Membrane fouling filtration applications

Cross-flow filtration systems utilize high liquid axial velocities to generate shear at the liquid-membrane interface. Shear is necessary to maintain acceptable permeate fluxes, especially with concentrated catalyst slurries. The degree of catalyst deposition on the filter membrane or membrane fouling is a function of the shear stress at the surface and particle convection with the permeate flow.16 Membrane surface fouling also depends on many application-specific variables, such as particle size in the retentate, viscosity of the permeate, axial velocity, and the transmembrane pressure. All of these variables can influence the degree of deposition of particles within the filter membrane, and thus decrease the effective pore size of the membrane. 

Some researchers [121, 126, 139] have demonstrated that intermittent application of AC or DC electric fields across MF or UF membranes during filtration can often promote displacement of polarization- or adherent fouling layers, with significant improvements in sustained permeation flux. The electrode is installed on either side of the membrane with the cathode on the permeate side and the anode on the feed side. Usually, the membrane support is made of stainless steel or the membrane itself is made of conductive materials to form the cathode. Titanium coated with a thin layer of a noble metal such as platinum could be one of the best anode materials [140], The electromagnetic field reduces fouling and biofilm development. 

It is important to generate the flux data on a continual basis as illustrated in Fig. 17. This type of information is very vital to identify any inconsistencies in the filtration performance and/or to determine if there is any irreversible membrane fouling. Reproducible performance will also be helpful to validate the membrane cleaning regimen for the application. 

G. Pearce, Fouling behaviour for different module formats in membrane filtration applications for surface water treatment, Desal. Water Treat. 8 (1-3) (2009) 36-38. 

Membrane fouling is one of most important problems for membrane processes related to filtration for food applications, since it can dramatically reduce the flow... 

Recently, several novel non-invasive techniques have been applied to characterize membrane fouling [1, 2]. Among them, optical and electron microscopic techniques have been recently used to visualize particle deposition, cake formation and membrane fouling. Conventional optical microscopy enables direct visualization of particle deposition during filtration, but its low resolution limits its applications. Additionally, conventional optical microscopy cannot be used to visualize cake structure and morphology since it has a very low axial resolution and requires ultrathin specimens to obtain a good visualization. 

Projector technique (PT), one early application of optical techniques to membrane fouling visualization, utilizes a projector and screen to monitor fouling deposition. This technique was applied to measure biofilm thickness on the silicone rubber tubular membrane during wastewater filtration [63]. The thickness was then measured and photographed from direct visual observation on the projector screen. 

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