Degradation regeneration method of waste reverse osmosis membrane

Abstract

The invention provides a degradation regeneration method of a waste reverse osmosis membrane, which comprises the following steps: cleaning the waste reverse osmosis membrane, fixing the waste reverse osmosis membrane in a flat state, and carrying out plasma treatment to obtain a degradation regeneration membrane. According to the regeneration method provided by the invention, the form of the polymer on the surface of the waste reverse osmosis membrane is regulated and controlled through the physical, chemical or physicochemical synergistic etching effect of the plasma, the waste membrane is converted into the nanofiltration membrane or the ultrafiltration membrane, meanwhile, compared with a commercial nanofiltration membrane or ultrafiltration membrane, the interception capacity of inorganic ions is improved, and in the treatment process, the treatment efficiency is improved. No chemical reagent is used, the process is simple, the treatment time is short, and the regeneration efficiency of the waste reverse osmosis membrane is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane treatment, and in particular relates to a degradation and regeneration method for a discarded reverse osmosis membrane. Background Art

[0002] Membrane technology has become one of the core technologies in the field of water treatment due to its advantages such as high efficiency, stability, and easy integration and automation. In particular, in the application of reverse osmosis membranes, its high desalination rate and pollutant retention capacity provide important support for seawater desalination and industrial wastewater reuse. However, with the surge in membrane usage, the accumulation of discarded reverse osmosis membranes has become increasingly prominent. Studies have shown that the abandonment of reverse osmosis membranes is mostly due to the irreversible attenuation of membrane flux after long-term operation or the degradation of performance caused by pollution, rather than the mechanical life of the membrane material itself. If such discarded membranes are directly landfilled or incinerated, it will not only cause a waste of resources, but the environmental degradation problems of their polymer materials (such as polyamide separation layer and polysulfone support layer) may also cause secondary pollution. Therefore, exploring the efficient regeneration and resource utilization technology of discarded reverse osmosis membranes has significant economic and environmental value.

[0003] At present, the mainstream idea of ​​regenerating waste reverse osmosis membranes is to downgrade and regenerate them into ultrafiltration (UF) or nanofiltration (NF) membranes by physical or chemical means. For example, CN111514758A discloses a method for regenerating ultrafiltration membranes from waste organic reverse osmosis membranes, using conventional reverse osmosis membrane cleaning liquid to chemically clean the waste organic reverse osmosis membrane original parts, then adding waste organic reverse osmosis membrane regeneration liquid for soaking treatment, and then using hydrochloric acid solution for cyclic soaking. CN112295412A discloses a method for ultrafiltration degradation and regeneration of waste reverse osmosis membranes by ultraviolet enhanced oxidation, using ultraviolet light irradiation and chlorine-containing solution soaking to modify the surface of the waste membrane, and further optimizing the filtration performance through one or more of surfactants, complexing agents, and chelating agents. CN117085511A discloses a method for converting and reusing waste polyamide reverse osmosis membranes, wherein the membrane assembly is cyclically cleaned and statically soaked in a cleaning agent, then soaked in an oxidant and rinsed with a low-pressure circulating flow, the polyamide layer is oxidized and degraded, and then a new modified layer is deposited layer by layer on the membrane surface.

[0004] The existing regeneration technologies for reverse osmosis membranes mainly include the cleaning method and the oxidation method. The cleaning method can only remove impurities on the surface of the waste membrane and it is difficult to achieve the downgraded regeneration of the membrane. The oxidation method restores the flux by destroying the cross-linked structure of the polyamide layer. However, the oxidation method has two main technical defects: on the one hand, the action of the oxidant is non-selective and will synchronously erode the support layer, resulting in a decrease in the mechanical strength of the membrane. The lack of a selective action mechanism for the separation layer and the support layer will make the performance of the regenerated membrane unstable; on the other hand, the oxidation operation process is complex, the process is cumbersome and time-consuming (usually requiring soaking for several days), and a large amount of oxidizing agents are used, with high energy consumption and secondary pollution. The residual oxidant may affect the safety and long-term stability of the regenerated membrane, making it impossible to balance the process simplicity and environmental friendliness.

[0005] Therefore, developing a simple, efficient, highly selective and non-secondary-pollution regeneration method is the key to promoting the resource utilization of waste reverse osmosis membranes and the low-carbon development of membrane technology. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a simple and precise downgraded regeneration method for waste reverse osmosis membranes. By etching the surface polymer layer of the waste reverse osmosis membrane, it is realized to downgrade and regenerate it into a nanofiltration membrane or an ultrafiltration membrane.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] The present invention provides a downgraded regeneration method for waste reverse osmosis membranes. The downgraded regeneration method includes the following steps:

[0009] After cleaning the waste reverse osmosis membrane sheet, fix the waste reverse osmosis membrane sheet in a flat state and perform plasma treatment to obtain a downgraded regenerated membrane.

[0010] The regeneration method provided by the present invention etches the waste reverse osmosis membrane, and uses ions or free radicals in the plasma generated by low-pressure discharge to etch the polymer on the surface of the waste reverse osmosis membrane, such as the polyamide layer, and simultaneously generates a physical and / or chemical synergistic etching effect, regulates the molecular structure and surface morphology of the polymer, converts the waste reverse osmosis membrane into a nanofiltration membrane or an ultrafiltration membrane, and improves its ion salt retention ability. Compared with chemical oxidation soaking, no chemical reagents are used during the process, there is no secondary pollution, and the treatment time is greatly reduced, improving the conversion and recycling efficiency of waste membranes.

[0011] Preferably, the pressure of the plasma treatment is 1×10 4 -5×10 5 Pa, for example, it can be 1×10 4 Pa, 5×10 4 Pa, 1×10 5Pa, 1.5×10 5 Pa, 2×10 5 Pa, 2.5×10 5 Pa, 3×10 5 Pa, 3.5×10 5 Pa, 4×10 5 Pa, 4.5×10 5 Pa or 5×10 5 Pa, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0012] Preferably, the power of the plasma treatment is 200 - 600 W. For example, it can be 200 W, 250 W, 300 W, 350 W, 400 W, 450 W, 500 W, 550 W or 600 W, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable. Preferably, it is 300 - 500 W.

[0013] Preferably, the working gas for the plasma treatment includes reactive gas and / or inert gas.

[0014] Preferably, the reactive gas includes any one or at least two combinations of nitrogen, oxygen or air. Typical but non - restrictive combinations include the combination of nitrogen and oxygen, the combination of oxygen and air, the combination of nitrogen and air, or the combination of nitrogen, oxygen and air.

[0015] Preferably, the inert gas includes argon and / or helium.

[0016] Preferably, the treatment method of the plasma treatment includes: the plasma is sprayed onto the surface of the waste reverse osmosis membrane through a nozzle for spraying treatment.

[0017] In the present invention, in the plasma treatment, when the nozzle sweeps the surface of the membrane, it is one - time spraying treatment.

[0018] The outlet pressure of the working gas for the plasma treatment is 0.5 MPa.

[0019] Preferably, the number of times of the spraying treatment is 1 - 3 times. For example, it can be 1 time, 2 times or 3 times.

[0020] Preferably, the cleaning method includes rinsing with water.

[0021] Preferably, the cleaning temperature is 10 - 50 °C. For example, it can be 10 °C, 20 °C, 30 °C, 40 °C or 50 °C, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0022] Preferably, the degradation and regeneration method further includes: soaking and storing the degraded and regenerated membrane in water.

[0023] Preferably, the soaking and storage time is 1 - 60 days.

[0024] As a preferred technical solution of the degradation and regeneration method provided by the present invention, the degradation and regeneration method includes the following steps:

[0025] (1) Cleaning the waste reverse osmosis membrane sheet with water at a cleaning temperature of 10 - 50°C until the surface dirt is removed to obtain a pretreated waste reverse osmosis membrane;

[0026] (2) Fixing the pretreated waste reverse osmosis membrane on a flat plate and placing it in the cavity of an atmospheric pressure plasma processor for atmospheric pressure plasma treatment. The parameters of the atmospheric pressure plasma treatment include: maintaining the cavity pressure at 1×10 4 -5×10 5 Pa. The working gas of the atmospheric pressure plasma treatment includes a reactive gas and / or an inert gas. The power of the atmospheric pressure plasma treatment is 200 - 600W. The plasma is sprayed onto the surface of the waste reverse osmosis membrane sheet through a nozzle. One spray treatment is completed when the nozzle sweeps across the surface of the membrane sheet. The number of spray treatments is 1 - 3 times. After the atmospheric pressure plasma treatment is completed, a degraded and regenerated membrane is obtained, and the degraded and regenerated membrane is placed in water for soaking and storage.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The regeneration method provided by the present invention regulates the polymer morphology on the surface of the waste reverse osmosis membrane through the physical, chemical, or physicochemical synergistic etching effect of the plasma, converts the waste reverse osmosis membrane into a nanofiltration membrane or an ultrafiltration membrane, and at the same time improves the interception ability of inorganic ions compared with nanofiltration membranes and ultrafiltration membranes. During the treatment process, no chemical reagents are used, the process is simple, the treatment time is shortened to the minute level, and the regeneration efficiency of the waste reverse osmosis membrane is greatly improved. Specific Embodiments

[0029] The technical solutions of the present invention will be further described below through specific embodiments.

[0030] To clearly illustrate the technical solutions of the present invention, in the specific embodiments, the treatment object used is the same waste reverse osmosis membrane module. The waste time of the waste reverse osmosis membrane is less than 6 months, and the storage state is intact. Under the conditions of a temperature of 25°C, a membrane pressing pressure of 1.2 MPa, and an operating pressure of 1 MPa, the water production flux of the waste reverse osmosis membrane for testing a NaCl solution (NaCl concentration is 2 g / L) is 6.67 L·m -2 ·h -1 .

[0031] Example 1

[0032] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. The downgrading and regeneration method includes the following steps:

[0033] (1) Separate the outer shell of the waste reverse osmosis membrane, unfold and lay flat the waste osmosis membrane into a waste reverse osmosis membrane sheet, cut the waste reverse osmosis membrane sheet, and then wash it with water at 25°C until the surface dirt is removed;

[0034] (2) Fix the washed waste reverse osmosis membrane sheet on a glass plate, keep it in a flat state, and place it in the cavity of an atmospheric pressure plasma processor;

[0035] (3) Perform atmospheric pressure plasma treatment on the waste reverse osmosis membrane sheet. The specific process is as follows: Keep the cavity pressure at 1.08×10 5 Pa, use nitrogen as the working gas, the treatment power is 350W, the plasma is sprayed onto the membrane sheet surface through a nozzle. When the nozzle sweeps across the surface of the waste reverse osmosis membrane sheet, it is one spraying treatment. A total of 3 spraying treatments are carried out. After the atmospheric pressure plasma treatment is completed, a regenerated reverse osmosis membrane is obtained, and the regenerated reverse osmosis membrane is placed in ultrapure water for soaking and preservation.

[0036] Example 2

[0037] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. The downgrading and regeneration method includes the following steps:

[0038] (1) Separate the outer shell of the waste reverse osmosis membrane, unfold and lay flat the waste osmosis membrane into a waste reverse osmosis membrane sheet, cut the waste reverse osmosis membrane sheet, and then wash it with water at 25°C until the surface dirt is removed;

[0039] (2) Fix the washed waste reverse osmosis membrane sheet on a glass plate, keep it in a flat state, and place it in the cavity of an atmospheric pressure plasma processor;

[0040] (3) Perform atmospheric pressure plasma treatment on the waste reverse osmosis membrane sheet. The specific process is as follows: Keep the cavity pressure at 1.08×10 5 Pa, use nitrogen as the working gas, the treatment power is 300W, the plasma is sprayed onto the membrane sheet surface through a nozzle. When the nozzle sweeps across the surface of the waste reverse osmosis membrane sheet, it is one spraying treatment. A total of 3 spraying treatments are carried out. After the atmospheric pressure plasma treatment is completed, a regenerated reverse osmosis membrane is obtained, and the regenerated reverse osmosis membrane is placed in water for soaking and preservation.

[0041] That is, compared with Example 1, the power of the atmospheric pressure plasma treatment is 300W, and the number of spraying treatments is 3 times.

[0042] Example 3

[0043] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Example 1, the power of the atmospheric pressure plasma treatment is 400 W, and the number of spraying treatments is 1 time. The rest are the same as in Example 1.

[0044] Example 4

[0045] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Example 1, the power of the atmospheric pressure plasma treatment is 400 W, and the number of spraying treatments is 2 times. The rest are the same as in Example 1.

[0046] Example 5

[0047] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Example 1, the power of the atmospheric pressure plasma treatment is 500 W, and the number of spraying treatments is 1 time. The rest are the same as in Example 1.

[0048] Example 6

[0049] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Example 1, the power of the atmospheric pressure plasma treatment is 200 W, and the number of spraying treatments is 3 times. The rest are the same as in Example 1.

[0050] Example 7

[0051] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Example 1, the power of the atmospheric pressure plasma treatment is 600 W, and the number of spraying treatments is 1 time. The rest are the same as in Example 1.

[0052] Example 8

[0053] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Example 1, the working gas is replaced with air. The rest are the same as in Example 1.

[0054] Example 9

[0055] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Example 1, the working gas is replaced with argon. The rest are the same as in Example 1.

[0056] Example 10

[0057] This example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Example 1, the working gas is replaced with a mixture of air and argon with a volume ratio of 1:1. The rest are the same as in Example 1.

[0058] Comparative Example 1

[0059] This comparative example provides a method for regenerating waste reverse osmosis membranes. Compared with Example 1, atmospheric pressure plasma treatment is not carried out, and the rest are the same as in Example 1. That is, after cleaning the waste reverse osmosis membrane, it is placed in ultrapure water and soaked for preservation.

[0060] Comparative Example 2

[0061] This comparative example provides a method for downgrading and regenerating waste reverse osmosis membranes. Compared with Example 1, the atmospheric pressure plasma treatment is replaced with oxidation treatment, and the rest are the same as in Example 1.

[0062] The specific process of the oxidation treatment is as follows: The waste reverse osmosis membrane is soaked in a sodium hypochlorite solution with an active chlorine concentration of 1000 mg / L for 24 h in a circulating manner.

[0063] Performance Test

[0064] The method for testing the membrane performance is as follows: Weigh 4 g of ionic salt and dissolve it in 2 L of ultrapure water to prepare a 2 g / L salt solution. A cross-flow permeation experiment is carried out using a reverse osmosis membrane test device. The temperature is set at 25 °C, the membrane pressing pressure is 1.2 MPa, and the operating pressure is 1 MPa to obtain the membrane rejection rate and flux data.

[0065] Table 1

[0066] <![CDATA[Flux (L·m -2 ·h -1 )]]> NaCl rejection rate (%) <![CDATA[MgSO4 rejection rate (%)]]> Example 1 26.89 91.76 95.41 Example 2 26.03 84.34 87.29 Example 3 9.87 85.23 90.44 Example 4 17.01 57.75 64.83 Example 5 15.35 72.58 86.15 Example 6 13.35 81.69 87.24 Example 7 21.25 13.36 21.82 Example 8 22.57 79.60 84.39 Example 9 21.46 87.34 89.5 Example 10 20.68 81.25 85.53 Comparative Example 1 6.67 95.8 93.1 Comparative Example 2 20.83 31.4 72.1

[0067] As can be seen from Table 1, the method for regenerating waste reverse osmosis membranes provided by the present invention can improve the flux of waste reverse osmosis membranes by performing plasma treatment on the surface of the membrane sheets, downgrade and regenerate waste reverse osmosis membranes into nanofiltration membranes or ultrafiltration membranes, reuse waste reverse osmosis membranes, and reduce solid waste. Under preferred conditions, the rejection rate of monovalent ions (NaCl) of the regenerated membrane after plasma treatment can reach 60%, or even 91.76%, and the rejection rate of divalent ions (MgSO4) can reach 60%, or even 95.41%. While improving the membrane flux, a good salt rejection effect is maintained. Under the same test conditions, the rejection rate of monovalent ions (NaCl) of the commercial ultrafiltration membrane Ande PS polysulfone membrane is only 2.45%, and the rejection rate of divalent ions (MgSO4) is only 8.75%. The salt rejection performance far exceeds that of commercial ultrafiltration membranes. Among them, under specific treatment conditions, its performance is close to the standard of high-performance commercial nanofiltration membranes. For example, under the same test conditions, the flux of DuPont NF 90-4040 is 10.88 L·m -2 ·h -1 , the rejection rate of monovalent ions (NaCl) is 96.5%, and the rejection rate of divalent ions (MgSO4) is 97.39%.

[0068] In Examples 1-8, the plasma treatment power and number of times are crucial for the performance of the degraded regenerated membrane. Under the condition of maintaining a certain power and number of treatments, good degraded regeneration effects are achieved. If the treatment power is too high, the flux of the regenerated membrane will be reduced instead, and the regeneration effect will be decreased; if the number of treatments is too large, the flux of the regenerated membrane will not be significantly improved, but the salt rejection rate will decrease significantly.

[0069] Compared with Example 1, in Comparative Example 1, only the physical cleaning method is used, and the membrane flux does not change, indicating that the physical cleaning method can only remove the dirt attached to the membrane surface and cannot achieve the degradation and regeneration of the reverse osmosis membrane. In Comparative Example 2, the oxidation treatment method is used. Although the flux of the regenerated membrane is increased, its salt rejection rate deteriorates significantly, and the regeneration effect is poor. At the same time, chemical reagents are likely to cause reagent pollution to the surface of the regenerated membrane and impose a burden on the environment.

[0070] In summary, the regeneration method provided by the present invention regulates the polymer morphology on the surface of the waste reverse osmosis membrane through the physical, chemical or physicochemical synergistic etching effect of the plasma, converts the waste membrane into a nanofiltration membrane or an ultrafiltration membrane, and at the same time improves the ion salt retention ability compared with the nanofiltration membrane and the ultrafiltration membrane. During the treatment process, no chemical reagents are used, the process is simple, the treatment time is short, and the regeneration efficiency of the waste membrane is greatly improved.

[0071] The specific embodiments described above further elaborate on the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for downgrading and regenerating waste reverse osmosis membranes, characterized in that, The degradation and regeneration method includes the following steps: After cleaning the waste reverse osmosis membrane sheet, the waste reverse osmosis membrane sheet is fixed in a flat state and subjected to plasma treatment to obtain a degraded and regenerated membrane.

2. The degradation regeneration method according to claim 1, wherein The pressure of the plasma treatment is 1×10 4 -5×10 5 Pa.

3. The degradation and regeneration method according to claim 1 or 2, characterized in that, The power of the plasma treatment is 200 - 600W.

4. The downgrading regeneration method according to any one of claims 1-3, characterized in that, The working gas for the plasma treatment includes a reactive gas and / or an inert gas.

5. The degradation regeneration method according to claim 4, wherein The reactive gas includes any one or a combination of at least two of nitrogen, oxygen, or air; Preferably, the inert gas includes argon and / or helium.

6. The degradation regeneration method according to any one of claims 1-5, characterized in that, The method of the plasma treatment includes: the plasma is sprayed onto the surface of the waste reverse osmosis membrane sheet through a nozzle for spraying treatment.

7. The degradation regeneration method according to claim 6, wherein The number of times of the spraying treatment is 1 - 3 times.

8. The degradation regeneration method according to any one of claims 1-7, characterized in that, The method of the cleaning includes rinsing with water; Preferably, the temperature of the cleaning is 10 - 50°C.

9. The degradation regeneration method according to any one of claims 1-8, characterized in that, The degradation and regeneration method further includes: soaking the degraded and regenerated membrane in water for storage.

10. The degradation regeneration method according to any one of claims 1-9, characterized in that, The degradation and regeneration method includes the following steps: (1) Cleaning the waste reverse osmosis membrane sheet with water at a temperature of 10 - 50°C until the surface dirt is removed to obtain a pretreated waste reverse osmosis membrane; (2) Fix the pretreated waste reverse osmosis membrane sheet on a flat plate and place it in the cavity of an atmospheric pressure plasma processor for atmospheric pressure plasma treatment. The parameters of the atmospheric pressure plasma treatment include: maintaining the cavity pressure at 1×10 4 -5×10 5 Pa. The working gas for the atmospheric pressure plasma treatment includes a reactive gas and / or an inert gas. The reactive gas includes any one or a combination of at least two of nitrogen, oxygen, or air. The inert gas includes argon and / or helium. The power of the atmospheric pressure plasma treatment is 200-600W. The plasma is sprayed onto the surface of the waste reverse osmosis membrane sheet through a nozzle. One pass of the nozzle over the membrane sheet surface is one spraying treatment, and the number of spraying treatments is 1-3 times. After the atmospheric pressure plasma treatment is completed, a degraded regenerated membrane is obtained. Place the degraded regenerated membrane in water for soaking and preservation.