Method for denitrification of ammonia-nitrogen wastewater by chlorine-oxygen radical

Abstract

A method for denitrifying ammonia nitrogen wastewater containing chlorine-oxygen free radicals is disclosed. The method uses ruthenium dioxide / titanium dioxide (RuO2 / Ti) as the anode and mesoporous carbon-modified carbon paper (CMK-3 / CP) as the cathode. Sodium sulfate, sodium chloride, and iron-modified graphene oxide as the particle electrode are added to the container containing ammonia nitrogen wastewater, forming a dual-electrode and particle-electrode electrochemical ammonia nitrogen denitrification system. Oxygen is then introduced into the cathode region, and the electrolysis current density is controlled to achieve denitrification of the ammonia nitrogen wastewater. This invention utilizes RuO2 / Ti to oxidize chloride ions to active chlorine (ClO2). ‑ Simultaneously, oxygen is reduced to hydrogen peroxide through mesoporous carbon-modified carbon paper, and the generated active chlorine and hydrogen peroxide are enriched in iron-modified graphene oxide particles. The hydrogen peroxide is further absorbed by the Fe atoms in the iron-modified graphene oxide particles. 2+ / Fe 3+ The cyclic catalytic process generates HO•, which can react with active chlorine to generate ClO•. ClO• can selectively oxidize ammonia nitrogen to nitrogen gas, generating high steady-state concentrations of chloroxygen free radicals, thus achieving efficient denitrification treatment of ammonia nitrogen wastewater.

Description

Technical Field

[0001] This invention relates to a technology in the field of environmental engineering, specifically a method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals. Background Technology

[0002] Ammonia nitrogen pollution is a significant cause of eutrophication in water bodies, and its treatment is one of the most challenging aspects of water treatment. Ammonia nitrogen denitrification is achieved through the oxidation of ammonia nitrogen by chloroxygen free radicals, and the use of active chlorine (HClO and ClO generated from the reaction of chlorine gas with water). - Compared with oxidation-based ammonia nitrogen removal, chlorination-based methods offer advantages such as better selectivity, faster N2 conversion rate, immunity to interference from strong oxides like H2O•, and lower levels of toxic byproducts, making them a promising future technology for ammonia nitrogen wastewater removal. ClO• is produced by active chlorine (HClO, ClO...). - ClO• is produced by the reaction of HClO with hydroxyl radicals (HO•) (HClO + HO• → ClO• + H2O). To prepare ClO•, current techniques employ a dual-anodine electrochemical system, where active chlorine (HClO and ClO•) is generated at the two anodes respectively. - (Anode 1) and HO• (Anode 2), then active chlorine reacts with HO• to generate ClO•, while the cathode undergoes a sacrificial hydrogen evolution reaction. Such a system leads to high energy consumption and a sacrificial reaction at the cathode. Furthermore, the formation efficiency and steady-state concentration of ClO• are constrained by the concentrations of HO• and active chlorine, particularly the steady-state concentration of HO•, because HO• has a short half-life, only 1 / 2000 that of ClO•, making it difficult to form a stable, high concentration of HO• in the system. These factors limit the application of ClO• in ammonia nitrogen removal. Summary of the Invention

[0003] This invention addresses the aforementioned shortcomings of existing technologies by proposing a method for denitrifying ammonia nitrogen wastewater containing chloride and oxygen free radicals. It utilizes a ruthenium dioxide / titanium (RuO2 / Ti) anode to oxidize chloride ions into active chlorine (ClO2). - HClO); simultaneously, oxygen is reduced to hydrogen peroxide through a carbon paper (CMK-3 / CP) cathode modified with mesoporous carbon; using iron-modified graphene oxide particles as particle electrodes, the generated active chlorine and hydrogen peroxide are enriched in the iron-modified graphene oxide particles, while the hydrogen peroxide is further absorbed by the Fe in the iron-modified graphene oxide particles. 2+ / Fe 3+ The cyclic catalytic process generates HO•; the generated HO• can react with active chlorine to generate ClO•; ClO• can selectively oxidize ammonia nitrogen in wastewater into nitrogen gas, thereby achieving efficient denitrification treatment of ammonia nitrogen wastewater.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals. The method uses ruthenium dioxide / titanium (RuO2 / Ti) as the anode and mesoporous carbon-modified carbon paper (CMK-3 / CP) as the cathode. Sodium sulfate, sodium chloride, and iron-modified graphene oxide as the particle electrode are added to a container containing ammonia nitrogen wastewater to form a dual-electrode and particle-electrode electrochemical ammonia nitrogen denitrification system. Oxygen is then introduced into the cathode region, and the electrolysis current density is controlled to achieve denitrification of the ammonia nitrogen wastewater.

[0006] The electrolytic constant current density is 2~5 mA cm⁻¹ -2 .

[0007] The concentration of sodium sulfate is 0.02~0.1 mol / L.

[0008] The concentration of sodium chloride is 0.05~0.15 mol / L.

[0009] The aforementioned particle electrode is prepared as follows: 60 mg of graphene oxide and 5-15 mg of nano-iron powder are ultrasonically dispersed in 30 mL of ultrapure water for 30-60 minutes. Then, 300 mg of ascorbic acid is added to the dispersion and stirred for 10-30 minutes to form a mixture. 3 mL of the mixture is placed in a sample vial and placed in a 95°C water bath for 2-3 hours to form a Fe-containing electrode. 2+ / Fe 3+ Iron-modified graphene oxide particle electrodes.

[0010] The cathode is prepared by mixing 40 mg of mesoporous carbon (CMK-3), 2 mL of pure water, 10 mL of ethanol and 250 μL of Nafion (5%) solution to form a precursor. 1-3 mL of the precursor is then uniformly drop-coated onto the hydrophilic layer of cleaned carbon paper. The carbon paper with the precursor drop-coated is then placed in a muffle furnace and heated at 360°C for 30 minutes to obtain the CMK-3 / CP cathode.

[0011] Technical effect

[0012] Compared to active chlorine-based ammonia nitrogen removal, ClO• oxidation of ammonia nitrogen to N2 offers better selectivity, faster denitrification rate, and is less affected by strong oxides such as HO•, with lower levels of toxic byproducts. However, existing electrochemical techniques for preparing ClO•, employing a dual-anodine electrochemical system, suffer from high energy consumption and low ClO• concentration, limiting their application and development in ammonia nitrogen wastewater denitrification. This invention designs the active chlorine and HO• required for the ClO• generation reaction directly / indirectly on the anode and cathode, respectively, fully utilizing the reduction potential of the cathode and avoiding complete sacrificial reactions at the cathode. This results in advantages such as low energy consumption and high ClO• concentration. In the cathode reaction design, oxygen-doped mesoporous carbon (CMK-3) material with abundant catalytic active centers is loaded onto the hydrophilic layer of carbon paper to enhance electron transport and catalytic activity at the cathode, thereby significantly improving the yield of H2O2 at the cathode. To increase the concentrations of active chlorine and H₂O₂ required for ClO₂• generation, this invention also introduces iron-modified graphene oxide particle electrodes into the electrochemical system. These iron-modified graphene oxide particle electrodes possess the functions of easy polarization, easy conduction, easy adsorption, and easy enrichment of active chlorine and H₂O₂. These functions synergistically promote the Fe₂O₃ formation of iron in the graphene particle electrode. 2+ / Fe 3+ The cyclic catalytic decomposition of H2O2 facilitates the generation of a large amount of HO•, which then reacts in situ with the active chlorine adsorbed on the particle electrode to produce a high concentration of ClO•, ultimately achieving a highly efficient ammonia nitrogen removal reaction. Compared with HO•, ClO• has advantages such as higher steady-state concentration, longer half-life, moderate oxidation potential, and higher reaction rate with ammonia nitrogen. Therefore, it can avoid interference from strong oxidizing substances such as HO•, exhibiting extremely high selectivity for ammonia nitrogen removal and significantly reducing the generation of toxic byproducts in ammonia nitrogen removal. Attached Figure Description

[0013] Figure 1 This is a comparison graph of the concentrations of hydroxyl radicals and chloroxylenoids in Example 1 and the concentrations in the control example;

[0014] Figure 2 This is the concentration change of various nitrogen-containing compounds during the ammonia nitrogen oxidation process in Example 1. Detailed Implementation

[0015] Example 1

[0016] This embodiment relates to a method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals. The electrochemical ammonia nitrogen denitrification system uses ruthenium dioxide / titanium (RuO2 / Ti) as the anode, mesoporous carbon-modified carbon paper (CMK-3 / CP) as the cathode, and iron-modified graphene oxide as the particle electrode. The treatment target is ammonia nitrogen wastewater with a concentration of 50 mg / L. The electrolytes are 0.05 mol / L sodium sulfate and 0.05 mol / L sodium chloride. By introducing oxygen into the cathode region and controlling the electrolysis constant current density, an electrochemical ammonia nitrogen denitrification system with dual electrodes and particle electrodes is formed to achieve the denitrification treatment of ammonia nitrogen wastewater.

[0017] The iron-modified graphene oxide particle electrode is prepared by ultrasonically dispersing 60 mg of graphene oxide and 10 mg of nano-iron powder in 30 mL of ultrapure water for 60 minutes, then adding 300 mg of ascorbic acid to the dispersion and stirring for 30 minutes to form a mixture. 3 mL of this mixture is then placed in a sample vial and placed in a 95°C water bath for 2 hours to form an electrode containing Fe. 2+ / Fe 3+ Iron-modified graphene oxide particle electrodes.

[0018] The cathode is prepared by uniformly mixing a solution containing 40 mg CMK-3, 2 mL of pure water, 10 mL of ethanol and 250 μL of Nafion (5%) to form a precursor, and then uniformly drop-coating 2 mL of the precursor onto the hydrophilic layer of cleaned carbon paper. The carbon paper with the precursor drop-coated is then placed in a muffle furnace and heated at 360°C for 30 minutes.

[0019] The aforementioned ammonia nitrogen removal is achieved by applying a constant current density of 4 mA cm⁻¹ to the cathode and anode. -2 Electrolysis is performed, causing the RuO2 / Ti anode to oxidize chloride ions to active chlorine (ClO2). - The CMK-3 / CP cathode reduces oxygen to hydrogen peroxide (HClO). The generated active chlorine and hydrogen peroxide are enriched in iron-modified graphene oxide particles, while the hydrogen peroxide is further absorbed by the Fe atoms in the iron-modified graphene oxide particles. 2+ / Fe 3+ The cyclic catalytic reaction generates HO•, which reacts with active chlorine to form ClO•. ClO• selectively oxidizes ammonia nitrogen to nitrogen gas. After 45 minutes of reaction, the ammonia nitrogen removal rate is 99.9%, with a nitrogen removal rate of 97.8% and an ammonia nitrogen removal rate of 1.09 mg / L. -1m in -1 .

[0020] The following uses a comparative example to illustrate the effect of Example 1:

[0021] As a control, with other conditions remaining unchanged in Example 1, FeSO4 solution was used instead of the iron-modified graphene oxide particle electrode as the Fe2SO4 decomposition electrode for hydrogen peroxide decomposition. 2+ / Fe 3+ The circulating catalyst, with all other conditions unchanged, served as the control group, and its performance was compared with that described by Nan Chen et al. in "Unveiling the Key Roles of Various Reactive Species for Ammonia Oxidation in an Efficient Three-Dimensional Electrocatalytic System and Enlarged Scale Study for the Treatment of Practical Wastewater" (ACS ES&TWater 2022, 2, 6, 1132-1142), as shown in Table 1.

[0022] Table 1. Comparison of parameters between Example 1, the control group, and the prior art.

[0023] As shown in Table 1, the present invention demonstrates better selectivity and removal rate.

[0024] like Figure 1 As shown, the concentrations of hydroxyl radicals and chloroxyl radicals in the bulk phase generated by the chloroxyl radical formation method designed in the example are significantly higher than the concentrations of radicals generated in the control group. Figure 2 As shown, the denitrification method for ammonia nitrogen wastewater based on chlorine-oxygen free radicals designed in Example 1 achieved a denitrification rate of 97.8%.

[0025] Example 2

[0026] This embodiment relates to a method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals. The electrochemical ammonia nitrogen denitrification system uses ruthenium dioxide / titanium (RuO2 / Ti) as the anode, mesoporous carbon-modified carbon paper (CMK-3 / CP) as the cathode, and iron-modified graphene oxide as the particle electrode. The treatment target is ammonia nitrogen wastewater with a concentration of 50 mg / L. The electrolytes are 0.02 mol / L sodium sulfate and 0.1 mol / L sodium chloride. By introducing oxygen into the cathode region and controlling the electrolysis constant current density, an electrochemical ammonia nitrogen denitrification system with dual electrodes and particle electrodes is formed to achieve the denitrification treatment of ammonia nitrogen wastewater.

[0027] The graphene oxide particles were prepared by ultrasonically dispersing 60 mg of graphene oxide and 5 mg of nano-iron powder in 30 mL of ultrapure water for 30 minutes, then adding 300 mg of ascorbic acid to the dispersion and stirring for 10 minutes to form a mixture. 3 mL of this mixture was then placed in a sample vial and placed in a 95°C water bath for 2 hours to solidify, forming a Fe-containing... 2+ / Fe 3+ Iron-modified graphene oxide particle electrodes.

[0028] The cathode is prepared by uniformly mixing a precursor containing 40 mg CMK-3, 2 mL ultrapure water, 10 mL ethanol and 250 μL Nafion (5%) solution, uniformly drop-coating 1 mL of the precursor onto the hydrophilic layer of cleaned carbon paper, and then placing the carbon paper coated with the precursor in a muffle furnace and heating it at 360°C for 30 minutes.

[0029] The aforementioned ammonia nitrogen removal is achieved by applying a constant current density of 2 mA cm⁻¹ between the cathode and anode. -2 Electrolysis is performed, causing the RuO2 / Ti anode to oxidize chloride ions to active chlorine (ClO2). - The CMK-3 / CP cathode reduces oxygen to hydrogen peroxide (HClO). The generated active chlorine and hydrogen peroxide are enriched in iron-modified graphene oxide particles, while the hydrogen peroxide is further absorbed by the Fe atoms in the iron-modified graphene oxide particles. 2+ / Fe 3+ The cyclic catalytic reaction generates HO•, which reacts with active chlorine to form ClO•. ClO• selectively oxidizes ammonia nitrogen to nitrogen gas. After 60 minutes of reaction, the ammonia nitrogen removal rate is 93.6%, with an ammonia nitrogen denitrification rate of 90.1% and an ammonia nitrogen removal rate of 0.78 mg / L. -1m in -1 .

[0030] Example 3

[0031] This embodiment relates to a method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals. The electrochemical ammonia nitrogen denitrification system uses ruthenium dioxide / titanium (RuO2 / Ti) as the anode, mesoporous carbon-modified carbon paper (CMK-3 / CP) as the cathode, and iron-modified graphene oxide as the particle electrode. The treatment target is ammonia nitrogen wastewater with a concentration of 50 mg / L. The electrolytes are 0.1 mol / L sodium sulfate and 0.15 mol / L sodium chloride. By introducing oxygen into the cathode region and controlling the electrolysis constant current density, an electrochemical ammonia nitrogen denitrification system with dual electrodes and particle electrodes is formed to achieve the denitrification treatment of ammonia nitrogen wastewater.

[0032] The graphene oxide particles were prepared by ultrasonically dispersing 60 mg of graphene oxide and 15 mg of nano-iron powder in 30 mL of ultrapure water for 60 minutes, then adding 300 mg of ascorbic acid to the dispersion and stirring for 30 minutes to form a mixture. 3 mL of this mixture was then placed in a sample vial and placed in a 95°C water bath for 3 hours to form a sample containing Fe. 2+ / Fe 3+ Iron-modified graphene oxide particle electrodes.

[0033] The cathode is prepared by uniformly mixing a precursor containing 40 mg CMK-3, 2 mL ultrapure water, 10 mL ethanol and 250 μL Nafion (5%) solution, and uniformly drop-coating 3 mL of the precursor onto the hydrophilic layer of cleaned carbon paper. The carbon paper coated with the precursor is then placed in a muffle furnace and heated at 360°C for 30 minutes.

[0034] The aforementioned ammonia nitrogen removal is achieved by applying a constant current density of 5 mA cm⁻¹ between the cathode and anode. -2 Electrolysis is performed, causing the RuO2 / Ti anode to oxidize chloride ions to active chlorine (ClO2). - The CMK-3 / CP cathode reduces oxygen to hydrogen peroxide (HClO). The generated active chlorine and hydrogen peroxide are enriched in iron-modified graphene oxide particles, while the hydrogen peroxide is further absorbed by the Fe atoms in the iron-modified graphene oxide particles. 2+ / Fe 3+ The cyclic catalytic reaction generates HO•, which reacts with active chlorine to form ClO•. ClO• selectively oxidizes ammonia nitrogen to nitrogen gas. After 30 minutes of reaction, the ammonia nitrogen removal rate is 94.67%, with an ammonia nitrogen denitrification rate of 92.8% and an ammonia nitrogen removal rate of 1.57 mg / L. -1m in -1 .

[0035] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals, characterized in that, With ruthenium dioxide / titanium as anode, mesoporous carbon modified carbon paper as cathode, adding sodium sulfate, sodium chloride and iron modified graphene oxide particle electrode containing Fe 2+ / Fe 3+ to the container containing ammonia nitrogen wastewater, a double electrode and particle electrode electrochemical ammonia nitrogen denitrification system are formed, oxygen is passed to the cathode area and the constant current density of electrolysis is controlled to realize the denitrification treatment of ammonia nitrogen wastewater.

2. The method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals according to claim 1, characterized in that, The electrolytic constant current density is 2~5 mA cm⁻¹ -2 .

3. The method for denitrification of ammonia nitrogen wastewater by chlorine and oxygen free radicals according to claim 1, characterized in that, The concentration of sodium sulfate is 0.02~0.1 mol / L.

4. The method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals according to claim 1, characterized in that, The concentration of sodium chloride is 0.05~0.15 mol / L.

5. The method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals according to claim 1, characterized in that, The aforementioned particle electrode is prepared as follows: 60 mg of graphene oxide and 5-15 mg of nano-iron powder are ultrasonically dispersed in 30 mL of ultrapure water for 30-60 minutes. Then, 300 mg of ascorbic acid is added to the dispersion and stirred for 10-30 minutes to form a mixture. 3 mL of the mixture is placed in a sample vial and placed in a 95°C water bath for 2-3 hours to form a Fe-containing electrode. 2+ / Fe 3+ Iron-modified graphene oxide particle electrodes.

6. The method for denitrifying ammonia nitrogen wastewater containing chlorine and oxygen free radicals according to claim 1, characterized in that, The cathode is prepared by mixing 40 mg CMK-3, 2 mL of pure water, 10 mL of ethanol and 250 μL of 5% Nafion solution to form a precursor. 1-3 mL of the precursor is then uniformly drop-coated onto the hydrophilic layer of cleaned carbon paper. The carbon paper with the precursor drop-coated is then placed in a muffle furnace and heated at 360°C for 30 minutes to obtain the CMK-3 / CP cathode.

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