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​Membrane Influence Factors
- Jun 28, 2018 -

Membrane influence factors


Effect of membrane surface velocity


Membrane filtration process usually adopts the operation method of cross-flow filtration. It is generally believed that increasing the flow rate can increase the flux. This is due to the increase of the flow rate, the increase of the shear force on the membrane surface, and the oil droplets deposited on the membrane surface are taken away. The thickness of the gel layer is small, and the effect of concentration polarization is reduced. When the flow rate is too high, the flux is reduced, which may be caused by the uneven operation pressure, or it may be in the membrane filter The residence time is too short, in addition, due to the increase in flow velocity, shear force increases, resulting in oil droplets deformed and squeezed into the membrane hole may also cause decreased flux.


Effect of temperature


Studies have shown that the effect of temperature on membrane flux is mainly related to the viscosity of feed liquid, the distribution of suspended solids in feed liquid, and the influence of feed liquid components and membrane surface forces. Appropriate increase in temperature can increase the flux of the membrane and increase with temperature. High, liquid viscosity decreases, solute diffusion coefficient increases, so the membrane flux increases.


Membrane cleaning


The composition of the oily wastewater is very complex, and there is no significant effect of a single pickling, caustic washing or oil washing. The analysis of the membrane surface pollutants is the key to find a practical and efficient cleaning method. When cleaning with light mineral oil, Although the oil on the membrane surface can be washed away, the mechanical impurities on the membrane surface cannot be washed down; when the alkali washing is used, the wastewater contains a large amount of calcium, magnesium and other metal ions that react with the alkali to form a flocculent precipitate and adhere to the membrane. Surface; When pickling, due to the protection of the oil pollution layer on the surface, can not effectively clean the surface of the film. Li Fayong using light mineral oil - pickling - caustic wash three-step cleaning method, each step cleaning 10min, after washing the film The flux is restored to 95% to 99% of the cleaning membrane flux; Zhang Zhicheng [23] regularly uses a tank washing solution containing detergent or surfactant in “Ultrafiltration Technology Research and Application” to clean the membrane and recover the flow of the membrane. Busca confirmed the effectiveness of surfactants to clean contaminated PVDF ultrafiltration membranes, and found that the temperature and concentration of cleaning agents play an important role in the effective removal of pollutants; Belkacem et al. reported the addition of a small amount of low molecular weight inorganics to wastewater. Salt can increase Flux due to the addition of inorganic salts, may reduce fouling at the membrane surface.


Therefore, studying the mechanism of membrane fouling, finding suitable cleaning methods and frequency have a profound impact on the successful application of membrane technology in the treatment of oily wastewater.