Method and device for treating nitrate radicals in high-salinity wastewater

Abstract

The invention relates to the technical field of harmless and resourceful treatment of wastewater, and discloses a method and a device for treating nitrate radicals in high-salinity wastewater. The treatment method comprises the following steps: selectively adsorbing nitrate radicals in wastewater to be treated by using an adsorbent; eluting the adsorbent adsorbed with the nitrate radicals by using a sodium chloride solution to obtain an eluent; in a decoupling membrane electrolytic tank of which the cathode and the anode are separated by a bipolar membrane, electrochemical reduction is carried out by taking the eluent as a cathode solution and taking a solution containing OH <-> and SO4 < 2-> as an anode solution, nitrate radicals are converted into ammonia gas and / or ammonium radicals at the cathode, and OH <-> is converted into oxygen at the anode. By adopting the method disclosed by the invention, the interference of high-concentration sodium chloride in the wastewater can be avoided, and the recycling and innocent treatment of nitrate radicals can be effectively realized.

Description

Technical Field

[0001] The present invention relates to the technical field of harmless and resourceful treatment of wastewater, and in particular to a method and device for treating nitrate in high-salt wastewater. Background Art

[0002] At present, in the water treatment and zero-discharge systems of coal chemical industry and petroleum industry, the removal of nitrate from high-salinity wastewater is a major difficulty due to the high solubility of nitrate. Traditional nitrate treatment methods mainly include biochemical method and physical adsorption method. When these methods are used to treat nitrate from high-salinity wastewater, the presence of high concentration of sodium chloride in the wastewater will affect the resource utilization and harmless treatment of nitrate, resulting in the following problems: (1) Microorganisms cannot normally perform denitrification in a high-salinity environment; (2) After the ion exchange adsorption method is used to treat nitrate wastewater, the subsequent treatment cost of a large amount of eluate is high, and the thermal solidification of the evaporated mother liquor consumes a lot of heat energy, which has high energy consumption cost, and it is difficult to achieve the separation and purification between chloride ions and nitrate ions, which affects the purity of resource-based products; (3) The traditional electrochemical method directly treats nitrate from high-salinity wastewater, which easily causes the chloride ions in the high-salinity wastewater to be oxidized at the anode to produce a large amount of chlorine gas, which is extremely dangerous and toxic.

[0003] For example, patent CN120398247A discloses a method for treating high-salt wastewater with electroactive microorganisms to recover nitrate. The method uses denitrifying microorganisms or electroactive microorganisms in a three-electrode single chamber, using nitrate in the wastewater as an electron acceptor to undergo denitrification or dissimilatory reduction to ammonium, so that the nitrate is oxidized to ammonium nitrogen for recycling. The microorganisms are in direct contact with the high-salt wastewater, and the high-salt environment easily inhibits the metabolic activity of the microorganisms, thereby affecting the efficiency of converting nitrate into ammonium. In addition, in the three-electrode single chamber, the Cl in the wastewater is directly - It may be oxidized to produce chlorine gas which is highly dangerous and toxic, which is not conducive to the harmless treatment of wastewater. Summary of the Invention

[0004] To address the technical issue of high-salinity wastewater, where the presence of high-concentration sodium chloride hinders the resource recovery and harmless treatment of nitrate, the present invention provides a method and apparatus for treating nitrate in high-salinity wastewater. The method of the present invention avoids interference from high-concentration sodium chloride in wastewater and effectively achieves resource recovery and harmless treatment of nitrate.

[0005] The specific technical solutions of the present invention are: In a first aspect, the present invention provides a method for treating nitrate in high-salt wastewater, comprising the steps of: S1: selectively adsorbing nitrate in the wastewater to be treated using an adsorbent; S2: using sodium chloride solution to elute the adsorbent adsorbed with nitrate to obtain an eluate; S3: electrochemical reduction in a decoupled membrane electrolytic cell in which the cathode is separated from the anode by a bipolar membrane, using the eluent as the catholyte and a solution containing OH - and SO4 2- as the anolyte, wherein nitrate is converted into ammonia and / or ammonium at the cathode and OH - is converted into oxygen at the anode.

[0006] The present application can realize the resource utilization and harmless treatment of nitrate in high-salinity wastewater by the above method, and the specific mechanism is as follows: (1) After selective adsorption of NO3 - in the wastewater in steps S1 and S2, the adsorbent is regenerated by using a sodium chloride solution as the regeneration liquid, the NO3 - concentration difference inside and outside the adsorbent is utilized, and the NO3 - inside the adsorbent is replaced into the solution by ion exchange, so as to realize the regeneration of the adsorbent, and the obtained eluent contains NO3 - and sodium chloride. Through the above process, selective enrichment of NO3 - can be realized, which is convenient for subsequent resource utilization of NO3 - by electrochemical reduction, and removal of most of the NO3 - in the wastewater.

[0007] (2) In step S3, the eluent is electrochemically reduced by using a decoupled membrane electrolytic cell with a bipolar membrane, so that NO3 - in the catholyte is reduced into ammonia and / or ammonium (NO3 - + 9H + + 8e - → NH3 + 3H2O, NH3 reacts with water to produce NH4 + ), and OH - in the anolyte is oxidized into oxygen (2OH - - 4e - → O2 + 2H + ). The cathode and the anode in the decoupled membrane electrolytic cell are separated by the bipolar membrane, and under the action of a micro-current, the bipolar membrane can provide H + for the cathode, improving the reduction efficiency of nitrate, and at the same time, the bipolar membrane can also provide OH - for the anolyte, maintaining the electrolyte concentration required for the anode oxidation reaction. SO4 2- in the anolyte can balance the ions in the cathode region and the anode region, avoiding too large difference in osmotic pressure between the two sides of the bipolar membrane and affecting the operation of the decoupled membrane electrolytic cell. In addition, since the wastewater to be treated is high-salinity wastewater, a small amount of Cl - may be adsorbed by the adsorbent in step S1, and the use of a sodium chloride solution in step S2 accelerates the replacement of NO3 -The eluent contains more Cl - If a conventional electrochemical reduction method is used, Cl - in the eluent is easy to be oxidized to produce a large amount of chlorine gas which is dangerous and toxic, and the special decoupling membrane electrolytic cell used in the present application, in combination with the specific cathode liquid and anode liquid design, can realize the reduction of NO3 - , avoid the oxidation of Cl - in the eluent to produce chlorine gas, and collect pure ammonia gas in the electrochemical reduction process, which can be converted into ammonia water, ammonium sulfate and other products, so as to realize the resource utilization of nitrate in wastewater, and the gas generated by the anode is only oxygen which can be directly discharged into the atmosphere.

[0008] The nitrate treatment method of the present application can effectively realize the resource utilization and harmless treatment of nitrate, avoid the interference of high-concentration sodium chloride in wastewater, and effectively reduce the operation energy consumption and cost.

[0009] As a preferred, in step S1, the concentration of sodium chloride in the wastewater to be treated is 10-20%, and the concentration of nitrate is 200-500 mg / L.

[0010] As a preferred, in step S1, the adsorbent includes one or more of chelating agent resin, macroporous anion resin and strong base anion resin.

[0011] As a preferred, in step S2, the concentration of sodium chloride solution is 8-12%, and the concentration of nitrate in the eluent is 4000-6500 mg / L; in step S3, the cathode liquid after electrochemical reduction is reused as sodium chloride solution to step S2.

[0012] In the process of electrochemical reduction in the decoupling membrane electrolytic cell, sodium chloride in the eluent is retained because it does not participate in the reaction, and the concentration of nitrate is greatly reduced, so it can be reused in step S2 to elute the adsorbent with adsorbed nitrate.

[0013] As a preferred, in step S3, in the process of electrochemical reduction, the current density is set to 50-200 mA / cm 2 , and the circulation flow rate of the cathode liquid and the anode liquid is 50-120 mL / min.

[0014] As a preferred, in step S3, the solution containing OH - and SO4 2- is a solution containing 1-4% sodium sulfate and 1-1.5 mol / L sodium hydroxide.

[0015] As preferred, in step S3, the process of converting the nitrate into ammonia gas at the cathode is carried out under the action of a reduction catalyst, which comprises one or more of Pb, Sn, Co, Fe and Mo; the OH - The process of converting into oxygen gas at the anode is carried out under the action of an oxidation catalyst, which comprises one or more of SnO2, Sb2O3, PbO2 and TiO2.

[0016] As preferred, in step S3, the ammonia gas generated at the cathode is pressurized and then absorbed with an absorption liquid; the absorption liquid is desalted water and / or dilute sulfuric acid.

[0017] In the second aspect, the application provides a device using the treatment method, which comprises: an adsorption tank containing an adsorbent, a NaCl solution storage tank in communication with the adsorption tank, a cathode chamber in communication with the adsorption tank, a decoupled membrane electrolysis cell, and an anode chamber; the decoupled membrane electrolysis cell comprises at least one electrolysis cell monomer, and each electrolysis cell monomer has the following structure: a cathode plate, an anode plate, and a bipolar membrane arranged between the cathode plate and the anode plate, wherein the cathode plate and the anode plate are each provided with a flow channel, and the anode face and the cathode face of the bipolar membrane face the anode plate and the cathode plate respectively; the cathode plate and the anode plate are in communication with the cathode chamber and the anode chamber respectively.

[0018] As preferred, in each electrolysis cell monomer, a cathode gas diffusion layer is arranged between the cathode plate and the bipolar membrane, and an anode gas diffusion layer is arranged between the anode plate and the bipolar membrane.

[0019] Further, the material of the cathode gas diffusion layer is a foam nickel loaded with a reduction catalyst; and the material of the anode gas diffusion layer is a foam nickel loaded with an oxidation catalyst.

[0020] As preferred, the decoupled membrane electrolysis cell comprises a plurality of parallel electrolysis cell monomers; the cathode plate and the anode plate of adjacent electrolysis cell monomers are combined to form a bipolar plate.

[0021] As preferred, the flow channel is a single-channel serpentine, a multi-channel serpentine, an interdigital shape or a straight-channel flat shape.

[0022] Compared with the prior art, the application has the following advantages: (1) After the nitrate in the wastewater is adsorbed, the application uses a sodium chloride solution for elution, and the eluate is electrochemically reduced by a special method, which can promote the desorption of the nitrate during elution by using sodium chloride, and at the same time, avoid the production of chlorine gas in the electrochemical reduction process caused by the introduction of sodium chloride, which is helpful to realize the resourceization and harmless treatment of the nitrate in high-salinity wastewater.

[0023] (2) The application uses a special decoupling membrane electrolytic cell, which is separated by a bipolar membrane between the cathode and the anode, so that the bipolar membrane can provide H+ for the cathode and OH- for the anode, promote the electrochemical reduction process, and facilitate the conversion of nitrate in the eluent into ammonia gas.

[0024] (3) In the electrochemical reduction process, the concentration of nitrate in the eluent is greatly reduced, and sodium chloride is retained, so that the sodium chloride solution as the adsorbent regeneration liquid can be regenerated after the electrochemical reduction is completed, thereby realizing recycling, and no regeneration liquid needs to be supplemented during the operation of the device.

[0025] (4) The main energy consumption in the whole operation process of the application is electric energy consumption, and there is no high energy consumption process (such as steam, high temperature and high pressure), which can reduce the operation energy consumption and cost. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a structural schematic view of a high-salinity wastewater nitrate treatment device in the application.

[0027] Figure 2 It is an exploded view of a single-stack decoupling membrane electrolytic cell in the application.

[0028] Figure 3 It is an exploded view of a multi-stack decoupling membrane electrolytic cell in the application.

[0029] Figure 4 It is the change of the nitrate concentration in the cathode liquid in the running process of the decoupling membrane electrolytic cell in Example 1~Example 3.

[0030] Figure 5 It is the change of the ammonia nitrogen concentration in the cathode liquid in the running process of the decoupling membrane electrolytic cell in Example 1~Example 3.

[0031] Figure 6 It is the change of the nitrate and ammonia nitrogen concentrations in the cathode liquid in the running process of the decoupling membrane electrolytic cell in Comparative Example 1.

[0032] The figure is marked as: nitrate enrichment module 1, eluent electro-reduction regeneration module 2, wastewater tank 3, wastewater to be treated 4, wastewater inlet pump 5, wastewater inlet valve 6, wastewater to be treated inlet pipe 7, adsorption tank 8, adsorbent 9, adsorption tank outlet pipe 10, outlet total valve 11, low-nitrate wastewater outlet valve 12, NaCl solution storage tank 13, NaCl solution 14, regeneration pipeline 15, regeneration pump 16, regeneration valve 17, eluent outlet pipe 18, eluent outlet valve 19, cathode chamber 20, catholyte 21, ammonia gas separation device 22, ammonia gas transfer pipeline 23, jet device 24, circulating pump 25, ammonia collection tank 26, ammonia gas absorption liquid 27, mixing pipeline 28, catholyte inlet pipe 29, catholyte inlet pump 30, catholyte inlet valve 31, cathode plate 32, decoupling membrane electrolytic cell 33, anode plate 34, direct current power supply 35, catholyte outlet pipe 36, catholyte outlet valve 37, anode chamber 38, anolyte 39, anolyte inlet pipe 40, anolyte inlet valve 41, anolyte inlet pump 42, anolyte outlet valve 43, anolyte outlet pipe 44, gas outlet pipeline 45, NaCl solution storage tank inlet pipe 46, NaCl solution storage tank inlet valve 47, flow channel 48, cathode gas diffusion layer 49, bipolar membrane 50, anode gas diffusion layer 51, bipolar plate 52. DETAILED DESCRIPTION

[0033] The application will be further described below in combination with examples.

[0034] A device for treating nitrate in high-salinity wastewater, comprising: an adsorption tank 8 containing an adsorbent 9, a NaCl solution storage tank 13 communicating with the adsorption tank 8, a cathode chamber 20 communicating with the adsorption tank 8, a decoupling membrane electrolytic cell 33, and an anode chamber 38; the decoupling membrane electrolytic cell 33 comprises at least one electrolytic cell monomer, and each electrolytic cell monomer has the following structure: comprising a cathode plate 32, an anode plate 34, and a bipolar membrane 50 arranged between the cathode plate 32 and the anode plate 34, the cathode plate 32 and the anode plate 34 are each provided with a flow channel 48, and the anode face and the cathode face of the bipolar membrane 50 face the cathode plate 32 and the anode plate 34 respectively; the cathode plate 32 and the anode plate 34 communicate with the cathode chamber 20 and the anode chamber 38 respectively.

[0035] In some embodiments, the decoupling membrane electrolytic cell 33 is a single-stack decoupling membrane electrolytic cell with only one electrolytic cell monomer. In other embodiments, the decoupling membrane electrolytic cell 33 is a multi-stack decoupling membrane electrolytic cell composed of multiple parallel electrolytic cell monomers, the cathode plate 32 and the anode plate 34 of adjacent electrolytic cell monomers are combined to form a bipolar plate 52, and in the bipolar plate 52, the flow channel 48 in the cathode plate 32 is only for the flow of catholyte, and the flow channel 48 in the anode plate 34 is only for the flow of anolyte, and the two liquids do not interfere with each other.

[0036] In some embodiments, in each of the electrolytic cell monomers, a cathode gas diffusion layer 49 is arranged between the cathode plate 32 and the bipolar membrane 50, and an anode gas diffusion layer 51 is arranged between the anode plate 34 and the bipolar membrane 50; the material of the cathode gas diffusion layer 49 is a foam nickel loaded with a reduction catalyst; and the material of the anode gas diffusion layer 51 is a foam nickel loaded with an oxidation catalyst.

[0037] In some embodiments, the flow channel 48 is a single-channel serpentine, a multi-channel serpentine, an interdigital shape, or a straight-channel flat shape.

[0038] A method for treating nitrate in high-salinity wastewater, comprising the steps of: S1: selectively adsorbing nitrate in the wastewater to be treated by an adsorbent; S2: eluting the adsorbent with a sodium chloride solution to obtain an eluate; S3: performing electrochemical reduction in a decoupled membrane electrolytic cell in which the cathode and the anode are separated by a bipolar membrane, using the eluate as the catholyte and a solution containing OH - and SO4 2- as the anolyte, so that the nitrate is converted into ammonia and / or ammonium at the cathode and OH - is converted into oxygen at the anode.

[0039] In some embodiments, in step S1, the concentration of sodium chloride in the wastewater to be treated is 10-20%, and the concentration of nitrate is 200-500 mg / L.

[0040] In some embodiments, in step S1, the adsorbent comprises one or more of a chelating agent resin, a macroporous anion resin, and a strong base anion resin.

[0041] In some embodiments, in step S2, the concentration of the sodium chloride solution is 8-12%, and the concentration of nitrate in the eluate is 4000-6500 mg / L.

[0042] In some embodiments, in step S3, the solution containing OH - and SO4 2- is a solution containing 1-4% sodium sulfate and 1-1.5 mol / L sodium hydroxide.

[0043] In some embodiments, in step S3, the conversion of the nitrate into ammonia gas at the cathode is performed under the action of a reduction catalyst, and the reduction catalyst comprises one or more of Pb, Sn, Co, Fe, and Mo.

[0044] In some embodiments, in step S3, the OH -The process of anode conversion into oxygen is carried out under the action of an oxidation catalyst, which includes one or more of SnO2, Sb2O3, PbO2 and TiO2.

[0045] In some embodiments, in step S3, the current density in the process of electrochemical reduction is set to 50-200 mA / cm 2 The circulation flow rate of the cathode liquid and the anode liquid is 50-120 mL / min.

[0046] In some embodiments, in step S3, the cathode liquid after electrochemical reduction is recycled to step S2 as a regeneration liquid.

[0047] In some embodiments, in step S3, the ammonia gas generated by the cathode is pressurized and absorbed by an absorption liquid; the absorption liquid is desalted water and / or dilute sulfuric acid.

[0048] The application will be described in detail below through specific examples. It should be understood that these examples are only used to illustrate the application and not to limit the scope of the application. Changes and advantages that can be thought of by those skilled in the art without departing from the spirit and scope of the application are included in the application, and the appended claims and any equivalents thereof are the protection scope of the application.

[0049] Example 1 The high-salinity wastewater nitrate treatment device of this example is composed of a nitrate enrichment module 1 and an eluent electro-reduction regeneration module 2, and the structure is as shown in Figure 1 The specific implementation is as follows: The nitrate enrichment module 1 is composed of a wastewater tank 3 containing the wastewater to be treated 4, an adsorption tank 8 filled with an adsorbent 9, and a NaCl solution storage tank 13 containing a NaCl solution 14. The adsorbent 9 is a macroporous anion resin. The lower part of the adsorption tank 8 is provided with a wastewater inlet, which is communicated with the wastewater tank 3 through a wastewater inlet pipe 7. The wastewater inlet pipe 7 is provided with a wastewater inlet pump 5 and a wastewater inlet valve 6. The lower part of the adsorption tank 8 is also provided with a NaCl solution inlet, which is communicated with the NaCl solution storage tank 13 through a regeneration pipeline 15. The regeneration pipeline 15 is provided with a regeneration pump 16 and a regeneration valve 17. The upper part of the adsorption tank 8 is provided with an eluent outlet, which is communicated with an adsorption tank outlet pipe 10. The adsorption tank outlet pipe 10 is provided with an outlet total valve 11, a branch point and a low-nitrate wastewater outlet valve 12 along the outlet direction in sequence. The branch point is communicated with an eluent outlet pipe 18, which is provided with an eluent outlet valve 19.

[0050] The eluent electro-reduction regeneration module 2 is composed of a decoupling membrane electrolytic cell 33, a cathode chamber 20 for storing the cathode liquid 21, an anode chamber 38 for storing the anode liquid 39, and an ammonia collection tank 26 filled with ammonia absorption liquid 27; the ammonia absorption liquid 27 is desalted water. Figure 2 The decoupling membrane electrolytic cell 33 is a single-stack decoupling membrane electrolytic cell with only one electrolytic cell monomer, and is composed of a cathode plate 32, a cathode gas diffusion layer 49, a bipolar membrane 50, an anode gas diffusion layer 51, and an anode plate 34 which are sequentially stacked, the anode face and the cathode face of the bipolar membrane 50 face the anode plate 34 and the cathode plate 32 respectively, the cathode plate 32 and the anode plate 34 are both provided with a single-channel serpentine flow channel 48, the cathode plate 32 and the anode plate 34 are connected with a direct current power supply 35, the cathode gas diffusion layer 49 is a foam nickel loaded with Pb, and the anode gas diffusion layer 51 is a foam nickel loaded with SnO2. The cathode chamber 20 is communicated with the eluent outlet pipe 18. The lower water outlet of the cathode chamber 20 and the lower water inlet of the cathode plate 32 are communicated through a cathode liquid water inlet pipe 29, the cathode liquid water inlet pipe 29 is provided with a cathode liquid water inlet pump 30 and a cathode liquid water inlet valve 31; the upper water inlet of the cathode chamber 20 and the upper water outlet of the cathode plate 32 are communicated through a cathode liquid water outlet pipe 36, the cathode liquid water outlet pipe 36 is provided with a cathode liquid water outlet valve 37; the lower water inlet and the upper water outlet of the cathode plate 32 are both communicated with the flow channel 48 in the cathode plate 32; the cathode liquid water inlet pipe 29 is communicated with the NaCl solution storage tank 13 through a NaCl solution storage tank water inlet pipe 46, the NaCl solution storage tank water inlet pipe 46 is provided with a NaCl solution storage tank water inlet valve 47. The bottom of the cathode chamber 20 is provided with an ammonia separation device 22, the ammonia separation device 22 is connected with a jet flow device 24 through an ammonia transfer pipeline 23, and the jet flow device 24 and the ammonia collection tank 26 form a circulation pipeline through a mixing pipeline 28 and a circulating pump 25. The lower water outlet of the anode chamber 38 and the lower water inlet of the anode plate 34 are communicated through an anode liquid water inlet pipe 40, the anode liquid water inlet pipe 40 is provided with an anode liquid water inlet valve 41 and an anode liquid water inlet pump 42; the upper water inlet of the anode chamber 38 and the upper water outlet of the anode plate 34 are communicated through an anode liquid water outlet pipe 44, the anode liquid water outlet pipe 44 is provided with an anode liquid water outlet valve 43; the lower water inlet and the upper water inlet of the anode plate 34 are both communicated with the flow channel 48 in the anode plate 34. The top of the anode chamber 38 is communicated with a gas outlet pipeline 45.

[0051] The device of the embodiment is used for treating nitrate in high-salinity wastewater, the concentration of sodium chloride in the wastewater to be treated is 15%, and the concentration of nitrate is 452.8 mg / L, and the wastewater treatment process is as follows: S1: Open wastewater inlet pump 5, wastewater inlet valve 6, main outlet valve 11, and low-nitrate wastewater outlet valve 12, and close eluent outlet valve 19, regeneration pump 16, and regeneration valve 17. The wastewater to be treated in wastewater tank 3 is passed into adsorption tank 8 at a flow rate of 4.8 BV / h. The wastewater to be treated is adsorbed by adsorbent 9, and the adsorbed wastewater flows out through adsorption tank outlet pipe 10. Testing shows that the average nitrate concentration of the wastewater to be treated after adsorption treatment is 3.53 mg / L, and the nitrate removal rate reaches 99.22%.

[0052] S2: After adsorbent 9 reaches saturation (nitrate concentration in the outlet of adsorption tank 8 exceeds 20 mg / L), wastewater inlet pump 5, wastewater inlet valve 6, and low-nitrate wastewater outlet valve 12 are closed. Outlet main valve 11, eluent outlet valve 19, regeneration pump 16, and regeneration valve 17 are opened. NaCl solution (sodium chloride concentration: 12%) in NaCl solution storage tank 13 is introduced into adsorption tank 8 at a flow rate of 1 BV / h. The solution then flows from bottom to top through adsorbent 9 within adsorption tank 8 to form an eluent. The eluent is then passed through eluent outlet pipe 18 and temporarily stored in cathode chamber 20. Testing reveals a nitrate concentration of 4930.27 mg / L in the eluent, and a nitrate elution rate of 90.47% from the adsorbent.

[0053] S3: Run the decoupled membrane electrolysis cell 33, so that the cathode liquid (eluent) circulates between the cathode chamber 20 and the cathode plate 32 at a circulation flow rate of 105 mL / min, and the total volume of the circulating cathode liquid is 100 mL; the anolyte (a mixed aqueous solution of sodium sulfate and sodium hydroxide, in which the concentrations of sodium sulfate and sodium hydroxide are 3% and 1 mol / L, respectively) circulates between the anode chamber 38 and the anode plate 34 at a circulation flow rate of 105 mL / min, and the total volume of the circulating cathode liquid is 100 mL; set the current density to 100 mA / cm 2 The decoupled membrane electrolysis cell 33 was operated continuously for 8 hours. During this period, samples were taken from the cathode chamber 20 every 2 hours to test the concentrations of nitrate and ammonia nitrogen (NH3-N) in the cathode liquid. The results are shown in Figure 4 and Figure 5 , Figure 4 and Figure 5 The results show that after 8 hours of operation, the nitrate concentration in the cathode liquid decreased from 4930.27 mg / L to 32.03 mg / L, with a removal rate of 99.35%; the ammonia nitrogen concentration increased to 1105.09 mg / L, with an ammonia conversion rate of 99.91%. - Removal rate and NO3 - The removal rate, as well as the voltage, current and energy consumption during operation are shown in Table 1. During operation, the gas discharged from the gas outlet pipe 45 was measured to be oxygen, and no chlorine gas was detected at the cathode and anode.

[0054] S4: The ammonia in the cathode liquid is removed by the ammonia gas separation device 22, enters the jet device 24 through the ammonia gas transfer pipeline 23 for pressurization, and then enters the ammonia collection tank 26 to contact with the ammonia gas absorption liquid. The mixture of the ammonia gas and the ammonia gas absorption liquid is circulated between the jet device 24 and the ammonia collection tank 26 through the mixing pipeline 28 and the circulating pump 25, so that the ammonia gas is fully absorbed by the ammonia gas absorption liquid, and the ammonia gas is collected and recycled.

[0055] S5: The cathode liquid after removing ammonia is introduced into the NaCl solution storage tank 13 through the NaCl solution storage tank inlet pipe 46 for recycling.

[0056] Example 2 The high-salinity wastewater nitrate treatment device of this example has the same structure as that of Example 1.

[0057] In this example, the eluent (nitrate concentration of 4930.27 mg / L) collected in Example 1 is subjected to electrochemical reduction by the following method: the decoupled membrane electrolytic cell 33 is operated to circulate the cathode liquid (eluent) between the cathode chamber 20 and the cathode plate 32, and the circulation flow rate is 95 mL / min, and the total volume of the cathode liquid in circulation is 100 mL; the anode liquid (a mixed aqueous solution of sodium sulfate and sodium hydroxide, wherein the concentrations of sodium sulfate and sodium hydroxide are 1% and 1.5 mol / L, respectively) is circulated between the anode chamber 38 and the anode plate 34, and the circulation flow rate is 95 mL / min, and the total volume of the cathode liquid in circulation is 100 mL; the current density is set to 100 mA / cm 2 . The decoupled membrane electrolytic cell 33 is continuously operated for 8 h, and the concentrations of nitrate and ammonia nitrogen (NH3-N) in the cathode liquid are tested every 2 h during the operation, and the results are shown in Figure 4 and Figure 5 , Figure 4 and Figure 5 : After 8 h of operation, the concentration of nitrate in the cathode liquid decreases from 4930.27 mg / L to 25.17 mg / L, with a removal rate of 99.49%; the concentration of ammonia nitrogen increases to 1104.3 mg / L, and the ammonia conversion rate is 99.7%. After 8 h of continuous operation, the removal rate of NO3 - and the removal rate of NO3 - , and the voltage, current and energy consumption during the operation are shown in Table 1. During the operation, the gas discharged from the gas pipeline 45 is oxygen, and no chlorine gas is detected at the cathode and anode.

[0058] Example 3 The high-salinity wastewater nitrate treatment device of this example has the same structure as that of Example 1, except that the decoupled membrane electrolytic cell 33 is a multi-stack decoupled membrane electrolytic cell composed of three parallel electrolytic cell monomers, and the structure is as shown in Figure 3As shown, each of the electrolytic cell monomers is composed of a cathode plate 32, a cathode gas diffusion layer 49, a bipolar membrane 50, an anode gas diffusion layer 51 and an anode plate 34 which are sequentially stacked, the anode face and the cathode face of the bipolar membrane 50 face the anode plate 34 and the cathode plate 32 respectively, the cathode plate 32 and the anode plate 34 are both provided with single-channel serpentine flow channels 48, the cathode plate 32 and the anode plate 34 are connected with a direct current power supply 35, the cathode gas diffusion layer 49 is a foam nickel loaded with Pb, and the anode gas diffusion layer 51 is a foam nickel loaded with Sn02; the cathode plate 32 and the anode plate 34 of adjacent electrolytic cell monomers are combined to form a bipolar plate 52, and in the bipolar plate 52, the flow channels 48 in the cathode plate 32 are only for the circulation of the catholyte, the flow channels 48 in the anode plate 34 are only for the circulation of the anolyte, and the two liquids do not interfere with each other.

[0059] The eluent (nitrate concentration of 4930.27 mg / L) collected in Example 1 was subjected to electrochemical reduction by the following method: running the decoupled membrane electrolytic cell 33, circulating the catholyte (eluent) between the cathode chamber 20 and the cathode plate 32 of each electrolytic cell monomer, the circulation flow rate was 100 mL / min, and the total volume of the catholyte in circulation was 100 mL; the anolyte (a mixed aqueous solution of sodium sulfate and sodium hydroxide, wherein the concentrations of sodium sulfate and sodium hydroxide were 2.5% and 1.3 mol / L, respectively) was circulated between the anode chamber 38 and the anode plate 34 of each electrolytic cell monomer, the circulation flow rate was 100 mL / min, and the total volume of the catholyte in circulation was 100 mL; the current density was set to 100 mA / cm 2 The decoupled membrane electrolytic cell 33 was continuously operated for 8 h, during which the concentrations of nitrate and ammonia nitrogen (NH3-N) in the catholyte were tested every 2 h by sampling from the cathode chamber 20, and the results are shown in Figure 4 and Figure 5 , Figure 4 and Figure 5 : after 8 h of operation, the concentration of nitrate in the catholyte decreased from 4930.27 mg / L to 13.68 mg / L, with a removal rate of 99.72%; the concentration of ammonia nitrogen increased to 1108.19 mg / L, with an ammonia conversion rate of 99.82%. After 8 h of continuous operation, the measured removal rate of NO3 - and the removal rate of NO3 - , as well as the voltage, current and energy consumption during the operation are shown in Table 1. During the operation, the gas discharged from the gas pipeline 45 was oxygen, and no chlorine was detected at the cathode and anode.

[0060] Comparative Example 1 The high-salinity wastewater nitrate treatment device of the present comparative example differs from that of Example 1 only in that the decoupling membrane electrolytic cell 33 is replaced by an anion exchange membrane electrolytic cell, in which an anion exchange membrane (AEM) is used instead of the bipolar membrane 50 in the decoupling membrane electrolytic cell 33, and the rest of the structure is the same as the decoupling membrane electrolytic cell 33 in Example 1.

[0061] The device of the present example is used to treat nitrate in high-salinity wastewater. The concentration of sodium chloride in the wastewater to be treated is 15%, and the concentration of nitrate is 362.5 mg / L. The wastewater treatment process is as follows: S1: Open the wastewater inlet pump 5, the wastewater inlet valve 6, the total outlet valve 11, and the low-nitrate wastewater outlet valve 12, and keep the eluent outlet valve 19, the regeneration pump 16, and the regeneration valve 17 closed. The wastewater in the wastewater tank 3 is fed into the adsorption tank 8 at a flow rate of 5 BV / h, and the adsorbent 9 is used to adsorb the wastewater to be treated. The wastewater after adsorption treatment flows out through the adsorption tank outlet pipe 10. After detection, the average concentration of nitrate in the wastewater to be treated after adsorption treatment is 2.3 mg / L, and the removal rate of nitrate is 99.36%.

[0062] S2: After the adsorbent 9 is saturated (the concentration of nitrate in the outlet of the adsorption tank 8 is higher than 20 mg / L), close the wastewater inlet pump 5, the wastewater inlet valve 6, and the low-nitrate wastewater outlet valve 12, and open the total outlet valve 11, the eluent outlet valve 19, the regeneration pump 16, and the regeneration valve 17. The NaCl solution (sodium chloride concentration of 10%) in the NaCl solution storage tank 13 is fed into the adsorption tank 8 at a flow rate of 1.8 BV / h, and the eluent is formed by flowing from bottom to top through the adsorbent 9 in the adsorption tank 8, and then the eluent enters the cathode chamber 20 through the eluent outlet pipe 18. After detection, the concentration of nitrate in the eluent is 5012.3 mg / L, and the elution rate of nitrate in the adsorbent is 90.5%.

[0063] S3: Run the decoupling membrane electrolytic cell 33 to circulate the cathode liquid (eluent) between the cathode chamber 20 and the cathode plate 32, with a circulation flow rate of 100 mL / min and a total volume of 100 mL in circulation; the anode liquid (a mixture of sodium sulfate and sodium hydroxide, with a concentration of 3% and 1 mol / L, respectively) circulates between the anode chamber 38 and the anode plate 34, with a circulation flow rate of 100 mL / min and a total volume of 100 mL in circulation; the current density is set to 110 mA / cm 2 . The decoupling membrane electrolytic cell 33 is continuously operated for 8 h, during which the concentrations of nitrate and ammonia nitrogen (NH3-N) in the cathode liquid are tested every 2 h from the cathode chamber 20, and the results are shown in Figure 6 , Figure 6The results show that after 8 hours of operation, the nitrate concentration in the cathode liquid decreased from 5012.3 mg / L to 1826 mg / L, with a removal rate of 63.57%; the ammonia nitrogen concentration increased to 702.3 mg / L. - Removal rate and NO3 - The removal rate, as well as the voltage, current and energy consumption during operation are shown in Table 1. During operation, the gas discharged from the gas outlet pipe 45 was measured to be oxygen, and no chlorine gas was detected at the cathode and anode.

[0064] S4: The ammonia in the cathode liquid is removed through the ammonia separation device 22, enters the ejector 24 through the ammonia transfer pipe 23 for pressurization, and then enters the ammonia collection box 26 to contact with the ammonia absorption liquid. The mixture of ammonia and ammonia absorption liquid is circulated between the ejector 24 and the ammonia collection box 26 through the mixing pipe 28 and the circulation pump 25, so that the ammonia is fully absorbed by the ammonia absorption liquid, thereby realizing the collection and resource utilization of ammonia.

[0065] S5: The cathode liquid after the ammonia removal is introduced into the NaCl solution storage tank 13 through the NaCl solution storage tank water inlet pipe 46 for reuse.

[0066] Table 1 Electrochemical reduction process operating data

[0067] It can be seen from Table 1 that in Examples 1 to 3, the NO3 in the cathode liquid (eluent) - The removal rate can reach more than 99%, and the removal rate can reach more than 610 mg·L / h, which is significantly higher than that of Comparative Example 1. In addition, the average voltage of the electrolytic cell during operation in Examples 1 to 3 is lower than that in Comparative Example 1. - -N) were reduced by 39.03%, 38.79% and 39.7% respectively compared with Comparative Example 1. The reason is that the nitrate reduction reaction in the cathode consumes a large amount of H + The oxidation reaction in the anode consumes a large amount of OH - In the electrolytic cell of comparative example 1, an anion exchange membrane is used, and H + The consumption of nitrate causes the pH value of the cathode liquid to rise rapidly, inhibiting the reduction of nitrate ions. At the same time, the OH in the anode liquid - The electrolytic cell of Example 1 to Example 3 uses a bipolar membrane, which can provide H for the cathode. + , providing OH to the anode - , thereby reducing resistance and promoting the electrochemical reduction process of nitrate.

[0068] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The materials, devices, and methods used in the present application are those that are conventionally employed in the art, unless specifically stated otherwise.

[0069] The above description is only the preferred embodiment of the present application, not any limitation to the present application, any simple modification, change and equivalent transformation to the above embodiment according to the technical essence of the present application are still within the protection scope of the technical solution of the present application.

Claims

1. A method for treating nitrate in high-salt wastewater, characterized in that the steps include: S1: selectively adsorbing nitrate in the wastewater to be treated using an adsorbent; S2: using sodium chloride solution to elute the adsorbent adsorbed with nitrate to obtain an eluate; S3: In a decoupled membrane electrolysis cell where the cathode and anode are separated by a bipolar membrane, the eluent is used as the cathode liquid and the OH - and SO4 2- The solution is the anolyte, and electrochemical reduction is carried out. Nitrate is converted into ammonia and / or ammonium at the cathode, and OH - Converted into oxygen at the anode.

2. The processing method according to claim 1, characterized in that In step S1, the concentration of sodium chloride in the wastewater to be treated is 10-20%, and the concentration of nitrate is 200-500 mg / L.

3. The processing method according to claim 1, characterized in that In step S1, the adsorbent includes one or more of a chelating resin, a macroporous anion resin, and a strong base anion resin.

4. The processing method according to claim 1 or 3, characterized in that In step S2, the concentration of the sodium chloride solution is 8-12%, and the nitrate concentration in the eluent is 4000-6500 mg / L; in step S3, the cathode liquid after the electrochemical reduction is reused as the sodium chloride solution in step S2.

5. The processing method according to claim 1, characterized in that In step S3, during the electrochemical reduction process, the current density is set to 50-200 mA / cm 2 The circulation flow rates of the cathode liquid and the anode liquid are both 50~120mL / min.

6. The processing method according to claim 1, characterized in that In step S3, the OH-containing - and SO4 2- The solution is a solution containing 1~4% sodium sulfate and 1~1.5mol / L sodium hydroxide.

7. The processing method according to claim 1, characterized in that In step S3, the process of converting nitrate into ammonia at the cathode is carried out under the action of a reduction catalyst, and the reduction catalyst includes one or more of Pb, Sn, Co, Fe and Mo; the OH - The process of converting into oxygen at the anode is carried out under the action of an oxidation catalyst, which includes one or more of SnO2, Sb2O3, PbO2 and TiO2.

8. A device using the treatment method according to any one of claims 1 to 7, characterized in that: include: An adsorption tank filled with an adsorbent, a NaCl solution storage tank connected to the adsorption tank, a cathode chamber connected to the adsorption tank, a decoupling membrane electrolytic cell, and an anode chamber; the decoupling membrane electrolytic cell includes at least one electrolytic cell unit, and the structure of each electrolytic cell unit is as follows: including a cathode plate, an anode plate and a bipolar membrane arranged between the cathode plate and the anode plate, the cathode plate and the anode plate are both provided with flow channels, the positive side and the negative side of the bipolar membrane are respectively facing the cathode plate and the anode plate; the cathode plate and the anode plate are respectively connected to the cathode chamber and the anode chamber.

9. The device according to claim 8, characterized in that In each electrolytic cell unit, a cathode gas diffusion layer is provided between the cathode plate and the bipolar membrane, and an anode gas diffusion layer is provided between the anode plate and the bipolar membrane.

10. The device according to claim 9, characterized in that The material of the cathode gas diffusion layer is foamed nickel loaded with a reduction catalyst; the material of the anode gas diffusion layer is foamed nickel loaded with an oxidation catalyst.

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