A Highly Efficient Chemical Cleaning Method for Ultrafiltration Membranes

Abstract

This application provides a highly efficient chemical cleaning method for ultrafiltration membranes. The method includes pretreating the ultrafiltration membrane module to be cleaned; injecting a chemical cleaning solution into the pretreated ultrafiltration membrane module for sequential recovery cleaning and direct current cleaning, during which nitrogen gas is introduced into the ultrafiltration membrane module for pulsed gas rinsing; after the chemical cleaning solution cleaning is completed, stopping the pulsed gas rinsing, and using clean water to rinse the ultrafiltration membrane module using a stepped pressure reduction method until the pH value and conductivity of the rinse water meet preset requirements and there are no obvious dirt particles; performing a backwashing operation on the ultrafiltration membrane module after the clean water rinsing, and switching the ultrafiltration membrane module to normal operation after the backwashing operation is completed. This application solves the problem of poor cleaning effect in existing ultrafiltration membrane cleaning technologies through the above method.

Description

Technical Field

[0001] This invention relates to the field of ultrafiltration membrane cleaning technology, and in particular to a highly efficient chemical cleaning method for ultrafiltration membranes. Background Technology

[0002] In the widespread application of ultrafiltration membrane technology, membrane fouling remains a core technical bottleneck restricting its long-term stable operation and impacting economic benefits. During long-term operation, various impurities in the raw water, including organic matter, microorganisms, colloids, and inorganic salt ions such as calcium and magnesium, accumulate on the surface of the membrane fibers and inside the membrane pores through physical adsorption, chemical bonding, or bioadhesion, eventually forming a dense fouling layer with complex structure and mixed components. This fouling layer not only significantly reduces membrane flux, forcing the system to operate under higher transmembrane pressure differentials, thus leading to a significant increase in energy consumption, but also accelerates the aging and deterioration of membrane materials, shortens the service life of membrane modules, and may pose a potential risk to the quality of the produced water.

[0003] Currently, the cleaning strategies commonly used in the industry are mainly divided into two categories: chemical cleaning and physical cleaning. Conventional chemical cleaning relies on the dissolving, complexing, or oxidizing effects of specific chemical agents (such as acids, alkalis, oxidants, surfactants, etc.) to remove contaminants.

[0004] However, when faced with complex fouling materials that are dense and chemically inert, simple chemical action often results in slow penetration and incomplete reactions, leading to less than ideal recovery rates of membrane flux after cleaning. Furthermore, prolonged high-concentration chemical immersion can cause irreversible damage to the membrane material itself. On the other hand, traditional physical cleaning methods, such as pressure-controlled backwashing or air scrubbing, typically operate at a macroscopic level, exhibiting problems such as uneven force distribution, difficulty in penetrating deep into the membrane pores, and limited physical removal capabilities for stubborn fouling, thus limiting cleaning effectiveness. In addition, in the design and operation of cleaning processes, how to effectively prevent secondary contamination caused by the circulation of cleaned-off fouling fragments within the system, how to ensure complete rinsing of chemical agents without residue, and how to maximize the protection of the delicate microstructure of the ultrafiltration membrane from mechanical damage while pursuing high-efficiency cleaning are all common challenges that have not yet been perfectly resolved in existing technologies. Summary of the Invention

[0005] This application provides a highly efficient chemical cleaning method for ultrafiltration membranes to solve the problem of poor cleaning effect in existing ultrafiltration membrane cleaning technologies.

[0006] The method includes: Pre-treatment is performed on the ultrafiltration membrane module to be cleaned; Chemical cleaning solution is injected into the pretreated ultrafiltration membrane module for sequential recovery cleaning and DC cleaning, and nitrogen gas is introduced into the ultrafiltration membrane module for pulse gas washing during the DC cleaning process. After the chemical cleaning solution is used to clean the ultrafiltration membrane module, the pulse air washing is stopped, and the ultrafiltration membrane module is flushed with clean water in a step-down pressure manner until the pH value and conductivity of the flushing water meet the preset requirements and there are no obvious dirt particles. The ultrafiltration membrane module is backwashed after being rinsed with clean water, and after the backwashing operation is completed, the ultrafiltration membrane module is switched to normal operation.

[0007] Preferably, the ultrafiltration membrane module includes an inlet valve, a product water valve, a backwash discharge valve, and a forward flush discharge valve, and the pretreatment step for the ultrafiltration membrane module to be cleaned includes: Close the inlet valve and the product water valve, and open the backwash discharge valve and the forward flush drain valve to drain the residual water in the ultrafiltration membrane module. After the residual water is drained, close the backwash discharge valve and the forward flush drain valve.

[0008] Preferably, the ultrafiltration membrane module further includes a corresponding chemical cleaning pump, a recovery valve, and a cleaning water tank, wherein the recovery cleaning step includes: The chemical cleaning solution is injected into the ultrafiltration membrane module through the chemical cleaning pump, and the circulation flow rate of the chemical cleaning solution is controlled within the range of 20t / h to 40t / h; during the cleaning process, the recovery valve is opened to collect the detached cleaning dirt, and the recovery valve is closed after at least 10 minutes. The DC cleaning includes: The chemical cleaning solution is switched to the cleaning water tank for circulation, and chemical cleaning continues for 60 minutes.

[0009] Preferably, the ultrafiltration membrane module further includes a nitrogen valve, and the step of introducing nitrogen into the ultrafiltration membrane module for pulse gas washing during DC cleaning includes: During the DC cleaning process, the nitrogen valve is slowly opened to introduce nitrogen into the ultrafiltration membrane module.

[0010] Preferably, the nitrogen gas introduced into the ultrafiltration membrane module has a purity of ≥99.5%, and the pressure of the nitrogen gas introduced into the ultrafiltration membrane module is 0.1-0.15 MPa.

[0011] Preferably, the step of flushing the ultrafiltration membrane module with clean water using a stepped pressure reduction method includes: Clean water is introduced into the membrane module, and a three-stage rinsing process is performed, including: In the first stage, the flushing pressure is 0.2-0.25 MPa, and it is maintained for 5-8 minutes; In the second stage, the flushing pressure is 0.15-0.18 MPa, and it is maintained for 8-10 minutes; In the third stage, the flushing pressure is 0.08-0.1 MPa, maintained for 10-15 minutes; the clean water flow rate in the first, second, and third stages is 1.5-2.5 m / s.

[0012] Preferably, the flushing pressure in the first stage is 0.22 MPa and the flushing time is 6 min; the flushing pressure in the second stage is 0.16 MPa and the flushing time is 9 min; the flushing pressure in the third stage is 0.1 MPa and the flushing time is 12 min; and the circulation flow rate of the chemical cleaning solution is 30 t / h.

[0013] Preferably, the chemical cleaning solution includes an alkaline cleaning system and an acidic cleaning system. When the membrane surface of the ultrafiltration membrane module is mainly contaminated with organic fouling and / or microbial fouling, the ultrafiltration membrane module is chemically cleaned using the alkaline washing system cleaning solution; the alkaline washing system cleaning solution is composed of NaClO, NaOH, sodium dodecylbenzenesulfonate and demineralized water. When the membrane surface of the ultrafiltration membrane module is mainly fouled by inorganic scale, the ultrafiltration membrane module is chemically cleaned using the acid washing system cleaning solution; the acid washing system cleaning solution is composed of HCl and demineralized water.

[0014] Preferably, the pH value of the alkaline washing system cleaning solution is in the range of 10-12; the pH value of the acid washing system cleaning solution is in the range of 1.5-2. The alkaline washing system contains a NaClO concentration of 0.15% and a NaOH concentration of 0.2% in the cleaning solution. The mass concentration of HCl in the pickling system cleaning solution is 0.25%.

[0015] As described above, this application provides a highly efficient chemical cleaning method for ultrafiltration membranes. The method includes pre-treating the ultrafiltration membrane module to be cleaned; injecting a chemical cleaning solution into the pre-treated ultrafiltration membrane module for sequential recovery cleaning and direct current cleaning, during which nitrogen gas is introduced into the ultrafiltration membrane module for pulsed gas rinsing; after completing the chemical cleaning solution cleaning, stopping the pulsed gas rinsing, and using clean water to rinse the ultrafiltration membrane module using a stepped pressure reduction method until the pH and conductivity of the rinse water meet preset requirements and there are no obvious dirt particles; performing a backwashing operation on the ultrafiltration membrane module after the clean water rinsing, and switching the ultrafiltration membrane module to normal operation after completing the backwashing operation. This application solves the problem of poor cleaning effect in existing ultrafiltration membrane cleaning technologies through the above method. Attached Figure Description

[0016] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a highly efficient chemical cleaning method for an ultrafiltration membrane according to this application. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that the brief descriptions of terms in this application are only for the convenience of understanding the embodiments described below, and are not intended to limit the embodiments of this application. Unless otherwise stated, these terms should be understood in their ordinary and common meaning.

[0020] It should be noted that, in this application, the terms "exemplary" or "for example" are used to indicate that something is being described as an example, illustration, or illustration. Any embodiment or design described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or design solutions. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0021] Figure 1 This is a flowchart of a highly efficient chemical cleaning method for an ultrafiltration membrane according to this application.

[0022] See Figure 1 As can be seen, this embodiment provides a highly efficient chemical cleaning method for ultrafiltration membranes, the method comprising: S1, Pre-treatment of the ultrafiltration membrane module to be cleaned.

[0023] Specifically, in this embodiment, the ultrafiltration membrane module to be cleaned is shut down, the inlet valve and the product water valve are closed, and the backwash discharge valve and the forward flush drain valve are opened to completely drain the residual water inside the ultrafiltration membrane; after the water is drained, the backwash discharge valve and the forward flush drain valve are closed to ensure that the system is sealed.

[0024] The method further includes: S2, chemical cleaning solution is injected into the pretreated ultrafiltration membrane module for sequential recovery cleaning and DC cleaning, and nitrogen gas is introduced into the ultrafiltration membrane module for pulse gas washing during the DC cleaning process.

[0025] Specifically, in this embodiment, the corresponding cleaning solution system is selected according to the type of fouling on the ultrafiltration membrane: When the membrane surface is mainly contaminated with organic dirt and microorganisms, an alkaline cleaning system is used: add a certain amount of NaClO, NaOH and sodium dodecylbenzenesulfonate to the cleaning tank. Sodium dodecylbenzenesulfonate acts as a surfactant, which can enhance the penetration and dispersion of dirt by the cleaning solution. Then add sufficient demineralized water, stir evenly and adjust the pH value of the system to 10-12 to form a mixed chemical cleaning solution. When the membrane surface is mainly fouled by inorganic scale (such as calcium and magnesium precipitates), an acid washing system is used for cleaning: add an appropriate amount of HCl and demineralized water to the cleaning water tank, adjust the pH value of the cleaning solution to 1.5-2.0, and form an acid washing cleaning solution. After preparation, open the cleaning solution inlet valve, return valve and recovery valve in sequence to establish a cleaning solution circulation path.

[0026] Preferably, in the alkaline washing system, the optimal mass concentration of NaClO is 0.15%, the optimal mass concentration of NaOH is 0.2%, and the pH value of the washing solution is 10-12.

[0027] Preferably, in the pickling system, the optimal mass concentration of HCl is 0.25%, and the pH value of the cleaning solution is 1.5-2.0.

[0028] Start the chemical cleaning pump to inject the chemical cleaning solution from the cleaning tank into the ultrafiltration membrane module. The chemical action dissolves the dirt on the membrane surface and internal channels. Adjust the outlet valve of the cleaning pump to control the circulation flow rate of the cleaning solution at 20-40 t / h, ensuring that the cleaning solution can fully cover the membrane surface and penetrate the membrane pores. After the cleaning solution flows out of the ultrafiltration membrane module, it first enters the recovery tank through the recovery valve, so that the cleaning solution carrying a large amount of detached dirt in the early stage is collected in a concentrated manner, preventing the dirt from circulating back into the membrane module and causing secondary pollution. After maintaining this state for 10 minutes, close the recovery valve to switch the cleaning solution to the cleaning tank for circulation and continue chemical cleaning.

[0029] Preferably, the optimal parameters for the chemical cleaning solution circulation cleaning are: a cleaning solution circulation flow rate of 30 t / h.

[0030] During the cleaning fluid circulation process, slowly open the nitrogen valve to introduce nitrogen into the circulation system. The nitrogen purity should be ≥99.5%, and the nitrogen inlet pressure should be controlled at 0.1-0.15 MPa.

[0031] This pressure range ensures that nitrogen gas can generate sufficiently strong bubble impact force while avoiding excessive pressure that could cause physical damage to the ultrafiltration membrane. Nitrogen gas and cleaning fluid are fully mixed in the system to form a gas-water mixture. Bubbles are continuously generated and burst on the membrane surface and in the membrane pores, generating pulse impact force that "explodes" the dense dirt layer that is difficult to dissolve with chemical cleaning fluid, thus achieving physical stripping and dispersion of dirt. Maintain the air-water mixture in a circulating cleaning state for 60 minutes to ensure the synergistic effect of air washing and chemical cleaning, and thoroughly remove membrane fouling.

[0032] Preferably, the optimal parameters for the nitrogen pulse gas scrubbing are: pulse pressure 0.1-0.15 MPa and total scrubbing time 60 min.

[0033] The method further includes: S3. After the chemical cleaning solution is used to clean the ultrafiltration membrane module, the pulse air washing is stopped, and the ultrafiltration membrane module is flushed with clean water in a step-down pressure manner until the pH value and conductivity of the flushing water meet the preset requirements and there are no obvious dirt particles.

[0034] Specifically, in this embodiment, after the nitrogen pulse gas washing is completed, the nitrogen valve is closed, and the residual nitrogen in the system is exhausted through the exhaust device; clean water is introduced into the membrane module, and flushing is carried out in a step-down manner: the initial flushing pressure is 0.2-0.25MPa, maintained for 5-8 minutes; then the pressure is reduced to 0.15-0.18MPa, maintained for 8-10 minutes; finally, it is reduced to 0.08-0.1MPa, maintained for 10-15 minutes; during the flushing process, the clean water flow rate is controlled at 1.5-2.5m / s.

[0035] By using a stepped pressure reduction method, it is possible to use higher pressure to flush out stubborn residual dirt, while lower pressure can be used in the later stages to prevent residual chemicals from being "pressed" into the depths of the membrane pores during the flushing process, ensuring thorough flushing and removing residual chemical cleaning agents and loose dirt particles.

[0036] Preferably, the optimal pressure gradient for the stepped pressure scouring is: 0.22MPa (6min) → 0.16MPa (9min) → 0.1MPa (12min).

[0037] The method further includes: S4, perform a backwashing operation on the ultrafiltration membrane module after rinsing with clean water, and switch the ultrafiltration membrane module to normal operation after completing the backwashing operation.

[0038] Specifically, in this embodiment, after the water is flushed at reduced pressure in a stepped manner, the pH value and conductivity of the flushing water are detected. When the pH value of the flushing water is close to that of the clean water, the conductivity is stable, and there are no obvious dirt particles, the flushing is deemed qualified. The cleaning solution inlet valve and return valve are closed, and the ultrafiltration membrane module is automatically backwashed to further remove any trace dirt that may remain. After the backwashing is completed, the relevant valves are closed, and the ultrafiltration membrane module is switched to normal operation, completing the entire chemical cleaning process.

[0039] This embodiment has the following advantages: This method achieves highly efficient synergy between chemical and physical cleaning, enhancing cleaning thoroughness. One of its core innovations lies in the simultaneous introduction of nitrogen gas for pulsed gas rinsing during the chemical cleaning solution circulation (DC cleaning). Nitrogen gas forms bubbles in the cleaning solution, which continuously generate and burst on the membrane surface and within the membrane pores, producing pulsed physical impact forces. This design allows the dissolution and decomposition of chemical agents to occur simultaneously and mutually reinforce the physical stripping and dispersion effects generated by bubble bursting. Especially effective against dense fouling layers that are difficult to treat alone with chemical cleaning, the physical pulse force can "explode" or loosen them, making it easier for the chemical cleaning solution to penetrate and react. This significantly improves the removal effect on complex and stubborn fouling, potentially leading to a greater recovery of membrane flux.

[0040] The cleaning process was optimized to effectively avoid secondary pollution: This method incorporates a "recycled cleaning" step, where, at the initial stage of chemical cleaning, the cleaning solution carrying a large amount of detached dirt is collected separately in a recycling tank instead of immediately participating in the system circulation. This step effectively prevents a large number of dirt fragments loosened by the chemical action at the beginning of cleaning from re-entering the circulation, re-adhering to the membrane surface, or clogging the membrane pores, thereby avoiding secondary pollution during the cleaning process and ensuring the effectiveness of subsequent cleaning steps.

[0041] A stepped pressure-reducing flushing process is employed to ensure thorough rinsing and protect the membrane elements: After chemical cleaning and air washing, this patented method uses a phased, gradually decreasing pressure approach for water rinsing. The initial higher pressure effectively removes stubborn residual dirt particles and chemical agents; the subsequent gradual pressure reduction prevents residual trace amounts of agents or fine particles from being "forced" deep into the membrane pores at the end of the flushing process, thus ensuring a more thorough rinse. This precise pressure control helps to efficiently remove residues while reducing potential mechanical stress on the membrane structure, protecting the delicate microstructure of the ultrafiltration membrane.

[0042] The method enhances the systematic nature and controllability of the cleaning process: from pretreatment, targeted solution preparation, combined chemical circulation and gas washing, step-down pressure rinsing, to final backwashing and recovery operation, it forms a complete and orderly cleaning process. Key steps such as the type of cleaning solution (selected based on the acidity or alkali of the contaminant), gas washing pressure, rinsing pressure, and time gradient have been clearly defined and optimized, making the cleaning operation more standardized and controllable, and helping to ensure the stability and repeatability of the cleaning effect.

[0043] For ease of explanation, the above description has been provided in conjunction with specific embodiments. However, the discussion in some embodiments is not intended to be exhaustive or to limit the embodiments to the specific forms disclosed above. Various modifications and variations can be obtained based on the above teachings. The selection and description of the above embodiments are for the purpose of better explaining the contents of this disclosure, thereby enabling those skilled in the art to better utilize the embodiments.

Claims

1. A highly efficient chemical cleaning method for ultrafiltration membranes, characterized in that, The method includes: Pre-treatment is performed on the ultrafiltration membrane module to be cleaned; Chemical cleaning solution is injected into the pretreated ultrafiltration membrane module for sequential recovery cleaning and DC cleaning, and nitrogen gas is introduced into the ultrafiltration membrane module for pulse gas washing during the DC cleaning process. After the chemical cleaning solution is used to clean the ultrafiltration membrane module, the pulse air washing is stopped, and the ultrafiltration membrane module is flushed with clean water in a step-down pressure manner until the pH value and conductivity of the flushing water meet the preset requirements and there are no obvious dirt particles. The ultrafiltration membrane module is backwashed after being rinsed with clean water, and after the backwashing operation is completed, the ultrafiltration membrane module is switched to normal operation.

2. The efficient chemical cleaning method for ultrafiltration membranes according to claim 1, characterized in that, The ultrafiltration membrane module includes an inlet valve, a product water valve, a backwash discharge valve, and a forward flush discharge valve. The pretreatment step for the ultrafiltration membrane module to be cleaned includes: Close the inlet valve and the product water valve, and open the backwash discharge valve and the forward flush drain valve to drain the residual water in the ultrafiltration membrane module. After the residual water is drained, close the backwash discharge valve and the forward flush drain valve.

3. The efficient chemical cleaning method for ultrafiltration membranes according to claim 2, characterized in that, The ultrafiltration membrane module also includes a corresponding chemical cleaning pump, a recovery valve, and a cleaning water tank. The recovery cleaning step includes: The chemical cleaning solution is injected into the ultrafiltration membrane module through the chemical cleaning pump, and the circulation flow rate of the chemical cleaning solution is controlled within the range of 20t / h to 40t / h; during the cleaning process, the recovery valve is opened to collect the detached cleaning dirt, and the recovery valve is closed after at least 10 minutes. The DC cleaning includes: The chemical cleaning solution is switched to the cleaning water tank for circulation, and chemical cleaning continues for 60 minutes.

4. The efficient chemical cleaning method for an ultrafiltration membrane according to claim 3, characterized in that, The ultrafiltration membrane module also includes a nitrogen valve, and the step of introducing nitrogen into the ultrafiltration membrane module for pulse gas washing during DC cleaning includes: During the DC cleaning process, the nitrogen valve is slowly opened to introduce nitrogen into the ultrafiltration membrane module.

5. The efficient chemical cleaning method for an ultrafiltration membrane according to claim 4, characterized in that, The nitrogen gas introduced into the ultrafiltration membrane module has a purity of ≥99.5%, and the pressure of the nitrogen gas introduced into the ultrafiltration membrane module is 0.1-0.15 MPa.

6. The efficient chemical cleaning method for an ultrafiltration membrane according to claim 4, characterized in that, The step of flushing the ultrafiltration membrane module with clean water using a stepped pressure reduction method includes: Clean water is introduced into the membrane module, and a three-stage rinsing process is performed, including: In the first stage, the flushing pressure is 0.2-0.25 MPa, and it is maintained for 5-8 minutes; In the second stage, the flushing pressure is 0.15-0.18 MPa, and it is maintained for 8-10 minutes; In the third stage, the flushing pressure is 0.08-0.1 MPa, maintained for 10-15 minutes; the clean water flow rate in the first, second, and third stages is 1.5-2.5 m / s.

7. The efficient chemical cleaning method for an ultrafiltration membrane according to claim 6, characterized in that, The flushing pressure in the first stage is 0.22 MPa and the flushing time is 6 min; the flushing pressure in the second stage is 0.16 MPa and the flushing time is 9 min; the flushing pressure in the third stage is 0.1 MPa and the flushing time is 12 min; and the circulation flow rate of the chemical cleaning solution is 30 t / h.

8. The efficient chemical cleaning method for an ultrafiltration membrane according to claim 1, characterized in that, The chemical cleaning solution includes alkaline cleaning system cleaning solution and acid cleaning system cleaning solution; When the membrane surface of the ultrafiltration membrane module is mainly contaminated with organic fouling and / or microbial fouling, the ultrafiltration membrane module is chemically cleaned using the alkaline washing system cleaning solution; the alkaline washing system cleaning solution is composed of NaClO, NaOH, sodium dodecylbenzenesulfonate and demineralized water. When the membrane surface of the ultrafiltration membrane module is mainly fouled by inorganic scale, the ultrafiltration membrane module is chemically cleaned using the acid washing system cleaning solution; the acid washing system cleaning solution is composed of HCl and demineralized water.

9. The efficient chemical cleaning method for an ultrafiltration membrane according to claim 8, characterized in that, The pH value of the alkaline washing system cleaning solution is in the range of 10-12; the pH value of the acid washing system cleaning solution is in the range of 1.5-2. The alkaline washing system contains a NaClO concentration of 0.15% and a NaOH concentration of 0.2% in the cleaning solution. The mass concentration of HCl in the pickling system cleaning solution is 0.25%.

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