KR101834438B1 - Apparatus and method for treating desulfurization waste water - Google Patents

Abstract

More particularly, the present invention relates to a wastewater treatment apparatus capable of efficiently treating ammonia nitrogen contained in a desulfurization wastewater, and a treatment method using the wastewater treatment apparatus.
According to the present invention, the ammonia stripping process and the electrolysis process are performed to remarkably reduce the total nitrogen content in the desulfurized wastewater by converting the high concentration of ammonia nitrogen into low concentration in a short time.
In addition, the total nitrogen content reduction is effective for improving the degradation efficiency by the microorganisms in the downstream bioreactor.

Description

[0001] The present invention relates to a desulfurization waste water treatment apparatus and a treatment method using the same,

More particularly, the present invention relates to a wastewater treatment apparatus capable of efficiently treating ammonia nitrogen contained in a desulfurization wastewater, and a treatment method using the wastewater treatment apparatus.

As the industry develops and the life is getting better, the electricity consumption is increasing every year, so the fossil fuel needed to produce electricity is consuming even more.

One of the major pollutants that occurs when fossil fuels are burned is SO ₂ , and the typical content of SO _{2 in} the flue gas ranges from 500 to 2000 ppm. The SO ₂ is a causative agent of acid rain, which directly affects the human body and has a great influence on animals and plants.

In general, the desulfurization wastewater contains a large amount of NS compounds due to the emission of NOx and SOx during the operation of the thermal power plant, and contains a high concentration of chlorine ions, toxic substances, hard substances (calcium ions, magnesium ions, etc.) have.

In order to treat such a desulfurization wastewater, conventionally, the M process is used, but the M process has a complicated process, has difficulty in maintenance, and has a high operation cost.

In particular, the M process has difficulties in operating a biological reactor due to high concentration of chlorine ions and toxins in the desulfurization wastewater, and is not sufficiently capable of removing nitrogen components. Physical methods such as filtration, reverse osmosis, ion exchange resin and evaporation concentration method are required to remove nitrogen in the desulfurization wastewater. However, these methods do not decompose nitrogen but merely separate nitrogen and concentrate It has a problem that post-processing is required.

In addition, NaOCl is injected to remove the NS COD in the process of removing the refractory wastewater. However, since the nitrogen is not completely decomposed, If it is released, it causes eutrophication, and if it is poured into the groundwater and people drink it, there is a problem that can cause cancer of the baby or blue baby syndrome of the infant.

Korean Unexamined Patent Publication No. 2003-0055827

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an apparatus and a device for treating a desulfurized wastewater which can remove ammonia nitrogen (NH ₄ -N) at a high concentration in a desulfurization wastewater and improve the stability and treatment efficiency of a downstream bioreactor And the like.

According to an aspect of the present invention, there is provided a desulfurization apparatus for a desulfurization apparatus, comprising: a flocculation reaction tank for flowing a desulfurization wastewater treated with suspended solids and heavy metals and removing hard substances in the desulfurization wastewater by a coagulation sedimentation reaction; An ammonia stripping tank for removing nitrogen through an ammonia stripping process, and an electrolysis tank for removing ammonia nitrogen, which has not been treated in the treatment water passed through the ammonia stripping tank, through an electrolysis reaction. ≪ / RTI >

The apparatus for treating desulfurized wastewater includes a bioreactor for removing a residual nitrogen component present in the treated water through the electrolytic bath by a bioreaction, and a flocculent material remaining in the treated water passing through the bioreactor through an adsorption reaction And further comprises an adsorption tank.

Wherein the ammonia stripping tank comprises: a first treatment water tank through which the treated water passing through the flocculation reaction tank flows, and air and a basic substance are introduced into the treated water to degas a part of the ammonia; And a scrubber tower for introducing the deaerated ammonia from the ammonia stripping tower and converting the ammonia into an ammonium salt by introducing an acidic substance into the ammonia, .

Wherein the electrolytic bath comprises an electrolytic bath into which the treated water passing through the ammonia stripping tank flows and which removes ammonia nitrogen which has not been treated in the treated water by an electrolysis reaction and an electrolytic bath through which the treated water is introduced, And a tertiary treatment water tank.

Wherein the bioreactor includes a denitrification tank into which the treated water flowing through the ammonia stripping tank flows and converts nitrate nitrogen and nitrite nitrogen present in the treated water by denitrification into nitrogen gas, And an aeration tank for removing the carbon source remaining in the treatment water through an oxidation reaction.

According to another aspect of the present invention, there is provided an ammonia stripping method comprising: (A) an ammonia stripping step of degassing ammonia nitrogen present in treated water from which sulfur suspended solids, heavy metals and hard substances are removed through ammonia stripping to ammonia, and B) an electrolysis step of removing the untreated ammonia nitrogen in the treated water after the ammonia stripping step by an electrolysis reaction.

The ammonia stripping step includes the steps of injecting air and a basic substance into the treated water from which the suspended solids, heavy metals and hard substances of the desulfurized wastewater have been removed and partially removing the water by degassing with ammonia, Temperature steam is supplied to raise the temperature of the treated water to degas the ammonia, and an acidic substance is added to the degassed ammonia to convert it into an ammonium salt to remove it.

Characterized in that the electrolysis step is carried out for 1 to 120 minutes at a current density of 1 to 5 A / dm < ² > at the electrode.

Further comprising a biological reaction step of removing a nitrogen component remaining in the treated water after the electrolysis step by a biological reaction, and an adsorption step of filtering the treated water having passed through the biological reaction step on activated carbon to remove the remaining suspended matter .

According to the present invention, the ammonia stripping process and the electrolysis process are performed to remarkably reduce the total nitrogen content in the desulfurized wastewater by converting the high concentration of ammonia nitrogen into low concentration in a short time.

In addition, the total nitrogen content reduction is effective for improving the degradation efficiency by the microorganisms in the downstream bioreactor.

1 is a schematic diagram illustrating an apparatus for treating a desulfurized wastewater according to an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the MLSS (mixed liquer suspended solid) concentration of the treated water after the ammonia stripping process and the electrolysis process, the treated water after the bioreaction process, and the treated water immediately after the ammonia stripping process without the electrolysis process Respectively. As shown in FIG.
FIG. 3 is a graph showing the relationship between the amount of total nitrogen (TN) present in each treatment water and the amount of ammonia stripping after the ammonia stripping process and immediately after the electrolysis process in the method of treating the desulfurization wastewater according to an embodiment of the present invention And the results are shown in FIG.
4 is sampled after the treatment may directly subjected to ammonia stripping process directly after the electrolytic process in the desulfurization waste water treatment method in accordance with one embodiment of the invention, the ammonium nitrogen present in the number of each treatment (NH ₃ -N ), And the results are shown in the graph.

Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.

"Stripping" used in the present invention means to separate and remove the gas dissolved in the liquid in all processes in contact with gas components such as heating, pressurization and air.

The 'desulfurization wastewater' referred to in the present invention refers to a wastewater containing a large amount of toxic substances including COD (Chemical Oxygen Demand) component and heavy metal component inevitably generated due to a desulfurization process in a flue gas desulfurization apparatus such as a thermal power plant It refers to waste water.

The nitrogen component in the desulfurization wastewater exists in the form of organic nitrogen and inorganic nitrogen, and the total nitrogen is called total nitrogen (T-N). Inorganic nitrogen is again divided into ammonia nitrogen (NHx) and nitrate nitrogen (NOx). In the present invention, the main purpose is to remove ammonia nitrogen present in the desulfurization wastewater.

1 is a schematic diagram illustrating an apparatus for treating a desulfurized wastewater according to an embodiment of the present invention.

Referring to FIG. 1, the apparatus for treating a desulfurized wastewater according to the present invention includes a flocculant tank 100 for removing hard substances in the desulfurized wastewater by flowing a desulfurized wastewater treated with suspended solids and heavy metals, The ammonia stripping tank 200 removes a large amount of ammonia nitrogen present in the treated water through the ammonia stripping process, and the ammonia stripping tank 200 removes the untreated ammonia nitrogen through the electrolysis reaction A bioreactor 400 for removing residual nitrogen components present in the treated water passed through the electrolytic bath 300 and the electrolytic bath 300 by a biological reaction, And the adsorbing tank 500 removes the adsorbed water from the adsorbent.

In the flocculation reaction tank 100, suspended solids and heavy metals-treated desulfurized wastewater are introduced and the hard substances are removed through a precipitation separation reaction as shown in the following reaction formula (1). The flocculation tank 100 includes a pH adjustment tank 110, an aggregation tank 120, and a first settling tank 130.

The above-mentioned hard substance is adhered to the electrode surface of the rear end electrolytic bath 300 to reduce the treatment efficiency and remarkably lower the durability of the electrode, and therefore must be removed in advance.

[Reaction Scheme 1]

Mg ²⁺ + (Ca (OH) ₂ , NaOH) Mg (OH) ₂ ↓ + (Ca ²⁺ , 2Na ⁺ )

Ca ²⁺ + Na ₂ CO ₃ → CaCO ₃ ↓ + 2Na ⁺

In the pH adjustment tank 110, the desulfurized wastewater is introduced, and the introduced desulfurized wastewater is adjusted to pH 9 to 13, which is a pH range at which the precipitation separation reaction can take place.

At this time, a pH adjuster is added to adjust the pH of the desulfurization wastewater, and Ca (OH) ₂ or NaOH is used as the pH adjustor.

At the same time as the pH adjuster is added, the magnesium ions are coagulated with the hydroxyl groups (OH ^- ) of NaOH, and the calcium ions are precipitated in the form of calcium carbonate (CaCO ₃ ) by the addition of sodium carbonate (Na ₂ CO ₃ ).

The pH of the flocculation tank 120 is adjusted through the pH adjustment tank 110, and treated water (hereinafter referred to as "first treated water") into which magnesium and calcium flocculate is introduced.

A coagulant is added to the first treated water to grow flocs of the coagulated hard material in the first treated water. Then, the first treated water containing the coagulated hard substance is transferred to the first sedimentation tank 130.

At this time, it is preferable to use polyaluminum chloride series as the coagulant, but it is not limited thereto.

The first treated water flowing through the flocculation tank 120 flows into the first sedimentation tank 130 and the coagulated hard substance is contained in the first treated water passed through the flocculation tank 120.

In the first settling tank 130, sedimentation of the agglomerated hard material occurs, and the precipitated hard material is conveyed to the thickening tank 600. Then, the non-precipitated supernatant is transferred to the ammonia stripping tank 200.

The precipitated hard substance transferred to the concentration tank 600 is concentrated to a certain water content or less and then transferred to the dehydrating tank 610, and the dehydrated precipitate is treated in the form of a dehydrated cake.

In the ammonia stripping tank 200, a large amount of ammonia nitrogen present in the treated water (hereinafter referred to as "second treated water") through which the hard substance is removed through the flocculation reaction tank 100 is removed.

The ammonia stripping tank 200 includes a first treated water tank 210, an ammonia stripping tower 220, and a scrubber tower 230.

The second treated water is introduced into the first treated water tank 210. The second treated water flows into the second treated water for 24 to 48 hours while air is being injected into the first treated water tank 210. The pH is adjusted to 10 or higher while NaOH, Some of the ammonium ions (NH ₄ ⁺ ) in the treated water are converted to ammonia (NH ₃ ), and some are deaerated and the remainder is transferred to the ammonia stripping tower 220 together with the wastewater.

The ammonia stripping tower 220 supplies steam and air at a temperature of 40 to 60 ° C to the second treated water that has passed through the first treated water tank 210 to raise the temperature of the second treated water to remove the ammonia stripping, .

Ammonia (NH ₃ ) is generated from the second treated water passing through the first treated water tank 210 through the ammonia stripping reaction. The generated ammonia is transferred to the scrubber tower 230, and the second treated water from which ammonia is removed is transferred to the electrolytic bath 300.

At this time, it is preferable that the supplied steam is maintained at a temperature of 40 to 60 ° C, which is a range in which the moving speed of the material is increased and the removal efficiency of ammonia is maximized, , The ammonia removal efficiency is lowered in the ammonia stripping tower. When the temperature is higher than 60 ° C, the economical efficiency against the rise in temperature is lowered, which is not preferable.

In the scrubber tower 230, an acidic substance is introduced into the ammonia gas generated through the ammonia stripping tower 220 to convert ammonia into ammonium salts. Then, the ammonium salt is transferred to a separate treatment tank and then removed. As the acidic substance, it is preferable to use sulfuric acid which can easily form an ammonium salt.

If an ammonia stripping process is performed without performing the electrolysis process described below and the biological reaction process is immediately carried out, undesired ammonia nitrogen may cause undesirable load on the biological reaction tank, which is a post-process.

The ammonia stripping process can be varied depending on the inflow temperature of the desulfurization wastewater, the amount of the inflow air, and the tower size. As the treatment efficiency of the ammonia stripping process becomes better, the size of the decomposition tank and the current supply amount in the downstream electrolysis process Thereby reducing the operating cost of the overall electrolysis process.

Therefore, the treated water passing through the ammonia stripping tank 200 can significantly reduce the amount of electricity required for electrolysis in the electrolytic bath 300 and the size of the electrolytic bath, because a large amount of ammonia nitrogen is removed.

The electrolytic bath 300 receives treated water (hereinafter referred to as "third treated water") from which a large amount of ammonia nitrogen has been removed through the ammonia stripping tank 200, and the third treated water contains untreated ammonia It is electrolyzed to remove nitrogen.

The electrolysis may be carried out for 1 to 120 minutes at a current density of 1 to 5 A / dm ² , preferably 1 to 5 A / dm ² , although it may vary depending on the operating conditions for the object to be treated. When the amount of current is less than 1 A / dm ² or less than 1 minute, the reactivity is lowered. If the current is more than 5 A / dm ² or more than 120 minutes, excessive generation of an oxidizing agent (NaOCl) The toxicity of the toxic substance due to the excessive amount of the reducing agent is increased and the operation ratio of the excessive amount of the reducing agent and the electric power ratio is increased.

Specifically, the electrolytic bath 300 includes an anode and a cathode. First, the electrolysis of water molecules present in the third treatment water is followed by the reaction of the following Schemes 2 to 4 sequentially.

That is, some of the chlorine (Cl ₂ ) gas produced by the following reaction scheme 2 is released, and a part of the chlorine (Cl ₂ ) gas is dissolved again with water. Then, hypochlorite ion (OCl ^- ) is generated by the reaction of the following reaction formula (3), and the generated hypochlorite ion (OCl ^- ) again reacts with ammonia to generate nitrogen gas.

[Reaction Scheme 2]

_{^{Cl - → Cl 2 (Dissolved +}} Gas) + 2e - ... ... ... (anode)

2H ₂ O + 2e ^- ? 2OH ^- + H ₂ ... ... ... (cathode)

[Reaction Scheme 3]

Cl ₂ + H ₂ O → HOCl + Cl ^- + H ⁺ ... ... (anode)

HOCl → OCl ^- + H ⁺ ... ... ... (cathode)

[Reaction Scheme 4]

2NH ₃ + 2OCl ^- → N ₂ ↑ + 2H ⁺ + 2Cl ^- + 2H ₂ O

That is, as shown in the above reaction formulas 2 to 4, the chlorine ions are partially converted into chlorine gas through electrolysis and then removed, and the remaining chlorine gas is dissolved again to promote the reaction of ammonia. The ammonia reacts with the hypochlorite ion to generate nitrogen gas, thereby removing the ammonia nitrogen present in the third treatment water.

By sequentially performing the ammonia stripping process and the electrolysis process, a large amount of ammonia nitrogen present in the desulfurization wastewater can be removed, and the reaction of the microorganisms in the bioreactor as a downstream process can be stabilized.

If the desulfurization wastewater not subjected to the ammonia stripping process and the electrolysis process is introduced into the bioreactor 400, there arises a problem that the decomposition efficiency of the microorganisms is lowered due to the nitrogen component at a high concentration.

Further, when the electrolysis process is used singly without performing the ammonia stripping process, the decomposition ability of the nitrogen component required in the electrolytic bath 300 is increased, so that the residence time is increased. When the residence time is increased, the required amount of electric power is increased along with the increase of the size of the electrolytic bath, and the efficiency is lowered.

Accordingly, since 60 to 80% or more of the ammonia nitrogen present in the desulfurization wastewater is treated through the ammonia stripping process and the untreated ammonia is treated through the electrolysis process, the scale of the electrolysis tank 300, Is minimized.

Since the pH of the treated water passed through the electrolytic bath 300 (hereinafter referred to as "fourth treated water") is in an alkaline state, the apparatus for treating a desulfurized wastewater according to the present invention comprises a second treated water tank Gt; 310 < / RTI >

In the second treatment water tank 310, it is preferable to adjust the pH to a level suitable for the biological treatment occurring in the biological treatment tank 400, which is a post-treatment.

That is, hydrochloric acid (HCl) is added to the fourth treated water to maintain the pH at 7 to 7.5. Acidic substances such as hydrochloric acid can be used without restrictions as long as they are soluble in water to produce H ⁺ .

(Hereinafter referred to as "fifth treated water") whose pH has been adjusted via the second treated water tank 310 flows into the bioreactor 400. [ In the bioreactor 400, the residual nitrogen component present in the fifth treated water is removed through the biological reaction.

The bioreactor 400 includes a denitrification tank 410, an aeration tank 420, and a second settling tank 430.

In the denitrification tank 410, the NO ₂ ^- and NO ₃ ^- components present in the fifth treated water are removed through the denitrification of denitrifying microorganisms as N ₂ .

The denitrifying microorganism may be, but not limited to, a breathable anaerobic microorganism or a denitrifying microorganism.

In the aeration tank 420, an external carbon source such as methanol existing in the fifth treated water passing through the denitrifying bath 410 is oxidized to oxidize a potential COD component.

The second settling tank 430 serves to transfer the precipitated microorganisms after the reaction to the thickening tank 600 as sludge, and to return the partially recovered microorganisms to the denitrifying tank 410 for reuse.

In the adsorption tank 500, treated water (hereinafter referred to as "sixth treated water") through which the nitrogen component is almost removed through the bioreactor 400 is introduced, and suspended matters remaining in the sixth treated water are removed.

The adsorption tank 500 is made of activated carbon, and the sixth treated water is passed through the activated carbon to adsorb residual suspended solids and organic substances present in the sixth treated water to the activated carbon. The sixth treated water having passed through the activated carbon to remove the residual suspended matter and the organic matter is finally discharged after adjusting the pH.

Test Example : Evaluation of Ammonia Treatment Efficiency

In order to evaluate the treatment efficiency of the ammonia nitrogen according to the apparatus and the treatment method of the desulfurization wastewater according to the present invention, the apparatus for treating the desulfurized wastewater was operated after constituting the reactor as shown in FIG.

The current and voltage were 60 A / 3.60 V, the current density was 2.3 A / dm ² , and the size of the electrode was 10.0 cmL × 11.0 cmH (the size of the electrolytic cell was 3.6 L and the electrolysis time was 10.0 min) × 1.2 T, and the number of electrodes was 12 electrolytic cells in anode and continuous operation, and the analysis was carried out in total of 6 times in 10 minute increments.)

FIG. 2 is a graph showing the relationship between the MLSS (mixed liquer suspended solid) concentration of the treated water after the ammonia stripping process and the electrolysis process, the treated water after the bioreaction process, and the treated water immediately after the ammonia stripping process without the electrolysis process Respectively. As shown in FIG.

Referring to FIG. 2, immediately after the biological reaction process, the MLSS concentration instantly decreased due to the impact load, but after about 6 hours, the MLSS concentration gradually increased and gradually increased.

Also, since the concentration of contaminants after the ammonia stripping process is higher than the recommended level of the bioreactor, it can be seen that the MLSS stabilization value is relatively low due to a large initial microbial kill rate.

On the contrary, after the ammonia stripping process and the electrolytic complex process, the concentration of contaminants was relatively low, and the recovery rate of the MLSS concentration, which was instantaneously decreased due to the impact load after flowing into the bioreactor as compared with the ammonia stripping process alone, And the number is also high.

FIG. 3 is a graph showing the results of measurement of the total amount of nitrogen (TN) present in each treated water immediately after the ammonia stripping process and immediately after the electrolysis process in the method of treating the desulfurized wastewater according to an embodiment of the present invention Fig.

FIG. 4 is a graph showing the relationship between ammonia nitrogen (NH ₃ -N) and ammonia nitrogen (NH ₃ -N) present in each treated water immediately after the ammonia stripping process and immediately after the electrolysis process in the method of treating the desulfurized wastewater according to an embodiment of the present invention. And the results are shown in the graph.

Referring to FIGS. 3 and 4, it can be seen that the amount of total nitrogen (T-N) is significantly decreased after the ammonia treatment step.

Generally, the allowable total nitrogen concentration into the bioreactor is limited to about 200-250 ppm. This is because when the total nitrogen above the allowable concentration is introduced into the bioreactor, the ability to degrade microorganisms is significantly reduced.

3 and 4, it can be confirmed that the total nitrogen content in the treated water after the ammonia stripping process and the electrolysis process is 250 ppm or less. Therefore, after the ammonia stripping process and the electrolysis process, It can be confirmed that the ammonia nitrogen is remarkably decreased.

Therefore, according to the present invention, the ammonia stripping process and the electrolysis process are performed to remarkably reduce ammonia nitrogen at a high concentration in a short time to a low concentration to reduce the total nitrogen content in the desulfurization wastewater.

According to the present invention, the ammonia stripping process and the electrolysis process are performed to treat the ammonia nitrogen in a short time, thereby reducing the processing load of the bioreactor and meeting the discharged water quality standard value.

100; Flocculation tank
110; pH adjustment tank
120; Coagulation tank
130; The first settling tank
200; Ammonia stripping tank
210; The first treatment water tank
220; Ammonia stripping tower
230; Scrubber tower
300; Electrolysis tank
310; The second treatment tank
400; Bioreactor
410; Denitrification tank
420; Aeration tank
430; The second settling tank
500; Adsorption tank
600; Thickener
610; Dehydration tank

Claims (9)

A flocculant tank for removing the hard substances in the desulfurized wastewater by flocculation and sedimentation reaction of the desulfurized wastewater treated with suspended solids and heavy metals;
An ammonia stripping tank for removing a large amount of ammonia nitrogen present in the treated water through the flocculation reaction tank through an ammonia stripping process;
An electrolysis tank for removing ammonia nitrogen, which has not been treated in the treatment water passed through the ammonia stripping tank, through an electrolysis reaction;
A bioreactor for removing a residual nitrogen component present in the treated water passed through the electrolytic bath by a biological reaction; And
And a adsorption tank for removing suspended solids remaining in the treated water through the bioreactor through an adsorption reaction,
In the ammonia stripping tank,
A first treatment water tank through which the treated water passing through the flocculation tank enters, the air is poured into the treated water for 24 to 48 hours, and then NaOH is added to degas a part of the ammonia;
An ammonia stripping tower for introducing treated water passing through the first treated water tank and supplying steam and air at 40 to 60 ° C to the treated water to raise water temperature of the treated water to degas ammonia; And
And a scrubber tower for introducing deaerated ammonia from the ammonia stripping tower and converting the ammonia into an ammonium salt by introducing an acidic substance into the ammonia,
Wherein electrolysis is performed for 1 to 120 minutes at a current density of 1 to 5 A / dm ^{2 in} the electrolysis tank.
delete delete The method according to claim 1,
In the electrolytic bath,
An electrolysis tank for introducing the treated water through the ammonia stripping tank and removing the ammonia nitrogen that has not been treated in the treated water by an electrolysis reaction; And
And a tertiary treatment water tank for introducing the treated water through the electrolytic bath and neutralizing the treated water.
The method according to claim 1,
The bioreactor includes:
A denitrification tank for converting nitrate nitrogen and nitrite nitrogen existing in the treated water into nitrogen gas by removing denitrification water flowing into the electrolytic bath; And
And an aeration tank for introducing the treated water through the denitrification tank and removing the carbon source remaining in the treated water through an oxidation reaction.
(A) an ammonia stripping step of removing ammonia nitrogen present in the treated water from which the suspended solids, heavy metals and hard substances of the desulfurized wastewater are removed through ammonia stripping to remove ammonia;
(B) an electrolysis step of removing the untreated ammonia nitrogen in the treated water through the ammonia stripping step by an electrolysis reaction;
(C) a biological reaction step of removing a nitrogen component remaining in the treated water after the electrolysis step by a biological reaction; And
(D) an adsorption step of filtering the treated water having undergone the biological reaction step with activated charcoal to remove residual suspended solids,
Wherein the ammonia stripping comprises:
Air is injected into the treated water from which the suspended solids, heavy metals and hard substances of the desulfurized wastewater have been removed for 24 to 48 hours, and then NaOH is injected and partially deaerated by removing ammonia;
Supplying steam at a temperature of 40 to 60 DEG C to the treated water in which the ammonia is partially deaerated to elevate the temperature of the treated water to degas ammonia; And
Introducing an acidic substance into the deaerated ammonia, converting the deacidified ammonia to an ammonium salt,
Wherein the electrolysis step is performed at a current density of 1 to 5 A / dm < ² > at an electrode for 1 to 120 minutes.

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