Ceramic membranes

Recently, submerged ceramic flat sheet membrane (CFM) draws attention, most notably those from Meidensha Co. (Japan). The overall appearance resembles Kubota’s EK cassette, where flat sheet modules are stacked in two-story cassette (Fig. 1c). Ceramic flat sheet membranes are attached in both sides of porous¬†polymeric support layer through which permeate is drawn (Fig. 1a). Each […]

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Dynamic membrane concept

Unlike the popular perception, it has been observed that pore size is not an important factor affecting permeate quality in MF and UF with possible exceptions with very tight membranes, e.g. molecular weight cut off (MWCO) < 100kDa. When MF and UF membranes with various pore sizes were compared in anaerobic digester broth filtration, there […]

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Cake layer compaction

Theory ¬† ¬†The cake layer formed on membrane surface acts as a filtration barrier. It increases TMP at a constant flux mode or decrease flux at a constant pressure mode. The pressure drop, , in cake layer can be calculated by Carmen-Kozeny equation given in Eq. (1). ¬† ¬† ¬† ¬†———————————— (1) where ¬† ¬† […]

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Resistance in series model

The relation between trans-membrane pressure (TMP) and flux can be described using a simple resistance in series model. The equation used in this model is inline with many other equations used in heat/mass transfer, electric current flow, air/water flow calculations,¬†etc., where flux is proportional to the driving force (TMP) and inversely proportional to the resistances […]

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Basics

¬† Resistance in series model The relation between trans-membrane pressure (TMP) and flux can be described using a simple resistance in series model. The equation used in this model is inline with many other equations used in heat/mass transfer, electric current flow, air/water flow calculations, etc., where flux is proportional to the driving force (TMP) […]

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Flux Definition

Flux indicates the productivity of membrane and defined as equation (1). Table 1 summarizes the three different units commonly used. ¬† ¬† ¬† ¬† ————————– (1) ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† ¬† […]

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Total back transport velocity

The particle back transport induced by Brownian diffusion is thermodynamically motivated and is effective whenever concentration gradient exists. The resulting particle back transport is weaker for larger particles due to the smaller Brownian diffusivity. On the other hand, the particle back transport induced by shear induced diffusion and the lateral migration is kinetically motivated and […]

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Effect on cake layer structure

Particle back-transport causes a stratification of cake layer with large particles in the bottom and small particles in the top. This phenomenon is more apparent in the constant pressure mode, where flux declines gradually over time. Under the declining flux condition, the large particles with high back-transport velocities can deposit mainly in the beginning of […]

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