Loose nanofiltration membrane for treating landfill leachate as well as preparation method and application of loose nanofiltration membrane

Abstract

The invention relates to the technical field of membrane separation, and particularly discloses a loose nanofiltration membrane for treating landfill leachate and a preparation method and application thereof.According to the preparation method, 1, 4, 7, 10-tetraazacyclododecane is used as a water-phase monomer, trimesoyl chloride is used as an oil-phase monomer, and the oil-phase monomer is used as an oil-phase monomer; an interfacial polymerization method is adopted for preparing the loose nanofiltration membrane with high flux and high selectivity, a polyamide active layer on the surface of the loose nanofiltration membrane is in a nodule shape, and the loose nanofiltration membrane keeps low interception on representative inorganic salt, has high interception on humus in landfill leachate which is applied to effluent after MBR treatment and has low interception on the inorganic salt; according to the present invention, the separation of the organic matter and the inorganic salt is achieved, and the membrane has excellent anti-pollution performance in the two-time cyclic pollution, can maintain the ideal stability in the long-term test, and has the application prospect in the landfill percolation treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and particularly discloses a loose nanofiltration membrane for treating landfill leachate, a preparation method thereof and an application thereof. Background Art

[0002] In recent years, with the continuous development of urbanization in China, the generation and treatment volume of municipal solid waste have been increasing year by year, which has also led to an increase in the generation volume of landfill leachate. At present, the annual generation volume of landfill leachate in China has exceeded 80 million tons. The current mature treatment process for landfill leachate generally adopts the method of "biochemical method + membrane separation" for treatment: the biodegradable organic matter and nutrients in the leachate are degraded and transformed in a multi-stage biological treatment system, while the organic pollutants and inorganic salts that are difficult to be biodegraded are intercepted by a membrane separation system (such as traditional nanofiltration will intercept inorganic salts with a valence of two or more, and reverse osmosis alone will intercept all inorganic salts). This kind of treatment method has good effects and stable operation. However, this kind of treatment method will bring a more difficult-to-treat by-product - membrane concentrated landfill leachate (hereinafter referred to as concentrated liquid). Such concentrated liquid contains high concentrations of difficult-to-biodegrade organic matter (mainly humus substances) and inorganic salts, and thus is difficult to be treated or utilized.

[0003] Loose nanofiltration membranes have widely attracted the interest of scholars due to their high water flux, high separation efficiency of organic matter and inorganic salts, excellent anti-fouling performance and other advantages, and the preparation methods, mechanisms, etc. of loose nanofiltration membranes have been explored. They are often applied to the separation research of organic matter and inorganic salts. To improve the treatment efficiency and save costs, it is also crucial to develop green and efficient loose nanofiltration membranes with better and more stable performance by optimizing the selective layer and adjusting the membrane structure and morphology.

[0004] Therefore, using a new membrane separation technology (loose nanofiltration membrane) to treat the landfill leachate after biochemical treatment and separate the difficult-to-biodegrade organic matter (humus) and inorganic salts therein, so that the inorganic salts do not accumulate in the concentrated liquid, can provide new ideas for the treatment or resource utilization of the concentrated liquid. Summary of the Invention

[0005] The object of the present invention is to provide a loose nanofiltration membrane for treating landfill leachate, its preparation method and application. Using a polyethersulfone (PES) membrane as the base membrane, a membrane preparation method of interfacial polymerization is adopted. 1,4,7,10-tetraazacyclododecane (Cyclen) with a dodecacyclic ring and a spatial conformation similar to piperazine (PIP) is used as the aqueous monomer, and trimesoyl chloride (TMC) is used as the oil-phase monomer to prepare a loose nanofiltration membrane (LNM). Cyclen has a larger spatial structure to effectively regulate the microstructure of the PA layer to form a loose active layer. The loose nanofiltration membrane prepared from the actual landfill leachate exhibits high water flux and high organic matter (humic substances) rejection rate while maintaining a low salt rejection rate. Compared with the NF270 commercial membrane, it shows excellent anti-fouling performance and long-term stability, exploring the feasibility of its application in the treatment of high-concentration wastewater such as landfill leachate, and providing a new strategy for the effective separation of organic matter / inorganic salts in landfill leachate.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A loose nanofiltration membrane for treating landfill leachate, which uses a PES membrane as the base membrane, Cyclen as the aqueous monomer, and TMC as the oil-phase monomer, and is prepared by an interfacial polymerization method to obtain a loose nanofiltration membrane with a nodular surface active layer, high flux and high selectivity.

[0008] A preparation method of a loose nanofiltration membrane for treating landfill leachate, comprising the following steps:

[0009] S1. Immerse the PES base membrane in deionized water for a period of time to remove the protective agent on the membrane surface;

[0010] S2. Dissolve 1,4,7,10-tetraazacyclododecane in ultrapure water to obtain an aqueous solution;

[0011] S3. Dissolve TMC in n-hexane to obtain an oil-phase solution;

[0012] S4. Immerse the PES base membrane in step S1 in the aqueous solution for a period of time, then take it out and remove the excess aqueous solution on the surface;

[0013] S5. Contact the membrane in step S4 with the oil-phase solution in step S3 to carry out an interfacial polymerization reaction;

[0014] S6. After reacting for a period of time, remove the oil-phase solution and let it stand at room temperature for a period of time;

[0015] S7. The prepared membrane is stored in deionized water for standby.

[0016] As a preferred method, in step S1, the PES base membrane is immersed in deionized water for not less than 12 h;

[0017] As a preferred method, in step S2, 1,4,7,10-tetraazacyclododecane is dissolved in ultrapure water with concentration gradients of 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 wt%.

[0018] As a preferred method, in step S3, TMC is dissolved in n-hexane with a concentration of 0.2 w / v%.

[0019] As a preferred method, in step S4, the PES-based membrane in step S1 is immersed in the aqueous solution and waits for 30 min.

[0020] As a preferred method, in step S5, the membrane in step S4 is contacted with the oil-phase solution in step S3 for 2 min to carry out an interfacial polymerization reaction.

[0021] As a preferred method, in step S6, after the interfacial polymerization reaction ends, the oil-phase solution is removed and left standing at room temperature for 5 min.

[0022] More preferably, in the aforementioned step S2, when the concentration of Cyclen is 0.6 wt% and in step S3 when the concentration of TMC is 0.2 wt%, it is the optimal reaction condition of the present invention.

[0023] In addition, the present invention also discloses an application of a loose nanofiltration membrane for treating landfill leachate. This loose nanofiltration membrane is applied to treat the landfill leachate from the effluent of MBR, separating the organic matter (humic substances) and inorganic salts in the landfill leachate, providing a new strategy for the effective separation of humic substances / inorganic salts in landfill leachate.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The present invention uses the interfacial polymerization method to prepare a high-flux and highly selective loose nanofiltration membrane with a nodular surface polyamide active layer. This membrane has low retention for representative inorganic salts. When applied to the landfill leachate from the effluent after MBR treatment, it has high retention for humic substances and low retention for inorganic salts in it, achieving the separation of organic matter and inorganic salts. This membrane has excellent anti-fouling performance in two cycles of pollution and maintains ideal stability in long-term tests, demonstrating its application prospects in landfill leachate treatment.

[0026] 2. The Cyclen / TMC loose nanofiltration membrane of the present invention demonstrates the application potential in landfill leachate treatment, providing new ideas for the resource utilization of landfill leachate, and also showing great application advantages in improving the selectivity of loose nanofiltration membranes and their application in the treatment of other high-concentration wastewater fields. Description of the Drawings

[0027] Figure 1 Schematic diagram of the preparation method of the loose nanofiltration membrane of the present invention;

[0028] Figure 2 Surface SEM morphology diagrams of Examples 1.1 to 1.6 and the PES-based membrane;

[0029] Figure 3 Cross-section SEM morphology diagrams of Examples 1.1 to 1.6 and the PES-based membrane;

[0030] Figure 4 ATR-FTIR diagrams of Membrane A3, A6 and the PES-based membrane;

[0031] Figure 5 AFM diagrams of Examples 1.1 to 1.6 and the PES-based membrane;

[0032] Figure 6 Water contact angle diagrams of Examples 1.1 to 1.6 and the PES-based membrane;

[0033] Figure 7 Zeta potential diagrams of Membrane A3, the PAS-based membrane and the NF270 commercial membrane;

[0034] Figure 8 Diagrams of (a) pure water flux and (b) inorganic salt rejection performance of Examples 1.1 to 1.6;

[0035] Figure 9 Molecular weight cut-off curve diagrams of Membrane A2, A3, A4, A5, A6;

[0036] Figure 10 Actual landfill leachate rejection performance diagrams of Examples 1.1 to 1.6 and the NF270 commercial membrane, where (a) humus and inorganic salt rejection rates in landfill leachate; (b) rejection rates of each component of landfill leachate; (c) three-dimensional fluorescence spectrum diagram of landfill leachate before treatment by Membrane A3; (c) three-dimensional fluorescence spectrum diagram of landfill leachate after treatment by Membrane A3;

[0037] Figure 11 Anti-fouling performance diagrams of Membrane A3 and the NF270 commercial membrane, where (a) line graph of the relationship between flux and time; (b) bar graph of water recovery rate (FRR), total fouling ratio (Rt), reversible fouling (Rr), irreversible fouling (Rir);

[0038] Figure 12 Long-term stability performance diagrams of Membrane A3 and the NF270 commercial membrane. Specific embodiments

[0039] The present invention will be specifically introduced below in conjunction with the accompanying drawings and specific embodiments.

[0040] Unless otherwise specified in the present invention, all raw materials used are commercially available. The preferred commercial sources are shown in Table 1 below:

[0041] Preferred commercial sources of each raw material in Table 1

[0042]

[0043]

[0044] The loose nanofiltration membrane is prepared by interfacial polymerization. The preparation process is schematically shown as Figure 1 shown below. The preparation steps are as follows:

[0045] (1) Immerse the PES substrate membrane in deionized water for a period of time to remove the protective agent on the membrane surface;

[0046] (2) Dissolve 1,4,7,10-tetraazacyclododecane in ultrapure water to obtain an aqueous solution;

[0047] (3) Dissolve TMC in n-hexane to obtain an oil-phase solution;

[0048] (4) Immerse the PES substrate membrane in step (1) in the aqueous solution for a period of time, then take it out and remove the excess aqueous solution on the surface;

[0049] (5) Contact the membrane in step (4) with the oil-phase solution in step (3) to carry out an interfacial polymerization reaction;

[0050] (6) After the interfacial polymerization reaction is completed, remove the oil-phase solution and let it stand at room temperature for a period of time;

[0051] (7) The prepared membrane is stored in deionized water for later use.

[0052] The preparation steps of the membranes in the following examples are the same as above, and the main difference lies in the amounts of raw materials used in the examples.

[0053] Example 1

[0054] Example 1 includes six sub-examples, denoted as Example 1.1, 1.2, 1.3, 1.4, 1.5, and 1.6 respectively. The main difference is the concentration of the aqueous monomer Cyclen. The membranes prepared are denoted as A1, A2, A3, A4, A5, and A6 respectively. See Table 2 for details:

[0055] Examples and monomer concentrations in Table 2

[0056]

[0057] Structure characterization

[0058] (1) SEM characterization

[0059] The surface morphology and cross-section of the membrane were characterized by SEM.

[0060] Figure 2 SEM surface morphology images of A1 of Example 1.1 to A6 of Example 1.6 and the PES-based membrane are shown. The PES-based membrane presents a smooth and uniform porous structure without obvious nodular structures. Obvious nodular structures appear in A1 to A6 and the porous structure is covered, indicating the successful formation of the active layer on the PES-based membrane. As the concentration of Cyclen increases, the nodular structures on the membrane surface gradually become denser and the wrinkles become more obvious, which is due to the interface instability caused by the increased release of reaction heat.

[0061] Figure 3 SEM cross-section morphology images of A1 of Example 1.1 to A6 of Example 1.6 and the PES-based membrane are shown. Compared with the PES-based membrane, obvious PA layers appear in the cross-section morphology of A1 to A6, and their thickness increases with the increase in the Cyclen concentration.

[0062] (2) ATR-FTIR infrared detection

[0063] The chemical composition of the membrane was characterized by ATR-FTIR.

[0064] Figure 4 ATR-FTIR spectra of A3 and A6 of Example 1.1 and the PES-based membrane are shown. Compared with the PES substrate, obvious peaks appear at 1606.03 cm -1 and 1398.16 cm -1 , which are caused by the stretching vibrations of amide bonds belonging to C=O groups and C-N groups respectively. The stretching vibration of the C-O group observed at 1060.78 cm -1 can be attributed to hydroxyl groups, indicating the successful preparation of the PA layer on the PES-based membrane.

[0065] (3) Surface properties

[0066] The surface roughness of the membrane was characterized using an atomic force microscope (AFM).

[0067] Figure 5 AFM images of A1 of Example 1.1 to A6 of Example 1.6 and the PES-based membrane are shown. Similar to the surface SEM results, as the concentration of Cyclen increases, the IP reaction becomes more intense, and the overall roughness and thickness show a gradually increasing trend. The difference in surface roughness is mainly caused by the diffusion rate of the aqueous-phase monomers.

[0068] The water contact angle of the membrane was measured using a water contact angle tester, and the zeta potential of the membrane was measured to evaluate the hydrophilicity of the membrane.

[0069] The water contact angles of A1 in Example 1.1 to A6 in Example 1.6 and the PES-based membrane are as follows Figure 6 shown. The water contact angle of the PES-based membrane is 61.26°. As the concentration of Cyclen increases, the water contact angle decreases from 44.43° of A1 to 17.51° of A6, indicating that the hydrophilicity of the membrane gradually increases. This is because the hydrolysis of unreacted acyl chloride groups increases, resulting in more carboxyl groups.

[0070] The zeta potentials of A3 in Example 1.3, the PES-based membrane, and the NF270 commercial membrane are as follows Figure 7 shown. The zeta potentials of A3, the PES-based membrane, and the NF270 commercial membrane all show a negative growth trend, and A3 and NF270 have more negative surface charges, indicating that A3 is more hydrophilic than the PES-based membrane, which is consistent with the water contact angle results.

[0071] Performance Test

[0072] In the performance test section, the membranes of Example 1 and the NF270 commercial membrane were tested and compared.

[0073] (1) Osmotic Separation Performance

[0074] Measured by a self-made cross-flow filtration system in the laboratory, the effective filtration area is 3.14 cm 2 , and the feed water used during pre-pressurization and testing is ultrapure water. The pressure during pre-pressurization is 6 bar and lasts for 0.5 h, and the pressure during measurement is 6 bar. The water flux and solute rejection rate of the membrane were evaluated using an inorganic salt (NaCl, MgCl2, MgSO4, 50 mmol / L) as the feed solution. The water flux (P, L m -2 h -1 bar -1 ) of the membrane was measured using the formula

[0075]

[0076] where V (L) is the permeated volume, A (m 2 ) is the effective filtration area, t (h) is the permeation time, and P (bar) is the measurement pressure.

[0077] The rejection rate (R, %) of the membrane was calculated using the formula

[0078]

[0079] where C f and C p are the solute concentrations in the feed solution and the permeate solution, respectively, and their concentrations were measured using a conductivity meter.

[0080] As shown in Figure 8Shown are the water fluxes of A1 of Example 1.1 to A6 of Example 1.6 and the rejection rates of (a) NaCl, (b) MgCl2, and (c) MgSO4, as Figure 8 (a) shows that when the Cyclen concentration is lower than 0.6 wt%, the pure water flux of the Cyclen / TMC membrane decreases significantly, from 122.82 L m -2 h -1 bar -1 at A1 to 31.73 L m -2 h -1 bar -1 at A3. As the Cyclen concentration increases, the pure water flux remains relatively stable. The increase in the hydrophilicity of the membrane surface is attributed to the active layer, and the presence of more nodular structures enhances the porosity and specific surface area, thus facilitating the formation of channels for promoting water molecule passage. The inorganic salt rejection rates of the Cyclen / TMC membrane are summarized in Figure 8 (b), where the rejection rates of A3 for NaCl, MgCl2, and MgSO4 are 10.15%, 19.60%, and 49.87% respectively

[0081] (2) Molecular weight cut-off of the membrane

[0082] The molecular weight cut-off of the membrane was studied by the solute migration method as Figure 9 shown. As the Cyclen concentration increases, the molecular weight cut-off (MWCO) decreases from 411 Da at A1 to 239 Da at A6, where the MWCO of A3 is 269 Da, indicating that A3 has a larger pore size compared to traditional nanofiltration, which can ensure its higher organic pollutant / salt selectivity and ideal water flux.

[0083] (3) Application of the membrane to actual landfill leachate

[0084] The separation performance of the Cyclen / TMC membrane was evaluated using landfill leachate from an actual waste incineration plant. Its water quality characteristics are shown in Table 1. Landfill leachate mainly consists of various dissolved non-biodegradable organic compounds (DOMs) such as humic acid (HA), fulvic acid (FA), hydrophilic components (HyI), and inorganic ions. First, the pH of the leachate was adjusted to below 3 to eliminate the potential influence of inorganic carbon on the obtained results, and then the solute concentration was measured and recorded as C T . Subsequently, the pH was adjusted to below 1.5 to promote the precipitation of humic acid (HA), and then centrifugation was carried out. The supernatant was collected after centrifugation to measure the solute concentration, denoted as C1, and its components are fulvic acid (FA) and hydrophilic components (HyI). The supernatant was mixed with an equal volume of resin, stirred to adsorb FA for 2 h, and the supernatant was separated by precipitation. The solute concentration in the separated part was measured and denoted as C2. This part contains HyI, and its calculation formula is

[0085] HA = C T -C1

[0086] FA = C1 - C2

[0087] HS = HA + FA

[0088] After the above treatment of the feed and effluent solutions, the total organic carbon analyzer was used to measure their concentrations and calculate the removal rate. The rejection rate (R, %) was calculated using the formula,

[0089]

[0090] where C f and C p are the solute concentrations in the feed solution and the permeate solution, respectively.

[0091] Table 3. Water quality characteristics of landfill leachate treated by MBR in this study

[0092]

[0093]

[0094] As Figure 10 (a) shows, the Cyclen / TMC membrane exhibits high humus (HS) rejection performance, while the rejection of inorganic salts is relatively low. From R HS = 78.11% and R salts = 2.75% for A1 to R HS = 94.48% and R salts = 13.60% for A6, when the Cyclen concentration exceeds 0.6 wt%, the rejection rate of HS is stable above 90%, and the rejection rate of inorganic salts is maintained at about 12%. As Figure 10 (b) shows, with the increase of the Cyclen concentration, the rejection rate of each component gradually increases. Due to the combined action of size exclusion and Donnan exclusion, the rejection rate of DOMs increases from 65.71% to 92.51%, the rejection rate of HA increases from 96.22% to 96.27%, the rejection rate of FA increases from 66.73% to 96.11%, and the rejection rate of HyI increases from 49.32% to 86.05%. The molecular weight relationship of HA, FA, and HyI is MW(HA) > MW(FA) > MW(HyI), and the rejection rates of these three components also show a decreasing trend (R HA > R FA > R HyI ), which is consistent with the rejection law of three different molecular weights. This indicates that the Cyclen / TMC membrane has the selective ability to remove organic matter in landfill leachate, including organic matter with different molecular weights. A3 has good HS / inorganic salt rejection performance (RHS = 96.36%, R salts = 9.65%), the rejection rate of DOMs was 92.52%, and the rejection rates of each component were R HA = 100%, R FA = 93.73%, R HyI = 77.84%. This indicates that the Cyclen / TMC membrane can effectively separate organic matter and inorganic salts from landfill leachate due to its thin and porous active layer. The rejection rate of NF270 for HS was 90.99%, the rejection rate of inorganic salts was 28.52%, and the rejection rates of other components were R DOMs = 90.25%, R HA = 83.98%, R FA = 95.3%, R HyI = 84.38%. The three-dimensional fluorescence spectra of the solution before and after treatment with A3 are shown in Figure 10 (c)–(d). Obviously, the humic acid-like substances in region V were effectively retained, leaving only a small part of the untreated small molecules. The above indicates that the Cyclen / TMC membrane exhibits significant separation performance with high HS retention and low inorganic salt retention.

[0095] (4) Fouling resistance test of the membrane

[0096] The problem of membrane fouling during operation and its impact on long-term stability cannot be ignored. Two fouling cycles were carried out using landfill leachate from an actual waste incineration plant to evaluate the fouling resistance of A3 and NF270 membranes. In Figure 11 (a), the fouling stage was due to the presence of high-molecular-weight organic matter in the landfill leachate, which blocked the membrane pores and formed a filter cake on the membrane surface. As a result, the membrane permeability decreased significantly. However, after a simple physical water cleaning process, both fouled membranes showed obvious water flux recovery. It should be noted that during the two fouling cycles, A3 showed a higher water flux compared to NF270. As shown in Figure 11As shown in (b), after two cycles, the flux recovery rate (FRR) of A3 exceeded 97% in both cases. In addition, the flux decline rate (Rt) remained at about 30%. The reversible fouling rate (Rr) decreased from 28.75% to 26.73%, and the irreversible fouling rate (Rir) was relatively low, being 2.05% and 2.99% respectively. The flux recovery rate (FRR) of NF270 increased from 89.78% to 97.76%, but the flux decline rate (Rt) reached over 60% in both cases, and the reversible fouling rate (Rr) also exceeded 55%, with the irreversible fouling rate (Rir) ranging from 10.21% to 2.23%. The higher FRR and lower Rir indicate that A3 has excellent anti-fouling performance and easy cleanability. The high hydrophilicity on the membrane surface promotes the adsorption of a large number of water molecules, thereby enhancing the interaction between the membrane surface and pollutants, and thus reducing the possibility of membrane fouling.

[0097] (5) Long-term stability of the membrane

[0098] Figure 12 The stability of A3 and NF270 within 12 hours of operation is shown. During the entire test period, the rejection rate of A3 for landfill leachate was above 97% and maintained a high flux. While NF270 showed a low flux while maintaining a high rejection rate. The above results indicate that the Cyclen / TMC membrane has great application potential in separation.

[0099] In the present invention, a loose nanofiltration membrane was prepared by interfacial polymerization using the macrocyclic polyamine monomer Cyclen and TMC for the selective separation of humic substances / inorganic salts in actual landfill leachate. The membrane was optimized by controlling the concentration of Cyclen in the aqueous phase. The optimal membrane A3 has a high pure water flux (pure water flux > 30 Lm -2 h -1 bar -1 ), has an excellent rejection rate for humic substances (rejection rate > 92%) and a low salt rejection rate (rejection rate < 10%). In addition, A3 has the properties of strong hydrophilicity and multiple negative charges, which can reduce the adhesion of pollutants on the membrane surface, thus showing excellent anti-fouling performance and also showing ideal stability under long-term operation.

[0100] In summary, the Cyclen / TMC loose nanofiltration membrane of the present invention demonstrates application potential in the treatment of landfill leachate, provides a new idea for the resource utilization of landfill leachate, and also shows application prospects in improving the selectivity of loose nanofiltration membranes and their application in the treatment of other high-concentration wastewater fields.

[0101] The above are only embodiments of the present invention, and do not thereby limit the patent scope of the present invention. Any equivalent structural or equivalent process transformations made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A loose nanofiltration membrane for treating landfill leachate, characterized in that: Using a polyethersulfone (PES) membrane as the base membrane, 1,4,7,10-tetraazacyclododecane (Cyclen) as the aqueous monomer, and trimesoyl chloride (TMC) as the oil-phase monomer, a high-flux and highly selective loose nanofiltration membrane with a nodular surface active layer was prepared by interfacial polymerization.

2. A preparation method of a loose nanofiltration membrane for treating landfill leachate as described in claim 1, characterized in that: The method includes the following steps: S1. Immerse the PES base membrane in deionized water for a period of time to remove the protective agent on the membrane surface. S2. Dissolve 1,4,7,10-tetraazacyclododecane in ultrapure water to obtain an aqueous solution. S3. Dissolve TMC in n-hexane to obtain an oil-phase solution. S4. Immerse the PES base membrane in step S1 in the aqueous solution for a period of time, then take it out and remove the excess aqueous solution on the surface. S5. Contact the membrane in step S4 with the oil-phase solution in step S3 to carry out an interfacial polymerization reaction. S6. After the interfacial polymerization reaction is completed, remove the oil-phase solution and let it stand at room temperature for a period of time. S7. Store the prepared membrane in deionized water for standby.

3. The preparation method of a loose nanofiltration membrane for treating landfill leachate according to claim 2, characterized in that: In step S1, immerse the PES base membrane in deionized water for at least 12 h.

4. The preparation method of a loose nanofiltration membrane for treating landfill leachate according to claim 2, characterized in that, In step S2, dissolve 1,4,7,10-tetraazacyclododecane in ultrapure water with concentration gradients of 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 wt%.

5. The preparation method of a loose nanofiltration membrane for treating landfill leachate according to claim 2, characterized in that, In step S3, dissolve TMC in n-hexane at a concentration of 0.2 w / v%.

6. The preparation method of a loose nanofiltration membrane for treating landfill leachate according to claim 2, characterized in that, In step S4, immerse the PES base membrane in step S1 in the aqueous solution and wait for 30 min.

7. The preparation method of a loose nanofiltration membrane for treating landfill leachate according to claim 2, wherein In step S5, contact the membrane in step S4 with the oil-phase solution in step S3 for 2 min to carry out an interfacial polymerization reaction.

8. The preparation method of a loose nanofiltration membrane for treating landfill leachate according to claim 2, wherein In step S6, after the interfacial polymerization reaction is completed, remove the oil-phase solution and let it stand at room temperature for 5 min.

9. Application of a loose nanofiltration membrane for treating landfill leachate, characterized in that, The loose nanofiltration membrane is applied to treat the effluent of MBR for landfill leachate to separate humus and inorganic salts in the landfill leachate.

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