Ultrafiltration membranes are a widely used configuration in ultrafiltration technology. Because of the continuous production of ultrafiltration membranes and their uniform quality, excellent membranes generally have no defects and a high density of membrane fillers, resulting in a smaller volume compared to other configurations (such as tube-shaped, plate-shaped, etc.). For ultrafiltration membrane packing components, the quality varies greatly, except for appearance, the intrinsic quality is different.
Under an inflation pressure of 0.1 to 0.2 MPa, there should be no bubbles leaking on the surface of the membrane. If bubbles exist, it indicates that the membrane has defects and its interception performance is inevitably poor.
At a certain temperature and pressure (0.1 MPa, 25 ℃), the pure water flux should be moderate, about 120-200 L/㎡/h. If the flux is too high, the membrane is prone to clogging, and if it is too low, the efficiency is low.
The pressure resistance strength (pressure difference between the inside and outside) of ultrafiltration membranes should be above 0.3 MPa. Sacrificing the strength of the membrane in order to increase water flux and reduce the thickness of the membrane and increase looseness is not advisable.
The interception performance is judged by determining the pollution index (SDI) of the water that passes through the membrane. Theoretically, when general turbidity enters the water, the SDI value of the ultrafiltration product water should be zero. However, due to sample collection, testing instruments, and environmental pollution, the SDI value is usually less than 2 and the normal value should be below 1.0.
The service life of ultrafiltration membrane components depends on the following factors:
High-quality ultrafiltration membranes with uniform pressure resistance, pore size, no defects, and smooth surface.
Correct process flow. Ultrafiltration devices, especially large-scale ones, must have pipeline and automatic control systems for backwashing, fast flushing, chemical flushing, and inflation flushing. Simple pipeline systems with one inlet and two outlets, although lower in equipment cost, seriously affect the service life of the membrane.
Good operation conditions. Operating conditions must be set based on the water quality of the feed water, such as operating pressure, the ratio of ultrafiltration water to concentrate water, backwashing frequency and intensity, chemical flushing cycle, selection of chemicals, and operating methods.
1. Use bactericide to kill bacteria and microorganisms in the feed water. Maintain appropriate residual chlorine levels;
2. Pre-filter to remove suspended solids and solid particles. When the colloidal content is high, use flocculation and precipitation pretreatment;
3. Regular backwashing and fast flushing, periodic chemical flushing;
4. Dynamic filtration, discharge concentrate water, recycling ratio depends on the water quality of the feed water;
5. Slowly raise and lower the pressure to prevent impact.