JPH11226576A - Method and apparatus for treating wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for removing nitrogen compounds from wastewater at an ordinary temperature and under an ordinary pressure without generating secondary waste. SOLUTION: Wastewater 7 containing nitrogen compounds is introduced into the anode chamber 4 of an electrolytic bath 6 in which a diaphragm having selective ion permeability is arranged between electrodes and electrolyzed. Reduces nitrogen compounds such as hydrazine and ammonium ions in the wastewater are oxidized by oxygen generated at an anode into nitrogen gas to be removed from the liquid. After the oxidation, the treated liquid is introduced into a cathode chamber 5 and electrolyzed again. Oxidized nitrogen compounds such as nitrate ions and nitrite ions in the liquid are reduced into nitrogen gas to be removed from the liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating a waste liquid, and more particularly, to a nitrogen reduction product (nitrogen hydride) such as hydrazine or ammonium ion, a nitrate ion or a nitrite ion. The present invention relates to a method for electrochemically oxidizing or reducing a nitrogen compound from a waste liquid containing a nitrogen compound such as a nitrogen oxide to form a nitrogen gas, and to remove the nitrogen compound. In this specification, the nitrogen compound, the nitrogen reduced product, and the nitrogen oxide each include those in an ionic state.

[0002]

2. Description of the Related Art In general, a deoxidizing (antioxidant) and anticorrosive treatment of a water supply system and a condensate system of a thermal power plant is performed by injecting a reducing volatile agent such as hydrazine or ammonia. I have. Therefore, added hydrazine or ammonia (ammonium ion) remains in the waste liquid generated from such a facility, and it is required that such a residue be subjected to some treatment to be removed.

Conventionally, methods for removing nitrogen compounds such as hydrazine and ammonium ions from a liquid include: 1) a method of oxidizing with an oxidizing agent such as hypochlorous acid, hydrogen peroxide, oxygen, 2) copper, A method of adding a catalyst such as lead and oxidizing under high temperature and high pressure.3) A method of pressure filtration using a reverse osmosis membrane.4) A large number of ion exchange membranes are arranged between the electrodes, and the ions are electrophoresed. Electrodialysis method for separation, and 5) oxidative decomposition using microorganisms that consume nitrogen components.

[0004]

However, in these methods, as described below, it is difficult to control the reaction, or secondary waste and by-products are newly generated due to the addition of an oxidizing agent or a catalyst. There was a problem.

[0005] That is, in the oxidation treatment method using an oxidizing agent, 1) not only is it difficult to handle the oxidizing agent, but also there is a problem that an overreaction generates by-products. There is a problem that not only may be a harmful secondary waste, but also it is difficult to control the reaction. In addition, 3) the pressure filtration method using a reverse osmosis membrane requires a small amount of treatment and further processing of the concentrated waste liquid, and 4) the method using electrodialysis cannot process anything other than charged ions. In addition, there is a problem that the concentrated ion component requires further treatment.

Therefore, at present, 5) the oxidative decomposition method using microorganisms is considered to be the most effective. However, this method requires a large amount of equipment area, requires a high level of skill in breeding microorganisms, and requires a large amount of organic feed. It is difficult to control the conditions of the water tank, and if the decomposition reaction is disturbed, it takes a long time to recover.

SUMMARY OF THE INVENTION The present invention has been made to solve these problems. Under normal temperature and normal pressure, hydrazine, ammonium ion, nitrate ion and nitrite ion can be produced from waste liquid without generating secondary waste. It is an object of the present invention to provide a method for treating a waste liquid for removing nitrogen compounds such as nitrogen gas and removing the same and a treatment apparatus.

[0008]

According to a first aspect of the present invention, there is provided a method for treating waste water, comprising: an anode chamber and a cathode chamber of an electrolytic cell having a diaphragm having selective permeability to ions between an anode and a cathode; A waste liquid containing a nitrogen compound is injected into at least one of them to perform electrolysis, and the nitrogen compound in the waste liquid is oxidized or reduced to nitrogen gas.

Further, according to a second aspect of the present invention, a waste liquid containing a nitrogen compound is injected into an anode chamber of an electrolytic cell in which a diaphragm having selective permeability to ions is disposed between an anode and a cathode. Performing a first electrolysis, oxidizing a nitrogen reductant in the waste liquid into nitrogen gas, and discharging the waste liquid oxidized by the first electrolysis step into a cathode chamber of the electrolytic cell. And a second electrolysis step of reducing the nitrogen oxides in the waste liquid into nitrogen gas by performing a second electrolysis.

[0010] In the waste liquid treatment apparatus of the present invention, a diaphragm having selective permeability for ions is disposed between an anode and a cathode, and an electrolytic cell separated into an anode chamber and a cathode chamber by the diaphragm; A DC power supply for applying a DC voltage between the battery and the cathode; a first liquid supply unit for supplying an electrolyte to the anode chamber of the electrolytic cell; and discharging the electrolyte from the anode chamber of the electrolytic cell. A second liquid supply means for supplying an electrolytic solution to the cathode chamber of the electrolytic cell, and a second liquid supply means for discharging the electrolytic solution from the cathode chamber of the electrolytic cell. And a gas discharging means for discharging gas generated by electrolysis from the gas phase of the anode chamber and / or the cathode chamber of the electrolytic cell.

In the present invention, an anion exchange membrane, a cation exchange membrane, an anion exchange membrane, and a cation are disposed between an anode and a cathode to divide the electrolytic cell into an anode compartment and a cathode compartment. A composite ion exchange membrane in which an exchange membrane is composited can be used. These ion exchange membranes are composed of a solid electrolyte, have selective permeability to ionic species, and block the movement of specific ions between the anode and cathode compartments. It is also possible to use a general-purpose solid electrolyte membrane such as silver iodide (α-AgI), alumina (β-Al ₂ O ₃ ), or stabilized zirconia.

In the present invention, the shape of the anode and the shape of the cathode can be not only a rod shape or a plate shape having a solid inside, but also a mesh shape or a porous shape. In addition, such an anode and a cathode can be arranged at appropriate positions in the anode chamber and the cathode chamber separated by the above-mentioned diaphragm, respectively, apart from each other,
The diaphragm may be arranged so as to sandwich the diaphragm closely. In particular, when electrolysis is performed by an electrolytic cell in which a mesh-shaped or porous anode and a cathode are arranged with a diaphragm interposed therebetween, the area of the contact interface between the electrode and the electrolyte is large, and Because the distance between and the cathode is short,
Electrochemical reactions tend to occur on the electrode surface. Therefore, the efficiency of the oxidation or reduction treatment of the nitrogen compound in the waste liquid is increased.

The nitrogen compounds to be electrolytically treated in the present invention include nitrogen reduced products (nitrogen hydride compounds) such as hydrazine and ammonium ions, and nitrogen oxides such as nitrate ions and nitrite ions. Is oxidized in the anode compartment of the electrolytic cell, and nitrogen oxide is reduced in the cathode compartment of the electrolytic cell. Further, as the nitrogen compound contained in the waste liquid, hydroxylamine, amine, diamine,
Amides, nitramides, tetrazenes, hyponitrite, -nitrogen oxide, -nitrous oxide, -nitrous oxide, nitrogen dioxide, nitrous oxide, nitrous oxide, nitride, azide, hypoazo, cyanide, nitrosyl salt, nitroyl salt And the like. These nitrogen compounds can also be oxidized or reduced by electrolysis in an anode chamber or a cathode chamber to be converted into nitrogen gas and removed.

In the first aspect of the present invention, water in the waste liquid injected into the anode compartment or the cathode compartment of the electrolytic cell is oxidized or reduced at the anode or the cathode as shown in the following reaction formula.

The ^{_{anode: 2Η 2 O-4e - →}} Ο 2 + 4Η + ^{_{cathode: 2Η 2 O + 2e - →}} H 2 + 2OΗ - Then, hydrazine contained in the effluent, ammonium ions, nitrate ions, nitrogen compounds such as nitrite Reacts with oxygen or hydrogen generated by the above-described anodic oxidation reaction or cathodic reduction reaction in an anode chamber or a cathode chamber of an electrolytic cell to generate nitrogen gas and water.

Here, the nitrogen reduced product (for example, hydrazine or ammonium ion) in the waste liquid reacts with oxygen generated at the anode in the anode chamber as shown in the following reaction formula to form nitrogen gas and water.

Ν ₂ Η ₄ + O ₂ → N ₂ ↑ + 2Η ₂ O ₄ ΝH ₄ ⁺ + 3O ₂ → 2Ν ₂ ↑ + 4 ⁺ + 6Η ₂ O Nitrogen oxides (eg, nitrate ions or nitrite ions) are removed from the cathode chamber. It reacts with hydrogen generated at the cathode as shown in the following reaction formula to form nitrogen gas and water.

2ΝO ₃ ⁻ + 5H ₂ → N ₂ ↑ + 2OH ⁻ + 4H ₂ Ο2ΝO ₂ ⁻ + 3H ₂ → N ₂ ↑ + 2OH ⁻ + 2H ₂ O The generated nitrogen gas moves from the liquid phase of the electrolytic cell to the gas phase,
It is further discharged and removed from the gas phase.

In the second aspect of the present invention, the waste liquid containing the nitrogen compound is first electrolyzed in the anode chamber of the electrolytic cell (first electrolysis step), and the nitrogen reductant in the waste liquid is oxidized. It becomes nitrogen gas and water. Next, the waste liquid oxidized in the first electrolysis step is injected into the cathode chamber of the electrolysis tank and electrolyzed (second electrolysis step), and nitrogen oxides in the waste liquid are reduced to nitrogen gas and water. Become. Thus, the nitrogen reduced product and the nitrogen oxide in the waste liquid can be respectively electrolyzed to nitrogen gas and removed from the liquid phase. In addition, in the electrolysis in the cathode chamber, the dissolved oxygen and the like in the liquid are reduced to water at the same time as the nitrogen oxides in the waste liquid are reduced, so that the amount of dissolved oxygen is reduced.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for treating waste liquid according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram for explaining a first embodiment of the waste liquid treatment method of the present invention.

In the first embodiment, as shown in FIG. 1, a diaphragm 3 made of alumina, which is a general-purpose solid electrolyte, is erected between an anode 1 and a cathode 2 each having a plate shape. 3
In the electrolytic cell 6 separating the anode chamber 4 and the cathode chamber 5 from each other, a waste liquid (waste aqueous solution) 7 containing at least one of hydrazine and ammonium ions is injected into the anode chamber 4, and pure water 8 flows through the cathode chamber 5. To perform electrolysis. Here, a waste liquid 7 containing at least one of hydrazine and ammonium ions
For example, a waste liquid generated from a thermal power plant is used.

The water in the waste liquid 7 injected into the anode chamber 4 is oxidized at the anode 1 as shown in the following reaction formula to generate oxygen.

2H ₂ O-4e ⁻ → O ₂ + 4Η ⁺ The nitrogen reduced product (hydrazine and / or ammonium ion) in the waste liquid 7 is converted into the following reaction formula by the oxygen generated at the anode 1 in the above reaction. As shown, nitrogen gas is generated by oxidation, and the generated nitrogen gas shifts from a liquid phase to a gas phase and is removed from the waste liquid 7.

N ₂ H ₄ + O ₂ → N ₂ ↑ + 2Η ₂ O ₄ ΝH ₄ ⁺ + 3O ₂ → 2N ₂ ↑ + 4Η ⁺ + 6Η ₂ O In the figure, reference numeral 9 denotes an oxidized liquid derived from the anode chamber 4. Is shown.

[0026] Figure 2, in such a first embodiment, the electrolyte area 0.75Dm ^2, current density 5~7A / dm ^2, the liquid amount 50
It is a graph showing the result of having measured the concentration of hydrazine and ammonium ion in the waste liquid 7 of the anode chamber 4 with time by performing electrolysis under the conditions of 0 ml and a liquid temperature of 25 to 35 ° C.

From this figure, it is seen that the waste liquid 7
It can be seen that hydrazine and ammonium ions in each of these can be efficiently removed, and their concentrations can be reduced below the detection limit.

Next, second to seventh embodiments of the present invention will be described.

FIG. 3 is a schematic configuration diagram for explaining a second embodiment of the present invention.

In the second embodiment, as shown in FIG. 3, an anion exchange membrane 3a is erected between the anode 1 and the cathode 2, and the anode compartment 4 and the cathode compartment 5 are formed by the anion exchange membrane 3a. In the electrolytic cell 6 which separates the wastewater and the wastewater, a waste liquid 7 containing a nitrogen reduced product such as hydrazine or ammonium ion is injected into the anode chamber 4, and pure water 8 flows through the cathode chamber 5 to perform electrolysis. Here, the anode 1 has a mesh shape in a structure in which platinum plating is applied to the surface of a titanium base material, and the cathode 2 is made of sus and has a mesh shape like the anode 1. These electrodes are used as anion exchange membranes (strongly basic anion exchange membranes) 3a
Are interposed therebetween and are arranged in close contact with the ion exchange membrane.

In the second embodiment, the nitrogen reduced product in the waste liquid 7 injected into the anode chamber 4 is oxidized by the oxygen generated at the anode 1 into nitrogen gas, and the generated nitrogen gas is
The liquid phase shifts to the gas phase and is removed from the waste liquid 7.

FIGS. 4A and 4B respectively show the second
It is the perspective view and disassembled perspective view which show the structure of the waste liquid processing apparatus used for the Example of FIG. In this processing apparatus, as shown in these figures, an anion exchange membrane 3a is closely arranged between an anode 1 and a cathode 2 having a mesh shape, and an anode chamber and a cathode chamber are formed by the anion exchange membrane 3a. And an external DC power supply 10 for applying a DC voltage between the anode 1 and the cathode 2, and a first solution for supplying a waste liquid 7 containing a nitrogen reduced product to the anode chamber of the electrolytic bath 6. A liquid supply pipe 11a, a first liquid discharge pipe 12a for discharging the oxidized liquid 9 from the anode chamber, a second liquid supply pipe 11b for supplying a liquid such as pure water 8 to the cathode chamber, and a cathode A second liquid discharge pipe 12b for discharging the liquid from the chamber 5 is provided. The first liquid supply pipe 11a and the first liquid discharge pipe 12a penetrate the anode chamber forming plate 13 forming the anode chamber, respectively, and are mounted so as to open into the anode chamber. The pipe 11b and the second liquid discharge pipe 12b respectively penetrate the cathode chamber forming plate 14 forming the cathode chamber, and are mounted so as to open into the cathode chamber. Further, the first liquid supply pipe 11a and the first liquid discharge pipe 12a are connected via a first liquid storage tank 15a and a first liquid circulation pump 16a, and the second liquid supply pipe 11b is connected to the second liquid supply pipe 11b. The second liquid discharge pipe 12b is
Liquid storage tank 15b and second liquid circulation pump 16b
Connected through. Further, a gas discharging means (not shown) for discharging nitrogen gas generated by the electrolysis is attached to the anode chamber side of the electrolytic cell 6. In the drawing, reference numeral 17 denotes an anode support forming the bottom side of the anode chamber 4, and reference numeral 18 denotes a cathode support forming the bottom side of the cathode chamber.

[0033] Figure 5, in such second embodiment, the electrolyte area 0.75Dm ^2, current density 5~7A / dm ^2, the liquid amount 50
It is a graph showing the result of having measured the concentration of hydrazine and ammonium ion in the waste liquid 7 of the anode chamber 4 with time by performing electrolysis under the conditions of 0 ml and a liquid temperature of 25 to 35 ° C.

From this figure, it can be seen that the waste liquid 7
It can be seen that the concentrations of hydrazine and ammonium ions in each can be reduced below the detection limit.

In the second embodiment, the anion exchange membrane 3a used as a diaphragm selectively permeates only anions in the liquid and does not transmit cations. The transfer of nitrogen reductant to 5 is blocked. Therefore, the oxidation reaction of the nitrogen reduced product in the anode chamber 4 can be efficiently performed. Further, the fixed ion effect in the ion-exchange membrane, Oita ^- so moves from the cathode chamber 5 to the anode chamber 4, Piita elevated accompanied liquid electrolyte at the cathode chamber 5 (Oita
^- the increase) is suppressed, decrease in current efficiency is suppressed.
Furthermore, Oita for transmitting and movement ^- for carry charge, loss due to electric resistance of the liquid becomes very small.

FIG. 6 shows the electrolysis area in the second embodiment.
0.75dm ^2, current density 2~ 3A / dm ^2, liquid volume 500 ml, liquid temperature 25
It is a graph showing the result of having performed electrolysis on conditions of -35 ° C, and measuring p ^ change of the solution in cathode room 5. From this figure,
When the anion exchange membrane 3a is used as the diaphragm, it can be seen that the pΗ rise of the liquid in the cathode chamber 5 due to electrolysis is small. In FIG. 6, for the purpose of comparison, the time-dependent change of pΗ in the case where a diaphragm made of alumina which is a general-purpose solid electrolyte is used and electrolysis is performed in the same manner as in the second embodiment is also shown in FIG.
Both are shown.

Further, in the second embodiment, since the anode 1 and the cathode 2 having a mesh shape are used, compared with the case where a solid rod or plate electrode is used,
The area of the contact interface between the electrode and the electrolyte has increased significantly. Further, the anode 1 and the cathode 2 having such a mesh shape are used.
However, since they are closely arranged with the anion exchange membrane 3a interposed therebetween, the distance between the electrodes is also reduced. Therefore, the electrode reaction easily occurs, and the oxidation of the nitrogen reduced product such as hydrazine or ammonium ion in the waste liquid 7 is efficiently performed in a short time.

FIG. 7 shows that pure water is injected into the anode chamber 4 and the cathode chamber 5 in an electrolytic cell 6 in which a mesh-shaped anode 1 and a cathode 2 are closely arranged with an anion exchange membrane 3a interposed therebetween. 5 is a graph showing the results of measuring the change over time in current when electrolysis is performed. The electrolysis was performed with an electrolysis area of 0.75 dm ² , an applied voltage of 10 V (constant), and a water temperature of 25 to 35 ° C.
The conditions were as follows. From this figure, it can be seen that the use of the mesh-shaped anode 1 and cathode 2 enables sufficient electrolysis even in pure water.

FIG. 8 is a schematic configuration diagram for explaining a third embodiment of the present invention.

In the third embodiment, as shown in FIG. 8, a cation exchange membrane 3b is erected between the anode 1 and the cathode 2, and the cation exchange membrane 3b allows the anode chamber 4 and the cathode chamber 5 to be formed. In the electrolytic cell 6 which separates the wastewater and the wastewater, a waste liquid 7 containing nitrogen oxides such as nitrate ions and nitrite ions is injected into the cathode chamber 5, and pure water 8 is flowed into the anode chamber 4 to perform electrolysis. Here, the anode 1 has a mesh shape in a structure in which platinum plating is applied to the surface of a titanium base material, and the cathode 2 is made of sus and has a mesh shape like the anode 1. Further, these electrodes are arranged with a cation exchange membrane (strongly acidic cation exchange membrane) 3b interposed therebetween and in close contact with the ion exchange membrane.

The water in the waste liquid 7 injected into the cathode chamber 5 is reduced at the cathode 2 as shown in the following reaction formula to generate hydrogen.

[0042] ^{_{2Η 2 O + 2e - → H}} 2 + 2OΗ - Then, nitrogen oxides in the effluent 7 (nitrate ion and / or nitrite ions), the hydrogen generated in the cathode 2 in each of the reaction, the following reaction formula As shown, nitrogen gas is generated by reduction, and the generated nitrogen gas shifts from a liquid phase to a gaseous phase and is removed from the waste liquid 7.

2ΝO ₃ ⁻ + 5H ₂ → N ₂ ↑ + 2OH ⁻ + 4H ₂ Ο2ΝO ₂ ⁻ + 3H ₂ → N ₂ ↑ + 2OH ⁻ + 2H ₂ O As described above, the nitrogen oxides in the waste liquid 7 are reduced in the cathode chamber 5. It becomes nitrogen gas and is removed. In addition,
In the figure, reference numeral 19 denotes a liquid that has been subjected to a reduction treatment and is led out of the cathode chamber 5.

FIGS. 9A and 9B respectively show the third
It is the perspective view and exploded perspective view which show the structure of the waste liquid processing apparatus used for the Example of FIG. In this processing apparatus, as shown in these figures, a cation exchange membrane 3b is closely arranged between an anode 1 and a cathode 2 having a mesh shape, and the cation exchange membrane 3b allows the anode chamber and the cathode chamber to be arranged. And an external DC power supply 10 for applying a DC voltage between the anode 1 and the cathode 2, and a first supply of a liquid such as pure water 8 to the anode chamber of the electrolytic bath 6. A liquid supply pipe 11a, a first liquid discharge pipe 12a for discharging liquid from the anode chamber, and a second liquid supply pipe 11 for supplying waste liquid 7 containing nitrogen oxide to the cathode chamber
b, and a second liquid discharge pipe 12 b for discharging the reduced liquid 19 from the cathode chamber 5. The first liquid supply pipe 11a and the first liquid discharge pipe 12a penetrate the anode chamber forming plate 13 forming the anode chamber, respectively, and are mounted so as to open into the anode chamber. The pipe 11b and the second liquid discharge pipe 12b respectively penetrate the cathode chamber forming plate 14 forming the cathode chamber, and are mounted so as to open into the cathode chamber. Further, the first liquid supply pipe 11a and the first liquid discharge pipe 12a are connected via a first liquid storage tank 15a and a first liquid circulation pump 16a, and the second liquid supply pipe 11b is connected to the second liquid supply pipe 11b. The second liquid discharge pipe 12b includes a second liquid storage tank 15b and a second liquid circulation pump 16b.
b. Further, a gas discharging means (not shown) for discharging nitrogen gas generated by electrolysis is attached to the cathode chamber side of the electrolytic cell 6. In the drawing, reference numeral 17 denotes an anode support forming the bottom side of the anode chamber, and reference numeral 18 denotes a cathode support forming the bottom side of the cathode chamber.

[0045] Figure 10, in such a third embodiment, the electrolytic area 0.75Dm ^2, the current density. 5 to 7A / dm ^2, the liquid volume 5
It is a graph showing the result of having measured the concentration of nitrate ion and nitrite ion in the waste liquid 7 of the cathode chamber 5 with time by performing electrolysis under the conditions of 00 ml and a liquid temperature of 25 to 35 ° C.

From this figure, it can be seen that the waste liquid 7
It can be seen that nitrate ions and nitrite ions in the medium were efficiently removed, and the concentrations of these ions could be reduced to below the detection limit.

FIG. 11 is a schematic configuration diagram for explaining a fourth embodiment of the present invention.

In the fourth embodiment, as shown in FIG.
In each case, a diaphragm 3 made of alumina is erected between the plate-like anode 1 and the cathode 2. In the electrolytic cell 6 in which the anode chamber 4 and the cathode chamber 5 are separated by the diaphragm 3, hydrazine and ammonium ions are separated. A waste liquid 7 containing at least one of them is injected into the anode chamber 4, and firstly, pure water is flowed into the cathode chamber 5 to perform first electrolysis, and nitrogen reduction products (hydrazine and / or
Or ammonium ions) are oxidized by oxygen generated at the anode 1 to form nitrogen gas. Next, the oxidized solution 9 is injected into the cathode chamber 5 and pure water is flown into the anode chamber 4 or a new waste liquid 7 is injected to perform a second electrolysis, and the oxidation in the waste liquid 7 is performed. The reducing substance is reduced. Here, as the waste liquid 7 containing at least one of hydrazine and ammonium ion, for example, a waste liquid generated from a thermal power plant is used. The electrolytic treatment of the waste solution 7 is a batch process. After the first electrolysis, the entire amount of the oxidized solution 9 in the anode chamber 4 is injected and supplied to the cathode chamber 5 to perform the second electrolysis. May be performed, but a continuous processing method may be employed. That is, the oxidized solution 9 is supplied to the anode chamber 4
The second electrolysis can be performed while continuously supplying the reduced solution 19 from the cathode chamber 5 and continuously supplying the reduced solution 19 from the cathode chamber 5.

In this embodiment, the nitrogen reduced product (hydrazine and / or ammonium ion) in the waste liquid 7 is
After being oxidized electrochemically in the anode chamber 4 and removed from the waste liquid 7 as nitrogen gas, the oxidizing substance in the waste liquid 7 is electrochemically reduced in the cathode chamber 5. When the waste liquid 7 contains nitrogen oxides such as nitrate ions and nitrite ions, the nitrogen oxides are reduced to nitrogen gas and removed from the waste liquid 7. Further, by the reduction treatment in the cathode chamber 5, dissolved oxygen and the like in the waste liquid 7 are simultaneously removed.

[0050] Figure 12, in such a fourth embodiment, the electrolytic area 0.75Dm ^2, the current density. 5 to 7A / dm ^2, the liquid volume 5
Waste water containing hydrazine and ammonium ions generated from a thermal power plant under the conditions of 00 ml and a liquid temperature of 25 to 35 ° C. 7
5 is a graph showing the results of continuously performing the electrolytic treatment of No. 7 and measuring the total nitrogen concentration in the waste liquid 7 over time. The measurement of the total nitrogen concentration was performed on the liquid continuously discharged from the cathode chamber 5. From this figure, according to the fourth embodiment,
It can be seen that the nitrogen component in the waste liquid 7 generated from the thermal power plant can be efficiently removed.

In the fifth embodiment, the same electrolytic cell 6 as in the fourth embodiment is used, and a waste liquid 7 containing at least one of hydrazine and ammonium ion and at least one of nitrate ion and nitrite ion is used. In the same manner as in the fourth embodiment, the electrolyte is first injected into the anode chamber 4 to perform first electrolysis, and hydrazine and / or ammonium ions in the waste liquid 7 are oxidized by oxygen generated at the anode 1 and then subjected to this oxidation treatment. The solution 9 thus obtained is injected into the cathode chamber 5 to perform the second electrolysis, thereby reducing nitrate ions and / or nitrite ions in the waste solution 7.

In this embodiment, hydrazine and / or ammonium ions, which are nitrogen reductants, in the waste liquid 7 are
After being electrochemically oxidized in the anode chamber 4 and removed as nitrogen gas from the waste liquid 7, nitrate ions and / or nitrite ions, which are nitrogen oxides, in the waste liquid 7 are converted into electricity in the cathode chamber 5. It is chemically reduced and becomes nitrogen gas and is removed from the waste liquid 7.

[0053] Figure 13, in such a fifth embodiment, electrolytic area 0.75Dm ^2, the current density. 5 to 7A / dm ^2, the liquid volume 5
It is a graph showing the result of performing electrolysis under the conditions of 00 ml and a liquid temperature of 25 to 35 ° C., and measuring the concentrations of nitrate ions and nitrite ions in the waste liquid 7 of the cathode chamber 5 with time. From this figure,
According to the fifth embodiment, it can be seen that nitrate ions and nitrite ions in the waste liquid 7 can be efficiently removed.

In the sixth embodiment, the same electrolytic cell 6 as in the fourth embodiment is used, which contains at least one of hydrazine and ammonium ions, at least one of nitrate ions and nitrite ions, and further contains The waste solution 7 containing each nitrogen compound is injected into the anode chamber 4 in the same manner as in the fourth embodiment to perform the first electrolysis, and then the oxidized solution 9 is injected into the cathode chamber 5 to perform the second electrolysis. , And the oxidation and reduction treatment of the nitrogen compound in the waste liquid 7 are sequentially performed.

In this embodiment, of the nitrogen compounds in the waste liquid 7, hydrazine and / or ammonium ions and other nitrogen reduction products are oxidized in the anode chamber 4,
Nitrate ions and / or nitrite ions and other nitrogen oxides can be reduced in the cathode chamber 5, all of which can be converted into nitrogen gas and water and removed from the waste liquid 7.

[0056] Figure 14, in this sixth embodiment, the electrolyte area 0.75Dm ^2, the current density. 5 to 7A / dm ^2, the liquid volume 5
It is a graph showing the result of having performed electrolytic treatment of the waste liquid 7 containing a nitrogen compound continuously on conditions of 00 ml and liquid temperature of 25-35 degreeC, and measuring the total nitrogen concentration in the waste liquid 7 with time. From this figure, it is understood that various nitrogen compounds in the waste liquid 7 can be efficiently removed by the sixth embodiment.

In the seventh embodiment, as shown in FIG.
A composite ion exchange membrane 3c in which an anion exchange membrane and a cation exchange membrane are combined is erected between the anode 1 and the cathode 2, and the anode chamber 4 and the cathode chamber 5 are separated by the composite ion exchange membrane 3c. In the separated electrolytic cell 6, a waste liquid 7 containing a nitrogen compound is injected into the anode chamber 4, and pure water is first flowed into the cathode chamber 5 so that the first
And the nitrogen reduced product in the waste liquid 7 is oxidized by the oxygen generated at the anode 1 to produce nitrogen gas. Next, the oxidized solution 9 is injected into the cathode chamber 5 to perform the second electrolysis, and the oxidizing substance in the waste solution 7 is reduced. Here, the anode 1 has a structure in which platinum plating is applied to the surface of a titanium base material and has a mesh shape, and the cathode 2 is made of sus.
Like the anode 1, it has a mesh shape. These electrodes are arranged with the composite ion exchange membrane 3c interposed therebetween and in close contact with the ion exchange membrane.

According to this embodiment, after the nitrogen reduced products such as hydrazine and ammonium ions in the waste liquid 7 are electrochemically oxidized in the anode chamber 4 to be removed from the waste liquid 7 as nitrogen gas. The oxidizing substance in the waste liquid 7 is electrochemically reduced in the cathode chamber 5. When the waste liquid 7 contains nitrogen oxides such as nitrate ions and nitrite ions, the nitrogen oxides are reduced to nitrogen gas and removed from the waste liquid 7.

FIGS. 16A and 16B are a perspective view and an exploded perspective view, respectively, showing the structure of a waste liquid treatment apparatus used in the seventh embodiment. In this processing apparatus, as shown in these figures, a composite ion exchange membrane 3c is closely arranged between an anode 1 and a cathode 2 having a mesh shape, and the composite ion exchange membrane 3c allows the anode chamber and the cathode chamber to be arranged. , An external DC power supply 10 for applying a DC voltage between the anode 1 and the cathode 2, and a first liquid for supplying a waste liquid 7 containing a nitrogen compound to the anode chamber of the electrolytic cell 6. A supply pipe 11a,
A first liquid discharge pipe 12a for discharging the oxidized liquid 9 from the anode chamber, a second liquid supply pipe 11b for supplying a waste liquid 7 containing a nitrogen compound to the cathode chamber 5, and a reduction processing from the cathode chamber 5. A second liquid discharge pipe 12b for discharging the liquid 19 which has been discharged. Then, the first liquid supply pipe 11a and the first liquid discharge pipe 12a respectively penetrate the anode chamber forming plate 13 forming the anode chamber,
The second liquid supply pipe 11b and the second liquid discharge pipe 12b penetrate the cathode chamber forming plate 14 forming the cathode chamber, respectively, and are mounted and opened in the cathode chamber. Have been. Also, the second
The liquid discharge pipe 12b and the first liquid supply pipe 11a are connected via a third liquid storage tank 15c and a third liquid circulation pump 16c, and the first liquid discharge pipe 12a and the second liquid supply pipe 11c are connected to each other. The liquid supply pipe 11b is connected via a fourth liquid circulation pump 16d. Then, the first electrolytic treatment in the anode chamber and the second electrolytic treatment in the cathode chamber are performed continuously. Further, gas discharging means (not shown) for discharging nitrogen gas generated by electrolysis is attached to each of the anode chamber side and the cathode chamber side of the electrolytic cell 6. In the figure, reference numeral 1
Reference numeral 7 denotes an anode support forming the bottom side of the anode chamber, and reference numeral 18 denotes a cathode support forming the bottom side of the cathode chamber.

[0060] Figure 17, in this seventh embodiment, the electrolyte area 0.75Dm ^2, the current density. 5 to 7A / dm ^2, the liquid volume 5
It is a graph showing the result of having performed the electrolytic treatment of the waste liquid 7 containing hydrazine and / or ammonium ion continuously under the conditions of 00 ml and the liquid temperature of 25 to 35 ° C., and measuring the total nitrogen concentration in the waste liquid 7 with time. . In addition, the measurement of the total nitrogen concentration
This was performed on the liquid continuously discharged from the cathode chamber 5.
From this figure, it can be seen that the seventh embodiment can efficiently remove nitrogen compounds such as hydrazine and ammonium ions in the waste liquid 7.

FIG. 18 is a graph showing the chronological change of the total nitrogen concentration in the waste liquid 7 when the waste liquid 7 containing nitrogen compounds generated from the thermal power plant in the seventh embodiment is treated in the same manner as described above. It is a graph showing the measurement result. From this figure, it is understood that various nitrogen compounds in the waste liquid 7 generated from the thermal power plant can be efficiently removed and the concentration of the nitrogen component can be significantly reduced by the seventh embodiment.

In the seventh embodiment, a composite ion exchange membrane 3c of a cation exchange membrane and an anion exchange membrane is provided as a diaphragm. And this composite ion exchange membrane 3
The cation exchange membrane constituting c selectively permeates only cations and blocks the permeation and movement of anions, and the anion exchange membrane selectively permeates only anions and permeates and permeates cations. Since the movement is blocked, the oxidation reaction in the anode chamber 4 and the reduction reaction in the cathode chamber 5 can be efficiently performed. Further, in both the anode chamber 4 and the cathode chamber 5, an increase in Η ⁺ or O Η ⁻ that reduces current efficiency is suppressed,
The change in pΗ of the liquid is suppressed.

In order to confirm such an effect, an aqueous solution of sodium sulfate was electrolyzed (electrolysis area: 0.75 dm ² , current: 10 μm) using an electrolytic cell having a composite ion exchange membrane of a cation exchange membrane and an anion exchange membrane. Density ^{2-3 A} / dm ² , liquid volume
500 ml, liquid temperature 25-35 ° C).

FIG. 19 is a graph showing the results of measuring the pΗ change of the solution in the anode compartment and the cathode compartment in the electrolysis of the aqueous sodium sulfate solution. From this figure, it can be seen that the composite ion-exchange membrane blocks the permeation and movement of both cations and anions, so that there is little pH change in both the anode compartment and the cathode compartment.

Next, the eighth and ninth embodiments of the present invention will be described.

In the eighth embodiment, the same electrolytic cell 6 as in the first embodiment is used, a waste liquid 7 containing hydrazine and ammonium ions is injected into the anode chamber 4, and pure water 8 is poured into the cathode chamber 5. The hydrazine and ammonium ions in the waste liquid 7 are oxidized in the anode chamber 4 and removed from the waste liquid 7 as nitrogen gas, and the hydrogen gas generated from the cathode 2 is recovered.

At the cathode 2, water is electrolyzed (reductively decomposed) as shown in the following reaction formula, and hydrogen is generated.

[0068] ^{_{2Η 2 O + 2e - → Η}} 2 + 2OΗ - thus produced hydrogen gas is recovered, the recovered hydrogen is recycled.

FIG. 20 is a graph showing an example of a change with time of the hydrogen gas generation amount electrochemically calculated in the eighth embodiment. From this figure, it can be seen that since hydrogen gas is constantly generated, recyclable hydrogen can be constantly obtained by recovering the hydrogen gas.

In the ninth embodiment, the same electrolytic bath 6 as that of the fourth embodiment is used, and a waste solution 7 containing hydrazine, ammonium ions and metal ions is first injected into the anode chamber 4 and the first electrolytic solution is discharged. Is performed to oxidize hydrazine and ammonium ions into nitrogen gas, and then the oxidized solution 9 is injected into the cathode chamber 5 to perform second electrolysis.

The metal ions (metal ions having a standard electrode potential lower than hydrogen) in the waste liquid 7 are reduced at the cathode 2 as shown in the following reaction formula to become metals, and are deposited on the surface of the cathode 2. By collecting the precipitated metal, metal ions in the waste liquid 7 can be removed.

M ⁺ + e ⁻ → M (metal) FIG. 21 shows a cathode chamber 5 according to the ninth embodiment.
3 is a graph showing the results of measuring the concentration of metal ions in the solution over time. From this figure, it can be seen that according to the ninth embodiment, metal ions in the waste liquid 7 can be deposited on the cathode 2 and recovered.

[0073]

As is apparent from the above description, in the present invention, the electrolysis is carried out by disposing a diaphragm having a selective permeability to ions such as an ion exchange membrane between the anode and the cathode. Under normal temperature and normal pressure, nitrogen compounds in waste liquid generated from a thermal power generation facility or the like can be converted to nitrogen gas and efficiently removed without generating secondary waste.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram for explaining a first embodiment of a waste liquid treatment method according to the present invention.

FIG. 2 is a graph showing changes over time in hydrazine concentration and ammonium ion concentration in the waste liquid in the anode chamber in the first embodiment.

FIG. 3 is a schematic configuration diagram for explaining a second embodiment of the present invention.

FIG. 4 shows a waste liquid treatment apparatus used in a second embodiment,
(A) is a perspective view, (b) is an exploded perspective view.

FIG. 5 is a graph showing changes over time in the hydrazine concentration and the ammonium ion concentration in the waste liquid in the anode chamber in the second embodiment.

FIG. 6 is a graph showing a change in pΗ of the liquid in the cathode chamber in the second embodiment.

FIG. 7 is a graph showing a change over time in current when electrolysis of pure water is performed in an electrolytic cell having a meshed anode and a cathode.

FIG. 8 is a schematic configuration diagram for explaining a third embodiment of the present invention.

FIG. 9 shows a waste liquid treatment apparatus used in the third embodiment,
(A) is a perspective view, (b) is an exploded perspective view.

FIG. 10 is a graph showing changes over time in nitrate ion concentration and nitrite ion concentration in the waste liquid in the cathode chamber in the third embodiment.

FIG. 11 is a schematic configuration diagram for explaining a fourth embodiment of the present invention.

FIG. 12 is a graph showing a change over time in a total nitrogen concentration in a waste liquid generated from a thermal power plant in a fourth embodiment.

FIG. 13 is a graph showing time-dependent changes in nitrate ion concentration and nitrite ion concentration in waste liquid in a cathode chamber in a fifth embodiment of the present invention.

FIG. 14 is a graph showing the change over time of the total nitrogen concentration in the waste liquid in the sixth embodiment of the present invention.

FIG. 15 is a schematic configuration diagram for explaining a seventh embodiment of the present invention.

16A and 16B show a waste liquid treatment apparatus used in the seventh embodiment, wherein FIG. 16A is a perspective view and FIG. 16B is an exploded perspective view.

FIG. 17 is a graph showing the change over time in the total nitrogen concentration in the waste liquid in the seventh embodiment.

FIG. 18 is a graph showing a change over time in a total nitrogen concentration in a waste liquid generated from a thermal power plant in a seventh embodiment.

FIG. 19 is a graph showing a change in pΗ of a solution in an anode chamber and a cathode chamber when an aqueous solution of sodium sulfate is electrolyzed in an electrolytic cell having a composite ion exchange membrane.

FIG. 20 is a graph showing the change over time in the amount of hydrogen gas generated electrochemically calculated in the eighth embodiment of the present invention.

FIG. 21 is a graph showing a change over time of a metal ion concentration in a liquid in a cathode chamber in a ninth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Anode 2 ... Cathode 3 ... Alumina diaphragm 3a ... Anion exchange membrane 3b ... Cation exchange membrane 3c ... Composite ion exchange membrane 4 ... Anode chamber 5 ... ... Cathode chamber 6... Electrolytic cell 7... Waste liquid 8... Pure water 9... Oxidized liquid 10... External DC power supply 11 a. .. Second liquid supply pipe 12a first liquid discharge pipe 12b second liquid discharge pipe 16a first liquid circulation pump 16b second liquid circulation pump 16c ... Third liquid circulation pump 16d Fourth liquid circulation pump 19 Liquid reduced

Claims (20)

[Claims] 1. An electrolytic cell in which a diaphragm having selective permeability to ions is disposed between an anode and a cathode, a waste liquid containing a nitrogen compound is injected into at least one of an anode chamber and a cathode chamber, and electrolysis is performed. A method for treating waste liquid, comprising oxidizing or reducing nitrogen compounds in the waste liquid to form nitrogen gas. 2. A first electrolysis is performed by injecting a waste liquid containing a nitrogen reduced product into an anode chamber of an electrolytic cell in which a diaphragm having selective permeability to ions is disposed between an anode and a cathode. 2. The method for treating waste liquid according to claim 1, wherein the nitrogen reduced product is oxidized into nitrogen gas. 3. A second electrolysis is performed by injecting a waste liquid containing nitrogen oxides into a cathode chamber of an electrolytic cell in which a diaphragm having selective permeability to ions is disposed between an anode and a cathode. 2. The method for treating waste liquid according to claim 1, wherein said nitrogen oxide is reduced to nitrogen gas. 4. A first electrolysis is performed by injecting a waste liquid containing a nitrogen compound into an anode chamber of an electrolytic cell in which a diaphragm having selective permeability to ions is disposed between an anode and a cathode. A first electrolysis step of oxidizing the nitrogen reductant to nitrogen gas, and injecting the waste liquid oxidized in the first electrolysis step into a cathode chamber of the electrolysis tank to perform a second electrolysis; A second electrolysis step of reducing nitrogen oxides in the waste liquid into nitrogen gas. 5. The waste liquid treatment method according to claim 2, wherein the waste liquid contains at least one of hydrazine and ammonium ion as a nitrogen reduced product. 6. The method according to claim 3, wherein the waste liquid contains at least one of nitrate ions and nitrite ions as nitrogen oxides. 7. The waste liquid treatment method according to claim 1, wherein the waste liquid is generated from a thermal power generation facility. 8. The method according to claim 1, wherein at least one of the anode and the cathode has a mesh shape or a porous shape, and the anode and the cathode are arranged so as to sandwich the diaphragm closely. The method for treating waste liquid according to any one of claims 1 to 4. 9. The method for treating waste liquid according to claim 1, wherein the diaphragm is an ion exchange membrane. 10. The method according to claim 9, wherein the diaphragm is an anion exchange membrane. 11. The method for treating waste liquid according to claim 9, wherein the diaphragm is a composite membrane of a cation exchange membrane and an anion exchange membrane. 12. The method according to claim 2, wherein hydrogen gas generated from the cathode is recovered in the first electrolysis step. 13. The method for treating waste liquid according to claim 3, wherein, in the second electrolysis step, metal ions contained in the waste liquid are deposited on a cathode and collected. 14. A diaphragm having selective permeability to ions is disposed between an anode and a cathode, and an electrolytic cell separated into an anode chamber and a cathode chamber by the diaphragm, and between the anode and the cathode. DC power supply for applying a DC voltage; first liquid supply means for supplying an electrolytic solution to the anode chamber of the electrolytic cell; and first liquid for discharging the electrolytic solution from the anode chamber of the electrolytic cell. Discharging means, second liquid supply means for supplying an electrolytic solution to the cathode chamber of the electrolytic cell, second liquid discharging means for discharging the electrolytic solution from the cathode chamber of the electrolytic cell, A waste liquid treatment apparatus comprising: gas discharging means for discharging gas generated by electrolysis from a gas phase of an anode chamber and / or a cathode chamber of an electrolytic cell. 15. A diaphragm having selective permeability to ions is disposed between an anode and a cathode, and an electrolytic cell separated into an anode chamber and a cathode chamber by the diaphragm, and between the anode and the cathode. A DC power supply for applying a DC voltage, and a first power supply for injecting a waste liquid containing a nitrogen compound into an anode chamber of the electrolytic cell.
A liquid supply means, a first liquid discharge means for discharging the oxidized waste liquid from the anode chamber of the electrolytic cell, and a second liquid discharge means for injecting a waste liquid containing a nitrogen compound into the cathode chamber of the electrolytic cell. A second liquid supply means, a second liquid discharge means for discharging the waste liquid subjected to the reduction treatment from the cathode chamber of the electrolytic cell, and electrolysis from the gas phase of the anode chamber and / or the cathode chamber of the electrolytic cell. 15. The waste liquid treatment apparatus according to claim 14, further comprising a nitrogen gas discharging means for discharging the nitrogen gas generated by the method. 16. The waste liquid processing apparatus according to claim 15, wherein said first liquid discharging means and said second liquid supplying means are directly connected. 17. The method according to claim 1, wherein at least one of the anode and the cathode has a mesh shape or a porous shape, and the anode and the cathode are arranged so as to sandwich the diaphragm therebetween. 16. The waste liquid treatment apparatus according to 14 or 15. 18. The apparatus for treating waste liquid according to claim 14, wherein the diaphragm is an ion exchange membrane. 19. The waste liquid treatment apparatus according to claim 18, wherein the diaphragm is an anion exchange membrane. 20. The waste liquid treatment apparatus according to claim 18, wherein the diaphragm is a composite membrane of a cation exchange membrane and an anion exchange membrane.