Application of cationic hydrophobic polyacrylamide flocculant for retarding membrane pollution

Abstract

The invention discloses an application of a cationic hydrophobic polyacrylamide flocculant for retarding membrane pollution, and cationic hydrophobic polyacrylamide is synthesized by a copolymerization method. A cationic hydrophobic polyacrylamide flocculant is added into raw water in the ultrafiltration water purification process, after the polyacrylamide flocculant reaches the surface of a membrane, the polyacrylamide flocculant is combined with the surface of the ultrafiltration membrane through a hydrophobic association effect, and a hydrophilic end and a cationic group expand outwards, so that the surface of the membrane can be effectively subjected to hydrophilic modification; the pollution of the ultrafiltration membrane and the removal of bacteria in the raw water are effectively slowed down.

Description

[0001] The present invention relates to the field of membrane pollution control in ultrafiltration water purification process, and in particular to an application of a cationic hydrophobic polyacrylamide flocculant to slow down membrane pollution. Background Art

[0002] With global water shortages and water pollution becoming increasingly serious, advances in water treatment technology are becoming increasingly important. Ultrafiltration, as a highly effective water treatment technology, is widely used due to its ability to effectively remove suspended solids, colloids, bacteria, and macromolecular organic matter. However, membrane fouling is one of the main issues limiting the application of ultrafiltration technology. It can lead to reduced membrane flux, increased cleaning frequency and costs, and shortened membrane life. To address this issue, various pretreatment technologies have been studied and applied, among which flocculation, as one of the pretreatment technologies, can mitigate membrane fouling by improving influent water quality.

[0003] Polyacrylamide is a widely used flocculant with excellent flocculation effects. However, conventional polyacrylamide flocculants are not very effective in mitigating membrane fouling because they have difficulty interacting with and modifying the membrane surface, and they lack effective bactericidal properties.

[0004] This patent aims to provide a method for mitigating membrane fouling during ultrafiltration using a cationic hydrophobic polyacrylamide flocculant. By optimizing the structure and properties of the flocculant, the flocculant binds to the membrane surface through hydrophobic association upon reaching it, thereby modifying the membrane's hydrophilicity. Furthermore, the flocculant's cationic groups can remove bacteria from the water, effectively mitigating membrane fouling. This method offers the advantages of simple operation, significant effectiveness, and low cost, and will provide strong technical support for the widespread application of ultrafiltration technology. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to slow down the pollution of ultrafiltration membranes during the ultrafiltration water purification process.

[0006] The present invention provides an application of using a cationic hydrophobic polyacrylamide flocculant to slow down membrane fouling. The preparation method and application include the following steps: (1) By weight, 1100-1200 parts of pure water, 260-270 parts of acrylamide, 20-50 parts of cationic monomer, and 2-20 parts of hydrophobic monomer were mixed evenly and then frozen to -2 °C. After nitrogen was introduced for 15 minutes, 0.01-0.02 parts of complexing agent, 0.3-0.5 parts of initiator, and 0.01-0.05 parts of chain transfer agent were added in sequence. After nitrogen was introduced for 5 minutes, 0.002-0.006 parts of oxidant were added. After 0.5 minutes, 0.002-0.006 parts of reducing agent were added. When the reaction started, nitrogen was stopped. After the reaction was completed and kept warm for 2 hours, the rubber block was taken out, granulated, dried, and ground to prepare a cationic hydrophobic polyacrylamide flocculant. (2) Dissolve 10-20 parts of kaolin, 5-10 parts of humic acid, 5-10 parts of bovine serum albumin, and 5-10 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the solution until the concentration reaches 10 6 -10 7 CFU / L; (3) First, prepare the cationic hydrophobic polyacrylamide in step (1) into a 1-2 g / L solution, and use a peristaltic pump to maintain the flow rate of the sewage in step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2 h), the hydraulic retention time in the ultrafiltration tank is 1 h, and the total surface area of ​​the fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the fiber membrane was soaked in pure water for 24 h to clean the fiber membrane. After filtration for 30 minutes, a water flow of 0.5 minutes (30 L / (m 2 Backwashing was performed using a combination of water and air bubbling (150 L / h). The fiber membrane was physically cleaned with a sponge at 12, 24, and 36 hours to remove the filter cake layer. The transmembrane pressure (TMP) was measured within 45-50 hours of the fiber membrane operation. The cationic monomer is allyltrimethylammonium chloride, the hydrophobic monomer is one of dodecyldimethylallylammonium chloride, allyltributylphosphine chloride, and (3,3-dimethylallyl)triphenylphosphine bromide, the complexing agent is pentasodium diethylenetriaminepentaacetate, the initiator is azobisisobutyronitrile, the chain transfer agent is sodium hypophosphite, the oxidant is tert-butyl hydroperoxide, and the reducing agent is sodium metabisulfite; The fiber membrane material is PVDF (polyvinylidene fluoride) or PES (polyether).

[0007] Compared with the prior art, the present invention has the following benefits: (1) By utilizing the hydrophobic effect of cationic hydrophobic polyacrylamide, after the flocculant reaches the membrane surface, it can combine with the membrane surface through hydrophobic association, modify the membrane surface to be hydrophilic, effectively blocking hydrophobic pollutants from reaching the membrane surface and slowing down membrane pollution.

[0008] (2) The bactericidal effect of the cationic group of the flocculant was utilized to effectively remove bacteria in the raw water and slow down biofilm pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a transmembrane pressure-time diagram of Example 1; Figure 2 This is a transmembrane pressure-time diagram of Example 2; Figure 3 This is a transmembrane pressure-time diagram of Example 3; Figure 4 This is a transmembrane pressure-time diagram of Example 4; Figure 5 This is a transmembrane pressure-time diagram of Example 5; Figure 6 This is a transmembrane pressure-time diagram of Example 6; Figure 7 is the transmembrane pressure-time diagram of Comparative Example 1; Figure 8 This is the transmembrane pressure-time diagram of Comparative Example 2; Figure 9 is the bacterial concentration of Examples 1-6 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0010] The following are specific embodiments of the present invention, which further describe the operating scheme of the present invention. The scope of protection includes but is not limited to these embodiments. All other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention. Example 1

[0011] (1) By mass, 1100 parts of pure water, 260 parts of acrylamide, 30 parts of allyltrimethylammonium chloride, and 5 parts of dodecyldimethylallyl ammonium chloride were mixed evenly and then frozen to -2 °C. After nitrogen was introduced for 15 minutes, 0.01 parts of diethylenetriamine pentaacetic acid pentasodium, 0.5 parts of azobisisobutyronitrile, and 0.02 parts of sodium hypophosphite were added in sequence. After nitrogen was introduced for 5 minutes, 0.002 parts of tert-butyl hydroperoxide were added. After 0.5 minutes, 0.002 parts of sodium metabisulfite were added. When the reaction started, nitrogen was stopped. After the reaction was completed and kept warm for 2 hours, the rubber block was taken out, granulated, dried, and ground to prepare a cationic hydrophobic polyacrylamide flocculant. The reaction formula is as follows: .

[0012] (2) Dissolve 10 parts of kaolin, 5 parts of humic acid, 5 parts of bovine serum albumin, and 5 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the solution until the concentration reaches 10 6 CFU / L.

[0013] (3) Prepare a 1 g / L solution of cationic hydrophobic polyacrylamide from step (1) and maintain the flow rate of the wastewater from step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2 h), the hydraulic retention time in the ultrafiltration tank is 1 h, and the total surface area of ​​the PVDF fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the PVDF fiber membrane was soaked in pure water for 24 h to clean the PVDF fiber membrane. The water flow rate (30 L / (m 2 The PVDF fiber membrane was physically cleaned with a sponge at 12, 24, and 36 h to remove the filter cake layer. The transmembrane pressure (TMP) was measured within 48 h of the fiber membrane operation. Example 2

[0014] (1) By mass, 1130 parts of pure water, 263 parts of acrylamide, 33 parts of allyltrimethylammonium chloride, and 5.3 parts of dodecyldimethylallyl ammonium chloride were mixed evenly and then frozen to -2 °C. After nitrogen was introduced for 15 minutes, 0.012 parts of diethylenetriamine pentaacetic acid pentasodium, 0.43 parts of azobisisobutyronitrile, and 0.022 parts of sodium hypophosphite were added in sequence. After nitrogen was introduced for 5 minutes, 0.0021 parts of tert-butyl hydroperoxide were added. After 0.5 minutes, 0.0022 parts of sodium metabisulfite were added. When the reaction started, nitrogen was stopped. After the reaction was completed and kept warm for 2 hours, the rubber block was taken out, granulated, dried, and ground to prepare a cationic hydrophobic polyacrylamide flocculant. The reaction formula is as follows: .

[0015] (2) Dissolve 10.5 parts of kaolin, 5.1 parts of humic acid, 5.5 parts of bovine serum albumin, and 5.3 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the solution until the concentration reaches 10 6 CFU / L.

[0016] (3) Prepare a 1 g / L solution of cationic hydrophobic polyacrylamide from step (1) and maintain the flow rate of the wastewater from step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2h), the hydraulic retention time in the ultrafiltration tank is 1 h, and the total surface area of ​​the PES fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the PES fiber membrane was soaked in pure water for 24 h to clean the PES fiber membrane. The water flow rate (30 L / (m 2 The PES fiber membrane was physically cleaned with a sponge at 12, 24, and 36 h to remove the filter cake layer. The transmembrane pressure (TMP) was measured within 48 h of the fiber membrane operation. Example 3

[0017] (1) By mass, 1140 parts of pure water, 265 parts of acrylamide, 23 parts of allyltrimethylammonium chloride, and 15 parts of allyltributylphosphine chloride were mixed evenly and then frozen to -2 °C. After nitrogen was introduced for 15 minutes, 0.015 parts of diethylenetriamine pentaacetic acid pentasodium, 0.45 parts of azobisisobutyronitrile, and 0.025 parts of sodium hypophosphite were added in sequence. After nitrogen was introduced for 5 minutes, 0.0021 parts of tert-butyl hydroperoxide were added. After 0.5 minutes, 0.0023 parts of sodium metabisulfite were added. When the reaction started, nitrogen was stopped. After the reaction was completed and kept warm for 2 hours, the rubber block was taken out, granulated, dried, and ground to prepare a cationic hydrophobic polyacrylamide flocculant. The reaction formula is as follows: .

[0018] (2) Dissolve 10.8 parts of kaolin, 5.7 parts of humic acid, 5.8 parts of bovine serum albumin, and 5.9 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the solution until the concentration reaches 10 6 CFU / L.

[0019] (3) Prepare a 1 g / L solution of cationic hydrophobic polyacrylamide from step (1) and maintain the flow rate of the wastewater from step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2 h), and the hydraulic retention time in the ultrafiltration tank is 1 h. The total surface area of ​​the PVDF fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the PVDF fiber membrane was soaked in pure water for 24 h to clean the PVDF fiber membrane. The water flow rate (30 L / (m 2 The PVDF fiber membrane was physically cleaned with a sponge at 12, 24, and 36 h to remove the filter cake layer. The transmembrane pressure (TMP) was measured within 48 h of the fiber membrane operation. Example 4

[0020] (1) By mass, 1150 parts of pure water, 268 parts of acrylamide, 26 parts of allyltrimethylammonium chloride, and 17 parts of allyltributylphosphine chloride were mixed evenly and then frozen to -2 °C. After nitrogen was introduced for 15 minutes, 0.014 parts of diethylenetriamine pentaacetic acid pentasodium, 0.46 parts of azobisisobutyronitrile, and 0.024 parts of sodium hypophosphite were added in sequence. After nitrogen was introduced for 5 minutes, 0.0022 parts of tert-butyl hydroperoxide were added. After 0.5 minutes, 0.0026 parts of sodium metabisulfite were added. When the reaction started, nitrogen was stopped. After the reaction was completed and kept warm for 2 hours, the rubber block was taken out, granulated, dried, and ground to prepare a cationic hydrophobic polyacrylamide flocculant. The reaction formula is as follows: .

[0021] (2) Dissolve 10.9 parts of kaolin, 5.5 parts of humic acid, 5.1 parts of bovine serum albumin, and 5.5 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the solution until the concentration reaches 10 6 CFU / L.

[0022] (3) Prepare a 1 g / L solution of cationic hydrophobic polyacrylamide from step (1) and maintain the flow rate of the wastewater from step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2 h), and the hydraulic retention time in the ultrafiltration tank is 1 h. The total surface area of ​​the PES fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the PES fiber membrane was soaked in pure water for 24 h to clean the PES fiber membrane. The water flow rate (30 L / (m 2 The PES fiber membrane was physically cleaned with a sponge at 12, 24, and 36 h to remove the filter cake layer. The transmembrane pressure (TMP) was measured within 48 h of the fiber membrane operation. Example 5

[0023] (1) By mass, 1120 parts of pure water, 264 parts of acrylamide, 20 parts of allyltrimethylammonium chloride, and 16 parts of (3,3-dimethylallyl)triphenylphosphonium bromide were mixed evenly and then frozen to -2 °C. After nitrogen was introduced for 15 minutes, 0.015 parts of diethylenetriamine pentaacetic acid pentasodium, 0.5 parts of azobisisobutyronitrile, and 0.02 parts of sodium hypophosphite were added in sequence. After nitrogen was introduced for 5 minutes, 0.002 parts of tert-butyl hydroperoxide were added. After 0.5 minutes, 0.002 parts of sodium metabisulfite were added. When the reaction started, nitrogen was stopped. After the reaction was completed and kept warm for 2 hours, the rubber block was taken out, granulated, dried, and ground to prepare a cationic hydrophobic polyacrylamide flocculant. The reaction formula is as follows: .

[0024] (2) Dissolve 11 parts of kaolin, 5.9 parts of humic acid, 6 parts of bovine serum albumin, and 5.8 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the solution until the concentration reaches 10 6 CFU / L.

[0025] (3) Prepare a 1 g / L solution of cationic hydrophobic polyacrylamide from step (1) and maintain the flow rate of the wastewater from step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2 h), the hydraulic retention time in the ultrafiltration tank is 1 h, and the total surface area of ​​the PVDF fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the PVDF fiber membrane was soaked in pure water for 24 h to clean the PVDF fiber membrane. The water flow rate (30 L / (m 2 The PVDF fiber membrane was physically cleaned with a sponge at 12, 24, and 36 h to remove the filter cake layer. The transmembrane pressure (TMP) was measured within 48 h of the fiber membrane operation. Example 6

[0026] (1) By mass, 1170 parts of pure water, 267 parts of acrylamide, 24 parts of allyltrimethylammonium chloride, and 19 parts of (3,3-dimethylallyl)triphenylphosphonium bromide were mixed evenly and then frozen to -2 °C. After nitrogen was introduced for 15 minutes, 0.01 parts of diethylenetriamine pentaacetic acid pentasodium, 0.5 parts of azobisisobutyronitrile, and 0.02 parts of sodium hypophosphite were added in sequence. After nitrogen was introduced for 5 minutes, 0.002 parts of tert-butyl hydroperoxide were added. After 0.5 minutes, 0.002 parts of sodium metabisulfite were added. When the reaction started, nitrogen was stopped. After the reaction was completed and kept warm for 2 hours, the rubber block was taken out, granulated, dried, and ground to prepare a cationic hydrophobic polyacrylamide flocculant. The reaction formula is as follows: .

[0027] (2) Dissolve 11.3 parts of kaolin, 5.5 parts of humic acid, 5.8 parts of bovine serum albumin, and 5.7 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the solution until the concentration reaches 10 6 CFU / L.

[0028] (3) Prepare a 1 g / L solution of cationic hydrophobic polyacrylamide from step (1) and maintain the flow rate of the wastewater from step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2 h), the hydraulic retention time in the ultrafiltration tank is 1 h, and the total surface area of ​​the PES fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the PES fiber membrane was soaked in pure water for 24 h to clean the PES fiber membrane. The water flow rate (30 L / (m 2 The PES fiber membrane was physically cleaned with a sponge at 12, 24, and 36 h to remove the filter cake layer. The transmembrane pressure (TMP) was measured within 48 h of the fiber membrane operation.

[0029] Comparative Example 1: (1) By mass, 1150 parts of pure water, 269 parts of acrylamide, and 5 parts of dodecyldimethylallyl ammonium chloride were mixed evenly and then frozen to -2 °C. After nitrogen was introduced for 15 minutes, 0.015 parts of diethylenetriamine pentaacetic acid pentasodium, 0.44 parts of azobisisobutyronitrile, and 0.025 parts of sodium hypophosphite were added in sequence. After nitrogen was introduced for 5 minutes, 0.0025 parts of tert-butyl hydroperoxide were added. After 0.5 minutes, 0.0021 parts of sodium metabisulfite were added. When the reaction started, nitrogen was stopped. After the reaction was completed and kept warm for 2 hours, the rubber block was taken out, granulated, dried, and ground to prepare polyacrylamide flocculant.

[0030] (2) Dissolve 12 parts of kaolin, 5.8 parts of humic acid, 5.3 parts of bovine serum albumin, and 5.7 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the solution until the concentration reaches 10 6 CFU / L.

[0031] (3) Prepare the polyacrylamide in step (1) into a 1 g / L solution, and maintain the flow rate of the wastewater in step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2h), the hydraulic retention time in the ultrafiltration tank is 1 h, and the total surface area of ​​the PVDF fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the PVDF fiber membrane was soaked in pure water for 24 h to clean the PVDF fiber membrane. The water flow rate (30 L / (m 2 The PVDF fiber membrane was physically cleaned with a sponge at 12, 24, and 36 h to remove the filter cake layer. The transmembrane pressure (TMP) was measured within 48 h of the fiber membrane operation.

[0032] Comparative Example 2: (1) By mass, 1170 parts of pure water, 265 parts of acrylamide, and 30 parts of allyltrimethylammonium chloride were mixed evenly and then frozen to -2 °C. After nitrogen was introduced for 15 minutes, 0.012 parts of diethylenetriamine pentaacetic acid pentasodium, 0.47 parts of azobisisobutyronitrile, and 0.025 parts of sodium hypophosphite were added in sequence. After nitrogen was introduced for 5 minutes, 0.0022 parts of tert-butyl hydroperoxide were added. After 0.5 minutes, 0.0023 parts of sodium metabisulfite were added. When the reaction started, nitrogen was stopped. After the reaction was completed and kept warm for 2 hours, the rubber block was taken out, granulated, dried, and ground to prepare polyacrylamide flocculant.

[0033] (2) Dissolve 11.8 parts of kaolin, 5.8 parts of humic acid, 6.2 parts of bovine serum albumin, and 6.1 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the solution until the concentration reaches 10 6 CFU / L.

[0034] (3) Prepare the polyacrylamide in step (1) into a 1 g / L solution, and maintain the flow rate of the wastewater in step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2 h), and the hydraulic retention time in the ultrafiltration tank is 1 h. The total surface area of ​​the PVDF fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the PVDF fiber membrane was soaked in pure water for 24 h to clean the PVDF fiber membrane. The water flow rate (30 L / (m 2 The PVDF fiber membrane was physically cleaned with a sponge at 12, 24, and 36 h to remove the filter cake layer. The transmembrane pressure (TMP) was measured within 48 h of the fiber membrane operation.

[0035] The transmembrane pressure-time results of the above examples and comparative examples are shown in the attached Figure 1-8As shown, Examples 1-6 respectively used cationic hydrophobic polyacrylamide to slow down membrane fouling during ultrafiltration water purification. The results showed that in the four stages of 0-12 h, 12-24 h, 24-26 h and 36-48 h, the transmembrane pressure of the embodiment rose relatively slowly, and after backwashing and physical cleaning, the transmembrane pressure quickly reached a very low level, indicating that most of the membrane fouling at this time was reversible membrane fouling and was easily removed by physical cleaning. This is because cationic hydrophobic polyacrylamide, after reaching the membrane surface, binds to the membrane surface through hydrophobic association, hydrophilically modifies the membrane surface, and effectively blocks hydrophobic pollutants from reaching the membrane surface. The polyacrylamide flocculant in Comparative Example 1 can bind to the membrane surface, but does not have good bactericidal ability, which increases the transmembrane pressure of the generated biofilm pollution, while the flocculant in Comparative Example 2 does not add hydrophobic monomers, making it difficult to effectively bind to the membrane surface and unable to hydrophilically modify the membrane surface, thus generating larger membrane fouling.

[0036] Attachment Figure 9 The bacterial concentrations in the supernatants of the ultrafiltration membrane tanks of Examples 1-6 and Comparative Examples 1-2 after stable operation are shown. The results indicate that since the flocculants in Examples 1-6 and Comparative Example 2 contain a large number of cationic groups, they are beneficial for removing bacteria in the water, while the polyacrylamide flocculant in Comparative Example 1 contains very few cationic groups, so more bacteria remain in the water.

Claims

1. An application of using a cationic hydrophobic polyacrylamide flocculant to slow down membrane fouling, characterized in that The steps include: (1) According to the mass fraction, 1100-1200 parts of pure water, 260-270 parts of acrylamide, 20-50 parts of cationic monomer, and 2-20 parts of hydrophobic monomer are mixed evenly and then frozen to -2 °C. After nitrogen is introduced for 15 minutes, 0.01-0.02 parts of complexing agent, 0.3-0.5 parts of initiator, and 0.01-0.05 parts of chain transfer agent are added in sequence. After nitrogen is introduced for 5 minutes, 0.002-0.006 parts of oxidant are added. After 0.5 minutes, 0.002-0.006 parts of reducing agent are added. When the reaction starts, nitrogen is stopped. After the reaction is completed and kept warm for 2 hours, the rubber block is taken out, granulated, dried, and ground to prepare a cationic hydrophobic polyacrylamide flocculant; (2) Dissolve 10-20 parts of kaolin, 5-10 parts of humic acid, 5-10 parts of bovine serum albumin, and 5-10 parts of sodium alginate in 1000 parts of pure water, and add Escherichia coli to the water until the concentration reaches 10. 6 -10 7 CFU / L; (3) First, prepare the cationic hydrophobic polyacrylamide in step (1) into a 1-2 g / L solution, and use a peristaltic pump to maintain the flow rate of the wastewater in step (2) at 25 L / (m 2 h), the flocculant flow rate was maintained at 2 L / (m 2 h), the hydraulic retention time in the ultrafiltration tank is 1 h, and the total surface area of ​​the fiber membrane in the ultrafiltration module is 300 cm 2 Before use, the fiber membrane was soaked in pure water for 24 h to clean the fiber membrane. After every 30 minutes of filtration, a 0.5-minute water flow (30 L / (m 2 The fiber membranes were backwashed with a combination of 240 mL / min and air bubbling (150 L / h). The fiber membranes were physically cleaned with sponges at 12, 24, and 36 h to remove the filter cake layer. The transmembrane pressure (TMP) was measured during the 45–50 h operation of the fiber membranes.

2. The use of a cationic hydrophobic polyacrylamide flocculant to slow down membrane fouling according to claim 1, characterized in that: The cationic monomer is allyltrimethylammonium chloride, the hydrophobic monomer is one of dodecyldimethylallylammonium chloride, allyltributylphosphine chloride, and (3,3-dimethylallyl)triphenylphosphine bromide, the complexing agent is pentasodium diethylenetriaminepentaacetate, the initiator is azobisisobutyronitrile, the chain transfer agent is sodium hypophosphite, the oxidant is tert-butyl hydroperoxide, and the reducing agent is sodium metabisulfite.

3. The use of a cationic hydrophobic polyacrylamide flocculant to slow down membrane fouling according to claim 1, characterized in that: The fiber membrane material is PVDF (polyvinylidene fluoride) or PES (polyether).

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