Membrane filtration ultrafiltration

Koyuncu et al. [56] presented pilot-scale studies on the treatment of pulp and paper mill effluents using two-stage membrane filtrations, ultrafiltration and reverse osmosis [56]. The combination of UF and RO resulted in very high removals of COD, color, and conductivity from the effluents. At the end of a single pass with seawater membrane, the initial COD, color and conductivity values were reduced to 10-20 mg/L, 0-100 PCCU (platinum cobalt color units) and 200-300 ps/cm, respectively. Nearly complete color removals were achieved in the RO experiments with seawater membranes. 

As the L/S ratio remains high, a concentration stage must be kept in the purification process. Evaporation is an expensive step that may be replaced by membrane filtration. Ultrafiltration was therefore investigated for its capability to achieve purification (in the same way as the alcohol precipitation) and concentration at the same time. Ultrafiltration was tested using differents membranes with an MWCO ranging from 1 to 50 kDa in order to obtain a minimum concentration ratio (CR) of 2 with a minimal organic matter loss. 

Researchers have recently developed four main types of processes to separate and purify whey proteins in an attempt to leave them in their more biologically active native forms. The types are selective precipitation, membrane filtration (ultrafiltration), selective adsorption, and selective elution (ion exchange). ... 

Membrane-retained components are collectively called concentrate or retentate. Materials permeating the membrane are called filtrate, ultrafiltrate, or permeate. It is the objective of ultrafiltration to recover or concentrate particular species in the retentate (eg, latex concentration, pigment recovery, protein recovery from cheese and casein wheys, and concentration of proteins for biopharmaceuticals) or to produce a purified permeate (eg, sewage treatment, production of sterile water or antibiotics, etc). Diafiltration is a specific ultrafiltration process in which the retentate is further purified or the permeable sohds are extracted further by the addition of water or, in the case of proteins, buffer to the retentate. 

Membrane Filtration. Membrane filtration describes a number of weU-known processes including reverse osmosis, ultrafiltration, nanofiltration, microfiltration, and electro dialysis. The basic principle behind this technology is the use of a driving force (electricity or pressure) to filter... 

Polymer Membranes These are used in filtration applications for fine-particle separations such as microfiltration and ultrafiltration (clarification involving the removal of l- Im and smaller particles). The membranes are made from a variety of materials, the commonest being cellulose acetates and polyamides. Membrane filtration, discussed in Sec. 22, has been well covered by Porter (in Schweitzer, op. cit., sec. 2.1). 

Recently, membrane filtration has become popular for treating industrial effluent. Membrane filtration includes microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse... 

Membrane filtration (reverse osmosis, nanofiltration, ultrafiltration, microfiltration)... 

Also included are sections on how to analyze mechanisms that affect flux feature models for prediction of micro- and ultrafiltration flux that help you minimize flux decline. Descriptions of cross-flow membrane filtration and common operating configurations clarify tf e influence of important operating parameters on system performance. Parameters irdlucnc irxj solute retention properties during ultrafiltration arc identified and discussed or treated in detail. 

Membrane-re tamed components are collectively called concentrate or retentate. Materials permeating the membrane are called filtrate, ultrafiltrate, or permeate. 

Figure 6.10 Effect of solute type and concentration on flux through the same type of ultrafiltration membrane operated under the same conditions [15]. Reproduced from M.C. Porter, Membrane Filtration, in Handbook of Separation Techniques for Chemical Engineers, P.A. Schweitzer (ed.), p. 2.39, Copyright 1979, with permission of McGraw-Hill, New York, NY...

Burba, R, Aster, B.,Nifant eva,T.,Shkinev, V., and Spivakov, B. Y. (1998). Membrane filtration studies of aquatic humic substances and their metal species A concise overview. Part 1. Analytical fractionation by means of sequential-stage ultrafiltration. Talanta 45, 977-988. 

Mass-transport limitations are common to all processes involving mass transfer at interfaces, and membranes are not an exception. This problem can be extremely important both for situations where the transport of solvent through the membrane is faster and preferential when compared with the transport of solute(s) - which happens with membrane filtration processes such as microfiltration and ultrafiltration - as well as with processes where the flux of solute(s) is preferential, as happens in organophilic pervaporation. In the first case, the concentration of solute builds up near the membrane interface, while in the second case a depletion of solute occurs. In both situations the performance of the system is affected negatively (1) solute accumulation leads, ultimately, to a loss of selectivity for solute rejection, promotes conditions for membrane fouling and local increase of osmotic pressure difference, which impacts on solvent flux (2) solute depletion at the membrane surface diminishes the driving force for solute transport, which impacts on solute flux and, ultimately, on the overall process selectivity towards the transport of that specific solute. 

Concentration of whev proteins. As mentioned earlier, microfiltration can be used to remove bacterias. In addition, they are capable of separating phospholipids, fats and casein fines of sweet whey or sour (acidified) whey. Ultrafiltration of whey has been well proven to provide an array of protein products of diverse compositions and properties. Inorganic membrane filtration can be used at different stages of the process to make whey protein concentrates (WPC) in powder form with a protein content reaching 50%. 

The individual membrane filtration processes are defined chiefly by pore size although there is some ovedap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafiltration (0.002—0.1 microns), and micro filtration (0.1—1.0 microns). Klectrodialysis uses dectric current to transport ionic species across a membrane. Micro- and ultrafiltration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and dectrodialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiU dilute streams, may require additional treatment or special disposal methods. 

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