Method for electrochemical removal of nitrate nitrogen from salt-containing wastewater

Abstract

The application discloses a treatment method for electrochemically removing nitrate nitrogen in salt-containing wastewater. The electrochemical reactor comprises a cathode reduction zone, an intermediate screen and an anode oxidation zone. The mesh of the intermediate screen is 50-300 meshes, and the thickness is 1.0-10.0 mm. The treatment method comprises the following steps: the salt-containing wastewater enters the reactor from the cathode reduction zone, and is subjected to a reduction reaction in an alkaline environment, then passes through the intermediate screen and enters the acid anode oxidation zone, and the hydroxyl radicals generated by the anode are used to convert the intermediate product of nitrate nitrogen in the wastewater into nitrogen, so that the purified wastewater is obtained. The method can improve the selectivity of the conversion of nitrate nitrogen into nitrogen, effectively alleviate the occurrence of the side reaction that the intermediate product of nitrate nitrogen is further oxidized into the original nitrate nitrogen, is more operable, and has a higher removal rate of nitrate nitrogen and total nitrogen.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for electrochemical removal of nitrate nitrogen from saline wastewater. Background Technology

[0002] Nitrate pollution has become a widespread environmental problem globally due to its high solubility, stability, and fluidity. Electrochemical technology, with its advantages of simple and controllable operation, high degree of automation, good safety, and no environmental pollution, has broad application prospects in the field of nitrate removal from high-salinity wastewater.

[0003] CN201510358016.X discloses a method for efficiently removing nitrates from groundwater using a Ti nanoelectrode. This method uses a prepared Ti nanoelectrode as the cathode and a Ti / Pt electrode as the anode to electroreducively treat nitrate nitrogen containing sodium sulfate. However, this method treats relatively low concentrations of nitrate nitrogen (25–100 mg / L) and low salt concentrations (0.1–1.0 g / L). Furthermore, the single-tank system carries the risk of further reduction of the nitrite nitrogen intermediate produced during reduction to nitrate nitrogen, and the reduction conditions at the cathode and oxidation conditions at the anode cannot be independently controlled, leading to a decrease in the removal rates of both nitrate nitrogen and total nitrogen.

[0004] CN201610010197.6 discloses a method for removing nitrates from water using bimetals as reducing agents. This method first involves adding iron-copper bimetallic flakes to wastewater to adjust its pH value. A primary reduction reaction occurs under air-isolated conditions, followed by filtration and collection of the filtrate. The pH value of the filtrate is then adjusted, and urea is added for a secondary reduction reaction under air-isolated conditions. CN201610010067.2 discloses a method for removing nitrate nitrogen from wastewater, which involves sequentially adding zinc-silver bimetallic fragments, disodium ethylenediaminetetraacetate, ferrous sulfate heptahydrate, and sodium sulfite to the wastewater to remove nitrate nitrogen. However, these methods often introduce impurities during nitrate nitrogen removal, posing a risk of secondary water pollution. Furthermore, these methods are relatively cumbersome and complex to operate. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for the electrochemical removal of nitrate nitrogen from saline wastewater. This method improves the selectivity of the direct reduction of nitrate nitrogen to nitrogen gas, effectively mitigates the side reaction of further oxidation of nitrite nitrogen intermediates back to original nitrate nitrogen, offers greater operability, and achieves higher removal rates of both nitrate nitrogen and total nitrogen.

[0006] The present invention provides an electrochemical method for removing nitrate nitrogen from saline wastewater. The electrochemical reactor comprises a cathode reduction zone, an intermediate partition screen, and an anodic oxidation zone. The intermediate partition screen has a mesh size of 50–300 mesh and a thickness of 1.0–10.0 mm, preferably 2.0–8.0 mm. The treatment method includes: saline wastewater entering the reactor from the cathode reduction zone, undergoing a reduction reaction in an alkaline environment, and then passing through the intermediate partition screen into an acidic anodic oxidation zone. Hydroxyl radicals generated at the anode convert the intermediate nitrate nitrogen in the wastewater into nitrogen gas, resulting in purified wastewater.

[0007] In this invention, an inlet is provided at the bottom of the cathode reduction zone and an outlet is provided at the bottom of the anodic oxidation zone in the electrochemical reactor.

[0008] In this invention, an intermediate partition is installed within the electrochemical reactor to divide the reaction zone into a cathodic reduction zone and an anodic oxidation zone. The cathodic reduction zone is equipped with a cathode, and the anodic oxidation zone is equipped with an anode.

[0009] In this invention, the volume ratio of the cathode reduction zone to the anodic oxidation zone is 10:1 to 4:1, preferably 9:1 to 5:1.

[0010] In this invention, the intermediate partition mesh can be one or more of the following: insulating ceramic mesh, rubber mesh, nylon mesh, PVC mesh, etc. The porosity of the intermediate partition mesh is 50%–95%, preferably 80%–95%.

[0011] In this invention, the cathode can be at least one of graphite electrode, platinum electrode, stainless steel electrode, iron electrode, zinc electrode, copper electrode, nickel electrode, titanium electrode, aluminum electrode, copper-nickel alloy electrode, copper-tin alloy electrode, etc., preferably at least one of stainless steel electrode, nickel electrode, titanium electrode, copper-nickel alloy electrode, etc.

[0012] In this invention, the anode can be at least one of diamond thin film electrode, lead dioxide electrode, tin dioxide electrode, manganese dioxide electrode, graphite electrode, platinum electrode, ruthenium-iridium electrode, iridium-tin electrode, ruthenium-tantalum electrode, ruthenium-iridium-tin electrode, ruthenium-iridium-tantalum electrode, etc., preferably at least one of diamond thin film electrode, lead dioxide electrode, tin dioxide electrode.

[0013] In this invention, preferably, at least one of persulfate, permonosulfate, hydrogen peroxide, and sodium percarbonate is exogenously added to the anodic oxidation zone, and more preferably at least one of persulfate and sodium percarbonate.

[0014] In this invention, the persulfate ion is in the form of S2O8. 2- Calculate and / or persulfate ions with HSO5 - Calculated with nitrate nitrogen as NO3 -The calculated molar ratio is 1:1 to 6:1, preferably 2:1 to 4:1.

[0015] In this invention, the hydrogen peroxide and / or sodium percarbonate react with nitrate nitrogen to form NO3. - The calculated molar ratio is 1:1 to 10:1, preferably 4:1 to 8:1.

[0016] In this invention, the total residence time of the wastewater is 10 to 120 minutes, and the ratio of the residence time of the wastewater in the cathode reduction zone to the residence time of the wastewater in the anodic oxidation zone is 10:1 to 4:1, preferably 9:1 to 5:1.

[0017] In this invention, the pH value of the cathode reduction zone is 9.0 to 11.5, and the pH value of the anodic oxidation zone is 2.5 to 5.0.

[0018] In this invention, the electrochemical reaction conditions are as follows: current density is 2–20 mA / cm². 2 The electrode spacing is 1.0–10.0 mm, and preferably, the current density is 8–14 mA / cm². 2 The electrode spacing is 2.0 to 10.0 mm.

[0019] In this invention, the salt content of the saline wastewater is 1000-100000 mg / L, preferably 2000-100000 mg / L, and the nitrate nitrogen concentration is 10-1000 mg / L, preferably 200-1000 mg / L.

[0020] The method of this invention can achieve a nitrate nitrogen removal rate of over 90% and a total nitrogen removal rate of over 50%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The method of the present invention separates the cathode reduction zone from the anodic oxidation zone by setting up an intermediate isolation net, and by controlling the operating conditions, it eliminates the need to add additional substances to adjust the pH value when treating saline wastewater. This allows the cathode reduction zone and the anodic oxidation zone to form a highly alkaline environment conducive to the reduction of nitrate nitrogen to nitrogen gas and an acidic environment conducive to the conversion of intermediate product ammonia nitrogen to nitrogen gas, respectively. This achieves an integrated operation in which both the reduction and oxidation of nitrate nitrogen species can be efficiently converted into nitrogen gas, resulting in a higher removal rate of nitrate nitrogen and total nitrogen. In particular, in the cathode reduction reaction zone, the side reaction of further oxidation of nitrite to nitrate by oxidizing active species during the electroreduction process can be effectively mitigated, improving the selectivity of nitrate nitrogen to nitrogen gas conversion in the cathode zone.

[0023] (2) The method of the present invention preferably increases the total nitrogen removal rate by separately adding persulfate and hydrogen peroxide in the anodic oxidation zone. The oxidation products are sulfate or water, which prevents the pollution problem caused by adding halogen ions such as chloride ions to generate chlorine gas through electrolysis.

[0024] (3) The method of the present invention can also alleviate the corrosion of the cathode by hydrogen ions generated at the anode and increase the service life of the electrode. Detailed Implementation

[0025] The method of the present invention will be further described in detail below through embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0027] In this invention, nitrate nitrogen was determined using the method specified in "Determination of Nitrate Nitrogen in Water - Phenolic Disulfonic Acid Spectrophotometric Method" (GB / 7480); nitrite nitrogen was determined using the method specified in "Determination of Nitrite Nitrogen in Water - Spectrophotometric Method" (GB / 7493); and ammonia nitrogen was determined using the method specified in "Determination of Ammonia Nitrogen - Gas Phase Molecular Absorption Spectrometry" (HJT195).

[0028] In this invention, the formulas for calculating the nitrate nitrogen residual rate, nitrite nitrogen formation rate, ammonia nitrogen formation rate, total nitrogen removal rate, and nitrate nitrogen removal rate are as follows:

[0029] Nitrate nitrogen residue rate:

[0030] Nitrite nitrogen formation rate:

[0031] Ammonia nitrogen formation rate:

[0032] Total nitrogen removal rate:

[0033] Nitrate nitrogen removal rate = 1 - nitrate nitrogen residue rate;

[0034] Among them, C(NO3) - -N)0—Initial concentration of nitrate nitrogen, C(NO3) - -N) t C(NO2) - -N) t C(NH4) + -N) tLet t be the instantaneous concentrations of nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen.

[0035] Example 1

[0036] The electrochemical reactor is divided into cathode and anode zones by an intermediate partition screen. A nickel electrode is selected as the cathode, and a lead dioxide electrode as the anode. The electrode spacing is 10 mm, and the PVC mesh is 100 mesh with a porosity of 90% and a thickness of 4.0 mm, resulting in a cathode-to-anode volume ratio of 8:1. It is used to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L.

[0037] The treatment method includes: saline wastewater enters the reactor from the cathode reduction zone, undergoes a reduction reaction in an alkaline environment (pH 10.8), and then passes through an intermediate partition mesh into an acidic anodic oxidation zone (pH 3.6) for oxidation to obtain purified wastewater. The controlled conditions are as follows: current density is 10 mA / cm³. 2 The total residence time was 60 min, with a residence time ratio of 8:1 between the cathode and anode regions. The reaction results showed that the removal rate of nitrate nitrogen reached 92.3%, and the removal rate of total nitrogen reached 61.6%.

[0038] Example 2

[0039] Unlike Example 1, persulfate ions were added to the anode region, wherein the persulfate ions were in the form of S2O8. 2- The amount of nitrate nitrogen in wastewater as NO3 - The molar ratio was 2:1, and other steps were the same, to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L. The reaction results showed that the nitrate nitrogen removal rate reached 94.2%, and the total nitrogen removal rate reached 82.5%.

[0040] Example 3

[0041] Unlike Example 1, sodium percarbonate was added to the anode region, wherein the sodium percarbonate reacts with nitrate nitrogen in the wastewater as NO3. - The molar ratio was 4:1, and other steps were the same, to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L. The reaction results showed that the nitrate nitrogen removal rate reached 92.6%, and the total nitrogen removal rate reached 74.4%.

[0042] Example 4

[0043] The electrochemical reactor is divided into cathode and anode zones by an intermediate partition screen. Stainless steel electrodes are selected as the cathode, and diamond thin-film electrodes as the anode. The electrode spacing is 8 mm. The nylon mesh with a mesh size of 200 mesh, a porosity of 89%, and a thickness of 4.0 mm provides a cathode-to-anode volume ratio of 5:1. It is used to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L.

[0044] The treatment method includes: saline wastewater enters the reactor from the cathode reduction zone, undergoes a reduction reaction in an alkaline environment (pH 11.0), and then passes through an intermediate partition mesh into an acidic anodic oxidation zone (pH 3.4) for oxidation to obtain purified wastewater. The controlled conditions are as follows: current density is 10 mA / cm³. 2 The total residence time was 60 min, with a cathode residence time to anode residence time ratio of 5:1. The reaction results showed that the removal rate of nitrate nitrogen reached 94.2%, and the removal rate of total nitrogen reached 68.9%.

[0045] Example 5

[0046] The electrochemical reactor is divided into cathode and anode zones by an intermediate partition screen. A nickel electrode is selected as the cathode, and a lead dioxide electrode as the anode. The electrode spacing is 10 mm, and the PVC mesh is 50 mesh with a porosity of 91% and a thickness of 8.0 mm, resulting in a cathode-to-anode volume ratio of 7:1. It was used to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L.

[0047] The treatment method includes: saline wastewater enters the reactor from the cathode reduction zone, undergoes a reduction reaction in an alkaline environment (pH 10.6), and then passes through an intermediate partition mesh into an acidic anodic oxidation zone (pH 3.9) for oxidation to obtain purified wastewater. The controlled conditions are as follows: current density is 10 mA / cm³. 2 The total residence time was 60 min, with a cathode residence time to anode residence time ratio of 7:1. The reaction results showed that the removal rate of nitrate nitrogen reached 91.8%, and the removal rate of total nitrogen reached 60.4%.

[0048] Example 6

[0049] The electrochemical reactor is divided into cathode and anode zones by an intermediate partition screen. A nickel electrode is selected as the cathode, and a lead dioxide electrode as the anode. The electrode spacing is 10 mm, and the PVC mesh is 300 mesh with a porosity of 86% and a thickness of 2.0 mm, resulting in a cathode-to-anode volume ratio of 4:1. It was used to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L.

[0050] The treatment method includes: saline wastewater enters the reactor from the cathode reduction zone, undergoes a reduction reaction in an alkaline environment (pH 10.2), and then passes through an intermediate partition mesh into an acidic anodic oxidation zone (pH 4.4) for oxidation to obtain purified wastewater. The controlled conditions are as follows: current density is 10 mA / cm³. 2 The total residence time was 60 min, with a cathode residence time to anode residence time ratio of 4:1. The reaction results showed that the removal rate of nitrate nitrogen reached 90.6%, and the removal rate of total nitrogen reached 57.7%.

[0051] Example 7

[0052] The electrochemical reactor is divided into a cathode and an anode zone by an intermediate partition screen. A nickel electrode is selected as the cathode, and a lead dioxide electrode as the anode. The electrode spacing is 10 mm, and the PVC mesh is 100 mesh with a porosity of 90% and a thickness of 4.0 mm, resulting in a cathode-to-anode volume ratio of 8:1. It is used to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 1000 mg / L.

[0053] The treatment method includes: saline wastewater enters the reactor from the cathode reduction zone, undergoes a reduction reaction in an alkaline environment (pH 10.9), and then passes through an intermediate partition mesh into an acidic anodic oxidation zone (pH 3.4) for oxidation to obtain purified wastewater. The controlled conditions are as follows: current density is 14 mA / cm³. 2 The total residence time was 80 min, with a cathode residence time to anode residence time ratio of 8:1. The reaction results showed that the removal rate of nitrate nitrogen reached 91.6%, and the removal rate of total nitrogen reached 60.5%. Increasing the initial nitrate nitrogen concentration and changing the reaction conditions maintained good removal efficiency for both nitrate nitrogen and total nitrogen.

[0054] Comparative Example 1

[0055] Compared to Example 1, the difference lies in that: no intermediate partition screen is installed in the electrochemical reactor, and a single electrolytic cell without a partition screen is used to treat the wastewater. The model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L was treated.

[0056] The treatment method includes: saline wastewater entering the reactor from the cathode area, reacting to obtain purified wastewater, wherein the control conditions are as follows: current density is 10 mA / cm². 2The total residence time was 60 min. The reaction results showed that the removal rate of nitrate nitrogen was 69.3%, and the removal rate of total nitrogen reached 48.1%. These results indicate that the electrolytic single-cell system without a partition screen leads to the occurrence of nitrite oxidation as a side reaction. Simultaneously, the alkalinity generated at the cathode and the acidity generated at the anode neutralize each other, causing both nitrate nitrogen reduction and ammonia nitrogen oxidation to occur under near-neutral conditions (pH 7.5), resulting in a decrease in the removal rates of both nitrate nitrogen and total nitrogen.

[0057] Comparative Example 2

[0058] Compared to Example 2, the difference lies in that: no intermediate partition screen is installed in the electrochemical reactor, and a single electrolytic cell without a partition screen is used to treat the wastewater. The model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L was treated.

[0059] The treatment method includes: saline wastewater entering the reactor from the cathode area, reacting to obtain purified wastewater, wherein the control conditions are as follows: current density is 10 mA / cm². 2 The total residence time was 60 min. The reaction results showed that the removal rate of nitrate nitrogen was 74.2%, and the removal rate of total nitrogen reached 52.2%. These results indicate that the introduction of persulfate into the single electrolytic cell without a partition increases nitrogen selectivity, but it also leads to the oxidation of nitrite as a side reaction. Furthermore, the added oxidizing persulfate exacerbates these side reactions, resulting in no significant increase in the efficiency of nitrate nitrogen removal.

[0060] Comparative Example 3

[0061] The electrochemical reactor is divided into cathode and anode zones by an intermediate partition screen. A nickel electrode is selected as the cathode, and a lead dioxide electrode as the anode. The electrode spacing is 10 mm, and the PVC mesh is 20 mesh with a porosity of 90% and a thickness of 4.0 mm, resulting in a cathode-to-anode volume ratio of 8:1. It is used to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L.

[0062] The treatment method includes: saline wastewater enters the reactor from the cathode reduction zone, undergoes a reduction reaction in an alkaline environment (pH 9.6), and then passes through an intermediate partition mesh into an acidic anodic oxidation zone (pH 5.3) for oxidation to obtain purified wastewater. The controlled conditions are as follows: current density is 10 mA / cm³. 2 The total residence time was 60 min, with a residence time ratio of 8:1 between the cathode and anode regions. The reaction results showed that the removal rate of nitrate nitrogen reached 78.6%, and the removal rate of total nitrogen reached 54.3%. These results indicate that a low mesh count in the intermediate septum results in poor separation between the anode and cathode regions.

[0063] Comparative Example 4

[0064] The electrochemical reactor is divided into cathode and anode zones by an intermediate partition screen. A nickel electrode is selected as the cathode, and a lead dioxide electrode as the anode. The electrode spacing is 10 mm, and the PVC mesh is 100 mesh with a porosity of 90% and a thickness of 0.4 mm, resulting in a cathode-to-anode volume ratio of 8:1. It was used to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L.

[0065] The treatment method includes: saline wastewater enters the reactor from the cathode reduction zone, undergoes a reduction reaction in an alkaline environment (pH 9.2), and then passes through an intermediate partition mesh into an acidic anodic oxidation zone (pH 5.8) for oxidation to obtain purified wastewater. The controlled conditions are as follows: current density is 10 mA / cm³. 2 The total residence time was 60 min, with a residence time ratio of 8:1 between the cathode and anode regions. The reaction results showed that the removal rate of nitrate nitrogen reached 75.0%, and the removal rate of total nitrogen reached 49.8%. These results indicate that a thinner intermediate separator significantly reduces the separation effect between the anode and cathode regions.

[0066] Comparative Example 5

[0067] The electrochemical reactor is divided into cathode and anode zones by an intermediate partition screen. A nickel electrode is selected as the cathode, and a lead dioxide electrode as the anode. The electrode spacing is 10 mm, and the PVC mesh is 100 mesh with a porosity of 90% and a thickness of 4.0 mm, resulting in a cathode-to-anode volume ratio of 3:1. It is used to treat model wastewater with a salt content of 10000 mg / L and a nitrate nitrogen concentration of 500 mg / L.

[0068] The treatment method includes: saline wastewater enters the reactor from the cathode reduction zone, undergoes a reduction reaction in an alkaline environment (pH 9.4), and then passes through an intermediate partition to enter the acidic anodic oxidation zone (pH 5.7) for an oxidation reaction to obtain purified wastewater. The controlled conditions are as follows: current density is 10 mA / cm³. 2 The total residence time was 60 min, with a cathode residence time to anode residence time ratio of 3:1. The reaction results showed that the nitrate nitrogen removal rate reached 72.6%, and the total nitrogen removal rate reached 46.7%. These results indicate that a small cathode-to-anode volume ratio leads to incomplete nitrate reduction in the cathode region, further limiting the oxidation steps in the anode region.

Claims

1. A method for electrochemically removing nitrate nitrogen from saline wastewater, wherein, The electrochemical reactor includes a cathode reduction zone, an intermediate partition screen, and an anodic oxidation zone. The intermediate partition screen has a mesh size of 50-300 mesh and a thickness of 1.0-10.0 mm. The treatment method includes: saline wastewater enters the reactor from the cathode reduction zone, undergoes a reduction reaction in an alkaline environment, and then passes through the intermediate partition screen into the acidic anodic oxidation zone. The hydroxyl radicals generated at the anode convert the nitrate nitrogen intermediates in the wastewater into nitrogen gas, thereby obtaining purified wastewater. The ratio of the residence time of wastewater in the cathode reduction zone to the residence time of wastewater in the anodic oxidation zone is 10:1 to 4:

1. The pH value of the cathode reduction zone is 9.0~11.5, and the pH value of the anodic oxidation zone is 2.5~5.0; The intermediate partition mesh is one or more of the following: insulating ceramic mesh, rubber mesh, nylon mesh, and PVC mesh; the porosity of the intermediate partition mesh is 50% to 95%. The anodic oxidation zone is exogenously added with at least one of persulfate, permonosulfate, hydrogen peroxide, and sodium percarbonate.

2. The method according to claim 1, characterized in that, The thickness of the intermediate partition mesh is 2.0~8.0 mm.

3. The method according to claim 1, characterized in that, The porosity of the intermediate partition mesh is 80%~95%.

4. The method according to claim 1, characterized in that, The cathode is at least one of graphite electrode, platinum electrode, stainless steel electrode, iron electrode, zinc electrode, copper electrode, nickel electrode, titanium electrode, aluminum electrode, copper-nickel alloy electrode, and copper-tin alloy electrode; and / or the anode is at least one of diamond thin film electrode, lead dioxide electrode, tin dioxide electrode, manganese dioxide electrode, graphite electrode, platinum electrode, ruthenium-iridium electrode, iridium-tin electrode, ruthenium-tantalum electrode, ruthenium-iridium-tin electrode, and ruthenium-iridium-tantalum electrode.

5. The method according to claim 4, characterized in that, The cathode is at least one of a stainless steel electrode, a nickel electrode, a titanium electrode, and a copper-nickel alloy electrode; and / or the anode is at least one of a diamond thin film electrode, a lead dioxide electrode, and a tin dioxide electrode.

6. The method according to claim 1, characterized in that, At least one of persulfate and sodium percarbonate is exogenously added to the anodic oxidation zone.

7. The method according to claim 1 or 6, characterized in that, The persulfate is in the form of S2O8 2- Calculate and / or persulfate to Calculated with nitrate nitrogen The molar ratio is 1:1 to 6:1; the hydrogen peroxide and / or sodium percarbonate are reacted with nitrate nitrogen in a ratio of 1:1 to 6:

1. The calculated molar ratio is 1:1 to 10:

1.

8. The method according to claim 7, characterized in that, The persulfate is in the form of S2O8 2- Calculate and / or persulfate to Calculated with nitrate nitrogen The molar ratio is 2:1 to 4:1; the hydrogen peroxide and / or sodium percarbonate are reacted with nitrate nitrogen in a ratio of 2:1 to 4:

1. The calculated molar ratio is 4:1 to 8:

1.

9. The method according to claim 1, characterized in that, The total residence time of the wastewater is 10 to 120 minutes, and the ratio of the residence time of the wastewater in the cathode reduction zone to the residence time of the wastewater in the anodic oxidation zone is 9:1 to 5:

1.

10. The method according to claim 1, characterized in that, The electrochemical reaction conditions are as follows: current density is 2~20 mA / cm². 2 The electrode spacing is 1.0~10.0 mm.

11. The method according to claim 10, characterized in that, The electrochemical reaction conditions are as follows: current density is 8~14 mA / cm². 2 The electrode spacing is 2.0~10.0 mm.

12. The method according to claim 1, characterized in that, The saline wastewater has a salt content of 1,000 to 100,000 mg / L and a nitrate nitrogen concentration of 10 to 1,000 mg / L.

13. The method according to claim 12, characterized in that, The saline wastewater has a salt content of 2000~100000 mg / L and a nitrate nitrogen concentration of 200~1000 mg / L.

14. The method according to claim 1 or 12, characterized in that, The removal rate of nitrate nitrogen reaches over 90%, and the removal rate of total nitrogen reaches over 50%.

15. The method according to claim 14, characterized in that, The total nitrogen removal rate reaches over 60%.

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