Ultrafiltration membrane cleaning method and cleaning system

Abstract

The invention provides an ultrafiltration membrane cleaning method and an ultrafiltration membrane cleaning system. The cleaning agent composition comprises a first cleaning component and a chemical cleaning component, wherein the first cleaning component comprises sodium hypochlorite and sodium hydroxide; the chemical cleaning component comprises a second cleaning component and a third cleaning component, the second cleaning component contains hydrochloric acid and organic acid, and the third cleaning component contains sodium hypochlorite, sodium hydroxide and sodium tripolyphosphate. The concentration of sodium hypochlorite is increased along with reduction of water temperature; different types of organic acids are selected according to different water temperatures; and when the water temperature is lower than the set temperature, sodium dodecyl benzene sulfonate is added. The cleaning method comprises the steps of detecting water temperature and inflow water quality, and selecting component concentration and cleaning frequency according to a detection result. According to the invention, the cleaning scheme can be dynamically adjusted according to the temperature and the inlet water quality, the transmembrane pressure difference of the membrane group is obviously reduced, the seawater flux is improved, efficient microbe removal is realized, the service life of the membrane is prolonged, the cleaning cost is reduced, and the environmental pollution is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of semipermeable membrane cleaning, and in particular to an ultrafiltration membrane cleaning method and a cleaning system. Background Art

[0002] Ultrafiltration membrane is an important filtration medium, widely used in water treatment, food processing, pharmaceutical manufacturing and other fields. In actual operation, the surface of ultrafiltration membrane is easily covered by pollutants such as organic matter, microorganisms, colloids and inorganic salts, forming a pollution layer, which leads to a decrease in membrane flux and an increase in transmembrane pressure difference, seriously affecting the operating efficiency of the ultrafiltration system.

[0003] The ultrafiltration membrane cleaning agents currently on the market usually use fixed formulas, without considering the impact of temperature and water quality changes on the cleaning effect. These conventional cleaning solutions have obvious shortcomings when facing different operating conditions. First, changes in water temperature will significantly affect the properties and degree of adhesion of membrane pollutants. When the water temperature decreases, the viscosity of the water increases, making it easier for pollutants to accumulate on the membrane surface, while also reducing the cleaning efficiency of conventional cleaning agents. Especially when the water temperature is low, the cleaning effect of conventional fixed formulas is significantly reduced, and pollutants on the surface of the ultrafiltration membrane cannot be effectively removed.

[0004] Secondly, seasonal changes in influent water quality also put forward different requirements for cleaning. Changes in parameters such as microbial content, organic matter concentration and turbidity in water require corresponding adjustments to the formulation of cleaning agents and the cleaning frequency. However, the cleaning schemes in the prior art often fail to make timely adjustments based on these changes, resulting in unstable cleaning effects, sometimes incomplete cleaning, and sometimes excessive cleaning, which increases membrane loss and operating costs.

[0005] In addition, existing cleaning solutions also have limitations in the selection of cleaning agent components. For example, in low-temperature environments, conventional cleaning agents are difficult to cope with the cleaning difficulties caused by increased water viscosity; for pollutants of different properties, such as organic matter and inorganic salt scale, the removal effect of a single cleaning agent is limited. Especially for microbial contamination, the sterilization efficiency of existing cleaning solutions is not high, which easily leads to repeated formation of biofilms and accelerates membrane contamination.

[0006] The existing ultrafiltration membrane cleaning technology has a relatively simple setting for the cleaning frequency, and lacks a mechanism for dynamic adjustment according to the actual operating conditions. This may lead to low efficiency, increased membrane loss and the use of chemical agents, increased operating costs, and increased burden on the environment. Summary of the invention

[0007] The object of the present invention is to provide an ultrafiltration membrane cleaning method and a cleaning system, which dynamically adjusts the components and concentrations according to changes in water temperature and influent water quality, thereby improving the cleaning effect and extending the service life of the ultrafiltration membrane.

[0008] In order to achieve the above technical objectives, the present invention provides an ultrafiltration membrane cleaning method, comprising:

[0009] Detect water temperature and inlet water quality;

[0010] Selecting cleaning agent components and their concentrations according to the water temperature and inlet water quality;

[0011] Determining the cleaning frequency according to the water temperature and the quality of the incoming water; and

[0012] Perform the first wash, second wash, and third wash.

[0013] Optionally, the first cleaning component used in the first cleaning comprises sodium hypochlorite and sodium hydroxide; the second cleaning component used in the second cleaning comprises hydrochloric acid and an organic acid; and the third cleaning component used in the third cleaning comprises sodium hypochlorite, sodium hydroxide and sodium tripolyphosphate;

[0014] Among them, the concentration of the sodium hypochlorite increases with the decrease of water temperature; the organic acid includes different types at different water temperatures; and the third cleaning component includes different types at different water temperatures or inlet water quality.

[0015] Optionally, the concentration of the sodium hydroxide is 400-800 ppm, the concentration of the sodium tripolyphosphate is 800-1000 ppm, the concentration of the hydrochloric acid is 400-1000 ppm, and the concentration of the organic acid is 600-1000 ppm.

[0016] Optionally, for every 1°C drop in water temperature or every 5%-10% increase in water viscosity, the concentration of the sodium hypochlorite in the third cleaning component is increased by 100 ppm until it reaches 1500 ppm.

[0017] Optionally, when the water temperature is not lower than the set temperature, the organic acid includes oxalic acid; when the water temperature is lower than the set temperature, the organic acid includes citric acid.

[0018] Optionally, when the water temperature is lower than the set temperature, the third cleaning component further comprises sodium dodecylbenzene sulfonate, and the concentration of the sodium dodecylbenzene sulfonate increases by 30 ppm for every 1° C. drop in the water temperature until it increases to 150 ppm.

[0019] Optionally, when the water temperature is not lower than the set temperature, the concentration of sodium hypochlorite in the first cleaning component is 400-600 ppm;

[0020] When the water temperature is lower than the set temperature, the concentration of sodium hypochlorite in the first cleaning component is 700-900 ppm;

[0021] When the water temperature is not lower than the set temperature, the concentration of sodium hypochlorite in the third cleaning component is 800-1200 ppm;

[0022] When the water temperature is lower than the set temperature, the concentration of the third cleaning component sodium hypochlorite is 1300-1500 ppm.

[0023] Optionally, when the water temperature is not lower than the set temperature, the first cleaning is performed every 30-40 hours;

[0024] When the water temperature is lower than the set temperature, the first cleaning is performed every 20-30 hours;

[0025] The first cleaning time is 1-3 hours / each time.

[0026] Optionally, when the water temperature is not lower than the set temperature, the second cleaning and the third cleaning are performed once a month;

[0027] When the water temperature is lower than the set temperature, the second cleaning and the third cleaning are performed 1-3 times per month, and the second cleaning and the third cleaning time are both 2-3 hours / each time.

[0028] The present invention also provides an ultrafiltration membrane cleaning system, comprising:

[0029] Detection unit, used to detect water temperature and inlet water quality;

[0030] A selection unit, for selecting cleaning agent components and their concentrations according to the water temperature and the quality of the inlet water, and determining the cleaning frequency;

[0031] A storage unit, used for storing cleaning components required for the first cleaning, the second cleaning and the third cleaning respectively;

[0032] an execution unit, used for executing a first cleaning, a second cleaning and a third cleaning;

[0033] Wherein, the selection unit is configured to increase the concentration of sodium hypochlorite and add sodium dodecylbenzene sulfonate to the components of the third cleaning when the water temperature is lower than the set temperature; select different types of organic acids according to the water temperature; and adjust the cleaning frequency according to changes in the inlet water quality.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] The cleaning method provided by the present invention dynamically adjusts the cleaning frequency and cleaning time by detecting the water temperature and the influent water quality, especially increasing the cleaning frequency in the low temperature season, and timely adjusting the chemical cleaning frequency according to the change of the influent water quality. This method can not only improve the cleaning effect, but also extend the service life of the ultrafiltration membrane, reduce maintenance costs, and improve the system operation efficiency. By reasonably matching conventional cleaning and the combination of acid cleaning and alkaline cleaning, different types of pollutants can be effectively removed, especially in the case of severe microbial contamination, showing a higher removal rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 1 is a flowchart of the steps of the ultrafiltration membrane cleaning method in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] A method for cleaning an ultrafiltration membrane and a cleaning system of the present invention will be described in more detail below in conjunction with the accompanying drawings, wherein preferred embodiments of the present invention are shown, and it should be understood that those skilled in the art may modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as being widely known to those skilled in the art and not as a limitation of the present invention.

[0038] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the accompanying drawings are in very simplified form and are not in exact proportions, and are only used to facilitate and clearly assist in illustrating the purpose of the embodiments of the present invention.

[0039] Embodiment 1

[0040] The embodiment of the present invention provides a formula for cleaning an ultrafiltration membrane, comprising a first cleaning component and a chemical cleaning component. The first cleaning component comprises sodium hypochlorite and sodium hydroxide; the chemical cleaning component comprises a second cleaning component and a third cleaning component, the second cleaning component comprises hydrochloric acid and an organic acid, and the third cleaning component comprises sodium hypochlorite, sodium hydroxide and sodium tripolyphosphate.

[0041] The concentrations of sodium hypochlorite in the first cleaning component and the chemical cleaning component both increase as the water temperature decreases; the organic acid includes different types at different water temperatures; and the third cleaning component includes different types at different water temperatures or influent water qualities.

[0042] When the water temperature is not lower than the set temperature, the organic acid includes oxalic acid; when the water temperature is lower than the set temperature, the organic acid includes citric acid. Oxalic acid and citric acid are both common organic acid cleaning agents, but they show different cleaning effects under different temperature conditions. Under higher water temperature conditions, oxalic acid has better solubility and cleaning ability; while under lower water temperature conditions, citric acid has more suitable solubility and cleaning ability.

[0043] When the water temperature is lower than the set temperature, the third cleaning component also contains sodium dodecylbenzene sulfonate (SDBS). For every 1°C drop in water temperature, the concentration of sodium dodecylbenzene sulfonate increases by 30ppm until it increases to 150ppm. Sodium dodecylbenzene sulfonate is a highly efficient surfactant that can effectively reduce water viscosity and improve cleaning efficiency. In a low temperature environment, the increase in water viscosity will affect the cleaning effect, so it is necessary to add a surfactant to improve the fluidity and permeability of the cleaning solution.

[0044] Further, when the water temperature is not lower than the set temperature, the concentration of sodium hypochlorite in the first cleaning component is 400-600 ppm; when the water temperature is lower than the set temperature, the concentration of sodium hypochlorite in the first cleaning component is 700-900 ppm; when the water temperature is not lower than the set temperature, the concentration of sodium hypochlorite in the third cleaning component is 800-1200 ppm; when the water temperature is lower than the set temperature, the concentration of sodium hypochlorite in the third cleaning component is 1300-1500 ppm.

[0045] The concentration of the sodium hydroxide is 400-800ppm, which is used to adjust the pH value of the cleaning solution to 11-12 and improve the cleaning ability of sodium hypochlorite. The concentration of the sodium tripolyphosphate is 800-1000ppm, which can effectively complex calcium and magnesium ions in the water as a chelating agent to prevent precipitation during the cleaning process. The concentration of the hydrochloric acid is 400-1000ppm, which is used for pickling to remove inorganic pollutants on the ultrafiltration membrane. The concentration of the organic acid is 600-1000ppm, which is used to remove organic pollutants and some inorganic pollutants.

[0046] For every 1°C drop in water temperature or 5%-10% increase in water viscosity, the concentration of sodium hypochlorite in the third cleaning component increases by 100ppm until it reaches 1500ppm. A drop in temperature will reduce the chemical reaction rate, while an increase in water viscosity will affect the penetration of the cleaning solution. Therefore, it is necessary to increase the concentration of sodium hypochlorite to compensate for the decrease in cleaning efficiency under low temperature conditions.

[0047] In a specific example, for high hardness influent water (high calcium and magnesium ion content), the concentration of sodium tripolyphosphate can be appropriately increased to 1000-1200 ppm to improve the chelating ability for calcium and magnesium ions.

[0048] In another specific example, for influent with a high organic content, the concentration of sodium hypochlorite in the first cleaning component can be increased to an upper limit, while the concentration of sodium hydroxide can be increased to 800 ppm to improve the oxidation and decomposition capabilities of the organic matter.

[0049] It should be noted that in this embodiment, the set temperature can be adjusted according to the actual water source characteristics, seasonal changes and regional differences. The temperature limit is not fixed and can be appropriately adjusted according to the specific application scenario and operating experience. According to the actual operating data and cleaning effect, the set temperature can be flexibly adjusted to obtain the best cleaning effect.

[0050] In one specific example, the set temperature is 15 degrees Celsius.

[0051] In summer (water temperature is not less than 15℃), the specific cleaning formula for a single membrane group is as follows:

[0052] First cleaning component: sodium hypochlorite: 500ppm; sodium hydroxide: 400ppm (satisfying pH value 11-12);

[0053] Cleaning frequency: once per set every 36 hours;

[0054] Cleaning time: about 1.5 hours;

[0055] Second cleaning component: hydrochloric acid: 600ppm; oxalic acid: 1000ppm;

[0056] Cleaning time: 2 hours;

[0057] Cleaning method: circulation, soaking, air wiping and reciprocating;

[0058] The third cleaning component: sodium hypochlorite: 1000ppm; sodium hydroxide: 400ppm; sodium tripolyphosphate: 1000ppm;

[0059] Cleaning time: 2 hours;

[0060] Cleaning method: circulation, soaking, air wiping and reciprocating;

[0061] Cleaning frequency: Once a month, adjusted according to incoming water quality and temperature changes.

[0062] Winter Cleaning Recipe Example

[0063] In winter (water temperature below 15°C), the specific cleaning formula for a single membrane group is as follows:

[0064] First cleaning component: Sodium hypochlorite: 800ppm, sodium hydroxide: 400ppm (satisfying pH value 11-12); cleaning frequency: once per set every 24 hours;

[0065] Cleaning time: about 1.5 hours;

[0066] Second cleaning component: hydrochloric acid: 600ppm, citric acid: 1000ppm;

[0067] Cleaning time: 2 hours;

[0068] Cleaning method: circulation, soaking, air wiping and reciprocating;

[0069] The third cleaning component: sodium hypochlorite: 1500ppm, sodium hydroxide: 400ppm, sodium tripolyphosphate: 1000ppm, sodium dodecylbenzene sulfonate: 150ppm;

[0070] Cleaning time: 2 hours;

[0071] Cleaning method: circulation, soaking, air wiping and reciprocating;

[0072] Cleaning frequency: 1-3 times per month, adjusted according to incoming water quality and temperature changes.

[0073] Embodiment 2

[0074] The present invention provides a method for cleaning an ultrafiltration membrane. Figure 1 , specifically including the following steps:

[0075] S1: Detect water temperature and inlet water quality.

[0076] Use temperature sensors to detect the inlet water temperature, and at the same time detect water quality parameters such as turbidity, organic matter content, and microbial content.

[0077] In a specific example, it can be obtained in real time through an online monitoring instrument, or through regular sampling and analysis.

[0078] S2: Select cleaning agent components and their concentrations according to the water temperature and inlet water quality.

[0079] According to the water temperature and water quality parameters obtained by S1, the cleaning agent components and their concentrations are selected.

[0080] Specifically:

[0081] When the water temperature is not lower than the set temperature, the organic acid includes oxalic acid; when the water temperature is lower than the set temperature, the organic acid includes citric acid.

[0082] When the water temperature is lower than the set temperature, sodium dodecylbenzene sulfonate is added to the third cleaning component, and the concentration increases as the temperature decreases. For every 1°C drop in water temperature, the concentration of sodium dodecylbenzene sulfonate increases by 30 ppm until it increases to 150 ppm.

[0083] And adjust the concentration of sodium hypochlorite according to the water temperature.

[0084] Specifically, when the water temperature is not lower than the set temperature, the concentration of sodium hypochlorite in the first cleaning is 400-600 ppm;

[0085] When the water temperature is lower than the set temperature, the concentration of sodium hypochlorite in the first cleaning is 700-900 ppm;

[0086] When the water temperature is not lower than the set temperature, the concentration of sodium hypochlorite in the third cleaning is 800-

[0087] 1200ppm;

[0088] When the water temperature is lower than the set temperature, the concentration of sodium hypochlorite in the third cleaning is 1300-1500 ppm.

[0089] S3: Determine the cleaning frequency according to the water temperature and the quality of the incoming water.

[0090] According to the water temperature and water quality parameters obtained by S1, the frequency of the first cleaning, the second cleaning and the third cleaning is determined. Specifically:

[0091] When the water temperature is not lower than the set temperature, the first cleaning is performed every 30-40 hours;

[0092] When the water temperature is lower than the set temperature, the first cleaning is performed every 20-30 hours;

[0093] When the water temperature is not lower than the set temperature, perform the second and third cleaning once a month;

[0094] When the water temperature is lower than the set temperature, perform the second and third cleaning 1-3 times a month;

[0095] When the inlet water quality deteriorates, increase the frequency of the second and third cleanings.

[0096] S4: Perform the first cleaning, the second cleaning, and the third cleaning.

[0097] The first cleaning, the second cleaning and the third cleaning are performed according to the frequency determined by S3 and using the cleaning agent composition and concentration selected by S2.

[0098] The first cleaning process lasts for 1-3 hours per cleaning, and is mainly used to remove sediment and organic matter on the surface of the ultrafiltration membrane.

[0099] In a specific example, the first cleaning includes the following sub-steps:

[0100] S4.1: injecting the first cleaning component into the ultrafiltration membrane system;

[0101] S4.2: Circulate cleaning at specified pressure;

[0102] S4.3: After cleaning, rinse with clean water.

[0103] The second cleaning and the third cleaning time are both 2-3 hours / each time.

[0104] The second cleaning and the third cleaning are chemical cleaning, which are mainly used to remove deep pollutants that cannot be removed by the first cleaning, such as heavy metal pollution and deeply deposited sediment.

[0105] In a specific example, the specific sub-steps of the second cleaning and the third cleaning time include:

[0106] S4.4: first perform acid washing, and inject the cleaning components of the second washing into the ultrafiltration membrane system;

[0107] S4.5: Pickling is performed by a reciprocating cycle of circulation, immersion and air rubbing;

[0108] S4.6: After pickling, rinse with clean water;

[0109] S4.7: Performing alkali washing again, injecting the cleaning components of the third washing into the ultrafiltration membrane system;

[0110] S4.8: Alkaline cleaning is performed by a reciprocating cycle of circulation, soaking and air rubbing;

[0111] S4.9: After alkaline cleaning, rinse with clean water.

[0112] Furthermore, the frequency of chemical cleaning needs to be increased when the inlet water quality shows any of the following conditions:

[0113] The ultrafiltration water production is significantly attenuated;

[0114] Increased turbidity of influent water;

[0115] Increased organic matter content in the influent; or

[0116] The microbial content of the influent increases.

[0117] In a specific example, for areas with large changes in water quality, a water quality monitoring and automatic adjustment system for cleaning frequency can be established to automatically adjust the cleaning frequency and cleaning agent formula based on real-time monitoring data to achieve the best cleaning effect.

[0118] In another specific example, for influent water that is seriously contaminated by microorganisms, a short-term (30-minute) flushing with high-concentration (1000 ppm) sodium hypochlorite can be added before chemical cleaning to improve the killing effect on microorganisms.

[0119] The ultrafiltration membrane cleaning method provided in the embodiment of the present invention can effectively deal with the ultrafiltration membrane pollution problem under various complex conditions by dynamically adjusting the cleaning agent formula and cleaning frequency according to the water temperature and the water quality of the inlet water. The ultrafiltration membrane cleaning method can reduce the transmembrane pressure difference after cleaning to 0.09MPa and increase the seawater flux to 298L / (m 2 h), the microbial removal rate reaches 96%, which is much better than the effect of a single cleaning method (such as conventional cleaning, acid cleaning or alkaline cleaning). In addition, through reasonable cleaning frequency and time arrangement, the service life of the ultrafiltration membrane can be extended, the operating cost can be reduced, and the overall efficiency of the system can be improved.

[0120] Embodiment 3

[0121] The embodiment of the present invention provides an ultrafiltration membrane cleaning system based on the second embodiment, comprising:

[0122] Detection unit, used to detect water temperature and inlet water quality;

[0123] A selection unit, for selecting cleaning agent components and their concentrations according to the water temperature and the quality of the inlet water, and determining the cleaning frequency;

[0124] A storage unit, used for storing cleaning agent components required for the first cleaning, the second cleaning and the third cleaning respectively;

[0125] An execution unit, used for sequentially executing a first cleaning, a second cleaning and a third cleaning;

[0126] Wherein, the selection unit is configured to increase the concentration of sodium hypochlorite and add sodium dodecylbenzene sulfonate to the components of the third cleaning when the water temperature is lower than the set temperature; select different types of organic acids according to the water temperature; and adjust the cleaning frequency according to changes in the inlet water quality.

[0127] In a specific example, the detection unit includes a temperature sensor and a water quality detection instrument, which is used to monitor the inlet water temperature, turbidity, organic matter content, microbial content and other parameters in real time. The temperature sensor is installed on the inlet pipe, and the water quality detection instrument regularly samples and analyzes the inlet water quality. The detection data is transmitted to the control center in real time.

[0128] The selection unit includes a controller and a decision module, which determines the cleaning agent composition, concentration and cleaning frequency based on the test data:

[0129] When the water temperature is lower than the set temperature, increase the concentration of sodium hypochlorite and add sodium dodecylbenzene sulfonate to the third cleaning component. For every 1°C drop in water temperature, the concentration increases by 30ppm, up to 150ppm. Change the organic acid from oxalic acid to citric acid. Adjust the frequency of the first cleaning from every 30-40 hours to every 20-30 hours, and adjust the frequency of chemical cleaning from once a month to 1-3 times a month.

[0130] When a significant increase in influent turbidity, organic matter content or microbial content is detected, choose to increase the cleaning frequency.

[0131] The storage unit includes multiple chemical storage tanks and metering systems: sodium hypochlorite storage tank, sodium hydroxide storage tank, hydrochloric acid storage tank, organic acid storage tank (oxalic acid and citric acid), sodium tripolyphosphate storage tank and sodium dodecylbenzene sulfonate storage tank.

[0132] Each storage tank is equipped with a liquid level sensor and a metering pump to accurately control the dosage of each reagent.

[0133] In a specific example, the execution unit executes the cleaning process according to the decision of the selection unit.

[0134] The cleaning system provided in this embodiment can detect water temperature and water quality, adjust the cleaning plan, deal with ultrafiltration membrane contamination problems under different conditions, improve cleaning efficiency, reduce manual intervention, extend the service life of the ultrafiltration membrane, and reduce operating costs.

[0135] Embodiment 4

[0136] The present invention provides a comparative experiment based on the cleaning method of Example 2 to verify the effectiveness of the ultrafiltration membrane cleaning method provided by the present invention. The comparative experiment is as follows:

[0137] The following 8 test formulas were used for cleaning respectively. The attenuated ultrafiltration membrane group was cleaned cyclically at the same time. The data before and after the membrane group cleaning were recorded as follows:

[0138]

[0139]

[0140] From the above experimental data we can get:

[0141] The cleaning effect of Experimental Example 1 (conventional washing + acid washing + alkaline washing) was the best. After cleaning, the transmembrane pressure difference decreased the most (down to 0.09 MPa), and the seawater flux increased most significantly, up to 298 L / (m 2 h), the microbial removal rate was the highest (96%).

[0142] Although the dosage of the reagents for acid cleaning and alkali cleaning was reduced in Experimental Examples 2 and 3, respectively, the cleaning effects were still much better than those of the comparative examples, indicating that the cleaning method of the present invention has good stability and adaptability.

[0143] The effects of the single cleaning method (Comparative Examples 1, 2, and 3) were all unsatisfactory, especially the acid cleaning method (Comparative Example 2) had the worst effect, with a microbial removal rate of only 62%.

[0144] Although the effects of conventional washing + acid washing (Comparative Example 4) and conventional washing + alkali washing (Comparative Example 5) are better than the single washing method, they are still obviously inferior to the three-step washing method of the present invention.

[0145] The comparative experimental data of the embodiments of the present invention fully demonstrate the effectiveness of the ultrafiltration membrane cleaning agent combination and cleaning method provided in Embodiment 1 and Embodiment 2. Through three-step cleaning, not only can various pollutants be effectively removed, the transmembrane pressure difference is reduced, and the seawater flux is increased, but also a microbial removal rate of 96% can be achieved, which is far superior to a single cleaning method or a two-step cleaning method.

[0146] In order to determine the optimal concentration range of each component under different conditions, the following concentration expansion range experiments were conducted:

[0147] Sodium hypochlorite concentration range experiment: Under the condition of keeping other conditions unchanged, the cleaning effects of 400ppm, 600ppm, 800ppm, 1000ppm, 1200ppm and 1500ppm sodium hypochlorite were tested respectively. The results show that when the water temperature is not lower than the set temperature, the sodium hypochlorite concentration in the range of 400-600ppm has a better effect; when the water temperature is lower than the set temperature, the sodium hypochlorite concentration needs to be increased to 700-900ppm (first cleaning) and 1300-1500ppm (third cleaning) to achieve the ideal effect.

[0148] Sodium hydroxide concentration range experiment: Under the condition of keeping other conditions unchanged, the cleaning effects of 300ppm, 400ppm, 600ppm and 800ppm sodium hydroxide were tested respectively. The results show that the sodium hydroxide concentration in the range of 400-800ppm can effectively adjust the pH value to 11-12 and achieve the ideal cleaning effect.

[0149] Sodium tripolyphosphate concentration range experiment: Under the condition of keeping other conditions unchanged, the cleaning effects of 600ppm, 800ppm, 1000ppm and 1200ppm sodium tripolyphosphate were tested respectively. The results show that sodium tripolyphosphate concentration in the range of 800-1000ppm can effectively complex calcium and magnesium ions in water and prevent precipitation formation during the cleaning process.

[0150] Hydrochloric acid concentration range experiment: Under the condition of keeping other conditions unchanged, the cleaning effects of 300ppm, 400ppm, 600ppm, 800ppm and 1000ppm hydrochloric acid were tested respectively. The results show that hydrochloric acid concentration in the range of 400-1000ppm can effectively remove inorganic pollutants on the ultrafiltration membrane without causing significant damage to the membrane material.

[0151] Organic acid concentration range experiment: Under the condition of keeping other conditions unchanged, the cleaning effects of oxalic acid and citric acid at 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm were tested respectively. The results show that organic acid concentrations in the range of 600-1000ppm can effectively remove organic pollutants and some inorganic pollutants without causing significant damage to the membrane material.

[0152] Sodium dodecylbenzene sulfonate concentration range experiment: Under low temperature conditions, the cleaning effects of 50ppm, 100ppm, 150ppm, and 200ppm sodium dodecylbenzene sulfonate were tested. The results show that sodium dodecylbenzene sulfonate concentrations in the range of 0-150ppm can effectively reduce water viscosity and improve cleaning efficiency without generating excessive foam that affects the cleaning process.

[0153] Based on the above experimental results, the optimal concentration range of each component was determined: Sodium hypochlorite: 400-1500ppm

[0154] Sodium hydroxide: 400-800ppm; Sodium tripolyphosphate: 800-1000ppm; Hydrochloric acid: 400-1000ppm; Organic acid: 600-1000ppm; Sodium dodecylbenzene sulfonate: 0-150ppm.

[0155] In summary, the present invention provides an ultrafiltration membrane cleaning method and cleaning system, which dynamically adjusts the cleaning agent components and their concentrations according to the water temperature and the inlet water quality, breaking the limitations of the traditional fixed addition scheme. Through three-step cleaning, a comprehensive and effective cleaning scheme is formed, which can effectively remove different types of pollutants (organic matter, inorganic matter, microorganisms, etc.). Comparative experimental data show that the effect of this three-step cleaning combination is far better than a single cleaning method or a two-step cleaning method. The cleaning frequency is adjusted according to the water temperature and the inlet water quality, while ensuring the cleaning effect, avoiding membrane damage and waste of reagents caused by excessive cleaning. Through scientific formula design and cleaning methods, the present invention has a microbial removal rate of up to 96%, significantly reduces the transmembrane pressure difference, greatly improves seawater flux, prolongs the service life of the ultrafiltration membrane, reduces operating costs, and reduces pollution to the environment. The present invention is suitable for various temperature conditions and inlet water quality conditions, especially in low temperature environments and when water quality fluctuates greatly.

[0156] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for cleaning an ultrafiltration membrane, characterized in that: include: Detect water temperature and inlet water quality; Selecting cleaning agent components and their concentrations according to the water temperature and inlet water quality; Determine the cleaning frequency according to the water temperature and inlet water quality; as well as Perform the first wash, second wash, and third wash.

2. The method according to claim 1, characterized in that The first cleaning component used in the first cleaning comprises sodium hypochlorite and sodium hydroxide; the second cleaning component used in the second cleaning comprises hydrochloric acid and an organic acid; the third cleaning component used in the third cleaning comprises sodium hypochlorite, sodium hydroxide and sodium tripolyphosphate; Among them, the concentration of the sodium hypochlorite increases with the decrease of water temperature; the organic acid includes different types at different water temperatures; and the third cleaning component includes different types at different water temperatures or inlet water quality.

3. The method according to claim 2, characterized in that The concentration of the sodium hydroxide is 400-800 ppm, the concentration of the sodium tripolyphosphate is 800-1000 ppm, the concentration of the hydrochloric acid is 400-1000 ppm, and the concentration of the organic acid is 600-1000 ppm.

4. The method according to claim 2, characterized in that: For every 1°C drop in water temperature or 5%-10% increase in water viscosity, the concentration of the sodium hypochlorite in the third cleaning component increases by 100 ppm until it reaches 1500 ppm.

5. The method according to claim 2, characterized in that: When the water temperature is not lower than the set temperature, the organic acid includes oxalic acid; when the water temperature is lower than the set temperature, the organic acid includes citric acid.

6. The method according to claim 2, characterized in that When the water temperature is lower than the set temperature, the third cleaning component further comprises sodium dodecylbenzene sulfonate, and the concentration of the sodium dodecylbenzene sulfonate increases by 30 ppm for every 1°C drop in the water temperature until it increases to 150 ppm.

7. The method according to claim 2, characterized in that When the water temperature is not lower than the set temperature, the concentration of sodium hypochlorite in the first cleaning component is 400-600 ppm; When the water temperature is lower than the set temperature, the concentration of sodium hypochlorite in the first cleaning component is 700-900 ppm; When the water temperature is not lower than the set temperature, the concentration of sodium hypochlorite in the third cleaning component is 800-1200 ppm; When the water temperature is lower than the set temperature, the concentration of sodium hypochlorite in the third cleaning component is 1300-1500 ppm.

8. The method according to claim 1, characterized in that When the water temperature is not lower than the set temperature, the first cleaning is performed every 30-40 hours; When the water temperature is lower than the set temperature, the first cleaning is performed every 20-30 hours; The first cleaning time is 1-3 hours / each time.

9. The method according to claim 1, characterized in that: When the water temperature is not lower than the set temperature, the second cleaning and the third cleaning are performed once a month; When the water temperature is lower than the set temperature, the second cleaning and the third cleaning are performed 1-3 times per month, and the second cleaning and the third cleaning time are both 2-3 hours / each time.

10. An ultrafiltration membrane cleaning system, characterized in that: include: Detection unit, used to detect water temperature and inlet water quality; A selection unit, for selecting cleaning agent components and their concentrations according to the water temperature and the quality of the inlet water, and determining the cleaning frequency; A storage unit, used for storing cleaning components required for the first cleaning, the second cleaning and the third cleaning respectively; An execution unit, used for executing a first cleaning, a second cleaning and a third cleaning; Wherein, the selection unit is configured to increase the concentration of sodium hypochlorite and add sodium dodecylbenzene sulfonate to the components of the third cleaning when the water temperature is lower than the set temperature; select different types of organic acids according to the water temperature; and adjust the cleaning frequency according to changes in the inlet water quality.

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