Method for off-line cleaning of hollow-fiber membrane for MBR using ozone micro-nano bubble

Abstract

To provide a method for off-line cleaning of a hollow-fiber membrane for MBR using ozone micro-nano bubble.SOLUTION: Ozone micro nano-bubbles generated by a micro nano-bubble generator are used for cleaning membrane. Therein, dissolved ozone concentration is controlled into 1 to 5 mg / L. A method for off-line cleaning of a hollow-fiber membrane dissolves such a problem that a residual amount of a chemical in water, in a conventional hollow-fiber off-line cleaning process and prevents waste liquid treatment problem after cleaning. further, ozone micro nano-bubbles have such advantages as high dissolving ability and high material transfer efficiency, and can generate OH radicals more than usual ozone water. Such problems that the ozone utilization factor is low and cleaning effect is also usual can be dissolved.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to the technical field of membrane cleaning, and particularly to a method for offline cleaning of hollow fiber membranes for MBR using ozone micro-nano bubbles.

Background Art

[0002] The cleaning of hollow fiber membranes for MBR is divided into online cleaning and offline cleaning. Online cleaning means that when membrane fouling is not severe, the membrane is periodically cleaned on-site using a chemical solution. When the performance of the membrane cannot be effectively restored by online cleaning, it is necessary to remove the membrane module from the treatment tank and immerse it in a chemical solution for offline cleaning. Conventional offline chemical cleaning of hollow fiber membranes for MBR generally uses acid and alkali chemicals, generating a large amount of acid and alkali cleaning waste liquid and harmful by-products, thus polluting the water quality.

[0003] Ozone has a strong oxidizing ability to oxidize organic and inorganic compounds, can oxidize most organic pollutants in wastewater, and is widely used in industrial wastewater treatment. Ozone oxidizes organic substances in two ways. The first is that ozone molecules selectively oxidize organic substances, that is, direct oxidation. The second is OH radicals generated by self-decomposition, which convert the pollutants on the membrane surface into intermediate products that are easily biodegradable, and oxidize organic substances quickly and non-selectively, that is, indirect oxidation. In the conventional method of cleaning membranes using ozone, the dissolved ozone concentration is generally relatively high, which is suitable for ozone-resistant membranes but has low applicability.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made in view of the above circumstances, and solves the problem that the residual amount of chemicals in water is excessive in the conventional offline cleaning process of hollow fiber membranes, avoids the problem of waste liquid treatment after cleaning, and ozone micro-nanobubbles have the advantages of high dissolution ability and high mass transfer efficiency, can generate more OH radicals than ordinary ozone water, and solves the problem that the ozone utilization rate generated by cleaning the membrane with ozone water is low and the cleaning effect is also ordinary. The purpose is to provide an offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles.

Means for Solving the Problems

[0005] To achieve the above object, the present invention is realized by the following technical means. An offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles, comprising the following steps. S1. In equipment connection,

[0006] The oxygen generator, ozone generator, and micro-nanobubble generator are connected in sequence via the first pipe and the second pipe. The liquid inlet of the micro-nanobubble generator is connected to the third pipe, and the gas outlet of the micro-nanobubble generator is connected to the fourth pipe. Both the third pipe and the fourth pipe extend into the cleaning tank. The hollow fiber membrane is immersed in the cleaning tank. The hollow fiber membrane is connected to a pressure sensor and a cleaning pump via the fifth pipe. The cleaning pump is further connected to the sixth pipe. The sixth pipe extends into the cleaning tank. The cleaning tank also cools the water in the tank by a cooling device. The oxygen generator is not particularly limited as long as it generates oxygen, for example, an oxygen generator, an industrial oxygen cylinder, etc. The cooling device is also not particularly limited as long as it plays a role in controlling the temperature of the cleaning liquid, for example, a cooling water circulation machine, a cooling water pipe, a low-temperature constant temperature bath, etc. During operation, the water temperature of the micro-nanobubble generator gradually rises, but the temperature has a great influence on the dissolution of ozone gas and the residence time of micro-nanobubbles in water, so the control of the water temperature is very important. S2. In membrane cleaning, 1) Turn on the oxygen generator and the ozone generator in sequence. The oxygen generated by the oxygen generator is sent into the ozone generator through the first pipe to generate ozone.

[0007] 2) Turn on the micro-nano bubble generator. Ozone is sent into the micro-nano bubble generator through the second pipe, and the water in the cleaning tank is sent into the micro-nano bubble generator through the third pipe. The generated ozone micro-nano bubbles are discharged into the cleaning tank through the fourth pipe, and the dissolved ozone concentration is 1 - 5 mg / L.

[0008] 3) Start the cleaning pump, and let the ozone micro-nano bubbles pass through the membrane in the forward direction for cleaning. In the method of "forward cleaning while immersed" or "alternate cleaning of immersion cleaning and forward cleaning", the cleaning can be stopped until the TMP displayed by the pressure sensor does not drop by more than 10% within 30 minutes.

[0009] Here, micro-nano bubbles refer to tiny bubbles with a diameter of less than 100 μm, and can be divided into micro-bubbles with a diameter of 1 - 100 μm and nano-bubbles with a diameter of less than 1 μm. Ozone micro-nano bubble technology refers to micro-nano level bubbles formed after ozone passes through the micro-nano bubble generator. Ozone micro-nano bubble technology utilizes the characteristics of large specific surface area, slow rising speed, negatively charged surface of micro-nano bubbles, and promoting ozone to generate more OH radicals.

[0010] Ozone micro-nano bubbles have high solubility in water and a long duration of ozone. At the same dissolved ozone concentration, the void ratio of ozone micro-nano bubbles is much higher than that of ozone macro-bubbles. As the dissolved ozone concentration increases, the difference in void ratio between the two becomes larger and larger.

[0011] The mass transfer efficiency of ozone micro-nano bubbles is high, and the saturated dissolved ozone concentration reached by ozone micro-nano bubbles is higher than that of ozone macro-bubbles. The time required for ozone micro-bubbles to reach the saturated dissolved ozone concentration is faster than that of ozone macro-bubbles.

[0012] Ozone micro-nano bubbles have high ozone utilization efficiency, generate a large amount of OH radicals, and have a high zeta potential on the surface. Therefore, compared with conventional ozone aeration, they can significantly promote the decomposition of organic pollutants, and have unique advantages in the membrane cleaning process due to the unique interface structure of ozone micro-nano bubbles.

[0013] Furthermore, the process of generating micro-nano bubbles is an exothermic process. During the operation of the micro-nano bubble generator, the water temperature gradually rises, and the temperature has a great influence on the dissolution of ozone gas and the residence time of micro-nano bubbles in water. Therefore, the control of water temperature is very important.

[0014] Also, the specific steps of the "sequential cleaning while immersed" method are as follows. Start the cleaning pump, and while the hollow fiber membrane is immersed in the cleaning solution, pass ozone micro-nano bubbles through the membrane in the forward direction for cleaning. Measure the dissolved ozone concentration, water temperature, and TMP (membrane differential pressure) during the membrane cleaning process of the ozone micro-nano bubble cleaning solution in the cleaning tank every 10 minutes. Cleaning can be stopped until the TMP displayed by the pressure sensor does not drop by more than 10% within 30 minutes, and the cleaning time is at most 2 hours. Also, the specific steps of the "alternate cleaning of immersion cleaning and sequential cleaning" method are as follows.

[0015] a. Start the cleaning pump, and while the hollow fiber membrane is immersed in the cleaning solution, pass ozone micro-nano bubbles through the membrane in the forward direction for 30 minutes of cleaning. Measure the dissolved ozone concentration, water temperature, and TMP (membrane differential pressure) during the membrane cleaning process of the ozone micro-nano bubble cleaning solution in the cleaning tank every 10 minutes.

[0016] b. Stop the cleaning pump, and immerse the hollow fiber membrane in ozone micro-nano bubbles for 30 minutes of immersion cleaning. Measure the dissolved ozone concentration, water temperature, and TMP during the membrane cleaning process of the ozone micro-nano bubble cleaning solution in the cleaning tank every 10 minutes.

[0017] c. Repeat steps a to b until the TMP displayed by the pressure sensor no longer drops by 10% or more within 30 minutes, at which point the cleaning can be stopped, and the maximum cleaning time is 2 hours. Also, keep the temperature of the cleaning liquid in the cleaning tank at 25°C ± 2°C using a cooling device.

[0018] In addition, on the upper part of the cleaning tank, there is a cleaning tank upper cover provided with a first insertion hole for the third pipe to pass through, a second insertion hole for the fourth pipe to pass through, a third insertion hole for the fifth pipe to pass through, and a fourth insertion hole for the sixth pipe to pass through. During use, each pipe is inserted into the cleaning tank through the corresponding insertion hole. The ozone waste gas treatment device is not particularly limited as long as it can discharge the treated ozone waste gas according to the standards.

[0019] Furthermore, on the cleaning tank upper cover, there is an ozone waste gas discharge hole further provided, which is connected to the ozone waste gas treatment device via the seventh pipe, and the generated waste gas is discharged after being treated by the ozone waste gas treatment device. Also, the cooling device is a low-temperature constant temperature bath, and the cleaning tank is arranged in the water tank of the low-temperature constant temperature bath. This method is suitable for cleaning small hollow fiber membranes.

[0020] Moreover, the cooling device includes a cooling water circulation device, an eighth pipe, a ninth pipe, and a cooling water pipe. The eighth pipe is connected to the cooling water inlet of the cooling water circulation device, the ninth pipe is connected to the cooling water outlet of the cooling water circulation device, the cooling water pipe is located in the cleaning tank and is provided along the wall surface, and both ends of the cooling water pipe are respectively connected to the eighth pipe and the ninth pipe. This method is suitable for cleaning large hollow fiber membranes.

[0021] In addition, above the cleaning tank, there is further provided a bubble uniform dispersion mechanism including a vertically provided connecting pipe, a plurality of horizontally provided flow guiding pipes, and a plurality of nozzles. The connecting pipe is connected to the fourth pipe, all of the plurality of flow guiding pipes communicate with the connecting pipe, the nozzles are evenly arranged on the flow guiding pipes, and the generated ozone micro-nano bubbles are evenly discharged into the cleaning tank through the plurality of nozzles.

Advantages of the Invention

[0022] Compared with the prior art, the method for offline cleaning of hollow fiber membranes for MBR using ozone micro-nano bubbles of the present invention has the following advantages:

[0023] 1. Environmentally friendly. When cleaning the membrane with ozone micro-nano bubbles, fewer halogenated disinfection by-products are generated compared to NaClO, solving the problem of excessive residual chemical agents in water during the offline cleaning process of conventional hollow fiber membranes and avoiding the problem of waste liquid treatment after cleaning. In terms of cost, the ozone micro-nano bubble technology uses water and ozone as raw materials and produces ozone on-site, so it does not require transportation and storage, and the cost can also be reduced. Ozone micro-nano bubbles do not require storage and the addition of chemical reagents, are instantly generated when water is used, and can be processed in real time. This improves the processing efficiency and shortens the waiting time during the processing process.

[0024] 2. None of the patents for cleaning with conventional ozone micro-nano bubbles or ozone micro-bubbles consider the exothermic process in the generation process of ozone micro-nano bubbles. If the temperature is too high, it will have a great impact on the residence time of micro-nano bubbles and the dissolution of ozone. In the present invention, a cooling device is used to control the temperature of the cleaning liquid so as not to affect the dissolution of ozone micro-nano bubbles.

[0025] 3. In the present invention, ozone micro-nano bubble water with a dissolved ozone concentration of 1-5 mg / L is selected. When cleaning the membrane in the "forward cleaning while soaking" method using ozone micro-nano bubble water with a dissolved ozone concentration of 1 mg / L, the cleaning effect is higher than that of sodium hypochlorite at 2000 ppm.

[0026] 4. The saturated dissolved ozone concentration of ozone micro-nano bubbles is higher than that of ozone macro-bubbles, and the required time is faster than that of ozone macro-bubbles. Compared with conventional ozone aeration, the more OH radicals generated by ozone micro-nano bubbles, the more significantly the decomposition of organic pollutants is promoted. The unique interface structure of ozone micro-nano bubbles has unique advantages in the membrane cleaning process.

[0027] 5. The present invention explores an optimal membrane passing method using ozone micro-nano bubbles, and it has been found that the effect of cleaning by passing ozone micro-nano bubbles through the membrane in the forward direction is higher than that of cleaning by passing them through the membrane in the reverse direction. Therefore, the membrane cleaning method using ozone micro-nano bubbles selects "forward cleaning while immersed", and considering energy consumption, "alternate cleaning of immersion cleaning and forward cleaning" is adopted. Different from the conventional cleaning methods of hollow fiber membranes, immersion cleaning with a cleaning liquid or cleaning by passing the cleaning liquid through the membrane in the reverse direction is not adopted.

Brief Description of the Drawings

[0028] The drawings constituting a part of the present invention are used for the purpose of further understanding the present invention. The schematic embodiments and their descriptions of the present invention are used to interpret the present invention and do not constitute an undue limitation to the present invention.

Figure 1

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Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0029] Note that when there is no contradiction, the examples and features in the examples in the present invention can be combined with each other.

[0030] The terms "center", "vertical direction", "horizontal direction", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. used in the present invention to indicate the orientation or positional relationship are the orientation or positional relationship shown based on the drawings, and are merely for the purpose of making it easier to simply explain the present invention. It does not indicate or imply that the indicated device or member must have a specific orientation or be configured and operated in a specific orientation, so it should not be understood as a limitation to the present invention. In addition, the terms "first" and "second" are merely used to describe the purpose, and it should not be understood that they indicate or imply relative importance or implicitly specify the number of the indicated technical features. Therefore, the features defined by "first", "second", etc. can explicitly or implicitly include one or more of the features. The term "plurality" used in the present invention means two or more unless otherwise specified.

[0031] Unless otherwise specifically defined or limited, the terms "attached", "coupled", "connected" used in the present invention should be interpreted in a broad sense. For example, it can be a connection and fixation, a removably connected connection, or an integrally connected connection, which can be a mechanical connection, an electrical connection, a direct connection, or an indirect connection through an intermediate element, and can also be a communication inside two elements. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific situation.

[0032] Hereinafter, with reference to the drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention. (Embodiment 1) The offline cleaning method of the hollow fiber membrane for MBR using ozone micro-nano bubbles includes the following steps. S1. In equipment connection,

[0033] The oxygen generator 1, the ozone generator 3, and the micro-nano bubble generator 5 are connected in sequence via the first pipe 2 and the second pipe 4. The liquid inlet of the micro-nano bubble generator 5 is connected to the third pipe 6, and the gas outlet of the micro-nano bubble generator 5 is connected to the fourth pipe 7. Both the third pipe 6 and the fourth pipe 7 extend into the cleaning tank 9. The hollow fiber membrane 10 is immersed in the cleaning tank 9. The hollow fiber membrane 10 is connected to the pressure sensor 12 and the cleaning pump 13 via the fifth pipe 11. The cleaning pump 13 is further connected to the sixth pipe 14. The sixth pipe 14 extends into the cleaning tank 9. The cleaning tank 9 also cools the water in the tank by the cooling device 8. The cooling device 8 is not particularly limited as long as it can control the temperature of the cleaning liquid. For example, it can be a cooling water circulation device, a cooling water pipe, a low-temperature constant temperature bath, etc. During operation of the micro-nano bubble generator 5, the water temperature gradually rises. Since the temperature has a great influence on the dissolution of ozone gas and the residence time of micro-nano bubbles in water, the control of the water temperature is very important. The cooling device 8 in this embodiment is a low-temperature constant temperature bath, and the cleaning tank is arranged in the water tank of the low-temperature constant temperature bath.

[0034] A cleaning tank upper cover 15 is provided on the upper part of the cleaning tank 9. As shown in FIG. 2, the cleaning tank upper cover is provided with a first insertion hole a for the third pipe 6 to pass through, a second insertion hole b for the fourth pipe 7 to pass through, a third insertion hole d for the fifth pipe 11 to pass through, and a fourth insertion hole e for the sixth pipe 14 to pass through. During use, each pipe is inserted into the cleaning tank 9 from the corresponding insertion hole.

[0035] The cleaning tank upper cover is connected to the ozone waste gas treatment device 17 via the seventh pipe 16, and an ozone waste gas discharge hole c is further provided for the generated waste gas to be discharged after being treated by the ozone waste gas treatment device 17. The connected devices are shown in FIG. 1. S2. In membrane cleaning,

[0036] 1) Turn on the oxygen generator 1 and the ozone generator 3 in sequence. The oxygen generated by the oxygen generator 1 is sent into the ozone generator 3 through the first pipe 2 to generate ozone.

[0037] 2) Turn on the micro-nano bubble generator 5. Ozone is sent into the micro-nano bubble generator 5 through the second pipe 4, and the water in the cleaning tank 9 is sent into the micro-nano bubble generator 5 through the third pipe 6. The generated ozone micro-nano bubbles are discharged into the cleaning tank 9 through the fourth pipe 7. Considering the difference in the degree of membrane contamination to be actually cleaned, it is preferable that the dissolved ozone concentration is 1-5 mg / L according to the actual situation. Place the cleaning tank 9 in the constant temperature tank of the cooling water circulation device, and keep the temperature of the cleaning liquid in the cleaning tank 9 at 25°C by the cooling device 8. 3) The hollow fiber membrane module is connected via the fifth pipe 11, the pressure sensor 12, and the cleaning pump 13. The water after membrane filtration is returned to the cleaning tank 9 through the sixth pipe 14.

[0038] Specifically, start the cleaning pump 13, pass the ozone micro-nano bubbles in the forward direction for membrane cleaning, and clean in the way of "forward cleaning while immersed" or "alternate cleaning of immersion cleaning and forward cleaning". Cleaning can be stopped until the TMP displayed by the pressure sensor 12 does not drop by more than 10% within 30 minutes.

[0039] 4) The ozone waste gas discharge hole c is connected to the ozone waste gas treatment device 17 through the seventh pipe 16, and the generated waste gas is discharged after being treated by the ozone waste gas treatment device 17.

[0040] Here, the specific steps of the "forward cleaning while immersed" method are as follows. Start the cleaning pump 13, keep the hollow fiber membrane 10 immersed in the cleaning liquid, pass the ozone micro-nano bubbles in the forward direction through the membrane for cleaning, measure the dissolved ozone concentration, water temperature, and TMP (membrane differential pressure) of the ozone micro-nano bubble cleaning liquid in the cleaning tank 9 every 10 minutes, and cleaning can be stopped until the TMP displayed by the pressure sensor 12 does not drop by more than 10% within 30 minutes. The cleaning time is at most 2 hours. The specific steps of the "alternate cleaning of immersion cleaning and forward cleaning" method are as follows.

[0041] a. Start the cleaning pump 13, and while the hollow fiber membrane 10 is immersed in the cleaning liquid, pass ozone micro-nano bubbles through the membrane in the forward direction for 30 minutes of cleaning. Measure the dissolved ozone concentration, water temperature, and TMP (membrane differential pressure) in the ozone micro-nano bubble cleaning liquid in the cleaning tank 9 every 10 minutes.

[0042] b. Stop the cleaning pump 13, and immerse the hollow fiber membrane in ozone micro-nano bubbles for 30 minutes of immersion cleaning. Measure the dissolved ozone concentration, water temperature, and TMP in the ozone micro-nano bubble cleaning liquid in the cleaning tank 9 every 10 minutes.

[0043] c. Repeat steps a to b, and the cleaning can be stopped until the TMP displayed by the pressure sensor 12 does not drop by more than 10% within 30 minutes. The maximum cleaning time is 2 hours. (Example 2)

[0044] An offline cleaning method for a hollow fiber membrane for MBR using ozone micro-nano bubbles, which is different from Example 1 in that there is a difference in the connection of the equipment in step S1. That is, for the cooling device 8, a cooling water circulation device, an eighth pipe 18, a ninth pipe 19, and a cooling water pipe 20 are used. The eighth pipe 18 is connected to the cooling water inlet of the cooling water circulation device, the ninth pipe 19 is connected to the cooling water outlet of the cooling water circulation device, the cooling water pipe 20 is located in the cleaning tank 9 and is arranged in a ring along the wall surface. Both ends of the cooling water pipe 20 are respectively connected to the eighth pipe 18 and the ninth pipe 19. As shown in FIGS. 3 and 4, a fifth insertion hole f and a sixth insertion hole f for the connection and insertion of the eighth pipe 18 and the ninth pipe 19 are respectively provided on the upper cover for the cleaning tank.

[0045] Above the cleaning tank 9, a bubble uniform dispersion mechanism that is hung on the edge of the inner tank of the cleaning tank is further provided. As shown in Fig. 5, the bubble uniform dispersion mechanism includes a vertically provided connecting pipe 21, a plurality of horizontally provided flow guiding pipes 22, and a plurality of nozzles 23. The connecting pipe 21 is connected to the fourth pipe 7, all of the plurality of flow guiding pipes 22 communicate with the connecting pipe, the nozzles 23 are evenly arranged on the flow guiding pipes 22, and the generated ozone micro-nano bubbles are evenly discharged into the cleaning tank 9 through the plurality of nozzles 23. (Test) This test example used the method described in Example 1.

[0046] The cleaned membrane is a PVDF hollow fiber membrane that has been continuously operated in the MBR membrane bioreactor for 9 months, and the sludge concentration of this MBR membrane bioreactor was 5000 mg / L. The effective volume of the cleaning liquid in the cleaning tank was 1 L. The effective area of the cleaned hollow fiber membrane was 15.1×10 -3 m 2 It was.

[0047] This test example compared the cleaning effects of the cleaning liquid in different membrane cleaning modes. The so-called "immersion cleaning" means that the membrane was immersed in the cleaning liquid. The "backwashing while immersed" means that the membrane was immersed in the cleaning liquid, and the cleaning liquid was pumped into the inside of the hollow fiber of the membrane by a cleaning pump, and the cleaning liquid was passed through the membrane from the inside to the outside of the hollow fiber of the membrane for cleaning. The so-called "forward washing while immersed" means that the membrane was immersed in the cleaning liquid, and then suction was performed by a cleaning pump, and the cleaning liquid was cleaned from the outside to the inside on the membrane surface of the hollow fiber membrane. The so-called "alternate cleaning of immersion cleaning and forward cleaning" means that the membrane was passed through in the forward direction every 30 minutes while being immersed in the cleaning liquid for cleaning. The membrane was immersed in the cleaning liquid, first the cleaning pump was started, the cleaning liquid was passed through the membrane in the forward direction for 30 minutes of cleaning, then the cleaning pump was stopped, and the membrane was simply immersed in the cleaning liquid for 30 minutes, and it was operated in a cycle according to the above rules. 1. In this test example, the cleaning effect of the membrane was evaluated by the cleaning efficiency. The cleaning efficiency was evaluated by the reduction rate of the membrane resistance of the hollow fiber membrane. The formula is as follows.

Number

[0048] In the formula, R 洗浄後 refers to the membrane resistance (m -1 ) after cleaning the contaminated membrane, and R 汚染後 refers to the membrane resistance (m -1 ) of the contaminated membrane, and R 初期 refers to the membrane resistance (m -1 ) of the original membrane. After immersing the original membrane in ultrapure water for 24 h, the permeation coefficient of pure water was measured. The resistance of the said membrane is calculated according to the following mathematical formula.

Number

[0049] In the formula, R refers to the resistance (m -1 ) of the membrane module, ΔP refers to the differential pressure between membranes (Pa), μ refers to the dynamic viscosity (Pa·s) of deionized water at 20 °C in this experiment, and it is selected to be 1.00×10 -3 , and J refers to the flux of the membrane module L / (m 2 ·h).

[0050] This test example compared the cleaning effects of ozone micro-nano bubbles, ordinary ozone water, and 2000 ppm NaClO on the MBR hollow fiber membrane. In order to ensure the accuracy of the experimental results, the test data were selected and calculated by repeating the test 3 times per cleaning experiment.

[0051] The membrane cleaning effects of ozone micro-nano bubbles and ordinary ozone water with the same dissolved ozone concentration in water were compared. Ozone gas and water were passed through the micro-nano bubble generator 5. After operating for half an hour, the cleaning liquid concentration was balanced, and ozone micro-nano bubbles with a dissolved ozone concentration of 1 mg / L in water were generated in the cleaning tank. Ozone gas was aerated into the cleaning tank through an aeration stone, and the ozone concentration in the ozone water measured after stabilization was 1 mg / L. The principle of the generation of the ozone micro-nano bubbles is gas dissolution and release, compression adjustment of the over-current cross-section, and sudden expansion. The generation of ordinary ozone water is carried out by dissolving ozone gas in water through an aeration stone.

[0052]

Table 1

[0053] From Table 1, it was found that the effects of "immersion cleaning", "alternate cleaning of immersion cleaning and forward cleaning", and "forward cleaning while immersed" of the hollow fiber membrane by ozone micro-nano bubbles were all higher than those of the hollow fiber membrane cleaned by ordinary ozone water and 2000 ppm NaClO. Since ozone micro-nano bubbles have a strong dissolving power in water, the ozone retention time is long. The ozone utilization efficiency is high, the generation of OH radicals is large, which is beneficial to the cleaning of membrane pores, and moreover, the unique interface structure of micro-nano bubbles is also beneficial to the cleaning of the membrane surface. 2. This test example compared the 1-hour cleaning efficiency of hollow fiber membranes by ozone micro-nano bubbles with dissolved ozone concentrations of 1, 3, 5, and 7 mg / L.

[0054]

Table 2

[0055]

Table 3

[0056] From Tables 2 and 3, regarding the cleaning effects of different cleaning methods at the same concentration, it was found that "forward cleaning while immersing" > "alternate cleaning of immersion cleaning and forward cleaning" > "immersion cleaning" > "reverse cleaning while immersing". Therefore, the conclusion can be drawn that the optimal cleaning method using ozone micro-nano bubbles is "performing forward cleaning while immersing". Considering the aspect of energy consumption, "alternate cleaning of immersion cleaning and forward cleaning" can be used.

[0057] From Tables 2 and 3, the membrane cleaning effects of dissolved ozone concentrations of 5 mg / L and 7 mg / L in ozone micro-nano bubbles are approximately the same. Moreover, the cleaning effect of 7 mg / L is slightly lower than that of 5 mg / L. It was found that when the dissolved ozone concentration in ozone micro-nano bubbles is 5 mg / L, it already meets the cleaning requirements of this membrane. Further increasing the ozone concentration will cause waste of resources, increase in costs, and also affect the performance of the membrane. Considering the differences in the degree of membrane pollution during actual cleaning and the actual situation, it is preferably 1 - 5 mg / L of the dissolved ozone concentration in ozone micro-nano bubbles. The membrane to be cleaned in the present invention is a PVDF hollow fiber membrane suitable for MBR water treatment.

[0058] Also, from Tables 2 and 3, it was found that for the contaminated membranes used in this test example, after cleaning for 1 h by passing the membrane in the forward direction simultaneously with immersion, the cleaning effects of all the membranes reached 90% or more.

[0059] 3. Changes in TMP during the processes of "forward cleaning while immersing" and "alternate cleaning of immersion cleaning and forward cleaning" using ozone micro-nano bubbles with dissolved ozone concentrations of 1, 3, and 5 mg / L in water.

[0060] Referring to FIGS. 7 and 8, it was found that the change in TMP had already stabilized 2 hours after membrane cleaning, indicating that the cleaning effect had reached saturation. Regarding the cleaning time criterion, considering the difference in the degree of membrane fouling, TMP during the membrane cleaning process was measured every 10 minutes, and the cleaning could be stopped until the TMP displayed by the pressure sensor did not drop by more than 10% within 30 minutes. The maximum cleaning time was 2 hours. Thus, even if the membrane fouling was severe, it could be cleaned within 2 hours of cleaning time. 4. Regarding the cleaning cost

[0061] [Table 4]

[0062] [Table 5]

[0063] [Table 6] The power consumption E = P * t, and the electricity cost was calculated at 0.8 yuan / kW·h.

[0064] From the above table, it was found that for the same cleaning method over the cleaning time, as the dissolved ozone concentration in the ozone micro-nano bubble cleaning solution used increased, the energy consumption increased, and the corresponding cleaning cost increased. The cleaning effect of the dissolved ozone concentration of 7 mg / L in the ozone micro-nano bubble was slightly lower than that of 5 mg / L. Moreover, regarding the cleaning cost, ozone micro-nano bubble (7 mg / L) > ozone micro-nano bubble (5 mg / L) > ozone micro-nano bubble (3 mg / L) > ozone micro-nano bubble (1 mg / L). Therefore, in terms of cost, a dissolved ozone concentration of 1 - 5 mg / L is preferred. 5. Regarding the analysis of the membrane surface morphology

[0065] As shown in Fig. 9, it is a schematic diagram of the membrane surface after cleaning the hollow fiber membrane 2h with ozone micro-nano bubbles with four different dissolved ozone concentrations. (a) Ozone micro-nano bubbles with a dissolved ozone concentration of 1 mg / L, (b) Ozone micro-nano bubbles with a dissolved ozone concentration of 3 mg / L, (c) Ozone micro-nano bubbles with a dissolved ozone concentration of 5 mg / L, (d) Ozone micro-nano bubbles with a dissolved ozone concentration of 7 mg / L. After cleaning the membrane with ozone micro-nano bubbles with a dissolved ozone concentration of 7 mg / L, cracks occurred on the membrane surface. It was found by analysis that ozone micro-nano bubbles with a dissolved ozone concentration of 7 mg / L are not suitable for cleaning the membrane for a long time. 6. Mechanical Strength after Membrane Cleaning

[0066] From Fig. 10 and Fig. 11, after cleaning the membrane with ozone micro-nano bubbles with a dissolved ozone concentration of 7 mg / L for 2 h, the tensile strength and elongation at break of the membrane decreased significantly, and the mechanical strength of the membrane became smaller. It was found that the performance of the membrane changed after cleaning the membrane with ozone micro-nano bubbles with this dissolved ozone concentration. However, it was discovered that cleaning the membrane with ozone micro-nano bubbles with a dissolved ozone concentration of 1 - 5 mg / L had no significant impact on the mechanical strength of the membrane. Therefore, from the above aspects and mechanical strength, ozone micro-nano bubbles with a dissolved ozone concentration of 1 - 5 mg / L are preferred.

[0067] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Modifications, substitutions by equivalents, and improvements made without departing from the spirit and principles of the present invention are included within the protection scope of the present invention.

Explanation of Reference Numerals

[0068] 10............... Hollow Fiber Membrane 1................. Oxygen Generator 11............... Fifth Pipe 12............... Pressure Sensor 13............... Cleaning pump 14............... Sixth pipe 15............... Upper cover for cleaning tank 16............... Seventh pipe 17............... Ozone waste gas treatment device 18............... Eighth pipe 19............... Ninth pipe 20............... Cooling water pipe 2................. First pipe 21............... Connecting pipe 22............... Deflector pipe 23............... Nozzle 3................. Ozone generator 4................. Second pipe 5................. Micronano bubble generator 6................. Third pipe 7................. Fourth pipe 8................. Cooling device 9................. Cleaning tank a................. First insertion hole b................. Second insertion hole c................. Ozone waste gas discharge hole d................. Third insertion hole e................. Fourth insertion hole f................. Fifth insertion hole g................. Sixth insertion hole

Claims

1. A method for offline cleaning of a hollow fiber membrane for MBR using ozone micro-nano bubbles, comprising the following steps. S1. In equipment connection, An oxygen generator, an ozone generator, and a micro-nano bubble generator are connected in sequence through a first pipe and a second pipe. The liquid inlet of the micro-nano bubble generator is connected to a third pipe, and the gas outlet of the micro-nano bubble generator is connected to a fourth pipe. Both the third pipe and the fourth pipe extend into a cleaning tank. The hollow fiber membrane is immersed in the cleaning tank. The hollow fiber membrane is connected to a pressure sensor and a cleaning pump in sequence through a fifth pipe. The cleaning pump is further connected to a sixth pipe. The sixth pipe extends into the cleaning tank. The cleaning tank also cools the water in the tank by a cooling device. S2. In membrane cleaning, 1) Turn on the oxygen generator and the ozone generator in sequence. The oxygen generated by the oxygen generator is sent into the ozone generator through the first pipe to generate ozone. 2) Turn on the micro-nano bubble generator. Ozone is sent into the micro-nano bubble generator through the second pipe, and the water in the cleaning tank is sent into the micro-nano bubble generator through the third pipe. The generated ozone micro-nano bubbles are discharged into the cleaning tank through the fourth pipe, and the dissolved ozone concentration is 1 - 5 mg / L. 3) Start the cleaning pump, and pass the ozone micro-nano bubbles through the membrane in the forward direction for cleaning. In the method of "forward cleaning while immersed" or "alternate cleaning of immersion cleaning and forward cleaning", the cleaning can be stopped until the TMP displayed by the pressure sensor does not drop by more than 10% within 30 minutes. A method for offline cleaning of a hollow fiber membrane for MBR using ozone micro-nano bubbles, characterized in that.

2. Start the cleaning pump. While the hollow fiber membrane is immersed in the cleaning liquid, pass the ozone micro-nano bubbles through the membrane in the forward direction for cleaning. Measure the dissolved ozone concentration, water temperature, and TMP (membrane differential pressure) during the membrane cleaning process of the ozone micro-nano bubble cleaning liquid in the cleaning tank every 10 minutes. The cleaning can be stopped until the TMP displayed by the pressure sensor does not drop by more than 10% within 30 minutes, and the cleaning time is at most 2 h. It is a specific step of the method of "forward cleaning while immersed", characterized in that the method for offline cleaning of a hollow fiber membrane for MBR using ozone micro-nano bubbles according to Claim 1.

3. a. Start the cleaning pump, and while the hollow fiber membrane is immersed in the cleaning solution, pass ozone micro-nano bubbles through the membrane in the forward direction for 30 minutes of cleaning. Measure the dissolved ozone concentration, water temperature, and TMP (membrane differential pressure) of the ozone micro-nano bubble cleaning solution in the cleaning tank every 10 minutes during the membrane cleaning process. b. Stop the cleaning pump, and immerse and clean the hollow fiber membrane in ozone micro-nano bubbles for 30 minutes. Measure the dissolved ozone concentration, water temperature, and TMP of the ozone micro-nano bubble cleaning solution in the cleaning tank every 10 minutes during the membrane cleaning process. c. Repeat steps a to b until the cleaning can be stopped when the TMP displayed by the pressure sensor does not drop by more than 10% within 30 minutes, and the cleaning time is at most 2 hours. The specific steps of the "alternate cleaning of immersion cleaning and forward cleaning" method, which is characterized in that it is the ozone micro-nano bubble used for offline cleaning of the hollow fiber membrane for MBR according to claim 1.

4. The method for offline cleaning of the hollow fiber membrane for MBR using ozone micro-nano bubbles according to claim 1, characterized in that the temperature of the cleaning solution in the cleaning tank is maintained at 25°C ± 2°C by a cooling device.

5. The upper cover for the cleaning tank is provided with a first insertion hole for the third pipe to pass through, a second insertion hole for the fourth pipe to pass through, a third insertion hole for the fifth pipe to pass through, and a fourth insertion hole for the sixth pipe to pass through. During use, each pipe is inserted into the cleaning tank through the corresponding insertion hole. The method for offline cleaning of the hollow fiber membrane for MBR using ozone micro-nano bubbles according to claim 1.

6. The upper cover for the cleaning tank is connected to an ozone waste gas treatment device via a seventh pipe, and an ozone waste gas discharge hole is further provided, through which the generated waste gas is discharged after being treated by the ozone waste gas treatment device. The method for offline cleaning of the hollow fiber membrane for MBR using ozone micro-nano bubbles according to claim 5.

7. The cooling device is a low-temperature constant temperature bath, and the cleaning tank is arranged in the water tank of the low-temperature constant temperature bath. The method for offline cleaning of the hollow fiber membrane for MBR using ozone micro-nano bubbles according to claim 1.

8. The cooling device includes a cooling water circulation device, an eighth pipe, a ninth pipe, and a cooling water pipe. The eighth pipe is connected to the cooling water inlet of the cooling water circulation device, the ninth pipe is connected to the cooling water outlet of the cooling water circulation device, the cooling water pipe is located in the washing tank and is provided along the wall surface, and both ends of the cooling water pipe are respectively connected to the eighth pipe and the ninth pipe. The method for offline cleaning of a hollow fiber membrane for MBR using ozone micro-nano bubbles according to claim 1 is characterized in that.

9. Above the washing tank, a bubble uniform dispersion mechanism including a vertically provided connecting pipe, a plurality of horizontally provided flow guiding pipes, and a plurality of nozzles is further provided. The connecting pipe is connected to the fourth pipe, all of the plurality of flow guiding pipes communicate with the connecting pipe, the nozzles are evenly arranged on the flow guiding pipes, and the generated ozone micro-nano bubbles are evenly discharged into the washing tank through the plurality of nozzles. The method for offline cleaning of a hollow fiber membrane for MBR using ozone micro-nano bubbles according to claim 8 is characterized in that.

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