Method for online cleaning of MBR hollow fiber membrane using ozone micro-nano bubbles

Abstract

The present invention provides a method for online cleaning of MBR hollow fiber membranes by utilizing ozone micro-nano bubbles. The method performs online maintenance cleaning by introducing ozone micro-nano bubbles with a dissolved ozone concentration of 0.1-1 mg / L. The method solves the problems of decreased activity of activated sludge, damage to membrane structure, and low utilization rate of ozone in actual engineering applications caused by traditional MBR online chemical cleaning. The method improves ozone utilization rate while reducing the impact on activated sludge and reduces waste gas emissions.

Description

Technical Field

[0001] The invention relates to the field of membrane cleaning, and in particular to a method for online cleaning of MBR hollow fiber membranes by utilizing ozone micro-nano bubbles. Background Art

[0002] Compared with the conventional activated sludge (CAS) process, the membrane bioreactor (MBR) is becoming more and more popular due to its small footprint, good effluent quality and low sludge production. However, the operation of MBR faces a huge challenge - membrane fouling. Membrane fouling refers to the formation of a thick gel layer on the membrane surface that blocks the membrane pores. At the same time, the filter cake layer gradually deposits on the gel layer, increasing the filtration resistance of the membrane, resulting in a decrease in membrane flux or an increase in transmembrane pressure difference. The main ways to alleviate membrane fouling are coagulation and membrane cleaning. MBR membrane cleaning can be divided into physical cleaning, chemical cleaning, biological cleaning, etc. according to the removal mechanism and the cleaning agent used; it can be divided into online cleaning and offline cleaning according to whether the membrane assembly leaves the MBR membrane pool during cleaning. Since online cleaning is easy to operate and can achieve more frequent cleaning, it is widely used in actual engineering applications. Due to the hollow structural characteristics of the hollow fiber membrane, backwashing and chemical enhanced backwashing are widely used in MBR hollow fiber membrane cleaning. However, as a physical cleaning method, backwashing can only remove reversible pollution, while the chemicals used in chemical enhanced backwashing will affect the activity of activated sludge in the MBR reactor, damage the membrane structure, and produce a large amount of acid and alkali cleaning waste liquid. In addition, a large amount of halogenated disinfection byproducts (DBPs) produced during the NaClO online chemical cleaning process of the MBR will inevitably enter the natural water body through the treated effluent.

[0003] Advanced oxidation processes (AOPs) mainly include Fenton oxidation, ultrasonic oxidation, photocatalytic oxidation and ozone oxidation, among which ozone oxidation is one of the most widely used advanced oxidation processes. Ozone is an unstable gas with a typical pungent odor. Its redox potential in alkaline solution is 2.07eV. It is a strong oxidant. Therefore, ozone can oxidize many inorganic and organic substances. In recent years, ozone has been applied to the cleaning of inorganic membranes such as ceramic membranes, the degradation of dyes, the degradation of organic compounds, sterilization and disinfection, and the degradation of drugs in water treatment. Due to the characteristics of ozone such as short half-life, low solubility in water, and poor mass transfer efficiency, this leads to low ozone utilization in actual engineering applications, which will increase the energy consumption and cost of operation.

[0004] Micro-nanobubble refers to tiny bubbles with a diameter of less than 100μm, which are further divided into microbubbles (MBs) with a diameter of 1 to 100μm and nanobubbles (NBs) with a diameter of less than 1μm. Micro-nanobubbles have the characteristics of high negative surface potential, high stability, high surface-to-volume ratio, and the generation of hydroxyl radicals when the bubbles burst. The above unique properties have made micro-nanobubbles receive more and more attention in various application fields, and it provides great opportunities to improve the existing water and wastewater treatment processes in various aspects. When using micro-nanobubble mass transfer, the bubble diameter is less than 100μm. According to the relationship between the theoretical mass transfer coefficient and the bubble diameter, it is generally believed that there is no mass transfer resistance in micro-nanobubbles. Therefore, the combination of ozone and micro-nanobubbles can prolong the residence time and mass transfer efficiency of ozone in water. In recent years, many researchers have applied ozone micro-nano bubbles in the field of water treatment, mainly in the fields of removal of organic pollutants, ozone disinfection, sludge ozonation, groundwater remediation, etc. However, as far as we know, ozone micro-nano bubbles have not been used in the field of online cleaning of MBR hollow fiber membranes. Summary of the invention

[0005] In view of this, the present invention aims to propose a method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles, so as to solve the problems of decreased activated sludge activity, membrane structure damage and low ozone utilization rate in actual engineering applications caused by traditional MBR online chemical cleaning, thereby reducing the impact on activated sludge while improving ozone utilization rate and reducing waste gas emissions.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles, the method comprising the following steps:

[0008] S1. Device connection

[0009] The oxygen generator, the ozone generator and the micro-nano bubble generator are connected in sequence. The water inlet and the water outlet of the micro-nano bubble generator are connected to the cleaning liquid reservoir. The cleaning liquid reservoir is connected to the MBR membrane assembly through a cleaning pump. An aeration device is provided at the bottom of the membrane pool where the MBR membrane assembly is placed. The cleaning liquid reservoir also cools the cleaning liquid by setting a cooling device.

[0010] S2. Membrane cleaning

[0011] 1) Before cleaning, the water inlet and outlet of the MBR hollow fiber membrane system should be stopped, and the aeration device should be turned on to keep the hollow fiber membrane system in the MBR membrane tank in a strong aeration state for 10-15 minutes to flush away the pollutants attached to the membrane. Then, the aeration device should be turned off to allow the system to stop and settle for 20 minutes;

[0012] 2) Turn on the oxygen generator, ozone generator and micro-nano bubble generator in sequence, pass the generated oxygen into the ozone generator to generate ozone, then pass the ozone and cleaning liquid into the micro-nano bubble generator for mixing, and release the generated cleaning liquid rich in ozone micro-nano bubbles into the cleaning liquid reservoir;

[0013] 3) Start the cooling device to cool the cleaning fluid, and start the cleaning pump after the temperature and dissolved ozone concentration are stable, and pump the ozone micro-nano bubble cleaning fluid into the MBR membrane assembly for online maintenance and cleaning;

[0014] During online backwashing, the cleaning liquid reversely permeates the membrane pores and directly contacts the activated sludge in the MBR membrane assembly. When using ozone micro-nano bubbles with high dissolved ozone concentration for online maintenance cleaning, some activated sludge microorganisms in the MBR membrane pool will be killed, resulting in a decrease in the pollutant removal effect of the MBR system. In order not to affect the activity of the activated sludge in the MBR system, the dissolved ozone concentration in the ozone micro-nano bubble cleaning liquid pumped into the MBR membrane assembly is 0.1-1 mg / L;

[0015] 4) After cleaning, let it stand for 30 minutes to allow the cleaning liquid to fully contact the membrane surface. After standing, turn on the aeration device to flush the membrane surface and the system will enter the normal operating cycle.

[0016] Ozone micro-nano bubble cleaning fluid with low dissolved ozone concentration has little effect on the activity of activated sludge in the MBR system, but its oxidation effect is poor, so it needs to be flushed more frequently. Ozone micro-nano bubble cleaning fluid with high dissolved ozone concentration has strong oxidizing properties but has a slightly greater impact on activated sludge, so the cleaning interval can be extended to reduce the impact on activated sludge.

[0017] Furthermore, when an ozone micro-nano bubble cleaning solution having a dissolved ozone concentration of 0.1-0.5 mg / L is used for maintenance cleaning, the cleaning interval is set to 12-24 hours.

[0018] Furthermore, when ozone micro-nano bubbles with a dissolved ozone concentration of 0.5-1 mg / L are used for online cleaning, the cleaning interval is set to 24-48 hours.

[0019] Furthermore, the amount of cleaning liquid introduced is also important for the cleaning effect and the activity of activated sludge in the MBR system. The amount of cleaning liquid introduced is controlled by controlling different cleaning durations. The flow rate during cleaning is 1.5-3 times the designed water flow rate of the MBR component, and the cleaning time is 3-10 minutes.

[0020] Furthermore, when the dissolved ozone concentration and cleaning interval are constant, shortening the cleaning time can extend the operation time of the MBR system; when the membrane pollution is relatively light, the selected cleaning time is 3-5 minutes.

[0021] The process of cutting large bubbles to produce micro-nano bubbles will do work. The liquid in the cleaning liquid reservoir will increase its temperature during the continuous circulation in the micro-nano bubble generator. The temperature has a great influence on the ozone concentration in the water, the ozone residence time and the existence time of micro-nano bubbles. Therefore, it is very important to control the temperature of the cleaning liquid.

[0022] Furthermore, the temperature of the cleaning liquid is maintained at 23°C ± 2°C by a cooling device.

[0023] Since ozone is relatively active and has a short half-life, the dissolved ozone concentration in the ozone micro-nano bubble cleaning fluid will gradually decrease during transportation in the cleaning fluid feed pipeline. Therefore, the dissolved ozone concentration in the cleaning fluid reservoir is slightly higher than the dissolved ozone concentration actually introduced into the MBR system.

[0024] Furthermore, the concentration of dissolved ozone in the ozone micro-nano bubble cleaning liquid in the cleaning liquid reservoir is 3-5 mg / L.

[0025] Furthermore, the top of the cleaning liquid storage tank is also connected to the exhaust gas treatment device through an eighth pipeline.

[0026] Furthermore, the cooling device is a cooling water circulation machine, a cooling water circulation pipe is provided inside the cleaning liquid storage tank, and the cooling water circulation pipe is connected to the cooling water circulation machine.

[0027] Furthermore, the cooling device is a cooling water circulation machine, and the cleaning liquid storage device is a cooling tank inside the cooling water circulation machine.

[0028] Furthermore, a temperature sensor and a liquid level meter are also arranged inside the cleaning liquid reservoir.

[0029] Compared with the prior art, the method of online cleaning of MBR hollow fiber membrane using ozone micro-nano bubbles described in the present invention has the following advantages:

[0030] 1. The combination of ozone and micro-nano bubble technology can prolong the residence time of ozone in water and increase the mass transfer efficiency of ozone. It can quickly make the water reach the required ozone concentration with a small amount of gas introduction, thereby improving the utilization rate of ozone and reducing waste gas emissions.

[0031] 2. The chemical agents used in the traditional MBR online chemical cleaning will affect the activity of the activated sludge, thereby affecting the removal rate of effluent pollutants. However, the dissolved ozone used in the present invention has a low concentration and has no significant effect on the removal rate of effluent pollutants and the activity of the activated sludge.

[0032] 3. Ozone has a short half-life. After cleaning is completed, the remaining ozone micro-nano bubble cleaning liquid in the cleaning liquid reservoir will turn into clean water after a certain period of time as the micro-nano bubbles burst and the ozone decomposes naturally, avoiding the problem of cleaning waste liquid treatment caused by traditional MBR online chemical cleaning.

[0033] 4. The methods currently reported in research to improve ozone mass transfer and utilization rate include: adding transfer promoters, surfactants and catalysts. Adding these chemicals to MBR online cleaning may have adverse effects on activated sludge. Micro-nano bubble technology has the advantages of simple process, high efficiency, fast degradation rate, and no need to add any chemicals. It has unique advantages in actual engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 This is a schematic diagram of the structure of the equipment used in the method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles as described in Example 1 of the present invention;

[0036] Figure 2 This is a schematic diagram of the structure of the equipment used in the method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles as described in Example 2 of the present invention;

[0037] Figure 3 This is the change diagram of the transmembrane pressure difference on both sides of the MBR hollow fiber membrane under the condition of online cleaning with clean water for 10 minutes;

[0038] Figure 4 This is the change diagram of the transmembrane pressure difference on both sides of the MBR hollow fiber membrane under the condition of ozone micro-nano bubble online cleaning with a dissolved ozone concentration of 1 mg / L for 10 minutes;

[0039] Figure 5 This is the change diagram of the transmembrane pressure difference on both sides of the MBR hollow fiber membrane under the condition of ozone micro-nano bubble online cleaning with a dissolved ozone concentration of 1 mg / L for 5 minutes;

[0040] Figure 6 This is the change diagram of the transmembrane pressure difference on both sides of the MBR hollow fiber membrane under the condition of ozone micro-nano bubble online cleaning for 3 minutes with a dissolved ozone concentration of 1 mg / L;

[0041] Figure 7 This is the change diagram of the transmembrane pressure difference on both sides of the MBR hollow fiber membrane under the condition of ozone micro-nano bubble online cleaning with a dissolved ozone concentration of 0.5 mg / L for 10 minutes;

[0042] Figure 8 This is the change diagram of the transmembrane pressure difference on both sides of the MBR hollow fiber membrane under the condition of ozone micro-nano bubble online cleaning with a dissolved ozone concentration of 1.5 mg / L for 10 minutes;

[0043] Fig. 9 This is the COD removal efficiency diagram of the MBR system before and after online cleaning with ozone micro-nano bubbles at dissolved ozone concentrations of 0.5 mg / L, 1 mg / L, and 1.5 mg / L;

[0044] Fig.10 This is the removal efficiency diagram of ammonia nitrogen of the MBR system before and after online cleaning with ozone micro-nano bubbles at dissolved ozone concentrations of 0.5 mg / L, 1 mg / L, and 1.5 mg / L;

[0045] Fig.11 The membrane surface morphology of the hollow fiber membrane after online cleaning with ozone micro-nano bubbles at dissolved ozone concentrations of 0.5 mg / L and 1 mg / L;

[0046] Fig.12 This is a comparison of the mechanical strength of the hollow fiber membrane after online cleaning with ozone micro-nano bubbles at dissolved ozone concentrations of 0.5 mg / L, 1 mg / L, and 1.5 mg / L;

[0047] Fig.13 This is a comparison chart of the hydrophilicity of the hollow fiber membrane surface after online cleaning with ozone micro-nano bubbles at dissolved ozone concentrations of 0.5 mg / L, 1 mg / L and 1.5 mg / L.

[0048] Description of reference numerals:

[0049] 1. Oxygen generator; 2. First pipeline; 3. Ozone generator; 4. Second pipeline; 5. Micro-nano bubble generator; 6. Third pipeline; 7. Cleaning liquid reservoir; 8. Fourth pipeline; 9. Cooling water circulation pipe; 10. Fifth pipeline; 11. Cooling water circulation machine; 12. Sixth pipeline; 13. Seventh pipeline; 14. Cleaning pump; 15. MBR membrane assembly; 16. Aeration device; 17. Eighth pipeline; 18. Tail gas treatment device. DETAILED DESCRIPTION

[0050] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0051] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0052] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] Example 1

[0055] A method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles, the method comprising the following steps:

[0056] S1. Device connection

[0057] like Figure 1As shown, the oxygen generator 1, the ozone generator 3, and the micro-nano bubble generator 5 are connected in sequence through the first pipe 2 and the second pipe 4, the water outlet of the micro-nano bubble generator 5 is connected to the cleaning liquid reservoir 7 through the third pipe 6, and the water inlet of the micro-nano bubble generator 5 is connected to the cleaning liquid reservoir 7 through the fourth pipe 8. A cooling water circulation pipe 9 is arranged inside the cleaning liquid reservoir 7, and the water outlet and the water inlet of the cooling water circulation pipe 9 are respectively connected to the cooling water circulation machine 11 through the fifth pipe 10 and the sixth pipe 12, and the MBR membrane assembly 15 is connected to the cleaning liquid reservoir 7 through the seventh pipe 13. The pump 14 provides power to transport the liquid in the seventh pipeline 13, and an aeration device 16 is provided at the bottom of the membrane pool; the process of cutting large bubbles to produce micro-nano bubbles will do work, and the liquid in the cleaning liquid reservoir 7 will increase its temperature during continuous circulation in the micro-nano bubble generator 5, and the temperature has a great influence on the ozone concentration in the water body, the ozone residence time and the existence time of the micro-nano bubbles. Therefore, it is very important to control the temperature of the cleaning liquid. In this embodiment, the cooling device uses a cooling water circulation machine, and the cooling water in the cooling water circulation machine is passed into the cooling water circulation pipe 9 in the cleaning liquid reservoir 7 to achieve cooling of the cleaning liquid.

[0058] The upper portion of the cleaning liquid reservoir 7 is also connected to an exhaust gas treatment device 18 via an eighth pipeline 17 .

[0059] S2. Membrane cleaning

[0060] 1) Before cleaning, the water inlet and outlet of the MBR hollow fiber membrane system should be stopped, and the aeration device should be turned on to keep the hollow fiber membrane system in the MBR membrane tank in a strong aeration state for 10-15 minutes to flush away the pollutants attached to the membrane. Then, the aeration device should be turned off to allow the system to stop and settle for 20 minutes;

[0061] 2) turning on the ozone generation system, and the oxygen generated by the oxygen generator is introduced into the ozone generator through the first pipeline to generate ozone;

[0062] 3) Turn on the micro-nano bubble generator, ozone is introduced into the micro-nano bubble generator through the second pipe, water in the cleaning liquid reservoir is introduced into the micro-nano bubble generator through the fourth pipe to mix with the ozone gas, and the generated cleaning liquid rich in ozone micro-nano bubbles is released into the cleaning liquid reservoir through the third pipe. The dissolved ozone concentration in the cleaning liquid reservoir is slightly higher than the dissolved ozone concentration actually introduced into the MBR membrane assembly, and the dissolved ozone concentration in the ozone micro-nano bubble cleaning liquid in the cleaning liquid reservoir is 3-5 mg / L;

[0063] 4) Start the cooling water circulation machine, and connect the cooling water to the cooling water circulation pipeline in the cleaning liquid reservoir through the fifth pipeline and the sixth pipeline, so that the cooling water circulates continuously in the circulation pipeline. After the temperature stabilizes, start the cleaning pump, and pump the ozone micro-nano bubble cleaning liquid into the MBR membrane assembly for online maintenance cleaning. The ozone concentration dissolved in the ozone micro-nano bubble cleaning liquid pumped into the MBR membrane assembly is 0.1-1 mg / L, and the cleaning liquid temperature in the cleaning liquid reservoir is maintained at 23°C±2°C;

[0064] 5) After cleaning, the MBR membrane assembly should be left to stand for 30 minutes to allow the cleaning liquid to fully contact the membrane surface. After the standing time is completed, the aeration device is turned on to flush the membrane surface and the system enters a normal operating cycle.

[0065] In order not to affect the activity of activated sludge in the MBR system, ozone micro-nano bubble cleaning liquid with a dissolved ozone concentration of 0.1-1 mg / L is used for online maintenance and cleaning;

[0066] When using ozone micro-nano bubble cleaning fluid with a dissolved ozone concentration of 0.1-0.5 mg / L for maintenance cleaning, the cleaning interval should be set to 12-24 hours; when using ozone micro-nano bubble cleaning fluid with a dissolved ozone concentration of 0.5-1 mg / L for online cleaning, the cleaning interval should be set to 24-48 hours.

[0067] The flow rate during cleaning should be 1.5-3 times the designed water flow rate of the MBR membrane assembly, and the cleaning duration is 3-10 minutes.

[0068] Example 2

[0069] The difference from Embodiment 1 is that the cooling device is different, the cooling device is a cooling water circulation machine, and the cleaning liquid storage device is a cooling tank built into the cooling water circulation machine. The rest is the same as Embodiment 1.

[0070] test

[0071] This test uses the method described in Example 1.

[0072] Table 1 Online cleaning MBR reactor configuration

[0073]

[0074] This test compared the changes in the MBR reactor operating cycle under the conditions of ozone micro-nano bubble online maintenance and cleaning, as well as the impact of direct contact between the ozone micro-nano bubble cleaning solution and the activated sludge on the removal rate of major pollutants in the MBR reactor. The membrane surface characteristics, mechanical strength, and hydrophilicity and hydrophobicity of the membrane after ozone micro-nano bubble online maintenance and cleaning were also analyzed.

[0075] 1. This test example compares the changes in transmembrane pressure difference of hollow fiber membranes under the conditions of online cleaning with ozone micro-nano bubbles at a cleaning interval of 24h, a cleaning duration of 3min-10min, and dissolved ozone concentrations of 0.5, 1, and 1.5mg / L.

[0076] pass Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 It was found that the operating cycle (0-30KPa) of the membrane backwashed with clean water was only 14 days, while when ozone micro-nano bubbles with dissolved ozone concentrations of 0.5mg / L and 1mg / L were used for online maintenance and cleaning, its operating cycle could reach 18-21 days.

[0077] pass Figure 4 , Figure 5 , Figure 6 It was found that when the dissolved ozone concentration and cleaning interval were the same, shortening the cleaning time could actually extend the operating time of the MBR system. This was mainly because after shortening the cleaning time, the amount of ozone micro-nano bubble cleaning liquid introduced into the MBR membrane pool was also reduced. Less ozone micro-nano bubble cleaning liquid introduced reduced the impact on the activated sludge in the MBR membrane pool.

[0078] pass Figure 8 It was found that when ozone micro-nano bubbles with a dissolved ozone concentration exceeding 1 mg / L were used for online cleaning, the operation time of the MBR system was 12 days. The reason for the rapid increase in the transmembrane pressure difference of the MBR system may be that the ozone micro-nano bubble cleaning liquid with a high dissolved ozone concentration killed the activated sludge microorganisms in the MBR membrane pool after it was introduced, causing the EPS in the microorganisms to be released, which made the activated sludge have a higher potential to adhere to the membrane surface, resulting in a rapid increase in the transmembrane pressure difference.

[0079] 2. Changes in the removal rate of major pollutants in the MBR reactor under the condition of ozone micro-nano bubble online cleaning with a dissolved ozone concentration of 1 mg / L

[0080] pass Fig. 9 , Fig.10It was found that after online cleaning with ozone micro-nano bubbles at dissolved ozone concentrations of 0.5 mg / L and 1 mg / L, the COD and ammonia nitrogen removal effects of the MBR reactor did not change significantly, which indicates that the ozone micro-nano bubble cleaning solution with dissolved ozone concentrations of 0.5 mg / L and 1 mg / L has little effect on the activity of activated sludge in the MBR membrane pool; after online cleaning with ozone micro-nano bubbles at a dissolved ozone concentration of 1.5 mg / L, the ammonia nitrogen removal rate of the MBR system dropped from 95% before cleaning to 89%, which indicates that the introduction of ozone micro-nano bubble cleaning solution with high dissolved ozone concentration affects the activity of nitrifying bacteria in the MBR membrane pool, thereby reducing the ammonia nitrogen removal effect of the MBR system.

[0081] 3. Cleaning costs

[0082] Table 2 Operating power of each equipment during cleaning process

[0083]

[0084] Table 3 Operating time of each equipment during cleaning process

[0085]

[0086] Table 4 Cleaning costs (yuan / m 2 )

[0087]

[0088] Power consumption E=P*t, electricity fee is calculated at 0.8 / kW•h

[0089] It can be seen from the above table that when the dissolved ozone concentration is 0.5-1mg / L, the ozone generator power increases from 59.4w to 63.8w, and the increase is small. Therefore, under the same cleaning time, the cost of online cleaning of ozone micro-nano bubbles with a dissolved ozone concentration of 0.5-1mg / L does not change much. At the same concentration, the cleaning cost increases with the increase of cleaning time. When the membrane is less contaminated, the recommended cleaning time is 3-5min.

[0090] 4. Membrane surface morphology analysis

[0091] Fig.11 Shown are the membrane surface morphologies of the hollow fiber membrane and the original membrane after online cleaning with ozone micro-nano bubbles at different dissolved ozone concentrations; (a) shows a new membrane, (b) shows ozone micro-nano bubbles with a dissolved ozone concentration of 0.5 mg / L, and (c) shows ozone micro-nano bubbles with a dissolved ozone concentration of 1 mg / L.

[0092] Analysis found that there was no morphological change on the surface of the membrane after online cleaning with ozone micro-nano bubbles at a dissolved ozone concentration of 0.5-1 mg / L, and the membrane pores did not increase significantly, indicating that ozone micro-nano bubbles in this concentration range will not have an adverse effect on the membrane and will not affect the function of the membrane.

[0093] 5. Mechanical strength of membrane after online cleaning

[0094] from Fig.12 It can be seen that after online cleaning with ozone micro-nano bubbles at a dissolved ozone concentration of 0.5-1 mg / L, the tensile strength and elongation at break of the membrane decreased slightly, which had little effect on the mechanical strength of the membrane overall. However, when the concentration was 1.5 mg / L, the tensile strength and elongation at break of the membrane decreased to a greater extent. Therefore, considering the above factors, the concentration was selected to be less than 1 mg / L.

[0095] 6. Hydrophilicity and hydrophobicity of membrane after online cleaning

[0096] The PVDF hollow fiber membrane used in this experiment is a hydrophilic membrane. The water contact angle of the original PVDF membrane surface is 74.3°. Fig.13 It can be seen that after online cleaning with ozone micro-nano bubbles at a dissolved ozone concentration of 0.5-1 mg / L, the water contact angle of the membrane increased slightly overall, but the increase was small, so online cleaning with ozone micro-nano bubbles at a dissolved ozone concentration of 0.5-1 mg / L had little effect on the hydrophilicity of the membrane.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles, characterized in that: The method comprises the following steps: S1. Device connection The oxygen generator, the ozone generator and the micro-nano bubble generator are connected in sequence. The water inlet and the water outlet of the micro-nano bubble generator are connected to the cleaning liquid reservoir. The cleaning liquid reservoir is connected to the MBR membrane assembly through a cleaning pump. An aeration device is provided at the bottom of the membrane pool where the MBR membrane assembly is placed. The cleaning liquid reservoir also cools the cleaning liquid by setting a cooling device. S2. Membrane cleaning 1) Before cleaning, the water inlet and outlet of the MBR hollow fiber membrane system should be stopped, and the aeration device should be turned on to keep the hollow fiber membrane system in the MBR membrane tank in a strong aeration state for 10-15 minutes to flush away the pollutants attached to the membrane. Then, the aeration device should be turned off to allow the system to stop and settle for 20 minutes; 2) Turn on the oxygen generator, ozone generator and micro-nano bubble generator in sequence, pass the generated oxygen into the ozone generator to generate ozone, then pass the ozone and cleaning liquid into the micro-nano bubble generator for mixing, and release the generated cleaning liquid rich in ozone micro-nano bubbles into the cleaning liquid reservoir; 3) Start the cooling device to cool the cleaning liquid, and start the cleaning pump after the temperature and dissolved ozone concentration are stable, and pump the ozone micro-nano bubble cleaning liquid into the MBR membrane assembly for online maintenance and cleaning; the dissolved ozone concentration in the ozone micro-nano bubble cleaning liquid pumped into the MBR membrane assembly is 0.1-1mg / L; when the ozone micro-nano bubble cleaning liquid with a dissolved ozone concentration of 0.1-0.5mg / L is used for maintenance and cleaning, the cleaning interval is set to 12-24h; when the ozone micro-nano bubble with a dissolved ozone concentration of 0.5-1mg / L is used for online cleaning, the cleaning interval is set to 24-48h; the flow rate during cleaning is 1.5-3 times the designed water flow rate of the MBR membrane assembly, and the cleaning time is 3-10min; when the dissolved ozone concentration and the cleaning interval are constant, shortening the cleaning time can extend the operation time of the MBR system; when the membrane is less polluted, the selected cleaning time is 3-5min; 4) After cleaning, let it stand for 30 minutes to allow the cleaning liquid to fully contact the membrane surface. After standing, turn on the aeration device to flush the membrane surface and the system will enter the normal operating cycle.

2. The method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles according to claim 1, characterized in that: The temperature of the cleaning liquid is maintained at 23℃±2℃ by a cooling device.

3. The method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles according to claim 1, characterized in that: The concentration of dissolved ozone in the ozone micro-nano bubble cleaning liquid in the cleaning liquid reservoir is 3-5 mg / L.

4. The method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles according to claim 1, characterized in that: The top of the cleaning liquid storage tank is also connected to the exhaust gas treatment device through an eighth pipeline.

5. The method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles according to claim 1, characterized in that: The cooling device is a cooling water circulation machine. A cooling water circulation pipe is arranged inside the cleaning liquid storage tank, and the cooling water circulation pipe is connected to the cooling water circulation machine.

6. The method for online cleaning of MBR hollow fiber membranes using ozone micro-nano bubbles according to claim 1, characterized in that: The cooling device is a cooling water circulation machine, and the cleaning liquid storage device is a cooling tank inside the cooling water circulation machine.

Images