Method for calculating diffusion coefficient of micropollutants in nanofiltration membrane based on adsorption quantity

Abstract

The invention discloses a method for calculating a diffusion coefficient of micro-pollutants in a nanofiltration membrane based on adsorption capacity in the technical field of membranes, which comprises the following steps: installing the nanofiltration membrane in a membrane pool filled with a salt solution, dissolving the micro-pollutants in the salt solution, and intercepting and adsorbing the micro-pollutants by the nanofiltration membrane in the membrane pool; and soaking the nanofiltration membrane which adsorbs the micro-pollutants in an elution solution to desorb the micro-pollutants. According to the method, the adsorption capacity of the micropollutants in the nanofiltration membrane is obtained through conventional micropollutant interception, adsorption and desorption experiments, the diffusion coefficient can be calculated, the testing method is simple, the mutual relation between the micropollutants and the membrane and the mutual relation between the micropollutants and the solvent are considered in the mass transfer model calculation process, and the calculation accuracy is high. The influence of the complex interaction force of the membrane-micropollutants on the mass transfer process of the micropollutants is introduced, so that the calculation of the diffusion coefficient of the micropollutants except ions in the membrane is more accurate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane technology, and particularly relates to a method for calculating diffusion coefficient of micro-pollutants in nanofiltration membrane based on adsorption amount. BACKGROUND

[0002] Micro-pollutants in water are various in types, high in toxicity and difficult to degrade. Although the concentration of micro-pollutants is extremely low (ng / L ~ μg / L level), long-term accumulation of micro-pollutants will cause serious threat to water environment safety and human health. The removal efficiency of micro-pollutants by traditional water treatment processes is limited and unstable. Nanofiltration, as a membrane separation technology between ultrafiltration and reverse osmosis, selectively removes micro-pollutants based on size sieving effect, Donnan effect and membrane-micro-pollutant interaction, and is a key technology for solving water environmental pollution. However, due to the incomplete understanding of the micro-pollutant removal mechanism by nanofiltration, the design of high-performance nanofiltration membranes is hindered. Precise and efficient determination of the diffusion coefficient of micro-pollutants in the membrane is crucial for analyzing the transmembrane transport mechanism of micro-pollutants.

[0003] The existing traditional pore flow model (such as DSPM-DE model) considers three mass transfer modes of convection, diffusion and electromigration in the nanofiltration process, describes the influence of steric effect, Donnan effect and dielectric effect on the transmembrane transport process of solutes, but ignores the membrane-solute interaction in the mass transfer process. Therefore, for micro-pollutants with complex interactions (such as hydrogen bond, π-π stacking and van der Waals force) with nanofiltration membranes, the DSPM-DE model cannot accurately predict the transmembrane transport of micro-pollutants, and cannot clearly show the influence of membrane-solute interaction on the transmembrane transport of solutes. SUMMARY

[0004] The present application aims to provide a method for calculating the diffusion coefficient of micro-pollutants in nanofiltration membrane based on adsorption amount, to solve the problem of unclear influence of membrane-solute interaction on the transmembrane transport of solutes.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme: A method for calculating the diffusion coefficient of micro-pollutants in nanofiltration membrane based on adsorption amount, comprising: installing the nanofiltration membrane in a membrane cell containing a salt solution, dissolving the micro-pollutants in the salt solution, and retaining and adsorbing the micro-pollutants by the nanofiltration membrane in the membrane cell; immersing the nanofiltration membrane adsorbed with micro-pollutants in an elution solution to desorb the micro-pollutants, and calculating the adsorption amount of micro-pollutants according to the concentration of micro-pollutants in the elution solution; calculating the diffusion coefficient of micro-pollutants in the nanofiltration membrane by using a mass transfer model according to the adsorption amount of micro-pollutants.

[0006] As a further scheme of the present application: the micro-pollutant adsorbed nanofiltration membrane is soaked in the elution solution for micro-pollutant desorption, and the micro-pollutant adsorption amount is calculated according to the concentration of the micro-pollutant in the elution solution, comprising: The elution solution comprises a methanol solution used for micro-pollutant elution. The nanofiltration membrane is soaked in the methanol solution, and after the elution reaches equilibrium, the concentration of the micro-pollutant in the elution solution is determined based on a mass spectrometer analysis method; and the micro-pollutant adsorption amount is calculated according to the volume of the methanol solution and the measured micro-pollutant concentration.

[0007] As a further scheme of the present application: the micro-pollutant comprises 4-chloroaniline, acetaminophen, trimethoprim, perfluorobutyl sulfonic acid and salicylic acid.

[0008] As a further scheme of the present application: the diffusion coefficient of the micro-pollutant in the nanofiltration membrane is calculated according to the micro-pollutant adsorption amount by using a mass transfer model, comprising: The diffusion coefficient of the micro-pollutant in the nanofiltration membrane , Wherein, is the friction coefficient of the micro-pollutant under diffusion conditions; is the diffusion coefficient of the micro-pollutant in the bulk phase.

[0009] As a further scheme of the present application: the hydrodynamic retardation factor and the correction factor are related; , Wherein, the correction factor is related to the ratio of the Stokes radius of the micro-pollutant to the membrane pore size of the nanofiltration membrane , and respectively represent the retardation coefficients between the micro-pollutant and the nanofiltration membrane and between the micro-pollutant and the salt solution, and the specific calculation process is, , , , Wherein, is the adsorption coefficient, is the hydrodynamic retardation factor; , Wherein, 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 further 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 2Fig. 1 is a schematic diagram of the micro-pollutant adsorption amount in the active layer per unit volume of the nanofiltration membrane NF270 according to the present application in Example 1. Figure 3 Fig. 2 is a schematic diagram of the micro-pollutant diffusion coefficient in the nanofiltration membrane NF270 calculated based on the adsorption amount according to the present application in Example 1. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0020] Embodiment: Please refer to Figure 1 In the embodiments of the present application, a method for calculating the micro-pollutant diffusion coefficient in a nanofiltration membrane based on the adsorption amount comprises the following steps: S1: installing the nanofiltration membrane in a membrane cell containing a salt solution, dissolving the micro-pollutant in the salt solution, and retaining and adsorbing the micro-pollutant by the nanofiltration membrane in the membrane cell; S2: soaking the nanofiltration membrane adsorbed with the micro-pollutant in an elution solution to desorb the micro-pollutant, and calculating the micro-pollutant adsorption amount according to the concentration of the micro-pollutant in the elution solution; S3: calculating the micro-pollutant diffusion coefficient in the nanofiltration membrane based on the mass transfer model according to the micro-pollutant adsorption amount, wherein the calculation process based on the mass transfer model is as follows: firstly, constructing a mass transfer model suitable for the nanofiltration membrane system, which fully considers the structural characteristics of the nanofiltration membrane and the transmission mechanism of the micro-pollutant in the membrane. In the model, the relevant boundary conditions and initial conditions are set, the micro-pollutant adsorption amount data obtained through experiments are substituted into the mass transfer model, the differential equations in the mass transfer model are solved by using the numerical calculation method, the mass transfer model is continuously iterated and adjusted to reach the best fitting state, and the micro-pollutant diffusion coefficient in the nanofiltration membrane is calculated.

[0021] Specifically, the concentration of the salt solution and the dissolution ratio of the micro-pollutant solution are accurately controlled to ensure that the nanofiltration membrane can effectively intercept and adsorb the micro-pollutants in a suitable environment, so as to reduce the influence of external factors on the adsorption process, desorb the micro-pollutants adsorbed on the nanofiltration membrane, accurately calculate the adsorption amount of the micro-pollutants according to the concentration of the micro-pollutants in the elution solution, and obtain the diffusion coefficient of the micro-pollutants in the nanofiltration membrane by using the mass transfer model to calculate the adsorption amount of the micro-pollutants. The method can obtain the adsorption amount of the micro-pollutants in the nanofiltration membrane through conventional micro-pollutant interception, adsorption and desorption experiments, and then calculate the diffusion coefficient. The test method is simple. The method considers the mutual relationship between the micro-pollutants and the membrane and the mutual relationship between the micro-pollutants and the solvent in the mass transfer model calculation process, introduces the influence of the complex interaction force between the membrane and the micro-pollutants on the mass transfer process of the micro-pollutants, and thus the calculation of the diffusion coefficient of the micro-pollutants in the membrane except for ions is more accurate.

[0022] Preferably, the nanofiltration membrane adsorbing the micro-pollutants is soaked in the elution solution to desorb the micro-pollutants, and the adsorption amount of the micro-pollutants is calculated according to the concentration of the micro-pollutants in the elution solution, including: The elution solution includes a methanol solution, and the methanol solution is used for elution of the micro-pollutants. The nanofiltration membrane is soaked in the methanol solution, after the elution reaches equilibrium, the concentration of the micro-pollutants in the elution solution is determined based on a mass spectrometer analysis method; the adsorption amount of the micro-pollutants is calculated according to the volume of the methanol solution and the measured concentration of the micro-pollutants, the nanofiltration membrane is soaked in the methanol solution under the conditions of a set temperature and time, so that the micro-pollutants are fully desorbed from the nanofiltration membrane into the methanol solution, after the elution reaches an equilibrium state, the nanofiltration membrane is taken out to avoid the solution from splashing out or the micro-pollutants remaining on the nanofiltration membrane from polluting the solution again, then, the concentration of the micro-pollutants in the elution solution is accurately determined by using the mass spectrometer analysis method, the adsorption amount of the micro-pollutants is accurately calculated according to the accurate volume of the methanol solution and the measured concentration of the micro-pollutants by using a calculation formula, and the calculation process is as follows: the adsorption amount of the micro-pollutants is equal to the product of the volume of the methanol solution and the concentration of the micro-pollutants in the elution solution, when calculating, it is necessary to ensure that the measurement of the volume of the methanol solution is accurate, and an accurate measurement tool is used to obtain the value; for the concentration of the micro-pollutants in the elution solution, the data obtained by the mass spectrometer analysis method is substituted, the accurately measured volume of the methanol solution is multiplied by the concentration of the micro-pollutants obtained by the mass spectrometer analysis, and thus the adsorption amount of the micro-pollutants can be accurately calculated.

[0023] Preferably, the micro-pollutants include 4-chloroaniline, acetaminophen, trimethoprim, perfluorobutyl sulfonic 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 inside the nanofiltration membrane is calculated using a mass transfer model based on the amount of micropollutants adsorbed.

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 diffusion coefficient of micropollutants within the nanofiltration membrane is calculated using a mass transfer model based on the adsorption capacity 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.

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 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.

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

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: 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.

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 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.

9. The method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity according to claim 8, 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.

10. The method for calculating the diffusion coefficient of micropollutants within a nanofiltration membrane based on adsorption capacity according to claim 9, characterized in that: The nanofiltration membrane was soaked in deionized water for 24 hours.

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