Offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles

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 field of membrane cleaning, and more particularly to an offline cleaning method for hollow fiber membranes for MBRs using ozone micro-nanobubbles. [Background technology]

[0002] The cleaning of hollow fiber membranes used in MBRs is divided into online cleaning and offline cleaning. Online cleaning refers to the periodic on-site cleaning of the membrane using chemicals when membrane contamination is not severe. If online cleaning cannot effectively restore the membrane's performance, the membrane module must be removed from the treatment tank and immersed in chemicals for offline cleaning. Conventional offline chemical cleaning of hollow fiber membranes used in MBRs generally involves the use of acidic and alkaline chemicals, which generate large amounts of acidic and alkaline cleaning wastewater and produce harmful byproducts, thus contaminating the water.

[0003] Ozone possesses a strong oxidizing ability that oxidizes both organic and inorganic compounds, and can oxidize most organic pollutants in wastewater, making it widely used in industrial wastewater treatment. Ozone oxidizes organic matter in two ways. First, ozone molecules selectively oxidize organic matter, i.e., direct oxidation. Second, OH radicals generated by autodecomposition convert pollutants on the membrane surface into easily biodegradable intermediate products, rapidly and non-selectively oxidizing organic matter, i.e., indirect oxidation. In conventional methods of cleaning membranes with ozone, the dissolved ozone concentration is generally relatively high, which is suitable for ozone-resistant membranes but has low applicability. [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention has been made in view of the above circumstances, and aims to provide an offline cleaning method for hollow fiber membranes for MBRs using ozone micro-nanobubbles that solves the problem of excessive residual chemicals in water in conventional offline cleaning processes for hollow fiber membranes, avoids the problem of wastewater treatment after cleaning, and solves the problem of low ozone utilization and ordinary cleaning effect when cleaning membranes with ozone water, as ozone micro-nanobubbles have advantages such as high dissolution capacity and high mass transfer efficiency, can generate more OH radicals than ordinary ozonated water. [Means for solving the problem]

[0005] To achieve the above objective, 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 device connection,

[0006] The oxygen generator, ozone generator, and micro-nanobubble generator are connected via the first and second pipes, respectively. 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 and fourth pipes extend into the cleaning tank, immersing the hollow fiber membrane in the cleaning tank. The hollow fiber membrane is connected to the pressure sensor and cleaning pump via the fifth pipe. The cleaning pump is further connected to the sixth pipe, which extends into the cleaning tank. The cleaning tank is a cooling system. The tank water is also cooled by the placement of the oxygen generator, and the oxygen generator is not particularly limited as long as it generates oxygen, for example, an oxygen production machine or an industrial oxygen cylinder. The cooling device is also not particularly limited as long as it plays a role in controlling the temperature of the cleaning solution, for example, a cooling water circulator, a cooling water pipe, or a low-temperature constant temperature bath. In the micro-nanobubble generator, the water temperature gradually rises during operation, but since temperature greatly affects the dissolution of ozone gas and the residence time of micro-nanobubbles in the water, controlling the water temperature is very important. S2, In membrane cleaning, 1) Turn on the oxygen generator and ozone generator in sequence. The oxygen generated by the oxygen generator is sent to the ozone generator through the first pipe to generate ozone.

[0007] 2) The micro-nanobubble generator is turned on, ozone is supplied to the micro-nanobubble generator through the second pipe, water in the cleaning tank is supplied to the micro-nanobubble generator through the third pipe, and the generated ozone micro-nanobubbles are released into the cleaning tank through the fourth pipe, with a dissolved ozone concentration of 1-5 mg / L.

[0008] 3) The cleaning pump is activated, and ozone micro-nanobubbles are passed through the membrane in a forward direction for cleaning. Cleaning can be stopped using the "forward cleaning while immersed" or "alternating cleaning of immersion and forward cleaning" method until the TMP displayed by the pressure sensor does not drop by more than 10% within 30 minutes.

[0009] Here, micro-nanobubbles refer to tiny bubbles with a diameter of less than 100 μm, and are divided into microbubbles with a diameter of 1 to 100 μm and nanobubbles with a diameter of less than 1 μm. Ozone micro-nanobubble technology refers to micro-nanobubbles that are formed after ozone passes through a micro-nanobubble generator. Ozone micro-nanobubble technology utilizes the properties of micro-nanobubbles, such as their large specific surface area, slow rising speed, negatively charged surface, and the fact that ozone promotes the generation of more OH radicals.

[0010] Ozone micro-nanobubbles have a high dissolution capacity in water and a long duration of ozone release. At the same dissolved ozone concentration, the void ratio of ozone micro-nanobubbles is far higher than that of ozone macrobubbles, and this difference in void ratios becomes even greater as the dissolved ozone concentration increases.

[0011] Ozone micro-nanobubbles have high mass transfer efficiency, and the saturated dissolved ozone concentration they reach is higher than that of ozone macrobubbles. The time required for ozone microbubbles to reach saturated dissolved ozone concentration is faster than that of ozone macrobubbles.

[0012] Ozone micro-nanobubbles have high ozone utilization efficiency, generate a large amount of OH radicals, and have a high surface zeta potential. Compared to conventional ozone aeration, they can significantly accelerate the decomposition of organic pollutants, and their unique interface structure offers unique advantages in membrane cleaning processes.

[0013] Furthermore, the process of generating micro-nanobubbles is an exothermic process, and the water temperature gradually rises while the micro-nanobubble generator is operating. Since temperature greatly affects the dissolution of ozone gas and the residence time of micro-nanobubbles in the water, controlling the water temperature is extremely important.

[0014] Furthermore, the specific steps of the "sequential cleaning while immersed" method are as follows: The cleaning pump is started, and while the hollow fiber membrane is immersed in the cleaning solution, ozone micro-nanobubbles are passed through the membrane in a forward direction for cleaning. Every 10 minutes, the dissolved ozone concentration in the ozone micro-nanobubble cleaning solution in the cleaning tank, the water temperature, and the TMP (transmembrane pressure difference) during the membrane cleaning process are measured. Cleaning can be stopped until the TMP displayed by the pressure sensor does not decrease by more than 10% within 30 minutes, and the maximum cleaning time is 2 hours. Furthermore, the specific steps of the "alternating immersion and sequential washing" method are as follows:

[0015] a. Start the cleaning pump and, while the hollow fiber membrane remains immersed in the cleaning solution, pass ozone micro-nanobubbles forward through the membrane for 30 minutes to clean it. Every 10 minutes, measure the dissolved ozone concentration in the ozone micro-nanobubble cleaning solution in the cleaning tank, the water temperature, and the TMP (transmembrane pressure difference) during the membrane cleaning process.

[0016] b. Stop the washing pump and immerse the hollow fiber membrane in ozone micro-nanobubbles for 30 minutes to wash it. Every 10 minutes, measure the dissolved ozone concentration in the ozone micro-nanobubble washing solution in the washing tank, the water temperature, and the TMP during the membrane washing process.

[0017] c. Repeat steps a to b, and 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 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 provided an upper cover for the cleaning tank 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] Moreover, on the upper cover for the cleaning tank, there is further provided an ozone waste gas discharge hole 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] In addition, 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] Furthermore, 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, the plurality of flow guiding pipes are all communicated with the connecting pipe, the nozzles are evenly arranged on the flow guiding pipes, and the generated ozone micronano 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 amounts of 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 heat generation process during 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 immersing" 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. Ozone micro-nano bubbles have a higher saturated dissolved ozone concentration than ozone macro-bubbles and take less time than 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 interfacial structure of ozone micro-nano bubbles has unique advantages in the membrane cleaning process.

[0027] 5. This invention explores the optimal membrane passage method using ozone micro-nanobubbles and found that ozone micro-nanobubbles are more effective at cleaning the membrane by passing through it in the forward direction than by passing through it in the reverse direction. Therefore, the membrane cleaning method using ozone micro-nanobubbles is "forward cleaning while immersed," and considering energy consumption, "alternating cleaning of immersion and forward cleaning" is adopted. Unlike conventional cleaning methods for hollow fiber membranes, this invention employs immersion cleaning with a cleaning solution and cleaning by passing the cleaning solution through the membrane in the reverse direction. [Brief explanation of the drawing]

[0028] The drawings, which constitute part of the present invention, are for the purpose of further understanding the present invention, and the schematic embodiments and descriptions of the present invention are for the purpose of interpreting the present invention and do not constitute an unreasonable limitation to the present invention. [Figure 1] This is a schematic diagram of the structure of the equipment used in the offline cleaning method for hollow fiber membranes for MBRs using ozone micro-nanobubbles according to Example 1 of the present invention. [Figure 2] This is a top view of the upper lid for the cleaning tank used in the offline cleaning method for hollow fiber membranes for MBRs using ozone micro-nanobubbles according to Example 1 of the present invention. [Figure 3] This is a schematic diagram of the structure of the equipment used in the offline cleaning method for hollow fiber membranes for MBRs using ozone micro-nanobubbles according to Example 2 of the present invention. [Figure 4] This is a top view of the upper lid for the cleaning tank of the offline cleaning method for hollow fiber membranes for MBRs using ozone micro-nanobubbles according to Example 2 of the present invention. [Figure 5] This is a schematic diagram of the bubble uniform dispersion mechanism of the offline cleaning method for hollow fiber membranes for MBRs using ozone micro-nanobubbles according to Example 2 of the present invention. [Figure 6] This is a schematic diagram of reverse and forward washing of a hollow fiber membrane. [Figure 7]This graph shows the change in TMP during the "forward washing" process of hollow fiber membranes using ozone micro-nanobubbles. [Figure 8] This graph shows the change in TMP during the "alternating immersion and sequential washing" process of hollow fiber membranes using ozone micro-nanobubbles. [Figure 9] This diagram shows the surface of a hollow fiber membrane after washing with ozone micro-nanobubbles of four different dissolved ozone concentrations: (a) ozone micro-nanobubbles with a dissolved ozone concentration of 1 mg / L, (b) ozone micro-nanobubbles with a dissolved ozone concentration of 3 mg / L, (c) ozone micro-nanobubbles with a dissolved ozone concentration of 5 mg / L, and (d) ozone micro-nanobubbles with a dissolved ozone concentration of 7 mg / L. [Figure 10] This is a comparison chart of the elongation at break after membrane washing. [Figure 11] This is a comparison chart of tensile strength after membrane cleaning. [Modes for carrying out the invention]

[0029] It should be noted that, where there is no contradiction, the embodiments and features of the present invention can be combined with each other.

[0030] The directions or positional relationships indicated by terms such as "center," "vertical," "horizontal," "up," "down," "front," "back," "left," "right," "perpendicular," "horizontal," "top," "bottom," "inside," and "outside" used in this invention are directions or positional relationships shown based on the drawings and are merely for the purpose of making the invention easy to explain. They do not indicate or suggest that the shown devices or components necessarily have a specific direction, or are composed of and operated in a specific direction, and should not be understood as limitations on the invention. Furthermore, the terms "first" and "second" are used merely to describe the purpose and should not be understood as indicating or suggesting relative importance, or implicitly indicating the number of technical features shown. Accordingly, features limited by "first," "second," etc., may explicitly or implicitly include one or more of those features. The term "multiple" used in this invention means two or more unless otherwise specified.

[0031] Unless otherwise specified or limited, the terms “attached,” “joined,” and “connected” as used in this invention should be interpreted broadly, and may include, for example, fixed connections, detachable connections, or integral connections; they may be mechanical, electrical, direct, indirect, or internal communication between two elements. Those skilled in the art will be able to understand the specific meaning of these terms in this invention depending on the specific circumstances.

[0032] The technical solutions in embodiments of the present invention will be described clearly and completely below with reference to the drawings of the embodiments of the present invention, but it will be clear that the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art without creative effort based on the embodiments of the present invention are all within the scope of the protection of the present invention. (Example 1) The offline cleaning method for hollow fiber membranes used in MBRs using ozone micro-nanobubbles includes the following steps. S1, In device connection,

[0033] The oxygen generator 1, ozone generator 3, and micro-nanobubble generator 5 are connected in order via the first pipe 2 and the second pipe 4, respectively. The liquid inlet of the micro-nanobubble generator 5 is connected to the third pipe 6, and the gas outlet of the micro-nanobubble generator 5 is connected to the fourth pipe 7. Both the third pipe 6 and the fourth pipe 7 extend to the cleaning tank 9, immersing the hollow fiber membrane 10 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, and the sixth pipe 14 is... The cleaning tank 9 is connected to the cooling device 8, which also cools the water inside the tank. The cooling device 8 is not particularly limited as long as it plays a role in controlling the temperature of the cleaning solution, and can be a cooling water circulation device, a cooling water pipe, a low-temperature constant-temperature bath, etc. During operation of the micro-nanobubble generator 5, the water temperature gradually rises, and since temperature greatly affects the dissolution of ozone gas and the residence time of micro-nanobubbles in the water, controlling the water temperature is very important. In this embodiment, the cooling device 8 is a low-temperature constant-temperature bath, and the cleaning tank is located in the water tank of the low-temperature constant-temperature bath.

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

[0035] The top cover for the washing tank is further provided with an ozone waste gas discharge port c, which is connected to an ozone waste gas treatment device 17 via a seventh pipe 16, and the generated waste gas is discharged after being treated by the ozone waste gas treatment device 17. The connected equipment is shown in Figure 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 to the ozone generator 3 through the first pipe 2 to generate ozone.

[0037] 2) The micro-nanobubble generator 5 is turned on, ozone is sent to the micro-nanobubble generator 5 through the second pipe 4, the water in the cleaning tank 9 is sent to the micro-nanobubble generator 5 through the third pipe 6, the generated ozone micro-nanobubbles are released into the cleaning tank 9 through the fourth pipe 7, the dissolved ozone concentration is preferably 1 to 5 mg / L depending on the actual situation, taking into account the difference in the degree of contamination of the membrane being cleaned, the cleaning tank 9 is placed in the constant temperature bath of the cooling water circulation system, and the temperature of the cleaning solution in the cleaning tank 9 is maintained at 25°C by the cooling device 8. 3) The hollow fiber membrane module is connected via the fifth pipe 11, pressure sensor 12, and washing pump 13, and the water after membrane filtration is returned to the washing tank 9 via the sixth pipe 14.

[0038] Specifically, the cleaning pump 13 is activated, ozone micro-nanobubbles are passed through the membrane in the forward direction for cleaning, and the cleaning can be stopped using the "forward cleaning while immersed" or "alternating cleaning of immersion and forward cleaning" method 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 port c is connected to the ozone waste gas treatment device 17 via the seventh pipe 16, and the generated waste gas is discharged after being treated in the ozone waste gas treatment device 17.

[0040] The specific steps of the "sequential cleaning while immersed" method are as follows: The cleaning pump 13 is started, and while the hollow fiber membrane 10 is immersed in the cleaning solution, ozone micro-nanobubbles are passed through the membrane in a forward direction to clean it. Every 10 minutes, the dissolved ozone concentration in the ozone micro-nanobubble cleaning solution in the cleaning tank 9, the water temperature, and the TMP (transmembrane pressure difference) during the membrane cleaning process are measured. Cleaning can be stopped until the TMP displayed by the pressure sensor 12 does not decrease by more than 10% within 30 minutes, and the maximum cleaning time is 2 hours. The specific steps for the "alternating immersion and sequential washing" method are as follows:

[0041] a. Start the cleaning pump 13 and, with the hollow fiber membrane 10 immersed in the cleaning solution, pass ozone micro-nanobubbles forward through the membrane for 30 minutes to clean it, and measure the dissolved ozone concentration of the ozone micro-nanobubble cleaning solution in the cleaning tank 9, the water temperature, and the TMP (transmembrane pressure difference) during the membrane cleaning process every 10 minutes.

[0042] b. Stop the washing pump 13 and immerse the hollow fiber membrane in ozone micro-nanobubbles for 30 minutes to wash it. Every 10 minutes, measure the dissolved ozone concentration in the ozone micro-nanobubble washing solution in the washing tank 9, the water temperature, and the TMP during the membrane washing process.

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

[0044] This is an offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles, and differs from Example 1 in that the equipment connection in step S1 is different, namely the cooling device 8 uses a cooling water circulation device, an 8th pipe 18, a 9th pipe 19, and a cooling water pipe 20, with the 8th pipe 18 connected to the cooling water inlet of the cooling water circulation device, the 9th pipe 19 connected to the cooling water outlet of the cooling water circulation device, the cooling water pipe 20 located inside the cleaning tank 9 and arranged in a ring along the wall surface, with both ends of the cooling water pipe 20 connected to the 8th pipe 18 and the 9th pipe 19 respectively, and the top cover for the cleaning tank is provided with a 5th insertion hole f and a 6th insertion hole f, respectively, for connecting and inserting the 8th pipe 18 and the 9th pipe 19, as shown in Figures 3 and 4.

[0045] Above the cleaning tank 9, a bubble uniform dispersion mechanism is further provided, which is attached to the edge of the inner tank of the cleaning tank. As shown in Figure 5, the bubble uniform dispersion mechanism comprises a vertically installed connecting pipe 21, a plurality of horizontally installed guide pipes 22, and a plurality of nozzles 23. The connecting pipe 21 is connected to the fourth pipe 7, all of the plurality of guide pipes 22 are in communication with the connecting pipe, and the nozzles 23 are evenly distributed in the guide pipes 22. The generated ozone micro-nanobubbles are evenly released into the cleaning tank 9 through the plurality of nozzles 23. (test) This test example uses the method described in Example 1.

[0046] The washed membrane was a PVDF hollow fiber membrane that had been continuously operated for 9 months in an MBR membrane bioreactor, and the sludge concentration in this MBR membrane bioreactor was 5000 mg / L. The effective volume of the cleaning solution in the cleaning tank was 1 L. The effective area of ​​the cleaned hollow fiber membrane was 15.1 × 10⁻⁶. -3 m 2 That was the case.

[0047] This test example compares the cleaning effect of cleaning solutions in different membrane cleaning modes. "Immersion cleaning" refers to immersing the membrane in the cleaning solution. "Backwashing while immersing" refers to immersing the membrane in the cleaning solution, injecting the cleaning solution into the fibers of the hollow fiber membrane with a cleaning pump, and cleaning the membrane by passing the cleaning solution from the inside out. "Forward cleaning while immersing" refers to immersing the membrane in the cleaning solution, then using a cleaning pump to draw in the solution, allowing the cleaning solution to clean the membrane surface of the hollow fiber membrane from the outside in. "Alternating cleaning of immersion cleaning and forward cleaning" refers to cleaning the membrane by passing it forward every 30 minutes while immersing it in the cleaning solution. The membrane was immersed in the cleaning solution, the cleaning pump was started, the cleaning solution passed through the membrane in the forward direction for 30 minutes, the cleaning pump was stopped, and the membrane was simply immersed for 30 minutes. The system operated in a cycle according to the above rules. 1. In this test example, the cleaning effect of the film was evaluated by cleaning efficiency. The aforementioned cleaning efficiency was evaluated by the rate of reduction in 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 membrane is calculated according to the following 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 MBR hollow fiber membranes with 2000 ppm NaClO. In order to ensure the accuracy of the experimental results, the test data were selected and calculated by repeating the test 3 times for each cleaning experiment.

[0051] The membrane cleaning effect of ozone micro-nanobubbles and normal ozonated water was compared, with the same dissolved ozone concentration in water being measured. Ozone gas and water were passed through a micro-nanobubble generator 5, and after half an hour of operation, the cleaning solution concentration was balanced, and ozone micro-nanobubbles with a dissolved ozone concentration of 1 mg / L in water were generated in the cleaning tank. Ozone gas was passed through the cleaning tank using an aeration stone, and the ozone concentration in the ozonated water measured after stabilization was 1 mg / L. The principle of ozone micro-nanobubble generation is gas dissolution and release, and the adjustment of pressure and sudden expansion of the overcurrent cross-section. Normal ozonated water is generated by dissolving ozone gas in water using an aeration stone.

[0052] [Table 1]

[0053] Table 1 shows that the effectiveness of ozone micro-nanobubble cleaning on hollow fiber membranes using "immersion cleaning," "alternating immersion cleaning and sequential cleaning," and "sequential cleaning while immersing" is higher than that of cleaning hollow fiber membranes with ordinary ozonated water and 2000 ppm NaClO. Ozone micro-nanobubbles have a strong solubility in water, resulting in a long ozone retention time. They have high ozone utilization efficiency, generate many OH radicals, which is advantageous for cleaning membrane pores, and the unique interface structure of micro-nanobubbles is also advantageous for cleaning the membrane surface. 2. This test example compares the 1-hour cleaning efficiency of hollow fiber membranes using ozone micro-nanobubbles with dissolved ozone concentrations of 1, 3, 5, and 7 mg / L.

[0054] [Table 2] This test example compares the 2-hour cleaning efficiency of hollow fiber membranes using ozone micro-nanobubbles with dissolved ozone concentrations of 1, 3, 5, and 7 mg / L.

[0055] [Table 3]

[0056] Tables 2 and 3 show that, at the same concentration, the cleaning effectiveness of different cleaning methods is as follows: "forward cleaning while immersing" > "alternating cleaning of immersion and forward cleaning" > "immersion cleaning" > "backward cleaning while immersing". Therefore, it can be concluded that the optimal cleaning method using ozone micro-nanobubbles is "forward cleaning while immersing". Considering energy consumption, "alternating cleaning of immersion and forward cleaning" can be used.

[0057] Tables 2 and 3 show that the membrane cleaning effects of dissolved ozone concentrations of 5 mg / L and 7 mg / L in ozone micro-nanobubbles are approximately the same, and the cleaning effect of 7 mg / L is slightly lower than that of 5 mg / L. It was found that a dissolved ozone concentration of 5 mg / L in ozone micro-nanobubbles already satisfies the membrane cleaning requirements, and further increasing the ozone concentration leads to resource waste, increased costs, and also affects membrane performance. Considering the differences in the degree of contamination of the membranes being cleaned, the dissolved ozone concentration in ozone micro-nanobubbles is preferably 1 to 5 mg / L depending on the actual situation, and the membrane used for cleaning in the present invention is a PVDF hollow fiber membrane suitable for MBR water treatment.

[0058] Furthermore, as shown in Tables 2 and 3, the contaminated membranes used in this test example were found to achieve a cleaning effect of 90% or more after being washed for 1 hour by passing the membrane forward while simultaneously being immersed.

[0059] 3. Changes in TMP during the "sequential washing while immersing" and "alternating washing with immersion and sequential washing" processes using ozone micro-nanobubbles with dissolved ozone concentrations of 1, 3, and 5 mg / L in water.

[0060] Referring to Figures 7 and 8, it was found that the change in TMP had already stabilized after 2 hours of membrane cleaning, indicating that the cleaning effect had saturated. The cleaning time criteria take into account the difference in the degree of membrane contamination. TMP is measured every 10 minutes during the membrane cleaning process, and cleaning can be stopped until the TMP displayed by the pressure sensor no longer drops by more than 10% within 30 minutes. The maximum cleaning time is 2 hours, and thus, even with severe membrane contamination, cleaning can be performed in 2 hours. 4. Regarding cleaning costs

[0061] [Table 4]

[0062] [Table 5]

[0063] [Table 6] The calculation was based on power consumption E = P * t and electricity cost of 0.8 yuan / kW·h.

[0064] The table above shows that, using the same cleaning method over a longer cleaning time, the dissolved ozone concentration in the ozone micro-nanobubble cleaning solution increases, leading to higher energy consumption and correspondingly higher cleaning costs. The cleaning effect of ozone micro-nanobubbles with a dissolved ozone concentration of 7 mg / L is slightly lower than that of 5 mg / L, and in terms of cleaning costs, ozone micro-nanobubbles (7 mg / L) > ozone micro-nanobubbles (5 mg / L) > ozone micro-nanobubbles (3 mg / L) > ozone micro-nanobubbles (1 mg / L). Therefore, from a cost perspective, a dissolved ozone concentration of 1 to 5 mg / L is preferable. 5. Analysis of film surface characteristics

[0065] As shown in Figure 9, the images show the surface of a hollow fiber membrane after washing with ozone micro-nanobubbles of four different dissolved ozone concentrations for 2 hours: (a) ozone micro-nanobubbles with a dissolved ozone concentration of 1 mg / L, (b) ozone micro-nanobubbles with a dissolved ozone concentration of 3 mg / L, (c) ozone micro-nanobubbles with a dissolved ozone concentration of 5 mg / L, and (d) ozone micro-nanobubbles with a dissolved ozone concentration of 7 mg / L. Analysis revealed that after washing the membrane with ozone micro-nanobubbles with a dissolved ozone concentration of 7 mg / L, cracks appeared on the membrane surface, indicating that ozone micro-nanobubbles with a dissolved ozone concentration of 7 mg / L are unsuitable for long-term membrane washing. 6. Mechanical strength after membrane cleaning

[0066] Figures 10 and 11 show that after washing the membrane with ozone micro-nanobubbles at a dissolved ozone concentration of 7 mg / L for 2 hours, the tensile strength and elongation at break of the membrane decreased significantly, and the mechanical strength of the membrane also decreased. This indicates that the performance of the membrane changed after washing with ozone micro-nanobubbles at this dissolved ozone concentration. However, it was found that washing the membrane with ozone micro-nanobubbles at a dissolved ozone concentration of 1 to 5 mg / L did not have a significant effect on the mechanical strength of the membrane. Therefore, considering the above-mentioned characteristics and mechanical strength, ozone micro-nanobubbles with a dissolved ozone concentration of 1 to 5 mg / L are preferred.

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

[0068] 10............... Hollow fiber membrane 1................. Oxygen generator 11.... Fifth pipe 12.... Pressure sensor 13... Washing pump 14............... 6th pipe 15.... Top cover for washing tank 16....7th pipe 17............... Ozone waste gas treatment equipment 18............... Pipe No. 8 19............... 9th pipe 20.......... Cooling water pipe 2................. First piping 21.... Connecting pipe 22........... Flow pipe 23............... Nozzle 3................. Ozone generator 4................. Second piping 5................. Micro-nanobubble generator 6................. Third pipe 7................. Fourth pipe 8.......... Cooling device 9................. Washing tank a................. First insertion hole b................. Second insertion hole c................. Ozone exhaust port d................. Third insertion hole e................. Fourth insertion hole f................. Fifth insertion hole g................. Sixth insertion hole

Claims

1. An offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles, comprising the following steps. S1. In device connection, The oxygen generator, ozone generator, and micro-nanobubble generator are connected in order via the first and second pipes, respectively. 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 and fourth pipes extend into the cleaning tank, immersing the hollow fiber membrane in the cleaning tank. The hollow fiber membrane is connected in order to the pressure sensor and cleaning pump via the fifth pipe. The cleaning pump is further connected to the sixth pipe, which extends into the cleaning tank. The cleaning tank is also cooled by a cooling device. S2, In membrane cleaning, 1) Turn on the oxygen generator and ozone generator in sequence. The oxygen generated by the oxygen generator is sent to the ozone generator through the first pipe to generate ozone. 2) The micro-nanobubble generator is turned on, ozone is supplied to the micro-nanobubble generator through the second pipe, water in the cleaning tank is supplied to the micro-nanobubble generator through the third pipe, and the generated ozone micro-nanobubbles are released into the cleaning tank through the fourth pipe, with a dissolved ozone concentration of 1 to 5 mg / L. 3) An offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles, characterized by starting a cleaning pump, passing ozone micro-nanobubbles forward through the membrane for cleaning, and ending the cleaning when the TMP (transmembrane pressure difference) displayed by a pressure sensor does not decrease by more than 10% in 30 minutes, using a method of "forward cleaning while immersed" or "alternating cleaning of immersion cleaning and forward cleaning".

2. The method for offline cleaning a hollow fiber membrane for an MBR using ozone micro-nanobubbles, as described in claim 1, is characterized by the following specific steps of the "forward cleaning while immersed" method: starting the cleaning pump, cleaning the hollow fiber membrane by passing ozone micro-nanobubbles forward through the membrane while it is immersed in the cleaning solution, measuring the dissolved ozone concentration of the ozone micro-nanobubble cleaning solution in the cleaning tank, the water temperature, and the TMP (transmembrane pressure difference) during the membrane cleaning process every 10 minutes, and terminating the cleaning when the TMP (transmembrane pressure difference) displayed by the pressure sensor does not decrease by more than 10% in 30 minutes, with a maximum cleaning time of 2 hours.

3. a. Start the cleaning pump and, while the hollow fiber membrane remains immersed in the cleaning solution, pass ozone micro-nanobubbles forward through the membrane for 30 minutes to clean it. Every 10 minutes, measure the dissolved ozone concentration in the ozone micro-nanobubble cleaning solution in the cleaning tank, the water temperature, and the TMP (transmembrane pressure difference) during the membrane cleaning process. b. Stop the cleaning pump and immerse the hollow fiber membrane in ozone micro-nanobubbles for 30 minutes to clean it. Every 10 minutes, measure the dissolved ozone concentration in the ozone micro-nanobubble cleaning solution in the cleaning tank, the water temperature, and the TMP during the membrane cleaning process. c. A method for offline cleaning hollow fiber membranes for MBRs using ozone micro-nanobubbles, as described in claim 1, characterized in that steps a to b are repeated, and cleaning is terminated when the TMP (transmembrane differential pressure) displayed by the pressure sensor does not decrease by more than 10% in 30 minutes, with a maximum cleaning time of 2 hours, which is a specific step of the "alternating cleaning of immersion cleaning and sequential cleaning" method.

4. An offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles 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 cleaning tank is provided with a top cover for the cleaning tank, which has a first insertion hole for a third pipe to pass through, a second insertion hole for a fourth pipe to pass through, a third insertion hole for a fifth pipe to pass through, and a fourth insertion hole for a sixth pipe to pass through, and each pipe is inserted into the cleaning tank through the corresponding insertion hole when in use, characterized in that an offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles is provided on the top of the cleaning tank, characterized in that each pipe is inserted into the cleaning tank through the corresponding insertion hole when in use, according to claim 1.

6. The method for offline cleaning of hollow fiber membranes for MBR using ozone micro-nanobubbles, as described in claim 5, is characterized in that the upper lid for the cleaning tank is further provided with an ozone waste gas discharge hole, which is connected to an ozone waste gas treatment device via a seventh pipe, and the generated waste gas is discharged after being treated by the ozone waste gas treatment device.

7. The method for offline cleaning hollow fiber membranes for MBR using ozone micro-nanobubbles according to claim 1, characterized in that the cooling device is a low-temperature constant-temperature bath, and the cleaning tank is located inside the water tank of the low-temperature constant-temperature bath.

8. The cooling device comprises a cooling water circulation device, an eighth pipe, a ninth pipe, and a cooling water pipe, wherein 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 inside the cleaning tank and provided along the wall surface, and both ends of the cooling water pipe are connected to the eighth pipe and the ninth pipe, respectively, characterized in that this is an offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles as described in claim 1.

9. A bubble uniform dispersion mechanism is further provided above the cleaning tank, comprising a vertically installed connecting pipe, a plurality of horizontally installed guide pipes, and a plurality of nozzles, the connecting pipe is connected to a fourth pipe, all of the plurality of guide pipes are in communication with the connecting pipe, the nozzles are evenly arranged in the guide pipes, and the generated ozone micro-nanobubbles are evenly released into the cleaning tank through the plurality of nozzles, characterized in that, an offline cleaning method for hollow fiber membranes for MBR using ozone micro-nanobubbles according to claim 8.

Images