Membrane cleaning method and cleaning system adopting normal-pressure-low-pressure cyclic cleaning

Abstract

The invention relates to a membrane cleaning method and cleaning system capable of circularly cleaning under normal pressure and low pressure, and the membrane cleaning method comprises the following steps: S1, infiltration: filling a cleaning solution into pores of a membrane module to be cleaned under first air pressure; and S2, low-pressure gassing cleaning: reducing the air pressure in the sealed space from the first air pressure to the second air pressure, and separating out the soluble gas. And S3, re-pressing vibration cleaning is conducted, specifically, the air pressure is increased to third air pressure, and the cleaning liquid generates violent vibration. Wherein the first air pressure and the third air pressure are respectively greater than the second air pressure, and the pressure difference between the first air pressure and the second air pressure is not less than 0.01 Mpa. The low-pressure gassing-re-pressing oscillation operation in the steps S2-S3 is executed for at least one time until the membrane cleaning target is completed. The technical problems that in the prior art, a membrane cleaning method adopting gas cleaning is low in cleaning efficiency, the membrane damage risk is high, and pollution is possibly caused to the environment can be solved.

Description

Technical Field

[0001] This invention relates to the field of membrane cleaning technology, and in particular to a membrane cleaning method and system employing atmospheric pressure-low pressure recirculating cleaning. Background Technology

[0002] Membrane separation technology, due to its advantages such as high efficiency, energy saving, and mild operating conditions, has been widely used in water treatment, food, pharmaceuticals, and biochemical industries. However, during the operation of membrane separation, pollutants such as suspended particles, colloids, dissolved organic matter, and microorganisms in the materials being treated will inevitably be adsorbed and deposited on the membrane surface and inside the membrane pores, leading to membrane fouling. This not only causes problems such as continuous decline in membrane flux, increased transmembrane pressure difference, and decreased membrane separation performance, but also significantly shortens the membrane's lifespan and increases the operating energy consumption and maintenance costs of the membrane separation system. Therefore, efficient and economical membrane cleaning technology is key to ensuring the stable operation of membrane separation processes and promoting their further development.

[0003] Currently, mainstream membrane cleaning technologies can be mainly divided into chemical cleaning, physical cleaning, and physical-chemical synergistic cleaning, which is a combination of the two.

[0004] 1. Chemical Cleaning Method: This is the most widely used cleaning method in existing technology. Chemical cleaning agents such as acids, alkalis, oxidants, and surfactants are added to the cleaning solution, causing reactions such as dissolution, hydrolysis, complexation, and saponification with contaminants on the membrane, thereby removing the contaminants. For example, CN106110895B discloses a method for cleaning ultrafiltration membranes used to treat oilfield produced water, which combines acid washing and alkaline washing to maintain membrane performance. While these chemical agents can achieve good cleaning results, they also have significant limitations: First, the large amount of chemical agents added makes these cleaning methods costly and requires substantial investment. Second, these chemicals can cause irreversible chemical damage to the membrane material, leading to permanent degradation of membrane performance. Furthermore, chemical cleaning generates a large amount of complex waste liquid, which, if not properly treated, can cause secondary environmental pollution and requires complex post-treatment before normal discharge.

[0005] 2. Physical Cleaning Methods: The core of physical cleaning methods is generally to utilize the shearing and impact effects of hydraulics or aerodynamics to remove contaminants and clean the membrane. Hydraulic cleaning typically involves increasing the water flow velocity or introducing a reverse flow, using the shear force of the water to wash the membrane surface. Examples include patents such as WO2022232691A1. However, this simple hydraulic cleaning has very limited effectiveness in removing stubborn contaminants tightly bound to the membrane surface and blockages within the membrane pores. To achieve sufficient cleaning results, a large amount of energy is usually required to generate strong shear force, which is energy-intensive and may damage the membrane, thus limiting its use. In practice, hydraulic cleaning is often combined with other cleaning methods to achieve a comprehensive cleaning effect (such as adding chemical agents like acids or alkalis to the cleaning solution).

[0006] Gas cleaning generally builds upon hydraulic cleaning by utilizing gas pulses and bubble sweeping. The gas pulse method involves periodically introducing pressurized gas into the membrane system, using the energy released by gas expansion and the agitation of the bubbles to clean the membrane surface. For example, patent EP1585590A2 proposes cleaning through short-duration pressurized gas release. However, this method is highly dependent on gas pressure, pulse frequency, and duration, requiring a complex control system and high energy input to maintain sufficient agitation intensity. Furthermore, the complexity and operating cost of this cleaning system are also high.

[0007] Bubble scouring typically introduces gas into the cleaning fluid through pressurization. As the cleaning fluid leaves the pressurized environment, it generates numerous bubbles during flow. These bubbles, generated and rising, create hydrodynamic disturbances as they flow through the membrane module, effectively stripping away contaminants. However, this method relies on a single pressure drop for gas release, resulting in spontaneous and localized bubble release. This leads to uneven cleaning distribution on the membrane surface, poor permeability, and insufficient removal of deeply deposited contaminants. Even when combined with hydraulic scouring, it fails to achieve adequate deep cleaning. Furthermore, existing technologies primarily depend on the macroscopic disturbances generated by a single gas release, resulting in relatively low cleaning efficiency.

[0008] Therefore, there is an urgent need in the field for a membrane cleaning method that causes less damage to the membrane, is less dependent on chemical agents, is environmentally friendly, and can achieve efficient and rapid cleaning. Summary of the Invention

[0009] (a) Technical problems to be solved

[0010] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a membrane cleaning method and system using atmospheric pressure-low pressure recirculating cleaning, which solves the technical problems of low cleaning efficiency, high risk of membrane damage and potential environmental pollution of the prior art using gas membrane cleaning methods.

[0011] (II) Technical Solution

[0012] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0013] In a first aspect, the present invention provides a membrane cleaning method employing atmospheric pressure-low pressure cyclic cleaning, characterized by comprising the following steps:

[0014] S1: Wetting: Under the first pressure, the cleaning solution fills the pores of the membrane module to be cleaned, resulting in a wetted membrane module; the cleaning solution is a gas-containing solution containing dissolved soluble gas; under the first pressure, the gas saturation of the dissolved soluble gas in the cleaning solution is not less than 60%;

[0015] S2: Low-pressure gas evolution cleaning: The gas pressure in the sealed space is reduced from the first gas pressure to the second gas pressure, causing the gas in the cleaning liquid distributed in the membrane module to explode and nucleate, thereby achieving low-pressure gas evolution cleaning of the membrane module.

[0016] S3: Re-pressure oscillation cleaning: The air pressure in the sealed space is increased to the third air pressure, causing the residual bubbles in S2 to break and the cleaning fluid to oscillate, thus achieving re-pressure oscillation cleaning;

[0017] Among them, the first pressure and the third pressure are greater than the second pressure, and the pressure difference between them and the second pressure is not less than 0.01 MPa;

[0018] The low-pressure gas evolution-repressurization oscillation operation of S2-S3 above shall be performed at least once until the membrane cleaning target is achieved.

[0019] According to a preferred embodiment of the present invention, in S1, the membrane module is filled with cleaning liquid by immersion or rinsing; the first gas pressure is 0.08-0.105 MPa; and the gas saturation of soluble gas in the cleaning liquid is 85%-100%.

[0020] The cleaning solution includes a solvent and a soluble gas; the Bunsen coefficient of the soluble gas in the solvent is not less than 0.6 under the conditions of 101.325 kPa and 0℃.

[0021] According to a preferred embodiment of the present invention, in S1, the solvent is water; the soluble gas is at least one of carbon dioxide, ozone, ammonia, and sulfur dioxide.

[0022] According to a preferred embodiment of the present invention, in S1, before immersion, a soluble gas is introduced into the sealed space so that the partial pressure of the soluble gas in the sealed space is not less than 0.08 MPa; the volume occupied by the membrane module to be cleaned and the cleaning liquid does not exceed 50% of the volume of the sealed space.

[0023] According to a preferred embodiment of the present invention, in S2, the air pressure in the sealed space is reduced by evacuation; in S3, the air pressure in the sealed space is increased by introducing soluble gas into the sealed space, and the soluble gas is dissolved in the cleaning liquid distributed in the membrane module (5) to complete the regeneration of the cleaning liquid; the soluble gas introduced into the sealed space is newly introduced soluble gas and / or the soluble gas extracted in S2.

[0024] According to a preferred embodiment of the present invention, in S2, the rate of decrease of the air pressure in the sealed space is 0.004-0.02 MPa / s; the second air pressure is 0.02-0.08 MPa.

[0025] In S3, the pressure increase rate within the sealed space is 0.01-0.02 MPa / s; the third pressure is 0.08-0.105 MPa.

[0026] The third pressure is greater than the second pressure, and the pressure difference between the third pressure and the second pressure is not less than 0.03 MPa.

[0027] According to a preferred embodiment of the present invention, the cleaning fluid is replaced in the sealed space every 1-3 cycles of S2-S3.

[0028] In a second aspect, the present invention also provides a cleaning system for implementing any of the membrane cleaning methods in the first aspect, comprising a cleaning chamber, a gas-liquid mixing device, a gas supply device, and a gas pressure regulating device.

[0029] The gas-liquid mixing device, the gas supply device, and the gas pressure regulating device are respectively connected to the cleaning chamber; the gas supply device is also connected to the gas supply device.

[0030] The cleaning chamber provides a sealed space for containing the cleaning fluid and membrane modules; the pressure regulating device is used to controllably increase or decrease the pressure in the sealed space; the gas-liquid mixing device is used to supply the sealed space with the cleaning fluid containing soluble gas; and the gas supply device is used to supply the sealed space and the gas-liquid mixing device with soluble gas.

[0031] According to a preferred embodiment of the present invention, the air pressure regulating device includes an air extraction module, an air storage module, and an injection module connected in sequence; the air extraction module is connected to the cleaning chamber and is used to extract gas from the cleaning chamber; the air storage module is used to store the gas extracted by the air extraction module; the injection module is connected to the cleaning chamber and is used to pressurize the gas stored in the air storage module and inject it into the cleaning chamber.

[0032] According to a preferred embodiment of the present invention, a water supply device is also included; the water supply device is connected to the gas-liquid mixing device and is used to provide the solvent required for the cleaning liquid to the gas-liquid mixing device; the cleaning chamber is also provided with a stirring unit for promoting the flow of liquid in the cleaning chamber and a gas injection unit for injecting soluble gas; the gas injection unit is connected to the gas supply device and the injection module respectively.

[0033] (III) Beneficial Effects

[0034] The beneficial effects of this invention are as follows: This invention provides a membrane cleaning method and system employing atmospheric pressure-low pressure recirculating cleaning. By using a method where soluble gas is dissolved in a solvent to form a cleaning solution under the same pressure, and then the cleaning solution is filled into the membrane module to be cleaned for wetting, this invention significantly improves the penetration depth and uniformity of soluble gas molecules compared to existing technologies. This allows soluble gas to penetrate deeply into the membrane pores and fouling layer in molecular form, providing sufficient and deep nucleation sites for subsequent low-pressure gas evolution cleaning. This enhances the cleaning effect during subsequent low-pressure gas evolution cleaning and avoids problems such as cleaning blind spots and insufficient cleaning depth caused by uneven bubble distribution or insufficient permeability.

[0035] Meanwhile, this invention also employs a pressure reduction method, causing the gas in the cleaning solution to rapidly generate microbubbles around the membrane module as the nucleation center. The membrane module is then cleaned through high-frequency local disturbances and shear forces generated by the merging, expansion, and quenching of these bubbles. Compared to existing technologies, this method, which uses microscale bubbles to simultaneously generate (or generate in large quantities within a short time) and quench (burst) a large number of bubbles within the membrane pores, directly destroys the contaminant adhesion structure, achieving efficient contaminant removal and realizing efficient, thorough, and uniform membrane cleaning. Furthermore, this method avoids the potential damage to the membrane material caused by chemical cleaning agents, high-pressure gas, or water flow impacts, and avoids the generation of complex chemical waste liquids, reducing membrane cleaning costs and preventing environmental pollution caused by complex waste cleaning solutions.

[0036] Furthermore, since this invention also re-dissolves soluble gases in the solvent and increases the pressure through re-pressure oscillation cleaning, it can simultaneously regenerate the cleaning solution and perform a secondary cleaning of the membrane module using residual bubbles and fluid backflushing. Compared to existing technologies, the reuse of the cleaning solution significantly reduces the amount of soluble gases and solvents consumed during cleaning, further reducing the cleaning cost of the membrane cleaning method. Moreover, utilizing the low pressure generated in the previous low-pressure gas evolution cleaning, this invention can also regenerate the cleaning solution and perform secondary cleaning of the membrane module with lower energy consumption during the re-pressure oscillation cleaning process. This allows the invention to achieve better cleaning results with lower energy consumption and realize cleaning solution regeneration, further reducing the cleaning and operating costs of the membrane cleaning method, improving energy utilization, and achieving more efficient, green, and energy-saving membrane cleaning. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the membrane cleaning method of the present invention, which employs atmospheric pressure-low pressure recirculating cleaning.

[0038] Figure 2 This is a schematic diagram of the cleaning chamber in the cleaning system of Embodiment 1 of the present invention.

[0039] [Explanation of Labels in the Attached Image]

[0040] 1: Cleaning chamber; 2: Liquid inlet; 3: Gas injection unit; 4: Pressure gauge; 5: Membrane module. Detailed Implementation

[0041] To better explain and facilitate understanding of the present invention, a detailed description of the invention is provided below with reference to the accompanying drawings and specific embodiments. In this document, directional terms such as "upper," "lower," etc., are used interchangeably with other directional terms. Figure 2 The orientation is used as a reference.

[0042] The invention provides a membrane cleaning method using atmospheric pressure-low pressure recirculating cleaning, comprising the following steps:

[0043] S1: Wetting: Under the first pressure, the cleaning solution fills the pores of the membrane module 5 to be cleaned, resulting in a wetted membrane module 5. The cleaning solution is a gas-containing solution containing dissolved gases. Under the first pressure, the gas saturation of the dissolved gases in the cleaning solution is not less than 60%.

[0044] In S1, through thorough immersion, the gas-rich cleaning solution can better penetrate into the pores of the membrane module 5, ensuring that it can penetrate into the inner layer of the fouling layer, the tiny pores of the membrane, and even smaller membrane pores. This allows the gas molecules (soluble gases) contained within to enter the membrane module 5 along with the cleaning solution, and to penetrate evenly into the tiny pores of the membrane module 5. This ensures that during the subsequent low-pressure gas separation cleaning process in S2, bubbles can be generated evenly and comprehensively within the membrane module 5, enabling thorough cleaning of the membrane module 5.

[0045] It is important to emphasize that, because the soluble gas in the cleaning solution permeates under initial pressure, it does not generate bubbles due to pressure changes during its wetting of membrane module 5. This ensures that the soluble gas, in the form of dissolved gas molecules, permeates evenly into the micropores of the membrane and into the contaminants within membrane module 5. This prevents premature bubble formation and ensures that the uniformly dispersed gas molecules can subsequently generate bubbles within the membrane pores and contaminants for comprehensive cleaning. If bubbles are generated during the entry process, the resulting disturbance may prevent sufficient wetting of the soluble gas, resulting in insufficient gas retention for subsequent cleaning and inadequate bubble generation within the pores of membrane module 5. Simultaneously, the saturation of the soluble gas needs to be controlled. Insufficient dissolved gas in the cleaning solution will prevent the generation of enough bubbles for subsequent cleaning, thus failing to achieve a sufficient cleaning effect. Conversely, oversaturation of the soluble gas should be avoided to prevent bubble generation and impaired permeation efficiency.

[0046] It should be further noted that the soluble gas can be directly dissolved into the cleaning solution at the first pressure, or a higher pressure can be used to assist in the dissolution of the soluble gas into the cleaning solution. This ensures that the cleaning solution remains stable during wetting of the membrane module, preventing the generation of a large number of bubbles and allowing sufficient permeation of the soluble gas. More preferably, the soluble gas can be directly dissolved into the cleaning solution at the first pressure. Dissolving and permeating the soluble gas under the same pressure further reduces the bubbles that may be generated during the flow and permeation of the cleaning solution, avoiding problems such as premature gas precipitation, improving the wetting effect, and reducing the complexity of pressure control. S2: Low-pressure gas separation cleaning: The pressure in the sealed space is reduced from the first pressure to the second pressure.

[0047] The decrease in gas pressure causes the gas in the cleaning fluid distributed in membrane module 5 to undergo explosive nucleation with membrane module 5 as the nucleation center (heterogeneous nucleation with membrane surface defects as the nucleation center), generating a large number of tiny bubbles on the surface and within the pores of membrane module 5 (the size of these bubbles is generally 0.1–10 micrometers or smaller, and generally does not exceed 100 micrometers). These bubbles further merge, expand, and / or quench, generating microjets. Since the bubbles are generated directly on the surface and within the pores of membrane module 5, during this process, these bubbles generate strong local high-frequency disturbances and burst shear forces on contaminants such as grease and colloids attached to the membrane surface and pores. This can quickly and effectively destroy the attachment structure of contaminants (such as organic gel layers, inorganic scale layers, or organic-inorganic composite fouling layers), tearing and peeling the contaminants from the membrane surface and pores. Meanwhile, the impact of this microscopic, localized disturbance and shearing is relatively small, confined to the microscopic scale. The intensity of the disturbance and shearing is far lower than that of high-speed water or gas impacts, and will not cause significant damage to the membrane structure, thus better maintaining membrane performance and greatly reducing damage to the membrane during cleaning. Furthermore, this high-frequency disturbance also generates a certain frequency of turbulent fluid, which, combined with the microjets generated by bubble bursting, can further flush and impact the fouling layer, making it easier to detach.

[0048] Furthermore, as the bubbles continuously move and diffuse to the outside (moving from the liquid phase to the gas phase under pressure changes and density differences), the large number of bubbles generated in the membrane module 5 can also adhere to / encapsulate and carry away the pollutants stripped from the membrane module 5, allowing them to detach from the pollutants and enter the cleaning liquid, thus achieving low-pressure gas separation cleaning of the membrane module 5.

[0049] S3: Re-pressure oscillation cleaning: The air pressure in the sealed space is rapidly increased to the third air pressure, causing the residual bubbles in S2 to burst instantly (within a few seconds or even one second) when the air pressure is increased, causing the cleaning liquid to oscillate violently, thus achieving re-pressure oscillation cleaning; after the pressure is increased to the third air pressure (or after the oscillation ends), the third pressure is maintained, and the sealed environment is maintained for a certain period of time, so that the soluble gas can be fully dissolved into the cleaning liquid distributed in the membrane module (5), thus completing the regeneration of the cleaning liquid.

[0050] At the end of S2 and during S3, under the rapid dissolution of new soluble gas and the rapid increase in gas pressure, the unruptured bubbles remaining in membrane module 5 will undergo further rapid dissolution and bursting during this process, which will again cause the soluble gas molecules and solvent molecules to undergo violent oscillation and shearing. This fluid combination of bursting, vibration, shearing and backflushing will jointly perform a second cleaning of the membrane, further improving the cleaning effect of the membrane cleaning method of the present invention on the membrane.

[0051] Furthermore, due to the use of soluble gases, during the pressure increase and maintenance process, both newly added soluble gases in the sealed space and those remaining in the solvent and sealed space can easily and quickly redissolve into the solvent, reforming the cleaning solution and resetting its cleaning capacity. This allows it to be used in subsequent cycle cleaning or cleaning of other membrane modules 5. This repeated use of soluble gases and solvents further reduces the repeated cleaning costs of the membrane cleaning process of this invention, eliminating the need to invest in and consume excessive amounts of solvents and soluble gases.

[0052] Secondly, during the repressurization and gas dissolution process, the fluid backflushing effect caused by the pressure rise can also drive the solvent and soluble gas (such as the soluble gas remaining in the sealed space after S2, the bubbles remaining in the membrane module 5, the recycling or new soluble gas, etc.) to flow in reverse into the membrane module 5 through the pressure gradient (after S2, a local low-pressure environment will be formed inside the membrane module 5). This efficiently flushes out the pollutants that have been decomposed, loosened or peeled off from the membrane module 5 from the membrane pores or gaps of the membrane module 5 and further carries them out of the membrane pores and channels, ensuring the internal cleanliness of the membrane module 5 and avoiding problems such as secondary deposition of the peeled pollutants.

[0053] Furthermore, it should be noted that when the re-pressure oscillation cleaning begins, the air pressure in the sealed space is a relatively low second air pressure. Under the action of the low second air pressure, it is not necessary to spend much energy to raise the air pressure in the sealed space to the third air pressure. The re-pressure oscillation cleaning process can be easily completed without consuming too much energy, which can further reduce the energy consumption required for the film cleaning method of the present invention and reduce the cleaning cost.

[0054] It is important to note that the first and third pressures are both greater than the second pressure, and the pressure difference between them is not less than 0.01 MPa, preferably not less than 0.2 MPa. This sufficiently large pressure difference ensures that in step S2, sufficient soluble gas is released and forms bubbles during the pressure reduction process, avoiding problems such as insufficient gas release or insufficient release volume that might occur with a smaller pressure difference, thus ensuring effective cleaning. Simultaneously, the sufficiently large pressure difference ensures the reflux of liquid and gas in step S3, as well as the disintegration of residual bubbles, ensuring thorough secondary cleaning, effectively removing the stripped contaminants, and allowing readily soluble gases to fully dissolve in the solvent.

[0055] The low-pressure gas evolution-repressurization oscillation operation of S2-S3 above shall be performed at least once until the membrane cleaning target is achieved.

[0056] After performing a single S2-S3 gas evolution-dissolved gas cleaning cycle, steps S2-S3 can be selectively repeated for cyclic cleaning, depending on the degree of membrane fouling after cleaning. During cyclic cleaning, building upon the microscopic channels created in the initial cycle, the fresh, gas-rich cleaning solution can penetrate deeper into the inner layer of the fouling layer and into smaller membrane pores, resulting in a deeper and more complete cleaning. With repeated cycles, the precipitated microbubbles will also generate and collapse deeper into the fouling layer and at more microscopic defects, effectively breaking down large fouling layers into smaller, transportable particles. It is important to note that the number of cycles is not a fixed value, but rather the physical criterion for termination is that the cleaning effect tends to stabilize. Specifically, the predetermined cleaning target can be confirmed based on apparent characteristics such as whether the turbidity of the cleaning solution in the sealed space or the discharged cleaning solution no longer increases, and whether the membrane's pure water flux (membrane flux) recovery rate reaches 80%-100% of its original level, and then it can be determined whether to terminate the cyclic cleaning process.

[0057] Because this invention can regenerate the cleaning solution through repeated pressure and oscillation cleaning, it greatly restores the cleaning ability of the cleaning solution. Furthermore, the membrane cleaning method of this invention causes minimal damage to the membrane, eliminating concerns about severe damage to the membrane module 5 from repeated cleaning. This invention can perform cyclic cleaning through multiple cycles in the S2-S3 manner, better restoring membrane flux while maintaining the integrity of the membrane structure, achieving a high cleaning effect. During the circulation process, the cleaning solution and its soluble gases can be reused, further reducing the investment required to achieve the desired cleaning effect and lowering cleaning costs.

[0058] Furthermore, it should be noted that, due to the superior cleaning efficiency and effectiveness of the membrane cleaning method of this invention, in most cases, membrane cleaning using this invention does not require circulation (i.e., only one S2-S3 process is needed to complete the membrane cleaning and achieve a good cleaning effect, restoring membrane flux. Only when dealing with certain difficult-to-treat membranes (such as membranes that have not been cleaned for a long time, membranes with long-term fouling and extremely strong hydrophobicity, membranes with special types of pollutants that are extremely tightly bound to the membrane) or when extremely deep cleaning is required, multiple circulations may be necessary to achieve a higher and more comprehensive cleaning effect.

[0059] This invention employs a method of dissolving soluble gas in a solvent under a first pressure to form a cleaning solution. This ensures that the gas in the cleaning solution is uniformly distributed in the liquid at the molecular level. While achieving efficient dissolution, it also prevents premature bubble formation, ensuring that during wetting, the soluble gas can deeply penetrate the membrane pores and the interior of the contaminant layer in molecular form, providing sufficient and deep nucleation sites for subsequent low-pressure gas evolution. Compared to existing technologies that rely solely on hydraulic rinsing or single gas evolution, this invention, by dissolving and wetting the gas under the same pressure, significantly improves the penetration depth and uniformity of gas molecules, enhancing the cleaning effect during subsequent low-pressure gas evolution cleaning and avoiding problems such as cleaning blind spots and insufficient cleaning depth caused by uneven bubble distribution or insufficient penetration.

[0060] Meanwhile, this invention also employs a pressure reduction method, causing the gas in the cleaning fluid to rapidly generate microbubbles around the membrane module 5 as the nucleation center. The membrane module 5 is then cleaned through high-frequency local disturbances and shear forces generated by bubble merging, expansion, and quenching. Compared to traditional gas cleaning methods, this method, which uses microscale bubbles to simultaneously generate and burst within the membrane pores, directly destroys the contaminant adhesion structure, achieving more efficient contaminant removal. It achieves good cleaning results without the need for chemical agents or high-speed impact, avoiding the potential damage to the membrane material caused by chemical cleaning, high-pressure gas, or water flow impact. Furthermore, since the bubbles are generated simultaneously within the membrane pores, it also solves the problem of low cleaning efficiency caused by uneven bubble distribution or insufficient bubble penetration in existing technologies, resulting in a significant improvement in cleaning efficiency. Simultaneously, since no chemical agents are required, this invention also avoids the problem of generating complex chemical waste liquids, reducing the treatment cost of membrane cleaning.

[0061] Furthermore, since this invention also re-dissolves soluble gases in the solvent and increases the pressure through re-pressure oscillation cleaning, while regenerating the cleaning solution, it utilizes residual bubbles and fluid backflushing to perform a secondary cleaning of the membrane module 5. Compared with the prior art, the reuse of the cleaning solution can significantly reduce the amount of soluble gases and solvents consumed during cleaning, further reducing the cleaning cost of the membrane cleaning method of this invention. Moreover, by utilizing the low pressure formed in the previous low-pressure gas evolution cleaning, this invention can regenerate the cleaning solution and perform a secondary cleaning of the membrane module 5 with lower energy consumption during the re-pressure oscillation cleaning process. This allows the invention to achieve a better cleaning effect with lower energy consumption and realize the regeneration of the cleaning solution, further reducing the cleaning and operating costs of the membrane cleaning method of this invention, improving energy utilization, and further achieving efficient, green, and energy-saving membrane cleaning.

[0062] Preferably, in S1, the cleaning solution includes a solvent and a soluble gas. In S1, the present invention does not have special requirements regarding the order in which the cleaning solution and the membrane module 5 to be cleaned are placed into the sealed space, the mixing order, or when the sealed space is sealed. This ensures that the sealed space is sealed before the pressure is reduced in S2, the pores in the membrane module 5 are fully filled with the cleaning solution, and the molecules of the soluble gas can deeply penetrate into the membrane module 5, thus enabling effective and uniform low-pressure gas separation cleaning.

[0063] Preferably, in step S1, the membrane module 5 is filled with cleaning fluid by soaking or rinsing. Specifically, soaking involves completely immersing the membrane module 5 in an aerated cleaning fluid, utilizing hydrostatic pressure and capillary action to ensure the cleaning fluid penetrates all membrane pores and complex flow channels, achieving thorough wetting. This method has high practicality and applicability. Rinsing involves spraying the cleaning fluid to evenly cover and flow over the membrane surface and interior, achieving the same effective filling purpose. This method is generally suitable for large-scale or fixed-installation membrane systems requiring continuous operation. Of course, other types of membrane modules 5 can also be treated in actual operation, depending on the specific circumstances.

[0064] In this invention, there is no strict requirement regarding the timing of dissolving the soluble gas in the cleaning solution. The soluble gas in the cleaning solution can be pre-dissolved in the solvent, or it can be prepared by dissolving the soluble gas in the solvent during the mixing of the solvent and membrane module 5. Specifically, the cleaning solution can be prepared by first mixing the solvent and the soluble gas, and then mixing and sealing the cleaning solution with the membrane module 5 for wetting. Alternatively, the membrane module 5 can be placed in a sealed space, mixed with the solvent, and then the soluble gas can be dissolved in the solvent to form the cleaning solution for wetting.

[0065] More preferably, the soluble gas in the cleaning solution is pre-dissolved in the solvent. After the soluble gas is dissolved in the solvent to form the cleaning solution, the cleaning solution is then filled into the pores of the membrane module 5. This method can more effectively improve the wetting effect of the soluble gas, allowing the soluble gas molecules to better penetrate into the membrane module 5 and ensuring the cleaning effect.

[0066] More preferably, by immersing the membrane module 5 in cleaning solution, the membrane module 5 is completely submerged in the cleaning solution during immersion. This ensures sufficient wetting while providing more soluble gas, further ensuring thorough cleaning of the membrane module 5 and guaranteeing the cleaning effect.

[0067] In addition, it should be noted that the cleaning solution regenerated after cleaning one membrane module 5 can be used as the cleaning solution for cleaning another membrane module 5 and reused. However, it is necessary to confirm the concentration of contaminants in the cleaning solution to ensure that it can still effectively clean. If the concentration of contaminants is too high, it cannot be reused.

[0068] In practical operation, the cleaning effect can be achieved as long as the magnitude of the first air pressure is sufficient to satisfy the difference between the first and second air pressures. However, considering issues such as the stability of the cleaning effect, the first air pressure is preferably 0.08-0.12 MPa, more preferably 0.08-0.105 MPa, or the local atmospheric pressure. Within the conventional air pressure range of 0.08-0.105 MPa, soluble gases generally exhibit high dissolution rates and solubility. Furthermore, this pressure range can be achieved and controlled in conventional equipment, eliminating the need for complex high-pressure systems and reducing equipment costs and operational risks associated with using this invention.

[0069] More preferably, atmospheric pressure, or local atmospheric pressure, is preferred. Atmospheric pressure is generally in the range of 0.08-0.105 MPa (in some high-altitude areas, the pressure may drop below 0.8, and in some high-pressure weather conditions, it may rise above 0.105), allowing for relatively rapid dissolution. Choosing atmospheric pressure as the first pressure eliminates the need for pressurized gas dissolution processes in S1; soluble gases can be dissolved directly under atmospheric pressure, yielding a cleaning solution with good cleaning effect without pressure control. The dissolution process does not require high energy expenditure for gas dissolution, significantly reducing the cleaning cost of the present invention. In the subsequent S2 process, simply reducing the pressure from atmospheric pressure to create a low-pressure environment achieves a good cleaning effect.

[0070] It should be noted that if the local atmospheric pressure is too low due to geographical reasons (such as below 0.6 MPa), the pressure can be appropriately increased to control the air pressure in the sealed space within the range of 0.08-0.105 MPa, which facilitates the dissolution of soluble gases and ensures sufficient cleaning effect.

[0071] Preferably, in S1, the gas saturation of soluble gas in the cleaning fluid is 85%-100%. Higher saturation further ensures that the cleaning fluid contains sufficient soluble gas, ensuring that in S2, the cleaning fluid has a sufficiently high supersaturation when the pressure is reduced, thereby triggering intense and dense bubble nucleation. Through the high-density bubble group, the cleaning area is increased and stronger disturbance is generated, thereby improving the cleaning intensity of S2 and improving the cleaning effect.

[0072] Preferably, the soluble gas used in this invention has a Bunsen coefficient of not less than 0.6 in a solvent at 101.325 kPa and 0°C. That is, under standard atmospheric pressure, the volume of the soluble gas that can dissolve in 1 unit volume (cubic meter) of liquid (solvent) is not less than 0.6 cubic meters, with units of standard cubic meters per cubic meter (dimensionless). More preferably, the Bunsen coefficient of the soluble gas in a solvent at 101.325 kPa and 0°C is not less than 1.7. By controlling the volume of the soluble gas dissolved in the solvent, it is further ensured that more bubbles are generated during low-pressure gas evolution, further ensuring the effectiveness of low-pressure gas evolution cleaning.

[0073] Note that in this invention, a mixture of gases with small Bunsen coefficients (such as gases with a Bunsen coefficient of less than 0.6 or even smaller) can be used as soluble gases. The sum of their Bunsen coefficients can be greater than 0.6 or larger. However, when using them, it is necessary to ensure that the saturation of these gases in the cleaning solution is not less than 85% to ensure that a large number of bubbles can be generated when performing low-pressure gas evolution.

[0074] More preferably, in S1, the solvent is water, which has higher environmental friendliness and lower cost, and wider applicability. The soluble gas is at least one of carbon dioxide, ozone, ammonia, sulfur dioxide, and chlorine dioxide, preferably at least one of carbon dioxide and ozone, and more preferably carbon dioxide. Among them, carbon dioxide and ozone have high dissolution rates and good solubility, and can dissolve into the solvent at a faster rate, increasing the gas dissolution rate in S1 and S3 and improving the treatment efficiency. At the same time, these gases themselves can also act as chemical agents, forming a weakly acidic / low-oxidizing environment in the cleaning solution. While improving the cleaning effect in synergy with bubbles, this weakly acidic and low-oxidizing environment also causes less damage to the membrane and will not cause significant damage to the membrane. When carbon dioxide is selected as the soluble gas, it has a high Bunsen coefficient (1.7), which can generate more bubbles. At the same time, as a gas with a high content in the air, carbon dioxide is not only cheaper, but also does not cause any pollution to the environment, which can further improve the environmental friendliness of the membrane cleaning method of the present invention and reduce its cost.

[0075] In addition, gases such as ammonia, sulfur dioxide, and chlorine dioxide, which have high Bunsen coefficients but may produce strong acid, strong alkali, or highly corrosive environments when dissolved in water, should be selected. When using these gases, their saturation should be further controlled to 60%-70%, preferably 60%-65%. Excessive use of these gases should be avoided as it could lead to a cleaning solution with strong acid, strong alkali, or strong corrosiveness, and the generation of chemical waste should also be prevented. These gases should only be used to create a weak acid / alkali / oxidizing environment to assist in cleaning.

[0076] Preferably, in step S1, during or before impregnation, a soluble gas is introduced into the sealed space to ensure that the partial pressure of the soluble gas in the sealed space is not less than 0.08 MPa. This higher partial pressure of the soluble gas ensures that a large amount of soluble gas does not escape into the gas phase environment of the sealed space during impregnation, ensuring uniform distribution of the soluble gas in the cleaning solution and avoiding problems such as local oversaturation or insufficient dissolution.

[0077] The volume occupied by the membrane module 5 to be cleaned and the cleaning liquid does not exceed 50% of the sealed space volume, and the volume occupied by the gas is not less than 50% of the sealed space volume. A sufficiently large gas phase space (>50% of the total volume) ensures that during the depressurization in S2 and the pressurization in S3, even a small change in gas volume can cause a rapid and significant change in system pressure. This further ensures efficient and rapid pressure regulation and circulation in the method of this invention, shortening the pressure regulation and circulation cycle time and improving cleaning efficiency. Simultaneously, the large gas phase space also serves as a buffer space, facilitating the maintenance of a relatively stable concentration of soluble gases in the gas phase during the pressure regulation and circulation process of S2-S3. This avoids drastic fluctuations in gas phase partial pressure caused by the precipitation or dissolution of gases in the liquid phase, thereby ensuring the stability of each pressure regulation and circulation, and facilitating precise control of parameters such as the pressure change rate.

[0078] Furthermore, it should be noted that this invention does not have strict requirements regarding the specific composition of the gas phase in the sealed chamber or the specific gas composition dissolved in the cleaning fluid, as long as the content of soluble gases meets the cleaning requirements. Both the gas phase and the cleaning fluid can contain gases other than soluble gases, such as oxygen and nitrogen. During low-pressure gas evolution operations, these gases can also generate bubbles, contributing to the cleaning effect. However, the amount of dissolved gas in these gases is generally less than that of soluble gases, and their contribution to the cleaning process is relatively small. Therefore, soluble gases are needed to ensure the cleaning effect.

[0079] More preferably, S1 also includes a pressure-enhancing impregnation process: when the membrane module 5 to be cleaned is impregnated with the cleaning solution, the air pressure in the sealed space is controlled to the fourth air pressure and maintained for a certain period of time. By adjusting the pressure in the sealed space, the cleaning solution is encouraged to penetrate into the pores of the membrane module 5, improving the impregnation effect and speed, and ensuring that the cleaning solution fully impregnates the membrane. After impregnation is completed, the air pressure in the sealed space is restored to the first air pressure. After confirming that no bubbles are generated, S2 is performed, or S2 is directly connected after impregnation is completed. The pressure-enhancing impregnation process can further improve the impregnation effect of the cleaning solution in S1. It should be clearly stated that the pressure-enhancing impregnation process is not a necessary step. In actual processing, pressure-assisted materials are generally suitable for membrane modules 5 with strong hydrophobicity and extremely poor water permeability, used to accelerate the impregnation speed of the membrane cleaning method of the present invention for these types of membranes. Even without the pressure-enhancing impregnation process, the cleaning solution in S1 can fully impregnate these types of membranes, only the impregnation speed is slower, and a similar impregnation effect can be achieved.

[0080] Meanwhile, the higher pressure difference between the fourth and second gas pressures after the pressurized immersion treatment can further improve the solubility and gas saturation of soluble gases in the solvent, and further improve the cleaning effect of low-pressure gas separation cleaning, but it will lead to problems such as increased energy consumption.

[0081] In addition, it should be noted that the duration and specific pressure of the pressurized immersion treatment need to be determined based on the actual immersion conditions, ensuring that membrane module 5 is fully immersed. Whether the membrane module is fully immersed depends on the type of membrane used (e.g., whether it is a hydrophobic membrane), the membrane porosity, and whether the membrane is spread, coiled, or in other states.

[0082] More preferably, the pressure of the fourth gas pressure is not lower than that of the first gas pressure, and the difference is 0-0.2 MPa, more preferably 0-0.1 MPa. The difference between the increased fourth gas pressure and the first gas pressure does not need to be too large, just enough to allow sufficient contact between the cleaning fluid and the difficult-to-penetrate membrane module 5. Excessive fourth gas pressure may lead to excessive energy consumption and energy waste.

[0083] More preferably, the fourth pressure is 0.09-0.13 MPa to avoid problems such as energy waste caused by excessively high fourth pressure.

[0084] Preferably, in step S2, the rate of pressure reduction in the sealed space is 0.005-0.02 MPa / s. The second pressure is 0.02-0.08 MPa, more preferably 0.02-0.06 MPa. Sufficiently low pressure ensures the cleaning fluid reaches a sufficiently high supersaturation ratio, ensuring effective precipitation of soluble gases. If the second pressure is too high (pressure difference too small), the driving force is insufficient, and bubble generation is inadequate. Controlling the pressure reduction rate within the range of 0.005-0.02 MPa / s ensures the cleaning fluid enters a supersaturated state at a relatively rapid rate, thereby inducing uniform and dense explosive nucleation at numerous weak nucleation sites on the membrane surface and within the membrane pores (such as the surface of contaminants and the edges of micropores), forming a high-density microbubble cluster. This results in more uniform interfacial adhesion and stronger disturbance and shearing, significantly improving the uniformity and intensity of cleaning. A rate exceeding 0.02 MPa / s may lead to overly vigorous nucleation, causing bubbles to rapidly merge into larger bubbles. This reduces the effective contact area of ​​the bubbles, hindering thorough cleaning of the membrane pores and potentially causing unnecessary stress damage to certain sensitive membrane structures. Conversely, a low rate of pressure reduction (<0.004 MPa / s) results in a slow increase in the supersaturation of the cleaning solution, which may cause soluble gas precipitation to tend to occur at a small number of specific strong nucleation sites (such as large defects). This leads to fewer and larger bubbles, resulting in a limited and uneven cleaning effect.

[0085] In addition, it should be noted that in S2, the second air pressure of 0.02-0.08 MPa is the optimal range selected based on the cleaning effect, energy consumption, equipment cost, etc. In actual use, a lower air pressure can be used to further increase the number of bubbles generated, thereby improving the membrane cleaning effect, especially for the cleaning effect of membrane module 5 which is more heavily polluted. However, the energy consumption will be significantly increased and a stronger vacuum equipment is required.

[0086] Preferably, in S3, the third air pressure is greater than the second air pressure, and the pressure difference between the third air pressure and the second air pressure is not less than 0.03 MPa. The air pressure increase rate within the sealed space is 0.01-0.02 MPa / s. The larger air pressure difference and higher third air pressure ensure both cleaning and gas dissolution effects in S3. Simultaneously, the faster pressurization rate allows the ambient pressure (air pressure) within the sealed space to quickly exceed the internal pressure of the residual bubbles, accelerating their dissolution process and causing rapid, synchronous collapse of bubbles, especially metastable microbubbles that did not fully grow in S2 (such as bubbles remaining in the pores of membrane module 5). This synchronous collapse generates stronger, more concentrated microjet impacts, resulting in stronger fluid backflushing and improving the cleaning effect of S3.

[0087] More preferably, the rate at which the air pressure increases in S3 is greater than the rate at which the air pressure decreases in S2, further ensuring the bubble bursting effect, improving the cleaning effect in S3, and shortening the processing time.

[0088] Preferably, the third pressure is 0.08-0.105 MPa or the local atmospheric pressure (normal pressure), with the local atmospheric pressure being more preferred. In actual operation, the third pressure can be the same as the first pressure, i.e., normal pressure can be selected. A normal pressure environment is easy to establish and maintain, reducing the difficulty of sealing and controlling the corresponding system using the method of this invention. Furthermore, since soluble gases are selected, at this pressure, the saturation of most soluble gases can quickly recover to a high level, ensuring effective redissolution of the soluble gases, rapidly completing the regeneration of the cleaning fluid, and facilitating the next cycle or reuse.

[0089] Furthermore, it should be noted that in S2-S3, the pressure and pressure change rate of the low-pressure gas evolution and re-pressure oscillating cleaning stages can be adjusted according to the fouling status of membrane module 5. The fouling status of membrane module 5 is determined by analyzing and testing indicators such as the pure water / wastewater flux decay rate (tested through methods such as pure water-wastewater-pure water filtration tests) and the initial fouling index, which will not be elaborated upon in this invention. Depending on the severity of the fouling of membrane module 5, different cleaning modes can be selectively performed. For example, if the water flux recovery rate after the pure water-wastewater-pure water filtration test is 50-80%, the membrane module 5 can be judged as lightly fouled; if the water flux recovery rate is 30-50%, it can be judged as moderately or heavily fouled. Among them, if the fouling level of membrane module 5 is judged to be relatively light, in S2-S3, multiple small-amplitude decreases and increases in air pressure can be selected to perform "high-frequency oscillating flushing". In S2, the pressure is reduced from the first pressure (normal pressure) to 0.04-0.05 MPa (second pressure), and then restored to the third pressure (normal pressure) in S3. This process is repeated multiple times, with rapid and small pressure fluctuations, which repeatedly generate and dissolve bubbles. This creates a certain frequency of turbulent fluid on the membrane surface, flushing away the fouling layer and making it easier to peel off. The small pressure changes further reduce the potential damage to the membrane module 5 during the cleaning process.

[0090] If the membrane module 5 is determined to be heavily fouled, one or more significant pressure reductions and increases can be performed in S2-S3 to clean it using a "rapid depressurization" method. For example, in S2, the first pressure (atmospheric pressure) is reduced to a lower second pressure (e.g., 0.01-0.02 MPa, or even lower or higher, depending on the actual equipment conditions and needs). This rapid depressurization causes the cleaning fluid to instantly reach a highly supersaturated state, resulting in a burst of microbubbles within the membrane pores and fouling layer in a very short time. The synchronous growth and violent collapse of these bubbles generate strong local shear forces and shock waves, sufficient to destroy the tough organic-inorganic composite fouling layer (such as the composite structure of organic gel layer and scale layer). Then in S3, the pressure is rapidly restored, causing some of the undone bubbles to collapse and dissolve again. The fluid backflushing effect caused by the rapid pressure recovery efficiently removes the decomposed and loosened contaminants from the membrane and carries them out of the membrane pores and channels, preventing secondary deposition of the stripped material and laying a better foundation for the next cycle.

[0091] By selecting and coordinating the first and third air pressures in S1 and S3, this invention can construct a complete, repeatable, and low-energy-consumption pressure cycle, which can greatly reduce the energy consumption and control difficulty in the pressure regulation process, and further realize a cyclic, efficient, and low-damage membrane cleaning method.

[0092] The present invention does not specify the method of reducing the air pressure in S2. The air pressure in the sealed space can be changed by extracting the gas in the sealed space or changing (increasing) the volume of the sealed space. However, due to factors such as cost, structural complexity, and stability, it is preferred that the air pressure in the sealed space be reduced by evacuation in S2 (such as actively expelling the gas in the sealed space by using a vacuum pump or other equipment).

[0093] The present invention does not specify the method of increasing the gas pressure in S3. The gas pressure in the sealed space can be changed by injecting gas into the sealed space or changing (reducing) the volume of the sealed space. However, due to factors such as cost, structural complexity, and stability, it is preferred that the gas pressure in the sealed space be increased by introducing soluble gas into the sealed space in S3.

[0094] Preferably, the soluble gas introduced into the sealed space is newly introduced soluble gas and / or the soluble gas extracted in S2. By collecting the gas extracted in step S2 (whose main component is the target soluble gas) and reusing it in the pressurization process of S3, a semi-closed or fully closed gas cycle is constructed, which can greatly reduce the consumption of soluble gas. This is especially true when using gases such as carbon dioxide or ozone, which require on-site preparation or are costly, significantly reducing operating costs and improving the cleaning efficiency and economy of this invention.

[0095] According to a preferred embodiment of the present invention, in S4, the cleaning solution is replaced once every 1-3 cycles or after repeated use of a certain cleaning solution more than 1-3 times. If the loss of soluble gas or severe contamination is significant, new soluble gas should also be replaced or replenished. By replacing the cleaning solution every 1-3 cycles, the liquid environment within the sealed space is ensured to remain clean, thereby guaranteeing the efficient dissolution and precipitation of soluble gas in the liquid phase and ensuring that contaminants stripped from the membrane are quickly removed from the vicinity of the membrane surface, avoiding secondary contamination and maintaining the efficiency and stability of the cleaning process until the membrane cleaning target is completely achieved. Of course, in actual use, if the cleaning solution and the soluble gas therein still have sufficient cleaning effect after 3 cycles or use (e.g., when cleaning a lightly contaminated membrane multiple times, the turbidity of the cleaning solution is generally not too high), the usage cycle (number of uses) can be appropriately extended, such as 3-6 times, as long as the cleaning effect of the cleaning solution is ensured.

[0096] Furthermore, it should be noted that all pressure-related statements mentioned in this invention refer to absolute pressure.

[0097] The present invention also provides a cleaning system for implementing the membrane cleaning method of the present invention, comprising a cleaning chamber 1, a gas-liquid mixing device, a gas supply device, and a gas pressure regulating device.

[0098] The gas-liquid mixing device, the gas supply device, and the gas pressure regulating device are all connected to the cleaning chamber 1. The gas supply device is also connected to another gas supply device.

[0099] The cleaning chamber 1 provides a sealed space to contain the cleaning fluid and the membrane module 5, and its structure, shape and size can be selected according to actual needs.

[0100] The pressure control device is used to controllably increase or decrease the pressure in the sealed space, and to achieve pressure control in low-pressure gas evolution and repressurized gas dissolution.

[0101] Gas-liquid mixing devices are used to provide cleaning fluid containing dissolved soluble gases to sealed spaces.

[0102] Gas supply devices are used to supply soluble gases to sealed spaces and / or gas-liquid mixing devices.

[0103] Preferably, the pressure control device includes a suction module, a gas storage module, and an injection module connected in sequence. The suction module is connected to the gas outlet on the cleaning chamber 1 and is used to extract gas from the cleaning chamber 1 at a predetermined rate, thereby achieving a rapid and controllable pressure reduction from the first gas pressure to the second gas pressure in S2. The suction module can adopt a conventional vacuum pump or similar structure, as long as it can meet the pressure control requirements.

[0104] The gas storage module is used to store the gas extracted by the extraction module, thus buffering soluble gases. The gas storage membrane vent can be constructed using conventional gas tanks or gas bags, as long as it can store the gas without affecting the operation of the extraction module.

[0105] The injection module is connected to the cleaning chamber 1 and is used to inject the gas stored in the gas storage module into the cleaning chamber at a predetermined pressure increase rate in S3, realizing the pressurization process from the second gas pressure to the third gas pressure and realizing the recycling of soluble gas. In actual use, since the cleaning chamber 1 is in a low-pressure environment after S2, it can automatically draw soluble gas from the high-pressure environment (such as the gas storage module). Therefore, under normal circumstances, the injection module can generally adopt a valve structure, and the connection between the cleaning chamber 1 and the gas storage module can be controlled by the opening and closing degree of the valve to achieve repressurization.

[0106] More preferably, a pressurization structure is provided in the injection module to accelerate the injection of soluble gas, ensuring that the pressure rise rate in the cleaning chamber 1 can reach the predetermined speed, and avoiding situations where there is insufficient suction power in the cleaning chamber 1 (such as when the pressure in the cleaning chamber 1 is limited by the dissolution rate of the soluble gas, when the pressure in the gas storage module is temporarily balanced with that in the cleaning chamber 1, or when the pressure in the gas storage module is low), or when the resistance during the injection of soluble gas is high, so that the gas cannot be effectively injected into the cleaning chamber 1.

[0107] Preferably, it also includes a water supply device for providing the solvent required for the cleaning fluid to the gas-liquid mixing device. Both the water supply device and the gas supply device are connected to the gas-liquid mixing device.

[0108] More preferably, the air pressure mixing device also includes an aeration device to further enhance the dissolution rate of soluble gases. Furthermore, it should be noted that because readily soluble gases dissolve relatively quickly, aeration devices are generally used in cleaning systems requiring the continuous use of large quantities of cleaning solution. This ensures that when preparing large quantities of cleaning solution, the soluble gases can be quickly and thoroughly dissolved, preventing uneven distribution of soluble gases and improving treatment efficiency. The aeration device can employ a conventional high-speed mixer or similar structure.

[0109] Preferably, the cleaning chamber 1 is further provided with a stirring unit for promoting the flow of liquid in the cleaning chamber and a gas injection unit 3 for injecting soluble gas.

[0110] The gas injection unit 3 is connected to the gas supply device and the injection module respectively. The gas supply device can introduce fresh soluble gas into the cleaning chamber 1 through the gas injection unit 3 to fill the gas phase space, maintain the partial pressure of soluble gas, or replenish the soluble gas lost during the recycling process.

[0111] The injection module connects to the injection unit to re-inject the soluble gas stored in the storage module into the cleaning chamber 1.

[0112] The stirring unit is located inside the cleaning chamber 1 to promote the gentle flow of liquid in the chamber during the cleaning process, accelerate the contact between the cleaning liquid and the membrane module 5 in S1, ensure sufficient and uniform wetting, and accelerate the dissolution of gas in S3.

[0113] More preferably, the cleaning system also includes a pressure detection unit for monitoring pressure changes within the cleaning chamber 1. In actual operation, a pressure gauge 4 or similar device can be installed at the top or inside the cleaning chamber 1 for monitoring.

[0114] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0115] Example 1:

[0116] This embodiment relates to a membrane cleaning method and system employing atmospheric pressure-low pressure recirculating cleaning. The cleaning system includes a cleaning chamber 1, a gas-liquid mixing device, a gas supply device, and a pressure regulating device. The pressure regulating device comprises a suction module, a gas storage module, and an injection module connected in sequence. The gas-liquid mixing device is connected to both the gas supply device and the water supply device. The outlet of the gas-liquid mixing device is connected to the inlet 2 of the cleaning chamber 1. The structure of the cleaning chamber 1 is as follows... Figure 2 As shown, an air injection unit 3 and a pressure gauge 4 are installed at the top of the cleaning chamber 1, and a membrane assembly 5 is installed inside the cleaning chamber 1.

[0117] The membrane cleaning method includes the following steps:

[0118] S01: System Preparation and Membrane Module 5 Installation:

[0119] The contaminated polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membrane module 5 was installed in the cleaning chamber 1. The effective membrane area of ​​the membrane module 5 is 1.0 m². 2 The initial water flux was reduced from the normal 200 L / (m²) 2 (·h·bar) decreased to 80L / (m 2 (·h·bar), the pollutants are mainly colloidal particles.

[0120] SO2: Preparation of saturated CO2 cleaning solution:

[0121] A saturated carbon dioxide aqueous solution (or a near-saturated solution with a saturation of greater than 98%) was prepared using a gas-liquid mixing device. 1.2 L of deionized water was added to the device, and food-grade carbon dioxide gas was introduced at a flow rate of 0.5 L / min. The system pressure was maintained at 0.1 MPa (at ambient pressure) for 25 minutes to obtain a saturated carbon dioxide aqueous solution with a saturation of >98%. The solution temperature was controlled at 25 ± 2 °C (room temperature).

[0122] S1: Introduce a saturated carbon dioxide aqueous solution into the cleaning chamber 1 at a flow rate of 0.3 L / min under a pressure of 0.1 MPa, immerse the membrane module 5, and continue immersing for 10 minutes to allow the solution to fully wet the inner and outer surfaces of the membrane and the membrane pores.

[0123] S2: Seal the cleaning chamber 1, start the air extraction module, and reduce the air pressure in the cleaning chamber 1 from 0.1MPa to 0.05MPa at a rate of 0.01MPa / s, and maintain it for 1 minute.

[0124] S3: Start the injection module to restore the pressure to 0.1 MPa at a rate of 0.01 MPa / s and maintain it for 1 minute. This completes one pressure cycle. This embodiment performs a total of 3 cycles.

[0125] After completing 3 cycles, drain the cleaning solution and rinse membrane module 5 with deionized water at a flow rate of 0.3 L / min for 5 minutes to complete the cleaning.

[0126] The membrane flux of membrane module 5 after cleaning was tested, and the clean water flux of membrane module 5 recovered to 188 L / (m²). 2 The flux recovery rate reached 94% (·h·bar). Contaminants on the membrane surface were basically removed, the membrane pore structure was intact, and there were no signs of chemical damage.

[0127] Example 2

[0128] This embodiment provides a membrane cleaning method and system using atmospheric pressure-low pressure recirculating cleaning. The difference from Embodiment 1 is that in this embodiment, the more heavily fouled membrane module 5 is cleaned. The same cleaning system as in Embodiment 1 is used in this embodiment.

[0129] The membrane cleaning method differs from that in Example 1 in that:

[0130] In S01, the more heavily polluted PVDF hollow fiber ultrafiltration membrane module 5 is placed in the cleaning chamber 1, with an effective membrane area of ​​1.0 m². 2 The initial water flux was reduced from the normal 200 L / (m²) 2 (·h·bar) decreased to 60L / (m 2 (·h·bar). The pollutant components include a complex of oils, colloidal particles, and microbial films.

[0131] In SO2, the soluble gas is a mixture of ozone and carbon dioxide, with an ozone volume concentration of 20% and a carbon dioxide volume concentration of 80%.

[0132] In S2, the depressurization rate is 0.015 MPa / s, the air pressure drops from 0.1 MPa to 0.03 MPa, is maintained for 2 minutes, and then the pressure is increased.

[0133] In step S3, the pressure increase rate is 0.02 MPa / s, recovering from 0.03 MPa to 0.1 MPa. The pressure is maintained for 2 minutes before depressurization. This embodiment performs a total of 5 cycles.

[0134] The cleaning fluid is replaced after every two pressure cycles, for a total of two replacements.

[0135] The membrane flux of membrane module 5 after cleaning was tested, and the clean water flux of membrane module 5 recovered to 184 L / (m²). 2 The flux recovery rate was 92% (·h·bar). The microbial film on the membrane surface was effectively removed, and the membrane pore permeability was significantly improved. Compared with Example 1, the membrane module 5 in this embodiment was more severely polluted, and the pollutants were more tightly attached. This embodiment effectively addressed the more severe complex pollution situation by appropriately increasing the number of pressure cycles, expanding the pressure differential range, and using a mixed gas containing ozone (to enhance the destructive effect on the biofilm).

[0136] Example 3

[0137] This embodiment provides a membrane cleaning method and system using atmospheric pressure-low pressure recirculating cleaning. The difference from Embodiment 1 is that in this embodiment, the less fouled membrane module 5 is cleaned. The same cleaning system as in Embodiment 1 is used in this embodiment.

[0138] The membrane cleaning method differs from that in Example 1 in that:

[0139] In step S01, a lightly fouled PVDF hollow fiber ultrafiltration membrane module 5 is placed in the cleaning chamber 1, with an effective membrane area of ​​1.0 m². 2 The initial water flux was reduced from the normal 200 L / (m²) 2 The volume of water (·h·bar) decreased to 120L / (m 2 (·h·bar). The main component of the pollutants is oil.

[0140] In SO2, the soluble gas is ammonia, and the gas saturation is 65%.

[0141] In S2-S3, the process of S2-S3 is performed only once.

[0142] The membrane flux of membrane module 5 after cleaning was tested, and the clean water flux of membrane module 5 recovered to 194 L / (m²). 2 The flux recovery rate reached 97% (·h·bar). Oil and contaminants on the membrane surface were almost completely removed, the membrane pore structure remained intact, and there were no obvious signs of damage.

[0143] Comparative Example 1

[0144] This comparative example provides a membrane cleaning method using gas-water backwashing, which differs from Example 1 in that it includes the following steps;

[0145] S1: System preparation and membrane module 5 installation

[0146] The PVDF hollow fiber ultrafiltration membrane module 5, sourced from the same origin as in Example 1, has an effective membrane area of ​​1.0 m² and an initial water flux of 200 L / (m²). 2 (·h·bar) decreased to 100L / (m 2 ·h·bar).

[0147] S2: High-pressure dissolved gas preparation of supersaturated solution

[0148] A supersaturated carbon dioxide aqueous solution was prepared at a pressure of 0.2 MPa using a gas-liquid mixing device. 1.2 L of deionized water was added to the device, and food-grade carbon dioxide gas was introduced at a flow rate of 1.0 L / min. The system pressure was maintained at 0.2 MPa for 20 minutes to obtain a supersaturated carbon dioxide aqueous solution, with the solution temperature controlled at 25 ± 2 °C.

[0149] S3: Atmospheric pressure backflushing cleaning

[0150] Membrane module 5 was placed in an atmospheric pressure environment, and the aforementioned supersaturated carbon dioxide aqueous solution was directly (in reverse) introduced into membrane module 5 at a flow rate of 200 L / h for backwashing. During the backwashing process, after the supersaturated carbon dioxide aqueous solution flowed out of the mixing device, the dissolved carbon dioxide gas rapidly precipitated and formed bubbles during the flow and upon contact with the membrane due to the decrease in ambient pressure from 0.2 MPa to atmospheric pressure (0.1 MPa). The backwashing process lasted for 120 minutes.

[0151] S4: Final Rinse

[0152] After backflushing, membrane module 5 is rinsed with deionized water at a flow rate of 0.5 L / min for 15 minutes to remove residual loose contaminants and air bubbles.

[0153] The test results are as follows: After cleaning, the clean water flux of membrane module 5 recovered to 154 L / (m²). 2The flux recovery rate was 77%, but some contaminants remained on the membrane surface, especially those deep within the membrane pores. Compared to Example 1, this method relies solely on a single pressure drop to achieve gas release, lacking the continuous disturbance effect of pressure cycling. Furthermore, the bubble release process is concentrated in the initial stage of backflushing; as cleaning progresses, the gas concentration in the solution decreases, significantly reducing bubble generation and preventing effective penetration into the membrane pores, thus failing to achieve sufficient cleaning upon contact with the membrane. Simultaneously, unidirectional backflushing is insufficient to effectively clean stubborn contaminants within the membrane pores, resulting in significantly poor cleaning performance. In addition, the cleaning process utilizes large amounts of cleaning fluid and carbon dioxide, leading to high costs and poor cleaning results.

[0154] In summary, the present invention can solve the technical problems of low cleaning efficiency, high risk of membrane damage, and potential environmental pollution caused by gas-based membrane cleaning methods in the prior art.

[0155] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0156] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0157] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that they are in indirect contact through an intermediate medium. Furthermore, "above," "over," or "on top" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," or "beneath" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0158] In the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0159] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A membrane cleaning method employing atmospheric pressure-low pressure recirculating cleaning, characterized in that, Includes the following steps: S1: Wetting: Under the first pressure, the cleaning solution is filled into the pores of the membrane module (5) to be cleaned to obtain a wetted membrane module (5); the cleaning solution is a gas-containing solution containing soluble gas; under the first pressure, the gas saturation of the soluble gas dissolved in the cleaning solution is not less than 60%; S2: Low-pressure gas evolution cleaning: The gas pressure in the sealed space is reduced from the first gas pressure to the second gas pressure, causing the gas in the cleaning liquid distributed in the membrane module (5) to explode and nucleate, thereby achieving low-pressure gas evolution cleaning of the membrane module (5); S3: Re-pressure oscillation cleaning: The air pressure in the sealed space is increased to a third air pressure, causing the residual bubbles in S2 to burst and the cleaning fluid to oscillate, thus achieving re-pressure oscillation cleaning; Among them, the first pressure and the third pressure are greater than the second pressure, and the pressure difference between them and the second pressure is not less than 0.01 MPa; The low-pressure gas evolution-repressurization oscillation operation of S2-S3 above shall be performed at least once until the membrane cleaning target is achieved.

2. The membrane cleaning method using atmospheric pressure-low pressure recirculating cleaning as described in claim 1, characterized in that, In S1, the membrane module (5) is filled with cleaning liquid by immersion or rinsing; the first gas pressure is 0.08-0.105 MPa; the gas saturation of soluble gas in the cleaning liquid is 85%-100%; The cleaning solution comprises a solvent and a soluble gas; the Bunsen coefficient of the soluble gas in the solvent is not less than 0.6 under the conditions of 101.325 kPa and 0°C.

3. The membrane cleaning method using atmospheric pressure-low pressure recirculating cleaning as described in claim 2, characterized in that, In S1, the solvent is water; the soluble gas is at least one of carbon dioxide, ozone, ammonia, and sulfur dioxide.

4. The membrane cleaning method using atmospheric pressure-low pressure recirculating cleaning as described in claim 1, characterized in that, In S1, before immersion, the soluble gas is introduced into the sealed space so that the partial pressure of the soluble gas in the sealed space is not less than 0.08 MPa; the volume occupied by the membrane module (5) to be cleaned and the cleaning liquid does not exceed 50% of the volume of the sealed space.

5. The membrane cleaning method using atmospheric pressure-low pressure recirculating cleaning as described in claim 1, characterized in that, In S2, the air pressure in the sealed space is reduced by evacuation; in S3, the air pressure in the sealed space is increased by introducing soluble gas into the sealed space, and the soluble gas is dissolved in the cleaning liquid distributed in the membrane module (5) to complete the regeneration of the cleaning liquid; the soluble gas introduced into the sealed space is the newly introduced soluble gas and / or the soluble gas extracted in S2.

6. The membrane cleaning method using atmospheric pressure-low pressure recirculating cleaning as described in claim 1, characterized in that, In S2, the rate of decrease of the air pressure in the sealed space is 0.004-0.02 MPa / s; the second air pressure is 0.02-0.08 MPa. In S3, the rate of increase of the air pressure in the sealed space is 0.01-0.02 MPa / s; the third air pressure is 0.08-0.105 MPa. The third air pressure is greater than the second air pressure, and the pressure difference between the third air pressure and the second air pressure is not less than 0.03 MPa.

7. The membrane cleaning method using atmospheric pressure-low pressure recirculating cleaning as described in claim 1, characterized in that, The cleaning fluid should be replaced once every 1-3 cycles of S2-S3.

8. The cleaning system used in any one of the membrane cleaning methods according to claims 1-7, characterized in that, Includes a cleaning chamber (1), a gas-liquid mixing device, a gas supply device, and a gas pressure regulating device; The gas-liquid mixing device, the gas supply device, and the gas pressure regulating device are respectively connected to the cleaning chamber (1); the gas supply device is also connected to the gas supply device. The cleaning chamber (1) provides a sealed space to contain the cleaning fluid and the membrane module (5); The pressure regulating device is used to controllably increase or decrease the pressure in the sealed space; the gas-liquid mixing device is used to provide the sealed space with a cleaning liquid containing soluble gas; and the gas supply device is used to provide soluble gas to the sealed space and the gas-liquid mixing device.

9. The cleaning system as described in claim 8, characterized in that, The air pressure control device includes an air extraction module, an air storage module, and an injection module connected in sequence; the air extraction module is connected to the cleaning chamber (1) and is used to extract the gas in the cleaning chamber (1); the air storage module is used to store the gas extracted by the air extraction module; the injection module is connected to the cleaning chamber (1) and is used to pressurize the gas stored in the air storage module and inject it into the cleaning chamber (1).

10. The cleaning system as described in claim 8, characterized in that, It also includes a water supply device; the water supply device is connected to the gas-liquid mixing device and is used to provide the solvent required for the cleaning liquid to the gas-liquid mixing device; the cleaning chamber (1) is also provided with a stirring unit for promoting the flow of liquid in the cleaning chamber (1) and an injection unit (3) for injecting the soluble gas; the injection unit (3) is connected to the gas supply device and the injection module respectively.

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