Hyperfiltration, membrane technology

Reverse Osmosis and Ultrafiltration. Reverse osmosis (qv) (or hyperfiltration) and ultrafilttation (qv) ate pressure driven membrane processes that have become well estabUshed ia pollution control (89—94). There is no sharp distinction between the two both processes remove solutes from solution. Whereas ultrafiltration usually implies the separation of macromolecules from relatively low molecular-weight solvent, reverse osmosis normally refers to the separation of the solute and solvent molecules within the same order of magnitude in molecular weight (95) (see also Membrane technology). 

Appropriate membrane technologies in the context of solid-liquid separation are microfiltration and the use of the more open membranes in ultrafiltration. Other membrane processes, including the pressure-driven processes of hyperfihration and reverse osmosis, are concerned primarily with the removal of dissolved species fi om a solvent and shall not be considered. The boundary between the finer end of microfiltration and the coarser end of ultrafiltration is not sharp, and ultrafiltration is used for fine colloid-liquid separation. The start of the regions of ndcrofiltratian, ultrafihration and hyperfiltration occurs, approximately, with the fihration of particles of diameter 10, 0.1 and 0.005 rm, respectively. 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Hyperfiltration (Reverse Osmosis) is a form of membrane distillation or desalination (desalting) operating with membrane pore sizes of perhaps 1 to 10 Angstrom units. The various individual RO component technologies have improved tremendously over the last 20 to 25 years, and resistance to fouling and permeate output rates have benefited. Nevertheless, all RO plants remain susceptible to the risk of fouling, and adequate pretreatment and operation is essential to minimize this problem. 

The SBP membrane filtration system concentrates contaminants and reduces the volume of contaminated groundwater, surface water, storm water, landfill leachates, and industrial process water. This hyperfiltration system consists of stainless steel tubes coated with a multilayered membrane, which is formed in-place using proprietary chemicals. The membrane filtration system can be used with an SBP bioremediation system or another technology as part of a treatment train. 

Two useful membranes developed by the group at the Oak Ridge National Laboratory have dominated the application of dynamic membranes the hydrous zirconium oxide ultrafilter and the hydrous zirconium oxide-poly(acrylic acid) hyperfilter. The technology of formation and utilization of zirconium oxide-poly(acrylic acid) dynamic membranes has been described in detail by Thomas ( ). The effects of molecular weight of the poly(acrylic acid), pore diameter of the porous support, formation cross-flow velocity, formation pressure, and pH of poly(acrylic acid) solution during initial deposition of the polyacid on the hyperfiltration performance are described and discussed. 

Whether we cail the process we have talked about during this week reverse osmosis or hyperfiltration or ultrafiltration is of little importance. The important thing is that the membrane invented by Loeb and Sourirajan slightly over 20 years ago is a marketable product and has a fantastic future. Too often we allow semantics to act as a barrier to our mutual understanding of this technology. 

Brandon, C. A. Closed-cycle Textile Dyeing Full-scale Hyperfiltration Demonstration presented at the Fifth Clemson Membrane Separation Technology Conference, Clemson University, Clemson, S.C. May 12-11+, I98O. 

The types of membrane separation technologies include reverse osmosis, hyperfiltration, ultrafiltration, and electrodialysis. At present, reverse osmosis is the only membrane separation technology that has been used as a mobile system and thus is the only such technology discussed in this section. 

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