CN111039361B - Electrochemical water treatment device capable of removing ammonia nitrogen and ammonia nitrogen oxidation by-products - Google Patents

Abstract

The invention relates to an electrochemical water treatment device capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen, wherein when the ammoniacal nitrogen in water is removed based on the electrochemical water treatment device, chemical reactions from (I) to (II) such as electrodialysis, electrochemical ammoxidation, ammoniacal breakpoint oxidation, electrochemical ammonia degassing, electrochemical direct ammonia oxidation, electrochemical nitrate nitrogen and chlorate reduction and the like are simultaneously realized in one electrochemical water treatment device, and the electrochemical water treatment process is controlled in a manner of mutually complementing the chemical reactions from (I) to (II), so that the ammoniacal nitrogen contained in water can be removed, and oxidation byproducts such as nitrate nitrogen, chlorate and the like generated in the oxidation process of the ammoniacal nitrogen can be effectively removed.

Description

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

technical field

The invention relates to an electrochemical water treatment device capable of removing ammonia nitrogen and oxidation by-products of ammonia nitrogen, more particularly, to an electrochemical water treatment device capable of removing ammonia nitrogen and oxidation by-products of ammonia nitrogen The treatment device, when removing ammonia nitrogen in water based on an electrochemical water treatment device, simultaneously realizes ① electrodialysis, ② electrochemical ammonia oxidation, ③ ammonia breakpoint oxidation, and ④ electrochemical ammonia degassing in one electrochemical water treatment device , ⑤ electrochemical ammonia direct oxidation, ⑥ electrochemical nitrate nitrogen and chlorate reduction, etc. ① to ⑥ chemical reactions, and control the electrochemical water treatment process in a way that the chemical reactions ① to ⑥ complement each other, so that not only can effectively It can effectively remove the ammonia nitrogen contained in the water, and can effectively remove the oxidation by-products such as nitrate nitrogen and chlorate in the oxidation process of the ammonia nitrogen.

[Notes on state support for research and development]

This research was carried out under the supervision of the Korea Institute of Science and Technology and supported by the Ministry of the Environment. Number: 1485015389).

Background technique

在水质和水量方面是非常稳定的替代水资源。被清洁处理后的排放水可以起到在枯水期间在中上游被污染的河流的稀释水作用，也可以用作高质量的工业用水，还可以以生态流量供给到由于城市化而干涸的城市河流中。然而，已知畜牧废水、食物废水等含高浓度氨态氮的废水即使经过厌氧消化等生物处理过程，也残留数百mg/L以上的浓度的氨态氮，通常使与其此连接的下水处理厂以高负荷运行而阻碍下水深度处理设施的性能。水中氨态氮是引起地表水的富营养化的营养盐类中的一种，未来将持续加强对处理下水和废水而得到的处理水中的氨态氮浓度的管理标准。Effluent water treated in environmental infrastructure such as sewage and wastewater treatment plants

It is a very stable alternative water resource in terms of water quality and quantity. The cleaned and treated discharge water can be used as dilution water for polluted rivers in the middle and upper reaches during dry seasons, it can also be used as high-quality industrial water, and it can also be supplied as ecological flow to urban rivers that have dried up due to urbanization. middle. However, it is known that even if the wastewater containing high-concentration ammonia nitrogen such as livestock wastewater and food wastewater is subjected to a biological treatment process such as anaerobic digestion, ammonia nitrogen with a concentration of several hundred mg/L or more remains, and the sewage connected to it is usually used. Treatment plants operate at high loads hindering the performance of advanced treatment facilities. Ammonia nitrogen in water is one of the nutrient salts that cause eutrophication of surface water. In the future, the management standards for ammonia nitrogen concentration in treated water obtained by treating sewage and wastewater will continue to be strengthened.

The technologies for treating high concentrations of ammonia nitrogen in sewage and wastewater generally include biological high-level treatment methods, adsorption, electrodialysis (Electrodialysis), electrochemical oxidation (Electrochemical Oxidation) and so on. The concentration of organic matter required in the biological nitrification/denitrification process of wastewater containing high concentration of ammonia nitrogen is seriously insufficient, and the cost of external carbon source injection and other costs is unavoidable. In addition, the adsorption method of ammonia nitrogen represented by the Korean Granted Patent No. 598596 etc. has limitations that it is not suitable for large-capacity wastewater treatment, and consumes high operating costs in terms of regeneration of the adsorbent. In this regard, electrodialysis in PCT Publication WO2015-164744A1, U.S. Publication US2016-0271562A1, etc. is to alternately configure ion exchange membranes that allow cations and anions such as ammonium ions to selectively pass, and then apply a DC voltage to increase the amount of ions passing through. The ion separation (desalination) speed of the exchange membrane, thereby producing the technology of treated water, can remove all kinds of ions. However, the limitation of electrodialysis water treatment methods is that the purpose of DC power application is fundamentally limited to increase the ion separation capacity by generating an electric field, during which the water splitting (generating oxygen and hydrogen) reactions take place at the anode and cathode. Cannot be used for water treatment.

Finally, the electrochemical highly oxidized water treatment method in Korean Authorized Patent No. 1833833 (the applicant's authorized patent), US Patent Publication US2013-0168262A1, US Authorized Patent US7160430, etc., is used in sewage and wastewater with high conductivity The oxidation and reduction reactions that occur after the oxidizing electrode (anode) and the reducing electrode (cathode) are installed and electrified can play the role of oxidizing ammonia nitrogen in wastewater or reducing nitrate nitrogen. However, this method has limitations in that when the concentration of chloride ions in the water to be treated is low, the efficiency is low, and oxidation by-products such as nitrate nitrogen and chlorate may be generated during the oxidation of ammonia nitrogen.

SUMMARY OF THE INVENTION

The present invention is accomplished in order to solve the above-mentioned problems, and its purpose is to provide an electrochemical water treatment device capable of removing ammonia nitrogen and oxidation by-products of ammonia nitrogen. When nitrogen is used, 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 and other chemical reactions ① to ⑥, and the electrochemical water treatment process is controlled in such a way that the chemical reactions ① to ⑥ complement each other, so that not only can the ammonia nitrogen contained in the water be effectively removed, but also the ammonia nitrogen contained in the water can be effectively removed. Nitrate nitrogen, chlorate and other oxidation by-products during the oxidation of ammonia nitrogen.

The electrochemical water treatment device capable of removing ammonia nitrogen and oxidation by-products of ammonia nitrogen according to the present invention for achieving the above object is an electrochemical water treatment device for removing ammonia nitrogen contained in raw water, characterized in that: It is composed of an electrochemical reaction tank, a first circulation reaction tank and a second circulation reaction tank, the electrochemical reaction tank has an anode region between the anode and the anion exchange membrane, and a cathode region between the cathode and the cation exchange membrane, and provides For the electrodialysis and electrochemical reaction space of raw water; the above-mentioned first circulation reaction tank induces ammonia breakpoint oxidation by circulating with the above-mentioned anode region, and induces the reduction of ammonia nitrogen oxidation by-products by circulating with the above-mentioned cathode region ; The above-mentioned second circulation reaction tank induces electrochemical ammonia degassing by circulating with the above-mentioned cathode region, and induces electrochemical ammonia direct oxidation by circulating with the above-mentioned anode region.

进行，在第一水处理步骤中，在上述电化学反应槽内进行电渗析和电化学氨氧化，并且通过第一循环反应槽与阳极区域的循环而进行氨折点氧化，通过第二循环反应槽与阴极区域的循环而进行电化学氨脱气，在第二水处理步骤中，通过第一循环反应槽与阴极区域的循环而进行氨态氮的氧化副产物的还原，通过第二循环反应槽与阳极区域的循环而进行电化学氨直接氧化。The first water treatment step and the second water treatment step are in time series

In the first water treatment step, electrodialysis and electrochemical ammonia oxidation are carried out in the above-mentioned electrochemical reaction tank, and ammonia breaking point oxidation is carried out through the circulation of the first circulation reaction tank and the anode region, and the second circulation reaction is carried out. The electrochemical ammonia degassing is carried out by the circulation of the tank and the cathode region, and in the second water treatment step, the reduction of the oxidation by-product of ammonia nitrogen is carried out through the circulation of the first circulation reaction tank and the cathode region, and the second circulation reaction is carried out. The electrochemical direct oxidation of ammonia is carried out by cycling the cell and the anode region.

Through the above electrodialysis, the _anions in the raw water move to the anode region, and the cations in the raw water move to the cathode region. , the chloride ion (Cl ^- ) moves to the anode region and the ratio of chloride ion/ammonia nitrogen in the raw water increases, and the generation efficiency of monochloramine (NH ₂ Cl) formed by chlorine radicals increases.

The monochloramine (NH ₂ Cl) generated in the anode region of the electrochemical reaction tank moves to the first circulation reaction tank, and the monochloramine (NH ₂ Cl) is converted into nitrogen (N ₂ ) and nitric acid through the above-mentioned ammonia breaking point oxidation nitrogen (NO ₃ ^- ).

The NH ₄ ⁺ that has moved to the cathode region of the electrochemical reaction cell by electrodialysis is converted into ammonia gas (NH ₃ ) by the hydroxide ions (OH ⁻ ) generated by the hydrogen generation reaction in the cathode region and circulated to the second circulation reaction cell Moving, a degassing device is provided on one side of the second circulation reaction tank, and the ammonia gas in the second circulation reaction tank passes through the degassing device to perform electrochemical ammonia degassing.

Through electrochemical ammonia degassing, NH 4 ^{+ remains in the second circulation reaction tank, and through the circulation of raw water between the anode region and the second circulation reaction tank, the residual NH 4 +} _in ^the second circulation reaction tank undergoes electrochemical reactions _. Ammonia is directly oxidized to nitrogen (N ₂ ).

Through electrochemical ammonia oxidation and ammonia breakpoint oxidation, the residual nitrate nitrogen (NO ₃ ^- ) and chlorate (ClO ₃ ^- ) in the first circulation reaction tank are circulated through the raw water between the cathode area and the first circulation reaction tank , the residual nitrate nitrogen (NO ₃ ^- ) and chlorate (ClO ₃ ^- ) in the first circulation reaction tank are reduced to nitrogen (N ₂ ) and chloride ion (Cl ^- ), respectively.

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

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

The raw water circulation method of the first water treatment step is that the first circulating reaction tank and the anode area are circulated and the second circulating reaction tank and the cathode area are circulated, and the raw water circulation method of the second water treatment step is that the first circulating reaction tank and The manner in which the cathode area circulates and the second circulation reaction tank circulates with the anode area.

In the first water treatment step, the control unit controls the DC power supply device to apply a power supply of 2.0 V or more to the anode in order to promote the generation of chlorine radicals, and in the second water treatment step, for electrochemical nitrate nitrogen and chlorine The acid salt reduction reaction was carried out, and the DC power supply device was controlled so that the voltage of -1.4V NHE or less was applied to the cathode.

The pH decrease rate per unit time (dpH/dt) of the raw water is the H ⁺ concentration increase rate, and the H ⁺ concentration increase rate is calculated by the following formula.

(Mode)

H ⁺ concentration increase rate (M/min) = log [J/F/(V/A) x 60]

(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 above-mentioned reference value is 2.3 to 3.2 pH change value/min.

The electrochemical water treatment device capable of removing ammonia nitrogen and oxidation by-products of ammonia nitrogen according to the present invention 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 in one electrochemical water treatment device, Therefore, not only can the ammonia nitrogen be effectively removed from the water, but also the secondary pollution problems of ammonia nitrogen concentrated water, nitrate nitrogen (NO ₃ ^- ), chlorate (ClO ₃ ^- ) and the like can be prevented.

的废水中氯离子/氨态氮的比率增加，在阳极周边设置参比电极来调节施加到阳极的电压，从而增加氯自由基(Cl·,Cl₂ ^-·)的生成量，从而能够增加电化学氨氧化速度。此外，在电化学氨氧化过程中生成的H⁺降低pH，从而能够得到在氨折点氧化过程中减少副产物硝态氮的生成的效果。into the anode compartment by electrodialysis

The ratio of chloride ion/ammonia nitrogen in the wastewater increases, and a reference electrode is set around the anode to adjust the voltage applied to the anode, thereby increasing the generation of chlorine radicals (Cl , Cl ₂ ^- ), which can increase the electricity Chemical ammonia oxidation rate. In addition, the H ⁺ generated during the electrochemical ammonia oxidation reduces the pH, so that the effect of reducing the generation of nitrate nitrogen by-product during the ammonia breakpoint oxidation can be obtained.

之间交替循环，从而使电化学氨直接氧化和硝态氮/氯酸盐还原反应容易发生。进而，通过控制部并基于反应槽内pH和电导率值来控制流路，从而能够防止除了氨态氮的去除以外的额外的能量消耗。At the same time, part of the inflow water is in the anode and cathode compartments

Alternating cycles between them, thus making the electrochemical ammonia direct oxidation and nitrate/chlorate reduction reactions easy to occur. Furthermore, by controlling the flow path based on the pH and conductivity values in the reaction tank by the control unit, it is possible to prevent additional energy consumption other than the removal of ammonia nitrogen.

Description of drawings

1 is a structural diagram of an electrochemical water treatment device capable of removing ammonia nitrogen and oxidation by-products of ammonia nitrogen according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a chemical reaction in an electrochemical water treatment apparatus for removing ammonia nitrogen.

FIG. 3 is a schematic diagram showing changes in the concentration of main ionic substances in the electrochemical water treatment device for removing ammonia nitrogen.

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

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

FIG. 6 is a flowchart showing a time-series flow of a first water treatment step and a second water treatment step.

Symbol Description

11: Anode 12: Cathode

13: Anion exchange membrane 14: Cation exchange membrane

15: Reference electrode 21: First circulation flow path

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

24: Bypass flow path 24a: On-off valve

31: pH sensor 32: Conductivity meter

110: Electrochemical reaction tank 111: Anode area

112: Cathode area 113: Raw water circulation area

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

140: Raw water circulation tank

Detailed ways

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

The ammonia removal technology according to the present invention is based on an electrochemical water treatment device, and by implementing 6 chemical reaction mechanisms in the electrochemical water treatment device, the ammonia nitrogen and the oxidation by-products occurring in the oxidation process of ammonia nitrogen can be effectively removed. product. The six chemical reaction mechanisms work independently and complement each other, ultimately improving the removal efficiency of ammonia nitrogen and oxidation by-products.

The six chemical reactions implemented in the electrochemical water treatment device according to the present invention are ① electrodialysis, ② electrochemical ammonia oxidation (electrochemical ammonia chlorination), and ③ ammonia breaking point oxidation (ammonia breaking point oxidation) point chlorination (breakpoint chlorination ofammonia), ④ electrochemical ammonia stripping (electrochemical ammonia stripping), ⑤ electrochemical ammonia direct oxidation (electrochemical ammonia direct oxidation), ⑥ electrochemical nitrate nitrogen and chlorate reduction (electrochemical reduction NO ₃ ^- and ClO ₃ ^- (electrochemical reduction of NO ₃ ^- and ClO ₃ ^- )).

The above-mentioned electrodialysis and the electrochemical reactions of ② to ⑥ will be described in detail with reference to the structure of the electrochemical water treatment apparatus described later.

Hereinafter, an electrochemical water treatment device capable of removing ammonia nitrogen and oxidation by-products of ammonia 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 device capable of removing ammonia nitrogen and ammonia nitrogen oxidation by-products according to an embodiment of the present invention includes an electrochemical reaction tank 110, a first circulation reaction tank 120, and a second circulation reaction tank 130 and raw water circulation tank 140.

The electrochemical reaction tank 110 described above provides a space for performing electrodialysis and electrochemical reactions. The electrochemical reaction cell 110 is spatially divided into an anode region (anodic compartment) 111 , a cathode region (cathodic compartment) 112 , and a raw water circulation region 113 . An anode 11 and a cathode 12 are respectively prepared on both ends of the electrochemical reaction tank 110 , and an anion exchange membrane 13 and a cation exchange membrane 14 are prepared in isolation between the anode 11 and the cathode 12 . Between the anode 11 and the anion exchange membrane 13 corresponds to the anode region 111 , between the cathode 12 and the cation exchange membrane 14 corresponds to the anode region 111 , and 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 is a membrane that selectively permeates only anions, and the cation exchange membrane 14 is a membrane that selectively permeates only cations.

The electrochemical reaction tank 110 described above includes an anion exchange membrane 13 and a cation exchange membrane 14, and can perform an electrodialysis process capable of separating cations and anions when power is applied. That is, when electrodialysis is performed by applying a power source in a state where the raw water is supplied to the electrochemical reaction tank 110, anions (for example, Cl ⁻ ) in the raw water move to the anode region 111 through the anion exchange membrane 13 , and cations (for example, Cl − ) in the raw water move to the anode region 111 . NH ₄ ⁺ ) moves through the cation exchange membrane 14 to the cathode region 112 .

The above-mentioned electrochemical reaction tank 110 basically provides a space for implementing electrodialysis, and at the same time provides the electrochemical reactions for implementing the above-mentioned ②～⑥, namely ② electrochemical ammonia oxidation, ③ ammonia breakpoint oxidation, and ④ electrochemical ammonia degassing , ⑤ electrochemical ammonia direct oxidation, ⑥ electrochemical nitrate nitrogen and chlorate reduction space.

In the above electrochemical reactions ① to ⑥, ① electrodialysis and ② electrochemical ammonia oxidation are carried out in the above electrochemical reaction tank 110, and the remaining ③ to ⑥, namely, ③ ammonia breaking point oxidation, ④ electrochemical ammonia degassing, ⑤ The electrochemical ammonia direct oxidation, ⑥ electrochemical nitrate nitrogen and chlorate reduction are carried out through the electrochemical reaction tank 110 and the first circulation reaction tank 120 in linkage, or the electrochemical reaction tank 110 and the second circulation reaction tank 130 are linked together conduct.

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 . In the case of circulation between the anode region 111 and the first circulation reaction tank 120, ③ ammonia breaking point oxidation is carried out, and in the case of circulation between the anode region 111 and the second circulation reaction tank 130, ⑤ electrochemical ammonia direct oxidation is carried out .

In addition, the raw water in the cathode region 112 of the electrochemical reaction tank 110 circulates between the cathode region 112 and the second circulation reaction tank 130 or between the cathode region 112 and the first circulation reaction tank 120 . In the case of circulation between the cathode region 112 and the second circulation reaction tank 130, ④ electrochemical ammonia degassing is performed, and in the case of circulation between the cathode region 112 and the first circulation reaction tank 120, ⑥ electrochemical nitrate state is performed Nitrogen and chlorate reduction.

In other words, the above-mentioned first circulation reaction tank 120 induces (3) ammonia breakpoint oxidation by circulating with the anode region 111 , and induces (6) electrochemical nitrate nitrogen and chlorate reduction by circulating with the cathode region 112 , the above-mentioned second circulation reaction tank 130 induces (4) electrochemical ammonia degassing by circulating with the cathode region 112 , and induces (5) electrochemical ammonia direct oxidation by circulating with the anode region 111 .

On the other hand, the raw water circulation tank 140 supplies raw water to the electrochemical reaction tank 110 , and the raw water in the raw water circulation area 113 of the electrochemical reaction tank 110 circulates between the raw water circulation area 113 and the raw water circulation tank 140 . When electrodialysis is performed in the electrochemical reaction tank 110 , as described above, anions in the raw water move to the anode region 111 , cations move to the cathode region 112 , and raw water with reduced ion species exists in the raw water circulation region 113 . The quality of the raw water circulating between the raw water circulation area 113 of the electrochemical reaction tank 110 and the raw water circulation tank 140 is improved when the electrochemical reactions of ② to ⑥ including the above electrodialysis are repeated. Here, that the water quality of the raw water is improved means that ammonia nitrogen and oxidation by-products of ammonia nitrogen contained in the raw water are reduced. For reference, raw water is supplied to the electrochemical reaction tank 110 through the raw water circulation tank 140 , and is simultaneously supplied to the first circulation reaction tank 120 and the second circulation reaction tank 130 .

The reactions of ① to ⑥ based on the above-mentioned electrochemical reaction tank 110, the first circulation reaction tank 120 and the second circulation reaction tank 130, namely ① electrodialysis, ② electrochemical ammonia oxidation, ③ ammonia breaking point oxidation, ④ electrochemical reaction The mechanisms of ammonia degassing, ⑤electrochemical ammonia direct oxidation, and ⑥electrochemical nitrate and chlorate reduction are described below.

①The electrodialysis is carried out as follows.

When a direct current power source is applied to the anode 11 and the cathode 12 of the electrochemical reaction tank 110 in a state where the raw water containing ammonia nitrogen is supplied to the electrochemical reaction tank 110 , anions (eg Cl ⁻ ) in the raw water pass through the anion exchange membrane 13 moves to the anode region 111 , and cations (eg NH ₄ ⁺ ) in the raw water move to the cathode region 112 through the cation exchange membrane 14 . By the electrodialysis as described above, raw water in which the concentration of ammonia nitrogen is reduced exists in the raw water circulation region 113 of the electrochemical reaction tank 110 .

②The electrochemical ammonia oxidation is carried out as follows.

The electrochemical reactions of ② to ⑥ including electrochemical ammonia oxidation are carried out together with electrodialysis.

When power is applied to the electrochemical reaction tank 110, chloride ions (2Cl ⁻ ) are changed into chlorine radicals (Cl·,Cl ₂ ⁻ · ) on the surface of the anode 11 (refer to Equation 1), which react with NH ₃ in water again to generate Monochloramine (NH ₂ Cl) (refer to formula 2). At this time, by electrodialysis, the negatively charged chloride ions (Cl ⁻ ) move to the anode region 111 , so that the ratio of chloride ions/ammonia nitrogen in the raw water flowing to the anode region 111 increases, so that the reaction rates of Equation 1 and Equation 2 are increased. rise. That is, as electrodialysis is combined with electrochemical ammonia oxidation, ammonia nitrogen removal efficiency increases. In addition, on the surface of the anode 11 , chloride ions are oxidized to free chlorine (Cl ₂ , HOCl) (refer to formula 3), and NH ₂ Cl (refer to formula 4) can also be produced. Therefore, it is preferable to induce the reaction of Formula 1 and Formula 2 rather than the reaction of Formula 3 and Formula 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 chloride ions, oxygen gas (O ₂ ) and H ⁺ are generated by the oxidation of water molecules, and the pH decreases (see Formula 5). In addition, chlorate (ClO ₃ ⁻ ) (Equation 6) may be generated on the surface of the anode 11 by further oxidation of free chlorine, which is removed by the ⑥ electrochemical nitrate and chlorate reduction mechanism described later.

(Formula 2) 2Cl·+NH ₃ →NH ₂ Cl+H ⁺ +Cl ⁻

(Formula 4) HOCl+NH ₃ →NH ₂ Cl+H ₂ O

(Formula 5) H ₂ O→1/2O ₂ +2H ⁺ +2e ⁻

(Formula 6) HOCl+2H ₂ O→ClO ₃ ^- +5H ⁺ +4e ^-

③The ammonia breaking point oxidation is carried out as follows.

The ammonia breaking point oxidation is performed in the process of circulating 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 .

The NH ₂ Cl generated in the anode region 111 of the electrochemical reaction tank 110 moves to the first circulation reaction tank 120 . Dichloramine (NHCl ₂ ) is produced by the reaction between NH ₂ Cl and residual free chlorine (refer to formula 7), which reacts with NH ₂ Cl again to produce nitrogen gas (N ₂ ) (refer to formula 8), and finally water Ammonia nitrogen removal. At the same time, a part of NH ₂ Cl is oxidized to nitrate nitrogen (NO ₃ ⁻ ) (see Formula 9), and it is preferable to reduce the rate of this reaction in terms of removal of total nitrogen in water. In this regard, in the present invention, the effect of reducing the pH and increasing the specific gravity of NHCl ₂ by the H ⁺ generated in the electrochemical ammonia oxidation process can be obtained, thereby further reducing the generation of nitrate nitrogen. In addition, by depleting the remaining free chlorine by the formula 7, it is possible to prevent the phenomenon that the anion exchange membrane is damaged by the free chlorine during the circulation to the anode region 111 .

(Formula 8) NH ₂ Cl+NHCl ₂ →N ₂ +3H ⁺ +3Cl ⁻

(Formula 9) NH ₂ Cl+3HOCl→NO ₃ ^- +4Cl ^- +5H ⁺

④ Electrochemical ammonia degassing is carried out as follows.

The 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 . One side of the second circulation reaction tank 130 is provided with a degassing device such as a blower capable of degassing ammonia gas in water.

On the surface of the cathode 12, hydroxide ions (OH ⁻ ) generated by the hydrogen generation reaction (refer to Equation 10) convert NH ₄ ⁺ moving to the cathode region 112 during electrodialysis into ammonia gas (NH ₃ ) (refer to the formula 10). formula 11). Raw water circulates between the cathode region 112 and the second circulation reaction tank 130, and a degasser capable of degassing ammonia gas is provided on one side of the second circulation reaction tank 130, so that the second circulation reaction tank can be degassed by the deaerator. Ammonia (NH ₃ ) in 130 was degassed. At this time, during the electrodialysis process, the temperature increase caused by the peripheral resistance of the cathode 12 has a positive effect on the degassing of ammonia. However, the degassing efficiency of ammonia is slow compared with the above-mentioned ammonia breakpoint oxidation, and the complete removal of ammonia nitrogen in water cannot be achieved.

(Formula 10) 2H ₂ O+2e ^- →H ₂ +2OH ^-

(Formula 11) NH ₄ ⁺ +OH ⁻ →NH ₃ +H ₂ O

⑤ The electrochemical ammonia direct oxidation is carried out as follows.

The electrochemical ammonia direct oxidation is performed in the process of circulating 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 ₄ ⁺ remains in the second circulation reaction tank 130 due to electrochemical ammonia degassing, and NH ₄ remains 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 130 ⁺ is directly oxidized to nitrogen (N ₂ ) as shown in formula 12. At this time, since the concentration of Cl ^- is relatively low and the concentration (pH) of OH ^- is increased by Equation 10, Equation 12 can be efficiently generated compared to the competing reactions of Equation 1, Equation 3, and Equation 5.

(Formula 12) NH ₃ +3OH ⁻ →1/2N ₂ +3H ₂ O+3e ⁻

⑥Electrochemical reduction of nitrate and chlorate is carried out as follows.

The electrochemical reduction of nitrate nitrogen and chlorate is performed during the 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 .

Through the above-mentioned (2) electrochemical ammonia oxidation and (3) ammonia breakpoint oxidation mechanism, the residual nitrate nitrogen (NO ₃ ^- ) and chlorate (ClO ₃ ^- ) in the first circulation reaction tank 120,

Through the raw water circulation between the cathode region 112 and the first circulation reaction tank 120, the nitrate nitrogen (NO ₃ ⁻ ) and chlorate (ClO ₃ ⁻ ) remaining in the first circulation reaction tank 120 are shown in Formula 13 and Formula 12, respectively. 14 is reduced to nitrogen (N ₂ ), chloride ion (Cl ⁻ ). At this time, by Equation 5, the concentration of H ⁺ is relatively high, so Equations 13 and 14 can occur efficiently compared to the competing reactions of Equation 10.

(Formula 13) NO ₃ ^- +6H ⁺ +5e ^- →1/2N ₂ +3H ₂ O

(Formula 14) ClO ₃ ^- +6H ⁺ +6e ^- →Cl ^- +3H ₂ O

The electrochemical reactions ① to ⑥ performed by 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 distinguished in time series. The ammonia nitrogen in the water is removed by the steps of ① to ④, and the residual ammonia nitrogen is removed by the subsequent steps of ⑤ to ⑥, and the nitrate nitrogen (NO ₃ ^- ) and chlorate, which are oxidation by-products of the ammonia nitrogen, can be removed. (ClO ₃ ^- ). Therefore, the reactions of ① to ④ are referred to as the first water treatment step (phase 1), and the reactions of ⑤ to ⑥ are referred to as the second water treatment step (phase 2).

The first water treatment steps (ie, the reactions of ① to ④) and the second water treatment steps (the reactions of ⑤ to ⑥), which are distinguished in time series, are also distinguished by the way of raw water circulation. Here, the raw water circulation system refers to a circulation system between the cathode region 112 and the anode region 111 of the electrochemical reaction tank 110 and the first circulation reaction tank 120 and the second circulation reaction tank 130 . In the first water treatment step, the anode region 111 and the first circulation reaction tank 120 are circulated, and the cathode region 112 and the second circulation reaction tank 130 are circulated. In the second water treatment step, the anode region 111 and the second circulation reaction tank are circulated The reaction tank 130 is circulated, and the circulation mode of the cathode region 112 and the first circulation reaction tank 120 changes the circulation mode of the raw water.

The time of distinction between the first water treatment step (phase 1) and the second water treatment step (phase 2), that is, the time at which the first water treatment step ends, is determined according to the degree of ammonia nitrogen removal. As described above, by the first water treatment step, ammonia nitrogen contained in the raw water is removed, and the second water treatment step is to remove ammonia nitrogen remaining in the raw water and nitrate nitrogen as an oxidation by-product of ammonia nitrogen ( NO ₃ ^- ) and chlorate (ClO ₃ ^- ).

The end time of the first water treatment step is determined based on the pH decrease rate per unit time of the raw water in the raw water circulation tank 140 . When the concentration of ammonia nitrogen in the first water treatment step is reduced by ① electrochemical ammonia oxidation and ③ ammonia breakpoint oxidation, the pH reduction rate (-dpH/dt) in the first circulation reaction tank 120 is accelerated. From this point of view, when the pH reduction 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, so that it can be converted into the second water processing steps.

The pH decrease rate per unit time (-dpH/dt) refers to the increase rate of the H ⁺ concentration, and the increase rate of the H ⁺ concentration was calculated by the following formula 15. The H ⁺ concentration increase rate mathematical formula according to Equation 15 is a function of current density (J), electrode area (A) and volume (V), taking into account the electrochemical oxidation reaction, the current density (J) of the mathematical formula applicable to the present invention ) is set at 20 to 40 mA/cm ² , and the volume of water (V/A) relative to the electrode area is set at 5 to 20 cm ³ /cm ² in consideration of the processing capacity of the electrochemical reaction tank 110 . The reference value of the pH decrease rate per unit time (dpH/dt) was set to 2.3 to 3.2 pH change value/min. However, considering that the pH increase rate is passivated due to the buffer capacity in water, it may be The reference value is set to 2.0 to 2.5 pH change value/min, more preferably, 2.5 pH change value/min can be set as the reference value.

(Equation 15) H ⁺ concentration increase rate (M/min) = log [J/F/(V/A) x 60]

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

The first water treatment step (phase 1) and the second water treatment step (phase 2) are carried out in time series according to an embodiment of the present invention The method for removing ammonia nitrogen and oxidation by-products is described in more detail, as follows (Refer to Figures 2 and 6).

The first water treatment step (phase 1) is carried out as follows.

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

For this purpose, raw water containing ammonia 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, and ③ ammonia breaking point oxidation is performed in the first circulation reaction tank 120, and the second ④ Electrochemical ammonia degassing is performed in the circulating reaction tank 130 . At this time, the raw water of the first circulation reaction tank 120 circulates with the anode region 111 of the electrochemical reaction tank 110, and the raw water of the second circulation reaction tank 130 circulates with the cathode region 112 of the electrochemical reaction tank 110 (S602).

During the first water treatment step, the raw water in the first circulation reaction tank 120 passes through the anode region 111 to form NH ₂ Cl through Formulas 1, 2 and 3, 4, and then circulates to the first circulation reaction tank 120 During the process, nitrogen gas and nitrate nitrogen are generated by formulas 7 to 9. At this time, the increase of chloride ions by electrodialysis competes with the decrease of chloride ions through the electrochemical reactions of Formulas 1 and 3. In addition, through further oxidation of free chlorine, chlorates can be formed. Finally, as shown in FIG. 3 , in the first water treatment step, the concentration of ammonia nitrogen in the first circulating reaction tank 120 continues to decrease, and the concentration of chloride ions is appropriately increased through electrodialysis, and then through the equations 1 and 3. The electrochemical reaction decreased, and the concentration of nitrate nitrogen and chlorate continued to increase. Here, the timing at which the concentration of chlorate begins to increase is similar to the timing at which the concentration of chloride ions begins to decrease.

The removal efficiency of ammonia nitrogen was doubled by electrodialysis and electrochemical ammonia oxidation in the first water treatment step, which was confirmed by experimental results. Figure 4 is a graph illustrating the comparison of changes in the concentration of ammonia nitrogen during electrochemical ammonia oxidation for subject water in the presence of 20 mM _NH4 ⁺ and 50, 100, 150 mM ^Cl- , respectively. At this time, Ti coated with Pt was used for the anode 11 , Ti was used for the cathode 12 , the volume of the target water relative to the electrode area was 1:10 cm ² /cm ³ , and the current density was 300 A/m ² . Referring to FIG. 4 , it can be confirmed that the higher the concentration of chloride ions in the water, the faster the decomposition rate of ammonia nitrogen. That is, by electrodialysis, negatively charged chloride ions (Cl ⁻ ) move to the anode region 111 and the reaction rate increases.

On the other hand, the NH ₂ Cl generated during the cycle of the anode region 111 is oxidized by the ammonia breaking point to generate nitrogen gas (N ₂ ) (refer to Equations 7 and 8), and the ammonia nitrogen in the water is finally removed, and at the same time , nitrate nitrogen (NO ₃ ^- ) can be generated by formula 9. FIG. 5 is a graph illustrating the comparison of nitrate concentration changes during electrochemical ammonia oxidation at pH 4, 7, and 10 for subject water in the presence of 20 mM NH ₄ ⁺ and 100 mM Cl ⁻ respectively. At this time, Ti coated with Pt was used for the anode 11 , Ti was used for the cathode 12 , the volume of the target water relative to the electrode area was 1:10 cm ² /cm ³ , and the current density was 200 A/m ² . Referring to FIG. 5 , it was confirmed that the higher the pH of the water, the faster the formation rate of nitrate nitrogen. That is, it was confirmed that the effect of reducing the pH and increasing the specific gravity of NHCl ₂ by H ⁺ generated during the electrochemical ammonia oxidation process can further reduce the generation of nitrate nitrogen.

During the formation of NH ₂ Cl by formulas 1, 2 and 3, 4 in the first water treatment step, the chlorine radicals (Cl , Cl ₂ ⁻ ) participating in formulas 1 and 2 and those participating in formulas 3 and 4 Free chlorine (Cl ₂ , HOCl) is relatively reactive. Therefore, it is necessary to induce the generation of chlorine radicals (Cl·, Cl ₂ ⁻ · ), and the generation of chlorine radicals (Cl·, Cl ₂ ⁻ · ) can be controlled by adjusting the voltage applied to the anode 11 . Specifically, the generation of chlorine-based radicals (Cl ₂ ⁻ ·, Cl·) depends on whether the voltage applied to the anode 11 satisfies the standard redox potential of chlorine-based radicals (Cl ₂ ⁻ ·, Cl·) .

【Table 1】

<Standard redox potential of chlorine-based oxidants>

Chlorine-based oxidant 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, it can be seen that the standard redox potential of hypochlorous acid (HOCl) is 1.48V NHE (normal hydrogen electrode), and the standard redox potential of dichloride radical ion (Cl ₂ ⁻ · ) is 2.0V NHE, the standard redox potential of chlorine radical (Cl·) is 2.4V NHE, in order to generate chlorine radical (Cl·) which is the strongest oxidant, it is necessary to apply a power supply of 2.4V or more to the anode 11, in order to generate dichloride For radical ions (Cl ₂ ⁻ · ), it is necessary to apply a power supply of 2.0 V or more 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 which are connected in parallel with an equal voltage by the DC power supply device. That is, it is necessary to supply a voltage of 2.4 V or more to the anode 11 and the cathode 12, respectively, and in consideration of the voltage loss, it is necessary to apply the cell voltage (cell voltage=[anode 11 voltage (+)]+[cathode 12 voltage (-)]+voltage loss ).

It is necessary to continuously confirm whether a voltage higher than the standard redox potential of chlorine-based radicals (Cl ₂ ⁻ ·, Cl · ), that is, a voltage of 2.0 V or more is applied to the anode 11 . The reference electrode 15 of the voltage applied to the anode 11 . The anode 11 voltage measured by the reference electrode 15 is transmitted to a control unit described later, and the control unit checks whether the measured anode 11 voltage is 2.0V or more, and when the measured anode 11 voltage is less than 2.0V, controls the DC power supply device A voltage of 2.0 V or more is supplied to the anode 11 .

On the other hand, in the first water treatment step, the raw water of the second circulation reaction tank 130 undergoes an electrochemical ammonia degassing process. Specifically, the hydroxide ion (OH ⁻ ) generated by Equation 10 changes NH ₄ ⁺ moved to the cathode region 112 during electrodialysis into ammonia gas (NH ₃ ) (refer to Equation 11). The degassing device provided in the second circulation reaction tank 130, for example, a blower, degass the ammonia gas dissolved in the water, and finally can remove the ammonia nitrogen in the water. As a result, as shown in FIG. 3 , the ammonia nitrogen concentration in the second circulation reaction tank 130 was initially increased by electrodialysis, and then decreased by electrochemical ammonia degassing. The pH is increased by the reaction of Equation 10, and its increase is passivated by the buffering capacity of ammonia nitrogen (Equation 11). It is predicted that the complete removal of ammonia nitrogen in the second circulation reaction tank 130 cannot be achieved in the first water treatment step, and the residual ammonia nitrogen can be completely removed by the second water treatment step.

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

The second water treatment step (phase 2) is carried out as follows.

In the second water treatment step, ⑤ electrochemical ammonia direct oxidation and ⑥ electrochemical nitrate nitrogen and chlorate reduction are performed. Through this process, the residual ammonia nitrogen in the second circulation reaction tank 130 is removed, while the first circulation Nitrate nitrogen (NO ₃ ⁻ ) and chlorate (ClO ₃ ⁻ ), which are oxidation by-products of ammonia nitrogen present in the reaction tank 120 , are 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 of the first circulation reaction tank 120 circulates with the cathode region 112 of the electrochemical reaction tank 110, and the raw water of the second circulation reaction tank 130 circulates with the anode region 111 of the electrochemical reaction tank 110 (S604).

The ⑥ electrochemical reduction of nitrate nitrogen and chlorate in the first circulation reaction tank 120 is performed as follows.

The NO ₃ ^- and ClO ₃ ^- present in the first circulation reaction tank 120 are in the process of cycling in the cathode region 112 of the electrochemical reaction tank 110 , and electrochemical nitrate is generated through the catalytic action of the Ni, Cu, and Ti components on the surface of the cathode 12 . Nitrogen and chlorate reduction reaction (refer to equations 13 and 14). The reduced pH in the first water treatment step facilitates Equations 13 and 14 to occur efficiently. At this time, it is known that the cathode 12 voltage for generating formula 13 is -1.0V NHE, and the cathode 12 voltage for generating formula 14 is -1.4V NHE. Therefore, in the present invention, a reference electrode 15 (Reference electrode) is provided on the peripheral side of the cathode 12 to adjust the voltage applied to the cathode 12, thereby creating an environment in which Equations 13 and 14 can be generated. The control unit confirms whether the measured voltage of the cathode 12 is -1.4V NHE or less, and when the absolute value of the measured cathode 12 voltage is less than 1.4V NHE, controls the DC power supply device so that the cathode 12 is supplied with -1.4V NHE or less voltage. As a result, in the second water treatment step, by electrodialysis, the concentration of ammonia nitrogen in the first circulation reaction tank 120 is partially increased, and the concentrations of nitrate nitrogen and chlorate ions are completely reduced. In this process, the concentration of chloride ions is partially rise. In addition, the pH is raised again by Equation 10 to return to the neutral region where it can be discharged.

On the other hand, NH ₄ ⁺ remaining in the second circulation reaction tank 130 circulates in the anode region 111 , and at the same time, the electrochemical ammonia direct oxidation reaction occurs by the catalytic action of the Pt component on the surface of the anode 11 (refer to Equation 12). At this time, the concentration of Cl ⁻ is relatively low, and the reaction of formula 10 has a high concentration (pH) of OH ⁻ , so that formula 12 can be efficiently generated compared with the competing reactions of formulas 1, 3, and 5. As a result, in the second water treatment step, the ammonia nitrogen concentration in the second circulation reaction tank 130 is completely reduced, and the chloride ion concentration is partially increased by electrodialysis. In addition, the pH is reduced again by Equation 5 to be able to return to the neutral region where it can be discharged. As described above, whether or not the concentration of ammonia nitrogen remaining in the second circulation reaction tank 130 is almost completely reduced can be confirmed by the change tendency of pH, and when the pH decrease rate per unit time (-dpH/dt) exceeds the reference value ( For example, when the pH change value is 2.5/min), it can be interpreted that the ammonia nitrogen in the second circulation reaction tank 130 is almost completely removed (S605).

The first water treatment step and the second water treatment step have been described above.

Ammonia nitrogen and nitrate nitrogen and chlorate which are oxidation by-products of ammonia nitrogen are removed by the first water treatment step and the second water treatment step, and the raw water after the second water treatment step can be discharged to the water system. To determine whether the raw water after the second water treatment step can be discharged can also be determined by measuring the electrical conductivity of the raw water. A conductivity meter is provided in the raw water circulation tank 140, whereby the concentrations of NH ₄ ⁺ and Cl ⁻ in the raw water can be indirectly measured. As an example, when it is determined that the electrical conductivity of the raw water is less than a certain level (usually 0.2 mS/cm or less) ( S606 ), it is determined that the concentration of ammonia nitrogen in the raw water circulation tank 140 has reached a dischargeable level, and the process can be terminated. The water treatment method according to the present invention (S607).

Above, the electrochemical water treatment device capable of removing ammonia nitrogen and ammonia nitrogen oxidation by-products according to an embodiment of the present invention has been described. In the above-described embodiments, the following detailed configurations can be limited.

When forming the electrochemical reaction tank 110 , the anode 11 and the cathode 12 may be formed in the form of a flat plate or a grid. In the case of the anode 11, it is preferable to select a material that can simultaneously realize electrodialysis, electrochemical ammonia oxidation, and electrochemical ammonia direct oxidation. The Pt particles are coated on the isoconductive support by methods such as Electrodeposition, Dip-coating, Chemical Vapor Deposition and Sputtering.

In the case of the cathode 12, it is preferable to select a material capable of simultaneously realizing electrochemical ammonia degassing and electrochemical nitrate nitrogen and chlorate reduction. Considering this aspect, 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 can electrochemically reduce nitrate nitrogen efficiently when the Cu content is in the range of 70 to 95%, and Ti, which is a conductive metal, is known to electrochemically reduce chloric acid Salt.

In addition, as the reference electrode 15, commonly used silver chloride (Ag/AgCl) electrodes, mercury (Hg/Hg ₂ SO ₄ ) electrodes, copper (Cu/CuSO ₄ ) electrodes, and Pt electrodes can be used. Meanwhile, as the cation exchange membrane 14 and the anion exchange membrane 13, a common ion exchange resin such as an ion exchange resin based on styrene divinyl-benzene (Styrene divinyl-benzene) can be used. For reference, FIG. 1 shows an example in which each of the cation exchange membrane 14 and the anion exchange membrane 13 is provided, but a plurality of exchange membranes may be alternately arranged.

In order to control the raw water circulation method, 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 area 113 of the electrochemical reaction tank 110 , and between the first circulation reaction tank 120 and the anode area 111 The second circulation channel 22 and the second circulation pump P2 are provided, and the third circulation channel 23 and the third circulation pump P3 are provided between the second circulation reaction tank 130 and the cathode region 112 . In addition, a bypass flow path 24 and an on-off valve 24 a are provided between the second circulation flow path and the third circulation flow path 23 . The first circulation reaction tank 120 can circulate with the anode region 111 or the cathode region 112, and the second circulation reaction tank 130 can circulate with the cathode region 112 or the anode region 111 by the operation of the opening and closing valve 24a and the bypass flow path 24.

One side of the first circulation reaction tank 120 and the second circulation reaction tank 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 for measuring the conductivity of the raw water (conductivity meter) 32.

In addition, one side of the electrochemical reaction tank 110 is provided with a DC power supply device and a control unit (not shown), and the DC power supply device applies power to the anode 11 and the cathode 12 . The said control part controls a raw-water circulation system and a DC power supply apparatus.

Specifically, the control unit measures the pH decrease rate per unit time (-dpH/dt) of the first circulation reaction tank 120, and when the measured pH decrease rate per unit time (-dpH/dt) exceeds a preset value When the reference value is reached, the raw water circulation method is switched from the first water treatment step to the second water treatment step. The raw water circulation method of the first water treatment step is that the first circulating reaction tank 120 circulates with the anode region 111 and the second circulating reaction tank 130 and the cathode region 112 circulate. The raw water circulation method of the second water treatment step is the first circulating reaction. The mode in which the tank 120 is circulated with the cathode region 112 and the second circulation reaction tank 130 is circulated with the anode region 111 . In the second water treatment step, the first circulating reaction tank 120 is connected to the cathode region 112 via the bypass flow path 24, and the second circulating reaction tank 130 is connected to the anode region 111 via the bypass flow path 24, for which the control unit controls Operation of the on-off valve 24a.

In addition, the above-mentioned control section 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, in order to promote the generation of chlorine radicals, the direct current power supply device is controlled to apply a power supply of 2.0V or more to the anode 11, and in the second water treatment step, in order to electrochemical nitrate nitrogen and chlorine. The acid salt reduction reaction is performed, and the DC power supply device is controlled so that a voltage of -1.4 V NHE or less is applied to the cathode 12 .

Claims (11)

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 electrochemical reaction space for raw water,

the electrochemical reaction tank further comprises a raw water circulation region located between the anion exchange membrane and the cation exchange membrane,

the first circulation reaction tank induces the oxidation of ammonia breakpoint through the circulation with the anode region and induces the reduction of oxidation by-products of ammoniacal nitrogen through the 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 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 carried out by the circulation of the first circulating reaction tank and the cathode region, and the electrochemical direct oxidation of ammonia is carried out by the circulation of the second circulating reaction tank and the anode region;

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 part measures the pH reduction speed per unit time of the first circulation reaction tank, namely-dpH/dt, and switches the raw water circulation mode from the first water treatment step to the second water treatment step when the measured pH reduction speed per unit time, namely-dpH/dt, exceeds a preset reference value;

the pH decrease rate per unit time of the raw water, i.e., dpH/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) x 60]

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.

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

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.

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

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 ^-。

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

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.

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

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。

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

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^-。

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

the raw water in the raw water circulation zone circulates between the raw water circulation zone and the raw water circulation 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.

8. The electrochemical water treatment apparatus according to claim 1, 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.

9. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen as claimed in claim 1, 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.

10. The electrochemical water treatment apparatus capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen as claimed in claim 1, 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.

11. The electrochemical water treatment device capable of removing ammoniacal nitrogen and oxidation byproducts of ammoniacal nitrogen as claimed in claim 1, wherein said reference value is 2.3-3.2 pH change value/min.

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