Membrane Bioreactor (mbr) as an Advanced Wastewater Treatment Technology
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TRICHLUCTHUADAT LIEN 1, TRICHLUCTHUADAT LIEN 1, TRICHLUCTHUADAT LIEN 1, TRICHLUCTHUADAT LIEN 1
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Membrane Fouling A decrease in the permeate flux or increase in TMP during a membrane process is generally understood by the term “fouling”. Fouling occurs as a consequence of interactions between the membrane and the mixed liquor, and is one of the principal limitations of the MBR process. There has been done a lot of research on this subject [9], so it is of interest to describe the fouling in more details. Fouling of membranes in MBRs is a very complex phenomenon with diverse relationships among its causes, and it is very dif- ficult to localize and define membrane fouling clearly. The main causes of membrane fouling are: 1. Adsorption of macromolecular and colloidal matter 2. Growth of biofilms on the membrane surface 3. Precipitation of inorganic matter 4. Aging of the membrane As a measure of fouling, resistance (R), which is inversely related to K, is often used. R is given by: R = ∆ P η J , (4) where η stands for permeate viscosity in (kg m –1 s –2 ). This total filtration re- sistance consists of a number of components, which can be divided as: mem- brane resistance, resistance of the fouling layer on the membrane surface, and resistance offered by the membrane-solution interfacial region. Mem- brane resistance is a function of characteristics of membrane material such as thickness and pore size, and it determines the flux through the membrane for filtration of one-component liquid, i.e., clean water. For MBRs, membrane resistance is often given as its inverse value called “clean water permeabil- ity”, which is normally within the range of a few hundred to a few thousand L m –2 h –1 bar –1 . The resistance of the fouling layer is associated with the fil- 48 J. Radjenovi´c et al. tration mechanism, which is dependent on the membrane characteristics and characteristics of filtered solids, while membrane-solution interfacial re- gion resistance is associated with concentration polarization. Concentration polarization is a phenomenon of solute tendency to accumulate within the boundary liquid layer of near-stagnant fluid adjacent to membrane surface. Since liquid velocity within this layer is close to zero, the only mode of mass transport is diffusion, which is significantly slower then convective transport in the bulk solution. As a consequence, resistance to filtration occurs. The thickness of the boundary layer is dependent on system’s hydrodynamics and can be decreased by promoting the turbulence of liquid flow. Fig. 9 Fouling mechanisms According to recognized mechanisms (Fig. 9), the fouling on the mem- brane occurs as: 1. Complete blocking caused by occlusion of pores by the particles with no tải về 0.95 Mb. Chia sẻ với bạn bè của bạn:
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