Ultrafiltration or microfiltration membrane cleaning device and cleaning method

Abstract

An ultrafiltration or microfiltration membrane cleaning device and cleaning method. The cleaning device comprises a cleaning container (1) for containing cleaning liquid medicine or clear water (2), an air inlet pipe (4), and an exhaust pipe (5). A membrane assembly to be cleaned is immersed in the cleaning liquid medicine or clear water (2) in the cleaning container (1), and the air inlet pipe (4) and the exhaust pipe (5) are communicated with a water production pipe (3) in the membrane assembly. The air inlet pipe (4) is connected to a compressed air source by means of an air inlet valve (6), and the exhaust pipe (5) is connected to an atmosphere or negative pressure system by means of an exhaust valve (7). According to the method, the problem of membrane filaments being unable to be in full contact with the cleaning liquid medicine during chemical cleaning is solved.

Description

Ultrafiltration or microfiltration membrane cleaning device and cleaning method thereof Technical Field

[0001] The present invention relates to the technical field of ultrafiltration or microfiltration membrane cleaning, in particular to an ultrafiltration or microfiltration membrane cleaning device and a cleaning method thereof. Background Art

[0002] Backwashing is a common cleaning method for ultrafiltration and microfiltration membranes. Backwashing involves using a pump to force cleaning water or chemicals through the membrane fibers from the product side toward the raw water side, effectively cleaning the membrane fibers in a countercurrent flow direction opposite to their normal filtration direction. This backwashing method is commonly used in column ultrafiltration, submerged ultrafiltration, and submerged membrane bioreactors (MBRs).

[0003] However, this backwashing method has several fatal disadvantages: First, when performing chemical backwashing, a large amount of chemicals will pass through the membrane and react with a large amount of substances (such as activated sludge) in the liquid on the membrane inlet side, and cannot fully react with the foreign dirt and blocking substances on the membrane fibers, thereby losing the cleaning effect. Therefore, when backwashing, the flow rate of the introduced chemicals must be controlled at a low level; although reducing the flow rate of the chemicals can reduce the ineffective flow of chemicals passing through the membrane fibers to a certain extent, because the membrane fibers are generally installed vertically, under lower flow control, the water pressure difference between the upper and lower ends of the membrane fibers will cause the cleaning chemicals to flow out only from the upper part, and cannot The water is passed into the bottom of the membrane filament, making it impossible to clean the membrane filament evenly from top to bottom, seriously reducing the cleaning efficiency; second, a backwash pump is used to suck the membrane produced water for membrane water backwashing. This method not only wastes a large amount of produced water, but also consumes energy; third, since the cleaning agent is mostly a stock solution of sodium hypochlorite and acid, it is difficult to filter out impurities before use. In the membrane filaments currently used in most of the market, the membrane pores are small on the raw water side and large on the produced water side. When the agent passes through the reverse direction from the produced water side of the membrane to the raw water side, the impurities in the agent are easily accumulated in the membrane pores with gradually decreasing diameters and cannot be discharged smoothly, resulting in membrane pollution.

[0004] In recent years, membrane cleaning technology has been improved to in-situ cleaning, that is, the raw water or activated sludge in the membrane pool is discharged, and then the membrane pool is filled with a cleaning solution prepared with produced water, and the membrane is cleaned by soaking the solution with chemicals and aerating and stirring.

[0005] However, this type of cleaning also has disadvantages. Since the water-producing side of the membrane fibers is usually filled with water or air, once the membrane fibers are severely contaminated, it is difficult for the reagent to pass through the membrane due to the effects of concentration polarization and air resistance, and to effectively clean the inner wall of the membrane pores and the inside of the membrane fibers.

[0006] The cleaning method disclosed in the invention patent with application number "202010074088.7" and titled "A method for cleaning an immersed ultrafiltration or microfiltration membrane" combines in-situ cleaning and backwashing. Not only is the operation more complicated, but the above-mentioned shortcomings also continue to exist.

[0007] Summary of the Invention

[0008] The purpose of the present invention is to provide a cleaning device and a cleaning method for ultrafiltration or microfiltration membranes to solve the problems existing in the prior art, overcome the problem of insufficient contact between the membrane filaments and the cleaning solution caused by concentration polarization and poor air-blocking water flow during cleaning with the cleaning solution, and also avoid the problem of impurities in the cleaning solution contaminating the membrane filaments.

[0009] To achieve the above-mentioned purpose, the present invention provides the following solution: The present invention provides a cleaning device for ultrafiltration or microfiltration membrane, comprising a cleaning container for containing cleaning liquid or clean water, an air inlet pipe and an exhaust pipe, the membrane assembly to be cleaned is immersed in the cleaning liquid or clean water, the air inlet pipe and the exhaust pipe are both connected to the water production pipe in the membrane assembly; the air inlet pipe is connected to the compressed air source through an air inlet valve, and the exhaust pipe is connected to the atmosphere or a negative pressure system through an exhaust valve.

[0010] Preferably, the pressure and flow rate of the compressed gas source are adjustable.

[0011] Preferably, the air intake pipe is connected to a compressed air source through the air intake valve, and the compressed air source is used to introduce compressed gas into the air intake pipe; the applicable gas pressure range is 0-300KPa.

[0012] Preferably, the compressed gas introduced by the compressed gas source is air, nitrogen or methane.

[0013] The present invention also discloses a method for cleaning an ultrafiltration or microfiltration membrane, comprising the following steps:

[0014] 1) Immerse the membrane assembly in a cleaning container with cleaning solution and close the water valve on the water pipe;

[0015] 2) Open the air inlet valve, close the exhaust valve, and introduce compressed gas into the water production pipe. The cleaning liquid or clean water in the membrane fibers is compressed by the compressed gas and discharged back into the raw water side of the membrane through the membrane pores on the membrane fiber wall;

[0016] 3) Close the air inlet valve and open the exhaust valve. The cleaning solution or clean water on the raw water side of the membrane enters the water-producing side of the membrane filaments from the membrane pores under the action of the water pressure difference between the inside and outside of the membrane filaments or the negative pressure suction. When the membrane assembly is chemically cleaned with a cleaning solution, the cleaning solution is kept in the membrane filaments for a certain period of time after entering the membrane filaments to allow the cleaning solution to fully contact and react with the impurities on the membrane filaments.

[0017] 4) Repeat steps 2) and 3) several times until the membrane assembly is cleaned.

[0018] Preferably, in step 3), the cleaning solution is maintained for 0.5 min to 30 min after entering the water-producing side of the membrane fibers.

[0019] Preferably, in step 2), the flow rate of the cleaning solution is 1 to 200 L / M 2 H.

[0020] Compared with the prior art, the present invention has achieved the following technical effects:

[0021] 1. The present invention repeatedly operates in a cycle of exhausting (liquid absorption) - standing - air intake (liquid drainage) on the water-producing side of the membrane filaments. This allows the cleaning solution or clean water in the cleaning container to be repeatedly transferred from the raw water side of the membrane through the membrane filaments to the water-producing side. Then, driven by the air pressure on the water-producing side of the membrane filaments, the cleaning solution or clean water is discharged from the membrane filaments back through the membrane filaments to the raw water side of the membrane filaments. This overcomes the problems of concentration polarization during chemical cleaning and the inability to effectively control the chemical around the membrane filaments, which prevents sufficient contact between the membrane filaments and the cleaning solution.

[0022] 2. In the process of absorbing cleaning liquid or clean water, the present invention utilizes the filtering effect of the membrane fibers themselves to block impurities in the cleaning liquid or clean water that can contaminate the membrane fibers on the raw water side of the membrane fibers, ensuring that the cleaning liquid or clean water entering the water production side of the membrane fibers no longer contains impurities larger than the pore size of the filter membrane. When compressed gas is injected into the water production side of the membrane fibers for backwashing, the problem of impurities in the cleaning liquid or clean water contaminating the membrane fibers can be avoided;

[0023] 3. The present invention solves the problems of waste water and difficulty in uniformly cleaning the membrane fibers in the prior art;

[0024] 4. The present invention immerses the membrane assembly in a cleaning solution for cyclic backwashing, which not only cleans the outer surface of the membrane fibers, the inner wall of the membrane pores, and the inner surface of the membrane fibers, but also increases the flow rate of the cleaning solution and improves the cleaning efficiency;

[0025] 5. The cleaning device of the present invention has a simple structure and the cleaning method is easy to operate, which is conducive to large-scale promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 is a diagram showing the state of compressed gas entering the membrane module;

[0028] FIG2 is a diagram showing the state of compressed gas when it is discharged from the membrane module;

[0029] Among them, 1. Cleaning container; 2. Cleaning solution or clean water; 3. Water production pipe; 4. Air inlet pipe; 5. Exhaust pipe; 6. Air inlet valve; 7. Exhaust valve; 8. Membrane wire; 9. Membrane hole. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] The purpose of the present invention is to provide a cleaning device and a cleaning method for ultrafiltration or microfiltration membranes to solve the problems existing in the prior art, overcome the problem of insufficient contact between the membrane filaments and the cleaning solution caused by concentration polarization and poor air-blocking water flow during cleaning with the cleaning solution, and also avoid the problem of impurities in the cleaning solution contaminating the membrane filaments.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] As shown in Figures 1 and 2, this embodiment provides a cleaning device for an ultrafiltration or microfiltration membrane, including a cleaning container 1 for containing cleaning liquid or clean water, an air inlet pipe 4 and an exhaust pipe 5. The cleaning liquid or clean water in the cleaning container 1 immerses the membrane assembly to be cleaned, and the air inlet pipe 4 and the exhaust pipe 5 are both connected to the water production pipe 3 in the membrane assembly; the air inlet pipe 4 is connected to the compressed air source through the air inlet valve 6, and the exhaust pipe 5 is connected to the atmosphere or the negative pressure system through the exhaust valve 7.

[0034] The membrane assembly to be cleaned in this embodiment can be a column membrane assembly, a curtain membrane assembly, or any other water purification assembly supported by ultrafiltration or microfiltration membranes. When the membrane assembly is a membrane fiber assembly in a column MBR, the shell of the column MBR serves as the cleaning vessel 1. When the membrane assembly is a curtain membrane assembly, a cleaning tank can serve as the cleaning vessel 1.

[0035] In this embodiment, the air inlet valve 6 and the exhaust valve 7 can be manual valves or electronically controlled valves. Preferably, the air inlet valve 6 and the exhaust valve 7 are both located above the liquid level of the cleaning solution or the clean water 2 for easy control.

[0036] The air inlet pipe 4 is connected to a compressed air source via an air inlet valve 6. The compressed air source is used to introduce compressed air into the air inlet pipe 4. The compressed air source can be a compressed air pump or a pressure gas cylinder. The compressed gas can be air, or other gases such as nitrogen or methane can be selected according to actual operating conditions.

[0037] This embodiment discloses a method for cleaning an ultrafiltration or microfiltration membrane, comprising the following steps:

[0038] 1) Fill the cleaning container 1 with cleaning liquid or clean water 2, immerse the membrane assembly in the cleaning liquid or clean water 2, and close the water production valve on the water production pipe 3.

[0039] 2) Open the air inlet valve 6, close the air outlet valve 7, and introduce compressed gas into the water production pipe 3. The cleaning liquid or clean water 2 in the membrane filaments 8 is compressed by the compressed gas and discharged back into the raw water side of the membrane filaments 8 through the membrane holes 9 on the wall of the membrane filaments 8, completing a cleaning of the interior of the membrane filaments 8 and the membrane holes 9, as shown in Figure 1.

[0040] 3) Close the air inlet valve 6 and open the air outlet valve 7. The cleaning solution or clean water 2 in the cleaning container 1 flows from the raw water side of the membrane filaments 8 through the membrane pores 9 into the water-producing side of the membrane filaments 8 due to the pressure difference between the inside and outside of the membrane filaments 8 or the negative pressure suction. As the cleaning solution or clean water 2 flows through the membrane pores 9, it can clean the membrane pores 9 again. At the same time, impurities in the cleaning solution or clean water 2 are blocked outside the membrane pores 9. The cleaning solution or clean water 2 entering the water-producing side of the membrane filaments 8 is a clean solution with impurity particle size smaller than the membrane pore size. When using chemical cleaning, the water-producing side of the membrane filaments 8 is fully filled with cleaning solution and maintained for a certain period of time to allow the cleaning solution or clean water 2 to fully react with impurities on the membrane filaments 8 to achieve a good cleaning effect, as shown in Figure 2.

[0041] 4) Repeat steps 2) and 3) several times until the membrane assembly is cleaned.

[0042] This embodiment repeatedly operates in a cycle of exhausting (liquid absorption) - standing - airing (liquid discharge) on the water-producing side of the membrane filaments 8, thereby repeatedly passing the cleaning solution or clean water 2 in the cleaning container 1 from the raw water side of the membrane through the membrane filaments 8 to the water-producing side. Then, driven by the air pressure on the water-producing side of the membrane filaments 8, the cleaning solution or clean water 2 is discharged from the water-producing side of the membrane filaments 8 back through the membrane filaments 8 to the raw water side of the membrane filaments 8. This overcomes the problems of concentration polarization during chemical cleaning and the inability to effectively control the reagent around the membrane filaments 8, which prevents the membrane filaments 8 from fully contacting the cleaning solution. Furthermore, during the absorption of the cleaning solution, the membrane filaments 8 utilize their own filtering effect to block impurities in the cleaning solution that are larger than the membrane pore size and could contaminate the membrane filaments 8, outside the membrane filaments 8. This ensures the cleanliness of the cleaning solution entering the water-producing side of the membrane filaments 8. When compressed gas is injected into the water-producing side of the membrane filaments 8 for backwashing, the problem of impurities in the cleaning solution contaminating the membrane filaments 8 can be avoided. This embodiment also solves the existing problems of waste water and difficulty in uniformly cleaning the membrane filaments 8. Furthermore, immersing the membrane assembly in a cleaning solution or clean water 2 for backwashing not only cleans the outer surfaces of the membrane filaments 8, the inner walls of the membrane pores 9, and the inner surfaces of the membrane filaments 8, but also increases the flow rate of the cleaning solution or clean water 2, improving cleaning efficiency. Furthermore, the cleaning device of this embodiment has a simple structure and an easy-to-use cleaning method, facilitating widespread adoption.

[0043] Furthermore, in step 3) of this embodiment, the cleaning solution or clean water 2 is maintained for 0.5 to 30 minutes after entering the water-producing side of the membrane filaments 8. The specific holding time can be determined according to the type of cleaning solution and the degree of membrane contamination.

[0044] Furthermore, in step 2) of this embodiment, under the pressure of compressed gas, the flow rate of the cleaning liquid or water 2 is 1 to 200 L / M 2 H, but it must be ensured that the pressure does not exceed the pressure range that the membrane can withstand; and the flow flux can be adjusted by adjusting the opening of the air inlet valve 6.

[0045] Adaptive changes based on actual needs are all within the scope of protection of the present invention.

[0046] It should be noted that it will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims, not the foregoing description, and it is intended that all variations within the meaning and range of equivalents of the claims be encompassed within the present invention. Any reference signs in the claims should not be construed as limiting the claim to which they relate.

Claims

1. A cleaning device for ultrafiltration or microfiltration membrane, characterized in that: It includes a cleaning container for containing cleaning solution or clean water, an air inlet pipe and an exhaust pipe. The membrane assembly to be cleaned is immersed in the cleaning solution or clean water. The air inlet pipe and the exhaust pipe are both connected to the water production pipe in the membrane assembly; the air inlet pipe is connected to the compressed air source through an air inlet valve, and the exhaust pipe is connected to the atmosphere or a negative pressure system through an exhaust valve.

2. The cleaning device for ultrafiltration or microfiltration membrane according to claim 1, characterized in that: The pressure and flow rate of the compressed gas source can be adjusted.

3. The cleaning device for ultrafiltration or microfiltration membrane according to claim 1, characterized in that: The air intake pipe is connected to a compressed air source through the air intake valve, and the compressed air source is used to introduce compressed gas into the air intake pipe.

4. The cleaning device for ultrafiltration or microfiltration membrane according to claim 1, characterized in that: The compressed gas introduced by the compressed gas source is air, nitrogen or methane.

5. The cleaning device for ultrafiltration or microfiltration membrane according to claim 1, characterized in that: The cleaning liquid or working liquid is a chemical solution for membrane cleaning, an activated sludge mixed liquid, water or various liquid filtering media.

6. A method for cleaning an ultrafiltration or microfiltration membrane, characterized in that: The following steps are involved: 1) Immerse the membrane assembly in a cleaning container with cleaning solution and close the water production valve on the water production pipe; 2) Open the air inlet valve, close the exhaust valve, and introduce compressed gas into the water production pipe. The cleaning liquid or clean water in the membrane fibers is discharged into the raw water side of the membrane through the membrane holes on the membrane fiber wall under the compression of the compressed gas; 3) Close the air inlet valve and open the exhaust valve. The cleaning solution or clean water on the raw water side of the membrane enters the water production side of the membrane from the membrane pores under the action of the water pressure difference between the inside and outside of the membrane or the negative pressure suction. When the membrane assembly is chemically cleaned with the cleaning solution, the cleaning solution is kept in the membrane for a certain period of time after entering the membrane so that the cleaning solution can fully contact and react with the impurities on the membrane. 4) Repeat steps 2) and 3) several times until the membrane assembly is cleaned.

7. The method for cleaning an ultrafiltration or microfiltration membrane according to claim 6, characterized in that: In step 2), the flow rate of the cleaning solution is 1 to 200 L / M 2 H.

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