CN111039361A

CN111039361A - Electrochemical water treatment device capable of removing ammoniacal nitrogen and oxidation by-products of ammoniacal nitrogen

Info

Publication number: CN111039361A
Application number: CN201811503677.1A
Authority: CN
Inventors: 洪锡垣; 崔在佑
Original assignee: Korea Advanced Institute of Science and Technology KAIST
Current assignee: Korea Advanced Institute of Science and Technology KAIST
Priority date: 2018-10-11
Filing date: 2018-12-10
Publication date: 2020-04-21
Anticipated expiration: 2038-12-10
Also published as: CN111039361B; KR102044195B1

Abstract

The present invention relates to an electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation by-products of ammoniacal nitrogen, wherein when ammoniacal nitrogen in water is removed by an electrochemical water treatment apparatus, chemical reactions ① to ⑥ such as ① electrodialysis, ② electrochemical ammonia oxidation, ③ ammonia breakpoint oxidation, ④ electrochemical ammonia degassing, ⑤ electrochemical ammonia direct oxidation, ⑥ electrochemical nitrate nitrogen and chlorate reduction are simultaneously performed in one electrochemical water treatment apparatus, and electrochemical water treatment processes are controlled so that chemical reactions ① to ⑥ complement each other, thereby not only removing ammoniacal nitrogen contained in water, but also effectively removing oxidation by-products such as nitrate nitrogen, chlorate and the like generated during oxidation of ammoniacal nitrogen.

Description

Electrochemical water treatment device capable of removing ammoniacal nitrogen and oxidation by-products of ammoniacal nitrogen

Technical Field

The present invention relates to an electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen, and more particularly, to an electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen, which is capable of effectively removing not only ammoniacal nitrogen contained in water but also oxidation byproducts such as nitrate nitrogen, chlorate and the like generated during oxidation of ammoniacal nitrogen by simultaneously performing chemical reactions ① to ⑥ such as ① electrodialysis, ② electrochemical ammonia oxidation, ③ ammonia breakpoint oxidation, ④ electrochemical ammonia degassing, ⑤ electrochemical direct ammonia oxidation, ⑥ electrochemical nitrate nitrogen and chlorate reduction in one electrochemical water treatment apparatus and controlling electrochemical water treatment processes so that the chemical reactions ① to ⑥ complement each other, when removing ammoniacal nitrogen in water using the electrochemical water treatment apparatus.

[ statement regarding national support for research and development ]

This study was conducted under the supervision of the korea institute of science and technology and was supported by the ministry of environment, under the name of top-level environmental technology development, worldwide, and under the name of electrochemical-based development of high-concentration organic substances and total nitrogen control technology (topic No. 1485015389).

Background

Effluent water treated in environmental infrastructure such as sewage and wastewater treatment plants

Is a very stable substitute water resource in the aspects of water quality and water quantity. The discharged water after the cleaning treatment can function as a dilution water of a river polluted at the midstream and upstream during the period of the dead water, can be used as a high-quality industrial water, and can be supplied to an urban river dried due to urbanization at an ecological flow rate. However, it is known that waste water containing ammonia nitrogen at a high concentration such as livestock waste water and food waste water still contains ammonia nitrogen at a concentration of several hundred mg/L or more even after a biological treatment process such as anaerobic digestion, and that a sewage treatment plant connected thereto is generally operated at a high load, which hinders the performance of a sewage advanced treatment facility. The ammoniacal nitrogen in the water is used as a guideOne of eutrophic nutritive salts of surface water will continue to increase the standard for controlling the concentration of ammoniacal nitrogen in treated water obtained by treating sewage and wastewater in the future.

Technologies for treating high-concentration ammoniacal nitrogen present in sewage and wastewater include, for example, biological high-level treatment methods, adsorption, Electrodialysis (electroanalysis), and electrooxidation (Electrochemical Oxidation). The wastewater containing ammonia nitrogen at a high concentration requires a seriously insufficient concentration of organic matters in the biological nitrification/denitrification process and inevitably consumes costs such as external carbon source injection. Further, the adsorption method of ammoniacal nitrogen represented by korean patent No. 598596 and the like has limitations that it is not suitable for large-capacity wastewater treatment, consumes high running costs in regeneration of the adsorbent, and the like. In this regard, electrodialysis in P CT patent publication WO2015-164744a1, U.S. patent publication US2016-0271562a1, and the like is a technique of producing treated water by alternately arranging ion exchange membranes through which cations such as ammonium ions and anions selectively pass, and then applying a direct current voltage to increase the speed of ion separation (desalination) by the ion exchange membranes, and thereby removing all kinds of ions. However, the water treatment method by the electrodialysis has a limitation in that the purpose of the application of the direct current power is fundamentally limited to the improvement of the ion separation capability by the generation of the electric field, during which the water splitting (oxygen and hydrogen generation) reaction occurring at the anode and the cathode cannot be applied to the water treatment.

Finally, the electrochemical high oxidation water treatment method in korean patent No. 1833833 (granted patent by the present applicant), U.S. patent publication No. US2013-0168262a1, U.S. patent No. US7160430, and the like can exert an effect of oxidizing ammonia nitrogen or reducing nitrate nitrogen in wastewater by utilizing oxidation/reduction reactions that occur after an oxidation electrode (anode) and a reduction electrode (cathode) are provided in wastewater and wastewater having high conductivity and power is supplied. However, this method has limitations that the efficiency is low when the concentration of chloride ions in the water to be treated is low, and oxidation by-products such as nitrate nitrogen and chlorate may be generated in the oxidation process of ammonia nitrogen.

Disclosure of Invention

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an electrochemical water treatment apparatus capable of removing ammonia nitrogen and oxidation byproducts of ammonia nitrogen, in which, when removing ammonia nitrogen in water using an electrochemical water treatment apparatus, chemical reactions ① to ⑥, such as ① electrodialysis, ② electrochemical ammonia oxidation, ③ ammonia breakpoint oxidation, ④ electrochemical ammonia degassing, ⑤ electrochemical ammonia direct oxidation, ⑥ electrochemical nitrate nitrogen and chlorate reduction, are simultaneously performed in one electrochemical water treatment apparatus, and the electrochemical water treatment process is controlled so that the chemical reactions ① to ⑥ complement each other, thereby not only effectively removing ammonia nitrogen contained in water, but also effectively removing oxidation byproducts such as nitrate nitrogen and chlorate generated during the oxidation of ammonia nitrogen.

An electrochemical water treatment apparatus according to the present invention for achieving the above object, which is capable of removing ammoniacal nitrogen and oxidation by-products of ammoniacal nitrogen, is an electrochemical water treatment apparatus for removing ammoniacal nitrogen contained in raw water, and is characterized by comprising an electrochemical reaction tank, a first circulation reaction tank, and a second circulation reaction tank, the electrochemical reaction tank having an anode region between an anode and an anion exchange membrane, a cathode region between a cathode and a cation exchange membrane, and providing an electrodialysis and an electrochemical reaction space for raw water; the first circulation reaction tank induces ammonia breakpoint oxidation by circulation with the anode region and induces reduction of oxidation by-products of ammoniacal nitrogen by circulation with the cathode region; the second circulation reaction tank induces electrochemical ammonia degassing by circulation with the cathode region, and induces electrochemical ammonia direct oxidation by circulation with the anode region.

The first water treatment step and the second water treatment step are performed in time series

In the first water treatment step, electrodialysis and electrochemical ammonia oxidation are performed in the electrochemical reaction tank, ammonia breakpoint oxidation is performed by circulation of the first circulation reaction tank and the anode region, and electricity is performed by circulation of the second circulation reaction tank and the cathode regionIn the second water treatment step, the oxidation by-product of ammoniacal nitrogen is reduced by circulation between the first circulation reaction tank and the cathode region, and electrochemical ammonia direct oxidation is performed by circulation between the second circulation reaction tank and the anode region.

By the electrodialysis, anions in the raw water move to the anode region and cations in the raw water move to the cathode region, and the ammonia nitrogen in the raw water is converted into monochloramine (NH) by the electrochemical ammonia oxidation₂Cl), by electrodialysis, chloride ion (Cl)^-) Monochloramine (NH) formed from chlorine radicals moving toward the anode region and increasing the ratio of chloride ions to ammoniacal nitrogen in the raw water₂Cl) is increased.

Monochloramine (NH) produced in the anodic region of an electrochemical reaction cell₂Cl) to the first recycle reaction tank, monochloramine (NH)₂Cl) is converted to nitrogen (N) by the above-mentioned ammonia breakpoint oxidation₂) And nitrate Nitrogen (NO)₃ ^-)。

NH moved by electrodialysis to the cathode region of an electrochemical cell₄ ⁺Hydroxyl ions (OH) generated by the hydrogen generation reaction are utilized in the cathode region^-) To ammonia (NH)₃) And moving the reaction mixture to a second circulation reaction tank, wherein a degasifier is provided on one side of the second circulation reaction tank, and the ammonia gas in the second circulation reaction tank is electrochemically degassed by the degasifier.

Residual NH in the second circulation reaction tank by electrochemical ammonia degassing₄ ⁺Residual NH in the second circulation reaction tank by the circulation of raw water between the anode region and the second circulation reaction tank₄ ⁺Undergoes electrochemical direct oxidation of ammonia to nitrogen (N)₂)。

Residual nitrate Nitrogen (NO) in the first circulation reaction tank through electrochemical ammonia oxidation and ammonia breakpoint oxidation₃ ^-) And chlorate (ClO)₃ ^-) Nitrate Nitrogen (NO) remaining in the first circulation reaction tank by the circulation of raw water between the cathode region and the first circulation reaction tank₃ ^-) And chlorate (ClO)₃ ^-) Are respectively reduced to nitrogen (N)₂) Chloride ion (Cl)^-)。

The electrochemical reaction tank is provided with a raw water circulation area between an anion exchange membrane and a cation exchange membrane, raw water in the raw water circulation area circulates between the raw water circulation area and the raw water circulation tank, a first circulation flow path and a first circulation pump (P1) are arranged between the raw water circulation area and the raw water circulation area, a second circulation flow path and a second circulation pump (P2) are arranged between the first circulation reaction tank and an anode area, a third circulation flow path and a third circulation pump (P3) are arranged between the second circulation flow path and a cathode area, a bypass flow path and an on-off valve are arranged between the second circulation flow path and the third circulation flow path, the first circulation reaction tank circulates with the anode area or the cathode area through the action of the on-off valve and the bypass flow path, and the second circulation reaction tank circulates with the cathode area or the anode area.

The first and second circulation reaction tanks are provided with a pH sensor for measuring the pH of the raw water on one side, the electrochemical reaction tank is provided with a DC power supply device on one side, and a control unit for measuring the rate of pH decrease (-dpH/dt) per unit time of the first circulation reaction tank and switching the raw water circulation system from the first water treatment step to the second water treatment step when the measured rate of pH decrease (-dpH/dt) per unit time exceeds a preset reference value.

The raw water circulation method of the first water treatment step is a method in which the first circulation reaction tank and the anode region are circulated and the second circulation reaction tank and the cathode region are circulated, and the raw water circulation method of the second water treatment step is a method in which the first circulation reaction tank and the cathode region are circulated and the second circulation reaction tank and the anode region are circulated.

The control unit controls the direct current power supply device to apply a power of 2.0V or more to the anode in order to promote the generation of chlorine radicals in the first water treatment step, and controls the direct current power supply device to apply a voltage of-1.4V or less NHE to the cathode in order to perform an electrochemical nitrate nitrogen and chlorate reduction reaction in the second water treatment step.

The pH drop per unit time of the raw waterLow speed (dpH/dt) is H⁺Rate of increase in concentration of the above H⁺The concentration increase rate was calculated by the following formula.

(formula (II))

H⁺The rate of increase in concentration (M/min) is log [ J/F/(V/A) x60]

(J is the current density, F is the Faraday constant, V is the sum of the anode area and the volume of R1, and A is the electrode area).

The reference value is 2.3-3.2 pH change value/min.

The electrochemical water treatment apparatus according to the present invention, which can remove ammoniacal nitrogen and oxidation by-products of ammoniacal nitrogen, has the following effects.

By simultaneously realizing chemical reactions such as electrodialysis, electrochemical ammonia oxidation, ammonia breakpoint oxidation, electrochemical ammonia degassing, electrochemical ammonia direct oxidation, electrochemical nitrate nitrogen and chlorate reduction and the like in one electrochemical water treatment device, ammonia nitrogen in water can be effectively removed, and ammonia nitrogen concentrated water and nitrate Nitrogen (NO) can be prevented₃ ^-) Chlorate (ClO)₃ ^-) And the like.

Flows into the anode chamber by electrodialysis

The ratio of chloride ion/ammonia nitrogen in the wastewater is increased, and a reference electrode is provided at the periphery of the anode to adjust the voltage applied to the anode, thereby increasing the chlorine radicals (Cl, Cl)₂ ^-Can increase the rate of electrochemical ammonia oxidation. In addition, H is formed during electrochemical ammoxidation⁺The pH is lowered, thereby obtaining the effect of reducing the generation of byproduct nitrate nitrogen in the ammonia breakpoint oxidation process.

At the same time, part of the influent water is in the anode and cathode chambers

Alternately cycling between them, thereby facilitating the electrochemical ammonia direct oxidation and nitrate nitrogen/chlorate reduction reactions. Further, the pH and the conductivity in the reaction tank are controlled by a control partThe flow path is controlled so that additional energy consumption other than the removal of ammoniacal nitrogen can be prevented.

Drawings

Fig. 1 is a block diagram of an electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation by-products of ammoniacal nitrogen according to an embodiment of the present invention.

Fig. 2 is a schematic diagram showing chemical reactions in the electrochemical water treatment apparatus for removing ammoniacal nitrogen.

Fig. 3 is a schematic diagram showing changes in the concentration of main ionic substances in the electrochemical water treatment apparatus for removing ammoniacal nitrogen.

Fig. 4 is a result of measuring a change in the removal efficiency of ammoniacal nitrogen according to the concentration of chloride ions in the anode chamber according to an embodiment of the present invention.

Fig. 5 is a result of measuring the generation rate of nitrate nitrogen according to pH in the anode chamber according to an embodiment of the present invention.

Fig. 6 is a flow chart showing a time-series flow of the first water treatment step and the second water treatment step.

Description of the symbols

11: anode 12: cathode electrode

13: anion exchange membrane 14: cation exchange membrane

15: reference electrode 21: first circulation flow path

22: second circulation flow path 23: a third circulation flow path

24: bypass flow path 24 a: opening and closing valve

31: the pH sensor 32: conductivity meter

110: electrochemical reaction tank 111: anode region

112: cathode region 113: raw water circulating area

120: first circulation reaction tank 130: second circulation reaction tank

140: raw water circulating tank

Detailed Description

The present invention shows a technique for removing ammoniacal nitrogen in water by an electrochemical water treatment apparatus. As described in the "background of the invention" above, there are many methods and mechanisms for removing ammoniacal nitrogen from water. The present invention shows an ammoniacal nitrogen removal technique based on an electrochemical water treatment device.

The ammonia removal technology according to the present invention is based on an electrochemical water treatment apparatus in which 6 chemical reaction mechanisms are realized, thereby enabling efficient removal of ammoniacal nitrogen and oxidation byproducts occurring during the oxidation of ammoniacal nitrogen. 6 chemical reaction mechanisms independently perform and simultaneously play a role of mutual complementation, and finally the removal efficiency of the ammoniacal nitrogen and the oxidation by-products is improved.

The 6 chemical reactions carried out in the electrochemical water treatment device according to the invention were ① electrodialysis (electrochemical), ② electrochemical ammonia oxidation (electrochemical ammonia chlorination), ③ break-point oxidation of ammonia (break-point chlorination of ammonia), ④ electrochemical ammonia degassing (electrochemical ammonia stripping), ⑤ electrochemical direct ammonia oxidation (electrochemical ammonia direct oxidation), ⑥ electrochemical nitrate nitrogen and chlorate reduction (electrochemical reduction of NO)₃ ^-And ClO₃ ^-(electrochemical reduction of NO₃ ^-and ClO₃ ^-))。

The ① electrodialysis and ② to ⑥ electrochemical reactions are explained in detail with reference to the structure of an electrochemical water treatment apparatus described later.

Next, an electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation by-products of ammoniacal nitrogen according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Referring to fig. 1, an electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen according to an embodiment of the present invention includes an electrochemical reaction tank 110, a first circulation reaction tank 120, a second circulation reaction tank 130, and a raw water circulation tank 140.

The electrochemical reaction tank 110 provides a space for performing electrodialysis and electrochemical reactions. The electrochemical reaction cell 110 is spatially divided into an anode region (anodic component) 111, a cathode region (cathodic component) 112, and a raw water circulation region 113. An anode 11 and a cathode 12 are respectively disposed at both ends of the electrochemical reaction tank 110, and an anion exchange membrane (anion exchange membrane)13 and a cation exchange membrane (cation exchange membrane)14 are separately disposed between the anode 11 and the cathode 12. A space between the anode 11 and the anion exchange membrane 13 corresponds to the anode region 111, a space between the cathode 12 and the cation exchange membrane 14 corresponds to the anode region 111, and a space between the anion exchange membrane 13 and the cation exchange membrane 14 corresponds to the raw water circulation region 113. The anion exchange membrane 13 selectively transmits only anions, and the cation exchange membrane 14 selectively transmits only cations.

The electrochemical reaction tank 110 includes an anion-exchange membrane 13 and a cation-exchange membrane 14, and can perform an electrodialysis step capable of separating cations and anions when a power source is applied. That is, when the electrodialysis is performed by applying power while the raw water is supplied to the electrochemical reaction tank 110, anions (for example, Cl) in the raw water^-) The cations (for example, NH) in the raw water move to the anode region 111 through the anion exchange membrane 13₄ ⁺) Moves through cation exchange membrane 14 to cathode region 112.

The electrochemical reaction tank 110 basically ① provides a space for performing electrodialysis, and at the same time provides a space for performing the electrochemical reactions ② - ⑥, i.e., ② electrochemical ammonia oxidation, ③ ammonia breakpoint oxidation, ④ electrochemical ammonia degassing, ⑤ electrochemical ammonia direct oxidation, and ⑥ electrochemical nitrate nitrogen and chlorate reduction.

In the electrochemical reactions ① to ⑥, ① electrodialysis and ② electrochemical ammonia oxidation are performed in the electrochemical reaction tank 110, and the other ③ to ⑥, that is, ③ ammonia breakpoint oxidation, ④ electrochemical ammonia degassing, ⑤ electrochemical ammonia direct oxidation, ⑥ electrochemical nitrate nitrogen and chlorate reduction are performed in a manner that the electrochemical reaction tank 110 and the first circulation reaction tank 120 are interlocked, or the electrochemical reaction tank 110 and the second circulation reaction tank 130 are interlocked.

The raw water in the anode region 111 of the electrochemical reaction tank 110 circulates between the anode region 111 and the first circulation reaction tank 120 or between the anode region 111 and the second circulation reaction tank 130, ③ -fold oxidation of ammonia is performed when the raw water circulates between the anode region 111 and the first circulation reaction tank 120, and ⑤ -electrochemical direct oxidation of ammonia is performed when the raw water circulates between the anode region 111 and the second circulation reaction tank 130.

The raw water in the cathode region 112 of the electrochemical reaction cell 110 is circulated between the cathode region 112 and the second circulation reaction cell 130 or between the cathode region 112 and the first

circulation reaction cell

120, ④ electrochemical ammonia degassing is performed when the raw water is circulated between the cathode region 112 and the second circulation reaction cell 130, and ⑥ electrochemical nitrate nitrogen and chlorate reduction is performed when the raw water is circulated between the cathode region 112 and the first circulation reaction cell 120.

In other words, the first circulation reaction tank 120 induces ③ the break point oxidation of ammonia by circulation with the anode region 111, ⑥ the electrochemical nitrate nitrogen and chlorate reduction by circulation with the cathode region 112, the second circulation reaction tank 130 induces ④ the electrochemical ammonia degassing by circulation with the

cathode region

112, and ⑤ the electrochemical ammonia direct oxidation by circulation with the anode region 111.

When the electrochemical reaction tank 110 performs electrodialysis, anions in the raw water move to the anode region 111, cations move to the cathode region 112, and raw water with reduced ionic substances exists in the raw water circulation region 113, the quality of raw water circulating between the raw water circulation region 113 of the electrochemical reaction tank 110 and the raw water circulation tank 140 is improved by repeating the electrochemical reactions ② to ⑥ including the electrodialysis as described above.

The mechanisms of the reactions ① to ⑥, namely, ① electrodialysis, ② electrochemical ammonia oxidation, ③ ammonia breakpoint oxidation, ④ electrochemical ammonia degassing, ⑤ electrochemical ammonia direct oxidation, and ⑥ electrochemical nitrate nitrogen and chlorate reduction, performed by the electrochemical reaction tank 110, the first circulating reaction tank 120, and the second circulating reaction tank 130 are described below.

① electrodialysis was carried out in the following manner.

When a direct current power supply is applied to the anode 11 and the cathode 12 of the electrochemical reaction cell 110 in a state where raw water containing ammoniacal nitrogen is supplied to the electrochemical reaction cell 110, anions (for example, Cl) in the raw water^-) The cations (for example, NH) in the raw water move to the anode region 111 through the anion exchange membrane 13₄ ⁺) Moves through cation exchange membrane 14 to cathode region 112. By the electrodialysis as described above, raw water with a reduced concentration of ammoniacal nitrogen is present in the raw water circulation zone 113 of the electrochemical reaction tank 110.

② electrochemical ammonia oxidation was carried out in the following manner.

An electrochemical reaction of ② - ⑥ comprising electrochemical ammonia oxidation is carried out together with electrodialysis.

When power is applied to the electrochemical reaction cell 110, chloride ions (2 Cl)^-) Chlorine radicals (Cl, Cl) are formed on the surface of the anode 11₂ ^-Cne) (see formula 1), which is reacted again with NH in water₃React to form monochloramine (NH)₂Cl) (see formula 2). At this time, chloride ions (Cl) having negative charges are generated by electrodialysis^-) Moving to the anode region 111, the ratio of chloride ion/ammonia nitrogen in the raw water flowing to the anode region 111 increases, and the reaction rates of formula 1 and formula 2 increase. That is, as electrodialysis is combined with electrochemical ammonia oxidation, the efficiency of removing ammoniacal nitrogen is improved. In addition, on the surface of the anode 11, chlorine ions are oxidized into free chlorine (Cl)₂HOCl) (see formula 3), and NH may be similarly formed₂Cl (see formula 4), which is known to have a lower velocity than formula 1 and formula 2. Therefore, it is preferable to induce the reactions of formulae 1 and 2 rather than the reactions of formulae 3 and 4, which can be achieved by adjusting the voltage applied to the anode 11, which will be described later.

On the other hand, on the surface of the anode 11, in addition to the oxidation of chlorine ions,oxygen (O) is generated by oxidation of water molecules₂) And H⁺And thus the pH decreases (refer to formula 5). In addition, chlorate (ClO) may be formed on the surface of the anode 11 by further oxidation of free chlorine₃ ^-) (equation 6), this is removed by the ⑥ electrochemical nitrate nitrogen and chlorate reduction mechanism described later.

(formula 2)2 Cl. cndot. + NH₃→NH₂Cl+H⁺+Cl^-

(formula 4) HOCl + NH₃→NH₂Cl+H₂O

(formula 5) H₂O→1/2O₂+2H⁺+2e^-

(formula 6) HOCl +2H₂O→ClO₃ ^-+5H⁺+4e^-

③ the ammonia breakpoint oxidation proceeds as follows.

The ammonia breakpoint oxidation is performed during the circulation of the raw water in the anode region 111 of the electrochemical reaction tank 110 between the anode region 111 and the first circulation reaction tank 120.

NH generated in the anode region 111 of the electrochemical reaction cell 110₂The Cl moves to the first circulation reaction tank 120. By NH₂Reaction between Cl and residual free chlorine to form dichloramine (NHCl)₂) (see formula 7), which is again reacted with NH₂Cl reacts to form nitrogen (N)₂) (see equation 8), the removal of ammoniacal nitrogen in water is finally achieved. At the same time, NH₂Part of the Cl is oxidized to nitrate Nitrogen (NO)₃ ^-) (see formula 9), in the water total nitrogen removal, preferably reduce the reaction rate. In this respect, H formed during the course of the electrochemical ammoxidation can be obtained in the present invention⁺Decreasing pH and increasing NHCl₂Thereby further reducing the effect of the formation of nitrate nitrogen. In addition, residual free chlorine is consumed by formula 7, so that it is possible to prevent a phenomenon in which the anion exchange membrane is damaged by the free chlorine during the circulation to the anode region 111.

(formula 8) NH₂Cl+NHCl₂→N₂+3H⁺+3Cl^-

(formula 9) NH₂Cl+3HOCl→NO₃ ^-+4Cl^-+5H⁺

④ electrochemical ammonia degassing is performed in the following manner.

Electrochemical ammonia degassing is performed during the circulation of the raw water in the cathode region 112 of the electrochemical reaction tank 110 between the anode region 111 and the second circulation reaction tank 130. A degasifier such as a blower (blower) capable of degassing ammonia gas in water is provided on one side of the second circulation reaction tank 130.

Hydroxyl ions (OH) generated by the hydrogen generation reaction (see formula 10) on the surface of the cathode 12^-) NH moving to the cathode region 112 during electrodialysis₄ ⁺To ammonia (NH)₃) (see formula 11). The raw water circulates between the cathode region 112 and the second circulation reaction tank 130, and ammonia gas (NH) in the second circulation reaction tank 130 can be degassed by a degasser provided on one side of the second circulation reaction tank 130₃) Degassing is carried out. In this case, the increase in temperature due to the resistance around the cathode 12 during the electrodialysis has a positive influence on the degassing of ammonia. However, the ammonia degassing efficiency is slower than the aforementioned ammonia breakpoint oxidation, and complete removal of ammoniacal nitrogen in water cannot be achieved.

(formula 10)2H₂O+2e^-→H₂+2OH^-

(formula 11) NH₄ ⁺+OH^-→NH₃+H₂O

⑤ electrochemical direct ammonia oxidation proceeds as follows.

The electrochemical ammonia direct oxidation is performed during the circulation of the raw water in the anode region 111 of the electrochemical reaction tank 110 between the anode region 111 and the second circulation reaction tank 130.

NH remains in the second circulation reaction tank 130 due to the electrochemical ammonia degassing₄ ⁺NH remaining in the second circulation reaction tank 130 due to the circulation of raw water between the anode region 111 and the second circulation reaction tank 130₄ ⁺As shown in formula 12, is directly oxidized to nitrogen (N)₂). At this time, Cl^-Is relatively low in concentration, OH^-Since the concentration (pH) of (a) is increased by formula 10, formula 12 can be efficiently generated as compared with the competing reactions of formula 1, formula 3, formula 5, and the like.

(formula 12) NH₃+3OH^-→1/2N₂+3H₂O+3e^-

⑥ electrochemical nitrate nitrogen and chlorate reduction proceeds as follows.

Electrochemical nitrate nitrogen and chlorate reduction is performed during circulation of raw water in the cathode region 112 of the electrochemical reaction tank 110 between the cathode region 112 and the first circulation reaction tank 120.

Nitrate Nitrogen (NO) remains in the first circulation reaction tank 120 by the mechanisms of the ② electrochemical ammonia oxidation and ③ ammonia breakpoint oxidation described above₃ ^-) And chlorate (ClO)₃ ^-)，

Nitrate Nitrogen (NO) remaining in the first circulation reaction tank 120 by the circulation of raw water between the cathode region 112 and the first circulation reaction tank 120₃ ^-) And chlorate (ClO)₃ ^-) Reduced to nitrogen (N) as shown in

formulas

13 and 14, respectively₂) Chloride ion (Cl)^-). In this case, the following formula 5, H⁺Is relatively high, and thus

formulas

13 and 14 can effectively occur compared to the competitive reaction of formula 10.

(formula 13) NO₃ ^-+6H⁺+5e^-→1/2N₂+3H₂O

(formula 14) ClO₃ ^-+6H⁺+6e^-→Cl^-+3H₂O

The electrochemical reactions ① to ⑥ performed in the electrochemical reaction tank 110, the first circulation reaction tank 120, and the second circulation reaction tank 130 have been described above.

On the other hand, in the present invention, the electrochemical reactions of ① to ⑥ can be differentiated in time series, and the removal of ammonia nitrogen in water by ① to ④, and the subsequent removal of residual ammonia nitrogen by ⑤ to ⑥, and the removal of nitrate Nitrogen (NO) which is an oxidation by-product of ammonia Nitrogen (NO) can be achieved₃ ^-) And chlorate (ClO)₃ ^-) Therefore, the reaction from ① to ④ is referred to as a first water treatment step (phase 1), and the reaction from ⑤ to ⑥ is referred to as a second water treatment step (phase 2).

The first water treatment step (i.e., reactions from ① to ④) and the second water treatment step (i.e., reactions from ⑤ to ⑥) which are separated in time series are also separated in a raw water circulation manner, where the raw water circulation manner refers to a circulation manner between the cathode region 112 and the anode region 111 of the electrochemical reaction tank 110 and the first and second

circulation reaction tanks

120 and 130. in the first water treatment step, the anode region 111 circulates through the first circulation reaction tank 120 and the cathode region 112 circulates through the second circulation reaction tank 130, and in the second water treatment step, the circulation manner is changed such that the anode region 111 circulates through the second circulation reaction tank 130 and the cathode region 112 circulates through the first circulation reaction tank 120.

The time of distinguishing the first water treatment step (phase 1) from the second water treatment step (phase 2), i.e., the time at which the first water treatment step ends, is determined according to the degree of removal of the ammoniacal nitrogen. As described above, the ammonia nitrogen contained in the raw water is removed by the first water treatment step, and the ammonia nitrogen remaining in the raw water and the nitrate Nitrogen (NO) which is an oxidation by-product of the ammonia nitrogen are removed by the second water treatment step₃ ^-) And chlorate (ClO)₃ ^-) The process (2).

From this viewpoint, when the pH lowering rate in the first circulation reaction tank 120 exceeds a preset reference value, it is determined that the ammonia nitrogen in the first circulation reaction tank 120 is almost completely removed, and the process can be switched to the second water treatment step.

The rate of pH decrease per unit time (-dpH/dt) is referred to as H⁺Rate of increase of concentration, H⁺The concentration increase rate was calculated by the following formula 15. H according to formula 15⁺The concentration increase rate is a function of current density (J), electrode area (A) and volume (V), and the current density (J) is set to 20-40 mA/cm in consideration of electrochemical oxidation reaction²Considering the treatment capacity of the electrochemical reaction tank 110, the volume of water discharged (V/A) relative to the electrode area is set to 5-20 cm³/cm². The pH decrease rate (dpH/dt) per unit time is set to a reference value of 2.3 to 3.2pH change/min, but in consideration of the fact that the pH increase rate is decreased due to the buffering capacity of water, the pH increase rate may be set to a reference value of 2.0 to 2.5pH change/min, and more preferably, the pH increase rate may be set to 2.5pH change/min.

(formula 15) H⁺The rate of increase in concentration (M/min) is log [ J/F/(V/A) x60]

(J is the current density, F is the Faraday constant, V is the sum of the volumes of anode region 111 and R1, and A is the electrode area).

A method of removing ammoniacal nitrogen and oxidation byproducts according to an embodiment of the present invention in which the first water treatment step (phase 1) and the second water treatment step (phase 2) are performed in time series will be described in more detail as follows (refer to fig. 2 and 6).

The first water treatment step (phase 1) was carried out in the following manner.

In the first water treatment step, electrochemical reactions from ① to ④, namely, ① electrodialysis, ② electrochemical ammonia oxidation, ③ ammonia breakpoint oxidation, and ④ electrochemical ammonia degassing, are performed.

To this end, raw water containing ammoniacal nitrogen is supplied to the raw water circulation tank 140, the first circulation reaction tank 120 and the second circulation reaction tank 130 (S601). in this state, when power is applied to the

electrochemical reaction tank

110, ① electrodialysis and ② electrochemical ammonia oxidation are performed in the electrochemical reaction tank 110, ③ break point oxidation is performed in the first

circulation reaction tank

120, and ④ electrochemical ammonia degassing is performed in the second circulation reaction tank 130. at this time, the raw water in the first circulation reaction tank 120 circulates with the anode region 111 of the electrochemical reaction tank 110, and the raw water in the second circulation reaction tank 130 circulates with the cathode region 112 of the electrochemical reaction tank 110 (S602).

In the course of performing the first water treatment step, NH is formed by

formulas

1, 2 and 3, 4 while the raw water of the first circulation reaction tank 120 passes through the anode region 111₂Cl, nitrogen gas and nitrate nitrogen are generated by formulas 7 to 9 during circulation to the first circulation reaction tank 120. At this time, the increase in chloride ions by electrodialysis is in competition with the decrease in chloride ions by the electrochemical reactions of formulas 1 and 3. In addition, chlorate may be formed by further oxidation of free chlorine. Finally, as shown in fig. 3, in the first water treatment step, the concentration of ammoniacal nitrogen in the first circulation reaction tank 120 is continuously decreased, the concentration of chloride ions is appropriately increased by electrodialysis, and is decreased by the electrochemical reactions of formulas 1 and 3, and the concentration of nitrate nitrogen and the concentration of chlorate are continuously increased. Here, the timing at which the concentration of the chlorate salt starts to increase is similar to the timing at which the concentration of the chloride ion starts to decrease.

The removal efficiency of ammoniacal nitrogen is doubled by performing electrodialysis simultaneously with electrochemical ammonia oxidation in the first water treatment step, which is confirmed by experimental results. FIG. 4 is a graph illustrating the presence of 20mM NH₄ ⁺And 50, 100, 150mM Cl respectively^-A graph comparing the change in the concentration of ammoniacal nitrogen in the electrochemical ammonia oxidation process. At this time, the anode 11 uses Ti coated with Pt, the cathode 12 uses Ti, and the volume of the subject water with respect to the electrode area is 1: 10cm²/cm³The current density was 300A/m². Referring to fig. 4, it can be confirmed that the higher the concentration of chloride ions in water, the higher the decomposition rate of ammoniacal nitrogen. Namely, by electrodialysis, chloride ions (Cl) having negative charges^-) Moves to the anode region 111 and increases the reaction rate.

On the other hand, in the above-mentioned anodeNH generated during cycling of region 111₂Cl forms nitrogen (N) by the aforementioned ammonia breakpoint oxidation₂) (see the expressions 7 and 8), the ammoniacal nitrogen in the water is finally removed, and at the same time, nitrate Nitrogen (NO) can be generated by the expression 9₃ ^-). FIG. 5 is a graph illustrating the presence of 20mM NH₄ ⁺And 100mM Cl respectively^-The target water of (1) is compared with the concentration change of nitrate nitrogen in the electrochemical ammonia oxidation process at pH4, 7, or 10. At this time, the anode 11 uses Ti coated with Pt, the cathode 12 uses Ti, and the volume of the subject water with respect to the electrode area is 1: 10cm²/cm³The current density used was 200A/m². Referring to FIG. 5, it was confirmed that the higher the pH of the water, the faster the nitrate nitrogen was produced. That is, it was confirmed that the following effects can be obtained: h formed during electrochemical ammoxidation⁺Lowering the pH to make NHCl₂It further reduces the production of nitrate nitrogen.

Formation of NH in a first Water treatment step by means of the

formulae

1, 2 and 3, 4₂In the course of Cl, the chlorine radicals (Cl, Cl) of the formulae 1, 2 are involved₂ ^-Of) with free chlorine (Cl) of formulae 3 and 4₂HOCl) is more reactive than HOCl). Therefore, it is necessary to induce chlorine radicals (Cl, Cl)₂ ^-Formation of the chlorine radical (Cl, Cl)₂ ^-Can be controlled by regulation of the voltage applied to the anode 11. Specifically, chlorine-based radical (Cl)₂ ^-Whether Cl is generated or not depends on whether or not the voltage applied to the anode 11 satisfies the chlorine-based radical (Cl)₂ ^-Cl.) standard redox potential.

[ TABLE 1 ]

< Standard Oxidation-reduction potential of chlorine-based oxidizing agent >

Chlorine-based oxidizing agent	Standard redox potential(E⁰,V NHE)
		ClO^-/Cl^-	0.81
Cl₂/Cl^-	1.36
		HOCl/Cl^-	1.48
Cl₂ ^-·/Cl^-	2.0
		Cl·/Cl^-	2.4

Referring to Table 1, hypochlorous acid (HOCl) had a standard redox potential of 1.48V NHE (normal hydrogen electrode) and a free radical dichloride ion (Cl)₂ ^-2.0V NHE, the standard redox potential of the chlorine radical (Cl.) is 2.4V NHE, a power source of 2.4V or more is required to be applied to the anode 11 in order to generate the chlorine radical (Cl.) as the strongest oxidizing agent, and a chlorine radical ion (Cl.) is generated₂ ^-·.) a power source of 2.0V or more needs to be applied to the anode 11. On the other hand, the power applied to the anode 11 and the cathode 12 is supplied by the dc power supply device as described above, and is applied to the anode 11 and the cathode 12 connected in parallel with a uniform voltage by the dc power supply device. That is, it is necessary to supply a voltage of 2.4V or more to the anode 11 and the cathode 12, respectively, and in consideration of a voltage loss, it is necessary to apply a cell voltage (cell voltage ═ anode 11 voltage (+)]+ [ cathode 12 Voltage (-)]+ loss of voltage).

Continuous confirmation of chlorine-based radical (Cl)₂ ^-Standard of. Cl.)Whether or not a voltage equal to or higher than the oxidation-reduction potential, i.e., a voltage equal to or higher than 2.0V, is applied to the anode 11, and therefore, a reference electrode 15 for measuring the voltage actually applied to the anode 11 is provided on one side of the anode 11. The voltage of the anode 11 measured by the reference electrode 15 is transmitted to a control unit described later, and the control unit checks whether or not the measured voltage of the anode 11 is 2.0V or more, and controls the dc power supply device to supply a voltage of 2.0V or more to the anode 11 when the measured voltage of the anode 11 is less than 2.0V.

On the other hand, the raw water of the second circulation reaction tank 130 is subjected to the electrochemical ammonia degassing process in the first water treatment step. Specifically, the hydroxide ion (OH) generated by formula 10^-) NH that will migrate to the cathode region 112 during electrodialysis₄ ⁺To ammonia (NH)₃) (see formula 11). The ammonia nitrogen in the water can be removed finally by degassing the ammonia gas dissolved in the water by a degassing device, such as a blower (blower), provided in the second circulation reaction tank 130. As a result, as shown in fig. 3, the ammonia nitrogen concentration in the second circulation reaction tank 130 initially increases by electrodialysis and then decreases by electrochemical ammonia degassing. The pH is increased by the reaction of formula 10 and then its increase is inactivated by the buffering capacity of ammoniacal nitrogen (formula 11). It is predicted that complete removal of ammoniacal nitrogen of the second circulation reaction tank 130 cannot be achieved in the first water treatment step and residual ammoniacal nitrogen can be completely removed by the second water treatment step.

The first water treatment step is explained above. When the first water treatment step is finished, the second water treatment step is performed, and the finishing time of the first water treatment step is judged by whether the pH decrease rate (-dpH/dt) per unit time exceeds a preset reference value (S603). As described above, the pH decreasing rate (-dpH/dt) in the first circulation reaction tank 120 is accelerated when the concentration of the ammonia nitrogen decreases, and when the pH decreasing rate in the first circulation reaction tank 120 exceeds a preset reference value, it is determined that the ammonia nitrogen in the first circulation reaction tank 120 is almost completely removed, and the process shifts to the second water treatment step.

The second water treatment step (phase 2) was carried out in the following manner.

⑤ electrochemical ammonia in the second water treatment stepDirect oxidation, ⑥ electrochemical nitrate nitrogen and chlorate reduction, by which residual ammoniacal nitrogen in the second circulating reaction tank 130 is removed while nitrate Nitrogen (NO), which is an oxidation by-product of ammoniacal nitrogen present in the first circulating reaction tank 120, is removed₃ ^-) And chlorate (ClO)₃ ^-) Is removed.

In the second water treatment step, ⑥ electrochemical nitrate nitrogen and chlorate reduction is performed in the first

circulation reaction tank

120, and ⑤ electrochemical ammonia direct oxidation is performed in the second circulation reaction tank 130. at this time, the raw water in the first circulation reaction tank 120 circulates with the cathode region 112 of the electrochemical reaction tank 110, and the raw water in the second circulation reaction tank 130 circulates with the anode region 111 of the electrochemical reaction tank 110 (S604).

The ⑥ electrochemical nitrate nitrogen and chlorate reduction of the first recycle reaction tank 120 proceeds as follows.

NO present in the first circulation reaction tank 120₃ ^-And ClO₃ ^-During circulation in the cathode region 112 of the electrochemical reaction cell 110, an electrochemical nitrate nitrogen and chlorate reduction reaction occurs by the catalytic action of the Ni, Cu, and Ti components on the surface of the cathode 12 (see formulas 13 and 14). The reduced pH in the first water treatment step facilitates the efficient occurrence of

formulas

13 and 14. At this time, it is known that the voltage of the cathode 12 for generating formula 13 is-1.0V NHE, and the voltage of the cathode 12 for generating formula 14 is-1.4V NHE. Therefore, in the present invention, Reference electrode 15(Reference electrode) is provided at the side of the periphery of cathode 12 to adjust the voltage applied to cathode 12, thereby creating an environment in which equations 13 and 14 can occur. The control unit checks whether the measured voltage of the cathode 12 is-1.4V NHE or less, and controls the DC power supply device so that the voltage of-1.4V NHE or less is supplied to the cathode 12 when the absolute value of the measured voltage of the cathode 12 is less than 1.4V NHE. As a result, in the second water treatment step, the ammonia nitrogen concentration of the first circulation reaction tank 120 is partially increased by the electrodialysis, the concentrations of the nitrate nitrogen and the chlorate ions are completely decreased, and the concentration of the chloride ions is partially increased in the process. Further, the pH can be restored to a neutral region where it can be discharged by rising again by the formula 10.

On the other hand, NH remaining in the second circulation reaction tank 130₄ ⁺While circulating in the anode region 111, an electrochemical ammonia direct oxidation reaction occurs by the catalytic action of the Pt component on the surface of the anode 11 (see formula 12). At this time, Cl^-By the reaction of formula 10, OH^-Is high, formula 12 can occur efficiently compared to competing reactions of

formulae

1, 3, 5, etc. As a result, in the second water treatment step, the ammonia nitrogen concentration of the second circulation reaction tank 130 is completely reduced, and the concentration of chloride ions is raised by the electrodialysis section. In addition, the pH can be restored to a neutral region where it can be discharged by decreasing again by formula 5. As described above, it can be confirmed whether the concentration of the ammoniacal nitrogen remaining in the second circulation reaction tank 130 is almost completely reduced by the tendency of pH change, and when the rate of pH decrease (-dpH/dt) per unit time exceeds a reference value (for example, 2.5pH change/min), it can be interpreted that the ammoniacal nitrogen in the second circulation reaction tank 130 is almost completely removed (S605).

The first water treatment step and the second water treatment step are explained above.

The raw water that completes the second water treatment step may be discharged to the water system by removing ammonia nitrogen and nitrate nitrogen, chlorate that is an oxidation by-product of the ammonia nitrogen by the first water treatment step and the second water treatment step. It is judged whether or not the raw water having completed the second water treatment step can be discharged, and it can also be judged by measuring the conductivity of the raw water. The raw water circulation tank 140 is provided with a conductivity meter, thereby indirectly measuring NH in the raw water₄ ⁺And Cl^-The concentration of (c). As an example, when it is determined that the conductivity of the raw water is less than a certain level (generally, 0.2mS/cm or less) (S606), it is determined that the concentration of ammoniacal nitrogen in the raw water circulation tank 140 becomes a dischargeable level, and the water treatment method according to the present invention may be ended (S607).

The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation by-products of ammoniacal nitrogen according to an embodiment of the present invention has been described above. In the above-described embodiments, the following detailed constitution may be defined.

In the case of forming the electrochemical reaction cell 110, the anode 11 and the cathode 12 may be formed in a flat plate or a mesh form. In the case of the anode 11, a material that can simultaneously realize electrodialysis, electrochemical ammonia oxidation, and electrochemical ammonia direct oxidation is preferably selected, and specifically, a material that can promote the Pt particles of formulas 1, 3, and 12 is preferably used, and the Pt particles can be coated on a conductive support such as Ti by a method such as Electrodeposition (electro-deposition), Dip-coating (Dip-coating), Chemical vapor deposition (Chemical vapor deposition), or Sputtering (Sputtering).

In the case of the cathode 12, it is preferable to select a material that can simultaneously realize electrochemical ammonia degassing and electrochemical nitrate nitrogen and chlorate reduction, and in this respect, it is preferable to coat the Ti support with an alloy of Cu and Ni. It is known that an alloy of Cu and Ni is electrochemically effective in reducing nitrate nitrogen in the range of 70 to 95% of Cu content, and Ti, which is a conductive metal, is electrochemically capable of reducing chlorate.

In addition, the reference electrode 15 may be a commonly used silver chloride (Ag/AgCl) electrode or mercury (Hg/Hg) electrode₂SO₄) Electrode, copper (Cu/CuSO)₄) Electrodes, Pt electrodes, etc. Meanwhile, as the cation-exchange membrane 14 and the anion-exchange membrane 13, a commonly used ion-exchange resin such as a Styrene divinyl-benzene (Styrene divinyl-benzene) based ion-exchange resin can be used. For reference, fig. 1 shows an example in which one cation exchange membrane 14 and one anion exchange membrane 13 are provided, respectively, but a plurality of exchange membranes may be alternately arranged.

In order to control the raw water circulation system, the first circulation flow path 21 and the first circulation pump P1 are provided between the raw water circulation tank 140 and the raw water circulation region 113 of the electrochemical reaction tank 110, the second circulation flow path 22 and the second circulation pump P2 are provided between the first circulation reaction tank 120 and the anode region 111, and the third circulation flow path 23 and the third circulation pump P3 are provided between the second circulation reaction tank 130 and the cathode region 112. Further, a bypass flow path 24 and an opening/closing valve 24a are provided between the second circulation flow path and the third circulation flow path 23. The first circulation reaction chamber 120 can circulate through the anode region 111 or the cathode region 112, and the second circulation reaction chamber 130 can circulate through the cathode region 112 or the anode region 111 by the operation of the opening/closing valve 24a and the bypass flow path 24.

One side of the first and second

circulation reaction tanks

120 and 130 may be provided with a pH sensor (pH meter)31 for measuring the pH of the raw water, and one side of the raw water circulation tank 140 may be provided with a conductivity meter (conductivity meter)32 for measuring the conductivity of the raw water.

The electrochemical reaction cell 110 includes a dc power supply device for applying power to the anode 11 and the cathode 12, and a control unit (not shown). The control unit controls the raw water circulation system and the DC power supply device.

Specifically, the controller measures the rate of pH decrease (-dpH/dt) per unit time in the first circulation reaction tank 120, and switches the raw water circulation system from the first water treatment step to the second water treatment step when the measured rate of pH decrease (-dpH/dt) per unit time exceeds a predetermined reference value. The raw water circulation system of the first water treatment step is a system in which the first circulation reaction tank 120 circulates the anode region 111 and the second circulation reaction tank 130 circulates the cathode region 112, and the raw water circulation system of the second water treatment step is a system in which the first circulation reaction tank 120 circulates the cathode region 112 and the second circulation reaction tank 130 circulates the anode region 111. In the second water treatment step, the first circulation reaction tank 120 is connected to the cathode region 112 via the bypass channel 24, and the second circulation reaction tank 130 is connected to the anode region 111 via the bypass channel 24, and the control unit controls the operation of the on-off valve 24 a.

The control unit controls the voltage applied to the anode 11 in the first water treatment step and the voltage applied to the anode 11 and the cathode 12 in the second water treatment step. In the first water treatment step, the dc power supply device is controlled so as to apply a power supply of 2.0V or more to the anode 11 in order to promote the generation of chlorine radicals, and in the second water treatment step, the dc power supply device is controlled so as to apply a voltage of-1.4V or less NHE to the cathode 12 in order to perform the electrochemical nitrate nitrogen and chlorate reduction reaction.

Claims

1. An electrochemical water treatment device capable of removing ammoniacal nitrogen and oxidation by-products of ammoniacal nitrogen, which is an electrochemical water treatment device for removing ammoniacal nitrogen contained in raw water, and is characterized by comprising an electrochemical reaction tank, a first circulating reaction tank and a second circulating reaction tank,

the electrochemical reaction tank has an anode region between an anode and an anion exchange membrane, a cathode region between a cathode and a cation exchange membrane, and provides an electrodialysis and an electrochemical reaction space for raw water;

the first circulation reaction tank induces ammonia breakpoint oxidation through circulation with the anode region, and induces reduction of oxidation by-products of ammoniacal nitrogen through circulation with the cathode region;

the second loop reactor induces electrochemical ammonia degassing by circulation with the cathode region and induces electrochemical ammonia direct oxidation by circulation with the anode region.

2. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and the oxidation by-products of ammoniacal nitrogen as claimed in claim 1,

the first water treatment step and the second water treatment step are performed in time series,

in the first water treatment step, electrodialysis and electrochemical ammonia oxidation are performed in the electrochemical reaction tank, ammonia breakpoint oxidation is performed by circulation between the first circulation reaction tank and the anode region, electrochemical ammonia degassing is performed by circulation between the second circulation reaction tank and the cathode region,

in the second water treatment step, the reduction of the oxidation by-product of ammoniacal nitrogen is performed by the circulation between the first circulating reaction tank and the cathode region, and the electrochemical direct oxidation of ammonia is performed by the circulation between the second circulating reaction tank and the anode region.

3. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and the oxidation by-products of ammoniacal nitrogen as claimed in claim 1 or 2,

by the electrodialysis, anions in the raw water move to the anode region and cations in the raw water move to the cathode region,

by the electrochemical ammonia oxidation, ammoniacal nitrogen in the raw water is changed into monochloramine, that is, NH₂Cl，

By electrodialysis, chloride ions, i.e. Cl^-Moving to the anode region, the raw water has an increased ratio of chloride ions to ammoniacal nitrogen, and monochloramine, NH, is formed from the chlorine radicals₂The efficiency of Cl generation increases.

4. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and the oxidation by-products of ammoniacal nitrogen as claimed in claim 1 or 2,

monochloramine, or NH, formed in the anode region of an electrochemical reaction cell₂The Cl moves to the first circulation reaction tank,

monochloramine or NH₂Cl is converted to nitrogen, N, by the ammonia breakpoint oxidation₂And nitrate nitrogen, i.e. NO₃ ^-。

5. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and the oxidation by-products of ammoniacal nitrogen as claimed in claim 1 or 2,

NH moved by electrodialysis to the cathode region of an electrochemical cell₄ ⁺OH, which is a hydroxyl ion generated by a hydrogen generation reaction, is used in the cathode region^-To ammonia gas, i.e. NH₃And moves to the second circulation reaction tank,

a degasifier is provided on one side of the second circulation reaction tank, and the ammonia gas in the second circulation reaction tank is electrochemically degassed by the degasifier.

6. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and the oxidation by-products of ammoniacal nitrogen as claimed in claim 1 or 2,

residual NH in the second circulation reaction tank by electrochemical ammonia degassing₄ ⁺，

Residual NH in the second circulation reaction tank by the raw water circulation between the anode region and the second circulation reaction tank₄ ⁺Is electrochemically directly oxidized with ammonia to nitrogen (N)₂。

7. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and the oxidation by-products of ammoniacal nitrogen as claimed in claim 1 or 2,

residual nitrate Nitrogen (NO) in the first circulation reaction tank through electrochemical ammonia oxidation and ammonia breakpoint oxidation₃ ^-And chlorates, i.e. ClO₃ ^-，

By the circulation of raw water between the cathode region and the first circulation reaction tank, nitrate Nitrogen (NO) remaining in the first circulation reaction tank₃ ^-And chlorates, i.e. ClO₃ ^-Are respectively reduced to nitrogen, i.e. N₂Chloride ion, i.e. Cl^-。

8. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and the oxidation by-products of ammoniacal nitrogen as claimed in claim 1,

the electrochemical reaction tank is provided with a raw water circulating area between an anion exchange membrane and a cation exchange membrane, raw water in the raw water circulating area circulates between the raw water circulating area and the raw water circulating tank,

a first circulation flow path and a first circulation pump (P1) are provided between the raw water circulation tank and the raw water circulation region, a second circulation flow path and a second circulation pump (P2) are provided between the first circulation reaction tank and the anode region, a third circulation flow path and a third circulation pump (P3) are provided between the second circulation reaction tank and the cathode region,

a bypass flow path and an on-off valve are provided between the second circulation flow path and the third circulation flow path, and the first circulation reaction tank circulates through the anode region or the cathode region and the second circulation reaction tank circulates through the cathode region or the anode region by operation of the on-off valve and the bypass flow path.

9. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and the oxidation by-products of ammoniacal nitrogen as claimed in claim 2,

one side of the first circulating reaction tank and one side of the second circulating reaction tank are provided with pH sensors for measuring the pH of raw water,

one side of the electrochemical reaction tank is also provided with a direct current power supply device and a control part,

the control unit measures a pH decrease rate per unit time, i.e., -dpH/dt, of the first circulation reaction tank, and switches the raw water circulation system from the first water treatment step to the second water treatment step when the measured pH decrease rate per unit time, i.e., -dpH/dt, exceeds a preset reference value.

10. The electrochemical water treatment apparatus according to claim 9, wherein the first water treatment step is a mode in which the first circulation reaction tank and the anode region are circulated and the second circulation reaction tank and the cathode region are circulated, and the second water treatment step is a mode in which the first circulation reaction tank and the cathode region are circulated and the second circulation reaction tank and the anode region are circulated.

11. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen as claimed in claim 9, wherein said control unit controls the direct current power supply device so as to apply a power of 2.0V or more to the anode in order to promote the generation of chlorine radicals in the first water treatment step.

12. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen as claimed in claim 9, wherein said control unit controls the direct current power supply apparatus so as to apply a voltage of-1.4V NHE or less to the cathode for the electrochemical nitrate nitrogen and chlorate reduction reaction in the second water treatment step.

13. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and an oxidation by-product of ammoniacal nitrogen as claimed in claim 9, wherein the raw water has a rate of pH decrease per unit time that isdpH/dt is H⁺Rate of increase in concentration of said H⁺The rate of increase in concentration is calculated by the following formula,

formula (II)

H⁺The rate of increase in concentration (M/min) is log [ J/F/(V/A) x60]

J is the current density, F is the Faraday constant, V is the sum of the anode area and the volume of R1, and A is the electrode area.

14. The electrochemical water treatment device capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen as claimed in claim 9, wherein said reference value is 2.3-3.2 pH change value/min.