Membranes micro-filtration

Traditional fermentation generally involves many process steps which are inefficient and uneconomical in terms of utilization of raw materials,recovery of product, and energy consumption. Continuous cross-flow membrane micro-filtration and ultrafiltration, when correctly introduced, have been shown to improve this process significantly. 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis 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 stiH dilute streams, may require additional treatment or special disposal methods. 

We wish to concentrate and achieve a solvent switch for a solution by batch crossflow micro filtration. The flux, jv, for the ceramic microfiltration membrane is 10 gal/(h-ft2). The initial solution volume is 1800 gal the final volume is 360 gal. The amount of protein present is 18.0 kg, and the molecular weight is 1,213.43 g/mole. The pressure drop is 30 psi (essentially 2 atm) and the operating temperature is 277 K. Calculate the area, A, required to complete the filtration in 2 h. 

In addition to the traditional deep bed filtration, other interesting examples of different processes and techniques can be described by the same basic principle (i) the tangential micro-filtration and ultra-filtration where a slow deep filtration produces the clogging of the membrane surface (ii) some processes of impregnation of porous supports with a sol in order to form a gel which, after precipitation, will form a membrane layer. Here the sol penetration inside the support is fundamental for the membrane quality. 

Ghayeni S.B.S., Beatson P.J., Fane A.G., and Schneider R.P., Bacterial passage through micro filtration membranes in wastewater applications. Journal of Membrane Science 153 1999 71-82. 

MaUubhotla H. and Belfort G., Flux enhancement during Dean vortex micro filtration. 8. Further diagnostics. Journal of Membrane Science 125 1988 75-91. 

Recent studies based on comparison between gel permeation chromatography and ultra/micro-filtration [119] have shown that whatever the chemical nature and shape of the model macromolecule used, it is possible to predict the cut-off value of a membrane by considering the hydrodynamic volume of the macromolecule. This parameter provides an appropriate definition of the effective solute size to be considered in hydrod)mamic models. 

Anton Steinecker Maschinenfabrik GmbH, Freising (BRD), Crossfow-micro-filtration with ceramic membranes. Company Product Bulletin, 1993. 

Hydrophobic membranes, e.g., PTFE, permit the efficient removal of volatile analytes from the sample matrix by diffusion though the micropores [257]. As these membranes have a high diffusion efficiency for many gaseous species, selectivity is usually low. For hydrophilic porous membranes, mass transference usually relies on dialysis, provided differences in donor and acceptor stream pressures are low [258] the chemical species originally in the donor stream migrate through the solvent in the interstitial volume of the membrane. Ionic species are therefore efficiently separated from the macromolecules in the sample matrix. Increasing the difference in pressures of both streams favours the micro-filtration process therefore, filtration and dialysis may occur simultaneously [259,260]. 

Clarifying fining lees tangential micro filtration, using membranes with pore diameters from 0.2 to 0.8 p.m, was compared with a rotary vacuum filter (Serrano, 1994). The flow rates were lower (50-100 1/h/m instead of 350-500 1/h/m ) but clarification was better, both in terms of much lower turbidity as well as the elimination of microorganisms. Wine losses were also lower ... 

Micro-filtration membranes are porous structures, which freely pass solvents (usually water) and molecularly dispersed solutes, including polymers. 

These interactions are only poorly understood and yet have major practical consequences for flux decline, membrane life time and the possibility of fractioning small particles by micro-filtration. 

Most micro-filtration membranes are made from modified, natural or synthetic polymers... 

MICRO FILTRATION - A membrane filtration process, which forces water through a porous barrier. Pores are usually between 0.1 to 20 m, when used for water purification. For filtering purposes, pore sizes are. 045 m. 

Increase re-use of treated fouled water Reduce water usage to minimum required Segregate different types of waste water streams and use localized treatment such as coagulation/flocculation followed by ultra/micro filtration/reverse osmosis membrane units. This can recycle 50% of the waste water as fresh water... 

Table 4.7 Some commercially available membranes for micro-filtration.

Separation processes such as ultrafiltration and micro filtration use porous membranes which allow the passage of molecules smaller than the membrane pore size. Ultrafiltration membranes have pore sizes from 0.001 to 0.1 )im while micro filtration membranes have pore sizes in the range of 0.02 to 10 im. The production of these membranes is almost exclusively based on non-solvent inversion method which has two essential steps the polymer is dissolved in a solvent, cast to form a film then the film is exposed to a non-solvent. Two factors determine the quality of the membrane pore size and selectivity. Selectivity is determined by how narrow the distribution of pore size is. In order to obtain membranes with good selectivity, one must control the non-solvent inversion process so that it inverts slowly. If it occurs too fast, it causes the formation of pores of different sizes which will be non-uniformly distributed. This can be prevented either by an introduction of a large number of nuclei, which are uniformly distributed in the polymer membrane or by the use of a solvent combination which regulates the rate of solvent replacement. 

Barrier membrane process. Processes in which one component, in a mixture, interacting with internal or external nanospaces of a membrane, present a barrier for another components, so that only the interacting component passes through the membrane. In the simplest case, a surface-active micro-filtration membrane, if saturated with a wetting liquid, is the barrier for a gas or a nonwetting liquid. Using lipophilic and lipophobic micro-filtration membranes, this phenomenon is applied in multiphase membrane contactors [7] and in the production of fine emulsions. 

Wakeman R.J., 1996. Fouling in crossflow ultra- and micro-filtration. Membrane Technol., 70,5. 

Mikulasek, P., Dolecek, P., Rambousek, V., Cakl, J. and Sed H., Testing of Micro-filtration Ceramic Membranes , Ceramics—Silikdty, 38(2), 99 (1994)... 

Water filtration using electrospun Ma et al. (2005c) regenerated cellulose nanofiber membranes studied and compared with commercial micro-filtration membranes. 

Micro filtration (MF) and ultrafiltration (MF) are typical low-driven pressure membrane processes widely applied in various chemical and biochemical processes thanks to their advantages over traditional filtration methods. They are generally a thermal and simple in concept and operation and do not involve phase changes or chemical additives. Additionally, they are modular, easy to scale-up and characterized by low energy consumptions (Mulder, 1998). 

Nataraj, S.K., Sridhar, S., Shaikha, I.N., Reddy, D.S. Aminabhavi, T.M. (2007) Membrane-based micro-filtration/electrodialysis hybrid process for the treatment of paper industry wastewater. Separation and Purification Technology, 57, 185-192. 

The conventional physical-chemical processes used for As removal can be classified on the basis of the principles involved (i) coagulation and filtration (Wickramasinghe et al., 2004) (ii) adsorption (iii) ion exchange and (iv) membrane technology, that includes reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and micro filtration (MF) (Choonga et al., 2007). Other methods like ozone oxidation, bioremediation, electrochemical treatments (Choonga et al., 2007) and natural zeolite (Baskan and Pal, 2011) are also used in the removal of As. 

---