Membrane pollution control method based on sacrificial protective coating

Abstract

The invention relates to the technical field of water treatment membranes, and provides a membrane pollution control method based on a sacrificial protective coating, which comprises the following steps: cross-flowing a persulfate aqueous solution into the surface of an active layer of a membrane assembly to form an activated membrane assembly; the iron-tannic acid coating liquid flows into the activated membrane assembly from the surface of the active layer in a staggered mode to complete coating loading; the membrane assembly loaded with the coating is used for sewage separation treatment, and the coating is disassembled after membrane pollution reaches a specific degree; a dismounting liquid flows into the polluted membrane module from the surface of the coating in a staggered manner, and the coating is dismounted; and coating loading / unloading is circularly carried out, so that continuous control on membrane pollution is realized. The method provided by the invention can avoid the contact between a membrane matrix material and pollutants, effectively controls the formation of irreversible membrane pollution, can be circularly applied to the membrane surface for a long time, does not damage the membrane matrix, and prolongs the service life of the membrane; good adaptability to various membrane materials is achieved, and practicability is high; and membrane pollution caused by various complex wastewater can be controlled without difference.

Description

Technical Field

[0001] The 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 is widely used in drinking water purification, seawater desalination and sewage treatment due to its energy-saving, environmental protection, simple operation and efficient separation. Compared with other water treatment technologies, membrane separation technology has the advantages of better treatment effect, more stable effluent water quality and no secondary pollution. However, an important obstacle to the application of membrane technology is the performance degradation and increased operating costs caused by membrane pollution. In particular, when treating wastewater with high concentration and complex matrix, irreversible membrane pollution is prone to occur, resulting in reduced membrane life. At present, the main ways to control membrane pollution are: pre-membrane pretreatment, physical / chemical cleaning and membrane modification. However, they also have problems such as difficult operation, high additional cost, membrane damage, difficulty in effectively controlling irreversible pollution and affecting the stability of membrane operation. Therefore, the membrane technology market still has a strong demand for efficient, convenient and low-cost membrane pollution control methods.

[0003] The sacrificial protective coating strategy is a new approach to solving the membrane pollution problem, and is particularly suitable for membrane application scenarios with serious irreversible pollution. This method first loads a protective layer on the membrane surface to isolate the membrane pollutants from direct contact with the membrane substrate during membrane operation. When the pollutants accumulate to a certain extent, a specific disassembly method is used to simultaneously remove the coating and the pollution layer, thereby completely restoring the original performance of the membrane, and obtaining a new sacrificial protective coating by reloading. The process is cyclically repeated 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 coating processes, long time consumption, high material costs, and high environmental risks, making it difficult to achieve large-scale applications. Summary of the invention

[0004]

Technical issues

[0005] The current methods for controlling membrane fouling have the problems of difficult operation, high additional cost, membrane damage, difficulty in effectively controlling irreversible fouling, and affecting the stability of membrane operation. There is an urgent need for an efficient, convenient, green, and low-cost membrane fouling control method that can protect the membrane from irreversible fouling without causing damage to the membrane matrix and prolonging the membrane life.

[0006]

Technical solution

[0007] Tannic acid molecules and multivalent metal ions can easily form a stable complex through coordination complexation. The complex has strong adhesion and can form a uniform and stable coating on the surface of various materials. In addition, the complex is sensitive to pH and can be quickly decomposed when the pH is lower than 3. Furthermore, the materials required for the complex are all cheap, easily available, non-toxic and harmless green natural substances. The present invention uses the coordination complex formed by tannic acid molecules and trivalent iron ions to establish a controllable loading / disassembly coating material application method, and uses it as a sacrificial protective coating on the membrane surface, forming a new method for effectively controlling membrane pollution, which is applicable to a variety of membrane materials, and the coating process is efficient and simple. The materials used are all natural, low-cost environmentally friendly materials, and have significant application potential.

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

[0009] S1, passing the persulfate aqueous solution into the membrane module in a cross-flow manner to contact the surface of the active layer of the membrane module to obtain an activated membrane module;

[0010] S2, passing the iron-tannic acid coating liquid from the surface of the active layer into the activated membrane assembly in a cross-flow manner to form a coating on the surface of the membrane active layer to obtain a coated membrane assembly;

[0011] 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 coating surface 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.

[0012] The cross-flow inflow is to make the flow direction of the incoming solution parallel to the surface of the membrane module.

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

[0014] In one embodiment of the present invention, in step S1, the membrane component is a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane or a reverse osmosis membrane.

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

[0016] In one embodiment of the present invention, 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.

[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 concentration of tannic acid is 0.1-1.0 mM, the concentration of trivalent iron ions is 0.1-2.0 mM, and the molar ratio of trivalent iron 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 into the tannic acid solution under stirring, and adjust the pH to 2-3.

[0020] In one embodiment of the present invention, in the method for preparing 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 dosage 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. Taking the water flux loss of the membrane module exceeding 5% to 30% as the critical point, the in-situ loading and disassembly of the membrane module coating are repeated according to steps S2 to S3, so as to achieve effective control of membrane fouling, especially irreversible membrane fouling.

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

[0028] Beneficial effects:

[0029] 1. The present invention utilizes the tannic acid-iron complex which is inexpensive, non-toxic, highly efficient and highly hydrophilic as the coating material, which can realize highly controllable coating loading and removal, and has a wide range of application potentials in membrane surface protection and avoiding membrane pollution.

[0030] 2. The highly controllable coating loading and disassembly method based on tannic acid-iron complex proposed in the present invention has good adaptability to various membrane materials, can be conveniently applied to various membrane treatment scenarios such as nanofiltration, ultrafiltration, reverse osmosis, etc., and the process is simple, does not require special conditions and equipment, can be quickly applied to existing membrane treatment processes, and has strong practicality.

[0031] 3. Based on the tannic acid-iron coating material with controllable loading and disassembly, the present invention establishes a membrane pollution control method based on sacrificial protective coating, which can avoid the contact between the membrane matrix material and pollutants and effectively control the formation of irreversible membrane pollution.

[0032] 4. The membrane pollution control strategy based on sacrificial protective coating proposed in the present invention can be applied indiscriminately to control membrane pollution caused by various membrane pollutants. This feature has significant advantages in the scenario of membrane treatment of complex wastewater (complex and diverse pollutants).

[0033] 5. The membrane pollution control strategy based on sacrificial protective coating proposed in the present invention can be applied on the membrane surface in a long-term cycle. While efficiently protecting the membrane from irreversible pollution, it will not cause damage to the membrane substrate, thereby greatly extending the service life of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0036] Figure 3 The appearances 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 It is the normalized flux change of the original membrane of comparative example 1 and the coating membrane of example 2 during the multi-cycle pollution process.

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

[0039] Test method:

[0040] Pure water is passed through the membrane module, 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. Pure water flux (Jw) calculation formula:

[0041]

[0042] V(L) is the volume of permeate, 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 pollution control method based on sacrificial protective coating comprises the steps of:

[0053] S1, passing the sodium persulfate aqueous solution into the 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 obtain an activated nanofiltration membrane;

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

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

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

[0057] The preparation method of the iron-tannic acid coating liquid is as follows: the tannic acid aqueous solution is slowly added dropwise to the ferric chloride hexahydrate aqueous solution under rapid stirring conditions (100 rpm), and then the mixture is stirred for 2 minutes, and the pH is adjusted with a 0.01 M NaOH aqueous solution;

[0058] The pressure of the iron-tannic acid coating liquid was 1 bar, the temperature was 25°C, the cross-flow rate was 3 m / s, and the time of introduction was 5 min.

[0059] S3, fix the coated nanofiltration membrane in the membrane pool, operate the coated membrane at a pressure of 2-3 bar, and test the flux level of the coated membrane;

[0060] S4, passing the disassembly liquid from the coating surface into the contaminated coating nanofiltration membrane assembly, and then passing deionized water to wash to obtain the nanofiltration membrane after the coating is disassembled, and testing the flux level of the membrane after the coating is disassembled under the same conditions as S3;

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

[0062] The pressure of the disassembly fluid was 1 bar, the temperature was 25°C, the cross-flow rate was 15 m / s, and the time of introduction was 30 min.

[0063] The deionized water was introduced at a pressure of 1 bar, a temperature of 25°C, a cross-flow rate of 15 m / s, and an introduction time of 30 min.

[0064] S5. Repeat steps S2 to S4.

[0065] By changing the activation conditions of the membrane surface, an unactivated coated nanofiltration membrane was obtained (compared with Example 1, step S1 was not performed and only step S2 was performed), and its appearance was as follows Figure 1 As shown in the left picture, the coating on the membrane surface is uneven and incomplete after the membrane is loaded with the coating without activation treatment. Figure 1 As shown in the right figure, a very uniform and complete coating is formed on the membrane surface of the coated nanofiltration membrane obtained in step S2 of Example 1. The membrane surface characteristics have a great influence on the coating loading efficiency and the uniformity and integrity of the formed coating. The pre-activation method proposed in the present invention breaks through the problem of the instability of the coating formed by 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 Table 1. Figure 2 C2, C1, and C0.3 indicate that the molar ratio of Fe:TA (molar ratio of ferric iron ion to tannic acid) is 2:1, 1:1, and 1:3, respectively; T5, T15, and T30 indicate that the coating loading time (the time for the iron-tannic acid coating liquid to be introduced) is 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 liquid 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 not lost, and no obvious coating formation is observed on the membrane surface. It is speculated that the coating has not been successfully loaded on the nanofiltration membrane. With the increase of the Fe:TA molar ratio in the iron-tannic acid coating liquid, the water flux of the coated nanofiltration membrane has a significant decrease, and at the same time, obvious uniform coating formation is observed on the membrane surface. Among them, the flux of the C1-T5-DL and C2-T5-DL coated nanofiltration membranes lose 14% and 20.3% respectively, indicating that the coating can be loaded and formed only when the Fe:TA molar ratio of the iron-tannic acid coating liquid is increased to 1:1 and 2:1. This is mainly due to the key complexation of Fe ions in the coating structure, and sufficient Fe ion cross-linking points are the key to ensure the stable formation of the coating. 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 losses 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] The disassembly liquid in step S4 of Example 1 was changed to a hydrochloric acid aqueous solution with a pH of 2 or a citric acid aqueous solution with a pH of 2, and the coating-loaded nanofiltration membrane was subjected to coating disassembly to obtain a series of nanofiltration membranes with coating disassembly. The pure water flux of the activated nanofiltration membrane was measured, recorded as Jw1; the pure water flux of the nanofiltration membrane loaded with coating was measured, recorded as Jw2; the pure water flux of the nanofiltration membrane with coating disassembly was measured, recorded as Jw3; the pure water flux of the nanofiltration membrane that was subjected to coating loading / disassembly again was measured, recorded as Jw4.

[0071] The results are shown in Table 2. Under the condition of pH = 2, the coating removal efficiency of hydrochloric acid + citric acid disassembly solution (Example 1) is the highest. After the coating is removed, the membrane flux is restored to 99% of the original membrane (untreated nanofiltration membrane), while the disassembly efficiency of hydrochloric acid disassembly solution or citric acid disassembly solution is significantly lower, 71.7% and 49.6% respectively. This shows that although they are both acidic solutions, their coating removal effects are completely different. Analyzing the reasons, the coordination complex structure of iron-tannic acid is unstable under acidic conditions and is easy to decompose. This is the basic premise for the detachable coating. However, in practical applications, the interaction between the iron-tannic acid complex and the membrane interface does not rely on the iron-tannic acid coordination complex. The hydrochloric acid disassembly solution can efficiently remove the iron-tannic acid body, but the removal effect on the combination between the complex and the membrane interface is not strong, so complete removal cannot be achieved. It was found during the experiment that although the citric acid aqueous solution had a poor removal effect on the iron-tannic acid coating, when it was mixed with hydrochloric acid, it exerted a higher removal efficiency than the hydrochloric acid aqueous solution. The possible reason is that the strong complexation between citric acid and metal ions is more effective in destroying the interaction between Fe ions and the membrane interface, so it forms a complementary disassembly effect with hydrochloric acid.

[0072] Table 2 Coating removal efficiency of removal fluids with different compositions

[0073]

[0074] The molar ratio of hydrochloric acid and citric acid in the stripping solution in step S4 of Example 1 was changed to pH 2 and 3, and the coating of the nanofiltration membrane loaded with the coating was stripped using the two stripping solutions, and the stripping effect was evaluated. The results are shown in Table 3. Compared with the stripping solution with pH = 2, the pure water flux of the nanofiltration membrane stripped with the coating treated with the stripping solution with pH = 3 was restored to a higher value (J W3 =13.79L / h·m 2 ), close to the pure water flux of activated nanofiltration membrane (J W1 =13.96L / h·m 2 ), indicating that the removal efficiency of pH=3 removal liquid is higher; after reloading the coating, the membrane flux recovery rate is as high as 98.52%, indicating that the coating can be reassembled on the membrane surface and recycled; while after removal with pH=2 removal liquid, the membrane flux after reloading the coating only recovered to 88.61%. The reason for this is that excessive acidity may cause the membrane pores of the nanofiltration membrane to shrink, thereby reducing the water flux of the membrane, and thus making the membrane flux unable to recover.

[0075] Selecting appropriate coating removal liquid composition and pH conditions is the key to achieving controllable and cyclic coating loading / removal and membrane pollution control through sacrificial protective coating in the present invention. The present invention determines that the optimal removal liquid 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 removal efficiency of hydrochloric acid + citric acid removal solution with different pH

[0077]

[0078] Figure 3 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 are compared. 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 removed through a simple process. The coating loading and removal effects are very stable during the multi-cycle cycle process, proving that the sacrificial protective coating application method of the present invention is simple, fast, efficient, and stable.

[0079] Example 2

[0080] A membrane pollution control method based on sacrificial protective coating comprises the steps of:

[0081] S1. Perform step S1 of Example 1;

[0082] S2, carry out step S2 of embodiment 1;

[0083] S3, fix the coated nanofiltration membrane in the membrane pool, pump the simulated sewage into the membrane test pool, filter the simulated sewage with the coated nanofiltration membrane at a temperature of 25°C and a pressure of 5 bar, collect the filtrate mass using an online electronic balance, and stop the sewage separation treatment when the membrane flux loss of the coated nanofiltration membrane reaches 30%;

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

[0085] S5. Repeat steps S2 to S4 to complete the multi-cycle contamination test.

[0086] Comparative Example 1

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

[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 is clearly observed that the normalized flux of the original membrane of Comparative Example 1 is gradually decreasing (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 attachment 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, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A membrane pollution control method based on sacrificial protective coating, characterized in that: Includes steps: S1, passing the persulfate aqueous solution into the membrane module in a cross-flow manner to contact the surface of the active layer of the membrane module to obtain an activated membrane module; S2, passing the iron-tannic acid coating liquid from the surface of the active layer into the activated membrane assembly in a cross-flow manner to form a coating on the surface of the membrane active layer to obtain 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 coating surface 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 pollution 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 pollution 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 pollution 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 trivalent iron ions is 0.1-2 mM, and the molar ratio of trivalent iron ions to tannic acid is 1:1-2:

1.

6. The membrane pollution 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 pollution 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 0.01-0.1M, and the concentration of citric acid is 0.01-0.1M.

8. The membrane pollution 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 sacrificial protective film pollution control method according to claim 1, characterized in that: After completing step S3, steps S2 to S3 are repeated.

10. Application of the sacrificial protective membrane pollution control method according to any one of claims 1 to 9 in the field of membrane filtration water treatment.

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