JPH08155463A - Method and apparatus for decomposing ammoniacal nitrogen nitric-nitrogen and/or nitrous-nitrogen - Google Patents

Abstract

PURPOSE: To provide an ammoniacal nitrogen or the like-decomposing method and apparatus for which halogen compounds are used and which involves the lessened number of processes and scarcely produces by products, in place of method which is proposed as an ammoniacal-nitrogen-decomposing method and for which hypochlorous acid produced by reaction with ozone and bromine is used involves a large number of processes and produces a large quantity of byproducts. CONSTITUTION: A solution 2 for treatment which contains ammoniacal nitrogen and an halogen ion electrolytically treated by using an electrode structural body in which a cathode 4, a diaphragm 5, and an anode 6 are layered successively to anodically oxidize and decompose the ammoniacal nitrogen. Since conversion of halogen ion into hypohalogenous acid, halogenic acid, etc., and contact of the hypohalogenous acid etc., with ammoniacal nitrogen are carried out in a single process without using ozone, the number of processes is lessened and byproducts are decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for decomposing and removing ammoniacal nitrogen, nitrate nitrogen and / or nitrite nitrogen accumulated in waste water or water.

[0002]

[Prior art and its problems] Environmental pollution is becoming more serious and there is an urgent need to solve it. Above all, the nitrogen component contained in wastewater promotes eutrophication of rivers and is also present in drinking water. If it is used as a carcinogen, it shows carcinogenicity, and further, accumulation in a closed system poses a problem even in aquaculture and human waste treatment. Thus, especially in the treatment of wastewater for human waste, sewage, etc., ammoniacal nitrogen has been an important treatment target, and biological treatment (eg, “Industrial water” No. 419, p. 37), aeration treatment, and chlorine oxidation have been conventionally performed. It is decomposed by treatment and removed from the wastewater for use.

The biological treatment is a well-established technique using microorganisms and has a high removal efficiency but is difficult to maintain and manage, and is not suitable for treating highly concentrated wastewater. The aeration process is a technique that aerates a liquid containing ammoniacal nitrogen to the air and keeps the pH alkaline to diffuse it into the atmosphere as gaseous ammonia and remove it, but the removal rate is low and ammonia is not processed. There is a problem that if it is released into the environment, it will cause new environmental pollution. Chlorine oxidation is a technology that converts chlorine into ammonia by injecting chlorine gas or hypochlorous acid, but it is performed in a closed system because harmful substances such as chloramine and nitric acid ions are generated by the reaction of chlorine and ammonia. There is a problem that it is difficult to do. In addition to these, an ion exchange method and a membrane filtration method have been proposed, but they are limited to specific applications in terms of price and maintenance.

Recently, bromine ions are oxidized with ozone to form bromate ions and hypobromite ions, and these ions and ammonia components are rapidly reacted to convert the latter into nitrogen and bromate ions such as bromine. A denitrification process using returning to ions has been proposed [new edition of new technology using ozone (Sanyu Shobo), Chapter 13]. However, this method has the drawback that by-products like nitrate and nitrate ions are produced during the reaction of bromate ions, and a device for generating ozone is required, which requires time and labor for maintenance.

[0005]

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned drawbacks of the technique of decomposing mainly ammoniacal nitrogen using bromine ions, and decomposes and removes ammoniacal nitrogen simply and reliably.
At the same time, it is an object to provide an electrochemical method and apparatus capable of decomposing and removing nitric acid and nitrite nitrogen as well.

According to the present invention, a solution to be treated containing ammoniacal nitrogen, nitrate nitrogen and / or nitrogenous acid nitrite, and halogen ions is electrolyzed to oxidize the halogen ions to form hypohalous acid. And / or an ammoniacal acid that produces a halogen acid and reacts the hypohalous acid and / or halogen acid with the ammoniacal nitrogen, nitrate nitrogen and / or nitrogen nitrite to convert to nitrogen and regenerate halogen ions. It is a method of removing nitrogen and the like, and a nitrogen-containing compound by-produced by electrolysis may be reduced and decomposed at the cathode. The present invention also provides an apparatus that can be used in the method.

Hereinafter, the present invention will be described in detail. The present invention
It is characterized by electrochemically decomposing ammoniacal nitrogen, nitrate nitrogen and / or nitrite nitrogen, which are nitrogen compounds that are difficult to decompose among various pollutants, into nitrogen. The present invention can be used not only for wastewater treatment but also for treatment of water for fish farms where it is desirable to remove ammoniacal nitrogen and the like. Although a local battery method using an oxygen gas diffusion electrode has been proposed as a method for oxidizing and removing hydrazine, formic acid, and formaldehyde in wastewater, an electrochemical method is not currently adopted for decomposing ammoniacal nitrogen and the like.

In the present invention, first, an electrolytic solution containing halogen ions such as bromine ions and chlorine ions is electrolytically oxidized at the anode to produce hypobromic acid, hypochlorous acid, bromic acid, chloric acid and the like.
Thus, depending on the catalyst, bromine and chlorine ions produce bromine and chlorine according to the formula and then they immediately react with water and produce hypobromite and hypochlorous acid according to the formula. Also, a small amount of bromic acid or chloric acid may be produced. Br ⁻ → Br ₂ + 2e ⁻ Cl ⁻ → Cl ₂ + 2e ⁻ Br ₂ + H ₂ O → HBrO + HBr Cl2 + H 2 O → HClO + HCl

Most of the other anodic reactions are oxygen generating reactions (partly ozone generating reactions) according to the formula, although it depends on the ionic species and the electrode catalyst that coexist. 2H ₂ O → O ₂ + 4H ⁺ + 4e When ammonia nitrogen is dissolved in a solution together with the halogen ion or ammonia nitrogen is added to an electrolytic solution in which the halogen ion is already dissolved to electrolyze, the halogen ion becomes hypobromic acid according to the formula. And hypochlorous acid, and these hypobromic acid and hypochlorous acid react with ammonia and form nitrogen according to the formula, and return to the original bromine ion and chlorine ion. Therefore, in the present invention, the halogen ion is not consumed even if the reaction proceeds and it is not necessary to add it. Although hypochlorous acid may produce chloramine and the like by reaction with ammonia, hypochlorous acid produces nitrogen almost quantitatively. Therefore, it is desirable to use bromine ion as the halogen ion.

3HBrO + 2NH ₃ → N ₂ + 3Br ⁻ + 3H ₂ O 3HClO + 2NH ₃ → N ₂ + 3Cl ⁻ + 3H ₂ O These reactions proceed on the alkaline side rather than the neutral side and partly N
Occasionally, intermediate products such as H ₂ Br and NBr ₃ are produced, and nitrate ions may be produced. Also, ammoniacal nitrogen does not react with hypobromite, etc.
Oxidized to Ox. These by-products are relatively small in amount and may not cause a problem if they are discharged as they are, but when they are relatively large, they are introduced into the cathode chamber of the electrolytic cell and subjected to reduction treatment.

Normally, at the cathode, hydrogen ions that have passed through the diaphragm are reduced to generate hydrogen, but the above-mentioned intermediate products, nitrate ions and NOx are reduced to nitrogen or ammonium ions at a base potential on the cathode. Further, when an oxygen-containing gas is supplied to the cathode side, the cathode reaction can be converted from a hydrogen generation reaction to a water generation reaction by reducing oxygen, which can reduce power consumption. As for the oxygen to be supplied, it is preferable that oxygen gas generated by the anodic reaction is captured by the water surface of the anolyte and sent to the cathode surface by an air pump.

According to the present invention, the oxidation of bromine ions, which has been conventionally performed by ozone treatment, can be performed electrolytically at the same time as the oxidation of ammonia nitrogen, etc., so that the number of steps is reduced and an ozone generator is not required, and moreover harmful impurities are eliminated. It can prevent the occurrence and can be processed more economically. The concentration of bromine and chlorine ions used in the present invention depends on the type of liquid to be treated, but it is preferably maintained at 1 to 1000 ppm.

For the electrode, the anode catalyst is preferably a noble metal such as platinum or iridium or an oxide thereof, and the cathode catalyst is preferably platinum, palladium, iridium, copper or silver. These catalysts should be 1 to 500 g / m ² on metal mesh having corrosion resistance such as carbon, titanium, stainless steel, powder sinter, metal fiber sinter by pyrolysis method or resin fixing method. Let it form. An ion exchange membrane is used as the diaphragm, and the ion exchange membrane may be either a fluororesin type or a hydrocarbon resin type. It is preferable that the electrode and the ion exchange membrane are fixed with a bolt and a nut in a tightening pressure of 3 to 100 kgf / cm ² in order to ensure continuity to form an electrode structure. The electrode structure may be formed by coating the particles on the ion exchange membrane. The ion exchange membrane has a function of preventing hypochlorous acid and hypobromite generated at the anode from being consumed at the cathode, and having a function of promptly promoting electrolysis even when the liquid to be treated has a low electric conductivity. . The current density of the reaction is preferably about 1-100 A / dm ² .

FIG. 1 is a vertical cross-sectional view showing an example of an apparatus for decomposing ammoniacal nitrogen or the like according to the present invention. Reference numeral 1 denotes a box-type electrolysis apparatus main body having an open top surface. Inside the main body 1, a liquid to be treated 2 containing ammoniacal nitrogen or the like and a metal halide salt such as sodium bromide, sodium chloride or potassium bromide 2
Is satisfied. Inside the apparatus main body 1, a cylindrical inner cylinder 3 is arranged so that the whole is immersed in the liquid to be treated 2 and the lower end does not contact the inner bottom surface of the main body 1, and the inner cylinder 3
Cathode 4-diaphragm (ion exchange membrane) from the bottom to the bottom inside
An electrode structure 8 which is laminated in the order of 5-anode 6 and which is fastened and integrated with a plurality of bolts 7 at appropriate places on the periphery is connected to the inner surface of the inner cylinder 3 and is supported in a fixed state.

When electricity is applied between both electrodes 4 and 6 of this decomposition apparatus, sodium bromide or the like dissolved in the liquid to be treated 2 is oxidized at the anode 6 and hypobromous acid is produced according to the above formula and. At this time, the gas generated at the same time rises in the inner cylinder 3, so that the liquid to be treated 2 circulates, and the liquid to be treated 2 and the electrodes are brought into contact smoothly. This hypobromous acid reacts with ammoniacal nitrogen and the like according to the above formula to convert most of it to harmless nitrogen. However, some are converted to harmful bromine compounds and nitrogen compounds. These harmful compounds are reduced at the cathode 4 and converted into harmless substances. In the apparatus shown in the figure, ozone is not used for the generation of hypobromous acid, so the generation of harmful impurities is reduced, and the generated impurities can also be decomposed and removed at the cathode, and effective treatment of ammoniacal nitrogen etc. can be achieved. .

FIG. 2 is a vertical cross-sectional view showing another example of the apparatus for decomposing ammoniacal nitrogen etc. according to the present invention. Reference numeral 11 denotes an electrolysis apparatus main body divided into an anode chamber 13 and a cathode chamber 14 by a diaphragm 12, and an anode 15 is closely attached to the anode chamber 13 side of the diaphragm 12 and a cathode 16 is closely attached to the cathode chamber 14 side. is set up.
The bottom surface of the cathode chamber 14 of the apparatus body 11 is connected with a liquid transfer pipe 19 for transferring a solution 17 to be treated in the cathode chamber 14 to a storage tank 18 located below the apparatus body 11, and the storage tank 18 The other end is immersed in the base end of the liquid to be treated supply pipe 21 whose other end is connected to the bottom surface of the anode chamber 13 via the pump 20.

The anode chamber 13 and the cathode chamber 14 are connected by a circulation pipe 22 connecting the upper surfaces thereof, so that the liquid to be treated 23 in the anode chamber 13 can be circulated toward the cathode chamber 14. A branch pipe 24 is branched to the circulation pipe 22, and a waste gas decomposition catalyst device 25 is installed in the branch pipe 24. This disassembly device
When electricity is applied between the both electrodes 15 and 16 of 11, the ammoniacal nitrogen or the like in the liquid 23 to be treated on the side of the anode chamber 13 is decomposed, as in the case of the example of FIG. Circulate to. At this time, the generated gas in the liquid to be treated is taken out from the branch pipe 24, decomposed in the waste gas decomposition catalyst device 25 to be harmless, and then released into the atmosphere.

In some cases, harmful impurities such as nitrate ions may be dissolved in the liquid to be treated supplied to the cathode chamber 14, and the impurities contact the cathode 16 and are decomposed. The liquid to be treated 17 in the cathode chamber 14 is supplied to the storage tank 18 through the liquid to be treated transfer pipe 19. At this point, the treated liquid which has been treated may be discarded, but if the removal of ammonia nitrogen in the liquid to be treated is not complete, it is circulated again to the anode chamber 13 through the treated liquid supply pipe 21. , The disassembly process can be continued. In the device shown in the figure, ozone is not used for the generation of hypobromous acid, and since the liquid to be treated can be repeatedly treated, the generation of harmful impurities is reduced, and the generated impurities are decomposed at the cathode. The target impurities can be completely removed.

[0018]

[Examples] Next, examples relating to the decomposition of ammoniacal nitrogen etc. of the present invention will be described, but the examples do not limit the present invention.

Example 1 1 liter of an aqueous solution in which 100 ppm of ammonium nitrate and 10 ppm of sodium bromide were dissolved was prepared.

A 1: 1 mixed solution of alcohol and lavender was prepared by dissolving platinum and palladium in a molar ratio of 1: 1.
mm, minor axis 2 mm, thickness 0.5 mm), the coating and firing at 500 ° C. were repeated until the total amount of platinum and palladium reached 20 g / m ² to obtain an anode. As the cathode, a glassy carbon porous body having an electrode area of 10 cm ² (Vitrocarbon of Nippon Carbon Co., Ltd., thickness 5 mm) was used, on which platinum was carried by the same method at 50 g / m ² .

Nafion 117 (manufactured by DuPont Japan Co., Ltd.) was used as an ion exchange membrane, and 4 holes were opened in the ion exchange membrane and the corresponding portions of the anode and cathode, and 5 kg / It was tightened with a pressure of m ² to be integrated, and it was housed in this electrode body and the electrolytic cell of FIG. The aqueous solution was contained in the electrolytic cell, and electrolysis was performed at a current density of 15 A / dm ² . Table 1 shows the concentration changes of ammonium ion and nitrate ion in the aqueous solution. After 15 hours, ammonium ion was reduced to 1 ppm and nitrate ion was also halved to 40 ppm.

[0021]

[Table 1]

[0022]

Comparative Example 1 An aqueous solution was electrolyzed under the same conditions as in Example 1 except that sodium bromide was not added, and Table 2 shows the concentration changes of ammonium ion and nitrate ion at that time. Nitrate ion decreased slightly, but ammonium did not change.

[0023]

[Table 2]

[0024]

INDUSTRIAL APPLICABILITY The present invention electrolyzes a liquid to be treated containing ammoniacal nitrogen, nitrate nitrogen and / or nitrous acid, and halogen ions to oxidize the halogen ions, thereby producing hypohalous acid and / or halogen acid. Is produced, and the hypohalous acid and / or halogen acid is reacted with the ammoniacal nitrogen, nitrate nitrogen and / or nitrogen nitrite to convert into nitrogen and regenerate halogen ions. This is a method of decomposing nitrogen and the like.

In the method of the present invention, ozone is not used for the production of hypohalous acid or halogenic acid used in the decomposition of ammoniacal nitrogen, and the formation of hypohalous acid and the like by the oxidation of halogen ions and ammoniacality are carried out. Since it can be performed electrolytically at the same time as the oxidation of nitrogen etc., it reduces the number of processes and eliminates the need for an ozone generator, and also prevents the generation of extra harmful impurities caused by the use of ozone, enabling more economical treatment. Become. Further, it is also possible to decompose and remove impurities that may be by-produced in addition to nitrogen by only electrolytic oxidation by circulating the anolyte to the cathode and performing cathode reduction. Further, in the device of the present invention, since the anode-diaphragm-cathode are integrated and easy to handle, the treatment efficiency of ammoniacal nitrogen and the like is further improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an example of an apparatus for decomposing ammoniacal nitrogen or the like according to the present invention.

FIG. 2 is a vertical cross-sectional view showing another example of the decomposing device for ammonia nitrogen according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electrolytic apparatus main body 2 ... Liquid to be treated 3 ... Inner cylinder 4 ... Cathode 5 ... Diaphragm 6 ... Anode 7 ...
.... Bolts 8 ... Electrolytic structure 11 ... Electrolytic device body 12 ... Separator 13 ... Anode chamber 14 ... Cathode chamber
15 ... Anode 16 ... Cathode 17 ... Liquid to be treated 18 ... Storage tank 19
・ ・ ・ Processed liquid transfer pipe 20 ・ ・ Pump 21 ・ ・ ・ Processed liquid supply pipe 22 ・ ・ ・ Circulation pipe 23 ・ ・ ・ Processed liquid 24 ・ ・ ・ Branch pipe 25 ・ ・ ・ Waste gas decomposition catalyst device

Claims (3)

[Claims] 1. A solution to be treated containing ammoniacal nitrogen, nitrate nitrogen and / or nitrogen nitrite, and halogen ions is electrolyzed to oxidize the halogen ions to generate hypohalous acid and / or halogen acid. Ammoniacal nitrogen and nitric acid characterized by reacting the hypohalogenous acid and / or halogenic acid with the ammoniacal nitrogen, nitrate nitrogen and / or nitrite nitrogen to convert into nitrogen and regenerate halogen ions. A method for decomposing nitrogen and / or nitrogen nitrite. 2. The method according to claim 1, wherein the nitrogen-containing compound by-produced by the oxidation of ammoniacal nitrogen, nitrate nitrogen and / or nitrogen nitrite is cathodically reduced. 3. A liquid to be treated containing ammoniacal nitrogen, nitrate nitrogen and / or nitrogen nitrite, and halogen ions in the main body of the electrolysis device has a gas-liquid permeable anode-diaphragm-gas liquid permeability. It is characterized in that the electrode structure integrated and laminated in the order of the cathode is immersed and housed, and the ammonia nitrogen, the nitrate nitrogen and / or the nitrite nitrogen are anodized and decomposed by applying an electric current between the electrodes. Decomposing device for ammoniacal nitrogen, nitrate nitrogen and / or nitrite.