Ultrafiltration membrane pore sizes

Papeterie du Rhin, Paper Roll Mill, France. In 1999, Veolia Water STI installed an MBR with Zeeweed ultrafiltration membranes (pore size 0.04 p.m) in Papeterie du Rhin s paper roll mill in France (Table 35.1). Recycled (not deinked) paper is used as the raw material. The bioreactor (1500 m ) is operated at a mixed liquor suspended solids (MLSS) content of 12-16 g/L. Brockmann and Praderie [58] report an average flux of 15 L/(m h) at a pressure of 0.15 bar over a 1 year filtration period. The wastewater from the mill is first prescreened with dmm screens, then sent to an equalization basin, from which it is pumped directly into the bioreactor. Table 35.6 summarizes the performance of the MBR process. The pressure used to draw the water through the membrane is 7-55 kPa. The filtrate is partly recycled as process water [27,57,58]. 

Once the cells have been removed, the enzyme broth is concentrated by evaporation or ultrafiltration. In ultrafiltration, membrane pore sizes are much smaller than in microfiltration, allowing only water and small molecules to travel through the membrane. Thus, enzymes can be concentrated under mild process conditions. Typical molecular weight cut off pore sizes for ultrafiltration membranes are 5000, 10,000, or 30,000 Daltons. 

Costa, A. R., and De Pinho, M. N. (2005) Effect of membrane pore size and solution chemistry on the ultrafiltration of humic substances solutions. /. Membr. Sci. 255,49-56. 

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. 

Ultrafiltration operates at lower pressures (0.2-1 MPa) than reverse osmosis and with higher permeate fluxes. It uses more porous membranes, pore size of 0.001-0.1 pm. In such a case, low-molecular weight dissolved compounds pass through the membrane, while colloid and suspended matters are rejected by UF membrane. 

Membranes are used for a wide variety of separations. A membrane serves as a barrier to some particles while allowing others to selectively pass through. The membrane pore size, shape, and electrostatic surface charge are fundamental to particle removal. Reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) relate to separation of ions, macromolecules and particles in the 0.001-10 pm range. 

In cross-flow flltration, the wastewater flows under pressure at a fairly high velocity tangentially or across the filter medium. A thin layer of solids form on the surface of the medium, but the high liquid velocity keeps the layer from building up. At the same time, the liquid permeates the membrane producing a clear filtrate. Filter media may be ceramic, metal (e.g., sintered stainless steel or porous alumina), or a polymer membrane (cellulose acetate, polyamide, and polyacrylonitrile) with pores small enough to exclude most suspended particles. Examples of cross filtration are microfiltration with pore sizes ranging from 0.1 to 5 pm and ultrafiltration with pore sizes from 1 pm down to about 0,001 pm. 

U. Goren, A. Aharoni, M. Kummel, R. Messalen, I. Mukmenev, A. Brenner, V. Gitis, Role of membrane pore size in tertiary flocculation/adsorption/ultrafiltration treatment of municipal wastewater. Separation and Purification Technology 2008,61, 193-203. 

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. 

Internal pressure hollow fiber ultrafiltration membrane was used in the experiment. The membrane material is modified PVC with effective membrane area of 40 m, the inner diameter and outer diameter of the hollow fiber is 1.0 mm and 1.5 mm, respectively, and the average membrane pore size is 0.01 xm, the molecular weight cutoff (MWCO) is 100 Ku. 

Separation processes such as ultrafiltration and microfiltration 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 pm while microfiltration membranes have pore sizes in the range of 0.02 to 10 pm. The production of these membranes is almost exclusively based on non-solvent inversion method which has two essen-... 

Ultrafiltration utilizes membrane filters with small pore sizes ranging from O.OlS t to in order to collect small particles, to separate small particle sizes, or to obtain particle-free solutions for a variety of applications. Membrane filters are characterized by a smallness and uniformity of pore size difficult to achieve with cellulosic filters. They are further characterized by thinness, strength, flexibility, low absorption and adsorption, and a flat surface texture. These properties are useful for a variety of analytical procedures. In the analytical laboratory, ultrafiltration is especially useful for gravimetric analysis, optical microscopy, and X-ray fluorescence studies. 

Ultrafiltration of micellar solutions combines the high permeate flows commonly found in ultrafiltration systems with the possibility of removing molecules independent of their size, since micelles can specifically solubilize or bind low molecular weight components. Characteristics of this separation technique, known as micellar-enhanced ultrafiltration (MEUF), are that micelles bind specific compounds and subsequent ultrafiltration separates the surrounding aqueous phase from the micelles [70]. The pore size of the UF membrane must be chosen such, that the micelles are retained but the unbound components can pass the membrane freely. Alternatively, proteins such as BSA have been used in stead of micelles to obtain similar enan-tioselective aggregates [71]. 

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