JPH08254597A - Method for treating waste liquid containing ammoniac nitrogen and organic substance - Google Patents

Abstract

PURPOSE: To inexpensively reduce the volume of a decontaminated waste liquid containing ammoniac nitrogen and organic substance. CONSTITUTION: A radioactive waste liquid 9, for example, containing heavy metal, a chelator and NH3 as well as scale including metal oxide such as iron oxide used to remove scale from a steam generator or other components at a nuclear power plant, is taken in an electrolyzer 4 and is electrolyzed by the anode 5 and the cathode 6 connected to a direct-current power source 10, keeping the temperature at 50 deg.C to the boiling point. The NH3 is separated from a complex by aerating the waste liquid 9 being electrolyzed from an diffusing pipe 8 and making a oxidizing decomposition of the complex made of the chelator and NH3 in the waste liquid, Furthermore, the diffusion of NH3 together with the air blown from the diffusing pipe 8 effectively decreases the volume of waste products.

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 waste liquid containing ammonia nitrogen and organic matter, and more particularly to ammonia nitrogen and water soluble organic matter such as steam generators and tanks for nuclear power plants. Wastewater containing ammonia and organic substances used for decontaminating the equipment of the equipment for volume reduction and removal treatment by electrolytic oxidation. Peroxidation of organic matter contained in the waste liquid in the presence of a catalyst. It is also used as a pretreatment process for a wet decomposition treatment process in which hydrogen is caused to oxidize and decompose.

[0002]

2. Description of the Related Art By operating a nuclear power plant,
Radioactive material is produced. Among these radioactive substances, for example, solids with high radioactivity generated from nuclear reactors, etc., if they are large in size, they are cut, and small ones are stored as they are in a predetermined container such as a drum tube and stored or discarded. It Also,
Liquids are also included in radioactive materials generated from nuclear power plants.The liquids include high conductivity waste liquids containing highly conductive salts, radioactive materials and detergents, steam generators and tanks. There are decontamination waste liquids that are generated when decontaminating various types of equipment.

The high-conductivity waste liquid is reduced in volume by evaporation and concentration, and then solidified with cement, asphalt or the like. On the other hand, in the decontamination waste liquid of equipment such as steam generators and tanks, heavy metal ions contained in the scale of the equipment, and these heavy metal ions and chelate compounds are also produced.
EDTA (Etylene DiamineTet) for removing heavy metals
ra Acetic acid: ethylenediaminetetraacetic acid) and NT
It contains a chelating agent such as A (Nitrilo Triacetic Acid Disodum), organic acids such as formic acid, oxalic acid and citric acid, and salts thereof. Moreover, in order to effectively remove the scale of decontaminated equipment, ammonium hydroxide (NH ₄ OH:
The pH of the decontaminating agent is set to about 9 with (ammonia water).

As in the case of the high-conductivity waste liquid, when the decontamination waste liquid is reduced in volume by evaporative concentration and then solidified with cement or the like and disposed on land, a carboxylic acid group is contained in the solidified treated substance. Since it contains a water-soluble chelating agent etc., the strength of the solidified body with cement decreases,
Further, when the solidified body comes into contact with water such as groundwater, there is a risk that radionuclides will be eluted.

As a method of decomposing such organic matter,
Many proposals have been made in the past. As one of them, the present applicant has disclosed in JP-A-61-104299 a wet decomposition method in which hydrogen peroxide (H ₂ O ₂ ) is caused to act in the presence of a catalyst to effect oxidative decomposition. This method is a safe and useful treatment method if it is allowed to consume expensive hydrogen peroxide, but if heavy metal is contained in the decontamination waste liquid, it is further treated in the oxidative decomposition step. A treatment for insolubilizing these heavy metals is required later.

US Pat. No. 4,537,666 discloses a method for cleaning a metal surface of a decontamination container containing metal ions and radioactively coated, and a decontaminating solution for cleaning the metal surface is a chelating agent. The flow of the decontamination liquid in the decontamination equipment is an organic acid containing
And it passes through the circulation path consisting of the decontamination solution tank and is circulated under pressure by a pump, and radioactive substances such as organic substances contained in the decontamination solution are adsorbed and removed by the ion exchange resin in this circulation path.
There is disclosed a purification method by electrolysis in which metal ions are removed by metal electrodeposition by a porous stainless steel electrode in an electrolytic cell to reduce metal ions.

Further, USP, No. 5,225,087 uses a chelating agent such as EDTA to remove metal contained in the waste liquid for chemical cleaning, cleaning of a steam generator, etc. In order to accelerate the reaction, pH adjustment is performed, and the pH is set to 2. Further, a technique for reusing EDTA contained in the waste liquid is disclosed. The waste liquid at this time is prepared by precipitating the metal and the radionuclide as a sulfide for environmental protection, or the radionuclide is removed by using an ion exchange resin.

The example of removing radioactive substances and the like by using the ion exchange resin has been described above. Generally, a method of treating the waste liquid by using the ion exchange resin to adsorb and remove ammonia, organic substances and radioactive substances in the waste liquid is carried out. It is being appreciated.

Further, conventionally, as a method for removing ammonia contained in the waste liquid, air stripping for inserting air by inserting a porous diffuser tube into a liquid container,
BACKGROUND ART An air exposure device by an air diffusion method is used in which ammonia dissolved in a waste liquid at a predetermined partial pressure is released to the outside air together with air. In the field of wastewater treatment, the nitrogen component is
₃ -N, NO ₃ -N, it is common to express divided into organic N, but referred ammonia in the case of performing the wastewater treatment and ammonia nitrogen, for simplicity, hereinafter simply referred to as ammonia.

However, in the prior art in which radioactive substances are adsorbed and removed using the above-mentioned ion exchange resin, after the decontamination waste liquid (hereinafter simply referred to as waste liquid) is treated, the used ion exchange resin is generated as secondary waste. In addition, NH that is contained as an ammonia salt by simply air stripping
We couldn't get rid of ₃ and how to deal with it has become a new issue. In order to solve this problem, the present inventor discloses in JP-A-4-66187 that by electrolyzing a waste liquid containing heavy metal ions and water-soluble organic matter in PH 4 to 9, the cathode side is Heavy metal ions are extracted as metal or hydroxide,
At the anode, a method for treating a waste liquid in which water-soluble organic matter is oxidatively decomposed and carbon dioxide and water are released is disclosed.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been made by the present inventor to further improve the method for treating a waste liquid containing a heavy metal and an organic substance disclosed in Japanese Patent Laid-Open No. 4-66187. . That is, according to the conventional waste liquid treatment method, the waste liquid contains NH ₃ in NH ₄ OH in addition to organic substances such as heavy metal ions and a water-soluble chelating agent, and forms a complex with the chelating agent. When NH ₃ which does not form a complex can be liberated alone, NH ₃ can be removed by air stripping. Thus, if the chelating agent in the waste liquid is EDTA, for example, under PH = 6 to 7, NH ₃ and EDTA form a complex with a molar ratio N of N = 3, so that a complex is formed. The volume of unreacted NH ₃ can be reduced, and there is a problem that a large amount of waste liquid containing a radioactive substance, a chelating agent, and salts such as ammonia salts is generated in addition to scales such as iron oxide and copper oxide.

In order to solve the above problems, the present invention provides N
A waste liquid containing H ₃ and a water-soluble organic substance is electrolyzed and oxidized, NH ₃ which has formed a complex with an organic substance is liberated, and the liberated NH ₃ is diffused and removed by the air blown from a diffuser pipe, The purpose is to reduce the volume of waste liquid.

[0013]

In order to solve the above-mentioned problems, the present invention is as follows: (1) A waste liquid containing ammoniacal nitrogen and a water-soluble organic substance is contained in an electrolytic cell provided with a diffuser pipe, and By applying a direct current to the waste liquid to perform electrolysis, the water-soluble organic matter is oxidatively decomposed at the anode, and at the same time, air is blown from the air diffuser to diffuse and remove ammoniacal nitrogen in the electrolytic cell. (2) In (1) above, the organic matter contained in the waste liquid is an organic acid, a salt of the organic acid, or a chelating agent, and (3) in (1) or (2) above. The electrolysis conditions of the waste liquid were such that the pH was in the range of 4 to 9, the temperature was in the range of 50 ° C. or higher and the boiling point or lower, and the current density was within 1 to 10 A / dm ^{2 at} an applied DC voltage of 4 to 8 V between the electrodes. Furthermore, (4 ) In any of the above (1) to (3), the waste liquid contains heavy metal ions, and (5) in any one of the above (1) to (4), the waste liquid is radiated. That it is polluted,
(6) In any one of (1) to (5), the treatment method of electrolytically oxidizing the waste liquid containing ammoniacal nitrogen and the water-soluble organic substance while blowing air into the waste liquid is used as a pre-stage process, and the waste liquid from the pre-stage process is treated. The wet decomposition method in which hydrogen peroxide is caused to act in the presence of a catalyst to cause oxidative decomposition is used as a post-process, and the pre-process and the post-process are combined.

[0014]

[Operation] To remove waste liquid containing ammonia nitrogen and organic matter, for example, scales (iron oxide, copper oxide) contaminated with radioactivity in steam generators of nuclear power plants,
A chelating agent that removes metals (DET) by making water-soluble chelate compounds that are extremely stable with the metals contained in the scale
A, NTA, etc.) is used.
The pH of the waste liquid is adjusted to 9 by adding H ₄ OH. Therefore other scales to decontaminated the waste contains radioactive materials, complexes and NH ₃ or the like between the chelate and NH _3. By electrolyzing such a waste liquid, heavy metal ions are converted into metal or hydroxide at the cathode of the electrolytic cell, and organic substances are oxidized and decomposed at the anode into carbon dioxide and water, and further NH ₄ + forming a complex is formed. Reduce to liberate NH ₃ . That is, NH ₃ in the waste liquid is combined with an organic acid or a chelating agent to form a complex, so that NH ₃ cannot be removed, but NH ₃ forming the complex is liberated by electrolysis. The released NH ₃ is diffused and removed by the air blown from the air diffuser provided at the bottom of the electrolytic cell to remove the decontaminating substance. That is, it is possible to suppress the generation of ammonium sulfate (which remains as a solid content and leads to an increase in a solidified body) generated by the neutralization of the waste liquid after the electrolytic treatment by adding H ₂ SO ₄ .

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram for explaining an example of a process for treating a waste liquid according to the present invention, in which 1 is a waste liquid supply tank, 2 is an acid supply tank, and 3 is an alkali supply tank. 4, electrolytic cell, 5 anode, 6 cathode, 7 PH detection electrode, 8 air diffuser, 9 waste liquid, 10 DC power source, 11, 12, 13
Is a pump, 14 is an air compressor, and 15 is a service air pipe.

In FIG. 1, as a waste liquid to be treated, a waste liquid 9 of a predetermined level is supplied from the waste liquid supply tank 1 into the electrolytic tank 4 by a pump 11. The electrolytic cell 4 has an external DC power source 1
An anode 5 and a cathode 6 connected to 0 are installed, and an air diffusing tube 8 is installed at the bottom. Air diffuser 8 has air compressor 1
The air supplied from the service air pipe 15 is pressure-fed by 4, and the air is blown into the electrolytic cell 4. Further, a PH detection electrode 7 for detecting the hydrogen ion concentration PH of the waste liquid 9 is inserted in the electrolytic bath 4, and sulfuric acid (H ₂ SO ₄₎ for adjusting the pH of the waste liquid 9 is provided outside the electrolytic bath _4. Acid supply tank 2 containing an acid solution such as), an alkaline solution tank 3 containing an alkaline solution such as ammonium hydroxide (NH ₄ OH) that is an aqueous solution of NH ₃ , is provided with a pump 12,
The acid or alkali solution is injected into the waste liquid 9 by driving 13
The pH of the waste liquid 9 can be set to a predetermined PH value based on the PH detection value.

As the electrode material, the material of the anode 5 which gives an oxidation reaction to the waste liquid is important, and when oxygen gas is generated in the anode 5, it does not contribute to the oxidation reaction and there is a possibility of electrode elution, so platinum (Pt), etc. Noble metals, iron oxide (Fe ₃ O ₄ ) and lead dioxide (PbO ₂ ) are used. In particular, PbO ₂ is useful for the oxidation of organic substances, and it is preferably supported by electrodeposition or other means on the outside of a material such as titanium (Ti) that can itself be used as an insoluble electrode. The cathode 6 may be made of any material, for example, stainless steel is used. The electrolysis operation can be carried out in either a batch system or a continuous system in which each process is carried out in a batch system.
Generally, if the processing amount is small and high-level processing is required, the batch system is used, but if the processing amount is large, the continuous system is applied.

The electrolysis conditions include PH value, pressure, waste liquid temperature, current density during electrolysis, voltage and the like. First, the PH value is measured by the pump 12 or 1 according to the detection value of the PH detection electrode 7.
3 from the acid supply tank 2 or the alkali supply tank 3
An acid such as ₂ SO ₄ or an alkaline solution such as aqueous ammonia is supplied into the electrolytic cell 4 to adjust the pH of the waste solution 9 within the range of 4 to 9. The PH value for insolubilizing metal ions is 4
This is because the above needs to be 9 or less in order to suppress the generation of oxygen gas. Usually, the pH value of the waste liquid 9 is 7-9. The waste liquid 9 contains an ammonium salt such as ammonium sulfate (NH ₄ ) ₂ SO ₄ or the like, and usually exhibits an electric conductivity suitable for electrolysis. However, when the salt concentration is low and the electric conductivity is small, for example, an electrolyte component is used. , A salt such as sodium sulfate (Na ₂ SO ₄ ) is added. As a matter of course, the salt to be added does not increase the amount of waste, because a part of the salt is recycled after the treatment liquid is neutralized and supplied.

Next, the outside air pressure as a pressure condition is a normal pressure, which is a preferable pressure from the viewpoint of safety. The temperature of the waste liquid 9 is about 50 ° C. or higher and not higher than the boiling point of the liquid. It is advantageous to raise the temperature within this temperature range in order to oxidize the organic matter. It is also advantageous for the removal of NH ₃ by air stripping in which air is blown into the inside. Next, the current density during electrolysis is usually 1
-10 A / dm ² is suitable, and if the current density is too low, the progress of electrolysis is slow and it is not practical, and the current efficiency is lowered even if it is excessive. The voltage at this time varies depending on the conditions such as the electric conductivity of the liquid, the current density and the distance between the electrodes.
It is about V.

By the electrolysis under the above-mentioned conditions, the oxidation reaction of the organic substance occurs in the anode 5 as follows.

[0021]

Embedded image

At the cathode 6, a metal electrodeposition or a hydroxide forming reaction occurs as shown in the following reaction formula.

[0023]

Embedded image

Further, the complex formed by EDTA and NH ₃ by electrolysis is electrooxidized. That is, in the neutral region where PH of EDTA is PH = 6 to 7, EDTA is decomposed, and thus ammonia ions (NH ₄ +) that have formed a complex with EDTA are liberated and NH ₃ is produced. Four
When air stripping is performed from the air diffusing tube 8 inside, NH ₃ is released together with air and NH ₃ can be removed. NH ₃ can also be collected and released by a scrubber.

At this time, the molar ratio of NH ₃ and EDTA N
Because be removed until N = 1, in which NH ₃ is contained alone in the waste, simply blowing air, NH ₃ as compared with the conventional method of so-called air stripping 1
It can be reduced to / 3. After the electrolysis, if necessary, an acid or alkali neutralizing agent is added from the acid supply tank 2 or the alkali supply tank 3 to neutralize the electrolytically treated liquid. However, in the case of a decontamination waste liquid, it is usually unnecessary to neutralize.

More specifically, in the conventional method, the weight percentage (Wt%) is, for example, when the conventional air stripping is not applied, the waste liquid contains 10% EDTA and 2.5% NH _3. When a volume of 100 m ^{3 is} generated at room temperature and pressure,
Only 80% of EDTA was decomposed, NH ₃ was neutralized with H ₂ SO _4, and ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) obtained as a whole remained as residual salt, the solid waste content was 23.4 Ton.
Met. On the other hand, according to the air stripped waste liquid treatment method of the present invention, when 70% of NH ₃ is air stripped, the solid waste content becomes 8.4 Ton.

Thus, the waste liquid according to the present invention is electrolyzed,
Furthermore, when the waste liquid treatment method with air stripping is used, the volume reduction ratio is (1 / 2.8) compared with the conventional waste liquid treatment method with no electrolysis, and the volume is greatly reduced. It Since the cost of waste disposal has been increasing recently, a reduction of about 1/3 means a significant reduction in waste disposal cost. Moreover, since no oxidizer and catalyst are used, the overall waste disposal cost is reduced.

Further, when the electrolytic oxidation means according to the present invention is used as the former stage process and the wet decomposition means is used as the latter stage process, since the heavy metals are removed by electrolysis in the former stage process, the metal insolubilization treatment is required in the latter stage process. In addition, since the amount of H ₂ O ₂ required for the oxidative decomposition of the chelating agent may be small, the amounts of the oxidizing agent and the catalyst used can be reduced in the subsequent process. Also,
The NH ₃ in the first stage process has H ₂ SO ₄ added in the _second stage process to bring the pH into an acidic condition, so that the total amount of NH ₃ is (N
H ₄ ) ₂ SO ₄ remains.

As the above-mentioned first-stage process, electrolytic oxidation is carried out,
By combining wet decomposition as the latter process, the chelating agent is decomposed by 50% or more in the former process, so that the consumption of H ₂ O ₂ is reduced. Since NH ₃ is removed by 70% or more in the previous stage, the residual amount of NH ₃ becomes 1/3 or less.

Concrete Example 1 FIG. 2 shows the EDTA concentration (to measure the TOC concentration) and the NH ₄ + concentration with time when the electrolysis and air stripping according to the present invention were performed and by the conventional waste liquid treatment method in which only electrolysis was performed. It is an example of experimental values for explaining the change, where the horizontal axis represents time and the vertical axis represents concentration, the results of the method of the present invention are shown by a solid line, and the results of the conventional method are shown by a dotted line.

FIG. 2 shows that 350 ml of waste liquid obtained by mixing EDTA with 10 g / l, NH ₃ with 2.6 g / l and Na ₂ SO ₄ with 30 g / l is electrolyzed in the electrolytic cell 4 shown in FIG. It was obtained by processing and the electrolysis conditions at this time were a cell voltage of 6
~ 7V, current 3A, liquid temperature at 50 ℃, PH during this period
Is in the range of 7-9. The air stripping condition of the present invention is as follows.
It is blowing in at a rate of n.

The EDTA concentration is TOC (Total Organic
c Carbon) The results obtained by measuring the concentration.

According to the results shown in FIG. 2, when air stripping was performed before the test, the decomposition rate based on the TOC concentration was 65%, and the NH ₃ removal rate reached 70%.
On the other hand, the NH ₃ removal rate in the conventional case where air stripping was not performed was only 35%.

Concrete Example 2 FIG. 3 shows an example of changes over time in the NH ₄ + and TOC concentrations when the anode used for electrolysis in the waste liquid treatment method according to the present invention is a material in which lead dioxide is electrodeposited on titanium. The experimental value is the same as in Example 1, except that 350 ml of waste liquid containing 10 g / l of EDTA and 1.7 g / l of NH ₃ in the electrolytic cell was used for a voltage of 6 to 7 V and a current of 3 A. Electrolyzed. The liquid temperature at this time was kept at 50 ° C and the air was adjusted to 5 ° C.
It was blown at a rate of 0 ml / min. PH = 8-
It was in the 9 range.

According to the results shown in FIG. 3, after the start of electrolysis, 6
After a lapse of time, the TOC decomposition rate reached 75% and the NH ₃ removal rate reached 75%.

Specific Example 3 FIG. 4 shows changes with time in the NH ₄ + and TOC concentrations when lead dioxide was used as the anode for electrolysis in the waste liquid treatment method of the present invention and the temperature of the liquid during electrolysis was 30 ° C. It is an experimental value showing an example, the electrolytic cell is the same as in Example 1, and the waste liquid contained in the electrolytic cell at a rate of 25 g / l of EDTA and 3.6 g / l of NH ₃ was applied at a voltage of 6 to 7 V and a current of 1. As air stripping at 5 A, air is blown out at a rate of 200 ml / min.

According to the results shown in FIG. 4, at the liquid temperature of 30 ° C., the TOC decomposition rate was 32 even after 8 hours had passed from the start of electrolysis.
%, The removal rate of NH ₃ is 40%, and even after 8 hours, the removal rate is only about half of that in the specific example 2 after 6 hours. It has been shown to have an impact.

[0038]

As is apparent from the above description, the present invention has the following effects. 1. Effect corresponding to claim 1 A waste liquid containing NH ₃ and a water-soluble organic substance is electrolyzed and oxidized, and NH ₃ which has formed a complex with NH ₃ is liberated and the liberated NH _{Since 3} was dissipated and removed by the air blown out by the air diffuser, the amount of NH ₃ was greatly reduced, and the volume of the waste liquid was reduced by this amount, enabling inexpensive waste liquid treatment. 2. Effect of organic substance corresponding to claim 2, in particular, when it contains a chelating agent, in the electrolytic cell form a complex with a chelating agent and NH _3, can not be removed NH ₃ , By electrolysis N
H ₃ can be released, the volume can be reduced, and the same effect as in claim 1 can be obtained. 3. Effect corresponding to claim 3 Since the temperature of the waste liquid in the electrolytic cell is in the range of 50 ° C or higher and the boiling point of the liquid or lower and the current is 1 to 10 A / dm ² or less, the efficiency of the waste liquid volume reduction is improved. . 4. Effect corresponding to claim 4 Since the heavy metal ions in the waste liquid are extruded as metal or hydroxide, the heavy metal ions in the waste liquid can be effectively removed. 5. Effect corresponding to claim 5 When the waste liquid is contaminated with radioactivity, NH ₃ complexed with the chelating agent by electrolysis and air stripping
And the metal having a radionuclide and the like can be removed, so that the volume of pollutants can be reduced. 6. Effect corresponding to claim 6 Since the electrolytic oxidation process is the first stage process and the wet decomposition process is the second stage, the cost of waste liquid treatment can be further reduced.

[Brief description of drawings]

FIG. 1 is a structural diagram for explaining an example of a process for treating a waste liquid according to the present invention.

FIG. 2 is an example of experimental values for explaining changes with time in EDTA concentration and NH ₄ + concentration.

FIG. 3 is an experimental value showing an example of changes over time in NH ₄ + and TOC concentrations when an anode used in electrolysis in the waste liquid treatment method according to the present invention is a material in which lead dioxide is electrodeposited on titanium.

FIG. 4 is an experimental value showing an example of changes over time in NH ₄ + and TOC concentrations when the anode used for electrolysis in the waste liquid treatment method according to the present invention is lead dioxide and the liquid temperature during electrolysis is 30 ° C. is there.

[Explanation of symbols]

1 ... Waste liquid supply tank, 2 ... Acid supply tank, 3 ... Alkali supply tank,
4 ... Electrolyzer, 5 ... Anode, 6 ... Cathode, 7 ... PH detection electrode,
8 ... Air diffuser, 9 ... Waste liquid, 10 ... DC power supply, 11, 12,
13 ... Pump, 14 ... Air compressor, 15 ... Service air piping.

Claims (6)

[Claims] 1. A waste liquid containing ammoniacal nitrogen and a water-soluble organic substance is stored in an electrolytic cell provided with an air diffuser,
By applying a direct current to the waste liquid to electrolyze, the water-soluble organic matter is oxidatively decomposed at the anode, and
At the same time, air is blown from the air diffuser to diffuse and remove ammoniacal nitrogen in the electrolytic cell to remove waste liquid containing ammoniacal nitrogen and organic matter. 2. The organic matter contained in the waste liquid is an organic acid,
The method for treating waste liquid containing ammoniacal nitrogen and organic matter according to claim 1, wherein the method is a salt of the organic acid or a chelating agent. 3. The electrolysis condition of the waste liquid is such that the pH is in the range of 4 to 9, the temperature is in the range of 50 ° C. to the boiling point, and the current density is 1 to 10 A / in the applied DC voltage of 4 to 8 V between the electrodes.
^{3. The} method for treating a waste liquid containing ammoniacal nitrogen and an organic matter according to claim 1 or 2, characterized in that it is in dm ² . 4. The method for treating a waste liquid containing ammonia nitrogen and organic matter according to claim 1, wherein the waste liquid contains heavy metal ions. 5. The method for treating a waste liquid containing ammonia nitrogen and an organic substance according to claim 1, wherein the waste liquid is radioactively contaminated. 6. A treatment method of electrolytically oxidizing a waste liquid containing ammoniacal nitrogen and a water-soluble organic substance while blowing air into the waste liquid, wherein the waste liquid from the previous process is treated with hydrogen peroxide in the presence of a catalyst. The waste liquid containing ammoniacal nitrogen and organic matter according to any one of claims 1 to 5, wherein the wet decomposition method of oxidative decomposition is used as a post-process, and the pre-process and the post-process are combined. Processing method.