HOW TO CLEAN THE ULTRAFILTRATION MEMBRANE
The structure of Ultrafiltration Membrane is divided into symmetrical and asymmetrical. The former is isotropic, there is no skin layer, and the pores in all directions are the same, which belongs to deep filtration; the latter has a denser surface layer and a finger-like structure-based bottom layer, with a surface thickness of 0.1 microns or less. It has well-arranged micropores, and the thickness of the bottom layer is 200-250 microns, which belongs to surface filtration. Ultrafiltration membranes used in industry are generally asymmetric membranes. The membrane materials of ultrafiltration membranes mainly include cellulose and its derivatives, polycarbonate, polyvinyl chloride, polyvinylidene fluoride, polysulfone, polyacrylonitrile, polyamide, polysulfone amide, sulfonated polysulfone, and cross-linked Polyvinyl alcohol, modified acrylic polymer, etc.
The ultrafiltration membrane screening process uses the pressure difference between the two sides of the membrane as the driving force, and the ultrafiltration membrane is used as the filter medium. Under a given pressure, when the original liquid flows through the membrane surface, the ultrafiltration membrane surface is densely covered with many small micropores Only water and small molecular substances are allowed to pass through and become permeate, while substances in the original solution whose volume is larger than the pore size of the membrane surface are trapped on the inlet side of the membrane and become a concentrated solution, thus achieving the purification, separation and concentration of the original solution purpose. There are about 6 billion 0.01 micron micropores on the wall of the ultrafiltration membrane per meter long, and its pore size only allows water molecules, beneficial minerals and trace elements in the water to pass, and the current known world’s lower limit of the volume of bacteria is 0.2 Micrometers, so bacteria and colloids, rust, suspended solids, silt, and macromolecular organics that are much larger than bacteria can be intercepted by the ultrafiltration membrane to achieve the purification process.
How to clean ultrafiltration membrane:
Physical cleaning mainly includes: positive washing, back washing, air washing (mainly including air scrubbing, air washing). Periodic physical cleaning mainly refers to a cleaning method that sets the system to run for a period of time to perform short positive washing, back washing and air washing, or a combination of these three methods.
1. Positive washing: The positive washing is to open the inlet valve and close the water production valve, so that the high flow rate of the flushing liquid will flow out from the drain valve on the concentrated water, so as to flush the surface of the membrane (hollow fiber curtain membrane) at high speed and reduce the membrane surface Concentration of pollutants.
Backwashing: This operation is the reverse of filtration, that is, the backwashing water enters the ultrafiltration fiber from the clear liquid side and flows through the membrane to the concentrated water side. The large flow of backwash water is used to flush the membrane pores and the surface of the Hollow Fiber Membrane. And drain the flushed pollutants through the lower drain valve.
2. Gas scrubbing: The contaminants on the surface of the membrane are removed by shaking the membrane filament with gas.
3. Air-water washing: the backwash water is pumped by ultrafiltration and backwashing from the clear liquid side of the ultrafiltration membrane (hollow fiber curtain membrane) tube into the concentration side and discharged, and at the same time, compressed air is intermittently passed through the filtration inlet of the Ultrafiltration Membrane Manufacturer, The combination of air and water for backwashing can effectively cause shearing force to more effectively peel off the particles contaminated on the membrane surface and take some particles out of the ultrafiltration membrane tube.
Each process is controlled through PLC. After running for a period of time, it can cooperate with forward washing, back washing and air washing, which can promptly and effectively remove the contaminants on the surface of the membrane (hollow fiber curtain membrane), which not only ensures the stable operation of the system, but also extends Chemical cleaning cycle.
4. Disperse chemical cleaning
Adding chemicals in backwashing (also called "dispersed medicine washing" or "chemically enhanced backwashing" in this system)
After the system sets the cumulative operation of each system for a fixed time, dosing backwash will be carried out, that is, a certain proportion of backwashing agent is added to the backwash liquid through the dosing pump, and the membrane (hollow fiber curtain membrane) is soaked for a short time In the cleaning mode, the operation of this process is automatic, but it is necessary to confirm that the medicine in the medicine box is sufficient. The added backwash agent depends on the quality of the treated water. For details, please consult Jiehan Environmental Protection Company.
5. Chemical cleaning
Chemical cleaning: After a period of normal operation, due to the contamination of the Ultrafiltration Membrane Modules by suspended particles, organic matter and other substances in the wastewater, the flow rate of the produced water decreases, and the pressure difference of the membrane (hollow fiber curtain membrane) increases (that is, the production The water pressure coefficient" drops). Moreover, this phenomenon cannot be recovered by physical methods or dispersed chemical cleaning. In order to restore the original performance of the membrane module, it must be chemically cleaned regularly. The specific cleaning plan should be determined by the characteristics of the pollutants and the degree of pollution.