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This paper introduced the definition and characteristic of membrane separates technology. Stated several conditional methods such as micro filtration, reverse osmosis, ultra filtration, nanofiltration, electro dialysis, liquid membrane, etc. Prospected the development of membrane separation technology. KEYWORD: Membrane separation technology; Wastewater treatment 4th International Conference on Mechanical Materials and Manufacturing Engineering (MMME 2016) © 2016. The authors Published by Atlantis Press 630 3 COMMON MEMBRANE SEPARATION TECHNOLOGY AND ITS CHARACTERISTICS Membrane separation technology has been widely used since it was invented, but the initial research and application of it are aimed at the field of water treatment. The current common membrane separation process mainly includes microfiltration, ultrafiltration, nanofiltration, electrodialysis, reverse osmosis, liquid film, pervaporation etc. Different membrane separation technology has different separation mechanism and application range. Some common membrane separation processes are listed in Table 1[6-9]. Table 1 Some common membrane separation processes Membrane Process Membrane Pore Size Driven Force Separation Mechanism Microfiltration 0.1-0.2μm pressure difference 100kPa mechanical screening Ultrafiltration 0.05-1μm pressure difference 0.1-1.0MPa size and shape of molecules nanofiltration 0.5-10nm pressure difference 0.5-1.0MPa screening and certain selectivity Reverse osmosis <1nm static pressure difference 1-10MPa selectivity of reverse osmosis membrane Electrodialysis potential difference selectivity of ion exchange membrane Liquid membrane technology concentration gradient chemical reaction and concentration difference Osmotic evaporation chemical reaction and concentration difference differences of solubility and diffusion coefficient 3.1 Microfiltration (MF) Microfiltration is a precise filtration process, as the same with reverse osmosis and ultrafiltration, they are all driven by pressure. The separated components are 0.1 to 0.2μm in diameter, mainly are fine microparticles, submicroparticles and nanoparticles. It is usually used for the terminal treatment of ultra pure water in the semiconductor industry, the first end pretreatment of the reverse osmosis. It was also used for the removal of microorganisms and odor impurities, etc. in the brewing of beer and other alcoholic drinks [6]. 3.2 Ultra filtration (UF) Ultrafiltration is similar to reverse osmosis, separating fractions with diameter of 0.005~10μm, which is between the reverse osmosis and microfiltration. Reverse osmosis, ultrafiltration and microfiltration formed a membrane separation process from the ions to particles. 3.3 Nanofiltration (NF) Nanofiltration membrane is a kind of pressure infiltration membrane with aperture between reverse osmosis and ultrafiltration membrane. It has a high retention performance for organic materials and high price, low price inorganic materials with molecular weight between 200 to 1000. Nanofiltration is widely used for water softening, organic bio active substances and dechlorination, purification, concentration, wastewater decoloration. Studies on nanofiltration technology began at the end of the 1980s, though it is still in the laboratory research and development stage and there is no products on the market [8]. 3.4 Reverse osmosis (RO) Membranes with substances selectivity is called semipermeable membrane, generally, Membranes only permitting solvent go through but not for the solute are known as ideal semipermeable membranes. When the same volume of dilute solution (e.g. freshwater) and concentrated solutions (e.g. saline) were placed on both sides of a semipermeable membrane, the solvent of dilute solution will spontaneously flow to the side of concentrated solution, this phenomenon is named permeate as shown in Figure 1[7]. Figure 1 Schematic diagram of the osmotic membrane When the infiltration process achieve balance, the liquid level of concentrated the solution side will be a certain higher than that of the dilute solution and there will format a differential pressure, known as the osmotic pressure. The value of osmotic pressure depends on the inherent nature of the solution, namely the solution species, concentration and tem-

Membrane Separation Technology for Wastewater Treatment and its Study Progress and Development Trend