A method for membrane fouling control based on sacrificial protective coating

Abstract

The present application relates to the technical field of water treatment membrane, and provides a membrane pollution control method based on sacrificial protective coating, which comprises the following steps: passing a persulfate aqueous solution into the surface of an active layer of a membrane module in cross flow to form an activated membrane module; passing a Fe-tannic acid coating liquid from the surface of the active layer into the activated membrane module in cross flow to complete coating loading; using the membrane module loaded with the coating for sewage separation treatment; and when the membrane pollution reaches a certain degree, carrying out coating disassembly; passing a disassembly liquid from the surface of the coating into the polluted membrane module in cross flow to disassemble the coating; and cyclically carrying out coating loading / disassembly to realize continuous control of membrane pollution. The method of the present application can avoid the contact between the membrane matrix material and pollutants, effectively control the formation of irreversible membrane pollution, be cyclically applied on the membrane surface for a long time, not cause damage to the membrane matrix, prolong the service life of the membrane, have good adaptability to various membrane materials, and have strong practicability; and can be used for controlling membrane pollution caused by various complex wastewaters without difference.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment membranes, and in particular to a membrane pollution control method based on sacrificial protective coatings. Background Art

[0002] Membrane separation technology, due to its energy-saving and environmentally friendly features, simple operation, and efficient separation, has been widely used in drinking water purification, seawater desalination, and wastewater treatment. Compared with other water treatment technologies, membrane separation technology offers advantages such as better treatment results, more stable effluent quality, and no secondary pollution. However, a major obstacle to the application of membrane technology is the performance degradation and increased operating costs caused by membrane fouling. This is particularly true when treating wastewater with high concentrations and complex matrices, which can easily lead to irreversible membrane fouling and shorten membrane life. Currently, the main methods for controlling membrane fouling include pre-membrane pretreatment, physical / chemical cleaning, and membrane modification. However, each of these methods presents challenges such as operational difficulty, high additional costs, membrane damage, difficulty in effectively controlling irreversible fouling, and impacts on membrane operational stability. Therefore, the membrane technology market remains in strong demand for efficient, convenient, and low-cost methods for controlling membrane fouling.

[0003] The sacrificial protective coating strategy is a new approach to solving the membrane fouling problem, and is particularly suitable for membrane application scenarios with severe irreversible fouling. This method first loads a protective layer on the membrane surface to isolate the membrane from direct contact between the membrane pollutants and the membrane substrate during membrane operation. When the pollutants accumulate to a certain level, the coating and the pollutant layer are removed simultaneously through a specific disassembly method, thereby completely restoring the original performance of the membrane. A new sacrificial protective coating is obtained by reloading, and the process is circulated to protect the membrane substrate. However, existing sacrificial protective coating methods, such as layer-by-layer self-assembly coatings and carboxymethyl chitosan coatings, still have problems such as high requirements for membrane surface properties, complex and time-consuming coating processes, high material costs, and high environmental risks, making them difficult to apply on a large scale. Summary of the Invention

[0004]

Technical Issues

[0005] Current methods for controlling membrane fouling are difficult to operate, have high additional costs, cause membrane damage, are difficult to effectively control irreversible fouling, and affect membrane operational stability. There is an urgent need for an efficient, convenient, green, and low-cost membrane fouling control method that protects membranes from irreversible fouling without damaging the membrane substrate and extending membrane life.

[0006]

Technical solution

[0007] The tannic acid molecules are easily combined with the polyvalent metal ions to form stable complex, which has strong adhesion and can form uniform and stable coating on various material surfaces; in addition, the complex is sensitive to pH, and can be quickly decomposed when the pH is lower than 3; furthermore, the materials required by the complex are cheap, easy-to-obtain, non-toxic and harmless green natural substances. The application utilizes the coordination complex formed by tannic acid molecules and ferric ions to establish a controllable loading / demolishing coating material application method, and uses the complex as a sacrificial protective coating on the membrane surface to form a new method for effectively controlling membrane pollution, which is suitable for various membrane materials, the coating process is efficient and simple, the materials used are natural and low-cost environment-friendly materials, and has significant application potential.

[0008] The first object of the application is to provide a membrane pollution control method based on sacrificial protective coating, comprising the steps of:

[0009] S1, a peroxysulfate aqueous solution is cross-flow passed into a membrane module to contact the surface of an active layer of the membrane module, so as to obtain an activated membrane module;

[0010] S2, an iron-tannic acid coating solution is cross-flow passed into the activated membrane module from the surface of the active layer to form a coating on the surface of the active layer of the membrane, so as to obtain a coated membrane module;

[0011] S3, the coated membrane module is used for sewage treatment, when the membrane flux loss reaches 5% to 30%, the sewage treatment is stopped, a demounting solution is cross-flow passed into the coating surface of the polluted coated membrane module to remove the coating on the surface in situ, the demounting solution is a mixed aqueous solution of hydrochloric acid and citric acid, and a coated membrane module is obtained.

[0012] The cross-flow passing is that the flow direction of the passing solution is parallel to the surface of the membrane module.

[0013] The surface of the active layer of the membrane module is the working surface of the membrane module for realizing selective separation of solutes.

[0014] In an embodiment of the application, in step S1, the membrane module is a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane or a reverse osmosis membrane.

[0015] In an embodiment of the application, in step S1, the concentration of peroxysulfate in the peroxysulfate aqueous solution is 0.01 to 0.05 M; the peroxysulfate is selected from one of sodium peroxysulfate (NH4S2O8), potassium peroxysulfate (K2S2O8) and ammonium peroxysulfate (Na2S2O8).

[0016] In an embodiment of the application, in step S1, the pressure of the peroxysulfate aqueous solution is 0.1 to 1 bar, the temperature is 20 to 40 DEG C, the cross-flow rate is 1 to 10 m / s, and the passing time is 30 to 60 min.

[0017] In one embodiment of the present invention, in step S2, the pH value of the iron-tannic acid coating liquid is 2-3, the tannic acid concentration is 0.1-1.0 mM, the ferric ion concentration is 0.1-2.0 mM, and the molar ratio of ferric ions to tannic acid is 1:1-2:1.

[0018] In one embodiment of the present invention, in step S2, ferric chloride hexahydrate is used to introduce trivalent iron ions.

[0019] In one embodiment of the present invention, in step S2, the preparation method of the iron-tannic acid coating liquid is to prepare a tannic acid aqueous solution and a trivalent iron ion aqueous solution respectively, add the trivalent iron ion solution dropwise to the tannic acid solution under stirring, and adjust the pH to 2-3.

[0020] In one embodiment of the present invention, in the preparation method of the iron-tannic acid coating liquid, a 5-15 mM NaOH aqueous solution is used to adjust the pH.

[0021] In one embodiment of the present invention, in step S2, the pressure of the iron-tannic acid coating liquid is 0.1-1 bar, the temperature is 20-40° C., the cross-flow rate is 1-10 m / s, and the introduction time is 1-5 min.

[0022] The sewage separation treatment is to separate water and pollutants in the sewage by utilizing the selective permeability of the membrane assembly.

[0023] In one embodiment of the present invention, in step S3, the pH of the disassembly solution is 2-3; the molar ratio of hydrochloric acid to citric acid in the disassembly solution is 1:1-3:1, the concentration of hydrochloric acid is 0.01-0.1M, and the concentration of citric acid is 0.01-0.1M.

[0024] In one embodiment of the present invention, the pH of the stripping solution is adjusted by adjusting the amount of hydrochloric acid and citric acid.

[0025] In one embodiment of the present invention, in step S3, the pressure of the disassembly liquid is 0.5-1 bar, the temperature is 20-40° C., the cross-flow rate is 10-20 m / s, and the time of introduction is 30-90 min.

[0026] In one embodiment of the present invention, after completing step S3, steps S2 to S3 are repeated. With the membrane module water flux loss exceeding 5% to 30% as the critical point, the membrane module coating is repeatedly loaded and removed in situ according to steps S2 to S3, thereby effectively controlling membrane fouling, especially irreversible membrane fouling.

[0027] The second object of the present invention is to provide application of the above-mentioned membrane fouling control method based on sacrificial protective coating in the field of membrane filtration water treatment.

[0028] Advantages:

[0029] 1、The tannin-iron complex is low in price, non-toxic and harmless, high in coating efficiency, and strong in hydrophilicity, and can be used as a coating material, so that highly controllable coating loading and removal can be realized, and the tannin-iron complex has wide application potential in film surface protection and pollution prevention.

[0030] 2、The highly controllable coating loading and removal method based on the tannin-iron complex has good adaptability to various membrane materials, can be conveniently applied to various membrane treatment scenes such as nanofiltration, ultrafiltration and reverse osmosis, and has the advantages of simple process, no special conditions and devices, and strong practicability.

[0031] 3、Based on the controllable loading and removal of the tannin-iron coating material, a membrane pollution control method based on a sacrificial protective coating is established, which can avoid the contact between the membrane matrix material and the pollutants, and effectively control the formation of irreversible membrane pollution.

[0032] 4、The membrane pollution control strategy based on the sacrificial protective coating can be applied to control the membrane pollution caused by various membrane pollutants without difference, and has significant advantages in the scene of treating complex wastewater (pollutants are complex and diverse).

[0033] 5、The membrane pollution control strategy based on the sacrificial protective coating can be applied on the membrane surface for a long time, which can effectively protect the membrane from irreversible pollution without damaging the membrane matrix, so that the service life of the membrane can be greatly prolonged. DETAILED DESCRIPTION

[0034] Figure 1 The appearance of the coated nanofiltration membrane under different activation conditions.

[0035] Figure 2 The pure water flux of the coated nanofiltration membrane under different coating loading conditions.

[0036] Figure 3 The appearance of the original membrane, the nanofiltration membrane after coating loading in Example 1, the nanofiltration membrane after coating removal in Example 1, and the membrane after five cycles of coating loading / removal in Example 1.

[0037] Figure 4 The normalized flux change of the original membrane in Comparative Example 1 and the coated membrane in Example 2 in the multi-cycle pollution process.

[0038] Figure 5 The schematic diagram of the sacrificial protective coating strategy. DETAILED DESCRIPTION

[0039] Test method:

[0040] Pure water is passed through the membrane module, and the permeate passing through the membrane module is collected and weighed. The permeate volume is calculated, and the pure water flux, coating removal efficiency, flux recovery rate and normalized flux are calculated. The pure water flux (Jw) calculation formula is:

[0041]

[0042] V(L) is the permeate volume, T(h) is the running time, A(m 2 ) is the effective area of ​​the membrane.

[0043] Flux recovery rate (FRR) calculation formula:

[0044]

[0045] Coating removal efficiency = Jw3 / Jw1

[0046] The pure water flux of the original membrane is recorded as Jw1; the pure water flux of the coating-loaded membrane is recorded as Jw2; the pure water flux of the coating-removed membrane is recorded as Jw3; the pure water flux of the coating-loaded / removed membrane again is recorded as Jw4

[0047] Normalized flux (J n )Calculation formula:

[0048] J n =J c / J0

[0049] J c is the real-time operating water flux of the membrane, and J0 is the initial pure water flux of the membrane.

[0050] The ferric chloride hexahydrate, tannic acid and hydrochloric acid involved in the following examples are all commercially available.

[0051] Example 1

[0052] A membrane fouling control method based on a sacrificial protective coating comprises the following steps:

[0053] S1, passing a sodium persulfate aqueous solution into a nanofiltration membrane assembly in a cross-flow manner, so that the sodium persulfate aqueous solution contacts the surface of the active layer of the nanofiltration membrane to prepare an activated nanofiltration membrane;

[0054] The sodium persulfate concentration of the sodium persulfate aqueous solution was 0.01 M; the pressure of the sodium persulfate aqueous solution was 0.5 bar, the temperature was 25° C., the cross-flow rate was 5 m / s, and the time of introduction was 30 min;

[0055] S2, cross-flowing the iron-tannic acid coating liquid from the surface of the active layer into the activated nanofiltration membrane, loading the active layer surface to form a coating, thereby preparing a coated nanofiltration membrane;

[0056] The pH value of the iron-tannic acid coating solution is 3, the molar ratio of ferric ion to tannic acid is 2:1, and the tannic acid concentration is 0.1 mM;

[0057] The preparation method of the iron-tannic acid coating solution is to slowly add a tannic acid aqueous solution drop by drop into a ferric chloride hexahydrate aqueous solution under rapid stirring (100 rpm), then mix and stir for 2 min, and adjust the pH with a 0.01M NaOH aqueous solution;

[0058] The pressure of the iron-tannic acid coating solution is 1 bar, the temperature is 25℃, the cross-flow rate is 3 m / s, and the time of passing in is 5 min;

[0059] S3, fix the coating nanofiltration membrane in a membrane cell, run the coating membrane under a pressure of 2-3 bar, and test the flux level of the coating membrane;

[0060] S4, pass the disassembly liquid cross-flow into the contaminated coating nanofiltration membrane assembly from the coating surface, then pass in deionized water for cleaning to obtain the nanofiltration membrane after disassembly of the coating, and test the flux level of the membrane after disassembly of the coating under the same conditions as S3;

[0061] The disassembly liquid is a mixed aqueous solution of hydrochloric acid and citric acid, the concentration of hydrochloric acid in the disassembly liquid is 0.05M, and the amount of citric acid is adjusted to make the pH of the disassembly liquid 3;

[0062] The pressure of the disassembly liquid is 1 bar, the temperature is 25℃, the cross-flow rate is 15 m / s, and the time of passing in is 30 min;

[0063] The pressure of the deionized water is 1 bar, the temperature is 25℃, the cross-flow rate is 15 m / s, and the time of passing in is 30 min;

[0064] S5, repeat the steps S2-S4.

[0065] The appearance of the unactivated coating nanofiltration membrane prepared by changing the membrane surface activation conditions (compared with Example 1, without step S1 and only step S2) is shown in the left figure. Figure 1 The membrane surface of the coating nanofiltration membrane obtained by step S2 of Example 1 forms a very uniform and complete coating, as shown in the right figure. Figure 1 The membrane surface characteristics have a great influence on the coating loading efficiency and the uniformity and integrity of the formed coating, and the pre-activation method proposed by the present application breaks through the problem of unstable coating of iron-tannic acid on different membrane materials, and lays an important foundation for establishing a sacrificial protective coating method.

[0066] By changing the molar ratio of ferric chloride to tannic acid and the coating loading time in step S2 of Example 1, a series of nanofiltration membranes loaded with coatings under different conditions were obtained. The loading conditions are shown in Table 1. The pure water flux thereof was tested. The results are shown in FIG. Figure 2 C2, C1, and C0.3 represent the Fe:TA molar ratio (the molar ratio of ferric ion to tannic acid) of 2:1, 1:1, and 1:3, respectively; T5, T15, and T30 represent the coating loading time (the time the iron-tannic acid coating solution is introduced) of 5, 15, and 30 min, respectively.

[0067] Table 1 Coating loading conditions of coated nanofiltration membranes

[0068]

[0069] From Table 1 and Figure 2 It can be seen that when the Fe:TA molar ratio of the iron-tannic acid coating solution is too low (C0.3-T5-DL, C0.3-T15-DL, C0.3-T30-DL), the pure water flux of the coated nanofiltration membrane is almost unchanged, and no obvious coating formation is observed on the membrane surface, suggesting that the coating has not been successfully loaded onto the nanofiltration membrane. As the Fe:TA molar ratio in the iron-tannic acid coating solution increases, the water flux of the coated nanofiltration membrane decreases significantly, while a clear, uniform coating formation is observed on the membrane surface. The flux of the C1-T5-DL and C2-T5-DL coated nanofiltration membranes decreases by 14% and 20.3%, respectively, indicating that the coating can only be loaded and formed when the Fe:TA molar ratio of the iron-tannic acid coating solution is increased to 1:1 and 2:1. This is mainly due to the key complexation effect of Fe ions in the coating structure, and sufficient Fe ion crosslinking points are key to ensuring stable coating formation. In addition, with the increase of coating loading time, the water flux loss of the coated nanofiltration membrane also increased significantly. The water flux of C1-T15-DL and C1-T30-DL membranes lost 19.0% and 29.6%, respectively, and the flux loss of C2-T15-DL and C2-T30-DL reached 26.1% and 40.5%, respectively. The coating loading time is a key factor in regulating the coating loading amount. In actual application, the coating loading time should be adjusted according to the specific situation, taking into account the coating protection effect and flux loss.

[0070] By changing the removal solution in step S4 of Example 1 to a pH-2 aqueous hydrochloric acid solution or a pH-2 aqueous citric acid solution, the coating-loaded nanofiltration membrane was subjected to coating removal, resulting in a series of coating-removed nanofiltration membranes. The pure water flux of the activated nanofiltration membrane was measured, recorded as Jw1; the pure water flux of the coating-loaded nanofiltration membrane was measured, recorded as Jw2; the pure water flux of the coating-removed nanofiltration membrane was measured, recorded as Jw3; and the pure water flux of the nanofiltration membrane that had undergone coating reloading / removal was measured, recorded as Jw4.

[0071] The results are shown in Table 2. Under the condition of pH = 2, the coating removal efficiency of the hydrochloric acid + citric acid stripping solution (Example 1) is the highest, the membrane flux after the coating is removed is restored to 99% of the original membrane (untreated nanofiltration membrane), while the stripping efficiency of the hydrochloric acid stripping solution or the citric acid stripping solution is obviously lower, being 71.7% and 49.6%, respectively. This shows that although they are both acidic solutions, their coating removal effects are completely different. The reason is analyzed as follows. The coordination complex structure of iron-tannic acid is unstable under acidic conditions and is easy to decompose, which is the basic prerequisite for the coating to be removable. However, the interaction between the iron-tannic acid complex and the membrane interface in actual application does not depend on the coordination complex of iron-tannic acid. The hydrochloric acid stripping solution can efficiently remove the iron-tannic acid main body, but the stripping effect on the combination between the complex and the membrane interface is not strong, so it cannot be completely removed. It is found in the experiment that although the stripping effect of the aqueous citric acid solution on the iron-tannic acid coating is not good, when it is used in combination with hydrochloric acid, it has a higher stripping efficiency than the aqueous hydrochloric acid solution. The possible reason is that the strong complexation of citric acid with metal ions is better for destroying the interaction between Fe ions and the membrane interface, so it forms a complementary stripping effect with hydrochloric acid.

[0072] Table 2 Coating removal efficiency of stripping solutions with different components

[0073]

[0074] The molar ratio of hydrochloric acid and citric acid in the stripping solution in step S4 of Example 1 is changed to make the pH be 2 and 3, the coating removal is carried out on the coating-loaded nanofiltration membrane with two kinds of stripping solutions, and the stripping effect is evaluated. The results are shown in Table 3. Compared with the stripping solution with pH = 2, the pure water flux of the coating-removed nanofiltration membrane treated with the stripping solution with pH = 3 is restored to a higher value (J W3 = 13.79 L / h·m 2 ), which is close to the pure water flux (J W1 = 13.96 L / h·m 2 ) of the activated nanofiltration membrane, indicating that the stripping efficiency of the stripping solution with pH = 3 is higher. After the coating is reloaded, the membrane flux recovery rate is as high as 98.52%, indicating that the coating can be reassembled on the membrane surface and recycled. After the coating is reloaded after being stripped by the stripping solution with pH = 2, the membrane flux is only restored to 88.61%, and the reason is analyzed as follows. The over-strong acidity may cause the membrane pores of the nanofiltration membrane to shrink, thereby reducing the water flux of the membrane, so that the membrane flux cannot be restored.

[0075] Selecting a suitable composition and pH condition of the coating stripping solution is the key to realizing the controllable and recyclable coating loading / removal and achieving the membrane pollution control by the sacrificial protective coating in the present application. The present application determines that the optimal stripping solution composition of the iron-tannic acid protective coating is hydrochloric acid + citric acid (1:1-1:3), and the pH is 3.

[0076] Table 3 Coating disassembly efficiency of hydrochloric acid + citric acid disassembly solution at different pH

[0077]

[0078] Figure 3 Picture comparison of the original membrane, the nanofiltration membrane after coating loading of Example 1, the nanofiltration membrane after coating disassembly of Example 1, and the membrane after five cycles of coating loading / disassembly. As can be seen from the figure, the coating can be uniformly loaded on the membrane surface through a simple and fast coating process, and can also be completely disassembled through a simple process. The loading and disassembly effect of the coating is very stable in the multi-cycle circulation process, proving that the application method of the sacrificial protective coating is simple, fast, efficient and stable.

[0079] Example 2

[0080] The membrane fouling control method based on the sacrificial protective coating comprises the following steps:

[0081] S1, perform step S1 of Example 1;

[0082] S2, perform step S2 of Example 1;

[0083] S3, fix the nanofiltration membrane loaded with the coating in a membrane cell, pump the simulated wastewater into the membrane cell, and then filter the simulated wastewater with the nanofiltration membrane loaded with the coating under the conditions of a temperature of 25℃ and a pressure of 5bar. An online electronic balance is used to collect the filtrate mass. When the membrane flux loss of the nanofiltration membrane loaded with the coating reaches 30%, stop the wastewater separation treatment;

[0084] S4, perform step S4 of Example 1 to disassemble the coating;

[0085] S5, repeat steps S2-S4 to complete the multi-cycle fouling test.

[0086] Comparative Example 1

[0087] In order to compare the difference in membrane fouling control effect between using the sacrificial protective coating and not using the sacrificial protective coating, a multi-cycle membrane fouling experiment was carried out on the original membrane, i.e., the original membrane was used to perform steps S3-S5 of Example 2.

[0088] Figure 4The normalized flux changes of the original membrane of Comparative Example 1 and the coating membrane of Example 2 during the multi-cycle pollution process. In the multi-cycle pollution experiment, it was clearly observed that the normalized flux of the original membrane of Comparative Example 1 gradually decreased (from 0.79 to 0.44), which indicates that the irreversible pollution on the original membrane is continuing to worsen. However, for the coating membrane of Example 2, after 6 cycles of pollution experiments, the normalized flux did not decrease significantly, and the normalized flux remained above 0.95 during the entire experiment. This result shows that the control of irreversible pollution of the membrane can be effectively achieved by applying the sacrificial protective coating strategy. This is because, Figure 5 As shown, the application of the sacrificial protective coating forms a protective layer on the membrane surface, which avoids direct contact between pollutants and the membrane substrate and prevents the adhesion of pollutants to the membrane substrate. The sacrificial protective coating with controllable disassembly function can be completely removed together with the pollutant layer attached thereto under specific conditions, thereby completely realizing the regeneration of the membrane and the restoration of its function.

[0089] The embodiments provided above are not intended to limit the scope of the present invention, nor are the steps described to limit their execution order. Any obvious improvements to the present invention made by those skilled in the art in combination with existing common knowledge shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A membrane fouling control method based on sacrificial protective coating, characterized in that: Including steps: S1, passing a persulfate aqueous solution into the membrane module in a cross-flow manner, contacting the persulfate aqueous solution with the active layer surface of the membrane module to prepare an activated membrane module; S2, cross-flowing the iron-tannic acid coating liquid from the surface of the active layer into the activated membrane assembly to form a coating on the surface of the membrane active layer to prepare a coated membrane assembly; S3. Use the coated membrane assembly for sewage treatment. When the membrane flux loss reaches 5% to 30%, stop the sewage treatment. Pass the dismantling liquid through the contaminated coated membrane assembly to remove the coating on the surface in situ. The dismantling liquid is a mixed aqueous solution of hydrochloric acid and citric acid to obtain a membrane assembly with the coating removed.

2. The membrane pollution control method based on sacrificial protective coating according to claim 1, characterized in that: In step S1, the membrane component is a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane or a reverse osmosis membrane.

3. The membrane fouling control method based on sacrificial protective coating according to claim 1, characterized in that: The persulfate concentration of the persulfate aqueous solution is 0.01-0.05 M; the persulfate is selected from one of sodium persulfate, potassium persulfate, and ammonium persulfate.

4. The membrane fouling control method based on sacrificial protective coating according to claim 1, characterized in that: In step S1, the pressure of the persulfate aqueous solution is 0.1-1 bar, the temperature is 20-40° C., the cross-flow rate is 1-10 m / s, and the time of introduction is 30-60 min.

5. The membrane fouling control method based on sacrificial protective coating according to claim 1, characterized in that: In step S2, the pH value of the iron-tannic acid coating liquid is 2-3, the concentration of tannic acid is 0.1-1.0 mM, the concentration of ferric ions is 0.1-2 mM, and the molar ratio of ferric ions to tannic acid is 1:1-2:

1.

6. The membrane fouling control method based on sacrificial protective coating according to claim 1, characterized in that: In step S2, the pressure of the iron-tannic acid coating liquid is 0.1-1 bar, the temperature is 20-40° C., the cross-flow rate is 1-10 m / s, and the time of introduction is 1-5 min.

7. The membrane fouling control method based on sacrificial protective coating according to claim 1, characterized in that: In step S3 , the pH of the disassembly solution is 2-3; the molar ratio of hydrochloric acid to citric acid in the disassembly solution is 1:1-3:1, the concentration of hydrochloric acid is 0.01-0.1 M, and the concentration of citric acid is 0.01-0.1 M.

8. The membrane fouling control method based on sacrificial protective coating according to claim 1, characterized in that: In step S3, the pressure of the disassembly liquid is 0.5-1 bar, the temperature is 20-40° C., the cross-flow rate is 10-20 m / s, and the time of introduction is 30-90 min.

9. The membrane fouling control method based on sacrificial protective coating according to claim 1, characterized in that: After completing step S3, repeat steps S2 to S3.

10. Use of the membrane fouling control method based on sacrificial protective coating according to any one of claims 1 to 9 in the field of membrane filtration water treatment.

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