Membrane separation technology in various types of sewage treatment
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Keywords: Membrane separation technology in various types of sewage treatment
Membrane separation principle and its characteristics:
Membrane separation technology is driven by external forces, using a special film with selective transmission performance as a barrier to select, allowing certain components of the mixture to be easily penetrated, and other components are difficult to permeate and retained to separate and purify. Condensation technology, its working principle is: First, according to the different components in the mixture of mass, size, size and geometry of the separation method used to separate them; Second, according to the different chemical properties of the mixture separation, material separation The speed of the film (dissolution rate) depends on the speed of entry into the film and the rate of diffusion (speed of diffusion) into the surface of the film to the other surface of the film, where the speed of dissolution depends entirely on the chemical nature of the material being separated from the film material. In general, the morphological structure of the membrane determines its separation mechanism and application. According to different structures, membranes can be divided into solid membranes and liquid membranes, and solid membranes can be divided into symmetrical membranes (column pore membranes, porous membranes, homogenous membranes) and asymmetric membranes (porous membranes, porous membranes with skin layers, composites). Membrane) Liquid membranes can be classified into two types, a liquid membrane existing in a solid porous supporting layer and a liquid membrane existing in the form of an emulsion.
At present, the commonly used membrane separation technology can be divided into reverse osmosis (ro), ultrafiltration (uf), microfiltration (mf), nanofiltration (nf), electrodialysis (ed) and membrane contactor (mc). In the process of use, the membranes need to be made into modules as the separation unit of the membrane separation device. The membrane modules commonly used in industry are in the form of plate frame, round tube, spiral coil and hollow fiber. The latter three are all tubular membranes, the difference being mainly in diameters: tubular membranes with a diameter of 10 mm in diameter, capillary membranes with a diameter of between 0.5 mm and 10 mm, and hollow fiber membranes with a diameter of less than 0.5 mm. The smaller the diameter of the tubular membrane, the larger the membrane area per unit volume. Membrane separation methods commonly used in wastewater treatment are shown in the table.
Compared with traditional separation techniques, membrane separation technology has the following characteristics: 1 Membrane separation is an efficient separation process that can separate relative molecular weights of thousands or even hundreds of substances. 2 The membrane separation process basically does not undergo "phase" changes, low energy consumption and high energy conversion rate. 3 Membrane separation process can be carried out at room temperature, suitable for the separation, grading, and concentration of heat-sensitive materials such as juices, enzymes, and drugs. 4 Membrane separation equipment has few moving parts, simple structure, convenient operation, control and maintenance. 5 The membrane separation efficiency is high, the equipment volume is small, the area is small, and the application scope is wide.