Efficient membrane cleaning process

Abstract

The invention discloses an efficient membrane cleaning process, and belongs to the field of industrial sewage treatment. According to the invention, a pre-washing, alkali washing and acid washing treatment process is adopted, solid impurities are effectively shaken off by adopting pre-washing, an effect of loosening a filter cake layer is achieved, and then the solid impurities are flushed out from membrane fibers by air-water backwashing; an alkali washing method is adopted, microorganisms on the surface of the membrane are removed firstly, and the wrapping effect of the microorganisms on hardness is reduced; metal ion attachments, such as calcium salt, magnesium salt and ferric salt, on the membrane are removed by adopting an acid pickling method, and finally, pollutants gathered on the membrane are thoroughly removed, so that the water production flux is improved, and meanwhile, the service life of the membrane is prolonged. According to the method, the ultrafiltration membrane cleaning effect is effectively improved, the transmembrane pressure difference is recovered to be 0.1 MPa or below, the ultrafiltration cleaning period can be prolonged to be about one month, and the overall recovery rate reaches 95% or above.

Description

Technical Field

[0001] The present invention relates to an efficient membrane cleaning process, belonging to the field of industrial sewage treatment. Background Art

[0002] The wastewater source of the membrane treatment system for the industrial wastewater of Taigang mainly comes from the wastewater generated in steel rolling and smelting production. The water quality indicators such as conductivity, hardness, bacteria, microorganisms, and organic matter in the water are relatively high and fluctuate greatly. Moreover, with the transformation of the company's water system and the continuous improvement of the water recycling rate, the water quality deterioration situation gradually increases. When ultrafiltration membranes operate in such sewage for a long time, it will cause physical, chemical, or mechanical interactions between macromolecular solutes such as particles, colloidal particles, organic matter, and microorganisms and the membrane, resulting in the adsorption and precipitation of pollutants on the membrane surface or in the pores, reducing the membrane pore size or blocking the pores. Conventional cleaning methods cannot thoroughly clean the pollutants accumulated on the membrane, so the water production flux drops sharply, and at the same time, the service life of the membrane is greatly shortened. Summary of the Invention

[0003] In order to overcome the above deficiencies, the present invention aims to provide an efficient membrane cleaning process to effectively remove the attachments of solid impurities, microorganisms, and metal ions on the membrane surface and in the membrane pores, such as pollutants like calcium salts, magnesium salts, iron salts, etc., improve the membrane flux, extend the membrane life, and ensure the normal operation of the membrane system.

[0004] The present invention provides an efficient membrane cleaning process, which successively adopts the processes of pre-cleaning, alkali cleaning, and acid cleaning to improve the membrane cleaning effect. The specific steps are as follows: (1) Adopt the pre-cleaning process. In the pre-washing stage, perform air scrubbing. Let low-pressure air enter the membrane fiber bundle. The high-velocity air flow can most effectively shake the membrane fibers and shake off the solid impurities intercepted on the membrane surface, and then perform air-water backwashing to flush the solid impurities out of the membrane fibers.

[0005] (2) Adopt the alkali cleaning process. First, remove the microorganisms on the membrane surface and reduce the wrapping effect of microorganisms on hardness. After chemical cleaning with an alkaline membrane cleaning solution, the flux recovery rate of the contaminated membrane for each separation component reaches more than 99%, indicating that the alkaline chemical cleaning agent has a good removal effect on the pollution layer formed by various DOMs on the membrane surface.

[0006] (3) Adopt the acid cleaning process to remove hardness pollution and remove the attachments of metal ions on the membrane, such as calcium salts, magnesium salts, iron salts, etc.

[0007] Through the application of the above steps and methods, it mainly prevents the deposition of particulate matter inside the membrane filaments, maintains the membrane flux, and is conducive to protecting the normal operation of the membrane system.

[0008] Carrying out in sequence according to the above three steps is the core technology to ensure the cleaning effect; the implementation effect is significantly better than the original process (acid pickling first and then alkali pickling). This process step adopts a working method from dynamic to static and from outside to inside, which can ensure the removal of pollutants. First, remove the microorganisms on the membrane surface to reduce the wrapping effect of microorganisms on hardness pollution (the hardness in water mainly refers to water scaling), and then use acid to clean the hardness pollution, making the cleaning targeted.

[0009] Furthermore, the inlet air pressure of the ultrafiltration membrane is 1.5 bar; the air scrubbing time is 1 min; after the air scrubbing is completed, the ultrafiltration membrane is backwashed 3 times.

[0010] Furthermore, the alkaline agent used in the alkali cleaning process is an aqueous solution prepared from NaOH and NaClO. The mass concentration of NaOH in the solution is 0.05%, and the mass concentration of NaClO is 0.3%; the temperature of the cleaning solution is controlled at 35°C - 38°C, and the pH is 11.5 - 12; Furthermore, the alkali cleaning process includes: chemical agent circulation, cleaning circulation, soaking, secondary circulation, and rinsing; specifically: (1) Chemical agent circulation for 5 min; (2) Circulating cleaning: (This step is air-water cleaning) ① Start the cleaning water pump for circulating cleaning. The inlet pressure is maintained at 1.0 - 1.5 bar, the flow rate is 120 m 3 / h, and the cleaning time is 30 - 60 min; ② When half of the cleaning time has elapsed: close the ultrafiltration cleaning return valve; build pressure to make all the cleaning liquid flow into the cleaning water tank from the product water return pipe; form a backflow; conduct enhanced cleaning on the fouling in the membrane pores for 10 min; ③ Conduct high-frequency short-time air scrubbing on the ultrafiltration membrane 5 times during the front, middle, and rear time periods of the circulation, each time for 15 seconds; scrub 5 times respectively during the front, middle, and rear time periods, and the interval time between each time is 15 seconds.

[0011] (3) Soaking: ① Close the cleaning circulation water pump. Let it stand and soak for 60 - 90 min. Determine the soaking time according to the fouling degree of the device.

[0012] ② After the soaking is completed, conduct air scrubbing: the air scrubbing air pressure is 1.5 bar; intake air for 8 seconds and stop for 15 seconds; then intake air for 8 seconds and stop for 15 seconds; circulate about 10 times; (4) Secondary circulation cleaning Conduct secondary circulation cleaning according to the above step (2); the time is 60 min; after the cleaning is completed, drain all the sewage inside the ultrafiltration; empty the cleaning water tank and pipelines, and rinse them clean with clean water.

[0013] (5) Rinsing Wash and rinse until the difference (the higher value) between the conductivity of the influent water and the product water is within 20 μs / cm.

[0014] Furthermore, during the circulating cleaning in the caustic washing process, the temperature is controlled at 35°C - 38°C and detected every 10 minutes. If the requirement is not met, heat up in time; the pH value is controlled at 11.5 - 12. Measure the pH once before circulation. If the pH does not meet the requirement, additional alkaline agents need to be added until the pH requirement is met; during cleaning, detect whether the pH value changes every 10 minutes. If there is a change, adjust appropriately to make the pH meet the requirement.

[0015] Further, the agent used in the pickling process is: 0.4% HCI solution; the temperature of the cleaning solution during the pickling process is controlled at 35°C - 38°C.

[0016] Further, the pickling process includes agent circulation, cleaning circulation, soaking, and secondary cleaning circulation; specifically: (1) Agent circulation for 5 minutes; (2) Circulating cleaning ① Start the cleaning water pump for circulating cleaning. The inlet pressure is maintained at 1.0 - 1.5 bar, and the flow rate is 120 m 3 / h, and the cleaning time is 30 - 60 minutes; ② When half of the cleaning time has passed: close the ultrafiltration cleaning return valve; build pressure so that all the cleaning liquid flows from the product water return pipe into the cleaning water tank to form a return flow for enhanced cleaning of the fouling inside the membrane pores for 20 minutes.

[0017] ③ Perform high - frequency short - time air scrubbing on the ultrafiltration membrane 5 times during the front, middle, and back periods of the circulation time, 15 seconds each time; scrub 5 times respectively during the front, middle, and back periods, and the interval time between each scrub is 15 seconds.

[0018] (3) Soaking: ① Turn off the cleaning circulation water pump; let it stand and soak for 60 - 90 minutes; determine the soaking time according to the fouling degree of the device.

[0019] ② After soaking, perform air scrubbing: the air scrubbing air pressure is 1.5 bar; intake air for 8 seconds and stop for 15 seconds; then intake air for 8 seconds and stop for 15 seconds; circulate about 10 times; (4) Secondary circulation cleaning Conduct secondary circulation cleaning according to step (2) above; the time is 60 minutes; after cleaning is completed, drain all the sewage inside the ultrafiltration; empty the cleaning water tank and pipelines, and rinse them clean with clean water.

[0020] Further, during the pickling process, during cyclic cleaning: the temperature is controlled at 35°C - 38°C, and it is detected every 10 minutes. If the requirement is not met, heat up in time; test the hardness of the cleaning solution once before cycling; test whether there is any change every 30 minutes during cleaning. During the pickling process, control the hardness of the cleaning solution ≤ 500 mg / l.

[0021] Advantages of the present invention: (1) The present invention adopts a treatment process of pre-cleaning + alkali cleaning + acid cleaning. Pre-cleaning effectively shakes off solid impurities, playing a role in loosening the filter cake layer, and then air-water backwashing flushes out the solid impurities from the membrane fibers; the alkali cleaning method is used to first remove microorganisms on the membrane surface and reduce the wrapping effect of microorganisms on hardness; the acid cleaning method is used to remove metal ion attachments on the membrane, such as calcium salts, magnesium salts, iron salts, etc. Finally, pollutants accumulated on the membrane are completely removed, thereby improving the water production flux and extending the service life of the membrane. (2) After implementation, the cleaning effect of the ultrafiltration membrane is effectively improved. The transmembrane pressure difference is restored to below 0.1 MPa, the ultrafiltration cleaning cycle can be extended to about 1 month, and the overall recovery rate reaches more than 95%. Specific embodiments

[0022] The present invention will be further described below through examples, but is not limited to the following examples. Example

[0023] Basic situation of the ultrafiltration membrane before cleaning: The pressure difference of the actual membrane system reached 0.50 - 0.60 MPa (the normal membrane pressure difference is generally within 0.25 MPa), the SDI of the effluent water quality exceeded the upper limit of measurement and could not be measured, and the membrane needed to be cleaned once every four days. It was urgent to clean the membrane.

[0024] The ultrafiltration membrane was cleaned by the method of the present invention, and the processes of pre-cleaning, alkali cleaning, and acid cleaning were sequentially adopted to improve the cleaning effect of the membrane. The specific steps are as follows: Step 1: Adopt the pre-cleaning process, and perform two processes of air scrubbing and backwashing in the pre-washing stage; the inlet air pressure of the ultrafiltration membrane is 1.5 bar; the air scrubbing time is 1 minute; after the air scrubbing is completed, the membrane is backwashed 3 times.

[0025] In this step, low-pressure air enters the membrane fiber bundle. The high-flow air stream can most effectively shake the membrane fibers and shake off the solid impurities intercepted on the membrane surface, and then air-water backwashing flushes out the solid impurities from the membrane fibers.

[0026] Step 2: Adopt an alkali washing process to first remove the microorganisms on the membrane surface and reduce the wrapping effect of microorganisms on hardness. After chemical cleaning with an alkaline membrane washing solution, the flux recovery rates of the contaminated membranes of each separation component reach over 99%, indicating that the alkaline chemical cleaning agent has a good removal effect on the pollution layers formed by various DOMs on the membrane surface. The alkaline agent used in the alkali washing process is an aqueous solution prepared from NaOH and NaClO. The mass concentration of NaOH in the solution is 0.05%, and the mass concentration of NaClO is 0.3%. Specifically, the alkali washing process includes: chemical agent circulation, cleaning circulation, soaking, secondary circulation, and rinsing; the steps are as follows: 1) Chemical agent circulation for 5 min: The cleaning pump adds the alkaline agent (an aqueous solution prepared from NaOH and NaClO) into the membrane for circulation. 2) Circulating cleaning: (This step is gas-water cleaning) ① Start the cleaning water pump for circulating cleaning. The inlet pressure is maintained at 1.0 - 1.5 bar, and the flow rate is 120 m 3 / h, and the cleaning time is 30 - 60 min; ② When half of the cleaning time has passed: Close the ultrafiltration cleaning return valve; build pressure to make all the cleaning liquid flow into the cleaning water tank from the product water return pipe; form a reflux; conduct enhanced cleaning of the fouling in the membrane pores for 10 min; ③ Conduct high-frequency short-time gas scrubbing on the ultrafiltration membrane 5 times at the front, middle, and end of the circulation period, 15 seconds each time; scrub 5 times respectively at the front, middle, and end periods, and the interval time between each time is 15 seconds.

[0027] 3) Soaking: ① Turn off the cleaning circulation water pump. Soak statically for 70 min. The soaking time is mainly determined according to the fouling degree of the device.

[0028] ② After soaking, conduct gas scrubbing: The gas scrubbing air pressure is 1.5 bar; intake air for 8 seconds and stop for 15 seconds; then intake air for 8 seconds and stop for 15 seconds; circulate 10 times; 4) Secondary circulation cleaning Conduct secondary circulation cleaning according to the above step (2); the time is 60 min; after cleaning is completed, drain all the sewage inside the ultrafiltration; empty the cleaning water tank and pipeline, and rinse them clean with clean water.

[0029] 5) Rinsing Conduct water washing and rinsing until the difference in conductivity between the influent and product water (the higher value) is within 20 μs / cm.

[0030] Step 3: Adopt an acid washing process to remove hardness pollution and the metal ion attachments on the membrane, such as calcium salts, magnesium salts, iron salts, etc.

[0031] The chemicals used in the pickling process are: 0.4% HCI solution; during the pickling process, the temperature of the cleaning solution is controlled at 35°C - 38°C. The pickling process includes chemical circulation, cleaning circulation, soaking, and secondary cleaning circulation; specifically: (1) Chemical circulation for 5 min: The cleaning pump adds acidic chemicals into the membrane for circulation. (2) Circulating cleaning ① Start the cleaning water pump for circulating cleaning. The inlet pressure is maintained at 1.0 - 1.5 bar, and the flow rate is 120 m 3 / h, and the cleaning time is 40 min. ② When half of the cleaning time has passed: Close the ultrafiltration cleaning return valve; build pressure so that all the cleaning solution flows into the cleaning water tank from the product water return pipe to form a return flow, for enhanced cleaning of the fouling in the membrane pores, with a time of 20 min.

[0032] ③ Perform high-frequency short-time air scrubbing on the ultrafiltration membrane 5 times during the front, middle, and back periods of the circulation, 15 seconds each time; scrub 5 times respectively during the front, middle, and back periods, with an interval of 15 seconds each time.

[0033] (3) Soaking: ① Turn off the cleaning circulation water pump; let it stand and soak for 65 min; determine the soaking time according to the fouling degree of the device.

[0034] ② After soaking, perform air scrubbing: The air scrubbing air pressure is 1.5 bar; intake air for 8 seconds and stop for 15 seconds; then intake air for 8 seconds and stop for 15 seconds; cycle 10 times. (4) Secondary circulation cleaning Perform secondary circulation cleaning according to step (2) above; the time is 60 min; after cleaning is completed, drain all the sewage inside the ultrafiltration; empty the cleaning water tank and pipeline, and rinse them clean with clean water.

[0035] As a preferred technical solution, during the alkali cleaning process and circulating cleaning, the temperature of the cleaning solution is controlled at 35°C - 38°C, and it is detected every 10 min. If it does not meet the requirements, heat it up in time; the pH value is controlled at 11.5 - 12. Measure the pH once before circulation. If the pH cannot meet the requirements, additional alkaline chemicals need to be added until the pH requirement is met; during cleaning, check whether the pH value changes every 10 min. If there is a change, adjust it appropriately to meet the pH requirement.

[0036] As a preferred technical solution, during the pickling process and circulating cleaning: The temperature is controlled at 35°C - 38°C, and it is detected every 10 min. If it does not meet the requirements, heat it up in time; test the hardness of the cleaning solution once before circulation; test whether it changes every 30 min during cleaning. During the pickling process, control the hardness of the cleaning solution ≤ 500 mg / l.

[0037] By applying the above steps and methods, it is mainly to prevent particulate matter from depositing inside the membrane filaments, maintain the membrane flux, and facilitate the normal operation of the membrane protection system.

[0038] Carrying out in sequence according to the above three steps is the core technology to ensure the cleaning effect; the implementation effect is significantly better than the original process (acid cleaning first and then alkali cleaning). The working method of this process step from dynamic to static and from outside to inside can ensure the removal of pollutants. First, remove the microorganisms on the membrane surface to reduce the wrapping effect of microorganisms on hardness pollutants (such as scale), and then use acid to clean the hardness pollution, making the cleaning targeted.

[0039] After adopting the cleaning method provided by the present invention, the membrane cleaning effect is effectively improved, the transmembrane pressure difference is restored to below 0.1 MPa, the ultrafiltration chemical cleaning cycle can be extended to about 1 month, the overall recovery rate reaches more than 95%, the effluent water quality SDI≤3 under normal conditions, and the performance of the ultrafiltration membrane is restored. After using the cleaning steps and methods of the present invention, the cleaning effect is effectively improved, and finally the cleaning standard for the application of UF system in steel wastewater is formed.

Claims

1. A high-efficiency membrane cleaning process, characterized in that: The pre-cleaning, alkali cleaning and acid cleaning processes are used in sequence to improve the cleaning effect of the membrane; specifically, the following steps are included: (1) Pre-cleaning process is adopted. Air scrubbing is performed in the pre-cleaning stage. Low-pressure air is used to enter the membrane fiber bundle. The high-velocity air flow shakes the membrane fibers and shakes off the solid impurities trapped on the membrane surface. Then, air-water backwashing is used to flush the solid impurities out of the membrane fibers. (2) The alkaline washing process is used to first remove the microorganisms on the membrane surface and reduce the encapsulation effect of the microorganisms on the hardness pollutants. After chemical cleaning with alkaline membrane washing liquid, the flux recovery rate of the contaminated membrane of each separation component is more than 99%; (3) Use pickling process to remove hardness pollution and metal ion attachment on the membrane.

2. The high-efficiency membrane cleaning process according to claim 1, characterized in that: The air inlet pressure of the ultrafiltration membrane is 1.5 bar; the air scrubbing time is 1 min; after the air scrubbing is completed, the ultrafiltration membrane is backwashed 3 times.

3. The high-efficiency membrane cleaning process according to claim 1, characterized in that: The alkaline agent used in the alkaline washing process is an aqueous solution prepared by NaOH and NaClO. The mass concentration of NaOH in the solution is 0.05%, and the mass concentration of NaClO is 0.3%; the temperature of the cleaning solution is controlled at 35℃-38℃, and the pH is 11.5-12.

4. The high-efficiency membrane cleaning process according to claim 3, characterized in that: The alkaline cleaning process includes: chemical circulation, circulation cleaning, soaking, secondary circulation cleaning, and rinsing; specifically: (1) The drug circulates for 5 minutes; (2) Circulation cleaning: ①Start the cleaning water pump for cyclic cleaning, with the inlet pressure maintained at 1.0-1.5 bar and the flow rate at 120m 3 / h, cleaning time is 30-60min; ② When the cycle reaches half of the cleaning time: close the ultrafiltration cleaning reflux valve; hold the pressure to allow all the cleaning liquid to flow from the produced water reflux pipe into the cleaning water tank; form a reflux; perform enhanced cleaning of the fouling in the membrane pores for 10 minutes; ③ The ultrafiltration membrane is scrubbed with high-frequency short-time air 5 times before, during and after the cycle period, each time for 15 seconds; the ultrafiltration membrane is scrubbed 5 times before, during and after the cycle period, each time with an interval of 15 seconds; (3) Soaking: ① Turn off the cleaning circulation water pump; let it soak for 60-90 minutes; determine the soaking time according to the degree of fouling of the device; ②After soaking, perform air scrubbing: the air scrubbing pressure is 1.5 bar; air is introduced for 8 seconds and then stopped for 15 seconds; air is introduced for 8 seconds and then stopped for 15 seconds; the cycle is repeated about 10 times; (4) Secondary cycle cleaning Perform secondary cycle cleaning according to the above step (2); the time is 60 minutes; after the cleaning is completed, drain the sewage inside the ultrafiltration; empty the cleaning water tank and pipeline, and rinse them with clean water; (5) Flushing Wash and flush until the conductivity difference between the inlet water and the product water is within 20μs / cm.

5. The high-efficiency membrane cleaning process according to claim 1, characterized in that: The reagent used in the pickling process is: 0.4% HCl solution; the temperature of the cleaning solution during the pickling process is controlled at 35℃-38℃.

6. The high-efficiency membrane cleaning process according to claim 5, characterized in that: The pickling process includes reagent circulation, circulation cleaning, soaking, and secondary cleaning cycle; specifically: (1) The drug circulates for 5 minutes; (2) Circulation cleaning ①Start the cleaning water pump, circulate and clean, keep the inlet pressure at 1.0-1.5bar, and the flow rate at 120m 3 / h, cleaning time 30-60min; ② When the cycle reaches half of the cleaning time: close the ultrafiltration cleaning reflux valve; hold the pressure to allow all the cleaning liquid to flow from the produced water reflux pipe into the cleaning water tank to form a reflux, and perform enhanced cleaning of the fouling in the membrane pores for 20 minutes; ③ Before, during and after the cycle, the ultrafiltration membrane is scrubbed with high-frequency short-time air for 5 times, each time for 15 seconds; scrubbed 5 times before, during and after the cycle, each time with an interval of 15 seconds; (3) Soaking: ① Turn off the cleaning circulation water pump; let it soak for 60-90 minutes; determine the soaking time according to the degree of fouling of the device; ②After soaking, perform air scrubbing: the air scrubbing pressure is 1.5 bar; air is introduced for 8 seconds and then stopped for 15 seconds; air is introduced for 8 seconds and then stopped for 15 seconds; the cycle is repeated about 10 times; (4) Secondary cycle cleaning Perform secondary cycle cleaning according to the above step (2); the time is 60 minutes; after the cleaning is completed, drain the sewage inside the ultrafiltration; empty the cleaning water tank and pipeline, and rinse them with clean water.

7. The high-efficiency membrane cleaning process according to claim 6, characterized in that: During the pickling process, when the cleaning cycle is running: the temperature is controlled at 35℃-38℃, and tested every 10 minutes. If it does not meet the requirements, heat it up in time; test the hardness of the cleaning liquid before the cycle; test every 30 minutes during cleaning to see if there is any change; during the pickling process, control the hardness of the cleaning liquid to ≤500mg / l.