Cleaning method for MBR membrane combined pollution

Abstract

The invention provides a cleaning method for combined pollution of an MBR (Membrane Bioreactor) membrane. The cleaning method for combined pollution of the MBR membrane comprises the following steps: firstly, soaking and cleaning the MBR membrane for the first time by using an acid solution, and then soaking and cleaning the MBR membrane for the second time by using an alkaline sodium hypochlorite solution; wherein the pH value of the acidic solution is 1-4, the available chlorine concentration of the alkaline sodium hypochlorite solution is 1000-5000 mg / L, and the pH value of the alkaline sodium hypochlorite solution is 10-13. According to the cleaning method disclosed by the invention, the acid solution is firstly used for soaking and cleaning so as to effectively remove inorganic pollutants on the MBR membrane and destroy connection among inorganic matters, organic matters and microorganisms, and then the alkaline sodium hypochlorite solution is used for soaking and cleaning so as to effectively remove organic matters and microbial pollution on the MBR membrane; and the composite membrane formed by interaction of inorganic matters, organic matters and microorganisms has a good pollution removal effect, and the filtration performance of the MBR membrane can be recovered.

Description

Technical Field

[0001] The invention relates to the technical field of sewage and wastewater treatment, and in particular to a cleaning method for MBR membrane composite pollution. Background Art

[0002] The membrane bioreactor (MBR) wastewater treatment process that couples biodegradation with micro / ultrafiltration membrane separation has the advantages of small footprint, stable and excellent effluent quality, and low excess sludge production. It is widely used in municipal sewage and industrial wastewater treatment at home and abroad. However, during the long-term operation of MBR, membrane pollution caused by the attachment and deposition of organic matter, inorganic matter and microorganisms in the membrane pores and on the membrane surface will lead to a decrease in membrane permeability, thereby affecting the technical and economic performance of MBR.

[0003] Chemical cleaning is a necessary measure to remove membrane pollution. Generally, low-concentration and high-frequency online chemical cleaning is used for maintenance cleaning, and high-concentration and low-frequency offline chemical cleaning is used for restorative cleaning. At present, low-concentration sodium hypochlorite solution is generally used for maintenance cleaning, and high-concentration sodium hypochlorite solution is generally used for restorative cleaning, followed by citric acid solution. The above cleaning measures are effective in removing membrane pollution mainly composed of organic matter and microorganisms, but the effect of removing composite membrane pollution composed of the interaction of inorganic matter, organic matter and microorganisms is average.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a cleaning method for MBR membrane (micro / ultrafiltration membrane in membrane bioreactor wastewater treatment process, referred to as MBR membrane) composite pollution, which has better cleaning effect on composite membrane pollution composed of inorganic matter, organic matter and microorganisms, and is conducive to restoring the filtration performance of MBR membrane.

[0006] The invention provides a cleaning method for composite pollution of MBR membrane, comprising: firstly soaking and cleaning the MBR membrane with an acidic solution, and then soaking and cleaning the MBR membrane with an alkaline sodium hypochlorite solution for a second time.

[0007] The pH value of the acidic solution is 1-4, preferably 2-3, and more preferably 2.5; the acidic solution includes an acid, and the acid is selected from at least one of hydrochloric acid, sulfuric acid, citric acid and oxalic acid. Preferably, the acidic solution is a citric acid solution or an oxalic acid solution, more preferably an oxalic acid solution. Further, the acidic solution also includes a complexing agent, such as disodium ethylenediaminetetraacetate, etc., and the concentration of the complexing agent in the acidic solution is 5-100 mg / L.

[0008] The first soaking and cleaning time is 4-8h, for example 8h. During the first soaking and cleaning process, small flow aeration is performed intermittently, the aeration volume of the small flow aeration is 10-20% of the aeration volume of the normal operation of the MBR, the aeration time of the small flow aeration is 4-6min, for example 5min, and the intermittent time of the small flow aeration is 50-70min, for example 1h.

[0009] The effective chlorine concentration of the alkaline sodium hypochlorite solution is 1000-5000 mg / L, preferably 1000-3000 mg / L, and more preferably 1500-2400 mg / L; the pH value of the alkaline sodium hypochlorite solution is 10-13, preferably 11-12, and more preferably 11-11.5, and the pH value of the alkaline sodium hypochlorite solution can be adjusted by adding a base such as sodium hydroxide.

[0010] The second soaking and cleaning time is 8-16 hours, for example, 16 hours. During the second soaking and cleaning process, small flow aeration is performed intermittently, the aeration volume of the small flow aeration is 10-20% of the aeration volume of the normal operation of the MBR, the aeration time of the small flow aeration is 4-6 minutes, for example, 5 minutes, and the intermittent time of the small flow aeration is 50-70 minutes, for example, 1 hour.

[0011] Furthermore, before the first immersion cleaning, the membrane group to be cleaned that has stopped filtering is aerated for 5-10 minutes to remove the mud accumulated on the membrane fibers.

[0012] In addition, there is no strict restriction on the cleaning method of the first immersion cleaning and the second immersion cleaning, and they can be performed by an in-situ cleaning method or an ex-situ cleaning method.

[0013] More specifically, the cleaning method for MBR membrane composite pollution of the present invention comprises the following steps:

[0014] 1) Stop the membrane group to be cleaned from producing water, aerate for 5-10 minutes to remove the sludge on the membrane fibers, then stop aeration, and perform in-situ cleaning according to steps 2) to 4) or perform ex-situ cleaning according to steps 5) to 7);

[0015] 2) The sludge mixed liquid in the membrane pool is drained by a sludge pump (the sludge mixed liquid is transferred to a standby pool or other membrane pools), and tap water or MBR produced water is injected to submerge the membrane group to be cleaned. At the same time, the corresponding reagent is added according to the injection volume and the concentration of the acid solution (the pH value is 1-4, preferably 2-3; optionally, a complexing agent such as disodium ethylenediaminetetraacetic acid with a low concentration of 5-100 mg / L is added) and mixed evenly through small flow intermittent aeration (10-20% of the normal aeration volume of the MBR), and soaked for cleaning for 4-8 hours. During this period, a small flow aeration is performed for 4-6 minutes every 50-70 minutes to promote effective contact between the liquid and the membrane fibers to improve the cleaning effect;

[0016] 3) After the acid solution cleaning is completed, the acid solution in the membrane pool is drained (the acid solution needs to be discharged after neutralization or returned to the water inlet for treatment together with the raw water), and tap water or MBR produced water is injected again to immerse the membrane group to be cleaned. At the same time, according to the injection volume and the concentration of alkaline sodium hypochlorite solution (effective chlorine concentration 1000-5000 mg / L, preferably 1000-3000 mg / L; adjust the pH value to 10-13, preferably 11-12 by adding alkali such as sodium hydroxide), add the corresponding reagent and use small flow intermittent aeration (10-20% of the normal aeration volume of MBR) to mix them evenly, soak and clean for 8-16 hours, during which a small flow aeration is performed every 50-70 minutes for 4-6 minutes to promote the effective contact between the liquid and the membrane to improve the cleaning effect;

[0017] 4) After the alkaline sodium hypochlorite solution is cleaned, the alkaline sodium hypochlorite solution in the membrane pool is drained (the alkaline sodium hypochlorite solution needs to be discharged after reduction and neutralization or returned to the water inlet for treatment together with the raw water), and the activated sludge mixed solution is re-injected to the designed liquid level. After air aeration for 5-10 minutes, the membrane group is started to produce water and put into normal operation;

[0018] 5) Open the aeration and water production pipe sections of the membrane group, transfer the membrane group to be cleaned to a special cleaning tank through the lifting system and connect the aeration pipeline, inject tap water or MBR produced water into the tank to immerse the membrane group to be cleaned, and add corresponding reagents according to the injection volume and the concentration of the acid solution (pH value is 1-4, preferably 2-3; optionally, a complexing agent such as 5-100 mg / L ethylenediaminetetraacetic acid disodium is added at a low concentration) and mix them evenly through small flow intermittent aeration (10-20% of the normal aeration volume of the MBR), soak and clean for 4-8 hours, during which a small flow aeration is performed for 4-6 minutes every 50-70 minutes to promote effective contact between the liquid and the membrane fibers to improve the cleaning effect;

[0019] 6) After the acid solution cleaning is completed, the acid solution in the membrane pool is drained (the acid solution needs to be discharged after neutralization or returned to the water inlet for treatment together with the raw water), and tap water or MBR produced water is injected again to immerse the membrane group to be cleaned. At the same time, according to the injection volume and the concentration of the alkaline sodium hypochlorite solution (effective chlorine concentration 1000-5000 mg / L, preferably 1000-3000 mg / L; adjust the pH value to 10-13, preferably 11-12 by adding alkali such as sodium hydroxide), add the corresponding reagent and use small flow intermittent aeration (10-20% of the normal aeration volume of MBR) to mix them evenly, soak and clean for 8-16 hours, during which a small flow aeration is performed every 50-70 minutes for 4-6 minutes to promote the effective contact between the liquid and the membrane to improve the cleaning effect;

[0020] 7) After the alkaline sodium hypochlorite solution is cleaned, the alkaline sodium hypochlorite solution in the membrane pool is drained (the alkaline sodium hypochlorite solution needs to be reduced and neutralized before being discharged or returned to the water inlet for treatment together with the raw water), the membrane group is transferred to the membrane pool through the lifting system, the aeration and water production pipelines of the membrane group are connected, and the membrane group is started to produce water after air aeration for 5-10 minutes, and put into normal operation.

[0021] The present invention analyzes the pollution properties of composite membranes (silicon, calcium, magnesium, aluminum, iron and other inorganic substances as nucleation and adsorption bridging media and microbial metabolites such as polysaccharides and proteins, natural organic substances such as humic acid and microbial cells form a stable pollution layer) through membrane dissection technology (electron microscopy observation, energy spectrum element analysis, infrared spectrum organic functional group analysis, contact angle hydrophilicity analysis, etc.), and proposes a high-efficiency and low-cost restorative cleaning method for composite pollution of MBR membranes through systematic research and testing. The method firstly adopts acid solution immersion cleaning to effectively remove inorganic pollutants on the MBR membrane and destroy the connection between inorganic substances and organic substances and microorganisms, and then adopts alkaline sodium hypochlorite solution immersion cleaning to effectively remove organic and microbial pollution on the MBR membrane. The method has better cleaning effect on composite membrane pollution formed by the interaction of inorganic substances, organic substances and microorganisms, and is beneficial to restoring the filtration performance of the MBR membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 The change of the clear water flux of the membrane group during the cleaning process of Example 1;

[0024] Figure 2 The change of the clear water flux of the membrane group during the cleaning process of Example 2;

[0025] Figure 3 The change of the clear water flux of the membrane group during the cleaning process of Example 3 and Comparative Example 2;

[0026] Figure 4 The change of the clear water flux of the membrane group during the cleaning process of Example 4 and Comparative Example 3;

[0027] Figure 5 This is the change in the clear water flux of the membrane group during the cleaning process of Control Example 1. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this description, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] The hollow fiber ultrafiltration membrane of an MBR sewage treatment plant that had been in operation for 2 years was dissected. The scanning electron microscope, energy spectrum analysis, infrared spectroscopy, contact angle and other advanced analytical methods revealed that the cause of membrane fouling was a composite membrane fouling composed of inorganic matter, organic matter and microorganisms (inorganic matter such as silicon, calcium, magnesium, aluminum and iron acted as nucleation and adsorption bridging media, together with microbial metabolites such as polysaccharides and proteins, natural organic matter such as humic acid and microbial cells to form a stable pollution layer).

[0033] This embodiment is directed to a cleaning method for MBR membrane composite pollution, and the steps are as follows:

[0034] 1) Stop the membrane group to be cleaned from producing water, aerate for 10 minutes to remove the sludge on the membrane fibers, and then stop aeration;

[0035] 2) Open the aeration and water production pipe sections of the membrane group, transfer the membrane group to a special cleaning tank through the lifting system and connect the aeration pipeline, inject tap water or MBR produced water into the tank until the membrane group to be cleaned is immersed, and at the same time, add citric acid according to the injection volume and the concentration of the citric acid solution (pH value is 2.5) and mix it evenly through small flow intermittent aeration (20% of the normal aeration volume of the MBR), soak and clean for 8 hours, during which a small flow aeration is performed for 10 minutes every 50 minutes to promote the effective contact between the citric acid solution and the membrane fibers to improve the cleaning effect;

[0036] 3) After the acid solution cleaning is completed, the citric acid solution in the membrane pool is drained, and tap water or MBR produced water is injected again to immerse the membrane group to be cleaned. At the same time, according to the water injection volume and the concentration of the alkaline sodium hypochlorite solution (effective chlorine concentration 1500 mg / L, sodium hydroxide is added to adjust the pH value to 11.5), the corresponding reagent is added and mixed evenly through small flow intermittent aeration (20% of the normal aeration volume of the MBR). Soak and clean for 16 hours, during which a small flow aeration is performed for 10 minutes every 50 minutes to promote the effective contact between the alkaline sodium hypochlorite solution and the membrane fibers to improve the cleaning effect;

[0037] 4) After the alkaline sodium hypochlorite solution is cleaned, the alkaline sodium hypochlorite solution in the membrane pool is drained, the membrane group is transferred to the membrane pool through the lifting system, the aeration and water production pipelines of the membrane group are connected, and the membrane group is started to produce water after air aeration for 10 minutes and put into normal operation.

[0038] The following detection method was used to measure the specific flux of clean water on the contaminated membrane before cleaning, the contaminated membrane after cleaning with citric acid solution, and the contaminated membrane after cleaning with alkaline sodium hypochlorite solution: the cleaning tank was filled with tap water and dead-end filtration was performed at constant pressure. The permeate flux of the membrane was measured under different pressures. The transmembrane pressure difference was used as the horizontal axis and the membrane flux was used as the vertical axis to plot the graph. The slope value obtained by linear fitting was the specific flux of clean water. The results are shown in Figure 1 .

[0039] Figure 1 The change of the membrane group clear water flux during the cleaning process of this embodiment is shown; the results show that the clear water membrane flux of the fouled membrane before cleaning, the fouled membrane after cleaning with citric acid solution, and the fouled membrane after cleaning with alkaline sodium hypochlorite solution all show a good linear growth with the transmembrane pressure difference (fitting coefficient R 2 are greater than 0.99), and the clean water specific flux (i.e., the fitting slope) is 4.06 L / m 2 / h / kPa, 5.18L / m 2 / h / kPa, 5.82L / m 2 / h / kPa, the increase in the specific flux of clean water of the polluted membrane after cleaning with citric acid solution and alkaline sodium hypochlorite solution was 1.12L / m 2 / h / kPa, 0.64L / m 2 / h / kPa.

[0040] Example 2

[0041] The process is the same as that of Example 1 except that the citric acid solution (pH value is 2.5) of Example 1 is replaced by the oxalic acid solution (pH value is 2.5).

[0042] The detection method of Example 1 was used to measure the clean water specific flux of the contaminated membrane before cleaning, the contaminated membrane after cleaning with oxalic acid solution, and the contaminated membrane after cleaning with alkaline sodium hypochlorite solution. The results are shown in Figure 2 . Figure 2 The change of the membrane group clear water flux during the cleaning process of this embodiment is shown; the results show that the clear water membrane flux of the contaminated membrane before cleaning, the contaminated membrane after cleaning with oxalic acid solution, and the contaminated membrane after cleaning with alkaline sodium hypochlorite solution all show a good linear growth with the transmembrane pressure difference (fitting coefficient R 2 are greater than 0.99), and the clean water specific flux (i.e., the fitting slope) is 4.07 L / m 2 / h / kPa, 5.29L / m 2 / h / kPa, 6.02L / m 2 / h / kPa, the increase in the specific flux of clean water of the polluted membrane after cleaning with oxalic acid solution and alkaline sodium hypochlorite solution was 1.22L / m 2 / h / kPa, 0.73L / m 2 / h / kPa.

[0043] Before cleaning, the clean water specific flux of the contaminated membrane group-3 in Example 2 is basically the same as that of the contaminated membrane group-2 in Example 1, indicating that the contamination status of the two membrane groups is basically the same and comparable. Compared with the method of first cleaning the contaminated membrane group-2 in Example 1 with a citric acid solution and then an alkaline sodium hypochlorite solution, the contaminated membrane group-3 in this example is first cleaned with an oxalic acid solution and then an alkaline sodium hypochlorite solution, and the clean water specific flux is increased from 1.76L / m 2 / h / kPa increased to 1.95L / m 2 / h / kPa, the increase value is further increased by 10.8%; the specific flux of clean water after cleaning with oxalic acid solution is 1.12L / m 2 / h / kPa increased to 1.22L / m 2 / h / kPa, the added value further increased by 8.93%.

[0044] In Example 1, the amount of citric acid (industrial grade, content 99%) used is about 180 kg and the cost is about 400 yuan. In this example, the amount of oxalic acid (industrial grade, content 99.6%) used is about 9 kg and the cost is about 23 yuan, both of which are reduced by about 95%. It can be seen that the technical and economic benefits of MBR membrane cleaning can be significantly improved by using oxalic acid solution first and then alkaline sodium hypochlorite solution for cleaning.

[0045] Example 3

[0046] The hollow fiber ultrafiltration membrane of an MBR sewage treatment plant which had been in operation for 3 years was dissected. The scanning electron microscope, energy spectrum analysis, infrared spectrum and other advanced analytical methods revealed that the membrane fouling was caused by composite membrane fouling composed of inorganic matter, organic matter and microorganisms.

[0047] This embodiment is directed to a cleaning method for MBR membrane composite pollution, and the steps are as follows:

[0048] 1) Stop the membrane group to be cleaned from producing water, aerate for 5 minutes to remove the mud accumulated on the membrane fibers, and then stop aeration;

[0049] 2) Open the aeration and water production pipe sections of the membrane group, transfer the membrane group to a special cleaning tank through the lifting system and connect the aeration pipe, inject tap water or MBR produced water into the tank to immerse the membrane group to be cleaned, and add oxalic acid according to the injection volume and the concentration of oxalic acid solution (pH value is 1.4) and mix it evenly through small flow intermittent aeration (10% of the normal aeration volume of MBR), soak and clean for 8 hours, during which small flow aeration is performed for 5 minutes every 70 minutes to promote effective contact between oxalic acid solution and membrane fibers to improve the cleaning effect;

[0050] 3) After the acid solution cleaning is completed, the oxalic acid solution in the membrane pool is drained, and tap water or MBR produced water is injected again to immerse the membrane group to be cleaned. At the same time, according to the water injection volume and the concentration of the alkaline sodium hypochlorite solution (effective chlorine concentration 2400 mg / L, sodium hydroxide is added to adjust the pH value to 11), the corresponding reagent is added and mixed evenly through small flow intermittent aeration (10% of the normal aeration volume of the MBR). Soak and clean for 12 hours, during which a small flow aeration is performed for 5 minutes every 70 minutes to promote the effective contact between the alkaline sodium hypochlorite solution and the membrane fibers to improve the cleaning effect;

[0051] 4) After the alkaline sodium hypochlorite solution is cleaned, the alkaline sodium hypochlorite solution in the membrane pool is drained, the membrane group is transferred to the membrane pool through the lifting system, the aeration and water production pipelines of the membrane group are connected, and the membrane group is started to produce water after air aeration for 5 minutes and put into normal operation.

[0052] The detection method of Example 1 was used to measure the clean water specific flux of the contaminated membrane before cleaning, the contaminated membrane after cleaning with oxalic acid solution, and the contaminated membrane after cleaning with alkaline sodium hypochlorite solution. The results are shown in Figure 3 . Figure 3 The change of the membrane group water flux during the cleaning process of this example is shown; the results show that the initial flux is 272L / m 2 / h / bar membrane group was first soaked and cleaned in pH=1.4 oxalic acid solution for 8 hours, and the specific flux increased to 365L / m 2 / h / bar, an increase of 34%; after being soaked and cleaned in sodium hypochlorite solution with an effective chlorine concentration of 2400mg / L and pH=11 for 12h, the specific flux continued to increase to 446L / m 2 / h / bar, with an overall increase of 64%.

[0053] Example 4

[0054] The hollow fiber ultrafiltration membrane of an MBR sewage treatment plant which had been in operation for 4 years was dissected. The scanning electron microscope, energy spectrum analysis, infrared spectrum and other advanced analytical methods revealed that the membrane fouling was caused by composite membrane fouling composed of inorganic matter, organic matter and microorganisms.

[0055] The cleaning method for the composite pollution of the MBR membrane in this embodiment is the same as that in Example 3; the detection method of Example 1 is used to measure the specific flux of clean water on the polluted membrane before cleaning, the polluted membrane after cleaning with oxalic acid solution, and the polluted membrane after cleaning with alkaline sodium hypochlorite solution. The results are shown in Figure 4 . Figure 4 The change of the membrane group water flux during the cleaning process of this example is shown; the results show that the initial flux is 98L / m 2 / h / bar membrane group was first soaked and cleaned in oxalic acid solution with pH = 1.4 for 8 hours, and the specific flux increased to 139L / m 2 / h / bar, an increase of 42%; after being soaked and cleaned in sodium hypochlorite solution with an effective chlorine concentration of 2400 mg / L and pH = 11 for 12 hours, the specific flux continued to increase to 273 L / m 2 / h / bar, with an overall increase of 179%.

[0056] Comparative Example 1

[0057] This comparative example adopts the cleaning method commonly used in MBR sewage treatment plants for off-line restorative cleaning, which is the same as Example 1 except that the cleaning order of the citric acid solution and the alkaline sodium hypochlorite solution is reversed.

[0058] The cleaning method for MBR membrane composite pollution in this comparative example has the following steps:

[0059] 1) Stop the membrane group to be cleaned from producing water, aerate for 10 minutes to remove the sludge on the membrane fibers, and then stop aeration;

[0060] 2) Open the aeration and water production pipe sections of the membrane group, transfer the membrane group to a special cleaning tank through the lifting system and connect the aeration pipe, inject tap water or MBR produced water into the tank until the membrane group to be cleaned is immersed, and at the same time, according to the injection volume and the concentration of alkaline sodium hypochlorite solution (effective chlorine concentration 1500 mg / L, sodium hydroxide is added to adjust the pH value to 11.5), add the corresponding reagent and use small flow intermittent aeration (20% of the normal aeration volume of MBR) to mix it evenly, soak and clean for 16 hours, during which a small flow aeration is performed for 10 minutes every 50 minutes to promote the effective contact between the alkaline sodium hypochlorite solution and the membrane fibers to improve the cleaning effect;

[0061] 3) After the alkaline sodium hypochlorite solution cleaning is completed, the alkaline sodium hypochlorite solution in the membrane pool is drained, and tap water or MBR produced water is injected again to immerse the membrane group to be cleaned. At the same time, citric acid is added according to the water injection volume and the concentration of the citric acid solution (pH value is 2.5) and mixed evenly through small flow intermittent aeration (20% of the normal aeration volume of the MBR). Soak and clean for 8 hours, during which a small flow rate aeration is performed for 10 minutes every 50 minutes to promote the effective contact between the citric acid solution and the membrane fibers to improve the cleaning effect;

[0062] 4) After the citric acid solution is cleaned, the citric acid solution in the membrane pool is drained, the membrane group is transferred to the membrane pool through the lifting system, the aeration and water production pipelines of the membrane group are connected, and the membrane group is started to produce water after air aeration for 10 minutes and put into normal operation.

[0063] The detection method of Example 1 was used to measure the clean water specific flux of the contaminated membrane before cleaning, the contaminated membrane after cleaning with alkaline sodium hypochlorite solution, and the contaminated membrane after cleaning with citric acid solution. The results are shown in Figure 5 . Figure 5 The change of the membrane group clear water flux during the cleaning process of this control example is shown; the results show that the clear water membrane flux of the fouled membrane before cleaning, the fouled membrane after cleaning with alkaline sodium hypochlorite solution, and the fouled membrane after cleaning with citric acid solution all show a good linear growth with the transmembrane pressure difference (fitting coefficient R 2 are greater than 0.99), and the clean water specific flux (i.e., the fitting slope) is 4.16 L / m 2 / h / kPa, 4.73L / m 2 / h / kPa, 5.33L / m 2 / h / kPa, the increase in the specific flux of clean water after cleaning with alkaline sodium hypochlorite solution and citric acid solution was 0.57L / m 2 / h / kPa, 0.6L / m 2 / h / kPa.

[0064] The difference in the clean water flux between the contaminated membrane group-2 of Example 1 and the contaminated membrane group-1 of this comparative example is small, indicating that the contamination status of the two membrane groups is not much different and they are comparable. Compared with the conventional method of first using alkaline sodium hypochlorite solution and then using citric acid solution to clean the contaminated membrane group-1 of this comparative example, the clean water flux of the contaminated membrane group-2 of Example 1, which is first cleaned with citric acid solution and then with alkaline sodium hypochlorite solution, is 1.17L / m 2 / h / kPa increased to 1.76L / m 2 / h / kPa, the added value increased by 50.43%, especially the specific flux of clean water after washing with citric acid solution increased from 0.6L / m 2 / h / kPa increased to 1.12L / m 2 / h / kPa, the added value increased by 86.67%.

[0065] Comparative Example 2

[0066] This comparative example adopts the cleaning method commonly used in MBR sewage treatment plants for off-line restorative cleaning, which is the same as Example 3 except that the cleaning order of the oxalic acid solution and the alkaline sodium hypochlorite solution is reversed.

[0067] The cleaning method for MBR membrane composite pollution in this comparative example has the following steps:

[0068] 1) Stop the membrane group to be cleaned from producing water, aerate for 5 minutes to remove the mud accumulated on the membrane fibers, and then stop aeration;

[0069] 2) Open the aeration and water production pipe sections of the membrane group, transfer the membrane group to a special cleaning tank through the lifting system and connect the aeration pipe, inject tap water or MBR produced water into the tank until the membrane group to be cleaned is immersed, and add corresponding reagents according to the injection volume and the concentration of alkaline sodium hypochlorite solution (effective chlorine concentration 2400 mg / L, sodium hydroxide is added to adjust the pH value to 11) and mix them evenly through small flow intermittent aeration (10% of the normal aeration volume of MBR), soak and clean for 12 hours, during which small flow aeration is performed for 5 minutes every 70 minutes to promote the effective contact between the alkaline sodium hypochlorite solution and the membrane fibers to improve the cleaning effect;

[0070] 3) After the alkaline sodium hypochlorite solution cleaning is completed, the alkaline sodium hypochlorite solution in the membrane pool is drained, and tap water or MBR produced water is injected again to immerse the membrane group to be cleaned. At the same time, oxalic acid is added according to the water injection volume and the concentration of oxalic acid solution (pH value is 1.4) and mixed evenly through small flow intermittent aeration (10% of the normal aeration volume of MBR). Soak and clean for 8 hours, during which a small flow aeration is performed for 5 minutes every 70 minutes to promote the effective contact between the oxalic acid solution and the membrane fibers to improve the cleaning effect;

[0071] 4) After the oxalic acid solution is cleaned, the oxalic acid solution in the membrane pool is drained, the membrane group is transferred to the membrane pool through the lifting system, the aeration and water production pipelines of the membrane group are connected, and the membrane group is started to produce water after air aeration for 5 minutes and put into normal operation.

[0072] The detection method of Example 1 was used to measure the clean water specific flux of the contaminated membrane before cleaning, the contaminated membrane after cleaning with alkaline sodium hypochlorite solution, and the contaminated membrane after cleaning with oxalic acid solution. The results are shown in Figure 3 ; The results show that: initial specific flux is 321L / m 2 / h / bar membrane group was first soaked and cleaned in alkaline sodium hypochlorite solution with effective chlorine concentration of 2400mg / L and pH=11 for 12h, and the specific flux increased to 420L / m 2 / h / bar, the increase was 31%; after being soaked and cleaned in oxalic acid solution with pH = 1.4 for 8 hours, the specific flux was slightly reduced to 401L / m 2 / h / bar, with an overall increase of only 27%.

[0073] Comparative Example 3

[0074] This control example adopts the cleaning method commonly used in MBR sewage treatment plants for offline restorative cleaning. Except for the fact that the cleaning order of oxalic acid solution and alkaline sodium hypochlorite solution is swapped, the rest is the same as Example 4. The cleaning method refers to Control Example 2.

[0075] The detection method of Example 1 was used to measure the clean water specific flux of the contaminated membrane before cleaning, the contaminated membrane after cleaning with alkaline sodium hypochlorite solution, and the contaminated membrane after cleaning with oxalic acid solution. The results are shown in Figure 4 ; The results show that: initial specific flux is 111L / m 2 / h / bar membrane group was first soaked and cleaned in alkaline sodium hypochlorite solution with effective chlorine concentration of 2400mg / L and pH=11 for 12h, and the specific flux increased to 246L / m 2 / h / bar, the increase reached 122%; after soaking and cleaning in pH=1.4 oxalic acid solution for 8h, the specific flux continued to increase to 272L / m 2 / h / bar, an overall increase of 146%.

[0076] comprehensive Figure 3 , Figure 4 It can be seen that the cleaning effect of the present invention, which first uses an acidic solution and then an alkaline sodium hypochlorite solution for cleaning, on polluted membrane groups with different operating years is better than the conventional MBR membrane cleaning method of first using alkali and then using acid.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cleaning method for MBR membrane composite pollution, characterized in that: include: The MBR membrane is firstly soaked and cleaned with an acidic solution, and then soaked and cleaned with an alkaline sodium hypochlorite solution for a second time.

2. The cleaning method according to claim 1, characterized in that: The pH value of the acidic solution is 1-4; the effective chlorine concentration of the alkaline sodium hypochlorite solution is 1000-5000 mg / L and the pH value is 10-13.

3. The cleaning method according to claim 1, characterized in that: The acidic solution includes an acid selected from at least one of hydrochloric acid, sulfuric acid, citric acid and oxalic acid.

4. The cleaning method according to claim 1, characterized in that: The acidic solution also includes a complexing agent, and the concentration of the complexing agent in the acidic solution is 5-100 mg / L.

5. The cleaning method according to claim 1, characterized in that: The first soaking and cleaning time is 4-8 hours.

6. The cleaning method according to claim 1, characterized in that: During the first immersion cleaning process, small flow aeration is performed intermittently. The aeration volume of the small flow aeration is 10-20% of the aeration volume of the normal operation of the MBR. The aeration time of the small flow aeration is 4-6 minutes, and the intermittent time of the small flow aeration is 50-70 minutes.

7. The cleaning method according to claim 1, characterized in that: The second soaking and cleaning time is 8-16h.

8. The cleaning method according to claim 1, characterized in that: During the second immersion cleaning process, small flow aeration is performed intermittently. The aeration volume of the small flow aeration is 10-20% of the aeration volume of the normal operation of the MBR. The aeration time of the small flow aeration is 4-6 minutes, and the intermittent time of the small flow aeration is 50-70 minutes.

9. The cleaning method according to claim 1, characterized in that: Before the first soaking and cleaning, aerate and flush the membrane group to be cleaned for 5-10 minutes after the filtration has stopped.

10. The cleaning method according to claim 1, characterized in that: The first immersion cleaning and the second immersion cleaning are performed by an in-situ cleaning method or an ex-situ cleaning method.

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