Pervaporation-membrane distillation coupling separation method for deep urine water reuse
By preparing a pervaporation functional layer on the surface of a hydrophobic membrane, a pervaporation-membrane distillation coupled separation method was developed, which solved the problems of membrane fouling and low ammonia retention in urine treatment, and achieved efficient water recovery and improved effluent quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2026-03-19
- Publication Date
- 2026-05-05
AI Technical Summary
Existing urine treatment technologies face membrane fouling and failure issues on space stations. In particular, traditional membrane distillation technology has limited effectiveness in retaining organic matter and ammonia in urine, resulting in low water recovery rates and poor effluent quality.
A pervaporation-membrane distillation coupled separation method is adopted. By preparing a pervaporation functional layer on the surface of a hydrophobic membrane to enhance hydrophilicity, and using a cross-flow liquid feeding device for urine treatment, selective separation of water, ammonia and organic matter is achieved.
It increased the water recovery rate of urine to 90%, reduced the conductivity of effluent, enhanced the ammonia retention capacity, solved the problems of membrane fouling and failure, and ensured the quality of effluent.
Smart Images
Figure CN121974441A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of water treatment technology, specifically relating to a pervaporation-membrane distillation coupled separation method for deep water reuse of urine. Background Technology
[0002] With the continuous expansion of space exploration and the development of the commercial space industry, sustainable water supply technology for space stations has become increasingly critical. Transporting water from Earth via spacecraft is not only costly but also limits the radius of space exploration. Since human urine is approximately 95% water, urine treatment and recycling have become the optimal strategy for replenishing water for space stations. An ideal urine treatment system should maximize water recovery and contaminant removal while minimizing equipment size. Unfortunately, complex endogenous substances in urine (such as salts, organic matter, and ammonia) can cause serious fouling and leakage risks to treatment devices, thus weakening the stability and recovery efficiency of urine treatment. For example, the Urine Treatment Apparatus (UPA) of the International Space Station (ISS) faces the challenges of low recovery rates and poor distilled water quality. Existing urine treatment technologies, including forward osmosis (FO) and reverse osmosis (RO), face multiple limitations (such as significant salinity dependence, low micro-contaminant rejection rates, and severe membrane fouling), restricting their application on space stations.
[0003] Membrane distillation (MD), a thermal-membrane coupling technology that utilizes hydrophobic membranes as the separation medium, can achieve near-complete retention of non-volatile substances. This technology is particularly suitable for urine treatment in the confined environment of the space station due to its small footprint, insensitivity to salinity, and ability to utilize low-grade heat sources (such as solar energy and waste heat). In recent years, the International Space Station has developed an MD-based brine treatment unit to compensate for the insufficient processing capacity of the Urine Treatment Apparatus (UPA). However, the organic / inorganic components in urine can cause complex synergistic fouling on the MD membrane, leading to membrane wetting and process failure. Furthermore, traditional distillation membranes have limited retention efficiency for volatile components. In particular, urea in urine hydrolyzes under the catalysis of urease, releasing large amounts of ammonia gas that diffuses through the hydrophobic membrane, causing effluent contamination. Therefore, existing membrane distillation urine treatment technologies are insufficient to meet the stable water supply requirements of the space station. Summary of the Invention
[0004] The purpose of this invention is to solve the problems of contamination and failure of distillation membranes in urine treatment, low ammonia nitrogen retention and low volatile organic compound retention, and to provide a pervaporation-membrane distillation coupled separation method for deep water reuse of urine.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0006] A pervaporation-membrane distillation coupled separation method for deep water recycling of urine, the method comprising:
[0007] Step 1: Immerse the microporous hydrophobic membrane in a strong alkaline solution with a concentration of 4-10 M and treat it at 60-80 ℃ for 4-6 hours; this will cause hydroxyl groups to grow on the surface of the microporous hydrophobic membrane, thereby enhancing the surface hydrophilicity.
[0008] Step 2: Prepare a pervaporation functional layer on the surface of the alkali-treated microporous hydrophobic membrane: Fix the alkali-treated microporous hydrophobic membrane in a frame to ensure that only one side of the microporous hydrophobic membrane is covered with the pervaporation functional layer (polyvinyl alcohol, chitosan, or polyimide, etc.). The pervaporation functional layer is a dense hydrophilic gel layer. Prepare a gel precursor solution by mixing gel monomers and crosslinking agents. Apply the gel precursor solution to the surface of the hydrophobic microporous membrane in the frame. Control the amount of gel precursor solution so that the thickness of the surface pervaporation functional layer is 1~2 μm.
[0009] Step 3: Stabilize the human urine to be treated using sulfuric acid as a stabilizer;
[0010] Step 4: The urine is treated using a cross-flow inlet device. The coupling separation membrane with a pervaporation functional layer and a hydrophobic substrate prepared in Step 2 is placed in an area with an effective working area of 10 cm². 2 In the membrane tank, gear pumps circulate urine (feed liquid) and pure water (condensate) on both sides of the separation membrane. The urine feed liquid side is heated to 60°C in a water bath, and 300-500 ml of pure water is used as the condensate, with the temperature controlled at 20°C using a condenser. After the cross-flow device starts operating, water, ammonia, and some organic matter in the urine enter the pervaporation functional layer on the coupling membrane surface through dissolution and diffusion. Because water molecules interact more strongly with the hydrophilic groups within the pervaporation functional layer, they more easily occupy these groups and complete pervaporation. Ammonia and organic matter are selectively retained because their diffusion sites are occupied by water molecules. Liquid water undergoes a vaporization phase change upon reaching the hydrophobic separation membrane / pervaporation functional layer interface, further achieving selective separation.
[0011] Step 5: After the urine has been treated to about 90% water recovery, replace the feed liquid with pure water to rinse the separation membrane. After rinsing, replace with new acid-stabilized urine feed liquid for recycling.
[0012] Furthermore, in step one, the microporous hydrophobic membrane is made of PVDF or PTFE material with a pore size of 0.22~0.45 micrometers and a thickness of 50~150 micrometers.
[0013] Further, in step two, the gel monomer is one or more of polyvinyl alcohol, acrylic acid, acrylamide, chitosan, and cellulose, and the crosslinking agent is one or more of glutaraldehyde, N,N'-methylenebisacrylamide, and ethylene glycol dimethacrylate, with a mass ratio of gel monomer to crosslinking agent of 5~50:1.
[0014] Furthermore, in step three, while monitoring the urine pH value with a pH meter, inorganic acid is added to the urine in small amounts multiple times to acidify it until the urine pH is adjusted to 2-3.
[0015] The advantages of this invention over the prior art are as follows:
[0016] 1. The pervaporation-membrane distillation urine treatment method proposed in this invention overcomes the problems of low water recovery rate and reclaimed water quality in the urine treatment process of traditional distillation membranes. The urine water reuse rate is greatly improved, the separation membrane does not wet, and the conductivity of the effluent is greatly reduced.
[0017] 2. The pervaporation-membrane distillation coupled separation membrane proposed in this invention exhibits significantly enhanced resistance to uric acid contamination, solving the problem of severe pore blockage and damage caused by uric acid contamination in traditional hydrophobic distillation membranes. The flux decrease of the coupled separation membrane during the treatment of acid-stabilized urine is far less than that of traditional hydrophobic membranes.
[0018] 3. The pervaporation-membrane distillation coupled separation membrane proposed in this invention significantly enhances the retention capacity of ammonia nitrogen in urine. This is mainly because water molecules occupy the dissolution-diffusion sites of ammonia molecules within the dense gel layer, achieving selective separation of water and ammonia. Attached Figure Description
[0019] Figure 1 The graph shows the flux change of the PVDF hydrophobic microporous membrane in the membrane distillation of urine.
[0020] Figure 2 The graph shows the conductivity of the effluent from the PVDF hydrophobic microporous membrane in the membrane distillation of urine.
[0021] Figure 3 This diagram shows the composition of the effluent from a PVDF hydrophobic microporous membrane used in membrane distillation of urine.
[0022] Figure 4 This figure shows the flux change of the composite separation membrane in the membrane distillation-pervaporization coupled urine treatment.
[0023] Figure 5 The graph shows the change in effluent conductivity of the composite separation membrane in the membrane distillation-pervaporization coupled urine treatment process.
[0024] Figure 6 This diagram shows the composition of the effluent from a composite separation membrane used in a membrane distillation-pervaporization coupled urine treatment process.
[0025] Figure 7 This is a diagram showing the membrane fouling of a PVDF hydrophobic microporous membrane after urine treatment by membrane distillation.
[0026] Figure 8This diagram shows the membrane fouling status of the composite separation membrane after urine treatment via membrane distillation-pervaporization coupling.
[0027] Figure 9 The image shows the infrared spectrum of the composite separation membrane surface after urine treatment via membrane distillation-pervaporization coupling.
[0028] Figure 10 This is the energy spectrum of the composite separation membrane surface after urine treatment via membrane distillation-pervaporization coupling. Detailed Implementation
[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.
[0030] Membrane distillation: A thermal membrane coupling separation technology that uses a hydrophobic membrane as the separation medium and the vapor pressure difference across the membrane as the driving force. Pervaporation: A separation technology that uses a chemical potential difference as the driving force and relies on the selective dissolution and diffusion of components through a membrane.
[0031] Example 1:
[0032] 1. Immerse a PVDF microporous hydrophobic membrane with a pore size of 0.45 μm in a 7.5 M sodium hydroxide solution and treat it at 70 °C for 6 hours. This causes hydroxyl groups to grow on the surface of the hydrophobic microporous membrane, thereby enhancing its surface hydrophilicity.
[0033] 2. A pervaporation functional layer was prepared on the surface of the microporous hydrophobic membrane after alkali treatment. The pervaporation functional layer was a dense PVA hydrophilic gel layer. The amount of gel precursor solution was controlled so that the thickness of the pervaporation functional layer on the surface was 1 μm.
[0034] 3. Stabilize the fresh human urine to be treated using an inorganic acid as a stabilizer. While monitoring the urine pH with a pH meter, add small amounts of sulfuric acid to the urine multiple times to acidify it until the urine pH is adjusted to 3.
[0035] 4. The urine is treated using a cross-flow inlet device. The coupling separation membrane, prepared in the previous step and containing a pervaporation functional layer and a hydrophobic substrate, is placed in an area with an effective working area of 10 cm². 2 In the membrane tank, the urine feed solution is heated to 60°C using a water bath, and 300-500 ml of pure water is used as the condensate, with the temperature controlled at 20°C using a condenser.
[0036] 5. After the cross-flow device starts operating, water, ammonia, and some organic matter in the urine enter the pervaporation functional layer on the surface of the coupling membrane through dissolution and diffusion. Because water molecules interact more strongly with the hydrophilic groups within the pervaporation functional layer, they more easily occupy these groups to complete pervaporation and diffusion. Ammonia and organic matter, however, are selectively retained because their diffusion sites are occupied by water molecules. Liquid water undergoes a vaporization phase transition upon reaching the hydrophobic separation membrane / pervaporation functional layer interface, further achieving selective separation. During this process, the conductivity of the effluent and the water flux of the membrane are recorded, and the ammonia nitrogen concentration in the effluent is determined using Nessler's reagent spectrophotometry. The fouling morphology and properties of the treated composite membrane are characterized using scanning electron microscopy, infrared spectroscopy, and X-ray diffraction spectroscopy. Compared with traditional hydrophobic membranes, the coupling membrane constructed in this work increases the urine recovery rate from 13% to 90% (see appendix). Figure 1 and 4 Meanwhile, the membrane does not wet, and the conductivity of the effluent decreases from 200 μS / cm to 6.26 μS / cm (see attached image). Figure 2 and 5 Traditional hydrophobic membrane effluent contains inorganic ions and organic matter, indicating membrane wetting and effluent fouling. Coupled membrane effluent, however, does not contain metal ions and exhibits lower concentrations of ammonia nitrogen and TOC, demonstrating superior effluent quality. (See appendix) Figure 3 and 6 When the coupling membrane recovers 90% of the water, the flux decreases by only 31.6%, while the traditional hydrophobic membrane experiences a 100% flux decrease when the water recovery rate is only 13% in the process of treating acid-stabilized urine. (Appendix) Figure 1 and 4 Traditional hydrophobic membranes exhibit significant fouling on both the surface and interior, resulting in severe damage to the membrane pores (see attached image). Figure 7 The coupling membrane showed the formation of a fouling layer, but the interior of the membrane was not contaminated or damaged (see attached image). Figure 8 ).
[0037] 6. After the urine has been treated to about 90% water recovery, replace the feed liquid with pure water to rinse the separation membrane. After rinsing, replace with new acid-stabilized urine feed liquid for recycling.
[0038] Example 2:
[0039] 1. A PVDF microporous hydrophobic membrane with a pore size of 0.22 μm was immersed in a 7.5 M sodium hydroxide solution and treated at 70 °C for 6 hours. This process caused hydroxyl groups to grow on the surface of the hydrophobic microporous membrane, thereby enhancing its surface hydrophilicity.
[0040] 2: A pervaporation functional layer was prepared on the surface of the microporous hydrophobic membrane after alkali treatment. The pervaporation functional layer was a dense PVA hydrophilic gel layer. The amount of gel precursor solution was controlled so that the thickness of the pervaporation functional layer on the surface was 2 μm.
[0041] 3. Stabilize the fresh human urine to be treated using an inorganic acid as a stabilizer. While monitoring the urine pH with a pH meter, add small amounts of sulfuric acid to the urine multiple times to acidify it until the urine pH is adjusted to 2.5.
[0042] 4. The urine was treated using a cross-flow inlet device. The coupling separation membrane, prepared in the previous step and containing a pervaporation functional layer and a hydrophobic substrate, was placed in an area with an effective working area of 10 cm². 2 In the membrane tank, the urine feed solution is heated to 60°C using a water bath, and 300-500 ml of pure water is used as the condensate, with the temperature controlled at 20°C using a condenser.
[0043] 5. After the cross-flow device starts operating, water, ammonia, and some organic matter in the urine enter the pervaporation functional layer on the surface of the coupling membrane through dissolution and diffusion. Because water molecules interact more strongly with the hydrophilic groups within the pervaporation functional layer, they more easily occupy these groups to complete pervaporation and diffusion. Ammonia and organic matter, however, are selectively retained because their diffusion sites are occupied by water molecules. Liquid water undergoes a vaporization phase transition upon reaching the hydrophobic separation membrane / pervaporation functional layer interface, further achieving selective separation. During this process, the conductivity of the effluent and the water flux of the membrane are recorded, and the ammonia nitrogen concentration in the effluent is determined using Nessler's reagent spectrophotometry. The morphology and properties of the fouling on the treated composite membrane are characterized using scanning electron microscopy, infrared spectroscopy, and X-ray diffraction spectroscopy. Traditional hydrophobic membranes exhibit crystalline contaminants on their surface after treating urine. Under unstable conditions, the main crystalline contaminant is sodium chloride, while under acid-stable conditions, it is mainly organic crystals containing C, N, and O (attached). Figure 10 After processing urine, the coupling membrane mainly adheres to contaminants containing carboxyl and amine groups on its surface. Figure 9 ), which corresponds to pollutants such as urea, creatinine, and uric acid in urine.
[0044] 6: After the urine has been treated to about 90% water recovery, replace the feed liquid with pure water to rinse the separation membrane. After rinsing, replace with new acid-stabilized urine feed liquid for recycling.
Claims
1. A pervaporation-membrane distillation coupled separation method for deep water recycling of urine, characterized in that: The method is as follows: Step 1: Immerse the microporous hydrophobic membrane in a strong alkaline solution with a concentration of 4-10 M and treat it at 60-80 °C for 4-6 h; Step 2: Prepare a gel precursor solution by mixing gel monomers and crosslinking agents. Apply the gel precursor solution to one side of the hydrophobic microporous membrane. Control the amount of gel precursor solution so that the thickness of the surface permeation vaporization functional layer is 1~2 μm. Step 3: Stabilize the human urine to be treated using sulfuric acid as a stabilizer; Step 4: The urine is treated using a cross-flow inlet device. The coupling separation membrane with a pervaporation functional layer and a hydrophobic substrate prepared in Step 2 is placed in an area with an effective working area of 10 cm². 2 In the membrane tank; urine (feed liquid) and pure water (condensate) are circulated on both sides of the separation membrane respectively; the urine feed liquid side is heated to 60 ℃ using a water bath, and 300~500 ml of pure water is used as condensate and its temperature is controlled at 20 ℃ using a condenser; Step 5: After the urine has been treated to about 90% water recovery, replace the feed liquid with pure water to rinse the separation membrane. After rinsing, replace with new acid-stabilized urine feed liquid for recycling.
2. The pervaporation-membrane distillation coupled separation method for deep water reuse of urine according to claim 1, characterized in that: In step one, the microporous hydrophobic membrane is made of PVDF or PTFE material with a pore size of 0.22~0.45 micrometers and a thickness of 50~150 micrometers.
3. The pervaporation-membrane distillation coupled separation method for deep water reuse of urine according to claim 1, characterized in that: In step two, the gel monomer is one or more of polyvinyl alcohol, acrylic acid, acrylamide, chitosan, and cellulose, and the crosslinking agent is one or more of glutaraldehyde, N,N'-methylenebisacrylamide, and ethylene glycol dimethacrylate. The mass ratio of gel monomer to crosslinking agent is 5~50:
1.
4. The pervaporation-membrane distillation coupled separation method for deep water reuse of urine according to claim 1, characterized in that: In step three, while monitoring the urine pH value with a pH meter, inorganic acid is added to the urine in small amounts multiple times to acidify it until the urine pH is adjusted to 2-3.