiding the first aqueous electrolyte discharged from the first anode chamber to the first cathode chamber. An apparatus for treating wastewater containing an oxidizable substance, comprising: 11. An anion exchange membrane, a first liquid chamber separated by the anion exchange membrane, into which waste water containing the oxidizable substance is introduced, and a second aqueous solution discharged from the first cathode chamber. A nitric acid recovery is provided which has a second liquid chamber into which an electrolytic solution is introduced, and moves nitrate ions in the second aqueous electrolytic solution from the second liquid chamber to the first liquid chamber through the anion exchange membrane to form nitric acid. Means, a second conduit for guiding the drainage to which the nitric acid is added to the first anode chamber, and a third conduit for guiding the second aqueous electrolyte discharged from the first cathode chamber to the second liquid chamber 11. A treatment device for wastewater containing an oxidizable substance according to claim 10, comprising a pipe. 12. An electrode which has an anion exchange membrane and a first electrode chamber and a second electrode chamber which are separated by the anion exchange membrane, and which is a cathode of the first electrode chamber and the second electrode chamber. In the electrode chamber in which is present, monovalent silver ions contained in the second aqueous electrolytic solution discharged from the second liquid chamber of the nitric acid recovery means are deposited on the electrode as metallic silver, and the first electrode chamber and In the electrode chamber of the second electrode chamber where an electrode serving as an anode exists, a means for guiding the wastewater supplied to the first anode chamber to elute metallic silver adhering to the latter electrode into the wastewater is provided. The apparatus for treating wastewater containing an oxidizable substance according to claim 11, comprising the silver recovery means having. 13. A means for switching between the polarity of a first electrode which is the electrode provided in the first electrode chamber and the polarity of a second electrode which is the electrode provided in the second electrode chamber, and Drainage introducing means for introducing the drainage into one of the first electrode chamber and the second electrode chamber, and an aqueous electrolyte introducing means for introducing the second aqueous electrolyte into one of the first electrode chamber and the second electrode chamber And when controlling the switching means such that the first electrode serves as an anode and the second electrode serves as a cathode, the drainage introducing means is controlled so as to guide the drainage to the first electrode chamber and the second When controlling the aqueous electrolytic solution introducing means so as to introduce the second aqueous electrolytic solution into the electrode chamber and controlling the switching means so that the first electrode serves as a cathode and the second electrode serves as an anode, The drainage introducing means is controlled so as to guide the drainage to the second electrode chamber. Wastewater treatment apparatus including the oxidizable material of claim 12, and a control means for controlling said aqueous electrolyte inlet means to direct the second aqueous electrolytic solution to said second electrode chamber while. 14. The apparatus for treating wastewater containing an oxidizable substance according to claim 11 or 12, wherein the anion exchange membrane is an anion exchange membrane that selectively permeates monovalent anions. 15. The method according to claim 10, further comprising means for supplying air, oxygen or ozone to the first cathode chamber.
Waste water treatment equipment containing oxidizable substances.