Membrane Module and Membrane Filter for Water Treatment
Existing membrane bioreactors can be divided into a split MBR and an integrated MBR according to the combined form of the membrane module and the bioreactor. The membrane module and bioreactor of the separate MBR are set separately. When working, the mixed liquid in the bioreactor is boosted by the circulation pump and hit the filter end of the membrane module. Under the action of pressure, the liquid in the mixed liquid penetrates the membrane. Become a system to treat water. The membrane module of the integrated MBR is placed inside the bioreactor. When working, most of the pollutants in the water body to be treated enter the membrane bioreactor are removed by the activated sludge in the mixed liquid, and then removed by the membrane filter under the action of pressure The component filters out water. Compared to the discrete MBR, the integrated MBR is usually smaller and has lower operating costs.
At present, the membrane elements used in the membrane module of the integrated MBR mainly include two types of plate membrane filters and hollow fiber membranes of the membrane filter. The plate membrane is a hollow plate-shaped or sheet-shaped membrane element. The appearance of membrane modules using plate membranes is similar to that of ordinary plate and frame filter presses. The hollow fiber membrane filter is a hollow fiber membrane element with an outer diameter of generally 40-250 microns and an inner diameter of generally 25-42 microns.
In the integrated MBR using hollow fiber membranes, the membrane module includes a fiber bundle composed of a large number of hollow fiber membranes, both ends of these fiber bundles are fixed by the device and the opening of the hollow fiber membrane is connected to the collecting chamber of the collecting member; The membrane module is directly placed in the bioreactor and immersed in the water body to be treated to form an immersion membrane bioreactor.
Plate membrane filter has high mechanical strength, long service life, and strong resistance to membrane pollution, but the production and use costs are high. Membrane modules using plate membranes are relatively simple to manufacture, easy to operate and operate, and easy to clean plate membranes. However, the packing density of plate membranes is relatively small, and large membrane areas often require large membrane modules. Hollow fiber membranes have low mechanical strength, are easily broken during use, and have a low resistance to membrane contamination, but have lower production and use costs.
Membrane modules using hollow fiber membranes are more sensitive to membrane fouling. Membrane pore-clogging and concentration polarization have a great influence on membrane separation performance. The pressure drop during filtration is large. However, the packing density of hollow fiber membranes is high and the unit volume The area of the lower membrane is generally up to 16000-30000m2 / m3. In general, compared with membrane modules using plate membranes, membrane elements using hollow fiber membranes have higher packing density but weaker anti-pollution ability.
The packing density of the hollow membrane filter is greatly benefited from its long shape. When a large number of hollow fiber membranes form fiber bundles, the total membrane area is naturally larger. However, because the gap between the hollow fiber membranes is very compact, the dirt intercepted by the hollow fiber membranes during filtration is likely to accumulate in the fiber bundle, which is also one of the reasons that the hollow fiber membranes are easily polluted and clogged.
In addition, the above-mentioned submerged membrane bioreactor specifically adopts that the upper end of the fiber bundle is connected to the current collecting member so that the opening of the hollow fiber membrane communicates with the current collecting chamber of the current collecting member, and the lower end of the fiber bundle is aerated The relatively fixed structure of the device, the two ends of the fiber bundle cannot move during operation, and the dirt formed by the filtration gradually gathers in the fiber bundle, and the aeration device often cannot effectively act on the upper end of the fiber bundle, which will eventually lead to the fiber The upper area of the bundle forms a dirt deposit area.