Preparation of a Janus composite membrane with a sandwich structure and its application in volume reduction of nuclear power plant decontamination wastewater.

Abstract

This invention discloses the preparation of a Janus composite membrane with a sandwich structure and its application in volume reduction of nuclear power plant decontamination wastewater. The Janus composite membrane consists of a hydrogel-like tannic acid / polypropylene glycol (PPG / TA) top layer, a highly adhesive biomimetic intermediate layer formed by polydopamine / polyethyleneimine / chitosan (PDA / PEI / CS), and a hydrophobic polytetrafluoroethylene (PTFE) substrate. Compared with traditional PTFE membranes, when the Janus composite membrane of this invention is applied to volume reduction of nuclear power plant decontamination wastewater, the asymmetric wettability of the Janus composite membrane prevents the foaming liquid of the decontamination wastewater from directly contacting the PTFE substrate and increases the capillary pressure at the membrane-liquid interface, thereby protecting its hydrophobic properties and continuously transporting water vapor. Compared with the monotonous negatively charged layer of the original commercial PTFE membrane, the rich hydrophilic functional groups of the modified layer of the Janus composite membrane further reduce the permeation rate of nuclides and other pollutants, with a nuclide rejection rate of over 99.95% and a permeate recovery rate of over 85%.

Description

Technical Field

[0001] This invention belongs to the field of radioactive wastewater treatment, and particularly relates to the preparation of a Janus composite membrane with a sandwich structure and its application in reducing the volume of decontamination wastewater from nuclear power plants. Background Technology

[0002] Besides spent fuel cooling water, decontamination wastewater is one of the main sources of liquid waste from nuclear power plants. It is a low-level radioactive waste generated from the removal of radioactive contaminants from the inner surfaces of instruments and equipment in contact with the coolant, as well as from floor cleaning, instrument maintenance, and personnel decontamination (including washing, laundry, etc.). Due to its high surfactant content, it typically exhibits unique characteristics such as easy aggregation and solubilization, easy formation of micelles and foaming, toxicity to aquatic organisms, and high reactivity with contaminants. Furthermore, surfactants can react with radionuclides such as Cs. + 、Sr 2+ Co 2+ The mixing process produces a significant synergistic effect, complicating the removal of radionuclides and posing new challenges to currently used treatment methods.

[0003] Membrane distillation relies on its separation principle: volatile components in the feed stream evaporate through a porous hydrophobic membrane according to a temperature gradient. Due to its high retention rate of radionuclides and excellent salt resistance, coupled with the low-grade waste heat generated by nuclear power plants, membrane distillation technology is increasingly used in the treatment of low-level radioactive wastewater. However, the presence of various surfactants significantly reduces the lifespan of commercial membrane materials, manifesting as rapid wetting of the membrane material (damage to the substrate hydrophobicity), thus creating a water pathway for pollutants and deteriorating the quality of the distillate. Compared to traditional hydrophobic membranes, composite Janus membranes offer better membrane distillation performance and have become a research hotspot. However, the additional layer introduced by composite membranes increases thermal resistance, exacerbating temperature polarization and reducing mass transfer driving force, resulting in severe membrane flux loss. Furthermore, the application performance of Janus membranes is inconsistent and difficult to handle complex real-world waste liquids. Therefore, achieving both stability and fouling resistance in modified membranes during engineering applications is a difficult problem. Therefore, developing a new high-efficiency hollow fiber membrane distillation material with almost no water flux loss, resistance to pollution and scaling is a pressing problem that needs to be solved in membrane distillation for reducing the volume of low-radioactive waste liquid from nuclear power plants.

[0004] Hydrogels are hydrophilic polymers with a three-dimensional network structure. However, traditional single-component gel groups are prone to drawbacks such as insufficient thermal stability and poor fouling rejection, leading to increasing research on composite hydrogels. Dopamine is a neurotransmitter widely present in organisms. Dopamine and its catechol derivatives, after oxidative polymerization under alkaline and aerobic conditions, can adhere to any substrate surface in an aqueous environment, forming a robust polydopamine layer. However, this layer is usually thin, resulting in less than ideal antifouling performance during membrane distillation. This paper presents for the first time the application of Janus hollow fiber membranes for vacuum membrane distillation and volume reduction of low-level radioactive waste from nuclear power plants, providing a new solution for the rational disposal of this waste. Summary of the Invention

[0005] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0006] To achieve these objectives and other advantages according to the present invention, a method for preparing a Janus composite membrane with a sandwich structure is provided, characterized by comprising the following steps:

[0007] Step 1: Cut polytetrafluoroethylene (PTFE) hollow fiber membrane filaments, soak them in anhydrous ethanol, rinse them with distilled water, and then dry them to make hollow fiber membrane modules.

[0008] Step 2: Prepare the biomimetic bio-adhesive and inject it into the hollow fiber membrane module using a syringe.

[0009] Step 3: Prepare the hydrogel, cool it, and then deposit it onto the hollow fiber membrane module using a syringe to obtain the Janus composite membrane.

[0010] Preferably, in step one, the soaking time is 20 minutes. The specific method for making the hollow fiber membrane module is as follows: a membrane module is made using a rigid polytetrafluoroethylene (PTFE) tube soaked in anhydrous ethanol and 5-15 PTFE hollow fiber membrane filaments 30-45 cm long. The PTFE hollow fiber membrane filaments are inserted into the rigid PTFE tube, and the gaps between the two ends of the rigid PTFE tube and the PTFE hollow fiber membrane filaments are sealed with epoxy resin. After the epoxy resin dries, the excess length of the PTFE hollow fiber membrane filaments and the glued end are cut off with a knife. It can be used normally after one night.

[0011] Preferably, in step two, the method for preparing the biomimetic bio-adhesive is as follows: dopamine hydrochloride (PDA), polyethyleneimine (PEI), and chitosan (CS) are dissolved in tris(hydroxymethyl)aminomethane buffer (Tris-HCl buffer solution) at 25°C, and then stirred uniformly at 200 rpm for 30 min.

[0012] Preferably, the biomimetic bio-adhesive contains dopamine hydrochloride, polyethyleneimine, and chitosan in a mass ratio of 1:1 to 1.5:0.5 to 1, with a concentration of 2 mg / ml, a Tris-HCl buffer solution concentration of 50 mmol / L, and a pH value of 8.5.

[0013] Preferably, in step two, the well-stirred biomimetic adhesive is drawn into the interior of the polytetrafluoroethylene hollow fiber membrane using a syringe, the sealing is checked, and the surface of the biomimetic adhesive is observed to prevent leakage, ensuring that the liquid is always maintained inside the entire component. After vertical contact for 12 to 24 hours, it is allowed to air dry for 6 to 12 hours.

[0014] Preferably, in step three, the hydrogel preparation method is as follows: tannic acid (PPF) and polypropylene glycol (TA) are mixed and stirred evenly at a mass ratio of 1:5 to 10, the stirring speed is 300 to 400 rpm, the stirring temperature is 85 to 90°C, and the stirring time is 6 to 8 hours.

[0015] Preferably, in step three, the deposition method is as follows: after the prepared hydrogel is cooled, the hydrogel is drawn into the hollow fiber membrane module obtained in step two using a syringe, then soaked for 5-10 minutes, and the residual liquid is squeezed out. The module is placed in a freezer for 2 hours, then at room temperature for 6-12 hours. The freeze-thaw cycle is repeated 2-3 times. Then, pure water is drawn into the membrane module using a syringe to fully swell the outermost layer.

[0016] This invention also provides a Janus composite membrane application for volume reduction of nuclear power plant decontamination waste liquid. The invention is characterized by a Janus hollow fiber membrane module composed of multiple Janus composite membranes connected to the output end of a concentrated waste liquid tank in a vacuum membrane distillation device via an intelligent peristaltic pump. The vacuum membrane distillation device further includes a pretreatment tank, and a heating jacket is fitted inside the concentrated waste liquid tank. The feed side of the Janus hollow fiber membrane module is connected to the intelligent peristaltic pump, and the permeate side of the Janus hollow fiber membrane module is externally connected to a condenser and a distillate collection tank. A reflux pipe is provided at the output end of the Janus hollow fiber membrane module, connecting it to the concentrated waste liquid tank.

[0017] Preferably, in the vacuum membrane distillation apparatus, the feed temperature of the exchange liquid is set to 70–80°C, the feed flow rate is 100–300 ml / min, the vacuum degree is -0.08–-0.09 MPa, and the condensation temperature is 8–10°C. The heat energy for heating the exchange liquid from room temperature to the feed temperature required for membrane distillation comes from the waste heat recovery system of the nuclear power plant reactor. The recovery method is a heat pump, regenerator, heater, etc., and no additional heating is required.

[0018] The present invention has at least the following beneficial effects:

[0019] (1) The method provided by the present invention can effectively reduce the volume of radioactive wastewater from nuclear power plants. From the perspective of membrane distillation technology, it solves the key problems of rapid membrane material fouling and short service life caused by the presence of surfactants. At the same time, the membrane distillation effect is stable. Once the device is running, no other operation is required from the beginning to the end of the concentration stage, which fundamentally reduces the time cost of personnel exposure to radiation.

[0020] (2) This invention can overcome the problem of substrate membrane pore wetting caused by surfactants with low surface tension by modifying the bifunctional layer of the sandwich structure; through the membrane distillation technology of Janus composite membrane material, the radioactive ion concentration of the effluent from the decontamination of radioactive wastewater from nuclear power plants is ≤0.012mg / L, the effluent conductivity is ≤5.08μS / cm, the water recovery rate is over 85%, the concentration factor is significantly improved compared with commercial membranes, and the radionuclide interception effect is higher than 99.95%.

[0021] (3) The Janus composite membrane provided by this invention has a composite pore structure with small pores covering large pores. According to the Young-Laplace equation, the micropores in the gel layer of the Janus composite membrane can significantly increase the ingress capillary pressure at the membrane-liquid interface, meaning that pollutants need to do more work to overcome them in order to achieve a penetration effect. Although the composite membrane is thicker, the intermediate water provided by the hydrogel layer and the highly adhesive hydrophilic groups in the intermediate layer can provide a higher vapor partial pressure. Therefore, the membrane flux is less damaged and can be kept at the same level as the original membrane flux.

[0022] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0023] Figure 1 The structural formulas of the materials prepared in each step of this invention are shown below;

[0024] Figure 2 This is a schematic diagram of a vacuum membrane distillation apparatus in an application example of the present invention;

[0025] Figure 3 This is a SEM image of the original polytetrafluoroethylene (PTFE) membrane in Example 1 of the present invention;

[0026] Figure 4 This is a SEM image of the Janus composite membrane finally obtained in Example 1 of the present invention;

[0027] Figure 5 The following are data graphs showing the simulated radioactive waste liquid treatment effects of Application Example 1 and Comparative Example 4 of this invention;

[0028] Figure 6 This is a graph showing the simulated radioactive waste liquid treatment effect data of Comparative Example 5 of the present invention;

[0029] Figure 7 The following are data graphs showing the simulated radioactive waste liquid treatment effects of Application Example 2 and Comparative Example 6 of this invention. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0031] Example 1

[0032] A method for preparing a Janus composite membrane with a sandwich structure includes the following steps:

[0033] Step 1: Cut 32cm long polytetrafluoroethylene (PTFE) hollow fiber membrane filaments and PTFE rigid tubing, soak them in anhydrous ethanol for 20 minutes, then rinse with distilled water and dry. Use the PTFE rigid tubing and 5 PTFE hollow fiber membrane filaments to make a membrane module: Insert the PTFE hollow fiber membrane filaments into the PTFE rigid tubing, and seal the gaps between the two ends of the PTFE rigid tubing and the PTFE hollow fiber membrane filaments with epoxy resin (do not contaminate the hollow channels of the hollow membrane). After the epoxy resin dries, use a knife to cut off the excess membrane length beyond the rigid tubing and the glued end, and leave it overnight.

[0034] Step 2: Measure 20 mL of Tris-HCl buffer solution (50 mmol / L, pH = 8.5), 40 mg of dopamine hydrochloride (PDA), 40 mL of polyethyleneimine (PEI), and 20 mg of chitosan (CS). Stir magnetically at 200 r / min for 30 min at 25℃ to obtain a biomimetic bio-adhesive (PDA / PEI / CS) reagent. Then, use a syringe to draw the biomimetic bio-adhesive reagent into the PTFE hollow fiber membrane filaments. Check the seal and observe that the biomimetic bio-adhesive liquid level does not leak, ensuring that the liquid is always maintained inside the entire component. After vertical contact with the component for 24 h, allow it to air dry for 12 h. After drying, the biomimetic bio-adhesive forms a very thin PDA / PEI / CS intermediate layer on the inner surface of the PTFE hollow fiber membrane filaments, and the PTFE hollow fiber membrane filaments still maintain their hollow structure.

[0035] Step 3: Weigh 2g of polypropylene glycol and 0.8g of tannic acid, place them in a magnetically heated stirring pot, set the stirring speed to 300rpm / min, the stirring temperature to 85℃, and the stirring time to 6h to obtain propylene glycol (PPG) and tannic acid (TA) hydrogels. After cooling, use a syringe to draw the hydrogel into the membrane module, soak it for 5min, and squeeze out the residual liquid. Place the membrane module in a freezer for 2h, then take it out and store it at room temperature for 6h. Repeat the freeze-thaw cycle twice, and then use a syringe to draw ultrapure water to soak it for 12h to allow the outermost layer to fully swell, thus obtaining the Janus composite membrane, which is stored in ultrapure water.

[0036] The structural formulas of the materials used in this embodiment are as follows: Figure 1 As shown, the SEM image of the PTFE membrane obtained in step one is as follows. Figure 3 As shown, the surface of the original PTFE substrate exhibits a porous microstructure characterized by crack lines formed by "fibrils" and particle agglomeration formed by "nodes." These fibril voids act as transmembrane channels for water vapor passage, with pore diameters ranging from 10 to 100 nm. The SEM image of the Janus composite membrane obtained in step three is shown below. Figure 4 As shown, the membrane surface becomes flat, and the micropores and fiber nodes are covered by a cross-linked network, forming a leaf vein-mesophyll structure similar to that of plant leaves. The top grains disappear significantly, presenting a smooth and defect-free dense layer.

[0037] Comparative Example 1

[0038] Using a commercially available PTFE membrane as a comparative example, five 32cm long commercial PTFE membranes were cut and processed according to step one in Example 1, without any further modification.

[0039] Comparative Example 2

[0040] Five commercial PTFE membranes, each 32 cm in length, were cut and processed according to steps one and two in Example 1, but step three was omitted, to obtain the PDA / PEI / CS-PTFE membrane.

[0041] Comparative Example 3

[0042] Five commercial PTFE membranes, each 32 cm in length, were cut and processed according to step one in Example 1. Then, step three was performed directly without step two to obtain the PPG / TA-PTFE membrane.

[0043] Application Example 1

[0044] The Janus composite membrane prepared in Example 1 was used as a membrane module to treat decontamination wastewater from a simulated nuclear power plant, including the following steps:

[0045] Building such Figure 2 The vacuum membrane distillation apparatus shown is used for volume reduction treatment of decontamination waste liquid from nuclear power plant equipment, and is configured with 100 mg / L Sr. 2+ Cs + Co 2+The process involved simulating radionuclides and using an industrial detergent (100 mg / L) to clean the inner walls of process equipment and instruments, along with chemical detergents oxalic acid (OA) and citric acid (30 mg / L), with a waste liquid volume of 0.5 L. The simulated component of the industrial detergent was a cationic surfactant, cetyltrimethylammonium bromide (CTAB), combined with a nonionic surfactant, polysorbate-80 (Tween-80). The feed liquid was poured into a waste liquid concentration tank and heated to 70°C. A peristaltic pump at a flow rate of 100 ml / min pumped the feed liquid into the lower end of the membrane module. The condensate circulation and vacuum pump were activated, and the unit operated for 24 hours. Samples were taken from the distillation tank every hour to measure changes in the effluent quality.

[0046] Comparative Example 4

[0047] Comparative Example 1 used a commercial PTFE membrane as a membrane module to treat decontamination wastewater from a simulated nuclear power plant, using the same method as in Application Example 1.

[0048] The results show that, Figure 5 As shown, after eight hours of operation of the vacuum membrane distillation unit, the commercial PTFE membrane experienced severe wetting, resulting in a rapid increase in flux and deterioration of effluent quality. The conductivity increased to 162.5 μS / cm, and the radionuclide rejection rate decreased to approximately 80%. In contrast, the Janus-PTFE membrane exhibited very stable performance, with a water flux almost identical to that of the unmodified PTFE membrane when the pores were not wetted (8 L / m). 2 / h), and the effluent stability remains close to 100%. The effluent conductivity during long-term operation is <3.69μs / cm, Sr 2+ Cs + Co 2+ The concentrations were all less than 0.012 mg / L, the rejection rate was >99.95%, and the water recovery rate was 88%. This proves that the membrane material achieved the purpose of reducing the volume of radioactive waste liquid containing detergents.

[0049] Comparative Example 5

[0050] The PDA / PEI / CS-PTFE membrane prepared in Comparative Example 2 and the PPG / TA-PTFE membrane prepared in Comparative Example 3 were used as membrane modules to treat the decontamination waste liquid from the simulated nuclear power plant in Application Example 1, including the following steps:

[0051] With the apparatus set up, both membranes were used for the simulated waste liquid in Application Example 1, and experiments were conducted under the same process conditions. The results showed that, as... Figure 6As shown, the exposure of the intermediate layer temporarily increased the membrane flux during the unwetting period due to its strong adhesion and hydrophilicity, which increased the contact area with water. However, after nine hours of operation, the PDA / PEI / CS-PTFE membrane underwent severe wetting, resulting in a rapid increase in flux and a deterioration in effluent quality. The conductivity increased to 80.46 μS / cm, and the radionuclide rejection rate decreased to approximately 90%. This indicates that the intermediate layer was insufficient to resist surfactant intrusion, and the membrane lifespan was only extended by about one hour compared to commercial membranes. Compared to the PPG / TA-PTFE membrane, the water flux during the unwetting period was almost the same as that of unmodified PTFE in the unwetting state (8 L / m). 2 The effluent stability remained close to 100% throughout the long-term operation ( / h). However, after 10 hours of operation, the effluent conductivity exceeded 10.75 μS / cm, the nuclide rejection rate dropped to 99.4%, and severe wetting occurred after 11 hours. This indicates that the composite membrane material with the gel layer lacked an intermediate layer for bonding, and the gel unstablely detached from the PTFE substrate, leading to interception failure.

[0052] Application Example 2

[0053] The Janus composite membrane prepared in Example 1 and the commercial PTFE membrane of Comparative Example 1 were used as membrane modules to treat decontamination wastewater from a simulated nuclear power plant, including the following steps:

[0054] Building such Figure 2 The vacuum membrane distillation apparatus shown is used in this application for volume reduction treatment of wastewater from nuclear power plant decontamination and laundry processes, with a concentration of 100 mg / L Sr. 2+ Cs + Co 2+ Simulated nuclides, along with 200 mg / L of detergent used for washing and showering staff uniforms, were used, resulting in a waste liquid volume of 0.5 L. The staff detergent consisted of a certain brand of laundry detergent and shower gel. The feed liquid was poured into a waste liquid concentration tank and heated to 70°C. A peristaltic pump at a flow rate of 100 ml / min pumped the feed liquid into the lower end of the membrane module. The condensate circulation and vacuum pump were activated, and the device operated for 24 hours. Samples were taken from the distillation tank every hour to measure changes in the effluent quality.

[0055] Comparative Example 6

[0056] Comparative Example 1 used a commercial PTFE membrane as a membrane module to treat decontamination wastewater from a simulated nuclear power plant, using the same method as in Application Example 2.

[0057] The results show that, Figure 7As shown, after seven hours of operation of the vacuum membrane distillation unit, the effluent quality of the commercial PTFE membrane deteriorated, with conductivity increasing to 156.7 μS / cm and radionuclide rejection decreasing to approximately 80%. In contrast, the Janus composite membrane performed remarkably well, with water flux almost identical to that of the unmodified PTFE membrane, and effluent stability consistently approaching 100%. During long-term operation, the effluent conductivity was <4.18 μS / cm, and the Sr... 2+ Cs + Co 2+ The concentrations were all less than 0.012 mg / L, the rejection rate was >99.95%, and the water recovery rate was 90%. This proves that the membrane material achieves the purpose of reducing the volume of low-level radioactive waste liquid containing personnel decontamination agents from nuclear power plants.

[0058] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a Janus composite membrane with a sandwich structure, characterized in that, Includes the following steps: Step 1: Cut polytetrafluoroethylene hollow fiber membrane filaments, soak them in anhydrous ethanol, rinse them with distilled water, and then dry them to make hollow fiber membrane modules. Step 2: Prepare the biomimetic bio-adhesive and inject it into the hollow fiber membrane module using a syringe. Step 3: Prepare the hydrogel, cool it, and then deposit it onto the hollow fiber membrane module using a syringe to obtain the Janus composite membrane; In step two, the method for preparing the biomimetic bio-adhesive is as follows: Dopamine hydrochloride, polyethyleneimine, and chitosan are dissolved in a Tris-HCl buffer solution at 25°C, and then stirred uniformly at 200 rpm for 30 min; the mass ratio of dopamine hydrochloride, polyethyleneimine, and chitosan in the biomimetic bio-adhesive is 1:1~1.5:0.5~1, the concentration of dopamine hydrochloride is 2 mg / ml, the concentration of the Tris-HCl buffer solution is 50 mmol / L, and the pH value is 8.5; In step three, the hydrogel preparation method is as follows: tannic acid and polypropylene glycol are mixed and stirred evenly at a mass ratio of 1:5~10, the stirring speed is 300~400 rpm, the stirring temperature is 85~90℃, and the stirring time is 6~8h.

2. The method for preparing the Janus composite membrane with a sandwich structure according to claim 1, characterized in that, In step one, the soaking time is 20 minutes. The specific method for making the hollow fiber membrane module is as follows: a membrane module is made using a rigid polytetrafluoroethylene (PTFE) tube soaked in anhydrous ethanol and 5-15 PTFE hollow fiber membrane filaments 30-45 cm long. The PTFE hollow fiber membrane filaments are inserted into the rigid PTFE tube, and the gaps between the two ends of the rigid PTFE tube and the PTFE hollow fiber membrane filaments are sealed with epoxy resin. After the epoxy resin dries, the excess length of the PTFE hollow fiber membrane filaments and the glued end are cut off with a knife. It can be used normally after one night.

3. The method for preparing the Janus composite membrane with a sandwich structure according to claim 1, characterized in that, In step two, the well-stirred biomimetic adhesive is drawn into the interior of the polytetrafluoroethylene hollow fiber membrane using a syringe. The sealing is checked, and the biomimetic adhesive liquid level is observed to ensure that it does not leak. The liquid is kept inside the entire component and then allowed to dry naturally for 6 to 12 hours after vertical contact.

4. The method for preparing the Janus composite membrane with a sandwich structure according to claim 1, characterized in that, In step three, the deposition method is as follows: after the prepared hydrogel is cooled, the hydrogel is drawn into the hollow fiber membrane module obtained in step two using a syringe, then soaked for 5-10 minutes, and the residual liquid is squeezed out. The module is placed in a freezer for 2 hours, then at room temperature for 6-12 hours. The freeze-thaw cycle is repeated 2-3 times. Then, pure water is drawn into the membrane module using a syringe to fully swell the outermost layer.

5. An application of a Janus composite membrane prepared according to any one of claims 1-4 for volume reduction of nuclear power plant decontamination wastewater, characterized in that, A Janus hollow fiber membrane module, composed of multiple Janus composite membranes, is connected to the output end of the concentrated waste liquid tank of a vacuum membrane distillation device via an intelligent peristaltic pump. The vacuum membrane distillation device also includes a pretreatment tank, and a heating jacket is installed inside the concentrated waste liquid tank. The feed side of the Janus hollow fiber membrane module is connected to the intelligent peristaltic pump, and the permeate side of the Janus hollow fiber membrane module is externally connected to a condenser and a distillate collection tank. The output end of the Janus hollow fiber membrane module is equipped with a reflux pipe connected to the concentrated waste liquid tank.

6. The application of the Janus composite membrane according to claim 5 for volume reduction of nuclear power plant decontamination wastewater, characterized in that, In the vacuum membrane distillation apparatus, the feed temperature of the exchange liquid is set at 70~80℃, the feed flow rate is 100~300ml / min, the vacuum degree is -0.08~-0.09Mpa, and the condensation temperature is 8~10℃. The heat energy of the exchange liquid, which is heated from room temperature to the feed temperature required for membrane distillation, comes from the waste heat recovery system of the nuclear power plant reactor. The recovery method is one of heat pump, regenerator, or heating furnace, and no additional heating is required.

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