Method for calculating diffusion coefficient of micro-pollutants in nanofiltration membrane based on adsorption amount

Abstract

The application discloses a kind of methods for calculating the diffusion coefficient of micro-pollutants in nanofiltration membrane based on adsorption capacity in the field of membrane technology, including installing nanofiltration membrane in membrane cell with salt solution, dissolving micro-pollutants in the salt solution, and nanofiltration membrane in the membrane cell intercepts and adsorbs micro-pollutants;Nanofiltration membrane adsorbed micro-pollutants is soaked in elution solution to desorb micro-pollutants.The application obtains the adsorption capacity of micro-pollutants in nanofiltration membrane by conventional micro-pollutant interception, adsorption and desorption experiment, and can calculate the diffusion coefficient, the test method is simple, the method considers the mutual relationship between micro-pollutants and membrane and micro-pollutants and solvent during mass transfer model calculation process, introduces the influence of membrane-micro-pollutant complex interaction force on micro-pollutant mass transfer process, and then the calculation of micro-pollutant diffusion coefficient in membrane except ion is also more accurate.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, specifically a method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity. Background Technology

[0002] Micropollutants in water bodies are diverse, highly toxic, and difficult to degrade. Although their concentrations are extremely low (ng / L ~ μg / L), their long-term accumulation poses a serious threat to aquatic environmental safety and human health. Traditional water treatment processes have limited and unstable removal efficiency for trace substances. Nanofiltration, as a membrane separation technology between ultrafiltration and reverse osmosis, selectively removes micropollutants primarily based on size sieving effects, the Donnan effect, and membrane-micropollutant interactions, making it a key technology for solving water pollution. However, the design of high-performance nanofiltration membranes is hindered by an incomplete understanding of the microscopic mechanisms by which nanofiltration removes micropollutants. Accurate and efficient determination of the diffusion coefficient of micropollutants within the membrane is crucial for elucidating the transmembrane transport mechanisms of micropollutants.

[0003] Existing traditional pore flow models (such as the DSPM-DE model) consider three mass transfer mechanisms in nanofiltration: convection, diffusion, and electromigration. They describe the effects of steric hindrance, Donnan effect, and dielectric effect on solute transmembrane transport, but neglect membrane-solute interactions during mass transfer. Therefore, for micro-pollutants with complex interactions with the nanofiltration membrane (such as hydrogen bonds, π-π stacking, and van der Waals forces), the DSPM-DE model cannot accurately predict their transmembrane transport and fails to clarify the impact of membrane-solute interactions on solute transmembrane transport. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity, in order to solve the aforementioned problem of failing to clarify the influence of membrane-solute interactions on solute transmembrane transport.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity includes: A nanofiltration membrane is installed in a membrane tank containing a salt solution, in which micro-pollutants are dissolved. The nanofiltration membrane in the membrane tank retains and adsorbs the micro-pollutants. The nanofiltration membrane that adsorbs micro-pollutants is immersed in an elution solution to desorb the micro-pollutants, and the amount of micro-pollutants adsorbed is calculated based on the concentration of micro-pollutants in the elution solution. The diffusion coefficient of micropollutants inside the nanofiltration membrane is calculated using a mass transfer model based on the amount of micropollutants adsorbed.

[0006] As a further aspect of the present invention: the step of immersing the nanofiltration membrane adsorbing micropollutants in an elution solution for micropollutant desorption, and calculating the amount of micropollutant adsorbed based on the concentration of micropollutants in the elution solution, includes: The elution solution includes a methanol solution, which is used for eluting micro-contaminants; The nanofiltration membrane was immersed in a methanol solution. After elution reached equilibrium, the concentration of micro-pollutants in the elution solution was determined by mass spectrometry. The amount of micro-pollutants adsorbed was calculated based on the volume of the methanol solution and the measured concentration of micro-pollutants.

[0007] As a further aspect of the present invention: the micro-pollutants include 4-chloroaniline, acetaminophen, trimethoprim, perfluorobutylsulfonic acid, and salicylic acid.

[0008] As a further aspect of the present invention: the diffusion coefficient of micropollutants within the nanofiltration membrane is calculated using a mass transfer model based on the adsorption amount of micropollutants, including: Nanofiltration membrane micro-pollutant diffusion coefficient , in, The friction coefficient of micro-pollutants under diffusion conditions; denoted as the diffusion coefficient of micro-pollutants in the bulk phase.

[0009] As a further aspect of the present invention: the With hydrodynamic retardation factor and correction factor Related; , Among them, correction factor The ratio of the Stokes radius of micropollutants to the pore size of the nanofiltration membrane. Related, and These represent the retardation coefficients between micropollutants and the nanofiltration membrane, and between micropollutants and the salt solution, respectively. The specific calculation process is as follows: , , , in, The adsorption coefficient is . It is the hydrodynamic retardation factor; , Where, 0 < <1; when ,

[0010]

[0011] when , , in, This represents the amount of micropollutants adsorbed per unit volume of the active layer when the nanofiltration membrane is saturated. This represents the concentration of micro-pollutants in the feed liquid. This represents the porosity of the nanofiltration membrane.

[0012] As a further aspect of the present invention: the micro-pollutants are desorbed using a centrifuge, the desorption time of the centrifuge is 24 hours, and the rotor speed of the centrifuge is 50 rpm.

[0013] As a further aspect of the present invention: the membrane tank is a cross-flow filtration system membrane tank, and the salt solution is a sodium chloride salt solution; A nanofiltration membrane is installed in the membrane tank of a cross-flow filtration system. The membrane tank contains a sodium chloride solution to dissolve micropollutants. The cross-flow filtration system is then activated, and the nanofiltration membrane in the membrane tank traps and adsorbs the micropollutants.

[0014] As a further aspect of the present invention: the micro-pollutants are intercepted and adsorbed in the membrane tank of the cross-flow filtration system at a pressure of 5 bar, the fluid velocity in the membrane tank of the cross-flow filtration system is 0.22 m / s, and the adsorption time in the membrane tank of the cross-flow filtration system is 12 h.

[0015] As a further aspect of the present invention, it also includes immersing the nanofiltration membrane in deionized water before installing the nanofiltration membrane in the membrane tank of the cross-flow filtration system.

[0016] As a further aspect of the present invention, the nanofiltration membrane is soaked in deionized water for 24 hours.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention uses conventional micro-pollutant retention, adsorption, and desorption experiments to obtain the amount of micro-pollutants adsorbed in a nanofiltration membrane, which can then be used to calculate the diffusion coefficient. The testing method is simple. This method considers the interaction between micro-pollutants and the membrane, and between micro-pollutants and the solvent during the mass transfer model calculation process. It introduces the influence of complex membrane-micro-pollutant interaction forces on the mass transfer process of micro-pollutants, thus making the calculation of the diffusion coefficient of micro-pollutants other than ions in the membrane more accurate. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2This invention provides a schematic diagram of the amount of micropollutants adsorbed per unit volume in the active layer of the nanofiltration membrane NF270 in Example 1; Figure 3 This invention provides a schematic diagram of the diffusion coefficient of micropollutants in nanofiltration membrane NF270, calculated based on adsorption amount, in Example 1 of this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example: Please see Figure 1 In this embodiment of the invention, a method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity includes: S1: Install a nanofiltration membrane in a membrane tank containing a salt solution. Dissolve micro-pollutants in the salt solution, and the nanofiltration membrane in the membrane tank will retain and adsorb the micro-pollutants. S2: The nanofiltration membrane that adsorbs micro-pollutants is immersed in the elution solution to desorb the micro-pollutants, and the amount of micro-pollutants adsorbed is calculated based on the concentration of micro-pollutants in the elution solution. S3: The diffusion coefficient of micropollutants within the nanofiltration membrane is calculated using a mass transfer model based on the adsorption amount of micropollutants. The calculation process based on the mass transfer model involves first constructing a mass transfer model suitable for the nanofiltration membrane system. This model fully considers the structural characteristics of the nanofiltration membrane and the transport mechanism of micropollutants within the membrane. Relevant boundary and initial conditions are set in the model. The micropollutant adsorption data obtained experimentally are substituted into the mass transfer model. Numerical calculation methods are used to solve the differential equations in the mass transfer model. Through continuous iteration and parameter adjustment, the mass transfer model reaches its best fit, and the diffusion coefficient of micropollutants within the nanofiltration membrane is calculated.

[0021] Specifically, by precisely controlling the concentration of the salt solution and the dissolution ratio of the micro-pollutant solution, the nanofiltration membrane can effectively retain and adsorb micro-pollutants under suitable conditions, thereby reducing the influence of external factors on the adsorption process. The micro-pollutants adsorbed on the nanofiltration membrane are then desorbed, and the adsorption amount is accurately calculated based on the concentration of micro-pollutants in the elution solution. The diffusion coefficient of micro-pollutants within the nanofiltration membrane is obtained by calculating the adsorption amount using a mass transfer model. This method, through conventional micro-pollutant retention, adsorption, and desorption experiments, calculates the diffusion coefficient by obtaining the adsorption amount of micro-pollutants in the nanofiltration membrane. The testing method is simple. This method considers the interactions between micro-pollutants and the membrane, and between micro-pollutants and the solvent during the mass transfer model calculation, introducing the influence of complex membrane-micro-pollutant interactions on the micro-pollutant mass transfer process. This makes the calculation of the diffusion coefficient of micro-pollutants (excluding ions) within the membrane more accurate.

[0022] Preferably, the nanofiltration membrane adsorbing micropollutants is immersed in an eluent to desorb the micropollutants, and the adsorption capacity of the micropollutants is calculated based on the concentration of the micropollutants in the eluent, including: The eluent includes a methanol solution, which is used for eluting micro-contaminants; A nanofiltration membrane was immersed in a methanol solution. After elution reached equilibrium, the concentration of micro-contaminants in the eluent was determined using mass spectrometry. The adsorption capacity of the micro-contaminants was calculated based on the volume of the methanol solution and the measured concentration. The nanofiltration membrane was immersed in the methanol solution under set temperature and time conditions to allow the micro-contaminants to fully desorb from the membrane into the solution. After elution reached equilibrium, the membrane was removed to avoid solution splashing or recontamination of the solution by residual micro-contaminants on the membrane. Subsequently, the concentration of micro-contaminants in the eluent was accurately determined using mass spectrometry. The adsorption amount of micropollutants is accurately calculated using a formula based on the precise volume of the methanol solution and the measured concentration of micropollutants. The calculation process is as follows: The adsorption amount of micropollutants is equal to the product of the methanol solution volume and the concentration of micropollutants in the elution solution. During the calculation, it is crucial to ensure the accurate measurement of the methanol solution volume using precise measuring instruments. For the concentration of micropollutants in the elution solution, data obtained from mass spectrometry analysis is substituted into the formula. By multiplying the accurately measured methanol solution volume by the concentration of micropollutants obtained from mass spectrometry analysis, the adsorption amount of micropollutants can be accurately calculated.

[0023] Preferably, the micro-contaminants include 4-chloroaniline, acetaminophen, trimethoprim, perfluorobutylsulfonic acid, and salicylic acid.

[0024] Specifically, micropollutants such as 4-chloroaniline, acetaminophen, trimethoprim, perfluorobutylsulfonic acid, and salicylic acid are typical examples in the environmental and water treatment fields. This invention provides crucial foundational data for accurately calculating the diffusion coefficient of micropollutants within the nanofiltration membrane by precisely measuring the adsorption capacity of these different types of micropollutants using a nanofiltration membrane. In the specific operation process, appropriate experimental conditions are controlled for micropollutants with different characteristics, such as the chemical stability of 4-chloroaniline, the polarity of acetaminophen, the molecular structure of trimethoprim, the persistence of perfluorobutylsulfonic acid, and the solubility of salicylic acid. This ensures the accuracy and reliability of the adsorption capacity measurement, thereby guaranteeing the precision of the diffusion coefficient calculation.

[0025] Preferably, the diffusion coefficient of micropollutants within the nanofiltration membrane is calculated using a mass transfer model based on the amount of micropollutants adsorbed, including: Nanofiltration membrane micro-pollutant diffusion coefficient , in, The friction coefficient of micro-pollutants under diffusion conditions; denoted as the diffusion coefficient of micro-pollutants in the bulk phase.

[0026] Preferred, With hydrodynamic retardation factor and correction factor Related; , Among them, correction factor The ratio of the Stokes radius of micropollutants to the pore size of the nanofiltration membrane. Related, and These represent the retardation coefficients between micropollutants and the nanofiltration membrane, and between micropollutants and the salt solution, respectively. The specific calculation process is as follows: , , , in, The adsorption coefficient is . It is the hydrodynamic retardation factor; , Where, 0 < <1; when ,

[0027]

[0028] when , , in, This represents the amount of micropollutants adsorbed per unit volume of the active layer when the nanofiltration membrane is saturated. This represents the concentration of micro-pollutants in the feed liquid. This represents the porosity of the nanofiltration membrane.

[0029] Specifically, by measuring key parameters such as the Stokes radius of micropollutants, the pore size of the nanofiltration membrane, the feed concentration of micropollutants, and the porosity of the nanofiltration membrane, a correction factor is calculated based on the relationship between the correction factor and the ratio of the Stokes radius of micropollutants to the pore size of the nanofiltration membrane. Then, based on the correction factor and the formulas for the retardation coefficients between micropollutants and the nanofiltration membrane and between micropollutants and the salt solution, and according to the formulas for the hydrodynamic retardation factor and related parameters, the hydrodynamic retardation factor is accurately calculated for different cases. Finally, by substituting the adsorption coefficient and the hydrodynamic retardation factor into the formulas, the adsorption correlation coefficient is obtained, and the diffusion coefficient of micropollutants within the nanofiltration membrane is accurately calculated. The calculation results are precise, clearly showing the influence of different interaction forces on the transmembrane transport of solutes. It can effectively take into account the interaction between micropollutants and membrane materials, and analyze the transmembrane mass transfer mechanism of organic micropollutants at the molecular level.

[0030] Preferably, the micro-pollutants are desorbed using a centrifuge, the desorption time of which is 24 hours and the rotor speed of the centrifuge is 50 rpm.

[0031] Specifically, during the desorption process, the centrifuge's operating parameters are strictly controlled to ensure that micro-pollutants can be fully desorbed from the nanofiltration membrane. After 24 hours of desorption treatment and centrifugation at a rotor speed of 50 rpm, a relatively pure desorption solution can be obtained. This provides a reliable guarantee for subsequent accurate measurement of key data such as the amount of micro-pollutants adsorbed per unit volume of the active layer when the nanofiltration membrane is saturated. Consequently, the process of calculating the diffusion coefficient of micro-pollutants in the nanofiltration membrane based on these data becomes more accurate and reliable.

[0032] Preferably, the membrane tank is a cross-flow filtration system membrane tank, and the salt solution is a sodium chloride solution; A nanofiltration membrane is installed in the membrane tank of a cross-flow filtration system. The membrane tank contains a sodium chloride solution to dissolve micropollutants. Once the cross-flow filtration system is started, the nanofiltration membrane in the membrane tank traps and adsorbs the micropollutants.

[0033] Specifically, during the operation of the cross-flow filtration system, by precisely controlling key parameters such as the flow rate, pressure, and temperature of the salt solution, the retention and adsorption process of micro-pollutants by the nanofiltration membrane is ensured to be stable and efficient. The precise control of the parameters of the cross-flow filtration system helps to improve the adsorption saturation of micro-pollutants by the nanofiltration membrane, thus laying a solid foundation for the subsequent accurate calculation of the diffusion coefficient of micro-pollutants in the nanofiltration membrane. At the same time, the design of the cross-flow filtration system can also effectively reduce the occurrence of concentration polarization, further improving the membrane separation performance.

[0034] Preferably, the retention and adsorption filtration pressure of micropollutants in the membrane tank of the cross-flow filtration system is 5 bar, the flow velocity of the fluid in the membrane tank of the cross-flow filtration system is 0.22 m / s, and the adsorption time in the membrane tank of the cross-flow filtration system is 12 h.

[0035] Specifically, the parameter settings of the membrane tank in the cross-flow filtration system not only ensure that the nanofiltration membrane has sufficient retention and adsorption effect on micro pollutants, allowing the entire filtration process to proceed in a relatively stable state, but also accurately simulate the effect of the nanofiltration membrane on micro pollutants in the actual water treatment environment. This creates favorable conditions for subsequently obtaining key data such as the amount of micro pollutants adsorbed per unit volume of the active layer when the nanofiltration membrane is saturated, thereby ensuring the accuracy and reliability of calculating the diffusion coefficient of micro pollutants within the nanofiltration membrane based on these data.

[0036] Preferably, the method further includes immersing the nanofiltration membrane in deionized water before installing it in the membrane tank of the cross-flow filtration system. Preferably, the nanofiltration membrane is immersed in deionized water for 24 hours.

[0037] Specifically, the nanofiltration membrane soaking time is set to 24 hours to remove impurities and residues that may be adsorbed during the production, transportation and storage of the nanofiltration membrane, to ensure the purity of the nanofiltration membrane, and to avoid these impurities and residues interfering with the subsequent interception and adsorption process of micro pollutants. This ensures that the adsorption effect of the nanofiltration membrane on micro pollutants in the membrane pool of the cross-flow filtration system is more accurate and reliable, and provides a strong guarantee for the subsequent accurate calculation of the diffusion coefficient of micro pollutants in the nanofiltration membrane.

[0038] Furthermore, the nanofiltration membrane can be a commercial or homemade polyamide nanofiltration membrane. Homemade polyamide nanofiltration membranes possess excellent separation performance and chemical stability, maintaining stable filtration effects in complex real-world water treatment environments. Commercial polyamide nanofiltration membranes undergo rigorous quality control, ensuring stable and reliable performance across all indicators; while homemade polyamide nanofiltration membranes can be customized to specific research needs and water quality characteristics, offering greater flexibility. Regardless of the type of nanofiltration membrane chosen, it can meet the requirements for the retention and adsorption of micropollutants, laying a solid foundation for the accurate calculation of the diffusion coefficient of micropollutants within the nanofiltration membrane.

[0039] Example 1: The nanofiltration membrane selected is the NF270 nanofiltration membrane. The NF270 is a polyamide composite membrane from Dow Chemical, with an effective membrane area of ​​400 ft. 2 (37m) 2 With a standard operating pressure of 225 psi (15.5 bar), the water production reaches 12,500 gpd (47 m³ / h). 3 / d), stable desalination rate (C1-) 99.5% (test conditions: 2000ppm NaCl, 25℃, pH=8, 15% recovery rate), continuous operation pH range 2-11, supports maximum temperature of 45℃ and water source below SDI5, suitable for long-term stable treatment of highly polluted water quality, combining economy and durability.

[0040] The specific implementation steps are as follows: S1: Install the NF270 nanofiltration membrane in the membrane tank of the cross-flow filtration system. Use a 10 mg / L sodium chloride solution as the background solution in the feed tank, and add a 200 µg / L micropollutant solution. Preferred micropollutants include 4-chloroaniline (PCA), acetaminophen (AP), trimethoprim (TMP), perfluorobutylsulfonic acid (PFBS), and salicylic acid (SA). Start the cross-flow filtration system; the nanofiltration membrane will retain and adsorb the micropollutants. The filtration pressure is 5 bar, the flow rate is 0.22 m / s, and the adsorption time is 12 h.

[0041] S2: The NF270 nanofiltration membrane, after adsorption saturation, was immersed in 20 mL of methanol solution for micropollutant desorption. The desorption time was 24 h, and the rotor speed was 50 rpm. After desorption, the concentration of micropollutants in the solution was determined using a high-performance triple quadrupole liquid chromatography-mass spectrometry (HPLC-MS / MS). The amount of micropollutant adsorbed was calculated based on the concentration of the solution after desorption.

[0042] S3: Calculate the intramembrane diffusion coefficient of micropollutants based on the adsorption amount using a mass transfer model. The specific calculation process is as follows: , in, and These represent the friction coefficient of the micro-pollutants under diffusion conditions and their diffusion coefficient in the bulk phase, respectively. The diffusion coefficients of the five micro-pollutants, PCA, AP, TMP, PFBS, and SA, in the bulk solution are 9.28 × 10⁻⁶. -10 m 2 / s, 8.46×10 -10 m 2 / s, 5.89×10 -10 m 2 / s, 6.45×10 -10 m 2 / s and 9.46×10 -10m 2 / s.

[0043] With blocking factor and correction factor The relevant calculation process is as follows: , Among them, correction factor The ratio of the Stokes radius of the micropollutants (0.23 nm, 0.26 nm, 0.37 nm, 0.34 nm, and 0.23 nm for PCA, AP, TMP, PFBS, and SA, respectively) to the membrane pore size (0.45 nm for nanofiltration membrane NF270). Related, and The specific calculation process for the hindrance coefficients representing the interactions between micro-pollutants and the membrane, and between micro-pollutants and the solvent, is as follows: , , , in, and These represent the adsorption coefficient and the hydrodynamic resistance factor, respectively. The specific calculation process is as follows: , when ,

[0044]

[0045] when , , in, This represents the amount of micropollutants adsorbed per unit volume of the active layer when the nanofiltration membrane is saturated. This represents the concentration of micro-pollutants in the feed liquid. This represents the porosity of the nanofiltration membrane (the porosity of nanofiltration membrane NF270 is 0.03).

[0046] See Figure 2 and Figure 3 In this embodiment, when the nanofiltration membrane NF270 is saturated, the amount of PCA, AP, TMP, PFBS, and SA adsorbed per unit volume of active layer is 6.49 × 10⁻⁶. 5 g / m 3 3.77×10 3 g / m 3 2.38×105 g / m 3 3.06×10 3 g / m 3 and 1.11×10 4 g / m 3 Based on the mass transfer model and the amount of adsorption, the diffusion coefficient within the nanofiltration membrane is calculated to be 6.55 × 10⁻⁶. -11 m 2 / s, 1.13×10 -10 m 2 / s, 8.40×10 -11 m 2 / s, 1.71×10 -10 m 2 / s and 1.00×10 -10 m 2 / s.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity, characterized in that, include: A nanofiltration membrane is installed in a membrane tank containing a salt solution, in which micro-pollutants are dissolved. The nanofiltration membrane in the membrane tank retains and adsorbs the micro-pollutants. The nanofiltration membrane that adsorbs micro-pollutants is immersed in an elution solution to desorb the micro-pollutants, and the amount of micro-pollutants adsorbed is calculated based on the concentration of micro-pollutants in the elution solution. The diffusion coefficient of micropollutants within the nanofiltration membrane is calculated using a mass transfer model based on the adsorption capacity of micropollutants. This includes: the diffusion coefficient of micropollutants within the nanofiltration membrane. , in, The friction coefficient of micro-pollutants under diffusion conditions; The diffusion coefficient of micro-pollutants in the bulk phase; The With hydrodynamic retardation factor and correction factor Related; ， Among them, correction factor The ratio of the Stokes radius of micropollutants to the pore size of the nanofiltration membrane. Related, and These represent the retardation coefficients between micropollutants and the nanofiltration membrane, and between micropollutants and the salt solution, respectively. The specific calculation process is as follows: , , ， in, The adsorption coefficient is . It is the hydrodynamic retardation factor; ， Where, 0 < <1; when , when , ， in, This represents the amount of micropollutants adsorbed per unit volume of the active layer when the nanofiltration membrane is saturated. This represents the concentration of micro-pollutants in the feed liquid. This represents the porosity of the nanofiltration membrane.

2. The method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity according to claim 1, characterized in that, The process of immersing the nanofiltration membrane that adsorbs micropollutants in an eluent to desorb them, and calculating the amount of micropollutant adsorbed based on the concentration of micropollutants in the eluent, includes: The elution solution includes a methanol solution, which is used for eluting micro-contaminants; The nanofiltration membrane was immersed in a methanol solution. After elution reached equilibrium, the concentration of micro-pollutants in the elution solution was determined by mass spectrometry. The amount of micro-pollutants adsorbed was calculated based on the volume of the methanol solution and the measured concentration of micro-pollutants.

3. The method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity according to claim 2, characterized in that: The micropollutants include 4-chloroaniline, acetaminophen, trimethoprim, perfluorobutylsulfonic acid, and salicylic acid.

4. The method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity according to claim 3, characterized in that: The micro-pollutants are desorbed using a centrifuge, the desorption time of which is 24 hours and the rotor speed of which is 50 rpm.

5. The method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity according to claim 4, characterized in that: The membrane tank is a cross-flow filtration system membrane tank, and the salt solution is a sodium chloride solution; A nanofiltration membrane is installed in the membrane tank of a cross-flow filtration system. The membrane tank contains a sodium chloride solution to dissolve micropollutants. The cross-flow filtration system is then activated, and the nanofiltration membrane in the membrane tank traps and adsorbs the micropollutants.

6. The method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity according to claim 5, characterized in that: The micropollutants are intercepted and adsorbed in the membrane tank of the cross-flow filtration system at a pressure of 5 bar, the fluid velocity in the membrane tank of the cross-flow filtration system is 0.22 m / s, and the adsorption time in the membrane tank of the cross-flow filtration system is 12 h.

7. The method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity according to claim 6, characterized in that: It also includes immersing the nanofiltration membrane in deionized water before installing it in the membrane tank of the cross-flow filtration system.

8. The method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity according to claim 7, characterized in that: The nanofiltration membrane was soaked in deionized water for 24 hours.

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