System and method for solar oxidation degradation of organic wastewater and hydrogen production

Abstract

The application discloses a system and method for solar oxidation degradation of organic wastewater and hydrogen production, and the whole system comprises a membrane separation subsystem, a solar heat collection subsystem and a multi-electrode reverse electrodialysis subsystem. The system takes solar energy as a driving force, takes high-salt organic wastewater as a working solution, realizes hydrogen production and organic matter degradation by means of a concentration difference of the working solution, separates the high-salt organic wastewater into high-salt wastewater and organic wastewater, and realizes effective utilization and efficient degradation of the high-salt organic wastewater by combining solar energy and reverse electrodialysis. That is, the system can completely mineralize the organic matter in the wastewater and produce high-purity hydrogen, and realizes efficient and high-quality utilization of solar energy.

Description

Technical Field

[0001] This invention belongs to the field of high-salt organic wastewater recycling technology, specifically a system and method for solar-powered oxidation degradation of organic wastewater and hydrogen production. Background Technology

[0002] Existing methods for treating organic wastewater fall into two main categories: biochemical degradation and advanced oxidative degradation. Biochemical degradation, including anaerobic and aerobic methods, utilizes the coordinated cooperation and metabolic processes of various microorganisms to decompose organic matter into environmentally harmless substances in anaerobic or aerobic environments. This method has been widely used to treat low-concentration organic wastewater with good results. However, it is difficult to effectively treat high-salinity organic wastewater discharged from processes such as pharmaceuticals, pesticides, dyeing and printing, refining, and coking using biochemical degradation methods.

[0003] To address this, various advanced oxidation methods for organic wastewater treatment have been proposed, including supercritical water oxidation, plasma advanced oxidation, Fenton reagent or electro-Fenton oxidation, ozone oxidation, photocatalytic oxidation, and ultrasound-assisted oxidation. However, these methods consume large amounts of electricity or chemical reagents, resulting in high treatment costs. Therefore, constructing novel degradation systems for high-salinity organic wastewater to achieve its effective utilization and efficient degradation is a key technical challenge that urgently needs to be overcome in the field of high-salinity organic wastewater treatment. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a system and method for solar-powered oxidation degradation of organic wastewater and hydrogen production; this system can completely mineralize the organic matter in the wastewater and generate high-purity hydrogen, while simultaneously achieving efficient and high-quality utilization of solar energy.

[0005] This invention is achieved through the following technical solution:

[0006] This invention provides a solar-powered system for oxidizing and degrading organic wastewater and producing hydrogen. The system uses solar energy as the driving force and high-salt organic wastewater as the working solution. It achieves hydrogen production and degradation of organic matter by utilizing the concentration difference of the working solution. The entire system includes a membrane separation subsystem, a solar thermal collection subsystem, and a multi-electrode reverse electrodialysis subsystem.

[0007] Furthermore, the membrane separation subsystem includes a high-salt organic wastewater input pump, a membrane separator, a high-salt wastewater output pump, and an organic wastewater output pump. The high-salt organic wastewater input pump is connected to the inlet pipe of the membrane separator, and the two outlet pipes of the membrane separator are respectively connected to the high-salt wastewater output pump and the organic wastewater output pump. The outlet of the organic wastewater output pump is connected to the organic wastewater storage tank.

[0008] Furthermore, the solar thermal collector subsystem includes a solar collector, a solution generator, a circulating working fluid pump, a solution spray pipe, an open tank, a dilute solution control valve, a dilute solution storage tank, a concentrated solution storage tank, and a dilute solution concentration regulating valve;

[0009] The outlet of the high-salt wastewater output pump of the membrane separation subsystem is connected to the inlet pipe of the solution generator. A circulating working fluid pump is installed between the solar collector and the solution generator. The high-salt wastewater flows out of the solution generator after heat exchange with the circulating working fluid heated by the solar collector. The two outlet pipes of the solution generator are respectively connected to an open tank and a dilute solution storage tank. A dilute solution control valve is also installed on the outlet pipe connecting the solution generator and the dilute solution storage tank. A solution spray pipe is installed in the open tank and connected to the concentrated solution storage tank. A dilute solution concentration regulating valve is installed on the pipe between the dilute solution storage tank and the concentrated solution storage tank.

[0010] Furthermore, the solution generator is a plate heat exchanger, and the circulating working fluid is water, a low-boiling-point alcohol, a thermally conductive silicone oil, or a halogenated hydrocarbon refrigerant.

[0011] Furthermore, the multi-electrode reverse electrodialysis subsystem includes several sets of reverse electrodialysis battery stacks, with each set of reverse electrodialysis battery stacks located between every two electrodes.

[0012] The reverse electrodialysis battery stack includes a gas-liquid separator, a hydrogen storage tank, a cathode liquid storage tank, an anode liquid pump I, a cation exchange membrane, an anion exchange membrane, an adjustable resistor, an organic wastewater storage tank, an anode liquid pump II, a concentrated solution flow channel S1 and a dilute solution flow channel S2, a cathode chamber S3 and an anode chamber S4.

[0013] The cation exchange membrane and anion exchange membrane allow only cations and anions from the salt solution to pass through, respectively. They are arranged alternately in the reverse electrodialysis stack. Any two ion exchange membranes can form a concentrated solution channel S1 and a dilute solution channel S2. The outermost two sides of the reverse electrodialysis stack are the cation exchange membrane and the anion exchange membrane, respectively. The outermost cation exchange membrane forms an anode chamber S4 with the adjacent electrode, and the outermost anion exchange membrane forms a cathode chamber S3 with the adjacent electrode.

[0014] The cathode chamber S3 is connected to a gas-liquid separator, which is connected to a hydrogen storage tank and a cathode liquid storage tank. The gas-liquid separator separates and purifies the hydrogen produced by the system from the electrode liquid it carries. The cathode liquid is returned to the cathode liquid storage tank. The organic wastewater is circulated in the anode chamber S4 and the organic wastewater storage tank. The wastewater is discharged from the system after the organic matter in the wastewater is completely degraded into clean water. The bottom of the reverse electrodialysis battery stack is also connected to a desalination device.

[0015] Furthermore, the cation exchange membrane is made of sulfonated polyether ether ketone, and the anion exchange membrane is made of polyepoxychloropropane.

[0016] Furthermore, each set of reverse electrodialysis cells between two electrodes contains 40 pairs of anion and cation exchange membranes, each membrane being 10 cm long and 10 cm wide, and the electrodes being boron-doped diamond electrodes or other inert electrodes.

[0017] Furthermore, both the concentrated solution flow channel S1 and the dilute solution flow channel S2 are provided with a septum layer with a thickness of 200 μm.

[0018] This invention also provides a method for solar-powered oxidation degradation of organic wastewater and hydrogen production, comprising the following steps:

[0019] Step 1: The high-salt organic wastewater input from the outside is separated into high-salt wastewater containing multiple inorganic salt ions and organic wastewater containing macromolecular organic pollutants through the membrane separation subsystem.

[0020] The high-salt organic wastewater discharged from the factory is pumped into the membrane separator by the high-salt organic wastewater input pump and separated into high-salt wastewater containing multiple inorganic salt ions and organic wastewater containing macromolecular organic pollutants. The high-salt wastewater enters the solar thermal collector subsystem under the action of the high-salt wastewater output pump, while the organic wastewater enters the multi-electrode reverse electrodialysis subsystem under the action of the organic wastewater output pump.

[0021] Step 2: Convert solar energy into salinity gradient energy of the working solution through a solar thermal collector system;

[0022] The high-salt wastewater output pump pumps the high-salt wastewater into the solution generator, where it exchanges heat with the circulating working fluid heated by the solar collector. After flowing out of the solution generator, part of the high-salt wastewater enters the dilute solution storage tank as a dilute solution, while another part is sprayed at the solution spray pipe in the open tank. The water vapor generated rises and exits the tank. The remaining concentrated high-salt wastewater enters the concentrated solution storage tank as a concentrated solution. By controlling the dilute solution concentration regulating valve, a small amount of concentrated solution can enter the dilute solution storage tank to achieve the regulation of the dilute solution conductivity.

[0023] Step 3: The concentration gradient energy of the concentrated and dilute solutions is converted into hydrogen energy and organic matter degradation energy through a multi-electrode reverse electrodialysis subsystem;

[0024] Driven by the potential difference across each membrane stack, hydrogen evolution and organic degradation reactions occur in the cathode chambers S3 and anode chambers S4 of the multi-electrode reverse electrodialysis battery stack. The generated hydrogen gas escapes from the top outlet of the anode chamber S3 and enters the gas-liquid separator. After passing through the gas-liquid separator, the gaseous hydrogen gas enters the hydrogen storage tank, while the liquid cathode liquid flows back to the cathode liquid storage tank. The organic wastewater circulates in the anode chamber S4 and the organic wastewater storage tank. After the organic matter in the wastewater is completely degraded into clean water, it is discharged from the system. The concentrated solution that has lost some ions and the dilute solution that has gained some ions flow out from the bottom outlet of the reverse electrodialysis battery stack and enter the desalination device, finally producing clean water and salt.

[0025] The beneficial effects of this invention are as follows:

[0026] 1) The system described in this invention comprises a membrane separation subsystem, a solar thermal collection subsystem, and a multi-electrode reverse electrodialysis subsystem, which separates high-salt organic wastewater into high-salt wastewater and organic wastewater, and combines solar energy and reverse electrodialysis to achieve effective utilization and efficient degradation of high-salt organic wastewater.

[0027] 2) The multi-electrode reverse electrodialysis stack of the present invention contains multiple electrode chambers and can simultaneously undergo hydrogen evolution reaction and degradation reaction. The overall hydrogen production efficiency and organic matter degradation rate of the system will be significantly improved compared with the traditional reverse electrodialysis stack. Furthermore, by directly adding electrodes to the stack, the resistance consumption of external wires is eliminated, resulting in higher energy efficiency.

[0028] 3) The electrodes in the reverse electrodialysis stack of the present invention are boron-doped diamond electrodes, which are inert electrodes with high oxygen evolution potential, strong conductivity and chemical stability.

[0029] 4) The system described in this invention can be applied to various high-salt organic wastewater treatment applications, such as leather making, printing and dyeing, textiles, and coking.

[0030] 5) The system described in this study will ultimately treat high-salt organic wastewater containing various inorganic salts and organic pollutants into clean water that can be directly discharged and recyclable inorganic salts, thus turning high-salt organic wastewater into a valuable resource. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0032] Reference numerals: 1. Solar collector; 2. Solution generator; 3. Circulating working fluid pump; 4. Dilute solution control valve; 5. Solution spray pipe; 6. Open tank; 7. Dilute solution storage tank; 8. Concentrated solution storage tank; 9. Dilute solution concentration regulating valve; 10. Dilute solution pump; 11. Concentrated solution pump; 12. Gas-liquid separator; 13. Hydrogen storage tank; 14. Cathode liquid storage tank; 15. Anode liquid pump I; 16. Electrode; 17. Cation exchange membrane; 18. Anion exchange membrane; 19. Adjustable resistor; 20. Anode liquid pump II; 21. Desalination device; 22. Organic wastewater storage tank; 23. Organic wastewater output pump; 24. High-salt organic wastewater input pump; 25. Membrane separator; 26. High-salt wastewater output pump; S1. Concentrated solution flow channel; S2. Dilute solution flow channel; S3. Cathode chamber; S4. Anode chamber. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Example

[0034] As shown in the attached figure, a solar-powered oxidation system for degrading organic wastewater and producing hydrogen includes the following three processes:

[0035] Step 1: Taking high-salt methyl orange dyeing wastewater as an example, the diameter of methyl orange molecules in the wastewater is approximately 6-8 nm, while the diameter of inorganic salt ions in the wastewater is approximately 0.1-0.4 nm, and the pore size of the ultrafiltration membrane can reach 1 nm. Therefore, when the high-salt methyl orange dyeing wastewater discharged from the factory is pumped into the membrane separation device 25 by wastewater pump 24, the membrane separation device 25, which uses ultrafiltration technology, can separate the wastewater into high-salt wastewater (concentration approximately 0.03 mol / kg) containing multiple inorganic salts and organic wastewater containing macromolecular organic pollutants. Then, the high-salt wastewater and organic wastewater enter the solar thermal collector subsystem and the multi-electrode reverse electrodialysis subsystem respectively via high-salt wastewater output pump 26 and organic wastewater output pump 23.

[0036] Step 2: After the high-salinity wastewater enters the solar collector subsystem, the hot water generated by the solar collector 1 enters the solution generator 2 to heat the low-concentration high-salinity wastewater and generate superheated steam. A portion of the high-salinity wastewater, as a dilute solution, enters the dilute solution storage tank 7. Another portion of the high-salinity wastewater enters the open tank 6, where it is sprayed through the solution spray pipe 5, releasing the superheated steam into the external environment. The concentrated high-salinity wastewater, as a concentrated solution, enters the concentrated solution storage tank 8. The conductivity of the dilute solution storage tank 7 is monitored. If the conductivity is less than 5 mS / cm, the concentration regulating valve 9 is opened, and a concentrated solution is supplied to the dilute solution storage tank 7 to adjust the conductivity to 5 mS / cm.

[0037] The third step involves using the concentrated solution pump 11 and the dilute solution pump 10 to pump the concentrated solution in the concentrated solution storage tank 8 and the dilute solution in the dilute solution storage tank 7 into the concentrated solution channel S1 and the dilute solution channel S2 separated by the cation exchange membrane 17 and the anion exchange membrane 18 in the multi-electrode reverse electrodialysis stack.

[0038] For ease of understanding, in this specific embodiment, the multi-electrode reverse electrodialysis stack uses three boron-doped diamonds as electrodes. The cation exchange membrane is mainly made of sulfonated polyether ether ketone, and the anion exchange membrane is mainly made of polyepoxychloropropane. Each set of anion and cation exchange membranes between two electrodes contains 40 pairs of anion and cation exchange membranes, each with a length of 10 cm and a width of 10 cm. The flow rates of the dilute and concentrated solutions entering the concentrated solution channels S1 (40 channels) and the dilute solution channels S2 (40 channels) are both controlled at approximately 0.1 cm / s, and the inflow is co-current. The concentrated solution pump 11 and the dilute solution pump 10 are preferably constant flow pumps (peristaltic pumps can also be used if cost is a constraint). In the aforementioned concentrated solution channels S1 and dilute solution channels S2, a septum layer with a thickness of 200 μm is arranged to provide flow guidance, support, and sealing.

[0039] Between the concentrated solution (3 mol / kg) in the concentrated solution channel S1 and the dilute solution (0.03 mol / kg) in the adjacent dilute solution channel S2, there exists a chemical potential difference that drives ion migration. Therefore, cations in the concentrated solution channel S1 migrate through the cation exchange membrane 18 to the adjacent dilute solution channel S2; while anions migrate through the anion exchange membrane 17 to the adjacent dilute solution channel S2 in the opposite direction. This accumulation creates a potential difference across the membrane stack. In this specific embodiment, the potential difference between any two electrodes can reach 5 V, thereby driving the simultaneous occurrence of hydrogen evolution reaction (theoretical potential approximately 0 V) ​​and degradation reaction (theoretical potential approximately 2.3 V) in the two anode chambers and two cathode chambers of the stack. Subsequently, the concentrated solution, having lost some ions, and the dilute solution, having gained some ions, flow out from the outlet of the reverse electrodialysis battery stack and enter the desalination unit to separate purified water and salt.

[0040] The principle of oxidative degradation of organic wastewater is as follows:

[0041] In RED battery stacks, the electrodes are boron-doped diamond electrodes or other inert electrodes. When the two ends of the RED battery stack form a closed circuit with an external load through the electrodes, under the action of the chemical potential difference in the solution, when organic wastewater flows through the anode chamber S4, strong oxidant hydroxyl radicals are generated on the anode surface to achieve mineralization of organic pollutants.

[0042]

[0043] In this example, methyl orange wastewater is circulated between organic wastewater storage tank 22 and anode chamber S4, and the methyl orange molecules in the wastewater are continuously mineralized into carbon dioxide and water by hydroxyl radicals. Finally, the methyl orange wastewater is degraded into clean water and discharged into the external environment.

[0044] The principle of hydrogen production is as follows:

[0045] In cathode chamber S3, the hydrogen production reaction can be carried out using an alkaline aqueous solution, or a neutral or acidic aqueous solution. In this embodiment, an alkaline aqueous solution is used as an example, and the specific reaction is as follows:

[0046] 2e- + 2H2O → 2OH- + H2↑

[0047] The generated hydrogen gas escapes from the top outlet of the cathode chamber S3 and enters the gas-liquid separator 13. The gas-liquid separator 13 has two outlets: a gas outlet located at the top, connected to the hydrogen storage tank 13; and a liquid outlet located at the bottom, connected to the cathode liquid storage tank 14. After passing through the gas-liquid separator 12, the gaseous hydrogen gas enters the hydrogen storage tank 13, while the entrained cathode liquid flows back into the cathode liquid storage tank 14. Thus, a solar-powered oxidation and degradation system for organic wastewater and hydrogen production has been successfully constructed, achieving the effective utilization and efficient degradation of high-salt organic wastewater through solar energy drive.

[0048] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope. All such changes and modifications fall within the scope of the present invention as claimed, which is defined by the appended claims and their equivalents.

Claims

1. A system for solar-powered oxidation degradation of organic wastewater and hydrogen production, characterized in that: This system uses solar energy as the driving force and high-salt organic wastewater as the working solution. It achieves hydrogen production and organic matter degradation by utilizing the concentration difference of the working solution. The entire system includes a membrane separation subsystem, a solar thermal collection subsystem, and a multi-electrode reverse electrodialysis subsystem. The membrane separation subsystem includes a high-salt organic wastewater input pump (24), a membrane separator (25), a high-salt wastewater output pump (26), and an organic wastewater output pump (23). The high-salt organic wastewater input pump (24) is connected to the inlet pipe of the membrane separator (25). The membrane separator (25) has two outlet pipes connected to a high-salt wastewater output pump (26) and an organic wastewater output pump (23), respectively. The outlet of the organic wastewater output pump (23) is connected to the organic wastewater storage tank (22). The solar thermal collector subsystem includes a solar collector (1), a solution generator (2), a circulating working fluid pump (3), a solution spray pipe (5), an open tank (6), a dilute solution control valve (4), a dilute solution storage tank (7), a concentrated solution storage tank (8), and a dilute solution concentration regulating valve (9). The outlet of the high-salt wastewater output pump (26) of the membrane separation subsystem is connected to the inlet pipe of the solution generator (2). A circulating working fluid pump (3) is installed between the solar collector (1) and the solution generator (2). The high-salt wastewater flows out of the solution generator (2) after heat exchange with the circulating working fluid heated by the solar collector (1). The two outlet pipes of the solution generator (2) are respectively connected to an open tank (6) and a dilute solution storage tank (7). A dilute solution control valve (4) is also installed on the outlet pipe connecting the solution generator (2) and the dilute solution storage tank (7). A solution spray pipe (5) is installed inside the open tank (6). The open tank (6) is connected to a concentrated solution storage tank (8). A dilute solution concentration regulating valve (9) is installed on the pipe between the dilute solution storage tank (7) and the concentrated solution storage tank (8). The multi-electrode reverse electrodialysis subsystem includes several sets of reverse electrodialysis battery stacks. Each pair of electrodes (16) contains a set of reverse electrodialysis battery stacks. The reverse electrodialysis battery stack includes a gas-liquid separator (12), a hydrogen storage tank (13), a cathode liquid storage tank (14), an anode liquid pump I (15), a cation exchange membrane (17), an anion exchange membrane (18), an adjustable resistor (19), an organic wastewater storage tank (22), an anode liquid pump II (20), a concentrated solution flow channel S1 and a dilute solution flow channel S2, a cathode chamber S3 and an anode chamber S4; The cation exchange membrane (17) and anion exchange membrane (18) allow only cations and anions in the salt solution to pass through. They are arranged alternately in the reverse electrodialysis stack. Any two ion exchange membranes can form a concentrated solution flow channel S1 and a dilute solution flow channel S2. The outermost two sides of the reverse electrodialysis stack are the cation exchange membrane (17) and the anion exchange membrane (18). The outermost cation exchange membrane (17) forms an anode chamber S4 with the adjacent electrode, and the outermost anion exchange membrane (18) forms a cathode chamber S3 with the adjacent electrode. The cathode chamber S3 is connected to a gas-liquid separator (12), which is connected to a hydrogen storage tank (13) and a cathode liquid storage tank (14). The gas-liquid separator (12) separates and purifies the hydrogen generated by the system from the electrode liquid it carries. The cathode liquid is returned to the cathode liquid storage tank (14). The organic wastewater is circulated in the anode chamber S4 and the organic wastewater storage tank (22). The wastewater is discharged from the system after the organic matter in the wastewater is completely degraded into clean water. The bottom of the reverse electrodialysis battery stack is also connected to a desalination device (21).

2. The system for solar-powered oxidation degradation of organic wastewater and hydrogen production according to claim 1, characterized in that: The solution generator (2) is a plate heat exchanger, and the circulating working fluid is water, low-boiling-point alcohol, thermally conductive silicone oil, or halogenated hydrocarbon refrigerant.

3. The system for solar-powered oxidation degradation of organic wastewater and hydrogen production according to claim 1, characterized in that: The cation exchange membrane (17) is made of sulfonated polyether ether ketone, and the anion exchange membrane (18) is made of polyepoxychloropropane.

4. The system for solar-powered oxidation degradation of organic wastewater and hydrogen production according to claim 1, characterized in that: Each set of reverse electrodialysis cells between two electrodes contains 40 pairs of anion and cation exchange membranes, each membrane being 10 cm long and 10 cm wide. The electrodes are boron-doped diamond electrodes or other inert electrodes.

5. The system for solar-powered oxidation degradation of organic wastewater and hydrogen production according to claim 1, characterized in that: Both the concentrated solution channel S1 and the dilute solution channel S2 are provided with a septum layer with a thickness of 200 μm.

6. A method for solar-powered oxidation degradation of organic wastewater and hydrogen production according to any one of claims 1 to 5, characterized in that: Includes the following steps: Step 1: Separate the high-salt organic wastewater from the outside into high-salt wastewater containing multiple inorganic salt ions and organic wastewater containing macromolecular organic pollutants through the membrane separation subsystem; The high-salt organic wastewater discharged from the factory is pumped into the membrane separator (25) by the high-salt organic wastewater input pump (24) and separated into high-salt wastewater containing multiple inorganic salt ions and organic wastewater containing macromolecular organic pollutants. The high-salt wastewater enters the solar thermal collector subsystem under the action of the high-salt wastewater output pump (26), while the organic wastewater enters the multi-electrode reverse electrodialysis subsystem under the action of the organic wastewater output pump (23). Step 2: Convert solar energy into salinity gradient energy of the working solution through a solar thermal collector system; The high-salt wastewater output pump (26) pumps the high-salt wastewater into the solution generator (2), where it exchanges heat with the circulating working fluid heated by the solar collector (1). After flowing out of the solution generator (2), a portion of the high-salt wastewater enters the dilute solution storage tank (7) as a dilute solution, while the other portion is sprayed at the solution spray pipe (5) in the open tank (6). The water vapor generated rises and exits the tank. The remaining concentrated high-salt wastewater enters the concentrated solution storage tank (8) as a concentrated solution. By controlling the dilute solution concentration regulating valve (9), a small amount of concentrated solution can enter the dilute solution storage tank (7), thereby achieving the regulation of the dilute solution conductivity. Step 3: The concentration gradient energy of the concentrated and dilute solutions is converted into hydrogen energy and organic matter degradation energy through a multi-electrode reverse electrodialysis subsystem; Driven by the potential difference across each membrane stack, hydrogen evolution reaction and organic degradation reaction occur in each cathode chamber S3 and anode chamber S4 of the multi-electrode reverse electrodialysis battery stack. The generated hydrogen gas escapes from the top outlet of the cathode chamber S3 and enters the gas-liquid separator (12). After passing through the gas-liquid separator (12), the gaseous hydrogen gas enters the hydrogen storage tank (13), while the liquid cathode liquid flows back to the cathode liquid storage tank (14). The organic wastewater circulates in the anode chamber S4 and the organic wastewater storage tank (22). After the organic matter in the wastewater is completely degraded into clean water, it is discharged from the system. The concentrated solution that loses some ions and the dilute solution that gains some ions flow out from the bottom outlet of the reverse electrodialysis battery stack and enter the desalination device (21), finally producing clean water and salt.

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