WO2020032312A1 - Method for treating nitrate nitrogen in water - Google Patents

Abstract

The present invention relates to a method for treating nitrate nitrogen in water and, particularly, to a method for treating nitrate nitrogen in wastewater, sewage, or purified water by electrolysis without using denitrifying microorganisms or chemicals. Preferably, the method for treating nitrate nitrogen in water, according to the present invention, is a method for treating nitrate nitrogen in water by using an electrolysis device, wherein nitrogen gas or ammonium ions are generated from a reduction reaction of nitrate nitrogen on the surface of a negative electrode, and the ammonium ions are reduced into nitrogen gas by chlorine gas generated at a positive electrode.

Description

How to Treat Nitric Acid Nitrogen in Water

The present invention relates to a method for treating nitrate nitrogen in water, and more particularly, to a method for treating nitrate nitrogen in wastewater, sewage, or purified water without using denitrifying microorganisms or chemicals.

With the development of various industrial environments, there are many cases where a large amount of nitrate nitrogen is contained in wastewater, sewage or purified water. In order to treat nitrate nitrogen in water, a method of reducing nitrate nitrogen using a denitrifying microorganism is generally used.

However, denitrifying microorganisms are of other nutrients and are sensitive to carbon sources, microbial toxic substances, dissolved oxygen concentrations, water temperatures, hydrogen ion concentrations, microbial concentrations, volume loads, and the like, and are difficult to recover when a trouble occurs.

Various documents have been published with regard to the treatment of nitrate nitrogen in water.

In Korean Patent No. 10-0980636, nickel or copper foam is plated with palladium (Pd), or copper (Cu) is plated with nickel and then palladium is plated using an electrolysis device having a negative electrode. A method of treating acidic nitrogen is disclosed. However, palladium is a very expensive metal, and since the electrode surface itself is close to zero dimension, the electrode specific surface area is not wide, which limits the application of high current density, and the hydrogen trapping ability is also lowered, so that the efficiency of removing nitrate nitrogen is not high. .

In addition, Korean Laid-Open Patent Publication No. 2006-0026510 discloses an apparatus and method for removing nitrogen components such as nitrate nitrogen by removing sludge from desulfurized wastewater, followed by direct electrolysis to remove bonds of hardly decomposable NS compounds. Doing.

It is an object of the present invention to provide a method for effectively treating nitrate nitrogen in wastewater, sewage or purified water using an electrolysis device.

The above problem is a method for treating nitric acid in water using an electrolysis device, wherein nitrogen gas or ammonium ions are generated by the reduction reaction of nitrate nitrogen on the surface of the cathode, and the ammonium ions are generated by chlorine gas generated at the anode. It is achieved by a process for treating nitric acid in water, characterized in that it is reduced to nitrogen gas.

Preferably, the cathode may be made of a plate, mesh or perforated titanium substrate and a nanostructure formed on the substrate.

Also preferably, the anode may be coated with iridium oxide or ruthenium oxide on a plate, mesh, or perforated titanium substrate.

Also preferably, the anode may be coated with a mixed solution of iridium oxide or ruthenium oxide and a binder on the titanium substrate.

The treatment method of the present invention has excellent economical efficiency compared to the treatment method using denitrification microorganisms, is easy to solve when a problem occurs, and can keep the water quality of the effluent constant.

1 schematically shows an electrolysis apparatus for treating nitrate nitrogen according to the present invention.

2 is a schematic diagram of the electrode modules 11 and 12 in one embodiment according to the present invention.

Figure 3 is a photograph of the negative electrode surface of the electrolysis device according to the present invention.

Figure 4 is a graph showing the composition of the anode and cathode of the electrolysis device according to the present invention and the treatment efficiency of nitrate nitrogen over time.

5 is a graph showing the configuration of the anode and cathode of the electrolysis device of the present invention and the treatment efficiency of nitrate nitrogen over time.

Figure 6 is a graph showing the treatment efficiency of the nitrate nitrogen according to the coating component difference of the positive electrode of the electrolysis device of the present invention.

Unless defined otherwise, all technical terms used in the present invention have the following definitions and conform to the meanings commonly understood by those skilled in the art in the relevant field of the present invention. In addition, although a preferred method or sample is described herein, similar or equivalent things are included in the scope of the present invention.

The term "about" means 30, 25, 20, 15, 10, 9, 8, 7, 6, 5, by reference quantity, level, value, number, frequency, percentage, dimension, size, amount, weight, or length. By amount, level, value, number, frequency, percentage, dimension, size, amount, weight or length, varying by 4, 3, 2 or 1%.

Throughout this specification, the terms "comprises" and "comprising", unless otherwise indicated in the context, include a given step or component, or group of steps or components, but any other step or component, or It is to be understood that it does not exclude a step or group of components.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

The present invention treats nitrate nitrogen in wastewater, sewage or purified water using an electrolysis device having an anode and a cathode. 1 schematically shows an electrolysis device 10 for treating nitric acid nitrogen according to the present invention. The electrolysis device 10 includes electrode modules 11 and 12, a chamber 13, and a rectifier 14, in which an anode and a cathode are arranged alternately, and inside and outside of the chamber 13 together with the electrode module. Baffles 15 for equalizing the flow rate are provided at the inlet and outlet, respectively. The electrolysis apparatus includes a plurality of electrode modules. The method of connecting the plurality of electrode modules is advantageous in the bipolar method of connecting the positive electrode and the negative electrode in series, but the monopolar method of connecting the positive electrode to the positive electrode and the negative electrode to the negative electrode is also possible. Do.

2 is a schematic diagram of the electrode modules 11 and 12 in one embodiment according to the present invention.

The anode may be prepared by coating a titanium group metal with iridium oxide (IrOx) or ruthenium oxide (RuOx) alone, or by coating a mixture of the platinum group metal oxide and a binder. The binder may be a transition metal, detanium (Ta) or titanium (Ti).

The manufacturing method of the positive electrode is as follows. First, the plate, mesh, or perforated titanium plate is sanded, and 40 to 100 ° C., 5 in acetone, hydrochloric acid, nitric acid, acetic acid, sulfuric acid, oxalic acid, or one or more mixed aqueous solutions (10 to 90% concentration) as a cleaning solution. Chemical etching is performed under immersion conditions for 10 minutes to 10 minutes. After the etching step, the plate is dried until all of the moisture evaporates under the conditions of 50 to 100 ° C., and the coating chemical is repeatedly coated several times by brush or dipping or spraying or electrostatic coating, and then pyrolyzed at 400 to 700 ° C. It can manufacture. The coating agent is H ₂ IrCl ₆ , IrCl _3, K ₂ IrCl ₆ as an iridium compound, but ruthenium oxide (RuOx) or RuCl ₃ as a ruthenium compound. Etc. can be used. According to one embodiment of the present invention, H ₂ IrCl ₆ , IrCl ₃ , K ₂ IrCl ₆ and the like dissolved in an organic solvent such as butanol or isopropyl alcohol at 50 ~ 500g / L to coat the titanium plate and thermally decompose An electrode of iridium oxide (IrO ₂ ) may be manufactured. According to another embodiment of the present invention, ruthenium oxide (RuOx) or RuCl ₃ is dissolved in 50-500 g / L butanol or isopropyl alcohol to coat the titanium plate, and pyrolyzed to electrode of ruthenium oxide (RuO ₂ ) Can be prepared.

In the preparation of the positive electrode, the ruthenium compound or the iridium compound may be mixed, and preferably, iridium is mixed with ruthenium in a molar ratio of 0.1: 99.9 to 99.9: 0.1, and 50 to 500 g / L is dissolved in butanol or isopropyl alcohol. And RuO ₂ / IrO ₂ mixed electrode can be prepared by coating, coating and pyrolysis. Preferably, iridium oxide or ruthenium oxide may be coated alone.

According to one embodiment of the present invention, in the preparation of the cathode coating drug, a ruthenium compound or an iridium compound and a binder material such as Ti, Ta, Sn may be mixed. However, when the content of the binder Ti, Ta, Sn in the coating chemicals is very small or absent, the efficiency of the reduction of nitrate nitrogen may be better.

The cathode is a titanium substrate formed with a nanostructure, and is produced by growing the nanostructure on the plate, mesh, or perforated titanium plate by anodizing method. Prior to the formation of the nanostructures, sand blast, which is a physical surface treatment, is used to secure roughness of 1 μm or more on the surface of the titanium substrate, and chemical etching is performed at 20 ° C. for 20 minutes using 20% hydrochloric acid as a chemical. In the step of forming the nanostructure, HF, NH ₄ F is added to the distilled water at a concentration of 0.1% or more to prepare an electrolyte solution, the titanium plate is immersed and a voltage of 8V or more, preferably 10 ~ 150V applied To form a nanostructure. The water temperature of the electrolyte solution may be in the range of 10 ~ 90 ℃, more preferably 20 ~ 50 ℃, the treatment time is preferably 1 hour to 3 hours. The size of the nanostructure is more than 30um in the depth direction is advantageous in terms of efficiency.

The nitrate nitrogen treatment process in the electrolysis tank having the positive electrode and the negative electrode is as follows.

First, raw water to be treated is introduced into the chamber and voltage is applied to the anode and cathode. At this time, the reduction reaction of nitrate nitrogen ions occurs on the surface of the cathode as shown in Schemes 1 and 2 below.

Scheme 1

^{_{NO 3 - + 3H 2 O +}} 5e - → 0.5N 2 + 6OH -

Scheme 2

^{_{NO 3 - + 7H 2 O +}} 8e - → NH 4 + + 10OH -

Both reactions occur at the electrode surface, and the reaction of directly reducing nitrogen gas (N ₂ ) as in Scheme 1 is effective in nitrogen treatment, but some are reduced to HN ₄ ⁺ as in Scheme 2. In most cases, Scheme 1 predominates.

At the positive electrode, the following reaction schemes 3 to 5 are generated to generate HOCl or OCl ⁻ .

Scheme 3

2Cl ^- → Cl ₂ + 2e ^-

Scheme 4

Cl ₂ + H ₂ O → HOCl + HCl

Scheme 5

HOCl ↔ OCl ^{- +} H +

HN ₄ ⁺ generated at the cathode reacts with OCl ⁻ generated at the cathode as shown in Scheme 6 below, eventually generating N ₂ to be removed.

Reaction Schemes 1 and 2 are reactions at the cathode surface, and the ratio of Reaction Scheme 1 predominates, and may be converted into NH ₄ ⁺ by some reactions of Scheme 2. NH ₄ ^{+ is} also a pollutant when discharged. However, Cl ₂ is generated by Scheme 3, the anodic reaction, and is finally present as HOCl or OCl ⁻ by the hydrolysis and ionization reactions of Schemes 4 and 5. At this time, since NH ₄ ⁺ is finally discharged from the water as N ₂ gas by the following Scheme 6, all of the nitrate nitrogen in the treated water can be removed.

Scheme 6

_{^{OCl - + HN 4 + + OH}} - → 0.5N 2 + H + + Cl - + 2H 2 O

Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited by these Examples.

Experimental Example 1

In the electrolysis apparatus of FIG. 1, the anode is a substrate coated with RuO ₂ / Ti on a titanium substrate, and the cathode is composed of a Ti or TiO ₂ nanostructured substrate, respectively. Example 1, the treated water was 3000 mg / L NaNO ₃ , the electrolyte was 0.5% Na ₂ SO ₄ , and in Example 2 the treated water was 3000 mg / L NaNO ₃ and the electrolyte was 1% NaCl. The treatment efficiency of nitrogen was measured. The current density was 0.04 A / cm ² , and the processing efficiency over time was measured and shown in FIGS. 4A (Example 1) and 4B (Example 2). 4A and 4B, when the negative electrode is titanium having a nano structure, it can be seen that the treatment efficiency of nitrate nitrogen is very excellent as compared with the case where the negative electrode is a titanium disc.

Experimental Example 2

In the electrolytic apparatus of FIG. 1, the anode is a substrate coated with RuO ₂ on a titanium substrate, the cathode is composed of a TiO ₂ nanostructured substrate (Example 3), and the anode is an IrO ₂ coated substrate on a titanium substrate. And the cathode constituted a case composed of a substrate having a TiO ₂ nanostructure (Example 4). The treated water was 3000 mg / L NaNO ₃ , the electrolyte was 0.5% Na ₂ SO ₄ or 1% NaCl, the current density was 0.04 A / cm ² , and the treatment efficiency over time was measured. 5A is a result graph of Example 3, and FIG. 5B is a result graph of Example 4. FIG. 5A and 5B, when ruthenium was used as the anode, both of the electrolytes were effective in NaCl and Na ₂ SO ₄ . In addition, in the case of using iridium as the anode, if the electrolyte is NaCl, the treatment efficiency is relatively unstable, but after 60 minutes, similar results to Na ₂ SO ₄ can be confirmed. Therefore, it can be seen that both the ruthenium anode and the iridium anode are effective for removing nitrate nitrogen.

Experimental Example 3

The difference in treatment efficiency according to the coating composition of the anode of the electrolysis device was measured.

In the electrolysis apparatus of FIG. 1, the cathodes were all composed of TiO ₂ nanostructures, and the composition of the coating solution of the anode was changed. The treated water was 3000 mg / L NaNO ₃ , the electrolyte was 0.5% Na ₂ SO ₄ , and the current density was 0.04 A / cm ² . 100% RuO ₂ /0% Ta ₂ O ₅ , 90% RuO ₂ /10% Ta ₂ O ₅ , 80% RuO ₂ /20% Ta ₂ O ₅ , 70% RuO ₂ /30% Ta ₂ O ₅ , 60% RuO ₂ /40% Ta ₂ O ₅ , 50% RuO ₂ /50% Ta ₂ O ₅ , and the nitrate nitrogen removal efficiency over time were measured and shown in FIG. 6A.

In addition, the positive electrode was 100% IrO ₂ /0% Ta ₂ O ₅ , 90% IrO ₂ /10% Ta ₂ O ₅ , 80% IrO ₂ /20% Ta ₂ O ₅ , 70% IrO ₂ /30% Ta ₂ It was composed of O ₅ , 60% IrO ₂ /40% Ta ₂ O ₅ , 50% IrO ₂ /50% Ta ₂ O ₅ , and the nitrate nitrogen removal efficiency over time was measured and shown in FIG. 6B. 6A and 6B, 100% RuO ₂ without binder in the coating solution of the positive electrode And in the case of 100% IrO ₂ , it is confirmed that the removal efficiency of the nitrate nitrogen is very excellent, the removal efficiency of the nitrate nitrogen decreases as the content of the binder increases.

Having described the specific part of the present invention in detail, it is apparent to those skilled in the art that such a specific technology is merely a preferred embodiment, and the scope of the present invention is not limited thereto. Therefore, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof.

Claims (4)

1. As a method for treating nitric acid in water using an electrolysis device,

   Nitrogen gas or ammonium ions are produced by the reduction reaction of nitrate nitrogen on the surface of the cathode, the ammonium ion is reduced to nitrogen gas by the chlorine gas generated at the anode, nitric acid treatment method in water.
2. The method of claim 1, wherein the cathode comprises a plate, mesh, or perforated titanium substrate and a nanostructure formed on the substrate.
3. The method of claim 1, wherein the anode is coated with iridium oxide or ruthenium oxide on a titanium substrate that is plate, mesh, or perforated.
4. The method of claim 3, wherein the anode is coated with a mixed solution of iridium oxide or ruthenium oxide and a binder on the titanium substrate.

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