Darcy's Law: Nonwoven Membrane Resistance In The Separation Process

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Darcy’s Law expresses flux of water without particles through a nonwoven membrane as follows: J=∆p/(μ.R_m )
(4)
where, J is the permeation flux (m3/m2s), ∆p is the transnonwoven pressure (Pa), μ is the viscosity (Pa.s), and Rm is the clean nonwoven membrane resistance or intrinsic resistance (1/m).
Since fouling is going to take place in the separation process, the permeation flux will always be lower than the flux given by Eq. 4. Cake resistance -formed by cake layer- and fouling resistance -formed due to pore blockage and particle adsorption onto the fibers- are the other main contributors to the total fouling. So, when all of effecting parameters are taken into account, the total nonwoven membrane resistance can be calculated as follows:
…show more content…
Recently, some innovative approaches have been applied for nonwoven fouling reduction(150–152). For a successful fouling control, fluid mechanics (shear stress), sludge properties (particle size, extracellular polymeric substance, surface charge), module design, membrane material (hydrophobicity, roughness, pore size, packing density), and operating conditions (pH, HRT, SRT, backwash cycle, F/M) should be taken into …show more content…
Pore characteristics are likely the most important parameter affecting the removal efficiency and flux/fouling behavior. Low cost microfiber nonwovens with diverse functionality, controlled characteristics, and enhanced flux offer many opportunities in microfiltration process. However, many limitations for nonwovens exist in microfiltration applications: they are relatively coarse pore size, wide pore size distribution, depth filter structure with tortuous pore path through the thickness, hydrophobic nature of melt processed fibers, high specific surface area, and rough surface. If the nonwovens are produced within the pore size range of the MF, the effluent quality or the removal efficiencies is expected to be similar to the typical microfiltration membranes with the help of the dynamic membrane formation. However, fouling problems such as flux reduction and flux recovery after backwash still remain as the major drawbacks during long-term filtration. Therefore, more study is required to understand fouling phenomenon of nonwovens. As a conclusion, nonwovens cannot yet replace microfiltration membranes in bioreactors for biomass separation; further studies are inevitable to produce low-fouling

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